Driving device

Abstract: A driving device includes a driving member (17) which is frictionally engaged with a driven member (1) or a member coupled to the driven member and which is movably supported on a fixed member (3), a piezoelectric element (12) disposed in contact with the driving member (17), and a driving circuit (18) for applying a voltage to the piezoelectric element (12) so as to make the speed of expansion of the piezoelectric element (12) different from the speed of contraction thereof.

Description: The present invention relates to a driving device for driving an object and, more particularly, to a driving device for driving a movable object incorporated in, for example, a precision machine or an imaging apparatus. A conventional example will be described below with reference to a lens driving device incorporated in a photographic apparatus, such as a video camera, which is one example of a precision machine or an imaging apparatus. Fig. 2 is a diagrammatic exploded perspective view of a conventional zoom lens mechanism incorporated in a video camera or the like. Referring to Fig. 2, a lens barrel 1 holds a lens, and a support plate 1h and an arm le project horizontally in opposite directions from the external peripheral surface of the lens barrel 1. Projections 1a and 1c project from one side of the support plate 1h at the front and rear end portions thereof, and holes 1b and 1d are formed so as to extend through the respective projections 1a and 1c in a direction parallel to the lens optical axis. A guide bar 2, which is secured to a support member (not shown), is relatively slidably inserted through the holes 1b and 1d. A follower pin 1g extends vertically downwardly from the underside of the portion of the support plate 1h which is near to the projection 1a. The follower pin 1g is arranged to be relatively slidably inserted into a cam slot formed in a cam plate 4 which will be described later. A lateral groove 1f which is U-shaped in cross section is formed in the extending end portion of the arm le of the lens barrel 1, and a guide bar 3 which is secured to a support member (not shown) is relatively slidably inserted through the groove If. Accordingly, the lens barrel 1 is supported by the guide bars 2 and 3 so that it can move in a direction parallel to the lens optical axis. The cam plate 4, which is horizontally disposed below the lens barrel 1, has a guide slot 4a which extends in a direction perpendicular to the axes of the guide bars 2 and 3, and a cam slot 4b which extends obliquely with respect to the axis of the slot 4a. Two guide pins 25 and 26 which project from a fixed member (not shown) are relatively slidably inserted into the guide slot 4a, and the cam plate 4 is supported on a fixed member (not shown) for movement in parallel with the slot 4a. Rack teeth 4c are formed along a rear end portion of the cam plate 4, and a gear 5 is meshed with the rack teeth 4c. The gear 5 is meshed with a small-diameter gear of a stepped gear 6, and a large-diameter gear of the stepped gear 6 is meshed with a pinion gear 7 secured to a shaft 8a of a motor 8. A slidable contact piece 9 is secured to the underside of the cam plate 4 with an electrically insulating sheet 11 interposed therebetween, and the slidable contact piece 9 has two arms 9a and 9b. Bent portions 9d and 9e are formed at the extending ends of the respective arms 9a and 9b, and the bent portions 9d and 9e are respectively in contact with a conductor part 10a and a resistor part 10b formed on a fixed detecting plate 10. The fixed detecting plate 10 has a construction in which the conductor part 10a and the resistor part 10b are formed on an electrically insulating board 10c. The conductor part 10a is connected to a power source by a lead wire 10f. Two lead wires 10d and 10e which lead from the resistor part 10b are connected via output terminals to input terminals of a microcomputer which will be described later. In a position detecting assembly consisting of the slidable contact piece 9 and the fixed detecting plate 10, its output varies depending on what portion of the resistor part 10b is in contact with the bent portion 9e of the arm 9b of the slidable contact piece 9. In other words, a voltage applied to the conductor part 10a through the lead wire 10f is divided according to the position of the bent portion 9e which is in contact with the resistor part 10b, and the divided voltage outputs are developed on the lead wires 10d and 10e. The operation of the conventional zoom lens mechanism having the above-described structure will be described below. When the motor 8 is activated by a control device (not shown), the pinion gear 7, the gear 6 and the gear 5 are made to rotate about their axes, and the cam plate 4 is made to move by the rack teeth 4c meshed with the gear 5 while it is being guided by the guide pins 5 and 6 in a direction perpendicular to the axes of the guide bars 2 and 3. During this time, the arms 9a and 9b of the slidable contact piece 9 slide on the conductor part 10a and the resistor part 10b, respectively. While the cam plate 4 is being made to move in parallel with the axis of the guide slot 4a, the follower pin 1g slides in the cam slot 4b, so that a force is applied to the lens barrel 1 via the follower pin 1g in a direction parallel to the lens optical axis. Accordingly, the lens barrel 1 is made to move in parallel with the lens optical axis while it is being