Optimal design and application of a low-cost wire-sensor system for the kinematic calibration of industrial manipulators

The paper presents the results of a research project whose aim is investigating, from both a theoretical and an experimental point of view, all the aspects connected to the optimal design and use of a 6 DoF draw-wire sensors based measuring system in the kinematic calibration of industrial robots context. One essential operation in calibration is the measurement of the pose of the robotic gripper in a predefined set of points inside the working space. For this purpose optical devices, like laser trackers, are usually employed due to their precision, although they are very expensive. Therefore, the study of a low-cost measuring system and the investigation of the reachable performances could represent a relevant outcome in the evolution of the calibration task. With this aim the design of a wire-sensors based measuring system was developed and applied to a six revolute degrees of freedom anthropomorphic robot. In a preliminary phase, with the aid of simulations tools, the measuring system was optimized to obtain isotropic accuracy and high sensitivity, while in the following experimental phase the same system was employed for the kinematic calibration of the robot, achieving an accuracy lower than the robot repeatability, which practically represents a physical limit.