Disk storage apparatus and disk storage apparatus control method

[0001] 1. Field of the Invention

[0002] The present invention relates to a disk storage apparatus for positioning a head to a target track of a disk which serves as a record medium, and to a technique of inhibiting a track dislocation of the head due to a disturbance to which the apparatus is subject.

[0003] 2. Description of the Related Art

[0004] A positioning control system reads servo information previously recorded on a disk using a head, and minimizes a position error signal for a target track. In this case, to improve positioning accuracy, there is known a method of setting control frequency at high level and thereby accelerating track following operation. However, if control frequency is set high, the positioning control system becomes unstable due to the inherent mechanical resonance of the actuator of the head. This results in a limit to the increase of control frequency. Considering this disadvantage, there is proposed reducing a disturbance (such as pivot bearing friction, an elastic force, and an inertia force due to shock/vibration) which acts on the actuator. That is, based on a head position signal obtained from servo information and a drive signal for the actuator, the disturbance is estimated and compensated by feed-forward control. By doing so, head positioning accuracy is improved.

[0005] However, the head position signal based on the servo information discretely recorded on the disk is not a continuous signal. A control band in which disturbance estimation means can estimate a disturbance is affected by the sampling frequency of a sector servo, and has an upper limit. It is difficult to correctly estimate the disturbance and to compensate the disturbance so that the disturbance has no effect on the actual use of the control system. Furthermore, if the resistance of the drive coil of the actuator fluctuates or the resistance is changed following temperature rise after a drive current is carried to the drive coil to heat the drive coil, the positioning control system including the disturbance estimation means becomes disadvantageously unstable.

[0006] To solve the above-stated disadvantages, the present invention takes the following measures. To negate a disturbance caused by a pivot bearing friction, an elastic force, an inertia force due to shock/vibration or the like exerted on actuator means, the magnitude of the disturbance is estimated. In estimating the magnitude of the disturbance, two elements are used. First, a voltage signal which is obtained as a detection result of detecting a voltage induced in driving the actuator means, is used. Second, a drive signal of the drive means for driving the actuator means is used. The drive signal of the drive means may be inputted into the drive means or outputted from the drive means. Alternatively, not the drive signal of the drive means but a position control signal, based on which the drive signal is produced, may be used. That is, disturbance estimation means for estimating the magnitude of the disturbance is provided. The disturbance estimation means receives a voltage signal, which is obtained by detecting the voltage induced in driving the actuator means by voltage detection means, and the drive signal or position control signal of the drive means, and produces a disturbance estimation signal. The disturbance estimation signal produced based on the two elements, correctly estimates the magnitude of the disturbance exerted on the head. As a result, it is possible to correctly estimate the magnitude of the disturbance exerted on the actuator means. The disturbance related to the estimation is indicated by the disturbance estimation signal. The disturbance estimation means produces the disturbance estimation signal based on either the drive signal or the position control signal and the voltage signal induced in driving the actuator means. The voltage induced in driving the actuator means is a continuous signal. Due to this, compared with conventional art for estimating a disturbance using a discontinuous head position signal as a result of reading servo information discretely recorded on the disk, it is possible to correctly estimate a disturbance.

[0007] Meanwhile, if there are fluctuations in the resistance value of the drive coil and changes of the resistance value, a phase with a gain crossover frequency with which open loop gain becomes zero, has no phase margin, with the result that a control system becomes unstable. To solve this disadvantage, according to the present invention, the drive signal is produced based on the position control signal for a head position and the disturbance estimation signal, the high frequency component of the disturbance estimation signal is cut off by filter means to thereby produce a filter signal. Thereafter, the position control signal for the head position is combined with the filter signal, thereby producing the drive signal.

[0008] By so constituting, the high frequency components of frequencies higher than a filter low-pass cut-off frequency are cut off by the filter means. The high frequency components of the disturbance estimation signal outputted from the disturbance estimation signal are not included equivalently in the drive signal. As a result, even if the resistance value of the drive coil of the actuator means is changed according to resistance fluctuation or temperature rise, it is possible to secure a phase margin with the gain crossover frequency and to constitute a stable head positioning control system.

[0009] Correction means combines the disturbance estimation signal after filtering (filter signal) with the position control signal from the position control means, and thereby produces a drive signal so as to negate the disturbance exerted on the actuator means using the disturbance estimation signal thus correctly estimated. By driving the actuator means of the head using the drive signal, it is possible to stably negate a disturbance such as a pivot bearing friction, an elastic force or an inertia force exerted on the actuator means. That is, it is possible to compensate the disturbance acting on the actuator means. Therefore, even if the fluctuation of the disturbance acting on the actuator means is large during following operation toward the target track, it is possible to stably control positioning the head to the target track. Furthermore, even if the resistance value of the drive coil of the actuator means is changed by resistance fluctuation or temperature rise, it is possible to stably control positioning the head to the target track. That is, it is possible to improve positioning accuracy against more diverse conditional change. In addition, as an effect resulting from this improvement, it is possible to substantially increase track density and to accelerate the embodiment of a large capacity disk storage apparatus.

[0010] As another means for solving the disadvantages, the present invention takes the following measures. The disturbance estimation means produces the disturbance estimation signal based on a signal obtained by multiplying the drive signal by k₁, where k₁ is a coefficient of a real number greater than 1, and the voltage signal. The correction means combines a signal obtained by multiplying the disturbance estimation signal by 1/k₂, where k₂ is a coefficient of a real number greater than 1, with the position control signal, and produces a drive signal. By doing so, the change of open loop gain from the position error signal to the head position can be suppressed to be small. As a result, even if the resistance value of the drive coil of the actuator means is changed according to resistance fluctuation or temperature rise, it is possible to stabilize the position control system. In this case, if the filter means is employed, it is possible to attain a more preferable effect.

[0011] The present invention explained above will be described more concretely.

[0012] As the first solving means, the disk storage apparatus according to the present invention comprises: actuator means for positioning a head with respect to a disk; drive means for driving the actuator means in accordance with an input drive signal; voltage detection means for detecting a voltage induced in driving the actuator means, and for outputting a voltage signal; disturbance estimation means for estimating a magnitude of a disturbance exerted on the head from the drive signal and the voltage signal, and for producing a disturbance estimation signal; filter means for cutting off a high frequency component of the disturbance estimation signal, and for outputting a filter signal; position detection means for producing a position error signal corresponding to a current position of the head from servo information previously recorded on the disk and detected by the head, and for outputting the position error signal; position control means for producing a position control signal corresponding to the position error signal, and for outputting the position control signal; and correction means for combining the position control signal with the filter signal to produce the drive signal, and for outputting the drive signal. With this constitution, the drive signal of the drive means may be a signal inputted into the drive means or a signal outputted from the drive signal. This applies hereafter.

[0013] The functions resulting from this first solving means are as follows. The disturbance estimation means can correctly estimate the magnitude of the disturbance exerted on the actuator means based on the drive signal applied to the drive means to drive the actuator means, and the voltage signal detected from the actuator means. A disturbance related to the estimation is a disturbance estimation signal. Here, it is particularly important that it is possible to correctly estimate the magnitude of the disturbance exerted on the actuator means from the drive signal and the voltage signal during following operation for allowing the head to follow up the target track. The reason is as follows. The voltage signal detected from the actuator means is a voltage induced in driving the actuator means. This signal, unlike servo information recorded on the disk discretely, is a continuous signal.

[0014] After the high frequency component of the disturbance estimation signal is cut off through the filter means so as to negate the disturbance exerted on the actuator means using the disturbance estimation signal thus correctly estimated, the resultant signal is combined with the position control signal outputted from the position control means to thereby produce the drive signal. By driving the actuator means using the drive signal, it is possible to stably negate the disturbance exerted on the actuator means. That is, since it is possible to compensate the disturbance exerted on the actuator means, the position control of the head toward the target track can be stable even if the fluctuation of the disturbance during the following operation for allowing the head to follow up the target track is large. In particular, even if the resistance value of the drive coil of the actuator means is changed by resistance fluctuation or temperature rise, in particular, it is possible to stably control positioning the head to the target track. That is, it is possible to improve positioning accuracy against more diverse conditional change.

[0015] The first solving means will be described as a disk storage apparatus control method as follows. That is, the method comprises the steps of: producing a position error signal corresponding to a current position of a head from servo information previously recorded on a disk and detected by the head; producing a position control signal corresponding to the position error signal; estimating a magnitude of a disturbance exerted on the head from a drive signal of actuator means for positioning the head and from a voltage signal induced in driving the actuator means, and producing a disturbance estimation signal; cutting off a high frequency component of the disturbance estimation signal, and producing a filter signal; combining the position control signal with the filter signal, and producing the drive signal; and positioning the head with respect to the disk by the drive signal. This disk storage apparatus control method can exhibit the same functions as stated above.

[0016] As the second solving means, the disk storage apparatus according to the present invention comprises: actuator means for positioning a head with respect to a disk; drive means for driving the actuator in accordance with an input drive signal; voltage detection means for detecting a voltage induced in driving the actuator means, and for outputting a voltage signal; position detection means for producing a position error signal corresponding to a current position of the head from servo information previously recorded on the disk and detected by the head, and for outputting the position error signal; position control means for producing a position control signal corresponding to the position error signal, and for outputting the position control signal; disturbance estimation means for estimating a magnitude of a disturbance exerted on the head from the voltage signal and the position control signal, and for producing a disturbance estimation signal; filter means for cutting off a high frequency component of the disturbance estimation signal, and for outputting a filter signal; and correction means for combining the position control signal with the filter signal to produce the drive signal, and for outputting the drive signal.

[0017] The functions resulting from this second solving means are as follows. The disturbance estimation means can correctly estimate the magnitude of the disturbance exerted on the actuator means based on the drive signal applied to the drive means to drive the actuator means, and the voltage signal detected from the actuator means. Here, it is particularly important that it is possible to correctly estimate the magnitude of the disturbance exerted on the actuator means from the drive signal and the voltage signal during following operation for allowing the head to follow up the target track. The reason is as follows. The voltage signal detected from the actuator means is, unlike servo information recorded on the disk discretely, a continuous signal.

[0018] After the high frequency component of the disturbance estimation signal is cut off through the filter means so as to negate the disturbance exerted on the actuator means using the disturbance estimation signal thus correctly estimated, the resultant signal is combined with the position control signal outputted from the position control means to thereby produce the drive signal. By driving the actuator means using the drive signal, it is possible to stably negate the disturbance exerted on the actuator means. That is, it is possible to compensate the disturbance exerted on the actuator means. Therefore, even if the fluctuation of the disturbance during the following operation for allowing the head to follow up the target track is large and even if the resistance value of the drive coil of the actuator means is changed according to resistance fluctuation or temperature rise, it is possible to stably control positioning the head to the target track. That is, it is possible to improve positioning accuracy against more diverse conditional change.

[0019] The second solving means will be described as a disk storage apparatus control method as follows. That is, the method comprises the steps of: producing a position error signal corresponding to a current position of a head from servo information previously recorded on a disk and detected by the head; producing a position control signal corresponding to the position error signal; estimating a magnitude of a disturbance exerted on the head from the position control signal and a voltage signal induced in driving actuator means for positioning the head, and producing a disturbance estimation signal; cutting off a high frequency component of the disturbance estimation signal, and producing a filter signal; combining the position control signal with the filter signal, and producing the drive signal; and positioning the head with respect to the disk by the drive signal. This disk storage apparatus control method can exhibit the same functions as stated above.

[0020] As the third solving means, the disk storage apparatus according to the present invention comprises: actuator means for positioning a head with respect to a disk; drive means for driving the actuator means in accordance with an input drive signal; voltage detection means for detecting a voltage induced in driving the actuator means, and for outputting a voltage signal; disturbance estimation means for estimating a magnitude of a disturbance exerted on the head from a signal obtained by multiplying the drive signal by k₁, where k₁ is a coefficient of a real number greater than 1, and from the voltage signal, and for producing a disturbance estimation signal; position detection means for producing a position error signal corresponding to a current position of the head from servo information previously recorded on the disk and detected by the head, and for outputting the position error signal; position control means for producing a position control signal corresponding to the position error signal, and for outputting the position control signal; and correction means for receiving the position control signal and the disturbance estimation signal, combining a signal obtained by multiplying the disturbance estimation signal by 1/k₂, where k₂ is a coefficient of a real number greater than 1, with the position control signal to produce the drive signal, and for outputting the drive signal.

