Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-09-14
2001-09-11
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S009000, C347S048000, C347S060000, C347S061000
Reexamination Certificate
active
06286924
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for heating an ink jet printhead, and more particularly, to an apparatus and method for heating a substrate of an ink jet printhead using pass transistors.
2. Description of the Prior Art
An ink jet printer is a device that produces images on paper by firing precisely sized droplets of ink at precisely defined positions. Ink jet printers form droplets of ink in different ways. The most popular technique used in the art is the bubble jet. In a bubble jet printer, small resistors or heaters are energized to create heat that vaporizes ink to from a bubble. The expansion that creates the bubble causes a droplet of ink to form and eject from the printhead. A typical bubble jet printhead has 64 or 128 or more nozzles, and all of them can be energized to fire a droplet of ink simultaneously or individually.
Quality of the printed images formed by the droplets fired is a function of the printed spot size. Because the size of the printed spots, among other factors, is dependant on the mass of the individual droplets, better control of the drop mass is desired to improve image quality.
The mass of the ejected droplet is, in turn, a strong function of the ink temperature. Temperature relates to the thermal energy in the ink and the size of the vapor bubble that drives the ink from the firing chamber. In addition, temperature affects the viscosity, which in turn also affects the mass of a drop because of viscous losses in the firing chamber.
Attempts have been made at controlling the temperature of a thermal printhead for the purpose of controlling drop mass and thereby to control spot size and image quality. One technique includes using the thermal drop forming system to heat the printhead when it is not being used to form drops.
Currently there are two approaches to heat the printhead for the purpose of temperature control. The first approach is to use the existing heating resistors to also heat the substrate. In this approach, reduced energy pulses are applied to the drop-creation resistors or heaters. The reduced energy pulses do not contain enough energy to cause bubble nucleation and growth, but are sufficient to increase the temperature of the printhead. A potential drawback of using the active heating resistors to maintain the substrate temperature is the added workload to an already highly stressed, highly cycled component of the printer, which increases the probability of failure.
The second approach is to use separate substrate heaters. These substrate heaters are large area devices. They can be connected to a separate power source. Alternatively, they can be driven by a single power source that also provides power to the drop forming heaters during margin operations of the printer as disclosed in U.S. Pat. No. 5,734,392, which is incorporated herein by reference for the purpose of providing background information only. However, using a separate power source increases production cost while using a single power source does not provide a continuous substrate heating mechanism.
Therefore, the need still exists in the art for alternative printhead heating mechanism so as to better control the temperature of a thermal ink printhead.
SUMMARY OF THE INVENTION
The present invention relates to an apparatus and method for heating an ink jet printhead. Among other things, the present invention relates to the use of at least one pass transistor for substrate heating, in addition to the use of it for controlling of ink drop firing. The present invention makes a switch-free, more reliable and cost-efficient ink jet printhead temperature controlling system possible.
In this regard, one aspect of the invention relates to a circuit for controlling an ink jet printhead nozzle, where the printhead nozzle is located in a substrate. In one embodiment of the invention, the circuit includes a drive transistor having a drain, a gate and a source. The drain of the drive transistor is electrically coupled to an ink heating resistor and the source of the drive transistor is grounded. The circuit also includes an enable transistor having a drain, a gate and a source. The drain of the enable transistor is electrically coupled to the gate of the drive transistor and the source of the enable transistor is grounded. Moreover, the circuit has a pass transistor with a drain, a gate and a source. The source of the pass transistor is electrically coupled to both the gate of the drive transistor and the drain of the enable transistor.
In this embodiment, the on resistances of the drive transistor, the enable transistor and the first pass transistor are selected such that in a first operation mode, the first pass transistor and the enable transistor are active thereby to allow a first current to flow through both the first pass transistor and the enable transistor sufficient to generate heat and warm the substrate, and to generate a voltage between the drain and source of the enable transistor sufficient to activate the drive transistor allowing a second current to pass through the heating resistor and the drive transistor to cause the printhead nozzle to fire. The circuit may be operated at the first operation mode by applying a logic high to the gate of the first pass transistor, and a logic high to the gate of the enable transistor. The drive transistor is activated when the voltage between the drain and source of the enable transistor is sufficient to constitute a logic high to the gate of the drive transistor.
Additionally, the on resistances of the drive transistor, the enable transistor and the first pass transistor may be selected such that in a second operation mode, the first pass transistor and the enable transistor are active thereby to allow a third current to flow through both the first pass transistor and the enable transistor sufficient to generate heat and warm the substrate, and to generate a voltage insufficient to activate the drive transistor so that no current passes the heating resistor to cause the printhead nozzle to fire. The circuit may be operated at the second operation mode by applying a logic high to the gate of the first pass transistor, and a logic high to the gate of the enable transistor, but the voltage between the drain and source of the enable transistor is not sufficient to constitute a logic high to the gate of the drive transistor.
Furthermore, the circuit can include a plurality of second pass transistors. Each second pass transistor has a drain, a gate and a source. The drains of the plurality of the second pass transistor are electrically coupled in common to the drain of the enable transistor, and the sources of the plurality of the second pass transistors are grounded. If the circuit is in the first operational mode, at least one of the plurality of second pass transistors is active to allow a fourth current to flow through both the first pass transistor and the at least one of the plurality of second pass transistors sufficient to warm the substrate. On the other hand, if the circuit is in the second operational mode, at least one of the plurality of second pass transistors is active to allow a fifth current to flow through both the first pass transistor and the at least one of the plurality of second pass transistors sufficient to warm the substrate.
Another aspect of the invention relates to an ink jet printhead. The ink jet printhead includes a plurality of individually controllable ink jet nozzles, wherein each of the controllable ink jet nozzles is positioned in a substrate. The ink jet printhead also includes a plurality of ink jet nozzle control circuits, wherein each of the plurality of ink jet nozzle control circuits is positioned near a corresponding one of the plurality of individually controllable ink jet nozzles. Each ink jet nozzle control circuit includes a first switch element having a command input, a current input and a current output. The current input of the first switch element is electrically coupled to a first current source through a h
Ahne Adam Jude
Anderson Frank Edward
Barlow John
Dudding Alfred E.
Lexmark International Inc.
Needle & Rosenberg P.C.
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