Dual roll dynamic rheology and heat distribution visual servoing method and system

Abstract

The application provides a double-roller dynamic rheology and thermal distribution visual servo method and system, relating to the field of calendering process control, which comprises: collecting infrared images and visible light images of a double-roller machine nip accumulation area and registering them to the same nip coordinate system; extracting a tumbling activity component from the visible light image, extracting a temperature gradient component from the infrared image, and fusing to obtain a melt stagnation index, indicating that the accumulation area has material stagnation when the tumbling activity component is lower than the activity threshold and the temperature gradient component is higher than the temperature threshold; in response to material stagnation, performing feedforward regulation on the speed difference of the double-roller machine roller and / or the feeding rate of the extruder to reconstruct the shear force distribution in the nip and resolve the material stagnation. The application fuses tumbling and temperature information to identify material stagnation, resolves it in time before irreversible thermal degradation of the material occurs through feedforward regulation, and improves the quality stability of continuous calendering.

Description

Technical Field

[0001] This application relates to the field of calendering process control, and in particular to a visual servo method and system for dynamic rheology and heat distribution of two rolls. Background Technology

[0002] A twin-roll mill is used to calender high-viscosity materials into sheets of uniform thickness. The material forms an accumulation zone in the gap between the two rollers, continuously being drawn in and tumbled by the rotation and speed difference of the rollers. The tumbling activity and temperature distribution of the material within the accumulation zone jointly determine the quality of the sheet. In continuous calendering of high-viscosity melts such as those containing physical matting agents, the roller gap remains constantly in operation without pause, and the material continuously endures heating and shearing from the roller surface.

[0003] When material stops tumbling and stagnates in a certain area of ​​the accumulation zone, it remains near the high-temperature roller surface for an extended period, causing continuous heat accumulation. Polymer melts degrade after the temperature exceeds their thermal degradation temperature and they remain there for a sufficient time, leading to charring, discoloration, and a decline in mechanical properties. This degradation is irreversible once it occurs. Since continuous calendering cannot be stopped midway to clean the roller surface, the identification and resolution of material stagnation in the accumulation zone can only be completed before degradation begins, leaving a limited time window for adjustment.

[0004] Existing roller gap condition monitoring methods mostly observe the material accumulation area using a single information mode. Since visible light images alone can only reveal the tumbling state of the material surface but not its temperature distribution, and temperature detection alone can only indicate the temperature level but cannot determine whether the material has stopped tumbling, a single mode cannot distinguish between accumulation stagnation caused by material accumulation thickness exceeding the normal range and stagnation caused by localized heating, thus failing to reliably determine the cause of stagnation. Furthermore, such monitoring methods often resort to stopping the machine to clean the rollers or only output a general judgment on whether adjustment is needed after an anomaly is detected. However, stopping the machine further aggravates coking during material processing, and the material accumulation area, which is the object of diagnosis, disappears. General post-adjustment lags behind the irreversible window of thermal degradation, and by the time stagnation is confirmed, coking has often already started. In addition, the roller gap extends linearly along the roller axis, and stagnation usually only occurs in localized sections. When adjusting with single axially acting quantities such as roller speed difference, increasing shear in the stagnant section will simultaneously change the shear state of other sections, making it difficult to take into account the unevenly distributed localized stagnation along the axial direction. Summary of the Invention

[0005] In order to identify and resolve material stagnation in areas that are difficult to observe from the outside before irreversible thermal degradation of the material occurs under continuous calendering conditions, this application provides a dual-roller dynamic rheology and heat distribution visual servoing method and system.

[0006] Firstly, this application provides a visual servoing method for dual-roller dynamic rheology and heat distribution, which adopts the following technical solution: A visual servoing method for dynamic rheology and heat distribution using dual rollers includes the following steps: S1. Infrared and visible light images of the material accumulation area in the roll gap of the twin-roll mill are acquired using an infrared acquisition unit and a visible light acquisition unit, respectively. The roll gap is formed between the two rolls of the twin-roll mill. The infrared and visible light images are registered to the same roll gap coordinate system. S2. Extract the tumbling activity component, which characterizes the tumbling activity of the material in the accumulation zone, from the visible light image; extract the temperature gradient component, which characterizes the surface temperature distribution of the accumulation zone, from the infrared image; fuse the tumbling activity component and the temperature gradient component to obtain the melt stagnation index, which characterizes the stagnation of the material in the accumulation zone. The melt stagnation index indicates that there is material stagnation in the accumulation zone when the tumbling activity component is lower than the corresponding activity threshold and the temperature gradient component is higher than the corresponding temperature threshold. S3. In response to the melt stagnation index indicating the presence of material stagnation in the accumulation zone, feedforward adjustment is performed on the roller speed difference of the twin-roll mill and / or the feed rate of the extruder to reconstruct the shear force distribution within the roll gap and resolve material stagnation.

[0007] By adopting the above technical solution, after the infrared image and the visible light image are registered to the same roller gap coordinate system, the tumbling activity component on the visible light side and the temperature gradient component on the infrared side correspond to each other in the same spatial position. The fused melt stagnation index reflects both the tumbling stagnation and the degree of heating of the material. The combined condition of the tumbling activity component being lower than the activity threshold and the temperature gradient component being higher than the temperature threshold is used as the stagnation criterion, so that the low-speed state of slowed tumbling but normal temperature and the state of heating up but still tumbling are not misjudged as stagnation. When the melt stagnation index indicates stagnation, the roller speed difference and the feeding rate are adjusted forward so that the shear force distribution in the roller gap is reconstructed before the material undergoes irreversible thermal degradation, and the material stagnation is resolved before the degradation begins.

[0008] Optionally, in S2, the material accumulation area is divided into multiple axial segments along the axial direction of the roller. The tumbling activity component and temperature gradient component are extracted and fused for each axial segment to obtain the melt stagnation index of each axial segment, so as to form a melt stagnation index distribution along the axial direction.

[0009] By adopting the above technical solution, the melt stagnation index is calculated segment by segment along the roller axis, so that the unevenly distributed local stagnation along the axis is not masked by the average of a single index of the whole roller, and provides spatial positioning for subsequent directional adjustment of the stagnation section.

[0010] Optionally, S3 includes sub-steps S31 to S33: S31. The axial segment in the melt stagnation index distribution that indicates the presence of material stagnation is identified as the target axial segment.

[0011] S32. Based on the temperature gradient component of the target axial segment, the accumulation thickness of the material profile in the visible light image, and the material tumbling speed, determine the cause of the material stagnation in the target axial segment. The causes of stagnation include excessive accumulation, local overheating, and insufficient shearing. The accumulation thickness is the distance from the top edge of the material profile in the target axial segment to the vertical direction of the roller gap in the visible light image. The excessive accumulation is the cause of stagnation where the accumulation thickness exceeds the corresponding thickness threshold and the material tumbling speed is lower than the corresponding speed threshold.

[0012] S33. Based on the cause of stagnation, the adjustment amount of the feedforward adjustment is diverted to the corresponding execution amount. For the case of excessive material accumulation, the feeding rate is reduced; for the case of insufficient shearing, the roller speed difference is adjusted; and for the case of local overheating, both the roller speed difference and the feeding rate are adjusted simultaneously.

[0013] By adopting the above technical solution, the cause of stagnation is first identified and then the adjustment amount is diverted to the corresponding execution amount. This allows the two to work together: reducing the feeding rate for the case of excessive material accumulation, adjusting the roller speed difference for the case of insufficient shearing, and coordinating the two for the case of local overheating. This avoids improper adjustment direction due to indiscriminate identification of the cause.

[0014] Optionally, S2 includes parallel sub-steps S2a and S2b: S2a. In response to the fact that the material outline in the visible light image is obscured and the tumbling activity component cannot be directly extracted, the tumbling activity of the material in the accumulation area is estimated based on the rate of change of temperature distribution over time in the infrared image, and the estimated value is used as the tumbling activity component to participate in the fusion of the melt stagnation index.

[0015] S2b. In response to interference with the infrared image, which prevents the direct extraction of the temperature gradient component, the surface temperature distribution of the accumulation area is estimated based on the flow velocity of the material texture in the visible light image. The estimated value is then used as the temperature gradient component to participate in the fusion of the melt stagnation index.

[0016] By adopting the above technical solution, when any spectral image cannot be directly extracted due to obstruction or interference, the component can be inferred by using another spectral image, so that the melt stagnation index can still be calculated even when a single spectrum fails for a short time.

