Mass center regulation and control device and method suitable for micro-thrust calibration torsional pendulum

Abstract

The invention discloses a mass center regulation and control device and method suitable for micro-thrust calibration torsional pendulum, the mass center precise regulation and control device comprises a double-bottom-plate torsional pendulum base arranged in a vacuum tank, the base is provided with a supporting frame, a pivot and a torsional pendulum, and the supporting frame supports the torsional pendulum through the pivot; the torsional pendulum inclination angle control mechanism is arranged on the driving side of the double-bottom-plate torsional pendulum base, and the mass center position adjusting mechanism is arranged on the double-bottom-plate torsional pendulum base and connected with one end of the torsional pendulum. The controller is arranged outside the vacuum tank; the method comprises the following steps: judging whether the offset s of the current centroid position is less than 10 microns or not, if so, finishing fine adjustment, and if not, continuing to control a torsional pendulum inclination angle # imgabs0 #, and then calculating the offset of the centroid position until the offset s is less than 10 microns; according to the invention, the torsional pendulum inclination angle control resolution of 5 [mu] rad level can be realized, and the centroid positioning precision of 1 [mu] m level can be synchronously reached; 1 [mu] m-level mass center position adjusting resolution can be achieved, and it is ensured that the deflection distance of the torsional pendulum mass center from a rotating shaft is not larger than 10 [mu] m.

Description

Technical Field

[0001] The present invention belongs to the field of aerospace propulsion technology, and specifically relates to a centroid control device and method applicable to a micro-thrust calibration torsion pendulum. Background Art

[0002] A micro-thrust calibration torsion pendulum is an important device for calibrating aerospace micro-thrusters. The centroid position of the torsion pendulum affects its anti-interference ability, and thus affects key indicators such as its resolution and noise power. The closer the centroid is to the rotation axis, the stronger the anti-interference ability of the torsion pendulum.

[0003] In the field of space gravitational wave detection, to achieve precise calibration of micro-Newton-level thrusters, it is necessary to ensure that the offset between the centroid of the torsion pendulum and the rotation axis is controlled within 10 μm. This index poses extremely high requirements for the sensing accuracy of centroid control, the control method, and the resolution of the actuator. Currently, the centroid control of the torsion pendulum mostly relies on manually adding or removing weights to balance the masses on both sides. Limited by atmospheric interference and human operation errors, the adjustment accuracy is low, and it is difficult to ensure that the centroid position meets the standard. Therefore, it is of great significance to study a high-precision and high-reliability centroid control method for the torsion pendulum. The purpose of the present invention is to achieve a micron-level centroid control accuracy for a micro-Newton-level thrust calibration device and provide a reliable test guarantee for micro-Newton-level thrusters. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention proposes a centroid control device and method applicable to a micro-thrust calibration torsion pendulum, aiming to solve the problem that for the precise calibration of micro-Newton-level thrusters, relying on manually adding or removing weights to balance the masses on both sides, the adjustment accuracy is low, and it is difficult to ensure that the offset between the centroid of the torsion pendulum and the rotation axis is controlled within 10 μm and the centroid position meets the standard.

[0005] The present invention proposes the following technical solutions to solve its technical problems:

[0006] A centroid precision control device applicable to a micro-thrust measurement device, characterized in that the centroid precision control device includes: a double-bottom torsion pendulum base disposed in a vacuum chamber, on which a support frame, a pivot, and a torsion pendulum are provided, the support frame supports the torsion pendulum through the pivot; a torsion pendulum inclination control mechanism disposed on the driving side of the double-bottom torsion pendulum base; a centroid position adjustment mechanism disposed on the double-bottom torsion pendulum base and connected to one end of the torsion pendulum; a controller disposed outside the vacuum chamber, the input end of the controller is respectively connected to the torsion pendulum and the displacement sensor of the torsion pendulum inclination control mechanism, and the output end is respectively connected to the motor of the centroid position adjustment mechanism and the piezoelectric actuator of the torsion pendulum inclination control mechanism; the torsion pendulum inclination control mechanism is used to control the inclination angle of the torsion pendulum, and this inclination angle is the inclination angle of the cross-section of the torsion pendulum along the direction of gravity; the centroid position adjustment mechanism is used to adjust the centroid position of the torsion pendulum; the controller is used to control the torsion pendulum inclination control mechanism and the centroid position adjustment mechanism.

