Control method for eliminating image dithering

Abstract

The invention provides a control method for eliminating image dithering, which is used for solving the problem of target loss caused by dramatic change of the motion state of a tracked target. The method comprises three stages: in the first stage, after the motion law of a tracked target is fully analyzed, the state of the tracked target is identified, a targeted control strategy is provided according to the state of the tracked target, and a preliminary control quantity is obtained, so that the tracked target is not lost; in the second stage, the initial control quantity is optimized, so that the tracked target is located in the center of the field of view; and in the third stage, amplitude limiting adjustment is carried out on the optimized control quantity, and final control output is output. The method is not limited by the type of the tracker, is simple and easy to implement, high in operability and convenient to popularize and use, and is short in debugging time and excellent in performance when being subjected to overall joint debugging with other external systems.

Description

Technical Field

[0001] The invention belongs to the field of servo control and relates to a control method for eliminating image jitter. Background Art

[0002] In combat scenarios, it is necessary to effectively track the target. When the optoelectronic tracker tracks a target at a long distance, once the target's motion state changes dramatically, such as sudden start and stop, the target is easy to be lost. In order to achieve effective tracking, the current mainstream strategy is to adjust the performance indicators of the tracker by directly improving the tracking algorithm of the tracker. The tracking algorithm in the tracker is embedded in the FPGA. Due to the large amount of FPGA modification content, the large number of debugging and modification times, the long FPGA compilation time, and the diverse and complex FPGA algorithm forms, the debugging time is too long and the technical difficulty is high. In addition, since trackers are mostly black boxes in practice, it is technically difficult to directly modify the control algorithm therein. Therefore, it is necessary to find a fast and simple method.

[0003] During the tracking process, the photoelectric tracker tracks the moving target through the cooperation of the servo control system. During this period, the staff monitors the movement of the target from the monitor. The control method of the existing servo control system is universal and simple, usually using PID control method, such as Figure 2 As shown, it specifically involves three loops: speed loop, position loop, and tracking loop, among which the speed loop is the innermost loop, the position loop is the middle loop, and the tracking loop is the outermost loop. The speed loop consists of four parts: controller, driver, motor (actuator), and gyroscope (speed sensor). When the servo controller receives the speed control command sent by the tracker, it forms a control signal for controlling the motor after passing through the internal algorithm. After being amplified by the driver, the motor is driven to rotate. The gyroscope transmits the rotation speed of the motor to the controller. The controller compares the current speed with the received speed value to form a new control quantity. It iterates in this way until the movement speed of the servo motor is the same as the speed output by the gyroscope, that is, the movement speed of the servo system is consistent with the target value.

[0004] The position loop is composed of a speed loop and a code disk (position sensor). When the servo controller receives the position signal from the tracker, it forms a control signal for the motor after calculation by the internal algorithm. After amplification by the driver, the motor is driven to rotate. The code disk transmits the position of the motor to the controller. The controller compares the current angle with the received position value to form a new control value. This iteration continues until the position of the servo motor is consistent with the position output by the code disk. That is, the rotation angle of the servo system is consistent with the target value.

[0005] The tracking loop consists of a tracker and a speed loop. When the servo controller receives the tracking deviation sent by the tracker, it calculates the internal algorithm to form a control signal for controlling the motor. After being amplified by the driver, the motor is driven to rotate. The tracker collects the current deviation pixel and compares it with the target deviation pixel to form a new control amount. This iteration continues until the tracking deviation pixel is zero, even if the tracking target position is in the field of view.

[0006] In summary, the servo control system can be combined to achieve fast and effective control of the photoelectric tracker's tracking and de-jittering. Summary of the invention

[0007] In view of this, the present invention proposes a control method for eliminating image jitter. The present invention no longer takes the tracking algorithm in the tracker as the improvement object, but specifically optimizes the control algorithm of the servo control system to solve the problem that the target is lost due to the drastic change in the motion state of the tracked target, and the existing technology cannot quickly achieve tracking and jitter elimination.

