PRINTING A DESIRED PATTERN ON A WORKPIECE SURFACE

Abstract: A system for identifying workpieces by scanning them and "reading" details of their configuration is adapted for applying a desired pattern of material in powder form (e.g. toner material or a hot melt adhesive) to the workpieces regardless of their location and orientation on a workpiece support (18), using an electrostatic printer (36) e.g. an ionographic printer. This is achieved by pattern data (relating to the desired pattern) selected from a store being modified in accordance with positional data (relating to the location and orientation of the workpiece) obtained during scanning (Figure 2), such modified pattern data being utilised to apply the desired pattern of powder to the surface of the printing member (roller 38) of the printer such that, when the roller and workpiece are brought together the powder is applied in its pattern to the desired locality of the workpiece.

Description: This invention is concerned with a method of an apparatus for printing a desired workpiece surface at a desired locality thereof using an operating tool constituted by an electrostatic printing device comprising a conductive member with a dielectric coating forming a printing surface. Where patterns are printed on workpiece surfaces it is customarily necessary for the workpieces to be located in a desired position in relation to the operating tool and also in the correct orientation in such position; where the workpieces are fed in a random orientation, it is thus customarily necessary to re-orientate them correctly and locate them at a desired position prior to feeding them to the operating tool. For an apparatus for thus re-orienting workpieces (but not in the context of a subsequent printing operation) see e.g. US-A 3356237. Using such an apparatus, however, there are limitations on the degree of mis-orientation of the workpiece which can be accomodated, while still allowing the workpiece to be properly presented to the operating tool. It is an object of the present invention to provide an improved method of printing a desired pattern on a workpiece surface at a desired locality thereof, wherein the need for any re-orientation is dispensed with prior to presentation to the operating tool. This object is resolved, in accordance with the present invention, in a method as set out in the first paragraph above, in that pattern data relating to the desired pattern is stored in a computer memory and is utilised for controlling the printing of the pattern by the operating tool while the workpiece is supported on a support across the width of which the printing surface extends whereby the workpiece on the support can be positioned in an operative relationship with the printing surface regardless of the location of the workpiece on the support, and further by the steps of obtaining positional data relating to the location and orientation of the workpiece on the support, and utilising the positional data to modify the pattern data such that, under the control of the modified pattern data, material in powder form is deposited on the printing surface in a pattern corresponding to the desired pattern and at a locality thereof which, when the printing surface enages the workpiece, corresponds to the desired locality on the latter, whereby the tool is caused to operate at the desired locality on the workpiece regardless of the location and orientation of the workpiece on the support. It will thus be appreciated that in using this method workpieces can be placed at random on the support and, in response to their location and orientation having been determined, the pattern to be applied is itself appropriately located and oriented on the printing surface, thus avoiding the need to physically re-orient the workpiece. The conductive member is conveniently in the form of a roller which is caused to rotate in timed relation with movement of the support. Furthermore, depending upon the type of electrostatic printer used pressure and/or heat may be applied to the workpiece as it is carried past the roller by the support. The electrostatic printing device used in carrying out a method as aforesaid may be of the xerographic type, but preferably comprises means for generating ions and forming them into a pattern on the printing surface under the control of the modified pattern data, the material in powder form, in this case toner material, being deposited on the printing surface in accordance with said pattern of ions; such a printing device is usually referred to as an ionographic printing device. Whereas the material in powder form is in this case toner material, it will be appreciated that e.g. adhesive in powder form could also be "printed" in this manner. The method in accordance with the invention referred to hereinbefore is suitably effected in combination with so-called pattern identification techniques, wherein the positional data is obtained by scanning the workpiece and thereby identifying it, using a computer which has been taught a plurality of workpiece shapes and comprises a store of data relevant thereto, and calculating the orientation of the workpiece on the support utilising such stored data. More particularly, preferably the workpiece is identified by compiling dimensional data from signals generated by scanning the workpiece and comparing such data with stored dimensional data for workpieces of known configuration (shape), and wherein stored pattern data is associated with the stored dimensional data for each