Shape memory alloy actuator and method of designing the same

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.