Self-referenced collimation optical path system based on polarized beam and method for calculating measured angle

Abstract

The present invention relates to a self-referenced collimating optical path system based on polarized light beams and a method for calculating a measured angle using the system. Light emitted by a light source is collimated into a parallel light beam and then irradiated onto a cross-shaped plate; a polarizing beam splitter prism splits the light beam irradiated onto the cross-shaped plate into two linearly polarized lights with mutually perpendicular polarization states; the linearly polarized light with a horizontal polarization direction passes through a quarter wave plate and a plane reflector, is reflected by a reference reflective surface, and returns to the polarizing beam splitter prism along the original path, and then is reflected by the polarizing beam splitter prism to enter a receiving optical path system for imaging; the linearly polarized light with a vertical polarization direction passes through a quarter wave plate, a window glass, and a measured reflective surface, is reflected by the measured reflective surface, and then returns to the polarizing beam splitter prism along the original path, and then is transmitted through the polarizing beam splitter prism to enter a receiving optical path system for imaging. The measured angle is calculated using the position difference between the reflected image of the measured surface and the reflected image of the reference surface, which effectively suppresses the influence of the change in the pointing direction of the laser beam on the measurement result.

Description

Technical Field

[0001] The invention belongs to the technical field of precision photoelectric measurement, and in particular relates to a self-reference collimating optical path system based on polarized light beams and a method for calculating a measured angle using the system. Background Art

[0002] The photoelectric autocollimator is an instrument that uses the principle of optical autocollimation to measure small angle changes. It can be divided into three parts: the autocollimation optical path system, the photoelectric receiving system, and the signal processing system. Among them, the autocollimation optical path system is used to emit and receive collimated light, the photoelectric receiving system is used to realize the conversion of photoelectric signals, and the signal processing system is used to complete signal preprocessing, target positioning, and calculation of deflection angles.

[0003] The basic principle of optical self-collimation angle measurement is: the light emitted by a monochromatic point light source is emitted parallel to the main optical axis after passing through the collimating optical system, and the emitted light is reflected by the object to be measured and returns to the optical system, and forms an image on the photosensitive surface of the photoelectric receiving system. If the reflective surface of the object to be measured is perpendicular to the main optical axis of the collimating optical system, the light returns along the original path, and the center of the image spot formed by the returning light on the photoelectric sensor is calibrated as the system zero position; when the normal direction of the reflective surface of the object to be measured is at an angle with the main optical axis of the optical system, there is a certain offset between the center of the reflected light image spot and the system zero position. According to the basic principles of geometric optics, the angle between the normal direction of the reflective surface of the object to be measured and the main optical axis of the optical system can be calculated through this offset.

[0004] Since semiconductor lasers have the advantages of good monochromaticity, strong energy, and easy to obtain optical systems with high resolution and long-distance measurement, semiconductor lasers are generally used as monochromatic light sources in high-precision autocollimation systems. However, the angular measurement accuracy of optical autocollimation systems that use semiconductor lasers as light sources is difficult to further improve, and inaccuracy occurs. The main reason for this phenomenon is that the semiconductor laser beam pointing has jitter, which is caused by the light-emitting mechanism of the semiconductor laser. The jitter of the beam pointing directly leads to the jitter of the collimated imaging position, which is the main obstacle to further improving the measurement accuracy of the autocollimation system. Therefore, how to reduce the impact of this beam pointing jitter on the measurement accuracy of the autocollimation system is the key to further improving the performance of the autocollimation system based on semiconductor lasers.

[0005] In addition, in the autocollimation system, affected by factors such as the reflective surface and distance, the light energy received by the photoelectric sensor varies greatly. Therefore, improving the dynamic range of the photoelectric sensor is the key to solving this problem. Summary of the invention

[0006] The purpose of the present invention is to provide a self-collimating optical path system with a self-reference function based on a polarized light beam and a method for calculating a measured angle using the system, which can effectively suppress the influence of the pointing jitter of a semiconductor laser light beam on the self-collimating optical system and improve the angle measurement accuracy of the self-collimating system.

