CN106526832A - Two-dimensional pointing servo control method and system - Google Patents

Abstract

The invention discloses a two-dimensional pointing mechanism servo control method and system based on image feedback and optical vector theory. By adding a measuring camera to the main optical path and using the fast image processing results of imaging as a feed source, an image servo closed loop is established. , actively control the fast-sweeping mirror through image feedback, complete the adjustment of the direction of the main optical axis of the camera, and achieve the search and gaze tracking functions of the imaging target. Improving the imaging efficiency of remote sensing cameras. By combining the optical vector reflection theory to design the servo control law, the nonlinear relationship between the motor rotation angle and the optical axis pointing is eliminated to improve the pertinence of the control, which is beneficial to improve the pointing accuracy of the fast-sweeping mirror and the stability of the imaging system.

Description

A two-dimensional pointing mechanism servo control method and system

technical field

The invention relates to a method and system for controlling a pointing mirror in a photoelectric detection system for searching and tracking, and specifically relates to a technique for using a measuring camera to detect and image, and using image processing results combined with optical vector theory to perform closed-loop control to drive the pointing mirror to precisely point .

Background technique

In recent years, many optical remote sensing instruments launched abroad have used pointing or scanning devices, and they are running well in orbit. The US GOES (Geosynchronous Environmental Satellite) series are meteorological satellites in geosynchronous geostationary orbit. Among them, the scanning imager IMAGER installed on the GOES-I/M that adopts the three-axis attitude stabilization method adopts the east-west scanning method of the pendulum mirror. It uses two inductive synchros to measure the mechanical angular displacement of the pendulum mirror. torque motor. Its working principle: the scanning controller is initialized according to the input command, and the angular position of the scanning mirror is determined according to the angle measurement signal of the induction synchronizer. When the angular displacement between the set position and the initial position is calculated, the drive motor drives at 10°/s The speed reaches the set position. When the east/west motors are in place, the north/south motors start to scan with a limited rotation angle according to the instructions. At the end of each scanning line, the control system issues a deceleration command to position the scanning mirror accurately and facilitate its retrace.

The US Landsat (Land Satellite) series are resource satellites in sun-synchronous orbit. The TM (Main Mapper) on Landsat-4 and 5 is a swing-broom multi-spectral scanning radiometer. Its two-way swing scanning system consists of a scanning drive device, a scanning mirror (Both sides are supported by flexure pivots), scan angle monitor, scan control system, double-page shock absorber and scan line correction device, etc. The scanning mirror scans back and forth in the direction of the track, and image data can be obtained by both positive and negative scanning.

SPOT-5 is a sun-synchronous orbit earth resource remote sensing satellite designed by CNES, and its payload includes two identical HRG (High Resolution Geometry) cameras. The HRG camera uses the pointing mirror mechanism to obtain oblique viewing angle observation capabilities, and the maximum side viewing angle is 27°. The pointing mirror drive control module (SCM) in the SPOT-5 satellite remote sensing system consists of two parts: one is the scanning belt selection (Strip-Selection) pointing mirror drive mechanism, and the actuator uses a stepping motor; the other is the motor refocusing and positioning The encoder uses a grating encoder to provide the position feedback signal required to control the stepper motor.

The scanning radiometer carried by my country's first-generation polar-orbiting meteorological satellite FY-1 (Fengyun-1) adopts a 45° rotating mirror scanning method. The optical axes of the system are in the same direction. The mirror rotates around the axis, the scanning plane is perpendicular to the orbital plane, and sweeps into the earth from the side of the back sun. When the satellite flies from north to south, the scanning mirror scans from west to east, and the optical instantaneous field of view receives the target radiation on both sides of the sub-satellite point. Obtain a two-dimensional view of the earth based on the movement of the satellite around the earth. The 45° rotating mirror scanning mode has the advantages of large observation range, the calibration source can be observed outside the scanning target range and the cold space for remote sensing instruments to be calibrated in flight, and the size is small.

