A nano-radian space gravitational wave detection beam pointing control system and method

Abstract

The present invention belongs to the field of control systems, and specifically relates to a nano-radian-level space gravitational wave detection beam pointing control system and method. The system includes a pointing mechanism controller, a pointing mechanism and an advance aiming beam monitoring unit; the input end of the pointing mechanism controller is respectively connected to an external host computer, a pointing mechanism and an advance aiming beam monitoring unit, and the output end is connected to the pointing mechanism. The pointing mechanism controller receives the pointing input signal sent by the host computer, the displacement feedback signal sent by the pointing mechanism and the pointing error signal sent by the advance aiming beam monitoring unit, obtains the pointing control signal according to the received signal and outputs it to the pointing mechanism; the pointing mechanism performs beam pointing control according to the pointing control signal and obtains the displacement feedback signal; the advance aiming beam monitoring unit detects the beam pointing and obtains the pointing error signal. The present invention adopts the advance aiming beam monitoring unit as the precision pointing control closed-loop feedback, which can realize the nano-radian-level angle deviation measurement.

Description

Technical Field

[0001] The present invention relates to a light beam pointing control system, and in particular to a nano-radian-level space gravitational wave detection light beam pointing control system and method. Background Art

[0002] The space laser interferometer gravitational wave detection plan can directly verify the general theory of relativity and provide a new observation window for cosmic exploration that electromagnetic waves cannot reach. my country's Taiji and Tianqin plans have also come into being. It is planned to launch a constellation of three gravitational wave detection satellites to the solar orbit to form an equilateral triangle configuration. In order to realize the detection of gravitational wave signals in the frequency band of 0.1mHz to 1Hz, the laser interferometer method will be used to measure the change in the length of the interference arm with picometer accuracy. Unlike the European LISA plan, the distance between two adjacent satellites is hundreds of thousands to millions of kilometers, and the sensitive frequency band is located in the range of 0.1mHz to 1Hz. Therefore, it has a more sensitive detection capability for the binary black hole orbiting and merging system with a total mass of hundreds to tens of thousands of solar masses involving the merger process of medium-mass black holes.

[0003] After the satellite is launched into the predetermined orbit, it is necessary to first capture the inter-satellite bidirectional laser signal and complete the construction of the inter-satellite laser link so that the four-quadrant detector can receive continuous laser signals. However, due to the orbital period changes between constellations and the random jitter of the satellite attitude, the laser pointing disturbance will be caused. If scientific measurements are to be carried out, the laser pointing stability needs to be controlled to the nanoradian level, which puts extremely stringent requirements on the precise pointing control system of the inter-satellite laser link.

[0004] At present, the classic beam pointing control technology cannot break through the nanoradian-level pointing control, which is mainly limited by the control system accuracy, precision compliant mechanism configuration, precision position, and angle feedback sensing technology. Therefore, the nanoradian-level space gravitational wave detection beam pointing control system will not only break through the ultra-high precision space laser beam pointing control technology, but also provide key technologies and theoretical foundations for my country's space gravitational wave detection. Summary of the invention

[0005] The purpose of the present invention is to solve the technical problem that the existing beam pointing control technology cannot achieve the purpose of nanoradian-level pointing control and is difficult to meet the requirements of high-precision space gravitational wave detection tasks, and to provide a nanoradian-level space gravitational wave detection beam pointing control system and method.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is:

[0007] A nano-radian-level space gravitational wave detection beam pointing control system, which is special in that:

[0008] It includes a pointing mechanism controller, a pointing mechanism and an advanced aiming beam monitoring unit DWS;

[0009] The input end of the pointing mechanism controller is respectively connected to the output end of the external host computer, the feedback end of the pointing mechanism and the output end of the advanced aiming beam monitoring unit DWS, and its output end is connected to the control end of the pointing mechanism. The pointing mechanism controller is used to receive the pointing input signal w(t) sent by the host computer, the displacement feedback signal sent by the pointing mechanism and the pointing error signal e(t) sent by the advanced aiming beam monitoring unit DWS, obtain the pointing control signal u(t) according to the pointing input signal w(t), the displacement feedback signal and the pointing error signal e(t), and output it to the pointing mechanism; the pointing mechanism is used to control the beam pointing according to the pointing control signal u(t) and obtain the displacement feedback signal; the detection end of the advanced aiming beam monitoring unit DWS is connected to the output end of the pointing mechanism, used to detect the beam pointing and obtain the pointing error signal e(t).

