GB2106243A - Optical measuring system employing coaxial illumination - Google Patents
Optical measuring system employing coaxial illumination Download PDFInfo
- Publication number
- GB2106243A GB2106243A GB08226390A GB8226390A GB2106243A GB 2106243 A GB2106243 A GB 2106243A GB 08226390 A GB08226390 A GB 08226390A GB 8226390 A GB8226390 A GB 8226390A GB 2106243 A GB2106243 A GB 2106243A
- Authority
- GB
- United Kingdom
- Prior art keywords
- light
- measuring system
- photodetector
- disposed
- lens
- Prior art date
- Legal status (The legal status 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 status listed.)
- Withdrawn
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
- G01B11/024—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness by means of diode-array scanning
-
- 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
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Length Measuring Devices By Optical Means (AREA)
Abstract
An optical measuring system employs coaxial illumination and is characterised in that it comprises a light source S coaxially illuminating an object (2) situated in front of a lens (3) in order to determine the dimensions or position of the object (2), a photodetector (4) being disposed on the image plane of the lens (3) at the location of the image of the object (2) under measurement. Reflecting surfaces may be provided at 5 or on the object itself. The detector which may be a photodiode, or a photodiode, photoresistor or CCD array, may be situated perpendicularly to the line of sight and cooperate with beam separator 9 and light trap 10. A light slit 8 and detector 4 may be at equal distances from lens 3. The main application of the invention is in the optical measuring industry. <IMAGE>
Description
SPECIFICATION
Optical measuring system employing coaxial illumination
This invention relates to an optical measuring system employing coaxial illumination. Optical measuring systems are already known in which contrast is improved by disposing a light source behind the object. This source is, however, always too bulky and requires complex adjustments.
The object of this invention is to obviate these disadvantages and proposes a universal contactless measuring system whereby it is possible to determine and measure the position of an object, its dimensions, or rapid phenomena such as the very rapid movement of an object.
Another object of the invention is to measure the dimensions or speeds of moving objects in the case of rapid movements or non-solid materials.
Another object of the invention is to provide an optical measuring system using photodetectors with high adaptability and good contrast so that the measurement is more reliable and insensitive to the ambient illumination, the measurements being made with a low power of illumination.
Finally, another object of the invention is to provide a lightweight and compact system incorporating the illumination and sighting means, the system being adapted to most industrial scientific conditions.
To this end, the invention relates to an optical measuring system employing coaxial illumination, characterised in that it comprises a light source coaxially illuminating an object and disposed in front of a lens in order to determine the dimensions or position of the object, a photodetector being disposed on the image plane of the lens at the location of the image of the object being measured.
According to another characteristic, the light source applies a beam of light on to rearwardly reflecting surfaces, the beam being returned to the photodetector, which is associated with an electronic system for processing the signal.
The use of rearwardly reflecting surfaces eliminates the need for, or simplifies, any installations situated behind the object requiring to be measured. Thus it is only necessary, for example, to mark the object with one or more sighting marks, which constitute the rearwardly reflecting surfaces, or to dispose a rearwardly reflecting surface behind the object.
According to another characteristic of the invention, the system comprises a condenser for the beam of light, in front of which there is disposed a screen formed with a slit, the beam of light passing through the slit to define a slit of light, and then passing through the lens in order to illuminate coaxially the object situated in front of a rearwardly reflecting surface.
According to another characteristic of the invention, the photodetector is disposed perpenducularly to the sighting axis and cooperates with a beam separator disposed between the photodetector and a light trap adapted to trap the unwanted beam.
Accordinq to another feature of the invention the light slit is larger than or equal to the photodetector in respect of its size.
According to another characteristic of the invention, the light slit and the photodetector are situated at equal distances from the lens.
Finally, according to another characteristic of the invention, the rearwardly reflecting surfaces are disposed either behind the illuminated object, or on the object itself.
The invention will be more readily understood from one embodiment of an optical measuring system according to the invention, which is shown diagrammatically by way of example without any limiting force in the accompanying drawings wherein:
Fig. lisa side elevation of the system and
Fig. 2 is a diagram showing the path of the rays of light.
