Multi-side-cylinder motion control method and hydraulic machine

Abstract

The invention provides a multi-side-cylinder motion control method and a hydraulic machine, and the method comprises the following steps: a, setting a virtual motion track under a standard condition for each hydraulic oil cylinder, and presetting the virtual motion track according to the actual working requirements of the hydraulic machine and the physical characteristics of the hydraulic oil cylinders; b, a hydraulic servo control technology is adopted, an intermediate relay is omitted, and a controller is directly connected with a solenoid valve coil so as to reduce response time; c, in the movement process, each hydraulic oil cylinder monitors the current position in real time through a high-precision displacement sensor, and the current position is compared with the virtual movement track under the standard condition. According to the multi-side-cylinder motion control method, when a single cylinder works, motion is stable, terminal point positioning is accurate, and the repeated positioning error is smaller than or equal to + / -0.03 mm; the synchronous precision of simultaneous working of multiple cylinders is smaller than or equal to + / -0.03 mm and far exceeds the traditional control level, an intermediate relay is omitted, the complex mechanical structure of the hydraulic machine is reduced, and the equipment cost and the maintenance difficulty are reduced.

Description

Technical Field

[0001] The invention relates to the field of single-cylinder and multi-cylinder control positioning and multi-cylinder synchronous motion control of a hydraulic press, and in particular to a multi-side cylinder motion control method and a hydraulic press. Background Art

[0002] Hydraulic presses are widely used in the field of pressure processing technology in mechanical engineering. They use liquid pressure to transfer energy and can realize forging, stamping, extrusion of metal materials, powder forming of powder metallurgy, and pressing and forming of non-metallic materials such as plastics and rubber products. However, there are many problems in the existing technology. When the hydraulic cylinder moves in a single cylinder or multiple cylinders, the overshoot phenomenon of the end point positioning is large (>0.50mm) and the error of repeated positioning accuracy is large (>0.50mm). When the multiple cylinders move, the synchronization accuracy and synchronization positioning accuracy are poor (>0.50mm). For the problems of single cylinder overshoot and repeated positioning, mechanical limit control is currently mainly used, which requires the operator to adjust the position by repeatedly testing the product based on experience, and also increases the mechanical structure of the hydraulic press. In terms of the synchronization accuracy and synchronization positioning accuracy of multi-cylinder movement, proportional servo control is mainly used, and servo closed-loop control is performed based on one of the cylinders, but the response time is too long when controlled by PLC, resulting in poor synchronization positioning.

[0003] Therefore, a multi-side cylinder motion control method and a hydraulic press are proposed. Summary of the invention

[0004] The present invention aims to solve the problems raised in the background technology and provides a multi-side cylinder motion control method and a hydraulic press to solve the problems of low positioning accuracy, poor synchronization accuracy and complex mechanical structure in the single-cylinder and multi-cylinder motion control of existing hydraulic presses. The hydraulic servo control technology is adopted and the intermediate relay is eliminated. The controller is directly connected to the solenoid valve coil, and the motion trajectory under standard conditions is set for each cylinder. Each cylinder compares the corresponding standard conditions in real time to perform position correction to achieve the purpose of precise control.

[0005] The specific technical solutions are as follows: A multi-side cylinder motion control method comprises the following steps: a. Setting a virtual motion trajectory under standard conditions for each hydraulic cylinder, which is pre-set according to the actual working requirements of the hydraulic press and the physical characteristics of the hydraulic cylinder; b. Adopt hydraulic servo control technology and cancel the intermediate relay, so that the controller is directly connected to the solenoid valve coil to reduce the response time; c. During the movement, each hydraulic cylinder monitors its current position in real time through a high-precision displacement sensor and compares it with the virtual motion trajectory under standard conditions; d. According to the comparison result, the PID control algorithm is used to correct the position of each hydraulic cylinder to achieve precise control. The PID control algorithm includes proportional control, integral control, and derivative control, and the position correction is achieved by adjusting the opening degree or opening time of the solenoid valve; Among them, the multi-side cylinder motion control method makes the motion process stable and the end-point positioning accurate when a single cylinder works, the repeated positioning error ≤ ±0.03 mm, and the synchronization accuracy ≤ ±0.03 mm when multiple cylinders work simultaneously.

