CN111323985A - Controller setting method for liquid crystal beam deflection system - Google Patents
Controller setting method for liquid crystal beam deflection system Download PDFInfo
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- CN111323985A CN111323985A CN202010138053.5A CN202010138053A CN111323985A CN 111323985 A CN111323985 A CN 111323985A CN 202010138053 A CN202010138053 A CN 202010138053A CN 111323985 A CN111323985 A CN 111323985A
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection
- G02F1/292—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection by controlled diffraction or phased-array beam steering
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B19/00—Programme-control systems
- G05B19/02—Programme-control systems electric
- G05B19/04—Programme control other than numerical control, i.e. in sequence controllers or logic controllers
- G05B19/042—Programme control other than numerical control, i.e. in sequence controllers or logic controllers using digital processors
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Abstract
The invention discloses a controller setting method for a liquid crystal beam deflection system. For a two-dimensional light beam deflection control system based on a liquid crystal spatial light modulator, an electrode phase difference signal needs to be transmitted to an HDMI driver based on an FPGA through a frequency response instrument. And a detector PSD is adopted to collect a light beam deflection miss distance signal, and the signal is fed back to the frequency response instrument. The transfer function of the controlled object is then obtained. In the stage of designing the PID controller, because the controlled object of the beam deflection system is based on the first-order transfer function with delay, under the condition of adopting the Ziegler integral method, the approximate PID controller can be effectively and quickly designed, and the method has important significance for the practical application of the liquid crystal beam control system.
Description
Technical Field
The invention relates to the technical field of beam deflection, in particular to a controller setting method for a liquid crystal beam deflection system.
Background
The beam deflection technology refers to a technology for accurately controlling the direction of a laser beam, and has a wide application background in various fields such as laser communication, spacecrafts, biomedicine, military and the like. With the mature laser technology and the global development informatization, the space laser communication technology with the advantages of large communication capacity, small volume, low power consumption, good confidentiality and the like is emphasized. In the space laser communication technology, the capture, tracking and Aiming (ATP) of the communication terminal is one of its key technologies, and is also an important guarantee for establishing a reliable communication link. Only on the basis of establishing a reliable communication link, the system can carry out communication with high reliability and strong anti-interference capability, so that the satellite-ground optical communication becomes an optimal scheme for satellite-ground large-capacity communication. In order to guarantee communication quality in actual situations such as a long distance and a relative motion state, the requirement on tracking precision of an ATP technique is very high, which is one of core technical problems of spatial optical communication. The traditional mechanical and semi-mechanical ATP technologies have the defects of large volume and weight, high power consumption, poor stability, slow response time, difficulty in combination with a driving circuit and the like, so that the control performance of a mechanical device is limited. With the development of space optics and information optics, the requirements of application fields represented by space optical communication, laser radar, infrared countermeasure, spacecraft, biomedicine and the like on the aspects of accuracy, flexible control, low power consumption and the like of a beam deflection technology are continuously improved.
The optical phased array technology can realize programmable control of the laser beam direction, can be used for beam deflection, and has the advantages of high scanning precision, random deflection, high response speed, low power consumption, good stability and the like. The optical phased array technology based on the liquid crystal material is the non-mechanical light beam deflection technology which is developed most rapidly, utilizes the principle that liquid crystal generates double refraction under the action of an electric field, and accurately changes the phase in real time by controlling the electric field intensity to enable light beams to form equal-phase wave fronts in a set direction to generate enhanced interference, so that high-intensity light beam energy is obtained to realize electric control scanning of the light beams, the scanning problems of rapid and flexible control of laser beam pointing and the like are solved, the system integration level is higher, and the manufacturing cost is lower. In the aspect of control, due to the limitation of the characteristics of the liquid crystal material and the delay of a common CCD detector and an external HDMI image display, the system bandwidth and the tracking precision are greatly reduced, and the requirement of the tracking performance of people can not be met. Meanwhile, the transfer function of the controlled object needs to be measured, and a PID controller needs to be designed for the model.
