Flexible magnetic tactile sensing device based on microstructured elastic layer, and three-dimensional force measurement device and measurement method

Abstract

Disclosed in the present invention are a flexible magnetic tactile sensing device based on a microstructured elastic layer, and a three-dimensional force measurement device and measurement method. The flexible magnetic tactile sensing device comprises a flexible magnetic film, a microstructured elastic layer, a Hall sensor, a PCB and a bottom housing, wherein the Hall sensor is mounted on the PCB; the flexible magnetic film, the microstructured elastic layer, the PCB and the bottom housing are stacked in sequence from top to bottom; and the microstructured elastic layer is of a non-planar structure. After the flexible magnetic film is deformed under a force, the deformation of the flexible magnetic film is transferred to the microstructured elastic layer, and the change in the strength of a triaxial magnetic field is measured by means of the Hall sensor and uploaded to a PC for data processing to achieve three-dimensional force measurement. The present invention can achieve three-dimensional force measurement. When a normal force is applied, the flexible magnetic film is locally deformed in the normal direction, and when a tangential force is applied, the flexible magnetic film is tangentially displaced; and on the basis of a quantitative analysis result, different suitable application scenarios for the microstructured elastic layer are provided.

Description

A flexible magnetic tactile sensing device, a three-dimensional force measuring device, and a measuring method based on a microstructure elastic layer. Technical Field

[0001] This invention relates to the fields of microstructured elastic layers and flexible magnetic tactile sensing, and in particular to a flexible magnetic tactile sensing device, a three-dimensional force measurement device, and a measurement method based on a microstructured elastic layer. Background Technology

[0002] In recent years, flexible tactile sensors have demonstrated significant application value in cutting-edge fields such as precise robot manipulation, tactile feedback for intelligent prosthetics, and safety control of human-computer interaction due to their excellent deformability and biocompatibility, driving the continuous development of tactile sensing technology towards flexibility and multidimensionality. According to different working principles, flexible multi-axis force sensors are mainly divided into the following two categories: (1) electrical sensors, including piezoresistive, capacitive, piezoelectric, and electromagnetic sensors; (2) optical sensors (light intensity modulation, phase modulation, and wavelength modulation). In recent years, magnetoelectric sensors have received widespread attention in three-dimensional force measurement due to their simple structure, low cost, and suitability for decoupling multiple physical signals. Traditional magnetic sensors mostly use a combination of rigid permanent magnets and magnetic sensitive elements to achieve force-magnetic conversion, but the presence of rigid magnets significantly limits their application in deformable scenarios. To achieve flexible force-magnetic sensing, a novel approach is to dope magnetic microparticles (such as NdFeB) into a flexible polymer matrix to construct a magnetoelastic composite film, and achieve specific magnetic responses through different magnetization methods. For example, one-dimensional sinusoidal magnetization, Halbach array magnetization, etc. Although the above-mentioned magnetic field distribution optimization methods have made some progress in force-magnetic conversion accuracy, they have overlooked a key factor: the mechanical conduction characteristics of the elastic layer. Its stress distribution characteristics not only affect the deformation mode of the magnetic film, but also determine the spatial distribution and linearity of the magnetic response, which is an important factor determining the sensor performance.

[0003] In summary, the current challenges of flexible magnetic tactile sensors are: firstly, the elastic layer is mostly planar, resulting in low stress transmission efficiency; secondly, the elastic layer is generally isotropic, making it impossible to distinguish between forces in the x and y directions; and thirdly, the microstructuring of the magnetic film, one-dimensional sinusoidal magnetization, and Halbach array magnetization methods lead to a more complex magnetic field distribution, increasing the complexity of magnetic field calculation. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a flexible magnetic tactile sensing device, a three-dimensional force measurement device and measurement method based on a microstructure elastic layer, which can quantitatively analyze the influence of hemispherical and pyramidal elastic layers on sensing performance and realize three-dimensional force measurement.

[0005] Technical Solution: The present invention discloses a flexible magnetic tactile sensing device based on a microstructured elastic layer, comprising a flexible magnetic film, a microstructured elastic layer, a Hall sensor, a PCB board, and a bottom shell. The Hall sensor is mounted on the PCB board. The flexible magnetic film, the microstructured elastic layer, the PCB board, and the bottom shell are stacked sequentially from top to bottom. The microstructured elastic layer has a non-planar structure. When the flexible magnetic film is deformed under force, the deformation of the flexible magnetic film is transmitted to the microstructured elastic layer. The Hall sensor measures the change in triaxial magnetic field strength and uploads the data to a PC for data processing to achieve three-dimensional force measurement.

[0006] Optionally, the microstructured elastic layer includes a planar substrate and a hemispherical array.

[0007] Optionally, the microstructured elastic layer includes a planar substrate and a pyramidal array.

