Abstract:
A lens driving apparatus which drives a first and a second lens group arranged in the optical axis by a first drive means and a second drive means, wherein the apparatus has a first and a second cam followers extending mutually parallel in a right angle direction to the optical axis from the first and second lens groups and cam member having first and second cams arranged along the optical axis and respectively engaging the first and second cam followers.

Description:
[0001]    This application is based on Patent Application No. 2000-385460 filed in Japan, the content of which is hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a lens driving apparatus, and specifically relates to a lens driving apparatus for driving a plurality of lens groups.  
           [0004]    2. Description of the Related Art  
           [0005]    A lens driving apparatus  18  for independently driving individual lens holders  5  and  6  via actuators  10   a  and  10   b  of a friction drive type which exert a drive force via friction bonding as shown in FIG. 1 has been proposed as a zoom lens for a compact photographic device.  
           [0006]    The actuators  10   a  and  10   b  have bases  1   a  and  1   b  and drive shafts  3   a  and  3   b  respectively attached to an end of piezoelectric elements  2   a  and  2   b  in the extension-contraction direction. The drive shafts  3   a  and  3   b  are friction bonded to lens holders  5  and  6  via a force exerted by flat springs  4   a  and  4   b  (only  4   b  is shown in the drawing) set in a channel in the lens holders  5  and  6 . When a drive voltage having, for example, a sawtooth pulse waveform is applied to the piezoelectric elements  2   a  and  2   b , the drive shafts  3   a  and  3   b  are oscillated at different speeds in the axial direction as indicated by the arrows  90  and  92 , such that the lens holders  5  and  6  are moved along the drive shafts  3   a  and  3   b . The lens holders  5  and  6  are guided in the optical axis direction by a guide shaft  8 , and the photographic element  7  is disposed on the focal plane of the optical system.  
           [0007]    In the lens driving apparatus  18 , since the lens holders  5  and  6  are independently and individually moved to optional positions by the respective actuators  10   a  and  10   b,  each lens holder  5  and  6  must have a specific positional relationship to obtain a desired photographic magnification and photographic distance. Particularly when zooming, the positions of the lens holders  5  and  6  must be detected with high precision in order to control the position of the lens holders  5  and  6 .  
           [0008]    Magnetic plates  11   a  and  11   b  are mounted on the respective lens holders  5  and  6 , and MR sensors  12   a  and  12   b  (only sensor  12   b  is shown in the drawing) are provided on the frame opposite these magnetic plates  11   a  and  11   b,  such that the position of the lens holders  5  and  6  can be measured. Furthermore, a signal processing device is also required to control the drive of the respective actuators  10   a  and  10   b  based on the measurement data. It is difficult to make the lens driving device compact and of simple structure due to the use of the sensors and signal processing device.  
         SUMMARY  
         [0009]    Accordingly, the technical problem resolved by the present invention is to provide a compact lens driving apparatus for driving a plurality of lenses, or a lens driving apparatus of simple structure.  
           [0010]    The present invention focuses on the fact that normally each lens holder need not necessarily be moved since the relationship between the photographic magnification and the lens holder position is completely determined, and provides a lens driving apparatus having the following structure.  
           [0011]    The lens driving apparatus is a type which drives in the optical axis direction a first and a second lens group arranged in the optical axis direction. The lens driving apparatus comprises first and second cam followers extending mutually parallel in a right angle direction to the optical axis from the first and second lens groups, cam member having first and second cams arranged along the optical axis and respectively engaging the first and second cam followers, first drive means for driving the first lens group in the optical axis direction, and second drive means for driving the second lens group in the optical axis direction.  
           [0012]    In this structure, the cam member is not limited to a plate cam, and also may be, for example, a cylindrical cam member (cam drum).  
           [0013]    According to this structure, for example, the second drive means exerts a supplemental force in the direction of movement of the second lens group, such that the second cam follower moves along the second cam of the cam member in conjunction with the drive of the first drive means, and the movement of the second cam follower is supplemented relative to the second cam of the cam member.  
           [0014]    In this way, a smooth drive is possible and the cam member and first drive means can be compact even when it is difficult for the second lens group to move because the pressure angle of the second cam is large, and a large drive force is required for only the first drive means.  
           [0015]    If the endface of the cam member is used as a cam (e.g., a plate cam), the cam member can be made even more compact by suitably controlling the first and second drive means so as to have the first and second cam follower follow the endface of the cam member.  
