A three-dimensional force detection method

Abstract

The present invention provides a split-type flexible magnetic tactile sensor with three-dimensional force sensing function and a detection method. The split-type flexible magnetic tactile sensor magnetizes the magnetic film by adopting a folding magnetization method to simulate ideal centripetal magnetization, and completes the three-dimensional decoupling of the folding magnetization through correction. This not only enhances the magnetic field strength and magnetic field gradient generated by the magnetic film at the position of the Hall sensor, enabling a relatively large distance to be maintained between the magnetic film of the tactile sensor and the Hall sensor for split-type sensing and realizing lossless split installation; at the same time, it also makes the tactile sensor have higher sensitivity compared with simple magnetization methods such as unidirectional magnetization. Through the above settings, the tactile sensor of the present invention can calculate and sense three-dimensional forces through only one unit according to the three-dimensional magnetic field strength in combination with the constructed three-dimensional force decoupling model, which is equivalent to the force sensing dimension of the human skin and has certain application potential in multiple fields such as bionic robots and flexible electronics.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible tactile sensors, and particularly relates to a split-type flexible magnetic tactile sensor with three-dimensional force sensing function and a detection method. Background Art

[0002] During the process of evolution, organisms have acquired sensory organs with a wide range of functions, enabling them to perceive the surrounding environment and prey and improve their survival ability. Among them, the tactile perception ability of three-dimensional mechanical forces enables humans and other animals to perform delicate operations and effective predation. With the continuous progress of algorithms, materials, and manufacturing technologies, researchers have developed various flexible tactile sensors by mimicking biological sensory organs, enabling robots or intelligent machines to have higher intelligence, better interactivity, and adaptability.

[0003] Currently, existing flexible tactile sensors include various principles such as piezoelectric, piezoresistive, capacitive, optical, triboelectric, etc. Most of these flexible tactile sensors have great advantages in high-precision perception and high-speed response. However, with the continuous improvement of the performance of flexible sensors, the complexity of their internal circuits has been increasing, which greatly increases the manufacturing difficulty of the sensors. Moreover, in frequent mechanical contacts, the built-in circuits of such flexible tactile sensors are prone to damage, making it difficult to ensure the stability of operation.

[0004] Flexible tactile sensors based on magnetic fields have the advantages of simple structure, high physical robustness, low cost, and wireless penetration, which can effectively make up for the above problems. In some existing solutions, hard permanent magnets are embedded to increase the magnetic field strength, but this reduces the flexibility of the sensor, making it easy to be damaged when applying large external impacts. Other solutions use flexible magnetic materials, but the magnetic field is weak and the sensing distance is short. Moreover, they do not fully utilize the advantage of wireless penetration of the magnetic field.

[0005] In addition, most of the existing flexible sensing units only have the ability to simultaneously sense one-dimensional force or two-dimensional force, and cannot identify the magnitude and direction of three-dimensional force. In many application scenarios, multi-dimensional perception can only be achieved by combining multiple sensing units in different directions, which brings certain limitations to many applications in fields such as bionic robots like human skin. Summary of the Invention

[0006] To solve the problems existing in the prior art, the present invention provides a split-type flexible magnetic tactile sensor with three-dimensional force sensing function and a detection method, which can achieve wireless sensing through split-type installation, make full use of the magnetic field sensing advantage of the centripetal magnetized magnetic film, and combine with the constructed three-dimensional force decoupling model. Only one unit can calculate the magnitude of the three-dimensional force received according to the magnetic field changes in any direction in the three-dimensional space.

[0007] A split-type flexible magnetic tactile sensor with three-dimensional force sensing function, comprising:

[0008] A flexible contact layer installed on the outside of the base body, the flexible contact layer includes a silicone flexible layer sequentially arranged on the outside of the base body and a square magnetic film magnetized centripetally; the cross-sectional size of the magnetic film is the same as the cross-sectional size of the silicone flexible layer, and the two are installed vertically aligned;

[0009] A three-dimensional Hall sensor, one side of the chip body of the Hall sensor is installed on the inside of the base body, and the chip body is parallel to the magnetic film and arranged on the same central axis.

[0010] In the above structure, the vertical alignment installation of the magnetic film and the silicone flexible layer means that each side of the two is vertically aligned. The base body is the application surface of the split-type flexible magnetic tactile sensor.

[0011] The split-type flexible magnetic tactile sensor of the present invention adopts a split-type installation of the flexible contact layer and the Hall sensor. The flexible contact layer is composed of a completely flexible magnetic film and a silicone flexible layer, without any electronic components and cables embedded, and does not directly contact the Hall sensor, which improves the upper limit of the force and physical impact of the flexible contact layer and has extremely strong physical robustness.

