An accelerometer system and control method based on variable duty cycle square wave modulation

Abstract

The application belongs to the field of precision measurement, and specifically discloses an accelerometer system based on variable duty cycle square wave modulation and a control method. The application adopts the technical means of generating a bipolar square wave signal with adjustable duty cycle as a carrier to be applied to the proof mass, avoids superimposing a direct current bias on the proof mass, realizes the integration of displacement sensing and electrostatic control circuit system functions, eliminates the electrostatic negative stiffness caused by the direct current bias, and overall reduces the electrostatic negative stiffness, thereby alleviating the problems of poor linearity and measurement distortion of the existing accelerometer system. The displacement sensing module detects the differential capacitance change based on the square wave signal, and the feedback control module generates a feedback voltage according to the output signal of the displacement sensing module, which, together with the carrier, generates an electrostatic feedback force to realize balance with the external inertial force and linearly represent the acceleration through the feedback voltage. Finally, the effect of significantly improving the measurement linearity and accuracy while keeping the system structure simple is realized.

Description

Technical Field

[0001] This application belongs to the field of precision measurement, specifically relating to an accelerometer system and control method based on variable duty cycle square wave modulation. Background Technology

[0002] Currently, capacitive electrostatic accelerometers typically employ differential capacitive displacement sensing and electrostatic feedback control technology, offering high accuracy and are widely used in space missions, inertial navigation, and scientific experiments. Their basic working principle involves detecting the change in differential capacitance caused by the displacement of a mass under external force, and using the electrostatic feedback force applied by the capacitor plates to maintain the mass in an equilibrium position. The external acceleration is then calculated by measuring this feedback force.

[0003] In differential capacitive accelerometer systems employing electrostatic feedback, a modulation signal is typically applied to the sensing quality of the accelerometer's sensitive probe to meet the functional requirements of capacitive sensing and electrostatic control. This is usually achieved by superimposing a high-frequency AC modulation signal and a DC bias voltage, working in conjunction with electronic units to realize differential capacitive displacement sensing and electrostatic feedback control. This approach has the following problems: adding a DC bias to the sensing quality introduces accelerometer closed-loop noise caused by DC voltage noise and a large electrostatic negative stiffness term. The closed-loop noise of the accelerometer is a reflection of its resolution; the lower the system's closed-loop noise, the higher the accelerometer resolution. To improve accelerometer resolution, it is necessary to minimize all system noise as much as possible.

[0004] Among them, electrostatic negative stiffness originates from the nonlinear nature of electrostatic force. When a feedback voltage is applied between the capacitor plates to generate electrostatic force, an electrostatic negative stiffness is generated whose magnitude varies with the feedback voltage value. This causes the sensitivity of the accelerometer to be not a constant, but to change with the magnitude of the input acceleration. This makes it impossible to maintain a strict linear relationship between the output voltage value of the accelerometer and the input acceleration.

[0005] Linearity is one of the key indicators for evaluating the performance of high-precision accelerometers. Poor linearity directly leads to measurement distortion, resulting in cumulative errors in applications such as navigation and attitude control, severely impacting the accuracy and reliability of the entire system. Due to the nature of electrostatic feedback force, electrostatic negative stiffness cannot be completely eliminated mechanistically. However, when designing closed-loop control schemes for accelerometer systems, it is necessary to minimize electrostatic negative stiffness as much as possible while ensuring high sensitivity, thereby effectively improving the linearity of the electrostatic accelerometer to meet the increasing demands of high-precision applications. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this application is to provide an accelerometer system and control method based on variable duty cycle square wave modulation. It utilizes bipolar square wave synchronization to achieve capacitive displacement sensing and electrostatic feedback control, aiming to solve the technical problems of existing accelerometer systems generally having a DC bias superimposed on the quality of the test, poor linearity due to electrostatic negative stiffness, resulting in measurement distortion and high noise.

[0007] The first aspect of this application relates to an accelerometer system based on variable duty cycle square wave modulation, comprising: a detection module, a carrier generation module, a displacement sensing module, and a feedback control module; the detection module includes a differential capacitor pair formed by a movable test mass and a fixed capacitor plate; the output terminal of the carrier generation module is connected to the test mass of the detection module; the input terminal of the displacement sensing module is connected to the fixed capacitor plate; the input terminal of the feedback control module is connected to the output terminal of the displacement sensing module; the output terminal of the feedback control module is connected to the fixed capacitor plate; the carrier generation module is configured to generate a bipolar capacitor with a duty cycle higher than 0.5. A bipolar square wave signal is used as the carrier signal for capacitive displacement sensing and applied to the inspection mass. The displacement sensing module is configured to detect the differential capacitance change of the inspection mass caused by displacement based on the bipolar square wave signal and output a displacement detection voltage signal. The feedback control module is configured to generate a feedback voltage signal based on the displacement detection voltage signal and apply it to the fixed capacitor plates. The inspection mass generates an electrostatic feedback force under the combined action of the bipolar square wave signal and the feedback voltage signal. The electrostatic feedback force is balanced with the inertial force of the inspection mass caused by external acceleration. The external acceleration is characterized by the feedback voltage signal.

[0008] In one embodiment, the carrier generation module is further configured to output a bipolar square wave signal with an adjustable duty cycle. By adjusting the duty cycle of the square wave signal, the sensitivity coefficient of the feedback actuator of the accelerometer system is changed, thereby adjusting the range of the accelerometer.