guided by the guide bars 2 and 3. The position of the lens barrel 1 which is in progressive movement is electrically detected by the position detecting assembly consisting of the slidable contact piece 9 and the fixed detecting plate 10. If the detection result becomes equal to a predetermined set value, the motor 8 is stopped by the control device (not shown), so that the lens held in the lens barrel 1 is automatically positioned at a desired location. However, the aforesaid conventional driving mechanism has a number of problems. For example, because it is necessary to use numerous parts such as a motor, gears and a cam mechanism, the conventional driving mechanism is excessively large in size and weight. Accordingly, it has been difficult to reduce the size and weight of an imaging apparatus provided with such a conventional driving mechanism and it has been impossible to greatly reduce manufacturing cost. In addition, since gears are used, the backlash of the gears has made it difficult to achieve highly accurate positioning of a lens and also to control the amount of movement of the lens with high accuracy. Moreover, from document EP-A-0 292 989 a drive device is known which comprises a moving member connected to a -piezoelectric element provided with an inertia member. This drive device uses an impact of the inertia member on the moving member, the former being accelerated and decelerated by the piezoelectric element supported on the moving member. In other words, this device uses the impact of a decelerated mass (inertia member) and is, in particular with respect to its accuracy, dependent on the field of gravity. Furthermore, the document US-A-3 808 488 discloses a drive device which is provided with a member to be moved which is interposed between two piezoelectric elements. A third piezoelectric element is arranged on the member to be moved for vibrating the latter. The vibration reduces the friction between the member to be moved and a fixed portion of the device. Then, the member to be moved is moved by activating the piezoelectric elements between which it is interposed. When the vibration is interrupted, the member to be moved is locked in its position by frictional forces. In this device, the moving distance of the member to be moved is limited by the expansion/contraction ability of the two piezoelectric elements. Furtheron, from the document US-A-4 195 243 a drive device for moving a wafer is known which comprises a transducer connected to a driving member on which the wafer is supported. The wafer is frictionally engaged with the driving member due to the weight of the wafer. The speeds of the expansion/contraction of the transducer are set to be different, so that, due to the inertia of the wafer, a rapid movement of the driving member is not transferred to the wafer, whereas a slow movement of the driving member leads to a common movement of the wafer and the driving member due to the frictional force acting between them. This known device suffers from the fact that the object to be moved must be horizontally supported on the driving member so as to achieve an appropriate frictional force therebetween. Consequently, an accurate operation of this device also strongly depends on its orientation in the field of gravity. Accordingly, it is the object of the invention to provide a compact and efficient drive device for moving an object with a high accuracy independent from gravity. The object is achieved with a drive device having the features of claim 1. Advantageous modifications are described in the dependent claims 2 to 15. The above and other objects, features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. Brief Description of the Drawings: Fig. 1 is a schematic view of a control system for the driving device according to the present invention; Fig. 2 is an exploded perspective view diagrammatically showing one example of a conventional zoom-lens driving device; Fig. 3 is a flowchart for explaining the operation of the control system shown in Fig. 1; Figs. 4(A), 4(B) and 4(C) are perspective views diagrammatically showing different examples of a leaf spring; Fig. 5 is a schematic cross-sectional view showing the state of mounting of the leaf spring shown in Fig. 4(b); Fig. 6 is a diagrammatic cross-sectional view showing a moving mechanism according to an embodiment of the present invention; Fig. 7 is a diagrammatic cross-sectional view showing a moving mechanism according to a further embodiment of the present invention; Fig. 8 is a diagrammatic cross-sectional view showing a moving mechanism according to a further embodiment of the present invention; Fig. 9 is a diagrammatic cross-sectional view showing a moving mechanism according to a further embodiment of the present invention; Fig. 10 is a diagrammatic cross-sectional view showing a moving mechanism according to a further embodiment of the present invention; Figs. 11 and 12 are waveform diagrams ; Figs. 13 and 14 are diagrammatic cross-sectional views showing modifications of the respective embodiments of Figs. 8 and 6; Fig. 15 is a diagrammatic cross-sectional view showing a moving mechanism according to a further embodiment of the present invention; Figs. 16 to 19 are diagrammatic cross-sectional views respectively showing further embodiments of the present invention; and Figs. 20 and 21 are waveform diagrams showing different waveforms of applied voltage. Detailed Description of the