Low disturbance differential device and method for micro-thrust measurement

Abstract

This invention discloses a low-interference differential device and method for micro-thrust measurement. The invention includes a measuring device and a measuring method. The measuring device includes a vibration isolation table; a thruster for generating a standard force; a long beam support fixed to the vibration isolation table; two cantilever beams of identical specifications fixed to the crossbeam support by clamps; strain gauges attached to the ends of the cantilever beams for measuring the bending strain of the beams; an impact hammer and an accelerometer fixed thereon; an embedded main control chip for acquiring data from the strain gauges and the accelerometer; and a host computer responsible for communicating with the main control chip and performing thrust calculations. The dual-beam differential measuring device designed in this invention has advantages such as improving the system's common-mode rejection ratio and reducing the impact of ambient temperature, vibration, and other common-mode noise on measurement stability.

Description

Technical Field

[0001] This invention belongs to the field of micro-thrust measurement technology, specifically relating to a low-interference differential device and method for micro-thrust measurement. Background Technology

[0002] Precision thrust measurement has important applications in satellite position control, gravitational wave detection, and other fields, and has become a key issue restricting the development of thrust technology. Spaceborne micro-thrusters are the foundation for micro- and nano-satellites to achieve precise attitude control, orbit control, and rapid maneuvering. Currently, both domestic and international researchers are actively engaged in research on micro-propulsion technologies suitable for the above missions, mainly including cold gas micro-propulsion, radio frequency ion micro-propulsion, field emission electric propulsion, colloidal ion micro-propulsion, tangential field micro-propulsion, and other novel micro-propulsion technologies. The thrust generated by these micro-propulsion technologies generally ranges from a few micronewtons to hundreds of micronewtons, with resolution requirements reaching the sub-micronewton level. This presents new challenges to the thrust measurement of micro-thrusters. While extensive thrust measurement research has been conducted both domestically and internationally, balancing heavy loads and accuracy remains difficult. The instability of ambient temperature, installation measurement errors, and uncertainties in mechanical structures also significantly affect the thrust measurement of thrust devices, adding considerable difficulty to micro-thrust measurement. Summary of the Invention

[0003] To address the aforementioned issues, this invention discloses a low-interference differential device and method for micro-thrust measurement. It employs a high-precision, high-resolution bending strain gauge as the sensing device for the vibration displacement of a cantilever beam, uses a combination of an impact hammer and an accelerometer as the excitation generation device, and a differential double beam as the response device. A thruster generates a standard force applied to a single beam. A microcontroller chip controls the data reading from the strain gauge and accelerometer, while a host computer performs data processing and thrust calculation. The differential double beam effectively suppresses external interference and accurately measures the thrust magnitude.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows:

[0005] A low-interference differential device for micro-thrust measurement includes a vibration isolation table, a thruster, a crossbeam support, a cantilever beam, an impact hammer, a main control chip, and a host computer. The crossbeam support is fixed to the vibration isolation table. Two cantilever beams of the same specifications are fixed to the crossbeam support by clamps. Strain gauges are attached to the ends of the cantilever beams. The thruster is aligned with the front middle of one of the cantilever beams, and the impact hammer is aligned with the front middle of both cantilever beams. An acceleration sensor is fixed on the impact hammer. The data from the strain gauges and the acceleration sensor are transmitted to the host computer through the main control chip.

[0006] As an improvement of the present invention, the cantilever beam is a thin sheet of 65Mn quenched spring steel.

[0007] As an improvement of the present invention, the cantilever beam has a thickness of 0.3 mm, a width of 40 mm, and a length of 240 mm, and the point of action of the impact hammer and the pusher is 1 cm from the front end of the cantilever beam.

[0008] As an improvement of the present invention, the impact hammer and the propeller act at the same point.

[0009] The thruster described in this invention is used to generate a standard force; a crossbeam support is fixed on a vibration isolation platform; two cantilever beams of the same specifications are fixed to the crossbeam support by clamps; strain gauges are attached to the ends of the cantilever beams to measure the bending strain of the beams; an impact hammer and an acceleration sensor fixed thereon; an embedded main control chip is used to collect data from the strain gauges and the acceleration sensor; and a host computer is responsible for communicating with the main control chip and performing thrust calculations.

