Capacitive Watch Battery Cover for Reliable Touch Detection

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Solution Overview

Problem

Wristwatches with capacitive touch zones made of non-electrically conductive materials face challenges in detecting finger presence due to fluctuating body potential, leading to unreliable operation, as the body is not set to the internal reference potential, unlike metal cases.

Innovation Solution

Incorporating an electrically conductive battery cover with a sealing gasket, such as a conductive particle-filled elastomer, to create a closed electrical loop between the user's finger, the watch crystal, printed circuit board, battery, and wrist, ensuring all elements are at the same potential, thus improving capacitance detection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a non-electrically conductive material is used for the watch case, then aesthetic freedom and material versatility are improved, but capacitance detection reliability deteriorates due to fluctuating body potential

Engineering Contradiction:

Improvematerial choice freedomVSAvoidcapacitance detection reliability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The battery cover is made electrically conductive and connected to the case to create an equipotential reference plane. This ensures that the body and all detection elements are at the same electrical potential, eliminating fluctuations and enabling reliable capacitance detection while maintaining the use of non-conductive case materials for aesthetic freedom

Inventive Principle:

Principle #12Equipotentiality

Solution Approach 2:

The conductive battery cover acts as an intermediary element between the battery and the case. It provides a stable electrical reference potential that mediates the capacitance detection process, allowing the system to function reliably without requiring the entire case to be conductive

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If a metal case is used, then capacitance detection reliability is improved by setting body potential to reference potential, but aesthetic freedom and material versatility are restricted

Engineering Contradiction:

Improvecapacitance detection reliabilityVSAvoidmaterial choice freedom

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

Instead of requiring the entire case to be conductive, only the battery cover is made electrically conductive. This localized approach provides the necessary reference potential for reliable detection while allowing the rest of the case to be made from aesthetically flexible non-conductive materials

Inventive Principle:

Principle #3Local quality

3Reliability

If conductive particles are added to plastic material, then capacitance detection reliability is improved, but color freedom deteriorates due to dark coloring

Engineering Contradiction:

Improvecapacitance detection reliabilityVSAvoidcolor choice freedom

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The electrical conductivity function is extracted from the case material itself and assigned to a separate conductive battery cover component. This separation allows the case to maintain its aesthetic color freedom while the conductive cover provides the necessary electrical reference for reliable detection

Inventive Principle:

Principle #2Taking out (Extraction)

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 stabilizes the capacitance variation detection, preventing fluctuations and ensuring accurate operation of the watch by setting all elements to the same electrical potential, enhancing the watch's ability to detect finger presence and perform intended operations.

Implementation Method 1

an electrically conductive sealing gasket between the battery cover and an electrode of the battery

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 2

the touch zones form the two armatures of a capacitor which has a certain capacitance value. This capacitance value is set by the sum of the various stray capacitances of the electronic system seen by an electrode forming a touch zone

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS9016935B2Watch with tactile zones of capacitive type comprising a battery hatch closed by an electrically conducting cover

Publication Date: 2015.04.28 ETA SA MFG HORLOGERE SUISSE

AI summary

A wristwatch with capacitive touch zones including a case made of a non electrically conductive material, the case including a housing in which a battery is housed and which is closed by an electrically conductive battery cover. The electrically conductive battery cover is mounted on the watch case with interposition of an electrically conductive sealing gasket between the battery cover and the battery.