Apparatus For Detecting And Measuring Yarn Defects And Irregularities

Abstract

Apparatus for detecting light reflections from yarn irregularities, such as broken filaments, fluffs, loops and the like which extend from the normal body of a moving yarn strand. The yarn strand is directly illuminated, and a shadowbar is positioned outside the path of light illumination between the yarn strand and the detection apparatus. The shadowbar is of such dimension as to be larger than the normal body diameter of the yarn strand so as to block reflection from the normal body of the yarn strand from the detection apparatus but enables reflected light from any yarn irregularities extending from the normal body of the yarn strand to be detected by the detection apparatus, such as a photomultiplier tube.

Description

BACKGROUND OF THE INVENTION

The present invention is directed to an apparatus for detecting light reflections from yarn irregularities, such as broken filaments, fluffs, loops and the like which extend from the normal body of a moving yarn strand.

Broken filaments in the production of continuous filament yarns, fluffs and other surface irregularities extending from yarn strands being processed are a major quality control problem.

One method for determining this quality parameter involves visual analysis sometimes known as "fluff counting." Although the method is accurate, it is extremely slow since individual packages of yarn selected on a predetermined basis must be taken to a testing location, be creeled, threaded and analyzed by trained operators at a rate not greater than 50 yards per minute.

Another method for detecting such yarn irregularities involves the use of apparatus such as disclosed in the Denyssen U.S. Pat. No. 2,413,486 wherein a light beam is directed against a shadow casting strip and in a manner so that it will not reach a photocell, and a yarn travels within the field of the photocell through a shadowed region of the light beam on the opposite side of the shadow casting strip. The shadowed region of the beam is controlled by the shadow casting strip so that the yarn normally travels in the dark. Any irregularities projecting from the yarn extend out of the shadowed region and into the path of the light beam, thereby reflecting light to the photocell. A disadvantage of this arrangement, however, is that diffracted light will pass around the shadow casting strip and will illuminate the body of the yarn, and the reflection from such illumination will be picked up in part by the photocell. Any variation in yarn shape or size will thus be falsely interpreted as a yarn defect or yarn irregularity.

Still another method for detecting such yarn irregularities involves the use of apparatus such as disclosed in the Duncan et al. U.S. Pat. No. 2,841,048 wherein a source of light is directed to illuminate a non-reflecting shadow bar, behind which a funicular structure (small cord or small rope structure) moves parallel to the shadow bar as the funicular structure passes through a light-tight closure. The funicular structure or yarn thus is to be shielded from light and only broken filaments, strip backs or fluffs balls extending from the yarn will protrude into the illuminate area and result in reflected light from such protrusions passing through a phototube triggering aperture. Although the shadowbar is said to be non-reflecting, it has been found by experimentation that there is still some reflection necessarily from the shadowbar as it is being directly focused upon by the light beam. This renders the apparatus somewhat less sensitive to the reflections from broken filaments and the like because such reflections as there are from the shadowbar will also be received through the phototube aperture and acted upon.

Applicants eliminate the light diffraction problem by directly illuminating the yarn body, and by positioning the shadowbar so that it lies outside the path of the light beam between the yarn and the viewing slit in front of a photomultiplier tube so that the photomultiplier tube will only see light reflections from yarn irregularities extending from the normal body of the yarn and beyond the light shielding effect of the shadowbar. Since the shadowbar is positioned outside the path of the light beam, the shadowbar will not be illuminated by the light beam, and hence there will be no diffraction or reflection of light effects such as is possible in the above described U.S. Pat. Nos. 2,413,486 and 2,841,048.

A further method employed in the prior art is that disclosed by the Van Dongeren U.S. Pat. No. 2,991,685 wherein light reflections from bulked yarn are continuously received by a photo-receiver unit mounted behind a screen, and any temporary interruptions of such continuous recording, due to the detection of the absence of such bulkiness, are recorded in order to indicate quality of the yarn being tested. In his arrangement a light source directly illuminates the moving yarn but is also directly in alignment with the screen and photo-receiver behind the screen. Light, therefore, is being transmitted directly into the photo-receiver. Such arrangement would not be suitable for detecting broken filaments for instance because any broken filament extending from the mass of bulked filaments being detected would cause such small signal change as to be not noticed. In applicants' invention, on the other hand, a relatively large signal results upon receipt of reflection of light from a single filament extending from the normal body of the yarn strand being examined. The invention therefore is far more sensitive to detection of such single filaments.

