Linkage differential measurement system and method suitable for micro thrust calibration

Abstract

The invention discloses a linkage differential measurement system and method suitable for micro thrust calibration. The system comprises a linkage differential measurement rack, a liquid metal radio frequency coaxial cable connector arranged on the rack, and a mass center precise regulation and control device arranged on the rack. The linkage differential measurement system provides micro-Newton-level micro thrust except environment common-mode noise; the method comprises the following steps: a torsional pendulum inclination angle control module controls a torsional pendulum inclination angle # imgabs0 #; the centroid position deviation calculation module is used for calculating centroid position deviation; judging whether the offset s of the current centroid position is less than 10 [mu] m or not; the mass center position adjusting module is used for adjusting the mass center position; the gravitational wave micro-thrust calibration torsional pendulum solves the problems that the gravitational wave thruster needs to calibrate thrust noise besides calibrating thrust, high rigidity of a coaxial cable can generate interference on motion of the gravitational wave micro-thrust calibration torsional pendulum, and the gravitational wave micro-thrust calibration torsional pendulum has extremely high requirements on sensing precision of mass center regulation and control.

Description

Technical Field

[0001] The present invention belongs to the field of aerospace propulsion technology, and particularly relates to a linkage differential measurement system and method suitable for micro-thrust calibration. Background Art

[0002] High-precision and low-noise micro-thrust measurement is one of the key technologies that need to be urgently broken through in space gravitational wave detection missions. It involves multi-disciplinary intersections and engineering technology breakthroughs. Its characteristics of high-precision, low-noise, and wide-bandwidth thrust measurement challenge the limits of existing technologies. Although micro-thrust measurement technology has been developed for many years, there is currently no measurement method that fully meets the requirements for ground calibration of micro-thrusters for space gravitational wave detection. The difficulty of micro-thrust measurement technology for space gravitational waves lies in how to achieve high-precision and low-noise micro-thrust calibration under ultra-low frequency bandwidths.

[0003] One of the design difficulties of the gravitational wave micro-thrust calibration torsion pendulum: Micro-thrusters are used for high-precision scientific exploration. Different from ordinary Hall thrusters, their thrust is extremely small, only dozens of nanonewtons or dozens of micronewtons. Conventional thrusters are in the millinewton level. The micro-newton thrusters used for high-precision and low-noise micro-thrust calibration have a thrust reduction of 3 orders of magnitude. Their thrust measurement is more difficult to achieve than conventional thrust measurement. Moreover, gravitational waves have a requirement that conventional thrusters do not have. For conventional thrusters, it is only necessary to calibrate the thrust magnitude. For gravitational wave thrusters, in addition to calibrating the thrust magnitude, it is also necessary to calibrate the thrust noise. For example, when the noise reaches 0.1 Hz, it is equivalent to measuring for 10,000 seconds. 10,000 seconds is equivalent to 3 hours. During these 3 hours, it is required that the equipment be in a very stable state, which is a very difficult thing.

[0004] The second design difficulty of the gravitational wave micro-thrust calibration torsion pendulum lies in: First, both radio frequency and microwave thrusters are electromagnetic waves, and coaxial cables are needed to achieve efficient transmission of radio frequency / microwave energy. Commonly used coaxial cables usually have relatively large stiffness. When using a torsion pendulum device to measure the thrust of a thruster, the high stiffness of the coaxial cable will interfere with the movement of the torsion pendulum. Seriously, it may even cause the torsion pendulum to be unable to accurately measure the thrust, greatly limiting the accuracy and reliability of the performance test of electric thrusters. Second, the spring of the pivot is extremely soft and can rotate with a little force. The stiffness of the coaxial cable is greater than that of the pivot, resulting in almost no change in force during the measurement process. Third, the coaxial cable is used for the transmission of radio frequency / microwave energy and will pass through relatively large radio frequency power or microwave power, so the cable will heat up. When the coaxial cable heats up, the radio frequency cable will creep, resulting in serious drift of the thrust measurement device and large measurement errors. For electric thrusters with a power of kilowatts, due to the influence of coaxial cables, etc., it is no longer possible to directly measure their thrust through a thrust measurement device, and the shooting method is mostly used to achieve indirect measurement of thrust. This measurement method has large errors and is not conducive to practical applications.

[0005] The third design difficulty of the gravitational wave micro-thrust calibration torsion pendulum: The gravitational wave thruster micro-thrust calibration torsion pendulum poses extremely high requirements for the sensing accuracy, control method, and actuator resolution of the centroid regulation. The centroid position of the gravitational wave thruster micro-thrust calibration torsion pendulum affects its anti-interference ability, and further affects key indicators such as its resolution and noise power. The closer the centroid is to the rotation axis, the stronger the anti-interference ability of the torsion pendulum. In the field of space gravitational wave detection, to achieve the precise calibration of micro-Newton thrusters, it is necessary to ensure that the offset between the centroid of the torsion pendulum and the rotation axis is controlled within 10 μm. This index poses extremely high requirements for the sensing accuracy, control method, and actuator resolution of the centroid regulation. Currently, the centroid regulation of the torsion pendulum mostly relies on manually adding or removing weights to balance the masses on both sides. Limited by atmospheric interference and human operation errors, the adjustment accuracy is low, and it is difficult to ensure that the centroid position meets the standard.

[0006] In summary, the design difficulties of the gravitational wave micro-thrust calibration torsion pendulum are as follows: The thrust is extremely small, and in addition to calibrating the thrust magnitude, the gravitational wave thruster also needs to calibrate the thrust noise; the high stiffness of the coaxial cable will interfere with the movement of the gravitational wave micro-thrust calibration torsion pendulum, and in severe cases, it may even cause the torsion pendulum to be unable to accurately measure the thrust; the gravitational wave micro-thrust calibration torsion pendulum poses extremely high requirements for the sensing accuracy, control method, and actuator resolution of the centroid regulation. Summary of the Invention

[0007] In order to solve the problems existing in the prior art, the present invention proposes a linkage differential measurement system and method applicable to micro-thrust calibration. The first objective is to solve the problems that the thrust is extremely small and that in addition to calibrating the thrust magnitude, the gravitational wave thruster also needs to calibrate the noise thrust. The second objective is to solve the problem that the high stiffness of the coaxial cable will interfere with the movement of the gravitational wave micro-thrust calibration torsion pendulum, and in severe cases, it may even cause the torsion pendulum to be unable to accurately measure the thrust. The third objective is to solve the problem that the gravitational wave micro-thrust calibration torsion pendulum poses extremely high requirements for the sensing accuracy, control method, and actuator resolution of the centroid regulation.

[0008] The present invention adopts the following technical solutions to solve its technical problems:

[0009] A linkage differential measurement system applicable to micro-thrust calibration, characterized in that: the system includes: a linkage differential measurement bench (1), a liquid metal radio frequency coaxial cable connector (2) disposed on the linkage differential measurement bench (1), and a centroid precision control device (3) disposed on the linkage differential measurement bench (1); the linkage differential measurement bench (1) provides a micro-thrust of the order of micronewtons excluding environmental common-mode noise for the linkage differential measurement system; the liquid metal radio frequency coaxial cable connector (2) provides a coaxial cable for micro-thrust measurement for the linkage differential measurement bench (1); the centroid precision control device (3) provides a torsional pendulum centroid control method with a precision of the order of micronewtons for the linkage differential measurement bench (1), so that the centroid of the torsional pendulum is concentric with the pivot of the torsional pendulum to reduce the interference of environmental common-mode noise on the linkage differential measurement system;

[0010] The linkage differential measurement bench (1) adopts two identical linkage torsional pendulums A and linkage torsional pendulums B, and is disposed on the same double-layer torsional pendulum base; among them, the thruster of one set of linkage torsional pendulums is ignited and working, and the thruster of the other set of linkage torsional pendulums is not ignited and working; the linkage differential measurement bench (1) is disposed inside and outside the vacuum chamber. The ones disposed inside the vacuum chamber are the linkage torsional pendulum A and the linkage torsional pendulum B, and the linkage torsional pendulum A and the linkage torsional pendulum B are symmetrically disposed along the X and Y directions on the double-bottom torsional pendulum base of the linkage differential measurement bench (1); the linkage torsional pendulum A or the linkage torsional pendulum B is used as a reference system, and the linkage torsional pendulum B or the linkage torsional pendulum A is used as a real thruster thrust measurement system; the one disposed outside the vacuum chamber is the differential signal processor of the sub-micronewton thrust linkage differential measurement system; the sub-micronewton thrust linkage differential measurement system provides a sub-micronewton-level micro-thrust excluding environmental common-mode noise for the linkage differential measurement system through the differential signal processor; the symmetrically disposed linkage torsional pendulum A and the linkage torsional pendulum B are connected to the support frame through their respective pivots, and then connected to the double-bottom torsional pendulum base through the support frame;

[0011] The liquid metal radio frequency coaxial cable connector (2) is disposed inside the vacuum chamber, one end of which is connected to the torsional pendulum of the linkage differential measurement bench (1), and the other end is connected to the double-bottom torsional pendulum base of the linkage differential measurement bench (1); the end connected to the torsional pendulum is a Type-N male head (2-1), and the end connected to the double-bottom torsional pendulum base is a Type-N female head (2-3); between the Type-N male head (2-1) and the Type-N female head (2-3) is liquid metal (2-2); the liquid metal (2-2) conducts the Type-N male head (2-1) and the Type-N female head (2-3) to achieve radio frequency / microwave power transmission, and the Type-N male head (2-1) rotates coaxially relative to the Type-N female head (2-3);

[0012] The centroid precision control device (3) is arranged inside and outside the vacuum chamber. The components arranged inside the vacuum chamber include a torsion pendulum tilt control mechanism and a centroid position adjustment mechanism, and the component arranged outside the vacuum chamber is a controller. The centroid position adjustment mechanism is arranged on the driving side of the double-bottom torsion pendulum base. The torsion pendulum tilt control mechanism is arranged on the two sides adjacent to the driving side of the double-bottom torsion pendulum base. The input ends of the controller are respectively connected to the torsion pendulum and the torsion pendulum tilt control mechanism, and the output ends are respectively connected to the centroid position adjustment mechanism and the torsion pendulum tilt control mechanism. The torsion pendulum tilt control mechanism is used to control the inclination angle of the torsion pendulum along the direction of gravity on the cross-section. The centroid position adjustment mechanism is used to adjust the centroid position of the torsion pendulum.

