Compact nonlinear six-dimensional force sensor

Abstract

The utility model 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. According to the utility model, the mounting requirements of humanoid robot joints and other space-limited scenes can be met, the multi-time rated load impact can be borne, and the movement safety and the complex task execution capability of the robot are improved.

Description

A compact nonlinear six-dimensional force sensor Technical Field

[0001] This utility model relates to the field of force sensor technology, and in particular to a compact nonlinear six-dimensional force sensor. Background Technology

[0002] As a core component in the field of humanoid robots, the performance of six-dimensional force sensors directly affects the robot's motion control accuracy, environmental interaction capabilities, and structural safety. When robots perform complex tasks such as grasping, walking, and collision perception, the sensors need to accurately measure force and torque information in three-dimensional space in real time, which places stringent requirements on their structural design, overload protection capabilities, and compact size.

[0003] Most existing six-dimensional force sensors employ cantilever beam structures. Common three- or four-beam designs attempt to balance mechanical connectivity with linear measurement characteristics through flexible connections between elastic sheets and the frame. However, an inherent drawback of this type of structure is its limited overload capacity: its safe overload is typically only about 50% of the rated load, and while the ultimate overload can reach 300%, it still falls short of the requirements of new devices such as robotic dogs and humanoid robots with jumping capabilities, which require overload capacities of more than five times. When a robot encounters a sudden impact or loses control of its movement, existing sensors are prone to permanent deformation or even breakage of the elastic structure due to overload, leading to overall machine failure or safety hazards.

[0004] To overcome the bottleneck of overload capacity, prior art has proposed I-beam and I-beam structures. These designs achieve decoupled measurement of axial force and moment through the bending deformation of a beam with a uniform cross-section. The structural symmetry reduces signal coupling, while optimized cross-sectional shape improves overload resistance. Experimental data shows that the ultimate overload capacity of this type of sensor is 2-3 times higher than that of traditional cantilever beam structures, while maintaining a high level of measurement accuracy (nonlinear error <1%). However, its structure is limited by the contradiction between the geometric dimensions of the uniform cross-section beam and the installation space—to ensure sufficient deformation to meet measurement sensitivity, the beam length usually needs to be greater than 30mm, making it difficult to compress the overall sensor volume to less than 50mm in diameter, thus failing to meet the integration requirements of space-constrained scenarios such as humanoid robot joints and end effectors. Therefore, this invention proposes a compact nonlinear six-dimensional force sensor. Summary of the Invention

[0005] The purpose of this invention is to address the problems in the background technology where existing six-dimensional force sensors have insufficient overload capacity of traditional cantilever beam structures and difficulty in miniaturizing novel I-beam and II-beam structures, thus failing to simultaneously meet the requirements of humanoid robots for high overload capacity and compact structure. Therefore, this invention proposes a compact nonlinear six-dimensional force sensor.

[0006] The technical solution of this utility model is as follows: a compact nonlinear six-dimensional force sensor, including an outer frame; a cross beam installed in the outer frame; a vertical beam vertically arranged at the center of the cross beam; a connecting block arranged at the end of the vertical beam away from the cross beam; the outer frame, cross beam, vertical beam, and connecting block are integrated into one piece; and a mounting plate installed on the connecting block.

[0007] Optionally, the connecting block has a stepped threaded hole.

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

[0009] Optionally, the connecting block has multiple sets of through slots, which extend through the inner and outer sides of the connecting block.

[0010] Optionally, the mounting plate has a connection hole corresponding to the connection block on the side near the outer frame.

[0011] Optionally, the mounting plate has multiple sets of second mounting holes, which are arranged in a ring array.

[0012] Optionally, the inner side of the outer frame is provided with multiple sets of first mounting holes, which are distributed in a ring array.

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

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

[0015] This invention utilizes the stress stiffening effect during deformation by fixing boundary conditions on both sides of the cross beam, enabling the sensor to maintain high sensitivity under small loads and automatically improve 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 outer frame, cross beam, vertical beam and connecting block design eliminates assembly gaps. While ensuring overload capacity, the volume is effectively reduced compared with the prior art I-beam structure, meeting the integration needs of space-constrained scenarios such as humanoid robot joints.

[0016] Furthermore, through the six-channel non-redundant structure of the cross beam four full bridge channel and the vertical beam double half bridge / full bridge, the cross interference of the six-dimensional force components is minimized through the independent decoupling algorithm, and the measurement repeatability error is controlled to a low value. The through slot design of the connecting block avoids the need to open threaded holes on the vertical beam through the radial expansion interference fit when the bolt is tightened. This maintains the integrity of the original cross section of the vertical beam and forms a self-locking assembly structure, which can capture transient mechanical signals such as robot jumping and collision in real time, providing accurate data support for force control closed loop control.

