Force-position sensing composite magnetic electronic skin for intelligent manipulator

Abstract

The invention discloses a force-position sensing composite magnetic electronic skin for an intelligent manipulator. The force-position sensing composite magnetic electronic skin comprises a magnetic thin film and a force sensor, wherein the magnetic thin film is prepared from magnetic conductive graphene powder, neodymium iron boron particles and a mixture of polydimethylsiloxane and silica gel; the flexible substrate is made of polydimethylsiloxane; the flexible printed circuit board is welded with a tunnel magnetoresistive element array; the magnetic film serves as a sensing part, and the internal magnetic field distribution changes after the magnetic film is stressed; the tunnel magnetoresistive element array serves as a detection part and is used for detecting magnetic field changes and converting the magnetic field changes into voltage signals through a bridge circuit to be output. The flexible substrate is arranged between the magnetic thin film and the tunnel magnetoresistive element array and used for buffering stress deformation and fixing the relative positions of all the parts. The device has the structural advantages of being high in sensitivity, narrow in lag and ultra-flexible, normal pressure stress and position sensing signals of a grabbed object are detected, and a measuring platform for static and dynamic force and plane position characteristics of the composite magnetic electronic skin is built.

Description

TECHNICAL FIELD

[0001] The present application is based on the magnetic graphite powder, neodymium iron boron magnetic particles (Nd2Fe 14 B1) and polydimethylsiloxane (PDMS) and silica polymer body design a high sensitivity, narrow hysteresis for intelligent manipulator force-position sensing composite magnetic electronic skin. BACKGROUND

[0002] Manipulator as the main way of information interaction between robots and the outside world, undertakes the important task of perceiving and identifying external stimuli. The electronic skin of the manipulator fingertips as the core component of the manipulator surface layer can perceive the size of the force loaded on the contacted object and the position information, so as to realize the real-time perception of the shape and movement trajectory of the contacted object, and realize the precise grasping work of the intelligent manipulator. The smooth progress of the precise grasping work of the intelligent manipulator puts forward the advantages of high sensitivity, narrow hysteresis and super flexibility for the composite magnetic electronic skin. The existing magnetic film is mainly composed of magnetic nanometer particles (MNPs) hydrogel (Hongwei Zhou, Zhaoyang Jin, Yang Gao, et al. Thermoresponsive, magnetic, adhesive and conductive nanocomposite hydrogels for wireless and non-contact flexible sensors, Colloids and Surfaces A: Physicochemical and Engineering Aspects, Volume 636, 2022). The magnetic nanometer particles are generally composed of a magnetic core composed of metal oxides such as iron, cobalt and nickel, and a high polymer wrapped outside the magnetic core (generally Fe3O4 or γ-Fe2O3 with superparamagnetic or ferromagnetic properties). This kind of magnetic hydrogel film has the problems of low sensitivity, the need for additional bias magnetic field, etc. The Hall effect of Hall element can convert the change of magnetic field into electric signal and amplify and output, but due to the poor anti-interference ability and low sensitivity of Hall element, the magnetic electronic skin has the problems of strong coupling effect, sensitive to working temperature, signal output changes with temperature, and the feedback of small force is not obvious, etc. SUMMARY

[0003] To address the aforementioned technical issues, this invention proposes a force-position sensing composite magnetic electronic skin for intelligent robotic arms. This enables real-time, precise monitoring and collection of normal compressive stress and force position data of the grasped object. The addition of magnetic graphene powder enhances the magnetism of the magnetic film prepared from neodymium iron boron magnetic particles. After this composite magnetic electronic skin is installed on the fingertips of the intelligent robotic arm, it can be used for precise grasping tasks such as industrial automation, complex parts, and medical supplies.

[0004] To achieve the above objectives, the present invention provides a force-position sensing composite magnetic electronic skin for intelligent robotic arms, comprising:

[0005] A magnetic thin film made of magnetic graphene powder, neodymium iron boron particles and a mixture of polydimethylsiloxane and silica gel;

[0006] A flexible substrate made of the aforementioned polydimethylsiloxane;

[0007] Flexible printed circuit board with a tunnel magnetoresistive element array welded on it;

[0008] The magnetic thin film, as a sensing element, undergoes a change in its internal magnetic field distribution after being subjected to force.

[0009] The tunnel magnetoresistive element array serves as the detection part, used to detect changes in the magnetic field and convert these changes into voltage signals through a bridge circuit for output.

[0010] The flexible substrate is disposed between the magnetic thin film and the tunnel magnetoresistive element array to buffer stress deformation and fix the relative positions of each part.

[0011] Optionally, the mixing ratio of the magnetic graphene powder, the neodymium iron boron particles, and the polydimethylsiloxane prepolymer is 1:3:1.

