JPH11149031A - Driving mechanism using electromechanical conversion element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving mechanism using an electromechanical conversion element whose durability is improved. SOLUTION: One end of a piezoelectric actuator 3 in an elongation and contraction deforming direction is fixed to a holding frame 14, and the other end is fixed to a guide shaft 18 movably held by the holding frames 14 and 15. A U-shaped spring 23 attached at a moving frame 22 is brought into linear contact with the guide shaft 18, so that the moving frame 22 is coupled with the guide shaft 18 by friction. Driving voltage to make extending deformation speed and contracting deformation speed different is applied to the piezoelectric actuator 3, and the moving frame 22 is stopped in a stopped state by the inertia of mass when the moving speed of the guide shaft 18 is high, and it is made to follow when the moving speed is low, so that the moving frame 22 is driven along the guide shaft 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving mechanism that uses an electromechanical transducer such as a piezoelectric actuator as a driving source, and drives a driven member by utilizing expansion and contraction of the element.

[0002]

2. Description of the Related Art Conventionally, as a driving mechanism of this type, for example, a mechanism used for zooming or focusing driving of a photographic lens of a camera is disclosed in Japanese Patent Laid-Open Publication No. Hei.
No. 69070. In this drive mechanism, one of two parallel guide shafts is configured to be movable in the axial direction with respect to the fixed member, and one end of the axially movable guide shaft is provided with a piezoelectric actuator mounted on the fixed member. The tip is fixed, and an arm formed on a lens holding frame as a driven member is attached to the outer peripheral surface of the guide shaft in a frictionally coupled state. Another arm formed on the lens holding frame is slidably attached to the other guide shaft.

In this drive mechanism, when the lens is driven, a drive pulse having a substantially sawtooth waveform is applied to the piezoelectric actuator so that the guide shaft is reciprocated continuously with a small stroke. The pulse waveform is different between the forward and backward movements of the guide shaft, and when the guide shaft moves in the direction of higher speed, the lens holding frame hardly moves due to the inertia of its mass, and the guide shaft moves in the opposite direction. It is defined that the lens holding frame moves with the guide shaft only when the lens holding frame moves slowly. Therefore, since the lens holding frame is repeatedly moved and stopped at a fine time pitch, it substantially continuously moves in one direction while a pulse is applied to the piezoelectric actuator.

[0004]

However, in the above configuration, when the ridge of the projection of the leaf spring attached to the lens holding frame makes point contact with the guide shaft, the lens holding frame and the guide shaft are frictionally coupled. Has become. Therefore, there is a problem that the contact portion is easily worn and the durability of the drive mechanism is not good.

Accordingly, a technical problem to be solved by the present invention is to provide a driving mechanism using an electromechanical transducer having improved durability.

[0006]

A driving mechanism according to the present invention comprises a holding member, an electromechanical transducer having one end fixed to the holding member, and a second end fixed to the electromechanical transducer. A movable member, a driven member frictionally coupled to the movable member, and a drive circuit for applying a drive voltage to the electromechanical transducer to cause expansion and contraction displacement at different speeds during expansion and contraction; Having a biasing member for providing a frictional force for coupling the movable member and the driven member,
The movable member and / or the driven member and the biasing member are configured to be in line contact or surface contact.

In the above structure, when a driving voltage such as a pulse having a sawtooth waveform is applied to the electromechanical transducer and the electromechanical transducer is deformed at a high speed in the direction of expansion or contraction, the driven member is driven. Does not follow the operation of the movable member due to the inertia of its mass, and remains at the same position. When the electromechanical transducer is deformed in the opposite direction at a lower speed, the driven member moves following the operation of the movable member. Therefore, the driven member continuously moves in one direction as the electromechanical transducer repeatedly expands and contracts.

In the above construction, the urging means is provided to apply a frictional force for coupling the movable member and the driven member.
Since the movable member and / or the driven member make line contact or surface contact, the contact portion is less likely to be worn as compared with the case of point contact.

