CN116841040A - Dual-tilting-mirror beam jitter suppression method based on serial hybrid control strategy - Google Patents
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- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
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Abstract
The invention discloses a double-tilting-mirror beam jitter suppression method based on a serial hybrid control strategy, which is characterized in that a jitter model is built on a beam jitter signal, power density analysis and spectrum identification are carried out according to the jitter signal of an actual system so as to obtain accurate jitter frequency, then the jitter signal is predicted and suppressed according to open-loop LQG control, and finally the suppressed jitter signal is subjected to closed-loop control of beam jitter by using a PI method. The method has the most remarkable advantages that LQG control can well inhibit high-frequency narrow-band beam jitter and PI control has good inhibition capability on low-frequency broadband beam jitter, correction residual errors are greatly reduced, control stability is improved, and real-time performance is high.
Description
Technical Field
The invention belongs to the field of wavefront processing control, and particularly relates to a double-tilting-mirror beam jitter suppression method based on a serial hybrid control strategy, which is suitable for wavefront control of a self-adaptive optical system.
Background
The phenomenon is called beam jitter, which is caused by the fact that the optical axis of a light beam deflects in the propagation process to continuously change the propagation direction of the light beam due to the interference of external factors such as low-frequency bandwidth disturbance caused by transmission media such as atmospheric turbulence and high-frequency narrow-band disturbance caused by vibration of mechanical devices, a light beam platform and the like. The traditional PI control has a good inhibition effect on low frequency bandwidth, does not have the prediction capability of time-varying disturbance, and has insufficient control capability on narrow-band disturbance. The optimal control technology LQG based on the state space model has phase prediction capability, and the substantial advantage of the optimal estimation of the state space is fully utilized, so that the high-frequency narrow-band beam jitter can be well restrained. In order to further improve the suppression capability of high-frequency bandwidth disturbance and solve the parallel coupling effect of the multi-control algorithm, a dual-tilting-mirror beam jitter suppression method based on a serial hybrid control strategy is provided.
Disclosure of Invention
The method aims at the problems of low-frequency bandwidth and high-frequency beam jitter caused by external factors in the adaptive optical system and the problems of poor coupling and pure LQG closed-loop stability of a hybrid control algorithm.
The invention provides the following technical scheme: a double-tilting-mirror light beam jitter suppression method based on a serial hybrid control strategy is realized by the following steps:
step 1: and obtaining far-field light spot centroid offset data containing noise through an image sensor corresponding to the first inclined mirror.
Step 2: to obtain the light beam jitter signalAnd establishing a model, carrying out model identification on far-field noise-containing light spot centroid offset data obtained by an image sensor corresponding to the first inclined mirror, and using an LQG algorithm to inhibit high-frequency and high-frequency narrow-band and partial low-frequency of light beam dithering of the first inclined mirror.
Step 3: the jitter optical signal after being restrained in the step 2 is processedAnd (3) transmitting the jitter signals into a second tilting mirror and a corresponding image sensor, and performing second suppression on the suppressed jitter signals by using PI control.
Further, the specific steps of modeling the optical beam dithering signal in the step 2 and performing model identification on far-field noise-containing spot centroid offset data obtained by the image sensor corresponding to the first tilting mirror are as follows:
step 2.1: establishing a second-order damped oscillation equation for the beam dithering signal, namely a second-order autoregressive system model:
wherein the method comprises the steps ofIs a wobble signal>Is the first and second time derivatives of the dither signal, K is the damping coefficient whose magnitude is related to the dither bandwidth and represents the width of the formant and the overshoot, G is the static gain, ζ is the oscillation source function, w 0 Representing the natural oscillation angular frequency.
Step 2.2: the discrete expression of equation (1) is:
wherein the method comprises the steps ofBeam-jittering signal, ζ, representing the time n n Zero mean Gaussian white noise representing time n, a 1 、a 2 Two parameters representing the discrete model are:
step 2.3: calculating the power spectral density of the beam dithering signal by a power spectral density calculation formula of a second-order autoregressive model using S (f i ) Expressed as:
wherein sigma 2 Power as forced vibration source function, where a 1 、a 2 Is the corresponding model parameter in equations (3) and (4), j is the imaginary unit.