[0017] Optionally, the roller gap of the twin-roll mill is provided with roller gap adjustment mechanisms at both ends of the roller axial direction; in S3, the feedforward adjustment also includes: determining the axial position of the axial segment where material stagnation occurs based on the melt stagnation index distribution, adjusting the difference in roller gap at both ends of the roller gap to actively form a roller gap wedge that gradually changes monotonically along the axial direction, so that the narrow end of the roller gap wedge is located at one end of the two ends of the axial direction closer to the axial position, so that the shear force in the roller gap increases towards the narrow end along the axial direction, and the roller speed difference is used to adjust the overall level of the shear force, and the roller gap wedge is used to adjust the distribution of the shear force along the axial direction.

[0018] By adopting the above technical solution, the overall level of shear force is adjusted by the roller speed difference, and the distribution of shear force along the axial direction is adjusted by the roller gap wedge. The two execution quantities act on the whole and the local respectively, so that the stagnant section is subjected to targeted shear enhancement, while the section far from the narrow end is relatively less affected.

[0019] Optionally, in S2, the correspondence between the melt stagnation index and the actual material stagnation degree in the accumulation zone is corrected online based on the current size of the roll gap wedge and the roll speed difference, so that after the roll gap wedge changes the geometry of the roll gap, the melt stagnation index still corresponds to the actual material stagnation degree in the accumulation zone.

[0020] By adopting the above technical solution, the current state of the roll gap wedge and the roll speed difference is written back to the interpretation benchmark of the melt stagnation index, so that the correspondence between the melt stagnation index and the actual degree of stagnation does not drift after the geometric shape is changed by the execution amount.

[0021] Optionally, in S3, while adjusting the difference in roller gap at both ends of the roller gap to form a roller gap wedge, the distribution of the feeding rate along the axial direction is coordinated to maintain the thickness integral of the output material of the twin-roll mill along the axial direction at a preset target cross-sectional area.

[0022] By adopting the above technical solution, the feeding rate is coordinated and distributed while reconstructing the shear distribution with the roller gap wedge, compensating for the influence of the wedge on the discharge, so that the thickness integral of the discharge along the axial direction is maintained at the target cross-sectional area.

[0023] Optionally, in S3, based on the melt stagnation index indicating that there is material stagnation in the accumulation area, the melt stagnation index of each axial segment is also constructed into a stagnation index sequence in chronological order. The upward trend of the melt stagnation index is identified according to the stagnation index sequence, and feedforward adjustment is performed on the axial segment only when the upward trend reaches the preset trend condition.

[0024] By adopting the above technical solution, the upward trend of the stagnation index over time is superimposed as a trigger threshold on the basis of satisfying the instantaneous stagnation criterion, filtering out instantaneous over-threshold caused by short-term fluctuations, and only performing feedforward adjustment on the continuously deteriorating axial segment.

[0025] Optionally, the axial segments located at both ends of the roller among the multiple axial segments are end dead zones; in S2, a material stagnation determination threshold independent of the other axial segments is used for the end dead zones; in S3, a discharge operation is periodically triggered for the end dead zones.

[0026] By adopting the above technical solution, an independent judgment threshold is set for the dead zone section at both ends of the roll gap, which is geometrically bound to be low speed due to its proximity to the material stop, and the material is discharged periodically, so as to avoid the end false triggering or missed detection of its chronic stagnation caused by a uniform threshold for the whole roll.

[0027] Optionally, the material in the accumulation zone is a high-viscosity melt of a physical matting agent under continuous calendering conditions.

[0028] By adopting the above technical solution and applying the above method to the continuous calendering of physical matting agents, the characteristics of the high-viscosity melt that is prone to local overheating due to stagnation are adapted.

[0029] Optionally, the tumbling activity component is at least one of the optical flow field amplitude of the material surface in the visible light image, the time rate of change of the material profile, and the displacement velocity of the surface texture of the accumulation area; the temperature gradient component is at least one of the spatial gradient of the surface temperature in the infrared image, the area of ​​the local hot spot, and the time rate of change of the surface temperature.

[0030] By adopting the above technical solution, multiple optional extraction sources are provided for the two components, enabling the fusion input to be selected according to the imaging conditions.

[0031] Optionally, the tumbling activity component and the temperature gradient component can be fused by weighting and summing, multiplying, or comparing the tumbling activity component and the temperature gradient component according to preset weights.

[0032] By adopting the above technical solutions, three fusion methods are proposed: weighted summation, product calculation, and ratio calculation, to adapt to different coupling relationships between tumbling stagnation and degree of heating.

[0033] Optionally, the cause of material stagnation in the target axial segment can be determined as follows: if the area of ​​local hot spots in the temperature gradient component exceeds the corresponding area threshold, it can be determined as local overheating; if the material profile's accumulated thickness exceeds the corresponding thickness threshold and the material tumbling speed is lower than the corresponding speed threshold, it can be determined as excessive material accumulation; if the material profile's accumulated thickness does not exceed the thickness threshold and the material tumbling speed is lower than the speed threshold, it can be determined as insufficient shearing.

[0034] By adopting the above technical solution, three types of causal criteria are given based on the combination of hot spot area, accumulation thickness and tumbling speed, so that the causal discrimination is based on specific characteristics.

[0035] Optionally, the axially oriented roll gap wedge can be formed by adjusting the roll gap adjustment mechanism at both ends of the roll gap to make the roll gap unequal, by making the axes of the two rollers slightly intersect each other, or by applying a bending moment to the axial ends of the rollers.

[0036] By adopting the above technical solutions, three methods for forming a wedge shape are provided: unequal roller spacing, slight axis crossing, and applying bending moment to the shaft end, which can be adapted to different roller system structures.

[0037] Optionally, in response to the simultaneous inability to extract the temperature gradient component and the tumbling activity component from both the infrared and visible light images for the same reason, the most recently obtained melt stagnation index is used, and an open-loop conservative deload is performed on the feed rate according to a preset process sequence until either the infrared or visible light image becomes usable again.

[0038] By adopting the above technical solution, when two images fail simultaneously for the same reason, the most recent effective index is used in conjunction with open-loop conservative load reduction to maintain safety. Once either image recovers, the feedforward adjustment based on the real-time melt stagnation index is resumed.

[0039] Optionally, for axial sections identified as having excessively thick material accumulation, the temperature gradient component of the axial section is monitored over time. In response to the increase of the temperature gradient component over time, the material stagnation in the axial section is determined to be a shift from excessively thick material accumulation to local overheating, and the feedforward adjustment of the axial section is upgraded in advance.

[0040] By adopting the above technical solution, the upward trend of the temperature gradient in the axial section of the material accumulation type is monitored, and the adjustment is upgraded in advance when the material accumulation type stops evolving into the local overheating type.

[0041] Optionally, the rollers of the twin-roll mill adopt a medium-high roller type with a diameter in the middle of the roller surface larger than that at both ends, in order to pre-compensate for the deflection of the rollers when they are under pressure, and to verify the residual compensation of the medium-high roller type for deflection by the melt stagnation index of the axial section located in the middle of the roller axis.

[0042] By adopting the above technical solution, the pressure-induced deflection of the roller is pre-compensated by the medium-high roller type, and the residual deflection after compensation is verified by the melt stagnation index of the middle axial section.

[0043] Optionally, based on the melt stagnation index of the axial section located in the middle of the roller's axis, the residual deflection of the roller as the working conditions change can be dynamically compensated by applying a bending moment to the roller or by making the axes of the rollers slightly intersect each other.

[0044] By adopting the above technical solution, bending moment is dynamically applied or axis intersection is adjusted based on the melt stagnation index in the central axial section to compensate for the residual deflection of the roller as the working conditions change.

[0045] Optionally, the discharge operation can be one of the following: briefly increasing the roller gap at the end dead section, briefly reversing the roller, or scraping the material at the end dead section.

[0046] By adopting the above technical solutions, three discharge methods are provided: increasing the roller gap, short-term reversal, and scraping, which are used to discharge the material stuck in the dead zone at the end.

[0047] Optionally, the infrared image and the visible light image can be registered to the same roll gap coordinate system, either for offline calibration based on a calibration target set in the roll gap or for online registration based on roll gap edge features.

[0048] By adopting the above technical solutions, two methods are presented: offline calibration based on the calibration target and online registration based on edge features, which are suitable for different field conditions.

