CN109831600B - Method for avoiding image motion in target approaching process of photoelectric tracking system - Google Patents
Method for avoiding image motion in target approaching process of photoelectric tracking system Download PDFInfo
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Abstract
The invention discloses a method for avoiding image motion of a photoelectric tracking system in a target approaching process, aiming at the problem that the image motion phenomenon can occur when the relative speed of a rack and a target is overlarge in the target approaching process of the photoelectric tracking system, an optimal step length image motion controller is added in front of a position ring controller in a control frame of the photoelectric tracking system to avoid the image motion problem. The method comprises the following specific implementation steps: firstly, an optimal step length image motion controller calculates the optimal step length input by a position ring controller at the current moment, and the step length enables the response of the system to be fastest under the condition of meeting the maximum allowable image motion of the system; and then, the optimal step size image shift controller determines the input of the position ring controller according to the current miss distance and the optimal step size and sends the input into the position ring. The method provided by the invention solves the problem of image motion of the photoelectric tracking system in the target approaching process, has the advantages of rapidity of response, small overshoot and the like, and is convenient for engineering realization.
Description
Technical Field
The invention belongs to the field of photoelectric tracking system control, and particularly relates to a method for reducing image motion of a photoelectric tracking system in a target approaching process.
Background
The image shift refers to relative motion of a target image point on a camera focal plane, and is a physical phenomenon which often occurs in the imaging process of a photoelectric system based on a moving carrier, such as a space camera, an aerial camera, a weapon sighting system and the like, and can cause the problems of trailing, fuzzy target edge, unreal gray scale and the like, thereby reducing the imaging quality. In order to improve the imaging quality, scientific researchers adopt different image motion compensation methods aiming at different application scenes. For a space remote sensing camera, Li Yongchang et al adopt a mode of adjusting a pendulum of a camera to offset image shift brought by satellite motion, namely an image shift speed model and a compensation strategy of a wide-field remote sensing camera, Wuhan university bulletin, 2018,43(8):1278 one-time material 1286), and for an aerial camera, Li Kerui et al adopt an angle reflector swing control system to compensate image shift (Fujinbao et al, an aerial camera image shift compensation composite control based on friction feedforward, an electronic measurement and instrument bulletin, 2014, 06; leersi et al, "research on image analysis-based detection method for image motion compensation mechanism of aerial camera", optics and optoelectronics, 2015,05.) zhangqing et al adopt a method of replacing a corresponding region of a current image with an image region of a previous frame closest to a target template in the current image to stabilize the image, aiming at the problem of image jitter in a low-altitude high-fire weapon sighting system. (Zhang Qing et al, image stabilization technology of low altitude high fire weapon sighting system, optical technology, 2002,03) in addition to this, there are mechanical image motion compensation method, integrated image motion compensation method, digital image motion compensation method (Zhang Yuxin et al, development and prospect of image motion compensation technology, Chinese optics and applied optics, 2010, 02.).
The photoelectric tracking system is used as high-precision tracking observation equipment and is widely applied to the fields of scientific research, aerospace, precision measurement and the like. In the target tracking process of the photoelectric tracking system, a camera acquires target image information, extracts miss distance and sends the miss distance to a position ring controller, and then the movement of the rack is controlled, so that the visual axis of the rack follows the sight line of a target, and finally the two are consistent. The process from the target entering the field of view of the photoelectric tracking system to the target miss amount being zero is called a target approaching process. In the process of approaching the target, if the relative speed of the frame and the target is too high, the photoelectric tracking system can also generate an image motion phenomenon. In an original photoelectric tracking system, in order to limit the relative angular speed of a visual axis of a rack and a target sight line, a method of limiting the Step length of a signal input by a position ring controller is generally adopted, namely a fixed Step length Step is specified, when the target miss distance delta theta is smaller than the Step, the miss distance delta theta is directly sent to the position ring controller, and when the miss distance delta theta is larger than the Step, the Step is sent to the position ring controller.
The method for avoiding the image motion of the photoelectric tracking system in the target approaching process is to design an optimal step image motion controller, calculate the optimal step (t)) at the current moment in real time, directly send the miss distance delta theta into the position ring controller when the target miss distance delta theta is smaller than step (t), and send step (t) into the position ring controller when the miss distance delta theta is larger than step (t). There is no similar method in the currently published literature for reducing image motion.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: in the target approaching process, if the relative speed of the frame and the target is too high, the moving distance of a target image point on a focal plane of the camera is large within the exposure time of the camera, the imaging quality is reduced, and the extraction of miss distance information is influenced.