[0007] Further, the controller is provided with: a centroid position offset calculation module for calculating the deviation position of the centroid of the torsion pendulum, a torsion pendulum inclination calculation module for calculating the inclination angle of the torsion pendulum, and a PID controller for controlling the inclination angle of the torsion pendulum;

[0008] The centroid position offset calculation module of the controller is used to calculate the deviation s between the centroid of the torsion pendulum and the rotating shaft. Its input ends are respectively connected to the torsion pendulum and the torsion pendulum inclination calculation module, obtaining the current rotation angle θ of the torsion pendulum from the torsion pendulum and the actual inclination angle of the torsion pendulum from the torsion pendulum inclination calculation module The output end is connected to the centroid position adjustment mechanism, and sends a motor drive instruction to the centroid position adjustment module;

[0009] The torsion pendulum inclination calculation module of the controller is used to calculate the inclination angle of the torsion pendulum Its input end is connected to the high-precision capacitance displacement sensor 1 and the high-precision capacitance displacement sensor 2 of the torsion pendulum inclination control mechanism. Through h1 and h2 of the respective measuring points of the high-precision capacitance displacement sensor 1 and the high-precision capacitance displacement sensor 2, the actual inclination angle between the upper bottom plate and the lower bottom plate of the double-bottom torsion pendulum base is obtained The output end of the torsion pendulum inclination calculation module is connected to the PID controller, and outputs the actual inclination angle of the torsion pendulum to the PID controller

[0010] The PID controller of the controller is used to output an instruction for the axial displacement of the piezoelectric actuator to the piezoelectric actuator; its input end is connected to the torsion pendulum inclination calculation module, and obtains the actual inclination angle of the torsion pendulum from the torsion pendulum inclination calculation module Compare it with the set inclination angle built in the controller The output end of the PID controller is connected to the piezoelectric actuator of the torsion pendulum inclination control module, and controls the voltage output by the piezoelectric actuator to the upper bottom plate of the double-bottom torsion pendulum base.

[0011] Further, the torsion pendulum inclination control mechanism includes: a piezoelectric actuator disposed on the driving side of the double-bottom torsion pendulum base, a pivot disposed on the rotational freedom side of the double-bottom torsion pendulum base and connecting the upper bottom plate and the lower bottom plate through the pivot, and the high-precision capacitance displacement sensor 1 and the high-precision capacitance displacement sensor 2 disposed on the bottom plate of the double-bottom torsion pendulum base and near both ends of the upper bottom plate; The piezoelectric actuator is used as a displacement source. When the piezoelectric actuator outputs an axial displacement voltage, it will cause the upper bottom plate to generate an inclination angle around the pivot The high-precision capacitance displacement sensor 1 and the high-precision capacitance displacement sensor 2 are symmetrically arranged at both ends of the double-bottom torsion pendulum base. Among them, the high-precision capacitance displacement sensor 1 is arranged at one end close to the driving side, and the high-precision capacitance displacement sensor 2 is arranged at one end close to the pivot. When the piezoelectric actuator outputs an axial displacement, the high-precision capacitance displacement sensor 1 and the high-precision capacitance displacement sensor 2 respectively measure the distances h1 and h2 between the upper bottom plate and the lower bottom plate, and send h1 and h2 to the torsion pendulum calculation module of the controller. The torsion pendulum calculation module obtains the tilt angle between the upper bottom plate and the lower bottom plate through h1 and h2