[0007] The technical solution of the present invention is to provide a self-referenced collimating optical path system based on polarized light beams, which is special in that it includes a light source 9, a first collimating optical system, a cross-reticle plate 11, a polarizing beam splitter prism 12, a measured optical path system, a reference optical path system and a receiving optical path system;

[0008] The first collimating optical system is used to collimate the light emitted by the light source 9 into a parallel beam and then illuminate the cross-reticle plate 11;

[0009] The polarization beam splitter prism 12 is used to split the light beam after irradiating the cross-reticle plate 11 into two linear polarized lights with polarization states perpendicular to each other, wherein one of the linear polarized lights is transformed into a linear polarized light with a horizontal polarization direction after passing through the polarization beam splitter prism 12, and serves as the parallel light of the second collimating optical system in the receiving optical path system, and the other linear polarized light is transformed into a vertical linear polarized light after being reflected by the polarization beam splitter prism 12;

[0010] The reference optical path system is located in the outgoing optical path of the linear polarized light with a horizontal polarization direction, and the measured optical path system is located in the outgoing optical path of the linear polarized light with a vertical polarization direction;

[0011] The reference optical path system includes a quarter wave plate 4, a plane reflector 3 and a reference reflective surface 2 arranged in sequence along the optical path. The linearly polarized light with a horizontal polarization direction passes through the quarter wave plate 4 and the plane reflector 3, and then is reflected by the reference reflective surface 2 and returns to the polarization beam splitter prism 12 along the original path. Since the light passes through the quarter wave plate 4 twice, the polarization state changes by 90 degrees, and finally is reflected by the polarization beam splitter prism 12 and enters the receiving optical path system for imaging.

[0012] The above-mentioned measured optical path system includes a 1 / 4 wave plate 4, a window glass 7 and a measured reflecting surface 1 arranged in sequence along the optical path. The linearly polarized light with a vertical polarization direction passes through the 1 / 4 wave plate 4, the window glass 7 and the measured reflecting surface 1, and returns to the polarization splitter prism 12 along the original path after being reflected by the measured reflecting surface 1. In the meantime, since it passes through the 1 / 4 wave plate 4 twice, the polarization state changes by 90 degrees, and finally passes through the polarization splitter prism 12 to enter the receiving optical path system for imaging.

[0013] The same graticule is used in the two-way optical system. After passing through the two-way optical system, the graticule will finally obtain two images in the photoelectric imaging system. The position difference between the two images is calculated using algorithms such as image processing and pixel subdivision, and the measured angle is calculated using this difference.

[0014] Preferably, the above-mentioned receiving optical path system includes a second collimating optical lens 5 and a photoelectric conversion device 6 arranged in sequence along the optical path. The photosensitive surface of the above-mentioned photoelectric conversion device 6 is located on the focal plane of the second collimating optical lens 5, the photosensitive surface of the photoelectric conversion device 6 is perpendicular to the optical axis, and the center of the photosensitive surface is located on the optical axis.

[0015] Preferably, because the collimating optical systems involved in the present invention are all two-dimensional systems, the photoelectric conversion device 6 of the present invention adopts a high-sensitivity area array photoelectric sensor, such as: EMCCD or SCMOS. At the same time, the use of a high-sensitivity area array photoelectric sensor can improve the dynamic range of measurement and maintain a high measurement accuracy when the reflected light intensity is weak.

[0016] Preferably, the system further comprises a pinhole stop 10, wherein the pinhole stop 10 is located between the light source 9 and the first collimating optical system.

[0017] Preferably, the first collimating optical system comprises a first collimating optical lens, and the light source 9 is located on the focal plane of the first collimating optical lens.

[0018] Preferably, the light source 9 is a monochromatic light source 9 .

[0019] The present invention also provides a method for calculating a measured angle using the self-reference collimating optical path system based on a polarized light beam, comprising the following steps:

[0020] Step 1: Adjust the direction of the reference reflective surface 2 so that the reference image is located at the center of the photosensitive surface of the receiving optical path system;

[0021] Step 2: collimate the light emitted by the light source 9 and illuminate the cross-shaped reticle 11;

[0022] Step 3: Use the polarization beam splitter prism 12 to split the light beam after irradiating the cross-reticle plate 11 into two linear polarized lights with polarization states perpendicular to each other, wherein one linear polarized light is reflected by the polarization beam splitter prism 12, and the other linear polarized light is transmitted by the polarization beam splitter prism 12;

