High-precision pupil optical axis stable compound control system with large dynamic range

Abstract

The invention discloses a large-dynamic-range high-precision pupil and optical axis stable compound control system which comprises a front-stage optical path system, a coarse-stage pupil correction assembly, a coarse-stage pupil error detection assembly, a fine-stage pupil and optical axis correction assembly, a spectroscope, a fine-stage pupil and optical axis error detection assembly, a processing controller and a rear-stage optical path system. Reasonable spatial arrangement is utilized to complete large-dynamic-range and high-precision correction of pupil optical axis stability errors. According to the system, coarse-level and fine-level pupil correction assemblies and an optical axis correction assembly are used as execution devices, coarse-level and fine-level error detection assemblies are used as detection feedback devices, a closed-loop system is formed through a control algorithm, and precise alignment of pupils and optical axes of front and rear optical systems is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of pupil optical axis stabilization error correction in a telescope optical system, and relates to a large dynamic range and high-precision pupil optical axis stabilization composite control system. Background Art

[0002] In complex optical systems such as space telescopes, there are often multiple sub-optical systems that are connected by optical paths to achieve the overall goal. The subsystems need to be fixed in different positions, but due to various factors, their pupils and optical axes may move during use, such as atmospheric disturbances, changes in the direction of gravity, assembly stress release of mechanical structures, and temperature changes in the environment, which can lead to uncoupling of the internal optical path and affect the operation of the overall optical system. For example, the stability error between the primary mirror and the secondary mirror in a space telescope can cause vignetting and defocusing in the image. Therefore, optical systems often need to be manually calibrated through instruments such as levels and interferometers, but for optical systems such as space telescopes, a special real-time optical path coupling system needs to be designed to correct the optical axis and align the pupil.

[0003] Traditional optical path correction and alignment systems mostly use two fast-control mirrors to achieve optical path alignment. The fast mirror uses piezoelectric ceramics to accurately adjust the angle of the reflection surface. It has high sensitivity and high response speed, which is very suitable for optical path coupling alignment systems. However, in practical applications, due to changes in the direction of gravity and the release of internal stress, the pupil often has low-frequency displacements, up to 5mm. Since the adjustment angle of the fast mirror is extremely small, for example, its correction dynamic range is 10', when the correction error is required to be 5mm, the distance between them needs to be no less than 2.7m, which leads to the traditional correction system occupying a large space and high cost. Summary of the invention

[0004] The technical problem to be solved by the present invention is: for the traditional pupil stabilization system, the disadvantage of its small pupil correction range is overcome, and a pupil stabilization composite control system with a large dynamic range is provided, which maintains the advantages of the original pupil stabilization system, such as fast correction response speed and high sensitivity, while greatly increasing the pupil correction dynamic range, solving the problem of low-frequency pupil disturbance errors in the optical system, and has the advantages of small space occupation and low cost.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A large dynamic range and high precision pupil optical axis stabilization composite control system, comprising:

[0007] Pre-stage optical system;

[0008] A coarse pupil correction component, used for correcting a low-frequency pupil error of a light beam from a preceding optical system;

[0009] A coarse pupil error detection component, comprising a coarse pupil measurement detector, detects the light beam corrected by the coarse pupil correction component and transmits it to a processing controller;

[0010] A fine pupil and optical axis correction component, used for correcting the optical axis error and high-frequency pupil error of the light beam from the coarse pupil error detection component;

[0011] A beam splitter, used to introduce the light beam into the precision pupil and optical axis error detection components and the subsequent optical system respectively;

[0012] A precision pupil and optical axis error detection component, comprising an optical axis measurement detector and a precision pupil measurement detector, detects the light beam corrected by the precision pupil and optical axis correction component, and transmits it to a processing controller;

[0013] A processing controller, used for calculating the optical axis and pupil error amounts according to the coarse pupil error detection component and the fine pupil and optical axis error detection component, thereby driving the coarse pupil correction component and the fine pupil and optical axis correction component to perform closed-loop control;

[0014] Post-stage optical system.

[0015] Beneficial effects:

[0016] 1. The present invention introduces a coarse pupil correction component, which realizes high dynamic range correction of the pupil by driving the reflector to translate, thereby greatly increasing the correction capability for low-frequency pupil errors.