Therefore, the durability can be improved.

[0010] Preferably, both ends of a contact portion between the movable member and / or the driven member and the urging member have no corners.

According to the above configuration, since there is no corner, it is possible to prevent the movable member and / or the driven member and the biasing member from being hindered from being hindered.

Preferably, the hardness of the movable member is different from that of the urging member.

According to the above configuration, since the hardness is different, it is possible to prevent one of the movable member and the urging member from being damaged by the other.

Further, the present invention provides a camera provided with the above-mentioned driving mechanism. Further, the present invention provides a photographic lens of a camera comprising the above driving mechanism.

[0015]

FIG. 1 shows a first embodiment of a camera provided with a drive mechanism using an electromechanical transducer according to the present invention.
This will be described in detail with reference to FIG. Note that this drive mechanism is an example configured to drive a photographing lens of a single-lens reflex camera.

FIG. 1 shows a piezoelectric ceramic PE formed of PZT (zircon / lead titanate) or the like. The piezoelectric ceramic PE has a property that the center of gravity of the positive charge and the center of gravity of the negative charge in the crystal lattice do not coincide with each other, and are themselves polarized, and have a property of expanding when a voltage E is applied in the polarization direction P. I have. However, since the distortion of the piezoelectric ceramic PE in this direction is very small and it is difficult to drive the driven object due to the amount of this distortion, a plurality of piezoelectric ceramic PEs are stacked as shown in FIG. Are provided as practical ones. In this embodiment, the laminated piezoelectric actuator is used as a drive source.

FIGS. 3A and 3B show the configuration of the taking lens of this camera. FIG. 3A shows the positions of the constituent lenses at the wide-angle end and FIG. 3B shows the positions of the constituent lenses at the telephoto end. As shown in the figure, this photographing lens is composed of five lenses from a first lens L1 to a fifth lens L5.

FIG. 4 is a block diagram schematically showing the circuit configuration of the camera. In the figure, reference numeral 1 denotes a microcomputer for controlling the driving of the taking lens. 2
Is a drive cylinder having a spiral cam groove (not shown) formed in the cam groove of the drive cylinder 2 and a fixed cylinder located on the inner surface side of the drive cylinder 2 along the optical axis. A pin (not shown) provided on a holding frame for integrally holding the third lens L3 and the fifth lens L5 is passed through both of the straight grooves (not shown), and the third and fifth lenses are rotated by the rotation of the driving cylinder 2. The lenses L3 and L5 are moved in the optical axis direction. Reference numeral 3 denotes a laminated piezoelectric actuator that drives the fourth lens L4, and reference numeral 4 denotes a driving cylinder 2
This is an electromagnetic motor that rotates. The multi-layer piezoelectric actuator 3 is connected to the microcomputer 1 via a D / A converter 5 and a drive amplifier 6, and a motor 4
Is connected to a microcomputer via a drive circuit 7. Further, the fourth lens L4 and the driving cylinder 2 are
Positions are detected by sensors such as photointerrupters used as the position detecting devices 8 and 9, respectively, and output signals of the position detecting devices 8 and 9 are input to the microcomputer 1.

Reference numeral 10 denotes an operation ring rotatably provided on the outer peripheral surface of the lens barrel.
A signal corresponding to the rotation direction and the amount of rotation is transmitted to the microcomputer 1, and based on the signal, the microcomputer 1 determines the direction and speed at which the lens should be zoomed, and the multilayer piezoelectric actuator 3 and the electromagnetic motor 4 are driven. Is done. Further, the microcomputer 1 has a memory 11 storing various data regarding the driving amount of zooming.
Is connected. The operation ring 10 may be replaced by another operation member such as a lever or a button.

FIG. 5 is a flowchart showing the flow of the operation during zooming of the taking lens. When the operation ring is operated and zooming is started in step # 01, in step # 02, the operation ring 10 is turned on.
An output signal corresponding to the rotation direction and the amount of rotation is supplied to the microcomputer 1 as zoom information such as a zoom direction and a zoom speed. In step # 03, the microcomputer 1 determines a target position for driving the lens according to the signal.

