EP0093865A1 - Feeler for detecting web seams - Google Patents

Abstract

To determine web seams (40; 40 ') in webs (19) processing e.g. Shearing machines, a scanning device is provided which has at least two detectors (34, 35, 36, 37) scanning the web at a distance from one another, the scanning signals of which are fed to a control circuit which only operates when the scanning signals of at least two detectors (eg 34, 37) coincide issues a control command to the machine control. The invention aims to provide a structurally simple device that is not able to detect web seams specially prepared for the measurement. This is achieved in that each detector consists of a potentiometer, which is machine-fixed with its resistance path, but adjustable transversely to the plane of the material path, and a probe head which can be placed on the material surface (17) and which is arranged with little play on a coupling element which is rigidly connected to the sliding contact of the potentiometer is. A particularly favorable scanning device, which also detects oblique (40) and special seams (40 '), is obtained according to a further embodiment in particular when two groups (32, 33) of two detectors (34, 35; 36, 37) each transverse to the direction of travel of the web (20) are arranged side by side in such a way that the two detectors of a group are arranged at a distance (39) transversely to the direction of the web and at a distance (38) in the direction of the web.

Description

The invention relates to a scanning device for determining web seams in web processing machines, e.g. Clippers, the control of which is to be acted upon in seam detection, with at least two detectors scanning the web at a distance from one another, the scanning signals of which are fed to a control circuit which, when the scanning signals of at least two detectors coincide, only issue a control command to the machine control.

For reasons of rationalization, a plurality of web sections are sewn or glued to one another for the mechanical processing of webs of goods in order to be able to capture a larger web stock in one goods pass. In almost all cases of processing such a web provided with seams, seam detection is necessary, e.g. in order to lift the shears from the web when the seam passes through a shearing machine and thus prevent damage to the shear blades.

The detection of seams has already been the subject of numerous considerations. For example, DE-PS 9 24 323 describes a device for determining a product connection seam, in which an electrical conductor, for example in the form of a metallic thread, is applied to the product web on one or both sides that causes a control pulse when two contacts connected to a control circuit are touched. Instead of using, for example, a metal thread through or surface-metallized textile thread, DE-PS 9 25 884 suggests treating the goods at the point to be taken into account, that is to say generally at the seam, with a conductive liquid, for example a salt solution or a weak acid to short-circuit the control circuit. According to DE-PS 9 30 442, a Geiger tube is used as the seam detector, the web being wetted in the seam area with a radioactive liquid. In the device for determining a product connection seam according to DE-AS 12 68 557, a thread impregnated with a fluorescent color is sewn into the seam, which is scanned by a photoelectric device comprising several detectors. DE-AS 24 28 112 deals with a seam monitor in which a high-frequency probe head with a probe and at least one receiving device is provided which responds to an electrical conductor incorporated in the seam, for example a metal or staniol strip or a conductive film applied to the material web.

The equipment expenditure of the known seam detection devices are - with the exception of those according to DE-PS 9 24 323 - relatively high. All seam detection devices are without exception the main disadvantage that the seam rich in the web must first be prepared in a suitable manner for the response of the seam detection device. These preparations are time-consuming and in any case involve an annoying additional effort.

In contrast, the object of the invention, based on a scanning device, in particular according to DE-AS 12 68 557, in the establishment of which the coincidence of at least two scanning signals is provided for acting on the machine control system, is to provide a device which is very simple in terms of its design, with which web seams can be scanned that have not previously been specially prepared for this purpose.

The invention is based on the knowledge that practically every seam - be it a glued paper seam or be it a sewn textile seam - is always noticeable by a local change in thickness in the material web and proposes to solve the aforementioned task that each detector consists of one with its resistance track, which is machine-fixed, but adjustable across the web level, there is a potentiometer and a probe that can be placed on the web surface, which is arranged with little play on a coupling element, which is rigidly connected to the sliding contact of the potentiometer.

Due to the low-play arrangement of the probe on the rigid and thus absolutely free of play With the sliding contact of the coupling element that is firmly connected to the machine, even with the precision of the potentiometer available today, even a change in the thickness of the material web of the order of magnitude of approximately 0.05 mm can be registered. The resistance changing due to the displacement of the sliding contact of the potentiometer can be used in the control circuit for the corresponding evaluation. However, it is a prerequisite that this utilization occurs only when the scanning signals of at least two detectors coincide, so that a locally limited unevenness in the web surface (front or back) is not already suggested as a seam.

