JP2005354830A - Control method for actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control method for an actuator which can shift a driven member accurately by applying the voltage of roughly saw-toothed drive pulses in specified timing to a plurality of piezoelectric elements. <P>SOLUTION: The piezoelectric elements 32A and 32B of the actuator 30 are arranged on both sides across the driven member 26. The end faces on one side in the displacement directions of the piezoelectric elements 32A and 32B are pressed by press plates 38A and 38B, and driving members 34A and 34B are attached to the other end faces. The driving members 34A and 34B are energized by a press spring 36 and are engaged frictionally. Voltage is applied to the piezoelectric elements 32A and 32B so that deformation velocity may be different between the time of elongation and the time of shrinkage of the piezoelectric elements 32A and 32B and that the timing may be qual between the piezoelectric elements 32A and 32B at low deformation velocity and the timing may be different between the piezoelectric elements 32A and 32B at high deformation velocity. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an actuator control method, and more particularly to an actuator control method that is mounted on a small precision device such as a digital camera or a mobile phone and drives a zoom lens and a focus lens.

  There is an actuator using a piezoelectric element as a driving device for a lens unit of a digital camera or the like. For example, in the actuator of Patent Document 1, a driving rod is fixed to the end face of a piezoelectric element, and a lens barrel is slidably supported by the driving rod. A leaf spring is attached to the lens barrel, and a frictional force acts between the plate spring and the drive rod by the elastic force of the leaf spring. A drive pulse having a substantially sawtooth waveform is applied to the piezoelectric element, and the piezoelectric element is deformed at different speeds in the extending direction and the contracting direction. For example, when the piezoelectric element is gently deformed, the lens barrel moves together with the drive rod. Conversely, when the piezoelectric element deforms quickly, the lens barrel stops at the same position due to the inertia of its mass. Therefore, the lens barrel can be moved intermittently at a fine pitch by repeatedly applying a drive pulse having a substantially sawtooth waveform to the piezoelectric element.

  However, since the actuator described in Patent Document 1 transmits the driving force through the long drive rod, the vibration of the piezoelectric element is absorbed and attenuated by the drive rod, and the lens barrel is moved accurately. There was a problem that I could not. In particular, high-frequency vibration has a large attenuation factor due to the drive rod, and therefore the response of the lens barrel is deteriorated. Therefore, the actuator of Patent Document 1 can be controlled only with a low-frequency drive pulse, and there is a problem that the number of movements of the lens barrel per unit time is reduced. For this reason, in order to increase the moving speed of the lens barrel in the actuator of Patent Document 1, it is necessary to increase the applied voltage to increase the amount of displacement of the piezoelectric element and to increase the amount of movement of the lens barrel once. .

  In Patent Document 2, by increasing the power supply voltage of 5 V to 30 V, the amount of movement at one time is increased, and the moving speed of the lens barrel is increased. For this reason, in patent document 2, there existed a problem that a pressure | voltage rise apparatus was needed, the apparatus enlarged, and complicated control was needed.

In the actuator described in Patent Document 3, an engagement member is attached to the end face of the piezoelectric element in the displacement direction, the engagement member is frictionally engaged with the moving plate, and the lens barrel is attached to the moving plate. . Then, by applying a driving pulse to the piezoelectric element, vibration is transmitted through the engaging member, and the moving plate and the lens barrel are moved.
Japanese Patent No. 2633066 Japanese Patent Laid-Open No. 2000-50660 Japanese Patent Laid-Open No. 10-232337

  By the way, the actuators described in Patent Documents 1 to 3 include the frictional force between the drive member (the drive member and the engagement member described above) and the driven member (the lens barrel and the movable plate described above) and the inertia of the driven member. The speed difference between when stretched and when shrunk must be set so that the magnitude relationship with the force is reversed between when the piezoelectric element is stretched and when it is shrunk. Therefore, there is a problem that it is very difficult to select a spring force that frictionally engages the driven member and the driving member with an appropriate friction force. In particular, in Patent Document 3, since the spring force is generated by the shape of the drive member (engagement member), it is very difficult to set an appropriate spring force. For this reason, in Patent Document 3, there is a risk that the driven member may not move accurately because the frictional force increases and the driven member does not slip, or the frictional force decreases and the driven member stops moving. was there.

