A rubber torsion spring for a robot flexible joint with non-linear stiffness

Abstract

The utility model provides a rubber torsion spring with nonlinear rigidity for robot flexible joint, including input metal piece and the output metal piece of sleeveing in the outer periphery of input metal piece, output metal piece has the outer ring and the inner ring of connecting in the inner side of outer ring through the connecting beam, is equipped with the strain gauge on the connecting beam and measures the torque, is equipped with the protruding beam of entering the recess of setting up in the outside of input metal piece on the inner ring, is equipped with cylindrical rubber between the both sides of protruding beam and the corresponding side of recess inner side wall, and cylindrical rubber's circumferential side is contacted and is matched with protruding beam and recess and shows pre -compression state. The utility model provides a rubber torsion spring structure that can realize big elastic deformation and has the nonlinear rigidity characteristic of " increasing with the increase of elastic deformation", the structure can avoid producing transmission gap, promotes robot joint under the torque control performance and environmental adaptability of complex working condition.

Description

Technical Field

[0001] This utility model relates to the field of robot joint design technology, specifically a rubber torsion spring for a robot flexible joint with nonlinear stiffness. Background Technology

[0002] Traditional robot joints often employ high-rigidity designs, relying on high-reduction-ratio reducers and high-performance servo motors to achieve precise position control. However, in unstructured environments or human-robot interaction scenarios, high-rigidity joints are prone to collision risks and lack adaptability to the environment. To address this, researchers have introduced elastic elements into the joints to create flexible joints, thereby improving the compliance and safety of torque control.

[0003] Currently, the elastic elements commonly used in robot joints are mostly made of metal, which has linear stiffness and limited deformation, making it difficult to adapt to complex load changes. Rubber materials are increasingly being introduced into joint design due to their high stiffness-to-mass ratio and customizability. In existing technologies, rubber elements are mostly block-shaped or fan-shaped, providing stiffness through shear or compression deformation, but this presents the following problems: Small elastic deformation and difficulty in pre-compression: Square or sector-shaped rubber is difficult to pre-compress effectively during installation, which can easily generate gaps during transmission, resulting in discontinuous torque transmission and reduced control accuracy; Single stiffness characteristics: The stiffness of existing rubber components is mostly linear or approximately linear, which cannot achieve the nonlinear stiffness characteristics of "high resolution under small load and high response under large load", thus limiting the robot's adaptability under dynamic loads. Structural layout limitations: Traditional rubber components have poor compactness, making it difficult to achieve both multi-path torque sensing and high elastic deformation within a limited space. Utility Model Content

[0004] The present invention aims to provide a rubber torsion spring for robot flexible joints with nonlinear stiffness. This torsion spring can achieve large elastic deformation and has the nonlinear stiffness characteristic of "increasing with the increase of elastic deformation". It can also avoid the generation of transmission backlash, thereby improving the torque control performance and environmental adaptability of robot joints under complex working conditions.

[0005] To solve the above technical problems, the specific solution adopted by this utility model is as follows: a rubber torsion spring for a robot flexible joint with nonlinear stiffness, including an input metal part and an output metal part fitted around the outer periphery of the input metal part. The output metal part has an outer ring and an inner ring connected to the inner side of the outer ring by a connecting beam. Multiple output connection holes for connecting the load end are provided at intervals on the outer ring. Multiple input connection holes for connecting to the power component are provided on the input metal part. Strain gauges for measuring torque are provided on the connecting beam. An extension beam is provided on the inner ring, extending into a groove opened on the outer side of the input metal part. Cylindrical rubber is provided between the inner walls of the corresponding sides of the extension beam and the groove. The circumference of the cylindrical rubber contacts and engages with the extension beam and the groove and is in a pre-compressed state. The side of the extension beam and the inner wall of the groove are both set as arc shapes adapted to the circumference of the cylindrical rubber.

[0006] Preferably, the wrap angles of the side of the protruding beam and the inner wall of the groove with respect to the circumference of the cylindrical rubber are both greater than 120°.

[0007] Preferably, the inner ring has a recess for connecting the connecting beam.

[0008] Preferably, the concave portion is an isosceles trapezoid, and the connecting beam is located at the center of the short base of the concave portion.

[0009] Preferably, it has two connecting beams, which are symmetrically distributed.

