Robotic Instrumented Complaint Wrist

A robotic complaint wrist which combines a passive compliance device and a displacement sensor has been developed and tested. The device provides the necessary flexibility to accommodate transitions between the position control and force control modes, and avoid large impact forces as a robot makes contact with parts, as well as correct positioning errors and allow the relaxation of tolerances in assembly and manufacturing operations. The device installed between a robot arm and end-effector is composed of two parts: a passive compliance device and a sensing mechanism. The passive compliance is provided by a rubber structure; its configuration can be arranged to yield the desired stiffness ratio along and about each axis. The sensing mechanism consists of a six-joint serial linkage with a transducer at each point. The measured deflection is used to actively control the contact forces and compensate for the positioning error during motion and contact. In this paper, the design features of two prototypes of the device are described. A systematic hybrid position/force control scheme incorporating the device is presented.