Disclosure of Invention
The invention discloses a controller setting method for a liquid crystal beam deflection system, which overcomes the defects of the prior art, solves the delay influence caused by hardware, and effectively improves the system bandwidth and the tracking precision.
The technical scheme adopted by the invention is as follows: a controller tuning method for a liquid crystal beam deflection system, the method comprising the steps of:
the method comprises the following steps: establishing a two-dimensional light beam deflection model to generate a corresponding gray level phase modulation graph;
step two: a light beam control experiment platform is built, and a data processing unit is formed by an HDMI driver based on an FPGA and a computer;
step three: the electrode phase difference in the sine form is transmitted to an HDMI driver based on the FPGA through a frequency response instrument, the driver generates a continuous phase modulation graph according to the phase difference, and the phase modulation graph is input to a liquid crystal spatial light modulator;
step four: collecting the deflection miss distance of a light beam by using a photoelectric Position Sensitive Device (PSD), feeding an output signal, namely continuous miss distance, back to a computer through a data processing unit, and performing fast Fourier transform on an input signal and an output signal through a frequency response instrument to obtain an amplitude-frequency phase-frequency characteristic curve;
step five: and calculating to obtain a controlled object model through an amplitude-frequency phase-frequency characteristic curve, and designing a PID (proportion integration differentiation) controller on the model through a Ziegler setting method.
Further, a two-dimensional light beam deflection model based on liquid crystal is established according to a liquid crystal target surface lattice type structure and by combining a microwave phased array principle.
Furthermore, a two-dimensional light beam deflection system experiment platform based on liquid crystal is built, the liquid crystal spatial light modulator adopts a Pluto series, and the HDMI driver and the computer are regarded as data processing units.
Further, the electrode phase difference in the sine form is transmitted to the HDMI driver based on the FPGA through the frequency response instrument, the driver generates a phase modulation diagram according to the received sine signal, and then the generated phase modulation diagram is input to the liquid crystal spatial light modulator, so that the phase modulation of the light wave is realized.
Furthermore, the miss distance is deflected by a non-imaging detection light beam of a photoelectric Position Sensitive Device (PSD), the centroid analysis of the miss distance is carried out by a data processing unit, digital signal processing is carried out, the output miss distance is fed back to the frequency response instrument, and meanwhile, the feedback delay can be reduced. And performing fast Fourier transform on the input signal and the output signal by using a frequency response instrument to obtain an amplitude-frequency phase-frequency characteristic curve.
Further, the amplitude-frequency-phase-frequency characteristic curve is regarded as a group of bode plots, and a corresponding model, namely a transfer function, is fitted according to the bode plots. And designing the PID controller for the transfer function through a Ziegler setting empirical formula. A PID controller is a linear controller with a transfer function of:
wherein k ispIs a proportionality coefficient, kiAs integral time coefficient, kdThe proportional link can effectively reduce deviation, the integral link can be used for eliminating static difference so as to improve the non-difference of the system, the differential link reflects the variation trend of a deviation signal, and an effective correction signal can be introduced before the deviation signal becomes too large so as to reduce the adjustment time. The Ziegler setting empirical formula is based on a first-order transfer function model with delay, and the controlled object model can be expressed as:
in the formula, the parameters k, L and T may be obtained by experimentally measuring a step response of the controlled object, and a is kL/T. And designing a corresponding PID controller according to a Ziegler tuning formula.
Compared with the prior art, the method has the following advantages:
(1) the phase difference of the electrodes can be directly transmitted to the HDMI driver based on the FPGA through the data processing unit, the defect of large delay of self-contained function of control software of the liquid crystal spatial light modulator is overcome, the phase modulation image can be quickly and timely transmitted to the liquid crystal spatial light modulator, and response delay can be reduced.
(2) The method overcomes the defect of large time delay of the mode of displaying the miss-target mass center acquisition by a common CCD detector, detects the miss-target mass center information by PSD non-imaging, can synchronously input the miss-target mass center information into a data processing unit, can reduce feedback time delay, and improves the system bandwidth and tracking precision.
(3) The invention can intuitively measure and extract the transfer function of the controlled object, and further designs the PID controller by a setting method.