[0017] 2. The present invention includes both coarse and fine correction components. The fine part has a small adjustment range, so that the distance between the two fast mirrors is small, the system structure is compact, the space occupied is small, and the cost is low.

[0018] 3. The conversion matrix in the present invention realizes real-time calculation of the optical axis measurement detector and the pupil measurement detector, which accelerates and facilitates the process of obtaining the adjustment angle of the fast reflection mirror.

[0019] 4. The present invention introduces a coarse-level and fine-level closed-loop control system to achieve correction for the external environment or external force, and has a strong ability to correct low-frequency errors.

[0020] 5. The error measurement detectors in the present invention are reasonably arranged, the optical axis measurement detector and the fine pupil measurement detector are only sensitive to their own measurement values, and the optical axis error has little effect on the coarse pupil measurement detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1The schematic diagram of a large dynamic range and high precision pupil and optical axis stabilization composite control system according to an embodiment of the present invention (1: front stage optical system; 2: coarse stage pupil correction component; 3: coarse stage pupil error detection component; 4: fine stage pupil and optical axis correction component; 5: spectroscope; 6: fine stage pupil and optical axis error detection component; 7: processing controller; 8: back stage optical system.)

[0022] Figure 2 Schematic diagram of a large dynamic range and high precision pupil and optical axis stabilization composite control system according to an embodiment of the present invention.

[0023] Figure 3 The figure is a simulation block diagram of a large dynamic range and high precision pupil and optical axis stabilization composite control system according to an embodiment of the present invention.

[0024] Figure 4 Graph showing simulation results of a composite control system according to an embodiment of the present invention (pupil residual error value).

[0025] Figure 5 Graph showing simulation results of a composite control system according to an embodiment of the present invention (optical axis residual error value).

[0026] Figure 6 This is a diagram of pupil error suppression capability when different frequency errors are input according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] Taking a large dynamic range and high precision pupil stabilization composite control system with an incident pupil diameter of 50 mm as an example, its main technical indicators are:

[0029] (1) Pupil diameter: 50 mm;

[0030] (2) Maximum pupil error: ±5mm;

[0031] (3) Maximum error of optical axis: ±3′;

[0032] (4) Pupil residual error < 0.2 mm;

[0033] (5) Optical axis residual error < 10″.

[0034] like Figure 2 As shown, the goal of the large dynamic range, high precision, pupil and optical axis stabilization composite control system of the embodiment of the present invention is to align the outgoing light beam of the preceding optical system to coincide with the incident light path of the subsequent optical system. Figure 1As shown, the large dynamic range high-precision pupil optical axis stabilization composite control system comprises: a front-stage optical system 1; a coarse-stage pupil correction component 2, used to correct the low-frequency pupil error of the light beam from the front-stage optical system 1; a coarse-stage pupil error detection component 3, used to detect the light beam corrected by the coarse-stage pupil correction component 2, and transmit it to the processing controller 7; a fine-stage pupil and optical axis correction component 4, used to correct the optical axis error and high-frequency pupil error of the light beam from the coarse-stage pupil error detection component 3; a spectroscope 5, used to introduce the light beam into the fine-stage pupil and optical axis error detection component 6 and the rear-stage optical system 8 respectively; the fine-stage pupil and optical axis error detection component 6, used to detect the light beam corrected by the fine-stage pupil and optical axis correction component 4, and transmit it to the processing controller 7; the processing controller 7, used to calculate the optical axis and pupil error amount according to the coarse-stage pupil error detection component 3 and the fine-stage pupil and optical axis error detection component 6, thereby driving the coarse-stage pupil correction component 2 and the fine-stage pupil and optical axis correction component 4 to perform closed-loop control; and the rear-stage optical system 8.

[0035] In the above system, the light beam output by the front optical system 1 passes through the coarse pupil correction component 2 and the fine pupil and optical axis correction component 4 and is aligned with the input pupil and optical axis of the rear optical system 8 .

