RU2362118C2 - Laser profile metre - Google Patents

Abstract

FIELD: instrument making.

SUBSTANCE: proposed laser profile metre serves to check up sophisticated-shape products, e.g. turbine blade, by light section method. The proposed instrument incorporate the blade lengthwise travel and fastening mechanism, two lasers with cylindrical lenses, for blade slot illumination, arranged in symmetry with the blade and on its both sides. The said lenses form flat light beams in the plane perpendicular to the blade lengthwise axis. It comprises TV camera and computer to process parametres of cross section under control. Additionally, the proposed metre comprises two lenses with their optical axes lying in the plane formed by the lasers axes and blade lengthwise axis. The said lenses are arranged in symmetry at angles α of the blade lengthwise axis. The metre includes also a beam splitter arranged between the first additional lens and TV camera lens, on its optical axis aligned with that of the first additional lens. It, further on, comprises the reflector, arranged in the plane perpendicular to that formed by lens axes at the point of intersection of the second additional lens optical axis, with perpendicular to TV camera lens axis, run through the point of its intersection with the splitter reflecting face in the plane, formed by the additional lens axes at the angle 2γ=(90°-2α)/2 to the second additional lens axis. Additionally introduced are two optical transparent plane-parallel plates made in material with its transmission spectrum maximum complying with the laser radiation wavelength, while its spectral transparency, outside the wavelength range, is minimum for the TV camera spectral sensitivity range. Aforesaid plates are fitted ahead of entrance pupils of additional lenses to revolve relative to mutually perpendicular axes crossing the additional lens optical axes. Thickness of the said plates B(mm) and refractivity are selected from the expression

. The plate material, constant and plate diametres D_n satisfy the requirement D_n≥D_K, where D_K is the diametres of additional lens entrance pupils.

EFFECT: higher accuracy of inspection.

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Description

The invention relates to non-destructive testing and can be used for non-contact control of the profile of products of complex shape, such as turbine blades, etc.

Known laser profilometer to control the profile of products of complex shape

[one]. Its essence lies in the fact that the known laser profilometer contains two additional lenses, the optical axes of which are located in the plane formed by the laser axes and the longitudinal axis of the blade, and are located symmetrically at angles α to the longitudinal axis of the blade, the optical axis of the camera lens coincides with the axis of the first additional lens, between these lenses a beam splitter is installed, at the intersection of the optical axis of the second additional lens with a perpendicular restored from the intersection point, I reflect a face of the beam splitter with the axis of the camera lens, a reflector is installed in the plane of the optical axes of the lenses perpendicular to this plane, the focal points of the additional lenses coincide with each other and with the intersection point of the laser axes and the longitudinal axis of the scapula.

It is proposed in a laser profilometer to control the profile of products of complex shape such as turbine blades by the light section method, containing a mechanism for fastening and longitudinal movement of the blade, two lasers with cylindrical lenses for slit illumination of the blade, located symmetrically relative to the blade from its opposite sides and forming flat light beams in the plane perpendicular to the longitudinal axis of the scapula, a camera, a computer for calculating the parameters of the controlled section, two lenses, the optical axis of which are located in the plane formed by the axes of the lasers and the longitudinal axis of the blade, located symmetrically at angles α to the longitudinal axis of the blade, a beam splitter located between the first additional lens and the camera lens on its optical axis coinciding with the axis of the first additional lens, and also a reflector located in the plane formed by the axes of the lenses at the point of intersection of the optical axis of the second additional lens with a perpendicular to the axis of the camera lens, drawn through the intersection point with a reflecting face of the beam splitter in the plane formed by the axes of the additional lenses at an angle β = (90 ° -2α) / 2 to the axis of the second additional lens, the focal points of the additional lenses coincide with each other and with the intersection point of the laser axes with the longitudinal axis of the blade, characterized in that two additional transparent transparent plane-parallel plates of material are introduced into it, the maximum transmission spectrum of which corresponds to the wavelength of the laser radiation, and the spectral transparency outside this region and the lengths are minimal in the spectral sensitivity range of the camera, the plates are mounted in front of the entrance pupils of additional lenses with the possibility of rotation relative to mutually perpendicular axes passing through the optical axes of the additional lenses, the axis of rotation of the first plate is parallel to the vertical diameter of the entrance pupil of the first additional lens, and the axis of rotation of the second plate is parallel the horizontal diameter of the entrance pupil of the second additional lens, the plate thickness In _mm , refractive index n are selected from the relation

,

,

- константа материала пластинки, Δ (мм) - требуемая минимальная величина смещения изображений световых профилей в плоскости объектов, γ(радиан) - угол поворота пластинки, соответствующий этому смещению, а диаметры D_n пластинок отвечают условиюWhere

is the constant of the plate material, Δ (mm) is the required minimum displacement of the images of light profiles in the plane of the objects, γ (radian) is the angle of rotation of the plate corresponding to this displacement, and the diameters D _{n of the} plates meet the condition

D _n ≥D _K , where D _K are the diameters of the entrance pupils of additional lenses.

