Abstract:
An inertial drive actuator includes a vibrating substrate configured to be reciprocally moved by small reciprocally displacements generated by a displacement generating unit arranged on a fixing member. The vibrating substrate has a first electrode on a plane of the vibrating substrate and an insulating layer on the first electrode. The inertial drive actuator further includes a mobile object arranged on the plane of the vibrating substrate and having a second electrode on a plane facing the first electrode through the insulating layer, a frictional force control unit configured to control frictional force between the vibrating substrate and the mobile object such that a potential difference is applied across the first electrode and the second electrode to cause electrostatic adsorptive force to act, and a frictional force applying unit configured to frictionally couple the mobile object and the vibrating substrate to each other by magnetic adsorptive force.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-109834, filed Apr. 12, 2006, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an inertial drive actuator which stepping-drives a mobile object. 
         [0004]    2. Description of the Related Art 
         [0005]    There is known an inertial drive actuator which supplies a saw-toothed drive pulse to an electromechanical conversion element coupled to a drive shaft to displace the drive shaft in an axial direction and to move a mobile object frictionally coupled to the drive shaft in the axial direction. 
         [0006]    This inertial drive actuator is disclosed in, for example, U.S. Pat. No. 5,225,941. As shown in FIG. 1 in the U.S. patent, a driving rod serving as a vibrating member is inserted into a hole formed in an upright portion of a supporting member and movably arranged in an axial direction of the vibrating member. One end of the vibrating member is fixed to one end of a piezoelectric element. The other end of the piezoelectric element is fixed to the supporting member. Therefore, with vibration of the piezoelectric element, the vibrating member vibrates in the axial direction. A lens barrel serving as a mobile object has two holes formed therein, and the vibrating member is inserted into the holes. Furthermore, a leaf spring is fitted on the mobile object from beneath, and a curved projection which is a projecting portion formed on the leaf spring is brought into press contact with the vibrating member. In this manner, the mobile object and the vibrating member are frictionally coupled to each other by being pressed by the leaf spring. 
         [0007]    In the inertial drive actuator, as shown in FIG. 3(A) in the U.S. patent, a drive voltage waveform has a sharply upright portion and a moderately fall portion. In the sharply upright portion, the piezoelectric element sharply extends to rapidly move the mobile object fixed to the piezoelectric element. However, the mobile object overcomes frictional coupling force between the mobile object and the vibrating member by the inertia to stay at the position without moving. When the piezoelectric element moderately shrinks, the vibrating member fixed to the piezoelectric element slowly moves. In this case, with frictional force between the mobile member brought into press contact with the leaf spring and the vibrating member, the mobile object moves along with movement of the vibrating member. 
         [0008]    As described above, the inertial drive actuator is an actuator which can move the mobile object by the frictional coupling between the mobile object and the vibrating member generated by the leaf spring and application of a voltage having the drive voltage waveform. 
         [0009]    When the leaf spring always brings the vibrating member into press contact with the mobile object to frictionally support the mobile member to keep the position thereof when the mobile object is stopped. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    According to an aspect of the present invention, there is provided an inertial drive actuator comprising: 
         [0011]    a fixing member; 
         [0012]    a displacement generating unit arranged on the fixing member and configured to generate small displacements in a first direction and a second direction opposing the first direction; 
         [0013]    a vibrating substrate configured to be reciprocally moved by the small displacements of the displacement generating unit and having a first electrode on a plane of the vibrating substrate and an insulating layer on the first electrode; 
         [0014]    a mobile object arranged on the plane of the vibrating substrate and having a second electrode on a plane facing the first electrode through the insulating layer; 
         [0015]    a frictional force control unit configured to control frictional force between the vibrating substrate and the mobile object such that a potential difference is applied across the first electrode and the second electrode to cause electrostatic adsorptive force to act; and 
         [0016]    a frictional force applying unit configured to frictionally couple the mobile object and the vibrating substrate to each other by magnetic adsorptive force. 
