Photoelectric autocollimator

Abstract

The photoelectric autocollimator comprises a beam splitter prism, a collimating objective lens located on one side, facing an object to be measured, of the beam splitter prism, a collimating ocular lens located on one side, back to the object to be measured, of the beam splitter prism, and a filter lens located on one side, facing an image plane of a detector, of the beam splitter prism, a reflector is arranged on one side, back to the beam splitter prism, of the collimator objective, the collimator objective is a transmission-type double-telecentric optical mechanism, and an aperture diaphragm is arranged in the middle of the collimator objective; a light source is arranged on one side, back to the spectroscope, of the collimating eyepiece, and the collimating eyepiece is a Cranisiden eyepiece; the centers of the collimator objective, the beam splitter prism and the collimator eyepiece are located on the same optical axis. Through transmission-type double-telecentric scheme design and athermal design calculation, different types of glass materials and structural materials are selected to be matched, and the temperature influence is eliminated through reasonable combination of the glass materials and the structural materials, so that the optical system is not influenced by the environment temperature, and the athermal effect is achieved.

Description

Technical Field

[0001] The present application relates to a photoelectric autocollimator, in particular to a photoelectric autocollimator with a long working distance, and belongs to the field of optical measuring instruments. Background Art

[0002] Photoelectric autocollimator is a precision optical measuring instrument, which is widely used in small angle measurement, parallelism and straightness measurement, base station flatness measurement, precision positioning measurement, small angle positioning, etc. Due to its advantages of high precision and ease of use, it occupies an important position in the field of precision measurement. However, the accuracy of existing photoelectric autocollimators is easily affected by the ambient temperature. When the ambient temperature changes suddenly, is too high or too low, the air mass will cause a slight refraction of the incident light, which is equivalent to placing a weak lens, causing a certain change in the position of the light spot, thereby affecting the measurement accuracy. Utility Model Content

[0003] In view of this, the present application provides a photoelectric autocollimator to solve the problem that the above-mentioned existing photoelectric autocollimator is easily affected by the ambient temperature and thus affects the measurement accuracy. The specific solution is:

[0004] A photoelectric autocollimator comprises: a beam splitter prism, a collimating objective lens located on the side of the beam splitter prism facing the object to be measured, a collimating eyepiece located on the side of the beam splitter prism facing away from the object to be measured, and a filter located on the side of the beam splitter prism facing the image plane of the detector;

[0005] A reflector is arranged on the side of the collimating objective lens facing away from the beam splitter prism, the collimating objective lens is a transmission type double telecentric optical structure, and an aperture stop is arranged in the middle of the collimating objective lens;

[0006] A light source is arranged on the side of the collimating eyepiece facing away from the beam splitter, and the collimating eyepiece is a Ramsden eyepiece;

[0007] The centers of the collimating objective lens, the beam splitting prism and the collimating eyepiece are located on the same optical axis.

[0008] Preferably, the collimating objective lens comprises: a first positive lens, a first negative lens, a second negative lens and a fourth positive lens, which are sequentially arranged along the optical axis from the object side to the imaging side of the beam splitter prism;

[0009] The aperture stop is disposed between the first negative lens and the second negative lens;

[0010] The reflecting mirror is located on a side of the first positive lens facing away from the first negative lens.

[0011] Preferably, the first positive lens is a biconvex lens;

[0012] The first negative lens is a biconcave lens with a notch facing the first positive lens;

[0013] The second negative lens and the second positive lens are meniscus lenses with opposite notches.

[0014] Preferably, the collimating eyepiece includes a third positive lens, a fourth positive lens and a graticule plate which are arranged in sequence along the optical axis from the light source to the imaging side of the dichroic prism; the light source is located on the side of the third positive lens facing away from the fourth positive lens.

[0015] Preferably, the third positive lens and the fourth positive lens are plano-convex lenses with convex surfaces facing each other, and the convex surface of the third positive lens faces the beam splitter prism;

[0016] The light source is located on one side of the plane of the third positive lens.

[0017] Preferably, the light source is an LED light source.

[0018] Preferably, the deflection angle of the reflector is determined according to the CMOS imaging situation.

[0019] Preferably, the first positive lens, the second negative lens and the second positive lens are all crown glass;

[0020] The first negative lens is made of flint glass.

[0021] The beneficial effects of this application include:

[0022] Through athermal design, different brands of optical glass materials are selected to match with structural materials such as aluminum alloy. The design ensures that the linear expansion coefficient of the supporting structure in direct contact with the optical element matches the linear expansion coefficient of the optical element, achieving the requirement that the optomechanical system can continue to maintain the overall performance of the optical system when the temperature changes, and solving the problem that the measurement accuracy is not affected by temperature changes.

