A linkage differential measurement system and method suitable for micro-thrust calibration

Abstract

The present invention discloses a linked differential measurement system and method suitable for micro-thrust calibration. The system comprises: a linked differential measurement platform, a liquid metal radio frequency coaxial cable connector arranged on the platform, and a center of mass precision control device arranged on the platform. The linked differential measurement system provides micro-thrust at the micro-newton level, excluding environmental common-mode noise. The method comprises: a pendulum inclination angle control module controlling the pendulum inclination angle #imgabs0#; a center of mass position deviation calculation module calculating the center of mass position offset; determining whether the current center of mass position offset s is less than 10 μm; and a center of mass position adjustment module adjusting the center of mass position. The present invention solves the problems that gravitational wave thrusters must calibrate thrust noise in addition to thrust magnitude, that the high stiffness of coaxial cables interferes with the motion of the gravitational wave micro-thrust calibration pendulum, and that the gravitational wave micro-thrust calibration pendulum places extremely high demands on the sensing accuracy of center of mass control.

Description

Technical Field

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

[0002] High-precision, low-noise microthrust measurement is one of the key technologies urgently needed for space gravitational wave detection missions. This multidisciplinary approach involves breakthroughs in engineering technology, and its high-precision, low-noise, and broadband thrust measurement capabilities challenge the limits of existing technologies. Despite years of development, microthrust measurement technology currently lacks a method that fully meets the requirements for ground-based calibration of microthrusters for space gravitational wave detection. The challenge of microthrust measurement technology for space gravitational waves lies in achieving high-precision, low-noise microthrust calibration within an ultra-low bandwidth.

[0003] One of the design challenges of the gravitational wave microthrust calibration pendulum is that microthrusters are used for high-precision scientific detection. Unlike ordinary Hall thrusters, they have extremely low thrust, only tens of nanonewtons or micronewtons. Conventional thrusters have thrust levels in the nanonewton range, while the micronewton thrusters used in high-precision, low-noise microthrust calibration have thrust levels three orders of magnitude lower, making thrust measurement more difficult than conventional thrust measurement. Furthermore, gravitational wave thrusters impose a requirement on thrusters that is not present in conventional thrusters. Conventional thrusters only require thrust calibration, but gravitational wave thrusters require both thrust calibration and thrust noise calibration. For example, when the noise reaches 0.1 Hz, the measurement is equivalent to 10,000 seconds, which is equivalent to three hours. During these three hours, the equipment must remain extremely stable, which is a very difficult task.

[0004] The second design difficulty of the gravitational wave microthrust calibration pendulum lies in the following: First, both RF and microwave thrusters utilize electromagnetic waves, requiring the use of coaxial cables for efficient transmission of RF / microwave energy. Commonly used coaxial cables are typically quite stiff. When using the pendulum device to measure thrust, the high stiffness of the coaxial cable interferes with the pendulum's motion. In severe cases, the pendulum can even fail to accurately measure thrust, significantly limiting the accuracy and reliability of electric thruster performance testing. Second, the pivot spring is extremely soft and can rotate with even the slightest force. The coaxial cable is even stiffer than the pivot, resulting in virtually no change in the force applied during measurement. Third, coaxial cables are used for RF / microwave energy transmission and carry both high and low RF power, which heats the cable. When the coaxial cable heats, the RF cable creeps, causing significant drift in the thrust measurement device and resulting in large measurement errors. For kilowatt-class electric thrusters, direct thrust measurement using thrust measurement devices is no longer possible due to the influence of coaxial cables, and the target shooting method is often used to achieve indirect thrust measurement. This measurement method has large errors and is not conducive to practical applications.

[0005] The third design difficulty of the gravitational wave microthrust calibration pendulum is that it places extremely high demands on the sensor accuracy, control method, and actuator resolution of the center of mass control mechanism. The center of mass position of the gravitational wave thruster microthrust calibration pendulum affects its anti-interference capability, which in turn affects key indicators such as resolution and noise power. The closer the center of mass is to the axis of rotation, the stronger the pendulum's anti-interference capability. In the field of space gravitational wave detection, to achieve accurate calibration of micronewton-class thrusters, it is necessary to ensure that the offset between the pendulum's center of mass and the axis of rotation is controlled within 10μm. This metric places extremely high demands on the sensor accuracy, control method, and actuator resolution of the center of mass control mechanism. Currently, center of mass control of the pendulum mostly relies on manually adding and removing weights to balance the masses on both sides. Limited by atmospheric interference and human error, the adjustment accuracy is low and it is difficult to ensure that the center of mass position meets the standard.

[0006] In short, the design difficulties of the gravitational wave microthrust calibration pendulum are: the thrust is extremely small, and the gravitational wave thruster not only needs to calibrate the thrust size but also the thrust noise; the high stiffness of the coaxial cable will interfere with the movement of the gravitational wave microthrust calibration pendulum, and in severe cases it may even cause the pendulum to be unable to accurately measure the thrust; the gravitational wave microthrust calibration pendulum places extremely high demands on the sensing accuracy, control method and actuator resolution of the center of mass control. Summary of the Invention

[0007] To address the problems existing in the prior art, the present invention proposes a linked differential measurement system and method suitable for micro-thrust calibration. The first purpose is to address the following issues: The thrust is extremely small, and in addition to calibrating the thrust size, the noise thrust of the gravitational wave thruster must also be calibrated. The second purpose is to address the fact that the high stiffness of the coaxial cable interferes with the motion of the gravitational wave micro-thrust calibration pendulum, which in severe cases may even prevent the pendulum from accurately measuring thrust. The third purpose is to address the problem that the gravitational wave micro-thrust calibration pendulum places extremely high demands on the sensing accuracy, control method, and actuator resolution of the center of mass control.

