Method for monitoring material adhesion of a steel belt in a continuous press and continuous press

Abstract

The invention relates to a method for monitoring material adhesion of at least one circulating steel belt (5a, 5b) in a continuous press (1) for material plates, in particular wooden material plates, wherein the steel belt (5a, 5b) is used to apply pressure to a press mat at a preselected belt speed to produce material plates, and the material adhesion of the circulating steel belt (5a, 5b) is monitored at least on one side of the steel belt (5a, 5b) via at least one photoelectric detector (2) by a light emitter (14) emitting a light pattern (16) onto the steel belt (5a, 5b) and a light receiver (15) receiving the light pattern (16) by reflection and transmitting it to an analysis evaluation unit (3), which determines changes. In order to keep the maintenance costs for finding harmful material adhesion small, it is provided that the material adhesion recognized on the steel belt (5a, 5b) after the start (27) of the detector measurement is transmitted to the analysis evaluation unit (3) together with absolute or relative to each other time or distance interval values.

Description

Technical Field

[0001] The invention relates to a method for monitoring the material adhesion of a circulating steel belt in a continuous press for material boards, in particular wood material boards, wherein pressure is applied to a pressing pad at a preselected belt speed with the aid of the steel belt to produce the material boards, and the material adhesion of the circulating steel belt is monitored at least on one side of the steel belt by means of at least one photodetector in such a way that a light emitter emits a light pattern onto the steel belt and a light receiver receives the light pattern by a reflection method and transmits it to an analysis and evaluation unit that determines the changes.

[0002] Furthermore, the present invention relates to a continuous press having a photoelectric detector for carrying out the method. Background Art

[0003] Typically a camera is used as the light receiver.

[0004] Material adhesion refers to the deposits of the detached parts of the press mat in the present invention, and these deposits adhere to the steel strip due to their characteristics. Below, these material adhesions are sometimes also referred to as scaling.

[0005] Typically, the material sheet is formed from, for example, wood fibers or sawdust in a continuous extrusion process, where the material, mixed with a binder and spread into a pressed mat, is shaped and solidified between two endless steel belts. However, other materials, such as plastic fibers, can also be used (in conjunction).

[0006] If parts of the press pad still have adhesive or bonding material attached, they can easily become lodged in the steel strip, resulting in unintended protrusions. The surface of the material sheet is particularly affected by the surface structure and surface quality of the steel strip. Under the applied pressure, local protrusions on the steel strip caused by material adhesion are pressed into the press pad with each cycle, causing localized defects in the subsequent sheet. A flat and uniform product surface is particularly desirable in the case of ultra-thin sheets, and material adhesion on the steel strip can negatively impact the product to the point where it can even result in scrap.

[0007] Furthermore, the steel belt is the most expensive single component of a continuous press. Due to its design and the high belt speeds of sometimes >2 m / s, manual monitoring of typical damage patterns during operation is virtually impossible. Harmful operating characteristics can only be identified by stopping the operation and inspecting the belt, and even this is difficult to achieve adequately due to the installation conditions. However, even continuously operating cleaning devices, such as those using a (rotating) cleaning brush with or without the addition of solvent, can only keep the steel belt surface clean to a certain extent. If this cleaning device is constantly acting on the steel belt, it can even lead to disturbing increased wear.

[0008] Furthermore, as soon as the steel strip enters the extrusion gap, the material deposits on the steel strip at these locations lead to higher pressures on the steel strip. This can negatively impact the steel strip and cause permanent damage, potentially leading to plastic deformations that are reflected in the finished material sheet.

[0009] Checking such a steel strip for material attachment during a stop is very time-consuming, as a single such steel strip can be up to 200 meters long. During the inspection of the steel strip, each attachment must be manually located and removed.

