Abstract:
Disclosed herein is a drive unit using a shape memory alloy including: a shape memory alloy member made from a shape memory alloy, the shape memory alloy member exhibiting superelasticity when being energized; a drive body connected to the shape memory alloy member, the drive body being moved from a stopping position to a specific operational position when the shape memory alloy member is energized; and a locking mechanism for retaining the drive body at the specific operational position. With this configuration, the drive unit using a shape memory alloy is capable of reducing the power consumption as well as miniaturizing the drive unit.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a drive unit using a shape memory alloy, and particularly to a drive unit for moving a drive body to a specific operational position by using a shape memory alloy which exhibits superelasticity when energized. 
     A drive unit generally includes a shape memory alloy member made from a shape memory alloy containing titanium (Ti) and nickel (Ni) and a drive body connected to the shape memory alloy member, wherein the drive body is moved by energizing the shape memory alloy member. 
     FIGS. 7 and 8 show a related art drive unit “a” using a shape memory alloy. 
     The drive unit “a” is composed of a shape memory alloy spring “b” made from a shape memory alloy, a drive body “c”, and a bias spring “d”. 
     The shape memory alloy spring “b” is arranged such that one end is connected to the left side surface of the drive body “c” and the other end is fixed to a first fixing wall “e”. The bias spring “d” is arranged such that one end is connected to the right side surface of the drive body “c” and the other end is fixed to a second fixing wall “f”. 
     The shape memory alloy spring “b” is electrically connected to a power source (not shown). When energized by the power source, the shape memory alloy spring “b” exhibits superelasticity, and is thereby contracted to move the drive body “c” in the direction A from a stopping position shown in FIG. 7 to an operational position shown in FIG.  8 . 
     When the energization of the shape memory alloy spring “b” is released, the drive body “c” is returned in the direction B from the operational position shown in FIG. 8 to the stopping position shown in FIG. 7 by the biasing force of the bias spring “d”. 
     The above-described related art drive unit “a”, however, has a problem. Since it is required to continue the energization of the shape memory alloy spring “b” for retaining the drive body “c” at the operational position, the power consumption becomes large. In particular, since the shape memory alloy containing Ti and Ni has a small inner resistance, the power consumption upon energization thereof becomes much larger. This brings a large obstacle to put the drive unit using the shape memory alloy into practical use. 
     The related art drive unit “a” also causes the following inconvenience: namely, in the case of retaining the drive body “c” at the operational position by continuing the energization of the shape memory alloy spring “b”, the drive body “c” tends to be oscillated, resulting in wobbling of the drive body “c” at the operational position. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is therefore to provide a drive unit using a shape memory alloy, which is capable of reducing the power consumption while overcoming the above mentioned problems. 
     To achieve the above object, according to the present invention, there is provided a drive unit using a shape memory alloy, including: a shape memory alloy member made from a shape memory alloy, the shape memory alloy member exhibiting superelasticity when being energized; a drive body connected to the shape memory alloy member, the drive body being moved from a stopping position to a specific operational position when the shape memory alloy member is energized; and a locking mechanism for retaining the drive body at the specific operational position. 
     With this configuration, since it is not required to continue the energization of the shape memory alloy member for retaining the drive body at the specific operational position, it is possible to significantly reduce the power consumption. 
     The locking mechanism may be provided with a locking portion, and the drive body may be integrally provided with a portion to be locked with the locking portion. With this configuration, it is possible to reduce the number of parts and to certainly retain the drive body at the specific operational position. 
     The locking mechanism may be additionally provided with a locking-releasing mechanism for releasing the retention of the drive body at the specific operational position. With this configuration, it is not required to provide a locking-releasing mechanism separately from the locking mechanism. Accordingly, it is possible to reduce the number of parts and simplify the mechanism, and hence to miniaturize the drive unit using a shape memory alloy and reduce the production cost of the drive unit. 
