Six-dimensional force / torque sensor and system based on multi-layer PCB and graphene material

Abstract

The application discloses a kind of six-dimensional force / torque sensor and system based on multilayer PCB and graphene material, sensor includes first to sixth PCB board, first PCB board is laid with reciprocating bending first parallel wire arranged along first direction, second PCB board is laid with reciprocating bending second parallel wire arranged along second direction, first direction and second direction are orthogonal, third PCB board is laid with reciprocating bending helical wire arranged with radial direction at preset angle, fourth PCB board and fifth PCB board are same in structure, and four orthogonal directions are respectively arranged with graphene piezoresistive sensing unit formed by graphene material, signal processing circuit is provided on the sixth PCB board, the signal processing circuit is connected with the first five PCB boards by wire, for collecting the resistance value of wire or graphene piezoresistive sensing unit on the first five PCB boards.The normal sensing capacity of the present application is stronger and more easily realized multidimensional decoupling.

Description

Technical Field

[0001] This invention relates to force / torque sensor technology, and more particularly to a six-dimensional force / torque sensor and system based on multilayer PCB and graphene materials. Background Technology

[0002] Force / torque sensors, as key components for sensing interactions between objects, play an irreplaceable role in the interactive control of modern intelligent systems. In the medical field, high-precision surgical tools rely on real-time force feedback to assist doctors in performing micron-level precision operations, ensuring surgical safety and reducing tissue damage. In industrial production, collaborative robot joints equipped with torque sensors can quickly detect and avoid harmful collisions with personnel, thereby ensuring the safety of human-robot collaborative environments. Furthermore, torque sensors are widely used in intelligent vehicles to trigger driver protection mechanisms by detecting abnormal road conditions. In precision manufacturing, lathes integrating force sensors can monitor cutting conditions in real time, improving workpiece surface quality and predicting tool wear; and pickup and placement robots, lacking high-precision torque feedback, cannot gently grasp fragile objects.

[0003] Traditional torque sensors primarily consist of a metal shaft and two resistance strain gauges bonded at ±45° angles along the longitudinal direction. While this resistance strain gauge-based technology has become mainstream due to its high linearity, simplicity, scalability, and cost-effectiveness, significant challenges remain in practical manufacturing and application. First, securing and precisely bonding tiny strain gauges to the curved surface of a cylindrical elastomer is an extremely difficult manufacturing process. Any minute alignment deviation, uneven adhesive layer thickness, or manufacturing defects can directly lead to a decrease in measurement accuracy and an increase in interdimensional coupling errors. Second, traditional six-dimensional force sensors typically employ complex metal machining structures (such as crossbeams or spoke structures), resulting in large sensor sizes and heavy weights, often reaching several kilograms. For lightweight collaborative robots or small biomimetic robots, this enormous mass and rotational inertia severely limit the system's dynamic response speed.

[0004] With the development of integrated circuit technology, printed circuit boards (PCBs) are no longer merely carriers of electronic components; the copper foil circuits on their surface have shown potential as sensing elements. Existing research has demonstrated that sinusoidal coils on the PCB surface can measure translational displacement, and this concept has been extended to the measurement of rotational displacement. Furthermore, researchers have discovered that applied torque can be measured by the deformation of the PCB itself. In one-dimensional torque measurement, by etching a special spiral sensing pattern on a PCB ring, the resistance change can be made proportional to the applied torque. Compared to traditional sensors, this PCB-based sensor exhibits the same excellent linearity over the same measurement range, while possessing better accuracy and a much smaller size. More importantly, it completely overcomes the alignment and bonding challenges of traditional sensors, providing more mounting possibilities and enabling the integration of peripheral electronic components onto a single circuit board. This innovative design provides an ideal force control option for general-purpose, mass-producible humanoid robots.