[0017] In summary, this utility model not only meets the installation requirements of humanoid robot joints and other space-constrained scenarios, but also can withstand impacts multiple times the rated load, thereby improving the robot's movement safety and ability to perform complex tasks. Attached Figure Description

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

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

[0020] Figure 3 is a schematic diagram of the cross beam structure;

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

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

[0023] Figure label:

[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 Implementation

[0028] The technical solution of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this utility model, but not all embodiments.

[0029] The components of the present invention embodiments described and shown in the accompanying drawings can typically be arranged and designed in a variety of 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 to illustrate selected embodiments of the invention.

[0030] Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0031] In the description of this utility model, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this utility model and simplifying the description, 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, and therefore should not be construed as a limitation of this utility model. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0032] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0033] Example

[0034] As shown in Figures 1 and 3, the present invention proposes a compact nonlinear six-dimensional force sensor, which includes an outer frame 1. The inner side of the outer frame 1 is provided with multiple sets of first mounting holes 11, which are arranged in a ring array. By setting the first mounting holes 11, the sensor can be quickly positioned and installed with the external structure, thereby improving assembly efficiency and facilitating the installation and connection of the force sensor.

[0035] Furthermore, referring to Figures 2 to 4, the aforementioned force sensor includes a cross beam 2 installed within the outer frame 1. The cross beam 2 has fixed boundary conditions on both sides, generating stress stiffening during deformation. Through a nonlinear structural stiffness adjustment mechanism, the sensor automatically increases its stiffness threshold when subjected to impact loads, improving its overload capacity. Through nonlinear calibration, it achieves high sensitivity under low loads and high rigidity under high loads, balancing micro-force sensing accuracy with strong impact protection capabilities. It possesses excellent buffering capacity, capable of withstanding impacts exceeding five times its rated load without permanent deformation, perfectly meeting the needs of applications such as humanoid robots or robotic dogs that require dexterity and jumping without overloading.

[0036] Furthermore, the aforementioned force sensor also includes a vertical beam 3 perpendicularly positioned at the center of the cross beam 2. Strain gauges are mounted on the sides of both the cross beam 2 and the vertical beam 3, employing a full-bridge / dual half-bridge circuit layout to improve the signal-to-noise ratio of the signal acquisition. At least one strain gauge is mounted on each side of the vertical beam 3. The strain gauges on two opposing sides are used to measure Fx and Fy, respectively. One strain gauge on each side forms a half-bridge channel, while two strain gauges on each side form a full-bridge channel. Two or four strain gauges are mounted on the two sides perpendicular to the cross beam 2 and the vertical beam 3, with the strain gauge positions corresponding to each other. Multiple strain gauges on the same side are symmetrical about the vertical beam 3. Two strain gauges on each side form a full-bridge channel for measuring Fz, while four strain gauges on each side form two full-bridge channels, improving the accuracy of Fz measurement. Simultaneously, four strain gauges are mounted on the two sides perpendicular to the cross beam 2 and the vertical beam 3. The four strain gauges on each side are arranged in a circular array around the vertical beam 3, with eight strain gauges forming two full-bridge channels for measuring Mx and My. Of the eight parallel sides of the cross beam 2 and the vertical beam 3, strain gauges are installed on four parallel sides to form a full-bridge channel for measuring Mz, or strain gauges are installed on all eight sides to form two full-bridge channels for measuring Mz. A total of six channels form a non-redundant and non-deficient structure. Through a six-dimensional force component independent decoupling algorithm, the cross-interference degree of multi-dimensional force measurements is ensured to be <0.5%, enabling the calculation of an accurate calibration matrix.

[0037] Specifically, as shown in Figure 4, the force sensor includes a connecting block 4 located at the end of the vertical beam 3 away from the cross beam 2. The outer frame 1, cross beam 2, vertical beam 3, and connecting block 4 are integrated into a single unit, employing a five-axis linkage CNC machining process to eliminate measurement errors caused by assembly gaps, thus avoiding assembly errors and improving accuracy. The measurement repeatability error can be controlled within ±0.1%FS, while ensuring synchronous deformation of the cross beam 2 and vertical beam 3. The dynamic response frequency can reach 500Hz, meeting the real-time measurement requirements of high-speed motion scenarios. The connecting block 4 has stepped threaded holes, and the four corners of the connecting block 4 are rounded for transition. Through finite element optimization design, the stress concentration factor is reduced by 40%, thus reducing stress concentration. Multiple through slots 41 are formed on the connecting block 4, penetrating both the inner and outer sides of the connecting block 4. The through slots 41 create an elastic deformation guiding structure, converting the bolt preload into a controllable radial expansion force. After the bolt is threaded into the stepped threaded hole in the connecting block 4, the bolt's rotation causes the connecting block 4 to deform, pressing against the inner wall of the connecting hole 51 to form an interference fit, thus completing the assembly of the mounting plate 5. This avoids the inability to install screws due to insufficient space and the damage to the elastomer caused by direct interference fit. Compared to traditional press-fitting processes, the installation space occupancy is reduced by 30%. Simultaneously, it avoids the impact of threaded holes in the vertical beam 3 on the elasticity of the vertical beam 3, maintaining the integrity of the original cross-section of the vertical beam 3.

