Fast steering mirror angle monitoring system and method based on three-point capacitive displacement sensor

Abstract

The application provides a fast swing mirror swing angle monitoring system and method based on a three-point capacitive displacement sensor, which comprises a capacitive displacement sensor, a signal conditioning circuit, a signal acquisition circuit, an FPGA angle calculation module and an upper computer. The three-point piezoelectric driving large-aperture fast swing mirror is a monitored component; three capacitive displacement sensors are distributed in an equilateral triangle around the center of the mirror surface, the included angle between each two actuators and the center connecting line is 120 DEG, the upper plate among them is installed at the bottom of the swing mirror, and the lower plate is installed to overlap with the upper plate on the support frame; the signal conditioning circuit converts the capacitive signal into a voltage signal, which is transmitted remotely through a current interface with the signal acquisition circuit; the signal acquisition circuit is connected with the FPGA angle calculation module; and the upper computer communicates with the FPGA. The application fully utilizes the high displacement detection precision of the capacitive sensor and the processing characteristics of the FPGA parallel calculation, and realizes high-precision and real-time swing mirror angle state monitoring of dynamic micro swing.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of sensors, and particularly relates to a fast steering mirror swing angle monitoring system and method based on a three-point capacitive displacement sensor. BACKGROUND

[0002] A large-aperture fast steering mirror (FSM) is a key component of a precise image stabilization system of a space telescope, which compensates for the optical shift of a fine guide sensor (FGS) detected and fed back, so as to ensure high-quality imaging and long-term stability of a detector of the telescope. The FSM works in a very complex on-orbit environment, and there is an error between a closed loop of an actuator and actual swinging, and the error is affected by various complex factors and changes. In order to ensure high-quality imaging and long-term stability of the detector of the telescope, a capacitive displacement sensor is used as an online monitoring means, and under the condition that the rigidity of the fast steering mirror is unchanged, the capacitive displacement sensor detects the change of a bottom plane of the FSM and a substrate, and monitors the swing angle and center displacement of the actuator.

[0003] The displacement measurement range of the capacitive displacement sensor is usually between 0.05 and 10 mm, and the precision can reach 0.005% of the full scale, which can meet the needs of various precision measurements. In addition, the capacitive displacement sensor has the advantages of high sensitivity, low zero drift, wide frequency response and small nonlinearity, so it becomes an indispensable testing instrument in precision production and control. However, the displacement output capacitance change of the capacitive displacement sensor is very weak, and the capacitance change is usually only a few pF or even a few fF, which puts high requirements on the resolution of the capacitive detection circuit.

[0004] Commonly used are inertial gyroscopes for measuring the angle and posture, but the precision is insufficient to detect the attitude change of the order of angle seconds; fine swing angle measurement usually directly measures by using a laser interference method, but for the on-orbit operation of a satellite, the volume, power consumption and complexity of a laser light source and its light path structure are large, and the factors of the emission and operation environment also cause the misadjustment of the measuring equipment, so the long-life operation requirement cannot be met, and therefore the on-orbit detection is not conducive. SUMMARY

[0005] To solve the above technical problems, the present application provides a fast steering mirror swing angle monitoring system and method based on a three-point capacitive displacement sensor.

[0006] Field Programmable Gate Array (FPGA) belongs to the highest integration of Application Specific Integrated Circuit (ASIC), which is composed of a large number of basic logic units. The I / O resource of FPGA is rich and can be flexibly configured, and can realize true parallel operation. The advanced FPGA currently contains a hardware core with digital signal processing function, which can realize the deployment of FPGA for complex angle calculation algorithm, and realize the fast swing mirror angle calculation of three-point capacitive displacement sensor.

[0007] In order to achieve the above purpose, the technical scheme adopted by the application is as follows:

[0008] A fast swing mirror swing angle monitoring system based on a three-point capacitive displacement sensor, comprising a three-point piezoelectric drive fast swing mirror mechanism, a capacitive displacement sensor, a signal conditioning circuit, a signal acquisition circuit, an FPGA angle calculation module and an upper computer.

