Abstract:
An actuator using the vibration caused by a piezoelectric element. The actuator includes: a base; a vibratory rod bonded to the base; an piezoelectric element bonded to the vibratory rod; and a contact body for contacting frictionally with the vibratory rod under an suitable frictional force exerting therebetween. The piezoelectric element is charged and discharged, so that the piezoelectric element is transformed in one direction relatively fast and in opposite direction relatively slow, and so that the contact body is driven along the vibratory rod in a set direction.

Description:
This application is based upon application No. 2000-280288 filed in Japan, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a drive mechanism employing an electromechanical transducer. More specifically, the present invention relates to the drive mechanism employing the electromechanical transducer or vibrating member, suitable for actuating a moving body equipped in an apparatus such as a precise device and a high-technology info tool, and for adapting a microactuator for minute operation. 
     2. Description of the Related Arts 
     Conventionally, there have been proposed some drive mechanisms employing electromechanical transducers. For example, in a drive mechanism as shown in FIG. 11, a moving body  51  contacts frictionally with a drive rod  53 , which is movably supported by stationary plates  62  and  63 . One end of the piezoelectric element  58  is fixed to the stationary plate  64 , and its opposite end is fixed to one of the ends of the drive rod  53 . In the arrangement, the piezoelectric element  18  expands at a first velocity and contracts at a second velocity, different from the first velocity, when the piezoelectric element  18  is supplied with drive pluses, for example, having a saw-teeth-shaped waveform. Thereby the drive rod  53  moves and the moving body  51  is driven along the drive rod  53  (See, for example, Japanese Non-examined Patent Publication No. 7-274544). 
     However, the strength of the piezoelectric element is low. Therefore, it is necessary to protect the piezoelectric element  58  from the excessive force. 
     Specifically, it is necessary to complicate the construction of the drive mechanism, and to limit the drive condition such as the drive velocity and the load, in order to prevent the external force from causing bending moment, torsion torque, compressive force, and tensile force to the piezoelectric element. 
     Additionally, it is necessary that expanding and contracting direction of the piezoelectric element  58  is precisely coincident with moving direction of the drive rod  53  moves. Therefore, it is difficult to assemble the drive mechanism, due to close tolerance of positioning the piezoelectric element  58  and drive rod  53 . 
     Moreover, the method for fixing the piezoelectric element  58  must be chosen from methods, in which no excessive force is exerted on the piezoelectric element  58 . The drive mechanism must be assembled without exerting the excessive force on the piezoelectric element  58 . Thus, it is difficult to assemble the drive mechanism efficiently. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a drive mechanism employing an electromechanical transducer, on which no excessive force is exerted. 
     In order to achieve the above objects, according to one aspect of the present invention, there is provided a drive mechanism, comprising: a stationary member; a drive member fixed to the stationary member; an electromechanical transducer fixed to the drive member; and a driven member which is driven by the drive member and which contacts frictionally with the drive member under a predetermined frictional force exerting therebetween, wherein the electromechanical transducer is supplied with drive pulses, so that the electromechanical transducer expands at a first velocity and contracts at a second velocity, different from the first velocity, and so that the driven member moves along the drive member in a predetermined direction. 
     In the construction, the electromechanical transducer (for example, electrostatic actuator, piezoelectric transducer, electrostriction transducer, magnetostriction transducer, and so on) changes the electrical energy (for example, electric voltage, electric current, electric field, electric charge, static electricity, magnetic field) supplied thereto into the mechanical energy (for example, transformation or strain such as prolonging, compressing, expanding, contracting, bending, twisting). 
     In the construction, even though the principle of driving is not completely clear, the driven member can be driven relative to the drive member in a predetermined direction, by means of supplying appropriate drive pulses, for example, having a saw-teeth-shaped waveform. Such drive pulses causes the transformation of the electromechanical transducer, so that the drive member vibrates with mutually different velocities, even if the drive member is fixed to the stationary member. Namely, the vibration of the drive member includes one component at relatively slow velocity proceeding in one direction, and the other component at relatively fast velocity proceeding in opposite direction. We reason; that the one component of the vibration does not cause the relative sliding between the drive member and the driven member; that the other component of the vibration causes the relative sliding therebetween; and that by repeating such a cycle, the driven member can be driven relative to the drive member in a predetermined direction. 
