Tendon post-processing method for a robot dexterous hand and application thereof

Abstract

The application discloses a tendon post-processing method for a robot dexterous hand and application thereof and belongs to the technical field of tendons. 3 ‑10 4 times of dynamic loading-unloading cycles; step 2, the tendon to be processed is tensioned at 30% of the rated load, is placed in liquid nitrogen at-196 DEG C for cryogenic treatment for 2-8 hours, is then warmed to room temperature at a rate of 5-8 DEG C / min, is again tensioned at the working load, is placed in liquid nitrogen at-196 DEG C for cryogenic treatment for 2-8 hours, and is then warmed to room temperature at a rate of 5-8 DEG C / min. The application eliminates the tiny internal stress or structural relaxation existing in the tendon after twisting and improves the structural stability of the tendon. In addition, the application completely releases the internal stress of the tendon, reduces the overall stress level of the tendon and improves the fatigue performance of the tendon.

Description

Technical Field

[0001] This invention belongs to the field of tendon rope technology, specifically relating to a post-processing method for tendon ropes used in robotic dexterity hands and its application. Background Technology

[0002] Technical Background: The prestressed cyclic-relaxation process is mainly used to improve the dimensional stability and stress retention capacity of materials during long-term service. By pre-applying cyclic loads and controlling the relaxation process, it reduces stress decay in actual use. This process combines two key steps: cyclic loading and stress relaxation control. Cyclic loading: Applying repeated tensile-release loads to prestressed steel or components activates the adaptive adjustment of the material's internal microstructure, reducing subsequent deformation potential. Relaxation control: Maintaining constant strain conditions for a certain period of time allows the material to complete part of the stress relaxation process ahead of time, thereby reducing long-term prestress loss after commissioning.

[0003] Cryogenic treatment is a material strengthening technique that involves placing metallic materials in an extremely low temperature environment ranging from -130℃ to -196℃ to improve their microstructure and overall properties. For example, after cryogenic treatment, conventional steel materials undergo a transformation of retained austenite into martensite and the precipitation of dispersed nanoscale carbides, significantly improving the material's hardness, wear resistance, dimensional stability, and fatigue strength. Another example is AZ61 magnesium alloy. After cryogenic treatment at -190℃ for 12 hours, fracture morphology analysis showed that the as-cast sample without cryogenic treatment exhibited typical brittle fracture characteristics at room temperature; after cryogenic treatment, the fracture morphology showed brittle fracture characteristics with some plastic deformation, indicating improved toughness.

[0004] A similar technical solution to this invention is described in Chinese Patent CN202110510491.4, which discloses a production process for synchronously rotating steel wire rope. This process involves subjecting the stabilized annealed steel wire rope to cryogenic treatment at -260°C for 12 hours to eliminate residual stress and improve toughness. As described in Chinese Patent CN202310344415.X, a two-step training method for efficiently improving the two-way shape memory effect of nickel-titanium alloys is disclosed. One step involves subjecting a nickel-titanium alloy strip to tensile cyclic loading to introduce dislocations, followed by thickness reduction to obtain a sample strip.

[0005] However, existing material post-processing methods cannot further improve the fatigue resistance and creep resistance of the materials during use. This invention creatively proposes a post-processing method for tendon cables used in dexterous hands, aiming to further improve the fatigue resistance and creep resistance of the tendon cables when used in dexterous hands. No prior art highly relevant to this invention was found. Summary of the Invention

[0006] The main problem solved by this invention is to provide a post-processing method for tendon ropes used in robot dexterity hands, which can improve the fatigue resistance and creep resistance limits of existing tendon ropes to a certain extent.

[0007] Meanwhile, this invention provides an application of a post-processing method for tendon ropes used in robot dexterity hands.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: The present invention proposes a post-processing method for tendon ropes used in robot dexterity hands, which mainly includes two steps: Step 1: Apply the tendon ligament to be treated to 50%-80% of its rated working tension for 10 minutes. 3 -10 4 The system uses a dynamic load-unload loop with a loading rate of 0.5-2.0 Hz.

