Hybrid impedance control in constraint coordinates using a disturbance observer

Many contact tasks are more easily defined in terms of constraint equations (and therefore constraint coordinates), rather than either Cartesian or joint coordinates. Deburring and grinding are examples of two such tasks. Hybrid impedance control has been a popular force control algorithm for these tasks. This paper gives a procedure to specify orthogonal subspaces in constraint coordinates. It is then easy to design a hybrid impedance controller in those constraint coordinates. To enhance the performance of the controller under model uncertainties and/or disturbances, a disturbance observer designed in the constraint frame is incorporated in the controller design. To show the performance improvement provided by the disturbance observer, this controller is compared to a common adaptive algorithm.