Hydraulic station for a numerical control lathe and control method thereof

Abstract

The application discloses a hydraulic station for a numerical control lathe and a control method thereof, and relates to the technical field of numerical control lathes. The hydraulic station for the numerical control lathe comprises an oil tank, a driving unit, a diaphragm accumulator, a filter, a high-pressure pipe and an oil distributor. The driving unit comprises a servo motor, a motor fixing block, a hydraulic pump and a pressure sensor. The output shaft of the servo motor is connected with the hydraulic pump. The pressure sensor is arranged on the output pipeline of the hydraulic pump. A flowmeter is arranged on the output pipeline of the hydraulic pump. The oil inlet of the hydraulic pump is connected with the oil tank. The output pipeline of the hydraulic pump, the diaphragm accumulator, the filter, the high-pressure pipe and the oil distributor are sequentially connected. The control method comprises the following steps: a feedforward-feedback compound control architecture is adopted to realize high-precision control of the hydraulic pump in combination with a fuzzy self-adaptive PID and a state observer. The application aims at reducing the vibration of the hydraulic station, so as to meet the needs of industrial scenes, such as super-precision lathes, aerospace actuators, precision injection molding machines and the like, which need multi-physical quantity accurate cooperative control.

Description

TECHNICAL FIELD

[0001] The present application relates to the hydraulic drive technology in the field of numerical control lathe, and particularly relates to a hydraulic station for numerical control lathe and a control method thereof. BACKGROUND

[0002] Numerical control lathe is a kind of high-precision and high-efficiency automatic machining equipment widely used in modern mechanical processing field. It can realize high-precision machining of complex parts by controlling the movement and processing of machine tool through numerical control system. The main components of numerical control lathe include spindle box, feed system, tool holder, bed and control system, etc. Its performance and precision directly affect the quality and production efficiency of products.

[0003] Hydraulic station is a kind of hydraulic equipment composed of hydraulic pump, motor, oil tank and solenoid valve, etc. It can provide corresponding flow direction, pressure and flow of hydraulic oil according to the needs of driving device, and is suitable for various machines with driving device separated from hydraulic station. By connecting hydraulic station and driving device with oil pipe, hydraulic system can realize various predetermined actions. Hydraulic station plays a crucial role in numerical control lathe. Many functions of numerical control lathe, such as spindle drive, feed system, tool holder movement, clamping device and cooling system, etc., rely on hydraulic station to realize. Hydraulic station converts hydraulic energy generated by hydraulic pump into mechanical energy to provide power for each component of machine tool. For example, hydraulic cylinder can realize rapid positioning and clamping of tool holder, and hydraulic motor can drive spindle to perform high-precision cutting. In addition, hydraulic system has the advantages of fast response speed, high precision and good stability, which can meet the strict requirements of numerical control lathe on precision and efficiency in the processing process.

[0004] The Chinese patent application document with publication number CN107327428A discloses a structure of numerical control machine tool hydraulic station. The device is provided on the base of numerical control machine tool and fixed to provide pressure guarantee. From left to right, it is provided with motor, hydraulic control valve, pressure regulating knob and pressure liquid level gauge. The motor adopts squirrel cage motor and is vertically installed on the hydraulic station platform through motor fastening flange. The hydraulic control valve is vertically fixed on the hydraulic station platform through bolt connection. The pressure regulating knob is vertically installed on the upper part and uses gap fit with the hydraulic station platform. The pressure liquid level gauge is installed on the upper left. However, the motor in the device adopts squirrel cage motor with large vibration, which has a great impact on the precision of ultra-precision lathe, and it is difficult to be applied to ultra-precision lathe, aerospace actuator, precision injection molding machine and other industrial scenes requiring accurate collaborative control of multiple physical quantities. SUMMARY

[0005] The technical problems solved by the present application: in view of the above problems of the prior art, a hydraulic station for a numerical control lathe and a control method thereof are provided, and the present application aims to reduce the vibration of the hydraulic station to meet the needs of ultra-precision lathes, aerospace actuators, precision injection molding machines and other industrial scenes that require multi-physical quantity accurate cooperative control.

[0006] To solve the above technical problems, the technical scheme adopted by the present application is:

[0007] A hydraulic station for a numerical control lathe, comprising an oil tank, a drive unit, a diaphragm accumulator, a filter, a high-pressure pipe and an oil distributor, the drive unit comprising a servo motor, a motor fixing block, a hydraulic pump and a pressure sensor, the output shaft of the servo motor being connected to the hydraulic pump through a shaft coupling, the pressure sensor being arranged on the output pipeline of the hydraulic pump, a flowmeter being arranged on the output pipeline of the hydraulic pump, the oil inlet of the hydraulic pump being connected to the oil tank, the output pipeline of the hydraulic pump, the diaphragm accumulator, the filter, the high-pressure pipe and the oil distributor being connected in sequence to output hydraulic oil through the oil distributor.

