Servo control method of airborne star tracker

Abstract

The invention provides a servo control method of an airborne star tracker. Based on airborne star tracker servo control of a variable gain PID (Proportion Integration Differentiation) controller, the requirements of the airborne star tracker on a servo system in different working modes are met. When the airborne star tracker is in a target switching working mode, only a PI controller is adopted, a larger Kp is selected to accelerate the response speed, and meanwhile, a smaller Ki is selected to prevent overshoot; when the airborne star tracker is in a target tracking working mode, the input can be simulated to be a sine function with a small amplitude. At the moment, small Kp can be selected to prevent system oscillation, large Ki can be selected to improve steady-state precision, Kd is added to achieve the purpose of advanced adjustment, the size of Kd is changed, and system oscillation caused by too large Kd is prevented.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-precision astronomical inertial navigation, and specifically relates to a servo control method for an airborne star tracker. Background Art

[0002] The star tracker is a complex multi-sensor system, and due to the airborne environment and navigation performance requirements, different working modes and performance requirements need to be considered. However, as far as its servo control system is concerned, the main tasks can be divided into two major tasks: target tracking and target switching.

[0003] The input instructions and requirements of the servo control system in the two working modes are:

[0004] When the airborne star tracker is in the target switching working mode: the star tracker calculates the positions of different stars and transmits the position difference to the servo system. Therefore, at this time, for the servo control system, the input command can be simulated as a step function with a large amplitude, and the requirement is a fast response;

[0005] When the airborne star tracker is in the target tracking working mode: due to various factors such as the engine and airflow, the aircraft will oscillate. Since the star needs to be tracked, the input command for the servo control system can be simulated as a sine function with a smaller amplitude, and the requirement is precise tracking.

[0006] PI (Proportional-Integral) control algorithm is a commonly used closed-loop control strategy, which is used to achieve error regulation of the system. The P controller combines only two control methods: proportional control (Proporional, P) and integral control (Integral, I). Proportional control directly converts the error into control output through proportional gain (Kp), while integral control integrates the error through integral gain (K) and accumulates the integral result as part of the control output. Comparative analysis shows that the input command parameters and working requirements of the servo control system in the target switching working mode and the target tracking working mode are quite different. If the traditional PI control method is used, it cannot be met at the same time. Summary of the invention

[0007] The purpose of this application is to provide a servo control method for an airborne star tracker, which automatically changes the variable gain of a PID controller by analyzing the working mode of the airborne star tracker, as well as the size of input command values ​​and feedback values, so that the servo system can complete the task requirements of the airborne star tracker.

[0008] To achieve the above object, a servo control method for an airborne star tracker is provided, which is characterized by comprising: when the airborne star tracker is in a target switching working mode, the input command can be simulated as a step function with a large amplitude, at this time only a PI controller is used, a larger proportional control is selected, the error is converted into a control output through a proportional gain Kp to speed up the response speed, the integral control performs integral control on the error through an integral gain Ki to eliminate the steady-state error, and the integral result is accumulated as a part of the control output;

[0009] When the airborne star tracker is in the target tracking working mode, a PID controller is used, and the input command can be simulated as a sine function with a small amplitude. At this time, the position error of the controller is small, but the frequency of change is high, that is, the differential of the position error is large. A smaller Kp is used to prevent the system from oscillating too large a steady-state error, and a larger Ki is selected to improve the steady-state accuracy. By identifying the size of the differential of the position error, the amplitude of the output signal is adjusted according to the rate of change of the position error signal, and the size of Kd is changed to prevent excessive Kd from causing system oscillation. The output signal is used as the output of the controller, and the output signal is converted into an actual control quantity through the actuator to act on the airborne star tracker; at the same time, the output signal of the airborne star tracker is used as a feedback command signal and compared with the reference signal to form a closed-loop control.

