CN108016027A - A kind of control method of BOPP bidirectional stretching systems - Google Patents

Abstract

The invention provides a control method of a BOPP bidirectional stretching system, for any three-motor subsystem in the stretching section of the system: including the front shaft, the first tension roller, the main drive shaft, the second tension roller, and the rear shaft , using two distributed controllers for control, wherein the front axle motor and the main drive axle motor are controlled by the first controller, and the main drive axle motor and the rear axle motor are controlled by the second controller. At the same time, the The first controller and the second controller share a part of output by superimposing control factors a and b to control the main drive shaft motor. In the method of the present invention, two continuous controllers share a part of the input and output by superimposing control factors, which can significantly improve the decoupling ability of the system speed and tension, and accordingly extend the above subsystem to the multi-motor roll of the biaxial stretching process In the winding system, the longitudinal and transverse thickness control models of the film are also designed to realize the synchronous and precise control of the speed, tension and thickness of the stretching process.

Description

A kind of control method of BOPP bidirectional stretching system

technical field

The invention relates to the technical field of control, in particular to a control method for a BOPP biaxial stretching system.

Background technique

BOPP is the abbreviation of "Biaxially Oriented Polypropylene", and BOPP film is a biaxially oriented polypropylene film. The production of BOPP film is to first make the melt of high molecular weight polypropylene through a narrow and long die into a sheet or a thick film, and then in a special stretching machine, at a certain temperature and a set speed, simultaneously or step by step A film made by stretching in two vertical directions (longitudinal and transverse) and undergoing appropriate cooling or heat treatment or special processing (such as corona, coating, etc.).

In the BOPP film winding transmission and stretching system, the main control objective is to independently control the speed and tension of each drive roller under the disturbance of the roll diameter and the change of the set value. However, these disturbance factors and control quantities often interact and cannot be described individually. The production process of casting sheet-longitudinal drawing-horizontal drawing-drawing-winding of the whole system includes a series of actuators (drive motors), and it is difficult to realize the control of multiple motors by using a global multi-variable controller.

Contents of the invention

The technical problem solved by the present invention is to provide a control method of the BOPP biaxial stretching system to reduce the longitudinal thickness deviation of the film.

In order to solve the above problems, the present invention adopts the following technical solutions:

A control method for a BOPP bidirectional stretching system. For any three-motor subsystem in the stretching section of the system: including the front shaft, the first tension roller, the main drive shaft, the second tension roller, and the rear shaft, two The distributed controller performs control, wherein, the front shaft motor and the main drive shaft motor are controlled by the first controller, and the main drive shaft motor and the rear shaft motor are controlled by the second controller. At the same time, the first controller Share a part of the output with the second controller by superimposing the control factors a and b to control the main drive shaft motor.

Further, the first controller takes the film tension setting value T _{u_ref} at the leading shaft and the film speed setting value V _ref at the main drive shaft as inputs, and according to the real-time tension T _u of the film at the first tension roller and the main The real-time velocity V of the film at the driving shaft is obtained from the tension control deviation value of the front shaft motor x _u =T _{u_ref} -T _u and the speed control deviation value x _v =V _ref -V, and then the torque control of the front shaft is obtained according to the following formula Signal u _u and main drive shaft motor torque control signal u _v1 :

Among them, P _u , P _v1 are proportional gain coefficients, T _iu , T _iv1 are integral time constants, i _u , _iv are mechanical transmission ratios of front shaft motor and main drive shaft motor, nu _u , n _v are front shaft motors Motor speed of shaft motor and main drive shaft motor;

The second controller takes the film speed set value V _ref at the main drive shaft and the film tension set value T _{w_ref} at the rear shaft as inputs, and according to the real-time speed V of the film at the main drive shaft and the film tension at the second tension roller For the real-time tension T _w of the film, the tension control deviation value of the rear shaft motor x _w =T _{w_ref} -T _w and the speed control deviation value x _v =V _ref -V are obtained, and then the torque control signal of the main drive shaft motor is obtained according to the following formula u _v2 and rear axle motor torque control signal u _w :

Among them, P _w , P _v2 are proportional gain coefficients, T _iw , T _iv2 are integral time constants, i _w , _iv are the mechanical transmission ratios of the rear shaft motor and the main drive shaft motor, n _w , n _v are the rear Motor speed of shaft motor and main drive shaft motor;

Afterwards, according to the overlapping control factors a and b, the main drive shaft motor control signal u _v =a·u _v1 +b·u _v2 is obtained.

