Constant-temperature hot pressing method and system for preparing PMMA light guide plate

Abstract

The invention provides a constant-temperature hot pressing method and system for preparing a PMMA light guide plate, and belongs to the technical field of light guide plate preparation. The method comprises the steps that S1, a mold is prepared; s2, adopting a PMMA plate as a raw material of the light guide plate; s3, preheating the raw material of the light guide plate; s4, the upper mold plate and the lower mold plate are heated to the corresponding preset temperatures; s5, the PLC adopts fuzzy PID to control the heating temperatures of the upper template and the lower template to be stabilized at the corresponding preset temperatures, and the PLC adopts fuzzy PID to control the hot pressing forming machine to perform hot pressing on the light guide plate raw material according to a preset pressure curve; s6, cooling treatment; and S7, demolding and post-processing the cooled light guide plate. By adopting the fuzzy PID control, the negative effect of a time delay link on the system control performance is avoided, so that the heating temperature and pressure are more accurately controlled, and the quality of the prepared PMMA light guide plate is effectively ensured.

Description

Technical Field

[0001] The invention relates to the technical field of light guide plate preparation, and in particular to a constant temperature hot pressing method and system for preparing a PMMA light guide plate. Background Art

[0002] Light guide plate is a key material used in LCD backlight module. Its main function is to evenly distribute light source to the liquid crystal surface, thereby improving the brightness and color uniformity of the entire LCD display device. Light guide plate is currently widely used in display devices such as laptops, flat-screen TVs, mobile phones, monitors and car displays. Light guide plate is usually made of plastic material, so some problems are prone to occur during processing, such as: plastic material itself has thermal stress and is easy to deform; mold is prone to internal stress during injection molding, causing deformation and loosening of light guide plate. In order to solve these problems, manufacturers usually use hot pressing process to process light guide plate. Specifically, hot pressing refers to placing the light guide plate in a high-temperature press, and then applying high pressure and high temperature to gradually release the residual stress in the light guide plate, thereby ensuring the flatness and stability of the light guide plate. Hot pressing can also change the composition structure of the surface of the light guide plate, improve its transparency and UV resistance, anti-loss and other properties, thereby improving the display effect and durability. Since hot pressing pressure, hot pressing temperature and hot pressing time are the three elements of hot pressing forming process, accurate control of hot pressing pressure, hot pressing time and hot pressing temperature is a necessary condition to ensure the quality of hot pressing forming. According to the prior art "Process Analysis of Isothermal Equivalent Alternative Hot Pressing Method for Forming Ultra-thin Light Guide Plate", the upper mold temperature is 100°C, the lower mold temperature is 95°C, and the pressure curve is as follows: Figure 2 The quality of the light guide plate obtained by processing as shown is the best. However, most of the existing temperature and pressure control systems are time-delay systems. Time lag can easily lead to reduced feedback performance and system oscillation of the system. The control of the time-delay system using ordinary PID control or improved PID control cannot fundamentally eliminate the adverse effects of the time-delay link on the system. Because the closed-loop characteristic equation of the system contains a time-delay term, it will inevitably cause the stability of the system to decrease. This will cause the ultra-thin light guide plate formed by this process to be prone to defects such as warping, bubbles, and wrinkles, affecting the molding quality.

[0003] The above problems need to be solved. Summary of the invention

[0004] The present invention aims to overcome at least one of the above-mentioned disadvantages of the prior art. On the one hand, a constant temperature hot pressing method for preparing a PMMA light guide plate is provided, and the method comprises: S1: preparing a mold, including an upper template and a lower template, wherein the upper template is a smooth plane, and the lower template has a microstructure corresponding to the microstructure of the bottom surface of the finished light guide plate; S2: using a PMMA plate as the raw material of the light guide plate, and cutting it into a specific size and shape; S3: using an oven or a hot plate to preheat the raw material of the light guide plate, so that the temperature of the raw material of the light guide plate is heated to a temperature close to that of the mold; S4: electrically connecting a PLC controller to a hot pressing molding machine so that it presses the upper template and the lower template is heated to a preset temperature corresponding thereto; S5: placing the raw material of the light guide plate in the mold, applying a preset temperature and pressure through a hot pressing molding machine, so that the raw material of the light guide plate contacts the surface of the mold and deforms, including: the PLC controller stabilizes the heating temperatures of the upper template and the lower template at the corresponding preset temperatures respectively through fuzzy PID control based on the received temperatures of the upper template and the lower template, the PLC controller controls the hot pressing molding machine to hot press the raw material of the light guide plate with a preset pressure curve through fuzzy PID control, and when it is detected that the mold is closed, the PLC controller controls the hot pressing molding machine to hold the pressure for a preset time, the fuzzy PID control includes a preset fuzzy control rule and an improved PID control rule, and the improved PID control rule includes:

[0005] u(k)=Δu(k)+u(k-1);

[0006] Δu(k)=K p ×ep(k)+K i ×ei(k)+K d ×ed(k);

[0007] ep(k)=e(k)-e(k-1);

[0008] e(k)=r(k)-y m (k);

[0009] y m (k)=-den[2]×y(k-1)+num[2]×u(k-1);