[0009] Eliminating initial nonlinear deformation of the material: Tendon chords may have minute internal stresses or structural relaxations during manufacturing and storage. This can be addressed by performing 10 [measurements] within the range of 50%-80% of the rated working tension. 3 -10 4 Dynamic loading-unloading cycles facilitate the initial adaptive deformation of materials, reducing unpredictable elongation or relaxation during subsequent use. This improves mechanical property stability: dynamic cyclic loading helps to evenly distribute the load between fibers, making the stress on each fiber more consistent, thereby improving overall tension transmission efficiency and fatigue life. It also simulates actual working conditions for pre-run-in: the loading rate is controlled at 0.5-2.0Hz, close to the actual operating frequency of most mechanical systems, equivalent to "pre-running in" the tendons and ligaments, exposing potential defects (such as local weakening, slippage, etc.) in advance, avoiding sudden failure in critical tasks. Furthermore, it optimizes system response accuracy: for high-precision transmission systems (such as dexterous hands, bionic robotic arms, etc.), pre-loading can significantly reduce motion hysteresis and return error, improving the repeatability and dynamic response consistency of the control system.

[0010] Step 2: Tension the tendon rope to be treated at 30% of the rated load, place it in liquid nitrogen at -196℃ for cryogenic treatment for 2-8 hours, and then warm it to room temperature at a rate of 5-8℃ / min; then tension it again with the working load, place it in liquid nitrogen at -196℃ for cryogenic treatment for 2-8 hours, and then warm it to room temperature at a rate of 5-8℃ / min.

[0011] Since the component needs to be immersed in liquid nitrogen after tensioning, the tensioning can be carried out by winding under a set tension. That is, one end of the tendon rope is fixed on the nickel-iron alloy component, and the other end is wound under a set tension. After reaching the second fixing point, the second end is fixed under tension using a pressure plate or nut. This will give the component a tendon rope that maintains a certain tension. Then the entire component can be immersed in liquid nitrogen.

[0012] Cryogenic treatment significantly improves the dimensional stability and mechanical properties of tungsten wire tendons, making it particularly suitable for high-precision transmission applications. This process optimizes the internal structure of the material through extreme low temperatures, with the specific benefits and principles as follows: Releasing residual stress and improving dimensional stability: Tungsten wire accumulates internal stress during drawing and braiding, leading to micro-deformation or preload reduction during use. Incubating in liquid nitrogen at -196℃ for 2-8 hours effectively relaxes these residual stresses, followed by a controlled reheating rate of 5-8℃ / min to room temperature, avoiding thermal shock and significantly enhancing the tendon rope's deformation resistance and positioning accuracy during long-term service.

[0013] Promotes tissue stabilization and improves wear resistance and fatigue resistance: The cryogenic environment promotes further densification of the tungsten filament lattice structure, reduces grain boundary defects, and may induce a uniform distribution of fine precipitates, thereby improving the material's hardness and fatigue resistance. This is particularly important for dexterity chord systems involving frequent reciprocating movements, effectively extending their service life.

[0014] Improve the synergy of composite structures and optimize load transfer: For composite tungsten wire tendons (such as metal / polymer coated structures), there are differences in the coefficients of thermal expansion between different components. Cryogenic treatment allows each layer of material to "synchronously shrink" at low temperatures, exposing potential interface defects; after warming, the interfaces adhere more tightly, improving the load transfer efficiency between fibers and reducing the risk of localized wear.

[0015] Simulate the stress state under actual working conditions: The first high-load deep cooling completes the macroscopic structural plastic shaping and metallographic phase transformation under high stress. The second low-working-tension deep cooling finely adjusts the residual stress of the lattice and locks the service state dimensions. The two deep coolings with graded load reduction control the structural deformation and microstructure transformation step by step, avoiding the drawbacks of single-load deep cooling, which may result in insufficient shaping or excessive deformation and brittleness.

[0016] The post-processing method of the present invention can improve the fatigue resistance and creep resistance of tendon ligaments during use.

[0017] Those in the metal wire rope industry know that a single steel wire undergoes two main stages during the stretching process: the elastic stretching stage and the plastic stretching stage. When the tension on the steel wire does not exceed the elastic deformation limit, the length of the steel wire will not change after the tension is released. The relationship between force and displacement in the elastic stage satisfies Hooke's Law, i.e., F=kx.

[0018] After multiple steel wires are twisted into rope products, the stretching stage is also divided into elastic stretching stage and plastic stretching stage. However, in the elastic stretching stage, this stage includes both the elastic deformation of the steel wire itself and the structural deformation of the steel wire rope. The structural elongation of steel wires with different structures is also different. In addition, the structural deformation of the steel wire rope only occurs under low load conditions.

[0019] However, whether it's the tensile curve of a steel wire rope or even the tensile curve of a single steel wire, it's difficult to achieve true pure elastic deformation in the elastic tensile stage. That is, in the force-displacement tensile curve, the elastic stage rarely achieves a truly proportional linear relationship. Therefore, researchers refer to this elastic tensile stage as the elastoplastic deformation stage. Understanding the actual deformation of the metal wire rope during the tensile process is essential to achieving the beneficial effects described in this invention—high creep resistance and high fatigue resistance—through the two steps mentioned above.

