Arrangement and method for marking defects

A method and device for marking defects in or on a substantially planar strip (70, 170), preferably a strip of polymeric film. The defect is marked by means of firstly illuminating the width across the strip (70, 170) by means of a light source (90, 190) and detecting defects in or on the strip (70, 170) by means of a detector (10, 300). The strip (70, 170) is placed in a plane in connection with the light source (90, 190) and wherein the incident light is reproduced on the detector (10, 300). Thereafter, the defect is marked by means of a marker (200) which is placed in connection with the defect. The marker (200) is placed on a label (62, 162), which is attached onto the strip (70, 170).

TECHNICAL FIELD
 The present invention pertains to a device and a method for marking defects
 in or on a strip, for example a strip of a polymeric film.
 BACKGROUND OF THE INVENTION
 It has long since been known how the occurrence of defects can be detected.
 The occurrence of defects in a film, for example a polymeric film, can be
 accomplished by means of a device which illuminates a film, for instance,
 from below with a light source. The film can be observed from above by a
 detector, for example by a line array. At the beginning and the end of the
 passage of a defect, the portion of the detector on which the present
 portion of the film is reproduced will not be equally illuminated, since
 the end and the beginning of the optically refracting defect temporarily
 break into the image of the non-radiating surface behind and in front of
 the light-radiating opening on the light table.
 An alternative design may be that a similar device is provided with a
 scanning beam of light (e.g. laser light) which illuminates a film and
 wherein the light beam is observed from the other side by a detector, e.g.
 a photo-detector. This detector is arranged so that the detection only
 verifies if there is light passing through the film. Should no light be
 detected, the light beam will accordingly have been refracted so that the
 light beam either passes in front of or behind the detector because of the
 defect which is present on the film.
 In order to find and analyze the defect, it can be marked with the aid of a
 marking device, for example of inkjet type, which marks the position of
 the defect on the strip by means of indicating, for example with ink,
 directly on the strip. The detector and the marking device can be
 electrically connected to each other, wherein the detector can transfer
 signals to the marking device in case a defect is detected. When a defect
 is detected, the marking device can mark this on the strip, for example by
 means of an inkjet printer.
 One way of detecting defects in a transparent plastic film is disclosed in
 U.S. Pat. No. 4,038,554. The defects are measured by means of a laser beam
 striking a mobile mirror, wherein the mirror performs a scanning movement
 across the film so that the laser beam can scan the entire width of the
 film. A light-collecting rod is situated underneath the plastic film and
 is provided with a light-refracting tape in the longitudinal direction of
 the rod and a photo-diode on one of the short sides of the rod.
 Another way of detecting defects on a transparent glass plate is disclosed
 in U.S. Pat. No. 3,989,387. The defects are measured by means of
 illuminating a glass plate with a light beam, wherein the light beam which
 has passed the glass plate is reflected onto a mirror. Accordingly, the
 light beam in the main can pass through the glass plate once more and be
 detected by a photo-electric cell. In order to obtain a suitable angle of
 reflection, the light beam is conducted through the glass at an angle up
 to 30.degree. in relation to a normal, which is perpendicular to the
 longitudinal direction of the glass.
 However, these documents only disclose how it is possible to detect defect
 and not how a defect can be marked on a strip. Furthermore, when marking
 of defects with the aid of inkjet printers is concerned, certain problems
 may occur such as the ink running on the strip. Furthermore, inkjet
 printers normally require high precision and maintenance, e.g. when
 cleaning out ink.
 One method of detecting and marking optically refracting defects in
 transparent glass plates is disclosed in U.S. Pat. No. 4,492,477 and is
 utilized for the preamble of claims 1 and 6. The defects in a glass plate
 can be detected by means of illuminating one side of the plate with a
 light source and detecting possible defects with a detector on the other
 side of the plate. A marking system can be arranged in connection with the
 detector, which can mark a defect directly on the plate. This marking
 system, however, only discloses how it is possible to utilize some kind of
 ink which is coated directly onto the plate. By means of coating the ink
 directly onto the plate, the ink can run on the plate. If the system is
 able to maintain high precision, it may be necessary to use special inkjet
 nozzles which require a special type of ink. The ink should be rapidly
 drying in order to avoid the ink running across the glass plate, which in
 turn contributes to another problem, namely that the ink inside the
 nozzles dries and, accordingly, they have to be cleaned. If this method
 were to be utilized for marking defects on a polymeric material, such as
 polyethylene or teflon, instead of glass as is disclosed in U.S. Pat. No.