Different configurations with special advantages are possible with regard to the arrangement of the detectors. Such an arrangement known per se provides that two detectors are provided at a distance from one another transversely to the direction of travel of the web. This arrangement, which is the simplest in its design, is suitable, for example, for recognizing straight transverse seams in paper webs in particular, the probe heads being deflected at the same time when the seam passes.

An increased measuring accuracy results from the fact that two detectors are arranged at a distance transversely to the direction of the web and at a distance from one another in the direction of the web. These two detectors, too, cannot be excited by the same, locally limited unevenness at the same time, but it is ahead setting that the bumps must occur in the distance from each other corresponding to the distance of the detectors transverse to the direction of travel of the web. The coincidence of the excitation of the detectors at a given web speed results from the distance between the detectors or from the time difference required at this speed between the excitation of the detector lying behind in the web direction and addressed first and the detector in the web direction at the front and second-most excited.

A universal and therefore particularly advantageous in the context of the invention scanning device, with which not only bevel seams, but almost all occurring seam shapes can be scanned with outstanding accuracy, consists quasi in a combination of the previously described alternative arrangements of two detectors in that two groups of each two detectors are arranged next to one another transversely to the direction of web travel in such a way that the two detectors of a group are arranged at a distance transversely to the direction of web travel and at a distance in the direction of web travel, it being further advantageous if the detectors of both groups arranged on a straight line transverse to the direction of web travel each have the same distance from each other. In order to trigger a machine control pulse, it is essential that each of the four detectors be energized. The control circuit falls in the essentially the task of recognizing whether all detectors are excited within a permissible time and / or path tolerance. Only if this is the case is the seam recognized correctly.

Although a rotary potentiometer could be used as a potentiometer, in which the coupling member could be designed as a pivoting lever carrying the probe, it has proven to be particularly advantageous if the potentiometer has a sliding contact that can be moved in a straight line and if the coupling member, which is essentially rod-shaped, moves in the direction of movement of the Sliding contact extends. The deflection of the probe then leads to a linearly proportional displacement of the sliding contact and thus enables a particularly precise and simple acquisition of the measured values. In addition, with such a "linear potentiometer", the backlash desired for the measuring accuracy can best be achieved in a particularly simple manner. The probe head is preferably designed as a low-radial play roller at the end of the coupling member, which prevents an otherwise also possible configuration of the probe head, e.g. As a skid, more favorable friction values and thus, in turn, more accurate measured values can be achieved.

Finally, for the purpose of a particularly simple adjustability of the scanning device, the invention provides that two potentiometers with opposite polarity to the control current are connected in such a way that, with the same deflection of the probes of these two detectors, the total measurement voltage is zero. This creates a self-adjusting scanning device which only presupposes that all detectors are arranged in a plane parallel to the plane of the web. This can be achieved in a simple manner by arranging all potentiometers at the same distance from a web support.

If, as is provided in accordance with a further advantageous feature, the potentiometers of one group or all potentiometers are arranged together in a carrier which is adjustable with respect to the plane of the web, a simple adjustment is e.g. by adjusting the support in such a way that the measuring voltage can be set to zero, which e.g. can easily be done with the help of a simple voltmeter.

• Fig. 1 eine schematische Seitenansicht einer einfachen Abtastvorrichtung,
• Fig. 2 eine Aufsicht auf die Vorrichtung nach Fig. 1,
• Fig. 3 eine der Fig. 1 entsprechende schematische Ansicht einer universell verwendbaren Abtastvorrichtung,
• Fig. 4 eine Aufsicht auf die Vorrichtung nach Fig. 3 und
• Fig. 5 ein Blockschaubild der elektrischen bzw. elektronischen Meßwerterfassung der Einrichtung nach den Fig. 3 und 4.

The invention is explained below with reference to several exemplary embodiments shown in the drawings. The drawings show:

• 1 is a schematic side view of a simple scanning device,
• 2 is a plan view of the device of FIG. 1,
• 3 is a schematic view corresponding to FIG. 1 of a universal scanning device,
• Fig. 4 is a plan view of the device according to Fig. 3 and
• 5 shows a block diagram of the electrical or electronic measured value acquisition of the device according to FIGS. 3 and 4.