[0020] The first step, "Cyclic Prestressing-Relaxation Acclimation," specifies a prestress of 50%-80% of the rated working tension in this invention. Generally, a tendon rope capable of bearing 60kg of force may have a rated working load of only 8kg, while in specific applications, the actual working load may only be 2kg. 50%-80% of the rated working tension represents the load range of the composite tendon rope in actual operation. This cyclic prestressing-relaxation acclimation, through multiple cycles, eliminates plastic deformation (both structurally and material-wise) of the tendon rope during the elastoplastic tensile stage, thereby improving its creep resistance during actual use.

[0021] The second step, "Cryogenic-Temperature Stabilization," involves the steel wires in the metal wire rope undergoing a transformation from straight wires into a three-dimensional, wave-like structure. Each wire contains torsional and tensile / compressive stresses. To illustrate this, a steel plate, fresh from rolling, can lie flat on the ground. However, after a period of time, such as after one side has been exposed to direct sunlight, the plate will bend. This change can be understood as the steel plate initially exhibiting opposite residual stresses on its front and back sides after rolling. These stresses are equal in magnitude but opposite in direction. As time passes, the residual stress on one side changes, disrupting the equilibrium and causing the plate to bend.

[0022] During the manufacturing process of metal wire ropes, to eliminate the residual stress in each filament after deformation, the industry commonly uses over-twisting devices and straighteners. However, after this stress elimination, the stress state between the individual filaments inside the wire rope is actually the same as in the case of the steel plate mentioned above—a state of stress equilibrium. This is why the torsion of a wire rope changes after it has been manufactured and left for a period of time.

[0023] The second step of this invention, the "low-temperature cryogenic-warming stabilization" treatment, differs from existing technologies primarily in that, firstly, the product needs to possess a certain tension (e.g., 30% of the rated load); and secondly, cryogenic treatment is performed under specific conditions. The cryogenic treatment in comparative document 1 (202510186066.2, A method for preparing steel strands for prestressed concrete) can improve the fatigue performance of the steel strands, mainly because it relaxes the absolute value of residual stress in the wires within the rope. In addition, this invention, due to the tensile state, during the residual stress relaxation process, the tension in the wires within the tendon rope is partially eliminated because the tendon rope remains in a tensile state. Therefore, after the tendon rope is removed from the cryogenic tank and the tensile tension is released, compressive stress is generated within the wires of the tendon rope. The presence of this compressive stress further enhances the tendon rope's creep resistance and fatigue performance during subsequent tensile work.

[0024] The main principle of the two-stage, load-bearing deep cryogenic operation of this invention is as follows: First process: High-load clamping and deep cooling (load > working tension, near yield) 1. Macroscopic structural level: Cryogenic + high-load synergistic compaction rope structure At room temperature and under high load, the gaps between rope strands can only be compacted by plastic extrusion; at low temperature and cryogenic conditions, the steel lattice contracts, plasticity decreases, and elastic modulus increases, under the constraint of external high load: 1) The twisting process causes the monofilaments to bend, the strands to loosen, and the weaving gaps to be forcibly compacted, exhausting the structural plastic elongation in one go and eliminating the source of subsequent structural creep in service. 2) High load forces each monofilament to be subjected to uniform force, which counteracts the residual internal stress of twisting and makes the initial prestress of the monofilament tend to be consistent.

[0025] 2. Microscopic metallographic level: Cryogenic phase transformation under high stress field After cold drawing and twisting, steel wire contains a large number of distorted crystal lattices and residual second phases. The external stress field generated by high load can induce the transformation of the residual second phase, and the phase transformation efficiency is much higher than that of stress-free deep cryogenic treatment.

[0026] However, the coexistence of high load and low temperature has risks: full-process high load deep cooling is prone to local stress concentration and low-temperature brittleness, and the working size cannot be determined directly in one step. Therefore, a second-stage de-load deep cooling correction is required.

[0027] Second process: Deep cooling with working tension clamping (load = actual service tension, lower than the previous high load) 1) Release residual stress under high load and lock in service stress state The first high load brings additional assembly stress, and after cooling and then heating, springback relaxation will occur. By changing to working tension constraint and deep cooling again, the lattice completes secondary relaxation under actual use stress, eliminating the excess internal stress left by the high load. After heating, the rope size fits the service conditions, preventing springback elongation after use.