[0009] The upper computer sends the angle control signal of the three-point piezoelectric drive fast swing mirror mechanism to the three-point piezoelectric drive fast swing mirror mechanism, and realizes the swing angle control by the target displacement of the three-point piezoelectric ceramic actuator uniformly distributed at an angle of 120° on the concentric circle of the mirror surface. The capacitive displacement sensor has 6 groups, each group has a main part and a backup part, and is located on both sides of the piezoelectric actuator at the same section to detect the displacement of the point position. The capacitive signal is converted to a voltage signal by the signal conditioning circuit, and is transmitted to the signal acquisition circuit for long distance transmission. After being amplified into a voltage signal, it is input into the FPGA angle calculation module for three-point displacement-swing angle calculation. The calculation result is transmitted to the upper computer to complete the real-time monitoring of the swing angle.

[0010] Further, the capacitive displacement sensor is composed of an upper plate and a lower plate, wherein the upper plate is installed below the three-point piezoelectric drive fast swing mirror mechanism, and the lower plate is installed on the base of the three-point piezoelectric drive fast swing mirror mechanism and overlaps with the upper plate. The main part and the backup part of the six capacitive displacement sensors are a group, located on both sides of the piezoelectric actuator, and distributed in an equilateral triangle around the center of the mirror surface. The included angle between each two actuators and the center line is 120°.

[0011] Further, the signal conditioning circuit and the signal acquisition circuit are composed of three independent channels, respectively used for detecting three displacement amounts, and the middle transmission is realized by V-I conversion and I-V conversion for long distance transmission of more than 1 meter. The three-point capacitive displacement is detected in parallel.

[0012] Further, the signal acquisition circuit comprises an amplification and filtering module, a single-end-differential conversion module and an analog-digital conversion module, the amplification and filtering module is used for denoising and amplifying the weak displacement signal detected by the signal conditioning circuit through a narrow-band Butterworth low-pass filter; the single-end-differential conversion module is used for improving the common-mode rejection capability and adapting the dynamic of the analog-digital conversion module; the analog-digital conversion module adopts a multi-channel 18 bits differential input type ADC, has a channel selection capability, and converts the displacement analog signal into a digital signal to access the FPGA angle calculation module.

[0013] Further, the angle of the three-point piezoelectric drive fast swing mirror mechanism is obtained through the FPGA angle calculation module and the 18 bits ADC analog-digital conversion, and is transmitted to the upper computer, so that the control result of the piezoelectric ceramic actuator is known.

[0014] Further, the conversion parameters of the FPGA angle calculation module are controlled by the closed-loop control of the three piezoelectric ceramic actuators to control the three-point piezoelectric drive fast swing mirror mechanism, and the star point information detected by the fine star finder is collected, and the coefficient conversion relationship between the capacitance acquisition signal and the angle is determined according to the spatial relationship of the information and the structure.

[0015] Further, the three-point piezoelectric drive fast swing mirror mechanism swings along the x-axis and the y-axis by the closed-loop control of the piezoelectric actuator, the maximum range of the swing angle is controlled, the change amount of the star point position collected by the fine star finder in the system is recorded, the conversion parameters of the FPGA angle calculation module are obtained according to the geometric relationship of the system, and the angle detection of the fast swing mirror is realized.

[0016] The application further provides a fast swing mirror swing angle monitoring method based on a three-point capacitance displacement sensor, comprising the following steps:

[0017] Step 1, the capacitance displacement sensor is installed on the frame, wherein the upper plate is installed below the three-point piezoelectric drive fast swing mirror mechanism, the lower plate is installed on the base of the three-point piezoelectric drive fast swing mirror mechanism and overlaps with the upper plate, and the three capacitance sensors are distributed in an equilateral triangle around the center of the mirror, and the included angle between each two actuators and the center connecting line is 120°.

[0018] Step 2, the dynamic measurement range of the capacitance displacement sensor is corrected, the output code value of the signal acquisition circuit of the three-point piezoelectric drive fast swing mirror mechanism three piezoelectric ceramic actuators at the minimum position and the maximum position is collected, if the dynamic range exceeds the effective range of the signal conditioning circuit and the capacitance displacement sensor, the parameter size of the differential capacitance chip is modified until the output code value dynamic range is in the effective value range.

