Twelve-beam six-dimensional force sensor

Abstract

The invention discloses a twelve-beam six-dimensional force sensor, and relates to the technical field of force sensing. The sensor effectively solves the problem of coupling interference in six-dimensional force measurement by optimizing the structural design of the elastic body, innovating the bridging mode of the strain gauges and accurately positioning the patches, and improves the measurement precision and stability. The sensor is of a twelve-beam elastomer structure, stress distribution under different loads is analyzed through COMSOL finite element simulation software, and the position of a strain sensitive area is determined; a group bridge circuit is designed through tension and compression strain characteristics of the symmetrical strain beams, and decoupling is achieved from the hardware level; mEMS silicon strain gauges are selected and accurately assembled, so that the measurement error is further reduced. Experimental data show that the crosstalk rate of the sensor under loads of all dimensions is as low as 2%, net output signals are stable, and the sensor can be widely applied to the fields of robots, precision manufacturing, aerospace and the like with high requirements on force measurement precision.

Description

Technical Field

[0001] This invention belongs to the field of force sensing technology, specifically relating to a twelve-beam six-dimensional force sensor. Background Technology

[0002] A six-dimensional force sensor is a device capable of simultaneously measuring three force components (Fx, Fy, Fz) and three torque components (Mx, My, Mz) acting on an object in three-dimensional space. It is currently the highest-dimensional and most comprehensive sensor type in the field of force sensing. Due to its ability to provide comprehensive force control information, six-dimensional force sensors play an irreplaceable role in fields with extremely high requirements for force control accuracy, such as precision assembly of industrial robots, medical surgical equipment, aerospace testing, and balance control of humanoid robots. However, traditional six-dimensional force sensors still face a series of key technical challenges in practical applications, severely limiting their measurement accuracy and reliability. These challenges are mainly manifested in the following aspects: 1. Severe Interdimensional Coupling Interference: Due to the nonlinear mechanical characteristics of six-dimensional force sensors, when one dimension is loaded, other dimensions often generate undesirable output signals. This phenomenon is called interdimensional coupling or crosstalk. An ideal six-dimensional force sensor requires independent outputs in each dimension, but in practice, coupling is difficult to avoid due to factors such as elastic body structure design and strain gauge bonding deviations. In traditional structural designs, the strain-sensitive area is not uniquely distributed, causing a single-dimensional load to induce strain in multiple regions, resulting in interference components from other dimensions mixed into the output signal. Although some designs attempt software decoupling through complex algorithms, these methods are computationally intensive, have poor real-time performance, and rely on high-performance processing units, making them unsuitable for high-dynamic scenarios.

[0003] 2. Insufficient strain gauge mounting accuracy and low signal acquisition quality: As the core sensitive element of a sensor, the mounting position of the strain gauge directly determines the sensitivity and accuracy of signal acquisition. Traditional sensor strain gauge mounting often relies on experience or simplified theoretical analysis, lacking guidance based on precise stress simulation positioning. This results in the strain gauge failing to cover the maximum strain area of ​​the elastic body. Furthermore, traditional metal foil strain gauges are large in size, making them difficult to adapt to miniaturization design requirements, and their poor temperature stability makes them susceptible to factors such as temperature drift and creep, further reducing signal reliability.

[0004] 3. Insufficient Dynamic Performance and Overload Protection: In practical applications, six-dimensional force sensors often need to handle high-speed, time-varying signals (such as robotic grinding and surgical force feedback), which places extremely high demands on the sensor's dynamic response characteristics. Traditional sensors mostly focus on static performance optimization, while research on dynamic performance is relatively weak, resulting in insufficient signal tracking capabilities under rapidly changing loads. At the same time, the mechanical overload protection structure design is complex, making it difficult to comprehensively protect the sensor while simultaneously ensuring accuracy and compactness.

[0005] 4. Complex calibration process and high cost: The calibration of six-dimensional force sensors requires specialized six-dimensional combined loading equipment to obtain the parameter mapping relationship needed for the decoupling algorithm through multi-dimensional composite loading. Such equipment is mostly non-standard customized, expensive, and the calibration process is easily affected by the nonlinear characteristics of inter-dimensional coupling, making it difficult to guarantee calibration accuracy. In addition, existing sensors lack systematic compensation for error factors such as temperature and creep, resulting in a decline in accuracy and stability during long-term use.

