PE protective film tensile property automatic detection device and use method thereof

Abstract

The invention relates to the technical field of protective film detection, and provides a PE protective film tensile property automatic detection device and a use method thereof.The device comprises a rack, a first clamping mechanism, a second clamping mechanism, a water spraying mechanism and an electric field generator fixedly installed on the water spraying mechanism; the first clamping mechanism and the second clamping mechanism are both used for clamping a to-be-tested protective film, the water spraying mechanism is used for spraying water flow to the surface of the to-be-tested protective film to form a water film, and the electric field generator is used for generating a direct-current electric field applied to the surface of the to-be-tested protective film, so that double electric layers are formed between the surface of the to-be-tested protective film and the water film; and leveling the surface of the to-be-detected protective film. The apparent contact angle of the to-be-detected protective film is reduced based on the electrowetting effect, the hydrophobicity of the to-be-detected protective film is weakened, the situation that a water film spontaneously shrinks into liquid drops due to the hydrophobicity can be avoided, and the detection accuracy of the tensile property of the PE protective film is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of protective film detection, in particular to a PE protective film tensile resistance automatic detection device and a use method thereof. BACKGROUND

[0002] PE protective film, full name Polyethylene, is the simplest high molecular organic compound. It is a special polyethylene (PE) plastic film as the base material, and is divided into high-density polyethylene protective film, medium-density polyethylene protective film and low-density polyethylene protective film according to the density. The hydrophobicity of plastic film is mainly determined by the surface chemical properties and microstructure. When the water contact angle (CA) is greater than 90°, the material is defined as hydrophobic. For example, polyethylene (PE), the electron distribution in the carbon-hydrogen main chain is uniform, and cannot form hydrogen bonds with water molecules, resulting in a contact angle usually greater than 90°.

[0003] The Chinese invention patent with the application number CN202411350654.7 discloses a PE protective film tensile resistance automatic detection device. Before testing, the uniform water flow sprayed by the water spray pipe forms a water film on the surface of the vertically released film body, the surface tension of the water film is used to repair the wrinkles on the surface of the film body, the surface flatness of the film body is improved, and the gravity of the water film itself is used to improve the verticality of the film body, and the accuracy of subsequent detection of tensile is improved.

[0004] However, the above-mentioned PE protective film tensile resistance automatic detection device has the following defects: the difference in surface energy of the PE protective film is not considered, the van der Waals force between water molecules and PE protective film surface molecules is smaller than the hydrogen bond force between water molecules, the water film spontaneously shrinks into droplets, cannot uniformly spread, the stress of the wrinkle area is uneven, and the PE protective film surface wrinkles cannot be effectively repaired by the water film tension. SUMMARY

[0005] Therefore, in order to solve the problem that the existing PE protective film tensile resistance automatic detection device cannot effectively repair the PE protective film surface wrinkles by water film tension, the present application provides a PE protective film tensile resistance automatic detection device and a use method thereof, and the specific technical solutions are as follows:

[0006] The application discloses an automatic tensile resistance detection device for a PE protective film, which comprises a rack, a first clamping mechanism, a second clamping mechanism, a water spraying mechanism and an electric field generator fixedly installed on the water spraying mechanism.

[0007] The automatic tensile resistance detection device for the PE protective film is characterized in that the electric field generator is installed on the water spraying mechanism, a direct-current electric field is applied to the surface of the protective film to be detected, a double electric layer is formed between the surface of the protective film to be detected and the water film, the apparent contact angle of the protective film to be detected is reduced based on the electro-wetting effect, the hydrophobicity is weakened, a small amount of ions in the water flow is directionally migrated, the water molecules are promoted to spread on the surface of the protective film to be detected, and the water film is prevented from spontaneously shrinking into droplets due to the hydrophobicity, so that the problem that the existing automatic tensile resistance detection device for the PE protective film cannot effectively repair the wrinkles on the surface of the PE protective film through the water film tension is solved, and the accuracy of the tensile resistance detection of the PE protective film is improved.

[0008] Preferably, the automatic tensile resistance detection device for the PE protective film further comprises a negative pressure generator and a suction mechanism installed on the rack, the suction mechanism is provided with a suction port, the negative pressure port of the negative pressure generator is in communication with the suction port, the suction mechanism is located on one side of the surface of the protective film to be detected, and the negative pressure generator and the suction mechanism are cooperatively operated to form the negative pressure acting on the surface of the protective film to be detected.

[0009] Preferably, the automatic tensile resistance detection device for the PE protective film further comprises a controller and a laser displacement sensor array installed on the rack, the laser displacement sensor array is used for collecting distance data of a plurality of sampling points on the surface of the protective film to be detected and feeding back to the controller, the controller is used for constructing a 3D topological map of the film surface according to the distance data and acquiring a real-time curvature of the film surface according to the 3D topological map of the film surface.

[0010] Preferably, the water spraying mechanism comprises a water inlet pipe, a water spraying pipe and a mesh plate, the water inlet pipe and the water spraying pipe are fixedly connected on the side away from the protective film to be detected and are in communication with each other, the water spraying pipe is provided with a water spraying port on the side facing the protective film to be detected, the mesh plate is embedded in the water spraying port, and the electric field generator is a ring electrode and is embedded in the water spraying port.

[0011] Preferably, the ring electrode comprises a conductive base and an insulating layer wrapped on the conductive base.

[0012] The application relates to a use method of an automatic detection device for the tensile property of a PE protective film, which is applied to the automatic detection device and comprises the following steps.

[0013] Unwinding is performed to move the lower end of the protective film to be detected to the lower side of the second clamping mechanism.

[0014] A water flow is sprayed to the surface of the protective film to be detected by a water spraying mechanism to form a water film.

[0015] A direct-current electric field applied to the surface of the protective film to be detected is generated by an electric field generator, so that a double electric layer is formed between the surface of the protective film to be detected and the water film.

[0016] After the flattening and dehydration treatment of the protective film to be detected, the tensile property detection is performed.

[0017] Preferably, the flattening and dehydration treatment of the protective film to be detected comprises the following steps.

[0018] When the water film covers the surface of the protective film to be detected, the water flow is stopped.

[0019] After the preset time is kept, the protective film to be detected is in a tension state.

[0020] The negative pressure generator is started, and the negative pressure generator and the adsorption mechanism are cooperatively operated to form negative pressure acting on the surface of the protective film to be detected, so that the surface of the protective film to be detected is dehydrated.

[0021] Preferably, the use method of the automatic detection device for the tensile property of the PE protective film further comprises the following steps.

[0022] Distance data of a plurality of sampling points on the surface of the protective film to be detected are collected.

[0023] A 3D topological graph of the film surface is constructed according to the distance data.

[0024] Real-time curvature of the film surface is obtained according to the 3D topological graph of the film surface.

[0025] Preferably, the use method of the automatic detection device for the tensile property of the PE protective film further comprises the following steps.

[0026] Real-time contact angles and target contact angles are obtained, and a contact angle error feedback term is obtained according to the real-time contact angles and the target contact angles.

[0027] Reference thickness and actual thickness of the PE protective film are obtained, and a film thickness correction term for representing the difficulty of electric field penetration to the film surface is obtained according to the reference thickness and the actual thickness.

[0028] A film thickness-curvature cross correction term for representing the surface tension gradient of the water film at the bending part is obtained according to the actual thickness and the real-time curvature of the film surface.

[0029] The output voltage of the electric field generator is obtained according to the contact angle error feedback term, the film thickness correction term, and the film thickness-curvature intersection correction term.

