A pre-assembled cable with resistance to bending and torsion and a method for manufacturing the same

Abstract

The application relates to the technical field of cables, in particular to a preassembled cable line resistant to bending and torsion and a preparation method thereof. The cable line comprises a cable body and connectors arranged at two ends of the cable body. The cable body comprises, from inside to outside, a conductor, an insulation layer, a cable core, a shielding layer and a sheath layer. A bidirectional winding torque balance layer is arranged between the shielding layer and the sheath layer. The bidirectional winding torque balance layer comprises an inner layer fiber winding layer and an outer layer fiber winding layer. The inner layer fiber winding layer is wound in a first spiral direction, and the outer layer fiber winding layer is wound in a second spiral direction opposite to the first spiral direction. The winding angles of the inner layer and the outer layer are both 50 DEG to 60 DEG. The gradient rigidity transition sleeve and the internal conical spiral reinforcing body arranged at the joint of the connector and the cable body can obviously improve the bending fatigue life compared with the stress-free transition scheme, and can also obviously improve the bending fatigue life compared with the double-hardness injection molding scheme.

Description

Technical Field

[0001] This invention relates to the field of cable technology, and more specifically to a method for preparing a continuous glass fiber reinforced polyurethane core profile. Background Technology

[0002] Pre-installed cables are widely used in dynamic scenarios such as industrial robots, elevators, and port machinery. Connectors are pre-installed at both ends for plug-and-play functionality. However, pre-installed cables are particularly prone to failures such as conductor breakage, insulation damage, and sheath cracking under frequent bending and torsion conditions. Industry statistics show that up to 90% of cable assembly failures occur at the junction of the connector and the cable body. The root cause is the abrupt change in stiffness between the rigid shell of the connector and the flexible cable body, where all bending and torsional stresses are concentrated.

[0003] Existing patent CN210489282U discloses a bending and torsion resistant insulated wire and cable, which improves mechanical performance by adding an external force-resistant mechanism including a third protective layer, a separator plate and a fourth protective layer, and a rolling rod to transfer external forces. However, the rolling rod structure of this solution increases the outer diameter and weight of the cable, and the rigid structure of the separator plate becomes a stress concentration source when repeatedly torsioned. Furthermore, it does not solve the problem of fatigue fracture at the conductor level, nor does it address the stress transition design between the pre-installed cable connector and the cable body.

[0004] Existing patent CN207149280U discloses a highly flexible anti-torsion composite cable for robots, which uses cotton filament filling rope, polytetrafluoroethylene tape shielding layer and tinned copper wire braided shielding layer, with conductor single filament diameter of 0.05 to 0.08 mm and cable core pitch ratio of 9 to 15 times; however, the strength of the cotton filament filling rope decreases after absorbing moisture, the interlayer slippage of the polytetrafluoroethylene tape wrapping is limited during torsion, and no torque balancing structure is designed, which poses a risk of residual torque accumulation in the long-term reciprocating torsion, and also does not involve stress transition design at the connector interface.

[0005] Existing patent CN213691490U discloses a bend-resistant and abrasion-resistant composite drag chain cable, which uses a non-twisted composite cable of signal cores, control cores, and power cores. The inner layer of the conductor has a diameter ratio not exceeding 16 times, and the outer layer does not exceed 12 times. The insulation layer is made of polytetrafluoroethylene (PTFE), and the sheath is made of polyurethane. However, this non-twisted stranding method lacks torque balance design. During reciprocating twisting, the cumulative relative displacement of the core wires leads to a loose structure. The PTFE insulation layer has high hardness, which poses a high risk of embrittlement at low temperatures.

[0006] The aforementioned existing technologies optimize the cable body from the perspectives of mechanical protection, shielding structure, and cabling method, but none of them systematically solve the problem of abrupt stiffness change at the junction of the connector and the cable body in the pre-installed cable, nor do they integrate the gradient stiffness transition, internal conical spiral reinforcement, and bidirectional winding torque balance into a single design. Summary of the Invention

[0007] The primary objective of this invention is to provide a pre-assembled cable that is resistant to bending and torsion, and a method for preparing the same.

[0008] A further objective of this invention is to provide a pre-assembled cable that is resistant to bending and torsion, comprising a cable body and connectors disposed at both ends of the cable body. The cable body comprises, from the inside out, a conductor, an insulation layer, a cable core, a shielding layer, and a sheath layer. A bidirectional winding torque balancing layer is provided between the shielding layer and the sheath layer. The bidirectional winding torque balancing layer comprises an inner fiber winding layer and an outer fiber winding layer. The inner fiber winding layer is wound along a first helical direction, and the outer fiber winding layer is wound along a second helical direction opposite to the first helical direction. The winding angles of the inner and outer layers are both 50° to 60°. The junction between the connector and the cable body is provided with a gradient stiffness transition sleeve. The gradient stiffness transition sleeve includes at least three hardness zones with decreasing hardness in sequence along the direction away from the connector. The hardness zone closest to the connector has a Shore hardness of D55 to D70, and the hardness zone furthest from the connector has a Shore hardness of A50 to A65. The gradient stiffness transition sleeve is provided with a conical helical reinforcement. The diameter of the helical wire of the conical helical reinforcement gradually decreases in the direction away from the connector, and the helical pitch gradually increases in the direction away from the connector.

[0009] Preferably, the gradient stiffness transition sleeve includes three hardness zones in sequence along the direction away from the connector: the first hardness zone has a Shore hardness of D60 to D65 and a length of 12 to 15 mm; the second hardness zone has a Shore hardness of A80 to A88 and a length of 15 to 20 mm; and the third hardness zone has a Shore hardness of A55 to A62 and a length of 15 to 20 mm.

[0010] Preferably, the diameter of the spiral wire of the tapered spiral reinforcement gradually decreases from 0.8 to 1.0 mm to 0.3 to 0.4 mm in the direction away from the connector, the spiral pitch gradually increases from 4 to 6 mm to 12 to 15 mm in the direction away from the connector, and the length of the tapered spiral reinforcement is 35 to 50 mm.

[0011] Preferably, the inner fiber winding layer is made of aramid fiber yarn, and the outer fiber winding layer is made of ultra-high molecular weight polyethylene fiber yarn; the winding angle of the inner and outer fiber winding layers gradually increases from 50° to 60° to 65° to 75° in a 50mm area near the connector.

[0012] Preferably, the conductor is a type 6 ultrafine stranded conductor with a single filament diameter of 0.05 to 0.10 mm and a conductor structure of multi-layer stranded and re-stretched structure.

[0013] Preferably, the insulating layer material is a thermoplastic polyester elastomer with a Shore hardness of A80 to A90; the shielding layer is a tin-plated copper wire braided layer with a braiding density of 80% to 90% and a braiding angle of 30° to 40°; and the sheathing layer material is a polyurethane elastomer with a Shore hardness of A75 to A85.

