Position closed-loop control method for fast reflector

Abstract

The invention relates to the technical field of optical machine control, and discloses a position closed-loop control method for a fast reflector, which comprises the following steps: acquiring frequency response data of the fast reflector based on frequency sweeping; fitting according to the frequency response data curve to obtain an open-loop transfer function of the fast reflector; constructing a correction model based on an open-loop transfer function, and enabling the controlled object to be in a standardized form in a working bandwidth range; establishing a generalized lag compensation PI controller; the correction model and a generalized lag compensation controller are connected in series and then act on the fast reflector, and position closed-loop control is achieved. According to the method, the open-loop transfer function and the correction model are obtained through frequency sweeping, and equivalent reverse compensation can be formed in a low-frequency band, so that the low-frequency following performance and the steady-state error convergence capability of the fast reflector are remarkably improved; moreover, the gain can be actively attenuated at a high frequency band through an additional first-order low-pass and second-order integral structure, thereby effectively suppressing the oscillation risk near the inherent frequency of the fast reflector, and improving the stability margin of the system.

Description

Technical Field

[0001] This invention relates to the field of optomechanical control technology, and in particular to a closed-loop control method for the position of a fast-reflecting mirror. Background Technology

[0002] A fast reflector is a high-speed, high-precision position servo system widely used in tracking and aiming optical systems, space optical communication, and laser communication, among other fields. The actuator of a fast reflector is either piezoelectric ceramic or voice coil motor. Because the deflection angle of a piezoelectric ceramic fast reflector is much smaller than that of a voice coil motor, voice coil motor fast reflectors are more widely used. A voice coil motor fast reflector typically consists of a voice coil motor, a flexible support, and a reflecting mirror. Its dynamic characteristics include high bandwidth, low natural frequency, and low damping.

[0003] Currently, proportional-integral (PI) controllers are commonly used in engineering to achieve closed-loop position control of fast reflectors. Traditional PI controllers have high high-frequency gain, which can easily excite the inherent high-frequency oscillation module of the fast reflector, resulting in insufficient stability margin of the fast reflector system. When external disturbances are strong, steady-state deviations or oscillations are likely to occur. Summary of the Invention

[0004] To solve the above problems, the technical solution adopted by the present invention is as follows: A closed-loop control method for the position of a fast reflector includes the following steps: S1: Obtain frequency response data of the fast reflector based on frequency sweeping; S2: Obtain the open-loop transfer function of the fast reflector by fitting the frequency response data curve; S3: Construct a correction model based on the open-loop transfer function to make the controlled object present a standardized form within the operating bandwidth. S4: Establish a generalized lag-compensated PI controller; S5: The correction model is connected in series with the generalized hysteresis compensation controller and then applied to the fast reflector to achieve closed-loop position control.

[0005] Furthermore, in step S1, the frequency sweep includes the following sub-steps: S101. Set the input frequency and input amplitude and record the phase; S102, Read the output amplitude and output phase; S103. Calculate the amplitude gain and phase difference based on the input amplitude and output amplitude; S104. Check if the output frequency has reached the preset frequency. If not, increase the input frequency. If it has, proceed to the next step. S105. Draw a Bode plot based on the amplitude gain and phase difference obtained each time.

[0006] Furthermore, the Bode plot includes an amplitude-frequency response comparison plot and a phase-frequency response comparison plot.

[0007] Furthermore, in step S2, the open-loop transfer function is:

[0008] In the formula, K is the gain coefficient of the proportional gain stage. It is the undamped natural frequency of a second-order system. The damping coefficient; The K,

[0009] Furthermore, the aforementioned for:

[0010] in, This is the resonant frequency in the Bode plot; for:

[0011] in, This represents the resonant peak gain in the Bode plot.

[0012] Furthermore, the correction model is as follows: .

[0013] Furthermore, the generalized hysteresis-compensated PI controller is:

[0014] in, For proportional gain, The integral time constant is... Let be the time constant for lag compensation, and s be the Laplace operator.

[0015] The beneficial effects of this invention are: By obtaining the open-loop transfer function and correction model through frequency sweeping, equivalent inverse compensation can be achieved in the low-frequency band, thereby significantly improving the low-frequency tracking performance and steady-state error convergence capability of the fast reflector. Furthermore, in the high-frequency band, the addition of a first-order low-pass filter and a second-order integral structure actively attenuates the gain, effectively suppressing the oscillation risk near the fast reflector's natural frequency and improving the system's stability margin. A generalized hysteresis-compensated PI controller effectively suppresses noise amplification, avoids exciting the fast reflector's resonant modes, and improves closed-loop stability. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of the invention.

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a control block diagram of the present invention; Figure 2 For Bode plots. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0020] Unless otherwise defined, the technical or scientific terms used in this disclosure shall have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms "first," "second," and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships, and these relative positional relationships may change accordingly when the absolute position of the described object changes.

[0021] A closed-loop control method for the position of a fast reflector includes the following steps: S1: Obtain frequency response data of the fast reflector based on frequency sweeping; S2: Obtain the open-loop transfer function of the fast reflector by fitting the frequency response data curve; S3: Construct a correction model based on the open-loop transfer function to make the controlled object present a standardized form within the operating bandwidth. S4: Establish a generalized lag-compensated PI controller; S5: The correction model is connected in series with the generalized hysteresis compensation controller and then applied to the fast reflector to achieve closed-loop position control.