Preferred Embodiments: Fig. 1 is a diagrammatic view showing a control system for the driving device according to the invention used with a lens. The control system shown in Fig. 1 includes a driving circuit 18 for applying a driving voltage to a piezoelectric element 12, a lens-barrel-position detector 19 consisting of a slidable contact piece 9 and a fixed detecting plate 10, a microcomputer 20 for receiving an output from the detector 19 and controlling the driving circuit 18, and focus decision means 30 for determining whether in-focus has been achieved. Fig. 3 is a flowchart showing the operation of the above-described control system. In Step S1, the focus decision means 30 determines whether in-focus has been achieved. If in-focus has not yet been achieved, the process proceeds to Step S2, where it is determined in which direction and by what amount the lens should be made to move to achieve in-focus. In Step S2, if it is determined that the state of focus is "near focus", the process proceeds to Step S3, while if it is determined that it is "far focus", the process proceeds to Step S4. In Step S3, the lens is driven to move in a first direction in which in-focus can be achieved in the case of the near focus, and the process proceeds to Step S5. In Step S4, the lens is driven to move in a second direction which in-focus can be achieved in the case of the far focus, and the process proceeds to Step S6. In Step S5 or S6, the microcomputer 20 detects whether the lens has moved by the amount of movement required to reach the in-focus position obtained in Step S2. The lens is made to move until in-focus is achieved, and if the in-focus is achieved, the process is brought to an end. In the above-described driving method, the relation between driving pulses and the amount of movement may not show coincidence due to vibrations, attitude difference or the like. For this reason, it is very effective to actually detect the state of movement by the lens-barrel-position detector 19 and carry out driving by feedback (a closed loop) of the detection result. A microcomputer constitutes a system controller in an imaging apparatus such as a camera, and outputs to lens driving circuits approximately sawtooth-shaped driving pulses. The lens driving circuits receive driving pulses of about 5V from the microcomputer and output driving pulses of the order of some tens of volts up to one hundred volts which are required to drive the piezoelectric elements. A potentiometer practically consists of a brush and a resistor board. Alternatively, a recess is formed in the head carriage or movable member in the vicinity of the front end thereof, and a light emitting element which has a bottom face serving as a light emitting face is disposed in the recess. A slit, which is elongated in a direction perpendicular to guide bars (that is, in a direction perpendicular to the direction of movement of the head carriage), is formed in the bottom of the recess to extend therethrough. Light emitted from the light emitting element passes through the slit and is projected downwardly from the head carriage as a narrow beam of light. A semiconductor position detecting element having a rectangular shape which is elongated in a direction parallel to the direction of movement of the head carriage is secured to a fixed member immediately below the path of movement of the head carriage. The semiconductor position detecting element is electrically connected to a driving circuit. The operation of the leaf spring 313 for causing a frictional force to act between the guide bar 303 and the head carriage 308 will be described below with reference to Fig. 5. To produce such a frictional force stably and to prevent the elastic force of the leaf spring 313 from acting in the direction of displacement of the head carriage, the curved projection 313c of U-shaped cross section is formed at the middle of the leaf spring 313 so that the elastic force of the leaf spring 313 can be applied to the guide bar 303 approximately perpendicularly. When the leaf spring 313 is elastically deformed in the direction of expansion or contraction of the piezoelectric element by the expansion or contraction of the same, the frictional force between the guide bar 313 and the head carriage varies and the elastic force acts in the direction of displacement of the head carriage, so that the displacement of the head carriage becomes unstable. To prevent this problem, the leaf spring 313 has flat portions 313d and 313e which extend parallel to the directions of expansion and contraction of the piezoelectric element, and is formed to have a high rigidity in these directions. Other examples of this leaf spring are shown in Figs. 4(A), 4(B), 4(C) and 5. Referring to Fig. 4(A), a leaf spring 318 of flat shape has holes 318a and 318b for securing the leaf spring 318 to the projections 308a and 308b of the head carriage. A frictional member 319 is formed of a material, such as metal or resin, which has a high rigidity at least in the directions of expansion and contraction of the piezoelectric element. The frictional member 319 is secured to the middle of the leaf spring 318. The example of Fig. 15(A) exhibits a high rigidity in the directions of expansion and contraction of the piezoelectric element. Fig. 4(B) shows a leaf spring which facilitates adjustment of frictional force. A leaf spring 320 has a hole 320a and a slot 320b for securing the leaf spring 320 