[0010] The use of photoelectric detectors for monitoring steel belts is well known in the papermaking industry. During the calendering process, the steel belt, which exerts pressure on the paper web, must be monitored. For example, EP 2304105 B1 describes such a method. However, adhesive deposits are rarely a concern in the papermaking industry, so the detectors described in EP 2304105 B1 are only used to detect cracks or deformations in the steel belt. Summary of the Invention

[0011] The object of the invention is to obtain automatic information about possible steel strip deposits and to facilitate cleaning operations by means of a simple method for detecting material deposits.

[0012] This object is achieved in terms of method by a method according to the invention for monitoring the buildup of material on a circulating steel belt in a continuous press for producing panels, in particular wood-based panels, wherein pressure is applied to a press mat at a preselected belt speed by means of the steel belt to produce the panels, and the buildup of material on the circulating steel belt is monitored at least on one side of the steel belt by means of at least one photodetector, in that a light emitter emits a light pattern onto the steel belt, and a light receiver receives the light pattern by reflection and transmits it to an evaluation unit that determines the change. According to the invention, material buildup detected on the steel belt after the start of the detector measurement is transmitted to the evaluation unit together with an absolute or relative time or distance interval value.

[0013] To detect material buildup, the continuity of the reflection pattern is monitored. If the reflective strip surface is covered by material buildup (mostly wood, which is non-reflective), the reflection pattern is interrupted at this point. Deviations from the original pattern are evaluated by a camera and corresponding evaluation software in the evaluation unit.

[0014] However, it is also known to remove individual material deposits on the steel strip that have been detected by detector measurements. After a single revolution of the steel strip, the same material deposits are always detected again. In continuous operation, the coordinates between the material deposits can be determined, for example, by calculating the time intervals using a preselected strip speed. This allows the precise position of the material deposits on the steel strip to be determined unambiguously. The size of the material deposits is determined by reflection measurements, making it possible to define a limit value, exceeding which requires intervention.

[0015] It is particularly advantageous if the steel strip is provided with a reference mark, which the photodetector uses as a starting point for the detector measurement.

[0016] Such a starting point can be, for example, a point in time or space at which the camera is directed when the strip starts. With the aid of a known speed increase and a known strip length, the instantaneous position of the point can be calculated at any time.

[0017] As a reference mark, a mark which is detected by the photodetector itself or a mark which is detected by another sensor which transmits this point to the evaluation unit can be used.

[0018] In the first case, for example, a dot-shaped or linear colored mark that contrasts sharply with the steel strip can be used as a reference mark, or a weld seam between the steel strips that is easily visible to a photoelectric detector system can be used as a reference mark. With each revolution of the steel strip, the reference mark is then detected again by the detector system like a trigger, and the time interval or distance interval to the material adhesion can be precisely determined continuously within just one steel strip revolution.

[0019] If the reference mark is not detected by the photodetector, it can also be recorded / photographed by another sensor and transmitted to the photodetector as a trigger signal. This could be, for example, an inductive sensor that responds to one or more notches in the strip. However, the drive signal of the motor driving the strip (e.g., via a strip deflection roller) could also be used to precisely trigger the starting point or reference point.

[0020] This eliminates slip-related deviations that could occur relative to the measurement starting point, which is determined only once when starting the continuous press. The starting point of the detector measurement is therefore reset with each revolution by the reference mark.

[0021] Preferably, each time the material passes the photoelectric detector, a time stamp is stored simultaneously.

[0022] Furthermore, it is advantageous if, during at least one further passage of the material deposit past the photodetector, the image size of the material deposit is compared with one of the previously occurring passages.

[0023] In this way, the dimensional development of the material attachment can be tracked over time. However, if a predefined limit value is exceeded or approached, a warning signal is automatically generated.

[0024] Real-time data is time-stamped and stored in a database. This allows local changes in the steel strip to be tracked over time. For example, if the steel strip experiences increasing material buildup over a short period of time, this can be compared with process parameters to identify possible causes and prevent further material buildup. This also makes it easy to monitor the overall condition and quality of the steel strip.

[0025] It should be noted that the evaluation unit can also be programmed to be self-learning, so that after a learning phase it can independently and automatically issue a warning signal when material adhesion develops to a certain extent.