[0036] In the above system, the light beam is emitted from the front-stage optical path system 1, passes through the coarse pupil correction component 2, and then is split by the coarse pupil error detection component 3 to the coarse pupil measurement detector inside the coarse pupil error detection component 3. The processing controller 7 is connected to the above coarse pupil measurement detector, and the optical axis and pupil error are calculated according to the measurement value thereof, thereby driving the coarse pupil correction component 2 to perform closed-loop control to achieve coarse correction of pupil error. The subsequent optical path passes through the fine pupil and optical axis correction component 4, and is output to the fine pupil and optical axis error detection component 6 and the rear-stage optical path system 8 respectively through the spectroscope 5. The former includes an optical axis measurement detector and a fine pupil measurement detector. The processing controller 7 is connected to the above two detectors, and the optical axis error and the residual error of pupil correction are calculated according to the measurement value thereof, thereby driving the coarse pupil correction component 2 and the fine pupil and optical axis correction component 4 to perform closed-loop control to achieve optical axis and fine pupil correction.

[0037] The coarse pupil correction component can complete the pupil error correction of the order of 10mm, and the fine pupil and optical axis correction component can realize sub-millimeter pupil error correction and sub-arcsecond optical axis error correction. When combined, the system can complete large dynamic range, high-precision pupil and optical axis stability error correction. At the same time, this solution can reduce the system's requirements for spatial size, making the system compact, small in space occupancy, and low in cost, and is especially suitable for space optical systems.

[0038] In one embodiment, the coarse pupil correction assembly 2 is composed of a first reflector and a second reflector, and the first reflector and the second reflector can also be replaced by right-angle prisms. The first reflector and the second reflector can achieve a linear motion of the order of 10 mm, and the driving method can be a stepper motor, a servo motor, or other driving methods that achieve the same functions and performance indicators. The working surfaces of the first reflector and the second reflector are perpendicular to each other, the driving surface of the former is parallel to the X-axis and is responsible for the X-axis correction of the pupil, and the driving surface of the latter is parallel to the Z-axis and is responsible for the Y-axis correction of the pupil. In one embodiment, the length and width of the first reflector and the second reflector are both 150 mm.

[0039] According to the actual application scenario, the appropriate drive system parameters are selected according to the maximum pupil offset to accurately compensate for the pupil offset at low frequencies and prevent the subsequent two fast mirrors from exceeding the adjustment range. The width of the first reflector and the second reflector are selected based on the maximum width of the input beam and the maximum pupil offset to ensure that the beam can completely pass through the reflector to the subsequent optical device under any circumstances.

[0040] In one embodiment, the fine pupil and optical axis correction component 4 includes a first fast reflex mirror and a second fast reflex mirror, which are installed parallel to the X-axis. The first fast reflex mirror receives the light beam that has been preliminarily corrected by the coarse stage, reflects it to the latter, and then outputs it to the fine pupil and optical axis error detection component 6 and the subsequent optical system 8 through the spectroscope 5. In terms of equipment selection, devices with high response speed and high angular resolution accuracy are preferred to complete high-frequency pupil and optical axis alignment tasks, and at the same time, the mechanical resonance frequency of the fast reflex mirror is avoided according to the task type. In one embodiment, the diameter of the first fast reflex mirror and the second fast reflex mirror is greater than 100 mm, and the correction dynamic range is 10'.

[0041] In one embodiment, the coarse pupil error detection component 3 includes a coarse pupil measurement detector for real-time detection of the pupil position of the light beam, and the coarse pupil measurement detector is coupled to the working surface of the second reflector. The coarse pupil measurement detector can use a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS).

[0042] The precision pupil and optical axis error detection component 6 includes an optical axis measurement detector and a precision pupil measurement detector, wherein the optical axis measurement detector detects the far-field focus of the light beam and is only sensitive to the angle change of the optical axis. The precision pupil measurement detector is coupled to the working surface of the second fast mirror, and the detector detection amount is linearly related to the amount of light beam movement on the surface. In addition, the correction center of the optical axis is the working surface of the second fast mirror, and the optical axis error has no effect on the precision pupil measurement. The optical axis measurement detector and the precision pupil measurement detector can use a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS).

[0043] The operation of the above-mentioned large dynamic range high-precision pupil optical axis stabilization composite control system includes the following three steps:

[0044] The first step is to lay out and install all system components. In one embodiment, in the coarse pupil correction component 2, it is necessary to ensure that the working planes of the two reflectors are perpendicular to each other, and at least ±10mm of mobile correction space is reserved. For the traditional pupil and optical axis correction component, when the maximum pupil error is ±5mm, at least 2.7m is left between the two fast mirrors, while for the fine pupil and optical axis correction component 4 in this embodiment, it only assists the coarse correction component to eliminate high-frequency errors, and the distance between the fast mirrors can be shortened to 0.2m.