(4) The improved control device is simple and easy to understand and is more suitable for practical application.
Drawings
FIG. 1 is a functional block diagram of a PID control system of the invention;
FIG. 2 is a beam deflection diagram of the present invention;
FIG. 3 is a schematic diagram of the calculation of a Ziegler tuning formula of the present invention;
fig. 4 is a schematic diagram of a beam deflection control system of the present invention.
Detailed Description
Embodiments of the present invention will be described below with reference to the accompanying drawings. The following examples are, however, only intended to illustrate the invention.
The invention relates to a controller setting method for a liquid crystal beam deflection system, which comprises the following specific steps:
as shown in fig. 1, the controller adopts a PID control algorithm, which is a linear controller, and the transfer function can be expressed as:
wherein Y(s) represents the output signal, U(s) represents the input signal, kpIs a proportionality coefficient, kiAs integral time coefficient, kdThe proportional part can effectively reduce deviation, the integral part can be used for eliminating static difference so as to improve the non-difference degree of the system, and the differential part reflects the deviation informationThe trend of the sign can introduce an effective correction signal before the deviation signal becomes too large, to reduce the adjustment time. The controlled object consists of an HDMI driver based on FPGA and a liquid crystal spatial light modulator;
as shown in FIG. 2, which is an experimental schematic diagram of a beam deflection system, the liquid crystal spatial light modulator is of a PLUTO-NIR-011 type, and the incident wavelength range of the modulator is 420-. In practical experiments, it should be noted that different wavelengths need to correspond to different phase modulation diagrams. Since the requirement of the liquid crystal material for the incident light is S-polarized light, P, S light decomposition needs to be performed through a polarizer before the laser reaches the liquid crystal spatial light modulator. The liquid crystal spatial light modulator is followed by a convergent lens, and the PSD target surface is positioned on the focal plane of the lens. The computer controls the frequency response instrument and transmits the input sine signal to the FPGA. And the FPGA generates a corresponding phase modulation graph according to the phase difference signal and transmits the graph to the liquid crystal spatial light modulator in real time. And beacon light mass centers of PSD non-imaging detection are transmitted into the FPGA through electric signals, digital signal processing is carried out, and output miss distance is fed back to the frequency response instrument. And (3) carrying out fast Fourier transform on the input signal and the output signal of the frequency response instrument through a computer to obtain a Bode diagram. The transfer function of the controlled object is then fitted by means of a bode diagram.
As shown in fig. 3, the parameters k, L and T in the formula (2) can be obtained by approximating the step response of the controlled object through experiment measurement. Then, a corresponding PID controller can be designed according to a Ziegler tuning formula.
As shown in fig. 4, the figure describes a closed-loop control circuit of a beam deflection system, an input signal is an electrode phase difference sequence, the input signal is adjusted by a PID controller, the adjusted electrode phase difference sequence is sent to an FPGA, a phase adjustment diagram is generated in real time and is sent to a liquid crystal spatial light modulator, a PSD non-imaging detection beam deflection miss amount with a fast response characteristic is utilized, and a data processing unit is used for carrying out miss amount centroid analysis to realize beam deflection closed-loop control, and the system bandwidth and tracking accuracy can be improved.
Claims (6)
1. A controller setting method for a liquid crystal beam deflection system is characterized by comprising the following steps: the method comprises the following steps:
the method comprises the following steps: establishing a two-dimensional light beam deflection model to generate a corresponding gray level phase modulation graph;
step two: a light beam control experiment platform is built, and a data processing unit is formed by an HDMI driver based on an FPGA and a computer;
step three: the electrode phase difference in the sine form is transmitted to an HDMI driver based on the FPGA through a frequency response instrument, the driver generates a continuous phase modulation graph according to the phase difference, and the phase modulation graph is input to a liquid crystal spatial light modulator;
step four: collecting the deflection miss distance of a light beam by using a photoelectric Position Sensitive Device (PSD), feeding an output signal, namely continuous miss distance, back to a computer through a data processing unit, and performing fast Fourier transform on an input signal and an output signal through a frequency response instrument to obtain an amplitude-frequency phase-frequency characteristic curve;
step five: and calculating to obtain a controlled object model through an amplitude-frequency phase-frequency characteristic curve, and designing a PID (proportion integration differentiation) controller on the model through a Ziegler setting method.