Next, in step # 04, the drive direction and drive amount of the drive cylinder are determined from the determined target position and current position. Then, in steps # 05 to # 07, the motor 4 is driven while counting the output pulses of the photointerrupter used as the position detection device 9 until the driving cylinder reaches the target zoom position, and the number of pulses becomes a predetermined number. Is reached, the motor stops in step # 08.

On the other hand, at the same time, the fourth lens L4 is driven. When the focal length of the lens changes, the position to be taken by the fourth lens L4 is stored in advance in the memory 11 for each focal length, and the fourth lens L4 corresponding to the target position is stored.
The position 4 is read in step # 09. Then, in step # 10, the number of driving pulses and the driving direction are determined from the difference from the current position, and based on that, steps # 11 to # 11 are performed.
At 13 the stacked pressure actuator is driven.

Next, details of the driving mechanism will be described with reference to FIGS. 6 is a sectional view of a main part of a lens barrel to which the driving mechanism is applied, FIG. 7 is a sectional view taken along line VII-VII of FIG. 6, and FIG. 8 is an exploded perspective view. As described above, the fixed barrel 12 is disposed on the inner surface side of the drive barrel 2, and the pin 16 of the holding frame (fixed side member) 13 that holds the third lens L 3 and the fifth lens L 5 has the drive barrel 2. Spiral cam groove 2a
And a straight groove 12a of the fixed cylinder 12 as a cam follower. The holding frame 13 includes a third lens L
The substantially cylindrical first holding frame 14 holding the pin 3 and having the pin 16 attached thereto, and the substantially disk-shaped second holding frame 15 holding the fifth lens L5 are fixed with screws 17 (FIG. 8) or the like. They are fixed to each other by means. First holding frame 1
4 has holes 14a and 14b at radially opposite positions,
The second holding frame 15 has holes 15a and 15b fixed on the first holding frame 14 and passing through the holes 14a and 14b and located on a line parallel to the optical axis. A first guide shaft (movable member) 18 is held in the holes 14a and 15a so as to be movable in the axial direction.
The second guide shaft 19 is held in the holes 14b, 15b with both ends regulated.

The first holding frame 14 has a flange 14c at an end opposite to the second holding frame 15, and the flange 14c is reinforced by a reinforcing plate 33 made of a high-strength material such as metal. . One end of the multilayer piezoelectric actuator 3 in the direction of expansion and contraction is fixed to the reinforcing plate 33 by bonding, and the other end of the multilayer piezoelectric actuator 3 is fixed to the first guide shaft 18 by bonding. Also, the second holding frame 1
5, a leaf spring 20 formed so as to cover the tip of the first guide shaft 18 is fixed with screws 21 at both ends in order to bias the first guide shaft 18 toward the piezoelectric actuator 3 side. The reinforcing plate 33 is provided so that when a voltage is applied to the piezoelectric actuator 3, the flange 14c is not deformed by an impact force at the time of expansion and contraction. Originally, if the first holding frame 14 is formed of a metal having high hardness, the reinforcing plate 33 is unnecessary, but if the first holding frame 14 must be formed of plastic or the like in terms of cost, weight, etc.
Without the reinforcing plate 33, the impact force of the piezoelectric actuator 3 is absorbed by the deformation of the flange 14c, and the driving efficiency is reduced.