     The locking-releasing mechanism may be provided with an extensible/contractible member which is made from a shape memory alloy and exhibits superelasticity when being electrified, whereby the retention of the drive body at the specific operational position is released by energizing the extensible/contractible member. With this configuration, it is possible to easily control the locking-releasing mechanism and certainly release the locking state of the drive body, and hence to ensure the desirable operational state of the drive unit. 
     The drive unit may further include a bias spring, connected to the drive body, for retaining the drive unit at the stopping position. With this configuration, it is possible to certainly retain the drive body at the stopping position and hence to optimize the operation of the drive unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a first embodiment of a drive unit using a shape memory alloy according to the present invention, showing a state in which a drive body is retained at a stopping position; 
     FIG. 2 is a schematic diagram of the drive unit shown in FIG. 1, showing a state in which the drive body is retained at an operational position; 
     FIG. 3 is a schematic diagram of the drive unit shown in FIG. 1, showing a state in which the locking state of the drive body by a locking mechanism is released; 
     FIG. 4 is a schematic diagram of a second embodiment of the drive unit using a shape memory alloy according to the present invention, showing a state in which a drive body is retained at a stopping position; 
     FIG. 5 is a schematic diagram of the drive unit shown in FIG. 4, showing a state in which the drive body is retained at an operational position on one side; 
     FIG. 6 is a schematic diagram of the drive unit shown in FIG. 4, showing a state in which the drive body is retained at an operational position on the other side; 
     FIG. 7 is a schematic diagram of a related art drive unit using a shape memory alloy, showing a state in which a drive body is retained at a stopping position; and 
     FIG. 8 is a schematic diagram of the drive unit shown in FIG. 7, showing a state in which the drive body is retained at an operational position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of a drive unit using a shape memory alloy according to the present invention will be described with reference to the accompanying drawings. In the drawings, members each being made from a shape memory alloy are schematically designated by thick lines for an easy understanding. 
     First, a drive unit  1  using a shape memory alloy according to the first embodiment will be described with reference to FIGS. 1 to  3 . 
     The drive unit  1  using a shape memory alloy according to the present invention is composed of a drive mechanism  2  and a locking mechanism  3 . The drive mechanism  2  includes a shape memory alloy member  4 , a drive body  5 , and a coil-shaped bias spring  6 . The shape memory alloy member  4  is configured as a shape memory alloy tensile coil spring. 
     The shape memory alloy member  4  is arranged such that one end is connected to the left side surface of the drive body  5  and the other end is fixed to a first fixing wall  7 . The shape memory alloy member  4  is electrically connected to a first power source (not shown). 
     The bias spring  6  configured as a tensile coil spring is arranged such that one end is connected to the right side surface of the drive body  5  and the other end is fixed to a second fixing wall  8 . Accordingly, the drive body  5  is usually biased in the direction X 2  shown in FIGS. 1 to  3  by the biasing force of the bias spring  6 . 
     The bottom surface of the drive body  5  has a notch-shaped recess as a portion  5   a  to be locked with the locking mechanism  3 . 
     The locking mechanism  3  includes an extensible/contractible member  9  made from a shape memory alloy, a locking member  10 , and a bias spring  11 . 
     The extensible/contractible member  9  is configured as a tensile coil spring extending in the vertical direction, and is fixed at its lower end to a third fixing wall  12 . The extensible/contractible member  9  is electrically connected to a second power source (not shown), and is energized by the second power source. 
     The locking member  10  is formed, for example, by bending a metal plate, and has a locking portion  10   a,  part thereof projecting upwardly. The locking member  10  is arranged such that one end is fixed to a fourth fixing wall  13  and the other end is connected to the upper end of the extensible/contractible member  9 . 
     The bias spring  11  is configured as a compression coil spring, and one end thereof is connected to a connection point between the extensible/contractible member  9  and the locking member  10 . The bias spring  11  retains, by its biasing force, the locking member  10  at an engagement position where the locking portion  10   a  of the locking member  10  can be engaged with the portion  5   a  to be locked of the drive body  5  (see FIG.  1 ). 
     The operation of the drive unit  1  using a shape memory alloy will be described below. 
