This paper examines the stability of the flexible-object impedance controller when coupled to an arbitrary passive environment. A simple representative system is developed to study the problem based on phenomena observed in a more complex, experimental system. Analysis of this representative system leads to several conclusions regarding factors that limit the achievable impedances of a multi-arm system grasping a common object. The filtering of the external force signals and the effective mass contributed by the manipulators prove to be two of the important factors. Some general guidelines are developed for the successful application of flexible-object impedance control to insure coupled system stability. These guidelines are applied to both the representative and experimental systems and verified.

This paper presents a control strategy for manipulation of flexible objects by multiple robot arms. The control policy developed in this paper for flexible objects is based on a controller developed previously for rigid objects: the object impedance controller. The controller compensates for the dynamics of both the arms and the object and responds to environmental forces with a fully programmable impedance relationship. For a class of flexible objects, the required extensions to object impedance control are outlined in this paper. The paper presents experimental results for a dual arm robotic system manipulating an object with a single flexible degree of freedom in both free-space and environmental contact tasks.>