Abstract:
An apparatus comprises first and second piezoelectric elements  25   a,    25   b  each extending and contracting in a driving direction, a fixed member  32  secured to one end of each of the first and second piezoelectric elements  25   a,    25   b,  first and second guide shafts  28   a,    28   b  secured to the other ends of the respective first and second piezoelectric elements  25   a,    25   b  to reciprocate with the extension and contraction of the aforesaid piezoelectric elements, first and second lens frames  21   a,    21   b  held frictionally by the first and second guide shafts  28   a,    28   b,  and a drive pulse generator for causing the slow and rapid displacements of each of the first and second piezoelectric elements  25   a,    25   b  and outputting drive pulses such that a period during which the first piezoelectric element  25   a  undergoes rapid displacement does not coincide with a period during which the second piezoelectric element  25   a  undergoes rapid displacement.

Description:
This application is based on application No. Hei 10-169474 filed in Japan, the content of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a driving apparatus and equipment comprising the driving apparatus. 
     The present invention relates to a driving apparatus and equipment for moving a member e.g. the lens of a camera by means of a plurality of electro-mechanical transducer such as piezoelectric elements. 
     2. Description of the Prior Art 
     A description will be given to a conventional driving apparatus which performs linear driving by means of piezoelectric elements with reference to FIG. 11 showing a lens unit for driving a plurality of lenses. FIG. 11 is a perspective view of the lens unit. 
       201 ,  205  denote lens barrels for holding lenses. Shafts  202 ,  203  for slidably guiding the lens barrels  201 ,  225  in the direction of an optical axis extend through projections  201   a,    201   c,    225   a,    225   c  formed integrally with the lens barrels  201 ,  225 . The shafts  202 ,  203  have their respective near-front and near-rear end portions held slidably lengthwise thereof in respective holes formed in the upright portions  213   a,    218   a  of support members  213 ,  218  and in respective holes formed in the upright portions  213   c,    218   c  of the support members  213 ,  218 . 
     The projections  201   a,    201   c,    225   a,    225   c  are provided with leaf springs  214 ,  219  attached thereto with screws. The leaf springs  214 ,  219  are pressed against the shafts  202 ,  203 , respectively. When the lens barrels  201 ,  225  move, therefore, they slide frictionally along the shafts  202 ,  203 . Piezoelectric elements  212 ,  217  are attached to the respective rear end portions of the shafts  202 ,  203 . The piezoelectric elements  212 ,  217  have respective rear end portions secured to the upright portions  213   e,    218   e  of the support members  213 ,  218 . The support members  213 ,  218  are secured to a common fixed portion. 
     The principle of operation of a moving mechanism using piezoelectric elements is disclosed in U.S. Pat. No. 5,225,941 or the like, which will be described briefly with reference to the schematic diagram shown in FIG.  2 . As shown in (a) section of FIG. 2, a shaft  53  is secured to one end of a piezoelectric element  52 , while a fixed portion  51  is secured to the other end thereof. A moving member  54  to be moved is held on the shaft  53  under a frictional force produced by spring biasing. The mass of the fixed portion  51  is sufficiently large compared with the mass of the moving member  54 . 
     When a voltage is applied to the piezoelectric element  52 , the inertial force of the fixed portion  51  prevents the piezoelectric element  52  from extending in the direction of the fixed portion  51 , so that the piezoelectric element  52  extends in the direction of the shaft  53  to move the shaft  53  to the left in the drawing. At this time, on a gentle rising edge of the applied voltage as shown in A section of FIG. 3, the moving member  54  moves by a distance x along with the shaft  53 , as shown in (b) section of FIG. 2, since the frictional force produced between the moving member  54  and the shaft  53  is larger than the inertial force of the moving member  54 . 
