A system for simultaneous monitoring of three-dimensional forces and identifying surface texture by three-dimensional magnetism

Abstract

This invention belongs to the field of robotics technology and discloses a system for simultaneously monitoring three-dimensional force and recognizing surface texture through three-dimensional magnetism. The system includes an artificial fingerprint film, a cylindrical magnet, a flexible elastomer, a circular protective shell, a flexible acquisition circuit board, and a rigid backplate. The artificial fingerprint film has a serrated ring structure; when it contacts and slides on a textured surface, it causes high-frequency vibrations in the serrated structure. The flexible elastomer deforms under three-dimensional static pressure. The magnetic field change of the cylindrical magnet is related to the vibration and deformation displacement. The flexible acquisition circuit board contains a chip that senses the three-dimensional magnetic field. The circular protective shell and rigid backplate prevent stress concentration at the chip. This invention can analyze the three-dimensional force experienced by the sensor and the texture of the contact surface by decoupling a single magnetic field signal, thus meeting the requirements of three-dimensional tactile perception and material discrimination for robotic fingers.

Description

Technical Field

[0001] This invention belongs to the field of robotics technology, and more specifically, relates to a system for simultaneously monitoring three-dimensional forces and identifying surface textures using three-dimensional magnetism. Background Technology

[0002] Robots need to interact with their surroundings through touch, and use feedback control to optimize this interaction. Touch sensation is typically captured by flexible tactile sensors. Existing flexible tactile sensors primarily focus on sensing quasi-static forces, such as shear forces during sliding or normal forces along the direction of motion, combining the magnitude and direction of these forces to adjust human-robot interaction control strategies in real time.

[0003] However, flexible tactile sensors still lack comprehensive perception of the characteristics of target objects. Taking human finger skin as an example, finger skin can not only sense the physical appearance and weight of objects, but also identify the surface material. Therefore, blind people who have lost their sight can still distinguish different objects of the same shape and weight by touch. Robots also need similar functions. For example, when a robot grasps ceramic cups and plastic cups of the same shape and weight, it needs to adopt different grasping strategies based on the different material properties.

[0004] For the skin of the human fingers, both slow-adapting receptors and fast-adapting receptors are tactile receptors responsible for receiving and transmitting tactile information from the external environment. These two types of receptors differ in their response characteristics and functions. Slow-adapting receptors are mainly distributed in the deeper layers of the skin, such as the dermis. They are more sensitive to sustained stimuli and can maintain a response to stimuli for a longer period. Slow-adapting receptors are primarily responsible for sensing sustained pressure, tactile localization, and changes in skin shape. For example, when touching an object, slow-adapting receptors perceive the object's shape, size, and texture. Fast-adapting receptors are mainly located in the superficial layers of the skin, such as the epidermis. They respond rapidly to brief, rapidly changing stimuli, and quickly cease responding when the stimulus disappears. Fast-adapting receptors are primarily responsible for sensing vibrations, light touches, and minute changes in the skin surface. For example, when the skin is slightly touched or vibrated, fast-adapting receptors quickly transmit this information to the brain and perceive dynamic changes in the external environment. Through these two different types of tactile receptors, the human body can comprehensively and accurately perceive the external world and make accurate judgments about the shape, size, texture, and dynamic changes of objects.

[0005] For robotics, identifying three-dimensional hydrostatic pressure and surface material using a single coupled signal remains challenging. This is because a single flexible tactile sensor struggles to simultaneously achieve highly sensitive three-dimensional hydrostatic pressure sensing and fast-response vibration frequency detection. Hydrostatic pressure detection involves sensing continuous pressure, while vibration detection requires rapid sensing and response to dynamic stimuli, such as minute vibrations or high-frequency surface movements. These two requirements for time response are contradictory. To effectively sense minute changes in three-dimensional features, the sensor needs high sensitivity. For example, the sensor must generate a perceptible signal under minute contact or pressure changes, allowing humans or robots to perceive subtle mechanical features. On the other hand, the sensor also needs a fast response to resolve minute high-frequency vibrations caused by the feature spacing of surface features. This fast response capability allows the sensor to sense and transmit information in a very short time, enabling flexible tactile sensors to accurately identify subtle changes in surface features. For example, in tactile systems, a fast response speed allows the sensor to sense the unevenness of an object's surface to detect its texture. Existing single flexible tactile sensors struggle to balance these two fast and slow characteristics within a single sensor. Therefore, two sensors are often used to couple and measure two signals, such as a capacitive strain sensor and a piezoelectric sensor to couple and measure axial hydrostatic pressure and vibration frequency, respectively. However, tactile sensors that acquire a single signal at high frequency and decouple three-dimensional force and vibration frequency through reverse coupling still need to be developed. Summary of the Invention