           [0016]    Accordingly, it is unnecessary to detect the position of each lens group or control the drive of each lens group, and the lens driving apparatus can be made more compact.  
           [0017]    It is desirable that the second cam of the cam member has first and second cam surfaces which are mutually opposed and have a gap therebetween wider than the second cam follower. The control means is linked to the drive of the first drive means, and the first and second drive means are controlled such that the second cam follower moves in the optical axis direction selectively along the one or another of the first or second cam surface of the second cam of the cam member.  
           [0018]    In this structure, the position of the second lens group relative to the first lens group is different when the second cam follower is along the first cam surface of the second cam of the cam member, and when the second cam follower is along the second cam surface of the second cam of the cam member.  
           [0019]    In this way, the lens groups can be moved in different modes, for example, for normal photography and macro photography.  
           [0020]    The technical idea of switching the cam surface abutting the cam follower is widely suited to lens driving apparatuses, and the present invention provides a lens driving apparatus having the following structure.  
           [0021]    The lens driving apparatus is a type which moves in the optical axis direction a first and a second lens group arranged in the optical axis direction. The lens driving apparatus comprises first and second cam followers, cam member, drive means, and force exerting means. The first and second cam followers extend in a right angle direction to the optical axis from the first and second lens groups. The cam member has first and second cams which respectively slide on the first and second cam followers. The second cam has first and second cam surfaces which are mutually opposed and have a gap therebetween wider than the second cam follower. The drive means drives the first lens group. The force exerting means selectively exerts a force on the second lens group in bilateral directions along the optical path such that the second cam follower selectively abuts the first or second cam surface of the second cam of the cam member.  
           [0022]    In this structure, the cam member is not limited to a plate cam, and also may be, for example, a cylindrical cam used in replaceable lenses of single lens reflex cameras. The force exerting means may be an actuator capable of driving the second lens group in bilateral directions along the optical path, and may switch the direct of the exerted force by, for example, a spring.  
           [0023]    According to this structure, the force exerting means switches the cam surface abutting the second cam follower by switching the direction of the force exerted on the second lens group, so as to drive the lens by selecting one of two modes of different positions of the second lens group relative to the first lens group.  
           [0024]    In the lens driving apparatus having the aforesaid structures, it is desirable that the drive means is a drive means of the friction drive type including a drive force generator for generating a drive force for driving the lens group, and a drive force transmitter for transmitting a drive force from the drive force generator to the lens group via a friction force.  
           [0025]    When a drive means of the friction drive type is used, the apparatus is easily made more compact. Furthermore, when a drive means is used for switching the cam surface abutting the cam follower, the control of the drive means is simple since any imbalance of the load is absorbed by sliding on the friction surface.  
           [0026]    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  
       [0027]    In the following description, like parts are designated by like reference numbers throughout the several drawings.  
         [0028]    [0028]FIG. 1 is a perspective view of the essential part of a conventional lens driving apparatus.  
         [0029]    [0029]FIG. 2 is a perspective view of the essential part of a lens driving apparatus of a first embodiment of the present invention.  
         [0030]    [0030]FIG. 3 is a perspective view of the essential part of a lens driving apparatus of a second embodiment of the present invention.  
         [0031]    [0031]FIG. 4 is a perspective view of the essential part of a lens driving apparatus of a third embodiment of the present invention.  
         [0032]    [0032]FIG. 5 is a perspective view of the essential part of a lens driving apparatus of a fourth embodiment of the present invention.  
         [0033]    [0033]FIG. 6 is a perspective view of the essential part of a lens driving apparatus of a fifth embodiment of the present invention.  
         [0034]    [0034]FIG. 7 is a plan view of the plate cam of FIG. 5.  
         [0035]    [0035]FIG. 8 illustrates the positional relationship of the plate cam and the lens holder.  
         [0036]    [0036]FIG. 9 illustrates the positional relationship of the plate cam and the lens holder.  
         [0037]    [0037]FIG. 10 illustrates the drive speed. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]    A lens driving apparatus  100  of the first embodiment is described with reference to FIGS. 2 and 8.  
         [0039]    The lens driving apparatus  100  shown in FIG. 2 drives lens groups of a compact photographic device such as a digital camera, a video camera, a cellular phone and a personal computer for as portable device. Two front and back lens holders  50  and  60  guided in the optical axis direction engage a cam via a plate cam  70 , and only the back lens holder  60  is driven by an actuator  10   b.    
