Patent Publication Number: US-2007096602-A1

Title: Impact drive actuator and lens drive device using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-319867, filed Nov. 2, 2005, the entire contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an impact drive actuator which drives a motion object, and to a lens drive device using the same.  
      2. Description of the Related Art  
      There is a known actuator in which an electromechanical transducer element linked to a drive shaft is supplied with drive pulses of a saw-tooth waveform to displace the drive shaft in an axial direction so that a movable member frictionally engaged with the drive shaft is moved in the axial direction. This kind of actuator will be hereinafter called an impact drive actuator.  
      This kind of impact drive actuator is disclosed in, for example, U.S. Pat. No. 5,589,723. Driving of the impact drive actuator is achieved by applying to a piezoelectric element a drive pulse having a waveform consisting of a gently rising part and a successive steep falling part. That is, the gently rising part of the drive pulse causes the piezoelectric element to extend gently in thickness directions, so that a drive shaft linked to the piezoelectric element is displaced in an axial direction (which is the first direction). Therefore, a motion object frictionally engaged with the drive shaft is moved in the same direction as the axial direction. The steep falling part of the drive pulse causes the piezoelectric element to contract rapidly in thickness directions, so that the drive shaft is displaced in another axial direction (which is the second direction opposite to the first direction). At this time, the motion object frictionally engaged with the drive shaft is not moved but stays substantially at the present position due to inertial force which overcomes frictional engagement force between the object and the drive shaft. In this case, use of the term “substantially” means including even a movement as follows. That is, the motion object moves following the drive shaft in both the first and second directions while causing a slippage between the object and the shaft, and the motion object moves as a whole in the first direction due to a difference in drive time. Styles of movements are determined under given frictional conditions.  
      By thus applying sequentially drive pulses having a waveform described above to a piezoelectric element, the motion object can be moved sequentially in the first direction.  
      On the contrary, movement of the motion object in the opposite direction (the second direction) to the first direction can be achieved by applying to the piezoelectric element drive pulses having a waveform consisting of a steep rising part and a successive gently falling part.  
     BRIEF SUMMARY OF THE INVENTION  
      According to a first aspect of the present invention, there is provided an impact drive actuator comprising:  
      a fixing member;  
      a vibrator fixed to the fixing member and configured to generate slight displacement in a first direction and a second direction opposite to the first direction;  
      a vibration substrate having a first flat face and configured to reciprocate by the slight displacement of the vibrator;  
      a motion object set on the first flat face of the vibration substrate and having a second flat face in a plane opposed to the first flat face;  
      an adsorption power control part configured to control adsorption power between the motion object and the vibration substrate; and  
      a motion object hold part having an end fixed to the fixing member, and provided along the vibration substrate, wherein  
      the motion object is supported clamped between the vibration substrate and the motion object hold part so as to be engaged with each of the vibration substrate and the motion object hold part, and  
      the adsorption power controlled by the adsorption power control part creates a difference between frictional force between the motion object and the vibration substrate and frictional force between the motion object and the motion object hold part.  
      According to a second aspect of the present invention, there is provided a lens drive device comprising:  
      an impact drive actuator including: 
          a fixing member;     a vibrator fixed to the fixing member and configured to generate slight displacement in a first direction and a second direction opposite to the first direction;     a vibration substrate having a first flat face and configured to reciprocate by the slight displacement of the vibrator;     a motion object set on the first flat face of the vibration substrate and having a second flat face in a plane opposed to the first flat face;     an adsorption power control part configured to control adsorption power between the motion object and the vibration substrate; and     a motion object hold part having an end fixed to the fixing member, and provided along the vibration substrate, wherein     the motion object is supported clamped between the vibration substrate and the motion object hold part so as to be engaged with each of the vibration substrate and the motion object hold part, and     the adsorption power controlled by the adsorption power control part creates a difference between frictional force between the motion object and the vibration substrate and frictional force between the motion object and the motion object hold part; and        

      an optical element provided on the motion object of the impact drive actuator.  
