A micro-nanometer newton force sensor and a multi-axis micro-nanometer newton force sensor with the same

Abstract

The present application relates to a kind of micro-nanometer force sensor and the multi-axis micro-nanometer force sensor with it, including device body, flexible connecting part and displacement detection component, flexible connecting part uses first flexible section and second flexible section that are arranged in series along the direction of force transmission, and both are parallel beam structure;Displacement detection component is arranged between first flexible section and second flexible section in non-contact mode.By the decoupling design of first flexible section and second flexible section, the first flexible section determining force resolution and measurement range and the second flexible section determining overall stiffness are separated, so that they can be independently optimized, thereby solving the problem that high resolution and high stiffness, strong anti-interference capability cannot be obtained in traditional sensor;The present application has nanometer high resolution, wide range, high linearity and good environmental adaptability.

Description

Technical Field

[0001] This invention relates to the field of force sensor technology, and in particular to a micro / nano Newton force sensor and a multi-axis micro / nano Newton force sensor having the same. Background Technology

[0002] In cutting-edge fields such as nanoindentation, atomic force microscopy, micro-nano manipulators, and bio-cell mechanics research, high-precision and high-stability measurement of forces ranging from micro-Newtons (μN) to nano-Newtons (nN) is of great significance. Currently, the mainstream technical approach to achieving micro-force measurement follows the basic principle of Hooke's Law: that is, by measuring the minute deformation or displacement produced by an elastic sensing structure with a known stiffness coefficient under the action of an unknown external force, the applied force value can be calculated.

[0003] Existing micro-force measurement technologies can be mainly classified into the following categories:

[0004] (1) Capacitive sensors: These sensors calculate displacement and force by detecting changes in capacitance caused by changes in the distance or area between movable and fixed electrodes connected to an elastic body due to external forces. Although these sensors have high sensitivity, a large sensor head is usually required to obtain sufficient initial capacitance and signal-to-noise ratio, which increases mass and makes the system extremely sensitive to environmental vibrations. The actual noise limit is usually only at the micronewton level. In addition, the measurement results are easily affected by the distributed capacitance and parasitic capacitance of the connecting cables, and recalibration is required after any system changes.

[0005] (2) Strain gauge sensor: It attaches a metal foil or semiconductor strain gauge to the strain-sensitive area of ​​an elastic body and indirectly obtains the strain of the structure by measuring the change in the resistance value of the strain gauge, thereby calculating the force value. This structure is relatively compact, but it is an indirect measurement, which has nonlinear error, and its performance is highly dependent on the bonding process of the strain gauge. In long-term use, the creep, aging and temperature effect of the adhesive will cause signal drift, requiring frequent calibration to maintain accuracy, and its long-term stability is insufficient.

[0006] (3) Optical interferometry: Represented by the optical lever or laser interferometry commonly used in atomic force microscopy, displacement is measured by detecting the position of the laser spot illuminating the elastic cantilever beam or the change in the intensity of the interference light. Although this method can achieve atomic-level resolution, the entire optical system is complex and expensive. It is also extremely sensitive to temperature, air pressure fluctuations, and air disturbances in the working environment, which can easily cause signal drift. Its stability and environmental robustness are poor, making it unsuitable for integrated application in industrial sites or long-term monitoring.

[0007] In summary, existing micro-force measurement schemes all have significant bottlenecks, making it difficult to achieve the following key performance indicators on a single sensor: achieving nano-Newton-level high resolution over a wide force measurement range (e.g., millinewyn to Newton levels); simultaneously possessing good long-term environmental stability, extremely low drift characteristics to reduce calibration frequency, and an overall structure that is simple, reliable, and easy to integrate. This multi-objective constraint limits the application of high-precision micro-force sensing technology in a wider range of scenarios. Summary of the Invention

[0008] This invention provides a micro / nano Newton force sensor and a multi-axis micro / nano Newton force sensor having the same, to solve the problem of the coupling between the resolution, measurement range and the overall structural stiffness of the force sensor in the existing micro-force measurement technology. It can adapt to different dynamic performance requirements and environmental anti-interference requirements by designing different stiffnesses.

[0009] The technical solution adopted by this invention to solve its technical problem is: a micro / nano Newton force sensor, comprising, The device body, used to transmit externally applied forces, includes a fixed end and a force-applying end; A flexible connection is disposed within the device body and located between the fixed end and the force-applying end. Externally applied forces are transmitted through the flexible connection. The flexible connection includes a first flexible segment and a second flexible segment connected in series along the force transmission direction. The first flexible segment is close to the fixed end, and the second flexible segment is close to the force-applying end. Both the first flexible segment and the second flexible segment are parallel beam structures. A displacement detection component is disposed between the first flexible segment and the second flexible segment for non-contact detection of the displacement of the first flexible segment under force. The first flexible segment is configured to determine the force resolution and measurement range of the device body; The second flexible segment is configured to determine the stiffness of the device body.

