Abstract: A method and apparatus to non-destructively inspect and quantify yarn crimp characteristics either off-line or on-line at speeds in excess of 2,000 yds./min. by acquiring images of yarn crimp on-line during the manufacturing process, then digitizing the images of yarn crimp and performing all data processing from the digital data required. Each image is segregated into features (e.g. valid crimp, low frequency oscillations, high frequency oscillations, edge oscillations, and unconfirmed oscillations with each parameter being analyzed separately. Features are segmented two dimensionally using techniques such as, but not limited to, local max/min intensity profiles and spatial intensity and frequency thresholding. Regions identified as abnormal are separated from areas of valid crimp before determining crimp frequency. Outputs of individual analysis are combined to determine global tow quality. This method provides a complete statistical analysis for each lane in the tow as well as the overall tow width.

Abstract: A label inspection system automatically inspects print on labels carried seriatim on a web. The system comprises a photoelectric sensing system including a light inspection sensor sensing reflected light and an electrical control circuit providing an output at a select first or second electrical state dependent upon sensed reflected light being above or below a select level. The sensor is mounted at a select transverse position in a path of movement of the web to sense reflected light along a select longitudinal path of the web, the select longitudinal path including a portion of the labels carried on the web intended to have print, the print acting to minimize reflected light. A detect sensor sense proximity of the inspection sensor relative to a select longitudinal portion of each successive label and provide an enable signal relative thereto.

Abstract: In a method of automatically determining flaws of an object of examination according to the invention, rays of light are transmitted through on object of examination, while adjusting the depth of observation to make it agree with the focal length of a detected flaw, go down deeper than the focal length and come up shallower than the focal length and the brightness of transmitted light for each depth of observation is converted into a corresponding electric signal. Portions of the generated signal that are found outside a predetermined range of intensity are taken out as flaw signals and the obtained flaw signals are compared with a number of binarized flaw patterns prepared from various flaws that have been detected in advance to accurately determine the type, number and size of the detected flaws.

Abstract: A yarn breakage detecting system includes yarn detectors for detecting warp yarns forming a warp and for providing yarn detection signals, and a signal processing unit for counting peaks in the yarn detection signals, representing the warp yarns and for providing a yarn breakage detection signal when the number of peaks is smaller than a predetermined number. The warp yarns are divided into a plurality of groups and the adjacent groups are spaced apart by a predetermined distance greater than the pitches of the warp yarns in the groups by spacers or demarcated by identifiers, and the yarn detectors are respectively assigned to the groups of warp yarns. Since the monitoring range of each yarn detector is relatively narrow, the yarn detector can accurately detect the warp yarns at a high resolution in a relatively short time.

Abstract: Method to detect manmade fibres, defective fibres and/or other foreign materials in the processing of silk waste and to classify and count the faults detected in the lap of silk fibres leaving a drawing frame for instance, the method arranging that a substantially defined zone of the lap of silk fibres (20) made substantially parallel is illuminated by transparency with white light (23) and is scanned by a telecamera (24) associated with a data processing system (27) and is also illuminated by transparency with polarized light (25) and is scanned at the same time by a telecamera (26), which too is associated with the data processing system (27), images (14-15) taken by the telecameras (24-26) being processed and compared to determine the quantity, position, type and length of the faults of manmade, foreign or defective fibres.

Abstract: A spectro photometer deflects a measuring beam off its original axis to pass through a long sample, and returns the measuring beam to its final direction after passing through the sample. The sample is guided along a path which is clear of a reference beam of the spectro photometer. This arrangement permits double-beam measurement of long samples, with good signal-to-noise ratio. Deflection is accomplished using a plurality of mirrors.

Abstract: Method and apparatus for inspecting the surface of a moving web of homogeneous material for anomalies, the apparatus including a light source for illuminating the web surface and a light sensitive detector for receiving data from the web surface. The data is representative of the light reflected from the surface, as the light is affected by surface anomalies and background information. Computational means are provided for receiving output data from the detector in response to the data the detector receives from the web surface, and for processing the output data in a manner that determines the presence of surface anomalies. The computation means includes a plurality of filters for transforming the surface data in a manner that effects substantial elimination of the background information, and means for establishing threshold levels for background information.

Abstract: In a method and system for the detection of faults in a length of textile fabric, the length of fabric is continuously scanned by an electro-optical sensor head. Light detectors located in a strip-form sensing zone of the sensor head are assembled in groups and emit group-specific fault signals. These fault signals are analyzed multi-dimensionally for the identification of spot faults and/or long faults, the criteria for analysis being the signal amplitude, the signal length, the recurrence of the signals and their periodic repeat at each revolution of the machine. Display, control counter devices and the like are energized as a function of the result of the analysis.