[0049] Secondly, the dual-roller dynamic rheology and heat distribution visual servoing system provided in this application adopts the following technical solution: A dual-roller dynamic rheology and heat distribution vision servo system includes: The dual-spectrum acquisition module includes an infrared acquisition unit and a visible light acquisition unit. The infrared acquisition unit is configured to acquire infrared images of the material accumulation area in the roll gap of the twin-roll mill, and the visible light acquisition unit is configured to acquire visible light images of the material accumulation area. An image registration module is configured to register infrared images and visible light images to the same roll gap coordinate system; The stagnation index extraction module is configured to extract the tumbling activity component from the visible light image and the temperature gradient component from the infrared image, fuse the tumbling activity component and the temperature gradient component to obtain the melt stagnation index, and determine that there is material stagnation in the accumulation area when the tumbling activity component is lower than the corresponding activity threshold and the temperature gradient component is higher than the corresponding temperature threshold. And a feedforward servo control module, which is configured to perform feedforward adjustment of the roller speed difference of the twin-roll mill and / or the feed rate of the extruder in response to material stagnation in the accumulation zone, in order to reconstruct the shear force distribution within the roll gap.

[0050] By adopting the above technical solution, the dual-spectrum acquisition module, image registration module, stagnation index extraction module and feedforward servo control module successively undertake image acquisition, image registration, melt stagnation index extraction and feedforward adjustment, so that the above-mentioned dual-roller dynamic rheology and heat distribution visual servo method is realized in the form of system modules.

[0051] In summary, this application includes at least one of the following beneficial technical effects: 1. The tumbling activity component of the visible light image and the temperature gradient component of the infrared image are fused into a melt stagnation index. Material stagnation is determined by the combined condition of low tumbling activity and high temperature gradient. Feedforward adjustment is performed on the roller speed difference and feeding rate before irreversible thermal degradation of the material occurs, so that material stagnation can be identified and resolved in a timely manner under the condition of continuous calendering without stopping the machine.

[0052] 2. Calculate the melt stagnation index in segments along the roller axis to locate local stagnation, identify the three types of causes: excessive material accumulation, local overheating, and insufficient shearing, and divert the adjustment amount to the corresponding execution amount. Combined with the adjustment of the shear force distribution along the axial direction by the roller gap wedge, the local stagnation with uneven distribution along the axial direction can be resolved in a targeted manner according to the cause.

[0053] 3. When a single spectral image fails due to occlusion or interference, the corresponding component is inferred from another spectrum. When both channels fail simultaneously, the nearest effective index is used in conjunction with open-loop load reduction to maintain safety. Furthermore, the upward trend and cause migration of the stagnation index are proactively identified, enabling visual servoing to remain continuously available under conditions of imaging disturbance and stagnation. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the overall process of the visual servoing method for dual-roller dynamic rheology and heat distribution in one embodiment of this application.

[0055] Figure 2 This is a schematic diagram of the roller system and dual-spectral acquisition arrangement of a twin-roll mill in one embodiment of this application.

[0056] Figure 3 This is a schematic diagram of the process for extracting the melt stagnation index and determining material stagnation in one embodiment of this application.

[0057] Figure 4 This is a schematic diagram of the process of cause identification and regulation diversion in feedforward regulation in one embodiment of this application.

[0058] Figure 5 This is a schematic diagram of the structure of a dual-roller dynamic rheology and heat distribution visual servo system in one embodiment of this application.

[0059] Explanation of reference numerals in the attached figures: 100, Twin-roll mill; 110, First roller; 120, Second roller; 130, Roller gap; 140, Material accumulation area; 150, Roller gap adjustment mechanism; 200, Extruder; 310, Infrared acquisition unit; 320, Visible light acquisition unit. Detailed Implementation

[0060] The present application will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the scope of the application.

[0061] This application discloses a visual servoing method for dynamic rheology and heat distribution of dual rollers. This method fuses the tumbling activity component (characterizing the material's tumbling activity in a visible light image) with the temperature gradient component (characterizing the material's surface temperature distribution in an infrared image) to form a melt stagnation index (characterizing the degree of material stagnation). When the melt stagnation index indicates material stagnation, feedforward adjustment is performed on the roller speed difference and feed rate to reconstruct the shear force distribution within the roller gap. First, infrared and visible light images of the material accumulation area in the roller gap are acquired using infrared and visible light acquisition units and registered to the same roller gap coordinate system. Then, the temperature gradient component and tumbling activity component are extracted from the two images respectively and fused to obtain the melt stagnation index, which is used to determine whether material stagnation exists in the accumulation area. Finally, feedforward adjustment is performed on the roller speed difference and feed rate to resolve stagnation before irreversible thermal degradation of the material occurs. Therefore, the shear force distribution within the roller gap can be reconstructed before irreversible thermal degradation is triggered by material stagnation.

[0062] The following section provides a detailed explanation of the terminology, main process, specific implementation of core steps, and system mapping.

[0063] For ease of understanding, the following will first explain some of the technical terms involved in the embodiments of this application.

[0064] The accumulation zone refers to the area above the gap between the two rollers in a continuous calendering mill, where material accumulates due to continuous feeding. This area extends along the axial direction of the rollers. The material entering the gap is first tumbled and mixed in the accumulation zone by the relative rotation of the two rollers, and then bitten into the gap and calendered into sheets.

[0065] The material profile buildup thickness refers to the amount of material accumulated in the accumulation zone, measured from a visible light image. The material in the accumulation zone piles up above the roll gap, and in the visible light image, the top edge of its profile extends along the axial direction of the rolls. The buildup thickness of the material profile is the distance measured vertically from the top edge of the material profile to the roll gap at each axial segment, where the roll gap is the minimum clearance between the two rolls. This distance is measured segment by segment along the axial direction of the rolls, reflecting the amount of material accumulated at each segment. The buildup thickness of the material profile is a different quantity from the output thickness of the sheet after rolling through the roll gap: the former is the height of the material accumulation above the roll gap, while the latter is the thickness of the sheet itself at the roll gap exit.

[0066] The tumbling activity component refers to a quantity extracted from a visible light image that characterizes the degree of tumbling activity of materials within the accumulation zone. The more active the tumbling of materials within the accumulation zone, the higher the degree to which the materials are continuously renewed by the rollers; a slowdown in tumbling may mean that the materials have stagnated at that point, but it may also simply mean that the materials are in a low-speed state overall.

[0067] The temperature gradient component refers to the quantity extracted from infrared images that characterizes the surface temperature distribution of the material accumulation zone. When the material stagnates in the accumulation zone, it generates heat due to the continuous shearing of the rollers. The heat cannot be carried away in time with the material turnover, resulting in a local temperature increase at the stagnation point, and the temperature gradient component increases accordingly. However, an increase in the temperature gradient may also be due to the overall warming of the operating conditions.

[0068] The melt stagnation index is a measure that characterizes the degree of material stagnation in the accumulation zone by combining the tumbling activity component and the temperature gradient component. Relying solely on tumbling activity or temperature gradient can lead to misjudgments: a state of slowed tumbling but normal temperature may simply indicate that the material is moving at a low speed overall, while a state of rising temperature but still tumbling may simply indicate that the operating conditions are too hot. The melt stagnation index combines the two, indicating that material stagnation exists in the accumulation zone only when the tumbling activity is low and the temperature gradient is high.

[0069] Feedforward regulation refers to the adjustment of roller speed difference and feed rate before irreversible thermal degradation of the material occurs, using material stagnation in the accumulation zone as a measurable disturbance. This adjustment is triggered by the real-time detection result of the melt stagnation index on material stagnation. It is feedforward relative to the controlled variable of the degree of thermal degradation of the material, meaning that the adjustment is applied before the controlled variable changes due to the disturbance, rather than after the material has already charred or discolored.

[0070] A roll gap wedge is a type of gap that gradually changes axially within the roll gap by making the distance between the two ends of the roll gap unequal. Roll gap wedges are used to adjust the distribution of shear force along the axial direction of the roll gap.

[0071] Based on the terminology mentioned above, the main flow of this method is described below. (Refer to...) Figure 1 This method includes steps S1 to S3.

[0072] In S1, infrared acquisition unit 310 and visible light acquisition unit 320 respectively acquire infrared and visible light images of the material accumulation area 140 in the roll gap of the twin-roll mill 100. The roll gap 130 is formed between the two rollers (first roller 110 and second roller 120) of the twin-roll mill, and the infrared and visible light images are registered to the same roll gap coordinate system. (Refer to...) Figure 2The infrared acquisition unit and the visible light acquisition unit are positioned facing the material accumulation area above the roller gap. The infrared acquisition unit acquires infrared thermal images of the surface of the material accumulation area, and the visible light acquisition unit acquires visible light images of the surface of the material accumulation area. The two acquisition units acquire images of the material accumulation area synchronously, so that the infrared image and the visible light image at the same moment correspond to the same material state in the material accumulation area. In the figure, the extruder 200 supplies material to the area above the roller gap between the two rollers to form the material accumulation area. Roll gap adjustment mechanisms 150 are provided at both ends of the roller axial direction. After the two images are registered to the same roller gap coordinate system, the same pixel position corresponds to the same spatial position of the material accumulation area in the roller gap coordinate system, so that the tumbling activity component and temperature gradient component extracted from the two images can be fused at the same spatial position.