[0010] ei(k) = e(k);

[0011] ed(k)=e(k)-2e(k-1)+e(k-2);

[0012] In the formula, u(k) is the output control quantity of the PID controller, Δu(k) is the control quantity increment, k is the sampling number, K p is the proportional adjustment coefficient, K i is the integral adjustment coefficient, K dis the differential adjustment coefficient, den is the denominator coefficient, the value is [1.00 -0.98], num is the numerator coefficient, the value is [0.00 12.68], e(k) is the error, ep(k) is the proportional term correction, ei(k) is the integral term correction, and ed(k) is the differential term correction; S6: Cooling the light guide plate after heating and hot pressing to solidify and stabilize its structure; S7: Demolding and post-processing the cooled light guide plate.

[0013] Furthermore, after step S5, the method further includes: detecting the micro-molding height h of the PMMA light guide plate online, sending the detected micro-molding height h to a PLC controller, and making the PLC controller compare the detected micro-molding height h with a preset theoretical micro-molding height h. ′ The preset temperature parameters and holding time parameters are automatically adjusted based on the comparison results.

[0014] Furthermore, the method includes: online detection of the micro-molding height h of the PMMA light guide plate by light scattering, wherein the micro-molding height h is judged by relying on different light receiving effects when light passes through PMMA light guide plates with different structures, including a light source and a light sensor.

[0015] Furthermore, the method comprises: when the detected micro-molding height h is equal to the preset theoretical micro-molding height h ′ When the difference between them meets the preset difference threshold, the corresponding temperature parameters and holding time parameters are recorded and saved.

[0016] Furthermore, the step S5 includes: a first temperature sensor and a second temperature sensor are respectively installed on the upper template and the lower template, the first temperature sensor and the second temperature sensor are respectively connected to the PLC controller, and the detected heating temperatures of the upper template and the lower template are sent to the PLC controller in real time. The PLC controller compares the temperature values ​​sent by the first temperature sensor and the second temperature sensor with the first preset temperature and the second preset temperature respectively, and based on the comparison result, the PID control is used to stabilize the heating temperature of the upper template at the first preset temperature, and the temperature of the lower template is stabilized at the second preset temperature.

[0017] Furthermore, the preset temperature in step S5 includes a first preset temperature and a second preset temperature, the first preset temperature corresponds to the heating temperature of the upper template, the second preset temperature corresponds to the heating temperature of the lower template, the first preset temperature is 100°C, and the second preset temperature is 95°C.

[0018] Furthermore, the pressure curve in step S5 is a pressure curve generated according to the properties and shape of the raw material of the light guide plate before hot pressing, and the hot pressing molding machine is pressurized by the pressure curve.

[0019] Furthermore, the holding time in step S5 is set to 20s, and the pressure range of the pressure curve is 0-100KN.

[0020] Furthermore, step S3 includes: a third temperature sensor is installed on the oven or hot plate, and the third temperature sensor is electrically connected to the PLC controller. The PLC controller compares the temperature value transmitted by the third temperature sensor with the third preset temperature, and then controls the heating temperature of the oven or hot plate to reach the third preset temperature.

[0021] In a second aspect, the present invention provides a constant temperature hot pressing system for preparing a PMMA light guide plate, the system comprising: a PLC controller, a preheating device, a hot pressing molding machine, a cooling device and a transmission device, the hot pressing molding machine comprising a mold system and a pressure driving system; the mold system comprises an upper template and a lower template, the upper template is a smooth plane, the lower template has a microstructure corresponding to the microstructure of the bottom surface of the finished light guide plate, the upper template is installed with a first electric heating plate, the lower template is installed with a second electric heating plate, which is used to heat the upper template and the lower template, the upper template is installed with a first temperature sensor, and the lower template is installed with a second temperature sensor; the PLC controller is electrically connected to the first temperature sensor, the second temperature sensor, the first electric heating plate and the second electric heating plate respectively, and is used to control the temperature of the first electric heating plate to be stable at a preset temperature through a PID based on the temperature value transmitted by the first temperature sensor, and to control the temperature of the first electric heating plate to be stable at a preset temperature through a PID based on the temperature value transmitted by the second temperature sensor ID controls the temperature of the second electric heating plate to be stable at a second preset temperature; the preheating device includes an oven or a hot plate, and the oven or the hot plate includes a third temperature sensor. The PLC controller is electrically connected to the third temperature sensor and the heating device of the oven or the hot plate, respectively, and is used to control the heating device to preheat the raw material of the light guide plate based on the temperature value transmitted by the third temperature sensor, so that the temperature of the raw material of the light guide plate is heated to a temperature close to that of the mold; the pressure drive system is electrically connected to the PLC controller, and the PLC controller controls the hot pressing molding machine to hot press the light guide plate raw material with a preset pressure curve. When it is detected that the mold is closed, the PLC controller controls the hot pressing molding machine to hold the pressure for a preset time; the PLC controller is electrically connected to the transmission device, and is used to control the transmission device to transmit the hot-pressed light guide plate raw material to the cooling device when the hot pressing molding machine holds the pressure for a preset time, and cool the light guide plate after heating and hot pressing to solidify and stabilize its structure.

