US3490253A

US3490253A - Stop motions for warp knitting machines

Info

Publication number: US3490253A
Application number: US666065A
Authority: US
Inventors: Erwin Sick; Winfried Piepenbrink
Original assignee: Individual
Current assignee: Individual
Priority date: 1966-09-10
Filing date: 1967-09-07
Publication date: 1970-01-20
Anticipated expiration: 1987-01-20
Also published as: DE1585348A1; DE1585349A1; GB1195897A; CH491232A; FR1538773A; DE1585348B2

Description

Jan. 20, 1970 E. SICK ET AL 3,490,253

I STOP MOTIONS FOR WARP KNITTING MACHINES Filed Sept. 7, 1967 4 Sheets-Sheet 1 IN VEN TORS M Mm -VW Jan. 20, 1970 E. SICK ET AL 3,490,253

STOP MOTIONS FOR WARP KNITTING MACHINES Filed Sept. '7, 1967 4 Sheets-Sheet 2 Fig. 6

Jan. 20, 1970 STOP MOTIONS FOR WARP KNITTING MACHINES Filed Sept. 7, 1967 4 Sheets-Sheet 3 IINSIEQVTORS: A BY WE; aw M MWW E. SICK. ET AL 3,490,253

Jan. 20, 1970 SICK ET AL 3,490,253

STOPQMOTIONS FOR WARP KNITTING MACHINES Filed Sept. 7, 1967 4 Sheets-Sheet 4 Fig. 8

INVENTORS:

F BY UM h United States Patent 3,490,253 STOP MOTIONS FOR WARP KNITTING MACHINES Erwin Sick, Icking, Isartal, and Winfried Piepenbr nk, Munich, Germany, assignors to Erwin Sick, Ickmg, Isartal, Germany Filed Sept. 7, 1967, Ser. No. 666,065 Claims priority, application Germany, Sept. 10, 1966, S 105,802; Oct. 12, 1966, S 106,453

Int. Cl. D04b 35/20 US. Cl. 66-166 Claims ABSTRACT OF THE DISCLOSURE To detect broken or missing threads in a knitted fabric having a plurality of parallel threads extending in a given direction with interstices therebetween, light is directed toward the fabric in a plane normal to said direction and at a very shallow angle to the surface of the fabric so that each thread will shade the interstice between it and the adjacent thread. If a thread is missing the shading effect will no longer occur and the light will pass through the opening in the fabric. Photoelectric means are provided to determine when the light passes through the fabric.

The invention relates to a warp knitting machine stop motion for the photo-electric spot scanning of knitted fabric.

In a warp knitting machine stop motion of the kind above referred to, the material on the knitting machine is inspected for defects immediately after the knitting operation, namely for the absence of a loop which would produce a gap in the knitted fabric. If this is the case, the warp knitting machine is shut down before substantial quantities of reject material are produced. In a known warp knitting machine stop motion this is done by means of a photo-electric scanning head which periodically traverses over the material. The scanning head contains an optical illuminating system which produces a light spot on the scanned material. The light, which is diffusely reflected by the aforementioned light spot, is photo-electrically received. For comparison purposes a second light spot, which may also be photo-electrically observed in the same manner, is produced in an adjacent position. If a defect occurs in the form of a missing loop, the diffusely reflected light diminishes in that light spot which just traverses the defective position while the other light spot, positioned on perfect material, is diffusely reflected in unchanged intensity. An error signal is derived from the above described conditions. The angles of light incidence and observation respectively in the known arrangement are extremely steep, that is to say they are at a small angle relative to the surface normal. In the arrangement described heretofore the perfect material also supplies a basic ripple in the diffusely reflected light flux, said ripple being undesirably close to a signal which occurs due to a defect, that is to say the defect signal exceeds that of the basic ripple only slightly, in particular if the defects are small. These difliculties occur mainly at the edge of the fabric webs because the fabric is distorted at the edges. A further difficulty is due to the fact that the described method is suitable for use with only unicoloured knitted fabric. When the known method is used for striped or patterned fabric, an error signal will occur if one light spot is disposed in the zone of a first colour tone while the second is already disposed in the zone of a second colour tone because different colour tones also vary the diffuse reflection.

