CN204564772U - A kind of vertical pulling type cold rolling experiment machine hydraulic pressure tension control system - Google Patents

Abstract

A hydraulic tension control system for a straight-pull cold rolling test machine belongs to the technical field of cold rolling tension control. The utility model includes a left tension hydraulic cylinder, a right tension hydraulic cylinder, a hydraulic pump, a constant back pressure control unit, a left tension control unit and a right tension control unit. Compared with the prior art, in the hydraulic tension control system, the utility model The overflow volume of the proportional relief valve on the outlet side and the inlet side can be greatly reduced, so that the tension control accuracy is greatly improved; when the proportional relief valve is working, it can effectively avoid the nonlinear zone and dead zone, It is beneficial to exert the performance of the proportional relief valve and improve the precision of tension control; the hydraulic tension control system of the utility model does not need to predict the forward slip rate and the rear slip rate, but by presetting the control amount of the servo valve, Combined with the pressure control of the proportional relief valve to achieve high-precision tension control, and ultimately enhance the robustness of the tension control system.

Description

A hydraulic tension control system of a straight-pull cold rolling test machine

technical field

The utility model belongs to the technical field of cold rolling tension control, in particular to a hydraulic tension control system of a straight-pull cold rolling test machine.

Background technique

The straight-pull cold rolling test machine is the key experimental equipment for the research and development of cold rolling process and rolled products. The tension hydraulic cylinders on the left and right sides of the cold rolling test machine apply tension to the rolled parts and perform constant tension rolling. .

However, it is not easy to achieve constant tension rolling. First, the precision of tension control must be guaranteed, and there are many factors that affect the precision of tension control, including the time-varying nature of the control object during the rolling process, nonlinearity, and left and right tension. Due to the strong coupling between them, it will become very difficult to achieve high-precision tension control.

In order to meet the requirements of constant tension rolling and realize high-precision tension control, those skilled in the art have disclosed an invention patent of "Proportion Control Hydraulic System Realizing Constant Tension Control in Strip Rolling", the patent application number is 200710010015.6, and This patent discloses a method of using a proportional relief valve to realize constant tension control in strip rolling. This method can have good steady-state control accuracy and high dynamics under conditions of low rolling speed and high tension. responding speed. However, in the actual application process, when the rolling speed is high and the tension is small, the effect of left and right tension control is not ideal, which is affected by the flow pressure characteristics, nonlinear zone and dead zone characteristics of the proportional relief valve. As the rolling speed increases, the overflow volume of the proportional relief valve will increase a lot, making it more difficult to adjust the proportional relief valve, resulting in tension fluctuations; when the tension is small, the input signal of the proportional relief valve is small , and the input signal is often in the nonlinear zone or even the dead zone of the proportional relief valve, which affects the tension control accuracy.

Those skilled in the art have also disclosed a patent for invention of "Speed Feedforward-Based Straight Pull Cold Rolling Tension Control Method", the patent application number is 201210048625.6, and a speed feedforward combined with tension feedback is disclosed in this patent PID control strategy, the purpose of this control strategy is to realize the precise matching between the tension hydraulic cylinder and the rolling speed, but this precise matching has a prerequisite, that is, the line speed of the rolling stock at the exit and entrance of the rolling mill is accurately predicted, and The main factors affecting the prediction accuracy include forward slip rate and back slip rate. In the cold rolling process, there are many factors that affect the front slip rate and the back slip rate, including the reduction rate, the thickness of the rolled piece, the friction coefficient, the roll diameter and the tension factor, etc. For different materials and different rolling processes, it will also affect the front slip rate. slip rate and back slip rate, which makes the high-precision prediction of front slip rate and back slip rate very difficult. Although during the rolling process, the forward slip rate and the rear slip rate can be calculated and corrected by the actual movement speed of the left and right tension hydraulic cylinders and the actual rotational speed of the rolling mill, but at the moment of starting the rolling process, the calculation has not yet started, and it is necessary to An initial prediction value is set for the forward slip rate and the rear slip rate, but the initial prediction value has uncertainty, which greatly affects the tension control accuracy in the start-up stage.

It can be seen that the robustness of the existing technology is not strong, which directly affects the precision of tension control. Therefore, a method that can effectively enhance the robustness of the tension control system is urgently needed to improve the precision of tension control.

Utility model content

Aiming at the problems existing in the prior art, the utility model provides a hydraulic tension control system of a straight-pull cold rolling testing machine, which can effectively enhance the robustness of the tension control system, thereby improving the precision of tension control.

In order to achieve the above purpose, the utility model adopts the following technical scheme: a hydraulic tension control system of a straight-pull cold rolling test machine, including a left tension hydraulic cylinder, a right tension hydraulic cylinder, a hydraulic pump, a constant back pressure control unit, a left tension control unit and right tension control unit;

The oil inlet of the constant back pressure control unit is connected with the oil outlet of the hydraulic pump, and the oil return port of the constant back pressure control unit is connected with the oil supply tank of the hydraulic pump; A first pressure measurement port and a second pressure measurement port are provided, a first pressure gauge is connected to the first pressure measurement port, and a second pressure gauge is connected to the second pressure measurement port; the oil outlet of the constant back pressure control unit The port is connected with the back pressure oil inlet of the left tension control unit and the back pressure oil inlet of the right tension control unit;