[0073] In some embodiments, the material in the accumulation zone is a high-viscosity melt of a physical matting agent under continuous calendering conditions. If this high-viscosity melt experiences localized stagnation in the accumulation zone, the heat generated by the continuous shearing of the rollers is not easily carried away with material turnover, leading to localized overheating at the stagnation point. Once the material reaches the temperature range for irreversible thermal degradation, the degradation becomes irreversible. Therefore, this method, in the continuous calendering scenario of this high-viscosity melt, resolves the continuous heat generation at the stagnation point by identifying material stagnation early and reconstructing the shear force distribution before thermal degradation.

[0074] In other embodiments, the infrared and visible light images are registered to the same roll gap coordinate system. This can be done offline based on a calibration target placed at the roll gap, or online based on roll gap edge features. Offline calibration based on the calibration target establishes the pixel correspondence between the two images during machine downtime using the target, suitable for situations where the roll geometry is relatively fixed. Online registration based on edge features extracts common features such as roll gap edges in real time during operation to align the two images, suitable for situations where the roll system experiences thermal expansion or pose drift. Both registration methods ensure pixel-by-pixel correspondence between the infrared and visible light images in the roll gap coordinate system.

[0075] In S2, the tumbling activity component, which characterizes the tumbling activity of the material in the accumulation zone, is extracted from the visible light image, and the temperature gradient component, which characterizes the surface temperature distribution of the accumulation zone, is extracted from the infrared image. The tumbling activity component and the temperature gradient component are fused to obtain the melt stagnation index, which characterizes the stagnation of the material in the accumulation zone. The melt stagnation index indicates that there is material stagnation in the accumulation zone when the tumbling activity component is lower than the corresponding activity threshold and the temperature gradient component is higher than the corresponding temperature threshold.

[0076] Specifically, refer to Figure 3 S2 includes sub-steps S21 to S24.

[0077] S21. Extract the tumbling activity component from the visible light image. The visible light image reflects the movement of the texture and contour of the material on the surface of the accumulation area over time. The more active the material tumbling, the more significant the displacement of the surface texture between adjacent images. Thus, the tumbling activity component, which characterizes the degree of material tumbling activity, can be extracted from the visible light image.

[0078] S22. Extract the temperature gradient component from the infrared image. The infrared image reflects the temperature distribution on the surface of the material accumulation area. The temperature of the material stagnating is higher than that of the surrounding normally renewed material due to continuous shear heating. Therefore, the temperature gradient component, which characterizes the surface temperature distribution of the material accumulation area, can be extracted from the infrared image.

[0079] S23. The tumbling activity component and the temperature gradient component are fused to obtain the melt stagnation index. Since the tumbling activity component and the temperature gradient component are extracted from visible light and infrared images respectively, and the two images are registered to the same roll gap coordinate system, they correspond to the same spatial position in the material accumulation area. The tumbling activity component and the temperature gradient component at this spatial position are synthesized according to a preset fusion relationship to obtain the melt stagnation index at that spatial position. The fusion relationship causes the melt stagnation index to increase as the tumbling activity decreases and as the temperature gradient increases, thus simultaneously reflecting the tumbling stagnation and the degree of heating of the material. The normalization before fusion can be achieved by linearly mapping the components to... The extreme values ​​of the interval are normalized, or the mean is subtracted and then the standard deviation is divided. The weights in the fusion relationship can be calibrated by collecting calibration data under normal operating conditions and known stagnation conditions, and aiming to make the melt stagnation index as divisible as possible for the two types of operating conditions, for example, making the inter-class interval of the melt stagnation index as large as possible under the two types of operating conditions.

[0080] S24. When the melt stagnation index indicates material stagnation, it is determined that material stagnation exists in the accumulation zone. In response to the tumbling activity component being lower than the corresponding activity threshold and the temperature gradient component being higher than the corresponding temperature threshold, the melt stagnation index indicates that material stagnation exists in the accumulation zone; in response to the above combined condition not being met, it is determined that there is no material stagnation in the accumulation zone. The combined condition of low tumbling activity and high temperature gradient is used as the stagnation criterion, ensuring that the low-speed state of slowed tumbling but normal temperature, and the state of heated but still tumbling, are not misjudged as stagnation: the former has low tumbling activity but no high temperature gradient, and the latter has a high temperature gradient but no low tumbling activity; neither of these conditions is satisfied simultaneously. The activity threshold and temperature threshold can be determined based on the value distribution of the tumbling activity component and temperature gradient component under normal and stagnation conditions, respectively. The activity threshold is set at the boundary between the tumbling activity distribution of the two types of conditions, and the temperature threshold is set at the boundary between the temperature gradient distribution of the two types of conditions, so that the combined criterion can correctly distinguish between the two types of conditions as much as possible.

[0081] Therefore, after the infrared image and the visible light image are registered to the same roller gap coordinate system, the tumbling activity component on the visible light side and the temperature gradient component on the infrared side correspond to each other in the same spatial position. The fused melt stagnation index reflects both the tumbling stagnation and the degree of heating of the material. The combined condition of low tumbling activity and high temperature gradient is used as the stagnation criterion to avoid two types of misjudgments under a single mode. When the melt stagnation index indicates stagnation, the roller speed difference and the feeding rate are adjusted forward so that the shear force distribution in the roller gap is reconstructed before the material undergoes irreversible thermal degradation, and the material stagnation is resolved before the degradation begins.

[0082] In some embodiments, the tumbling activity component is at least one of the following: the amplitude of the optical flow field on the material surface in the visible light image, the time rate of change of the material contour, and the displacement velocity of the surface texture of the accumulation area. The amplitude of the optical flow field reflects the motion velocity of each pixel in the visible light image at adjacent moments; the more active the material tumbling, the larger the amplitude of the optical flow field. The time rate of change of the material contour reflects how quickly the material accumulation shape changes over time. The displacement velocity of the surface texture of the accumulation area reflects the movement speed of the surface texture feature points. Correspondingly, the temperature gradient component is at least one of the following: the spatial gradient of the surface temperature in the infrared image, the area of ​​local hot spots, and the time rate of change of the surface temperature. The spatial gradient of the surface temperature reflects the steepness of the temperature difference between adjacent areas on the surface of the accumulation area; the area of ​​local hot spots reflects the size of the high-temperature zone where the temperature exceeds that of the surrounding area; the time rate of change of the surface temperature reflects how quickly the temperature rises over time. Each of the above sources can be used as the basis for extracting the corresponding component, and one or more of them can be selected according to the imaging conditions and material characteristics.

[0083] In other embodiments, the tumbling activity component and the temperature gradient component are fused. This can be achieved by weighting and summing, multiplying, or ratioing the tumbling activity component and the temperature gradient component according to preset weights. All three fusion methods result in the melt stagnation index increasing as the tumbling activity component decreases and as the temperature gradient component increases, thus aligning with the physical meaning of slowed tumbling and rising temperature indicating material stagnation. Taking weighted summation as an example, the tumbling activity component and the temperature gradient component are first normalized separately. Then, the normalized temperature gradient component and the normalized tumbling activity component are weighted and summed according to preset weights to obtain the melt stagnation index, denoted as: ; in, The melt stagnation index. The normalized roll activity component, These are the normalized temperature gradient components. and The weights are preset to be non-negative. The stagnation index represents the tendency for tumbling to stagnate; the lower the tumbling activity, the larger this term. Therefore, the melt stagnation index increases with decreasing tumbling activity and increasing temperature gradient. The product method uses the product of the normalized temperature gradient component and the stagnation tendency to represent the degree of stagnation, while the ratio method uses the ratio of the normalized temperature gradient component to the tumbling activity component to represent the degree of stagnation. Both methods also satisfy the aforementioned monotonic relationship. The normalization of the two components in the above fusion methods can use extreme value normalization or standardization, with the weights in the weighted summation... and Calibration can be performed by collecting calibration data under normal operating conditions and known stagnation conditions, with the goal of making the melt stagnation index as divisible as possible under the two types of conditions.