Referring to Fig. 1, the optical measuring system 1 employing coaxial illumination comprises a light source S coaxially illuminating an object 2 disposed in front of a lens 3. A.
photodetector 4 is disposed on the image plane of the lens 3 at the location of the image of the object 2 under measurement.
The system 1 also comprises reflecting surfaces 5 disposed behind the object although they may be disposed on the object itself in the form of sighting marks. The function of the reflecting surface is to return the beam of light emitted by the source S to the photodetector 4 with only low illumination power.
The beam of light emitted by the light source S first passes through a condenser 6 where it is applied to a screen 7 formed with a light slit 8. The dimensions of the slit 8 are greater than or at least equal to the dimensions of the photodetector 4.
Slit 8 and photodetector 4 are also disposed at equal distances from the lens 3. Photodetector 4 is also disposed perpendicularly to the sighting axis and co-operates with a beam separator 9 situated on the line of sight X between the photodetector 4 and a light trap 10 intended, to trap the unwanted beam of light. Thus the beam of light emitted by the light source S is reflected by the rearwardly reflecting surface 5 to the beam separator 9 which applies some of this beam art a right angle to the photodetector 4, the other part, which is deflected perpendicularly upwards by the beam separator 9, being trapped by the light trap 10. Photodetector 4 is connected to an electronic signal processing system not shown in the drawing.
The system 1 thus makes it possible to determine the size or position of an object disposed in front of the lens 3 by forming the image of this object on a photodetector 4. The latter may, for example, be a photodiode, a CCD photodiode, photo resistor or similar array. In the case of a CCD photodiode array connected to an electronic signal processing system, the video signal is logicalized in a comparator which discriminates the illuminated diodes and the dark diodes. A counter defines either the dimensions of the measured zone or its position in relation to the photo-detector origin.
The system 1 coaxially illuminates the object 2 by means of the taking lens 3, the beam of light being condensed and then passing through a light slit 8 before passing through a beam separator 9.
The latter may comprise a semi-transparent plate, a Lumer cube, or a Fresnel prism or the like. The reflected beam of light is separated by the semitransparent plate 9, for example downwardly to the photodetector 4 and upwardly to the light trap for the unwanted beam. The light trap 10 also reduces interference effects.
The rearwardly reflecting surfaces 5 improve the sighting contrast, being disposed either on the background behind the object, which then appears dark on a light background, or being disposed on the sighted object itself, e.g. in the form of sighting
marks, so that the position or the limits of this object can be defined. The object then appears
light on a dark background.
The rearwardly reflecting surface 5 may be in the form of an easily fitted adhesive plastic or
paint. It may also be in the form of catadioptric
plastic blocks adapted to be secured by adhesive
or screws. The use of these rearwardly reflecting
surfaces requires a minimum of work. When they
are disposed behind the object, they become
larger than the image spot of the light source S.
These reflecting surfaces are also relatively
insensitive to the angle of incidence of the light
over a range depending upon the technique used for their production.
Referring to Fig. 2 the system 1 illustrates the
path of the beam of light E. This is emitted by the
light source S and then passes to the condenser 6
before passing through the light slit 8 and the semi-transparent plate 9 and lens 3 to illuminate the object and impinge on the rearwardly
reflecting surface 5, from which a beam E is
returned. The reflected beam is returned to the beam separator 9, consisting of a semitransparent plate where the unwanted beam is
applied at right angles to the line of sight X to the
light trap 10 where this part of the beam is trapped. The light trap 10 is disposed above the semi-transparent plate 9 in relation to the line of
sight X.
The wanted beam is fed to the photodetector 4
situated below the line of sight X. Photodetector 4
is connected to an electronic signal processing
system 11 which allows either the dimensions of
the object 2 or its position or movement to be
measured.
System 1 enables the properties of the
rearwardly reflecting surfaces to be used to the
optimum of their efficiency, i.e. for zero divergence
between the incident and reflected beams. An
impression of the photodetector is thus obtained with a good efficiency, using only low and very localized illumination power. The use of the rearwardly reflecting surfaces provides high constrast, which allows accurate measurements with the different types of detectors, the ambient illumination having little influence.
