DE3231001A1 - Method for determining the thickness of the wedge of a material upstream of a pair of rollers - Google Patents

Abstract

The thickness of the wedge (8) of a material upstream of a pair of rollers through the gap of which the material is being moved is measured using a diode-row camera (9). The wedge is illuminated and scanned by means of the diode-row camera (9), which generates a video signal (24, 40) which is evaluated. The evaluation includes investigating whether the video signal is above or below a prescribable threshold. The signals below the threshold are evaluated as wedge ends. The integration time of the diode-row camera (9) is regulated in such a way that a video signal value measured at a selected scanning point is held constant. <IMAGE>

Description

Method for determining the thickness of the kneading of a material a pair of rollers The invention relates to a method of detection the thickness of the kneading of a material in front of a pair of rollers, through their gap the material is moved through, the kneading along at least one over its A wide line is illuminated and scanned with a diode line camera which generates a video signal from which the kneading thickness is obtained.

PVC foils are mainly produced on calenders.

A high film quality can thus be achieved. PVC chunks or a PUC strand will be in the gap between a first pair of calender rolls transported.

The rollers compress the PVC. This creates on one of the Rolls a coating, the so-called skin, which is fed to a further nip becomes that is smaller.

There can be several pairs of calender rolls between which In each case, smaller and smaller roller gaps are provided in the transport direction of the plastic are.

A characteristic of the calendering process is the mass kneading process the nips.

In addition to the uniform thickness, the surface texture is a essential quality feature of calendered film. Here is the knead, the excess melt in front of the roll gap, an important influencing variable.

For these reasons, the smallest possible, uniform kneading is used desired, its amount of melt in a reasonable relation to the time constant of the entire system.

In most cases, the dough is in the shape of a cigar and shows a rotational movement, which often consists of spiraling movements of the surface is superimposed.

Since the kneading directly influences the film quality, is a metrological detection of the kneading geometry aimed at, for example, a To avoid too large kneading diameter, because the stored material is too large is slowly exchanged. Due to the friction of the rollers, the knead also occurs Shear forces, which are converted into mechanical energy. Therefore shows the Kneads at a higher temperature than the skin on the roller.

The kneading geometry is influenced by many factors. There are Dependencies, for example, on the degree of filling of the material feed, on the roll gaps, from roll bending and tilting, as well as from friction.

The triangulation method can be used for contactless recording of the kneading dimensions be used. With this method, a light spot appears on the kneading surface projected, the size of which changes depending on the kneading diameter. However, it can only colored plasticine can be measured, as only then will the light mark on the surface be good is visible.

The Using a line scan camera. The kneading is done along at least one line illuminated along which the kneading dimensions are to be recorded. The illuminated Place is observed with a diode line camera connected to evaluation electronics connected. The diode line camera is aimed at the center of the clay.

The invention is based on the object of a method of the above described type to the effect that the thickness of the kneading independently determined by the color of the kneading and the illuminance on the kneading surface can be.

This object is achieved by the measures described in claim 1 solved. With this method, the video signal is set to values above and below the Threshold evaluated. The kneading thickness corresponds to the width of the video signal in the Middle between the signal components lying below the threshold. The others Signals above the threshold are masked out. That when scanning between Knead and roller occurring signal minimum of the video signal is lower than that at The signal minimum resulting from the scanning between the clay and the skin. One cause is to see in the fact that clay and fur are the same color. With the claim 1, the influence of disturbances on the measurement result is reduced. In particular, the impairment of the measurement accuracy due to color and 9 Illuminance influences avoided, which would change the width between the Can cause minima of the video signal.