[0013] Further, the linkage torsion pendulum A or the linkage torsion pendulum B is respectively provided with two parallel swing arms A or two parallel swing arms B. The center of the lower surface of each swing arm of the swing arm A or the swing arm B is connected to a pivot, and then each is connected to the double-bottom torsion pendulum base through the pivot. Symmetrical connecting rods A are provided at both ends in the length direction of the swing arm A, namely a left connecting rod A and a right connecting rod A. The left connecting rod A is added with a counterweight and a displacement sensor A, and the right connecting rod A is added with a thruster A and a standard force device A. Symmetrical connecting rods B are provided at both ends in the length direction of the swing arm B, namely a left connecting rod B and a right connecting rod B. The left connecting rod B is added with a counterweight and a displacement sensor B, and the right connecting rod B is added with a thruster B and a standard force device B. The standard force device A or the standard force device B is used to provide a standard force. Through this standard force, the relationship between the standard force and the displacement of the displacement sensor can be obtained, so as to realize the calibration of the standard force. The thruster A or the thruster B is used to provide the current micro-thrust, including the micro-thrust generated by the environmental working mode noise when the thruster has no thrust output, and the sum of the thrust of the thruster and the thrust generated by the environmental working mode noise when the thruster has thrust output.

[0014] Further, when the linkage torsion pendulum A is used as a reference system and the linkage torsion pendulum B is used as a real thruster thrust measurement system, the thruster of the right connecting rod A has no thrust output and the thruster of the right connecting rod B has thrust output. At this time, the micro-thrust obtained by the differential signal processor through the displacement sensor A is the micro-thrust generated by the environmental working mode noise, and the micro-thrust obtained by the differential signal processor through the displacement sensor B is the sum of the micro-thrust generated by the environmental working mode noise and the micro-thrust generated by the thruster B. When the linkage torsion pendulum B is used as a reference system and the linkage torsion pendulum A is used as a real thruster thrust measurement system, the thruster of the right connecting rod B has no thrust output and the thruster of the right connecting rod A has thrust output. At this time, the micro-thrust obtained by the differential signal processor through the displacement sensor B is the micro-thrust generated by the environmental working mode noise; the micro-thrust obtained by the differential signal processor through the displacement sensor A is the sum of the micro-thrust generated by the environmental working mode noise and the micro-thrust generated by the thruster B.

[0015] Further, the sub-micro-newton thrust linkage differential measurement system of the linkage differential measurement bench (1) includes: a thruster, a micro-thrust combined differential measurement bench, a sub-micro-newton level standard force generation and calibration device, and a differential signal processor; the thruster includes a thruster with no thrust output and a thruster with thrust output; the micro-thrust combined differential measurement bench includes bench displacement data with no thrust output and bench displacement data with thrust output; the sub-micro-newton level standard force generation and calibration device includes calibration data A based on the proportional relationship between the standard force A generated by the standard force device A and the displacement sensor A, and calibration data B based on the proportional relationship between the standard force B generated by the standard force device B and the displacement sensor B. The differential signal processor obtains the current micro-thrust excluding environmental common-mode noise interference according to the displacement sensor displacement data with no thrust output, the displacement sensor displacement data with thrust output, and the calibration data A and calibration data B.

[0016] Further, the Type-N male head (2-1) of the liquid metal radio frequency coaxial cable connector (2) has three layers inside and outside: the outer layer has two parts up and down: the male outer thread (2-1-1) near the end of the male head and the male outer conductor (2-1-2) below the outer thread; the middle layer is the male insulator (2-1-3); the inner layer is the inner conductor pin (2-1-4), and a shielding layer (2-1-5) is also provided radially between the inner conductor pin (2-1-4) and the male outer conductor (2-1-2); the Type-N female head (2-3) has three layers inside and outside: the outer layer has the female outer thread (2-3-5) near the end of the female head and the female outer conductor (2-3-4) below the female outer thread; the middle layer has the female insulator (2-3-2); the inner layer has the female inner conductor pin seat (2-3-3); a liquid pool (2-3-1) is also provided on the female outer conductor (2-3-4). The liquid pool (2-3-1) is divided into two layers inside and outside, the female outer conductor liquid pool (2-3-1-1) on the female outer conductor and the female inner conductor liquid pool (2-3-1-2) on the female inner conductor pin seat. The female outer conductor liquid pool (2-3-1-1) is axially docked with the shielding layer (2-1-5) of the Type-N male head (2-1); the female inner conductor liquid pool (2-3-1-2) is axially docked with the inner conductor pin (2-1-4) of the Type-N male head (2-1).

[0017] Further, the liquid metal (2-2) of the liquid metal radio frequency coaxial cable connector adopts a gallium-indium-tin alloy, which has the characteristics of low melting point, high precision, low volatility, good electrical and thermal conductivity, etc., and is non-toxic, pollution-free and has good liquid fluidity. Its precision is 6.44 g / mL, viscosity 0.0024 PAS, melting point 6-10 °C, electrical conductivity 3.46×106 S / M, and volatility 0.001%; the male insulator (1-3) and the female insulator (3-2) are made of polytetrafluoroethylene.

[0018] Furthermore, the cable impedance of the RF coaxial cable connector of the liquid metal RF coaxial cable connector is 50 Ω. According to the characteristic impedance calculation formula of a single-core coaxial cable:

[0019]

[0020] In the formula, D T is the inner diameter of the outer conductor of the coaxial cable, d T is the outer diameter of the inner conductor. The inner diameters of the male head outer conductor (2-1-2) and the female head outer conductor (2-3-4) are D T ; the outer diameters of the inner conductor pin (2-1-4) and the female head inner conductor socket (2-3-3) are d T . The inner and outer diameters of the male head insulator (2-1-3) and the female head outer conductor (2-3-4) both need to meet the requirements of the above formula.

[0021] Furthermore, the Type-N male head (1) is coaxially installed with the torsion pendulum, and the Type-N female head (3) is coaxially installed with the torsion pendulum pivot.

[0022] Furthermore, the controller of the centroid precision control device is provided with: a centroid position offset calculation module for calculating the deviation position of the centroid of the torsion pendulum, a torsion pendulum inclination calculation module for calculating the inclination angle of the torsion pendulum, and a PID controller for controlling the inclination angle of the torsion pendulum; the centroid position offset calculation module of the controller is used to calculate the deviation s between the centroid of the torsion pendulum and the rotation axis. Its input ends are respectively connected to the torsion pendulum and the torsion pendulum inclination calculation module, obtaining the current rotation angle θ of the torsion pendulum from the torsion pendulum and the actual torsion pendulum inclination angle from the torsion pendulum inclination calculation module The output end is connected to the centroid position adjustment mechanism, sending a motor drive instruction to the centroid position adjustment module;

[0023] The torsion pendulum inclination calculation module of the controller is used to calculate the inclination angle of the torsion pendulum Its input end is connected to the high-precision capacitive displacement sensor 1 and the high-precision capacitive displacement sensor 2 of the torsion pendulum inclination control mechanism. Through h1 and h2 at the respective measuring points of the high-precision capacitive displacement sensor 1 and the high-precision capacitive displacement sensor 2, the actual torsion pendulum inclination angle between the upper and lower bottom plates of the double-bottom torsion pendulum base is obtained The output end of the torsion pendulum inclination calculation module is connected to the PID controller, outputting the actual torsion pendulum inclination angle to the PID controller

[0024] The PID controller of the controller is used to output an instruction for the axial displacement of the piezoelectric actuator to the piezoelectric actuator; its input end is connected to the torsion pendulum inclination calculation module, and the PID controller has a set inclination angle Obtaining the actual torsion pendulum inclination angle from the torsion pendulum inclination calculation module Compare it with the set inclination angle built in the controller The output end of the PID controller is connected to the piezoelectric actuator of the torsion pendulum inclination control module to control the voltage output by the piezoelectric actuator to the upper plate of the double-bottom torsion pendulum base.

[0025] Furthermore, the torsion pendulum inclination control mechanism of the centroid precision regulation device includes: a piezoelectric actuator arranged on the driving side of the double-bottom torsion pendulum base, a pivot arranged on the rotational freedom side of the double-bottom torsion pendulum base and connecting the upper plate and the lower plate through the pivot, and a high-precision capacitance displacement sensor 1 and a high-precision capacitance displacement sensor 2 arranged on the bottom plate of the double-bottom torsion pendulum base and close to both ends of the upper plate; the piezoelectric actuator serves as a displacement source. When the piezoelectric actuator outputs an axial displacement voltage, the upper plate will be tilted around the pivot The high-precision capacitance displacement sensor 1 and the high-precision capacitance displacement sensor 2 are symmetrically arranged at both ends of the double-bottom torsion pendulum base. Among them, the high-precision capacitance displacement sensor 1 is arranged at one end close to the driving side, and the high-precision capacitance displacement sensor 2 is arranged at one end close to the pivot; when the piezoelectric actuator outputs an axial displacement, the high-precision capacitance displacement sensor 1 and the high-precision capacitance displacement sensor 2 respectively measure the distances h1 and h2 between the upper plate and the lower plate, and send h1 and h2 to the torsion pendulum calculation module of the controller. The torsion pendulum calculation module obtains the inclination angle between the upper plate and the lower plate through h1 and h2

[0026] Furthermore, the centroid position adjustment mechanism of the centroid precision regulation device includes: a fine-threaded screw, a counterweight mass block, and a motor; the motor is coaxial with the counterweight mass block; one end of the fine-threaded screw is fixed along the torsion pendulum axis and on one side of the torsion pendulum, and the other end passes through the central hole of the counterweight mass block and is threadedly connected to the central hole of the counterweight mass block; guide through holes are symmetrically opened on both sides of the counterweight mass block, and two thinner guide shafts pass through the guide holes and are fixed on the motor; the central part of the counterweight mass block is prefabricated with internal threads and forms a precise fit with the screw; when the motor rotates, the two guide shafts will drive the counterweight mass block to rotate on the fine-threaded screw; the fine-threaded screw converts the angular displacement of the counterweight mass block into an axial linear displacement, causing the counterweight mass block to move along the torsion pendulum axis, thereby changing the centroid distribution of the torsion pendulum and completing a single adjustment of the deviation of the centroid position.

