Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/89—Investigating the presence of flaws or contamination in moving material, e.g. running paper or textiles
  • G01N21/8901—Optical details; Scanning details

Definitions

• the present invention relates to an automatic surface inspection method of a moving strip, in particular a laminated sheet, or of plates moving at high speed, for the detection of surface defects.
• a first conventional technique for inspecting the surface of a strip consists in carrying out a visual inspection of the surface of this strip.
• Another known technique of surface inspection consists in automatically checking the surface condition of the strip by means of, on the one hand, a camera whose optical axis is directed towards the surface to be inspecting and forming on said surface a line of sight transverse with respect to the direction of travel of the strip and, on the other hand, of a lighting system illuminating the width of the strip at the level of the line of sight, and finally, a signal processing unit for real-time analysis of the images delivered by the camera.
• Conventional lighting systems for automatic surface inspection devices produce lighting whose radiated rays are, in the transverse direction, perpendicular to the strip. It follows that, at each point of the transverse line of sight, the direction of observation of the camera forms with the reflected specular ray a variable angle.
• one solution consists in providing lighting whose rays do not. are no longer emitted perpendicular to the strip.
• there are systems capable of producing such a type of lighting the main emission angle of the rays of which is constant in the direction perpendicular to the direction of travel of the strip.
• the application of these systems has two major drawbacks.
• the visibility of a given defect is not constant as a function of the position of this defect along the line of sight and, on the other hand, the signal recorded by the camera and constituting the image of the strip has amplitude variations in the transverse direction.
• the object of the invention is to avoid these drawbacks by proposing an automatic inspection device which allows a significant increase in the visibility of faults and the obtaining of a constant signal in the transverse direction recorded by a camera. , thereby improving the detection thereof.
• the subject of the invention is therefore an automatic surface inspection device for a moving strip, for the detection of surface defects, of the type comprising, on the one hand, at least one camera, the optical axis is directed towards the surface to be inspected and forming with said surface a transverse line of sight with respect to the direction of travel of the strip and, on the other hand, at least one lighting system whose incident rays are directed towards the transverse line of sight and distributed over the entire length of said line, characterized in that at each point of the transverse line of sight, the direction of observation of the camera forms with the reflected ray specular at said point at a constant angle.
• the specular reflected ray on the line of sight forms with the normal to the surface to be inspected an angle whose value varies continuously along the line of sight, its minimum value corresponding to the center of this line of sight and its maximum value at the end of said line of sight,
• said lighting system is formed by at least one row of optical fibers, - said lighting system is formed by at least one row of light-emitting diodes,
• said lighting system is formed by a linear light source associated with at least one optical element for directing the incident rays towards the transverse line of sight,
• the camera is inclined, relative to an axis perpendicular to the surface to be inspected and passing through the point of intersection of the optical axis of said camera on said surface, by an angle between 0 and 70 °.
• FIG. 1 is a schematic perspective view of a device for inspecting the surface of a moving strip, according to the invention
• FIG. 2 is a schematic view showing the optical configuration of the inspection device according to the invention.
• the device shown in FIG. 1 is intended to inspect a surface of a strip 1 during high-speed scrolling, for example a laminated strip leaving a rolling line, to detect surface defects.
• a surface of the strip 1 is inspected by means of a camera 10 whose optical axis Xi X 2 is directed towards the surface to be inspected.
• the device comprises a single camera 10 directed on one of the surfaces of the strip 1, but of course, the device can be equipped with two cameras suitable for forming images of each surface of said strip 1.
• the camera 10 can be constituted by any type of camera suitable for the intended use, such as for example a camera forming on the surface of the strip 1 a transverse line of sight L with respect to the direction of travel of said strip 1.
• the field width of the camera 10 is equal to or slightly greater than the width of the inspection area of the strip 1.
• the transverse line of sight L is equal to or slightly greater than the width of the strip 1.
• the camera 10 acquires the image of the surface of the strip 1 as it travels and to improve the visibility of possible defects on this surface to be inspected, such as for example scratches or scratches, the inspection device also comprises at least one lighting system such as a light bar 15.