The object of the invention is to provide a photoelectric warp knitting machine stop motion which will permit better differentiation between error signal and basic ripple and which is also suitable for striped or patterned fabric.

According to the invention the knitted fabric is illuminated at a shallow angle and an error signal can be triggered by the transmitted light.

Where the light incidence occurs at an angle, practically no light will be transmitted through perfect material because the individual filaments cover the intermediate gaps as seen in the direction of the optical path. However, if owing to a knitting defect a filament is absent and, given a suitable choice of the angle of light incidence, light will be transmitted through the resultant gap to produce an error signal. If the light were to be allowed to pass practically perpendicularly in the manner of the known arrangement, it would not be possible to operate with transmitted light when processing conventional knitted fabric because owing to the gaps between the individual filaments a relatively large light flux would pass through the fabric so that the signal resulting from the occurrence of a defect would be small relative to that produced by the light transmitted through the perfect fabric. This disadvantage cannot be avoided by reducing the size of the light spot as such a procedure would lead to increased basic ripple. The use of transmitted light for this purpose becomes possible only by virtue of the incident light falling at an angle and the covering effect achieved thereby.

It is known to detect tears or the like in webs of material by photo-electric means and by transmitted light. However, this does not apply to the inspection of knitted fabric where such inspection would not readily be possible by means of transmitted light since the aforementioned method applies to the inspection of homogeneous and substantially opaque webs such as paper, film and the like. The light incidence is substantially perpendicular to the surface of the material.

The prior art also discloses inspection apparatus for paper web or sheets in which the paper surface is illuminated at a shallow angle. This is done for the purpose of improving fold detection but not in order to utilise a covering effect as in the invention. In the system just described, observation takes place in the reflected light at an even smaller angle than that of the illumination.

Embodiments of the inventions will now be described by way of example with reference to the accompanying diagrammatic drawings in which:

FIGURE 1 is a first embodiment of the invention illustrating operation with an autocollimated optical path;

FIGURE 2 illustrates a second embodiment using illumination from an elongated light source;

FIGURE 3 shows a third embodiment of the invention in side elevation;

FIGURE 4 is a path view thereof;

FIGURES 5 and 6 illustrate modifications of the arrangement of FIGURE 1 with different reversing reflectors;

FIGURE 7 shows an embodiment in which the light is transmitted to the photo-electric receiver by means of a light guide rod extending over the width of the knitted fabric;

FIGURE 8 shows the transmitter and receiver part, and

FIGURE 9 shows the two scanning slides of a further embodiment of the invention, said slides being traversible over the Web to be monitored.

In the embodiment according to FIGURE 1 a light source 1 is provided from which a light beam is projected through an objective lens 2, said light beam falling at a shallow angle on to the knitted fabric 3 to be inspected and in whose plane it produces a light spot. If a knitting defect occurs at the location of the light spot, the light beam will pass as shown through the knitted material 3 to fall upon areflector 5 having surfaces disposed in a sawtooth pattern and being covered with .a reflecting emulsion or film. These surfaces are disposed substantially perpendicularly to the direction of the illuminating light beam so that adequate reversal reflection with low light losses is ensured despite the angle of incidence of the light. The light beam is reflected into itself, condensed by the objective lens 2 and passes through a semi-reflecting mirror 6, inclined relative to the'optical path, onto a photo-electric receiver 7 where it triggers an error signal.

