Development of Hydraulic Control Technology in Hydraulic Press Brake
The development of hydraulic control technology in hydraulic press brakes has gone through three different control stages: pressure ratio control, flow servo proportional control, and the hybrid control technology of electro-hydraulic integration. This process reflects the pursuit of control accuracy, energy-saving, and cost-effective synchronization, from simple control to precise control. After the adoption of electro-hydraulic hybrid technology in hydraulic press brakes, there has also been a technological evolution from rough to refined.
Review of the Development of Electro-Hydraulic Hybrid Technology
When electro-hydraulic hybrid technology was first introduced, influenced by the upper-level numerical control systems and technological understanding, it simply replaced asynchronous motors with servo motors and used a simple multi-speed control method. The corresponding motor speed was set based on a rough estimate of the hydraulic flow requirements for each step in the bending machine's processing cycle. Because it was an estimate, the servo motor-driven oil pump would inevitably produce flow exceeding the demand, which had to be relieved through overflow valves, resulting in energy loss. At the same time, this control method lacked stability, couldn't meet the requirements of various processing techniques, had inflexible slide speed control, and high manufacturing costs.
With the improvement of electro-hydraulic pump control technology and the accumulation of experience in multiple industries, it has been further optimized for torque-limited control schemes in hydraulic press brakes.
This control scheme can solve the basic occurrence of overflow and further eliminate the need for pressure proportional valves, saving some hydraulic system costs. Currently, this scheme is mainly used in numerical control systems that support hydraulic flow analog commands. However, there are still some numerical control systems in the market that do not support this dual analog mode (hydraulic flow and hydraulic pressure) and can only use combinations of switch quantities to form multi-speed flow control combined with pressure analog commands. In addition to this obvious defect, the torque-limited control scheme also has another important drawback. Let's briefly describe the working principle of torque-limited control on hydraulic press brakes.
Mapping the system pressure to the motor output torque and achieving pressure control through simple PID control. The principle is simple and easy to understand, but in practical implementation, there is not a simple linear relationship between pressure commands, torque limit values, and actual pressure values. It needs to be corrected through point-by-point mapping in the numerical control system. The higher the pressure accuracy requirement, the more mapping points are needed, and the more adjustment time is required. If the mapping points are reduced, there will be an increase in pressure deviation.
To address the above-mentioned deficiencies in these two practical applications, we have proposed corresponding solutions.
Full Closed-Loop Pressure Control Mode
By adding a pressure sensor in the control system to provide real-time feedback of the system pressure, the advantage is that there is no overflow generated. It truly meets the real-time flow demand of the process, outputs as much as needed, and the pressure accuracy can be controlled within 0.1 MPa, significantly reducing adjustment time.
Multi-Stage Flow Pressure Closed-Loop Mode
In response to the existing market where many numerical control systems for bending machines only support flow switch quantity commands, the control firmware of the hydraulic-electric servo drive is optimized. This enables bending machines using such numerical control systems to achieve precise pressure control without generating overflow, thereby improving accuracy, reducing energy consumption, and lowering costs.
Practical Case
In actual bending processes, under the holding pressure state, the pressure output and set demand are essentially aligned, and the output flow is automatically adjusted according to the actual process.
Segments: A - Fast Down; B - Work Feed; C - Holding Pressure; D - Pressure Release; E - Fast Up.
Light blue line: Pressure command; Pink line: Actual pressure; Blue line: Output flow; Brown line: Output torque.
With the same control effect, this solution addresses the overflow issue that exists in the simple multi-speed control scheme during different process stages while ensuring precise pressure control, resulting in significant economic benefits.
Segments: A - Fast Down; B - Work Feed; C - Holding Pressure; D - Pressure Release; E - Fast Up.
Red line: Pressure command; Green line: Actual pressure; Blue line: Flow command; Yellow line: Actual flow.
Compared to the commonly used electro-hydraulic control technology, our company's hydraulic press brake pump control technology solution provides a better control mechanism. Without significantly increasing costs, it can effectively achieve the requirements of no overflow, reduced oil temperature, decreased noise, and improved accuracy. It also reduces costs and increases efficiency for bending machine manufacturers and end users, making it an ideal solution for hydraulic press brake electro-hydraulic control technology.
