A method and system for monitoring the coaxiality between axes of a horizontal solar telescope

Abstract

The present application belongs to the technical field of optomechanical adjustment and precision tracking control of astronomical telescopes. The present invention discloses a method and system for monitoring the coaxiality between the axis systems of an horizontal solar telescope, and uses the method and system to measure and monitor the changes of the axis systems of the horizontal solar telescope, thereby reducing the range of movement of the optical axis within the Coode focal plane, improving the long-term tracking accuracy of the telescope for the target observed on the solar surface, and ensuring the smooth development and normal operation of the telescope. The present invention solves the difficult problem of real-time monitoring of the coaxiality between the axis systems of an horizontal solar telescope, and provides a technical means for monitoring the coaxiality and its changes between the axis systems during the optomechanical adjustment and operation stages of the development of the horizontal solar telescope. Based on the optomechanical structural characteristics of large solar telescopes at home and abroad, and combined with the current development of related technologies, the present invention proposes a quick method and corresponding system for real-time monitoring of the coaxiality between the axis systems of an horizontal solar telescope.

Description

Technical Field

[0001] The present application belongs to the technical field of optical-mechanical adjustment and precision tracking control of astronomical telescopes, and in particular to a method and system for monitoring the coaxiality between the axes of a horizontal solar telescope. Background Art

[0002] A solar telescope is an astronomical device for observing the sun. It has complex and precise filters, spectrometers, polarization measurement and other terminal scientific instruments installed at the focal plane of its imaging, which are used to obtain, process and analyze solar information, and then provide it to scientists for solar research. Since solar telescopes have very high requirements for the stability of these terminal scientific instruments, large-aperture (meter-level) solar telescopes usually use Gregorian optical systems, and place their terminal scientific instruments on the Coode focal plane that does not rotate with the telescope frame. A thermal stop is placed at the Gregorian focus for heat treatment to limit most of the sunlight from entering the back-end system, so that only a local area on the solar disk can be observed. In order to reduce the heating of the atmosphere in the optical path of the telescope by the thermal stop, which generates random turbulence and deteriorates the imaging quality of the telescope, the solar telescope requires a special design: first, the main body of the optical system is installed in a vacuum tube, such as my country's one-meter New Vacuum Solar Telescope NVST and Sweden's 1-meter SST; second, the main body of the optical system adopts an off-axis optical system, such as my country's one-meter AIMS and the United States' 1.6-meter GST and 4-meter DKIST; third, the main body of the optical system adopts a solar telescope with a symmetrical optical path, but the thermal control system at the Gregorian focus has very high requirements, such as my country's 1.8-meter CLST, Germany's 1.5-meter GREGOR, etc.

[0003] On the other hand, in order to offset the apparent diurnal motion of celestial bodies caused by the rotation of the earth and ensure that the observed target is always stable in the center of the telescope's field of view, the astronomical telescope requires that the various axis systems of the telescope rotate precisely and smoothly, cooperate with each other to achieve accurate pointing (alignment) of the observed target and track it for a long time with high precision. Pointing and tracking accuracy is one of the important indicators to measure the performance of an astronomical telescope. The RMS value of the pointing error is usually required to be less than 10 arc seconds, and the RMS value of the tracking error is usually required to be less than 1 arc second. However, the pointing and tracking accuracy is affected by many factors. First, it is related to the observed target. For example, for a solar telescope, in addition to considering the apparent diurnal motion of the earth, it is also necessary to consider the revolution of the earth and the rotation of the sun; secondly, it is closely related to the optical and mechanical structure of the telescope. In terms of structure, astronomical telescopes mainly have equatorial device structures and horizontal device structures. When tracking the apparent diurnal motion of celestial bodies rising in the east and setting in the west, the equatorial telescope is simple to control, and only requires the right ascension axis to rotate at a constant speed. The tracking of horizontal telescopes is complicated. The azimuth axis and the altitude axis need to perform non-uniform non-uniform acceleration non-linear motion at the same time to achieve the precise tracking of celestial bodies by the telescope. Moreover, when the horizontal telescope passes the zenith, the running speed and acceleration of the azimuth axis become infinite, so there is an observation blind spot. In addition, there is also a rotation of the field of view during the tracking process of the telescope, which causes the celestial body image at the focal plane to rotate continuously. However, due to the superior mechanical properties and compact structure of the horizontal telescope, astronomical telescopes usually adopt the horizontal structure, especially large and medium-sized astronomical telescopes. In optics, the optical system of the solar telescope is usually more complicated than that of the night telescope. Generally, the Gregorian system is adopted, while the night telescope usually adopts the RC system. The Gregorian system needs to extend the Gregorian focus (relative to the RC's card focus) to the Kude focus of the Kude room through a complex extended optical path (i.e., the folded axis optical path) to install large focal surface scientific instruments. From the Gregorian focus to the Coode focus, the main optical axis of the telescope optical system extends through the folded-axis optical path and passes through the telescope's altitude axis, azimuth axis and derotation axis in turn, and the main optical axis is required to completely coincide with the three axis systems of the telescope's altitude mechanical axis, azimuth mechanical axis and derotation mechanical axis. However, due to the inevitable errors in telescope manufacturing and optical-mechanical adjustment, it is impossible for the main optical axis and the rotation centers of these three axis systems to coincide. Therefore, in the process of the telescope tracking the sun, the main optical axis of the folded-axis optical path will make very complex movements around the telescope's altitude axis, azimuth axis and derotation axis, resulting in a complex translational motion of the solar image on the Coode focal plane that varies with time, similar to the tracking error, usually called the secondary tracking error, which reduces the tracking accuracy of the solar telescope on the Coode focal plane. The better the coaxiality between these axis systems, the smaller the tracking error. Summary of the invention

[0004] The present invention aims at the technical problems raised by the background technology and proposes a method for monitoring the coaxiality between the axis systems of an azimuth-type solar telescope. The present invention proposes a method and a corresponding system for real-time monitoring of the coaxiality and its changes between the axis systems of an azimuth-type solar telescope based on the optical-mechanical structural characteristics of large solar telescopes at home and abroad and in combination with the development of current related technologies.