The entire unit comprising the lamp 1, the objective lens 2, the mirror 6 and the receiver 7 traverses across the knitted fabric 3 so that said fabric is scanned on a spot-by-spot basis. When the light strikes perfect material and neglecting dispersion and diffraction, no light will pass through the material because the individual filaments or threads conceal intermediate gaps in the direction of the light beam. When being observed from the light source 1, the gaps between the filaments cannot be seen at all. The angle of light incidence must be so selected that the aforementioned covering effect occurs with perfect fabric while a gap resulting from a missing filament is seen, i.e., it permits the transmission of the light beam.

FIGURE 2 illustrates another method which does not involve the use of an autocollimated optical path. A fluorescent tubular lamp 8, extending transversely across the material to be inspected, serves as light source. The fluorescent lamp 8 has disposed in front of it a raster 8 comprising a plurality of diaphragms disposed in parallel to each other and at a shallow angle relative to the fabric 9 so that only that light which strikes at an angle will also strike the material 9. Observation is by means of an objective lens 11 through which a spot and the material plane is projected on a photo-electric receiver 12 by means of a light beam extending at an angle relative to the plane of the material. If a knitting defect 10 occurs at the position of the projected spot, light will strike the receiver and trigger an error signal. In this case too, the objective lens 11 together with the receiver 12 is periodically traversed across the knitted fabric to be inspected.

In the arrangement according to FIGURES 3 and 4, a spot light source 13 (lamp filament) produces an illuminating beam by means of an objective lens 14, said beam once again striking the knitted fabric 15 to be monitored at a shallow angle and producing in the plane of said fabric a light spot traversing across the said knitted fabric. The knitted fabric 15 is backed by a reflector 17 comprising a substantial number of concave mirrors 18. The concave mirrors 18 are also disposed in sawtooth fashion, similar to the reflecting surfaces in FIGURE 1. Their optical axes are disposed substantially in one plane at the angle of incidence of the light relative to the knitted fabric 15 but are slightly twisted relative to the light incidence direction. From the light beam passing through a knitting defect 16 the concave mirrors 18 produce a light spot upon the knitting defect 16 (FIGURE 4) but with slight lateral displacement relative to the illuminated light spot. The light beam which thus passes to and fro through a knitting defect is condensed by a concave mirror 19 on a photo-electric receiver 20. However, this optical path would be obtained only if the knitting defect 16 were disposed accurately in the plane containing the optical axis of the concave mirror 18 and being inclined at the light incidence angle relative to the knitted fabric 15 as indicated in FIGURE 3. The first light spot produced by the objective lens 14 on the knitting defect 16 would not otherwise be projected by the concave mirror on the knitting defect 16 in the manner shown. This difficulty is avoided by the reflector executing a pivoting motion in the scanning direction as indicated in FIGURE 3 by the double arrow. During the pivoting motion the optical axis of the concave mirror will traverse at least once through the knitting defect 16 to generate a light flash on the receiver 20.

FIGURES 5 and 6 are modifications of the arrangement of FIGURE 1. The scanning head which traverses over knitted

fabric

19 or 21 respectively is constructed as indicated in FIGURE 1; Instead of the reflector 5 with reversal reflecting surfaces disposed in sawtooth fashion, this embodiment provides for a series of individual optical reversing reflectors whose optical axes in each case coincide with the light incidence direction. In FIG- .URE 5 these elements are the convex lenses 20. In FIG- URE 6 they are thetriple reflectors 22. having one front element each by meanss of which the light spot is once again projected in the plane of the material 21.

In the embodiment illustrated in FIGURE 7 a light beam from a light source 23 is conducted at a shallow angle by means of the objective lens 24 on to the material 25 to produce a light spot thereon. The scanning head with the objective lens 24 and the light source 23 is traversed in the paper plane across the knitted fabric 25. When a knitting defect 26 is detected the light passes through the material 25. A light-conducting rod 27, provided at the top with saw-tooth light entry surfaces 28 whose surface normals coincide substantially with the light incidence direction, is disposed behind the material. The light-conducting rod conducts the transmited light to the right in FIGURE 2 where it emerges on the end face of the light-conducting rod. Since the light enters the light-conducting rod 27 at a defined angle, it also leaves the said light-conducting rod substantially at a defined angle (upwardly or downwardly, depending on the number of reflections) as indicated in FIGURE 7. The emerging light is aligned substantially in parallel to the longitudinal axis of the light-conducting-rod 27 by means of a prism 29. Thelight then strikes a concave mirror 30 in the focal point of which the photo-electric receiver 31 is disposed.