[0023] Step 4: Adjust the polarization state of the linear polarized light reflected by the polarization beam splitter prism 12 and then irradiate the measured reflective surface 1 through the window glass 7, and then return to the polarization beam splitter prism 12 along the original path after being reflected by the measured reflective surface 1, and then be transmitted by the polarization beam splitter prism 12 and imaged on the photoelectric sensor after being collimated;

[0024] After adjusting the polarization state of the linearly polarized light transmitted by the polarization beam splitter prism 12, the linearly polarized light is irradiated on the reference reflection surface 2, and then reflected by the reference reflection surface 2 and returned to the polarization beam splitter prism 12 along the original path. After being reflected by the polarization beam splitter prism 12, the linearly polarized light is collimated and imaged on the photoelectric sensor.

[0025] Step 5: Use image processing and pixel subdivision algorithm to calculate the position difference between the two images obtained in step 4, and use the difference to calculate the measured angle.

[0026] During the measurement process, if there is a large difference in brightness between the measured image and the reference image, the measured image is collected using the high-gain mode of the high-sensitivity area array photoelectric sensor, and the reference image is collected using its low-gain mode.

[0027] The present invention also provides a photoelectric autocollimator, which is special in that it comprises the above-mentioned self-reference collimation optical path system based on polarized light beam.

[0028] Before measuring the angle, the measured reflective surface and the reference reflective surface can be adjusted to be parallel. The specific method is to adjust the reference reflective surface until the images formed by the reference reflective surface and the measured reflective surface overlap. If the reference reflective surface and the measured reflective surface are not adjusted to be parallel before measurement, the position difference between the images formed by the reference reflective surface and the measured reflective surface is first recorded before measurement, and the position difference between the two is recorded again after measurement, and finally the measurement angle is calculated using the two position differences.

[0029] The beneficial effects of the present invention are:

[0030] 1. The present invention uses the position difference between the reflected image of the measured surface and the reflected image of the reference surface to calculate the measured angle. When the direction of the laser beam changes, the reflected image of the measured surface and the reflected image of the reference surface move at the same time and in the same direction, which effectively suppresses the influence of the change of the laser beam direction on the measurement result;

[0031] 2. The present invention uses a high-sensitivity array photoelectric sensor device 6 as a receiving device to improve the signal-to-noise ratio of the receiving system, improve the dynamic range of detection, and ultimately improve the use range of the measurement system. When the reflected light intensity is weak, it still maintains a high measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the optical path of the present invention;

[0033] The reference numerals in the figure are: 1-measured reflecting surface, 2-reference reflecting surface, 3-plane reflecting mirror, 4-1 / 4 wave plate, 5-second collimating optical lens, 6-photoelectric conversion device, 7-window glass, 8-first collimating optical lens, 9-light source, 10-pinhole aperture, 11-cross-grid plate, 12-polarization splitter prism. DETAILED DESCRIPTION

[0034] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0035] from Figure 1It can be seen that the present invention has a high-precision, high signal-to-noise ratio self-collimating optical path system with a self-reference function, including a light source 9, a pinhole aperture 10, a first collimating optical lens 8, a cross-graticule plate 11, a polarization beam splitter prism 12, a measured optical path system, a reference optical path system and a receiving optical path system; this optical path system can be used for a photoelectric autocollimator.

[0036] The receiving optical path system includes a second collimating optical lens 5 and a photoelectric conversion device 6 which are sequentially arranged along the optical path. The photosensitive surface of the photoelectric conversion device 6 is arranged on the focal plane of the second collimating optical lens 5. The photosensitive surface of the photoelectric conversion device 6 is perpendicular to the optical axis of the optical system, and the center of the photosensitive surface is located on the optical axis. The photoelectric conversion device 6 adopts a high-sensitivity array photoelectric sensor, such as EMCCD or SCMOS.

[0037] The measured optical path system includes a 1 / 4 wave plate 4, a window glass 7 and a measured reflective surface 1 arranged in sequence along the optical path; the reference optical path system includes a 1 / 4 wave plate 4, a plane reflector 3 and a reference reflective surface 2 arranged in sequence along the optical path.