     In the construction, the electromechanical transducer is fixed to (or restrained by) only the drive member, and thereby, no excessive force is exerted on the electromechanical transducer. 
     As an embodiment, expansion and contraction of the electromechanical transducer makes the drive member vibrate, so that a cycle of the vibration of the drive member causes one state in which the driven member slides along (or is slidable along) the drive member in a predetermined direction, resisting the frictional force exerting therebetween, and another state in which the driven member does not slide along (or is unslidable along, or remains stationary against) the drive member with the frictional force exerting therebetween. 
     As an embodiment, the drive member has a pair of ends, so that a portion near one of the ends of the drive member is fixed to the stationary member, and so that the electromechanical transducer is fixed to the other of the ends of the drive member. 
     According to the embodiment, it is possible to prevent the drive member from moving, and to have a driving range of the driven member along the drive member between one positions fixed to the stationary member and the other position fixed to the electromechanical transducer, without any stopper for preventing the driven member from moving beyond the driving range. 
     As an embodiment, the drive member has a pair of ends, so that a portion near one of the ends of the drive member is fixed to the stationary member, and so that the electromechanical transducer is fixed to the one of the ends of the drive member. 
     According to the embodiment, it is possible to increases the space around the driven member. 
     As an embodiment, another portion near the other of the ends of the drive member is supported by the stationary member. 
     According to the embodiment, it is possible to prevent the drive member from moving, and to have a driving range of the driven member along the drive member between one position fixed to the stationary member and the other position supported by the stationary member, without any stopper for preventing the driven member from moving beyond the driving range. 
     As an embodiment, another portion near the other of the ends of the drive member is fixed to the stationary member. 
     According to the embodiment, it is possible to prevent the drive member from moving, and to have a driving range of the driven member along the drive member between two positions fixed to the stationary member, without any stopper for preventing the driven member from moving beyond the driving range. 
     As an embodiment, the stationary member is fixed to a lens barrel, and wherein the driven member holds a lens. 
     As an embodiment, the drive member is fixed to the stationary member by one of caulking, press fitting, fusion bonding, adhesive bonding, screw fastening, and welding. 
     As an embodiment, the drive member is formed with elastic material. 
     In order to achieve the above object, according to another aspect of the present invention, there is provided a drive mechanism, comprising: a stationary member; a drive member, having a pair of ends, fixed to the stationary member; a first electromechanical transducer fixed to one of the ends of the drive member; a second electromechanical transducer fixed to the other of the ends of the drive member; and a driven member which is driven by the drive member and which contacts frictionally with the drive member under a predetermined frictional force exerting therebetween, wherein at least one of the first electromechanical transducer and the second electromechanical transducer is supplied with drive pulses, so that the at least one thereof expands at a first velocity and contracts at a second velocity, different from the first velocity, and so that the driven member moves along the drive member in a predetermined direction. 
     In the construction, the electromechanical transducers are fixed to (or strained by) only both ends of the drive member, and thereby, no excessive force is exerted on the electromechanical transducers. 
     Moreover, in the construction, it is possible to drive the driven member identically in one direction and opposite direction, for example, by supplying same drive pulses to either one of the electromechanical transducers selectively. 
     As an embodiment, expansion and contraction of the at least one of the first electromechanical transducer and the second electromechanical transducer makes the drive member vibrate, so that a cycle of the vibration of the drive member causes one state in which the driven member slides along (or is slidable along) the drive member in a predetermined direction, resisting the frictional force exerting therebetween, and another state in which the driven member does not slide along (or is unslidable along, or remains stationary against) the drive member with the frictional force exerting therebetween. 
     As an embodiment, a portion near the one of the ends of the drive member and another portion near the other of the ends thereof are fixed to the stationary member. 
     According to the embodiment, it is possible to prevent the drive member from moving, and to have a driving range of the driven member along the drive member between two positions fixed to the stationary member, without any stopper for preventing the driven member from moving beyond the driving range. 
