Drive unit

[0001] The present invention relates to a drive unit for driving a movable object incorporating mainly an optical component, such as a lens being used in a camera, a DVD drive, a CD drive, an MD drive, an endoscope or the like.

[0002] As a drive unit that uses an electromechanical transducer, such as a piezoelectric element, which changes its dimension (expands or contracts) when a voltage is applied, the drive unit shown in an exploded perspective view in FIG. 1A and in an assembled perspective view in FIG. 1B, for example, is known (U.S. Pat. No. 6,016,231).

[0003] A piezoelectric element 4 comprises multiple piezoelectric plates stacked. One end 4a thereof in the expansion/contraction direction is secured to a base 1, and the other end 4b thereof is secured to the first end 5a of a rod (supporting member) 5. The rod 5 is slidably supported on supporting sections 2 and 3 integrated with the base 1.

[0004] The rod 5 is held between the main unit 10a and the cap 10b of a movable object 10, and a hold-down spring 10c exerts an urging force to the main unit 10a and the cap 10b in the holding direction. The movable object 10 is thus supported so as to be slidable along the rod 5.

[0005] A voltage control circuit is connected to the piezoelectric element 4. For example, when a predetermined drive voltage having a rectangular waveform or the like is applied to the piezoelectric element 4, the piezoelectric element 4 vibrates with a displacement, the shape of which is nearly the same as that of the drive voltage. Because the rod 5 is flexible, the rod 5 vibrates with a displacement having a sawtooth shape in the direction of its length in response to the displacement of the piezoelectric element 4 (see FIG. 2).

[0006] More specifically, in period A, the piezoelectric element 4 expands relatively slowly in the gradually rising inclined section 101 of a first vibration displacement 100, and the rod 5 moves slowly in the direction indicated by arrow I shown in FIG. 1B. Next, in period B, the piezoelectric element 4 contracts abruptly and its length returns to its initial length (as shown by the waveform section indicated by the falling inclined section 102). The rod 5 thus moves abruptly in the direction indicated by arrow II.

[0007] Movements similar to those described above are repeated hereafter. As a result, the rod 5 repeats the slow movement in direction I and the abrupt movement in direction II, thereby vibrates. Hence, the rod 5 vibrates with a displacement having a sawtooth vibration waveform characterized by a gradual rise and a rapid fall as shown in FIG. 2.

[0008] The spring force of the hold-down spring 10c of the movable object 10 (the frictional connection force applied from the movable object 10 to the rod 5) is adjusted so that the movable object 10 moves together with the rod 5 when the rod 5 moves slowly (in period A), and so that the movable object 10 stays where it is due to inertia (or moves by an amount smaller than that of the rod 5) when the rod 5 moves abruptly (in period B), as shown in FIG. 3. Hence, the movable object 10 moves in direction I relatively with respect to the base 1 while the rod 5 vibrates.

[0009] In the case that the movable object 10 is moved in the direction indicated by arrow II shown in FIG. 1B, the vibration waveform of the rod 5 should be the reverse of that shown in FIG. 2, that is, a waveform having a rapidly rising section and a gradually falling section. The movement principle of the movable object 10 in this case is similar to that of the above-mentioned case. In this case, the vibration displacement of the rod can be reversed from that shown in FIG. 2 by changing the duty ratio of the rectangular wave applied to the piezoelectric element 4.

[0010] The movable object 10 of the drive unit can be moved relatively with respect to the base (stationary base) 1. Hence, the drive unit can be used as the lens drive unit of a camera, for example. In other words, with a configuration in which the movable object 10 is connected to a lens frame, the lens can be moved simultaneously with the movement of the movable object 10.

[0011] In the case that the drive unit that uses such a piezoelectric element having the movement principle described above is used to move an optical member, the positional control of the movable object 10 becomes important. In the positional control of the movable object 10, the position of the movable object 10 should be detected at all times so that the movable object 10 can be stopped accurately at a position immediately before the end of the movable range. However, it is difficult to accurately carry out positional control for the drive unit that uses such a piezoelectric element. Hence, the supporting section 3 that supports the rod is used as a restricting member that restricts the movement range of the movable object, and the movable object is securely made contact with the supporting section 3 that restricts the movement of the movable object (see FIG. 4A).