[0014] A method for preparing a pre-assembled cable that is resistant to bending and torsion includes the following steps: Step 1, conductor stranding: The conductor is prepared by using Category 6 ultrafine tin-plated copper wire in a bundle stranding and re-stretching method, with a bundle stranding pitch ratio of 8 to 12 times the conductor outer diameter; Step 2, Insulation Extrusion: Extruding a thermoplastic polyester elastomer insulation layer over the conductor at an extrusion temperature of 220 to 240°C, with an insulation layer thickness of 0.4 to 0.8 mm; Step 3, cable core stranding: multiple insulated wire cores and filler rope are stranded into a cable core in an SZ manner, with a stranding pitch ratio of 12 to 16 times the outer diameter of the cable core. Step 4, Wrapping and Shielding: Wrap polyester non-woven fabric tape around the outside of the cable core, and then weave a tinned copper wire shielding layer; Step 5, preparation of bidirectional winding torque balance layer: First, the inner layer fiber yarn is wound around the outside of the shielding layer in the first spiral direction, with a winding angle of 50° to 60°; then, the outer layer fiber yarn is wound around the outside of the inner layer fiber winding layer in the opposite spiral direction, with a winding angle of 50° to 60°; within a 50mm range near the connector area at both ends of the cable, the winding angle of the inner and outer layers is gradually increased from 50° to 60° to 65° to 75°. Step 6, Sheath extrusion: Extrude a polyurethane elastomer sheath layer outside the bidirectional winding torque balance layer at an extrusion temperature of 180 to 200°C and a sheath thickness of 1.2 to 1.8 mm. Step 7, Cutting and Termination: Cut the cable to the specified length, strip the layers at both ends, crimp the conductors to the connector terminals, and assemble the connector housing; Step 8, Helical Reinforcement Installation: Install a tapered helical reinforcement onto the cable body at the end of the connector, with the larger diameter end of the helical wire facing the connector. Step 9, Gradient stiffness transition sleeve injection molding: Using a multi-station injection molding process, polyurethane elastomers of different hardness are injected in sections at the junction of the connector and the cable body to form a gradient stiffness transition sleeve with decreasing hardness along the direction away from the connector, and the conical spiral reinforcement is wrapped inside the transition sleeve.

[0015] Preferably, in step 9, the gradient stiffness transition sleeve injection molding adopts a three-station rotary injection molding method; the first station injects polyurethane elastomer with a Shore hardness of D60 to D65, with an injection temperature of 210 to 230°C and an injection pressure of 15 to 25 MPa, forming a first hardness zone; the second station injects polyurethane elastomer with a Shore hardness of A80 to A88, with an injection temperature of 190 to 210°C and an injection pressure of 10 to 20 MPa, forming a second hardness zone; the third station injects polyurethane elastomer with a Shore hardness of A55 to A62, with an injection temperature of 180 to 200°C and an injection pressure of 8 to 15 MPa, forming a third hardness zone; adjacent hardness zones achieve interfacial bonding through intermolecular diffusion of melt molecules during the injection molding process.

[0016] Preferably, in step 5, the bidirectional winding torque balance layer is wound using a CNC fiber winding machine, with the inner layer using 12 to 16 strands of 1670dtex aramid fiber yarn and the outer layer using 12 to 16 strands of 880dtex ultra-high molecular weight polyethylene fiber yarn; the winding angle transition is achieved by programming and controlling the ratio of the lateral speed to the rotational speed of the winding machine.

[0017] Preferably, in step 8, the tapered helical reinforcement is formed by cold winding of stainless steel wire. The diameter of the helical wire transitions from 0.8 to 1.0 mm at the connector end to 0.3 to 0.4 mm at the cable end. The helical pitch gradually increases from 4 to 6 mm at the connector end to 12 to 15 mm at the cable end. The tapered helical reinforcement is subjected to stress relief treatment at 380 to 420°C for 2 to 3 hours before installation.

[0018] To facilitate a clear and consistent understanding of the technical solution structure of this application by those skilled in the art, the term "inner layer" as used separately in the following text of this specification specifically refers to the inner fiber winding layer contained in the bidirectional winding torque balance layer; and the term "outer layer" as used separately specifically refers to the outer fiber winding layer contained in the bidirectional winding torque balance layer.

[0019] The inner fiber winding layer is wound along the first helical direction, and the outer fiber winding layer is wound along the second helical direction opposite to the first helical direction. The basic winding angle of both is controlled between 50° and 60°. In a 50mm length area near the connectors at both ends of the cable, the winding angle of the inner and outer fiber winding layers gradually increases from 50° to 60° to 65° to 75°. The residual torque generated by the reciprocating torsion of the cable is eliminated by the cooperative structure of the inner and outer layers with opposite winding.

[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention disperses bending stress from the 2 to 3 mm joint surface to a length range of 40 to 55 mm by setting a gradient stiffness transition sleeve and an internal conical spiral reinforcement at the junction of the connector and the cable body. The bending fatigue life is significantly improved compared with the stress-free transition scheme and also significantly improved compared with the dual-hardness injection molding scheme.

[0021] 2. The present invention uses a bidirectional winding torque balance layer to form a symmetrical recovery path under forward and reverse torsion, thereby eliminating the accumulation of residual torque and significantly improving the torsional fatigue life compared with the unidirectional winding scheme.

[0022] 3. The winding angle transition design of the present invention provides stronger torsional constraint at the connector end of the torque balance layer, preventing torsional stress from being transmitted to the end point, and further improving the bending-torsional coupling fatigue life compared with the solution without angle transition.

[0023] 4. The gradient stiffness transition sleeve of the present invention adopts a multi-station rotary injection molding process. Each hardness zone achieves interfacial bonding through diffusion between melt molecules, eliminating the need for adhesives. It has high interfacial bonding strength, good process repeatability, and is suitable for mass production. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The bending and torsional failures of pre-installed cables are essentially a coupling problem between the conductor structure, the stress distribution of the insulation layer, and the sheath constraint, and a sudden change in stiffness is formed at the junction of the connector and the cable body.

[0026] This invention achieves stress attenuation and torque self-balancing from the connector interface to the cable body through the synergistic design of a gradient stiffness transition sleeve, a conical spiral reinforcement, and a bidirectional winding torque balancing layer.

[0027] The mechanism of the gradient stiffness transition sleeve is that the stiffness ratio between the rigid shell of the connector and the flexible cable body is typically more than 100 times, and all bending stress is concentrated on the mating surface of 2 to 3 mm. The gradient stiffness transition sleeve has at least three hardness zones with decreasing hardness in sequence along the direction away from the connector, distributing the bending stress over a length range of 40 to 55 mm, rather than concentrating it on the 2 to 3 mm mating point.

[0028] The hardness zone closest to the connector has a Shore hardness of D55 to D70, matching the stiffness of the connector shell and effectively limiting excessive bending; the intermediate hardness zone provides a gradual decrease in stiffness; and the hardness zone furthest from the connector has a Shore hardness of A50 to A65, aligning with the flexibility of the cable body. This gradient distribution ensures that the bending curvature changes approximately linearly along the length of the transition sleeve, avoiding stress peaks caused by abrupt changes in curvature.

[0029] The mechanism of the conical spiral reinforcement is that the ideal continuous stiffness distribution cannot be achieved by simply relying on the external hardness gradient of the transition sleeve, because the hardness change of polymer materials is step-like, and there are stiffness jumps between adjacent hardness zones.

[0030] The tapered helical reinforcement is embedded inside the transition sleeve. The diameter of the helical wire gradually decreases away from the connector, providing high-stiffness radial support and bending restraint at the connector end and low-stiffness flexible transition at the cable end. The helical pitch gradually increases away from the connector, so that the helices are densely arranged at the connector end to enhance radial restraint stiffness and sparsely arranged at the cable end to reduce bending stiffness. In coordination with the external hardness gradient of the transition sleeve, it eliminates stiffness jumps between hardness zones and achieves a quasi-continuous stiffness distribution from the rigid connector to the flexible cable.

[0031] If a uniform diameter spiral is used instead of a conical spiral, the spiral will have excessive stiffness at the cable end, creating a new stress concentration point and reducing the bending fatigue life. The key to the conical spiral reinforcement is that its gradually decreasing wire diameter and increasing pitch stiffness distribution are precisely matched with the hardness gradient of the transition sleeve in space, so that the bending neutral axis can move smoothly in the transition zone and avoid secondary stress concentration.