[0009] In one embodiment, under the condition that only a bipolar square wave signal without DC bias is applied to the inspection quality, the expression for the electrostatic force on the inspection quality is as follows: ; in, F It is electrostatic force; x To verify the displacement of the mass from its equilibrium position; C 0 and d 0 represents the capacitance value and plate spacing of the two sets of capacitors when the inspection quality is in equilibrium. n + and V p represents the duty cycle and amplitude of the square wave signal, respectively. V f is the feedback voltage calculated by the system; where 2 C 0 V p(2n+ -1) / d 0 represents the sensitivity coefficient of the feedback actuator.

[0010] In one embodiment, the carrier generation module includes: a first control unit and a power supply unit; the output terminal of the first control unit is connected to the controlled terminal of the power supply unit; the output terminal of the power supply unit is connected to a quality check; the first control unit is configured to output a control signal to the power supply unit to control the power supply unit to output a bipolar square wave signal with adjustable amplitude, frequency, and duty cycle.

[0011] In one embodiment, the first control unit is configured to execute the following range adjustment logic: when it is necessary to increase the sensitivity coefficient of the feedback actuator of the accelerometer system, the amplitude of the bipolar square wave signal is kept constant and the result is achieved by adjusting the duty cycle; when the required sensitivity coefficient cannot be obtained by adjusting the duty cycle alone, the amplitude of the square wave signal is increased, and the target sensitivity coefficient is obtained again by adjusting the duty cycle based on the increased amplitude.

[0012] In one embodiment, the duty cycle is adjusted by increasing or decreasing the deviation of the square wave signal's duty cycle from 0.5.

[0013] In one embodiment, the displacement sensing module includes: a modulation and demodulation unit and a first signal processing unit; the input terminal of the modulation and demodulation unit is connected to a fixed capacitor plate; the output terminal of the modulation and demodulation unit is connected to the input terminal of the first signal processing unit; the output terminal of the first signal processing unit is connected to the input terminal of a feedback control module; the modulation and demodulation unit is configured to modulate the capacitance change of the differential capacitor pair into a current signal and demodulate it to output to the first signal processing unit; the first signal processing unit is configured to convert the current signal into a voltage signal, and amplify, perform differential operations and filtering on the voltage signal, and finally output a displacement detection voltage signal proportional to the displacement of the inspected mass.

[0014] In one embodiment, the feedback control module includes: a second control unit and a second signal processing unit; the input terminal of the second control unit is connected to the output terminal of the displacement sensing module; the output terminal of the second control unit is connected to the input terminal of the second signal processing unit; the output terminal of the second signal processing unit is connected to a fixed capacitor plate; the second control unit is configured to receive a displacement detection voltage signal and calculate and generate an initial feedback control signal according to a control algorithm; the second signal processing unit is configured to process the initial feedback control signal, generate and output a pair of feedback voltage signals with equal amplitude and opposite polarity applied to the fixed capacitor plate to form a closed-loop feedback control.

[0015] The second aspect of this application relates to a control method for an accelerometer system, comprising: step S10, acquiring the target duty cycle of a bipolar square wave signal based on the required range, generating a bipolar square wave signal according to the target duty cycle, and applying the square wave signal to a movable test mass of the accelerometer system; step S20, detecting the differential capacitance change caused by the displacement of the test mass based on the bipolar square wave signal, and outputting a displacement detection voltage signal; step S30, generating a pair of feedback voltage signals according to the displacement detection voltage signals, and applying them respectively to fixed capacitor plates on both sides of the test mass, so that the test mass generates an electrostatic feedback force under the combined action of the bipolar square wave signal and the feedback voltage signal, the electrostatic feedback force being balanced with the inertial force of the external acceleration acting on the test mass, and the external acceleration being characterized by the feedback voltage signal.

[0016] In one embodiment, the step S10 of obtaining the target duty cycle of the bipolar square wave signal based on the required range includes: increasing the deviation of the target duty cycle from 0.5 when it is necessary to increase the accelerometer range; and decreasing the deviation of the target duty cycle from 0.5 when it is necessary to decrease the accelerometer range, so as to match the accelerometer range with the external input.

[0017] In summary, the technical solution proposed in this application replaces the traditional method of applying a voltage with an AC carrier superimposed with a DC bias by using a bipolar square wave signal with an adjustable duty cycle (not equal to 50%) as the carrier applied to the test quality. This solves the problems of poor linearity and measurement distortion caused by the superimposed DC bias in the prior art, and achieves the technical effect of improving the linearity of accelerometer measurements. Specifically, by eliminating the need for an additional DC bias voltage, the direct noise source introduced by the DC bias voltage is eliminated at its source, thereby reducing the closed-loop noise of the accelerometer. Simultaneously, the voltage signal applied to the test mass no longer contains a DC component. This means that the expression for the electrostatic negative stiffness force acting on the test mass no longer includes a term composed of the square of the DC bias voltage, effectively reducing the electrostatic negative stiffness of the system and thus improving the linearity of the accelerometer system.