 4,492,477, it may furthermore be necessary to use another type of ink.
 This implies that the method will be difficult to apply to different types
 of materials, since it is not always possible to use the same type of ink.
 SUMMARY OF THE INVENTION
 Accordingly, one object of the present invention is to provide a method and
 a device for marking and analyzing defects on a strip in a simple way,
 which eliminates the above-mentioned problems.
 In accordance with the present invention, the above-mentioned object is
 achieved by means of providing a method in accordance with claim 1 and a
 device in accordance with claim 6.
 Preferred embodiments of the method and the device, in accordance with the
 invention, are defined in detail in the dependent claims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
 With reference to FIG. 1, a first embodiment of a device for detecting
 defects in a substantially planar strip 70 is shown, the strip preferably
 being a strip of a polymeric film or the like, which in this embodiment is
 transparent. The device is arranged with a light source 90, for example a
 scanning laser or a diffuse light source, in order to illuminate
 substantially the width across the transparent strip 70. In order to
 delimit or direct the light from the light emitted from the light source,
 an aperture, preferably a slit (not shown), is arranged in front of the
 light source. Furthermore, the device is provided with focusing means 50,
 which for example comprise a lens system and an optical axis, for focusing
 the light which passes through the transparent strip and a detector 10
 provided with one or several detector elements (not shown), which for
 example may be constituted of a CCD-camera or a single detector element
 (e.g. a photo-diode), detecting light from a mirror which rotates in the
 main across the width of the film, for detecting defects on the strip 70.
 This detector 10 can be of a scanning type, i.e. the detector in the main
 can scan across the light which passes the transparent strip, for example
 by means of mounting the detector on a mobile axis and setting this in
 motion either manually or by means of a motor (not shown). The detector 10
 can achieve an image of an occurring defect and the light which passes
 through the strip. Furthermore, the strip 70 can be displaced in its
 longitudinal direction, past the detector, by means of displacement means
 80, which for example can be constituted by one or several electrical
 motors provided with rollers which drive the strip 70 forwards. Other
 detectors 10 than CCD cameras may of course also be utilized, for example
 photo-diodes and other types of photo-cells can be utilized. By means of
 these detectors, a monochromatic scale of the achieved image may
 furthermore be obtained.
 The detector 10 can further comprise an electronic unit, which is provided
 with a main circuit connection (for power supply to the detector), first
 means for controlling the light source, and second means for controlling
 the sensitivity of the detector. The first means can e.g. control the
 intensity of the light source, indicate malfunction of the lamp, etc. In
 order to enable the focusing means 50 to obtain the same amount of light,
 independently of the thickness of the strip, the first means can
 automatically or manually control the intensity of the lamp so that equal
 quantity of light passes through the focusing means 50.
 The second means can further transmit signals to a marking device 60, for
 example an electronic printer, for marking the position of the defect on
 the strip by means of a marker 200, see also FIG. 2. The detector and the
 marking device can be connected to each other, e.g. by means of an
 electrical cable 100 or in a wireless way, wherein the detector can
 transfer signals to the marking device if a defect is detected.
 The sensitivity/detectability can be varied by means of the second means in
 order to make it possible to increase or reduce the detectability of a
 defect with another accuracy. Furthermore, the detector 10 can be arranged
 with a focusing indicator 20 and an exposure meter 40.