      According to a third aspect of the present invention, there is provided a lens drive device comprising:  
      an impact drive actuator including: 
          a fixing member;     a vibrator fixed to the fixing member and configured to generate slight displacement in a first direction and a second direction opposite to the first direction;     a vibration substrate having a first flat face and configured to reciprocate by the slight displacement of the vibrator;     a motion object set on the first flat face of the vibration substrate and having a second flat face in a plane opposed to the first flat face;     an adsorption power control part configured to control adsorption power between the motion object and the vibration substrate; and     a motion object hold part having an end fixed to the fixing member, and provided along the vibration substrate, wherein     the motion object is supported clamped between the vibration substrate and the motion object hold part so as to be engaged with each of the vibration substrate and the motion object hold part, and     the adsorption power controlled by the adsorption power control part creates a difference between frictional force between the motion object and the vibration substrate and frictional force between the motion object and the motion object hold part;        

      plural fixed lenses provided at the motion object hold part of the impact drive actuator, the motion object hold part having a function as a lens barrel; and  
      one of an optical element set on the motion object of the impact drive actuator and an optical element linked to the motion object by a link member formed on the motion object of the impact drive actuator, the optical element provided to be movable along an axial direction of the lens barrel inside the lens barrel.  
      According to a fourth aspect of the present invention, there is provided an impact drive actuator comprising:  
      a fixing member;  
      a vibrator fixed to the fixing member and configured to generate slight displacement in a first direction and a second direction opposite to the first direction;  
      a vibration substrate having a first flat face and configured to reciprocate by the slight displacement of the vibrator;  
      a motion object set on the first flat face of the vibration substrate and having a second flat face in a plane opposed to the first flat face;  
      a first electrode provided on the first flat face;  
      a second electrode provided on the motion object, opposed to the first electrode;  
      a guide member having an end fixed to the fixing member, and provided along the vibration substrate, the motion object is supported clamped between the vibration substrate and the guide member so as to be engaged with each of the vibration substrate and the guide member; and  
      a controller configured to control adsorption power between the motion object and the vibration substrate by applying a potential difference between the first and second electrodes, the adsorption power being generated by the first and second electrodes and causing a difference between frictional force between the motion object and the vibration substrate and frictional force between the motion object and the guide member.  
      According to a fifth aspect of the present invention, there is provided an impact drive actuator comprising:  
      a fixing member;  
      displacement generation means fixed to the fixing member and for generating slight displacement in a first direction and a second direction opposite to the first direction;  
      a vibration substrate having a first flat face and for reciprocating by the slight displacement of the displacement generation means;  
      a motion object set on the first flat face of the vibration substrate and having a second flat face in a plane opposed to the first flat face;  
      adsorption power controlling means for controlling adsorption power between the motion object and the vibration substrate; and  
      motion object holding means having an end fixed to the fixing member, and provided along the vibration substrate, wherein  
      the motion object is supported clamped between the vibration substrate and the motion object holding means so as to be engaged with each of the vibration substrate and the motion object holding means, and  
      the adsorption power controlled by the adsorption power controlling means creates a difference between frictional force between the motion object and the vibration substrate and frictional force between the motion object and the motion object holding means.  
      Advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
      The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
       FIG. 1A  is a perspective view of an impact drive actuator according to a first embodiment of the present invention;  
       FIG. 1B  is an cross-sectional view of the impact drive actuator according to the first embodiment;  
       FIG. 1C  is a side view of the impact drive actuator according to the first embodiment;  
       FIG. 2  is a view for explaining traces of motion of a motion object;  
       FIG. 3  is a cross-sectional view of an engagement part between the motion object and a vibration member;  
       FIG. 4  is a cross-sectional view of an engagement part between a motion object and a vibration member according to a modification of the first embodiment;  
       FIG. 5  is a cross-sectional view of an engagement part between a motion object and a vibration member according to another modification of the first embodiment;  
       FIG. 6  is a cross-sectional view of an engagement part between a motion object and a guide member;  
       FIG. 7A  is a perspective view of a lens drive device using an impact drive actuator according to a second embodiment of the present invention;  
       FIG. 7B  is a plan view of a lens drive device according to the second embodiment;  
       FIG. 7C  is a cross-sectional view observed from a side of the lens drive device according to the second embodiment;  
       FIG. 8  is a cross-sectional view of an engagement part between a motion object and a vibration member;  
       FIG. 9  is a cross-sectional view of an engagement part between a motion object and a guide member;  
       FIG. 10A  is a perspective view of a lens drive device using an impact drive actuator according to a third embodiment of the present invention;  
       FIG. 10B  is a cross-sectional view of the lens drive device according to the third embodiment, observed from a side of the device;  
       FIG. 10C  is an A-A cross-sectional view of  FIG. 10B ;  
       FIG. 11A  is a perspective view of a lens drive device using an impact drive actuator according to a fourth embodiment of the present invention;  
       FIG. 11B  is a cross-sectional view of the lens drive device according to the fourth embodiment, observed from a side of the device;  
       FIG. 11C  is an A-A cross-sectional view of  FIG. 11B ; and  
       FIG. 11D  is a B-B cross-sectional view of  FIG. 11B . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Hereinafter, best modes for carrying out the present invention will be described with reference to the drawings.  