[0030] Preferably, the dehydration treatment of the surface of the protective film to be tested comprises:

[0031] The free water on the surface of the protective film to be tested is removed by the first gradient negative pressure value;

[0032] The bound water on the surface of the protective film to be tested is removed by the second gradient negative pressure value;

[0033] The micropore water on the surface of the protective film to be tested is removed by the third gradient negative pressure value;

[0034] The first gradient negative pressure value > the second gradient negative pressure value > the third gradient negative pressure value. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a schematic diagram of the overall structure of a PE protective film tensile resistance automatic detection device in an embodiment of the present application;

[0036] Figure 2 is a schematic diagram of the structural relationship between the support plate, the water spraying mechanism, and the adsorption mechanism in an embodiment of the present application;

[0037] Figure 3 is a schematic diagram of the structural relationship between the water spraying pipe, the mesh plate, and the electric field generator in an embodiment of the present application;

[0038] Figure 4 is a schematic diagram of the overall process of a PE protective film tensile resistance automatic detection device usage method in an embodiment of the present application;

[0039] Figure 5 is a schematic diagram of the process of flattening and dehydration treatment of the protective film to be tested in an embodiment of the present application;

[0040] Figure 6 is a schematic diagram of the process of gradient negative pressure dehydration in an embodiment of the present application;

[0041] Figure 7 is a schematic diagram of the overall process of a PE protective film tensile resistance automatic detection device usage method in another embodiment of the present application Figure 1 ;

[0042] Figure 8 is a schematic diagram of the overall process of a PE protective film tensile resistance automatic detection device usage method in another embodiment of the present application Figure 2 ;

[0043] Figure 9is a flow diagram of optimizing a pressure gradient curve based on a hybrid neural network in an embodiment of the present application;

[0044] Figure 10 is a simulation effect diagram of the pressure gradient curve of the PE protective film with different thicknesses in the dehydration process in an embodiment of the present application;

[0045] Figure 11 is a training loss curve diagram of the hybrid neural network in an embodiment of the present application.

[0046] Legend:

[0047] 1, rack; 2, first clamping mechanism; 3, second clamping mechanism; 4, water spraying mechanism; 5, electric field generator; 6, first moving mechanism; 7, second moving mechanism; 8, third moving mechanism; 9, adsorption mechanism; 10, air suction port; 11, support plate; 12, protective film winding mechanism; 13, protective film to be measured; 40, water spraying pipe; 41, mesh plate; 42, water spraying port. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical scheme and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with its embodiments.

[0049] Before explaining the embodiments of the present application, a brief introduction to the prior art is given. The PE protective film has low surface energy (typical contact angle ≈ 90°) and shows hydrophobicity. The Van der Waals force between water molecules and PE surface molecules is smaller than the hydrogen bond force between water molecules, resulting in spontaneous shrinkage of the water film into droplets and inability to spread uniformly. The water film wrinkle repair in the Chinese invention patent No. CN202411350654.7 “PE protective film tensile resistance automatic detection device” relies on gravity and capillary action, which does not take into account the difference in surface energy of the PE protective film, cannot overcome the high-energy barrier contact angle threshold of the PE protective film, and leads to spontaneous shrinkage of the water film into droplets and inability to spread uniformly. In addition, the PE protective film tensile resistance automatic detection device injects airflow generated by an external air blower into a blowing pipe, and then a pair of blowing pipes located on both sides of the film body are moved from top to bottom by a vertical displacement mechanism to blow and clean the water film on the surface of the film body. If the airflow is too strong, the surface tension gradient of the non-uniform water film is also prone to induce secondary wrinkles of the film body during strong airflow dehydration.

[0050] In order to solve the problem that the existing PE protective film tensile resistance automatic detection device cannot effectively repair the surface wrinkles of the PE protective film by water film tension,

[0051] For example, Figure 1 , Figure 2 andFigure 3 As shown, an embodiment of the present application provides a kind of PE protective film tensile property automatic detection device, it includes rack 1, first clamping mechanism 2, second clamping mechanism 3, water spraying mechanism 4 and electric field generator 5 fixedly installed on the water spraying mechanism 4.The first clamping mechanism 2 and second clamping mechanism 3 are all installed on the rack 1 and are used to clamp the protective film 13 to be measured.The first clamping mechanism 2 and second clamping mechanism 3 are the same structure, including two oppositely arranged clamping plates and the clamping drive mechanism for driving the relative movement of two clamping plates.Two clamping plates are driven by clamping drive mechanism to approach each other, and the end of the protective film 13 to be measured is clamped.

[0052] The PE protective film tensile property automatic detection device further includes first moving mechanism 6 for driving first clamping mechanism 2 to move along the length direction of protective film 13 to be measured, second moving mechanism 7 for driving second clamping mechanism 3 to move along the length direction of protective film 13 to be measured, and protective film winding mechanism 12 for winding PE protective film, which are all installed on the rack 1.When the protective film 13 to be measured is placed vertically, the length direction refers to the vertical direction, and when the protective film 13 to be measured is placed horizontally, the length direction refers to the horizontal direction.The protective film 13 to be measured is preferably arranged in the vertical direction.Because the first clamping mechanism 2, second clamping mechanism 3, first moving mechanism 6, second moving mechanism 7 and protective film winding mechanism 12 all belong to the conventional technical means in the art, they will not be described here.

[0053] The water spraying mechanism 4 is installed on the rack 1 and is used to spray water flow towards the surface of the protective film 13 to be measured to form a water film.The water spraying mechanism 4 is located on one side of the protective film 13 to be measured, and the water flow sprayed by the water spraying mechanism 4 is perpendicular to the surface of the protective film 13 to be measured.The electric field generator 5 is used to generate a direct current electric field applied to the surface of the protective film 13 to be measured, so that a double electric layer is formed between the surface of the protective film 13 to be measured and the water film, to perform flattening treatment on the surface of the protective film 13 to be measured.

[0054] For PE protective film, its surface energy is low, and the typical contact angle is about 90°, showing hydrophobicity 5.The van der Waals force between water molecules and PE surface molecules is smaller than the hydrogen bond force between water molecules, resulting in spontaneous contraction of the water film into droplets, which cannot spread uniformly.That is to say, the hydrophobicity of the surface of the PE protective film causes the local contraction of the water film, forming microdroplets instead of a continuous film, and the problem of uneven stress in the wrinkle area is prone to occur.The relationship between dielectric layer and contact angle follows Young-Lippmann equation (i.e., Young's equation) cos θ = cos θ0 + (ε0ε r V 2 ) / (2dγ).Wherein, θ is the contact angle after applying voltage, θ0 is the initial contact angle (about 90°), ε0 is the vacuum permittivity, ε rwherein k is the water dielectric constant (about 78.36 at 25℃), d is the double layer thickness (in nm), g is the water-air interfacial tension, and V is the applied voltage. Thus, the electric field force can reduce the apparent contact angle of the PE protective film and promote the spreading of the water film. It should be noted that the applied voltage parameter should be lower than the water breakdown threshold to avoid water molecule ionization or damage to the PE protective film. Based on the electrowetting effect, a direct current voltage is applied to the electric field generator 5 to form a direct current electric field. The water flow (as a dielectric) sprayed from the water spraying mechanism 4 contacts the surface of the protective film 13 to be tested, which induces the aggregation of electric charges at the PE protective film-water film interface to form a double layer. The electric field force acts through the double layer to reduce the apparent contact angle of the PE protective film and weaken the hydrophobicity of the PE protective film, making the water film more easily spread.