[0028] 2) Complete the remaining phase transition and stabilize long-term creep performance. The high-load phase transformation of the first stage is limited by high stress, and there is still a small amount of untransformed residual structure; the low-load deep cryogenic process has no risk of overload, further refines the structure, and suppresses long-term aging creep and temperature-induced expansion and contraction.

[0029] 3) Repairing minor localized micro-damage caused by primary cryogenic treatment High load and low temperature conditions can easily generate micro-stress microcracks on the surface of the wire; under low load and low temperature conditions, the crystal lattice shrinks uniformly, the microcracks close, and the fatigue resistance and wear resistance are improved.

[0030] Existing technology suggests that, traditionally, simple cyclic prestressing followed by relaxation typically promotes dislocation slip, localized softening, or damage accumulation, potentially weakening creep resistance. However, the "cyclic prestressing-relaxation acclimatization" combined with two stages of "low-temperature cryogenic-warming stabilization" in this invention allows the stress in each monofilament of the entire tendon cord to reach a balanced state. In existing technologies, once this balance is disrupted during tendon cord use, it leads to a rapid decrease in fatigue life. This invention, however, can maintain this monofilament stress balance even after 5 million or more uses, thus improving creep resistance and fatigue resistance.

[0031] The present invention has the following beneficial effects: Because robotic dexterous hands require force transmission within confined spaces, the friction pairs driving the tendons through repeated stretching have small diameters. Consequently, the bending radius of the tendons on these friction pairs is small. To ensure sufficient lifespan, the tendons need to possess adequate flexibility, which necessitates smaller diameter metal monofilaments used to compose them. Furthermore, the twist pitch is also small, leading to increased structural elongation.

[0032] For example, a common 7×7×7 tungsten wire tendon cord in existing technology, with a total diameter of 0.63mm, is composed of 343 single filaments of 0.023mm each, with a minimum twist pitch of 0.8mm. In this complex multi-strand tendon cord, each wire experiences different torsional stresses during the twisting process due to its different position within the cord. Some single filaments undergo three twists, some two, and some only one. These varying torsional stresses result in different contributing stresses. These stresses are difficult to completely eliminate using existing straighteners and overtwisters during tendon cord manufacturing; the goal is only to achieve a stress balance among the single filaments. Once this balance is disrupted during use, it leads to a rapid decrease in fatigue life.

[0033] The post-treatment method for tendon cords of the present invention uses "cyclic prestressing-relaxation acclimatization" and two-stage "low temperature cryogenic-warming stabilization" treatments to eliminate the minute internal stress or structural relaxation that exists inside the tendon cord after twisting, thereby improving the structural stability of the tendon cord. On the other hand, it completely releases the internal stress of the tendon cord, reduces the overall stress level of the tendon cord, and improves the fatigue performance of the tendon cord. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure for tensioning tendons and ligaments according to the present invention; Figure 2 This is a schematic diagram of an embodiment of the present invention immersed in liquid nitrogen; Figure 3 This is a schematic diagram of the main body of the composite tendon rope used in the present invention for fatigue testing. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are only for explaining the invention and are not intended to limit the invention. Example 1

[0036] A complex multi-strand tendon cord with a 7×7×7 structure, wherein each metal wire in the tendon cord is a high-purity tungsten wire doped with trace amounts of lanthanum oxide, with a tungsten content greater than 99.95% and a diameter of 0.024 mm. It is produced through multiple heat processing steps. The basic properties of the tendon cord are shown in Table 1.

[0037] Table 1 Basic Properties of Composite Tendon Rosette

[0038] Table 2 compares the performance test data of the tendon ropes in Table 1 before and after the post-treatment method of the present invention. During the fatigue test, the tested tendon ropes were fixed at both ends 7A and 7B and maintained with a certain load. With the repeated rotation of the bending test element 6, the tested tendon ropes were repeatedly bent on the test element 6 until they broke; or after reaching a certain number of fatigue cycles, the sample was removed and the change in distance L between 7A and 7B was measured. It can be seen from the table that the fatigue limit of the tendon ropes in Examples 1 and 2 was improved and the creep rate was well controlled after the post-treatment method of the present invention. Comparative Example 1 only implemented the "cyclic prestress-relaxation acclimatization" treatment of the present invention, so its creep resistance performance was acceptable, but still not as good as Examples 1 and 2; Comparative Example 2 only implemented the "low temperature cryogenic-warming stabilization" treatment of the present invention, so its fatigue resistance performance was acceptable, but still not as good as Examples 1 and 2; Comparative Example 3 did not implement the post-treatment method of the present invention, and its creep resistance and fatigue resistance performance were both poor.