[0012] The present invention can install the flexible contact layer and the Hall sensor on an installation base body without damage. In some closed environments and situations where there are requirements for non-damage to the installation location, it has excellent application capabilities. For example, in the high-pressure environment of the extreme deep sea, tactile perception can be realized while maintaining the integrity of the submersible cabin or the robot shell.

[0013] In addition, the present invention magnetizes the magnetic film by means of centripetal magnetization, so that a symmetric magnetic field is generated around the magnetic film. When the magnetic film is subjected to an external force, the magnetic film moves in a plane, and then the silicone flexible layer is squeezed and / or pulled to generate deformation. The magnetic film generates a position offset relative to the Hall sensor, causing a change in the magnetic field of the magnetic film at the position of the Hall sensor. By analyzing and calculating the change in the three-dimensional magnetic field sensed by the Hall sensor, the three-dimensional position offset of the magnetic film can be obtained, and then according to the material properties such as the Young's modulus of the silicone flexible layer, the magnitude and direction of the external force can be obtained, realizing the perception of three-dimensional force.

[0014] It should be noted that when the magnetic film is subjected to an external force, it needs to maintain planar movement, that is, there should be no depression, tilt or rotation. It is required that the contact area between the acting object and the magnetic film is large enough, and generally the contact area is required to be the area of the magnetic film.

[0015] To achieve the three-dimensional decoupling of the magnetic field and then calculate the three-dimensional force, the present invention proposes the concept of ideal centripetal magnetization. The so-called ideal centripetal magnetization direction is from the edge of the magnetic film to the center of the magnetic film, but this ideal state is difficult to achieve in actual operation. Preferably, the square magnetic film is centripetally magnetized in the following manner:

[0016] First, fold the square magnetic film to form an arrow cluster structure, and then magnetize the folded magnetic film; after the magnetic film is flattened, the creases formed by folding are four linear structures evenly distributed at equal angles along the center of the magnetic film.

[0017] By using the above method of folding the magnetic film first and then magnetizing it, a magnetic film with approximate centripetal magnetization is obtained to replace the ideal centripetal magnetization magnetic film.

[0018] Preferably, when a larger sensing range is required in a single direction, the chip body can be translated relative to the magnetic film in that direction for implementation, and only one calibration is required. Different from the three-dimensional force sensing function obtained by fitting many experimental calibration data, the three-dimensional force sensing function of the present invention only requires one calibration after the device is installed, greatly reducing the workload.

[0019] Preferably, the three-dimensional Hall sensor is an MLX90393 three-dimensional Hall sensor, including an MLX90393 chip body, a PCB board, and pin headers.

[0020] Preferably, the magnetic film can be prepared from the following materials by weight percentage:

[0021]

[0022] As a further preference, the preparation process of the centripetally magnetized square magnetic film is as follows:

[0023] Mix the SE1700 substrate, SE1700 catalyst, Ecoflex 00-30B component, nano-silica particles, and neodymium iron boron magnetic particles by stirring and then pre-degassing to obtain a clay-like mixture;

[0024] Place the evenly mixed clay-like mixture between two glass plates and squeeze it into a thin film. Control the thickness of the thin film by placing gaskets with a set thickness at the edge, then place the glass plates and the thin film together in a constant temperature oven for curing, and finally cut out a square thin film with a set size;

[0025] Fold the square thin film into an arrow cluster shape and place it in a strong magnetic coil for magnetization, thus obtaining the centripetally magnetized square magnetic film.

[0026] Preferably, the silicone flexible layer can be prepared from the following materials by weight percentage:

[0027] Component A of Ecoflex 00-30: 40%

[0028] Component B of Ecoflex 00-30: 40%

[0029] Dimethyl silicone oil with a viscosity of 5: 20%.

[0030] As a further preference, the preparation process of the silicone flexible layer includes:

[0031] After stirring and premixing the Component A of Ecoflex 00-30, the Component B of Ecoflex 00-30 and the dimethyl silicone oil with a viscosity of 5 and then pre-degassing, they are injected into a mold for degassing in a vacuum, and then cured at room temperature to obtain the silicone flexible layer.