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

[0009] A linkage differential measurement system suitable for micro-thrust calibration is characterized in that the system comprises: a linkage differential measurement platform (1), a liquid metal radio frequency coaxial cable connector (2) arranged on the linkage differential measurement platform (1), and a mass center precision control device (3) arranged on the linkage differential measurement platform (1); the linkage differential measurement platform (1) provides the linkage differential measurement system with micro-thrust at the micro-newton level excluding environmental common-mode noise; the liquid metal radio frequency coaxial cable connector (2) provides the linkage differential measurement platform (1) with a coaxial cable for micro-newton level measurement; and the mass center precision control device (3) provides the linkage differential measurement platform (1) with a micro-newton level precision torsion pendulum mass center control method, so that the torsion pendulum mass center is concentric with the torsion pendulum pivot, thereby reducing the interference of environmental common-mode noise on the linkage differential measurement system.

[0010] The linkage differential measurement rig (1) uses two sets of identical linkage pendulums A and linkage pendulums B, and is arranged on the same double-layer pendulum base; wherein, the propellers of one set of linkage pendulums are ignited 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); Linked pendulum A or linked pendulum B serves as a reference system, and linked pendulum B or linked pendulum A serves as a real thruster thrust measurement system. A differential signal processor of a sub-micronewton thrust linked differential measurement system is arranged outside the vacuum tank. The sub-micronewton thrust linked differential measurement system provides the linked differential measurement system with sub-micronewton microthrust after removing environmental common-mode noise via the differential signal processor. The symmetrically arranged linked pendulums A and B are connected to a support frame via their respective pivots, and are then connected to a double-baseplate pendulum base via the support frame.

[0011] 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 located between the Type-N male connector (2-1) and the Type-N female connector (2-3); the liquid metal (2-2) connects 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);

[0012] The center of mass precision control device (3) is arranged inside and outside the vacuum tank, the torsion pendulum tilt control mechanism and the center of mass position adjustment mechanism are arranged inside the vacuum tank, and the controller is arranged outside the vacuum tank; the center of mass 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 both 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 center of mass 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 torsion pendulum along the direction of gravity on the cross section; the center of mass position adjustment mechanism is used to adjust the center of mass position of the torsion pendulum.

[0013] Furthermore, 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 the 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 A and a right connecting rod A. Rod B and right connecting rod B, left connecting rod B plus counterweight and displacement sensor B, right connecting rod B plus thruster B and standard force device B; the standard force device A or 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 thruster B is used to provide the current microthrust, including the microthrust 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.

[0014] Furthermore, when the linked pendulum A serves as the reference system and the linked pendulum B serves as the real thrust measurement system, the thruster of the right link rod A has no thrust output and the thruster of the right link rod B has thrust output. At this time, the microthrust obtained by the differential signal processor through the displacement sensor A is the microthrust generated by the environmental tool noise, and the microthrust obtained through the displacement sensor B is the sum of the microthrust generated by the environmental tool noise and the microthrust generated by thruster B. When the linked pendulum B serves as the reference system and the linked pendulum A serves as the real thrust measurement system, the thruster of the right link rod B has no thrust output and the thruster of the right link rod A has thrust output. At this time, the microthrust obtained by the differential signal processor through the displacement sensor B is the microthrust generated by the environmental tool noise; the microthrust obtained through the displacement sensor A is the sum of the microthrust generated by the environmental tool noise and the microthrust generated by thruster B.

[0015] Furthermore, the sub-micronewton thrust linkage differential measurement system of the linkage differential measurement rig (1) comprises: a thruster, a microthrust combined differential measurement rig, 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 combined differential measurement rig comprises rig displacement data without thrust output and rig displacement data with thrust output; the sub-micronewton standard force generation and calibration device comprises 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 microthrust after removing the interference of the common mode noise of the environment 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.

[0016] Furthermore, the Type-N male connector (2-1) of the liquid metal radio frequency coaxial cable connector (2) is provided with three inner and outer layers: the outer layer is provided with two parts, an upper and lower part: 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 inner and outer layers: 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 (2-3-6) below the female external thread. -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), and the liquid pool (2-3-1) is divided into an inner and outer layers, 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 axially connected to the shielding layer (2-1-5) of the Type-N male connector (2-1); the female inner conductor liquid pool (2-3-1-2) is axially connected to the inner conductor pin (2-1-4) of the Type-N male connector (2-1).

[0017] Furthermore, the liquid metal (2-2) of the liquid metal RF coaxial cable connector adopts 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℃, 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.

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

[0019]

[0020] 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.

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

[0022] Furthermore, 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 pendulum, a pendulum inclination calculation module for calculating the inclination angle of the pendulum, and a PID controller for controlling the inclination angle of the pendulum; the mass center position offset calculation module of the controller is used to calculate the deviation s between the mass center of the pendulum and the rotation axis, and its input end is connected to the pendulum and pendulum inclination calculation modules respectively, and the current pendulum rotation angle θ is obtained from the pendulum, and the actual pendulum inclination angle is obtained from the 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;

[0023] 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 high-precision capacitive displacement sensor 2 of the torsion pendulum angle control mechanism, and the actual torsion pendulum angle between the upper and lower base plates of the double-base 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 angle calculation module is connected to the PID controller to output the actual torsion pendulum angle to the PID controller.

[0024] 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 angle calculation module, and the PID controller has its own setting angle 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 and oscillation angle control module to control the voltage output by the piezoelectric actuator to the bottom plate on the double bottom plate torsion and oscillation base.

[0025] Furthermore, the torsion and tilt 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 tilt base, a pivot arranged on the rotational freedom side of the double-bottom plate torsion and tilt 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 tilt base and close to both ends of the upper base; the piezoelectric actuator serves as a displacement source, and when the piezoelectric actuator outputs an axial displacement voltage, it will cause the upper base to 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 both 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 and lower base plates, 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 and lower base plates through h1 and h2.