     As an embodiment, the stationary member is fixed to a lens barrel, and wherein the driven member holds a lens. 
     As an embodiment, the drive member is fixed to the stationary member by one of caulking, press fitting, fusion bonding, adhesive bonding, screw fastening, and welding. 
     As an embodiment, the drive member is formed with elastic material. 
     In order to achieve the above object, according to still another aspect of the present invention, there is provided a drive mechanism, comprising: a first member; a second member for contacting frictionally with the first member under a predetermined frictional force exerting therebetween; and an electromechanical transducer fixed to the first member, wherein the electromechanical transducer is supplied with drive pulses, so that the electromechanical transducer expands at a first velocity and contracts at a second velocity, different from the first velocity, and so that one of the first member and the second member moves relative to the other thereof in a predetermined direction. 
     In the construction, the electromechanical transducer vibrates the first member with mutually different velocities. Namely, the vibration of the first member includes one component at relatively slow velocity proceeding in one direction, and the other component at relatively fast velocity proceeding in opposite direction. The one component of the vibration does not cause the relative sliding between the first member and the second member. On the other hand, the other component of the vibration causes the relative sliding therebetween. By repeating such a cycle, in case that one of the first member and the second member is fixed to the stationary member, the other thereof is driven relative to the one thereof in a predetermined direction. 
     In the construction, the electromechanical transducer is restrained by only the first member, and thereby, it is possible to exert no excessive force on the electromechanical transducer. 
     As an embodiment, expansion and contraction of the electromechanical transducer makes the first member vibrate, so that a cycle of the vibration of the first member causes one state in which the one of the first member and the second member moves along (or is movable along) the other thereof in a predetermined direction, resisting the frictional force exerting therebetween, and another state in which the one thereof does not move along (or is unmovable along, or remains stationary against) the other thereof with the frictional force exerting therebetween. 
     In order to achieve the above object, according to still another aspect of the present invention, there is provided a drive mechanism, comprising: a stationary member; a first drive member fixed to the stationary member; a first electromechanical transducer fixed to the fist drive member; a first driven member which is driven by the first drive member and which contacts frictionally with the first drive member under a predetermined frictional force exerting therebetween; a second drive member fixed to the first driven member; a second electromechanical transducer fixed to the second drive member; a second driven member which is driven by the second drive member and which contacts frictionally with the second drive member under a predetermined frictional force exerting therebetween; a third drive member fixed to the second driven member; a third electromechanical transducer fixed to the third drive member; a third driven member which is driven by the third drive member and which contacts frictionally with the third drive member under a predetermined frictional force exerting therebetween, wherein each of the first electromechanical transducer, the second electromechanical transducer, and the third electromechanical transducer is supplied with drive pulses, so that each thereof expands at a first velocity and contracts at a second velocity, different from the first velocity, respectively, and so that each of the first driven member, the second driven member, and the third driven member moves relative to each of the first drive member, the second drive member, and the third drive member in a predetermined direction, respectively. 
     In the construction, the third driven member can be driven at three or more degrees of freedom in three-dimensional space. 
     As an embodiment, expansion and contraction of each of the first electromechanical transducer, the second electromechanical transducer, and the third electromechanical makes each of the first drive member, the second drive member, and the third drive member vibrate respectively, so that a cycle of the vibration of each thereof causes one state in which each of the first driven member, the second driven member, and the third driven member moves along (or is movable along) each of the first drive member, the second drive member, and the third drive member in a predetermined direction, resisting the frictional force exerting therebetween, respectively, and another state in which each of the first driven member, the second driven member, and the third driven member does not move along (or is unmovable along, or remains stationary against) each of the first drive member, the second drive member, and the third drive member with the frictional force exerting therebetween, respectively. 
     As an embodiment, the first drive member, the second drive member, and the third drive member are arranged, so that the moving directions of the first driven member, the second driven member, and the third driven member are substantially perpendicular to each other. 
     In the construction, the vibration in one of the driven members exerts no influence on the other thereof, and therefore the drive mechanism can be driven efficiently. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This and other objects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying the drawings. 
     FIG. 1 is a perspective view of a drive mechanism according to a first embodiment of the present invention. 