[0018] The displacement sensing module detects changes in differential capacitance based on the square wave signal and outputs a displacement detection voltage signal. The feedback control module generates a feedback voltage based on the displacement signal, which, together with the square wave carrier, produces an electrostatic feedback force, achieving balance with the inertial force of external acceleration. Thus, the acceleration is linearly characterized through the feedback voltage. Compared with existing technologies, this approach significantly improves measurement linearity and accuracy while maintaining a simple system structure.

[0019] Furthermore, by adjusting the duty cycle of the square wave signal, the average value of the square wave voltage can be changed, thereby linearly adjusting the sensitivity coefficient of the system feedback actuator to achieve range switching. Within a certain range adjustment range, this can be achieved by simply changing the duty cycle without increasing the square wave amplitude, thus avoiding the problem of a squared increase in electrostatic negative stiffness caused by increasing the amplitude. This allows the system to maintain high linearity even when the range is expanded. Attached Figure Description

[0020] Figure 1 This is a structural block diagram of an accelerometer system based on variable duty cycle square wave modulation provided in an embodiment of this application; Figure 2 This is a schematic diagram of a bipolar square wave signal with adjustable duty cycle provided in an embodiment of this application; Figure 3 This is a basic selection diagram of an accelerometer system based on variable duty cycle square wave modulation provided in the embodiments of this application; Figure 4 This is a schematic diagram illustrating the principle of accelerometer range switching provided in an embodiment of this application; Figure 5 This is a flowchart illustrating the control method of the accelerometer system provided in the embodiments of this application.

[0021] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 10 is the detection module; 11 is the quality inspection module; 12 is the capacitor plate; 20 is the carrier generation module; 21 is the first control unit; 22 is the power supply unit; 30 is the displacement sensing module; 31 is the modulation and demodulation unit; 32 is the first signal processing unit; 40 is the feedback control module; 41 is the second control unit; 42 is the second signal processing unit. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0023] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A existing alone, A and B existing simultaneously, and B existing alone. In this application, the symbol " / " indicates that the related objects are in an "or" relationship, for example, A / B means A or B.

[0024] In this application, the terms "first" and "second," etc., are used to distinguish different objects, not to describe a specific order of objects. For example, "first response message" and "second response message," etc., are used to distinguish different response messages, not to describe a specific order of response messages. The term "connection" in this application can refer to a direct circuit connection or signal transmission via a communication protocol.

[0025] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0026] In the description of the embodiments of this application, unless otherwise stated, "multiple" means two or more, for example, multiple processing units means two or more processing units, multiple elements means two or more elements, etc.

[0027] Currently, accelerometer systems generally incorporate a DC bias for quality control, which leads to poor linearity due to the influence of electrostatic negative stiffness and measurement distortion.

[0028] Based on this, this application proposes an embodiment of an accelerometer system based on variable duty cycle square wave modulation. Please refer to... Figure 1 , Figure 1 This is a structural block diagram of an accelerometer system based on variable duty cycle square wave modulation provided in an embodiment of this application.

[0029] In this embodiment, the accelerometer system includes: a detection module 10, a carrier generation module 20, a displacement sensing module 30, and a feedback control module 40.

[0030] It should be noted that the detection module 10 includes a differential capacitor pair formed by a movable inspection mass 11 and a fixed capacitor plate 12. The movable inspection mass 11 is a movable structure fabricated using microelectromechanical systems (MEMS) technology, typically formed by etching silicon-based material. It is connected to the substrate via a support beam and can move freely along the acceleration-sensitive direction. The fixed capacitor plate 12 is a conductive metal layer deposited on the substrate and is positioned opposite the movable inspection mass 11, forming two independent capacitors that constitute a differential structure. When an external acceleration is applied to the movable inspection mass 11, the inertial force causes it to displace along the sensitive direction, resulting in a change in the difference between the two capacitors. This difference is positively correlated with the magnitude of the acceleration.

[0031] The output of the carrier generation module 20 is connected to the inspection quality 11 of the detection module 10; the input of the displacement sensing module 30 is connected to the fixed capacitor plate 12; the input of the feedback control module 40 is connected to the output of the displacement sensing module 30; and the output of the feedback control module 40 is connected to the fixed capacitor plate 12.

[0032] It is understood that an electrical connection is formed between the output of the carrier generation module 20 and the movable test mass 11 of the detection module 10. This connection is used to apply an excitation potential to the movable test mass 11. In specific implementations, this connection can be achieved through conductive wire bonding or silicon-to-silicon technology to transmit the carrier signal to the movable test mass 11. Since the movable test mass 11 is typically made of semiconductor silicon material, which has good conductivity, this connection, serving as the common electrode of the differential capacitor, allows the square wave carrier signal to be loaded onto the movable structure, thereby establishing an alternating electric field between the fixed capacitor plate 12 and the movable test mass 11. This connection method ensures that the excitation signal can directly drive the movable mass block, which is the basis for realizing capacitance detection.

[0033] Understandably, the input terminal of the displacement sensing module 30 is connected to the fixed capacitor plate 12, forming a signal pickup path. The fixed capacitor plate 12 is typically divided into a first fixed plate and a second fixed plate. The input terminal of the displacement sensing module 30 is electrically connected to these two sets of plates to acquire changes in the differential capacitance. In practical applications, the input terminal of the pre-amplifier circuit (such as a charge amplifier) ​​of the displacement sensing module 30 is connected to the pads of the fixed capacitor plate 12 via metal traces. This connection method allows the displacement sensing module 30 to monitor in real time the capacitance fluctuations caused by the displacement of the movable test mass 11 and convert it into an easily processed voltage or current signal, the amplitude of which is positively correlated with the displacement caused by acceleration.