[0010] More specifically, the device body includes a first connecting part, a second connecting part, and a third connecting part. The first connecting part and the second connecting part form a first flexible segment, and the second connecting part and the third connecting part form a second flexible segment. The displacement detection component is disposed on the second connecting part. The end of the first connecting part away from the second connecting part is a fixed end, and the end of the third connecting part away from the second connecting part is a force-applying end.

[0011] More specifically, the parallel beam structure includes at least two parallel beams arranged parallel to each other along the direction of force transmission.

[0012] More specifically, the material of the device body is selected from titanium alloy, single crystal silicon or other low thermal expansion materials.

[0013] More specifically, when the device body is made of metal, it is prepared using wire cutting or laser cutting processes; when the device body is made of single-crystal silicon, it is prepared using semiconductor micromachining processes.

[0014] More specifically, the displacement detection component includes an optical encoder scale and an optical reading head. The optical encoder scale is disposed on the device body and moves with the device body, while the optical reading head is disposed on the outer shell of the device body.

[0015] More specifically, a force-applying step is provided at the force-applying end.

[0016] More specifically, the stiffness of the second flexible segment is adjusted so that the stiffness of the device body is controlled between 50-500000 N / m.

[0017] A multi-axis micro / nano Newton force sensor is composed of multiple micro / nano Newton force sensors as described above; the multiple micro / nano Newton force sensors are connected in series end to end, and the device body of each micro / nano Newton force sensor extends in a different direction.

[0018] The beneficial effects of this invention are: 1. By connecting the first and second flexible segments in series, the force resolution, which determines the static measurement performance of the sensor, and the overall structural stiffness, which determines its dynamic mechanical performance, are separated. The resolution and range are optimized by designing the first flexible segment, achieving high resolution at the nanonewton (nN) level within a wide force range (e.g., millinewyn to Newton). The required overall stiffness and dynamic response are set by designing the second flexible segment, thereby achieving high natural frequency, good resistance to mechanical vibration interference, and fast dynamic response.

[0019] 2. The first flexible segment can be easily adapted to different application requirements, from ultra-precision static measurement to high-speed dynamic force monitoring, by being paired with a second flexible segment of different stiffness. In static experiments requiring extremely high resolution, a low-stiffness second flexible segment can be configured to filter environmental vibrations. In dynamic operations requiring fast response, a high-stiffness second flexible segment can be configured to ensure bandwidth.

[0020] 3. Non-contact displacement measurement is adopted, which avoids the creep and aging problems caused by strain gauge bonding, and the measurement is more direct and has better linearity. Attached Figure Description

[0021] Figure 1 This is a three-dimensional schematic diagram of the structure of the micro / nano Newton force sensor of the present invention; Figure 2 This is a schematic diagram of the front view structure of the micro / nano Newton force sensor of the present invention; Figure 3This is a schematic diagram of the deformation structure of the micro / nano Newton force sensor of the present invention; Figure 4 This is a schematic diagram of the structure of the biaxial micro / nano Newton force sensor of the present invention.

[0022] In the figure: 10, Device body; 11, First connecting part; 12, Second connecting part; 13, Third connecting part; 14, Force application step; 21, First flexible section; 22, Second flexible section; 31, Optical encoder scale; 32, Optical reading head; 101, Fixed end; 102, Force application end. Detailed Implementation

[0023] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The direction of movement is also relative and is not limited to an absolute direction of movement. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0025] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. Furthermore, the technical features involved in the different embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0026] In the design of micro / nano Newtonian force sensors, the force resolution depends on its sensitivity, i.e., the displacement produced per unit force. To improve resolution, the stiffness of the elastic body needs to be reduced so that it can produce a sufficiently large displacement detectable by an optical system even under small forces. However, excessively low overall structural stiffness makes the sensor itself "soft," reducing its natural frequency and making it susceptible to environmental vibration interference, resulting in poor dynamic response performance and difficulty in stable operation in scenarios requiring high bandwidth or containing mechanical noise. Conversely, increasing overall stiffness to enhance anti-interference capability and dynamic response sacrifices resolution. In existing designs, sensitivity (resolution) and overall stiffness are coupled and inversely related, requiring a trade-off between the two during design, which severely limits the application range of the sensor.

