Stacked Metal and Elastomeric Dome for Thin Key Switches
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Solution Overview
Problem
Existing keyboards face challenges in achieving a thin, aesthetically pleasing design while maintaining tactile feedback and user functionality, particularly in portable computing devices, where conflicting design goals of reduced thickness and functionality need to be balanced.
Innovation Solution
A low-travel keyboard design incorporating a metal dome and an elastomeric dome, where the key cap deforms both domes in a serial or parallel fashion to activate electrical switch circuitry, providing a positive tactile response with reduced travel distance, and a scissor mechanism for additional stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a traditional rubber dome switch is used, then tactile feedback is provided, but the keyboard thickness increases
Solution Approach 1:
The single dome structure is segmented into two separate domes: a metal dome and a rubber dome. Each dome serves a specific function - the metal dome provides the primary switching action with shorter travel, while the rubber dome enhances tactile feedback. This segmentation allows the keyboard to maintain reduced thickness while preserving tactile feedback quality.
Solution Approach 2:
The invention uses a composite dome structure combining metal and rubber materials. The metal dome provides structural rigidity and precise switching characteristics, while the rubber dome adds compliance and tactile feedback. This composite approach enables the keyboard to achieve thin profile without sacrificing user experience.
2Length of moving object
If the key travel distance is reduced for a thin profile, then keyboard thickness is reduced, but tactile feedback quality deteriorates
Solution Approach 1:
The key travel distance is segmented into two phases: the first phase involves the metal dome deformation providing initial resistance and switching action, and the second phase involves the rubber dome deformation providing enhanced tactile feedback. This segmentation allows reduced overall travel distance while maintaining perceptible tactile feedback through the two-stage deformation process.
3Device complexity
If a single dome structure is used, then device complexity is reduced, but functional performance is insufficient
Solution Approach 1:
The switching function is segmented between two domes with distinct roles. The metal dome handles the primary electrical switching with its precise deformation characteristics, while the rubber dome provides tactile feedback and ensures reliable contact. This functional segmentation improves switching reliability without excessive complexity.
Solution Approach 2:
The dual-dome structure uses composite materials (metal and rubber) to achieve complementary performance characteristics. The metal provides structural integrity and precise switching point, while the rubber provides compliance and tactile response. This material composite approach enhances overall switching performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The combination of metal and elastomeric domes allows for a keyboard with less than 1.5 mm travel distance while maintaining desirable tactile feedback, achieving a balance between reduced thickness and tactile feel, suitable for thin-profile computing devices.
Implementation Method 1
the key cap deforms the elastomeric dome when a user pushes down on the key cap, and the elastomeric dome then deforms the metal dome in a serial fashion
Implementation Method 2
the metal dome can activate electrical switch circuitry below the metal dome when the metal dome is deformed
Data Source
AI summary
A low travel keyboard and methods of fabrication are described. The low-travel keyboard is suitable for a thin-profile computing device, such as a laptop computer, netbook computer, desktop computer, etc. The keyboard includes a key cap positioned over stacked elastomeric and metal domes. The quick force drop of the metal dome provides the crisp “snappy” feel for the user and the elastomeric dome provides the ability for longer travel than the metal dome alone. The metal dome also activates the switch circuitry of the membrane on printed circuit board. The stacking of the elastomeric metal domes takes advantage of the abrupt force drop in the metal dome buckling and applies it to the elastomeric dome force, making it possible to design a low-travel key while still maintaining or improving the tactile feeling of the key switch.