[0034] Understandably, the input terminal of the feedback control module 40 is connected to the output terminal of the displacement sensing module 30, and this connection is used to transmit an error signal characterizing the magnitude of acceleration. The analog voltage signal output by the displacement sensing module 30 is transmitted to the input terminal of the analog-to-digital converter or comparator of the feedback control module 40 via a signal line. Structurally, this connection can be a metal interconnect within an integrated circuit or an external circuit connection after chip packaging. Through this connection, the feedback control module 40 can acquire the current displacement state and calculate the correction amount required to maintain system balance based on a preset control algorithm (such as a PID algorithm), thereby achieving closed-loop signal processing.

[0035] Understandably, the output of the feedback control module 40 is connected to the fixed capacitor plate 12, forming the force feedback execution path. Based on the feedback voltage signal output from this connection, the feedback control module 40 applies an electrostatic force to the fixed capacitor plate 12 to balance the inertial force generated by the acceleration of the movable inspection mass 11. In a specific implementation, this output can generate a DC or low-frequency voltage proportional to the displacement detection signal. After being applied to the fixed capacitor plate 12, the electrostatic attraction pushes the movable inspection mass 11 back to its zero position. This connection method achieves closed-loop control of the system, significantly improving the system's dynamic range and anti-interference capability, and avoiding nonlinear distortion caused by large displacements.

[0036] Therefore, the carrier generation module 20 is configured to generate a bipolar square wave signal with a duty cycle higher than 0.5 and apply the square wave signal as a carrier signal to the inspection mass 11; the displacement sensing module 30 is configured to detect the differential capacitance change of the inspection mass 11 caused by displacement based on the bipolar square wave signal and output a displacement detection voltage signal; the feedback control module 40 is configured to generate a feedback voltage signal based on the displacement detection voltage signal and apply it to the fixed capacitor plate 12; wherein, the inspection mass 11 generates an electrostatic feedback force under the combined action of the bipolar square wave signal and the feedback voltage signal, and the electrostatic feedback force is balanced with the inertial force of the external acceleration acting on the inspection mass 11, and the external acceleration is characterized by the feedback voltage signal.

[0037] It is understood that the core of this embodiment lies in the fact that the carrier generation module 20 is configured to generate a bipolar square wave signal with a duty cycle higher than 0.5. This configuration means that the module internally contains a programmable logic device or an application-specific integrated circuit (ASIC) for controlling the duty cycle parameter of the output waveform. A bipolar square wave signal refers to a pulse signal whose signal level periodically jumps between positive and negative voltages, and whose high-level duration is not equal to its low-level duration. In specific implementations, the carrier generation module 20 can be implemented using a microcontroller's PWM peripheral in conjunction with a level conversion circuit, or using a field-programmable gate array (FPGA) combined with a digital-to-analog converter (DAC).

[0038] Specifically, please refer to Figure 2 , Figure 2 This is a schematic diagram of a bipolar square wave signal with adjustable duty cycle provided in an embodiment of this application. Wherein, V p It represents the amplitude of the square wave; positive and negative signs indicate polarity. T The period of the square wave; T p The width of the positive pulse of the square wave; T n It represents the negative pulse width of a square wave. Its amplitude, duty cycle, and frequency can all be freely adjusted.

[0039] Understandably, a bipolar square wave signal with a duty cycle higher than 0.5 determines the average voltage across the test mass. This average value arises from the asymmetry in the duration of the positive and negative voltage levels. Under an ideally symmetrical square wave (duty cycle 0.5), the integral areas of the positive and negative voltage levels on the test mass are equal throughout a complete cycle, resulting in a net average voltage of zero. However, when the duty cycle deviates from 0.5, the integral areas of the positive and negative half-cycles differ, accumulating a non-zero DC voltage component over time—the average voltage. This seemingly minor difference in average value plays a decisive role in the electrostatic feedback mechanism.

[0040] First, this average voltage component provides a stable electrostatic feedback bias basis for the system. In the differential capacitor structure, the magnitude of the electrostatic force is proportional to the square of the voltage between the plates. When the displacement sensing module 30 detects a small amplitude displacement of the test mass 11 and outputs an error signal, the feedback control module 40 generates a corresponding feedback voltage signal based on this error and applies it to the fixed capacitor plate 12. Due to the asymmetry of the carrier duty cycle, the bipolar square wave loaded on the test mass 11 has a specific average value, which allows a stable DC bias electric field to be established between the fixed plate and the test mass 11. Superimposing an AC detection signal on this bias electric field can significantly improve the signal-to-noise ratio of the system and optimize the detection sensitivity of small capacitance changes.

