RU2369835C1 - Laser profilometre - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: application: for contact-free control of complex-shaped item profiles. Laser profilometre comprises mechanisms for fixation and longitudinal displacement of blade, laser sources of blade slot illumination installed symmetrically relative to blade on its opposite sides and forming flat light beams in plane, which is perpendicular to longitudinal axis of blade, TV camera and computer for calculation of controlled section parametres, moreover, it additionally comprises collimator lens, axis of which corresponds to longitudinal axis of blade and is parallel to optical axis of TV camera lens, and its front focus matches point of blade longitudinal axis crossing with plane of blade slot illumination laser sources distribution, between collimator lens and lens of TV camera there is a periscopical system, which consists of mirror and beam divider, reflecting surfaces of which are parallel to each other and are installed in planes, which are perpendicular to plane created by optical axis of collimator lens and axes of leaser sources of blade slot illumination and are installed at the angle of 45° to axis of collimator lens symmetrically relative to this axis, centres of mirror and beam divider are installed on axis, which is perpendicular to axis of TV camera lens, parallel to axes of laser sources of slot illumination and passing through point of TV camera lens axis crossing with centre of beam divider.

EFFECT: improved metrological characteristics.

3 dwg

Description

The invention relates to non-destructive testing and can be used for non-contact control of the profile of products of complex shape, for example, blades for gas turbine engines, screws, rolled products, etc.

A device for controlling the profile of the blades by the light section method, comprising a blade attachment mechanism, the optical axis of the lens of which coincides with the longitudinal axis of the controlled blade, sources of slot illumination of the blade in a plane perpendicular to its longitudinal axis and forming a thin light belt from its surface in a given section, outlining the contour of this section, which is projected onto the screen, as well as the mechanism for moving the blade along its longitudinal axis [1].

The disadvantage of this device is the inability to obtain the contour of the blades of complex shape, for example, with double curvature and / or with a device for mounting them in the rotor due to the effect of screening the contour with these elements.

A known laser profilometer containing laser sources of slit illumination of the product in a plane perpendicular to the longitudinal axis of the object, a television camera and symmetric optical systems located on different sides of the product to form images of individual sections of the cross-section of the section, connected optically to a single image in the plane of the CCD camera matrix [2].

The disadvantage of this device is the complexity of the design, high I cost, low metrological characteristics due to the non-identical optical characteristics of the channels.

The purpose of the invention is the elimination of disadvantages.

- угол между оптической осью объектива и направлением визирования контролируемого сечения, при котором отсутствует его экранирование элементами лопатки высотой t′, расположенными на расстоянии Δ от контролируемого сечения, между коллиматорным объективом и объективом телекамеры расположена перископическая система, состоящая из зеркала и светоделителя, отражающие поверхности которых параллельны друг другу и расположены в плоскостях, перпендикулярных плоскости, образованной оптической осью коллиматорного объектива и осями лазерных источников щелевой подсветки лопатки, и установлены под углом 45° к оси коллиматорного объектива симметрично относительно этой оси, центры зеркала и светоделителя расположены на оси, перпендикулярной оси объектива телекамеры, параллельной осям лазерных источников щелевой подсветки и проходящей через точку пересечения оси объектива телекамеры с центром светоделителя, расстояние L между центрами зеркала и светоделителя выбирается из соотношения L<D_k, фокурное расстояние коллиматорного объектива выбирают из соотношения

максимальная высота контролируемого сечения, f₀ - фокусное расстояние объектива телекамеры, d - размер ПЗС-матрицы телекамеры, k=(0,8÷0,9) - коэффициент запаса, размер S стороны светоделительного кубика выбирается из соотношения S≥D₀, где D₀ - диаметр объектива телекамеры, а размеры зеркала А×В выбираются из соотношений A≥D₀ и

For this, a device containing a mechanism for fixing the blade and its movement along its longitudinal axis, laser sources of slot illumination of the blade in the plane perpendicular to the longitudinal axis of the blade, a television camera with a lens and an optical information system for images of sections of contour elements, an additional collimator lens with a diameter D _k and with a focal length f _k, whose optical axis coincides with the longitudinal axis of the blade and parallel to the optical axis of the camera lens, and its front focus coincides with the Coy intersection of the longitudinal axis of the blade with the plane of propagation of laser sources slit illumination lens diameter defined by the expression D _k ≥f _k · tgα, wherein

