Fuzzy based active stiffness control of a synergistically compliant variable stiffness shape memory actuator

Abstract

Shape Memory Alloy (SMA) based actuator has proven to be very convenient in variable stiffness and active compliance applications viz. robotics and bio-medical devices. The unique attractive feature of SMA is its stiffness varying property during phase transformation, in addition to its high force to weight ratio, mechanical simplicity and flexibility; all desirable for the design of new actuation technologies. Stiffness variation in the SMA based actuator using direct stiffness feedback for scaled down applications is comparatively loftier than in the conservatively designed variable stiffness actuator. The stiffness control performance of a newly developed synergistically operated translational compliant variable stiffness actuator (STCVSA) is determined and presented in this paper, for which system identification technique is employed to achieve the actuator model. Adaptive control algorithms (fuzzy PID and fuzzy Sliding Mode Control (SMC)) are considered for implementing the stiffness feedback control. The simulation results of fuzzy SMC and fuzzy PID controller is shown and is concluded that Fuzzy SMC has a robust nature capable to model uncertainties, disturbances and parameter variations.