     Next, when the piezoelectric element  52  releases a voltage on a steep falling edge as shown in B section of FIG. 3, the inertial force of the moving member  54  becomes larger than the frictional force produced between the moving member  54  and the shaft  53 , so that the moving member  54  remains in place and only the shaft  53  moves by the distance x toward the initial position, as shown in (c) section of FIG.  2 . By applying a sawtooth drive pulse to the piezoelectric element  52  to cause it to repeat this action, the moving member  54  can be moved to a specified position. To move the moving member  54  in the opposite direction, a drive pulse with a steep rising edge and with a gentle falling edge is applied properly. 
     If the frequency of a waveform as shown in FIG. 3 is increased to increase a frequency for extending and contracting an electro-mechanical transducer, a transition is made to a state in which a skid occurs between the driving frictional member (shaft) and the moving member which are frictionally combined with each other upon each of the extension and contraction of the electro-mechanical transducer. In this case, since a relative skid occurring between the driving frictional member and the moving member upon the extension of the electro-mechanical transducer is different in direction and magnitude from the skid occurring therebetween upon the contraction of the electro-mechanical transducer, the moving member can be driven in a desired direction relative to the fixed portion. 
     In the lens driving apparatus having a structure as shown in FIG. 11, the piezoelectric elements  212 ,  217  extend and contract when a sawtooth drive pulse is applied thereto for a specified period of time, thereby causing the forward and backward movements of the shafts  202 ,  204 . The order relationship between the frictional force between the shafts  202 ,  203  and the leaf springs  214 ,  219  and the inertial force resulting from the masses of the lenses and the lens barrels  201 ,  225  vary depending on the moving speeds of the shafts  202 ,  203 , so that the lenses are moved to specified positions. It is to be noted that the force applied to the fixed portion upon the extension or contraction of the piezoelectric elements  212 ,  217  causes the fixed portion to reciprocate along with the support members  213 ,  218 , though it is indistinct because of the relatively large mass of the fixed portion. 
     In FIG. 4, the vertical axis represents the magnitude of a voltage and the horizontal axis represents time. In the case where the drive pulses applied to the two piezoelectric elements  212 ,  217  have waveforms G 1 , G 2  shown in FIG. 4 in which portions with abrupt voltage changes B 1 , B 2  are coincident with each other, the forces are applied simultaneously to the fixed portion so that the respective driving operations interfere with each other. 
     For example, the fixed portion experiences an increased amount of elastic deformation and an increased amount of travel compared with the case where a single piezoelectric element and a single shaft are provided, so that the shafts  202 ,  203  (driving shafts) undergo a lower degree of acceleration. 
     occasionally, the inertial forces of the lens barrels  201 ,  225  (moving members) become smaller than the frictional forces, which deteriorates driving properties. As a result, the speeds of the lens barrels  201 ,  225  are lowered or, in some cases, the lens barrels  201 ,  225  are not moved at all. This leads to such a problem as an elongated time required to dispose the lenses at desired positions, which degrades the operability of a camera used in conjunction with the lens unit. Similar problems occur when three or more piezoelectric elements are used. 
     Although the description has thus been given to the case where the common fixed portion is used, interference occurs even when fixed portions are provided for individual piezoelectric elements on a one-by-one basis if the fixed portions are at positions close to each other. That is, if the voltages applied to the piezoelectric elements have the waveforms G 1 , G 2  in which the portions B 1 , B 2  with abrupt voltage changes are coincident with each other, as shown in FIG. 4, the forces are applied simultaneously to the fixed portions and therefore the forces are applied simultaneously to the lens unit in which the fixed portions are disposed. 
     This also deteriorates the driving properties for the lens barrels (moving members), similarly to the foregoing case. If the fixed portions contain elastic bodies such as plastic moldings, in particular, the fixed portions are likely to warp and move, so that the amount of elastic deformation experienced by the fixed portions is increased and the influence given to the driving of the moving members becomes greater. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a driving apparatus for moving a moving member by means of two or more electro-mechanical transducers and equipment comprising the driving apparatus, wherein the driving properties for the moving member are prevented from deteriorating. 