[0012] Further, the centroid position adjustment mechanism includes: a fine-threaded screw, a counterweight mass block, and a motor; the motor is coaxial with the counterweight mass block; one end of the fine-threaded screw is fixed on one side along the axis of the torsion pendulum, and the other end passes through the central hole of the counterweight mass block and is threadedly connected to the central hole of the counterweight mass block; guide through holes are symmetrically opened on both sides of the counterweight mass block, and two guide shafts with smaller diameters pass through the guide holes and are fixed on the motor; the central prefabricated internal thread of the counterweight mass block forms a precise fit with the screw; when the motor rotates, the two guide shafts will drive the counterweight mass block to rotate on the fine-threaded screw; the fine-threaded screw converts the angular displacement of the counterweight mass block into an axial linear displacement, so that the counterweight mass block moves along the axis of the torsion pendulum, thereby changing the centroid distribution of the torsion pendulum and completing a single adjustment of the deviation of the centroid position

[0013] Further, the torsion pendulum tilt angle calculation module obtains the tilt angle between the upper bottom plate and the lower bottom plate through h1 and h2 Specifically as follows: Set the distance between the two measurement points of the high-precision capacitance displacement sensor 1 and the high-precision capacitance displacement sensor 2 as L. Assume that the clearances on the high and low sides in the tilted state are h1 and h2 respectively. The tilt angle calculation formula is

[0014]

[0015] Thus, the tilt angle of the torsion pendulum can be accurately measured

[0016] Further, the centroid position deviation calculation module calculates the deviation s between the centroid of the torsion pendulum and the rotation axis as follows

[0017] When the centroid of the torsion pendulum deviates from the rotation axis, the torsion pendulum will rotate under the action of the moment generated by the gravity component in the tilted state. Assume that the total mass of the torsion pendulum is M, the pivot stiffness coefficient is k, and the distance between the centroid and the rotation axis is s. If the tilt angle of the upper bottom plate around the pivot increases After that, the change in the rotation angle of the torsion pendulum is θ, then the mechanical equilibrium equation of the moment of the gravity component and the restoring moment of the pivot is

[0018]

[0019] where g is the acceleration due to gravity. Under the small - angle assumption (when θ is small enough, cosθ = 1), the deviation of the center of mass of the torsion pendulum from the axis of rotation can be obtained as

[0020]

[0021] In this equation, θ is precisely measured through the angular displacement measurement function of the torsion pendulum itself, k is obtained by calibrating the torsion pendulum, and M can be directly measured with a balance. Therefore, the key to calculating the deviation position of the center of mass is to output the axial displacement through the piezoelectric actuator to make the upper base plate of the double - base torsion pendulum produce a controllable inclination angle around the pivot

[0022] A method for precise adjustment of the center of mass applicable to a micro - thrust measurement device, characterized in that it includes the following steps:

[0023] Step 1: Determine that the current center - of - mass offset s belongs to the fine - adjustment range;

[0024] Step 2: The torsion - pendulum inclination - angle control module controls the inclination angle of the torsion pendulum for control;

[0025] Step 3: The center - of - mass position deviation calculation module calculates the center - of - mass position offset;

[0026] Step 4: Determine whether the current center - of - mass position offset s is less than 10 μm. If so, complete the fine - adjustment and proceed to Step 6; if not, continue to Step 5;

[0027] Step 5: The center - of - mass position adjustment module adjusts the center - of - mass position and returns to Step 2;

[0028] Step 6: The fine - adjustment ends.

[0029] The torsion - pendulum inclination - angle control in Step 2 includes the following process:

[0030] 1) The input end of the PID controller receives the set inclination angle and the actual inclination angle

[0031] 2) Determine whether there is a difference between the set inclination angle and the actual inclination angle If not, proceed to process 7); if so, continue to process 3);

[0032] 3) The PID controller outputs a voltage to the piezoelectric actuator. When the piezoelectric actuator outputs an axial displacement, the upper base plate of the double - base torsion - pendulum base tilts around the pivot to produce an inclination angle

[0033] 4) The high - precision capacitance displacement sensor 1 and the high - precision capacitance displacement sensor 2 feed back h1 and h2 at their respective measurement points to the inclination - angle calculation module of the controller;

[0034] 5) The inclination angle calculation module feeds back the actual inclination angle to the input end of the PID controller;

[0035] 6) The PID controller calculates the difference based on the set inclination angle and the actual inclination angle at the input end, and returns to process 2)

[0036] 7) End.