The calender operator therefore always has a measure of the kneading diameter to disposal. The kneading thickness can be optimally adjusted by taking appropriate measures will. This eliminates the problems that occur when the kneading thickness is too large or too small Avoid disadvantages. If the kneading diameter is too large, the material becomes in the core zone is exchanged only slowly, so that the melt thermally due to the long residence time can be harmed. In addition, when rotating a large kneading bead Air bubbles become trapped. To keep the thermal load on the material low a short dwell time in the knead is therefore desirable, i.e. H. small kneading diameter. On the other hand, too little kneading has on the one hand only little mixing of the melt result. On the other hand, it harbors the risk of demolition because of the material supply in the kneading must be in reasonable proportion to the material flow.

The material supply in the kneading must be adapted to the time constant of the system be.

In a preferred embodiment it is provided that the predeterminable Threshold during successive scans of the kneading with the diode line camera, starting from a low threshold, as long as to higher thresholds is shifted until two signals lying on both sides of the kneading center are detected that are below the threshold. This automatically increases the threshold adjusted to the most favorable value for the respective material. The kneading thickness can also can still be measured in cases where the maximum of the video signal is in the middle of the kneading is not very pronounced.

In another advantageous embodiment it is provided that the shift of the threshold value is carried out separately for each kneading half and that when the respective kneading half is scanned when the value falls below the threshold value occurring signal is evaluated as the thickness of the kneading half.

With the measures explained above, the effect becomes more different Signal minima when scanning the transition point from knead to roller and from skin too putty on the measurement result eliminated.

Preferably, the video signals are several consecutive Samples of the kneading (8) superimposed on each other, the obtained from the superposition Signal with the predeterminable threshold for detecting those below the threshold Values corresponding to the kneaders are compared.

With this embodiment difficulties are eliminated in the measurement of kneading occur when the material is intended for transparencies is. It has been found that the calendering of transparencies is extremely glassy Play dough. The light of the lighting penetrates into the interior with such kneading a. As the clay rotates occur constantly changing conditions in relation to the light reflected back to the diode line camera. This leads to, that not only the transitions between putty and skin and between putty and roller Cause signal minima that are below the threshold.

The minima at the kneading ends remain on that due to several scans predetermined time scale, which is preferably several seconds, to the same Places, while the minima occurring due to disturbances are averaging. Therefore, the minima corresponding to the kneaders can be easily recognized.

The invention is illustrated below with reference to a drawing Embodiment described in more detail, from which further features and advantages result. 1 shows a device for calendering film in the scheme, FIG. 2 shows an arrangement for measuring the kneading thickness in the scheme, FIG. 3 shows the structure of a of the arrangement according to FIG. 2 in the kneading thickness measurement for a number of materials 4 shows the structure of a video signal generated by the arrangement according to FIG video signal generated during the kneading thickness measurement with other materials, Fig. 5 a device with two monitoring kneading between two calender rolls Diode line cameras.

A device for calendering film contains calender rolls, of which in Fig. 1, the rollers 1, 2, 3 and 4 are designated in more detail. Via a conveyor belt 5 plastic parts 6 are transported into the space between the two rollers 1, 2, their axes in a horizontal plane are arranged. The plastic parts 6 are pressed together by the rollers 1, 2. It is formed after that between the two Rolls prevailing gap a covering 7 made of plastic on the roller 2. This covering 7, which is also referred to as "skin", comes to a roll gap between the two rollers 2 and 3 is arranged. This roll gap is smaller than the gap between rollers 1 and 2.

Therefore a kneading 8 occurs in front of the roll gap. The roll 3 is transported the covering coming from the roll gap to another roll gap between the rolls 3 and 4. The roll gap between rolls 3 and 4 is smaller than the gap between the rollers 2 and 3. In front of the gap between the rollers 3 and 4, there is again a Knead 8. The mass knead 8 is a characteristic of the calendering process.

In most cases it is shaped like a cigar and shows one Rotational movement, which is often superimposed by spiral-shaped movements of the surface will.

To measure the putty 8, a diode line camera is used in each case 9 used. The kneading compound 8 is provided by a light source 10, which is preceded by an optical system 11 is illuminated at least along a line extending in the direction of the thickness of the mastic 8 extends. The illuminated line is made with the diode line camera 9 observed.

