Abstract:
A driving device capable of multidimensional positioning by the single device has a shaft-like driving member  4,  an electromechanical transducer  3  which has a plurality of expandable portions  11, 12  and which holds one end of the driving member  4,  the expandable portions being provided in parallel so that each of the expandable portions can separately expands and contracts in a axial direction of the driving member  4,  and a movable member  5  which frictionally engages on the driving member  4  and which can displace slidingly on the driving member  4,  and a drive circuit which applies to some of the expandable portions  11, 12  a low change rate of direct-current voltage component different from that applied to other expandable portions  11, 12,  and which applies to all the expandable portions  11, 12  a common alternating voltage component fluctuating with a common period.

Description:
[0001]    This application is based on application No. 2009-110945 filed in Japan, the contents of which are hereby incorporated by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a driving device. 
       BACKGROUND ART 
       [0003]    As disclosed in JP 2000-78861 A, there are publicly known driving devices of vibration type which cause asymmetrical vibrations of a driving member and slide displacement of a movable member engaged frictionally with the driving member. 
         [0004]    As disclosed in JP 2008-178209 A, JP 2008-172885 A and JP 2007-325466 A, there are also known driving devices (truss actuators) which frictionally drive a movable member held movably by guides or the like, using contact members which make elliptical motions through agency of a plurality of piezoelectric elements. 
         [0005]    In JP 2000-78861 A, JP 2008-178209 A, JP 2008-172885 A and JP 2007-325466 A are disclosed techniques for achieving a two-dimensional motion using a rotary motion through agency of a piezoelectric element in which a plurality of piezoelectric elements are integrally formed, in other words, in which electrodes are separately provided so that different portions of the one piezoelectric element can separately be expanded and contracted. 
       SUMMARY OF INVENTION 
       [0006]    Any of the driving devices described in the above mentioned Japanese patent literatures capable of performing only one-dimensional driving, and it is thus necessary to combine two or more driving devices or three or more driving devices in order to attain two-dimensional driving or three-dimensional driving, respectively. 
         [0007]    An object of the present invention is to provide a driving device capable of achieving multidimensional positioning by the single device. 
         [0008]    In order to achieve the objects of the present invention, there is provided a driving device comprising a shaft-like driving member, an electromechanical transducer which has a plurality of expandable portions and which holds one end of the driving member, the expandable portions being provided in parallel so that each of the expandable portions can separately be expanded and contracted in an axial direction of the driving member and can independently be controlled, and a movable member which is frictionally engaged on the driving member and which can be displaced slidingly on the driving member. 
         [0009]    According to this configuration, expansion and contraction of the electromechanical transducer with a short period cause vibrations of the driving member and the slide displacement of the movable member in the direction of the axis of the driving member, and imbalanced slow expansion and contraction of the expandable portions cause an inclination of the driving member while retaining the engagement of the movable member. That is, a moving radius of the movable member in a polar coordinate system is determined by a position thereof in the direction of the axis of the driving member and an argument (azimuth angle) θ of the movable member in the polar coordinate system is determined by the inclination of the driving member. Thus multidimensional positioning can be attained by the single driving device of the present invention. 
         [0010]    In the driving device of the present invention, a number of the expandable portions may be not less than three. 
         [0011]    According to this configuration, three-dimensional positioning can be attained because the driving member can be inclined in any of three or more directions and because the arguments in two or more directions can be determined. 
         [0012]    The driving device of the present invention may further have a drive circuit which applies to some of the expandable portions a direct-current voltage component different from that applied to other expandable portions, and which applies to all the expandable portions a common alternating voltage component periodically fluctuating, wherein the direct-current voltage component can be varied in voltage at a low change rate so as to prevent the slide displacement of the movable member. 
         [0013]    According to this configuration, the driving member can be inclined by the direct-current voltage component and the slide displacement of the movable member on the driving member can be caused by the alternating voltage component. 
         [0014]    In the driving device of the present invention, an even number of the expandable portions may be provided around a center axis of the electromechanical transducer which extends in the direction of the axis of the driving member, and the drive circuit may apply the direct-current voltage component opposite in polarity to the expandable portions facing across the center axis. 
         [0015]    According to this configuration, the inclination of the driving member can be increased by expansion of one of the facing expandable portions and contraction of the other. 