[0006] For the above multi-side cylinder motion control method, where: the PID control algorithm generates a control signal by calculating the current error (proportional term), the integral of the error (integral term), and the derivative of the error (derivative term), so as to achieve precise control of the hydraulic cylinder. The PID control algorithm equation is as follows: ; Where: u(t) is the control signal (i.e., the signal output to the solenoid valve coil); e(t) is the current error, that is, the deviation between the actual position of the hydraulic cylinder and the preset virtual motion trajectory; Kp is the proportional coefficient, which determines the proportional relationship between the control signal and the current error; Ki is the integral coefficient, which determines the proportional relationship between the control signal and the integral of the error and is used to eliminate the static error; Kd is the derivative coefficient, which determines the proportional relationship between the control signal and the rate of change of the error and is used to improve the response speed and stability of the system; In practical applications, since the control system is discrete (i.e., the sampling time interval is fixed), it is necessary to discretize the PID control algorithm. The discretized PID control algorithm equation is as follows: ; Where: u(k) is the control signal at the kth sampling moment; e(k) is the error at the kth sampling moment; is the integral of the error from the 0th sampling moment to the kth sampling moment; e(k)−e(k−1) is the rate of change of the error at the kth sampling moment; In the control system, the main control unit (such as a high-performance PLC or DSP) will regularly sample the signal of the displacement sensor, calculate the current error, and calculate the control signal according to the discretized PID control algorithm equation. Then, this control signal will be output to the high-speed solenoid valve coil to adjust the motion state of the hydraulic cylinder.

[0007] The above multi-side cylinder motion control method, wherein: the hydraulic servo control technology adopts a closed-loop control mode to achieve precise control of the hydraulic cylinder.

[0008] The above multi-side cylinder motion control method, wherein: the controller is a programmable logic controller (PLC) or a digital signal processor (DSP).

[0009] The above multi-side cylinder motion control method, wherein: it further includes step e: after the motion ends, record the actual motion trajectory of each hydraulic cylinder and compare it with the virtual motion trajectory under standard conditions to evaluate the control effect.

[0010] The above multi-side cylinder motion control method, wherein: the position correction is achieved by adjusting the opening degree or opening time of the solenoid valve.

[0011] The above multi-side cylinder motion control method, wherein: it further includes step f: according to the evaluation result, correct the virtual motion trajectory under standard conditions to improve the accuracy of subsequent control.

[0012] The above multi-side cylinder motion control method, wherein: the hydraulic cylinder is a side cylinder of a pipe forming hydraulic press.

[0013] The present invention also provides a hydraulic press adopting the above multi-side cylinder motion control method.

[0014] The above hydraulic press, wherein: it further includes a control system for implementing the multi-side cylinder motion control method, and the control system includes: A main control unit, adopting a high-performance controller, responsible for receiving sensor signals, executing a PID control algorithm, and outputting control signals; A high-precision displacement sensor for real-time monitoring of the position information of the hydraulic cylinder; A high-speed solenoid valve coil for achieving fast response and precise control; A human-machine interface for providing an intuitive data display and a graphical operation interface to facilitate parameter setting, status monitoring, and fault diagnosis operations by the operator; Wherein, the main control unit processes and analyzes the displacement sensor signals received through a preset PID control program, calculates a correction signal according to the deviation between the actual position of the current cylinder and the preset virtual motion trajectory, and outputs it to the high-speed solenoid valve coil, thereby achieving precise control of the cylinder motion.

[0015] The multi-side cylinder motion control method provided by the present invention has the following beneficial effects: 1. Improved positioning accuracy: When a single cylinder works, the motion is stable, the end-point positioning is accurate, and the repeat positioning error ≤ ±0.03 mm; when multiple cylinders work simultaneously, the synchronization accuracy ≤ ±0.03 mm, far exceeding the traditional control level.