[0006] To address the technical challenge of existing flexible tactile sensors in acquiring single signals at high frequencies and decoupling three-dimensional force and vibration frequency, this invention presents a three-dimensional force and surface texture recognition system based on a single magnetic field node. This sensing system monitors the movement of a magnet above the node and calculates the magnitude of the three-dimensional force acting on the node. High sensitivity is achieved through the use of a soft, elastic material, realizing a spatial resolution of tens of micrometers of undulation. Furthermore, the selection of low-hysteresis materials, the design of the surface microstructure, and the high sampling frequency enable the sensing system to rapidly respond to high-frequency vibrations caused by artificial fingerprints on the surface. Therefore, the changes in the coupled magnetic field caused by magnet displacement and vibration are sensed by a chip on the flexible circuit board.

[0007] To achieve the above objectives, according to the present invention, a system for simultaneously monitoring three-dimensional force and identifying surface texture through three-dimensional magnetism is provided. The system includes an artificial fingerprint film, a cylindrical magnet, a flexible elastomer, a circular protective shell, a flexible acquisition circuit board, and a rigid backplate.

[0008] The flexible elastomer has an island structure in the middle, and a reserved hole is provided in the middle of the island. A cylindrical magnet is inserted into the reserved hole and sealed with silicone adhesive. The artificial fingerprint film is attached to the island of the flexible elastomer with silicone adhesive.

[0009] A flexible acquisition circuit board is set at the bottom of a flexible elastomer. A magnetoresistive chip for sensing a three-dimensional magnetic field is installed on the flexible acquisition circuit board. The magnetoresistive chip communicates with the host computer through four wires on the flexible acquisition circuit board and outputs magnetic field information in real time. A circular protective shell and a rigid back plate are attached to the top and bottom surfaces of the flexible acquisition circuit board with light-curing resin. The circular protective shell protects the magnetoresistive chip inside.

[0010] The flexible elastomer has pre-drilled holes that mate with the circular protective shell. The flexible acquisition circuit board is coated with silicone adhesive and is connected to the flexible elastomer by mates with the pre-drilled holes in the flexible elastomer and the circular protective shell.

[0011] Furthermore, the surface of the artificial fingerprint film has multiple concentric circular raised peaks, just like a real fingerprint. When it contacts and slides on a textured object surface, it will cause high-frequency vibration of the sawtooth structure. The flexible elastic body will deform under three-dimensional static pressure. The magnetic field change of the cylindrical magnet is related to the vibration and deformation displacement. The flexible acquisition circuit board has a magnetoresistive chip that senses the three-dimensional magnetic field. The circular protective shell and hard back plate prevent stress concentration at the chip.

[0012] Furthermore, the signal analysis of the sensing system uses a two-level model. The first level low-pass filters the original signal and calculates the three-dimensional force by combining the magnetic field magnitude with the three-dimensional force calibration model. The second level high-pass filters the original signal and identifies the texture of the material by combining the magnetic field vibration frequency and the material type calibration model.

[0013] Furthermore, the sensing system analyzes the three-dimensional force experienced by the sensor and the texture of the contact surface by decoupling a single magnetic field signal.

[0014] Furthermore, the artificial fingerprint film is made of PDMS material and is cast into a resin mold; the ratio of silicone and catalyst in PDMS is between 10:1 and 5:1.

[0015] Furthermore, the diameter of the cylindrical magnet is less than or equal to 3 mm to prevent the magnet from deflecting and thus becoming unable to decouple.

[0016] Furthermore, the flexible elastomer is made using ecoflex10, ecoflex20, or ecoflex30.

[0017] The present invention also provides a method for manufacturing the tactile sensing system as described above, the method comprising the following steps:

[0018] (1) Pour ecoflex10 into a mold and cure it at room temperature for 1 hour to obtain a flexible elastomer;

[0019] (2) Insert a cylindrical magnet with a diameter of 1 mm into the reserved hole of the island of the flexible elastomer and seal it with silicone adhesive.

[0020] (3) Mix PDMS and catalyst in a 5:1 ratio, pour into a mold to form an artificial fingerprint, and use silicone adhesive to attach the artificial fingerprint to the island of flexible elastomer.

[0021] (4) Use photocurable resin to attach the circular protective shell and the rigid back plate to both sides of the flexible acquisition circuit board; the side of the flexible acquisition circuit board that is in contact with the flexible elastomer is the circular protective shell.

