Constant current mode firing circuit for thermal inkjet-printing nozzle

Patent metadata

Field	Value
Publication number	US-9283750-B2
Application number	US-13401505-A
Country	US
Kind code	B2
Filing date	May 20, 2005
Priority date	May 20, 2005
Publication date	Mar 15, 2016
Grant date	Mar 15, 2016

Abstract

A firing circuit for a thermal inkjet-printing nozzle includes a heater resistor and a switch. The heater resistor heats ink to cause the ink to be ejected from the nozzle. The heater resistor has a first end and a second end, the second end connected to a ground. The switch controls activation of the heater resistor. The switch has a first end connected to a voltage source and a second end connected to the first end of the heater resistor. The switch operates in a constant current mode, such that an at least substantially constant current flows through the heater resistor upon activation.

First claim

We claim:

1. An inkjet-printing device comprising:
a plurality of inkjet-printing nozzles;
a plurality of firing circuits corresponding to the inkjet-printing nozzles;
a first voltage source at which a parasitic resistance of the firing circuits is concentrated;
a ground,
wherein each firing circuit comprising:
a heater resistor to heat ink to cause the ink to be ejected from the nozzle, the heater resistor having a first end and a second end, the second end connected to the ground; and,
a switch to control activation of the heater resistor, the switch having a first end connected to the first voltage source and a second end connected to the first end of the heater resistor,
wherein the switch operates in a constant current mode, such that an at least substantially constant current flows through the heater resistor upon activation,
wherein the switch is a transistor having a gate, a body, a drain, and a source, the source being the second end of the switch, the drain being the first end of the switch connected to the voltage source, the body connected to the source, and a turn-on voltage applied to the gate to control activation of the heater resistor,
wherein a voltage at the first end of the heater resistor tracks a voltage at the gate, and a current through the heater resistor remains constant, regardless of any fluctuation to voltage provided by the first voltage source at the drain; and

a controller to selectively activate the firing circuits to cause the nozzles to eject ink, such that for each firing circuit that is activated a difference between a voltage at the gate and a voltage at the drain is less than or equal to a voltage between the gate and the source, regardless of the parasitic resistance decreasing the voltage at the drain, the parasitic resistance based on and increasing in correspondence with a number of the firing circuits that are currently firing,
wherein the gate is connected to a turn-on voltage circuit including a second voltage source different than the first voltage source to provide the turn-on voltage greter than a threshold voltage defined between the gate and the source,
and wherein the voltage at the gate when the heater resistor is activated is greater than a voltage at the first voltage source by at most the threshold voltage of the transistor, so that operation of the switch remains in the constant current mode.

2. The inkjet-printing device of claim 1 , wherein operation of the switch in the constant current mode causes the heater resistor to have a voltage at the first end thereof regulated.

3. The inkjet-printing device of claim 1 , wherein the ground to which the second end of the heater resistor is connected is a local ground, such that a voltage at the second end of the heater resistor is unregulated.

4. The inkjet-printing device of claim 1 , wherein the ground to which the second end of the heater resistor is connected is an absolute ground, such that a voltage at the second end of the heater resistor is regulated to zero volts.

5. The inkjet-printing device of claim 1 , wherein the switch operates in a source follower mode so that operation of the switch remains in the constant current mode.

6. The inkjet-printing device of claim 1 , further comprising the turn-on voltage circuit to translate a firing logic signal to a greater voltage needed to turn on the switch to activate the heater resistor.

7. The inkjet-printing device of claim 1 , wherein the transistor is a laterally diffused metal-oxide semiconductor (LDMOS) transistor.

8. The inkjet-printing device of claim 1 , further comprising a conductive plate disposed next to the heater resistor, the conductive plate in physical contact with the ink, the conductive plate being connected to the second ground so that the ink is electrically connected to the second ground.

9. The inkjet-printing device of claim 1 , wherein the parasitic resistance is a first parasitic resistance, a second parasitic resistance at the ground minimized as compared to the first parasitic resistance.

10. An inkjet-printing device comprising:
an inkjet-printing nozzle;
a firing circuit corresponding to the inkjet-printing nozzle;
a first voltage source at which a first parasitic resistance of the firing circuit is concentrated;
a ground at which a second parasitic resistance of the firing circuit is minimized in comparison to the first parasitic resistance;
a heater resistor to heat ink to cause the ink to be ejected from the nozzle, the heater resistor having a first end and a second end, the second end connected to a ground;
a switch to control activation of the heater resistor via a turn-on voltage being applied to the switch, the switch having a first end connected to the first voltage source and a second end connected to the first end of the heater resistor,
wherein the switch operates in a constant current mode, such that an at least substantially constant current flows through the heater resistor upon activation,
wherein the switch is a transistor having a drain at the first end, a source at the second end, and a gate connected to a turn-on voltage circuit, a threshold voltage of the transistor defined between the gate and the source when the transistor is on,
wherein the transistor further has a body connected to the source of the transistor; and
a controller to selectively active the firing circuit to cause the inkjet-printing nozzle to eject ink such that a difference between a voltage at the gate of the transistor and a voltage at the drain of the transistor is less than or equal to the threshold voltage,
wherein the gate is connected to a turn-on voltage circuit a threshold voltage of the transistor defined between the gate and the source,
and wherein is greater than a voltage at the first voltage source by at most the threshold voltage of the transistor, so that operation of the switch remains in the constant current mode.

11. The inkjet-printing device of claim 10 , further comprising a conductive plate disposed next to the heater resistor, the conductive plate in physical contact with the ink, the conductive plate being connected to the second ground so that the ink is electrically connected to the second ground.

Assignees

• Liao Hang
• Yeh Bao
• Kawamoto Galen H
• Schloeman Dennis J
• Clark Richard R
• Hewlett Packard Development Co

Inventors

• Liao Hang
• Yeh Bao
• Kawamoto Galen H
• Schloeman Dennis J
• Clark Richard R

Classifications

• B41J2/0458 Primary

  controlling heads based on heating elements forming bubbles · CPC title

• B41J2/0455

  Details of switching sections of circuit, e.g. transistors · CPC title

• B41J2/0457

  Power supply level being detected or varied · CPC title

• B41J2/04555

  detecting current · CPC title

• B41J2/04541 Primary

  Specific driving circuit · CPC title