Ink level sensor and related methods

Patent metadata

Field	Value
Publication number	US-9599500-B2
Application number	US-201114123522-A
Country	US
Kind code	B2
Filing date	Jun 27, 2011
Priority date	Jun 27, 2011
Publication date	Mar 21, 2017
Grant date	Mar 21, 2017

Abstract

In an embodiment, a method of sensing an ink level includes applying a pre-charge voltage Vp to a sense capacitor to charge the sense capacitor with a charge Q 1 , sharing Q 1 between the sense capacitor and a reference capacitor, causing a reference voltage Vg at the gate of an evaluation transistor, and determining a resistance from drain to source of the evaluation transistor that results from Vg.

First claim

What is claimed is:

1. An ink level sensor comprising:
a sense capacitor whose capacitance changes with a level of ink in a chamber;
a first switch to apply a voltage Vp to the sense capacitor, placing a charge on the sense capacitor;
a second switch to share the charge between the sense capacitor and a reference capacitor, resulting in a reference voltage Vg; and
an evaluation transistor configured to provide a drain to source resistance in proportion to the reference voltage.

2. An ink level sensor as in claim 1 , wherein the sense capacitor comprises:
a metal plate;
a passivation layer over the metal plate; and
substance within a chamber above the passivation layer.

3. An ink level sensor as in claim 2 , wherein the substance is selected from the group consisting of ink, ink and air, and air.

4. An ink level sensor as in claim 1 , wherein the reference capacitor comprises gate capacitance of the evaluation transistor.

5. An ink level sensor as in claim 1 , further comprising a sense structure that includes the sense capacitor, the chamber, a nozzle, a metal plate firing element disposed within the fluid chamber, a passivation layer over the firing element, and an insulating layer on a silicon substrate.

6. An ink level sensor as in claim 1 , further comprising a clearing resistor to purge ink residue from the chamber.

7. An ink level sensor as in claim 2 , wherein the metal plate comprises a resistor firing element.

8. An ink level sensor as in claim 2 , further comprising a parasitic elimination element to eliminate a parasitic capacitance formed under the metal plate.

9. An ink level sensor as in claim 8 , wherein the parasitic elimination element comprises a conductive poly silicon layer.

Assignees

• Ge Ning
• Benjamin Trudy
• Neo Teck-Khim
• Torgerson Joseph M
• Banerjee Neel
• Corrigan Iii George H
• Hewlett Packard Development Co Lp

Inventors

• Ge Ning
• Benjamin Trudy
• Neo Teck-Khim
• Torgerson Joseph M
• Banerjee Neel
• Corrigan Iii George H

Classifications

• G01F23/263 Primary

  by measuring variations in capacitance of capacitors · CPC title

• B41J2/14153 Primary

  Structures including a sensor · CPC title

• B41J2/175 Primary

  Ink supply systems {; Circuit parts therefor} · CPC title

• B41J2/17566

  Ink level or ink residue control · CPC title

• B41J2002/17579

  Measuring electrical impedance for ink level indication · CPC title