[0022] (5) Apply silicone adhesive to the flexible acquisition circuit board and bond it together with the hole reserved in the flexible elastomer and the circular protective shell to obtain the sensing system.

[0023] The present invention also provides an application of the sensing system described above in the skin of a robot finger, which meets the requirements of the robot to perceive three-dimensional touch and distinguish the material of objects.

[0024] In summary, compared with the prior art, the tactile sensing system provided by the present invention has the following advantages:

[0025] 1. Enhanced Overall Performance. Compared to existing tactile sensing systems that require multiple sensors coupled together to measure three-dimensional force and surface texture, this invention achieves both functions using a single node, simplifying the system structure. By integrating multiple functions into one system, not only is the system's complexity and size reduced, but its overall performance and stability are also improved, making the robot more reliable and efficient in practical applications.

[0026] 2. High spatial and temporal resolution. This invention utilizes highly sensitive flexible materials, magnets, and the high-resolution magnetoresistive chip MMC5603NJ to achieve a spatial resolution of tens of micrometers in the sensing system; and leverages surface microstructure and a high sampling rate of 1000Hz to achieve a temporal resolution of vibration signals from 0 to 500Hz. This means the sensing system can detect minute changes in force and surface texture, enabling the robot to interact more accurately with its surroundings, thereby improving the robot's operational precision and efficiency.

[0027] 3. The system is simple and low-cost to manufacture. This invention provides a detailed manufacturing method, including material selection, manufacturing process, and assembly procedures. Using readily available materials and a simple manufacturing process makes the manufacturing of the sensing system much easier, reducing manufacturing costs and difficulty compared to the currently used strain-based three-dimensional force sensing system (ATI mini40) which costs tens of thousands of dollars. This will help promote the application and popularization of this technology and advance the development of robotics.

[0028] 4. Optimized Coupled Signal Analysis Algorithm. This invention employs a two-level model for signal analysis, effectively decoupling three-dimensional force and vibration frequency. The first-level model is used for low-pass filtering and force calibration to calculate the three-dimensional force; the second-level model is used for high-pass filtering and texture recognition to calculate the vibration frequency and map material texture. This enables the sensing system to analyze the signals received by the sensor more accurately, improving the precision and accuracy of signal processing.

[0029] 5. Wide range of applications. The tactile sensing system provided by this invention is applicable to multiple fields such as artificial limbs and robotic finger skin, meeting the requirements of artificial limbs and robots for three-dimensional tactile perception and material differentiation. This technology has broad application prospects and can be applied to various aspects of grasping, manipulation, perception, and interaction in artificial limbs and robots, providing important support for the development of artificial limb and robotics technologies. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the tactile sensing system provided by the present invention;

[0031] Figure 2 This is a schematic diagram of a magnet model;

[0032] Figure 3 This is a schematic diagram of the three-dimensional force monitoring mechanism according to an embodiment of the present invention;

[0033] Figure 4 This is a schematic diagram of the surface texture monitoring mechanism;

[0034] Figure 5 This is a schematic diagram of the Earth's magnetic field shielding along the x-axis;

[0035] Figure 6 This is a schematic diagram of the y-axis geomagnetic field shielding;

[0036] Figure 7 This is a schematic diagram of the geomagnetic field shielding along the z-axis;

[0037] Figure 8 This is a flowchart illustrating the manufacturing process of a tactile sensing system.

[0038] Figure 9 This is a schematic diagram of a decoupling algorithm for coupled signals;

[0039] Figure 10 This is a schematic diagram of the X-direction coupling signal obtained by the present invention.

[0040] Figure 11 This is a schematic diagram of the Y-direction coupled signal obtained by the present invention.

[0041] Figure 12This is a schematic diagram of the Z-method coupling signal obtained by the present invention.

[0042] Figure 13 This is a schematic diagram of a three-dimensional force calibration platform;

[0043] Figure 14 This is a schematic diagram of the force signal in the X direction obtained by the present invention;

[0044] Figure 15 This is a schematic diagram of the force signal in the Y direction obtained by the present invention;

[0045] Figure 16 This is a schematic diagram of the force signal in the Z direction obtained by the present invention;

[0046] Figure 17 It is a calibration platform for vibration frequency and material type;

[0047] Figure 18 This is a schematic diagram of the average power frequency (MPF) signal obtained by passing through two materials in the X direction according to the present invention;

[0048] Figure 19 This is a schematic diagram of the average power frequency (MPF) signal obtained by passing through two materials in the Y direction according to the present invention;

[0049] Figure 20 This is a schematic diagram of the average power frequency (MPF) signal obtained by passing through two materials in the Z direction according to the present invention;