[0016] 2. Simplification of mechanical structure: The intermediate relay is cancelled, reducing the complex mechanical structure of the hydraulic press and lowering the equipment cost and maintenance difficulty. Description of the Drawings

[0017] Figure 1 It is a schematic flow chart of the multi-side cylinder motion control method provided by the embodiment of the present invention. Detailed Embodiments

[0018] The technical solution of the present invention will be further described below with reference to the drawings and through specific embodiments.

[0019] Among them, the drawings are only for illustrative purposes, showing only schematic diagrams rather than physical drawings, and should not be construed as a limitation to this patent; in order to better illustrate the embodiments of the present invention, some components in the drawings will be omitted, enlarged or reduced, which do not represent the dimensions of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0020] In the drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if terms such as "upper", "lower", "left", "right", "inner", "outer", etc. are used to indicate the orientation or positional relationship, it is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only for illustrative purposes and should not be construed as a limitation to this patent. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0021] In the description of the present invention, unless otherwise clearly defined and limited, if terms such as "connection" are used to indicate the connection relationship between components, this term should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] Embodiment 1 The multi-side cylinder motion control method provided in this embodiment, as Figure 1 shown, includes the following steps: a. Set a virtual motion trajectory under standard conditions for each hydraulic cylinder, and this virtual motion trajectory is preset according to the actual working requirements of the hydraulic press and the physical characteristics of the hydraulic cylinder; Among them, the setting process needs to consider factors such as the stroke range of the oil cylinder, the variation law of the movement speed, and the characteristics of the processed material. Through precise calculation and simulation, the optimal movement trajectory curve of each oil cylinder under standard working conditions is obtained, and this curve should be stored in the storage unit of the controller for ready call during the working process; b. Adopt hydraulic servo control technology and cancel the intermediate relay, so that the controller is directly connected to the solenoid valve coil to reduce the response time; Among them, the connection method of the controller to the solenoid valve coil should ensure the stability and timeliness of signal transmission. Its connection line needs to use a wire with good shielding performance to reduce the influence of electromagnetic interference on the control signal and ensure the accuracy of control; c. During the movement process, each hydraulic oil cylinder monitors its current position in real time through a high-precision displacement sensor and compares it with the virtual movement trajectory under standard conditions; d. According to the comparison result, use the PID control algorithm to correct the position of each hydraulic oil cylinder to achieve precise control. The PID control algorithm includes proportional control, integral control, and derivative control, and realizes position correction by adjusting the opening degree or opening time of the solenoid valve; e: After the movement ends, record the actual movement trajectory of each hydraulic oil cylinder and compare it with the virtual movement trajectory under standard conditions to evaluate the control effect; f: According to the evaluation result, correct the virtual movement trajectory under standard conditions to improve the accuracy of subsequent control.

[0023] Among them, a high-precision position sensor is installed on the oil cylinder. The measurement accuracy of the position sensor should reach within ±0.01 mm, which can accurately detect the actual position of the oil cylinder in real time and transmit the position signal to the controller in a timely manner. The controller compares and analyzes the received actual position signal with the pre-stored movement trajectory under standard conditions and calculates the position deviation amount.

[0024] Among them, the built-in PID control algorithm of the controller has the characteristics of high precision and fast response. According to the magnitude and change trend of the position deviation amount, it can accurately calculate the current or voltage adjustment value required for the solenoid valve coil, ensuring that the oil cylinder can quickly and accurately return to the movement trajectory under standard conditions and achieve precise control.

[0025] Among them, the multi-side cylinder movement control method makes the movement process of a single cylinder stable, the end point positioning accurate, the repeat positioning error ≤ ±0.03 mm, and the synchronization accuracy ≤ ±0.03 mm when multiple cylinders work simultaneously.

