Orthodontic force measuring device and method based on MEMS capacitive sensor

Abstract

The invention discloses an orthodontic force measuring device and method based on an MEMS capacitive sensor, and belongs to the technical field of wireless sensing. The orthodontic force measuring device comprises a normal force sensor and a tangential force sensor, the normal force sensor is used for measuring the normal force of a vertical tooth surface, the tangential force sensor is used for measuring the tangential force of a parallel tooth surface, a capacitor assembly and an induction coil are connected in series to form an LC oscillation circuit, an oscillation signal is generated through excitation of external equipment, and the oscillation signal is transmitted to the external equipment. And the frequency changes along with the capacitance change. Strain caused by orthodontic force is sensed through the polar distance changing type capacitance structure, passive force value detection is achieved in combination with an LC oscillation circuit and near field communication, and the oral cavity environment is adapted by adopting biological compatible material packaging and an anti-abrasion coating. The orthodontic force of vertical and parallel tooth surfaces can be accurately measured, the problem that traditional orthodontics depends on experience evaluation is solved, the orthodontic precision is improved, and the recurrence rate is reduced.

Description

Technical Field

[0001] This invention belongs to the field of wireless sensing technology and relates to an orthodontic force measurement device and method based on MEMS capacitive sensors, and more particularly to a device and measurement method for real-time detection of orthodontic force using MEMS capacitive strain sensors. Background Technology

[0002] In current orthodontic treatment, the assessment of orthodontic force relies on the doctor's experience and static imaging examinations, which can lead to tooth relapse due to improper force application or misjudgment of the endpoint. Traditional measurement methods cannot monitor dynamic orthodontic force in real time, and imported solutions have drawbacks such as high cost and insufficient resistance to interference from the oral environment.

[0003] In the prior art, Chinese invention patent CN117705322A discloses a wireless measurement system for orthodontic force, which uses an LC wireless passive planar capacitive pressure sensor that can be housed between the teeth and the orthodontic appliance. However, this solution uses a single-layer planar capacitor design, which cannot distinguish between the directions of normal and tangential forces, making it difficult to cope with the complex mechanical distribution in the oral cavity. In terms of communication and power supply, the frequency sweep signal transmission of this technology requires continuous excitation from an external device, making operation cumbersome.

[0004] Chinese invention patent CN119818222A discloses a real-time orthodontic pressure detection device integrating MEMS sensors. It achieves multi-point force measurement through a MEMS sensor array and an ASIC chip, employing ultra-wideband wireless transmission. However, this solution relies on active chips and a wireless power module, increasing system size and power consumption, and faces the challenge of miniaturization versus biocompatibility. Furthermore, it lacks a clearly defined corrosion-resistant packaging design for the moist and hot environment of the oral cavity, raising concerns about long-term stability. While its array design can measure three-dimensional force distribution, it requires complex algorithm decoupling, and its accuracy is easily affected by dynamic noise in the oral cavity.

[0005] Based on the aforementioned technical bottlenecks, those skilled in the art have been continuously exploring targeted solutions: How to achieve multi-directional measurement of orthodontic forces through structural innovation? How to optimize passive communication mechanisms to balance miniaturization and signal stability? And how to construct a long-lasting encapsulation system adapted to the oral environment?

[0006] Therefore, there is an urgent need for a miniaturized, high-precision, passive orthodontic force measurement device that is adapted to the oral environment. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention aims to solve the problems of reliance on experience, insufficient accuracy, and weak anti-interference capabilities in current orthodontic force measurement. It provides a MEMS capacitive sensor measurement device and method that enables directional detection, passive communication, and adaptation to the oral environment. This invention includes two configurations: a normal force sensor and a tangential force sensor. It senses the strain caused by the orthodontic force through a variable-gap capacitor structure, and achieves passive force detection by combining an LC oscillation circuit with near-field communication. It employs biocompatible materials for encapsulation and an anti-wear coating to adapt to the oral environment. This invention can accurately measure the orthodontic force perpendicular to and parallel to the tooth surface, solving the problem of reliance on experience-based assessment in traditional orthodontics, improving correction accuracy, and reducing relapse rates.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] An orthodontic force measurement device based on a MEMS capacitive sensor is disclosed. The device comprises an LC oscillation circuit formed by a capacitor assembly and an induction coil connected in series. An oscillation signal is generated by external excitation, and the frequency changes with the capacitance, requiring no internal power supply. The device includes two configurations: a normal force sensor and a tangential force sensor. The normal force sensor measures the normal force perpendicular to the tooth surface, while the tangential force sensor measures the tangential force parallel to the tooth surface. Specifically:

[0010] The normal force sensor includes an induction coil 1, a flexible support mesh 2, a capacitor assembly, a polyimide encapsulation 5, and orthodontic adhesive 6. The capacitor assembly includes an upper capacitor plate 3 and a lower capacitor plate 4. Specifically, both the upper and lower capacitor plates 3 and 4 are square ceramic capacitor plates. The induction coil 1 is arranged on the upper side of the upper capacitor plate 3. The periphery of the upper capacitor plate 3 is connected to the side wall of the lower capacitor plate 4 through the flexible support mesh 2. The induction coil 1, the upper capacitor plate 3, and the lower capacitor plate 4 together form an LC oscillation circuit. The induction coil 1, the flexible support mesh 2, the upper capacitor plate 3, and the lower capacitor plate 4 are all enclosed within a square polyimide encapsulation 5 with an open top. The polyimide encapsulation 5 is entirely enclosed within a square orthodontic adhesive 6 with an open top. The orthodontic adhesive 6 is used to bond the tooth surface and the orthodontic appliance.

[0011] Furthermore, the polyimide package 5 is a box structure with an opening at the top.

[0012] Furthermore, the lower capacitor plate 4 is a box structure with an opening at the top.

[0013] Furthermore, the flexible support mesh 2 is composed of multiple SU-8 photoresist support pillars, with each SU-8 photoresist support pillar having its two ends connected to the outer side of the upper capacitor plate 3 and the inner wall of the lower capacitor plate 4, respectively.

[0014] The tangential force sensor includes a top polyimide encapsulation 7, an induction coil 1, a capacitor assembly, a flexible support 9, a bottom polyimide encapsulation 11, and orthodontic adhesive 6. The capacitor assembly includes an upper capacitor assembly 8 and a lower capacitor assembly 10. Specifically, the upper capacitor assembly 8 consists of eight upper capacitor groups and a square upper fixing plate, with each upper capacitor group fixed to the upper fixing plate. Each upper capacitor group consists of six capacitor plates arranged longitudinally, and the capacitor plates are ceramic capacitor plates. The lower capacitor assembly 10 consists of eight lower capacitor groups and a square lower fixing plate, with each lower capacitor group fixed to the lower fixing plate. Each lower capacitor group consists of six capacitor plates arranged longitudinally, and the capacitor plates are ceramic capacitor plates. The induction coil 1 is arranged on the upper side of the upper capacitor assembly 8. The flexible support 9 is arranged in a vertical column and fixed between the upper capacitor assembly 8 and the lower capacitor assembly 10, and the height of the flexible support 9 is greater than the distance between the upper and lower fixing plates. The induction coil 1, the upper capacitor assembly 8, and the lower capacitor assembly 10 together form an LC oscillation circuit for responding to external excitation signals. The induction coil 1, upper capacitor assembly 8, lower capacitor assembly 10, and flexible support 9 are all encased between the top polyimide encapsulation 7 and the bottom polyimide encapsulation 11, and are entirely encased within orthodontic adhesive 6, which is used to bond the tooth surface and the orthodontic appliance. Furthermore, both the upper capacitor assembly 8 and the lower capacitor assembly 10 are composed of eight parallel capacitors, which are evenly distributed in a ring at 45-degree intervals. Each capacitor group contains six capacitor plates, which are arranged in a straight line at equal intervals perpendicular to the plate surface.

[0015] Furthermore, the flexible support 9 is a hollow square structure composed of multiple support units arranged together, with the upper capacitor assembly 8 and the lower capacitor assembly 10's upper and lower capacitor groups located within the hollow square structure. The support unit is an S-shaped support pillar made of SU-8 photoresist using ultraviolet lithography, arranged vertically. Furthermore, the top polyimide package 7 is a box structure with an open bottom, and the bottom polyimide package 11 is a box structure with an open top; the internal space after their assembly is used to house the induction coil 1, the upper capacitor assembly 8, the lower capacitor assembly 10, and the flexible support 9.