workpiece of known configuration, the associated pattern data to be utlised for a given workpiece being selected according to its identification. For effecting such pattern identification (or pattern recognition), an apparatus may be used as is described in GB-A 2067326, which apparatus comprises a workpiece support, a scanning device, means for effecting relative movement between the scanning device and the workpiece support whereby a workpiece supported by the workpiece support is scanned by the scanning device, and compiling means responsive to signals emitted by the scanning device for compiling positional data relating to both the location and the orientation of the workpiece on the workpiece support It is a further object of the invention to provide an improved apparatus for effecting a printing operation on a workpiece whereby a desired pattern can be printed at a desirable locality on the workpiece surface regardless of the location and orientation of the workpiece. This object is resolved in accordance with the present invention in an apparatus being the features set out in the last paragraph but one, by data storage means for storing the positional data and also pattern data relating to the desired surface treatment pattern, data modifying means whereby the pattern data is modified using the positional data, an electrostatic printing device comprising a conductive member with a dielectronic coating forming a printing surface which extends across the width of the support, pattern locating means for determning, in accordance with the modified pattern data, a location on the printing surface which, when the printing surface engages the workpiece surface, corresponds to the desired location on the workpiece surface, and depositing means whereby material in powder form is applied, in accordance with the modified data, to said location on the printing surface, and means for effecting relative movement between the printing surface and the workpiece support whereby the surface of a workpiece on said support and the printing surface are brought into an operative relationship for a printing operation to be performed at the desired location on the workpiece surface. For assisting in the retrieval of data from the data storage means and also the matching of pattern data with positional data as aforesaid, conveniently the data storage means comprises a first permanent store of dimensional data relating to workpieces of different configuration and also a second permanent store of pattern data relating to different patterns to be followed, selected pattern data from the second store being associated with the dimensional data for each such workpiece, and the compiling means also compiles dimensional data relating to the workpiece scanned by the scanning device, the apparatus further comprising comparator means for comparing the compiled dimensional data with the data in the first permanent store thus to identify the scanned workpiece, and selector means for selecting from the second permanent store the pattern data associated with the workpiece as identified. There now follows a detailed description, to be read with reference to the accompanying drawings, of a method and an apparatus in accordance with the invention. It will be appreciated that this method and this apparatus have been selected for description merely by way of non-limiting example of the invention. In the accompanying drawings:- Fig. 1 is a schematic view indicating the lay-out of the apparatus in accordance with the invention; and Fig. 2 is a flowchart setting out schematically the software controlling the method in accordance with the invention. The apparatus in accordance with the invention (Fig. 1) comprises a pattern recognition system located at a pattern recognition station generally designated A and a printing apparatus located at a printing station generally designated B, both being controlled by a central processor unit CPU. The pattern recognition system is generally similar, except as hereinafter described, to the system described in GB-A 2067326 and comprises two conveyor belts 18, 20 between which is a narrow gap 12 which can be bridged by a workpiece W being fed in the direction of the arrow F through the stations A, B. Aligned with the gap 12, beneath the conveyor belts 18, 20, is an array of filament lamps 10, while disposed in opposed relationship with said lamps, above the level of the workpiece-carrying surfaces of the belts 18, 20, is an array of light detectors 14 arranged to receive light emitted by the lamps 10 and focussed onto the detectors by a high-resolution lens 16; the array 14 and lens 16 are generally referred to as a "camera". It will thus be appreciated that the optical paths of the light will be interrupted upon the passage of a workpiece across the gap 12, the advancing movement of the workpiece being progressive whereby the workpiece is "scanned" by the array 14 as it is fed. For moving the conveyor belts 18, 20 a numerically controlled motor drive system generally designated 22 is provided. The system 22 typically comprises a stepping motor SM having an output shaft 24 carrying a pulley which is connected by a timing belt 26 with a corresponding pulley on a shaft supporting the drive pulleys for the conveyor belt 18. Similarly, a timing belt 28 connects the output shaft 30, itself connected by a timing belt 32 to a drive pulley associated with the conveyor belt 20. In this way, the two conveyor belts 18, 20 are driven synchronously under the stepping motor