[0026] Particularly preferably, the evaluation unit generates a preferably two-dimensional unfolded image of the steel strip on a display, the unfolded image including a display of material adhesion.

[0027] The coordinates of each material attachment can be entered into this rectangular representation of the steel strip at a known position. The provided time scrolling option allows for rapid identification of the development of each material attachment. Identifying the point in time when a material attachment occurred significantly simplifies the identification of its cause.

[0028] Preferably, taking into account the time or distance interval values ​​stored in the evaluation unit relative to the detector's measurement starting point, the harmful material deposit is moved to a suitable cleaning location and stopped there. There, the material deposit is at least partially removed manually or using a cleaning device. The cleaning device can, for example, be an adjustable rotating brush that does not need to extend across the entire strip width but can, depending on the specific situation, be designed for transverse movement. In addition or as an alternative, a cleaning agent or solvent can be sprayed onto the strip.

[0029] Because each material buildup is detected and stored, for example, its distance from a reference mark, any material buildup identified as serious and requiring repair can be easily moved to a specified position at a specified (slow) strip feed speed, where it can be easily reached and cleaned. This makes it particularly easy for maintenance personnel to locate and remove the material buildup. Software provisions allow for this to be made by simply clicking on the material buildup on a two-dimensional strip display using a pointing device (mouse). If the user decides to remove the material buildup on the strip, they can select the scale in the visual display, which causes the system control system to move the affected area to a preselected cleaning position. There, the area can be cleaned manually or using the cleaning device described as an example. The cleaning device should then be activated only when the material buildup is in the cleaning position, or only then, to avoid continuous stress on the strip. Material contact between the cleaning device and the strip causes natural wear on the strip surface due to abrasion. Therefore, it is desirable to keep intervention time as short as possible. The present invention makes this possible without requiring any intervention by the system operator.

[0030] The color and / or brightness of the light emitter is preferably adjusted by means of a calibration device within the field of view of the light receiver.

[0031] This minimizes environmental influences that interfere with the camera system, such as changing workshop lighting, sidelighting, changing ambient color temperature, and the varying properties of the current steel strip. To this end, the light emitter is adapted to emit any wavelength (e.g., by using RGB LEDs). By adjusting the light intensity and hue, corresponding environmental influences can be compensated. For example, in the case of slightly reddish ambient light, a blue light pattern should be selected to achieve maximum contrast with the surroundings. To determine the environmental conditions, a specially printed calibration disc, for example, is placed in the camera's field of view as a calibration device. Since the hue of the light pattern on this calibration disc is known, the environmental conditions can be determined using software.

[0032] In terms of equipment, the object is achieved by a continuous press comprising

[0033] at least one circulating steel belt for compacting the moving press mat by pressure applied by a pressure applicator;

[0034] A control system for regulating the speed of the steel strip; and

[0035] a photodetector comprising a light emitter which emits a light pattern onto the steel strip and a light receiver which is adapted to receive the light pattern by reflection and transmit it to an evaluation unit which determines the change,

[0036] The continuous press is used to implement the method according to the invention described above and is particularly characterized in that the steel strip has a starting point for detector measurement, and all further identified material attachments together with time interval values ​​or distance interval values ​​from the starting point for detector measurement can be transmitted to an analysis and evaluation unit and can be stored in the analysis and evaluation unit.

[0037] In the method of the present invention, it is also preferred that

[0038] - at least one detected material adhering to the photoelectric detector shall be configurable with a time stamp in the evaluation unit each time it passes the photoelectric detector, and / or

[0039] - the two-dimensional image of the steel strip should be displayable together with the material adhesion on a display connected to the evaluation unit, and / or

[0040] The drive of the steel strip should be adapted, by means of a control system for regulating the steel strip speed, to move severe material deposits to a repair or maintenance station based on the recorded distance between the starting point of the detector measurement and the material deposit.

[0041] Furthermore, it is advantageous if at least one light line extending across the width of the strip is used as the light pattern. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be described in detail below with reference to the accompanying drawings.