[0026] Furthermore, the center of mass position adjustment mechanism of the center of mass precision control device includes: a fine-thread screw, a counterweight mass block and a motor; the motor is coaxial with the counterweight mass block; one end of the fine-thread screw is fixed to one side along the pendulum axis and the 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 opened 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, which 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-thread screw; the fine-thread screw converts the angular displacement of the counterweight mass block into axial linear displacement, so that the counterweight mass block moves along the axial direction of the pendulum, thereby changing the center of mass distribution of the pendulum and completing a single adjustment of the center of mass position deviation.

[0027] Furthermore, the torsion and tilt angle calculation module of the center of mass precision control device obtains the tilt 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, and set the gaps on the high and low sides in the tilt state to h1 and h2 respectively. The inclination angle calculation formula is:

[0028]

[0029] In this way, the inclination angle of the torsion pendulum can be accurately measured.

[0030] Furthermore, the center of mass position deviation calculation module calculates the deviation s between the center of mass of the pendulum and the rotation axis as follows:

[0031] When the center of mass of the torsion pendulum deviates from the axis of rotation, 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 axis of rotation 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

[0032]

[0033] Where g is the acceleration due to gravity. Under the assumption of a small angle (θ is small enough, cosθ = 1), the deviation between the center of mass of the pendulum and the axis of rotation is

[0034]

[0035] In this equation, θ is accurately measured using the angular displacement measurement function of the torsion pendulum, k is obtained by calibrating the torsion pendulum, and M can be directly measured using a balance. Therefore, the key to calculating the center of mass deviation is to output axial displacement through the piezoelectric actuator to produce a controllable tilt angle around the pivot.

[0036] A method for precisely controlling the center of mass of a micro-thrust measuring device is characterized by comprising the following steps:

[0037] Step 1: Determine whether the current center of mass offset s is within the fine-tuning range;

[0038] Step 2: The torsion and tilt angle control module controls the torsion and tilt angle to exercise control;

[0039] Step 3: The center of mass position deviation calculation module calculates the center of mass position offset;

[0040] Step 4: Determine whether the current center of mass position offset s is less than 10 μm. If yes, complete fine adjustment and proceed to step 6. If not, proceed to step 5.

[0041] Step 5: The center of mass position adjustment module adjusts the center of mass position and returns to step 2;

[0042] Step 6: Fine-tuning is completed.

[0043] The yaw angle control in step 2 includes the following steps:

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

[0045] 2) Determine the set inclination angle and actual inclination Is there a difference? If not, go to process 7); if yes, continue with process 3);

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

[0047] 4) High-precision capacitive displacement sensor 1 and high-precision capacitive displacement sensor 2 feed back h1 and h2 of their respective measuring point positions to the controller's inclination angle calculation module;

[0048] 5) The inclination calculation module calculates the actual inclination Feedback to the PID controller input;

[0049] 6)PID controller is based on the set inclination angle of the input and actual inclination Do the difference calculation and return to process 2)

[0050] 7) End.

[0051] The calculation of the center of mass position offset s in step 3 includes the following steps:

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

[0053]

[0054] B. According to the The relationship between the pendulum mass center and the rotation axis is obtained by the formula:

[0055]

[0056] C. Send the deviation s to the center of mass position adjustment module.

[0057] The center of mass position adjustment module in step 5 performs center of mass position adjustment, and the specific steps are as follows:

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

[0059] 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.

[0060] Advantages and effects of the present invention

[0061] 1. The linked differential measurement rig of the present invention ensures the consistency of the dynamic characteristics of the two sets of 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 rig of the present invention converts the micro-thrust generated by the thruster into the displacement of the thrust rig through torsion, and the displacement is accurately measured by the high-stability micro-displacement information acquisition device; the sub-micronewton and standard force generation and calibration device provides high-precision sub-micronewton standard force for calibration of the measurement rig and closed-loop measurement of a large range of thrust; the integrated thermal / electromagnetic shielding ultra-quiet and ultra-stable experimental platform provides a low-noise, high-stability experimental environment for measurement experiments, ensuring the accuracy of the measurement results; and the multi-task intelligent real-time measurement and control software receives data information from each device, performs data processing and analysis, and controls the standard force output of the sub-micronewton standard force generation and calibration device.

[0063] 3. The linkage differential measurement rig of the present invention proposes a symmetrical dual-arm linkage measurement method to decouple the thruster configuration from the thrust measurement, reduce the difficulty of thruster assembly and debugging, eliminate the influence of errors such as arm calibration, thrust action center measurement, and plume non-uniformity on thrust measurement, and achieve thrust measurement accuracy that cannot be achieved by conventional methods.

[0064] 4. The linkage differential measurement rig of the present invention adopts a differential measurement method and designs a dual-symmetrical linkage differential measurement structure to reduce the requirements for the test environment and solve the problem of low-frequency thrust noise measurement. Through debugging, the consistency requirements of the dynamic characteristics of the two sets of linkage torsion pendulums are achieved, and a higher common-mode noise suppression ratio is achieved to reduce the impact of common-mode noise on the measurement results.

[0065] 5. The linkage differential measurement rig 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 micro-thrust dynamic measurement performance.

[0066] 6. The liquid metal RF coaxial cable connector of the present invention improves measurement accuracy: by adopting liquid metal bridging and zero-stiffness coaxial cable connection, the influence of the coaxial cable on the torsion pendulum stiffness is significantly reduced, so that the torsion pendulum can more accurately measure the tiny thrust of the thruster, thereby 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 RF coaxial cable connector of the present invention realizes efficient RF transmission: the connector design based on liquid metal realizes good impedance matching, ensures efficient transmission of RF / microwave power, reduces losses during signal transmission, and improves the working efficiency of the electric thruster.

[0068] 8. The liquid metal RF coaxial cable connector of the present invention has broad application prospects: it is not only suitable for existing microwave / RF ion electric thruster thrust testing, but can also be promoted and applied to other fields that require low-rigidity coaxial cable connections and RF energy transmission, such as satellite communications, radar systems, etc., and has broad market application prospects.

[0069] 9. The center of mass precision control device of the present invention, based on a closed-loop control architecture constructed with a piezoelectric actuator and a high-precision capacitive displacement meter, can achieve a 5μrad level torsion and tilt angle control resolution and simultaneously achieve a center of mass positioning accuracy of 1μm.