[0005] However, most existing research on PCB-based mechanical sensors is limited to single-dimensional torque (Mz) measurement. In actual complex operation tasks, single-dimensional torque information alone is insufficient. Robot end effectors or joints need to simultaneously acquire thrust (Fx, Fy, Fz) in three directions and torque (Mx, My, Mz) in three directions to achieve compliant control. Current PCB sensing solutions have the following bottlenecks in achieving six-dimensional force perception: (1) Structural uniformity: It is difficult for a single-layer PCB to distinguish force signals of different dimensions through a single trace scheme. The signals generated in each dimension are prone to aliasing, making it difficult to achieve hardware-level decoupling. (2) Insufficient sensitivity of normal force sensing: Traditional copper foil strain gauges have a relatively weak response to pressure (Fz) perpendicular to the PCB plane. Summary of the Invention

[0006] To address the problems existing in the prior art, the purpose of this invention is to provide a six-dimensional force / torque sensor and system based on multilayer PCB and graphene materials, which has stronger normal sensing capabilities and is easier to achieve multi-dimensional decoupling.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] A six-dimensional force / torque sensor based on multilayer PCBs and graphene materials includes a first to a sixth PCB board. The first PCB board has a first parallel wire arranged along a first direction with reciprocating bending. The second PCB board has a second parallel wire arranged along a second direction with reciprocating bending. The first and second directions are orthogonal. The third PCB board has a spiral wire arranged at a preset angle to the radial direction with reciprocating bending. The fourth and fifth PCB boards have the same structure, and graphene piezoresistive sensing units formed of graphene material are arranged in four orthogonal positions. The sixth PCB board is provided with a signal processing circuit, which is connected to the first five PCB boards through wires and is used to collect the resistance values ​​of the wires or graphene piezoresistive sensing units on the first five PCB boards.

[0009] Furthermore, each PCB board is a circular PCB board. The outer ring of the circular PCB board has several through holes. The first to sixth PCB boards are fixed as a whole by a fixing device passing through the through holes. The inner ring of the circular PCB board is the external load loading area, and the annular area between the outer and inner rings is the strain sensing area, which is used to lay wires or signal processing circuits.

[0010] Furthermore, the first PCB board, the second PCB board, the third PCB board, the fourth PCB board, the fifth PCB board, and the sixth PCB board are stacked sequentially from top to bottom.

[0011] Furthermore, the first direction is the X-axis direction and the second direction is the Y-axis direction, or the first direction is the Y-axis direction and the second direction is the X-axis direction.

[0012] Furthermore, the angle between the inner loop of the spiral conductor and the radial direction is a preset angle. The angle between the outer loop of the spiral conductor and the radial direction is . .

[0013] Furthermore, the preset angle for .

[0014] Furthermore, the fourth PCB board and the fifth PCB board Graphene piezoresistive sensing units are arranged in different directions.

[0015] Furthermore, the signal processing circuit specifically includes:

[0016] The Wheatstone bridge circuit unit connects the wires of the first five PCB layers and is used to convert the resistance changes of each PCB layer into voltage signals.

[0017] The signal processing chip is used to amplify, regulate, and convert the voltage signal output from the Wheatstone bridge circuit unit into an analog-to-digital signal.

[0018] Digital output circuitry is used to analyze and output signals from signal processing chips.

[0019] Furthermore, the main body of each PCB board is made of composite material FR-4.

[0020] A six-dimensional force / torque sensor system based on multilayer PCB and graphene material includes the aforementioned sensor and a decoupling module connected to the signal processing circuit for performing the following calculations:

[0021] The first-dimensional force is calculated using the following formula:

[0022]

[0023] In the formula, This represents the first-dimensional force obtained by decoupling. This represents the equivalent cross-sectional area of ​​the area where the first parallel conductor is laid on the first PCB board. , These represent the real-time resistance value and resistance change value of the first parallel conductor acquired by the signal processing circuit when an external load is applied, respectively. This indicates the shear modulus of the PCB board material. These represent the sensitivity coefficients of the conductors;

[0024] The second-dimensional force is calculated using the following formula:

[0025]

[0026] In the formula, This represents the second-dimensional force obtained through decoupling. , These represent the real-time resistance value and resistance change value of the second parallel conductor acquired by the signal processing circuit when an external load is applied;

[0027] The first-dimensional torque is calculated using the following formula:

[0028]

[0029] In the formula, , These represent the real-time resistance value and resistance change value of the spiral conductor on the third PCB board, respectively, acquired by the signal processing circuit when an external load is applied. These are the fitting coefficients;

[0030] The third-dimensional force is calculated using the following formula:

[0031]

[0032] In the formula, This represents the third-dimensional force obtained through decoupling. These are the fitting coefficients. These represent the resistance changes of the four graphene piezoresistive sensing units on the fourth PCB board when an external load is applied.

