Abstract:
The present invention concerns a method for visually inspecting tubular garments such as socks, sleeves, stockings, panties or the like. The article is loaded onto or unloaded from a support or stretcher, and the article is checked or inspected by means of a computer-aided vision system during the loading onto or unloading off of the support or stretcher.

Description:
This is a continuation-in-part of co-pending Internationl Application PCT/ES97/00259 filed on Nov. 3, 1997 designating the United States. 
    
    
     FIELD OF THE INVENTION 
     The present invention concerns a method for visually inspecting all kinds of tubular textile garments such as socks, sleeves, stockings, panties or the like, of the type comprising a first stage in which the article is loaded onto or unloaded from a support or stretcher, and a second stage in which said article is checked or inspected by means of a computer-aided vision system operating by means of an image acquisition stage and a final stage in which the acquired images are processed for thus detecting the flaws. 
     The devices of the above-mentioned type do generally comprise a contactless inspection based on a digital processing of images taken from different positions by means of a traveling motion executed with a mechanical system for positioning the system for the digital acquisition of said images. 
     RELATED PRIOR ART 
     As a background of the invention can be cited the report entitled “Inspección visual de prendas a gran velocidad”, published in the magazine  Automática e Instrumentación , October  1994, no. 47, pages 70-74, A. Llorens Castelló, A. Sanfeliu, J. J. Souto, describing a system for automatically inspecting panties for flaws, said system consisting of three main modules: 
     a mechanical module for automatically loading the garment onto a support and moving a lighting and camera assembly; 
     a circuitry module consisting of three circuit cards: a memory card with a 16 MB RAM with a line scan CCD camera input, an image preprocessing card whose core is comprised of the INP1000 systolic processor specially developed for the system, and a card for the visualization of the panty images, together with the corresponding software programs for access to the cards; 
     the image processing software programs implementing all the algorithms for processing said images and detecting the flaws for their ulterior rating. 
     The system operates as follows: The undyed panty is vertically mounted on a stretcher thus allowing to illuminate it and to acquire its image during the vertical travel of a line scan CCD camera of 1024 “pixels” (picture elements) capturing the image line by line at right angles to the stretcher. The digititalized data are stored in the memory card, from where they are sent to the preprocessing card to be transmitted from there to a module for the extraction of characteristics and for their ulterior rating. Said stretcher has been provided to be shifted to place itself in front of the lighting and camera assembly, as well as to be turned such that the camera can thus when moving scan both sides of the garment. 
     The number and variety of the flaws to be controlled, and the frequency of the false alarms produced by seam shadows, overstressing of the fiber and other causes result in a very complex and costly image processing system. 
     One of the most significant problems inherent in the above-mentioned application derives from the need to correctly rate the flaws regardless of the type of material, garment size, finish and above all the tension to which the garment is subjected during the automatic mounting process, this entailing a high degree of parametrization of the algorithms implemented. 
     It is apparent that the described embodiment consists in a specialized machine, the system not being hence designed to be applied in textile or other machines already operating in the market. 
     The traveling motion of the lighting and camera assembly requires a space availability for said function requiring a predetermined free area. 
     The use of a line scan CCD camera (that scans the area to be inspected) involves long process times. 
     The lighting means employed by the described system comprise several fluorescent lamps strategically placed to obtain a correct illumination during the whole travel of the camera, this again imposing limitations when it comes to generalizing this application for its use with the standard machines that are commercially available in the market. 
     SUMMARY OF THE INVENTION 
     The object of the present invention consists in a method and system for visually inspecting tubular textile garments allowing to obviate the above-mentioned problems and to notably improve the efficiency of the system, and also allowing its implementation by means of a stationary image acquisition device of reduced dimensions. 
     The system being herein provided is essentially characterized in that it comprises a stationary camera and light source on an inspection area wherein the article to be checked is moved being kept under a predeterminated tension o a support or stretcher, and the method consists essentially in carrying out the inspection simultaneously with the introduction or egression of the finished article, tinted or not, onto or from a support such as a stretcher, with the essential particularity that said introduction of the article is carried out in the inspection area while being focused by said camera, uniformly illuminated and under a predetermined tension that is kept constant throughout the process. This results in said preset, constant tension giving the textile a uniform texture such that the distance between two filling or warp yarns is at all times smaller than a portion of any one of the flaws to be detected, which can thus be then correctly discriminated. 
     The stages of the method are detailed in claim  2  (20), and other particularities of the process appear in appended claims  3  (21) to  6  (24). 
     The essential characteristics of the system are on heir part detailed in claim  7  (25). 
     Other details of interest of the proposed system appear in appended claims  8  (26) to  18  (36). 
    
