Seek trajectory adaptation in sinusoidal seek servo hard disk drives

[0002] The present application is a non-provisional application of a provisional application entitled “SEEK TRAJECTORY ADAPTATION IN SINUSOIDAL SEEK SERVO OF HARD DISK DRIVES”, assigned Provisional Application Serial No. 60/232,647, and filed Sep. 14, 2000.

[0003] 1. Field of the Invention

[0004] The present invention relates generally to disk drives and more particularly to a method, apparatus, and computer readable program product for improving the performance of hard disk drive servomechanisms.

[0005] 2. Description of the Related Art

[0006] Hard disk drives include a plurality of magnetic transducers that can write and read information by magnetizing and sensing the magnetic field of a rotating disk(s), respectively. The information is typically formatted into a plurality of sectors that are located within an annular track. There are a number of tracks located across each surface of the disk. A number of vertically similar tracks are sometimes referred to as a cylinder. Each track may therefore be identified by a cylinder number.

[0007] Each transducer is typically integrated into a slider that is incorporated into a head gimbal assembly (HGA). Each HGA is attached to an actuator arm. The actuator arm has a voice coil located adjacent to a magnet assembly which together define a voice coil motor. The hard disk drive typically includes a driver circuit and a controller that provide current to excite the voice coil motor. The excited voice coil motor rotates the actuator arm and moves the transducers across the surfaces of the disk(s).

[0008] When writing or reading information, the hard disk drive may perform a seek routine to move the transducers from one cylinder (track) to another cylinder. During the seek routine the voice coil motor is excited with a current to move the transducers to the new cylinder location on the disk surfaces. The controller also performs a servo routine to insure that the transducer is at the center of the track.

[0009] The assignee of the present invention has introduced disk drives that utilize a sinusoidal seek algorithm where the transducer is moved according to a sinusoidal trajectory.

[0010] The present invention comprises a method, apparatus, and computer program product for a hard disk drive. In one embodiment, the apparatus comprises a disk which has a surface, a spindle motor to rotate the disk, a transducer to write information onto the disk and read information from the disk, an actuator arm to move the transducer across the surface of the disk, and a controller. The controller, in response to a command to seek from a first track to a second track, can determine a seek length from the first track to the second track, determine a seek time based on the seek length, scale the seek time in response to a velocity error between a calculated velocity and a design velocity for the seek length, and control the actuator arm to move said transducer across said disk surface from the first track to the second track using an acceleration trajectory.

[0011] FIG. 1 is a top view of an embodiment of a hard disk drive of the present invention;

[0012] FIG. 2 is a schematic of an electrical system which controls the hard disk drive;

[0013] FIG. 3 is a schematic of a servo control system of the disk drive;

[0014] FIGS. 4A through 4C show exemplary graphs of the acceleration, velocity, and position trajectories of a sinusoidal seek.

[0015] FIG. 5 illustrates a flow diagram of an initialization method, according to one embodiment of the present invention.

[0016] FIG. 6 illustrates a flow diagram of a method for adjusting a scaling value, according to one embodiment of the present invention.

[0017] FIG. 7 illustrates a flow diagram of a method 700 for adjusting the seek time based on the scaling value, according to one embodiment of the present invention.

[0018] The present invention comprises a method, apparatus, and computer program product for a hard disk drive. In one embodiment, a hard disk drive includes a disk which has a surface, a spindle motor that rotates the disk, and a transducer which can write information onto the disk and read information from the disk. The transducer may be integrated into a slider that is incorporated into a head gimbal assembly (HGA). The HGA may be mounted to an actuator arm which can move the transducer across the disk surface. The movement of the actuator arm and the transducer may be controlled by a controller.

[0019] The controller may move the transducer from a present track to a new track in accordance with a seek routine and a servo control routine. During the seek routine, the controller can determine a seek length from the first track to the second track, determine a seek time based on the seek length, adjust the seek time in response to a velocity error between a calculated velocity and a design velocity for the seek length, and control the actuator arm to move the transducer across the disk surface from the present track to the new track using the acceleration trajectory. In one embodiment, the acceleration trajectory is a sinusoidal acceleration trajectory. The acceleration trajectory may take other forms such as a bang-bang acceleration trajectory.

[0020] Referring to the drawings more particularly by reference numbers, FIG. 1 shows an embodiment of a hard disk drive 10. The drive 10 includes at least one magnetic disk 12 that is rotated by a spindle motor 14. The drive 10 may also include a transducer 16 located adjacent to a disk surface 18.

[0021] The transducer 16 can write and read information on the rotating disk 12 by magnetizing and sensing the magnetic field of the disk 12, respectively. There is typically a transducer 16 associated with each disk surface 18. Although a single transducer 16 is shown and described, it is to be understood that there may be a write transducer for magnetizing the disk 12 and a separate read transducer for sensing the magnetic field of the disk 12. The read transducer may be constructed from a magneto-resistive (MR) material.

[0022] The transducer 16 can be integrated into a slider 20. The slider 20 may be constructed to create an air bearing between the transducer 16 and the disk surface 18. The slider 20 may be incorporated into a head gimbal assembly (HGA) 22. The HGA 22 may be attached to an actuator arm 24 which has a voice coil 26. The voice coil 26 may be located adjacent to a magnet assembly 28 to define a voice coil motor (VCM) 30. Providing a current to the voice coil 26 will generate a torque that rotates the actuator arm 24 about a bearing assembly 32. Rotation of the actuator arm 24 will move the transducer 16 across the disk surface 18.

[0023] Information is typically stored within annular tracks 34 of the disk 12. Each track 34 typically contains a plurality of sectors. Each sector may include a data field and an identification field. The identification field may contain Gray code information which identifies the sector and track (cylinder). The transducer 16 is moved across the disk surface 18 to write or read information on a different track. Moving the transducer to access a different track is commonly referred to as a seek routine.

[0024] FIG. 2 shows an electrical system 40 which can control the hard disk drive 10. The system 40 may include a controller 42 that is coupled to the transducer 16 by a read/write (R/W) channel circuit 44 and a pre-amplifier circuit 46. The controller 42 may be a digital signal processor (DSP), microprocessor, microcontroller, and the like. The controller 42 can provide control signals to the read/write channel 44 to read from the disk 12 or write information to the disk 12. The information is typically transferred from the R/W channel 44 to a host interface circuit 46. The host circuit 46 may include buffer memory and control circuitry which allow the disk drive to interface with a system such as a personal computer.

[0025] The controller 42 may also be coupled to a VCM driver circuit 48 which provides a driving current to the voice coil 26. The controller 42 may provide control signals to the driver circuit 48 to control the excitation of the VCM and the movement of the transducer 16.

[0026] The controller 42 may be connected to a non-volatile memory such as a read only memory (ROM) or flash memory device 50, and a random access memory (RAM) device 52. The memory devices 50 and 52 may contain instructions and data that are used by the controller 42 to perform software routines. One of the software routines may be a seek routine to move the transducer 16 from one track to another track. The seek routine may include a servo control routine to insure that the transducer 16 moves to the correct track. In one embodiment, the memory device 50 contains the acceleration, velocity, and position trajectory equations, as discussed hereinbelow, where such equations may be loaded into memory device 52 at startup. Moreover the memory device 50 may include one or more software routines that allow(s) for adaptation of the seek trajectory and one or more tables, all of which may be loaded into the memory device 52 at startup.

[0027] FIG. 3 shows a servo control system 60 that is implemented by the controller 42, which may be implemented in hardware and/or software. The servo control system 60 insures that the transducer 16 is accurately located on a desired track of the disk 12. When the controller 42 performs a seek routine the transducer 16 is moved from a first track to a new track located a distance X_SKfrom the first track. The Gray codes of one or more tracks located between the new and first tracks are read as the transducer 16 moves across the disk 16. This allows the controller 42 to periodically determine whether the transducer 16 is moving at a desired speed or acceleration, or both, across the disk surface.

[0028] The control system 60 includes an estimator 62, which may be implemented in software and/or hardware. The estimator 62 can determine the actual distance or position X_athat the transducer has moved from the first track. The position can be determined by reading the Gray code of a track beneath the transducer 16. The estimator 62 can also determine the actual velocity V_aand actual acceleration A_aof the transducer 16. The Gray codes can be periodically sampled as the transducer 16 moves to the new track location so that the controller 42 can correct the movement of the transducer 16 with the control system 60.