[0084] In some embodiments, in S2, the material accumulation area is divided into multiple axial segments along the roller axis. The tumbling activity component and temperature gradient component are extracted from each axial segment and fused to obtain the melt stagnation index for each segment, thus forming a melt stagnation index distribution along the roller axis. The stagnation of material along the roller axis within the material accumulation area is not uniform; stagnation may occur only in a localized section while material continues to be replenished normally in other sections. If only a single melt stagnation index is calculated for the entire material accumulation area, the stagnation in that localized section will be diluted by the average of the other normal sections and difficult to detect. By dividing the material accumulation area along the axial axis and calculating the melt stagnation index segment by segment, the stagnation in a localized section is independently reflected in the melt stagnation index of that segment. For example, if the material accumulation area is uniformly divided into several axial segments along the roller axis, when the melt stagnation index of one axial segment is significantly higher than that of the other axial segments, it indicates that material stagnation has occurred in that axial segment, while material in the other axial segments is normal. The axial segment can be divided uniformly along the axial length, or it can be divided non-uniformly according to the temperature distribution of the roll surface or the structural characteristics of the roll system, such as by denser division in the middle or end of the roll where stagnation is likely to occur. Thus, the melt stagnation index is calculated segment by segment along the roll axis, ensuring that unevenly distributed local stagnation along the axial direction is not masked by the averaging of a single index across the entire roll. This also provides spatial positioning for subsequent stagnation segment analysis, wedge adjustment, and trend identification based on axial location.

[0085] In other embodiments, S2 includes parallel sub-steps S2a and S2b for inferring the component from another spectral image when direct extraction of the corresponding component in S21 or S22 fails.

[0086] S2a. In response to the obstruction of the material outline in the visible light image, making it impossible to directly extract the tumbling activity component, the tumbling activity of the material in the accumulation zone is estimated based on the rate of change of temperature distribution over time in the infrared image. The estimated value is then used as the tumbling activity component to participate in the fusion of the melt stagnation index. When the material tumbles in the accumulation zone, its surface continuously contacts the rollers for heat exchange. The more active the tumbling, the more drastic the temperature fluctuation at the same location over time. Therefore, the tumbling activity of the material can be inferred from the rate of change of temperature over time in the infrared image. This estimation is maintained even when the tumbling activity component cannot be directly extracted from the visible light image due to obstruction by steam, oil, or reflections.

[0087] S2b. In response to interference with the infrared image, which prevents direct extraction of the temperature gradient component, the surface temperature distribution of the accumulation area is estimated based on the flow velocity of the material texture in the visible light image. The estimated value is then used as the temperature gradient component in the fusion of the melt stagnation index. As the material temperature increases, its apparent viscosity decreases and its fluidity increases. The flow velocity of the texture in the visible light image changes accordingly. Based on this, the surface temperature distribution can be inferred from the flow velocity of the texture in the visible light image. This estimation of the temperature gradient component is maintained even when the infrared image cannot be directly extracted due to water mist, lens contamination, or environmental heat source interference.

[0088] The mapping relationships between the rate of temperature change and the degree of tumbling activity, and between the texture flow velocity and the surface temperature, upon which the aforementioned cross-modal back-inference is based, can be obtained through empirical regression fitting of data simultaneously acquired from two images under normal operating conditions, or can be established based on a material rheological and heat transfer physical model. The empirical regression can employ least-squares linear regression or polynomial regression, using the temperature change rate and tumbling activity, and the texture flow velocity and surface temperature, acquired simultaneously under normal operating conditions as sample pairs, to fit the corresponding mapping relationships and their coefficients. Therefore, when any spectral image cannot directly extract the corresponding component due to occlusion or interference, the component can be back-inferred using another spectral image, allowing the melt stagnation index to continue to be calculated even when a single spectrum is temporarily unavailable; once the unavailable spectral image is restored to usability, the system switches back to directly extracting the corresponding component.

[0089] Optionally, in response to the simultaneous inability to extract the temperature gradient component and tumbling activity component from both the infrared and visible light images for the same reason, the most recently obtained effective melt stagnation index is used, and an open-loop conservative deload is applied to the feed rate according to a preset process sequence until either the infrared or visible light image becomes available again. When both images fail simultaneously for the same reason (e.g., the accumulation area is completely obscured by a large area of ​​splashed material, or both illumination and thermal imaging fail), the aforementioned cross-modal back-engineering cannot be performed because both images are unavailable. The melt stagnation index loses its observable diagnostic basis, making it impossible to determine whether the accumulation area is stagnant or where the stagnation occurs. Therefore, the most recently obtained effective melt stagnation index is used to maintain the judgment, and an open-loop conservative deload is applied to the feed rate according to a preset process sequence to reduce the material accumulation rate in the accumulation area and avoid irreversible stagnation overheating during the period of blindness. Once either image becomes available again, the feedforward adjustment based on the real-time melt stagnation index is resumed.

[0090] In some embodiments, S2 further corrects the correspondence between the melt stagnation index and the actual material stagnation degree in the accumulation zone based on the current size of the roll gap wedge and the roll speed difference. This ensures that even after the roll gap wedge changes its geometry, the melt stagnation index still corresponds to the actual material stagnation degree in the accumulation zone. The melt stagnation index is calibrated based on the tumbling and heating behavior of the material under a specific roll gap geometry, and its value corresponds to the actual stagnation degree. However, in S3, adjusting the roll gap wedge to reconstruct the shear force distribution changes the roll gap geometry, causing the same material stagnation degree to exhibit different tumbling activity and temperature gradients under the changed geometry. This causes the correspondence between the melt stagnation index and the actual stagnation degree to drift. Without correction, the melt stagnation index used for feedforward adjustment will deviate from the actual stagnation degree, potentially leading to inappropriate direction or amplitude of feedforward adjustment, or even counterproductive results from continuing adjustment in already alleviated sections. Therefore, the current size of the roll gap wedge and the roll speed difference are used as inputs and written back to the interpretation benchmark of the melt stagnation index relative to the actual stagnation degree. The correspondence between the two is then corrected online. This correction relationship can be calibrated by collecting the melt stagnation index and the corresponding actual stagnation degree under different roll gap wedges and roll speed differences, and stored in the form of a lookup table or a parameterized function with the roll gap wedge and roll speed difference as independent variables. Thus, by writing back the current state of the roll gap wedge and roll speed difference to the interpretation benchmark of the melt stagnation index, the correspondence between the melt stagnation index and the actual stagnation degree does not drift after the geometry is changed, avoiding inappropriate direction of feedforward adjustment due to drift of the interpretation benchmark.

[0091] In S3, in response to the melt stagnation index indicating material stagnation in the accumulation zone, feedforward adjustment is performed on the roller speed difference of the twin-roll mill and / or the feed rate of the extruder to reconstruct the shear force distribution within the roll gap and resolve material stagnation. The roller speed difference refers to the difference in the rotational linear velocities of the two rollers in the twin-roll mill; the feed rate refers to the rate at which the extruder supplies material to the accumulation zone; and the shear force distribution within the roll gap refers to the spatial distribution of the shear force exerted on the material by the relative shearing of the two rollers within the roll gap. In practice, adjusting the roller speed difference changes the relative shear strength of the material by the two rollers, thereby altering the shear force exerted on the material within the roll gap; adjusting the feed rate changes the amount of material accumulated in the accumulation zone, thereby changing the filling and shearing state of the material within the roll gap. Both of these factors affect the shear force distribution within the roll gap, causing the stagnant material to be re-sheared and renewed.

[0092] After the material stagnates in the accumulation zone, it continues to be subjected to shear heat. Once the temperature enters the range of irreversible thermal degradation, the thermal degradation becomes irreversible, and the degraded material cannot be restored through post-processing. Therefore, this method performs feedforward regulation when the melt stagnation index indicates stagnation, but before the material enters the irreversible thermal degradation stage. This reconstructs the shear force distribution within the roll gap before degradation begins, thus resolving the material stagnation before it evolves into irreversible degradation.

[0093] Feedforward regulation can be applied to either the roller speed difference or the feed rate, or both simultaneously. Adjusting only the roller speed difference directly enhances shear at the stagnation point by changing the relative shear strength between the two rollers. Adjusting only the feed rate reduces material accumulation at the stagnation point, thus restoring shear renewal. When both are applied simultaneously, both shear strength and accumulation are changed concurrently. The appropriate approach can be chosen from these three options depending on the specific stagnation situation, reconstructing the shear force distribution within the roller gap using different execution paths. As a result, after the shear force distribution is reconstructed, the material at the stagnation point is re-driven by roller shearing and renewed, resolving material stagnation before irreversible thermal degradation begins.