[0041] Secondly, by adjusting the duty cycle to change the average voltage on the inspection mass 11, the sensitivity coefficient of the system feedback actuator is adjusted, thereby changing the electrostatic acceleration measurement range to achieve precise control and closed-loop balance of the electrostatic force. In actual operation, external acceleration acts on the inspection mass 11, generating inertial force that causes it to deviate from its initial equilibrium position, resulting in differential capacitor imbalance. The displacement sensing module 30 captures this change and converts it into a displacement detection voltage signal. The feedback control module 40 quickly calculates the required restoring force and adjusts the feedback voltage output to the fixed capacitor plate 12. At this time, the average square wave value on the inspection mass 11 interacts with the feedback voltage on the fixed plate, generating an electrostatic balance force of equal magnitude and opposite direction. When the system reaches a stable closed-loop state, the inspection mass 11 is firmly locked near its initial zero position, with almost zero displacement, effectively avoiding nonlinear errors caused by large displacements and significantly improving the system's linearity and dynamic range.

[0042] Furthermore, due to the alternating positive and negative characteristics of this square wave signal, the average voltage it generates on the test quality 11 is strictly controllable and highly stable. Compared to traditional unipolar pulse or pure sine excitation, this controllable average voltage value can perfectly cooperate with the subsequent synchronous demodulation circuit to extract the weak inertial force signal from the high-frequency carrier without distortion, while filtering out noise caused by manufacturing process errors. Finally, the magnitude of the external acceleration is accurately mapped to the amplitude of the feedback voltage signal. By performing simple calibration and conversion on this feedback voltage, a high-precision acceleration output value can be obtained.

[0043] In summary, this application proposes an electrostatic accelerometer based on square wave duty cycle modulation. It replaces the traditional scheme of superimposed DC bias by changing the duty cycle of the bipolar square wave to change the measurement range of the electrostatic accelerometer. This reduces the closed-loop acceleration noise introduced by DC voltage noise and improves the linearity of the accelerometer by reducing the electrostatic negative stiffness.

[0044] Next, this application will further elaborate on the specific implementation methods.

[0045] In this embodiment, the carrier generation module 20 includes: a first control unit 21 and a power supply unit 22; the output terminal of the first control unit 21 is connected to the controlled terminal of the power supply unit 22; the output terminal of the power supply unit 22 is connected to the test quality 11; the first control unit 21 is configured to output a control signal to the power supply unit 22 to control the power supply unit 22 to output a bipolar square wave signal with adjustable amplitude, frequency and duty cycle.

[0046] In this embodiment, the displacement sensing module 30 includes: a modulation and demodulation unit 31 and a first signal processing unit 32; the input terminal of the modulation and demodulation unit 31 is connected to the fixed capacitor plate 12; the output terminal of the modulation and demodulation unit 31 is connected to the input terminal of the first signal processing unit 32; the output terminal of the first signal processing unit 32 is connected to the input terminal of the feedback control module 40; the modulation and demodulation unit 31 is configured to modulate the capacitance change of the differential capacitor pair into a current signal and demodulate it to output to the first signal processing unit 32; the first signal processing unit 32 is configured to convert the current signal into a voltage signal, and amplify, perform differential operation and filtering on the voltage signal, and finally output a displacement detection voltage signal proportional to the displacement of the inspection mass 11.

[0047] In this embodiment, the feedback control module 40 includes: a second control unit 41 and a second signal processing unit 42; the input terminal of the second control unit 41 is connected to the output terminal of the displacement sensing module 30; the output terminal of the second control unit 41 is connected to the input terminal of the second signal processing unit 42; the output terminal of the second signal processing unit 42 is connected to the fixed capacitor plate 12; the second control unit 41 is configured to receive the displacement detection voltage signal and calculate and generate an initial feedback control signal according to the control algorithm; the second signal processing unit 42 is configured to process the initial feedback control signal, generate and output a pair of feedback voltage signals with equal amplitude and opposite polarity applied to the fixed capacitor plate 12 to form a closed-loop feedback control.

[0048] Specifically, the first control unit 21 and the power supply unit 22 together realize the function of the square wave generator. The carrier generation scheme includes, but is not limited to, the method of switching the reference source using an analog switch and the method of controlling the DAC generation using a controller such as FGPA.

[0049] Specifically, the detection module 10 selects an accelerometer mechanical sensitive probe, which consists of an intermediate inspection mass 11 and surrounding fixed capacitor plates 12, forming a differential capacitor pair with the surrounding plates. When the inspection mass 11 is displaced relative to the capacitor plates 12, it will cause a change in the differential capacitance value.

[0050] Specifically, the modulation and demodulation unit 31 and the first signal processing unit 32 constitute a charge-discharge type capacitor displacement sensing circuit. This circuit uses a square wave signal generated by a square wave generator to charge and discharge the differential capacitor under test, and modulates the differential capacitor signal into the current generated during the charging and discharging process.

[0051] It should be noted that, please refer to Figure 3 , Figure 3 This is a basic selection diagram of an accelerometer system based on variable duty cycle square wave modulation provided in the embodiments of this application.

[0052] In the charge-discharge capacitive displacement sensing circuit, the modulation and demodulation unit 31 includes a switching diode and a transimpedance amplifier. The switching diode demodulates the modulated current, and the transimpedance amplifier converts the demodulated current signal into a differential voltage signal. The first signal processing unit 32 includes a differential amplifier and a low-pass filter. The differential amplifier converts the differential voltage signal into a single-ended voltage signal, and the low-pass filter yields a DC voltage value proportional to the differential capacitance value.