[0005] The present invention provides a method for monitoring the coaxiality between the axes of a horizontal solar telescope, which specifically comprises the following steps:

[0006] First, an optical imaging system is designed on the Coode focal plane of the telescope to image the entrance pupil of the solar telescope, and the image of the entrance pupil of the telescope is collected by a camera and input into the computer;

[0007] Image processing is then performed to calculate the center of the pupil image, and the center is approximated as the center of the telescope's field of view or the position of the main optical axis; finally, the telescope's altitude axis, azimuth axis, and derotation axis are rotated respectively, and the changes in the pupil image center and the rotation angles of the telescope's axes are recorded in real time. Then, based on the trajectory of the pupil image center, the center of the circle is fitted to obtain the mechanical rotation center position of each axis system. The degree of dispersion of the mechanical rotation center position of each axis system is the coaxiality between the telescope's axis systems. The change in the axis system is obtained from the changes in the mechanical rotation center corresponding to each axis system.

[0008] The present invention also discloses a monitoring system for the coaxiality between the axis systems of a horizontal solar telescope, which comprises a solar telescope system, a focal plane system, a pupil plane imaging system and an image acquisition and data processing system in sequence;

[0009] The solar telescope system is composed of a main optical system, a guiding optical system, a telescope pointing and tracking system, and a de-rotation control system in sequence.

[0010] The main optical system is a Gregorian optical system, which images the sun. Its main and secondary mirror systems are the main imaging systems, which image the sun at the Gregorian focus. A thermal stop is placed at the Gregorian focus to perform heat treatment on the system. The optical axis of the main and secondary mirror systems is the main optical axis of the entire system, and the main mirror or the secondary mirror is the entrance pupil of the system.

[0011] The guiding optics system is to extend the image of the sun at the Gregorian focus to the Coode focus;

[0012] The guiding optical system is mainly composed of a plurality of plane reflectors, and the main optical axis of the telescope passes through the altitude mechanical axis, the azimuth mechanical axis and the de-rotation mechanical axis of the telescope, and the main optical axis theoretically coincides with the rotation centers of the altitude mechanical axis, the azimuth mechanical axis and the de-rotation mechanical axis;

[0013] The telescope pointing tracking control system is used to implement precise motion control of the telescope's altitude axis and azimuth axis, and provide attitude information of the telescope's altitude axis and azimuth axis to other systems of the telescope, including but not limited to rotation angle information;

[0014] The derotation control system of the telescope is used to eliminate the image field rotation of the Coode focal plane, and at the same time provide attitude information of the derotation axis to other systems of the telescope, including but not limited to rotation angle information.

[0015] Preferably, the focal plane system is arranged on the Coode focal plane platform of the horizontal solar telescope;

[0016] The light coming out of the Coode focal plane can be split into two paths by a beam splitter, one path entering the terminal scientific instrument system and the other entering the pupil imaging system.

[0017] Preferably, the pupil plane imaging system 30 is composed of a pupil plane imaging optical path 301 and an industrial camera 302, and is used to image and receive the entrance pupil of the main optical system of the telescope, wherein the pupil plane imaging optical path 301 is used to image the entrance pupil of the telescope, and is composed of a collimator, a neutral density film and an imaging mirror lens group.

[0018] Preferably, the image adoption and data processing system consists of an axis information calculation module, an image acquisition and image preprocessing module, a telescope attitude information acquisition module, a derotator attitude acquisition module, an axis information real-time display module and an axis information storage module, and runs on an industrial computer.

[0019] Preferably, the axis system information calculation module is responsible for calculating the mechanical rotation center position of each axis system, so as to obtain their coaxiality, and the coordinates of the mechanical rotation center position of each axis system are calibrated by the camera target surface;

[0020] The image acquisition and image preprocessing module is used to acquire images from a camera in a pupil plane imaging system, and then perform flat field and dark field preprocessing to obtain an image that can be used for pupil plane center calculation;

[0021] The telescope attitude information acquisition module acquires the rotation angles of the azimuth axis and the altitude axis of the telescope from the telescope pointing tracking system 103 via local area network communication.

[0022] The de-rotation posture information acquisition module communicates with the de-rotation control system 104 via the local area network to obtain the rotation angle of the de-rotation axis;

[0023] The axis system information real-time display module is used to display the coordinates of the optical axis, the azimuth mechanical axis rotation center, the altitude mechanical axis rotation center and the de-rotation mechanical axis rotation center;

[0024] The axis system information storage module is used to store the coordinates of the optical axis, the azimuth mechanical axis rotation center, the altitude mechanical axis rotation center and the derotation mechanical axis rotation center.

