Abstract:
A measuring device useful for measuring mechanical properties of highly flexible or limp sheet materials. The device includes a base, a pair of clamping members, with one of the clamping members being movable away from and toward the second clamping member. A load sensor is mounted in one of the clamping means for measurement of the required mechanical properties.

Description:
This invention relates to the measurement of the mechanical properties of highly flexible or limp sheet material, for example paper, textile material, plastics and composite materials. In particular, the invention relates to the measurement of the tensile, shear, buckling, and compression strengths, sheet thickness, bending stiffness and surface qualities such as friction and roughness. The purpose of such testing, under normal loading without destruction of the sample of the material under test, is to determine the performance of the material in use, e.g. clothing fabrics during normal wear. 
     BACKGROUND OF THE INVENTION 
     To date, such measurements have generally been made independently on different samples of the material to be tested. For example, there is the widely accepted Kawabata Evaluation System for Fabric (KESF) for textile fabrics. With this system, different samples of the fabric to be tested are required to be placed in several different devices in order to make the measurements of the various properties listed above. One sample of the fabric to be tested is placed in a device which measures tensile and shear properties by clamping the sample at two spaced locations and moving the clamps apart and laterally relative to each other. This device has to be calibrated for each measurement on a sample. Bending strength, but not buckling, is measured by placing a different sample of the fabric in a second device. In this device the sample is mounted vertically and the device is very difficult to set up in trying to achieve an even tension in the fabric. One clamp makes a circumferential movement in order to measure the bending strength. Thickness measurement requires another measuring device. In this case a head moves vertically relative to the fabric in order to measure the thickness of the material and then its compressibility. For surface properties, a further sample of the material is clamped under load in a further device in which a head lowers and the material is then moved laterally relative to the head. Different probes on the head measure surface roughness and friction. It is very expensive to have all of these devices and very time consuming to place the different samples in the different devices in order to make all of the measurements. Another system is the Fabric Assurance by Simple Testing (FAST) system. 
     This is a simplified version of the KESF system, but at least two different samples are needed. 
     Thickness and compression are measured in one device at two positions of a movable head. 
     Bending is measured in another device in which the fabric is laid on a bed and is traversed by a moving plate on top of the fabric until the fabric extends over the edge of the bed and cuts a light beam. For tensile strength, the fabric is placed between two clamps in a further device, the lower one of the clamps being on an arm which is pivoted and has a weight on the other end. When the arm is released, the device registers the load in the fabric. The results from these tests are limited to the measured loads only and cannot provide full stress/strain profiles of the test samples. In addition the results from the two test systems are not very reproducible, due to the need for different sample sizes and the manual handling for each test. In the cosmetics and medical fields it is desirable to determine the effect cosmetic or medical creams and the like have on the human skin. To this end a fabric which has similar characteristics to human or animal skin is treated with the cream and the mechanical properties of fabric are then measured. For such an application the KESF and FAST systems are considered too expensive and too complicated. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a single apparatus for the measurement of the mechanical properties of a single sample of a limp sheet material in order to reduce the equipment costs compared with that of the number of existing devices required. It is also an object of the present invention to reduce the time and complexity of making such measurements and to increase the accuracy and reproducibility of such measurements compared with the existing methods. 
     The invention provides a device for the measurement of the mechanical properties of a limp sheet material, comprising a base, a pair of clamping members operable to clamp the sheet material to the base at spaced locations, load sensing means on at least one clamping member, at least one of the clamping members being movable away from and towards the other in the plane of the sheet material and laterally of the other in said plane, and a head assembly having a sensing device spaced from the base and movable theretowards and laterally of the plane of the sheet material. 
     One clamping member may be the at least one movable clamping member and the load sensing means may be mounted on the other clamping member. Two load sensing means having differing ranges of measurement may be mounted on the one clamping member, the first load sensing means being adapted to measure tensile load and the second load sensing means being adapted to measure buckling load. The measurement device may comprise a third load sensing means adapted to measure shear loads. The sensing device may comprise a further load sensing means and a surface characteristics sensing means. 
     Preferably the base is a plate which is disposed substantially horizontally, in which case the clamping members may be disposed above the base plate and positionally adjustable to clamp the sheet material. The measuring device may comprise position indicating means adapted to indicate the position of the at least one movable clamping member relative to a datum position. The at least one movable clamping member may be mounted on low friction slideways, and the slideways may be disposed remote from the axes of movement of the at least one movable clamping member. The head assembly may be disposed between the clamping members, and may be mounted on the base plate. The head assembly may comprise a slide part on which the sensing device is mounted for movement towards the base plate and, together with the slide part, laterally of the sheet material. 