[0023] The collimating eyepiece, the beam splitter prism and the collimating objective lens involved in the present application are arranged on the same optical axis, wherein the collimating objective lens is a transmissive double telecentric optical structure, and an aperture diaphragm is arranged in the middle of the collimating objective lens, so that the light entering and exiting the double telecentric lens must pass through the aperture center point of the aperture diaphragm, ensuring that the main light rays of the object side and the image side must enter the optical system parallel to the optical axis, so that the incident parallel light has a sufficiently large depth of field range, and the light coming out of the lens is parallel light, thereby ensuring that even if the working distance changes within the depth of field, the imaging height (i.e., the magnification) will not change, effectively solving the problems of low linearity within the measurement range and large changes in measurement accuracy when the measurement distance changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of the structure of a photoelectric autocollimator for this application;

[0025] Figure 2 Schematic diagram of the point diagram at the best image plane of the lens shown in Table 1 under normal temperature and pressure conditions in the embodiment of the present application;

[0026] Figure 3 Schematic diagram of the enclosing circle energy curve at the best image plane of the lens shown in Table 1 under normal temperature and pressure conditions in the embodiment of the present application;

[0027] Figure 4 Schematic diagram of the modulation transfer function MTF curve at the best image plane of the lens shown in Table 1 under normal temperature and pressure conditions in the embodiment of the present application;

[0028] Figure 5 Schematic diagram of the field curvature / distortion curve at the best image plane of the lens shown in Table 1 under normal temperature and pressure conditions in the embodiment of the present application;

[0029] Figure 6 Schematic diagram of the magnification chromatic aberration curve at the best image plane of the lens shown in Table 1 under normal temperature and pressure conditions in the embodiment of the present application;

[0030] Figure 7 Schematic diagram of the modulation transfer function MTF curve at the best image plane of the lens shown in Table 1 under the conditions of -40°C and normal pressure in the embodiment of the present application;

[0031] Figure 8 Schematic diagram of the modulation transfer function MTF curve at the best image plane of the lens shown in Table 1 under the conditions of -20°C and normal pressure in the embodiment of the present application;

[0032] Fig. 9 Schematic diagram of the modulation transfer function MTF curve at the best image plane of the lens shown in Table 1 under 0°C and normal pressure in the embodiment of the present application;

[0033] Fig.10 Schematic diagram of the modulation transfer function MTF curve at the best image plane of the lens shown in Table 1 under +40°C and normal pressure in the embodiment of the present application;

[0034] Fig.11 Schematic diagram of the modulation transfer function MTF curve at the best image plane of the lens shown in Table 1 under +60°C and normal pressure in the embodiment of the present application;

[0035] Fig.12 Schematic diagram of the modulation transfer function MTF curve at the best image plane of the lens shown in Table 1 under +80°C and normal pressure in the embodiment of the present application;

[0036] Fig.13 Schematic diagram of the modulation transfer function MTF curve at the best image plane of the lens shown in Table 1 under +100°C and normal pressure conditions in the embodiment of the present application;

[0037] Fig.14 Schematic diagram of the modulation transfer function MTF curve at the best image plane of the lens shown in Table 1 under normal temperature and pressure conditions in the embodiment of the present application when the object distance is infinite;

[0038] Fig.15 This is a schematic diagram of the modulation transfer function MTF curve at the best image plane of the lens shown in Table 1 when the object distance is 50m under normal temperature and pressure conditions in the embodiment of the present application;

[0039] Fig.16 This is a schematic diagram of the modulation transfer function MTF curve at the best image plane of the lens shown in Table 1 when the object distance is 10m under normal temperature and pressure conditions in the embodiment of the present application;

[0040] Fig.17 This is a schematic diagram of the modulation transfer function MTF curve at the best image plane of the lens shown in Table 1 when the object distance is 5m under normal temperature and pressure conditions in the embodiment of the present application;

[0041] Fig.18 Schematic diagram of the modulation transfer function MTF curve at the best image plane of the lens shown in Table 1 under normal temperature and pressure conditions in the embodiment of the present application when the object distance is 1m;

[0042] Fig.19 This is a schematic diagram of the modulation transfer function MTF curve at the best image plane of the lens shown in Table 1 when the object distance is 0.5m under normal temperature and pressure conditions in the embodiment of the present application;

[0043] Fig. 20 This is a schematic diagram of the modulation transfer function MTF curve at the best image plane of the lens shown in Table 1 when the object distance is 0.1m under normal temperature and pressure conditions in the embodiment of the present application;