The moving frame 22 for holding the fourth lens L4 is
Boss 22b having hole 22a to be fitted to first guide shaft 18
And a U-shaped notch 22 into which the second guide shaft 19 fits.
has c. By the way, in recent years, interchangeable zoom lenses for single-lens reflex cameras have been increasing in magnification and downsizing.
Along with this, the position error of each lens has been greatly affecting the optical performance of the taking lens.
In the camera of this embodiment, since the sensitivity to the position error of the fourth lens L4 with respect to the third and fifth lenses L3 and L5 is large, the camera is fixed after removing the inclination and the parallel eccentricity with respect to the moving frame 22. Further, the third and fifth lenses L3, L5
The U-shaped spring 23 is used to reduce the “gap” of the fitting portion between the moving frame 22 and the two guide shafts 18 and 19 so as not to cause tilting or eccentricity during the movement of the fourth lens L4 with respect to And the moving frame 22 using the L-shaped spring 24.
Are pressed against guide shafts 18 and 19 in one direction. As a result, the guide shafts 18, 19 and the moving frame 22
Is always kept in a frictionally connected state. The U-shaped spring 23 is fitted in a groove 22d formed in the boss 22b, and the L-shaped spring 24 is fixed to the moving frame 22 with a screw 25.

In the above configuration, the U-shaped spring 23 slides on the guide shaft 18 when the moving frame 22 operates. Here, if the cross-sectional shape of the U-shaped spring 23 is circular, the guide shaft 18 and the spring 23 come into point contact with each other, and depending on the state of the guide shaft 18, the guide shaft 18 may be caught and the driving of the moving frame 22 may be performed. There is a possibility that it will hinder. Further, in that case, the contact portion may be worn quickly, and the durability may be reduced. Therefore, in this embodiment, the cross section of the spring 23 is formed in an oval shape, and
3 is in line with the first guide shaft 18 and has no corners at both ends (it may be configured to make surface contact). In this embodiment, the surface hardness of the spring 23 is set lower than the hardness of the first guide shaft 18 in order to prevent the first guide shaft 18 from being damaged.

On the other hand, the first guide shaft 18 is also urged against the holding frame 13 in one direction by a spring 34 fixed by a screw 35 to prevent rattling therebetween. The same configuration is also taken between the guide shaft 19 and the moving frame 22 and between the guide shaft 19 and the holding frame 13.

Next, a method of driving the moving frame 22 by this mechanism will be described. In general, the laminated piezoelectric actuator 3 has a small amount of displacement when a voltage is applied, but generates a large force and has a sharp response. Therefore, as shown in FIG. 9A, when a pulse voltage having a substantially sawtooth waveform with a sharp rise and a slow fall is applied, the piezoelectric actuator 3
Expands sharply at the rise of the pulse and shrinks more slowly at the fall. Therefore, when the piezoelectric actuator 3 is extended, the first guide shaft 1
6 is pushed rightward in FIG. 6, but the moving frame 22 holding the fourth lens L4 does not move together with the guide shaft 18 due to inertia due to its own mass. Causes a slip and stops at that position. On the other hand, when the pulse falls, the first guide shaft 18 returns slowly compared to when the pulse rises.
8 and moves leftward in FIG. 6 integrally with the guide shaft 18. Therefore, by applying a pulse whose frequency is set to several hundreds to tens of thousands of hertz, the moving frame 22 is set.
Can be continuously moved at a desired speed. Also, as shown in FIG. 9 (b), if a pulse with a slowly rising voltage and a sharp falling voltage is applied, the moving frame 22
Can be moved to the right in the figure.

In this embodiment, a pulse having a sawtooth waveform is generated by converting a signal output from the microcomputer 1 into an analog signal by the D / A converter 5 and amplifying the analog signal by the amplifier 6. Done. The signal representing the waveform shape is stored in the memory 11 in advance according to the zooming direction and speed set by operating the operation ring 10. The stored data includes, for example, the maximum voltage Vmax, the voltage hold times t1 and t2, the number of rising and falling stages, and the one-step hold time Δt at that time shown in FIG. In FIG. 9, a portion where the voltage changes relatively slowly is shown by a straight line, but strictly speaking, a pulse having this waveform is obtained by outputting a stepwise signal from the microcomputer 1.

