RU2369048C1 - Laser centraliser for x-ray emitter - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention can be used in aligning an X-ray emitter relative an object. The laser centraliser for an X-ray emitter has a housing in which there is a laser, a mirror made from organic glass, mounted at the intersection of the axes of the laser and X-ray beams and which directs the laser beam onto the object, which coincides with the axis of symmetry of the X-ray beam, which forms a point image on the image, which determines the centre of the illumination zone of the object with X-rays, an ultrasonic range finder, the axis of the radiation beam of which is parallel to the axis of the X-ray beam, a digital still camera, the axis of which is parallel to the axis of the X-ray beam, a lens, the optical axis of which coincides with the optical axis of the laser, and a circular matrix of semiconductor microlasers, mounted in front of the lens on its back focus side. The axis of symmetry of the matrix coincides with the axis of the laser, and a circular structure of laser points is formed on the object, the diametre of which corresponds to the diametre of the zone on the object, illuminated with X-rays. A laser range finder is also included, the optical axis of which is parallel to the axis of the X-ray beam and the axis of radiation of the ultrasonic range finder. Measuring bases of both range finders lie on the same level. The wavelength of the radiation of the laser range finder lies in the wavelength range, in which liquid medium over the object is transparent and has minimal light scattering.

EFFECT: provision for version of determining thickness of the layer of liquid over the object.

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Description

The invention relates to the field of non-destructive testing of materials and products of the aerospace industry, pipeline systems for transporting oil and gas, etc. objects using the radiographic method.

A known laser centralizer for an x-ray emitter, comprising a housing in which a central laser is placed, the optical axis of which is parallel to the longitudinal axis of the x-ray emitter, a plexiglass mirror mounted at the intersection of the axes of the laser and x-ray beams perpendicular to the plane formed by them and directing the laser beam coinciding with the object the axis of symmetry of the x-ray beam, to determine the center of the zone of transmission of the object by x-ray radiation, an ultrasonic range finder, the axis of the beam of radiation which is parallel to the axis of the X-ray beam, a digital camera whose axis is parallel to the axis of the X-ray beam, a lens whose optical axis coincides with the optical axis of the laser, and an annular matrix of semiconductor microlasers mounted in front of the lens from its back focus side, the axis of symmetry of which coincides with the axis of the central laser, and on the object forms an annular structure of laser dots to visualize the area of the object exposed to x-ray radiation [1].

However, this centralizer has several disadvantages. For example, in cases of frequent radiography of objects under a layer of water, oil, alcohol, acids, chemical solutions or another liquid, it is necessary not only to estimate the distance from the object to the centralizer, but also to determine the thickness of the liquid layer above the object, since this greatly affects the quality of x-rays due to the strong scattering of x-rays in liquid media. However, ultrasonic rangefinders can only determine the distance from the centralizer to the outer surface of the liquid medium.

Measuring the depth of a liquid layer by mechanical means (measuring rails, plumb, etc.) is laborious, not accurate, not operational, and in the case of aggressive liquids (acids, etc.) it is dangerous.

Laser rangefinders can measure the distance to an object in two-phase media (water-air), but their readings depend on the optical thickness of the liquid layer, i.e. from the product of its geometric thickness to the refractive index of the liquid. As a rule, the share of the path traveled by a laser beam in a liquid medium is not known in the rangefinder readings, which leads to uncertainty of the measurement results, in particular to overestimation of distances.

The purpose of the invention is the elimination of this disadvantage.

α - угол расходимости пучка рентгеновского излучения, которая формирует на объекте кольцевую структуру лазерных точек, для визуализации положения и размера зоны, просвечиваемой рентгеновским излучением, дополнительно введены лазерный дальномер, оптическая ось которого параллельна оси рентгеновского пучка и оси излучения ультразвукового дальномера, измерительные базы обоих дальномеров расположены на одном уровне, длина волны излучения лазерного дальномера выбирается в диапазоне длины волны, в котором жидкая среда над объектом прозрачна и имеет минимальное светорассеивание, а расстояние от объекта до центратора вычисляется по формулеTo do this, into a laser centralizer for an x-ray emitter, comprising a housing in which a central laser is placed, the optical axis of which is parallel to the longitudinal axis of the x-ray emitter, a plexiglass mirror mounted at the intersection of the axes of the laser and x-ray beams perpendicular to the plane formed by them and directing the laser beam onto the object, coinciding with the axis of symmetry of the x-ray beam to determine the center of the zone of transmission of the object, a digital camera and an ultrasonic range finder, the axes of which are parallel Yelnia axis x-ray beam, an annular array of semiconductor microlasers with a diameter D, mounted on a central axis in the region of the laser (A + B) of the mirror center of plexiglass, where A - distance from the center of the mirror to focus the x-ray tube,

