Space-to-plane decoupling method for six-degree-of-freedom motion measurements

The advantages of the Stewart platform in bearing capacity, dynamic response, structural rigidity, and stability make it widely used in many fields, such as motion simulators, parallel machine tools, assembly docking. In order to ensure that the spatial positioning accuracy of the Stewart platform to meet the application requirements in various fields, it is necessary to measure its pose in real time. However, the six degrees of freedom are highly coupled, it is difficult to obtain reliable six-degree-of-freedom information through mathematical decoupling. In this study, a machine vision measurement method based on physical decoupling is proposed. The spatial motion measurement of the Stewart platform is mapped to the plane motion measurement by three feature points through the laser pointer and the rear-projection screen. It realizes the dimension reduction equivalently, and simplifies the mathematical model. A lot of experimental analyses show that the proposed method can reliably achieve high-precision real-time measurement of six-degree-of-freedom, which has the accuracy of 0.21 mm (displacement) and 0.045° (rotation) at frequency between 0.1 and 1 Hz. In addition, the space-to-plane decoupling method provides a new way to implement the traceability of the six-degree-of-freedom spatial motion measurement.