[0027] like Figure 1 and Figure 2 The present invention provides a micro-nano Newton force sensor with independently decoupled resolution and overall stiffness, which is used to achieve high-precision measurement of forces in the range of micro-Newton (μN) to nano-Newton (nN); the micro-nano Newton force sensor includes a device body 10, a flexible connection part, and a displacement detection component.

[0028] The device body 10 is an integral structure used to transmit externally applied forces. Its material is preferably a material with a low coefficient of thermal expansion, low internal friction, and high elasticity, such as titanium alloy. Using titanium alloy can effectively avoid deformation hysteresis and zero-point drift. In other embodiments, the device body 10 can also be made of other low thermal expansion materials such as single-crystal silicon. When a metal material is used, it can be integrally formed by precision machining processes such as wire cutting or laser cutting. When single-crystal silicon is used, it can be fabricated using semiconductor micromachining technology to achieve a finer structure at the submicron scale, thereby obtaining lower stiffness.

[0029] The device body 10 includes, in sequence along the force transmission direction, a fixed end 101, a first connecting part 11, a second connecting part 12, a third connecting part 13, and a force-applying end 102; the fixed end 101 is used to install the entire sensor onto an external base or positioning platform, and the force-applying end 102 is used to bear or apply the force to be measured; in this application, a force-applying step 14 is provided at the force-applying end 102 to facilitate the installation of probes or docking with other components.

[0030] The flexible connection is disposed inside the device body 10, located between the fixed end 101 and the force-applying end 102. External force is transmitted through it and generates elastic deformation. The flexible connection includes a first flexible segment 21 and a second flexible segment 22 arranged in series along the force transmission direction. The first flexible segment 21 is connected between the first connection part 11 and the second connection part 12 and is disposed near the fixed end 101. The second flexible segment 22 is connected between the second connection part 12 and the third connection part 13 and is disposed near the force-applying end 102. External force is applied to the force-applying end 102 and transmitted to the fixed end 101 along the third connection part 13, the second flexible segment 22, the second connection part 12, the first flexible segment 21, and the first connection part 11.

[0031] In this application, both the first flexible segment 21 and the second flexible segment 22 are parallel beam structures, meaning that each flexible segment contains at least two beams arranged parallel to each other along the force transmission direction, i.e., parallel beams; for example Figure 2 The diagram illustrates a double parallel beam structure. Multiple parallel beam structures, such as three, four, or five parallel beams, can also be implemented depending on specific requirements. The function of the parallel beam structure is to strictly constrain the degrees of freedom of motion, such as... Figure 3 As shown, when an external force is applied, the parallel beam structure allows the device body 10 to produce an approximate translation (i.e., an approximate vertical displacement) during deformation, thereby suppressing torsion and lateral deflection to the maximum extent and ensuring a highly linear and single mapping relationship between the force and displacement signals. If a non-parallel arrangement (such as an inclined or curved beam) is used, it will lead to significant tilting deformation and rotation, introducing coupling errors and affecting measurement accuracy.

[0032] The displacement detection component is disposed non-contactly between the first flexible segment 21 and the second flexible segment 22, specifically on the second connecting part 12, for detecting the displacement of the first flexible segment 21 under external force. In this application, the displacement detection component includes an optical encoder scale 31 fixed on the second connecting part 12 and an optical reading head 32 fixed on a housing (not shown in the figure) outside the device body 10. The optical encoder scale 31 moves with the movement of the second connecting part 12, while the optical reading head 32 remains stationary. Therefore, relative motion occurs between the two during measurement. The optical reading head 32 and the optical encoder scale 31 are disposed opposite to each other but do not contact each other, forming a non-contact displacement measurement structure. It has sub-nanometer displacement resolution, and by avoiding the adhesive layer of traditional strain gauge sensors, it eliminates the hysteresis and zero-point drift problems caused by adhesive creep and aging, ensuring long-term stability and high repeatability of the measurement.

[0033] This invention achieves functional decoupling between the two through the design of a two-segment flexible structure.

[0034] The stiffness (denoted as k1) of the first flexible segment 21 independently determines the force resolution and measurement range of the micro-nano Newton force sensor. According to Hooke's Law (F=kx), under the premise of fixed displacement detection resolution, the smaller the value of k1, the smaller the force required to generate a unit displacement, that is, the higher the force resolution, and the smaller the force that can be detected. Therefore, by designing the thickness, length, and width of the parallel beam of the first flexible segment 21, its stiffness k1 can be controlled within a low and optimized range, thereby obtaining a high force resolution, for example, the force resolution can be controlled between 25nN and 250uN. At the same time, k1 also determines the lower limit of the sensor's range, which can cover the force measurement range from 100nN to 100mN. The first flexible segment 21 can independently focus on optimizing the force resolution without having to consider the overall dynamic performance.