[0021] The functions resulting from this third solving means are as follows. Besides the same functions as those resulting from the first solving means, it is possible to suppress the change of open loop gain from the position error signal to the head position to be small since the drive signal is applied to the disturbance estimation means after being multiplied by k₁ (k₁>>1) and the disturbance estimation signal is applied to the correction means after being multiplied by 1/k₂ (k₂>>1). As a result, even if the resistance value of the drive coil of the actuator means is changed according to resistance fluctuation or temperature rise, it is possible to stabilize the position control system. That is, it is possible to improve positioning accuracy against more diverse conditional change. In this case, if the filter means provided by the first solving means is used, it is possible to obtain a more preferable effect.

[0022] The third solving means will be described as a disk storage apparatus control method as follows. That is, the method comprises the steps of: producing a position error signal corresponding to a current position of a head from servo information previously recorded on a disk and detected by the head; producing a position control signal corresponding to the positon error signal; estimating a magnitude of a disturbance exerted on the head from a signal obtained by multiplying a drive signal of actuator means for positioning the head by k₁, where k₁ is a coefficient of a real number greater than 1, and from a voltage signal induced in driving the actuator means, and producing a disturbance estimation signal; combining a signal obtained by multiplying the disturbance estimation signal by 1/k₂, where k₂ is a coefficient of a real number greater than 1, with the position control signal, and producing the drive signal; and positioning the head with respect to the disk by the drive signal. This disk storage apparatus control method can exhibit the same functions as stated above.

[0023] As the fourth solving means, the disk storage apparatus according to the present invention comprises: actuator means for positioning a head with respect to a disk; drive means for driving the actuator means in accordance with an input drive signal; voltage detection means for detecting a voltage induced in driving the actuator means, and for outputting a voltage signal; position detection means for producing a position error signal corresponding to a current position of the head from servo information previously recorded on the disk and detected by the head, and for outputting the position error signal; position control means for producing a position control signal corresponding to the position error signal, and for outputting the position control signal; disturbance estimation means for estimating a magnitude of a disturbance exerted on the head from a signal obtained by multiplying the position control signal by k₁, where k₁ is a coefficient of a real number greater than 1, and from the voltage signal, and for producing a disturbance estimation signal; and correction means for receiving the position control signal and the disturbance estimation signal, combining a signal obtained by multiplying the disturbance estimation signal by 1/k₂, where k₂ is a coefficient of a real number greater than 1, with the position control signal to produce the drive signal, and for outputting the drive signal.

[0024] With this constitution, the disturbance estimation means can correctly estimate the magnitude of the disturbance exerted on the actuator means based on the position control signal outputted from the position control means so as to be applied to the drive means for driving the actuator means and the voltage signal detected from the actuator means. It is possible to correctly estimate the magnitude of the disturbance exerted on the actuator means from the position control signal and the voltage signal particularly during following operation for allowing the head to follow up the target track. The disturbance estimation signal is combined with the position control signal outputted from the position control means so as to negate the disturbance exerted on the actuator means using the disturbance estimation signal thus correctly estimated, to thereby produce the drive signal. By driving the actuator means of the head using the drive signal, it is possible to stably negate the disturbance exerted on the actuator means. That is, it is possible to compensate the disturbance exerted on the actuator means. Therefore, even if the fluctuation of the disturbance is large during the following operation for allowing the head to follow up the target track and even if the resistance value of the drive coil of the actuator means is changed according to resistance fluctuation or temperature rise, it is possible to stably control positioning the head to the target track. That is, it is possible to improve positioning accuracy against more diverse conditional change.

[0025] The fourth solving means will be described as a disk storage apparatus control method as follows. That is, the method comprises the steps of: producing a position error signal corresponding to a current position of a head from servo information previously recorded on a disk and detected by the head; producing a position control signal corresponding to the position error signal; estimating a magnitude of a disturbance exerted on the head from a signal obtained by multiplying the position control signal by k₁, where k₁ is a coefficient of a real number greater than 1, and from a voltage signal induced in driving actuator means for positioning the head, and producing a disturbance estimation signal; combining a signal obtained by multiplying the disturbance estimation signal by 1/k₂, where k₂ is a coefficient of a real number greater than 1, with the position control signal, and producing the drive signal; and positioning the head with respect to the disk by the drive signal. This disk storage apparatus control method can exhibit the same functions as stated above.

[0026] Alternatively, the first solving means may be combined with the third solving means. The second solving means may be combined with the fourth solving means. These combination means are fifth and sixth solving means, respectively.

[0027] As the fifth solving means, the disk storage apparatus according to the present invention comprises: actuator means for positioning a head with respect to a disk; drive means for driving the actuator means in accordance with an input drive signal; voltage detection means for detecting a voltage induced in driving the actuator means, and for outputting a voltage signal; disturbance estimation means for estimating a magnitude of a disturbance exerted on the head from a signal obtained by multiplying the drive signal by k₁, where k₁ is a coefficient of a real number greater than 1, and from the voltage signal, and for producing a disturbance estimation signal; position detection means for producing a position error signal corresponding to a current position of the head from servo information previously recorded on the disk and detected by the head, and for outputting the position error signal; position control means for producing a position control signal corresponding to the position error signal, and for outputting the position control signal; and correction means for receiving the position control signal and the disturbance estimation signal, cutting off a high frequency component of a signal, which is obtained by multiplying the disturbance estimation signal by 1/k₂, where k₂ is a coefficient of a real number greater than 1, to produce a filter signal, combining the position control signal with the filter signal to produce the drive signal, and for outputting the drive signal.

[0028] The fifth solving means will be described as a disk storage apparatus control method as follows. That is, the method comprises the steps of: producing a position error signal corresponding to a current position of a head from servo information previously recorded on a disk and detected by the head; producing a position control signal corresponding to the position error signal; estimating a magnitude of a disturbance exerted on the head from a signal obtained by multiplying a drive signal of actuator means for positioning the head by k₁, where k₁ is a coefficient of a real number greater than 1, and from a voltage signal induced in driving the actuator means, and producing a disturbance estimation signal; cutting off a high frequency component of a signal, which is obtained by multiplying the disturbance estimation signal by 1/k₂, where k₂ is a coefficient of a real number greater than 1, and producing a filter signal; combining the position control signal with the filter signal, and producing the drive signal; and positioning the head with respect to the disk by the drive signal.

[0029] Further, as the sixth solving means, the disk storage apparatus according to the present invention comprises: actuator means for positioning a head with respect to a disk; drive means for driving the actuator means in accordance with an input drive signal; voltage detection means for detecting a voltage induced in driving the actuator means, and for outputting a voltage signal; position detection means for producing a position error signal corresponding to a current position of the head from servo information previously recorded on the disk and detected by the head, and for outputting the position error signal; position control means for producing a position control signal corresponding to the position error signal, and for outputting the position control signal; disturbance estimation means for estimating a magnitude of a disturbance exerted on the head from a signal obtained by multiplying the position control signal by k₁, where k₁ is a coefficient of a real number greater than 1, and from the voltage signal, and for producing a disturbance estimation signal; and correction means for receiving the position control signal and the disturbance estimation signal, cutting off a high frequency component of a signal, which is obtained by multiplying the disturbance estimation signal by 1/k₂, where k₂ is a coefficient of a real number greater than 1, to produce a filter signal, combining the position control signal with the filter signal to produce the drive signal, and for outputting the drive signal.

[0030] The sixth solving means will be described as a disk storage apparatus control method as follows. That is, the method comprises the steps of: producing a position error signal corresponding to a current position of a head from servo information previously recorded on a disk and detected by the head; producing a position control signal corresponding to the position error signal; estimating a magnitude of a disturbance exerted on the head from a signal obtained by multiplying the position control signal by k₁, where k₁ is a coefficient of a real number greater than 1, and from a voltage signal induced in driving actuator means for positioning the head, and producing a disturbance estimation signal; cutting off a high frequency component of a signal, which is obtained by multiplying the disturbance estimation signal by 1/k₂, where k₂ is a coefficient of a real number greater than 1, and producing a filter signal; combining the position control signal with the filter signal, and producing the drive signal; and positioning the head with respect to the disk by the drive signal.

[0031] The fifth and sixth solving means have synergistic effects. That is, even if the change width of the resistance value of the drive coil is quite large, it is possible to implement stable head positioning control over higher control frequency bands.

[0032] According to the third to sixth solving means, it is preferable that the coefficients k₁ and k₂ are set almost equal to each other.

[0033] By doing so, in the substantial transfer function from the position control signal to the drive current to the actuator means, components related to the resistance value of the drive coil of the actuator means can be ignored. Accordingly, even if the resistance value of the drive coil of the actuator means is changed by resistance fluctuation or temperature rise, it is possible to sufficiently, stably control positioning the head to the target track.

[0034] According to the first, third or fifth solving means in which the drive signal out of the drive signal and the position control signal is applied to the disturbance estimation means, it is preferable to constitute the apparatus as follows. The disturbance estimation means comprises: comparison means for receiving the voltage signal detected by the voltage detection means; first multiplication means for multiplying the drive signal or a signal obtained by multiplying the drive signal by k₁, by a coefficient consisting of a first transfer function; second multiplication means for multiplying an output of the comparison means by a coefficient consisting of a second transfer function; first integration means for integrating the output of the comparison means; and second integration means for integrating a value obtained by subtracting the added value of the output of the second multiplication means and the output of the first integration means from the output of the first multiplication means, and the comparison means is configured to compare the voltage signal with the output of the second integration means, and to output a comparison result to the second multiplication means and the first integration means.

[0035] The functions resulting from this constitution are as follows. The output of the first multiplication means which inputs the drive signal or a signal obtained by multiplying the drive signal by k₁, becomes a drive torque estimation signal corresponding to the drive torque acting on the actuation means. The output of the second integration means becomes a feedback element for the voltage signal inputted from the voltage detection means. The output of the comparison means which obtains the difference between the voltage signal and the feedback element from the second integration means, is applied to the first integration means and the second multiplication means. The output of the first integration means which integrates the difference, becomes a disturbance estimation signal corresponding to the disturbance exerted on the actuator means. The output of the second multiplication means obtained by multiplying the difference by a predetermined coefficient, is added to the disturbance estimation signal. The added value is subtracted from the drive torque estimation signal and the result is applied to the second integration means.

[0036] As a result, the disturbance estimation signal outputted from the first integration means corresponds to the correct estimate of the disturbance exerted on the actuator means. Further, using the disturbance estimation signal thus correctly estimated, feed-forward control is implemented so as to negate the disturbance exerted on the actuator means. It is, therefore, possible to compensate the disturbance acting on the actuator means during following operation. Even if the fluctuation of the disturbance in the actuator means is large during the following operation, and even if the resistance value of the drive coil of the actuator means is changed according to resistance fluctuation or temperature rise, it is possible to stably control positioning the head to the target track, and to improve positioning accuracy against more diverse conditional changes.

[0037] According to the second, fourth or sixth solving means in which the position control signal out of the drive signal and the position control signal is applied to the disturbance estimation means, it is preferable to constitute the apparatus as follows. The disturbance estimation means comprises: comparison means for receiving the voltage signal detected by the voltage detection means; first multiplication means for multiplying the position control signal or the signal, which is obtained by multiplying the position control signal by k₁, by a coefficient consisting of a first transfer function; second multiplication means for multiplying an output of the comparison means by a coefficient consisting of a second transfer function; first integration means for integrating the output of the comparison means; and second integration means for integrating a value obtained by subtracting the output of the second multiplication means from the output of the first multiplication means, and the comparison means compares the voltage signal with the output of the second integration means, and outputs a comparison result to the second multiplication means and the first integration means.

[0038] The functions resulting from this constitution are as follows. The output of the first multiplication means which inputs the position control signal from the position control means signal or a signal obtained by multiplying the position control signal by k₁, becomes a drive torque estimation signal corresponding to the drive torque acting on the actuation means. The output of the second integration means becomes a feedback element for the voltage signal inputted from the voltage detection means. The output of the comparison means which obtains the difference between the voltage signal and the feedback element from the second integration means, is applied to the first integration means and the second multiplication means. The output of the first integration means which integrates the difference, becomes a disturbance estimation signal corresponding to the disturbance exerted on the actuator means. The output of the second multiplication means obtained by multiplying the difference by a predetermined coefficient, is subtracted from the drive torque estimation signal and the result is applied to the second integration means.

