A Photoelectric Tracking Control Method Based on Feedforward Improved Smith Predictor

Abstract

The invention discloses an optoelectronic tracking control method of a feedforward improved Smith predictor, and relates to the technical field of target tracking control of an optoelectronic tracking system. Firstly, an optical fiber gyroscope is installed on an optoelectronic tracking platform to obtain the rotational angular velocity of the optoelectronic tracking platform moving in an inertial space, and a high-precision speed object model of the optoelectronic tracking platform is obtained by using a frequency response tester and a frequency domain fitting method; a CCD image sensor is installed on a tracking device to obtain target miss amount information with a time lag; then a corresponding speed controller is designed according to the obtained high-precision speed object model; a position controlled object model is obtained according to a designed speed closed loop, and a position controller is designed; a negative feedback integral link is added to the position controller, and an intermediate signal is obtained by superimposing the CCD miss amount and a speed given signal through the output of the position object model; and the intermediate signal is superimposed with the output of the position controller after being de-noised by a differential and low-pass filter.

Description

Technical Field

[0001] The invention belongs to the technical field of target tracking control of an optoelectronic tracking system, and in particular relates to an optoelectronic tracking control method of a feedforward improved Smith predictor. Background Art

[0002] With the continuous development of science and technology, in optoelectronic tracking systems, target tracking is based on the off-target error information extracted from the CCD image sensor. Since CCD clear imaging requires a long exposure time, the control system closed loop will contain non-negligible delay, which will cause phase attenuation and have a negative impact on control stability. In order to ensure that the system has sufficient margin, the controller gain is usually limited to a small range, which directly leads to insufficient tracking ability of the system. In order to reduce the impact of delay on control stability, predecessors introduced a delay compensation method called Smith predictor, which is widely used in the field of industrial control, in optoelectronic tracking systems. Smith predictor is based on the internal model principle. By eliminating the output early feedback of the delayed object model, the delay is approximately separated from the closed-loop system, thereby improving the controller gain and improving the tracking ability of the system. The literature "Improved Smithpredictor control for fast steering mirrorsystem" (Iop Conference Series:Earth&Environmental Science, 2017) uses the speed closed loop constructed by gyroscope as the controlled object model to construct a Smith predictor, which improves the control performance of the Smith predictor under parameter perturbations; the literature "Stabilization Control of Electro-Optical Tracking System with Fiber-Optic Gyroscope Based on Modified Smith Predictor Control Scheme" (IEEE Sensors Journal, Vol(18), 2018) constructs an improved Smith predictor with disturbance observation performance in the speed closed loop, which can simultaneously reduce the negative impact of delay and external interference on the control system.

[0003] However, although the above method can enhance the tracking capability of the system by improving the gain ability of the Smith predictor, the model mismatch in the system will still limit the extent of the gain improvement, resulting in the system transfer characteristics still being less than ideal and the system tracking capability still failing to meet the requirements; for this reason, a feedforward improved Smith predictor optoelectronic tracking control method is proposed. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide an optoelectronic tracking control method of a feedforward improved Smith predictor, which solves the technical problem in the prior art that the traditional Smith predictor cannot significantly improve the controller gain due to model mismatch, resulting in insufficient tracking performance.

[0005] The object of the present invention can be achieved by the following technical solution: a photoelectric tracking control method of a feedforward improved Smith predictor, the method comprising the following steps:

[0006] A fiber optic gyroscope is installed on the optoelectronic tracking platform to obtain the rotational angular velocity of the optoelectronic tracking platform in inertial space. A frequency response tester is used to obtain a high-precision velocity object model of the optoelectronic tracking platform by frequency domain fitting.

[0007] The CCD image sensor is installed on the tracking device to obtain the target miss distance information with time lag;

[0008] According to the high-precision speed object model obtained design The corresponding speed controller C v , realize the speed closed loop; according to the designed speed closed loop, the position controlled object model is obtained And design the position controller C p , realize position closed loop;

[0009] The classic Smith predictor structure is constructed in the position loop, and a negative feedback integral link 1 / s is added to the position controller to construct a fast position loop; the CCD miss distance and the speed given signal are converted into the position object model. The output of is superimposed to obtain the intermediate signal r, which is used as the input of the fast position loop;

[0010] After the intermediate signal r is differentiated and denoised by a low-pass filter F, it is used as a feedforward input and is connected to the position controller C p The output of is superimposed as the given of the speed loop.

[0011] Furthermore, the fiber optic gyroscope has a high sampling rate and a small lag time.

[0012] Furthermore, the lag time of the fiber optic gyroscope is negligible.

[0013] Furthermore, the CCD image sensor has low noise, large dynamic range and low sampling rate.

[0014] Furthermore, the lag time of the CCD image sensor cannot be ignored.

