A new pose measuring system based on a spatial four bar linkage with RSSR chain

This paper proposes a new low cost procedure for the simultaneous measure of all the six coordinates of the pose of a body with respect to a given reference frame. One of the fields in which this feature can be applied is the robot calibration where the actual pose of the gripper must be measured over the workspace of the robot. The proposed measuring system consists in a spatial four bar mechanism with a symmetrical (RSSR) kinematic structure. The pose is estimated measuring the rotation of the two revolute joints. The paper develops the estimation procedure in analytical form and derives the uncertainty of the estimation caused by the limited repeatability of the used sensors. A numerical example of the achievable measuring range and uncertainty is also given.