On the design and simulation-based validation of an active compliance law for multi-arm robots

A special active compliance law is presented as the feedback element in a non-master/slave (i.e. symmetric) coordination strategy with explicit force distribution for robots with multiple cooperating arms. The method used to design the compliance controller comprise a structural design phase and dynamics design phase. The proposed controller structure simplifies the design problem as it maps the multivariate system onto two decoupled SISO loops with PI controllers describing internal and external compliance behavior. The conditions for the validity of this conceptual system model are discussed and the significance of task parameters such as grasp configuration, force distribution law and mechanical compliance values for the controller structure is explored. The dynamic behavior of internal and external compliance is determined in the second design phase by the choice of gain and integral action time of the respective controllers. An example shows the applicability of classical SISO control system design tools such as the root locus technique. The validity of the design method has been verified by means of the multi-arm robot simulation program MAROSIM, which is also presented in the paper.