Piezoelectric Element Tapered Vibration Portion Stress Distribution
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Solution Overview
Problem
Piezoelectric elements in liquid ejecting heads, such as ink jet recording heads, face challenges with stress concentration at the end portions, leading to potential fracture due to the difficulty in forming beam portions near the ends, which affects the reliability and displacement of the vibrating plates.
Innovation Solution
A piezoelectric element design featuring a vibrating plate with a second vibration portion having a taper part with increased thickness towards the first vibration portion, and a first electrode with a similar thickness variation, helps in distributing stress and preventing fracture by increasing the thickness at the end portions where stress is concentrated.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a beam portion with reduced thickness is provided at the arm to increase vibrating plate displacement, then the displacement is improved, but the piezoelectric element may be fractured due to stress concentration at the end portion
Solution Approach 1:
The patent applies local quality by creating a thickness gradient in the vibrating plate - the plate has reduced thickness at the arm portion for high displacement, but gradually increases thickness toward the end portion where the piezoelectric element is located. This local variation in thickness provides both the displacement benefit of thin sections and the stress distribution benefit of thick sections near the piezoelectric element, preventing fracture while maintaining performance.
2Reliability
If the thickness of the vibrating plate is increased at the end portion, then the fracture resistance is improved, but the displacement of the vibrating plate is reduced
Solution Approach 1:
The vibrating plate is segmented into multiple regions with different thickness characteristics: a thin arm portion for displacement, a gradual transition zone, and a thicker end portion for stress resistance. This segmentation allows each region to optimize its function - the thin portion maximizes displacement while the thick portion minimizes stress concentration, resolving the contradiction between displacement and fracture resistance.
3Reliability
If a beam portion is formed in the vicinity of the end portion of the piezoelectric element, then the stress concentration is reduced, but it is difficult or impossible to form the beam portion at the end portion
Solution Approach 1:
Instead of forming a beam portion in the planar dimension near the end portion (which is difficult or impossible), the patent transitions to the thickness dimension by creating a gradual thickness increase from the arm toward the end portion. This dimensional approach to stress distribution avoids the manufacturing difficulties of forming beam structures at the end portion while still achieving the goal of reducing stress concentration.
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 design enhances the reliability of the piezoelectric element by reducing the likelihood of fracture and maintaining satisfactory displacement during deformation, thereby improving the ejecting characteristics of the liquid ejecting head.
Implementation Method 1
a piezoelectric element which includes a vibrating plate, a first electrode provided over the vibrating plate, a piezoelectric layer provided over the first electrode, and a second electrode provided over the piezoelectric layer
Data Source
AI summary
Provided are a vibrating plate, a first electrode provided over the vibrating plate, a piezoelectric layer provided over the first electrode, and a second electrode provided over the piezoelectric layer are provided. The piezoelectric layer is interposed between the first electrode and the second electrode. The piezoelectric layer includes an active portion of which at least one end portion is defined by the first electrode, and a non-active portion provided on an outside of the end portion of the first electrode for defining the active portion. The vibrating plate includes a first vibration portion under the non-active portion and a second vibration portion on an outside of the first vibration portion. The second vibration portion includes a taper part having the thickness which is increased toward the first vibration portion.