     To attain the above object, one aspect of the present invention comprises: first and second electro-mechanical transducers each extending and contracting in a driving direction; first and second fixed portions secured to one ends of the respective first and second electro-mechanical transducers; first and second shafts secured to the other ends of the respective first and second electro-mechanical transducers to reciprocate with the extension and contraction of the aforesaid electro-mechanical transducers; first and second moving members held frictionally by the first and second shafts; and a drive pulse generator for causing the slow and rapid displacements of each of the first and second electro-mechanical transducers and outputting drive pulses such that a period during which the first electro-mechanical transducer undergoes rapid displacement does not coincide with a period during which the second electro-mechanical transducer undergoes rapid displacement. 
     In the arrangement, the drive pulses outputted from the drive pulse generator cause the slow and rapid displacements of each of the first and second electro-mechanical transducers and the first and second shafts undergo repeated slow and rapid displacements in association therewith, which moves the first and second moving members held frictionally by the first and second shafts. At this time, since the drive pulses are outputted such that the period during which the first electro-mechanical transducer undergoes rapid displacement does not coincide with the period during which the second electro-mechanical transducer undergoes rapid displacement, the forces exerted during the rapid displacements are prevented from being applied simultaneously to the first and second fixed members. 
     In another aspect of the present invention, the first and second electro-mechanical transducers in the aforesaid structure are piezoelectric elements. 
     In still another aspect of the present invention, the first and second fixed members are composed of a single member. 
     If the fixed members are formed of the single member, interference is more likely to occur. However, since the drive pulses are outputted such that the period during which the first electro-mechanical transducer undergoes rapid displacement does not coincide with the period during which the second electro-mechanical transducer undergoes rapid displacement, the forces exerted during the rapid displacements are prevented from being applied simultaneously to the single fixed member. 
     In yet another aspect of the present invention, a drive pulse for driving the second electro-mechanical transducer is outputted during the period in which no change occurs in the voltage applied the first electro-mechanical transducer. 
     In the arrangement, the period during which the drive pulse for the first electro-mechanical transducer is outputted is not coincident with the period during which the drive pulse for the second electro-mechanical transducer is outputted, so that the forces exerted by the first and second electro-mechanical transducers under slow and rapid displacements are prevented from being applied simultaneously to the fixed members. 
     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 a perspective view showing a structure of the driving apparatus commonly used in the following embodiments; 
     FIG. 2 is a view for illustrating the principle of operation of the driving apparatus of FIG. 1; 
     FIG. 3 is a view showing an example of the waveform of a voltage applied to an electro-mechanical transducer of FIG. 1; 
     FIG. 4 is a view showing the waveform of the voltage applied to the electro-mechanical transducer of FIG. 1; 
     FIG. 5 is a perspective view showing another structure of the driving apparatus; 
     FIG. 6 is a control block diagram for the embodiments of the present invention; 
     FIG. 7 is a view showing the waveform of a voltage applied to an electro-mechanical transducer in the first embodiment of the present invention; 
     FIG. 8 is a view showing the waveform of a voltage applied to an electro-mechanical transducer in the second embodiment of the present invention; 
     FIG. 9 is a view showing the waveform of a voltage applied to an electro-mechanical transducer in the third embodiment of the present invention; 
     FIG. 10 is a view showing the waveform of a voltage applied to an electro-mechanical transducer in the fourth embodiment of the present invention; and 
     FIG. 11 is a view showing prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, the embodiments of the present invention will be described. 
     FIG. 1 shows a structure of an interchangeable lens for a camera, which is common to the individual embodiments. 
       21   a,    21   b  denote respective lens frames for holding lenses L 1 , L 2 . Guide shafts  28   a,    28   b  for slidably guiding the respective lens frames  21   a,    21   b  in the direction of an optical axis extend through respective bearing portions  33   a,    33   b  disposed above the lens frames. The guide shafts  28   a,    28   b  have their respective near-front and near-rear end portions held slidably lengthwise thereof in shaft holes  30   a,    30   b  formed in a front wall  30   f  of a fixed frame  30  and in shaft holes  30   a ′,  30   b ′ (of which  30   b ′ is not shown) formed in an inner wall  30   m  of the fixed frame  30 . 