[0044] List of parts and reference numerals:

[0045] 1. First positive lens; 2. First negative lens; 3. Aperture stop; 4. Second negative lens; 5. Second positive lens; 6. Beam splitter; 7. Filter; 8. Detector; 9. Beam splitter plate; 10. Fourth positive lens; 11. Third positive lens; 12. Light source. DETAILED DESCRIPTION

[0046] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0047] As attached Figure 1 The photoelectric autocollimator shown comprises a collimating eyepiece, a beam splitter prism 6, a collimating objective lens and a reflector which are sequentially arranged along the illumination light path of the light source;

[0048] The detector is located on one side of the folding surface of the beam splitter prism 6 (i.e., the side perpendicular to the optical axis), and a filter 7 is provided between the folding surface of the beam splitter prism 6 and the image plane of the detector 8;

[0049] The centers of the collimating eyepiece, the beam splitter prism 6, the collimating objective lens and the reflector are located on the same straight line (i.e., on the same optical axis);

[0050] In this embodiment, the light source 12 is an LED light source. The scattered light emitted by the light source is projected onto the beam splitter plate 9 of the collimating eyepiece through the collimating eyepiece, and then emitted in parallel to the reflector after passing through the collimating objective lens; then the reflector reflects the light signal carrying the angle deflection information back to the collimating objective lens, which is folded by the beam splitter prism 6 and focused on the CMOS image sensor to form an image.

[0051] In the present application, the collimating eyepiece includes: a third positive lens 11 with positive focal length, a fourth positive lens 10 with positive focal length, and a beam splitter plate 9, which are sequentially arranged along the optical axis from the irradiation direction of the light source to the direction of the beam splitter prism 6;

[0052] The beam splitter 9 is a scribed beam splitter graticule, which is located between the fourth positive lens and the beam splitter prism 6, and the light source 12 is located on the side of the third positive lens 11 facing away from the fourth positive lens 10;

[0053] The first positive lens and the second positive lens are plano-convex lenses with convex surfaces arranged opposite to each other, so that the object focus of the eyepiece is located outside the lens, which is convenient for setting the beam splitter plate 9; the Ramsden eyepiece form is used in the design of the two, which can correct the aberration well and ensure that the outgoing light beam after passing through the eyepiece can evenly illuminate the beam splitter plate 9.

[0054] The collimating objective lens comprises a first positive lens 1 with positive focal power, a first negative lens 2 with negative focal power, a second negative lens 4 with negative focal power, and a second positive lens 5 with positive focal power, which are sequentially arranged along the optical axis from the object side to the imaging side of the dichroic prism 6;

[0055] The reflector is located on the side of the first positive lens 1 with positive optical power facing away from the beam splitter prism 6;

[0056] The first positive lens 1 is a double convex lens, and its main function is to bear a large focal length, greatly change the trajectory of the incident light, and make the light converge; the first negative lens 2 is a double concave lens with the notch facing the first positive lens 1, which can diverge the light processed by the first lens, so that the incident angle of the light entering the subsequent lens becomes smaller; the second negative lens 4 and the second positive lens 5 are meniscus lenses with opposite notches, and the two are used in combination, so that the main light of the outgoing light beam is parallel to the optical axis on the image side, and a good telecentricity is obtained; thus, a transmission-type double telecentric optical structure is formed, and the aberration of the final image surface is basically 0;

[0057] At the same time, the aperture stop 3 is arranged between the first negative lens 2 and the second negative lens 4, and the centers of the first positive lens 1, the first negative lens 2, the aperture stop 3, the second negative lens 4 and the second positive lens 5 are all located on the same optical axis, so that the main light rays entering and exiting the double telecentric lens must pass through the center point of the aperture, thereby ensuring that the main light rays of the object side and the image side must enter the optical system parallel to the optical axis, leaving a sufficiently large depth of field range for the incident parallel light, so that the light coming out of the lens is parallel light, thereby ensuring that even if the working distance changes significantly within the depth of field range, the imaging height (i.e., the magnification) will not change, effectively solving the problem of low linearity within the measurement range and large changes in measurement accuracy when the measurement distance changes;