[0032] As a preference, the flexible magnetic tactile sensor further includes a single-chip microcomputer that is signal-connected to the Hall sensor, and the single-chip microcomputer calculates the three-dimensional force through the following three-dimensional force decoupling model:

[0033]

[0034]

[0035]

[0036] In the formula, S represents the magnetic film contact area; H represents the thickness of the silicone flexible layer; G represents the shear modulus of the silicone flexible layer; E represents the elastic modulus of the silicone flexible layer; k = 2π / λ, k represents the sine wave number, and λ is equal to the side length of the magnetic film; (x0, y0, z0) represents the initial coordinates of the center point of the magnetic film;

[0037] (x1, y1, z1) represents the coordinates of the center point of the magnetic film after displacement; a1, a2, and a3 are respectively the compensation coefficients of the shear modulus and the elastic modulus; b1, b2, and b3 are respectively the calibration error compensation coefficients;

[0038] Rx, Ry, and Sz respectively represent the decoupling parameters in the three-dimensional directions, and the calculation formulas are as follows:

[0039]

[0040]

[0041]

[0042] In the formula, B x 、B y 、B z respectively represent the magnetic flux densities in the three-dimensional directions at the coordinates (x, y, z); k1, k2, c1, and c2 respectively represent the decoupling compensation coefficients.

[0043] The present invention also provides a three-dimensional force detection method, which obtains the magnetic field intensities in three-dimensional directions by using the split-type flexible magnetic tactile sensor with three-dimensional force sensing function described in any one of the above, and calculates the forces in three-dimensional directions respectively through the following three-dimensional force decoupling model:

[0044]

[0045]

[0046]

[0047] In the formula, S represents the magnetic film contact area; H represents the thickness of the silicone flexible layer; G represents the shear modulus of the silicone flexible layer; E represents the elastic modulus of the silicone flexible layer; k = 2π / λ, k represents the sine wave number, and λ is equal to the side length of the magnetic film; (x0, y0, z0) represents the initial coordinates of the center point of the magnetic film; (x1, y1, z1) represents the coordinates of the center point of the magnetic film after displacement; a1, a2, and a3 are respectively the compensation coefficients of the shear modulus and the elastic modulus; b1, b2, and b3 are respectively the calibration error compensation coefficients;

[0048] Rx, Ry, and Sz respectively represent the decoupling parameters in three-dimensional directions, and the calculation formulas are as follows:

[0049]

[0050]

[0051]

[0052] In the formula, B x , B y , B z respectively represent the magnetic flux densities in three-dimensional directions at the coordinate (x, y, z); k1, k2, c1, and c2 respectively represent the decoupling compensation coefficients.

[0053] It should be noted that (x0, y0, z0) and (x1, y1, z1) can represent the initial coordinates and the coordinates after displacement of any point on the magnetic film. For the convenience of description, they are uniformly written as the initial coordinates and the coordinates after displacement of the center point of the magnetic film in this article.

[0054] The construction process of the above three-dimensional force decoupling model is as follows:

[0055] Assume that there is an ideal centripetally magnetized square magnetic film with a thickness of d in the x-y plane. The upper and lower surfaces of the magnetic film are located at z = d and z = 0 respectively. The centripetal magnetization arrangement of the magnetic film is the superposition of two orthogonal sine curves on the x-y plane. The remanent magnetization in the magnetic film can be expressed as:

[0056] mx = m0sin(kx), m y = m0sin(ky), m z = 0 (1)

[0057] where k = 2π / λ, representing the wave number; λ is equal to the side length of the square magnetic film; m0 represents the maximum value of m x and m y (since it is a square magnetic film, the maximum values of m x and m y are equal).

[0058] The magnetization arrangement of the ideally centripetally magnetized magnetic film is as shown in (a) of Figure 6 where the magnetic potential Φ obeys the Poisson equation inside the magnetic film and the Laplace equation outside the magnetic film:

[0059]

[0060]

[0061] Therefore, the particular solution of formula (2b) is -m0k(cos(kx) + cos(ky)); the general solution of formulas (2a) and (2b) is:

[0062] Φ outside = (A1e -kz + B1e kz )cos(kx) + (A2e -kz + B2e kz )cos(ky) (3a)

[0063]

[0064] The above general solution obeys the following four boundary conditions: (1) When z approaches infinity, the magnetic field and magnetic potential must approach zero; (2) The tangential magnetic field must match on the surface; (3) The normal magnetic flux density on the surface must be continuous; (4) The magnetic potential is symmetric about the plane z = d / 2, that is:

[0065] Φ outside | z→±∞ = 0 (4a)

[0066] Φ outside | z＝0 = Φ inside | z＝0 (4b)

[0067]

[0068] Φ inside (x, y, z) = Φ inside (x, y, d - z) (4d)

[0069] Using the above general solution and the four boundary conditions, the following solution can be calculated:

[0070]

[0071]

[0072] The magnetic field H is the negative gradient of the scalar potential Φ (magnetic potential), and when the remanent magnetization M outside the magnetic film is 0, the magnetic flux density B is proportional to H, i.e.:

[0073]

[0074] In the formula, μ0 represents the magnetic permeability of vacuum.