[0016] Furthermore, when the tangential force sensor is subjected to force, it senses the force value through the change in the electrode spacing of each capacitor plate on the upper capacitor assembly 8 and the lower capacitor assembly 10. The initial electrode spacing in the detection direction of the capacitor assembly is much smaller than the initial electrode spacing in the non-detection direction, so as to achieve a near-linear response between capacitance change and displacement. Since the upper capacitor assembly 8 and the lower capacitor assembly 9 intersect each other, each capacitor plate will form a capacitor with the capacitor plates on both sides. At this time, the spacing is adjusted so that the capacitor spacing on one side is significantly smaller than that on the other side, and the capacitor on one side is significantly larger than that on the other side. The initial electrode spacing in the detection direction refers to the initial spacing between the capacitor plates that form a larger capacitor in the capacitor group structure composed of multiple capacitor plates arranged along the direction of the tangential force. The initial electrode spacing in the non-detection direction refers to the initial spacing between the capacitor plates that form a smaller capacitor in the capacitor group structure composed of multiple capacitor plates arranged along the direction of the tangential force.

[0017] Furthermore, the encapsulation of each part of the orthodontic force measuring device, including the polyimide encapsulation 5, the top polyimide encapsulation 7, and the bottom polyimide encapsulation 11, is made of biocompatible materials and encapsulated with polyimide material to ensure biocompatibility, corrosion resistance, and insulation performance.

[0018] A method for measuring orthodontic force based on a MEMS capacitive sensor, implemented using the aforementioned orthodontic force measuring device, wherein the device employs near-field communication (NFC) to achieve non-contact detection of oscillation signals, mapping the capacitance value and corresponding orthodontic force. The method includes the following steps:

[0019] The first step is to select a matching normal force sensor or tangential force sensor from the orthodontic force measuring device based on the target force direction of the tooth to be measured, which is either the normal force perpendicular to the tooth surface or the tangential force parallel to the tooth surface. Then, the selected sensor is placed in the preset installation position on the tooth surface and fixed with the orthodontic adhesive 6 that comes with the orthodontic force measuring device. Then, the orthodontic appliance is installed on the orthodontic adhesive to ensure that the sensor fits tightly and is stable between itself and the tooth surface and the orthodontic appliance, providing a basis for subsequent force value detection.

[0020] The second step is to apply a pulse excitation signal to the induction coil 1 built into the installed normal force sensor or tangential force sensor using an external NFC device after the sensor is installed and fixed. Since the upper capacitor plate 3 and lower capacitor plate 4 of the normal force sensor or the upper capacitor assembly 8 and lower capacitor assembly 10 of the tangential force sensor of the orthodontic force measuring device are connected in series with the induction coil 1 to form an LC oscillation circuit, the LC oscillation circuit will generate an oscillation signal with specific frequency characteristics under the action of the excitation signal.

[0021] The third step involves non-contact detection of the oscillation signal generated by the LC oscillation circuit using an external NFC device to obtain the real-time frequency data of the oscillation signal. This frequency data is then mapped into the "frequency-corrective force value" calibration curve of the orthodontic force measurement device to obtain the real-time corrective force value corresponding to the frequency change.

[0022] Furthermore, in the third step, the "frequency-corrective force value" calibration curve of the orthodontic force measuring device is obtained by fitting the frequency change under different known force values. Specifically, six equally spaced calibration points are selected, and equally spaced known forces are applied to each calibration point while simultaneously measuring the frequency value fed back by the sensor. After collecting multiple sets of calibration data, the calibration curve of the sensor is obtained through polynomial fitting. The horizontal axis of this calibration curve represents the magnitude of the force, and the vertical axis represents the frequency.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) The present invention uses a flexible support network for a normal force sensor + dual capacitor plates and a flexible support column for a tangential force sensor + annular distributed capacitor group + asymmetric plate spacing to respond to forces perpendicular to or parallel to the tooth surface, thereby solving the crosstalk problem of a single sensor in principle and improving detection accuracy.