[0010] Furthermore, the pointing mechanism includes a mounting base, a first rotating shaft pivot, a mounting platform, a reflector, a transmission member, a second rotating shaft pivot, a piezoelectric ceramic actuator and a displacement detector; the number of the first rotating shaft pivots is two, and the two first rotating shaft pivots are arranged on the mounting base opposite to each other, one end of each first rotating shaft pivot is respectively connected to the mounting base, and the other end is respectively connected to the side wall of the mounting platform; the reflector is arranged at a position where the mounting base is located between the two first rotating shaft pivots, and is installed on the front side of the mounting platform; the transmission member is arranged at a position where the mounting base is located on the back side of the mounting platform, and one end of each first rotating shaft pivot is connected to the back side of the mounting platform; the piezoelectric ceramic actuator and the displacement detector are arranged on the mounting base. The detectors are respectively installed at the position of the mounting base located at the other end of the transmission member. The output end of the piezoelectric ceramic actuator is connected to the upper side of the other end of the transmission member through the second rotating shaft pivot. The detection end of the displacement detector is located at the lower side of the other end of the transmission member, and is used to obtain a displacement feedback signal by detecting the displacement of the other end of the transmission member; the input end of the piezoelectric ceramic actuator is connected to the output end of the pointing mechanism controller, and is used to control the reflection angle of the reflector according to the pointing control signal u(t) to realize the light beam pointing control; the output end of the displacement detector is used as the feedback end of the pointing mechanism, and is connected to the input end of the pointing mechanism controller.

[0011] Furthermore, the first rotating axis pivot and the second rotating axis pivot each include two reeds that are asymmetrically cross-arranged and equal in length; the two reeds are located on one side of the intersection with the same length and are greater than the length on the other side of the intersection; the parts of the two reeds located on one side of the intersection constitute the long axis, and the parts on the other side constitute the short axis; the short axes of the two reeds in the first rotating axis pivot are respectively connected to the mounting base, and the long axes are respectively connected to the mounting table; the short axes of the two reeds in the second rotating axis pivot are respectively connected to the transmission members, and the long axes are respectively connected to the output ends of the piezoelectric ceramic actuators.

[0012] Furthermore, the intersection of the two reeds in the first rotating shaft pivot constitutes the deflection center, and the mirror rotation center of the reflector is located on the line connecting the deflection centers of the two first rotating shaft pivots; the intersection of the two reeds in the second rotating shaft pivot constitutes the driving point of the piezoelectric ceramic actuator, and the driving point of the piezoelectric ceramic actuator is located in the same plane as the deflection center.

[0013] Furthermore, the thickness of the spring leaf is 0.42 mm to 0.43 mm; the intersection angle of the long axis in the first rotation axis pivot and the second rotation axis pivot is 27.20° to 27.40°; the length of the short axis in the first rotation axis pivot and the second rotation axis pivot is 3.30 mm to 3.50 mm.

[0014] Furthermore, the mounting base, the first rotating axis pivot and the mounting table are integrated and adopt slow-wire integrated processing. In the slow-wire integrated processing, the thickness error of the two springs of the first rotating axis pivot is ±0.013mm, the crossing angle error is ±0.05°, and the short axis length error is ±0.03mm.

[0015] Furthermore, the mounting base includes a top plate and a bottom plate, both of which are U-shaped parts, the two arms of the top plate are respectively connected to the two arms of the bottom plate through the middle plate, the two arms of the top plate and the corresponding arms of the bottom plate and the corresponding middle plate form two grooves, the two first rotating shaft pivots are respectively arranged in the two grooves, and the short axes of the two first rotating shaft pivots are respectively connected to the middle plate; a light beam pointing window of the reflector is formed between the top plate and the bottom plate, and the reflector is arranged in the light beam pointing window; the displacement detector is arranged between the bottom plate and the transmission member; an actuator mounting plate is provided on one side of the top plate, and one end of the piezoelectric ceramic actuator is connected to the actuator mounting plate.

[0016] Furthermore, the displacement detector is a capacitive sensor.