[0027] Furthermore, the torsion pendulum inclination calculation module of the centroid precision regulation device obtains the inclination angle between the upper plate and the lower plate through h1 and h2 Specifically as follows: Set the distance between the two measuring points of the high-precision capacitance displacement sensor 1 and the high-precision capacitance displacement sensor 2 as L, and set the gaps on the high and low sides in the inclined state as h1 and h2 respectively. The inclination angle calculation formula is

[0028]

[0029] Thus, the inclination angle of the torsion pendulum can be accurately measured.

[0030] Further, the centroid position deviation calculation module calculates the deviation s between the centroid of the torsion pendulum and the rotation axis as follows:

[0031] When the centroid of the torsion pendulum deviates from the rotation axis, the torsion pendulum will rotate under the action of the torque generated by the gravity component in the inclined state. Let the total mass of the torsion pendulum be M, the pivot stiffness coefficient be k, and the distance between the centroid and the rotation axis be s. If the inclination angle of the upper base plate around the pivot increases After that, if the rotation angle change of the torsion pendulum is θ, the mechanical equilibrium equation of the torque of the gravity component and the restoring torque of the pivot is

[0032]

[0033] where g is the acceleration due to gravity. Under the small angle assumption (when θ is small enough, cosθ = 1), the deviation between the centroid of the torsion pendulum and the rotation axis can be obtained as

[0034]

[0035] In this equation, θ is accurately measured through the angular displacement measurement function of the torsion pendulum itself, k is obtained by calibrating the torsion pendulum, and M can be directly measured with a balance. Therefore, the key to calculating the centroid deviation position is to output an axial displacement through the piezoelectric actuator to make the upper base plate generate a controllable inclination angle around the pivot

[0036] A method for precise centroid regulation applicable to a micro-thrust measurement device, characterized by comprising the following steps:

[0037] Step 1: Determine that the current centroid offset s belongs to the fine-tuning range;

[0038] Step 2: The torsion pendulum inclination control module controls the inclination angle of the torsion pendulum for control;

[0039] Step 3: The centroid position deviation calculation module calculates the centroid position deviation;

[0040] Step 4: Determine whether the current centroid position deviation s is less than 10 μm. If so, complete the fine adjustment and go to Step 6. If not, continue with Step 5;

[0041] Step 5: The centroid position adjustment module adjusts the centroid position and returns to Step 2;

[0042] Step 6: The fine adjustment ends.

[0043] The torsion pendulum inclination control in Step 2 includes the following process:

[0044] 1) The input end of the PID controller receives the set inclination angle and the actual inclination angle

[0045] 2) Determine the set inclination angle and the actual inclination angle Whether there is a difference. If not, go to process 7). If so, continue process 3);

[0046] 3) The PID controller outputs voltage to the piezoelectric actuator. When the piezoelectric actuator outputs an axial displacement, the upper base plate of the double-bottom pendulum base generates an inclination angle around the pivot

[0047] 4) The high-precision capacitance displacement sensor 1 and the high-precision capacitance displacement sensor 2 feedback h1 and h2 at their respective measurement point positions to the inclination angle calculation module of the controller;

[0048] 5) The inclination angle calculation module feeds back the actual inclination angle to the input end of the PID controller;

[0049] 6) The PID controller performs a difference calculation based on the set inclination angle and the actual inclination angle at the input end, and returns to process 2)

[0050] 7) End

[0051] The calculation of the centroid position offset s in step three includes the following steps:

[0052] A. Establish a relationship between the inclination angle generated by the piezoelectric actuator and the change θ of the pendulum rotation angle;

[0053]

[0054] B. Obtain the deviation S of the pendulum centroid from the rotation axis according to the relationship between and the θ

[0055]

[0056] C. Send the deviation s to the centroid position adjustment module

[0057] The centroid position adjustment module in step five performs centroid position adjustment, and the specific steps are as follows:

[0058] 1) The centroid position offset calculation module of the controller sends a drive command to the motor of the centroid position adjustment module according to the offset;

[0059] 2) When the motor rotates, the guide shaft will drive the mass block to rotate to complete a single adjustment of the centroid position deviation

[0060] Advantages and effects of the present invention

[0061] 1. The linked differential measurement bench of the present invention ensures the consistency of the dynamic characteristics of the two torsion pendulums through system debugging, can achieve a common-mode rejection ratio of more than two orders of magnitude, greatly reduce the background noise of the micro-thrust measurement system, and achieve efficient suppression of environmental common-mode noise.

[0062] 2. The linked differential measurement bench of the present invention converts the micro-thrust generated by the thruster into the displacement of the thrust bench through the torsion pendulum, and this displacement is accurately measured by a high-stability micro-displacement information acquisition device; the sub-micro-newton and standard force generation and calibration device provides a high-precision sub-micro-newton-level standard force for the calibration of the measurement bench and the closed-loop measurement of large-range thrust; the integrated thermal / electromagnetic shielding ultra-quiet and ultra-stable experimental platform provides a low-noise and high-stability experimental environment for the measurement experiment to ensure the accuracy of the measurement results; and the multi-task intelligent real-time measurement and control software receives the data information from each device, performs data processing and analysis, and controls the standard force output of the sub-micro-newton-level standard force generation and calibration device.

[0063] 3. The linked differential measurement bench of the present invention proposes a symmetric double-arm linked measurement method, realizes the decoupling of the thruster configuration and thrust measurement, reduces the difficulty of thruster assembly and debugging, eliminates the influence of errors such as force arm calibration, measurement of the thrust action center, and plume non-uniformity on thrust measurement, and achieves a thrust measurement accuracy that cannot be achieved by conventional methods.

[0064] 4. The linked differential measurement bench of the present invention adopts a differential measurement method, designs a double-symmetric linked differential measurement structure, reduces the requirements for the test environment, and solves the problem of low-frequency thrust noise measurement; through debugging, the consistency requirements of the dynamic characteristics of the two linked torsion pendulums are realized, and a high common-mode noise rejection ratio is achieved to reduce the influence of common-mode noise on the measurement results.

[0065] 5. The linked differential measurement bench of the present invention proposes a micro-thrust response measurement method based on torsion pendulum dynamics inversion and thrust closed-loop control, which improves the dynamic measurement performance of micro-thrust.

[0066] 6. The liquid metal radio frequency coaxial cable connector of the present invention improves the measurement accuracy: by adopting the liquid metal bridging and zero-stiffness coaxial cable connection method, the influence of the coaxial cable on the torsion pendulum stiffness is significantly reduced, enabling the torsion pendulum to more accurately measure the micro-thrust of the thruster, improving the accuracy of thrust measurement, and providing reliable data support for the performance optimization and research of electric thrusters.

[0067] 7. The liquid metal radio frequency coaxial cable connector of the present invention realizes efficient radio frequency transmission: based on the connector design of liquid metal, good impedance matching is achieved, ensuring the efficient transmission of radio frequency / microwave power, reducing the loss during signal transmission, and improving the working efficiency of electric thrusters.

[0068] 8. The liquid metal radio frequency coaxial cable connector of the present invention has broad application prospects: it is not only applicable to the thrust test of existing microwave / radio frequency ion thrusters, but can also be extended to other fields that require low-rigidity coaxial cable connection and radio frequency energy transmission, such as satellite communication, radar systems, etc., and has broad market application prospects.

[0069] 9. The centroid precision control device of the present invention, based on the closed-loop control architecture constructed by piezoelectric actuators and high-precision capacitance displacement gauges, can achieve a torsional pendulum tilt angle control resolution of 5 μrad, and simultaneously reach a centroid positioning accuracy of 1 μm;

[0070] 10. The centroid precision control device of the present invention can achieve a centroid position adjustment resolution of 1 μm by changing the mass distribution through the axial displacement of the mass counterweight on the fine-threaded screw, ensuring that the distance between the centroid of the torsional pendulum and the rotation axis does not exceed 10 μm, thereby effectively suppressing the interference of disturbances such as ground vibration on the torsional pendulum, reducing the noise floor of the torsional pendulum, improving the measurement resolution, and providing a reliable guarantee for the test calibration of micro-Newton thrusters;

[0071] 11. The centroid precision control device of the present invention has a mature software implementation scheme for the entire process, can be operated when the torsional pendulum is in a vacuum environment, reduces atmospheric disturbances, improves the centroid adjustment accuracy, and simplifies the operation complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1a is the functional block diagram of the linkage differential measurement system applicable to micro-thrust calibration of the present invention;

[0073] Figure 1b is the layout schematic diagram of the linkage differential measurement system applicable to micro-thrust calibration of the present invention;

[0074] Figure 2a is the schematic diagram of the existing technology measurement bench;

[0075] Figure 2b is the linkage differential measurement bench applicable to micro-thrust calibration of the present invention;

[0076] Figure 2c is the schematic diagram of the sub-micro-Newton thrust linkage differential measurement system of the present invention;

[0077] Figure 3a is the assembly schematic diagram of the coaxial connector of the present invention;

[0078] Figure 3b is the male head structure schematic diagram of the coaxial connector of the present invention;

[0079] Figure 3c is the female head structure schematic diagram of the coaxial connector of the present invention;

[0080] Figure 4a Structural diagram of the centroid precision control device applicable to micro-thrust calibration of the present invention;

[0081] Figure 4b Schematic diagram of the centroid precision adjustment module of the present invention: Figure (a) is a side view, and Figure (b) is a top view;

[0082] Figure 4c Schematic diagram - perspective view of the inclination control system of the present invention;

[0083] Figure 4d Side view of the torsion pendulum inclination control mechanism of the present invention;

[0084] Figure 4e Centroid position adjustment mechanism of the present invention, Figure (a) is a side view, and Figure (b) is a right view;

[0085] Figure 4f Overall flow chart of the centroid position adjustment mechanism of the present invention;

[0086] Figure 4g Flow chart of "torsion pendulum inclination control" of the present invention;

[0087] Figure 4h Flow chart of "centroid offset adjustment" of the present invention.

