A micro-newton level force value measuring device and method based on a double capacitor structure

Abstract

The application discloses a kind of micro-newton level force value measuring device and method based on double capacitor structure, the device includes flexible pivot structure, flexible pivot structure is by upper, lower, left, right 4 connecting rods and is connected by 4 flexible hinges, load tray is installed in the upper end of right connecting rod, for the loading and unloading of force value to be measured, the inner electrode of main capacitor is installed in the lower end of right connecting rod, the inner electrode of auxiliary capacitor is installed in the lower end of left connecting rod, and differential laser interferometer is used to measure the relative displacement amount of inner electrode and outer electrode of main capacitor;The measurement light of two laser range finders is reflected by two plane mirrors respectively, the absolute distance of two plane mirrors and two laser range finders can be measured, and the point of two absolute distances is equal as initial zero of capacitance gradient and force value measurement.The application can realize the accurate measurement of capacitance gradient near initial zero, ensure the consistency of capacitance gradient measurement path and force value measurement path, and improve the measurement accuracy of micro-newton level force value.

Description

Technical Field

[0001] This invention belongs to the field of micro-Newton force measurement, specifically relating to a micro-Newton force measurement device and method based on a dual-capacitor structure. Background Technology

[0002] Fields such as space payload attitude control, micro-cantilever probe contact force measurement, and MEMS (Micro-Electro-Mechanical Systems) micro-nano measurement and control technologies all place high demands on the measurement range and accuracy of micro-Newton-level forces. Existing micro-Newton-level force measurement devices employ electrostatic force reproduction, measuring the capacitance gradient and applied voltage of a capacitor by fixing the inner electrode and reciprocating the outer electrode along the axis under the drive of a precision displacement stage, thereby calculating the minute force value. However, when measuring the capacitance gradient, the measurement path is inconsistent with the force measurement path, resulting in a discrepancy between the zero point of the capacitance gradient measurement and the zero point of the minute force measurement. During measurement, it is necessary to establish a curve fitting of the experimental capacitance gradient value based on the relationship between the unit electrostatic force and the unit weight of the weight, and extend it to the zero point. This means that the capacitance gradient is not directly measured, ultimately affecting the accuracy of micro-Newton-level force measurement. Summary of the Invention

[0003] The purpose of this invention is to address the problem that existing micro-Newton force measurement devices cannot directly measure the capacitance gradient at the measurement zero point, resulting in excessive capacitance gradient measurement errors and low accuracy of electrostatic force reproduction. This invention provides a micro-Newton force measurement device and method based on a dual-capacitor structure, which can accurately measure the capacitance gradient near the initial zero point, ensure the consistency between the capacitance gradient measurement path and the force measurement path, and improve the accuracy of micro-Newton force measurement.

[0004] One aspect of the present invention provides a micro-Newton force measurement device based on a dual-capacitor structure, comprising a flexible pivot structure, a support base, a load tray, a main capacitor, an auxiliary capacitor, a level adjustment block, two horizontal position adjustment stages, two plane mirrors, two laser rangefinders, a support platform, and a differential laser interferometer;

[0005] The flexible pivot structure consists of four links (upper, lower, left, and right) connected by four flexible hinges. At the symmetrical center of the upper and lower links, one flexible hinge fixes the flexible pivot structure to the support base. The flexible pivot structure is quadrilateral and can swing around the geometric center of the structure.

[0006] The load tray is installed at the upper end of the right connecting rod for loading and unloading the force to be measured. The main capacitor and the auxiliary capacitor have the same structure, including an inner electrode and an outer electrode respectively. The inner electrode of the main capacitor is installed at the lower end of the right connecting rod, and the inner electrode of the auxiliary capacitor is installed at the lower end of the left connecting rod. The horizontal adjustment block is installed at the lateral position of the left connecting rod for adjusting the levelness of the flexible pivot structure.

[0007] Two horizontal position adjustment stages are connected to the external electrodes of the main capacitor and the auxiliary capacitor, respectively, and are used to adjust the positions of the external electrodes of the main capacitor and the auxiliary capacitor in the horizontal plane. The differential laser interferometer is used to measure the relative displacement of the inner and outer electrodes of the main capacitor.