[0008] Optionally, the oil tank is cuboid, and fixing plates are welded on both sides and the back of the oil tank for mounting on the numerical control lathe by threads, a platform side plate is arranged on the outer side of the side wall of the oil tank, a pressure liquid level gauge, an observation port and a refueling port are arranged on the platform side plate, the flowmeter is fixedly installed on the top of the oil tank, and a thermometer for detecting the temperature of the hydraulic oil is also fixedly installed on the top of the oil tank.

[0009] A control method applied to the hydraulic station for a numerical control lathe, comprising:

[0010] S1, obtaining a feedforward signal from the flow signal detected by the flowmeter using a feedforward controller ;

[0011] S2, calculating the error signal E and the error change rate EC of the flow, and dynamically correcting the control parameters of the PID controller using a fuzzy controller according to the error signal E and the error change rate EC of the flow to obtain the first corrected proportional gain K p , integral gain K i and differential gain K d ;

[0012] S3, observing the flow estimation value z1, the pressure estimation value z2 and the pressure change rate estimation value z3 respectively by a third-order state observer, correcting the integral gain K i of the PID controller using the flow estimation value z1, correcting the proportional gain K p of the PID controller using the pressure estimation value z2, and correcting the differential gain K d of the PID controller using the pressure change rate estimation value z3 to obtain the second corrected proportional gain Kp , integral gain K i , and derivative gain K d ;

[0013] S4, obtaining a corresponding reference signal based on the second corrected proportional gain K p , integral gain K i , and derivative gain K d and the error signal E of the input flow, and summing the reference signal and the feedforward signal to obtain a control voltage u of the hydraulic pump to control the working state of the hydraulic pump.

[0014] Optionally, the function expression of the feedforward controller is:

[0015] , ,

[0016] wherein, is the output of the feedforward controller at time t, is the input of the feedforward controller at time t, is the feedforward transfer function of the feedforward controller, is the transfer function of the feedforward controller.

[0017] Optionally, when the control parameters of the PID controller are dynamically corrected by the fuzzy controller, the control process of the numerical control machine tool is divided into three stages, i.e., a control initial stage, a control middle stage, and a steady state adjustment later stage, and the fuzzy controller dynamically corrects the proportional gain K p In the fuzzy rules adopted, a preset higher proportional gain K p is adopted in the control initial stage to improve the dynamic tracking ability of the system by using the fast response characteristic thereof; the proportional gain K p is reduced after entering the control middle stage to suppress the overshoot phenomenon while maintaining the response efficiency of the system; the proportional gain K p is increased again in the steady state adjustment later stage to improve the steady state accuracy in combination with the integral element.

[0018] Optionally, when the control parameters of the PID controller are dynamically corrected by the fuzzy controller, the fuzzy controller dynamically corrects the integral gain K i In the fuzzy rules adopted, a preset lower integral gain K i is adopted in the control initial stage to suppress the integral intensity to avoid the initial overshoot risk; the integral gain K i is gradually increased after entering the control middle stage to balance the error correction demand and the phase margin until entering the control middle stage; the integral gain K i is continuously increased in the steady state adjustment later stage to improve the control accuracy by exerting the cumulative error elimination characteristic thereof.

[0019] Optionally, when the fuzzy controller is used to dynamically modify the control parameters of the PID controller, the fuzzy controller dynamically modifies the differential gain K d The fuzzy rules used include a preset higher differential gain K in the initial stage of control. d In order to utilize its advanced compensation effect to effectively suppress overshoot and enhance the rapid response; after entering the mid-term control, reduce the differential gain K d To balance the contradiction between dynamic correction requirements and noise sensitivity; after entering the late stage of steady-state regulation, increase the differential gain K again d To form a secondary damping enhancement mechanism to improve anti-interference ability.

[0020] Optionally, the function expression of the third-order state observer is:

[0021] ,

[0022] , ,

[0023] ,

[0024] ,

[0025] , , , ,

[0026] in, ~ are the first, second, third and fourth control state variables of the hydraulic station, is the flow rate of the hydraulic station, is the internal pipeline pressure of the hydraulic station, is the pressure change in the internal pipeline of the hydraulic station, is the total disturbance, The relative control voltage of the hydraulic station flow The partial derivative of is the flow gain of the hydraulic pump, is the pressure difference between the inlet and outlet of the hydraulic pump, ~ for ~ The derivative of is the flow change of the hydraulic station, To control the voltage variation, is the change of flow disturbance, is the effective bulk modulus of the oil, is the effective volume of the control chamber of the hydraulic pump, is the load flow, is the pressure estimation error, Estimated flow rate The first derivative of Estimated pressure value The first derivative of is the estimated value of the pressure change rate The first derivative of is the disturbance estimate The first derivative of ~ is the intermediate variable, is the bandwidth of the third-order state observer.

[0027] Optionally, the flow estimation value z1 is used to modify the integral gain K of the PID controller. i , use the pressure estimate z2 to modify the proportional gain K of the PID controller p , use the estimated value of pressure change rate z3 to modify the differential gain K of the PID controller d Includes: If the flow estimate z1 increases, reduce the integral gain K i To improve steady-state accuracy, if the flow estimate z1 decreases, increase the integral gain K i Otherwise, reduce the integral gain K i To improve stability; if the pressure estimate z2 increases, reduce the proportional gain K p Otherwise, increase the proportional gain K p To avoid overshoot; if the pressure change rate estimate z3 exceeds the preset threshold, increase the differential gain K d Otherwise, reduce the differential gain K d To suppress vibration.