[0008] The technical solution of the present invention is as follows

[0009] The present invention is based on a system composed of a servo system and an optoelectronic tracker, and the control target is to track a target without losing it and to make the tracked target be in the center of the field of view; specifically, it includes three stages: in the first stage, a preliminary control amount is obtained by selecting a control strategy to ensure that the tracked target is not lost; in the second stage, the preliminary control amount is optimized to ensure that the tracked target is in the center of the field of view; in the third stage, the optimized control amount is limited and adjusted to output the final control amount; wherein, the first stage includes that after the optoelectronic tracker tracks the target, the tracking deviation is sent to the servo controller, and the tracking deviation refers to the pixel deviation of the position of the tracked target from the center of the field of view in the imaging field of view, and the servo system converts the tracking deviation into three judgment indicators, namely, the deviation angle, the deviation angular velocity, and the deviation angular acceleration; according to the three judgment indicators, it is judged whether the tracked object is in a sudden start-stop state; for the sudden start-stop state, the controller in the servo system adopts proportional control, and for the non-sudden start-stop state, the controller in the servo system adopts proportional integral control, thereby obtaining the preliminary control amount;

[0010] Judging whether the tracked object is in a sudden start-stop state according to the three judgment indicators specifically includes:

[0011] When the deviation angle is large, the tracked object is in a state of sudden start and stop;

[0012] When the deviation angle is small and the deviation angular velocity is large, the tracked object is in a sudden start-stop state;

[0013] When the deviation angle is small, the deviation angular velocity is small, and the deviation angular acceleration is large, the tracked object is in a sudden start-stop state;

[0014] When the deviation angle is small, the deviation angular velocity is small, and the deviation angular acceleration is small, the tracked object is not in a sudden start-stop state;

[0015] When the tracked object is not in a sudden start-stop state, the motion state is relatively stable, and the tracked object is in the center of the field of view. At this time, the deviation angle, deviation angular velocity, and deviation angular acceleration are all within a very small range. Once a sudden start-stop occurs, the deviation angular acceleration will first change dramatically, then cause a dramatic change in the deviation angular velocity, and finally lead to a dramatic change in the deviation angle, and the tracked object will obviously deviate from the center of the field of view. The present invention divides the sudden start-stop state into three stages: initial, development, and end according to the law of motion change, and proposes the above three judgment conditions corresponding to the sudden start-stop state.

[0016] Furthermore,

[0017] The smaller amount of the three judgment indicators is: the minimum identification parameter of each judgment indicator obtained by the hardware device in the servo system;

[0018] For example: the minimum recognition speed of the gyroscope is 1° / s; the minimum pixel that the tracker can recognize is 2 pixels, the output accuracy of the code disk is 0.01 degrees, etc.

[0019] The larger amount of the three judgment indicators is: 4-7 times the corresponding smaller amount;

[0020] The control goal of the second stage is to keep the tracked target in the center of the field of view. The optimization process of the preliminary control quantity includes:

[0021] Corresponding to the initial control amount of the sudden start-stop state, it is judged whether the initial control amount will cause the mechanical angle servo of the servo system to cross the boundary. If it crosses the boundary, the initial control amount is optimized by proportional control to ensure that the tracked target is as close to the center of the field of view as possible under the premise that the servo does not cross the boundary, thereby obtaining the optimized control amount; if it does not cross the boundary, the initial control amount is optimized by proportional integral control to ensure that the tracked target is in the center of the field of view, thereby obtaining the optimized control amount;

[0022] Corresponding to the preliminary control quantity of the non-sudden start-stop state, it is judged whether the integral time in the preliminary control quantity is greater than the servo data conversion time.

[0023] If it is greater than, it means that the integral time is too long, and the controller is always in the state of calculating the integral time, and the integral calculation cannot be realized, and the integral term cannot be sent out. Then, the preliminary control amount is proportionally controlled, and the value of the control amount is changed through the proportional term to obtain the appropriate control amount, so as to ensure that the servo control amount is continuous during the tracking process, the servo system does not overshoot, and the servo system runs smoothly according to the change of the tracking deviation, and finally the tracking target is in the center of the field of view, thereby obtaining the optimized control amount;

[0024] If it is not greater than, it is determined whether the initial control amount will cause the mechanical angle servo of the servo system to exceed the limit.