     FIGS. 2A through 2F are waveform charts of drive pulses supplied to the piezoelectric element in the drive mechanism as shown in FIG.  1 . 
     FIG. 3 is a schematic exploded view of a drive mechanism according to a second embodiment of the present invention. 
     FIG. 4 is a schematic exploded view of a drive mechanism according to a third embodiment of the present invention. 
     FIG. 5 is a schematic exploded view of a drive mechanism according to a fourth embodiment of the present invention. 
     FIG. 6 is a schematic exploded view of a drive mechanism according to a fifth embodiment of the present invention. 
     FIG. 7 is a sectional perspective view of main part of a drive mechanism according to a sixth embodiment of the present invention. 
     FIG. 8 is a sectional view of main part of a drive mechanism according to a seventh embodiment of the present invention. 
     FIG. 9 is a perspective view of a drive mechanism according to a eighth embodiment of the present invention. 
     FIG. 10 is a perspective view of a manipulator according to a ninth embodiment of the present invention. 
     FIG. 11 is an exploded perspective view of a conventional drive mechanism using a piezoelectric element  18 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before the description of each of the preferred embodiments according to the present invention proceeds, it is to be noted that like or corresponding parts are designated by like reference numerals throughout the accompanying drawings. 
     A detailed description is made below upon drive mechanisms of the preferred embodiments, with reference to FIG.  1  through FIG.  10 . 
     First, referring to FIGS. 1 and 2, the description is made below in detail on a drive mechanism, according to a first embodiment of the present invention. FIG. 1 is a perspective view showing a construction of the drive mechanism  100 . The drive mechanism  100  comprises a piezoelectric element  1 , a drive rod  2 , a contact body  3 , and a stationary member  4 . Each of the piezoelectric element  1  and the drive rod  2  has a pair of ends. One end of the drive rod  2  is adhered to one end of the piezoelectric element  1 . The opposite end of the drive rod  2  is fixed to the stationary member  4 . The contact body  3  frictionally contacts with the drive rod  2 . 
     Specifically, the drive rod  2  has an approximately prismatic shape. The contact body  3  has an L-shape section, extending along two planes crossing at a sharp corner of the drive rod  2 , so as to slidably contact with the drive rod  2  without rotating respect to the drive rod  2 . The contact body  3  can move along the drive rod  2  longitudinally. An urging spring  5  is fixed to the contact body  3  by bolts  6 . The urging spring  5  contacts with a round corner of the drive rod  2 , opposite to the sharp corner thereof, so that the contact body  3  contacts frictionally with the drive rod  2  under an appropriate frictional force exerting therebetween. 
     A principle of operation of the driven mechanism  100  is supposed as follows. The piezoelectric element  1  repeats expanding and contracting in directions indicated by an arrow X in FIG. 1, responding to appropriate drive pulses supplied thereto, and thus vibrates. Such vibration of the piezoelectric element  1  is transmitted to the drive rod  2 , and makes the drive member  2  vibrate. Then, the contact body  3  moves in either one of directions indicated by an arrow Y in FIG.  1 . The direction and the velocity of motion of the contact body  3  can be controlled by means of changing drive pulses supplied to the piezoelectric element  1 . 
     Specifically, when drive pulses (or pules voltage), for example, having a generally saw-teeth-shaped waveform with pairs of a slowly raising portion and a rapidly falling portion as shown in FIG. 2A, is supplied (or applied) to the piezoelectric element  1 , the piezoelectric element  1  repeats expanding slowly in one of both directions indicated by the arrow X in FIG. 1, and contracting rapidly in the other thereof, in a same cycle as that of drive pulses. Such vibration of the piezoelectric element  1  causes the drive rod  2  to vibrate. 
     The drive rod  2  vibrates at least in its longitudinal directions with mutually different velocities. That is to say, the waveform of such a vibration is not symmetric about an axis parallel to a time axis. The contact body  3  slides or moves along the drive rod  2  in either one of directions shown by the arrow Y in FIG.  1 . 
