Rotary Shaver Inner Blade with Concave Cutting Edge
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Solution Overview
Problem
The inner blade of rotary electric shavers faces a conflicting problem of decreasing the rake angle and increasing the erecting angle, leading to issues such as remaining hair on the end side of cut hair, poor shaving performance, increased sliding resistance, and reduced comfort due to the trade-off between blade length and angle configurations.
Innovation Solution
The inner blade is designed with a small blade formed by erecting a metal plate at an acute angle, featuring a concave portion on the front side in the rotation direction, where the upper end edge defined by the upper end surface and the concave portion functions as a blade edge, allowing for a larger erecting angle without compromising rigidity or increasing sliding resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the erecting angle is decreased to reduce the rake angle and prevent remaining hair, then the small blade length must be increased, but this causes poor rigidity, deflection, vibrations, and hindered close contact with the outer blade
Solution Approach 1:
The small blade is segmented into multiple regions: a support portion (plate surface) and a blade portion (erected portion with concave portion). This segmentation allows the support portion to provide structural rigidity while the blade portion achieves the necessary cutting geometry, resolving the conflict between rigidity and cutting precision.
Solution Approach 2:
The invention transitions from a flat plate configuration to a three-dimensional structure by erecting the blade portion at an acute angle and forming a concave portion. This dimensional change enables the blade to achieve both rigidity (through the erected structure) and precise cutting (through the concave portion geometry) simultaneously.
2Manufacturing precision
If the small blade length is increased to decrease the rake angle, then cutting precision improves, but sliding resistance against the outer blade increases, causing noise and increased power consumption
Solution Approach 1:
By segmenting the blade into support and blade portions with distinct functions, the invention reduces the sliding surface area in the blade portion while maintaining sufficient length for precise cutting. This segmentation allows optimization of each region independently, reducing overall sliding resistance while preserving cutting precision.
Solution Approach 2:
The concave portion creates local quality variations in the blade structure, concentrating the cutting function in a specific region with optimized geometry. This local optimization reduces the overall sliding surface area while maintaining cutting precision, thereby reducing power consumption and noise.
3Reliability
If the erecting angle is increased to improve blade rigidity and close contact with outer blade, then shaving performance improves, but the rake angle increases causing remaining hair on the end side of cut hair
Solution Approach 1:
The segmentation into support portion and blade portion allows the support portion to provide rigidity and close contact (improving reliability) while the blade portion with its concave geometry maintains the necessary rake angle for precise cutting (preventing remaining hair). Each segment optimizes for its specific function.
Solution Approach 2:
The concave portion creates local quality in the blade region that maintains precise cutting geometry independent of the overall erecting angle. This allows the support portion to be erected at a higher angle for rigidity while the blade portion maintains the optimal rake angle for cutting precision.
Data Source
AI summary
An inner blade of a rotary electric shaver decreases a rake angle and increases an erecting angle in a small blade, which can prevent remaining hair from appearing on one end side in a cross section of hair, and which can prevent poor shaving performance and increased sliding resistance against an outer blade. An inner blade of a rotary electric shaver includes an outer blade whose upper surface functions as an annular shaving surface having multiple hair inlets, and the inner blade having a plurality of small blades which rotate while coming into sliding contact with a lower surface of the outer blade. The small blade is formed by erecting a portion of a metal plate so that an angle of a front side in a rotation direction with respect to a plate surface of the metal plate becomes an acute angle, the front side in the rotation direction has a concave portion having a shape hollowed toward a lower end portion from an upper end surface which comes into sliding contact with the outer blade, and an upper end edge defined by the upper end surface and the concave portion functions as a blade edge.