[0026] To ensure the performance of single-cylinder operation, high-precision flow control valves and pressure control valves are set in the hydraulic system. The flow regulation accuracy of the flow control valve should reach within ±0.1 L / min, and the pressure regulation accuracy of the pressure control valve should reach within ±0.1 MPa to accurately control the movement speed and pressure of the hydraulic cylinder, thus ensuring a smooth movement process and accurate end-point positioning.

[0027] Among them, the solenoid valve coil is made of materials with high temperature resistance and corrosion resistance. The insulating material of the solenoid valve coil is selected from materials with good high temperature resistance (long-term working temperature not less than 150 °C) and corrosion resistance (able to withstand the erosion of chemical substances in hydraulic oil), such as polyimide, etc., to ensure that the solenoid valve coil can work stably for a long time in a harsh working environment and reduce the probability of failures.

[0028] Among them, there is a reliable communication interface between the controller and external devices, such as Ethernet interface, RS485 interface, etc.

[0029] The communication interface should support standard communication protocols, such as ModbusTCP protocol, ModbusRTU protocol, etc., in order to achieve interconnection and interoperability with the host computer or other control systems, facilitate remote monitoring and control, and improve the automation level and management efficiency of production.

[0030] Among them, the movement trajectory under standard conditions can be adjusted and optimized according to different processing technologies and materials; when the processing technology or material changes, the operator can input relevant parameters through the human-machine interface of the controller. The controller recalculates and generates the movement trajectory under standard conditions according to the new parameters and stores it in the storage unit. The human-machine interface should have the characteristics of simple and intuitive operation, facilitating the operator to set parameters and adjust the trajectory. Specifically, in this embodiment: The PID control algorithm generates a control signal by calculating the current error (proportional term), the integral of the error (integral term), and the derivative of the error (differential term), so as to achieve precise control of the hydraulic cylinder. The PID control algorithm equation is as follows: ; Among them: u(t) is the control signal (i.e., the signal output to the solenoid valve coil); e(t) is the current error, that is, the deviation between the actual position of the hydraulic cylinder and the preset virtual movement trajectory; Kp is the proportional coefficient, which determines the proportional relationship between the control signal and the current error; Ki is the integral coefficient, which determines the proportional relationship between the control signal and the integral of the error and is used to eliminate the static error; Kd is the differential coefficient, which determines the proportional relationship between the control signal and the rate of change of the error and is used to improve the response speed and stability of the system; In practical applications, since the control system is discrete (i.e., the sampling time interval is fixed), it is necessary to discretize the PID control algorithm. The equation of the discretized PID control algorithm is as follows: ; Where: u(k) is the control signal at the k-th sampling moment; e(k) is the error at the k-th sampling moment; is the integral of the error from the 0-th sampling moment to the k-th sampling moment; e(k)−e(k−1) is the rate of change of the error at the k-th sampling moment; In the control system, the main control unit (such as a high-performance PLC or DSP) will regularly sample the signal of the displacement sensor, calculate the current error, and calculate the control signal according to the discretized PID control algorithm equation. Then, this control signal will be output to the high-speed solenoid valve coil to adjust the motion state of the hydraulic cylinder.

[0031] The performance of the PID control algorithm depends to a large extent on the selection of the proportional coefficient Kp, the integral coefficient Ki, and the differential coefficient Kd. These parameters usually need to be debugged and optimized according to the characteristics of the actual system and the control requirements.

[0032] Specifically, in this embodiment: The hydraulic servo control technology adopts a closed-loop control method to achieve precise control of the hydraulic cylinder.

[0033] Specifically, in this embodiment: The controller is a programmable logic controller (PLC) or a digital signal processor (DSP), which has powerful computing capabilities and fast data processing speeds, and can respond to the feedback signal from the cylinder position sensor in an extremely short time and generate precise control instructions.

[0034] Specifically, in this embodiment: To facilitate position correction, the position correction is achieved by adjusting the opening degree or the opening time of the solenoid valve.

[0035] Specifically, in this embodiment: To better meet the use of the hydraulic press for pipe fitting forming, the hydraulic cylinder set is the side cylinder of the hydraulic press for pipe fitting forming.