[0006] In summary, existing six-dimensional force sensors have significant shortcomings in terms of structural design, signal decoupling, dynamic response, and calibration accuracy, making them particularly inadequate for high-precision force control applications such as robotic manipulation and medical surgery. Therefore, there is an urgent need for a sensor design solution that incorporates systematic innovations in elastomer structure, patch positioning, and bridging methods to fundamentally reduce inter-dimensional coupling and improve signal quality and dynamic performance. Summary of the Invention

[0007] This invention provides a twelve-beam six-dimensional force sensor, which aims to solve the problems of low accuracy and insufficient stability in current six-axis detection.

[0008] The present invention is implemented as follows: a twelve-beam six-dimensional force sensor includes an elastic body, a central loading platform, and strain gauges. The central loading platform is provided with positioning holes. The elastic body includes an outer frame, a central loading platform, and twelve elastic beams connected between the two. The twelve elastic beams include four T-shaped main beams and eight L-shaped secondary beams. The four T-shaped main beams are evenly distributed around the central loading platform, and the L-shaped secondary beams are symmetrically distributed on both sides of each T-shaped main beam. The strain gauges are attached to the strain-sensitive area of ​​the elastic beam, which is the region with the largest strain under a specific dimensional load, as determined by finite element simulation analysis. The strain gauges are connected to form a measuring bridge. The bridge is assembled by dividing the strain gauges on a symmetrical strain beam that produces strains of equal magnitude and opposite properties under load in a specific direction into two groups, which are then connected to adjacent arms of the measuring bridge.

[0009] Preferably, the central loading platform is provided with a threaded hole, and the external load is transmitted to the elastomer through the inner wall of the threaded hole.

[0010] Preferably, the central loading platform has a cuboid structure.

[0011] Preferably, the T-shaped main beam has a rectangular cross-section, and the L-shaped secondary beam has an L-shaped cross-section.

[0012] Preferably, a total of 24 strain gauges are attached to the elastomer, with 4 strain gauges corresponding to each dimensional load, forming six Wheatstone full-bridge circuits.

[0013] Preferably, the finite element simulation analysis refers to plotting the stress path and selecting the region of maximum strain when the elastic body is subjected to loads of Fx, Fz, My, and Mz.

[0014] Preferably, the central loading stage is rigidly connected to the elastomer via four screws. The loading stage has threaded holes, allowing external loads (such as robot end effector forces or test piece reaction forces) to be transmitted to the elastomer through the inner side of the threaded holes, ensuring a stable load transmission path and preventing additional errors caused by loose connections. Strain gauges: MEMS silicon strain gauges are selected, measuring 1.3mm × 0.15mm, featuring high sensitivity, good temperature stability, and small size, adapting to the miniaturization requirements of the elastomer's strain-sensitive area. A total of 24 strain gauges are attached, with 4 strain gauges corresponding to each dimensional load (Fx, Fy, Fz, Mx, My, Mz), arranged in six Wheatstone bridges. The measurement bridge is designed based on the tensile and compressive strain characteristics of the strain gauges, achieving hardware decoupling through a specific bridge configuration, reducing software algorithm dependence, and improving measurement real-time performance and accuracy.

[0015] Compared with related technologies, the twelve-beam six-dimensional force sensor provided by this invention has the following beneficial effects: 1. Significantly Reduced Crosstalk and High Measurement Accuracy: Through an innovative twelve-beam elastic structure design (including four T-shaped main beams and eight L-shaped secondary beams), combined with strain-sensitive zone positioning determined by finite element simulation, and hardware bridging decoupling design utilizing the tensile and compressive strain characteristics of symmetrical strain beams, this invention effectively suppresses coupling interference during force / torque measurement in all dimensions from the structural source and signal acquisition stage. Experimental data shows that the crosstalk rate of this sensor can be as low as 2%FS (full scale) under various dimensional loads. For example, the crosstalk rate is 2% under Fx load, -2% under Fy load, 2% under Fz load, and 2% under Mx, My, and Mz loads, achieving high-precision six-dimensional force measurement.

[0016] 2. Hardware Decoupling Enhances Real-Time Performance and Stability: This invention achieves preliminary decoupling of force signals in various dimensions at the hardware level through a specific bridging method (dividing strain gauges on a symmetrical strain beam that produces equal and opposite strain under load in a specific direction into two groups, each connected to an adjacent arm of a measuring bridge). This design reduces reliance on complex software decoupling algorithms, lowers data processing complexity, and improves measurement real-time performance, making it particularly suitable for dynamic applications requiring rapid force feedback, such as precision assembly and polishing in robots. Simultaneously, hardware decoupling reduces the possibility of additional errors introduced by algorithm model errors or environmental interference, improving measurement stability and reliability.