Abstract: A surface defect detector for detecting a gentle wavy defect and a minute rough defect on a surface of an object. The detector has a conveyer to move the object in a linear direction, a laser beam generator to irradiate a laser beam onto the object in a direction perpendicular to the linear direction, two photoreceptors to generate two different signals in accordance with a reflection of the laser beam from the object, a separator to optically separate the photoreceptors, and a processor to process the signals from the photoreceptors to detect the gentle wavy defect and the minute rough defect.

Abstract: A tubular illuminator for focusing a bright line of approximately specular illumination onto the surface of a web moving at high speed to detect defects usually in the surface of the web.

Abstract: The apparatus comprises at least one light source (3) and a plurality of test channels with in each case one optoelectronic converter (4a, 4b). In the light path between the light source and the converter is provided at least one light channel (5a, 5b) and the test material (1). The light channels are constructed as optical elements for bounding or defining a light bundle. A plurality of light channels is juxtaposed in a common casing (6a, 6b) on at least part of the light path. In each light channel can be provided a beam splitter element (12) and together form a single beam splitter (12) removably arranged in the casing. The converters (4a) can be juxtaposed on the same casing as the beam splitter (12) and each is associated with a light channel (5a). Two casings (6a, 6b) can be provided, the light source (3) in the first casing (6a) and the converters (4b) in the second casing (6b) are juxtaposed and associated with in each case one light channel (5a, 5b).

Abstract: According to the present invention, an optical inspection apparatus which can observe a light-transmitted portion and a light-reflected portion within objects of inspection, distinguishable from each other within the same field of vision, is provided.

Abstract: A method for detecting both separated and non-separated edge cracks on a travelling product, such as a continuous paper web, and the like, and an apparatus for performing the invented method. The method includes directing air onto a travelling product with sufficient force to separate non-separated edge cracks and utilizing an optical signal device to detect edge cracks in the travelling product. A preferred embodiment of the method includes directing two streams of air toward opposite surfaces of the travelling product to effectively separate the non-separated edge cracks and orienting the optical device so that the direction of emitted optical signals forms an angle other than a right angle with the direction in which the product is travelling. The air used to separate the non-separated cracks is also directed across the optical signal device to prevent the build-up of foreign particles, thus improving the integrity of the method.

Abstract: Information is received from an image on a moving substrate. Flash exposure is used, defining operating or exposure cycles. The reflection or a representation of the image is subdivided into a matrix having n columns and m rows or lines. The sensor is a charge coupled device (CCD), arranged to have a sensing area (11) with n columns and m rows or lines, and a storage region or section (12), likewise arranged to have storage cells of n and m columns and rows or lines. Information of any one image element, upon sensing, is shifted by a line transfer pulse by one image line. The line transfer pulses are synchronized with web movement of the substrate and operate as shift pulses. The m line, at the first transfer line shift pulse, is shifted into the first line or row of the matrix of the storage portion of the CCD. For each operating cycle, at least one line transfer pulse is used. The information of the image elements can be read out serially from the storage portion (12) at high speed.

Abstract: The detection of abrupt changes in opacity of a moving sheet resulting from, for example, an overlap type splice is provided. The web material is fed between two identical light emitter/detector pairs such that its opacity is measured. An abrupt change in web thickness passing through one light emitter/detector pair is sensed as a change in web opacity. The difference and resulting imbalance with the opacity signal from the other light emitter/detector pair, not yet interrupted with the abrupt change, is utilized to indicate the presence of the defect which, in this application, could be an overlap splice. The disclosed invention, although adaptable to thicker textile webs, specifically relates to a device for the detection of overlap splices in a moving sheet representative of all the paper types required by the cigarette, printing, and labeling industries.

Abstract: The invention relates to an optical inspection apparatus comprising an illuminating means which has a linear light source (11) and a concave cylindrical mirror (10) which forms an image of the light source (11), with the cylindrical axis of the cylindrical mirror extending essentially parallel to the light source (11) in order to generate an illuminated strip (31) on a web (12) to be monitored, with the illuminated strip preferably extending over the entire width of the web (12). By means of an optical system (24) a light receiving means forms an image of an inspection line (32) extending on the material web (12) at the center of the illuminated strip (31) on a row-like photoreceiver arrangement (25), so that light emerging from the material web (12) is detected. The photoreceiver arrangement (25) is connected to an electronic processing circuit (26).

