Co-injected Cross-Country Ski Boot Element for Rigidity-Weight Balance
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Solution Overview
Problem
Cross-country ski boots face challenges in balancing rigidity for force transmission with comfort and weight reduction, while also requiring impact resistance and thermoformability, all while maintaining reasonable manufacturing costs.
Innovation Solution
The cross-country ski boot element employs a rear stiffener with a sandwich structure of co-injected plastic materials of varying rigidity, where the more rigid material is used in stress-bearing areas for efficient impulse transmission and the softer material in contact areas for comfort, and a rotating joint for the 'skating step' technique, optimizing both performance and comfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If rigid elements are incorporated into the cross-country ski boot to improve force transmission efficiency, then the boot's rigidity is improved, but the boot weight increases leading to faster fatigue
Solution Approach 1:
The patent applies local quality by creating zones of different rigidity within the boot shell. The co-injected plastic materials form regions with varying stiffness - harder material in areas requiring structural support and force transmission, softer material in areas contacting the foot for comfort. This localized differentiation allows the boot to be rigid where needed without uniformly increasing weight throughout the entire structure.
Solution Approach 2:
The patent uses composite materials through co-injection of two different plastic materials with distinct rigidity properties. This creates a composite structure where the harder plastic provides structural integrity and force transmission pathways, while the softer plastic reduces weight and improves comfort. The composite approach allows optimization of the strength-to-weight ratio by strategically distributing material properties throughout the boot shell.
2Strength
If rigid elements are used in the cross-country ski boot to improve force transmission, then impulse transmission to the ski is improved, but comfort deteriorates when foot or lower leg presses against hard sections
Solution Approach 1:
The patent implements local quality by differentiating the mechanical properties of the boot shell in specific zones. The co-injected harder plastic material is positioned in structural areas responsible for transmitting impulses from the foot to the ski, while the softer plastic material is placed in zones that directly contact the foot and lower leg. This spatial differentiation of material properties allows efficient force transmission without compromising comfort in contact areas.
Solution Approach 2:
The composite structure formed by co-injecting plastics with different rigidities enables simultaneous achievement of impulse transmission and comfort. The harder plastic phase creates rigid pathways for force transmission, while the softer plastic phase provides cushioning in contact zones. This composite approach resolves the contradiction by allowing both hard and soft characteristics to coexist in different locations within the same boot shell.
3Reliability
If the cross-country ski boot is designed with optimized mechanical properties for performance, then force transmission and comfort are improved, but manufacturing cost increases
Solution Approach 1:
The patent merges multiple functions and material layers into a single co-injection molding process. Instead of manufacturing separate components with different rigidities and then assembling them (which would increase manufacturing complexity and cost), the invention combines the structural and comfort layers into one integrated shell produced in a single injection molding operation. This merging of processes maintains boot performance while controlling manufacturing costs through process integration.
Solution Approach 2:
The co-injection of composite plastic materials is achieved through a standardized manufacturing process that, while technically sophisticated, produces a single integrated component. The composite structure is created during the molding process itself rather than requiring post-manufacturing assembly steps. This approach balances the complexity of producing optimized mechanical properties with the simplicity of a single-step manufacturing process, thereby controlling costs while achieving high performance.
4Reliability
If the cross-country ski boot element uses co-injected plastic materials with different rigidities, then optimal force transmission and comfort are achieved, but device complexity increases
Solution Approach 1:
The patent merges the complexity of multiple materials and structures into a single integrated component produced by co-injection molding. Rather than creating a complex assembly of separate parts with different rigidities that would require multiple manufacturing steps and assembly operations, the invention combines everything into one shell produced in a single process. This merging reduces device complexity by eliminating interfaces and assembly requirements while maintaining the differentiated material properties needed for performance and comfort.
Data Source
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AI summary
Element (10, 30, 40) of cross-country ski boot (1, 21) comprising an inner lateral part and an outer lateral part, characterized in that it comprises a first zone (Z1) comprising two plastic materials (M11, M12) co-injected in its thickness, a second zone (Z2) comprising either two plastic materials (M21, M22) co-injected in its thickness, or a single plastic material, and a third zone (Z3) comprising only the second plastic material (M12, M21) of the first and/or second zone (Z1, Z2), the first zone (Z1) extending into one lateral part, the second zone (Z2) extending into the other lateral part, the third zone (Z3) extending between the first zone (Z1) and the second zone (Z2).