Independent torque and stiffness adjustment of a pneumatic direct rotary soft-actuator for adaptable human-robot-interaction

An important property of rehabilitation robots required for safe and human-like interaction is compliant actuation combined with light-weight design. This requirement can be fulfilled by fluidic soft-actuators like pneumatic muscles due to inherent passive compliancy and high power to weight ratio. However because of the nonlinear dependency on actuator chamber contraction and air pressure as well as friction effects control of such actuator type still remains challenging, even for common position or force control. For human-robot-interaction (HRI) it is necessary to adapt the actuator output characteristics appropriately depending on the manipulation task and/or the capabilities of the individual person. This paper presents an approach to independently adjust torque and compliance/stiffness of a soft-actuator with direct acting antagonistic rotary elastic chambers (REC) and illustrates a possible example of application with an exoskeleton robot for lower extremities training.