Abstract:
A driving apparatus includes an electromechanical transducer that is connected to a drive pulse generating means and that expands and contracts, a driven member that is connected to one end of the transducer, a friction member that is connected to the other end of the transducer and a guide unit that is in frictional contact with the friction member. The friction member has an elastic deforming mechanism that elastically presses against and comes into frictional contact with the guide unit, and the elastic deforming mechanism is constructed such that its elastic deformation stress vector perpendicularly crosses the directions of expansion and contraction of the transducer.

Description:
This application is based on application No. Hei 9-143998 filed in Japan, the content of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to a driving apparatus that uses as a drive source a member that expands and contracts, and more particularly, to a driving apparatus that employs an electromechanical transducer such as a piezoelectric element, e.g., to a driving apparatus used for the precision driving of an X-Y drive table, a camera image recording lens, or a probe of a scanning tunneling electron microscope. 
     2. Description of the Related Art 
     Conventional examples of a driving apparatus using a piezoelectric element include driving apparatus  10   a  in which movable unit  20   a  moves along shaft  14 , as shown in FIGS. 1 through 3, and driving apparatus  10   b  in which movable unit  20   b  moves along guide groove  18 , as shown in FIGS. 4 through 6. In these driving apparatuses  10   a  and  10   b , an elastic deforming mechanism is constructed by pressing protrusion  24   a  or  25   a  of plate spring  24  or  25 , which is a friction member connected to one end of piezoelectric element  22 , against the outer surface of shaft  14  or against the inner surface of guide groove  18 , such that a frictional force may be created. A driving apparatus of the type in which the friction member has an elastic deforming mechanism which creates frictional force is superior to a driving apparatus of the type in which a frictional force is created by applying external force to the friction member by means of a spring member, as shown in U.S. Pat. No. 5,589,723, in that the construction may be simplified. 
     In either driving apparatus  10   a  or  10   b , the elastic deformation stress vector that occurs during the elastic deformation of protrusion  24   a  or  25   a  of plate spring  24  or  25  runs in the directions indicated by bi-directional arrow  82  or  84  in FIG. 3 or  6 , where stress is applied that has a component that works in the directions of expansion and contraction of piezoelectric element  22 , as shown by bi-directional arrow  80 . In other words, deflection occurs in plate spring  24  or  25 , the friction member, in the directions of expansion and contraction of piezoelectric element  22 , between the area that is fixed to piezoelectric element  22  and the area that is in frictional contact with shaft  14  or guide groove  18 , and plate spring  24  or  25  elastically deforms in expansion and contraction directions  80  of piezoelectric element  22 . 
     Therefore, if the frequency of the pulse voltage that is applied to piezoelectric element  22  is increased in order to move movable unit  20   a  or  20   b  of driving apparatus  10   a  or  10   b  at a high rate of speed, the change in position that occurs at one end  22   a  of piezoelectric element  22  can no longer be communicated to the frictional contact point via plate spring  24  or  25  in the same manner as before. FIGS. 7 and 8 are graphs that show the transfer function G=Y/X, i.e., the relationship between the transfer of the change in position X of piezoelectric element  22  and the change in position Y of the frictional contact point between friction member  24  or  25  and shaft  14  or groove  18 . In other words, as shown in FIGS. 7 and 8, when the frequency increases, the gain decreases and the phase changes. Therefore, as shown in FIG. 9, with conventional driving apparatuses  10   a  and  10   b , when the frequency increases to a certain level, the drive speed of movable units  20   a  and  20   b  decreases, as a result of which the drive speed cannot be increased by increasing the frequency. 
     SUMMARY OF THE INVENTION 
     The technological issue to be resolved by the present invention, therefore, is to improve the frequency characteristic of the transfer function governing the relationship between the change in position of the piezoelectric element and the change in position of the friction member&#39;s frictional contact point, so as to provide a driving apparatus capable of high speed driving in a high frequency range. 
     The present invention provides a driving apparatus having the following construction in order to resolve the technological issue described above. 
     The driving apparatus comprises (i) an electromechanical transducer that is connected to a drive pulse generating means and that expands and contracts, (ii) a first unit that is either fixed or movable and that is connected to one expansion end of said electromechanical transducer, (iii) a friction member that is connected to the other expansion end of said electromechanical transducer, and (iv) a second unit that is either movable or fixed that comes into frictional contact with said friction member, wherein said friction member has an elastic deforming mechanism that elastically presses against and comes into frictional contact with said second unit, said electromechanical transducer is expanded or contracted by means of said drive pulse generating means such that it drives said movable unit in a prescribed direction relative to said fixed unit, and said elastic deforming mechanism is constructed such that its elastic deformation stress vector vertically crosses the directions of expansion and contraction of said electromechanical transducer. 