The system 1 is also adaptable to all focusing distances and distances of the measured object.
Thus if the lens is moved for a different focus, the light source S remains in focus as soon as the image of the object 2 is distinct on the photo detector 4. This greatly simplifies adjustment operations.
Claims (10)
1. An optical measuirng system employing coaxial illumination, characterised in that it comprises a light source coaxially illuminating an object disposed in front of a lens in order to determine the dimensions or position of the object, a photodetector being disposed on the image plane of the lens at the location of the image of the object being measured.
2. A measuring system according to claim 1, characterised in that the light source passes a beam of light on to rearwardly reflecting surfaces, the beam being returned to the photodetector, which is associated with an electronic signal processing system.
3. A measuring system according to claims 1 and 2, characterised in that it comprises a condenser for the beam of light, in front of which there is disposed a screen formed with a slit, the beam of light passing through the slit to define a slit of light, and then passing through the lens in order coaxially to illuminate the object situated in front of a rearwardly reflecting surface.
4. A measuring system according to any one of claims 1 to 3, characterised in that the photodetector is disposed perpendicularly to the line of sight and co-operates with a beam separator disposed between the photodetector and a light trap intended to trap the unwanted beam.
5. A measuring system according to any one of claims 1 to 4, characterised in that the light slit is of dimensions greater than or equal to those of the photodetector.
6. A measuring system according to any one of claims 1 to 5, characterised in that the light slit and the photodetector are situated at equal distances from the lens.
7. A measuring system according to any one of claims 1 to 6, characterised in that the beam separator is a semi-transparent plate, a Lumer cube, a Fresnel prism or the like.
8. A measuring system according to any one of claims 1 to 7, characterised in that the photodetector comprises a photodiode or a photodiode,
photo-resistor or similar CCD array.
9. A measuring system according to any one of claims 1 to 8, characterised in that the rearwardly reflecting surfaces are disposed either behind the illuminated object or on the object itself.
10. An optical measuring system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FR8117525A FR2512949A1 (en) | 1981-09-16 | 1981-09-16 | OPTICAL MEASURING DEVICE BY COAXIAL LIGHTING |
Publications (1)
Publication Number | Publication Date |
---|---|
GB2106243A true GB2106243A (en) | 1983-04-07 |
Family
ID=9262205
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB08226390A Withdrawn GB2106243A (en) | 1981-09-16 | 1982-09-16 | Optical measuring system employing coaxial illumination |
Country Status (3)
Country | Link |
---|---|
DE (1) | DE3234382A1 (en) |
FR (1) | FR2512949A1 (en) |
GB (1) | GB2106243A (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2144536A (en) * | 1983-08-04 | 1985-03-06 | Nanometrics Inc | Optical dimension measuring system |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4742217A (en) * | 1986-06-02 | 1988-05-03 | Honeywell Inc. | Projection alignment and focusing aid |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE2153950A1 (en) * | 1971-10-29 | 1973-05-03 | Licentia Gmbh | PHOTOELECTRIC BARRIER |
DE2208228A1 (en) * | 1972-02-22 | 1973-08-30 | Licentia Gmbh | PHOTOELECTRIC BARRIER |
SE376966B (en) * | 1973-10-12 | 1975-06-16 | Aga Ab |
-
1981
- 1981-09-16 FR FR8117525A patent/FR2512949A1/en active Pending
-
1982
- 1982-09-16 GB GB08226390A patent/GB2106243A/en not_active Withdrawn
- 1982-09-16 DE DE19823234382 patent/DE3234382A1/en not_active Withdrawn
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2144536A (en) * | 1983-08-04 | 1985-03-06 | Nanometrics Inc | Optical dimension measuring system |
Also Published As
Publication number | Publication date |
---|---|
DE3234382A1 (en) | 1983-04-14 |
FR2512949A1 (en) | 1983-03-18 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |