CN106767545A - A kind of high accuracy high-space resolution angel measuring instrument and angle measurement method - Google Patents

Abstract

The invention discloses a kind of high accuracy high-space resolution angel measuring instrument and angle measurement method.Measuring instrument of the invention includes：Light source, produces locational space and all uniform light field in angle space；Light bar, confine optical beam bore；Camera lens, for the light beam that focused subbeams and collection are turned back；Speculum to be measured；Spectroscope, for that will turn back, light beam reflexes to detector plane；Detector array, the image for recording light beam pattern of being turned back on front focal plane；Data processing display module.Structure of the present invention can solve the problem that and measured at sample surfaces that existing optical angle measurement instrument (such as autocollimator etc.) is faced the big problem of spot size, further, this equipment can be scanned for long-range profile, so as to obtain the face graphic data of testing sample.Meanwhile, position or defocus error of the system to sample, lens aberration are insensitive, are adapted to the high-acruracy survey of a small range.

Description

A high-precision and high-spatial resolution angle measuring instrument and angle measuring method

technical field

The invention relates to angle measurement based on optical means, which can be expanded to measure mirror surface shape, and in particular relates to an angle measuring instrument with high precision and high spatial resolution and an angle measuring method.

Background technique

High-precision angle measurement technology has very important application value in many engineering fields. For example, high-precision equipment requires high-precision attitude adjustment. Especially in the field of synchrotron radiation, the surface of the component can be obtained by measuring and integrating the inclination of the surface Face shape etc. Angle measuring devices based on optical methods have the great advantage of being non-contact and not affecting the characteristics of the workpiece/system, and are widely used. The main angle measurement equipment includes electronic autocollimator and angle measurement method based on laser interferometry. Since they use a collimated beam to scan the sample, in order to ensure sufficient signal-to-noise ratio and positioning accuracy, the spot size of the scanning beam or the sampling spot size on the sample surface is generally relatively large. For example, the optical head structure in the long-range surface profiler uses the angle measurement method of laser interference. Since the size of the sampling spot is 1–2mm, for each sampling point, the measured angle is the average result of the illumination area of the spot .

In short, if the lateral period of the profile change is less than 1mm (rapid change), this change cannot be accurately measured. From a frequency perspective, higher frequency surface information cannot be measured. However, this information is very important for the quality assessment of the specular surface shape and the performance assessment of the system to which it is applied.

Contents of the invention

Aiming at the technical problems existing in the prior art, the object of the present invention is to provide a high-precision and high-spatial-resolution angle measuring instrument and an angle measuring method. The optical system architecture of the present invention includes:

The light source 11 generates a light field that is uniform in position space and angular space. Realization methods: (1) For incoherent light sources, such as LEDs, use optical fiber or other methods to uniformly light to produce light with uniform spatial distribution and uniform distribution of exit angles; use small holes to limit the area of the light source. (2) The coherent light source is transmitted and output through a single-mode polarization-maintaining optical fiber.

Light barrier 12, limiting beam aperture;

The lens 14 is used to focus the illumination beam, generate a small sampling spot, and collect the beam returned from the reflector 15 to be tested;

The position of the mirror 15 to be tested can be adjusted at will, and can be on the imaging surface of the lens 14. At this time, the test sampling spot is the smallest, so the spatial resolution is higher. It can also be used in other defocus planes, only the spatial resolution will be changed, and the test accuracy will not be affected;

The beam splitter 13 separates the illumination light path and the detection light path, that is, the illumination light beam is transmitted, and the reentrant light beam is reflected to the detection unit plane;

The detector unit 16 is a detector array, located on the front focal plane of the lens, for recording the image of the reentrant light beam;

The data processing component 17 calculates the relative displacement of the light spot caused by the angle change of the mirror under test according to the recorded image, and then deduces the angle change of the mirror under test based on this, and displays the final measurement result.

Function realization mechanism:

The divergent light emitted by the light source first passes through the fixed aperture, and then the illuminating beam of a certain caliber passes through the beam splitter and reaches the lens. After being focused by the lens, it irradiates the surface of the mirror to be tested. The distance between the position of the mirror to be tested and the distance of the converging point determines the size of the sampling spot.