my country's first-generation geostationary geostationary meteorological satellite FY-2 (Fengyun-2) adopts a spin stabilization method, its spin axis is perpendicular to the equatorial plane, and its spin speed is 100r/min. The main optical axis of the R-C optical system of the FY-2 satellite multi-channel scanning radiometer is perpendicular to the satellite spin axis and parallel to the earth's equatorial plane, and the sub-satellite point points to the equator. dimension scan. The radiometer scans the earth from west to east as the satellite rotates. Every time the satellite rotates once, the telescope steps from north to south once, with a step angle of 140μrad, to complete a line scan. It takes 25 minutes to scan 2,500 lines for each map of the earth’s disk, and it takes 25 minutes to sweep across 20° from north to south. After completing a global scan, the telescope takes 2.5 minutes to return to the north limit position from south to north. The scanning radiometer has a folding mirror between the main optical system and the rear optical path. When the telescope moves in steps in the north-south direction, the folding mirror should also step at the same time. The stepping direction of the telescope barrel and the folding mirror is the same, because the folding mirror reflects twice the angle of the incident light, the stepping angle of the folding mirror is half of the stepping angle of the telescope barrel.

In the current existing examples, the characteristic of the control method of the two-dimensional pointing mirror is that the scanning trajectory is preset by the program, which can only complete the periodic scanning of the target area, and cannot complete the active search and staring of the target.

Contents of the invention

The problem solved by the technology of the present invention is: the control of the traditional fast-sweeping mirror is periodical-sweeping, its pointing track is determined, and it does not have the function of staring and tracking. A two-dimensional pointing mechanism servo control method and system based on image feedback and optical vector theory of the present invention, that is, a detection camera is added to the main optical path, and the fast image processing result of imaging is used as a feed source to establish an image servo closed-loop loop, which is fast The sweeping mirror is actively controlled to complete the adjustment of the direction of the main optical axis of the camera to achieve the search and gaze tracking functions of the imaging target.

Technical solution of the present invention: a two-dimensional pointing mechanism servo control method based on image feedback and optical vector theory, the implementation steps are as follows:

Step 1. Using the angle relationship of the optical system and the basic theory of the optical reflection vector, the pointing characteristic equation of the azimuth axis, the pitch axis and the imaging optical axis of the fast-sweeping mirror is established;

Step 2, using the pointing characteristic equation obtained in step 1, combining information such as the focal length f from the swing mirror to the focal plane, the pixel size d, and the like to establish a mapping relationship between the rotation angle of the pointing mirror and the line-of-sight angle of the exit optical axis;

Step 3: Combining the mapping relationship between the pointing mirror rotation angle and the line-of-sight angle of the exit optical axis with the control theory, designing a pointing control law, adjusting the transfer function characteristics of the pointing control system, and making the system stable.

In the first step, using the angular relationship of the optical system and the basic theory of the optical reflection vector, the pointing characteristic equations of the azimuth axis, the pitch axis and the imaging optical axis of the fast sweeping mirror are established as follows:

I ₀ ′ is the visual axis direction of the system, I ₀ is the incident light, R is the reflection matrix, and G ₁₀ is the rotation auxiliary matrix. is the boresight azimuth, θ is the elevation angle.

In the second step, the mapping relationship between the pointing mirror rotation angle and the line-of-sight angle is established as follows:

α is the rotation angle of the azimuth axis of the two-dimensional pointing mirror, β is the rotation angle of the pitch axis of the two-dimensional pointing mirror, Δ ₁ and Δ ₂ are infinitesimal quantities, K ₁ and K ₂ are the linear gains from the rotation angle of the pointing mirror to the line-of-sight angle.

In the third step, design the directional control law and adjust the transfer function characteristics of the system as follows:

G _cl is the pointing control rate transfer function, G _c is the PID controller, G _p is the two-dimensional pointing mechanism model, G _v is the inner loop speed feedback controller, K ₁ and K ₂ are linear gains.

