Position/force control of a manipulator with unknown constraints

The control of force as well as position of the end-effector in a manipulator has become a common requirement in many applications. The force exerted by the end-effector is usually controlled in a direction normal to the constraint surface, while the position of the end-effector is maintained in the tangential direction. In this paper, the position/force control of a manipulator over unknown surfaces is studied. The position and force degrees of freedom are specified for unknown constraint surfaces depending on the type of contact. Three types of contact (point, line, and plane) are considered. The type of contact is determined based on the point of contact which is calculated from information received from a wrist force/torque sensor. The reduced order position/force control method is then applied to effectively control the manipulator in orthogonal directions considering the type of contact. An example is presented to demonstrate the technique