[0088] In the figure, 1: Linkage differential measurement bench; 2: Liquid metal RF coaxial cable connector; 2-1: Type-N male head; 2-1-1: External thread of male head; 2-1-2: Outer conductor of male head; 2-1-3: Insulator of male head; 2-1-4: Inner conductor pin; 2-1-5: Shielding layer; Inner conductor pin; 2-2: Liquid metal; 2-3: Type-N female head; 2-3-1: Liquid pool; 2-3-1-1: Liquid pool of outer conductor of female head; 2-3-1-2: Liquid pool of inner conductor of female head; 2-3-2: Insulator of female head; 2-3-3: Inner conductor pin seat; 2-3-4: Outer conductor of female head, 2-3-5: External thread of female head; 3: Centroid precision control device. Specific implementation manners

[0089] Innovation points of the present invention

[0090] 1. One of the innovation points: The linkage rod of the linkage differential measurement bench ① is changed from translational motion to rotational motion. Before the improvement, the linkage rod of the measurement bench could only move up and down translationally. After the improvement, the linkage rod can rotate by an angle θ. The linkage rod before the improvement is as Figure 2aAs shown in the figure, a standard force device is arranged below the linkage rod. The permanent magnet is placed on the linkage rod, and the other end is placed on the coil. An electromagnetic force is generated between the coil and the permanent magnet to calibrate the relationship between the displacement and the force of the linkage rod. Before the improvement, the linkage rod was connected to the pivot. The linkage rod could only perform translational motion, one moving up and the other moving down, and could not rotate. After the improvement, after calibrating the relationship between the displacement and the force, a thruster is arranged on the driving side of the double-bottom base. When the thruster generates thrust, it will cause the upper bottom plate on the driving side of the double-bottom swing base to generate an upward displacement relative to the lower bottom plate. After the upper bottom plate moves upward, an angle is generated between the upper bottom plate and the lower bottom plate. Since the torsion pendulum is arranged on the upper bottom plate, the cross-section of the torsion pendulum will also generate a torsion pendulum inclination angle with the displacement of the upper bottom plate. Torsion pendulum inclination angle After it is generated, if the center of mass of the torsion pendulum is not on the rotation axis, the torsion pendulum with a greater gravity on both sides of the rotation axis will rotate in the direction of the gravity component, and a torsion pendulum rotation angle θ will be generated. According to the mechanical equilibrium equation, the torsion pendulum tilt angle can be obtained. The relationship with the rotation angle θ. Once this relationship is obtained, the deviation s of the center of mass of the torsion pendulum from the axis of rotation can be obtained. When the offset s = 0 is adjusted, the center of mass of the torsion pendulum is concentric with the axis of rotation. At this time, the torsion pendulum is least affected by the environmental common-mode noise, so that the measured micro-thrust reaches the accuracy requirement of the micro-newton level. ② Two sets of upper and lower linkage plates are adopted. One is the linkage swing arm A and the other is the linkage swing arm B. Two identical things are installed on the same double-layer torsion pendulum base. Among them, only the thruster B of the linkage swing arm B is ignited and working, and the thruster A is not working, and one is ignited and working. The advantage of doing this is that the interference force of the environmental common-mode noise can be measured. The double-layer torsion pendulum base is placed inside the vacuum chamber. The vacuum chamber will vibrate. The vacuum chamber is placed on the foundation, and the foundation will also be affected by the vibrations of external vehicles and the like. The vibration noise will all be transmitted in. This kind of vibration noise is generally common-mode noise. The common-mode noise has the same response when the linkage swing arm A and the linkage swing arm B are adjusted to be consistent. The same response means that when the common-mode noise is transmitted to the linkage swing arm A and the linkage swing arm B through the double-layer torsion pendulum base, A and B have the same movement trend. Therefore, after the torsion pendulum displacement sensor A and the torsion pendulum displacement sensor B measure the displacements and then take the difference between the two points, the common-mode noise can be eliminated. For example, when the linkage swing arm A has no thrust output and the linkage swing arm B has thrust output, the linkage swing arm A is only affected by the interference force of the environmental common-mode noise. The linkage swing arm B is affected by not only the interference force of the environmental common-mode noise but also the micro-thrust of the thruster A. At this time, the displacement of the displacement sensor B - the displacement of the displacement sensor A is the displacement that eliminates the interference of the environmental common-mode noise. Then, through the corresponding relationship between the displacement and the standard force, the micro-thrust received by the linkage swing arm B after removing the interference of the environmental common-mode noise can be calculated. The common-mode noise such as temperature noise and vibration noise. The temperature noise is due to the fact that the temperature changes all day long. The linkage swing arm A and the linkage swing arm B will also have temperature drifts as the temperature changes. If the linkage swing arm A and the linkage swing arm B are adjusted well and the temperature drifts are the same, after adjusting for 3 hours, the temperature drifts can be deducted after taking the difference.

[0091] 2. The second innovation point: The adjustment mechanism of the center of mass of the torsion pendulum: Establish the inclination angle of the torsion pendulum and the relationship with the rotation angle θ of the torsion pendulum, and then calculate the displacement offset s. First, the inclination angle of the torsion pendulum ≠ the rotation angle θ of the torsion pendulum. Two conditions are required for the torsion pendulum to rotate. The center of mass deviates from the center point and is affected by the gravity component. This gravity component is shown in the left figure of Figure 2. When both of these two conditions, that is, the generation of the gravity component and the deviation of the center of mass of the torsion pendulum, are met, the torsion pendulum will generate the rotation angle θ. Assume that the center of mass of the torsion pendulum does not deviate. At this time, any given inclination angle of the torsion pendulum even if the inclination angle of the torsion pendulum is degrees, which is close to 90 degrees. Even so, the pendulum will not produce a rotation angle θ. Because the center of mass position has not deviated at this time, the pendulums on both sides of the pivot are subject to the same gravitational force from the earth, so the pendulums on both sides of the pivot maintain a horizontal posture, that is, the rotation angle θ is zero. Second, the center of mass of the pendulum is adjusted by the center of mass adjustment mechanism; third, the adjustment of the center of mass position of the pendulum is not completed once, but several times, but after each adjustment, the rotation angle θ of the pendulum will become smaller and smaller; fourth, each adjustment of the center of mass position requires two steps. The first step is to adjust the inclination angle of the previous pendulum. and the torsion pendulum rotation angle θ are reset to zero; in the second step, the PID controller resets the set inclination angle The set inclination The inclination angle can be set with the last setting Same or different, set the torsion tilt angle The purpose of the gravity component is to generate a gravity component, the size of which determines the sensitivity of the pendulum to rotate. However, the sensitivity of the pendulum is only one aspect. Only when the center of mass of the pendulum deviates will the gravity component have an effect on the rotation of the pendulum. The degree of deviation of the center of mass of the pendulum determines the size of the rotation angle θ of the pendulum. The smaller the deviation of the center of mass of the pendulum, the smaller the rotation angle θ. The inclination angle of the pendulum The size of determines the sensitivity of the torsion pendulum, which is related to the gravity component. The larger the gravity component, the stronger the sensitivity of the torsion pendulum. It can’t be too small or too large. It just needs to meet the sensitivity of the torsion yaw. If it is too small, the sensitivity of the torsion will be poor.

[0092] 3. Innovation point 3: RF coaxial cable connector based on liquid metal

[0093] ①One of the innovation points: Using liquid metal as the connection medium. This RF coaxial cable connector based on liquid metal designs a male head and a female head. There is no mechanical contact between the two heads. There is a pin hole inside. The female head is installed on the base through threads, and the male head is arranged on the swing rod through threads. After being inserted, it cannot move translationally but can only rotate. The male head will also rotate slightly relative to the female head. There is a shielding head and an insulator outside the male head. The female head also has a shielding shell and an insulator. The blank area between the male head and the female head is empty, and the middle is separated by an insulator to form a liquid pool. There is a hollow column in the concentric circle. The liquid is metal liquid. When the metal liquid comes into contact with brass, it conducts electricity. There is also a liquid pool outside. The metal liquid outside is separated from the middle inside. The outer shell is made of stainless steel. When the outer shell is connected to the metal liquid outside, it conducts electricity. After the pin is inserted, the metal liquid outside becomes a little higher. When the pin contacts the metal liquid, it conducts electricity with two brass conductors, and the outer shielding layer also conducts electricity, which is equivalent to being connected inside and outside. The insulation size of the RF coaxial cable connector based on liquid metal has physical requirements and needs to satisfy this physical formula. Coaxial cables generally have 25 ohms, 70 ohms, and 50 ohms. In this embodiment, 50-ohm coaxial cables are used. There are requirements for the outer diameter of the inner core and the inner diameter of the outer core of the coaxial cable. Only by designing these parameters well can the requirement of 50 ohms be achieved. Actually, it is 50.76 ohms, and a difference of 1 - 2 ohms is within the allowable range.