[0022] On the other hand, the present invention provides a computer-readable storage medium, wherein one or more instructions are stored in the computer-readable storage medium, and the computer instructions are used to enable the computer to execute the above-mentioned constant temperature hot pressing method for preparing PMMA light guide plates.

[0023] On the other hand, the present invention provides an electronic device, comprising: a memory and a processor; the memory stores at least one program instruction; the processor implements the above-mentioned constant temperature hot pressing method for preparing a PMMA light guide plate by loading and executing the at least one program instruction.

[0024] The beneficial effects of the present invention are as follows: the present invention provides a constant temperature hot pressing method and system for preparing PMMA light guide plates. The PLC controller controls the heating temperatures of the upper template and the lower template based on the received temperatures of the upper template and the lower template through PID control, so that the heating temperatures of the upper template and the lower template are stabilized at the corresponding preset temperatures, respectively, so as to break through the ideological constraints of "high temperature hot pressing-low temperature demoulding" in the prior art, that is, a constant temperature mold is used instead of a variable temperature mold, so that the mold temperature of the entire imprinting process is maintained at a preset temperature, and the microstructure of the mold is copied to the surface of the substrate with high precision under appropriate pressure by utilizing the solid-state characteristics of the polymer, while completing the hot pressing molding process of the PMMA light guide plate. The hot pressing molding machine is controlled by fuzzy PID to hot press the light guide plate raw material with a preset pressure curve, and to heat it at a preset temperature. By improving the PID control rule, the time lag link in the original PID control rule is eliminated, avoiding the negative effect of the time lag link on the system control performance, making the control of the heating temperature and pressure more accurate, and effectively ensuring the quality of the prepared PMMA light guide plate. In addition, a targeted pressure curve is generated based on the material properties and shape of PMMA during the hot pressing process of the PMMA light guide plate, and pressure is applied during the hot pressing process based on the pressure curve to ensure the uniformity and stability of the pressure and avoid bubbles or deformation of the light guide plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0026] Figure 1 This is a flow chart of a constant temperature hot pressing method for preparing a PMMA light guide plate provided in Example 1 of the present invention.

[0027] Figure 2 It is a schematic diagram of the customized pressure curve provided in Example 1 of the present invention.

[0028] Figure 3a This is a time-temperature simulation curve generated by the fuzzy PID control provided in Example 1 of the present invention.

[0029] Figure 3bThis is a time-temperature simulation curve generated by the original PID control provided in Example 1 of the present invention.

[0030] Figure 4 It is a comparison chart of the sinusoidal response simulation results of PID and fuzzy PID control under a sinusoidal signal with a frequency of 1 Hz provided in Example 1 of the present invention.

[0031] Figure 5 It is a schematic diagram of the structure of the fuzzy PID controller provided in Example 1 of the present invention.

[0032] Figure 6a is the membership function of the error e provided in Example 1 of the present invention.

[0033] Figure 6b It is the membership function of the error change rate ec provided in Example 1 of the present invention.

[0034] Figure 6c is the proportional coefficient correction value ΔK provided in Example 1 of the present invention p The membership function of .

[0035] Figure 6d is the integral coefficient correction value ΔK provided in Example 1 of the present invention i The membership function of .

[0036] Figure 6e is the differential coefficient correction value ΔK provided in Example 1 of the present invention d The membership function of .

[0037] Figure 7 It is a working principle diagram of the pressure servo control system of the hot pressing molding machine provided in Example 1 of the present invention.

[0038] Figure 8a It is a microscope schematic diagram of the light guide plate microstructure manufactured based on the prior art provided in Example 1 of the present invention.

[0039] Figure 8b It is a microscope schematic diagram of the light guide plate microstructure prepared based on this scheme provided in Example 1 of the present invention.

[0040] Fig. 9 It is a structural schematic diagram of a constant temperature hot pressing system for preparing a PMMA light guide plate provided in Example 2 of the present invention.

[0041] Fig.10 This is a partial block diagram of an electronic device provided in Example 4 of the present invention. DETAILED DESCRIPTION

[0042] It should be mentioned before discussing the exemplary embodiments in more detail that some exemplary embodiments are described as processes or methods depicted as flow charts. Although the flow charts describe the operations as sequential processes, many of the operations therein can be implemented in parallel, concurrently or simultaneously. In addition, the order of the operations can be rearranged. The process can be terminated when its operation is completed, but can also have additional steps not included in the accompanying drawings. The process can correspond to a method, function, procedure, subroutine, subprogram, etc.

[0043] It should be understood that, although the terms "first", "second", etc. may be used herein to describe various units, these units should not be limited by these terms. These terms are used only to distinguish one unit from another unit. For example, without departing from the scope of the exemplary embodiments, the first unit may be referred to as the second unit, and similarly the second unit may be referred to as the first unit. The term "and / or" used herein includes any and all combinations of one or more of the listed associated items.

[0044] Example 1

[0045] refer to Figure 1 , shows a flow chart of a constant temperature hot pressing method for preparing a PMMA light guide plate.

