Motor, motor device, and lens drive mechanism using the same

An arrangement of the invention includes a base block 16, a cylindrical cam 14, as a rotary member, which is rotatably supported on the base block 16, and includes a contact portion on an outer periphery thereof for outputting a rotating force, a drive gear 21, as an oscillatory ring, which includes a contact portion on an inner periphery thereof, and is oscillated on a plane perpendicular to a rotation axis of the cylindrical cam 14 in contact with the contact portion of the cylindrical cam 14, parallel springs 23 through 26, as a position retainer, for retaining the position of the drive gear 21, and three or more shape metal alloy actuators (SMA) wires 35 through 38, as expandable and contractible actuators, with both ends of the each SMA wire being fixed to the base block 16 for contact with the drive gear 21.

This application is based on Japanese Patent Application No. 2005-155498 and No. 2006-25885 filed on May 27, 2005, and Feb. 2, 2006, respectively, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motor for generating a rotation driving force using a shape memory alloy, a motor device, and a lens drive mechanism incorporated with the motor for use in an image sensing apparatus.

2. Description of the Related Art

The shape memory alloy (SMA) is generally used for an actuator which is actuated in response to a change of ambient temperature. For instance, the SMA is used for a valve portion to regulate the temperature of hot water in a hot water system, or for the purpose of varying a ventilating opening in accordance with a temperature change of external air. In the above usage, it is often the case that the SMA is molded into a coil spring, which is used in combination with a rectilinear reciprocating mechanism.

Japanese Unexamined Patent Publication No. 7-327380 discloses an SMA actuator which is designed to generate heat with its own Joule heat by energization thereto for actuation. As an example of the SMA actuator, there is disclosed an electric motor incorporated with rotary actuators, wherein the linear type SMA actuators are provided. Specifically, the electric motor adopts a crank mechanism, in which one ends of the substantially U-shaped SMA actuators are circumferentially and equidistantly supported on a disk-like base block, and the other ends thereof are circumferentially and equidistantly supported on a rotary drive member, which is rotatably mounted on a rotor at an eccentric position of the rotor. As the SMA actuators are sequentially expanded and contracted, the distance between the other end of the corresponding SMA actuator, and the rotary drive member is varied, thereby rotating the rotor.

In the above conventional crank mechanism, a displacement amount of each SMA actuator is significantly small, and a sufficient pivotal rotation of the rotor is difficult by the mechanism having the small number of SMA actuators as proposed in the conventional arrangement. Also, if the number of the SMA actuators is decreased, the crank diameter of the crank mechanism is decreased, which means generation of a small torque. The increased number of the SMA actuators leads to generation of a large torque, however, it may lower the rotation number of the rotor, make the assembling of the crank mechanism complicated, and raise the production cost. Increasing the axis diameter of the SMA actuator may avoid complex assembling of the mechanism to some extent. However, a required response time may be unduly extended in view of a relation between the volume and the surface area of the SMA actuators, with the result that the rotating speed of the rotor may be lowered, as compared with a case where an increased number of SMA actuators is used. Also, increasing the length of the SMA actuator may increase the size of the actuator itself.

In the electric motor employing the rotary actuators, a crank rod is provided at a center of rotation of the rotor. Accordingly, it is impossible to arrange the electric motor coaxially with a lens optical system, considering driving of the lens optical system, and it is necessary to dispose the electric motor on the side of a lens barrel, for instance. This may lead to increase the size of an image sensing apparatus incorporated with the electric motor.

SUMMARY OF THE INVENTION

In view of the above problems residing in the prior art, it is an object of the present invention to provide an SMA-based quiet and compact motor that enables to generate a large rotation driving force, and be assembled into a cylindrical configuration so as to drive a lens element substantially coaxially with an optical system, as well as a motor device, and a lens drive mechanism incorporated with the motor.

According to an aspect of the invention, a motor comprises: a base block; a rotary member which is rotatably supported on the base block, and includes a contact portion on an outer periphery thereof for outputting a rotating force; an oscillatory ring which includes a contact portion on an inner periphery thereof, and is oscillated on a plane perpendicular to a rotation axis of the rotary member in contact with the contact portion of the rotary member; a position retainer for retaining a position of the oscillatory ring; and three or more expandable and contractible actuators each in the form of a wire or a belt, the each actuator having both ends thereof being fixed to the base block for contact with the oscillatory ring.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the invention are described referring to the drawings.

First Embodiment

FIG. 1is a perspective view showing a construction of a zoom unit for use in an image sensing apparatus, which serves as a lens drive mechanism in accordance with a first embodiment of the invention. The zoom unit1includes ring frames11,12for supporting an unillustrated lens element on respective inner surfaces thereof, a fixed cylinder13, a cylindrical cam14, and a driver assembly15. The zoom unit1is mounted on a base block16.

The ring frames11and12has three projections11aand12b, respectively. The ring frames11and12are accommodated in the fixed cylinder13and the cylindrical cam14in this order in such a manner that the projections11aof the ring frame11are received in a through groove13aof the fixed cylinder13and in corresponding through grooves14aof the cylindrical cam14, and the projections12bof the ring frame12are received in a through groove13bof the fixed cylinder13and in corresponding through grooves14bof the cylindrical cam14. The fixed cylinder13is fixed to the base block16. The through grooves13aand13bof the fixed cylinder13each has such a configuration that its axial displacement is converted into a circumferential rotation thereof. On the other hand, the through grooves14a,14bof the cylindrical cam14extend in an axial direction of the cylindrical cam14. As will be described later, in response to rotational driving of the cylindrical cam14, each of the projections11aof the ring frame11is moved along an intersection of the corresponding through groove14aof the cylindrical cam14and the through groove13aof the fixed cylinder13, and each of the projections12aof the ring frame12is moved along an intersection of the corresponding through groove14bof the cylindrical cam14and the through groove13bof the fixed cylinder13. Thereby, the distance between the ring frames11and12is varied to thereby adjust the focal length of an optical system.

The cylindrical cam14, as a rotary cylinder and an output rotary member, is rotatably supported on the base block16. Teeth14cas a contact portion are formed along an outer circumference of a base end of the cylindrical cam14. A part of the teeth14cis allowed to be meshed with a part of teeth21c, which serve as a contact portion. The teeth21cis formed along an inner circumference of a drive gear21, which serves as an oscillatory ring or an oscillatory member of the driver assembly15. The drive gear21is mounted on the base block16, and is housed in an annular intermediate frame22having an inner diameter larger than an outer diameter of the drive gear21in such a manner that the drive gear21is allowed to be movable solely in y-direction i.e. vertical directions on the plane ofFIG. 1within an accommodating space22adefined in the intermediate frame22by a pair of parallel springs23and24. The intermediate frame22is supported on an annular wall of the base block16, and is allowed to be movable solely in x-direction i.e. transverse directions on the plane ofFIG. 1by a pair of parallel springs25and26. Thus, the drive gear21is oscillatory supported on the base block16, with its rotation being restrained, namely, the position thereof being retained.

FIG. 2is an illustration schematically showing the driver assembly15in the zoom unit1having the above construction. Four cylindrical projections31,32,33, and34are attached circumferentially and substantially equidistantly away from each other by 90° about the center of rotation of the cylindrical cam14. Longitudinally and substantially middle parts of shape metal alloy (SMA) actuators35,36,37, and38each in the form of a wire or a belt (hereinafter, called as “SMA wires”) are wound over the cylindrical projections31,32,33, and34, respectively. Both ends of each SMA wire35,36,37,38are caulked by terminals39, respectively. Thus, the SMA wires35through38are fixed to the base block16at the respective fixed positions in such a manner that each SMA wire35,36,37,38is bent into a substantially L-shape at the corresponding cylindrical projection.