  The present invention has been made in view of such circumstances, and it is an object of the present invention to provide an actuator control method capable of accurately moving a driven member.

  In order to achieve the above object, the invention described in claim 1 is frictionally engaged with the plurality of piezoelectric elements, the plurality of driving members integrally attached to the plurality of piezoelectric elements, and the plurality of driving members. And a driven member extending in the driving direction and a control unit that applies a voltage of a pulse waveform to the plurality of piezoelectric elements at a predetermined timing. The deformation speed is different between the expansion and contraction of the element, the timing is the same for the plurality of piezoelectric elements when the deformation speed is slow, and the timing is different for the plurality of piezoelectric elements when the deformation speed is high. A voltage is applied to the capacitor.

  According to the first aspect of the present invention, since the deformation speed of the piezoelectric element is different between when stretched and when contracted, the driven member moves together with the driving member when the deformation speed is low, and when the deformation speed is high Then, the driven member slides against the driving member and stops. Therefore, the driven member can be moved in one direction.

  According to the first aspect of the present invention, since the timing is made equal by a plurality of piezoelectric elements at a slow deformation speed, the driven member is driven by the plurality of driving members. The member can be reliably moved with a large driving force. Since the timing is different among the plurality of piezoelectric elements at a high deformation speed, the driving member can move individually, and the driven member can be prevented from moving with the driving member, and the driven member can be reliably Can be stopped. Therefore, according to the first aspect of the present invention, the driven member can be accurately moved. In addition, since the difference in driving force between the expansion and contraction of the piezoelectric element is increased, it is easy to set the frictional force between the driven member and the driving member.

  According to the first aspect of the present invention, since the driven member extends in the driving direction, the friction engagement surface between the driven member and the driving member is always at a constant position with respect to the piezoelectric element. To be kept. Therefore, the friction engagement surface can always be arranged in the vicinity of the piezoelectric element. Thereby, the vibration of the piezoelectric element is transmitted to the driven member without being attenuated by the driving member, so that the driven member can be reliably moved even when a high-frequency driving pulse is applied to the piezoelectric element. Therefore, the driven member can be moved at high speed even with a low voltage.

  According to a second aspect of the present invention, in the first aspect of the invention, the actuator is a lens moving actuator that moves a lens frame integrally attached to the driven member along an optical axis. And

  According to the actuator control method of the present invention, the deformation speed is different between when the piezoelectric element is stretched and when the piezoelectric element is contracted, and when the deformation speed is slow, the timing is equal among the plurality of piezoelectric elements, and the deformation speed is high. At this time, since the voltages are applied so that the timings are different among the plurality of piezoelectric elements, the driven member can be moved accurately.

  Hereinafter, preferred embodiments of a method for controlling an actuator according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a perspective view showing the configuration of a lens apparatus to which the actuator control method of the present invention is applied. The lens device shown in FIG. 1 has a box-shaped case composed of a case body 12 and a lid 14, and a fixed lens 16 is attached to the side surface of the case body 12.

  Two lens frames 18 and 20 are provided inside the case body 12, and movable lenses such as a zoom lens and a focus lens are held in the two lens frames 18 and 20. The two lens frames 18 and 20 are supported by two guide rods 22 and 24 arranged in parallel with the optical axis of the fixed lens 16 so as to be slidable in the optical axis direction. That is, a guide portion 23 is formed to project from the outer peripheral surface of the lens frame 18, and the guide rod 24 is inserted and guided through the through hole of the guide portion 23, and is projected to the opposite side of the guide portion 23. When the guide rod 22 is engaged with the U-shaped groove of the engaging portion (not shown), the lens frame 18 is supported slidably in the optical axis direction. Similarly, a guide portion 25 is formed on the outer peripheral surface of the lens frame 20 so as to be guided by being inserted through the through hole of the guide portion 25, and protrudes on the opposite side of the guide portion 25. When the guide rod 24 is engaged with the U-shaped groove of the formed engaging portion 27, the lens frame 20 is supported slidably in the optical axis direction.