      [First Embodiment] 
      As shown in  FIGS. 1A  to  1 C, in an impact drive actuator according to a first embodiment of the invention, an end of a vibrator  10  as a displacement means constituted by a piezoelectric element is fixed to a fixing member  12 . A vibration member  14  as a vibration substrate is attached to another end of the vibrator  10 . A voltage supplied to the vibrator  10  from a driver  16  causes the vibrator  10  to be displaced slightly in a first direction and in a second direction opposite to the first direction. This slight displacement causes the vibration member  14  to be displaced slightly in the same directions.  
      The vibration member  14  has a first flat face on which a motion object  18  is set to be movable in a predetermined direction relative to the fixed member  12 . The motion object  18  is supported clamped between the fixing member  12  and a guide member  20  which is a motion object hold means fixed to the fixing member  12  and provided along the vibration member  14 . Therefore, not only the motion object  18  and the vibration member  14  are frictionally engaged with each other but also the motion object  18  and the guide member  20  are frictionally engaged with each other. A second flat face of the motion object  18 , which is opposite the first flat face of the vibration member  14 , and this first flat face of the vibration member  14  contact each other. Therefore, as shown in  FIG. 2 , the motion object  18  does not stop even if the motion axis  22  of the vibration member  14  and a motion direction  24  of the motion object  18  do not correspond to each other. As a result, the motion object  18  is able to follow traces as indicated by broken lines in the figure. In other words, the motion object  18  is freely movable in the first flat face formed by the vibration member  14 .  
      An opposite side of the vibration member  14  to the side in which the member  14  is attached to the vibrator  10  is pressed toward the vibrator  10  by an elastic member  26  such as a spring.  
      As shown in  FIG. 3 , the vibration member  14  is formed by layering an electrode  28  (hereinafter called a first electrode) and an insulating material  30  on a substrate  27  forming the first flat face. An electrode  32  (hereinafter called a second electrode) is formed on an opposite face of the motion object  18  to the vibration member  14 . The first electrode  28  provided on the vibration member  14 , and the second electrode  32  formed on the opposite face (second flat face) thereof to the vibration member  14  are opposed to each other through the insulating material  30 . The insulating material  30  may be formed in bottom of the second electrode  32  instead of forming it on the first electrode  28 .  
      This structure constitutes an adsorption power control part  34  which controls adsorption power between the motion object  18  and the vibration member  14 . That is, frictional force between the motion object  18  and vibration member  14  can be changed if electrostatic force is generated by making a potential difference between the first electrode  28  and the second electrode  32  from a controller  36 . This change in frictional force causes a difference in friction force between the motion object  18  and the vibration member  14  and between the motion object  18  and the guide member  20 . Therefore, the motion object  18  is made movable by applying a predetermined waveform to the vibrator  10  by the driver  16 . In the structure using electrostatic force as described above, each electrode can be formed thin so that the actuator can be downsized.  
      Although the adsorption power control part  34  is changed by electrostatic force, the present invention is not limited to this structure. For example, as shown in  FIG. 4 , the vibration member  14  may be made of a permanent magnet and the motion object  18  may be made of a magnetic material such as iron. This kind of structure need not include an electrode in the vibration member  14  or motion object  18 . Further, neither the controller  36  nor a wiring for applying a voltage from the controller  36  to an electrode is required. Accordingly, the structure is simplified.  
      As shown in  FIG. 5 , it is quite possible that the vibration member  14  is made of a permanent magnet and an electromagnet using a coil  38  is used for the motion object  18 . By thus using an electromagnet for the motion object  18 , a great force can be generated such as cannot be generated electrostatically. Accordingly, more stable driving can be achieved.  