         [0017]    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 
         [0018]    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. 
           [0019]      FIG. 1A  is a perspective view showing a configuration of an inertial drive actuator according to a first embodiment of the present invention; 
           [0020]      FIG. 1B  is a plan view showing the configuration of the inertial drive actuator according to the first embodiment; 
           [0021]      FIG. 1C  is a sectional view showing the configuration of the inertial drive actuator according to the first embodiment; 
           [0022]      FIG. 2A  is a waveform chart showing waveforms of applied voltages to respective parts of the inertial drive actuator according to the first embodiment when a mobile object is moved to the left in  FIG. 1C ; 
           [0023]      FIG. 2B  is a waveform chart showing waveforms of applied voltages to the respective parts of the inertial drive actuator according to the first embodiment when the mobile object is moved to the right in  FIG. 1C ; 
           [0024]      FIG. 3  is a sectional view showing a configuration of a modification of the inertial drive actuator according to the first embodiment; 
           [0025]      FIG. 4  is a sectional view showing a configuration of an inertial drive actuator according to a second embodiment of the present invention; 
           [0026]      FIG. 5  is a sectional view showing a configuration of a modification of the inertial drive actuator according to the second embodiment; 
           [0027]      FIG. 6  is a sectional view showing a configuration of an inertial drive actuator according to a third embodiment of the present invention; 
           [0028]      FIG. 7A  is a waveform chart showing waveforms of applied voltages to respective parts of the inertial drive actuator according to the third embodiment when a first mobile object is moved to the left in  FIG. 6  and a second mobile object is moved to the right in  FIG. 6  independently of each other; and 
           [0029]      FIG. 7B  is a waveform chart showing waveforms of applied voltages to the respective parts of the inertial drive actuator according to the third embodiment when the first mobile object is moved to the right in  FIG. 6  and the second mobile object is moved to the left in  FIG. 6  independently of each other. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    A best mode for carrying out the present invention will be described below with reference to the accompanying drawings. 
       First Embodiment 
       [0031]    In an inertial drive actuator according to a first embodiment of the present invention, as shown in  FIGS. 1A to 1C , one end of a piezoelectric element  10  is fixed to a fixing member  12 , and the other end of the piezoelectric element  10  is fixed to one end of a vibrating substrate  14 . A mobile object  16  which can move in a vibration direction of the piezoelectric element  10  is arranged on the vibrating substrate  14 . A first electrode  18  is formed on a plane of the vibrating substrate  14  facing the mobile object  16 , and a second electrode  20  is formed on a plane of the mobile object  16  facing the vibrating substrate  14 . The first electrode  18  and the second electrode  20  are in contact with each other through an insulating film  22  formed on the first electrode  18  to face each other. When a potential generating unit  24  applies a potential difference across the first electrode  18  and the second electrode  20 , electrostatic adsorptive force acts between the electrodes  18  and  20 . 
         [0032]    On the side of the vibrating substrate  14  opposing the side on which the mobile object  16  is arranged, a permanent magnet  26  is arranged to extend in the vibration direction of the vibrating substrate  14 . On the mobile object  16 , an adsorbed member  28  having magnetism is arranged. For this reason, magnetic adsorptive force acts between the permanent magnet  26  and the mobile object  16 . The permanent magnet  26  and the adsorbed member  28  are arranged to make it possible to stop the mobile object  16 . Furthermore, even though electrostatic adsorptive force does not act between the first electrode  18  and the second electrode  20 , the mobile object  16  can be held at the position due to frictional force even in a stopped state. Since the permanent magnet  26  is not in contact with the adsorbed member  28 , frictional force can be supplied without being influenced by abrasion or the like. For this reason, the actuator can be stably driven. 
         [0033]    The other end of the vibrating substrate  14  is biased toward the piezoelectric element  10  by a bias spring  30 . A drive voltage to displace the piezoelectric element  10  is applied from a drive circuit  32  to the piezoelectric element  10 . 