[0025] (2) The present invention uses an LC oscillation circuit composed of a capacitor component and an induction coil, combined with NFC external excitation, without the need for an internal power supply module, which simplifies the sensing structure and controls the sensor size to the sub-millimeter level.

[0026] (3) This invention can be implemented by embedding orthodontic glue between the appliance and the tooth surface without modifying the existing appliance, and the implementation cost is low.

[0027] (3) The core components of this invention are encapsulated with polyimide and fixed with orthodontic adhesive to meet the requirements of more than 3 years of use; the flexible support structure can buffer high-frequency vibration noise, avoid false triggering, and ensure detection stability;

[0028] (4) This invention uses NFC to detect the oscillation frequency in real time and combines it with the calibration curve to obtain the force value, which helps doctors to accurately adjust the force parameters, reduce tooth deviation, reduce the rebound rate and shorten the treatment cycle. Attached Figure Description

[0029] Figure 1 This is an exploded view of the normal force sensor structure.

[0030] Figure 2 This is an exploded view of the tangential force sensor structure.

[0031] Figure 3 This is a diagram showing the arrangement of the capacitor array for the tangential force sensor.

[0032] Figure 4 This is a schematic diagram of the wireless measurement principle of the present invention;

[0033] Figure 5 This is a calibration curve of a normal force sensor according to an embodiment of the present invention;

[0034] Figure 6 This is a schematic diagram of the normal force sensor structure;

[0035] Figure 7 This is a schematic diagram of the tangential force sensor structure;

[0036] In the diagram: 1. Induction coil; 2. Flexible support mesh; 3. Upper capacitor plate; 4. Lower capacitor plate; 5. Polyimide encapsulation; 6. Orthogonal adhesive; 7. Top polyimide encapsulation; 8. Upper capacitor assembly; 9. Flexible support; 10. Lower capacitor assembly; 11. Bottom polyimide encapsulation. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] The embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0039] This invention relates to an orthodontic force measurement device based on a MEMS sensor. The device comprises an LC oscillation circuit formed by a capacitor assembly and an induction coil connected in series. An oscillation signal is generated by external excitation, and the frequency changes with the capacitance, eliminating the need for an internal power supply. The device includes two configurations: a normal force sensor and a tangential force sensor. The normal force sensor measures the normal force perpendicular to the tooth surface, while the tangential force sensor measures the tangential force parallel to the tooth surface. Specifically:

[0040] The normal force sensor includes an induction coil 1, a flexible support mesh 2, a capacitor assembly, a polyimide encapsulation 5, and orthodontic adhesive 6. The capacitor assembly includes an upper capacitor plate 3 and a lower capacitor plate 4. Specifically, both the upper and lower capacitor plates 3 and 4 are square ceramic capacitor plates. The induction coil 1 is positioned on the upper side of the upper capacitor plate 3. The outer periphery of the upper capacitor plate 3 is connected to the side wall of the lower capacitor plate 4 via the flexible support mesh 2. The induction coil 1, the upper capacitor plate 3, and the lower capacitor plate 4 together form an LC oscillation circuit for… The induction coil 1, the flexible support mesh 2, the upper capacitor plate 3, and the lower capacitor plate 4 are all enclosed within a square polyimide encapsulation 5 with an open top. The polyimide encapsulation 5 is entirely enclosed within a square orthodontic adhesive 6 with an open top. The orthodontic adhesive 6 is used to bond the tooth surface to the orthodontic appliance.

[0041] Furthermore, the polyimide package 5 is a box structure with an opening at the top.

[0042] Furthermore, the lower capacitor plate 4 is a box structure with an opening at the top.

[0043] Furthermore, the flexible support mesh 2 is composed of multiple SU-8 photoresist support pillars, with each SU-8 photoresist support pillar having its two ends connected to the outer side of the upper capacitor plate 3 and the inner wall of the lower capacitor plate 4, respectively.