On a frame of a machine that processes webs, e.g. a clipper, two carriers 11 for one detector 12 and 13 each are arranged in such a way that they are each height-adjustable (double arrow 14) and pivotally adjustable about an axis 15 (double arrow 16). Each carrier 11 is located with the associated detector 12 or 13 above a table 18 provided with a fabric support 17, over which a web 19 is guided in the web running direction 20. The web 19 shows two sections 21 and 22 which are connected by a seam 23.

The detectors 12 and 13 each comprise a linear potentiometer 22 with a resistance track (not shown) fixed in the housing and thus fixed on the carrier 11 and a sliding contact indicated by 25. This is rigidly connected to a rod-shaped coupling member 26, on the free end of which a preferably roller-mounted roller 27 acts as a probe head 28 is ordered. Each change in the thickness of the web 19, in particular the seam 23, causes a deflection of the probe head 28 and, associated therewith, a displacement of the sliding contact 25 upwards. The resulting change in resistance influences the electrical values of the control circuit to which the respective detector is connected at 29.

As FIG. 2 shows, two detectors 12 and 13 are arranged at a distance 30 transversely to the direction of web travel 20. The control command to the machine control is issued when the scanning signals of these two detectors 12 and 13 coincide, i.e. that is, when both detectors are excited simultaneously by an unevenness of the material web in the arrangement shown in FIG. 2. This very simple device according to FIGS. 1 and 2 is very well suited for the seam detection on essentially smooth surface webs with seam 23 arranged perpendicular to the web running direction 20, in particular e.g. for machines processing paper webs.

The arrangement described is less suitable for the scanning of such webs that have regular patterns, for example transverse grooves or waffle patterns on the back (which is usually scanned). Straight seams of such webs could, however, be scanned, for example, by moving one of the two detectors 12 or 13 relative to the other detector 13 or 12 in web direction 20 orders. This is illustrated in FIG. 2 with the detector 13 'taking the place of the detector 13, which is offset by the distance 31 in the direction of web travel 20 from the other detector 12. With this arrangement, transverse seams can also be detected on patterned or profiled webs, the only requirement being that the pattern repeat has a dimension different from the distance 31. The electronics here have to hold on to the pulse generated by the first-responding detector 12 by changing the resistance until, in accordance with the set fabric running speed, the time has elapsed that a seam would at least need to reach the second detector 13 '. If this second detector 13 'then responds, the seam is recognized; if it does not respond, no control impulse is passed on to the machine control. In many cases, even with such a device, cross seams of the type of seam 23 can be detected with sufficient reliability.

The detector arrangements described above also have the disadvantage that oblique or special seams cannot be detected, at least not with sufficient reliability. However, this is easily possible with the device shown in FIGS. 3 and 4. Here two groups 32 and 33 of two detectors 34, 35 and 36, 37 are arranged such that the detectors 34 in the direction of web travel 20 and 35 and the detectors 36 and 37 are at a distance 38 from one another and are each offset by a distance 39 in the direction transverse to the direction of web travel. An arrangement is provided in the vicinity of both web edges, as corresponds to that last described with reference to FIG. 2.

The mode of operation is understood as follows with reference to FIG. 5. As soon as the oblique seam 40 excites the detector 34 and, as a result of the change in the resistance set by its potentiometer, this supplies the differential logic 41 with a pulse, the path / pulse generator 42 keeps the pulse caused by the detector 34 usable at least until the seam - if it is is one - the detector 35 should have reached. The same happens with regard to the detector group 33 having the detectors 36 and 37, in whose circuit a differential logic 43 is also connected, which is also linked to the path / pulse generator 42.

The following explains the following characteristic conditions:

1st example

At the points denoted by 50 and 51 and lying in line with the detectors 34 and 35, the material web has unevenness, which in the device according to FIGS. 1 and 2, if in line with the detectors 12 and 13 or 13 ' lying down would result in the recognition of a straight seam. This is where the detector 34 is energized and the detector 35 is excited with a time delay. The differential logic connected to these two detectors 34 and 35 initially recognizes on standard seam. However, since neither the detector 36 nor the detector 37 are energized, the differential logic 43, which is connected to these detectors, cannot detect at the seam. The link logic 44, which only receives a seam detection from the difference logic 41, can no longer detect seams due to the missing message from the difference logic 43 and does not give a control pulse to the machine controller 45.