[0017] 3. Structural Optimization and Precise Strain Gauge Placement Enhance Signal Quality and Sensitivity: The twelve-beam symmetrical structure design results in a more uniform load distribution, reduces local stress concentration, and provides space for the independent placement of strain-sensitive zones in each dimension, improving the structure's stability and load-bearing capacity. By analyzing the stress distribution under different loads using finite element simulation software such as COMSOL, the region of maximum strain was precisely determined as the strain-sensitive zone for strain gauge placement, ensuring that the strain gauge can effectively acquire the target signal. A 1.3mm × 0.15mm MEMS silicon strain gauge was selected, featuring high sensitivity, good temperature stability, and small size, further improving signal acquisition sensitivity and signal-to-noise ratio, and reducing measurement errors.

[0018] 4. Excellent overall performance and broad application prospects: The sensor of this invention possesses comprehensive advantages such as high precision (low crosstalk), high stability (hardware decoupling reduces algorithm dependence, MEMS silicon strain gauge has good temperature stability), fast response (hardware decoupling improves real-time performance), and compact structure (twelve-beam design, small MEMS strain gauge). Its net output signal is stable with low crosstalk, making it highly suitable for fields requiring high force measurement accuracy, such as force control of industrial robot end effectors, assembly and inspection in precision manufacturing, and component testing in the aerospace field. Attached Figure Description

[0019] Figure 1 This is a three-dimensional schematic diagram of the overall structure of the twelve-beam six-dimensional force sensor of the present invention; Figure 2 This is a stress distribution cloud diagram of the sensor of the present invention when an Fx load is applied; Figure 3 This is a stress distribution cloud diagram of the sensor of the present invention when an Fz load is applied; Figure 4 This is a stress distribution cloud diagram of the sensor of the present invention when an Mx load is applied; Figure 5 This is a stress distribution cloud diagram of the sensor of the present invention when an Mz load is applied; Figure 6 This is a schematic diagram showing the distribution of strain gauge patch positions in the sensor of the present invention.

[0020] In the diagram: 1. Positioning hole; 2. T-shaped main beam; 3. Central loading platform; 4. L-shaped secondary beam. Detailed Implementation

[0021] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments. The following embodiments or drawings are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0022] In this embodiment, it should be understood that the terms "middle," "upper," "lower," "top," "right side," "left end," "above," "back," "center," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0023] Furthermore, unless otherwise specified in this specific embodiment, the connection or fixing method between components can be achieved by bolt fixing, pin fixing, or pin connection commonly used in the prior art. Therefore, it will not be described in detail in this embodiment.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein in the specification of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and foregoing drawings of this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification, claims, or foregoing drawings of this application are used to distinguish different objects, not to describe a particular order.

[0025] Example 1 A preferred embodiment of the twelve-beam six-dimensional force sensor provided by the present invention is as follows: Figures 1 to 6 As shown: The sensor includes an elastic body, a central loading platform 3, and strain gauges. The central loading platform 3 has positioning holes 1. The elastic body consists of an outer frame, the central loading platform 3, and twelve elastic beams connecting the two. Four T-shaped main beams 2 are evenly distributed around the circumference of the central loading platform 3, and eight L-shaped secondary beams 4 are symmetrically connected to both sides of each T-shaped main beam 2. The central loading platform 3 is a cuboid structure with a threaded hole at its center for connecting external loads via bolts. In both simulation analysis and actual measurement, the inner wall of the threaded hole is used as the load transfer reference point to ensure accurate and stable force path.

[0026] Figure 6 The markings R1 to R24 indicate the specific locations of the twenty-four strain gauges attached to the elastic body. These strain gauges are connected according to their strain-sensitive regions and a specific hardware decoupling bridging principle to form six Wheatstone full-bridge circuits, which are used to measure force / torque signals in six dimensions: Fx, Fy, Fz, Mx, My, and Mz.

[0027] The strain gauges are MEMS silicon strain gauges (1.3mm × 0.15mm), 24 in total, which are attached to the strain-sensitive area of ​​the elastic beam. The strain-sensitive area was determined by analysis using COMSOL finite element simulation software: single loads Fx, Fz, My, and Mz were applied respectively, stress paths were plotted and the location-strain relationship was analyzed, and the coordinate region corresponding to the maximum strain was selected as the patch placement location (see...). Figures 2-5 High-precision positioning fixtures are used during strain gauge placement to ensure that the deviation between the strain gauge and the simulation position is less than 0.1mm.