[0055] As a preferred technical solution, the water spraying mechanism 4 includes a water inlet pipe, a water spraying pipe 40, and a mesh plate 41. The water inlet pipe is fixedly connected to the water spraying pipe 40 away from the protective film 13 to be tested and is in communication with the water spraying pipe 40. The water spraying pipe 40 is provided with a water spraying port 42 on the side facing the protective film 13 to be tested. The mesh plate 41 is embedded in the water spraying port 42 and the four peripheral edges of the mesh plate 41 completely fit the side wall of the water spraying port 42. The electric field generator 5 is a ring electrode embedded in the water spraying port 42 and completely fitted with the side wall of the water spraying port 42 on the outside of the mesh plate 41. When the water flow passes through the ring electrode, it is pre-polarized by the direct current electric field, the directional arrangement of water molecules is enhanced, and the water flow can form interaction with the PE protective film surface more quickly after reaching the PE protective film surface, reducing the droplet shrinkage caused by hydrophobicity.

[0056] The water spraying pipe 40 is horizontally arranged, specifically in a transverse circular tube structure, and the mesh plate 41 is nested in the water spraying port 42. The outer side of the water spraying pipe 40 is in communication with the external water supply pump through the water inlet pipe, and the whole is controlled by the controller. The ring electrode is embedded in the four peripheral inner walls of the water spraying port 42. The water flow sprayed by the water spraying mechanism 4 has a conductivity of 5-50 μS / cm. In this way, the electric field generated by the ring electrode can better make a small amount of ions in the water flow migrate directionally to the PE protective film interface to form an ion diffusion layer, promote the spreading of water molecules on the PE protective film, and avoid droplet shrinkage caused by hydrophobicity.

[0057] Exemplarily, the ring-shaped electrode comprises a conductive substrate and an insulating layer coated on the conductive substrate. The conductive substrate can be made of platinum, titanium or titanium alloy with corrosion resistance and stable conductivity, and a nano-silicon dioxide insulating layer or polytetrafluoroethylene (thickness ≈ 200 nm) is coated on the surface of the conductive substrate as an insulating layer to block the direct electron transfer path, avoid direct conduction between the electrode and the water flow causing electric field loss, and also avoid metal ion pollution of the water film. The direct current voltage applied to the ring-shaped electrode is between 0.5-1kV. The direct current voltage is synchronized with the water film standing time, and continues to act after the water film is formed until clamping, ensuring the stable existence of the electric double layer, strengthening the repair effect of the water film on the wrinkle, and after the standing (such as 2 or 3 minutes) is completed, the first clamping mechanism 2 and the second clamping mechanism 3 are used to clamp the water film containing the protective film 13 to be tested.

[0058] The PE protective film tensile property automatic detection device further comprises a third moving mechanism 8 installed on the rack 1 for driving the water spraying mechanism 4 to move up and down in the vertical direction. The third moving mechanism 8 includes but is not limited to a pneumatic cylinder and a linear module, and the water spraying mechanism 4 is installed on the third moving mechanism 8 through a support plate 11. The water spraying mechanism 4 sprays water flow to form a water film to repair the film surface wrinkle, and the electric field generated by the ring-shaped electrode can enhance the adhesion between the water film and the PE protective film, reduce the shrinkage of the water film, and cooperate with the third moving mechanism 8 to drive the up and down reciprocating movement of the water spraying pipe 40, so that the film surface of the protective film 13 to be tested can be more evenly covered, the film surface flattening effect is strengthened, and the wrinkle repair efficiency is improved. The water spraying pipe is a metal conductive pipe, which can be destaticized by connecting an electric wire. When the ring-shaped electrode of the water spraying pipe 40 applies a direct current voltage and forms a direct current electric field between the protective film 13 to be tested, the static electricity generated by the friction of the PE protective film can also be reduced, avoiding the film body curling caused by static electricity, and forming synergy with the destaticization function of the water spraying pipe, further ensuring the uniformity of the water film.

[0059] Further, a low concentration of surfactant (non-ionic surfactant) such as polyoxyethylene octylphenyl ether can be added to the water flow to reduce the surface tension of the water and promote the spreading of the water film. Adding a low concentration of surfactant to the water flow can further reduce the contact angle at the same voltage, enhancing the spreading effect. For the low concentration of surfactant, a micro-metering pump and a surfactant storage tank can be added between the water inlet pipe and the external water supply pump, which are controlled by the controller to synchronize the operation of the micro-metering pump and the water spraying pipe 40, and the concentration of the surfactant is accurately controlled between 0.05%-0.2% by controlling the operation of the micro-metering pump.

[0060] Further, a plurality of low-temperature plasma nozzles can be additionally arranged on the side of the support plate 11 facing the protective film 13 to be tested, and controlled by the controller to be started several seconds (e.g. 10-30 seconds) before water spraying, so as to use argon or oxygen plasma to bombard the surface of the PE protective film, introduce hydrophilic groups such as hydroxyl (-OH) and carboxyl (-COOH), temporarily reduce the surface contact angle (from 90° to below 60°), and significantly improve the hydrophilicity in a short time. By precisely controlling the plasma treatment intensity, such as controlling the plasma power to be between 50-100 W and the treatment time to be less than 1 minute, the surface of the PE protective film is prevented from being excessively oxidized to change the performance. The water spraying pipe 40 is started immediately after the low-temperature plasma treatment of the protective film 13 to be tested is completed, and the temporary hydrophilicity of the surface is used to form a stable water film.

[0061] The mesh plate 41 adopts a gradient aperture structure, and the aperture gradually increases from the top to the bottom, such as from 0.1 mm to 0.3 mm, so that the pressure of the water flow sprayed to the protective film 13 to be tested gradually increases from top to bottom. Therefore, the upper low pressure can prevent the water flow from causing the film to shake, and the lower high pressure can promote the water film to spread to the edge. In combination with the third moving mechanism 8 driving the water spraying mechanism 4 to move in the vertical direction from bottom to top, the water flow can form a uniform water film in the manner of “low pressure coverage first and high pressure spreading later”. Of course, the apertures of the mesh plate 41 can also be uniformly set, so that the water flow of the water spraying pipe 40 can be uniformly sprayed after passing through the mesh plate 41.

[0062] In summary, the PE protective film tensile resistance automatic detection device can form a double electric layer between the surface of the protective film 13 to be tested and the water film by installing the electric field generator 5 on the water spraying mechanism 4 and applying a direct current electric field to the surface of the protective film 13 to be tested, which can reduce the apparent contact angle of the protective film 13 to be tested based on the electro-wetting effect, weaken the hydrophobicity, and make a small amount of ions in the water flow directional migration, promote the spread of water molecules on the protective film 13 to be tested, and avoid the spontaneous shrinkage of the water film into droplets due to hydrophobicity, thereby solving the problem that the existing PE protective film tensile resistance automatic detection device cannot effectively repair the wrinkles on the surface of the PE protective film through the water film tension, and improving the accuracy of the PE protective film tensile resistance detection.

[0063] In order to solve the problem of secondary wrinkle of the film body caused by the surface tension gradient of the non-uniform water film in the prior art by strong air flow dehydration, as an preferred technical scheme, the automatic detection device for the tensile resistance of the PE protective film further comprises a negative pressure generator and an adsorption mechanism 9 installed on the rack 1, the adsorption mechanism 9 is provided with an air suction port 10, the negative pressure port of the negative pressure generator is communicated with the air suction port 10, and specifically, the negative pressure port of the negative pressure generator is communicated with the air suction port 10 through a negative pressure cavity arranged in the adsorption mechanism. The adsorption mechanism 9 is located on one side of the surface of the protective film 13 to be detected, and the negative pressure generator and the adsorption mechanism 9 cooperate to form a negative pressure acting on the surface of the protective film 13 to be detected.