[0012] Optionally, the preparation process of the magnetic film includes: pouring the uniformly mixed prepolymer into a mold, performing step-by-step heating and curing in a nitrogen environment, and finally cooling.

[0013] Optionally, the stepped temperature curing process includes: initial curing at 80°C; followed by continued curing at 120°C to remove air bubbles.

[0014] Optionally, the tunnel magnetoresistive element array consists of nine tunnel magnetoresistive elements arranged in a 3x3 configuration.

[0015] Optionally, the tunnel magnetoresistive elements are spaced 7 mm apart in the row direction and 2.5 mm apart in the column direction.

[0016] Optionally, the output end of the flexible printed circuit board is arranged in a single row and is arranged in the direction of the double pins of the tunnel magnetoresistance element.

[0017] Optionally, the magnetic film is subjected to multi-pole magnetization treatment before installation and use, so as to form a plurality of magnetic poles corresponding to the positions of the array of tunnel magnetoresistance elements.

[0018] Technical effects of the present application:

[0019] 1. The magnetic film made of neodymium iron boron magnetic particles with high magnetic performance, light specific gravity and high shape freedom and flexible polydimethylsiloxane is used as a sensing part, a high-sensitivity TMR element is selected as a detection part, a magnetic electronic skin is formed, and accurate sensing of touch is realized. Figure 4 The corresponding relationship between the pressure F applied vertically on the electronic skin and the output voltage U is that when the applied pressure is 0-1N, the peak output voltage of the magnetic electronic skin is 423.941mV, and when the pressure reaches 5N, the peak output voltage is 1601.183mV, which is greatly improved in sensitivity compared with the existing magnetic electronic skin. Figure 5 It can be seen that the actual output value of the electronic skin is basically consistent with the theoretical value, and the electronic skin can meet the needs of the manipulator in high-precision tasks.

[0020] 2. The 9 TMR elements are welded on the flexible printed circuit board in a 3x3 manner, the TMR elements and the flexible printed circuit board are covered under the PDMS, the flexibility of the whole electronic skin is increased, the electronic skin can be completely attached to the surface of the phalanx when installed inside the three-fingered manipulator, the maximum bending degree can reach 120°, and the flexibility and accuracy of the manipulator are improved. When attached to the skin surface, it can closely adhere to the human skin, deform with the skin, and have good flexibility.

[0021] 3. The high flexibility and high sensitivity of the electronic skin can make it perfectly adhere to and more accurately distinguish different shapes and different hardness of objects. The results of the grabbing experiment show that when the electronic skin is installed on the three-fingered manipulator to grab two cylinders with different hardness (the difference in Shore hardness is 10 degrees), the average outputs of 4-6 TMR in the electronic skin are 708.29mV and 760.11mV respectively, which can accurately distinguish the hardness of different objects and provide accurate tactile sensing information for the manipulator.

[0022] 4. The TMR element is assembled in a free covering manner. The PDMS is cured around the TMR, which fixes the TMR position at the most suitable working magnetic field strength while playing a protective buffering role, improves the sensitivity of the electronic skin, and more effectively transmits information.

[0023] 5. The PDMS flexible substrate of the electronic skin is formed by casting and curing, which reduces the distance between the TMR and the magnetic film, allows the TMR to work in the optimal magnetic field, and leaves sufficient space for the deformation of the magnetic film. The force on the electronic skin is increased to 5N, and the overall space of the skin is reduced.

[0024] 6. Integrate the magnetic film of the electronic skin and the PDMS flexible substrate onto a flexible printed circuit board with TMR soldered on it. The output terminals are in the direction of the TMR dual pins, which reduces output interference and improves the efficiency of the circuit board, making it easy to install onto a robotic arm. Attached Figure Description

[0025] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0026] Figure 1 This is a schematic diagram of a force-position sensing composite magnetic electronic skin for an intelligent robotic arm according to an embodiment of the present invention;

[0027] Figure 2 Hysteresis loop diagrams of NdFeB-graphene magnetic films and NdFeB magnetic films according to embodiments of the present invention;

[0028] Figure 3 The output voltage waveforms of NdFeB-graphene and NdFeB magnetic electronic skin under different stresses are shown in the embodiments of the present invention.

[0029] Figure 4 The static force sensitivity curves of NdFeB-graphene and NdFeB magnetic electronic skin under different stresses are shown in the embodiments of the present invention.

[0030] Figure 5 The output voltage waveforms of NdFeB-graphene magnetic electronic skin under different frequencies and under N stress are shown in Embodiment 1 of the present invention.

[0031] Figure 6 The output voltage waveforms of the neodymium iron boron-graphene magnetic electronic skin under stress of 20N and frequency of 4Hz in Embodiment 1 of the present invention are shown.

[0032] Figure 7 The output voltage waveforms of the neodymium iron boron-graphene magnetic electronic skin under stress pulse excitation in Embodiments 1-20N of the present invention are shown.

[0033] Figure 8 The output voltage waveforms of the neodymium iron boron-graphene magnetic electronic skin under 2000 cycles of stress in Embodiments 1-N of the present invention are shown. Detailed Implementation

[0034] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0036] like Figure 1 As shown, this embodiment provides a force-position sensing composite magnetic electronic skin for intelligent robotic arms, comprising:

[0037] A magnetic thin film made of magnetic graphene powder, neodymium iron boron particles and a mixture of polydimethylsiloxane and silica gel;

[0038] A flexible substrate made of the aforementioned polydimethylsiloxane;

[0039] Flexible printed circuit board with a tunnel magnetoresistive element array welded on it;

[0040] The magnetic thin film, as a sensing element, undergoes a change in its internal magnetic field distribution after being subjected to force.

[0041] The tunnel magnetoresistive element array serves as the detection part, used to detect changes in the magnetic field and convert these changes into voltage signals through a bridge circuit for output.

[0042] The flexible substrate is disposed between the magnetic thin film and the tunnel magnetoresistive element array to buffer stress deformation and fix the relative positions of each part.

[0043] Furthermore, the mixing ratio of the magnetic graphene powder, the neodymium iron boron particles, and the polydimethylsiloxane prepolymer is 1:3:1.

[0044] Furthermore, the preparation process of the magnetic thin film includes: pouring the uniformly mixed prepolymer into a mold, performing step-by-step heating and curing in a nitrogen atmosphere, and finally cooling.

[0045] Furthermore, the stepped temperature curing process includes: initial curing at 80°C; and continued curing at 120°C to remove air bubbles.

[0046] Furthermore, the tunnel magnetoresistive element array consists of nine tunnel magnetoresistive elements arranged in a 3x3 configuration.

[0047] Furthermore, the spacing between the tunnel magnetoresistive elements is 7 mm in the row direction and 2.5 mm in the column direction.

[0048] Furthermore, the output terminals of the flexible printed circuit board are arranged in a single row and positioned in the direction of the dual pins of the tunnel magnetoresistive element.

[0049] Furthermore, the magnetic thin film undergoes multi-pole magnetization treatment before installation and use to form multiple magnetic poles corresponding to the positions of the tunnel magnetoresistive element array.

[0050] This invention relates to an electronic skin designed based on the magnetic effect of neodymium iron boron (NdFeB) magnetic particles and magnetically permeable graphene, combined with the tunneling magnetoresistance (TMR) effect of TMR elements. The electronic skin comprises a NdFeB-graphene magnetic film, a PDMS flexible substrate, TMR elements, and a flexible printed circuit board. It can accurately sense static and dynamic forces of varying magnitudes. The multi-pole magnetized NdFeB-graphene magnetic film provides a stable magnetic field distribution. When pressure is applied to the magnetized film, it deforms, altering the internal magnetic field distribution and consequently changing the surrounding magnetic field distribution. The underlying TMR element senses this subtle change in the magnetic field and converts the signal into a change in internal magnetoresistance via the tunneling magnetoresistance effect. This change is then converted into a voltage value via a bridge circuit for output. The output voltage value is acquired by a dynamic signal acquisition card, and the acquired signal is processed for data visualization on a computer. Nine TMR elements are soldered in a 3×3 configuration onto the surface of the flexible printed circuit board, with the entire TMR array covering the interior of the PDMS film. The electronic skin is then installed on the inside of the fingertips of a three-finger mechanical device to detect the force applied to the fingertips when grasping an object and to determine the physical properties of the grasped object. Its high sensitivity allows the robotic arm to quickly and accurately sense changes in force; its high flexibility allows it to completely adhere to the surface of an object for information recognition when grasping it; and its small size ensures unimpeded grasping, restoring the inherent flexibility of the robotic arm.

[0051] The process for preparing the high-permeability magnetic hydrogel graphene composite material in this invention combines solution treatment of graphene oxide with in-situ generation of iron oxide. The specific steps are as follows: First, using graphene oxide as a precursor, it is dispersed in water and ultrasonically treated to form a uniform and transparent graphene oxide colloidal solution (the recommended mass-to-volume ratio concentration is controlled at 0.3-0.6 mg / mL). Subsequently, iron salt (FeCl3·6H2O) is introduced. By controlling its addition amount (0.42 g FeCl3·6H2O) and combining it with a hydrothermal reaction (temperature 170-190℃, time 10-13 hours), Fe3O4 nanoparticles are generated in-situ on the graphene oxide surface, simultaneously promoting the formation of a three-dimensional porous hydrogel structure. During the hydrothermal process, the iron salt can be converted into iron oxide particles under alkaline or specific reaction conditions. The size of these particles is controllable (e.g., the Fe2O3 particle size can be adjusted to 300-500 nm or 1.2 μm), and they are uniformly loaded onto the graphene sheet surface through electrostatic adsorption or chemical bonding. After the reaction, the system is allowed to cool naturally, and then washed with deionized water and ethanol to remove unreacted impurities. Finally, the three-dimensional porous structure of the hydrogel is preserved by low-temperature drying (e.g., 70-80℃) or freeze-drying technology, resulting in a Fe3O4-modified graphene hydrogel composite material with both high magnetic permeability and electrical conductivity. This method simplifies the process by using an aqueous phase system, avoids organic solvent contamination, and ensures uniform dispersion of iron oxide particles, thereby improving the magnetic field uniformity of the material.

