This invention relates to fabric testing apparatus, for the objective measurement of certain properties of fabrics that are important to the tailorability of the fabric.

Devices presently available for this purpose are relatively expensive and have the following inherent limitations and drawbacks: (1) The tests that are done with them are destructive in that small samples of specific sizes must be cut from a piece of fabric for testing. After testing the samples are useless.

(2) Because the tests are destructive, they cannot be used to assess the way in which fabric properties vary from place to place in a piece of fabric, nor to measure fabric properties during the fabric and garment manufacturing process.

(3) The tests are time consuming. Cutting and preparation of samples can take up to half of the total time required for testing.

The physical and mechanical properties of fabric that are important to the garment manufacturing industry include (i) relaxation shrinkage, (ii) hygral expansion, (iii) formability, (iv) extensibility, (v) bending rigidity, (vi) shear rigidity, (vii) thickness, (viii) compressibility, and (ix) surface characteristics.

At least some of these properties are inter- related for a specific type of fabric. For example, the relaxation shrinkage of a light-weight wool fabric is highly related to the difference between the extensibility of the relaxed and unrelaxed fabric.

Also, the hygral expansion of wool fabric is highly related to the extensibility of the relaxed fabric. By measuring the extensibility of a wool fabric as received and after relaxation, one can thus predict the

relaxation shrinkage and hygral expansion of the fabric.

Furthermore, the bending rigidity of light- weight wool fabrics is related to the thickness and initial Young's modulus of the fabric, and the shear rigidity is highly related to the extensibility in the bias direction.

Thus, by simply measuring the extensibility of a fabric in a number of different directions, and its thickness and compressibility, a number of properties of the fabric that are important to the tailorability of the fabric can be determined.

It is an object of the present invention to provide apparatus for objectively measuring the extensibility, thickness, and compressibility of a fabric, in a rapid and non-destructive manner, and from these measurements to determine certain properties of the fabric that are important to the tailorability of the fabric.

According to one aspect of the invention there is provided fabric testing apparatus comprising first means for measuring the extensibility of a fabric, said first means comprises a pair of clamping devices for clamping the fabric to be tested in spaced apart positions, tensioning means for varying the distance between the clamping devices, and tension sensing means for determining the tension in the fabric between the clamping devices.

The clamping devices may be electro-magnetic clamping devices, each comprising a pair of opposed magnetic core halves defining between them a gap in which the fabric can be placed, and a coil for magnetising the core halves, whereby, when the coil is energized, the core halves are drawn towards one another magnetically, to clamp the fabric between them.

The apparatus may comprise a base plate of non-magnetic material, the opposed core halves of each

of the clamping devices being mounted one underneath the base plate and the other on a cantilever arm above the base plate.

The tensioning means may comprise a stepper motor. The tension sensing means may comprise a load cell.

The apparatus may further comprise data acquisition and processing means, the coil of each clamping device, the stepper motor, and the load cell being coupled to the data acquisition and processing means for control and data acquisition purposes. The data acquisition and processing means may comprise a suitably programmed computer.

The apparatus may further comprise second means for measuring the thickness and compressibility of the fabric, said second means comprising a pressure plate mounted above the base plate so as to be parallel to and displaceable towards and away from the base plate, the pressure plate and the base plate defining between them a gap in which the fabric can be placed, the pressure plate being biased towards the base plate, and the pressure plate being coupled to position sensing means for determining the distance between the pressure plate and the base plate.

The pressure plate may be biased gravitationally towards the base plate. To this end the pressure plate may be adapted to have one or more loading weights placed removably thereon.

The position sensing means may comprise a distance-to-voltage transducer. The position sensing means may be coupled to the data acquisition and processing means.

According to another aspect of the invention there is provided fabric testing apparatus comprising first means for measuring the extensibility of a fabric, and second means for measuring the thickness and compressibility of the fabric, the second means

comprising a base plate, a pressure plate mounted above the base plate so as to be parallel to and displaceable towards and away from the base plate, the pressure plate and the base plate defining between them a gap in which the fabric can be placed, the pressure plate being biased towards the base plate, and the pressure plate being coupled to position sensing means for determining the distance between the pressure plate and the base plate.

The invention will now be described in more detail, by way of example, with reference to the accompanying drawings.