[0029] The controller 42 computes a design position X_i, a design velocity V_iand a design acceleration A_iof the transducer 16 each time the transducer reads the Gray code of a track 34. The controller 42 computes the difference between the design position X_iand the actual position X_aat summing junction 64. In block 66, the controller 42 then computes a position correction value E_xwith a proportional plus integral control algorithm and the output of the summing junction 64.

[0030] The actual velocity V_ais subtracted from the sum of the design velocity V_iand the position correction value E_xat summing junction 68. In block 70, the controller 42 computes a velocity correction value E_vwith a proportional plus integral control algorithm and the output of the summing junction 68.

[0031] An acceleration correction value E_ais computed by subtracting the actual acceleration A_afrom the sum of the design acceleration A_iand the velocity correction value E_vat summing junction 72. The acceleration correction value E_ais used to increase or decrease the current provided to the voice coil 26 and to vary the acceleration of the movement of the transducer 16.

[0032] The acceleration correction value E_amay also be provided to the estimator 62 to generate a feedforward acceleration value A′_a. The feedforward acceleration value A′_acan be provided to sunning junction 72 to provide a feedforward control loop.

[0033] The design acceleration A_i, velocity V_i, and position X_iwaveforms provided at the respective summing junction 72, 68, and 64 are described and shown below.

[0034] In one embodiment, the acceleration trajectory comprises a sinusoidal acceleration trajectory, as defined by the following equation: $\begin{array}{cc}a\left(t\right)=K_A{I}_M\sin \left(\frac{2\pi }{T_{\mathrm{SK}}}t\right),& \left(1\right)\end{array}$

[0035] where;

[0036] K_A=acceleration constant;

[0037] I_M=maximum current provided to the voice coil; and

[0038] T_SK=seek time required to move the transducer from the old track to the new track.

[0039] The following ideal velocity equation can be derived by integrating the acceleration equation. $\begin{array}{cc}v\left(t\right)={\int }_o^{i}a\left(t\right)dt=K_A{I}_M\frac{T_{\mathrm{SK}}}{2\pi }\left[1-\cos \left(\frac{2\pi }{T_{\mathrm{SK}}}t\right)\right].& \left(2\right)\end{array}$

[0040] Additionally, the following ideal position equation can be derived by integrating the velocity equation. $\begin{array}{cc}x\left(t\right)={\int }_o^{t}v\left(t\right)dt=K_A{I}_M\frac{T_{\mathrm{SK}}}{2\pi }\left[t-\frac{T_{\mathrm{SK}}}{2\pi }\sin \left(\frac{2\pi }{T_{\mathrm{SK}}}t\right)\right].& \left(3\right)\end{array}$

[0041] FIGS. 4A through 4C show exemplary graphs of the acceleration, velocity, and position trajectories of a sinusoidal seek. When the disk drive is in operation, the disk drive may receive a command to store or read information. The command may require that the transducer be moved from a first track to a new track in accordance with a seek routine. During a seek routine, the new track and corresponding distance (seek length X_SK) to the new track from the first track can be determined by the controller 42. The seek time may be initially computed before the ideal acceleration, ideal velocity, and ideal position are computed. The following relationship between T_SKand X_SKcan be generated from equation (3) by setting t=T_SK. $\begin{array}{cc}{T}_{\mathrm{SK}}=\sqrt{\frac{2\pi X_{\mathrm{SK}}}{K_A{I}_M}}.& \left(4\right)\end{array}$

[0042] Instead of performing a square root operation, the controller can compute T_SKfrom X_SKby generating a number of sample points N between t=0 and t=T_SKand storing the samples in a lookup table having N entries, and using the following linear interpolation algorithm to determine the seek time between sample points. $\begin{array}{cc}{T}_{\mathrm{SK}}=T_{\mathrm{SK}}^I+\frac{T_{\mathrm{SK}}^{I+1}-T_{\mathrm{SK}}^I}{X_{\mathrm{SK}}^{I+1}-X_{\mathrm{SK}}^I}\left(X_{\mathrm{SK}}-X_{\mathrm{SK}}^I\right).& \left(5\right)\end{array}$

[0043] Table 1 provides an exemplary format of the X_skv. T_sklookup table.

