Modeling and Evaluation of a Twist Drive Actuator for Soft Robotics

Abstract

Robotic technology is widening its scope into applications where robots coexist with humans and other living beings in a common space, and where cooperative and other physical interactions between the robots and the living beings are anticipated and actually occur. Safety of living beings and of robots in such an environment calls for solutions in robot mechanisms that are different from the recently used ones in industrial robotics. In this paper we present an actuator named a Twist Drive, which uses two strings that by twisting on each other generate a pulling force. The mechanism can be used to replace gear reducers in robot joints with benefits that originate in its muscle-like operation and in its nonlinear characteristics. A mathematical model to describe the kinematic transmission characteristics of the mechanism is presented and compared to experimental data. A passive characteristic of kinematic stiffness is discussed and evaluated in the paper. Experimental results show the adequacy of the proposed models. Durability of commercially available strings was tested and the results reported. Application in a robot's joint is briefly presented by an example.