[0037] The calculation of the centroid position offset s in step three includes the following steps:

[0038] A. Establish a relationship between the inclination angle generated by the piezoelectric actuator and the change θ of the rotation angle of the torsion pendulum;

[0039]

[0040] B. Obtain the deviation amount S of the centroid of the torsion pendulum from the rotation axis according to the relationship between the and the θ

[0041]

[0042] C. Send the deviation amount s to the centroid position adjustment module.

[0043] The centroid position adjustment module in step five adjusts the centroid position, and the specific steps are as follows:

[0044] 1) The centroid position offset calculation module of the controller issues a driving instruction to the motor of the centroid position adjustment module according to the offset;

[0045] 2) When the motor rotates, the guide shaft drives the mass block to rotate, completing a single adjustment of the centroid position deviation.

[0046] Advantages and effects of the present invention

[0047] 1. Based on the closed-loop control architecture constructed by the piezoelectric actuator and the high-precision capacitance displacement meter, the torsion pendulum inclination angle control resolution of 5 μrad can be achieved, and the centroid positioning accuracy of 1 μm can be synchronously achieved;

[0048] 2. By changing the mass distribution through the axial displacement of the mass block on the fine-thread screw, the centroid position adjustment resolution of 1 μm can be achieved, ensuring that the distance between the centroid of the torsion pendulum and the rotation axis does not exceed 10 μm, thereby effectively suppressing the interference of disturbances such as ground vibration on the torsion pendulum, reducing the noise floor of the torsion pendulum, improving the measurement resolution, and providing a reliable guarantee for the test and calibration of the micro-newton thruster;

[0049] 3. The whole process has a mature software implementation solution, which can be operated when the torsion pendulum is in a vacuum environment, reducing atmospheric disturbances, improving the centroid adjustment accuracy, and simplifying the operation complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 Structural diagram of the centroid precision control device applicable to micro-thrust calibration of the present invention;

[0051] Figure 2 Schematic diagram of the centroid precision adjustment module of the present invention: Figure (a) is a side view, and Figure (b) is a top view;

[0052] Figure 3 Schematic diagram - perspective view of the inclination control system of the present invention;

[0053] Figure 4 Side view of the torsion pendulum inclination control mechanism of the present invention;

[0054] Figure 5 Centroid position adjustment mechanism of the present invention, Figure (a) is a side view, and Figure (b) is a right view;

[0055] Figure 6 Overall flow chart of the centroid position adjustment mechanism of the present invention;

[0056] Figure 7 Specific process of "torsion pendulum inclination control" of the present invention;

[0057] Figure 8 Specific process of "centroid offset adjustment" of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0058] Design principle of the present invention

[0059] I. Innovation points of the present invention: Establish the relationship between the torsion pendulum inclination angle and the torsion pendulum rotation angle θ, and then calculate the displacement offset s. A thruster is arranged on the driving side of the double-bottom base. When the thruster generates thrust, it will cause the upper bottom plate on the driving side of the double-bottom torsion pendulum base to displace upward relative to the lower bottom plate. After the upper bottom plate displaces upward, an angle is generated between the upper bottom plate and the lower bottom plate. Since the torsion pendulum is arranged on the upper bottom plate, the cross-section of the torsion pendulum will also generate a torsion pendulum inclination angle with the displacement of the upper bottom plate. Torsion pendulum inclination angle After the torsion pendulum inclination angle is generated, if the centroid of the torsion pendulum is not on the rotation axis, the torsion pendulum with a greater gravity on both sides of the rotation axis will rotate in the direction of the gravity component, generating a torsion pendulum rotation angle θ; according to the mechanical equilibrium equation, the torsion pendulum tilt angle can be obtained. The relationship with the rotation angle θ. Once this relationship is obtained, the deviation s of the centroid of the torsion pendulum from the axis of rotation can be obtained. When the offset s = 0 is adjusted, the centroid of the torsion pendulum is concentric with the axis of rotation. At this time, the torsion pendulum is least affected by the environmental common-mode noise, so that the measured micro-thrust reaches the accuracy requirement of the micro-newton level.