[0046] As an example, the method includes: S1: preparing a mold, including an upper template and a lower template, wherein the upper template is a smooth plane, and the lower template has a microstructure corresponding to the microstructure of the bottom surface of the finished light guide plate; S2: using a PMMA plate as a raw material of the light guide plate, and cutting it into a specific size and shape; S3: using an oven or a hot plate to preheat the raw material of the light guide plate, so that the temperature of the raw material of the light guide plate is heated to a temperature close to that of the mold; S4: electrically connecting a PLC controller to a hot pressing molding machine, so that it heats the upper template and the lower template to a preset temperature corresponding thereto; S5: placing the raw material of the light guide plate in the mold, and applying a preheating agent through the hot pressing molding machine The temperature and pressure set are set to make the raw material of the light guide plate contact with the mold surface and deform, including: the PLC controller stabilizes the heating temperatures of the upper template and the lower template at the corresponding preset temperatures based on the received temperatures of the upper template and the lower template through fuzzy PID control, the PLC controller controls the hot pressing molding machine to hot press the light guide plate raw material with a preset pressure curve through fuzzy PID control, and when it is detected that the mold is closed, the PLC controller controls the hot pressing molding machine to hold the pressure for a preset time; S6: cooling the light guide plate after heating and hot pressing to solidify and stabilize its structure; S7: demolding and post-processing the cooled light guide plate.

[0047] Preferably, combined Figure 5As shown, the fuzzy PID control in step S5 includes a preset fuzzy control rule and an improved PID control rule, and the improved PID control rule includes:

[0048] u(k)=Δu(k)+u(k-1);

[0049] Δu(k)=K p ×ep(k)+K i ×ei(k)+K d ×ed(k);

[0050] ep(k)=e(k)-e(k-1);

[0051] e(k)=r(k)-y m (k);

[0052] y n (k)=-den[2]×y(k-1)+num[2]×u(k-1);

[0053] ei(k) = e(k);

[0054] ed(k)=e(k)-2e(k-1)+e(k-2);

[0055] In the formula, u(k) is the output control quantity of the PID controller, Δu(k) is the control quantity increment, k is the sampling number, K p is the proportional adjustment coefficient, K i is the integral adjustment coefficient, K d is the differential adjustment coefficient, den is the denominator coefficient, the value is [1.00 -0.98], num is the numerator coefficient, the value is [0.00 12.68], e(k) is the error, ep(k) is the proportional term correction, ei(k) is the integral term correction, and ed(k) is the differential term correction.

[0056] Preferably, combined Figure 6a-6e As shown, the input variables of the preset fuzzy rule are the error e and the error change rate ec, and the output variable is the correction value ΔK of the three parameters of PID p , ΔK i , ΔK d , the domains of the input and output variables are: e: [-6, 6]; ec: [-3, 3]; ΔK p :[-0.03,0.03];ΔK i :[-0.003,0.003];ΔK d:[-0.003,0.003], their fuzzy subsets are evenly divided into 7 fuzzy levels within the domain: {FD, FZ, FX, LG, ZX, ZZ, ZD}, namely negative large, negative medium, negative small, zero, positive small, positive medium, positive large. The knowledge base contains p , K i , K d Table of adjusted fuzzy control rules:

[0057] Table 1: Proportional coefficient correction ΔK p Fuzzy rule table

[0058]

[0059] Table 2: Proportional coefficient correction ΔK i Fuzzy rule table

[0060]

[0061] Table 3: Proportional coefficient correction ΔK d Fuzzy rule table

[0062]

[0063] Finally, the three correction parameters ΔK of the fuzzy PID controller are obtained: P , ΔK I , ΔK d The fuzzy value of ΔK P , ΔK I , ΔK d The fuzzy quantity is defuzzified by weighted average method, and finally the three correction parameters ΔK of the fuzzy adaptive PID controller are obtained. P , ΔK I , ΔK d The kth sampling time is set as:

[0064] K p =K p0 +ΔK p ;

[0065] K i =K i0 +ΔK i ;

[0066] K d =K d0 +ΔK d Among them, K p0 , K i0 , K d0 are the initial values ​​of PID parameters tuned by the ZN method, which are 0.325, 0.04, and 0.02 respectively.