     In the construction described above, the fixed unit is fixed and the movable unit may move relative to the fixed unit. In the driving apparatus, the electromechanical transducer slowly changes its position in a first direction and said second unit which is either movable or fixed, changes its position in the first direction due to the electrostatic friction between itself and the friction member, but when the electromechanical transducer suddenly changes its position in a second direction, the inertial force of the second unit overcomes the frictional force between itself and the friction member, causing the second unit to slip, as a result of which only the friction member returns to the original position, for example. Step driving of the driving apparatus can be achieved by repeating this process. Where the movable unit is fixed to one expansion end of the electromechanical transducer, to perform driving it is necessary for the mass of the movable unit to be smaller than the mass of the friction member that is fixed to the other expansion end of the electromechanical transducer. 
     Using the construction described above, the elastic deforming mechanism elastically deforms in directions that are perpendicular to the directions of expansion and contraction of the electromechanical transducer and does not deform in directions that are parallel to said directions of expansion and contraction. Consequently, the change in position of the electromechanical transducer caused by its expansion and contraction may be directly communicated to the frictional contact point of the friction member even when the driving frequency applied to the electromechanical transducer increases. 
     Therefore, the frequency characteristic of the function governing the transfer of the change in position of the piezoelectric element to the change in position of the friction member&#39;s frictional contact point may be improved and high-speed driving in the high frequency range becomes possible. 
     These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following description, like parts are designated by like reference numbers throughout the several drawings. 
     FIG. 1 is an exploded perspective view of a conventional driving apparatus. 
     FIG. 2 is an overall perspective view of the driving apparatus shown in FIG.  1 . 
     FIG. 3 is a partial enlargement of the frictional contact area of the driving apparatus shown in FIG.  1 . 
     FIG. 4 is an exploded perspective view of a conventional driving apparatus. 
     FIG. 5 is an overall perspective view of the driving apparatus shown in FIG.  4 . 
     FIG. 6 is a partial enlargement of the frictional contact area of the driving apparatus shown in FIG.  4 . 
     FIG. 7 is a graph showing the frequency-gain relationship in a conventional driving apparatus. 
     FIG. 8 is a graph showing the frequency-phase relationship in a conventional driving apparatus. 
     FIG. 9 is a graph showing a frequency-speed relationship in a conventional driving apparatus. 
     FIG. 10 is an exploded perspective view of a driving apparatus of a first embodiment pertaining to the present invention. 
     FIG. 11 is an overall perspective view of the driving apparatus shown in FIG.  10 . 
     FIG. 12 is a partial enlargement of the frictional contact area of the driving apparatus shown in FIG.  10 . 
     FIG. 13 is a perspective view of the important components of a driving apparatus of a second embodiment pertaining to the present invention. 
     FIG. 14 is a perspective view of the important components of a driving apparatus of a third embodiment pertaining to the present invention. 
     FIG. 15 is a drawing showing three sides of a friction member of a fourth embodiment pertaining to the present invention. 
     FIG. 16 is a perspective view of the friction member shown in FIG.  15 . 
     FIG. 17 is a perspective view of the important components of the driving apparatus of the fourth embodiment. 
     FIG. 18 is an exploded perspective view of a driving apparatus of a fifth embodiment pertaining to the present invention. 
     FIG. 19 is an overall perspective view of the driving apparatus shown in FIG.  18 . 
     FIG. 20 is a drawing showing three sides of the frictional contact area of the driving apparatus shown in FIG.  18 . 
     FIG. 21 is a graph showing the frequency-gain relationship in a driving apparatus of the present invention. 
     FIG. 22 is a graph showing the frequency-phase relationship in a driving apparatus of the present invention. 
     FIG. 23 is a graph showing the frequency-speed relationship in a driving apparatus of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Driving apparatuses in which the present invention is applied are explained below with reference to the accompanying drawings. 
     Driving apparatus  10   s , a first embodiment, of the type in which driving occurs along a shaft, will first be explained. 
     As shown in the exploded perspective view of FIG.  10  and the assembled perspective view of FIG. 11, this driving apparatus  10   s  is constructed in essentially the same manner as driving apparatus  10   a , the conventional example shown in FIG.  1 . In other words, in driving apparatus  10   s , shaft  14  is fixed by means of screws  13  in a pair of fixed blocks  12  that are fixed onto a base, and movable unit  30  is movably supported by shaft  14 . 
