Use of Hidden Robot Concept for Calibration of an Over-Constrained Mechanism

Abstract

Overconstrained mechanisms prove useful in applications where high stiffness and low weight is required against high amount of forces while keeping high precision. This study issues a planar two degrees-of-freedom overconstrained parallel manipulator for positioning the end-effector with high acceleration values (>5g) with a positioning precision in the order of 30 micrometers. Since the manufacturing errors were compatible with the end-effector positioning errors, it was required to perform some system identification before the precision and repeatability tests. For the system identification, the end-effector position and motor input values are recorded. However, since the mechanism is overconstrained, the link lengths could not be obtained due to the lack of analytical inverse kinematics solution. In order to cope with this problem, the hidden robot concept is utilized in order to fit a simple kinematic model between the task space and the joint space of the manipulator. Further calibration studies are carried out using the error correction matrix. The test results are presented.