[0050] Among them: 1-Artificial fingerprint film, 2-Cylindrical magnet, 3-Flexible elastomer, 4-Circular protective shell, 5-Photocurable resin, 6-MMC5603NJ magnetoresistive chip, 7-FPCB circuit board, 8-Hard back plate, 9-Surface texture of object; 10-ATI three-dimensional force sensor; 11-Flexible tactile sensor; 12-Second type of fabric; 13-First type of fabric. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0052] The monitoring of tactile signals has always been a key issue in robotics research. Tactile signals are characterized by redundancy and complexity. To acquire high-fidelity tactile signals, researchers have employed methods such as capacitance measurement, piezoresistive effect measurement, ultrasonic measurement, and piezoelectric measurement. Each of these signal detection methods can represent tactile information in a certain aspect. Single pressure detection cannot fully reflect the force situation experienced by the robot. For example, tangential force plays an important role in human-robot interaction, especially in cases involving cyclic impacts and heavy loads. The reaction force between the robot and the ground involves normal force and tangential force, which are closely related to stability and traction. Composite force perception allows robots to adjust their movements, avoid slipping, maintain balance, and adapt to various terrains. However, robots often fail to perceive surface textures due to insufficient spatial and temporal resolution of multidimensional tactile sensors. This may lead to the robot ignoring the material properties of objects (such as eggs) when grasping them, resulting in unnecessary damage or inaccurate operations. This invention, by mimicking the analysis of composite signals by human skin, achieves a tactile sensor with decoupling from single signals, low complexity, and high sensitivity and response for three-dimensional force recognition and surface material recognition.

[0053] Force-magnetic model establishment:

[0054] The force and frequency sensing of this invention is achieved by measuring the magnetic field changes of a cylindrical magnet, and a model is established to analyze the magnet displacement caused by three-dimensional force and the changes in the three-dimensional magnetic field.

[0055] like Figure 2 As shown, let the length of the cylindrical magnet be h and the radius be a. A surface current distribution exists on the cylindrical surface with only axial flow. A cylindrical coordinate system is established with the central axis of the cylindrical magnet as the axis and the center of the middle surface as the origin. The cylindrical magnet is embedded in the upper surface of an elastic layer with thickness L and cross-sectional area A, and the upper surface is subjected to three-dimensional forces (Fx, Fy, Fz). Under the action of these three-dimensional forces, the cylindrical magnet and its cylindrical coordinate system move.

[0056] The hyperelastic properties of elastic bodies are typically described by the Mooney-Rivlin constitutive model, with the strain energy density function expressed as:

[0057] w = C 10 (I1-3)+C 01 (I2-3)

[0058] Where w is the strain energy density, I1 is the first invariant of the strain tensor, I2 is the second invariant of the strain tensor, and C... 01 and C 10 Here are the material parameters. The relationship between stress σ and strain ε can be expressed as:

[0059]

[0060] Within the desired deformation range, the relationship between stress and strain is approximately linear. Therefore, the displacement from the center of the magnet to the center of the chip can be characterized as follows:

[0061]

[0062] Where E is the elastic modulus and υ is Poisson's ratio.

[0063] Therefore, the displacement of the cylindrical magnet and its cylindrical coordinate system is...

[0064]

[0065] Next, we calculate the magnetic field of the chip center relative to the magnet after the displacement change.

[0066] The magnetic field excited by the magnetic sheet can be described by the EMC model. In this model, the magnetic field in the space outside the permanent magnet is assumed to be generated by the current in the side-bound surface.

[0067] Biot-Sava's law is a fundamental law in electromagnetic field theory. In principle, this law can be used to calculate the magnetic field produced by an arbitrary distribution of steady current. In a vacuum, when the current distribution (surface distribution) is known, the magnetic flux density at any point in the magnetic field can be calculated using Biot-Sava's law as follows:

[0068]

[0069] Where Q and P represent the source and field points, respectively; S represents the region of current distribution; dS(Q) represents the area element around the source point; Js(Q) represents the surface current density of Q; R = |rr′| represents the distance between the source and field points; R = rr′ represents the distance vector from the source point to the field point; μ0 = 4π × 10 -7 H / m represents the permeability of free space. The magnetic flux density produced by a cylindrical magnet is calculated using Biotsava's law.

