Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-12-16
2001-12-18
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S019000
Reexamination Certificate
active
06331040
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for and a method of driving an ink jet record head wherein ink droplets of different sizes may be spouted from each nozzle, and also to a printing apparatus with such a driving apparatus.
2. Discussion of the Background
An ink jet printer converts an image, which is to be printed, into binary codes or multi-value codes and controls the creation of dots on a recording medium by respective nozzles on a print head, based on the dot on-off signals obtained as the results of the multi-value coding. The structure of the ink jet printer causes the plurality of nozzles on the record head to respectively spout ink droplets at a predetermined timing and thereby form dots on the surface of a recording medium, such as a recording sheet of paper, so as to implement the recording. The fundamental technique for ink spouting pressurizes ink in an ink conduit, which is connected to each nozzle, for an extremely short time period and causes the pressurized ink to spout as an ink droplet from the end of the nozzle. There are several known mechanisms for generating the pressure that is applied to the ink; for example, a system that utilizes piezoelectric elements to generate the pressure and a system that takes advantage of bubbles produced by heating to apply the pressure. No matter which mechanism is applied, however, the ink jet technique can only control the spout or non-spout of ink droplets from the ends of the respective nozzles, that is, the on-off state of the dots. It is thus extremely difficult to continuously and freely regulate the weight of ink in each spouted ink droplet and record the halftone.
Several techniques have been proposed to express the halftone; for example, the area tone method, the dither method, and the error diffusion method. The area tone method, for example, expresses each pixel with a plurality of dots like 4×4 or 8×8 to record the halftone. The expression of one pixel with the 4×4 dot matrix results in the representation of the density by the gradation of 16 tones (or 17 tones including complete white). An increase in resolving power of the pixel ensures a more minute tone expression. An increase in tone without varying the diameter of the recorded dots, however, lowers the practical resolution. The larger diameter of the dots recorded on the recording paper makes the granularity undesirably conspicuous in a low density area. It is accordingly necessary to decrease the weight of each ink droplet and reduce the diameter of the recorded dots.
A known technique for spouting ink droplets of a smaller weight to reduce the dot diameter first expands and then contracts the volume of a pressure chamber connected to the ink conduit, which is generally referred to as the ‘drawing shot’, as described in, for example, JAPANESE PATENT LAID-OPEN GAZETTE No. 55-17589. The expansion of the volume of the pressure chamber cancaves the ink interface (meniscus) inward the nozzle and causes a smaller ink droplet to be spouted from the nozzle under pressure, thereby reducing the diameter of the recorded dots.
The smaller diameter of the recorded dots makes the granularity substantially inconspicuous in a low density area and enhances the recording quality, but significantly lowers the recording rate. By way of example, where using only the smaller diameter dots having a dot diameter about half the standard dot diameter requires approximately four times the recording time, compared with using dots of a standard dot diameter. The possible measures to prevent the lowered recording rate increase the driving frequency for spouting ink droplets by four times and increase the number of nozzles by four times. Neither of these measures is, however, easily actualized.
One proposed technique causes ink droplets of different weights to be spouted from one identical nozzle and enables the tone expression (see, for example, the specification of the U.S. Pat. No. 5,285,215). This technique generates a plurality of identical pulse signals in one recording period and thereby makes a plurality of minute ink droplets. Before reaching the recording paper, the plurality of minute ink droplets join to produce a large ink droplet.
This proposed technique controls the spout of minute ink droplets and the spout of a large ink droplet obtained by uniting the plurality of minute ink droplets. A lot of conditions, such as the distance between the nozzle end and the recording paper and the relationship between the spouting rate of the ink droplets and the driving rate of the head, must be fulfilled to securely unite the plurality of ink droplets having substantially the same size before the ink droplets reach the recording paper. Another disadvantage is a narrow variable range of the recorded dot diameter.
The object of the present invention is thus to solve the above problems and provide an apparatus for and a method of driving an ink jet record head that widens the variable range of the recorded dot diameter, as well as a printing apparatus with this recording head driving apparatus.
SUMMARY OF THE INVENTION
At least part of the above problems is solved by the present invention. The present invention is directed to an apparatus for driving an ink jet record head, wherein a pressure generating element provided corresponding to each opening of a plurality of nozzles is actuated to cause an ink droplet to be spouted from the opening of each nozzle. The apparatus includes:
a driving signal generation unit that generates a driving signal, which includes a first driving pulse for causing a first ink droplet to be spouted from the plurality of nozzles and a second driving pulse for spouting a second ink droplet that is greater in size than the first ink droplet to be spouted from the plurality of nozzles;
a driving pulse selection unit that selects at least one driving pulse from the first driving pulse and the second driving pulse in one recording period corresponding to the recording of one pixel;
an element driving unit that drives the pressure generating element in response to the driving signal including the selected driving pulse; and
a larger dot creation unit that, when it is required to create a larger dot than dots formed by the first and the second ink droplets, causes the pulse selection unit to select both the first driving pulse and the second driving pulse in one recording period, so as to create the larger dot by an ink droplet corresponding to both the first and the second driving pulses on a recording medium.
The present invention is also directed to a method corresponding to the apparatus for driving the record head. The present invention accordingly provides a method of driving an ink jet record head, wherein a pressure generating element provided corresponding to each opening of a plurality of nozzles is actuated to cause an ink droplet to be spouted from the opening of each nozzle. The method includes the steps of:
generating a driving signal, which includes a first driving pulse for causing a first ink droplet to be spouted from said plurality of nozzles and a second driving pulse for spouting a second ink droplet that is greater in size than the first ink droplet to be spouted from said plurality of nozzles;
selecting at least one driving pulse from the first driving pulse and the second driving pulse in one recording period corresponding to the recording of one pixel;
when it is required to create a larger dot than dots formed by the first and the second ink droplets, selecting both the first driving pulse and the second driving pulse in one recording period; and
driving said pressure generating element in response to the driving signal including the selected driving pulse.
The apparatus for and the method of driving the ink jet record head selects at least one driving pulse out of the two driving pulses, which respectively correspond to a first ink droplet and a second ink droplet having different sizes, in one recording period, and drive the pressure generating element in r
Kosugi Yasuhiko
Yonekubo Shuji
Barlow John
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seiko Epson Corporation
Stewart Jr. Charles W.
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