[0094] ②Another innovation point: The innovative application of liquid metal in the field of RF coaxial cable connectors. Currently, no one at home or abroad has thought about using a coaxial connector based on liquid metal to solve the problem of the influence of the stiffness of coaxial cables on measurement. Many people have thought about using liquid metal to achieve the connection of a single cable, but using it on coaxial cables has never been thought of by anyone. In this embodiment, the RF coaxial cable connector based on liquid metal, due to the connection of metal liquid, only has damping when rotating and will not cause stiffness problems. The pin of the male head inserts into the surface of the metal liquid instead of a mechanical connection.

[0095] ③Technical key points: First, coaxial installation: Liquid metal is mostly applied to mechanical parts, pipelines, engine cylinders, welding, manufacturing of complex shapes, nerve connections, electronic ink, etc. This invention transfers it to the coaxial cable of a micro-newton-level thrust measurement torsion pendulum. It is necessary to overcome difficulties that do not exist in the prior art, that is, not only to achieve the bridging of metal liquid but also to ensure the coaxial installation of the male head, female head, and torsion pendulum pivot, which is relatively difficult to achieve; Second, when purchasing coaxial cables on the market, only coaxial cables with the required ohm number need to be selected. However, for the coaxial cable of this invention based on metal liquid, it is necessary to achieve the requirement of a predetermined ohm number through the cooperation of the dimensions of each part, including the inner diameter D of the outer conductor 1 - 2 of the male head and the outer conductor 3 - 4 of the female head T design; the outer diameter d of the inner conductor pin 1 - 4 and the inner conductor pin seat 3 - 3 of the female head TFor the design, the inner and outer diameters of the male insulator 1-3 and the female outer conductor 3-4 need to meet the requirements of formula (1).

[0096] Based on the above invention principle, the present invention designs a linkage differential measurement system applicable to micro-thrust calibration, as Figure 1a , 1b shown. Its characteristics are: the system includes: a linkage differential measurement bench 1, a liquid metal radio frequency coaxial cable connector 2 arranged on the linkage differential measurement bench 1, and a centroid precision control device 3 arranged on the linkage differential measurement bench 1; the linkage differential measurement bench 1 provides a micro-Newton level micro-thrust for the linkage differential measurement system except for environmental common-mode noise; the liquid metal radio frequency coaxial cable connector 2 provides a coaxial cable for micro-Newton level measurement for the linkage differential measurement bench 1; the centroid precision control device 3 provides a torsion pendulum centroid control device and method with micro-Newton level precision for the linkage differential measurement bench 1, so that the torsion pendulum centroid is concentric with the pivot of the torsion pendulum to reduce the interference of environmental common-mode noise on the linkage differential measurement system;

[0097] As Figure 2a , 2b shown, the linkage differential measurement bench 1 adopts two identical linkage torsion pendulums A and linkage torsion pendulums B, and is arranged on the same double-layer torsion pendulum base; among them, the thruster of one set of linkage torsion pendulums is ignited and working, and the thruster of the other set of linkage torsion pendulums is not ignited and working; the linkage differential measurement bench 1 is arranged inside and outside the vacuum chamber. The ones arranged inside the vacuum chamber are the linkage torsion pendulum A and the linkage torsion pendulum B. The linkage torsion pendulum A and the linkage torsion pendulum B are symmetrically arranged along the X and Y directions on the double-bottom torsion pendulum base of the linkage differential measurement bench (1); the linkage torsion pendulum A or the linkage torsion pendulum B is used as a reference system, and the linkage torsion pendulum B or the linkage torsion pendulum A is used as a real thruster thrust measurement system; the one arranged outside the vacuum chamber is the differential signal processor of the sub-micro-Newton thrust linkage differential measurement system; the sub-micro-Newton thrust linkage differential measurement system provides a sub-micro-Newton level micro-thrust for the linkage differential measurement system except for environmental common-mode noise through the differential signal processor; the symmetrically arranged linkage torsion pendulum A and the linkage torsion pendulum B are connected to the support frame through their respective pivots, and then connected to the double-bottom torsion pendulum base through the support frame;

[0098] As Figure 3a , 3bAs shown in Fig. 3c, the liquid metal radio frequency coaxial cable connector 2 is disposed inside the vacuum chamber. One end of it is connected to the torsion pendulum of the linkage differential measurement bench 1, and the other end is connected to the double-bottom torsion pendulum base of the linkage differential measurement bench 1. The end connected to the torsion pendulum is a Type-N male head 2-1, and the end connected to the double-bottom torsion pendulum base is a Type-N female head 2-3. Between the Type-N male head 2-1 and the Type-N female head 2-3 is liquid metal 2-2. The liquid metal 2-2 conducts the Type-N male head 2-1 and the Type-N female head 2-3 to achieve radio frequency / microwave power transmission. The Type-N male head 2-1 rotates coaxially relative to the Type-N female head 2-3.

[0099] As Figure 4a shown, the centroid precision control device 3 is disposed both inside and outside the vacuum chamber. The part disposed inside the vacuum chamber includes a torsion pendulum inclination control mechanism and a centroid position adjustment mechanism, and the part disposed outside the vacuum chamber is a controller. The centroid position adjustment mechanism is disposed on the driving side of the double-bottom torsion pendulum base. The torsion pendulum inclination control mechanism is disposed on the two sides adjacent to the driving side of the double-bottom torsion pendulum base. The input ends of the controller are respectively connected to the torsion pendulum and the torsion pendulum inclination control mechanism, and the output ends are respectively connected to the centroid position adjustment mechanism and the torsion pendulum inclination control mechanism. The torsion pendulum inclination control mechanism is used to control the inclination of the torsion pendulum along the direction of gravity on the cross section. The centroid position adjustment mechanism is used to adjust the centroid position of the torsion pendulum.

[0100] As Figure 2a shown, the linkage torsion pendulum A or the linkage torsion pendulum B is respectively provided with two parallel swing arms A or two parallel swing arms B. The center of the lower surface of each swing arm of the swing arm A or the swing arm B is connected to a pivot, and then each is connected to the double-bottom torsion pendulum base through the pivot. At both ends of the length direction of the swing arm A, there are symmetrically arranged linkage rods A, namely a left linkage rod A and a right linkage rod A. The left linkage rod A is added with a weight and a displacement sensor A, and the right linkage rod A is added with a thruster A and a standard force device A. At both ends of the length direction of the swing arm B, there are symmetrically arranged linkage rods B, namely a left linkage rod B and a right linkage rod B. The left linkage rod B is added with a weight and a displacement sensor B, and the right linkage rod B is added with a thruster B and a standard force device B. The standard force device A or the standard force device B is used to provide a standard force. Through this standard force, the relationship between the standard force and the displacement of the displacement sensor can be obtained, and thus the calibration of the standard force can be realized. The thruster A or the thruster B is used to provide the current micro-thrust, including the micro-thrust generated by the ambient industrial mode noise when the thruster has no thrust output, and the sum of the thrust of the thruster and the thrust generated by the ambient industrial mode noise when the thruster has thrust output.

[0101] As Figure 2aAs shown in the figure, when the linkage torsion pendulum A is used as the reference system and the linkage torsion pendulum B is used as the true thruster thrust measurement system, the thruster of the right connecting rod A has no thrust output and the thruster of the right connecting rod B has thrust output. At this time, the micro-thrust obtained by the differential signal processor through the displacement sensor A is the micro-thrust generated by the environmental industrial mode noise, and the micro-thrust obtained by the differential signal processor through the displacement sensor B is the sum of the micro-thrust generated by the environmental industrial mode noise and the micro-thrust generated by the thruster B; when the linkage torsion pendulum B is used as the reference system and the linkage torsion pendulum A is used as the true thruster thrust measurement system, the thruster of the right connecting rod B has no thrust output and the thruster of the right connecting rod A has thrust output. At this time, the micro-thrust obtained by the differential signal processor through the displacement sensor B is the micro-thrust generated by the environmental industrial mode noise; the micro-thrust obtained by the differential signal processor through the displacement sensor A is the sum of the micro-thrust generated by the environmental industrial mode noise and the micro-thrust generated by the thruster B.

[0102] As Figure 2b shown, the sub-micro-newton thrust linkage differential measurement system of the linkage differential measurement bench includes: a thruster, a micro-thrust combined differential measurement bench, a sub-micro-newton standard force generation and calibration device, and a differential signal processor; the thruster includes a thruster with no thrust output and a thruster with thrust output; the micro-thrust combined differential measurement bench includes bench displacement data with no thrust output and bench displacement data with thrust output; the sub-micro-newton standard force generation and calibration device includes calibration data A based on the proportional relationship between the standard force A generated by the standard force device A and the displacement sensor A, and calibration data B based on the proportional relationship between the standard force B generated by the standard force device B and the displacement sensor B. The differential signal processor obtains the current micro-thrust excluding environmental common-mode noise interference according to the displacement sensor displacement data with no thrust output, the displacement sensor displacement data with thrust output, and the calibration data A and calibration data B.

[0103] As Figure 3a , Figure 3b , Figure 3cAs shown, the Type-N male head 2-1 of the liquid metal radio frequency coaxial cable connector is provided with three layers inside and outside: the outer layer has two parts up and down: the male outer thread 2-1-1 near the end of the male head and the male outer conductor 2-1-2 below the outer thread; the middle layer is the male insulator 2-1-3; the inner layer is the inner conductor pin 2-1-4, and a shielding layer 2-1-5 is also provided radially between the inner conductor pin 2-1-4 and the male outer conductor 2-1-2; the Type-N female head 2-3 is provided with three layers inside and outside: the outer layer has the female outer thread 2-3-5 near the end of the female head and the female outer conductor 2-3-4 below the female outer thread; the middle layer is provided with the female insulator 2-3-2; the inner layer is provided with the female inner conductor pin base 2-3-3; a liquid pool 2-3-1 is also provided on the female outer conductor 2-3-4, and the liquid pool 2-3-1 is divided into two layers inside and outside, the female outer conductor liquid pool 2-3-1-1 on the female outer conductor and the female inner conductor liquid pool 2-3-1-2 on the female inner conductor pin base, and the female outer conductor liquid pool 2-3-1-1 is axially docked with the shielding layer 2-1-5 of the Type-N male head 2-1; the female inner conductor liquid pool 2-3-1-2 is axially docked with the inner conductor pin 2-1-4 of the Type-N male head 2-1.