[0008] Optionally, the flexible magnetic film has axial magnetization properties.

[0009] Optionally, the center of the flexible magnetic film and the microstructure elastic layer is located on the same vertical line as the center of the Hall sensor.

[0010] The present invention discloses a three-dimensional force measurement device, comprising: a flexible magnetic tactile sensing device, a three-axis displacement stage, a planar probe, a force measurement system, and a magnetic flux density measurement system. The flexible magnetic tactile sensing device is fixed on the upper surface of the three-axis displacement stage, and the planar probe is fixed to the force measurement system. During the contact process between the planar probe and the top flexible magnetic film of the flexible magnetic tactile sensing device, the three-dimensional force causing the change in three-dimensional magnetic flux density is simultaneously measured by the force measurement system and the magnetic flux density measurement system.

[0011] The present invention provides a three-dimensional force measurement method based on the aforementioned three-dimensional force measurement device, comprising the following steps:

[0012] (1) Gradually increase the loading displacement in the z-direction, with equal intervals between each loading displacement. The force sensor measures a total of n sets of z-direction pressure data applied to the flexible magnetic membrane, denoted as F. z1 F z2 ..., F zn Similarly, n sets of x-direction and y-direction displacements were applied in the x-direction and y-direction respectively, and the x-direction shear force F applied to the flexible magnetic membrane was recorded. x1 F x2 ..., F xn and the y-axis shear force F applied to the flexible magnetic membrane y1 F y2 ..., F yn ;

[0013] (2) Under the z-axis pressure F of group n z1 F z2 ..., F znDuring the loading process, the Hall sensor measures n sets of magnetic flux densities in the z-direction, denoted as B. z1 B z2 ... B zn Similarly, the Hall sensor measures the magnetic flux density in the x and y directions, denoted as B. x1 B x2 ... B xn and B y1 B y2 ... B yn ;

[0014] (3) Collect the force value F according to steps (1) and (2). x F y F z and magnetic flux density B x B y B z A one-to-one correspondence dataset, for each force value F x1 F x2 ..., F xn F y1 F y2 ..., F yn F z1 F z2 ..., F zn Each has a corresponding magnetic flux density value B x1 B x2 ... B xn B y1 B y2 ... B yn B z1 B z2 ... B zn Based on the collected data, a three-dimensional force (F) was established using a linear fitting method. x F y F z ) and three-dimensional magnetic flux density (B x B y B z The functional relationship between them;

[0015] (4) Based on the functional relationship between the three-dimensional force and the three-dimensional magnetic flux density obtained by fitting, the magnetic flux density value (B) measured by the Hall sensor is used. x B y B z Substituting the fitted function into the equation, we can calculate the force value in each direction (F). x F y F z ).

[0016] Furthermore, in step (1), during the normal loading and unloading process, the flexible magnetic tactile sensing device is driven upward by controlling the z-axis motion stage of the three-axis displacement stage to obtain the z-axis loading displacement. The normal force is measured using a force measurement system, and combined with the three-dimensional magnetic flux density, the force value is changed by adjusting the z-axis loading displacement to obtain the change in the z-axis magnetic flux density ΔB. z The normal force F of the force measuring system z The data.

[0017] Furthermore, in step (1), during the shear force loading and unloading process, a triaxial displacement stage is used to apply horizontal displacement to the flexible magnetic membrane in the x or y direction. When the planar probe contacts the side of the flexible magnetic membrane, the applied shear force and the change in magnetic induction along the three axial directions are simultaneously recorded by the force measurement system and the magnetic flux density measurement system, thus obtaining the applied x-direction shear force and the corresponding magnetic flux density change ΔB in the x-direction. x The linear relationship between them was determined, and the applied y-direction shear force and the corresponding magnetic flux density change ΔB in the y-direction were obtained. y A linear relationship exists between them.

[0018] Furthermore, the functional relationship between the three-dimensional force and the three-dimensional magnetic flux density obtained in step (3) is: F x =k1B x +b1 F y =k2B y +b2 F z =k3B z +b3

[0019] Among them, F x F y F z B represents the force in the x, y, and z directions in a three-dimensional force, respectively. x B y B z They represent the components in the x, y, and z directions of the three-dimensional magnetic flux density, respectively. k1, k2, k3, b1, b2, and b3 are coefficients obtained through linear fitting.