         [0040]    The actuator  10   b  driving the back lens holder  60  is a friction drive type actuator.  
         [0041]    The actuator  10   b  includes a base  1   b,  piezoelectric element  2   b , and drive shaft  3   b . The piezoelectric element  2   b  is arranged such that the extension-contraction direction matches the optical axis direction, and the base  1   b  is attached at one end in the extension-contraction direction and the shaft endface of the drive shaft  3   b  is attached at the other end in the extension-contraction direction. The drive shaft  3   b  is arranged in the optical axis direction, and friction-engages the lens holder  60  via a force exerted by a flat spring  4   b  on a channel of the back lens holder  60 .  
         [0042]    The front lens holder  50  is supported so as to freely move in parallel to the optical axis direction as indicated by the arrow  90  via a common guide shaft  8  and a special guide shaft  3   g  arranged in the optical axis direction. The common guide shaft  8  also engages the back lens holder  60 , and guides and supports as indicated by the arrow  92 . The special guide shaft  3   g  is attached to one end of the base la and passes through a guide hole  58  in the front lens holder  50 .  
         [0043]    The lens holders  50  and  60  are provided with cam pins  54  and  64  which protrude mutually parallel in a right angle direction to the optical axis.  
         [0044]    The plate cam  70  is arranged parallel to the optical axis and adjacent to the lens holders  50  and  60 , and is supported so as to be freely rotatable as indicated by the arrow  94  via a support shaft  78  parallel to cam pins  54  and  64 . The plate cam  70  has cam holes  72  and  74  formed therein, such that cam pins  64  and  54  are inserted therethrough. In this way, the front and back lens holders  50  and  60  engage the cam and are moved in linkage therewith.  
         [0045]    An image sensing element  7   b  for photoelectrically converting a photographic image and outputting image signals is provided at the image forming plane of the optical system including the lens groups supported by the lens holders  50  and  60 .  
         [0046]    The operation of the lens driving apparatus  100  is described below.  
         [0047]    A drive voltage having a specific waveform is applied to the piezoelectric element  2   b  of the actuator  10   b  by a drive circuit not shown in the drawing, and the drive shaft  3   b  is oscillated in the axis direction, such that the lens holder  60  which is friction bonded to the drive shaft  3   b  is driven in the optical axis direction along the drive shaft  3   b.    
         [0048]    For example, a drive voltage having a sawtooth pulse waveform is applied to the piezoelectric element  2   b  to reciprocatingly move the drive shaft  3   b  in the optical axis direction at different speeds depending on the direction. In this way, when the drive shaft  3   b  moves relatively slowly, the lens holder  60  moves integratedly together with the drive shaft  3   b  via the friction force between the drive shaft  3   b  and the lens holder  60 . On the other hand, when the drive shaft  3   b  moves relatively rapidly in the opposite direction, sliding is generated between the drive shaft  3   b  and the lens holder  60 , such that only the drive shaft  3   b  moves, and the lens holder  60  remains stationary. In this way, the lens holder  60  can be moved along the drive shaft  3   b.    
         [0049]    Since the front and back lens holder  50  and  60  engage the plate cam  70  and are linked when the back lens holder  60  is moved in the optical axis direction by the actuator  10   b , the front lens holder  50  also moves in the optical axis direction while maintaining a specific relationship with the back lens holder  60 .  
         [0050]    [0050]FIG. 8 shows an example of the movement of the front and back lens holders  50  and  60  via the movement of the plate cam  70 . Curve A represents the position of the front lens holder  50 , and curve B represents the position of the back lens holder  60 .  
         [0051]    That is, when the back lens holder  60  is driven by the actuator  10   b,  the movement is transmitted to the front lens holder  50  linked to the plate cam  70 , and the mutual positional relationship of the lens holders  50  and  60  is completely determined as shown in FIG. 8 via the shape of the cam holes  72  and  74  of the plate cam  70 . Therefore, sensors for detecting the position of each lens holder, and a signal processing device for controlling the movement of the lens holders  50  and  60  while maintaining a constant relationship are unnecessary.  
         [0052]    A lens driving apparatus  102  of a second embodiment is described below with reference to FIGS. 3 and 8.  