[0015] Furthermore, the speed controller C is designed using the zero-pole cancellation method.v , the compensated open-loop object is constructed into a type I system. Considering the high bandwidth of the speed closed-loop, the transfer function of the speed closed-loop is converted into Idealized as transfer model 1, the position object model is obtained as follows: where τ m is the model of the system delay τ obtained by identification, and the position controller C p Designed as a proportional controller.

[0016] Furthermore, the obtained system error transfer function is as follows:

[0017]

[0018] Where τ ≈ τ m <<1, when s→0, due to Error Transfer Function

[0019] Furthermore, the system error transfer function is improved as follows:

[0020]

[0021] Where τ ≈ τ m <<1, when s→0, due to And the low-pass filter F→1, the error transfer function S1=0.

[0022] Furthermore, S1<S0 indicates that the introduced feedforward can significantly improve the system's low-frequency tracking capability.

[0023] Beneficial effects of the present invention:

[0024] During the use of the present invention, a fiber optic gyroscope is first installed on the photoelectric tracking platform to obtain the rotational angular velocity of the photoelectric tracking platform in the inertial space, and a high-precision velocity object model of the photoelectric tracking platform is obtained by using a frequency response tester and a frequency domain fitting method. Then the CCD image sensor is installed on the tracking device to obtain the target miss distance information with time lag; then according to the obtained high-precision speed object model design The corresponding speed controller C v , realize the speed closed loop; according to the designed speed closed loop, the position controlled object model is obtained And design the position controller C p , realize the position closed loop; build the classic Smith predictor structure in the position loop, add the negative feedback integral link 1 / s in the position controller to build a fast position loop; integrate the CCD miss distance and the speed given signal through the position object model The output of the intermediate signal r is superimposed to obtain the intermediate signal r as the input of the fast position loop; the intermediate signal r is de-noised by differential and low-pass filter F and then combined with the position controller C p The output of the speed loop is superimposed as the given of the speed loop; the problem of insufficient low-frequency transfer characteristics of the Smith predictor due to model mismatch is solved. By introducing feedforward, the transfer characteristics of the system are further improved. The model information of the controlled object can be reused, and additional feedforward branches can be built based on the model to continue to explore the potential of the system; the idea is clear, the structure is simple, and it is easy to implement in engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 is a control block diagram of the present invention;

[0027] Figure 2 It is a comparison chart of the error suppression capability of the dual closed loop of speed and position and the dual closed loop with the traditional Smith predictor added. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] like Figure 1 As shown, a photoelectric tracking control method of a feedforward improved Smith predictor comprises the following steps:

[0030] A fiber optic gyroscope is installed on the optoelectronic tracking platform to obtain the rotational angular velocity of the optoelectronic tracking platform in inertial space. A frequency response tester is used to obtain a high-precision velocity object model of the optoelectronic tracking platform by frequency domain fitting.

[0031] The CCD image sensor is installed on the tracking device to obtain the target miss distance information with time lag;

[0032] According to the high-precision speed object model obtained design The corresponding speed controller C v, realize the speed closed loop; according to the designed speed closed loop, the position controlled object model is obtained And design the position controller C p , realize position closed loop;

[0033] The classic Smith predictor structure is constructed in the position loop, and a negative feedback integral link 1 / s is added to the position controller to construct a fast position loop; the CCD miss distance and the speed given signal are converted into the position object model. The output of is superimposed to obtain the intermediate signal r, which is used as the input of the fast position loop;

[0034] After the intermediate signal r is differentiated and denoised by a low-pass filter F, it is used as a feedforward input and is connected to the position controller C p The output of is superimposed as the given of the speed loop.

[0035] It needs to be further explained that, in a specific implementation process, the fiber optic gyroscope has a high sampling rate and a small lag time.

[0036] It should be further explained that, in the specific implementation process, the lag time of the fiber optic gyroscope is negligible.

[0037] It should be further explained that, in a specific implementation process, the CCD image sensor has low noise, a large dynamic range and a low sampling rate.

[0038] It needs to be further explained that, in the specific implementation process, the lag time of the CCD image sensor cannot be ignored.

[0039] It should be further explained that in the specific implementation process, the zero-pole cancellation method is used to design the speed controller C v , the compensated open-loop object is constructed into a type I system. Considering the high bandwidth of the speed closed-loop, the transfer function of the speed closed-loop is converted into Idealized as transfer model 1, the position object model is obtained as follows: where τ m is the model of the system delay τ obtained by identification, and the position controller C p Designed as a proportional controller.

[0040] It needs to be further explained that, in the specific implementation process, the system error transfer function obtained is as follows:

[0041]

[0042] Where τ ≈ τ m <<1, when s→0, due to Error Transfer Function

[0043] It should be further explained that, in the specific implementation process, the system error transfer function is improved as follows:

[0044]

[0045] Where τ ≈ τ m <<1, when s→0, due to And the low-pass filter F→1, the error transfer function S1=0.