[0052] After atomization, the NdFeB magnetic particles have a particle size of approximately 100 μm, ensuring a well-preserved crystalline structure. First, a PDMS polymer is prepared by mixing the main agent and curing agent in a 15:1 ratio. NdFeB magnetic particles, magnetically conductive graphene, and PDMS prepolymer are then mixed in a 3:1:1 ratio and stirred for 120 minutes to ensure uniform particle distribution and sufficient contact between the PDMS main agent and curing agent, thus preparing the PDMS prepolymer. A layer of PDMS release agent is sprayed into a cuboid mold to form a micron-sized semi-permanent film on its surface. The PDMS prepolymer is poured into the mold and cured at 80°C under nitrogen for 120 minutes for initial curing. Then, curing continues at 120°C under nitrogen for 60 minutes to completely remove air bubbles from the composite film. Finally, the film is cooled at 25°C for 60 minutes to fully cure, yielding a flexible NdFeB-graphene film. The obtained flexible film was magnetized in a magnetizer. To enable decoupling, the film underwent multi-pole magnetization to obtain a NdFeB-graphene magnetic film. A flexible printed circuit board with nine TMR elements soldered on it was placed in a cuboid mold and laid flat on the bottom surface of the mold. A 3mm thick PDMS prepolymer layer was poured onto the circuit board, and the NdFeB-graphene magnetic film was placed on top of the PDMS prepolymer. The film was supported by the mold and maintained good contact with the top of the PDMS prepolymer. The entire mold was placed in a high-temperature nitrogen atmosphere for curing, followed by cooling at room temperature to obtain a complete magnetic electronic skin.

[0053] The high-sensitivity electronic skin in this embodiment consists of one thin-film sensing part and nine TMR detection parts. The sensing part is a neodymium iron boron (Nd2Fe) film with a length of 30 mm, a width of 20 mm, and a height of 0.5 mm. 14B) - A magnetic graphene film with a detection component consisting of a TMR2503 element along the Z-axis magnetic sensing direction, packaged in SOT23-5 format, measuring 3mm × 3mm × 1.45mm. Both the NdFeB-PDMS magnetic film and the TMR element are horizontally placed, parallel to the flexible printed circuit board, with identical spacing between each TMR element and the magnetic film. The spacing between the TMR elements is also identical, with a longitudinal spacing of 7mm and a transverse spacing of 2.5mm. All nine TMR elements completely cover the PDMS flexible substrate. When an external force is applied to the surface of the magnetic film, the film deforms, causing changes in the internal magnetic domains, which in turn lead to changes in the magnetic field strength. The TMR element converts these changes in the surrounding magnetic field strength into a voltage signal, thereby accurately sensing the magnitude of the force. Experimental results show that when the film is subjected to a pressure of 1N, the average output voltage of each TMR of the electronic skin is 423.941mV, and the sensitivity is 423mV / N. When the pressure is 5N, the average output voltage of each TMR is 1601.183mV, and the sensitivity within the range of 1-5N is 294mV / N, which can provide precise tactile perception for the robotic arm. Nine TMR sensing units are soldered in a 3×3 configuration onto the surface of a flexible printed circuit board, forming an electrical connection between the TMR and the circuit board. This forms a highly sensitive magnetic electronic skin that is covered within a cast PDMS flexible substrate.

[0054] The magnetic electronic skin structure of this invention is as follows: Figure 1 As shown, the electronic skin is 30mm long, 20mm wide, and 3.6mm high. When a pressure of 20N is applied, the magnetic film of the electronic skin deforms downwards, descending a distance of 1.0mm. After the pressure is removed, it can quickly return to its original shape. Within the effective force measurement range, the film will not touch the internal TMR element. It is composed of a neodymium iron boron-graphene magnetic film 1, a PDMS substrate 2, a flexible printed circuit board 3, and a TMR element 3-1.