[0017] At the same time, the present invention also provides a nano-radian space gravitational wave detection beam pointing control method, based on the aforementioned nano-radian space gravitational wave detection beam pointing control system, characterized in that it includes the following steps:

[0018] Step 1: receiving the pointing input signal w(t) sent by the host computer, the displacement feedback signal sent by the pointing mechanism, and the pointing error signal e(t) sent by the advanced aiming beam monitoring unit DWS through the pointing mechanism controller, obtaining the pointing control signal u(t) according to the pointing input signal w(t), the displacement feedback signal, and the pointing error signal e(t), and outputting it to the pointing mechanism;

[0019] Step 2: The pointing mechanism controls the beam pointing according to the pointing control signal u(t), and obtains a displacement feedback signal to feed back to the pointing mechanism controller;

[0020] Step 3: Detect the beam pointing through the advanced aiming beam monitoring unit DWS, obtain the pointing error signal e(t), and send it to the pointing mechanism controller to achieve closed-loop control.

[0021] Furthermore, in step 1, the pointing control signal u(t) is calculated using the following formula:

[0022] ;

[0023] Where: e(t)=w(t)-displacement feedback signal; is the proportional control constant; is the integral control constant; is the differential control constant; t is the time.

[0024] The beneficial effects of the present invention are:

[0025] 1. The present invention adopts the advanced aiming beam monitoring unit DWS as the precision pointing control closed-loop feedback, which can realize the angle deviation measurement at the nanoradian level, thereby improving the control accuracy of the system and realizing the nanoradian level pointing control to meet the task requirements of high-precision space gravitational wave detection.

[0026] 2. The pointing mechanism provided by the present invention adopts an asymmetric cross spring as a rotating axis pivot, and the parasitic displacement of the deflection center of the spring is minimized by specially designing the thickness, cross angle, and short axis length (ratio of the long axis to the short axis). The designed pointing mechanism can achieve a control accuracy of 1.1pm of parasitic displacement within a deflection range of ±500μrad. Compared with the existing pointing mechanisms, the parasitic displacement is 30μm within a deflection range of ±500μrad; the leading angle pointing mechanism used for the European Space Agency's Laser Interferometer Space Antenna (LISA) mission has a parasitic displacement of 240pm at a maximum deflection angle of 412μrad. In summary, the pointing mechanism provided by the present invention introduces almost no parasitic displacement during the pointing process, basically realizes the "absolute rotation" movement of the reflector, and greatly reduces the interference of changes in the optical path difference on the beam transmission.

[0027] 3. The present invention adopts contactless capacitive sensing technology to achieve precise displacement measurement and monitor the displacement of the pointing mechanism, thereby further improving the accuracy of pointing control.

[0028] 4. The pointing mechanism provided by the present invention, through the design of asymmetric cross springs, makes the deflection center of the spring coincide with the mirror rotation center of the reflector, avoiding the translation of the outgoing light path and ensuring the pointing accuracy of the pointing mechanism.

[0029] 5. The pointing mechanism of the controllable parasitic displacement light beam of the mirror rotation center provided by the present invention has its deflection deformation mainly based on the elastic deformation of the weak link of the asymmetric cross spring, which completely eliminates the mechanical friction and viscosity in the movement, and the pointing mechanism can realize high-frequency, high-precision and high-resolution deflection adjustment within the range of elastic deformation; also, because its deflection deformation mainly depends on elastic deformation, there is no special lubrication requirement, and additional interference and pollution of the optical system are completely avoided; in addition, the asymmetric cross spring does not require maintenance and can be used in a variety of extreme environments such as vacuum, high and low temperature, and has a wide range of application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a structural schematic diagram of an embodiment of a nano-radian-level space gravitational wave detection beam pointing control system of the present invention;

[0031] Figure 2 It is a structural schematic diagram of a pointing mechanism in an embodiment of a nano-radian-level space gravitational wave detection beam pointing control system of the present invention;

[0032] Figure 3 It is a cross-sectional view of a pointing mechanism in an embodiment of a nano-radian-level space gravitational wave detection beam pointing control system of the present invention;

[0033] Figure 4 It is a schematic structural diagram of a first rotating axis pivot in an embodiment of a nano-radian-level space gravitational wave detection beam pointing control system of the present invention;

[0034] Figure 5 It is a schematic diagram of various parameters when the existing symmetrical cross-type spring is deflected.

