A practical approach to enhance positioning accuracy for industrial robots

Robot calibration plays a significantly important role in enhancing robot positioning accuracy, and it is known that inaccurate kinematic parameters and deflection due to elasticity of each joint take majority of error source of uncalibrated robots. This paper presents a practical approach for improving the accuracy of industrial robots by compensating the deflected angles as well as the kinematic parameters. The key idea of this paper is that robot controllers are able to generate accurate commands if the kinematic parameters and joint stiffness parameters generated by calibration process were reflected. A new robot calibration algorithm was developed, which is able to identify both the kinematic and stiffness parameters simultaneously, and the deflection compensators using the stiffness of robot axes were developed for forward and inverse kinematics embedded in robot controllers. Also HRCAL(Hyundai Robot Calibration), Windows based software, was implemented with the algorithm. For real-time applications, since it is not desirable to use an iterative method for inverse kinematics in the controller, only some kinematic parameters not affecting analytical inverse kinematics were calibrated with joint stiffness parameters. Then the calibrated parameters were reflected in the controller of the system. Finally the effectiveness of this method was verified by some experiments with the HS165 robot system designed and manufactured by Hyundai Heavy Industries Co., Ltd.