Abstract:
A driving mechanism is disclosed that utilizes a shape-memory alloy. In particular, mechanical components are movably positioned by a member composed of shape-memory alloy, which changes shape when heated. The present invention reduces the number of mechanical components in a driving mechanism, thereby reducing size and improving performance. One of many applications of the present invention is a camera application.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field of the Invention 
     This application is based on applications Nos. 9-113804, 9-118177, 9-118178, and 10-69667, filed in Japan, the contents of which are hereby incorporated by reference. 
     The present invention relates to a driving mechanism, and particularly to a driving mechanism which utilizes changes in the shape of a shape-memory alloy for various mechanical actions. 
     2. Description of Related Art 
     There are many different kinds of mechanical actions, and driving mechanisms for these actions are respectively designed in accordance with different purposes. However, while various appliances are desired to be multifunctional and high speed, demands which are contradictory to each other and thus difficult to accomplish, such as minimization, higher precision, quietness of the actions, have been increased. Taking cameras as the example, some of the conventional driving mechanisms as well as their problems will be hereinafter described. 
     A built-in pop-up flash of a camera is constructed as shown in FIG. 1, in which a flash  102  is urged upwardly by a spring  104  but is normally retained in a housed position (initial position) by a lever  111  against the force of the spring  104 . The lever  111  is urged by a spring  113  to remain in a locking position, and when the lever  111  is released from this state, the flash  102  is popped up by the force of the spring  104 . Such release is made either manually with an operative member or automatically in accordance with automatic measurement of light. 
     FIG. 2 shows a sequence of actions in the flash pop-up mode in which the case using a plunger  113  shown in FIG. 1 is taken as an example. First, an electric current is applied to the electromagnetic plunger  117 , by which the lever  111  releases a hold of the flash  102 , which is freed and popped up by the urging force of the spring  104  from the housed position shown in FIG. 1A to a state shown in FIG.  1 B. At the same time a switch  119  is turned off, and the application of the electric current to the electromagnetic plunger  117  is ended by this switch-off signal, whereby the camera is set to a standby mode. When the electricity to the electromagnetic plunger  117  is shut off, the lever  111  is freed and returned to the locking position by the urging force of the spring  113  as shown in FIG. 1C so as to prepare for the next locking action when the flash  102  is housed again. In this example, the flash  102  is housed by pushing it in by a hand. 
     In such a construction, however, the camera cannot be further minimized in dimensions since the plunger has a large volume and needs to be disposed on an upper part of the camera. It is possible to provide a motor instead of the plunger to allow the lock of the flash to be released by a rotational force of the motor. However, such provision of the motor specially for the lock releasing action would be also disadvantageous for minimization of the camera. The necessity of providing an additional motor may be obviated by using a part of rotation of a motor for charging shutter, but in that case it will be further necessary to provide a linking mechanism and a drive force switchover mechanism and the like between the two, leading to an increase in number of components as well as causing the structure to be complicated, thus ending up to be disadvantageous for minimization of the mechanism and reduction of cost. 
     A second example of driving mechanism is designed for a film feeding system and a zooming system of cameras, which are driven by a drive force switched over from a single motor and transmitted to either of them depending on needs. Such driving mechanism allows a multifunctional camera to have fewer number of motors. 
     In the zooming system, a lens tube is driven tele- and wide-scopically, instantly responding to operations by a user. 
     In the film feeding system, for example, in the case of an advanced photo system camera, since the film is pushed out from a cartridge or rewound into the cartridge, a fork shaft which is engaged with a cartridge spool needs to be rotated in both regular and reverse directions. A take-up spool inside the camera also needs to be rotated in a film take-up direction for a so-called thrust drive when the fork is rotated in a direction to push out the film from the cartridge. For satisfying these demands, rewinding of the film is achieved by the rotation of the motor in one direction, and the thrust drive and spool take-up drive are achieved by the rotation in the reverse direction in an ordinary mechanism. 
     In such a case, it is necessary to switch over the rotation of the motor in normal and reverse directions to the zooming system and the film feeding system. A switchover means which the applicant of the present invention has previously proposed as disclosed in Japanese Published Unexamined Patent Application No. 1-287648 employs a friction planet gear mechanism. As the transmission is changed over from one to another by the rotation of motor in either one of directions in this mechanism, it is necessary to lock the planet gear so as to prevent the transmission from being changed over when transmitting a drive force and to release the lock of the planet gear when changeover of transmission is required. Such locking and releasing may be achieved using actions of an electromagnetic plunger. However, as a plunger takes up a lot of space, its usage is limited within a compact camera. Also, it is necessary to supply electricity to two loads at the same time since the changeover of the planet gear is performed such that an electric current is applied to the motor while electricity is also applied to the plunger. This increases the load on a battery, and the capacity of motor will have to be reduced, which will result in decrease in driving speed. 
     For focusing lenses in cameras, it is required to move a focusing lens to a predetermined position and stop it there in accordance with the distance to an object to be photographed. Also, for driving a zooming action of a flash, it is required to move a reflector umbrella to a prescribed position and stop it there in accordance with a zooming action of a photographing lens. Each are generally driven by a motor which is supplied with electricity from a battery. The motor is electrically controlled according to position detecting signals from a position detector which judges whether a driven member is located at the prescribed position, whereby the driven member is moved to a desired position and stopped there. 
     However, the motor has a large volume and requires a gear or the like for transmitting the rotation thereof to the driven member, and may further require a motion converting mechanism for converting rotation into a linear movement in case the movement of the driven member is reciprocating motion of one dimension. It is possible to employ another driving mechanism cooperatively with the motor to avoid increase in volume, in which case the construction will be any way complicated because a drive switchover mechanism and a transmission mechanism are necessary. 
     Further, when a motor or a gear is employed, since motors emit vibration sounds and gears emit noises generated by toothed gears meshing with each other, they are unsuitable for use under a quiet circumstance. Also, in the case of using gears, position control of the driven member will be more difficult due to backlash that is specific to a gear transmission system. It is especially disadvantageous for driving reciprocating motions such as when zooming tele- or wide-scopically. 
     These problems are not limited to cameras but commonly found in other driving mechanisms under similar circumstances for various purposes. 
     BRIEF SUMMARY OF THE INVENTION 
     In view of the foregoing, it is a primary object of the present invention to provide a driving mechanism which is capable of favorable drive in accordance with various demands as described above utilizing a shape change stroke of a shape-memory alloy back to its memorized shape. 
     The above said object is addressed by one aspect of the present invention which provides a novel driving mechanism including a driven member biased toward one direction from an initial position, a locking mechanism for retaining the driven member at the initial position against a biasing force, a shape-memory alloy of which transformation into a memorized shape by electric heating is used for lock release operation for releasing the lock by the locking mechanism, and a controller by which electric heating of the shape-memory alloy for releasing the lock is completed after a predetermined period of time has passed since the start of electricity supply. 
     To accomplish the said object, a driving mechanism for driving a plurality of driven members selectively according to another aspect of the present invention comprises a first driving power source which is a motor, a second driving power source which is a shape-memory alloy, a transmission changeover mechanism for selectively transmitting a drive force from the first driving power source to a specific one of the plurality of driven members, wherein the transmission changeover mechanism performs a transmission changeover action by utilizing a shape change of the second driving power source. 
     A driving mechanism according to yet another aspect of the present invention comprises a driven member, a shape-memory alloy having a predetermined memorized shape, a driver for driving the driven member utilizing transformation of the shape-memory alloy, a sensor for detecting displacement of the driven member, and a controller for controlling the driver based on data from the sensor which detects displacement of the driven member. 
