RU2769305C1 - Autocollimator - Google Patents

Abstract

FIELD: optical equipment.

SUBSTANCE: invention can be used to measure the angles of rotation of objects relative to two mutually perpendicular axes. The autocollimator includes an optical system for generating an autocollimation image of a stamp on a photodetector from a radiation source, a capacitor, a mark, a beam splitter, a lens, an autocollimation mirror and a photodetector with a signal processing unit. The mark and the photodetector are installed in the focal planes of the lens. A semi-transparent plane-parallel plate is additionally installed between the lens and the autocollimator mirror, located to the sighting axis of the autocollimator at an angle ϕ selected from the condition: ϕ<b/kf, where b is the characteristic size of the photodetector, mm; f is the focal length of the lens, mm; k≥4. The signal processing unit is made calculating the position of the autocollimator mirror based by signals generated by several mark images.

EFFECT: increase in measurement accuracy, a reduction in dimensions and an increase in functionality.

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Description

The invention relates to measuring technology using optical measuring instruments, in particular to optoelectronic devices that allow the autocollimation method to measure the angles of rotation of objects relative to two mutually perpendicular axes.

It is known that for angular measurements of the position of objects, visual autocollimators are widely used, which are convenient and easy to use. These include, in particular, the widespread autocollimators AKU-1, AKU-0.5 and AKU-0.2, which are produced by the Federal State Unitary Enterprise PO Novosibirsk Instrument-Making Plant (Number in the State Register of Measuring Instruments 10714-05). They contain a source of radiation, a condenser and a test mark in the form of a crosshair, installed in the focal plane of the objective. The radiation from the test mark, having passed through the beam splitter, is directed by the lens to an autocollimation mirror mounted on the object, reflected from it, and projected through the lens and the beam splitter onto a special scale, also installed in the focal plane of the lens and made in the form of a grid of threads. The image of the test mark on the scale is viewed using an eyepiece. Measurements are made by determining the position of the test mark image relative to a fixed scale.

These autocollimators do not have high measurement accuracy, do not measure the angular position of the mirror in dynamics, and do not allow automation of the measurement process.

Known autocollimator (see Pat. RF No. 2353960, IPC GO2B 27/30, prior. 11/19/2007) consisting of an illuminator placed along the condenser beam, a brand, a beam splitter, a lens, an autocollimating mirror installed with the possibility of adjustment in two coordinates, a matrix photodetector and an information processing unit, wherein the mark and the photodetector are installed in conjugate focal planes of the lens, while part of the mark field is made in the form of a slit raster, and part is in the form of a stroke, and in front of the part of the matrix photodetector, which registers the image of the mark field in the form multi-element raster, an additional slit raster is installed close to it. When an autocollimation image of the mark raster is superimposed on an additional raster, a moiré pattern is formed, which is recorded by a matrix photodetector, and when the autocollimation mirror is rotated, the linear displacement of the extrema of the moiré pattern turns out to be greater than the movement of the stroke and depends on the selected ratio of the frequencies of the raster raster and the additional raster and the angle between them. A rough reading in the autocollimator is taken from the displacement of the mark stroke image, an accurate reading is taken from the displacement of the extrema of the moiré pattern. Data on the position of the stroke and the moiré pattern from the photodetector are fed to a personal computer, in which the position of the autocollimation mirror is calculated, taking into account all influencing factors.

However, such an autocollimator does not allow measurements in two coordinates, it requires the development of a specialized program for a personal computer, and the adjustment of the optical scheme of the autocollimator is complicated.

Known autocollimator (see Pat. RF No. 2455668, IPC G02B 27/30, prior. 05/20/2010), chosen by us as a prototype for most essential features.