According to the present embodiment, since the movable frame 22 and the guide shafts 18 and 19 are urged in one direction by the respective springs, the movable frame 22 is substantially "wobbled" with respect to the holding frame 13. Can be driven without any Further, as described above, the moving frame 22 is moved relative to the guide shafts 18 and 19 by the springs 23 and 24.
, And a frictional force is generated in the meantime, so that "play" can be prevented from occurring even after repeated driving, and a large change does not occur in the frictional force.

As described above, according to the present embodiment, the moving frame 22
Since the “gap” hardly occurs, the height of the driven object such as the moving frame 22 is higher than that of a conventional drive mechanism using a motor or the like, which has to provide the “gap” to reduce the driving torque. It is possible to commercialize a lens that can be driven with high precision and has better optical performance than before. In addition, the moving frame 22 can be driven at an arbitrary speed by appropriately setting the frequency of the pulse to be applied. Therefore, a speed reduction mechanism is not required, and the camera can be downsized. In this embodiment, since the distal end of the guide shaft 18 is urged toward the piezoelectric actuator 3 by the leaf spring 20, the lens can be driven when the lens barrel is set vertically, or when the lens is turned upward or downward. Thus, when the camera is placed on a desk, it is possible to prevent the adhesive portions at both ends of the piezoelectric actuator from peeling off.

In the above embodiment, the drive cylinder is described as being driven by an electromagnetic motor, but a laminated piezoelectric actuator may be used instead of the electromagnetic motor. Therefore, as a second embodiment, a mechanism for driving a driving cylinder by a laminated piezoelectric actuator will be described with reference to FIGS.

FIG. 10 is a central longitudinal sectional view of this mechanism, and FIG.
FIG. 11 is a sectional view taken along line XI-XI in FIG. 10. Driving cylinder 2 is fixed cylinder 1
2, it is mounted movably in the rotational direction without being moved in the axial direction by a coupling method such as bayonet coupling. Also,
As described above, the cam groove 2a provided in the drive cylinder 2;
The pins 16 attached to the holding frame 22 (FIG. 6) are passed through both the straight grooves 12a provided in the fixed barrel 12, and the holding frame 22 moves in the optical axis direction by the rotation of the driving barrel 2. ing. Since the lenses L3 to L5 are highly sensitive to positional errors, the cam groove 2a, the linear groove 12a and the pin 1
6 and the “play” between the fixed barrel 12 and the drive barrel 2 are set to be extremely small.

The drive cylinder 2 and the fixed cylinder 12 have flange portions 2b and 12b facing each other, and a pressure contact member (movable member) 26 is mounted on both flange portions 2b and 12b. Although the press contact member 26 is shown as a U-shaped integral part in the figure, the arms 26a and 26b are movable in directions of approaching or separating from each other, and a spring 27 is provided.
Are biased in a direction to approach each other. Therefore, the drive cylinder 2 is configured so that "play" hardly occurs in the optical axis direction with respect to the fixed cylinder 12. In addition, each member 2,
Reference numerals 12 and 26 denote a flange portion 2b of the drive cylinder 2 and the pressing member 26.
Is relatively large between the drive cylinder 2 and the fixed cylinder 12, and between the flange 12b of the fixed cylinder 12 and the pressure contact member 26.
The material is selected so that the frictional force between them is relatively small.

As shown in FIG. 11, one end of a piezoelectric actuator 28 disposed substantially parallel to the tangential direction of the outer peripheral surface of the drive cylinder 2 is fixed to one end of the pressure contact member 26.
The other end of the piezoelectric actuator 28 is fixed to a holding member 30 fixed to the fixed cylinder 12 with screws 29. Further, an L-shaped leaf spring 31 is screwed on the fixed cylinder 12 on the opposite side of the pressure contact member 26 from the piezoelectric actuator 28.
And presses the pressure contact member 26 elastically against the piezoelectric actuator 28.