Further, the real-time tension of the film at the first tension roller place T ₁ is the tension of the film between the front shaft and the first tension roller, and T ₂ is the tension _Tu of the film between the first tension roller and the main drive shaft; the real-time tension of the film at the second tension roller place T ₃ is the tension of the film between the driving shaft and the second tension roller, T ₄ is the tension of the film between the second tension roller and the rear shaft; T ₁ , T ₂ , T ₃ , T ₄ and the main driving shaft The real-time velocity V of the film is obtained by the following formula:

Among them, Ω _k = V _k / R _k is the rotational speed of the kth roller, K _k is the motor torque constant, U _k is the motor torque, J _k is the moment of inertia, R _k is the roll diameter, C _f is the friction torque , V ₀ is the rated film speed of the film at the exit of the front shaft, T _k and L _k are the tension and film length between the k-1 roller and the k roller, V ₀ is the ideal film speed, T ₀ is the ideal film speed Tension, E is the Young's modulus of elasticity of the film material, S is the cross-sectional area of the film; the real-time speed of the film at the main drive shaft V=V ₃ .

Further, the five parts of the BOPP biaxial stretching system, including casting, longitudinal drawing, transverse drawing, traction and winding, include a total of 12 shaft drive motors from M1 to M12, wherein the motor M1 drives the cooling roll, and the motors M2, M3, M4 drives the three stretching rollers in the longitudinal stretching area, motor M5 drives the stretching rollers in the transverse stretching area, M6, M7, M8, M9 and M10 drive 5 sets of traction guide rollers, and motors M11 and M12 drive two sets of each other as spares the reel;

The above 12 shaft drive motors and their corresponding 12 shafts are divided into 5 subsystems, each subsystem includes 3 motors and corresponding 3 shafts; the 3 shafts in each subsystem are respectively abstracted as the front shaft, main drive shaft and rear shaft are controlled by 2 PID controllers.

Further, the method of the present invention also includes a lateral thickness deviation control model and a longitudinal thickness deviation control model, wherein the lateral thickness deviation control model includes the following steps:

S1. Detect the thickness of the biaxially stretched film through the first thickness gauge configured in the traction part;

S2. Comparing the thickness detected by the first thickness gauge with the thickness setting value to obtain a thickness difference;

S3. The cast sheet PID controller calculates the correction value according to the thickness difference, and adjusts it through the bolt temperature control PID controller to change the temperature of the heat-sensitive die head bolts so that the opening degree of the lip of the membrane head changes, and the adjustment sheet The thickness of the material; among them,

The correction parameters of the lip opening of the membrane head are obtained through the following transfer function:

Among them, W is the correction parameter of the mouth opening of the membrane head, Ky is the target change amount of the mouth opening of the membrane head, K _x is the adjustment amount of the bolt, ma _is the displacement ratio parameter, and G _p is the enlargement of the cross-sectional shape of the mouth of the membrane head coefficient, T ₀ is the thickness setting value, and T _m is the film thickness value detected by the first thickness gauge.

Further, the BOPP biaxial stretching system is equipped with 32 sets of heat-sensitive die bolts to adjust the extrusion volume of the BOPP raw polymer melt in different regions, and each heat-sensitive die bolt is controlled by an independent control loop.

Further, the longitudinal thickness deviation control model includes the following steps:

S1. Detect the thickness of the formed slab at the outlet of the chill roll through the second thickness gauge configured in the casting part;

S2. Comparing the film thickness measured by the second thickness gauge with the set value to obtain an error signal;

S3. According to the error signal, change the linear speed of the chill roll through the chill roll PID regulator, so as to control the longitudinal thickness deviation of the film.

According to the film thickness control method of the BOPP biaxial stretching system of the present invention, the tension of the whole system can be kept constant, and the decoupling ability of the system speed and tension is improved, and the longitudinal thickness deviation and transverse thickness deviation of the film are reduced.

Description of drawings

Figure 1 is a schematic diagram of the composition of the BOPP biaxial stretching system.

Fig. 2 is a schematic diagram of a three-motor overlapping control model in the control method of the present invention.

Fig. 3 is a diagram of the experimental results of the three-motor overlapping control model in Fig. 2 .

Fig. 4 is a schematic diagram of a multi-motor semi-decentralized overlapping control model in the control method of the present invention.

Fig. 5 is a schematic diagram of the composition of the longitudinal thickness deviation control loop in the control method of the present invention.

Fig. 6 is a schematic composition diagram of the longitudinal and transverse thickness deviation control loops in the control method of the present invention.

Fig. 7 is a comparison chart of lateral thickness deviation data detected by the thickness gauge in the existing control method and the control method of the present invention.

Fig. 8 is a comparison chart of longitudinal thickness deviation data detected by the thickness gauge in the existing control method and the control method of the present invention.

Detailed ways

In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only to further illustrate the features and advantages of the present invention, rather than limiting the claims of the present invention.

First, the BOPP biaxially stretched system will be described. As shown in Figure 1, the BOPP biaxial stretching system includes six subsystems: extrusion, casting, longitudinal stretching, transverse stretching, traction and winding.