[0053] Specifically, the second control unit 41 and the second signal processing unit 42 constitute a feedback control circuit. The feedback control circuit includes, but is not limited to, an analog PID controller composed of operational amplifiers and a follower inverter, and a digital controller composed of modules such as ADC, DAC, and FPGA. It calculates the required feedback voltage value of the two plates based on the output voltage value of the capacitor displacement sensing circuit, and injects the feedback voltage into the capacitor plates around the inspection mass, so that the inspection mass is kept in a balanced position under the action of electrostatic force.

[0054] Understandably, the capacitive sensing and electrostatic control scheme used in traditional accelerometers involves applying an AC carrier superimposed with a DC bias voltage to the quality of the test, and injecting feedback voltages into the two plates respectively. V f and- V f When the electrostatic force on the quality is inspected, it can be expressed as: .

[0055] in, x To verify the displacement of the mass from its equilibrium position, C 0 and d 0 represents the capacitance value and plate spacing of the two sets of capacitors when the inspection quality is in equilibrium. and v p,rms These are the mean and RMS values ​​of the AC carrier signal, respectively. V b It is the DC bias superimposed on the carrier signal, where the first term is the feedback driving force and the second term is the electrostatic negative stiffness force.

[0056] In the control scheme of this application, when the durations of the positive and negative levels of the square wave are not equal, due to... Since the value is not zero, it is not necessary to superimpose a DC bias onto the square wave signal to obtain the feedback driving force. The electrostatic force on the quality inspection is: .

[0057] Here and v p,rms Let be the mean and RMS values ​​of the square wave signal, respectively, and their expressions are as follows: ; .

[0058] Therefore, the complete expression for the electrostatic force F acting on the intermediate plate of the accelerometer is: .

[0059] Specifically, the first term in the complete expression is the feedback restoring force, and the second term is the electrostatic negative stiffness force, where... x To verify the displacement of the mass from its equilibrium position, C 0 and d 0 represents the capacitance value and plate spacing of the two sets of capacitors when the inspection quality is in equilibrium. n + and V p These represent the duty cycle and amplitude of the square wave signal, respectively. V f This is the feedback voltage calculated by the system.

[0060] Specifically, 2 C 0 V p (2 n + -1) / d 0 represents the sensitivity coefficient of the feedback actuator, which can be adjusted not only by changing the amplitude of the square wave but also by changing the duty cycle of the square wave.

[0061] The feedback restoring force and electrostatic negative stiffness force can be further expressed as: ; .

[0062] Compared to traditional solutions, the electrostatic negative stiffness is reduced. V Item b2 clearly shows that the electrostatic negative stiffness caused by DC bias has been eliminated, and the overall electrostatic negative stiffness has been reduced, alleviating the problems of poor linearity and measurement distortion caused by electrostatic negative stiffness in existing accelerometer systems.

[0063] Furthermore, according to Figure 4 As shown, Figure 4 This is a schematic diagram illustrating the principle of accelerometer range switching provided in this application embodiment. Without adjusting the amplitude and frequency of the square wave modulation signal, the carrier generation module 20 is further configured to change the sensitivity coefficient of the accelerometer's feedback actuator by adjusting the duty cycle of the square wave signal, thereby switching the accelerometer range. Different square wave duty cycles correspond to different ranges.

[0064] It is understandable that when this coefficient is large, the feedback voltage is small. V f This generates an electrostatic force sufficient to balance the inertial force of large accelerations, making the system suitable for measuring large ranges and low sensitivity scenarios. Conversely, when this coefficient is small, the same feedback voltage can only generate a small force, making the system suitable for small ranges and high sensitivity scenarios. Therefore, adjusting this coefficient is equivalent to adjusting the measurement range.

[0065] In addition, the first control unit 21 can be configured to execute the following range adjustment logic: when it is necessary to increase the sensitivity coefficient of the feedback actuator of the accelerometer system, the amplitude of the bipolar square wave signal is kept constant and the duty cycle is adjusted; when the required sensitivity coefficient cannot be obtained by adjusting the duty cycle alone, the amplitude of the square wave signal is increased, and the target sensitivity coefficient is obtained again by adjusting the duty cycle based on the increased amplitude.

[0066] Understandably, according to the expression for feedback restoring force, when the square wave duty cycle is 0.5, the sensitivity coefficient of the feedback actuator is 0, and the accelerometer is in open-loop operation. When the square wave duty cycle is not 0.5, the accelerometer is in closed-loop operation. Using a square wave duty cycle of 0.5 as a baseline, increasing the square wave duty cycle increases the sensitivity coefficient of the feedback actuator, and the greater the deviation of the adjusted square wave duty cycle from 0.5, the greater the sensitivity coefficient. In other words, the range adjustment is achieved by increasing or decreasing the deviation of the square wave signal duty cycle from 0.5.

[0067] In addition, this application also proposes a control method for an accelerometer system. Please refer to... Figure 5 , Figure 5 This is a flowchart illustrating the control method for the accelerometer system provided in an embodiment of this application. The method includes: Step S10: Obtain the target duty cycle of the bipolar square wave signal based on the required range, generate the bipolar square wave signal according to the target duty cycle, and apply the square wave signal to the movable test quality of the accelerometer system.

[0068] In this embodiment, a bipolar square wave signal refers to a pulse waveform in which the signal level periodically jumps between positive and negative potentials, and the widths of the positive and negative pulses are not equal. The target duty cycle refers to the ratio of the duration of the positive level within a single cycle to the total time of the cycle. n + The signal is generated by the carrier generation module 20, which can be controlled by the first control unit 21, such as an FPGA or MCU, to output the power supply unit 22, such as a DAC or a programmable gain amplifier.