[0008] Two plane mirrors are symmetrically fixed on the lower surface of the lower connecting rod. The normals of the two plane mirrors are equidistant from the horizontal distance of the support base. Two laser rangefinders are symmetrically mounted on the support platform, corresponding to the two plane mirrors. The measuring light from the two laser rangefinders is reflected by the two plane mirrors respectively, which can measure the absolute distance between the two plane mirrors and the two laser rangefinders. The two points with equal absolute distances are used as the initial zero points for the measurement of capacitance gradient and force value.

[0009] Another aspect of the present invention provides a method for measuring micro-Newton force based on a dual-capacitor structure, wherein the micro-Newton force is measured using the aforementioned apparatus, and the method includes:

[0010] Step S1: Adjust the inner and outer electrodes of the main capacitor and the auxiliary capacitor to be coaxial.

[0011] Step S2: Adjust the leveling block of the flexible pivot structure so that the leveling error of the flexible pivot structure is less than 10 mrad;

[0012] Step S3: Zero the readings of the two laser rangefinders and set the point where the difference between the readings of the two laser rangefinders is equal to zero as the initial zero point for capacitance gradient and force value measurement;

[0013] Step S4: Measure the capacitance values ​​of the inner and outer electrodes of the main capacitor. C ;

[0014] Step S5: Measure the vertical displacement values ​​of the inner and outer electrodes of the main capacitor using a differential laser interferometer. z ;

[0015] Step S6: Apply voltage to the inner and outer electrodes of the auxiliary capacitor to generate an electrostatic force along the axis of the auxiliary capacitor, which drives the inner electrode of the auxiliary capacitor to move up and down, thereby causing the inner electrode of the main capacitor to move up and down. At the same time, collect the capacitance value and displacement value of the main capacitor and obtain the capacitance gradient of the initial zero position by fitting.

[0016] Step S7: Apply voltage to the inner and outer electrodes of the main capacitor. This generates electrostatic force in the main capacitor, driving the inner electrode to move. The applied voltage value is changed using PID control to drive the inner electrode back to its initial zero position. The applied voltage at this point is... V U The generated electrostatic force is F e1 ;

[0017] Step S8: Apply the micro-Newton force to be measured vertically to the tray. Under the guidance of the flexible pivot structure, the inner electrode of the main capacitor moves vertically, increasing the relative displacement between the inner and outer electrodes. The applied voltage is then changed via PID control to restore the relative vertical position of the inner and outer electrodes to their initial zero position. The applied voltage at this point is... V L The generated electrostatic force is F e2 ;

[0018] Step S9: Calculate the micro-Newton force value to be measured as follows. F m :

[0019] .

[0020] According to the above-described aspects of the present invention, the micro-Newton force measurement device and method based on a dual-capacitor structure can achieve accurate measurement of the capacitance gradient near the initial zero position, ensure the consistency between the capacitance gradient measurement path and the force measurement path, and improve the measurement accuracy of the micro-Newton force. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort:

[0022] Figure 1 This is a schematic diagram of a micro-Newton force measurement device based on a dual-capacitor structure according to an embodiment of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0024] One embodiment of the present invention provides a micro-Newton force measurement device based on a dual-capacitor structure, such as... Figure 1 As shown, the micro-Newton force measurement device based on a dual-capacitor structure in this embodiment of the invention includes a flexible pivot structure, a support base 16, a load tray 1, a main capacitor, an auxiliary capacitor, two horizontal position adjustment platforms, two plane mirrors, two laser rangefinders, a high-precision level, a level adjustment block 17, a differential laser interferometer 11, and a plane reflector 10.

[0025] The main capacitor includes, from the inside out, a first inner electrode 7, a first outer electrode 8, and a first protective electrode 9. The auxiliary capacitor includes, from the inside out, a second inner electrode 18, a second outer electrode 19, and a second protective electrode 20.