Among them, the extrusion system is mainly composed of primary extrusion, secondary extrusion, first auxiliary extrusion, second auxiliary extrusion and filter. Specifically, the function of the first-stage main extrusion is to make the material receive the heat from the external heater, and reach a semi-molten state under the shear and compression of the screw, and quantitatively supply the material to the second-stage main extrusion. The secondary main extrusion is mainly composed of a molten material compression zone and a metering zone. Its function is to fully melt and plasticize the polymer, and through high shearing, the materials are uniformly mixed and metered for extrusion. After the material enters the first-stage main extrusion from the hopper, it is plasticized and compressed through the feeding area, compression area, and metering area, and then sent to the second-level main extrusion. The first-stage main extrusion screw is driven by two motors, and the second-stage main extrusion screw is driven by one motor. Adjusting the screw speed can change the discharge pressure of the extruder and control the melting temperature of the material. The first auxiliary extrusion and the second auxiliary extrusion are driven by a single-screw extruder. Its main function is to continuously convey, melt, mix, exhaust, and pressurize the solid resin, and to uniformly plasticize the melt. Constant pressure and quantitative extrusion into the molding die.

The casting system is mainly composed of membrane head, heating bolt, chill roll and 1# thickness gauge. "Cast sheet" means that the molten plastic is forced to pass through the long die under the pressure, and under the action of external force (static electricity, air flow, etc.), the molten plastic is quickly attached to the surface of the cold drum and made into a solid state. Sheet process. Among them, the film head is the key device of cast casting, which directly determines the uniformity of the shape and thickness of the casting, and the opening of the die is initially adjusted by several push-pull differential bolts with heating coils. The 1# thickness gauge can automatically measure the thickness of the cast slab, and feed back the thickness value of the cast slab to the control system. Heating bolts: including 32 sets of differential heating bolts, the extrusion volume and film thickness deviation can be adjusted and controlled by manual adjustment + automatic adjustment. Manual adjustment method: manually rotate the bolt, and the opening of the die lip will increase or decrease [m1-m2] every time the bolt rotates once (assuming that the pitch of the outer thread of the differential bolt is m1, and the pitch of the inner thread is m2). The controller system adjusts the thickness of the cast sheet detected by the 1# thickness gauge, adjusts the temperature of the heating bolt of the die head in real time, and fine-tunes the opening of the die lip. The cooling roll is used to quickly cool the BOPP melt flowing out of the die below its glass transition temperature, forming a glassy cast sheet with uniform thickness. The purpose of rapid cooling is to make the thick sheet form an amorphous structure and minimize its crystallization, so as to avoid adverse effects on the next stretching process. The cold roll is driven by the motor M1, and the control system adjusts the speed of the cold roll according to the requirements of stretching thickness control. Cooling water at about 30°C is passed through the cooling roll to ensure that the cast sheet is cooled to below 60°C.

The longitudinal stretching system is used to stretch the slab from the casting machine to a certain number of longitudinal stretches in a heated state. The longitudinal stretching system is divided into four zones: preheating zone, stretching zone, shaping zone and cooling zone, which is composed of preheating roller, stretching roller, cooling roller, rubber pressing roller, temperature control system, sheet feeding system, etc. Among them, the temperature control system uses low-pressure steam heating in the preheating zone, and high-temperature and high-pressure water heating in the stretching zone, shaping zone and cooling zone. There are three stretching rollers arranged in the stretching area, which are respectively driven by motors M2, M3, and M4.

The horizontal tension system is composed of oven, chain clamp and guide rail, static pressure box, chain tensioner, guide rail width adjustment device, opening and closing clamp, hot air circulation system, lubrication system and EPC. The horizontal stretching mechanism is composed of functional sections such as film feeding, preheating, tentering, buffering, shaping and cooling, and the heating temperature of each section is not higher than 190°C. The function of the horizontal stretching machine is to complete the transverse stretching of the film through preheating, tentering, heat setting and cooling in the horizontal stretching machine. The transverse stretching roller is driven by a motor M5.

Traction system: It is composed of several traction guide rollers, cooling rollers, flattening rollers, tension rollers, tracking rollers, edge trimming devices, edge material crushing systems, 2# thickness gauges, and corona treatment machines. Among them, the 2# thickness gauge is used to measure the transverse thickness of the stretched BOPP film online. The corona treater applies a high-frequency and high-voltage current to the electrode to cause the electrode to generate a corona discharge, and the gas ionizes to generate high-energy ions, which impact the surface of the plastic film under the action of a strong electric field to activate the surface of the film to increase the surface wet tension of the film. The traction guide rollers include 5 sets of traction guide rollers, which are driven by motors M6, M7, M8, M9 and M10.

