Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
1999-11-01
2001-09-18
Hilten, John S. (Department: 2854)
Incremental printing of symbolic information
Ink jet
Medium and processing means
C400S579000, C400S582000
Reexamination Certificate
active
06290351
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to printers such as ink jet printers, and more particularly to such a printer including a precision sheet transport control method and apparatus for minimizing printed image misregistration and other observable printed image defects.
An ink jet printer of the type frequently referred to as drop-on-demand, has at least one printhead from which droplets of ink are directed towards a recording medium. Within the printhead, the ink is contained in a plurality of channels. Piezoelectric devices or power pulses cause the droplets of ink to be expelled as required, from orifices or nozzles located at the end of the channels. In thermal ink jet printing, the power pulses are usually produced by resistors also known as heaters, each located in a respective one of the channels. The heaters are individually addressable to heat and vaporize the ink in the channels. As a voltage is applied across a selected heater, a vapor bubble grows in that particular channel and ink bulges from the channel nozzle. At that stage, the bubble begins to collapse. The ink within the channel retracts and then separates from the bulging ink thereby forming a droplet moving in a direction away from the channel nozzle and towards the recording medium whereupon hitting the recording medium a spot is formed. The channel is then refilled by capillary action which, in turn, draws ink from a supply container of liquid ink.
The ink jet printhead may be incorporated into either a carriage type printer or a page width type printer. The carriage type printer typically has a relatively small printhead containing the ink channels and nozzles. The printhead is usually sealingly attached to a disposable ink supply cartridge and the combined printhead and cartridge assembly is attached to a carriage which is reciprocated to print one swath of information (equal to the length of a column of nozzles) at a time on a stationary recording medium, such as a sheet of paper or a transparency.
After each such swath is printed, the sheet of paper is transported or advanced forwardly (usually the movement involves stepping or indexing) a distance that is equal to the height of the printed swath or of a portion thereof so that the next printed swath is properly registered in an overlapping or contiguous manner therewith. The procedure is then repeated until an entire page on the sheet is printed.
Conventional sheet transporting or advancing systems in such printers typically have limited precision due to the limited precision of the mechanical components that make up the system. The predictable and inescapable result of such limited precision is image misregistration. It has been found that when printed material includes misregistration defects of even one-half pixel, such defects will be observable. This is becoming more and more of a problem as the printing industry pushes for lower and lower cost printers with finer and finer levels of pixel resolution, (which has now reached and is exceeding 600 dpi). The reason a one-half pixel misregistration defect is observable is because at 600 dpi a one-half pixel error is equal to about 21 microns.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, there is provided a printer for producing precise registered images is provided and includes a sheet transport and control assembly for moving a sheet of paper along a sheet path through a printing zone. The sheet transport and control assembly includes drive device; a moveable sheet carrying web member having a first edge and a second edge having an array of precision holes, including adjacent holes spaced a precise distance apart, formed through at least the first edge and the second edge. The sheet transport and control assembly also includes a programmable controller connected to the drive device, and a dual sensor assembly mounted along the sheet path and connected to the programmable controller for responsively generating and inputting precision hole position signals to the programmable controller. The dual sensor assembly includes a first sensor for generating a first increasing and decreasing signal, and a second sensor for generating a second increasing and decreasing signal that increases and decreases oppositely relative to the first signal. The programmable controller controls the moving device to move and stop the web member responsively to a desired value of a ratio of the first signal to the second signal, thereby ensuring precise moving and stopping of a sheet of paper on the web member through the printing zone.
Pursuant to another aspect of the invention, there is provided a method of transporting and controlling a sheet for precise image printing through a printing zone of a printing machine. The method includes the steps of mounting within the printing machine a moveable web assembly including a drive device, and an endless sheet carrying web member having a constant path of movement through the printing zone, and a series of holes formed at desired locations along at least one edge thereof; attaching a sheet for image printing onto the web member; and mounting a first sensor, and a second sensor along constant path of movement, for respectively producing a first signal that increases and decreases, and a second signal that increases and decreases oppositely relative to the first signal. The method then includes the steps of connecting a programmable controller to the drive device and to the first and second sets of sensors; and moving and stopping the web member through the printing zone responsively to a desired ratio of the second signal to the first signal, thereby minimizing misregistration and other observable printed image defects in printed images.
REFERENCES:
patent: 5260725 (1993-11-01), Hammond
patent: 5272493 (1993-12-01), Hubble, III et al.
patent: 5947617 (1999-09-01), Kondo
patent: 6059285 (2000-05-01), Suga et al.
patent: 6106090 (2000-08-01), Uchida et al.
Crenshaw Marvin P
Hilten John S.
Nguti Tallam I.
Xerox Corporation
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