In Fig. 2, the kneading 8 between the rollers 2, 3 is again in detail Shown in advertising connection with the arrangement for measuring the KnetLicke. One not The line of the kneading 8, designated in more detail, is shown by the camera 9 via an objective 12 a line of photodiodes 13 shown. The diode row 13 preferably contains 256 Diodes spaced 25 pm apart. Reading out the line of photodiodes 13 is controlled by an arranged in the camera 9 electronics 14, which via a Terminal 15 control clocks are supplied, which are fed by a cable 16 with the Camera 9 connected evaluation circuit 17 come. The line of photodiodes 13 feeds a video amplifier 18, the a comparator 19 is connected downstream is whose second input via an unspecified trigger to a Terminal 20 is connected, which is connected to evaluation circuit 17. The exit of the comparator 19 is also connected to the evaluation circuit via a connection 21 17 in connection. The output signal of the video amplifier 13 is via another Terminal 22 can be tapped, to which a viewing device 23 is connected via the cable 16 is. The connection 22 is also connected to the evaluation circuit 17.

When the knead 8 is scanned, the not closer appears on the screen designated oscilloscope tube of the viewing device a video signal of the in Fig. 3 Type shown. This video signal 24 consists of a central part 25 with high signal values. The video signal 24 also contains two minima 26, 27 on both sides of the minima 26, 27, the video signal 24 shows two areas 28, 29 with increasing Signal values. The maximum signal level 30 of the video signal 24 arises during the scanning the middle 31 of the kneading 8. The minima 27, 25 each occur when the Transition 32 between the skin 33 on the roller 2 and the kneading 8 and the transition 34 between the kneading 8 and the roller 3.

The video signal 24 is given by a signal via the input 20 adjustable trigger threshold 35 evaluated.

The comparator 19 therefore emits a binary data signal 36, which at Video signal 24 lying above threshold 35 has a binary value, for example "1", and if the video signal 24 is below the threshold, the other binary value, for example 0, has.

13 is set to the middle 31 of the kneading 8. The middle 37 of the Data signal 36 is evaluated for determining the kneading thickness, the kneading thickness corresponds to the distance between the edges 37 and 38 of the data signal 36. This The time interval is based on the traversed at a certain scanning speed Line on the surface of the modeling clay 8 and based on the geometric Arrangement between camera 9 and kneading 8 in the evaluation circuit 17 calculated.

The integration time of the camera 9 depends on the scanning speed away. One at a selected point of the kneading 8, preferably at the kneading center 31, the occurring value of the video signal 24 is used for additional signal processing selected. This value, which is preferably the signal value 30, is kept at a constant value by influencing the integration time. The integration time is set so that despite different materials with different reflection properties and different illuminance levels the signal value 30 remains constant. This makes the measurement of the kneading thickness independent of lighting fluctuations and different optical properties of the calendered Materials. For the regulation, it is expedient in the evaluation circuit 17 the setpoint value for the signal value 30 from the actual value tapped from the connection 22 subtracted. The control deviation is applied to a clock generator 39, which the control clocks generated for the camera 9.

The predeterminable threshold 35 is during successive scans of the kneading 8 changed at the beginning of the measurement. The initial value is a low one Predetermined threshold. From sample to sample, the threshold 35 increases a little receives. During the scans, the data signal 36 is monitored to determine whether the values corresponding to the minima 26, 27 occur in each case. Isn't this the one If so, a new sampling with an increased threshold 35 is carried out in each case. If the minima 26, 27 are established, then the threshold 35 can be increased once a safety addition must be increased before they are used for further scans is kept constant. The threshold 35 is increased in the evaluation circuit 17. So that the kneading thickness measurement can be adjusted automatically to the circumstances adapt to the respective material.

The method explained above is expedient to that effect modified so that it is carried out in two sections. The first section will only the area on one side of the kneading center 31 is scanned or evaluated.