[0055] The NdFeB-graphene magnetic film 1 is composed of NdFeB, magnetically conductive graphene, and PDMS in a 3:1:1 ratio. PDMS is a mixture of PDMS main agent and curing agent in a 15:1 ratio. After multipole magnetization, it can generate 9 pairs of N and S poles, corresponding to the positions of 9 TMR elements. Compared with magnetic films composed of NdFeB and PDMS in a 3:1 ratio, the high conductivity of graphene powder in the NdFeB-graphene magnetic film can synergize with the magnetic properties of NdFeB, improving electromagnetic compatibility in certain applications and reducing interference from magnetic materials prepared from pure NdFeB under electromagnetic fields. Simultaneously, the addition of magnetically conductive graphene powder makes the response of the composite magnetic material under a magnetic field more uniform, reducing the internal magnetic field gradient and local demagnetization effect, and avoiding magnetic instability caused by local aggregation. Compared to films without magnetically conductive graphene, neodymium iron boron-graphene magnetic films increase magnetic induction intensity and widen the hysteresis loop, thereby improving overall magnetic properties, such as...Figure 2 As shown. Accordingly, the prepared composite magnetic electronic skin, due to the addition of highly magnetic graphene powder, makes the sensor more sensitive to changes in external magnetic fields or forces.

[0056] The PDMS flexible substrate 2 is made by mixing PDMS main agent and curing agent in a 15:1 ratio. It is a cuboid with the edge of the PDMS substrate flush with the flexible printed circuit board 3. The magnetic film is placed at the center above the PDMS flexible substrate, and 3×3 TMR elements 3-1 are fixed below it. The projection in the vertical direction completely covers the 3×3 TMR elements.

[0057] The flexible printed circuit board 3 has a polyimide substrate, and the circuit is distributed on the substrate. The TMR component is 3mm long, 3mm wide, and 1.45mm high, completely covering the interior of the PDMS flexible substrate. The TMR components are arranged in a 3×3 pattern on the surface of the circuit board, with a spacing of 7mm in the X direction and 2.5mm in the Y direction. Each TMR component has a set of pads below it, namely VCC pad, GND pad, empty pad, V+ pad, and V- pad. Each VCC pad is connected in series, and each GND pad is connected in series. The flexible printed circuit board has a planar size of 30mm×20mm. A 1×20 output is set on the upper side of the base plate, which can be completely attached to the tip of the Robotiq three-finger mechanical finger.

[0058] Example 1: Using a TMR element as the sensing component, the relationship between pressure and output voltage of a 30mm long and 20mm wide magnetic film within the range of 0-20N was tested. The main purpose of this example is to study the input-output correspondence and pressure sensitivity of the electronic skin.

[0059] Experimental platform setup: according to Figure 1 and Figure 2 The electronic skin assembly is shown. The composite magnetic electronic skin is directly fixed below the digital push-pull force gauge. By shaking the joystick, the drive rod of the push-pull force gauge is aligned with a TMR component in the electronic skin and brought into contact with its surface. Continuing to shake the joystick sets the push-pull force gauge to apply a static force to the electronic skin. A DC regulated power supply provides a stable 5V voltage to the electronic skin. The output of the electronic skin is connected to the sampling port of the DH-8303 dynamic data acquisition card, acquiring differential voltage signals at a sampling frequency of 5kHz. The signal output of the dynamic data acquisition card is connected to a computer, and the acquired data is displayed in real time on the computer screen for subsequent data analysis and processing.

[0060] Experimental Procedure and Results: A digital push-pull force gauge was used to gradually apply a force of 0-20N to the electronic skin at 1N intervals. The force gauge contacts compressed the thin film portion of the electronic skin, causing deformation. The arrangement of magnetic domains within the deformed film changed, resulting in a change in the generated magnetic field. The TMR element below detected the slight change in magnetic field strength, and the internal magnetoresistance changed, which was then output as a voltage signal after passing through a bridge circuit. Within the 0-20N range, pressure was applied to the electronic skin at 1N intervals, and the output voltage was as follows: Figure 4 As shown in the diagram, the electronic skin can quickly return to its original shape after the applied external force is removed, demonstrating good durability and stability. The sensitivity is 687.51 mV / N when the pressure is 1-5 N; 154.321 mV / N when the pressure is 5-12 N; and 22.89 mV / N when the pressure is 12-20 N. The sensitivity and flexibility of this electronic skin are significantly higher than current NdFeB magnetic thin-film sensors, exhibiting excellent characteristics.

[0061] Example 2: In engineering applications, in order to ensure that the electronic skin has better performance and stability in the working state of the intelligent robotic arm, it is necessary to further analyze the dynamic characteristics of the composite magnetic electronic skin.