     It is possible to move the contact body  3  in opposite direction by changing drive pulses supplied to the piezoelectric element  1 . For example, a generally saw-teeth-shaped waveform, having pairs of a rapidly raising portion and a slowly falling portion, as shown in FIG. 2B are supplied to the piezoelectric element  1 . 
     Drive pulses, having square waveforms as shown in FIGS. 2C and 2D, may be supplied to the piezoelectric element  1 . It is possible to change the moving direction of moving the contact body  3 , by changing the duty of square waves. 
     In case that drive pulses have saw-teeth waveforms or square waveforms, it is possible to change the moving direction of the contact body  3  by means of changing the period of drive pulses without changing the type of waveforms. Drive pulses are rot limited to saw-teeth waveforms or square waveforms, but it may be any waveforms so as to vibrate the drive rod  3  with mutually different velocities. 
     Furthermore, it is possible to move the contact body  3  by a small amount, when drive pulses, having intermittent waveforms as shown in FIGS. 2E and 2F, are supplied to the piezoelectric element  1 . 
     As shown in the above described embodiment, only one end of the piezoelectric element  1  is adhered to the drive rod  2 , and thus, the number of portions where the piezoelectric element  1  is strained is reduced to one. Since the mechanical strength of the drive rod  2  can be high and the drive rod  2  does not: need to be able to move longitudinally, the drive rod  2  can be fixed firmly to the stationary member  4 . Therefore, it is possible to simplify the construction of the drive mechanism  100 , without conventional urging or holding member for removing the play of the drive rod relative to the supporting portion therefor. 
     Moreover, since the piezoelectric element  1  is blocked from the external force and the working load, no excessive force is exerted on the piezoelectric element  1 , and thereby, it is possible to make the drive mechanism  100  strong and rigid. Specifically, although, in the conventional drive mechanism, there is a problem about peeling at the boundaries adhered between the piezoelectric element and the stationary member and between the piezoelectric element and the drive rod, such a problem is not caused in the drive mechanism  100 . 
     Furthermore, since at least one portion of the drive rod  2  may be fixed on the stationary member  4  and at least another portion of the drive rod  2  may be adhered to the piezoelectric element  1 , it is easy to assemble the drive mechanism  100 . Since the mechanical strength of the drive rod  2  can be high, as described above, the way having easy operations can be selected, in order to fix the drive rod  2  to the stationary member  4 . Moreover, since it is sufficient that the adhesive strength between the piezoelectric element  1  and the drive rod  2  is so strong as to prevent the piezoelectric element  1  from peeling from the drive rod  2  during the operation, the way having easy operations can be selected, in order to fix the piezoelectric element  1  to the drive rod  2 . Thus, the drive mechanism  100  can be assembled more easily. 
     In one specific example of the embodiment, the piezoelectric element  1  is a rectangular solid, having a height and a depth of 3 mm each and a width of 5 mm. 
     In the above example, the drive rod  2  is formed with fiberglass reinforced plastic, including 50 weight percent carbon fiber. The drive rod  2  is generally rectangular solid, which section is generally square 3.5 mm on a side, and which length is 20 mm. One of corners of the section is rounded by 3.5 mm. Young&#39;s modulus of the drive rod  2  is nearly 0.6 time as many as that of the metal (steel). The drive rod  2  is as heavy as the piezoelectric element  1 . Alternatively, any material other than fiberglass reinforced plastic can be used for the drive rod  2 , if Young&#39;s modulus and density thereof fall in the range in which the power of the piezoelectric element  1  can cause appropriate longitudinal vibration in the drive rod  2 . 
     In case that drive pulses, which frequency is nearly similar to natural frequency in a cantilever model about the drive mechanism  100 , are supplied to the piezoelectric element  1 , it is possible to actuate the contact body  3  efficiently. In the cantilever model, one end of a cantilever, corresponding to the drive rod  2 , is fixed (or build-in) and the other end thereof has the mass, corresponding to the piezoelectric element  1 . In the above example, especially efficient frequency of drive pulses fell in the range generally between 130 kHz and 150 kHz. The frequency of drive pulses is not limited to the range near the natural frequency of longitudinal vibration, but may be the range near the frequency causing high frequency resonance or subharmonic resonance, or may be the frequency forcing the vibration irrelevant to the harmonic resonance. 