Each SMA wire35,36,37,38has a thin string-like shape, with a shorter size in cross-section in a direction perpendicular to a longitudinal direction thereof, i.e. a smallest diameter, of e.g. 100 μm or less. Each SMA wire35,36,37,38is made of e.g. Ni—Ti—Cu alloy. The SMA wire made of Ni—Ti—Cu alloy has a distortion amount of about 4%. Assuming that the length of each SMA wire35,36,37,38is 40 mm, a stroke of 1.6 mm can be obtained. If each SMA wire35,36,37,38is wound on the drive gear21with a bent angle of 120° at the corresponding cylindrical projection, an eccentricity amount of the drive gear21is about 1.715 mm, which provides precision sufficient for designing a drive mechanism. In the example ofFIGS. 1 and 2, the four cylindrical projections are arranged away from each other by 90° about the center of rotation of the cylindrical cam14. Alternatively, three projections, or more than four projections may be provided. Also, the middle parts of the SMA wires35through38may be interconnected to the drive gear21by way of a sleeve engagement, a resilient hinge, or a like engagement, in place of using the cylindrical projections31through34.

The both ends of each SMA wire35,36,37,38are caulked by the terminals39, respectively. The terminals39each is constituted of a conductive member, and connected to an unillustrated drive circuit. With this arrangement, the SMA wires35through38are energizable individually by the drive circuit. The SMA wires35through38each memorizes its contraction amount of a certain size in advance. When each SMA wire35,36,37,38generates heat in response to energization thereto by the drive circuit, the temperature of each SMA wire35,36,37,38reaches a certain temperature. Thereby, each SMA wire35,36,37,38is contracted into its memorized initial shape. On the other hand, when each SMA wire35,36,37,38is de-energized, the temperature thereof is lowered, and as a result, the elastic modulus thereof is lowered.

FIGS. 3A through 3Dare timing charts describing energization controls of the SMA wires35through38, respectively. At the timing t1, a current is supplied to none of the SMA wires35through38. Accordingly, the SMA wires35through38pull each other with a moderate force in a well-balanced manner, and retain their initial states where energization to the SMA wires35through38is suspended. In this state, the drive gear21is not interconnected to the cylindrical cam14.

At the timing t2, when one of the SMA wires35through38is energized, (hereinafter, the control is described by taking an example of the SMA wire35), and heat is generated, the energized SMA wire35is contracted into its memorized shape against resilient forces of the SMA wire36through38to which the current is not supplied. The restoring force capable of restoring the shape of the SMA wire to its memorized shape differs depending on the temperature of the SMA wire. Accordingly, it is possible to regulate the restoring force of each SMA wire35,36,37,38by controlling the current value for energization so as to regulate the heat generating temperature of each SMA wire35,36,37,38.

The energization to the SMA wire35is continued until the timing t3, at which the energization is suspended.FIG. 2shows a state that the energization to the SMA wire35is suspended at the timing t3. Since the SMA wire35is contracted from its initial shape, the drive gear21receives a force in y direction, whereby the drive gear21is interconnected to the cylindrical cam14. Then, at the timing t3, the SMA wire36is started to be energized. When a current is supplied to the SMA wire36, similarly to the case of the SMA wire35, the SMA wire36is contracted against resilient forces of the non-energized SMA wires35,37, and38. At this time, since the drive gear21has already been interconnected to the cylindrical cam14, the cylindrical cam14is rotated counterclockwise as shown by the arrow CC inFIG. 2due to the contraction force of the SMA wire36.

The energization to the SMA wire36is continued until the timing t4, at which the energization is suspended. Thereafter, similarly to the above control, the SMA wire37is energized until the timing t5, and then, the SMA wire38is energized until the timing t6, thereby enabling to keep rotating the cylindrical cam14counterclockwise. In other words, the cylindrical cam14is rotated counterclockwise by energizing the SMA wires in the order of35,36,37, and38in clockwise direction. A rotation angle δ of the cylindrical cam14in this driving is represented by the following equation, assuming that Z1represents the number of the teeth21cof the drive gear21, and Z2represents the number of the teeth14cof the cylindrical cam14.
δ=(Z1−Z2)/Z2×360°

Conversely to the above, the cylindrical cam14is rotated clockwise by energizing the SMA wires in the order of38,37,36, and35in counterclockwise direction. Thus, the cylindrical cam14as the output rotary member, the base block16, the drive gear21constituting the driver assembly15, the intermediate frame22, and the SMA wires35through38constitute a motor. The motor capable of changing its rotating direction merely by changing the order of driving the SMA wires in the embodiment is useful because there is no need of detecting the position of the SMA wire whose energization is suspended in the previous driving, and specifying the SMA wire whose energization is to be started.

Now, the above driving is observed in the aspect of phase. Assuming that a period from the point of time when a first-time energization to the SMA wire35is started to the point of time when the energization to the SMA wire35is resumed is defined as a cycle T, a time interval between the timings t2and t3, between the timings t3and t4, between the timings t4and t5, and between the timings t5and t6(or t2) corresponds to a time duration obtained by dividing the cycle T by four. In other words, energization to the SMA wires35through38is conducted by phase displacement of 90°. Specifically, the energization timing for the respective SMA wires35through38is determined in conformity to the angular displacement (=90°) of the cylindrical projections31through34. Accordingly, if three cylindrical projections are disposed away from each other by 120°, it is possible to perform a driving similar to the above driving by using three SMA wires and by shifting the energization timing for the respective SMA wires by 120° in phase.

In the embodiment, the energization period Ton for the respective SMA wires35through38is made coincident to the time duration obtained by dividing the cycle T by four. Alternatively, the energization period Ton may be shortened. A shortened energization period may decrease a torque to be generated, but lowers a required electric power, which is effective in energy saving. In other words, it is optional to define the energization period Ton relative to the time duration obtained by dividing the cycle T by four. It is possible to control the characteristics of the motor based on the energization period Ton. The rotating speed of the cylindrical cam14can be varied by varying the cycle T.

With the above arrangement, the contraction and expansion of the linear-type SMA wire35,36,37,38having a high responsive rate and capable of generating a large force can be converted into a rotating force by the oscillatory drive gear21with its rotation being restrained, namely, the position thereof being retained, whereby the cylindrical cam14can be drivingly rotated. This enables to produce the compact and less costly zoom unit1. The zoom unit1is incorporated in a lens barrel of an unillustrated lens device. It is needless to say that the lens device can be arbitrarily designed with use of well-known means.

The above description is made on a premise that the teeth14cof the cylindrical cam14are external teeth, and the teeth21cof the drive gear21are internal teeth. Alternatively, a bevel gear or an equivalent member may be used so that the teeth14cof the cylindrical cam14and the drive gear21are meshed with each other in the optical axis direction of the zoom unit1. The teeth may have an arbitrary shape such as a cycloid, in place of the involute teeth as shown inFIG. 1.

Second Embodiment

FIG. 4is an illustration schematically showing a construction of a driver assembly15′ in a zoom unit for use in an image sensing apparatus, which serves as a lens drive mechanism in accordance with a second embodiment of the invention.FIG. 5is a cross-sectional view taken along the line X-X inFIG. 4. Elements inFIG. 4which are equivalent to those inFIG. 2and have the same arrangement as the arrangement inFIG. 2are denoted by the same reference numerals, and elements inFIG. 4whose arrangement is similar to those inFIG. 2are denoted by the like reference numerals with an apostrophe ′ attached thereto. In the driver assembly15′, a drive gear21is directly supported on a base block16′ by a support rod41, in place of the intermediate frame22and the parallel spring pairs23,24; and25,26.