     Other and further objects, features and advantages of the invention will appear more fully from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A-1C are cross-sectional views illustrating states of a conventional flash section in action including a lock release mechanism, in which  1 A shows a state where the flash is housed,  1 B shows a state when the lock is released and the flash is popped up, and  1 C shows a state where a locking lever is returned to its initial position after the lock release; 
     FIG. 2 is a flowchart of a sequence of actions for releasing the lock of the flash in FIG. 1; 
     FIGS. 3A-3C are cross-sectional views illustrating states of a flash section in action including a lock release mechanism according to one embodiment of the present invention, in which  3 A shows a state where the flash is housed,  3 B shows a state when the lock is released and the flash is popped up, and  3 C shows a state where a locking lever is returned to its initial position after the lock release; 
     FIG. 4 is a front view of a camera having the flash section of FIG. 3 in a state where the flash is housed in the camera; 
     FIG. 5 is a front view of a camera having the flash section of FIG. 3 in a state where the flash is popped out from the camera; 
     FIG. 6 is a flowchart of a sequence of actions for releasing the lock of the flash in FIG. 3; 
     FIG. 7 is a side view showing a lock release mechanism of a second embodiment of the present invention; 
     FIG. 8 is a front view of a camera representative of one of the embodiments according to the present invention; 
     FIG. 9 is a top plan view of the camera of FIG. 8; 
     FIG. 10 is a bottom plan view of the camera of FIG. 8; 
     FIG. 11 is a plan view showing a transmission changeover state of a transmission changeover mechanism in a driving mechanism of the camera of FIG. 8 in which a film feed system is selected; 
     FIG. 12 is a plan view showing a lock release state of the transmission changeover mechanism of FIG. 11 under the transmission changeover state in which the film feed system is selected; 
     FIG. 13 is a plan view showing a transmission changeover state of the transmission changeover mechanism of FIG. 11 in which a zoom system is selected from the transmission changeover state in which the film feed system is selected; 
     FIG. 14 is a plan view showing the transmission changeover mechanism which is locked to be in the transmission changeover state of FIG. 11; 
     FIG. 15 is a block diagram showing a control unit of a driving mechanism; 
     FIG. 16 is a flow chart of a sequence showing a first example of transmission changeover operation; 
     FIG. 17 is a flow chart of a sequence showing a second example of transmission changeover operation; 
     FIG. 18 is a flow chart of a sequence showing a third example of transmission changeover operation; 
     FIG. 19 is a flow chart of a sequence showing a fourth example of transmission changeover operation; 
     FIG. 20 is a plan view showing a transmission changeover state of a transmission changeover mechanism in a driving mechanism of a fifth example in which the film feed system is selected; 
     FIG. 21 is a block diagram showing a control unit of the driving mechanism of FIG. 20; 
     FIG. 22 is a flow chart of a sequence of transmission changeover operation of the control unit shown in FIG. 21; 
     FIG. 23 is a plan view showing a transmission changeover state of a transmission changeover mechanism in a driving mechanism of a sixth example in which the film feed system is selected; 
     FIG. 24 is a block diagram showing a control unit of the driving mechanism of FIG. 23; 
     FIG. 25 is a flow chart of a sequence of transmission changeover operation of the control unit shown in FIG. 24; 
     FIG. 26 is a plan view showing a transmission changeover state of a transmission changeover mechanism in a driving mechanism of a seventh example in which the zoom drive system is selected; 
     FIG. 27 is a plan view showing a transmission changeover state of a transmission changeover mechanism in the driving mechanism of FIG. 26 in which the film feed system is selected; 
     FIG. 28 is a plan view showing a transmission changeover state of a transmission changeover mechanism in a driving mechanism of an eighth example in which the zoom drive system is selected; 
     FIGS. 29A and 29B are plan views showing a state of the transmission changeover mechanism of the driving mechanism of FIG. 28 in which changeover has started from a state wherein the zoom drive system is selected to a state wherein the film feed system is selected, respectively illustrating a state of feeding a ratchet toothed wheel by supplying electricity to the shape-memory alloy and a state of returning the ratchet toothed wheel by shutting off electricity to the shape-memory alloy; 
     FIG. 30 is a plan view showing a transmission changeover state of a transmission changeover mechanism in a driving mechanism of FIG. 28 in which the film feed system is selected; 
     FIG. 31 is a plan view showing a transmission changeover state of a transmission changeover mechanism in a driving mechanism of a ninth example in which the zoom drive system is selected; 
     FIG. 32 is a plan view showing a transmission changeover state of a transmission changeover mechanism in a driving mechanism of FIG. 31 in which the film feed system is selected; 
     FIG. 33 is a perspective view of a camera to which a fourth embodiment of the present invention is applied; 
     FIGS. 34A and 34B are diagrams showing a focusing mechanism of the camera of FIG. 33; 
     FIG. 35 is a flow chart of shooting action which involves the focusing mechanism of FIG. 34; 
     FIG. 36 is a diagram showing a focusing mechanism in a fifth embodiment of the present invention; 
     FIG. 37 is a flow chart of shooting action which involves the focusing mechanism of FIG. 36; 
     FIG. 38 is a diagram showing a focusing mechanism in a sixth embodiment of the present invention; 
     FIG. 39 is a flow chart of shooting action which involves the focusing mechanism of FIG. 38; 
     FIG. 40 is a diagram showing a focusing mechanism in a seventh embodiment of the present invention; 
     FIG. 41 is a flow chart of shooting action which involves the focusing mechanism of FIG. 40; 
     FIG. 42 is a diagram showing a focusing mechanism in an eighth embodiment of the present invention; 
     FIG. 43 is a diagram showing a zooming mechanism of a lash in a ninth embodiment of the present invention; and 
     FIG. 44 is a diagram showing a zooming mechanism in a tenth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be hereinafter described in conjunction with the accompanying drawings. 
     (First Embodiment) 
     FIGS. 3A-3C to FIG. 6 show a first embodiment of the resent invention, in which an object to be driven is an electronic flash  2  incorporated in a camera  1  as shown in FIG.  4  and FIG. 5. A main body  2   a  of the flash  2  is supported to a camera body  1   a  around a shaft  3  so that it can rotate between a housed position shown in FIG. 3A and a popped-up position shown in FIGS. 3B,  3 C, and FIG. 5, and is urged by a spring  4  in one direction from its housed position as an initial position towards the popped-up position. The spring  4  is mounted such as to surround the shaft  3  and applied between a shaft  5  on the camera body  1   a  and a shaft  6  on the flash main body  2   a.  It is of course possible to variously modify the style of movement of the flash  2  and its supporting structure, as well as the type of spring  4  and the way of its application. 
     The flash  2  has a luminous panel  2   b  at its distal end facing to the front side in the popped-up state, as shown in FIGS. 3B,  3 C, and FIG. 5, through which light is emitted from a light source  2   e  in synchronism with shutter release. Light adjustment control may be further performed in accordance with measurement of light or distance depending on cases. 
     On the front side of the flash main body  2   a  is a hook-like catching piece  2   c,  which is for example integrally formed thereon, to be coupled with a locking lever  11  on the camera body  1   a  side for retaining the flash  2  in its housed position. The locking lever  11  in this embodiment is a bell crank type supported on the camera body  1   a  around a shaft  12 , but any other appropriate configurations may be employed in accordance with the size or shape of an available inner space of the camera body  1   a.  The locking lever  11  is mounted around the shaft  12  and urged by a spring  13 , which is inserted to act between the locking lever  11  and a shaft  15  in an upper part of the camera body  1   a,  to stay in its locking position shown in FIGS. 3A and 3C. By this arrangement, at the last stage of pressing the flash  2  by a hand from the popped-up position to the housed position, when the catching piece  2   c  comes into contact with an end of the locking lever  11 , they slide with each other by their respective sliding surfaces  11   a  and  2   d  which are rounded or inclined, so that the locking lever  11  is pushed against the force of the spring  13  from the locking position shown in FIG. 3A toward the lock release side shown in FIG. 3B before the flash  2  reaches its housed position. When the flash  2  comes to the housed position, the catching piece  2   c  is released from the end of the locking lever  11 , by which the freed locking lever  11  returns to its locking position by the force of the spring  13 , where it couples with the caching piece  2   c  of the flash main body  2   a  which is now housed, so as to hold the flash  2  in its housed position shown in FIG.  3 A. The locking position of the locking lever  11  is restricted by a stopper  14 . 
     A shape-memory alloy  21  in a linear form is employed as an actuator for an automatic lock release operation of the locking lever  11 . One end of the shape-memory alloy  21  is connected to the proximal end of the locking lever  11 , whereas the other end is connected to a fixed portion  1   c  of the camera body  1   a  such as would keep a tense state between both ends. Electric power supply to the shape-memory alloy  21  is controlled with an electric current control circuit  22 , and when an electric current is applied to the shape-memory alloy  21 , it heats itself to a higher temperature to change into a memorized shape. In this first embodiment, the shape-memory alloy  21  shrinks and changes from the stretched state shown in FIG. 3A to be the contracted form shown in FIG. 3B which is the memorized shape. Due to this shape change, the shape-memory alloy  21  pulls the proximal end of the locking lever  11  toward the fixed portion  1   c  side, causing the locking lever  11  to rotate in a clockwise direction in FIGS. 3A-3C to be released from the catching piece  2   c.  The lock of the flash  2  at its housed position is thereby released, and the flash  2  pops up by the force of the spring  4  to be in its popped-up position shown in FIG.  3 B. 
     When the electric current supply is shut off, the shape-memory alloy  21  stops generating heat, and when its temperature lowers, the retaining force for remaining in the memorized shape also decreases, so it returns to its stretched form by the force of the spring  13  so as to cause the locking lever  11  to return to its locking position shown in FIG.  3 C and stand by the next time when the flash  2  is housed. Normally, it requires a longer time for the temperature to fall, and thus the shape-memory alloy  21  returns to the initial shape at a quite low rate as compared to the speed of its transformation into the contracted form. However, the flash  2  is not housed again immediately after it is popped up in most cases, so it hardly happens that the flash  2  cannot be locked when it is housed again under normal uses. There will be less limitation depending on selection of materials of the shape-memory alloy  21  or on development of new materials in future. 
     The shape-memory alloy  21  causes the locking lever  11 , which is a locking mechanism for retaining the driven member or the flash  2  at its initial position, to move to a lock release position to release the lock by transforming to the memorized shape when heated by electricity so that the flash  2  is moved to the popped-up position by the force of the spring  4 . Here, since the transformation of the shape-memory alloy  21  is made linearly, the volume required for the mechanism is small and, for example, the mechanism can be installed between an upper cover of the camera body  1   a  and the main body, by which the space is saved, preventing the appliances such as cameras incorporating the mechanism from becoming bulky. Specifically in the first embodiment which utilizes linear transformation of the shape-memory alloy  21 , there is an advantage of having such other possibilities of arrangement that the shape-memory alloy  21  can even be disposed in a curved gap within the camera body  1   a  with the provision of a roller or a wall or any such guiding members for guiding the shape-memory alloy  21  to stretch and contract in a linear form while tension is maintained at the curved portion. 
     The transformation stroke may be variously set according to the length or other properties of the shape-memory alloy  21 , or a required stroke length may be fulfilled by arranging the proportion of levers such as the locking lever  11 . It is also possible to employ a locking mechanism for locking the driven member such as the flash  2  or the like and for releasing the lock which does not use a lever, or to employ a mechanism which uses a locking member which moves linearly. Also, the present invention can be applied to any other driven members other than the flash  2 , as long as it is urged by a spring to remain at an initial position toward one direction, and styles of movement of the driven member from the initial position toward one direction or a specific supporting structure may be freely designed. 