[0067] The temperature and pressure of the hot pressing machine are controlled by the fuzzy PID controller mentioned above. Figure 3a-3b As shown in the figure, this design solves the adverse effect of time lag on the stability of the control system and greatly improves the accuracy of temperature control. Figure 4 As shown, in the process of controlling the pressure, the response speed and following characteristics under the fuzzy PID control strategy are better than those of the ordinary PID control strategy, and the fuzzy PID control can effectively reduce the time lag phenomenon; at the same time, PID has a certain amplitude attenuation, while the fuzzy PID has almost no amplitude attenuation. After the frequency of the sinusoidal signal increases, the following property and stability of the system under the fuzzy PID control are also excellent, almost completely fitting the target curve. Furthermore, by adopting the fuzzy PID control strategy, the heating temperature and pressure can be accurately controlled during the hot pressing process of preparing PMMA, so that the produced light guide plate can be more in line with the actual needs, avoiding the phenomenon that the ultra-thin light guide plate is prone to defects such as warping, bubbles, and wrinkles, which affect the molding quality. Preferably, after the step S5, it also includes: by online detecting the micro-molding height h of the PMMA light guide plate, sending the detected micro-molding height h to the PLC controller, so that the PLC controller compares the detected micro-molding height h with the preset theoretical micro-molding height h ′ The micro-molding height h of the PMMA light guide plate is detected online by light scattering, wherein the micro-molding height h is judged by the different light receiving effects when light passes through the PMMA light guide plate with different structures, including a light source and a light sensor. When the detected micro-molding height h is different from the preset theoretical micro-molding height h ′ When the difference between the measured micro-molding height h and the preset theoretical micro-molding height h meets the preset difference threshold, the corresponding temperature parameter and holding time parameter are recorded and saved. ′ When the difference between the two meets the preset difference threshold, it proves that the quality of the hot-pressed PMMA light guide plate meets the requirements. Therefore, the temperature parameters (including the first preset temperature, the second preset temperature and the third preset temperature) and the holding time parameters at this time are recorded and stored, so that the temperature parameters and the holding time parameters can be directly referenced in the subsequent production of the PMMA light guide plate. By adaptively adjusting the temperature parameters and the holding time parameters in the hot-pressing process based on online detection, the relevant parameter settings can be continuously optimized in the process of preparing the PMMA light guide plate, forming a closed-loop parameter optimization system, so that the quality of the PMMA light guide plate finally produced meets the actual requirements.

[0068] Preferably, step S5 comprises: the upper template and the lower template are respectively installed with a first temperature sensor and a second temperature sensor, the first temperature sensor and the second temperature sensor are respectively connected to a PLC controller, and the detected heating temperatures of the upper template and the lower template are sent to the PLC controller in real time, the PLC controller compares the temperature values ​​sent by the first temperature sensor and the second temperature sensor with the first preset temperature and the second preset temperature respectively, and controls the heating temperature of the upper template to be stabilized at the first preset temperature and the temperature of the lower template to be stabilized at the second preset temperature through PID based on the comparison result. That is, since the working requirements of the upper template and the lower template in the actual hot pressing process are different, that is, the hot pressing process corresponding to the template is a smooth plane, and the hot pressing process corresponding to the lower template is a plane with a microstructure, the corresponding heating temperatures are also different due to their different hot pressing purposes. Specifically, by heating the upper template temperature to 100°C and the lower template temperature to 95°C, the molding quality of the microstructure of the light guide plate can be improved while ensuring the compression molding of the smooth surface of the light guide plate. It should be noted that the heating temperature here is the optimal temperature parameter in the processing of the PMMA light guide plate obtained by researchers after a large number of experiments.

[0069] Preferably, in order to avoid temperature changes during the heating process of the upper and lower templates, the heating plates of the upper and lower templates can be heated at the beginning of hot pressing to make their temperatures reach the first preset temperature and the second preset temperature. This avoids the situation in which the temperature constantly changes during the actual hot pressing process, which prolongs the entire cycle of the light guide plate embossing and reduces the production efficiency of the product, and further avoids the stress changes inside the PMMA raw material caused by the constant temperature changes during the hot pressing process, which leads to quality defects such as bubbles in the PMMA light guide plate.

[0070] Preferably, the preset temperature in step S5 includes a first preset temperature and a second preset temperature, the first preset temperature corresponds to the heating temperature of the upper template, the second preset temperature corresponds to the heating temperature of the lower template, the first preset temperature is 100°C, and the second preset temperature is 95°C.

[0071] Preferably, the pressure curve in step S5 is a pressure curve generated according to the properties and shape of the raw material of the light guide plate before hot pressing, and the hot pressing molding machine is pressurized by the pressure curve. Figure 2 As shown, during the hot pressing process, the PLC controller controls the hot pressing molding machine to apply pressure to the mold using a pre-generated pressure curve, which can avoid the situation in the prior art where the constant pressure method is used, which leads to uneven pressure distribution of the raw materials during the hot pressing process, and further avoids bubbles or deformation of the light guide plate. More specifically, the working principle of the hot pressing molding machine pressure servo control system is as follows: Figure 6dAs shown, when the servo control system starts working, the permanent magnet synchronous servo motor drives the gear pump to rotate, and the direction of the cylinder piston movement is changed by changing the left and right positions of the electromagnetic reversing valve, so that the cylinder rises or falls, and the oil pressure and oil flow in the cylinder are controlled by adjusting the speed of the permanent magnet synchronous servo motor itself, thereby controlling the pressure applied to the template.

[0072] Preferably, a balance regulator may be added to the hot pressing machine. By adding the balance regulator, uniform distribution of force on the hot pressing machine can be achieved, thereby avoiding uneven force on the hot pressing machine.

[0073] Preferably, step S3: preheat the raw material of the light guide plate using an oven or a hot plate, so that the temperature of the raw material of the light guide plate is heated to a temperature close to that of the mold. By preheating the PMMA raw material, it is possible to avoid the impact of the hot pressing molding machine on the material caused by a large difference between the temperature of the raw material and the temperature of the mold during the hot pressing process. That is, by preheating the raw material to a temperature close to that of the mold before hot pressing, the impact of the hot press on the material can be effectively reduced, and the uneven force can be reduced.

