Controlling the contact compliance via internal forces on objects held by dual-arm robots

When two robot arms holding an object together they form a closed kinematic chain which enables generation and control of arbitrary internal forces on the object. The internal forces balance within the closed kinematic chain and therefore do not contribute to the resultant force that generates motion. However, they change the effective compliance realized on the object. Therefore when the object held by the robots makes a contact with a rigid environment the compliance at the contact location does not only depend on the inherent compliances and the posture of each robot arm but also depends on the internal forces exerted on the object. In cases when the contact location moves relative to each robot´s tip, the compliance at the contact depends also on the variation of the contact location. In this study we propose a method that utilizes the internal forces to keep the contact compliance in primarily important directions close to the desired values regardless of the variation of the contact location and robots´ posture