A model assisted feedforward controller design method and apparatus for visual electro-optical tracking systems

Abstract

The application discloses a model-assisted feedforward controller design method and device for a visual photoelectric tracking system and belongs to the field of target tracking control of photoelectric tracking systems. In view of the input lag of the visual-based servo system, the gain design of the position controller is limited, the method firstly gives a design scheme of the position controller to complete a position closed loop, on the basis of the position closed loop, the position controller output is used, and the influence of model mismatch is considered, and under the condition of meeting stability, a design scheme of an optimal feedforward controller is given. The method belongs to a controller optimization method, and under the condition of a prior model, the error suppression capability and the anti-interference capability of the system are simultaneously improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of visual photoelectric tracking system control, and particularly relates to a model-assisted feedforward controller design method and device for a visual photoelectric tracking system. BACKGROUND

[0002] System tracking accuracy is an important indicator in photoelectric tracking, which is directly reflected in the size of line of sight (LOS) error. Controlling LOS requires two equally important requirements, one is to track the target so that it is in the field of view, and the other is to reject disturbances to stabilize the LOS in the inertial space. High control bandwidth is generally beneficial to tracking and anti-interference.

[0003] However, because the visual-based photoelectric tracking system needs a strong exposure time to obtain high-quality images through a CCD, the system will contain a non-negligible delay, which limits the control bandwidth. Since the delay will limit the gain of the controller, it is difficult to obtain sufficient pointing accuracy only by relying on basic feedback control. Therefore, a control strategy specially designed to overcome the impact of delay must be used to overcome the diffraction limit of the optical system as much as possible.

[0004] In order to balance the sharp contradiction between the controller gain and the phase angle margin of the system with time delay, researchers consider adding an additional feedforward branch to improve the control performance of the system. Since the image sensor can only obtain the LOS error of feedback control, the difficulty of using feedforward lies in obtaining the target information required for feedforward control. Scholars try to combine the LOS error with the platform angle provided by the encoder or other sensors to synthesize the target trajectory, and then forward it to the system after delay compensation prediction. However, the traditional feedforward control is used to improve the tracking performance with the help of additional sensors, but it is invalid for the disturbance of the LOS in the inertial space, and cannot guarantee high-precision tracking in a strong disturbance environment. Moreover, no specific feedforward controller design scheme is given, which may lead to non-optimal design of the system and cannot guarantee the stability of the system in the case of serious mismatch. SUMMARY

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a model-aided feedforward controller design method and device for visual photoelectric tracking systems. Unlike traditional feedforward methods that only improve tracking capability, this method is actually a composite structure of tracking and interference feedforward, which can simultaneously improve both tracking and anti-interference capabilities. Furthermore, considering delay mismatch, an optimal feedforward controller satisfying stability conditions is designed based on the small gain theorem. To address the gain limitation of the position controller due to delay, compensation based on position controller-assisted feedforward control is added, breaking the traditional requirement of an additional position encoder for feedforward. Moreover, feedforward controllers are often designed empirically without a quantitative design scheme. This method, based on the designed position controller, provides an optimal feedforward controller design scheme satisfying stability conditions under the condition of delay mismatch. This method can simultaneously improve the system's error suppression and anti-interference capabilities.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A model-aided feedforward controller design method for a visual photoelectric tracking system includes the following steps:

[0008] Step (1): Based on the CCD vision sensor on the servo platform, the target miss distance is obtained to form a closed-loop control, and the transfer function of the controlled object is obtained by fitting the frequency domain response. ;

[0009] Step (2): Transfer function of the controlled object based on the photoelectric tracking system The position controller was designed by using the zero-pole cancellation method, which constitutes the position feedback controller, and the error transfer function of photoelectric tracking was further obtained.

[0010] Step (3): Based on the established position feedback controller, considering the mismatch between the controlled object model and the actual object, design the optimal feedforward position controller that satisfies the stability condition.

[0011] A model-aided feedforward controller design device for a visual photoelectric tracking system includes:

[0012] Fitting module: Based on the CCD vision sensor on the servo platform, it acquires the target's miss distance to form a closed-loop control, and obtains the transfer function of the controlled object through frequency domain response fitting. ;

[0013] Transfer function acquisition module: Transfer function of the controlled object based on the photoelectric tracking system The position controller was designed by using the zero-pole cancellation method, which constitutes the position feedback controller, and the error transfer function of photoelectric tracking was further obtained.

[0014] Optimal feedforward position controller design module: based on the established position feedback controller, considering the mismatch between the controlled object model and the actual object, design the optimal feedforward position controller under the stability condition.

[0015] An electronic device includes one or more processors; memory for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the method.

[0016] A computer readable storage medium having stored thereon executable instructions that, when executed by a processor, cause the processor to perform the method.

[0017] Compared with the prior art, the present application has the beneficial effects:

[0018] The present application gives an optimal position controller design method under delay condition compared with traditional experience design and uses model output synthesis trajectory for feedforward. Compared with traditional feedforward, the system has sufficient directional accuracy even in strong interference environment, and does not need to use redundant sensors, so it is lighter and saves hardware cost.