[0025] 1. The present invention solves the problem that the coaxiality between the axis systems of the horizontal solar telescope can only be measured by professionals using professional optical adjustment equipment during the optical and mechanical adjustment of the telescope. After adopting the present invention, the coaxiality between the axis systems can be measured during the optical and mechanical adjustment of the telescope and when the telescope is in operation. By monitoring the changes in the optical axis in real time, the changes in the coaxiality can be understood, and these measurement data can be stored and compared for a long time to evaluate the changes in the axis systems of the telescope.

[0026] 2. The method and system of the present invention were used in the field installation of the AIMS one-meter solar telescope in my country to carry out actual measurement experiments, measure the change of the center position of the optical axis of the telescope and the mechanical rotation center of each axis system, and analyze the coaxiality between them. The present invention can assist the optical and mechanical installation of the telescope, monitor the change of the optical axis during operation, and measure the coaxiality between the axis systems of the telescope at any time as needed. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 This is the system structure intention provided by the present application to realize the coaxiality monitoring between the axis systems of the horizontal solar telescope;

[0029] Figure 2 It is a schematic diagram of the system structure on the AIMS one-meter solar telescope provided by this application;

[0030] Figure 3 This is a rendering of the effect of an embodiment of the present application on the AIMS one-meter solar telescope. DETAILED DESCRIPTION

[0031] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0032] It is very important to monitor the coaxiality between the axes in the optical and mechanical system of the solar telescope:

[0033] On the one hand, during the optical-mechanical assembly stage, a method for detecting the center of rotation of the axis system is provided. Based on the detection data, the coaxiality between these axis systems is controlled as much as possible to improve the assembly accuracy of the telescope and reduce the secondary tracking error of the Coode focal plane. On the other hand, during the use stage of the telescope, a monitoring method is provided for the coaxiality between the axis systems and its changes during the operation of the telescope, so as to understand the changes in the axis systems. If the coaxiality between the axis systems deteriorates, resulting in an excessive decrease in tracking accuracy, necessary optical-mechanical adjustments can be made.

[0034] With the development of many large solar telescopes in my country, the significance of this invention will become more significant. At present, in terms of the development of large solar telescopes in my country, there are: the one-meter New Vacuum Solar Telescope (NVST) built by Yunnan Observatory; the two-meter ring solar telescope (2MRST) under development at Yunnan Observatory, the one-meter off-axis solar telescope (AIMS) for the mid-infrared solar magnetic field measurement system of the National Astronomical Observatory, and the 2.5-meter day and night telescope of Nanjing University; the 8-meter China Giant Solar Telescope (CGST) planned for Yunnan Observatory. These solar telescopes all use horizontal tracking frames, and except for 2MRST, their optical systems all use Gregorian systems. So how to monitor the coaxiality and changes between the axis systems of these telescopes is very important for the development and operation and maintenance of these large solar telescopes.

[0035] Regarding the technology of monitoring the coaxiality between telescope axes, the current method is to introduce crosshairs and other marks in the optical system by rotating the various axes of the telescope during the optical and mechanical adjustment, and then use professional detection and adjustment equipment such as autocollimation telescopes, 4D interferometers, and laser trackers to observe and measure the changes of crosshairs and other marks with the rotation of the axis system at certain specific positions of the optical path to determine the rotation center and coaxiality of the axis system. Through continuous adjustment of the optical machine and rotation of different axes, the measurement of the changes of crosshairs and other marks with the rotation of each axis system is within the minimum or allowable error range, indicating that the adjustment meets the requirements and the coaxiality between the axes meets the requirements. However, these methods require professional optical adjustment equipment, professional adjustment personnel, and related methods and experience, and the engineering application is professional and complex. Moreover, after the telescope is adjusted and put into operation, the adjustment equipment will be dismantled and the professional adjustment personnel will be evacuated, so it will be difficult to detect the coaxiality and its changes between the telescope axes.

[0036] The present invention adopts a real-time imaging and image and data processing technology to solve the difficult problem of real-time monitoring of the coaxiality between the axis systems of the horizontal solar telescope. The specific technical scheme is: firstly, an optical imaging system is designed on the Coode focal plane of the telescope to image the entrance pupil of the solar telescope, and the image of the entrance pupil of the telescope is collected by a camera and input into a computer; then, image processing is performed to solve the center of the pupil surface image, and the center is approximated as the field of view center or the main optical axis position of the telescope; finally, the altitude axis, azimuth axis and derotation axis of the telescope are rotated respectively, and the change of the pupil surface image center and the rotation angle of each axis of the telescope are recorded in real time, and then the center of the circle is fitted according to the trajectory of the pupil surface image center, so as to obtain the mechanical rotation center position of each axis system, and the dispersion degree of these mechanical rotation center points is the coaxiality between the axis systems of the telescope, and the change of the mechanical rotation center corresponding to each axis system is the change of the axis system.

[0037] The present invention utilizes the optical and mechanical structural features of the horizontal solar telescope:

[0038] First, the entrance pupil of the horizontal solar telescope is the primary mirror or the secondary mirror.

[0039] The second is to use the entrance pupil center as the position of the main optical axis of the main and sub-systems. The third is that when the optical axis is not concentric with the mechanical axis system, the pupil center (main optical axis) will rotate around the mechanical axis system.

[0040] The difference between the present invention and the solution usually adopted in the optical and mechanical adjustment of telescopes is:

[0041] The optical-mechanical system uses professional equipment such as autocollimation telescopes, 4D interferometers, and laser trackers, which are relatively expensive and require the design of some auxiliary devices and professional adjustment personnel. The equipment in this solution is mainly a relatively simple pupil imaging optical system, industrial-grade camera, computer and processing algorithm. The equipment is relatively cheap and easy to use.