[0035] The stiffness of the second flexible segment 22 (denoted as k2) independently determines the overall stiffness of the device body 10 to match different application environments and dynamic requirements. The overall stiffness of the sensor is determined by k2 and k1 in series, but k2 plays a dominant role. By independently designing k2, force control from extremely fine to a large range can be achieved, effectively expanding the usable force range and adaptability of the sensor. By increasing the stiffness of the second flexible segment 22, the overall natural frequency of the sensor can be increased, enhancing its resistance to high-frequency mechanical vibration interference and obtaining a better dynamic response bandwidth, making it suitable for high-speed, high-bandwidth scenarios. In scenarios where filtering of low-frequency vibrations or large amplitude fluctuations is required, mechanical low-pass filtering can be achieved by reducing k2. The effect is to significantly improve the signal-to-noise ratio. The adjustment of the overall stiffness has virtually no impact on the force resolution determined by the first flexible segment 21. In this application, the stiffness k2 of the second flexible segment 22 is greater than, equal to, or less than the stiffness k1 of the first flexible segment 21, and is ultimately determined according to the specific actual working conditions. In this application, the stiffness of the device body 10 is controlled within the range of 50 N / m to 500,000 N / m by adjusting the stiffness k2, but it is not limited to this. The overall stiffness of the device 10 can also be adjusted by adjusting the stiffness k1 or by simultaneously adjusting the stiffness k1 and k2. Depending on the different application scenarios, the overall dynamic performance can be matched by replacing the device body 10 with one having a different k2.

[0036] This application provides three specific embodiments, taking silicon material as an example, a double parallel beam structure, and employing photolithography + deep reactive ion etching (DRIE) semiconductor process. Three configurations were actually fabricated and verified: Example 1: High resolution, small range configuration.

[0037] Material: Monocrystalline silicon (elastic modulus E≈110 GPa); Manufacturing method: The pattern is generated using photolithography, and the silicon is etched using DRIE technology; Optical encoder resolution: 0.5 nm; First flexible section (21): Parallel beam length L1=17mm, width w1=1mm, thickness t1=0.1mm, stiffness k1≈45.5N / m; Second flexible segment (22): Parallel beam length L2=17mm, width w2=1mm, thickness t2=4.8mm, stiffness k2≈1.34×10 6 N / m; The overall stiffness is calculated using the formula: keq≈45.5 N / m (<50 N / m); Force resolution: 45.5 N / m (K1) × 0.5 nm = 22.75 nN; Measurement range: Silicon fracture strength 1GPa, safety factor 10, maximum range = 45.5N / m×(t1×w1×L1) / (E×w1×t1²)×10≈40mN.

[0038] In this embodiment, the resolution and range of the proof force can be achieved at the nanonewton level by adjusting the size of the first flexible section; while the overall stiffness is determined by both k1 and k2, and the overall stiffness can be adjusted to below 50 N / m by adjusting the stiffness k2.

[0039] Example 2: High stiffness, large range configuration.

[0040] Material: Monocrystalline silicon (elastic modulus E≈110 GPa); Manufacturing method: The pattern is generated using photolithography, and the silicon is etched using DRIE technology; Optical encoder resolution: 0.5 nm; First flexible segment (21): L1=7.8mm, w1=3mm, t1=0.8mm, k1≈5×10 5 N / m; Second flexible segment (22): L2=2.5mm, w2=3mm, t2=4.8mm, k2≈5.8×10 7 N / m; The overall stiffness is calculated using the formula: keq≈5×10 5 N / m; Force resolution = 5 × 10 5 N / m × 0.5 nm = 250 μN; Measuring range: Maximum range ≈ 12.5N; In this embodiment, the resolution and range of the proof force can be adjusted to the micro-Newton and Newton levels by adjusting the size of the first flexible segment; while the overall stiffness is determined by both k1 and k2, and the overall stiffness can be adjusted to 5 × 10⁻⁶ by adjusting the stiffness k2. 5 N / m.

[0041] Example 3: Based on Example 2, the overall stiffness is adjusted by changing the stiffness k2.

