SU1522029A1 - Method and apparatus for measuring thickness of walls olf trasparentt tubes - Google Patents

Abstract

The invention relates to measuring technique and can be used to measure the wall thickness of pipes. The aim of the invention is to improve the measurement accuracy by eliminating the effect of pipe displacement relative to the optical system. For this purpose, a beam of radiation is directed to the surface 6 in the form of a narrow strip from the source 1 of the pipe. The optical system 2 builds in the plane of the photodetector 5 images of light beams reflected from the outer and inner surfaces of the tube 6. By means of a collimator and spatial filter 4, the reflected beams are limited to paraxial ones. 2 sec. f-ly, 1 zp f-ly, 3 ill.

Description

SP K9 Yu

ABOUT

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The invention relates to a control measuring technique, namely, an optoelectronic measuring device, and can be used to measure the wall thickness of glass, quartz, or transparent plastic pipes.

The purpose of the invention is to improve the measurement accuracy by eliminating the effect of displacement of the test tube and its transfer relative to the optical system.

FIG. 1 shows the device, overall view; in fig. 2 - section A-A on | u. 1 j in FIG. 3 - “section BB in FIG. one.

The device contains a source .1 of a directional radiation beam, an image transfer optical system 2 (a cylindrical lens), a cylindrical lens 3, a spatial filter (slit diaphragm) 4 and a scanning photodetector 5 (a line of photodiodes in which the functions of the scanning unit and the photodetector are combined). The optical axes of the radiation source 1 and the optical system 2 are located in the XOY plane formed by the axis of the tube and the axis of the illuminating beam under the angle 2o / to each other. Between the radiation source 1 and the optical signal. Subject 2 of the image transfer at the point of intersection of their optical axes of the wall of the test tube 6.

The method is carried out; in the following way.

A controllable tube; 6 is installed between the radiation source 1 and the image transfer optical system 2. From the radiation source 1, a beam of radiation in the form of a narrow and light stripe perpendicular to the XOY plane is directed to the surface of the pipe 6. oscillation range of the tube during measurement). The optical system 2 builds in the plane 5) of the receiver 5 an image of two light beams reflected from the outer and inner surfaces of the pipe wall. The cylindrical optical system 2 is positioned so that the radii of curvature of its refracting surfaces lie in the XOY plane, and it itself works as an image transfer system. Reflected from the walls

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five

Beam tubes are limited by aperture using a collimator consisting of lens 3 and spatial filter 4. In the image plane, the photoreceiver 5 scans the images of reflected beams and transforms them into electrical signals (a sequence of two short pulses), which determine the wall thickness pipes. The time interval between pulses is proportional to the wall thickness of the pipe.

The cylindrical lens 3 is positioned in such a way that its optical axis coincides with the axis of the optical system 2, and the radii of curvature of the refractive surfaces lie in a plane perpendicular to the XOY plane. In the XOY plane, the lens 3 operates as a plane-parallel plate, which practically does not change the parameters of the image transfer system and the magnitude of the equivalent focal length of the optical system. A spatial filter 4 is located in the rear focal plane of the lens 3, which has the shape of a slit diaphragm, the long side of which is parallel to the XOY plane. 2 - as a plane-parallel plate, which practically does not change the equivalent focal length of the collimator. In this case, the lens 3 collects on the slits of the spatial filter 4 only the light rays reflected from certain sections of the tube, in this case from its top (point B), which propagate parallel to the optical axis of the lens. Rays reflected from adjacent pipe sections at different angles to the optical axis (q | 0) are shielded by spatial filter 4 and do not reach the photodetector 5. Due to this scheme, when the pipe is displaced relative to the optical system by an amount L, from the same sections of the pipe, in this case from its top (point B). In this case, the distance between the images of the light rays reflected from the outer and inner surfaces of the pipe wall remains unchanged, and therefore does not change.

and the result of measuring the wall thickness of the pipe.

The distance t between the axes of the light beams in the plane of the photodetector 5 is related to the thickness of the pipe wall and the angle of incidence illuminating the dependence:

t 2.S-V -coso tg / 3,

where S pipe wall thickness}

V is the magnification factor of the optical system;

, / sini v p, - arcs in C) - the angle between

the direction of propagation of the fractured beam and the plane of the cross section of the pipe

n is the refractive index of the pipe material.

The value of t reaches the maximum value at the angle of incidence with a0. Near this angle, the distance t between the axes of the recorded light beams reaches the maximum value, and its partial derivative is zero.

jt Qd

0

Consequently, near the angle o / opt the maximum sensitivity of the device to changes in wall thickness is achieved and the sensitivity to the inclination of the tube relative to the optical circuit is minimal. The optimal angle of incidence is the root of this equation, which after differentiation and identical transformations takes the form:

one

Vni - - sinV) O

According to the proposed method, the angle t / is chosen equal to the root of equation (1). Due to this, the device has the lowest possible sensitivity to the inclination of the tube relative to the optical circuit, which improves the accuracy of measuring the wall thickness of the tube during oscillations and inclinations of the tube.

In the device, the image transfer system can be made of

two spherical lenses. A cylindrical lens 3 located between these lenses operates in the XOY plane as a plane-parallel plate that does not change the equivalent focal length of the image transfer system. The role of the collimator in the plane perpendicular to the XOY plane is performed by spherical and cylindrical lenses and a spatial filter 4 located in their equivalent focal plane F.

The aberration calculation of the optical circuit of the device showed that the image transfer system has the smallest field aberration 1. MI, and therefore a higher accuracy of image transmission in the event that it is made with a single increase in a symmetric scheme with telecentric ray path. In such a scheme, the field aberrations of the first spherical lens are co-sensitized by the equal and reverse aberrations of the second lens, which ensures a constant distance of the tube with respect to the optical circuit

between the images of the reflected rays.

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Claims (3)

Invention Formula 1, A method for measuring the wall thickness of transparent pipes, which means sending a beam of radiation to the pipe to be measured at an angle of 0 ° x 90 to the plane of its cross section, forms images of two beams reflected from the outer wall of the pipe in the plane photodetectors, scan the received images. h and convert them into electrical signals, which determine the thickness of the pipe wall, and with the fact that, in order to improve the measurement accuracy, the reflected beams are limited Over the aperture to the paraxial beams in the direction perpendicular to the plane formed by the axis of the tube and the axis of the illuminating beam, and the angle is determined from the equation one Vn - sinV (t cos " g sin o ( - ) ABOUT, where n is the refractive index of the material of the pipe. 2. A device for measuring the wall thickness of transparent tubes, comprising a radiation source, an illumination beam forming system, an optical image transfer system and a scanning receiver, arranged so that the axis of the optical image transfer system is at an angle to the axis of the illumination beam forming system, moreover, the angle Y lies in the range of 0 ° (90 a photo-receiver is located in the image plane of the optical system, characterized in that, in order to improve the accuracy, it is equipped with a collimator, located m between optical transfer system izobra- voltage and photodetector and configured as a series arrangement of the lens and the spatial filtered / 7о BepxHocnf mptjSt The lens is made of spherical or cylindrical lenses and is oriented so that the radii of curvature of the lenses are located in a plane perpendicular to the plane formed by the axis of the illumination beam forming system and the axis of the optical image transfer system, and the spatial filter is installed in the equivalent focal plane of the lens and optical system a) image transfer, aligned with the plane, of the photodetector. 3. A device according to claim 2, characterized in that the optical image transfer system is implemented in a symmetrical pattern with a single magnification and telecentric ray path both in the space of objects and in the space of images. g, h