Improvement in Position Response of Laser Focus Controlled Magnetic Actuator Based on Mixed Sensitivity Robust Control

The relative position between the laser beam and the nozzle is controlled by laser-focus-controlled magnetic actuators to achieve non-coaxial laser cutting and improve laser cutting efficiency. In this paper, a 3-DOF (degrees of freedom) magnetic actuator is designed to solve the inconsistency of the laser beam focus and the nozzle focus in off-axis laser cutting. A mixed sensitivity robust controller is designed, and its simulation analysis and experimental research are carried out. First, the kinetic mathematical equations are established according to the structure of the actuator. Then, a mixed sensitivity robust controller is designed and analyzed using MATLAB/Simulink. The control performance is simulated and analyzed under 20% parameter variation and pulse disturbance with an uncertain mathematical model and external disturbance, respectively. Finally, the experimental study of the step response of the actuator is carried out. The experimental results show that the step response of the actuator in the Y, X, and θ directions can quickly reach the steady-state value. Furthermore, the steady-state error in the X is 1.6%; the steady-state error in the Y is 0.39%; the steady-state error in the θ is 0.45%. Their errors are all less than 0.025 mm, so they meet the position performance requirements. It can provide technical support for laser off-axis cutting.