[0028] Compared with the prior art, the present application mainly has the following beneficial effects: in order to reduce the vibration of the hydraulic station, in order to meet the needs of the industrial scene requiring accurate cooperative control of multiple physical quantities such as ultra-precision lathe, aerospace actuator, precision injection molding machine, etc., the hydraulic station for numerical control lathe of the present application comprises an oil tank, a driving unit, a diaphragm accumulator, a filter, a high-pressure pipe and an oil distributor, the driving unit comprises a servo motor, a motor fixing block, a hydraulic pump and a pressure sensor, the output shaft of the servo motor is connected with the hydraulic pump through a shaft coupling, the pressure sensor is arranged on the output pipeline of the hydraulic pump, a flowmeter is arranged on the output pipeline of the hydraulic pump, the oil inlet of the hydraulic pump is connected with the oil tank, the output pipeline of the hydraulic pump, the diaphragm accumulator, the filter, the high-pressure pipe and the oil distributor are connected in sequence to output hydraulic oil through the oil distributor, the servo motor is used to replace the original squirrel cage motor, compared with the original motor, the device has small size, low energy consumption, is more environmentally friendly and clean, and in combination with the diaphragm accumulator and the filter, the vibration of the hydraulic station can be reduced, digital integration is easier to realize, rapid response under different working conditions can be completed, and the needs of the industrial scene requiring accurate cooperative control of multiple physical quantities such as ultra-precision lathe, aerospace actuator, precision injection molding machine, etc. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a schematic diagram of the three-dimensional structure of the hydraulic station of the embodiment of the present application.

[0030] Figure 2 It is a schematic diagram of the three-dimensional structure of the driving unit in the embodiment of the present application.

[0031] Figure 3 It is a schematic diagram of the control principle of the hydraulic station of the embodiment of the present application.

[0032] Legend: 1, fixed plate; 10, flowmeter; 11, thermometer; 12, observation port; 13, oil filling port; 2, pressure liquid level gauge; 3, platform side wall; 4, oil distributor; 5, high-pressure pipe; 6, filter; 7, diaphragm accumulator; 8, driving unit; 800, servo motor; 801, motor fixing block; 802, hydraulic pump; 803, pressure sensor; 9, oil tank. DETAILED DESCRIPTION

[0033] In order to enable personnel in the technical field to better understand the technical solutions of the present application, the technical solutions of the present application will be further described in detail below in combination with the drawings in the embodiments of the present application.

[0034] As Figure 1 And Figure 2As shown, the hydraulic station for the numerical control lathe in the embodiment comprises an oil tank 9, a driving unit 8, a diaphragm accumulator 7, a filter 6, a high-pressure pipe 5 and an oil distributor 4. The driving unit 8 comprises a servo motor 800, a motor fixing block 801, a hydraulic pump 802 and a pressure sensor 803. The output shaft of the servo motor 800 is connected to the hydraulic pump 802 through a shaft coupling. The pressure sensor 803 is arranged on the output pipeline of the hydraulic pump 802. A flow meter 10 is arranged on the output pipeline of the hydraulic pump 802. The oil inlet of the hydraulic pump 802 is connected to the oil tank 9. The output pipeline of the hydraulic pump 802, the diaphragm accumulator 7, the filter 6, the high-pressure pipe 5 and the oil distributor 4 are sequentially connected to output hydraulic oil through the oil distributor 4. Since the vibration of the squirrel cage motor will affect the precision of the ultra-precision lathe, the driving unit 8 in the embodiment comprises the servo motor 800, the motor fixing block 801, the hydraulic pump 802 and the pressure sensor 803. The driving unit 8 is used to replace the squirrel cage motor. The diaphragm accumulator 7 is used for energy storage and release. The working principle of the diaphragm accumulator 7 is as follows: the diaphragm accumulator 7 comprises a sealed container which is divided into a liquid cavity and a gas cavity by an elastic diaphragm. When the system pressure rises, the hydraulic oil enters the liquid cavity through the liquid valve, compresses the gas cavity on the other side of the elastic diaphragm, the gas volume decreases and the pressure rises, and the energy is stored in the form of gas compression energy. When the system pressure drops, the high-pressure nitrogen gas in the gas cavity expands to push the hydraulic oil in the liquid cavity back to the system to supplement the flow or maintain the pressure. In the embodiment, the diaphragm accumulator 7 temporarily stores the high-pressure fluid energy in the hydraulic system. When the system needs instantaneous large flow, the diaphragm accumulator 7 releases energy to supplement the insufficient liquid supply of the pump. In addition, the diaphragm accumulator 7 can also absorb pressure impact. When the valve is suddenly closed or the pump is started and stopped, the system may generate pressure pulsation phenomenon. The diaphragm accumulator 7 absorbs the impact by compressing the gas to protect the pipeline and components.