[0042] The method used when assembling the optical-mechanical system is that the equipment is dismantled after the telescope is installed, and it is impossible to monitor the axis changes when the telescope is working. This solution can be used not only when assembling the optical-mechanical system of the telescope, but also during the operation of the telescope.

[0043] The method used when assembling the optical-mechanical system cannot record the coaxiality data for a long time and systematically. However, this solution can record the coaxiality change data between the axis systems for a long time to facilitate subsequent analysis and processing, and analyze the changes in the axis systems of the telescope. Therefore, this solution is simpler and more practical.

[0044] According to the method adopted by the present invention, combined with the Gregorian optical system commonly used in the horizontal solar telescope and the optical path of the rear-end Coode focal plane platform, the horizontal tracking frame and the de-rotation principle of the Coode focal plane, the system structure and working principle of the present invention are:

[0045] 1. System structure

[0046] The system of the present technical solution comprises: a large horizontal solar telescope for implementing coaxiality monitoring between axis systems and the main body of the system structure of the present invention.

[0047] The telescope includes its Gregorian optomechanical system, control system and Coode focal plane instrument system. The Gregorian optical system is composed of the main optical system and the guiding optical system. The control system includes the pointing tracking system of the telescope frame and the derotation control system for eliminating the rotation of the field of view. The Coode focal plane instrument system mainly includes the terminal scientific instrument system of the telescope and the spectroscope of the Coode focal plane. The main body of the system structure of the present invention includes a pupil image acquisition system and an image acquisition and data processing system. The pupil image acquisition system includes a pupil imaging optical path and an industrial camera for image acquisition. The image acquisition and data processing system includes image adoption and image preprocessing, telescope attitude and derotator attitude acquisition, axis rotation center solution system, axis center position and coaxiality information display and storage. The telescope system transmits the required optical signal, telescope attitude and derotator attitude to the main system of the present invention, and the main system solves the coaxiality and its change between the telescope axis systems.

[0048] 2. Working Principle

[0049] During the operation of the horizontal solar telescope, the optical system forms an image of the sun at the Coode focal plane. However, due to factors such as the telescope's optical and mechanical manufacturing and installation errors, during the pointing, tracking and derotation of the telescope, the main optical axis of the optical system, the telescope's altitude mechanical axis, the azimuth mechanical axis and the derotation system's mechanical axis cannot completely coincide, which will cause relative movement between these axis systems.

[0050] From the perspective of the Coode focal plane, one is that the image of the sun on the Coode focal plane will move slowly, which is the secondary tracking error; the other is that the entire light spot on the Coode focal plane will move, that is, the movement of the optical axis or the movement of the pupil image.

[0051] Since the Coode focal plane tracking error is not only a secondary tracking error component, but also affected by many factors such as the telescope frame, the change of the telescope axis system cannot be inferred from the tracking error alone. However, the movement of the pupil image of the Coode focal plane is completely caused by the different axes between the axis systems, so the movement and change of the pupil image can reflect the different axis degrees and changes between the telescope axis systems. Considering that the clear image of the Coode focal plane is the image of the sun, and the image of the pupil is the image of the primary mirror or the secondary mirror, an optical system is first designed to clearly image the entrance pupil of the telescope, and then the pupil image is collected by a camera. The collected image is sent to the computer for processing, mainly including flat field and dark field preprocessing, noise removal, and obtaining a high-quality pupil image. Next, the center of the pupil image is calculated, and the change of the center of the circle with each axis system is obtained according to the trajectory of the center of the circle, the attitude of the telescope (rotation angle of the azimuth axis and the altitude axis), and the attitude of the derotation system (rotation angle of the derotator).

[0052] Since the center of the circle is the center of the pupil image, it represents the position of the main optical axis of the telescope optical system. The change trajectory of the main optical axis is refitted to calculate the mechanical rotation center of the telescope azimuth axis, altitude axis and derotation axis. The distribution of the coordinates of the rotation center of these axes on the camera target surface represents the coaxiality between these axis systems. Finally, this information is displayed in real time and stored for a long time. The information processing system will also compare historical data to calculate the trend of coaxiality changes between telescope axis systems to monitor changes in the telescope axis systems.

[0053] The system has two working modes: independent measurement mode and real-time monitoring mode.

[0054] When working in independent test mode, the positions of the mechanical rotation centers of the telescope's altitude axis, azimuth axis, and derotation axis can be measured separately to obtain the coaxiality between them. Each axis system includes the altitude axis, azimuth axis, and derotation axis.

[0055] The specific working steps are:

[0056] First, point the solar telescope toward the sky so that even sky light enters the solar telescope;

[0057] Second, rotate the azimuth axis, altitude axis or derotation axis of the solar telescope separately. Rotate the axis you want to measure and keep the other two axes stationary.

[0058] Third, every time the corresponding axis rotates a certain angle, such as five or ten degrees, a set of pupil images is collected through an industrial camera, and the rotation angle of the axis at this time is recorded;

[0059] Fourth, calculate the center position of the pupil image corresponding to each rotation angle of the axis, that is, the coordinates on the camera target surface, and repeat the third and fourth steps until all data collection of the axis is completed;

[0060] Fifth, according to the changing trajectory of the center position of the pupil image, the center of the circle is fitted, and this center is the mechanical rotation center of the corresponding axis system. By measuring the rotation centers of the altitude axis, azimuth axis and anti-rotation axis, their coaxiality can be determined.

[0061] In real-time monitoring mode, the optical axis changes caused by the different axis of the telescope's mechanical axis system can be measured.