     In a state in which the shape memory alloy member  4  of the drive mechanism  2  is not energized, the drive body  5  is retained at a stopping position by the biasing force of the bias spring  6  (see FIG.  1 ). In this state, as described above, the locking member  10  of the locking mechanism  3  is retained, by the biasing force of the bias spring  11 , at the engagement position where the locking portion  10   a  can be engaged with the portion  5   a  to be locked of the drive body  5  (see FIG.  1 ). 
     When energized by the first power source, the shape memory alloy member  4  exhibits superelasticity, and is thereby contracted to move the drive body  5  in the direction X 1  shown in the figures against the biasing force of the bias spring  6 . 
     When the drive body  5  is moved in the direction X 1  until part of the drive body  5  is brought into contact with the locking portion  10   a  of the locking member  10  located at the engagement position, the locking portion  10   a  is deflected downwardly. When the drive body  5  is further moved in the direction X 1  until the drive body  5  reaches an operational position, the locking portion  10   a  having been deflected is returned to the original state to be engaged with the portion  5   a  to be locked (see FIG.  2 ). 
     When the locking portion  10   a  is engaged with the portion  5   a  to be locked, the energization of the shape memory alloy member  4  by the first power source is released. At this time, since the portion  5   a  to be locked of the drive body  5  is engaged with the locking portion  10   a  of the locking member  10 , the movement of the drive body  5  in the direction X 2  by the biasing force of the bias spring  6  is restricted by the locking portion  10   a,  with a result that the drive body  5  is retained at the operational position. 
     When the extensible/contractible member  9  of the locking mechanism  3  is energized by the second power source in the state in which the drive body  5  is retained at the operational position, the extensible/contractible member  9  exhibits superelasticity and is thereby contracted to displace the locking member  10  downwardly against the biasing force of the bias spring  11 . When the locking member  10  is displaced downwardly, the engagement between the locking portion  10   a  and the portion  5   a  to be locked of the drive body  5  is released. As a result, the drive body  5  is moved in the direction X 2  by the biasing force of the bias spring  6  to be returned to the stopping position (see FIG.  3 ). Accordingly, the locking mechanism  3  also has a function as a locking-releasing mechanism for releasing the locking state of the drive body  5  retained at the operational position. 
     According to this embodiment, since the locking mechanism  3  serves as the locking-releasing mechanism as described above, it is not required to provide a locking-releasing mechanism separately from the locking mechanism  3 . Accordingly, it is possible to reduce the number of parts and simplify the mechanism, and hence to miniaturize the drive unit  1  using a shape memory alloy and reduce the production cost of the drive unit  1 . 
     When the locking member  10  is displaced downwardly and the engagement between the locking portion  10   a  and the portion  5   a  to be locked is released, the energization of the extensible/contractible member  9  by the second power source is released, and the extensible/contractible member. 9  having been contracted is returned to the original state. As a result, the locking member  10  is returned to the engagement position by the biasing force of the bias spring  11 . 
     The drive unit  1  using a shape memory alloy according to this embodiment has the following advantages: 
     Since the drive unit  1  is provided with the locking mechanism  3  for retaining the drive body  5  at the operational position, it is not required to continue the energization of the shape memory alloy member  4  for retaining the drive body  5  at the operational position, so that it is possible to significantly reduce the power consumption. 
     Since the drive body  5  is provided with the portion  5   a  to be locked with the locking portion  10   a  of the locking member  10 , it is possible to reduce the number of parts and to certainly retain the drive body  5  at the operational position. 
     Since the drive unit  1  using a shape memory alloy is provided with the extensible/contractible member  9  which exhibits superelasticity when energized as the locking-releasing mechanism, it is possible to easily control the locking-releasing mechanism and certainly release the locking state of the drive body  5 , and hence to ensure the desirable operational state of the drive unit  1 . 
     Since the drive unit  1  using a shape memory alloy is provided with the bias spring  6  for retaining the drive body  5  at the stopping position, it is possible to certainly retain the drive body  5  at the stopping position and hence to optimize the operation of the drive unit  1 . 