[0064] Specifically, the adsorption mechanism 9 is preferably a porous adsorption plate, which is fixedly installed on the support through a support plate 11, and the air suction port 10 is arranged on the porous adsorption plate. The pore diameter of the air suction port 10 can be 0.5 mm, and the distance between two adjacent air suction ports 10 is 5 mm, so as to ensure uniform adsorption. The automatic detection device further comprises a fourth moving mechanism installed on the third moving mechanism and used for adjusting the relative distance between the support plate 11 and the protective film 13 to be detected. Through the fourth moving mechanism, the distance between the adsorption mechanism and the water spraying mechanism relative to the protective film to be detected can be better adjusted, so as to facilitate better flattening of the protective film to be detected. Through the negative pressure generator and the adsorption mechanism 9, the protective film 13 to be detected after flattening is subjected to dehydration treatment, replacing the impact defects of the traditional strong air flow dehydration, and the water film is removed efficiently through step-by-step and uniform negative pressure adsorption, while the secondary wrinkle of the protective film 13 to be detected is avoided.

[0065] Here, the automatic detection device for the tensile resistance of the PE protective film further comprises a controller and a laser displacement sensor array installed on the rack 1, the laser displacement sensor array is used for collecting distance data of a plurality of sampling points on the surface of the protective film 13 to be detected and feeding back to the controller, and the controller is used for constructing a film surface 3D topological map according to the distance data and acquiring a film surface real-time curvature according to the film surface 3D topological map.

[0066] Specifically, the laser displacement sensor array is fixedly installed on the support plate 11, and is installed on the rack 1 through the support plate 11. An infrared sensor can also be installed on the support plate 11, and the water film thickness is monitored in real time by calculating the infrared absorption peak intensity of water, so as to judge the water film removal progress. The infrared sensor and the laser displacement sensor array cooperate to work, and the flattening effect of the protective film 13 to be detected can be monitored by monitoring the water film removal progress and the film surface real-time curvature in real time.

[0067] After the surface of the protective film 13 to be tested is treated by the direct current electric field, a double electric layer is formed between the surface of the protective film 13 to be tested and the water film, and the water film is uniformly spread on the film surface by capillary force. When the film surface contacts the negative pressure field, the air pressure difference (one side of the film surface is negative pressure, and the other side is atmospheric pressure) on the surface of the water film will overcome the solid-liquid interfacial tension between the water film and the protective film 13 to be tested, and the water film will be “pulled away” from the film surface. Compared with the strong airflow impact type water film removal, the problem of vibration of the film body caused by the kinetic energy of the airflow, and even the deformation of the PE protective film, the direction of the negative pressure force is perpendicular to the film surface (parallel to the water film peeling direction), the disturbance to the film body is smaller, the water film can be efficiently removed, and the secondary wrinkling of the protective film 13 to be tested is avoided.

[0068] An embodiment of the present application also provides a use method of the PE protective film tensile resistance automatic detection device, which is applied to the automatic detection device, as shown in Figure 4 The use method comprises the following steps:

[0069] S1, unwinding, moving the lower end of the protective film to be tested below the second clamping mechanism.

[0070] S2, spraying water flow on the surface of the protective film to be tested by the water spraying mechanism to form a water film.

[0071] Specifically, the protective film to be tested is released by the protective film winding mechanism, when the lower end of the protective film to be tested moves below the second clamping mechanism, the external water supply pump and the third moving mechanism are controlled to move up and down along the vertical direction by the controller. The external water supply pump pumps water to the water spraying pipe through the water inlet pipe, and sprays water flow on the surface of the protective film to be tested under the action of the mesh plate to form a water film.

[0072] S3, generating a direct current electric field applied to the surface of the protective film to be tested by the electric field generator, so that a double electric layer is formed between the surface of the protective film to be tested and the water film.

[0073] The electric field generator is preferably a ring electrode embedded in the inner wall of the water spraying port. Before the water spraying mechanism sprays water flow, it is confirmed that the surface of the ring electrode is not scaled. Scaling will cause uneven electric field distribution. If there is dirt, remove the dirt before spraying water flow on the protective film to be tested and applying power to the ring electrode. While the water spraying mechanism sprays water flow on the surface of the protective film to be tested to form a water film, the controller controls the ring electrode to work, applies a direct current voltage to the ring electrode, and under the action of the direct current electric field, a double electric layer is formed between the surface of the protective film to be tested and the water film, so as to reduce the apparent contact angle of the PE protective film and weaken the hydrophobicity of the PE protective film, so that the water film is more easily spread, and the wrinkles and uneven places on the surface of the protective film to be tested are flattened. At the same time, when the water flow passes through the ring electrode, it will be polarized by the electric field, the water molecules are arranged in a certain direction to enhance the interaction between the water molecules and the PE protective film surface, and the liquid droplet contraction caused by the hydrophobicity is reduced.

[0074] S4, after the flattening and dehydration treatment of the protective film to be tested, the tensile property detection is performed.

[0075] In the tensile property detection, the tensile force data and deformation data in the tensile property detection process of the protective film to be tested are detected by a tensile force sensor and an infrared distance sensor respectively, the controller is signal connected with the tensile force sensor and the infrared distance sensor, the controller receives the tensile force data and the deformation data, and automatically completes the detection analysis of the tensile property of the protective film to be tested based on the obtained tensile force data and deformation data. The tensile force data includes the maximum tensile force, and the deformation data includes the original length of the protective film to be tested, the breaking length of the protective film to be tested and the cross-sectional area. The tensile property includes the tensile strength and the breaking elongation rate, the tensile strength = the maximum tensile force / the cross-sectional area, and the breaking elongation rate = (the breaking length-the original length) / the original length x 100%. Since the specific installation mode of the tensile force sensor and the infrared distance sensor, and the detection analysis of the tensile property based on the obtained tensile force data and deformation data all belong to the conventional technical means in the art, they will not be described here.

[0076] The contact angle on the surface of the protective film to be tested can be measured every 10 seconds. If the contact angle is greater than a preset first contact angle threshold (such as 65°), it indicates that the electro-wetting effect is insufficient, and the voltage of the ring electrode needs to be increased. If the contact angle is less than a preset second contact angle threshold (such as 55°), it indicates that the electro-wetting effect is too strong, and the voltage of the ring electrode needs to be appropriately reduced.

[0077] As shown in FIG. 1, the flattening and dehydration treatment of the protective film to be tested includes the following steps: Figure 5

[0078] S41, when the water film covers the surface of the protective film to be tested, the water flow is stopped. While the water flow is sprayed to the protective film to be tested, the profile image of the liquid droplet in contact with the solid can be captured by a high-speed camera based on the principle of optical imaging, and the baseline is automatically fitted and the contact angle value is calculated by combining the analysis software.

[0079] S42, after standing for a preset time, the protective film to be tested is in a tension state. Specifically, the protective film to be tested is clamped by the first clamping mechanism and the second clamping mechanism, the first clamping mechanism is driven to move upward and / or the second clamping mechanism is driven to move downward, and the protective film to be tested is pre-tensioned to avoid the wrinkles on the protective film to be tested recovering after the water film is removed.

