Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-05-21
2004-02-24
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S068000
Reexamination Certificate
active
06695437
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an inkjet recording head for recording characters and images by ejection of ink droplets, and manufacturing and driving methods thereof, and an inkjet recording apparatus having such an inkjet recording head.
2. Description of the Related Art
In recent years, an impact recording process has attracted much attention for its small noise in recording and a high recording speed thereof. Among other impact recording processes, an inkjet recording process used in inkjet printers has been in wide use. The inkjet printer allows ink droplets to be ejected from the recording head and attached onto recording paper so that characters, figures and photographs are printed at a high speed. The inkjet printer is capable of recording the images onto plain paper without using a special fixation processing. According to a known inkjet recording process called drop-on-demand inkjet recording scheme, an electromechanical transducer such as a piezoelectric actuator is used to generate pressure waves (acoustic waves) in pressure chambers filled with ink, thereby allowing ink droplets to be ejected from the nozzles disposed in communication with the pressure chambers.
An inkjet recording head using the drop-on-demand inkjet scheme is described in JP Patent Publication No. Sho. 53-12138 and JP Patent Laid-Open Publication No. Hei. 10-193587.
FIG. 34
is a sectional view of a recording head in an inkjet recording apparatus such as described in these publications. The inkjet recording apparatus includes a plurality of pressure chambers
51
, a plurality of nozzles
52
each in communication with a corresponding one of the pressure chambers
51
, a plurality of ink supply passage
54
for supplying ink from an ink reservoir through a common ink passage
53
. A diaphragm
55
is fixed onto the bottom of the pressure chambers
51
.
In the above inkjet recording apparatus, at the time of ink droplet ejection, the diaphragm
55
is displaced (or flexibly deformed) by a piezoelectric actuator
56
disposed outside the pressure chamber
51
to change the volume in the pressure chamber
51
, thereby generating a pressure wave in the pressure chamber
51
. The pressure wave causes part of the ink filled in the pressure chamber
51
to be ejected outside the pressure chamber
51
through the nozzle
52
as an ink droplet
57
. The ejected ink droplets arrive at a recording medium such as a recording paper sheet to form recording dots (pixels) thereon. The process of forming the recording dots is iteratively performed based on image data so that characters or images are formed on the recording medium.
It is desired that the drop-on-demand inkjet recording apparatus achieve both high speed recording and high image quality recording. In the conventional inkjet recording apparatus, however, achieving both high speed recording and high image quality recording at the same time is in fact extremely difficult. If, for example, the resolution is degraded in order to achieve high speed recording, high image quality is not provided. On the other hand, if the resolution is increased in order to achieve high image quality recording, the high speed recording cannot be obtained. In other words, high speed recording and high image quality recording are tradeoff against each other.
The necessary conditions to achieve both “high speed recording” and “high image quality recording” in the inkjet recording apparatus will be described hereinafter. Two particularly important conditions to achieve the “high speed recording” are as follows:
(1) to lower the recording resolution, and
(2) to increase the number of nozzles disposed (or to increase the nozzle density).
If the condition (1), i.e., to lower the resolution is satisfied, a unit area can be recorded with less ink droplets, and therefore the time required for recording can be reduced. When recording resolutions of 300 dpi (dots/inch) and 1200 dpi are compared against each other, the necessary number of ink dots for 300 dpi is {fraction (1/16)} as many as that for the resolution of 1200 dpi to record the same area. It should be noted that, for the same frequency of ejected ink droplets (driving frequency), the recording speed obtained at 300 dpi resolution is about 16 times as high as that obtained at 1200 dpi resolution.
However, if the recording resolution is set to be lower, the image quality is lowered, and therefore there is a lower limit for the reduction in the recording resolution. In consideration of human eyesight, it is most suitable that the recording resolution be set in the range roughly from 300 to 600 dpi (1 dot/inch =39.37 dots/m) in order to achieve high speed recording without significantly lowering the image quality (character and line qualities). The recording resolution is preferably set to be lower than the usual resolution (700 to 2400 dpi) of typical inkjet recording apparatuses generally used heretofore, in view of improvement of the recording speed. It should be noted, however, that in order to set a lower recording resolution, ink droplets having a corresponding large size should be ejected.
More specifically, in order to form large ink dots in accordance with the high speed recording corresponding to the lower recording resolution, ink droplets having a corresponding large volume should be ejected. The relation between the recording resolution and a necessary droplet volume changes to some extent depending on the types of ink or recording paper used. With a typical ink and typical recording paper used in the conventional inkjet recording apparatus, an ink droplet volume in the range from 15 to 30 pl (1 pico-liter=10
−15
m
3
) is generally adopted to provide a sufficient recording density together with a recording resolution in the range from 300 to 600 dpi. This is about 1.5 to 3 times as much as the ink droplet volume (about 10 pl) necessary for the resolution of 1200 dpi.
In order to increase the recording speed, the number of nozzles should be increased as in the above condition (2). A larger number of nozzles increases the number of dots formed per unit time length, which improves the recording speed. Therefore, in typical inkjet recording apparatuses, a multi-nozzle recording head is generally employed which includes a number of such ink ejecting mechanisms (ejectors) coupled together.
FIG. 35
shows the multi-nozzle recording head. In the recording head shown, an ink reservoir
67
is coupled with a common ink passage
63
, to which a plurality of pressure chambers
61
are coupled through respective ink supply passages (not shown). Thus, in this head structure, by arranging ejectors
68
one-dimensionally along the common ink passage
63
, the number of ejectors
68
(or the number of nozzles
62
) is increased up to about 30 to 100.
Another inkjet recording head having ejectors arranged two-dimensionally in a matrix (hereinafter referred to as “matrix head”) to further increase the number of ejectors is described in, for example, JP Patent Laid-Open Publication No. 1-208146 and JP National Phase PCT Publication No. 10-508808.
FIG. 36
shows a matrix head such as described in these publications. In the matrix head, the common ink passage includes a main passage
73
and a plurality of branch passages
78
, wherein a plurality of ejectors
79
are connected to a single branch passage
78
. The matrix head structure is advantageous in increasing the number of ejectors
89
(or the number of nozzles
72
). If, for example, there are 26 branch passages
78
disposed in the matrix head, and ten ejectors
79
are connected to each of the branch passages
78
, then 260 ejectors can be arranged altogether. It should be noted that
FIG. 36
shows only 36 ejectors among them.
As described above, the matrix head is advantageous for increasing the number of nozzles, while the dimensions of the recording head as a whole increases unless the density of the pressure chambers
71
arranged is not increased. This may increase the cost for manufacturing t
Nakamura Hirofumi
Okuda Masakazu
Fuji 'Xerox Co., Ltd.
Nguyen Thinh
Scully Scott Murphy & Presser
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