A direct-drive, robot parts, and tooling gripper with high-performance force feedback control

The authors present the design of a direct-drive parts and tooling gripper for use in robotic assembly operations. The gripper design incorporates three-dimensional force vector sensing and both force and position control with extremely-low-friction, direct linear motor drives. The authors present a state-variable approach to force control and discuss the design techniques required for a manipulator to achieve high-performance force control. They introduce an underlying principle in force control by demonstrating that the contact stiffness between the environment and the manipulator must be known and of an optimum range to provide good force control. To verify the techniques, a servo-controlled manipulator with compliant vector force sensing was developed. The manipulator features direct-drive, linear motors and compliant, vector force sensors. Force resolution was optimized by eliminating friction sources. Inertia was kept to a minimum to allow command following performance. A compliant vector force sensor provides the known contact stiffness between the manipulator and the workpiece environment. Experimental results show that force sensor stiffness is a key element in force loop control design and that robust force control dynamics are comparable to robust position control loop dynamics