[0033] The second and third-dimensional torques are calculated using the following formula:

[0034]

[0035]

[0036] In the formula, , This represents the second and third-dimensional torques obtained from decoupling. , These are the fitting coefficients. These represent the resistance changes of the four graphene piezoresistive sensing units on the fifth PCB board when an external load is applied. These represent the real-time resistance values ​​of the four graphene piezoresistive sensing units on the fifth PCB board when an external load is applied.

[0037] Compared with the prior art, the beneficial effects of this invention are:

[0038] (1) Extremely high linearity and accuracy: By utilizing the stack-up space routing capability of multi-layer PCBs, the complex six-dimensional signal is split into different physical layers, reducing the pressure of algorithm compensation, making it easier to achieve six-dimensional decoupling, and achieving higher accuracy;

[0039] (2) Higher sensitivity: Traditional copper foil strain gauges perform poorly in normal force detection. This invention introduces graphene piezoresistive material and utilizes its ultra-high sensitivity coefficient to obtain high signal-to-noise ratio signals under small displacements.

[0040] (3) Structural integration, lighter weight: Traditional sensors obtain deformation through metal elastomers (such as cross beams), resulting in a large rotational inertia of the system. This invention utilizes a multi-layer PCB board as both a circuit carrier and an elastic sensing element, greatly reducing thickness and weight, resulting in a lighter weight;

[0041] (4) Higher precision: Traditional sensors rely on manual pasting of strain gauges, which is greatly affected by the operator's skill and has poor alignment accuracy. This invention uses high-precision PCB etching technology to directly grow the sensing units (parallel wires, spiral wires and graphene piezoresistive sensing units) on the elastic substrate, ensuring absolute accuracy of geometric position;

[0042] (5) Low cost and easy to mass-produce quickly: Relying on a mature, precise and automated PCB supply chain, this invention can achieve low-cost large-scale production. Attached Figure Description

[0043] Figure 1 This is an exploded decomposition diagram of the overall structure of a six-dimensional force / torque sensor based on multilayer PCB and graphene material provided in an embodiment of the present invention;

[0044] Figure 2 yes Figure 1 A schematic diagram of the structure of the first PCB board in the middle;

[0045] Figure 3 yes Figure 1 Schematic diagram of the structure of the second PCB board;

[0046] Figure 4 yes Figure 1 Schematic diagram of the structure of the third PCB board;

[0047] Figure 5 yes Figure 1 Schematic diagram of the fourth PCB board in the middle;

[0048] Figure 6 yes Figure 1 Schematic diagram of the sixth PCB board;

[0049] Figure 7 This is a circuit diagram of the signal processing circuit provided in an embodiment of the present invention; In the diagram, 1: First PCB board, 1-1: Inner ring loading hole, 1-2: Through hole, 1-3: Middle annular area, 1-4: First parallel wire, 2: Second PCB board, 2-1: Second parallel wire, 3: Third PCB board, 3-1: Spiral wire, 4: Fourth PCB board, 4-1: Graphene piezoresistive sensing unit, 4-2: Wire, 5: Fifth PCB board, 6: Sixth PCB board, 6-1: Signal processing chip, 6-2: Wheatstone bridge circuit unit. Detailed Implementation

[0050] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0051] Example 1

[0052] This invention provides a six-dimensional force / torque sensor based on multilayer PCB and graphene materials, such as... Figure 1As shown, the PCBs are stacked sequentially from top to bottom, namely, PCB 1, PCB 2, PCB 3, PCB 4, PCB 5, and PCB 6. In other embodiments, the top-to-bottom arrangement of the PCBs can be changed without affecting the final result. The substrate of all PCBs is made of FR-4 composite material. FR-4 is a composite material composed of woven fiberglass cloth and flame-retardant epoxy resin adhesive, possessing excellent electrical insulation properties and mechanical strength. Their parameters are as follows:

[0053] External parameters: The sensor body is a circular disc structure with a diameter of 100mm and a total thickness of approximately 1.6mm to 2.0mm.