2. A controller tuning method for a liquid crystal beam deflection system according to claim 1, wherein:
in the first step, a two-dimensional light beam deflection model based on liquid crystal is established according to a liquid crystal target surface lattice type structure and by combining a microwave phased array principle.
3. A controller tuning method for a liquid crystal beam deflection system according to claim 1, wherein:
and step two, a two-dimensional light beam deflection system experiment platform based on liquid crystal is built, the liquid crystal spatial light modulator adopts a Pluto series, and the HDMI driver and the computer are regarded as data processing units.
4. A controller tuning method for a liquid crystal beam deflection system according to claim 1, wherein:
in the third step, the electrode phase difference in the sine form is transmitted to the HDMI driver based on the FPGA through the frequency response instrument, the driver generates a phase modulation diagram according to the received sine signal, and then the generated phase modulation diagram is input to the liquid crystal spatial light modulator, so that the phase modulation of the light wave is realized.
5. A controller tuning method for a liquid crystal beam deflection system according to claim 1, wherein:
in the fourth step, the miss distance is deflected through a non-imaging detection light beam of a photoelectric Position Sensitive Device (PSD), the centroid analysis of the miss distance is carried out through a data processing unit, digital signal processing is carried out, the output miss distance is fed back to a frequency response instrument, meanwhile, the feedback delay can be reduced, and fast Fourier transform is carried out on input signals and output signals through the frequency response instrument to obtain an amplitude-frequency phase-frequency characteristic curve.
6. A controller tuning method for a liquid crystal beam deflection system according to claim 1, wherein:
and fifthly, regarding the amplitude-frequency phase-frequency characteristic curve as a group of bode diagrams, fitting a corresponding model, namely a transfer function, according to the bode diagrams, and then designing a PID (proportion integration differentiation) controller for the transfer function through a Ziegler setting empirical formula, wherein the PID controller is a linear controller, and the transfer function is as follows:
wherein k ispIs a proportionality coefficient, kiAs integral time coefficient, kdThe proportional element can effectively reduce deviation for differentiating time coefficient, the integral element can be used for eliminating static difference to raise the non-difference degree of system, the differential element can reflect the variation trend of deviation signal, and can introduce an effective correction signal before the deviation signal becomes too large to reduce regulation time, the Ziegler setting empirical formula is based on the first-order transfer function model with delay, and the controlled object model can be expressed as：
In the formula, the parameters k, L and T can be obtained by measuring and obtaining the step response of the controlled object through experiments, a is kL/T, and the corresponding PID controller can be designed according to a Ziegler setting formula.
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|---|---|---|---|---|
| CN102073290A (en) * | 2010-12-13 | 2011-05-25 | 宋四海 | Zigbee protocol based proportion integration differentiation (PID) parameter tuning controller |
| CN109856873A (en) * | 2017-11-30 | 2019-06-07 | 帕洛阿尔托研究中心公司 | Use the LC variable delayer of liquid crystal cells with different thickness |
| CN110286541A (en) * | 2019-07-08 | 2019-09-27 | 中国科学院光电技术研究所 | A kind of beam deflection system control method based on liquid crystal |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102073290A (en) * | 2010-12-13 | 2011-05-25 | 宋四海 | Zigbee protocol based proportion integration differentiation (PID) parameter tuning controller |
| CN109856873A (en) * | 2017-11-30 | 2019-06-07 | 帕洛阿尔托研究中心公司 | Use the LC variable delayer of liquid crystal cells with different thickness |
| CN110286541A (en) * | 2019-07-08 | 2019-09-27 | 中国科学院光电技术研究所 | A kind of beam deflection system control method based on liquid crystal |
Non-Patent Citations (1)
| Title |
|---|
| 杜升平: "应用于空间光通信的液晶光束偏转技术研究", 《中国科学院大学博士学位论文》 * |
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