α is the angle of divergence of the x-ray beam, which forms an annular structure of laser dots on the object, to visualize the position and size of the zone illuminated by x-ray radiation, an additional laser rangefinder is introduced, the optical axis of which is parallel to the axis of the x-ray beam and the radiation axis of the ultrasonic range finder, measuring bases of both rangefinders located at the same level, the wavelength of the laser rangefinder radiation is selected in the wavelength range in which the liquid medium above the object is transparent ANT and has a minimum light scattering, and the distance from the object to the centralizer is calculated by the formula

,

,

where H _knots are the readings of the ultrasonic range finder equal to the distance from the centralizer to the surface of the liquid medium with the refractive index n, Δ is the distance from the focus of the x-ray tube to the measuring bases of the range finders, N _l is the readings of the laser range finder, the readings of both range finders are taken in a single scale of linear measuring units , for example, in meters, and the thickness h of the liquid layer is determined by the expression

A diagram of the laser centralizer is shown in the drawing.

равному половине угла расходимости рентгеновского пучка, и сходятся на оси центрального лазера 6 в точке, отстоящей на расстоянии А от центра зеркала 3, а затем после отображения от него, формируют конической сноп лучей, соосный с рентгеновским пучком и имеющий одинаковый с ним угол раскрытия. При этом на объекте возникает кольцевая структура лазерных пятен, с помощью которой можно оценить положение и размер зоны объекта, просвечиваемой рентгеновским излучением. Пятно от центрального лазера обозначает центр этой зоны.It contains an X-ray emitter 1, to which the housing 2 is attached. In housing 2 there is a Plexiglas mirror 3 mounted at the intersection of the laser and X-ray axes, a translucent mirror 4 mounted on the laser axis between the Plexiglas mirror and a ring matrix with a diameter D = 2R of semiconductor microlasers 5, the rays of which are inclined to the axis of the central laser 6 at an angle

equal to half the angle of divergence of the x-ray beam, and converge on the axis of the central laser 6 at a point spaced at a distance A from the center of mirror 3, and then, after displaying from it, form a conical sheaf of rays, coaxial with the x-ray beam and having the same opening angle with it. In this case, an annular structure of laser spots appears on the object, with the help of which it is possible to evaluate the position and size of the zone of the object exposed to x-ray radiation. A spot from the central laser indicates the center of this zone.

Ultrasonic 8 and laser 7 rangefinders are mounted on the body 2, the axes of which are parallel to each other and the axis of the X-ray beam, and the measuring bases are at the same distance Δ from the focus of the X-ray emitter.

In the housing 2 there are also a digital camera, consisting of a filter 9, a lens 10 and a CCD matrix 11 with a display 12. The object 13 is in a liquid medium with a refractive index n and a thickness h.

The centralizer works as follows. The microlasers of the matrix 5 are turned on, the central laser 6 is turned on and the x-ray emitter is directed at the contour zone of object 13, controlling the centralizer pointing process on the display screen 12. A necessary condition for the centralizer to work effectively is that the liquid must be clean, transparent in the laser emission band, with a calm surface .

Then include rangefinders, take readings and calculate the distance from the object to the centralizer and the thickness of the liquid layer with a known refractive index according to the above formulas.

Calculations can be performed manually or automatically. In the latter case, a computer or other auxiliary device is introduced into the centralizer.

If the refractive index of the liquid is unknown, it is determined by standard refractometers or using look-up tables [2, 3].

For water, the laser wavelength is usually selected in the visible wavelength range (λ = 0.4 ÷ 0.7 μm).

The refractive index of water, both fresh and marine, is well known and with sufficient x-ray control for practice, n = 1.33.

For other liquids (oil, liquid nitrogen, acids, gasoline, kerosene, special compounds, etc.), the refractive index is determined individually. Usually it is equal to H = 1.35 ÷ 1.45 [2].