[0058] The collimating objective lens is designed after fully examining the problems of existing instruments, and a transmission type double telecentric design and athermal design calculation are selected. In this application, the first positive lens 1, the second negative lens 4, and the second positive lens 5 are all crown glass; the first negative lens 2 is flint glass. The structural material is steel (that is, the fixed structural member connecting each lens is aluminum alloy). According to the matching of each lens and the structural member, the thermal expansion and contraction caused by temperature are guaranteed, and the system can automatically compensate, so that different types of glass materials of each lens are matched with the structural member materials, and the temperature influence is eliminated through a reasonable combination of the two. Several characteristic temperature points are selected within the use temperature range, and an evaluation function is constructed for calculation and analysis. According to the calculation results, a suitable material is selected, which can ensure that the linear expansion coefficient of the supporting structural member in direct contact with the optical element matches the linear expansion coefficient of the optical element, and passive compensation of the optical system is realized to ensure that the optical system can continue to maintain the overall performance requirements of the system when the temperature changes, solve the problem that the measurement accuracy is not affected by temperature changes, and realize athermal design. It has the characteristics of simple and reliable structure, high assembly efficiency, etc., and is suitable for mass production.

[0059] In this embodiment, the beam splitter is a cubic beam splitter with a beam splitting ratio of R:T=5:5, which can transmit the measuring light beam emitted from the collimated eyepiece and reflect the light beam with the test data after being reflected by the reflector to be measured, thus realizing a dual light path design; the filter is used to selectively transmit a light beam of a specific wavelength and refuse to transmit the rest, thus effectively filtering out light waves not needed for imaging and improving the accuracy of the test results;

[0060] It should be noted that:

[0061] The photoelectric autocollimator in the present application adopts a reverse design, that is, the actual light is emitted by the LED light source, and after being homogenized and converged by the collimating eyepiece, it is projected onto the graticule at the focal plane of the collimating objective lens. After the light beam is collimated into a parallel light beam by the collimating objective lens, it is incident on the plane reflector in front. Then, the measuring light beam reflected by the plane reflector is emitted from the object side again. After passing through the collimating eyepiece, the main light of the outgoing light beam is parallel to the optical axis on the image side. After being reflected by the oblique surface of the dichroic prism, it is received by the focal plane of the detector, that is, the collimating objective lens can realize the sending and receiving functions at the same time.

[0062] Specifically, the actual light source is an output light beam from an LED light source 12, which passes through the third positive lens 11, the fourth positive lens 10, the beam splitter plate 9, the beam splitter prism 6, the second positive lens 5, the second negative lens 4, the aperture diaphragm 3, the first negative lens 2, the first positive lens 1, and is irradiated to the plane reflector in front of the first positive lens 1. Then the reflected light beam of the reflector passes through the first positive lens 1, the first negative lens 2, the aperture diaphragm 3, the second negative lens 4, the second positive lens 5, the beam splitter prism 6, the filter 7, and is received by the detector 8.

[0063] During actual testing, the deflection angle of the reflector can be determined through different situations of CMOS imaging. If the reflector is installed on the optical axis of the instrument, it can be determined whether the axis is horizontal. Specifically, the scattered light emitted by the light source is projected onto the graticule at the focal plane of the collimating eyepiece after passing through the collimating eyepiece, and then emitted in parallel after passing through the collimating eyepiece. The parallel light is irradiated onto the reflector to be measured, and the reflector reflects the light signal carrying the angle deflection information back to the collimating eyepiece, which is folded by the beam splitter and focused on the CMOS image sensor (i.e., the focal plane of the detector) to form an image. Then, the coordinates of the target image point are extracted by image processing means, and converted into angle information through geometric optics.

[0064] In one embodiment of the present application, as shown in Table 1, it is a basic parameter table of the collimating lens of the photoelectric autocollimator, wherein the units of the radius of curvature, thickness, and focal length are all in millimeters (mm);

[0065] Table 1 Basic parameters of collimating objective lens

[0066]

[0067] As shown in Table 2, it is a basic parameter table of the collimating eyepiece of the photoelectric autocollimator, where the units of the radius of curvature, thickness, and focal length are all in millimeters (mm);

[0068] Table 2 Basic parameters of collimating eyepiece

[0069]

[0070]

[0071] In order to verify that the function of the collimating lens of this application is not affected by the ambient temperature, the image quality of the collimating lens is evaluated through the following items:

[0072] Image quality evaluation of the collimating objective lens shown in Table 1 under normal temperature and pressure conditions:

[0073] As attached Figure 2 Shown is a schematic diagram of the point diagram at the best image plane of the collimating objective lens shown in Table 1 under normal temperature and pressure conditions.

[0074] Attached Figure 3 It is a schematic diagram of the modulation transfer function MTF curve at the best image plane of the collimating objective lens shown in Table 1 under normal temperature and pressure conditions.

[0075] Attached Figure 4 It is a schematic diagram of the field curvature / distortion curve at the best image plane of the collimating objective lens shown in Table 1 under normal temperature and pressure conditions.