     The base plate may have an edge to a side of the at least one movable clamping member remote from the other clamping member, over which edge the sheet material may be moved to cantilever thereover. The measurement device may comprise a beam transmitting device and a beam sensing device operable to receive the transmitted beam and detect when the sheet material interrupts the beam. The beam may be directed from beneath and spaced from the edge of the base plate at an angle of between 30° and 60° to the horizontal. 
     Preferably the beam is directed at an angle of 41.5° to the horizontal. The base plate may be formed to have a shallow recess between the spaced locations to reduce the frictional contact between the sheet material and the base plate. 
     The measurement device may comprise control means operable to control the sequence of movement of the at least one movable clamping member and the sensing device. The control means may also be operable to render operable the first or second load sensing means for measuring tensile load or buckling load respectively dependent on the direction of movement from the datum position of the at least one movable clamping member. The control means may be operable to vary the length of time between successive movements of the at least one movable clamping member and the sensing device. The control means may also be operable to adjust the speed of movement of the at least one movable clamping member and the sensing device. The control means may comprise programmable means for the selection of the measurements to be made, the speed of movement of the at least one movable clamping member and the sensing device, and the timing of the movements. 
     The movement of the at least one movable clamping member and the sensing device may be effected by respective stepper motors. The clamping members may also be moved between respective sample material release positions and their clamping positions by respective stepper motors. 
     In another aspect, the invention relates to methods and apparatus for the assessment of seam pucker and other surface irregularities. 
     Assessment of surface irregularities, particularly seam pucker, is at present largely a subjective matter. Attempts to introduce objectivity into the assessment have, to date, not been so successful as the result is non-standard. The same is true for measurements, generally, of surface irregularities of which seam pucker is typical—with the exception, possibly, of microscopic surface roughness measurements, necessarily automated and standardized because of inaccessibility to the naked eye—surface irregularity is “judged” rather than objectively measured. 
     The invention provides an objective assessment for seam pucker and other, comparable surface irregularities. 
     The invention comprises a method for the assessment of seam pucker and other surface irregularities comprising directing at the surface a line beam from an illuminator, imaging the line on the surface formed by the line beam and analysing data of the image to produce an objective indication of the degree of irregularity of the surface. 
     Parallel line beams may be directed at the surface. For the assessment of seam pucker, the parallel line beams may be directed to form lines on the surface parallel to and either side of the seam, and at an angle from the plane perpendicular to the surface. 
     The illuminator may comprise a line beam laser. 
     The line on the surface may be imaged by a pixel image such as a CCD array camera. 
     The image may be analysed in a computer programmed with image analysis software. The result of analysing the image may be a display of a distribution of severity of deviation of the surface from flat. 
     The surface may be that of a limp material, such as a textile fabric, mounted on a flat support base. The base may, for the assessment, be inclined steeply with the material clamped uppermost and resting against the base below the clamping location. 
     For consistency of measurement the material is preferably the same size as the bed, so no additional irregularity is occasioned by edge effects. A sample for assessment may be cut to size using the bed as a template. 
     The invention also comprises surface irregularity assessment apparatus comprising 
     a line beam illuminator; 
     a support arrangement for the surface under assessment such that the line beam illuminator is directed at the surface to illuminate a line thereon; 
     an imaging arrangement adapted to image the line illuminated on the surface, by the line beam illuminator; and 
     analysis means adapted to receive image data to produce an objective indication of the degree of irregularity of the surface. 
     There may be one, two or more line beam illuminators casting parallel beams. Beams may be cast in different arrangements to provide further information. 
     The imaging arrangement may comprise a pixel imaging arrangement, and may comprise a CCD array. 
     The line illuminator may be a laser. 