- the angle between the optical axis of the lens and the direction of sight of the controlled section, at which it is not shielded by blade elements of height t ′ located at a distance Δ from the controlled section, between the collimator lens and the camera lens there is a periscope system consisting of a mirror and a beam splitter, the reflecting surfaces of which parallel to each other and located in planes perpendicular to the plane formed by the optical axis of the collimator lens and the axes of the laser the sources of the slit illumination of the scapula, and are installed at an angle of 45 ° to the axis of the collimator lens symmetrically with respect to this axis, the centers of the mirror and the beam splitter are located on an axis perpendicular to the axis of the camera’s lens, parallel to the axes of the laser sources of the slit illumination and passing through the intersection of the axis of the camera’s lens with the center of the beam splitter , the distance L between the centers of the mirror and the beam splitter is selected from the relation L <D _k , the focal distance of the collimator lens is selected from the relation

the maximum height of the monitored section, f ₀ is the focal length of the camera lens, d is the size of the CCD matrix of the camera, k = (0.8 ÷ 0.9) is the safety factor, the size S of the side of the beam splitter is selected from the relation S≥D ₀ , where D ₀ - the diameter of the camera lens, and the dimensions of the mirror A × B are selected from the relations A≥D ₀ and

The device diagram is shown in figures 1-3.

The profilometer consists of mounting angles 2 and longitudinal movement 3 of the blade 1 along its longitudinal axis, two symmetrical laser slit illuminators on both sides of the blade, consisting of lasers 4 and 4 ′ and cylindrical lenses 5 and 5 ′, forming narrow light on the side surfaces of the blade strips visualizing the profile of the scapula in a given section. Flat light rays formed by laser illuminators lie in the same plane perpendicular to the longitudinal axis of the scapula. The optical axes of the lasers 4 and 4 ′ lie on one straight line passing through the point of intersection of the longitudinal axis of the blade with the plane of propagation of plane laser beams.

In the plane formed by the longitudinal axis of the blade and the axes of the lasers, the optical axis of the collimator lens 6 of diameter D _k and focal length f _k coincides with the longitudinal axis of the blade. The foci of the lenses 6 are aligned with the intersection point of the laser axes with the longitudinal axis of the blades.

In front of the collimator lens 6, a beam splitter 8 and a television camera are mounted sequentially on its optical axis, comprising a lens 9 with a focal length f ₀ and a diameter D ₀ and a CCD matrix of size d × d installed in the focal plane of the lens 9. A profile image of the blade is observed on a video monitor 11 .

The beam splitter 8 is made in the form of a prism-cube with sides S, the translucent reflecting surface of which coincides with the diagonal plane of the prism-cube, oriented at an angle of 45 ° to the axis of the lens 9 and perpendicular to the plane of the optical axes of the laser and collimator lens 6.

The distance t between the lenses 6 and 9 is selected from the relation t≥S · p, where p = (1.2 ÷ 1.3) is the design tolerance for the installation size of the prism-cube 8.

The center of the periscope mirror 7, size A × B, is installed at a distance L from the center of the beam splitter on an axis passing through the point of intersection with the axis of the lens 9 perpendicular to it, in a plane formed by the axis of the lens 9 and the laser axes.

The device operates as follows.

With the longitudinal movement of the blade along its axis, two laser slit illuminators form images of thin light strips that accurately display the cross-sectional profile of the blade in a given plane.

The collimator lens 6 forms parallel beams of rays that are spatially aligned by the reflector 7, and the beam splitter 8, and the lens 9 and are focused on the surface of the CCD matrix 10, forming the profile profile of the blade, consisting of two optically aligned parts (figure 3). When setting up the optical system of the profilometer, the exact combination of these separate images is made by quotation turns of the reflector 7 using the appropriate mechanisms not shown in the diagram due to common knowledge [3].

The need to observe the different sides of the blade with two lenses, located at an angle to the longitudinal axis of the blade, is due to the presence on the front edges of modern blade mounts for installation in turbine casings and / or double curvature of the blade, which leads to screening of sections located in close proximity to these elements (figure 2). The choice of angle α is made from the obvious relation α> arctan (t / Δ), where t 'is the height of the shielding element, Δ is the distance from it to the controlled section.

