JP2005354868A - Actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an actuator which can be moved at high speed even with a low voltage by providing piezoelectric elements at the opposite ends of a drive rod thereby preventing oscillation of the piezoelectric element from damping through the drive rod. <P>SOLUTION: The actuator is arranged such that a driven section 28 is formed integrally with a lens frame 20 and engages frictionally with a drive rod 24. The drive rod 24 is arranged in the direction of optical axis and piezoelectric elements 32A and 32B are provided at the opposite ends thereof. The piezoelectric elements 32A and 32B are applied synchronously with drive pulses of opposite phase. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an actuator, and more particularly to an actuator 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 drive rod is fixed to the end face of a piezoelectric element, and a lens barrel is slidably supported by the drive rod. A leaf spring is attached to the lens barrel, and a frictional force acts between the lens barrel 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.
Japanese Patent No. 2633066

  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 tip of the drive rod is mirrored. There was a problem that the cylinder could not be moved accurately. 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 displacement amount of the piezoelectric element, and to increase the single moving amount of the lens barrel. At low voltage, the lens barrel could not be moved at high speed.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an actuator that can be moved at high speed even with a low voltage.

  In order to achieve the object, the invention according to claim 1 is a piezoelectric element, a driving member integrally attached to the piezoelectric element and extending along a displacement direction of the piezoelectric element, and the driving member A driven member that is frictionally engaged with the piezoelectric element, and an actuator that moves the driven member along the driving member by applying a voltage to the piezoelectric element, wherein the piezoelectric element includes both end portions of the driving member. It is provided in.

  According to the first aspect of the present invention, since the piezoelectric elements are provided at both ends of the driving member, the vibration of the piezoelectric elements is transmitted to the driving member from both ends. Therefore, the vibration of the piezoelectric element is reliably transmitted to the entire drive member. Thereby, since the vibration of the piezoelectric element is transmitted without being attenuated, the movement of the driven member can be accurately controlled. Therefore, control by high-frequency drive pulses is possible, and 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 present invention, one of the piezoelectric elements provided at both ends of the driving member has a polarity reversed with respect to the other piezoelectric element. A drive pulse voltage is applied.

  According to a third aspect of the invention, in the first or second aspect of the invention, the actuator is an actuator for moving a lens that moves a lens frame integrally attached to the driven member along an optical axis. It is characterized by.

  According to the actuator of the present invention, since the piezoelectric elements are provided at both ends of the driving member, the movement of the driven member can be accurately controlled.

  Hereinafter, preferred embodiments of an actuator according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a perspective view showing a configuration of a lens device of a small precision device such as a mobile phone to which the actuator according to the present invention is applied. The lens device shown in FIG. 1 has a box-shaped case 12 constituting a lens unit body, and a fixed lens 16 is attached to the front surface of the case 12. A lens frame 20 holding a moving lens (for example, a zoom lens or a focus lens) 18 is provided inside the case body 12.

  On the outer peripheral surface of the lens frame 20, an engaging portion 22 is formed so as to protrude. A U-shaped groove 23 is formed in the engaging portion 22, and the guide rod 24 is engaged with the groove 23. The guide rod 24 is disposed in the optical axis direction and is fixed to the case 12.

  Further, as shown in FIG. 2, a guide portion 26 and a driven portion 28 are integrally formed on the lens frame 20. A through hole 27 is formed in the guide portion 26 in the optical axis direction, and the drive rod 30 is inserted into the through hole 27. The drive rod 30 is formed in a cylindrical shape with a light and strong material, for example, ceramic, and is disposed in parallel with the optical axis.

  A U-shaped groove 29 is formed in the driven portion 28, and a driving rod 30 is engaged with the groove 29. Four corner portions 34, 34... Of the driven portion 28 are formed to protrude upward. A friction plate 38 is provided in a range surrounded by the corner portions 34, 34. The friction plate 38 is bent in an arc shape in accordance with the side surface shape of the drive rod 30 and is placed on the drive rod 30.

  A presser spring 36 is attached to the driven portion 28. The presser spring 36 is formed to bend so as to sandwich the driven portion 28 from above and below, and the presser spring 36 urges the friction plate 38 downward. As a result, the friction plate 38 is frictionally engaged with the side surface of the drive rod 30. The friction plate 38 is prevented from falling off from the driven portion 28 by the corner portions 34, 34. Note that the friction plate 38 may be frictionally engaged with the drive rod 30 by using another biasing means, for example, an elastic body such as a compression spring or rubber, instead of the presser spring 36. Further, the frictional force between the friction plate 38 and the drive rod 30 is such that the frictional force becomes larger than the driving force when a driving pulse with a gradual voltage change is applied to the piezoelectric elements 32A and 32B. When a driving pulse having a rapid voltage change is applied to 32A and 32B, the frictional force is set to be smaller than the driving force.

