Motion Analysis and Orientation Holding Control of a 3-RRR Rigid-Flexible Coupling Mechanism for Photovoltaic Panel Assembly

Abstract

This article is concerned with the design and control of a 3-Revolute-Revolute-Revolute Parallel Manipulator (3-RRR) rigid-flexible coupling mechanism, to meet the high flexibility and stability requirements for holding control in photovoltaic (PV) panel assembly. A mathematical model is established including forward, inverse, and differential kinematics, which is collapsed into the standard state-space equations. The relationship between the spherical workspace of a 3-RRR rigid-flexible coupling mechanism and the size of its orientation transformations is analyzed. Due to the orientation holding requirements in the PV panel assembly process, a quasi-sliding mode control (QSMC) is designed for orientation adjustment of the 3-RRR mechanism. The effectiveness of the algorithm is verified through simulation and experiment, compared with the traditional PID control. An industrial robot is connected with the 3-RRR rigid-flexible coupling mechanism and programmed to exert continuous disturbance and step signals. The motion capture cameras are adopted to capture the end orientation transformations in real time as feedback. Compared with the traditional PID control method, the mean absolute errors with QSMC are reduced by 64.55% and 65.54% in α and β orientations, respectively. The maximum convergence time in α and β orientations subject to the step signals is accelerated by 52.98% and 54.36%, respectively.