  The lens frames 18 and 20 are integrally formed with driven plates (corresponding to driven members) 26 and 26, respectively. The driven plate 26 is formed in an elongated rectangular shape, and is arranged so that its longitudinal direction is parallel to the optical axis. The material of the driven plate 26 is not particularly limited, but a light and strong material such as ceramic is selected.

  Actuators 30 and 30 are disposed on each driven plate 26 and 26. Each actuator 30, 30 is fixed by being fitted into the opening of the lid 14.

  FIG. 2 is a perspective view for explaining the basic structure of the actuator 30. Hereinafter, an example of the actuator 30 that drives the lens frame 18 will be described, but the actuator 30 that drives the lens frame 20 is configured similarly.

  As shown in FIG. 2, the actuator 30 is mainly composed of piezoelectric elements 32A and 32B, driving members 34A and 34B, a pressing spring 36, and pressing plates 38A and 38B. The piezoelectric elements 32A and 32B are arranged on both sides of the driven plate 26. The piezoelectric elements 32A and 32B are arranged such that the displacement direction thereof is the longitudinal direction of the driven plate 26 (that is, the driving direction). The pressing plates 38A and 38B fixed to the case lid 14 (see FIG. 1) are attached to one end face in the displacement direction of each piezoelectric element 32A and 32B, and the driving members 34A and 34B are integrally formed on the other end face. Attached. The drive members 34A and 34B are formed in a substantially rectangular block shape, and are made of a light and rigid material such as ceramic, like the driven plate 26 described above. The driving members 34A and 34B are formed with recesses 35A and 35B on the side surface opposite to the side facing the driven plate 26, and the presser spring 36 is engaged with the recesses 35A and 35B. The presser spring 36 is a plate spring that sandwiches the two drive members 34 </ b> A and 34 </ b> B, and the drive members 34 </ b> A and 34 </ b> B are pressed against the driven plate 26 by the biasing force of the presser spring 36. As a result, the drive members 34 </ b> A and 34 </ b> B are frictionally engaged with the driven plate 26.

  2 shows an example in which the presser spring 36 is used as a biasing means for biasing the driving members 34A and 34B to the driven plate 26, but other biasing means such as a compression spring or rubber is used. The driving members 34A and 34B may be individually urged by an elastic body.

  FIG. 3 is a block diagram illustrating a configuration of a control unit that applies a voltage to the piezoelectric elements 32A and 32B at a predetermined timing. As shown in the figure, amplifiers 31A and 31B are connected to the piezoelectric elements 32A and 32B, and are further connected to the CPU 29 via D / A converters 33A and 33B. The CPU 29 outputs a control signal at a predetermined timing. This signal is D / A converted by the D / A converters 33A and 33B, and then amplified by the amplifiers 31A and 31B to generate a rectangular-wave drive pulse signal. . The drive pulse signal of the piezoelectric element 32A and the drive pulse signal of the piezoelectric element 32B are generated as rectangular waves having the same timing of one of the rising edge or the falling edge and the other timing of the rising edge or the falling edge. The

  4A and 4B show examples of drive pulse signals applied to the piezoelectric elements 32A and 32B. 4A is a drive pulse signal for moving the lens frame 18 of FIG. 2 in the left direction, and FIG. 4B is a drive pulse signal for moving the lens frame 18 of FIG. 2 in the right direction. It is.