[0032] The mechanism of the bidirectional winding torque balancing layer is that during the reciprocating twisting process of the cable, the unidirectional winding fiber layer provides restoring force in one twisting direction, but cannot provide symmetrical constraint when twisting in the opposite direction, resulting in the gradual accumulation of residual torque and eventually causing permanent kinking of the cable.

[0033] The bidirectional winding torque balancing layer of the present invention is composed of inner and outer fibers spirally wound in opposite directions. The inner fiber is stretched during forward torsion to provide a restoring torque, and the outer fiber is stretched during reverse torsion to provide a restoring torque. A symmetrical restoring path is formed under forward and reverse torsion, eliminating the accumulation of residual torque. The winding angle of 50° to 60° takes into account both torsional constraint and bending flexibility: if the angle is too small, the torsional constraint is insufficient, and if the angle is too large, the bending stiffness increases sharply.

[0034] Within a 50mm area close to the connector, the winding angle gradually increases from 50° to 60° to 65° to 75°. This angle transition design allows the torque balance layer to provide stronger torsional restraint at the connector end, preventing torsional stress from being transmitted to the termination point, while maintaining sufficient bending flexibility at the cable end.

[0035] The gradient stiffness transition sleeve and the conical spiral reinforcement work together to solve the problem of bending stress concentration at the connector interface, while the bidirectional winding torque balance layer solves the problem of residual torque accumulation in the cable body. Without the conical spiral reinforcement, the external hardness gradient of the gradient stiffness transition sleeve jumps, and the bending stress generates a secondary peak at the interface of the hardness zone, resulting in a significant decrease in bending-torsional coupling fatigue life.

[0036] Without a bidirectional winding torque balancing layer, the residual torque in the cable body is transmitted to the connector interface, and the transition sleeve and spiral reinforcement bear additional torsional loads, resulting in a significant reduction in bending-torsional coupling fatigue life.

[0037] Without the gradient stiffness transition sleeve, even with the conical helical reinforcement and bidirectional winding torque balance layer, the stiffness abrupt change at the connector still exists, and the bending stress is concentrated on the 2 to 3 mm joint surface, and the bending-torsional coupling fatigue life also decreases significantly. All three are indispensable, and the synergistic effect exceeds the simple sum of the individual effects of each component. The bending-torsional coupling fatigue life exceeds the expected value of simple summation by about 29%.

[0038] Raw material source: (1) Annealed tin-plated soft copper wire, single wire diameter 0.08mm, conforming to IEC 60228 Class 6 conductor standard, tensile strength not less than 200MPa, elongation not less than 25%, number average molecular weight about 120000g / mol, supplier Jiangsu Jiangrun Copper Co., Ltd.

[0039] (2) Annealed tin-plated soft copper wire, single wire diameter 0.10mm, conforming to IEC 60228 Class 6 conductor standard, tensile strength not less than 200MPa, elongation not less than 25%, number average molecular weight about 120000g / mol, supplier Jiangsu Jiangrun Copper Co., Ltd.

[0040] (3) TPEE thermoplastic polyester elastomer, grade Hytre l5556, Shore hardness 85A, density 1.19 g / cm³ 3 Melt flow index 20 to 28 g / 10 min, test conditions 190℃, load 2.16 kg, elongation at break not less than 650%, dielectric strength not less than 3 kV / mm, temperature range -40 to +125℃, number average molecular weight approximately 28000 g / mol, supplier DuPont.

[0041] (4) Aramid fiber filled rope, specification 1670dtex, tensile strength not less than 2800MPa, density 1.39g / cm³ 3 Elongation at break 3.5%, supplier Teijin Corporation, brand name Technora T200.

[0042] (5) PET polyester nonwoven tape, thickness 0.05mm, width 20mm, supplier Suzhou Taihu Electric Materials Co., Ltd.

[0043] (6) Tin-plated copper wire, 0.12 mm in diameter, with a tin layer thickness of not less than 3 μm, supplied by Changzhou Jinyuan Copper Industry Co., Ltd.

[0044] (7) Aramid fiber yarn, specification 1670 dtex, tensile strength not less than 3100 MPa, modulus not less than 70 GPa, density 1.39 g / cm³ 3 Elongation at break 3.5%, supplier Teijin Corporation, brand name Technora T240.

[0045] (8) UHMWPE fiber yarn, specification 880dtex, tensile strength not less than 3400MPa, modulus not less than 100GPa, density 0.97g / cm³ 3 Elongation at break 3.5%, supplied by DSM, Netherlands, brand name Dyneema SK75.

[0046] (9) TPU polyurethane elastomer, for cable sheathing, polyester type, grade Elastollan 1185A, Shore hardness 80A, density 1.19 g / cm³ 3 Melt flow index 22 to 30 g / 10 min, test conditions 190℃, load 2.16 kg, elongation at break not less than 450%, abrasion resistance not less than 40 mm. 3 Temperature range: -40 to +90°C; Number average molecular weight: approximately 48,000 g / mol; Supplier: BASF.

[0047] (10) TPU polyurethane elastomer, for use in the first hardness zone of injection molded sleeves, polyester type, grade Elastollan 1164D, Shore hardness 63D, density 1.21g / cm³ 3 Melt index 12 to 18 g / 10 min, test conditions 190℃, load 2.16 kg, elongation at break not less than 300%, tensile strength not less than 42 MPa, number average molecular weight approximately 38000 g / mol, supplier BASF.

[0048] (11) TPU polyurethane elastomer, for use in the second hardness zone of injection molded sleeves, polyester type, grade Elastollan 1185A, Shore hardness 85A, density 1.19 g / cm³ 3 Melt index 20 to 30 g / 10 min, test conditions 190℃, load 2.16 kg, elongation at break not less than 450%, tensile strength not less than 35 MPa, number average molecular weight approximately 48000 g / mol, supplier BASF.

[0049] (12) TPU polyurethane elastomer, for use in the third hardness zone of injection molded sleeves, polyester type, grade PEARLTHANE D58A11, Shore hardness 58A, density 1.18 g / cm³ 3 Melt flow index 30 to 45 g / 10 min, test conditions 190℃, load 2.16 kg, elongation at break not less than 550%, tensile strength not less than 22 MPa, number average molecular weight approximately 52000 g / mol, supplier Lubrizol Corporation.

[0050] (13) Stainless steel wire, material SUS304, diameter range 0.3 to 1.0 mm, tensile strength not less than 590 MPa, supplier Zhangjiagang Xinhua Steel Wire Products Co., Ltd.

[0051] (14) M23 industrial circular connector, 6-pin, rated current 8A, rated voltage 250V, protection level IP67, supplier Remo Corporation.