     The bearing portions  33   a,    33   b  are provided with holding plates  31   a,    31   b  (of which the holding plate  31   b  is hidden in the drawing) configured as leaf springs and attached to the bearing portions  33   a,    33   b  with screws. The holding plates  31   a,    31   b  are pressed against the guide shafts  28   a,    28   b.  Accordingly, the lens frames  21   a,    21   b  slide frictionally along the guide shafts  28   a,    28   b  when the lens frames  21   a,    21   b  move. Piezoelectric elements  25   a,    25   b  are attached to the respective rear end portions of the guide shafts  28   a,    28   b.  A fixed member  32  is secured to each of the rear end portions of the piezoelectric elements  25   a,    25   b.  The fixed member  32  is attached to the fixed frame  30 . 
     FIG. 6 is a control block diagram, which is common to the individual embodiments. A drive control circuit  10  controls a first drive pulse generating circuit  11   a  for generating a first drive pulse applied to the first piezoelectric element  25   a  and a second drive pulse generating circuit  11   b  for generating a second drive pulse applied to the second piezoelectric element  25   b.  The first and second drive pulses extend or contract the piezoelectric elements  25   a,    25   b  and thereby move the lens frames  21   a,    21   b.    
     FIG. 7 shows respective pulses for driving the two piezoelectric elements  25   a,    25   b,  which are generated by the first and second drive pulse generating circuits  11   a,    11   b,  i.e., first and second drive pulses G 1 , G 3  in the first embodiment of the present invention. The vertical axis represents the magnitude of a voltage and the horizontal axis represents time, similarly to the second to fourth embodiments which will be described later. As shown in the drawing, the drive pulse G 1  for the piezoelectric element  25   a  is shifted in phase from the drive pulse G 3  for the piezoelectric element  25   b  such that the portion B 1  with an abrupt voltage change of the drive pulse G 1  does not coincide with the portion B 3  with an abrupt voltage change of the drive pulse G 3 . 
     In the arrangement, even during rapid displacements under which the piezoelectric elements  25   a,    25   b  abruptly extend or contract to cause enhanced acceleration, the fixed member  32  receives a force from either one of the piezoelectric elements  25   a,    25   b.  As a result, the inertial mass of the fixed member  32  is used effectively without being distributed, so that the guide shafts  28   a,    28   b  are efficiently accelerated. This permits the lens frames  21   a,    21   b  and the lenses L 1 , L 2  to be moved at high speed to specified positions, similarly to the case where the shaft for driving is only one, i.e., only one piezoelectric element, one shaft, and one moving member are provided. 
     FIG. 8 shows respective drive pulses G 1 , G 4  for two piezoelectric elements  25   a,    25   b  according to a second embodiment of the present invention. As shown in the drawing, the drive pulse G 1  for the piezoelectric element  25   a  and the drive pulse G 4  for the piezoelectric element  25   b  have different cycles. In this case also, the same effect as achieved by the first embodiment can be achieved by shifting the drive pulse G 1  from the drive pulse G 4  such that the portion B 1  with an abrupt voltage change of the drive pulse G 1  does not coincide with the portion B 4  with an abrupt voltage change of the drive pulse G 4 . 
     FIG. 9 shows respective drive pulses G 1 , G 5  for two piezoelectric elements  25   a,    25   b  according to a third embodiment of the present invention. According to the drawing, the pulse P 5  of the drive pulse G 5  for the piezoelectric element  25   b  is generated during the period t 1  in which no voltage change occurs in the drive pulse G 1  for the piezoelectric element  25   a.    
     The arrangement prevents the portion B 5  with an abrupt voltage change of the drive pulse G 5  from coinciding with the portion B 1  with an abrupt voltage change of the drive pulse G 1  and further prevents the portion A 5  with a gentle voltage change of the drive pulse G 5  from coinciding with the portion B 1  with an abrupt voltage change of the drive pulse G 1 . This achieves the effect of preventing the degree of acceleration of the guide shaft  28   a  from being lowered due to the force applied by the piezoelectric element  25   b  to the fixed member  32  under slow displacement (see FIG. 1) when the piezoelectric element  25   a  is under rapid displacement, in addition to the same effect as achieved by the first embodiment. As a result, the distribution of the inertial mass of the fixed portion  32  is further suppressed, while the guide shaft  28   a  is accelerated more efficiently. 