The passbands of specific liquids are given in a number of reference books or are determined experimentally. For carbohydrates, for example, the bandwidths usually lie in the infrared region of the spectrum (λ = 0.9–8 μm), in which numerous industrial lasers emit.

To increase the accuracy of measurements, it is advisable to calibrate the laser rangefinder in real conditions by measuring the thickness of a layer of water or liquid using measuring rulers, poles, etc. devices with an accuracy not worse than ± 1 mm.

To illustrate, we present the test results of a centralizer with a laser rangefinder of the Leika company (Austria) of the Disto brand and an ultrasonic range finder of the FIT brand (England) in the pool. The depth was 2 m, the thickness of the water layer varied from 0 to 2 m.

Rangefinders were located at a constant distance of 3 m from the pool.

The measurement results are given in table. 1. The refractive index is taken equal to n = 1.33.

The measurement error of both rangefinders did not exceed ± 0.01 m (1 cm).

As you can see, the readings of the laser rangefinder strongly depend on the thickness of the water layer, and the ultrasonic rangefinder measures the distance only to the water surface.

The results of the experiment fully confirmed the validity of the technical solution underlying the invention.

Table 1 The thickness of the water layer, m Range Finder Indications Estimated Values KM Laser h, m N, m 0 3.00 3.00 0 3.00 one 2.00 3.33 1.01 3.01 2 1.00 3.65 2.00 2.99

The pool was filled with clean tap water with a temperature of t = + 20 ° C. The measurements were carried out in the summer, outdoors, under normal weather conditions (clear weather, noon, no wind, water surface, atmospheric pressure 760 mm Hg, air temperature + 23 ° C, humidity W≈70%). The wavelength of the laser rangefinder λ = 0.63 μm, the radiation power of 3 mW.

The error in measuring the thickness of the water layer and the distance from the object (pool bottom) to the centralizer did not exceed ± 1.5 cm in absolute measure or not more than 0.5% in relative units.

The thickness of the water layer was determined by standard roulette with a division price of 1 mm and using a measuring pole.

In table 1, N is the distance to the object, calculated by the formulas above in the description of the invention, h is the calculated thickness of the water layer.

Literature

1. Patent RU N 2263421 C1. Laser centralizer for x-ray emitter.

2. Ioffe B.V. Refractometric methods of chemistry, L .: Chemistry, 1983, 352 p.

3. Zolotarev V. M. et al. Optical constants of natural and technical media, Directory, L .: Chemistry, 1984, 360 pp.

Claims (1)

A laser centralizer for an X-ray emitter, comprising a housing in which a laser is placed, the optical axis of which is parallel to the longitudinal axis of the X-ray emitter, a Plexiglas mirror mounted at the intersection of the axes of the laser and X-ray beams perpendicular to the plane formed by them and directing the laser beam at the object coinciding with the axis of symmetry an x-ray beam that forms an image of a black dot on the object that defines the center of the area of the object's x-ray transmission, ultrasonic number, the axis of the radiation beam of which is parallel to the axis of the x-ray beam, a digital camera, the axis of which is parallel to the axis of the x-ray beam, a lens whose optical axis coincides with the optical axis of the laser, and a ring matrix of semiconductor microlasers mounted in front of the lens from the back focus side, the axis of symmetry of the matrix coincides with the axis of the laser, and with its help an annular structure of laser dots is formed on the object, the diameter of which corresponds to the diameter of the zone of the object that is exposed to x-ray radiation characterized in that an additional laser rangefinder is introduced into it, the optical axis of which is parallel to the axis of the x-ray beam and the radiation axis of the ultrasonic rangefinder, the measuring bases of both rangefinders are at the same level, the wavelength of the laser rangefinder radiation is selected in the wavelength range in which the liquid medium above the object is transparent and has minimal light scattering, and the geometric distance from the object to the centralizer is calculated by the formula

,
where H _knots are the readings of the ultrasonic rangefinder equal to the distance from the centralizer to the surface of the liquid medium with the refractive index n, Δ is the distance from the focus of the x-ray tube to the measuring bases of the rangefinders, N _l is the readings of the laser rangefinder, while the readings of both rangefinders are taken in a single linear scale measuring units, for example, in meters, and the thickness h of the liquid layer is determined by the expression