[0038] Furthermore, as shown in Figures 1 and 5, the force sensor includes a mounting plate 5 installed on the connecting block 4. The mounting plate 5 has connecting holes 51 corresponding to the connecting block 4 on the side near the outer frame 1, facilitating the fixing of the mounting plate 5 through the connecting holes 51 after the connecting block 4 is bolted open, forming a self-locking assembly structure. The mounting plate 5 has multiple sets of second mounting holes 52 arranged in a circular array, compatible with standardized flange interfaces, adaptable to mainstream robot joint modules, and facilitating the installation and connection of the force sensor.

[0039] In this embodiment, the sensor is fixed to the robot joint or end effector base through the first mounting holes 11 of the annular array on the inner side of the outer frame 1, achieving standardized flange installation and ensuring an axis alignment accuracy of ≤0.05mm. The mounting plate 5 is installed onto the connecting block 4 through the connecting hole 51. The bolts are screwed into the stepped threaded holes of the connecting block 4. As the bolts are tightened, the through groove 41 of the connecting block 4 undergoes radial expansion deformation, so that the outer side of the connecting block and the inner wall of the connecting hole 51 form an interference fit. 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 collision, the external three-dimensional force / torque is transmitted to the connecting block 4 through the mounting plate 5. The axial force (Fz) acts directly on the vertical beam 3, causing it to undergo axial tensile / compressive deformation; the tangential force (Fx / Fy) and torque (Mx / My / Mz) are transmitted to the cross beam 2 through the connecting block 4, causing the cross beam 2 to undergo combined bending and torsional 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 nonlinear 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. Under small loads, linear deformation is the main process, while under large loads, the stiffness automatically increases. When the overload is 5 times, the deformation only increases by 15%. The buffering capacity is improved through the nonlinear constitutive relationship of the material.

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

[0043] The four full-bridge channels of the cross beam 2 (up, down, left, and right) collect strain signals in the Fx / Fy / Mx / My directions, respectively, while the dual half-bridge / full-bridge channels of the vertical beam 3 collect Fz / Mz signals. Six channels are sampled simultaneously at a sampling frequency of 10kHz. The strain gauges convert mechanical strain into voltage signals, which are transmitted to the back-end conditioning circuit via shielded cables. The signal-to-noise ratio is >60dB, and the electromagnetic interference immunity meets industrial-grade standards.

[0044] The six-channel raw voltage signal is input to the calibration matrix calculation unit. Based on the non-redundant and non-deficient structural mathematical model, the three-dimensional force (Fx / Fy / Fz) and three-dimensional torque (Mx / My / Mz) components are obtained by least squares method. 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 via RS485 / CAN bus with a communication delay of <1ms. It is used for scenarios such as trajectory planning, force control closed loop, or collision detection, with a typical application response time of <10ms.

[0046] The above specific embodiments are merely optional embodiments of this utility model. Based on the technical solution of this utility model and the relevant teachings 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 nonlinear six-dimensional force sensor, characterized in that, include: Outer frame (1); cross beam (2) installed in the outer frame (1); A vertical beam (3) is set vertically at the center of the cross beam (2); a connecting block (4) is set at the end of the vertical beam (3) away from the cross beam (2); the outer frame (1), cross beam (2), vertical beam (3) and connecting block (4) are an integral design; and an mounting plate (5) is installed on the connecting block (4).

2. A compact nonlinear six-dimensional force sensor according to claim 1, characterized in that, The connecting block (4) has a stepped threaded hole.

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

4. A compact nonlinear six-dimensional force sensor according to claim 3, characterized in that, The connecting block (4) has multiple sets of through slots (41) which penetrate the inner and outer sides of the connecting block (4).

5. A compact nonlinear six-dimensional force sensor according to claim 4, characterized in that, The mounting plate (5) has a connection hole (51) corresponding to the connecting block (4) on the side near the outer frame (1).

6. A compact nonlinear six-dimensional force sensor according to claim 1, characterized in that, The mounting plate (5) has multiple sets of second mounting holes (52), which are arranged in a ring array.

7. A compact nonlinear six-dimensional force sensor according to claim 1, characterized in that, The outer frame (1) has multiple sets of first mounting holes (11) on its inner side, and the multiple sets of first mounting holes (11) are arranged in a ring array.

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

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