Enhanced cascade control approach for non-orthogonal shafting laser tracking systems based on fuzzy control techniques

Abstract The non-orthogonal shafting design is motived by the growing demand for large-scale measurement instrument, and the matching laser tracking technology is required to be completed to improve the automation and flexibility. While, due to the complexity and nonlinearity of non-orthogonal shafting architecture, it is difficult to calculate the rotation angles of the two axes based on the tracking deviation in the absence of distance information, and traditional proportional, integral and differential method cannot enable the system to adapt to unknown sudden target movement efficiently. Thus, the enhanced cascade control method for non-orthogonal shafting laser tracking system based on fuzzy control theories is proposed in this paper. Firstly, a position loop fuzzy prediction and tracking algorithm is proposed. Based on the current motion state of the target, the fuzzy controller predict the motion trend and calculate the tracking speed of the two axes. By implementing a two-stage model of coarse adjustment and fine adjustment, the responsiveness and stability of the laser tracking system have been improved. Secondly, the particle swarm optimization algorithm is adopted to conduct offline iterative optimization of the parameters of the scaling factor in the variable universe fuzzy control, achieving the rapid adaptability of the speed loop. The simulation results show that, compared with cascade PI control, this method has a faster response speed and a smaller tracking error. The experimental results show that the average dynamic tracking error and average static tracking error of this method are 1.873 58 mm and 0.026 89 mm respectively, and the fastest tracking speed of the non-orthogonal system is better than 7° s −1 .