Method and device of contact-free optical measurement of object's sizes

FIELD: measurement technology.

SUBSTANCE: according to method of contact-free optical measurement the object is placed between laser radiation source and photoreceiver. Power of laser radiation P is measured and compared with preset level of power P0 . Laser radiation is optically scanned into beam of parallel rays at the area where object finds its place and size of object is found from size of shade of object onto photoreceiver while correcting time of exposure from value of difference (P0-P). Device for realizing the method has laser, beam-splitting plate, short-focused cylindrical lens, output cylindrical lens, collimating lens, CCD, data processing unit, photoreceiving threshold unit.

EFFECT: improved precision of measurement.

5 cl, 1 dwg

 

The invention relates to measurement techniques, in particular for contactless optical measurement of the geometrical sizes of various objects.

A known method of non-contact optical measuring sizes of objects, also called the shadow, which is the placement of the investigated object between the laser and multielement photodetector, the sweep of the laser beam into a beam of parallel rays in the zone of location of the object and determining the size of the object according to the amount of shadow cast them on the photodetector. Devices that implement the known method, laser shadow gauges are composed of a laser light source, a lens system that forms from the original beam by the optical scanner beam of parallel rays, and multi-element photodetector, connected to the processing unit. The number of transmission of the pixels on the sensor on the CCD linear array determines the size of the object (1, 2).

Using the optical scanner allows you to apply for continuous reading information of the multi-element photodetector on the line CCD and implement information retrieval within one frame, the duration of which is regulated within wide limits, up to 0.1 microsecond. This fact gives the possibility to use laser shadow gauges for measuring parameters the s objects moving with great speed.

As a prototype of the proposed technical solution chosen method of non-contact optical measuring sizes of objects, which consists in placing the investigated object between the laser and the photodetector, optical scanning of the laser radiation into a beam of parallel rays in the zone of location of the object and determining the size of the object according to the size of the shadow from the object on the sensor. A device that implements a known way, comprises a laser light source, lens system, optical scanner, multi-element photodiode line, schema information processing and computer (3).

The disadvantages of this method and a device which implements the method, due to the following. The accuracy of the measurement when using the known method depends primarily on the accuracy of determining the boundaries of the contour of the object. Diffraction effects cause the transition from light to shadow on the surface of the photodetector is characterized by a certain length, which is used in practice photodetectors on the line CCD is typically a few pixels. Blurring the boundaries between light and shadow reduces the accuracy of determining the size of the object, and the influence of this factor will be greater, the smaller the size of the object.

As b is lo shown above, the size of the object is determined by the number of transmission (shaded) of pixels on the CCD linear array. Blackout is the pixel, the video signal is less than a certain threshold.

It can be shown that the size of the part will be determined by the number of pixels to which the voltage Utmore threshold Uthen

,

where Emaxthe maximum power of the laser radiation;

r is the current radius of the laser beam on the CCD linear array;

raboutis the radius of the laser beam at the radiation power density in the e2times smaller compared to the intensity at the center;

Tex- the exposure time;

RC is a parameter specific to the line CCD.

From the expression (1) implies that the size of the object depends on the laser power and the exposure time.

During the exposure the number of pixels by which the Ut≥Uthenwill be determined by the power of the laser radiation, since the luminance of each pixel and, therefore, the slew rate of charge it depends on the laser power. As a consequence, determine the size of the object will depend on the magnitude of the laser power. Therefore, in the known laser meter when the fluctuations of the power and accuracy of determination of the size of the object decreases.

C the house, solved by the invention, the improved accuracy of the measurements.

This task is solved in that in the method of non-contact optical measuring sizes of objects, which consists in placing the object between the laser light source and a photodetector, optical scanning of the laser radiation into a beam of parallel rays in the zone of location of the object and determining the size of the object according to the size of the shadow from the object on the sensor, measure the laser power P, compare it with a given level of Paboutand largest (Pabout-R) carry out adjustment of the exposure time of the photodetector. The device for implementing the method that contains the source of the laser beam, optical means to scan the laser beam, a photodetector, connected to the first input of the processing unit and the object is located between the source of laser beam and photodetector equipped with a beam splitter disposed between the laser beam source and means of the optical scanner, and photodetector threshold device, the output of which is connected to the second input of the processing unit. Tools of the optical laser beam scanning is made in the form of a cylindrical lens, and a beam splitter in the form of a translucent plate.

