WO1991005983A1 - A method and a device for measuring the height of material pieces - Google Patents

A method and a device for measuring the height of material pieces Download PDF

Info

Publication number
WO1991005983A1
WO1991005983A1 PCT/FI1990/000242 FI9000242W WO9105983A1 WO 1991005983 A1 WO1991005983 A1 WO 1991005983A1 FI 9000242 W FI9000242 W FI 9000242W WO 9105983 A1 WO9105983 A1 WO 9105983A1
Authority
WO
WIPO (PCT)
Prior art keywords
shadow
material piece
height
measuring
angle
Prior art date
Application number
PCT/FI1990/000242
Other languages
French (fr)
Inventor
Seppo Korhonen
Pertti Puumalainen
Original Assignee
Iggesund Pulp Fibre Oy Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Iggesund Pulp Fibre Oy Ab filed Critical Iggesund Pulp Fibre Oy Ab
Publication of WO1991005983A1 publication Critical patent/WO1991005983A1/en

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
    • G01B11/0608—Height gauges

Definitions

  • the present invention relates to a method of measuring the height of material pieces positioned on a surface, such as wood chips, wherein the material piece is illuminated and a shadow caused by the material piece is measured.
  • the sources of light is positioned beside the surface on which the material piece rests so that it emits light beams parallel with the surface, it is possible to measure the height of the material piece by means of a detector which is positioned on the shadow side of the material piece and which records the height of the shadow.
  • the prior art methods described above operate satisfactorily if the material pieces are positioned one after another on the surface, in most cases a conveyor belt. If the conveyor belt supports a great number of material pieces which are positioned in an arbitrary order on the belt and many of which are positioned side by side in the transverse direction of the belt, the above-described height measuring method cannot be used, since the method measures only the highest one of the material pieces which are positioned side by side.
  • the object of the present invention is to provide a method which enables simple measuring of the height of material pieces resting in great numbers in an arbitrary order on a . surface.
  • the main characteristic features of the method of the invention are disclosed in the attached claim 1.
  • the material pieces When the material pieces are illuminated obliquely from above, they cast a short shadow upon the surface beside, the material piece.
  • the height of the material piece over the surface is measured by means of the length of the shadow. ⁇
  • the height can- be measured irrespective of the order of the material pieces on the surface. As to the position of the material pieces with respect to each other, it is only required that the distance between the material pieces exceeds the length of the shadow in the direction in which the shadows are formed.
  • the light beams are directed towards the surface in such a manner that the angle between the light beams and the surface is smaller than the angle between the surface and that side of the material piece beside which the shadow is formed.
  • the angle between the light beams and the surface is between 20° and 50°, preferably about 35°.
  • the invention is also concerned with a device for measuring the height of material pieces posi ⁇ tioned on a surface, such as wood chips, comprising a source of light which illuminates the material piece, and a detector which measures the shadow caused by the material piece. The characteristic features of the device appear from the attached claim 4.
  • FIG. 1 is a general view of the measuring device of the invention
  • Figure 2 illustrates on an enlarged scale the principle for measuring the shape of a material piece
  • Figure 3 illustrates generally the measuring of the height of a material piece.
  • Figure 1 shows a conveyor belt 1 which supports and transports wood chips 2 arbitrarily positioned on its upper horizontal surface.
  • Two cameras 3 and 4 are arranged above the upper surface of the conveyor belt 1.
  • the cameras are positioned above the central line of the belt in such a way that the camera 3 is posi ⁇ tioned in front of the camera 4 in the direction of travel of the belt.
  • the field of view of the cameras extends up to the edges of the belt, as shown in the figure.
  • the cameras are preferably CCD cameras and they are directed directly downwards perpendicular to the surface of the conveyor belt.
  • the device further comprises two sources of light formed by lamps 5 and 6, which illuminate the wood chips 2 within the field of view of the cameras 3 and 4, respectively.
  • the con ⁇ veyor belt 1 is transparent, which enables the light from the lamp 5 to penetrate through it and cause a shadow of the wood chip to be cast towards the camera 3.
  • the shadow side of the wood chip is thereby out ⁇ lined against the illuminated conveyor belt, which enables the recording of the shape of the wood chip, see the arrow A.
  • the dimensions of the wood chip in the plane of the conveyor belt can alternatively be measured by illuminating the upper side of the chip so that the illuminated side is outlined against the dark con- veyor belt.
  • the height of the upper side of the material piece over the surface of the conveyor belt is measured, which height, with wood chips, corresponds substantially to the thick- ness of the chip, as shown in Figure 3.
  • the wood chip is illuminated obliquely from above by the lamp 6, which is positioned above the conveyor belt and which is directed toward the conveyor belt so that it illuminates the belt within the field of view of the camera 4.
  • Light beams from the lamp 6 form an acute angle with the upper surface of the conveyor belt 1. This angle varies between 20° and 50°, being prefer ⁇ ably about 35°, when the material pieces are wood chips. The angle depends on the shape of the material piece the height of which is to be measured.
  • the light beams should be directed towards the conveyor belt in such a way that the angle they form with the belt is smaller than the angle between the belt and that side of the material piece beside which the shadow is formed. In this way it is ensured that a shadow is always formed upon the upper surface of the conveyor belt 1.
  • the shadow is indicated with the reference numeral 7 and it is formed beside a side 8 an upper edge 9 of which forms the edge 10 of the shadow.
  • the length of the shadow that is, the dis ⁇ tance between the edge 9 and the edge 10 in a plane parallel to the conveyor belt, is indicated with the arrow B.
  • the length of the shadow is measured by means of the camera 4 which also observes possible length variation caused by variation in the height of the edge 9 over the conveyor belt. Combined information from the two cameras 3, 4 gives a good picture of the shape and volume of the wood chips.
  • the position of the cameras can differ from that described above as well as the position of the source of light 6. It is of primary importance for the invention that the shadow formed upon the surface on which the material piece is positioned can be imaged by a camera.
  • the method of the invention can be applied with material pieces of many different types. Since the material pieces are normally arbitrarily positioned on the surface, the shadow 7 is often formed beside two or more sides of the material piece, which, however, does not affect the measuring result.
  • the cameras 3, 4 can be replaced with other suitable detectors which are directed per- pendicular to the conveyor belt similarly as the cameras 3, 4 or which are obliquely positioned with respect to the belt.
  • the surface need not, of course, be a conveyor belt.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Length Measuring Devices By Optical Means (AREA)

Abstract

The invention relates to a method and a device for measuring the height of material pieces. It is previously known to measure the height of a material piece (2) by illuminating it from the side and measuring the width of a shadow falling on a detector (4). If several material pieces lie side by side on a surface (1), this prior art method cannot be applied. The height of the material pieces (2) can be measured individually by illuminating the material piece (2) obliquely from above in such a manner that a shadow (7) is formed upon the surface beside the material piece (2), and the length (B) of the shadow is measured. The length (B) of the shadow (7) gives the height of the material piece.

Description

A method and a device for measuring the height of material pieces
The present invention relates to a method of measuring the height of material pieces positioned on a surface, such as wood chips, wherein the material piece is illuminated and a shadow caused by the material piece is measured.
Various industrial processes use piece material as raw material. Such processes include ore dressing and cooking of cellulose. In these cases, it is usually very important to know the size and shape of the material pieces as these values affect the pro¬ cess time and the amount of chemicals. The size and shape of wood chips also provide information on the condition of the chopper.
There are two main types of optical measuring methods known from the prior art: those in which a detector measures the light reflected from the sur- face of the material piece, and those in which the size of a shadow caused by the material piece in the detector is measured. These measuring methods usually provide information on the shape and dimensions of the material piece in one plane. Finnish Patent Specification 61758 describes a method in which a material piece is illuminated from four different sides. The material piece thereby casts four shadows, which are imaged by four dif¬ ferent detectors. As one of the sources of light is positioned beside the surface on which the material piece rests so that it emits light beams parallel with the surface, it is possible to measure the height of the material piece by means of a detector which is positioned on the shadow side of the material piece and which records the height of the shadow.
The prior art methods described above operate satisfactorily if the material pieces are positioned one after another on the surface, in most cases a conveyor belt. If the conveyor belt supports a great number of material pieces which are positioned in an arbitrary order on the belt and many of which are positioned side by side in the transverse direction of the belt, the above-described height measuring method cannot be used, since the method measures only the highest one of the material pieces which are positioned side by side. The object of the present invention is to provide a method which enables simple measuring of the height of material pieces resting in great numbers in an arbitrary order on a. surface. The main characteristic features of the method of the invention are disclosed in the attached claim 1.
When the material pieces are illuminated obliquely from above, they cast a short shadow upon the surface beside, the material piece. The height of the material piece over the surface is measured by means of the length of the shadow. ■ As the shadow is formed upon the surface beside the material piece, the height can- be measured irrespective of the order of the material pieces on the surface. As to the position of the material pieces with respect to each other, it is only required that the distance between the material pieces exceeds the length of the shadow in the direction in which the shadows are formed. To ensure that the edge of the formed shadow is posi¬ tioned on the surface, it is to be preferred that the light beams are directed towards the surface in such a manner that the angle between the light beams and the surface is smaller than the angle between the surface and that side of the material piece beside which the shadow is formed.
For most material pieces it is preferable that the angle between the light beams and the surface is between 20° and 50°, preferably about 35°. The invention is also concerned with a device for measuring the height of material pieces posi¬ tioned on a surface, such as wood chips, comprising a source of light which illuminates the material piece, and a detector which measures the shadow caused by the material piece. The characteristic features of the device appear from the attached claim 4.