In this embodiment, at least one e.g. four support rods41are provided. In the case where the plural support rods41are provided, the support rods41are substantially equidistantly arranged along a circumference of a drive gear21. Each support rod41has an elasticity in x-direction and y-direction, but is devoid of elasticity in a torsional direction. With this arrangement, the drive gear21is allowed to be movable solely in x-direction and y-direction with respect to the base block16′, and the drive gear21is oscillated with its rotation being restrained, namely, the position thereof being retained.

In the arrangement described in the second embodiment, expansion and contraction of linear-type SMA wires35through38made of a shape metal alloy can be converted into a rotating force by the drive gear21which is oscillated with its position retained, thereby enabling to drivingly rotate a cylindrical cam14.

Third Embodiment

FIG. 6is an exploded perspective view showing an example of an arrangement of a focus lens drive mechanism (hereinafter, called as “focus unit”) in accordance with a third embodiment of the invention. The focus unit2includes a bias spring51, a rectilinear guide cylinder52, a focus lens element53, a cylindrical cam54, an annular gear55, a position retaining guide56, and a base block57. In this arrangement, the focus lens element53is guided merely in an optical axis direction of the focus unit2by the rectilinear guide cylinder52. Also, the focus lens element53comes into pressing contact with the cylindrical cam54by an urging force of the bias spring51acting in a forward direction along the optical axis of the focus unit2. The cylindrical cam54has a cam surface541extending in the optical axis direction, and an outer cycloid gear542at a radially outer position. The cylindrical cam54is rotatably supported about the optical axis.

The ring-like annular gear55is arranged around an outer surface of the cylindrical cam54. The annular gear55has an inner cycloid gear551. The inner cycloid gear551of the annular gear55and the outer cycloid gear542of the cylindrical gear54are interconnected to each other by gear engagement. Also, rotation of the annular gear55about the optical axis is restrained by the position retaining guide56. The position retaining guide56is, for instance, a substantially L-shaped guide rod or a guide member. An end portion561and the other end portion562of the position retaining guide56are loosely received in the annular gear55, specifically, in a through-hole5521, serving as a receiving portion, of a support member552formed on the annular gear55, and in the base block57provided around the outer surface of the annular gear55, specifically, in a through-hole5711, serving as a receiving portion, of a support member571formed on the base block57, respectively, so that the position retaining guide56is slidably movable in the respective axial directions of the one end portion561and the other end portion562. With this arrangement, the base block57and the annular gear55are made slidably movable in orthogonal directions to each other. In other words, the guide member, and the receiving portions constitute a guide mechanism, which is adapted to retain the position of the annular gear55relative to the base block57i.e. the focus unit2.

Four cylindrical projections553each extending in the optical axis direction are arranged circumferentially and substantially equidistantly away from each other by 90°. Four SMA wires58a,58b,58c, and58dare provided on the base block57in a state that each SMA wire58a,58b,58c,58dis wound into a substantially L-shape over the corresponding cylindrical projection553, with a certain tension force being applied thereto. Substantially middle parts of the respective SMA wires58a,58b,58c,58dcome into contact with the corresponding cylindrical projection553. Both ends of each SMA wire58a,58b,58c,58dare jointed to SMA retaining blocks572fixedly attached to an upper circumferential surface of the base block57. In this embodiment, eight SMA retaining blocks572are provided. The substantially L-shaped SMA wire58a,58b,58c,58dis obtained by angularly displacing the SMA wires from each other by 90° about the optical axis. Each SMA retaining block572is connected to an unillustrated drive circuit so that a current is selectively supplied to the SMA retaining blocks572. The base block57is fixed to an unillustrated fixing member to support the SMA wires58athrough58d, and the position retaining guide56.

FIG. 7is an illustration schematically showing a drive state of the focus unit2shown inFIG. 6, viewed from the optical axis direction, in which the respective parts are assembled together. InFIG. 7, the bias spring51and the SMA retaining blocks572are not illustrated. Also, as shown inFIG. 7, the two support members571are formed on the base block57.

FIGS. 8A through 8Dare timing charts showing energization timings for the SMA wires58athrough58d, respectively. The upper through the lower timing charts are timing charts for supplying a current to the SMA wires58a,58b,58c, and58din this order. Each SMA wire58a,58b58c,58dmemorizes its contraction amount of a certain size. The SMA wires58athrough58dare so configured that when the temperature of each SMA wire58a,58b,58c,58dreaches a certain temperature by energization thereto, each SMA wire58a,58b,58c,58dis restored into its memorized shape.

Referring toFIGS. 7 and 8, as well asFIG. 9to be described later, a driving operation of the annular cam54and the annular gear55of the focus unit2is described. Referring toFIGS. 8A through 8D, a current is supplied to none of the SMA wires58athrough58dat the timing t1. Accordingly, the SMA wires58athrough58dpull each other with a moderate force in a well-balanced manner, and retain their initial states where energization to the SMA wires58athrough58dis suspended. In this state, the annular gear55is not interconnected to the cylindrical cam54.

At the timing t2, a current Id is started to be supplied to the SMA wire58afor energization. In response to heat generation by the current supply, the SMA wire58ais contracted into its memorized shape against resilient forces of the SMA wires58b,58c, and58dto which the current is not supplied. The energization to the SMA58ais controlled in such a manner that the current Id is temporarily lowered to a current Ih at the timing t3, and then, the energization by the supply of the current Ih is continued until the timing t4, at which the current supply is suspended. Since the SMA wire58ais contracted from its initial state, the cylindrical projection553i.e. a cylindrical projection553aover which the SMA wire58ais wound is subjected to the contraction force. As a result, the annular gear55is interconnected to the cylindrical cam54by gear engagement.

Subsequently, at the timing t3, energization to the SMA wire58bis started.FIG. 7shows a state of the SMA wire58bimmediately after start of the energization by supply of a current Id thereto. When the current Id is supplied to the SMA wire58b, the SMA wire58bis contracted against resilient forces of the SMA wires58a,58c, and58din a similar manner as in the case where the SMA58ais contracted. Since the annular gear55has already been interconnected to the cylindrical cam54by gear engagement at this time, the cylindrical cam54is rotated counterclockwise by a contraction force of the SMA wire58b. If a stress of the SMA58ais gone before energization to the SMA58bis started, the annular gear55may be disengaged from the cylindrical cam54due to an action of the annular gear55to return to its balanced position. In view of this, supplying a little current to the SMA wire58aenables to securely suppress the returning action of the annular gear55in light of a hysteresis of the SMA wire, thereby eliminating the gear disengagement (seeFIG. 9, which will be described later). Similarly to the control of the SMA wire58a, the energization to the SMA wire58bis temporarily lowered from the supply of the current Id to the supply of a current Ih at the timing t4, and the supply of the current Ih is continued until the timing t5, at which the current supply is suspended.

Similarly to the above, driving is performed in such a manner that energization to the SMA wire58cis continued until the timing t6, and then, energization to the SMA wire58dis continued until the timing t7, whereby the cylindrical cam54is kept on rotating counterclockwise. Specifically, the cylindrical cam54is rotated counterclockwise by energizing the SMA wires in the order of58a,58b,58c, and58din clockwise direction. A rotation angle δ of the cylindrical cam54in this driving is represented by the following equation, assuming that Z1represents the number of the teeth of the annular gear55, and Z2represents the number of the teeth of the cylindrical cam54.
δ=(Z1−Z2)/Z2×360°

Conversely to the above, the cylindrical cam54is rotated clockwise by energizing the SMA wires in the order of58a,58d,58c, and58bin counterclockwise direction.

