ISFET Printhead Ink Property Sensing

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Solution Overview

Problem

Inkjet printing technologies face challenges in accurately monitoring and adjusting ink properties, such as pH, over time due to variations in ion concentrations, which can affect print quality and reliability.

Innovation Solution

Integration of ion-sensitive field effect transistors (ISFETs) within the printhead, capacitively coupled with electrodes, to detect changes in ink ion concentrations, enabling real-time measurement and analysis of ink properties like pH, using a print controller and computer-based analysis.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If inkjet printing is performed over time, then productivity increases, but ink property stability deteriorates due to ion concentration changes

Engineering Contradiction:

Improveprinting outputVSAvoidink property stability

Core Design Contradiction:

ProductivityVSStability of the object's composition

Solution Approach 1:

The system continuously monitors ink properties using ISFET sensors integrated into the printhead and adjusts printing parameters based on detected changes in ion concentration or pH, creating a closed-loop feedback system that maintains print quality despite ink degradation over time

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The printhead performs self-diagnosis by integrating sensing capabilities directly into the printing component, allowing it to autonomously detect ink property changes and trigger appropriate responses without external intervention

Inventive Principle:

Principle #25Self-service

2Measurement precision

If ink is monitored externally, then measurement capability is provided, but device complexity and loss of time increase

Engineering Contradiction:

Improveink property detectionVSAvoidsystem complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The sensing functions are merged with the printhead structure itself, integrating ISFET sensors and electrodes directly into the printing component rather than using separate external monitoring systems, thereby reducing overall system complexity and improving measurement speed

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The printhead is designed to perform multiple functions simultaneously: it acts as both the printing device and the sensing device, with the same component structure used for both ink ejection and property monitoring

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Device complexity

If ink properties are not monitored, then device complexity is reduced, but print quality reliability deteriorates

Engineering Contradiction:

Improvesystem simplicityVSAvoidprint quality reliability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The system replaces complex mechanical or chemical monitoring methods with solid-state ISFET sensors that provide reliable electrical signals for detecting ink property changes, maintaining simplicity while improving reliability

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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

Enables precise monitoring and adjustment of ink properties, ensuring consistent print quality by detecting shifts in threshold voltage corresponding to ion concentration changes, thereby improving the reliability and performance of inkjet printing systems.

Implementation Method 1

An electrode is disposed in each of the chambers having an ISFET and capacitively coupled to said ISFET through a dielectric

Methodology Applied

Scientific EffectCapacitive coupling: Capacitance

Implementation Method 2

At least one ion-sensitive field effect transistor (ISFET) is disposed in a respective at least one of the chambers. The ISFET can be configured to be responsive to particular ion concentrations in the ink, such as pH

Methodology Applied

Scientific EffectIon-sensitive field effect transistor sensing:

Implementation Method 3

An electrical current is passed through the heating element. As the heating element generates heat, a small portion of the fluid within the firing chamber is vaporized

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 4

The vapor rapidly expands forcing a small droplet out of the firing chamber and nozzle. The electrical current is then turned off and the heating element cools. The vapor bubble rapidly collapses, drawing more fluid into the firing chamber

Methodology Applied

Scientific EffectVaporization and condensation: Phase Change

Data Source

PatentUS9908332B2Ink property sensing on a printhead

Publication Date: 2018.03.06 HEWLETT PACKARD DEVELOPMENT COMPANY LP

AI summary

Ink property sensing on a printhead is described. In an example, a substrate for a printhead includes a cap layer having bores. Chambers are formed beneath the cap layer in fluidic communication with the bores. Fluid ejectors are disposed in at least a portion of the chambers. At least one ion-sensitive field effect transistor (ISFET) is disposed in a respective at least one of the chambers. An electrode is disposed in each of the chambers having an ISFET and capacitively coupled to said ISFET through a dielectric.