The winding system is composed of touch roller, 1# winding shaft, 2# winding shaft, turret and automatic film cutting knife. 1# winding shaft and 2# winding shaft are spare for each other, driven by M11 and M12 respectively, and the turret is driven by M13. When the 1# winding shaft is close to the full set, the turret will rotate the 1# winding shaft to the spare station, the film cutter will cut off the film, the winding system will switch to the 2# winding shaft, and the operator will turn the 1# winding shaft The finished film is hoisted and shipped out.

The above-mentioned BOPP biaxial stretching system adopts a biaxially oriented flat film stepwise stretching method. The longitudinal stretching system has 10 preheating rolls, 4 stretching rolls and 2 setting rolls. The horizontal stretching system adopts four-zone preheating, three-zone stretching, two-zone setting, and one-zone cooling. The longitudinal stretching of the system adopts single-point stretching with small gaps, and the stretching ratio can be set and adjusted arbitrarily from 1:1 to 1:6, and the maximum horizontal stretching ratio can reach 1:11. Tension sensors are used for speed synchronization between the cold drum and longitudinal stretching slow rolls and cross stretching, and between longitudinal stretching fast rolls and cross stretching. The speed setting from the cold drum to the traction unit is in a speed chain relationship to ensure that the speed of the production line is synchronized. In order to realize the stable control of the above system, the present invention provides a control method of the BOPP biaxial stretching system.

One aspect of the present invention provides a stretch control method. Let's start with a simpler model.

As shown in Figure 2, for any three-motor subsystem in the stretching section of the system: including the front shaft, the first tension roller, the main drive shaft, the second tension roller, and the rear shaft, two distributed controllers are used to implement control, wherein the front shaft motor and the main drive shaft motor are controlled by the first controller, and the main drive shaft motor and the rear shaft motor are controlled by the second controller, and at the same time, the first controller and the second controller A part of the output is shared by superimposing the control factors a and b to control the main drive shaft motor.

Specifically, the first controller takes the film tension set value T _{u_ref} at the front shaft and the film speed set value V _ref at the main drive shaft as inputs, and according to the real-time tension _{Tu_ref} of the film at the first tension roller and the main drive shaft The real-time speed V of the film at the position, the tension control deviation value of the front shaft motor x _u = T _{u_ref} -T _u and the speed control deviation value x _v = V _ref -V are obtained, and then the torque control signal u of the front shaft is obtained according to the following formula _u and main drive shaft motor torque control signal u _v1 :

Among them, P _u , P _v1 are proportional gain coefficients, T _iu , T _iv1 are integral time constants, i _u , _iv are mechanical transmission ratios of front shaft motor and main drive shaft motor, nu _u , n _v are front shaft motors Motor speed of shaft motor and main drive shaft motor;

The second controller takes the film speed set value V _ref at the main drive shaft and the film tension set value T _{w_ref} at the rear shaft as inputs, and according to the real-time speed V of the film at the main drive shaft and the film at the second tension roller Real-time tension T _w , obtain the tension control deviation value of the rear shaft motor x _w = T _{w_ref} -T _w and the speed control deviation value x _v = V _ref -V, and then obtain the torque control signal u _v2 of the main drive shaft motor according to the following formula And the rear axle motor torque control signal u _w :

Among them, P _w , P _v2 are proportional gain coefficients, T _iw , T _iv2 are integral time constants, i _w , _iv are the mechanical transmission ratios of the rear shaft motor and the main drive shaft motor, n _w , n _v are the rear Motor speed of shaft motor and main drive shaft motor;

Afterwards, according to the overlapping control factors a and b, the main drive shaft motor control signal u _v =a·u _v1 +b·u _v2 is obtained.

In the above calculation, the real-time tension of the film at the first tension roller T ₁ is the tension of the film between the front shaft and the first tension roller, and T ₂ is the tension _Tu of the film between the first tension roller and the main drive shaft; the real-time tension of the film at the second tension roller place T ₃ is the tension of the film between the driving shaft and the second tension roller, T ₄ is the tension of the film between the second tension roller and the rear shaft; T ₁ , T ₂ , T ₃ , T ₄ and the main driving shaft The real-time velocity V of the film is obtained by the following formula:

Among them, Ω _k = V _k / R _k is the rotational speed of the kth roller, K _k is the motor torque constant, U _k is the motor torque, J _k is the moment of inertia, R _k is the roll diameter, C _f is the friction torque , V ₀ is the rated film speed of the film at the exit of the front shaft, T _k and L _k are the tension and film length between the k-1 roller and the k roller, V ₀ is the ideal film speed, T ₀ is the ideal film speed Tension, E is the Young's modulus of elasticity of the film material, S is the cross-sectional area of the film; the real-time speed of the film at the main drive shaft V=V ₃ .

As shown in Figure 3, it is the experimental result graph after using the above control model. It can be seen that both the unwinding tension and winding tension, and the speed of the main drive shaft have good stability.