The technical scheme adopted by the invention for solving the technical problems is as follows: designing a variable step size image motion controller, calculating the optimal step size step (t) of the input quantity of the position ring controller at the current moment in real time, directly sending the miss distance delta theta into the position ring controller when the target miss distance delta theta is less than step (t), and sending step (t) into the position ring controller when the miss distance delta theta is more than step (t). The relative movement speed of the visual axis of the frame and the target sight line is limited by adjusting the input of the position ring controller, so that the moving distance of a target image point on a camera focal plane in the exposure time of the camera is reduced, the image motion is reduced, and the imaging quality is improved.
The control system framework adopted by the invention is shown as the attached figure 1: thetaTIs the target visual axis angular position, theta is the current frame visual axis angular position, delta theta is the miss distance detected by the CCD camera, CimIs an image shift controller, Delta thetapGiven for the position ring, CpBeing position loop controllers, omegaTGiven for the velocity ring, CvIs a speed loop controller, GvIs the controlled object of the velocity loop and ω is the current gantry velocity.
The invention relates to a method for avoiding image motion in a target approaching process of a photoelectric tracking system, which is realized by adopting the following steps:
step (1), adding an optimal step length image shift controller in front of a position ring controller in a control frame of a photoelectric tracking system;
and (2) setting M as the maximum imaging position of the target allowed by the photoelectric tracking system on the focal plane of the cameraInter-frame pixel difference, TsIs the sampling period, | G of the camerap(t) | is the current gain of the position loop controller, and the image shift controller calculates the optimal step length at the current moment
Step (3), limiting the input delta theta of the position loop controller by the image motion controller according to the current optimal step length step (t)p(t): when the target miss distance delta theta is less than step (t), directly sending the miss distance into a position ring controller, namely delta thetap(t) ═ Δ θ; when the miss distance is larger than step (t), sending step (t) to a position ring controller, namely delta thetap(t)＝Step(t)。
The invention realizes the principle that: the target approaching process is as shown in fig. 2, and the position ring controller adjusts the position of the rack according to the target miss distance at the present moment, so that the target miss distance Δ θ is reduced to 0. In this process, let Δ θ have components in the X-axis and Y-axis directions of the image as Δ θ, respectivelyx_o、Δθy_o，Δθx(ΔTs)、Δθy(ΔTs) For the distance moved in the X-axis and Y-axis directions of the image for each sampling period of the target, if Δ θx(ΔTs)、Δθy(ΔTs) If the length of the step length M is not more than the fixed length of the step length M, the image motion of the target is within the allowable range, and the imaging quality is not influenced; otherwise, the image shift of the target exceeds the allowable range, which may reduce the imaging quality and further affect the extraction of the target miss distance. The invention adds a image shift controller in front of the position ring controller in the system control block diagram, which ensures that the image shift of the target in the exposure time does not exceed M pixels, namely:
to ensure the implementation of equation (1), Δ θ is first input by the controllerpTo a target miss distance delta theta open loop transfer function G collected by a CCD camerap_openComprises the following steps:
in the above formula, e-τsIs the CCD sampling delay. In practical systems, the speed loop bandwidth is much higher than the position loop gain, so within the operating bandwidth of the position loop, the speed loop can be equivalent to an amplifier with a gain of 1, and therefore equation (2) can be simplified as follows:
input Δ θpStep response ofi(t) is:
in the above formula L-1A pull-type inverse transform is represented.
Setting the sampling period of the position loop as TsThe CCD exposure period is also TsThe condition for ensuring the image to be clear is that the image movement does not exceed M pixels within the exposure time:
|Δθi(nTs)-Δθi[(n-1)Ts]|≤δ(nTs)M,(i＝x,y) (5)
the transformation into the complex frequency domain is:
in order to ensure that the target is as close to the center of the image as possible under the condition of clear image, an image shift controller C is designedimLet Δ θp(s)＝Cim[Δθ(s)]：
Returning to the time domain, the function Δ θp(t)＝Cim[Δθ(t)]The method is designed as a limiting function, the limiting value is Step, and the expression is as follows:
from the above equation, | Δ θ (t) | > Step (6) may become:
in an actual system, in order to ensure the phase margin of a position ring, the controller adopts an inertia link to replace an integral link:
so in the open-loop state, CpGiven ω for a velocity ring at a Step response of magnitude StepT：
Angular velocity omega of the frameTThe time-dependent curve is shown in fig. 3, and it can be seen that even if the position loop is given a step signal of fixed amplitude, ωTStill increases with time t, with a lower limit of Step kpUpper limit of
The relationship between Step size and image motion is shown in FIG. 4. If Step > M/TskpThen the image shift problem cannot be avoided anyway; if it is not
Whether there is an image motion problem is time-varying; if it is not
The image shift problem can be avoided but the response can be very slow. Practical systemIn the system, the setup of Step is as large as possible in consideration of the requirement of rapidity of response. To ensure omegaT(t)≤M/TsDesigning the time-varying optimal step size step (t) such that:
in the above formula | Gp(t) | is the position loop real-time gain, and the expression is
The image shift controller is realized by firstly obtaining the optimal step length step (t) at the current moment and then limiting and calculating the input delta theta of the position loop controller according to the optimal step lengthp(t) is carried out sequentially, and a program framework of the concrete implementation is shown in FIG. 5.
