Towards variable stiffness control of antagonistic twisted string actuators

This paper shows the possibility of using two antagonistic twisted strings actuators as a new type of variable stiffness actuator. Variable stiffness model of the twisted string actuator is identified empirically, and the control strategy is proposed for simultaneous position and stiffness control of the actuator. A variable stiffness linear joint actuated by antagonistic twisted string actuators is proposed as a target system. The proposed model and control strategy make it possible to control the position and the stiffness of the joint without position and force sensor at the load side. The developed variable stiffness linear joint can be effectively used in applications where weight distribution is vital, such as exoskeleton systems and low weight manipulators.