Dynamic model of cable-conduit actuation for interaction with non-passive environments

Remote actuation is useful in human-interacting robots to reduce dynamic loading on distal joints. Cable-conduit transmissions, sometimes referred to as Bowden cable or tendon-sheath actuation, are a lightweight option for transferring power to a distal joint from a remotely located actuator. However, the nature of such transmissions causes the system to suffer from diminished efficiency and high reflected impedance as a result of distributed frictional effects between cable and conduit. A dynamic model is useful to produce controllers capable of accurately tracking force or displacement at the system's output. In this paper, we present a new computational model for cable-conduit systems that describes interaction with non-passive environments. Unlike previous models, our model features bi-directional propagation of motion within the cable-conduit system. This allows for simulation of human-interacting systems where both the human and the robot have the capability to impose motion or force. Because of this feature, the developed model is applicable to a wide range of physical systems. The model is validated in a physical prototype through experiments involving physical interaction with a human subject. We show that our model accurately predicts behaviors observed in the experimental system.