Hair-Cutting Unit With Trailing-Edge Retention Reducing Skin Irritation
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Solution Overview
Problem
Existing hair-cutting units suffer from excessive skin doming, leading to skin irritation and reduced hair-catching performance due to large slot angles and constant shearing angles, as seen in WO 2019/211128.
Innovation Solution
A hair-cutting unit with external cutting members featuring hair-entry slots with a slot angle of 0° to 20° and internal cutting members with cutting edges at 55° to 85°, combined with a hair-retaining structure along the trailing edge, maintains hairs in a stationary position for slicing motion, enhancing hair-catching and reducing skin irritation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the slot angle of hair-entry slots is increased to reduce skin doming, then skin irritation is reduced, but hair-catching performance deteriorates
Solution Approach 1:
The patent applies local quality by creating different functional zones within the hair-entry slot structure. The trailing edge features a hair-retaining structure with a specific geometric configuration (protrusions or increased thickness) that locally enhances hair retention capabilities, while the main body of the slot maintains a smaller angle for optimal hair catching. This localized structural modification allows the trailing edge to perform differently from the rest of the slot, resolving the contradiction between skin protection and hair-catching efficiency.
2Productivity
If the cutting-edge angle is decreased to improve hair-cutting efficiency, then hair-cutting performance is improved, but wear on cutting edges increases
Solution Approach 1:
The patent optimizes the cutting-edge angle parameter to a specific range (55° to 85°) that balances cutting efficiency with edge durability. This parameter change represents a departure from conventional sharper angles, accepting a moderate trade-off in cutting speed to significantly reduce wear and extend the operational life of the cutting edges. The optimized angle range maintains sufficient sharpness for effective hair cutting while distributing mechanical stress more favorably across the edge geometry.
3Object-affected harmful factors
If the slot angle is increased to minimize skin contact, then skin irritation is reduced, but hair manipulation capability deteriorates
Solution Approach 1:
The patent segments the hair-entry slot into distinct functional regions: a main slot body with a smaller angle for effective hair manipulation and guiding, and a trailing edge region with a hair-retaining structure for final hair positioning before cutting. This segmentation allows each region to be optimized for its specific function, with the trailing edge providing skin protection while the main body maintains superior hair manipulation capabilities through its geometric configuration.
Data Source
AI summary
A hair-cutting unit (9a) comprises an external cutting member (11a) and an internal cutting member (13a) rotatable relative to the external cutting member about a central axis. The external cutting member comprises hair-entry slots (35) having a slot angle (α) in a range from 0° to 20° in each radial position of the hair-entry slot. The internal cutting member comprises cutting elements (59a, 59b, 59c) each having a cutting edge (45a, 45b, 45c) having a cutting-edge angle (β) in a range from 55° to 85°. A trailing edge (43) of each hair-entry slot is provided with a hair-retaining structure (47) having an array of hair-abutment surfaces (53) extending transversely relative to the trailing edge and facing the central axis (19).