The high-pressure oil inlet of the left tension control unit is connected with the high-pressure oil input port, and the oil return port of the left tension control unit is connected with the high-pressure oil supply tank; The pressure measuring port, the first working oil port, the second working oil port and the pressure measuring port of the first rod cavity, the first oil pressure sensor is connected to the first back pressure measuring port, the first working oil port and the left tension hydraulic cylinder The rodless cavity of the left tension hydraulic cylinder is connected with the second working oil port, and the second oil pressure sensor is connected to the pressure measuring port of the first rod cavity;

The high-pressure oil inlet of the right tension control unit is connected with the high-pressure oil input port, and the oil return port of the right tension control unit is connected with the high-pressure oil supply tank; The pressure measuring port, the third working oil port, the fourth working oil port and the pressure measuring port of the second rod cavity, the fourth oil pressure sensor is connected to the second back pressure measuring port, the third working oil port and the right tension hydraulic cylinder The rod chamber of the second rod chamber is connected, the fourth working oil port is connected with the rodless chamber of the right tension hydraulic cylinder, and the third oil pressure sensor is connected to the pressure measurement port of the second rod chamber.

The constant back pressure control unit includes a first one-way valve, a first relief valve and a second relief valve, the oil inlet of the constant back pressure control unit is connected to the inlet of the first one-way valve, the first relief valve The inlet is connected with the second pressure measuring port of the constant back pressure control unit, the outlet of the first check valve is connected with the inlet of the second relief valve, the oil outlet of the constant back pressure control unit and the first pressure measuring port, and the first The outlet of the relief valve is connected with the outlet of the second relief valve and the oil return port of the constant back pressure control unit.

The left tension control unit includes a first filter, a second one-way valve, a third one-way valve, a first accumulator, a first servo valve and a first proportional overflow valve, the back of the left tension control unit The pressure oil inlet is connected with the first back pressure measuring port and the first working oil port, the high pressure oil inlet of the left tension control unit is connected with the first filter inlet, and the first filter outlet is connected with the second one-way valve inlet The outlet of the second check valve is connected with the pressure oil port of the first servo valve and the first accumulator; the working oil port of the first servo valve is connected with the inlet of the first proportional relief valve and the left tension control unit The second working oil port and the pressure measuring port of the first rod chamber are connected, the outlet of the first proportional relief valve is connected with the oil return port of the first servo valve and the inlet of the third check valve, and the outlet of the third check valve It is connected with the oil return port of the left tension control unit.

The right tension control unit includes a second filter, a fourth one-way valve, a fifth one-way valve, a second accumulator, a second servo valve and a second proportional relief valve, the back of the right tension control unit The pressure oil inlet is connected with the fourth working oil port and the second back pressure measurement port, the high pressure oil inlet of the right tension control unit is connected with the second filter inlet, and the second filter outlet is connected with the fifth one-way valve inlet The outlet of the fifth check valve is connected with the pressure oil port of the second servo valve and the second accumulator; the working oil port of the second servo valve is connected with the inlet of the second proportional relief valve and the right tension control unit The pressure measuring port of the second rod chamber of the second rod chamber is connected with the third working oil port, the outlet of the second proportional relief valve is connected with the oil return port of the second servo valve and the inlet of the fourth check valve, and the outlet of the fourth check valve It is connected with the oil return port of the right tension control unit.

Adopting the control method of the hydraulic tension control system of the straight-pull cold rolling testing machine may further comprise the steps:

Step 1: Start the hydraulic pump, and at the same time connect the high-pressure oil input port to high-pressure oil;

Step 2: When the hydraulic system is running for the first time, manually adjust the set pressure of the first relief valve and the second relief valve in the constant back pressure control unit. The specific process is as follows:

① Input positive control signals to the first servo valve and the second servo valve at the same time, so that the working oil port of the first servo valve is connected with the oil return port of the first servo valve, and the working oil port of the second servo valve is connected with the oil return port of the first servo valve. The oil return ports of the two servo valves are connected, and the pistons of the left tension hydraulic cylinder and the right tension hydraulic cylinder extend to the limit position under the push of the back pressure of the rodless chamber, and maintain a static state;

② Manually adjust the first relief valve to the set pressure Py11, manually adjust the second relief valve to the set pressure Py12, and make Py11=Py12;

Step 3: Input the rated control signal to the first proportional relief valve and the second proportional relief valve, and use the first servo valve, the second servo valve, the first displacement sensor and the second displacement sensor to make the left tension hydraulic cylinder and The right tension hydraulic cylinder works in the position closed-loop state and clamps the test piece to be rolled;

Step 4: Determine the control volume SV1 of the first servo valve, the control volume SV2 of the second servo valve, the control signal PVz of the first proportional overflow valve and the control signal PVy of the second proportional overflow valve. The specific process is as follows:

① Determine the set rolling speed Vs and rolling direction according to the rolling regulations, and calculate the control volume SV1 of the first servo valve and the control volume SV2 of the second servo valve respectively by setting the rolling speed Vs and rolling direction, and actually control the first servo valve and the second servo valve;

Among them, the calculation process of the control quantity SV1 of the first servo valve and the control quantity SV2 of the second servo valve is as follows:

1) When the rolling direction is from left to right, the first servo valve is in the state of oil flow from the working oil port to the oil return port, and the second servo valve is in the state of oil flow from the pressure oil port to the working oil port;