[0044] During the servo routine, the system may take a number of samples which correlate to the different positions, velocities, and accelerations of the transducer as the transducer moves from one track to another track. It is desirable to discretize the ideal trajectories to correspond with the sampling of Gray codes so that the actual values can be subtracted from the ideal values at the summing junctions of the servo control shown in FIG. 3. To discretize the trajectories, equations (1), (2), and (3) are transformed into a sample domain (n) and equation (4) is substituted into the amplitude terms to generate the following equations. $\begin{array}{cc}a\left(n\right)=\frac{2\pi X_{\mathrm{SK}}}{N_{\mathrm{SK}}^2{T}_{\mathrm{SM}}^2}\sin \left(\frac{2\pi }{N_{\mathrm{SK}}}n\right),& \left(6\right)\\ v\left(n\right)=\frac{X_{\mathrm{SK}}}{N_{\mathrm{SK}}{T}_{\mathrm{SM}}}\left[1-\cos \left(\frac{2\pi }{N_{\mathrm{SK}}}n\right)\right],\mathrm{and}& \left(7\right)\\ x\left(n\right)=\frac{X_{\mathrm{SK}}}{N_{\mathrm{SK}}}n-\frac{X_{\mathrm{SK}}}{2\pi }\sin \left(\frac{2\pi }{N_{\mathrm{SK}}}n\right),& \left(8\right)\end{array}$

[0045] where;

[0046] T_sm=the sampling time, computed from equation (5);

[0047] N_SK=the total number of samples; and

[0048] n=sample number.

[0049] The sine and cosine values can be computed by utilizing look-up tables that are stored in memory. Alternatively, the sine and cosine values can be computed with the state equation and initial value of the following recursive sine wave generation algorithm. $\begin{array}{cc}\left[\begin{array}{c}{x}_c\left(n+1\right)\\ x_s\left(n+1\right)\end{array}\right]=\left[\begin{array}{c}\cos \left(\frac{2\pi }{N_{\mathrm{SK}}}\right)-\sin \left(\frac{2\pi }{N_{\mathrm{SK}}}\right)\\ \sin \left(\frac{2\pi }{N_{\mathrm{SK}}}\right)\cos \left(\frac{2\pi }{N_{\mathrm{SK}}}\right)\end{array}\right]\left[\begin{array}{c}{x}_c\left(n\right)\\ x_s\left(n\right)\end{array}\right],\left[\begin{array}{c}{x}_c\left(0\right)\\ x_s\left(0\right)\end{array}\right]=\left[\begin{array}{c}M\\ 0\end{array}\right],& \left(9\right)\end{array}$

[0050] which utilizes the following known trigonometric identities. $\begin{array}{cc}\cos \left(\frac{2\pi }{N_{\mathrm{SK}}}\left(n+1\right)\right)=\cos \left(\frac{2\pi }{N_{\mathrm{SK}}}\right)\cos \left(\frac{2\pi }{N_{\mathrm{SK}}}n\right)-\sin \left(\frac{2\pi }{N_{\mathrm{SK}}}\right)\sin \left(\frac{2\pi }{N_{\mathrm{SK}}}n\right),\mathrm{and}& \left(10\right)\\ \sin \left(\frac{2\pi }{N_{\mathrm{SK}}}\left(n+1\right)\right)=\sin \left(\frac{2\pi }{N_{\mathrm{SK}}}\right)\cos \left(\frac{2\pi }{N_{\mathrm{SK}}}n\right)-\cos \left(\frac{2\pi }{N_{\mathrm{SK}}}\right)\sin \left(\frac{2\pi }{N_{\mathrm{SK}}}n\right).& \left(11\right)\end{array}$

[0051] During the servo routine, the controller 42 computes the ideal position, ideal velocity, and ideal acceleration of the transducer at a first sample time, determines the actual position, velocity, and acceleration values and then processes the data in accordance with the control loop shown in FIG. 3 and described above. Second, third, etc. samples are taken and the process is repeated to provide a servo routine that controls the movement of the transducer 16.