[0054] Inner ring loading hole 1-1: An inner ring circumference with a radius of 10mm, used to connect the input shaft at the force-bearing end and bear external loads.

[0055] Outer ring fixing holes: There are 8 through holes 1-2 with a diameter of 4.5mm evenly distributed on the outer ring circumference with a radius of 42.5mm. These holes are used to connect the output shaft of the fixing base and fix the first to sixth PCB boards as a whole.

[0056] Sensitive area: The intermediate annular area 1-3 located between the inner ring and the outer ring, that is, the area with a radius between 15mm and 37.5mm, is the strain sensing area of ​​the present invention, which is used to lay wires or signal processing circuits.

[0057] Manufacturing process requirements: The conductors laid on the PCB are made of copper foil, with a standard copper foil thickness of 17.5μm. The designed copper foil linewidth is 100μm, and the minimum spacing is 100μm. In the actual etching process, due to over-etching, the linewidth may be slightly reduced to approximately 90μm. This deviation will be compensated for in subsequent circuit calibration.

[0058] like Figure 2 As shown, a first parallel conductor 1-4, arranged along the X-axis, is laid on the first PCB board 1, with reciprocating bends. The main body of the first parallel conductor 1-4 is parallel to the X-axis, and the bending direction is along the Y-axis. Therefore, when the sensor is subjected to shear force F along the positive and negative X-axis directions... x The central annular region experiences shear strain along the X-axis. During this process, the length and cross-sectional area of ​​the first parallel conductors 1-4, arranged along the X-axis, change due to the stretching or compression of the substrate, resulting in a change in resistance. The resistance F can then be calculated from this change in resistance. x .

[0059] like Figure 3As shown, a second parallel conductor 2-1, arranged along the Y-axis, is laid on the second PCB board 2, with reciprocating bends. The main direction of the second parallel conductor 2-1 is parallel to the Y-axis, and the bending direction is along the X-axis. Specifically, the laying rule of the second parallel conductor 2-1 is the same as that of the first parallel conductor 1-4, only the angle is rotated by 90 degrees. The orthogonal layout of the first PCB board 1 and the second PCB board 2 ensures that the second PCB board 2 only experiences the shear force component F in the Y-axis direction. y Highly sensitive. Through physical isolation and direction locking between the first PCB board 1 and the second PCB board 2, F-axis sensitivity is achieved in the early stages of signal generation. x With F y The initial hardware decoupling avoids severe coupling of bidirectional signals in a single plane, minimizes cross-interference, and thus improves the measurement accuracy of forces in the X and Y axes.

[0060] In other embodiments, the wiring directions of the first PCB board 1 and the second PCB board 2 can be interchanged without affecting the final result.

[0061] like Figure 4 As shown, the third PCB board 3 is covered with helical wires 3-1 that are bent back and forth and arranged at a preset angle to the radial direction. Specifically, the angle between the inner loop of the helical wire 3-1 and the radial direction is a preset angle. The angle between the outer ring and the radial direction is called the angle between the outer ring and the radial direction. preset angle for , Figure 4 As shown Spiral sensing pattern. Traditional radial routing. Although it responds to torque, its resistance change cannot distinguish whether the torque is clockwise or counterclockwise. Tangential routing. Therefore, it has almost no length response to torque. This invention employs a length-independent design with respect to the radial radius. A clockwise torque on a spiral wire will compress the spiral wire, reducing resistance. A counterclockwise torque will stretch the spiral wire, increasing resistance. The third PCB board 3 is a crucial component for realizing rotational torque sensing in this invention. It features a specially designed spiral copper foil sensing pattern for measuring the torque M around the Z-axis. z It can accurately capture shear strain caused by torsion and can distinguish between clockwise and counterclockwise torque by the direction of resistance change.