[0026] The flexible pivot structure consists of four links connected by four flexible hinges. Figure 1 In this embodiment, the four links are upper link 2, right link 3, lower link 4, and left link 5. At the symmetrical center of upper link 2 and lower link 4, a flexible pivot structure is fixed to the support base 16 by a flexible hinge 6. The entire flexible pivot structure is quadrilateral and can swing slightly around the geometric center of the structure.

[0027] In this embodiment, the flexible hinge 6 is a spring-type flexible hinge. The spring-type flexible hinge 6 can swing within a range of ±10° through its internal elastic structure, thereby achieving a small-amplitude swing of the flexible pivot structure. Through holes are machined at the symmetrical center positions of the upper connecting rod 2 and the lower connecting rod 4, as well as on the support base 16. The diameter of the through holes is equal to the diameter of the spring-type flexible hinge 6. By installing the spring-type flexible hinge 6 in the through holes, the flexible pivot structure is fixed to the support base 16. Alternatively, an integrally machined elliptical flexible hinge can be used instead of the spring-type flexible hinge.

[0028] A load tray 1 is installed at the upper end of the right connecting rod 3 for loading and unloading the force to be measured. The inner electrode 7 of the main capacitor is installed at the lower end of the right connecting rod 3. A horizontal adjustment block 17 is installed at the lateral position of the left connecting rod 5 as a counterweight to adjust the levelness of the flexible pivot structure. The horizontal adjustment block 17 includes a threaded rod and a mass block with a threaded hole. One end of the threaded rod is fixed to the left connecting rod 5, and the other end is equipped with the mass block. By rotating the mass block, its horizontal position on the threaded rod can be adjusted, thereby adjusting the overall levelness of the flexible pivot structure. The inner electrode 18 of the auxiliary capacitor is installed at the lower end of the left connecting rod 5. Before the experiment, the levelness of the flexible pivot structure is measured using a high-precision level. The levelness of the flexible pivot structure is adjusted using the level adjustment block 17. The position where the levelness of the flexible pivot structure is less than 10 mrad is set as the initial zero point of the micro-Newton force measurement device, which is also the initial zero point for subsequent capacitance gradient measurement and force measurement.

[0029] Two plane mirrors (first plane mirror 13 and second plane mirror 15) are fixed at the center of symmetry on the lower surface of the lower connecting rod 4. The normals of the two plane mirrors are both 13 and 15 at a horizontal distance from the support base 16. l 2. Two laser rangefinders (first laser rangefinder 12 and second laser rangefinder 14) are mounted on the support platform 23 corresponding to two plane mirrors. The measuring optical paths are reflected by the two plane mirrors, allowing for the measurement of the absolute distances between the two plane mirrors and the two laser rangefinders. During the experiment, the two plane mirrors and two laser rangefinders enable precise positioning of the zero points for capacitance gradient measurement and force measurement, reducing measurement errors at the micro-Newton level for capacitance gradient and force.

[0030] The first external electrode 8 and the first protective electrode 9 of the main capacitor are fixed on the first horizontal position adjustment platform 21, and the second external electrode 19 and the second protective electrode 20 of the auxiliary capacitor are fixed on the second horizontal position adjustment platform 22. The first protective electrode 9 is mainly used to protect the first external electrode 8, and the second protective electrode 20 is mainly used to protect the second external electrode 19 to prevent electromagnetic interference during the experiment. The first horizontal position adjustment platform 21 and the second horizontal position adjustment platform 22 are mainly used to adjust the position of the external electrodes of the main capacitor and the auxiliary capacitor in the horizontal plane, thereby adjusting the relative position of the inner and outer electrodes of the main capacitor and the auxiliary capacitor to prevent the inner and outer electrodes from colliding during the movement.

[0031] The inner surfaces of the inner and outer electrodes (first inner electrode 7 and first outer electrode 8) of the main capacitor are designed with high reflectivity coatings. Two circular holes of the same diameter are machined on the support platform 23. The two measuring optical paths of the differential laser interferometer 11 are incident on the inner surfaces of the inner and outer electrodes of the main capacitor through the circular holes via the plane mirror 10. When the inner and outer electrodes move relative to each other, the relative displacement of the inner and outer electrodes can be calculated by the two measuring optical path signals of the differential laser interferometer 11. When measuring micro-Newton force values, after the force to be measured is loaded and unloaded, the loading voltage of the main capacitor is controlled by PID to keep the inner and outer electrodes at the initial zero position, thereby improving the measurement accuracy of micro-Newton force values.