[0010] Preferably, the connecting beam is provided with strip-shaped through holes distributed along its longitudinal direction.

[0011] Preferably, it has four protruding beams and four corresponding grooves, with the four grooves arranged in pairs, and the two groups of grooves are symmetrically distributed with the longitudinal line connecting the two connecting beams as the center line.

[0012] Preferably, the output connection hole is a threaded hole and the input connection hole is a countersunk through hole.

[0013] Beneficial effects 1. Traditional square or fan-shaped rubber exhibits severe stress concentration at its corners. When compressed, the force preferentially concentrates at these sharp corners, potentially causing microcracks to form in these areas during the early stages of deformation, thus limiting the maximum safe deformation. This invention, however, uses cylindrical rubber with a continuous, smooth curved surface and no sharp corners. When compressed, stress can be evenly transmitted inward along its curved surface, allowing the material to expand freely and uniformly in all directions (Poisson effect), preventing stress concentration in any particular area. This uniform stress distribution allows for larger and more uniform deformation without premature localized tearing or damage, resulting in a greater compressive deformation capacity.

[0014] 2. Under torque, the cylindrical rubber in this invention exhibits a nonlinear characteristic where stiffness increases with deformation. First, in the initial stage of small deformation, the cylindrical rubber exhibits low stiffness. The smooth cylindrical surface allows for uniform distribution of compressive stress, avoiding stress concentration at corners, thus allowing the rubber to easily and almost linearly begin to deform. At this stage, the structural design primarily aims to "not hinder" the material's low stiffness characteristics. Then, in the subsequent stage of large deformation, the cylindrical rubber exhibits greater stiffness, tightly confined within the narrow space formed by the "inner wall of the groove" and the "side wall of the protruding beam." As the amount of compressive deformation increases, the radial expansion of the rubber is strongly restricted by the surrounding metal walls. This restriction is no longer free expansion but rather the filling of a closed space. To be further compressed, the rubber must be forcibly "stuffed" into this almost completely filled fixed space. This results in extremely high hydrostatic pressure inside the rubber. At this point, the force required to overcome this extremely high internal pressure increases dramatically. The structural constraints transform the material's incompressibility into a strong stiffness hardening effect. The nonlinear stiffness curve in this invention is intentionally designed by combining a cylindrical structure with tight spatial constraints. The cylinder, due to its lack of sharp edges, is best suited to withstand this comprehensive constraint without premature damage. It is precisely this specific design of the "constrained cylindrical rubber" that reliably and repeatedly achieves the desired intelligent mechanical behavior of "hardening under pressure."

[0015] 3. This invention applies pre-compression to the cylindrical rubber in its initial neutral state, ensuring it remains under pressure throughout forward and reverse rotation. This completely avoids the transmission gap problem caused by the small elastic deformation and difficulty in pre-compression of traditional block or sector-shaped rubber, thus improving the continuity and smoothness of torque transmission. As mentioned earlier, the maximum safe deformation of block and sector-shaped rubber is relatively small. To achieve pre-compression (i.e., a certain amount of compression at zero torque), it needs an initial, considerable deformation. For these components with inherently poor deformation capacity, this initial deformation may approach or even exceed their safety limit, easily leading to permanent damage or a sharp drop in fatigue life. To achieve pre-compression, external force is needed during assembly to "stuff" the component into a space smaller than its natural state. Because block and sector-shaped components have sharp edges and are not easily deformed, this assembly process is very difficult, requires a lot of force, and is prone to jamming or damage. The cylindrical rubber in this invention has a large deformation capacity and can be easily compressed to a suitable preload within a reasonable tolerance range. This eliminates gaps without reaching the damage limit, and assembly is relatively easy, thus avoiding the problem of transmission gaps.