[0039] As a result, the disturbance estimation signal outputted from the first integration means corresponds to the correct estimate of the disturbance exerted on the actuator means. Further, using the disturbance estimation signal thus correctly estimated, feed-forward control is implemented so as to negate the disturbance exerted on the actuator means. It is, therefore, possible to compensate the disturbance acting on the actuator means during following operation. Even if the fluctuation of the disturbance in the actuator means is large during the following operation, and even if the resistance value of the drive coil of the actuator means is changed according to resistance fluctuation or temperature rise, it is possible to stably control positioning the head to the target track, and to improve positioning accuracy. Besides, the addition of the first integration means and the second multiplication means which the first solving means requires, is unnecessary. It is, therefore, possible to omit addition means and to thereby simplify the constitution.

[0040] Further, according to the above-stated invention, it is preferable that an estimation frequency of the disturbance estimation signal produced by the disturbance estimation means is set at a value larger than a control frequency band of the position control means.

[0041] The functions resulting from the above are as follows. To widen the control frequency band of the positioning control system means to increase proportional gain. However, the gain has an upper limit by the sampling frequency of the sector servo of the disk storage apparatus or the inherent mechanical resonance frequency of the actuator means. In contrast, the disturbance estimation means is not affected by the sampling frequency of the sector servo of the disk storage apparatus. Accordingly, in the disturbance estimation means, it is possible to set the estimation frequency band of the disturbance estimation signal produced by the disturbance estimation means, higher than the control frequency band of the positioning control system. As a result, it is possible to make the head correctly follow up the target track over higher control frequency bands.

[0042] Further, according to the above-stated invention, it is preferable that a cut-off frequency of the filter means is set at a value smaller than a control band of the position control means.

[0043] The functions resulting from this are as follows. Normally, there is a fluctuation in the resistance value of the drive coil of the actuator means. In addition, by conducting a drive current to the drive coil, the drive coil is heated to raise temperature and the temperature rise changes the resistance value. Consequently, the change of the resistance value of the drive coil of the actuator means makes the positioning control system including the disturbance estimation means unstable, with the result that the system oscillates with frequency near the control band of the position control means. To solve this disadvantage, the drive signal is produced based on the position control signal for the head position and the disturbance estimation signal. The high frequency component of the disturbance estimation signal is cut off by the filter means to thereby produce a filter signal. The position control signal for the head position is combined with the filter signal to thereby produce the drive signal. In this case, if the cut-off frequency of the filter signal by the filter means or correction means is set lower than the control band of the position control means, then the disturbance estimation signal having higher frequency components than the cut-off frequency is cut off by the filter means and not fed back to the positioning control system. Therefore, even if the resistance value of the drive coil of the actuator means is changed according to resistance fluctuation or temperature rise, it is possible to stabilize the position control system.

[0044] Furthermore, according to the above-stated invention, it is preferable that the actuator means is configured by a permanent magnet fixedly attached to at least one yoke of a pair of yokes in a cavity of the pair of yokes opposite to each other through the cavity, and a drive coil provided in a magnetic cavity formed by the permanent magnet and the yokes, and that a circuit having a capacitor and a resistor connected in series, is connected to the drive coil in parallel.

[0045] The functions resulting from this are as follows. Normally, the drive coil which constitutes the actuator means contains not only a resistance component but also an inductance component. Since the inductance component is smaller than the coil resistance, it is difficult to accurately constitute a circuit therefor. Further, since the inductance component is a derivative element, it tends to be affected by noise. As a result, if the control band of the disturbance estimation means is set high, the control system becomes unstable due to the influence of this inductance. This results in a limit in increasing the control band of the disturbance estimation means. Considering this disadvantage, the circuit having the capacitor and the resistor connected in series is connected to the drive coil in parallel, whereby the influence of the inductance of the drive coil can be eliminated and the control band thereof can be set higher than the control band of the positioning control system. As a result, it is possible to make the head correctly follow up the target track over higher control bands. In addition, in the constitution of a circuit, it is unnecessary to take account of the inductance component which requires high accuracy, so that the voltage detection means can be simplified.

[0046] Moreover, according to the above-stated invention, it is preferable that the capacitor and the resistor connected to the drive coil in parallel are set to have a capacitance value C and a resistance value r as expressed by CLa/Ra², and rRa, or approximate to CLa/Ra², and rRa, respectively, wherein Ra is a resistance value of the drive coil.

[0047] By so setting, the composite impedance of the impedance of the drive coil and that of the parallel circuit becomes substantially equal to the resistance of the drive coil, making it possible to equivalently negate the inductance component of the drive coil. Accordingly, even if there is a fluctuation in the inductance component which tends to be affected by the noise because it is a derivative element, it is possible to stably implement positioning control without being influenced by the noise.

[0048] As is obvious from the above explanation, the position control means, the disturbance estimation means, the correction means, and the filter means, which are the constituent elements of the disk storage apparatus, may be configured by hardware or software.

[0049] Additionally, as is evident from the above explanation, the comparison means, the respective multiplication means, and the respective integration means, which are the constituent elements of the disk storage apparatus, may be by hardware or software.

[0050] While the present invention functions most advantageously if being applied to a magnetic disk storage apparatus, the present invention is not limited to the magnetic disk storage apparatus but can be applied to the other information recording apparatuses such as an optical disk storage apparatus and a magneto-optical storage apparatus.

[0051] The foregoing and other aspects will become apparatus from the following description of the invention when considered in conjunction with the accompanying drawing figures.

[0052] FIG. 1 is a block diagram showing the configuration of a disk storage apparatus in the first embodiment according to the present invention;

[0053] FIG. 2 is a block diagram showing the whole configuration of the positioning control system of the disk storage apparatus in the first embodiment according to the present invention;

[0054] FIG. 3A is a block diagram for explaining the disturbance estimation operation of the disturbance estimation means of the disk storage apparatus in the first embodiment according to the present invention, FIG. 3B is a block diagram obtained by equivalently transforming the block diagram of FIG. 3A, and FIG. 3C is a block diagram collectively expressing the block diagram of FIG. 3A;

[0055] FIG. 4A is a block diagram for explaining an operation of inhibiting a disturbance exerted on the disk storage apparatus in the first embodiment according to the present invention, and FIG. 4B is a block diagram obtained by equivalently transforming the block diagram of FIG. 4A;

[0056] FIG. 5 is a cut-off frequency characteristic graph for the disturbance exerted on the disk storage apparatus in the first embodiment according to the present invention;

[0057] FIG. 6A is a waveform chart of the fluctuation of the disturbance exerted on the disk storage apparatus and a disturbance estimation signal outputted from the disturbance estimation means with respect to time response in the first embodiment according to the present invention, FIG. 6B is a waveform chart of a drive current with respect to time response in a case where the disturbance estimation signal outputted from the disturbance estimation means is inputted into correction means and in a case where the distance estimation signal is not inputted into the correction means, and FIG. 6C is a waveform chart of a track error with respect to time response in a case where the disturbance estimation signal outputted from the disturbance estimation means is inputted into the correction means to negate the fluctuation of the disturbance;

[0058] FIG. 7A is a frequency gain characteristic view of the open loop of a positioning control system in a case where the disturbance estimation means of the disk storage apparatus in the first embodiment according to the present invention takes account of the inductance of a drive coil, and FIG. 7B is a frequency to phase characteristic view corresponding to FIG. 7A;

[0059] FIG. 8A is a frequency gain characteristic view of the open loop of a positioning control system in a case where the disturbance estimation means of the disk storage apparatus in the first embodiment according to the present invention does not take account of the inductance of the drive coil, and FIG. 8B is a frequency to phase characteristic view corresponding to FIG. 8A;

[0060] FIG. 9 is a circuit configuration view of a capacitor and a resistance connected in parallel to the drive coil of the disk storage apparatus in the first embodiment according to the present invention;

[0061] FIG. 10 is a block diagram showing the changed parts of the disturbance estimation means of the disk storage apparatus in the first embodiment according to the present invention;

[0062] FIG. 11A is a frequency gain characteristic view of the open loop of the positioning control system of the disk storage apparatus in the first embodiment according to the present invention in a case where a filter is not inserted between the output of the disturbance estimation means and the input of the correction means (indicated by a solid line) and in a case where the disturbance estimation means does not take account of the inductance of the drive coil (indicated by a broken line), and FIG. 11B is a frequency phase characteristic view corresponding to FIG. 11A;

[0063] FIG. 12 is a block diagram showing the configuration of a disk storage apparatus in the second embodiment according to the present invention;

[0064] FIG. 13 is a block diagram showing the whole configuration of the positioning control system of the disk storage apparatus in the second embodiment according to the present invention;

[0065] FIG. 14 is a block diagram showing the configuration of a disk storage apparatus in the third embodiment according to the present invention;

[0066] FIG. 15 is a block diagram showing the whole configuration of the positioning control system of the disk storage apparatus in the third embodiment according to the present invention;

[0067] FIG. 16A is a frequency gain characteristic view of the open loop of the positioning control system in a case where the resistance value of the drive coil is not equal to a nominal value in the disturbance estimation means in the third embodiment according to the present invention, and FIG. 16B is a frequency phase characteristic view corresponding to FIG. 16A;

[0068] FIG. 17A is a block diagram showing the whole configuration of the positioning control system of the disk storage apparatus in the third embodiment according to the present invention, FIG. 17B is a block diagram obtained by equivalently transforming the block diagram of FIG. 17A, and FIG. 17C is a block diagram showing the changed parts of the positioning control system in a case where the resistance value of the drive coil is not equal to the nominal value;

[0069] FIG. 18 is a re-drawn block diagram of the configuration of the disk storage apparatus (FIG. 14) in the third embodiment according to the present invention;

[0070] FIG. 19 is a re-drawn block diagram of the whole configuration of the positioning control system (FIG. 15) of the disk storage apparatus in the third embodiment according to the present invention;

[0071] FIG. 20 is a block diagram showing the configuration of a disk storage apparatus in the fourth embodiment according to the present invention;

[0072] FIG. 21 is a block diagram showing the whole configuration of the positioning control system of the disk storage apparatus in the fourth embodiment according to the present invention;

[0073] FIG. 22 is a re-drawn block diagram of the configuration of the disk storage apparatus (FIG. 14) in the third embodiment according to the present invention;

[0074] FIG. 23 is a re-drawn block diagram of the whole configuration of the positioning control system (FIG. 15) of the disk storage apparatus in the third embodiment according to the present invention;

[0075] FIG. 24 is a block diagram showing the configuration of a disk storage apparatus in an embodiment which is a combination of the first and third embodiments according to the present invention; and

[0076] FIG. 25 is a block diagram showing the configuration of a disk storage apparatus in an embodiment which is a combination of the second and fourth embodiments according to the present invention.

[0077] In all these figures, like components are indicated by the same numerals.

[0078] With reference to the drawings, concrete embodiments of a disk storage apparatus and a disk storage apparatus control method according to the present invention will be explained hereinafter in detail. It is noted that components having the same functions are denoted by the same reference numerals, respectively.

[0079] First Embodiment

[0080] FIG. 1 is a block diagram showing the configuration of an example of a disk storage apparatus of the present invention in the first embodiment.

[0081] In FIG. 1, the numeral 1 indicates a magnetic disk rotated by a spindle motor (not shown); the numeral 2, a magnetic head for recording/reproducing data for the disk 1; and the numeral 3, an arm which moves the head 2 to a target track on the disk 1 by pivoting the head 2 mounted on the one end of the arm 3 around a bearing 4. The numeral 5 indicates a drive coil provided on the rear end of the arm 3; and the numeral 6, a stator (yoke) in which a magnet (a permanent magnet, not shown) is arranged on the surface opposite to the drive coil 5. The stator 6 consists, through a gap, of a pair of opposite yokes, and within the gap, the above-mentioned magnet is fixed to at least one of the yokes. The interaction between the magnetic flux generated by the magnet arranged on the stator 6 and the magnetic field produced by the current conducted through the drive coil 5 causes the arm 3 to be subject to a rotational force. An actuator 7 is configured by the arm 3, the bearing 4, the drive coil 5 and the stator 6.