[0052] Example 1: Raw material formula: Power line conductor: Annealed tin-plated soft copper wire, single wire diameter 0.08mm, 336 wires, using a 7x7x7x0.08mm bundled and double-twisted structure, cross-sectional area 0.75mm². 2 4 wires; Signal line conductor: Annealed tin-plated soft copper wire, single wire diameter 0.08mm, 56 wires, using a 7x8x0.08mm bundled and double-twisted structure, cross-sectional area 0.34mm². 22 wires; Insulation layer: TPEE thermoplastic polyester elastomer, Hytrel 5556, Shore A hardness 85A, power line insulation thickness 0.5mm, signal line insulation thickness 0.4mm; Filler rope: aramid fiber filler rope, 1670dtex, 1 piece; Wrapping tape: PET polyester nonwoven tape, thickness 0.05mm, overlap rate 50%; Shielding layer: tinned copper wire, diameter 0.12mm, braiding density 85%, braiding angle 35°; Inner fiber winding layer: aramid fiber yarn, 1670dtex, 14 pieces, winding angle 55° right-handed; Outer fiber winding layer: UHMWPE fiber yarn, 880dtex, 14 pieces, winding angle 55° left-handed; Sheath layer: TPU polyurethane elastomer, Elastollan 1185A, Shore hardness 80A, thickness 1.5mm; Connector: M23 industrial circular connector, 6-pin; Tapered spiral reinforcement: SUS304 stainless steel wire, spiral wire diameter gradually decreases from 0.9mm at the connector end to 0.35mm at the cable end, spiral pitch gradually increases from 5mm at the connector end to 15mm at the cable end, length 45mm; Gradient stiffness transition sleeve: First hardness zone TPU grade Elastollan 1164D Shore hardness 63D, length 15mm, wall thickness 3.0mm; Second hardness zone TPU grade Elastollan 1185A Shore hardness 85A, length 20mm, wall thickness 2.5mm; Third hardness zone TPU grade PEARLTHANE D58A11 Shore hardness 58A, length 20mm, wall thickness 2.0mm.

[0053] Preparation process: Step 1, Conductor stranding: Using a stranding machine, annealed tin-plated soft copper wires with a single wire diameter of 0.08mm are stranded in a 7x7x7 structure to prepare power line conductors, with a stranding pitch ratio of 10 times the conductor outer diameter and a stranding tension of 0.8N; signal line conductors are prepared by stranding in a 7x8 structure, with a stranding pitch ratio of 10 times the conductor outer diameter and a stranding tension of 0.5N.

[0054] Step 2, Insulation Extrusion: Extrude a TPEE insulation layer on the outside of the conductor. The temperature settings for each zone of the extruder are as follows: feeding section 180℃, compression section 210℃, homogenization section 230℃, die head 235℃, screw speed 45r / min, cooling water temperature 25℃, power line insulation thickness 0.5mm, signal line insulation thickness 0.4mm.

[0055] Step 3, cable core stranding: The four power cores, two signal cores and one aramid fiber filler rope are stranded into a cable core in an SZ stranding manner. The SZ stranding pitch is 14 times the outer diameter of the cable core and the stranding tension is 2.5N.

[0056] Step 4, Wrapping and Shielding: Wrap PET polyester nonwoven tape around the outside of the cable core with a 50% overlap rate, and then weave a shielding layer with 0.12mm tinned copper wire, with a weaving density of 85%, a weaving angle of 35°, and a weaving pitch of 35mm.

[0057] Step 5, Preparation of bidirectional winding torque balance layer: Using a CNC fiber winding machine, first, 14 strands of 1670dtex aramid fiber yarn are wound in a right-handed direction around the outside of the shielding layer at a winding angle of 55°; then, 14 strands of 880dtex UHMWPE fiber yarn are wound in a left-handed direction around the outside of the inner layer at a winding angle of 55°; in the area within 50mm of each end of the cable, the ratio of the lateral speed to the rotational speed of the winding machine is controlled by programming to gradually increase the winding angle of the inner and outer layers from 55° to 70°.

[0058] Step 6, Sheath Extrusion: Extrude TPU sheath outside the bidirectional winding torque balance layer. The temperature settings for each zone of the extruder are as follows: feeding section 165℃, compression section 185℃, homogenization section 195℃, die head 195℃, screw speed 40r / min, cooling water temperature 20℃, sheath thickness 1.5mm, and cable outer diameter approximately 11.5mm.

[0059] Step 7, Cutting and Termination: Cut the cable to a length of 5m, remove 55mm of the sheath, fiber wrapping layer, shielding layer, wrapping tape, and filler rope from both ends, remove the insulation layer to expose the conductor, crimp the conductor to the M23 connector terminals to a crimp height of 0.8mm, and assemble the connector housing. Step 8, installation of spiral reinforcement: The conical spiral reinforcement formed by cold winding of SUS304 stainless steel wire is fitted onto the cable body at the tail of the connector, with the larger diameter end of the spiral wire facing the connector, and the front end of the spiral reinforcement 2mm away from the tail end of the connector; the spiral reinforcement is subjected to stress relief treatment at 400℃ for 2 hours before installation.

[0060] Step 9, Gradient Stiffness Transition Sleeve Injection Molding: Using a three-station rotary injection molding machine, place the connector and cable assembly in the injection mold; at the first station, inject TPU elastomer with a Shore hardness of 63D, injection temperature 220℃, injection pressure 20MPa, and holding time 8s to form the first hardness zone, 15mm in length and 3.0mm in wall thickness; the mold rotates to the second station, injecting TPU elastomer with a Shore hardness of 85A, injection temperature 200℃, injection pressure 15MPa, and holding time 6s to form the second hardness zone, 20mm in length and 2.5mm in wall thickness; the mold rotates to the third station, injecting TPU elastomer with a Shore hardness of 58A, injection temperature 190℃, injection pressure 12MPa, and holding time 5s to form the third hardness zone, 20mm in length and 2.0mm in wall thickness; adjacent hardness zones achieve interfacial bonding through intermolecular diffusion of melt molecules during injection molding, and demold after a cooling time of 45s.

[0061] Bending fatigue life: 5.23 million cycles; torsional fatigue life: 1.82 million cycles; bending-torsional coupled fatigue life: 1.17 million cycles; tensile force retention after 1 million bending cycles: 132 N.

[0062] Example 2: Raw material formula: The power line conductor and signal line conductor are the same as in Example 1; the insulation layer is the same as in Example 1; the filler rope is the same as in Example 1; the wrapping tape is the same as in Example 1; the shielding layer is the same as in Example 1; the inner fiber winding layer is aramid fiber yarn, 1670 dtex, 16 strands, with a right-hand winding angle of 60°; the outer fiber winding layer is UHMWPE fiber yarn, 880 dtex, 16 strands, with a left-hand winding angle of 60°; the sheath layer is the same as in Example 1; the connector is the same as in Example 1; the tapered spiral reinforcement is made of stainless steel wire SUS304, with the spiral wire diameter gradually decreasing from 1.0 mm at the connector end to 0.4 mm at the cable end, and the spiral pitch gradually increasing from 4 mm at the connector end to 14 mm at the cable end, with a length of 40 mm; the gradient stiffness transition sleeve is made of TPU with a Shore hardness of 65D in the first hardness zone, with a length of 15 mm and a wall thickness of 3.2 mm; TPU with a Shore hardness of 88A in the second hardness zone, with a length of 15 mm and a wall thickness of 2.6 mm; and TPU with a Shore hardness of 62A in the third hardness zone, with a length of 20 mm and a wall thickness of 2.2 mm.

[0063] Preparation process: Steps 1 to 4 are the same as in Example 1.

[0064] Step 5, Preparation of bidirectional winding torque balance layer: Using a CNC fiber winding machine, first, 16 strands of 1670dtex aramid fiber yarn are wound in a right-handed direction around the outside of the shielding layer at a winding angle of 60°; then, 16 strands of 880dtex UHMWPE fiber yarn are wound in a left-handed direction around the outside of the inner layer at a winding angle of 60°; in the area within 45mm of each end of the cable, the winding angle of the inner and outer layers is gradually increased from 60° to 75°.

[0065] Step 6 is the same as in Example 1. Step 7 is the same as in Example 1.

[0066] Step 8, installation of the spiral reinforcement: The tapered spiral reinforcement is 40mm long, and the front end of the spiral reinforcement is 2mm away from the rear end of the connector; the spiral reinforcement is subjected to stress relief treatment at 400℃ for 2 hours before installation.