[0062] Experimental Platform Setup: A dynamic characteristic testing platform for the composite magnetic electronic skin was built based on a signal generator, power amplifier, exciter, mounting plate, transmission rod, and quartz force sensor. The dynamic response, hysteresis, and stability of the composite magnetic electronic skin were analyzed. In the dynamic characteristic test, the signal generator produced a sine wave signal with a frequency of 1-4Hz, which was amplified by the power amplifier and transmitted to the exciter. The exciter drove the transmission rod to apply a dynamic force to the composite magnetic electronic skin. Simultaneously, a DC regulated power supply provided a stable 5V voltage to the composite electronic skin. A dynamic signal acquisition card collected the output voltage signal data of the electronic skin and transmitted it to a computer for real-time display and recording.

[0063] Experimental process and results: such as Figure 5 The figure shows the dynamic output voltage characteristics of the magnetic electronic skin when the normal force is 1N and the excitation frequency is 1-4Hz. As the frequency increases, the output voltage deviation rate does not exceed 3.74%. Furthermore, normal forces of the same frequency but different magnitudes are applied to the magnetic electronic skin... Figure 6 As shown, at the same frequency of 4Hz, the output voltage signal increases significantly with increasing normal pressure, and the output voltage value remains the same under the same normal force. Figure 7 As shown, the response and recovery times of the magnetic electronic skin under different normal forces were 39 ms and 38 ms, respectively. Furthermore, the cyclic stability of the composite magnetic electronic skin was tested. Figure 8As shown, when a cyclic normal force of 1N is applied (over 2000 cycles), the output voltage of the electronic skin does not exhibit significant jumps throughout the entire cycle, with a deviation not exceeding 3.17%. This indicates that this magnetic electronic skin possesses good durability and stability, making it suitable for long-term monitoring of pressure signals.

[0064] Example 3: High-sensitivity magnetic electronic skin is installed on the inner side of the fingertips of a Robotiq three-finger robotic hand (one piece of electronic skin is installed on each of the three fingertips). The electronic skin can fit snugly against the robotic fingertips. The three-finger robotic hand is connected to the Universal Robots UR5e six-axis robotic arm, which is equipped with a control panel. A DC regulated power supply provides a stable operating voltage for the TMR components in the electronic skin. The 9 pairs of V+ and V- correspond to the 9 channels of the dynamic data acquisition card. The output voltage of the electronic skin is acquired by the acquisition card and displayed on the computer. The computer calculates the grasping force, speed, and grasping displacement to maintain consistency during the grasping process. The robotic hand grasps wooden cuboids (40mm×40mm×52mm) and wooden cylinders (40mm base diameter, 52mm height) of different shapes, as well as two rubber cylinders (40mm base diameter, 52mm height) with a Shore hardness difference of 10 degrees.

[0065] Experimental Procedure and Results: The gripping angle and position of the three-finger manipulator were adjusted to ensure that the electronic skin at the fingertips could completely adhere to the surface of the object being gripped, guaranteeing output from each TMR. When gripping a wooden cuboid, the output voltage of each TMR ranged from 516.74mV to 534.03mV, with an average output voltage of 526.30mV. Within the allowable error range, the output voltages of each TMR element can be considered equal. When gripping a wooden cylinder, the output voltages of TMR elements 1-3 and 7-9 ranged from 356.83mV to 369.15mV, with an average output voltage of 364.04mV. The output voltage of TMR element 4-6 ranged from 730.95mV to 740.28mV, with an average output voltage of 737.03mV. Within the allowable error range, the output voltages of TMR elements 1-3 and 7-9, and TMR elements 4-6, can be considered equal. Analysis of the output voltages of each TMR element... By comparing the sizes, the surface shape of the object being grasped can be preliminarily determined. The greater the difference in output between the 4-6 TMR elements and the other 6 TMR elements, the greater the surface curvature of the grasped cylinder. When grasping a rubber cylinder, the output voltage of each TMR element is as follows: the output voltage of TMR elements 1-3 and 7-9 is between 303.21mV and 319.15mV, with an average output voltage of 312.85mV; the output voltage of TMR elements 4-6 is between 700.67mV and 715.33mV, with an average output voltage of 708.30mV. Analysis of the output shows that when the robotic arm grasps objects of different hardness, this electronic skin can accurately identify the hardness. The higher the output voltage, the greater the hardness of the grasped object, thus leveraging the high sensitivity of this electronic skin.

[0066] This invention proposes a composite magnetic electronic skin composed of magnetic graphene powder, neodymium iron boron particles, a mixture of polydimethylsiloxane (PDMS) and silicone, and tunnel magnetoresistive elements (TMR). Based on a biomimetic strategy of human skin, this composite magnetic electronic skin has a laminated layered structure. The first layer is the sensing part of the electronic skin, which is a magnetic thin film made of magnetic graphene powder, neodymium iron boron particles, PDMS and silicone to form the "epidermis" of the force-magnetic electronic skin, and is magnetized along the thickness direction of the magnetic film using a multi-pole magnetization method. The second layer is a flexible substrate of PDMS and silicone to buffer the deformation of the magnetic film under stress, forming the "dermis" of the electronic skin. The third layer is a sensing array made of 3×3 TMR 2853 element units soldered on a flexible printed circuit board for force-magnetic signal conversion and output, forming the "subcutaneous tissue" of the electronic skin, in which the TMR element units constitute the "neurons" of the electronic skin.