[0035] In the figure: 1-mounting base, 11-top plate, 12-bottom plate, 13-middle plate, 14-actuator mounting plate, 2-first rotating shaft pivot, 3-reflector, 4-transmission member, 5-second rotating shaft pivot, 6-piezoelectric ceramic actuator, 7-capacitive sensor, 8-mounting table. DETAILED DESCRIPTION

[0036] In order to make the purpose, advantages and features of the present invention more clear, the following is a further detailed description of a nano-radian space gravitational wave detection beam pointing control system and method proposed by the present invention in combination with the accompanying drawings and specific embodiments. The advantages and features of the present invention will be more clear according to the following specific implementation methods.

[0037] See also Figure 1 The present embodiment provides a nano-radian-level space gravitational wave detection beam pointing control system, which mainly includes a pointing mechanism controller, a pointing mechanism and an advanced aiming beam monitoring unit DWS.

[0038] The input end of the pointing mechanism controller is respectively connected to the output end of the external host computer, the feedback end of the pointing mechanism and the output end of the advanced aiming beam monitoring unit DWS, and the output end of the pointing mechanism controller is connected to the control end of the pointing mechanism. The pointing mechanism controller receives the pointing input signal w(t) sent by the host computer, the displacement feedback signal sent by the pointing mechanism and the pointing error signal e(t) sent by the advanced aiming beam monitoring unit DWS, obtains the pointing control signal u(t) according to the pointing input signal w(t), the displacement feedback signal and the pointing error signal e(t), and outputs it to the pointing mechanism; the pointing mechanism performs beam pointing control according to the pointing control signal u(t) and obtains the displacement feedback signal; the detection end of the advanced aiming beam monitoring unit DWS is connected to the output end of the pointing mechanism to detect the beam pointing and obtain the pointing error signal e(t).

[0039] See also Figure 2 and Figure 3 Specifically, the pointing mechanism includes a mounting base 1, a first rotating shaft pivot 2, a reflector 3, a transmission member 4, a second rotating shaft pivot 5, a piezoelectric ceramic actuator 6 and a displacement detector.

[0040] The mounting base 1, the first rotating shaft 2 and the mounting platform 8 are integrated, and the three constitute an integrated base, and the integrated base is processed by slow wire cutting.

[0041] Specifically, the mounting base 1 includes a top plate 11 and a bottom plate 12, both of which are U-shaped parts. The two arms of the top plate 11 are respectively connected to the two arms of the bottom plate 12 through the middle plate 13, and the two arms of the top plate 11 and the corresponding arms of the bottom plate 12 and the corresponding middle plate 13 form two grooves.

[0042] There are two first rotating shaft pivots 2, which are respectively arranged in two grooves, and one end of the two first rotating shaft pivots 2 is respectively connected to the middle plate 13. The two arms of the mounting platform 8 are also respectively arranged in two grooves, and are respectively connected to the other ends of the two first rotating shaft pivots 2. A gap is provided between the two arms of the mounting platform 8 and the arms of the top plate 11 and the arms of the bottom plate 12, which are close to each other. The gap meets the beam pointing control requirements of the reflector 3, and in this embodiment, it is preferably 1.5 mm.

[0043] See also Figure 3 and Figure 4, the first rotating axis pivot 2 includes two springs of equal length and arranged asymmetrically and crosswise; the lengths of the two springs on one side of the intersection are the same and greater than the lengths on the other side of the intersection; the parts of the two springs on one side of the intersection constitute the long axis, the parts on the other side constitute the short axis, and the intersection constitutes the deflection center; the short axis is the fixed end, and the long axis is the free end. The short axes of the two springs in the first rotating axis pivot 2 are connected to the mounting base 1, and the long axis is connected to the mounting table 8. The thickness error of the two springs in the integrated processing of slow wire walking is ±0.013mm, the crossing angle error is ±0.05°, and the short axis length error is ±0.03mm.