[0082] The numeral 10 indicates drive means; and the numeral 11, voltage detection means, which is included in the drive means 10, detects a voltage generated across the drive coil 5, and outputs a voltage signal E_d. The numeral 12 indicates disturbance estimation means which estimates a disturbance torque _d exerted on the arm 3 from the voltage signal E_d outputted by the voltage detection means 11 and from a drive signal u as an input of the drive means 10, and outputs a disturbance estimation signal _dest. A position signal of the track, which has been previously recorded as servo information on respective sectors of the disk 1, is read by the head 2. Position detection means 13 detects a current position of the head 2 from the position signal read by the head 2, and produces a position error signal e indicating a difference from a target position r of the target track. Position control means 14 receives the position error signal e produced by the position detection means 13, amplifies and phase compensates the signal, and produces a position control signal c.

[0083] The numeral 16 indicates filter means which cuts off high frequency components of the disturbance estimation signal _dest applied from the disturbance estimation means 12 to correction means 15 and which does not output the high frequency components to the correction means 15 so as to stabilize a positioning control system. The filter means 16 outputs a filter signal f obtained by cutting off the high frequency components from the disturbance estimation signal _dest, to the correction means 15.

[0084] The numeral 15 indicates the correction means which receives the position control signal c from the position control means 14 and the filter signal f from the filter means 16. The correction means 15 performs a correction computation, and then outputs the drive signal u to the drive means 10.

[0085] The drive means 10 is configured such that it conducts a drive current I_a to the drive coil 5 in response to the inputted drive signal u, pivots the arm 3 about the bearing 4 as a center, rotationally moves the head 2 mounted on the top end of the arm 3, and positions, with high accuracy, the head 2 to the target track formed at narrow track pitches in order to record/reproduce data on the disk 1.

[0086] Using FIG. 2, the operation of the positioning control system of the disk storage apparatus in the first embodiment will be explained hereinafter. FIG. 2 is a block diagram showing the whole configuration of the positioning control system of the disk storage apparatus in the first embodiment.

[0087] A portion 30 surrounded with a single-dot chain line in the figure is a block of the disturbance estimation means 12. Similarly, a portion 47 surrounded with a single-dot chain line in the figure is a block of correction means 15. A portion 55 surrounded with a single-dot chain line in the figure is a block of the voltage detection means 11. In FIG. 2, the symbol s indicates Laplace operator. In FIG. 2, hold elements by the sampling of the sector servo are omitted to simplify the explanation.

[0088] In FIG. 2, expressing the current track position detected by the head 2 as x, the position error signal e with respect to the target track position r is expressed by formula 1, which position error signal e is obtained at a comparator (which is also referred to as comparison means) 20.

[0089] The position control means 14 expressed by a block 21 in FIG. 2 applies a digital filter processing of a transfer function Gx (z) to the position error signal e outputted from the comparator 20, produces the position control signal c, and outputs it to the correction means 15 expressed by a block 47. The positioning control system is applied with a normal PID control, and the transfer function of the position control means 14 can be expressed by formula 2: $\begin{array}{cc}{G}_X\left(z\right)=K_X\left\{1+a_d\left(1-z^{-1}\right)+a_1\frac{z^{-1}}{1-z^{-1}}\right\}& \left(2\right)\end{array}$

[0090] Here, the symbol z¹ indicates a one-sample delay, and the symbol K_x indicates a proportional gain of the positioning control system. The coefficients a_d, a_l indicate constants for expressing frequency characteristic, in which the coefficient a_d is a derivative coefficient, while the coefficient a₁ is an integral coefficient. The position control signal c passes through an adder 46, and becomes the drive signal u. The drive signal u is converted from the voltage signal to a g_m-time current signal at the drive means 10 of a block 22 (the transfer function is g_m), where the drive current I_a is outputted. In the actuator 7 expressed by a block 23, the drive current I_a is converted by a transfer function K_t to the drive torque by an interaction between the magnetic field produced by the drive current I_a and the above-mentioned magnetic flux of the stator 6. Here, the transfer function K_t is a torque constant of the actuator 7. A transfer function (L_b/Js) of a block 24 expresses a transfer characteristic from the drive torque exerted on the arm 3 to a moving velocity v of the head 2. Here, the symbol J indicates an inertia moment of the arm 3, and the symbol L_b indicates a distance from the bearing 4 of the arm 3 to the head 2. A block 25 indicates an integrator (which is also referred to as integration means), where the transfer function is expressed by 1/s, and the moving velocity v of the head 2 is converted to the current track position x.

[0091] In the actuator 7, a block 26 outputs an induced voltage E_a generated across the drive coil 5 by the rotation of the actuator 7, while a block 27 outputs a voltage drop (R_aL_as) I_a generated by the conduction of the drive current I_a into the drive coil 5, and outputs a terminal voltage Va of the actuator 7 by adding the induced voltage and the voltage drop to each other at an adder 28. That is, the relationship therebetween is as follows:

[0092] Wherein R_a indicates coil resistance of the drive coil 5 and L_a indicates the inductance of the drive coil 5.

[0093] A disturbance _d exerted on the arm 3 such as a pivot bearing friction of the actuator 7, an elastic force of an FPC connecting the actuator 7 with an electronic circuit board, and an inertia force received by the actuator 7 due to shock or vibration exerted on the disk storage apparatus from the outside can be expressed as a form inputted into the front stage of the block 24 at a comparator 29.

[0094] The portion 55 surrounded with a single-dot chain line in FIG. 2 shows the detail of the voltage detection means 11, which block 55 includes a block 39 having the same transfer function as that of the block 27 included in the actuator 7, and a subtracter 36. The block 39 outputs voltage drop (R_anL_ans)I_a which is generated by conducting the drive current I_a to the drive coil 5, and outputs the drive signal E_d by subtracting the voltage drop from the terminal voltage Va of the actuator 7 using the subtracter 36.

[0095] The portion 30 surrounded with a single-dot chain line in FIG. 2 shows the detail of the disturbance estimation means 12, which block 30 includes a block 32 having the same transfer function as that of the block 22 as the drive means 10, a block 33 having the same transfer function as that of the block 23 as the actuator 7, a block 34 having the same transfer function as that of the block 24, and a block 35 having the same transfer function as that of the block 26. The first multiplier (which is also referred to as multiplication means) 41 is configured by the combination of the block 32 and the block 33. The numeral 43 indicates a first integrator and 44 indicates a second multiplier. The second integrator 42 is configured by the combination of the block 34 and the block 35. Here, respective constants with the suffix n in the block 30 indicate nominal values, and variables with the suffix _est indicate estimates.

[0096] The drive signal u inputted into the block 22 is also inputted into the block 32 constituting the disturbance estimation means 12, and a multiplication of g_mnK_tn times the drive signal u in the block 32 and the block 33 causes the same drive torque estimation signal _est as the drive torque exerted on the arm 3 to be obtained.

[0097] In FIG. 2, a velocity estimation signal v_est is outputted from the block 34. In the block 35, an induced voltage estimation signal E_aest obtained by increasing the velocity estimation signal v_est by K_vn times is inputted into a comparator 37 and is compared with the voltage signal E_d actually detected. A resultant deviation signal (E_aestE_d) is inputted into the first integrator 43 and the second multiplier 44. The first integrator 43 integrates the deviation signal by g₂ times, and outputs a disturbance estimation signal _dest for disturbance. The deviation signal is inputted into the second multiplier 44, and increased by g₁ times, and then added to an adder 38. The output of the adder 38 is inputted into a subtracter 31, where a resultant value obtained by subtracting the output of the adder 38 from the drive torque estimation signal _est outputted from the block 33 is outputted to the block 34.

[0098] A coefficient g₁ of the second multiplier 44 and a coefficient g₂ of the first integrator 43 are constants for stabilizing the operation of the disturbance estimation means 12, the detail of which will be described later.

[0099] In FIG. 2, a block 54 is a block diagram of the filter means 16. The filtermeans 16 expressed by the block 54 subjects the disturbance estimation signal _dest outputted from the disturbance estimation means 12 to a filter processing of a transfer function F(s), generates a filter signal f, and outputs the filter signal f to the correction means 15 expressed by the block 47. The transfer function of the filter means 16 can be expressed by formula 4: $\begin{array}{cc}F\left(s\right)=\frac{1}{1+T_{X}s}& \left(4\right)\end{array}$

[0100] Here, T_x indicates a time constant of a filter and T_x and a filter low-pass cut-off frequency f_x hold the following relationship: $\begin{array}{cc}{T}_X=\frac{1}{2\mathrm{fx}}& \left(5\right)\end{array}$

[0101] In FIG. 1, a state in which the filter signal f is outputted from the filter means 16 to the correction means 15 is shown.

[0102] The filter of the block 54 is to stabilize the operation of the positioning control system of the disk storage apparatus in the first embodiment, the detail of which will be described later.

[0103] In FIG. 2, a block 47 surrounded with a single-dot chain line is a block diagram of the correction means 15. A block 45 included in the correction means 15 produces a correction signal to the drive means 10 required to make the arm 3 generate a drive force having a magnitude equivalent to the disturbance estimation signal _dest by increasing the disturbance estimation signal _dest by 1/(g_mnK_tn) times. The correction signal is added to the position control signal c at an adder 46.

[0104] With reference to FIG. 3, the operation of the disturbance estimation means 12 of the block 30 will be explained hereinafter.

[0105] FIG. 3A is a block diagram obtained by changing the block 30 of FIG. 2, and shows the transfer from the input of the drive signal u to the output of the disturbance estimation signal _dest. FIG. 3B is a block diagram obtained in the block diagram of FIG. 3A by transfer moving equivalently the input position (at the comparator 37) of the voltage signal E_d, thereby transforming the block diagram of FIG. 3A. Here, to simplify the explanation, assuming that the value g_m of the block 22 is equal to the value g_mn of the block 32 in FIG. 2 as shown in the following formula, the drive current I_a (g_mu) is considered to be equal to the estimation current I_aest (g_mnu).

[0106] By increasing the magnitude of the voltage signal E_d by (J_ns)/(L_bnK_vn) times, the input position of the comparator 37 of FIG. 3A can be equivalently move to the input position of a subtracter 48 shown in FIG. 3B.

[0107] Noting the subtracter 48 of FIG. 3B, the value as the output of the subtracter 48 is expressed as shown in formula 7: $\begin{array}{cc}=K_{\mathrm{tn}}{I}_a-\frac{J_{n}s}{L_{\mathrm{bn}}{K}_{\mathrm{vn}}}{E}_a& \left(7\right)\end{array}$

[0108] Here, to simplify the formula 7, assuming that there exists a relationship as shown in formulas 8 and 9 as ideal conditions:

[0109] Noting the subtracter 36 and substituting the formula (3), the voltage signal E_d is expressed by the following formula 10: $\begin{array}{cc}\begin{array}{c}{E}_d=V_a-\left(R_{\mathrm{an}}+L_{\mathrm{an}}s\right)I_a\\ =E_a+\left(R_a+L_{a}s\right)I_a-\left(R_{\mathrm{an}}+L_{\mathrm{an}}s\right)I_a\\ =E_a\end{array}& \left(10\right)\end{array}$

[0110] Then, noting the comparator 29, and the blocks 24 and 26 of FIG. 2, there exists a relationship as shown in the formula 11: $\begin{array}{cc}{E}_a=\frac{L_b{K}_v}{Js}\left(K_t{I}_a-d\right)& \left(11\right)\end{array}$

[0111] Here, assuming the relationships shown in formulas 12 and 13 as ideal conditions, and substituting the formulas 10, 6, and 7 in the formula 7, the formula 7 is transformed as shown in the formula 14:

K_tK_th(12) $\begin{array}{cc}\frac{L_b{K}_v}{J}=\frac{L_{\mathrm{bn}}{K}_{\mathrm{vn}}}{J_n}& \left(13\right)\end{array}$ _d(14)

[0112] d

[0113] That is, the value as the output of the subtracter 48 is equal to the disturbance _d exerted on the arm 3.

