Compact nonlinear six-dimensional force sensor

Abstract

The invention relates to the technical field of force sensors, in particular to a compact nonlinear six-dimensional force sensor. In order to solve the problems that the overload capacity of a traditional cantilever beam structure is insufficient, a novel I-shaped beam and II-shaped beam structure is difficult to miniaturize and the requirements of a humanoid robot for high overload capacity and a compact structure cannot be met at the same time, the following technical scheme is provided: the six-dimensional force sensor comprises an outer frame; the cross beam is mounted in the outer frame; the vertical beam is vertically arranged at the central position of the cross beam; the connecting block is arranged at one end, far away from the cross-shaped beam, of the vertical beam; the outer frame, the cross-shaped beam, the vertical beam and the connecting block are integrally designed; and the mounting plate is mounted on the connecting block. The mounting requirements of humanoid robot joints and other space-limited scenes are met, multi-time rated load impact can be borne, and the movement safety and the complex task execution capacity of a robot are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of force sensors, and particularly to a compact non-linear six-dimensional force sensor. Background Art

[0002] As a core component in the field of humanoid robots, the performance of a six-dimensional force sensor directly affects the motion control accuracy, environmental interaction ability, and structural safety of the robot. When the robot performs complex tasks such as grasping, walking, and collision perception, the sensor needs to accurately measure the force and torque information in three-dimensional space in real time, which poses strict requirements on its structural design, overload protection ability, and size compactness.

[0003] Most existing six-dimensional force sensors adopt a cantilever beam structure. The common three-beam or four-beam design attempts to balance the mechanical connection function and the linear measurement characteristics through the flexible connection between the elastic sheet and the frame. However, the inherent defect of such a structure is limited overload capacity: its safety overload is usually only about 50% of the rated load, and although the ultimate overload can reach 300%, it is still difficult to meet the requirements of new devices such as mechanical dogs and humanoid robots with jumping functions for an overload capacity of more than 5 times. When the robot encounters sudden impacts or motion out of control, the existing sensors are prone to permanent deformation or even fracture of the elastic structure due to overload, which may lead to overall machine failures or safety hazards.

[0004] To break through the bottleneck of overload capacity, the prior art has proposed I-beam and II-beam structures. This type of design realizes the decoupled measurement of axial force and torque through the bending deformation of the equal-section beam, reduces the signal coupling degree by virtue of structural symmetry, and improves the overload resistance performance by optimizing the cross-sectional shape. Experimental data shows that the ultimate overload capacity of such sensors is 2-3 times higher than that of the traditional cantilever beam structure, and the measurement accuracy remains at a high level (non-linear error < 1%). However, its structure is restricted by the contradiction between the geometric size of the equal-section beam and the installation space - to ensure sufficient deformation to meet the measurement sensitivity, the beam length usually needs to be greater than 30 mm, resulting in the overall volume of the sensor being difficult to be compressed to less than 50 mm in diameter, and unable to meet the integration requirements of space-limited scenarios such as humanoid robot joints and end effectors. In view of this, the present invention proposes a compact non-linear six-dimensional force sensor. Summary of the Invention

[0005] The object of the present invention is to address the problems in the background art that existing six-dimensional force sensors have insufficient overload capacity in the traditional cantilever beam structure and are difficult to miniaturize in the new I-beam and II-beam structures, and cannot simultaneously meet the requirements of humanoid robots for high overload capacity and compact structure, and to propose a compact non-linear six-dimensional force sensor.

[0006] Technical solution of the present invention: A compact non-linear six-axis force sensor, comprising an outer frame; a cross beam installed in the outer frame; a vertical beam vertically arranged at the center position of the cross beam; a connecting block arranged at one end of the vertical beam away from the cross beam, and the outer frame, cross beam, vertical beam, and connecting block are integrally designed; a mounting plate installed on the connecting block.

[0007] Optionally, a stepped threaded hole is provided in the connecting block.

[0008] Optionally, the four corners of the connecting block are rounded.

[0009] Optionally, multiple groups of through grooves are provided on the connecting block, and the through grooves penetrate the inner and outer sides of the connecting block.

[0010] Optionally, a connection hole corresponding to the connecting block is provided on the side of the mounting plate close to the outer frame.

[0011] Optionally, multiple groups of second mounting holes are provided on the mounting plate, and the multiple groups of second mounting holes are distributed in an annular array.