Compared with the prior art, the invention has the following advantages:
1. the method provided by the invention aims at the image motion phenomenon of a photoelectric tracking system in the target approaching process, and the conventional image motion control method only aims at the image motion phenomenon of a moving carrier camera.
2. The method provided by the invention adjusts the limited step length of the input signal according to the real-time gain of the position loop controller, can realize the optimization of the step length, and can realize the requirements of rapidity and minimum image motion to the maximum extent.
Drawings
FIG. 1 is a schematic diagram of a control framework of an electro-optical tracking system;
FIG. 2 is a schematic diagram of a target approximation process;
FIG. 3 is a position loop controller CpWhen Step signal with amplitude of Step is input, omega is outputT(ii) a change;
FIG. 4 is a diagram illustrating the relationship between Step size and image motion;
FIG. 5 is a flowchart of an optimal step size image shift controller routine;
fig. 6 is a simulation experiment result of the target approximation process in the embodiment of the present invention.
Detailed Description
The following describes embodiments of the present invention. The following examples are only for explaining the present invention, the scope of the present invention shall include the full contents of the claims, and the full contents of the claims of the present invention can be realized by those skilled in the art through the following examples.
Position ring controller for photoelectric tracking system
Sampling period TsThe minimum image shift to ensure image sharpness is M3 pix, 0.02 s. Can decompose out kp＝12、kI29.4, a 0.04. Respectively adopting three control structures of an image shift controller, an optimal step image shift controller and a fixed step image shift controller, and comparing step responses in the target approaching process, wherein the expression of the fixed step image shift controller is as follows:
the method provided by the invention is implemented according to the following steps:
step (1), adding an optimal step length image shift controller in front of a position ring controller in a control frame of a photoelectric tracking system;
step (2), the optimal step length image shift controller calculates the optimal step length of the current moment
Step (3), limiting the input delta theta of the position loop controller by the image motion controller according to the current optimal step length step (t)p(t)：
For a step signal with an amplitude value of 128pixl (a pixel value), a simulation experiment result is shown in fig. 6, a given time of the system without the image shift controller for the first time is 0.18 seconds, the overshoot is 11%, the maximum frame-to-frame difference of the miss distance is 31pixl, and obviously, the image shift phenomenon is relatively serious. The system adopting the optimal step length image motion controller has the first arrival time of 0.84 seconds, 7% overshoot, the maximum miss distance of 3pixl and image motion within the control range. The system adopting the fixed step image motion controller has the advantages that the first arrival time of the system is 0.98 second, the overshoot is 19.5 percent, the maximum miss distance between frames is 4pixl, and the slight image motion phenomenon exists.
The experimental results show that: the method for avoiding image motion in the target approaching process of the photoelectric tracking system provided by the invention has good rapidity under the condition of ensuring that the image motion is in a specified range, and the overshoot is lower than that of other two methods.
Parts of the invention not described in detail are well known in the art.
Claims (1)
1. A method for avoiding image motion in the target approaching process of an optoelectronic tracking system is characterized by comprising the following steps:
step (1), adding an optimal step length image shift controller in front of a position ring controller in a control frame of a photoelectric tracking system;
and (2) setting M as the maximum inter-frame pixel difference T of the target allowed by the photoelectric tracking system at the imaging position of the focal plane of the camerasIs the sampling period, | G of the camerap(t) | is the current gain of the position loop controller, and the optimal step length image shift controller calculates the optimal step length at the current moment
Step (3), the optimal step size image motion controller limits the input delta theta of the position ring controller according to the current optimal step size step (t)p(t): when the target miss distance delta theta is less than step (t), directly sending the miss distance into a position ring controller, namely delta thetap(t) ═ Δ θ; when the miss distance is larger than step (t), sending step (t) to a position ring controller, namely delta thetap(t)＝Step(t)。
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