Next, the above control model is applied to the entire BOPP biaxial stretching system. As shown in Figure 4, the five parts of the entire BOPP biaxial stretching system, including casting, longitudinal drawing, transverse drawing, traction and winding, include a total of 12 shaft drive motors from M1 to M12. Among them, the motor M1 drives the cooling roll, and the motor M2, M3 and M4 drive the three stretching rollers in the longitudinal stretching zone, motor M5 drives the stretching rollers in the transverse stretching zone, motors M6, M7, M8, M9 and M10 drive 5 sets of traction guide rollers, and motors M11 and M12 drive Two mutually spare rewinding shafts; the above 12 shaft drive motors and their corresponding 12 shafts are divided into 5 subsystems, each subsystem includes 3 motors and corresponding 3 shafts; 3 in each subsystem The root shafts are respectively abstracted into the front shaft, the main drive shaft, and the rear shaft, and are controlled by two PID controllers. Among them, the two winder shafts are only used as the rear shafts of the last unit in the working state.

On the other hand, in the stretching process, whether the crystallization and orientation are uniform and whether the degree is appropriate depends on the uniformity and stability of the material temperature. In order to ensure the control accuracy of the temperature field, the system design adopts the PID temperature control method. The thickness control technology of the system uses two thickness gauges to detect the thickness of thick sheet and film products respectively, and feeds the measured data back to the control system to calculate the longitudinal and transverse thickness deviation, and control the extruder screw according to the longitudinal thickness deviation of the film Speed correction amount, and at the same time control the temperature of the bolts at the corresponding parts of the extruder head according to the film transverse thickness deviation to realize the automatic control of thick sheet and film thickness.

Based on this, another aspect of the present invention also provides a film thickness control method. Specifically, the film thickness control method of the present invention adopts the following scheme including a lateral thickness deviation control model and a longitudinal thickness deviation control model:

Wherein, as shown in Figure 5, the longitudinal thickness deviation control model in the film thickness control method of the present invention comprises the following steps:

First, through the second thickness gauge configured in the casting system, the thickness of the formed slab at the exit of the chill roll is detected;

Then compare the film thickness measured by the second thickness gauge with the set value to obtain an error signal;

Then, according to the error signal, the linear speed of the chilled roll is changed through the chilled roll PID regulator to control the longitudinal thickness deviation of the film.

At the same time, as shown in Figure 6, the film thickness control method of the present invention further includes a lateral thickness deviation control model, which specifically includes the following steps:

First, through the first thickness gauge configured in the traction system, the thickness of the film after biaxial stretching is detected;

Then compare the thickness detected by the first thickness gauge with the thickness setting value to obtain the thickness difference;

Then the cast sheet PID controller calculates the correction value according to the thickness difference, and adjusts it through the bolt temperature control PID controller to change the temperature of the heat-sensitive die head bolt, and use the temperature change of the heat-sensitive bolt to control the extruder film head , causing the bolts to thermally expand and contract, causing the opening of the membrane head lip to change, and adjusting the thickness of the sheet; among them,

The correction parameters of the lip opening of the membrane head are obtained through the following transfer function:

Among them, Ky is the target variation of the opening degree of the membrane head lip, K _x is the bolt adjustment amount, _ma is the displacement ratio parameter, G _p is the magnification factor of the membrane head lip section shape, T ₀ is the thickness setting value, T _m is the film thickness value detected by the first thickness gauge.

In the above process, the temperature control of the machine head bolt adopts the direct feedback method, and the control system performs real-time calculation according to a certain period, and adjusts the voltage and energization rate of the machine head bolt intermittently, so as to adjust the bolt temperature—change the opening degree of the membrane head lip— The process of adjusting the amount of extrusion.

Preferably, 32 sets of heat-sensitive die head bolts are configured in the above-mentioned BOPP biaxial stretching system to adjust the extrusion volume of BOPP raw polymer melt in different regions, and each heat-sensitive die head bolt is controlled by an independent control loop.

The implementation effects of the above-mentioned film thickness control method of the present invention are shown in FIGS. 7-8 . Among them: Figure 7(a) shows the lateral thickness deviation value of the BOPP film at a certain time point detected by the thickness gauge when the existing control method is adopted. It can be seen from this that the lateral thickness deviation of the film fluctuates relatively large, and there are many The lateral thickness deviation value exceeds the upper and lower thresholds. Fig. 7 (b) adopts the control method of the present invention, the lateral thickness deviation value of the BOPP film at a certain time point detected by the thickness gauge, as can be seen from it, the lateral thickness deviation fluctuation of the film is much smaller than the existing control method, The thickness deviation only exceeds the upper and lower limit thresholds at the edge of the film, and the average thickness is closer to the set value of 3.22 μm. The control method of adjusting the lateral thickness deviation of the film by controlling the temperature of the head bolts has achieved a significant control effect.

