Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-07-30
2001-07-10
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S010000, C347S014000, C347S015000, C347S037000
Reexamination Certificate
active
06257689
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique of printing an image on a printing medium, and more specifically to a printing technique that records two pixels adjoining to each other in a main scanning direction with a plurality of ink droplets.
2. Description of the Related Art
Ink jet printers that eject ink droplets from a head are widely used as an output device of a computer. The conventional ink jet printers reproduce each pixel by only two values, that is, the on state and the off state. Multi-value printers, which have been proposed recently, on the other hand, reproduce each pixel by three or greater values.
One of such multi-value printers selectively ejects a first ink droplet, which has a relatively small quantity of ink, and a second ink droplet, which has a greater quantity of ink than that of the first ink droplet, in the area of one pixel. This configuration enables reproduction of four tones, that is, the state of no dot creation where neither the first ink droplet nor the second ink droplet is ejected, the state of small dot creation where only the first ink droplet is ejected, the state of medium dot creation where only the second ink droplet is ejected, and the state of large dot creation where both the first ink droplet and the second ink droplet are ejected. The arrangement of ejecting the two different types of ink droplets is actualized by driving the print head in response to a driving signal, which may selectively include a first driving pulse and a second driving pulse within one printing period corresponding to one pixel in printing.
In the prior art technique, there are some cases in which two different types of dots are created respectively in two pixels adjoining to each other in the main scanning direction in response to different driving pulses selected out of the first and the second driving pulses. The positions of these two adjoining dots in the main scanning direction created by the prior art technique are, however, varied to cause a positional deviation. Namely there is a difference between a first state, in which a dot is created in the first pixel in response to the first driving pulse and a dot is created in the latter pixel in response to the second driving pixel, and a second state, in which a dot is created in the first pixel in response to the second driving pulse and a dot is created in the latter pixel in response to the first driving pixel. The subsequent image processing does not practically distinguish between the first state and the second state. The prior art technique accordingly fails in faithful reproduction of print data of interest generated as a result of the image processing, which causes deterioration of the picture quality of the resulting printed image.
FIG. 25
shows the positions of two different types of dots, a small dot and a medium dot, created in the first state and in the second state. Lattices in
FIG. 25
represent boundaries of pixel areas, and each square area defined by a lattice corresponds to the area of one pixel. An ink droplet is ejected from a print head (not shown) into each pixel, while the print head moves in the main scanning direction. In the example of
FIG. 25
, recording is carried out in the first state with regard to two pixels, a k-th pixel and a (k+1)-th pixel (where k is a positive number), that are included in a first raster line L
1
and adjoin to each other in the main scanning direction. Recording is carried out in the second state, on the other hand, with regard to two pixels, a k-th pixel and a (k+1)-th pixel, that are included in a second raster line L
2
and adjoin to each other in the main scanning direction.
As clearly understood from the drawing of
FIG. 25
, in the prior art technique, the hitting positions of the two ink droplets ejected in the two adjoining pixels, the k-th and (k+1)-th pixels, on the first raster line L
1
are different from those on the second raster line L
2
. The ink droplet for recording the k-th pixel in the main scanning direction hits on the left half of the pixel area in the first raster line L
1
, but hits on the right half of the pixel area in the second raster line L
2
. On the contrary, the ink droplet for recording the (k+1)-th pixel hits on the right half of the pixel area in the first raster line L
1
, but hits on the left half of the pixel area in the second raster line L
2
. The subsequent image processing does not distinguish between the two dots on the first raster line L
1
and the two dots on the second raster line L
2
. The small dot is, however, apart from the medium dot on the first raster line L
1
, whereas the medium dot is close to or even integrated with the small dot on the second raster line L
2
. This results in a density difference and roughness in the resulting reproduced image.
In the conventional multi-value ink jet printer, the hitting positions of the two different types of ink droplets in the main scanning direction, which are ejected in the two adjoining pixels, are varied in the first state and in the second state discussed above. The variation in hitting positions unfavorably deteriorates the picture quality of the resulting printed image.
SUMMARY OF THE INVENTION
The object of the present invention is thus to prevent deterioration of the picture quality of a resulting printed image, which is ascribed to a variation in hitting positions of two different types of ink droplets ejected in two pixels, which adjoin to each other in a main scanning direction, in response to different driving pulses selected out of a first driving pulse and a second driving pulse in a state where a dot is created in a first pixel in response to the first driving pulse and a dot is created in a latter pixel in response to the second driving pulse and in an inverted state.
At least part of the above and the other related objects is attained by a first printer that prints an image on a printing medium while carrying out a main scan that moves a print head relative to the printing medium. The first printer includes: the print head that has a plurality of nozzles and a plurality of pressure generating elements, which respectively correspond to the plurality of nozzles, each of the pressure generating elements being driven in response to a driving signal, so as to cause an ink droplet to be ejected from the corresponding nozzle against the printing medium; and a head driving control unit that controls the driving signal output to the print head and thereby causes the print head to print an image on the printing medium. The head driving control unit includes: a driving signal generating unit that generates the driving signal that selectively includes a first driving pulse and a second driving pulse in one printing period corresponding to one pixel in printing, a first driving pulse causing a first ink droplet to be ejected from each of the nozzles, a second driving pulse following the first driving pulse and causing a second ink droplet to be ejected from each of the nozzles; and a driving signal specification unit that specifies the first driving pulse and the second driving pulse, in order to cause three factors, that is, an ejecting speed of the first ink droplet towards the printing medium, an ejecting speed of the second ink droplet towards the printing medium, and a variation in time difference between the first driving pulse and the second driving pulse when the first driving pulse and the second driving pulse are respectively output to adjoining pixels in this sequence and in an inverted sequence, to satisfy a predetermined relationship, which depends upon a distance from a nozzle of interest to the printing medium, thereby causing a variation in distance between a hitting position of the first ink droplet and a hitting position of the second ink droplet when the first driving pulse and the second driving pulse are respectively output to the adjoining pixels in this sequence and in the inverted sequence to be within a preset value.
In the first printer of the abo
Barlow John
Dudding Alfred
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seiko Epson Corporation
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