         [0016]    In the driving device of the present invention, no direct-current voltage component may be applied to at least any of the expandable portions. 
         [0017]    According to this configuration, lack of forces for the expansion and contraction in some of the expandable portions makes it possible to adjust a direction in which the forces for the expansion and contraction of the electromechanical transducer are balanced and to widen choices for the direction of inclination of the driving member. 
         [0018]    According to the invention, the slide displacement of the movable member on the driving member can be caused by uniform expansion and contraction of the plurality of expandable portions of the electromechanical transducer with a short period and the driving member can be inclined by nonuniform slow expansion and contraction of the expandable portions. Thus multidimensional positioning of the movable member in the polar coordinate system can be attained. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0019]    These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: 
           [0020]      FIG. 1  is a side view of a driving device of a first embodiment of the present invention; 
           [0021]      FIG. 2  is a view of a cross-section of the driving device of  FIG. 1 , taken along line A-A; 
           [0022]      FIG. 3  is a view of a cross-section of the driving device of  FIG. 1 , taken along line B-B; 
           [0023]      FIG. 4  is a side view of the driving device of  FIG. 1  in which a driving member is inclined; 
           [0024]      FIG. 5  is a circuit diagram of a drive circuit for the driving device of  FIG. 1 ; 
           [0025]      FIG. 6  is a circuit diagram of an alternative drive circuit for the driving device of  FIG. 2 ; 
           [0026]      FIG. 7  is a view of a cross-section of a piezoelectric element of a driving device in accordance with a second embodiment of the present invention, taken along a direction perpendicular to an axis thereof; 
           [0027]      FIG. 8  is a diagram showing positions of an extremity of a driving member of the driving device in accordance with the second embodiment of the present invention; 
           [0028]      FIG. 9  is a configuration diagram of an optical device using the second embodiment of the present invention; and 
           [0029]      FIG. 10  is a view of a cross-section of a piezoelectric element of a driving device in accordance with a third embodiment of the present invention, taken along a direction perpendicular to an axis thereof. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0030]    Hereinbelow, embodiments of the present invention will be described with reference to the drawings.  FIGS. 1 through 3  show a driving device  1  of a first embodiment of the present invention. The driving device  1  comprises of a weight  2 , a piezoelectric element (electromechanical transducer)  3  having one end fixed to the weight  2 , a shaft-like driving member  4  having one end fixed to the other end of the electromechanical transducer  3 , and a movable member  5  which is engaged frictionally on the driving member  4  so as to be capable of slidingly displacing. 
         [0031]    As shown in  FIGS. 2 and 3 , the piezoelectric element  3  is formed of a sheet-like piezoelectric layer  6  on which two print electrodes  7 ,  8  are printed and which is laminated in a axial direction of the driving member  4 , and external electrodes  9   a,    9   b,    10   a,    10   b  which alternately connects the print electrodes  7 ,  8 . In the piezoelectric element  3 , an expandable portion  11  in which the print electrodes  7  are interposed expands and contracts in accordance with a voltage applied between the external electrodes  9   a - 9   b,  and an expandable portion  12  in which the print electrodes  8  are interposed expands and contracts in accordance with a voltage applied between the external electrodes  10   a - 10   b.  That is, the expandable portion  11  and the expandable portion  12  are provided in parallel so as to be capable of separately expanding and contracting in the axial direction of the driving member  4 . 
         [0032]    When the expandable portion  11  is expanded by application of a positive voltage between the external electrodes  9   a - 9   b  and the expandable portion  12  is contracted by application of a negative voltage between the external electrodes  10   a - 10   b,  as shown in  FIG. 4 , the piezoelectric element  3  curves so that an extremity of the element  3  on a side to which the driving member  4  is fixed tilts in a direction of the expandable portion  12 . Thus the driving member  4  is inclined and the movable member  5  is swung to a side of the expandable portion  12 . 
         [0033]    With application to the external electrodes  9   a - 9   b  and  10   a - 10   b  short-period alternating voltages which cause slow expansion and subsequent rapid contraction of the expandable portions  11 ,  12 , the movable member  5  slidingly displaces on the driving member  4  in a direction such that the movable member  5  goes away from the piezoelectric element  3 . 
         [0034]    Thus the driving device  1  is capable of positioning the movable member  5  on a polar coordinate (r, θ), wherein a moving radius r is a position on the driving member  4  and an argument θ is an angle of inclination of the driving member  4 . 