     Next, referring to FIG. 3, a description is made below in detail on a drive mechanism, according to a second embodiment of the present invention. The drive mechanism  102 , as shown in FIG. 3, is used for moving a lens L. The lens frame  11  for holding the lens L contacts frictionally with a drive rod  13  by means of a frictional plate  12 . Specifically, the frictional plate  12  is urged toward the lens frame  11  by a curved portion  14   b  of an urging spring  14 . The urging spring  14  is fixed to the lens frame  11  by bolts  14   a . Holding plates  15  and  16 , fixed to the lens frame  11  by bolts  15   a , prevent the frictional plate  12  from removing from the lens frame  11 . 
     The drive rod  13  penetrates between the lens frame  11  and the friction plate  12 , and is pressed therebetween by the urging spring  14 . Thus, the drive rod  13  contacts with the lens frame  11  and the frictional plate  12  under an appropriate frictional force exerting contact surfaces thereof. 
     A stationary member  21  has holding plates  22  and  23 . The drive rod  13  penetrates through a small opening  23   a  of one of the holding plate  23  and is fixed thereto. Such a fixation may be performed by means of adhesive bonding, press fitting, fusion bonding, and so on. The piezoelectric element  18  is fixed to the one end of the drive rod  13  outside of the holding plate  23 . Such fixing may be performed by means of adhesive bonding, press fitting, and so on. Although there is a small clearance between the piezoelectric element  18  and the holding plate  23 , the piezoelectric element  18  may be contacted with the holding plate  23 , or may be fixed to the holding plate  23  by means of adhesive and the like. The other end of the drive rod  13  loosely fits within a small hole  22   a  of the other of the holding plate  22 , due to easy assembling. Alternatively, the drive rod  13  may tightly fits within the small hole  22   a  or fixed thereto. 
     In the drive mechanism  102 , for example, supplying drive pulses as shown in FIGS. 2A-2F to the piezoelectric element  18  causes the piezoelectric element  18  to vibrate. Such a vibration seems to make the drive rod  13  vibrate at least longitudinally. Therefore, the lens frame  11  moves along the drive rod  13 . The moving direction of the lens frame  11  may be controlled by changing the waveform of drive pulses. 
     Since the piezoelectric element  18  is connected with only the drive rod  13  in the drive mechanism  102 , the external forces, such as bending moment and so on, exerting to the piezoelectric element  18  are reduced widely, so as to limit to the weight of the piezoelectric element  18  and the force exerted by the wires connected to the piezoelectric element  18 . Thus, the mechanical strength of the drive mechanism  102  can be improved without any members for reinforcing the piezoelectric element  18 . 
     Next, referring to FIG. 4, a description is made below in detail on a drive mechanism, according to a third embodiment of the present invention. The drive mechanism  104  as shown in FIG. 4 is generally similar to the drive mechanism  102  as shown in FIG.  3 . It is, however, different from the drive mechanism  102  as shown in FIG. 3, that another piezoelectric element  19  is connected with the other end of the drive rod  13 , that the drive rod  13  is fixed to the small opening  23   a  of the holding plate  23 , and that there is a small clearance between the piezoelectric element  19  and the holding plate  22  as well as that between the piezoelectric element  18  and the holding plate  23 . 
     In the drive mechanism  104 , for example, supplying drive pulses, as shown in FIGS. 2A-2F, to both of the piezoelectric elements  18  and  19  at one time, or to either one thereof selectively, causes the vibration of the piezoelectric elements  18  and/or  19 . Such vibration is transmitted to the drive rod  13 , and then the lens frame  11  moves. Since the piezoelectric elements  18  and  19  are arranged at both ends of the drive rod  13 , the moving direction of the zooming lens frame  11  can be changed by supplying drive pulses to whether one of the piezoelectric elements  18  and  19 . Thus, the moving amounts and the moving velocities of the lens frame  11  in one direction and in opposite direction can be controlled similarly or symmetrically, by selecting either one of the piezoelectric elements  18  and  19  for supplying drive pulses thereto. Moreover, it is possible to drive the lens frame  11  in both directions, by supplying the same drive pulses to either one of the piezoelectric elements  18  and  19 . Thus, the circuit for generating drive pulses can be simplified, without providing different circuits for each moving direction of the lens frame  11 . 