[0019] Step 3, set the swing angle conversion parameter of the FPGA angle solution module, wherein the three-point piezoelectric drive fast swing mirror mechanism needs to be controlled to swing along the x-axis and the y-axis by a closed-loop piezoelectric actuator, the maximum range of the swing angle is controlled, the star point position variation collected by the fine star finder is recorded, the conversion parameter of the FPGA angle solution module is obtained according to the geometric relationship of the system, and the angle detection of the fast swing mirror is realized.

[0020] Further, in the step 2, the differential capacitance chip is used to realize the signal reading of the capacitive displacement sensor, and the calculation formula of the output voltage is:

[0021] ;

[0022] Wherein, is an analog amplification factor; is a capacitive-to-voltage conversion factor; is a reference voltage; = CS2IN + CS2, = CS1IN + CS1, CS1IN and CS2IN are differential inputs of the capacitive displacement sensor to be detected, and CS1 and CS2 are adjustable compensation capacitors in the HJ3110 chip, which are used to adjust the bias caused by the asymmetry of the input capacitors; is the integration capacitance of the charge integrator; after parameter adjustment and displacement correction, the change of the capacitor can be converted into the spacing d of the two plates.

[0023] Beneficial effects:

[0024] The present application can directly measure the actual displacement of the three detection points of the fast swing mirror, so as to calculate the swing angle of the mirror surface, by converting the spacing displacement between the bottom surface of the fast swing mirror structure and the support frame into a small change of the capacitor through the capacitive sensor. The method has the advantages of simple structure, high measurement accuracy, and does not need additional light source, and can meet the needs of long-term detection of the swing angle of the order of angle-second on orbit. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a schematic diagram of the fast swing mirror swing angle monitoring system based on the three-point capacitive displacement sensor of the present application.

[0026] Figure 2 It is a functional block diagram of the differential capacitance chip (taking the HJ3110 chip as an example).

[0027] Figure 3 It is an installation schematic diagram of the capacitive sensor.

[0028] Figure 4 It is a side view of the three-point piezoelectric drive fast swing mirror mechanism with the capacitive sensor.

[0029] Figure 5Block diagram of a space telescope precise image stabilization system.

[0030] Wherein, the figure mark is: three-point piezoelectric drive fast swing mirror mechanism 1, capacitance displacement sensor 2, signal conditioning circuit 3, signal acquisition circuit 4, FPGA angle solution module 5, host computer 6. DETAILED DESCRIPTION

[0031] 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 not to 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.

[0032] As shown in Figure 1 A three-point capacitance displacement sensor-based fast swing mirror swing angle monitoring system of the present application includes a three-point piezoelectric drive fast swing mirror mechanism 1, a capacitance displacement sensor 2, a signal conditioning circuit 3, a signal acquisition circuit 4, an FPGA angle solution module 5 and a host computer 6.

[0033] The host computer 6 sends the angle control signal of the three-point piezoelectric drive fast swing mirror mechanism 1 to the three-point piezoelectric drive fast swing mirror mechanism 1 through the 422 communication interface, and realizes swing angle control by using the target displacement of the three-point piezoelectric ceramic actuator. The included angle of the three-point piezoelectric ceramic actuator is 120° and is uniformly distributed on the concentric circle of the mirror surface. The capacitance displacement sensor 2 has a total of 6, every 2 as a group of main and backup, respectively located on both sides of the piezoelectric actuator at the same section, detects the displacement of the point position, and the capacitance signal is converted to voltage signal by the signal conditioning circuit 3, which is transmitted to the signal acquisition circuit 4, and then the voltage signal is amplified and input to the FPGA angle solution module 5 for three-point displacement-swing angle calculation. The calculation result is transmitted to the host computer 6 through the 422 communication interface, and the real-time monitoring of the swing angle is completed.

[0034] As shown in Figure 4 The capacitance displacement sensor 2 is composed of an upper plate and a lower plate, wherein the upper plate is installed below the FSM (three-point piezoelectric drive fast swing mirror mechanism 1), and the lower plate is installed on the base of the FSM and overlaps with the upper plate. The three capacitance displacement sensors 2 are distributed in an equilateral triangle around the center of the mirror surface, and the included angle between each two actuators and the center is 120°.