[0062] like Figure 5 As shown, the fourth PCB board 4 has four orthogonal orientations. Each of the graphene piezoresistive sensing units 4-1 is formed of graphene material and is connected by a wire 4-2 to realize the sensing of the Z-axis force F. zHigh-sensitivity measurement. Specifically, graphene conductive ink is integrated into the reserved window area using screen printing technology or in-situ coating process to form graphene piezoresistive sensing unit 4-1. Compared with traditional copper foil traces, graphene material has a higher sensitivity coefficient, reaching tens or even hundreds, and can detect minute normal deformations. When the inner ring is subjected to pressure or tension in the Z-axis direction, the four graphene piezoresistive sensing units 4-1 generate strain in the same direction, and then the Z-axis force F can be calculated based on the resistance change caused by the strain. z .

[0063] The fifth PCB board 5 has the same structure as the fourth PCB board 4, but their decoupling principles differ. The fifth PCB board 5 is mainly used to measure the X and Y axis torques. When a torque is generated around the X-axis, the torque located on the Y-axis... Graphene piezoresistive sensing unit and The graphene piezoresistive sensing unit generates strain of opposite sign. Graphene piezoresistive sensing unit and The differential calculation of strain in the graphene piezoresistive sensing unit enables measurement and cancellation of common-mode interference, thereby realizing the X-axis torque M. x Similarly, measurement can be based on Graphene piezoresistive sensing unit and Differential calculation of strain in graphene piezoresistive sensing unit to realize Y-axis torque M y Measurement.

[0064] like Figure 6 As shown, a signal processing circuit is installed on the sixth PCB board 6. This signal processing circuit is connected to the first five PCB boards via wires and is used to collect the resistance values ​​of the wires or graphene piezoresistive sensing units on the first five PCB boards, converting the weak resistance changes into digital signals that can be read by a computer. The signal processing circuit is as follows... Figure 7 As shown, it specifically includes:

[0065] The Wheatstone bridge circuit unit 6-2 connects the wires of the first five PCB layers and is used to convert the resistance changes of each PCB layer into voltage signals. Since over-etching in the PCB etching process may cause uneven trace widths (such as from 100μm to 90μm), a balancing potentiometer can also be integrated into the circuit to adjust the initial zero-point balance.

[0066] The signal processing chip (HX711) 6-1, integrated on the PCB, includes a low-noise programmable gain amplifier (x128 gain) PGA, an internal voltage regulator, and a 24-bit high-resolution analog-to-digital converter (ADC). It amplifies, regulates, and converts the voltage signal output from the Wheatstone bridge circuit. The internal voltage regulator provides a stable drive voltage to the bridge. The low-noise programmable gain amplifier can be set to 128 times to amplify the microvolt-level bridge output signal. The 24-bit ADC converts the analog signal into a high-resolution digital signal.

[0067] The digital output circuit connects to the signal processing chip via digital signals. It is used to analyze and output the signals output by the signal processing chip. Specifically, an MCU (such as Arduino Uno) is used to analyze the data. Its output rate can reach 80Hz, which is sufficient to meet the collision detection needs of most collaborative robots.

[0068] The signal processing circuit is calibrated with a 24-bit ADC and a balanced potentiometer, which enables a low discrimination threshold and effectively suppresses temperature drift and electromagnetic interference through a differential bridge.

[0069] Example 2

[0070] This embodiment provides a six-dimensional force / torque sensor system based on multilayer PCB and graphene material, including the sensor of Embodiment 1, and further including a decoupling module. The decoupling module is connected to the signal processing circuit and is used to perform the following calculations:

[0071] S1. The X-axis force is calculated using the following formula:

[0072]

[0073] In the formula, This represents the X-axis force obtained after decoupling. This represents the equivalent cross-sectional area of ​​the area where the first parallel conductor is laid on the first PCB board. , These represent the real-time resistance value and resistance change value of the first parallel conductor acquired by the signal processing circuit when an external load is applied, respectively. This indicates the shear modulus of the PCB board material. This indicates the sensitivity coefficient of the conductor.