[0080] S43, the negative pressure generator is started, and the negative pressure generator and the adsorption mechanism work together to form a negative pressure acting on the surface of the protective film to be tested, and the surface of the protective film to be tested is dehydrated.

[0081] ​Traditional negative pressure dehydration is mostly based on constant negative pressure value, which has the problem that initial high negative pressure will cause water film to shrink rapidly, causing uneven local tension on the film surface, such as the water film in the wrinkle area being sucked away first, which will cause the protective film to shrink towards that area.

[0082] To solve the above problems, as a preferred technical solution, the embodiment is dehydrated by gradient negative pressure, and the negative pressure is increased from low to high. Specifically, in step S43, as shown in the figure, gradient negative pressure dehydration includes the following steps: Figure 6

[0083] S431, remove the free water on the surface of the protective film to be tested by the first gradient negative pressure value. This is the low negative pressure stage, and the first gradient negative pressure value is the low negative pressure value. Exemplarily, the negative pressure value is between -10 and -20 kPa. This stage removes the free water on the film surface (the surface of the protective film to be tested), i.e. the water layer not closely combined with the film surface, at this time the surface tension of the water film has not been completely released, and the film body remains flat.

[0084] S432, remove the bound water on the surface of the protective film to be tested by the second gradient negative pressure value. This is the medium negative pressure stage, and the second gradient negative pressure value is the medium negative pressure. Exemplarily, the negative pressure value is between -30 and -40 kPa. This stage removes the bound water, i.e. the water layer combined with the film surface through hydrogen bonds or van der Waals forces, at this time the curvature of the film surface can be monitored in real time by infrared-laser coupling sensing, if the curvature exceeds 2°, the pressure increase is paused to avoid deformation of the protective film to be tested.

[0085] S433, remove the micropore water on the surface of the protective film to be tested by the third gradient negative pressure value. This is the high negative pressure stage, and the second gradient negative pressure value is the high negative pressure. Exemplarily, the negative pressure value is between -50 and -60 kPa. This stage removes the micropore water, i.e. the water in the small pores on the surface of the protective film to be tested. At this time the water film has been basically stripped, and the high negative pressure only acts on the residual moisture and will not cause the protective film to be tested to shrink.

[0086] Among the above three, the first gradient negative pressure value > the second gradient negative pressure value > the third gradient negative pressure value. Exemplarily, in the low negative pressure stage, the vacuum pump is started, and the initial pressure of the negative pressure cavity in the suction mechanism is adjusted to -10 kPa by the electric regulating valve. The free water moves along the capillary channel of the water film to the air suction port under the action of the negative pressure difference, and when the water film thickness is reduced to 0.05 mm by monitoring with an infrared sensor or no obvious water film flow is monitored for 20 seconds by shooting a water film image with a high-speed camera, it is judged that the free water has been removed, and the low negative pressure stage is terminated.

[0087] ​In the medium negative pressure stage, the negative pressure is increased to-30 kPa by the electric regulating valve in a gradient increasing-10 kPa / min manner to avoid pressure mutation, and the laser displacement array is started to draw a 3D topological map of the film surface in real time at a sampling frequency of 10 Hz. If the curvature of a certain area is greater than 3°, it indicates that the wrinkle in the area is not completely repaired, and the system automatically triggers local water spraying by driving the third moving mechanism to move towards the corresponding area to supplement the water film tension to repair the wrinkle. After the curvature is restored to less than 1°, the negative pressure is continued to be increased. In this stage, if the water film thickness is reduced to 0.02 mm or the overall flatness error of the film surface is less than 0.5 mm, it can be understood that the combined water has been removed, and the medium negative pressure stage is terminated.

[0088] In the high negative pressure stage, the negative pressure is increased to-50 kPa and is used as the final pressure, and is maintained for 10 seconds to avoid long-time high negative pressure leading to stretching of the protective film to be tested. At this time, the microporous water is sucked out through the "Laplace pressure" of the gas-liquid interface under high negative pressure, and at this time the water film has been completely peeled off, and only a small amount of water remains on the film surface, and the water film thickness is less than 0.01 mm. When the water film thickness is less than 0.01 mm or the air pumping amount of the vacuum pump is reduced to 10% of the initial value, it indicates that there is no significant water extraction, and the high negative pressure stage is terminated.

[0089] After the high negative pressure stage is completed, the vacuum pump is turned off, and the negative pressure is slowly released through the pressure relief valve to avoid the rebound of the protective film to be tested caused by the sudden disappearance of the negative pressure. At this time, the curvature of the film surface is detected again through the laser displacement sensor array, and if the real-time curvature is less than 1°, it is determined that the dehydration is qualified, otherwise the protective film to be tested is re-flattened and dehydrated until the real-time curvature of the film surface is less than 1°.

[0090] The present embodiment is based on gradient negative pressure to dehydrate the surface of the protective film to be tested, and the core is gradient pressure plus directional adsorption. By adjusting the negative pressure intensity in stages and monitoring the real-time curvature state of the surface of the protective film to be tested in real time, the balance between the gradual peeling of the water film and the shape maintenance of the film body is realized.

[0091] For the direct current voltage applied to the ring electrode, if a high voltage such as 1kV is directly applied, due to the sudden change of surface tension, it is easy to cause the water film to shrink instantaneously, so that the water film cannot be uniformly spread. Therefore, the form of gradient voltage adjustment is adopted to stage the voltage, so that the water film can adapt to the electric field effect, and uniform wetting is realized. Exemplarily, in the first voltage increasing stage, the voltage is gradually increased from 0.5kV to 0.8kV with a step of 0.1kV, each step is kept for 30 seconds, and the change of the water film contact angle is observed. When the contact angle decreases from 90° to 75°, the current voltage value is recorded, for example, 0.6kV. In the second voltage increasing stage, the voltage is fine-tuned from 0.7kV to 1.0kV with a step of 0.05kV, each step is kept for 10 seconds, and whether the contact angle breaks through the threshold of 60° is monitored. If the contact angle is stable at 60°±2°, the current voltage is locked, for example, 0.85kV.

[0092] After the current voltage is locked, the water film thickness is dynamically monitored. If the local water film is too thick (such as >0.3mm), the voltage is automatically increased by 0.05kV; if the water film is too thin (such as <0.15mm), the voltage is decreased by 0.03kV. At the same time, the contact angle is continuously monitored (such as once every 5 minutes). If the contact angle rises (such as due to the change of water flow), the voltage is slightly adjusted (±0.05kV) to maintain the contact angle between 60°±2°. If bubbles appear due to electrolysis caused by too high voltage, the voltage needs to be immediately reduced, for example, to 0.8kV, and the water quality is checked to determine whether the conductivity is too high. After the test is completed, the electric field voltage is decreased to 0kV, and the voltage-contact angle curve of this adjustment is recorded for reference for the next test.

[0093] In summary, the PE protective film tensile resistance automatic detection device uses the method of installing an electric field generator on the water spraying mechanism. By applying a direct current electric field to the surface of the protective film to be tested, a double electric layer is formed between the surface of the protective film to be tested and the water film. On the one hand, the apparent contact angle of the protective film to be tested is reduced based on the electro-wetting effect, and the hydrophobicity is weakened. On the other hand, a small amount of ions in the water flow is directionally migrated, and the water molecules are spread on the protective film to be tested, which avoids the spontaneous shrinkage of the water film into droplets due to hydrophobicity. The problem that the existing PE protective film tensile resistance automatic detection device cannot effectively repair the wrinkles on the surface of the PE protective film through the water film tension is solved, and the accuracy of the PE protective film tensile resistance detection is improved.