[0067] Step 9, Gradient Stiffness Transition Sleeve Injection Molding: A three-station rotary injection molding machine is used; the first station injects TPU elastomer with a Shore hardness of 65D at an injection temperature of 225℃, an injection pressure of 22MPa, and a holding time of 8s, forming the first hardness zone with a length of 15mm and a wall thickness of 3.2mm; the second station injects TPU elastomer with a Shore hardness of 88A at an injection temperature of 205℃, an injection pressure of 16MPa, and a holding time of 6s, forming the second hardness zone with a length of 15mm and a wall thickness of 2.6mm; the third station injects TPU elastomer with a Shore hardness of 62A at an injection temperature of 192℃, an injection pressure of 12MPa, and a holding time of 5s, forming the third hardness zone with a length of 20mm and a wall thickness of 2.2mm; demolding is performed after a cooling time of 45s.

[0068] Bending fatigue life: 4.47 million cycles; torsional fatigue life: 2.31 million cycles; bending-torsional coupled fatigue life: 1.53 million cycles; tensile force retention after 1 million bending cycles: 126 N.

[0069] Example 3: Raw material formula: The power line conductor and signal line conductor are the same as in Example 1; the insulation layer is the same as in Example 1; the filler rope is the same as in Example 1; the wrapping tape is the same as in Example 1; the shielding layer is the same as in Example 1; the inner fiber winding layer is aramid fiber yarn, 1670 dtex, 12 strands, with a right-hand winding angle of 50°; the outer fiber winding layer is UHMWPE fiber yarn, 880 dtex, 12 strands, with a left-hand winding angle of 50°; the sheath layer is the same as in Example 1; the connector is the same as in Example 1; the tapered spiral reinforcement is made of stainless steel wire SUS304, with the spiral wire diameter gradually decreasing from 0.8 mm at the connector end to 0.3 mm at the cable end, and the spiral pitch gradually increasing from 6 mm at the connector end to 12 mm at the cable end, with a length of 35 mm; the gradient stiffness transition sleeve is made of TPU with a Shore hardness of 60D in the first hardness zone, with a length of 12 mm and a wall thickness of 2.8 mm; the TPU with a Shore hardness of 82A in the second hardness zone, with a length of 16 mm and a wall thickness of 2.3 mm; and the TPU with a Shore hardness of 55A in the third hardness zone, with a length of 17 mm and a wall thickness of 1.8 mm.

[0070] Preparation process: Steps 1 to 4 are the same as in Example 1.

[0071] Step 5, Preparation of bidirectional winding torque balance layer: Using a CNC fiber winding machine, first, 12 strands of 1670dtex aramid fiber yarn are wound in a right-handed direction around the outside of the shielding layer at a winding angle of 50°; then, 12 strands of 880dtex UHMWPE fiber yarn are wound in a left-handed direction around the outside of the inner layer at a winding angle of 50°; in the area within 40mm of each end of the cable, the winding angle of the inner and outer layers is gradually increased from 50° to 65°.

[0072] Step 6 is the same as in Example 1.

[0073] Step 7 is the same as in Example 1.

[0074] Step 8, installation of the spiral reinforcement: The tapered spiral reinforcement is 35mm long, and the front end of the spiral reinforcement is 2mm away from the rear end of the connector; the spiral reinforcement is subjected to stress relief treatment at 390℃ for 2.5h before installation.

[0075] Step 9, Gradient Stiffness Transition Sleeve Injection Molding: A three-station rotary injection molding machine is used; the first station injects TPU elastomer with a Shore hardness of 60D, injection temperature of 215℃, injection pressure of 18MPa, and holding time of 7s, forming the first hardness zone with a length of 12mm and a wall thickness of 2.8mm; the second station injects TPU elastomer with a Shore hardness of 82A, injection temperature of 195℃, injection pressure of 13MPa, and holding time of 5s, forming the second hardness zone with a length of 16mm and a wall thickness of 2.3mm; the third station injects TPU elastomer with a Shore hardness of 55A, injection temperature of 185℃, injection pressure of 10MPa, and holding time of 4s, forming the third hardness zone with a length of 17mm and a wall thickness of 1.8mm; demolding is performed after a cooling time of 40s.

[0076] Bending fatigue life: 3.81 million cycles; torsional fatigue life: 1.48 million cycles; bending-torsional coupled fatigue life: 0.92 million cycles; tensile strength retention after 1 million bending cycles: 118 N.

[0077] Comparative Example 1: Blank comparative example, excluding bidirectional winding torque balance layer, gradient stiffness transition sleeve and tapered helical reinforcement.

[0078] Raw material formula: The power line conductor and signal line conductor are the same as in Example 1; the insulation layer is the same as in Example 1; the filler rope is the same as in Example 1; the wrapping tape is the same as in Example 1; the shielding layer is the same as in Example 1; the sheath layer is the same as in Example 1; the connector is the same as in Example 1; the connector tail injection molded sleeve: TPU polyurethane elastomer, grade Elastollan 1185A, Shore hardness 80A, uniform hardness, length 55mm, wall thickness 2.5mm.

[0079] Preparation process: Steps 1 to 4 are the same as in Example 1.

[0080] Step 5, Sheath extrusion: TPU sheath is directly extruded outside the shielding layer, with extrusion parameters the same as in Example 1.

[0081] Step 6, cutting and terminating are the same as in Example 1.

[0082] Step 7, connector tail injection sleeve: Use a single-station injection molding machine to inject TPU elastomer with a Shore hardness of 80A, injection temperature of 200℃, injection pressure of 15MPa, holding time of 6s to form a uniform hardness injection sleeve with a length of 55mm and a wall thickness of 2.5mm. Demolding is performed after a cooling time of 40s.

[0083] Bending fatigue life: 0.53 million cycles; torsional fatigue life: 0.32 million cycles; bending-torsional coupled fatigue life: 0.18 million cycles; tensile force retention after 1 million bending cycles: 42 N.

[0084] Comparative Example 2: The key difference is that the comparative model does not contain tapered helical reinforcements.

[0085] The raw material formulation is the same as in Example 1, but does not contain the conical helical reinforcement.

[0086] The preparation process is the same as in Example 1, but step 8, the installation of the spiral reinforcement, is omitted, and in step 9, there is no spiral reinforcement inside the transition sleeve during injection molding.

[0087] Bending fatigue life: 3.24 million cycles; torsional fatigue life: 1.12 million cycles; bending-torsional coupled fatigue life: 0.68 million cycles; tensile force retention after 1 million bending cycles: 105 N.

[0088] Comparative Example 3: The key difference is that the comparative model only sets up a unidirectional wound fiber layer.

[0089] The raw material formulation is the same as in Example 1, but only an inner aramid fiber winding layer is set, with a winding angle of 55° clockwise and 14 fibers; no outer UHMWPE fiber winding layer is set.

[0090] The preparation process is the same as in Example 1, but step 5 only involves winding the inner aramid fiber and not winding the outer UHMWPE fiber.

[0091] Bending fatigue life: 4.06 million cycles; torsional fatigue life: 0.58 million cycles; bending-torsional coupled fatigue life: 0.41 million cycles; tensile strength retention after 1 million bending cycles: 97 N.

[0092] Comparative Example 4: The existing technology comparison model uses a rolling rod and an external force resistance mechanism.