[0035] The signal conditioning circuit 3 and the signal acquisition circuit 4 are composed of three independent channels, and the middle transmission is realized by V-I conversion and I-V conversion to realize more than 1 meter of long-distance transmission. The displacement of the three-point capacitance position is detected in parallel.

[0036] The signal acquisition circuit 4 comprises an amplification and filtering module, a single-ended-differential conversion module and an analog-digital conversion module, the amplification and filtering module is used for denoising and amplifying the weak displacement signal detected by the signal conditioning circuit 3 through a narrow-band Butterworth low-pass filter; the single-ended-differential conversion module is used for improving the common-mode rejection capability and adapting the dynamic of the analog-digital conversion module; the analog-digital conversion module adopts a multi-channel 18 bits differential input type ADC, has a channel selection capability, and converts the displacement analog signal into a digital signal to access the FPGA angle calculation module 5.

[0037] The application adopts a three-point capacitive displacement sensor to detect the swing angle of the FSM, utilizes the signal conditioning circuit 3 and the signal acquisition circuit 4 to amplify the signal of the capacitive voltage in parallel, and performs analog-digital conversion through the 18 bits ADC, obtains the angle of the FSM through the FPGA angle calculation module 5, and transmits the angle to the upper computer 6, so that the control result of the piezoelectric ceramic actuator can be known.

[0038] The capacitive displacement sensor (Capacitance displacement sensor, CS) is a non-contact micro displacement measuring instrument based on the flat plate capacitance principle, comprises an upper plate and a lower plate, and the installation mode is as shown in Figure 2 The working principle is as shown in the following formula:

[0039] ;

[0040] Wherein, C is the capacitance sensor capacity, is the dielectric constant, S is the relative coverage area between the plates, d is the distance between the plates, is the relative dielectric constant, is the vacuum dielectric constant, and the value is 8.85fF / m.

[0041] The differential capacitance chip can be used to realize the signal reading of the capacitive displacement sensor, for example, the HJ3110 chip, and the structure is as shown in Figure 3 The output voltage calculation formula is:

[0042] ;

[0043] Wherein, is the analog amplification factor; is the conversion coefficient of capacitance to voltage; is the reference voltage; =CS2IN+CS2, =CS1IN+CS1, CS1IN and CS2IN are differential inputs of the detected capacitive displacement sensor, and CS1 and CS2 are adjustable compensation capacitors in the HJ3110 chip, which are used to adjust the bias caused by the asymmetry of the input capacitance. The integral capacitor of the charge integrator; after parameter adjustment and displacement correction, the change of the capacitor can be converted into the distance d between the two plates.

[0044] As shown in Figure 4 , the piezoelectric ceramic actuator is based on piezoelectric ceramic as the basic element, and outputs displacement and force through external mechanical structure, and the resistance strain gauge sensor (SGS) is installed in the actuator as a micro-displacement detection sensor of the piezoelectric actuator, and through the displacement output of the piezoelectric actuator and the measurement of the SGS, closed-loop control of the piezoelectric actuator can be realized.

[0045] Through the uniform distribution of the three piezoelectric actuators on the circumference of the FSM, closed-loop control of the FSM angle can be realized, and further combined with the measurement and processing of the star point by the guide star instrument, the fast swing mirror swing angle can be calibrated and further controlled in a closed loop. The upper plate of the capacitive displacement sensor is installed below the FSM structure, and the lower plate is installed on the FSM base and overlaps with the upper plate, and as shown in Figure 5 , the three capacitive sensors are distributed in an equilateral triangle around the center of the mirror surface, the included angle between each two piezoelectric actuators and the center line is 120°, and the capacitance reflects the displacement between the FSM structure below and the FSM base. Through 18 bits ADC, the displacement of the three points is converted into digital signals, and the displacement is taken as the swing micro-angle detection sensor of the fast swing mechanism by the FPGA angle calculation module 5.