The autocollimator contains a radiation source, a condenser, a test mark, a beam splitter, an objective, an autocollimation mirror, a photodetector with a reading device, located along the beam, the mark and the photodetector are installed in the focal planes of the lens. The radiation from the test mark, reflected by the beam splitter, is directed by the lens to the autocollimating mirror, reflected from it, and projected by the same lens through the beam splitter onto the photodetector. The photodetector contains a CCD matrix with a device for generating a standard video signal. The reading device is made in the form of a computer with an application program for calculating the angular position of the autocollimating mirror. The test mark is made in the form of a round diaphragm, the diameter of which is calculated according to the stated formula.

When changing the angular position of the autocollimating mirror relative to the optical axis of the autocollimator, the coordinates of the center of the image of the test mark on the surface of the CCD array change, which is the basis for performing measurements. The measurements are performed using a specially developed application software that determines the desired angular position of the autocollimating mirror relative to the optical axis of the autocollimator.

However, such an autocollimator does not have a sufficiently high measurement accuracy. It also has other disadvantages: large overall dimensions, the need to use a specially developed application computer program, and there is no possibility to change the sensitivity of the autocollimator and the measurement range.

The technical effect of the proposed device is to increase the accuracy of measurements, reduce the size and increase functionality.

As a result of our studies, we found that a semitransparent plane-parallel plate (PPP) located between the lens and an autocollimation mirror (ACM) at a given angle ϕ to the sighting axis of the autocollimator (AC) forms additional images of the mark in the photodetector (PC) plane, and some of them have increased sensitivity to the rotation of the AKZ, which makes it possible to increase the accuracy of measurements. We have also shown that the use of additional images of the mark allows you to change the conversion factor and the range of measurements of AC. And the use of an additional image formed by the rays after the first reflection from the SPP as a reference makes it possible to exclude some systematic errors, which also increases the accuracy of AK measurements.

To solve this problem, in the proposed autocollimator, which includes an optical system for forming an autocollimation image of a mark on a photodetector from a radiation source, placed along the beam of a condenser, a mark, a beam splitter, an objective, an autocollimation mirror and a photodetector with a signal processing unit, the mark and photodetector are installed in the focal planes of the lens, what is new is that between the lens and the autocollimation mirror on the optical axis, a semitransparent plane-parallel plate is additionally installed, located to the sighting axis of the autocollimator at an angle ϕ, selected from the condition:

ϕ<b/kf,

where

b is the characteristic size of the photodetector, mm;

f - focal length of the lens, mm;

k≥4;

and the signal processing unit is configured to calculate the position of the autocollimation mirror from the signals generated by several brand images.

In FIG. 1 shows a schematic diagram of the claimed autocollimator, where the radiation source 1, condenser 2, brand 3, beam splitter 4, lens 5, translucent plane-parallel plate 6, autocollimation mirror 7, photodetector 8, signal processing unit 9;

O - O ₁ - sighting axis of the autocollimator.

In FIG. 2 shows the course of rays upon reflection from an autocollimating mirror installed perpendicular to the optical axis of the autocollimator and a translucent plane-parallel plate installed with an inclination ϕ in the vertical plane, where the objective is 5, the translucent plane-parallel plate 6, the autocollimating mirror 7;

i ₀ - rays after reflection from a translucent plane-parallel plate;

i ₁ , i ₂ , i ₃ - rays after the first, second and third reflection from the autocollimating mirror.

In FIG. Figure 3 shows a variant of the location of the images of marks in the plane of the photodetector in the initial position and when the autocollimation mirror is rotated through an angle α in the horizontal plane, where

photodetector - 8;

I ₀ - the image of the brand, which remains motionless when the autocollimation mirror is rotated, formed by rays reflected from a translucent plane-parallel plate;

I ₁ , I ₂ , I ₃ - the first, second and third images of the brand;

I' ₁ , I' ₂ , I' ₃ - the first, second and third images of the mark when the autocollimation mirror is rotated by an angle α.

The claimed autocollimator works as follows.