control. The stepping motor SM is controlled by the CPU. The CPU is also operable, after each unit distance of movement, to record which of the array of detectors 14 has detected a workpiece as aforesaid. The unit distance is typically in the order of 300 microns. The printing station B is arranged "downstream" of the gap 12 (viewed along the direction F), the conveyor belt 20 passing through the printer station B and out at the opposite side. Arranged in a suitable cabinet 34 at the printing station B is a printer generally designated 36 of the electrostatic type, more particularly an ionographic printing device. Such a device is generally similar, except as hereinafter described, to the apparatus described in US-A 4267556 and comprises a print roller 38 which is coated with a suitable dielectric material, a charging head 40 by means of which a latent electrostatic image, in a desired pattern, is provided on the dielectric layer and toner applying means, including a toner applicator head 42 by which charged, coloured particulate material is applied to the latent image. The print roller 38 is arranged above the workpiece-supporting surface of the belt 20 such that a workpiece supported by said surface is engaged by the print roller. For applying suitable pressure to the workpiece to effect the transfer of the toner material, a further, presser, roller 44 is provided, this latter roller being desirably coated with a thermoplastic material. The two rollers 38, 44 are synchronously driven using a gear and timing belt drive arrangement generally designated 46, so that they rotate in contrary directions, and further the drive arrangement 46 is itself connected to the drive arrangement 22 in such a manner (not shown) that the two rollers 38, 44 rotate at a peripheral speed which matches that of the conveyor belt 20. In the operation of this apparatus, in carrying out the method in accordance with the invention, a workpiece W is placed on the conveyor belt 18 in any orientation and is advanced across the gap 12 onto the upper reach of the belt 20, the camera 14, 16 being effective to scan the workpiece as it crosses the gap and thereby identify it. As described in detail in GB-A 2067326, the camera is connected to the CPU the data storage means of which comprises a first permanent store of dimensional data relating to workpieces of different configuration, and which also comprises comparator means for comparing compiled dimensional data for the particular workpiece with the data in the first permanent store. The CPU, in identifying a workpiece, also determines, from the signals from the camera 14, 16, positional data relating to both the location of the workpiece on the conveyor belt and further the orientation of the workpiece. Thus, when the workpiece has reached the conveyor belt 20, both its identity and also its location and orientation on the belt 20 are "known". The data storage means of the CPU also comprises a second permanent store of pattern data relating to different desired patterns which are to be applied to workpieces being treated in the apparatus. Furthermore, the data storage means also identifies to which workpiece configuration any given pattern whose pattern data is thus stored is to be applied. Thus, when a workpiece of a given configuration is identified as aforesaid, selector means in the CPU is effective to select its associated pattern data from the second permanent store. The pattern data selected is then processed by the CPU according to the location and orientation of the workpiece using data modifying means forming part of the CPU and appropriate signals are then supplied by the CPU to the charging head 40 of the printing device 36 in accordance with the modified pattern data. The latent image is then formed on the surface of the dielectric layer on the print roller 38, at a location on said surface which, when the surface engages the workpiece surface to be printed, corresponds to the desired location on the workpiece surface. The latent image is then toned, as described in US-A 4267556, and the toned image is then pressed against the workpiece surface to effect a printing operation thereon. Whereas in using an ionographic printer, it is necessary to apply pressure to the pattern of the toner material, in other electrostatic printers, e.g. laser printers and xerographic printers, it is desirable to apply heat. Fig. 2 is a flowchart setting out in more detail a preferred method in accordance with the invention for effecting shape recognition and for controlling the print operation. At step 200 the workpiece W placed on the conveyor belt 18 is passed across the gap 12 as aforesaid and scanned using the camera 14, 16. The camera, at step 202, effects an edge detection process using 3 × 3 convolution techniques. That is to say, the region scanned is sub-divided into nine pixels and each pixel is scanned as to whether it is registering light detection, a "0" signal, or no light, a "1" signal. Where there is a "1", then the adjacent pixels are scanned for further "1" signals, which would indicate the presence of an edge. In this way the edge configuration of the workpiece is built up as the workpiece progresses through the gap 12. At step 204 the edge points are passed to the CPU. From this information the CPU calculates various characteristics of the workpiece (step 206). In particular, the area is calculated by summing all the "1" signals (sigma a). In addition, the first moment of area is calculated (sigma ax, sigma ay) with respect