summary:
To address the issue of excessive inertial force caused by grinding wheel position disturbance, and the influence of the grinding head's own weight, friction, and inertial force on the system output force, an improvement method was proposed. This method involves superimposing closed-loop control on the pressure control based on a three-way proportional pressure reducing valve. A grinding head pressing control system with a programmable logic controller (PLC) as its core was developed. Position and pressure composite control was employed during the pressing process, improving work efficiency. An incremental PID controller with integral separation was introduced for closed-loop pressure control, achieving precise control of the grinding head pressing force. This ensures the system maintains good following characteristics under position disturbances, meeting performance requirements, and has been successfully applied to the domestically produced MG215-H5 slab grinding machine.
Keywords:
Steel billet grinding machine; hydraulic pressing system; PLC; closed-loop control; PID
Chinese Library Classification Numbers: TH137; TG580
0. Introduction
To ensure the final quality and yield of steel products, removing defects, scale, and decarburized layers from the surface of steel billets before rolling is a crucial process. The primary method is grinding wheel regrinding. Steel billet surfaces are generally uneven, while the scale thickness is relatively uniform. Therefore, during regrinding, to thoroughly remove the scale while minimizing metal removal and avoiding unnecessary waste, the grinding wheel must adapt to the uneven surface of the billet. This requires the grinding wheel's head pressing system to have excellent following characteristics, achieving uniform thickness grinding. Since the grinding depth is directly proportional to the grinding pressure, maintaining a constant pressure between the grinding wheel and the billet surface is essential during the regrinding process.
Currently, domestically produced billet grinding machines are mainly controlled by centralized computers, concentrating the detection, data processing, display, and control of hundreds or thousands of signals from the industrial site onto a single computer. This results in long control cycles and the inability to achieve closed-loop control. Based on this, this paper proposes a hierarchical control approach. The bottom layer consists of distributed, independent control units, which can easily allocate control functions of different devices to appropriate control units. This allows for modular modification and debugging of each control unit as needed, facilitating management. Each control unit is installed near the controlled equipment, saving cabling, improving control speed, and enabling closed-loop control. Furthermore, its sampling period is unaffected by other control units. The upper layer is an operation and monitoring computer system that issues operation commands and parameters to the bottom-level computers and receives data and information from them. They exchange information via a data bus.
1. Working principle of the hydraulic pressing system
Controlling the pressure of the grinding head pressing system in a billet grinding machine is extremely difficult. The main reason for the instability of the system's output force is the positional disturbance of the grinding wheel. This disturbance not only introduces excess inertial force into the system but also significantly affects the system's output force due to the weight, friction, and inertial forces inherent in the mechanism itself. When using open-loop pressure control, the system output force fluctuates considerably. Therefore, an improvement method is proposed, which involves superimposing closed-loop control on top of pressure control using a three-way proportional pressure reducing valve.
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