[0070] 10. The center of mass precision control device of the present invention achieves a 1μm-level center of mass position adjustment resolution by changing the mass distribution due to the axial displacement of the mass counterweight on the fine-thread screw, ensuring that the deviation of the pendulum's center of mass from the rotating axis is no more than 10μm. This effectively suppresses the interference of disturbances such as ground vibration on the pendulum, reduces the noise floor of the pendulum, and improves the measurement resolution, providing reliable guarantee for the testing and calibration of micro-newton thrusters.

[0071] 11. The center of mass precision control device of the present invention has a mature software implementation solution for the entire process and can be operated when the pendulum is in a vacuum environment, reducing atmospheric disturbances, improving the center of mass adjustment accuracy, and simplifying the operation complexity. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0073] Figure 1b Schematic diagram of the layout of the linkage differential measurement system suitable for micro-thrust calibration of the present invention;

[0074] Figure 2a This is a schematic diagram of a measurement bench in the prior art;

[0075] Figure 2b The invention is a linkage differential measurement stand suitable for micro-thrust calibration;

[0076] Figure 2c Schematic diagram of the sub-micronewton thrust linkage differential measurement system of the present invention;

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

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

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

[0080] Figure 4a This is a structural diagram of the center of mass precision control device suitable for micro-thrust calibration of the present invention;

[0081] Figure 4b The schematic diagram of the center of mass precision adjustment module of the present invention is as follows: Figure (a) is a side view, and Figure (b) is a top view;

[0082] Figure 4c This is a schematic diagram of the tilt control system of the present invention - a three-dimensional diagram;

[0083] Figure 4d A side view of the torsion and yaw angle control mechanism of the present invention;

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

[0085] Figure 4f This is the overall flow chart of the center of mass position adjustment mechanism of the present invention;

[0086] Figure 4g This is a flow chart of the "torsion and sway angle control" of the present invention;

[0087] Figure 4h This is the flow chart of “center of mass offset adjustment” of the present invention.

[0088] In the figure, 1: Linked differential measurement bench; 2: Liquid metal RF coaxial cable connector; 2-1: Type-N male connector; 2-1-1: Male external thread; 2-1-2: Male outer conductor; 2-1-3: Male insulator; 2-1-4: Inner conductor pin; 2-1-5: Shielding layer; Inner conductor pin; 2-2: Liquid metal; 2-3: Type-N female connector; 2-3-1: Liquid pool; 2-3-1-1: Female outer conductor liquid pool; 2-3-1-2: Female inner conductor liquid pool; 2-3-2: Female insulator; 2-3-3: Inner conductor needle holder; 2-3-4: Female outer conductor, 2-3-5: Female external thread; 3: Center of mass precision control device. DETAILED DESCRIPTION

[0089] Innovation of the present invention

[0090] 1. Innovation 1: Linkage differential measuring platform ① The linkage rod is changed from translation to rotation. Before the improvement, the linkage rod of the measuring platform could only move up and down. After the improvement, the linkage rod can rotate at an angle of θ. Figure 2aAs shown, a standard force device is arranged under the linkage rod, a 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, which is used to calibrate the relationship between the displacement and force of the linkage rod. Before the improvement, the linkage rod was connected to the pivot, and the linkage rod could only move horizontally, one upward and the other downward, and could not rotate. After the improvement, after the relationship between displacement and force is calibrated, a thruster is arranged on the driving side of the double-bottom-plate base. When the thruster generates thrust, the upper base plate on the driving side of the double-bottom-plate torsion pendulum base will generate an upward displacement relative to the lower base plate. After the upper base plate moves upward, an angle is generated between the upper and lower base plates. Since the torsion pendulum is arranged on the upper base plate, the cross section of the torsion pendulum will also generate a torsion pendulum inclination angle as the upper base plate moves. yaw angle After the pendulum is generated, if the center of mass of the pendulum is not on the axis, the pendulum with greater gravity on both sides of the axis will rotate in the direction of the gravity component, and generate a pendulum rotation angle θ; according to the mechanical equilibrium equation, the pendulum inclination angle can be obtained The relationship between the rotation angle θ and the center of mass of the torsion pendulum and the rotation axis can be determined by understanding this relationship. When the offset s = 0, the center of mass of the torsion pendulum is concentric with the rotation axis. At this point, the torsion pendulum is minimally affected by environmental common-mode noise, enabling the measured microthrust to achieve micronewton-level accuracy. (2) Two linkage plates are used: one linkage arm A and one linkage arm B. These two identical sets are mounted on the same double-layer torsion pendulum base. Only thruster B of linkage arm B is ignited; thruster A is inactive. This approach allows for the measurement of the interference force of environmental common-mode noise. The double-layer torsion pendulum base is placed inside a vacuum tank, which vibrates. The vacuum tank is placed on a foundation, which is also affected by external vibrations, such as from cars, transmitting vibration noise. This vibration noise is generally common-mode noise, meaning that the response is identical when linkage arms A and B are tuned identically. The responses are identical, meaning that when common-mode noise is transmitted to linkage arms A and B through the double-layer torsion pendulum base, A and B exhibit the same motion trend. Therefore, the common-mode noise can be eliminated by subtracting the displacements measured by torsion pendulum displacement sensors A and B. For example, when linkage arm A is not outputting thrust and when linkage arm B is outputting thrust, linkage arm A is only subject to the interference force of the environmental common-mode noise. Linkage arm B, in addition to the interference force of the environmental common-mode noise, is also subject to the microthrust of thruster A. At this point, the displacement of displacement sensor B minus the displacement of displacement sensor A is the displacement that eliminates the interference of the environmental common-mode noise. Using the correspondence between displacement and standard force, the microthrust experienced by linkage arm B, excluding the interference of the environmental common-mode noise, can be calculated. The common mode noise includes temperature noise and vibration noise. The temperature noise is caused by the temperature changing throughout the day. The linkage swing arm A and the linkage swing arm B will also have temperature drift as the temperature changes. If the linkage swing arm A and the linkage swing arm B are well debugged, the temperature drift will be consistent. After adjusting for 3 hours and making the difference, the temperature drift can be deducted.

