Generalized contact force estimator for a robot manipulator

In this work, we present implementation and experiment of the theory of dynamic force sensing for robotic manipulators. In the robot manipulation context, end-effector contact forces may be difficult to measure due to tool interference, yet indirect measurement such as from wrist-mounted force sensors provide force measurement contaminated by inertial forces of the tool distal to the force sensor. In order to extract the contact force exerted by the robot, it is necessary to separate the contact forces from inertial forces. We propose a complete formulation and implementation of a new control strategy based on multi-sensor fusion with three different sensors-that is, encoders mounted at each joint of the robot with six degrees of freedom, a wrist force sensor and accelerometers-whose goal is to obtain a suitable contact force estimator. These new observers contribute to overcome many of the difficulties of uncertain world models and unknown environments, which limit the domain of application of contemporary robots used without external sensory feedback; in addition, the final observer can be applied to any kind of real robot system. An impedance control scheme was proposed to verify the improvement. The experiments were carried out on an industrial Staubli RX60 manipulator with open control system architecture.