Effect of Vibration on Twisted String Actuation Through Conduit at High Bending Angles This paper studies an effect of vibration on twisted string actuation through conduit at high bending angles. In our previous work 1, we have demonstrated that twisted string actuators can be used to transmit power even at significant deflection angles of the conduit. However, several undesirable effects, namely pullback, hysteresis, and chattering, were present during actuation due to friction between strings and the internal sheath of the conduit. This paper reports the results of experimental study on effects of vibration on twisted string actuation inside deflected conduits. We have demonstrated that applying vibration generated near natural frequency of the system during the later stages of twisting and untwisting cycles helped reduce pullback and hysteresis and increase string contraction. In case when sheath was deflected by 180xc2xb0 under a constant load of 3 kg, we were able to achieve over 70% decrease in pullback and 30% decrease in hysteresis, compared with no vibration case.

A ClosedLoop Controller for CableDriven HyperRedundant Manipulator with Joint Angle Sensors * A cabledriven hyperredundant manipulator is especially suited for manipulations in confined spaces. In most of the existing approaches, a controller is often designed to actuate the joints by pulling the corresponding cables without the feedback from remote sensors at the joints. The unmodeled elongations of these cables due to unknown tensions often cause a decrease in control precision. To improve the performance of such a manipulator, this paper presents an investigation where miniature potentiometers are integrated into the joints for angle feedback. Furthermore, a pullerfollower controller is developed to control the three cables of a universal joint for not only closed loop joint angle control but also cable tension preservation. Applying the Hookexe2x80x99s Law, the cable tension is represented by its deformation. In this way, the controller is designed to realize both the desired angles and the cable deformations, without force sensing on the cables. Finally, experiments on a single joint and multiple joints were conducted to verify the effectiveness of this proposed controller.