[0091] 2. Innovation point 2: Adjustment mechanism of the center of mass of the torsion pendulum: Establishing the torsion pendulum inclination angle The relationship between the torsion pendulum angle θ and the displacement offset s is calculated. ≠The rotation angle θ of the torsion pendulum. The rotation of the torsion pendulum requires two conditions: the center of mass deviates from the center point and is subjected to a gravity component. The gravity component is as follows Figure 2a As shown in the figure, the pendulum will rotate at an angle θ only when both the gravity component and the center of mass of the pendulum are deviated are met. Assuming that the center of mass of the pendulum does not deviate, at this time, an arbitrary pendulum inclination angle is given. Even if the pendulum angle is 80 degrees 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 pendulum from the previous step. 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 angle Can be compared with the last set inclination The same or different, set the torsion tilt angle The purpose of the force is to generate a gravity component, the magnitude of which determines the sensitivity of the pendulum to rotation. However, the sensitivity of the pendulum is only one aspect; the gravity component will only affect the pendulum's rotation when the pendulum's center of mass deviates. The degree of deviation of the pendulum's center of mass determines the magnitude of the pendulum's rotation angle θ. The smaller the deviation of the pendulum's center of mass, the smaller the rotation angle θ. 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. Therefore, the inclination angle of the torsion pendulum is It can’t be too small or too large. As long as it can meet the sensitivity of the torsion pendulum, the torsion pendulum angle 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] ① One of the innovations: using liquid metal as the connecting medium. This liquid metal-based RF coaxial cable connector features a male and female connector with no mechanical contact. The connector has a pinhole inside. The female connector is threaded onto the base, while the male connector is threaded onto the pendulum. Once plugged in, it can only rotate, not move linearly. The male connector also rotates slightly relative to the female connector. The male connector is surrounded by a shield and an insulator. The female connector also has a shield and an insulator. The space between the male and female connectors is empty, separated by an insulator to form a liquid pool. A hollow column is located in the middle of the concentric circles. The liquid is molten metal, which becomes conductive when it comes into contact with the brass. The outer shell is also a liquid pool, separated from the inner shell by a stainless steel shell. When the outer shell and the outer liquid metal are connected, the outer shell becomes conductive. When the pin is inserted, the outer metal liquid rises slightly. When the pin contacts the liquid metal, the two brass wires become conductive, and the outer shielding layer also becomes conductive, effectively connecting the inside and the outside. The insulation dimensions of liquid metal-based RF coaxial cable connectors have physical requirements and must meet these physical formulas. Coaxial cables are generally available in 25 ohm, 70 ohm, and 50 ohm ratings. This embodiment uses 50 ohm coaxial cables. Coaxial cables have requirements for both the outer diameter of the inner core and the inner diameter of the outer core. These parameters must be carefully designed to achieve the 50 ohm requirement. The actual value is 50.76 ohms, with a difference of 1-2 ohms being acceptable.

[0094] ② Innovation point 2: Innovative application of liquid metal in the field of RF coaxial cable connectors. Currently, no one at home or abroad has considered using liquid metal-based coaxial connectors to solve the problem of the influence of coaxial cable stiffness on measurement. Many people have thought of using liquid metal to achieve single cable connections, but no one has considered using it on coaxial cables. This embodiment is based on the liquid metal RF coaxial cable connector. Since it is a metal liquid connection, there is only damping during rotation, and there will be no stiffness issues. The male pin is inserted into the surface of the metal liquid instead of a mechanical connection.

[0095] ③ Key technical points: First, coaxial installation: Liquid metal is mostly used in mechanical parts, pipelines, engine cylinders, welding, complex shape manufacturing, neural connections, electronic ink, etc. The present invention transfers it to the coaxial cable for micro-newton thrust measurement and torsion. It is necessary to overcome the difficulties that the existing technology does not have, that is, not only to realize the bridging of the metal liquid, but also to ensure the coaxial installation of the male head, female head and torsion pivot, which is more difficult to achieve; second, when purchasing coaxial cables on the market, you only need to choose the one that meets the required ohm number, but the coaxial cable based on the metal liquid of the present invention must meet the requirements of the predetermined ohm number by matching the sizes of each part, including the inner diameter D of the male outer conductor 1-2 and the female outer conductor 3-4. T Design; the outer diameter d of the inner conductor pins 1-4 and the female inner conductor pin seat 3-3 TIn the design, the inner and outer diameters of the male insulator 1-3 and the female outer conductor 3-4 must meet the requirements of formula (1).

[0096] Based on the above invention principle, the present invention designs a linkage differential measurement system suitable for micro-thrust calibration, such as Figure 1a 、 1b As shown, its characteristics are: the system includes: a linkage differential measurement platform 1, a liquid metal radio frequency coaxial cable connector 2 arranged on the linkage differential measurement platform 1, and a center of mass precision control device 3 arranged on the linkage differential measurement platform 1; the linkage differential measurement platform 1 provides a micro-thrust 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 platform 1; the center of mass precision control device 3 provides a device and method for controlling the center of mass of the torsion pendulum with micro-newton level precision for the linkage differential measurement platform 1, so that the center of mass of the torsion pendulum is concentric with the pivot axis of the torsion pendulum, thereby reducing the interference of environmental common-mode noise on the linkage differential measurement system;

[0097] like Figure 2a 、 2b As shown, the linkage differential measurement rig 1 uses two sets of identical linkage pendulums A and linkage pendulums B, and is arranged on the same double-layer pendulum base; wherein, the propeller of one set of linkage pendulums is ignited and the propeller of the other set of linkage pendulums is not ignited; 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); Linked pendulum A or linked pendulum B serves as a reference system, and linked pendulum B or linked pendulum A serves as a real thruster thrust measurement system. A differential signal processor of a sub-micronewton thrust linked differential measurement system is arranged outside the vacuum tank. The sub-micronewton thrust linked differential measurement system provides the linked differential measurement system with sub-micronewton microthrust after removing environmental common-mode noise via the differential signal processor. The symmetrically arranged linked pendulums A and B are connected to a support frame via their respective pivots, and are then connected to a double-baseplate pendulum base via the support frame.