The light beam returned by the reflector passes through the lens, is reflected by the beam splitter, and finally reaches the detector plane and is photoelectrically converted into an electronic image. According to the displacement (Δx, Δy) of the light spot in the image detected by the detector before and after the angle change of the mirror to be tested, the angle change information (Δx/2f, Δy/2f) of the test mirror can be obtained, where f is the focal length of the lens.

Compared with prior art, positive effect of the present invention is:

This structure can solve the problem of large measurement spot size on the sample surface faced by existing optical angle measuring instruments (such as autocollimators, etc.), and further, this device can be used for long-distance surface scanning to obtain the sample surface data. At the same time, the system is insensitive to sample position or defocus error, lens aberration, and is suitable for high-precision measurement in a small range.

As shown in FIG. 4 , the present invention has higher spatial resolution capability. The spot size used in the example is 0.1mm, and the sampling step is 0.1mm. The angular distribution on such a small spatial scale can be clearly observed.

Description of drawings

Fig. 1 is angle measuring instrument of the present invention;

Among them, 10-scanning optical head, 11-light source, 12-optical barrier, 13-beam splitter, 14-lens, 15-mirror to be tested, 16-detection unit, 17-data processing component, 18-illumination light, 19 - return beam;

Fig. 2 is a structural diagram of the light source of the present invention;

(a) is a coherent light source system, wherein, 21-laser, 22-coupling lens, 23-optical fiber;

(b) is an incoherent light source system, wherein, 24-light-emitting diodes, small hole aperture-25;

Fig. 3 is the surface profiler scanning system;

Among them, 31-object to be measured, 32-high-precision air bearing translation stage, 33-large-diameter mirror, 34-electronic autocollimator;

Figure 4 is the measurement result of the surface profiler;

(a) The measured surface slope curve, (b) the result of the integral processing of the curve.

detailed description

The present invention is described in further detail below in conjunction with accompanying drawing:

The angle measuring instrument with high precision and high spatial resolution of the present invention is as shown in Figure 1, and its structure comprises: light source 11, produces the all uniform light field of position space and angle space; Focusing the illumination beam and collecting the returned beam; the reflector to be tested; the spectroscope 13, used to reflect the returned beam to the detector plane; the detector array 16, used to record the image of the returned beam shape on the front focal plane; data processing Component 17 calculates the relative displacement of the spot caused by the angle change of the mirror to be measured according to the recorded image, and then deduces the angle change of the mirror 15 to be tested based on this, and displays the final measurement result; centroid method, correlation algorithm, etc. can be used The method calculates the change of the center of mass, and the present invention adopts an algorithm based on the center of mass.

Displacement and angle algorithm: record the images A, B before and after the angle change of the mirror to be tested. Use the centroid method to calculate the centroid of the spot separately, that is, calculate

Where I _i,j is the optical signal intensity of the (i,j)th pixel, x _i,j and y _i,j are the spatial coordinates of the (i,j)th pixel, M and N are used for data processing The number of horizontal and vertical pixels of the image. The centroids in image A and image B are (x _A , y _A ) and (x _B , y _B ) calculated sequentially, and finally the angle of the test mirror can be obtained as:

where f is the focal length of the lens.

The specific structure of the light source 11 of the present invention is as shown in Figure 2, and the implementation method: (1) adopt a coherent light source as shown in Figure 2 (a), including a laser 21, a coupling lens 22 and an optical fiber 23, and directly couple the light of the laser 21 into the optical fiber , is transmitted and output through the optical fiber, and the optical field can be generated under the premise that the optical fiber is long enough and the end surface is smooth. (2) Adopting an incoherent light source as shown in FIG. 2( b ), including a light emitting diode 24 and an aperture diaphragm 25 . Or use optical fiber or other methods to homogenize the light to produce light with uniform spatial distribution and uniform distribution of exit angles; use small holes to limit the area of the light source.

Applications:

(1) Angle measurement (in principle, only angle measurement)

Measure the angle of rotation of the target mirror as previously described

(2) Surface shape measurement (application, angle measurement, integration to obtain)

Referring to FIG. 3 , the high spatial resolution long-range surface shape detection system includes: an object to be measured 31 , a high-precision air bearing translation stage 32 , a scanning optical head 10 , a large-diameter mirror 33 , and an electronic autocollimator 34 .