[0019] Considering that the system delay will change in real time, resulting in mismatch between fixed delay models, the optimal feedforward controller design scheme under the condition of model mismatch is given. BRIEF DESCRIPTION OF DRAWINGS

[0020] The accompanying drawings, which form a part of the specification, illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application.

[0021] Referring to the drawings, the present application can be more clearly understood in light of the following detailed description, in which:

[0022] Figure 1 Is the model assisted feedforward control block diagram of the photoelectric tracking system of the present application;

[0023] Figure 2 Is the intermediate function value graph in the process of designing the feedforward controller in the embodiment of the present application;

[0024] Figure 3 Is the error suppression capability comparison graph in the embodiment of the present application;

[0025] Figure 4 Is the anti-disturbance capability comparison graph in the embodiment of the present application. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other. In order to achieve the above purpose, the technical scheme of the present application is as follows.

[0027] Example 1

[0028] Figure 1 is a flow chart of a model-assisted feedforward controller design method for a visual photoelectric tracking system, which comprises a position controller and a model-assisted feedforward controller. Among them, represents the transfer function mathematical model of the controlled object, C is the position controller, and F is the feedforward controller, is the system delay, is the added artificial delay, is the equivalent model of the controlled object G, , and h is the synthesized target trajectory with delay.

[0029] Figure 1 The control block diagram shown in the figure comprises the following steps:

[0030] Step (1): Install a CCD visual sensor on the servo platform to obtain the target off-target amount to constitute a closed-loop control. The transfer function of the controlled object is obtained by fitting the frequency domain response. Because of high fitting accuracy, the estimated controlled object obtained by fitting can be regarded as the real object;

[0031] Step (2): Based on the transfer function of the controlled object identified by the system , the zero-pole cancellation method is used to complete the design of the position controller and constitute a single position feedback controller;

[0032] Step (3): Based on the established position feedback controller, considering the mismatch between the controlled object model and the actual model, an optimal feedforward controller is designed to meet the stability condition.

[0033] Further, based on the transfer function mathematical model of the photoelectric tracking system, the zero-pole cancellation method is used to expand the system bandwidth. Assuming that the crossover frequency of the compensated open-loop object characteristic is , the gain frequency is , B is the open-loop transfer function of the system, and according to the requirements of the phase angle margin and the amplitude margin of the system stability, the following can be obtained:

[0034] ;

[0035] The position controller is designed as:

[0036]

[0037] The error transfer function and the disturbance transfer function of the single position feedback controller can be obtained as: where the gain is limited by the delay size, The designed position controller C can make the system obtain a phase margin of more than 60 degrees and an amplitude margin of more than 6 decibels.

[0038] The error transfer function and the disturbance transfer function of the single position feedback controller can be obtained as:

[0039]

[0040] Further, the synthesized trajectory is: Figure 1

[0041]

[0042] The synthesized trajectory is: It can be seen that the synthesized target trajectory of the present example is not the trajectory of the target in the inertial space, but the trajectory of the target relative to the visual axis of the platform.

[0043] The error transfer function and the disturbance transfer function of the model-assisted feedforward control of the visual photoelectric tracking system in the present example are:

[0044]

[0045] The error transfer function and the disturbance transfer function of the traditional feedforward control under the condition of adding an encoder are:

[0046]

[0047]

[0048] Comparing the error transfer function and the disturbance transfer function of the single position feedback, the traditional feedforward and the present example, it can be seen that the error suppression ability and the disturbance resistance ability of the system are both enhanced. Considering that the new term in the denominator has an adverse effect on stability in the face of delay mismatch, F should be designed to ensure the stability of the system.

[0049] Further, because of the uncertainty of the delay, a feedforward controller that satisfies the stability of the system needs to be designed under the condition of model mismatch.

[0050] The error transfer function and the disturbance transfer function of the model-assisted feedforward control of the photoelectric tracking system in the present example can be simplified as: ​​​​​​​​​​​

[0051] ;

[0052] The design of the position controller has made the denominator stable, according to the small gain theorem, the condition for the system to be stable is:

[0053] ;

[0054] F is designed as a first-order low-pass filter , T is the time constant, let Convert to the frequency domain to obtain:

[0055] ;

[0056] Let , , , , obtain , it is easy to get when , Take the minimum value.

[0057] Let represent the delay uncertainty, and perform Euler expansion to obtain:

[0058] ;

[0059] Let , define , a sufficient condition to ensure that the above formula is as follows:

[0060] ;

[0061] Obtain:

[0062] ;

[0063] A sufficient condition to ensure that the formula is as follows:

[0064] ;

[0065] Finally, the condition to meet the stability is:

[0066] ;

[0067] Again through the amplitude of the error transfer function and the disturbance transfer function of the example:

[0068] ;

[0069] When , the system obtains optimal performance.

[0070] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

[0071] Example 2:

[0072] This embodiment uses a photoelectric tracking system as an example to verify the model-assisted feedforward method of the visual photoelectric tracking system provided in Embodiment 1.