BRIEF SUMMARY OF THE INVENTION

The invention therefore is directed to an apparatus wherein a moving yarn strand is directly illuminated, and reflected light from broken filaments and the like which extend from the surface of the normal body of the yarn strand are detected and measured or counted as desired. Reflected light from the normal body of the yarn strand is prevented from being detected by a shadowbar which is positioned between the moving yarn strand and the light reflection detection apparatus. The shadowbar is positioned so as to be located beyond the path of illumination that is illuminating the yarn strand, and is of such dimension as to be larger than the normal body diameter of the yarn strand so as to block off reflected light from the normal body of the yarn strand.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a perspective view of the overall apparatus including the detection apparatus and the registering apparatus with the cover assembly of the detection apparatus shown in closed portion in phantom line and in the open position in solid line and illustrating the yarn passing in front of the shadowbar and viewing slit;

FIG. 2 is a cross-sectional view in side elevation of the detection apparatus taken along line 2--2 of FIG. 1;

FIG. 3 is a diagrammatic illustration of the detection apparatus and illustrating the path that light would follow from the light source through the collimating diaphragms for subsequent illumination of the yarn strand and into the light absorbing well, and further illustrating the path reflected light from a defect extending from the normal body diameter of the yarn strand follows in passing the shadowbar and entering through the viewing slits to the photomultiplier tube, and still further illustrating reflected light from the edge of one of the collimating diaphragms being trapped by one of the wall members defining a viewing slit; and

FIG. 4 is a cross-sectional view taken along line 4--4 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In reference to the drawings, 10 designates the detection apparatus and 12 designates the registering apparatus that may be operatively connected to the detection apparatus. It will be appreciated that apparatus having functions other than a registering function may also be used without departing from the scope of the invention.

The detection apparatus 10 has a housing 14 that is divided into three main light-tight compartments. Compartment 16 (FIG. 2) has housed therein a light sensitive photomultiplier tube 18 which is electrically coupled through an appropriate circuit to the registering apparatus 12. Compartment 20, adjacent to compartment 16, houses the light source 22, suitably supported by a light support bracket 24, and a lens 26, suitably supported by a lens support 28. The third compartment 30 is also adjacent to compartment 16 and is located above compartment 20. This third compartment is formed by light shield walls 32 and a hinged cover assembly 34 that closes over the top of the light shield walls to form with the light shield walls a light baffled entryway for the yarn strand 36 being inspected. The entryway consists of a pair of opposed slots 38 formed in the light shield walls and a pair of opposed slots 40 in the hinged cover assembly, the slots 40 being offset (FIG. 4) with respect to the slots 38 so as to prevent light from entering with the yarn strand. Each pair of slots is provided, respectively, with wear resistant yarn guides 42, 44.

The third compartment 30 houses a shadowbar 46 that is positioned parallel to the path to be followed by the yarn strand 36 when it passes through compartment 30. The shadowbar is of such dimension as to be larger than the normal body diameter of yarn strand that is to be inspected. This dimension can be changed if larger or smaller yarn strands are to be inspected. The dimension of the shadowbar also bears a relation to the distance the shadowbar is spaced from the path of the yarn strand, for reasons which will become evident from subsequent description.

An aperture 48 is provided between compartments 30 and 20 so that light from light source 22 may be beamed into compartment 30 for illuminating the yarn strand 36 when it passes along its path through compartment 30. The beam of light is collimated or made parallel-like by at least one collimating diaphragm 50. Although the detection apparatus could be operated with one such collimated diaphragm, the use of a second collimating diaphragm 52 serves to minimize stray light reflection and to render the light beam more parallel. The diagrammatic illustration in FIG. 3 serves to show how part of the light that has spread (as indicated at X) is blocked by collimating diaphragm 52.

An aperture 54 is provided between compartments 30 and 16 so that desired reflected light can pass therethrough, and at least one diaphragm member 56 defining a viewing slit 58 is provided across aperture 54 between compartments 30 and 16. The viewing slit is located perpendicular to the light beam from the light source 22 and is directly opposite the yarn strand path. Although the detection apparatus has been operated effectively with a single such diaphragm member, a second diaphragm member 60 with viewing slit 62 serves to minimize stray light reflection such as might be reflected from the edge of the aperture in the collimating diaphragm 50, as demonstrated in FIG. 3 at Y. Diaphragm member 60 blocks off light reflection Y and thus serves to render the photomultiplier tube 18 more effective in performing its desired function.