Abstract: In a cobwebbing detection device of the type in which light illuminates the end surface of a package and a cobwebbed yarn is detected by photographing the end surface by a CCD camera, a cobwebbing detection device has a binary encoder which converts each pixel of the image data into a binary coded data, a storage device, for storing the binary-coded pixel data, and a detection circuit which detects each pixel [1] or [0] in each scanning.

Abstract: A defect detection system for the optical inspection of defects in transparent and translucent sheets of materials. The system utilizes the differing optical properties of different defects to distinguish between such defects as fisheye defects, speck defects and scratches.

Abstract: Yarn is guided along a linear path through a light beam which is directed toward a photoelectric detector. Non-uniformities in the surface texture of the yarn cause the intensity of the light received by the detector to fluctuate rapidly as long as the yarn is moving. If the yarn stops moving as a result of breakage, the intensity of the light remains constant, and the detector produces an electrical signal indicative of the breakage.

Abstract: The invention consists in using a transmitter (23) of light to reproduce, in the plane of an optical detector (24), the profile of an object or a set of objects in contact or overlapping on a conveyor belt (21), e.g. newspapers (20), the profile being reproduced in the form of a function Y=f(X), then in scanning the profile by means of two receivers (27, 28) delimited by two slots (30, 31) in such a manner that the intersections of the function Y and the lines representing the two receivers are reduced approximately to two points with the distance between the two points being as small as possible, and finally in permanently determining the derivative Y'(X) and in actuating an electronic circuit associated with the detector (24) to generate an output signal proportional to the value of the derivative Y'(X).

Abstract: A device to monitor a moving yarn for irregularities is described. A first sensor head (2) with a recess (6) and a second sensor head (3) with a recess (7) are arranged in the direction of yarn movement. The cross-sectional depth of the recess (7) in second sensor head (3) is deeper than that of the recess (6) of sensor head (2). It is therefore possible, for example, to record separately slubs and projecting fibers. The monitoring device can be automated and used for quality control of any type of yarn.

Abstract: An engineered lighting system for high speed video inspection includes an array of light emitting diodes including light emitting diodes for use in time delay integration (TDI) inspection of web materials. The light emitting diodes of the array are selectively controllable to accomplish sequential illumination and carefully controllable imaging of a specified section of a continuously moving specimen or specimens. The system also includes an array of optional backlighting elements to aid in illumination of semi-opaque specimens to accomplish inspection thereof.

Abstract: The invention features a real time system for detecting streaks or scratches which occur substantially parallel to the direction of motion of a continuous web of material. The system can also be used to inspect sheets of material that may have been cut from such webs. An energy source such as an incandescent lamp or a bank of lamps generates electromagnetic energy that impinges upon the continuous web of material. CCD cameras receive reflected specular radiation from the web and generate video signals. The CCD cameras are disposed opposite the energy source and within 5.degree. of the plane perpendicular to the continuous web plane. Alternatively, the energy sources may transmit energy through the web material, which energy can be received by the CCD cameras. A processor is connected to the CCD cameras to process the video signals and to generate an enhanced signal-to-noise ratio signal that represents a streak or scratch on the web.

Abstract: Holes, tears and missing portions in a sheet, such as a banknote, are detected. The sheet is irradiated with radiation so that the radiation passes through the sheet with a relatively low degree of attenuation in areas where holes, tears and missing portions do not exist and with a relatively high degree of attenuation in areas where holes, tears and missing portions exist. The attenuated radiation is retroreflective back through the sheet and is then received by appropriate photodetectors. Since the sheet is relatively opaque and the radiation passes through the same points in the sheet twice, the contrast between the received radiation having passed through the holes, tears and missing portions and the received radiation passing through the relatively opaque sheet is very high making it simple to differentiate between those areas and thereby to positively detect holes, tears and missing portions in the sheet.

Abstract: A method and apparatus for detecting flaws in continuous web material illuminated by a light source and optically scanned to produce a digitalized electronic image of said material. The digitized image data representative of the continuous web material is stored in memory. The image data is also applied to a digital signal processor which identifies areas of the image which represent potential flawed areas of the continuous web material. A variety of spatial matched filters are employed to detect the flaws. Information concerning the locations of the potential flaws is transferred to a computer which analyzes in detail portions of the stored image in the vicinity of the identified areas. The processing performed in the computer verifies the presence of flaws in the material.