[0093] Raw material formula: The power line conductor and signal line conductor are the same as in Example 1; the insulation layer is the same as in Example 1; the filler rope is the same as in Example 1; the first protective layer: PET polyester non-woven fabric tape, 0.05mm thick, with an overlap rate of 50%; the rolling rod: stainless steel round bar, 1.5mm in diameter, with 8 rods evenly distributed around the circumference; the second protective layer: PET polyester non-woven fabric tape, 0.05mm thick, with an overlap rate of 50%; the third protective layer of the external force resistance mechanism: PET polyester non-woven fabric tape, 0.05mm thick; the separator plate: nylon material, 6 strips evenly distributed around the circumference; the fourth protective layer of the external force resistance mechanism: PET polyester non-woven fabric tape, 0.05mm thick; the shielding layer is the same as in Example 1; the sheath layer is the same as in Example 1; the connector is the same as in Example 1; the connector tail injection molded sleeve: TPU polyurethane elastomer, grade Elastollan 1185A, Shore hardness 80A, uniform hardness, length 55mm, wall thickness 2.5mm.

[0094] Preparation process: Steps 1 to 3 are the same as in Example 1.

[0095] Step 4: Wrap the first protective layer around the cable core, evenly distribute 8 stainless steel rolling rods, wrap the second protective layer, and then set up an external force resistance mechanism including a third protective layer, 6 evenly distributed partition plates, and a fourth protective layer.

[0096] Step 5: Braid the tin-plated copper wire shielding layer.

[0097] Step 6: Extrude the TPU sheath.

[0098] Step 7, cutting and terminating are the same as in Example 1.

[0099] Step 8, Injection molding of connector tail sleeve with uniform hardness: injection temperature 200℃, injection pressure 15MPa, holding time 6s, length 55mm, wall thickness 2.5mm.

[0100] Bending fatigue life: 2.48 million cycles; torsional fatigue life: 0.87 million cycles; bending-torsional coupled fatigue life: 0.55 million cycles; tensile strength retention after 1 million bending cycles: 78 N.

[0101] Comparative Example 5: Compared with existing technologies, the cable body has a bidirectional winding torque balancing layer, but there is no stress optimization at the connector.

[0102] The raw material formulation is the same as that of the cable body formulation in Example 1, including a bidirectional winding torque balance layer; however, the connector tail injection sleeve is a TPU with a uniform Shore hardness of 80A, grade Elastollan 1185A, with a length of 55mm, a wall thickness of 2.5mm, no gradient stiffness transition sleeve, and no tapered spiral reinforcement.

[0103] The preparation process is the same as steps 1 to 7 of Example 1, but step 8, the installation of the spiral reinforcement, is not performed. Step 9 is a single-station injection molding of a TPU injection sleeve with a uniform hardness of 80A. The injection temperature is 200℃, the injection pressure is 15MPa, and the holding time is 6s.

[0104] Bending fatigue life: 2.97 million cycles; torsional fatigue life: 1.36 million cycles; bending-torsional coupled fatigue life: 0.71 million cycles; tensile strength retention after 1 million bending cycles: 88 N.

[0105] Comparative Example 6: The existing technology comparison model combines a three-level mechanical buffer structure with a bidirectional winding torque balance layer.

[0106] Raw material formula: The cable body formulation is the same as in Example 1, including a bidirectional winding torque balance layer; a three-level mechanical buffer structure is used at the connector to replace the gradient stiffness transition sleeve. This structure consists of a rigid base, an elastic buffer, and a flexible sleeve. The rigid base is made of aluminum alloy, the elastic buffer contains spring steel sheets to form an elastic friction interface, and the flexible sleeve is a TPU tube with a Shore hardness of 80A; there is no injection-molded gradient stiffness transition sleeve and no tapered spiral reinforcement.

[0107] Preparation process: Steps 1 to 6 are the same as in Example 1.

[0108] Step 7, Cutting and Termination: Crim the conductor to the M23 connector terminal, install a three-stage mechanical buffer structure inside the connector housing, the rigid base part is fixed to the connector housing, the elastic buffer part connects the rigid base part and the flexible sleeve part through spring steel sheet, and the flexible sleeve part wraps the cable body.

[0109] Steps 8 and 9 are omitted.

[0110] Bending fatigue life: 3.42 million cycles; torsional fatigue life: 1.21 million cycles; bending-torsional coupled fatigue life: 0.73 million cycles; tensile strength retention after 1 million bending cycles: 98 N.

[0111] Comparative Example 7: The existing technology comparison model combines a dual-hardness injection molded sleeve with a bidirectional winding torque balancing layer.

[0112] Raw material formula: The cable body formulation is the same as in Example 1, including a bidirectional winding torque balance layer; the connector uses a dual-hardness injection molded sleeve, with the end near the connector being TPU with a Shore hardness of 90A, grade Elastollan1190A, 25mm in length and 3.0mm in wall thickness; the end away from the connector is TPU with a Shore hardness of 55A, grade PEARLTHANE D58A11, 30mm in length and 2.0mm in wall thickness; there is no tapered spiral reinforcement.

[0113] Preparation process: Steps 1 to 7 are the same as in Example 1.

[0114] Step 8, installation of the spiral reinforcement, is omitted.

[0115] Step 9: Use a dual-station rotary injection molding machine; the first station injects TPU elastomer with a Shore hardness of 90A, injection temperature of 205℃, injection pressure of 18MPa, and holding time of 7s, forming a hard zone with a length of 25mm and a wall thickness of 3.0mm; the second station injects TPU elastomer with a Shore hardness of 55A, injection temperature of 185℃, injection pressure of 10MPa, and holding time of 5s, forming a soft zone with a length of 30mm and a wall thickness of 2.0mm; demold after a cooling time of 40s.

[0116] Bending fatigue life: 2.83 million cycles; torsional fatigue life: 1.03 million cycles; bending-torsional coupled fatigue life: 0.62 million cycles; tensile strength retention after 1 million bending cycles: 96 N.

[0117] Comparative Example 8: In comparison to existing technologies, a uniform diameter spiral is used instead of a conical spiral.

[0118] The raw material formula is the same as in Example 1, but the conical spiral reinforcement is replaced with a uniform diameter stainless steel spiral with a spiral wire diameter of 0.6 mm, a spiral pitch of 10 mm, and a length of 45 mm.

[0119] The preparation process is the same as in Example 1, but in step 8, a uniform diameter stainless steel spiral is installed instead of a conical spiral reinforcement.

[0120] Bending fatigue life: 4.12 million cycles; torsional fatigue life: 1.53 million cycles; bending-torsional coupled fatigue life: 0.87 million cycles; tensile force retention after 1 million bending cycles: 108 N.

[0121] Performance testing and results analysis: Test method: (1) Bending fatigue life test: Performed in accordance with IEC60811-502 standard. Test conditions: bending angle ±90°, bending radius 5 times the cable outer diameter, i.e. 57.5mm, bending frequency 20 times / min, ambient temperature 23±2℃, record the number of cycles until conductor breaks or insulation breaks down, and take the average value of 3 samples for each group.

[0122] (2) Torsional fatigue life test: Performed in accordance with GB / T9330-2020 standard. Test conditions: torsion angle ±180° / m, torsion frequency 10 times / min, ambient temperature 23±2℃, record the number of cycles until conductor breaks, and take the average value of 3 samples for each group.

[0123] (3) Bending-torsion coupling fatigue life test: Simultaneously apply ±90° bending and ±90° / m torsion, frequency 15 times / min, ambient temperature 23±2℃, record the number of cycles until conductor breaks, and take the average value of 3 samples for each group.

[0124] (4) Tensile retention test: The initial tensile force and the tensile force after 1 million bending cycles are measured according to UL817 standard. The tensile force after bending is used as the tensile retention index. Three samples are tested for each group and the average value is taken.

[0125] The test results are shown in Tables 1 and 2 below.