There are two ways to do this. The first is that only those diodes of the photodiode row 13 that correspond to the side up to the kneading center 31, be switched through to the video amplifier 18. These diodes are therefore in read out consecutive sampling cycles, from sampling cycle to sampling cycle the threshold value 35 is increased and it is checked whether a minimum, i. H. a signal below the specified threshold is present. The first area is, for example to the right of the maximum value 30. This method step then results in the position of the minimum 27 is determined, which corresponds to the transition from kneading B to skin 33. In Another possibility is to determine the minimum by setting the threshold from the maximum The value in the middle is gradually decreased. If the minimum 27 is found, then the threshold 35 set for this purpose is increased by a safety margin and kept constant for the further scans. The same process is used for repeats the area to the left of signal value 30.

The threshold value determined in this area for the minimum 26 35 is also saved after increasing by a safety margin and for the further scans are used. With this measure, the influence becomes different large minima 26, 27 on the measurement result eliminated. The differences in the minima 26, 27 result from the different relationships at the transitions between Roller 3 and kneading 8 as well as between skin 33 and kneading 8.

The other option mentioned earlier is to use the entire Area to be scanned, but first only one half of the data signal 36 and then to examine the other half for the occurrence of the respective minimum 26, 27.

When calendering cling film, extremely glassy kneading can occur 8 occur. The light generated by the light source 10 enters this kneading material and is there by random structures that appear vesicular due to the formation of eddies, thrown back. When such a clay is scanned, a video signal is produced of the type shown in Fig. 4, which has a strong structure. This video signal 40 not only has minima at the transitions between kneading 8 and roller 3 or between Knead 8 and Fell 33, but also further minima that are below the trigger threshold 41 lying. The transitions between kneading 8 and roller 3 or between kneading 8 and skin 33 correspond to the minima 42, 43. The further minima 44, 45 result from the special proportions of the materials used for transparent foils.

The data signal at the output of the comparator 19 shows changes in the signal 46, 47 the minima 42, 43 and by signal changes 48, 49 further minima. the Minima 44, 45 falsify the measurement if there is no clear assignment between the respective minimum and the end of the kneading 8 can be determined.

When kneading, which produce video signals in the manner of FIG. 4, are the video signals resulting from several successive scans are mutually exclusive superimposed.

The scans expediently extend over several seconds. The result of the superposition represents the mean value of the video signal in the above mentioned sampling period. This mean value of the video signal is with the previously explained signal thresholds checked.

The first correspond from the kneading center below the respective Threshold values lying minima of the kneading ends 32, 34.

Because of the rotation of the kneading 8 notches, as denoted by 44, 45 are present only for a short time, while the minima 42, 43 occur constantly, these can be recorded and evaluated for the determination of the kneading thickness.

With the aforementioned measures, the video signals 24, 40 processed analogously by the comparator 19. It is useful to track the video signals 24, 40 to convert into digital data. The video signals 24, 40 are scanned in the process and the samples are in quantized form, for example with a data width of 8 bits, entered into a short-term memory. A number of dates for each several consecutive kneading scans are made for the different scanning points added up. The changing minima are thus averaged out. The thus obtained The shape of the curve is now examined for minima by specifying a threshold. These Minima then correspond to the kneading ends. The distance between the minima and the center of the kneading 31 can be specified in the number of diodes up to the middle of the photodiode line 13. With a conversion factor that depends on the geometric structure of the measuring system, from this the kneading thickness can be determined in absolute units. In addition, the kneading thickness are monitored for certain min / max values, if they are below or exceeded an alarm is triggered.

In the arrangement shown in FIG. 5, two diode line cameras are used 50, 51 used for observing a kneading 8 between two rollers 52, 53. The kneading 8 is located at two points 54, 55 on both sides of the kneading center Light sources 56, 57 illuminated. The optical systems of the light sources 56, 57 and the diode line cameras 50, 51 are related to the rollers 52, 53 and the knead 8 arranged at the same altitude. The altitude preferably corresponds to the ones of modeling clay 8.