Abstract: The device contains a measuring gap, which is provided for the passage of the test material, the measuring gap having two side walls each of which is provided with a measuring electrode forming part of a capacitive measuring element. An optical measuring element having a light source arranged on one side of the measuring gap and having a photoelectric element is provided in addition to the capacitive measuring element, and both measuring elements form part of a common measuring head. The fluctuations in accuracy of previous measuring heads having only one measuring element are thereby reduced and automatic checking of the measuring head output can be preformed. In addition, parameters which could not be determined with previous measuring heads can be measured and monitored in accordance with the present invention.

Abstract: A method and apparatus for detecting foreign matter on a sample by illuminating a stripe-shaped region with linearly polarized light. Some of the light reflected by the sample is intercepted by a light intercepting stage, and the rest of the light reflected by the sample, which passes through the light intercepting stage is directed to a detecting optical system, to be detected by a photo-detector. The sample is illuminated obliquely at a predetermined angle with respect to a group of straight lines constituting a primary pattern on the sample. The angle is selected so that the diffraction light reflected by the group of straight lines does not enter the detecting optical system. A polarizing spatial filter using a liquid crystal element may be disposed in a predetermined restricted region in a spacial frequency region, or Fourier transformation plane, within the detecting optical system.

Abstract: An annunciator system and method for indicating when the number of detected flaws in a moving web is greater than a preselected threshold. The method and system includes a controllable display comprising a matrix of areas each corresponding to one type of the plurality of flaws and each capable of displaying any one of a first, second and third color. Signals corresponding to different detected flaws are received for controlling the display to initially display all of the areas in the first color, to individually change the color of an area to the second color in response to the detection of a first preselected threshold value of flaws of a type corresponding to the area and to individually change the color of an area from the second color to the third color in response to the detection of a second preselected threshold value of corresponding type flaws, which is higher than the first preselected threshold value.

Abstract: A joint inspection apparatus comprises a light irradiating device for irradiating light to a tape joint at which two tape edge portions are joined together, and a light receiving device for receiving the light irradiated by the light irradiating device to the tape joint and passing through the tape joint or reflected by the tape joint. A judgment device is provided for judging the extent of a deviation of the two tape edge portions from each other in the tape width direction at the tape joint on the basis of information on the optical amount of the light received by the light receiving device on both sides of the tape joint.

Abstract: A web drive control apparatus for continuously driving a web at a constant speed and stopping it at a desired position along a web drive line, comprises a web surface inspector for detecting a predetermined significant surface condition of a surface of the web. This inspector outputs an appropriate electric signal as a timing signal and a drive controller causes the web drive to start a deceleration of the web upon receiving the timing signal so as to stop part of the web where the significant surface condition is detected at a predetermined station along the web drive line. An activator, which is manually turned on and off, is provided to provide the line controller with an activation signal to enable the line controller to perform the decleration of the web.

Abstract: A method and apparatus are disclosed for nondestructively measuring the density and orientation of crystalline and other micro defects on and directly below the surface of a properly prepared material such as a semiconductor wafer. The material surface is illuminated with a probe beam of electromagnetic radiation which is limited to a nondestructive power level or levels. Polarization and wavelength or wavelengths of the electromagnetic radiation are selected according to certain characteristics of the material so that penetration depth is controlled. Specific orientation of the material with respect to the probe beam and the detector is required to detect that portion of the probe beam scattered from the defects of interest, surface or subsurface, without interference from other scatter sources and to identify the orientation of the defects. Maps of scatter intensity versus position are made according to the density of the defects encountered.

Abstract: The present disclosure describes an apparatus and a method for detecting the presence of flaws in a moving sheet of material. The apparatus comprises a light source for projecting a light beam; a beam shaping unit for shaping the light beam into a predetermined structured light pattern, and projecting the structured light pattern onto a portion of the surface of the sheet; an optical unit for collecting light emitted from the portion of the surface; and a light detecting unit for receiving the light collected by the optical unit and generating an electrical signal indicative of the intensity of the light generated from the portion of the surface. A signal processing unit is provided for filtering the electrical signal, the signal processing unit having predetermined characteristics specifically adapted to match an expected electrical signal corresponding to the predetermined structured light pattern.

Abstract: Apparatus and a method records a flaw in a fabric web during a flaw inspection. The flaw is recorded by a mark placed on the fabric web along with the X- and Y-values of a system of points defining a boundary line around the flaw. The mark and a side edge of the fabric web, respectively, serve as reference points for these X-and Y-values.