[0069] Understandably, step S10 includes obtaining the target duty cycle of the bipolar square wave signal based on the required range.

[0070] Understandably, the required range refers to the measurement interval set by the user based on the dynamic range of the acceleration to be measured. This is because the sensitivity coefficient and duty cycle of the feedback actuator... n The relationship between n and n+ is linear, and the sensitivity coefficient of the feedback actuator can be changed by adjusting n+.

[0071] Specifically, the first control unit 21 has a pre-stored set of mapping relationships that define the target duty cycle values ​​corresponding to different ranges. When the system starts up or switches ranges, the first control unit 21 looks up the corresponding target duty cycle or calculates it based on the input required range. n + In this way, the measurement range can be flexibly switched through software configuration without changing the circuit structure, and the square wave amplitude is maintained. V p The constant stability effectively suppresses the increase in electrostatic negative stiffness, ensuring measurement linearity across the entire measurement range.

[0072] In addition, when it is necessary to increase the accelerometer range, the deviation of the target duty cycle from 0.5 is increased; when it is necessary to decrease the accelerometer range, the deviation of the target duty cycle from 0.5 is decreased, so that the accelerometer range matches the external input.

[0073] It should be noted that applying a square wave signal to the movable test mass 11 aims to use this signal as a carrier to establish an alternating electric field between the test mass and the fixed capacitor plates 12 on both sides. The duty cycle of this signal determines the average component of the electric field, providing a bias basis for subsequent electrostatic feedback, while avoiding the introduction of an independent DC bias voltage.

[0074] Step S20: Based on the bipolar square wave signal, detect the change in differential capacitance caused by the displacement of the test mass, and output the displacement detection voltage signal.

[0075] Understandably, this step is implemented through the displacement sensing module 30. Specifically, the modulation and demodulation unit 31 modulates and demodulates the differential capacitance change caused by the displacement of the inspection mass based on the bipolar square wave signal applied to the inspection mass, converting it into a current signal. Subsequently, the first signal processing unit 32 converts the current signal into a voltage signal and performs amplification, differential operation, and filtering. Since the sensitivity coefficient of this sensing circuit depends only on the amplitude and frequency of the square wave signal and is independent of the duty cycle, this step can stably output a displacement detection voltage signal proportional to the displacement of the inspection mass 11 regardless of subsequent range adjustments, ensuring the linearity of the detection.

[0076] Step S30: Based on the displacement detection voltage signal, generate a pair of feedback voltage signals and apply them to the fixed capacitor plates on both sides of the inspection mass, so that the inspection mass generates electrostatic feedback force under the combined action of the bipolar square wave signal and the feedback voltage signal. The electrostatic feedback force is balanced with the inertial force of the external acceleration acting on the inspection mass. The external acceleration is characterized by the feedback voltage signal.

[0077] Understandably, the feedback control module 40 performs this step. The second control unit 41 receives the displacement detection voltage signal and calculates and generates an initial feedback control signal according to a preset control algorithm. The second signal processing unit 42 processes the signal to generate a pair of feedback voltage signals with equal amplitude and opposite polarity, which are then applied to the fixed capacitor plates 12 on both sides. At this time, the inspection mass 11 carries a bipolar square wave voltage, which interacts with the feedback voltage on the fixed plates to generate an electrostatic feedback force. F When the system reaches steady state, the electrostatic feedback force is equal in magnitude and opposite in direction to the inertial force generated by the external acceleration, locking the inspection mass at the equilibrium position. At this time, the feedback voltage signal... V f The magnitude of the external acceleration is linearly represented.

[0078] Compared with the prior art, the beneficial effects of the control method for the accelerometer system provided in this application are the same as those of the accelerometer system based on variable duty cycle square wave modulation provided in the above embodiments, and will not be repeated here.

[0079] It should be understood that expressions such as “comprising” and “may include” used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as “comprising” and / or “having” are to be interpreted as indicating a particular characteristic, number, operation, constituent element, component, or combination thereof, but not to exclude the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0080] Furthermore, in this application, the expression "and / or" includes any and all combinations of the associated listed words. For example, the expression "A and / or B" may include A, may include B, or may include both A and B.

[0081] The above description is merely a specific embodiment of this application, but the scope of protection of this application 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 application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An accelerometer system based on variable duty cycle square wave modulation, characterized in that, include: The module consists of a detection module, a carrier generation module, a displacement sensing module, and a feedback control module. The detection module includes a differential capacitor pair formed by a movable inspection mass and a fixed capacitor plate; The output of the carrier generation module is connected to the quality check of the detection module; the input of the displacement sensing module is connected to the fixed capacitor plate. The input terminal of the feedback control module is connected to the output terminal of the displacement sensing module; the output terminal of the feedback control module is connected to the fixed capacitor plate. The carrier generation module is configured to generate a bipolar square wave signal with a duty cycle higher than 0.5, and apply the square wave signal as a carrier signal to the test quality. The displacement sensing module is configured to detect the differential capacitance change of the inspection mass caused by displacement based on the bipolar square wave signal and output a displacement detection voltage signal. The feedback control module is configured to generate a feedback voltage signal based on the displacement detection voltage signal and apply it to the fixed capacitor plate. The inspection mass generates an electrostatic feedback force under the combined action of the bipolar square wave signal and the feedback voltage signal. The electrostatic feedback force is balanced with the inertial force of the inspection mass caused by external acceleration. The external acceleration is characterized by the feedback voltage signal.