      As described above, the guide member  20  can support the motion object  18  so as to raise a degree of freedom in motion. Further, as shown in  FIG. 6 , a coil spring  42  as an elastic member may be inserted between an upper face of a vertical part  40  of the motion object  18  and the guide member  20 . By adopting this structure, (pressing) force for supporting the motion object  18  can be managed easily so that desired pressing force can be supplied stably to the motion object  18 . That is, frictional force between the motion object  18  and the guide member  20  can be managed easily.  
      Although the coil spring  42  is used in the above case, the structure may be constituted by any member such as a plate spring as long as the member is an elastic member.  
      [Second Embodiment] 
      As shown in  FIGS. 7A  to  7 C, a lens drive device using an impact drive actuator according to a second embodiment of the present invention drives a lens L 2  among three lenses of L 1 , L 2 , and L 3 .  
      That is, the basic structure of the impact drive actuator according to this embodiment is the same as that of the first embodiment described above. However, in the lens drive device in the present embodiment, the motion object  18  of such an impact drive actuator serves also as a support frame for supporting the lens L 2 . In addition, a front lens frame  44  in which a fixed lens L 1  is set, and a rear lens frame  46  in which a fixed lens L 3  is set are attached to the fixing member  12 .  
      As in the first embodiment, the motion object  18  and the vibration member  14  are frictionally engaged with each other, as well as the motion object  18  and the guide member  20  are frictionally engaged with each other, in the lens drive device according to the present embodiment. Therefore, if the guide member  20  is a guide shaft, the motion object  18  and the vibration member  14  contact each other on faces of their own, so that the motion object  18  is movable in a face of the vibration member  14 . Accordingly, the motion object  18  can be moved stably and accurately along the guide shaft.  
      As shown in  FIGS. 8 and 9 , if the impact drive actuator is used in a lens drive device, a coil spring  42  is inserted between the motion object  18  and the guide member  20 , as in the first embodiment described above. Thus, stable pressing is achieved, and accuracy of movement based on frictional engagement with the guide shaft is guaranteed.  
      To make the lens drive mechanism as compact as possible, the adsorption power control part  34  is constructed as a simple structure as shown in  FIG. 8  which causes electrostatic force to act. Of course, it is quite possible to use a mechanism in which electromagnetic force is caused to act using an electromagnet and a permanent magnet without using electrostatic force, as described in the first embodiment.  
      [Third Embodiment] 
      As shown in  FIGS. 10A  to  10 C, a lens drive device using an impact drive actuator according to a third embodiment of the present invention drives a lens L 2  among three lenses of L 1 , L 2 , and L 3 , as in the second embodiment described above.  
      In the lens drive device according to this embodiment, a guide groove  48  for guiding the motion object  18  is provided in the fixing member  12 . That is, the fixing member  12  is constructed so as to serve also as a guide shaft for a lens.  
      By thus providing the guide groove  48  in the fixing member  12 , the vibration member  14  is displaced along the guide groove  48 . Therefore, motion of the motion object is more stable and guarantees high operation accuracy.  
      [Fourth Embodiment] 
      As shown in  FIGS. 11A  to  11 D, a lens drive device using an impact drive actuator according to a fourth embodiment of the present invention drives a lens L 2  among three lenses of L 1 , L 2 , and L 3 , like in the second embodiment described above.  
      In the lens drive device according to this embodiment, the guide member  20  serves also as a lens barrel which fixes fixed lenses L 1  and L 3 . In this lens barrel, a lens hold member  50  including a lens L 2  provided to be freely movable in axial directions thereof is linked to the motion object  18  with a predetermined clearance maintained therebetween by a link member  52  formed on the motion object  18 .  
      In this case, the motion object  18  is frictionally engaged with the lens barrel having an optical axis, and the motion object  18  and the vibration member  14  contact each other on flat faces of their own, as in the third embodiment described above. Thus, the degree of freedom in motion of the motion object  18  is raised.  
      Accordingly, if the lens is arranged to have an optical axis corresponding to the optical axis of the lens barrel, the lens can be moved coaxially to the optical axis of the lens barrel without moving the actuator along the optical axis as long as the lens hold member  50  can be moved by the link member  52 .  
      Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, and representative devices shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.