2nd example

The special seam 40 ′ shown in FIG. 4 passes through the scanning device. This means that the detectors are excited by the thickenings 50 to 53 in the order 34, 36, 35 and 37. Accordingly, the difference logic 41 first detects a seam, with a slight time delay the difference logic 43 also determines a seam. Since the logic logic 44 has now received a seam message from the two difference logics 41 and 43, it also recognizes the seam and responds to the machine control 45.

It is understandable that diagonal seams of the type of diagonal seam 40 can of course also be recognized with the device according to FIGS. 3 and 4. The path / pulse generator 42 is closed only for this ensure that unevenness of the material web that is too far apart in terms of time or distance may no longer be recognized as a seam.

The logic function essentially has the task of not accepting a seam as reported by only one detector group 32 or 33 via the associated difference logic 41 or 43, unless the other difference logic is also available at a later time according to the setting of the path / pulse generator Seam reports. On the other hand, it has the task of recognizing a seam when the difference logics 41 and 43 report a seam, either at the same time or with a time delay.

The detectors 34 and 35 on the one hand and the detectors 36 and 37 on the other hand are each connected to the control circuit with different polarities. If the detectors 35/35 and 26/37 of a group 32 or 33 are acted upon in the same direction, the resistance of one detector is to be reduced thereby, while that of the other is increased by the same amount. An adjustment of a detector group 32 or 33 is therefore possible in a simple manner by adjusting the total measurement voltage to zero. This is possible in a simple manner by the pivot adjustment arrangement of the supports 11 for the corresponding detectors described at the beginning.

Claims (9)

1. Scanning device for determining web seams in web processing machines, e.g. Clippers, the control of which is to be acted upon in seam detection, with at least two detectors scanning the web at a distance from one another, the scanning signals of which are fed to a control circuit which, only when the scanning signals of at least two detectors coincide, give a control command to the machine control, characterized in that each detector (12, 13, 13 ', 34, 35, 36, 37) consists of a potentiometer (24) which is machine-fixed with its resistance track, but adjustable transversely to the plane of the web, and a probe (28) which can be placed on the web surface and which has little play on a coupling element (26) is arranged, which is rigidly connected to the sliding contact (25) of the potentiometer (24). 2. Scanning device according to claim 1, characterized in that - in a known arrangement - two detectors (12, 13) at a distance (30) from one another are provided transversely to the direction of web travel (20). 3. Scanning device according to claim 1, characterized in that two detectors (12, 13) at a distance (30) transverse to the web direction (20) and at a distance (31) in the web direction (20) from each other. 4. Scanning device according to claim 1 to 3, characterized in that two groups (32; 33). of two detectors (34, 35; 36, 37) are arranged next to each other transversely to the direction of web travel (20) such that the two detectors (24, 35; 36, 37) of a group (32, 33) are spaced apart (39) are arranged transversely to the direction of web travel (20) and at a distance (38) in the direction of web travel (20). 5. A scanning device according to claim 4, characterized in that the detectors (34, 36; 35, 37) of both groups (32; 33), each arranged on a straight line transverse to the direction of web travel (20), are each at the same distance (46) from one another . 6. Scanning device according to claim 1 to 5, characterized in that the potentiometer (24) has a rectilinearly movable sliding contact (25) and that the essentially rod-shaped coupling member (26) extends in the direction of movement of the sliding contact (25). 7. Scanning device according to claim 6, characterized in that the probe (28) is designed as a radial clearance arm at the end of the coupling member (26) roller bearing roller (27). 8. Scanning device according to claim 1 or one of the following, characterized in that the potentiometers (24) of two detectors (34, 35; 35, 36) with opposite polarity are connected to the control circuit (29) such that, with the same deflection of the probes (28) of the two detectors (34, 35; 36, 37) the total measuring voltage is zero. 9. Scanning device according to claim 1 or one of the following, characterized in that the potentiometers (24) each of a group (32; 33) or all potentiometers (24) are arranged together in an adjustable with respect to the plane of the web support (11).

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