[0074] The derivation of the above calculation formula is as follows:

[0075] According to elasticity analysis, when the sensor is subjected to a unidirectional shear force along the x-axis... At this time, shear strain will occur in the sensitive area. According to the theory of thin plate mechanics, the average shear stress caused by shear force is... It can be represented as:

[0076]

[0077] Due to the deformation of the PCB substrate under pressure, the length l of the conductor changes slightly by Δl. According to the law of resistance... , Let S be the resistivity of the conductor material, and S be the cross-sectional area of ​​the conductor. The first parallel conductor 1-4 zigzags back and forth along the main X-axis direction; this serpentine wiring method causes its linear strain in the X-axis direction. Most sensitive.

[0078] The relationship between the rate of change of resistance and the applied force is as follows:

[0079]

[0080] Will After substituting and performing formal transformations, we can obtain... The calculation formula.

[0081] S2. The Y-axis force is calculated using the following formula:

[0082]

[0083] In the formula, This represents the Y-axis force obtained after decoupling. , These represent the real-time resistance value and resistance change value of the second parallel conductor, respectively, acquired by the signal processing circuit when an external load is applied. The derivation process is similar to that of the first-dimensional force calculation unit and will not be repeated here.

[0084] S3. The Z-axis torque is calculated using the following formula:

[0085]

[0086] In the formula, This represents the Z-axis torque obtained after decoupling. , These represent the initial resistance value and the resistance change value of the spiral wire on the third PCB board, respectively, acquired by the signal processing circuit when an external load is applied. The fitting coefficients are denoted as .

[0087] The derivation of the above calculation formula is as follows:

[0088] Assuming the inner diameter of the PCB ring is The outer diameter is When the outer ring is fixed, the inner ring is subjected to a torque about the Z-axis. When applied, in-plane shear stress is generated inside the ring. According to the equilibrium equations of elasticity in axisymmetric polar coordinates, the differential equation under pure torsion is:

[0089]

[0090] Integrate the differential equation and combine it with the inner loop boundary conditions (torque). (Equivalent to distributed shear force on the inner ring boundary), the shear stress can be obtained. The distribution law with radius r is as follows:

[0091]

[0092] Where t is the thickness of the annulus. This formula shows that the shear stress decreases inversely with the square of the radius. To maximize the capture of the deformation caused by this stress, this embodiment uses a helical trace at a 45° angle to the radial direction on the third PCB board. Mechanically, the 45° direction is precisely the direction of the principal strain under pure shear conditions. The rate of change of total resistance generated by the helical conductor under this stress field is the strain integral along its path. Due to the local strain and torque... The relationship is linear, therefore the overall resistance change rate is... With applied torque It exhibits extremely high linear correlation:

[0093]

[0094] Introducing comprehensive fitting coefficients The above calculation formula and fitting coefficient can then be obtained. The value of this coefficient can be obtained through experiments. Specifically, a known torque is applied to the sensor, and then the resistance value is measured.

[0095] S4. The Z-axis force is calculated using the following formula:

[0096]

[0097] In the formula, This represents the z-axis force obtained after decoupling. These are the fitting coefficients. These represent the resistance changes of the four graphene piezoresistive sensing units on the fourth PCB board when an external load is applied.

[0098] The derivation of the above formula is as follows:

[0099] First, we analyze the force response of a single graphene piezoresistive sensing unit: when the sensor is subjected to a Z-axis force perpendicular to the plane... When this occurs, the sensor core structure, made of flexible materials such as PDMS (polydimethylsiloxane) or silicone, will undergo normal compressive deformation. This deformation is directly transmitted to the graphene piezoresistive pad on the fourth-layer PCB, causing it to experience out-of-plane strain. According to the piezoresistive effect equation of graphene material, the relative resistance change rate of the i-th sensing unit is related to the local strain at its location. Proportional.

[0100] Let the initial resistances of the four graphene piezoresistive sensing units be respectively The rate of change of resistivity and strain of graphene materials Satisfies the piezoresistive effect equation:

[0101]

[0102] in, The sensitivity coefficient of graphene materials is typically much greater than that of copper foil conductors. ).

[0103] Within the linear elastic range, local strain and local normal load Proportional, that is:

[0104]

[0105] in, This is the structural deformation transmission coefficient at that location.

[0106] Analysis of the array synthesis effect of the four sensing units: In this embodiment, the four graphene piezoresistive sensing units are symmetrically distributed at 90°. To amplify the signal characteristics of the central Z-axis force and average out local material inhomogeneities, the measurement is achieved by calculating the algebraic sum of the changes in the four signals.