  In the case of FIG. 4A, a substantially sawtooth drive pulse that gently rises from time α1 to time α2 and falls sharply at time α3 is applied to the piezoelectric element 32A. The piezoelectric element 32B is applied with a substantially sawtooth drive pulse that rises gently from time α1 to time α2 and falls sharply at time α4. Accordingly, from time α1 to time α2, the piezoelectric elements 32A and 32B are gently extended at the same time, so that the drive members 34A and 34B in FIG. 2 move slowly to the left. At this time, since the driving members 34A and 34B move gently, the driven plate 26 is held by the frictional force with the driving members 34A and 34B, and moves to the left together with the driving members 34A and 34B. On the other hand, only the piezoelectric element 32A contracts rapidly at time α3, and only the piezoelectric element 32B contracts rapidly at time α4. Accordingly, at time α3 and time α4, the drive members 34A and 34B in FIG. 2 each move independently and suddenly move to the right. When the driving members 34A and 34B move suddenly in this way, slip occurs between the driven plate 26 and only the driving members 34A and 34B move while the driven plate 26 is stopped. Therefore, at the time α3 and the time α4, the piezoelectric elements 32A and 32B can be contracted and returned to the original state while the driven plate 26 is stopped. From the above, when the driving pulse of FIG. 4A is repeatedly applied, the driven plate 26 of FIG. 2 repeats the movement and the stop in the left direction, so that the lens frame 18 can be moved in the left direction.

  In the case of FIG. 4B, a substantially sawtooth drive pulse that gently falls from time α5 to time α6 and suddenly rises at time α7 is applied to the piezoelectric element 32A. Then, a substantially sawtooth drive pulse that gently falls from time α5 to time α6 and suddenly rises at time α8 is applied to the piezoelectric element 32B. Therefore, from time α5 to time α6, the piezoelectric elements 32A and 32B are gradually contracted simultaneously, so that the driving members 34A and 34B in FIG. 2 move gently in the right direction. At this time, since the driving members 34A and 34B move gently, the driven plate 26 is held by the frictional force with the driving members 34A and 34B and moves to the right together with the driving members 34A and 34B. On the other hand, only the piezoelectric element 32A rapidly expands at the time α7, and only the piezoelectric element 32B rapidly expands at the time α8. Therefore, at time α7 and time α8, the drive members 34A and 34B in FIG. When the driving members 34A and 34B move suddenly in this way, slip occurs between the driven plate 26 and only the driving members 34A and 34B move while the driven plate 26 is stopped. Therefore, at time α7 and time α8, the piezoelectric elements 32A and 32B can be extended and returned to the original state while the driven plate 26 is stopped. From the above, when the driving pulse in FIG. 4B is repeatedly applied, the driven plate 26 in FIG. 2 repeats the movement and the stop in the right direction, so that the lens frame 18 can be moved in the right direction.

  Next, the operation of the actuator according to the present invention will be described.

  Hereinafter, a comparative example in which voltages are applied to the piezoelectric elements 32A and 32B of the actuator 30 shown in FIGS. 1 and 2 in a substantially sawtooth shape as shown in FIGS. 5A and 5B will be described.

  In the case of FIG. 5A, a drive pulse having the same shape, that is, a substantially sawtooth drive pulse that rises gently from time β1 to time β2 and falls sharply at time β3 is applied to the piezoelectric elements 32A and 32B. Yes. Therefore, at time β3, the piezoelectric elements 32A and 32B are rapidly contracted at the same timing.

  Similarly, in the case of FIG. 5B, the piezoelectric elements 32A and 32B have the same shaped drive pulse, that is, a substantially sawtooth drive pulse that gently falls from time β4 to time β5 and rises rapidly at time β6. Applied. Therefore, at time β6, the piezoelectric elements 32A and 32B are rapidly expanded at the same timing.

  When the piezoelectric elements 32A and 32B are suddenly deformed at the same timing as described above, the driving members 34A and 34B move simultaneously while holding the driven plate 26, so that the driven plate 26 is driven by the driving members 34A and 34B. It becomes easy to move with. Therefore, the deformation speed when the piezoelectric elements 32A and 32B are extended and contracted is set strictly or the frictional force between the driven plate 26 and the drive members 34A and 34B is set so that the moved plate 26 is surely stopped. Must be set strictly. Therefore, it becomes very difficult to select the pulse shape and the spring constant of the presser spring 36. Further, when the selection of the pulse shape and the selection of the spring constant of the presser spring 36 are not performed accurately, the driven plate 26 moves both when the piezoelectric elements 32A and 32B are expanded and contracted. It becomes impossible to move the driven plate 26 accurately.

