Developing a novel continuum module actuated by shape memory alloys

Abstract

Developing continuum manipulators is very useful for special robotic applications. One of the practical usages is medical tools such as endoscope or colonscope. In such applications, a maneuverable thin and flexible manipulator is highly required. In this paper, a basic module is designed which can be used as an element of a continuum manipulator in a modular configuration. Furthermore, the module can simultaneously be utilized both as a joint and actuator in a mechanism. In the structure of the module, three springs of shape memory alloy (SMA) are uniformly distributed and mounted around a bias spring with an angle of 120°. Stimulating SMA springs individually or together provides different rotation regimes. Brinson model and normal compression spring behavior are used for modeling of SMA and bias spring, respectively. Afterward, the model of SMAs and bias spring are integrated to describe the behavior of the actuated module. The modeled module is simulated in Matlab software by which the proper control strategy can be designed. Due to the complex and nonlinear behavior of SMAs, design an appropriate control scheme is a real challenge. In this paper, a new control strategy is developed for regulating a desired position for the two degrees of freedom actuator module. Through the provided test bed, the performance of the strategy is verified. The results present a reasonable performance of the controller and reveal the merits of the developed module in continuum robotic manipulators or flexible joint actuator.