GB2243847A - Visual inspection of fabric faults - Google Patents

Abstract

Fabric inspection apparatus comprises a screen (7) or wire frame spreader (60), preferably elliptical in shape, over which fabric (1) is drawn as it is wound onto a take-up roller (3). The screen (7) or spreader (60) is supported on rollers (5), through the fabric (1), and is lightweight in construction containing no light source. Light is transmitted to the interior of the screen or spreader, for illumination of the tubular fabric (1) from within the tube, by shining light from a light source (12) through one ply of fabric and through the top (9) or bottom of the spreader or of the screen which is transparent. Illumination is more uniform than if the light source were mounted within the screen or spreader; the handling is easier because the screen or spreader can be made light in weight; the strain on the fabric is less; and problems in powering the light source are solved.

Description

TITLE Fabric Fault Inspection Apparatus DESCRIPTION Field of the Invention The invention relates to fault inspection apparatus for the inspection of continuous tubular fabric.

Background Art Apparatus is known for permitting the continuous visual inspection of tubular fabric over its whole circumference as it is wound past an inspection station. The fabric is normally taken from a roller where the tubular formation is flattened and wound as a double ply roll, and the known apparatus involves illuminating the fabric between the front and back plies, using a light box which is inserted into the fabric tube at the inspection station, and over which the fabric is drawn as it is wound past the inspection station.

The light box is supported at its edges and its base by rollers, with the tubular fabric passing between the light box and those rollers. The light box is thus completely enclosed, and isolated from any physical connection with a power source. A problem therefore exists in passing power to the illumination source inside the light box.

This problem has been overcome in currently available and commercially used apparatus by means of a light box which is a flat double-sided screen, the sides of which are made from panels of translucent plastics material between which is mounted a bank of fluorescent tubes. Between the panels of the screen and connected to the fluorescent tubes there is mounted a transducer which converts a changing electromagnetic field into electrical power to illuminate the tubes. Alongside the screen, but separated therefrom by a small air gap, is a source of the electromagnetic field which transmits power across the air gap and through the fabric and screen wall to the transducer.

There are disadvantages associated with the use of the above apparatus. The fact that the light box has to carry its own fluorescent tubes and power source means that it is heavy, and its weight is an inconvenience when initially setting up the inspection apparatus (at which time a leading end of the fabric must be drawn over the light box which must then be balanced on its supporting rollers) and when running the apparatus (at which time the weight of the light box pulls at the fabric and opposes the free motion of fabric through the apparatus) . Also, the apparatus does involve the generation of a high intensity electromagnetic field in the close vicinity of an operator. Shielding of the field is not a certain means of preventing operator exposure, and there is a significant potential health problem in the lonq term operation of the apparatus.

Finally, it will be appreciated that much of the cost of the apparatus is associated with the transmission of the power as a varying electromagnetic field across the air gap and into the light box. Any solution which reduced that expense would therefore be most beneficial.

Summary of the Invention The invention provides apparatus for the visual inspection of faults in continuous tubular fabric, comprising a series of rollers for winding the fabric continuously past an inspection station, a double sided screen of transparent or translucent material for insertion into the fabric tube in the vicinity of the inspection station, and a light source for shining light through the fabric and into a screen volume defined between the opposite sides of the screen from a position immediately above or below the screen and externally of the fabric tube to illuminate the fabric tube internally.

The principal advantage of the apparatus of the invention is that it does not require expensive high energy sources of fluctuating electromagnetic field to generate electrical energy within the tubular fabric. The screen used in the apparatus of the invention incorporates no transducer at all, and the light source is positioned externally of the fabric and of the screen. As a result the screen can be made very substantially lighter than the light box of the prior art, which causes less of a pull on the fabric as it is drawn over the screen during inspection. Very surprisingly, the much simpler apparatus according to the invention gives superior visual inspection conditions. The illumination of the fabric tube is more uniform than when using a light box positioned within the tube as in the prior art.Even when the prior art light box is provided with sophisticated diffusers, the operative sees areas in front of each fluorescent tube which are brighter than areas between tubes. On the contrary, the use of a screen illuminated from without as in the invention produces a remarkably even illumination over the whole screen area, even when the screen is made from clear transparent material. The consistency of the illumination across the screen can be improved, at the expense of some small reduction in the level of that illumination, by making the screen with side walls of a translucent or optically diffusing material. Preferably however the top or bottom wall through which the light enters the interior of the screen is both clear and transparent.

The apparatus of the invention preferably further comprises a support bracket mechanism for the light source which permits that light source to be pivoted away from the rollers to permit threading up of the apparatus with a new fabric tube to be inspected.

Preferably the screen in use is supported through the fabric by rollers beneath and on each side of the screen.

Mirrors may be provided to enable an operative to inspect the fabric on both sides of the screen simultaneously as the fabric is drawn over the screen. Faults are readily detectable because they appear as a line or blemish on the fabric which moves over the surface of the screen with the moving fabric: and the human eye is better able to detect movement than to detect static differences in light and shade. The operative is preferably provided with a speed control to permit variation of the rate at which the fabric is wound over the screen. If desired a dimmer or intensity control can also be provided.

