Study on observability of a parallel-typed machining center using a single planar table and digital indicators

This paper presents a fully observable and global kinematic calibration method for a parallel manipulator. A constraint operator is introduced to constrain a mobile platform with a planar table and digital indicators. Taking calibration data from the optimal configurations makes the kinematic parameters fully observed while shifting a constraint plane leads to the global calibration. We eliminate the concern over the poor parameter observability due to the constrained movements and the local calibration due to a single planar constraint. The low-cost and high-accuracy digital indicators are used as a device to check if the constrained movement is completed. Using only one planar table for a mechanical fixture avoids the misalignment of multiple constraint planes. We apply the calibration method to the Stewart–Gough platform. Calibration results verify that the method, which improves the robustness under the constrained movements, is a fully observable and global calibration manner.