Since the focal plane of the collimator lens 6 coincides with the plane of the object, parallel beams are formed at its output, which are then focused by the lens 9, forming in the image plane of the CCD matrix 10 the image of the light contour of the scapula in the selected section.

In this case, by the property of telescopic systems with parallel ray paths between components [3], the difference in optical beams between lenses 6 and lens 9 does not change the scale of the images formed by these elements of the optical system.

The image scale of the cross section in the plane of the CCD matrix for an optical system with a parallel path of rays between the I components, as is known, is m = f ₀ / f _k [3].

, то условие выбора фокусного расстояния дополнительных объективов можно записать в виде

, где k=(0,6÷0,9) - конструктивный коэффициент запаса, учитывающий случайные смещения изображения.In this case, the image H of the cross section of the blade of the maximum size should not go beyond the receiving area of the CCD matrix of size d, taking into account the tolerance for possible displacements of this image due to variation in the size of the blades and various technological factors (Fig. 2). Because

, then the condition for choosing the focal length of additional lenses can be written as

where k = (0.6 ÷ 0.9) is the structural safety factor taking into account random image displacements.

For accurate measurement of cross-sectional dimensions, the profilometer is pre-calibrated using test samples of known size. Calibration is performed for two mutually perpendicular directions in order to exclude the influence of angle distortion on the measurement results due to the fact that the cross-sectional dimension in the direction perpendicular to the axis of the lenses (H _α ) is related to its true value H by the obvious relation H _α = H cos α.

Corresponding corrections are automatically taken into account by the computer included in the profilometer.

It is significant that images of sections of opposite sides of the scapula are deformed by the same lens. This provides high metrological characteristics of the optical system of the profilometer. The periscope can be made in the form of a compact monoblock of two glued prisms (in this case, instead of mirror 7, a rectangular prism of total internal reflection is used). Given the high accuracy of optical technology (the tolerance on the angles of prisms is 1 ″ ÷ 2 ″ ang. Sec) this will further improve the accuracy and stability of the profilometer.

LITERATURE

1. Rabinovich A.N. Devices and systems for automatic control of the dimensions of machine parts. Kiev. Technique, 1970, 206 p.

2. Patent RU 2 285 234 C2. Laser profilometer.

3. Reference designer of optical-mechanical devices. / Ed. Kruger M.Ya. M .: Engineering, 1980, 742 p.

Claims (1)

A laser profilometer for controlling a profile of a complex shape such as blades of gas turbine engines by the light section method, containing mechanisms for fastening and longitudinal movement of the blade, laser sources of slot illumination of the blade located symmetrically relative to the blade from its opposite sides and forming flat light beams in a plane perpendicular to the longitudinal axis of the blade, a television camera and a computer for calculating the parameters of the controlled section, characterized in that it additionally contains collimator nth lens with a focal length f _k , whose axis coincides with the longitudinal axis of the blade and parallel to the optical axis of the camera’s lens, and its front focus coincides with the point of intersection of the longitudinal axis of the blade with the propagation plane of the laser sources of slot illumination of the blade, the diameter of the collimator lens is determined by the expression D _k ≥ 2f _k · tgα, where

- the angle between the optical axis of the collimator lens and the direction of sight of the controlled section, at which it is not shielded by blade elements of height t ′ located at a distance Δ from the controlled section, between the collimator lens and the camera lens there is a periscope system consisting of a mirror and a beam splitter, reflecting surfaces which are parallel to each other and are located in planes perpendicular to the plane formed by the optical axis of the collimator lens and the axes of the laser sources of slit illumination of the blade and are mounted at an angle of 45 ° to the axis of the collimator lens symmetrically with respect to this axis, the centers of the mirror and the beam splitter are located on the axis perpendicular to the axis of the lens of the camera, parallel to the axes of the laser sources of slit illumination and passing through the center of the axis of the camera lens with the center the beam splitter, the distance L between the centers of the mirror and the beam splitter is selected from the ratio L≤D _k , the focal length of the collimator lens is selected from the ratio

where H is the maximum height of the monitored section, f ₀ is the focal length of the camera lens, d is the size of the CCD matrix of the camera, k = (0.8 ÷ 0.9) is the safety factor, the size S of the beam splitting cube side is selected from the relation S≥D ₀ , where D ₀ is the diameter of the camera lens, and the dimensions of the mirror A × B are selected from the relations A≥D ₀ and

Images