     Movable unit  30  comprises (i) movable member  26  that is movably supported by shaft  14 , (ii) piezoelectric element  22  located such that one expansion end is connected to one end of movable member  26  and its direction of layering is parallel to the axis of shaft  14 , and (iii) friction member  32  that is connected to the other expansion end of piezoelectric element  22  and is aligned in the direction of shaft  14 . Friction member  32  is a block member having a construction different from that of plate spring  24  of the conventional driving apparatus  10   a . That is, friction member  32  comprises main body or driving member  32   s  that is connected to piezoelectric element  22  and a pair of semi-cylindrical protrusions  32   a  that protrude toward shaft  14  from a side of main body  32   s . The pair of protrusions  32   a  elastically grasp shaft  14  from both above and below, as shown in FIG. 11, and are in frictional contact with shaft  14 . When protrusions  32   a  grasp shaft  14 , an elastic deformation stress vector occurs along the circumference of the shaft, as indicated by arrows  86  in the partial enlargement of FIG.  12 . Directions  86  in which the stress runs are essentially perpendicular to the directions of expansion and contraction of piezoelectric element  22  indicated by bi-directional arrow  80 . 
     Therefore, because friction member  32  does not elastically deform in directions that are parallel to the directions of expansion and contraction of piezoelectric element  22 , the change in position of piezoelectric element  22  due to its expansion or contraction can be accurately transmitted to the frictional contact point even when the driving frequency increases. 
     A driving apparatus of a second embodiment pertaining to the present invention will now be explained. 
     In driving apparatus  10   s  of the first embodiment described above, the frictional contact point is not in the line of force governing the expansion and contraction of piezoelectric element  22 , and consequently, moment is applied to connection surface  22   a  between piezoelectric element  22  and friction member  32 , but this moment can be removed in the second embodiment. 
     FIG. 13 is an enlargement of the important components of driving apparatus  30   a  using two shafts  15 . This driving apparatus of the second embodiment has a pair of parallel shafts  15 , and movable member  26   a  is movably supported on them. Piezoelectric element  22  and friction member  34  are located between the pair of shafts  15 . Friction member  34  is a driving member with two pairs of protrusions  34   a  that grasp a respective shaft  15  on either side. In this driving apparatus  30   a , frictional contact areas at which friction member  34  engages with shafts  15  exist on either side of piezoelectric element  22 , and consequently, the moment that is applied to piezoelectric element  22  by each frictional contact area is kept in balance by the other, and consequently no net moment works on piezoelectric element  22 . 
     FIG. 14 is an enlargement of the important components of driving apparatus  30   b  of a third embodiment, using two piezoelectric elements  22 . This driving apparatus of the third embodiment has a single shaft  14 , and movable member  26  is movably supported by this shaft  14 . Two piezoelectric elements  22  are located one on either side of shaft  14 , and one expansion end of each piezoelectric element  22  is connected to one end of movable member  26 . Friction member  36 , which is located such that it crosses shaft  14 , is connected to the other expansion end of the two piezoelectric elements  22 . Friction member  36  has a pair of protrusions  36   a  at its center that grasp shaft  14 . In this variation, the two piezoelectric elements  22  expand and contract synchronously and move friction member  36  along the shaft  14 . Therefore, no net moment works on piezoelectric elements  22 . 
     Driving apparatus  30   c  of a fourth embodiment, shown in FIGS. 15 through 17, is an example in which friction member  38  is simplified relative to the third embodiment described above. FIG. 15 shows three sides of friction member  38 . 
     FIG. 16 is a perspective view of friction member  38 , and FIG. 17 is a perspective view of the important components of driving apparatus  30   c . Friction member  38  is essentially a triangular block. Piezoelectric elements  22  are connected to bottom surface  38   a . Pass-through hole  38   t , which passes through the center of the block, is formed such that it runs from top surface  38   b  to bottom surface  38   a , and slit  38   s  is also formed through pass-through hole  38   t  such that pass-through hole  38   t  will elastically grasp shaft  14 . In this embodiment, the friction member  38  may be made lightweight, highly elastic, highly movable and very hard by using an aluminum alloy treated with anode oxide coating. 
     Driving apparatus  10   t  of a fifth embodiment of the type in which the movable member moves along a groove will now be explained. 
