Rotary Shaver Cutter Concave Face Shearing Angle

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Solution Overview

Problem

Conventional electric rotary shaver cutter units with domed shaving tracks face challenges in maintaining a constant shearing angle, leading to discomfort and snagging, as conventional angled cutters with convex upper faces and flat forward faces struggle to maintain a consistent cutting edge across the width of the shaving track, especially when the shaving track is domed.

Innovation Solution

A cutter unit with a concave forward face and a convex upper face, where the cutting edge lies in a vertical plane, allowing for a constant shearing angle over the radial extent of the cutter, achieved by shaping the cutter disk with upstanding legs and forming the cutting edge to intersect at a specific angle, reducing variations in the cutting edge's angle with respect to the radial direction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a domed shaving track is used, then skin comfort is improved, but maintaining a constant shearing angle becomes difficult

Engineering Contradiction:

Improveskin comfortVSAvoidshearing angle consistency

Core Design Contradiction:

Ease of operationVSManufacturing precision

Solution Approach 1:

The cutter forward face is made concave (curved inward) to match the domed shape of the shaving track. This curvature allows the cutting edge to maintain a constant shearing angle relative to the hair across the entire width of the domed track, resolving the contradiction between using a domed track for comfort and maintaining cutting precision.

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Ease of manufacture

If conventional angled cutters with convex upper faces and flat forward faces are used, then manufacturing is simpler, but the cutting edge angle varies across the shaving track width

Engineering Contradiction:

Improvecutter manufacturing simplicityVSAvoidcutting edge angle consistency

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The forward face is changed from flat to concave curved, which maintains a consistent cutting edge angle across the domed shaving track width, improving precision while remaining manufacturable through cold-forming processes.

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Manufacturing precision

If curved slots are formed in the cap to match the cutter, then shearing angle consistency is improved, but manufacturing complexity and cost increase significantly

Engineering Contradiction:

Improveshearing angle consistencyVSAvoidmanufacturing process complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

Instead of curving the slots in the cap to match the cutter (which would be complex), the invention inverts the approach by making the cutter's forward face concave while keeping the slots straight. This achieves the same shearing angle consistency with much simpler manufacturing for both the cutter and cap.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The forward face geometry is changed from flat to concave, which fundamentally alters how the cutting edge interacts with the domed track, enabling constant shearing angle without requiring curved slots.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9873204B2Shaving head with doming control

Publication Date: 2018.01.23 KONINKLIJKE PHILIPS NV

AI summary

A cutter unit (1) for a rotary shaver is formed by an outer cutting element or cap (2) which interacts with a rotating inner cutting element or cutter (4) to trap and cut hairs. The cap has an annular shaving track (8) of domed cross-section having slots (30) through which the hairs may protrude. The cutter has a convex upper face (22) to engage the shaving track and a concave forward face (26).