[0016] 5. This invention features symmetrically arranged strain gauges on both sides of the connecting beam, combined with a strip-shaped through-hole design, enhancing the strain concentration effect and improving the sensitivity and signal-to-noise ratio of torque sensing, making it particularly suitable for the precise detection of minute torques. Creating a strip-shaped through-hole in the connecting beam is equivalent to creating a "weak link" or "elastic hinge" in the beam. When torque is transmitted, the force flow lines bypass this hole, causing the material at the edge of the hole to be forced to bear greater strain (deformation). The strain gauge is precisely attached to this high-strain area. Under the same torque, the strain here is much greater than that of a solid beam without the hole. Therefore, the resistance change (output signal) of the strain gauge is more significant, enabling the system to detect minute torque changes and improving sensitivity. Furthermore, the useful strain signal is amplified, while irrelevant noise such as thermal noise and electromagnetic interference from the circuit itself is not amplified proportionally. Therefore, the signal-to-noise ratio (SNR) is improved, making the measurement results clearer and more accurate, particularly beneficial for the detection of minute torques, and effectively improving the SNR. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the main structure of a rubber torsion spring with nonlinear stiffness for a robot flexible joint according to the present invention. Figure 2 This is a three-dimensional structural diagram of a rubber torsion spring with nonlinear stiffness for a robot flexible joint according to the present invention. Figure 3 This is a three-dimensional structural diagram of the input metal component in a rubber torsion spring with nonlinear stiffness for a robot flexible joint according to the present invention. Figure 4 This is a three-dimensional structural diagram of the output metal component in a rubber torsion spring with nonlinear stiffness for a robot flexible joint according to the present invention. Figure 5 A schematic diagram illustrating the nonlinear characteristic of the cylindrical rubber in this invention where "stiffness increases with the amount of deformation"; The markings in the diagram are: 1. Input metal part, 2. Recess, 3. Strain gauge, 4. Strip-shaped through hole, 5. Connecting beam, 6. Output metal part, 601. Outer ring, 602. Inner ring, 7. Groove, 8. Protruding beam, 9. Cylindrical rubber, 10. Input connection hole, 11. Output connection hole. Detailed Implementation

[0018] like Figures 1 to 4 As shown, the present invention provides a rubber torsion spring for a robot flexible joint with nonlinear stiffness, which mainly includes an input metal part 1, an output metal part 6, a cylindrical rubber 9, and a strain gauge 3.

[0019] The input metal part 1 has four grooves 7 on its outer periphery, and two cylindrical rubbers 9 are symmetrically arranged in each groove. The inner sidewall of the groove 7 is arc-shaped with a wrap angle greater than 120° to ensure full contact with the periphery of the cylindrical rubbers 9. The input metal part 1 also has multiple countersunk through holes as input connection holes 10 for connecting to the output end of the motor or reducer.

[0020] The output metal component 6 includes an outer ring 601 and an inner ring 602, which are connected by two symmetrically arranged connecting beams 5. The connecting beams 5, the outer ring 601, and the inner ring 602 are integrally formed. The inner ring 602 has four protruding beams 8 extending inwards. Each protruding beam 8 extends into a corresponding groove 7 of the input metal component 1, and its side is also arc-shaped, tightly fitting with the cylindrical rubber 9. The wrap angle with the cylindrical rubber 9 is not less than 120°. The outer ring 601 has multiple threaded holes as output connection holes 11 for connecting the load end.

[0021] Each connecting beam 5 has a strip-shaped through hole 4 distributed along its longitudinal direction, and a strain gauge 3 is attached to each side to detect strain changes caused by torque. The inner ring 602 has a recess 2 for connecting the connecting beams 5. The recess 2 is an isosceles trapezoid, and the connecting beam 5 is connected to the center of its short base to optimize stress distribution.

[0022] Four sets of protruding beams 8 and grooves 7 are symmetrically arranged, working in conjunction with trapezoidal recesses 2 and symmetrical connecting beams 5 to achieve uniform torque distribution. This embodies the principles of symmetry and force flow balance in mechanical design, with the four sets of structures centrally symmetrically distributed. Regardless of the direction of the torque, the load is simultaneously and evenly distributed to all four contact points. This avoids localized overload caused by excessive local stress at only one or two points. Connecting beams 5 are the critical path for torque transmission from the inner ring to the outer ring. The symmetrical arrangement of the two connecting beams 5 ensures that the force transmission path from the center to both sides is symmetrical and of equal length. The design of the trapezoidal recesses 2, especially the connection at the center of the short base, allows the force to flow smoothly from the wider root (inner ring) to the narrower connecting beams 5, optimizing the stress transmission path and avoiding stress concentration caused by sudden changes in cross-section. In other words, this design, through symmetrical layout and optimized force flow path, ensures that all cylindrical rubbers 9 share the load, thereby preventing premature fatigue failure of individual components and extending the service life of the entire torsion spring.

