Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-12-08
2003-11-25
Meier, Stephen D. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S014000, C347S019000
Reexamination Certificate
active
06652056
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink-jet recording apparatus in which an image with a high quality image can always be formed. The invention can be applied to all equipment that uses recording media such as a sheet, a cloth, a non-woven fabric, or an OHP sheet, e.g., business equipment and mass-production equipment such as a printer, copying machine, or facsimile apparatus.
2. Description of the Related Art
In association with the widespread use of information processing equipment such as a copying machine, a word processor, and a computer and, further, of communication equipment, an ink-jet recording apparatus for recording a digital image by an ink-jet method has rapidly spread as one type of output apparatus for forming (recording) images processed by the information processing equipment or the communication equipment.
A conventional ink-jet recording apparatus comprises a recording head (hereinlater, referred to as a multi-head) which is formed by aligning a plurality of ink discharge nozzles. The nozzles of the recording head discharge ink, and the ink adheres to a recording medium, thereby forming an image. Generally, the ink-jet recording apparatus comprises a plurality of the multi-heads corresponding to colors for the purpose of recording a color image. The conventional ink-jet recording apparatus having the recording heads has excellent characteristics that enables an image with higher quality to be formed or recorded at a higher speed, more quietly, and more inexpensively, as compared with that in accordance with other recording methods.
However, the conventional ink-jet recording apparatus has various problems as described in the following paragraphs numbered (1) to (6).
(1) In the step of producing the recording head, slight differences in the shape of a discharge port of the recording head and in the performance of an electricity-to-heat converter (discharge heater) are produced and, thus, the discharge amounts and the discharging directions of the ink which is discharged from the discharge port are varied. There is a problem (first problem) that unevenness of density occurs in an image and an image quality deteriorates when the discharge amounts and the discharging directions of the ink vary, as mentioned above. A specific example will be described with reference to
FIGS. 15A
to
15
C and
FIGS. 16A
to
16
C. Referring to
FIG. 15A
, reference numeral
91
denotes a multi-head which comprises eight multi-nozzles
92
. Reference numeral
93
denotes ink droplets which are discharged by the multi-nozzles
92
and, ideally, an equal amount of discharged ink should be discharged in the indicated direction as shown in the figure. If the ink is discharged in the aforementioned manner, dots having the same size are shot on a sheet (as shown in
FIG. 15B
) and an even image having no unevenness of density as a whole can be obtained (as shown in FIG.
15
C). However, the discharge amounts and the discharging directions are actually varied depending on the nozzles, so that if printing is executed in the manner similar to the foregoing, the size and the direction of ink droplets which are discharged from the nozzles are varied as shown in
FIG. 16A
, and dots are shot on a sheet as shown in FIG.
16
B. Referring to
FIGS. 16A and 16B
, there is a blank portion which cyclically satisfies no area factor of 100%, on the contrary, dots are overlapped more than required, and a white streak is caused at the center. The dots which are shot in the above-described state produces a density distribution for the nozzle and the discharged direction shown in FIG.
16
C. Consequently, the phenomenon is usually detected as unevenness of density from the eyes of a human.
(2) The amount of discharged ink from one discharge port changes as a function of time, so that there is problem that the unevenness of density occurs in an image and, an image having a proper density cannot be recorded (second problem). Specifically speaking, when an image is scanned in the main scanning direction by the recording head and the image is recorded, energy for driving the discharge accumulates over time and the temperature of the head rises. In accordance therewith, the viscosity of ink decreases and the amount of discharged ink increases. In particular, according to an ink-jet method known as the (hereinafter, bubble jet method, abbreviated to the BJ method) for forming a flying fluid droplet by use of thermal energy and for recording an image, a foaming force increases due to the increase in temperature of the ink and the amount of discharged ink increases remarkably. Consequently, in general, the density of the image is higher on the side of the end of recording in the main scan than that on the side of the start thereof. Although the phenomenon causes a problem for the typical image, a low-density portion at the start of writing may come into contact with a high-density portion at the end of writing, especially in the case of reciprocating recording and thus, the density difference becomes more remarkable. In accordance with the increase in the number of discharge times, a burnt deposit on the heater unit according to the BJ method causes the amount of discharged ink to decrease.
(3) The amount of discharged ink from a discharge port changes because of dirt near the discharge port which is caused by ink mist and sheet powder or dust, the mixture of bubbles and dust within the discharge port, and the thickening by evaporation of an ink solvent, etc. This causes a problem that an image having a proper density cannot be recorded (third problem).
(4) When the phenomenon noted in paragraph (3) occurs is remarkable, that is, the discharge port is clogged and a non-discharge nozzle is caused, there is a problem that a clear white streak appears in the image and the quality of the image degrades. When the appearance of burnt deposit (“koga”) is remarkable according to the BJ recording method, the discharge also becomes defective and the amount of discharged ink excessively decreases, thereby causing the occurrence of the white streak (fourth problem).
(5) There is a possibility of a stoppage of discharge (non-discharge) which is caused by a short circuit due to corrosion, etc. of a power supply line to the nozzles or by a short circuit of a discharge heater in the recording head according to the BJ method. This causes a problem that a clear white streak appears due to the non-discharge and the quality of the image degrades (fifth problem).
(6) If a large part of ink in the ink tank is consumed and there is a small amount of ink remaining in the ink tank, this causes a problem that a patchy portion appears in the whole image and the quality of the image deteriorates (sixth problem).
Conventional ink-jet recording systems cope with the problems (1) to (6) as follows.
Against problem (1), there are methods for recording a test pattern cyclically
on-cyclically, reading it, determining a state of the recording head, and adjusting a method of image processing as disclosed in Japanese Patent Laid-Open No. 57-41965, Japanese Patent Publication No. 2708439, and Japanese Patent Publication No. 2711011. These methods are used when a user sees an image which is usually recorded and determines that the image is degraded. If specific handling which is different from the usual use such as exchanging of the head or exchanging of an ink tank, is required, the adjustment is executed. As mentioned above, all of the nozzles are adjusted so as to eliminate the variations of the amount of discharged ink and the discharging direction of the discharge ports.
Against problems (2) and (3), there is a method for cyclically
on-cyclically wiping and cleaning the discharge ports. The method is performed when a user judges that the image is degraded, the head is exchanged, the ink tank is exchanged, or the head is unused for a predetermined time period. As described above, against problems (2) and (3), all of the nozzles are subjected to recovering processes such as wiping and clea
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Mouttet Blaise
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