A two-dimensional pointing mechanism servo control system based on image feedback and optical vector theory, including main imaging camera, measuring camera, fast image processor, pointing controller, D/A conversion, pointing mirror driver, two-dimensional pointing mirror 7 and Main lens; the imaging target beam enters from the main lens, and after passing through the same optical path, enters the main imaging camera and the measuring camera. Using the image data of the measuring camera, the image is processed in real time in the fast image processor, and then it is processed in the pointing controller. Calculate and generate the driving information of the two-dimensional pointing mirror, and perform angle servo on the two-dimensional pointing mirror to control the pointing of the optical path, measure the acquisition of the camera to obtain new image data, and process the image in real time in the fast image processor to form a closed-loop control .

The advantage of the present invention compared with prior art is:

(1) Using the image processing results of the detection camera imaging as the feed source, the closed-loop control of the fast sweeping mirror can be performed to complete the high-precision optical axis pointing of the imaging target, which improves the imaging efficiency of the remote sensing camera.

(2) By combining the optical vector reflection theory to design the servo control law, the nonlinear relationship between the motor rotation angle and the optical axis pointing is eliminated, so as to improve the pertinence of the control, which is conducive to improving the pointing accuracy of the fast-sweeping mirror and the stability of the imaging system sex.

Description of drawings

Figure 1 is a two-dimensional pointing control diagram based on image feedback and optical vector theory;

Figure 2 is the reference coordinate system;

Fig. 3 is the optical path structure diagram of the incident light reflected by the two-dimensional pointing mirror to the focal plane for imaging;

Fig. 4 and Fig. 5 are the variation curves of the pitch angle of the boresight axis after the outer ring is fixed, and then the inner ring is swayed, and the change relationship of the azimuth angle of the boresight axis after the inner ring is fixed and the outer ring is swayed;

Fig. 6 is the scan trajectory on the focal plane when the pitch axis is fixed to rotate the azimuth axis and the scan trajectory on the focal plane when the azimuth axis is fixed to rotate the pitch axis;

Fig. 7 is a structural block diagram of the position loop;

Fig. 8 is a block diagram of the image loop structure;

Fig. 9 is a system Bode diagram of a class of image closed-loop;

Fig. 10 is a step response curve of a kind of image closed-loop system.

detailed description

The present invention includes an optical system, which is composed of a main optical lens, a main imaging camera 1, a measuring camera 2, a fast image processor 3, a pointing controller 4, a pointing mirror driver 6, and a two-dimensional pointing mirror 7. The composition of the system is shown in Figure 1.

The concrete implementation steps of the present invention are as follows:

Step 1: Establish an optical system as shown in FIG. 1 , the imaging optical axis of the measurement camera 2 is the same as that of the main imaging camera 1 or the optical path relationship is determined. Optical parameters are determined, including parameters such as the inclination angle of the two-dimensional pointing mirror 7 and the imaging focal length.

Step 2: Using the angle relationship shown in Figure 2 in the reference coordinate system and the basic theory of optical reflection vectors, establish the pointing characteristic equations of the azimuth axis, pitch axis, and imaging optical axis of the fast-sweeping mirror.

The equation is calculated as follows:

N represents the mirror normal unit vector, A represents the incident vector, A' represents the reflection vector, the linear transformation relationship between the image vector and the incident vector can be expressed as A'=R·A, R is the reflection matrix

Among them, N _x , N _y and N _z are the projections of the normal vector of the plane mirror in the reference coordinate system respectively.

The vector A rotates an angle θ around the rotation axis unit vector P to become a vector A', which is written in the matrix form A'=S _p,θ ·A, where S _p,θ represents the rotation matrix around the vector P by θ.