[0020] Beneficial effects: Compared with the prior art, the significant technical effects of the present invention are as follows: (1) By constructing flexible magnetic tactile sensors with three elastic layers, the z-direction sensitivity of the hemispherical and pyramidal elastic layers is increased by 2.12 times and 2.47 times, respectively, and the x-direction sensitivity is increased by 4.28 times and 5.34 times, respectively, compared with the planar elastic layer; (2) The sensing device can realize three-dimensional force measurement. When the normal force is applied, the flexible magnetic film will produce local deformation in the normal direction, and when the tangential force is applied, the flexible magnetic film will produce tangential displacement. Due to its anisotropy, the pyramidal elastic layer has inconsistent sensitivity in the x and y directions. The y-direction sensitivity is 1.3 times that of the x-direction sensitivity, so the direction of the tangential force can be distinguished according to the magnitude of the tangential sensitivity; (3) According to the quantitative analysis results, the application scenarios suitable for the three different microstructure elastic layers are given. The planar structure is most suitable for applications with a wide measurement range, but its sensitivity is the lowest. In contrast, the pyramidal structure has the highest sensitivity and is very suitable for small signal detection applications. The hemispherical structure achieves a balance between all key performance parameters and is suitable for general sensing tasks. Attached Figure Description

[0021] Figure 1 is a schematic diagram of a flexible magnetic tactile sensing device based on a microstructure elastic layer, where (a) is a schematic diagram of a hemispherical structure and (b) is a schematic diagram of a pyramidal structure.

[0022] Figure 2 is a schematic diagram of a square permanent magnet model;

[0023] Figure 3 is a schematic diagram of the manufacturing and magnetization of flexible magnetic films;

[0024] Figure 4 is a schematic diagram of the magnetic field of the flexible magnetic film;

[0025] Figure 5 is a schematic diagram of the fabrication of three microstructure elastic layers;

[0026] Figure 6 is a schematic diagram of PCB packaging;

[0027] Figure 7 shows a schematic diagram of three types of flexible magnetic tactile sensors with different microstructure layers: (a) hemispherical, (b) pyramidal, and (c) planar.

[0028] Figure 8 is a schematic diagram of a three-dimensional force measurement device;

[0029] Figure 9 is a schematic diagram of the application of normal force;

[0030] Figure 10 is a schematic diagram of the normal force measurement curve, where (a) is a schematic diagram of the measurement results and (b) is a schematic diagram of the hysteresis curve.

[0031] Figure 11 is a schematic diagram of the application of shear force;

[0032] Figure 12 is a schematic diagram of the tangential force measurement curve, where (a) is a schematic diagram of the measurement results and (b) is a schematic diagram of the hysteresis curve;

[0033] Reference numerals: 1: Flexible magnetic film, 2-1: Planar substrate, 2-2: Hemispherical array, 2-3: Pyramid array, 3: Hall sensor, 4: PCB board, 5: Bottom shell, 6: Acquisition board, 7: PC terminal, 8: Right-angle fixing block, 9: Optical platform, 10: Six-axis force sensor, 11: Planar probe, 12: Flexible magnetic tactile sensing device, 13: Three-axis displacement stage, 14: Force acquisition card. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0035] To address the problems of existing technologies, this invention proposes a flexible magnetic tactile sensing device based on the microstructure of an elastic layer. It compares different geometric units (such as hemispheres and pyramids) with planar structures, analyzing the impact of different elastic layer structures on the sensitivity and measurement range of the sensing device. The flexible magnetic tactile sensing device has a layered structure, mainly including an axially magnetized flexible magnetic film, a microstructured elastic layer, and a PCB for mounting a Hall sensor. The flexible magnetic film is axially magnetized under a 5T strong magnetic field. When subjected to forces in the x, y, and z directions, the flexible magnetic film undergoes corresponding deformations. These deformations are transmitted to the microstructured elastic layer, thereby changing the magnetic flux density. The Hall sensor measures the three-dimensional magnetic flux density change, and the magnetic field signal is then transmitted to a PC (Personal Computer) via a data acquisition card. The acquired three-dimensional magnetic flux signal is processed to establish a mathematical model between the three-dimensional magnetic flux density and the three-dimensional force, thus realizing three-dimensional force measurement. When a three-dimensional force is applied to the flexible magnetic membrane, the force is transmitted to the microstructure elastic layer. Due to the inconsistent deformation of the elastic layers with the three types (hemispherical, pyramidal, and planar) under stress, the three-dimensional magnetic flux density of the flexible magnetic membrane changes inconsistently, thus affecting the sensitivity and measurement range of the flexible magnetic tactile sensing device. Experimental data are processed to quantitatively analyze the impact of the elastic layer's geometry on sensor performance (sensitivity and measurement range).