     The flash pop-up mode is implemented according to the sequence of actions, for example, as shown in FIG. 6, and a temperature sensor  23  for detecting environmental temperature of the camera body  1   a  and a key switch  8   a  of an operative button  8  provided on the front side of the camera body  1   a  for manual flash pop-up operation are connected to the electric current control circuit  22 . 
     A microcomputer installed in the camera body  1   a  for controlling actions may be commonly used as the electric current control circuit  22 . However, it is not limited to this, and a special control unit may be used, as well as other control units may be commonly used. 
     Description of the flash pop-up mode will now be made in accordance with the sequence of actions shown in FIG.  6 . First it is judged whether the operative button  8  has been operated or not, and when the operative button  8  has been operated, it is started to heat the shape-memory alloy  21  by electricity after a certain period of time has lapsed, which is counted by an inner timer function or the like of the electric current control circuit  22 . The timing for starting electric heating of the shape-memory alloy  21  with respect to the operation timing of the operative button  8  can be freely set by determining this certain period of time. Particularly in this embodiment, the period of time is altered by the electric current control circuit  22  in accordance with, for example, a certain table corresponding to environmental temperature of the camera body  1   a  detected by the temperature sensor  23 . More specifically, when the temperature is high, the period of time is set shorter, and when the temperature is low, the period of time is set longer. The transformation speed of the shape-memory alloy  21  into the memorized shape by electric heating is thereby prevented from varying depending on differences in temperature, and it is avoided that the time between the operation of the operative button  8  and the lock release varies, which would annoy the user of the camera. In other words, the period of time is set such as to be the longest time for the shape-memory alloy  21  to transform into the memorized shape from the moment when the operative button  8  is operated. 
     In case of an automatic flash pop-up mode without operation of the operative button  8 , such consideration as mentioned above is unnecessary, and it is favorable to set such that the flash  2  pops up as quickly as possible. Thus the electric heating of the shape-memory alloy  21  may be immediately started when it is judged that the flash  2  needs to be popped up by automatic settings. However, it is not limited to this, and it is of course possible to control the timing similarly in the case of manual operation of the operative button  8 . 
     The electric heating of the shape-memory alloy  21  is ended after a certain period of time has lapsed. The timing of ending the electric current supply to the shape-memory alloy  21  can also be set using the inner timer function of the electric current control circuit  22 , eliminating the necessity of providing an additional switch. It is thus not only advantageous from the viewpoint of space saving, but also helps reduce the cost with fewer number of components and assembling steps. 
     Particularly in this embodiment, the period of time is altered by the electric current control circuit  22  in accordance with, for example, a certain table corresponding to environmental temperature of the camera body  1   a  detected by the temperature sensor  23 . More specifically, when the temperature is high, the period of time is set shorter, and when the temperature is low, the period of time is set longer. By varying the certain period of time between the start and the end of the electric heating, it is ensured that the lock of the flash  2  is reliably released so that the flash  2  is certainly moved by the urging force of the spring, whereas the time of electric heating is reduced to a minimum depending on the temperature thereby saving electricity, so it is advantageous in the case of using an electric power source built in the camera  1 . 
     When electric current supply to the shape-memory alloy  21  is finished, the flash  2  stands by photographing under the flash mode. Meanwhile, the shape-memory alloy  21  starts to cool after the end of the electric heating and returns to be its initial form. 
     (Second Embodiment) 
     FIG. 7 shows a second embodiment, in which a heater  25  is provided to heat the shape-memory alloy  21 , and an electric current is applied to the heater  25  by the electric current control circuit  22 . By heating the shape-memory alloy  21  by means of the heater  25 , a complicated operation of connecting a current circuit to the shape-memory alloy  21  can be avoided, as compared with a case of directly heating the shape-memory alloy  21  by electricity. 
     The heater  25  is coiled around the shape-memory alloy  21 . However, it is not limited to this configuration, and the heater may be just touched with the shape-memory alloy, or the shape-memory alloy may be interposed between heaters or covered with a tube-like heater, or any other various arrangements may be employed. 
     (Third Embodiment) 
     This embodiment is an example of a driving mechanism in which a plurality of driven members are selectively driven by one motor, the drive transmission being changed over from one to another by using a friction planet gear mechanism in a camera. For example, in a camera  1  of an advanced photo system type shown in FIG. 8 to FIG. 10, the rotation of a motor  31  is selectively transmitted to a zoom system  33  and a film feed system  34  by an action of a transmission changeover unit  32  shown in FIG. 11 to FIG. 14 as one example of transmission changeover means. 
     When the transmission changeover unit  32  is connected to a zoom system gear  61  for transmitting a drive force to the zoom system  33  as shown in FIG. 14, a barrel  36  is extended or retracted by means of, for example, a reversible rotation of the motor  1  as a first driving power source, via a zoom drive system  35  shown in FIG. 10 to FIG. 14 for achieving the zoom driving. 
     When the transmission changeover unit  32  is connected to a film feed system gear  62  for transmitting a drive force to the film feed system  34  as shown in FIG. 11, a fork shaft  42  is rotated by the reversible rotation of the motor  31  through a fork transmission gear  73 , a rewind/thrust transmission train  37  of a rewind/thrust transmission system  50 , a transmission shaft  38 , a transmission shaft gear  39 , and a rewind/thrust drive mechanism  41  shown in FIG. 8 to FIG. 14, and the rotation of the motor  31  is also transmitted to a cartridge spool  48  of a cartridge  46  via another transmission system (not shown). 
     The fork gear  42  is rotated counterclockwise via the rewind/thrust drive mechanism  41  by the clockwise rotation of the transmission shaft gear  39 . A fork shaft  44  is integrally provided to the fork gear  42 , and the fork shaft  44  is provided with a retractable fork key  45 , which couples with a spool key groove  48   a  of the cartridge spool  48 . The cartridge spool  48  is rotated counterclockwise by the rotation of the fork gear  42  in the same direction which is driven by the clockwise rotation of an output gear (not shown) of the motor  31 , by which a film  49  shown in FIG. 9 is rolled into the cartridge  46 . 
     When the cartridge spool  48  is rotated clockwise by the clockwise rotation of the fork gear  42  which is driven by a counterclockwise rotation of the output gear of the motor  31 , the film  49  is pushed out from the cartridge  46  and fed toward a take-up spool  52  shown in FIG. 8 to FIG. 14 within the camera  1 . 
     In the film feed system  34 , the take-up spool  52  shown in FIG. 8 to FIG. 10 within the camera  1  is rotated clockwise by the rotation of the motor  31  in the same direction via a spool transmission gear  72  of a take-up drive system  51 , and the transmission of the drive force from the motor  31  to the spool  52  is cut by the reverse rotation of the motor  31  in the take-up drive system  51 . 
     A roller (not shown) is pressed against the take-up spool  52 , by which the film  49  being fed thereto is pressed against the spool  52  to generate a frictional force therebetween, so that the film  49  is pulled by the spool  52  rotating in the take-up direction and rolled around the spool  52 . 
     A perforation sensor  53  shown in FIG. 8 is an optical sensor, of which output varies depending on existence of perforations in the film  49 . 
     As shown in FIG. 11 to FIG. 14, the transmission changeover unit  32  has a sun gear  47  which is linked to the output gear of the motor  31  and a planet lever  55  which is provided on an identical shaft of the sun gear  47 . A planet gear  56  which meshes with the sun gear  47  is axially supported on the planet lever  55 . A friction mechanism is further provided either between the sun gear  47  and the planet lever  55  or between the planet lever  55  and the planet gear  56 . When the planet lever  55  is in a free state, the planet lever  55  and the planet gear  56  rotate integrally with the sun gear  47  by frictional resistance of the friction mechanism. By this means, the planet lever  55  and the planet gear  56  are pivotally reciprocated between stoppers  57 ,  58  by the reversible rotation of the motor  31 , so that it is changed over appropriately such that the planet gear  56  selectively meshes with the zoom system gear  61  for transmitting the drive force to the zoom system  33  or with the film feed system gear  62  for transmitting the drive force to the film feed system  34 , respectively shown in FIG.  11  and FIG.  14 . 
     In these connected states shown in FIG.  11  and FIG. 14, when the rotation of the planet lever  55  is stopped, the rotation of the sun gear  47  overcomes the frictional resistance of the friction mechanism and is transmitted to the planet gear  56  which is axially supported on the planet lever  55 . By this means, the rotation is transmitted to the zoom system gear  61  or the film feed system gear  62  being meshed with the planet gear  56 , so as to drive either the zoom system  33  or the film feed system  34  as mentioned above. 
     A lock lever  63  is used for locking the planet lever  55  at its transmission changeover position shown in FIG.  11  and FIG.  14 . This lock lever  63  is urged clockwise by a spring  65  so as to be always located at the lock position shown in FIG. 11 where it contacts to a stopper  66 . In the state shown in FIG. 11, a connected state is maintained in which a contact portion  63   a  of the lock lever  63  is in contact with a contact portion  55   a  of the planet lever  55  so as to lock the planet lever  55  to be in contact with the stopper  58  and prevent the planet lever  55  to rotate clockwise, and the rotation of the motor  31  in both directions is transmitted to the film feed system  34 . 
     Here, a shape-memory alloy  64  as a second driving power source is linearly disposed, one end of which is attached to the lock lever  63  while the other end is connected to the camera body  1   a.  The memorized shape of the shape-memory alloy  64  is shorter than the length shown in FIG. 11, and when an electric current is applied from a current control circuit  67  to the shape-memory alloy  64 , it generates heat and returns to its original shorter form. When the shape-memory alloy  64  is shortened, the lock lever  63  is rotated counterclockwise against the force of the spring  65  to cause its contact portion  63   a  to depart from the contact portion  55   a  of the planet lever  55  as shown in FIG. 12, so as to allow the planet lever  55  to rotate clockwise. Also, when the lock lever  63  is rotated counterclockwise, a switch  69  is turned off, by which it is detected that the amount of transformation of the shape-memory alloy  64  has reached a predetermined value and the lock lever  63  has been released to allow the transmission to be changed over. 