In the following a preferred embodiment of the invention will be described in greater detail with reference to the attached drawing, in which Figure 1 is a general view of the measuring device of the invention;
Figure 2 illustrates on an enlarged scale the principle for measuring the shape of a material piece; and Figure 3 illustrates generally the measuring of the height of a material piece.
Figure 1 shows a conveyor belt 1 which supports and transports wood chips 2 arbitrarily positioned on its upper horizontal surface. Two cameras 3 and 4 are arranged above the upper surface of the conveyor belt 1. The cameras are positioned above the central line of the belt in such a way that the camera 3 is posi¬ tioned in front of the camera 4 in the direction of travel of the belt. The field of view of the cameras extends up to the edges of the belt, as shown in the figure. The cameras are preferably CCD cameras and they are directed directly downwards perpendicular to the surface of the conveyor belt.
The device further comprises two sources of light formed by lamps 5 and 6, which illuminate the wood chips 2 within the field of view of the cameras 3 and 4, respectively.
To achieve a three-dimensional image of the wood chip 2, one measures both the shape of the wood chip according to Figure 2 and its thickness or height over the conveyor belt 1 according to Figure
3.
In the' embodiment shown in Figure 2 the con¬ veyor belt 1 is transparent, which enables the light from the lamp 5 to penetrate through it and cause a shadow of the wood chip to be cast towards the camera 3. The shadow side of the wood chip is thereby out¬ lined against the illuminated conveyor belt, which enables the recording of the shape of the wood chip, see the arrow A.
The dimensions of the wood chip in the plane of the conveyor belt can alternatively be measured by illuminating the upper side of the chip so that the illuminated side is outlined against the dark con- veyor belt.
According to the invention the height of the upper side of the material piece over the surface of the conveyor belt is measured, which height, with wood chips, corresponds substantially to the thick- ness of the chip, as shown in Figure 3. The wood chip is illuminated obliquely from above by the lamp 6, which is positioned above the conveyor belt and which is directed toward the conveyor belt so that it illuminates the belt within the field of view of the camera 4. Light beams from the lamp 6 form an acute angle with the upper surface of the conveyor belt 1. This angle varies between 20° and 50°, being prefer¬ ably about 35°, when the material pieces are wood chips. The angle depends on the shape of the material piece the height of which is to be measured. As a general rule, it can be said that the light beams should be directed towards the conveyor belt in such a way that the angle they form with the belt is smaller than the angle between the belt and that side of the material piece beside which the shadow is formed. In this way it is ensured that a shadow is always formed upon the upper surface of the conveyor belt 1.
In Figure 3, the shadow is indicated with the reference numeral 7 and it is formed beside a side 8 an upper edge 9 of which forms the edge 10 of the shadow. The length of the shadow, that is, the dis¬ tance between the edge 9 and the edge 10 in a plane parallel to the conveyor belt, is indicated with the arrow B.
The length of the shadow is measured by means of the camera 4 which also observes possible length variation caused by variation in the height of the edge 9 over the conveyor belt. Combined information from the two cameras 3, 4 gives a good picture of the shape and volume of the wood chips.
The position of the cameras can differ from that described above as well as the position of the source of light 6. It is of primary importance for the invention that the shadow formed upon the surface on which the material piece is positioned can be imaged by a camera. The method of the invention can be applied with material pieces of many different types. Since the material pieces are normally arbitrarily positioned on the surface, the shadow 7 is often formed beside two or more sides of the material piece, which, however, does not affect the measuring result. The cameras 3, 4 can be replaced with other suitable detectors which are directed per- pendicular to the conveyor belt similarly as the cameras 3, 4 or which are obliquely positioned with respect to the belt. The surface need not, of course, be a conveyor belt.