[0036] As shown in Figures 1(a) and 1(b), the flexible magnetic tactile sensing device based on a microstructured elastic layer of the present invention has a layered structure, mainly including: a flexible magnetic film 1, a microstructured elastic layer, a Hall sensor 3, a PCB board 4, and a bottom shell 5. The flexible magnetic film 1, the microstructured elastic layer, the PCB board 4, and the bottom shell 5 are stacked sequentially from top to bottom. The flexible magnetic film is located on the upper layer of the microstructured elastic layer, the microstructured elastic layer is located on the upper layer of the PCB board, the Hall sensor 3 is mounted on the PCB board, and the PCB board is fixed above the bottom shell. As shown in Figure 8, when the flexible magnetic film is deformed by force, the deformation of the flexible magnetic film is transmitted to the microstructured elastic layer. The Hall sensor measures the change in the triaxial magnetic field strength, and the magnetic field signal is transmitted to the PC (Personal Computer) terminal 7 through the acquisition board 6. The three-dimensional force measurement is realized through data processing on the PC terminal.

[0037] The acquisition board 6 is connected and communicates with the PCB board and PC via DuPont wires and USB respectively. The acquisition board 6 transmits the three-dimensional magnetic flux signal output by the flexible magnetic tactile sensing device to the PC for processing.

[0038] Preferably, the microstructure elastic layer adopts a non-planar structure, including a planar substrate 2-1 and a hemispherical array 2-2, or it may include a planar substrate 2-1 and a pyramidal array 2-3. Compared with a planar structure, the non-planar structure has a larger deformation under the same force, thereby enhancing the sensitivity of the sensing device.

[0039] Preferably, the top flexible magnetic film 1 is axially magnetized, which has a lower cost and produces a simpler magnetic field.

[0040] The flexible magnetic film 1 is made by mixing a flexible polymer and magnetic powder. In this embodiment, it is made by mixing PDMS (polydimethylsiloxane) and NdFeB (neodymium iron boron) magnetic powder, with a thickness of 2 mm. After curing, the film is axially magnetized using a 5T strong magnetic field. The microstructure elastic layer is made of PDMS and comes in three shapes: hemispherical, pyramidal, and planar. The hemispherical and pyramidal types are both 4×4 arrays, with a planar substrate height of 1 mm, a radius of 1.5 mm for a single hemisphere, a height of 1.5 mm for a single pyramid, and a center-to-center spacing of 3.75 mm between hemispherical or pyramidal arrays. The planar type has a height of 2.5 mm, and the length and width of the microstructure elastic layer for the hemispherical, pyramidal, and planar types are all 15 mm. The bottom shell 5 is manufactured using 3D printing and is made of high-performance resin. The flexible magnetic film and microstructure elastic layer are assembled using PDMS-specific adhesive. The Hall sensor 3 uses the commercially available MLX90393, and its sensitivity is adjustable. In order to achieve consistent measurement ranges in the x and y directions, the center of the magnetic pole of the flexible magnetic film 1 needs to be aligned with the center of the Hall sensor 3.

[0041] The flexible magnetic film is approximated as a square permanent magnet model, as shown in Figure 2. The permanent magnet is magnetized along the z-direction to achieve uniform and complete magnetization, reaching saturation. According to the Ampere-molecular current hypothesis, the magnetic field at any point in the external space of the magnet is generated by a closed current loop on its side. Taking the origin coordinates of the permanent magnet's magnetic field as (x0, y0, z0) and the coordinates of the field point P as (x, y, z), the formula for calculating the magnetic flux density B at any point on the surface of the square permanent magnet can be obtained as follows:

[0042] Where M is the magnetization, μ0 = 4π × 10 -7 It is the permeability of free space, with units of H / m, where H is Henry and m is meter. x (x, y, z) represents the x-component of the magnetic field produced by a square magnet at a point in space, B. y (x, y, z) represents the y-component of the magnetic field produced by a square magnet at a point in space, B. z (x, y, z) represents the z-component of the magnetic field produced by a square magnet at a point in space. The functions F1 and F2 are defined as follows:

[0043] Where a is half the length of the square permanent magnet in the x-direction, b is half the length of the square permanent magnet in the y-direction, and c is half the length of the square permanent magnet in the z-direction.

[0044] The preparation process of the flexible magnetic film is shown in Figure 3. The flexible magnetic film is composed of NdFeB magnetic powder and PDMS (Dow Corning Incorporated, USA, 184). First, the basic components of PDMS and the curing agent are mixed evenly at a ratio of 10:1. Then, NdFeB magnetic powder is added at a mass ratio of 2:1. After mixing evenly, the mixture is poured into a mold, vacuum degassing is performed, and the film is cured and demolded. The size of the magnetic film is 15mm × 15mm × 2mm. The flexible magnetic film is axially magnetized using a 5T strong magnetic field. The schematic diagram of the magnetized magnetic field is shown in Figure 4.

