US 3169193 A
Description (OCR text may contain errors)
Feb. 9, W65 J. M. STRANG SJGWIW PHOTOSENSITIVE APPARATUS FOR SENSING THE ORIENTATION OF FINE MESH'MATERIAL. Filed March '7, 1961 4 Sheets-Sheet 1 H o\\\ DIFFRACTION /-V/V PATTERN F/G./.
I n v e n t o r 1/00 MET/Al Jim/w waf wmae Attorneys Feb. 9, W65 J. M. STRANG PHOTOSENSITIVE APPARATUS FOR SENSING THE ORIENTATION OF FINE MESH MATERIAL Filed March 7, 1961 4 Sheets-Sheet 2 F/GZ.
I n ven tor day/v MET/AI Jim/v6 Attorneys Feb. 9, 1965 J. M. STRANG J J PHOTOSENSITIVE APPARATUS FOR SENSING THE oaxsu'rmou OF FINE MESH MATERIAL Filed March 7. 1961 4 Sheets-Sheet 5 37 a A 4 JL fi' ll BISTABLE PRE-AMPLIFIERS TRANSISTOR INTEGRATING PHOTOCELLS CIRCUITS cmcuns x 2 37 3e- EEBEISISTOR v SWITCHES INTEGRATING CIRCUITS BISTABLE TRANSISTOR CIRCUITS Inventor Ja /v 444mm fire/W6 i wwmw Attorneys Feb. 9, 1965 J. M. STRANG 3,169,193
PHOTOSENSITIVE APPARATUS FOR SENSING THE ORIENTATION OF FINE MESH MATERIAL Filed March 7. 1961 4 Sheets-Sheet 4 F/GQQ.
MOTOR DIFFEFE TIA GEARN L SS-DIFFERENTIAL In ven tor 54 do/m/ Mom/v Sum A Horn e ys ilnitcd States This invention relates to a method of and apparatus for sensing the orientation of mesh material; for example, textile fabric or mesh of wire or synthetic resin during conveyance through a machine. Such mesh material comprises a series of moreor less opaque elements defining spaces between them. The elements may for example be yarns or threads formed from textile fibres or they may be wires or filaments of metal or synthetic resin.
According to the present invention there is provided apparatus for sensing the orientation of mesh material, comprising a light source for directing a beam of light through said material, means for forming an image of the source in light diffracted by said material, and means for examining said image whereby the orientation of the material may be sensed. I
Further according to the present invention there is provided apparatus for sensing and controlling the orientation of a moving web of regular mesh material in accordance with its deviation from a predetermined orientation, comprising a light source for directing a beam of light through said material, means for forming a diffraction image by said mesh material, the orientation of said diffraction image being dependent on the orientation of the mesh material, means for examining said image and producing an electrical signal in accordance with its orientation, and guide means adapted to act to return the web to its predetermined orientation, said guide means being controlled by said electrical signal.
The invention is primarily applicable to regular mesh material, in which the elements define mesh spaces in a regularpattem disposed in parallel rows, not necessarily in a rectangular arrangement. Infrequent irregularities such as knots or small holes are unimportant and do not substantially effect the sensing of the image. However, the invention may also be of use where the mesh'space pattern is not exactly regular but of a repetitive nature.
Theoretically the mesh may be very co-ar's'e provided that the element thickness is not small, nor very large, in relation to the size of the spaces, but in practice, owing to limitations of light intensity and pinhole size, in general,
materials having less than ten elements per inch are too coarse to form a satisfactory diflraction image. On the other hand successful tests with materials having one hundred elements per inch have been made,
Further, according to the present invention there is provided a method of sensing the orientation of regular mesh material having successive rows of greater or lesser translucency, comprising passing a beam of light through the material to form a diffraction pattern, forming a further enlarged image thereof, and examining the image to establish the orientation of the material.
An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: 1
FIG. 1 shows the formation of diffraction image pattern;
FIG. 2 is a perspective view showing a further-diffraction image;
FIG. 3 is a perspective view showing a diiferent diffraction image;
amiss Patented Feb. 9, 1985 FIG. 4 is a perspective view showing another diflfrac- 'tion image;
FIG. 5 shows schematically part of an application of the invention;
FIG. 6 shows part of a typical diffraction image;
FIG. 7 shows a circuit used in the invention;
FIG. 8 shows a modified circuit; I
FIG; 9 shows schematically part of the apparatus used in conjunction with the modified circuit; and
FIG. 10 shows a stenter in combination with orientation sensing apparatus.
FIG. 1 shows an enlarged section of finely meshed material 11. A beam of light is projected through the finely meshed material and as a result of the regular pattern of apertures formed between the weft threads 12 and the warp a Fraunhofer diffraction image is produced. As this image is formed at infinity a lens 13 is introduced to focus the image in its focal plane, the image being concentrated at specific points 1 I I hereinafter referred to as the maxima. I is formed on the axis of the lens 13 and is the Zero order maximum. I is the first order maximum and is formed at a distance from I dependent on the spacing of the apertures in the material and the focal length of the lens 13. I2 is the second order maximum, being of much less brightness than 1 and formed at a distance still further away from I For the purposes of this application I and higher order maxima may be neglected.