Figure 8(a) shows the longitudinal thickness deviation value of the BOPP film detected by the thickness gauge when using the existing control method, where each column represents the maximum value (highest red point) and minimum value ( lowest red point) and average (black point). It can be seen that the longitudinal thickness deviation of the film fluctuates relatively large, and the longitudinal thickness deviation values in many places exceed the upper and lower limit thresholds. Fig. 8 (b) adopts the control method of the present invention, the vertical thickness deviation value of the BOPP film that the thickness gauge detects, can find out from it, the maximum value, the minimum value and the average value fluctuation of the longitudinal thickness of the film are smaller than before transformation a lot of. The method of adjusting the longitudinal thickness deviation of the film by controlling the screw speed of the extruder has a significant control effect.

The descriptions of the above embodiments are only used to help understand the method and core idea of the present invention. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, some improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims (7)

1. A control method for a BOPP bidirectional stretching system, characterized in that: for any three-motor subsystem in the stretching section of the system: comprising a front shaft, a first tension roller, a main drive shaft, a second tension roller, a rear The shaft is controlled by two distributed controllers, wherein the front shaft motor and the main drive shaft motor are controlled by the first controller, and the main drive shaft motor and the rear shaft motor are controlled by the second controller. At the same time, The first controller and the second controller share a part of output by superimposing control factors a and b to control the main drive shaft motor. 2. the control method of BOPP biaxial stretching system as claimed in claim 1, is characterized in that: The first controller takes the film tension set value T _{u_ref} at the front shaft and the film speed set value V _ref at the main drive shaft as inputs, and according to the real-time tension T _u of the film at the first tension roller and the film speed at the main drive shaft For the real-time speed V of the film, the tension control deviation value of the front shaft motor x _u =T _{u_ref} -T _u and the speed control deviation value x _v =V _ref -V are obtained, and then the front shaft torque control signal u _u is obtained according to the following formula And the torque control signal u _v1 of the main drive shaft motor: <mrow><msub><mi>u</mi><mi>u</mi></msub><mo>=</mo><mfrac><mn>1</mn><msub><mi>P</mi><mi>u</mi></msub></mfrac><mrow><mo>(</mo><msub><mi>x</mi><mi>u</mi></msub><mo>+</mo><mfrac><mn>1</mn><msub><mi>T</mi><mrow><mi>i</mi><mi>u</mi></mrow></msub></mfrac><mo>&amp;Integral;</mo><msub><mi>x</mi><mi>u</mi></msub><mi>d</mi><mi>t</mi><mo>)</mo></mrow><mo>&amp;CenterDot;</mo><mo>&amp;lsqb;</mo><mfrac><mrow><mn>30</mn><msub><mi>i</mi><mi>u</mi></msub><mi>V</mi></mrow><mrow><msub><mi>&amp;pi;n</mi><mi>u</mi></msub></mrow></mfrac><mo>&amp;rsqb;</mo><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow></mrow> <mrow><msub><mi>u</mi><mrow><mi>v</mi><mn>1</mn></mrow></msub><mo>=</mo><mfrac><mn>1</mn><msub><mi>P</mi><mrow><mi>v</mi><mn>1</mn></mrow></msub></mfrac><mrow><mo>(</mo><msub><mi>x</mi><mi>v</mi></msub><mo>+</mo><mfrac><mn>1</mn><msub><mi>T</mi><mrow><mi>i</mi><mi>v</mi><mn>1</mn></mrow></msub></mfrac><mo>&amp;Integral;</mo><msub><mi>x</mi><mi>v</mi></msub><mi>d</mi><mi>t</mi><mo>)</mo></mrow><mo>&amp;CenterDot;</mo><mo>&amp;lsqb;</mo><mfrac><mrow><mn>30</mn><msub><mi>i</mi><mi>v</mi></msub><mi>V</mi></mrow><mrow><msub><mi>&amp;pi;n</mi><mi>v</mi></msub></mrow></mfrac><mo>&amp;rsqb;</mo><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>2</mn><mo>)</mo></mrow></mrow> Among them, P _u , P _v1 are proportional gain coefficients, T _iu , T _iv1 are integral time constants, i _u , _iv are mechanical transmission ratios of front shaft motor and main drive shaft motor, nu _u , n _v are front shaft motors Motor speed of shaft motor and main drive shaft motor; The second controller takes the film speed set value V _ref at the main drive shaft and the film tension set value T _{w_ref} at the rear shaft as inputs, and according to the real-time speed V of