Dynamics and control of a free-floating space robot in presence of nonzero linear and angular momenta

Abstract

Common control methods for free-floating robots assume zero initial linear and angular momenta, for which a reduced joint dynamics equivalent to that of a fixed-base robot can be obtained. On the other hand, a disturbance is induced in the system dynamics when the linear or angular momenta are not zero, leading to a deviation of the end effector. In this work the dynamics of the free-floating robot in presence of momentum is analyzed and a torque feedback control is proposed. An operational space formulation is considered to identify the disturbing Coriolis/centrifugal forces and to cancel them by feedback. A stability proof for the proposed controller is developed using a time-varying approach. The effectiveness of the control is shown in simulation for a seven degrees-of-freedom arm connected to a floating-base under the effect of linear and angular momenta considering model parameters uncertainties.