Pump Control Technology: It Brings Performance Upgrade to Hydraulic Press Brake

The development of hydraulic press brake’s hydraulic control technology has gone through 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 quest for control from simple control to precise control to simultaneous energy and usage cost savings.

After the adoption of electro-hydraulic hybrid technology in hydraulic bending machines, there is in fact a change of technology from rough to fine.

Review of the development of electro-hydraulic mixing technology

When the electro-hydraulic hybrid technology was first introduced, it was influenced by the superior CNC system and technical knowledge, but simply replaced the asynchronous motor with a servomotor, and used a simple multi-stage speed control method to set the corresponding motor speed by roughly estimating the hydraulic flow demand for each executive step in the bending cycle.

Because of the estimation, the oil pump driven by the servomotor must end up producing more flow than required.

It still has to overflow through the relief valve, causing energy loss.

At the same time, this control method is not stable enough to adapt to the requirements of a variety of processing techniques, the ram speed control is not flexible, and the manufacturing cost is high.

With the improvement of electro-hydraulic pump control technology and the accumulation of experience in a number of industries, the hydraulic press brake is further optimized for torque limiting control scheme, as shown in Figure 1.

framework diagram of torque limiting control scheme

Figure 1 Framework diagram of torque limiting control scheme

This control scheme can not only solve the basic situation of overflow, but also further reduce the pressure proportional valve, saving part of the hydraulic system cost.

At present, this program is used more in support of the hydraulic flow analog command of the NC system.

But there are still some CNC systems on the market that do not support this dual analog work (hydraulic flow and hydraulic pressure), can only use the combination of switching to form a multi-stage speed of the flow control with pressure analog command.

In addition to this obvious shortcoming, the torque limiting control scheme has another important shortcoming.

Let’s first briefly describe the working principle of torque limiting control on a hydraulic press brake machine, as shown in Figure 2.

Correspondence between pressure and torque

Figure 2 Correspondence between pressure and torque

The system pressure is mapped to the motor output torque, and the pressure control is achieved through simple PID control.

The principle is simple and easy to understand, but there is also a non-simple linear relationship between the pressure command, the torque limit value, and the actual pressure value during specific implementation.

It needs to be corrected by drawing points in the CNC system,

The higher the pressure accuracy requirement, the more tracepoints are needed, and the corresponding adjustment man-hours will be more.

If the tracepoints are reduced, the pressure deviation will increase.

In view of the above two practical application defects, we propose corresponding solutions.

Full closed loop pressure control mode

Add a pressure sensor to the control system to feedback the system pressure in real-time.

The advantage is that there is no overflow at all, which can truly meet the real-time flow demand of the process.

It outputs as much as it actually needs, and the pressure accuracy can be controlled to within 0.1 MPa to significantly reduces the adjustment time, as shown in Figure 3.

Framework diagram of full closed loop pressure control mode

Figure 3 Framework diagram of full closed loop pressure control mode

Pressure closed loop mode of multistage flow

Aiming at the many CNC systems for press brake machines that only support flow switching commands in the stock market, it optimizes the control firmware of the hybrid servo drive, which makes the press brake machine adopt this kind of numerical control system.

It also realizes precise pressure control without overflow and achieves the purpose of improving accuracy, reducing energy consumption, and reducing costs.

Framework diagram of the multistage flow control

Figure 4 Framework diagram of the multistage flow control

Actual case

The specific configuration and technical requirements of the scheme are shown in Table 1.

Table 1 Configuration and technical requirements

NO. Name Number Technique requirements
1 CNC system 1
2 Oil-electric servo motor 1 Maximum system pressure 30MPa
3 Oil-electric servo driver 1 Maximum motor speed 2000rpm
4 Rear damper servo driver 1 Ram fast down speed 150mm/s
5 Rear damper servo motor 1 Ram slow down speed 10mm/s
6 Pressure Sensor 1 Ram fast up speed 120mm/s
7 Inner gear oil pump 1

It can be seen 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 be automatically adjusted according to the actual process.

Among them:

  • A section-fast down;
  • B section-feeding;
  • C section-pressure holding;
  • D section-pressure relief;
  • E section-fast up.

Full closed loop pressure control mode

Figure 5 Full closed loop pressure control mode

  • light blue line: pressure command;
  • pink line: actual pressure;
  • blue line: output flow;
  • brown line: output torque.

It can be seen from Figure 6 that the same control effect solves the problem of overflow in different processes in the simple multistage speed control scheme, while ensuring the accuracy of pressure control and bringing good economic benefits.

Multistage flow pressure control mode

Figure 6 Multistage flow pressure control mode

Among them:

  • A section-fast down;
  • B section-feeding;
  • 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 technique provides a better control mechanism.

Without significantly increasing the cost, it can meet the requirements of no overflow, oil temperature reduction, noise reduction, and accuracy improvement at the same time.

At the same time, it can reduce costs and increase benefits for press brake manufacturers and end-users, which is an ideal solution for electro-hydraulic control technology of hydraulic press brake.

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