[0052] The velocity of the transducer should not exceed a maximum value so that the transducer can accurately read Gray codes from the disk. From equation (2) the maximum velocity can be computed as follows: $\begin{array}{cc}{V}_{\mathrm{MAX}}=K_A{I}_M\frac{T_{\mathrm{SK}}}{\pi }.& \left(12\right)\end{array}$

[0053] Using equation (4) the maximum seek time and maximum seek length can be determined as follows. $\begin{array}{cc}{T}_{\mathrm{SK}}^M=\frac{\pi }{K_A{I}_M}{V}_{\mathrm{MAX}},\mathrm{and}& \left(13\right)\\ X_{\mathrm{SK}}^M=\frac{\pi }{2K_A{I}_M}{V}_{\mathrm{MAX}}^2.& \left(14\right)\end{array}$

[0054] When the seek length X_SKexceeds the maximum seek length X_SK^M, a coast period must be introduced where the acceleration of the transducer is zero, so that the transducer velocity does not exceed the maximum value. The coast time can be defined by the following equation. $\begin{array}{cc}{T}_{CST}=\frac{X_{SK}-X_{SK}^M}{V_{\mathrm{MAX}}}.& \left(15\right)\end{array}$

[0055] For a seek length greater than X_SK^Mthe ideal position, ideal velocity, and ideal acceleration trajectories may be defined in (n) domain by the following equations. $\begin{array}{cc}a\left(n\right)=\frac{2\mathrm{\pi 2}{X}_{ACC}}{N_{SK}^{M^2}{T}_{SM}^2}\sin \left(\frac{2\pi }{N_{SK}^M}n\right),& \left(16\right)\\ v\left(n\right)=\frac{2X_{ACC}}{N_{SK}^M{T}_{SM}}\left[1-\cos \left(\frac{2\pi }{N_{SK}^M}n\right)\right],\mathrm{and}& \left(17\right)\\ x\left(n\right)=\frac{2X_{ACC}}{N_{SK}^M}n-\frac{2X_{ACC}}{2\pi }\sin \left(\frac{2\pi }{N_{SK}^M}n\right)& \left(18\right)\end{array}$

[0056] when the transducer is accelerating;

[0057] a(n)=0,  (19)

[0058] V(n) V_MAX, and  (20)

[0059] x(n)=X_ACC+V_MAXT_SM(n−N_SK^M/2)   (21)

[0060] when the transducer is coasting; and $\begin{array}{cc}a\left(n\right)=\frac{2\mathrm{\pi 2}{X}_{DEC}}{N_{SK}^{M^2}{T}_{SM}^2}\sin \left(\frac{2\pi }{N_{SK}^M}\left(n-N_{CST}\right)\right),& \left(22\right)\\ v\left(n\right)=\frac{2X_{DEC}}{N_{SK}^M{T}_{SM}}\left[1-\cos \left(\frac{2\pi }{N_{SK}^M}\left(n-N_{CST}\right)\right)\right],\mathrm{and}& \left(23\right)\\ \begin{array}{c}x\left(n\right)=X_{ACC}+X_{CST}+\frac{2X_{DEC}}{N_{SK}^M}\left(n-N_{CST}-N_{SK}^M/2\right)-\\ \frac{2X_{DEC}}{2\pi }\sin \left(\frac{2\pi }{N_{SK}^M}\left(n-N_{CST}\right)\right)\end{array}& \left(24\right)\end{array}$

[0061] when the transducer is decelerating

[0062] where;

[0063] X_CST=T_CSTV_MAXfor T_CSTat coast phase,  (25)

[0064] X_ACC=(X_SK−X_CST)/2 for T_SK^M/2 at acceleration phase, and   (26)

[0065] X_DEC=X_SK−X_ACC−X_CSTfor T_SK^M/2 at deceleration phase.   (27)

[0066] When the seek length exceeds X_SK^M, the controller computes the ideal position, ideal velocity, and ideal acceleration in accordance with equations (15) through (27), and then utilizes the ideal values in the control loop of FIG. 3.