     Furthermore, in case of supplying the drive pulses to both of the piezoelectric elements  18  and  19 , it is possible to improve the performance of the moving velocity, the driving force, the resolution of movement, and so on, by means of adjusting respective timing to supply drive pulses to the piezoelectric elements  18  and  19 , combining different drive pulses for respective piezoelectric elements  18  and  19 , and so on. 
     Next, referring to FIG. 5, a description is made below in detail on a drive mechanism  106 , according to a fourth embodiment of the present invention. The drive mechanism  106  as shown in FIG. 5 is generally similar to the drive mechanism  102  as shown in FIG.  3 . It is, however, different from the drive mechanism  102  in FIG. 3 that only one end of the drive rod  13  is fixed to the hole  23   a  of the holding plate  23 , and the other end thereof is not supported or fixed. Since the other end of the drive rod  13  is a free end, it is possible to make the construction of the drive mechanism  106  small and light. Such construction is suitable for driving extremely light loading, for example, a small lens, and a micro lens. 
     Next, referring to FIG. 6, a description is made below in detail on a drive mechanism  108 , according to a fifth embodiment of the present invention. The drive mechanism  108  as shown in FIG. 6 is generally similar to the drive mechanism  102  in FIG.  3 . It is, however, different from the drive mechanism  102  in FIG. 3 that one end of the drive rod  13  is not fixed or supported, and only the other end thereof is fixed to the hole  22   a  of the holding plate  22 . Since the one end of the drive rod  13  is a free end, it is possible to make the construction of the drive mechanism  108  small and light. Such a construction is suitable for driving extremely light loading, for example, a small lens, and a micro lens. Additionally, another piezoelectric element may be bonded to the other end of the drive rod  13 , similar to the drive mechanism  104  of the third embodiment. 
     Next, referring to FIG. 7, a description is made below in detail on a drive mechanism  110 , according to a sixth embodiment of the present invention. The drive mechanism  110  is used for moving a second lens L 2  relative to a first lens L 1  and a third lens L 3 . The lenses L 1 , L 2 , and L 3  are held by a holding member  36 . The holding member  36  has a cam follower pin  39 , which engages both a cam groove of a driving barrel  32  and a straight groove of a stationary barrel  34  so as to drive the holding member  36  in a direction of optical axis by the relative rotation of the driving barrel  32  and the stationary barrel  34 . A first lens frame  38  for holding the first lens L 1  and a third lens frame  37  for holding the third lens L 3  are fixed to the lens holding member  36 . A second lens frame  44  for holding the second lens L 2  is slidably held by the drive rod  2  and a guide rod  40 . One end of the drive rod  2  penetrates a hole  38 a of the first lens frame  38  and fixed to the first lens frame  38  by the adhere  42 . The other of the drive rod  13  penetrates a hole  37   a  of the third lens frame  37 , and is adhered to one end of the piezoelectric element  18  in expanding and contracting directions. 
     Alternatively, the piezoelectric element  18  may be adhered to the one end of the drive rod  13 , or a pair of piezoelectric elements may be adhered to both ends thereof. One end of the guide rod  40  is fixed to the hole  38   b  of the first lens frame  38 , and the other end thereof is fixed to the hole  37   b  of the third lens frame  37 . The second lens frame  44  contacts frictionally with the drive rod  13  and without play, by means of urging springs  44   s ,  44   e . Supplying the appropriate drive pulses to the piezoelectric element  18  causes the vibration of the piezoelectric element  18 , which vibrates the drive rod  13  longitudinally so as to move the second lens frame  44  along the drive rod  13 . 
     Next, referring to FIG. 8, a description is made below in detail on a drive mechanism  112 , according to a seventh embodiment of the present invention. The drive mechanism  112  as shown in FIG. 8 is generally similar to the drive mechanism  110  as shown in FIG.  7 . It is, however, deferent from the drive mechanism  110  in FIG. 7 that the one end of the drive rod  13  is fixed to the first lens frame  38 , not by adhesive  42 , but by a bolt  48 . 