Wherein, the calculation formula of the control variable SV1 of the first servo valve is:

$\mathrm{<span\; class="notranslate">\; SV</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; SV</span>}\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; 0.55</span>}\mathrm{<span\; class="notranslate">\; vs.</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; Ay</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}$

In the formula, SV1max is the rated control signal of the first servo valve, Vs is the set rolling speed, Ay1 is the effective area of the rod chamber of the piston of the left tension hydraulic cylinder, Q _N1 is the rated flow rate of the first servo valve, ΔP _N1 is the rated pressure difference of the valve port of the first servo valve, and ΔP1 is the actual pressure difference of the valve port of the first servo valve;

Wherein, the calculation formula of the control quantity SV2 of the second servo valve is:

$\mathrm{<span\; class="notranslate">\; SV</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; SV</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; 1.05</span>}\mathrm{<span\; class="notranslate">\; vs.</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; Ay</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}$

In the formula, SV2max is the rated control signal of the second servo valve, Vs is the set rolling speed, Ay2 is the effective area of the rod cavity of the piston of the right tension hydraulic cylinder, Q _N2 is the rated flow rate of the second servo valve, ΔP _N2 is the rated pressure difference of the valve port of the second servo valve, and ΔP2 is the actual pressure difference of the valve port of the second servo valve;

2) When the rolling direction is from right to left, the first servo valve is in the state of oil flow from the pressure oil port to the working oil port, and the second servo valve is in the state of oil flow from the working oil port to the oil return port;

Wherein, the calculation formula of the control variable SV1 of the first servo valve is:

$\mathrm{<span\; class="notranslate">\; SV</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; SV</span>}\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; 1.05</span>}\mathrm{<span\; class="notranslate">\; vs.</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; Ay</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}$

In the formula, SV1max is the rated control signal of the first servo valve, Vs is the set rolling speed, Ay1 is the effective area of the rod chamber of the piston of the left tension hydraulic cylinder, Q _N1 is the rated flow rate of the first servo valve, ΔP _N1 is the rated pressure difference of the valve port of the first servo valve, and ΔP1 is the actual pressure difference of the valve port of the first servo valve;

Wherein, the calculation formula of the control quantity SV2 of the second servo valve is:

$\mathrm{<span\; class="notranslate">\; SV</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; SV</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; 0.55</span>}\mathrm{<span\; class="notranslate">\; vs.</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; Ay</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}$

In the formula, SV2max is the rated control signal of the second servo valve, Vs is the set rolling speed, Ay2 is the effective area of the rod cavity of the piston of the right tension hydraulic cylinder, Q _N2 is the rated flow rate of the second servo valve, ΔP _N2 is the rated pressure difference of the valve port of the second servo valve, and ΔP2 is the actual pressure difference of the valve port of the second servo valve;

②According to the rolling regulations, determine the left tension setting value T1 and the right tension setting value T2, and calculate the preset signal PV11 of the first proportional relief valve according to the left tension setting value T1 and the right tension setting value T2 And the preset signal PV12 of the second proportional relief valve, and through the difference between the left tension setting value T1 and the left actual tension value feedback, the right tension setting value T2 and the right actual tension value feedback difference, the first The regulator of the proportional relief valve calculates the adjustment signal PV21 of the first proportional relief valve, and the regulator of the second proportional relief valve calculates the regulation signal PV22 of the second proportional relief valve, and the first proportional relief valve The preset signal PV11 of the valve is added to the adjustment signal PV21, which is used as the control signal PVz of the first proportional relief valve, and the preset signal PV12 of the second proportional relief valve is added to the adjustment signal PV22, which is used as the second proportional relief valve Valve control signal PVy, the specific calculation process is as follows:

1) The calculation formula of the preset signal PV11 of the first proportional relief valve is:

$\mathrm{<span\; class="notranslate">\; PV</span>}\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; Python</span>}\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; Aw</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; Ay</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; PV</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}{{\mathrm{<span\; class="notranslate">\; Python</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}$

In the formula, T1 is the set value of the left tension, Py11 is the manually set pressure value of the first relief valve, Aw1 is the effective area of the rodless chamber of the piston of the left tension hydraulic cylinder, and Ay1 is the rod of the piston of the left tension hydraulic cylinder cavity effective area, PV1 _N is the rated control signal of the first proportional relief valve, Py1 _N is the rated control pressure of the first proportional relief valve;

Therefore, the control signal PVz of the first proportional relief valve is:

PVz=PV11+PV21

In the formula, PV11 is the preset signal of the first proportional relief valve, and PV21 is the adjustment signal of the first proportional relief valve;

2) The calculation formula of the preset signal PV12 of the second proportional relief valve is:

$\mathrm{<span\; class="notranslate">\; PV</span>}\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; Python</span>}\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; Aw</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Ay</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; PV</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}{{\mathrm{<span\; class="notranslate">\; Python</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}$

In the formula, T2 is the set value of the right tension, Py12 is the manually set pressure value of the second relief valve, Aw2 is the effective area of the rodless chamber of the piston of the right tension hydraulic cylinder, and Ay2 is the rod of the piston of the right tension hydraulic cylinder cavity effective area, PV2 _N is the rated control signal of the second proportional relief valve, Py2 _N is the rated control pressure of the second proportional relief valve;

Therefore, the control signal PVy of the second proportional relief valve is:

PVy=PV12+PV22

In the formula, PV12 is the preset signal of the second proportional relief valve, and PV22 is the adjustment signal of the second proportional relief valve.