[0012] However, in the case that the movable object is made contact with the restricting member (the supporting section 3) and stopped, if the driving of the piezoelectric element is not stopped immediately after the movable object is made contact with the restricting member, there is a problem in which the movable object is tilted as shown in FIG. 4B. In other words, in the case of a drive unit that is actually used in the lens barrel of a camera or the like, the diameter of the rod is appropriately 1 mm, but the diameter of the lens frame 11 connected to the movable object is appropriately 10 mm. Hence, the sizes and weights of the members extending from the movable object are larger than those of the movable object. For this reason, if the state in which the movement of the movable object 10 is restricted using the restricting member 3 continues while the piezoelectric element 4 is driven to move the movable object 10, the movable object 10 is apt to be tilted. Although the tilting of the movable object is very slight, in the case of the drive unit connected to an optical member, such as a lens 12, the tilting becomes a cause of significant deterioration in the performance of the optical system.

[0013] For the purpose of solving this problem, the restricting member is made larger or a sensor capable of accurately detecting the position of the movable object is provided, whereby it is possible to prevent the tilting of the movable object. However, such a configuration in which the restricting member is made larger and a sensor is provided is not desirable from the viewpoint of downsizing the optical system, such as a lens barrel, in recent years. Furthermore, providing a sensor causes a problem of increasing cost.

[0014] Accordingly, for the purpose of solving the technical problem described above, the present invention is intended to provide a drive unit capable of preventing the tilting of the movable object thereof in the case that the movable object is stopped at the position where the movable object makes contact with the restricting member.

[0015] For the purpose of solving the technical problem described above, the present invention provides a drive unit configured as described below.

[0016] A first aspect of the present invention provides a drive unit comprising:

[0017] an electromechanical transducer capable of expanding/contracting by drive signal application,

[0018] a supporting member that is connected to the electromechanical transducer and displaced together with the electromechanical transducer,

[0019] a movable object that is slidably supported on the supporting member and moves along the supporting member owing to a vibration of the supporting member by virtue of the expansion/contraction of the electromechanical transducer,

[0020] restricting member that restricts a movable range of the movable object,

[0021] a drive circuit that applies to the electromechanical transducer a first wave drive signal for vibrating the supporting member so that a difference occurs between the expansion and contraction of the supporting member when the movable object is moved to a position where the movable object makes contact with the restricting member, and applies to the electromechanical transducer a second wave drive signal for vibrating the supporting member so that the movable object is not moved substantially after the movable object is made contact with the restricting member.

[0022] In the configuration described above, the second wave drive signal can have a rectangular waveform having a duty ratio of 0.5.

[0023] In addition, the first wave drive signal can have a rectangular waveform having a duty ratio other than 0.5.

[0024] Furthermore, the restricting member is provided at a reference position where the position of the movable object of the drive unit is detected.

[0025] Moreover, the movable object is urged by an urging force against the supporting member.

[0026] Still further, the drive circuit is configured to apply the second wave drive signal after the first wave drive signal is applied for a predetermined time. In the configuration described above, it is preferable that the predetermined time should be a time sufficient to allow the movable object to reach the restricting member, regardless of the position of the movable object in the movable range thereof.

[0027] A second aspect of the present invention provides a drive unit comprising:

[0028] an electromechanical transducer capable of expanding/contracting by drive signal application,

[0029] a supporting member that is secured to an end of the electromechanical transducer in an expansion/contraction direction thereof,

[0030] a movable object slidably supported on the supporting member,

[0031] an urging member that exerts an urging force to urge the movable object toward the supporting member, a restricting member provided to make contact with the movable object at an end of a movable range of the movable object, and

[0032] a drive circuit that applies to the electromechanical transducer a first wave drive signal for vibrating the supporting member so that the movable object moves relatively with reference to the supporting member against an urging force when the movable object is moved to a position where the movable object makes contact with the restricting member, and applies to the electromechanical transducer a second wave drive signal for vibrating the supporting member so that the movable object is not moved substantially with respect to the supporting member after the movable object is made contact with the restricting member.