[0043] Figure 1 The inlet of the continuous press is shown and the detector and the analytical evaluation unit are schematically shown;

[0044] Figure 2 A light emitter is shown;

[0045] Figure 3 shows the light pattern on the steel strip;

[0046] Figures 4a to 4c shows the change in the reflected light pattern during movement of a steel strip with material attached; and

[0047] Figure 5 A diagram of a steel strip on a display is shown. DETAILED DESCRIPTION

[0048] exist Figure 1The figure shows the inlet area of ​​a continuous double-belt press 1, such as that used to produce material boards, particularly those made of wood. The continuous press 1, shown in its basic structure, comprises an upper press part 1a with a heated upper platen 7a and a lower press part 1b with a heated lower platen 7b. A frame 12 connects the upper and lower press parts 1a, 1b, and the pressure applicator 8 for applying pressure is also supported within the frame. In the upper and lower press parts 1a, 1b, circulating steel belts 5a and 5b are guided, forming a press nip for a press cushion (not shown). The steel belts 5a and 5b are supported on the platens 7a and 7b with rollers 10 interposed between them. The rollers 10 are guided on a circulating roller chain (not shown) via roller bearing pins. The chain is guided via chain deflection rollers 11, indicated by dotted lines.

[0049] The steel strips 5a, 5b are guided in a circular motion via upper and lower steel strip deflecting rollers 9a, 9b. Similarly, similar steel strip deflecting rollers are provided at the press ends (not shown). For reasons of clarity, the overall diagram of the continuous double-belt press 1 is not shown, as the steel strips 5a, 5b can be up to two hundred meters long.

[0050] In the inlet region of the continuous press 1 shown, the upper steel belt 5 a and the lower steel belt 5 b form a wedge-shaped inlet region for a press mat (not shown), which is also referred to as an inlet opening 6 .

[0051] In the illustrated embodiment, a photodetector 2 is arranged in front of each deflecting roller 9a, 9b. This photodetector 2 consists of a light emitter 14 (e.g., an LED strip) and a light receiver 15 (e.g., a camera system). Depending on the press width, the images from multiple cameras across the width can be combined to form a single image. The light emitter 14 consists of at least one light source that directly or indirectly projects a light pattern 16 onto the reflective strip surface. In this embodiment, the light pattern 16 is projected toward the outer surface of the deflecting rollers 9a, 9b and thereby impinges on the strip surface of the upper or lower strip 5a, 5b. High strip tension exists on the deflecting rollers 9a, 9b, so that the strips 5a, 5b rest directly on the outer surface. The camera system 15 detects both the projected light pattern 16 and the surrounding strip surface within the camera's viewfinder. Due to the uniform reflective properties of the intact and clean strips 5a, 5b, the projected light pattern 16 is reflected without distortion and detected by the camera system 15. The light pattern 16 can be designed in a variety of different shapes. A checkerboard pattern, raster lines, or color image projections can be used. In this embodiment, at least one horizontal line should be displayed across the width of the light strip. However, in principle, the light pattern can also be projected onto other locations of the steel strips 5a, 5b that do not extend straight around the deflecting rollers 9a, 9b.

[0052] The reflections recorded by the camera system are transmitted to an evaluation unit 3 and can be checked there for changes. They can also be displayed on a display 17. If material buildup obscures the area where the light pattern 16 (a line in this example) projected by the light emitter 14 onto the steel strip surface is projected, the reflections received / photographed by the camera system 15 will change or even disappear completely.

[0053] For example, Figure 2 A light emitter 14 is shown, and Figure 3 The diagram shows a light pattern 16 on the steel strip. The light emitter comprises, for example, a light source 19 in the form of a strip of LEDs the same width as the steel strip, a light shield 21, and a diffuser 20. The arrows indicate the emission of two light rays. These rays are imaged as two lines on the steel strips 5, 5a, 5b as the light pattern 16. Also indicated is a camera frame 23, for example, which actually monitors this reflected light pattern as the steel strips 5, 5a, 5c move.