The screen is preferably elliptical in section, with rounded edges to avoid snagging the fabric. The side walls of the screen may be transparent or translucent but surprisingly good and uniform illumination is achieved with transparent side walls. The top or bottom wall through which the interior of the screen is illuminated from the light source is preferably clear and transparent.

DRAWINGS Figure 1 is a schematic vertical section to apparatus of the invention; Figure 2 is a schematic perspective view of the screen of Figure .1; Figure 3 is a general plan view of the operator position and inspection station of the apparatus of Figure 1; Figure 4 is a plan view of one form of light unit of Figure 1; and Figure 5 is a plan view of another form of the light unit of Figure 1.

Referring first to Figure 1, the general arrangement of the apparatus of the invention is illustrated during use with a roll of tubular fabric being inspected passing through the apparatus. The fabric 1, shown in chain-hyphen dotted lines, is shown as being drawn from a delivery roller 2 and ultimately wound onto a take-up roller 3. The fabric is guided through the apparatus by passing it over a top roller 4 and between the nip of a pair of bottom rollers 5.

The speed of rotation of the bottom rollers 5 is variable from a control unit 6 which is under operator control.

Between the delivery roller 2 and the top roller 4; and the bottom rollers 5 and the take-up roller 3 the fabric is folded flat on itself into a two-ply band of fabric.

Between the top roller 4 and the bottom rollers 5 the two plies of the fabric tube are separated and pass around a screen 7 which comprises opposite side walls 8 of transparent or translucent material, a transparent top wall 9 and a bottom wall 10 which mounts a pair of support rollers 11. The support rollers 11 support the screen 7 through the fabric 1 on the bottom rollers 5, and additional lateral support (not shown) is provided by edge rollers contacting the vertical edges of the screen 7 above and below the plane of the paper in Figure 1.

The preferred shape of the screen 7 is illustrated in Figure 2, which illustrates a screen generally elliptical in vertical section. Preferably all the edges are rounded to avoid snagging the fabric as it is drawn over the screen, and the screen is preferably made of a relatively lightweight plastics material such as perspex, acrylic resin or polycarbonate resin.

Reverting to Figure 1, there is illustrated a light unit 12 mounted on pivotal frame member 13 immediately above the screen 7. The frame member 13 is pivoted at 14 and includes a trailing arm 13a which is pivotally connected to a spring loaded strut 15 which is in compression and, in parts, a bias on the frame member 13 axially of the strut 15. The frame member 13 is thus pivotable overcentre between the position shown in solid line and the position shown in broken line in Figure 1. The former position is defined by a locating stop 16, the latter is defined by a locating stop 17. The frame member can be raised and lowered by means of a handle 18.

The light unit carried by the frame member 13 comprises a light source 19 which is illustrated as a bank of two fluorescent tubes. Clearly any source of high intensity light would be suitable, but fluorescent tubes are preferred because the heat generated is small. The light generated by the tubes shines through a diffuser 20 of the light unit, through one ply of the fabric 1, and through the top 9 of the screen 7 to illuminate the interior of the screen.

Figure 3 illustrates how an operator 30, seated at one side of the screen 7, can view the fabric passing down both sides of the screen from a single inspection position using a pair of angled mirrors 31.

Figure 4 illustrates how a housing 40 for the light unit 12 can be made of generally rectangular plan section, but with opaque masks 41 over the diffuser screen 20 to ensure that light from the light unit does not spill over the outside of the fabric as it is drawn down over the screen 7.

Tubular fabrics can be knitted in a variety of different diameters, and a different sized screen 70 would be needed to suit each different diameter of fabric to be examined.

Economies of tooling can be obtained by constructing the light unit 12 as a number of modular sections 40a, 40b, 40c as shown in Figure 5, so that the appropriate number of modules can be placed end to end to match the width of the screen 7 used for any particular fabric inspection. It may then be appropriate to mask some but not all of the modular sections as shown at 41 in Figure 5.

Claims (9)

1. Apparatus for the visual inspection of faults in continuous tubular fabric, comprising a series of rollers for winding the fabric continuously past an inspection station, a double sided screen of transparent or translucent material for insertion into the fabric tube in the vicinity of the inspection station, and a light source for shining light through the fabric and into a screen volume defined between the opposite sides of the screen from a position immediately above or below the screen and externally of the fabric tube to illuminate the fabric tube internally.

2. Apparatus according to claim 1, wherein the screen is generally elliptical in section, with transparent or translucent side walls and at least one transparent end wall through which the interior of the screen is illuminated.

3. Apparatus according to claim 2, wherein the side walls are transparent.

4. Apparatus according to any preceding claim, wherein the screen is made from perspex, acrylic resin or polurethane resin.

5. Apparatus according to any preceding claim, wherein the light source is mounted on a support bracket mechanism which permits the light source to be pivoted away from the rollers to permit threading up of the apparatus with a new fabric tube to be inspected.

6. Apparatus according to any preceding claim, further comprising rollers beneath and on each side of the screen for supporting the screen through the fabric.

7. Apparatus according to any preceding claim, further comprising a pair of angled mirrors to enable an operative to inspect the fabric on both sides of the screen simultaneously as the fabric is wound over the screen.

8. Apparatus according to any preceding claim, further comprising a speed control to permit variation of the rate at which the fabric is wound over the screen.

9. Apparatus for the visual inspection of faults in continuous fabric, substantially as described herein with reference to the drawings.