The use of reversal reflectors, or concave mirrors disposed in saw-tooth fashion, and the use of a light-conducting rod with saw-tooth light entry surfaces, requires a high precision of the component which, in practice, increases the cost of manufacture. Moreover, active parts of the arrangements described heretofor (lamps, photocells), must be traversed over the knitted fabric webs to be monitored and must therefore be connected via a flexible cable, spiral cable, which has a disturbing effect. In order to operate with stationary active elements requiring a power supply in Warp knitting machine stop motions, so that spiral cable connections and the like and the previously described manufacturing problems are avoided, the apparatus may be so constructed that a pencil of light extending in parallel across the knitted fabric is produced by a stationary first optical collimator system, while an optical projection system is disposed in a first slide, traversable along the pencil light, so that the light is focused and ducted at a shallow angle upon the knitted fabric, and/ or that a second optical collimator system is disposed on asecond slide which is traversable on the other side of the knitted fabric in synchro-nism with the first slide, so that the light passing through the knitted fabric is parallelly directed upon a stationary optical condenser system. which collects the pencil of lightfor transmission to a photo-electricreceiver.

The active elements, that is to say, the light source and photo-electric receivers, may be disposed stationarily and may be permanently wired at the edge of the knittted fabric to be scanned. The slides contain only passive optical elements. The radiation energy is transferred without wire by the parallel light beams through the air to the moving slides and from these back to the stationary receiver. To ensure that the light flux which strikes the receiver in the event of a knitting fault is the same at any position of the scanned material, it is advantageous if the aperture of the first optical collimator system is made substantially larger than that of the optical projection system and the aperture of the aforementioned optical condenser system is constructed to be larger than that of the second optical collimator system. Furthermore, the optical elements are appropriately so dimensioned that the ratio of light source diameter to focal length of the first optical collimator system is smaller than the ratio of the pupil diameter of the first optical collimator system, relative to the scanning width of the knitted fabric.

The light source, which has a finite diameter, is projected by the first optical collimator system at infinity and at an angle determined by the ratio of light source diameter at focal length of the optical collimator system. If the first slide is moved away from the first optical collimator system, it being assumed that the optical projection system has at first an infinitely small aperture, so that the said optical collimator system is displayed at a progressively diminishing angle, this will result in vignetting and therefore lead to a reduction of the light flux if the optical collimator system appears at a smaller angle than the light source projected by the optical collimator at infinity (limiting distance). Light from all points of the light source will no longer pass through the pupil of the first optical collimator system to the point of observation. The relationships become even less favourable if the finite aperture of the optical project system is allowed for. An effort must therefore be made to construct the aperture of the first optical collimator system as large as possible and to select a substantially smaller aperture for the optical projection system. Within the limiting distance explained 'hereabove, such procedure will permit the transmission of a substantially constant light flux.

The optical projection system may be of a spherical type. However, it is advantageous if the optical projection system is constructed from an optical cross-cylinder system.

The slides may be magnetically coupled to each other via the knitted fabric. l

In order to eliminate errors due to spurious light effects when light energy is transmitted over relatively long distances, it is appropriate if the pencil of light is periodically chopped.