[0033] In the configuration described above, it is preferable that first and second waves of the first and second wave drive signal are rectangular waves and that the first and second waves have different duty ratios. For example, the second wave can have a duty ratio of 0.5.

[0034] In the configuration described above, the restricting member slidably supports the supporting member.

[0035] In addition, the drive circuit applies a predetermined number of pulses as the first wave drive signal to the electromechanical transducer.

[0036] With the present invention, in the case that the movable object is stopped at the position where the movable object is made contact with the restricting member, the tilting of the movable object owing to the contact of the movable object with the restricting member can be corrected. In other words, the tilting of the movable object, caused when the movable object makes contact with the restricting member, can be corrected by vibrating the supporting member so that the movable object is not moved substantially after the movable object is made contact with the restricting member. Hence, the movable object can be positioned without using a sensor or the like. Furthermore, the displacement of the optical axis due to the displacement of the optical member provided in the movable object can be prevented.

[0037] In addition, the movable object can be brought to a state in which the movable object is not moved while the vibration of the electromechanical transducer is obtained securely, by applying a rectangular drive signal having a duty ratio of 0.5 as the second wave drive signal. Hence, the tilting of the movable object can be corrected, without changing the position of the movable object.

[0038] Furthermore, the movable object can be moved at high speed in a predetermined direction by applying a rectangular wave drive signal having a duty ratio other than 0.5 as the first wave drive signal.

[0039] Still further, because the position of the movable object being in contact with the restricting member can be detected accurately, the positional detection of the movable object can be carried out easily using the position of the movable object as a reference position.

[0055] Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. A drive unit according to an embodiment of the present invention will be described below referring to the drawings.

[0056] FIG. 5A is a schematic view showing a configuration of a drive unit according to this embodiment of the present invention. The drive unit 20 according to this embodiment is used to drive a lens frame 31 in which an optical lens 32 being used in a lens barrel of a camera is provided.

[0057] The drive unit 20 drives a movable object 30 on the basis of the same principle as that of the drive unit that uses a piezoelectric element 4 shown in FIG. 1. The piezoelectric element 24 of the drive unit 20 comprises multiple piezoelectric plates stacked. One end thereof in an expansion/contraction direction is secured to a frame 21, and the other end thereof is secured to an end of a rod 25. The rod 25 is slidably supported on supporting sections 22 and 23 integrated with the frame 21. The rod 25 is held between the main unit 30a and the cap 30b of a movable object 30, and a hold-down spring 30c exerts an urging force to the main unit 30a and the cap 30b in the holding direction. The movable object 30 is thus supported so as to be slidable along the rod 25.

[0058] For example, the rod 25 is held between the main unit 30a and the cap 30b of the movable object 30, and a hold-down spring 30c exerts an urging force to the main unit 30a and the cap 30b in the holding direction to achieve frictional connection between the rod 25 and movable object 30. The movable object 30 is thus supported so as to be slidable along the rod 25. The lens frame 31 is secured to the movable object 30 and is moved simultaneously with the movement of the movable object. Because the movable object 30 is urged toward the rod 25 by hold-down spring, when the movable object 30 is tilted with respect to the rod 25, a force is exerted to correct the tilting of the movable object 30.

[0059] A drive circuit 33 is connected to the piezoelectric element 24. Under the control from a control section 34, the drive circuit 33 applies a rectangular wave drive voltage having a predetermined duty ratio to the piezoelectric element 24. In other words, the control section 34 controls the drive circuit 33 to apply a rectangular wave drive voltage having a predetermined duty ratio depending on the direction and speed of the movement of the movable object 30, thereby adjusting the position of the movable object 30.

