FORCE CONTROL OF KINEMATICALLY CONSTRAINED MECHANISMS IN THE PRESENCEOF CONTACT POINT DISTURBANCES

This paper presents a discussion of the issues related to force contro l in closed-loop kinematically constrained mechanisms. Unlike many of the analyses presented in robotics literature, which tend to model the contact with a stiff, but finite, compliance, the analysis in this pa per focuses on the issues particular to mechanisms in which the contac t relationship is kinematic. Motions of these kinematically constraine d points thus give rise to contact force fluctuations which are relate d to both the inertial properties of the mechanism and the nonlinear k inematics. By modelling the constrained system as a closed-loop mechan ism, it is possible to take into account both the kinematic constraint and the dynamic properties of the mechanism in order to derive force control laws which can be used to regulate contact forces even in the presence oi contact point disturbances. Simulations and experiments wi th a simple one-link constrained mechanism underscore the importance o f inertial force and contact point disturbance consideration in force control.