     Although each of the shape memory alloy member  4  and the bias spring  6  in the drive unit  1  is configured as a tensile coil spring, it may be configured as a compression coil spring. Further, the shape memory alloy member  4  is not limited to the coil-shaped spring but also may be a strand-shaped spring or a wire-shaped spring. 
     The portion  5   a  to be locked of the drive body  5 , which is configured as the notch-like recess in this embodiment, may be configured as a projection. 
     Further, in the drive unit  1  using a shape memory alloy according to this embodiment, the release of the engagement between the locking portion  10   a  of the locking member  10  and the portion  5   a  to be locked of the drive body  5  is performed by energizing the extensible/contractible member  9  made from a shape memory alloy; however, the release of the engagement between the locking portion  10   a  and the portion  5   a  to be locked may be performed by using a mechanical locking-releasing mechanism. In this case, since a power required for releasing the engagement is saved, it is possible to further reduce the power consumption. 
     Next, a drive unit  1 A using a shape memory alloy according to a second embodiment will be described with reference to FIGS. 4 to  6 . 
     The drive unit  1 A is different from the above-described drive unit  1  in that two locking mechanism  3 A and  3 B are provided; the bias spring  6  is not provided and a drive body  5 A is connected to two shape memory alloy members  4 A and  4 B and is kept in balance by these members  4 A and  4 B; and the drive body  5 A is provided with two portions  5   a  to be locked. In the following description of the drive unit  1 A using a shape memory alloy, therefore, only parts different from those of the drive unit  1  will be described, and the same parts as those of the drive unit  1  are designated by the same characters and the overlapped description thereof is omitted. 
     The drive unit  1 A using a shape memory alloy is composed of a drive mechanism  2 A and the two locking mechanism  3 A and  3 B. The drive mechanism  2 A includes the two shape memory alloy members  4 A and  4 B, and the drive body  5 A. 
     The shape memory alloy member  4 A is arranged such that one end is connected to the left side surface of the drive body  5 A and the other end is fixed to a first fixing wall  7 , and can be energized by a power source (not shown). Similarly, the shape memory alloy member  4 B is arranged such that one end is connected to the right side surface of the drive body  5 A and the other end is fixed to a second fixing wall  8 , and can be energized by a power source (not shown). 
     The two portions  5   a  to be locked are formed on the lower surface of the drive body  5 A in such a manner as to be right/leftwise symmetrical. 
     The locking mechanisms  3 A and  3 B, each of which has the same configuration as that of the locking mechanism  3  in the first embodiment, are spaced from each other in such a manner as to be right/leftwise symmetrical with respect to a stopping position of the drive body  5 A. 
     The operation of the drive unit  1 A using a shape memory alloy will be described below. 
     In a state in which the shape memory alloy members  4 A and  4 B of the drive mechanism  2 A are not energized, the drive body  5 A is retained at the stopping position by the balance between the shape memory alloy members  4 A and  4 B (see FIG.  4 ). In this state, the locking members  10  of the locking mechanism  3 A and  3 B are retained, by the biasing forces of bias springs  11 , at positions where the locking portions  10   a  can be engaged with the portions  5   a  to be locked of the drive body  5 A (see FIG.  4 ). 
     When only the shape memory alloy member.  4 A is energized, it exhibits superelasticity and is thereby contracted to move the drive body  5 A in the direction X 1  shown in the figures. 
     When the drive body  5 A is moved in the direction X 1  until part of the drive body  5 A is brought into contact with the locking portion  10   a  of the locking member  10  provided for the locking mechanism  3 A located at the engagement position, the locking portion  10   a  is deflected downwardly. When the drive body  5 A is further moved in the direction X 1  until the drive body  5 A reaches an operational position on the direction X 1  side, the locking portion  10   a  having been deflected is returned to the original state to be engaged with the portion  5   a  to be locked on the left side (see FIG.  5 ). 