[0025] If it is out of bounds, the initial control amount is adjusted using proportional control to ensure that the target is as close to the center of the field of view as possible without the servo going out of bounds, thereby obtaining the optimized control amount;

[0026] If it does not cross the boundary, due to the accumulation of integral terms in the preliminary control quantity, it is necessary to determine again whether the integral time is greater than the servo data conversion time to prevent the integral term from being unable to be output or the output integral term from being too large. If it is greater, the preliminary control quantity is optimized using proportional control to obtain the optimized control quantity, so that the tracking target is in the center of the field of view; if it is not greater, the preliminary control quantity is optimized using proportional integral control to finally achieve the tracking target in the center of the field of view, so as to obtain the optimized control quantity;

[0027] In the third stage, the optimized control quantity is output with limited amplitude;

[0028] Furthermore, the boundary value of the control quantity is determined by the amplification factor of the servo system driver involved and the performance index of the motor.

[0029] in,

[0030] The integral time refers to the time required when the output formed by the integral action is equal to the output formed by the proportional action;

[0031] Servo data conversion time refers to the time from when the servo controller receives the control command from the host computer to when it outputs the control quantity to the motor;

[0032] The integral time refers to the sum of the time from a certain starting point to a certain end point on the time axis. The integral time is a parameter used to indicate the strength of the integral control effect. The shorter the integral time, the stronger the integral effect. Conversely, the longer the integral time, the weaker the integral effect. In PID, I refers to the compensation of the accumulated error over the past period of time, because the P compensation is not continuous under discrete time. Assuming that e is a function of time, then the P compensation is Pe(t)-Pe(t+1), where t+1 is not 1 second added to the time, but the number of compensations added once. It is easy to conclude that the error between this time and the last time cannot be equal to 0, so it is necessary to calculate the continuous integral over the past period of time to eliminate this error. That is, the integral I controls the past changes of the controlled quantity, the proportional P controls the current changes of the controlled quantity, and the differential D controls the future changes of the controlled quantity.

[0033] Beneficial Effects

[0034] 1) Based on the working principle of the servo system, the present invention proposes a control method for tracking and de-jittering of an optoelectronic tracker according to the basic characteristics of the tracking loop and the control principle of the servo system, which can effectively improve the tracking performance of the tracked target under sudden start-stop conditions.

[0035] 2) In the first stage, after fully analyzing the movement law of the tracked target, the present invention effectively identifies the state of the tracked target based on three judgment indicators, and proposes a targeted control strategy based on the state of the tracked target, thereby solving the problem of tracking loss when the tracked deviation changes greatly in a short period of time.

[0036] 3) The second stage of the optimization control strategy, for the initial control quantity of the sudden start-stop state, when the initial control quantity causes the mechanical angle servo of the servo system to cross the boundary, proportional control is used for optimization. Proportional control can respond to the deviation signal in time without lag, and can quickly adjust the mechanical angle so that it does not cross the boundary, and ensure that the servo control quantity is continuous during the tracking process, the servo system does not overshoot, and the servo system runs smoothly according to the change of the tracking deviation. When it does not cross the boundary, proportional integral is used for optimization. Proportional control responds to the deviation signal in time without lag, and integral control automatically eliminates static error, that is, error-free regulation. When it does not cross the boundary, it can respond to the change of the current deviation in time and eliminate the steady-state error. This can ensure that the servo system has good performance indicators, small overshoot, and stable operation.

[0037] For the initial control quantity in the non-sudden start-stop state, two integral time judgments were performed to ensure that the control quantity can be effectively output.

[0038] 4) By limiting the control amount, the servo control system can be prevented from oscillating and the service life of the system can be extended.

[0039] 5) The present invention is not limited by the model of the tracker, is simple and easy to operate, and has strong operability.