[0044] The tangential force sensor includes a top polyimide encapsulation 7, an induction coil 1, a capacitor assembly, a flexible support 9, a bottom polyimide encapsulation 11, and orthodontic adhesive 6. The capacitor assembly includes an upper capacitor assembly 8 and a lower capacitor assembly 10. Specifically, the upper capacitor assembly 8 consists of eight upper capacitor groups and a square upper fixing plate, with each upper capacitor group fixed to the upper fixing plate. Each upper capacitor group consists of six capacitor plates arranged longitudinally, and the capacitor plates are ceramic capacitor plates. The lower capacitor assembly 10 consists of eight lower capacitor groups and a square lower fixing plate, with each lower capacitor group fixed to the lower fixing plate. Each lower capacitor group consists of six capacitor plates arranged longitudinally, and the capacitor plates are ceramic capacitor plates. The induction coil 1 is arranged on the upper side of the upper capacitor assembly 8. The flexible support 9 is arranged in a vertical column and fixed between the upper capacitor assembly 8 and the lower capacitor assembly 10, and the height of the flexible support 9 is greater than the distance between the upper and lower fixing plates. The induction coil 1, the upper capacitor assembly 8, and the lower capacitor assembly 10 together form an LC oscillation circuit for responding to external excitation signals. The induction coil 1, upper capacitor assembly 8, lower capacitor assembly 10, and flexible support 9 are all encased between the top polyimide encapsulation 7 and the bottom polyimide encapsulation 11, and are entirely encased within orthodontic adhesive 6, which is used to bond the tooth surface and the orthodontic appliance. Furthermore, both the upper capacitor assembly 8 and the lower capacitor assembly 10 are composed of eight parallel capacitors, which are evenly distributed in a ring at 45-degree intervals. Each capacitor group contains six capacitor plates, which are arranged in a straight line at equal intervals perpendicular to the plate surface.

[0045] Furthermore, the flexible support 9 is a hollow square structure composed of multiple support units arranged together, with the upper capacitor assembly 8 and the lower capacitor assembly 10's upper and lower capacitor groups located within the hollow square structure. The support unit is an S-shaped support pillar made of SU-8 photoresist using ultraviolet lithography, arranged vertically. Furthermore, the top polyimide package 7 is a box structure with an open bottom, and the bottom polyimide package 11 is a box structure with an open top; the internal space after their assembly is used to house the induction coil 1, the upper capacitor assembly 8, the lower capacitor assembly 10, and the flexible support 9.

[0046] Furthermore, when the tangential force sensor is subjected to force, it senses the force value through the change in the electrode spacing of each capacitor plate on the upper capacitor assembly 8 and the lower capacitor assembly 10. The initial electrode spacing in the detection direction of the capacitor assembly is much smaller than the initial electrode spacing in the non-detection direction, so as to achieve a near-linear response between capacitance change and displacement. Since the upper capacitor assembly 8 and the lower capacitor assembly 9 intersect each other, each capacitor plate will form a capacitor with the capacitor plates on both sides. At this time, the spacing is adjusted so that the capacitor spacing on one side is significantly smaller than that on the other side, and the capacitor on one side is significantly larger than that on the other side. The initial electrode spacing in the detection direction refers to the initial spacing between the capacitor plates that form a larger capacitor in the capacitor group structure composed of multiple capacitor plates arranged along the direction of the tangential force. The initial electrode spacing in the non-detection direction refers to the initial spacing between the capacitor plates that form a smaller capacitor in the capacitor group structure composed of multiple capacitor plates arranged along the direction of the tangential force.

[0047] Furthermore, the encapsulation of each part of the orthodontic force measuring device, including the polyimide encapsulation 5, the top polyimide encapsulation 7, and the bottom polyimide encapsulation 11, is made of biocompatible materials and encapsulated with polyimide material to ensure biocompatibility, corrosion resistance, and insulation performance.

[0048] Specifically, the capacitor plate of the normal force sensor is made of 0.1mm thick copper foil, the flexible support is made of SU-8 photoresist, and the induction coil is an 11-turn copper hollow coil with a diameter of 2mm.

[0049] Specifically, the array capacitor sheet of the tangential force sensor has a size of 0.46mm×0.1mm, the corrugated support column is made of SU-8 photoresist and formed by photolithography, and the induction coil is an 11-turn copper hollow coil with a diameter of 2mm.