         [0034]    A guide may be arranged not to move the mobile object  16  in a direction other than the vibration direction of the piezoelectric element  10 . 
         [0035]    An operation of the inertial drive actuator having the above configuration will be described below. 
         [0036]    A driving principle will be described first with reference to  FIG. 2A . In  FIG. 2A , an applied voltage waveform I denotes an applied voltage from the drive circuit  32  to the piezoelectric element  10 , an applied voltage waveform II denotes an applied voltage from a potential difference generating unit  24  to the first electrode  18 , and an applied voltage waveform III denotes an applied voltage from the potential difference generating unit  24  to the second electrode  20 . 
         [0037]    In a period from time point A to time point B shown in  FIG. 2A , an applied voltage from the drive circuit  32  to the piezoelectric element  10  is sharply upright, and the piezoelectric element  10  is sharply displaced to the left in  FIG. 1C . Accordingly, the vibrating substrate  14  also sharply moves to the left. At this time, simultaneously, by the potential difference generating unit  24 , an applied voltage to the first electrode  18  arranged on the vibrating substrate  14  and an applied voltage to the second electrode  20  arranged on the mobile object  16  have a potential difference. For this reason, electrostatic adsorptive force acts between the vibrating substrate  14  and the mobile object  16  to increase frictional force. Therefore, with the displacement of the vibrating substrate  14 , the mobile object  16  moves to the left. 
         [0038]    In a period from time point C to time point D in  FIG. 2A , in contrast to the above, an applied voltage to the piezoelectric element  10  sharply falls. When the piezoelectric element  10  sharply shrinks, the vibrating substrate  14  sharply moves to the right in  FIG. 1C . At this time, since an applied voltage to the first electrode  18  of the vibrating substrate  14  and an applied voltage to the second electrode  20  of the mobile object  16  are equal voltages, electrostatic adsorptive force is not generated between the electrodes  18  and  20 . Therefore, due to inertia of the mobile object  16 , the mobile object  16  overcomes frictional force between the vibrating substrate  14  and the mobile object  16  generated by magnetic adsorptive force between the permanent magnet  26  and the mobile object  16  on which the adsorbed member  28  is installed, to stay at the position. 
         [0039]    By repeating this operation, the mobile object  16  moves to the left with respect to the vibrating substrate  14 . 
         [0040]    When the mobile object  16  is moved to the right in  FIG. 1C , as shown in  FIG. 2B , a potential difference may be applied across the first and second electrodes  18  and  20  when the piezoelectric element  10  is sharply shrunk. 
         [0041]    The above is a basic drive principle of the inertial drive actuator according to the embodiment. Since friction is given in synchronism with piezoelectric vibration, the mobile object  16  moves only when the friction increases, and thus the drive efficiency is improved. At the same time, the actuator can be inertially driven without reciprocally changing a displacement rate of the piezoelectric element  10 . As a result, driving waveforms can be simplified. 
         [0042]    When the moving mobile object  16  is stopped, if driving of the piezoelectric element  10  and supply of the potential difference across the first and second electrodes  18  and  20  are stopped, the frictional force between the vibrating substrate  14  and the mobile object  16  by the magnetic adsorptive force between the permanent magnet  26  and the adsorbed member  28  can stop the mobile object  16  and hold the mobile object  16  at the position. 
         [0043]    As described above, in the first embodiment, the frictional force applying unit which frictionally couples the mobile object  16  and the vibrating substrate  14  to each other by the magnetic adsorptive force is arranged to always constantly apply frictional force and to make it possible to stably drive the actuator. 
         [0044]    In the embodiment, although the permanent magnet  26  is arranged under the vibrating substrate  14 , the vibrating substrate  14  itself may be constituted by a permanent magnet. When the vibrating substrate  14  is a permanent magnet, parts constituting the inertial drive actuator can be reduced in number, and a simple configuration can be achieved. 