The hinged cover assembly 34 is further provided with a recessed light-absorbing well 64 which when the cover assembly is in operative position, as shown in FIGS. 2 and 3, will be in direct alignment with the light source 22. The light that extends beyond the yarn strand will be absorbed in the light absorbing well, which is deep enough to prevent any stray light reflection from reaching the photomultiplier tube 18.

In operation, as yarn strand 36 passes through the light-tight chamber defined by compartment 30, the yarn strand is directly illuminated by light source 22. Any light reflection directly abeam of and from the normal body diameter of the yarn strand is blocked by the shadowbar 46, which is spaced outside the path of the collimated light beam and is between the yarn strand, when moving through the light-tight chamber, and the viewing slit 58.

Any yarn irregularities, such as broken filaments, fluffs, loops and the like which extend from the normal body diameter of the moving yarn strand will reflect light beyond and behind the shadowbar and will be picked up or detected through the viewing slit or slits by the photomultiplier tube 18. Yarn defect 66 is shown as reflecting light through the viewing slits for reception by the photomultiplier tube 18. The photomultiplier tube will respond in turn and generate a predetermined electrical signal and actuate the registering apparatus or whatever apparatus happens to be operatively connected to the photomultiplier tube for registering and counting each electrical signal.

The registering apparatus may be a solid state instrument having a pulse counting and integrating module which will process the signal from the photomultiplier tube in order to count and integrate voltage peaks due to yarn defects or irregularities. The signal, for instance, may first pass through a gain control and filter and then into a voltage follower which would prevent loading of the photomultiplier tube. A diode could be used to clip the positive-going portion of the signal, following which the signal could then be fed into both an integrating amplifier and a one-shot multi-vibrator which would trigger an electrical impulse counter. The one-shot multivibrator could have an adjustable triggering threshold which would allow a choice of the pulse height to be counted.

It will now be evident that with the arrangement disclosed the photomultiplier tube 18 will receive essentially zero light illumination until a defect protrudes beyond the normal body diameter of the yarn strand and beyond the shielding effect of the shadowbar 46. In this manner the photomultiplier tube will be rendered more sensitive to a single broken filament, loop and the like. This apparatus, therefore, will be able to measure staple yarn fuzz density or detect broken filaments in continuous filament yarn.

Tests run on this apparatus have established that 55 and 150 denier acetate yarn, for example, may be inspected at speeds up to 2,100 feet per minute. Thus the apparatus may be a high speed detector of defects in single ends of acetate yarn.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims

We claim:

1. An apparatus for detecting reflected light from yarn irregularities in a moving yarn strand as the yarn strand moves along a predetermined path and comprising:

wall means defining a light-tight chamber;

means for guiding the moving yarn strand through the wall means into, across and out of the light-tight chamber;

means including a light source for directing a collimated light beam from said light source into the light-tight chamber, to illuminate the yarn strand when the yarn strand is moving through the chamber;

one of the wall means defining therethrough a viewing slit that is located outside the path of the light beam and perpendicular to the axis of the collimated light beam and directly opposite the yarn strand path;

a shadowbar positioned outside the path of the collimated light beam and between the yarn strand when moving through the light-tight chamber and the viewing slit, the shadowbar being of such dimension as to be larger than the normal body diameter of the yarn strand so as to block reflected light from the normal body of the yarn strand from the viewing slit, but enabling reflected light from any yarn irregularities extending from the normal body of the yarn strand to enter through said viewing slit; and

means on the opposite side of said viewing slit and responsive to reflected light entering through said viewing slit from said yarn irregularities to generate a predetermined electrical signal proportional to said reflected light.

2. An apparatus as defined in claim 1 and wherein said means for guiding the moving yarn strand include light baffle means to exclude light from entering into the light-tight chamber along the path of the yarn strand as it enters and leaves said light-tight chamber.

3. An apparatus as defined in claim 1 and wherein said means responsive to reflected light include a photomultiplier tube.

4. An apparatus as defined in claim 1 and further comprising an electrical counting system responsive to each electrical signal generated for registering and recording each said electrical signal.

5. An apparatus as defined in claim 1 and wherein the wall means defines through one of said wall means an opening through which said collimated light beam enters into the light-tight chamber, the wall means opposite said one of said wall means defining a recessed light absorbing well for shielding any undesired reflected light from entering through said viewing slit.

6. An apparatus as defined in claim 5, and wherein the opening through said one of said wall means is defined by at least one collimating diaphragm.

7. An apparatus as defined in claim 1, and wherein a second viewing slit is provided between the viewing slit and the last recited means.