[0010] The working principle of this invention is to use two cantilever beams of the same specifications as a comparison for differential thrust measurement. First, a standard static force is generated on one of the cantilever beams by a thruster, and a bending response will occur at the fixed end of the cantilever beam. The response output is instantaneously recorded by a strain gauge, communicated through the main control chip and collected on the host computer, and the linear relationship between displacement and response is calibrated. Next, the cantilever beams are struck by an impact hammer, and the acceleration sensor records the acceleration excitation. The strain gauges produce bending strain as the response output. Mathematical models of the two cantilever beams are established according to the system identification, and the inverse system equation is obtained. Then, a standard thrust is applied to one cantilever beam by a thruster, while no thrust is applied to the other. The strain gauge responses are recorded for each beam. The thrust input signal is derived through the inverse system, and the thrust magnitude is obtained by differential calculation of the two.

[0011] The aforementioned impact hammer generates an acceleration pulse signal that acts at the midpoint of the free end of the cantilever beam. The impact hammer and the thruster act at the same point. The cantilever beam's spring plates undergo elastic deformation according to the horizontal and directional thrust. A bending strain gauge is used to measure the displacement response at the fixed end of the cantilever beam. The strain gauge's output signal is instantaneously recorded by the main control chip via a serial port. The thruster continuously generates thrust, typically within the micro-Newton range. When a static thrust is applied to the bottom end of the leaf spring, the elastic force of the leaf spring is generated at the free end of the cantilever beam, resulting in maximum displacement at the free end. According to the cantilever beam's vibration equation, the elastic force is linearly related to the displacement at the free end of the cantilever beam and is also directly proportional to the bending response at the fixed end. Therefore, the magnitude of the thruster's thrust can be determined by measuring the displacement of the cantilever beam.

[0012] Secondly, this invention also provides a thrust measurement method based on linear system identification and inverse systems. In practical problems, systems are subject to random disturbances, making it impossible to directly and accurately obtain many state parameters. Instead, it is necessary to obtain the true thrust signal amidst various random disturbances. For some complex systems, accurately analyzing the internal behavior characteristics using mechanistic methods is extremely difficult or impossible. Statistical identification methods, also known as black-box modeling methods, are experimentally based and rely solely on a large amount of observational data obtained from the system's inputs and outputs for computational analysis to identify the system's structure and parameters. Using linear system identification methods, the response characteristics of the differential beam can be effectively obtained, leading to the system's state-space equations. Then, the excitation for applying the thrust can be obtained through the inverse transformation of the state-space parameters.

[0013] An impact hammer applies an impulse response δ(t) to the bottom end of a cantilever beam on one side, generating a bending strain x1(t) at the fixed end. The Laplace transform of the unit impulse force is 1. The system response under a unit impulse is obtained, and the transfer function of the measurement system can be obtained by performing a Laplace transform. Due to structural errors and other reasons, the impulse excitation cannot be a standard impulse function. Therefore, a mathematical model of the measurement system is established through identification. The system order is preset to be 2, the excitation signal is the output signal of the accelerometer, and the response signal is the displacement signal of the bending strain gauge.

[0014] Two sets of modal parameters, including the inherent damping ω, were identified for the two cantilever beams respectively. r Modal damping ζ r Modal vectors and mode matrix The state equation of the cantilever beam measurement system can then be obtained as follows:

[0015]

[0016] Where X(t) is the input vector, Y(t) is the output vector, and U(t) is the state vector, this system is stable, invertible, controllable, and observable, then its inverse system is...

[0017]

[0018] When measuring the thrust, the thruster applies a thrust f(t) at the midpoint of the bottom end of the left cantilever beam, while no excitation is applied to the right cantilever beam. The responses y1(t) and y2(t) of the two bending strain gauges are obtained. The input responses U1(t) and U2(t) are obtained according to the inverse system state-space equations obtained above. The magnitude of the thrust applied by the thruster can be obtained by the difference between the two.

