Small-Diameter Composite Cable Structure for Bending Endurance
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Solution Overview
Problem
Small-diameter medical cables, such as endoscopic signal cables, often fail in bending endurance tests due to disconnection of shield strands or cracking of the sheath, necessitating a solution for enhanced bending resistance while maintaining a diameter of 2 mm or less.
Innovation Solution
A composite cable design featuring a binder layer, a shield layer with a specific amount of metal conductor, and a sheath, where the amount of metal conductor in the shield layer is between 0.4 and 0.7 times that of the wires, and the sheath thickness is between 1.4 and 3 times the shield strand diameter, using thin shield strands with high tensile strength and appropriate wire configurations to achieve high bending resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the cable diameter is reduced to 2 mm or less for medical applications, then the cable can be used in small-diameter medical devices, but the bending resistance deteriorates due to shield strand disconnection or sheath cracking
Solution Approach 1:
The patent changes the physical parameters of the shield layer by controlling the amount of metal conductor per unit length to be 0.4 to 0.7 times that of the plural wires, and specifying the wire diameter to be 0.03 to 0.05 mm. These parameter adjustments optimize the shield layer's contribution to bending resistance while maintaining the small cable diameter of 2.0 mm or less.
Solution Approach 2:
The patent employs a composite structure where the shield layer combines metal conductor strands with a resin coating layer. This composite material approach provides both electrical shielding function and mechanical strength enhancement, improving bending resistance without significantly increasing cable diameter. The resin coating protects the metal strands and contributes to overall cable flexibility and durability.
2Strength
If the amount of metal conductor in the shield layer is increased to improve bending resistance, then the cable maintains structural integrity during bending, but the cable diameter exceeds 2 mm
Solution Approach 1:
The patent optimizes the parameter of metal conductor amount in the shield layer to be 0.4 to 0.7 times that of the plural wires, which is less than the conventional 1:1 ratio. This parameter reduction allows achieving adequate bending resistance while keeping the cable diameter within 2.0 mm, resolving the contradiction between strength and size.
Solution Approach 2:
The patent applies local quality enhancement by specifying the wire diameter of shield strands to be 0.03 to 0.05 mm, which is thinner than conventional shields. This localized thinning of shield wires, combined with optimized shielding coverage, achieves the required bending resistance with reduced overall cable diameter.
3Volume of moving object
If thin shield strands are used to reduce cable diameter, then the cable fits small-diameter applications, but the shield strands are prone to disconnection during bending
Solution Approach 1:
The patent uses composite material construction where thin metal conductor strands (0.03 to 0.05 mm diameter) are coated with resin to form a composite shield layer. The resin coating reinforces the thin metal strands, preventing disconnection during bending while maintaining the overall thin profile necessary for 2.0 mm cable diameter.
Solution Approach 2:
The resin coating on the shield strands provides beforehand cushioning and protection against mechanical stress during bending. This protective layer prevents the thin metal strands from breaking or disconnecting under bending loads, ensuring reliability despite the reduced strand diameter.
Data Source
AI summary
A composite cable is provided with plural wires each having a metal conductor and an insulator, a binder layer that bundles the plural wires together, a shield layer composed of a metal conductor and arranged around the binder layer, and a sheath covering around the shield layer. An outer diameter of the sheath is 2.0 mm or less. An amount of the metal conductor per unit length used in the shield layer is 0.4 times or more and 0.7 times or less than an amount of the metal conductor per unit length used in the plural wires.