[0073] 1) An estimate of the controlled object model is obtained through frequency domain response fitting. Because of its high fitting accuracy, this estimated model can be used as the real object during the design process. The CCD image sensor has a sampling rate of 50Hz, and the time delay obtained through frequency domain fitting is 0.02s. The estimated controlled object model obtained through fitting is:

[0074] ;

[0075] 2) The position controller designed using the transfer function of the controlled object is:

[0076] ;

[0077] 3) For the design of the feedforward controller, we need to find ,exist The minimum value within the interval is taken as 50% of the delay uncertainty, i.e. The graph of L's values ​​within the interval is shown below. Figure 2 As shown, it can be seen that Then the feedforward controller T is designed as follows:

[0078] ;

[0079] The final feedforward controller design is as follows:

[0080] ;

[0081] Depend on Figure 3 and Figure 4The Bode diagram of error transfer function and disturbance transfer function of different control methods shows that the model assisted feedforward control of the visual photoelectric tracking system has higher error suppression capability and disturbance resistance than single position feedback control and traditional feedforward control, and does not need to add extra sensors, thereby greatly saving hardware cost. The above-described specific embodiments further specifically describe the purposes, technical solutions and beneficial effects of the present application, and it should be understood that the above-described specific embodiments are only for the purpose of the present application, and are not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A model aided feedforward controller design method for a visual electro-optical tracking system, characterized in that, Includes the following steps: Step (1): Based on the CCD vision sensor on the servo platform, the target off-target amount is obtained to constitute a closed-loop control, and the transfer function of the controlled object is obtained by fitting the frequency domain response ; Step (2): The transfer function of the controlled object based on the photoelectric tracking system The position controller is designed by using the zero-pole cancellation method, a position feedback controller is constituted, and the error transfer function of the photoelectric tracking is further obtained. Step (3): Based on the established position feedback controller, considering the mismatch between the controlled object model and the actual object, design an optimal feedforward position controller that meets the stability condition; the imaging information obtained by the CCD vision sensor through the image processing unit obtains the target miss distance, which is equivalent to obtaining the control error, and constitutes a closed-loop control. The target miss distance contains the delay time ​ The transfer function of the photoelectric tracking system controlled object derived from step (1) The position controller is designed by using zero-pole cancellation method, the crossover frequency of the open-loop transfer function characteristics of the system containing the position controller after compensation is , the gain frequency is , and the open-loop transfer function of the system containing the position controller after compensation is B ； Design the position controller as follows: ； obtained and wherein denotes the inverse of the fitted model of the plant G, is the delay time, the position feedback controller is constituted by adding negative feedback to the position controller, and the error transfer function of the photoelectric tracking system is 。 2. The model-aided feedforward controller design method for a visual photoelectric tracking system according to claim 1, characterized in that, A feedforward controller is formed from the off-target amount and position controller outputs, and an error transfer function of an optoelectronic tracking system formed from the feedforward controller and a position feedback controller and a disturbance transfer function is: ； where F is a feed forward controller, C is a position controller, is a system delay, is an added artificial delay, .

3. A model based feed forward controller design method for visual electro-optical tracking systems according to claim 2, characterized in that, Considering delay mismatch, design the optimal feedforward controller; the error transfer function and disturbance transfer function are simplified to: ； The conditions for system stability are: 。 4. The model-aided feedforward controller design method for a visual photoelectric tracking system according to claim 3, characterized in that, F is designed as a first-order low-pass filter T is a time constant, such that Converting to the frequency domain gives: ； make , , , , and thus , get when , Obtain the minimum value; make Representing the uncertainty of delay, we obtain the following Euler expansion: ； make ,definition A sufficient condition for the above equation to hold true is as follows: ； get: ； The sufficient condition for this expression to hold is as follows: ； Finally, the condition for satisfying stability is obtained: ； The magnitudes of the error transfer function and the disturbance transfer function: ； when At that time, the system achieves optimal performance.

5. A model-aided feedforward controller design device for a visual photoelectric tracking system, comprising the method described in any one of claims 1-4, characterized in that, include: Fitting module: Based on the CCD vision sensor on the servo platform, it acquires the target's miss distance to form a closed-loop control, and obtains the transfer function of the controlled object through frequency domain response fitting. ; Transfer function acquisition module: Transfer function of the controlled object based on the photoelectric tracking system The position controller was designed by using the zero-pole cancellation method, which constitutes the position feedback controller, and the error transfer function of photoelectric tracking was further obtained. Optimal feedforward position controller design module: Based on the established position feedback controller, considering the mismatch between the controlled object model and the actual object, design an optimal feedforward position controller that satisfies the stability conditions.

6. An electronic device, characterized in that, include: One or more processors; A memory for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors cause the one or more processors to implement the method of any one of claims 1 to 4.

7. A computer-readable storage medium, characterized in that, It stores executable instructions that, when executed by a processor, cause the processor to implement the method described in any one of claims 1 to 4.

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