On-line acquisition of link deformations for the robot of accuracy
Repeatability and accuracy of the robot operation are two distinct specifications of the robot capacity. Repeatability measures the precision with which the manipulator revisits a taught point, while the accuracy discloses how closely the manipulator visits a computed point. The accuracy of a taught point is limited by the resolution of the operator’s eyes. On the other hand, the accuracy of the computed point is limited by nothing other than the computer rounding errors. The computed point defines the desired position via forward and backward kinematics of the rigid manipulator. Unfortunately, no manipulator is rigid. Static deformation exists. As a result, the computed point deviates from the position where the manipulator actually visits. To remedy this problem, compensation methods have been explored. They require the link deformation to be identified on-line. No such method exists to date. This thesis explores a novel method which acquires link deflection and angular bending on-line. To facilitate the acquisition method, laser light source, partial-pass reflectors and sensor arrays are aligned on the link. Positions where the laser beams project on the sensor arrays are measured to calculate the link deformations. The sensitivity analysis is also performed. In addition, computation examples illustrate the on-line acquisition method. The feasibility of its adoption using today’s equipment is addressed.