Now, the above driving is observed in the aspect of phase. Assuming that a period from the point of time when a first-time energization to the SMA wire58ais started to the point of time when the energization to the SMA wire58ais resumed is defined as a cycle T, a time interval between the timings t2and t3, between the timings t3and t4, between the timings t4and t5, and between the timings t5and t6(or t2) corresponds to a time duration obtained by dividing the cycle T by four. In other words, energization to the SMA wires58athrough58dis conducted by phase displacement of 90°. Specifically, the energization timing for the respective SMA wires58athrough58dis determined in conformity to the angular displacement (=90°) of the cylindrical projections. Accordingly, if three cylindrical projections are disposed away from each other by 120°, it is possible to perform a driving similar to the above driving by using three SMA wires and by shifting the energization timing for the respective SMA wires by 120° in phase.

FIG. 9is a hysteresis graph on current-to-distortion characteristic, representing a relation between a current to be supplied to the respective SMA wires, and a displacement thereof. The currents A and B shown in the characteristic graph ofFIG. 9correspond to the currents Id and Ih described in the foregoing section referring toFIG. 8, respectively. As an energization amount is increased, the SMA wire is abruptly contracted when the energization reaches a certain level. When the contraction amount of the SMA wire reaches a certain degree, or the contraction is suspended, the amount of the current supply keeps on increasing, without changing the distortion. Conversely, as the energization amount is gradually decreased, the distortion is not decreased until the amount of the current supply falls below a certain level, as compared with the case where the amount of the current to be supplied keeps on increasing. The current Id used for heating the SMA wire, i.e., the heating current indicated by the arrow A, and the current Ih used for retaining the temperature of the SMA wire, i.e., the retaining current indicated by the arrow B, for instance, are determined based on the hysteresis of the SMA wire. This control enables to retain the distortion i.e. a contact of the cylindrical cam54with the annular gear55, with a less current, as compared with the case where the heating current is supplied.

Utilizing the hysteresis as mentioned above enables to simultaneously energize adjacent two SMA wires among the SMA wires, for instance, by shifting the SMA wires for the simultaneous energization in such an order that the SMA wires58aand58bare energized, then, the SMA wires58band58care energized, and then the SMA wires58cand58dare energized, and then, the SMA wires58dand58aare energized. In this arrangement, the respective energization amounts to energize the adjacent two SMA wires may be an energization amount to be obtained by supply of a first current capable of attaining a temperature equal to or larger than a deformation start temperature at which the SMA wire is started to be deformed, and an energization amount to be obtained by supply of a second current, which is smaller than the first current, and is capable of retaining the substantially same deformed state as the above deformed state. Specifically, the current supply is controlled, for instance, in such an order that the first current is supplied to the SMA wire58a, and the second current is supplied to the SMA wire58b; then, the first current is supplied to the SMA wire58b, and the second current is supplied to the SMA wire58c; then, the first current is supplied to the SMA wire58c, and the second current is supplied to the SMA wire58d; and then, the first current is supplied to the SMA wire58d, and the second current is supplied to the SMA wire58a. With this arrangement, an electric power can be saved by the amount corresponding to a difference between the first current and the second current, as compared with an arrangement that the same current, in this case, the first current is supplied to the respective SMA wires58athrough58d.

Utilizing the hysteresis provides substantially the same effect as a technique of flowing a minute electric current, without likelihood that distortion may become substantially zero immediately after completion of the energization to the respective SMA wires in the sequential energization as shown inFIG. 3. In particular, the same effect can be obtained in a high-temperature condition, even if an energization interval is extended, as compared with the example inFIG. 3, namely, even if a next energization start timing is set within a cooling period following the point of time of completion of the previous energization. Specifically, as shown inFIGS. 10A through 10D, an energization control may be performed in such a manner that energization to the next SMA wire i.e. the SMA wire58bis started upon lapse of a certain period T1(hereinafter, also called as “shape-retaining non-energization period”) from the timing t3, indicated by the symbol C, at which the first-time energization to a certain SMA wire i.e. the SMA wire58ahas been completed. The energization start timing to the succeeding SMA wire can be defined in a similar manner as mentioned above. A required distortion amount is secured even if actual energization is not conducted in the shape-retaining non-energization period T1. In the above energization control, a shape retaining effect i.e. a distortion amount retaining effect can be obtained, similarly to the energization control as shown inFIG. 3. Thereby, an energy-saving-oriented device superior in energy efficiency can be realized.

In the focus unit2of the embodiment, a temperature detector such as a temperature sensor (not shown) for detecting the temperature of the respective SMA wires is provided in the vicinity of the SMA wires in order to accurately detect the temperature of the respective SMA wires. The temperature detector is connected to a drive circuit. The drive circuit controls an energization time and an energization interval of the respective SMA wires based on the temperature information detected by the temperature detector. Specifically, in the case where it is judged that the temperature of the respective SMA wires itself which has been detected by the temperature sensor, or the ambient temperature around the SMA wires is higher than a predetermined threshold value (this state is referred to as “high temperature condition”), as shown inFIGS. 10A through 10D, the energization control of delaying the energization start timing by the period T1is performed to extend the energization interval of sequentially energizing the SMA wires i.e. SMA actuators, or to shorten the energization time for the respective SMA actuators.

In the case where it is judged that the temperature of the respective SMA wires itself which has been detected by the temperature sensor is lower than a predetermined threshold value (this state is referred to as “low temperature condition”), as shown inFIGS. 11A through 11D, for instance, an energization control may be performed in such a manner that energization to a next SMA wire i.e. the SMA wire58bis started at a timing earlier than the timing t3, indicated by the symbol C, at which the first-time energization to the SMA wire58ahas been completed, by a certain period T2(hereinafter, also called as “preparatory energization period T2”) in order to shorten the energization interval for energizing the respective SMA actuators or to extend the energization time for the respective SMA actuators in the sequential energization. It should be noted that the threshold temperature in the low temperature condition may be identical to or different from the threshold temperature for use in judging whether the detected temperature lies in the high temperature condition. The energization start timing for the succeeding SMA wire can be defined in a similar manner as mentioned above. Thereby, the energization time i.e. the heating time for the respective SMA wires can be extended by the preparatory energization period T2, as compared with the arrangement shown inFIG. 3. In other words, it is possible to start the energization earlier than the arrangement shown inFIG. 3by the preparatory energization period T2. This enables to securely obtain a required distortion amount of the respective SMA wires even in the low temperature condition, thereby enabling to accurately perform driving rotation of the motor by the drive mechanism.

The foregoing description is made on a premise that a high transmission efficiency is secured between the cylindrical cam54and the annular gear55, and a quiet and friction-resistive cycloid gear is used. The requirements may not be indispensable. Alternatively, an involute gear, which is easily processable and producible with a low cost, or a frictional engagement may be used. The modification is described in the following.