In the driving mechanism configured as described above,
When a pulse voltage having the waveform shown in FIG. 9A is applied to the piezoelectric actuator 28 in the same manner as described above, the piezoelectric actuator 2
When 8 is suddenly extended, the pressing member 26 moves to the left in FIG. 11, but the driving cylinder 2 remains at the same position due to inertia due to its mass. When the piezoelectric actuator 28 contracts more slowly, the driving cylinder 2 moves to the right in the figure together with the press-contact member 26. Therefore, the driving cylinder 2 can be continuously driven in the right direction in the figure by the continuous pulse. If the pulse having the waveform shown in FIG. 9B is used, the driving cylinder 2 can be driven continuously to the left in the drawing. Also in this embodiment, since the driving cylinder 2 can be driven with almost no backlash with respect to the fixed cylinder 12,
Since the positional accuracy of the lens is excellent and the pressing member 26 is urged toward the piezoelectric actuator 28 by the leaf spring 31, the piezoelectric actuator 28 can be prevented from peeling from the fixed cylinder 12 and the pressing member 26.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a piezoelectric element.

FIG. 2 is a perspective view showing a laminated piezoelectric actuator used in the drive mechanism according to the first embodiment of the present invention.

FIG. 3 is a diagram showing the configuration and operation of a photographing lens of a camera to which the driving mechanism is applied.

FIG. 4 is a block diagram schematically showing a circuit configuration of the camera.

FIG. 5 is a flowchart schematically showing the operation of the camera.

FIG. 6 is a central longitudinal sectional view of a taking lens barrel to which the driving mechanism is applied.

FIG. 7 is a sectional view taken along the line VII-VII of FIG. 6;

FIG. 8 is an exploded perspective view of the taking lens barrel.

FIG. 9 is a diagram showing a waveform of a pulse applied to a piezoelectric actuator.

FIG. 10 is a central longitudinal sectional view of a drive mechanism according to a second embodiment.

11 is a sectional view taken along line XI-XI in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Microcomputer 2 Drive cylinder 2a Cam groove 2b Flange part 3 Laminated piezoelectric actuator (electromechanical conversion element) 4 Motor 5 D / A converter (drive circuit) 6 Drive amplifier (drive circuit) 7 Drive circuit 8,9 Position detecting device DESCRIPTION OF SYMBOLS 10 Operation ring 11 Memory 12 Fixed cylinder 12a Straight groove 12b Flange part 13 Holding frame (holding member) 14 First holding frame 14a, 14b hole 14c flange 15 Second holding frame 15a, 15b hole 16 Pin 17 Screw 18 First guide shaft (Movable member) 19 Second guide shaft 20 Leaf spring 21 Screw 22 Moving frame (driven member) 22a Hole 22b Boss 22c Notch 23 Spring (biasing member) 24 Spring 25 Screw 26 Press-contact member 26a, 26b Arm 27 Spring 28 piezoelectric actuator 29 screw 30 holding member 31 leaf spring 32 screw 3 Reinforcing plate 34 spring 35 bis

Claims (5)

[Claims] 1. A holding member (13), and an electromechanical transducer (3) having one end fixed to the holding member.
And a movable member (1) fixed to the other end of the electromechanical transducer.
8); a driven member (22) frictionally coupled to the movable member; and a drive for applying a drive voltage to the electromechanical transducer to cause expansion and contraction displacement at different speeds when the electromechanical transducer is expanded and contracted. A circuit (5, 6), and a biasing member (23) for applying a frictional force for coupling the movable member and the driven member, wherein the movable member and / or the driven member; A driving mechanism, wherein the urging member is configured to be in line contact or surface contact. 2. The drive mechanism according to claim 1, wherein both ends of a contact portion between the movable member and / or the driven member and the urging member are formed without corners. 3. The drive mechanism according to claim 1, wherein the movable member and the urging member have different hardnesses. 4. A camera comprising the driving mechanism according to claim 1, 2 or 3. 5. A photographic lens for a camera, comprising the driving mechanism according to claim 1, 2 or 3.