[0104] The liquid metal 2-2 of the liquid metal radio frequency coaxial cable connector uses a gallium indium tin alloy, which has the characteristics of low melting point, high precision, low volatility, good electrical and thermal conductivity, etc., and is non-toxic, pollution-free and has good liquid fluidity. Its precision is 6.44 g / mL, viscosity 0.0024 PAS, melting point 6-10 °C, conductivity 3.46×106 S / M, and volatility 0.001%; the male insulator (1-3) and the female insulator (3-2) are made of polytetrafluoroethylene.

[0105] The cable impedance of the radio frequency coaxial cable connector of the liquid metal radio frequency coaxial cable connector is 50 Ω. According to the characteristic impedance calculation formula of a single-core coaxial cable:

[0106]

[0107] In the formula, D T is the inner diameter of the outer conductor of the coaxial cable, d T is the outer diameter of the inner conductor. The inner diameters of the male outer conductor 2-1-2 and the female outer conductor 2-3-4 are D T ; the outer diameters of the inner conductor pin 2-1-4 and the female inner conductor pin base 2-3-3 are d T , and the inner and outer diameters of the male insulator 2-1-3 and the female outer conductor 2-3-4 need to meet the requirements of the above formula.

[0108] The Type-N male head (1) is coaxially installed with the torsion pendulum, and the Type-N female head (3) is coaxially installed with the torsion pendulum pivot.

[0109] As shown Figure 4a in the figure, the controller of the centroid precision control device is provided with: a centroid position offset calculation module for calculating the deviation position of the centroid of the torsion pendulum, a torsion pendulum inclination calculation module for calculating the inclination angle of the torsion pendulum, and a PID controller for controlling the inclination angle of the torsion pendulum; the centroid position offset calculation module of the controller is used to calculate the deviation s between the centroid of the torsion pendulum and the rotating shaft, and its input ends are respectively connected to the torsion pendulum and the torsion pendulum inclination calculation module, obtaining the current rotation angle θ of the torsion pendulum from the torsion pendulum and the actual inclination angle of the torsion pendulum from the torsion pendulum inclination calculation module The output end is connected to the centroid position adjustment mechanism, and sends a motor drive instruction to the centroid position adjustment module;

[0110] As shown Figure 4a in the figure, the torsion pendulum inclination calculation module of the controller is used to calculate the inclination angle of the torsion pendulum Its input end is connected to the high-precision capacitance displacement sensor 1 and the high-precision capacitance displacement sensor 2 of the torsion pendulum inclination control mechanism, and the actual inclination angle between the upper bottom plate and the lower bottom plate of the double-bottom torsion pendulum base is obtained through h1 and h2 of the respective measuring points of the high-precision capacitance displacement sensor 1 and the high-precision capacitance displacement sensor 2 The output end of the torsion pendulum inclination calculation module is connected to the PID controller, and outputs the actual inclination angle of the torsion pendulum to the PID controller

[0111] As shown Figure 4a in the figure, the PID controller of the controller is used to output an instruction for the axial displacement of the piezoelectric actuator to the piezoelectric actuator; its input end is connected to the torsion pendulum inclination calculation module, and the PID controller has a set inclination angle Obtain the actual inclination angle of the torsion pendulum from the torsion pendulum inclination calculation module Compare it with the set inclination angle built in the controller The output end of the PID controller is connected to the piezoelectric actuator of the torsion pendulum inclination control module, and controls the voltage output by the piezoelectric actuator to the upper bottom plate of the double-bottom torsion pendulum base

[0112] As shown Figure 4d in the figure, the torsion pendulum inclination control mechanism of the centroid precision control device includes: a piezoelectric actuator arranged on the driving side of the double-bottom torsion pendulum base, a pivot arranged on the rotational freedom side of the double-bottom torsion pendulum base and connecting the upper bottom plate and the lower bottom plate through the pivot, and the high-precision capacitance displacement sensor 1 and the high-precision capacitance displacement sensor 2 arranged on the bottom plate of the double-bottom torsion pendulum base and close to both ends of the upper bottom plate; the piezoelectric actuator is used as a displacement source, and when the piezoelectric actuator outputs an axial displacement voltage, it will cause the upper bottom plate to tilt around the pivot The high-precision capacitance displacement sensors 1 and 2 are symmetrically arranged at both ends of the double-bottom torsion pendulum base. Among them, the high-precision capacitance displacement sensor 1 is arranged at one end close to the driving side, and the high-precision capacitance displacement sensor 2 is arranged at one end close to the pivot. When the piezoelectric actuator outputs an axial displacement, the high-precision capacitance displacement sensors 1 and 2 respectively measure the distances h1 and h2 between the upper bottom plate and the lower bottom plate, and send h1 and h2 to the torsion pendulum calculation module of the controller. The torsion pendulum calculation module obtains the tilt angle between the upper bottom plate and the lower bottom plate through h1 and h2.

[0113] As Figure 4e shown, the centroid position adjustment mechanism of the centroid precision control device includes: a fine-threaded screw, a counterweight mass block, and a motor; the motor is coaxial with the counterweight mass block; one end of the fine-threaded screw is fixed on one side along the axis of the torsion pendulum, and the other end passes through the central hole of the counterweight mass block and is threadedly connected to the central hole of the counterweight mass block; guide through holes are symmetrically opened on both sides of the counterweight mass block, and two smaller-diameter guide shafts pass through the guide holes and are fixed on the motor; the central part of the counterweight mass block is prefabricated with internal threads and forms a precise fit with the screw; when the motor rotates, the two guide shafts will drive the counterweight mass block to rotate on the fine-threaded screw; the fine-threaded screw converts the angular displacement of the counterweight mass block into an axial linear displacement, causing the counterweight mass block to move along the axis of the torsion pendulum, thereby changing the centroid distribution of the torsion pendulum and completing a single adjustment of the deviation of the centroid position.

[0114] The torsion pendulum tilt angle calculation module of the centroid precision control device obtains the tilt angle between the upper bottom plate and the lower bottom plate through h1 and h2. Specifically as follows: Set the distance between the two measuring points of the high-precision capacitance displacement sensor 1 and the high-precision capacitance displacement sensor 2 as L. Let the clearances on the high and low sides in the tilted state be h1 and h2 respectively. The tilt angle calculation formula:

[0115]

[0116] Thus, the tilt angle of the torsion pendulum can be accurately measured.

[0117] The centroid position deviation calculation module calculates the deviation s between the centroid of the torsion pendulum and the rotation axis as follows:

[0118] When the centroid of the torsion pendulum deviates from the rotation axis, the torsion pendulum will rotate under the action of the moment generated by the gravity component in the tilted state. Let the total mass of the torsion pendulum be M, the pivot stiffness coefficient be k, and the distance between the centroid and the rotation axis be s. If the tilt angle of the upper bottom plate around the pivot increases After that, the change in the rotation angle of the torsion pendulum is θ, then the mechanical equilibrium equation of the moment of the gravity component and the restoring moment of the pivot is

[0119]

[0120] where \(g\) is the acceleration due to gravity. Under the small-angle assumption (when \(\theta\) is small enough, \(\cos\theta = 1\)), the deviation of the center of mass of the torsion pendulum from the axis of rotation can be obtained as

[0121]

[0122] In this equation, \(\theta\) is accurately measured through the angular displacement measurement function of the torsion pendulum itself, \(k\) is obtained by calibrating the torsion pendulum, and \(M\) can be directly measured with a balance. Therefore, the key to calculating the deviation position of the center of mass is to output an axial displacement through the piezoelectric actuator to generate a controllable inclination angle of the upper base plate around the pivot

[0123] Based on the above center-of-mass precision control device, the present invention designs a center-of-mass precision control method applicable to a micro-thrust measurement device, which is characterized by including the following steps:

[0124] Step 1: Determine that the current center-of-mass offset \(s\) belongs to the fine-tuning range;

[0125] Step 2: The torsion pendulum inclination control module controls the inclination angle of the torsion pendulum for control;

[0126] Specifically, it includes the following processes:

[0127] 1) The input end of the PID controller receives the set inclination angle and the actual inclination angle

[0128] 2) Determine whether there is a difference between the set inclination angle and the actual inclination angle If not, transfer to process 7); if so, continue with process 3);

[0129] 3) The PID controller outputs a voltage to the piezoelectric actuator. When the piezoelectric actuator outputs an axial displacement, the upper base plate of the double-bottom torsion pendulum base rotates around the pivot to generate an inclination angle

[0130] 4) The high-precision capacitance displacement sensor 1 and the high-precision capacitance displacement sensor 2 feed back \(h1\) and \(h2\) at their respective measurement points to the inclination angle calculation module of the controller;

[0131] 5) The inclination angle calculation module feeds back the actual inclination angle to the input end of the PID controller;

[0132] 6) The PID controller calculates the difference based on the set inclination angle and the actual inclination angle at the input end and returns to process 2)

[0133] 7) End.

[0134] Step 3: The centroid position deviation calculation module calculates the centroid position offset;

[0135] Specifically, it includes the following steps:

[0136] A. Establish the relationship between the tilt angle generated by the piezoelectric actuator and the change in the rotation angle θ of the torsion pendulum;

[0137]

[0138] B. Obtain the deviation S between the centroid of the torsion pendulum and the rotation axis according to the relationship between and the θ;

[0139]

[0140] C. Send the deviation s to the centroid position adjustment module.