  On the other hand, in the present invention, as shown at time α3 and time α4 in FIG. 4A or at time α7 and time α8 in FIG. 4B, the two piezoelectric elements 32A and 32B are suddenly deformed. The timing to make is shifted. Accordingly, the drive member 34B is stopped when the drive member 34A moves, and the drive member 34A is stopped when the drive member 34B moves. For this reason, the driven plate 26 is not easily moved by being driven by the driving members 34A and 34B, and the driven plate 26 can be surely stopped. Therefore, by applying the pulse-shaped voltage shown in FIGS. 4A and 4B to the piezoelectric elements 32A and 32B, the movement and stop of the driven plate 26 can be reliably controlled. 26 drive control can be performed accurately.

  Further, when the control is performed as described above, the difference in driving force between when the driven plate 26 is moved and when the driven plate 26 is stopped increases, so that an unstable factor in driving control is reduced, and the driven plate 26 and the driving member 34A are reduced. , 34B can be easily set. Therefore, the driven plate 26 can be controlled stably and reliably.

  Further, according to the present embodiment, the driven plate 26 extends in the driving direction, and the friction engagement surfaces between the driving members 34A and 34B and the driven plate 26 are always constant with respect to the piezoelectric elements 32A and 32B. Since the structure is maintained in a positional relationship, the friction engagement surface can always be disposed in the vicinity of the piezoelectric elements 32A and 32B. Thereby, the vibrations of the piezoelectric elements 32A and 32B can be reliably transmitted to the driven plate 26, and control by high-frequency driving pulses becomes possible. Therefore, the driven plate 26 can be moved at a high speed even with a low voltage.

  In the above-described embodiment, the driven member is driven in the optical axis direction. However, the driving direction of the driven member is not limited to this. For example, the lens device shown in FIG. 6 is an example of driving in a direction orthogonal to the optical axis. This lens device includes a lens frame 52 that holds a lens group including a moving lens 50 and a lens frame 56 that holds a lens group including a moving lens 54. Each lens frame 52, 56 is slidably supported by two guide rods 58, 60 arranged in the optical axis direction. The lens frames 52 and 56 are provided with cam pins 62 and 64, respectively. The cam pins 62 and 64 are engaged with cam grooves 68 and 70 formed in the moving plate 66. The moving plate 66 is supported so as to be slidable in the vertical direction in FIG. 6 (that is, the direction orthogonal to the optical axis), and the actuator 30 is attached to the moving plate 66. The piezoelectric elements 32A and 32B of the actuator 30 are provided on both sides of the moving plate 66, and are arranged to expand and contract in the vertical direction. Drive members 34A and 34B are attached below the piezoelectric elements 32A and 32B. A pressing spring 36 is attached to the driving members 34 </ b> A and 34 </ b> B, and the driving members 34 </ b> A and 34 </ b> B are frictionally engaged with the moving plate 66 by the urging force of the pressing spring 36. Therefore, when the voltage of the driving pulse described above is applied to the piezoelectric elements 34A and 34B, the moving plate 66 is driven in the vertical direction, and the lens frames 52 and 56 are moved back and forth in the optical axis direction. Also in the lens apparatus configured as described above, the moving plate 66 can be stably and accurately moved by applying the pulse-shaped voltage shown in FIGS. 4 (A) and 4 (B).

  In the lens device shown in FIG. 7, cam pins 62 and 64 formed on the lens frames 52 and 56 are engaged with cam grooves 74 and 76 formed on the swing plate 72. A hole 78 is formed in the swing plate 72, and the swing plate 72 is swingably supported through a shaft member (not shown) inserted through the hole 78. In the actuator 30, drive members 34 </ b> A and 34 </ b> B are arranged on both sides of the swing plate 72, and are frictionally engaged with the swing plate 72 from both sides by a presser spring 36. Also in this case, the oscillating plate 72 can be moved stably and accurately in the oscillating direction by applying the pulse-shaped voltage shown in FIGS. 4 (A) and 4 (B).