[0010] Furthermore, the error value between the input command and the feedback command is identified. When the difference is greater than 2°, it is identified that the airborne star tracker is in the target switching working mode. Only the PI controller is used, and a larger Kp is selected to speed up the response speed, and a smaller Ki is selected to prevent overshoot. When the difference is less than 2°, it is identified that the airborne star tracker is in the target tracking working mode. At the same time, according to the size of the differential component of the error value, the external jitter condition of the airborne star tracker is judged to adjust the parameters, and the parameter size of the PID value is switched to achieve the control effect.

[0011] Further, external jitter compensation processing is performed, including: a jitter measurement component, which is configured to receive rate data output by the sensor device, and a jitter compensation component, which is configured to adjust the operation of the measurement component to compensate for the measurement value changes caused by the jitter determined by the jitter measurement component.

[0012] Furthermore, the jitter measurement component is based on inertial sensor technology, or non-inertial sensor technology, or a combination of inertial and non-inertial sensor technology, and is integrated in a closed space of the aircraft.

[0013] Further, the jitter measurement component uses a multi-stage filtering method to calculate a measure of jitter severity. In a first stage, upon receiving each new example of rate data from the sensor device, a difference between a weighted average of previously received rate data and a historical intermediate instance of the received rate data is determined; in a second stage, a measure of the jitter severity of the new example of rate data is determined as the difference between a weighted average of the previously determined differences and a difference determined in the history.

[0014] Further, the weighted average is determined using an already used symmetrical weighted distribution of the received rate data, the symmetrical weighted distribution including a half-sine wave distribution or a uniform weighted distribution.

[0015] Further, the jitter measurement component also includes a third filtering stage having a uniformly weighted low pass filter for determining the jitter severity measurement; upon receiving new example data of rate data from the sensor device, estimating the average rate of change of the object's orientation over an estimated time period before the effective time point of the new example data of rate data, and integrating the average rate of change over the estimated integration time period to give an estimate of the object's orientation, and adding the estimated orientation change to the orientation determined by integrating the received new example data of rate data to give a predicted orientation of the object.

[0016] Further, the jitter compensation component adjusts at least one of the estimation time period and the integration time period of the predictor component according to the determined measure of jitter severity to perform compensation, and then outputs instruction data to the PID control algorithm for precise control.

[0017] The beneficial effects of this application include:

[0018] The invention has the beneficial effect of automatically changing the variable gain of the PID controller by analyzing the working mode of the airborne star tracker, the size of the input command value and the feedback value, thereby improving the servo capability of the star tracker, enabling the star tracker to stably follow the star and improving the accuracy of astronomical inertial navigation. Through multi-stage filtering, the jitter data is compensated and transmitted to the PID algorithm control to achieve the purpose of optimal and precise control. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0020] Attached Figure 1 This is a schematic diagram of the control flow of a traditional star tracker;

[0021] Attached Figure 2 A schematic flow chart of a servo control method for an airborne star tracker in the present invention;

[0022] Attached Figure 3 This is a flow chart of the variable gain PID algorithm in the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. It should be noted that, in the absence of conflict, the various features in the embodiments of the present application can be combined with each other, and the combined embodiments are still within the scope of protection of the present application.

[0024] Attached Figure 1 This is a schematic diagram of the traditional star tracker control process, which consists of three PI loops: position-speed-current. When the airborne star tracker is in the target switching working mode: for the servo control system, the input command can be simulated as a step function with a large amplitude; when the airborne star tracker is in the target tracking working mode, for the servo control system, the input command can be simulated as a sine function with a small amplitude. Comparative analysis shows that the input command values ​​and working requirements of the servo control system in the two working modes are quite different. If the traditional PI control method is used, it is impossible to meet both working modes at the same time.

[0025] The present invention proposes a servo control method for an airborne star tracker, which is based on a variable gain PID controller to control the airborne star tracker servo system to meet the requirements of the airborne star tracker for the servo system in different working modes. Figure 2 The figure shows a flow chart of the servo control method of the airborne star tracker of the present invention. Compared with the traditional PI control method, the present invention changes the PID parameters of the position loop by analyzing the working mode of the airborne star tracker.