[0074] Preferably, the holding time in step S5 is set to 20s, and the pressure range of the pressure curve is 0KN-100KN.

[0075] Preferably, step S3 includes: a third temperature sensor is installed on the oven or hot plate, the third temperature sensor is electrically connected to the PLC controller, and the PLC controller compares the temperature value transmitted by the third temperature sensor with the third preset temperature, thereby controlling the heating temperature of the oven or hot plate to reach the third preset temperature.

[0076] Preferably, the step S6: cooling the light guide plate after heating and hot pressing to solidify and stabilize its structure includes: the cooling process generally adopts natural cooling or water cooling, and the temperature rise speed and uniformity are controlled during the cooling process, which can effectively avoid stress and cracks inside the light guide plate.

[0077] Preferably, the step S7 of demolding and post-processing the cooled light guide plate includes: demolding the light guide plate is the process of removing the formed light guide plate from the mold, and at the same time, the demolded light guide plate also needs to be post-processed, including removing scraps, polishing, cleaning the surface, inspecting optical properties and other steps to ensure that the product meets the requirements.

[0078] Preferably, Figure 8a-8b As shown, it can be seen that the PMMA light guide plate prepared by the above method of the present application has good molding quality and clear microstructure.

[0079] The above embodiment uses a PLC controller to control the heating temperature of the upper template and the lower template through PID based on the received temperature of the upper template and the lower template, so that the heating temperature of the upper template and the lower template is stabilized at the corresponding preset temperature, thereby breaking through the ideological constraint of "high temperature hot pressing-low temperature demolding" in the prior art, that is, a constant temperature mold is used instead of a variable temperature mold, so that the mold temperature is kept at a preset temperature during the entire imprinting process, and the microstructure of the mold is copied to the surface of the substrate with high precision under appropriate pressure by utilizing the solid-state characteristics of the polymer, while completing the hot pressing molding process of the PMMA light guide plate. The hot pressing molding machine is controlled by the PLC controller to hot press the light guide plate raw material with a preset pressure curve, and when the mold is detected to be closed, the PLC controller controls the hot pressing molding machine to hold the pressure for a preset time. In the hot pressing molding process of the PMMA light guide plate, a targeted pressure curve is generated based on the material properties and shape of PMMA, and pressure is applied during the hot pressing process based on the pressure curve, ensuring the uniformity and stability of the pressure, and avoiding bubbles or deformation of the light guide plate.

[0080] Example 2

[0081] like Fig. 9 As shown, a schematic diagram of the structure of a constant temperature hot pressing system for preparing a PMMA light guide plate is shown.

[0082] As an example, the system includes: a PLC controller 1 , a preheating device 2 , a hot press molding machine 3 , a cooling device 4 and a transmission device 5 , wherein the hot press molding machine 3 includes a mold system 310 and a pressure driving system 320 .

[0083] The mold system 310 includes an upper template 3101 and a lower template 3102. The upper template 3101 is a smooth plane, and the lower template 3102 has a microstructure corresponding to the microstructure of the bottom surface of the finished light guide plate. A first electric heating plate 31011 is installed on the upper template 3101, and a second electric heating plate 31021 is installed on the lower template for heating the upper template 3101 and the lower template 3102. A first temperature sensor 31012 is installed on the upper template 3101, and a second temperature sensor 31022 is installed on the lower template.

[0084] The PLC controller 1 is electrically connected to the first temperature sensor 31012, the second temperature sensor 31022, the first electric heating plate 31011 and the second electric heating plate 31021 respectively, and is used to control the temperature of the first electric heating plate 31011 to be stable at a first preset temperature through a PID based on the temperature value received from the first temperature sensor 31012, and to control the temperature of the second electric heating plate 31021 to be stable at a second preset temperature through a PID based on the temperature value received from the second temperature sensor 31022.

[0085] The preheating device 2 includes a heating device 210, including an oven or a hot plate, and the oven or the hot plate includes a third temperature sensor 220. The PLC controller 1 is electrically connected to the third temperature sensor 220 and the heating device 210, respectively, and is used to control the heating device to preheat the raw material of the light guide plate based on the temperature value transmitted by the third temperature sensor 220, so that the temperature of the raw material of the light guide plate is heated to a temperature close to that of the mold.

[0086] The pressure driving system 320 is electrically connected to the PLC controller 1. The PLC controller 1 controls the hot pressing molding machine 3 to hot press the light guide plate raw material with a preset pressure curve. When it is detected that the mold is closed, the PLC controller 1 controls the hot pressing molding machine to hold the pressure for a preset time.

[0087] The PLC controller 1 is electrically connected to the transmission device 5, and is used to control the transmission device 5 to transmit the hot-pressed light guide plate raw material to the cooling device 4 when the holding time of the hot pressing molding machine 3 reaches a preset time, and cool the light guide plate after heating and hot pressing to solidify and stabilize its structure.