• the incident rays Rj are directed towards the transverse line of sight L and distributed over the entire length of this line of sight.
• the lighting system 15 is designed such that at each point of the transverse line of sight L, the direction of observation y of the camera 10 forms with the reflected ray R r specular at said point a constant angle ⁇ .
• the reflected ray R r specular is the reflected ray which forms with a normal to the point of impact on the surface of the strip 1, an angle which is equal to the angle formed by the incident ray Rj at said point with this normal.
• Fig. 2 we have chosen, by way of example, two points respectively Pi and P 2 , located on the transverse line of sight L and on either side of the optical axis Xi X 2 of the apparatus shooting 10.
• the point Pi is at a distance di from the optical axis X ⁇ X of the camera 10 and the point P 2 is at a distance d from this optical axis which is less than the distance di.
• the incident ray Rj emitted by the light source 15 at the point Pi forms an angle ⁇ with the normal i at the surface of the strip 1 at the point P and the direction of observation Yi of the camera 10 forms with this normal Ni at the point Pi an angle ai.
• the reflected ray R r specular at point Pi forms with the direction of observation Yi at point Pi an angle ⁇ .
• the incident ray Ri emitted by the light source 15 forms at point P 2 with the normal N 2 at this point P 2 an angle ⁇ 2 and the direction of observation Y 2 of the camera 10 forms with said normal N at point P 2 an angle 2 .
• The. reflected ray R r specular forms with the direction of observation Y 2 at point P 2 , an angle ⁇ equal to the angle ⁇ formed with the reflected ray R r specular and the direction of observation Y 1 of said camera 10 at the point Pi.
• the incident rays form with a normal at each point of the transverse line of sight, an angle which varies continuously along said light source.
• the reflected ray R r specular and obviously the incident ray Rj at a point taken on the line of sight L forms an angle ⁇ whose value varies continuously along said line.
• the maximum value of this angle is located in the center of the line of sight L and its minimum value at the end of said line of sight.
• the angle of the reflected ray R r specular or of the incident ray Ri varies on the line of sight L between 30 and 60 ° and this for each half-band between a point located on the shore and a point located on the optical axis ⁇ X 2 of said camera 10.
• the angle of the reflected ray R r or of the incident ray Rj varies between 15 ° and 30 ° and this for each quarter of the tape.
• the lighting system 15 is formed by at least one row of optical fibers or by at least one row of light-emitting diodes so as to be able to tilt the incident ray at an angle determined as a function of the point of the transverse line of sight on which is directed said incident beam.
• the lighting system 15 is formed by a linear light source associated with at least one optical element for directing the incident rays towards the transverse line of sight and for giving these incident rays the desired inclination according to the point located on said transverse line of sight.
• the camera 10 is inclined, relative to an axis perpendicular to the surface to be inspected of the strip 1 and passing through the point of intersection of the optical axis Xi X 2 of said camera on said surface, an angle between 0 and 70 °.
• the inspection device using a lighting system illuminating the surface to be inspected of the strip from the side relative to the direction of travel of this strip allows a significant increase in the visibility of certain types of defects, such as for example long mechanical defects in the rolling direction.
• this device makes it possible to obtain a maximum and constant visibility of the defects over the entire width of a strip, such as for example a strip of two meters wide in movement, and this regardless of the position of the fault on this strip. .
• the reliability of the tape quality controls is increased, thus allowing rapid intervention in the tape manufacturing process to correct these defects as soon as possible and avoid significant scrap.

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• Engineering & Computer Science (AREA)
• Textile Engineering (AREA)
• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)

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• 2000
  • 2000-12-11 FR FR0016093A patent/FR2817964B1/fr not_active Expired - Lifetime
• 2001
  • 2001-12-10 EP EP01270764A patent/EP1346204A1/de not_active Withdrawn
  • 2001-12-10 BR BRPI0115787-6B1A patent/BR0115787B1/pt active IP Right Grant
  • 2001-12-10 MX MXPA03005075A patent/MXPA03005075A/es active IP Right Grant
  • 2001-12-10 CA CA002431256A patent/CA2431256C/fr not_active Expired - Lifetime
  • 2001-12-10 JP JP2002549953A patent/JP3822567B2/ja not_active Expired - Lifetime
  • 2001-12-10 AU AU2002217230A patent/AU2002217230A1/en not_active Abandoned
  • 2001-12-10 WO PCT/FR2001/003904 patent/WO2002048695A1/fr active Application Filing
  • 2001-12-10 US US10/415,421 patent/US6995838B2/en not_active Expired - Lifetime

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