The invention is illustrated in the drawing, which shows schematically the device from what omashu which implements the inventive method. It includes a laser 1, a semi-transparent beam splitting plate 2, tools of the optical scanner of the laser beam, consisting of a short-focus cylindrical lens 3 and the output of the cylindrical lens 4, the collimating lens 5, the photodetector on the line CCD 6, connected to the first input of the processing unit 7 and the photodetector threshold device 8 connected to the second input unit 7, and represents a photodetector with a comparison circuit. Beam-splitting plate 2 and photodetector threshold device 8 to form a channel, adjust the exposure time. Beam-splitting plate 2 is located at an angle to the path of the laser beam 1 in order to ensure the removal of the radiation power on the photodetector threshold device 8. The object to be measured 9 is placed between the lenses 4 and 5.

The inventive method is carried out as follows. The laser light 1 falls on the beam splitter plate 2. Part of the radiation is deflected by the plate 2 on the photodetector threshold device 8, and the remainder passes into the optical system of lenses 3 and 4, performing a scan of the radiation in the beam of parallel rays. In the investigated object 9 is exposed flat beam and the photodetector 6 is formed image of the object corresponding to the shadow cast by the object 9 to the surface of the photodetector 6. In Blake processed image signal and determining an object's size 9. In the threshold device 8 compares the part of the laser radiation power received by the device 8, with the threshold value corresponding to a given radiation power. If the magnitude of power other than specified, at the output of the threshold device 8 will form a differential signal is supplied to the second input unit 7. In accordance with the magnitude of the received signal unit 7 corrects the exposure time of the photodetector 6. If the actual power of the laser radiation is greater than the specified, unit 7 reduces the exposure time, if it's smaller increases.

As a consequence, the adjustment to the charge time of the pixel even in the face of fluctuations of the laser power provides high accuracy measurements.

Thus, the inventive method and device by adjusting the exposure time depending on the laser power provide is compared with the device-prototype - improving the accuracy of measuring the size of objects.

LITERATURE

1. Asennettu, Wendelken, Dstool, Avemaria. The application of laser techniques to control the parameters of the coupler and spring. New technologies for rail transport. The collection of scientific articles with international participation, part 4. Omsk 2000, s-233.

2. V.N.Demrin, D.S.Dokov, V.N.Tereshkin, A.Z.Venediktov. Optical control of geometrical dimensions for railwa cars automatic coupling. Third Internat. Workshop on New Approaches to High-Tech: Nondestructive Testing and Computer Simulations in Science and Engineering. Proceedings of SPAS, Vol. 3. 7-11 June 1999, St. Petersburg, p. A17.

3. Yea, Mpharane. Non-contact laser measuring geometric dimensions of the rollers. New technologies for rail transport. The collection of scientific articles with international participation, part 4. Omsk 2000, s-213 (prototype).

1. Method for the contactless measurement of object sizes, which consists in placing the object between the laser light source and a photodetector, optical scanning of the laser radiation into a beam of parallel rays in the zone of location of the object, and determining the size of the object according to the size of the shadow from the object to the sensor, wherein the measured laser power P, compare it with a given level of Paboutand largest (Pabout-R) carry out adjustment of the exposure time of the photodetector.

2. Device for the contactless optical measurement of objects containing the source of the laser beam, optical means to scan the laser beam, a photodetector, connected to the first input of the processing unit and the object is located between the means of the optical scanner of the laser beam and a photodetector, characterized in that it is provided with a beam splitter disposed between the optical source) the treatment and means of the optical scanner and optically associated with the photodetector threshold device the output of which is connected to the second input of the processing unit.

3. The device according to claim 2, characterized in that the optical means of the laser beam scanning is made in the form of a cylindrical lens.

4. The device according to claim 2, characterized in that the beam splitter is made in the form of a translucent plate.



 

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