to the projections 308a and 308b of the head carriage by means of the respective screws 314 and 315. Fig. 5 is a diagrammatic view showing the assembled state of the leaf spring 320. The leaf spring 320 is tightly secured to the projection 308a by the screw 314 at the position of the hole 320a. The frictional member 319 is pressed against the guide bar 303 by the leaf spring 320. The screw 315 is screwed into the projection 308b through the slot 320b, and the tightening strength of the screw 315 can be adjusted to change the state of bend of the leaf spring 320, thereby adjusting the pressure of an elastic member against the guide bar 303. After this adjustment has been performed, the screw 315 is fixed by an adhesive. Fig. 4(C) shows a leaf spring 321 having one flat portion to which the frictional member 319 is secured. The leaf spring 321 is secured to the projection 308a by the screw 314 passed through a hole 321a. Fig. 6 is a schematic cross-sectional view showing a further embodiment, and Figs. 11 and 12 are diagrams showing different waveforms of a voltage applied to a piezoelectric element. In Fig. 6, reference numeral 401 denotes a fixed portion consisting of, for example, a frame, reference numeral 404 denotes a vibration shaft which is longitudinally movably supported and guided by the fixed portion 401, and reference numeral 402 denotes a movable object having mass. The movable object 402 is supported and guided by the vibration shaft 404 and the fixed portion 401 with the direction of movement of the movable object 402 restricted by them. A piezoelectric element 403 is held by the fixed portion 401 in such a manner that the directions of expansion and contraction (lamination direction) of the piezoelectric element 403 coincide with the directions indicated by arrows A and B of Fig. 6. One end face of the piezoelectric element 403 relative to the directions of expansion and contraction of the piezoelectric element 403 abuts against one end of the vibration shaft 404, and the piezoelectric element 403 and the vibration shaft 404 are integrally bonded by an adhesive. A first leaf spring 405 is secured to the movable object 402 to urge the fixed portion 401 by a constant force, thereby producing a frictional force between the fixed portion 401 and the movable object 402. A second leaf spring 408 is secured to the movable object 402 to urge the vibration shaft 404 by a constant force, thereby producing a frictional force between the movable object 402 and the vibration shaft 404. To prevent the movable object 402 from moving down by its own weight, the sum of the frictional forces produced by the leaf springs 405 and 408 are set to be greater than gravitational force acting on the movable object 402. Also, the frictional force produced by the second leaf spring 408 is set to be greater than that produced by the first leaf spring 405. If the first leaf spring 405 is omitted, the movable object 402 can be made to move, and if the frictional force produced by the second leaf spring 408 is made greater than the gravitational force applied to the movable object 402, it is also possible to prevent the movable object 402 from moving down by its own weight. In this arrangement, however, the frictional force by the second leaf spring 408 becomes excessively large with respect to the mass of the movable object 402, thus lowering the speed of movement of the movable object 402. Accordingly, in this embodiment, both the leaf springs 405 and 408 are used to impart frictional force to the movable object 402. Referring to Figs. 11 and 12, reference numerals 410 and 411 denote different voltage waveforms which are applied for driving of a piezoelectric element. The voltage waveform 410 shown in Fig. 11 has a rapid voltage rise 410a and a relatively slow voltage drop 410b, and the voltage waveform 411 of Fig. 12 has a relatively slow voltage rise 411a and a rapid voltage drop 411b. Referring back to Fig. 6, a voltage waveform adjusting circuit 412 serves as a voltage controlling circuit, and is connected to a power source 413 and the piezoelectric element 403 by electric wires, respectively. The operation of the moving mechanism having the above-described arrangement will be described below. For example, if the voltage waveform shown in Fig. 11 is applied to the piezoelectric element 403, the piezoelectric element 403 rapidly expands in the direction of the arrow A at the rapid voltage rise 410a and the vibration shaft 404 is also made to move in the direction of the arrow A by an amount equivalent to the expansion of the piezoelectric element 403. During this time, the movable object 402 hardly moves since it does not follow the movement of the vibration shaft 404 by the inertia of the movable object 402 due to the own weight thereof and by the frictional force produced by the first leaf spring 405. Then, at the relatively slow voltage drop 410b, the piezoelectric element 403 slowly contracts in accordance with the voltage drop. During this time, the vibration shaft 404 is made to move slowly in the direction of the arrow B, and the movable object 402 is also made to move in the direction of the arrow B because the frictional force produced by the second leaf spring 408 is greater than that produced by the first leaf spring 405. The above-described sequence of operations is repeated and the movable object 402 is made to move in the direction of the arrow B. If the voltage waveform shown in Fig. 12 is applied to the piezoelectric element 403, the piezoelectric element 403 slowly expands at the relatively slow voltage rise 411a in the direction of the arrow A as viewed in Fig. 6 in accordance with the voltage rise, and the vibration shaft 404 is also made to move in the direction of the arrow A. During this time, the movable object 402 moves together with the vibration shaft 404 in the direction of the arrow A owing to the frictional force produced by the second leaf spring 408. Then, the piezoelectric element 404 rapidly contracts at the rapid voltage drop 411b and the vibration shaft 404 is made to move rapidly in the direction of the arrow B by an amount equivalent to the contraction of the piezoelectric element 403. During this time, the movable object 402 hardly moves since it does not follow the movement of the vibration shaft 404 by the inertia of the movable object 402 due to the own weight thereof and by the frictional force produced by the first leaf spring 405. In other words, the movable object 402 is made to move in the direction of the arrow A by the application of the voltage waveform shown in Fig. 12. In the aforesaid embodiment, the piezoelectric element 403 and the vibration shaft 404 are fixed to each other by the adhesive so that the movement of the vibration shaft 404 follows the expansion and contraction of the piezoelectric element 403. As shown in Fig. 7, a coil spring 406 is provided on a side opposite to the piezoelectric element 403, and the vibration shaft 404 and the piezoelectric element 403 are maintained in contact with each other. The vibration shaft 404 is at all times pressed in contact with the piezoelectric element 403 by the spring force of the coil spring 406 so that the vibration shaft 404 is prevented from moving away from the piezoelectric element 403 by the expansion or contract of the piezoelectric element 403. The rotation of the movable object 402 about the vibration shaft 404 is restricted by the fixed portion 401. However, a similar effect can be obtained by fitting the movable object 401 onto a guide shaft 407 as shown in Fig. 8. Fig. 9 shows an embodiment consisting of a combination of the embodiments shown in Figs. 7 and 8. The movable object 402 is supported by the vibration shaft 404 which is inserted through the movable object 402. To obtain a similar effect, the movable object 402 may also be supported and guided by the guide shaft 407 and the fixed portion 401 as shown in Fig. 10. The first leaf spring 405 may be provided on the fixed portion 401 as shown in Fig. 13 and the second leaf spring 408 on the vibration shaft 404 as shown in Fig. 14. In this arrangement as well, a similar effect can be obtained. Although a leaf spring is used as friction means for producing frictional forces for the movable object, an elastic member such as a coil spring or a rubber may also be employed. As is apparent from the foregoing description, in accordance with each embodiment, an electrical-mechanical energy converting element, for example a piezoelectric element, can be utilized to constitute a moving mechanism having an extremely simple structure, whereby it is possible to provide a miniaturized moving mechanism. In addition, it is possible to achieve, by the application of a voltage, a large amount of movement with respect to an extremely small amount of displacement of the piezoelectric element. Further, since the amount of displacement of the piezoelectric element is extremely small at the application of a voltage, it is possible to position the movable object with extremely high accuracy. Further, since the sum of the frictional forces produced by the leaf springs 405 and 408 is greater than gravitational force applied to the movable object, the movable object does not move down by its own weight even if the direction of the movement thereof is set to any direction. As is apparent from the foregoing description, the moving mechanism according to each of embodiment makes it possible to realize a desired amount of displacement and to effectively miniaturize the device. Fig. 15 is a diagrammatic view showing a moving mechanism according to a further embodiment of the present invention. In Fig. 15, reference numeral 601 denotes a fixed portion, reference numeral 602 denotes a movable object, and reference numerals 603a and 603b denote piezoelectric elements. The piezoelectric elements 603a and 603b are held against the fixed portion 601 in such a manner that the directions of their expansion and contraction (their lamination directions) coincide with the directions indicated by the arrows A and B of Fig. 15. Both ends of a vibration shaft 604 are maintained in contact with the respective piezoelectric elements 603a and 603b, or they are opposed to the respective piezoelectric elements 603a and 603b with small gaps interposed therebetween. These gaps are selected to be smaller than the amounts of expansion of the respective piezoelectric elements 603a and 603b by the application of a voltage. The vibration shaft 604 is held by the fixed portion 601 for movement in the direction of each of the arrows A and B of Fig. 15. A first leaf spring 605 is secured to the movable object 602, and urges the vibration shaft 604 with a constant spring force to produce a frictional force between the movable object 602 and the vibration shaft 604. A second leaf spring 606 is secured to the movable object 602, and urges the fixed portion 601 with a constant spring force to produce a frictional force between the movable object 602 and the fixed portion 601. To prevent the movable object 602 from moving down by its own weight, the resultant of the frictional forces produced by the first and second leaf springs 605 and 606 are set to be greater than gravitational force acting on the movable object 602. If the second leaf spring 606 is omitted, the movable object 602 can be made to move, and if the frictional force produced by the first leaf spring 605 is made greater than the gravitational force applied to the movable object 602, it is also possible to prevent the movable object 602 from moving down by its own weight. In this arrangement, however, the frictional force by the first leaf spring 605 becomes excessively large with respect to the mass of the movable object 602, thus lowering the speed of movement of the movable object 602. Accordingly, in this embodiment, the first and second leaf springs 605 and 606 are used to impart frictional force to the movable object 602. A voltage waveform adjusting circuit 612 is arranged to convert a voltage from a power source 613 into a waveform 610 or 611 having a rapid voltage rise 610a or 611a as shown in Fig. 20 or 21 and apply such a waveform to the piezoelectric elements 603a and 603b. There is also provided a selecting circuit for selectively and alternately applying the waveforms 610 and 611 to the piezoelectric elements 603a and 603b. In the moving mechanism having the above-described arrangement, if, for example, the waveform 610 shown in Fig. 20 is applied to the piezoelectric element 603a by the voltage waveform adjusting circuit 612, the piezoelectric element 603a rapidly expands in the direction of the arrow A as viewed in Fig. 15 to instantaneously impart a large acceleration (impact) to the vibration shaft 604 in the direction of the arrow A. At this time, the movable object 602 hardly moves since it does not follow the movement of the vibration shaft 604 owing to the inertia of the movable object 602 due to the own weight thereof. Then, as the voltage applied to the piezoelectric element 603a drops, the piezoelectric element 603a contracts and the vibration shaft 604 is made to return to its original position by a reaction to the impact imparted by the piezoelectric element 603b. During this time, the movable object 602 moves together with the vibration shaft 604 since a frictional force which is produced between the vibration shaft 604 and the movable object 602 by the first leaf spring 605 is greater than a frictional force produced by the second leaf spring 606. In other words, the movable object 602 is made to move in the direction of the arrow B by a small amount. Subsequently, the movable object 602 is made to progressively move in the direction of the arrow B by repeating the above-described operation (cycle T). If the voltage of the above-described waveform is applied to the piezoelectric element 603b, the movable object 602 is made to move in the opposite direction indicated by the arrow A. In the above-described embodiment, the impact which has been imparted to the vibration shaft 604 by one piezoelectric element is applied to the other piezoelectric element. To avoid this problem, as shown in Fig. 16, stepped portions may be formed at the opposite end portions of the vibration shaft 604 and engaged with the fixed portion 601 so as to prevent the impact of the vibration shaft 604 from being applied to the other piezoelectric element. Although the second leaf spring 606 is provided on the moving object 602, it may also be provided on the fixed portion 601 as shown in Fig. 17 or on both the moving object 602 and the fixed portion 601. Although in the embodiment shown in Fig. 15 the first leaf spring 605 is provided on the moving object 602, it may also be provided on the vibration shaft 604 as shown in Fig. 18 or on both the moving object 602 and the vibration shaft 604. Alternatively, as shown in Fig. 19, the movable object 602 may be fitted onto a guide shaft 607 alone and a frictional force may be produced between the movable object 602 and the vibration shaft 604 by the first leaf spring 605 provided on the vibration shaft 604. Although in each of the embodiments a leaf spring is used as friction means, an elastic member, such as a coil spring or a rubber, or a magnet may also be employed. As is apparent from the foregoing description, in accordance with each embodiment of the present invention, a piezoelectric element can be employed to constitute a moving mechanism having an extremely simple structure. Accordingly, it is possible to provide a miniaturized moving mechanism and it is also possible to achieve, by the application of a voltage, a large amount of movement with respect to an extremely small amount of displacement of the piezoelectric element. Further, since the amount of displacement of the piezoelectric element is extremely small at the application of a voltage, it is possible to position the movable object with extremely high accuracy. Furthermore, since the resultant of the frictional forces produced by first and second friction means consisting of leaf springs or the like is selected to be greater than gravitational force applied to the movable object, it is possible to prevent the movable object from moving down by its own weight even if the direction of movement of the movable object is set to any direction.

Claims: A drive device comprising: a driving member (404, 604) being operatively engaged with at least one piezoelectric element (403, 603a, 603b) so as to be movable in accordance with an expansion/contraction of the same, a control means for controlling the expansion/ contraction of said piezoelectric element such that the speed of expansion is different from the speed of contraction, and a driven member (402, 602) being frictionally engaged with said driving member (404, 604) via a first friction means (408, 605), characterized in that said driven member (402, 602) frictionally contacts a fixed portion (401, 601) via a second friction means (405, 606), wherein the sum of the friction generated by said first (408, 605) and said second (405, 606) friction means is greater than the gravitational force of said driven member (402, 602), and wherein the friction generated by said first friction means (408, 605) is greater than the friction generated by said second friction means (405, 606). A drive device according to claim 1, wherein said first and said second friction means (408, 605, 405, 606) comprises a leaf spring frictionally contacting a member disposed in opposition thereto with a springy portion thereof. A drive device according to claim 1 or 2, wherein said driving member (604) is provided with a piezoelectric element (603a, 603b) at each end thereof, said piezoelectric elements (603a, 603b) being arranged so as shift said driving member (604) in response to expansion/contraction signals from said controlling means. A drive device according to claim 1 or 2, wherein one end of said driving member (404) is provided with a piezoelectric element (403), the opposite end of said driving member (404) being provided with a spring means (406) elastically engaged with said fixed portion. A drive device according to claim 1, 2, 3 or 4, wherein said driving member (404, 604) comprises a driving shaft passing through an opening provided in said driven member (402, 602). A drive device according to claim 5, wherein said driving shaft (404, 604) is loosely fitted in said opening, and a first friction means (408, 605) being arranged on said driven member (402, 602) frictionally contacts said driving shaft (404, 604). A drive device according to claim 5, wherein said opening accomodates said driving shaft (404, 604) and said first friction means (408, 605). A drive device according to claim 7, wherein said first friction means (408, 605) is arranged on said driving shaft (404, 604) and frictionally contacts the inner wall of said opening in said driven member (402, 602). A drive device according to any one of the preceding claims, comprising a guide means (407, 607) for guiding said driven member (402, 602) along a predetermined moving path thereof. A drive device according to claim 9, wherein said guide means comprises a guide shaft (407, 607) passing through an opening provided in said driven member (402, 602). A drive device according to claim 10, wherein said driving shaft (404, 604) is adapted to guide said driven member (402, 602). A drive device according to any one of the preceding claims, wherein said second friction means (405, 606) is arranged on said driven member (402, 602) and frictionally contacts said fixed portion. A drive device according to any one of the preceding claims, wherein said second friction means (405, 606) is arranged on said fixed portion and frictionally contacts said driven member (402, 602). A drive device according to any one of the preceding claims, wherein said driven member (402, 602) is adapted to move an optical element. A drive device according to any one of the preceding claims, wherein said driven member (402, 602) is adapted to move a head for reading and/or writing information.

Inventors: NAGANO MASATOSHI, SAITO SCHUICHIRO, NAGANO, MASATOSHI, SAITO, SCHUICHIRO, NAGANO, MASATOSHI, CANON KABUSHIKI KAISHA, SAITO, SCHUICHIRO, CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: G05B19
IPC codes: G02B7, H01L41, B23Q1, B23Q5