Claims

Claims:
1. A method of measuring the height of material pieces positioned on a surface, such as wood chips, wherein the material piece (2) is illuminated and a shadow (7) caused by the material piece is measured, c h a r a c t e r i z e d in that the material piece (2) is illuminated obliquely from above in such a manner that a shadow (7) is formed upon the surface (1) beside the material piece, the length (B) of the shadow being measured.
2. A method according to claim 1, c h a r a c ¬ t e r i z e d in that the light beams are directed towards the surface (1) in such a manner that the angle they form with the surface (1) is smaller than the angle between the surface (1 ) and that side (8) of the material piece (2) beside which the shadow is formed.
3. A method according to claim 2, c h a r a c - t e r i z e d in. that the angle between the light beams and the surface is between 20° and 50°, prefer¬ ably about 35° .
4. A device for measuring the height of material pieces' positioned on a surface, such as wood chips, comprising a source of light (5) which il¬ luminates the material piece (2) , and a detector (4) which measures the shadow (7) caused by the material piece, c h a r a c t e r i z e d in that the source of light (6) is arranged to illuminate the material piece (2) obliquely from above so that a shadow (7 ) is formed upon the surface ( 1 ) beside the material piece, the detector (4) being arranged to measure the length (B) of the shadow.
5. A device according to claim 4, c h a r a c - t e r i z e d in that the source of light (6) is arranged to illuminate the material piece (2) at an angle with the material piece which is smaller than the angle between the surface and that side (8) of the material piece beside which the shadow (7) is formed.
6. A device according to claim 5, c h a r a c ¬ t e r i z e d in that the angle between the light beams and the surface is between 20° and 50°, prefer¬ ably about 35"C, the detector being formed by a camera (4) which is directed substantially perpen¬ dicular to the surface.
PCT/FI1990/000242 1989-10-18 1990-10-17 A method and a device for measuring the height of material pieces WO1991005983A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI894962A FI894962A0 (en) 1989-10-18 1989-10-18 FOERFARANDE OCH ANORDNING FOER HOEJDMAETNING AV MATERIALSTYCKEN.
FI894962 1989-10-18

Publications (1)

Publication Number Publication Date
WO1991005983A1 true WO1991005983A1 (en) 1991-05-02

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WO (1) WO1991005983A1 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2251937B (en) * 1990-12-27 1994-08-03 Sharp Kk Semiconductor chip position detector
WO2007113166A1 (en) * 2006-03-30 2007-10-11 Siemens Aktiengesellschaft Device for determining the size of an object in particular an essentially parallelepiped packet
CN116494023A (en) * 2023-04-11 2023-07-28 中国航空制造技术研究院 Device and method for measuring and correcting geometrical parameters of machining electrode of electro-hydraulic beam machine tool

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3976382A (en) * 1972-11-14 1976-08-24 A/S Kongsberg Vapenfabrik Procedure and apparatus for determining the geometrical shape of a surface
GB2032618A (en) * 1978-09-18 1980-05-08 Eastman Kodak Co Inspection of elongate articles for surface irregularities

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3976382A (en) * 1972-11-14 1976-08-24 A/S Kongsberg Vapenfabrik Procedure and apparatus for determining the geometrical shape of a surface
GB2032618A (en) * 1978-09-18 1980-05-08 Eastman Kodak Co Inspection of elongate articles for surface irregularities

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2251937B (en) * 1990-12-27 1994-08-03 Sharp Kk Semiconductor chip position detector
WO2007113166A1 (en) * 2006-03-30 2007-10-11 Siemens Aktiengesellschaft Device for determining the size of an object in particular an essentially parallelepiped packet
CN116494023A (en) * 2023-04-11 2023-07-28 中国航空制造技术研究院 Device and method for measuring and correcting geometrical parameters of machining electrode of electro-hydraulic beam machine tool
CN116494023B (en) * 2023-04-11 2024-03-22 中国航空制造技术研究院 Device and method for measuring and correcting geometrical parameters of machining electrode of electro-hydraulic beam machine tool

Also Published As

Publication number Publication date
FI894962A0 (en) 1989-10-18

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