Piezoelectric Locking Mechanism for Watch Hands

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Solution Overview

Problem

Electro-mechanical watches face challenges in maintaining time indication hands at high unbalance during mechanical shocks due to high positioning torque requirements, which can lead to shifting and increased electrical consumption.

Innovation Solution

A mechanism using a piezoelectric actuator or electro-active polymer to lock a wheel of the gear wheels between motor activations, allowing for reduced electrical consumption and improved shock resistance by blocking the wheel directly or in combination with a lock, enabling the electric motor to maintain needle position without excessive torque.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high positioning torque is used to maintain hand position during shocks, then hand stability is improved, but electrical consumption increases

Engineering Contradiction:

Improvehand stability during shockVSAvoidelectrical consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent replaces the traditional mechanical spring-based locking system with a piezoelectric actuator that uses electro-mechanical conversion to achieve locking and unlocking functions. This substitution reduces the continuous electrical torque required while maintaining hand stability during shocks, as the piezoelectric element provides intermittent mechanical locking only when needed.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The piezoelectric actuator operates periodically by applying voltage only during critical moments (when locking is needed to prevent hand displacement during shocks), rather than maintaining continuous electrical torque. This periodic activation significantly reduces overall electrical consumption while ensuring hand stability when required.

Inventive Principle:

Principle #19Periodic action

2Reliability

If high positioning torque is used to prevent hand shifting, then shock resistance is improved, but the electric motor cannot rotate

Engineering Contradiction:

Improveshock resistanceVSAvoidmotor rotation capability

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent replaces the continuous mechanical torque transmission system with a piezoelectric locking mechanism that provides intermittent mechanical constraint. This allows the electric motor to rotate freely during normal operation without resistance, while still providing shock resistance when the piezoelectric actuator activates to lock the gear train.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The locking system transitions from a static high-torque mechanical connection to a dynamic piezoelectrically-controlled locking mechanism. The system is flexible during normal operation (allowing motor rotation) but becomes rigid when locking is required (providing shock resistance), optimizing both motor operation and shock protection.

Inventive Principle:

Principle #15Dynamics

3Reliability

If a traditional locking mechanism is used between motor activations, then hand position stability is improved, but device complexity increases

Engineering Contradiction:

Improvehand position stabilityVSAvoidlocking mechanism complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces complex multi-component mechanical locking mechanisms with a single piezoelectric actuator that achieves the same locking function through electro-mechanical conversion. This simplification reduces the number of parts, assembly steps, and potential failure points while maintaining hand position stability between motor activations.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 reduces electrical consumption and enhances the watch's ability to maintain time indication hands at high unbalance during shocks, with the piezoelectric actuator providing a strong locking force and efficient energy use.

Implementation Method 1

A mechanism using a piezoelectric actuator or electro-active polymer to lock a wheel of the gear wheels between motor activations

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

an electro-active polymer element or a shape-memory alloy element, which heats up when an electric current passes through it and thus deforms

Methodology Applied

Scientific EffectElectro-active polymer effect: Electroactive Polymer

Implementation Method 3

an electro-active polymer element or a shape-memory alloy element, which heats up when an electric current passes through it and thus deforms

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentEP2735923B1Drive mechanism for the hands of an electro-mechanical watch, provided with a locking device

Publication Date: 2019.04.24 ETA SA MFG HORLOGERE SUISSE

Figure 1
Figure 2a~3b
Figure 4a~5b

AI summary

The mechanism (1) has a set of gear wheels (3-7) connected to an electric motor (2) to move the hands forward or backward on each actuation of the electric motor. A locking device (20) includes a piezoelectric actuator (21) for locking a wheel between actuations of the electric motor in a rest mode via a bolt (22). The piezoelectric actuator releases the set of gear wheels when actuated by electrical signal at the moment of each actuation of the electric motor to move the hands forward or backward.