[0040] 6) The present invention has been verified in the photoelectric tracker, and the effect is remarkable, and it is easy to promote and use. When it is overall coordinated with other external systems, the debugging time is short and the performance is excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A program flow chart of a control method for eliminating image jitter

[0042] Figure 2 Principle block diagram of existing servo control system. DETAILED DESCRIPTION

[0043] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0044] like Figure 1As shown, the present invention proposes a photoelectric tracker tracking de-jitter control method, comprising the following steps:

[0045] Step 1: Read the tracking command word, and the servo system enters the tracking state;

[0046] Step 2: Read the tracking deviation and convert the tracking deviation into deviation angle, deviation angular velocity and deviation angular acceleration;

[0047] Step 21: Calculate the tracking deviation angle based on the TV focal length sent by the tracker

[0048] A_err=-57.3*arctan(6.45*0.001*(A_err_track) / bjfk);

[0049] Where: A_err is the tracking deviation angle;

[0050] A_err_track is the tracking deviation given by the tracker;

[0051] bjfk gives the TV focal length value for the tracker;

[0052] Step 22: Calculate the deviation angular velocity according to the calculated tracking deviation angle;

[0053] A_speed=A_err(t)-A_err(t-1);

[0054] Where: A_speed is the deviation angular velocity;

[0055] A_err(t) is the deviation angle at the current moment;

[0056] A_err(t-1) is the deviation angle at the previous moment;

[0057] Note: A_err(t) and A_err(t-1) differ by 1 second;

[0058] Step 23: Calculate the deviation angular acceleration according to the calculated deviation angular velocity;

[0059] A_a=A_speed(t)-A_speed(t-1);

[0060] Where: A_a is the deviation angular acceleration;

[0061] A_speed(t) is the deviation angular velocity at the current moment;

[0062] A_speed(t-1) is the deviation angular velocity at the previous moment;

[0063] Note: A_speed(t) and A_speed(t-1) differ by 1s;

[0064] Step 3: The servo system converts the tracking deviation into deviation angle, deviation angular velocity, and deviation angular acceleration, and obtains the preliminary control quantity by judging and adopting the corresponding control strategy;

[0065] Step 31: Determine the tracking deviation angle. If the tracking deviation angle is less than the deviation range of 1°, that is, the tracked object is not at the sudden start-stop moment, proceed to step 32;

[0066] If the tracking deviation angle is greater than the deviation range of 5°, that is, the tracked object is at a sudden start or stop moment, the control strategy in the servo system adopts integral clearing, and the control algorithm output of P;

[0067] Step 32: Determine the tracking deviation angular velocity. If the tracking deviation angular velocity is less than the deviation range of 1° / s, that is, the tracked object is not at the sudden start-stop moment, proceed to step 33;

[0068] If the tracking deviation angular velocity is greater than the deviation range of 5° / s, that is, the tracked object is at a sudden start or stop moment, the control strategy in the servo system adopts integral clearing, and the control algorithm output of P;

[0069] Step 33: Determine the tracking deviation angular acceleration. If the angular acceleration is less than the deviation range of 1° / s2, that is, the tracked object is not at the moment of sudden start and stop, the control strategy in the servo system adopts the control algorithm output of PI;

[0070] If the angular acceleration is greater than the deviation range of 5° / s2, that is, the tracked object is at a sudden start or stop moment, the control strategy in the servo system adopts integral clearing, and the control algorithm output of P;

[0071] Step 4: Further optimize the preliminary control quantity obtained in step 3. The optimization process is as follows:

[0072] Step 41: Determine whether the integral time in the preliminary control amount is greater than the servo data conversion time 0.8s;

[0073] 1) If it is greater than, the integral time is reset to zero and the P control algorithm is used for output;

[0074] 2) If not greater than, proceed to step 42;

[0075] The initial control amount corresponding to the sudden start-stop state has no integral control, so it directly enters step 42;

[0076] Step 42: Determine if the mechanical angle servo is out of bounds.