the film at the main drive shaft and the film tension at the second tension roller For the real-time tension T _w of the film, the tension control deviation value of the rear shaft motor x _w =T _{w_ref} -T _w and the speed control deviation value x _v =V _ref -V are obtained, and then the torque control signal of the main drive shaft motor is obtained according to the following formula u _v2 and rear axle motor torque control signal u _w : <mrow><msub><mi>u</mi><mi>w</mi></msub><mo>=</mo><mfrac><mn>1</mn><msub><mi>P</mi><mi>w</mi></msub></mfrac><mrow><mo>(</mo><msub><mi>x</mi><mi>w</mi></msub><mo>+</mo><mfrac><mn>1</mn><msub><mi>T</mi><mrow><mi>i</mi><mi>w</mi></mrow></msub></mfrac><mo>&amp;Integral;</mo><msub><mi>x</mi><mi>w</mi></msub><mi>d</mi><mi>t</mi><mo>)</mo></mrow><mo>&amp;CenterDot;</mo><mo>&amp;lsqb;</mo><mfrac><mrow><mn>30</mn><msub><mi>i</mi><mi>w</mi></msub><mi>V</mi></mrow><mrow><msub><mi>&amp;pi;n</mi><mi>w</mi></msub></mrow></mfrac><mo>&amp;rsqb;</mo><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>3</mn><mo>)</mo></mrow></mrow> <mrow><msub><mi>u</mi><mrow><mi>v</mi><mn>2</mn></mrow></msub><mo>=</mo><mfrac><mn>1</mn><msub><mi>P</mi><mrow><mi>v</mi><mn>2</mn></mrow></msub></mfrac><mrow><mo>(</mo><msub><mi>x</mi><mi>v</mi></msub><mo>+</mo><mfrac><mn>1</mn><msub><mi>T</mi><mrow><mi>i</mi><mi>v</mi><mn>2</mn></mrow></msub></mfrac><mo>&amp;Integral;</mo><msub><mi>x</mi><mi>v</mi></msub><mi>d</mi><mi>t</mi><mo>)</mo></mrow><mo>&amp;CenterDot;</mo><mo>&amp;lsqb;</mo><mfrac><mrow><mn>30</mn><msub><mi>i</mi><mi>v</mi></msub><mi>V</mi></mrow><mrow><msub><mi>&amp;pi;n</mi><mi>v</mi></msub></mrow></mfrac><mo>&amp;rsqb;</mo><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>4</mn><mo>)</mo></mrow></mrow> Among them, P _w , P _v2 are proportional gain coefficients, T _iw , T _iv2 are integral time constants, i _w , _iv are mechanical transmission ratios of rear shaft motor and main drive shaft motor, n _w , n _v are rear shaft motors Motor speed of shaft motor and main drive shaft motor; Afterwards, according to the overlapping control factors a and b, the main drive shaft motor control signal u _v =a·u _v1 +b·u _v2 is obtained. 3. The control method of BOPP biaxial stretching system as claimed in claim 2, is characterized in that: the real-time tension of film at the first tension roller place T ₁ is the tension of the film between the front shaft and the first tension roller, and T ₂ is the tension _Tu of the film between the first tension roller and the main drive shaft; the real-time tension of the film at the second tension roller place T ₃ is the tension of the film between the driving shaft and the second tension roller, T ₄ is the tension of the film between the second tension roller and the rear shaft; T ₁ , T ₂ , T ₃ , T ₄ and the main driving shaft The real-time velocity V of the film is obtained by the following formula: <mrow><mfrac><mrow><mi>d</mi><mrow><mo>(</mo><msub><mi>J</mi><mi>k</mi></msub><msub><mi>&amp;Omega;</mi><mi>k</mi></msub><mo>)</mo></mrow></mrow><mrow><mi>d</mi><mi>t</mi></mrow></mfrac><mo>=</mo><msub><mi>R</mi><mi>k</mi></msub><mrow><mo>(</mo><msub><mi>T</mi><mrow><mi>k</mi><mo>+</mo><mn>1</mn></mrow></msub><mo>-</mo><msub><mi>T</mi><mi>k</mi></msub><mo>)</mo></mrow><mo>+</mo><msub><mi>K</mi><mi>k</mi></msub><msub><mi>U</mi><mi>k</mi></msub><mo>+</mo><msub><mi>C</mi><mi>f</mi></msub><mo>,</mo><mrow><mo>(</mo><mi>k</mi><mo>=</mo><mn>1</mn><mo>,</mo><mn>2</mn><mo>,</mo><mn>3</mn><mo>,</mo><mn>4</mn><mo>)</mo></mrow><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>5</mn><mo>)</mo></mrow></mrow> <mrow><msub><mi>L</mi><mi>k</mi></msub><mfrac><mrow><msub><mi>dT</mi><mrow><mi>k</mi><mo>+</mo><mn>1</mn></mrow></msub></mrow><mrow><mi>d</mi><mi>t</mi></mrow></mfrac><mo>=</mo><mrow><mo>(</mo><mi>E</mi><mi>S</mi><mo>+</mo><msub><mi>T</mi><mn>0</mn></msub><mo>)</mo></mrow><mrow><mo>(</mo><msub><mi>V</mi><mrow><mi>k</mi><mo>+</mo><mn>1</mn></mrow></msub><mo>-</mo><msub><mi>V</mi><mi>k</mi></msub><mo>)</mo></mrow><mo>+</mo><msub><mi>V</mi><mn>0</mn></msub><mrow><mo>(</mo><msub><mi>T</mi><mi>k</mi></msub><mo>-</mo><msub><mi>T</mi><mrow><mi>k</mi><mo>+</mo><mn>1</mn></mrow></msub><mo>)</mo></mrow><mo>,</mo><mrow><mo>(</mo><mi>k</mi><mo>=</mo><mn>1</mn><mo>,</mo><mn>2</mn><mo>,</mo><mn>3</mn><mo>,</mo><mn>4</mn><mo>)</mo></mrow><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>6</mn><mo>)</mo></mrow></mrow> Among them, Ω _k = V _k / R _k is the rotational speed of the kth roller, K _k is the motor torque constant, U _k is the motor torque, J _k is the moment of inertia, R _k is the roll diameter, C _f is the friction torque , V ₀ is the rated film speed of the film at the exit of the front shaft, T _k and L _k are the tension and film length between the k-1 roller and the k roller, V ₀ is the ideal film speed, T ₀ is the ideal film speed Tension, E is the Young's modulus of elasticity of the film material, S is the cross-sectional area of the film; the real-time speed of the film at the main drive shaft V=V ₃ . 