Accurate controlled shape memory alloy actuator for minimally invasive surgery

With the development of minimally invasive surgery (MIS), the surgical robot has been required to offer big output with a minimized volume. Shape memory alloys (SMA) Actuator exhibits large strain and high energy density, which shows good potential to be applied in the surgical robot. This paper proposes an accurate controlled SMA actuator with one degree of freedom (DOF). The system is actuated by two SMA springs, angle feedback system is used initially. After the parameters are regulated, PID controller shows very accurate control. To meet the need of demanding miniature applications, it is better to reduce the number of additional sensing devices. Previous research shows the electric resistance of SMA has approximate linear relationship with the strain, which make accurate self sensing become possible. A self-sensing model based on the SMA rotation angle to resistance curve has been established. The curve is modeled by fitted polynomial. Self sensing control is demonstrated through step response, the small pretension stress and the bad consistency of the SMA springs reduced the precision. More modification is worth to be done in the future to improve the self control model.