FIG. 2 shows the diffraction image 19 obtained when a beam of light from a source is passed through a series of horizontal slits l5, and focussed by a lens 16; the image 19 takes the form of a series of point maxima extending in a direction normal to the direction of the slits.
FIG. 3, shows the image 2d resulting when a beam of light from a source 14 is passed through a series of vertical slits 17 and focussed by a lens to. The image 24) again takes the form of a series of point inaxima and extends in a direction normal to the direction of the slits.
FIG. 4 shows the effect when the slits of FIG, 2 and FIG. 3 are combined to form a mesh as is found in woven material. A beam of light passing through the mesh 18 becomes diffracted, the dilfraction image being focussed by the lens 16 and taking the form of a central point corresponding to the zero order maximum su'rrounded by higher order maXima arranged in a square,
rectangular, or rhornbic figure. The lines that couldbe drawn joining these point maxima are perpendicular to the lines defining the apertures in the material.
As a result of this, if the mesh 18 is angularly displaced or re-orientated the points in the diffraction image will be displaced angularly through the saine angle. Examination of the image 21 can therefore determine the orientation of the mesh 18.
The invention may be applied for exampleto the control of a woven fabric web passing through a stenter where it is important to prevent misalignment or skew of the fabric prior to being pinned or otherwise secured to the stenter guide chains. In such an applicationat least one beam of light is passed through the web normal to its plane and a diifraction image is formed of the mesh pattern of the fabric. In the present embodiment an electronic apparatus then detects and indicates any misalignment of the image and may translate same into an amplii ed signal which is used to control the operation of guiding means positioning the web on the stenter chains so as to correct the misalignment. An apparatus such as this will be described with reference to FIGS. 5 to 10.
r 3 26 which is tested for misalignment. A further object lens 27 collects transmitted and refracted light to form an image 28 consisting of a number of diffraction images of the pinhole arranged in a regular lattice the form of which, is related to the structure of the material being examined. If multichromatic light is used, all points of the lattice other than the central one are spectra of the source. The primary image 28 is projected by the relay or lens combination 29, which produces a considerably enlarged image in the vicinity of the reflecting prisms 30a and 30b. These prisms select spectra on either side of the central (zero order) maximum along one of the principal directions of the lattice.
It is convenient to use a parallel beam of light in the formation of the diffraction image, as with this the distance of the source has no effect on the axial position of the image 28. However it is not essential that the beam of light be parallel; for example, a source of small angular size would be suitable.
FIG. 6 shows a representation of such a lattice with the two selected spectra surrounded by dotted squares. The prisms 30a and 30b reflect these selected spectra on to scanning discs 31 driven from a comon spindle rotated by a motor 35. If the material tilts, the diffraction image 28 rotates about its centre by the same angle, and a slot cut in each scanning disc 31 will encounter the image earlier or later depending on the direction of rotation of the material. Immediately behind the scanners lie field lenses 32 which collect all incident light into a highly reduced image of the objective lens 27 on each of the two photocells 33 and 34.
With the scanning disc arrangement described above, if the cloth is at an angle to the axis of the photocells 33 and 34, a pulse of light will fall on one photocell followed some time later by pulse on the second photocell. The time interval between these pulses is a function of the orientation of the cloth, and each light pulse will puroduce a corresponding electrical pulse in the photocell output. The outputs from the two photocells are fed through pre-amplifiers 36 and then into two bistable transistor circuits A and B, as shown in FIG. 7. Such bistable transistor circuits may be of the types disclosed at pages 324-336 of Transistor Circuit Engineering, edited by Richard F. Shea, and published by John Wiley & Sons, Inc., 1957. The outputs from the bistable circuits are integrated by circuits 37 to provide voltages proportional to the time that the respective bistable circuit was on and fed into a voltmeter 38 calibrated to indicate misalignment of the web.
A bistable circuit is one in which a constant output voltage can be produced when an input pulse is applied to one part of the circuit, and the output voltage can be reduced to zero when a second pulse is applied to another part of the circuit. Thus a voltage is produced at the output from bistable circuit A when photocell 33 receives a pulse of light. This voltage continues until a pulse of light is received on photocell 34. The second bistable circuit B is operated by photocell 34 and cut off by photocell 33, that is, it produces a voltage output when the angle of misalignment of the web is opposite to that which energised the first circuit.
In the first case, when photocell 34 switches off the bistable circuit A, it will switch on the bistable circuit B. To prevent this, a switch must be provided for both bistable circuits as shown in FIG. 8, which opens when the slit in the respective scanning disc passes the axis of the photocells 33 and 34.