As can be seen from Fig. 5, the kneading 8 has approximately the shape of a Cigar on. The video signals of the two diode line cameras 50, 51 are not only evaluated for determining the kneading thickness at the respective point, but also compared with each other.

The comparison takes place with a reference value that is determined by empirical values is determined, which occur with excessive kneading. If the reference values are exceeded, then this is an indication that the kneading is over the edges of the rollers 52, 53 can run out. Such a disturbance can therefore be detected from the video signals and be reported.

It is also possible to use those determined at the two scanned locations Subtract kneading thicknesses from each other. If the difference exceeds a specifiable one Threshold value, then this indicates an impermissible asymmetry of the kneading 8.

Preferably at the last roll gap a tapered one in the middle Training clay. Therefore, here the kneading becomes the kneading center and one The diode line camera scans the dough close to the edge of the roller.

Claims (10)

Claims two methods for determining the thickness of the kneading of a material in front of a pair of rollers, through the gap of which the material moves is, wherein the knead along at least one running across its width line is illuminated and scanned with a diode line camera that emits a video signal produced, from which the kneading dough is obtained, wd characterized by the fact that the Video signal (24, 40) is compared with a predeterminable threshold (35, 41) with the two occurring on both sides of the kneading center (31) during scanning, below the threshold values (26, 27) are obtained, which are at the ends of the kneading (8) arise and that the integration time of the diode line camera (9) as a function from the exposure of the clay to constant values of the video signal (24, 40) is regulated. 2. The method according to claim 1, characterized in that a one selected point (31) of the kneading (8) corresponding value (30) of the video signal (24, 40) by regulating the integration time to a constant value is regulated. 3. The method according to claim 1 or 2, characterized in that the predeterminable threshold (35) during successive scans of the kneading (8) with the diode line camera (9), starting from a low threshold value, as long as is shifted to higher threshold values until two on both sides of the kneading center (31) lying signals (26, 27) are detected which are below the threshold (35) lie. 4. The method according to claim 3, characterized in that the displacement of the threshold value is carried out separately for each kneading half and that at the scanning of the respective kneading half when falling below the threshold value Signal is evaluated as the thickness of the kneading half. 5. The method in particular according to claim 1 or one of the following Claims, characterized in that the video signals of several successive Samples of the kneading (8) are superimposed and that from the superposition received signal with the predefinable threshold for detecting the below the threshold lying values is compared, which correspond to the kneaders. 6. The method according to claim 1 or one of the following claims, characterized characterized in that the video signal (24, 40) is converted into quantized values, each for several consecutive scans in a short-term memory are entered that then the digital ones obtained at the same sampling points Values are summed up and that then the summed up values by means of a predetermined Threshold value (41) to the situation under- examined halfway through the threshold will. 7. The method according to claim 1 or one of the following claims, characterized in that the kneading thickness from the distance between the flanks (37, 38) sensing diodes of the photodiode line (13) from the middle of the line, from the distance the camera (9) from the kneading (8) and from the geometry of the optics of the camera (9) will. 8. The method according to claim 1 or one of the following claims, characterized characterized in that the kneading (8) by two points (54, 55) on both sides of the Diode line cameras (50, 51) directed towards the kneading center are monitored, the video signals of which are monitored for asymmetries lying above specifiable limits. 9. The method according to claim 1 or one of the following claims, characterized in that the kneading device (8) is monitored by two diode line cameras one on the middle of the clay and the other on one near the edge of the rollers lying point of the kneading (8) is directed and that the video signals of the two diode line cameras to asymmetries that are above predeterminable limits be monitored. 10. The method according to claim B, characterized in that the for both points (54, 55) determined kneading thicknesses are subtracted from one another and that in the case of a difference exceeding a predetermined limit, there is a disturbance is reported.