[0060] II. Design principle of the centroid control device: First, the inclination angle of the torsion pendulum ≠ the rotation angle θ of the torsion pendulum. Two conditions are required for the torsion pendulum to rotate. The centroid deviates from the center point and is subject to the gravity component. As shown in the left figure of Figure 2 , when both of these two conditions, namely the generation of the gravity component and the deviation of the centroid of the torsion pendulum, are met, the torsion pendulum will generate the rotation angle θ. Assume that the centroid of the torsion pendulum does not deviate. At this time, any given inclination angle of the torsion pendulum Even if the inclination angle of the torsion pendulum is degrees, which is close to 90 degrees. Even so, the torsion pendulum will not generate the rotation angle θ. Because at this time the centroid position does not deviate, the gravitational forces on both sides of the pivot axis of the torsion pendulum are the same, so the torsion pendulum on both sides of the pivot axis remains in a horizontal posture unchanged, that is, the rotation angle θ is zero. Second, adjust the centroid of the torsion pendulum through the centroid adjustment mechanism; Third, the adjustment of the centroid position of the torsion pendulum is not completed in one go, but several times. However, after each adjustment, the rotation angle θ of the torsion pendulum will become smaller and smaller; Fourth, each adjustment of the centroid position requires two steps. The first step is to clear the previous inclination angle and the rotation angle θ of the torsion pendulum; The second step is that the PID controller gives a new set inclination angle This set inclination angle can be the same as or different from the inclination angle set in the previous time . The purpose of setting the inclination angle of the torsion pendulum is to generate the gravity component. The magnitude of this gravity component determines the sensitivity of the torsion pendulum to rotate. However, the sensitivity of the torsion pendulum is only one aspect. Only when the centroid of the torsion pendulum deviates, this gravity component will act on the rotation of the torsion pendulum. The deviation degree of the centroid of the torsion pendulum determines the magnitude of the rotation angle θ of the torsion pendulum. The smaller the deviation degree of the centroid of the torsion pendulum, the smaller the rotation angle θ. The magnitude of the inclination angle of the torsion pendulum determines the sensitivity of the torsion pendulum. The sensitivity is related to the gravity component. The greater the gravity component, the stronger the sensitivity of the torsion pendulum. Therefore, the inclination angle of the torsion pendulum cannot be too small or too large. As long as it can meet the sensitivity of the torsion pendulum. If the inclination angle of the torsion pendulum is too small, the sensitivity of the torsion pendulum will be poor.

[0061] Based on the above principles, the present invention designs a centroid precision control device applicable to a micro-thrust measurement device, as shown in Figure 1As shown in the figure, the centroid precision control device includes: a double-bottom torsion pendulum base arranged in a vacuum chamber, a support frame, a pivot, and a torsion pendulum are provided on the base, the support frame supports the torsion pendulum through the pivot, a torsion pendulum inclination control mechanism arranged on the driving side of the double-bottom torsion pendulum base, and a centroid position adjustment mechanism arranged on the double-bottom torsion pendulum base and connected to one end of the torsion pendulum; a controller arranged outside the vacuum chamber, the input ends of the controller are respectively connected to the torsion pendulum and the displacement sensors of the torsion pendulum inclination control mechanism, and the output ends are respectively connected to the motor of the centroid position adjustment mechanism and the piezoelectric actuator of the torsion pendulum inclination control mechanism; the torsion pendulum inclination control mechanism is used to control the inclination angle of the torsion pendulum, and this inclination angle is the inclination angle of the cross-section of the torsion pendulum along the direction of gravity; the centroid position adjustment mechanism is used to adjust the centroid position of the torsion pendulum; the controller is used to control the torsion pendulum inclination control mechanism and the centroid position adjustment mechanism.