     The analysis means may comprise a computer programmed with image analysis software. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     Embodiments of the invention will now be further described with references to the accompanying drawings in which: 
     FIG. 1 is a front elevation, 
     FIG. 2 is a view on line  2 — 2  of FIG. 1, 
     FIG. 3 is a perspective view of an apparatus for measuring seam pucker, in simplified form; 
     FIG. 4 is a view of an illuminated sample in the apparatus of FIG. 3; and 
     FIG. 5 is a block diagram of the apparatus of FIG.  3 . 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIGS. 1 and 2, there is shown a measurement device  10  comprising a substantially horizontally disposed base plate  11  on which a sample  12  of the material to be tested is placed. A ‘fixed’ clamping member  13  and a ‘movable’ clamping member  14  are mounted on respective supports  15 ,  16  and are movable by respective stepper motors  17 ,  18  from their respective sample material release positions as shown downwardly towards the base plate  11  to clamp the sample  12 . At this initial stage the ‘movable’ clamping member  14  and its ‘movable’ support  16  are in the ‘datum position and the end of the sample  12  is aligned with the end  19  of the base plate  11 . Mounted on a head support  20  is a head assembly comprising a slide part  20   a  which is movable by means of stepper motor  21  and lead screw laterally of the sample  12  in slideways  22  and a sensing part  20   b  which is movable by means of a stepper motor  23  vertically in slideways  24 . The sensing part  20   b  has a sensing device  25  which incorporates load sensing means  26  and a surface characteristics sensing means  27 . A position sensor  28  is provided on the support  20  to measure the height of the head assembly  20  relative to the base plate  11 . 
     The ‘movable’ support  16  is mounted on the base plate  11  in low friction slideways  29  disposed remote from the axis  30  of movement of the ‘movable’ support  16  to minimise the effects of friction on the operation and measurement sensitivity of the measurement device  10 . The ‘movable’ support  16  is movable by means of stepper motor  31  and lead screw  32  away from and towards the ‘fixed’ support  15 , and a position sensor  33  indicates the position of the ‘movable’ support  16  relative to a datum position. The upper part  16   a  of the ‘movable’ support  16  is movable in slideways  34  in lower part  16   b  by stepper motor  35  laterally of the base plate  11 . A position sensor  36  indicates the lateral position of the ‘movable’ support  16  relative to a datum central position. In fact, the ‘fixed’ support  15  is also mounted on the slideways  29  and is movable from its datum position  16  under the effect of a change in the tension in the sample  12 . Any such change in tension is detected by load cells  37 ,  38 . The ‘movable’ support  16  may be extended as shown to support the sample  12  when it is moved towards the edge  19  of the base plate  12  for the bending test described below. 
     Located adjacent the edge  19  of the base plate  12  is a beam transmitting device  39  and a beam sensing device  40  operable to receive the transmitted beam  41  and detect when the sample  12  interrupts the beam  41 . The beam transmitting device  39  is mounted at the edge  19  and the beam  41  is directed downwardly towards the base plate  11  at an angle of 41.5° to the horizontal. 
     A control device  42 , including programmable means  43  is provided to control automatically the operation of the measuring device  10 , which is as follows. The prepared sample  12  of the material to be tested is placed in the measuring device  10  on the base plate  11  so that the end of the sample aligns with the edge  19  of the base plate  11 . The control device  42  is activated and the clamping members  13 ,  14  are lowered by their motors  17 ,  18  to clamp the sample  12 . Load cell  37 , having a range of measurement appropriate to the measurement of tension in the sample  12  is brought into operation by the control means  42  and the other load cell  38  is taken out of operation. The motor  31  is then operated to move the ‘movable’ support  16  from its datum position in a direction away from the ‘fixed’ support  15 . This movement applies a tensile load to the sample  12 , which is measured by the load cell  37 . A shallow recess  44  in the base plate  11  under the sample  12  reduces the effect of friction between the sample  12  and the base plate  11 . The distance moved by the ‘movable’ support  16  is measured by the position sensor  33 , so that a ‘load-extension’ relationship for the sample  12  can be determined. The control means  42  reverses the motor  31  to return the ‘movable’ support  16  to its datum position. The load sensor  37  is taken out of operation and the load cell  38 , having a range of measurement appropriate to the measurement of buckling load in the sample  12 , is brought into operation. Further movement of the ‘movable’ support  16  towards the ‘fixed’ support  15  enables the load in the sample  12  as it buckles to be measured by the load cell  38 . The ‘movable support  16  is then again returned to its datum position. 