[0044] The deflection center of the first rotating shaft pivot 2 is the intersection point (cross point) of the asymmetric cross springs, and its translation along the normal direction of the mirror surface of the reflector 3 during rotation is the parasitic displacement. During the one-dimensional deflection of the pointing mechanism, the mirror surface rotation center of the reflector 3 will translate along the normal direction of the mirror surface, and the deflection center of the first rotating shaft pivot 2 will also produce displacement in the same direction. In order to avoid the superposition of the parasitic displacements generated by the two in the direction of the optical path, it is necessary to make the mirror surface rotation center of the reflector 3 coincide with the deflection center of the first rotating shaft pivot 2 to minimize the parasitic displacement.

[0045] The structural design of the asymmetric cross spring is as follows:

[0046] Figure 5 This is a schematic diagram of the parameters of the existing symmetrical cross spring deflection. The normal direction of the mirror surface is defined as x The two connection points of the positive axis, the short axis and the middle plate are y Two points on the axis make a rectangular coordinate system x - y , the straight line where the deflection center is located ( x The intersection of the axis and the fixed end is the origin O, then the coordinates of the deflection center are , the coordinates of the midpoint of the free end are , the offset angle is θ E .

[0047] Among them, the initial position of the deflection center is C r , the initial position of the midpoint of the free end is E0, C r The initial distance to E0 is n 0; the offset position E1 of the midpoint of the free end is parallel to the normal direction of the free end. x The intersection of the two axes, with the intersection point (the offset position of the deflection center) marked as T, is the offset spacing. n E (The distance between points T and E1) and n 0, then C r The distance to T is the parasitic displacement d T .

[0048] Parasitic displacement dT The calculation method is as follows:

[0049] According to the Euler-Bernoulli equation:

[0050]

[0051] in: is the torsion angle, parameter , is the pure moment approximately acting on the free end, is the elastic modulus, is the moment of inertia, It is the length from the fixed end to the free end.

[0052] Separating the variables and integrating them, we get:

[0053]

[0054] Solve for the free end torsion angle .

[0055] According to the chain rule of differentiation, dx / ds = , dy / ds = ,get:

[0056]

[0057] Solve the free end coordinate formula:

[0058]

[0059]

[0060]

[0061] From the deflection center C r The change in position when moving to T represents the magnitude of the parasitic displacement, and we get:

[0062]

[0063] From the above formula, we can see that the parasitic displacement d T With parameters (That is, the moment of inertia ) is related, and the moment of inertia Depending on the cross-sectional shape of the asymmetric cross reed, there are three key parameters: reed thickness , Cross Angle , short axis length (That is, the ratio of the major axis to the minor axis, with the major axis length fixed and the minor axis length used as a variable).

[0064] Three key parameters and parasitic displacement d T The relationship between them is nonlinear, and there is a certain correlation between the three. The three need to be designed to minimize the parasitic displacement.

[0065] According to the size of the reflector 3 and the integrated base, the long axis length is 6 mm and the thickness of the fixed spring is , Cross Angle The value of the minor axis length The adjustment range is 0~6mm ( =6mm is a symmetrical cross spring); at this time, the short axis length The parasitic displacement d varies in the range of 0~6mm. T Follow The increase is first decreased and then increased, so it can be deduced that there is a minimum value of parasitic displacement. Varies in the range of 0.2mm~0.5mm, and the cross angle There is a minimum parasitic displacement in the range of 15°~45°.

[0066] Because the parasitic displacement is sensitive to three key parameters S Existence relationship ,in, is the parasitic displacement versus reed thickness sensitivity, is the parasitic displacement versus the minor axis length sensitivity, is the parasitic displacement versus the crossover angle The sensitivity of the three key parameters is taken into account, and the coupling relationship between the three key parameters is comprehensively considered. The three key parameters are adjusted at the minimum value of the parasitic displacement. At the same time, the size of the reflector 3 and the integrated base is considered, and the ranges of the three key parameters are designed to be:

[0067]

[0068]

[0069]

[0070] In other embodiments of the present invention, the above three key parameters may also have other value ranges, and the design may be specifically based on the dimensions of components such as the reflector 3, the integrated base, the transmission member 4, and the above principles.

[0071] A beam pointing window of the reflector 3 is formed between the top plate 11 and the bottom plate 12. The reflector 3 is arranged in the beam pointing window, and the reflector 3 is mounted on the front of the mounting platform 8. The transmission member 4 is arranged on the back of the mounting platform 8, and one end thereof is connected to the back of the mounting platform 8.