     In this state, when the sun gear  47  is rotated clockwise by the drive force from the motor  31 , the planet lever  55 , which is in a free state, is integrally rotated clockwise with the sun gear  47  due to the frictional resistance by the friction mechanism, until the planet lever  55  strikes the stopper  57  as shown in FIG. 13, by which the clockwise rotation of the planet lever  55  is stopped. In a state that the planet lever  55  is in contact with the stopper  57 , the planet gear  56  is meshed with the zoom system gear  61 . 
     When the electric current supply to the shape-memory alloy  64  is stopped, its temperature gradually decreases, thus reducing its transforming force, in accordance with which the urging force of the spring  65  overcomes the force from the shape-memory alloy  64 . As a result, the lock lever  63  is rotated clockwise by the force of the spring  65 , bringing its contact portion  63   b  into contact with the contact portion  55   b  of the planet lever  55  as shown in FIG. 14 so as to retain the planet lever  55  at the position for driving the zoom system  33 . When the lock lever  63  comes to the position for locking the planet lever  55  as shown in FIG. 14, the transmission of the force to the zoom drive system  35  by the counterclockwise rotation of the sun gear  47  is enabled. The switchover of transmission from the zoom system  33  driving state shown in FIG. 14 to the film feed system  34  driving state shown in FIG. 11 is achieved by reversely performing the actions that have been described above. 
     As set forth above, the transmission changeover unit  32  is capable of switching over transmission of the force from the motor  31  to one of a plurality of driven members such as the zoom system  33  and the film feed system  34  selectively, utilizing thermal transformation of the shape-memory alloy  64 . Since the shape-memory alloy  64  changes its shape by heat quickly, transmission changeover can be achieved without much dead time. Even when the heating of the shape-memory alloy  64  is stopped at the same time when the transmission changeover by the motor  31  is started, since it restores slowly and thus does not obstruct the transmission changeover by the motor  31 , the time for applying electricity can be minimized as in this embodiment in which the heating is achieved by electricity supply. Moreover, since the transformation of the shape-memory alloy  64  is made linearly as in this embodiment, the volume required for the mechanism is small and, for example, the mechanism can be installed between a bottom cover of the camera  1  and the camera body  1   a,  by which the space is saved, permitting the camera to be compact. 
     Furthermore, the mechanism is free from unfavorable properties of a holding mechanism which utilizes attraction consisting of an electromagnet and an armature, which is susceptible to shocks and easily decreased in attracting force by dust. A mechanism with a plunger or an electromagnet has a disadvantage that its driving force is declined as its electromagnetic force decreases with the fall of the voltage from the electric power source while applying electricity, whereas the shape-memory alloy  64  keeps generating a certain amount of transforming force even during a longer heating time, thus assuring stable actions. 
     In order for implementing the above described transmission changeover and various driving actions, a CPU is used as a control unit  68  in this embodiment, to which the motor  31  and the electric current control circuit  67  are connected as well as the switch  69 , which detects whether the amount of transformation of the shape-memory alloy  64  has reached a predetermined value or whether the lock by the lock lever  63  has been released. Also connected is the perforation sensor  53  for correctly rewinding and taking up the film  49 . Further, a zoom switch  71  which detects a zooming position of the barrel  36  is connected to the CPU for performing a correct driving action of the zoom system  33 . The CPU which controls overall actions of the camera  1  or any other control units may be commonly used as the control unit  68 , or a special unit may be additionally provided. 
     In a first example of sequence of actions shown in FIG. 16, the camera is in a state shown in FIG. 11 at step {circle around (1)}, and when electricity supply to the shape-memory alloy is started at step {circle around (2)}, the alloy is heated and transforms to the memorized length, with which the lock lever  63  starts to rotate counterclockwise. 
     At step {circle around (3)}, the lock lever  63  leaves the planet lever  55  and further rotates counterclockwise until the switch  69  is turned off as shown in FIG.  12 . 
     In response to the switch  69  being turned off, the electricity supply to the shape-memory alloy  64  is stopped at step {circle around (4)}. 
     At step {circle around (5)}, as the electricity to the shape-memory alloy  64  is ended, the transforming force of the shape-memory alloy  64  decreases with its temperature goes down, as a result of which the lock lever  63  rotates clockwise by the force of the spring  65  as shown in FIG. 13, but since it takes time for the lock lever  63  to come into the track of the planet lever  55 , it is started to apply electricity to the motor  31  to cause the planet lever  55  to rotate in a clockwise direction, so as to change over the planet lever  55  from the film feed system  34  to the zoom system  33 . 
     At step {circle around (6)}, the action proceeds to the next sequence. Here, as the planet lever  55  is locked at the zoom system driving position by the lock lever  63  after a predetermined period of time has lapsed since the end of electricity supply to the shape-memory alloy  64 , the driving of the zoom system  33  in both directions is performed after the locking is completed as shown in FIG.  14 . This is because the planet lever  55  would be changed over to the film feed system  34  if the sun gear  47  were rotated counterclockwise before the lock lever  63  reaches the position for locking the planet lever  55 . The timing of driving in the next sequence may be set such as to be started when the switch  69  is turned on, or according to a timer setting by counting the time from when the electricity supply to the shape-memory alloy  64  is shut off. In the case of using a timer, the timer setting may be altered according to the temperature detected by a temperature sensor (not shown) provided in the camera  1 . This is because the cooling time of the shape-memory alloy varies depending on the ambient temperature. 
     As set forth above, when changing over transmission, it is possible to prevent such a disadvantage as to apply electricity to the motor  31  and to the shape-memory alloy  64  at the same time, as well as to achieve the transmission changeover reliably by starting electricity supply to the motor  31  after the electric heating of the shape-memory alloy  64  is stopped. 
     Further, the shape change of the shape-memory alloy  64  or the switchover actions of the lock lever  63  is detected by the switch  69 , by which the electric current to the shape-memory alloy  64  is shut off at the time when or after the amount of transformation of the shape-memory alloy  64  by electric heating has reached a predetermined value. It is thus possible to save electricity by minimizing the time for applying an electric current to the shape-memory alloy  64  and to ensure that the transmission changeover is certainly achieved by the transformation of the shape-memory alloy  64  by electric heating. 
     In a second example of sequence of actions shown in FIG. 17, the camera is in a state shown in FIG. 11 at step {circle around (1)}, and when electricity supply to the shape-memory alloy  64  is started at step {circle around (2)}, the alloy is heated and transforms to the memorized length, with which the lock lever  63  starts to rotate counterclockwise. 
     At step {circle around (3)}, it is judged whether a predetermined period of time which is set in a timer has lapsed since the start of electricity supply to the shape-memory alloy  64 , by which it is supposed that the lock lever  63  left the planet lever  55  and reached the position shown in FIG.  12 . 
     After the predetermined time has lapsed, the electric current to the shape-memory alloy  64  is shut off at step {circle around (4)}. The timer setting time, i.e., the above mentioned predetermined period of time may be changed according to the temperature detected by a temperature sensor (not shown) provided in the camera  1 . This is because the cooling time of the shape-memory alloy varies depending on the ambient temperature. 
     At step {circle around (5)}, as the electricity to the shape-memory alloy  64  is shut off, the transforming force of the shape-memory alloy  64  decreases with its temperature goes down, as a result of which the lock lever  63  rotates clockwise by the force of the spring  65  as shown in FIG. 13, but since it takes time for the lock lever  63  to come into the track of the planet lever  55 , it is started to apply electricity to the motor  31  to cause the planet lever  55  to rotate in a clockwise direction, so as to change over the planet lever  55  from the film feed system  34  to the zoom system  33 . 
     At step {circle around (6)}, the action proceeds to the next sequence. Here, as the planet lever  55  is locked at the zoom system driving position by the lock lever  63  after a predetermined period of time has lapsed since the end of electricity supply to the shape-memory alloy  64 , the driving action of the zoom system  33  in both directions is performed after the locking is completed as shown in FIG.  14 . This is because the planet lever  55  would be changed over to the film feed system  34  if the sun gear  47  were rotated counterclockwise before the lock lever  63  reaches the position for locking the planet lever  55 . The timing of driving in the next sequence may be set such as to be started when the switch  69  is turned on, or according to a timer setting by counting the time from when the electricity supply to the shape-memory alloy  64  is shut off. In the case of using a timer, the timer setting may be altered according to the temperature detected by a temperature sensor (not shown) provided in the camera  1 . This is because the cooling time of the shape-memory alloy varies depending on the ambient temperature. 
     As set forth above, the second example is different from the first example in that the timing for stopping electric heating of the shape-memory alloy  64  is set such as to be after a predetermined period of time has lapsed since the start of heating of the shape-memory alloy  64 , by which it is assured that the transmission changeover by the transformation of the shape-memory alloy  64  is reliably achieved before the electric heating is stopped without any special detecting means, thanks to an inner counting function provided in the control unit  68  shown in FIG.  15 . By changing the time setting according to the ambient temperature, it is prevented that the amount of transformation of the shape-memory alloy  64  by electric heating varies depending on the ambient temperature, by which it is avoided that, due to such variation of the amount of transformation, the transmission changeover is not achieved because the timing of ending electric heating is too early, or that the timing is too late and electric power is wasted. 
