A Two-Step Self-calibration Method with Portable Measurement Devices for Industrial Robots Based on POE Formula

A two-step self-calibration method based on portable calibration devices is proposed in this paper. In the first step, the distance errors in a large-range workspace is utilized to calibrate the manipulator. In the second step, the position errors is utilized to calibrate an external world frame to describe all the coordinate systems in a robot cell and further enhance the calibration results in the first step. For each step, a linear and simplified calibration model is then formulated by employing the local POE formula and introducing the position adjoint conversion matrix. Based on the calibration model, portable and cost-effective self-calibration devices are designed, which consist of a spherical center measuring device, a movable ball bar and Tri-ball plate. The calibration devices presented can obtain distance errors in a large-range workspace and position errors in a local workspace of a manipulator, which enhance the reliability of the calibration results and set an external reference frame. Finally, an accurate kinematic model with respect to the external user-defined frame is given, which enables the off-line programming to be more accurate and effective. The simulation results demonstrate that the proposed two-step self-calibration algorithm is effective and robust.