     FIG. 10 shows respective drive pulses G 8 , G 9  for two piezoelectric elements  25   a,    25   b  according to a fourth embodiment of the present invention. As shown in the drawing, the plural pulses P 9  of the drive pulse G 9  for the piezoelectric element  25   b  are generated during the period t 8  in which no voltage change occurs in the drive pulse G 8  for the piezoelectric element  25   a,  while the plural pulses P 8  of the drive pulse G 8  for the piezoelectric element  25   a  are generated during the period t 9  in which no voltage change occurs in the drive pulse G 9  for the piezoelectric element  25   b.    
     This not only achieves the same effect as achieved by the third embodiment but also prevents, even if the respective drive pulses for the two piezoelectric elements  25   a,    25   b  have different frequencies, the forces exerted by one piezoelectric element  25   b  under rapid displacement (B 9 ) and under slow displacement (A 9 ) from being applied to the fixed member  32  when the other piezoelectric element  25   a  is under rapid displacement, as indicated by B 8 . As a result, it becomes possible to prevent the degree of acceleration of the guide shaft  28   a  from lowering. 
     Although the description has thus been given to the driving apparatus shown in FIG. 2, which has shafts in two systems including two piezoelectric elements  25   a,    25   b  secured to one fixed member  32 , the same structure can be implemented if shafts in three or more systems are provided and the same effect can be achieved. 
     The same effect can be achieved even in the case where fixed members  32   a,    32   b  are provided for the individual piezoelectric elements  25   a,    25   b  on a one-by-one basis, as shown in FIG.  5 . This prevents the forces from being applied simultaneously to the fixed members  32   a,    32   b  and thereby prevents an increased force from being applied to the fixed frame  30  on which the fixed members  32   a,    32   b  are mounted. As a result, it becomes possible to move the lens frames  21   a,    21   b  and the lenses L 1 , L 2  at high speed to specified positions by efficiently accelerating each of guide shafts  28   a,    28   b.  The effect is particularly remarkable when the fixed frame is composed of an elastic body. 
     In each of the foregoing arrangements, when a plurality of electro-mechanical transducers are used to move moving members under repeated slow and rapid displacements, the rapid displacements of the respective electro-mechanical transducers do not coincide with each other, so that the member or portion on which the fixed member is mounted never receives the large forces applied simultaneously thereto. This prevents the lowering of the degree of acceleration of the shaft or guide shaft and the deterioration of the driving properties of the moving member, such as a lens. The effect of preventing the lowering of the degree to which the shaft is accelerated is particularly remarkable when the member on which the fixed portion is mounted is composed of an elastic body, such as a resin. Hence, it becomes possible to prevent the degradation of the operability of equipment on which the driving apparatus is mounted. 
     In using a plurality of electro-mechanical transducers to move moving members under repeated slow and rapid displacements, the rapid displacements of the respective electro-mechanical transducers do not coincide with each other, so that the fixed member never receives the large forces applied simultaneously thereto. This prevents the lowering of the degree of acceleration of the shaft or guide shaft and the deterioration of the driving properties of the moving member, such as a lens. 
     Furthermore, it becomes possible to prevent, when one electro-mechanical transducer is under rapid displacement, the fixed member or the member on which the fixed member is mounted from being accelerated by the other electro-mechanical transducer under rapid and slow displacements. Accordingly, the effect of preventing the lowering of the degree to which the shaft is accelerated is further enhanced, which permits more efficient acceleration of the shaft and further prevents the deterioration of the driving properties of the moving member, such as a lens. 
     Although each of the foregoing embodiments is a replacement lens for a camera, it will easily be appreciated that the present invention is also applicable to any equipment such as an X-Y table or a binocular. 
     Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.