The beneficial effects of the utility model:

Compared with the prior art, the utility model can greatly reduce the overflow volume of the proportional overflow valves on the outlet side and the inlet side in the hydraulic tension control system, and the tension control precision is greatly improved accordingly; when the proportional overflow valve When the flow valve is working, it can effectively avoid the nonlinear zone and dead zone, which is beneficial to the performance of the proportional relief valve and improves the precision of tension control; the hydraulic tension control system of the utility model does not need to predict the forward slip rate and the rear slip rate , but by pre-setting the control amount of the servo valve, combined with the pressure control of the proportional relief valve to achieve high-precision tension control, and ultimately enhance the robustness of the tension control system.

Description of drawings

Fig. 1 is a schematic diagram of a hydraulic tension control system of a straight-pull cold rolling testing machine of the present invention;

Fig. 2 is the actual tension control curve diagram of the left tension hydraulic cylinder;

Fig. 3 is the actual tension control curve diagram of the right tension hydraulic cylinder;

Fig. 4 is the actual tension control error diagram of the left tension hydraulic cylinder;

Fig. 5 is the actual tension control error diagram of the right tension hydraulic cylinder;

In the figure, I—constant back pressure control unit, II—left tension control unit, III—right tension control unit;

1—left tension hydraulic cylinder, 2—right tension hydraulic cylinder, 3—hydraulic pump, 4—first pressure gauge, 5—second pressure gauge, 6—first oil pressure sensor, 7—second oil pressure sensor, 8 - the third oil pressure sensor, 9 - the fourth oil pressure sensor, 10 - the first one-way valve, 11 - the first relief valve, 12 - the second relief valve, 13 - the first filter, 14 - the second Check valve, 15—the third check valve, 16—the first accumulator, 17—the first servo valve, 18—the first proportional relief valve, 19—the second filter, 20—the fourth check valve , 21—the fifth one-way valve, 22—the second accumulator, 23—the second servo valve, 24—the second proportional overflow valve, 25—the first displacement sensor, 26—the second displacement sensor;

K1—oil inlet port of constant back pressure control unit, K2—oil return port of constant back pressure control unit, K3—first pressure measurement port, K4—second pressure measurement port, K5—oil outlet of constant back pressure control unit K6—back pressure oil inlet of left tension control unit, K7—high pressure oil inlet of left tension control unit, K8—oil return port of left tension control unit, K9—first back pressure measurement port, K10—first One working oil port, K11—the second working oil port, K12—the pressure measuring port of the first rod chamber, K13—the high pressure oil inlet of the right tension control unit, K14—the oil return port of the right tension control unit, K15—right The back pressure oil inlet of the tension control unit, K16—the pressure measuring port of the second rod chamber, K17—the third working oil port, K18—the fourth working oil port, K19—the second back pressure measuring port, Ps—high pressure oil Input port, Pp—oil outlet port of hydraulic pump;

A10—inlet of the first one-way valve, B10—outlet of the first one-way valve, P11—inlet of the first relief valve, T11—outlet of the first relief valve, P12—inlet of the second relief valve, T12—second overflow Flow valve outlet, A13—inlet of the first filter, B13—outlet of the first filter, A14—inlet of the second one-way valve, B14—outlet of the second one-way valve, A15—inlet of the third one-way valve, B15—inlet of the first one-way valve Outlet of three check valves, P17—pressure oil port of the first servo valve, B17—working oil port of the first servo valve, T17—oil return port of the first servo valve, P18—inlet of the first proportional relief valve, T18 —Outlet of the first proportional relief valve, A19—inlet of the second filter, B19—outlet of the second filter, A20—inlet of the fourth one-way valve, B20—outlet of the fourth one-way valve, A21—fifth one-way valve Inlet, B21—the outlet of the fifth check valve, P23—the pressure oil port of the second servo valve, B23—the working oil port of the second servo valve, T23—the oil return port of the second servo valve, P24—the second proportional overflow Flow valve inlet, T24—second proportional relief valve outlet.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment the utility model is described in further detail.

As shown in Figure 1, a hydraulic tension control system for a straight-pull cold rolling test machine includes a left tension hydraulic cylinder 1, a right tension hydraulic cylinder 2, a hydraulic pump 3, a constant back pressure control unit I, a left tension control unit II and Right tension control unit III;

The oil inlet K1 of the constant back pressure control unit 1 is connected with the oil outlet Pp of the hydraulic pump 3, and the oil return port K2 of the constant back pressure control unit 1 is connected with the oil supply tank of the hydraulic pump 3; The constant back pressure control unit 1 is also provided with a first pressure measuring port K3 and a second pressure measuring port K4, the first pressure measuring port K3 is connected with a first pressure gauge 4, and the second pressure measuring port K4 is connected with a second pressure measuring port K4. Pressure gauge 5; the oil outlet K5 of the constant back pressure control unit I communicates with the back pressure oil inlet K6 of the left tension control unit II and the back pressure oil inlet K15 of the right tension control unit III;