    
     BRIEF EXPLANATION OF THE DRAWINGS 
     For a better understanding of the invention follows a detailed description of a possible embodiment cited only by way of an illustrative, non limiting example with reference to two sheets of drawings accompanying this specification. 
     In said drawings: 
     FIG. 1 shows a perspective view of a textile garment being laded onto a support or stretcher; 
     FIG. 2 is a cross-sectional drawing illustrating the different arrangements that can be adopted by the image capturing means and the lighting means as per this invention; 
     FIG. 3 is a block diagram explaining how the process stages follow each other in the method for visually inspecting tubular textile garments; and 
     FIG. 4 exemplifies a graph representing the evolution of the grey levels assigned to the digitalized signal from each array light sensitive sensor (photosensor) of the camera throughout a given inspection. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     At numeral  1  is indicated in FIG. 1 a support or stretcher onto which a tubular textile garment  2  (a panty in this case) is being loaded in order to be inspected by means of image capturing means and lighting means simultaneously with said loading operation. In order to obtain a constant loading speed and most importantly a constant tension in the textile of the garment to be inspected both in the transversal and longitudinal direction throughout the whole operation mechanical loading mans have ben provided including in this example a driving roller  3  driven by a motor (not shown) and a driven roller  4  that can turn freely while opposing a frictional resistance to be preset as a function of each article, said rollers  3 ,  4  being arranged under stretcher  1  adjacent to distal ends of garment  2  between which the area to be scanned is defined. This results in the garment being grabbed between each of said rollers  3 ,  4  and the stretcher  1 . Driving roller  3  is positioned ahead of driven roller  4 , such that when said driving roller  3  turns in the advancing direction it drives by friction garment  2  thus advancing it in the direction shown by the arrow in FIG. 1, whereas driven roller  4  is driven by said garment  2  thus turning while opposing a predetermined resistance to the turning motion, said resistance providing a constant tension (both in the transversal and longitudinal direction) in the textile of said garment  2  while this latter advances with a uniform speed. FIG. 1 shows as well a partially or totally opaque plane  5  whose function will be described below. The inspection process can be equally carried out during the loading or unloading of garment  2  onto or from the support or stretcher  1 , both on one only side or simultaneously on both sides of said garment  2 . 
     FIG. 2 illustrates image capturing means comprising, for example, a line or matrix scan CCD or MOS camera  6  (although other technologies are also feasible such as that of the CMOS camera), and lighting means consisting in a fluorescent or laser light source  7 , said CCD camera  6  and light source  7  being stationary and being each arranged in one of the quadrants delimited by the plane on which the garment to be inspected is stretched (plane of the support stretcher  1 ) and a vertical plane that is perpendicular to the area to be scanned and centrally located with respect to it. With such an arrangement the textile of garment  2  reflects the light emitted by light source  7 , said light being then captured by the CCD camera  6 . The CCD camera  6  and the light source  7  can be positioned in different positions, since for example the CCD camera  6  can be positioned in a quadrant above the textile of garment  2 , and a light source  8  can be situated in the same quadrant behind the camera itself in order not to dazzle it, and can advantageously have a ring shape. It is also to be noted that this system offers the possibility of simultaneously scanning both sides of an article, for such a purpose arranging both above and below said garment an assembly formed by a camera  6 ,  6   a  and a light source  7 ,  7   a  in each case situated in opposite quadrants. Since in this latter case the light sources are directly facing the cameras of the opposite side, in the case of transparent articles to be inspected it has been foreseen to interpose a totally or partially opaque plane  5  in order to avoid the occurrence of glaring phenomena in the corresponding cameras  6 . The upper and lower cameras  6  and  6   a  can also in this arrangement comprise each a rear annular light source  8 . 
     Block diagram of FIG. 3 allows to graphically follow the stages through which an image captured by the CCD camera  6  is processed up to the rating of the detected flaw types. In said diagram numeral  16  indicates an image captured by the CCD camera  6  which is firstly subjected to a digitilizing  17  in order to thus allow said image  16  to be processed in a computer system. The texture of the textile  23  is thereupon eliminated in block  18  by means of an image  16  filtering process after which only those elements representing alterations in the textile  23  are visible, this process being uniquely facilitated by the application of a constant tension to the garment in the area to be scanned, this allowing to eliminate the image background by comparison with standards. After a flaw emphasizing process in block  19  the flaw detection and extraction is thereupon carried out in block  20  by means of a simultaneous double threshold technique to be described below. In block  21  the flaw characterization is finally carried out by comparison with predetermined patterns or standards thus then arriving to a rating  22  of said flaws. 
     FIG. 4 shows a graph on coordinate axes displaying the evolution of the proportion of light which after having been emitted by light source  7  and reflected by the yarns of textile  23  is captured by the CCD camera  6  throughout the inspection. To such an effect each signal (voltage level) from an individual light sensitive element (CCD phototransistor) of the camera is once digitalized assigned a value of a grey level scale. Said values thus form the grey level graph  9  where the grey level is plotted against the axis of ordinates  14  and the inspected length of the garment is plotted against the axis of abscissae  15 . Due to the fact that the tension of textile  23  remains essentially uniform on the support or stretcher  1  throughout the inspection the yarn density in said textile  23  is also essentially constant, this resulting in the proportion of light reflected by said yarns and captured by the CCD camera  6  remaining in a grey level graph  9  between an upper threshold  10  an a lower threshold  11 , said upper and lower threshold being also constant (see FIG.  4 ). Wherever there is a flaw in textile  23 , said flaw brings about an alteration in the quantity of light reflected by the yarns forming said textile  23 , said alteration being captured by the CCD camera  6  and being thus reflected in the grey level graph  9  in form of a peak reaching values above the upper threshold  10  or below the lower threshold  11  depending on the type of flaw having caused the alteration. Thus when the flaw consists in a smaller yarn density in textile  23  as is the case when there is a hole, a rip or a “run” the reflected proportion of light is smaller than the normal one, and therefore a dark flaw peak  12  appears in the grey level graph  9  below the lower threshold  11 . On the contrary, if the flaw consists in a clustering of yarns exceeding the usual arrangement the quantity of reflected light will be bigger, and a light flaw peak  13  will appear in the grey level graph  9  above the upper threshold  10 . 
     It is to be finally pointed out that the scope of the invention shall also encompass those variations in details not modifying the essence of the invention, such as in particular the use of mechanical driving assemblies for introducing or withdrawing the garment to be checked onto or from a support with diverse holding means such as a roller, a suction nozzle or a friction generating element such as a resiliently loaded hold-down applied on an area spaced apart from the garment driving area.