Shape memory alloy actuator and method of designing the same
원문보기
IPC분류정보
국가/구분
United States(US) Patent
등록
국제특허분류(IPC7판)
C22C-019/03
C22K-001/00
출원번호
US-0162399
(2002-06-05)
우선권정보
JP-0189861 (2001-06-22)
발명자
/ 주소
Homma, Dai
출원인 / 주소
Toki Corporation Kabushiki Kaisha
대리인 / 주소
Birch, Stewart, Kolasch & Birch, LLP
인용정보
피인용 횟수 :
4인용 특허 :
7
초록▼
The present invention employs a shape memory alloy that exhibits a two-way shape memory effect and that has a stress-strain property that, in a stress-strain diagram, the stress-strain curve comprises a gentler gradient portion extending with relatively small gradients and a steeper gradient portion
The present invention employs a shape memory alloy that exhibits a two-way shape memory effect and that has a stress-strain property that, in a stress-strain diagram, the stress-strain curve comprises a gentler gradient portion extending with relatively small gradients and a steeper gradient portion extending with relatively great gradients. The shape memory alloy is operated in the region surrounded by the gentler gradient portion, the steeper gradient portion, a practical stress limit line, a straight line connecting the intersection of the practical stress limit line and a strain limit line near shape recovery completion on which the strain of the shape memory alloy reaches a specified value in a state close to the shape recovery completion and the point where the strain is zero at a low temperature in the stress-strain diagram.
대표청구항▼
1. A method of designing a shape memory alloy actuator, using a shape memory alloy exhibiting a two-way shape memory effect and having a stress-strain property that, in a stress-strain diagram with the stress plotted in ordinate, the upward direction taken as the positive direction, and the strain p
1. A method of designing a shape memory alloy actuator, using a shape memory alloy exhibiting a two-way shape memory effect and having a stress-strain property that, in a stress-strain diagram with the stress plotted in ordinate, the upward direction taken as the positive direction, and the strain plotted in abscissa, the rightward direction taken as the positive direction, the stress-strain curve at a low temperature comprises a gentler gradient portion extending from the position at which the strain is zero to the right with relatively small gradients, in the area in which the stress is negative or approximately along the line on which the stress is zero, and a steeper gradient portion extending upward to the right with relatively great gradients on the right of said gentler portion, the method comprising the step of: setting said shape memory alloy to be operated in the region surrounded by said gentler gradient portion, said steeper gradient portion, a practical stress limit line on which the stress in said shape memory alloy reaches a specified practical limit, a straight line connecting the intersection of said practical stress limit line and a strain limit line near shape recovery completion on which the strain of said shape memory alloy reaches a specified value in a state close to the shape recovery completion and the point where the strain is zero at a low temperature in said stress-strain diagram. 2. A method of designing a shape memory alloy actuator as set forth in claim 1, comprising setting said shape memory alloy to be operated in the region surrounded by said gentler gradient portion, said steeper gradient portion, said practical stress limit line and said strain limit line near shape recovery completion in said stress-strain diagram.3. A method of designing a shape memory alloy actuator as set forth in claim 2, wherein the region in which said shape memory alloy is to be operated is simplified down to the region surrounded by the line on which the stress is zero, a straight line by which said steeper gradient portion is approximated, said practical stress limit line and said strain limit line near shape recovery completion in said stress-strain diagram.4. A method of designing a shape memory alloy actuator as set forth in claim 1, wherein the region in which said shape memory alloy is to be operated is simplified down to the region surrounded by the line on which the stress is zero, a straight line by which said steeper gradient portion is approximated, said practical stress limit line, and the straight line connecting the intersection of said practical stress limit line and said strain limit line near shape recovery completion and the point where the stress and the strain are zero in said stress-strain diagram.5. A method of designing a shape memory alloy actuator as set forth in claim 1, wherein said shape memory alloy exhibits a two-way shape memory effect with a strain of 2% or more in tensile strain equivalent.6. A method of designing a shape memory alloy actuator as set forth in claim 1, wherein said shape memory alloy exhibits a two-way shape memory effect over almost the whole range in which the strain is recoverable.7. A method of designing a shape memory alloy actuator as set forth in claim 1 further comprising the step of: providing biasing means for biasing said shape memory alloy in a direction to impart a deformation thereto so that a line representing characteristics of said biasing means crosses said region in which said shape memory alloy is operated in said stress-strain diagram. 