         [0035]      FIG. 5  shows a drive circuit  13  of the driving device  1 . The drive circuit  13  has a bridge circuit  15  capable of switching a direct-current power supply  14  and applying a power supply voltage with a desired polarity between the external electrodes  9   a - 9   b  and a bridge circuit  16  capable of applying a power supply voltage with a desired polarity between the external electrodes  10   a - 10   b.  The bridge circuits  15 ,  16  are controlled by a control circuit  17  comprised of a microcomputer, and the control circuit  17  is capable of adjusting the power supply voltage of the direct-current power supply  14 . 
         [0036]    When positioning the movable member  5  of the driving device  1 , the control device  17  initially causes the bridge circuits  15 ,  16  to output alternating voltages with rectangular waves in phase with each other so as to expand and contract the expandable portions  11 ,  12  of the piezoelectric element  3  in phase with each other and so as to place the movable member  5  with a desired moving radius r with slide displacement thereof. Subsequently, the control device  17  causes the bridge circuits  15 ,  16  to continue applying the power supply voltages in opposed directions to the expandable portions  11 ,  12  and adjusts the power supply voltage of the direct-current power supply  14  so as to cause a bend of the piezoelectric element  3  at a desired angle, thereby inclining the driving member  4  at a desired argument θ. Thus the movable member  5  is positioned on the desired polar coordinate (r, θ). 
         [0037]      FIG. 6  shows an alternative drive circuit  18  for the driving device  1 . The drive circuit  18  has output of a pulse shaper  19  for shaping a waveform of a periodic alternating voltage for causing slide displacement of the movable member  5  relative to the driving member  4  by axial expansion and contraction of the piezoelectric element  3 , and a DA converter  20  for producing a voltage signal proportional to a voltage required for bending the piezoelectric element  3  to incline the driving member  4 . The pulse shaper  19  and the DA converter  20  are controlled by a microcomputer not shown. 
         [0038]    The drive circuit  18  has an adder  21  for adding output of the pulse shaper  19  and output of the DA converter  20  in a specified ratio and amplifying the output with inversion thereof, a subtractor  22  for subtracting the output of the DA converter  20  from the output of the pulse forming device  19  and amplifying the result with inversion thereof, and amplifiers  23 ,  24  for inverting and amplifying output of the adder  21  and output of the subtractor  22  with the same gains. Output of the amplifiers  23 ,  24  makes a voltage resulting from superposition of a periodic alternating voltage component obtained from amplification of output waveform of the pulse shaper  19  by a specified amplification factor and a direct-current voltage component obtained from amplification of output waveform of the DA converter  20  by a specified amplification factor. The direct-current voltage component in the amplifier  23  and the direct-current voltage component in the amplifier  24  differ in positiveness/negativeness. 
         [0039]    In the drive circuit  18 , in which the direct-current voltage component and the alternating voltage component can independently be controlled, the moving radius r of the movable member  5  can be adjusted by the pulse shaper  19  while the argument  0  of the movable member  5  can be adjusted by the DA converter  20 . 
         [0040]      FIG. 7  shows a cross-section of a piezoelectric element  31  of a driving device  1  in accordance with a second embodiment of the present invention. The following embodiment is the same as the first embodiment except for a configuration of the piezoelectric element  31  and duplicate description is omitted. In the driving device  1  of the present embodiment, the piezoelectric element  31  has four expandable portions  32 ,  33 ,  34 ,  35  which are separately capable of expanding and contracting in a axial direction of a driving member  4  and which are obtained from division of the prism-like piezoelectric element  31  into quarters around a center axis C thereof. 
         [0041]      FIG. 8  shows positions of an extremity of the driving member  4  of the driving device  1  in accordance with the present embodiment, on a plane orthogonal to the axis of the driving member  4 . In the present embodiment, a positive or negative power supply voltage or no voltage can be applied separately to each of the expandable portions  32 ,  33 ,  34 ,  35  by bridge circuits (not shown) corresponding to the expandable portions  32 ,  33 ,  34 ,  35 , for instance. In the positions of the extremity of the driving member  4  in the drawing, the voltages applied to the expandable portions  32 ,  33 ,  34 ,  35  for obtainment of each of the positions are designated by signs “+”, “−”, and “0”. 