The high-pressure oil inlet K7 of the left tension control unit II is connected with the high-pressure oil input port Ps, and the oil return port K8 of the left tension control unit II is connected with the high-pressure oil supply tank; in the left tension control unit II It is also provided with a first back pressure measurement port K9, a first working oil port K10, a second working oil port K11 and a first rod cavity pressure measuring port K12, and a first oil pressure sensor is connected to the first back pressure measuring port K9 6. The first working oil port K10 is connected with the rodless chamber of the left tension hydraulic cylinder 1, the second working oil port K11 is connected with the rod chamber of the left tension hydraulic cylinder 1, and the pressure measurement port K12 of the first rod chamber A second oil pressure sensor 7 is connected;

The high-pressure oil inlet K13 of the right tension control unit III is connected with the high-pressure oil input port Ps, and the oil return port K14 of the right tension control unit III is connected with the high-pressure oil supply tank; in the right tension control unit III The second back pressure measuring port K19, the third working oil port K17, the fourth working oil port K18 and the second rod chamber pressure measuring port K16 are also provided, and the fourth oil pressure sensor is connected to the second back pressure measuring port K19 9. The third working oil port K17 is connected with the rod chamber of the right tension hydraulic cylinder 2, the fourth working oil port K18 is connected with the rodless chamber of the right tension hydraulic cylinder 2, and the pressure measurement port K16 of the second rod chamber A third oil pressure sensor 8 is connected.

The constant back pressure control unit I includes a first one-way valve 10, a first relief valve 11 and a second relief valve 12, and the oil inlet K1 of the constant back pressure control unit I is connected to the first one-way valve 10. The inlet A10, the inlet P11 of the first overflow valve 11 and the second pressure measurement port K4 of the constant back pressure control unit I are connected, the outlet B10 of the first check valve 10 is connected with the inlet P12 of the second overflow valve 12, and the constant back pressure control The oil outlet K5 of the unit I is connected with the first pressure measuring port K3, the outlet T11 of the first relief valve 11 is connected with the outlet T12 of the second relief valve 12 and the oil return port K2 of the constant back pressure control unit I.

The left tension control unit II includes a first filter 13, a second one-way valve 14, a third one-way valve 15, a first accumulator 16, a first servo valve 17 and a first proportional overflow valve 18, so The back pressure oil inlet K6 of the left tension control unit II is connected with the first back pressure measurement port K9 and the first working oil port K10, and the high pressure oil inlet K7 of the left tension control unit II is connected with the first filter 13 inlet A13 The outlet B13 of the first filter 13 is connected with the inlet A14 of the second one-way valve 14, and the outlet B14 of the second one-way valve 14 is connected with the pressure oil port P17 of the first servo valve 17 and the first accumulator 16 ; The working oil port B17 of the first servo valve 17 is connected with the inlet P18 of the first proportional relief valve 18, the second working oil port K11 of the left tension control unit II and the first pressure measuring port K12 of the rod chamber. The outlet T18 of a proportional relief valve 18 communicates with the oil return port T17 of the first servo valve 17 and the inlet A15 of the third check valve 15, and the outlet B15 of the third check valve 15 communicates with the oil return port K8 of the left tension control unit II connected.

The right tension control unit III includes a second filter 19, a fourth one-way valve 20, a fifth one-way valve 21, a second accumulator 22, a second servo valve 23 and a second proportional overflow valve 24, so The back pressure oil inlet K15 of the right tension control unit III is connected with the fourth working oil port K18 and the second back pressure measurement port K19, and the high pressure oil inlet K13 of the right tension control unit III is connected with the second filter 19 inlet A19 The outlet B19 of the second filter 19 is connected with the inlet A21 of the fifth one-way valve 21, and the outlet B21 of the fifth one-way valve 21 is connected with the pressure oil port P23 of the second servo valve 23 and the second accumulator 22 ; The working oil port B23 of the second servo valve 23 communicates with the inlet P24 of the second proportional relief valve 24, the second rod chamber pressure measurement port K16 of the right tension control unit III and the third working oil port K17. The outlet T24 of the second proportional overflow valve 24 communicates with the oil return port T23 of the second servo valve 23 and the inlet A20 of the fourth one-way valve 20, and the outlet B20 of the fourth one-way valve 20 communicates with the oil return port K14 of the right tension control unit III connected.

In this embodiment, a 350 mm straight-pull cold rolling test machine is used. The piston diameter D of the left tension hydraulic cylinder 1 and the right tension hydraulic cylinder 2 of the test machine is 80 mm, the diameter d of the piston rod is 56 mm, and the maximum stroke L is 2100mm, the maximum tension Tmax is 50kN, and the maximum rolling speed Vmax is 0.4m/s; the pressure of the high-pressure oil fed into the high-pressure oil input port Ps is 23.5MPa, the set pressure Py11 of the first relief valve 11 and the setting pressure of the second relief valve 11 The set pressure Py12 of the flow valve 12 is both 2.0MPa, and the first relief valve 11 and the second relief valve 12 are all selected cartridge relief valves, the model of which is DBDS20K10B/50; the first one-way valve 10, The second one-way valve 14, the third one-way valve 15, the fourth one-way valve 20 and the fifth one-way valve 21 all use cartridge type one-way valves, the model of which is M-SR20KE05-10/B; the hydraulic pump 3 The vane pump is selected, and its model is T6C-014-1R01-A1; the first filter 13 and the second filter 19 are both high-pressure filters, and its model is ZU-H-250×3FP; the first accumulator 16, The second accumulator 22 is a bladder-type accumulator with a model of NXQ1-4L/31.5-F-A; the first servo valve 17 and the second servo valve 23 are both servo valves with a model of D661-4538C/G35JOAA4VSX2H; The models of the first oil pressure sensor 6 and the fourth oil pressure sensor 9 are HDA3844-A-100-000, the models of the second oil pressure sensor 7 and the third oil pressure sensor 8 are HDA3844-A-250-000; the first displacement The model of the sensor 25 and the second displacement sensor 26 is RHM2150MD701S1G2100; the model of the first proportional relief valve 18 and the second proportional relief valve 24 is RZMO-A-030/315; the hydraulic tension control system of the straight-pull cold rolling testing machine Siemens S7-400PLC is adopted, and the CPU unit used is CPU416-2DP+FM458-1DP, and the regulators of the first proportional overflow valve 18 and the second proportional overflow valve 24 are all run in FM458-1DP.