This switch 39 can take the form of a transistor gate as used in computer technique, an example of which may be found at page 320 of Transistor Circuit Engineering, heretofore identified. FIG. 9 shows the optical arrangement with the addition of a light source 40, focussing lenses 43, a phototransistor 41 and a disc 42 mounted on the same spindle as the scanning discs 31. The disc 42 allows light to fall on the switching phototransistor 4 41 when the slit on the scanning disc passes the axis of the photocells 33 and 34; the slit on the disc 41 extends over a sector and thus the photo-transistor 41 would be illuminated for about 90 of its rotation.
As indicated in FIG. 10, the output from the integrating circuits can be used to control a motor 50 or other device for example a brake mechanism, acting to advance or retard the carriage of a differential gear 51 to speed up or slow down one of the usual stenter chains 52. The stenter chains are driven through the differential 55 by the input shaft 53. The light beam for forming the diffraction image may be positioned as indicated in dotted lines at 54. The orientation of the web may be adjusted by means of the arrangements described in the preceding description.
The invention may be utilised for example in aligning woven material in preparation for printing.
1. Apparatus for sensing the orientation of mesh material having openings capable of producing a diffraction pattern from light passing therethrough, comprising a light source means for directing a beam of light through the material to form a diffraction pattern therefrom, means for forming a diffractive image from the diffraction pattern formed by the material having a plurality of substantially point maxima whose angular positions relative to the center of the diftractive image varies as a function of the orientation of the mesh material, and means for sensing angular changes in position of at least a pair of said point maxima in said diffractive image relative to preselected reference positions therefor to produce an indication of the orientation of the material.
,2. Apparatus as claimed in claim 1, in which said means for sensing comprises photo-sensitive means adapted to emit an electric signal which is a function of the orientation of the diffractive image.
3. Apparatus as claimed in claim 2, including scanning means permitting the photo-sensitive means to View the dilfractive image only at intervals.
4. Apparatus for sensing the orientation of mesh material, comprising a light source for directing a beam of light through the material, means for forming a diffractive image by the material which comprises a central zero order maximum surrounded by at least a series of first order maxima at anequal distance from the zero order maximum, means for examining a diffractive image whereby the orientation of the material may be sensed including photosensitive means adapted to emit an electric signal which is a function of the orientation of the dilfractive image, and scanning means permitting the photosensitive means to view the diffractive image only at intervals, the photo-sensitive means comprising two photo-electric cells, and said scanning means including two rotatable slotted discs adapted to permit each photo electric cell to examine part of the image at intervals, whereby, dependent on the orientation of the image, said plailoto-electric cells emit electrical signals at varying interv s.
5. Apparatus as claimed in claim 4, in which a bistable circuit is coupled to each photo-electric cell and each bistable circuit is adapted to be initially triggered to provide an output voltage by a pulse from the photoelectric cell coupled thereto, a second pulse from the other photo-electric cell reducing the output from the bistable circuit to zero.
6. Apparatus as claimed in claim 5, in which there is provided an integrating circuit coupled to each bistable circuit which produces an output voltage proportional to the length of time between the first pulse and the second pulse.
7. Apparatus for sensing the angular orientation of mesh material having openings therein capable of producing a diffraction pattern from light passing therethrough, comprising light source means for directing a substantially collimated beam of light through the material to form a diffraction pattern therefrom, means forming an enlarged image of the dilfraction pattern producing a diifractive image having a plurality of substantially point maxima Whose angular positions relative to the center of the diffractive image varies as a function of the orientation of the mesh material, and sensing means responsive to angular changes in position of at least a pair of said point maxima in the enlarged difi'ractive image relative to preselected reference positions therefor to produce an output indication of the orientation of the mesh material.
8. Apparatus for sensing the orientation of a web of mesh fabric during conveyance thereof along a processing feed path wherein the mesh fabric has sufficiently small openings to form a diffraction pattern from light trans mitted therethrough, comprising a substantially point source of light, means for directing a beam of light from said source through the mesh fabric to form a diffraction pattern therefrom, means forming an enlarged diifractive image of said diifraction pattern at a selected image plane having a central maximum and at least a selected pair of maxima of corresponding order at angular positions about said central maximum which vary in determinable relation to the orientation of said fabric, and means for sensing said selected pair of maxima responsive to the angular positions thereof relative to selected reference positions therefor for generating signals indicative of the orientation of the fabric.
References Cited by the Examiner UNITED STATES PATENTS 2,106,612 1/38 LaPierre et al. 2651.5 2,355,465 8/44 Oberkirk 26-515 X 2,623,262 12/52 Berry 26-515 2,777,069 1/57 Saeman 250-219 2,861,345 11/58 Spencer 18-14 2,886,717 5/59 Williamson et al.
2,966,593 12/60 Leimer et a1 250*219 2,972,794 2/61 Saul et al. 2651.5 3,054,902 9/62 Timms et al 250-237 RALPH G. NILSON, Primary Examiner. RUSSELL C. MADER, Examiner.