Print head drive scheme

Details Print head drive scheme Print head drive scheme

2000-06-08

2002-08-13

Barlow, John (Department: 2853)

Incremental printing of symbolic information

Ink jet

Controller

C347S058000

Reexamination Certificate

active

06431677

ABSTRACT:

TECHNICAL FIELD
The invention relates generally to ink jet printers. More particularly, the invention relates to an improved method and apparatus for addressing nozzles in an inkjet printhead through address lines, quadrature lines and primitive lines.
BACKGROUND OF THE INVENTION
An ink jet print head cartridge has a number of nozzles on a printhead that are used to expel drops of ink onto a printing surface. As the printhead cartridge body scans across a printing surface at a predetermined speed, the nozzles on the printhead are fired at precisely determined times to expel drops of ink and produce an image on the printing medium. Due to design constraints, an ink jet printhead can only fire a certain number of nozzles in a given amount of time. Thus, the time required to print an image is fixed by the rate at which the printhead can fire the nozzles. One way to decrease the time required to print an image with an ink jet printer is to address and fire an increased number of nozzles in a given amount of time as the ink jet printhead cartridge body moves across the page to be printed. However, for any given clock rate, more input data lines are required to address and fire an increased number of nozzles in a fixed amount of time. Unfortunately as the number of input lines to the ink jet printhead increases, so does the cost and complexity of manufacturing the printhead. Thus, increasing the number of data lines leads to a more expensive printhead that is capable of firing more nozzles in a fixed amount of time.
Typically, printing a higher resolution image requires more nozzle firings per unit area than does printing a lower resolution image. One way to increase the number of nozzle firings per unit area is to fire more nozzles in a fixed amount of time as the printhead cartridge body passes over the printing medium as discussed above. However, a low cost alternative for printing a higher resolution image is to have the ink jet printhead cartridge body make multiple passes over the same print region. For example, if a printhead can fire all of its nozzles simultaneously, it can print a full resolution image in one pass. However, if the printhead only has enough address lines to fire one quarter of the nozzles in one pass, the printhead will have to make four passes before printing a full resolution image. Thus, the number of address lines required to print an image can be decreased by having the ink jet printhead cartridge body make multiple passes over the printing region. While such a printhead drive scheme allows an image to be printed with a decreased number of address lines, the time required to print the image is increased. Thus, having the ink jet printhead cartridge body make multiple passes is a low cost alternative for minimizing the number of address lines to the ink jet printhead.
Prior three-dimensional addressing techniques provide an addressing dimension by switching the ground connection at the drain of the power FET. Switching the ground increases the impedance losses in the heater resistor path, which requires a higher voltage be used to maintain the same energy delivered to the heater. The higher voltage makes greater demands on the voltage breakdown requirements of the heater chip logic. Further, additional active devices in the heater path increase the variance in the energy delivered to the heater which results in poor print quality.
What is needed, therefore, is a three-dimensional addressing scheme that does not require ground switching and thereby does not require a high voltage driver.
SUMMARY OF THE INVENTION
The foregoing and other needs are met by an improved printhead drive scheme for activating printing elements on a printhead of an ink jet printer. The invention provides a method of selectively activating a printing element within an array of printing elements on a printhead of an ink jet printer. The method is used with a printhead that includes pass-gate devices and power devices associated with corresponding printing elements. The pass-gate devices and power devices each have a source, drain, and gate, where the source of each pass-gate device is connected to the gate of a corresponding one of the power devices, and where the source of each power device is connected to a corresponding one of the printing elements. According to the method, a quadrant selection signal is provided to a subset of the pass-gate devices, and a subset of printing elements are identified in the array of printing elements based on the quadrant selection signal. An address signal is provided to a group of the power devices, and a group of printing elements is identified within the subset of printing elements based on the address signal. A primitive signal is provided to the group of printing elements on the printhead, and a printing element is activated within the group based on the primitive signal.
In another aspect, the invention provides an ink jet printing apparatus for generating a printed image on a print medium. The apparatus includes an array of resistive heating elements for heating adjacent ink and thereby causing the ink to be expelled onto the print medium. A subset selection circuit selects subsets of the resistive heating elements to be activated based on subset selection signals. A group selection circuit selects groups of the resistive heating elements within a selected subset to be activated based on group selection signals. A primitive selection circuit provides primitive selection signals to resistive heating elements within a selected group, where the primitive selection signals activate individual resistive heating elements within the selected group. The apparatus also includes power switching devices for controlling activation of corresponding resistive heating elements based on the group selection signals, and pass switching devices for providing the group selection signals to corresponding power switching devices based on the subset selection signals.
The above discussed method and apparatus for addressing and activating the resistive heating elements of an ink jet printhead allow for a greater number of resistive heating elements to be addressed and activated with a reduced number of data lines running between the printhead and the printer controller. Reducing the number data lines decreases the complexity and the production cost of the ink jet printhead. Since most ink jet printhead assemblies are designed to be disposable, a method and apparatus which reduces their cost represents a substantial improvement over the prior art.
The invention further provides a three dimensional addressing scheme that does not require ground switching in order to address the third dimension of circuitry elements. The integrated circuit on the printhead utilizes a pass gate design to switch on/off a power FET in the current path of the heater resistor. The address lines are connected to the drain side of the pass device, and the quad lines are connected to the gate of the same pass device. The source of the pass device is used to drive the gate of the power FET connected to the heater resistor. Thus, when the address, quad, and primitive lines for a particular heater resistor are all high, the resistor is energized. This technique provides three-dimensional addressing without switching the ground at the power FET drain.


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