A new method for fully autonomous calibration of parallel manipulators using a constraint link

Kinematic calibration is a process whereby the actual values of geometric parameters are estimated so as to minimize the error in absolute positioning. Fully autonomous methods of calibration are cost effective, fast and easy to implement. This paper presents a new method for fully autonomous calibration that can be applied to 6 degree-of-freedom fully parallel manipulators. The proposed method uses a link of fixed length, having spherical joints at both of it ends, to restrain the motion of the end-effector over spherical surface with arbitrary orientations. The end-effector, therefore, has 5 degrees of freedom. However, the measurement data is collected from 6 actuator sensors. This redundancy of sensory information is utilized for calibrating the geometric parameters without using any extra sensing device. The calibration procedure can be completely automated for the six kinematic chains of the manipulator. Simulations have been performed to show the effectiveness of the proposed method