Piezoelectric Actuator Plate with Composite Damping Layers
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Solution Overview
Problem
Piezoelectric actuators in ultrasonic motors face inefficiencies due to low coupling coefficients from elastic materials, high stress concentrations, audible noise, slow speeds, high operating voltages, and manufacturing complexities, limiting miniaturization and performance.
Innovation Solution
A piezoelectric actuator with a plate shape and three layers of uniformly polarized material, featuring specific electrode configurations for independent excitation of longitudinal and fourth bending modes, allowing for a thinner design and reduced layer count, which minimizes manufacturing costs and enhances displacement efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If elastic material is used in the vibrating stator element, then the structure can be simpler, but the coupling coefficient decreases resulting in lower efficiency
Solution Approach 1:
The patent uses a composite structure combining piezoelectric material layers with a viscoelastic damping layer. The piezoelectric material (e.g., PZT ceramic) provides high coupling coefficient and efficiency, while the viscoelastic layer provides damping and stress distribution. This composite approach resolves the contradiction by achieving both structural simplicity and high efficiency simultaneously.
2Device complexity
If piezoelectric and elastic elements are bonded together, then the structure can be integrated, but stress concentration occurs at the bonding layer causing detachment
Solution Approach 1:
The patent introduces a viscoelastic damping layer with specific material parameters (loss factor, thickness) between the piezoelectric and elastic elements. This layer changes the stress distribution parameters at the bonding interface, reducing stress concentration and preventing detachment while maintaining structural integration.
Solution Approach 2:
The viscoelastic damping layer acts as an intermediary between the piezoelectric and elastic elements. It mediates the mechanical stress transfer, distributing loads evenly and preventing stress concentration at the bonding interfaces, thus ensuring bonding stability while maintaining integration.
3Force
If multilayer actuators are used to generate sufficient displacement, then the actuator can produce required force, but the number of layers increases making the structure complex and costly
Solution Approach 1:
The patent optimizes the parameters of individual layers, particularly the thickness and material properties of the piezoelectric and viscoelastic layers. By carefully selecting these parameters, sufficient displacement and force are achieved with a reduced number of layers, simplifying the structure while maintaining performance.
4Force
If high number of layers are used to generate sufficient displacement, then the actuator can produce required force, but high operating voltages are still needed
Solution Approach 1:
The composite structure with optimized piezoelectric and viscoelastic layers improves the overall electromechanical coupling efficiency. This allows the actuator to generate sufficient displacement at lower operating voltages compared to traditional multilayer designs, reducing energy consumption while maintaining force output.
5Volume of moving object
If the actuator is designed for miniaturization, then the size can be reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent optimizes the thickness parameters of individual layers to achieve miniaturization. By carefully selecting and controlling these parameters within specific ranges, the actuator size is reduced while maintaining manufacturability and performance, balancing miniaturization with manufacturing precision requirements.
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 actuator achieves significant thickness reduction, improved displacement, and reduced manufacturing costs, while maintaining performance and reliability, enabling higher speeds and quieter operation.
Implementation Method 1
at least three layers of uniformly polarized piezoelectric material stacked in its thickness direction... capable of independently exciting vibrations in a longitudinal mode and a fourth bending mode
Implementation Method 2
capable of independently exciting vibrations in a longitudinal mode and a fourth bending mode... The excited second bending modes are either in thickness or in width direction
Implementation Method 3
At one of the main surfaces, at least one friction element is arranged, which is intended for mechanical or friction contact with an element to be driven by the piezoelectric actuator
Data Source
Figure 1
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AI summary
Disclosed is a piezoelectric actuator (1) for an ultrasonic motor in the shape of a plate with two main surfaces (2) representing the largest surfaces of the plate, where at least one friction element (16) is arranged at one of said main surfaces, two longer side surfaces (3) running in the length direction of the plate and two shorter side surfaces (4) running in the width direction of the plate, the plate having at least three layers (5) of uniformly polarized piezoelectric material stacked in its thickness direction and at least one electrode layer (6) arranged at a main surface constituting outer electrodes (7) and at least two electrode layers (8) each arranged between two adjacent piezoelectric material layers and constituting inner electrodes (9), with the inner electrodes comprising exciting electrodes (10) and common electrodes (11) and with the outer electrodes (7) comprising exciting electrodes (10) and at least one common electrode (11), and with at least one exciting electrode having two first channel electrodes (12) and two second channel electrodes (13) with the first channel electrodes and the second channel electrodes alternately arranged along the length direction of the plate in a spaced manner and thus defining four separate and equally sized sections (14) of the plate, each section representing a generator (15) for a standing wave, and with the polarization direction of adjacent piezoelectric material layers of each generator being opposite to each other.