[0098] like Figure 3a 、 3bAs shown in 3c, the liquid metal RF coaxial cable connector 2 is arranged in a vacuum tank, one end of which is connected to the torsion pendulum of the linked differential measurement rig 1, and the other end is connected to the double-bottom-plate torsion pendulum base of the linked differential measurement rig 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; between the Type-N male connector 2-1 and the Type-N female connector 2-3 is liquid metal 2-2; the liquid metal 2-2 connects the Type-N male connector 2-1 and the Type-N female connector 2-3 to realize RF / microwave power transmission, and the Type-N male connector 2-1 rotates coaxially relative to the Type-N female connector 2-3;

[0099] like Figure 4a As shown, the center of mass precision control device 3 is arranged inside and outside the vacuum tank. The ones arranged inside the vacuum tank are the torsion pendulum tilt control mechanism and the center of mass position adjustment mechanism, and the one arranged outside the vacuum tank is the controller; the center of mass 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 both 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 center of mass position adjustment mechanism and the torsion pendulum tilt control mechanism; the torsion pendulum tilt control mechanism is used to control the inclination angle along the gravity direction on the cross section of the torsion pendulum; the center of mass position adjustment mechanism is used to adjust the center of mass position of the torsion pendulum.

[0100] like Figure 2a As shown, 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 the 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, the left connecting rod B and right connecting rod B, left connecting rod B plus counterweight and displacement sensor B, right connecting rod B plus thruster B and standard force device B; the standard force device A or 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 thruster B is used to provide the current microthrust, including the microthrust 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.

[0101] like Figure 2aAs shown in FIG, when linkage pendulum A is used as the reference system and linkage pendulum B is used as the real thrust measurement system, the thruster of the right linkage rod A has no thrust output, while the thruster of the right linkage rod B has thrust output. At this time, the microthrust obtained by the differential signal processor through displacement sensor A is the microthrust generated by the environmental tool noise, and the microthrust obtained through displacement sensor B is the sum of the microthrust generated by the environmental tool noise and the microthrust generated by thruster B. When linkage pendulum B is used as the reference system and linkage pendulum A is used as the real thrust measurement system, the thruster of the right linkage rod B has no thrust output, while the thruster of the right linkage rod A has thrust output. At this time, the microthrust obtained by the differential signal processor through displacement sensor B is the microthrust generated by the environmental tool noise, and the microthrust obtained through displacement sensor A is the sum of the microthrust generated by the environmental tool noise and the microthrust generated by thruster B.

[0102] like Figure 2b As shown, the sub-micronewton thrust linkage differential measurement system of the linkage differential measurement rig includes: a thruster, a microthrust combined differential measurement rig, a sub-micronewton standard force generation and calibration device, and a differential signal processor; the thruster includes a thruster without thrust output and a thruster with thrust output; the microthrust combined differential measurement rig includes rig displacement data without thrust output and rig displacement data with thrust output; the sub-micronewton 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 microthrust after removing the environmental common-mode noise interference based on 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.

[0103] like Figure 3a 、 Figure 3b 、 Figure 3cAs shown, the Type-N male connector 2-1 of the liquid metal RF coaxial cable connector has three layers: the outer layer has two parts, the upper and lower parts: the male external thread 2-1-1 near the end of the male connector and the male outer conductor 2-1-2 below the external 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 further provided in the radial direction between the inner conductor pin 2-1-4 and the male outer conductor 2-1-2; the Type-N female connector 2-3 has three layers: the outer layer has the female external thread 2-3-5 near the end of the female connector and the female outer conductor 2-3-6 below the female external thread -3-4; the middle layer is provided with a female insulator 2-3-2; the inner layer is provided with a female inner conductor needle seat 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 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, and the female outer conductor liquid pool 2-3-1-1 is axially connected to the shielding layer 2-1-5 of the Type-N male connector 2-1; the female inner conductor liquid pool 2-3-1-2 is axially connected to the inner conductor pin 2-1-4 of the Type-N male connector 2-1.

[0104] 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℃, 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.

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

[0106]

[0107] Where D T is the inner diameter of the coaxial cable outer conductor, d T The inner diameter of the inner conductor is D. 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.

[0108] The Type-N male connector (1) is mounted coaxially with the oscillator, and the Type-N female connector (3) is mounted coaxially with the oscillator pivot.

[0109] like Figure 4a As shown, 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 pendulum, a pendulum inclination calculation module for calculating the inclination angle of the pendulum, and a PID controller for controlling the inclination angle of the pendulum; the mass center position offset calculation module of the controller is used to calculate the deviation s between the mass center of the pendulum and the rotation axis, and its input end is connected to the pendulum and pendulum inclination calculation modules respectively, and the current pendulum rotation angle θ is obtained from the pendulum, and the actual pendulum inclination angle is obtained from the 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;

[0110] like Figure 4a As shown, 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 high-precision capacitive displacement sensor 2 of the torsion pendulum angle control mechanism, and the actual torsion pendulum angle between the upper and lower base plates of the double-base 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 angle calculation module is connected to the PID controller to output the actual torsion pendulum angle to the PID controller.

[0111] like Figure 4a As shown, 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 angle calculation module, and the PID controller has its own setting angle 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 and oscillation angle control module to control the voltage output by the piezoelectric actuator to the bottom plate on the double bottom plate torsion and oscillation base.