It is of course most appropriate if the light flux which passes from a stationary light source to the first slide, as well as the light flux which passes from the second slide to a stationary receiver is transmitted'in the manner described here above by means of parallel pencils of light. It is of course also advantageous if one or the other procedure is adopted by itself, so that either light passes from a stationary light source to a moving slide by virtue of the transmission of a parallel pencil of light, or only a parallel pencil of light is transmitted from the second, that is to say, receiver side slide to the stationary receiver. For example, illumination could be obtained by means of a stationary parallel pencil of light directed on to the entire knitted fabric under test, while observation is performed, spot by spot, by means of a movable slide or head. Conversely, observation could be performed by means of a light-conducting rod, given spot by spot illumination with a movable slide or, head containing an optical illumination system.

Such an arrangement is illustrated in FIGURES 8 and 9.

The light emitted by lamp 31 is displayed via a condenser 32 on a chopper disk 33 in a diaphragm 34. A first optical collimator system, in the form of an objective lens 35, projects the chopped light spot infinity. Projection should be of high quality. Achromatic lenses were used in a practical embodiment.

An optical projection system in the form of a system of crossed cylindrical lenses is disposed on a first slide 36. The system of crossed cylindrical lenses comprises a cylindrical lens 37 and a cylindrical concave mirror 38, disposed at right angles thereto. The concave mirror 38 ducts the light under a shallow angle on to the knitted fabric. The system of crossed cylindrical lenses obtains from the relatively large and substantially parallel light beam, a small zone 40 of, for example, 10 millimetre diameter. The light source (diaphragm 34) appears in the

optical system

37, 38 on the slide in the form of a star, which is seen at a finite angle and is disposed at infinity. The light flux remains uniform, irrespective of the position of the slide 36, relative to the optical collimator system. These conditions apply only to a certain limiting distance which maybe the larger, the larger the pupil of the optical collimator system 35. For example, if the diaphragm 34, functioning asa light source, appears at an angle of 1:100, the limiting distance will be approximately equal to one hundred times the pupil diameter of the optical system objective lens 35. The system of crossed

cylindrical lenses

37, 38 focuses the light sharply on the material to be monitored. After transmission illumination of the fault position 39, the light is transmitted via the deflecting mirrors 41 and 42 to the second optical collimator system 43, which once again aligns the pencil of light in parallel and transmits it in parallel to the leading pencil of light to the transmitter and receiver unit (FIGURE 8). At this position, the returning parallel pencil of light is collected by an optical condenser system 44 and transferred to a photo-electric receiver 45. The

numerals

46 and 47 are deflecting mirrors of the transmitter and receiver part. The pencil of light 1, emerging from the second optical collimator system 43, is substantially smaller than the aperture of the optical condenser system 44. Substantially the same conditions apply as those which refer to the optical collimator system 35 and the

optical projection system

37, 38.

The

mirrors

41 and 42 and the lens 43 are disposed on a second slide 48. The two slides 36 are coupled to each other via the knitted fabric, by means of magnets 49. One of the two slides is traversed across the width of the web to be scanned by means of a rope drive or the like. The other is driven by the magnets.

The invention is claimed as follows:

1. In a stop motion apparatus for knitted fabrics having a plurality of generally parallel threads positioned in one direction with respect to the fabric with interstices between adjacent threads wherein the apparatus has a detection device including a light source with relative motion being provided between the device and the fabric so that the area of the fabric inspected continuously changes, the improvement in said device comprising:

light directing means between the light source and the fabric to form the light rays into a beam and to direct the beam toward the fabric along a line inclined at a shallow angle with respect to the fabric, which line is in a plane approximately normal to said thread direction and is inclined at such a shallow angle with respect to the fabric that each thread shadows the interstice between that thread and the adjacent thread to prevent substantial light from passing through the interstice and when the beam is directed at a portion of the fabric where a thread is missing due to a defect in the fabric said shadowing effect will not occur and the beam will pass through the fabric indicating the presence of the defect; and

light detection means for determining when said beam passes through said fabric, said detection means having at least a portion thereof positioned along said line and on the other side of said fabric from said light directing means to intercept the beam so passing through said fabric.