[0072] An actuator mounting plate 14 is provided on one side of the top plate 11 close to the transmission member 4, and one end of the piezoelectric ceramic actuator 6 is connected to the actuator mounting plate 14. The structure of the second rotating shaft pivot 5 is the same as that of the first rotating shaft pivot 2, and its short axis is connected to the upper side of the other end of the transmission member 4, and its long axis is connected to the output end of the piezoelectric ceramic actuator 6. The piezoelectric ceramic actuator 6 provides a vertical downward driving displacement, and the transmission member 4 converts the vertical displacement into the rotation of the reflector 3. The input end of the piezoelectric ceramic actuator 6 is electrically connected to the output end of the pointing mechanism controller, and is used to control the reflection angle of the reflector 3 according to the pointing control signal u(t) to achieve beam pointing regulation.

[0073] The intersection of the two springs in the second rotating shaft 5 is used as the driving point of the piezoelectric ceramic actuator 6. In this embodiment, the driving point of the piezoelectric ceramic actuator 6 is 1 / 200 m from the mirror rotation center of the reflector 3. L , then the driving displacement and torsion angle The relationship is:

[0074]

[0075] According to the detection of gravitational waves, the deflection range of the pointing mechanism mirror (i.e. the torsion angle ), the required driving displacement can be calculated by this formula , that is, the driving stroke of the piezoelectric ceramic actuator 6.

[0076] In this embodiment, the thickness of the transmission member 4 is set to 4 mm, and thus the driving point of the piezoelectric ceramic actuator 6 is set 2 mm away from the upper surface of the transmission member 4, so that the driving point of the piezoelectric ceramic actuator 6 is in the same plane as the offset center of the first rotating shaft pivot 2 to reduce parasitic displacement.

[0077] In this embodiment, a piezoelectric ceramic actuator 6 is selected as a driving element, and an asymmetric cross spring is used as a pointing mechanism to achieve the purpose of high-precision one-dimensional deflection of the light beam by the reflector 3 with minimal parasitic displacement, thereby improving the performance indicators of the optical system.

[0078] The displacement detector is installed between the bottom plate 12 and the transmission member 4 and is located at the lower side of the other end of the transmission member 4. The displacement feedback signal is obtained by detecting the displacement of the other end of the transmission member 4. The output end of the displacement detector serves as the feedback end of the pointing mechanism and is electrically connected to the input end of the pointing mechanism controller.

[0079] In this embodiment, the displacement detector is preferably a capacitive sensor 7. The capacitive sensor 7 is a non-contact capacitive principle precision measuring instrument, which is responsible for cooperating with the transmission member 4 in the system design to detect the displacement of the transmission member 4 and realize non-contact precision displacement measurement.

[0080] Compared with conventional laser, ultrasonic or resistance sensors, the advantages of using the contactless capacitive sensor 7 in the present invention are:

[0081] 1) Non-contact measurement: No physical contact is required between the capacitive sensor 7 and the object to be measured, thus avoiding wear and damage, and is suitable for precise measurement and detection of fragile objects.

[0082] 2) High sensitivity; the capacitive sensor 7 is very sensitive to small changes and can detect very small displacements or deformations, with a maximum resolution better than 1nm.

[0083] 3) Fast response: The response speed of the capacitive sensor 7 can be in the order of megahertz or even higher, which is very helpful for real-time control of laser pointing.

[0084] Currently, there are three main methods for using lasers to measure small angles: optical lever measurement, multi-path heterodyne interferometry, and advance aiming beam monitoring.

[0085] The optical lever measurement is based on the spot position measurement, and the angle is measured by measuring the movement of the spot position on the detector surface caused by the deflection of the reflecting surface;

[0086] Multi-path heterodyne interferometry converts rotation measurement into displacement measurement through multiple measurement points;

[0087] The advanced aiming beam monitoring is based on the laser wavefront measurement, which derives the angular change of the wavefront by comparing the interference phases in different quadrants;

[0088] Table 1 shows the sensitivity of the three methods in the range of 1mHz to 1Hz:

[0089] Table 1

[0090]

[0091] Due to the requirement of ultra-high precision measurement in the range of 1 mHz to 1 Hz for space gravitational wave detection, the measurement method in this embodiment is advanced aiming beam monitoring, that is, an advanced aiming beam monitoring unit DWS is used.