         [0042]    In the present embodiment, in this manner, angles (θ, φ) of inclination of the driving member  4  in the two directions can be adjusted. With addition of a position (r) of the movable member  5  on the driving member  4 , the driving device  1  is capable of attaining three-dimensional positioning in a spherical coordinate system (r, θ, φ). 
         [0043]    In particular, the application of the direct-current voltage opposite in polarity to the expandable portions  32 ,  33 ,  34 ,  35  facing across the center axis C causes great deformation of the piezoelectric element  3  so as to increase an angle of inclination of the driving member  4 . Furthermore, the application of no direct-current voltage to some of the expandable portions  32 ,  34  or  33 ,  35  increases a number of directions in which the driving member  4  can be inclined. 
         [0044]    In the driving device  1  of the present embodiment also, an alternating voltage component may be applied to the expandable portions  32 ,  33 ,  34 ,  35  in common and an adjustable direct-current component voltage may selectively be applied to the desired expandable portions  32 ,  33 ,  34  and/or  35 . Though the direct-current component voltages may be made separately variable for each of the expandable portions  32 ,  33 ,  34 ,  35 , one power supply voltage may be made variable, and only directions (positiveness or negativess) and execution or non-execution of application of the direct-current component voltage may be selected. 
         [0045]      FIG. 9  shows a laser module  36  using the driving device  1  for the spherical coordinate system, as an example. The laser module  36  has a laser diode  37  for producing an infrared laser beam, an alignment lens  38  which guides the laser beam and is held by the movable member  5  of the driving device  1 , a second harmonic generator  39  as a light receiving member for receiving the laser beam and producing a green half-wave laser beam, and an emission lens  40  for emitting output of the second harmonic generator  39 . The alignment lens  38  undergoes positioning that is performed by the driving device  1  in a plane orthogonal to an optical axis of the laser beam. 
         [0046]    The laser module  36  further has a beam splitter  41  for splitting the output beam from the second harmonic generator  39 , a power monitor  42  composed of a sensor such as photodiode for converting an output level of the split output beam from the second harmonic generator  39  into a voltage signal, and a control circuit  44  for controlling operation of a drive circuit  43  for the driving device  1  in response to output of the power monitor  42 . 
         [0047]    A light receiving portion of the second harmonic generator  39  has an aperture on the order of 1 to 3 μm. The alignment lens  38  condenses the laser beam so that the laser beam has a diameter on the same order as the light receiving portion of the second harmonic generator  39 , and aligns the optical axis of the laser beam with a center of the light receiving portion of the second harmonic generator  39 . On condition where the laser beam is sufficiently condensed and where the optical axis of the laser beam is aligned with the center of the second harmonic generator  39 , all energy of the laser beam is inputted into the second harmonic generator  39 , so that output of the second harmonic generator  39  and output of the power monitor  42  are maximized. That is, the driving device  1  performs three-dimensional positioning of the movable member  5  so as to maximize the output of the power monitor  42 . 
         [0048]      FIG. 10  shows a piezoelectric element  51  of a driving device  1  in accordance with a third embodiment of the present invention. In the present embodiment, the piezoelectric element  51  is shaped like a hexagonal cylinder and has trigonal-prism-like expandable portions  52 ,  53 ,  54 ,  55 ,  56 ,  57  obtained from division thereof into sixths around a center axis C. In the present embodiment, a pair of external electrodes of each of the expandable portions  52 ,  53 ,  54 ,  55 ,  56 ,  57  are provided side by side on the same outer surface of the piezoelectric element  51 . 
         [0049]    As in the present embodiment, increase in number of the expandable portions in parallel in the piezoelectric element allows finer selection of the direction of inclination of the driving member. In a method of selecting the direction of inclination, for instance, there may be selected an asymmetrical pattern of voltage application such as application of a positive voltage to the expandable portions  52 ,  53 , a negative voltage to the expandable portion  54 , and no voltage to the expandable portions  55 ,  56 ,  57  in the present embodiment. 
         [0050]    Even if the number of the expandable portions in parallel is decreased to three, the direction of inclination of the driving member can be selected in a two-dimensional manner, so that three-dimensional positioning of the movable member can be attained. 
         [0051]    Although the present invention has been fully described in connection with the preferred embodiment thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.