[0036] Embodiment 2 This embodiment provides a hydraulic press that adopts the multi-side cylinder motion control method in Embodiment 1. The hydraulic press further includes a control system for implementing the multi-side cylinder motion control method. The control system includes: a main control unit, a high-precision displacement sensor, a high-speed solenoid valve coil, and a human-machine interface.

[0037] The main control unit, adopting a high-performance controller, is responsible for receiving sensor signals, executing the PID control algorithm, and outputting control signals; A high-precision displacement sensor is used to monitor the position information of the hydraulic cylinder in real time; A high-speed solenoid valve coil is used to achieve fast response and precise control; A friendly human-machine interface is used to provide an intuitive data display and a graphical operation interface, facilitating operators to perform parameter settings, status monitoring, and fault diagnosis operations; Among them, the main control unit processes and analyzes the displacement sensor signals received through a preset PID control program, calculates a correction signal based on the deviation between the actual position of the current cylinder and the preset virtual motion trajectory, and outputs it to the high-speed solenoid valve coil, thereby achieving precise control of the cylinder movement.

[0038] In summary, the multi-side cylinder motion control method provided in this embodiment has the following advantages: 1. Improved positioning accuracy: When a single cylinder works, the movement is stable, the end-point positioning is accurate, and the repeat positioning error ≤ ±0.03mm; when multiple cylinders work simultaneously, the synchronization accuracy ≤ ±0.03mm, far exceeding the traditional control level.

[0039] 2. Simplified mechanical structure: The intermediate relay is cancelled, reducing the complex mechanical structure of the hydraulic press, and lowering the equipment cost and maintenance difficulty.

[0040] 3. Enhanced system performance: The reliable communication interfaces (such as Ethernet, RS485, etc.) between the controller and external devices support standard protocols (such as ModbusTCP, ModbusRTU, etc.), enabling remote monitoring and control, and improving production automation and management efficiency; at the same time, the high-precision flow and pressure control valves in the hydraulic system ensure precise control of the cylinder movement speed and pressure, further stabilizing the system performance.

[0041] Working principle: This multi-side cylinder motion control method realizes precise control of hydraulic cylinders based on hydraulic servo control technology and advanced control algorithms. First, a virtual motion trajectory under standard conditions is preset for each hydraulic cylinder according to the working requirements of the hydraulic press and the physical characteristics of the cylinder, and stored in the controller. During operation, a high-precision displacement sensor (with an accuracy within ±0.01 mm) is used to monitor the position of the cylinder in real time, and the deviation is obtained by comparing it with the preset trajectory. The controller uses a discretized PID control algorithm to calculate the control signal according to the proportional, integral, and differential coefficients (Kp, Ki, Kd), and outputs it to the high-speed solenoid valve coil that is resistant to high temperature and corrosion (insulating materials such as polyimide, with a temperature resistance of not less than 150 °C). By adjusting its opening degree or opening time, the position of the cylinder is corrected to achieve precise control. During this process, the controller (such as a high-performance PLC or DSP) quickly responds to the sensor feedback with its powerful computing and processing capabilities, and the control system adopts a closed-loop structure to ensure the control accuracy.

[0042] Workflow 1. Preset trajectory: Comprehensively consider the cylinder stroke, motion speed law, and processing material characteristics, etc., accurately calculate and simulate the optimal motion trajectory of each cylinder under standard conditions, and store it in the storage unit of the controller.

[0043] 2. Hardware connection and startup: Cancel the intermediate relay, connect the controller and the solenoid valve coil with wires having good shielding performance, and start the system using hydraulic servo control technology.

[0044] 3. Real-time monitoring and correction: During motion, the sensor monitors the position of the cylinder and transmits it to the controller. After comparing it with the preset trajectory, the control signal is calculated by the PID algorithm to drive the solenoid valve to adjust the motion of the cylinder.

[0045] 4. Effect evaluation and optimization: After the motion ends, compare the actual and preset trajectories to evaluate the control effect, and correct the preset trajectory according to the results to improve the subsequent control accuracy.