[0092] Compared with the commonly used optical lever measurement method, the advantages of the advanced aiming beam monitoring method are:

[0093] 1. The advanced aiming beam monitoring adopts phase-sensitive detection technology, and its detection accuracy is three to four orders of magnitude higher than differential power detection.

[0094] 2. In the advanced aiming beam monitoring, the conversion factor between phase information and beam angle can be as high as several thousand, which is much higher than the optical lever measurement. When the phase measurement accuracy of the advanced aiming beam monitoring reaches the μrad level, the nrad level off-target detection accuracy required for gravitational wave detection can be obtained.

[0095] 3. The advanced aiming beam monitoring can realize the distance measurement function through the average phase while realizing the angle measurement. It effectively avoids the light intensity dispersion and shot noise increase caused by separate distance measurement and angle measurement, making the overall design of the control system more reasonable.

[0096] This embodiment provides a nanoradian-level space gravitational wave and detection beam pointing control method, which specifically includes the following steps:

[0097] Step 1: Receive the pointing input signal w(t) sent by the host computer, the displacement feedback signal sent by the pointing mechanism, and the pointing error signal e(t) sent by the advance aiming beam monitoring unit DWS through the pointing mechanism controller, obtain the pointing control signal u(t) according to the pointing input signal w(t), the displacement feedback signal and the pointing error signal e(t), and output it to the pointing mechanism.

[0098] The pointing error signal e(t) is calculated using the following formula:

[0099] e(t)=w(t)-displacement feedback signal

[0100] The pointing control signal u(t) is calculated using the following formula:

[0101]

[0102] Where: is the proportional control constant; is the integral control constant; is the differential control constant; t is the time.

[0103] Integral control can reduce the steady-state error of the control system, while differential control plays a leading role in reducing overshoot. Control constant They can be flexibly debugged to reduce overshoot and steady-state error to achieve the expected control performance indicators.

[0104] Step 2: The pointing mechanism controls the beam pointing according to the pointing control signal u(t), and obtains a displacement feedback signal to feed back to the pointing mechanism controller.

[0105] Step 3: Detect the beam pointing through the advanced aiming beam monitoring unit DWS, obtain the pointing error signal e(t), and send it to the pointing mechanism controller to achieve closed-loop control.

Claims

1. A nano-radian space gravitational wave detection beam pointing control system, characterized in that: It includes a pointing mechanism controller, a pointing mechanism and an advanced aiming beam monitoring unit DWS; The input end of the pointing mechanism controller is respectively connected to the output end of the external host computer, the feedback end of the pointing mechanism and the output end of the advanced aiming beam monitoring unit DWS, and the output end is connected to the control end of the pointing mechanism. The pointing mechanism controller is used to receive the pointing input signal w(t) sent by the host computer, the displacement feedback signal sent by the pointing mechanism and the pointing error signal e(t) sent by the advanced aiming beam monitoring unit DWS, obtain the pointing control signal u(t) according to the pointing input signal w(t), the displacement feedback signal and the pointing error signal e(t), and output it to the pointing mechanism; The pointing mechanism is used to control the light beam pointing according to the pointing control signal u(t) and obtain a displacement feedback signal; The pointing mechanism comprises a mounting base (1), a first rotating shaft pivot (2), a mounting platform (8), a reflector (3), a transmission member (4), a second rotating shaft pivot (5), a piezoelectric ceramic actuator (6) and a displacement detector; The number of the first rotating shaft pivots (2) is two, and the two first rotating shaft pivots (2) are arranged opposite to each other on the mounting base (1), one end of each first rotating shaft pivot is connected to the mounting base (1), and the other end of each first rotating shaft pivot is connected to the side wall of the mounting platform (8); The reflector (3) is arranged at a position of the mounting base (1) between the two first rotating shaft pivots (2), and is mounted on the front side of the mounting platform (8); The transmission member (4) is arranged at a position of the mounting base (1) located on the back of the mounting platform (8), and one end of the transmission member (4) is connected to the back of the mounting platform (8); The piezoelectric ceramic actuator (6) and the displacement detector are respectively mounted on the mounting base (1) at a position located at the other end of the transmission member (4); the output end of the piezoelectric ceramic actuator (6) is connected to the upper side of the other end of the transmission member (4) via a second rotating shaft pivot (5); the detection end of the displacement detector is located at the lower side of the other end of the transmission member (4) and is used to obtain a displacement feedback signal by detecting the displacement of the other end of the transmission member (4); The input end of the piezoelectric ceramic actuator (6) is connected to the output end of the pointing mechanism controller and is used to control the reflection angle of the reflector (3) according to the pointing control signal u(t) to achieve light beam pointing regulation; The output end of the displacement detector is used as a feedback end of the pointing mechanism and is connected to the input end of the pointing mechanism controller; The detection end of the advanced aiming beam monitoring unit DWS is connected to the output end of the pointing mechanism, and is used to detect the beam pointing and obtain the pointing error signal e(t).

