Twisted-string actuation devices have been adopted in various robotic systems due to their advantages of compact size and simple\nstructure. To precisely control the displacement of such devices, a dual-direction actuating mechanism, which provides both\nextension and contraction of two strings simultaneously, must be implemented. Due to the physical properties of twisted string,\nthe actuator has problems of nonlinear length variation and cross-coupled relationships between two strings. In this study, two\ncontrollers (PID-FC and LQR-FC) were synthesized with the consideration of cross-coupling dynamics between the two axes. The\nexperimental results demonstrate the performance of both tracking and synchronization responses of these two types of controllers.
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