[0035] The filter 6 can reduce the vibration of the hydraulic station, greatly improve the space utilization, is convenient to install, is suitable for scenes with limited space, can effectively improve the speed regulation precision by using the motor to replace the motor for oil supply, is easier to realize digital integration, and can complete the rapid response under different working conditions. Compared with the original motor, the device has lower energy consumption and is more environmentally friendly and clean, and can meet the needs of industrial scenes such as ultra-precision lathes, aerospace actuators, precision injection molding machines and the like which need multi-physical quantity accurate cooperative control.

[0036] As Figure 1As shown, the oil tank 9 is cuboid in this embodiment, and the two sides and the rear of the oil tank 9 are welded with the fixing plate 1 for being installed on the numerical control lathe by screwing, and the outer side of the side wall of the oil tank 9 is provided with the platform side wall 3, and the pressure liquid level gauge 2, the observation hole 12 and the oil filling port 13 are arranged on the platform side wall 3, the flow meter 10 is fixedly installed on the top of the oil tank 9, and the thermometer 11 for detecting the temperature of the hydraulic oil is also fixedly installed on the top of the oil tank 9. In this embodiment, the fixing plate 1 is fixed on the machine tool by screwing, the pressure liquid level gauge 2 is vertically close to the upper left side of the oil tank 9, the oil distributor 4 is horizontally installed on the hydraulic station platform 14 and connected with the high-pressure pipe 5, the oil distributor 4 is divided into three pipe lines and connected with different pipes, the filter 6 is vertically fixed on the oil tank 9 by screwing, the diaphragm accumulator 7 is vertically fixed on the fixing plate 1 by screwing, the flow meter 10 is vertically fixed on the hydraulic station platform 14 by welding, the temperature sensor is horizontally fixed on the hydraulic station platform by screwing, the driving unit 8 is horizontally fixed on the hydraulic station platform 14 by bolts, the observation hole 12 is designed on the upper right side, and the oil filling port 13 is designed below the oil tank 9. In this embodiment, the servo motor 800 of the driving unit 8 is horizontally fixed on the motor fixing block 801 by bolts and connected with the hydraulic pump 802 through the coupling, the motor fixing block 801 is horizontally installed on the hydraulic station platform 14 and connected by screwing, and the hydraulic pump 802 is horizontally installed on the motor fixing block 801 and connected by screwing. The pressure sensor 803 is connected with the hydraulic pump 802 by a nut and sealed by a sealing ring. Specifically, the hydraulic pump 802 adopts a bidirectional gear pump in this embodiment, and other pumps can also be used according to the needs, the flow rate of the hydraulic pump 802 is maintained at 20-150 L / min in this embodiment, and the pressure is set at 20-250 bar. In this embodiment, the servo motor 800, the hydraulic pump 802 and the pressure sensor 803, and the closed-loop control system composed of the flow meter 10 on the output pipe line of the hydraulic pump 802. Among them, the servo motor 800 is directly connected with the hydraulic pump 802 through the elastic coupling, so as to basically stabilize the pressure and the amount of oil supply.

[0037] For the hydraulic station for the numerical control lathe in this embodiment, the motor dynamics equation and the hydraulic station flow and pressure equation can be established as follows:

[0038] ,

[0039] ,

[0040] ,

[0041] Among them, is the flow rate of the hydraulic station, is the valve flow gain, is the control voltage, is the valve port pressure difference, Flow disturbances, including leakage and oil viscosity changes; is the pressure change of the pipeline in the hydraulic station, is the effective bulk modulus of the oil, To control the effective volume of the cavity, is the load flow, is the servo motor moment of inertia, and are the first-order and second-order positions of the motor angle respectively, is the motor viscous friction coefficient, is the pressure drop proportionality coefficient, is the current, It is the pressure disturbance caused by sudden load changes, including temperature and other effects.

[0042] like Figure 3 As shown, this embodiment also provides a control method for the hydraulic station for a CNC lathe, including using a feedforward-feedback composite control architecture combined with a fuzzy adaptive PID and a state observer to achieve high-precision control of the hydraulic pump 802:

[0043] S1, the flow signal detected by the flow meter 10 is used to obtain a feedforward signal by a feedforward controller ;

[0044] S2, calculate the flow error signal E and error change rate EC, according to the flow error signal E and error change rate EC, use the fuzzy controller to dynamically correct the control parameters of the PID controller, and obtain the proportional gain K after the first correction p , integral gain K i and differential gain K d ;

[0045] S3, through the third-order state observer, respectively observes the flow estimation value z1, pressure estimation value z2 and pressure change rate estimation value z3, and uses the flow estimation value z1 to correct the integral gain K of the PID controller i , use the pressure estimate z2 to modify the proportional gain K of the PID controller p , use the estimated value of pressure change rate z3 to modify the differential gain K of the PID controller d , get the second corrected proportional gain K p , integral gain K i and differential gain K d ;

[0046] S4, through the PID controller based on the proportional gain K after the second correction p , integral gain K i and differential gain K dThe error signal E of the input flow is obtained, and a corresponding reference signal is obtained, and the reference signal and the feedforward signal The control voltage u of the hydraulic pump 802 is obtained by summation to control the working state of the hydraulic pump 802.