[0046] The conversion parameters of the FPGA angle calculation module 5 need to control the FSM by closed-loop control of the three piezoelectric actuators, and the star point information detected by the fine guide star instrument (FGS) is collected, and according to the geometric relationship of the space telescope precise image stabilization system, the coefficient conversion relationship between the capacitive collection signal and the angle is determined, and the space telescope precise image stabilization system block diagram is shown in Figure 5 , specifically, the signal of the guide star is folded back on the main focal plane of the FGS through the off-axis three-mirror structure and the FSM, and the FSM is swung along the x-axis and the y-axis through the precise image stabilization controller to realize the closed-loop control of the piezoelectric actuator, so as to realize the coordinate position change of the guide star on the FGS. The swing angle of the FSM is controlled to swing in the maximum range, and the star point position change (i.e. Figure 5 ) collected by the FGS in the system is recorded, and according to the geometric relationship of the system, the conversion parameters of the FPGA angle calculation module 5 are obtained, and the angle detection of the fast swing mirror is realized. Thus, in the subsequent use, the swing angle of the fast swing mirror can be monitored in real time according to the measurement value of the collection circuit.

[0047] The application also provides a fast swing mirror swing angle monitoring method based on a three-point capacitive displacement sensor, which comprises the following steps:

[0048] Step 1, install the capacitive displacement sensor on the frame, wherein the upper plate is installed below the FSM structure, the lower plate is installed on the FSM base and overlaps with the upper plate, three capacitive sensors are distributed in an equilateral triangle around the center of the mirror, and the included angle between each actuator and the center connecting line is 120°;

[0049] Step 2, correct the dynamic measurement range of the capacitive displacement sensor, collect the output code value of the signal acquisition circuit of the three piezoelectric actuators of the fast steering mirror mechanism 1 at the minimum position and the maximum position, if the dynamic range exceeds the effective range of the signal conditioning circuit and the capacitive displacement sensor, modify the parameter size of the differential capacitive chip until the output code value dynamic range is in the effective value range;

[0050] Step 3, set the swing angle conversion parameters of the FPGA angle calculation module, wherein the piezoelectric actuators need to be controlled in a closed loop to realize the swing of the FSM along the x-axis and the y-axis, control the maximum range of the swing angle, record the star point position change amount collected by the FGS, obtain the conversion parameters of the FPGA angle calculation module according to the geometric relationship of the system, and realize the angle detection of the fast steering mirror.

Claims

1. A system for monitoring the swing angle of a fast-swinging mirror based on a three-point capacitive displacement sensor, characterized in that, It includes a three-point piezoelectric driven fast-swing mirror mechanism, a capacitive displacement sensor, a signal conditioning circuit, a signal acquisition circuit, an FPGA angle calculation module, and a host computer; The host computer sends the angle control signal of the three-point piezoelectric driven fast swing mirror mechanism to the three-point piezoelectric driven fast swing mirror mechanism. The target displacement of the three-point piezoelectric ceramic actuators, which are evenly distributed in concentric circles on the mirror surface with an included angle of 120°, is used to achieve swing angle control. There are a total of 6 capacitive displacement sensors, with 2 sensors forming a main and backup group, located on both sides of the same cross section of the piezoelectric actuator. The displacement of the detection point is converted into a voltage signal by the signal conditioning circuit. The signal is then transmitted to the signal acquisition circuit over a long distance through VI conversion and IV conversion. The displacement of the three-point capacitor position is detected in parallel. After being converted into a voltage signal and amplified, the signal is input into the FPGA angle calculation module to calculate the three-point displacement-swing angle. The calculation result is transmitted to the host computer to complete the real-time monitoring of the swing angle. Two capacitive displacement sensors are arranged in an equilateral triangle around the center of the mirror, and the angle between the line connecting each two actuators and the center is 120°. The signal acquisition circuit includes an amplification and filtering module, a single-ended to differential conversion module, and an analog-to-digital conversion module. The analog-to-digital conversion module converts the displacement analog signal into a digital signal and inputs it into the FPGA angle calculation module. The conversion parameters of the FPGA angle calculation module are controlled by three piezoelectric ceramic actuators through closed-loop control to control the three-point piezoelectric drive fast swing mirror mechanism. At the same time, star point information detected by the fine guide star instrument is collected. Based on the star point information and the spatial relationship of the structure, the coefficient conversion relationship between the capacitor acquisition signal and the angle is determined.

