Piezoelectric Ejection Head Reinforcing Film for Crack Prevention
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Solution Overview
Problem
Existing liquid ejecting heads with reinforcing films on diaphragms still face stress concentration at the ends of the reinforcing film, leading to potential cracks despite the film's presence, as the diaphragm vibrates at points other than the boundary where the film is provided.
Innovation Solution
A liquid ejecting head design where the reinforcing film is formed along a direction perpendicular to the lamination direction, overlapping the boundary between the partition wall and pressure chamber, and adhering to specific thickness and slope conditions defined by Formulas (1) and (2), thereby dispersing stress and reducing concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reinforcing film is provided on the diaphragm to suppress cracks at the boundary section, then the reliability of the diaphragm is improved, but stress concentration occurs at the end portion of the reinforcing film where it meets the diaphragm, creating a new risk of cracks
Solution Approach 1:
The patent changes the thickness parameter of the reinforcing film from uniform to variable. The film thickness is set to decrease from the boundary section toward the pressure chamber center, with specific slope constraints (a1 and a2) to ensure smooth stress transition. This gradual thickness reduction eliminates abrupt stiffness changes at the film ends, preventing stress concentration while maintaining crack suppression at the boundary section.
2Ease of manufacture
If the reinforcing film is formed with constant thickness to simplify manufacturing, then the ease of manufacture is improved, but stress concentration occurs at the ends of the film, reducing the reliability
Solution Approach 1:
The patent transitions from a constant thickness parameter to a variable thickness parameter with controlled gradients. By defining specific slope constraints (a1 at the boundary and a2 toward the center), the design achieves smooth thickness variation that can be manufactured using conventional techniques while eliminating stress concentration at the film ends.
3Reliability
If the reinforcing film covers the entire diaphragm surface to maximize protection, then the reliability is improved, but the device complexity and material usage increase
Solution Approach 1:
The patent applies local quality by concentrating the reinforcing film only where stress concentration occurs (at the boundary section between the partition wall and pressure chamber) rather than uniformly across the entire diaphragm. The variable thickness design with controlled slopes ensures adequate reinforcement at critical locations while reducing or eliminating the film at non-critical areas, optimizing both reliability and structural simplicity.
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 design effectively reduces stress concentration and prevents cracks by uniformly distributing stress, enhancing the durability and reliability of the diaphragm.
Implementation Method 1
a piezoelectric element that includes a first electrode, a piezoelectric layer, and a second electrode, which are laminated in a lamination direction, and that deforms when a voltage is applied
Data Source
AI summary
A liquid ejecting head includes a piezoelectric element, a diaphragm, a reinforcing film, and a pressure chamber substrate. The reinforcing film is formed along a first direction, overlaps a boundary between the partition wall and the pressure chamber, and satisfies Y1>Y2 and 0<a1<a2 where Y1 is a first thickness of the reinforcing film in the lamination direction at a first position, Y2 is a second thickness of the reinforcing film in the lamination direction at a second position closer to the center of the pressure chamber than the first position, a1 is an absolute value of a slope of a first tangent line, to an inclined surface as a surface of the reinforcing film that is not in contact with the diaphragm, at the first position, and a2 is an absolute value of a slope of a second tangent line at the second position.