[0045] The fabrication process of the three microstructured elastic layers is shown in Figure 5. First, three molds are manufactured using 3D printing technology. Then, PDMS components and curing agents are mixed evenly at a ratio of 10:1 and poured into the molds. After vacuum degassing, the mixture is cured and demolded. The Hall sensor used is Melexis' MLX90393. To ensure flatness, the PCB is placed in the mold, and PDMS is poured into the upper surface for encapsulation. Finally, the mold is demolded, as shown in Figure 6. After the three-layer structure is fabricated, the three layers are bonded together using PDMS adhesive. The schematic diagrams of the flexible magnetic tactile sensing devices with the three microstructured elastic layers are shown in Figures 7(a), (b), and (c).

[0046] The performance of the flexible magnetic tactile sensing device can be further altered by changing the materials of the three microstructure elastic layers, such as Ecoflex, to improve sensitivity, hysteresis, and measurement range.

[0047] The measurement method based on the aforementioned flexible magnetic tactile sensing device includes the following steps:

[0048] (1) Gradually increase the loading displacement in the z-direction, with equal intervals between each loading displacement. The force sensor measures a total of n sets of z-direction pressure data applied to the flexible magnetic membrane, denoted as F. z1 F z2 ..., F zn Similarly, corresponding displacement operations were performed in the x and y directions, respectively. n sets of x- and y-direction displacements were applied using a triaxial displacement stage, and the x-direction shear force F applied to the flexible magnetic membrane was recorded. x1 F x2 ..., F xn and the y-axis shear force F applied to the flexible magnetic membrane y1 F y2 ..., F yn .

[0049] (2) Under the z-axis pressure F of group n z1 F z2 ..., F zn During the loading process, the Hall sensor measures n sets of magnetic flux densities in the z-direction, denoted as B. z1 B z2 ... B zn Similarly, the Hall sensor measures the magnetic flux density in the x and y directions, denoted as B. x1 B x2 ... B xn and B y1 B y2 ... B yn .

[0050] (3) The force value F is collected through the measurements in steps (1) and (2). x F y F z and magnetic flux density B x B y B z A one-to-one correspondence dataset. Each force value (F) x1 F x2 ..., F xn F y1 F y2 ..., F yn F z1 F z2 ..., F znEach of these has a corresponding magnetic flux density value (B). x1 B x2 ... B xn B y1 B y2 ... B yn B z1 B z2 ... B zn Based on the collected data, a three-dimensional force (F) was established using a linear fitting method. x F y F z ) and three-dimensional magnetic flux density (B x B y B z The functional relationship between force and magnetic flux density is established as follows: F x =k1B x +b1 (6) F y =k2B y +b2 (7) F z =k3B z +b3 (8)

[0051] In the formula, F x F y F z B represents the force in the x, y, and z directions in a three-dimensional force, respectively. x B y B z They represent the components in the x, y, and z directions of the three-dimensional magnetic flux density, respectively. k1, k2, k3, b1, b2, and b3 are coefficients obtained through linear fitting.

[0052] (4) Based on the fitted expressions (6), (7) and (8), the magnetic flux density value (B) measured by the Hall sensor is used. x B y B z Substituting the values ​​into the linear fitting formula, the force values ​​(F) in each direction can be calculated. x F y F z ).

[0053] As shown in Figure 8, the three-dimensional force measurement device mainly includes a flexible magnetic tactile sensing device 12, a three-axis displacement stage 13, a force measurement system, and a magnetic flux density measurement system. A six-axis force sensor 10 from Kunwei Technology Co., Ltd., model KWR36A, is used as the standard force gauge, with a maximum range of 3 kgf and an accuracy of 0.5% FS. The three-axis displacement stage has a travel of ±6.5 mm along the X / Y axes and a travel of 10 mm along the Z axis, with an accuracy of 0.01 mm. The flexible magnetic tactile sensing device 12 is fixed to the upper surface of the three-axis displacement stage 13. The six-axis force sensor 10 is fixed above the flexible magnetic tactile sensing device using right-angle fixing blocks 8. The 3D-printed planar probe 11 is fixed to the upper surface of the six-axis force sensor 10 using screws. The force measurement system includes a six-axis force sensor 10 and a force acquisition card 14, and transmits force values ​​to a PC 7 via Ethernet. The magnetic flux density measurement system includes an acquisition board 6 (Arduino UNO model) and a PC 7. All devices are mounted on an optical platform 9. During the contact between the planar probe 11 and the top flexible magnetic film, the three-dimensional force causing the change in three-dimensional magnetic flux density is simultaneously measured using both the force measurement system and the magnetic flux density measurement system, as shown in Figure 9. Force and magnetic flux density are measured simultaneously during normal loading and unloading. In the normal loading experiment, the planar probe 11 on the upper surface of the six-axis force sensor 10 is positioned directly above the flexible magnetic film. The flexible magnetic tactile sensing device is driven upwards by controlling the z-axis motion stage, with a z-axis loading displacement of 1 mm and a step size of 0.05 mm. By measuring the normal force using the six-axis force sensor 10 and combining it with the three-dimensional magnetic flux density, the force value is changed by adjusting the z-axis loading displacement, yielding the change in magnetic flux density (ΔB) in the z-axis of three different elastic layers. Z ) and the normal force F of the six-axis force sensor z The data is shown in Figure 10(a). Sensitivity is defined as follows:

[0054] Where S represents sensitivity, ΔB represents the change in magnetic flux density, ΔF represents the change in applied external force, B0 is the initial magnetic flux density without external force, and B represents the magnetic flux density with external force. F represents the applied external force. As can be seen from Figures 10(a) and (b), among the three elastic layer structures, the pyramid-shaped elastic layer has the highest sensitivity, while the planar elastic layer has the lowest. Compared to the planar design, the hemispherical and pyramid-shaped elastic layers undergo greater deformation under the same load, resulting in higher sensitivity. In the first stage (0-0.55mm), the sensitivities of the planar, hemispherical, and pyramid-shaped elastic layers are 1.16 μT / gf (0-770gf), 2.87 μT / gf (0-310gf), and 6.20 μT / gf (0-150gf), respectively. That is, the sensitivities of the hemispherical and pyramid-shaped structures are 2.47 times and 5.34 times that of the planar structure, respectively. In the second stage (0.55-1 mm), the sensitivities were 0.83 μT / gf (770-1,700 gf), 1.66 μT / gf (310-780 gf), and 3.24 μT / gf (150-380 gf), respectively. In the second stage, the sensitivities of the hemispherical and pyramidal types were 2 and 3.9 times that of the planar type, respectively. However, the planar elastic layer had the largest measurement range, with the normal measurement ranges of the three elastic layers being 1,700 gf, 780 gf, and 380 gf (based on a total loading displacement of 1 mm). The piecewise linear fitting expressions between the normal force and magnetic flux density of the three different elastic layers, obtained from the calibration results, are shown in Table 1. When an external force is applied, hysteresis occurs due to the elastic recovery characteristics of the elastomer and the magnetic film. As shown in Figure 10(b), the loading and unloading curves of the three elastic layers clearly demonstrate the response and recovery capabilities of the flexible magnetic tactile sensor after the release of the normal force. The lag value can be calculated using the following formula:

[0055] Where H represents hysteresis, and B... loading and B unloading These represent the magnetic flux density under a specific force value during loading and unloading, respectively. B max B0 represents the magnetic flux density at full-scale output, and B0 represents the initial magnetic flux density without external force loading. Measurements showed that the hysteresis errors in the normal direction for the three elastic structures were 4.8%, 4.4%, and 7.2%, respectively.

[0056] Table 1. Expression for Piecewise Linear Fitting Relationship between Normal Force and Magnetic Field

[0057] In Table 1, F z This represents the pressure (i.e., normal force) applied to the flexible magnetic membrane in the z-direction, B. zThis represents the component B of the three-dimensional magnetic flux density in the z-direction. z .

[0058] Specifically, in the piecewise fitting expression for the normal force-magnetic flux density of the planar structure, k3 is 1.16 and b3 is 28.32 in the range of 0-770gf, and k3 is 0.83 and b3 is 274.01 in the range of 770-1700gf. In the piecewise fitting expression for the normal force-magnetic flux density of the hemispherical structure, k3 is 2.87 and b3 is 31.49 in the range of 0-310gf, and k3 is 1.66 and b3 is 399.88 in the range of 310-780gf. In the piecewise fitting expression for the normal force-magnetic flux density of the pyramid-shaped structure, k3 is 6.20 and b3 is 53.40 in the range of 0-150gf, and k3 is 3.24 and b3 is 459.29 in the range of 150-380gf. At the boundary points (770gf, 310gf, 150gf), either coefficient from the two stages can be used. The fitting curves for all three structures are piecewise linear; the first segment represents a loaded displacement of 0-0.55mm, and the second segment represents a loaded displacement of 0.55-1mm.