[0039] Table 2 Fatigue Performance Test Results

[0040] Figure 1 This is a method for immersing in liquid nitrogen and maintaining tension during the process of an embodiment of the present invention. In the figure, 1 is a tendon rope, 2 is the fixed end of the tendon rope, and 3 is a nickel-iron alloy element. Since it is necessary to immerse in liquid nitrogen after tensioning, tensioning can be implemented by winding under a set tension, that is, the tendon rope 1 is under the nickel-iron alloy element 3 (below). Figure 1 One end is fixed on the nickel-iron alloy element 3 (as shown), and the other end is wound under a set tension. After reaching the second fixing point, the second end (i.e., the tendon rope fixing end 2) is fixed under tension using a pressure plate 2 or nut, so that a tendon rope is obtained on the nickel-iron alloy element 3 under a certain tension condition. Then, the entire nickel-iron alloy element 3 is placed into liquid nitrogen.

[0041] Figure 2 This is a schematic diagram of step 2 of the present invention, which involves immersion in liquid nitrogen. In the diagram, 4 represents liquid nitrogen. Figure 3 This is a schematic diagram of the main body of the composite tendon rope for fatigue testing in this invention, where 5 is the composite tendon rope, 6 is the bidirectional bending test element, R in the test element is the bending radius, and 7A and 7B are the two ends of the bidirectional bending test.

[0042] The post-processing method described in this embodiment is applied to improve the fatigue resistance and creep resistance of metal wire rope products. The metal wire rope products include tungsten wire tendon ropes or composite tungsten wire tendon ropes.

[0043] This embodiment describes the application of tendon cables in a high-precision transmission system for a robot's dexterous hand. The high-precision transmission system includes a dexterous hand or a bionic robotic arm.

[0044] Example 2

[0045] The only difference between this embodiment and Embodiment 1 is that: in step 1, the rated working tension is 80%; in step 2, the temperature in the temperature control chamber is restored to room temperature at a rate of 8℃ / min.

[0046] The tendon rope for the robot dexterous hand obtained in this embodiment has a fatigue life of ≥5 million cycles under working tension, and the change in L after 1 million fatigue tests is 0.001%.

[0047] Example 3

[0048] The only difference between this embodiment and Embodiment 1 is that: in step 1, the rated working tension is 60%; in step 2, the temperature in the temperature control chamber is restored to room temperature at a rate of 6℃ / min.

[0049] The tendon rope for the robot dexterous hand obtained in this embodiment has a fatigue life of ≥5 million cycles under working tension, and the change in L after 1 million fatigue tests is 0.001%.

[0050] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for post-processing tendon cables used in a robot dexterous hand, characterized in that, Includes the following steps: Step 1: Apply the tendon ligament to be treated to 50%-80% of its rated working tension for 10 minutes. 3 -10 4 The dynamic load-unload loop has a loading rate of 0.5-2.0Hz. Step 2: Tension the tendon rope to be treated at 30% of the rated load, place it in liquid nitrogen at -196℃ for cryogenic treatment for 2-8 hours, and then warm it to room temperature at a rate of 5-8℃ / min; then tension it again with the working load, place it in liquid nitrogen at -196℃ for cryogenic treatment for 2-8 hours, and then warm it to room temperature at a rate of 5-8℃ / min.

2. The post-processing method according to claim 1, characterized in that, Tendon chords include tungsten wire tendon chords or composite tungsten wire tendon chords.

3. The post-processing method according to claim 2, characterized in that, Composite tungsten wire tendon cords are structures in which tungsten wire tendon cords are coated with polymer materials.

4. The tendon rope for a robot dexterous hand obtained by the post-processing method according to any one of claims 1-3.

5. The tendon rope for a robot dexterous hand according to claim 4, characterized in that, The fatigue life under working tension is ≥5 million cycles, and the change in L after 1 million fatigue tests is 0.001-0.002%.

6. The application of the post-processing method according to any one of claims 1-3 in improving the fatigue resistance and creep resistance of metal wire rope products.

7. The application according to claim 6, characterized in that, Metal wire rope products include tungsten wire tendon ropes or composite tungsten wire tendon ropes.

8. The application of the tendon rope for robot dexterity hand according to claim 4 in a high-precision transmission system.

9. The application according to claim 8, wherein the high-precision transmission system comprises a dexterous hand or a bionic robotic arm.

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