         [0053]    As shown in FIG. 3, the lens driving apparatus  102  has a structure largely similar to that of the lens driving apparatus  100  of the first embodiment, with the exception that an actuator  10   a  is provided for the front lens holder  50  and not only for the back lens holder  60 . In the following description like parts are designated by like reference numbers, and the description focuses on the dissimilarities.  
         [0054]    When the lens holders  50  and  60  are linked through the plate cam  70 , the part of the largest pressure angle of the cam, e.g., the part represented by the symbol Ax in FIG. 8, is such that the pressure angle increases even more as the plate cam  70  is made more compact. When the pressure angle of the cam increases, it becomes difficult to smoothly drive the front lens holder  50  via the drive of the back lens holder  60 .  
         [0055]    In the lens driving apparatus  102  of the second embodiment, an actuator  10   a  is provided for supplementally driving the front lens holder  50 , as shown in FIG. 3. The actuator  10   a  has a structure identical to the actuator  10   b  for driving the back lens holder  60 . A base la and drive shaft  3   a  are attached at bilateral ends of a piezoelectric element  2   a  in the extension-contraction direction. The drive shaft  3   a  is friction bonded via a force exerted by a flat spring (not shown) on the channel  52  of the lens holder  50 .  
         [0056]    Although the lens driving apparatus  102  can simultaneously use the two actuators  10   a  and  10   b  to drive the lens holders  50  and  60 , the actuator  10   b  on the back lens holder  60  aside is used for the main drive, and the actuator  10   a  on the front lens holder  50  side is used supplementally. That is, even when the cam pressure angle increases and the front lens holder  50  becomes difficult to move, the actuator  10   a  on the front lens holder  50  side provides a slight supplemental drive to smoothly drive the front lens holder  50 . For example, when actuator  10   b  on the back lens holder  60  side is driven at a 5 V drive voltage, the actuator  10   a  on the front lens holder  50  side is supplementally driven at a 2 V drive voltage.  
         [0057]    When the actuator  10   a  is used supplementally, a drive lag (delay and advance) is generated between the two actuators  10   a  and  10   b,  however, because the actuators  10   a  and  10   b  and the lens holders  50  and  60  are friction bonded, sliding is generated by the friction bonded part, such that the drive lag can be absorbed. In other words, even though there is a difference between the speed of the front lane holder  50  when the cam pin  54  completely follows the cam hole  74  of the plate cam  70  rotated by the actuator  10   b  and the speed of the front lens holder  50  driven by the actuator  10   a,  the speed difference is absorbed by the sliding between the drive shafts  3   a  and  3   b  and the lens holders  50  and  60 . The front and back lens holders  50  and  60  are driven smoothly while a constant relationship is maintained by following the cam holes  74  and  72  of the plate cam  70 .  
         [0058]    Accordingly, the front and back lens holders  50  and  60  can be driven smoothly by simple controls such as providing a simple drive force or difference in drive speed between the actuators  10   a  and  10   b.  Furthermore, since the front and back lens holders  50  and  60  can be driven even when the cam pressure angle increases, the plate cam can be made more compact, and the entire apparatus can be made more compact.  
         [0059]    A lens driving apparatus  104  of a third embodiment is described below with reference to FIG. 4.  
         [0060]    The lens driving apparatus  104  has a structure largely similar to that of the lens driving apparatus  102  of the second embodiment, with the exception of the shape of the plate cam  70   a.    
         [0061]    The plate cam  70   a  is an endface cam; the front and back endfaces  74   a  and  72   a  in the optical axis direction connect with the cam pins  54  and  64  of the respective front and back lens holders  50  and  60 .  
         [0062]    The method of operation of the lens driving apparatus  104  is described below.  
         [0063]    Actuators  10   a  and  10   b  must provide a drive such that the cam pins  54  and  64  do not separate from the endfaces  74   a  and  72   a  of the plate cam  70   a.    
         [0064]    For this reason, when driving a lens group to the object side (left side in the drawing), the actuator  10   b  on the back lens holder  60  side, for example, is driven by a 5 V drive voltage, and the actuator  10   a  on the front lens holder  50  side is driven by a 2 V drive voltage. In this way, the cam pins  54  and  64  both move to the object side, but since the cam pin  54  on the front lens holder  50  side is delayed relative to the cam pin  64  on the back lens holder  60  side, the plate cam  70   a  is rotated in a counterclockwise direction in the drawing with both cam pins  54  and  64  engaged.  