     When the locking portion  10   a  is engaged with the portion  5 a to be locked, the energization of the shape memory alloy member  4 A is released. At this time, the drive body  5 A is biased in the direction X 2  by the shape memory alloy member  4 B; however, since the portion  5   a  to be locked of the drive body  5 A is engaged with the locking portion  10   a  of the locking member  10 , the movement of the drive body  5 A in the direction X 2  is restricted, with a result that the drive body  5 A is retained at the operational position on the direction X 1  side (see FIG. 5) 
     When only an extensible/contractible member  9  of the locking mechanism  3 A is energized in the state in which the drive body  5 A is retained at the operational position, the extensible/contractible member  9  exhibits superelasticity and is thereby contracted to displace the locking member  10  downwardly against the biasing force of the bias spring  11 . When the locking member  10  is displaced downwardly, the engagement between the locking portion  10   a  and the portion  5   a  to be locked of the drive body  5 A is released. As a result, the drive body  5 A is moved in the direction X 2  by the biasing force of the shape memory alloy member  4 B to be returned to the stopping position (see FIG.  4 ). 
     When the locking member  10  of the locking mechanism  3 A is displaced downwardly and the engagement between the locking portion  10   a  and the portion  5   a  to be locked is released, the energization of the extensible/contractible member  9  is released, and the extensible/contractible member  9  having been contracted is returned to the original state. As a result, the locking member  10  is returned to the engagement position by the biasing force of the bias spring  11 . 
     When only the shape memory alloy member  4 B is energized in the state in which the drive body  5 A is retained at the stopping position (see FIG.  4 ), the shape memory alloy member  4 B exhibits superelasticity and is thereby contracted to move the drive body  5 A in the direction X 2  shown in the figures. As a result, the portion  5   a  to be locked on the right side of the drive body  5 A is engaged with the locking portion  10   a  of the locking member  10  of the locking mechanism  3 B (see FIG.  5 ). Accordingly, the movement of the drive body  5 A in the direction X 1  is restricted by the locking mechanism  3 B, with a result that the drive body  5 A is retained at an operational position on the direction X 2  side (see FIG.  6 ). 
     When only an extensible/contractible member  9  of the locking mechanism  3 B is energized in the state in which the drive body  5 A is retained at the operational position, the extensible/contractible member  9  exhibits superelasticity and is-thereby contracted to release the engagement between the locking portion  10   a  of the locking member  10  and the portion  5   a  to be locked of the drive body  5 A. As a result, the drive body  5 A is moved in the direction X 1  by the biasing force of the shape memory alloy member  4 A so as to be returned to the stopping position (see FIG.  4 ). Then, the energization of the extensible/contractible member  9  of the locking mechanism  3 B is released, so that the locking member  10  is returned to the engagement position by the biasing force of the bias spring  11 . 
     The drive unit  1 A using a shape memory alloy according to this embodiment has the following advantages: 
     Like the drive unit  1  in the first embodiment, the drive unit  1 A is provided with the locking mechanisms  3 A and  3 B for retaining the drive body  5 A at the operational positions. Accordingly, since it is not required to continue the energization of the shape memory alloy member  4 A or  4 B for retaining the drive body  5 A at the operational position either on the direction X 1  side or on the direction X 2  side, it is possible to significantly reduce the power consumption. 
     Since the drive unit  1 A is configured such that the drive body  5 A can be retained at the operational positions in the two directions, it is possible to use the drive unit  1 A as a multifunctional unit. 
     In addition, the drive body  5 A is moved in the X 1  and X 2  directions in this embodiment; however, it may be moved in a direction different therefrom, or may be moved in three or more directions. 
     In the drive unit  1 A using a shape memory alloy, each of the shape memory alloy members  4 A and  4 B is configured as a tensile coil spring; however, it may be configured as a compression coil spring. Further, each of the shape memory alloy members  4 A and  4 B is not limited to the coil-shaped spring but may be a strand-shaped spring or a wire-shaped spring. 
     Further, the release of the engagement between the locking portion  10   a  of the locking member  10  and each portion  5   a  to be locked of the drive body  5 A may be performed by using a mechanical locking-releasing mechanism. 
     While the preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.