[0012] Optionally, multiple groups of first mounting holes are provided on the inner side of the outer frame, and the multiple groups of first mounting holes are distributed in an annular array.

[0013] Optionally, strain gauges are installed on the sides of the cross beam and the vertical beam.

[0014] In summary, the present application includes at least one of the following beneficial technical effects:

[0015] Through the design of fixed boundary conditions on both sides of the cross beam in the present invention, the stress stiffening effect during deformation is utilized to enable the sensor to maintain high sensitivity under small loads and automatically increase the structural stiffness under large loads. Compared with the traditional cantilever beam structure, the overload capacity is increased by more than 2 times. At the same time, the integrated design of the outer frame, cross beam, vertical beam, and connecting block eliminates the assembly gap. On the premise of ensuring the overload capacity, the volume is effectively reduced compared with the prior art I-beam structure, meeting the integration requirements of space-limited scenarios such as humanoid robot joints;

[0016] Furthermore, through the six-channel non-redundant structure of the four full-bridge channels of the cross beam and the double half-bridge / full-bridge of the vertical beam, the cross-interference degree of the six-axis force components is made extremely small through an independent decoupling algorithm, and the measurement repeatability error is controlled at a low value. The through groove design of the connecting block forms a radial expansion interference fit when the bolt is tightened, avoiding the opening of threaded holes on the vertical beam, maintaining the integrity of the original cross-section of the vertical beam, and forming a self-locking assembly structure, which can capture transient mechanical signals such as robot jumps and collisions in real time, providing accurate data support for force control closed-loop control;

[0017] In summary, the present invention not only meets the installation requirements of space - limited scenarios such as the joints of humanoid robots, but also can withstand impacts of multiple times the rated load, improving the motion safety and complex task execution ability of the robot. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic structural diagram of a compact non - linear six - dimensional force sensor;

[0019] Figure 2 is Figure 1 a schematic cross - sectional structural diagram of;

[0020] Figure 3 is a schematic structural diagram of a cross - beam;

[0021] Figure 4 is a schematic structural diagram of a connecting block;

[0022] Figure 5 is a schematic structural diagram of a mounting plate.

[0023] REFERENCE MARKS:

[0024] 1. Outer frame; 11. First mounting hole;

[0025] 2. Cross - beam; 3. Vertical beam;

[0026] 4. Connecting block; 41. Through - slot;

[0027] 5. Mounting plate; 51. Connecting hole; 52. Second mounting hole. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention.

[0029] Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents the selected embodiments of the present invention.

[0030] All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0031] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0032] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0033] Example

[0034] like Figure 1 and Figure 3 As shown, a compact nonlinear six-dimensional force sensor proposed in the present invention includes an outer frame 1, and a plurality of groups of first mounting holes 11 are arranged on the inner side of the outer frame 1. The plurality of groups of first mounting holes 11 are distributed in a ring array. Through the arrangement of the first mounting holes 11, the sensor and the external structure can be quickly positioned and installed, the assembly efficiency is improved, and the installation and connection of the force sensor are convenient.

[0035] For further information, see Figures 2 to 4 The force sensor includes a cross beam 2 installed in the outer frame 1. The cross beam 2 is a fixed boundary condition on both sides, and generates stress stiffening when deformed. Through the nonlinear adjustment mechanism of structural stiffness, the sensor automatically increases the stiffness threshold when subjected to impact load, thereby improving the overload capacity. Through nonlinear calibration, high sensitivity under small load and high rigidity under large load are achieved, taking into account both micro-force sensing accuracy and strong impact protection capabilities. It has very good buffering capacity and can withstand more than 5 times the rated load impact without permanent deformation. It is very suitable for humanoid robots or robot dogs that can be used in applications where they can be operated flexibly and jump without overloading.