In the drawings: Figure 1 is a pictorial view of testing apparatus in accordance with the invention; Figure 2 is a plot showing a typical load- extension curve for a fabric; Figure 3 is a plot showing the relationship between relaxation shrinkage and the difference in extensibility of a relaxed and unrelaxed fabric for a series of commercial fabrics (warp and weft values); Figure 4 is a plot showing the relationship between hygral expansion and extensibility (500gf/cm) of relaxed fabrics; Figure 5 is a plot showing the relationship between fabric bending rigidity on the one hand and thickness and extensibility of the fabric on the other hand, in the warp direction of the fabric; Figure 6 is a plot similar to Figure 5 but showing the fabric bending rigidity in the weft direction of the fabric; Figure 7 is a plot showing the variation of extensibility of a fabric with direction; Figure 8 illustrates the forces that act on an undistorted fabric when determining the extensibility of the fabric; and Figure 9 is similar to Figure 8 but shows the

forces in respect of a distorted fabric.

Referring first to Figure 1, reference numeral 10 generally indicates fabric testing apparatus in accordance with the invention, for the objective measurement, and in a non-destructive manner, of certain properties of a fabric that are important to the tailorability of the fabric. The apparatus comprises a portable instrument 12 which includes a section 14 where measurements of thickness and compressibility are carried out, and a section 16 where measurements of extensibility are carried out. The apparatus further comprises a suitably programmed desk- top computer 18 for control and data acquisition purposes.

The instrument 12 comprises a cover 20 which encloses various parts of the instrument, and a cantilever arm 22. The cover 20 has a base plate 21 at the top and is cut away for purposes of illustration, to show the various parts housed in the cover. The front end of the cantilever arm 22 is positioned above the base plate 21. The cover 20 and the various parts of the instrument that are housed in the cover are mounted on a base (not shown), and the rear end (not shown) of the cantilever arm 22 is fixed to the base.

The section 14 where measurements of thickness and compressibility are carried out comprises a fixed part 24 and a movable core 26 which can move up and down in the fixed part. The fixed and movable parts 24,26 together form a linearly variable differential transformer which acts as a linear distance-to-voltage transducer designated 27. The fixed part 24 is mounted on a bracket 28 which is fixed to the cantilever arm 22. The core 26 has a pressure plate in the form of a disc 30 at its lower end. A weight 32 of copper or other non-magnetic material can be stacked on top of the disc 30. In the example illustrated, the combined mass of the core 26 and the

disc 30 is lOg, and the surface area of the lower face of the disc is 5cm2. The mass of the weight 32 is 490g. The transducer 27 is connected to the computer 18, as indicated by the dashed line 34.

The cantilever arm 22 has a pair of cross arms 36 fixed thereto. Suspended from the cross arms 36 there are two steel blocks 38.1 and 38.2. The blocks 38.1 and 38.2 are connected to the cross arms 36 by means of spring mountings (not shown), so that they are able to move vertically with respect to the cross arms. Furthermore, the blocks 38.1 and 38.2 are mounted in such a manner that they are able to move freely with respect to the cross arms 36 in the direction of arrows A, i. e. in the longitudinal direction of the cross arms. This can, for example, be achieved by mounting the blocks 38.1 and 38.2 on rails (not shown). The blocks 38.1 and 38.2 are thus suspended above the base plate 21, the spring mountings maintaining a gap between the blocks 38.1 and 38.2 on the one hand and the base plate 21 on the other hand.

Underneath the base plate 21, below the blocks 38.1 and 38.2, there are a pair of E-cores 40.1 and 40.2 respectively, each having a coil 42 wound onto the central limb thereof. The block 38.1 and the E-core 40.1 form a first clamp 44.1 between which fabric can be clamped. Likewise, the block 38.2 and the E-core 40.2 form a second clamp 44.2 between which the fabric can be clamped. The base plate 21 is of a non-magnetic material such as, for example, copper, bronze, or aluminium so that, when the coils 42 are energized, the blocks 38.1 and 38.2 are attracted to the E-cores 40.1 and 40.2 respectively. The current required to energize the coils 42 is controlled by the computer 18, as indicated by the dashed line 46.

The E-core 40.1 is supported on a support 48, in such a manner that it can slide in the direction of arrows A with respect to the support. The E-core 40.1

is connected to a load cell 50 by means of a rod 52.

The load cell 50 is connected to the computer 18 as indicated by the dashed line 54.

The E-core 40.2 is mounted on a carriage 56.

The carriage 56 is supported on a support 58 so that the carriage can be displaced with respect to the support in the direction of arrows A. The carriage 56 is connected to a stepper motor (not shown) via a rod 60. The stepper motor is controlled by the computer 18, as indicated by the dashed line 62.

During testing, fabric that is to be tested is placed on the base plate 21, so that it is underneath the disc 30 and also underneath the steel blocks 38.1 and 38.2.