[0075] Combining formulas (5a), (5b) and (6), the magnetic flux densities in the three-axis directions at any coordinate point (x, y, z) can be calculated as follows:

[0076] B x =-Ke kz sin(kx) (7)

[0077] B y =-Ke kz sin(ky) (8)

[0078] B z =Ke kz (cos(kx)+cos(ky)) (9)

[0079] In the formula,

[0080] According to formulas (7) to (9), the relationship between the position (x, y, z) below the magnetic film and the magnetic flux densities B x , B y , and B z can be obtained:

[0081]

[0082]

[0083]

[0084] Therefore, the relative displacements Δx, Δy, and Δz of the magnetic film in the three-axis directions can be calculated through formulas (10) to (12):

[0085]

[0086]

[0087]

[0088] In the formula, (x0, y0, z0) represents the initial coordinates of the center point of the magnetic film; (x1, y1, z1) represents the coordinates of the center point of the magnetic film after displacement.

[0089]

[0090]

[0091]

[0092] As can be seen from the above, the magnetic film with ideal centripetal magnetization can achieve complete three-dimensional decoupling. Through three-dimensional decoupling, the decoupling parameters Rx, Ry, and Sz calculated are independently related to the x-axis displacement, y-axis displacement, and z-axis displacement of the magnetic film respectively. That is, Rx only changes with the change of the x-axis displacement of the magnetic film, and Rx remains constant when the y-axis and z-axis displacements change; Ry only changes with the change of the y-axis displacement of the magnetic film, and Ry remains constant when the x-axis and z-axis displacements change; Sz only changes with the change of the z-axis displacement of the magnetic film, and Sz remains constant when the x-axis and y-axis displacements change. Therefore, the measurements of the three-axis displacements of the magnetic film are all independent of each other. Moreover, because the silicone flexible layer 3 is isotropic, the magnitudes of the component forces in each axial direction received by the tactile sensor can also be independently measured according to the magnitudes of Rx, Ry, and Sz. Based on this theory, the split-type flexible magnetic tactile sensor proposed by the present invention can realize the perception and calculation of three-dimensional forces in space.

[0093] However, the ideal centripetal magnetization method is difficult to achieve in actual operation. Therefore, the present invention adopts an approximate folded centripetal magnetization method to simulate ideal centripetal magnetization.

[0094] The present invention compares the magnetic field distributions of the magnetic film with ideal centripetal magnetization and the folded centripetal magnetization magnetic film proposed by the present invention through COMSOL simulation. As Figure 6 shown in (a) and (b), they are respectively schematic diagrams of the internal remanent magnetization distributions of ideal centripetal magnetization and the folded centripetal magnetization of the present invention; Figure 7 is the magnetic field comparison of the magnetic film with ideal centripetal magnetization and the folded centripetal magnetization magnetic film of the present invention in the plane where z = -20 mm. It can be seen from Figure 7 that the magnetic flux densities generated by the two magnetization methods are very similar, especially B x (average deviation 3.50 μT), By (average deviation 3.58 μT), and the magnetic field direction in the x-y plane (average deviation 0.14°). The main difference between the magnetic fields generated by the two magnetization methods lies in the magnetic field on the z-axis. B z has an average deviation of 26.70 μT, with a relatively large difference. Therefore, in order to better achieve three-dimensional decoupling for actual folded centripetal magnetization, it is necessary to correct B z .

[0095] According to Ampere's circulation hypothesis, the magnetic field inside the magnetic film can be equivalent to the circular currents on the upper and lower surfaces of the magnetic film. The external magnetic fields generated by them are superimposed on each other to obtain the magnetic field around the centripetally magnetized magnetic film. The magnetic field distribution of the circular current can be calculated by Biot-Savart law:

[0096]

[0097] In the formula, μ0 represents the magnetic permeability in vacuum; I represents the source current; represents the vector from the current element to the field point to be calculated; represents the infinitesimal line element of the source current; r represents the modulus of the vector .

