Manipulators Constrained by Stiff Contact: Dynamics, Control, and Experiments

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Abstract
The problem of concurrent motion and force control for ma nipulator tasks with continuous contact between end effector and environment is addressed in this article. In contrast to previous work, no compliance is assumed between end effec tor and contacted object, but instead the contact is modeled to be stiff. A convenient formulation of dynamic equations for constrained manipulators is presented that allows for a very simple inclusion of kinematic constraints resulting from stiff contact. The formulation is also applicable in situations where the compliance frame and/or the contacted object are moving. Based on the resulting dynamic equations, two separate compensators for the nonlinear and time-variant manipulator dynamics in the motion- and force-controlled subspaces are derived. Suitable discrete-time controllers for motion control and for force control are presented. The re sulting control scheme was implemented on an experimental high-speed manipulator, and results are given and discussed.

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