[0046] The above are only the preferred embodiments of the present invention, and do not limit the implementation manners and protection scope of the present invention accordingly. For those skilled in the art, it should be able to realize that all the equivalent replacements and obvious changes made by using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A multi-side cylinder motion control method, characterized in that: The following steps are involved: a. Setting a virtual motion trajectory under standard conditions for each hydraulic cylinder, which is pre-set according to the actual working requirements of the hydraulic press and the physical characteristics of the hydraulic cylinder; b. Adopt hydraulic servo control technology and cancel the intermediate relay, so that the controller is directly connected to the solenoid valve coil to reduce the response time; c. During the movement, each hydraulic cylinder monitors its current position in real time through a high-precision displacement sensor and compares it with the virtual motion trajectory under standard conditions; d. According to the comparison results, the PID control algorithm is used to correct the position of each hydraulic cylinder to achieve precise control. The PID control algorithm includes proportional control, integral control and differential control. The position correction is achieved by adjusting the opening or opening time of the solenoid valve.

2. The multi-side cylinder motion control method according to claim 1, characterized in that: The PID control algorithm generates a control signal by calculating the current error, the integral of the error, and the differential of the error, thereby achieving precise control of the hydraulic cylinder. The PID control algorithm equation is as follows: ； in: u(t) is the control signal; e(t) is the current error; Kp is the proportionality coefficient; Ki is the integration coefficient; Kd is the differential coefficient; In practical applications, since the control system is discrete, the PID control algorithm needs to be discretized. The discretized PID control algorithm equation is as follows: ； in: u(k) is the control signal at the kth sampling moment; e(k) is the error at the kth sampling moment; is the error integral from the 0th sampling moment to the kth sampling moment; e(k)−e(k−1) is the error change rate at the kth sampling moment; In the control system, the main control unit will periodically sample the signal of the displacement sensor, calculate the current error, and calculate the control signal according to the discretized PID control algorithm equation. Then, the control signal will be output to the high-speed solenoid valve coil to adjust the motion state of the hydraulic cylinder.

3. The multi-side cylinder motion control method according to claim 1, characterized in that: The hydraulic servo control technology adopts a closed-loop control method to achieve precise control of the hydraulic cylinder.

4. The multi-side cylinder motion control method according to claim 1, characterized in that: The controller is a programmable logic controller or a digital signal processor.

5. The multi-side cylinder motion control method according to claim 1, characterized in that: The method also includes step e: after the movement is completed, the actual movement trajectory of each hydraulic cylinder is recorded and compared with the virtual movement trajectory under standard conditions to evaluate the control effect.

6. The multi-side cylinder motion control method according to claim 1, characterized in that: The position correction is achieved by adjusting the opening degree or opening time of the electromagnetic valve.

7. The multi-side cylinder motion control method according to claim 1, characterized in that: The method further comprises step f: correcting the virtual motion trajectory under standard conditions according to the evaluation result to improve the accuracy of subsequent control.

8. The multi-side cylinder motion control method according to claim 1, characterized in that: The hydraulic cylinder is a side cylinder of a pipe forming hydraulic press.

9. A hydraulic press using the multi-side cylinder motion control method according to any one of claims 1 to 8.

10. The hydraulic press according to claim 9, characterized in that It also includes a control system for implementing the multi-side cylinder motion control method, the control system comprising: The main control unit is responsible for receiving sensor signals, executing the PID control algorithm and outputting control signals; High-precision displacement sensor, used to monitor the position information of hydraulic cylinder in real time; High-speed solenoid valve coils for fast response and precise control; Human-machine interaction interface, used to provide intuitive data display and graphical operation interface, so that operators can perform parameter setting, status monitoring and fault diagnosis operations; Among them, the main control unit processes and analyzes the received displacement sensor signal through a preset PID control program, calculates the correction signal according to the deviation between the actual position of the current cylinder and the preset virtual motion trajectory, and outputs it to the high-speed solenoid valve coil, thereby realizing precise control of the cylinder movement.

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