[0098] As Figure 8 shown, taking AB as an example, the position of the current element on AB is (b, y0, h), and the current magnitude is I = J·db, where J represents the current density; it can be obtained that:

[0099]

[0100] The external magnetic field generated by the current AB can be expressed as:

[0101]

[0102] Similarly, it can be obtained that:

[0103]

[0104]

[0105]

[0106]

[0107]

[0108]

[0109]

[0110] In the formula, db represents the current width; x0, y0, and z0 respectively represent the position coordinates of the current element on the current to be calculated; x, y, and z represent the coordinates of the field point to be calculated;

[0111] Therefore, the magnetic fields generated by the upper and lower circular currents at a distance b from the center of the magnetic film surface are as follows:

[0112] B b= B(AB) + B(BC) + B(CD) + B(DA) + B(A'B') + B(B'C') + B(C'D') + B(D'A') (20)

[0113] The external magnetic field generated by the equivalent current of the folded centripetal magnetized magnetic film can be expressed as:

[0114]

[0115] The three-dimensional magnetic field at any point in the external space of the folded centripetal magnetized magnetic film can be accurately calculated from formula (21).

[0116] To quantitatively evaluate the decoupling effect, the present invention introduces an index D, which represents the difference between the standard deviation of the decoupling parameter values in the decoupling plane divided by the average value of the decoupling parameter values in the two normal offset planes of ±0.25 mm, as shown in formula (22):

[0117]

[0118] In addition, the present invention also selects the index CV (coefficient of variation, also known as relative standard deviation) to assist in evaluating the decoupling effect, which represents the standard deviation of the decoupling parameter values in the decoupling plane divided by the average value of the decoupling parameters, as shown in formula (23):

[0119]

[0120] According to formula (21), the three-dimensional magnetic field values (magnetic flux density) at the required positions within the space range can be calculated. Substitute the obtained three-dimensional magnetic field values into formulas (16) - (18) to calculate the magnitudes of the decoupling effect evaluation indices D and CV, and use this to correct the decoupling formula for ideal centripetal magnetization, as far as possible eliminating the deviation between the ideal model and the actual model, and obtaining the accurate decoupling formula for the folded magnetized magnetic film.

[0121] In addition, it should be noted in actual perception that the magnetic film needs to maintain translational motion during the force application process to reduce the perception error. Considering the deformation degree of the silicone flexible layer and the range of formula correction implementation, the displacement working range of the sensor is: -3 mm ≤ Δx, Δy ≤ 3 mm, 0 mm ≤ Δz ≤ 3 mm. Taking the magnetic film size of 20 mm * 20 mm * 1 mm and the distance between the magnetic film and the chip body of 23 mm as an example (i.e., z = -23 mm below the magnetic film), within a range larger than the actual working range (Δx, Δy = ±5 mm, Δz = 0 - 6 mm), the D and CV obtained directly using the three-dimensional decoupling formulas (16) - (18) for ideal centripetal magnetization are D Rx = 0.344, D Ry = 0.344, D Sz = 0.256 and CV Rx= 6.68%, CV Ry = 6.68%, CV Sz = 0.25%.

[0122] In order to further reduce the data fluctuations of Rx, Ry, and Sz in the corresponding decoupling planes, the present invention introduces two decoupling compensation coefficients k and z to compensate for B z , obtaining the formulas shown in (24)-(26):

[0123]

[0124]

[0125]

[0126] Wherein, k1 and c1 represent the decoupling compensation coefficients on the x-y plane; k2 and c2 are the decoupling compensation coefficients in the z direction;

[0127] Taking the minimum of D as the objective, it can be solved to obtain: k1 = 1.65, c1 = 140 μT, k2 = 0.84, c2 = -17 μT, and then the complete folded centripetal magnetization three-dimensional decoupling formula is obtained.

[0128] After the above correction, the evaluation indexes of Rx, Ry, and Rz are respectively reduced to D Rx = 0.044, D Ry = 0.044, D Sz = 0.097 and CV Rx = 0.88%, CV Ry = 0.88%, CV Sz = 0.09%, and already has a good decoupling effect.

[0129] The sensor indirectly senses the magnitude of the force by the displacement of the magnetic film to sense the deformation of the flexible layer. According to Hooke's law, the applied external force is linearly related to the displacement corresponding to the elastic material. The components F x , F y and F z of the external force in the three-dimensional directions can be calculated by the following formulas:

[0130]

[0131]

[0132]

[0133] Wherein, S is the magnetic film contact area, H is the thickness of the silicone flexible layer, γ, ε, G, and E are respectively the tangential strain, normal strain, shear modulus, and elastic modulus of the silicone flexible layer. For an isotropic silicone elastomer, G = E / (2(1 + v)), where v is the material Poisson ratio.