[0026] When the airborne star tracker is in the target switching working mode, the input command can be simulated as a step function with a large amplitude. At this time, the position error of the controller is large, which can be seen by analyzing the functions of the parameters Kp, Ki, and Kd in the PID controller structure. Only the PI controller can be used, and a larger proportional control can be selected to convert the error into the control output through the proportional gain Kp to speed up the response speed and be more sensitive; while the integral control integrates the error through the integral gain (Ki) to eliminate the steady-state error, and accumulates the integral result as part of the control output to make the system output more stable.

[0027] When the airborne star tracker is in the target tracking working mode, the PID controller is used, and the input command can be simulated as a sine function with a small amplitude. At this time, the position error of the controller is small, but the frequency of change is high, that is, the differential of the position error is large. At this time, a smaller Kp can be selected to prevent the system from oscillating too large in the steady-state error. At the same time, a larger Ki can be selected to improve the steady-state accuracy and add Kd to achieve the purpose of advance regulation. It is necessary to identify the size of the differential of the position error, adjust the amplitude of the output signal according to the rate of change of the position error signal, change the size of Kd, and prevent excessive Kd from causing system oscillation. The output signal is used as the output of the controller, and the output signal is converted into the actual control quantity through the actuator (such as the motor driver) to act on the airborne star tracker. At the same time, the output signal of the airborne star tracker is used as the feedback command signal and compared with the reference signal to form a closed-loop control.

[0028] Attached Figure 3 This is a flow chart of the variable gain PID algorithm in the present invention, which identifies the error value between the input command and the feedback command. When the difference is greater than 2°, it is identified that the airborne star tracker is in the target switching working mode, and only the PI controller is used, and a larger Kp is selected to speed up the response speed, and a smaller Ki is selected to prevent overshoot; when the difference is less than 2°, it is identified that the airborne star tracker is in the target tracking working mode, and according to the size of the differential component of the error value, the external jitter condition of the airborne star tracker is judged to adjust the parameters, and the parameter size of the PID value is switched to achieve the control effect.

[0029] Due to the dynamic randomness or dynamic non-randomness of external jitter conditions, even if the parameters of the PID value are dynamically adjusted, the airborne star tracker cannot achieve the best control effect. In order to better control the airborne star tracker, it is also necessary to compensate for the external jitter, based on a relatively stable (less external disturbance) input command, and achieve the best actual control effect through the variable gain PID algorithm.

[0030] The invention provides a method for compensating for external jitter, comprising: a jitter measurement component configured to receive rate data output by a sensor device, and a jitter compensation component configured to adjust the operation of the measurement component to compensate for measurement value changes introduced by jitter determined by the jitter measurement component.

[0031] The jitter measurement component is based on inertial sensor technology, or non-inertial sensor technology, or a combination of inertial and non-inertial sensor technology, and is integrated in the enclosed space of the aircraft.

[0032] The jitter measurement component uses a two-stage filtering method to calculate a measure of jitter severity. In a first stage, upon receiving each new example of rate data from the sensor device, a difference between a weighted average of previously received rate data and a historical intermediate instance of received rate data is determined. In a second stage, a measure of jitter severity for the new example of rate data is determined as the difference between the weighted average of the previously determined differences and the differences determined in the history. In a specific calculation method, the weighted average is determined using an already used symmetrical weighted distribution of the received rate data, which may include a half-sine wave distribution or a uniform weighted distribution.

[0033] More precisely, the jitter measurement assembly further comprises a third filtering stage, having a uniformly weighted low pass filter, for determining the measure of jitter severity. Upon receiving a new example of velocity data from the sensor device, an average rate of change of the orientation of the object over an estimation time period preceding the valid time point of the new example of velocity data is estimated, and the average rate of change over an estimated integration time period is integrated to give an estimate of the orientation of the object. The estimated change in orientation is added to the orientation determined by integrating the received new example of velocity data to give a predicted orientation of the object.