[0054] To detect such material buildup, various operating principles can be employed. Geometric deformations in the steel strip surface alter the reflection angle of the light pattern 16, thus optically bending the projected light pattern. However, typically, when the light pattern travels over a material buildup, it is no longer reflected at all. Deviations from the original pattern are detected by the light receiver 15 and corresponding evaluation software in the evaluation unit 3.

[0055] Because the positions of light emitter 14 and light receiver 15 (camera system) are fixed, the position of light pattern 16 relative to camera viewfinder 23 is initially constant. As the steel strip continues to circulate, the light pattern repeatedly scans every surface point of the strip. If a material adheres to the light pattern, the effect just described occurs.

[0056] By converting the unreflected strip or face segments in the image into the actual strip width, the location of the material attachment relative to the strip width is determined. Software can also be used to determine the position along the direction of travel. This requires, for example, tracking the strip's path using a reference mark or simply starting from its starting point. Furthermore, existing features, such as weld seams, can be used as synchronization features, acting like triggers. Because the speed of the strip 5 is continuously measured by sensor 13 and the strip length is already known, accurately determining the location of the material attachment relative to the strip length from the starting point or reference point of the detector measurement is not a problem.

[0057] To better understand the reflection phenomenon, Figures 4a to 4c The images as a time sequence, ie in fact as individual frames of a video, show how material adhesion can be detected and evaluated. Figure 4a A possible camera frame 23 can be seen in the figure, which shows a straight line as a light pattern 16 on the steel strip 5, wherein the light pattern 16 just misses the material deposit 25. The arrow here indicates the direction of the steel strip's circulation. Above this straight line, i.e., close to the light pattern, there is a geometric material deposit 25 on the steel strip surface. This material deposit then becomes tangential to the light pattern, i.e., the straight line 16, at its edge region, due to the steel strip's circulation. Thus, until the center of the material deposit lies on the light pattern line, a reflection interruption can be determined (cf. Figure 4b ).Show Figure 4c It shows how the material attachment leaves the light pattern 16 and the light pattern continues to extend again.

[0058] When material adhesion is detected, its location and size are stored in the database of the evaluation unit 3. A report can then be sent to the plant operator on request based on predefined rules. The plant operator can manually assess the condition of the steel strip via an optional display 17 and determine the need for local repairs.

[0059] Figure 5 The steel strip 5 with its material attachments is schematically shown on the display 17 in the unfolded state. The left edge 27 of the steel strip corresponds to the detection starting point. After the system is stopped, by clicking on a corresponding material attachment 25 with the mouse (see the cursor 26 shown), the software can output the exact coordinates 29 related to the detection starting point 27. In addition, the steel strip 5 can be moved to a previously determined cleaning position 18 via an interface to the system control system 4. Figure 1 As shown in FIG, the cleaning position 18 can be equipped with a cleaning brush 18a that can be adjusted toward the steel strips 5, 5a, 5b. However, any other type of cleaning agent / cleaning device can also be selected, including spraying liquid solvents. This saves the operator from having to manually find the location where the material is attached.

[0060] Regarding the clicked material attachment, not only are the exact coordinates 29 shown on the expanded view 24, but a time mark 30 is also provided on the right side of the display, for example, at which the material attachment 25 had the shown dimensions, wherein the development of the dimensions can be traced via the time selection key 28.

[0061] Reference Signs List

[0062] 1 Continuous double belt press 1a Upper press section 1b Lower press part 2 Photodetector 3 Analysis and Evaluation Unit 4 Steel belt speed control system 5a Upper steel belt 5b Lower steel belt 6 Import port 7a Upper pressure plate 7b Lower pressure plate 8 Pressure applicator 9a Upper belt turning roller 9b Lower belt turning roller 10 Roller 11 Chain steering roller 12 frame 13 Steel belt speed sensor 14 Optical Transmitter 15 Optical receiver, camera system 16 Light pattern, straight line here 17 monitor 18 Cleaning location 18a Attachable cleaning brush 19 light source 20 diffuser 21 visor 22 Calibration device 23 Camera viewfinder 24 Expanded view of steel strip 5 25 Material Adhesion 26 cursor 27 Detection starting point 28 Time selection key 29 coordinate 30 Time stamp