     In the above described drive mechanism  112 , at least one position of the drive rod  13  may be fixed, and the piezoelectric element  18  may be connected to only the drive rod  13 . Thus, it is easy to assemble the drive mechanisms. Moreove, since the mechanical strength of the drive rod  13  is high, it is possible to choose any efficient method for fixing the drive rod  13 , such as caulking, press fitting, fusion bonding, adhesive bonding, screw fastening, welding. 
     Next, referring to FIG. 9, a description is made below in detail on a mechanism  114 , according to a eighth embodiment of the present invention. The drive mechanism  114  as shown in FIG. 9 is generally similar to the drive mechanism  100  as shown in FIG.  1 . It is, however, different from the drive mechanism  100  in FIG. 1 that not the drive rod  2 , but the contact body  3  is fixed to the stationery member  4 . 
     The vibration of the piezoelectric element  1  in directions indicated by an arrow X, caused by supplying appropriate drive pulses, causes longitudinal vibration, having asymmetric waveform respective to time axis direction, of the drive rod  2 . Since the contact body  3  is fixed to the stationary  4 , it is possible to move the drive rod  2  together with the piezoelectric element  1 , in either one of both directions indicated by an arrow Y. It is possible to move the drive rod  2  together with the piezoelectric element  1  in opposite direction, by means of changing the drive pulses. 
     Next, referring to FIG. 10, a description is made below in detail on a manipulator  120 , according to a ninth embodiment of the present invention. The manipulator  120  is combined with three drive mechanisms  122 ,  124 ,  126  so as to drive the arm  7  in three dimensions. 
     Specifically, as for a first drive mechanism  122 , one end of a drive rod  2   a  is fixed to the stationary member  4 , and the other end thereof is fixed to a piezoelectric element  1   a . The contact body  3   a  contacts frictionally with the drive rod  2   a , so as to move along the drive rod  2   a  without rotating, when the drive rod  2   a  vibrates longitudinally by the vibration of the piezoelectric element  1   a , as well as the drive mechanism  100  in FIG.  1 . 
     As for a second drive mechanism  124 , one end of a drive rod  2   b  is fixed to the contact body  3   a  of the first drive mechanism  122 , and the other end thereof is fixed to a piezoelectric element  1   b . The contact body  3   b  contacts frictionally with the drive rod  2   b , so as to move along the drive rod  2   b  without rotating, when the drive rod  2   b  vibrates longitudinally by the vibration of the piezoelectric element  1   b.    
     Similarly, as for a third drive mechanism  126 , one end of a drive rod  2   c  is fixed to the contact body  3   b  of the second drive mechanism  124 , and the other end thereof is fixed to a piezoelectric element  1   c . The contact body  3   c  contacts frictionally with the drive rod  2   c , so as to move along the drive rod  2   c  without rotating, when the drive rod  2   c  vibrates longitudinally by the vibration of the piezoelectric element  1   c . A fixing portion  9  of an arm  7  is fixed to the contact body  3   c . The tip portion  8 , to which an object (not shown) is fixed, of the arm  7  can rotate relative to the fixing portion  9 . Thus, the manipulator  120  can move the object with four degrees of freedom in three-dimensional space. Preferably, neighboring drive rods  2   a ,  2   b ;  2   b ,  2   c  cross each other at right angles, so that the longitudinal vibration of either one of the drive rod  2   a ,  2   b ,  2   c  exerts no influence on neighboring drive mechanism  122 ,  124 ,  126 . 
     As described above, the piezoelectric element is fixed to only the drive rod, and may not be fixed to the other member such as the stationary member. Therefore, no excessive force is exerted on the piezoelectric element. Thereby, it is possible to simplify the construction of the drive mechanism, without considering any construction for protecting the piezoelectric element. 
     Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are also apparent to those skilled in the art. 
     For example, there are many variations about fixing of the drive rod, connecting or engaging between the drive rod and the contact body, waveform of drive pulses, timing for supply drive pulses to the piezoelectric elements, and so on.