[0059] Similarly, shear experiments were conducted on three elastic layers to evaluate the shear performance of the sensing device. It is evident that the planar and hemispherical structures exhibit consistent shear force responses in both the x and y directions, as these two structures are isotropic in the x and y directions. Therefore, only the test results in the x direction are presented. However, due to the anisotropy of the pyramid structure, significant differences exist in the response when shear force is applied separately in the x and y directions. Therefore, measurements in both directions are crucial for accurately capturing its mechanical behavior under different shear forces. In the shear experiments, a triaxial displacement stage was used to apply a 2 mm horizontal displacement to the flexible magnetic membrane in either the x or y direction, with a step size of 0.05 mm. During the experiment, a planar probe was placed on the side of the flexible magnetic tactile sensing device. When the planar probe contacts the side of the flexible magnetic membrane, as shown in Figure 11, the applied shear force and the change in magnetic flux density along the three axial directions are simultaneously recorded by the force measurement system and the magnetic flux density measurement system. Figure 12(a) shows the applied x-direction shear force and the corresponding change in magnetic flux density (ΔB) in the x-direction. XThe linear relationship between the two is shown. For shear sensing tests, the sensitivities of the three elastic layer structures in the first stage (0-0.75mm) are 2.89 μT / gf (0-190gf), 5.37 μT / gf (0-100gf), 9.62 μT / gf (0-55gf), and 12.60 μT / gf (0-40gf), respectively, corresponding to planar, hemispherical, pyramidal-x, and pyramidal-y structures. The sensitivities of the hemispherical and pyramidal structures are 1.86 times, 3.33 times, and 4.36 times that of the planar structure, respectively. In the second stage (0.75-2 mm), the corresponding sensitivities were 2.00 μT / gf (190-600 gf), 4.24 μT / gf (100-300 gf), 8.56 μT / gf (55-150 gf), and 11.46 μT / gf (40-115 gf), respectively, indicating that the sensitivities in the x and y directions for the hemispherical and pyramidal structures were 2.12 times, 4.28 times, and 5.73 times higher than those for the planar structure, respectively. For the pyramidal structure, the sensitivities in the x and y directions were not the same. Specifically, in the first and second stages, the sensitivity in the y direction was approximately 1.3 times that in the x direction. Therefore, the direction of the shear force could be determined by this difference in sensitivity. Although the planar structure had the lowest sensitivity, it had the largest measurement range. The shear measurement ranges for the planar, hemispherical, and pyramidal elastic layers were 600 gf, 300 gf, and 150 gf, respectively (based on a total loaded displacement of 2 mm). Similarly, based on the tangential experimental data, the piecewise linear fitting expressions between the tangential force and magnetic flux density of the three different elastic layers are shown in Table 2. Figure 12(b) shows the loading and unloading curves of the magnetic tactile sensors of the three elastic layers in the tangential direction. According to Equation (4), the hysteresis errors of the three elastic structures in the tangential direction are 1.3%, 5.2%, and 6.2%, respectively.

[0060] Table 2. Expressions for Piecewise Linear Fitting Relationship between Tangential Force and Magnetism

[0061] In Table 2, F x This represents the x-axis shear force applied to the flexible magnetic membrane, B. x This represents the component of the three-dimensional magnetic flux density in the x-direction; F y This represents the y-axis shear force applied to the flexible magnetic membrane, B. y This represents the component of the three-dimensional magnetic flux density in the y-direction.

[0062] Specifically, in the piecewise fitting expression for the tangential force-magnetic flux density of the planar structure, k1 is -2.89 and b1 is -31.96 in the range of 0-190gf, and k1 is -2 and b1 is -188.16 in the range of 190-600gf. For the hemispherical structure, k1 is -5.37 and b1 is -18.78 in the range of 0-100gf, and k1 is -4.24 and b1 is -115.27 in the range of 100-300gf. For the pyramidal structure, k1 is -9.62 and b1 is 11.42 in the x-direction tangential force-magnetic flux density range of 0-55gf, and k1 is -8.56 and b1 is -74.48 in the range of 55-150gf. In the piecewise fitting expression of tangential force-magnetic flux density in the y-direction for the pyramid-shaped structure, k² is -12.60 and b² is 0.79 in the range of 0-40 gf, and -11.46 and -74.87 in the range of 40-115 gf. The fitting curves for all three structures are piecewise linear; the first segment represents the loaded displacement from 0 to 0.75 mm, and the second segment represents the loaded displacement from 0.75 to 2 mm. The planar and hemispherical structures are centrally symmetric, so the fitting expressions for the x-direction and y-direction tangential forces can be considered consistent. However, the pyramid-shaped structure is not centrally symmetric, so separate expressions for the x-direction and y-direction tangential forces are required.

[0063] Based on experimental data in both normal and tangential directions, planar structures are best suited for applications with wide measurement ranges in terms of sensitivity, measurement range, and hysteresis, but they have the lowest sensitivity. In contrast, pyramidal structures offer the highest sensitivity and are ideal for applications requiring small signal detection. Hemispherical structures achieve a balance among all key performance parameters and are suitable for general-purpose sensing tasks.

Claims

1. A flexible magnetic haptic sensing device based on a microstructured elastic layer, characterized in that, The flexible magnetic touch sensor device comprises a flexible magnetic film, a microstructure elastic layer, a Hall sensor, a PCB board and a bottom shell, the Hall sensor is installed on the PCB board, the flexible magnetic film, the microstructure elastic layer, the PCB board and the bottom shell are stacked in sequence from top to bottom, the microstructure elastic layer is a non-planar structure, when the flexible magnetic film is deformed under force, the deformation of the flexible magnetic film is transmitted to the microstructure elastic layer, the change of the three-axis magnetic field intensity is measured through the Hall sensor, and the change is uploaded to a PC end for data processing to realize three-dimensional force measurement.