8. A method of designing a shape memory alloy actuator as set forth in claim 7, wherein, said line representing characteristics of said biasing means is made to cross said steeper gradient portion and said strain limit line near shape recovery completion.9. A shape memory alloy actuator comprising: a shape memory alloy exhibiting a two-way shape memory effect and having a stress-strain property that, in a str ess-strain diagram with the stress plotted in ordinate, the upward direction taken as the positive direction, and the strain plotted in abscissa, the rightward direction taken as the positive direction, the stress-strain curve at a low temperature comprises a gentler gradient portion extending from the position at which the strain is zero to the right with relatively small gradients, in the area in which the stress is negative or approximately along the line on which the stress is zero, and a steeper gradient portion extending upward to the right with relatively great gradients on the right of said gentler portion; said shape memory alloy being operated in the region surrounded by said gentler gradient portion, said steeper gradient portion, a practical stress limit line on which the stress in said shape memory alloy reaches a specified practical limit, a straight line connecting the intersection of said practical stress limit line and a strain limit line near shape recovery completion on which the strain of said shape memory alloy reaches a specified value in a state close to the shape recovery completion and the point where the strain is zero at a low temperature in said stress-strain diagram. 10. A shape memory alloy actuator as set forth in claim 9, wherein said shape memory alloy is operated in the region surrounded by said gentler gradient portion, said steeper gradient portion, said practical stress limit line and said strain limit line near shape recovery completion in said stress-strain diagram.11. A shape memory alloy actuator as set forth in claim 9, wherein said shape memory alloy exhibits a two-way shape memory effect with a strain of 2% or more in tensile strain equivalent.12. A shape memory alloy actuator as set forth in claim 9, wherein said shape memory alloy exhibits a two-way shape memory effect over almost the whole range in which the strain is recoverable.13. A shape memory alloy actuator as set forth in claim 9 further comprising biasing means for biasing said shape memory alloy in a direction to impart a deformation thereto, a line representing characteristics of said biasing means crossing said region where said shape memory alloy is operated in said stress-strain diagram.14. A shape memory alloy actuator as set forth in claim 13, wherein in said stress-strain diagram said line representing characteristics of said biasing means crosses said steeper gradient portion and said strain limit line near shape recovery completion.15. A shape memory alloy actuator as set forth in claim 9, further comprising stress-limiting means for preventing the stress in said shape memory alloy from exceeding said practical limit.16. A shape memory alloy actuator as set forth in claim 15, wherein said stress-limiting means comprises an alloy supporting member for supporting said shape memory alloy, said alloy supporting member being displaced in a direction to relieve the stress in said shape memory alloy when the stress is about to exceed said practical limit.17. A shape memory alloy actuator as set forth in claim 16, wherein said alloy supporting member has elasticity and is deformed in the direction to relieve the stress in said shape memory alloy when the stress is about to exceed said practical limit.18. A shape memory alloy actuator as set forth in claim 16, wherein said stress-limiting means comprises a spring that normally holds said alloy supporting member at a predetermined position, while allowing said alloy supporting member to displace from said predetermined position in the direction to relieve the stress in said shape memory alloy when the stress is about to exceed said practical limit.19. A shape memory alloy actuator as set forth in claim 15, wherein said shape memory alloy is driven by an electric current passed therethrough and said stress-limiting means interrupts the current to said shape memory alloy when the stress in said shape memory alloy is about to exceed said practical limit.20. A shape memory alloy actuator as set forth in claim 19, wherein said stress-limiting means comprises a reference shape memory alloy that carries an electric current in common with said shape memory alloy operated in said region and said stress-limiting means interrupts the electric current to said shape memory alloy operated in said region when the stress in said reference shape memory alloy is about to exceed a predetermined value corresponding to said practical limit.21. A shape memory alloy actuator as set forth in claim 9, further comprising strain-limiting means that prevents said shape memory alloy from performing shape recovery beyond said strain limit line near shape recovery completion.22. A shape memory alloy actuator as set forth in claim 21, wherein said shape memory alloy is driven by an electric current passed therethrough and said strain-limiting means interrupts the electric current to said shape memory alloy when said shape memory alloy is about to perform shape recovery more than a determined level.23. A shape memory alloy actuator as set forth in claim 22, wherein said strain-limiting means comprises a reference shape memory alloy that carries an electric current in common with said shape memory alloy operated in said region and said strain-limiting means interrupts the electric current to said shape memory alloy operated in said region when said reference shape memory alloy is about to perform shape recovery more than a determined level.
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