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    Servo System Controlling in CNC Bending Machine

    CNC Bending Machine is a machine to process metal plates and it mainly uses hydraulic system to blend panels into different shapes. Hydraulic system of traditional CNC bending machines generally adopts common three-phase asynchronous motor, thus it has big energy consumption, high temperature and low efficiency, and its parts are vulnerable. With energy saving and emission reduction is concerned by more and more people, new CNC bending machine which uses electric-hydraulic servo system to drive oil pump has emerged. Combination of servo drives and servo motors and adjustment of electro-hydraulic servo of CNC bending machine hydraulic system can reduce system energy consumption and temperature-rising of hydraulic oil and improve operational reliability of equipment at the same time.
    CNC bending machine

    Introduction of techniques
    A work cycle of CNC bending machines can be divided into several states like fast drop, slow drop, pressure maintaining, unload and kickback. When the equipment is working, the system will control oil pump to work, coordinating with work of hydraulic oil circuit control units, and then control the flow of hydraulic system, to reach the reasonable pressure value under different working states. The specific work procedures are as follows:
    1. When sliding blocks of machines drop fast, pressure oil will enter into upper compartment of oil cylinder through hydraulic valve and oil in lower compartment will return back to hydraulic pump through hydraulic valve. In this way, sliding blocks of machines will decline rapidly due to self-weight, and the open prefill valve will charge upper compartment of oil cylinder.
    2. When sliding blocks of machines operate in a slow speed, pressure oil will enter into upper compartment of oil cylinder through hydraulic valve to continue to push sliding blocks to drop.
    3. when sliding blocks of machines return back, pressure oil will enter into lower compartment of oil cylinder through hydraulic valve, rod of oil cylinder will pull sliding blocks to rise and oil in upper compartment of oil cylinder will flow back to oil tank through open prefill valve.
    Thus a work cycle has just finished.

    Application of servo system
    Hydraulic system of traditional bending machines adjusts flow of the system through dosing pump and proportional reversing valve. Since actual flow needed by the system changes while discharge of oil pump is constant, a part of flow will definitely overflow and generate energy loss. Moreover, setting pressure of valve controlling hydraulic system is always higher than actual pressure demanded, which will also cause energy loss. Meanwhile, throttle governing modes have overflow in main pressure valve, which will cause noise, a large calorific value of hydraulic oil, rising temperature, reduction of service life of hydraulic oil and increasing maintenance cost.
    In view of defects of hydraulic system of traditional bending machine and characteristics of forming techniques and processes of equipment, it adopts servo drive, servo motor, and gear pump to adjust control system of flow and pressure of hydraulic system. The details are as follows:
    According to position feedback of linear scale, CNC system will obtain values of flow and pressure needed by the system through algorithm characteristics, output 0~±10V analog control signals to servo drives, adjust speed of oil pump in real time and coordinate with work of hydraulic oil circuit control unit to meet demands of different process terminals on pressure and flow. The program adopts the principles of volumetric speed control and changes flow of oil pump and system pressure by adjusting speed of servo motor, thus avoiding energy consumption caused by traditional throttle governing schemes. Especially at the stage of pressure maintaining and unloading, output of oil is less and oil pump can almost stop operate, which will greatly reduce energy consumption. Meanwhile, response time of servo driven system is shorter and speed of fast drop and return when equipment is working is faster and has a higher efficiency.

    In conclusion, the program can effectively reduce system consumption, has less operation noise and a faster system response, and improves efficiency, and its operation is stable and reliable, its protection function is strong and its operation is simple and convenient. Thus it can not only meet requirements of forming techniques of bending machines and improve product quality and output, but also reduce maintenance costs of equipment, creating favorable economic benefits to users.

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