[0134] According to formulas (13) to (15) and (27) to (29), and introducing six error correction coefficients:

[0135]

[0136]

[0137]

[0138] Wherein, a1, a2, and a3 are respectively the compensation coefficients of the shear modulus and the elastic modulus. Since the shear modulus and the elastic modulus are affected by the bonding situation of the magnetic film, silicone, and glue, and there may be certain manufacturing defects. b1, b2, and b3 are respectively the calibration error compensation coefficients used to compensate for the initial calibration error caused by the installation offset.

[0139] After the split-type flexible magnetic tactile sensor of the present invention is installed, the specific parameters of the three-dimensional force decoupling model can be obtained through one calibration.

[0140] Compared with the prior art, the beneficial effects of the present invention are:

[0141] The flexible magnetic tactile sensor of the present invention magnetizes the magnetic film by adopting the way of folding magnetization to simulate the ideal centripetal magnetization, and completes the three-dimensional decoupling of the folding magnetization through correction. It not only enhances the magnetic field strength and magnetic field gradient generated by the magnetic film at the position of the Hall sensor, enables a relatively large distance to be maintained between the magnetic film and the Hall sensor of the tactile sensor for split-type sensing, and realizes lossless split installation; at the same time, it also makes the tactile sensor have higher sensitivity compared with simple magnetization methods such as unidirectional magnetization. Through the above settings, the tactile sensor of the present invention can calculate and sense the three-dimensional force through only one unit according to the three-dimensional magnetic field strength in combination with the constructed three-dimensional force decoupling model, which is equivalent to the force sensing dimension of the human skin and has certain application potential in many fields such as bionic robots and flexible electronics. BRIEF DESCRIPTION OF THE DRAWINGS

[0142] Figure 1 It is the front view structural schematic diagram of the embodiment of the present invention;

[0143] Figure 2 It is the three-dimensional structural schematic diagram of the embodiment of the present invention;

[0144] Figure 3Schematic diagram of the three-dimensional structure of the three-dimensional Hall sensor in the embodiment of the present invention;

[0145] Figure 4 Schematic diagram of the method for magnetizing the folded magnetic film in the embodiment of the present invention;

[0146] Figure 5 Schematic diagram of the magnetization direction of the magnetic film in the embodiment of the present invention;

[0147] Figure 6 Magnetic field distributions of the ideal centripetal magnetized magnetic film and the folded centripetal magnetized magnetic film proposed by the present invention in COMSOL simulation; among them, (a) is a schematic diagram of the internal remanence distribution of the ideal centripetal magnetized magnetic film; (b) is a schematic diagram of the internal remanence distribution of the folded centripetal magnetized magnetic film;

[0148] Figure 7 Magnetic field comparison between the ideal centripetal magnetized magnetic film and the folded centripetal magnetized magnetic film; among them, (a) is the magnetic field strength and horizontal direction in the x-y plane near the position of the three-dimensional Hall sensor under the ideal centripetal magnetized magnetic film; (b) is the magnetic field strength and horizontal direction in the x-y plane near the position of the three-dimensional Hall sensor under the folded centripetal magnetized magnetic film; (c) is the magnetic film magnetic field distribution in the plane of z = -20 mm under the ideal magnetization condition; (d) is the magnetic film magnetic field distribution in the plane of z = -20 mm under the folded centripetal magnetization of the present invention; (e) is the distribution of the magnetic film magnetic field difference between the two magnetization methods in the plane of z = -20 mm;

[0149] Figure 8 Schematic diagram of the equivalent current on the surface of the folded centripetal magnetized magnetic film;

[0150] Figure 9 Signal diagram generated by the sensing unit under the action of forces in different directions in the embodiment of the present invention.

[0151] In the figure: 1 - substrate, 2 - magnetic film, 3 - silicone flexible layer, 4 - PCB board, 5 - pin, 6 - MLX90393 chip. Detailed implementation manners

[0152] As Figure 1 and 2 shown, the split-type flexible magnetic tactile sensor with three-dimensional force sensing function proposed by the present invention mainly includes two parts, namely a flexible contact layer and a three-dimensional Hall sensor, which are respectively installed on the outer side and the inner side of the substrate.

[0153] The flexible contact layer is composed of a square magnetic film 2 magnetized centripetally and a silicone flexible layer 3. The silicone flexible layer 3 and the magnetic film 2 are sequentially installed on the outer side of the substrate. They have the same size and structure in the x-y plane (cross-section), and their edges are aligned up and down.