[0114] Therefore, determining a transfer function from the disturbance _d exerted on the arm 3 to the disturbance estimation signal _dest, the function is obtained as shown in the formula 15: $\begin{array}{cc}{}_{\mathrm{dest}}=\frac{\frac{L_{\mathrm{bn}}}{J_n}{K}_{\mathrm{vn}}{g}_2}{s^2+\frac{L_{\mathrm{bn}}}{J_n}{K}_{\mathrm{vn}}{g}_{1}s+\frac{L_{\mathrm{bn}}}{J_n}{K}_{\mathrm{vn}}{g}_2}{}_d& \left(15\right)\end{array}$ $\mathrm{dest}=\frac{\frac{\mathrm{Lbn}}{\mathrm{Jn}}\mathrm{Kvn}\mathrm{g2}}{s^2+\frac{\mathrm{Lbn}}{\mathrm{Jn}}\mathrm{Kvn}\mathrm{g1}s+\frac{\mathrm{Lbn}}{\mathrm{Jn}}\mathrm{Kvn}\mathrm{g2}}d$

[0115] From the formula 15, the disturbance estimation means 12 is understood that the actual disturbance _d can be estimated in a secondary delay system from the drive signal u and the voltage signal E_d by the loop in the block 30 surrounded with a single-dot chain line of FIG. 2.

[0116] Here, expressing the natural angular frequency (estimated angular frequency) of the secondary delay system as ₀ and the damping factor as ₀, the constants g₁ and g₂ to stabilize the operation of the disturbance estimation means 12 are expressed by the following formulas 16 and 17, respectively: $\begin{array}{cc}{g}_1=2{}_o{}_o\frac{J_n}{L_{\mathrm{bn}}{K}_{\mathrm{vn}}}& \left(16\right)\\ \begin{array}{c}{g}_2={}_o^2\frac{J_n}{L_{\mathrm{bn}}{K}_{\mathrm{vn}}}\\ \mathrm{g2}=o^2\frac{J_n}{L_{\mathrm{bn}}{K}_{\mathrm{vn}}}\end{array}& \left(17\right)\end{array}$

[0117] Here, setting the estimated angular frequency ₀ at a value higher than a position control band fc, and selecting the damping factor as ₀ as 0.7 through 1, the disturbance _d such as a pivot bearing friction, an elastic force and an inertia force can be correctly estimated by the disturbance estimation means 12.

[0118] Transforming the formula 15 by the use of the formulas 16 and 17, the following formula 18 is obtained: $\begin{array}{cc}\begin{array}{c}{}_{\mathrm{dest}}=\frac{{}_O^2}{s^2+2{}_O{}_{O}s+{}_O^2}{}_d\\ d_{\mathrm{est}}=\frac{o^2}{s^2+2oos+o^2}d\end{array}& \left(18\right)\end{array}$

[0119] That is, the block diagram of the disturbance estimation means 12 of FIG. 3A can be simplified as shown in a block 52 of FIG. 3C.

[0120] With reference to FIG. 4, the operation of the correction means 15 shown in the block 47 will be explained in detail hereinafter, on the assumption that the transfer function F(s) of the filter means 16 is 1 to simplify the explanation. This corresponds to the operation of the positioning control system with a basic configuration in which the filter means 16 is not provided between the disturbance estimation means 12 and the correction means 15.

[0121] The block 47 of a portion surrounded with a single-dot chain line of FIG. 2 indicates the detail of the correction means 15. The block 45 outputs the correction signal obtained by increasing the disturbance estimation signal _dest by 1/(g_mnK_tn) times to the adder 46. That is, by increasing the disturbance estimation signal _dest by 1/(g_mnK_tn) times, the correction signal required to make the actuator 7 generate a drive force having a magnitude equivalent to the disturbance estimation signal _dest is outputted to the adder 46. Further, the correction signal is increased g_mnK_tn times by the blocks 22 and 23, so that the disturbance estimation signal _dest is previously increased 1/(g_mnK_tn) times to match the magnitude with each other.

[0122] Concluding the above explanation, it can be said that the disk storage apparatus of the first embodiment is configured such that the disturbance estimation signal _dest is made to be exerted on the actuator 7 in a manner to negate the disturbance _d due to a pivot bearing friction of the actuator 7, an elastic force of FPC connecting the actuator 7 with an electronic circuit board, an inertia forces exerted on the actuator 7 by a shock or vibration exerted on the disk storage apparatus from the outside, and the like.

[0123] FIG. 4A is a block diagram obtained by picking portions from the adder 46 to the comparator 29, and the block 24 relating the operation of the correction means 15. FIG. 4B is a block diagram in which the disturbance _d exerted on the comparator 29 and the one exerted on a block 52 are integrated into one disturbance _d. Components having the same function as those in the block diagram of FIG. 2 are indicated by the same symbols to omit a duplicated explanation.

[0124] In the block diagram of FIG. 4A, the block 52 is equivalent to the block 52 of FIG. 3C, and has a transfer function expressed by the formula 15.

[0125] Therefore, from FIG. 4B, the disturbance _d exerted on the arm 3 from the outside can be considered to be exerted through a filter expressed by a transfer function of the formula 19 on the head positioning control system. $\begin{array}{cc}\begin{array}{c}{G}_d\left(s\right)=1-\frac{{}_O^2}{s^2+2{}_O{}_{O}s+{}_O^2}\\ =\frac{s^2+2{}_O{}_{O}s}{s^2+2{}_O{}_{O}s+{}_O^2}\\ G_d\left(s\right)=1-\frac{{}_o^2}{s^2+2{}_o{}_{o}s+{}_o^2}\\ =\frac{s^2+2{}_o{}_{o}s}{s^2+2{}_o{}_{o}s+{}_o^2}\end{array}& \left(19\right)\end{array}$

[0126] FIG. 5 shows the frequency characteristic of a transfer function G_d(s) expressed by the formula 19 as a polygonal line approximation. From the frequency characteristic of the transfer function G_d(s) shown in FIG. 5, at an angular frequency lower than the angular frequency ₀ the gain is 0 dB or less, and as the angular frequency drops, the gain is damped at a damping ratio of 20 dB/decade. The decade means ten times. That is, from FIG. 5, transfer function G_d(s) has a low frequency cut-off filter characteristic capable of inhibiting a frequency lower than the angular frequency ₀.

[0127] That is, the disk storage apparatus of the first embodiment is configured such that even when the disturbance _d due to a pivot bearing friction, an elastic force, an inertia force or the like is exerted on the arm 3, the disturbance _d is estimated by the disturbance estimation means 12, and controlled in a manner to negated the disturbance _d exerted from the outside with the disturbance estimation signal _dest. Therefore, the disturbance _d exerted from the outside acts as if the disturbance _d is exerted through a filter having the cut-off frequency characteristic of the formula 19 and FIG. 5 on the head positioning control system.

[0128] Therefore, at a frequency lower than the angular frequency ₀, the first-order low frequency cut-off characteristic can inhibit the disturbance due to a pivot bearing friction of the actuator 7, an elastic force of FPC connecting the actuator 7 with an electronic circuit board, an inertia forces exerted on the actuator 7 by a shock or vibration exerted on the disk storage apparatus from the outside, and the like.

[0129] That is, even when a vibration or a shock is applied to the apparatus to cause the disturbance _d to be exerted on the actuator 7, the disturbance _d is estimated by the disturbance estimation means 12, and controlled in a manner to negated the disturbance _d exerted from the outside, so that there is an effect as if the disk storage apparatus is provided with a mechanical vibration-proof mechanism.

[0130] FIGS. 6A to 6C are time response waveform views for explaining the disturbance inhibiting effect of the disturbance estimation means 12 of the disk storage apparatus in the first embodiment in more detail.

[0131] FIG. 6A shows a waveform 61 (shown by the broken line) of the disturbance _d due to an inertia force exerted on the actuator 7 and a waveform 62 of the disturbance estimation signal _dest outputted by the disturbance estimation means 12 when a half-sine wave-shaped rotational shock with the maximum angular acceleration d₀/dt of 5000 radian/sec² is exerted on the disk storage apparatus from the outside. Expressing an inertia moment J about the bearing 4 of the actuator 7 as 0.1 gcm², the maximum value of the disturbance _d becomes as follows: $\begin{array}{cc}\begin{array}{c}{}_{d\max }=J\frac{{}_O}{t}\\ =500\mathrm{dyn}\mathrm{cm}\\ d_{\max }=J\frac{{}_o}{t}\end{array}& \left(20\right)\end{array}$

[0132] Here, selecting the values of an estimation frequency f_o (_o2f_o) and a damping factor ₀ for determining control parameters of the formulas 16 and 17 as 3 kHz and 1, respectively, and setting the control band of the positioning control system at 800 Hz, a simulation has been performed.

[0133] The disturbance estimation means 12 estimates the disturbance torque _d exerted on the actuator 7 from the drive signal u as the input of the drive means 10 and from the voltage signal E_d outputted by the voltage detection means 11, and outputs the disturbance estimation signal _dest substantially similar to the actual disturbance _d, though a little time delay exists.

[0134] FIG. 6B shows a waveform 64 of the drive current I_a when the disturbance estimation signal _dest has been exerted on the actuator 7 in a manner that the disturbance estimation signal _dest outputted by the disturbance estimation means 12 is inputted into the correction means 15 to negate a fluctuation due to the disturbance _d, and shows a simulation result of a waveform 63 of the drive current I_a when the disturbance estimation signal _dest is not inputted into the correction means 15. The torque constant K_t of the actuator 7 is 23 dyncm/mA.

[0135] Servo information recorded on the disk 1 has been recorded on the disk in a discrete condition having a certain sampling period, so that the head position signal is not a continuous signal. Therefore, the position control signal c of the position control means 14 for implementing digital processing is changed into a step-shaped one. As a result, the waveform of the drive current I_a of the actuator 7 when the disturbance estimation signal _dest is not inputted into the correction means 15 becomes the same waveform as that of the position control signal c, so that the waveform is changed into a step-shaped one as shown in the waveform 63 of FIG. 6B (I_ag_mcg_mu). The waveform 64 of the drive current I_a of the actuator 7 when the disturbance estimation signal _dest has been inputted into the correction means 15 is produced by adding the disturbance estimation signal _dest of the disturbance estimation means 12 to the control signal c of the position control means 14 by the correction means 15, so that the time delay thereof from a point (t0) when a rotational shock is exerted on the disk storage apparatus is smaller than that of the waveform 63 of FIG. 6B. In addition, the waveform 64 is changed smoothly.

[0136] FIG. 6C shows a waveform 66 of the track position error signal e when the disturbance estimation signal _dest has been exerted on the actuator 7 in a manner that the disturbance estimation signal _dest outputted by the disturbance estimation means 12 is inputted into the correction means 15 to negate a fluctuation due to the disturbance, and shows a simulation result of a waveform 65 of the position error signal e when the disturbance estimation means 12 is not applied. Even when a half-sine wave-shaped rotational shock is exerted on the disk storage apparatus from the outside, if the disturbance estimation means 12 is applied, the position error signal e is not largely fluctuated as with the waveform 66, so that compared to the waveform 65 when the disturbance estimation means 12 is not applied, the disturbance inhibiting effect has been improved.

[0137] As a result, the disk storage apparatus of the first embodiment correctly detects the disturbance due to an inertia force exerted on the actuator 7 by a vibration or a shock exerted from the outside by the use of the disturbance estimation means 12 to allow a track dislocation due to the disturbance to be inhibited, whereby the head 2 is controlled at a high accuracy to be positioned to the target track. Therefore, the tracking control stable against the shock or vibration can be implemented, thereby improving the reliability of the disk storage apparatus.

[0138] FIGS. 7A and 7B are open loop frequency characteristic views showing the transfer from the position error signal e to a head position x in the block diagram of the positioning control system of the disk storage apparatus of the first embodiment shown in FIG. 2. As can be understood from the gain characteristic view of FIG. 7A, a gain crossover frequency f_c with which the open loop gain becomes zero is 800 Hz. In addition, as can be understood from the phase characteristic view of FIG. 7B, with the gain crossover frequency f_c, a phase margin _m is 50 degrees, thus constituting a stable head positioning control system. The reason is as follows. In the block 55 of the voltage detection means 11 surrounded with a single-dot chain line shown in FIG. 2, the block 39 with the voltage drop (R_anL_ans) is faithfully expressed to obtain the voltage drop of a coil resistance R_an and a coil inductance L_an generated by conducting the drive current I_a to the drive coil 5. Using the formula 10, the voltage signal E_d of the voltage detection means 11 is the pure output of a induced voltage E_a induced across the drive coil 5 by the rotation of the actuator 7.

