粉末成形液压机自适应鲁棒运动控制

在粉末冶金零件成形生产中,压坯产品的质量取决于粉末成形工艺的完成度,这依赖于成形液压机的运动控制性能。然而控制粉末成形液压机运动的电液系统是一种具有参数不确定性的非线性系统,且整个运动控制系统在粉末致密化加压成形过程中还受到了负载压制力的强非线性干扰。针对以上难题,研究中建立了负载压制力的非线性模型,将其与电液系统的动力学模型相结合,基于此包含负载动力学的控制设计模型利用自适应鲁棒控制理论设计了粉末成形液压机的压制运动控制器。理论上,该控制器保证了鲁棒瞬态性能和稳态跟踪精度。实验结果表明,所设计的电液控制器可以实现对铁基粉末成形圆柱体压坯单向变速压制工艺压制运动曲线的精确跟踪控制,并表现出良好的控制性能。

Adaptive Robust Motion Control of Powder Compaction Press

High-performance pressing motion control of powder compaction press for improving the quality of green compacts was considered. With the aim to realize precise motion trajectory tracking control, physical modeling of the compacting force in powder densification process was developed and validated by iron-based powder compressibility test. A control oriented model was constructed to describe the system dynamics of the electro-hydraulic system of the powder compaction press by using the solenoid valves. Then a motion controller based on adaptive robust control (ARC) method was synthesized by back-stepping design with Lyapunov function. The controller took into consideration of the effect of parameter variations with the strongly nonlinear disturbance of compacting force coming from the powder press molding process and various hydraulic parameters as well as the effect of hard-to-model nonlinearities and uncertainties. The stability, tracking transient and final tracking accuracy of the system can be guaranteed by the controller. Experimental study was also carried out through a 1 000 kN powder compaction press prototype. The pressing motion control of the prototype machine in the iron-based powder forming cylinder compact process was used as a case study. The analysis and experimental results showed that the proposed control method achieved satisfying control performance for the powder compaction press, validating the effectiveness of the proposed control approach in practical applications. In powder forming process the tracking errors were reduced almost down to the measurement resolution level (±0.04 mm). Furthermore, the dimensional accuracy in the height direction and the density uniformity of the compacts were improved.