[0094] In some embodiments, refer to Figure 4 S3 includes sub-steps S31 to S33, used to first determine the cause of material stagnation and then distribute the adjustment amount to the corresponding execution amount according to the cause. Material stagnation can be divided into three categories according to its cause: excessive material accumulation, local overheating, and insufficient shear. Excessive material accumulation refers to the situation where too much feed causes the material to accumulate in the accumulation area to exceed the corresponding thickness threshold, and the bottom material is difficult to be driven by the roller and thus stagnates. Local overheating refers to the situation where the material has been heated due to stagnation, causing the local temperature to rise significantly. Insufficient shear refers to the situation where the shear strength of the roller on the material is insufficient, resulting in sluggish material tumbling. The adjustment directions required for the three types of causes are not the same. If the same method is used to adjust them all without distinguishing the causes, the adjustment direction may be incorrect: for example, if the roller speed difference is increased for the excessive material accumulation type, it will further aggravate shear heat generation when the accumulation thickness has exceeded the thickness threshold.

[0095] S31. Determine the axial segment in the melt stagnation index distribution that indicates material stagnation as the target axial segment. Based on the melt stagnation index distribution along the roller axis obtained in S2, select the axial segment that indicates material stagnation as the target axial segment to be adjusted.

[0096] S32. Based on the temperature gradient component of the target axial segment, the accumulation thickness of the material profile in the visible light image, and the material tumbling speed, determine the cause of material stagnation in the target axial segment. Stagnation causes include excessive material accumulation, localized overheating, and insufficient shearing. The temperature gradient component reflects whether the target axial segment has been significantly heated, the accumulation thickness of the material profile reflects the amount of material accumulated in that segment, and the material tumbling speed reflects the degree to which the material in that segment is driven by the rollers. Combining these three factors allows for the determination of the cause of stagnation.

[0097] S33. Based on the cause of stagnation, the adjustment amount of the feedforward regulation is diverted to the corresponding execution amount. For the excessively thick material accumulation type, the feeding rate is reduced; for the insufficient shearing type, the roller speed difference is adjusted; and for the local overheating type, both the roller speed difference and the feeding rate are adjusted simultaneously. For the excessively thick material accumulation type, the main cause is that the material accumulation thickness exceeds the thickness threshold, so the feeding rate is reduced to thin the accumulation. For the insufficient shearing type, the main cause is insufficient shear strength, so the roller speed difference is adjusted to enhance shearing. For the local overheating type, the material has been significantly heated, so the feeding rate is reduced to thin the accumulation, and the roller speed difference is adjusted to improve shearing, so that the two work together to resolve the problem as quickly as possible.

[0098] In S32, the determination of the cause of stagnation can be based not only on the combination rule of the temperature gradient component, the accumulation thickness of the material profile, and the material tumbling speed, but also on using the above three features as inputs and a pre-trained classifier to determine the cause of stagnation. Therefore, by first determining the cause of stagnation and then diverting the adjustment amount to the corresponding execution amount, the stagnation can be addressed by reducing the feeding rate for excessive material accumulation, adjusting the roller speed difference for insufficient shearing, and coordinating the adjustment for localized overheating, thus avoiding inappropriate adjustment direction due to indiscriminate identification of the cause.

[0099] In other embodiments, the cause of material stagnation in the target axial segment can be determined according to the following criteria: If the area of ​​local hot spots in the temperature gradient component exceeds the corresponding area threshold, it is classified as local overheating, where the material has formed a significant high-temperature zone due to stagnation and heating. If the material profile's accumulated thickness exceeds the corresponding thickness threshold and the material tumbling speed is lower than the corresponding speed threshold, it is classified as excessive material accumulation, where the material's accumulated thickness exceeds the thickness threshold and tumbling is sluggish, but it has not yet been significantly heated. If the material profile's accumulated thickness does not exceed the thickness threshold and the material tumbling speed is lower than the speed threshold, it is classified as insufficient shear, where the material's accumulated thickness does not exceed the thickness threshold but tumbling is sluggish, indicating that the stagnation originates from insufficient shear strength rather than excessive material accumulation. The above criteria, based on a combination of local hot spot area, material profile accumulated thickness, and material tumbling speed, distinguish the three types of stagnation causes. The thickness threshold is determined as follows: Under normal calendering conditions of the twin-roll mill, the accumulated thickness of the material profile is collected for each axial segment, and its average value over a period of time is taken as the baseline of the accumulated thickness of that axial segment; the thickness threshold of that axial segment is taken as 1.2 to 2.0 times its accumulated thickness baseline. Accordingly, the term "excessive material accumulation" in this application refers to the accumulated thickness of the material profile at that axial segment reaching more than 1.2 times its accumulated thickness baseline. The lower limit of 1.2 times is used to prevent fluctuations in the accumulated thickness under normal operating conditions from being misjudged as excessive material accumulation; the upper limit of 2.0 times is used to prevent the situation where the accumulated thickness has clearly exceeded the normal range and the bottom material is indeed difficult to be moved by the rollers from being missed. The accumulated thickness baselines of each axial segment may not be equal due to their different positions on the roller axis, therefore the thickness threshold is determined separately for each axial segment. In addition, the above-mentioned discrimination thresholds can also be determined by collecting known stagnant samples belonging to the local overheating type, the material accumulation thickness type, and the insufficient shear type, and taking the discrimination values ​​that make the three types of causes as distinguishable as possible in terms of local hot spot area, material outline accumulation thickness, and material tumbling speed.

[0100] In some embodiments, for axial sections identified as having excessive material accumulation, the temperature gradient component of that axial section is monitored over time. In response to the increase in the temperature gradient component over time, the material stagnation in that axial section is determined to be a transition from excessive material accumulation to localized overheating, and the feedforward adjustment for that axial section is upgraded in advance. Although the material in the excessively thick section has not yet been significantly heated, the material thickness exceeding the thickness threshold will trap the continuously input shear heat from the rollers, making it difficult for it to dissipate. As heat accumulates, the temperature in this section gradually rises, and the cause of stagnation evolves from excessive material accumulation to localized overheating. If the original adjustment is maintained only for the initially identified excessive material accumulation, the material temperature may already be close to the temperature range of irreversible thermal degradation by the time it evolves into localized overheating. Therefore, by monitoring the rising trend of the temperature gradient component of the axial section with excessive material accumulation over time, the section can be identified as a potential migration point in the early stages of the evolution from excessive material accumulation to local overheating. The feedforward adjustment of this section can be upgraded in advance, for example, from simply reducing the feed rate to simultaneously reducing the feed rate and adjusting the roller speed difference, so as to accelerate the resolution before it evolves into local overheating.

[0101] In other embodiments, the roll gap of the twin-roll mill is provided with roll gap adjustment mechanisms at both ends of the axial direction of the rolls. The roll speed difference acts on the entire roll gap, and adjusting the roll speed difference will simultaneously change the shear intensity at various points along the axial direction of the roll gap. However, material stagnation often only occurs in a local section along the axial direction. If the shear of the stagnant section is enhanced only by the global execution amount of the roll speed difference, the shear of the other normal sections of the roll gap will also be enhanced, which may introduce excessive shearing and heat generation in the normal sections. In order to enhance the shear of the stagnant section while reducing the disturbance to the other sections, the feedforward adjustment in S3 also includes: determining the axial position of the axial section where material stagnation occurs based on the melt stagnation index distribution, adjusting the difference in roll gap at both ends of the axial direction to actively form a roll gap wedge that is monotonically gradually changing along the axial direction, so that the narrow end of the roll gap wedge is located at the end closer to the axial position, so that the shear force in the roll gap increases towards the narrow end along the axial direction, and the overall level of shear force is adjusted by the roll speed difference, and the distribution of shear force along the axial direction is adjusted by the roll gap wedge.

[0102] The roller gap adjustment mechanism is located at both ends of the roller gap along the axial direction, used to adjust the distance between the two ends of the roller gap. When the distances at both ends are unequal, the roller gap forms a gradually changing wedge-shaped gap along the axial direction, i.e., a roller gap wedge. The axial distance of the roller gap is determined by the difference in roller gaps at both ends and is monotonically gradually changing, with its narrow end located at one of the two ends of the axial direction. The smaller the roller gap distance, the stronger the compression and shearing of the material within the roller gap. Therefore, by adjusting the difference in roller gaps at both ends so that the narrow end of the roller gap wedge is located at the end of the axial direction closest to the stagnant axial section, the shearing force within the roller gap increases axially towards that narrow end, thereby creating a directional shear enhancement in the stagnant axial section. In this way, the roller speed difference adjusts the overall level of the shearing force within the roller gap, and the roller gap wedge adjusts the axial distribution of the shearing force. These two actuators act on the overall and local distribution of the shearing force, respectively. Their orthogonal cooperation allows the stagnant section to receive targeted shear enhancement, while the section far from the narrow end is relatively less affected. The size of the roll gap wedge, which is the difference in the distance between the two rolls, has a corresponding relationship with the increase in shear force at the stagnant position. The required wedge size can be determined based on the degree of stagnation. This relationship can be calibrated by simulating or measuring the shear force distribution within the roll gap under different wedge sizes. Thus, by adjusting the overall level of shear force using the roll speed difference and adjusting the axial distribution of shear force using the roll gap wedge, these two actuations act on the whole and the local respectively, enabling targeted shear enhancement in the stagnant section, while the section far from the narrow end is relatively less affected.

