Pump control technology brings performance upgrades to press brake
The development of hydraulic control technology for hydraulic press brake has experienced three different control stages .
From pressure proportional control to flow servo proportional control, and then to electro-hydraulic hybrid control technology.
This process embodies the process from simple control to precise control to synchronization . It saves the pursuit of energy and cost control. After the hydraulic press brake adopts electro-hydraulic hybrid technology, there are actually technical changes from rough to fine.
When the electro-hydraulic hybrid technology began to use, affected by the upper CNC system and technical cognition.
The asynchronous motor simply replace with a servo motor, and use a simple multi-speed control method
Set the corresponding motor speed according to the hydraulic flow demand of each execution step. Because it is an estimate, the oil pump will eventually have a flow that exceeds the demand. Or it must overflow through the overflow valve, causing energy loss.
At the same time, the stability of this control method is not good enough to meet the requirements of various processing techniques.
The speed control of the slider is not flexible, and the manufacturing cost is not low.
With the improvement of electro-hydraulic pump control technology and the accumulation of experience in multiple industries;
The hydraulic bending machine further optimize as a torque limit control scheme, as shown in Figure 1.
This control scheme can solve the basic situation of overflow, and can further reduce the pressure proportional valve. So can save part of the hydraulic system cost.
At present, this scheme mostly use on CNC systems that support hydraulic flow analog commands. However, there are still some on the market that do not support this dual-analog work mode ;
and can only use the combination of switch variables to form multi-speed flow control with pressure analog commands.
In addition to this obvious defect, the torque limit control scheme has another important shortcoming.
First briefly describe the working principle of the torque limit control on the hydraulic bending machine, as shown in Figure 2.
The system pressure maps to the motor output torque, and the pressure control achieves through simple PID control.
The principle is simple and easy to understand, but in the specific implementation,
There is also a non-simple linear relationship between the pressure command, the torque limit value, and the actual pressure value.
It needs to correct in the CNC system by drawing points, and the pressure requires accuracy . The higher the value, require the more scanning points , and the corresponding adjustment man-hours. If reduce the scanning points , the pressure deviation will increase.
Full closed loop pressure control mode
Adding a pressure sensor in the control system to feedback the system pressure in real time has the advantage that there is no overflow at all, and it can truly meet the real-time flow demand of the process.
The output is as much as the actual need. The pressure accuracy can controll within 0.1MPa, which significantly reduces the adjustment time ,As shown in Figure 3.
Multi-access pressure closed-loop mode
Aiming at the many CNC systems for bending machines in the stock market that only support flow switching commands, by optimizing the control firmware of the oil-electric servo drive, the bending machines using this type of CNC system also achieve precise pressure control without overflow , And achieve the purpose of accuracy improvement, consumption reduction, energy saving, and cost reduction.
It can see from Figure 5 that in the actual bending process, the pressure output and the demand setting basically coincide in the pressure holding state, and the output flow will automatically adjust according to the actual process.
Among them: A section-fast down; B section-work advance; C section-pressure holding; D section-pressure relief; E section-fast up.
Light blue line: pressure command;
pink line: actual pressure;
blue line: output flow;
brown line: output torque.
It can see from Figure 6 that the same control effect solves the problem of overflow in different processes in the simple multi-stage speed control scheme, while ensuring the accuracy of pressure control and bringing good economic benefits.
Among them: A section-fast down; B section-work advance; C section-pressure holding; D section-pressure relief; E section-fast up.
Red line: pressure command; green line: actual pressure; blue line: flow command; yellow line: actual flow.
Compared with the commonly used electro-hydraulic control technology, our company’s hydraulic press brake pump control technology solution provides a better control mechanism, and can achieve excellent non-overflow at the same time without significantly increasing the cost.
Reduce oil temperature, reduce noise, improve accuracy requirements, and reduce costs and increase benefits for bending machine manufacturers and end users. It is an ideal solution for hydraulic bending electro-hydraulic control technology.