[0139] Actually, however, since the coil inductance L_an is lower than the coil resistance R_an, it is difficult to accurately configure a circuit. Further, since L_ans is a derivative element, it tends to be particularly influenced by noise and attention should be particularly taken to configure a circuit.

[0140] FIGS. 8A and 8B are open loop frequency characteristic views showing the transfer from the position error signal e to the head position x if only the voltage drop of the coil resistance R_an is considered among those generated by conducting the drive current I_a to the drive coil 5 while ignoring the voltage drop of the coil inductance L_an in the block 39 included in the voltage detection means 11 in the block diagram of the positioning control system shown in FIG. 2.

[0141] As is obvious from the gain characteristic view of FIG. 8A and the phase characteristic view of FIG. 8B, if the coil inductance L_an of the drive coil 5 is omitted for simplification in the block 39 included in the voltage detection means 11, the head positioning control system including the disturbance estimation means 12 becomes unstable. That is, as can be understood from the gain characteristic view of FIG. 8A, the gain crossover frequency fc with which the open loop gain becomes zero is 900 Hz and the phase at that time is a lag phase from 180 degrees, so that the control system becomes unstable. The voltage drop caused by the coil inductance L_an included in the drive coil 5 is smaller than that caused by the coil resistance R_an. However, the term (L_ans) included in the block 39 included in the voltage detection means 11 is an important element to stabilize the positioning control system shown in FIG. 2.

[0142] The positioning control system shown in FIG. 2 becomes unstable if the term (L_ans) included in the block 39 is omitted for the following reason. Although the actual drive coil 5 contains the component of the coil resistance R_a and that of the coil inductance L_a, the voltage detection means 11 does not include the component of the coil inductance L_an. Therefore, to stabilize the positioning control system, the coil inductance of the drive coil 5 may be made equivalently zero.

[0143] FIG. 9 shows a circuit configuration to stabilize the positioning control system, in which a circuit having a capacitor C and a resistor r connected in series is connected to the drive coil 5 in parallel. In FIG. 9, a composite impedance Z_a if the circuit having the capacitor C and the resistor r connected in series is connected to the drive coil 5 in parallel is expressed by the following formula 21. In the formula 21, R_a indicates the coil resistance of the drive coil 5 and L_a indicates the inductance thereof. $\begin{array}{cc}{Z}_a=\frac{\left(R_a+L_{a}s\right)\left(r+\frac{1}{Cs}\right)}{R_a+r+L_{a}s+\frac{1}{Cs}}& \left(21\right)\end{array}$

[0144] Selecting the values of the resistor r and the capacitor C as shown in formulas 22 and 23, respectively, Za in the formula 21 can be expressed by formula 24.

rR_a(22) $\begin{array}{cc}C=\frac{L_a}{R_a^2}& \left(23\right)\end{array}$ Z_aR_a(24)

[0145] That is, if the values of the resistor r and the capacitor C which constitute the circuit shown in FIG. 9 are set at those shown in the formulas 22 and 23, respectively, the composite impedance Z_a generated across the drive coil 5 is equal to a resistance R_a as seen in the formula 24, so that the drive coil 5 does not equivalently include the coil inductance L_a. Therefore, as shown in FIG. 9, by connecting the circuit having the resistor r and the capacitor C connected in series, to the drive coil 5 in parallel, it suffices to consider only the voltage drop caused by the coil resistance R_an generated by the conductance of the drive current I_a to the drive coil 5 in the block 39 included in the voltage detection means 11 in the block diagram of the positioning control system shown in FIG. 2, and to use a block 49 shown in FIG. 10 instead of the block 39 included in the voltage detection means 11 shown in FIG. 2. As a result, it is possible to configure the voltage detection means 11 more simply.

[0146] In FIGS. 8A and 8B, waveforms indicated by dotted lines are open loop frequency characteristics which show the transfer from the position error signal e to the head position x if the block 39 is replaced by the block 49 shown in FIG. 10 and if the circuit having the resistor r and the capacitor C, expressed by the formulas 22 and 23, respectively, connected in series is connected in parallel to the drive coil 5 of the actuator 7 across the coil 5, in the block diagram of the positioning control system of the disk storage apparatus of the first embodiment shown in FIG. 2. As can be understood from FIGS. 8A and 8B, the open loop frequency characteristics are almost equal to those shown in FIGS. 7A and 7B.

[0147] In the above-mentioned explanation, the stability of the positioning control system if the coil resistance R_an of the block 49 included in the voltage detection means 11 is equal to the coil resistance R_a of the drive coil 5 of the actuator 7, i.e., the formula 8 (R_aR_an) is satisfied and the transfer function F(s) of the filter means 16 is 1, is shown.

[0148] However, the coil resistance R_a of the drive coil 5 of the actuator 7 has a fluctuation of resistance value and the resistance value is changed following temperature rise after a drive current I_a is carried to the drive coil 5 to heat the drive coil 5. Therefore, even if the coil resistance R_a of the drive coil 5 of the actuator 7 is initially equal to a nominal value R_an, the resistance value of the drive coil 5 is changed by the temperature rise during the operation, with the result that the formula 8 (R_aR_an) is not satisfied.

[0149] In FIGS. 11A and 11B, waveforms indicated by solid lines are open loop frequency characteristics which show the transfer from the position error signal e to the head position x if the coil resistance R_a of the drive coil 5 of the actuator 7 is not equal to the nominal value R_an, in the block diagram of the positioning control system shown in FIG. 2. In a simulation, the component of a coil inductance L_an is omitted in the block 39 included in the voltage detection means 11, and frequency characteristics if the coil resistance R_a of the drive coil 5 of the actuator 7 is larger than the nominal value R_an by 5% is obtained while the circuit having the resistor r and the capacitor c connected in series and determined by the formulas 22 and 23 is connected in parallel to the drive coil (FIG. 9). That is, as can be understood from the gain characteristic view of FIG. 11A, the gain crossover frequency fc with which the open loop gain becomes zero is 500 Hz. As shown in FIG. 11B, phase at that time is approximately 180 degrees. Because of insufficient phase margin, the control system is unstable.

[0150] Next, the significance of providing the filter means 16 between the disturbance estimation means 12 and the correction means 15 will be described.

[0151] In the disk storage apparatus in the first embodiment shown in FIG. 2, if the disturbance estimation signal _dest outputted from the disturbance estimation means 12 is applied to the positioning control system as it is through the correction means 15 while the coil resistance R_a of the drive coil 5 of the actuator 7 is not equal to the nominal value R_an, the positioning control system becomes unstable. To stabilize the positioning control system, therefore, the disturbance estimation signal _dest outputted from the disturbance estimation means 12 expressed by the block 30 in FIG. 2 is outputted to the correction means 15 of the block 47 through the filter means 16 of the block 54.

[0152] The filter means 16 conducts filter processing as expressed by the transfer function F(s) of the formulas 4 and 5, produces a filter signal f, and inputs the filter signal into the correction means 15. That is, the high frequency components higher in frequency than the filter low-pass cut-off frequency f_x are cut off by the filter means 16. As a result, the high frequency components of the disturbance estimation signal _dest outputted from the disturbance estimation means 12 are not equivalently outputted to the correction means 15. That is the significance of providing the filter means 16 between the disturbance estimation means 12 and the correction means 15. The significance will be described concretely below.

[0153] In FIGS. 11A and 11B, waveforms indicated by dotted lines are open loop frequency characteristics which show the transfer from the position error signal e to the head position x if the disturbance estimation signal _dest outputted from the disturbance estimation means 12 is outputted to the correction means 15 of the block 47 through the filter means 16 of the block 54, in the block diagram of the positioning control system of the disk storage apparatus in the first embodiment shown in FIG. 2.

[0154] In a simulation, frequency characteristics if the filter low-pass cut-off frequency f_x is set at 400 Hz in the block 54 showing the filter means 16, and the coil resistance R_a of the drive coil 5 of the actuator 7 is higher than the nominal value R_an by 5%. As can be understood from the gain characteristic view of FIG. 11A, the gain crossover frequency fc with which the open loop gain becomes zero is 500 Hz. In addition, as can be understood from the phase characteristic view of FIG. 11B, with the gain crossover frequency fc, the phase margin _m is 40 degrees, thus constituting a stable head positioning control system.

[0155] That is, by inserting the filter means 16 between the output of the disturbance estimation means 12 and the input of the correction means 15, it is possible to stabilize the positioning control system even if the coil resistance R_a of the drive coil 5 of the actuator 7 is not equal to the nominal value R_an due to the change of the resistance value by the resistance fluctuation or temperature rise.

[0156] The disk storage apparatus of the first embodiment explained above is configured such that the drive signal u outputted from the block 47 is inputted as one of the input signals for the disturbance estimation means 12. Needless to say, the same effect can be attained even if the drive current I_a outputted from the drive means 10 outputted from the block 22 instead of the drive signal u is used.

[0157] Second Embodiment

[0158] FIG. 12 is a block diagram showing the configuration of a magnetic disk storage apparatus which is one example of a disk storage apparatus in the second embodiment according to the present invention. FIG. 13 is a block diagram showing the whole configuration of a head positioning control system in the magnetic disk storage apparatus in the second embodiment. It is noted that components having the same functions as those in the first embodiment are denoted by the same reference numerals, respectively and will not be repeatedly explained.

[0159] The disk storage apparatus in the second embodiment of FIG. 12 is different from that in the first embodiment of FIG. 1 in a signal inputted into the disturbance estimation means. While the first embodiment of FIG. 1 has been configured such that the voltage signal E_d and the drive signal u produced by the voltage detection means 11 are inputted into the disturbance estimation means 12, in the second embodiment of FIG. 12, the voltage signal E_d produced by the voltage detection means 11 and the position control signal c produced by the position control means 14 are inputted into disturbance estimation means 17.

[0160] The disturbance estimation signal _dest produced by the disturbance estimation means 17 of FIG. 12 is inputted into the correction means 15 through the filter means 16. The correction means 15, into which the position control signal c outputted from the position control means 14, the disturbance estimation signal _dest produced by the disturbance estimation means 17, and the filter signal f passing through the filter means 16 are inputted, implements a correction computing and then outputs the drive signal u to the drive means 10.

[0161] The block 60 surrounded with a single-dot chain line in FIG. 13 is a block diagram of the disturbance estimation means 17. Inputted into the disturbance estimation means 17 are the voltage signal E_d produced by the voltage detection means 11 as the output of the adder 36 and the position control signal c produced by the position control means 14 expressed by the block 21.

[0162] In the above-mentioned disturbance estimation means 12 of the first embodiment, the computing has been implemented as follows: A signal obtained by multiplying a deviation signal from a comparator 37 by the coefficient g₂/s of the first integrator 43, and a signal obtained by multiplying a deviation signal by the coefficient g₁ of the second multiplier 44 are added to each other at the adder 38. A signal obtained by the addition and the drive torque estimation signal _est produced by multiplying a drive signal u by the coefficient g_mnK_tn of the first multiplier 41 are inputted into the subtracter 31. The signal obtained by the subtraction of the subtracter 31 has been inputted into the second integrator 42. That is, the drive signal u obtained by adding the correction signal to the control signal c has been inputted into the disturbance estimation means 12, so that the adder 38 of FIG. 2 has been required.

[0163] However, the disturbance estimation means 17 of the second embodiment is configured such that the position control signal c is inputted before the correction signal is added, so that the adder 38 as shown in FIG. 2 is not required.

[0164] Compared to the operation of the disturbance estimation means 12 of the first embodiment, the operation of the disturbance estimation means 17 of the disk storage apparatus of the second embodiment configured as explained above will be explained hereinafter referring to FIGS. 2 and 13.