The disc 30 is allowed to bear down on the fabric. The output of the transducer 27 then provides a measure of the distance between the disc 30 and the base plate 21, and thus of the thickness of the fabric between them. The thickness of the fabric is measured when the weight 32 is not on the disc 30 (in which event the fabric is subjected to a pressure of 2g/cnr), and when the weight 32 is on the disc (in which event the fabric is subjected to a pressure of lOOg/cm'-).

To carry out extensibility measurements a software program in the computer 18 will first instruct the instrument to close the clamps 44.1 and 44.2, and then starts the stepper motor that is connected to the E-core 40.2. This extends the fabric in the direction of arrows A while imposing a load on the load cell 50.

Upon reaching a predetermined maximum load or extension, the software program instructs the stepper motor to turn in the other direction, to return the E- core 40.2. The number of steps through which the stepper motor is stepped are counted by the computer 18, whereas the load on the fabric is measured by the load cell 50 and recorded by the computer. A typical load versus extension curve obtained in this manner is

illustrated in Figure 2.

By placing the fabric in the instrument in different directions, the low-stress tensile properties of the fabric in different directions can be determined. The bias extensibility may be used to calculate the shear rigidity.

Once the difference in extensibility of the fabric when in the relaxed and unrelaxed conditions is known, the relaxation shrinkage of the fabric can be determined according to the relationship shown in Figure 3, which plots the values of relaxation shrinkage (W) against difference in extensibility at 500gf/cm.

Furthermore, the hygral expansion of the fabric can be determined according to the relationship shown in Figure 4, which plots values of hygral expansion (W) against extensibility (W) at 500gf/cm.

Furthermore, the bending rigidity of the fabric in the warp and weft directions respectively can be determined according to the relationships shown in Figures 5 and 6, which plot values of bending rigidity against fabric thickness to the third power divided by extensibility in the warp or weft direction as the case may be.

The system can also be used to detect the degree of fabric distortion, i. e. bow and skewness.

Fabric distortion is not only a problem with check fabrics, but also with single-colour and stripe fabrics. Distorted check fabrics are obviously not acceptable because of problems in check matching.

Although distorted single-colour or stripe fabrics do not suffer from problems such as check matching, because the distortion is hardly visible, they can cause much difficulty in making-up. To determine the degree of distortion, it is normally necessary in conventional testing procedures to tear the fabric, causing considerable waste. As a result, conventional

tests to determine fabric distortion can only be carried out at the end of a fabric sample, and this cannot really represent the overall degree of distortion of the sample.

With the apparatus of the present invention, fabric distortion is measured by measuring the extensibility in different directions. As illustrated in Figure 7, the extensibility of a fabric normally varies with direction, reaching a maximum in the bias direction and minimums in the warp and weft directions.

If the fabric is not distorted, as illustrated in Figure 8, the extensibility (Eb) in the B-B direction, which is at an angle-3 (e. g.-15°) to the weft direction (A-A in the drawing), is very similar to that (Ec) in the C-C direction which is at an angle +0 to the weft direction. If the fabric is distorted, as illustrated in Figure 9, the extensibility in the B-B direction (Eb) is very different from that in the C-C direction (Ec). In practice, if (Eb-Ec)/Eb is higher than a predetermined tolerance limit, the fabric can be considered as unacceptably distorted. This general principle also holds for single-colour or stripe fabrics whose extensibility does not vary greatly in different directions because, for such fabrics, fabric distortion does not cause any making-up problems.

The apparatus described herein can have the following uses: (a) Quality assurance of finished fabrics. For a specific range of finished fabrics, most of the important physical and mechanical properties of the fabric, related to making-up performance of the fabric, can be predicted from the extensibilities in the warp, weft and bias directions, before relaxation and after relaxation, and from the thickness and compressibility. These values can all be measured by the apparatus. The measured and calculated

properties of finished fabrics can be compared with the specified tolerance limits to assess the quality.

(b) On-line quality control of fabrics during finishing. The thickness, compressibility, extensibility, and shear rigidity of fabrics can be checked before and after every stage of the finishing process. As a result, preventative and corrective action can be taken during the finishing process, to produce a finished product of high and consistent quality.

(c) Assessment of the effectiveness of finishing processes. This can be done by comparing the test results with the predetermined or desired levels and tolerances.

(d) On-line quality control during making-up.

The distortion (i. e. bow & skewness) of single colour and stripe fabrics can be checked without tearing the fabric. The variation of the fabric in terms of various physical and mechanical properties along the length can be determined.

(e) A tool for analysing garment problems. Tests can be performed on garments in a non-destructive manner, to determine, for example, the reasons for non-performance.