 In order to be able to mark defects in or on the strip, the defect should
 initially be detected. This may for example be achieved by means of
 illuminating the width across the strip 70 by means of the light source
 90. The light passing the strip 70 can further be focused through the
 focusing means 50, which can be provided with an optical axis. The strip
 70 is placed in a first plane between the light source 90 and the focusing
 means 50, wherein the optical axis is placed in a second plane and focuses
 the incident light to the detector 10 through the focusing means 50. In
 this a way, a possible defect in or on the strip 70 can be detected by
 means of the detector 10. Thereafter, the marking device 60 can mark the
 defect by means of a marker, which is placed in connection with the
 defect. This marker is placed on a label 62, wherein the label is attached
 to the strip. In addition to the marker, the marking device can print out
 the dimensions of the defect and/or the position of the defect on the
 strip, i.e. detailed information in the form of letters, numbers,
 characters, etc. The label can for example be constituted of a patch
 provided with an adhesive material, e.g. some kind of glue, on one side.
 The label can either be placed in a predetermined position on the strip or
 be laterally displaced when the marker is placed in a predetermined
 position on the label, i.e. the marker is placed in a predetermined
 position on the strip.
 By means of selecting a patch of a suitable material, i.e. of paper,
 plastic or a composite of similar materials, which can have a certain
 absorbency, an inkjet printer will be perfectly usable since the ink does
 not run on the patch because it has a certain absorbency. Other types of
 printer can of course also be utilized, such as e.g. a laser-printer, a
 thermal printer or the like, wherein the patch does not have to possess a
 certain absorbency but may for example be constituted of an impervious
 plastic surface.
 In FIG. 2, an embodiment of the appearance of a label is shown, which a
 marking device 60 has printed out by means of an electronic printer. The
 marker is denoted 200, whereas the dimensions of the defect, and/or the
 position of the defect on the strip, are denoted 210 and 220.
 In FIG. 3, a second embodiment of a device for detecting defects in a
 substantially planar strip 170 is shown, said strip being for example a
 strip of polymeric film, which can be transparent, or a film of an opaque
 or partially transparent material, wherein said device can be arranged
 with a light source 190, for example a laser or a diffuse light source,
 for illuminating substantially the width across said strip 170.
 Furthermore, the device can be provided with focusing means 150, which for
 example comprise a lens system and an optical axis, for focusing the light
 which strikes the strip and a detector 300 provided with one or several
 detector elements (not shown), which for example can be constituted of a
 CCD-camera or a single detector element (e.g. a photo-diode) detecting
 light from a mirror which rotates in the main across the width of the
 film, for detecting defects on said strip 170. This detector 300 can be of
 a scanning type, i.e. implying that the detector can in the main scan
 across the light which strikes the strip, for example by means of mounting
 the detector on a mobile axis and setting this in motion either manually
 or by means of a motor (not shown). The detector 300 can achieve an image
 of an occurring defect and the light striking the strip. Furthermore, the
 strip 170 can be displaced in its longitudinal direction by means of
 displacement means (not shown). Other detectors 300 than CCD-cameras can
 of course also be utilized, for example photo-diodes and other types of
 photo-cells may be utilized. By means of these detectors, a monochromatic
 scale of the achieved image may furthermore be obtained.
 In a corresponding way, the detector member 300 may, as shown in the first
 embodiment, transmit signals to a marking device 160, for example an
 electronic printer, for marking where the defect is located on the the
 strip by means of a marker 200, see also FIG. 2. This marker is placed on
 a label 162, wherein the label is attached to the strip 170. The detector
 member 300 and the marking device 160 can be connected to each other, e.g.
 by means of an electrical cable 310 or in a wireless way, wherein the
 detector member 300 can transfer signals to the marking device 160 in case
 a defect is detected.
 Although the shown embodiments of the present invention have been described
 in detail with reference to the accompanying drawings, it should be
 understood that the invention is not limited to these specific embodiments
 and that different changes or modifications can be achieved by a skilled
 person, without departing from the scope which is defined by the following
 claims. For instance, it need not necessarily be a printer which prints
 out a marker on a label, but it can instead be a device which attaches a
 marker, in the form of a smaller label, onto the label which is intended
 to be attached to the strip. Another optional marker can be to punch one
 or several holes into the label.