[0032] In one embodiment, the main capacitor and the auxiliary capacitor are cylindrical capacitors. Planar capacitors can also be used instead of cylindrical capacitors, which can also achieve the same result of driving the main capacitor to move along the axis and measuring the capacitance gradient at the initial zero position.

[0033] The operation steps of the micro-Newton force measurement device based on a dual-capacitor structure according to this invention are as follows:

[0034] Step S1: Adjust the inner and outer electrodes of the two sets of capacitors to a coaxial state using the horizontal position adjustment platform for the outer electrodes of the main capacitor and the auxiliary capacitor.

[0035] Step S2: Adjust the level adjustment block 17 of the flexible pivot structure using a high-precision level to make the level error of the flexible pivot structure less than 10mrad;

[0036] Step S3: Record the readings of the left and right laser rangefinders as Δ1 and Δ2 respectively. When the level of the flexible pivot structure is adjusted to the ideal state, reset the readings of the two laser rangefinders to zero at the same time. In subsequent steps, make the readings of the two laser rangefinders equal, that is, the point where the reading difference (Δ1-Δ2) is equal to zero is taken as the initial zero point for the capacitance gradient and force value measurement.

[0037] Step S4: Connect the capacitance bridge to the inner and outer electrodes of the main capacitor, and measure the capacitance values ​​of the inner and outer electrodes of the main capacitor. C ;

[0038] Step S5: Adjust the incident and reflected light paths of the differential laser interferometer to project the beams onto the inner surfaces of the inner and outer electrodes of the main capacitor, respectively, to achieve vertical displacement values ​​of the inner and outer electrodes. z Measurement;

[0039] Step S6: Connect the output terminal of the DC voltage source to the inner and outer electrodes of the auxiliary capacitor. Changing the DC voltage applied to the auxiliary capacitor can cause the auxiliary capacitor to generate an electrostatic force along the axis, driving the inner electrode of the auxiliary capacitor to move up and down. Due to the central symmetry design of the quadrilateral of the flexible pivot structure, the inner electrode of the main capacitor can also move up and down. By precisely controlling the applied voltage value, the main capacitor can be driven to move within the range of ±200μm from the initial zero position. At the same time, the capacitance value and displacement value of the main capacitor are collected. The capacitance gradient of the initial zero position can be obtained by fitting.

[0040] Step S7: Connect DC voltage source #2 to the inner and outer electrodes of the main capacitor to generate electrostatic force in the main capacitor to drive the inner electrode to move. Use a PID control program to change the voltage value to drive the inner electrode to its initial zero position, and record the applied voltage at this time. V U The generated electrostatic force is F e1 ,

[0041] Step S8: Apply the force to be measured vertically to the tray. Under the guidance of the flexible pivot structure, the inner electrode of the main capacitor will move vertically, increasing the relative displacement between the inner and outer electrodes. The PID control program changes the potential difference between the inner and outer electrodes of the main capacitor, restoring their vertical relative position to its initial zero position. Let the voltage across the main capacitor at this time be... V L The generated electrostatic force is F e2 ;

[0042] Step S9: The above operation process can be used to measure the micro-Newton force value. F m The electrostatic force converted to the main capacitor can be expressed by formula (1):

[0043] (1)

[0044] As described above, the micro-Newton force measurement device based on a dual-capacitor structure in this embodiment of the invention adopts a single-degree-of-freedom structural design. After the force to be measured is applied, it can only displace along the direction of gravity. By using flexible hinges to construct a flexible pivot structure, the overall load-bearing capacity of the structure can be improved while meeting the single-degree-of-freedom design requirements. The flexible pivot structure adopts a centrally symmetrical design, with four links connected by flexible hinges. A pair of capacitors, namely the main capacitor and the auxiliary capacitor, are installed at the lower ends of the left and right links. Laser rangefinders are installed at symmetrical positions on the left and right sides of the flexible pivot structure to measure the relative position deviation of the flexible pivot structure. When measuring the capacitance gradient, the auxiliary capacitor drives the inner electrode of the main capacitor to move along the axis. When measuring the micro-Newton force, a PID program is used to control the applied voltage of the main capacitor to achieve the measurement of the micro-Newton force. During the above measurement process, the measurement data of the relative position deviation of the flexible pivot structure by the laser rangefinder is used to confirm whether the overall structure is in its initial zero position.

