Piezoelectric Driving Device Torque Stability via Frequency Inversion

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Solution Overview

Problem

Piezoelectric driving devices face challenges in generating large torque due to peaky driving characteristics when resonance frequencies of longitudinal and bending vibrations are close, limiting the range of appropriate driving frequencies and making precise control difficult.

Innovation Solution

A piezoelectric driving device is configured with a piezoelectric vibrating body that includes a contact and two piezoelectric elements generating bending and longitudinal vibrations, where the resonance frequency of longitudinal vibration is higher than that of bending vibration, and a driving circuit sets the driving frequency equal to or higher than the resonance frequency of longitudinal vibration to stabilize torque generation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the resonance frequency of bending vibration is set higher than that of longitudinal vibration, then the driving efficiency is improved, but the range of appropriate driving frequency becomes extremely narrow and control becomes difficult

Engineering Contradiction:

Improvedriving efficiencyVSAvoidrange of appropriate driving frequency

Core Design Contradiction:

ProductivityVSAdaptability or versatility

Solution Approach 1:

The patent inverts the traditional frequency relationship by setting the longitudinal vibration resonance frequency higher than the bending vibration resonance frequency. This parameter change expands the usable frequency range from between the two resonances (when bending > longitudinal) to above the longitudinal resonance frequency, allowing broader frequency adaptation while maintaining driving efficiency.

Inventive Principle:

Principle #35Parameter changes

2Speed

If the piezoelectric element is driven in tension driving mode, then the operation can be performed above bending vibration resonance frequency, but the driving force is reduced and large torque cannot be produced

Engineering Contradiction:

Improvedriving frequency rangeVSAvoiddriving force

Core Design Contradiction:

SpeedVSForce

Solution Approach 1:

The patent inverts the conventional approach by raising the longitudinal resonance frequency above the bending resonance frequency. This inversion allows the system to operate in push driving mode (which generates large torque) at frequencies above the longitudinal resonance, rather than being forced into tension driving mode with reduced force.

Inventive Principle:

Principle #13The other way round (Inversion)

3Force

If the piezoelectric element is driven in extrusion driving mode, then large torque can be produced, but the driving frequency must be between the two resonance frequencies which becomes extremely narrow

Engineering Contradiction:

ImprovetorqueVSAvoiddriving frequency range

Core Design Contradiction:

ForceVSAdaptability or versatility

Solution Approach 1:

By changing the parameter relationship between resonance frequencies (making longitudinal > bending), the patent expands the frequency range for extrusion driving mode from a narrow band between two close frequencies to a broader range above the longitudinal resonance frequency, while maintaining large torque production capability.

Inventive Principle:

Principle #35Parameter changes

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 configuration allows for stable generation of large torque and improved control by maintaining a gentle frequency dependence, enabling efficient operation across a broader range of frequencies.

Implementation Method 1

a first piezoelectric element which generates bending vibration in a direction intersecting with the first direction in accordance with a first driving voltage supplied from the driving circuit

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

a second piezoelectric element which generates longitudinal vibration in the first direction in accordance with a second driving voltage supplied from the driving circuit

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS11482661B2Piezoelectric driving device, driving method of piezoelectric driving device, robot, electronic component transport apparatus, printer, and projector

Publication Date: 2022.10.25 SEIKO EPSON CORP

AI summary

A piezoelectric driving device includes a piezoelectric vibrating body and a driving circuit. The piezoelectric vibrating body includes a contact which extends in a first direction and comes into contact with a driven member, a first piezoelectric element which generates bending vibration in a direction intersecting with the first direction in accordance with a first driving voltage, and a second piezoelectric element which generates longitudinal vibration in the first direction in accordance with a second driving voltage. The piezoelectric vibrating body is configured such that a resonance frequency of the longitudinal vibration is higher than a resonance frequency of the bending vibration. The driving circuit sets a driving frequency of each of the first driving voltage and the second driving voltage to be equal to or higher than the resonance frequency of the longitudinal vibration.