[0034] The jitter compensation component adjusts at least one of the estimation time period and the integration time period of the predictor component according to the determined measure of jitter severity to perform compensation, and then outputs instruction data to the PID control algorithm for precise control.

[0035] The parts not involved in the present application are the same as the prior art or can be implemented by using the prior art.

[0036] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A servo control method for an airborne star tracker, characterized in that: Including: When the airborne star tracker is in the target switching working mode, the input command can be simulated as a step function with a large amplitude. At this time, only the PI controller is used, and a larger proportional control is selected. The error is converted into a control output through the proportional gain Kp to speed up the response speed. The integral control integrates the error through the integral gain Ki to eliminate the steady-state error, and the integral result is accumulated as part of the control output; When the airborne star tracker is in the target tracking working mode, a PID controller is used, and the input command can be simulated as a sine function with a small amplitude. At this time, the position error of the controller is small, but the frequency of change is high, that is, the differential of the position error is large. A smaller Kp is used to prevent the system from oscillating too large a steady-state error, and a larger Ki is selected to improve the steady-state accuracy. By identifying the size of the differential of the position error, the amplitude of the output signal is adjusted according to the rate of change of the position error signal, and the size of Kd is changed to prevent excessive Kd from causing system oscillation. The output signal is used as the output of the controller, and the output signal is converted into an actual control quantity through the actuator to act on the airborne star tracker; at the same time, the output signal of the airborne star tracker is used as a feedback command signal and compared with the reference signal to form a closed-loop control.

2. The method according to claim 1, characterized in that: Identify the error value between the input command and the feedback command. When the difference is greater than 2°, identify that the airborne star tracker is in the target switching working mode. Only use the PI controller, and select a larger Kp to speed up the response speed, and select a smaller Ki to prevent overshoot. When the difference is less than 2°, identify that the airborne star tracker is in the target tracking working mode. At the same time, according to the size of the differential component of the error value, judge the external jitter condition of the airborne star tracker to adjust the parameters, and switch the parameter size of the PID value to achieve the control effect.

3. The method according to claim 2, characterized in that: The invention provides a method for compensating for external jitter, comprising: a jitter measurement component configured to receive rate data output by a sensor device, and a jitter compensation component configured to adjust the operation of the measurement component to compensate for measurement value changes introduced by jitter determined by the jitter measurement component.

4. The method according to claim 3, characterized in that: The jitter measurement component is based on inertial sensor technology, or non-inertial sensor technology, or a combination of inertial and non-inertial sensor technology, and is integrated in the enclosed space of the aircraft.

5. The method according to claim 3, characterized in that: The jitter measurement component uses multi-stage filtering to calculate a measure of jitter severity, wherein in a first stage, upon receipt of each new instance of rate data from the sensor device, a difference between a weighted average of previously received rate data and a historical intermediate instance of received rate data is determined; In the second stage, a measure of the severity of jitter for a new example of the rate data is determined as the difference between a weighted average of previously determined differences and the differences determined historically.

6. The method according to claim 3, characterized in that: The weighted average is determined using an already used symmetrical weighted distribution of the received rate data, including a half-sine wave distribution or a uniform weighted distribution.

7. The method according to claim 5, characterized in that: The jitter measurement component also includes a third filtering stage having a uniformly weighted low pass filter for determining a measure of jitter severity; upon receiving a new example of rate data from the sensor device, estimating the average rate of change of the object's orientation over an estimated time period before the valid time point of the new example of rate data, and integrating the average rate of change over an estimated integration time period to give an estimate of the object's orientation, and adding the estimated orientation change to the orientation determined by integrating the received new example of rate data to give a predicted orientation of the object.

8. The method according to claim 5, characterized in that: The jitter compensation component adjusts at least one of the estimation time period and the integration time period of the predictor component according to the determined measure of jitter severity to perform compensation, and then outputs instruction data to the PID control algorithm for precise control.

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