Step 2.4: the detected beam jitter data is used for carrying out identification calculation on model parameters by using a least square fitting according to a formula (5) in the step 2.3 to obtain a 1 、a 2 Sum sigma 2 。
Step 2.5: the state equation based on LQG control is as follows:
X n+1 ＝AX n +V n (7)
y n ＝CX n +ω 0 (8)
C＝D(0，1，0，1，…，0，1) (9)
wherein m represents m dither signals, n represents the nth time, A is a coefficient matrix composed of the single frequency beam dither model coefficients obtained in step 4, y n Is the centroid offset, D is the response matrix of the wavefront sensor, N is the response function of the tilting mirror, u n-2 Is the control voltage at time n-2, w 0 Is the detection noise of the wavefront sensor and C is the measurement matrix.
Step 2.6: and predicting the centroid offset by using a Kalman filter, wherein the optimal estimation formula is as follows:
wherein formula (10)Represents the time of n to X n Estimate of->Is n-1 time to X n Is estimated by H ∞ Representing the Kalman filter asymptotic gain matrix, the optimal predicted state of n time to n+1 time can be obtained through formulas (11) and (12)Thereby obtaining the optimal control voltage u n 。
Further, the second suppression of the suppressed jitter signal by PI control in step 3 is specifically as follows:
step 3.1: the PI is utilized to complete closed-loop control, and the time domain expression is as follows:
u n ＝a*u n-1 +b*u e (13)
wherein u is e ＝u n -u n-1 Is an error control signal.
Step 3.2: the LQG open loop control and PI closed loop control are connected in series to suppress beam wobble.
Compared with the prior art, the invention has the following advantages: according to the invention, different inclined mirrors are respectively controlled by using an LQG method and a PI algorithm serial mixed control strategy, the inhibition of high-frequency narrow-band beam jitter caused by mechanical vibration and the like is realized by using LQG control, the inhibition of low-frequency wide-band beam jitter caused by atmospheric turbulence and other factors is realized by using PI, the problem of jitter inhibition capability reduction caused by mixed control coupling is solved in a serial mode, and meanwhile, the control bandwidth of a system can be further improved by using open-loop LQG control.
Drawings
Fig. 1 is a schematic diagram of beam-jitter signal suppression according to the present invention.
Fig. 2 is a schematic diagram of beam dithering signal suppression control.
Fig. 3 is a plot of jitter signal fit and spectral identification.
FIG. 4 is a plot of centroid offset comparisons for spots after identification using LQG algorithm open loop control and PI closed loop control, and LQG open and closed loops.
Reference numerals illustrate:
1 is a parallel light source generating device, 2 is a linear polaroid, 3 is a third inclined mirror, 7 is a first inclined mirror, 8 is a second inclined mirror, 4 is a beam splitting prism, 5 is a first lens, 9 is a second lens, 6 is a first image sensor, and 10 is a second image sensor.
Detailed Description
In order to make the object and technical scheme of the present invention more clear and intuitive, the present invention is further described in detail below with reference to the accompanying drawings in conjunction with specific embodiments.
Fig. 1 is a schematic diagram of beam-jitter signal suppression according to the present invention. As shown in fig. 1, the specific principle is as follows: obtaining far-field light spot centroid offset data containing noise, namely light beam jitter signals, through image sensors corresponding to first inclined mirrorsFor beam wobble signal->Modeling and obtaining far-field noise content for the image sensor corresponding to the first inclined mirrorPerforming model identification on the acoustic facula centroid offset data, and then using an LQG algorithm to inhibit high-frequency and high-frequency narrow-band and partial low-frequency beam dithering of the first inclined mirror; the suppressed wobble optical signal +.>And detecting by using a second tilting mirror and a corresponding image sensor, and performing second suppression on the suppressed jitter signals by using PI control, wherein signal acquisition and recognition are completed in a Linux+Xenomai real-time system. The schematic diagram of the control of suppressing the beam wobble signal is shown in fig. 2, in which a parallel light beam is generated by a parallel light source generating device 1, the parallel light beam is split into two light beams by a splitting prism 4 after passing through a linear polarizer 2 and a third inclined mirror 3, one light beam is received by a first sensor through a first lens 5, and the other light beam is received by a second image sensor 10 after being reflected by a first inclined mirror 7 and a second inclined mirror 8 and passing through a second lens 9. Wherein the third tilting mirror 3 generates a dither signal, the generated dither signal is model-recognized by the first image sensor 6, the recognition result is shown in (a) and (b) of fig. 3, and then the first tilting mirror 7 is controlled by the LQG algorithm control unit to suppress the dither signal->The second image sensor 10 is used for detection, and finally the PI algorithm control unit is used for closed-loop control of the second tilting mirror 8, so that series hybrid control of beam dithering is realized, the inhibition effect is as shown in fig. 4, the stability of the closed loop is improved compared with that of pure LQG, and the tilting mirror is protected to a certain extent.