[0107]

[0108] In actual manufacturing processes, the initial resistance of the four symmetrically arranged graphene units is approximately equal, i.e. With a constant initial resistance Deformation transmission coefficient and sensitivity coefficient Constants are uniformly merged into the comprehensive fitting coefficients. In, that is:

[0109]

[0110] The Z-axis force can be directly calculated by summing the absolute changes in the resistance of the four circuits:

[0111]

[0112] S5. The second and third-dimensional torques are calculated using the following formula:

[0113]

[0114]

[0115] In the formula, , This represents the X and Y axis torques obtained after decoupling. , These are the fitting coefficients. These represent the resistance changes of the four graphene piezoresistive sensing units on the fifth PCB board when an external load is applied. These represent the real-time resistance values ​​of the four graphene piezoresistive sensing units on the fifth PCB board when an external load is applied.

[0116] The derivation of the above formula is as follows:

[0117] First, we analyze the force response of the flexible core structure under torque: when the sensor is subjected to a flipping torque around the X-axis... At this time, the core layer, composed of flexible materials such as PDMS or silicone, will exhibit asymmetrical "seesaw" deformation. Specifically, the area located on the positive Y-axis (e.g., at 90°) is compressed, while the area on the negative Y-axis (e.g., at 270°) is stretched (or its deformation is reduced). This asymmetrical deformation is transmitted to the corresponding graphene piezoresistive pad on the fifth PCB layer, causing it to produce equal local strains of opposite signs. According to the single-point derivation logic in S4, the local equivalent normal load... Its absolute change in resistance Proportional:

[0118]

[0119] Analysis of the differential calculation effect of the symmetrical sensing unit: In the mechanical model, the torque about the X-axis This can be equivalent to a pair of couples acting on a symmetrical sensing unit. Let d be the equivalent force arm from the corresponding sensing unit to the central X-axis; then the torque can be expressed as the product of the differences in the normal loads on both sides:

[0120]

[0121] To accurately extract torque And effectively cancel common-mode interference, substitute into the normal load expression of each element to perform differential calculation:

[0122]

[0123] In actual processes, the parameters of symmetrically arranged graphene units are highly consistent, that is... Furthermore, the deformation conductivity of the PDMS / silicone structure at symmetrical positions... .

[0124] With a constant lever arm d and initial resistance , conductivity k and graphene sensitivity Constants are uniformly merged into the comprehensive fitting coefficients. In, that is:

[0125]

[0126] The torque around the X-axis can be directly calculated from the difference in the absolute changes of the two resistances:

[0127]

[0128] Similarly, the derivation can be obtained by calculating the difference between element 1 and element 3 on the X-axis:

[0129]

[0130] In other embodiments, the calculation processes of S1 to S5 described above can be combined into a matrix algorithm, and the five digital output signals of the sensor can be set as S=[ ], , = Six-dimensional force / torque F=[F x ,F y ,F z M x M y M z The relationship between the two satisfies:

[0131]

[0132] in This is the decoupling matrix obtained through experimental calibration. Because this invention addresses F at the physical level... x ,F y M z Distributed on different PCB layers, decoupling matrix It exhibits good diagonal characteristics, which significantly reduces computational complexity and crosstalk error.

[0133] It should be understood that the embodiments and descriptions above are only the principles, main features and advantages of the present invention. Various changes and modifications can be made to the present invention without departing from the spirit and scope of the invention, and all such changes and modifications fall within the protection scope of the present invention.

Claims

1. A six-dimensional force / torque sensor based on multilayer PCB and graphene material, characterized in that, The system includes six PCB boards. The first PCB board has a first parallel wire arranged in a first direction with reciprocating bends. The second PCB board has a second parallel wire arranged in a second direction with reciprocating bends. The first and second directions are orthogonal. The third PCB board has a spiral wire arranged in a predetermined angle with the radial direction with reciprocating bends. The fourth and fifth PCB boards have the same structure, and graphene piezoresistive sensing units formed of graphene material are arranged in four orthogonal positions. The sixth PCB board is equipped with a signal processing circuit, which is connected to the first five PCB boards through wires and is used to collect the resistance values ​​of the wires or graphene piezoresistive sensing units on the first five PCB boards.