[0042] Material: Monocrystalline silicon (elastic modulus E≈110 GPa); Manufacturing method: The pattern is generated using photolithography, and the silicon is etched using DRIE technology; Optical encoder resolution: 0.5 nm; First flexible segment (21): L1=7.8mm, w1=3mm, t1=0.8mm, k1≈5×10 5 N / m; Second flexible segment (22): L2=4.5mm, w2=3mm, t2=0.8mm, k2≈1.86×10 6 N / m; The overall stiffness is calculated using the formula: keq ≈ 3.9 × 10⁻⁶ 5 N / m; Force resolution = 5 × 10 5 N / m × 0.5 nm = 250 μN; Measuring range: Maximum range ≈ 12.5N; This embodiment demonstrates that the overall stiffness can be adjusted by adjusting the stiffness k2, while the force resolution and maximum range remain essentially unchanged.

[0043] Based on the aforementioned micro / nano Newton force sensor, this invention also provides a multi-axis micro / nano Newton force sensor; this multi-axis micro / nano Newton force sensor is composed of multiple aforementioned micro / nano Newton force sensors. Specifically, the multiple micro / nano Newton force sensors are connected in series end to end, that is, the force-applying end 102 of the previous sensor is connected to the fixed end 101 of the next sensor. Furthermore, the extension direction (i.e., the force transmission direction) of the device body 10 of each micro / nano Newton force sensor is different, for example, they can be perpendicular to each other, thereby forming a sensor capable of simultaneously measuring two (e.g., Figure 4 A multi-axis force sensor that displays force components in the X and Y axes (as shown) or in three orthogonal directions (X-axis, Y-axis, and Z-axis).

[0044] In summary, this invention, through a two-segment series parallel beam flexible structure combined with a non-contact displacement detection component, physically decouples the first flexible segment 21, which determines force resolution, from the second flexible segment 22, which determines dynamic performance, and allows for independent design. This not only achieves high resolution, wide measurement range, high linearity, and long-term stability, but also, through the independent design of the rigidity of the second flexible segment 22, allows users to flexibly configure it according to specific application scenarios, solving the problem of mutual constraints and difficulty in balancing resolution and stiffness in existing technologies.

[0045] It should be emphasized that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A micro / nano Newton force sensor, characterized in that, include, The device body (10) is used to transmit externally applied force and includes a fixed end (101) and a force-applying end (102). A flexible connection is disposed within the device body (10) and located between the fixed end (101) and the force-applying end (102). Externally applied forces are transmitted through the flexible connection. The flexible connection includes a first flexible segment (21) and a second flexible segment (22) arranged in series along the force transmission direction. The first flexible segment (21) is close to the fixed end (101), and the second flexible segment (22) is close to the force-applying end (102). Both the first flexible segment (21) and the second flexible segment (22) are parallel beam structures. The parallel beam structure includes at least two parallel beams arranged in parallel along the force transmission direction. The displacement detection component is disposed between the first flexible segment (21) and the second flexible segment (22) for non-contact detection of the displacement of the first flexible segment (21) under force. The first flexible segment (21) is configured to determine the force resolution and measurement range of the device body (10); The second flexible segment (22) is configured to determine the stiffness of the device body (10); The device body (10) includes a first connecting part (11), a second connecting part (12) and a third connecting part (13). The first connecting part (11) and the second connecting part (12) are connected by a first flexible segment (21), and the second connecting part (12) and the third connecting part (13) are connected by a second flexible segment (22). The displacement detection component is disposed on the second connecting part (12). The end of the first connecting part (11) away from the second connecting part (12) is a fixed end (101), and the end of the third connecting part (13) away from the second connecting part (12) is a force-applying end (102).

2. The micro / nano Newton force sensor according to claim 1, characterized in that, The material of the device body (10) is selected from titanium alloy, single crystal silicon or other low thermal expansion materials.

3. The micro / nano Newton force sensor according to claim 1, characterized in that, When the device body (10) is made of metal, it is prepared by wire cutting or laser cutting; when the device body (10) is made of single crystal silicon, it is prepared by semiconductor micromachining.

4. The micro / nano Newton force sensor according to claim 1, characterized in that, The displacement detection component includes an optical encoder scale (31) and an optical reading head (32). The optical encoder scale (31) is disposed on the device body (10) and moves with the device body (10). The optical reading head (32) is disposed on the outer shell of the device body (10).

5. The micro / nano Newton force sensor according to claim 1, characterized in that, A force-applying step (14) is provided at the force-applying end (102).

6. The micro / nano Newton force sensor according to claim 1, characterized in that, Adjust the stiffness of the second flexible segment (22) so that the stiffness of the device body (10) is controlled between 50-500000 N / m.

7. A multi-axis micro / nano Newton force sensor, characterized in that, It is composed of multiple micro-nano Newton force sensors as described in any one of claims 1-6; multiple micro-nano Newton force sensors are connected in series end to end, and the device body (10) of each micro-nano Newton force sensor extends in a different direction.

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