[0076] Attached Figure 5 It is a schematic diagram of the magnification chromatic aberration curve at the best image plane of the collimating objective lens shown in Table 1 under normal temperature and pressure conditions.

[0077] The modulation transfer function (MTF) represents the relationship between the modulation degree and the number of line pairs per millimeter in the image, and can be used to reflect the imaging quality of the optical system. In particular, for the imaging system, it is the most comprehensive criterion for all performance judgments. Therefore, this application provides MTF curves at different temperatures (specifically: -40°C, -20°C, 0°C, +40°C, +60°C, +80°C and +100°C) to determine whether the imaging quality of the photoelectric autocollimator is qualified.

[0078] As attached Figure 6-13 Shown is a schematic diagram of the modulation transfer function MTF curve at the best image plane of the collimating objective lens shown in Table 1 under normal pressure conditions and temperatures of -40°C, -20°C, 0°C, +40°C, +60°C, +80°C and +100°C respectively.

[0079] Modulation transfer function (MTF) represents the relationship between modulation and the number of line pairs per millimeter in the image. It can be used to reflect the imaging quality of the optical system, especially for the imaging system. It is the most comprehensive criterion of all performance judgments. Figure 6-13 It can be seen that the MTF curves are all close to the diffraction limit, and the values ​​of the MTF curves at different operating temperatures (-40°C to +100°C) and the MTF curves at normal temperature and pressure do not change significantly. It can be concluded that the measurement accuracy of the photoelectric autocollimator involved in the present application is not affected by temperature changes.

[0080] Attached Figure 14-20The following are schematic diagrams of the modulation transfer function MTF curves at the best image plane of the lens shown in Table 1 under normal temperature and pressure conditions, when the object distance is infinite, when the object distance is 50m, when the object distance is 10m, when the object distance is 5m, when the object distance is 1m, when the object distance is 0.5m, and when the object distance is 0.1m;

[0081] This achieves two functions: one is to solve the temperature effect, and the other is to solve the problem of inaccurate measurement results when the distance between the reflector and the collimating lens (i.e., object distance) changes. The effect of object distance change is solved by the double telecentric structure, which is matched with the athermal design of temperature effect.

[0082] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A photoelectric autocollimator, characterized in that: include: A beam splitter prism, a collimating objective lens located on the side of the beam splitter prism facing the object to be measured, a collimating eyepiece located on the side of the beam splitter prism facing away from the object to be measured, and a filter lens located on the side of the beam splitter prism facing the image plane of the detector; A reflector is arranged on the side of the collimating objective lens facing away from the beam splitter prism, the collimating objective lens is a transmission type double telecentric optical structure, and an aperture stop is arranged in the middle of the collimating objective lens; A light source is arranged on the side of the collimating eyepiece facing away from the beam splitter, and the collimating eyepiece is a Ramsden eyepiece; The centers of the collimating objective lens, the beam splitting prism and the collimating eyepiece are located on the same optical axis.

2. A photoelectric autocollimator according to claim 1, characterized in that: The collimating objective lens comprises: a first positive lens, a first negative lens, a second negative lens and a second positive lens which are sequentially arranged along the optical axis from the object side to the imaging side of the beam splitter prism; The aperture stop is disposed between the first negative lens and the second negative lens; The reflecting mirror is located on a side of the first positive lens facing away from the first negative lens.

3. A photoelectric autocollimator according to claim 2, characterized in that: The first positive lens is a biconvex lens; The first negative lens is a biconcave lens with a notch facing the first positive lens; The second negative lens and the second positive lens are meniscus lenses with opposite notches.

4. The photoelectric autocollimator according to claim 1, characterized in that: The collimating eyepiece comprises a third positive lens, a fourth positive lens and a scribed graticule arranged in sequence along the optical axis from the light source to the imaging side of the beam splitter prism; the light source is located on the side of the third positive lens facing away from the fourth positive lens.

5. A photoelectric autocollimator according to claim 4, characterized in that: The third positive lens and the fourth positive lens are plano-convex lenses with convex surfaces facing each other, and the convex surface of the third positive lens faces the beam splitter prism; The light source is located on one side of the plane of the third positive lens.

6. The photoelectric autocollimator according to claim 1, characterized in that: The light source is an LED light source.

7. The photoelectric autocollimator according to claim 1, characterized in that: The deflection angle of the reflector is determined according to the CMOS imaging situation.

8. The photoelectric autocollimator according to claim 2, characterized in that: The first positive lens, the second negative lens and the second positive lens are all crown glass; The first negative lens is made of flint glass.

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