[0112] like Figure 4d As shown, the torsion and tilt angle control mechanism of the center of mass precision control device includes: a piezoelectric actuator arranged on the driving side of the double-base torsion and tilt base, a pivot arranged on the rotational freedom side of the double-base torsion and tilt base and connecting the upper base and the lower base 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-base torsion and tilt base and close to the two ends of the upper base; the piezoelectric actuator serves as a displacement source, and when the piezoelectric actuator outputs an axial displacement voltage, it will cause the upper base to 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 both 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 and lower base plates, 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 and lower base plates through h1 and h2.

[0113] like Figure 4e As shown, the center of mass position adjustment mechanism of the center of mass precision control device includes: a fine-thread screw, a counterweight mass block and a motor; the motor is coaxial with the counterweight mass block; one end of the fine-thread screw is fixed on one side along the pendulum axis and the 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 opened 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, which 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-thread screw; the fine-thread screw converts the angular displacement of the counterweight mass block into axial linear displacement, so that the counterweight mass block moves along the axial direction of the pendulum, thereby changing the center of mass distribution of the pendulum and completing a single adjustment of the center of mass position deviation.

[0114] The torsion and tilt angle calculation module of the center of mass precision control device obtains the tilt 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, and set the gaps on the high and low sides in the tilt state to h1 and h2 respectively. The inclination angle calculation formula is:

[0115]

[0116] In this way, the inclination angle of the torsion pendulum can be accurately measured.

[0117] 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:

[0118] When the center of mass of the torsion pendulum deviates from the axis of rotation, 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 axis of rotation 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

[0119]

[0120] Where g is the acceleration due to gravity. Under the assumption of a small angle (θ is small enough, cosθ = 1), the deviation between the center of mass of the pendulum and the axis of rotation is

[0121]

[0122] In this equation, θ is accurately measured using the angular displacement measurement function of the torsion pendulum, k is obtained by calibrating the torsion pendulum, and M can be directly measured using a balance. Therefore, the key to calculating the center of mass deviation is to output axial displacement through the piezoelectric actuator to produce a controllable tilt angle 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 suitable for a micro-thrust measurement device, which is characterized by comprising the following steps:

[0124] Step 1: Determine whether the current center of mass offset s is within the fine-tuning range;

[0125] Step 2: The torsion and tilt angle control module controls the torsion and tilt angle to exercise control;

[0126] The specific process includes the following:

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

[0128] 2) Determine the set inclination angle and actual inclination Is there a difference? If not, go to process 7); if yes, continue with process 3);

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

[0130] 4) High-precision capacitive displacement sensor 1 and high-precision capacitive displacement sensor 2 feed back h1 and h2 of their respective measuring point positions to the controller's inclination angle calculation module;

[0131] 5) The inclination calculation module calculates the actual inclination Feedback to the PID controller input;

[0132] 6)PID controller is based on the set inclination angle of the input and actual inclination Do the difference calculation and return to process 2)

[0133] 7) End.

[0134] Step 3: The center of mass position deviation calculation module calculates the center of mass position offset;

[0135] Specifically, it includes the following steps:

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

[0137]

[0138] B. According to the The relationship between the pendulum mass center and the rotation axis is obtained by the formula:

[0139]

[0140] C. Send the deviation s to the center of mass position adjustment module.

[0141] Step 4: Determine whether the current center of mass position offset s is less than 10 μm. If yes, complete fine adjustment and proceed to step 6. If not, proceed to step 5.

[0142] Step 5: The center of mass position adjustment module adjusts the center of mass position and returns to step 2;

[0143] The specific steps are as follows:

[0144] 1) The center of mass position offset calculation module of the controller sends a drive instruction to the motor of the center of mass 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 center of mass position deviation.

[0146] Step 6: Fine-tuning is completed.

[0147] It should be emphasized that the above specific embodiments are merely explanations of the present invention and are not limitations of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the above embodiments as needed, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A linkage differential measurement system suitable for micro-thrust calibration, characterized by: The system comprises: a linkage differential measurement stand (1), a liquid metal radio frequency coaxial cable connector (2) arranged on the linkage differential measurement stand (1), and a mass center precision control device (3) arranged on the linkage differential measurement stand (1); the linkage differential measurement stand (1) provides a micro-thrust 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 stand (1); and the mass center precision control device (3) provides a micro-newton level precision torsion pendulum mass center control method for the linkage differential measurement stand (1), so that the mass center of the torsion pendulum is concentric with the pivot axis 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, and is arranged on the same double-layer pendulum base; wherein, the propeller of one set of linkage pendulums is ignited and the propeller of the other set of linkage pendulums is not ignited and is arranged inside and outside the vacuum tank, wherein 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 pendulum A or the linkage pendulum B serves as a reference system, and the linkage pendulum B or the linkage pendulum A serves as a real thrust measurement system for the thrust of the thruster; a differential signal processor of a 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 microthrust after removing the environmental common-mode noise through the differential signal processor; the symmetrically arranged linkage pendulum A and linkage pendulum B are connected to a support frame through their respective pivots, and then connected to a double-bottom-plate 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 located between the Type-N male connector (2-1) and the Type-N female connector (2-3); the liquid metal (2-2) connects 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 center of mass precision control device (3) is arranged inside and outside the vacuum tank, the torsion pendulum tilt control mechanism and the center of mass position adjustment mechanism are arranged inside the vacuum tank, and the controller is arranged outside the vacuum tank; the center of mass 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 both 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 center of mass 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 torsion pendulum along the direction of gravity on the cross section; the center of mass position adjustment mechanism is used to adjust the center of mass 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, the left connecting rod B and the right connecting rod B, the left connecting rod B plus the counterweight and the displacement sensor B, and the right connecting rod B plus the thruster B and the 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. The linkage differential measurement system suitable for micro-thrust calibration according to claim 2, characterized in that: When linkage pendulum A serves as the reference system and linkage pendulum B serves as the actual thrust measurement system, the thruster of the right linkage rod A has no thrust output, while the thruster of the right linkage rod B has thrust output. At this time, the microthrust obtained by the differential signal processor through displacement sensor A is the microthrust generated by the environmental tool noise, and the microthrust obtained through displacement sensor B is the sum of the microthrust generated by the environmental tool noise and the microthrust generated by thruster B. When linkage pendulum B serves as the reference system and linkage pendulum A serves as the actual thrust measurement system, the thruster of the right linkage rod B has no thrust output, while the thruster of the right linkage rod A has thrust output. At this time, the microthrust obtained by the differential signal processor through displacement sensor B is the microthrust generated by the environmental tool noise, and the microthrust obtained through displacement sensor A is the sum of the microthrust generated by the environmental tool noise and the microthrust generated by thruster B.