[0088] It is not difficult to find that this embodiment is a system embodiment corresponding to the first embodiment, and this embodiment can be implemented in conjunction with the first embodiment. The relevant technical details mentioned in the first embodiment are still valid in this embodiment, and in order to reduce repetition, they are not repeated here. Accordingly, the relevant technical details mentioned in this embodiment can also be applied in the first embodiment.

[0089] It is worth mentioning that all units involved in this embodiment are logical units. In practical applications, a logical unit can be a physical unit, a part of a physical unit, or a combination of multiple physical units. In addition, in order to highlight the innovative part of the present invention, this embodiment does not introduce units that are not closely related to solving the technical problem proposed by the present invention, but this does not mean that there are no other units in this embodiment.

[0090] Example 3

[0091] The embodiment of the present invention further provides a storage medium, on which a constant temperature hot pressing method for preparing a PMMA light guide plate is stored, and when the constant temperature hot pressing program for preparing a PMMA light guide plate is executed by a processor, the steps of the constant temperature hot pressing method for preparing a PMMA light guide plate as described above are implemented. Since the storage medium adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be repeated here one by one.

[0092] Example 4

[0093] See also Fig.10 An embodiment of the present invention further provides an electronic device, comprising: a memory and a processor; the memory stores at least one program instruction; the processor loads and executes the at least one program instruction to implement the constant temperature hot pressing method for preparing the PMMA light guide plate provided in Example 1.

[0094] The memory 702 and the processor 701 are connected in a bus manner, and the bus may include any number of interconnected buses and bridges, and the bus connects various circuits of one or more processors 701 and the memory 702 together. The bus can also connect various other circuits such as peripheral devices, voltage regulators, and power management circuits, which are well known in the art and are therefore not further described herein. The bus interface provides an interface between the bus and the transceiver. The transceiver can be one element or multiple elements, such as multiple receivers and transmitters, providing a unit for communicating with various other devices on a transmission medium. The data processed by the processor 701 is transmitted on a wireless medium via an antenna, and further, the antenna also receives data and transmits the data to the processor 701.

[0095] The processor 701 is responsible for managing the bus and general processing, and can also provide various functions, including timing, peripheral interfaces, voltage regulation, power management and other control functions. The memory 702 can be used to store data used by the processor 701 when performing operations.

[0096] The above is only an embodiment of the present invention. The common sense such as the known specific structure and characteristics in the scheme is not described in detail here. The ordinary technicians in the relevant field know all the common technical knowledge in the technical field of the invention before the application date or priority date, can obtain all the existing technologies in the field, and have the ability to apply the conventional experimental means before that date. The ordinary technicians in the relevant field can improve and implement this scheme in combination with their own abilities under the enlightenment given by this application. Some typical known structures or known methods should not become obstacles for ordinary technicians in the relevant field to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, which will not affect the effect of the implementation of the present invention and the practicality of the patent. The protection scope required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A constant temperature hot pressing method for preparing a PMMA light guide plate, characterized in that: The method comprises: S1: preparing a mold, including an upper mold and a lower mold, wherein the upper mold is a smooth plane, and the lower mold has a microstructure corresponding to the microstructure of the bottom surface of the finished light guide plate; S2: Use PMMA sheet as the raw material of the light guide plate and cut it into specific size and shape; S3: preheating the raw material of the light guide plate by using an oven or a hot plate, so that the temperature of the raw material of the light guide plate is heated to a temperature close to that of the mold; S4: The PLC controller is electrically connected to the hot pressing forming machine so that it heats the upper mold plate and the lower mold plate to corresponding preset temperatures; S5: placing the raw material of the light guide plate in the mold, applying preset temperature and pressure through the hot pressing molding machine, so that the raw material of the light guide plate contacts the surface of the mold and deforms, including: the PLC controller stabilizes the heating temperature of the upper template and the lower template at the corresponding preset temperature through fuzzy PID control based on the received temperature of the upper template and the lower template, the PLC controller controls the hot pressing molding machine through fuzzy PID to hot press the raw material of the light guide plate with a preset pressure curve, and when it is detected that the mold is closed, the PLC controller controls the hot pressing molding machine to hold the pressure for a preset time, and the fuzzy POD control includes preset fuzzy control rules and improved PID control rules, and the improved PID control rules include: u(k)=Δu(k)+u(k-1); Δu(k)=K p ×ep(k)+K i ×ei(k)+K d ×ed(k); ep(k)=e(k)-e(k-1); e(k)=r(k)-y m (k); and m (k)=-den[2]×y(k-1)+num[2]×u(k-1); ei(k) = e(k); ed(k)=e(k)-2e(k-1)+e(k-2); In the formula, u(k) is the output control quantity of the POD controller, Δu(k) is the control quantity increment, k is the sampling number, K p is the proportional adjustment coefficient, K i is the integral adjustment coefficient, K d is the differential adjustment coefficient, den is the denominator coefficient, the value is [1.00-0.98], num is the numerator coefficient, the value is [0.00 12.68], e(k) is the error, ep(k) is the proportional term correction, ei(k) is the integral term correction, and ed(k) is the differential term correction; S6: cooling the light guide plate after heating and hot pressing to solidify and stabilize its structure; S7: demolding and post-processing the cooled light guide plate.

