High-Bandwidth Control of Twisted String Actuators

Twisted string actuators are an emerging type of transmission systems that may benefit various applications of robotics and mechatronics. However, control of TSAs in applications that require high bandwidth has attracted comparatively little interest from research community, mainly due to complexity of twisted string behavior. This paper proposes a new adaptive control methodology that allows to sufficiently increase bandwidth of TSA-based systems. We reformulate mathematical model of the TSA into a suitable form for online parameter estimation, outline adaptive estimation methods and propose a method to design variable controller gain that rectifies nonlinearities in the system. We present experimental comparison of proposed adaptive control strategies with two conventional TSA control techniques. Experimental results demonstrated that the proposed adaptive control architecture with feedforward speed term was nearly insensitive to increase in input signal frequency while reducing position tracking error by 80%. Proposed algorithm can be applied in any TSA control system that has input and output signal measurements.