Payload estimation based on identified coefficients of robot dynamics - With an application to collision detection

We revisit the classical problem of estimating the dynamic parameters of an unknown payload rigidly held by the robot end effector. The approach relies on the analysis of the symbolic expressions of the robot dynamic coefficients (i.e., combinations of dynamic parameters) when working with and without payload, with no special assumptions on payload structure. The linearity of the associated changes in the dynamic coefficients due to the payload addition is exploited so as to estimate the gravity and inertial parameters of the payload. The procedure is illustrated in simulation on a planar 2R robot with asymmetric payload and through experiments on a 7R KUKA LWR arm with medium payloads. Accurate estimates of non-inertial payload parameters can be obtained even by running the identification scheme on few small motions in a restricted area. The results are shown to be useful for improving the sensorless collision detection capabilities of a robot arm in the presence of an a priori unknown payload.