Abstract: A method and apparatus for detecting flaws in web material such as fabric comprises an array of optical sensors arranged in closely spaced relationship into at least one row spanning the web to be inspected. A light source is mounted in spaced parallel relationship relative to the sensor array and the web passes between the light source and the sensors. Each sensor produces a voltage signal that is proportional to intensity of light falling thereon and, therefore, to the amount of light transmitted by the portion of the web passing adjacent the sensor. The sensors are connected to a microprocessor that is programmed to compare their signals to standards representing signals produced by flawless fabric. A predetermined number of comparison results are combined and transformed into a single representative value that is compared with a preselected threshold value. If the representative value exceeds the threshold, a signal indicative of a flaw is produced by the microprocessor.

Abstract: A method and device for determining the strength of a sheet material, such as paper, utilizing floc size and the variability of the local basis weight of the sheet. The force required to deflect the moving sheet out of a nominal position, the distance the sheet is deflected by said force and the average tension applied to the sheet may also be utilized in the above determination of sheet strength.

Abstract: Method of determining the quality characteristic of running yarns, in which the number of yarn imperfections is ascertained with the aid of fluff counters, wherein the thread passes through at least three fluff sensors of the same type arranged one after another, whose counting pulses, which are emitted upon passage, by a yarn section of the freely selectable length L, are converted into a length-related average R, highly deviant individual measurement results being regarded as outlier values and not being included in the averaging.

Abstract: A method and apparatus are disclosed for nondestructively measuring the density and orientation of crystalline and other micro defects directly below the surface of a properly prepared material such as a semiconductor wafer. The material surface is illuminated with a probe beam of electromagnetic radiation which is limited to a nondestructive power level and with a wavelength, or wavelengths, selected according to certain characteristics of the material so that penetration depth is controlled. Specific orientation of the material with respect to the probe beam and the detector is required to detect that portion of the probe beam scattered from the subsurface region without interference from the surface scatter and to identify the orientation of the defects. Maps of scatter intensity versus position are made according to the density of the defects in the subsurface.

Abstract: An on-line method of and apparatus for inspecting an apertured mask sheet to be formed into a shadow mask for a color cathode ray tube are disclosed. In one of several embodiments described the mask sheet is linearly scanned by a laser spot transverse to the direction of advancement of the mask sheet. The peak values of the grey levels of the laser light transmitted by the mask sheet are detected and the data is convoluted electronically to form a series of convolution windows. The grey levels of the successively formed convolution windows are compared to at least one reference value and an output is produced at least in those cases where an error in the mask aperture size is detected.

Abstract: An optical slub catcher, particularly suitable for open-end process weaving machines, comprises a special optical head for the measurement of yarn diameter, the analog signal of which is cleaned of the disturbances due to ambient light. This analog signal is furthermore normalized by an original compensating and normalizing unit, and is then digitized. The slub catcher of the present invention is also provided with the following: a detector unit for the detection of Moire defects, a detector unit for the detection of the % VC irregularities, and a unit for spectrogram processing.In addition, the slub catcher of the present invention compensates for dirt build-up, thermal drifts, and aging of the optical head which affect the performance of the slub catchers of the prior art.

Abstract: An apparatus for examining the surface of a substrate comprises irradiating means for supplying a light beam which scans the surface of the substrate, first and second light-receiving means for individually receiving scattered lights travelling in different first and second directions from the surface of the substrate and individually producing first and second output signals conforming to the intensities of the received lights, and means for discriminating the directional characteristics of the scattered lights on the basis of the time phase shift between the first and second output signals.

Abstract: A method of cutting out pieces which are to be assembled from a length of check fabric 1 in order to obtain continuity or alignment in the design on the fabric at at least some of the assembly points includes the steps of placing a length of fabric on a cutting-out table 2, storing the shapes, positions, and orientations of the pieces to be cut out in a computer memory, with a margin having a width equal to one half of a design element being reserved around some of the pieces in one or two directions, and also storing the positions of points A, B which are to coincide when the pieces are assembled. A pair of images of the fabric, each centered on a corresponding one of the points, are displayed on a screen 8 side by side, and linear and/or angular offsets between the designs are observed, whereafter any offsets are corrected such that the designs correspond in at least one direction.

Abstract: A system to detect the angle of pile lay of the fibers on the face side of a pile fabric by scanning the fibers with an infra red light source and measuring the intensity of the reflected infra red light beam. This is accomplished by using a rotating mirror system to deflect the infra red light beam onto the fabric and direct the infra red light beam reflected from the pile fibers on the fabric to a detector.