FIG. 12is a partially enlarged perspective view of a modified arrangement, in which a frictional engagement by frictional members i.e. a cylindrical cam54aand an annular gear55ais employed, in place of the gear engagement using a cycloid gear or a like member in the drive mechanisms of the first through third embodiments. In the modification, the cylindrical cam54ahas a radially outwardly protruding circumferential portion540, serving as a contact portion, in place of the external teeth of the cycloid gear. The circumferential portion540is made of e.g. a rubber material having a required frictional coefficient i.e. capable of exhibiting a required frictional force. The annular gear55ais formed with a V-shaped recess portion555, serving as a contact portion, around the inner circumference thereof, in place of the external teeth of the cycloid gear. The recess portion555is made of e.g. a rubber material having a required frictional coefficient i.e. capable of exhibiting a required frictional force, similar to the circumferential portion540of the cylindrical cam54a. With this arrangement, the V-shaped recess portion555is brought to a frictional engagement with the circumferential portion540. This arrangement is provided to increase a contact area of the frictional members so as to enhance a frictional force of the frictional engagement. Alternatively, the contact portion may have a shape such as a flat shape other than the protruding shape or the V-shape. The advantages of the frictional engagement are that the gear can be made smaller by a size corresponding to the tooth height, and that processing of the gear is easy. It is required to strengthen the contact between the frictional members in order to utilize the advantages. As mentioned above, a contact pressure can be secured by energization to a SMA wire having a phase different from the phase of the SMA wire used for generating a driving force. A further advantage of the frictional engagement is that the gear mechanism is usable as a torque limiter for limiting a load. Specifically, the frictional engagement enables to protect the parts in the gear mechanism in the case where an external force is exerted to the gear mechanism, or enables to suppress an output of the motor by restricting a transmission force to the motor if the output exceeds an allowable level. The frictional members each is made of a resin material e.g. a rubber having a large frictional force or a resilient force. The frictional engagement mechanism constituted of the annular gear55aas a drive member, and the cylindrical cam54aas a driven member, as shown inFIG. 12, is applicable to the below-mentioned fourth and fifth embodiments.

Fourth Embodiment

As mentioned above, the contact of the cylindrical cam with the annular gear enables to transmit the driving force of the annular gear generated by energization to the SMA wires to the cylindrical cam to thereby rotate the cylindrical cam. It is preferable to maintain the contact of the cylindrical cam with the annular gear in order to perform a desirable rotational driving of a motor. In view of this, a drive mechanism in accordance with a fourth embodiment of the invention is provided with a contact retainer for retaining a contact of a cylindrical cam with an annular gear. In the following, an example of using magnets is described as the contact retainer.

FIG. 13is an illustration of a focus unit2′ provided with magnets as a contact retainer, viewed from the same direction as shown inFIG. 7. As shown inFIG. 13, a certain number of magnets544are substantially equidistantly arranged around an outer circumference of a cylindrical cam54away from each other by a certain pitch, for instance. The magnets544have predetermined polarities thereof directed in a radial direction of the cylindrical cam54. Likewise, magnets557of the same number as the magnets544are substantially equidistantly arranged around an inner circumference of an annular gear55away from each other by a certain pitch, for instance. Polarities of the respective magnets557are directed in the radial direction opposite to those of the corresponding magnets544. In other words, the magnets544and557are arranged individually in such a manner that the polarities of the counterpart magnets544and557are opposite to each other between the cylindrical cam54and the annular gear55, or between the cylindrical cam54and a base block57, which will be described later, so as to generate an attraction force i.e. a contact force of attracting the cylindrical cam54and the annular gear55, or the cylindrical cam54and the base block57to each other at a contact position of these two members where these two members come closest to each other.

When SMA wires58athrough58dare in a de-energized state, the cylindrical cam54and the annular gear55are eccentrically displaced from each other due to an action of the magnets544and557whose polarities are opposite to each other, and stabilized at a site indicated by the symbol F inFIG. 13where the cylindrical54and the annular gear55are contacted to each other in a state that teeth of the cylindrical cam54and teeth of the annular gear55are meshed. When the SMA wire (in this case, SMA wire58d) adjacent the contact site F is energized, the annular gear55is moved parallel to the cylindrical cam54in contact with the outer surface of the cylindrical cam54due to an effect of an L-shaped position retaining guide56. At this time, the position retaining guide56slidably moves. Since the annular gear55and the cylindrical cam54are interconnected to each other by gear engagement, the cylindrical cam54is rotated without sliding over the annular gear55. This operation is continued until a clearance near a pressing contact site of the energized SMA wire58dagainst a corresponding cylindrical projection is gone. The number of the magnets are four inFIG. 13. Accordingly, four sites where the inner-disposed magnets544and the outer-disposed magnets557are opposed to each other, and four sites corresponding to the middle between the adjacent ones of these four opposing sites, namely, eight sites in total, are provided as stable positions where the cylindrical cam54and the annular gear55are stably meshed with each other. Vectors of magnetic force are constantly directed radially outwardly in intermediate areas between the adjacent ones of these eight stable positions. Accordingly, there is no likelihood that the cylindrical cam54may be disengaged from the annular gear55. Similarly to the above, when the succeeding SMA wire i.e. the SMA wire58cis energized, a movement similar to the movement described above is performed, whereby the cylindrical cam54is continuously rotated. As the rotation of the cylindrical cam54progresses, the phases of the magnets544and557may be displaced from each other. However, since the vectors of magnetic force are constantly directed radially outwardly as mentioned above, the arrangement is free from a drawback resulting from phase displacement.

In this embodiment, the magnets are arranged on the cylindrical cam54and the annular gear55. Alternatively, a similar effect as in the embodiment can be obtained by arranging magnets on the base block57and the annular gear55. In the modification, magnets of a certain number are arranged substantially equidistantly around the outer circumference of the annular gear55, with predetermined polarities thereof being directed in the radial direction of the annular gear55, and magnets of the same number as those on the annular gear55are arranged substantially equidistantly on the inner circumference of the base block57, with polarities thereof opposite to those of the corresponding magnets on the annular gear55being directed in the radial direction. The magnets on the annular gear55and the magnets on the base block57at the side opposite to the side where the annular gear55and the cylindrical cam54are meshed with each other are attracted to each other. Accordingly, a magnetic force acts in such a direction as to strengthen the gear engagement of the annular gear55and the cylindrical cam54. When the annular gear55is slidably moved around the cylindrical cam54, the counterpart magnets closest to each other on the annular gear55and the base block57are shifted one after another. However, if three or more magnets are provided for each on the annular gear55and the base block57, a magnetic force to strengthen the gear engagement of the annular gear55and the base block57acts owing to resultant forces of the magnets in intermediate areas between the adjacent ones of the opposing sites of the counterpart magnets on the annular gear55and the base block57, as in the arrangement of the embodiment. Also, the modification is free from the phase displacement of magnets as mentioned in the foregoing section. The energizing approach for the SMA wires58athrough58das described in the first embodiment referring toFIG. 3may be applicable to the fourth embodiment and to the modification thereof. It is possible to use charge retaining members capable of acquiring magnetic poles i.e. lines of magnetic force, in place of the magnets.

Fifth Embodiment

In this section, an arrangement is described, wherein a crank rod is used as an example of the contact retainer described in the fourth embodiment.FIG. 14is an illustration primarily showing a cylindrical cam, an annular gear, and a base block in a focus unit3provided with the crank rod in the fifth embodiment. In this embodiment, a cylindrical cam61, an annular gear62, and a base block63are provided. The cylindrical cam61has a cam surface extending in an optical axis direction of the focus unit3, and external teeth (not shown) at a radially outer position. The cylindrical cam61is rotatably supported about the optical axis. The ring-like annular gear62is provided around the outer surface of the cylindrical cam61. The annular gear62has internal teeth, which is interconnected to the external teeth of the cylindrical cam61by gear engagement. Axially extending four cylindrical projections (not shown) are circumferentially and substantially equidistantly attached to the annular gear62by a certain pitch i.e. by 90°. Four SMA wires (not shown) are fixed on the annular gear62in a state that each SMA wire is wound into a substantially L-shape over the corresponding cylindrical projection, with a certain tension force being applied thereto. Substantially middle parts of the respective SMA wires come into contact with the corresponding cylindrical projection. Both ends of each SMA wire are jointed to SMA retaining blocks (not shown) attached to the base block63, which is fixed to a fixing member (not shown), and is provided around the outer surface of the annular gear62. In this embodiment, eight SMA retaining blocks are provided. The substantially L-shaped SMA wire is obtained by angularly displacing the SMA wires from each other by 90° about the optical axis. Each SMA retaining block is connected to an unillustrated drive circuit so that a current is selectively supplied to the SMA retaining blocks.