[0103] Optionally, the axially oriented wedge-shaped roll gap can be formed by adjusting the roll gap adjustment mechanism at both ends of the roll gap to make the roll gap unequal, by slightly intersecting the axes of the two rollers, or by applying a bending moment to the ends of the roller shafts. Making the roll gap unequal at both ends is achieved by directly changing the distance between the two ends using the roll gap adjustment mechanism; slightly intersecting the axes of the two rollers involves deflecting the axes of the two rollers by a small angle in the horizontal plane, causing the roll gap distance to gradually change axially; applying a bending moment to the ends of the roller shafts causes a slight bending deflection in the rollers, resulting in a gradually changing roll gap distance axially. All three methods create a gradually changing wedge-shaped gap within the roll gap, and one method can be selected based on the roller system structure.

[0104] In some embodiments, in S3, while adjusting the difference in roller spacing at both ends of the roller gap to form a roller gap wedge, the axial distribution of the feeding rate is simultaneously adjusted to maintain the thickness integral of the output material along the axial direction at a preset target cross-sectional area. The thickness integral is the cross-sectional area of ​​the output material along the axial direction, representing the output amount per unit output length of the twin-roll mill. Forming a roller gap wedge changes the axial spacing distribution of the roller gap, and the roller gap spacing directly determines the thickness of the output material at that point. Therefore, while the wedge enhances shearing in the stagnant section, it also makes the thickness of the output material along the axial direction uneven. To compensate for the wedge's effect on the output, while adjusting the difference in roller spacing, the axial distribution of the feeding rate is simultaneously adjusted. In sections where the roller gap spacing is reduced, the material supply at those sections is adjusted accordingly, maintaining the thickness integral of the output material along the axial direction at a preset target cross-sectional area. Thus, while reconstructing the shear distribution with a roller gap wedge, the feeding rate is simultaneously distributed to compensate for the wedge's effect on the output material, maintaining the thickness integral of the output material along the axial direction at the target cross-sectional area.

[0105] In other embodiments, the rollers of the twin-roll mill employ a medium-high roller profile with a larger diameter in the middle of the roller surface than at both ends. This is to pre-compensate for the deflection of the rollers under pressure, and the residual compensation for deflection by the medium-high roller profile is verified by the melt stagnation index of the axial section located in the middle of the roller's axis. When calendering materials, the rollers bear axially distributed pressure, causing a bending deflection in the middle of the rollers away from the roll gap. This results in an increased roll gap in the middle, weakened shearing of the material in the middle, and a tendency for stagnation. The roll gap wedges formed by the roller gap adjustment mechanisms located at both ends of the axial direction act on the ends of the roll gap, making it difficult to compensate for the deflection in the middle of the rollers. By employing a medium-high roller profile with a larger diameter in the middle of the roller surface than at both ends, the larger diameter in the middle of the roller pre-compensates for the deflection in the middle after pressure, making the roll gap more uniform along the axial direction after pressure. Because the deflection under pressure fluctuates with operating conditions, the fixed convexity of the medium-high roll type may not perfectly compensate for the current deflection. Therefore, the melt stagnation index of the axial section located in the middle of the roll's axis is used as an indicator of residual compensation: if the melt stagnation index of the middle axial section is still too high, it indicates that the middle roll gap is still too large and the compensation is insufficient. The convexity can be determined according to the bending deflection of the roll under typical calendering load, so that the convexity at the two ends of the middle of the roll surface compensates for the deflection at the two ends of the middle of the roll under the typical load, thereby making the roll gap after pressure tend to be uniform along the axial direction under typical load.

[0106] Optionally, based on the melt stagnation index of the axial section located in the middle of the roller's axis, residual deflection of the roller due to changes in operating conditions is dynamically compensated by applying a bending moment to the roller or by slightly intersecting the roller axes. The central convexity of the medium-high roller type is fixed during roller manufacturing and can only compensate for deflection under a specific load. When the calendering load changes with material quantity, viscosity, or process conditions, the fixed central convexity will overcompensate under low loads and undercompensate under high loads, leaving residual deflection that varies with operating conditions. Therefore, based on the melt stagnation index of the middle axial section, which reflects the shear condition in real time, a bending moment is dynamically applied to the roller or the intersection angle of the two roller axes is dynamically adjusted, so that the central roll gap is compensated in real time for changes in load: compensation is increased when the central melt stagnation index is high and decreased when it is low. The correspondence between the melt stagnation index in the central axial section and the required dynamic compensation amount can be established by calibration under different rolling loads, while the compensable range for applying bending moment or adjusting axis intersection is determined by the stroke of the bending roll mechanism or the adjustable angle range of the axis intersection mechanism.

[0107] In some embodiments, in step S3, based on the melt stagnation index indicating material stagnation in the accumulation area, a stagnation index sequence is constructed for each axial segment in chronological order. The upward trend of the melt stagnation index is identified based on this sequence, and feedforward adjustment is performed on the axial segment only when the upward trend reaches a preset trend condition. Using only whether the melt stagnation index exceeds a threshold at a certain moment as the stagnation criterion may result in short-term threshold exceedances due to instantaneous fluctuations in material tumbling or image noise. Immediate adjustment based on this could frequently apply unnecessary adjustments to segments that are not actually continuously deteriorating. To filter out such short-term fluctuations, the melt stagnation index of each axial segment is arranged in chronological order to form a stagnation index sequence. This sequence identifies whether the melt stagnation index shows a continuous upward trend, and feedforward adjustment is performed on the axial segment only when the upward trend reaches a preset trend condition, thus only acting on segments where stagnation is continuously worsening. The upward trend can be identified by the stagnation index sequence rising at a slope exceeding a threshold within a preset time window, or by the number of consecutive rises reaching a preset number. Considering that thermal degradation occurs after the material temperature enters the irreversible range, the preset time window and threshold can be set so that the total delay from identification to triggering is less than the time required for the material to rise from its current temperature to the irreversible thermal degradation temperature. The latter can be estimated from the irreversible thermal degradation temperature of the material and the heating rate of the accumulation zone to ensure that the feedforward adjustment is completed before degradation.

[0108] In other embodiments, the axial segments located at both ends of the roller among multiple axial segments are designated as end dead zones. In S2, a material stagnation determination threshold independent of the other axial segments is applied to the end dead zones. In S3, a discharge operation is periodically triggered on the end dead zones. Baffles are typically installed at both ends of the roller gap to prevent material overflow. Material in close contact with the baffles is restricted in flow due to the baffles, resulting in a geometrically lower tumbling speed. Even under normal process conditions, the tumbling activity at this point is low. If a uniform stagnation determination threshold applicable to the other normal sections is used to measure the ends, the ends will be continuously misjudged as stagnant due to their geometrically inherently low tumbling activity. Conversely, if the threshold for the entire roller is relaxed to accommodate the ends, true stagnation in other sections will be missed. Therefore, the axial segments at both ends of the roller gap are designated as end dead zones, and an independent material stagnation determination threshold is applied to them to distinguish them from the geometrically inherently low speed of the other sections. Simultaneously, a discharge operation is periodically triggered on the end dead zones to discharge the material slowly stagnating at the ends, preventing overheating due to prolonged stagnation. The independent judgment threshold for the dead zone at the end can be determined by collecting the baseline of the tumbling activity at the end under normal working conditions and relaxing the activity judgment threshold at the end below the baseline, so that the geometrically necessary low tumbling activity at the end due to its proximity to the stop is not misjudged as stagnation.

[0109] Optionally, the discharge operation can be one of the following: briefly increasing the roller gap at the end dead section, briefly reversing the rollers, or scraping the material at the end dead section. Briefly increasing the roller gap at the end dead section allows the material stuck there to fall and be discharged; briefly reversing the rollers carries the material away from its original position; scraping the material at the end dead section involves directly scraping the material off the roller surface using a scraper. All three methods are used to discharge material stuck in the end dead section, and one can be selected based on the roller system structure.