[0050] Furthermore, the encapsulation bodies 5, 7, and 11 of the orthodontic force measuring device are made of biocompatible materials and encapsulated with polyimide material to ensure biocompatibility, corrosion resistance, and insulation performance.

[0051] Specifically, during the pretreatment optimization of the polyimide encapsulation material, deionized water is used for ultrasonic cleaning to remove particulate matter, anhydrous ethanol is used for ultrasonic cleaning to remove organic residues, and oxygen plasma treatment is used to achieve surface hydroxylation.

[0052] Specifically, the coating process for polyimide encapsulation uses a medical-grade polyimide precursor solution, filtered through a pre-filter membrane to remove impurities. The coating process is divided into low-speed spreading and high-speed thickness control stages, with the coating thickness controlled by adjusting the rotation speed. Curing is performed in stages: soft baking removes the solvent, pre-curing completes initial cyclization, and full curing is performed under high-temperature nitrogen protection with temperature control to prevent cracking.

[0053] A method for measuring orthodontic force based on a MEMS capacitive sensor, implemented using the aforementioned orthodontic force measuring device, wherein the device employs near-field communication (NFC) to achieve non-contact detection of oscillation signals, mapping the capacitance value and corresponding orthodontic force. The method includes the following steps:

[0054] The first step is to select a matching normal force sensor or tangential force sensor from the orthodontic force measuring device based on the target force direction of the tooth to be measured, which is either the normal force perpendicular to the tooth surface or the tangential force parallel to the tooth surface. Then, the selected sensor is placed in the preset installation position on the tooth surface and fixed with the orthodontic adhesive 6 that comes with the orthodontic force measuring device. Then, the orthodontic appliance is installed on the orthodontic adhesive to ensure that the sensor fits tightly and is stable between itself and the tooth surface and the orthodontic appliance, providing a basis for subsequent force value detection.

[0055] The second step is to apply a pulse excitation signal to the induction coil 1 built into the installed normal force sensor or tangential force sensor using an external NFC device after the sensor is installed and fixed. Since the upper capacitor plate 3 and lower capacitor plate 4 of the normal force sensor or the upper capacitor assembly 8 and lower capacitor assembly 10 of the tangential force sensor of the orthodontic force measuring device are connected in series with the induction coil 1 to form an LC oscillation circuit, the LC oscillation circuit will generate an oscillation signal with specific frequency characteristics under the action of the excitation signal.

[0056] The third step involves non-contact detection of the oscillation signal generated by the LC oscillation circuit using an external NFC device to obtain the real-time frequency data of the oscillation signal. This frequency data is then mapped into the "frequency-corrective force value" calibration curve of the orthodontic force measurement device to obtain the real-time corrective force value corresponding to the frequency change.

[0057] Furthermore, in the third step, the "frequency-corrective force value" calibration curve of the orthodontic force measurement device is obtained by fitting the frequency change under different known force values ​​through previous experiments. Specifically, six equally spaced calibration points are selected, and equally spaced known forces are applied to each calibration point, while the frequency value fed back by the sensor is measured simultaneously. After collecting multiple sets of calibration data, the calibration curve of the sensor is obtained through polynomial fitting. The horizontal axis of this calibration curve represents the magnitude of the force, and the vertical axis represents the frequency.

[0058] The following is an example of calibration data for a normal force sensor. Six calibration points with stresses of 0 MPa, 0.3 MPa, 0.6 MPa, 0.9 MPa, 1.2 MPa, and 1.5 MPa were selected. The corresponding known forces were applied to the normal force sensor, and the frequency of the sensor's feedback was measured. The following calibration data was obtained:

[0059]

[0060]

[0061] The calibration curve obtained by polynomial fitting of the calibration data is as follows:

[0062] f = -0.1845x 2 -0.5518x+9.9511

[0063] The independent variable x represents the magnitude of the force, and the dependent variable f represents the frequency fed back by the normal force sensor.

[0064] Figure 5 This is an offline calibration curve. Based on this curve, the real-time corrective force value can be obtained according to the measured frequency.