[0036] Furthermore, the above force sensor further includes a vertical beam 3 vertically disposed at the center of the cross beam 2. Strain gauges are installed on the sides of both the cross beam 2 and the vertical beam 3. A full bridge / dual half-bridge circuit layout is adopted to improve the signal acquisition signal-to-noise ratio. At least one strain gauge is installed on each side of the vertical beam 3. The strain gauges on two opposite sides are respectively used to measure Fx and Fy. When one strain gauge is installed on each side, a half-bridge channel is formed. When two strain gauges are installed on each side, a full-bridge channel is formed. Two or four strain gauges are installed on two opposite sides of the cross beam 2 perpendicular to the vertical beam 3, and the positions of the strain gauges on the two sides correspond. The multiple strain gauges on the same side are symmetric about the vertical beam 3. When two strain gauges are installed on both sides, a full-bridge channel is formed to measure Fz. When four strain gauges are installed on both sides, two full-bridge channels are formed to improve the measurement accuracy of Fz. At the same time, four strain gauges are installed on two opposite sides of the cross beam 2 perpendicular to the vertical beam 3, and the four strain gauges on both sides are arranged in a circular array centered on the vertical beam 3. The eight strain gauges are used to form two full-bridge channels to measure Mx and My. Among the eight sides of the cross beam 2 and the vertical beam 3 that are parallel to each other, strain gauges are installed on four of the parallel sides to form a full-bridge channel to measure Mz, or strain gauges are installed on all eight sides to form two full-bridge channels to measure Mz. There are a total of six channels, forming a non-redundant and non-deficient structure. Through a six-dimensional force component independent decoupling algorithm, it is ensured that the cross-interference degree of multi-dimensional force measurement < 0.5%, and an accurate calibration matrix can be obtained.

[0037] Specifically, as Figure 4 shown, the above force sensor includes a connection block 4 disposed at one end of the vertical beam 3 away from the cross beam 2. The outer frame 1, the cross beam 2, the vertical beam 3, and the connection block 4 are integrally designed. A five-axis linkage numerical control machining process is adopted to eliminate the measurement error caused by the assembly gap, avoid assembly errors, facilitate improving the accuracy. The measurement repeatability error can be controlled within ±0.1% FS. At the same time, it ensures that the cross beam 2 and the vertical beam 3 deform synchronously, and the dynamic response frequency can reach 500 Hz, meeting the real-time measurement requirements of high-speed motion scenarios. A stepped threaded hole is provided in the connection block 4, and the four corners of the connection block 4 are rounded. The rounding method is used for transition. Through finite element optimization design, the stress concentration coefficient is reduced by 40%, reducing stress concentration. A plurality of through grooves 41 are provided on the connection block 4. The through grooves 41 penetrate the inner and outer sides of the connection block 4. By providing the through grooves 41, an elastic deformation guiding structure is formed, converting the bolt pre-tightening force into a controllable radial expansion force. After the bolt is threadedly connected to the stepped threaded hole in the connection block 4, as the bolt rotates, it drives the connection block 4 to deform and squeeze the inner wall of the connection hole 51 to form an interference fit, completing the assembly of the mounting plate 5. It avoids the situation that the screw cannot be installed due to insufficient space and the damage to the elastic body caused by direct interference fit. Compared with the traditional press-fitting process, the installation space occupation is reduced by 30%. At the same time, it avoids opening threaded holes in the vertical beam 3, which affects the elasticity of the vertical beam 3 and maintains the integrity of the original cross-section of the vertical beam 3.

[0038] Further, as Figure 1 and Figure 5 shown, the above force sensor includes a mounting plate 5 mounted on the connecting block 4. A connecting hole 51 corresponding to the connecting block 4 is provided on one side of the mounting plate 5 close to the outer frame 1, which is convenient for fixing the mounting plate 5 through the connecting hole 51 after the connecting block 4 is expanded by bolts, forming a self-locking assembly structure. A plurality of groups of second mounting holes 52 are provided on the mounting plate 5, and the plurality of groups of second mounting holes 52 are distributed in a circular array, compatible with a standardized flange interface, adapted to mainstream robot joint modules, and convenient for the installation and connection of the force sensor.

[0039] In this embodiment, the sensor is fixed to the robot joint or the end effector base through the circular array of first mounting holes 11 on the inner side of the outer frame 1 to achieve standardized flange mounting, ensuring that the axis alignment accuracy ≤ 0.05 mm. The mounting plate 5 is mounted on the connecting block 4 through the connecting hole 51, and the bolt is screwed into the stepped threaded hole of the connecting block 4. As the bolt is tightened, the through groove 41 of the connecting block 4 generates radial expansion deformation, so that an interference fit is formed between the outer side of the connecting block and the inner wall of the connecting hole 51. No additional axial pressure is required during the assembly process, and rapid installation can be completed within 30 seconds.