[0165] First, in FIG. 2, expressing the input of the second integrator 42 constituting the disturbance estimation means 12 of the first embodiment as , by noting the subtracter 31, the signal is expressed as follows:

[0166] While by noting the adder 46 of FIG. 2, the drive signal u is expressed by the formula 26: $\begin{array}{cc}\begin{array}{c}u=c+\\ =c+\frac{1}{g_{\mathrm{mn}}{K}_{\mathrm{th}}}{}_{\mathrm{dest}}\\ u=c+\\ =c+\frac{1}{g_{\mathrm{mn}}{K}_{\mathrm{tn}}}{d}_{\mathrm{est}}\end{array}& \left(26\right)\end{array}$

[0167] Therefore, from the formulas 25 and 26, the signal can be expressed by the formula 27:

[0168] Based on the formula 27, the block diagram 30 of the disturbance estimation means 12 of the first embodiment shown in FIG. 2 is changed to the block diagram 60 of the disturbance estimation means 17 shown in FIG. 13. As shown in FIG. 13, the position control signal c produced by the position control means 14 (block 21) is inputted into the multiplier 32, and the output of the multiplier 32 is inputted into the multiplier 33. Hence, multiplying the position control signal c by the coefficient g_mnK_tn allows the drive torque estimation signal _est to be obtained.

[0169] On the other hand, the disturbance estimation signal _dest is inputted into the correction means 15 expressed by the block 47 through the filter means 16 expressed by the block 54. Therefore, similarly the first embodiment, the disk storage apparatus of the second embodiment estimates the disturbance torque acting on the arm 3 from the voltage signal E_d produced by the voltage detection means 11 and the position control signal c produced by the position control means 14, and outputs the disturbance estimation signal _dest by the function of the disturbance estimation means 17. The disturbance estimation signal _dest is inputted into the correction means 15 so as to negate the disturbance _d such as a pivot bearing friction, an elastic force, and an inertia force exerted on the arm 3.

[0170] Further, similarly to the disk storage apparatus of the first embodiment, since the filter means 16 is inserted between the output of the disturbance estimation means 17 and the input of the correction means 15, it is possible to stabilize the positioning control system even if the coil resistance R_a of the drive coil 5 of the actuator 7 is not equal to the nominal value R_an due to the change of the resistance value by the resistance fluctuation or temperature rise.

[0171] Therefore, the disk storage apparatus of the second embodiment can correctly detect the disturbance such as an inertia force acting on the actuator 7 due to shock/vibration applied from the outside by the disturbance estimation means 17. This disk storage apparatus is configured such that even if the disturbance _d acts on the actuator 7, such as pivot bearing friction, an elastic force of the FPC, and an inertia force due to shock/vibration exerted from the outside, the disturbance estimation means 17 is controlled to estimate this disturbance _d and the disturbance _d exerted from the outside is negated by the disturbance estimation signal _dest thus estimated. Therefore, similarly to the first embodiment, the disturbance _d exerted from the outside acts as if the disturbance _d is exerted through a filter having the cut-off frequency characteristic of the formula 19 and FIG. 5 on the positioning control system. Hence, according to the disk storage apparatus of the second embodiment, with a frequency lower than the angular frequency ₀, it is possible to inhibit the disturbance by the first-order low frequency cut-off characteristic, and to inhibit a track dislocation due to the disturbance, whereby the head 2 is controlled at a high accuracy to be positioned to the target track. Therefore, the tracking control stable against the shock or vibration can be implemented, thereby improving the reliability of the disk storage apparatus.

[0172] As can be seen, according to the disk storage apparatus of the second embodiment, the number of adders required to constitute the disturbance estimation means 17 can be reduced compared with the disk storage apparatus of the first embodiment. Therefore, compared with the first embodiment, the disk storage apparatus of the second embodiment can estimate the disturbance _d acting on the arm 3 such as a pivot bearing friction, an elastic force and an inertia force acting on the head positioning control system as the disturbance, by simple configuration, stably control head positioning, and position the head 2 to the target track formed at narrow track pitches with high accuracy.

[0173] Furthermore, according to the disk storage apparatus of the second embodiment, the number of the adders can be reduced, so that when the positioning control system is embodied with a hardware such as an analog circuit, the adjustment of such circuit can be simplified. Further, when the positioning control system is embodied with a software, the computing time delay by computing process can be shortened.

[0174] The disturbance estimation means 12 configured similarly to the block 30 shown in FIG. 2, is not affected by the sampling frequency of the sector servo of the disk storage apparatus. Therefore, the control band of the disturbance estimation means 12 can be set higher than that of the positioning control system.

[0175] Moreover, according to the disk storage apparatus of the second embodiment, the number of the adders constituting the disturbance estimation means 17 can be reduced. Therefore, when the control system is embodied with a hardware such as an analog circuit, the adjustment of such circuit can be simplified. Further, when the control system is embodied with a software, the computing time delay by computing process can be shortened, thereby making it possible to set the control band higher.

[0176] Additionally, according to the disk storage apparatus of the second embodiment, by inserting the filter means 16 between the output of the disturbance estimation means 12 and the input of the correction means 15, it is possible to stabilize the positioning control system even if the coil resistance R_a of the drive coil 5 of the actuator 7 is not equal to the nominal value R_an due to the change of the resistance value by the resistance fluctuation or temperature rise.

[0177] Third Embodiment

[0178] FIG. 14 is a block diagram showing the configuration of a magnetic disk storage apparatus which is one example of a disk storage apparatus in the third embodiment according to the present invention. FIG. 15 is a block diagram showing the whole configuration of the positioning control system of the magnetic disk storage apparatus in the third embodiment. In the third embodiment, the filter means 16 and the block 54 having the transfer function F(s) in the first embodiment are not provided. Disturbance estimation means 12A and correction means 15A partially differ from the disturbance estimation means 12 and cosrrection means 15 in the first embodiment. The configurations of the other components are the same as those in the first embodiment shown in FIGS. 1 and 2. It is noted that components or members having the same functions as those shown in the first embodiment are denoted by the same numerals, respectively and will not be repeatedly explained herein.

[0179] Next, the operation of the positioning control system of the disk storage apparatus in the third embodiment will be explained hereinafter.

[0180] In FIGS. 16A and 16B, waveforms indicated by broken lines are open loop frequency characteristics which show the transfer from the position error signal e to the head position x if the coil resistance R_a of the drive coil 5 of the actuator 7 is not equal to the nominal value R_an, in the block diagram of the positioning control system shown in FIG. 15. In a simulation, frequency characteristics if the component of the coil inductance L_an is omitted in the block 39 included in the voltage detection means 11 and if the coil resistance R_a of the drive coil 5 of the actuator 7 is larger than the nominal value R_an by 5%, is obtained. That is, as can be understood from the gain characteristic view indicated by a broken line in FIG. 16A, the gain crossover frequency f_C with which the open loop gain becomes zero is 300 Hz and the phase is almost equal to 210 degrees. Because of lack of phase margin, the positioning control system is unstable.

[0181] Next, explanation will be given to a case where the gain crossover frequency with which the open loop gain becomes zero is greatly decreased from that shown in FIG. 7 (R_aR_an) if the coil resistance R_a of the drive coil 5 of the actuator 7 is higher than the nominal value R_an by 5%.

[0182] If the coil resistance R_a of the drive coil 5 of the actuator 7 is not equal to the nominal value R_an, the voltage signal E_d is expressed by the following formula 28:

[0183] That is, the coil resistance R_a of the drive coil 5 of the actuator 7 is not equal to the nominal value R_an due to the change of the resistance value caused by the resistance fluctuation or temperature rise, the voltage signal E_d of the voltage detection means 11 is equal to the output of the addition result of adding the induced voltage E_a induced across the drive coil 5 by the rotation of the actuator 7 to the voltage drop (R_aR_an)I_a generated by the conduction of the drive current I_a into the drive coil 5.

[0184] FIGS. 17A and 17B are block diagrams for explaining that the gain changes if the coil resistance R_a of the drive coil 5 of the actuator 7 is not equal to the nominal value R_an due to the change of the resistance value caused by the resistance fluctuation or temperature rise.

[0185] FIG. 17A is a block diagram obtained by changing the block diagram of FIG. 3B while noting the second term of the formula 28. FIG. 17B is a block diagram equivalently transformed from the block diagram of FIG. 17A. FIG. 17C is a block diagram obtained by changing a part of the block diagram of FIG. 15 based on the block diagram of FIG. 17B. That is, if R_a is not equal to R_an, this is equivalent to the addition of the negative feedback loop of the blocks 54, 52 and 45 to the block 22 (the transfer function is g_m) in the block diagram of FIG. 15.

[0186] In the block diagram of FIG. 17C, the composite transfer frequency G_m(s) from the position control signal c to the drive current I_a is expressed by the following formula 29. $\begin{array}{cc}{G}_m\left(s\right)=\frac{g_m}{1+\frac{g_m}{g_{\mathrm{mn}}}\frac{J_n\left(R_a-R_{\mathrm{an}}\right)}{L_{\mathrm{bn}}{K}_{\mathrm{vn}}{K}_{\mathrm{th}}}\frac{{}_O^2}{s^2+2{}_O{}_{O}s+{}_O^2}s}& \left(29\right)\end{array}$

[0187] In the formula 29, the estimation frequency f_o (_o/2) is set sufficiently higher than the position control band f_c, so that formula 30 is established. As a result, the formula 29 can be simplified to formula 31. $\begin{array}{cc}\frac{{}_O^2}{s^2+2{}_O{}_{O}s+{}_O^2}=1& \left(30\right)\\ G_m\left(s\right)=\frac{g_m}{1+\frac{g_m}{g_{\mathrm{mn}}}\frac{J_n\left(R_a-R_{\mathrm{an}}\right)}{L_{\mathrm{bn}}{K}_{\mathrm{vn}}{K}_{\mathrm{th}}}s}& \left(31\right)\end{array}$

[0188] In the formula 31, at R_aR_an, G_m(s)g_m; however, at R_aR_an, the gain G_m(s) decreases.

[0189] Here, if g_mn is substituted as shown in the following formula 32, the formula 31 is transformed to formula 33.

g_mnkg_m(32) $\begin{array}{cc}{G}_m\left(s\right)=\frac{g_m}{1+\frac{1}{k}\frac{J_n\left(R_a-R_{\mathrm{an}}\right)}{L_{\mathrm{bn}}{K}_{\mathrm{vn}}{K}_{\mathrm{th}}}}& \left(33\right)\end{array}$

[0190] Here, selecting, as the coefficient k of a real number, a number sufficiently greater than 1 (k>>1), the term including (R_aR_an) in the denominator of the formula 33 can be regarded as 0. Even if R_aR_an, the formula 33 can be expressed by formula 34 by approximation.

[0191] As stated above, according to the third embodiment, even if the coil resistance R_a of the drive coil 5 of the actuator 7 is not equal to the nominal value R_an due to the change of the resistance value by the resistance fluctuation or temperature rise, the composite transfer function G_m(s) from the position control signal c to the drive current I_a does not change and the formula 34 is always established by setting the coefficient k of the actual number sufficiently greater. The significance of this formula is that it does not include R_a and R_an. Therefore, even if the coil resistance R_a changes due to the resistance fluctuation or temperature rise, the open loop gain of the positioning control system does not greatly change, making it possible to stabilize the positioning control system.

[0192] In FIGS. 16A and 16B, waveforms indicated by solid lines are open loop frequency characteristics which show the transfer from the position error signal e to the head position x if the coefficient k of the formula 32 is 50 in the block diagram of the positioning control system shown in FIG. 15. In a simulation, similarly to the cases indicated by broken lines (k1) in FIGS. 16A and 16B, frequency characteristics are obtained if the coil resistance R_a of the drive coil 5 of the actuator 7 is higher than the nominal value R_an by 5%. As can be understood from the gain characteristic view indicated by the solid line in FIG. 16A, the gain crossover frequency f_C with which the open loop gain becomes zero is 800 Hz. In addition, as can be understood from the phase characteristic view indicated by the solid line in FIG. 16B, with the gain crossover frequency f_C, the phase margin _m is 50 degrees, thus constituting a stable head positioning control system.

[0193] That is, setting the coefficient g_mn of the block 32 in the block 30A of the disturbance estimation means 12A and the coefficient g_mn of the denominator of the block 45 of the correction means 15A shown in FIG. 15 to be k times (k>>1) of the transfer function g_m of the block 22, it is possible to stabilize the positioning control system even if the coil resistance R_a of the drive coil of the actuator 7 is not equal to the nominal value R_an due to the change of the resistance value by the resistance fluctuation or temperature rise.

[0194] In the block 30A of the disturbance estimation means 12A in FIG. 15, the block 32 of the first multiplier 41 into which the drive signal u is inputted has a coefficient g_mn, meaning that the block 32 multiplies the drive signal u by g_mn. This g_mn is expressed by approximation (g_mnkg_mn) in the formula 32.