The invention is illustrated in figures 1-3.

The profilometer consists of attachment points 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.

. Фокусы объективов 5 и 5' совмещены с точкой пересечения осей лазеров с продольной осью лопатки.In the plane formed by the longitudinal axis of the blade and the axes of the lasers, the optical axes of two additional lenses 6 and 6 'of diameter D _k with focal lengths are located at angles α to the longitudinal axis of the blade

. The foci of the lenses 5 and 5 'are aligned with the intersection point of the laser axes with the longitudinal axis of the blade.

и диаметром D₀ и ПЗС-матрицу размером d×d₁, установленную в фокальной плоскости объектива 9.In front of the first additional lens 6, a beam splitter 8 and a color camera containing a lens 9 with a focal length are sequentially mounted on its optical axis

and a diameter D ₀ and a CCD matrix size d × d ₁ mounted in the focal plane of the lens 9.

к оптической оси второго дополнительного объектива 6'.The beam splitter 8 is made in the form of a prism-cube, the translucent reflecting surface of which coincides with the diagonal plane of the prism-cube, is oriented at an angle of 45 ° to the axis of the lens 9 and is perpendicular to the plane of the optical axes of the additional lenses 6 and 6 '. At the intersection of the optical axis of the second additional lens 6 'and the perpendicular restored from the point of intersection of the reflecting surface of the prism-cube with the axis of the lens 9, a reflector 7 is installed in the plane of the optical axes of the lenses 6 and 6' perpendicular to this plane, the normal to which is located at an angle

to the optical axis of the second additional lens 6 '.

The diameters D _{to the} lenses 6 and 6 'are selected from the condition D _to ≤D ₀ in accordance with the requirements for the allowable value of the geometric transformation of the image of the light section of the object with a maximum value of H.

Processing of the measurement results is carried out using a computer 11 with a display 12.

Plane-parallel plates 13 and 13 'are installed in front of the entrance pupils of the lenses 6 and 6'.

Since the focal planes of the lenses 6 and 6 'coincide with the plane of the object, parallel beams are formed at their output, which are then focused by the lens 9, forming images of the light contour of the scapula in the selected section in the image plane of the CCD matrix 10. Moreover, by the property of telescopic systems with parallel ray paths between components [2], differences in optical paths between lenses 6 and 6 'and lens 9 do not change the sharpness and scale of images formed by these elements of the optical system.

For accurate measurement of cross-sectional dimensions, the profilometer is pre-calibrated according to the test object. 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 lens axis (Hα) is related to its true value H by the obvious relation Hα = H · cosα.

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

Plane-parallel plates 13 and 13 'are mounted in front of the lenses 6 and 6' perpendicular to their optical axes with the possibility of angular turns with respect to mutually perpendicular axes. For the first plate 13, the axis of rotation is perpendicular to the plane formed by the optical axes of the lenses 6 and 6 ', and parallel to the vertical diameter of the entrance pupil of the lens 6. The axis of rotation of the second plate 13' lies in the plane formed by the axes of the lenses 6 and 6 ', and parallel to the horizontal diameter of the input pupil of the lens 6. The turning mechanisms in figure 1 are not shown due to the well-known technical solutions [2].

Adjustment i.e. the combination of the light sections of the opposite sides of the blade 1 is made in the following sequence.

First, the turns of the reflector 7 is a preliminary beam-splitting of images. Then, by turning one of the plates, for example 13, the vertical sections are aligned (Fig. 2, a). After that, the image is horizontally aligned with the turns of the second plate 13 '(Fig.2, b) until they are completely merged (Fig.2, c). Combining control by the operator of the image on the display section 12 to within Δ _B (vertical) and delta _T (horizontal). Usually

Δ _B = Δ _G.

Consider a numerical example of the proposed mechanism for combining elements of the light section of the scapula.

In the pilot sample of the profilometer, KS-19 brand red glass plates were used, the light transmission of which at the radiation wavelength of lasers 4 and 4 '(λ = 0.63 μm) is not less than τ = 0.8 with the plate thickness B = 2 mm, and is equal to τ≤0,1 wavelengths less than λ≤0,63 μm (figure 3), because the spectrum of background radiation (sun, fluorescent lamps, etc.) mainly contains radiation in the wavelength range of 0.4 ÷ 0.6 μm. They are effectively selected by glass of plates, which provides a high contrast image of the light section regardless of fluctuations in the intensity of background radiation.

