Overcurrent Detection for Piezoelectric Printheads
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Solution Overview
Problem
Piezoelectric inkjet printheads are prone to electrical shorts and overcurrent conditions due to defects or deterioration in electrical paths, leading to damage and inoperativity of multiple ink nozzles, which can cascade into failure of entire driver chips.
Innovation Solution
Incorporating a transistor with a diode connected to the piezoelectric actuator and a detection circuit to identify overcurrent conditions, disabling the transistor when excessive voltage is detected to prevent damage and isolate affected units, thereby preventing cascading failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If piezoelectric actuators and ASICs are packed into a small area to increase productivity, then the number of nozzles per unit area increases, but electrical shorts and overcurrent conditions occur more frequently due to defects or deterioration in electrical paths
Solution Approach 1:
The invention divides the electrical connection system into isolated segments, with each nozzle having its own dedicated transistor and detection circuit. This segmentation prevents electrical faults from propagating across the entire array, allowing high-density packaging while maintaining reliability through electrical isolation of individual elements
Solution Approach 2:
The invention introduces individual transistors as intermediary components between the ASIC and each piezoelectric actuator. These transistors serve as protective mediators that can be individually disabled to isolate faults, preventing direct electrical shorts from affecting multiple nozzles simultaneously
2Reliability
If overcurrent detection is implemented to prevent damage to individual units, then reliability of individual nozzles improves, but device complexity increases due to additional detection circuits and transistors
Solution Approach 1:
The invention merges multiple functions into the transistor component: it serves as both the drive switch for the piezoelectric actuator and the overcurrent protection element. The detection circuit reuses existing voltage detection capabilities already present in the driver architecture, avoiding the need for separate complex protection circuits
Solution Approach 2:
The transistor is designed to perform multiple functions: normal operation as a drive switch, overcurrent detection through voltage monitoring at the drain, and automatic protection through gate voltage reduction. This multi-functionality reduces the need for additional dedicated protection components
3Reliability
If electrical shorts occur in densely packed nozzles, then multiple nozzles can become damaged and rendered inoperative, but implementing individual isolation circuits increases manufacturing complexity
Solution Approach 1:
Each nozzle is electrically segmented with its own transistor and detection circuit, allowing faults to be isolated to individual elements. This segmentation is implemented using standard semiconductor fabrication processes, maintaining ease of manufacture while achieving fault isolation
Solution Approach 2:
The system implements self-service protection where the detection circuit automatically detects overcurrent conditions and the transistor automatically reduces its gate voltage to protect itself and connected nozzles. This automatic self-protection eliminates the need for complex external protection circuits or manual intervention
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
Individual fluid ejection units can be disabled to prevent collateral damage to other units, reducing the need for head replacement and maintaining functionality of remaining ASIC outputs.
Implementation Method 1
each including a pumping chamber connected to a nozzle. The piezoelectric material can be electrically coupled to an application-specific integrated circuit (ASIC). The ASIC drives the piezoelectric material, which actuates the pumping chamber and ejects the ink from the associated nozzle.
Implementation Method 2
a detection circuit configured to detect whether a voltage at the drain of the transistor is above a predefined voltage
Data Source
Figure 1
Figure 2
Figure 3A~3C
AI summary
An apparatus, method, and a fluid ejection system for detecting electrical shorts in piezoelectric printheads are described. An apparatus includes a piezoelectric actuator, a transistor whose drain is connected to the piezoelectric actuator, a diode that is connected to a source and the drain of the transistor, a detection circuit configured to detect whether a voltage at the drain of the transistor is above a predefined voltage, and a disabling circuit configured to turning off the transistor in response to detecting that voltage at the drain of the transistor is above the predefined voltage.