[0019] The beneficial effects of this invention are:

[0020] This invention presents a low-interference differential device and method for micro-thrust measurement. Compared to traditional torsional thrust measurement, its overall structure is simpler and applicable to more complex measurement scenarios. Furthermore, through a reasonable differential structure design and a thrust measurement method based on linear system identification and inverse systems, the influence of temperature drift and structural dimensional errors is reduced, enabling dynamic and accurate thrust measurement. Attached Figure Description

[0021] Figure 1 This is a device architecture diagram of the present invention.

[0022] Figure 2 This is a flowchart of the present invention based on linear system identification and inverse system thrust measurement.

[0023] List of identifiers in attached diagrams:

[0024] 1. Vibration isolation table, 2. Thruster, 3. Crossbeam support, 4. Cantilever beam, 5. Fixture, 6. Strain gauge, 7. Impact hammer, 8. Accelerometer, 9. Main control chip, 10. Host computer. Detailed Implementation

[0025] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0026] like Figure 1 As shown, this invention proposes a low-interference differential device for micro-thrust measurement, including a vibration isolation table 1 as a base plate; a thruster 2 for generating a standard force; a crossbeam support 3 fixed on the vibration isolation table 1; two cantilever beams 4 of the same specifications, fixed on the crossbeam support 3 by clamps 5, with strain gauges 6 attached to the ends of the cantilever beams for measuring the bending strain of the beams; an impact hammer 7 and an acceleration sensor 8 fixed thereon; an embedded main control chip 9 for acquiring data from the strain gauges and the acceleration sensor 8; and a host computer 10 responsible for communicating with the main control chip 9 and performing thrust calculation.

[0027] The impact hammer 7 generates an acceleration pulse signal that acts on the midpoint of the free end of the left cantilever beam. At this time, a bending response will occur at the fixed end of the cantilever beam. The response output is instantaneously recorded by the strain gauge 6 and communicated with the main control chip 9 via I2C and collected on the host computer 10.

[0028] The cantilever beam's four spring plates undergo elastic deformation according to the horizontal and directional thrust. A bending strain gauge is used to measure the displacement response at the fixed end of the cantilever beam. The strain gauge's output signal is instantaneously recorded by the main control chip via a serial port. The thruster continuously generates thrust, typically within the micronewton range. When a static thrust is applied to the bottom end of the cantilever beam's four spring plates, an elastic force is generated at the free end of the cantilever beam, resulting in maximum displacement at the free end. According to the cantilever beam's vibration equation, the elastic force is linearly related to the displacement at the free end of the cantilever beam and directly proportional to the bending response at the fixed end. Therefore, the thrust of the thruster can be determined by measuring the displacement of the cantilever beam.

[0029] like Figure 2 As shown, the present invention also provides a thrust measurement method based on linear system identification and inverse system.

[0030] After the system is powered on, the impact hammer applies an impulse response δ(t) to the bottom end of the cantilever beam on one side, generating a bending strain x1(t) at the fixed end. The Laplace transform of the unit impulse force is 1, and the system response under a unit impulse is obtained. The transfer function of the measurement system can be obtained by performing a Laplace transform. Due to structural errors and other reasons, the impulse excitation cannot be a standard impulse function. Therefore, a mathematical model of the measurement system is established through identification. The system order is preset to be 2, the excitation signal is the output signal of the accelerometer, and the response signal is the displacement signal of the bending strain gauge.

[0031] Two sets of modal parameters, including the inherent damping ω, were identified for the two cantilever beams respectively. r Modal damping ζ r Modal vectors and mode matrix The state equation of the cantilever beam measurement system can then be obtained as follows:

[0032]

[0033] Where X(t) is the input vector, Y(t) is the output vector, and U(t) is the state vector, this system is stable, invertible, controllable, and observable, then its inverse system is...