[0094] As a preferred technical solution, the use method further comprises introducing machine learning (such as CNN convolutional neural network), training through a large amount of dehydration data, realizing adaptive adjustment of pressure gradient, and realizing automatic optimization of pressure curve according to the film thickness and surface energy of the PE protective film. Exemplarily, the nonlinear relationship between the input features and the output (pressure gradient curve) is learned through a hybrid neural network, the feature weights are dynamically allocated combined with an attention mechanism, and finally an adaptive pressure curve conforming to the physical law is output. More specifically, as shown in Figure 9 true (t) and the effect index (such as wrinkle recovery rate R) to construct a training data set, and trains the hybrid neural network according to the training data set, with a loss function L = λ1·|P(t)-P true (t)|+λ2·R, λ1, λ2 represent loss function weight coefficients, generally 0.7 and 0.3 respectively. The optimizer uses Adam with a learning rate of 0.001.

[0095] The input features include PE protective film parameters, real-time monitoring data, and historical optimization data. The PE protective film parameters include, but are not limited to, the film thickness h pe (mm) affecting the rigidity and tensile strength of the film body, and the surface energy γ pe (mN / m) determining the water film wettability. The real-time monitoring data includes, but is not limited to, the contact angle θ(t) (°) reflecting the wettability of the water film and the film surface, and the water film thickness h w (t) (μm) for real-time feedback of water film removal progress. The historical optimization data includes, but is not limited to, the pressure curve P prev (t) of the last dehydration and the corresponding effect index (such as wrinkle recovery rate R prev , fracture strength retention rate σ ret , etc.).

[0096] The output target is the pressure gradient curve, which is set as a piecewise nonlinear pressure curve function P(t) here, covering the three stages of dehydration (low negative pressure → medium negative pressure → high negative pressure), and the pressure value and duration of each stage are dynamically optimized by the neural network. Specifically, P1(t) is the low negative pressure stage, which aims to remove free water, P2(t) is the medium negative pressure stage, which aims to remove bound water, and P3(t) is the high negative pressure stage, which aims to remove micropore water. T1, T2, T3 are the time thresholds of each stage, and P1(t) < P2(t) < P3(t) in absolute value.

[0097] The hybrid neural network structure is CNN+LSTM+attention. In order to deal with the fusion problem of time series data (contact angle and water film thickness) and static features (film thickness and surface energy), CNN is used to extract local dynamic features (such as the change rate of contact angle dθ / dt, the gradient of water film thickness dh w / dt), LSTM is used to capture time dependencies (such as the sequential nature of the dehydration stages), and an attention layer is used to assign feature weights (such as the weight of the contact angle in the low negative pressure stage is higher than the surface energy). Specifically, the CNN layer inputs real-time time series data including contact angle and water film thickness, extracts local features (such as the mutation point of the contact angle θ) through a 1D convolution kernel (size 3), and outputs a feature map. The input of the LSTM layer is the feature map output by the CNN layer. By processing the long-term dependencies of the time series (such as the trend of the contact angle θ decreasing from 90° to 60° during the dehydration process), the hidden state H is output. LSTM The attention layer combines the static features including film thickness and surface energy with the hidden state, and calculates the feature attention weight w=softmax(W·[h pe ,γ pe ,H LSTM ]+b), where W and b are learnable parameters. The output layer outputs the pressure value (P1, P2, P3) and time threshold (T1, T2, T3) of each stage through the fully connected layer, and the activation function uses the constrained ReLU function (P i ∈[-60kPa,-10kPa]), to avoid pressure exceeding the tensile strength of the PE protective film.

[0098] For example, to achieve dynamic weighting of features, a piecewise nonlinear function is designed to combine attention weights with physical parameters to output pressure values ​​at each stage. Among them, α1 represents the proportional coefficient of the low negative pressure stage, which is used to control the pressure level of the low negative pressure stage and can be learned by the neural network or set by technicians based on experience. θ 、w hw 、w hpe 、w γpe represents the feature weight of the attention layer output and w θ +w hw +w hpe +w γpe =1, which reflects the importance of each feature in the low negative pressure stage. σ(·) represents a constrained activation function, such as σ(x) = ReLu(x)-1, which is used to limit the output to a reasonable negative pressure range. β1 is a learnable parameter used to control the nonlinear combination of physical parameters, such as Reflects the correction of the contact angle due to surface energy. In order to prevent the pressure from exceeding the tensile strength of the PE film, a constraint condition is added: the absolute value of the pressure at any stage ≤ (tensile strength / film thickness) × safety factor. The safety factor is generally taken as 0.8, leaving 20% ​​strength redundancy. This constraint is integrated into the neural network training through projected gradient descent to ensure that the pressure output by the neural network conforms to the laws of physics. Based on the incremental update method, after each dehydration is completed, new data such as film thickness, surface energy, contact angle, and water film thickness are added to the training data set, and the neural network parameters are updated using a small batch gradient descent method to achieve self-optimization of the hybrid neural network model.

[0099] The adaptive adjustment method of the pressure gradient is reflected in the following aspects: 1. Intra-stage adaptation: dynamically adjust the feature weights through the attention layer, such as the contact angle weight is high in the low negative pressure stage, and the water film thickness weight is high in the medium negative pressure stage; 2. Inter-batch adaptation: integrate historical optimization data (such as the pressure curve of the previous batch and the corresponding effect indicators), and update the neural network parameters through incremental learning. For example, when the wrinkle recovery rate is too high, reduce the pressure value in the high negative pressure stage; 3. Individual adaptation: output personalized pressure curves based on the inherent parameters of different PE protective films. For example, thick films correspond to higher negative pressures because thick films have greater stiffness.

[0100] In general, the hybrid neural network incorporates a dynamic attention mechanism, breaking through the limitations of traditional fixed weights and allowing the neural network to automatically learn the importance of different features in different dehydration stages. This is more in line with actual scenarios than manually designed weights. Through iterative updates of historical data, the neural network can adapt to parameter fluctuations in different batches of PE membranes (such as a thickness deviation of ±0.01mm for the same model of membrane), without the need to retrain the model, reducing the maintenance cost of industrial applications. Different function structures are designed for the three stages of dehydration, which can better capture stage specificity than a single function (such as emphasizing the adjustment of contact angle in the low negative pressure stage and the removal of water film thickness in the high negative pressure stage), thereby improving the targetedness of the pressure curve.

[0101] Here, the above-mentioned method of obtaining the pressure gradient curve based on the hybrid neural network is experimentally simulated, and the experimental environment parameters include: temperature controlled at 20±2°C, humidity controlled at 50±5%RH, and negative pressure accuracy of ±0.02MPa. Figure 10 The following are the pressure gradient curves of PE protective films with different thicknesses during the dehydration process. Figure 10It can be seen that the pressure response difference in the dehydration process of the PE protective film with different thicknesses is significant. Therefore, if a fixed pressure gradient is used, the dehydration quality and efficiency of the protective film to be tested are easily reduced, thereby causing the protective film to be tested to be excessively stretched or the wrinkle recovery to be insufficient. In another aspect, the present application obtains a pressure gradient curve with an adaptive adjustment function based on a hybrid neural network, which can avoid the problems of excessive stretching or insufficient wrinkle recovery of the protective film to be tested in the dehydration process, and can adapt to the performance changes caused by different thicknesses, surface energies and other parameter differences, thereby improving the accuracy of the tensile property detection of the PE protective film.