     In a third example of sequence of actions shown in FIG. 18, the camera is in a state shown in FIG. 11 at step {circle around (1)}, and when electricity supply to the shape-memory alloy is started at step {circle around (2)}, the alloy is heated and transforms to the memorized length, with which the lock lever  63  starts to rotate counterclockwise. 
     At step {circle around (3)}, the lock lever  63  leaves the planet lever  55  and further rotates counterclockwise until the switch  69  is turned off as shown in FIG.  12 . 
     In response to the switch  69  being turned off, the electricity supply to the motor  61  is started at step {circle around (4)} for rotating the sun gear  47  in a clockwise direction so as to cause the planet lever  55  to rotate clockwise as shown in FIG.  12 . 
     At step {circle around (5)}, it is awaited until a predetermined period of time, which is set in the timer, passes after the start of electricity supply to the motor  31 . This period may be the time necessary for the planet gear  56  of the planet lever  55  to uncouple the film feed system gear  62  and to mesh with the zoom system gear  61 . 
     At step {circle around (6)}, as the predetermined time has passed, the electric current to the shape-memory alloy  64  is shut off, with which the transforming force of the shape-memory alloy  64  decreases as its temperature goes down, and the lock lever  63  starts to rotate clockwise by the force of the spring  65  as shown in FIG.  13 . 
     At step {circle around (7)}, the action proceeds to the next sequence. Here, as the planet lever  55  is locked at the zoom system driving position by the lock lever  63  after a predetermined period of time has lapsed since the end of electricity supply to the shape-memory alloy  64 , the driving action of the zoom system  33  in both directions is performed after the locking is completed as shown in FIG.  14 . This is because the planet lever  55  would be changed over to the film feed system  34  if the sun gear  47  were rotated counterclockwise before the lock lever  63  reaches the position for locking the planet lever  55 . The timing of driving in the next sequence may be set such as to be started when the switch  69  is turned on, or according to a timer setting by counting the time from when the electricity supply to the shape-memory alloy  64  is shut off. In the case of using a timer, the timer setting may be altered according to the temperature detected by a temperature sensor (not shown) provided in the camera  1 . This is because the cooling time of the shape-memory alloy varies depending on the ambient temperature. 
     In a fourth example of sequence of actions shown in FIG. 19, the camera is in a state shown in FIG. 11 at step {circle around (1)}, and when electricity supply to the shape-memory alloy is started at step {circle around (2)}, the alloy is heated and transforms to the memorized length, with which the lock lever  63  starts to rotate counterclockwise as shown in FIG.  12 . 
     At step {circle around (3)}, the lock lever  63  leaves the planet lever  55  and further rotates counterclockwise until the switch  69  is turned off as shown in FIG.  12 . 
     In response to the switch  69  being turned off, the electricity supply to the motor  61  is started at step {circle around (4)} for rotating the sun gear  47  in a clockwise direction so as to cause the planet lever  55  to rotate clockwise as shown in FIG.  13 . 
     At step {circle around (5)}, it is detected whether the planet lever  55  has reached a predetermined transmission changeover position shown in FIG. 13 with a sensor (not shown) which detects positions of the planet lever  55 . 
     At step {circle around (6)}, when it is detected that the planet lever  55  has reached the predetermined position by the planet lever position sensor (not shown), the electric current to the shape-memory alloy  64  is shut off, with which the transforming force of the shape-memory alloy  64  decreases as its temperature goes down, and the lock lever  63  starts to rotate clockwise by the force of the spring  65  as shown in FIG.  13 . 
     At step {circle around (7)}, the action proceeds to the next sequence. Here, as the planet lever  55  is locked at the zoom system driving position by the lock lever  63  after a predetermined period of time has lapsed since the end of electricity supply to the shape-memory alloy  64 , the driving action of the zoom system  33  in both directions is performed after the locking is completed as shown in FIG.  14 . This is because the planet lever  55  would be changed over to the film feed system  34  if the sun gear  47  were rotated counterclockwise before the lock lever  63  reaches the position for locking the planet lever  55 . The timing of driving in the next sequence may be set such as to be started when the switch  69  is turned on, or according to a timer setting by counting the time from when the electricity supply to the shape-memory alloy  64  is shut off. In the case of using a timer, the timer setting may be altered according to the temperature detected by a temperature sensor (not shown) provided in the camera  1 . This is because the cooling time of the shape-memory alloy varies depending on the ambient temperature. 
     The third and fourth examples are different from the first and second examples in that electricity is applied to the motor  31  and the shape-memory alloy  64  at the same time, which is effective when the battery has a sufficient capacity of electric power for such simultaneous electricity supply to both members, and specifically, it is possible to ensure that the transmission changeover is certainly achieved because the lock lever  63  can be retained at its lock release position by the shape-memory alloy  64  even during the switchover action of the planet lever  55 . 
     Although the electricity supply to the motor  31  is started when the switch  69  is turned off in the third and fourth examples, it is also possible to count the timing with a timer from the start of electricity supply to the shape-memory alloy  64 , and also to start applying an electric current to the motor  31  at the same time depending on cases. By this means, the motor  31  can be warmed up by electricity from the process in which the transmission changeover is performed by electric heating of the shape-memory alloy  64 , which means that the transmission changeover action by the motor  31  can be started simultaneously with the completion of transmission changeover preparation, thus eliminating a delay in transmission changeover actions caused by warming up for driving. In the case of using a timer for counting the timing of starting electricity supply to the motor  31 , the timer setting may be altered according to the temperature detected by a temperature sensor (not shown) provided in the camera  1 . This is because the cooling time of the shape-memory alloy varies depending on the ambient temperature. 
     In addition to time counting with a timer as described above, the timing of ending electricity supply to the shape-memory alloy  64  may be determined by detecting resistance value when an electric current is applied to the shape-memory alloy  64  or by detecting temperature. 
     When the shape-memory alloy  64  heats up by electricity, the resistance value decreases in a certain relationship with this temperature. Also, the increase in temperature by electricity and an amount of shrinkage of the shape-memory alloy  64  have a certain relation. Thus, even more precise control is possible than with the time counting by the timer. 
     FIG. 20 to FIG. 22 show a fifth example in which the resistance is detected. As shown in FIG.  20  and FIG. 21, a resistance detection sensor  81  is provided for detecting the resistance of the shape-memory alloy  64 , according to which the timing of ending electricity supply to the shape-memory alloy  64  is determined. For this purpose, the resistance outputted from the resistance detection sensor  81  is inputted to the control unit  68  as shown in FIG.  21 . The control unit  68  judges whether the resistance inputted from the sensor  81  is a predetermined value as in the step {circle around (3)} in the flowchart of FIG. 22, and if it is the predetermined value, the electric current to the shape-memory alloy  64  is shut off. The control unit  68  performs such judgment with an inner function such as a microcomputer, but it is not limited to this. As other structures are more or less the same as the first example, like elements are given the same reference numerals, and the description thereof will be omitted. 
     FIG. 23 to FIG. 25 show a sixth example in which the temperature is detected. As shown in FIG.  23  and FIG. 24, a temperature sensor  82  is provided for detecting the temperature of the shape-memory alloy  64 , according to which the timing of ending electricity supply to the shape-memory alloy  64  is determined. For this purpose, the temperature outputted from the temperature sensor  82  is inputted to the control unit  68  as shown in FIG.  24 . The control unit  68  judges whether the temperature inputted from the sensor  82  is a predetermined value as in the step {circle around (3)} in the flowchart of FIG. 25, and if it is the predetermined value, the electric current to the shape-memory alloy  64  is shut off. The control unit  68  performs such judgment with an inner function such as a microcomputer, but it is not limited to this. As other structures are more or less the same as the first example, like elements are given the same reference numerals, and the description thereof will be omitted. 
     It is of course possible to apply such method of judging a state of transformation of the shape-memory alloy  64  by detection of temperature or resistance in the fifth and sixth examples to the detection of timings in accordance with transformation of the shape-memory alloy  64  in the third and fourth examples. 
     The member for locking the planet lever for transmission changeover is not limited to a lever, and other members which act linearly may be employed. However, by employing a lever, the transformation stroke of shape-memory alloy  64  can be variously converted by changing the proportion of lever lengths, and it is possible to minimize the necessary transformation stroke of the shape-memory alloy  64 . Also, the shape-memory alloy  64  can be disposed along a curved or crooked gap within the camera, as long as there is provided a guide such as a roller or a wall by which a linear transformation thereof can be utilized. Further, the shape-memory alloy  64  may be heated by a heater to which electricity is applied. Such heater may be coiled around the shape-memory alloy  64 , arranged in the form of a cylinder, touched at the alloy  64 , or disposed in the vicinity of the alloy  64 . It is also possible to heat the shape-memory alloy  64  other than by electricity depending on cases. 
     In the above described examples 1 to 6, the transformation of shape-memory alloy  64  is used for changing over the transmission changeover unit  32  into a state of being able to switch over transmission, and the actual transmission changeover action is performed by the motor  31 . 
     On the other hand, in a seventh example shown in FIG.  26  and FIG. 27, transmission changeover is achieved using the transformation of shape-memory alloy  64  for directly driving a transmission changeover means. For this purpose, the shape-memory alloy  64  is connected to the planet lever  55 , as well as a spring  83  for restoration is acted between the planet lever  55  and the camera body  1   a.  The shape-memory alloy  64  and the spring  83  are both connected to a lever piece  55   c  extending from a base of the planet lever  55 , but the way of connection may be freely selected. Other structures are substantially identical to those of the first to sixth examples except for specific action control of transmission changeover. Thus, like elements are given the same reference numerals and the description thereof will be omitted. 