[0047] In this embodiment, the function expression of the feedforward controller is:

[0048]

[0049] wherein, is the output of the feedforward controller at time t, is the input of the feedforward controller at time t, is the feedforward transfer function of the feedforward controller, is the transfer function of the feedforward controller.

[0050] In this embodiment, when the error signal E of the flow and the error change rate EC are calculated, the error signal E is the difference between the flow signal detected by the flow meter 10 and the target flow, and the error change rate EC is the change rate of the error signal E.

[0051] The dynamic characteristics of the PID control system are mainly affected by the synergistic effect of the three parameters of the proportional gain K p , the integral gain K i and the differential gain K d In this embodiment, when the control parameters of the PID controller are dynamically corrected by the fuzzy controller, the control process of the numerical control machine tool is divided into three stages: the initial control stage, the middle control stage and the steady-state adjustment stage. The fuzzy controller dynamically corrects the proportional gain K p In the fuzzy rules adopted, if the error signal E of the flow is NB, and the error change rate EC of the flow is NB, NM, NS, ZO, PS, PM or PB, the proportional gain K p is PB, PB, PM, PM, PS, ZO or ZO, respectively; if the error signal E of the flow is NM, and the error change rate EC of the flow is NB, NM, NS, ZO, PS, PM or PB, the proportional gain K p is PM, PB, PM, PS, PS, ZO or NS, respectively; if the error signal E of the flow is NS, and the error change rate EC of the flow is NB, NM, NS, ZO, PS, PM or PB, the proportional gain K p is PM, PM, PM, PS, ZO, ZO or NS, respectively; if the error signal E of the flow is ZO, and the error change rate EC of the flow is NB, NM, NS, ZO, PS, PM or PB, the proportional gain K p ​​PM, PM, PS, ZO, ZO, NS or NM, respectively; if the flow error signal E is PS, and the flow error change rate EC is NB, NM, NS, ZO, PS, PM or PB, the proportional gain K p PM, PM, PS, ZO, ZO, NS or NM, respectively; if the flow error signal E is PS, and the flow error change rate EC is NB, NM, NS, ZO, PS, PM or PB, the proportional gain K p PM, PM, PS, ZO, ZO, NS or NM, respectively; if the flow error signal E is PS, and the flow error change rate EC is NB, NM, NS, ZO, PS, PM or PB, the proportional gain K p ZO, ZO, NS, NM, NM, NM or NB, as shown in Table 1.

[0052] Table 1: Dynamic correction of the proportional gain K p Fuzzy rule table adopted

[0053]

[0054] Referring to Table 1, the time-varying characteristics of the proportional gain K p are optimized in this embodiment: a preset higher proportional gain K p is used in the initial stage of control to improve the dynamic tracking ability of the system by using its fast response characteristics; the proportional gain K p is appropriately reduced in the middle stage of control to effectively suppress the overshoot phenomenon by weakening the strength of the proportional action, while maintaining the response efficiency of the system; when the system enters the later stage of steady-state regulation, the proportional gain K p is increased again, and the integral element is used to improve the steady-state accuracy.

[0055] The adjustment mechanism of the integral element directly affects the steady-state error elimination ability of the system. In the fuzzy controller of this embodiment, if the flow error signal E is NB, and the flow error change rate EC is NB, NM, NS, ZO, PS, PM or PB, the integral gain K i is NB, NB, NM, NM, NS, ZO or ZO, respectively; if the flow error signal E is NM, and the flow error change rate EC is NB, NM, NS, ZO, PS, PM or PB, the integral gain K i is NB, NB, NM, NM, NS, ZO or ZO, respectively; if the flow error signal E is NS, and the flow error change rate EC is NB, NM, NS, ZO, PS, PM or PB, the integral gain K i is NB, NB, NM, NM, NS, ZO or ZO, respectively; if the flow error signal E is NS, and the flow error change rate EC is NB, NM, NS, ZO, PS, PM or PB, the integral gain K iNB, NM, NS, ZO, PS, PM or PB; if the flow error signal E is PS and the flow error change rate EC is NB, NM, NS, ZO, PS, PM or PB, the integral gain K i NB, NM, NS, ZO, PS, PM or PB; if the flow error signal E is PS and the flow error change rate EC is NB, NM, NS, ZO, PS, PM or PB, the integral gain K i NM, NM, NS, PS, ZO, PM or PM; if the flow error signal E is PM and the flow error change rate EC is NB, NM, NS, ZO, PS, PM or PB, the integral gain K i ZO, NS, ZO, PS, PS, PM or PB; if the flow error signal E is PB and the flow error change rate EC is NB, NM, NS, ZO, PS, PM or PB, the integral gain K i ZO, ZO, PS, PM, PS, PS or PB, as shown in Table 2.