[0062] The specific working steps are:

[0063] First, point the solar telescope toward the sun and track it, while also turning on the de-racing control system;

[0064] Second, at certain intervals, such as two minutes or five minutes, a pupil image is captured by the camera, and the axis rotation angle corresponding to each pupil image is recorded, including the telescope's altitude angle, azimuth angle, and derotation angle;

[0065] Third, calculate the changing trajectory of the pupil image center position, that is, the coordinate on the camera target surface. The changing trajectory of the coordinate is the change of the optical axis caused by the different axes between the mechanical axis systems of the telescope.

[0066] Furthermore, it is possible to obtain its changes over time or along a certain axis. By monitoring for a long time and comparing it with historical data, it is possible to monitor the change state of the telescope axis system and the changes in the optical axis caused by it.

[0067] The specific components of the system, such as Figure 1 FIG. 1 is a schematic diagram of a system structure for realizing the monitoring of the coaxiality between the axis systems of a horizontal solar telescope and the changes in the axis system states as described in the present invention.

[0068] The system comprises four parts, namely, a solar telescope system 10 , a focal plane system 20 , a pupil plane imaging system 30 and an image acquisition and data processing system 40 .

[0069] The solar telescope system 10 and the focal plane system 20 are large-scale horizontal solar telescopes to be implemented, which are circled with dotted lines.

[0070] The pupil imaging system 30 and the image acquisition and data processing system 40 are the main components of the system structure and are circled in bold solid lines.

[0071] The telescope system 10 refers to a solar telescope for implementing coaxiality monitoring between axis systems, and the structural system adopted is a horizontal frame, and the optical system is a Gregorian optical system, which can be a symmetrical Gregorian system or an off-axis Gregorian optical system.

[0072] The solar telescope system 10 is composed of a main optical system 101 , a guiding optical system 102 , a telescope pointing and tracking system 103 , and a de-rotation control system 104 in sequence.

[0073] The main optical system 101 is a Gregorian optical system, which images the sun. Its main and secondary mirror systems are the main imaging systems, which image the sun at the Gregorian focus. A thermal aperture is placed at the Gregorian focus to perform heat treatment on the system. The optical axis of the main and secondary mirror systems is the main optical axis of the entire system, and the main mirror or the secondary mirror is the entrance pupil of the system.

[0074] The guiding optical system 102 extends the solar image at the Gregorian focus to the Coode focus.

[0075] The guiding optical system 102 is mainly composed of a plurality of plane mirrors, which direct the main optical axis of the telescope through the altitude mechanical axis, azimuth mechanical axis and derotation mechanical axis of the telescope. Theoretically, the main optical axis is required to be as consistent as possible with the rotation centers of these three mechanical axis systems. However, due to manufacturing and processing errors, it is impossible to achieve complete consistency in engineering.

[0076] The telescope pointing tracking control system 103 is responsible for implementing precise motion control on the telescope's altitude axis and azimuth axis, and provides attitude information (rotation angle information) of the telescope's altitude axis and azimuth axis to other systems of the telescope.

[0077] The derotation control system 104 of the telescope is responsible for eliminating the image field rotation of the Coode focal plane, and at the same time provides the attitude information (rotation angle information) of the derotation axis to other systems of the telescope.

[0078] The focal plane system 20 is arranged on the Coode focal plane platform of the horizontal solar telescope, and the precise scientific instruments with very high requirements on environment and stability are placed on the focal plane platform.

[0079] The light from the Coode focal plane 201 can be divided into multiple paths by a beam splitter to meet different scientific instruments or other usage requirements. In this system, the beam splitter 202 divides the light from the Coode focal plane into two paths, one path entering the terminal scientific instrument system 203 and the other path entering the pupil imaging system 30.

[0080] The pupil imaging system 30 is composed of a pupil imaging optical path 301 and an industrial camera 302, and performs imaging and reception of the entrance pupil of the main optical system of the telescope;

[0081] Among them, the pupil imaging optical path 301 images the entrance pupil of the telescope, and it is composed of a collimator, a neutral density film and an imaging lens group. The imaging quality of the optical system needs to meet the image quality requirements and clearly image the pupil of the telescope.

[0082] The industrial camera 302 is used to receive pupil surface images and transmit the images to the image acquisition and image preprocessing system 402. The camera must have a high signal-to-noise ratio. The images from the camera are transmitted to the control computer behind it. The computer is a general industrial computer. The connection line between the camera and the computer uses a special cable or a specified cable provided by the camera manufacturer. It is best to use an Ethernet industrial camera. The image transmission uses Ethernet to meet the transmission distance requirements.

[0083] The optical system and camera of the pupil imaging system 30 must match each other to meet the field of view requirements and ensure that the pupil image does not move out of the camera target surface when the axes rotate. It is best to reserve a space of more than 3 arc minutes. At the same time, the resolution of the system cannot be too low and needs to reach the arc second level to meet the resolution and accuracy requirements of the pupil center coordinate solution.

[0084] The image acquisition and data processing system 40 is the core of this system. The hardware is an industrial computer. The software module consists of six parts, which are the axis information calculation module 401, the image acquisition and image preprocessing module 402, the telescope attitude information acquisition module 403, the derotator attitude acquisition module 404, the axis information real-time display module 405 and the axis information storage module 406. These software modules run on an industrial computer, WINDOWS10 and above platform, and the hard disk of the industrial computer reaches a capacity of two TB to meet the capacity requirements of the information storage database.