         [0045]    When a material having magnetism is used as the mobile object  16 , even though the adsorbed member  28  is not additionally arranged, not only an effect equivalent to that of the embodiment but also a simpler configuration can be obtained. In this case, as a magnetic material used in the mobile object  16 , iron, a nickel alloy, stainless steel, or the like is typically used. 
         [0046]    Dimensions of the inertial drive actuator are typically 20 mm in length×3 mm in width×3 mm in height. 
         [0047]    As shown in  FIG. 3 , the position of the permanent magnet  26  may be arranged under the fixing member  12 . In order to simplify the drawing, the potential difference generating unit  24  and the drive circuit  32  are omitted in  FIG. 3  (as in  FIGS. 4 to 6  described later). 
         [0048]    In this manner, the permanent magnet  26  is arranged under the fixing member  12  to prevent the vibrating substrate  14  and the permanent magnet  26  from being in contact with each other. For this reason, abrasion of the permanent magnet  26  caused by vibration generated by the vibrating substrate  14  is eliminated. Furthermore, in this case, when the fixing member  12  consists of the magnetic material, the permanent magnet  26  can be fixed to the fixing member  12  by magnetic adsorptive force, and adhesive bonding or the like is not required. For this reason, the inertial drive actuator can be easily assembled. 
       Second Embodiment 
       [0049]    In an inertial drive actuator according to a second embodiment of the present invention, unlike in the first embodiment, the permanent magnet  26  is not arranged on the fixing member  12  side, and the permanent magnet  26  is arranged on the mobile object  16  side as shown in  FIG. 4 . 
         [0050]    In this manner, the permanent magnet  26  is arranged on the mobile object  16  side to make it possible to stably generate magnetic adsorptive force regardless of the position of the mobile object  16 . 
         [0051]    As shown in  FIG. 5 , the fixing member  12  may consist of a magnetic material. 
         [0052]    When the fixing member  12  consists of the magnetic material as described above, a simpler configuration is obtained because an adsorbed member  28  is not necessary. In this case, as the magnetic material used in the fixing member  12 , iron, a nickel alloy, stainless steel, or the like is used. However, the magnetic material is not limited to these materials, and any material having magnetism may be used. 
       Third Embodiment 
       [0053]    In an inertial drive actuator according to a third embodiment of the present invention, as shown in  FIG. 6 , a first mobile object  16 A and a second mobile object  16 B are arranged on a vibrating substrate  14 . In this case, each of the mobile objects  16 A and  16 B has the same configuration as that of the mobile object  16  in the first embodiment. More specifically, in the first mobile object  16 A, a second electrode  20 A is formed through an insulating film  22  to face a first electrode  18  of the vibrating substrate  14 , and an adsorbed member  28 A having magnetism is also arranged. Similarly, in the second mobile object  16 B, a second electrode  20 B is formed through the insulating film  22  to face the first electrode  18  of the vibrating substrate  14 , and an adsorbed member  28 B having magnetism is arranged. The other configurations are the same as those in the modification of the first embodiment. 
         [0054]    An operation of the inertial drive actuator according to the embodiment will be described below with reference to  FIGS. 7A and 7B . In these drawings, an applied voltage waveform I denotes an applied voltage from a drive circuit  32  to a piezoelectric element  10 , an applied voltage waveform II denotes an applied voltage from a potential difference generating unit  24  to the first electrode  18 , an applied voltage waveform III denotes an applied voltage from the potential difference generating unit  24  to the second electrode  20 A of the first mobile object  16 A, and an applied voltage waveform IV denotes an applied voltage from the potential difference generating unit  24  to the second electrode  20 B of the second mobile object  16 B. 