In this embodiment, high-strength steel DP550 is used as raw material, its thickness is 3.3 mm, width is 200 mm, and length is 650 mm. The rolling schedule is shown in Table 1, and the first pass is rolling from left to right.

Table 1

Adopting the control method of the hydraulic tension control system of the straight-pull cold rolling testing machine may further comprise the steps:

Step 1: start the hydraulic pump 3, and at the same time, connect the high-pressure oil input port Ps to the high-pressure oil, and the pressure of the high-pressure oil is 23.5MPa;

Step 2: When the hydraulic system is running for the first time, manually adjust the set pressures of the first relief valve 11 and the second relief valve 12 in the constant back pressure control unit I, the specific process is as follows:

① Input a positive control signal to the first servo valve 17 and the second servo valve 23 at the same time, make the working oil port B17 of the first servo valve 17 communicate with the oil return port T17 of the first servo valve 17, and make the second servo valve The working oil port B23 of 23 is connected with the oil return port T23 of the second servo valve 23, the pistons of the left tension hydraulic cylinder 1 and the right tension hydraulic cylinder 2 extend to the limit position under the push of the back pressure of the rodless chamber, and keep still state;

②Manually adjust the first overflow valve 11 to the set pressure Py11, manually adjust the second overflow valve 12 to the set pressure Py12, and make Py11=Py12=2.0MPa;

Step 3: Input the rated control signal 10V to the first proportional relief valve 18 and the second proportional relief valve 24, while using the first servo valve 17, the second servo valve 23, the first displacement sensor 25 and the second displacement sensor 26 , so that the left tension hydraulic cylinder 1 and the right tension hydraulic cylinder 2 work in a position closed-loop state and clamp the test piece to be rolled;

Step 4: Determine the control volume SV1 of the first servo valve 17, the control volume SV2 of the second servo valve 23, the control signal PVz of the first proportional relief valve 18 and the control signal PVy of the second proportional relief valve 24, the specific process as follows:

① Determine the set rolling speed Vs and rolling direction according to the rolling regulations, and calculate the control volume SV1 of the first servo valve 17 and the control volume of the second servo valve 23 respectively by setting the rolling speed Vs and rolling direction SV2, and actually control the first servo valve 17 and the second servo valve 23;

Wherein, the calculation process of the control variable SV1 of the first servo valve 17 and the control variable SV2 of the second servo valve 23 is as follows:

Taking the third rolling pass as an example, when the rolling direction is from left to right, the first servo valve 17 is in the state of oil flow from the working oil port B17 to the oil return port T17, and the second servo valve 23 is in the state of oil flow from the pressure oil port P23 to the oil return port T17. The state of working oil port B23 through oil;

Wherein, the calculation formula of the control variable SV1 of the first servo valve 17 is:

$\mathrm{<span\; class="notranslate">\; SV</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; SV</span>}\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; 0.55</span>}\mathrm{<span\; class="notranslate">\; vs.</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; Ay</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}$

In the formula, SV1max is the rated control signal of the first servo valve 17, Vs is the set rolling speed, Ay1 is the effective area of the rod cavity of the piston of the left tension hydraulic cylinder 1, and Q _N1 is the rated flow rate of the first servo valve 17 , ΔP _N1 is the rated pressure difference at the valve port of the first servo valve 17, and ΔP1 is the actual pressure difference at the valve port of the first servo valve 17;

Wherein, the calculation formula of the control variable SV2 of the second servo valve 23 is:

$\mathrm{<span\; class="notranslate">\; SV</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; SV</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; 1.05</span>}\mathrm{<span\; class="notranslate">\; vs.</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; Ay</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}$

In the formula, SV2max is the rated control signal of the second servo valve 23, Vs is the set rolling speed, Ay2 is the effective area of the rod cavity of the piston of the right tension hydraulic cylinder 2, and Q _N2 is the rated flow rate of the second servo valve 23 , ΔP _N2 is the rated pressure difference of the valve port of the second servo valve 23, and ΔP2 is the actual pressure difference of the valve port of the second servo valve 23;

According to the selected models of the first servo valve 17, the second servo valve 23, the left tension hydraulic cylinder 1 and the right tension hydraulic cylinder 2 in this embodiment, the parameters that can be determined are: SV1max= _SV2max =10mA, QN1=Q _N2 = 90l/min, ΔP _N1 = ΔP _N2 = 3.5MPa, Ay1 = Ay2 = 1/4π(D ² -d ² ) = 2563.5mm ² , then:

$\mathrm{<span\; class="notranslate">\; SV</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 9.4</span>}\mathrm{<span\; class="notranslate">\; vs.</span>}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 3.5</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}$

$\mathrm{<span\; class="notranslate">\; SV</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 17.9</span>}\mathrm{<span\; class="notranslate">\; vs.</span>}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 3.5</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}$

Wherein, the set rolling speed Vs of the third rolling speed-up section is taken as 0.1m/s, ignoring the oil return back pressure, it can be obtained: ΔP1=P1, P1 is the pressure at the working oil port B17 of the first servo valve 17 The pressure is approximately equal to the pressure in the rod cavity of the left tension hydraulic cylinder 1, and is measured by the second oil pressure sensor 7. The measured value is ΔP1=P1=18.76MPa; where, ΔP2=Ps-P2=23.5-P2, P2 is the pressure at the working oil port B23 of the second servo valve 23, which is approximately equal to the pressure in the rod chamber of the right tension hydraulic cylinder 2, and is measured by the third oil pressure sensor 8. The measured value is P2=18.83MPa, and ΔP2 can be obtained =4.67MPa; finally available: SV1=0.41mA, SV2=-1.55mA;

②According to the rolling regulations, determine the left tension setting value T1 and the right tension setting value T2, and calculate the preset signal of the first proportional relief valve 18 according to the left tension setting value T1 and the right tension setting value T2 PV11 and the preset signal PV12 of the second proportional relief valve 24, and through the difference between the left tension setting value T1 and the left actual tension value feedback, the right tension setting value T2 and the right actual tension value feedback difference, by The regulator of the first proportional relief valve 18 calculates the regulation signal PV21 of the first proportional relief valve 18, the regulator of the second proportional relief valve 24 calculates the regulation signal PV22 of the second proportional relief valve 24, and The preset signal PV11 of the first proportional overflow valve 18 is added to the adjustment signal PV21 as the control signal PVz of the first proportional overflow valve 18, and the preset signal PV12 of the second proportional overflow valve 24 is added to the adjustment signal PV22 Added together, as the control signal PVy of the second proportional relief valve 24, the specific calculation process is as follows:

1) The calculation formula of the preset signal PV11 of the first proportional overflow valve 18 is:

$\mathrm{<span\; class="notranslate">\; PV</span>}\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; Python</span>}\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; Aw</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; Ay</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{{\mathrm{<span\; class="notranslate">\; PV</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}{{\mathrm{<span\; class="notranslate">\; Python</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}$

In the formula, T1 is the left tension setting value of 38kN, Py11 is the manual setting pressure value of the first relief valve 11, and it is known that Py11=2.0MPa, and Aw1 is the effective effect of the piston rodless cavity of the left tension hydraulic cylinder 1 Area, Ay1 is the effective area of the rod cavity of the piston of the left tension hydraulic cylinder 1, which can be obtained according to the model selected in this embodiment of the left tension hydraulic cylinder 1, Aw1=1/4πD ² =5026.5mm ² , and Ay1= 2563.5mm ² , PV1 _N is the rated control signal of the first proportional relief valve 18, PV1 _N = 10V, Py1 _N is the rated control pressure of the first proportional relief valve 18, Py1 _N = 31.5MPa; then substitute the above parameters into After the formula, it can be obtained: PV11=3.459V;

In the present embodiment, the regulator of the first proportional overflow valve 18 adopts a PI regulator, wherein the P parameter is 0.08, and the I parameter is 450ms, then the adjustment signal PV21 calculated by the regulator of the first proportional overflow valve 18= -0.201V, finally the control signal PVz of the first proportional relief valve 18 can be obtained as: PVz=PV11+PV21=3.258V;

2) The calculation formula of the preset signal PV12 of the second proportional relief valve 24 is:

$\mathrm{<span\; class="notranslate">\; PV</span>}\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; Python</span>}\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; Aw</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Ay</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{{\mathrm{<span\; class="notranslate">\; PV</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}{{\mathrm{<span\; class="notranslate">\; Python</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}$

In the formula, T2 is the right tension setting value of 36kN, Py12 is the manual setting pressure value of the second relief valve 12, and it is known that Py12=2.0MPa, and Aw2 is the effective effect of the piston rodless chamber of the right tension hydraulic cylinder 2 Area, Ay2 is the effective area of the rod chamber of the piston of the right tension hydraulic cylinder 2, which can be obtained according to the model selected in this embodiment of the right tension hydraulic cylinder 2, Aw2=1/4πD ² =5026.5mm ² , Ay2=2563.5 mm ² , PV2 _N is the rated control signal of the second proportional relief valve 24, PV2 _N = 10V, Py2 _N is the rated control pressure of the second proportional relief valve 24; Py2 _N = 31.5MPa; then substitute the above parameters into the formula After that, we can get: PV12=3.212V;

In the present embodiment, the regulator of the second proportional relief valve 24 adopts a PI regulator, wherein the P parameter is 0.08, and the I parameter is 450ms, then the regulation signal PV22 calculated by the regulator of the second proportional relief valve 24= 0.053V, finally the control signal PVy of the second proportional overflow valve 24 can be obtained as: PVy=PV12+PV22=3.265V.