The scanning optical head 10 is shown in FIG. 3 . The scanning optical head 10 and the large-aperture mirror 33 move with the high-precision air bearing translation stage 32 . The focused light beam 35 formed by the internal optical path structure of the scanning optical head 10 scans the object 31 to be measured, and the returned light beam 36 enters the scanning optical head 10 again and is detected. The electronic autocollimator 34 is fixed outside the scanning optical head 10 , and the electronic autocollimator 34 measures the angle change of the beam emitted by the electronic autocollimator 34 after being reflected by the large-aperture mirror 33 , so as to obtain the rotation angle error β _OH of the scanning optical head 10 . The beam position change measured by the detector in the optical head can be expressed as:

x _samp = 2x _{0, samp} +2f(β _sut +β _OH )

During the scanning process, the constant Const=2× _{0, samp} will not reflect the change of the surface inclination of the object 31 to be measured. Finally, the inclination change of the surface of the object 11 to be measured can be obtained as:

Figure 4 shows the results of a sample inclination measurement with a scan step of 0.1 mm. Figure 4(a) is the measured surface inclination curve, and Figure 4(b) is the differential calculation of the curve in Figure 4(a), the statistical standard deviation is 40nrad rms.

Claims (10)

1. a high-precision high-spatial resolution angle measuring instrument is characterized in that, comprising a light source (11), a beam splitter (13), a lens (14), a detector unit (16) and a data processing assembly (17), wherein, The light emitted by the light source (11) enters the lens (14) through the beam splitter (13); The lens (14) is used to focus the incident light of the beam splitter (13) to the reflector (15) to be measured, and to collect the return light beam from the reflector (15) to be measured; A beam splitter (13), used to reflect the returned light beam to the detector unit (16); A detector unit (16), used to record the image of the returned light beam; The data processing component (17) is connected with the detector unit (16), and is used for calculating the angle change of the reflector (15) to be measured according to the recorded image. 2. The high-precision and high-spatial-resolution angle measuring instrument according to claim 1, characterized in that, the light source (11) is a light source capable of generating a light field that is uniform in positional space and angular space. 3. the high precision high spatial resolution angle measuring instrument as claimed in claim 1 or 2, is characterized in that, described light source (11) is a coherent light source system, and it comprises laser (21), coupling lens (22) and optical fiber (23); wherein, the laser light output by the laser (21) is incident into the optical fiber (23) through the coupling lens (22), and the light emitted through the optical fiber (23) enters the lens (14) through the beam splitter (13). 4. the high precision and high spatial resolution angle measuring instrument as claimed in claim 1 or 2, is characterized in that, described light source (11) is an incoherent light source system, and it comprises light-emitting diode (24) and pinhole diaphragm ( 25); wherein, the laser light output by the light-emitting diode (24) is incident on the beam splitter (13) through the aperture diaphragm (25). 5. The high-precision and high-spatial resolution angle measuring instrument according to claim 1, characterized in that a light bar (12) is arranged between the light source (11) and the beam splitter (13). 6. high precision high spatial resolution angle measuring instrument as claimed in claim 1, is characterized in that, detector unit (16) is positioned on the front focal plane of lens (14); Reflector to be measured (15) is positioned at lens (14) ) on the imaging plane or the defocused plane. 7. A method for measuring angles with high precision and high spatial resolution, the steps of which are: 1) The light emitted by the light source (11) enters the lens (14) through the beam splitter (13); 2) the lens (14) focuses the incident light through the beam splitter (13) to the reflector (15) to be tested, and the reentrant light beam from the reflector to be measured (15) is incident to the beam splitter (13); 3) The beam splitter (13) reflects the returned light beam to the detector unit (16); 4) The detector unit (16) sends the image of the returned light beam to the data processing component (17); 5) Adjust the angle of the mirror to be tested (15), and the detector unit (16) regenerates the image of the reflected beam of the mirror to be tested (15) and sends it to the data processing component (17); 6) The image received twice by the data processing component (17) is calculated to obtain the angle change of the mirror to be measured (15). 8. The method according to claim 7, characterized in that the light source (11) is a light source capable of generating a light field that is uniform in position space and angular space. 9. The method according to claim 7, characterized in that a light barrier (12) is provided between the light source (11) and the beam splitter (13). 10. method as claimed in claim 7 is characterized in that, detector unit (16) is positioned on the front focal plane of lens (14); on the focal plane.