[0110] The aforementioned dual-roller dynamic rheology and heat distribution visual servoing method can be implemented by a corresponding dual-roller dynamic rheology and heat distribution visual servoing system. (Refer to...) Figure 5 The system includes a dual-spectrum acquisition module, an image registration module, a stagnation index extraction module, and a feedforward servo control module. Each module is responsible for image acquisition, image registration, melt stagnation index extraction, and feedforward adjustment, respectively, in the aforementioned methods. In the figure, the material state of the twin-roll mill is continuously acquired by the dual-spectrum acquisition module, serving as the measurable disturbance on which the feedforward adjustment is based.

[0111] The dual-spectrum acquisition module includes an infrared acquisition unit and a visible light acquisition unit. The infrared acquisition unit is used to acquire infrared images of the material accumulation area in the roll gap of the twin-roll mill, and the visible light acquisition unit is used to acquire visible light images of the material accumulation area, corresponding to the image acquisition in S1 of the above method.

[0112] The image registration module is used to register the infrared image and the visible light image to the same roll gap coordinate system, corresponding to the image registration in S1 of the above method, so that the tumbling activity component and the temperature gradient component extracted from the two images correspond to each other in the same spatial position.

[0113] The stagnation index extraction module is used to extract the tumbling activity component from the visible light image and the temperature gradient component from the infrared image. The tumbling activity component and the temperature gradient component are fused to obtain the melt stagnation index. When the tumbling activity component is lower than the corresponding activity threshold and the temperature gradient component is higher than the corresponding temperature threshold, it is determined that there is material stagnation in the accumulation area, which corresponds to the extraction, fusion and determination in S2 of the above method.

[0114] The feedforward servo control module is used to perform feedforward adjustment on the roller speed difference of the twin-roll mill and / or the feed rate of the extruder in response to the presence of material stagnation in the accumulation zone, so as to reconstruct the shear force distribution in the roll gap, corresponding to the feedforward adjustment in S3 of the above method.

[0115] The modules described above are responsible for image acquisition, image registration, melt stagnation index extraction, and feedforward adjustment, respectively, so that the above method is implemented in the form of system modules. The optional implementations in the embodiments of the above method are respectively reflected as extensions of the functions of each module, which will not be elaborated here.

[0116] The same or similar parts in the various embodiments of this application may be referred to each other; the technical features of each embodiment may be combined with each other to form new embodiments without conflict.

[0117] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is used as an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above.

[0118] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A visual servoing method for dual-roller dynamic rheology and heat distribution, characterized in that, Includes the following steps: S1. Infrared and visible light images of the material accumulation area in the roll gap of the twin-roll mill are acquired using an infrared acquisition unit and a visible light acquisition unit, respectively. The roll gap is formed between the two rolls of the twin-roll mill. The infrared image and the visible light image are registered to the same roll gap coordinate system. S2. Extract the tumbling activity component, which characterizes the degree of material tumbling activity in the accumulation area, from the visible light image; extract the temperature gradient component, which characterizes the surface temperature distribution of the accumulation area, from the infrared image; fuse the tumbling activity component and the temperature gradient component to obtain the melt stagnation index, which characterizes the degree of material stagnation in the accumulation area. The melt stagnation index indicates that there is material stagnation in the accumulation area when the tumbling activity component is lower than the corresponding activity threshold and the temperature gradient component is higher than the corresponding temperature threshold. S3. In response to the melt stagnation index indicating that there is material stagnation in the accumulation zone, feedforward adjustment is performed on the roller speed difference of the twin-roll mill and / or the feed rate of the extruder to reconstruct the shear force distribution in the roll gap and resolve the material stagnation; In step S2, the material accumulation area is divided into multiple axial segments along the axial direction of the roller. The tumbling activity component and the temperature gradient component are extracted and fused for each axial segment to obtain the melt stagnation index of each axial segment, thereby forming a melt stagnation index distribution along the axial direction. S3 includes the following sub-steps: S31. The axial segment in the melt stagnation index distribution that indicates the presence of material stagnation is determined as the target axial segment; S32. Based on the temperature gradient component of the target axial segment, the accumulation thickness of the material profile in the visible light image, and the material tumbling speed, determine the cause of stagnation of the material in the target axial segment. The causes of stagnation include excessive accumulation, local overheating, and insufficient shearing. The accumulation thickness is the distance from the top edge of the material profile in the target axial segment in the visible light image to the vertical direction of the roller gap. The excessive accumulation is a stagnation cause where the accumulation thickness exceeds the corresponding thickness threshold and the material tumbling speed is lower than the corresponding speed threshold. S33. Based on the cause of the stagnation, the adjustment amount of the feedforward adjustment is diverted to the corresponding execution amount, wherein for the excessively thick material accumulation type, the feeding rate is reduced; for the insufficient shearing type, the roller speed difference is adjusted; and for the local overheating type, both the roller speed difference and the feeding rate are adjusted simultaneously. In step S3, based on the melt stagnation index indicating that there is material stagnation in the accumulation area, the melt stagnation index of each axial segment is further arranged in chronological order to form a stagnation index sequence. The upward trend of the melt stagnation index is identified according to the stagnation index sequence, and the feedforward adjustment is performed on the axial segment only when the upward trend reaches the preset trend condition.

2. The dual-roller dynamic rheology and heat distribution visual servoing method according to claim 1, characterized in that, S2 includes S2a and S2b, which are parallel: S2a. In response to the material outline being obscured in the visible light image and the inability to directly extract the tumbling activity component, the tumbling activity of the material in the accumulation area is estimated based on the rate of change of temperature distribution over time in the infrared image, and the estimated value is used as the tumbling activity component to participate in the fusion of the melt stagnation index. S2b. In response to interference with the infrared image, making it impossible to directly extract the temperature gradient component, the surface temperature distribution of the accumulation area is estimated based on the flow velocity of the material texture in the visible light image, and the estimated value is used as the temperature gradient component to participate in the fusion of the melt stagnation index.

3. The dual-roller dynamic rheology and heat distribution visual servoing method according to claim 1, characterized in that, The roller gap of the twin-roll mill is provided with roller gap adjustment mechanisms at both ends of the axial direction of the rollers; in S3, the feedforward adjustment further includes: determining the axial position of the axial segment where material stagnation occurs based on the melt stagnation index distribution, adjusting the difference in roller gap between the two ends of the roller gap to actively form a roller gap wedge that monotonically changes along the axial direction, so that the narrow end of the roller gap wedge is located at the end of the two ends of the axial direction closer to the axial position, so that the shear force in the roller gap increases towards the narrow end along the axial direction, and the roller speed difference is used to adjust the overall level of the shear force, and the roller gap wedge is used to adjust the distribution of the shear force along the axial direction.

4. The dual-roller dynamic rheology and heat distribution visual servoing method according to claim 3, characterized in that, In step S2, the correspondence between the melt stagnation index and the actual material stagnation degree in the accumulation zone is corrected online based on the current size of the roll gap wedge and the roller speed difference, so that after the roll gap wedge changes the geometry of the roll gap, the melt stagnation index still corresponds to the actual material stagnation degree in the accumulation zone.

5. The dual-roller dynamic rheology and heat distribution visual servoing method according to claim 3, characterized in that, In step S3, while adjusting the difference in roller spacing at both ends of the roller gap to form the roller gap wedge, the distribution of the feeding rate along the axial direction is coordinated to maintain the thickness integral of the output material of the twin-roll mill along the axial direction at a preset target cross-sectional area.

6. The dual-roller dynamic rheology and heat distribution visual servoing method according to claim 1, characterized in that, Among the plurality of axial segments, the axial segments located at both ends of the roller are end dead zones; in S2, a material stagnation determination threshold independent of the other axial segments is applied to the end dead zones; in S3, a discharge operation is periodically triggered for the end dead zones.

7. A dual-roller dynamic rheology and heat distribution vision servo system, characterized in that, The dual-roller dynamic rheology and heat distribution visual servoing method as described in any one of claims 1-6 includes: A dual-spectrum acquisition module includes an infrared acquisition unit and a visible light acquisition unit. The infrared acquisition unit is configured to acquire infrared images of the material accumulation area in the roll gap of a twin-roll mill, and the visible light acquisition unit is configured to acquire visible light images of the material accumulation area. An image registration module is configured to register the infrared image and the visible light image to the same roll gap coordinate system; The stagnation index extraction module is configured to extract a tumbling activity component from the visible light image and a temperature gradient component from the infrared image, fuse the tumbling activity component and the temperature gradient component to obtain a melt stagnation index, and determine that there is material stagnation in the accumulation area when the tumbling activity component is lower than the corresponding activity threshold and the temperature gradient component is higher than the corresponding temperature threshold. And a feedforward servo control module configured to perform feedforward adjustment on the roller speed difference of the twin-roll mill and / or the feed rate of the extruder in response to material stagnation in the accumulation zone, so as to reconstruct the shear force distribution in the roll gap.

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