to an arbitrary datum and from this information the location of the centroid is calculated: Also at this stage second moments of area are calculated (sigma ax², sigma ay², sigma axy). At step 208, using the parallel axis theorem, second moments of area are then calculated about the centroid. As a further calculation, at step 210 the orientation of the principal axes, about which the second moments of area have minimum and maximum values respectively, are calculated. It will of course be appreciated that the orientation of the axes is ambiguous in so far as they are capable of two positions which differ by 180°. To overcome this, also in this step the longest side of the major axis is established and this is the final part of determining the orientation of the workpiece unambiguously. As a final part of the calculation, at step 212 the furthest edge point along each of a number of equispaced radii emanating from the centroid is determined and in each case the square of the distance along the radius is used as a "candidate" feature, i.e. a feature of the set of information which subsequently will be used to identify the workpiece. Up to this stage, the apparatus operates in the same manner whether the workpiece configuration (shape) is being taught or whether the workpiece is being recognised. At step 214 this question is asked. If the reply is "Taught" then at step 216 the whole of the database is reprocessed adding the new data and re-calculating the feature sets stored for each workpiece in order to ensure that each remains unique. This calculation is based upon the "minimum distance" feature set out in GB-A 2067326. If the answer at step 214 is "Recognised", then at step 218 the dimensional data thus obtained as aforesaid is compared feature by feature with the data stored in the first permanent store of the data storage means of the CPU. In order to limit the search, the first comparison is one of area. At step 220 the question is posed whether there are sufficient identical features between the workpiece and the compared data to satisfy the minimum distance requirements. If the answer is "No", then step 218 is returned to for further features to be compared, and this process continues until the identity of the workpiece is established. At the same time the positional data relating to the identified workpiece is determined and stored (step 222). More particularly, the location of the centroid is stored and also the orientation of the principal axes calculated at step 210. The selecting means of the computer control means is then effective to select from the second permanent store of the data storage means the pattern data which is associated with the dimensional data in the first permanent store (step 224). At this stage the workpiece W is advancing to the printing station B. It is of course important also at this stage to ensure that the workpiece does not lose registration in terms of its location on the conveyor belt 20 and its orientation. To this end, therefore, the belt 20 may be perforated and pass over a suction chamber whereby the workpiece W is maintained in position on the workpiece-supporting surface of the belt. The pattern data in the data storage means is in the form of a set of x and y coordinates, which are related to a datum, said relationship reflecting the relationship between the centroid to which the pattern is to be applied and the position of such pattern in relation to the centroid. At step 226 transformation is applied to the pattern data in accordance with the stored data relating to the location and orientation of the workpiece on the workpiece-supporting surface of the conveyor belt 20. The transformed (modified) data is then passed at step 228 to a controller which controls the operation of the electrostatic printing device 36. The controller then executes the printing operation (step 230), that is to say, the data is utilised to form on the dielectric layer providing the surface of the print roller 38 a latent electrostatic image corresponding to the desired pattern at a location which is so arranged that it corresponds to the location and orientation of the workpiece on the workpiece-supporting surface, whereby, as the workpiece is advanced and the print roller is rotated, the latent image picks up toner material and applies it to the workpiece surface at the desired locality thereof. It will thus be appreciated that, in carrying out said method in accordance with the invention, the positional data which is obtained relating to the location and orientation of the workpiece, which has been identified as aforesaid, is utilised to modify the pattern data which has been selected for application to such identified workpiece, and the operating tool, in this case the print roller, is caused to operate at the desired location on the workpiece surface regardless of the location and orientation of the workpiece on the workpiece-supporting surface. It will of course be appreciated that the pattern which is printed on the workpiece surface may be for decorative or other purposes. One non-decorative example would be stitch-marking, that is to say marking on the surface of the workpiece (constituted e.g. by a shoe upper component) a marking, e.g. a delible line marking, which serves to locate a further workpiece in relation to the printed workpiece prior to securing the two together by stitching. Alternatively, instead of toner material, adhesive, e.g. hot melt adhesive, in powder material may be applied using the foregoing method.