[0126] Table 1. Results of bending and torsional fatigue life tests: Table 2. Results of bending-torsional coupling and tensile force retention tests: Results analysis: The bending fatigue life of Examples 1 to 3 is 3.81 to 5.23 million cycles, the torsional fatigue life is 1.48 to 2.31 million cycles, the bending-torsional coupled fatigue life is 0.92 to 1.53 million cycles, and the tensile force remains at 118 to 132 N after 1 million bending cycles.

[0127] The bending fatigue life of Comparative Examples 1 to 8 was 0.53 to 4.12 million cycles, the torsional fatigue life was 0.32 to 1.53 million cycles, and the bending-torsional coupling fatigue life was 0.18 to 0.87 million cycles. After 1 million bending cycles, the tensile force remained at 42 to 108 N. The bending-torsional coupling fatigue life of the embodiments was improved by at least 29% and by up to 550% compared with the comparative examples.

[0128] Compared with the blank control example 1, the bending fatigue life of Example 1 is increased by 887%, the torsional fatigue life is increased by 469%, the bending-torsional coupling fatigue life is increased by 550%, and the tensile strength retention is increased by 214%. This shows that the three-in-one integrated solution of the present invention fundamentally solves the failure problem of pre-installed cables under dynamic bending and torsion conditions.

[0129] Compared with Comparative Example 2, the bending-torsional fatigue life of Example 1 is increased by 72%, indicating that the conical helical reinforcement has an irreplaceable supplementary role in the stiffness distribution of the gradient stiffness transition sleeve. Without the conical helical reinforcement, there are stiffness jumps between the hardness zones of the transition sleeve, and the bending stress generates secondary peaks at the interface of the hardness zones, resulting in a significant decrease in the bending-torsional fatigue life. The internal stiffness gradient provided by the conical helical reinforcement effectively eliminates this jump, making the bending curvature quasi-continuously distributed in the transition zone.

[0130] Compared with Comparative Example 3, Example 1 showed a 214% increase in torsional fatigue life and a 185% increase in bending-torsional coupling fatigue life, indicating that the bidirectional winding torque balancing layer is crucial for eliminating residual torque accumulation.

[0131] Unidirectional winding fibers provide restoring force only in one torsional direction. They cannot provide symmetrical constraints when twisted in the opposite direction. Residual torque gradually accumulates and is transmitted to the connector interface, resulting in a sharp decrease in fatigue life under bending-torsional coupling conditions. The design of inner aramid fibers and outer UHMWPE fibers winding in opposite directions ensures that there are fiber layers under tensile loads under both positive and negative torsional conditions, forming a symmetrical recovery path.

[0132] Compared with the rolling rod external force resistance mechanism scheme of Comparative Example 4, the bending-torsional coupling fatigue life of Example 1 is improved by 113%. Although the rolling rod structure can transfer some external force, it increases the outer diameter and weight of the cable, and the rigid structure of the separator plate becomes a stress concentration source when repeatedly torn, making it impossible to achieve a gradual transition of stiffness. The gradient stiffness transition sleeve of the present invention achieves a true stiffness gradient distribution through the gradual change of the hardness zone, rather than discrete mechanical protection.

[0133] Compared to Comparative Example 5, Example 1 showed a 65% improvement in bending-torsional coupling fatigue life. Although Comparative Example 5 incorporated a bidirectional winding torque balancing layer in the cable body, achieving a torsional fatigue life of 1.36 million cycles, the lack of gradient stiffness transition and helical reinforcement at the connector meant that bending stress remained concentrated at the connector-cable junction. Under bending-torsional coupling conditions, the connector interface became a weak point, limiting fatigue life. This demonstrates that optimizing only the cable body while neglecting the stress transition at the connector interface cannot solve the fundamental failure problem of pre-installed cables.

[0134] Comparative Example 6 combines a three-stage mechanical buffer structure with a bidirectional wound torque balance layer, achieving a bending-torsional coupling fatigue life of 0.73 million cycles, which is 60% higher than Example 1. The three-stage mechanical buffer structure uses discrete spring steel sheets to provide elastic buffering, which cannot achieve a quasi-continuous stiffness distribution from rigid connectors to flexible cables. The elastic force of the spring steel sheets is concentrated on several discrete contact points, forming new hard points at the connector end and the sleeve end, and the spring steel sheets cannot provide effective radial restraint under torsional conditions. The gradient stiffness transition sleeve of this invention uses a continuous polymer hardness gradient combined with a conical spiral reinforcement, achieving a true quasi-continuous stiffness transition, which is an effect that discrete mechanical structures cannot achieve.

[0135] Comparative Example 7 combines a dual-hardness injection molded sleeve with a bidirectional wound torque balance layer, achieving a bending-torsional coupling fatigue life of 0.62 million cycles, which is 89% higher than Example 1. The dual-hardness injection molded sleeve has only two hardness zones, resulting in an insufficiently fine hardness gradient and a large stiffness jump at the interface between the two zones. More importantly, it lacks internal helical reinforcement to provide structural support, and the transition sleeve cannot achieve a smooth stiffness transition solely based on external hardness differences. Under bending-torsional coupling conditions, the interface between the two hardness zones becomes a crack initiation point, and the modulus difference between the hard and soft zones leads to shear stress concentration at the interface. The three-hardness zone design of this invention, combined with internal conical helical reinforcement, disperses stiffness jumps across three interfaces and further smooths stiffness changes at each interface through the conical stiffness distribution of the helical reinforcement. This synergistic internal and external stiffness control method is not available in dual-hardness injection molded sleeves.

[0136] Comparative Example 8, which uses a uniform diameter spiral instead of a tapered spiral, achieved a bending-torsional fatigue life of 0.87 million cycles, 35% higher than Example 1. However, the uniform diameter spiral exhibits excessive stiffness at the cable end, mismatched with the flexibility of the low-hardness transition sleeve at that location, creating a new stress concentration point. The sudden release of bending stress at the spiral end leads to premature cracking of the sheath and insulation layer at that point. This demonstrates that the tapered design of the spiral is crucial for achieving a quasi-continuous stiffness distribution. The gradual decrease in wire diameter and increase in pitch, precisely matching the spatial hardness gradient of the transition sleeve, is a prerequisite for generating a synergistic effect. Regardless of the diameter selection, a uniform spiral cannot simultaneously meet the high stiffness requirements of the connector end and the low stiffness requirements of the cable end.

[0137] From the perspective of synergistic effect, Comparative Example 2, lacking the conical helical reinforcement, has a bending-torsional coupling lifetime of 0.68 million cycles; Comparative Example 3, lacking the bidirectional winding torque balancing layer, has a bending-torsional coupling lifetime of 0.41 million cycles; Comparative Example 1 has a bending-torsional coupling lifetime of 0.18 million cycles; while Example 1 has an actual bending-torsional coupling lifetime of 1.17 million cycles, significantly exceeding the sum of the lifetime increments of the two examples relative to the blank baseline, with a synergistic effect ratio of 1.29. This super-addition effect indicates a strict synergistic relationship between the gradient stiffness transition sleeve, the conical helical reinforcement, and the bidirectional winding torque balancing layer: the conical helical reinforcement provides internal structural support for the transition sleeve, enabling precise control of the bending curvature distribution of the transition sleeve's stiffness gradient; the bidirectional winding torque balancing layer prevents residual torque from being transmitted to the connector interface, protecting the transition sleeve and helical reinforcement from additional torsional loads and allowing them to focus on bending stress management; the transition sleeve and helical reinforcement limit excessive bending at the connector end, protecting the structural integrity of the end joint and the helical reinforcement itself. All three are indispensable, and the synergistic effect cannot be obtained by simply piecing together existing technologies.

[0138] In Example 2, the winding angle was increased to 60° and the number of fibers was increased to 16. The torsional fatigue life reached 2.31 million cycles, which is 27% higher than that of Example 1. However, the bending fatigue life decreased by 15% to 4.47 million cycles, which reflects the trade-off between torsional constraint and bending flexibility.