[0067] During normal operation, the disk drive exhibits good seek performance using the sinusoidal seek method. In extreme conditions, however, such as, for example, when the disk drive is subjected to high temperature or is operated in a low voltage environment, the disk drive may exhibit a seek overrun condition. For example, at high temperatures, the resistance of the voice coil motor tends to increase causing a larger voltage drop across the voice coil motor, and thus a smaller voltage to drive the obtained current command E_a. As a result, a voltage saturation condition arises resulting in a different VCM current from the current command E_a. This can cause overshoot during settling.

[0068] To obtain stable seek performance both at normal and extreme conditions, the present invention adaptively adjusts the seek time based on the available voltage. Since the available voltage may be hard to determine, the seek time is adaptively adjusted based on the voltage error signal V_err. If there is sufficient voltage to drive the VCM, the VCM current is substantially the same as the current command E_a. In this case, the actual velocity is substantially the same as the velocity profile calculated from the current command. Consequently, the maximum of velocity error V_errbetween the actual velocity and design velocity will be below a selectable threshold THLD₁. However, if there is not sufficient voltage to drive the VCM, the actual VCM current is different than the design current, and the actual velocity is different than the design velocity. Thus, if the maximum of velocity error V_errduring a seek operation is greater than the threshold THLD₁, it can be concluded that there is not sufficient voltage to drive the VCM. To compensate for the lack of sufficient voltage to drive the VCM, the seek time T_SKis increased, resulting in a smaller current command for the seek length in the next seek operation. FIGS. 5 through 7 illustrate an exemplary embodiment of this mechanism.

[0069] FIG. 5 illustrates a flow diagram of an initialization method 500, according to one embodiment of the present invention. The initialization method is typically executed during power on self-test, or at some time prior to operation of the adaptive technique. Referring to FIG. 5, the method 500 commences at block 510 where a K_scaletable having N entries is created in memory (e.g., memory 52, FIG. 2). The size of the K_scaletable is equal to the size of Table 1. At block 515, all entries in the K_scaletable are set to one. In one embodiment, the K_scaletable may be part of Table 1.

[0070] FIG. 6 illustrates a flow diagram of a method 600 for adjusting a scaling value, according to one embodiment of the present invention. In one embodiment, the method 600 is executed for each seek. In this method, the maximum velocity error V_erris calculated and compared with two thresholds. If V_erris larger than a first threshold THLD₁, K_scaleis increased to provide a slower seek time. On the other hand, if V_erris smaller than a second threshold THLD₂, K_scaleis decreased to provide faster seek time.

[0071] Referring to FIG. 6, the method 600 commences at block 605 where X_skand I are determined. X_sk, which is the distance between a current track and a new track, may be determined by table lookup. Once X_skis determined, I is determined from Table 1. For example, if X_skis equal to the fifth entry in Table 1 (X_sk5), then I is equal to five. If, on the other hand, X_skis at a value between two entries (e.g., between X_sk20and X_sk21), then I may be set to either entry (e.g., twenty or twenty-one). The method 600 continues to block 610 where a variable V_errmaxis initialized to zero. At block 615, at a first sample time during the seek, the velocity error V_err, which is the output of summing junction 68, is calculated. The method 600 then moves to block 620 where the absolute value of V_err(ABS(V_err)) is compared to V_errmax. If ABS(V_err) is greater than V_errmax, then the method continues to block 625 where V_errmaxis set to the ABS(V_err), otherwise the process skips block 625. At block 630, the method 600 determines whether the seek is complete. If so, the process continues to block 640. If not, the process moves to block 635, where the method waits for the next servo interrupt at the next sample time. Blocks 615, 620, and/or 625 are executed for each sample time until the seek is complete, at which time the highest value of the velocity error is stored in V_errmax.

[0072] Continuing with FIG. 6, at block 640, V_errmaxis compared to a first predetermined threshold THLD₁. This block determined whether the highest value of the velocity error is above a predetermined value. The predetermined threshold may be set to any value or range of values. The predetermined threshold THLD₁may be a number or a percentage. For example, the predetermined threshold may be 5%, 10%, 15%, or higher. The predetermined threshold may be set to a lower value or percentage. Thus, during a seek, if the biggest different between an actual velocity and ideal velocity is less than the predetermined threshold (e.g., 10%), the process moves to block 650. Otherwise, the process moves to block 645 where the I-th element in the K_scaletable is increased by a predetermined value δ. This new value will be used to increase the seek time T_SKduring the next seek that has the same seek length (for the same entry I in Table 1). The designer may set the value and/or granularity of δ. For example, the seek time may be increased by 1%, 5%, 10%, or higher.