Plural crank rods64, which are so-called eccentric rods, and serve as eccentric cylindrical projections, e.g. three crank rods64as shown inFIG. 13, are received both in the annular gear62and in the base block63. Each crank rod64is pivotally supported by the annular gear62and the base block63for crank rotation. With this arrangement, the annular gear62and the base block63are eccentrically movable relative to each other. The crank rods64singly define the position of the annular gear62to the base block63, and a trajectory of the annular gear62. Specifically, providing the crank rods64enables to retain the position of the annular gear62relative to the base block63in rotational driving, i.e. allow the arrangement with the crank rods64to function as a guide mechanism, and simultaneously enables to retain the contact of the annular gear62with the cylindrical cam61.

When the SMA wire adjacent the site where the cylindrical cam61and the annular gear62are contacted to each other is energized, the annular gear62is moved parallel to the cylindrical cam61, while contacting the outer surface of the cylindrical cam61due to the effect of the crank rods64. Since the annular gear62and the cylindrical cam61are interconnected to each other by gear engagement, the cylindrical cam61is rotated without sliding over the annular gear62. This operation is continued until a clearance near a pressing contact site of the energized SMA wire against the corresponding cylindrical projection is gone. Similarly to the above, when the succeeding SMA wire is energized, a movement similar to the movement described above is performed, whereby the cylindrical cam61is continuously rotated. The energization approach for the respective SMA wires in the embodiment may be the same as described in the first embodiment referring toFIG. 3.

In the fifth embodiment, the arrangement provided with the position retaining function and the contact retaining function is realized with use of the plural e.g. three crank rods64. Alternatively, an arrangement similar to the above may be realized with use of a position retainer constituted of a single crank rod and a position retaining guide, for instance.

Sixth Embodiment

In this section, an arrangement is described, wherein a cycloid gear is used as an example of the contact retainer.FIG. 15is an illustration primarily showing a cylindrical cam, an annular gear, and a base block in a focus unit4provided with the cycloid gear in the sixth embodiment. In this embodiment, a cylindrical cam71, an annular gear72, and a base block73are provided. The focus unit4has a position retaining guide74and an intermediate arcuate ring75. The cylindrical cam71has a cam surface extending in an optical axis direction of the focus unit4, and an external cycloid gear at a radially outer position. The cylindrical cam71is rotatably supported about the optical axis. The ring-like annular gear72is provided around the outer surface of the cylindrical cam71. The annular gear72has an internal cycloid gear with the tooth number larger than the tooth number of the external cycloid gear of the cylindrical cam71by one. The external cycloid gear of the cylindrical cam71is interconnected to the internal cycloid gear of the annular gear72by gear engagement.

The annular gear72has its rotation about the optical axis restrained by the position retaining guide74. The position retaining guide74has e.g. two pairs of parallel link levers serving as linking members, as shown inFIG. 15. One of the parallel link lever pairs is provided between the annular gear72and the intermediate arcuate ring75partly surrounding the outer circumference of the annular gear72, and the other one of the parallel link lever pairs is provided between the intermediate arcuate ring75and the base block73surrounding the outer circumference of the intermediate arcuate ring75. Both ends741of each parallel link lever are attached to the corresponding members i.e. the annular gear72, the base block73, or the intermediate arcuate ring75by a pivot pin or a like member so that each parallel link lever is pivotally rotatable about the corresponding pivot pin.

Similarly to the fifth embodiment, axially extending four cylindrical projections (not shown) are circumferentially and substantially equidistantly attached to the annular gear72by a certain pitch i.e. by 90°. Four SMA wires (not shown) are fixed on the annular gear72in a state that each SMA wire is wound into a substantially L-shape over the corresponding cylindrical projection, with a certain tension force being applied thereto. Substantially middle parts of the respective SMA wires come into contact with the corresponding cylindrical projection. Both ends of each SMA wire are jointed to SMA retaining blocks (not shown) attached to the base block73, which is fixed to a fixing member (not shown), and is provided around the outer surface of the annular gear72. In this embodiment, eight SMA retaining blocks are provided. The substantially L-shaped SMA wire is obtained by angularly displacing the SMA wires from each other by 90° about the optical axis. Each SMA retaining block is connected to an unillustrated drive circuit so that a current is selectively supplied to the SMA retaining blocks.

Generally, cycloid gears with a tooth number difference of one each has contacts by the number corresponding to the tooth number thereof. The phases of the tooth planes of the respective cycloid gears are displaced from each other at the respective contacts by the angle obtained by dividing 360° by the tooth number. Accordingly, the relative movement of the cycloid gears is singly defined in light of the above phase displacement. Actually, defining at least two positions is sufficient to determine the trajectory of the gear, because rotation of the gear is restrained, namely, the position of the gear is retained. Accordingly, the gears to be used in the embodiment may be cycloid gears with a tooth number difference of one, and constitute so-called unmating gears having a feature that one of the gears has at least two teeth. In this arrangement, since the position of the annular gear72is retained by the parallel link lever pairs, the annular gear72is moved parallel to the cylindrical cam71, whereby the cylindrical cam71is rotated.

Energizing the SMA wire which is expected to exhibit a maximal force among the SMA wires in a tangential direction at a contact point where a tangential line including a contact point of the cylindrical cam71and the annular gear72is substantially parallel to a tangential line on an imaginary circle711defined by rotation of the cylindrical cam71about its rotation axis, enables to move the annular gear72parallel to the cylindrical cam71while rotating the cylindrical cam71due to a relative restraining effect of the cycloid gears with the tooth number difference of one. Similarly to the above, when the succeeding SMA wire is energized, a movement similar to the movement described above is performed, whereby the cylindrical cam71is continuously rotated.

The arrangement in the sixth embodiment is advantageous because the contact retainer provided in the fourth and fifth embodiments can be eliminated, thereby enabling to produce a compact and less costly drive mechanism. Also, in the sixth embodiment, since there is no need of energizing two SMA wires adjacent to each other in order to keep the contact of the cylindrical cam with the annular gear, as recited in the third embodiment, the arrangement in the sixth embodiment enables to perform driving at a low power consumption. The energization approach for the respective SMA wires in the sixth embodiment may be the one as recited in the first embodiment described referring toFIG. 3.

To summarize the invention, in the motor of the embodiments corresponding to the zoom unit1, and the focus units2,2′, and4, a rotary member corresponding to the cylindrical cam14and the cylindrical cam54has a contact portion on the outer periphery thereof, and is rotatably supported on a base block corresponding to the base blocks16,16′,57, and73for outputting a rotating force. An oscillatory ring, corresponding to the drive gear21and the annular gear55, with a contact portion on the inner periphery thereof, is oscillated on the plane perpendicular to the rotation axis of the rotary member in contact with the contact portion of the rotary member. Also, a position retainer, corresponding to the parallel springs23through26, the position retaining guide56, the through holes5521,5711, the position retaining guide74, and the like, retains the position of the oscillatory ring. The oscillatory ring is brought into contact with three or more wire- or belt-shaped expandable and contractible actuators, corresponding to the SMA wires35through38, and the SMA wires58athrough58d, with both ends of the each actuator being fixed to the base block.