     The sensing part  20   b  of the head support  20  is then lowered by means of the motor  23  until contact between the sample  12  and the surface characteristics sensing means  27 . The height of the surface characteristics sensing means  27  above the base plate  11  is indicated by the position sensor  28  so as to determine the thickness of the sample  12 . Further lowering of the sensing part  20   b  will apply a compressive load to the sample  12 , as determined by the load cell  26 . Correlation of the readings of the load cell  26  and the position sensor  28  will provide a ‘Load-compression’ relationship for the sample  12 . The sensing part  20   b  is then raised to the position of contact between the sample  12  and the surface characteristics sensing means  27 . Lateral movement of the slide part  20   a  along slideways  22  by means of motor  21  causes the surface characteristics sensing means  27  to measure the friction between it and the sample  12  and also the surface roughness of the sample  12 . The sensing part  20   b  is then raised to its original position. 
     The control means  42  then activates motor  36  to move the upper part  16   a  of the ‘movable’ support  16  laterally of the base plate  11 . This induces a shear in the sample  12 , and the shear load is indicated by a further load cell  45 . Correlation of the readings of the load cell  45  and the position sensor  36  will provide a ‘Load-shear’ relationship for the sample  12 . 
     To determine the bending characteristics of the sample  12 , the control means  42  now activates motors  17  and  18  to raise the ‘fixed’ and ‘movable’ clamping members  13 ,  14  to release the sample  12 . Motor  31  is then activated to move the ‘movable’ support  16  and the sample  12  away from the ‘fixed’ support  15 . During this movement the sample  12  is supported by the extended support  16   c . This causes the end of the sample  12  to cantilever over the edge  19  of the base plate  11 , eventually to bend and hang downwardly  50  as to interrupt the beam  41 . The position sensor  33  indicates the amount of sample  12  extending over the edge  19  of the base plate  11  when the beam  41  is interrupted, this amount being dependent on the stiffness of the material of the sample  12 . 
     If not all of the above measurements are required, suitable programming of the programmable means  43  can cause the control means  42  only to activate the relevant motors for the measuring device to perform the required operations. Furthermore, if the effect of the speed of application of any load to the sample  12  is required, the programmable means  43  can be programmed to alter the speed of operation of the relevant motor or motors. As a further benefit of the measuring device  10 , cyclic loading of the sample  12  may be effected by suitable programming of the programmable means  43 . 
     Alternative embodiments of measuring device according to the invention will be apparent to persons skilled in the art. For example, as an alternative to stepper motors, the movements of the movable parts of the measurement device may be effected by pneumatic or hydraulic cylinders or by linear motors. As another alternative construction, the slide and sensing parts  20   a ,  20   b  may be mounted on the upper part  16   a  of the ‘movable’ support  16 . By means of the present invention measurements of tensile, shear, buckling, and compression strengths, sheet thickness, bending stiffness and surface qualities such as friction and roughness can be made on a single sample of a limp sheet material in a single measuring device, thereby reducing the time involved in performing the tests and the initial cost of purchasing the necessary equipment. 
     FIGS. 3 to  5  of the drawings illustrate a fabric sample  311  with a seam  312  giving rise to seam pucker—undulations  13  in the fabric either side of the seam  312 —held by a clamp  314  on a support base  315  inclined steeply so the fabric rests on the base rather than hangs freely, but otherwise without any constriction that would give rise to specious undulation or flattening and of any pucker that might be present. A bridge  315   a  on the support base  315  restricts movement of the sample  311  during monitoring. 
     The base  315  is removable from an enclosure in which the assessment is carried out and may be used as a template in cutting a sample for assessment from a larger piece. 
     Two parallel line beam lasers  316 ,  317  are directed at the sample  311  so that they illuminate lines  318  either side of the seam  312 . 
     As seen in FIG. 4, these lines take on a undulating appearance because of the seam pucker. The sample is imaged by a CCD camera  319 , which is arranged at such a distance from the sample that the distortions due to seam pucker in the lines  318  are visible in the image. 
     The whole is enclosed, for the assessment, in a box, and should, to prevent laser light escaping that might damage eyes be viewed directly, there being an interlock arrangement to ensure the lasers cannot operate unless the box is closed. 
     The image from the camera  319  is fed to a computer  321 , FIG. 5, with a vision card  322  and software capable of analysing the image by suitable routines to assess the degree and spatial frequency of any undulation caused by seam pucker. 
     Clearly a similar set-up can be employed to assess other types of surface irregularity. 
     The apparatus may readily be miniaturized and presented as a hand-held arrangement for portable use.