[0060] The movable object 30 moves along the rod as the piezoelectric element 24 expands and contracts by drive signal application. The movable range of the movable object 30 is between the two supporting sections 22 and 23. In other words, the rod 25 is required to be configured so that its length is larger than the movable range, and the size of the rod 25 is designed depending on the movable range of the movable object 30. In addition, the position where the movable object 30 makes contact with the supporting section 22 is used as the origin for positional control. In other words, in the positional control of the movable object 30, the origin that is used to detect the position of the movable object 30 can be detected by making the movable object 30 come into contact with the supporting section 22. With a configuration in which the supporting sections 22 and 23 are made sufficiently larger than the movable object, the movement of the movable object 30 can be restricted without causing the tilting of the movable object 30 during origin detection described later. However, in this embodiment, the supporting sections are made small so that the drive unit is configured to be small in size.

[0061] A sensor 23a, provided at the end of the movable range on the side of the supporting section 23, detects that the movable object 30 makes contact with the supporting section 23. The output of the sensor 23a is input to the control section 34.

[0062] FIG. 6 shows a configuration example of the drive circuit 33 that is included in the drive unit shown in FIG. 5A and applies a voltage to the piezoelectric element. In the drive circuit 33, four switches Q1 to Q4 and two capacitors C1 and C2 form an H-bridge circuit, and the drive circuit 33 applies a drive voltage to the piezoelectric element 24. The switches Q1 and Q2 are formed of P-channel MOS FETs, and the switches Q3 and Q4 are formed of N-channel MOS FETs.

[0063] The source of the switch Q1 is connected to a terminal Vp, and the gate thereof is connected to the terminal Sc1 of the control section 34. The source of the switch Q2 is connected to the terminal Vp, and the gate thereof is connected to the terminal Sc2 of the control section. The drain of the switch Q3 is connected to the drain of the switch Q1, and the source thereof is grounded. In addition, the gate of the switch Q3 is connected to the terminal Sc3 of the control section 34. The drain of the switch Q4 is connected to the drain of the switch Q2, and the source thereof is grounded. Furthermore, the gate of the switch Q4 is connected to the terminal Sc4 of the control section 34.

[0064] One terminal of the piezoelectric element 24 is connected to the drains of the switches Q1 and Q3, and the other terminal thereof is connected to the drains of the switches Q2 and Q4. In addition, the capacitors C1 and C2 are connected in parallel with the switches Q3 and Q4, respectively, as shown in FIG. 6. The capacitance of each of the capacitors C1 and C2 is equal to the capacitance of the piezoelectric element 24. The control section 34 switches voltages to be input to the switches Q1 to Q4, thereby controlling the voltages to be applied to the piezoelectric element 24. More specifically, for example, when a voltage (high) is applied to the switches Q1 and Q3 and when no voltage (low) is applied to the switches Q2 and Q4, voltage −Vp is applied to the piezoelectric element. On the other hand, when no voltage (low) is applied to the switches Q1 and Q3 and when a voltage (high) is applied to the switches Q2 and Q4, voltage Vp is applied to the piezoelectric element 24.

[0065] The control section 34 turns ON/OFF the voltages applied to the drains of the switches Q1 to Q4 as described above, thereby controlling the voltage to be applied to the piezoelectric element 24 and inputting a rectangular wave drive voltage to the piezoelectric element 24 via the drive circuit 33. More specifically, when the gate voltages of the switches Q1 to Q4 are controlled as shown in FIG. 7, the drive voltage to be applied to the piezoelectric element 24 has a rectangular waveform shown by Load in FIG. 7. As understood from FIG. 7, ta to td respectively designate voltage application time periods, and these time periods ta to td form one cycle.

[0066] First, in the time period ta, the switches Q2 and Q4 become high, and the switches Q1 and Q3 become low. On the other hand, in the time period tc, the switches Q2 and Q4 become low, and the switches Q1 and Q3 become high. Hence, the voltage applied to the piezoelectric element 24 in the time period ta and the voltage applied thereto in the time period tc are equal in absolute value, but opposite in sign.

[0067] In the time periods tb and td, because all the switches Q1 to Q4 become high, the voltage applied to the piezoelectric element 24 is zero. Hence, when the cycle from ta to td is repeated, the rectangular wave drive voltage shown in FIG. 7 is applied periodically to the piezoelectric element 24. During the time periods tb and td, the shape of the piezoelectric element 24, having been changed, is returned to its original shape. The time periods tb and td are significantly shorter than the time periods ta and tc, and the time periods tb and td can be set to zero. The ratio between the time periods ta and tc only are adjusted to change the duty ratio of the drive voltage.

