The Puller-Follower Control of Compliant and Noncompliant Antagonistic Tendon Drives in Robotic Systems

This paper proposes a new control strategy for noncompliant and compliant antagonistic tendon drives. It is applied to a succession of increasingly complex single-joint systems, starting with a linear and noncompliant system and ending with a revolute, nonlinearly tendon coupled and compliant system. The last configuration mimics the typical human joint structure, used as a model for certain joints of the anthropomimetic robot ECCEROBOT. The control strategy is based on a biologically inspired puller-follower concept, which distinguishes the roles of the agonist and antagonist motors. One actuator, the puller, is considered as being primarily responsible for the motion, while the follower prevents its tendon from becoming slack by maintaining its tendon force at some non-zero level. Certain movements require switching actuator roles; adaptive co-contraction is used to prevent tendons slackening, while maintaining energetic efficiency. The single-joint control strategy is then evaluated in a multi-joint system. Dealing with the gravitational and dynamic effects arising from the coupling in a multi-joint system, a robust control design has to be applied with on-line gravity compensation. Finally, an experiment corresponding to object grasping is presented to show the controller's robustness to external disturbances.