Claims

1. A method for monitoring the material adhesion of at least one circulating steel strip (5a, 5b) in a continuous press (1) for producing material sheets, wherein pressure is applied to a press pad by means of the steel strip (5a, 5b) at a preselected strip speed to produce the material sheet, and the material adhesion of the circulating steel strip (5a, 5b) is monitored via at least one photodetector (2) at least on one side of the steel strip (5a, 5b) in such a way that a light emitter (14) emits a light pattern (16) onto the steel strip (5a, 5b) and a light receiver (15) receives the light pattern (16) by a reflection method and transmits it to an evaluation unit (3), which determines the changes, characterized in that: The material deposits detected on the steel strip (5a, 5b) after the start of the detector measurement are transmitted to the evaluation unit (3) together with absolute or relative time interval values ​​or distance interval values.

2. The method according to claim 1, wherein: The steel strips (5a, 5b) have reference marks which are used by the photodetector as starting points (27) for the detector's measurements.

3. The method according to claim 1 or 2, characterized in that: Each time a material deposit (25) passes the photodetector (2), a time stamp (30) is stored simultaneously.

4. The method according to claim 1 or 2, characterized in that: When the material deposit (25) passes the photodetector (2) at least one more time, the image size of the material deposit (25) is compared with one of the previously occurring passes.

5. The method according to claim 1 or 2, characterized in that: The evaluation unit (3) generates a spread (24) of the steel strip (5a, 5b) on a display (17), the spread including a material adhesion display.

6. The method according to claim 3, wherein: Taking into account the time interval values ​​or distance interval values ​​stored in the evaluation unit (3) relative to the starting point (27) of the detector measurement, the harmful material deposits (25) are moved to a suitable cleaning position (18) and at least partially removed there manually or using a cleaning device.

7. The method according to claim 1 or 2, characterized in that: The color and / or brightness of the light emitter (14) is adjusted by means of a calibration device (22) within the field of view of the light receiver (15).

8. The method according to claim 1 or 2, characterized in that: The material board is a wooden material board.

9. The method according to claim 5, characterized in that: The expanded view (24) is a two-dimensional expanded view.

10. A continuous press comprising: at least one circulating steel belt (5a, 5b) for compacting the moving pressing mat by means of pressure applied by a pressure applicator (8); A control system for regulating the speed of the steel strip (4); and a photodetector (2) comprising a light emitter (14) which emits a light pattern (16) onto the steel strip (5a, 5b) and a light receiver (15) which is adapted to receive the light pattern (16) by reflection and transmit it to an evaluation unit (3) which determines the change, The continuous press is used to implement the method according to any one of claims 1 to 9, Its characteristics are: The steel strip (5a, 5b) has a starting point (27) of the detector measurement, and all further detected material adhesions together with time interval values ​​or distance interval values ​​from the starting point of the detector measurement can be transmitted to the evaluation unit (3) and can be stored in the evaluation unit.

11. The continuous press according to claim 10, characterized in that: At least one detected material deposit (25) can be assigned a time stamp (30) in the evaluation unit (3) each time it passes the photodetector (2).

12. The continuous press according to claim 10 or 11, characterized in that: The two-dimensional image of the steel strip (5a, 5b) can be displayed as a development image (24) together with the material adhesion on a display (17) connected to the evaluation unit (3).

13. The continuous press according to claim 10 or 11, characterized in that: The drive of the steel strips (5a, 5b) is adapted to move heavy material deposits to a cleaning position by means of a control system (4) for regulating the speed of the steel strips, depending on the registered distance between the starting point (27) measured by the detector and the material deposit.

14. The continuous press according to claim 10 or 11, characterized in that: At least one light line extending across the width of the steel strip is used as the light pattern (16).

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