[0068] FIG. 8 shows an example of the relationship between the duty ratio and the movement speed of the movable object 30. As the duty ratio increases from zero, the movement speed of the movable object 30 increases in the positive direction, and reaches the positive maximum value when the duty ratio is 0.3. Furthermore, as the duty ratio exceeds 0.3, the speed lowers gradually, and reaches zero when the duty ratio is 0.5. At this time, the expansion and contraction speeds of the rod 25 are equal, and the movable object has room for movement microscopically. However, because the movement amounts during expansion and contraction are the same, the movable object is in a state in which its speed is zero, relatively. In addition, as the duty ratio becomes larger than 0.5, the movement speed of the movable object increases in the negative direction, and reaches the negative maximum value when the duty ratio is 0.7. Furthermore, as the duty ratio exceeds 0.7, the negative speed lowers gradually, and the movable object stops when the duty ratio is 1.0. In this embodiment, the positive direction is a direction in which the movable object 30 is moved toward the supporting section 22, and the negative direction is a direction in which the movable object 30 is moved toward the supporting section 23.

[0069] Next, the drive control of the drive unit according to this embodiment will be described below. As described above, the drive unit moves the movable object 30 along the rod 25 in a desired direction by applying the rectangular wave drive voltage having a predetermined duty ratio determined using the control section 34. For the purpose of moving the movable object 30 at high speed, it is preferable that the duty ratio of the drive voltage at this time should be appropriately 0.3 or 0.7. In other words, when the duty ratio is 0.3, the movable object 30 moves at high speed toward the supporting section 22, and when the duty ratio is 0.7, the movable object 30 moves at high speed toward the supporting section 23.

[0070] If the drive voltage is applied to the piezoelectric element 24 when the movable object 30 has moved to an end of its movable range, that is, when the movable object 30 is in contact with the supporting section 22 or 23, the movable object 30 is tilted. The drive unit according to this embodiment carries out the following control to prevent or eliminate the tilting.

[0071] The sensor 23a carries out positional detection when the movable object 30 makes contact with the end of the movable range on the tip side of the drive unit, that is, the supporting section 23. In other words, when the sensor 23a detects that the movable object 30 has made contact with the supporting section 23, the application of the drive voltage to the piezoelectric element 24 is stopped. As a result, the drive voltage is not applied when the movable object 30 is in contact with the supporting section 23, whereby the tilting of the movable object 30 is prevented.

[0072] On the other hand, when the movable object 30 makes contact with the end of the movable range on an element side of the drive unit, that is, the supporting section 22, the following processing is carried out. The limit position of the movable range, restricted using the supporting section 22 as described above, is used as the origin for the positional control of the movable object 30, and serves as the standby position of the movable object 30. In other words, when the power supply of a camera incorporating the drive unit is turned OFF or when the power supply is turned ON and the state of the camera is reset, the movable object 30 is controlled so as to make contact with the supporting section 22 on the element side, and origin detection is carried out.

[0073] FIG. 9 is a flowchart showing origin detection processing for detecting the position of the movable object 30. First, for the purpose of detecting the origin of the movable object, a predetermined first wave drive voltage having a rectangular waveform and having a duty ratio in the range of 0 to 0.5 is applied to the piezoelectric element 24 to move the movable object 30 toward the element side (at step 1). FIG. 10A is a view showing the waveform of the drive voltage having a duty ratio of 0.3, as an example of the first wave drive signal. In the processing being carried out at this time, pulses are applied to the piezoelectric element 24 a predetermined number of times stored beforehand in the control section 34, regardless of the position of the movable object 30 on the rod 25. The predetermined number of pulses is a number of pulses capable of securely obtaining the movement amount that allows the movable object 30 to make contact with the supporting section 22, regardless of the position of the movable object 30 in the movable range. The specific value of the number has been set beforehand depending on the length of the rod 25, the displacement amount of the piezoelectric element 24, and the like.