  Piezoelectric elements 32A and 32B are provided at both ends of the drive rod 30 described above. The piezoelectric elements 32A and 32B are arranged so that the displacement direction is parallel to the optical axis. Then, the end face of the drive rod 30 is fixed to one end face in the displacement direction of the piezoelectric elements 32A, 32B, and the other end face of the piezoelectric elements 32A, 32B is brought into contact with the case 12 (see FIG. 1).

  3A and 3B show examples of driving pulses applied to the piezoelectric elements 32A and 32B. 3A is a drive pulse for moving the lens frame 20 of FIG. 1 to the left, and FIG. 3B is a drive pulse for moving the lens frame 20 of FIG. 2 to the right. .

  As shown in FIGS. 3 (A) and 3 (B), driving pulses having opposite phases are applied to the two piezoelectric elements 32A and 32B. In the case of FIG. 3A, a substantially sawtooth drive pulse that gently rises from time β1 to time β2 and suddenly falls at time β3 is applied to the piezoelectric element 32A. Then, a substantially sawtooth drive pulse that gently falls from time β1 to time β2 and suddenly rises at time β3 is applied to the piezoelectric element 32B. Therefore, from time β1 to time β2, the piezoelectric element 32A is gently expanded and the piezoelectric element 32B is gradually contracted, so that the drive rod 30 is displaced in the left direction in FIG. At this time, since the drive rod 30 is gently displaced, the driven portion 28 moves together with the drive rod 30. Thereby, the driven part 28 can be moved in the left direction of FIG. At time β3, the piezoelectric element 32A contracts rapidly and the piezoelectric element 32B expands rapidly, so that the drive rod 30 is displaced in the right direction in FIG. At that time, since the driving rod 30 is suddenly displaced, only the driving rod 30 moves while the driven portion 28 is stopped at that position due to inertia. Therefore, by repeatedly applying the sawtooth drive pulse shown in FIG. 3A, the driven portion 28 in FIG. 2 repeats the movement and stop in the left direction, so that the lens frame 20 is moved in the left direction. be able to.

  In the case of FIG. 3B, a substantially sawtooth drive pulse that gently falls from time β4 to time β5 and rapidly rises at time β6 is applied to the piezoelectric element 32A. Then, a substantially sawtooth drive pulse that gently rises from time β4 to time β5 and suddenly falls at time β6 is applied to the piezoelectric element 32B. Therefore, from time β4 to time β5, the piezoelectric element 32A is gradually contracted and the piezoelectric element 32B is gently expanded, so that the drive rod 30 is displaced in the right direction in FIG. At this time, since the drive rod 30 is gently displaced, the driven portion 28 moves together with the drive rod 30. Thereby, the driven part 28 can be moved rightward in FIG. At time β6, the piezoelectric element 32A expands rapidly and the piezoelectric element 32B contracts rapidly, so that the drive rod 30 is displaced leftward in FIG. At that time, since the driving rod 30 is suddenly displaced, only the driving rod 30 moves while the driven portion 28 is stopped at that position due to inertia. Therefore, by repeatedly applying the sawtooth drive pulse shown in FIG. 3B, the driven portion 28 of FIG. 2 repeats the movement and stop in the right direction, so that the lens frame 20 is moved in the right direction. be able to.

  As described above, in the actuator of the present embodiment, the piezoelectric elements 32A and 32B are disposed at both ends of the drive rod 30, and drive pulses having opposite phases are applied to the piezoelectric elements 32A and 32B in synchronization. As a result, the entire drive rod 30 can be reliably displaced. Therefore, the driven part 28 can be reliably moved at any position of the driving rod 30. Thereby, the position of the lens frame 20 can be accurately controlled.

  In the present embodiment, the piezoelectric elements 32A and 32B are arranged so that the displacement directions are opposite to each other. Therefore, since the hysteresis characteristics of the piezoelectric elements 32A and 32B act so as to cancel each other, errors due to the hysteresis of the piezoelectric elements 32A and 32B can be suppressed. Thereby, the position of the lens frame 20 can be controlled more accurately.

  The application of the actuator according to the present invention 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 at a high frequency of about 20 kHz, and the lens frame 20 can be driven at a high speed of 2 mm / s or more. It can be moved with. 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 device to which an actuator according to the present invention is applied. The perspective view which shows the structure of the actuator of 1st Embodiment. Waveform diagram of drive pulse applied to piezoelectric element of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Lens frame, 28 ... Driven part, 30 ... Drive rod, 32A, 32B ... Piezoelectric element, 34A, 34B ... Drive member, 36 ... Pressing spring, 38 ... Friction plate

Claims (3)

A piezoelectric element; a driving member that is integrally attached to the piezoelectric element and that extends along a displacement direction of the piezoelectric element; and a driven member that is frictionally engaged with the driving member. In an actuator that moves the driven member along the driving member by applying a voltage to the driving member,
The actuator, wherein the piezoelectric element is provided at both ends of the driving member.   The drive pulse voltage with the polarity reversed is applied to one of the piezoelectric elements provided at both ends of the drive member with respect to the other piezoelectric element. Item 10. The actuator according to Item 1.   3. The actuator 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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