[0154] As Figure 3As shown, the three-dimensional Hall sensor includes the MLX90393 chip body 6, the PCB board 4, and the pins 5 of the pin header.

[0155] The material ratio for preparing the magnetic film 2 is: 11.71 wt% of SE1700 substrate, 1.17 wt% of SE1700 catalyst, 21.78 wt% of Ecoflex 00-30B component, 2.72 wt% of nano-silica particles, and 62.62 wt% of neodymium iron boron magnetic particles.

[0156] Mix the above components in a blender at a speed of 2000 revolutions per minute for 3 minutes, then defoam at the same speed for 2 minutes. Place the evenly mixed clay-like mixture between two glass plates and squeeze it into a film. Control the thickness of the film by placing 1-mm spacers at the edges, then place them together in a constant-temperature oven at 120 °C for 1.5 h of curing. Finally, cut out a 20-mm × 20-mm square film. Fold the film into the arrow cluster shape as shown in Figure 4 and place it in a 4-T strong magnetic coil to complete centripetal magnetization. The magnetization direction of the unfolded magnetic film 2 is as shown in Figure 5 and the creases formed by folding are four straight lines evenly distributed at equal angles along the center of the magnetic film.

[0157] The material ratio of the silicone flexible layer 3 is: 40 wt% of Ecoflex 00-30A component, 40 wt% of Ecoflex 00-30B component, and 20 wt% of 5-viscosity dimethyl silicone oil. Mix the foregoing components in a blender at a speed of 2000 revolutions per minute for 2 minutes and defoam for 2 minutes. Inject the mixture into a pre-prepared mold of 20 mm × 20 mm × 10 mm, then defoam in a vacuum and place it at room temperature for 6 h of curing. After the silicone flexible layer 3 is demolded, evenly coat the upper surface with silicone soft glue (Ding Lifeng DL-1020), then flatly attach the centripetally magnetized magnetic film 2 to the upper surface of the silicone flexible layer, and align their edges through a mold. Let it stand at room temperature for 24 h to completely cure the glue and connect the magnetic film 2 and the silicone flexible layer 3 to obtain a flexible contact layer.

[0158] The three-dimensional Hall sensor is composed of the PCB board 4, the pin header 5, and the MLX90393 chip 6. The size of the PCB board is 21 mm × 21 mm × 1 mm, and the size of the MLX90393 chip 6 is approximately 3 mm × 3 mm × 1 mm, which is located at the center of the PCB board 4.

[0159] In this embodiment, the substrate 1 used for display is a 3D-printed PLA plastic block with dimensions of 30 mm × 30 mm × 12 mm. The silicone flexible layer 3 is first pasted on the upper surface (outer side) of the substrate 1 through silicone soft glue, and then the Hall sensor is attached to the lower surface (inner side) of the substrate 1 and the chip is translated. At the same time, the Z-axis magnetic field intensity (B z ) value is measured and observed. The position directly below the center of the magnetic film is where the B z value is the largest. After determining the position, the Hall sensor is also pasted on the lower surface of the substrate 1 using silicone soft glue. After the flexible magnetic tactile sensor is installed, the distance between the magnetic film 2 and the MLX90393 chip 6 is 23 mm.

[0160] Based on the proposed ideal centripetal magnetic film decoupling theory, the mathematical modeling and analysis of the spatial magnetic field distribution below the folded centripetal magnetized magnetic film are carried out using Ampere's circulation hypothesis and Biot-Savart law. Thus, three decoupling parameters corresponding to the three-axis displacement of the magnetic film are obtained:

[0161]

[0162] Among them, B x , B y and B z are the three-axis magnetic field intensities measured by the MLX90393 sensor respectively. k1, k2, c1, and c2 are all decoupling compensation coefficients. In this embodiment, k1, k2, c1, and c2 are calculated to be 1.65, 0.84, 140 μT, and -17 μT respectively.

[0163] The above flexible magnetic tactile sensor further includes a single-chip microcomputer that is signal-connected to the Hall sensor. The single-chip microcomputer calculates the components of the external force received by the magnetic film in the three-dimensional directions through the following three-dimensional force decoupling model:

[0164]

[0165]

[0166]

[0167] In the formula, S represents the magnetic film contact area; H represents the thickness of the silicone flexible layer; G represents the shear modulus of the silicone flexible layer; E represents the elastic modulus of the silicone flexible layer; k = 2π / λ, k represents the sine wave number, and λ is equal to the side length of the magnetic film; (x0, y0, z0) represents the initial coordinates of the center point of the magnetic film; (x1, y1, z1) represents the coordinates of the center point of the magnetic film after displacement; a1, a2, and a3 are the compensation coefficients of the shear modulus and the elastic modulus respectively; b1, b2, and b3 are the calibration error compensation coefficients respectively.

