Piezoelectric Element Protection Circuit for Inkjet Print Heads
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Solution Overview
Problem
Piezoelectric elements in liquid discharge apparatuses, such as ink jet printers, are prone to reduced piezoelectric characteristics and breakage due to the application of reverse-polarity electric fields, especially when using thin-film piezoelectric bodies, which can lead to leakage and operational failures.
Innovation Solution
Incorporating a second switch that can electrically connect or disconnect the first and second electrodes of the piezoelectric element, allowing for the suppression of reverse-polarity electric fields by maintaining a predetermined potential difference and using a comparison unit to control the switching based on electrode potentials, thereby preventing excessive or high reverse-polarity electric field applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the potentials of the lower electrodes of the piezoelectric elements are set to a predetermined potential differing from ground potential, then leak current between the upper electrodes and the lower electrodes is suppressed, but reverse-polarity electric fields may be easily applied to the piezoelectric elements causing breakage or reduced piezoelectric characteristics
Solution Approach 1:
A protection portion is introduced as an intermediary component between the drive signal supply circuit and the piezoelectric element. This protection portion includes a switch that mediates the electrical connection, allowing the system to benefit from both leak current suppression (by maintaining predetermined potential) and reverse-polarity protection (by controlling switch state based on potential comparisons).
Solution Approach 2:
The system implements feedback control by using a comparison unit to continuously monitor the potentials of the upper and lower electrodes. Based on the comparison result, a control unit adjusts the switch state to prevent reverse-polarity electric fields from being applied to the piezoelectric element, while still allowing the predetermined potential to be maintained for leak current suppression.
2Productivity
If thin-film piezoelectric bodies are used, then the discharge portions can be manufactured by MEMS technique with high density, but the piezoelectric bodies are easily broken due to application of electric fields having polarity reverse to that in the poling
Solution Approach 1:
The protection portion acts as a protective intermediary that shields the thin-film piezoelectric body from harmful reverse-polarity electric fields. This allows the system to achieve high discharge portion density through MEMS manufacturing techniques while protecting the fragile thin-film piezoelectric bodies from breakage.
Solution Approach 2:
The system applies beforehand cushioning by proactively preventing reverse-polarity electric fields from reaching the piezoelectric elements through the protection portion's switch control mechanism. This advance protection prevents breakage before it can occur, enabling the use of thin-film piezoelectric bodies in high-density configurations.
3Reliability
If a protection portion with switch is added to suppress reverse-polarity electric fields, then piezoelectric element breakage is prevented, but device complexity increases
Solution Approach 1:
The protection portion is designed to serve multiple functions: it protects against reverse-polarity electric fields, maintains the predetermined potential for leak current suppression, and integrates with the existing drive signal supply circuit. This multi-functionality reduces the need for separate complex protection circuits.
Solution Approach 2:
The protection portion is merged with the existing drive signal supply circuit structure. The switch, comparison unit, and control unit are integrated into the circuit that already supplies drive signals to the piezoelectric elements, combining the protection function with the existing signal delivery infrastructure to minimize additional complexity.
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 solution effectively suppresses the application of reverse-polarity electric fields, reducing the risk of piezoelectric element breakage and maintaining high piezoelectric performance, even in high-density discharge configurations with thin-film piezoelectric bodies.
Implementation Method 1
The piezoelectric elements are displaced by, for example, supplying a drive signal to the upper electrodes and applying a voltage in accordance with the drive signal to between the upper electrodes and the lower electrodes
Data Source
AI summary
A liquid discharge apparatus includes a piezoelectric element that has a first electrode, a piezoelectric body, and a second electrode, a first switch that is capable of switching whether to supply a drive signal for driving the piezoelectric element to the first electrode, and a second switch that is arranged electrically in parallel with the piezoelectric element and is capable of switching whether to electrically connect the first electrode and the second electrode to each other.