[0067] The purpose of this invention is to address the problems of low sensitivity, severe hysteresis, poor anti-interference ability, and high requirements for the working environment in current flexible electronic skins. Based on the magnetic properties of magnetic graphene powder and neodymium iron boron particles, a high-sensitivity, narrow-hysteresis, and ultra-flexible composite magnetic electronic skin is proposed. This electronic skin is composed of magnetic graphene powder, neodymium iron boron particles, polydimethylsiloxane-silicone polymer, and tunneling magnetoresistive elements. A magnetic thin film (magnetic graphene powder-neodymium iron boron-PDMS-Silica composite magnetic thin film) is prepared by mixing magnetic graphene powder, neodymium iron boron particles, and polydimethylsiloxane-silicone polymer in a certain proportion, serving as the sensing part of the magnetic electronic skin. When external pressure is applied, the deformation of the composite magnetic skin causes a change in the relative positions of the NdFeB particles, resulting in a change in magnetic induction intensity. Simultaneously, the magnetic permeability of the graphene powder synergizes with the magnetism of the NdFeB, increasing the remanence (Br) of the hybrid magnet compared to a pure NdFeB magnet. This helps to increase the magnetic energy product (BH)max, enabling the magnet to exhibit stronger magnetic properties in practical applications. It also improves coercivity and thermal stability, resulting in better magnetic response under normal compressive stress in the composite magnetic film material. Furthermore, the addition of magnetically permeable graphene powder makes the response of the composite magnetic material under magnetic field conditions more uniform, reducing the internal magnetic field gradient and local demagnetization effects, avoiding magnetic instability caused by local aggregation, thereby improving overall magnetic performance. Therefore, the prepared composite magnetic electronic skin, due to the inclusion of highly conductive graphene powder, makes the sensor more sensitive to changes in external magnetic fields or forces. Due to its superior performance, such as high sensitivity, low power consumption, and strong anti-interference ability, the tunnel magnetoresistive element is used as a detection component. Changes in the magnetic field will cause changes in the internal magnetoresistive resistance of the element. The change in resistance is converted into an electrical signal by a bridge circuit, thereby detecting the change in the magnitude of the pressure signal.

[0068] The composite magnetic electronic skin of the present invention has the advantages of high sensitivity, narrow hysteresis and ultra-flexible structure. It can realize the detection of normal compressive stress and position sensing signals of the grasped object, and build a measurement platform for the static, dynamic force and planar position characteristics of the composite magnetic electronic skin.

[0069] The high-sensitivity magnetic electronic skin disclosed in this invention consists of four parts: a neodymium iron boron-graphene magnetic film, a PDMS substrate, TMR elements, and a flexible printed circuit board. It can be completely adhered to the inner side of a mechanical finger bone or human skin, and can identify and judge the hardness and surface shape of different objects. Three × three TMR elements in the electronic skin substrate are soldered onto the flexible printed circuit board. The magnetized NdFeB-PDMS magnetic film deforms under force, and the deformation is converted into a change in magnetic field through the magnetic permeability effect. The TMR element detects the weak change in the magnetic field signal, converts it into a change in magnetoresistance through the tunneling magnetoresistance effect, and then converts it into an electrical signal for output through a bridge circuit. The NdFeB-PDMS magnetic film is used to sense changes in external forces and provide a stable bias magnetic field, keeping the TMR element in its linear operating range. The PDMS flexible substrate is used to fix the relative position of the NdFeB-PDMS magnetic film and the TMR element, buffering the applied force and protecting the entire electronic skin. The magnetic electronic skin is installed on a three-finger robotic hand to grasp objects of different hardness and shape. The acquired signals are received by a dynamic signal acquisition card and output to a computer screen for data visualization. By comparing the shape of the output voltage, the hardness and shape of different objects can be distinguished.

[0070] The beneficial effects of this invention are as follows:

[0071] 1. Using neodymium iron boron magnetic particles with high magnetic properties, light weight, and high degree of shape freedom, and a magnetic thin film made of highly flexible polydimethylsiloxane as the sensing part, and selecting a high-sensitivity TMR element as the detection part, a magnetic electronic skin is formed to achieve precise tactile perception. Figure 4 To illustrate the relationship between the pressure F applied vertically to the electronic skin and the output voltage U, when the applied pressure is between 0 and 1 N, the peak output voltage of the magnetic electronic skin is 423.941 mV, and when the pressure reaches 5 N, the peak output voltage is 1601.183 mV, which is a significant improvement in sensitivity compared to existing magnetic electronic skins. Figure 5 It can be seen that the actual output value of the electronic skin is basically consistent with the theoretical value, and the electronic skin can meet the needs of the robotic arm when performing high-precision tasks.