With this arrangement, a motor capable of continuously rotating in forward and backward directions is realized by sequentially energizing the actuators for expansion and contraction. Also, this arrangement constitutes a speed reduction mechanism, wherein the rotary member is allowed to rotate merely by the length corresponding to the trajectory of the oscillatory ring. This arrangement enables to generate a force sufficient for drivingly rotating the rotary member even with use of the wire- or belt-shaped expandable and contractible actuators e.g. wire- or belt-shaped expandable and contractible actuators made of a shape metal alloy, for instance. Also, use of the actuators having an elongated shape with a small size in cross section enables to increase the cooling rate and at the same time to secure an output, by utilizing the actuators made of the shape metal alloy having a property that the actuators are contracted as a result of heat generation. This enables to realize a quiet and compact motor capable of generating a large rotational driving force, with use of the shape metal alloy. Also, in this arrangement, all the constituent elements are arranged in close contact with the outer surface of the rotary member. Accordingly, providing an optical system on the rotary member and assembling the optical system including relevant peripheral elements thereof into a concentrically cylindrical configuration, for instance, enables to realize a motor capable of driving a lens element with a substantially coaxial arrangement with the optical system. Since all the constituent elements are arranged around the rotary member, it is possible to mount the wire- or belt-shaped actuators along the outer circumference of the rotary member, which provides an improved assembling.

Also, the contact of the rotary member with the oscillatory ring is retained by a contact retainer corresponding to the magnets544,557, the crank rods64, or an equivalent element. With this arrangement, the oscillatory ring is securely oscillated in contact with the rotary member due to the contact force exerted by the contact retainer to retain the contact of the rotary member with the oscillatory ring, namely, a centripetal force exerted by the oscillatory ring to the rotary member. Specifically, in the case where the rotary member and the oscillatory ring are interconnected to each other by gear engagement using the cycloid gear542and the like, collision of tooth tips of the gears is avoided due to a stabilized distance between the center positions of the respective gears, which enables to perform smooth rotational driving i.e. output a rotating force due to stabilized rotation of the rotary member.

Also, the expandable and contractible actuators each is in the form of a thin shape metal alloy wire having a shorter size in cross section of 100 μm or less. This arrangement enables to produce a compact and light-weighted motor, and to increase the cooling rate of the shape metal alloy, in other words, to keep the reactive rate of the shape metal alloy i.e. the expandable and contractible rate of the actuators high.

Also, at least one position retainer is provided between the base block and the oscillatory ring, and a guide member, corresponding to the position retaining guide56, for slidably moving the base block and the oscillatory ring in directions orthogonal to each other, and receiving portions, corresponding to the through-holes5521,5711, in which the guide member is slidably received, constitute a guide mechanism. This enables to realize the position retainer with a simplified arrangement constituted of the guide member and the receiving portions.

Also, as shown inFIG. 13, the contact retainer is constituted of magnets, corresponding to the magnets544,577, or the charge retaining members, wherein the magnets are arranged individually on the rotary member corresponding to the cylindrical54and the oscillatory ring corresponding to the annular gear55, or on the rotary member and the base block corresponding to the base block57, with their polarities opposite to each other between the rotary member and the oscillatory ring, or between the rotary member and the base block, so as to generate a contact force at a contact position of the rotary member and the oscillatory ring where the rotary member and the oscillatory ring come closest to each other. This enables to realize the contact retainer with a simplified arrangement constituted of the magnets or the charge retaining members.

Also, as shown inFIG. 14, at least one contact retainer is provided between the base block corresponding to the base block63, and the oscillatory ring corresponding to the annular gear62, and an eccentric drive mechanism is constituted of eccentric rods corresponding to the crank rods64and the eccentric cylindrical projections, wherein the base block and the oscillatory ring are eccentrically movable relative to each other. This enables to realize the contact retainer with a simplified arrangement constituted of the eccentric rods, and to allow the contact retainer to function as the position retainer as well.

Also, as shown inFIG. 15, the oscillatory ring corresponding to the annular gear72is oscillated in contact with the cycloid gear formed on the outer periphery of the rotary member in a state that the cycloid gear formed on the inner periphery of the oscillatory ring has the tooth number larger than the tooth number of the cycloid gear formed on the outer periphery of the rotary member corresponding to the cylindrical cam71by one. This arrangement enables to perform a function of retaining the contact of the rotary member with the oscillatory ring.

Also, as shown inFIG. 15, the contact retainer is constituted of linking members corresponding to the position retaining guide74and the parallel linking levers, wherein at least one pair of the linking members is provided each between the oscillatory ring, and an intermediate arcuate ring corresponding to the intermediate arcuate ring75partly surrounding the outer circumference of the oscillatory ring, and between the intermediate arcuate ring, and the base block corresponding to the base block73surrounding the outer circumference of the intermediate arcuate ring. The linking members in pair are arranged parallel to each other, and both ends of the each linking member are pivotally connected to the oscillatory ring and the intermediate arcuate ring, or to the intermediate arcuate ring and the base block, respectively. This enables to realize the contact retainer with a simplified arrangement constituted of the at least two linking member pairs, with each linking pair having the parallel arrangement, in the arrangement where the oscillatory ring is oscillated in contact with the cycloid gear formed on the outer periphery of the rotary member in a state that the cycloid gear formed on the inner periphery of the oscillatory ring has the tooth number larger than that of the cycloid gear formed on the outer periphery of the rotary member by one.

Also, in the motor device of the embodiments corresponding to the zoom unit1, and the focus units2,2′, and4, a rotary member corresponding to the cylindrical cam14and the cylindrical cam54has a contact portion on the outer periphery thereof, and is rotatably supported on a base block corresponding to the base blocks16,16′,57, and73for outputting a rotating force. An oscillatory ring, corresponding to the drive gear21and the annular gear55, with a contact portion on the inner periphery thereof, is oscillated on the plane perpendicular to the rotation axis of the rotary member in contact with the contact portion of the rotary member. Also, a position retainer, corresponding to the parallel springs23through26, the position retaining guide56, the through holes5521,5711, the position retaining guide74, and the like, retains the position of the oscillatory ring. The oscillatory ring is brought into contact with three or more wire- or belt-shaped expandable and contractible actuators, corresponding to the SMA wires35through38, and the SMA wires58athrough58d, with both ends of the each actuator being fixed to the base block, and a substantially middle part thereof being in contact with the oscillatory ring. The actuators may be called as energization contractible actuators, for instance, in light of the fact that the actuators are contracted by energization thereto. The actuators adjacent to each other are sequentially energized by an energization controller corresponding to the unillustrated drive circuit connected to the SMA wires35through38or the SMA wires58athrough58d.

With this arrangement, a motor device capable of continuously rotating in forward and backward directions is realized by causing the energization controller to sequentially energize the actuators adjacent to each other for contraction. Also, this arrangement constitutes a speed reduction mechanism, wherein the rotary member is allowed to rotate merely by the length corresponding to the trajectory of the oscillatory ring. This arrangement enables to generate a force sufficient for drivingly rotating the rotary member even with use of the wire- or belt-shaped expandable and contractible actuators e.g. wire- or belt-shaped expandable and contractible actuators made of a shape metal alloy, for instance. Also, use of the actuators having an elongated shape with a small size in cross section enables to increase the cooling rate and at the same time to secure an output, by utilizing the actuators made of the shape metal alloy having a property that the shape metal alloy is contracted as a result of heat generation by energization. This enables to realize a quiet and compact motor device capable of generating a large rotational driving force, with use of the shape metal alloy. Also, in this arrangement, all the constituent elements are arranged in close contact with the outer surface of the rotary member. Accordingly, providing an optical system on the rotary member and assembling the optical system including relevant peripheral elements thereof into a concentrically cylindrical configuration, for instance, enables to realize a motor device capable of driving a lens element with a substantially coaxial arrangement with the optical system. Since all the constituent elements are arranged around the rotary member, it is possible to mount the wire- or belt-shaped actuators along the outer circumference of the rotary member, which provides an improved assembling.

