Normally Closed Dome Switch with Pivoting Contact Segments
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Solution Overview
Problem
Newer generation nurse call devices require a normally closed dome switch that opens upon actuation, which is not addressed by the existing metallic dome switches designed as normally open switches.
Innovation Solution
A normally closed dome switch is designed with a printed circuit board and a conductive switch dome, where the switch dome is unpressed to form a closed circuit between two contact areas and pressed to open the circuit by pivoting contacting portions out of contact, utilizing a spacer layer and fulcrums to achieve this functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If metallic dome switches are designed as normally open switches (closing upon actuation), then the switch structure is simple and manufacturing is easy, but the requirement for normally closed switches in nurse call devices cannot be met
Solution Approach 1:
The dome switch is segmented into multiple contacting portions (first, second, third, and fourth contacting portions) that can independently contact different contact areas. This segmentation allows the switch to provide normally closed functionality while maintaining compatibility with standard dome switch structures, resolving the contradiction between adaptability and complexity.
Solution Approach 2:
Instead of designing a normally open switch that closes upon actuation, the patent inverts the logic by creating a normally closed switch that opens upon actuation. The dome switch is configured to contact both first and second contact areas in its unactuated state, and upon actuation, the contacting portions pivot to remove contact with at least one contact area, thereby opening the circuit.
2Reliability
If a normally closed dome switch is designed to open upon actuation, then the nurse call device requirement is met, but the switch mechanism becomes more complex requiring additional components
Solution Approach 1:
The patent merges the dome switch structure with the spacer layer by forming fulcrums on the spacer layer itself. The spacer layer serves dual purposes: providing mechanical support/spacing and creating the fulcrum points for the contacting portions to pivot upon actuation. This integration reduces overall component count while maintaining reliable normally closed operation.
Solution Approach 2:
The spacer layer acts as an intermediary element between the dome switch and the contact areas. It provides the fulcrum mechanism that enables the contacting portions to pivot during actuation, mediating the transition from closed to open state without requiring complex additional mechanisms.
3Ease of operation
If the switch dome uses multiple contacting portions to maintain closed circuit, then normally closed functionality is achieved, but the manufacturing precision requirements increase
Solution Approach 1:
The dome switch structure is designed to self-align during assembly. The contacting portions are configured to naturally contact the first and second contact areas when the dome is in its unactuated state, without requiring precise manual adjustment. The resilient nature of the dome ensures consistent contact pressure and alignment, reducing manufacturing precision requirements while maintaining ease of operation.
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 solution provides a reliable normally closed dome switch that meets the requirements of newer nurse call devices, ensuring proper operation by opening the switch when pressed and closing it when unpressed, enhancing user control and device functionality.
Implementation Method 1
The switch dome is resiliently pressable to urge the central portion of the switch dome toward the printed circuit board
Implementation Method 2
A spacer layer adhered to the printed circuit board has cut-out regions over the arc-shaped segments of the switch trace and provides a fulcrum radially adjacent each arc-shaped segment such that when the central portion of the switch dome is pressed toward the printed circuit board, each of the contacting portions is pivoted about the fulcrum out of contact with the corresponding first or second contact area of the switch trace
Data Source
AI summary
A normally closed dome switch comprises a printed circuit board including a switch trace having first and second contact areas electrically insulated from one another, and a conductive switch dome having a central portion spaced from the printed circuit board and a plurality of contacting portions extending from the central portion such that each of the first and second contact areas is contacted by at least one of the contacting portions when the switch dome is unpressed such that the unpressed switch dome forms a closed switch between the first and second contact areas. The switch dome is resiliently pressable to urge the central portion toward the printed circuit board and pivot the contacting portions about a corresponding fulcrum to remove the plurality of contacting portions of the switch dome from contact with at least one of the first and second contact areas to open the switch.