[0045] The second step is to calibrate the expected incident light path of the system. A collimated light beam that completely coincides with the expected pupil optical axis is used to be incident on the pupil optical axis stabilization composite control system. The data of the coarse pupil measurement detector, the optical axis measurement detector and the fine pupil measurement detector are collected through the processing controller 7, and the center point value of the reference beam on each detector is calculated and recorded.

[0046] The third step is to start the closed-loop control system of the fast mirror. The coarse pupil correction closed-loop control starts after receiving the outgoing light beam from the previous optical system. The two mirrors are driven to move and participate in the correction in real time according to the error value. When the coarse error value approaches a certain small amount, the fine pupil correction closed-loop starts, and the error values ​​in all directions are calculated in real time. The expected deflection angle of the fast mirror is obtained through the conversion matrix calculation, and the driving voltage is input into the closed-loop circuit to realize the closed-loop of fine control.

[0047] Subsequently, by repeating the third step above, real-time correction of the pupil and the optical axis between the systems is achieved.

[0048] The optical axis measurement detector and the precision pupil measurement detector are the core components of the precision pupil and optical axis error detection assembly 6. They determine the difference between the current light beam and the target light path based on the basic principle of two points in one line. The center of the optical axis measurement detector is calibrated to the far field center point of the target light path, and the center value of the X-axis mark is recorded as ; The center of the pupil measurement detector is calibrated to the near-field center of the target optical path, and the center value of the X-axis mark is recorded as .

[0049] The calculation formula for the beam mark center value is:

[0050] ,

[0051] in, is the center value of the reference beam, represents the total number of pixels of the detector, represents the light intensity at the mth row and nth column in the detector, It represents the X-axis value of the pixel at the mth row and nth column in the detector, and the same is true for the center value of the beam mark in the Y-axis direction.

[0052] From this, we can determine the error value of the light beam on the optical axis and pupil measurement detector:

[0053] ,

[0054] in, Represent the beam offset in the far field and near field along the X-axis, represents the total number of pixels of the detector, represents the light intensity at the i-th row and j-th column in the detector, It represents the X-axis value of the pixel at the i-th row and j-th column in the detector. The same is true for the beam offset in the Y-axis direction.

[0055] In practical applications, the adjustment angle of the fast mirror in the correction system is extremely small. Therefore, under this condition, the adjustment angle and the adjustment amount of the light beam on the X and Y axes can be regarded as a linear relationship. In order to convert the signal on the detector into the desired adjustment angle of each axis on each fast mirror in real time, the following conversion matrix is ​​constructed in the X-axis direction:

[0056] ,

[0057] in, , They are the error values ​​after measurement and solution by the optical axis measurement detector and the precision pupil measurement detector, Respectively represent the adjustment angles of the first fast reflex mirror and the second fast reflex mirror along the vertical axis, They represent the ratio between the adjustment angle of the fast mirror and the corresponding beam offset. Similarly, the conversion matrix can also be constructed in the Y-axis direction.

[0058] Through the closed-loop control algorithm, the expected adjustment angle of the fast mirror obtained in real time is converted into the driving voltage of the two fast mirrors. The actual angle of the fast mirror is controlled by the driver output to correct the optical path. Assume that the driving voltage of the X-axis driver of the first fast mirror and the second fast mirror is , can be calculated by the following closed-loop formula:

[0059] ,

[0060] ,

[0061] in, are the driving voltage of the upper wheel control cycle, are the integral coefficients of the corresponding closed-loop controllers, The adjustment angle is obtained by calculating the conversion matrix, and the same is true for the Y-axis control loop.

[0062] For the closed-loop control of coarse pupil correction, the X-axis error of the coarse pupil measurement detector can be calculated by the same logic: , let the expected displacement of the first reflector be , can be calculated by the following closed-loop formula:

[0063] ,

[0064] in, is the linear coefficient of the corresponding error value and the expected displacement of the first reflecting mirror. After the expected displacement of the first reflecting mirror is calculated, the corresponding stepping motor can be driven to make real-time adjustments.