Claims: Method of printing a desired pattern on a workpiece surface (W) at a desired locality thereof, using an operating tool constituted by an electrostatic printing device (36) comprising a conductive member (38) with a dielectric coating forming a printing surface, characterised in that pattern data relating to the desired pattern is stored in a computer memory and is utilised for controlling the printing of the pattern by the operating tool (36) while the workpiece (W) is supported on a support (18, 20) across the width of which the printing surface extends, whereby the workpiece on the support can be positioned in an operative relationship with the printing surface regardless of the location of the workpiece on the support, and further characterised by the steps of obtaining positional data relating to the location and orientation of the workpiece on the support (18, 20), and utilising the positional data to modify the pattern data such that, under the control of the modified pattern data, material in powder form is deposited on the printing surface in a pattern corresponding to the desired pattern and at a locality thereof which, when the printing surface engages the workpiece, corresponds to the desired locality on the latter, whereby the tool (36) is caused to operate at the desired locality on the workpiece (W) regardless of the location and orientation of the workpiece on the support (18, 20). A method according to Claim 1 wherein the conductive member is in the form of a roller (38) which is caused to rotate in timed relation with advancing movement of the support (18, 20). A method according to Claim 2 wherein heat and pressure are applied to the workpiece as it is carried past the roller (38) by the support (18, 20). A method according to any one of the preceding Claim 1 wherein the printing device (36) comprises means (40) for generating ions and forming them into a pattern on the printing surface under the control of the modified pattern data, the material in powder form being deposited on the printing surface in accordance with said pattern of ions. A method according to any one of the preceding Claims wherein the material in powder form is constituted by toner material. A method according to any one of the Claims 1 to 5 wherein the material is powder form is constituted by a hot melt adhesive. Apparatus for effecting a printing operation on a workpiece (W) at a desired location on the workpiece surface and in accordance with a desired pattern, comprising a workpiece support (18, 20), a scanning device (14, 16), means (22) for effecting relative movement between the scanning device (14, 16) and the workpiece support (18, 20) whereby a workpiece (W) supported by the workpiece support is scanned by the scanning device, and compiling means responsive to signals emitted by the scanning device (14, 16)for compiling positional data relating to both the location and the orientation of the workpiece on the workpiece support (18, 20) are obtained, and said apparatus being characterised by data storage means for storing the positional data and also pattern data relating to the desired surface treatment pattern, data modifying means for modifying the pattern data using the positional data, an electrostatic printing device (36) comprising a conductive member (38) with a dielectric coating forming a printing surface which extends across the width of the support (18, 20), pattern locating means (40) for determining, in accordance with the modified pattern data, a location on the printing surface which, when the printing surface engages the workpiece surface, corresponds to the desired location on the workpiece surface, and depositing means (42) for applying material in powder form, in accordance with the modified data, to said location on the printing surface, and means (22) for effecting relative movement between the printing surface (38) and the workpiece support (18, 20) whereby the surface of the workpiece (W) on said support and the printing surface are brought into an operative relationship for a printing operation to be performed at the desired location on the workpiece surface. Apparatus according to Claim 7 wherein the printing device (36) comprises means (40) for generating ions and forming them into a pattern on the printing surface under the control of the modified pattern data, and means (42) for depositing the material in powder form on the printing surface, the powder being, thus deposited in accordance with said pattern of ions. Apparatus according to either on of Claims 7 and 8 wherein the workpiece support (18, 20) is movable along a path to carry a workpiece supported thereby past the scanning device (14, 16) and the electrostatic printing device (36), and wherein the conductive member (38) of said device (36) is in the form of a roller (38) which is caused to rotate in timed relation with advancing movement of the support (18, 20). Apparatus according to any one of Claims 7 to 9 wherein the data storage means comprises a first permanent store of dimensional data relating to workpieces of different configuration and also a second permanent store of pattern data relating to different patterns to be followed, selected pattern data from the second store being associated with the dimensional data for each such workpiece, and wherein the compiling means also compiles dimensional data relating to the workpiece scanned by the scanning device (14, 16), the apparatus further comprising comparator means for comparing the compiled dimensional data with the data in the first permanent store thus to identify the scanned workpiece, and selector means for selecting from the second permanent store the pattern data associated with the workpiece as identified.

Inventors: PREECE, CLIVE, REEDMAN, DAVID CREYKE
Applicants: BRITISH UNITED SHOE MACHINERY LIMITED
Application year: 1987
Main classification: G05B19
IPC codes: B43L13, B41J2, G05B19, A43D119, A43D8, B41M5, A43D1