         [0065]    When a lens group is driven to the photographic element  7  side (right side in the drawing), the actuator  10   b  on the back lens holder  60  side, for example, is driven by a 2 V drive voltage, and the actuator  10   a  on the front lens holder  50  side is driven by a 5 V drive voltage. In this way, since the front cam pin  54  advances more than the back cam pin  64 , the plate cam  70   a  is rotated in a clockwise direction in the drawing with both cam pins  54  and  64  engaged.  
         [0066]    The plate cam  70   a  can be made even more compact by having the cam pins  54  and  64  of the front and back lens holders  50  and  60  press against the endfaces  72   a  and  74   a  of the plate cam  70   a  via the drive of the actuators  10   b  and  10   a.    
         [0067]    The lens driving apparatus of a fourth embodiment is described below with reference to FIGS. 5, 7,  9 , and  10 .  
         [0068]    As shown in FIG. 5, a lens driving apparatus  106  has a structure largely similar to that of the lens driving apparatus  102  of the second embodiment, with the exception of the shape of the plate cam  70   b.    
         [0069]    That is, the plate cam  70   b  has cam holes  74   b  and  72   b  through which pass the cam pins  54  and  64  of the front and back lens holders  50  and  60 . The front and back lens holders  50  and  60  move in the optical axis direction as indicated by the arrows  90  and  92  relative to the rotation of the plate cam  70   b  represented by the arrow  94 .  
         [0070]    As shown in FIG. 7, the width of the cam hole  72   b  through which is inserted the cam pin  64  on the back lens holder  64  side is approximately equal to the major diameter of the cam pin  64  passing therethrough, and no play is generated in the engagement of the hole and the pin.  
         [0071]    The cam hole  74   b  through which passes the cam pin  54  of the front lens holder  54  allows play when the cam pin  54  passes therethrough. That is, the width of the cam hole  74   b  is larger than the major diameter of the cam pin  54 . The cam pin  54  follows either the front and back cam surfaces  74   x  or  74   y  opposite the optical axis direction of the cam hole  74   b , so as to be capable of performing two operations wherein the position of the lens holder  54  differs relative to the back lens holder  64 .  
         [0072]    For example, as shown in FIG. 9, the position of the back lens holder  64  is represented by curve B relative to the rotation angle of the plate cam  70   b . On the other hand, the position of the front lens holder  54  is represented by curve A 1  when the cam pin  54  abuts the front cam surface  74   x,  and is represented by curve A 2  when the cam pin  54  abuts the back cam surface  74   y.  For example, normal photography is performed by combining curves A 2  and B, and macro photography is performed by combining curves A 1  and B.  
         [0073]    The method of operation of the lens driving apparatus  106  is described below.  
         [0074]    [0074]FIG. 10 is a graph showing the relationship between the rotation angle of the plate cam  70   b  and the speed of the cam pins  54  and  64 . When the cam pin  54  of the front lens holder  50  is not engaged with the cam hole  74   b  of the plate cam  70   b , and the cam pin  64  of the back lens holder  60  is driven at constant speed as represented by the symbol vT, the speed of the cam pin  54  of the front lens holder  50 , i.e., the ideal speed of the cam pin  54  of the front lens holder  50 , changes as represented by the curve vS when it is assumed that the cam pin  54  of the front lens holder  50  moves completely in accordance with the cam hole  74   b  of the plate cam  70   b . In this case, to simplify, we do not distinguish between the cam pin  54  of the front lens holder  50  sliding on either of the front and back cam surface  74   x  or  74   y  of the cam hole  74   b  of the plate cam  70   b . In the entire range of rotation of the plate cam  70   b , a speed normally greater than the ideal speed of the cam pin  54  of the front lens holder  50  is designated vA, and a speed normally slower is designated vB.  
         [0075]    When driven in accordance with the curves A 2  and B of FIG. 9, for example during normal photography, the drive operation is as described below.  
         [0076]    In FIG. 7, when the plate cam  70   b  is rotated in a counterclockwise direction, the actuator  10   a  on the front lens holder  50  side drives at the speed vB (e.g., 2 V), and the actuator  10   b  on the back lens holder  60  side drives at a constant speed vT (e.g., 5 V). In this way, since the cam pin  54  on the front lens holder  50  side is slow relative to the cam pin  64  on the back lens holder  60  side, the cam pin  54  abuts the back cam surface  74   y  as indicated by the solid line in FIG. 7. Accordingly, the cam pin  54  slides along the back cam surface  74   y  of the plate cam  70   b.    