[0065] In summary, the coarse pupil correction component 2 in the composite closed-loop control controls the two driving devices in the coarse correction through the coarse pupil error in a closed-loop manner, and the fine pupil and optical axis error detection component 6 calculates the optical axis error and the pupil correction residual error through the conversion matrix to obtain the desired angles of the first fast reflex mirror and the second fast reflex mirror, and drives the first fast reflex mirror and the second fast reflex mirror in a closed-loop manner, and the two are combined to jointly control the light beam to achieve the goal.

[0066] According to the above process, if Figure 3 As shown in the figure, the simulation system was designed and verified. The pupil optical axis error and Gaussian noise of the high, medium and low frequency mixture were input. The final correction result is shown in Figure 4 , Figure 5As shown in the figure, the pupil residual is 0.101mm (3σ), and the optical axis residual is 4.97″(3σ), which meets the original requirements. In addition, the error suppression capability of the system for different frequency inputs is tested. For frequencies less than 1000Hz, the pupil error suppression capability is less than -13dB. The results are shown in the figure below. Figure 6 shown.

Claims

1. A large dynamic range and high precision pupil and optical axis stabilization composite control system, characterized in that: include: Pre-stage optical system (1); A coarse pupil correction component (2) for correcting a low-frequency pupil error of a light beam from a preceding optical system (1); A coarse pupil error detection component (3) is used to detect the light beam corrected by the coarse pupil correction component (2) and transmit it to a processing controller (7); A fine pupil and optical axis correction component (4) for correcting the optical axis error and high-frequency pupil error of the light beam from the coarse pupil error detection component (3); A beam splitter (5) for respectively introducing the light beam into the precision pupil and optical axis error detection component (6) and the subsequent optical system (8); A precision pupil and optical axis error detection component (6) is used to detect the light beam corrected by the precision pupil and optical axis correction component (4) and transmit it to a processing controller (7); A processing controller (7) is used to calculate the optical axis and pupil error amounts based on the coarse pupil error detection component (3) and the fine pupil and optical axis error detection component (6), thereby driving the coarse pupil correction component (2) and the fine pupil and optical axis correction component (4) to perform closed-loop control; Post-stage optical system (8).

2. The large dynamic range high precision pupil optical axis stabilization composite control system according to claim 1 is characterized in that: The coarse pupil correction component (2) is composed of a first reflector and a second reflector. The first reflector and the second reflector can achieve a linear motion of the order of 10 mm. The driving method is a stepper motor or a servo motor. The working surfaces of the first reflector and the second reflector are perpendicular to each other. The driving surface of the first reflector is parallel to the X-axis and is responsible for the X-axis correction of the pupil. The driving surface of the second reflector is parallel to the Z-axis and is responsible for the Y-axis correction of the pupil.

3. The large dynamic range high precision pupil optical axis stabilization composite control system according to claim 2 is characterized in that: The fine-level pupil and optical axis correction component (4) comprises a first fast-reflection mirror and a second fast-reflection mirror, which are installed parallel to the X-axis. The first fast-reflection mirror receives the light beam that has undergone preliminary coarse-level correction, reflects it to the latter, and then outputs it to the fine-level pupil and optical axis error detection component (6) and the subsequent optical system (8) through a beam splitter (5).

4. The large dynamic range high precision pupil optical axis stabilization composite control system according to claim 3 is characterized in that: The coarse pupil error detection component (3) comprises a coarse pupil measurement detector for detecting the pupil position of the light beam in real time. The coarse pupil measurement detector is coupled to the working surface of the second reflector. The coarse pupil measurement detector uses a charge coupled device or a complementary metal oxide semiconductor.

5. The large dynamic range high precision pupil optical axis stabilization composite control system according to claim 3 is characterized in that: The precision pupil and optical axis error detection component (6) comprises an optical axis measurement detector and a precision pupil measurement detector, wherein the optical axis measurement detector detects the far-field focus of the light beam and is only sensitive to the angle change of the optical axis. The precision pupil measurement detector is coupled to the working surface of the second fast reflection mirror, and the optical axis measurement detector and the precision pupil measurement detector use a charge coupled device or a complementary metal oxide semiconductor.

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