[0072] 2. Nine TMR components are soldered onto a flexible printed circuit board in a 3×3 configuration. The TMR components and the flexible printed circuit board are covered under the PDMS, increasing the overall flexibility of the electronic skin. When installed on the inside of a three-finger robotic hand, it can completely conform to the surface of the finger bones, with a maximum bending angle of 120°, improving the robotic hand's flexibility and precision. When applied to the skin surface, it can closely conform to human skin, bending and deforming with the skin, exhibiting excellent flexibility.

[0073] 3. The high flexibility and high sensitivity of the electronic skin allow it to perfectly conform to and more accurately distinguish objects of different shapes and hardnesses when in contact. Grasping experiments show that when the electronic skin is installed on a three-finger robotic hand to grasp two cylinders of different hardness (a Shore hardness difference of 10 degrees), the average outputs of the 4-6 TMR components in the electronic skin are 708.29 mV and 760.11 mV respectively. This allows for precise differentiation of the hardness of different objects, providing the robotic hand with accurate tactile perception information.

[0074] 4. The TMR element adopts free-coverage assembly. PDMS is directly cured around the TMR, which not only provides protection and buffering but also fixes the TMR position at the optimal working magnetic field strength, improving the sensitivity of the electronic skin and transmitting information more effectively.

[0075] 5. The PDMS flexible substrate of the electronic skin is formed by casting and curing, which reduces the distance between the TMR and the magnetic film, allows the TMR to work in the optimal magnetic field, and leaves sufficient space for the deformation of the magnetic film. The force on the electronic skin is increased to 5N, and the overall space of the skin is reduced.

[0076] 6. Integrate the magnetic film of the electronic skin and the PDMS flexible substrate onto a flexible printed circuit board with TMR soldered on it. The output terminals are in the direction of the TMR dual pins, which reduces output interference and improves the efficiency of the circuit board, making it easy to install onto a robotic arm.

[0077] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A force-position sensing composite magnetic electronic skin for intelligent robotic arms, characterized in that, include: A magnetic thin film made of magnetic graphene powder, neodymium iron boron particles and a mixture of polydimethylsiloxane and silica gel; A flexible substrate made of the aforementioned polydimethylsiloxane; Flexible printed circuit board with a tunnel magnetoresistive element array welded on it; The magnetic thin film, as a sensing element, undergoes a change in its internal magnetic field distribution after being subjected to force. The tunnel magnetoresistive element array serves as the detection part, used to detect changes in the magnetic field and convert these changes into voltage signals through a bridge circuit for output. The flexible substrate is disposed between the magnetic thin film and the tunnel magnetoresistive element array to buffer stress deformation and fix the relative positions of each part.

2. The force-position sensing composite magnetic electronic skin for intelligent robotic arms as described in claim 1, characterized in that, The mixing ratio of the magnetic graphene powder, the neodymium iron boron particles, and the polydimethylsiloxane prepolymer is 1:3:

1.

3. The force-position sensing composite magnetic electronic skin for intelligent robotic arms as described in claim 1, characterized in that, The preparation process of the magnetic thin film includes: pouring the uniformly mixed prepolymer into a mold, performing step-by-step heating and curing in a nitrogen environment, and finally cooling.

4. The force-position sensing composite magnetic electronic skin for intelligent robotic arms as described in claim 3, characterized in that, The stepped temperature curing process includes: initial curing at 80℃; and continued curing at 120℃ to remove air bubbles.

5. The force-position sensing composite magnetic electronic skin for intelligent robotic arms as described in claim 1, characterized in that, The tunnel magnetoresistive array consists of nine tunnel magnetoresistive elements arranged in a 3x3 configuration.

6. The force-position sensing composite magnetic electronic skin for intelligent robotic arms as described in claim 5, characterized in that, The tunnel magnetoresistive elements are spaced 7 mm apart in the row direction and 2.5 mm apart in the column direction.

7. The force-position sensing composite magnetic electronic skin for intelligent robotic arms as described in claim 1, characterized in that, The output terminals of the flexible printed circuit board are arranged in a single row and positioned in the direction of the dual pins of the tunnel magnetoresistive element.

8. The force-position sensing composite magnetic electronic skin for intelligent robotic arms as described in claim 1, characterized in that, The magnetic thin film undergoes multi-pole magnetization before installation and use to form multiple magnetic poles corresponding to the positions of the tunnel magnetoresistive element array.

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