Thus, the plates 13 and 13 'perform two functions - filtering the background radiation and fine alignment shift of fragments of the light section.

As is known, the image shift in the plane of objects when rotating a plate of thickness B by an angle γ is determined by the relation

,

,

where n is the refractive index of the plate material.

The actual required accuracy of image alignment in the plane of the object is Δ = ± 0.01 mm. At the same time, in order to confidently perform the operation of combining image fragments, the rotation angle of the plate γ corresponding to a given Δ value should be of the order of γ≥2 ÷ 3 ° and γ = 0.04 ÷ 0.06 radians, which is due to both ergonomic requirements and requirements for radiation accuracy of manufacturing the mechanism of rotation of the plates.

, здесь

- константа материала пластинки (для стекла КС-19 n≅1,50 и K≅3,0). Для Δ=0,01 мм, K=0,3 и γ=0,02 рад имеем

, что практически вполне приемлемо.Therefore, the thickness of the plate should be selected taking into account the ratio obtained from the above formula

, here

is the constant of the plate material (for KS-19 glass n≅1.50 and K≅3.0). For Δ = 0.01 mm, K = 0.3 and γ = 0.02 rad, we have

which is almost completely acceptable.

This example illustrates the sensitivity of the alignment mechanism.

Note that when using reflector 7 as an adjustment element, the required value of its angular displacement to ensure the same alignment accuracy Δ = 0.01 mm is Δβ = 0.0001 rad, which makes the requirements for the accuracy of manufacturing of the corresponding mechanism of its rotation practically impossible.

Actually, the value of the mismatch of the fragments of the light section during preliminary alignment using the reflector 7 is ± 0.1 ÷ 0.3 mm in the plane of the object. The rotation range of the plates for night alignment of fragments with the above parameters of the plates (B≈1.5 mm, n = 1.50) is γ≅0.6 ÷ 0.8 rad, or γ≈ ± 10 °, which is also practically acceptable and not causes noticeable aberrations in images of sectional fragments.

LITERATURE

1. Laser profilometer. The decision to grant a patent on the application 2004131383/28, dated 28.10.2004, IPC G01B 11/24 (2006.01).

2. Handbook of the designer of optical-mechanical devices, ed. Kruger M.Ya., Mechanical Engineering, 1980.742 p.

Claims (1)

A laser profilometer for controlling the profile of products of complex shape such as turbine blades by the light section method, containing a mechanism for attaching and longitudinally moving the blades, two lasers with cylindrical lenses for slit illumination of the blades, located symmetrically relative to the blade from its opposite sides and forming flat light beams in a plane perpendicular the longitudinal axis of the blade, a camera, a computer for calculating the parameters of a controlled cross section, two additional lens whose optical axis are in the plane formed by the axes of the lasers and the longitudinal axis of the blade, located symmetrically at angles α of the longitudinal axis of the blade, a beam splitter located between the first additional lens and the camera lens on its optical axis coinciding with the axis of the first additional lens, and also a reflector located in the plane perpendicular to the plane formed by the axes of the lenses at the point of intersection of the optical axis of the second additional lens with a perpendicular to the axis of the camera lens, through the point of its intersection with the reflecting face of the beam splitter in the plane formed by the axes of the additional lenses at an angle 2γ = (90 ° -2α) / 2 to the axis of the second additional lens, the focal points of the additional lenses coincide with each other and with the intersection point of the laser axes with the longitudinal axis of the blade, characterized in that it additionally contains two transparent transparent plane-parallel plates of material, the maximum transmission spectrum of which corresponds to the wavelength of the laser radiation, and transparency outside this section of wavelengths is minimal in the range of spectral sensitivity of the camera, the plates are mounted in front of the entrance pupils of additional lenses with the possibility of rotation relative to mutually perpendicular axes passing through the optical axes of the additional lenses, the axis of rotation of the first plate is parallel to the vertical diameter of the entrance pupil of the first additional lens, and the axis rotation of the second plate is parallel to the horizontal diameter of the entrance pupil of the second additional lens, plate thickness B (mm), refractive index n are selected from the ratio

where

is the constant of the plate material, Δ (mm) is the required minimum displacement of the images of light profiles in the plane of the objects, γ (radian) is the angle of rotation of the plate corresponding to this displacement, and the diameters D _{n of the} plates correspond to the condition D _n ≥D _K , where D _K - diameters of the entrance pupils of additional lenses.

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