Kinematic identification of a closed-chain manipulator using a laser interferometry based sensing technique

This paper focuses on a technique for the identification of parameters needed for kinematic modeling of an industrial manipulator, Motoman SK 120, with a parallel five-bar mechanism. Two classical estimation techniques, nonlinear and linear least squares, are employed to determine the parameters from a number of manipulator end point positions measured by a high precision laser tracking system with a single beam laser interferometer. The kinematics parameters of the five-bar mechanism in the topology of the manipulator are considered during kinematic modeling and parameter identification procedure. Numerical results presented demonstrate that the root mean square position error can be improved by at least 60% with the identified parameters. Although slightly different parameters are obtained from both estimation techniques, the resulting root mean square position errors remain the same. When the kinematics parameters of the five-bar mechanism are not included in the model for parameter estimation, the improvement in the root mean square position errors has been limited to 35%.