         [0055]    In a period from time point A to time point B shown in  FIG. 7A , the applied voltage waveform from the drive circuit  32  to the piezoelectric element  10  is sharply upright, and the vibrating substrate  14  also rapidly moves to the left in accordance with rapid displacement of the piezoelectric element  10  to the left in  FIG. 6 . At this time, simultaneously, by the potential difference generating unit  24 , an applied voltage to the first electrode  18  arranged on the vibrating substrate  14  and an applied voltage to the second electrode  20 A arranged on the first mobile object  16 A have a potential difference. For this reason, electrostatic adsorptive force acts between the vibrating substrate  14  and the first mobile object  16 A to increase frictional force. Therefore, with the displacement of the vibrating substrate  14 , the first mobile object  16 A moves to the left. On the other hand, with respect to the second mobile object  16 B, since the applied voltage to the first electrode  18  of the vibrating substrate  14  and the applied voltage to the second electrode  20 B of the second mobile object  16 B are equal voltages, electrostatic adsorptive force is not generated between the electrodes. Therefore, since the inertial force of the second mobile object  16 B overcomes frictional force between the vibrating substrate  14  and the second mobile object  16 B, the second mobile object  16 B stays at the position. 
         [0056]    In a period from time point C to time point D in  FIG. 7A , in contrast to the above, an applied voltage waveform to the piezoelectric element  10  sharply falls. When the piezoelectric element  10  sharply shrinks, the vibrating substrate  14  sharply moves to the right in  FIG. 6 . At this time, since an applied voltage to the first electrode  18  of the vibrating substrate  14  and an applied voltage to the second electrode  20 A of the first mobile object  16 A are equal voltages, electrostatic adsorptive force is not generated between the electrodes. Therefore, since the inertial force of the first mobile object  16 A overcomes frictional force between the vibrating substrate  14  and the first mobile object  16 A, the first mobile object  16 A stays at the position. In contrast to this, with respect to the second mobile object  16 B, since the applied voltage to the first electrode  18  arranged on the vibrating substrate  14  and the applied voltage to the second electrode  20 B arranged on the second mobile object  16 B have a potential difference, electrostatic adsorptive force acts between the vibrating substrate  14  and the second mobile object  16 B to increase frictional force. Therefore, with displacement of the vibrating substrate  14 , the second mobile object  16 B moves to the right. 
         [0057]    By repeating this operation, the first mobile object  16 A moves to the left with respect to the vibrating substrate  14 , and the second mobile object  16 B moves to the right with respect to the vibrating substrate  14 . 
         [0058]    In this manner, a waveform obtained by inverting the waveform applied to the first mobile object  16 A is applied to the second mobile object  16 B to make it possible to independently move the first mobile object  16 A to the left and the second mobile object  16 B to the right. 
         [0059]    When the second mobile object  16 B is moved to the left simultaneously with the movement of the first mobile object  16 A to the right, as shown in  FIG. 7B , a potential difference may be applied across the first electrode  18  and the second electrode  20 A when the piezoelectric element  10  is sharply shrunk, and a potential difference may be applied across the first electrode  18  and the second electrode  20 B when the piezoelectric element  10  is sharply extended. 
         [0060]    As a matter of course, when waveforms having equal phases are applied to the first mobile object  16 A and the second mobile object  16 B, respectively, the two mobile objects  16 A and  16 B move in the same direction. The waveform is applied only to a mobile object to be moved to make it possible to move only one mobile object as a matter of course. 
         [0061]    In this manner, two or more mobile objects can be independently moved without changing the size of the inertial drive actuator. 
         [0062]    As in this embodiment, the above modifications described in the first embodiment can be achieved as a matter of course. 
         [0063]    As in the second embodiment, the permanent magnet  26  may be arranged on a mobile object side. 
         [0064]    The present invention has been described with reference to the embodiments. However, the present invention is not limited to the embodiments, and various changes and applications can be effected without departing from the spirit and scope of the invention as a matter of course. 
         [0065]    For example, the piezoelectric element  10  is used as a displacement generating unit. However, the displacement generating unit is not limited to the piezoelectric element  10 . An electrostatic actuator, an electromagnetic actuator, an electrostrictive actuator, and the like may be used. 
         [0066]    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 embodiments 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.