2. The microstructured elastomeric layer-based flexible magneto-tactile sensing device of claim 1, wherein, The microstructure elastic layer comprises a planar base and a hemispherical array.

3. The microstructured elastomeric layer-based flexible magneto-tactile sensing device of claim 1, wherein, The microstructure elastic layer comprises a planar base and a pyramid array.

4. The microstructured elastomeric layer-based flexible magneto-tactile sensing device of claim 1, wherein, The flexible magnetic film has axial magnetization performance.

5. The microstructured elastomeric layer-based flexible magneto-tactile sensing device of claim 1, wherein, The center of the flexible magnetic film and the center of the microstructure elastic layer are located on the same vertical line.

6. A three-dimensional force measuring device, characterized by The flexible magnetic touch sensor device, the three-axis displacement table, the planar probe, the force measuring system and the magnetic flux density measuring system are used to measure the three-dimensional force causing the change of the three-dimensional magnetic flux density through the force measuring system and the magnetic flux density measuring system in the process that the planar probe contacts the top flexible magnetic film of the flexible magnetic touch sensor device. The method comprises the following steps:

7. A method of three-dimensional force measurement based on the apparatus of claim 6, characterized by, The function relationship between the three-dimensional force and the three-dimensional magnetic flux density obtained through the fitting in step (3) is as follows: (1) gradually increase the loading displacement in z direction, each loading displacement is equal interval, force sensor measures n groups of z direction pressure data applied on flexible magnetic film, recorded as F z1 , F z2 , ..., F zn ; similarly, respectively load n groups of x direction and y direction displacement in x direction and y direction respectively, record x direction shear force F x1 , F x2 , ..., F xn and y direction shear force F y1 , F y2 , ..., F yn applied on flexible magnetic film; (2) During the loading process of n sets of z-direction pressure F z1 , F z2 ,..., F zn , the Hall sensor measures n sets of z-direction magnetic flux density, denoted as B z1 , B z2 ,..., B zn ; Similarly, the Hall sensor measures the x-direction and y-direction magnetic flux density, denoted as B x1 , B x2 ,..., B xn and B y1 , B y2 ,..., B yn ; (3) Collecting force values F according to step (1) and step (2) x , F y , F z , and magnetic flux density B x , B y , B z , a one-to-one data set, each force value F x1 , F x2 , …, F xn , F y1 , F y2 , …, F yn , F z1 , F z2 , …, F zn has a corresponding magnetic flux density value B x1 , B x2 , …, B xn , B y1 , B y2 , …, B yn , B z1 , B z2 , …, B zn ; based on the collected data, using linear fitting method, respectively, the function relationship between three-dimensional force (F x , F y , F z ) and three-dimensional magnetic flux density (B x , B y , B z ); (4) According to the function relationship between the three-dimensional force and the three-dimensional magnetic flux density obtained by fitting, the magnetic flux density value (B x , B y , B z ) measured by the Hall sensor is substituted into the function relationship obtained by fitting, that is, the force value in each direction (F x , F y , F z ) is calculated.

8. The three-dimensional force measuring device of claim 7, wherein, In step (1), the flexible magnetic tactile sensor device is driven upward by controlling the z-direction motion table of the triaxial displacement table during the normal loading and unloading process, the z-direction loading displacement is obtained, the normal force is measured by using the force measurement system, the change amount ΔB of the magnetic flux density in the z-direction is obtained by adjusting the z-direction loading displacement to change the force value, in combination with the three-dimensional magnetic flux density z and the data of the normal force F of the force measurement system. z ​ 9. The three-dimensional force measuring device of claim 7, wherein, In step (1), during the loading and unloading of shear force, a triaxial displacement table is used to apply horizontal displacement to the flexible magnetic film in the x or y direction. When the plane probe contacts the side of the flexible magnetic film, the applied shear force and the change in magnetic induction along the three axis directions are recorded simultaneously by the force measuring system and the magnetic flux density measuring system, obtaining the linear relationship between the applied x-direction shear force and the corresponding magnetic flux density change ΔB x x, and obtaining the linear relationship between the applied y-direction shear force and the corresponding magnetic flux density change ΔB y y.

10. The three-dimensional force measurement method of claim 7, wherein, ​ F x = k1B x + b1 F y = k2B y + b2 F z = k3B z + b3 where F x , F y , F z represent forces in x, y, z directions of three-dimensional force respectively, B x , B y , B z represent components in x, y, z directions of three-dimensional magnetic flux density respectively, k1, k2, k3, b1, b2, b3 are coefficients obtained by linear fitting.

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