[0141] Step 4: Determine whether the current centroid position offset s is less than 10 μm. If so, complete the fine adjustment and go to Step 6; if not, continue with Step 5;

[0142] Step 5: The centroid position adjustment module adjusts the centroid position and returns to Step 2;

[0143] The specific steps are as follows:

[0144] 1) The centroid position offset calculation module of the controller sends a drive command to the motor of the centroid position adjustment module according to the offset;

[0145] 2) When the motor rotates, the guide shaft will drive the mass block to rotate, completing a single adjustment of the centroid position deviation.

[0146] Step 6: The fine adjustment ends.

[0147] It should be emphasized that the above specific embodiments are only explanations of the present invention, and they are not limitations of the present invention. Those skilled in the art can make modifications to the above embodiments without creative contributions according to needs after reading this specification, but as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

Claims

1. A linkage differential measurement system suitable for micro-thrust calibration, characterized in that: The system comprises: a linkage differential measurement bench (1), a liquid metal radio frequency coaxial cable connector (2) arranged on the linkage differential measurement bench (1), and a mass center precision control device (3) arranged on the linkage differential measurement bench (1); the linkage differential measurement bench (1) provides a micro-thrust force of micro-newton level excluding environmental common mode noise for the linkage differential measurement system; the liquid metal radio frequency coaxial cable connector (2) provides a coaxial cable for micro-newton level measurement for the linkage differential measurement bench (1); the mass center precision control device (3) provides a method for controlling the mass center of a torsion pendulum with micro-newton level accuracy for the linkage differential measurement bench (1), so that the mass center of the torsion pendulum is concentric with the pivot of the torsion pendulum, thereby reducing the interference of environmental common mode noise on the linkage differential measurement system; The linkage differential measurement rig (1) uses two sets of identical linkage pendulums A and linkage pendulums B, which are arranged on the same double-layer pendulum base; wherein the propellers of one set of linkage pendulums are ignited and work, and the propellers of the other set of linkage pendulums are not ignited and work; the linkage differential measurement rig (1) is arranged inside and outside the vacuum tank, and the linkage pendulums A and B are arranged inside the vacuum tank, and the linkage pendulums A and B are symmetrically arranged along the X and Y directions on the double-bottom plate pendulum base of the linkage differential measurement rig (1); wherein In the embodiment, the linkage torsion pendulum A or the linkage torsion pendulum B is used as a reference system, and the linkage torsion pendulum B or the linkage torsion pendulum A is used as a real thruster thrust measurement system; the differential signal processor of the sub-micronewton thrust linkage differential measurement system is arranged outside the vacuum tank; the sub-micronewton thrust linkage differential measurement system provides the linkage differential measurement system with sub-micronewton micro-thrust after removing the environmental common mode noise through the differential signal processor; the symmetrically arranged linkage torsion pendulum A and linkage torsion pendulum B are connected to a support frame through their respective pivots, and then connected to a double bottom plate torsion pendulum base through the support frame; The liquid metal radio frequency coaxial cable connector (2) is arranged in a vacuum tank, one end of which is connected to the torsion pendulum of the linkage differential measurement stand (1), and the other end is connected to the double-bottom-plate torsion pendulum base of the linkage differential measurement stand (1); one end connected to the torsion pendulum is a Type-N male connector (2-1), and one end connected to the double-bottom-plate torsion pendulum base is a Type-N female connector (2-3); liquid metal (2-2) is provided between the Type-N male connector (2-1) and the Type-N female connector (2-3); the liquid metal (2-2) conducts the Type-N male connector (2-1) and the Type-N female connector (2-3) to achieve radio frequency / microwave power transmission, and the Type-N male connector (2-1) coaxially rotates relative to the Type-N female connector (2-3); The mass center precision control device (3) is arranged inside and outside the vacuum tank. The torsion pendulum tilt control mechanism and the mass center position adjustment mechanism are arranged inside the vacuum tank, and the controller is arranged outside the vacuum tank. The mass center position adjustment mechanism is arranged on the driving side of the double-bottom plate torsion pendulum base. The torsion pendulum tilt control mechanism is arranged on two sides adjacent to the driving side of the double-bottom plate torsion pendulum base. The input end of the controller is respectively connected to the torsion pendulum and the torsion pendulum tilt control mechanism, and the output end is respectively connected to the mass center position adjustment mechanism and the torsion pendulum tilt control mechanism. The torsion pendulum tilt control mechanism is used to control the tilt angle of the cross section of the torsion pendulum along the gravity direction; the mass center position adjustment mechanism is used to adjust the mass center position of the torsion pendulum.

2. A linkage differential measurement system suitable for micro-thrust calibration according to claim 1, characterized in that: The linked torsion pendulum A or the linked torsion pendulum B is respectively provided with two parallel swing arms A or two parallel swing arms B; the center of the lower surface of each swing arm of the swing arm A or the swing arm B is connected to a pivot, and then each is connected to a double-bottom plate torsion pendulum base through a pivot; symmetrical connecting rods A are provided at both ends of the length direction of the swing arm A, namely a left connecting rod A and a right connecting rod A, the left connecting rod A is added with a counterweight and a displacement sensor A, and the right connecting rod A is added with a thruster A and a standard force device A; symmetrical connecting rods B are provided at both ends of the length direction of the swing arm B, namely a left connecting rod B and a right connecting rod B, a left connecting rod B plus a counterweight and a displacement sensor B, and a right connecting rod B plus a thruster B and a standard force device B; the standard force device A or the standard force device B is used to provide a standard force, through which the relationship between the standard force and the displacement of the displacement sensor can be obtained, thereby realizing the calibration of the standard force; the thruster A or the thruster B is used to provide the current micro-thrust, including the micro-thrust generated by the environmental working mode noise when the thruster has no thrust output, and the sum of the thrust of the thruster and the thrust generated by the environmental working mode noise when there is thrust output.

3. A linkage differential measurement system suitable for micro-thrust calibration according to claim 2, characterized in that: When the linkage torsion pendulum A is used as the reference system and the linkage torsion pendulum B is used as the thrust measurement system of the real thruster, the thruster of the right linkage rod A has no thrust output and the thruster of the right linkage rod B has thrust output. At this time, the micro-thrust obtained by the differential signal processor through the displacement sensor A is the micro-thrust generated by the environmental working mode noise, and the micro-thrust obtained through the displacement sensor B is the sum of the micro-thrust generated by the environmental working mode noise and the micro-thrust generated by the thruster B; when the linkage torsion pendulum B is used as the reference system and the linkage torsion pendulum A is used as the thrust measurement system of the real thruster, the thruster of the right linkage rod B has no thrust output and the thruster of the right linkage rod A has thrust output. At this time, the micro-thrust obtained by the differential signal processor through the displacement sensor B is the micro-thrust generated by the environmental working mode noise; the micro-thrust obtained through the displacement sensor A is the sum of the micro-thrust generated by the environmental working mode noise and the micro-thrust generated by the thruster B.

4. A linkage differential measurement system suitable for micro-thrust calibration according to claim 2, characterized in that: The sub-micronewton thrust linkage differential measurement system of the linkage differential measurement bench (1) comprises: a thruster, a microthrust joint differential measurement bench, a sub-micronewton standard force generation and calibration device, and a differential signal processor; the thruster comprises a thruster without thrust output and a thruster with thrust output; the microthrust joint differential measurement bench comprises bench displacement data without thrust output and bench displacement data with thrust output; the sub-micronewton standard force generation and calibration device comprises calibration data A based on the proportional relationship between a standard force A generated by a standard force device A and a displacement sensor A, and calibration data B based on the proportional relationship between a standard force B generated by a standard force device B and a displacement sensor B; the differential signal processor obtains the current microthrust with the common mode noise interference of the environment removed according to the displacement data of the displacement sensor without thrust output, the displacement data of the displacement sensor with thrust output, the calibration data A and the calibration data B.

5. The linkage differential measurement system suitable for micro-thrust calibration according to claim 1, characterized in that: The Type-N male connector (2-1) of the liquid metal radio frequency coaxial cable connector (2) is provided with three layers, inner and outer: the outer layer is provided with two parts, upper and lower: a male external thread (2-1-1) near the end of the male connector and a male external conductor (2-1-2) below the external thread; the middle layer is a male insulator (2-1-3); the inner layer is an inner conductor pin (2-1-4), and a shielding layer (2-1-5) is further provided in the radial direction between the inner conductor pin (2-1-4) and the male external conductor (2-1-2); the Type-N female connector (2-3) is provided with three layers, inner and outer: the outer layer is provided with a female external thread (2-3-5) near the end of the female connector and a female external conductor (2-3- 4); a female insulator (2-3-2) is provided in the middle layer; a female inner conductor needle seat (2-3-3) is provided in the inner layer; a liquid pool (2-3-1) is also provided on the female outer conductor (2-3-4); the liquid pool (2-3-1) is divided into two layers, an inner and outer layer, a female outer conductor liquid pool (2-3-1-1) on the female outer conductor and a female inner conductor liquid pool (2-3-1-2) on the female inner conductor needle seat; the female outer conductor liquid pool (2-3-1-1) is connected to the shielding layer (2-1-5) of the Type-N male connector (2-1) along the axial direction; the female inner conductor liquid pool (2-3-1-2) is connected to the inner conductor pin (2-1-4) of the Type-N male connector (2-1) along the axial direction.

6. A linkage differential measurement system suitable for micro-thrust calibration according to claim 5, characterized in that: The liquid metal (2-2) of the liquid metal radio frequency coaxial cable connector is made of gallium indium tin alloy, which has the characteristics of low melting point, high precision, low volatility, good electrical and thermal conductivity, and is non-toxic, pollution-free and has good liquid fluidity. Its precision is 6.44g / mL, viscosity is 0.0024PAS, melting point is 6-10°C, conductivity is 3.46×106S / M, and volatility is 0.001%; ​​the male insulator (1-3) and the female insulator (3-2) are made of polytetrafluoroethylene.