[0062] As Figure 1 , 7 shown in the figure, the controller is provided with: a centroid position offset calculation module for calculating the deviation position of the centroid of the torsion pendulum, a torsion pendulum inclination calculation module for calculating the inclination angle of the torsion pendulum, and a PID controller for controlling the inclination angle of the torsion pendulum;

[0063] As Figure 1 shown in the figure, the centroid position offset calculation module of the controller is used to calculate the deviation s between the centroid of the torsion pendulum and the rotation axis, its input ends are respectively connected to the torsion pendulum and the torsion pendulum inclination calculation module, obtains the current rotation angle θ of the torsion pendulum from the torsion pendulum, and obtains the actual torsion pendulum inclination angle from the torsion pendulum inclination calculation module, and the output end is connected to the centroid position adjustment mechanism, and sends a motor drive command to the centroid position adjustment module;

[0064] As Figure 1 shown in the figure, the torsion pendulum inclination calculation module of the controller is used to calculate the inclination angle of the torsion pendulum its input end is connected to the high-precision capacitive displacement sensor 1 and the high-precision capacitive displacement sensor 2 of the torsion pendulum inclination control mechanism, and obtains the actual torsion pendulum inclination angle between the upper bottom plate and the lower bottom plate of the double-bottom torsion pendulum base through h1 and h2 of the respective measuring points of the high-precision capacitive displacement sensor 1 and the high-precision capacitive displacement sensor 2 the output end of the torsion pendulum inclination calculation module is connected to the PID controller, and outputs the actual torsion pendulum inclination angle to the PID controller

[0065] As Figure 1 shown in the figure, the PID controller of the controller is used to output an instruction for the axial displacement of the piezoelectric actuator to the piezoelectric actuator; its input end is connected to the torsion pendulum inclination calculation module, and obtains the actual torsion pendulum inclination angle from the torsion pendulum inclination calculation module compares it with the set inclination angle built in the controller Compare; the output end of the PID controller is connected to the piezoelectric actuator of the torsion pendulum inclination control module to control the voltage output by the piezoelectric actuator to the upper plate of the double-bottom torsion pendulum base.

[0066] As Figure 4 shown, the torsion pendulum inclination control mechanism includes: a piezoelectric actuator arranged on the driving side of the double-bottom torsion pendulum base, a pivot arranged on the rotational freedom side of the double-bottom torsion pendulum base and connecting the upper plate and the lower plate through the pivot, and high-precision capacitance displacement sensors 1 and 2 arranged on the bottom plate of the double-bottom torsion pendulum base and close to both ends of the upper plate; the piezoelectric actuator serves as a displacement source. When the piezoelectric actuator outputs an axial displacement voltage, the upper plate will be tilted around the pivot. The high-precision capacitance displacement sensors 1 and 2 are symmetrically arranged at both ends of the double-bottom torsion pendulum base. Among them, the high-precision capacitance displacement sensor 1 is arranged at one end close to the driving side, and the high-precision capacitance displacement sensor 2 is arranged at one end close to the pivot; when the piezoelectric actuator outputs an axial displacement, the high-precision capacitance displacement sensors 1 and 2 respectively measure the distances h1 and h2 between the upper plate and the lower plate, and send h1 and h2 to the torsion calculation module of the controller. The torsion calculation module obtains the inclination angle between the upper plate and the lower plate through h1 and h2.

[0067] As Figure 5 shown, the centroid position adjustment mechanism 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 along the torsion pendulum axis and on one side of the torsion pendulum, and the other end passes through the central hole of the counterweight mass block and is threadedly connected to the central hole of the counterweight mass block; guide through holes are symmetrically opened on both sides of the counterweight mass block, and two smaller-diameter guide shafts pass through the guide holes and are fixed on the motor; the central part of the counterweight mass block is prefabricated with internal threads to form a precise fit with the screw; when the motor rotates, the two guide shafts will drive the counterweight mass block to rotate on the fine-thread screw; the fine-thread screw converts the angular displacement of the counterweight mass block into an axial linear displacement, so that the counterweight mass block moves along the torsion pendulum axis, thereby changing the centroid distribution of the torsion pendulum and completing a single adjustment of the deviation of the centroid position.