While the invention has been described with respect to specific embodiments thereof, it will be appreciated that the invention is not limited thereto, but rather encompasses modifications and substitutions within the scope of the present invention as will be appreciated by those skilled in the art.
Claims (3)
1. A double-tilting-mirror light beam jitter suppression method based on a serial hybrid control strategy is characterized by comprising the following steps of: the method uses a control strategy combining an open loop and a closed loop to eliminate beam jitter based on the structure of the adaptive optical system, and is realized by the following steps:
step 1: obtaining far-field light spot centroid offset data containing noise, namely optical dithering signals, through a first image sensor corresponding to a first tilting mirror
Step 2: for the obtained beam dithering signalPerforming model building, performing model identification on far-field noise-containing light spot centroid offset data obtained by an image sensor corresponding to the first inclined mirror, and then using an LQG algorithm to realize light beam dithering signals for the first inclined mirror>Jitter signal with suppressed high frequency and high frequency narrowband and partial low frequency suppression +.>
Step 3: the jitter signal after being restrained in the step 2 is processedDetection using a second tilting mirror and a corresponding image sensor, suppressed wobble signal +.>A second inhibition was performed.
2. The dual tilt mirror beam dithering suppression method based on a serial hybrid control strategy as recited in claim 1, wherein: the step 2 is to dither the light beamModeling and mapping the image corresponding to the first inclined mirrorThe specific steps of obtaining far-field noise-containing light spot centroid offset data by the sensor for model identification are as follows:
step 2.1: for beam dithering signalsEstablishing a second-order damped oscillation equation, namely a second-order autoregressive system model:
wherein the method comprises the steps ofIs a wobble signal>Is the first and second time derivatives of the dither signal, K is the damping coefficient of a magnitude related to the dither bandwidth and represents the width of the formant and the overshoot, G is the static gain, ζ is the oscillation source function, ω 0 Represents the natural oscillation angular frequency;
step 2.2: the discrete expression of equation (1) is:
wherein the method comprises the steps ofBeam-jittering signal, ζ, representing the time n n Zero mean Gaussian white noise representing time n, a 1 、a 2 The two parameters representing the discrete model are respectively:
wherein T represents a sampling period;
step 2.3: calculating a light beam shaking signal through a power spectrum density calculation formula of a second-order autoregressive modelIs determined by the power spectral density of S (f i ) Expressed as:
wherein sigma 2 Power as forced vibration source function, where a 1 、a 2 Is the corresponding model parameter in formulas (3) and (4), i is the imaginary unit;
step 2.4: the detected beam jitter signal data is used for carrying out identification calculation on model parameters by using a least square fitting according to a formula (5) in the step 2.3 to obtain a 1 、a 2 Sum sigma 2 ；
Step 2.5: the state equation based on LQG control is as follows:
X n+1 ＝AX n (7)
y n ＝CX n +w 0 (8)
C＝D(0，1，0，1，…，0，1) (9)
wherein m represents m dither signals, n represents the nth time, A is a coefficient matrix, and the coefficients of the beam dither models with different frequencies obtained in the step 2.4 are y n Is the centroid offset, D is the response matrix of the wavefront sensor, N is the response function of the tilting mirror, u n-2 Is the control voltage at time n-2, w o Is the detection noise of the wavefront sensor, C is the measurement matrix;
step 2.6: and predicting the centroid offset by using a Kalman filter, wherein the optimal estimation formula is as follows:
wherein formula (10)Represents the time of n to X n Estimate of->Is n-1 time to X n Is estimated by H ∞ Representing the Kalman filter asymptotic gain matrix, the optimal prediction state +.about.1 for n time to n+1 time can be obtained by formulas (11) and (12)>Thereby obtaining the optimal control voltage u n 。
3. The dual tilt mirror beam dithering suppression method based on a serial hybrid control strategy as recited in claim 1, wherein: and 3, performing second suppression on the suppressed jitter signal by using PI control, wherein the method comprises the following specific steps of:
step 3.1: the PI is utilized to complete closed-loop control, and the time domain expression is as follows:
u n ＝a*u n-1 +b*u e (13)
wherein u is e ＝u n -u n-1 Alpha is a proportional control coefficient, and b is an integral control coefficient;
step 3.2: the LQG open loop control and PI closed loop control are connected in series to suppress beam wobble.
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