[0168] After the installation of the split-type flexible magnetic tactile sensor is completed, calibrate the device once to obtain:

[0169] F x = 4.391·ΔR x

[0170] F y = 4.391·ΔR y

[0171] F z = 31.49·ΔS z

[0172] Demonstration of the sensor's perception effect:

[0173] Apply one-dimensional forces (F along the z-axis +z , F along the y-axis +y and F along the x-axis -x ), two-dimensional forces (F in the y-z plane +z+y and F in the x-y plane +y-x ) and three-dimensional forces (F in space +z+y-x ) on the above-mentioned flexible magnetic tactile sensor respectively using a three-dimensional moving platform. The aforementioned one-dimensional forces, two-dimensional forces, and three-dimensional forces are all applied according to the magnitude of ; The change values of the three-dimensional decoupling parameter values obtained from the flexible magnetic tactile sensor and the decoupling formula (1) relative to the initial position are as shown in Figure 9 . It can be seen that the three output signals are independently related to the external forces in the three axes respectively, and the directions are consistent with the directions of the applied forces. Therefore, the tactile sensor in this embodiment can well sense the component forces in each axis and calculate the resultant force according to the magnitude of the output signal.

[0174] Substitute Figure 9 ΔR obtained in x = ΔR y = 0.179, ΔS z = 0.221 into the three-dimensional force decoupling model after the above calibration respectively, and the measured forces in the three-dimensional directions are obtained as follows: It can be seen that the measured forces in the x and y directions are consistent with the magnitudes of the actual applied forces, and the error between the measured force in the z direction and the actual applied force is only 3.3%; from this, it can be known that the flexible magnetic tactile sensor of this application can not only realize the perception and calculation of three-dimensional forces, but also has high calculation accuracy.

Claims

1. A three-dimensional force detection method, characterized in that: The three-dimensional magnetic field strength is obtained using a split flexible magnetic tactile sensor with three-dimensional force sensing function. The three-dimensional force is calculated using the following three-dimensional force decoupling model: Where S is the contact area of the magnetic film; H is the thickness of the silicone flexible layer; G is the shear modulus of the silicone flexible layer; E is the elastic modulus of the silicone flexible layer; k = 2π / λ, k is the number of sine waves, and λ is equal to the side length of the magnetic film; (x0, y0, z0) is the initial coordinate of the center point of the magnetic film; (x1, y1, z1) is the coordinate of the center point of the magnetic film after displacement; a1, a2, and a3 are the compensation coefficients of the shear modulus and elastic modulus, respectively; b1, b2, and b3 are the calibration error compensation coefficients, respectively. Rx, Ry, and Sz represent the decoupling parameters in the three-dimensional directions, and the calculation formulas are as follows: where B x , B y , B z respectively represent the magnetic flux densities in the three-dimensional directions at the coordinates (x, y, z); k1, k2, c1, and c2 respectively represent the decoupling compensation coefficients; The split-type flexible magnetic tactile sensor with three-dimensional force sensing function includes: A flexible contact layer is installed on the outside of the base, the flexible contact layer comprising a silicone flexible layer and a centripetally magnetized square magnetic film, which are sequentially arranged on the outside of the base; the cross-sectional dimensions of the magnetic film are the same as the cross-sectional dimensions of the silicone flexible layer, and the two are installed in an aligned manner. A three-dimensional Hall sensor is provided, wherein one side of a chip body of the Hall sensor is mounted on the inner side of a substrate, and the chip body is parallel to the magnetic film and arranged on the same central axis.

2. The three-dimensional force detection method according to claim 1, characterized in that, The square magnetic film is centripetally magnetized in the following manner: First, the square magnetic film is folded to form an arrow cluster structure, and then the folded magnetic film is magnetized; after the magnetic film is flattened, the folding marks are four straight lines distributed at equal angles along the center of the magnetic film.

3. The three-dimensional force detection method according to claim 1, characterized in that, When a larger sensing range is required in a single direction, the chip body can be translated relative to the magnetic film in that direction to achieve this.

4. The three-dimensional force detection method according to claim 1, characterized in that: The split flexible magnetic tactile sensor with three-dimensional force sensing function also includes a single-chip microcomputer connected to the Hall sensor signal, and the single-chip microcomputer calculates the three-dimensional force through the three-dimensional force decoupling model.

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