[0065] This invention achieves precise measurement of orthodontic force through directional structural design, passive communication, and adaptation to the oral environment. It can be integrated into invisible aligners or metal brackets and is suitable for various orthodontic scenarios.

[0066] The above embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. An orthodontic force measurement device based on a MEMS capacitive sensor, characterized in that, The orthodontic force measuring device consists of an LC oscillation circuit formed by a capacitor assembly and an induction coil connected in series. An oscillation signal is generated by external excitation, and the frequency changes with the capacitance, requiring no internal power supply. The orthodontic force measuring device includes two configurations: a normal force sensor and a tangential force sensor. The normal force sensor measures the normal force perpendicular to the tooth surface, while the tangential force sensor measures the tangential force parallel to the tooth surface. Specifically: The normal force sensor includes an induction coil (1), a flexible support mesh (2), a capacitor assembly, a polyimide encapsulation (5), and orthodontic adhesive (6), wherein the capacitor assembly includes an upper capacitor plate (3) and a lower capacitor plate (4). The tangential force sensor includes a top polyimide encapsulation (7), an induction coil (1), a capacitor assembly, a flexible support (9), a bottom polyimide encapsulation (11), and orthodontic adhesive (6), wherein the capacitor assembly includes an upper capacitor assembly (8) and a lower capacitor assembly (10). When the tangential force sensor is subjected to force, it senses the force value by changing the distance between the capacitor plates on the upper capacitor assembly (8) and the lower capacitor assembly (10).

2. The orthodontic force measurement device based on a MEMS capacitive sensor according to claim 1, characterized in that, Specifically, the normal force sensor is as follows: the upper capacitor plate (3) and the lower capacitor plate (4) are both square ceramic capacitor plates. The induction coil (1) is arranged on the upper side of the upper capacitor plate (3). The upper capacitor plate (3) is connected to the lower capacitor plate (4) through the flexible support net (2). The induction coil (1), the upper capacitor plate (3), and the lower capacitor plate (4) together form an LC oscillation circuit. The induction coil (1), the flexible support net (2), the upper capacitor plate (3), and the lower capacitor plate (4) are all wrapped in a square polyimide package (5) with an opening at the top. The polyimide package (5) is completely wrapped in a square orthodontic adhesive (6) with an opening at the top. The orthodontic adhesive (6) is used to bond the tooth surface and the orthodontic appliance.

3. The orthodontic force measurement device based on a MEMS capacitive sensor according to claim 2, characterized in that, The polyimide package (5) is a box structure with an open top; the lower capacitor plate (4) is a box structure with an open top.

4. The orthodontic force measurement device based on a MEMS capacitive sensor according to claim 2, characterized in that, The flexible support mesh (2) is composed of multiple SU-8 photoresist support pillars, with each SU-8 photoresist support pillar having its two ends connected to the outer side of the upper capacitor plate (3) and the inner wall of the lower capacitor plate (4), respectively.

5. The orthodontic force measurement device based on a MEMS capacitive sensor according to claim 1, characterized in that, Specifically, the tangential force sensor comprises: the upper capacitor assembly (8) consisting of multiple upper capacitor groups and a square upper fixing plate, wherein the upper capacitor groups are fixed on the lower surface of the upper fixing plate, and each upper capacitor group is composed of multiple capacitor plates arranged longitudinally, wherein the capacitor plates are ceramic capacitor plates; the lower capacitor assembly (10) consists of multiple lower capacitor groups and a square lower fixing plate, wherein the lower capacitor groups are fixed on the upper surface of the lower fixing plate, and each lower capacitor group is composed of multiple capacitor plates arranged longitudinally, wherein the capacitor plates are ceramic capacitor plates; the induction coil (1) is arranged on the upper capacitor assembly (8). On the upper side, the flexible support (9) is arranged in a vertical row and fixed between the upper capacitor assembly (8) and the lower capacitor assembly (10); the induction coil (1), together with the upper capacitor assembly (8) and the lower capacitor assembly (10), constitutes an LC oscillation circuit for responding to external excitation signals; the induction coil (1), the upper capacitor assembly (8), the lower capacitor assembly (10) and the flexible support (9) are all wrapped between the top polyimide encapsulation (7) and the bottom polyimide encapsulation (11), and are completely wrapped in orthodontic adhesive (6), which is used to bond the tooth surface and the orthodontic appliance.