[0070] The coordinates of the chip in the magnetic field are the field point. Take any source point on the current distribution surface of the cylindrical magnet. The surface current density vector at that point is Then the position vector r′ of the source point and the position vector r of the field point can be expressed as follows:

[0071]

[0072] The vector distance R and the distance R from the source point Q to the field point P are respectively:

[0073]

[0074] vector product

[0075]

[0076] Using the vector transformation matrix from rectangular coordinates to cylindrical coordinates,

[0077]

[0078] Write it as an expression in cylindrical coordinates

[0079]

[0080] in,

[0081] Depend on Figure 2 It can be seen that the axial coordinates of the upper and lower edges of the cylindrical magnet are h / 2 and -h / 2, respectively. According to Biot's law, the magnetic induction intensity of the cylindrical magnet at the field point P is:

[0082]

[0083] From this, we can obtain the radial component B of the magnetic induction intensity. ρ Circumferential components and axial component B z The expression is

[0084] The radial component is,

[0085] in,

[0086]

[0087] The circumferential component is, The axial component is, in,

[0088]

[0089] Then, using a vector transformation matrix, the coordinates are transformed from cylindrical coordinates to Cartesian coordinates.

[0090]

[0091] Therefore, in conclusion

[0092] The magnetic field component in the X direction is

[0093]

[0094] The magnetic field component in the Y direction is

[0095]

[0096] The magnetic field component in the Z direction is:

[0097]

[0098] Working principle of coupling sensors:

[0099] Please see Figure 1 , Figure 3 and Figure 4 Based on the above, the present invention provides a coupled sensing system capable of simultaneously acquiring vibration frequencies caused by three-dimensional forces and surface textures. The sensing system includes an artificial fingerprint film 1, a cylindrical magnet 2, a flexible elastomer 3, a circular protective shell 4, a photocurable resin 5, an MMC5603NJ magnetoresistive chip 6, an FPCB circuit board 7, and a rigid backplate 8.

[0100] The MMC5603NJ magnetoresistive chip 6 is bonded to a circular protective shell 4 and a rigid backplate 8 via photocurable resin 5, reinforcing the flexible FPCB circuit board 7 surrounding the chip and preventing stress concentration at the four pins connecting the chip to the flexible circuit board. The MMC5603NJ magnetoresistive chip 6 communicates with the host computer ESP32 via four wires on the FPCB circuit board 7, outputting magnetic field information in real time. The flexible elastomer 3 is bonded to the FPCB circuit board 7 with silicone adhesive, with the central cylindrical elastomer island bearing three-dimensional force. The cylindrical magnet 2 is located directly above the MMC5603NJ magnetoresistive chip 6 and embedded in the upper surface of the flexible elastomer 3. The artificial fingerprint film 1 is attached to the cylindrical magnet 2, sensing the vibration of the artificial fingerprint film 1.

[0101] in, Figure 3 The cylindrical magnet 2 and the flexible elastomer 3 of the sensing system are shown to withstand a three-dimensional force F. Figure 4 The image shows the contact pattern between the artificial fingerprint film 1 and the surface texture 9 of the object. When the artificial fingerprint film 1 slides on the surface texture 9, the finger peak of the artificial fingerprint film 1 sweeps across the surface texture 9, causing microscopic uneven terrain and generating a high-frequency vibration signal. The vibration signal is transmitted to the cylindrical magnet 2 that is attached to the artificial fingerprint film 1, causing high-frequency vibration of the magnetic field. The MMC5603NJ magnetoresistive chip 6 analyzes the frequency and amplitude of the vibration through high-frequency sampling at 1000Hz.

[0102] Geomagnetic field shielding:

[0103] exist Figures 5-7 In the process, the baseline of the uncompensated sensor data from one node exhibits significant fluctuations in signal due to interference from the geomagnetic field during rotation along the xyz axes, such as... Figures 5-7The original data showed standard deviations of signal fluctuations of 63.3 μT, 73.9 μT, and 82.8 μT. A node 10 mm away was then introduced as a geomagnetic reference node. By subtracting the geomagnetic signal from the measured node, the standard deviations of signal fluctuations were reduced to 8.7 μT, 12.65 μT, and 11.53 μT. Compared to the ±3000 μT sensing range of the flexible tactile sensor, the baseline fluctuations in the sensing data became negligible after introducing the reference node, indicating that the sensor exhibited robustness and stability in the presence of external interfering magnetic fields.

[0104] Sensor manufacturing process:

[0105] Please see Figure 8 The present invention also provides a method for fabricating the tactile sensing system as described above, the method mainly comprising the following steps:

[0106] S1: Spray a release agent onto the resin-printed 3D mold, then pour the mixed silicone into the mold and cure it in a 50-degree heating oven for 1 hour to obtain a flexible elastomer.

[0107] Preferably, the silicone can be ecoflex-10, or the type of silicone can be selected according to the working environment and the required range.