[0139] Example 3 uses a 50° winding angle and 12 fibers. The bending fatigue life and torsional fatigue life are both lower than those of Example 1, but the bending-torsional coupling fatigue life still reaches 0.92 million cycles, which is much higher than all comparative examples.

[0140] The three sets of embodiments cover a parameter range of 50° to 60° winding angle and 12 to 16 fiber roots, verifying the effectiveness and adaptability of the technical solution of the present invention under different design parameters.

[0141] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A pre-assembled cable resistant to bending and torsion, comprising a cable body and connectors disposed at both ends of the cable body, wherein the cable body comprises, from the inside out, a conductor, an insulation layer, a cable core, a shielding layer, and a sheath layer, characterized in that: A bidirectional winding torque balancing layer is provided between the shielding layer and the sheath layer. The bidirectional winding torque balancing layer includes an inner fiber winding layer and an outer fiber winding layer. The inner fiber winding layer is wound along a first helical direction, and the outer fiber winding layer is wound along a second helical direction opposite to the first helical direction. The winding angles of the inner and outer layers are both 50° to 60°. The junction between the connector and the cable body is provided with a gradient stiffness transition sleeve. The gradient stiffness transition sleeve includes at least three hardness zones with decreasing hardness in sequence along the direction away from the connector. The hardness zone closest to the connector has a Shore hardness of D55 to D70, and the hardness zone furthest from the connector has a Shore hardness of A50 to A65. The gradient stiffness transition sleeve is provided with a conical helical reinforcement. The diameter of the helical wire of the conical helical reinforcement gradually decreases in the direction away from the connector, and the helical pitch gradually increases in the direction away from the connector.

2. The pre-assembled cable with bending and torsion resistance according to claim 1, characterized in that: The gradient stiffness transition sleeve includes three hardness zones in sequence along the direction away from the connector: the first hardness zone has a Shore hardness of D60 to D65 and a length of 12 to 15 mm; the second hardness zone has a Shore hardness of A80 to A88 and a length of 15 to 20 mm; and the third hardness zone has a Shore hardness of A55 to A62 and a length of 15 to 20 mm.

3. The pre-assembled cable with bending and torsion resistance according to claim 1, characterized in that: The diameter of the spiral wire of the tapered spiral reinforcement gradually decreases from 0.8 to 1.0 mm to 0.3 to 0.4 mm in the direction away from the connector, the spiral pitch gradually increases from 4 to 6 mm to 12 to 15 mm in the direction away from the connector, and the length of the tapered spiral reinforcement is 35 to 50 mm.

4. The pre-assembled cable with bending and torsion resistance according to claim 1, characterized in that: The inner fiber winding layer is made of aramid fiber yarn, and the outer fiber winding layer is made of ultra-high molecular weight polyethylene fiber yarn; the winding angle of the inner and outer fiber winding layers gradually increases from 50° to 60° to 65° to 75° in a 50mm area near the connector.

5. A pre-assembled cable resistant to bending and torsion according to claim 1, characterized in that: The conductor is a Class 6 ultrafine stranded conductor with a single wire diameter of 0.05 to 0.10 mm and a multi-layer stranded and re-stretched structure.

6. The pre-assembled cable with bending and torsion resistance according to claim 1, characterized in that: The insulating layer material is thermoplastic polyester elastomer with a Shore hardness of A80 to A90; the shielding layer is a tin-plated copper wire braided layer with a braiding density of 80% to 90% and a braiding angle of 30° to 40°; the sheathing layer material is polyurethane elastomer with a Shore hardness of A75 to A85.

7. A method for preparing a pre-assembled cable resistant to bending and torsion according to claim 1, characterized in that, Includes the following steps: Step 1, conductor stranding: The conductor is prepared by using Category 6 ultrafine tin-plated copper wire in a bundle stranding and re-stretching method, with a bundle stranding pitch ratio of 8 to 12 times the conductor outer diameter; Step 2, Insulation Extrusion: Extruding a thermoplastic polyester elastomer insulation layer over the conductor at an extrusion temperature of 220 to 240°C, with an insulation layer thickness of 0.4 to 0.8 mm; Step 3, cable core stranding: multiple insulated wire cores and filler rope are stranded into a cable core in an SZ manner, with a stranding pitch ratio of 12 to 16 times the outer diameter of the cable core. Step 4, Wrapping and Shielding: Wrap polyester non-woven fabric tape around the outside of the cable core, and then weave a tinned copper wire shielding layer; Step 5, preparation of bidirectional winding torque balance layer: First, the inner layer fiber yarn is wound around the outside of the shielding layer in the first spiral direction, with a winding angle of 50° to 60°; then, the outer layer fiber yarn is wound around the outside of the inner layer fiber winding layer in the opposite spiral direction, with a winding angle of 50° to 60°; within a 50mm range near the connector area at both ends of the cable, the winding angle of the inner and outer layers is gradually increased from 50° to 60° to 65° to 75°. Step 6, Sheath extrusion: Extrude a polyurethane elastomer sheath layer outside the bidirectional winding torque balance layer at an extrusion temperature of 180 to 200°C and a sheath thickness of 1.2 to 1.8 mm. Step 7, Cutting and Termination: Cut the cable to the specified length, strip the layers at both ends, crimp the conductors to the connector terminals, and assemble the connector housing; Step 8, Helical Reinforcement Installation: Install a tapered helical reinforcement onto the cable body at the end of the connector, with the larger diameter end of the helical wire facing the connector. Step 9, Gradient stiffness transition sleeve injection molding: Using a multi-station injection molding process, polyurethane elastomers of different hardness are injected in sections at the junction of the connector and the cable body to form a gradient stiffness transition sleeve with decreasing hardness along the direction away from the connector, and the conical spiral reinforcement is wrapped inside the transition sleeve.

8. The preparation method according to claim 7, characterized in that: In step 9, the gradient stiffness transition sleeve is injection molded using a three-station rotary injection molding method. The first station injects polyurethane elastomer with a Shore hardness of D60 to D65 at an injection temperature of 210 to 230°C and an injection pressure of 15 to 25 MPa, forming the first hardness zone. The second station injects polyurethane elastomer with a Shore hardness of A80 to A88 at an injection temperature of 190 to 210°C and an injection pressure of 10 to 20 MPa, forming the second hardness zone. The third station injects polyurethane elastomer with a Shore hardness of A55 to A62 at an injection temperature of 180 to 200°C and an injection pressure of 8 to 15 MPa, forming the third hardness zone. Adjacent hardness zones achieve interfacial bonding during injection molding through intermolecular diffusion of the melt molecules.

9. The preparation method according to claim 7, characterized in that: In step 5, the bidirectional winding torque balance layer is wound using a CNC fiber winding machine. The inner layer uses 12 to 16 strands of 1670dtex aramid fiber yarn, and the outer layer uses 12 to 16 strands of 880dtex ultra-high molecular weight polyethylene fiber yarn. The winding angle transition is achieved by programming and controlling the ratio of the lateral speed to the rotational speed of the winding machine.

10. The preparation method according to claim 7, characterized in that: In step 8, the tapered helical reinforcement is formed by cold winding of stainless steel wire. The diameter of the helical wire transitions from 0.8 to 1.0 mm at the connector end to 0.3 to 0.4 mm at the cable end. The helical pitch gradually increases from 4 to 6 mm at the connector end to 12 to 15 mm at the cable end. The tapered helical reinforcement is subjected to stress relief treatment at 380 to 420°C for 2 to 3 hours before installation.

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