4. The control method of the BOPP biaxial stretching system according to any one of claims 1-3, characterized in that: the five parts of the BOPP biaxial stretching system are casting, longitudinal stretching, horizontal stretching, traction and winding Including M1-M12, a total of 12 shaft drive motors, among which, motor M1 drives the cold roll, motors M2, M3, M4 drive the three stretching rolls in the longitudinal stretching area, motor M5 drives the stretching rolls in the transverse stretching area, M6, M7, M8, M9 and M10 drive 5 sets of traction guide rollers, and motors M11 and M12 drive two rewinding shafts that are spare for each other; The above 12 shaft drive motors and their corresponding 12 shafts are divided into 5 subsystems, each subsystem includes 3 motors and corresponding 3 shafts; the 3 shafts in each subsystem are respectively abstracted as the front shaft, main drive shaft and rear shaft are controlled by 2 PID controllers. 5. The control method of BOPP biaxial stretching system as claimed in claim 4, is characterized in that: also comprise transverse thickness deviation control model and longitudinal thickness deviation control model, wherein transverse thickness deviation control model comprises the steps: S1. Detect the thickness of the biaxially stretched film through the first thickness gauge configured in the traction part; S2. Comparing the thickness detected by the first thickness gauge with the thickness setting value to obtain a thickness difference; S3. The cast sheet PID controller calculates the correction value according to the thickness difference, and adjusts it through the bolt temperature control PID controller to change the temperature of the heat-sensitive die head bolts so that the opening degree of the lip of the membrane head changes, and the adjustment sheet The thickness of the material; among them, The correction parameters of the lip opening of the membrane head are obtained through the following transfer function: <mrow><mi>W</mi><mo>=</mo><mfrac><msub><mi>K</mi><mi>y</mi></msub><msub><mi>K</mi><mi>x</mi></msub></mfrac><mo>=</mo><mfrac><mrow><msub><mi>m</mi><mi>a</mi></msub><mo>&amp;CenterDot;</mo><msub><mi>G</mi><mi>p</mi></msub><mrow><mo>(</mo><msub><mi>T</mi><mn>0</mn></msub><mo>-</mo><msub><mi>T</mi><mi>m</mi></msub><mo>)</mo></mrow></mrow><msub><mi>K</mi><mi>x</mi></msub></mfrac></mrow> Among them, W is the correction parameter of the lip opening of the membrane head, K _y is the target change of the lip opening of the membrane head, K _x is the adjustment amount of the bolt, _ma is the displacement ratio parameter, and G _p is the cross-sectional shape of the lip of the membrane head Amplification factor, T ₀ is the thickness setting value, T _m is the film thickness value detected by the first thickness gauge. 6. The control method of the BOPP biaxial stretching system as claimed in claim 5, characterized in that: 32 groups of heat-sensitive die head bolts are configured in the BOPP biaxial stretching system, and the extrusion of the BOPP raw material polymer melt is zonally adjusted The amount, and each heat-sensitive die head bolt is controlled by an independent control loop. 7. The control method of the BOPP biaxial stretching system as claimed in claim 5 or 6, is characterized in that, described longitudinal thickness deviation control comprises the steps: S1. Detect the thickness of the formed slab at the outlet of the chill roll through the second thickness gauge configured in the casting part; S2. Comparing the film thickness measured by the second thickness gauge with the set value to obtain an error signal; S3. According to the error signal, change the linear speed of the chill roll through the chill roll PID regulator, so as to control the longitudinal thickness deviation of the film.