2 In an apparatus as set forth in claim 1, wherein said detection means includes:

as said portion an autocollimation reflector, said refiector being positioned to reflect the light fromsaid other side of said fabric back along said line; and means positioned on the same side of said fabric as 7 said light directing means to intercept said reflected "light, separate it from said beam and to produce an electricalsignal-as a resultof the light so reflected.

3. In an apparatus as set forth in claim 1, wherein said light detection means pivots with respect tosaid fabric so that said line moves in a curvedpathfwith respect to-the' fabric; and

said detection means includes:

'as's'aid portion a reflectorcomprising a substantial number of concave mirrors disposed in sawtooth fashion and "having optical axes inclined at the angle of inclination of said line and slightly twisted relative to said plane, and means positioned on the same side of said fabric as said light directing means for intercepting the reflected light and producing an electrical signal as a result of the light so intercepted,

4. In an apparatus as set forth in claim 1, wherein said :ource is elongated in the direction of the width of the fabric, said light directing means includes a plurality of liaphragm means positioned between the source and the fabric, positioned adjacent and parallel to each other and positioned at said angle to the fabric for restricting the .ight striking the fabric to substantially said angle, and ;aid light detection means includes a photoelectric dezector at the other side of the fabric and optical means between the detector and the fabric with its optical axis Jeing inclined at said angle with respect to the fabric.

5. In an apparatus as set forth in claim 1, wherein said light detection means includes:

a light conducting rod extending transversely of the fabric and having, on the side thereof adjacent the fabric, a plurality of light entry surfaces arranged in sawtooth fashion, said surfaces being approximately normal to said line, said rod having a light emitting end; and

photoelectric means positioned at said end for receiving the emitted light and producing an electrical signal in response to the receipt of emitted light.

6. In an apparatus as set forth in claim 1, wherein said light directing means includes:

stationaryoptical collimator means for producing a pencil of light extending across said fabric at right angles to said direction,

first slide means movable along said pencil of light, and

8 means on said firstslide means for intercepting said pencil of light anddirecting it along sai I line-with respect to the "fabric, and I I I said light detection means includes: J scond slide means positioned on the-oppositeside of thefa'bric'fror'n the first slide means, '-parallel r -'to 'the first slide means and intersecting said line, said second slide means'being movable in sync'hronis'rn with' said first slide r'neans', photoelectric means, i i second optical collimator means having" atleast a portion thereof on said-second slideme'a'ns for intercepting the-light passing through the fabbric and 'dir'ectingit to said photoelectricmeans. *7. In an apparatus as set forth "in claim 6, 'wherein said stationary optical collimator means has an aperture of a given size, said means ori' said first slide'means includes optical projectionrneans having an 'aperturesm'aller than said given size, and'saicl second'op'tical collimator means has an aperture smaller than said given size.

8. In an apparatus asset forth inclaim7, wherein said optical projection means comprises"a*system of cylindrical cross lenses.

9. In an apparatus'as set forth in claim 6, wherein said first and second slide means each includes'magnetic ineans coupling the two slide 'means for movement in synchronisrn. *T I 10. In an apparatus assetforth in claim 6, including means to periodically chop s'aid pencil'of'light.

Photoelektronische Fehlerefassung Bei Gemusterter Kettenwirkware,pp.,156158.. 4

MERVIN STEIN, Primary Examiner 'U.S. c1;v X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 90,253 Dated January 20, 1970 Inventor(s) Erwin Sick and Winfried Pipenbrink It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 56, "path" should read --plan--;

Column 4, line 28, "FIGURE 2" should read ---FIGURE 7---: Column 5, line 26, "project" should read --projection--; Column 7, line 38, after "and" insert --for--;

Column 8, line 3, after "fabric" insert -semico1on-;

SIGNED AN SEALED sea-197g (SEAL) Am Edward M. Fletcher, Ir.

Ameting Officer WILLIAM E. swarm? J11. Commissioner of Patents :nnu nnJnan 110.55

UsCOMM-DC 60876-960