[0056] Table 2: Dynamic correction of integral gain K i Fuzzy rule table adopted

[0057]

[0058] Referring to Table 2, the dynamic correction of integral gain K i in the present embodiment is as follows: in the initial stage of control, a weak integral action is applied, i.e. a preset lower integral gain K i is adopted to suppress the integral strength and avoid the risk of initial overshoot; in the middle stage of system dynamic adjustment, the integral gain K i is gradually increased to a specified range to balance the error correction requirement and phase margin maintenance; in the later stage of steady-state tracking, the integral action strength is strengthened, i.e. the integral gain K i is continuously increased to fully exert its cumulative error elimination characteristics and improve the control accuracy.

[0059] The dynamic compensation characteristics of the derivative element directly affect the transient response quality of the system. The dynamic correction of derivative gain K d adopted by the fuzzy controller in the present embodiment is as follows: if the flow error signal E is NB and the flow error change rate EC is NB, NM, NS, ZO, PS, PM or PB, the derivative gain K d is PS, NS, NB, NB, NB, NM or PS; if the flow error signal E is NM and the flow error change rate EC is NB, NM, NS, ZO, PS, PM or PB, the derivative gain K dZO, NS, NM, NM, NS, or ZO, respectively; if the flow error signal E is ZO and the flow error change rate EC is NB, NM, NS, ZO, PS, PM, or PB, the differential gain K d ZO, NS, NM, NM, NS, or ZO, respectively; if the flow error signal E is ZO and the flow error change rate EC is NB, NM, NS, ZO, PS, PM, or PB, the differential gain K d ZO, NS, NM, NM, NS, or ZO, respectively; if the flow error signal E is ZO and the flow error change rate EC is NB, NM, NS, ZO, PS, PM, or PB, the differential gain K d ZO, NS, NM, NM, NS, or ZO, respectively; if the flow error signal E is ZO and the flow error change rate EC is NB, NM, NS, ZO, PS, PM, or PB, the differential gain K d ZO, NS, NM, NM, NS, or ZO, respectively; if the flow error signal E is ZO and the flow error change rate EC is NB, NM, NS, ZO, PS, PM, or PB, the differential gain K d ZO, NS, NM, NM, NS, or ZO, respectively; if the flow error signal E is ZO and the flow error change rate EC is NB, NM, NS, ZO, PS, PM, or PB, the differential gain K

[0060] Table 3: Dynamic correction of differential gain K d fuzzy rule table

[0061]

[0062] Referring to Table 3, the dynamic correction of differential gain K d achieved by using time-varying differential gain: in the initial stage of control, a strong differential action is configured, i.e., a preset higher differential gain K d is used to effectively suppress overshoot and enhance response rapidity by using its lead compensation effect; in the middle stage of regulation, the differential gain is moderately attenuated, i.e., the differential gain K d is reduced to balance the contradiction between the demand for dynamic correction and noise sensitivity; when approaching the steady state stage, the differential strength is again increased, i.e., the differential gain K d is increased again to form a secondary damping enhancement mechanism to improve the anti-interference ability.

[0063] In Table 1 to Table 3, NB, NM, NS, ZO, PS, PM, PB are fuzzy language variables, NB represents "negative big", NM represents "negative medium", NS represents "negative small", ZO represents "zero", PS represents "positive small", PM represents "positive medium", and PB represents "positive big". It should be noted that the fuzzy controller maps the error signal E and the error change rate EC of the flow to the fuzzy language variables NB, NM, NS, ZO, PS, PM, PB, and maps the fuzzy language variables NB, NM, NS, ZO, PS, PM, PB of the proportional gain K p , the integral gain K i and the differential gain K d three parameters to the corresponding actual values. The existing known method of the fuzzy controller is used, and the implementation details are not described in detail here.

[0064] According to the valve port flow equation Q= , the hydraulic system is essentially nonlinear, the hydraulic station system of the machine tool has nonlinear friction and valve core hysteresis phenomenon, the third-order state observer has more degrees of freedom, which can be changed , , , according to the actual situation to meet the control requirements. In this embodiment, the function expression of the third-order state observer is:

[0065] ,

[0066] , ,

[0067] ,

[0068] ,

[0069] , , , ,

[0070] wherein, ~ are the first, second, third and fourth control state variables of the hydraulic station, is the flow of the hydraulic station, is the internal pipeline pressure of the hydraulic station, is the internal pipeline pressure change of the hydraulic station, is the total disturbance, is the partial derivative of the flow of the hydraulic station with respect to the control voltage , is the flow gain of the hydraulic pump 802, ​is the inlet and outlet pressure difference of the hydraulic pump 802, ~ for ~ The derivative of is the flow change of the hydraulic station, To control the voltage variation, is the change of flow disturbance, is the effective bulk modulus of the oil, is the effective volume of the control chamber of the hydraulic pump 802, is the load flow, is the pressure estimation error, Estimated flow rate The first derivative of Estimated pressure value The first derivative of is the estimated pressure change rate The first derivative of is the disturbance estimate The first derivative of ~ is the intermediate variable, is the bandwidth of the third-order state observer. Since the hydraulic oil in the machine tool hydraulic station will increase the temperature during the flow process, the third-order observation adds a compensation term, and the observer introduces a total disturbance The core advantage of third-order state observers in hydraulic control lies in compensating for system nonlinearities and disturbances through algorithms, reducing reliance on high-cost hardware such as ultra-high-precision sensors, and improving the reliability and miniaturization of hydraulic station systems.