[0102] Figure 11 The training loss curve of the hybrid neural network is shown. From the training loss curve of the hybrid neural network, it can be seen that the overall loss value of the hybrid neural network model is small after 45 rounds of training, and a balance between accuracy and speed is obtained. Figure 11 It can be seen that the hybrid neural network model has a small overall loss value after 45 rounds of training, and a balance between accuracy and speed is obtained.

[0103] As a preferred technical solution, as shown in the figure, the method for using the PE protective film tensile property automatic detection device further includes the following steps: Figure 7

[0104] S5, collecting distance data of a plurality of sampling points on the surface of the protective film to be tested.

[0105] Specifically, the laser displacement sensor array is a detection system composed of a plurality of laser displacement sensors arranged in a certain rule (such as one-dimensional linear array, two-dimensional surface array). It collects the distance data of a plurality of sampling points on the film surface synchronously, and provides the original input for the construction of the film surface 3D topological graph. Among them, the one-dimensional linear array (such as 10-20 sensors arranged in a row) is suitable for detecting the linear wrinkle (such as edge curl) of the film surface, and the cost is low but the coverage is limited; the two-dimensional surface array (such as 10x10 or 20x20 matrix) can cover the entire film surface and generate a complete 3D model, which is the mainstream choice for large-area detection of PE protective film and the like. Exemplarily, the resolution of the laser displacement sensor array is greater than or equal to 1 μm to realize the detection of the thin wrinkle of the PE protective film with a thickness of 0.01-0.1 mm, and the frame rate is greater than or equal to 1 kHz to capture the dynamic changes of the film surface wrinkle, meeting the real-time requirements.

[0106] S6, constructing a film surface 3D topological graph according to the distance data.

[0107] ​The point cloud data (3D coordinates of multiple sampling points on the film surface) collected by the laser displacement sensor array is pre-processed and reconstructed into a curved surface to generate a 3D3D topology map of the film surface, which can intuitively reflect the concave-convex, wrinkles and other shapes of the film surface. Generally, it includes the following steps: 1. Each sensor in the laser displacement sensor array synchronously collects the distance data of the corresponding point on the film surface at a set frequency (such as 1 kHz), such as 20x20 array with 400 points, each point containing X / Y (sensor position), Z (distance) coordinates, forming the original point cloud; 2. Remove environmental light, film surface reflection and other noise interference by using Gaussian filtering or statistical filtering, and align the point cloud with the reference coordinate system (such as the initial plane of the film surface) by using ICP (Iterative Closest Point) algorithm to ensure the accuracy of the model; 3. For triangular mesh, use Delaunay triangulation to convert point cloud to triangular mesh, which is fast in calculation and suitable for real-time detection; for NURBS surface, use non-uniform rational B-spline to fit the point cloud to generate a smooth surface, which has high accuracy and small model error.

[0108] S7, obtaining the real-time curvature of the film surface according to the 3D topology map of the film surface.

[0109] Curvature is an index to measure the degree of bending of the film surface, and real-time curvature calculation is to analyze the bending degree of the wrinkle area through the 3D topology map model of the film surface. For triangular mesh curvature, calculate the average curvature of each triangle, and for NURBS curvature, calculate the principal curvature through the second derivative matrix. According to the characteristics of PE protective film, set the curvature threshold, such as the maximum allowable curvature of PE protective film is 5°, then set the curvature threshold to 5°. When the real-time curvature of a certain area exceeds the curvature threshold, reduce the negative pressure value in the gradient negative pressure dehydration process, such as from high negative pressure to medium or low negative pressure. Continuously monitor the area, and when the real-time curvature decreases to below the curvature threshold, restore the high negative pressure value.

[0110] By constructing the 3D topology map of the film surface and obtaining the real-time curvature of the film surface, dynamically adjusting the negative pressure value in the gradient negative pressure dehydration process based on the real-time curvature of the film surface, it is beneficial to improve the dehydration efficiency and quality of the film surface, and to better optimize the detection accuracy of the tensile property of the PE protective film.

[0111] As a preferred technical solution, as shown in Figure 8 The method for using the PE protective film tensile property automatic detection device further includes the following steps:

[0112] S8, obtaining the real-time contact angle θ real and the target contact angle θ target , obtaining the contact angle error feedback term according to the contact angle and the target contact angle.

[0113] Based on the electrowetting effect, the contact angle of the protective film to be tested is proportional to the square of the voltage. The purpose of applying an electric field to the protective film to be tested by the electric field generator is to reduce the initial contact angle of the hydrophobic PE protective film, such as from the original 90° to about 60°, to ensure the spreading of the water film. Therefore, the contact angle of the protective film to be tested is the key feedback signal of the input voltage of the electric field generator. Specifically, based on the Young equation cos θ = cos θ0+ (ε0ε r V 2 ) / (2dγ), to stabilize θ at the target contact angle (such as 60°), the contact angle error Δθ = θ target -θ real is defined. Exemplarily, the contact angle error feedback term adopts an exponential decay function to enhance the adjustment accuracy when the error is small, expressed as Kθ·f(Δcosθ). Wherein, f(Δcosθ) = Δcosθ·e -α·|Δcosθ| represents the nonlinear feedback coefficient of the contact angle error, K θ represents the first calibration coefficient, which can be fitted by experiment. α represents the nonlinear decay factor, which can be calibrated by experiment, such as equal to 5. When Δcosθ is large, such as the real-time contact angle >> 60°, e -α·|Δcosθ| is small, which can limit the sudden increase of the voltage; when Δcosθ is small, such as the real-time contact angle ≈ 60°, e -α·|Δcosθ| is close to 1, which can improve the adjustment accuracy. The contact angle error feedback term adopts cosθ as the key feedback variable, combined with the exponential decay function, which is more in line with the physical law of the electrowetting effect, avoiding the nonlinear error of the linear feedback of the contact angle θ.

[0114] S9, obtaining the reference thickness t0 and the actual thickness t of the PE protective film, and obtaining a film thickness correction term for characterizing the difficulty of the electric field penetrating to the film surface according to the reference thickness and the actual thickness.

[0115] The thicker the protective film to be tested, the more difficult the electric field penetrates to the surface, so a higher voltage is required to maintain the surface charge density. That is, the input voltage of the electric field generator is proportional to the actual thickness of the protective film to be tested. Exemplarily, the film thickness correction term is expressed as K t ·g(t). Exemplarily, g(t) = t-t0 represents the film thickness correction factor, K t represents the second calibration coefficient, which can be fitted by experiment. When the actual thickness is greater than the reference thickness, the protective film to be tested can be identified as a thick film, the film thickness correction factor is greater than 0, and the voltage is increased; when the actual thickness is less than the reference thickness, the protective film to be tested can be identified as a thin film, the film thickness correction factor is less than 0, and the voltage is reduced to avoid film damage caused by overvoltage. Of course, the film thickness correction factor can also be defined as the natural logarithm of the actual thickness minus the natural logarithm of the actual thickness, and the film thickness correction term is defined as the product of the film thickness correction factor and the second calibration coefficient, and the second calibration coefficient is calibrated by experiment.