In the reference coordinate system, the image vector of the incident light vector A ₀ reflected by the two-dimensional pointing mirror is A ₀ ′, and the transformation relationship between the two is obtained according to the optical reflection vector theory

From the previous derivation, it can be seen that the rotation matrix of the pointing mirror rotated by an angle α around the Z0 axis, and rotated by an angle β around the Y0 axis is

G ₁₀ =S _Z0,α ·S _Y0,β

Here, the azimuth axis vector P _z =[0 0 1]′, the pitch axis vector P _y =[0 1 0]′, and can be substituted into the formula

Step 3: Establish the mapping relationship from the angle of the pointing mirror to the angle of view. The optical path structure diagram of the incident light after being reflected by the two-dimensional pointing mirror and then imaging on the focal plane is shown in Figure 3. The method is as follows:

When the pointing mirror rotates around the Z0 axis and the Y0 axis at the same time, if the angle between the normal vector of the pointing mirror at the initial position and the X0 axis is β ₀ , then the normal vector is , and the rotation direction is defined as the upward deflection around the Y0 axis as a positive direction.

N ₀ ＝(cosβ ₀ ,0,sinβ ₀ )

At the zero position, the angle between the horizontal outgoing light and the X0 axis is γ ₀ , so the outgoing vector is expressed as

O ₀ ＝[cosγ ₀ -sinγ ₀ 0]

According to the reflection vector theorem, the incident ray vector at zero position can be obtained

I ₀ ＝R ⁻¹ ·O ₀

Assuming that under the action of the incident light I ₀ , the pointing mirror rotates around the pitch axis and the azimuth axis at angles α and β at the same time, then the unit outgoing image vector reflected by the pointing mirror is I ₀ ′, and the direction of the image vector is the direction of the system boresight. can be obtained by calculation

If the boresight azimuth It is defined as the angle between the projection of the viewing axis on the horizontal plane and the X0 axis, and the pitch angle θ is defined as the angle between the viewing axis and the horizontal plane OX0Y0, then the relationship between the viewing angle of the optical axis of the pointing mirror and the motor rotation angle is expressed as

If the focal length from the swinging mirror to the focal plane is defined as f, and the pixel size is d, then the off-target amount of the incident light vector under the projection of the image plane is

The above formula can be organized as

u and v are the control quantities of the azimuth axis and the pitch axis respectively.

It can be seen that when the field of view range is very small, the variation of the viewing axis of the swing mirror and the amount of focal plane miss are linear, that is,

Figures 4 and 5 respectively show the change curve of the pitch angle of the boresight axis after the outer ring is fixed and the inner ring is swung, and the relationship between the azimuth angle of the boresight axis after the inner ring is fixed and the outer ring is swung.

Figure 6 shows the scanning trajectory on the focal plane when the pitch axis is fixed and the azimuth axis is rotated, and the scanning trajectory on the focal plane when the azimuth axis is rotated by a fixed azimuth axis. From the figure, we can see that there is a relationship between the line-of-sight angle of the outgoing optical axis and the motor rotation angle A certain linear relationship can be expressed as

_Δ1 and _Δ2 are infinitesimal quantities.

Step 4: Design pointing controller;

Open-loop transfer function pointing to a single axis of a mirror:

In the formula, J is the total moment of inertia converted from the system to the motor shaft; θ is the rotation angle of the motor output shaft, in rad; K _n is the torsional stiffness of the flexible pivot, in N·m·A ^-1 ; K _m is Motor current torque coefficient, unit N·m·A ^-1 , L is the equivalent inductance of the motor armature, unit H; R is the equivalent resistance of the motor armature, unit Ω; E is the input voltage, unit V, K _b is the counter electromotive force coefficient, unit V·s·rad ^-1 .

Figure 7 shows the structural block diagram of the position loop. The position loop takes the motor azimuth axis and pitch axis motor rotation angle calculated from the received sun vector angle as input signals, and drives the voice coil motor through the controller to realize pointing control. In the figure, G _p is the two-dimensional pointing mechanism model, G _c is the PID controller, and G _v is the inner loop speed feedback controller. The closed loop transfer function is

Figure 8 shows the block diagram of the image loop. The image loop takes the focal plane off-target amount as a given input, and the controller drives the motor to rotate to ensure that the focal plane off-target amount converges to zero. In the control structure, it is assumed that the mapping relationship between the motor rotation angle and the optical axis is as follows: Linear, directly control the rotation of the motor through the amount of focal plane miss, which reduces the difficulty of calculation and solution, and is easier to implement.