4. The 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 rig (1) comprises: a thruster, a microthrust combined differential measurement rig, 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 combined differential measurement rig comprises rig displacement data without thrust output and rig displacement data with thrust output; the sub-micronewton standard force generation and calibration device comprises 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 microthrust after removing the interference of the common mode noise of the environment 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: the outer layer is provided with two parts, the upper and lower parts: the male external thread (2-1-1) near the end of the male connector and the 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: the outer layer is provided with a female external thread (2-3-5) near the end of the female connector and the 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), and the liquid pool (2-3-1) is divided into 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 axially connected to the shielding layer (2-1-5) of the Type-N male connector (2-1); the female inner conductor liquid pool (2-3-1-2) is axially connected to the inner conductor pin (2-1-4) of the Type-N male connector (2-1).

6. The 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 and the female insulator are made of polytetrafluoroethylene.

7. The linkage differential measurement system suitable for micro-thrust calibration according to claim 5, characterized in that: The cable impedance of the liquid metal RF coaxial cable connector is 50Ω. According to the calculation formula of the characteristic impedance of the single-core coaxial cable: Where D T is the inner diameter of the coaxial cable outer conductor, d T The inner diameter of the inner conductor is D, 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 mounted coaxially with the sway bar, and the Type-N female connector (2-3) is mounted coaxially with the sway bar 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 pendulum, a pendulum inclination calculation module for calculating the inclination angle of the pendulum, and a PID controller for controlling the inclination angle of the pendulum; the mass center position offset calculation module of the controller is used to calculate the deviation s between the mass center of the pendulum and the rotation axis, and its input end is connected to the pendulum and pendulum inclination calculation modules respectively, and the current pendulum rotation angle θ is obtained from the pendulum, and the actual pendulum inclination angle is obtained from the 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 high-precision capacitive displacement sensor 2 of the torsion pendulum angle control mechanism, and the actual torsion pendulum angle between the upper and lower base plates of the double-base 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 angle calculation module is connected to the PID controller to output the actual torsion pendulum 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 angle calculation module, and the PID controller has its own setting angle 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 and oscillation angle control module to control the voltage output by the piezoelectric actuator to the bottom plate on the double bottom plate torsion and oscillation base.

10. The linkage differential measurement system suitable for micro-thrust calibration according to claim 9, characterized in that: The torsion and tilt angle control mechanism of the mass center precision control device includes: a piezoelectric actuator arranged on the driving side of the double-base torsion and tilt base, a pivot arranged on the rotational freedom side of the double-base torsion and tilt base and connecting the upper base and the lower base 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-base torsion and tilt base and close to the two ends of the upper base; the piezoelectric actuator serves as a displacement source, and when the piezoelectric actuator outputs an axial displacement voltage, it will cause the upper base to 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 both 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 and lower base plates, 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 and lower base plates 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-thread screw, a counterweight mass block and a motor; the motor is coaxial with the counterweight mass block; one end of the fine-thread screw is fixed to one side along the pendulum axis and the 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 opened 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, which 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-thread screw, and the fine-thread screw will convert the angular displacement of the counterweight mass block into axial linear displacement, so that the counterweight mass block moves along the axial direction of the pendulum, thereby changing the center of mass distribution of the 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 tilt angle calculation module of the center of mass precision control device obtains the tilt 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, and set the gaps on the high and low sides in the tilt state to h1 and h2 respectively. The inclination angle calculation formula is: In this way, the inclination angle of the torsion pendulum can be accurately measured.

13. The 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 axis of rotation, 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 axis of rotation 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, θ is small enough so that cosθ = 1. The deviation between the center of mass of the pendulum and the axis of rotation is: In this equation, θ is accurately measured using the angular displacement measurement function of the torsion pendulum, k is obtained by calibrating the torsion pendulum, and M can be directly measured using a balance. Therefore, the key to calculating the center of mass deviation is to output axial displacement through the piezoelectric actuator to produce a controllable tilt angle around the pivot.

14. A method for precisely controlling the center of mass of a micro-thrust measurement device based on a linkage differential measurement system suitable for micro-thrust calibration according to 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 tilt angle control module controls the torsion and tilt angle to exercise control; Step 3: The center of mass position deviation calculation module calculates the center of mass position offset; Step 4: Determine whether the current center of mass position offset s is less than 10 μm. If yes, complete fine adjustment and proceed to step 6. If not, proceed to step 5. Step 5: The center of mass position adjustment module adjusts the center of mass 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 yaw angle control in step 2 includes the following steps: 1) The PID controller input receives the set inclination angle and actual inclination 2) Determine the set inclination angle and actual inclination Is there a difference? If not, go 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 of the double-base torsion pendulum base generates an inclination angle around the pivot. 4) High-precision capacitive displacement sensor 1 and high-precision capacitive displacement sensor 2 feed back h1 and h2 of their respective measuring point positions to the controller's inclination angle calculation module; 5) The inclination calculation module calculates the actual inclination Feedback to the PID controller input; 6)PID controller is based on the set inclination angle of the input and 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 center of mass 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 θ; B. According to the The relationship between the pendulum mass center and the rotation axis is obtained by the formula: 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 center of mass position adjustment module in step 5 performs center of mass position adjustment, and the specific steps are as follows: 1) The center of mass position offset calculation module of the controller sends a drive 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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