An actuator of two-way behavior by using two kinds of shape memory polymers with different Tgs

A novel operating method for shape memory polymer (SMP) actuators has been developed and characterized. Since the shape memory effect works in one way, an external force to deform SMP has been used in conventional SMP actuators. Our actuators use only the shape memory effect to reproduce a specific behavior. Our operating method is as follows. Two kinds of SMPs with different glass transition temperatures (Tg1 and Tg2 (Tg1 < Tg2)) are used. After a memory shape relating to Tg1 is formed, the memory shape relating to Tg2 cancels the previous memory shape at Tg2, i.e., the memory shape of Tg2 is set to the reverse shape of the memory shape of Tg1. This method needs only the temperature cycle of heating and cooling to operate the actuator and this simple operating method is suitable for small size actuators. SMPs of polyurethane series are chosen for being able to tailor the Tgs. We confirmed that the proposed operating principle functioned experimentally by using two kinds of proto-type actuators of a cantilever beam and a diaphragm and examined the characteristics of them.