The fine tracking system transfer function is

In the formula, E is the input voltage of the motor, U is the off-target amount of the output optical axis on the focal plane, ω is the rotation angle of the motor shaft, and θ is the direction of the output optical axis

The closed loop transfer function is

Adjust the parameters to adjust the transfer function characteristics of the system to make the system stable; optimize the parameters to make the performance of the system meet the performance index requirements. Figure 9 and Figure 10 show a system Bode diagram and step response curve of a kind of image closed loop.

The contents not described in detail in the specification belong to the well-known technologies of those skilled in the art.

Claims (5)

1. a kind of two-dimensional pointing mechanism method of servo-controlling, it is characterised in that realize that step is as follows：

The basic theories of step one, the angular relationship using optical system and optical reflection vector, sets up the side of quick sweeping mirror Position axle, pitch axis and the directional property equation for being imaged optical axis；

Step 2, using the directional property equation obtained by step one, focal length f, pixel dimension d with reference to pendulum mirror to focal plane etc. believe Breath sets up the mapping relations for pointing to mirror corner to the emergent light axis angle of sight；

Step 3, mirror corner will be pointed to control theory is combined to the mapping relations of the emergent light axis angle of sight, design sensing control law, The transfer function characteristics of pointing control system are adjusted, system stability is made.

2. two-dimensional pointing mechanism method of servo-controlling according to claim 1, it is characterised in that：In the step one, utilize The basic theories of the angular relationship of optical system and optical reflection vector, set up the azimuth axis of quick sweeping mirror, pitch axis with into The directional property equation of picture optical axis is as follows：

$I_0^{\′}=\left[\begin{array}{c}{I}_x^{\′}\\ I_y^{\′}\\ I_z^{\′}\end{array}\right]=(G_{10}\·R\·G_{10}^{-1})\·I_0$

I′₀For system boresight direction, I₀For incident ray, R is reflection matrix, G₁₀For rotating companion matrix.For optical axis orientation Angle, θ are the angle of pitch.

3. two-dimensional pointing mechanism method of servo-controlling according to claim 1, it is characterised in that：In the step 2, build The vertical mapping relations for pointing to mirror corner to the angle of sight are as follows：

α be scan mirror orientation Shaft angle, β be scan mirror pitching Shaft angle, Δ₁With Δ₂For dimensionless, K₁、K₂For Mirror corner is pointed to the linear gain of the angle of sight.

4. two-dimensional pointing mechanism method of servo-controlling according to claim 1, it is characterised in that：In the step 3, if Meter points to control law, and the transfer function characteristics of regulating system are specific as follows：

$G_{cl}=\frac{G_c{G}_p{K}_1{K}_2}{1+G_p{G}_v+G_c{G}_p{K}_1{K}_2}$

G_clFor pointing to control rate transmission function, G_cFor PID controller, G_pFor two-dimensional pointing mechanism model, G_vFeed back for inner loop velocity Controller, K₁、K₂For linear gain.

5. a kind of two-dimensional pointing mechanism servo-control system, it is characterised in that：Including main image camera, measurement camera, quick figure As processor, pointing controller, D/A conversions, sensing mirror driver, scan mirror 7 and main lens；Imageable target light beam is by leading Camera lens is entered, Jing after identical light path, into main image camera and measurement camera, using the view data of measurement camera, fast Real-time processing is carried out to image in fast image processor, is calculated in pointing controller, generate the driving of scan mirror Information, and angle servo is carried out to scan mirror, control light path is pointed to, and measure camera collects new view data, Real-time processing is carried out in fast image processing device to image, closed loop control is formed.