[0073] The process continues to block 650 where V_errmaxis compared to a second predetermined threshold THLD₂. That is, if the highest value of the velocity error during the seek is below a second predetermined threshold, indicating that the seek time can be decreased while still maintaining stable seek performance, the I-th element in the K_scaletable is decreased by α (block 655). The value α may be equal to δ.

[0074] It is to be noted that variations to the method 600 exist. For example, instead of storing the highest value of V_erras V_errmax, the average of V_errfor all sample times during a seek may be stored as V_erravg. Moreover, V_error V_erravgcan be compared to more than one threshold level. For example, if V_error V_erravgis greater than a first threshold THLD_1Abut smaller than a second threshold THLD_1B, the entry in the K_scaletable can be increased by a first amount δ₁, and if V_error V_erravgis greater than the second threshold THLD_1Bbut smaller than a third threshold THLD_1C, the entry in the K_scaletable can be increased by a second, larger amount δ₂and so on. A similar mechanism may be used for the second threshold THLD₂.

[0075] FIG. 7 illustrates a flow diagram of a method 700 for adjusting the seek time, according to one embodiment of the present invention. The method 700 is executed prior to calculation of the ideal position, velocity, and acceleration trajectories, and prior to the current command E_a.

[0076] Referring to FIG. 7, the method 700 commences at block 710, where the distance X_skbetween the current track and new track is determined. This may be determined by searching a lookup table. At block 715, the value of I is determined using Table 1 (lookup table). At block 720, T_skis determined by matching T_skto X_skin Table 1, and using linear interpolation (Equation 5), if necessary. At block 725, T_skis adjusted. In one embodiment, T_skis adjusted by multiplying T_skby K_scale[I], the I-th entry in the K_scaletable. If the value of K_scale[I] is greater than 1, indicating insufficient voltage to drive the VCM for the seek length of X_sk, then T_skis increased; if the value of K_scale[I] is equal to one, indicating sufficient voltage to drive the VCM for the seek length of X_sk, then T_skis unchanged; and if K_scale[I] is less than one, indicating that additional voltage is available to drive the VCM, T_skis decreased.

[0077] As can be seen, the present invention provides a method and apparatus for adaptively adjusting seek trajectories based on voltage available to drive the voice coil motor. During a seek, if the highest value of the velocity error, which indicates the difference between the ideal velocity and actual velocity, is greater than a predetermined threshold, it can be safely assumed that there is not sufficient voltage to drive the voice coil motor. As a result, the seek time is increased to cause a smaller current command for the same seek length in the next seek operation. This reduces the possibility of a seek overrun. The present invention may be implemented in any sinusoidal seek hard disk drive servomechanisms such as those described in co-pending applications having application Ser. No. 09/552,112, entitled GENERALIED FOURIER SEEK METHOD AND APPARATUS FOR A HARD DISK DRIVE SERVOMECHANISM, and application Ser. No. 09/609,630, entitled AN OPTIMIZATION METHOD AND APPARATUS FOR A GENERALIZED FOURIER SEEK TRAJECTORY FOR A HARD DISK DRIVE SERVOMECHANISM, the contents of which are fully incorporated herein by reference.

[0078] The present invention may be implemented as a method, apparatus, system, computer program product, etc. When implemented in software, the elements of the present invention are essentially the code segments to perform the necessary tasks. The program or code segments can be stored in a processor readable medium or transmitted by a computer data signal embodied in a carrier wave over a transmission medium or communication link. The “processor readable medium” may include any medium that can store or transfer information. Examples of the processor readable medium include an electronic circuit, a semiconductor memory device, a ROM, a flash memory, an erasable ROM (EROM), a floppy diskette, a CD-ROM, an optical disk, a hard disk, a fiber optic medium, a radio frequency (RF) link, etc. The computer data signal may include any signal that can propagate over a transmission medium such as electronic network channels, optical fibers, air, electromagnetic, RF links, etc.

[0079] While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.