Let us assume that the sighting axis OO1 of the AK is directed perpendicular to the plane of the ACS 7, the PPP 6 is installed in front of the lens 5 perpendicular to the sighting axis of the autocollimator in the horizontal plane and at an angle ϕ in the vertical plane (see Fig. 1).

The angle ϕ is determined from the condition of location on the sensitive surface of the AF 8 of the reference image formed by the rays reflected only by the PPP 6, and the estimated number of images formed by the reflection of the rays from the ACS 7.

The reflection coefficients R and transmission T PPP is determined from the condition that the estimated number of brand images on the surface of the FP 8 will have a brightness that allows them to be processed.

The principles for calculating the positions of brand images formed in the focal plane of the lens in an optical system with reflectors in the form of SPP and ACD are known.

The beam of light from the radiation source 1 (see Fig. 1) through the condenser 2 and mark 3 falls on the beam splitter 4. The part of the light reflected from the beam splitter 4, passing through the lens 5, is converted into a parallel beam of rays, which partially passes through the PPP 6 and falls on AKZ 7, and is partially reflected from the PPP 6. Part of the rays reflected from the PPP 6 passes through the lens 5 in the opposite direction and through the beam splitter 4 forms an image of mark 3 on the AF 8, which is stable and motionless and does not depend on the position of the AKZ 7 (I ₀ in Fig. 3). This image of the brand in the calculations is taken as a reference, and when measuring with a reference channel, relative to it, the position of other images formed on the FP 8 is calculated.

Rays that have passed PPP 6 are reflected by ACZ 7, partially re-pass through PPP 6, and partially reflected from PPP 6 and again fall on ACZ 7. The percentage ratio of the intensity of the transmitted and reflected rays from PPP 6 will be determined by the reflection coefficients R and transmission T of the PPP.

Part of the rays reflected from the AKZ 7 and passed through the PPP 6 passes in the opposite direction of the lens 5, in the focal plane of which, that is, on the FP 8, the image of mark 3 is built. from it and returns to PPP 6, partially passes through it and builds a new image of brand 3 on FP 8 through lens 5, and is partially reflected from PPP 6 and again falls on APC 7. The process of re-reflection between APC 7 and STP 6 is repeated many times and depends on coefficients R and T of the PPP 8, dimensions and location of the AKZ 7 and PPP 6 relative to each other and the sighting axis of the lens 5. After multiple reflections from the PPP 6 and AKZ 7 towards the lens 5, several parallel beams of rays emerge, pairwise differing in the directions of propagation at an angle of 2ϕ (see Fig. 2).

As a result, several images of brand 3 are obtained on the FP 8 (see Fig. 3) with brightness decreasing as the serial number of the image increases.

An expression is known that relates the magnitude of the image shift and the angle of rotation of the mirror in the autocollimator:

d=2ftgα,

where

d - linear displacement of the brand image in the FP plane relative to the initial position, mm;

f - focal length of the lens, mm;

α is the angle of rotation of the mirror.

In the proposed AK, when rotating AKZ 7, several images of brand 3, formed by rays reflected from AKZ 7, are displaced in the area of AF 8 by an amount proportional to the tangent of the rotation angle (see Fig. 3). In this case, the linear displacement of the 1st image of the brand relative to the initial position when the mirror is rotated through an angle α is equal to:

di=ftg2α,

2nd:

d ₂ =2(ftg2α),

3rd:

d ₃ =3(ftg2α).

Total offset of n images:

D=N(ftg2α),

where N=(1+2+…+n) is the sum of the sequence numbers of the images used in the calculations.

From the above formulas, it can be seen that when using the second image of the brand to calculate the position of the AKZ, the sensitivity of the AK increases by 2 times, the third image - by 3 times, simultaneously the 1st, 2nd and 3rd - 6 times compared to AK, built according to a standard optical scheme, in which only one image of the brand is used.