[0045] In summary, the micro-Newton force measurement device based on a dual-capacitor structure of this invention addresses the problem in existing micro-Newton force measurement devices where the capacitance gradient is measured by fixing the inner electrode and having the outer electrode reciprocate along the axis under the drive of a precision displacement stage. This results in an inconsistency between the capacitance gradient measurement path and the force measurement path, making it impossible to measure the capacitance gradient at the initial zero point and introducing measurement errors during force measurement. The dual-capacitor structure design installs capacitors of the same structure at symmetrical positions at the center of the flexible pivot structure. By applying a voltage to drive the inner electrode of the auxiliary capacitor, the inner electrode of the main capacitor moves along the axis, achieving accurate measurement of the capacitance gradient near the initial zero point. This process does not affect the stiffness of the flexible pivot structure, ensuring that the capacitance gradient measurement path is consistent with the movement path for micro-Newton force measurement. Furthermore, by installing a laser rangefinder at symmetrical positions on the flexible pivot structure, the zero points for both capacitance gradient and force measurement are accurately located, reducing measurement errors for both the capacitance gradient and micro-Newton force.

[0046] The micro-Newton force measurement device based on the dual capacitor structure of the present invention has at least the following advantages: (1) the coaxiality of the inner and outer electrode axes of the capacitor and the stiffness of the flexible pivot structure along the vertical direction are not affected during the measurement process, ensuring the consistency between the capacitance gradient measurement path and the force measurement path; (2) the initial zero position is fixed during the measurement process and can be adjusted non-contactly. When there is a deviation in the initial zero position, the position of the initial zero position can be adjusted by applying and unloading voltage on the auxiliary capacitor.

[0047] The micro-Newton force measurement device of this invention reproduces the force value to be measured by electrostatic force, which can trace the force value to the quantized voltage, displacement and capacitance values, suppress the uncertainty of force measurement and improve the measurement accuracy of micro-Newton force values.

[0048] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A micro-Newton force measurement device based on a dual-capacitor structure, characterized in that, It includes a flexible pivot structure, a support base, a load tray, a main capacitor, an auxiliary capacitor, a leveling adjustment block, two leveling adjustment platforms, two plane mirrors, two laser rangefinders, a support platform, and a differential laser interferometer; The flexible pivot structure consists of four links (upper, lower, left, and right) connected by four flexible hinges. At the symmetrical center of the upper and lower links, one flexible hinge fixes the flexible pivot structure to the support base. The flexible pivot structure is quadrilateral and can swing around the geometric center of the structure. The load tray is installed at the upper end of the right connecting rod for loading and unloading the force to be measured. The main capacitor and the auxiliary capacitor have the same structure, including an inner electrode and an outer electrode respectively. The inner electrode of the main capacitor is installed at the lower end of the right connecting rod, and the inner electrode of the auxiliary capacitor is installed at the lower end of the left connecting rod. The horizontal adjustment block is installed at the lateral position of the left connecting rod for adjusting the levelness of the flexible pivot structure. Two horizontal position adjustment stages are connected to the external electrodes of the main capacitor and the auxiliary capacitor, respectively, and are used to adjust the positions of the external electrodes of the main capacitor and the auxiliary capacitor in the horizontal plane. The differential laser interferometer is used to measure the relative displacement of the inner and outer electrodes of the main capacitor. Two plane mirrors are symmetrically fixed on the lower surface of the lower connecting rod. The normals of the two plane mirrors are equidistant from the horizontal distance of the support base. Two laser rangefinders are symmetrically mounted on the support platform, corresponding to the two plane mirrors. The measuring light from the two laser rangefinders is reflected by the two plane mirrors respectively, which can measure the absolute distance between the two plane mirrors and the two laser rangefinders. The two points with equal absolute distances are used as the initial zero points for the measurement of capacitance gradient and force value.

