Closed Loop Control of Melt Pool Width in Laser Directed Energy Deposition Process Based on PSO-LQR

Abstract

A closed-loop controller was proposed to adjust the laser power to maintain melt pool stability based on the linear quadratic regulator (LQR) control theory. The melt pool width acquisition system was built based on complementary metal oxide semiconductor (CMOS), and the captured melt pool image was processed using an image processing algorithm to obtain the melt pool width. The laser power was used as the input variable and the melt pool width as the output variable. The state space spatial model was identified using the subspace method to identify the experimental data. The LQR controller was designed based on the state space equation, to improve the controller’s performance and reduce the hassle of selecting the weighting matrix ${Q}$ in LQR. A particle swarm optimization (PSO) algorithm was used to optimize the control weighting matrix globally, and the optimal control weighting matrix was obtained. The controller performance was evaluated by constant-width and variable-width thin-wall deposition samples, and the results showed that the algorithm is simple, efficient, and able to maintain the melt pool width stable in real-time. It can effectively reduce reliance on manual experience.

Keywords

• Laser directed energy deposition
• melt pool width control
• optimal control
• particle swarm optimization