2. The constant temperature hot pressing method for preparing a PMMA light guide plate according to claim 1, characterized in that: After step S5, the step further includes: detecting the micro-molding height h of the PMMA light guide plate online, sending the detected micro-molding height h to the PLC controller, and making the PLC controller calculate the micro-molding height h based on the detected micro-molding height h and the preset theoretical micro-molding height h. ′ The preset temperature parameters and holding time parameters are automatically adjusted based on the comparison results.

3. The constant temperature hot pressing method for preparing a PMMA light guide plate according to claim 2, characterized in that: The method comprises: online detection of the micro-molding height h of the PMMA light guide plate by light scattering, wherein the micro-molding height h is judged by relying on different light receiving effects when light passes through PMMA light guide plates with different structures, and comprises a light source and a light sensor.

4. The constant temperature hot pressing method for preparing a PMMA light guide plate according to claim 2, characterized in that: The method comprises: when the detected micro-molding height h is equal to the preset theoretical micro-molding height h ′ When the difference between them meets the preset difference threshold, the corresponding temperature parameters and holding time parameters are recorded and saved.

5. The constant temperature hot pressing method for preparing a PMMA light guide plate according to claim 1, characterized in that: The step S5 includes: a first temperature sensor and a second temperature sensor are respectively installed on the upper template and the lower template, the first temperature sensor and the second temperature sensor are respectively connected to the PLC controller, and the detected heating temperatures of the upper template and the lower template are sent to the PLC controller in real time. The PLC controller compares the temperature values ​​sent by the first temperature sensor and the second temperature sensor with the first preset temperature and the second preset temperature respectively, and controls the upper template heating temperature to be stabilized at the first preset temperature and the lower template temperature to be stabilized at the second preset temperature through PID based on the comparison result.

6. The constant temperature hot pressing method for preparing a PMMA light guide plate according to claim 1, characterized in that: The preset temperature in step S5 includes a first preset temperature and a second preset temperature, the first preset temperature corresponds to the heating temperature of the upper template, the second preset temperature corresponds to the heating temperature of the lower template, the first preset temperature is 100°C, and the second preset temperature is 95°C.

7. The constant temperature hot pressing method for preparing a PMMA light guide plate according to claim 1, characterized in that: The pressure curve in step S5 is a pressure curve generated according to the properties and shape of the raw material of the light guide plate before hot pressing, and the hot pressing molding machine is pressurized by the pressure curve.

8. The constant temperature hot pressing method for preparing a PMMA light guide plate according to claim 1, characterized in that: The holding time in step S5 is set to 20s, and the pressure range of the pressure curve is 0-100KN.

9. The constant temperature hot pressing method for preparing a PMMA light guide plate according to claim 1, characterized in that: The step S3 includes: a third temperature sensor is installed on the oven or hot plate, the third temperature sensor is electrically connected to the PLC controller, the PLC controller compares the temperature value transmitted by the third temperature sensor with the third preset temperature, and then controls the heating temperature of the oven or hot plate to reach the third preset temperature.

10. A constant temperature hot pressing system for preparing a PMMA light guide plate, characterized in that: The system comprises: a PLC controller, a preheating device, a hot pressing molding machine, a cooling device and a transmission device, wherein the hot pressing molding machine comprises a mold system and a pressure driving system; The mold system includes an upper template and a lower template, the upper template is a smooth plane, the lower template has a microstructure corresponding to the microstructure of the bottom surface of the finished light guide plate, the upper template is installed with a first electric heating plate, the lower template is installed with a second electric heating plate, used to heat the upper template and the lower template, the upper template is installed with a first temperature sensor, and the lower template is installed with a second temperature sensor; The PLC controller is electrically connected to the first temperature sensor, the second temperature sensor, the first electric heating plate and the second electric heating plate respectively, and is used to control the temperature of the first electric heating plate to be stable at a preset temperature through PID based on the temperature value transmitted by the first temperature sensor, and to control the temperature of the second electric heating plate to be stable at a second preset temperature through PID based on the temperature value transmitted by the second temperature sensor; The preheating device includes an oven or a hot plate, and the oven or the hot plate includes a third temperature sensor. The PLC controller is electrically connected to the third temperature sensor and the heating device of the oven or the hot plate, respectively, and is used to control the heating device to preheat the raw material of the light guide plate based on the temperature value transmitted by the third temperature sensor, so that the temperature of the raw material of the light guide plate is heated to a temperature close to that of the mold; The pressure driving system is electrically connected to the PLC controller, and the PLC controller controls the hot pressing molding machine to hot press the light guide plate raw material with a preset pressure curve. When it is detected that the mold is closed, the PLC controller controls the hot pressing molding machine to hold the pressure for a preset time; The PLC controller is electrically connected to the transmission device, and is used to control the transmission device to transmit the hot-pressed light guide plate raw material to the cooling device when the holding time of the hot pressing molding machine reaches a preset time, and to cool the light guide plate after heating and hot pressing to solidify and stabilize its structure.

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