[0028] The external loads include three translational forces Fx, Fy, and Fz, and three rotational torques Mx, My, and Mz. When each load acts independently, the corresponding net output signal is output through the measurement bridge, and the crosstalk rate satisfies the following conditions: crosstalk rate is 2% under Fx load, -2% under Fy load, 2% under Fz load, 2% under Mx load, 2% under My load, and 2% under Mz load.

[0029] The bridging method is based on hardware decoupling design: Taking the measurement of Mx as an example, under the load of Mx, the symmetrically distributed T-shaped main beam 2 generates opposite strains of "tension and compression". The strain gauges that generate tensile strain (such as R1, R3) and the strain gauges that generate compressive strain (such as R2, R4) are respectively connected to the adjacent arms of the Wheatstone bridge. When Mx is applied, the resistance changes of the strain gauges in the adjacent arms are opposite, and the output signals are superimposed and enhanced; the same-direction resistance changes caused by other loads (such as Fy) are canceled out in the bridge subtraction operation, thus achieving decoupling. Each load is bridged according to this principle, forming a total of six independent full-bridge circuits.

[0030] Specifically, the sensor decoupling is analyzed using the measuring bridge of Mx as an example. When subjected to three-dimensional force and three-dimensional torque, the strain sensed by strain gauges R1, R2, R3, and R4 used to measure Mx in actual operation is the superposition of the strain εFx caused by the force in the x-direction, the strain εFy caused by the force in the y-direction, the strain εFz caused by the force in the z-direction, the strain εMx caused by the torque around the x-axis, the strain εMy caused by the torque around the y-axis, the strain εMz caused by the torque around the z-axis, and the strain εT caused by temperature change. Specifically, the strain reading of each strain gauge can be written as: ; Considering the symmetry (or antisymmetry) of the elastic body structure and internal forces, the strain induced by the external load at symmetrical locations is the same (or opposite). Therefore, the strain reading of the Wheatstone bridge can ultimately be simplified to: ; Similarly, we can obtain: ; Therefore, interdimensional coupling can be eliminated by appropriately designing the chip location.

[0031] Preferably, to address the coupling problem under loads in various dimensions, this invention innovatively designs a bridge configuration to achieve decoupling at the hardware level. Observation through strain contour plots reveals that under a single-dimensional load, multiple strain gauges in the elastic body will generate strain, meaning the strain-sensitive area is not unique, leading to coupling interference from other dimensions mixed into the measurement signal. Utilizing the characteristic that a load in a specific direction generates opposite strains (tension and compression) on a symmetrical strain gauge, strain gauges generating tensile strain and those generating compressive strain are divided into two groups, each connected to adjacent arms of the measuring bridge. When a load in a specific direction is applied, the strain gauges in adjacent arms generate opposite resistance changes, resulting in effective signal superposition and enhancement during bridge subtraction. Conversely, coupling signals from loads in other directions cause adjacent arm strain gauges to generate resistance changes in the same direction, canceling each other out during subtraction, thus achieving decoupling.

[0032] Specifically, by Figure 2 Strain contour plot analysis reveals that stress concentration mainly occurs at the sides and corners of "cross-shaped" or "frame-shaped" components connecting the internal and external parts of the structure. These locations are critical paths for force transmission in the x-direction, and stress concentration is easily generated due to abrupt changes in geometry (such as the transition from wide to narrow components). The overall stress level is relatively dispersed. From the color gradient, the high-stress areas (red, yellow, etc.) are relatively small, indicating that the stress distribution of the structure under the action of Fx is relatively uniform, with significant stress concentration only in locally critical stress areas.

[0033] Depend on Figure 3 Strain contour plot analysis reveals that significant stress concentrations occur in the vertical portions of the "cross-shaped" components within the structure and at the connection nodes with the outer ring structure. Forces in the z-direction result in a relatively even distribution of stress in both the vertical and horizontal directions, leading to a low overall strain level, but localized symmetrical tensile / compressive strain concentrations exist.

[0034] Depend on Figure 4 Strain contour plot analysis reveals that stress concentration occurs at the two edges of the "cross-shaped" component inside the structure, exhibiting a symmetrical distribution. A moment in the x-direction causes bending deformation around the x-axis, with the two sides of the "cross-shaped" component under tension and compression respectively, resulting in stress concentration at the edges. The strong symmetry of the stress distribution conforms to the mechanical laws governing structural deformation and stress distribution under moment, i.e., a moment around a certain axis will cause symmetrical stress and strain in the structure within a plane perpendicular to that axis.

