Force Tracking Impedance Control for Robot Manipulators with an Unknown Environment: Theory, Simulation, and Experiment

In impedance control for force tracking, it is well known that the reference trajectory of the robot is calculated from known environmental stiffness. The authors present a simple technique for determining the reference trajectory under the condition that the environment is unknown. The technique is developed based on the replacement of the unknown stiffness with a function of the measured force. Combining this technique with the impedance function yields the force tracking impedance function. Robot dynamic uncertainties are assumed to be compensated by a robust position control method based on time-delayed control. The local stability at equilibrium points is analyzed with respect to uncertainty in environmental position. Computer simulation studies demonstrate that force tracking using the proposed technique is excellent for unknown environment and dynamics uncertainty. The practicality of the technique is also verified experimentally using a PUMA 560 manipulator.