[0074] Depending on the position of the movable object 30, it is conceivable that the movable object 30 makes contact with the supporting section 22 before the application of the predetermined number of pulses. However, the control section 34 applies the predetermined number of pulses, regardless of whether the movable object 30 is in contact with the supporting section 22. In other words, because of the application of the predetermined number of pulses to the piezoelectric element 24, the movable object 30 can be made contact with the supporting section 22 on the element side, regardless of the position of the movable object 30 at the time of the start of the processing (at step 3). There is a case in which the piezoelectric element 24 is driven by this operation although the movable object 30 is in contact with the supporting section 22. In this case, the tilting of the movable object 30 may occur.

[0075] Next, after the application of the predetermined number of pulses is completed, the control section 34 changes the duty ratio of the drive voltage to 0.5 (at step 4), and the application of the predetermined number of pulses to the piezoelectric element is carried out. With this processing, the piezoelectric element 24 can vibrate without changing the position of the movable object 30, and the tilting of the movable object 30 can be corrected by the urging force exerted to the movable object 30 (at step 5). FIG. 10B is a view showing the waveform of the drive voltage having a duty ratio of 0.5, as an example of a second wave drive signal.

[0076] As the number of pulses of the drive voltage having a duty ratio of 0.5 being set at step 4, a value in the range of several to several tens can be selected as necessary depending on the design of the drive unit. In this embodiment, it has been confirmed that the tilting of the movable object 30 is corrected by applying 60 pulses.

[0077] As described above, with the drive unit according to the embodiment of the present invention, the operation for detecting the origin of the movable object 30 can be carried out easily and securely without providing auxiliary devices, such as a sensor. In addition, the tilting of the movable object 30, caused when the movable object 30 is made contact with the supporting section 22 for origin detection, can be corrected by carrying out simple processing.

[0078] The present invention is not limited to the embodiment described above, but the present invention can be implemented using other various embodiments. For example, the embodiment described above is configured so that, for the purpose of moving the movable object 30 to a limit position in the movable range, the drive voltage having a duty ratio of 0.5 is applied only when the positional detection on the element side is carried out, whereby the tilting is corrected. However, this processing may be carried out on both ends of the movable range. In other words, by the use of this processing instead of providing the sensor 23a, the tilting of the movable object 30, caused by the contact, can also be corrected at the supporting section 23 on the tip side. In this case, it is preferable that the duty ratio of the first wave drive voltage may be larger than 0.5 and less than 1.0, and that the duty ratio of the second wave drive voltage may be 0.5.

[0079] In addition, both the control for making the movable object come into contact with the supporting section and the control for correcting the tilting of the movable object in the embodiment described above are carried out by changing the number of pulses, but may be carried out by changing the application time of the drive voltage.

[0080] Furthermore, the second wave drive voltage that is applied to correct the tilting is not limited to the rectangular wave voltage having a duty ratio of 0.5, but may be a voltage having a sine waveform, a triangular waveform or a trapezoidal waveform, for example. Generally speaking, the drive voltage may only be a drive voltage having a waveform capable of causing vibration so that the speeds of the expansion and contraction of an electromechanical transducer are equal.

[0081] Moreover, although the drive unit is configured so that the lens used in the lens barrel of a camera is moved, the drive unit is not limited to this configuration. For example, the drive unit can also be used as an actuator for driving a lens used in an MD drive, a CD drive, a DVD drive or the like.

[0082] Still further, the supporting member is not limited to have a rod shape, but may be formed into a plate shape, for example. Moreover, although the movable object and the supporting member in the embodiment described above are moved relatively by abruptly moving the supporting member, a mechanism that cancels the urging force exerted from the movable object to the supporting member may be provided when the movable object is moved relatively with respect to the supporting member.

[0083] By appropriate combination of any of the various embodiments described above, the effects of the respective embodiments can be produced.

[0084] The entire disclosure of Japanese Patent Application No. 2005-235824 filed on Aug. 16, 2005, including specification, claims, drawings, and abstract are incorporated herein by reference in its entirety.

[0085] Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.