[0035] Depend on Figure 5Strain contour plot analysis reveals that stress concentration is primarily located at the upper and lower edges of the "cross-shaped" components within the structure, as well as in the connection areas with the periphery. The moment in the z-direction causes torsional or bending deformation around the z-axis, with the upper and lower edges of the "cross-shaped" components becoming key points for moment transmission, thus leading to stress concentration. High-stress areas exhibit a symmetrical distribution along the upper and lower edges of the "cross-shaped" components, which matches the deformation mode of the structure under the action of Mz. The deformation caused by the moment subjects these edge areas to significant shear or bending stress. The strain contour plot of the elastic body clearly shows that the action of force tends to generate localized stress concentration along the force transmission path, while the action of moment, due to the bending and torsional deformation of the structure, generates stress concentration at the edges or symmetrical locations of the components, and the stress distribution under moment action exhibits a more pronounced symmetry.

[0036] As shown in Tables 1-6, this invention discloses the net output and crosstalk of each output channel of the sensor when force and torque are applied in a single direction. When all single-channel inputs are applied, there is some crosstalk in the output of non-target channels, but the overall crosstalk is at a low level (<2%FS), which meets the "decoupling" requirement of six-dimensional force measurement and can be used for accurate detection of multi-component forces / torques.

[0037] Table 1 Output of applying Fx ; Table 2 Output of applying Fy ; Table 3 Output of applying Fz ; Table 4 Output of applying Mx ; Table 5 Output of applying My ; Table 6 Output of applying Mz ; It should be understood that the disclosed apparatus can be implemented in other ways, as illustrated in the embodiments provided in this application. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units described above is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or communication connections shown or discussed may be through some interfaces; the indirect coupling or communication connections between devices or units may be telecommunications or other forms.

[0038] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still combine, add, delete, or otherwise adjust the features of the various embodiments of the present invention according to the circumstances without conflict or creative effort, thereby obtaining different technical solutions that do not fundamentally depart from the concept of the present invention. These technical solutions also fall within the scope of protection of the present invention.

Claims

1. A twelve-beam six-dimensional force sensor, comprising an elastic body, a central loading stage (3), and strain gauges, characterized in that: The central loading platform (3) is provided with positioning holes (1); The elastic body includes an outer frame, a central loading platform (3), and twelve elastic beams connected between the two; the twelve elastic beams include four T-shaped main beams (2) and eight L-shaped secondary beams (4), the four T-shaped main beams (2) are evenly distributed around the central loading platform (3), and the L-shaped secondary beams (4) are symmetrically distributed on both sides of each T-shaped main beam (2). The strain gauges are attached to the strain-sensitive area of ​​the elastic beam, which is the region with the largest strain under a specific dimensional load, as determined by finite element simulation analysis. The strain gauges are connected to form a measuring bridge. The bridge is assembled by dividing the strain gauges on a symmetrical strain beam that produces strains of equal magnitude and opposite properties under load in a specific direction into two groups, which are then connected to adjacent arms of the measuring bridge.

2. The twelve-beam six-dimensional force sensor according to claim 1, characterized in that: The central loading platform (3) is provided with a threaded hole, and the external load is transmitted to the elastic body through the inner wall of the threaded hole.

3. The twelve-beam six-dimensional force sensor according to claim 1, characterized in that: The central loading platform (3) has a cuboid structure.

4. The twelve-beam six-dimensional force sensor according to claim 1, characterized in that: The T-shaped main beam (2) has a rectangular cross-section, and the L-shaped secondary beam (4) has an L-shaped cross-section.

5. The twelve-beam six-dimensional force sensor according to claim 1, characterized in that: The strain gauge is a MEMS silicon strain gauge.

6. The twelve-beam six-dimensional force sensor according to claim 1, characterized in that: A total of 24 strain gauges are attached to the elastomer, with 4 strain gauges corresponding to each dimensional load, forming six Wheatstone full-bridge circuits.

7. The twelve-beam six-dimensional force sensor according to claim 1, characterized in that: The finite element simulation analysis refers to plotting the stress path and selecting the region of maximum strain when the elastic body is subjected to loads of Fx, Fz, My, and Mz.

8. The twelve-beam six-dimensional force sensor according to claim 5, characterized in that: The MEMS silicon strain gauge has a size of 1.3mm × 0.15mm.

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