2. The fast-swing mirror swing angle monitoring system based on a three-point capacitive displacement sensor according to claim 1, characterized in that, The capacitive displacement sensor consists of an upper electrode plate and a lower electrode plate. The upper electrode plate is installed below the three-point piezoelectric driven fast-swing mirror mechanism, and the lower electrode plate is installed on the base of the three-point piezoelectric driven fast-swing mirror mechanism, overlapping the upper electrode plate.

3. The fast-swing mirror swing angle monitoring system based on a three-point capacitive displacement sensor according to claim 1, characterized in that, The signal conditioning circuit and signal acquisition circuit consist of three independent channels, which are used to detect three displacement quantities respectively.

4. The fast-swing mirror angle monitoring system based on a three-point capacitive displacement sensor according to claim 1, characterized in that, The amplification and filtering module is used to denoise and amplify the weak displacement signal detected by the signal conditioning circuit through a narrowband Butterworth low-pass filter; the single-ended to differential conversion module is used to improve the common-mode rejection capability and adapt to the dynamics of the analog-to-digital conversion module; the analog-to-digital conversion module adopts a multi-channel 18-bit differential input ADC with channel selection capability.

5. The fast-swing mirror swing angle monitoring system based on a three-point capacitive displacement sensor according to claim 1, characterized in that, The angle of the three-point piezoelectric driven fast-swing mirror mechanism is obtained through the 18-bit ADC and the angle calculation module of the FPGA, and then transmitted to the host computer to understand the control result of the piezoelectric ceramic actuator.

6. The fast-swing mirror angle monitoring system based on a three-point capacitive displacement sensor according to claim 5, characterized in that, The closed-loop control piezoelectric actuator enables the three-point piezoelectric drive of the fast swing mirror mechanism to swing along the x and y axes, controlling the maximum range of the swing angle. It records the changes in star position collected by the fine guide star instrument in the system, and obtains the conversion parameters of the FPGA angle calculation module based on the geometric relationship of the system, thereby realizing the angle detection of the fast swing mirror.

7. A method for monitoring the swing angle of a fast-swinging mirror based on a three-point capacitive displacement sensor, implemented using the three-point capacitive displacement sensor-based swing angle monitoring system according to any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Install the capacitive displacement sensor on the frame. The upper electrode plate is installed below the three-point piezoelectric driven fast swing mirror mechanism, and the lower electrode plate is installed on the base of the three-point piezoelectric driven fast swing mirror mechanism, overlapping with the upper electrode plate. The three capacitive sensors are distributed in an equilateral triangle around the center of the mirror surface, and the angle between the line connecting each two actuators and the center is 120°. Step 2: Correct the dynamic measurement range of the capacitive displacement sensor. Collect the output code values ​​of the signal acquisition circuit of the three piezoelectric ceramic actuators of the three-point piezoelectric driven fast swing mirror mechanism at the minimum and maximum positions. If the dynamic range exceeds the effective range of the signal conditioning circuit and the capacitive displacement sensor, modify the parameter size of the differential capacitor chip until the dynamic range of the output code value is within the effective value range. Step 3: Set the swing angle conversion parameters of the FPGA angle calculation module. This requires closed-loop control of the piezoelectric actuator to realize the three-point piezoelectric drive of the fast swing mirror mechanism to swing along the x-axis and y-axis, control the maximum range of the swing angle, record the change in star position collected by the fine guide star instrument, and obtain the conversion parameters of the FPGA angle calculation module based on the geometric relationship of the system to realize the angle detection of the fast swing mirror.

8. The method for monitoring the swing angle of a fast-swinging mirror based on a three-point capacitive displacement sensor according to claim 7, characterized in that, In step 2, a differential capacitor chip is used to read out the signal from the capacitive displacement sensor. The formula for calculating the output voltage is as follows: ； in, To simulate magnification; This is the conversion factor from capacitance to voltage; Reference voltage; =CS2IN+CS2, =CS1IN+CS1, CS1IN and CS2IN are the differential inputs of the detected capacitive displacement sensor, and CS1 and CS2 are the adjustable compensation capacitors inside the HJ3110 chip, used to adjust the bias caused by the asymmetry of the input capacitance. The capacitor is the integrating capacitor of the charge integrator; after parameter adjustment and displacement correction, the change in capacitance can be converted into the distance d between the two plates.

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