Abstract: An optical surface inspection apparatus for material webs comprises an illuminating means (11) for generating a strip of light (12) on the surface (19) to be inspected and a light receiving means (13) which receives the light emitted (diffusely reflected) from the surface region illuminating by the strip of light (12) and directs it to a photoreceiving arrangement, which delivers a signal representative of web faults to an electronic processing circuit (16). The light receiving means (13) has at least one row camera (14) which receives light remitted from a line illuminated by the strip of light (12) and forms an image of the line on the diode row (15). The light receiving means is also arranged at such a shallow observing angle .alpha. relative to the tangential plane to the surface at the location of the strip of light (12) that faults (20) which project slightly out of the surface appear to the row camera (14) in shadow outline against the light background of the strip of light (12).

Abstract: A joint inspection apparatus comprises a light irradiating device for irradiating light to a tape joint at which two tape edge portions are joined together, and a light receiving device for receiving the light irradiated by the light irradiating device to the tape joint and passing through the tape joint or reflected by the tape joint. A judgment device is provided for judging the presence or absence of an overlap of the two tape edge portions one upon the other at the tape joint on the basis of information on the optical amount of the light received by the light receiving device in the vicinity of the tape joint.

Abstract: The invention is a process and an apparatus for measuring the weft threads and draft angle for a continuously moving textile sheet. At least one long narrow section of the sheet is monitored by transmitted or reflected illumination. The long narrow section has a small width and long length in comparison with the thickness of the weft threads. The longitudinal axis of the section has a defined, constant angle in relation to the transport direction. The illuminated section is monitored by a sensor array. The brightness values within the section are divided in two classes (bright, dark), and those sensors within the field in which brightness values are the same, and that there be determined either the number of (total) length of the sensors within the same class or speed at which the sensors of one class move in the section, and that the draft angle of the weft thread is determined therefrom.

Abstract: An apparatus usable with an object having surfaces, for examining the states of the surfaces, includes on irradiating system for irradiating the surfaces of the object with a single light beam, and a plurality of light-receiving systems provided in association with the surfaces of the object, respectively, the plural light-receiving systems being arranged to receive light scatteringly reflected from the surfaces of the object, respectively, and to produce outputs corresponding to the states of the surfaces of the object, respectively.

Abstract: A method of testing security papers with respect to the positions of a safety thread and water marks to detect errors in the paper is performed by a linewise scanning of a finished paper web. The web has at least two point like measuring marks inserted into it in addition to the water marks, whereby impulses which are originated from these measuring marks are evaluated and the sheet width and the sheet distortion are calculated by comparing the x-y positions of the individual measuring marks with each other. The measuring marks are sharpe edged and rich in contrast. The given edge impulse is evaluated.

Abstract: The specification describes a method for measuring the offset between regular images of, for instance, halftone dots and double images thereof, in which a test screen pattern is printed along an edge of the paper web to be printed which consists of two rows of test pattern strips representing a fishbone pattern. Using two sensors the gray values of the two test pattern rows are scanned and supplied to a double element printing measuring device. On the basis of the results of measurement and the geometrical relationships of the test strips and of the test edges arising owing to double printing phenomena the degree of double print offset may be determined. The method may be used for on line measurement of the degree of double print offset during the operation of the printing press.

Abstract: Printed webs leaving a printing press at speeds above 500 feet per minute are inspected with precision across the full width of the web by a stroboscope method and apparatus. Each repetitive image or design imprinted on the high speed web is rendered stationary relative to the eyes of a viewer at a web inspection station by bright short flashes of light emitted by an elongated xenon flash tube or tubes spanning the web transversely of its path of movement. Light flashes triggered by an improved strobe circuit which is synchronized with the images at all times permits an inspector to inspect any number of images, spaced around the press cylinder, whether or not the images are equally spaced. Additionally, the system can be used in either an image lock mode for side-by-side comparison with a standard or in a controlled pan or scroll mode to allow optimal inspection of entire impression sequences.

Abstract: Apparatus for detecting discontinuities in a radiation diffusing surface (10) such as paper. Radiation is passed to the surface and a radiation collector (19) receives the diffused radiation (18) from a limited area of the surface (10). The radiation collector receives the diffuse radiation from a limited area only and from within predetermined angular limits other than normal to the surface. The radiation collector (19) defines said predetermined angular limits through total internal reflection.