Modeling and observation of hysteresis lost motion in elastic robot joints

In this paper the modeling and observation of elastic robot joints with hysteresis is addressed. An adequate model of the joint torque transmission which could capture the hysteresis lost motion is of outstanding interest for design and control of flexible joint robots. A method of describing the significant joint nonlinearities such as dynamic friction and state-dependent stiffness with hysteresis is proposed. The joint dynamics is considered as an interplay between the propulsion and reactive torque. Direct and inverse hysteresis models of state-variant joint stiffness are introduced and identified from experiments. The proposed joint torque observer can serve as a “virtual” sensor of hysteresis lost motion without measuring the joint output.