Also, the contact of the rotary member with the oscillatory ring is retained by a contact retainer corresponding to the magnets544,557, the crank rods64, or an equivalent element. With this arrangement, the oscillatory ring is securely oscillated in contact with the rotary member due to the contact force exerted by the contact retainer to retain the contact of the rotary member with the oscillatory ring, namely, a centripetal force exerted by the oscillatory ring to the rotary member. Specifically, in the case where the rotary member and the oscillatory ring are interconnected to each other by gear engagement, collision of tooth tips of the gears is avoided due to a stabilized distance between the center positions of the respective gears, which enables to perform smooth rotational driving i.e. output a rotating force due to stabilized rotation of the rotary member.

Also, as shown inFIG. 12, the rotary member corresponding to the cylindrical cam54a, and the oscillatory ring corresponding to the annular gear55aeach includes a contact portion having such a shape that the rotary member and the oscillatory ring are interconnectable to each other by a frictional force. This enables to interconnect the rotary member to the oscillatory ring by frictional engagement. Further, as compared with a case where the rotary member and the oscillatory ring are gear-connected, for instance, this arrangement enables to make the gear smaller by a size corresponding to the tooth height, and make the gear arrangement simple, i.e. make the gear processing easy. Also, this arrangement enables to transmit the driving force between the rotary member and the oscillatory ring by way of the frictional engagement i.e. a frictional force, and to provide a function as a torque limiter for limiting a load.

Also, an energization controller, corresponding to the unillustrated drive circuit connected to the SMA wires35through38or the SMA wires58ato58d, simultaneously energizes adjacent two actuators among the actuators while shifting the actuators for the simultaneous energization one after another. Since the energization control is performed in such a manner that the adjacent two actuators are simultaneously energized while shifting the actuators for the simultaneous energization sequentially, an improved energy saving effect can be obtained, as compared with a case where a single current e.g. a first current is supplied for energization of the actuators, by supply of two different kinds of currents for the simultaneous energization, namely, supply of the first current, corresponding to the heating current Id indicated by the arrow A inFIG. 9, for instance, which is capable of attaining a temperature equal to or larger than a deformation start temperature at which the actuator is started to be deformed, and a second current, corresponding to the retaining current Ih indicated by the arrow B inFIG. 9, which is smaller than the first current, and is capable of retaining substantially the same deformed state as the above deformed state, with use of the hysteresis (seeFIG. 9) of the shape metal alloy, in the case where the actuators are made of the shape metal alloy. This enables to realize a motor device having an improved energy efficiency.

Also, energization amounts for energizing the adjacent two actuators respectively are a first energization amount to be obtained by supply of the first current which is capable of attaining the temperature equal to or higher than the deformation start temperature at which the deformation of the actuator is started, and a second energization amount to be obtained by supply of the second current, which is smaller than the first current, and is capable of retaining substantially the same deformed state as the above deformed state. This arrangement enables to provide an improved energy saving effect, as compared with the case where energization is performed merely with supply of a single current e.g. the first current, by the amount corresponding to a difference between the first energization amount and the second energization amount. This enables to realize a motor device having an improved energy efficiency.

Also, a temperature detector corresponding to the temperature sensor detects the temperature relating to the actuators, and an energization controller controls an energization interval and an energization time based on temperature information detected by the temperature detector to sequentially energize the actuators. Thus, the energization control is performed in such a manner that the actuators are sequentially energized, while controlling the energization interval and the energization time based on the temperature information detected by the temperature detector. This enables to provide an improved energy saving effect by extending the energization interval of the respective actuators i.e. shortening the energization time of the respective actuators in the sequential energization, and to stabilize the deformation by shortening the energization interval of the respective actuators i.e. extending the energization time of the respective actuators in the sequential energization in accordance with a temperature rise of the respective actuators. Thereby, a motor device capable of performing optimal drive control depending on the purpose of use can be easily provided.

Also, as shown inFIGS. 10A through 10D, the energization controller controllably extends the energization interval as the temperature of the respective actuators by the energization is raised. This enables to accomplish energy saving in driving of the motor by extending the energization interval of the respective actuators i.e. by shortening the energization time of the respective actuators in the sequential energization, in other words, by performing energization control of delaying the energization start time by a predetermined period in accordance with the temperature rise of the respective actuators.

Also, as shown inFIGS. 11A through 11D, the energization controller controllably shortens the energization interval as the temperature of the respective actuators by the energization is raised. This enables to stabilize the deformation i.e. contraction of the respective actuators by shortening the energization interval of the respective actuators i.e. by extending the energization time of the respective actuators in the sequential energization, in other words, by performing energization control to set the energization start time earlier by a predetermined period in accordance with the temperature rise of the respective actuators.

Also, in the lens drive mechanism of the embodiments corresponding to the focus units2,2′, and4, a rotary cylinder i.e. a rotary member, corresponding to the cylindrical cam54and the rectilinear guide cylinder52has a contact portion on the outer periphery thereof, and is rotatably supported on a base block corresponding to the base block57while holding a lens element corresponding to the focus lens element53thereon for outputting a rotating force. An oscillatory ring, corresponding to the annular gear55, with a contact portion on the inner periphery thereof, is oscillated on the plane perpendicular to the rotation axis of the rotary member in contact with the contact portion of the rotary member. Also, a position retainer, corresponding to the position retaining guide56, the through holes5521,5711, and the like, retains the position of the oscillatory ring. The contact of the rotary member with the oscillatory ring is retained by a contact retainer corresponding to the magnets544,557, the crank rods64, and the like. The oscillatory ring is brought into contact with three or more wire- or belt-shaped expandable and contractible actuators, corresponding to the SMA wires58athrough58d, with both ends of the each actuator being fixed to the base block, and a substantially middle part thereof being in contact with the oscillatory ring.

With this arrangement, a lens drive mechanism capable of continuously rotating the rotary member carrying the lens element in forward and backward directions is realized by sequentially energizing the actuators for expansion and contraction. Also, this arrangement constitutes a speed reduction mechanism, wherein the rotary member is allowed to rotate merely by the length corresponding to the trajectory of the oscillatory ring. This arrangement enables to generate a force sufficient for drivingly rotating the rotary member even with use of the wire- or belt-shaped expandable and contractible actuators e.g. wire- or belt-shaped expandable and contractible actuators made of a shape metal alloy, for instance. Also, use of the actuators having an elongated shape with a small size in cross section enables to increase the cooling rate and at the same time to secure an output, by utilizing the actuators made of the shape metal alloy having a property that the shape metal alloy is contracted as a result of heat generation. This enables to realize a quiet and compact lens drive mechanism capable of generating a large rotational driving force, with use of the shape metal alloy.

Also, with this arrangement, the oscillatory ring is securely oscillated in contact with the rotary member due to the contact force exerted by the contact retainer to retain the contact of the rotary member with the oscillatory ring, namely, a centripetal force exerted by the oscillatory ring to the rotary member. Specifically, in the case where the rotary member and the oscillatory ring are interconnected to each other by gear engagement, collision of tooth tips of the gears is avoided due to a stabilized distance between the center positions of the respective gears, which enables to perform smooth rotational driving i.e. output a rotating force due to stabilized rotation of the rotary member.

Also, in this arrangement, all the constituent elements are arranged in close contact with the outer surface of the rotary member. Accordingly, providing an optical system on the rotary member and assembling the optical system including relevant peripheral elements thereof into a concentrically cylindrical configuration, for instance, enables to realize a lens drive mechanism capable of driving a lens element with a substantially coaxial arrangement with the optical system. Since all the constituent elements are arranged around the rotary member, it is possible to mount the wire- or belt-shaped actuators along the outer circumference of the rotary member, which provides an improved assembling.