     In the state shown in FIG. 26, electricity is not supplied to the shape-memory alloy  64  from the electric current control circuit  67 . Thus, the shape-memory alloy  64  is in an elongated state, and the planet lever  55  is retained at a position contacting to the stopper  57  by the force of the spring  83  in the clockwise direction so as to cause the planet gear  56  to mesh with the zoom system gear  61 . Accordingly, the rotation of the motor  31  in both directions is transmitted to the zoom drive system  35 . 
     In the state shown in FIG. 27, the shape-memory alloy  64  is supplied with electricity from the electric current control circuit  67 . Thus, the shape-memory alloy  64  is contracted to the memorized length to cause the planet lever  55  to rotate counterclockwise from the position shown in FIG. 26 against the force of the spring  83 . By this rotation, the planet lever  55  is maintained at a position contacting to the stopper  58  so as to cause the planet gear  56  to mesh with the film feed system gear  62 . Accordingly, the rotation of the motor  31  in both directions is transmitted to the rewind/thrust transmission system  50  and to the spool  52 . 
     When electricity from the current control circuit  67  to the shape-memory alloy  64  is shutoff under the state shown in FIG. 27, the unit  32  returns to the state shown in FIG. 26 due to the shape-memory alloy  64  stretching back to a predetermined length coupled with the pulling force of the spring  83 . 
     Control timings for starting and ending electricity supply to the shape-memory alloy  64 , rotating the motor  31  in both directions or stopping the rotation may be appropriately set according to the cases, where applicable, in the examples 1 to 6 described above. 
     In an eighth example shown in FIG. 28 to FIG. 30, transmission changeover is achieved by the transmission changeover unit  32  using extension and contraction of the shape-memory alloy  64  by electricity supply in corporation with the spring  83  via a ratchet mechanism  84 . The ratchet mechanism  84  includes a ratchet toothed wheel  85  comprising an eccentric cam  85   a  which couples to a fork  55   d  provided at one end of the planet lever  55  without play and a rotation shaft  85   b  in its center, and a movable table  86  which holds a ratchet lever  87  and is moved leftward and rightward in the figure for driving the ratchet toothed wheel  85  in a counterclockwise direction. For this reciprocating motion, the shape-memory alloy  64  is connected to the movable table  86  on a side toward which the movable table moves from the position shown in FIG. 28 to another shown in FIG. 29, whereas the spring  83  is connected to the other side toward which the movable table  86  returns from the position shown in FIG. 29 to another shown in FIG.  28 . Although not shown, it will be favorable for more stable actions if a guide for guiding the reciprocating movement of the movable table  86  is provided. The ratchet lever  87  is supported around a shaft  91  on the movable table  86  and maintained at a position where a hooked portion  87   a  at one end thereof is contacted to a stopper surface  89  of the movable table  86  by the counterclockwise force of a spring  88  so that the ratchet lever  87  is coupled with the ratchet toothed wheel  85 . The ratchet toothed wheel  85  is anyway provided with a proper means for preventing reverse rotation such as a leaf spring  92 . 
     Other structures are substantially identical to those of the first to sixth examples except for specific action control of transmission changeover. Thus, like elements are given the same reference numerals and the description thereof will be omitted. 
     In the state shown in FIG. 28, electricity is not supplied to the shape-memory alloy  64  from the electric current control circuit  67 , and the movable table  86  is located at its returned position. The planet lever  55  is located at a position where the planet gear  56  meshes with the zoom system gear  61 , and the eccentric cam  85   a  is stably retained in the position shown in the figure between the fork  55   d  of the planet lever  55 , contacting at two points P 1  and P 2  in a rotating direction to the fork  55   d.  The relation between the contacting positions of the eccentric cam  85   a  and the fork  55   d  remains identical irrespective of rotating position of the planet lever  55 , so the eccentric cam  85   a  is held stably throughout the rotation of the planet lever  55 . In the state shown in FIG. 28, the rotation of the motor  31  in both directions is transmitted to the zoom drive system  35 . 
     In the state shown in FIG. 28, when the shape-memory alloy  64  is supplied with electricity from the electric current control circuit  67 , the shape-memory alloy  64  is contracted to the memorized length to cause the movable table  86  to move leftward against the force of the spring  83 . By this movement, the ratchet lever  87  coupling with the ratchet toothed wheel  85  drives it to rotate counterclockwise by one pitch as shown in FIG.  29 A. Subsequently, when the electricity to the shape-memory alloy  64  from the current control circuit  67  is shut off, the shape-memory alloy  64  stretches back to its original length from the state shown in FIG.  29 A and causes the movable table  86  to return to the position shown in FIG. 28 in corporation with the spring  83 . At this time, the ratchet lever  87 , with the rotating movement around the shaft  91  against the force of the spring  88 , slides over one tooth of the ratchet toothed wheel  85  in a returning direction as shown in FIG. 29B, after which it returns to the position shown in FIG. 28 by the pulling force of the spring  88 . 
     Such rotation drive of the ratchet toothed wheel  85  by one pitch is achieved every time the start and the end of electricity supply to the shape-memory alloy  64  is repeated with the rotation of the eccentric cam  85   a,  and as the ratchet toothed wheel  85  rotates, the eccentric cam  85   a  coupling to the fork  55   d  causes the planet lever  55  to rotate counterclockwise. The planet gear  56  is thereby gradually disengaged from the zoom system gear  61  and comes to mesh with the film feed system gear  62  as shown in FIG. 30 when the ratchet toothed wheel  85  is rotated substantially a half round. At this point, by stopping rotation drive of the ratchet toothed wheel  85 , the rotation of the motor  31  in both directions is transmitted to the rewind/thrust transmission system  50  and to the spool  52 . 
     When the ratchet toothed wheel  85  is further driven to rotate counterclockwise as described above from the state shown in FIG. 30, the planet lever  55  is this time rotated clockwise from the position shown in FIG. 30 to cause the planet gear  56  to approach the zoom system gear  61  and eventually mesh therewith when the ratchet toothed wheel  85  is rotated substantially a half round as shown in FIG.  28 . At this point, by stopping rotation drive of the ratchet toothed wheel  85 , the unit  32  returns to the state where the rotation of the motor  31  in both directions is transmitted to the zoom drive system  35 . 
     Since the ratchet toothed wheel  85  has twelve teeth in the illustrated example, transmission is changed over from the state shown in FIG. 28 to the state shown in FIG.  30  and vice versa repeatedly in sequence by driving the ratchet toothed wheel  85  by six pitches. However, such number of rotation drive of the ratchet toothed wheel  85  for one switchover action may be variously determined, and it is possible to achieve the changeover by one rotation drive depending on cases. 
     Here, the start and end of the rotation drive of the ratchet toothed wheel  85  in the eighth example correspond to the start and end of electricity supply to the shape-memory alloy  64  in the examples 1 to 6. Thus, by interpreting the start and end of electricity supply to the shape-memory alloy  64  in the examples 1 to 6 as the start and end of the rotation drive of the ratchet toothed wheel  85  in the eight example, the control timings for rotating the motor  31  in both directions or stopping the motor  31  may be set according to the cases, where applicable, in the examples 1 to 6 described above. Further, in this embodiment where the eccentric cam  85   a  performs a switching over action, the stoppers  57 ,  58  as in the other examples are unnecessary. 
     In a ninth example shown in FIG.  31  and FIG. 32, transmission changeover is achieved using transformation of a shape-memory alloy  94  which is provided as a part of the transmission changeover unit  32 . In the illustrated example, the shape-memory alloy  94  is linked to a part of the planet lever  55  at one end, and its shape change which occurs between the plane t lever  55  side and other mounting portion on the camera body  1   a  side is used for transmission changeover. For example, shape change in a bending state such as a widened U-shaped form shown in FIG. 31 and a narrowed U-shaped form shown in FIG. 32 is used. A shape-memory alloy  94  of such configuration is also applicable as a part of the lock lever  63  in the first example for performing transmission changeover actions by changing over the lock lever  63  between the locking position and lock release position as required. Other structures are more or less the same as those of the seventh example. Thus, like numerals are given the same reference numerals and the description thereof will be omitted. 
     In the state shown in FIG. 31, electricity from the current control circuit  67  to the shape-memory alloy  94  is shut off. Thus, the shape-memory alloy  94  is bent in a wider U-shaped form, and the planet lever  55  is maintained at a position contacting to the stopper  57  by the force of the spring  83  in the clockwise direction so as to cause the planet gear  56  to mesh with the zoom system gear  61 . Accordingly, the rotation of the motor  31  in both directions is transmitted to the zoom drive system  35 . 
     In the state shown in FIG. 32, electricity is supplied from the current control circuit  67  to the shape-memory alloy  94 . Thus, the shape-memory alloy  94  changes its form to the memorized narrower U-shaped state to cause the planet lever  55  to rotate against the force of the spring  83  from the position shown in FIG. 31 in the counterclockwise direction. The planet lever  55  is maintained at a position contacting to the stopper  58  by this rotation to cause the planet gear  56  to mesh with the film feed system gear  62 . Accordingly, the rotation of the motor  31  in both directions is transmitted to the rewind/thrust transmission system  50  and to the spool  52 . 
     When electricity from the current control circuit  67  to the shape-memory alloy  94  is stopped under a state shown in FIG. 32, the shape-memory alloy  94  broadens to a predetermined wider U-shaped form, and the transmission changeover unit  32  returns to the state shown in FIG. 31 in corporation with the force of the spring  83 . 
     Control timings for starting and ending electricity supply to the shape-memory alloy  94 , rotating the motor  31  in both directions or stopping the rotation may be appropriately set according to the cases, where applicable, in the examples 1 to 6 described above. 
