Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-10-26
2001-06-19
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C345S012000, C358S461000
Reexamination Certificate
active
06247786
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally directed to mechanism management in an ink jet printer. More particularly, the present invention is directed to adjusting the amount of image data to be printed during a pass of ink jet print heads in an ink jet printer based on the current available capacity of a pass buffer in the printer and the amount of data available from a host computer.
BACKGROUND OF THE INVENTION
Generally, an ink jet printer prints an image on a page by ejecting droplets of ink from one or more vertical columns of nozzles on a print head. The droplets are ejected to form a matrix of dots as the print head passes horizontally across the page. For each dot which makes up the image, there is image data describing which nozzle is to print the dot during a particular pass and describing the horizontal position on the page at which to print the dot. Typically, prior to a pass of the print head across the page, the image data is temporarily stored in a memory location, sometimes referred to as a pass buffer. As the print head makes a pass, the image data is transferred from the pass buffer to the print head.
The amount of image data to be stored in a pass buffer depends on the print resolution (number of dots per inch), the page width, and the number of nozzles on the print head. As the number of nozzles on the print head increases, so does the demand for pass buffer space to store the image data. Since pass buffer capacity is limited by hardware design considerations, depending on the particular characteristics of the image to be printed, it may not be possible to store a full pass of image data in the pass buffer all at once.
One approach to handling the problem of limited pass buffer capacity or limited data available from the host is to load as much image data into the pass buffer as it will hold, or as much data as is available, which may be only a portion of a pass, and then print that portion of the pass using the entire print head height. When the print head has printed the portion of the pass, the print head pauses while the pass buffer is refilled with image data. This approach is problematic because it reduces print quality. To obtain the highest print quality using an ink jet printer, it is important not to stop the print head while printing a page. Pausing the print head within a pass causes mechanical difficulties because the print head must be repositioned precisely when the pass is completed after stopping. Pausing at either margin causes variations in ink drying time. Uneven drying times cause undesirable print defects. Further, pausing the print head is perceptually undesirable to the user.
Therefore, a system is needed for managing image data in the pass buffer of an ink jet printer to prevent pass buffer overflow and to prevent undesirable pauses while printing an image.
SUMMARY OF THE INVENTION
The foregoing and other needs are met by a method for transferring to an ink jet print head data that describes an image, and for printing the image on a print medium. The method is used with a print head having n number of nozzles in a vertical array for sequentially ejecting vertical columns of ink droplets onto the print medium as the print head scans horizontally across the image. The vertical columns of ink droplets ejected during a single pass of the print head collectively comprise a swath of the image. The method includes the steps of receiving the data from a data source, and determining an amount of memory space, such as in a pass buffer, needed to hold the an amount of data required to print a swath of the image using all n of the nozzles. The method determines a current available capacity of a memory device, such as a pass buffer, to be used for storing the data. A ratio
1
is calculated according to:
ratio
1
=
current
available
capacity
of
the
memory
device
memory
space
needed
to
hold
data
required
to
print
a
swath
using
all
n
nozzles
,
(
1
)
and a value ratio is determined according to:
ratio=ratio
1
. (2)
A portion of the data that describes a swath of the image to be printed using a number m of the nozzles is transferred to the memory device, where:
m≦ratio×n, for ratio<1, and (3)
m=n, for ratio≧1, and where (4)
The portion of the data that describes the swath of the image to be printed using the m number of the nozzles is transferred from the memory device to the print head, and the swath of the image is printed on the print medium using the m number of the nozzles.
Thus, for those passes in which the amount of data required to print a full swath using all n of the nozzles is larger than the pass buffer capacity, only a lesser number, m, of the nozzles are used. In this way, the invention ensures that no more data is written to the pass buffer than the pass buffer can hold for the next swath to be printed. This prevents the print head from being forced to stop during or between passes to wait for the pass buffer to reload. By avoiding undesirable pauses in the printing of an image, the invention provides for consistent ink drying times from pass to pass, thus improving the overall printed image quality. Another consequence of this method is that the print head moves continuously, which is more satisfying to the user than a method that causes the print head to make obvious pauses.
Preferred embodiments of the invention can choose to use only a portion of the vertical print head height based upon the amount of data available from the host at the time that the print head completes a pass and is ready to accept data for the next pass. According to these embodiments of the invention, an amount of the image data received from the data source is determined, and a ratio
2
is calculated according to:
ratio
2
=
amount
of
image
data
received
from
the
data
source
amount
of
image
data
required
to
print
a
swath
using
all
n
nozzles
.
(
5
)
In this embodiment, ratio is the lesser of ratio
1
and ratio
2
, and is calculated according to:
ratio min[ratio
1
, ratio
2
]. (6)
Thus, based on the value of ratio calculated according to equations (2) or (6), a partial pass of the print head can be made using the subset m of the possible n nozzles without pausing the movement of the print head.
In an extreme case where the value of ratio is less than some predetermined minimum value, preferred embodiments of the invention pause the print head motion until either the amount of available memory space or the amount of image data are great enough to cause the value of ratio to be larger than the predetermined minimum.
REFERENCES:
patent: 5347617 (1994-09-01), Webb et al.
patent: 5511890 (1996-04-01), Momose
patent: 5563712 (1996-10-01), Nahata
patent: 5619233 (1997-04-01), Harrington
patent: 5696888 (1997-12-01), Ikeda
patent: 5760807 (1998-06-01), Yamazaki et al.
patent: 5764867 (1998-06-01), Sato
patent: 5816714 (1998-10-01), Hori
patent: 5970222 (1999-10-01), Gusmano et al.
patent: 6028676 (2000-02-01), Nakao
Booth James Ronald
Rivers Martin Geoffrey
Le N.
Lexmark International Inc.
Neely, Esq. Andrew S.
Nguyen Lamson D.
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