[0071] In this embodiment, the flow rate estimation value z1 is used to modify the integral gain K of the PID controller. i , use the pressure estimate z2 to modify the proportional gain K of the PID controller p , use the estimated value of pressure change rate z3 to modify the differential gain K of the PID controller d Includes: If the flow estimate z1 increases, reduce the integral gain K i To improve steady-state accuracy, if the flow estimate z1 decreases, increase the integral gain K i Otherwise, reduce the integral gain K i To improve stability; if the pressure estimate z2 increases, reduce the proportional gain K p Otherwise, increase the proportional gain K p To avoid overshoot; if the pressure change rate estimate z3 exceeds the preset threshold, increase the differential gain K d Otherwise, reduce the differential gain K d To suppress oscillation. In this embodiment, the proportional gain K of the PID controllerp 0.01-0.5 between, integral gain K i Between 0.05-1s, differential gain K d Between 0.1-0.5s.

[0072] The control method of the hydraulic station of the numerical control lathe in this embodiment combines fuzzy feedforward PID control with a third-order state observer, a third-order state observer is designed, and the flow estimate value of the hydraulic station is obtained through the observer , the pressure estimate value , the pressure rate estimate value and the disturbance estimate value , the flow estimate value z1 is used to correct the integral gain K of the PID controller i , the pressure estimate value z2 is used to correct the proportional gain K of the PID controller p and the pressure and flow of the hydraulic station are controlled by the PID control, which can effectively suppress disturbances and quickly respond to changes in the set value, and complete closed-loop control in the controller. The dynamic control algorithm in this embodiment adopts an adaptive fuzzy PID control strategy, estimates the load inertia change in real time through a third-order state observer, eliminates the steady-state error caused by the valve port pressure difference through a feedforward compensation algorithm, and can achieve high positioning accuracy and stable flow control. It is especially suitable for industrial scenarios such as ultra-precision lathes, aerospace actuators, precision injection molding machines and other industrial scenarios that require accurate collaborative control of multiple physical quantities. Through experimental verification, the system's comprehensive energy efficiency is improved by 82%, the force control accuracy is ±0.5% FS, and the maintenance cycle is extended by 4000 working hours compared with traditional hydraulic systems.

[0073] In addition, the embodiment also provides a control system for the hydraulic station of the numerical control lathe, which comprises a microprocessor and a memory connected to each other, and the microprocessor is programmed or configured to execute the control method for the hydraulic station of the numerical control lathe. The embodiment also provides a computer readable storage medium having a computer program or instructions stored therein, which are programmed or configured to execute the control method for the hydraulic station of the numerical control lathe by a processor. The embodiment also provides a computer program product comprising a computer program or instructions programmed or configured to execute the control method for the hydraulic station of the numerical control lathe by a processor.

[0074] The above is only the preferred embodiment of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiments. Any technical solutions falling within the concept of the present application shall fall within the protection scope of the present application. It should be noted that, for ordinary skilled persons in the art, some improvements and refinements without departing from the principles of the present application shall also be considered as the protection scope of the present application.

Claims

1. A control method for a hydraulic station of a numerically controlled lathe, characterized in that, The hydraulic station comprises an oil tank (9), a driving unit (8), a diaphragm accumulator (7), a filter (6), a high-pressure pipe (5) and an oil distributor (4), the driving unit (8) comprises a servo motor (800), a motor fixing block (801), a hydraulic pump (802) and a pressure sensor (803), the output shaft of the servo motor (800) is connected with the hydraulic pump (802) through a shaft coupling, the pressure sensor (803) is arranged on the output pipeline of the hydraulic pump (802), a flowmeter (10) is arranged on the output pipeline of the hydraulic pump (802), the oil inlet of the hydraulic pump (802) is connected with the oil tank (9), the output pipeline of the hydraulic pump (802), the diaphragm accumulator (7), the filter (6), the high-pressure pipe (5) and the oil distributor (4) are sequentially connected to output hydraulic oil through the oil distributor (4); the control method comprises the following steps: S1, obtaining a feedforward signal by using a feedforward controller to process a flow signal detected by the flowmeter (10) ; S2, calculating an error signal E and an error change rate EC of the flow, and dynamically correcting control parameters of a PID controller by using a fuzzy controller according to the error signal E and the error change rate EC of the flow, to obtain a first-corrected proportional gain K p , integral gain K i and differential gain K d ; S3, observing a flow estimation value z1, a pressure estimation value z2 and a pressure change rate estimation value z3 by using a three-order state observer, respectively, correcting the integral gain K i of the PID controller by using the flow estimation value z1, correcting the proportional gain K p of the PID controller by using the pressure estimation value z2, correcting the differential gain K d of the PID controller by using the pressure change rate estimation value z3, to obtain a second-corrected proportional gain K p , integral gain K i and differential gain K d ; S4, obtaining a corresponding reference signal by using the PID controller based on the second-corrected proportional gain K p , integral gain K i and differential gain K d and the input error signal E of the flow, and summing the reference signal and a feedforward signal to obtain a control voltage u of the hydraulic pump (802) to control the working state of the hydraulic pump (802). The function expression of the third order state observer is: ， ， ， ， ， ， ， ， ， in, ~ are the first, second, third and fourth control state variables of the hydraulic station, is the flow rate of the hydraulic station, is the internal pipeline pressure of the hydraulic station, is the pressure change in the internal pipeline of the hydraulic station, is the total disturbance, The relative control voltage of the hydraulic station flow The partial derivative of is the flow gain of the hydraulic pump (802), is the inlet and outlet pressure difference of the hydraulic pump (802), ~ for ~ The derivative of is the flow change of the hydraulic station, To control the voltage variation, is the change of flow disturbance, is the effective bulk modulus of the oil, is the effective volume of the control chamber of the hydraulic pump (802), is the load flow, is the pressure estimation error, Estimated flow rate The first derivative of Estimated pressure value The first derivative of is the estimated value of the pressure change rate The first derivative of is the disturbance estimate The first derivative of ~ is the intermediate variable, is the bandwidth of the third-order state observer.