7. A linkage differential measurement system suitable for micro-thrust calibration according to claim 5, characterized in that: The cable impedance of the RF coaxial cable connector of the liquid metal RF coaxial cable connector is 50Ω, according to the single-core coaxial cable characteristic impedance calculation formula: Where D T is the inner diameter of the coaxial cable outer conductor, d T The inner diameter of the male outer conductor (2-1-2) and the female outer conductor (2-3-4) is D T The outer diameter of the inner conductor pin (2-1-4) and the female inner conductor pin seat (2-3-3) is d T The inner and outer diameters of the male insulator (2-1-3) and the female outer conductor (2-3-4) must meet the requirements of the above formula.

8. The linkage differential measurement system suitable for micro-thrust calibration according to claim 5, characterized in that: The Type-N male connector (2-1) is coaxially mounted with the oscillator, and the Type-N female connector (2-3) is coaxially mounted with the oscillator pivot.

9. The linkage differential measurement system suitable for micro-thrust calibration according to claim 1, characterized in that: The controller of the mass center precision control device is provided with: a mass center position offset calculation module for calculating the deviation position of the mass center of the torsion pendulum, a torsion pendulum inclination calculation module for calculating the inclination angle of the torsion pendulum, and a PID controller for controlling the inclination angle of the torsion pendulum; the mass center position offset calculation module of the controller is used to calculate the deviation s between the mass center of the torsion pendulum and the rotation axis, and its input end is respectively connected to the torsion pendulum and the torsion pendulum inclination calculation module, and the current rotation angle θ of the torsion pendulum is obtained from the torsion pendulum, and the actual torsion pendulum inclination angle is obtained from the torsion pendulum inclination calculation module. The output end is connected to the mass center position adjustment mechanism to send the motor drive instruction to the mass center position adjustment module; The controller's torsion pendulum angle calculation module is used to calculate the torsion pendulum angle Its input end is connected to the high-precision capacitive displacement sensor 1 and the high-precision capacitive displacement sensor 2 of the torsion pendulum tilt angle control mechanism, and the actual torsion pendulum tilt angle between the upper bottom plate and the lower bottom plate of the double bottom plate torsion pendulum base is obtained through the h1 and h2 of the high-precision capacitive displacement sensor 1 and the high-precision capacitive displacement sensor 2 respectively. The output end of the torsion pendulum inclination angle calculation module is connected to the PID controller to output the actual torsion pendulum inclination angle to the PID controller. The PID controller of the controller is used to output the axial displacement instruction of the piezoelectric actuator to the piezoelectric actuator; its input end is connected to the torsion pendulum inclination angle calculation module, and the PID controller has its own inclination setting function. Get the actual yaw angle from the yaw angle calculation module Compare it with the controller's built-in tilt setting Comparison; the output end of the PID controller is connected to the piezoelectric actuator of the torsion pendulum tilt control module to control the voltage output by the piezoelectric actuator to the bottom plate on the double bottom plate torsion pendulum base.

10. A linkage differential measurement system suitable for micro-thrust calibration according to claim 9, characterized in that: The torsion and yaw angle control mechanism of the mass center precision control device includes: a piezoelectric actuator arranged on the driving side of the double-bottom plate torsion and yaw base, a pivot arranged on the rotational freedom side of the double-bottom plate torsion and yaw base and connecting the upper and lower bases through the pivot, and a high-precision capacitive displacement sensor 1 and a high-precision capacitive displacement sensor 2 arranged on the bottom plate of the double-bottom plate torsion and yaw base and close to the two ends of the upper base; the piezoelectric actuator is used as a displacement source, and when the piezoelectric actuator outputs an axial displacement voltage, the upper base will generate an inclination angle around the pivot. The high-precision capacitive displacement sensor 1 and the high-precision capacitive displacement sensor 2 are symmetrically arranged at the two ends of the double-bottom plate torsion pendulum base, wherein the high-precision capacitive displacement sensor 1 is arranged at the end close to the driving side, and the high-precision capacitive displacement sensor 2 is arranged at the end close to the pivot; when the piezoelectric actuator outputs axial displacement, the high-precision capacitive displacement sensor 1 and the high-precision capacitive displacement sensor 2 respectively measure the distances h1 and h2 between the upper bottom plate and the lower bottom plate, and send h1 and h2 to the torsion pendulum calculation module of the controller, and the torsion pendulum calculation module obtains the inclination angle between the upper bottom plate and the lower bottom plate through h1 and h2.

11. The linkage differential measurement system suitable for micro-thrust calibration according to claim 9, characterized in that: The center of mass position adjustment mechanism of the center of mass precision control device includes: a fine-pitch screw, a counterweight mass block and a motor; the motor is coaxial with the counterweight mass block; one end of the fine-pitch screw is fixed on one side along the torsion pendulum axis and the torsion pendulum, and the other end passes through the center hole of the counterweight mass block and is threadedly connected to the center hole of the counterweight mass block; guide through holes are symmetrically provided on both sides of the counterweight mass block, and two guide shafts with smaller diameters pass through the guide holes and are fixed to the motor; the center of the counterweight mass block is prefabricated with an internal thread to form a precise fit with the screw; when the motor rotates, the two guide shafts will drive the counterweight mass block to rotate on the fine-pitch screw; the fine-pitch screw converts the angular displacement of the counterweight mass block into an axial linear displacement, so that the counterweight mass block moves along the axial direction of the torsion pendulum, thereby changing the center of mass distribution of the torsion pendulum and completing a single adjustment of the center of mass position deviation.

12. The linkage differential measurement system suitable for micro-thrust calibration according to claim 9, characterized in that: The torsion and pendulum angle calculation module of the mass center precision control device obtains the inclination angle between the upper base plate and the lower base plate through h1 and h2. The details are as follows: Set the distance between the two measuring points of high-precision capacitive displacement sensor 1 and high-precision capacitive displacement sensor 2 to L, set the gaps on the high and low sides of the tilt state to h1 and h2 respectively, and the inclination angle calculation formula is: In this way, the inclination angle of the torsion pendulum can be accurately measured.

13. A linkage differential measurement system suitable for micro-thrust calibration according to claim 12, characterized in that: The center of mass position deviation calculation module calculates the deviation s between the center of mass of the torsion pendulum and the rotation axis as follows: When the center of mass of the torsion pendulum deviates from the rotation axis, the torsion pendulum will rotate under the action of the torque generated by the gravity component in the tilted state. Assume that the total mass of the torsion pendulum is M, the pivot stiffness coefficient is k, and the distance of the center of mass deviating from the rotation axis is s. If the tilt angle of the upper base plate around the pivot increases After that, the rotation angle of the torsion pendulum changes to θ, then the mechanical equilibrium equation of the moment of the gravity component and the restoring moment of the pivot is Where g is the acceleration of gravity. Under the assumption of a small angle (cosθ=1 when θ is small enough), the deviation between the center of mass of the torsion pendulum and the axis of rotation is In this equation, θ is accurately measured by the angular displacement measurement function of the torsion pendulum, k is obtained by calibrating the torsion pendulum, and M can be directly measured with the help of a balance. Therefore, the key to calculating the deviation of the center of mass is to output the axial displacement through the piezoelectric actuator to make the upper base plate produce a controllable inclination angle around the pivot.

14. A method for precisely controlling the center of mass of a micro-thrust measuring device based on a linkage differential measurement system suitable for micro-thrust calibration as claimed in any one of claims 9 to 13, characterized in that: The following steps are involved: Step 1: Determine whether the current center of mass offset s is within the fine-tuning range; Step 2: The torsion and sway angle control module controls the torsion and sway angle To exercise control; Step 3: The centroid position deviation calculation module calculates the centroid position offset; Step 4: Determine whether the current centroid position offset s is less than 10um. If yes, complete fine adjustment and proceed to step 6. If no, proceed to step 5. Step 5: The centroid position adjustment module adjusts the centroid position and returns to step 2; Step 6: Fine tuning is completed.

15. A method for precisely controlling the center of mass of a micro-thrust measurement device according to claim 14, characterized in that: The torsion yaw angle control in step 2 includes the following process: 1) The PID controller input receives the set inclination angle and the actual inclination 2) Determine the set inclination angle and the actual inclination Is there a difference? If not, proceed to process 7); if yes, continue with process 3); 3) The PID controller outputs voltage to the piezoelectric actuator. When the piezoelectric actuator outputs axial displacement, the upper base plate of the double-base torsion pendulum base generates an inclination angle around the pivot. 4) The high-precision capacitive displacement sensor 1 and the high-precision capacitive displacement sensor 2 feed back h1 and h2 of their respective measuring point positions to the inclination angle calculation module of the controller; 5) The inclination calculation module converts the actual inclination Feedback to the PID controller input; 6)PID controller according to the set inclination angle of the input and the actual inclination Do the difference calculation and return to process 2) 7) End.

16. A method for precisely controlling the center of mass of a micro-thrust measurement device according to claim 15, characterized in that: The calculation of the mass center position offset s in step 3 includes the following steps: A. Establish the inclination angle generated by the piezoelectric actuator and the relationship between the pendulum rotation angle change θ; B. According to the The relationship between the center of mass of the torsion pendulum and the axis of rotation S is obtained by the relationship between θ and C. Send the deviation s to the center of mass position adjustment module.

17. A method for precisely controlling the center of mass of a micro-thrust measurement device according to claim 14, characterized in that: The centroid position adjustment module in step 5 performs centroid position adjustment, and the specific steps are as follows: 1) The center of mass position offset calculation module of the controller sends a driving instruction to the motor of the center of mass position adjustment module according to the offset; 2) When the motor rotates, the guide shaft will drive the mass block to rotate, completing a single adjustment of the center of mass position deviation.

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