     As shown in the exploded perspective view of FIG.  18  and the assembled perspective view of FIG. 19, this driving apparatus  10   t  is constructed in essentially the same manner as the conventional driving apparatus  10   b . In driving apparatus  10   t , movable unit  31  is located in guide groove  18  of guide block  16  that is fixed on a base, such that friction member  40  of movable unit  31  comes into movable contact with the vertical surfaces of guide groove  18 . Movable unit  31  comprises piezoelectric element  22 , movable member  27  that is connected to one expansion end of piezoelectric element  22 , and friction member  40  that is connected to the other expansion end of piezoelectric element  22 . The construction of friction member  40  differs from that of the friction member in the conventional driving apparatus  10   b.    
     In other words, friction member  40  comprises elastic member  42 , which is a rubber plate, and a pair of contact members  44  formed of carbon fiber, as shown in the three-sided drawing of FIG.  20 . Each of the pair of contact members  44  comprises a base piece  44   b  having the configuration of a small cylinder split in the middle along the axis, and contact piece  44   a  having the configuration of a large cylinder split in the middle along the axis, the two of them being connected such that they share the same axis. Base pieces  44   b  of the pair of contact members  44  are fixed to each other, and the ends opposite from the ends connected to contact pieces  44   a  are fixed to expansion end  22   a  of piezoelectric element  22 . For friction member  40 , elastic member  42  is sandwiched between contact pieces  44   a  of the pair of contact members  44  such that (i) both contact pieces  44   a  face the vertical surfaces of guide groove  18 , and (ii) elastic member  42  is parallel to the vertical surfaces of guide groove  18 . 
     When movable unit  31  is placed in guide groove  18 , contact pieces  44   a  of contact members  44  are elastically pressed against the vertical surfaces of guide grooves  18  due to the force of elastic member  42 , and as a result, friction member  40  comes into frictional contact with guide block  16 . Contact members  44  are made of carbon fiber, and thus experience virtually no elastic deformation along their length, i.e., in the directions of expansion and contraction of piezoelectric element  22 . In other words, the elastic deformation stress vector of friction member  40  runs perpendicular to the directions of expansion and contraction of piezoelectric element  22 , and no elastic deformation occurs in directions that are parallel to the directions of expansion and contraction of piezoelectric element  22 . Therefore, this driving apparatus  10   t  can also be driven at a high rate of speed using a high frequency. 
     Friction member  40  is made lightweight, very rigid, highly movable and very hard by using carbon fiber. On the other hand, the optimal elasticity to create frictional force can be easily provided to contact members  44  by selecting the most suitable rubber characteristic for elastic member  42 . 
     The effect of the present invention is shown in FIGS. 21 through 23 with regard to the driving apparatuses of the first through fifth embodiments. FIG. 21 is a graph showing the transfer function G=Y/X, just as with regard to FIG. 7, showing the function governing the transfer of change in position X of the piezoelectric element to change in position Y of the frictional contact point between friction member  32 ,  34 ,  36 ,  38  or  40  and shaft  14  or groove  18 . The vertical axis represents the gain, while the horizontal axis represents the frequency of the voltage applied to the piezoelectric element. FIG. 22 is a graph showing the transfer function G=Y/X, just as with regard to FIG. 8, and the vertical axis represents the phase, while the horizontal axis represents the frequency of the voltage applied to the piezoelectric element. Comparing FIG. 21 with FIG. 7 regarding the conventional examples, the frequency level at which the gain starts to decrease is higher. Comparing FIG. 22 with FIG. 8 regarding the conventional examples, phase change does not occur until a higher frequency is applied. FIG. 23 is a graph showing the characteristic of the present invention in terms of the frequency (the horizontal axis) and the drive speed (the vertical axis). In other words, using driving apparatus  10   s  or  10   t  of the present invention, the drive frequency can be increased to increase the drive speed. 
     In the embodiments described above, a movable unit equipped with piezoelectric element  22  moves. However, it is also acceptable if the movable unit is fixed on a base and shaft  14  or  15  or guide block  16  moves instead. In addition, the present invention is not limited to said embodiments, but may be implemented in various other forms. 
     For example, as shown in U.S. Pat. No. 5,589,723, the same effect is obtained if the driving apparatus used is of the type in which one end of a piezoelectric element is fixed to a base, and a shaft, connected to the other end of the piezoelectric element, is moved back and forth such that a movable member that is in friction contact with the shaft is driven, or is of the type that performs rotation instead of linear movement. Needless to say, an electromechanical transducer other than a piezoelectric element may also be used in its place. 
     Although preferred embodiments of the invention have been described in the foregoing detailed description and illustrated in the accompanying drawings, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions of parts and elements without departing from the spirit of the invention. Accordingly, the present invention is intended to encompass such rearrangements, modification and substitutions of parts and elements as fall within the spirit and scope of the invention.