Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2001-01-22
2002-08-13
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S009000, C347S011000
Reexamination Certificate
active
06431676
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique that generates driving waveforms to actuate driving elements of a print head.
2. Description of the Related Art
A color ink jet printer that ejects several color inks from a print head is one of the output devices of the computer. The ink jet printer expresses multiple tones by distribution of dots. In order to attain the smoother tone expression, some ink jet printers create variable size dots in respective pixels. Some ink jet printers carry out printing in both forward and backward passes of main scan, thereby enhancing printing speed.
The ink jet printer regulates the weight of ink droplets ejected from nozzles of the print head to create the respective dots. For example, the print head with piezoelectric elements regulates the size of each dot by controlling the meniscus or the shape of the ink surface at the nozzle opening and adjusting the ejection timing of the ink droplet. The driving waveform to drive the piezoelectric elements is varied to attain such control and adjustment.
FIG. 18
illustrates a prior art driving waveform to create the variable size dots. The driving waveform includes two element waveforms W
1
and W
2
that are output intervalically. The driving waveform has a interval T corresponding to one pixel division. The first element waveform W
1
is used to create small size dots, and the second element waveform W
2
is used to create medium size dots.
Large size dots are formed in response to both the first element waveform W
1
and the second element waveform W
2
.
Various driving waveforms can be generated by a programmable signal generation circuit. The programmable signal generation circuit intervalically accumulates a preset value of voltage change in the driving waveform, that is, quantities of voltage change per unit time, with an adder, so as to determine the level of the driving waveform.
FIG. 19
is a block diagram illustrating the internal structure of a programmable signal generation circuit
100
.
FIG. 20
shows a process of generating a driving waveform by the prior art programmable generation. The driving waveform generation circuit
100
includes a memory
102
, an accumulator
104
, and a digital-to-analog (D-A) converter
106
. Driving waveform data &Dgr;V
1
, &Dgr;V
2
, and &Dgr;V
3
, each representing a rate of voltage change in the driving waveform, are stored in the memory
102
. Each of the driving waveform data corresponds to a quantity of voltage change in the driving waveform per interval t of a clock signal CLK. The driving waveform data &Dgr;V
1
, &Dgr;V
2
, and &Dgr;V
3
read from the memory
102
are successively accumulated in synchronism with the clock signal CLK by the accumulator
104
. The arithmetic operation gives 18-bit data as the result of accumulation. The upper 10 bits out of the 18-bit result of accumulation are subjected to the D-A conversion carried out by the D-A converter
106
, so as to generate a driving waveform.
The number of reproducible tone levels increases as the number of available dot sizes and, in turn, as the number of element waveforms. There is, however, generally a restriction on the number of element waveforms included in one interval T. The prior art print head accordingly enables only a restricted number of different types of usable dots to be created.
SUMMARY OF THE INVENTION
The object of the present invention is to increase the number of different types of dots usable for printing.
At least part of the above and the other related objects is attained by a technique that selectively generates one of a plurality of different driving waveforms having different shapes at predetermined intervals of selection to actuate driving elements of a print head. The selective use of the plurality of different driving waveforms enables a variety of dots to be created without restriction on the number of element waveforms included in one interval.
In the technique of generating the driving waveforms in a programmable manner, changing the set of driving waveform data varies the resulting driving waveform. The switchover of the driving waveform is accordingly attained by appropriately rewriting the set of driving waveform data stored in the memory according to the desired driving waveform to be generated. This method, however, lengthens the time interval required for switching over the driving waveform. This is because no driving waveform is generated until the writing operation of a next set of driving waveform data is completed. The longer time interval required for the switchover may lower the printing speed and deteriorate the usability of the printing apparatus.
The technique of the present invention provides a specific number of memory areas, which are at least two memory areas and do not overlap one another at least partly, and changes over a working memory area used to generate the driving waveform, thereby switching over the resulting driving waveform. A set of driving waveform data used to generate each of the plurality of different driving waveforms is stored in each of the specific number of memory areas. This arrangement does not require the switchover operation of the working driving waveform to wait for the completion of the writing operation of the driving waveform data, thus attaining the high-speed switchover of the working driving waveform.
In the present invention, the predetermined interval of selection may corresponds to one pixel division. This arrangement effectively increases the number of different types of dots created in one pixel division during one pass of the main scan.
Here the term ‘one pixel division’ represents a time interval required for creating a dot at one pixel. The expression ‘one pixel division’ accordingly corresponds to the interval T of outputting the element waveforms W
1
and W
2
of the driving waveform shown in FIG.
18
. The same principle is adopted in the case where the driving waveform includes three or more factor waveform element waveforms.
The term ‘one pixel division’ also has the following meaning. Printing is generally implemented by creating dots at respective pixel positions specified by a recording resolution. According to the relationship between the velocity of main scan and the driving speed of the print head, dots may be created on a raster line at a pitch of two or more pixels during one pass of the main scan. In one example, it is assumed that dots are created on a printing medium in a pattern shown in
FIG. 1B
in response to a driving waveform COM, which is output repeatedly at a interval T shown in FIG.
1
A. The driving waveform COM output at the interval T enables dots to be created at every other pixel as shown in FIG.
1
B. It is required to create dots in the residual alternate pixels by another pass of the main scan. In this case, the interval T still represents the time interval required for creating a dot at one pixel. The interval T accordingly corresponds to ‘one pixel division’.
The predetermined intervals of selection can be set at a variety of length, for example, intervals of different change rate of the driving waveform or intervals corresponding to one pass of the main scan of the print head.
The switchover of the driving waveform according to the present invention is implemented by a variety of embodiments discussed below.
A first embodiment provides a specific number of memory areas that corresponds to the number of different driving waveforms, and stores a set of driving waveform data corresponding to each of the plurality of different driving waveforms into each of the memory areas. In this arrangement, the sets of driving waveform data corresponding to the available driving waveforms are stored separately in the individual memory areas. This arrangement does not require the writing operation of the driving waveform data prior to the switch over of the working driving waveform, thereby having high speed of generating the working driving waveform.
In a second embodiment, a reading/writing operation of each memory area
Asauchi Noboru
Otsuki Koichi
Barlow John
Dudding Alfred
Seiko Epson Corporation
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