[0085] The image acquisition and data processing system 40 is responsible for data acquisition and information processing. These data and information come from pupil image data, telescope attitude data, derotator attitude data and historical data in the information storage system. It finally calculates the coaxiality between the axis systems of the telescope and its changes with the telescope attitude and derotator attitude, and displays and stores the information in real time.

[0086] The axis system information calculation module 401 is responsible for calculating the mechanical rotation center position of each axis system, so as to obtain their coaxiality. The center position coordinates of these axis systems are calibrated with the camera target surface.

[0087] The image acquisition and image preprocessing module 402 acquires images from the camera in the pupil imaging system, and then performs preprocessing such as flat field and dark field to obtain an image that can be used for pupil center calculation.

[0088] The telescope attitude information acquisition module 403 acquires the rotation angles of the azimuth axis and the altitude axis of the telescope from the telescope pointing tracking system 103 using local area network communication.

[0089] The de-rotation attitude information acquisition module 404 communicates with the de-rotation control system 104 via a local area network to acquire the rotation angle of the de-rotation axis.

[0090] Finally, the information of the system image preprocessing module 402, the telescope attitude information acquisition module 403 and the derotator attitude acquisition module 404 is input into the axis system information solving module 401; when necessary, the axis system information solving module 401 obtains historical data from the axis system information storage module 406 for comparative analysis.

[0091] The axis system information real-time display module 405 is responsible for displaying the coordinates of the optical axis, the azimuth mechanical axis rotation center, the altitude mechanical axis rotation center and the de-rotation mechanical axis rotation center.

[0092] The axis information storage module 406 is responsible for storing the coordinates of the optical axis, the azimuth mechanical axis rotation center, the altitude mechanical axis rotation center and the derotation mechanical axis rotation center. Example

[0093] More specifically, let's use a case to illustrate. Figure 2 As shown, the system structure is:

[0094] The AIMS solar telescope system 10 is composed of a main optical system 101 and a guide optical system 102 in sequence.

[0095] The AIMS main optical system 101 is an off-axis Gregorian optical system that images the sun.

[0096] The AIMS main optical system 101 consists of a primary mirror M1 and a secondary mirror M2, and the focus of the primary and secondary mirror systems is the Gregorian focus.

[0097] The guiding optical system 102 extends the image at the Gregorian focus to the Coode focus.

[0098] The guiding optical system 102 of AIMS is composed of a secondary mirror M3, a plane mirror M4, a plane mirror M5, a plane mirror M6, a de-racemic K mirror system, a M7 mirror, a M8 mirror and a M9 mirror.

[0099] Plane mirror M4 guides the main optical axis to the altitude axis and coincides with the altitude mechanical rotation axis. The main optical axis of the outgoing light from plane mirror M6 coincides with the telescope azimuth mechanical rotation axis and the de-rotated K mirror mechanical axis.

[0100] The secondary mirror M2 is the entrance pupil of the telescope system 10 .

[0101] The light coming out of the Coode focal plane secondary imaging system 20 passes through the beam splitter 202 , and then enters the terminal scientific instrument system 203 , and then enters the pupil surface imaging system 30 .

[0102] The pupil imaging system 30 is composed of a lens group 301 and an image acquisition camera 302; the lens group 301 is mainly composed of a collimator, a neutral density film, and a beam splitter.

[0103] The image acquisition camera 302 adopts the industrial camera of AVT of Germany, the specific model is GT2050, the image target surface is 2048×2048 pixels, the pixel size is 5um, and the image acquisition adopts GIE gigabit network to send the image to the industrial computer in the system 40.

[0104] The image acquisition and data processing system 40 is composed of six parts in sequence, namely, an axis information calculation module 401, an image acquisition and image preprocessing module 402, a telescope attitude acquisition module 403, a derotator attitude acquisition module 404, an axis information real-time display module 405 and an axis information storage module 406. These six modules constitute a software system and run on an industrial computer with a Windows 10 platform.

[0105] The image acquisition and image preprocessing module 402 acquires the image from the camera 302 via Ethernet and performs flat-dark preprocessing.

[0106] The telescope attitude acquisition module 403 acquires the azimuth axis rotation angle and the altitude axis rotation angle of the telescope from the telescope pointing tracking system 103 via Ethernet. The derotator attitude acquisition module 404 acquires the derotation axis rotation angle from the derotation control system 104 via Ethernet.

[0107] The axis system information calculation module 401 calculates the center of the pupil image, that is, the optical axis, and then fits the mechanical rotation center position of the axis system, that is, the coaxiality between the axis systems. Finally, the position of the optical axis and the center of each axis system is displayed in the form of coordinates of the camera target surface in the axis system information real-time display module 405 and stored in the axis system information storage module 406.

[0108] Working method:

[0109] The AIMS telescope mainly measures the magnetic field of the sun in the mid-infrared band, and also conducts imaging observations of the sun in the mid-infrared. The terminal scientific instruments are all placed on the Kuder focal platform.

[0110] In the process of tracking the sun, due to the manufacturing and installation errors of the optical-mechanical system, the optical axis of the telescope cannot be completely consistent with the mechanical rotation axis of altitude, azimuth, and derotation, which causes the pupil image (main optical axis) to move and change on the Coode focal plane platform, and eventually causes the image of the Coode focal plane to slowly deviate from the center of the field of view over time. By monitoring the movement of the pupil image, the mechanical rotation center of each axis system can be solved, the coaxiality between the axis systems can be obtained, and the operation of the optical-mechanical system of the AIMS telescope can be monitored.