[0040] When the robot performs actions such as grasping and colliding, the external three-dimensional force / moment is transmitted to the connecting block 4 through the mounting plate 5. The axial force (Fz) directly acts on the vertical beam 3, causing it to produce axial tensile / compressive deformation; the tangential force (Fx / Fy) and the moment (Mx / My / Mz) are conducted to the cross beam 2 through the connecting block 4, causing the cross beam 2 to undergo a combined bending and torsion deformation. The fixed boundary conditions on both sides of the cross beam 2 cause the deformation to concentrate in the middle of the beam, and the strain gradient is increased by 2 times.

[0041] The cross beam 2 undergoes non-linear bending deformation under the action of tangential force and moment. Due to the fixed boundary conditions on both sides, a stress stiffening effect is generated - mainly linear deformation under small loads, and the stiffness automatically jumps when the load is large. When the overload is 5 times, the deformation amount only increases by 15%. The buffering capacity is improved through the material non-linear constitutive relationship.

[0042] The vertical beam 3 produces linear telescopic deformation under the action of axial force. Its double half-bridge / full-bridge strain gauge layout ensures that the linearity of axial force measurement > 99.5%. The strain gauge paste position is optimized by finite element simulation to eliminate the interference of lateral force.

[0043] The four full-bridge channels on the upper, lower, left, and right of the cross beam 2 respectively collect the strain signals in the Fx / Fy / Mx / My directions, and the double half-bridge / full-bridge channels of the vertical beam 3 collect the Fz / Mz signals. Six-channel synchronous sampling is performed, and the sampling frequency reaches 10 kHz. The strain gauge converts mechanical strain into a voltage signal, which is transmitted to the backend conditioning circuit through a shielded cable. The signal-to-noise ratio > 60 dB, and the anti-electromagnetic interference ability meets the industrial standard.

[0044] The six-channel original voltage signal is input into the calibration matrix calculation unit. Based on the non-redundant and non-deficient structure mathematical model, the three-dimensional force (Fx / Fy / Fz) and three-dimensional torque (Mx / My / Mz) components are calculated by least squares solution. The decoupling error is <1% FS, and the cross sensitivity is <0.5%.

[0045] The decoupled and compensated six-dimensional force data is transmitted to the robot control system through the RS485 / CAN bus. The communication delay is <1ms, which is used in scenarios such as trajectory planning, force control closed-loop or collision detection. The response time of typical application scenarios is <10ms.

[0046] The above specific embodiments are only an optional embodiment of the present invention. Based on the technical solution of the present invention and the relevant revelations of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A compact non-linear six-axis force sensor, characterized in that, Comprising: An outer frame (1); A cross beam (2) installed in the outer frame (1); A vertical beam (3) vertically arranged at the central position of the cross beam (2); A connection block (4) arranged at one end of the vertical beam (3) far from the cross beam (2), and the outer frame (1), cross beam (2), vertical beam (3), and connection block (4) are of an integrated design; A mounting plate (5) installed on the connection block (4).

2. The compact nonlinear six-axis force sensor according to claim 1, characterized in that, A stepped threaded hole is provided in the connection block (4).

3. A compact nonlinear six-axis force sensor according to claim 2, characterized in that, The four corners of the connection block (4) are rounded.

4. A compact non-linear six-axis force sensor according to claim 3, characterized in that, Multiple groups of through slots (41) are provided on the connection block (4), and the through slots (41) penetrate the inner and outer sides of the connection block (4).

5. A compact non-linear six-axis force sensor according to claim 4, characterized in that, Connection holes (51) corresponding to the connection block (4) are provided on one side of the mounting plate (5) close to the outer frame (1).

6. A compact non-linear six-axis force sensor according to claim 1, characterized in that, Multiple groups of second mounting holes (52) are provided on the mounting plate (5), and the multiple groups of second mounting holes (52) are distributed in an annular array.

7. A compact non-linear six-axis force sensor according to claim 1, characterized in that, Multiple groups of first mounting holes (11) are provided on the inner side of the outer frame (1), and the multiple groups of first mounting holes (11) are distributed in an annular array.

8. A compact non-linear six-axis force sensor according to claim 1, characterized in that, Strain gauges are installed on the sides of the cross beam (2) and the vertical beam (3).

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