Structural design method of rotation gear actuated by shape memory alloys

Shape memory alloys (SMA) are highly active actuators. When shape memory alloys are used to realize a two-way actuation with a large driving force and a long driving stroke, a bias mechanism should be added to finish the symmetrical movement. When a spring is used as a bias mechanism, continuous energy input is required to keep the deformation. To overcome this shortcoming, a structural design method of rotation gear actuated by shape memory alloys based on constraint condition of strain is put forward. The structure is realized by sprocket feed and one-way shape memory effect and a two-way actuation is finished by the bias mechanism made up of shape memory alloy itself. Space of sprocket drive can be erased by the contraction of SMA. According to the feature of this structure, the formulas of geometric parameter design and torque are given. Under the constraint condition of strain, relations between stress and strain of shape memory alloys are studied through experiment. A strain dead zone existing during the actuation is given and an angle design function is corrected.