Hermetically Sealed Capacitive Switch for Outdoor Request Buttons
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Solution Overview
Problem
Existing capacitive switches for triggering devices like traffic lights and train/bus doors are prone to malfunction due to exposure to environmental influences such as moisture and heat, leading to leakage currents and unintended switching operations.
Innovation Solution
The capacitive switch features an electrically conductive layer applied to an insulating material plate, which is then embedded and hermetically sealed within the injection molding material of the device's cover, ensuring protection from dirt, moisture, and temperature fluctuations, with the option of using transparent insulating materials for visual inspection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the electrically conductive layer is glued to the inside of the housing or cover, then the capacitive switch can be manufactured, but the conductive layer is exposed to environmental influences such as moisture and heat, leading to leakage current and unintended switching operations
Solution Approach 1:
The electrically conductive layer is embedded within the injection molding material of the cover, nesting the conductive element inside the protective housing structure. This embedding process hermetically seals the conductive layer, protecting it from environmental influences while maintaining manufacturing efficiency through integration of the conductive layer into the molding process.
Solution Approach 2:
The injection molding material acts as an intermediary substance between the electrically conductive layer and the external environment. This intermediate layer hermetically seals the conductive layer, preventing direct exposure to moisture and heat, thereby eliminating leakage current issues while maintaining the capacitive switch's functionality.
2Ease of operation
If the electrically conductive layer is exposed on the housing, then the capacitive switch can be operated, but it becomes detached from the wall of the cover due to temperature fluctuations, impairing functionality
Solution Approach 1:
The electrically conductive layer is nested within the injection molding material, which provides mechanical anchoring and thermal stability. This embedding prevents the conductive layer from detaching during temperature fluctuations while maintaining its capacitive functionality for touch operation.
Solution Approach 2:
The electrically conductive layer is merged with the injection molding material through embedding, creating a unified structure where the conductive layer and housing become integrated. This combination ensures thermal expansion compatibility and prevents detachment, maintaining both operational functionality and structural stability.
3Reliability
If the electrically conductive layer is hermetically sealed by embedding in injection molding material, then protection from environmental influences is achieved, but the manufacturing process becomes more complex
Solution Approach 1:
The manufacturing process merges the embedding of the electrically conductive layer with the injection molding process itself. By integrating these steps, the hermetic sealing is achieved as part of the standard manufacturing workflow rather than as a separate complex process, thereby maintaining reliability while minimizing added complexity.
Solution Approach 2:
The injection molding material serves multiple functions: it forms the housing structure, provides hermetic sealing for the conductive layer, and offers mechanical support. This multi-functionality eliminates the need for separate sealing components or processes, achieving high reliability without significantly increasing device complexity.
4Ease of repair
If a transparent insulating material is used for the cover, then visual inspection of the electrically conductive layer is possible, but the material selection becomes more restricted
Solution Approach 1:
The insulating material is selected to be transparent or translucent, allowing visual inspection of the electrically conductive layer for defects such as cracks or damage. This optical property enables quality control and maintenance activities while the material still provides the necessary electrical insulation and mechanical protection.
Solution Approach 2:
The transparency requirement is applied locally to the cover material rather than imposing universal constraints on all components. This allows the use of transparent insulating materials specifically where visual inspection is needed, while other parts of the device can use more versatile materials, balancing inspection capabilities with overall material adaptability.
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
This solution guarantees long-term functionality by shielding the capacitive sensor from environmental factors and preventing detachment, ensuring reliable operation under various conditions, including exposure to dirt, moisture, heat, and external loads.
Implementation Method 1
the plate provided with the electrically conductive layer is embedded with its side having the electrically conductive layer and the associated peripheral edge of the electrically conductive layer in the injection molding material forming the cover (2), so that the electrically conductive layer is hermetically sealed
Implementation Method 2
the insulating material is transparent. This makes it possible to check whether the electrically conductive layer was damaged, for example by cracks or the like
Data Source
Figure 1~4
AI summary
The device comprises a capacitive switch with an electrically conductive layer which is arranged on housing of a request device. An electrically conductive layer is applied on a plate with an insulating material, where the plate is embedded in the housing for forming an injection molding material with its side having the electrically conductive layer and an associated circumferential edge of the electrically conductive layer, so that the electrically conductive layer is hermetically sealed. An independent claim is included for a method for producing a device, particularly a request device for initiating a switching procedure for a traffic light or for a door of a train or bus.