[0068] The torsion pendulum inclination calculation module obtains the inclination angle between the upper plate and the lower plate through h1 and h2. Specifically as follows: Set the distance between the two measuring points of the high-precision capacitance displacement sensors 1 and 2 as L, and set the clearances on the high and low sides in the inclined state as h1 and h2 respectively. The inclination angle calculation formula:

[0069]

[0070] Thus, the inclination angle of the torsion pendulum can be accurately measured.

[0071] The centroid position deviation calculation module calculates the deviation s between the centroid of the torsion pendulum and the rotation axis as follows:

[0072] When the centroid of the torsion pendulum deviates from the rotation axis, the torsion pendulum will rotate under the action of the moment generated by the gravity component in the inclined state. Let the total mass of the torsion pendulum be M, the pivot stiffness coefficient be k, and the distance between the centroid and the rotation axis be s. If the inclination angle of the upper base plate around the pivot increases After that, if the rotation angle change of the torsion pendulum is θ, the mechanical equilibrium equation of the moment of the gravity component and the restoring moment of the pivot is

[0073]

[0074] where g is the acceleration due to gravity. Under the small angle assumption (when θ is small enough, cosθ = 1), the deviation between the centroid of the torsion pendulum and the rotation axis can be obtained as

[0075]

[0076] In this equation, θ is accurately measured through the angular displacement measurement function of the torsion pendulum itself, k is obtained by calibrating the torsion pendulum, and M can be directly measured with a balance. Therefore, the key to calculating the centroid deviation position is to output an axial displacement through the piezoelectric actuator to make the upper base plate of the double-bottom torsion pendulum base generate a controllable inclination angle around the pivot

[0077] A centroid precision control method applicable to a micro-thrust measurement device, as Figure 6 shown, is characterized by including the following steps:

[0078] Step 1: Determine that the current centroid offset s belongs to the fine-tuning range;

[0079] Step 2: The torsion pendulum inclination control module controls the inclination angle of the torsion pendulum for control;

[0080] including the following processes:

[0081] 1) The input end of the PID controller receives the set inclination angle and the actual inclination angle

[0082] 2) Determine whether there is a difference between the set inclination angle and the actual inclination angle If not, go to process 7), if so, continue with process 3);

[0083] 3) The PID controller outputs a voltage to the piezoelectric actuator. When the piezoelectric actuator outputs an axial displacement, the upper base plate of the double-bottom torsion pendulum base generates an inclination angle around the pivot

[0084] 4) The high-precision capacitance displacement sensor 1 and the high-precision capacitance displacement sensor 2 feedback h1 and h2 at their respective measuring point positions to the inclination calculation module of the controller;

[0085] 5) The inclination calculation module feedbacks the actual inclination to the input end of the PID controller;

[0086] 6) The PID controller calculates the difference according to the set inclination at the input end and the actual inclination and returns to process 2)

[0087] Step Three: The centroid position deviation calculation module calculates the centroid position offset;

[0088] It includes the following links:

[0089] A. Establish the relationship between the inclination generated by the piezoelectric actuator and the change θ of the torsional pendulum rotation angle;

[0090]

[0091] B. Obtain the deviation amount S between the centroid of the torsional pendulum and the rotation axis according to the relationship between the

[0092]

[0093] C. Send the deviation amount s to the centroid position adjustment module.

[0094] Step Four: Determine whether the current centroid position offset s is less than 10 um. If it is, the fine adjustment is completed and go to Step Six. If not, continue with Step Five;

[0095] Step Five: The centroid position adjustment module adjusts the centroid position and returns to Step Two;

[0096] The specific links are as follows:

[0097] 1) The centroid position offset calculation module of the controller sends a driving instruction to the motor of the centroid position adjustment module according to the offset;

[0098] 2) When the motor rotates, the guide shaft will drive the mass block to rotate to complete a single adjustment of the centroid position deviation;

[0099] Step Six: The fine adjustment ends.