2. The six-dimensional force / torque sensor based on multilayer PCB and graphene material according to claim 1, characterized in that, Each PCB board is a circular PCB board. The outer ring of the circular PCB board has several through holes. The first to sixth PCB boards are fixed as a whole by a fixing device that passes through the through holes. The inner ring of the circular PCB board is the external load loading area, and the annular area between the outer and inner rings is the strain sensing area, which is used to lay wires or signal processing circuits.

3. The six-dimensional force / torque sensor based on multilayer PCB and graphene material according to claim 1, characterized in that, The first PCB board, the second PCB board, the third PCB board, the fourth PCB board, the fifth PCB board, and the sixth PCB board are stacked sequentially from top to bottom.

4. The six-dimensional force / torque sensor based on multilayer PCB and graphene material according to claim 1, characterized in that, The first direction is the X-axis direction and the second direction is the Y-axis direction, or the first direction is the Y-axis direction and the second direction is the X-axis direction.

5. The six-dimensional force / torque sensor based on multilayer PCB and graphene material according to claim 1, characterized in that, The angle between the inner loop of the spiral conductor and the radial direction is a preset angle. The angle between the outer loop of the spiral conductor and the radial direction is . .

6. The six-dimensional force / torque sensor based on multilayer PCB and graphene material according to claim 5, characterized in that, The preset angle The for .

7. The six-dimensional force / torque sensor based on multilayer PCB and graphene material according to claim 1, characterized in that, The fourth PCB board and the fifth PCB board Graphene piezoresistive sensing units are arranged in different directions.

8. The six-dimensional force / torque sensor based on multilayer PCB and graphene material according to claim 1, characterized in that, The signal processing circuit specifically includes: The Wheatstone bridge circuit unit connects the wires of the first five PCB layers and is used to convert the resistance changes of each PCB layer into voltage signals. The signal processing chip is used to amplify, regulate, and convert the voltage signal output from the Wheatstone bridge circuit unit into an analog-to-digital signal. Digital output circuitry is used to analyze and output signals from signal processing chips.

9. The six-dimensional force / torque sensor based on multilayer PCB and graphene material according to claim 1, characterized in that, The main body of each PCB board is made of composite material FR-4.

10. A six-dimensional force / torque sensor system based on multilayer PCB and graphene material, characterized in that, The sensor, comprising any one of claims 1 to 9, further comprises a decoupling module connected to the signal processing circuit, the decoupling module being used to perform the following calculations: The first-dimensional force is calculated using the following formula: , In the formula, This represents the first-dimensional force obtained by decoupling. This represents the equivalent cross-sectional area of ​​the area where the first parallel conductor is laid on the first PCB board. , These represent the real-time resistance value and resistance change value of the first parallel conductor acquired by the signal processing circuit when an external load is applied, respectively. This indicates the shear modulus of the PCB board material. These represent the sensitivity coefficients of the conductors; The second-dimensional force is calculated using the following formula: , In the formula, This represents the second-dimensional force obtained through decoupling. , These represent the real-time resistance value and resistance change value of the second parallel conductor acquired by the signal processing circuit when an external load is applied; The first-dimensional torque is calculated using the following formula: , In the formula, , These represent the real-time resistance value and resistance change value of the spiral conductor on the third PCB board, respectively, acquired by the signal processing circuit when an external load is applied. These are the fitting coefficients; The third-dimensional force is calculated using the following formula: , In the formula, This represents the third-dimensional force obtained through decoupling. These are the fitting coefficients. These represent the resistance changes of the four graphene piezoresistive sensing units on the fourth PCB board when an external load is applied. The second and third-dimensional torques are calculated using the following formula: , , In the formula, , This represents the second and third-dimensional torques obtained from decoupling. , These are the fitting coefficients. These represent the resistance changes of the four graphene piezoresistive sensing units on the fifth PCB board when an external load is applied. These represent the real-time resistance values ​​of the four graphene piezoresistive sensing units on the fifth PCB board when an external load is applied.

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