     The present invention is applicable to cases where more than three driven members are selectively driven by a single motor, and not limited to the above described embodiments or examples. For example, by dividing the shape-memory alloy  64  into a plurality of parts and controlling electricity supply to each part individually, a stroke consisting of several stages can be obtained, whereby it is possible to move the planet lever  55  to a plurality of positions for selectively transmitting a drive force to more than three driven members. 
     It is also to be noted that the transmission changeover mechanism which has been described above can be employed not only as a mechanism in cameras but also used, for example, for transmission changeover between popping-up and retracting actions and swinging actions of a side mirror in an automobile, and that the mechanism is favorably used in various other devices in which a plurality of driven members are selectively driven by a single drive power source. Also, transformation of the shape-alloy memory to its memorized shape is not limited to the above described cases which are caused by heating depending on its material or properties. 
     (Fourth Embodiment) 
     In a fourth embodiment, the present invention is applied to a lens shutter camera as shown in FIG.  33 . With this camera, a picture is taken by operating a shutter release button  7  provided at one end on the upper surface of a camera body  1   a  through a lens barrel  203  on the front face of the camera body  1   a.    
     The lens barrel  203  is provided with a focusing lens  204  as shown in FIG. 34, which is fixedly supported by a focusing lens support  205 . 
     The focusing lens support  205  is supported by the lens barrel  203  in such a way that the focusing lens  204  can move in a direction along an optical axis  207  of a filming lens system  206 . Other optical lenses of the filming lens system  206  are fixedly supported with respect to the lens barrel  203 . 
     The position of the focusing lens  204  along the direction of the optical axis  207  is detected by a position sensor  208 . The position sensor  208  detects the position of the focusing lens  204  by an optical, electric, or electromagnetic method and inputs data to a control unit  209 . The position sensor  208  illustrated in the figure is constructed to detect the position of the focusing lens support  205  with an optical method, and for example, the position of the focusing lens support  205  may be detected by the combination of an optical pattern (not shown) provided to the focusing lens support  205  and an optical sensor (not shown) disposed at a predetermined position of the lens barrel  203 . The position of the focusing lens support  205  may be also detected with an electric method, for example, by the combination of an electric pattern provided to a prescribed position of the lens barrel  203  and a brush contact piece provided on the focusing lens support  205  side. 
     In order to move the focusing lens  204  along the direction of the optical axis  207  for focusing, a shape-memory alloy  211  is directly mounted to the focusing lens support  205  at one end thereof in this embodiment. The other end of the shape-memory alloy  211  is connected to the lens barrel  203  which supports the focusing lens support  205 . 
     Although the shape-memory alloy  211  is directly connected to the focusing lens support  205  in this embodiment, in the case where the direction of displacement of the shape-memory alloy  211  and that of the focusing lens support  205  as a driven member in this embodiment are different from each other due to a restricted layout, the shape-memory alloy  211  may be bent on its middle part using a guide such as a pulley (not shown), or the direction of movement, i.e., the direction of stroke may be converted using a lever (not shown). If the movement of the driven member is a rotation, the direction of the stroke may be converted with a motion converting mechanism such as a rack and pinion. Also, as required, the amount of displacement of the shape-memory alloy  211  may be converted by changing, for example, the proportion of lever lengths in the case of using a lever or of pinion diameter in the case of using a rack and pinion. It is also possible to convert and transmit other motional properties such as displacement speed depending on motion converting mechanisms. The control unit  209  is a CPU which controls actions of the camera, but it is not limited to this, and other various control circuits may be used. 
     An electric wiring  221  is provided to the shape-memory alloy  211  so as to control application of an electric current to the shape-memory alloy  211  by controlling current on/off switching member  212  such as an electromagnetic switch or a switching element by the control unit  209 . 
     As shown in FIG. 34B, although the shape-memory alloy  211  is heated by directly applying an electric current thereto in this embodiment, a heater  271  such as a Nichrome wire which is heated by applying an electric current may be disposed in the vicinity of the shape-memory alloy  211 , and the heating control of the shape-memory alloy  211  may be achieved by controlling electricity supply to such heater. It is also possible to heat the shape-memory alloy  211  other than electricity depending on cases, or to cause the alloy to displace without heating it depending on materials or types of the shape-memory alloy  211 . 
     Next, a shooting action of the camera with focusing operation is described in accordance with the flow chart of FIG.  35 . 
     When the shutter release button  7  shown in FIG. 33 is operated, a release operation switch  214  is turned on, and this turn-on signal is inputted to the control unit  209 . In response to this, the control unit  209  prepares for shooting an object to be photographed, i.e., detects a distance to the object by a measuring means (not shown) and calculates a position where the focusing lens support  205  should be located. When this calculation is completed, the control unit  209  turns on the electric current on/off switching member  212 , and starts controlling electric heating of the shape-memory alloy  211 . When heated, the shape-memory alloy  211  shrinks so as to cause the focusing lens support  205  to move rightward from its home position shown in FIG.  34 . The position of the focusing lens support  205  is detected by the position sensor  208 , and when the focusing lens support  205  reaches a prescribed position which has been determined by the data from the measuring means, the electric current on/off switching member  212  is turned off to shut electricity to the shape-memory alloy  211 . After that, a shutter (not shown) opens and closes and completes exposure to a film, by which the shooting action is ended. 
     As set forth above, the focusing lens support  205  as one example of driven member can be driven and moved to a position at which it needs to be located that is determined by measurement of distance, using transformation of the shape-memory alloy  211  by heating. Especially in this case, the condition of the shape-memory alloy  211  heated by the electric wiring  221  as one example of heating means is controlled by the control unit  209  as one example of a controlling means based on data on the position of the focusing lens support  205  with the position sensor  208 . Thus, it is possible not only to move the focusing lens support  205  to a requested position by the transformation of the shape-memory alloy  211  by heating, but also to cause the same to remain at the same position, without generating any noises which would be caused by vibration of motors or toothed gears meshing with each other. Also, unlike a gear transmission system, there is no such disadvantage as to errors in position control caused by backlash. Since the transformation of the shape-memory alloy  211  is made linearly, the volume required for the mechanism is small and, for example, the mechanism can be installed between a cover and the main body of the camera, by which the space is saved, permitting the camera to be compact. 
     Also, as the shape-memory alloy  211  is directly connected at its one end to a lens barrel  203  side which is a support member for movably supporting the focusing lens support  205  as a driven member and directly fixed at the other end to the focusing lens support  205  which is the driven member, the transformation of the shape-memory alloy  211  by heating can be directly acted for driving and moving the focusing lens support  205  to a required position, the structure is simplified, errors in movement will be minimized, and response speed will be increased. 
     (Fifth Embodiment) 
     In a fifth embodiment, as shown in FIG. 36, the shape-memory alloy  211  between the focusing lens support  205  which fixedly supports the focusing lens  204  and the lens barrel  203  is divided into several parts, and provided with electric wiring  221  for partial electricity supply. 
     As shown, the shape-memory alloy  211  is divided into four parts a, b, c, and d. 
     When a first switch  212   a  of the electric current on/off switching member  212  is turned on, the shape-memory alloy  211  is supplied with an electric current through all the parts a-d, and the shape-memory alloy  211  is shortened by a certain amount Δ 1 , to cause the focusing lens support  205  to move rightward by the amount Δ 1 . 
     When a second switch  212   b  is turned on, parts a to c of the shape-memory alloy  211  are supplied with an electric current, and the shape-memory alloy  211  is shortened by a certain amount Δ 2 , to cause the focusing lens support  205  to move rightward by the amount Δ 2 . 
     When a third switch  212   c  is turned on, parts a to b of the shape-memory alloy  211  are supplied with an electric current, and the shape-memory alloy  211  is shortened by a certain amount Δ 3 , to cause the focusing lens support  205  to move rightward by the amount Δ 3 . 
     When a fourth switch  212   d  is turned on, the part a of the shape-memory alloy  211  is supplied with an electric current, and the shape-memory alloy  211  is shortened by a certain amount Δ 4 , to cause the focusing lens support  205  to move rightward by the amount Δ 4 . 
     Since there is a relation of Δ 1 &gt;Δ 2 &gt;Δ 3 &gt;Δ 4  between these parts a to d, a predetermined amount of displacement of the focusing lens support  205  can be obtained by selectively turning on the switches  212   a  to  212   d.    
     As described above, dividing a shape-memory alloy  211  of a straight form which transforms to its memorized shape linearly into a plurality of parts and heating these parts selectively permit choices of displacement amount of the shape-memory alloy  211 . But then, if the shape-memory alloy  211  is divided into parts a to d with different lengths or different transformation amount into a memorized shape, various kinds of displacement amount as many as the number of divided parts can be achieved only by selecting one part to which electricity is supplied. Combining this with the selection of numbers of parts to which electricity is supplied will permit an even wider range of choices of displacement amount. 
     Other structures and effects are substantially identical to those of the fourth embodiment. Like elements are given the same reference numerals and the description thereof will be omitted. 
     Next, a shooting action of the camera with focusing operation is described in accordance with the flow chart of FIG.  37 . 
     When the shutter release button  7  is operated, a distance to the object to be photographed is detected by a measuring means (not shown) and a position where the focusing lens support  205  should be located is calculated, in response to which the control unit  209  decides which switches  212   a  to  212   d  of the electric current on/off switching member  212  should be turned on. When the switch which has been selected by the control unit  209  is turned on and electricity is supplied to the shape-memory alloy  211 , the part of the alloy to which electricity is supplied shrinks so as to cause the focusing lens support  205  to move rightward from its home position shown in FIG.  36 . After a predetermined period of time for allowing the shape-memory alloy  211  to transform has passed, electricity supply to the shape-memory alloy  211  is shut off by controlling the electric current on/off switching member  212 . After that, a shutter (not shown) opens and closes and completes exposure to a film, by which the shutter release action is ended. 