[0195] Here, the block 32 can be considered while dividing the block 32 into a block having a coefficient g_m and a block having a coefficient k₁ (k) . In this case, similarly to the formula 6 in the first embodiment, the following formula 35 can be set:

[0196] If changing FIG. 15 by changing the block 32 to a block having the coefficient g_mn equal to the coefficient g_m and the block 71 to a block having the coefficient having a coefficient k₁, a block diagram as shown in FIG. 19 is obtained. The coefficient of the block 45, into which the disturbance estimation signal _dest is inputted from the first integrator 43, is (1/g_mnK_tn) and includes g_mn. Therefore, in FIG. 19, a block 72 having a coefficient (1/k₂) is arranged between the first integrator 43 and the block 45. Here, the relationship between k₁ of the block 71 and k₂ of the block 72 is basically as shown in the following formula 36.

[0197] Practically, however, the condition of the formula 36 is not always essential but k₁ and k₂ may be approximate to each other with a certain degree of allowance. That is, ks can be expressed by formula 37 wherein an allowance coefficient is close to 1.

[0198] The concrete value of the allowance coefficient may be appropriately set according to the specification of the actual apparatus. Empirically, the allowance coefficient may be in a range of 0.7 to 1.3, preferably 0.8 to 1.2, more preferably 0.9 to 1.1. These can be expressed as shown in formulas 38, 39 and 40, respectively.

[0199] It is ideal that the coefficient is 1.0.

[0200] If changing FIG. 14 to correspond to FIG. 19, the block diagram becomes that shown in FIG. 18. That is, the disturbance estimation means 12A of the third embodiment is the combination of the disturbance estimation means 12 of the first embodiment and the first correction multiplication means 18 of the third embodiment. In addition, the correction means 15A of the third embodiment is the combination of the correction means 15 of the first embodiment and the second correction multiplication means 19 of the third embodiment. The first correction multiplication means 18 having the transfer function of k₁ is inserted into the path for transferring the drive signal u from the correction means 15 to the disturbance estimation means 12, and the second correction multiplication means 19 having the transfer function of k₂ is inserted into the path for transferring the disturbance estimation signal _dest from the disturbance estimation means 12 to the correction means 15. In FIG. 19, the block 71 corresponds to the first correction multiplication means 18, and block 72 corresponds to the second correction multiplication means 19.

[0201] If the third embodiment is described based on FIGS. 18 and 19, the disturbance estimation means 12A is configured to generate the disturbance estimation signal _dest from the signal obtained by multiplying the drive signal u by k₁ and the voltage signal E_d. The correction means 15A is configured to combine the position control signal c with the signal obtained by multiplying the disturbance estimation signal _dest by 1/k₂.

[0202] The disk storage apparatus in the third embodiment is configured such that the drive signal u outputted from the block 47A is inputted into one of the input signals for the disturbance estimation means 12A. Needless to say, the same effect can be attained even if the drive current I_a outputted from the drive means 10 outputted from the block 22 instead of the drive signal u is used.

[0203] Fourth Embodiment

[0204] FIG. 20 is a block diagram showing the configuration of a magnetic disk storage apparatus which is one example of a disk storage apparatus in the fourth embodiment according to the present invention. FIG. 21 is a block diagram showing the whole configuration of the positioning control system of the magnetic disk storage apparatus in the fourth embodiment. In the fourth embodiment, the filter means 16 and the block 54 having the transfer function F(s) in the second embodiment are not provided. Inputs to the disturbance estimation means 17A of the fourth embodiment differ from those of the disturbance estimation means 12A of the third embodiment. That is, the voltage signal E_d from the voltage detection means 11 and the position control signal c from the position control means 14 are inputted into the disturbance estimation means 17A. The configurations of the other components are the same as those in the third embodiment shown in FIGS. 14 and 15. It is noted that components or members having the same functions as those shown in the third embodiment are denoted by the same numerals, respectively and will not be repeatedly explained herein.

[0205] The relationship between the disk storage apparatus of the fourth embodiment shown in FIG. 20 and that of the third embodiment shown in FIG. 14 corresponds to the relationship between the disk storage apparatus of the second embodiment shown in FIG. 12 and that of the first embodiment shown in FIG. 1. However, the filter means 16 is not provided. In the third embodiment shown in FIG. 14, the voltage signal E_d produced by the voltage detection means 11 and the drive signal u are inputted into the disturbance estimation means 12A. In the fourth embodiment shown in FIG. 20, the voltage signal E_d produced by the voltage detection means 11 and the position control signal c produced by the position control means 14 are inputted into the disturbance estimation means 17A.

[0206] Therefore, in the fourth embodiment, the formulas 25 to 27 are established. Accordingly, if the block 30A of the disturbance estimation means 12A of the third embodiment shown in FIG. 15 is changed, it becomes equal to the block 60A of the disturbance estimation means 17A shown in FIG. 21. This corresponds to FIG. 13 in the second embodiment. However, the block 54 corresponding to the filter 16 is not provided.

[0207] Further, by configuring the apparatus similarly to the third embodiment, the formulas 28 to 40 are established in the fourth embodiment. In the formula 32, by setting the coefficient k of the actual number sufficiently greater, it is possible to stabilize the positioning control system even if the coil resistance R_a of the drive coil 5 of the actuator 7 is not equal to the nominal value R_an due to the change of the resistance value by the resistance fluctuation or temperature rise.

[0208] As a result, according to the disk storage apparatus of the fourth embodiment, the disturbance such as an inertia force acting on the actuator 7 due to shock/vibration exerted from the outside can be correctly detected by the disturbance estimation means 17A. Even if the disturbance _d acts on the actuator 7, such as pivot bearing friction, an elastic force of the FPC, and an inertia force due to shock/vibration exerted from the outside, the disturbance estimation means 17A is controlled to estimate this disturbance _d and the disturbance _d exerted from the outside is negated by the disturbance estimation signal _dest thus estimated. Therefore, similarly to the third embodiment, the disturbance _d exerted from the outside acts as if the disturbance _d is exerted through a filter having the cut-off frequency characteristic of the formula 19 and FIG. 5 on the positioning control system. Hence, according to the disk storage apparatus of the fourth embodiment, with a frequency lower than the angular frequency _o, it is possible to inhibit the disturbance by the first-order low frequency cut-off characteristic, and to inhibit a track dislocation due to the disturbance, whereby the head 2 is controlled at a high accuracy to be positioned to the target track. Therefore, the tracking control stable against the shock or vibration can be implemented, thereby improving the reliability of the disk storage apparatus.

[0209] As can be seen, according to the disk storage apparatus of the fourth embodiment, the number of adders required to constitute the disturbance estimation means 17A can be reduced compared with the disk storage apparatus of the third embodiment. Therefore, compared with the third embodiment, the disk storage apparatus of the fourth embodiment can estimate the disturbance _d acting on the arm 3 such as a pivot bearing friction, an elastic force and an inertia force acting on the head positioning control system as the disturbance, by simple configuration, stably control head positioning, and position the head 2 to the target track formed at narrow track pitches with high accuracy. Furthermore, according to the disk storage apparatus of the fourth embodiment, the number of the adders can be reduced, so that when the positioning control system is embodied with a hardware such as an analog circuit, the adjustment of such circuit can be simplified. Further, when the positioning control system is embodied with a software, the computing time delay by computing process can be shortened.

[0210] Similarly to the third embodiment, the disturbance estimation means 17A is not affected by the sampling frequency of the sector servo of the disk storage apparatus. Therefore, the control band of the disturbance estimation means 17A can be set higher than that of the positioning control system.

[0211] Moreover, according to the disk storage apparatus of the fourth embodiment, the number of the adders constituting the disturbance estimation means 17A can be reduced. Therefore, when the control system is embodied with a hardware such as an analog circuit, the adjustment of such circuit can be simplified. Further, when the control system is embodied with a software, the computing time delay by computing process can be shortened, thereby making it possible to set the control band higher.

[0212] If changing FIGS. 20 and 21 using the coefficients k₁ and k₂ similarly to the third embodiment, the block diagrams become those shown in FIG. 22 and 23, respectively. That is, the disturbance estimation means 17A of the fourth embodiment is the combination of the disturbance estimation means 17 of the second embodiment and the first correction multiplication means 18 of the fourth embodiment. In addition, the correction means 15A of the fourth embodiment is the combination of the correction means 15 of the second embodiment and the second correction multiplication means 19 of the fourth embodiment. The first correction multiplication means 18 having the transfer function of k₁ is inserted into the path for transferring the drive signal u from the correction means 15 to the disturbance estimation means 17, and the second correction multiplication means 19 having the transfer function of k₂ is inserted into the path for transferring the disturbance estimation signal _dest from the disturbance estimation means 17 to the correction means 15. In FIG. 23, the block 71 corresponds to the first correction multiplication means 18, and block 72 corresponds to the second correction multiplication means 19.

[0213] If the fourth embodiment is described based on FIGS. 22 and 23, the disturbance estimation means 17A is configured to generate the disturbance estimation signal _dest from the signal obtained by multiplying the position control signal c by k₁ and the voltage signal E_d. The correction means 15A is configured to combine the position control signal c with the signal obtained by multiplying the disturbance estimation signal _dest by 1/k₂.

[0214] The following embodiments may be employed besides the above-mentioned embodiments. As shown in FIG. 24, the first and third embodiments may be combined. As shown in FIG. 25, the second and fourth embodiments may be combined. That is, in either embodiment, the filter means 16 for cutting off the high frequency components of the disturbance estimation signal _dest is added to the correction means 15A.

[0215] In the disk storage apparatus in the first to fourth embodiment explained so far, the multipliers and integrators are configured by analog filters. Alternatively, they can be configured by digital filters. Further, the respective components constituting the positioning control system in each embodiment may be embodied in a software by a microcomputer.

[0216] While the disk storage apparatuses of the first to fourth embodiments have been explained as the magnetic disk storage apparatuses, the present invention is not limited to this, and can be applied to the other information recording apparatuses such as an optical disk storage apparatus and a magneto-optical disk storage apparatus.

[0217] As stated so far, according to the disk storage apparatus of the present invention, to estimate the disturbance such as a pivot bearing friction, an elastic force or an inertia force exerted on the actuator means, the disturbance estimation signal is produced by combining one of the drive signal and the position control signal with the voltage signal induced across the drive coil of the actuator means. Since the voltage signal is a continuous signal, it is possible to correctly detect the disturbance, compared with the conventional art using discrete servo information. Accordingly, even if the fluctuation of the disturbance during following operation directed toward the target track is large, it is possible to surely compensate this fluctuation and to improve the positioning accuracy of the head with respect to the target track. Besides, by negating the inertia force exerted on the actuator means due to shock/vibration from the outside, it is possible to improve the shock resistance characteristic of the disk storage apparatus and to stably implement head positioning control.

[0218] According to the disk storage apparatus of the present invention, besides the above-stated functions and effects, to produce the drive signal based on the position control signal for the head position and the disturbance estimation signal, the high frequency components of the disturbance estimation signal are cut off by the filter means to thereby produce a filter signal, and the filter signal is combined with the position control signal for the head position to thereby produce the drive signal. Therefore, it is possible to stabilize the positioning control system even if the coil resistance of the drive coil of the actuator means is not equal to the nominal value due to the change of the resistance value by the resistance fluctuation or temperature rise.

[0219] Moreover, the disturbance estimation means is configured to produce the disturbance estimation signal based on the signal obtained by multiplying the drive signal or position control signal by k₁ and the voltage signal, and the correction means is configured to produce the drive signal by combining the signal obtained by multiplying the disturbance estimation signal by 1/k₂ with the position control signal (k₁>>1, k₂>>1). By so configuring, it is possible to stabilize the positioning control system even if the coil resistance of the drive coil of the actuator means is not equal to the nominal value due to the change of the resistance value by the resistance fluctuation or temperature rise.

[0220] Hence, particularly if the influence of the disturbance, which is exerted on the actuator means, on the positioning control system increases as the actuator means is made small in size and light in weight and the resistance fluctuation of the drive coil and the change of the resistance value occur, the disk storage apparatus of the present invention can deal with more diverse conditional changes by improving the head positioning accuracy and improve the track density compared from the conventional apparatus. It is, therefore, possible to realize a large capacity disk storage apparatus.