[0116] S10, obtaining a film thickness-curvature cross correction term K

[0117] The greater the curvature, the more curved the film surface, and the water film is prone to gather at the concave part and shrink at the convex part, so the electric field needs to be enhanced to optimize the water film spreading. Since the electric field demand of the thick film in the high curvature area is nonlinear superposition, the input voltage of the electric field generator is adjusted in combination with the film thickness and the curvature. Exemplarily, the film thickness-curvature cross correction term K th ·h(t,k) is obtained. Wherein, h(t,k) = k 2 ·t represents a cross correction factor, K th represents a third calibration coefficient, which can be fitted by experiment. k represents the real-time curvature of the film surface, reflecting the bending degree of the film surface, and the greater the value, the greater the surface tension gradient of the water film at the bending part. k 2 is used to amplify the influence of high curvature, and the influence can be ignored when the curvature is small, and is significantly enhanced when the curvature is large. k 2 ·t can be understood as a film thickness correction term in combination, and the voltage demand of the thick film in the high curvature area is greater. Therefore, this film thickness-curvature cross correction term captures the nonlinear demand of the thick film in the high curvature area, which is more in line with the actual situation than the independent parameter addition.

[0118] S11, obtaining the output voltage of the electric field generator according to the contact angle error feedback term, the film thickness correction term, and the film thickness-curvature cross correction term.

[0119] Exemplarily, the output voltage V of the electric field generator is V = sat[V0+ K θ ·f(Δcosθ) + K t ·g(t) + K th ·h(t,k)]. Wherein, sat represents a hard package and function, which is used to limit the output voltage to 0.5-1kV, avoiding overvoltage or invalid voltage. For the first calibration coefficient, the second calibration coefficient, and the third calibration coefficient, the method of orthogonal experiment is used for fitting. First, three film thicknesses (such as t = 0.05mm, t = 0.1mm, and t = 0.15mm) are selected, three curvatures (such as k = 0m -1 , k = 5m -1 , and k = 10m -1 ), a total of 9 groups of experiments, then for each group of experiments, the output voltage data required to reduce the contact angle from 90° to 60° is measured, and finally the experimental data is substituted into the output voltage formula, and the first calibration coefficient, the second calibration coefficient, and the third calibration coefficient are fitted by using the method of multivariate nonlinear regression.

[0120] It should be noted that the function form of the contact angle error feedback term, the film thickness correction term and the film thickness-curvature cross correction term includes but is not limited to linear function, polynomial, exponential function and quadratic function, etc., which can be selected according to the actual situation and determined by experimental calibration.

[0121] The output voltage function V=sat[V0+K θ ·f(Δcosθ)+K t ·g(t)+K th ·h(t,k)] first integrates the contact angle, the film thickness, the real-time curvature and the three core parameters, realizes the accurate regulation of the voltage through the creative nonlinear function, conforms to the physical law of the electrowetting effect, and can significantly improve the water film spreading effect and the detection stability in the tensile performance detection of the PE protective film.

[0122] The above-mentioned embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as the limitation of the scope of the patent. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A device for automatically testing the tensile strength of a PE protective film, comprising a frame, a first clamping mechanism, a second clamping mechanism, and a water spraying mechanism, wherein the first clamping mechanism and the second clamping mechanism are both mounted on the frame and used to clamp the protective film to be tested, and the water spraying mechanism is mounted on the frame and used to spray water toward the surface of the protective film to be tested to form a water film, characterized in that: It also includes an electric field generator fixedly installed on the water spray mechanism, which is used to generate a DC electric field applied to the surface of the protective film to be tested, so that a double electric layer is formed between the surface of the protective film to be tested and the water film, so as to level the surface of the protective film to be tested.

2. The automatic detection device for the tensile strength of a PE protective film according to claim 1, characterized in that: It also includes a negative pressure generator and an adsorption mechanism installed on the frame, the adsorption mechanism is provided with an air suction port, the negative pressure port of the negative pressure generator is connected to the air suction port, the adsorption mechanism is located on one side of the surface of the protective film to be tested, and the negative pressure generator and the adsorption mechanism work together to form a negative pressure acting on the surface of the protective film to be tested.

3. The automatic detection device for the tensile strength of a PE protective film according to claim 2, characterized in that: It also includes a controller and a laser displacement sensor array installed on the frame. The laser displacement sensor array is used to collect distance data of multiple sampling points on the surface of the protective film to be measured and feed it back to the controller. The controller is used to construct a 3D topological map of the film surface based on the distance data, and obtain the real-time curvature of the film surface based on the 3D topological map of the film surface.

4. The automatic detection device for the tensile strength of a PE protective film according to claim 3, characterized in that: The water spray mechanism includes a water inlet pipe, a water spray pipe and a mesh plate. The water inlet pipe is fixedly connected to the side of the water spray pipe away from the protective film to be tested and is communicated with the water spray pipe. The side of the water spray pipe facing the protective film to be tested is provided with a water spray outlet. The mesh plate is embedded in the water spray outlet. The electric field generator is a ring electrode and is embedded in the water spray outlet.

5. The automatic detection device for the tensile strength of a PE protective film according to claim 4, characterized in that: The annular electrode includes a conductive substrate and an insulating layer coated on the conductive substrate.

6. A method for using an automatic detection device for the tensile strength of a PE protective film, applied to the automatic detection device according to any one of claims 1 to 5, characterized in that: The steps include: Unwinding the protective film to be tested so that the lower end thereof moves to the bottom of the second clamping mechanism; Spraying water toward the surface of the protective film to be tested by a water spraying mechanism to form a water film; Generating a DC electric field applied to the surface of the protective film to be tested by an electric field generator, so that a double electric layer is formed between the surface of the protective film to be tested and the water film; After the protective film to be tested is flattened and dehydrated, the tensile strength test is performed.

7. The method for using the automatic detection device for the tensile strength of a PE protective film according to claim 6, characterized in that: The leveling and dehydration treatment of the protective film to be tested includes: When the water film covers the surface of the protective film to be tested, the water jet is stopped; After standing for a preset time, the protective film to be tested is in a tensioned state; The negative pressure generator is started, and the negative pressure generator cooperates with the adsorption mechanism to form a negative pressure acting on the surface of the protective film to be tested, so as to dehydrate the surface of the protective film to be tested.

8. The method for using the automatic detection device for the tensile strength of a PE protective film according to claim 7, characterized in that: The following steps are also included: Collect distance data of multiple sampling points on the surface of the protective film to be tested; Constructing a 3D topological map of the membrane surface according to the distance data; The real-time curvature of the membrane surface is obtained according to the 3D topological map of the membrane surface.

9. The method for using the automatic detection device for the tensile strength of a PE protective film according to claim 8, characterized in that: The following steps are also included: Acquire a real-time contact angle and a target contact angle, and obtain a contact angle error feedback item according to the contact angle and the target contact angle; Obtaining a reference thickness and an actual thickness of the PE protective film, and obtaining a film thickness correction term for characterizing the difficulty of the electric field penetrating the film surface based on the reference thickness and the actual thickness; Obtaining a film thickness-curvature cross correction term for characterizing the surface tension gradient of the water film at the bend according to the actual thickness and the real-time curvature of the film surface; The output voltage of the electric field generator is obtained according to the contact angle error feedback term, the film thickness correction term and the film thickness-curvature cross correction term.

10. The method for using the automatic detection device for the tensile strength of a PE protective film according to claim 9, characterized in that: Dehydrating the surface of the protective film to be tested includes: Removing free water from the surface of the protective film to be tested by a first gradient negative pressure value; removing bound water on the surface of the protective film to be tested by a second gradient negative pressure value; Removing microporous water on the surface of the protective film to be tested by a third gradient negative pressure value; Among them, the first gradient negative pressure value>the second gradient negative pressure value>the third gradient negative pressure value.

Images