[0111] The specific steps of the system in this embodiment on the AIMS telescope are: first, a light path is separated by the beam splitter 201 in the focal plane system 20, and the light enters the pupil imaging light path 301 in the pupil imaging system 30; the pupil imaging light path 301 images the entrance pupil (secondary mirror M2) in the telescope optical system; the pupil camera 302 receives the pupil image and transmits it to the image acquisition and image preprocessing in the image acquisition and data processing system 40 through the network; the image acquisition and image preprocessing module 402 is a software module, which runs on the industrial computer in the image acquisition and data processing system 40.

[0112] After the image acquisition and image preprocessing module 402 acquires the pupil surface image, it performs flat dark field image preprocessing, and then sends the preprocessed image to the axis information solving module 401.

[0113] At the same time, the axis system information solving module 401 also receives the telescope attitude from the module 403, receives the derotator attitude from the module 404, and also receives the axis system history information in the axis system information storage module 406 during comparative analysis. Finally, the axis system information solving module 401 displays the coaxiality information of the axis system in the axis system information real-time display module 405 and stores it in the axis system information storage module 406.

[0114] The specific working mode and process of the system in this embodiment on the AIMS telescope.

[0115] The system has two working modes:

[0116] One is the measurement mode and the other is the monitoring mode.

[0117] In the measurement mode, the mechanical rotation centers of the telescope's azimuth axis, altitude axis and derotation axis can be measured to obtain their coaxiality.

[0118] In monitoring mode, the changes in the pupil image (or optical axis) of the telescope during operation can be monitored and compared with historical data to provide long-term changes in the telescope's optical-mechanical axis system.

[0119] The specific working steps of the measurement mode are:

[0120] First, point the telescope to the sky, so that uniform sky light enters the AIMS solar telescope system 10, the Coode focal plane secondary imaging system 20 and the pupil plane imaging optical path 301 of the telescope;

[0121] Second, the azimuth axis, altitude axis or derotation axis of the telescope is rotated separately through the telescope pointing tracking system 103 and the derotation control system 104. The axis to be measured is rotated, and the other two axes are kept stationary.

[0122] Third, every time the corresponding axis rotates a certain angle, such as five degrees or ten degrees, a group of pupil images are collected through the industrial camera 302 and the image acquisition and image preprocessing 402, and the rotation angle of the axis at this time is recorded through 403 and 404;

[0123] Fourth, the center position of the pupil image corresponding to each rotation angle of the axis is calculated by 401, that is, the coordinates on the camera target surface, and the third and fourth steps are repeated until all data collection of the axis is completed;

[0124] Fifth, according to the changing trajectory of the pupil image center position, the axis information solving module 401 fits the center of the circle, which is the mechanical rotation center of the corresponding axis. By measuring the rotation centers of the altitude axis, azimuth axis and derotation axis, their coaxiality can be determined.

[0125] In real-time monitoring mode, the optical axis changes caused by the different axis of the telescope's mechanical axis system can be measured.

[0126] The specific working steps are:

[0127] First, the solar telescope system 10, the focal plane system 20 and the pupil plane imaging optical path 301 are pointed toward the sun and tracked, and the de-racing control system is also turned on;

[0128] Second, at certain intervals, such as two minutes or five minutes, the image acquisition and image preprocessing module 402 acquires a pupil image through the industrial camera 302, and at the same time, the telescope attitude information acquisition module 403 and the derotator attitude acquisition module 404 record the axis rotation angle corresponding to each pupil image, including the telescope's altitude angle, azimuth angle, and derotation angle;

[0129] Third, the axis information calculation module 401 calculates the change trajectory of the pupil image center position, that is, the coordinates on the camera target surface. The change trajectory of the coordinates is the change of the optical axis caused by the different axes between the mechanical axis systems of the telescope. Further, its change over time or with a certain axis can be obtained. Through long-term monitoring and comparison with the historical data in the axis information storage module 406, the change state of the telescope axis system and the resulting change of the optical axis can be monitored.

[0130] like Figure 3 As shown, the experiment is a set of data measured during the field installation of the AIMS telescope. The invention works in the measurement mode and carries out the measurement of the coaxiality of the axis system within the mechanical rotation limit range of each axis of the telescope.

[0131] Extreme rotation range of the altitude axis (20° to 89°, 0° at ground level);

[0132] Azimuth axis extreme rotation range (60° to 300°, due north 0°);

[0133] The rotation range of the de-rotation axis (0° to 180°, the de-rotation characteristic of the K mirror is: 2 times relationship, that is, the K mirror rotates 180°, and the pupil image rotates 360°. The specific experimental process is:

[0134] 1. Make the invention work in measurement mode;

[0135] Second, let the telescope face the sky, rotate the azimuth axis, altitude axis and derotation axis respectively. Every time the axis rotates 10°, sample a frame of pupil image and calculate the center of pupil image (optical axis);

[0136] 3. Fit the optical axis trajectory with a circle to obtain the rotation center and radius of each mechanical axis. The positional relationship of the coordinates of each center on the camera target surface represents the coaxiality between the axis systems, and the size of the radius represents the coaxiality between the optical axis and each mechanical axis.