2. The nano-radian space gravitational wave detection beam pointing control system according to claim 1, characterized in that: The first rotating shaft pivot (2) and the second rotating shaft pivot (5) both comprise two reeds that are asymmetrically arranged and cross-arranged and have equal lengths; The lengths of the two reeds on one side of the intersection are the same and greater than the lengths on the other side of the intersection; the parts of the two reeds on one side of the intersection constitute the major axis, and the parts on the other side constitute the minor axis; The short axes of the two spring leaves in the first rotating shaft pivot (2) are respectively connected to the mounting base (1), and the long axes are respectively connected to the mounting platform (8); the short axes of the two spring leaves in the second rotating shaft pivot (2) are respectively connected to the transmission member (4), and the long axes are respectively connected to the output end of the piezoelectric ceramic actuator (6).

3. The nano-radian space gravitational wave detection beam pointing control system according to claim 2, characterized in that: The intersection of the two spring leaves in the first rotating shaft pivot (2) constitutes a deflection center, and the mirror surface rotation center of the reflector (3) is located on the line connecting the deflection centers of the two first rotating shaft pivots (2); The intersection point of the two spring leaves in the second rotating shaft pivot (5) constitutes the driving point of the piezoelectric ceramic actuator (6), and the driving point of the piezoelectric ceramic actuator (6) is located in the same plane as the deflection center.

4. The nano-radian space gravitational wave detection beam pointing control system according to claim 3, characterized in that: The thickness of the reed is 0.42 mm to 0.43 mm; The intersection angle of the long axes of the first rotating axis pivot (2) and the second rotating axis pivot (5) is 27.20° to 27.40°; The length of the short axis of the first rotating shaft pivot (2) and the second rotating shaft pivot (5) is 3.30 mm to 3.50 mm.

5. The nano-radian space gravitational wave detection beam pointing control system according to claim 4, characterized in that: The mounting base (1), the first rotating shaft pivot (2) and the mounting platform (8) are integrated and processed by wire-cutting integrated processing. In the wire-cutting integrated processing, the thickness error of the two springs of the first rotating shaft pivot (2) is ±0.013 mm, the cross angle error is ±0.05°, and the short axis length error is ±0.03 mm.

6. The nano-radian space gravitational wave detection beam pointing control system according to claim 2, characterized in that: The mounting base (1) comprises a top plate (11) and a bottom plate (12), both of which are U-shaped parts, the two arms of the top plate (11) are respectively connected to the two arms of the bottom plate (12) through the middle plate (13), the two arms of the top plate (11) and the corresponding arms of the bottom plate (12) and the corresponding middle plate (13) form two grooves, the two first rotating shaft pivots (2) are respectively arranged in the two grooves, and the short axes of the two first rotating shaft pivots (2) are respectively connected to the middle plate (13); A light beam pointing window of the reflector (3) is formed between the top plate (11) and the bottom plate (12), and the reflector (3) is arranged in the light beam pointing window; the displacement detector is arranged between the bottom plate (12) and the transmission member (4); An actuator mounting plate (14) is provided on one side of the top plate (11), and one end of the piezoelectric ceramic actuator (6) is connected to the actuator mounting plate (14).

7. The nano-radian space gravitational wave detection beam pointing control system according to claim 1, characterized in that: The displacement detector is a capacitive sensor (7).

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