2. The control method of the hydraulic station for a numerically controlled lathe according to claim 1, characterized in that, The oil tank (9) is cuboid, both sides and rear of the oil tank (9) are welded with fixing plates (1) for being installed on a numerical control lathe through threads, the outer side of the side wall of the oil tank (9) is provided with a platform side wall (3), the platform side wall (3) is provided with a pressure liquid level gauge (2), an observation hole (12) and a filling hole (13), the flow meter (10) is installed and fixed on the top of the oil tank (9), and the top of the oil tank (9) is also installed and fixed with a thermometer (11) for detecting the temperature of the hydraulic oil.

3. The control method of the hydraulic station for a numerically controlled lathe according to claim 1, characterized in that, The function expression of the feedforward controller is: ， ， wherein is the output of the feedforward controller at time t, is the input of the feedforward controller at time t, is the feedforward transfer function of the feedforward controller, is the transfer function of the feedforward controller.

4. The control method of the hydraulic station for a numerically controlled lathe according to claim 1, characterized in that, The control parameter of the PID controller is dynamically corrected by the fuzzy controller, including dividing the control process of the numerical control lathe machining into three stages of initial control, middle control and steady state adjustment, dynamically correcting the proportional gain K p The fuzzy rules include using a preset higher proportional gain K p in the initial control stage, and using the fast response characteristic to improve the dynamic tracking ability of the system; after entering the middle control stage, the proportional gain K p is reduced to weaken the strength of the proportional action to suppress the overshoot phenomenon while maintaining the response efficiency of the system. Re-increase the proportional gain K after entering the late stage of steady-state regulation p to improve the steady-state accuracy by combining the integral element.

5. The control method of the hydraulic station for a numerically controlled lathe according to claim 1, characterized in that, The control parameter of the PID controller is dynamically corrected by the fuzzy controller i In the fuzzy rules, a preset lower integral gain K is adopted in the initial control stage i To suppress the integral strength and avoid the initial overshoot risk; gradually increase the integral gain K after entering the middle control stage i To balance the error correction demand and the phase margin until the middle control stage is entered; continue to increase the integral gain K after entering the late stage of steady-state regulation i To exert its cumulative error elimination characteristics to improve control accuracy.

6. The control method of the hydraulic station for a numerically controlled lathe according to claim 1, characterized in that, The control parameters of the PID controller are dynamically corrected by the fuzzy controller d In the fuzzy rules, a preset higher differential gain K is used in the initial stage of control d The differential gain K is reduced in the middle stage of control to effectively suppress overshoot and enhance response rapidity by using the lead compensation effect thereof d The differential gain K is increased again in the later stage of steady state regulation to balance the contradiction between dynamic correction requirement and noise sensitivity d A secondary damping enhancement mechanism is formed to improve the anti-interference ability 7. The control method of the hydraulic station for a numerically controlled lathe according to claim 1, characterized in that, The integral gain K of the PID controller is corrected by using the flow rate estimation value z1 i The proportional gain K of the PID controller is corrected by using the pressure estimation value z2 p The differential gain K of the PID controller is corrected by using the pressure rate of change estimation value z3 d It includes lowering the integral gain K if the flow rate estimation value z1 is raised i to improve the steady state accuracy, raising the integral gain K if the flow rate estimation value z1 is lowered i , lowering the integral gain K if the pressure estimation value z2 is lowered i to improve the stability; lowering the proportional gain K if the pressure estimation value z2 is raised p , raising the proportional gain K if the pressure estimation value z2 is lowered p to avoid overshoot; increasing the differential gain K if the pressure rate of change estimation value z3 exceeds a preset threshold value d , decreasing the differential gain K if the pressure rate of change estimation value z3 is below the preset threshold value d to suppress oscillation.

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