[0137] The conclusions drawn from this AIMS field test are:

[0138] The position of the mechanical rotation center of the azimuth axis on the camera target surface is (921.0, 1092.6), the position of the mechanical rotation center of the altitude axis on the camera target surface is (939.0, 1111.9), and the position of the mechanical rotation center of the de-raculation axis on the camera target surface is (927.3, 1098.0). The azimuth axis and the de-raculation axis are very close, and the altitude axis is far away from the azimuth axis and the de-raculation axis. The coaxiality between the azimuth axis and the de-raculation axis is better than that between them and the altitude axis. From the radius point of view, the rotation radius of the optical axis around the altitude axis is 18.9PIX (pixel), the rotation radius of the optical axis around the azimuth axis is 44.3PIX, and the rotation radius of the optical axis around the de-raculation axis is 37.8PIX. It can be seen that the optical axis is closer to the altitude axis, and the coaxiality between them is better than the coaxiality between the optical axis and the azimuth axis and the de-raculation axis. The measurement results show that AIMS needs to continue to be adjusted this time to try to make the mechanical rotation centers of the azimuth axis, altitude axis and derotation axis coincide with each other and achieve the ideal result of the optical axis rotation radius being zero.

[0139] The above shows that the invention has achieved the desired effect in the field adjustment experiment of the AIMS one-meter solar telescope.

[0140] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0141] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for monitoring the coaxiality between the axes of a horizontal solar telescope, characterized in that: The specific steps include: First, an optical imaging system is designed on the Coode focal plane of the telescope to image the entrance pupil of the solar telescope, and the image of the telescope entrance pupil is collected by a camera and input into the computer; then image processing is performed to calculate the center of the pupil image, and the center is approximated as the center of the field of view or the position of the main optical axis of the telescope; finally, the altitude axis, azimuth axis and derotation axis of the telescope are rotated respectively, and the changes in the center of the pupil image and the rotation angles of the axes of the telescope are recorded in real time; then, according to the trajectory of the center of the pupil image, the center of the circle is fitted to obtain the mechanical rotation center position of each axis system. The degree of dispersion of the mechanical rotation center position of each axis system is the coaxiality between the axis systems of the telescope. The change of the axis system is obtained from the change of the mechanical rotation center corresponding to each axis system.

2. A system for implementing the method for monitoring the coaxiality between the axes of a horizontal solar telescope as claimed in claim 1, characterized in that: It comprises a solar telescope system, a focal plane system, a pupil plane imaging system and an image acquisition and data processing system in sequence; the solar telescope system comprises a main optical system, a guiding optical system, a telescope pointing tracking system and a derotation control system in sequence.

3. The system according to claim 2, characterized in that The main optical system is a Gregorian optical system, which images the sun. Its main and secondary mirror systems are the main imaging systems, which image the sun at the Gregorian focus. A thermal stop is placed at the Gregorian focus to perform heat treatment on the system. The optical axis of the main and secondary mirror systems is the main optical axis of the entire system, and the main mirror or the secondary mirror is the entrance pupil of the system. The guiding optics is to extend the image of the sun at the Gregorian focus to the Coode focus; The guiding optical system is mainly composed of a plurality of plane reflectors, and the main optical axis of the telescope passes through the altitude mechanical axis, the azimuth mechanical axis and the de-rotation mechanical axis of the telescope, and the main optical axis theoretically coincides with the rotation centers of the altitude mechanical axis, the azimuth mechanical axis and the de-rotation mechanical axis; The telescope pointing tracking control system is used to implement precise motion control of the telescope's altitude axis and azimuth axis, and provide attitude information of the telescope's altitude axis and azimuth axis to other systems of the telescope, including but not limited to rotation angle information; The derotation control system of the telescope is used to eliminate the image field rotation of the Coode focal plane, and at the same time provide attitude information of the derotation axis to other systems of the telescope, including but not limited to rotation angle information.

4. The system according to claim 2, characterized in that The focal plane system is set on the Kuder focal plane platform of the horizontal solar telescope; The light coming out of the Coode focal plane can be divided into two paths by a beam splitter, one path entering the terminal scientific instrument system and the other entering the pupil imaging system.

5. The system according to claim 2, characterized in that The pupil imaging system consists of a pupil imaging optical path and an industrial camera, and is used to image and receive the entrance pupil of the main optical system of the telescope. The pupil imaging optical path is used to image the entrance pupil of the telescope, and is composed of a collimator, a neutral density film, and an imaging lens group.

6. The system according to claim 2, characterized in that The image acquisition and data processing system consists of an axis information calculation module, an image acquisition and image preprocessing module, a telescope attitude information acquisition module, a derotator attitude acquisition module, an axis information real-time display module and an axis information storage module, and runs on an industrial computer.

7. The system according to claim 6, characterized in that The axis system information calculation module is responsible for calculating the mechanical rotation center position of each axis system, so as to obtain their coaxiality. The coordinates of the mechanical rotation center position of each axis system are calibrated by the camera target surface; The image acquisition and image preprocessing module is used to acquire images from a camera in a pupil plane imaging system, and then perform flat field and dark field preprocessing to obtain an image that can be used for pupil plane center calculation; The telescope attitude information acquisition module acquires the rotation angles of the azimuth axis and the altitude axis of the telescope from the telescope pointing tracking system through local area network communication; The derotator attitude information acquisition module communicates with the derotation control system through a local area network to obtain the rotation angle of the derotation axis; The axis system information real-time display module is used to display the coordinates of the optical axis, the azimuth mechanical axis rotation center, the altitude mechanical axis rotation center and the de-rotation mechanical axis rotation center; The axis system information storage module is used to store the coordinates of the optical axis, the azimuth mechanical axis rotation center, the altitude mechanical axis rotation center and the derotation mechanical axis rotation center.

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