  The lens apparatus shown in FIG. 8 has a fixed cylinder 80, and a lens frame 84 of a moving lens 82 is supported inside the fixed cylinder 80 so as to be slidable in the optical axis direction. A driving cylinder 86 is rotatably supported outside the fixed cylinder 80, and the lens frame 84 is configured to move back and forth in the optical axis direction by rotating the driving cylinder 86. . A flange 88 is formed on the drive cylinder 86, and the actuator 30 is attached to the flange 88. In the actuator 30, the drive members 34 </ b> A and 34 </ b> B are disposed on both sides of the flange 88, and are frictionally engaged with the flange 88 from both sides by the presser spring 36. Also in this case, the drive cylinder 86 can be stably and accurately moved in the rotation direction by applying the pulse-shaped voltage shown in FIGS. 4 (A) and 4 (B).

  Further, in the above-described embodiment, the example in which the two piezoelectric elements 32A and 32B are provided has been described. However, three or more piezoelectric elements may be provided. For example, FIG. 9 shows an example in which four piezoelectric elements 32A to 32D are provided. The piezoelectric elements 32A and 32C are arranged on the opposite side of the piezoelectric elements 32B and 32D with respect to the driven plate 26, respectively. Drive members 34A to 34D are integrally attached to the four piezoelectric elements 32A to 32D, respectively. The drive members 34A to 34D are urged by the presser springs 26 and 26, and are frictionally engaged with the driven plate 26. Has been. Driving pulses as shown in FIGS. 10A and 10B are applied to the four piezoelectric elements 32A to 32D. That is, in the case of FIG. 10A, the piezoelectric elements 32A to 32D are given substantially sawtooth drive pulses that rise gently simultaneously from time γ1 to time γ2 and fall sharply at different times from time γ3 to time γ6. Applied. Similarly, in the case of FIG. 10 (B), the piezoelectric elements 32A to 32D have substantially saw-tooth drive pulses that simultaneously gradually fall from time γ7 to time γ8 and rise sharply at different times from time γ9 to time γ12. Applied. By shifting the timing of suddenly deforming the piezoelectric elements 32A to 32D in this way, accurate drive control can be performed even when the four piezoelectric elements 32A to 32D are used.

  The application of the actuator described above can be applied to small precision devices such as digital cameras and mobile phones. In particular, the cellular phone needs to be driven at a low voltage of 3 V or less, but by using the actuator of the present invention, it can be driven even at a high frequency of about 20 kHz, and the lens frame 20 can be driven at 2 mm / s or more. It can be moved at high speed. Therefore, even a zoom lens that needs to move about 10 mm can be moved quickly.

1 is an exploded perspective view showing a configuration of a lens apparatus to which an actuator of the present invention is applied. Perspective view explaining the basic principle of the actuator Block diagram showing the configuration of the controller Waveform diagram of drive pulse applied to piezoelectric element of FIG. Waveform diagram of drive pulse different from FIG. The perspective view which shows the main structures of the lens apparatus different from FIG. The perspective view which shows the main structures of the lens apparatus different from FIG. The perspective view which shows the main structures of the lens apparatus different from FIG. A perspective view explaining the basic principle of an actuator provided with four piezoelectric elements Waveform diagram of drive pulse applied to piezoelectric element of FIG.

Explanation of symbols

  18, 20 ... Lens frame, 26 ... Driven plate, 32A, 32B ... Piezoelectric element, 34A, 34B ... Drive member, 36 ... Presser spring

Claims (2)

A plurality of piezoelectric elements; a plurality of driving members integrally attached to the plurality of piezoelectric elements; a driven member frictionally engaged with the plurality of driving members and extending in a driving direction; In a method for controlling an actuator comprising a control unit that applies a voltage of a pulse waveform to the piezoelectric element at a predetermined timing,
The control unit is configured so that the deformation speeds of the piezoelectric elements are different at the time of expansion and contraction, and the timing is the same for the plurality of piezoelectric elements when the deformation speed is low, and when the deformation speed is high, the control elements A method of controlling an actuator, wherein a voltage is applied so that timing is different between piezoelectric elements.   2. The actuator control method according to claim 1, wherein the actuator is a lens moving actuator that moves a lens frame integrally attached to the driven member along an optical axis.

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