[0022] In this invention, such as Figure 1 As shown, the fast reflector current loop uses an analog circuit to achieve a higher current loop bandwidth. The fast reflector actuator is a voice coil motor, and the feedback signal is provided by an angle sensor. The control algorithm adopts a PID control algorithm, where igive is the current command signal and i_f is the current feedback signal output by the angle sensor.

[0023] Specifically, in step S1, the frequency sweep includes the following sub-steps: S101. Set the input frequency and input amplitude and record the phase; S102, Read the output amplitude and output phase; S103. Calculate the amplitude gain and phase difference based on the input amplitude and output amplitude; S104. Check if the output frequency has reached the preset frequency. If not, increase the input frequency. If it has, proceed to the next step. S105. Draw a Bode plot based on the amplitude gain and phase difference obtained each time.

[0024] Specifically, such as Figure 2 As shown, the Bode plot includes an amplitude-frequency response comparison chart and a phase-frequency response comparison chart; and the first part of the stable segment is the proportional gain stage in the low-frequency band, while the second part is the oscillation stage in the high-frequency band.

[0025] Specifically, in step S2, the open-loop transfer function is:

[0026] In the formula, K is the gain coefficient of the proportional gain stage. It is the undamped natural frequency of a second-order system. The damping coefficient; The K,

[0027] Specifically, the aforementioned for:

[0028] in, This is the resonant frequency in the Bode plot, i.e., the peak frequency of the oscillating element; for:

[0029] in, This represents the resonant peak gain in the Bode plot, i.e., the peak gain of the oscillating element.

[0030] Specifically, the correction model is as follows:

[0031] Where f is the frequency.

[0032] In this invention, such as Figure 2 As shown, the amplitude-frequency gain exhibits a resonant peak around 13Hz. Since the fast reflector is a second-order system with a small damping coefficient and a significant natural frequency, the presence of this resonant peak makes it difficult for traditional PID control to achieve the desired control effect. The fast reflector is a second-order underdamped system; the smaller the damping ratio, the larger the overshoot and the slower the response time. Therefore, by correcting the model... (High-pass filter) artificially adds "virtual damping" to improve the phase margin of the system in the high-frequency band and enhance stability.

[0033] Specifically, the generalized hysteresis-compensated PI controller is:

[0034] in, For proportional gain, The integral time constant is... Let be the time constant for lag compensation, and s be the Laplace operator. When the frequency is lower than the cutoff frequency of the lag element... When the amplitude is close to 1, the controller approaches a standard PID controller, enabling the fast reflector to obtain a higher low-frequency gain, thereby reducing steady-state deviation and improving position accuracy. When the frequency is higher than the cutoff frequency, the amplitude of the hysteresis element decays as the frequency increases, causing the controller to automatically reduce the gain in the mid-to-high frequency range, thus effectively suppressing noise amplification, avoiding excitation of the resonant modes of the fast reflector actuator and structural components, and improving closed-loop stability.

[0035] (1) Unless otherwise defined, the same reference numerals in the embodiments and drawings of this disclosure have the same meaning.

[0036] (2) The accompanying drawings of the embodiments of this disclosure only involve the structures involved in the embodiments of this disclosure. Other structures can be referred to the general design.

[0037] (3) For clarity, components or areas are enlarged in the drawings used to describe embodiments of the present disclosure. It will be understood that when an element is referred to as being “above” or “below” another element, the element may be “directly” located “above” or “below” the other element, or there may be an intermediate element.

[0038] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A closed-loop control method for the position of a fast-reflecting mirror, characterized in that: Includes the following steps: S1: Obtain frequency response data of the fast reflector based on frequency sweeping; S2: Obtain the open-loop transfer function of the fast reflector by fitting the frequency response data curve; S3: Construct a correction model based on the open-loop transfer function to make the controlled object present a standardized form within the operating bandwidth. S4: Establish a generalized lag-compensated PI controller; S5: The correction model is connected in series with the generalized hysteresis compensation controller and then applied to the fast reflector to achieve closed-loop position control.

2. The closed-loop position control method for a fast-reflecting mirror according to claim 1, characterized in that: In step S1, the frequency sweep includes the following sub-steps: S101. Set the input frequency and input amplitude and record the phase; S102, Read the output amplitude and output phase; S103. Calculate the amplitude gain and phase difference based on the input amplitude and output amplitude; S104. Check if the output frequency has reached the preset frequency. If not, increase the input frequency. If it has, proceed to the next step. S105. Draw a Bode plot based on the amplitude gain and phase difference obtained each time.

3. The closed-loop position control method for a fast-reflecting mirror according to claim 2, characterized in that: The Bode plot includes a comparison plot of amplitude-frequency response and a comparison plot of phase-frequency response.

4. The closed-loop position control method for a fast-reflecting mirror according to claim 2, characterized in that: In step S2, the open-loop transfer function is: ； In the formula, K is the gain coefficient of the proportional gain stage. It is the undamped natural frequency of a second-order system. The damping coefficient; The K, and All were calculated using Bode plots.

5. The closed-loop position control method for a fast-reflecting mirror according to claim 4, characterized in that: The for: ； in, This is the resonant frequency in the Bode plot; for: ； in, This represents the resonant peak gain in the Bode plot.

6. The closed-loop position control method for a fast-reflecting mirror according to claim 4, characterized in that: The correction model is: 。 7. The closed-loop position control method for a fast-reflecting mirror according to claim 4, characterized in that: The generalized hysteresis-compensated PI controller is: ； in, For proportional gain, The integral time constant is... Let be the time constant for lag compensation, and s be the Laplace operator.

Images