[0108] S2: Select a cylindrical magnet and embed it into the groove reserved on the upper surface of the elastomer. Leave a certain margin in the groove, and then fill the groove with silicone adhesive.

[0109] Preferably, the selected cylindrical magnet has a diameter of 1 mm and a height of 0.5 mm. The 1 mm diameter prevents the magnetic field from being too strong and exceeding the measurement range of the MMC5603NJ chip, while the 0.5 mm height makes the magnet itself slightly flat, preventing inverse calculation errors caused by magnet deflection.

[0110] S3: Pour PDMS into a resin mold manufactured using micro-nano technology to form an artificial fingerprint. Use silicone adhesive to attach the artificial fingerprint to the upper surface of the island of flexible elastomer.

[0111] Preferably, the PDMS used is composed of silicone and catalyst in a 5:1 ratio, with an elastic modulus of approximately 7 MPa and a hardness of approximately Shore A 60. The resin mold for the artificial fingerprint film is manufactured using a micro-nano 3D printer, wherein the artificial fingerprint film has a diameter of 5 mm and a total thickness of 310 μm. The artificial fingerprint film contains concentric circular peaks, with the height of the peaks ranging from 150 μm to 400 μm, and the distance between the concentric circular peaks ranging from 150 μm to 350 μm.

[0112] S4: Apply UV-curable resin to the corresponding position on the back of the chip on the flexible FPCB board, and attach a rigid backplate with a diameter of 5mm and a thickness of 0.5mm. Then, apply UV-curable resin to the chip on the flexible FPCB board and cover it with a circular protective shell with a diameter of 5mm and a depth of 1mm. Then, use a UV lamp to irradiate both sides for 5 minutes each.

[0113] Preferably, the rigid backplate and circular protective shell are manufactured by 3D printing to prevent the chip from being subjected to positive pressure and shear force.

[0114] S5: Using a cotton swab, apply silicone adhesive to the flexible acquisition circuit board and bond it together with the pre-drilled holes in the flexible elastomer and the circular protective shell to obtain the sensing system. Then cure at room temperature for 15 minutes.

[0115] Preferably, the pre-drilled holes on the flexible elastomer need to have a certain margin to allow for proper positioning and installation. Decoupling algorithm for coupled signals:

[0116] like Figure 9 The decoupling algorithm of this invention was discussed. A two-level model was used for signal analysis of the sensing system.

[0117] The first-level model performs a low-pass filter on the original signal to remove high-frequency noise, interference, and vibrations, while retaining the low-frequency components. This helps extract signal components related to the magnitude of the magnetic field. The low-pass filtered magnetic field signal is then combined with a three-dimensional force calibration model to calculate the value of the three-dimensional force, determining the magnitude and direction of the force acting on the tactile sensor. The second-level model performs a high-pass filter on the original signal to remove low-frequency components, retaining the high-frequency components. This helps highlight rapidly changing parts of the signal, such as vibrations. The high-pass filtered magnetic field signal is then combined with a calibration model based on vibration frequency and material type to identify the material's texture. This helps determine the surface texture features of the object, such as roughness and smoothness.

[0118] Through these two levels of models, the sensing system can more comprehensively analyze the original signal, extract key information, and realize the recognition and analysis of the three-dimensional force and texture of the object.

[0119] Display of coupled signals:

[0120] A flexible tactile sensor is worn on the robot's finger to simultaneously collect three-dimensional force and vibration signals. The robot's finger is controlled to lightly touch the fabric surface, pause for about 8 seconds, then glide across a 200mm section of the fabric surface at a speed of 20mm / s, pause for about 8 seconds, and then remove the robot's finger from the fabric surface.

[0121] like Figures 10-12It is easy to observe that when the robot's finger contacts the fabric surface, there are abrupt changes in force along the XYZ directions. The force in the X direction changes from approximately 0 N to approximately 0.2 N, the force in the Y direction changes from approximately 0 N to approximately 0.1 N, and the force in the Z direction changes from approximately 0 N to approximately 0.9 N. The force in the Z direction is normal force, which changes significantly, while the force in the XY directions is shear force, typically normal force multiplied by the coefficient of friction, and changes less. During the robot's finger's 20 mm / s sliding motion on the fabric surface, the force signal in the XYZ directions generates high-frequency vibrations. This vibration signal is caused by the coupling between the fabric surface texture and the artificial fingerprint film. Then, when the robot's finger stops and leaves the fabric surface, the three-dimensional force signal returns to zero. This demonstrates that the tactile sensor can simultaneously and accurately acquire both the three-dimensional force signal and the vibration frequency caused by the surface texture.