[0038] The light source 9 is a monochromatic light source, which refers to laser light generated by a semiconductor laser, etc. The point light source 9 emitted through the pinhole aperture 10 is located in the light path of the light source and is arranged on the focal plane of the first collimating optical lens 8.

[0039] The system includes a two-path collimation imaging system based on the same light source 9, wherein the first path is used for measuring the collimation imaging of the measured reflection surface 1, and its optical path process is as follows: point light source 9-pinhole aperture 10-first collimation optical lens 8-cross-graticule plate 11-polarization beam splitter prism 12-1 / 4 wave plate 4-window glass 7-measured reflection surface 1-window glass 7-1 / 4 wave plate 4-polarization beam splitter prism 12-second collimation optical lens 5-photoelectric receiving system; the second path is used for collimation imaging of the reference reflection surface 2, and its optical path process is as follows: point light source 9-pinhole aperture 10-first collimation optical lens 8-cross-graticule plate 11-polarization beam splitter prism 12-1 / 4 wave plate 4-plane reflector 3-reference reflection surface 2-plane reflector 3-1 / 4 wave plate 4-polarization beam splitter prism 12-second collimation optical lens 5-photoelectric receiving system.

[0040] The measurement process is as follows: the light source 9 emits light, which forms a point light source after passing through the pinhole diaphragm 10, and is collimated into a parallel light beam by the first collimating optical lens 8, and then irradiates the cross-shaped graticule 11, and then passes through the polarization beam splitter prism 12, and the parallel light beam is divided into two linearly polarized lights, one of which becomes a horizontally polarized linearly polarized light after transmission (corresponding to the e-light emitted by the birefringent crystal), and the other is reflected and becomes a vertically linearly polarized light (corresponding to the o-light emitted by the birefringent crystal).

[0041] Among them, the horizontal linear polarized light (i.e., e-light) transmitted by the polarization beam splitter prism 12 passes through the 1 / 4 wave plate 4, is reflected by the plane reflector 3 and the reference reflective surface 2, and then returns to the original path. After passing through the 1 / 4 wave plate 4 again, it becomes vertical linear polarized light (corresponding to the o light emitted by the birefringent crystal). The vertical linear polarized light (i.e., o light) is reflected by the polarization beam splitter prism 12 and enters the second collimating optical lens 5. The second collimating optical lens 5 images the parallel light on the photosensitive surface of the photoelectric converter of the light receiving system (reference image); on the other hand, the vertical linear polarized light (i.e., o light) reflected by the polarization beam splitter prism 12 passes through the 1 / 4 wave plate 4, passes through the device window glass 7, and then returns from the measured reflective surface 1, passes through the window glass 7 and the 1 / 4 wave plate 4 again, becomes e light, and after transmitting through the polarization beam splitter prism 12, it is imaged on the photosensitive surface of the photoelectric sensor by the second collimating optical lens 5 (measured image).

[0042] Before measurement, adjust the direction of the reference reflective surface 2 so that the reference image is located at the center of the photosensitive surface. During measurement, if the brightness difference between the measured image and the reference image is large, use the high-gain mode of the high-sensitivity array photoelectric sensor to collect the measured image, and use its low-gain mode to collect the reference image. During measurement, the measured angle is calculated based on the position difference between the measured image and the reference image and the optical system parameters.