     (Sixth Embodiment) 
     In a sixth embodiment shown in FIG. 38, the focusing lens support  205  to which the shape-memory alloy  211  is connected is provided with a spring  231  which biases the support  205  toward a direction opposite to the direction of movement of the shape-memory alloy  211  when transformed by heating. The shape-memory alloy  211  is normally transformed by the pulling force of the spring  231  and stretched longer than the memorized shape, retaining the focusing lens support  205  at its home position contacting to a stopper  232 . 
     Other structures and effects are substantially identical to those of the fourth embodiment. Thus, like elements are given the same reference numerals and the description thereof will be omitted. 
     Next, a shooting action of the camera with focusing operation is described in accordance with the flow chart of FIG.  39 . 
     When the shutter release button  7  is operated, a distance to the object to be photographed is detected by a measuring means (not shown) and a position where the focusing lens support  205  should be located is calculated, in response to which the control unit  209  starts control of electric heating to the shape-memory alloy  211 . When heated, the shape-memory alloy  211  shrinks so as to cause the focusing lens support  205  to move rightward from its home position shown in FIG. 38 against the force of the spring  231 . The position of the focusing lens support  205  is detected by the position sensor  208 , and when the focusing lens support  205  reaches a prescribed position which has been determined by the data from the measuring means, the electric current on/off switching member  212  is turned off to shut electricity to the shape-memory alloy  211 . When electricity is shut off, the shape-memory alloy  211  cools down gradually and decreases its transforming force, in accordance with which the focusing lens support  205  moves leftward in FIG. 38 by the force of the spring  231 . Since this movement is detected by the position sensor  208 , if the focusing lens support  205  is displaced from a position determined by the data from the measuring means, electricity supply to the shape-memory alloy  211  is restarted by controlling the electric current on/off switching member  212 . It is thus possible to maintain the focusing lens support  205  to stay at a predetermined position by controlling on/off switchover of electricity based on the data from the position sensor  208 . 
     There is another such possible method as described below, in which heating element such as the electric wiring  221  is controlled based on the data from a displacement detecting means of the shape-memory alloy  211  such as the position sensor  208 . 
     When the shutter release button  7  is operated, a distance to the object to be photographed is detected by a measuring means (not shown) and a position where the focusing lens support  205  should be located is calculated, in response to which the control unit  209  starts control of electric heating to the shape-memory alloy  211 . When heated, the shape-memory alloy  211  shrinks so as to cause the focusing lens support  205  to move rightward from its home position shown in FIG. 38 against the force of the spring  231 . The position of the focusing lens support  205  is detected by the position sensor  208 , and when the focusing lens support  205  reaches a prescribed position which has been determined by the data from the measuring means, an electric current supply to the shape-memory alloy  211  is adjusted by controlling the electric current on/off switching member  212 . Although the focusing lens support  205  is biased leftward in FIG. 38 by the spring  231 , the pulling force of the spring  231  and the transforming force of the shape-memory alloy  211  are balanced by adjusting the electric current so as to maintain the focusing lens support  205  to be at a predetermined position. The electric current amount may be varied depending on the position of the focusing lens support  205 , i.e., the force of the spring  231 . 
     While the focusing lens support  205  is retained at a predetermined location, a shutter (not shown) opens and closes and completes exposure to a film, by which the shutter release action is ended. After that, electricity supply to the shape-memory alloy  211  is shut off by controlling the electric current on/off switching member  212 , by which the shape-memory alloy  211  cools down gradually and decreases its transforming force. In accordance with this, the focusing lens support  205  moves leftward in FIG. 38 by the force of the spring  231 , until it strikes the stopper  232 , which is its home position. 
     (Seventh Embodiment) 
     In a seventh embodiment shown in FIG. 40, the shape-memory alloy  211  of the fifth embodiment which is divided into parts a to d is employed in the configuration of the sixth embodiment, by which electricity is supplied partially by the switches  212   a  to  212   d  of the electric current on/off switching member  212 . Other structures and effects are substantially identical to those of the sixth embodiment. Thus, like elements are given the same reference numerals and the description thereof will be omitted. 
     Next, a shooting action of the camera with focusing operation is described in accordance with the flow chart of FIG.  41 . 
     When the shutter release button  7  is operated, a distance to the object to be photographed is detected by a measuring means (not shown) and a position where the focusing lens support  205  should be located is calculated, in response to which the control unit  209  decides which switches  212   a  to  212   d  of the electric current on/off switching member  212  should be turned on. When the switch which has been selected by the control unit  209  is turned on and electricity is supplied to the predetermined part from a to d of the shape-memory alloy  211 , this part of the alloy to which electricity is supplied shrinks so as to cause the focusing lens support  205  to move rightward from its home position shown in FIG.  40 . After a predetermined period of time for allowing the shape-memory alloy  211  to transform has passed, a shutter (not shown) opens and closes and completes exposure to a film, by which the shutter release action is ended. 
     After that, electricity supply to the shape-memory alloy  211  is shut off by controlling the electric current on/off switching member  212 , by which the shape-memory alloy  211  cools down gradually and decreases its transforming force. In accordance with this, the focusing lens support  205  moves leftward in FIG. 40 by the force of the spring  231 , until it strikes the stopper  232 , which is its home position. 
     (Eighth Embodiment) 
     In an eighth embodiment shown in FIG. 42, the focusing lens support  205  as the driven member to which the shape-memory alloy  211  is connected is provided with a second shape-memory alloy  241  which transforms by heating such as to drive the focusing lens support  205  in a direction opposite to the driving direction of the shape-memory alloy  211 . This second shape-memory alloy  241  is also provided with an electric wiring  242  for supplying electricity, and on/off switchover is controlled by the control unit  209  by controlling an electric current on/off switching member  243  provided to the electric wiring  242 , similarly like the first shape-memory alloy  211 . 
     Other structures and effects are substantially identical to those of the fourth embodiment. Thus, like elements are given the same reference numerals and the description thereof will be omitted. 
     In such a configuration, after heating the shape-memory alloy  211  for driving by its transformation the focusing lens support  205  to move to a predetermined position, the second shape-memory alloy  241  is heated, by which the focusing lens support  205  can be swiftly returned to its home position due to the quick transformation of the alloy. Accordingly, it is possible to prepare promptly for a next shooting action. 
     (Ninth Embodiment) 
     In a ninth embodiment shown in FIG. 43, the driven member is applied to zoom drive of an electronic flash  251  in cameras. A position control driving mechanism which is substantially the same as that provided to the focusing lens support  205  in the seventh embodiment is acted to a zooming flash support  254  which supports a light source  252  for the flash  251  and a reflection umbrella  253 . More specifically, the zooming flash support  254  is connected to the shape-memory alloy  211  which is divided into four parts a to d for causing the support  254  from its home position to a position according to a distance to an object to be photographed which is detected by the measuring means, and further provided with the spring  231  for causing the zooming flash support  254  to return to the home position which is defined by the stopper  232 . The control unit  209  decides which part of the shape-memory alloy  211  should be supplied with electricity, and controls electricity supply through the electric current on/off switching member  212 . 
     By this configuration, when zooming operation is performed to the camera, a position where the zooming flash support  254  needs to be located is calculated together with the necessary position of the zooming lens support, and the control unit  209  decides which of the switches  212   a  to  212   d  of the electric current on/off switching member  212  should be turned on. When the switch which has been selected by the control unit  209  is turned on and electricity is supplied to a predetermined part from a to d of the shape-memory alloy  211 , this part of the alloy to which electricity is supplied shrinks so as to cause the zooming flash support  254  to move rightward from its home position shown in FIG. 43 to prepare for the shooting. In this state, a shutter (not shown) opens and closes and completes exposure to the film, by which the shutter release action is ended. At the same time, electricity supply to the shape-memory alloy  211  is shut off and the zooming flash support  254  is returned to the home position by the force of the spring  231 . 
     (Tenth Embodiment) 
     In a tenth embodiment shown in FIG. 44, the driven member is applied to zoom drive of a zooming lens system  261  of cameras. A position control driving mechanism which is substantially the same as that provided to the focusing lens support  205  in the seventh embodiment is acted to a zooming lens support  262  which supports the zooming lens system  261 . More specifically, the zooming lens support  262  is connected to the shape-memory alloy  211  which is divided into four parts a to d for causing the support  262  from its home position to a position according to a distance to an object to be photographed which is detected by the measuring means, and further provided with the spring  231  for causing the zooming lens support  262  to return to the home position which is defined by the stopper  232 . The control unit  209  decides which part of the shape-memory alloy  211  should be supplied with electricity, and controls electricity supply through the electric current on/off switching member  212 . 
     By this configuration, when zooming operation is performed to the camera, a position where the zooming lens support  262  needs to be located is calculated, and the control unit  209  decides which of the switches  212   a  to  212   d  of the electric current on/off switching member  212  should be turned on. When the switch which has been selected by the control unit  209  is turned on and electricity is supplied to a predetermined part from a to d of the shape-memory alloy  211 , this part of the alloy to which electricity is supplied shrinks so as to cause the zooming lens support  262  to move rightward from its home position shown in FIG. 44 to prepare for the shooting. 
     In this state, a shutter (not shown) opens and closes and completes exposure to the film, by which the shutter release action is ended. At the same time, electricity supply to the shape-memory alloy  211  is shut off, and the zooming lens support  262  is returned to its home position by the force of the spring  231 . 
     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.