         [0077]    When the plate cam  70   b  is rotated in the reverse direction (clockwise direction), the actuator  10   a  on the front lens holder  50  side drives in the reverse direction at a speed of vA (e.g., 4 V), and the actuator  10   b  on the back lens holder  60  side drives in the reverse direction at a constant speed vT (e.g., 5 V). Since the cam pin  54  on the front lens holder  50  side advances relative to the cam pin  64  on the back lens holder  60  side, the cam pin  54  slides along the back cam surface  74   y  of the plate cam  70   b.    
         [0078]    When driven in accordance with the curves A 1  and B of FIG. 9, for example during macro photography, the drive operation is as described below.  
         [0079]    When the plate cam  70   b  is rotated in a counterclockwise direction in FIG. 7, the actuator  10   a  on the front lens holder  50  side drives at the speed vA (e.g., 4 V), and the actuator  10   b  on the back lens holder  60  side drives at a constant speed vT (e.g., 5 V), such that the cam pin  54  on the front lens holder  50  side advances more than the cam pin  64  on the back lens holder  60  side, and the cam pin  54  abuts the front cam surface  74   x  as indicated by the dotted line  54   s  in FIG. 7.  
         [0080]    When the plate cam  70   b  is rotated in the clockwise direction, the actuator  10   a  on the front lens holder  50  side drives in the reverse direction at a speed of vB (e.g., 2 V), and the actuator  10   b  on the back lens holder  60  side drives in the reverse direction at a constant speed vT (e.g., 5 V), such that the cam pin  54  on the front lens holder  50  side is slower than the cam pin  64  on the back lens holder  60  side, and the cam pin  54  abuts the front cam surface  74   x  of the plate cam  70   b  as indicated by the dotted line  54   s  in FIG. 7.  
         [0081]    A lens driving apparatus  108  of a fifth embodiment is described below with reference to FIG. 6.  
         [0082]    The lens driving apparatus  108  is largely similar to the lens driving apparatus  106  of the fourth embodiment, with the exception that an actuator is not provided for the back lens holder  60  and the plate cam  70   b  is driven by a motor  80 .  
         [0083]    A gear  79  is provided on the peripheral surface of a rotating shaft  78  supporting the plate cam  70   b , and a gear  82  attached to the output shaft of a motor  80  engages the gear  79 , and the plate cam  70   b  is rotated via the motor  80 . The back lens holder  60  is supported so as to be freely movable in the optical axis direction by a common guide shaft  8  and a special guide shaft  3   g′.    
         [0084]    The lens driving apparatus  108  is capable of driving in two modes, by switching the drive of the motor  80  and the actuator  10   a  similar to the lens driving apparatus  106  of the fourth embodiment, such that the cam pin  54  of the front lens holder  50  abuts the front cam surface  74   x,  or abuts the back cam surface  74   y,  of the cam hole  74   b  of the plate cam  70   b.    
         [0085]    The lens driving apparatuses  100 ,  102 ,  104 ,  106 , and  108  of each embodiment described above is capable of maintaining a normal mutual positional relationship of a lens holder  50  and lens holder  60  in a specific relationship by controlling the movement of the lens holder  50  relative to the other lens holder  60  by combining a plate cam  70 ,  70   a , or  70   b  between two lens holders  50  and  60 . In this way, sensors and signal processing devices which are required when individually driving individual lens groups become unnecessary.  
         [0086]    Accordingly, the structure of the lens driving apparatuses  100 ,  102 ,  104 ,  106 ,  108  can be simplified and made more compact.  
         [0087]    The present invention is not limited to the above described embodiment, and may be variously modified.  
         [0088]    For example, an actuator of a type other than the friction drive type used in the embodiments may be used, e.g., an ultrasonic motor can be used with similar effectiveness to slide on a friction surface transmitting a drive force.  
         [0089]    In the fifth embodiment, a spring or the like may be substituted fro the actuator  10   a  to switch the contact of the cam pin  54  relative to the front and back cam surfaces  74   x  and  74   y  by switching the direction of an exerted force. Furthermore, a drum cam or the like may be substituted for the plate cam  70   b.    
         [0090]    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.