[0023] The cylindrical rubber 9 is in a pre-compressed state in its initial neutral state (when the torque is zero), ensuring that no gaps appear during forward and reverse rotation. It has a large compression deformation, and its stiffness increases with the amount of deformation, forming a shape like... Figure 5The diagram illustrates the nonlinear stiffness characteristics. These nonlinear stiffness characteristics enable robot joints to exhibit a "soft contact-hard response" intelligent behavior pattern, making them particularly suitable for scenarios requiring dynamic adaptation to human movement, such as bionic robots and exoskeletons. The soft contact phase (small load / low stiffness stage) refers to the initial small load when a robot joint (such as the knee joint of an exoskeleton) contacts a human leg or begins movement. At this time, the torsion spring is in the low stiffness region, and the joint behaves very "softly," easily being moved. This provides comfort, avoids the harshness of mechanics, and absorbs minor impacts during initiation. The hard response phase (large load / high stiffness stage) refers to the rapid increase in load when supporting human weight or performing actions such as taking large steps or standing up quickly. At this time, the torsion spring is compressed to the high stiffness region, and the joint instantly "hardens," providing strong support and responding quickly and stably to large torque demands, preventing the user from falling due to insufficient support. Furthermore, when this invention is applied to bionic robots, it makes the robot's movement more like that of a living organism, with light steps (soft contact) and rapid force when pushing off the ground (hard response). When applied to exoskeletons, this invention provides gentle assistance and conforms to nature during the swaying phase of a patient's walk, while providing strong support and helping to bear weight during the support phase. This adaptive stiffness perfectly matches the changes in torque requirements during human movement.

Claims

1. A rubber torsion spring for a robot flexible joint with nonlinear stiffness, characterized in that: The device includes an input metal part (1) and an output metal part (6) fitted around the outer periphery of the input metal part (1). The output metal part (6) has an outer ring (601) and an inner ring (602) connected to the inner side of the outer ring (601) by a connecting beam (5). The outer ring (601) is provided with a plurality of output connection holes (11) for connecting the load end at intervals. The input metal part (1) is provided with a plurality of input connection holes (10) for connecting to the power component. The connecting beam (5) is provided with a strain gauge for measuring torque. (3) An extension beam (8) is provided on the inner ring (602) and extends into the groove (7) opened on the outside of the input metal part (1). A cylindrical rubber (9) is provided between the inner walls of the extension beam (8) on both sides and the corresponding side of the groove (7). The periphery of the cylindrical rubber (9) contacts and fits with the extension beam (8) and the groove (7) and is in a pre-tightened state. The side of the extension beam (8) and the inner wall of the groove (7) are both set as arcs that fit the periphery of the cylindrical rubber (9).

2. The rubber torsion spring for a robot flexible joint with nonlinear stiffness as described in claim 1, characterized in that: The wrap angles of the side of the protruding beam (8) and the inner wall of the groove (7) to the periphery of the cylindrical rubber (9) are both greater than 120°.

3. A rubber torsion spring with nonlinear stiffness for a robot flexible joint as described in claim 1, characterized in that: The inner ring (602) has a recess (2) for connecting the connecting beam (5).

4. A rubber torsion spring with nonlinear stiffness for a robot flexible joint as described in claim 3, characterized in that: The concave part (2) is an isosceles trapezoid, and the connecting beam (5) is connected at the center of the short base of the concave part (2).

5. A rubber torsion spring with nonlinear stiffness for a robot flexible joint as described in claim 1, characterized in that: It has two connecting beams (5), which are symmetrically distributed.

6. A rubber torsion spring with nonlinear stiffness for a robot flexible joint as described in claim 5, characterized in that: The connecting beam (5) is provided with strip-shaped through holes (4) distributed along its own longitudinal direction.

7. A rubber torsion spring with nonlinear stiffness for a robot flexible joint as described in claim 5, characterized in that: It has four protruding beams (8) and four corresponding grooves (7). The four grooves (7) are distributed in pairs, and the two groups of grooves (7) are symmetrically distributed with the longitudinal line connecting the two connecting beams (5) as the center line.

8. A rubber torsion spring with nonlinear stiffness for a robot flexible joint as described in claim 1, characterized in that: The output connection hole (11) is a threaded hole, and the input connection hole (10) is a countersunk through hole.

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