2. The accelerometer system based on variable duty cycle square wave modulation as described in claim 1, characterized in that, The carrier generation module is also configured to output a bipolar square wave signal with an adjustable duty cycle. By adjusting the duty cycle of the square wave signal, the sensitivity coefficient of the feedback actuator of the accelerometer system is changed, thereby adjusting the range of the accelerometer.

3. The accelerometer system based on variable duty cycle square wave modulation as described in claim 2, characterized in that, Under the condition that only a bipolar square wave signal without DC bias is applied to the inspection mass, the expression for the electrostatic force on the inspection mass is as follows: ； in, F It is electrostatic force; x To verify the displacement of the mass from its equilibrium position; C 0 and d 0 represents the capacitance value and plate spacing of the two sets of capacitors when the inspection quality is in equilibrium. n + and V p represents the duty cycle and amplitude of the square wave signal, respectively. V f is the feedback voltage calculated by the system; Among them, 2 C 0 V p(2n+ -1) / d 0 represents the sensitivity coefficient of the feedback actuator.

4. The accelerometer system based on variable duty cycle square wave modulation as described in claim 1, characterized in that, The carrier generation module includes: a first control unit and a power supply unit; The output terminal of the first control unit is connected to the controlled terminal of the power supply unit; the output terminal of the power supply unit is connected to the inspection quality. The first control unit is configured to output a control signal to the power supply unit to control the power supply unit to output a bipolar square wave signal with adjustable amplitude, frequency, and duty cycle.

5. The accelerometer system based on variable duty cycle square wave modulation as described in claim 4, characterized in that, The first control unit is configured to execute the following range adjustment logic: When it is necessary to increase the sensitivity coefficient of the feedback actuator of the accelerometer system, the amplitude of the bipolar square wave signal is kept constant and the duty cycle is adjusted. When the required sensitivity coefficient cannot be obtained by adjusting the duty cycle alone, the amplitude of the square wave signal is increased, and the target sensitivity coefficient is obtained again by adjusting the duty cycle based on the increased amplitude.

6. The accelerometer system based on variable duty cycle square wave modulation as described in claim 5, characterized in that, The duty cycle is adjusted by increasing or decreasing the deviation of the square wave signal's duty cycle from 0.

5.

7. The accelerometer system based on variable duty cycle square wave modulation as described in claim 1, characterized in that, The displacement sensing module includes: a modulation and demodulation unit and a first signal processing unit; The input terminal of the modulation and demodulation unit is connected to the fixed capacitor plate; the output terminal of the modulation and demodulation unit is connected to the input terminal of the first signal processing unit; the output terminal of the first signal processing unit is connected to the input terminal of the feedback control module. The modulation and demodulation unit is configured to modulate the capacitance change of the differential capacitor pair into a current signal and demodulate it to output to the first signal processing unit. The first signal processing unit is configured to convert the current signal into a voltage signal, and to amplify, differentially process, and filter the voltage signal, and finally output a displacement detection voltage signal that is proportional to the displacement of the inspection mass.

8. The accelerometer system based on variable duty cycle square wave modulation as described in claim 1, characterized in that, The feedback control module includes: a second control unit and a second signal processing unit; The input terminal of the second control unit is connected to the output terminal of the displacement sensing module; the output terminal of the second control unit is connected to the input terminal of the second signal processing unit; the output terminal of the second signal processing unit is connected to the fixed capacitor plate. The second control unit is configured to receive the displacement detection voltage signal and calculate and generate an initial feedback control signal according to the control algorithm; The second signal processing unit is configured to process the initial feedback control signal, generate and output a pair of feedback voltage signals with equal amplitude and opposite polarity applied to the fixed capacitor plates, so as to form a closed-loop feedback control.

9. A control method for an accelerometer system, characterized in that, The accelerometer system based on variable duty cycle square wave modulation as described in any one of claims 1 to 8 includes: Step S10: Obtain the target duty cycle of the bipolar square wave signal based on the required range, generate the bipolar square wave signal according to the target duty cycle, and apply the square wave signal to the movable test quality of the accelerometer system. Step S20: Based on the bipolar square wave signal, detect the change in differential capacitance caused by the displacement of the test mass, and output the displacement detection voltage signal; Step S30: Based on the displacement detection voltage signal, generate a pair of feedback voltage signals and apply them to the fixed capacitor plates on both sides of the inspection mass, so that the inspection mass generates an electrostatic feedback force under the combined action of the bipolar square wave signal and the feedback voltage signal. The electrostatic feedback force is balanced with the inertial force of the external acceleration acting on the inspection mass. The external acceleration is characterized by the feedback voltage signal.

10. The control method for the accelerometer system as described in claim 9, characterized in that, Step S10, which involves obtaining the target duty cycle of the bipolar square wave signal based on the required range, includes: When it is necessary to increase the accelerometer range, increase the deviation of the target duty cycle from 0.5; When it is necessary to reduce the accelerometer range, reduce the deviation of the target duty cycle from 0.5 to match the accelerometer range with the external input.

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