During the entire rolling process, as shown in Figures 2 and 3, they are the actual tension control curves of the left tension hydraulic cylinder 1 and the actual tension control curves of the right tension hydraulic cylinder 2 respectively. It can be clearly seen in the figures that Large tension control deviation appears in the process of starting and stopping, and increases with the increase of the maximum rolling speed.

In the fifth rolling pass, the maximum rolling speed is 0.4m/s. During the starting process and the parking process, as shown in Figures 4 and 5, they are the actual tension control error diagrams of the left tension hydraulic cylinder 1 And the actual tension control error diagram of the right tension hydraulic cylinder 2, it can be clearly seen in the figure that the maximum control deviation of the left and right tension is about within ± 1.0kN, and then the effectiveness of the utility model is verified.

The schemes in the embodiments are not intended to limit the patent protection scope of the present utility model, and all equivalent implementations or changes that do not deviate from the utility model are included in the patent scope of the present case.

Claims (4)

1. A hydraulic tension control system for a straight-pull cold rolling testing machine, characterized in that: it comprises a left tension hydraulic cylinder, a right tension hydraulic cylinder, a hydraulic pump, a constant back pressure control unit, a left tension control unit and a right tension control unit; The oil inlet of the constant back pressure control unit is connected with the oil outlet of the hydraulic pump, and the oil return port of the constant back pressure control unit is connected with the oil supply tank of the hydraulic pump; A first pressure measurement port and a second pressure measurement port are provided, a first pressure gauge is connected to the first pressure measurement port, and a second pressure gauge is connected to the second pressure measurement port; the oil outlet of the constant back pressure control unit The port is connected with the back pressure oil inlet of the left tension control unit and the back pressure oil inlet of the right tension control unit; The high-pressure oil inlet of the left tension control unit is connected with the high-pressure oil input port, and the oil return port of the left tension control unit is connected with the high-pressure oil supply tank; The pressure measuring port, the first working oil port, the second working oil port and the pressure measuring port of the first rod cavity, the first oil pressure sensor is connected to the first back pressure measuring port, the first working oil port and the left tension hydraulic cylinder The rodless cavity of the left tension hydraulic cylinder is connected with the second working oil port, and the second oil pressure sensor is connected to the pressure measuring port of the first rod cavity; The high-pressure oil inlet of the right tension control unit is connected with the high-pressure oil input port, and the oil return port of the right tension control unit is connected with the high-pressure oil supply tank; The pressure measuring port, the third working oil port, the fourth working oil port and the pressure measuring port of the second rod cavity, the fourth oil pressure sensor is connected to the second back pressure measuring port, the third working oil port and the right tension hydraulic cylinder The rod chamber of the second rod chamber is connected, the fourth working oil port is connected with the rodless chamber of the right tension hydraulic cylinder, and the third oil pressure sensor is connected to the pressure measurement port of the second rod chamber. 2. The hydraulic tension control system of a straight-pull cold rolling testing machine according to claim 1, wherein the constant back pressure control unit includes a first check valve, a first overflow valve and a second overflow valve. flow valve, the oil inlet of the constant back pressure control unit communicates with the first check valve inlet, the first overflow valve inlet and the second pressure measurement port of the constant back pressure control unit, and the first check valve outlet communicates with the The inlet of the second relief valve, the oil outlet of the constant back pressure control unit and the first pressure measuring port are connected, and the outlet of the first relief valve is connected with the outlet of the second relief valve and the oil return port of the constant back pressure control unit . 3. The hydraulic tension control system of a straight-pull cold rolling testing machine according to claim 1, wherein the left tension control unit includes a first filter, a second one-way valve, and a third one-way valve , the first accumulator, the first servo valve and the first proportional relief valve, the back pressure oil inlet of the left tension control unit communicates with the first back pressure measurement port and the first working oil port, the left tension control The high-pressure oil inlet of the unit is connected with the inlet of the first filter, the outlet of the first filter is connected with the inlet of the second one-way valve, and the outlet of the second one-way valve is connected with the pressure oil port of the first servo valve and the first energy storage The working oil port of the first servo valve is connected with the inlet of the first proportional relief valve, the second working oil port of the left tension control unit and the pressure measuring port of the first rod chamber, and the first proportional relief valve The outlet of the valve is connected with the oil return port of the first servo valve and the inlet of the third one-way valve, and the outlet of the third one-way valve is connected with the oil return port of the left tension control unit. 4. The hydraulic tension control system of a straight-pull cold rolling testing machine according to claim 1, wherein the right tension control unit includes a second filter, a fourth one-way valve, and a fifth one-way valve , the second accumulator, the second servo valve and the second proportional relief valve, the back pressure oil inlet of the right tension control unit communicates with the fourth working oil port and the second back pressure measurement port, and the right tension control unit The high-pressure oil inlet of the unit is connected with the inlet of the second filter, the outlet of the second filter is connected with the inlet of the fifth one-way valve, the outlet of the fifth one-way valve is connected with the pressure oil port of the second servo valve and the second energy storage The working oil port of the second servo valve is connected with the inlet of the second proportional relief valve, the pressure measuring port of the second rod chamber of the right tension control unit and the third working oil port, and the second proportional relief valve The outlet of the valve is connected with the oil return port of the second servo valve and the inlet of the fourth one-way valve, and the outlet of the fourth one-way valve is connected with the oil return port of the right tension control unit.