[0046] It needs to be further explained that in the specific implementation process, S 1 ＜S 0 shows that the introduced feedforward can significantly improve the system's low-frequency tracking ability.

[0047] The design process and experimental results of the present invention are described in detail below using a photoelectric tracking platform system as an example:

[0048] (1) The velocity transfer function model of the system is obtained by frequency domain response fitting as follows. Due to the high fitting accuracy, the fitting model can be treated as a real object during the design process.

[0049]

[0050] (2) The sampling rate of the CCD image sensor is 50 Hz, and the time lag obtained by frequency domain fitting is 0.02 s.

[0051] (3) According to the speed model, using the zero-pole cancellation method, the speed controller is designed as follows:

[0052]

[0053] After the speed closed loop is constructed, the position object model is approximately The position controller gain is designed to be C p =20.

[0054] (4) After adding the Smith predictive controller, the gain of the position controller can be increased to C p =50.

[0055] (5) Differentiate the target trajectory signal at the current moment, filter and denoise it, and use it as a feedforward input, which is superimposed with the output of the position controller as the given signal of the speed closed loop. The filter selected is

[0056] Under the same experimental conditions, the error suppression residuals of the speed and position double closed loop, the traditional Smith predictor, and the feedforward improved Smith predictor control methods are compared. Figure 2This is a comparison chart of the error suppression capability of the present invention, which is plotted by taking the logarithm of the amplitude ratio between the error and the given input at different frequencies. Compared with the speed and position dual closed-loop structure, the low-frequency error suppression capability is improved after adding the traditional Smith predictor, but the error suppression capability is still limited. After using the feedforward improved Smith predictor, the system's error suppression capability at low frequencies is further improved. Although the differential in the feedforward will partially amplify the noise at high frequencies and cause the high-frequency suppression capability to decrease, the suppression effect of the present invention on low-frequency errors is particularly suitable for tracking long-distance targets whose signals are mainly distributed at low frequencies.

[0057] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0058] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited by the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A photoelectric tracking control method based on feedforward improved Smith predictor. It is characterized in that The method comprises the following steps: A fiber optic gyroscope is installed on the optoelectronic tracking platform to obtain the rotational angular velocity of the optoelectronic tracking platform in inertial space. A frequency response tester is used to obtain a high-precision velocity object model of the optoelectronic tracking platform by frequency domain fitting. The CCD image sensor is installed on the tracking device to obtain the target miss distance information with time lag; According to the high-precision speed object model obtained design The corresponding speed controller C v , realize the speed closed loop; according to the designed speed closed loop, the position controlled object model is obtained And design the position controller C p , realize position closed loop; The classic Smith predictor structure is constructed in the position loop, and a negative feedback integral link 1 / s is added to the position controller to construct a fast position loop; the CCD miss distance and the speed given signal are converted into the position object model. The output of is superimposed to obtain the intermediate signal r, which is used as the input of the fast position loop; After the intermediate signal r is differentiated and denoised by a low-pass filter F, it is used as a feedforward input and is connected to the position controller C p The output of is superimposed as the given value of the speed loop; Design of speed controller C using zero-pole cancellation method v , the compensated open-loop object is constructed into a type I system. Considering the high bandwidth of the speed closed-loop, the transfer function of the speed closed-loop is converted into Idealized as transfer model 1; The position object model is obtained as where τ m is the model of the system delay τ obtained by identification, and the position controller C p Designed as a proportional controller; The resulting system error transfer function is as follows: Where τ ≈ τ m =1, when s→0, due to The system error transfer function is obtained 2. The photoelectric tracking control method of the feedforward improved Smith predictor according to claim 1, It is characterized in that The fiber optic gyroscope has a high sampling rate and a small lag time.

3. The photoelectric tracking control method of the feedforward improved Smith predictor according to claim 2, It is characterized in that The lag time of the fiber optic gyroscope is negligible.

4. The photoelectric tracking control method of the feedforward improved Smith predictor according to claim 1, It is characterized in that The CCD image sensor has low noise, large dynamic range and low sampling rate.

5. The photoelectric tracking control method of the feedforward improved Smith predictor according to claim 4, It is characterized in that The lag time of the CCD image sensor cannot be ignored.

6. The photoelectric tracking control method of the feedforward improved Smith predictor according to claim 1, It is characterized in that The system error transfer function is improved as follows: Where τ ≈ τ m =1, when s→0, due to And the low-pass filter F→1, the system error transfer function S 1 =0.

7. The photoelectric tracking control method of the feedforward improved Smith predictor according to claim 6, It is characterized in that S 1 <S 0 This shows that the introduced feedforward can significantly improve the system's low-frequency tracking capability.

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