Claims

1. A self-referenced collimation optical path system based on polarized beams, Features: It comprises a light source (9), a first collimating optical system, a cross-reticle plate (11), a polarization beam splitting prism (12), a measured optical path system, a reference optical path system and a receiving optical path system; The first collimating optical system is used to collimate the light emitted by the light source (9) into a parallel light beam and then illuminate the cross-reticle plate (11); The polarization beam splitter prism (12) is used to split the light beam irradiated by the cross-reticle plate (11) into two beams of linear polarized light with polarization states perpendicular to each other, wherein one beam of linear polarized light is transformed into linear polarized light with a horizontal polarization direction after being transmitted through the polarization beam splitter prism (12), and the other beam of linear polarized light is transformed into vertical linear polarized light after being reflected by the polarization beam splitter prism (12); The reference optical path system is located in the outgoing optical path of linear polarized light with a horizontal polarization direction, and the measured optical path system is located in the outgoing optical path of linear polarized light with a vertical polarization direction; The reference optical path system comprises a quarter wave plate (4), a plane reflector (3) and a reference reflective surface (2) which are sequentially arranged along the optical path; linearly polarized light with a horizontal polarization direction passes through the quarter wave plate (4) and the plane reflector (3), is reflected by the reference reflective surface (2) and returns along the original path to the polarization beam splitter prism (12), and then is reflected by the polarization beam splitter prism (12) and enters the receiving optical path system for imaging; The measured optical path system comprises a quarter wave plate (4), a window glass (7) and a measured reflective surface (1) arranged in sequence along the optical path; linearly polarized light with a vertical polarization direction passes through the quarter wave plate (4), the window glass (7) and the measured reflective surface (1), is reflected by the measured reflective surface (1) and returns to the polarization beam splitter prism (12) along the original path, and then is transmitted through the polarization beam splitter prism (12) into the receiving optical path system to form an image.

2. A self-referenced collimating optical path system based on polarized light beam according to claim 1, Features: The receiving optical path system comprises a second collimating optical lens (5) and a photoelectric conversion device (6) arranged in sequence along the optical path, wherein the photosensitive surface of the photoelectric conversion device (6) is located on the focal plane of the second collimating optical lens (5), the photosensitive surface of the photoelectric conversion device (6) is perpendicular to the optical axis, and the center of the photosensitive surface is located on the optical axis.

3. A self-referenced collimated optical path system based on polarized light beam according to claim 2, Features: The photoelectric conversion device (6) adopts a high-sensitivity array photoelectric sensor.

4. A self-referenced collimating optical path system based on polarized light beam according to claim 3, Features: The high-sensitivity area array photoelectric sensor is EMCCD or SCMOS.

5. A self-referenced collimating optical path system based on polarized light beam according to claim 4, Features: It also comprises a pinhole stop (10), wherein the pinhole stop (10) is located between the light source (9) and the first collimating optical system.

6. A self-referenced collimating optical path system based on polarized light beam according to claim 5, Features: The first collimating optical system comprises a first collimating optical lens (8), and the light source (9) is located on the focal plane of the first collimating optical lens (8).

7. A self-referenced collimating optical path system based on polarized light beam according to any one of claims 1 to 6, Features: The light source (9) is a monochromatic light source.

8. A method for calculating a measured angle using a self-referenced collimated optical path system based on a polarized light beam as described in any one of claims 1 to 7, It is characterized in that The following steps are involved: Step 1: Adjust the direction of the reference reflective surface so that the reference image is located at the center of the photosensitive surface of the receiving optical path system; Step 2: Collimate the light emitted by the light source and illuminate the cross-reticle; Step 3: Use a polarization beam splitter prism to split the light beam after irradiating the cross-reticle into two linear polarized lights with polarization states perpendicular to each other, one of which is reflected by the polarization beam splitter prism, and the other is transmitted by the polarization beam splitter prism; Step 4: Adjust the polarization state of the linear polarized light reflected by the polarization beam splitter prism and then illuminate the measured reflective surface through the window glass. After being reflected by the measured reflective surface, it returns to the polarization beam splitter prism along the original path. After being transmitted by the polarization beam splitter prism, it is collimated and imaged on the photoelectric sensor. After adjusting the polarization state of the linearly polarized light transmitted by the polarization beam splitter prism, the light is irradiated on the reference reflection surface, and then reflected by the reference reflection surface, returns to the polarization beam splitter prism along the original path, and after being reflected by the polarization beam splitter prism, is collimated and imaged on the photoelectric sensor; Step 5: Use image processing and pixel subdivision algorithm to calculate the position difference between the two images obtained in step 4, and use the difference to calculate the measured angle.

9. A method for calculating a measured angle using a self-referenced collimated optical path system based on a polarized light beam according to claim 8, Features: During the measurement process, if there is a large difference in brightness between the measured image and the reference image, the measured image is collected using the high-gain mode of the high-sensitivity area array photoelectric sensor, and the reference image is collected using its low-gain mode.

10. A photoelectric autocollimator, Features: It comprises the self-referenced collimating optical path system based on polarized light beam as described in any one of claims 1-7.

Images