[0077] 1) If the azimuth mechanism is not within the range of -180°~+180°, and the pitch mechanism is not within the range of -16°~

[0078] +66°, the integral term is cleared, and the P control algorithm is used to ensure that the mechanical angle servo does not exceed the limit;

[0079] 2) If the azimuth mechanism is in the range of -180° to +180° and the pitch mechanism is in the range of -16° to +66°, the integral term is accumulated and the process goes to step 43; the initial control amount corresponding to the sudden start-stop state has no integral control, so the process goes directly to step 43;

[0080] Step 43: Determine whether the integration time is greater than the servo data conversion time;

[0081] 1) If the integral time is greater than the servo data conversion time of 0.8s, the integral time is reset and the P control algorithm is used for output; pure proportional is used during the pre-servo conversion time to prevent tracking steps and large overshoot during initial tracking;

[0082] 2) If the integral time is not greater than the servo data conversion time of 0.8s, the PI control algorithm is used for output;

[0083] Step 5: For the optimized control quantity obtained in step 4, determine the boundary value of the control quantity according to the gain of the servo system driver and the performance index of the motor. If it does not exceed the boundary value, the optimized control quantity is the final control quantity; if it exceeds the boundary value, the boundary value is used as the final control quantity output.

Claims

1. A control method for eliminating image jitter, characterized in that: In the first stage, the initial control quantity is obtained by selecting the control strategy so that the tracking target is not lost; In the second stage, the preliminary control amount is optimized to place the tracked target in the center of the field of view; In the third stage, the optimized control quantity is limited and adjusted to output the final control output; wherein, the first stage includes, the photoelectric tracker sends the tracking deviation to the servo controller, the tracking deviation refers to the pixel deviation of the position of the tracked target from the center of the imaging field of view, and the servo controller converts the tracking deviation into three indicators, namely, the deviation angle, the deviation angular velocity, and the deviation angular acceleration; according to the three indicators, it is judged whether the tracked object is in a sudden start-stop state; for the sudden start-stop state, the controller in the servo system adopts proportional control, and for the non-sudden start-stop state, the controller in the servo system adopts proportional integral control, thereby obtaining the preliminary control quantity.

2. The control method for eliminating image jitter according to claim 1, characterized in that: The following three indicators are used to determine whether the tracked object is in a sudden start-stop state: When the deviation angle is large, the tracked object is in a state of sudden start and stop; When the deviation angle is small and the deviation angular velocity is large, the tracked object is in a sudden start-stop state; When the deviation angle is small, the deviation angular velocity is small, and the deviation angular acceleration is large, the tracked object is in a sudden start-stop state; When the deviation angle is small, the deviation angular velocity is small, and the deviation angular acceleration is small, the tracked object is not in a sudden start-stop state.

3. The control method for eliminating image jitter according to claim 2, characterized in that: The smaller amount of the three judgment indicators is: the minimum identification parameter of each judgment indicator obtained by the hardware device in the servo system; The larger amount of the three judgment indicators is: 4-7 times the corresponding smaller amount.

4. A control method for eliminating image jitter according to claim 1, 2 or 3, characterized in that: The second phase further includes, Corresponding to the initial control amount of the sudden start-stop state, it is judged whether the initial control amount will cause the mechanical angle servo of the servo system to cross the boundary. If it crosses the boundary, the initial control amount is optimized by proportional control to obtain the optimized control amount, so that the tracked target is as close to the center of the field of view as possible without crossing the boundary of the servo; If it does not cross the boundary, the initial control quantity is optimized by using proportional integral control to make the tracked target in the center of the field of view; Corresponding to the preliminary control quantity of the non-sudden start-stop state, it is judged whether the integral time in the preliminary control quantity is greater than the servo data conversion time. If it is greater than, the initial control amount is optimized by proportional control to make the tracking target in the center of the field of view; If it is not greater than, it is determined whether the initial control amount will cause the mechanical angle servo of the servo system to exceed the limit. If it is out of bounds, the initial control amount is adjusted using proportional control to keep the tracked target in the center of the field of view as much as possible without the servo going out of bounds; If it does not cross the limit, it is determined again whether the integration time is greater than the servo data conversion time. If it is, the initial control amount is optimized by proportional control to make the tracked target as close to the center of the field of view as possible. If it is not greater than, the initial control amount is optimized by using proportional integral control to make the tracking target in the center of the field of view; in, The integral time refers to the time required when the output formed by the integral action is equal to the output formed by the proportional action; The servo data conversion time refers to the time from when the servo controller receives the control command from the host computer to when it outputs the control quantity to the motor.

5. The control method for eliminating image jitter according to claim 4, characterized in that: The boundary value of the control quantity is determined by the amplification factor of the servo system driver involved and the performance indicators of the motor.

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