2. The apparatus as claimed in claim 1, characterized in that, The flexible hinge is a spring-type flexible hinge, which can swing within a range of ±10° through its internal elastic structure.

3. The apparatus as described in claim 1 or 2, characterized in that, Through holes are machined at the symmetrical center positions of the upper and lower connecting rods and on the support base. The diameter of the through holes is equal to the diameter of the spring-type flexible hinge. The flexible pivot structure is fixed to the support base by installing the spring-type flexible hinge in the through holes.

4. The apparatus as described in claim 1 or 2, characterized in that, The main capacitor and the auxiliary capacitor also include protective electrodes for protecting the external electrodes. The protective electrodes of the main capacitor and the auxiliary capacitor are respectively fixed on two horizontal adjustment platforms.

5. The apparatus as described in claim 1 or 2, characterized in that, It also includes a high-precision level, which is used in conjunction with a leveling block to measure the levelness of a flexible pivot structure.

6. The apparatus as claimed in claim 1 or 2, characterized in that, The leveling block includes a threaded rod and a mass block with a threaded hole. One end of the threaded rod is fixed to the left connecting rod, and the other end is equipped with the mass block. By rotating the mass block, its horizontal position on the threaded rod can be adjusted, thereby adjusting the levelness of the flexible pivot structure.

7. The apparatus as described in claim 1 or 2, characterized in that, It also includes a plane mirror, and the inner surfaces of the inner and outer electrodes of the main capacitor are coated with a high reflectivity coating. Two circular holes of the same diameter are machined on the support platform. The two beams of measurement light from the differential laser interferometer are incident on the inner surfaces of the inner and outer electrodes of the main capacitor through the plane mirror and the circular holes, thereby measuring the relative displacement of the inner and outer electrodes.

8. A method for measuring micro-Newton-level force based on a dual-capacitor structure, characterized in that, Measuring microNewton-level force using the apparatus of any one of claims 1-7, the method comprising: Step S1: Adjust the inner and outer electrodes of the main capacitor and the auxiliary capacitor to be coaxial. Step S2: Adjust the leveling block of the flexible pivot structure so that the leveling error of the flexible pivot structure is less than 10 mrad; Step S3: Zero the readings of the two laser rangefinders and set the point where the difference between the readings of the two laser rangefinders is equal to zero as the initial zero point for capacitance gradient and force value measurement; Step S4: Measure the capacitance values ​​of the inner and outer electrodes of the main capacitor. C ; Step S5: Measure the vertical displacement values ​​of the inner and outer electrodes of the main capacitor using a differential laser interferometer. z ; Step S6: Apply voltage to the inner and outer electrodes of the auxiliary capacitor to generate an electrostatic force along the axis of the auxiliary capacitor, which drives the inner electrode of the auxiliary capacitor to move up and down, thereby causing the inner electrode of the main capacitor to move up and down. At the same time, collect the capacitance value and displacement value of the main capacitor and obtain the capacitance gradient of the initial zero position by fitting. Step S7: Apply voltage to the inner and outer electrodes of the main capacitor. This generates electrostatic force in the main capacitor, driving the inner electrode to move. The applied voltage value is changed using PID control to drive the inner electrode back to its initial zero position. The applied voltage at this point is... V U The generated electrostatic force is F e1 ; Step S8: Apply the micro-Newton force to be measured vertically to the tray. Under the guidance of the flexible pivot structure, the inner electrode of the main capacitor moves vertically, increasing the relative displacement between the inner and outer electrodes. The applied voltage is then changed via PID control to restore the relative vertical position of the inner and outer electrodes to their initial zero position. The applied voltage at this point is... V L The generated electrostatic force is F e2 ; Step S9: Calculate the micro-Newton force value to be measured as follows. F m : 。 9. The method as described in claim 8, characterized in that, In step S6, the main capacitor is moved within a range of ±200μm from its initial zero position by controlling the applied voltage value.

Images