The AK signal processing unit provides calculation of the AKZ rotation angle taking into account the above formulas and for each specific case allows you to quickly change the sensitivity and measurement range using one image of the brand, several images or all images of the brands that are in the field of view of the AK, depending on the problem being solved. specific task.

The calculation principles for determining the coordinates of the center of gravity of brand images, taking into account averaging over rows (columns) and over time relative to the coordinates of the matrix, are known.

раз, где n - число используемых при расчете изображений. При использовании 3-х изображений чувствительность возрастает в

раз.Also, to increase the sensitivity of the AK leads to a greater number of images used in the calculation of the angular position of the AKZ, compared with the prototype. In general, the sensitivity increases with

times, where n is the number of images used in the calculation. When using 3 images, the sensitivity increases in

once.

Thus, the calculation shows that when processing three images used in the proposed AK when determining the angular position of the AKZ, the overall sensitivity of the AK increases by about 10 times.

It is known that when measurements are taken with the required accuracy of fractions of an arc second, errors due to the displacement of elements in the optical path (CCD array, lens, etc.) for a conventional AK can reach comparable values. In practice, this leads to the need for a long preheating of the device, careful stabilization of the position of the AC itself during measurements.

In the claimed AK when measuring with a reference channel eliminates the systematic error associated with changing the position of the autocollimator or its elements. In this case, the measurements of the position of the AKZ take place relative to the position of the PPP, the stability of which is much easier to ensure, since it does not have internal heat sources, has smaller dimensions, and can be placed on an independent base. A slight shift of the AF, the optical elements of the AK or the AK itself during the measurement process leads to the fact that the images of the brand from the PPP and from the AKZ are shifted by the same amount, which eliminates the occurrence of a systematic error.

Also, systematic errors are partially compensated due to the uneven sensitivity of the FP elements and (or) point inhomogeneities of the optical elements due to the different location of the brand images on the FP site.

The claimed autocollimator makes it possible to obtain high sensitivity and, accordingly, high measurement accuracy in combination with high reliability of these measurements, since some systematic errors are excluded, with the small dimensions of the device itself.

According to the scheme (see Fig. 1), a model of a high-precision two-coordinate photoelectric autocollimator was created. An infrared LED (λ=0.87 µm) is used as a radiation source. The lens has a focal length of 300 mm; the photodetector is a CCD array of 1200×1920 photosensitive elements 4.8×4.8 µm in size. AK uses a stamp with a diameter of 0.1 mm. A PPP with a light diameter of 60 mm and a thickness of 10 mm is installed in front of the lens, on one side of which a dielectric coating is applied with a reflection coefficient of R = 40% and a transmission coefficient of T = 60% at a wavelength of 0.87 μm, on the other side - an antireflection coating with a reflection coefficient 0.1%. The PPP is installed perpendicular to the sighting axis of the AK in the horizontal plane and at an angle ϕ=5 arc. min. in the vertical plane. The signal processing unit calculates the angles of rotation of the ACZ from the signals received from the three images. The sensitivity to a change in the angle of the AKZ, when the AK is located at a distance of 100 mm from it, is 0.04 arc. sec. The measurement range of the horizontal angle is ± 6 arc. min, vertical angle - ± 1.5 arc. min.

Claims (7)

Autocollimator, including an optical system for forming an autocollimation image of a mark on a photodetector from a radiation source, placed along the beam of a condenser, a mark, a beam splitter, an objective, an autocollimation mirror and a photodetector with a signal processing unit, the mark and photodetector are installed in the focal planes of the lens, characterized in that between the lens and the autocollimation mirror on the optical axis, a semitransparent plane-parallel plate is additionally installed, located to the sighting axis of the autocollimator at an angle ϕ, selected from the condition: ϕ<b/kf, where b is the characteristic size of the photodetector, mm; f - focal length of the lens, mm; k≥4; and the signal processing unit is configured to calculate the position of the autocollimation mirror from the signals generated by several brand images.

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