[0100] 7) End.

Claims

1. A center of mass control device suitable for micro-thrust calibration torsion pendulum, characterized in that: The center of mass precision control device includes: a double-bottom plate torsion pendulum base arranged in a vacuum tank, the base is provided with a support frame, a pivot, and a torsion pendulum, and the support frame supports the torsion pendulum through the pivot; a torsion pendulum inclination control mechanism arranged on the driving side of the double-bottom plate torsion pendulum base, and a center of mass position adjustment mechanism arranged on the double-bottom plate torsion pendulum base and connected to one end of the torsion pendulum; a controller arranged outside the vacuum tank, the input end of the controller is respectively connected to the torsion pendulum and the displacement sensor of the torsion pendulum inclination control mechanism, and the output end is respectively connected to the motor of the center of mass position adjustment mechanism and the piezoelectric actuator of the torsion pendulum inclination control mechanism; the torsion pendulum inclination control mechanism is used to control the torsion pendulum inclination, which is the inclination of the torsion pendulum cross section along the direction of gravity; the center of mass position adjustment mechanism is used to adjust the center of mass position of the torsion pendulum; the controller is used to control the torsion pendulum inclination control mechanism and the center of mass position adjustment mechanism.

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

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

4. A mass center control device suitable for micro-thrust calibration torsion pendulum according to claim 1, characterized in that: The center of mass position adjustment mechanism includes: a fine-pitch screw, a counterweight mass block and a motor; the motor is coaxial with the counterweight mass block; one end of the fine-pitch screw is fixed on one side along the torsion pendulum axis and the torsion pendulum, and the other end passes through the center hole of the counterweight mass block and is threadedly connected to the center hole of the counterweight mass block; guide through holes are symmetrically provided on both sides of the counterweight mass block, and two guide shafts with smaller diameters pass through the guide holes and are fixed to the motor; the center of the counterweight mass block is prefabricated with an internal thread to form a precise fit with the screw; when the motor rotates, the two guide shafts will drive the counterweight mass block to rotate on the fine-pitch screw; the fine-pitch screw converts the angular displacement of the counterweight mass block into an axial linear displacement, so that the counterweight mass block moves along the axial direction of the torsion pendulum, thereby changing the center of mass distribution of the torsion pendulum and completing a single adjustment of the center of mass position deviation.

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

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

7. A method for precise center of mass control of a micro-thrust measuring device based on the center of mass control device for micro-thrust calibration torsion pendulum as claimed in any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1: Determine whether the current center of mass offset s is within the fine-tuning range; Step 2: The torsion and sway angle control module controls the torsion and sway angle To exercise control; Step 3: The centroid position deviation calculation module calculates the centroid position offset; Step 4: Determine whether the current centroid position offset s is less than 10um. If yes, complete fine adjustment and proceed to step 6. If not, proceed to step 5. Step 5: The centroid position adjustment module adjusts the centroid position and returns to step 2; Step 6: Fine tuning is completed.

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

9. A method for controlling the center of mass of a micro-thrust calibration torsion pendulum according to claim 8, characterized in that: The calculation of the mass center position offset s in step 3 includes the following steps: A. Establish the inclination angle generated by the piezoelectric actuator and the relationship between the pendulum rotation angle change θ; B. According to the The relationship between θ and the center of mass of the torsion pendulum and the axis of rotation is obtained by C. Send the deviation s to the center of mass position adjustment module.

10. The method for controlling the center of mass of a micro-thrust calibration torsion pendulum according to claim 7, characterized in that: The centroid position adjustment module in step 5 performs centroid position adjustment, and the specific steps are as follows: 1) The center of mass position offset calculation module of the controller sends a driving instruction to the motor of the center of mass position adjustment module according to the offset; 2) When the motor rotates, the guide shaft will drive the mass block to rotate, completing a single adjustment of the center of mass position deviation.

Images