基于预测控制的连续平压机热压板升降系统同步控制

Synchronization Control of the Hot Platen Lifting System in Continuous Flat Press Based on Predictive Control

【目的】针对连续平压机热压板升降系统被控对象多且具有非线性、强耦合性等特点,提出基于广义预测控制的环形耦合同步控制方法,以降低热压板升降系统在上升和下降过程中各路液压缸的同步运动误差,确保热压板在升降过程中保持在同一水平面上,减小因不同步对热压板及相关元器件的损害。【方法】建立热压板升降系统同步控制模型,采用广义预测控制算法对每路液压缸的控制量进行优化,构建包含同步误差影响的热压板升降系统优化性能指标函数,导出各子系统基于预测控制的环形耦合同步控制规律。为降低计算复杂性,将优化函数进行分解,在各路液压缸的优化控制性能指标中引入该液压缸和相邻一侧液压缸同步误差的影响,对控制参数在线滚动优化,抑制扰动和随机噪声,采用环形耦合方式对各路液压缸进行同步控制。在系统控制模型基础上进行Matlab仿真试验,并与基于PID的主从控制方式进行对比,分析2种控制方式的位置跟踪、同步误差和抗扰动能力。【结果】环形耦合同步控制方法可保证单路液压缸的跟踪精度,使相邻液压缸之间的同步跟踪误差趋于零,能够实现各路液压缸之间的同步控制,解决某路液压缸受扰动时无法与其他液压缸精确同步的问题。Matlab仿真试验结果表明,与常规主从控制方法相比,基于预测控制的环形耦合同步控制方法具有更好的位置跟踪精度、同步性能、抗扰动能力和响应速度,对于升降过程中的系统扰动和参数突变,系统能迅速恢复稳定,体现出算法的鲁棒性和适应性。【结论】环形耦合同步控制方法更适用于被控对象多的系统,且系统的复杂程度不随被控对象增多而增加,预测控制算法与环形耦合同步控制的结合可实现连续平压机热压板升降系统中对液压缸较高的位置跟踪和同步控制精度,有利于减小因液压缸不同步造成的对设备的损害。

【Objective】The lifting system of the continuous flat press has such characteristics as multiple controlled objects,nonlinear,strong coupling.In order to reduce the synchronous motion error of multiple hydraulic cylinders,ensure the hot platen be kept at the same level during the lifting and descending period respectively,and reduce the damage to hot platen and related components caused by non-synchronization,a ring coupling synchronization control method based on generalized predictive control(GPC)was proposed in this paper.【Method】Firstly,the synchronous control model of the hot platen lifting system was established,and the generalized predictive control algorithm was used to optimize the control parameters of each cylinder.The optimal performance index function influenced by the synchronization error of the hot platen lifting system was established,and the ring coupling synchronization control law based on predictive control was derived for each subsystem.To reduce computational complexity,the optimal index function was decomposed,the synchronization error between the hydraulic cylinder and its adjacent one was added in each hydraulic cylinder’s optimal control index function,and the disturbance and random noise were suppressed by on-line rolling optimization of control parameters,then a ring coupling control method was adopted to achieve the synchronization control for all hydraulic cylinders.Moreover,based on the established system control model,a simulation experiment was carried out using Matlab.The position tracking,synchronization error and anti-disturbance ability were compared between the PID based master-slave control method and our proposed method.【Result】The ring coupling synchronization control method proposed in this paper could ensure the tracking accuracy of each cylinder.Meanwhile,the synchronization error between the adjacent subsystems could converge to zero,hence the synchronization control of multi-channel hydraulic cylinder was achieved.The results of the Matlab simulation showed that the ring coupling synchronization control based on predictive control method resulted in a better position tracking accuracy,synchronization performance,anti-disturbance ability and response speed compared with the conventional master-slave control method.For the system disturbance and sudden changes of parameters during the lifting processes,the system could recover stability quickly,which reflected the robustness and adaptability of the control algorithm proposed in this paper.【Conclusion】Ring coupling control mode was much more suitable for the multi-objects controlled system,and the system complexity would not increase along with the number of the controlled objects.By combining the prediction control algorithm with ring coupling synchronization control strategy,the desirable position tracking precision and synchronization accuracy of the hot platen in continuous flat press could be obtained.Meanwhile,the damage to the equipment caused by non-synchronous hydraulic cylinders could be reduced.