[0034]

[0035] When measuring the thrust, the thruster applies a thrust f(t) at the midpoint of the bottom end of the left cantilever beam, while no excitation is applied to the right cantilever beam. The responses y1(t) and y2(t) of the two bending strain gauges are obtained. The input responses U1(t) and U2(t) are obtained according to the inverse system state-space equations obtained above. The magnitude of the thrust applied by the thruster can be obtained by the difference between the two.

[0036] It should be noted that the above content merely illustrates the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various improvements and modifications can be made without departing from the principle of the present invention, and all such improvements and modifications fall within the scope of protection of the claims of the present invention.

Claims

1. A low-interference differential device for micro-thrust measurement, characterized in that: The system includes a vibration isolation table (1), a thruster (2), a crossbeam support (3), a cantilever beam (4), an impact hammer (7), a main control chip (9), and a host computer (10). The crossbeam support (3) is fixed on the vibration isolation table (1). Two cantilever beams (4) of the same specifications are fixed on the crossbeam support (3) by a clamp (5). Strain gauges (6) are pasted on the ends of the cantilever beams. The thruster (2) is aligned with the middle of the front end of one of the cantilever beams. The impact hammer (7) is aligned with the middle of the front end of both cantilever beams (4). An acceleration sensor (8) is fixed on the impact hammer (7). The data from the strain gauges (6) and the acceleration sensor (8) are transmitted to the host computer (10) through the main control chip (9).

2. The low-interference differential device for micro-thrust measurement according to claim 1, characterized in that: The cantilever beam (4) is a sheet of 65Mn quenched spring steel.

3. The low-interference differential device for micro-thrust measurement according to claim 2, characterized in that: The cantilever beam (4) has a thickness of 0.3 mm, a width of 40 mm, and a length of 240 mm. The impact hammer (7) and the pusher (2) are applied at a point 1 cm from the front end of the cantilever beam.

4. The low-interference differential device for micro-thrust measurement according to claim 1, characterized in that: The impact hammer (7) and the propeller (2) act at the same point.

5. A low-interference differential device for micro-thrust measurement according to claim 1, characterized in that: The working principle involves using two identical cantilever beams for differential thrust measurement. First, a standard static force is applied to one cantilever beam using a thruster, causing a bending response at the fixed end. The response output is instantaneously recorded by strain gauges, communicated with the main control chip, and collected on the host computer to calibrate the linear relationship between displacement and response. Next, one cantilever beam is struck with an impact hammer, and an acceleration sensor records the acceleration excitation. The strain gauges then produce bending strain as the response output. Mathematical models of the two cantilever beams are established based on system identification, and the inverse system state-space equation is obtained. Then, a standard thrust is applied to one cantilever beam using a thruster, while no thrust is applied to the other. The strain gauge responses are recorded for both beams, and the thrust input signal is derived through the inverse system. The magnitude of the thrust is obtained by differential calculation of the two.

6. A thrust measurement method based on the low-interference differential device for micro-thrust measurement as described in claim 1, characterized in that: An impact hammer applies an impulse response δ(t) to the bottom end of a cantilever beam on one side, generating a bending strain x1(t) at the fixed end. The Laplace transform of the unit impulse force is 1, and the system response under the unit impulse is obtained. The transfer function of the measurement system can be obtained by performing a Laplace transform. A mathematical model of the measurement system is established through identification. The system order of the identification is preset to be 2, the excitation signal is the output signal of the accelerometer, and the response signal is the displacement signal of the bending strain gauge. Two sets of modal parameters and inherent damping were identified for the two cantilever beams respectively. Modal damping Modal vectors and mode matrix Then the state equation of the cantilever beam measurement system is obtained as follows: in, For the input vector, For the output vector, Let be the state vector. If this system is stable, invertible, controllable, and observable, then its inverse system state-space equation is: When measuring the thrust, the thruster applies a thrust f(t) at the midpoint of the bottom end of the left cantilever beam, while no excitation is applied to the right cantilever beam. The responses y1(t) and y2(t) of the two bending strain gauges are obtained. The input responses U1(t) and U2(t) are obtained according to the inverse system state-space equations obtained above. The magnitude of the thrust applied by the thruster can be obtained by the difference between the two.

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