[0122] Calibration and characterization of three-dimensional force signals, and calibration and characterization of vibration frequencies:

[0123] The first step is the calibration and characterization of the three-dimensional force signal. Force calibration requires a three-dimensional moving platform, a six-axis sensor (ATIMini40), a force data acquisition card (NIUSB-6251), a magnetic field acquisition unit (STM32F407GT6), and a personal computer. The ATI sensor has three-axis ranges of Fx: ±80N, Fy: ±80N, and Fz: 240N, with X and Y sensing accuracies of 0.02N and Z-axis accuracy of 0.04N, offering good pressure resolution and sensitivity. The six-axis sensor is fixed to the three-dimensional moving platform using a fixture. The sensor to be tested is fixed to the base below. A three-dimensional load is applied by controlling the three-dimensional moving platform, such as... Figure 13 As shown, the force data sensor and magnetic field acquisition unit establish a connection with the host computer after power-on and transmit data at a frequency of 50Hz. To achieve high calibration accuracy, it is necessary to acquire the magnetic induction intensity and corresponding three-dimensional force throughout the entire deformation space of the magnetoelastic body. The acquisition space is a cylinder with a height of 2mm and a diameter of 3mm. The normal and radial intervals of the acquisition points are both set to 0.2mm, with a 1-second pause between sampling points.

[0124] In establishing the force-magnetic model, the relationship between the external load and the magnetic induction intensity is described from the perspective of force and magnetic field models. Due to the complexity and difficulty in solving the theoretical formulas, a three-layer neural network structure is adopted to balance solution speed and model accuracy, with ReLU activation functions used between the hidden layers. The three-dimensional vector of magnetic induction intensity is used as the model input, and the three-dimensional force is used as the model label.

[0125] Using the sensor's magnetic flux density value as input, simulated values ​​were calculated through calibration and compared with experimental values ​​measured by ATI commercial sensors. The results are as follows: Figures 14-16The predicted three-dimensional force from the magnetic field is highly consistent with the actual three-dimensional force, with an absolute error of 0.081 N in the X direction, 0.049 N in the Y direction, and 0.053 N in the Z direction. This demonstrates that the tactile sensing system can accurately perceive three-dimensional force.

[0126] Next is the calibration and characterization of the vibration frequency. Vibration calibration requires the use of different types of cloth, 36×36×13.6mm lead blocks, traction cables, rotary servos, servo control boards, and personal computers. For example... Figure 17 As shown, the side of the tactile sensor with the artificial fingerprint contacts the fabric surface. A lead weight of approximately 200 grams is attached to the flexible FPCB on the back of the sensor to ensure full contact between the fingerprint and the fabric. A traction rope is attached to the lead weight. A servo motor pulls the traction rope, causing the tactile sensor to slide across the fabric at a speed of 20 mm / s, with a total sliding path of 200 mm. The tactile sensor passes through two types of fabric: one relatively rough and one relatively smooth.

[0127] When the tactile sensor glides across the fabric, high-frequency vibrations are generated in the XYZ axes. Vibration signals in these three dimensions are collected, and each signal is high-pass filtered with a cutoff frequency of 100Hz. The signals are then subjected to a Fast Fourier Transform (FFT) to calculate the average power frequency (MPF), and the differences in high-frequency vibration frequencies of different materials are analyzed to distinguish different surface textures.

[0128] Depend on Figures 18-20 It can be seen that when moving from one type of fabric to another, the frequency collected by the tactile sensor changes significantly (over approximately 5 seconds), and the average values ​​of the two changes are noticeably different. The baseline vibration frequency in the X-direction changes from 227Hz to 253Hz, in the Y-direction from 235Hz to 270Hz, and in the Z-direction from 250Hz to 281Hz. This demonstrates that the tactile sensing system can accurately perceive the texture of different materials.