6. The orthodontic force measurement device based on a MEMS capacitive sensor according to claim 5, characterized in that, In the tangential force sensor: The upper capacitor assembly (8) and the lower capacitor assembly (10) are both composed of 8 sets of parallel capacitors. The 8 sets of parallel capacitors are evenly distributed in a ring at 45-degree intervals. Each set of capacitors contains 6 capacitor plates, and the 6 capacitor plates are arranged in a straight line at equal intervals in the direction perpendicular to the plate surface. The flexible support (9) is a hollow square structure composed of multiple support units arranged together. The upper capacitor assembly (8) and the lower capacitor assembly (10) are located inside the hollow square structure. The support unit is an S-shaped support column made of SU-8 photoresist by ultraviolet lithography and arranged vertically. The height of the flexible support (9) is greater than the distance between the upper and lower fixed plates; The capacitor plates of the upper capacitor assembly (8) and the lower capacitor assembly (9) intersect each other, and each capacitor plate will form a capacitor with the capacitor plates on both sides.

7. The orthodontic force measurement device based on a MEMS capacitive sensor according to claim 5, characterized in that, The polyimide encapsulation (5), top polyimide encapsulation (7), and bottom polyimide encapsulation of the orthodontic force measuring device are all made of biocompatible materials and are encapsulated using polyimide material.

8. The orthodontic force measurement device based on a MEMS capacitive sensor according to claim 1, characterized in that, In the orthodontic force measuring device, the initial plate spacing of the capacitor assembly in the detection direction is smaller than that in the non-detection direction, thereby achieving a near-linear response between capacitance change and displacement. The initial plate spacing in the detection direction refers to the initial spacing between capacitor plates that make up a larger capacitor in a capacitor bank structure composed of multiple capacitor plates arranged along the direction of the tangential force. The initial plate spacing in the non-detection direction refers to the initial spacing between the capacitor plates that make up the smaller capacitor in a capacitor bank structure composed of multiple capacitor plates, arranged along the direction of the tangential force.

9. A method for measuring orthodontic force based on a MEMS capacitive sensor, characterized in that, The orthodontic force measurement method is implemented based on the orthodontic force measurement device according to any one of claims 1-8. The orthodontic force measurement device uses near-field communication (NFC) to achieve non-contact detection of oscillation signals, mapping the capacitance value and the corresponding orthodontic force; it includes the following steps: First, select a matching normal force sensor or tangential force sensor from the orthodontic force measuring device according to the target force direction of the tooth to be measured, which is either the normal force perpendicular to the tooth surface or the tangential force parallel to the tooth surface; then, place the selected sensor in the preset installation position on the tooth surface and fix the sensor with the orthodontic adhesive (6) that is matched with the orthodontic force measuring device; then install the orthodontic appliance on the orthodontic adhesive. The second step is to use an external NFC device to apply a pulse excitation signal to the induction coil (1) built into the normal force sensor or tangential force sensor; under the action of the excitation signal, the LC oscillation circuit generates an oscillation signal with specific frequency characteristics; The third step involves non-contact detection of the oscillation signal generated by the LC oscillation circuit using an external NFC device to obtain the real-time frequency data of the oscillation signal. This frequency data is then mapped into the "frequency-corrective force value" calibration curve of the orthodontic force measurement device to obtain the real-time corrective force value corresponding to the frequency change.

10. The orthodontic force measurement method based on a MEMS capacitive sensor according to claim 9, characterized in that, In the third step, the "frequency-corrective force value" calibration curve of the orthodontic force measuring device is obtained by fitting the frequency change under different known force values. Specifically, six equally spaced calibration points are selected, and equally spaced known forces are applied to each calibration point, while the frequency value fed back by the sensor is measured simultaneously. After collecting multiple sets of calibration data, the calibration curve of the sensor is obtained by polynomial fitting. The horizontal axis of the calibration curve is the magnitude of the force, and the vertical axis is the frequency.

Images