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
  • G01N21/892—Investigating the presence of flaws or contamination in moving material, e.g. running paper or textiles characterised by the flaw, defect or object feature examined
  • G01N21/898—Irregularities in textured or patterned surfaces, e.g. textiles, wood
  • G01N21/8986—Wood
• • 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
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/46—Wood
• • 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
  • G01N2021/8905—Directional selective optics, e.g. slits, spatial filters

Definitions

• the present invention relates to a method and a measuring system for detection of defects within a prescribed measurement zone on the surface of a piece of wood, said measuring system comprising at least one light source for spot illumination of the surface of the wood within the measurement zone and at least one optical detection member for detecting the light reflected from the wood surface and connected to a microprocessor, as well as means for displacing the wood surface through the measurement zone.
• Sawmills usually make an end adjustment of the butt end of the boards in such a way that defects in the form of pick ⁇ ups, rot, splits, warping, cupping and knots are cut off. From an economical point of view it is important that this cutting adjustment occurs without unnecessary waste so that no first-rate timber is lost. Until now the end adjustment has occurred manually by the boards being fed forwards on a transporter whilst lying transversely to the transp ⁇ orter's longitudinal direction, past an inspection station where an inspector visually inspects the passing boards. The inspector makes a judgement of a suitable cutting position for each board and moves the same to said cutting position in line with a cutting device.
• One object of the present invention is therefore to achieve a method and a measuring system which, with comparatively simple and cheap components, enables the detection of defects and the determination of a suitable cutting point.
• the wood sur ace is spot-illuminated with a number of light beams which are parallel and have known respective separation distances, said beams being made to pass the measurement zone and presenting a certain in ⁇ tensity, and in that the light intensity and the position of the spots in which the light beams illuminate the piece of wood during displacement within the measurement zone are detected in a series of exposures.
• the measuring system according to the invention is charac ⁇ terized in that the light source comprises means to emit a number of light beams which are parallel and directed towards the wood surface and which have known respective separation distances, and in that the microprocessor is arranged to control the detection means in such a way that a series of exposures, in which the light intensity and the position for the illuminated spots on the wood surface are detected, are made at small intervals when the piece of wood passes the measurement zone.
• FIG. 1 shows a schematic end view of a measuring system according to the invention which comprises two measuring units
• Fig. 2 shows a side view of the internals of one of the measurement units shown in fig. 1
• Fig. 3 depicts the detection method schematically
• Fig. 4 depicts diagrammatically the light levels of a scanned exposure
• Fig. 5 shows a board-end with a split and a skew cut in perspective
• Fig. 6 depicts diagrammatically the result of the detec ⁇ tion of the board-end shown in fig. 5
• Fig. 7 shows a curved and cupped board-end
• Fig. 8 depicts diagrammatically the result of the detec ⁇ tion of the board-end shown in fig. 7.
• the measurement units 10 shown in fig. 1 are mounted on the upper and lower side of a light trans issive transporter which is not shown in the figures but can be constituted by a normal chain transporter which feeds forwardly boards which lie transverse to the longitudinal direction of the transporter.
• Each measurement unit comprises a box-formed casing 11 which contains a complete detection unit.
• the two measurement units 10 are completely alike and cooperate in such a way that they inspect the upper and lower side respectively of a piece of wood 13 via a glazed window 12 arranged in respective casings.
• the measurement system is intended to determine the cutting point on the butt end of dried boards which can for example have a width of 75-200 mm and a thickness of 15-75 mm.
• the equipment can for example be dimensioned for a measurement zone of 310 mm in length and 100 mm in thickness.
• each measurement unit comprises three laser tubes 14 or laser diodes each of which emits a narrow beam of preferably pulse modulated light.
• the beam from respective laser tubes are fed via a mirror
• the beams 17 are directed so that they impinge on the wood surface perpendicularly and are oriented so that they form a row which extends essentially transversely to the forward-feed direction of the piece of wood 13.
• a luminous tube 18 is also mounted in the casing 11 so that it spreads a diffuse light through the window glass 12. Additionally there is an optical detection means 19 mounted in the casing 11 for detecting the light reflected from the surf ce of the wood 13 via the window glass 12 and a mirror 20 mounted inwardly of this within the casing 11.
• the detection means 19 is of the array type and comprises a series of light-sensitive elements which, in the shown embodiment, are arranged to cover a measurement zone of 0- 5000 pixels.
• the casing 11 also contains a microprocessor 21, an electrical supply device 22 for the electronics and for the luminous tube, three electrical supply devices 23 for the laser tubes 14 and a display arrangement 24.
• the microprocessor 21 is arranged to control the exposure of the detection means 19 for collection of a series of measured values from each board 13 which passes the inspection station. The series of measured values then forms the basis for a judgement carried out by the micro ⁇ processor for determining the optimal cutting point having regard to the defects which are present in the measurement zone.
• Each unit 10 can be provided with a nozzle (non-depicted) for blowing pressurized air in order to keep the window 12 clean.
• Fig. 4 shows graphically in an X-Y diagram how this is represented in the detection means 19 with an exposure time of circa 2 ms, whereby the X-axis defines the number of pixels and the Y-axis the illumination intensity.
• the left zone thus shows the number of laser beams which impinge upon the board.
• the distance between two laser beams is 10 mm, which corresponds to circa 140 pixels on the array if the board is planar.
• the reference numeral 25 indicates the end point of the board.
• the resolution for this point is circa 0 ,1 mm for determination of the position horizontally and vertically whereby the two last laser beams which impinge upon the board are used as a reference.
• the distance between these is 10 mm, which corresponds to circa 140 pixels.
• Fig. 5 depicts a complete measurement collection from a board end which presents a split 26, a skew-cut portion 27 and a certain cupping.
• a series of exposures are made during the passage of the board past the row of laser beams in the direction of movement as in ⁇ dicated by arrow 28.
• the exposure time is for example 2 ms and each exposure, is saved until the board has passed the row of laser beams.
• the condition for starting a measure ⁇ ment collection is that at least one laser beam has to be detected.
• the measurement collection is terminated when no beam is detected any more.
• Fig. 6 shows the measurement collection graphically in an X-Y diagram whereby the X-axis defines the distance from a re erence beam in pixels and the Y-axis exposure occurrenc ⁇ es. All the lines are slightly curved. This is due to the fact that the board is cupped. The blip in line four and five originates from the end of the drying split 26. The split 26 is so large at lines six to nine that the laser beams disappear into the split during the whole exposure time. The lines ten to thirteen being interrupted is due to the fact that the board is a skew cut. This board should be cut at 30 mm. If the drying split 26 had not been present cutting should have occurred at 92 mm.
• Figs. 7 and 8 show in a corresponding manner a board and respectively a diagram coming from the measurement of this board.
• the board is bent upwardly and cupped downwardly. Due to the fact that the board is bent upwardly the distance between the lines increases towards the right in the diagram. The lines in the diagram bend moreover to the left as a result of the cupping.

Landscapes

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

Applications Claiming Priority (2)

Publications (1)

Family

ID=20386034

Family Applications (1)

Country Status (2)

Cited By (4)

Citations (4)

• 1992
  • 1992-04-23 SE SE9201277A patent/SE510242C2/sv not_active IP Right Cessation
• 1993
  • 1993-04-23 WO PCT/SE1993/000352 patent/WO1993022659A1/en active Application Filing

Patent Citations (4)

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