[0129] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A system for simultaneously monitoring three-dimensional force and identifying surface texture using three-dimensional magnetism, characterized in that, The system includes an artificial fingerprint film, a cylindrical magnet, a flexible elastomer, a circular protective shell, a flexible acquisition circuit board, and a rigid backplate. The flexible elastomer has an island structure in the middle with a pre-drilled hole. The cylindrical magnet is inserted into the pre-drilled hole and sealed with silicone adhesive. The artificial fingerprint film is adhered to the island of the flexible elastomer using silicone adhesive. The flexible acquisition circuit board is located at the bottom of the flexible elastomer. A magnetoresistive chip for sensing a three-dimensional magnetic field is installed on the flexible acquisition circuit board. The magnetoresistive chip communicates with a host computer through four wires on the flexible acquisition circuit board, outputting magnetic field information in real time. A circular protective shell and a rigid backplate are bonded to the top and bottom surfaces of the flexible acquisition circuit board using photocurable resin; the circular protective shell protects the magnetoresistive chip inside; holes are pre-drilled on the flexible elastomer to mate with the circular protective shell; silicone adhesive is applied to the flexible acquisition circuit board, and the connection with the flexible elastomer is achieved through the pre-drilled holes on the flexible elastomer and the mating with the circular protective shell; using the sensor's magnetic induction intensity value as input, the simulation value is calculated through calibration, and the vibration frequency is calibrated and characterized. For vibration calibration, different types of cloth, 36×36×13.6mm lead blocks, traction wires, rotary servos, servo control boards, and personal computers are required. The side of the tactile sensor with the artificial fingerprint contacts the cloth surface, and the flexible FPCB on the back of the tactile sensor... A lead weight of about 200 grams is attached to the fabric to ensure full contact between the artificial fingerprint and the fabric surface. A traction rope is attached to the lead weight, and a servo motor drives the tactile sensor to slide across the fabric surface at a speed of 20 mm / s, with a total sliding path of 200 mm. When the tactile sensor slides across the fabric surface, there will be high-frequency vibrations in the XYZ directions. Vibration signals in the three dimensions are collected, and the signals are high-pass filtered with a cutoff frequency of 100 Hz. Then, the signals are fast Fourier transformed and the average power frequency (MPF) is calculated. The differences in high-frequency vibration frequencies of different materials are analyzed to distinguish different surface textures.

2. The system for simultaneously monitoring three-dimensional force and identifying surface texture through three-dimensional magnetism according to claim 1, characterized in that, The artificial fingerprint film has multiple concentric circular protrusions on its surface. When it contacts and slides on a textured surface, it causes high-frequency vibrations in the serrated structure. The flexible elastic body will deform under three-dimensional static pressure. The magnetic field change of the cylindrical magnet is related to the vibration and deformation displacement. The circular protective shell and hard backplate prevent stress concentration at the chip.

3. A system for simultaneously monitoring three-dimensional force and identifying surface texture using three-dimensional magnetism according to claim 1 or 2, characterized in that, The signal analysis of the sensing system uses a two-level model. The first level low-pass filters the original signal and calculates the three-dimensional force by combining the magnetic field magnitude with the three-dimensional force calibration model. The second level high-pass filters the original signal and identifies the texture of the material by combining the magnetic field vibration frequency and the material type calibration model.

4. The system for simultaneously monitoring three-dimensional force and identifying surface texture through three-dimensional magnetism according to claim 3, characterized in that, The sensing system analyzes the three-dimensional force and the texture of the contact surface of the sensor by decoupling a single magnetic field signal.

5. A system for simultaneously monitoring three-dimensional force and identifying surface texture using three-dimensional magnetism according to claim 4, characterized in that, The artificial fingerprint film is made of PDMS material and is cast into a resin mold; the ratio of silicone and catalyst in PDMS is between 10:1 and 5:

1.

6. The system for simultaneously monitoring three-dimensional force and identifying surface texture through three-dimensional magnetism according to claim 5, characterized in that, The diameter of the cylindrical magnet is less than or equal to 3 mm to prevent the magnet from deflecting and becoming unable to decouple.

7. A system for simultaneously monitoring three-dimensional force and identifying surface texture using three-dimensional magnetism according to claim 6, characterized in that, The flexible elastomer is made using ecoflex10, ecoflex20, or ecoflex30.

8. A method for manufacturing a tactile sensing system as described in any one of claims 1-7, characterized in that, The process includes the following steps: (1) Pour ecoflex10 into a mold and cure it at room temperature for 1 hour to obtain a flexible elastomer; (2) Insert a cylindrical magnet with a diameter of 1 mm into the reserved hole of the island of the flexible elastomer and encapsulate it with silicone adhesive; (3) Mix PDMS and catalyst at a ratio of 5:1, pour it into a mold to form an artificial fingerprint, and use silicone adhesive to attach the artificial fingerprint to the island of the flexible elastomer; (4) Use photocurable resin to attach the circular protective shell and the rigid back plate to both sides of the flexible acquisition circuit board; the side of the flexible acquisition circuit board that contacts the flexible elastomer is the circular protective shell; (5) Apply silicone adhesive to the flexible acquisition circuit board and achieve bonding by matching the reserved hole in the flexible elastomer with the circular protective shell to obtain the sensing system.

9. The application of a sensing system as described in any one of claims 1-7 in the skin of a robot finger, which satisfies the robot's requirements for perceiving three-dimensional tactile sensation and distinguishing object materials.

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