Force-controlled assembly with a two-arm robot: How and where to perform it within the workspace

The use of a two-arm robot for assembling two objects, with each being held by one arm, is presented. More precisely, the authors propose some solutions for determining how and where such an assembly task should be performed. For the approach phase (before contact), they define the motion of one end-effector with respect to the other, without reference to any fixed frame. This allows them to take advantage of the two-arm robot redundancy. For the insertion phase, they use a symmetric hybrid control scheme. Real experiments with two PUMA robots have shown that the success of the assembly is highly dependent on the location where the assembly is performed. This is due to the control of contact forces between the objects, which can be done more or less properly. This problem is treated by using the concept of manipulability, represented by ellipsoids.