Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-11-13
2003-03-18
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
C347S098000
Reexamination Certificate
active
06533382
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink-jet recording apparatus and ink-jet recording method, for recording images on a recording medium using ink containing color material and a liquid essentially containing no color material.
2. Description of the Related Art
As photocopiers, word processors, computers and other information processing equipment, and communication devices come into common use, ink-jet recording apparatuses are rapidly becoming commonplace as one type of output device thereof, for performing recording of digital images using the ink-jet method. With such recording apparatuses, recording heads made up of multiple ink discharging nozzles in integrated arrays with multiple ink discharge openings and liquid channels are used to improve recording speed, and further, in recent years, arrangements containing a plurality of such recording heads are often used to deal with color which is becoming commonplace.
The ink-jet recording method performs recording of dots by forming flying droplets of ink as the recording liquid and landing these on a recording medium such as paper or the like, and has a low noise factor due to being a non-contact method. Also, high resolution and high-speed recording is enabled by the increased density of the ink discharge nozzles. Further, no special processing such as developing or fixing is necessary for recording media such as plain paper or the like, so high-quality images can be obtained at low cost. Accordingly, this method has become widespread in recent years. Particularly, on-demand type ink-jet recording apparatuses can be easily arranged to deal with color, and further the apparatus itself can be easily reduced in size and complexity, so the demand thereof in the future is expected to be great. Also, as such color becomes commonplace, even higher image quality and speed are being required.
In the present state of such high image quality being required, there are various methods being proposed regarding improving image quality. One method for improving image quality involves making the droplets of discharged ink smaller. Reducing the diameter of the nozzles is the most effective method for reducing the size of the droplets, and improved image quality is achieved by arraying the ink discharging nozzles with small nozzle diameters in high density. The reason that reducing the size of the discharged ink droplets leads to higher image quality is that the dots are not as conspicuous, and the number of gradients which can be represented without increasing the matrix size of one pixel can be increased. In other words, reducing the size of the discharged ink droplets enables the number of gradients to be increased without losing resolution. Incidentally, the higher the density of the arrayed nozzles is, the higher the output resolution is, but there is a limit to how high the density can be, due to restrictions in the manufacturing process. This is also true for reducing the size of the discharged ink droplets, and currently, due to restrictions in the manufacturing process, the limit on how little the amount discharged can be is 1 to several picoliters (several nanograms), and 20 to 40 &mgr;m recorded dot diameters on the recording medium.
Also, as another method for improving image quality, there is a method of using concentration ink which is ink of the same color in different ink concentrations. With this method, highlight portions (portions with low concentration) are recorded with low-concentration ink so as to make the grainy appearance of the recording dots less conspicuous. This also enables a great number of gradients to be represented, by using ink with low and high concentration according to the gradients. Thus, using ink with low and high concentration enables high-quality images. Also, as another method for making the grainy appearance of the recording dots less conspicuous in highlight portions, Japanese Patent Laid-Open No. 59-115853 discloses a method wherein transparent ink is recorded over the recorded dots so as to thin the concentration of the recorded dots and represent an overall light color. According to this Japanese Patent Laid-Open No. 59-115853, the number of gradients represented is not being increased, but the grainy appearance in the highlight portions is reduced, ultimately leading to high quality.
Also, as another method for improving image quality, there is a method wherein the size of the recording dots is controlled by pulse modulation, thereby increasing the number of gradients which can be represented. This is a method wherein the dot recording area is changed per unit area by changing the diameter of the dots, thereby changing the apparent concentration, and consequently representing gradients.
Also, there are methods for high quality images other than recording images with gradation (i.e., wherein the gradient level is not constant) with high quality, i.e., methods aiming to improve the quality of characters. As one method for such improvement in character quality, there is edge enhancing wherein the edge portions of characters are enhanced. For example, Japanese Patent Laid-Open No. 1-212176 discloses a method wherein image signals are subjected to secondary differentiation and computation is performed with original image signals and smoothed data, thereby enhancing the edge portions. Also, Japanese Patent Laid-Open No. 8-72236 discloses a method wherein the amount of ink discharged at the edge portions is greater than the non-edge portions, thereby raising the concentration at the edge portions. Performing such edge enhancing allows characters with clear outlines to be formed.
Though various methods are being proposed for realizing high image quality as described above, these methods have various problems, as described below.
{circle around (1)} Reducing the size of discharged ink droplets increases the resolution, but the area covered by each ink dot is reduced. This means that the number of ink dots necessary for covering a certain area on the recording medium increases, leading to reduction in printing speed. That is to say, reducing the size of the discharged ink droplets contributes to high image quality but contradicts high speed.
{circle around (2)} Arraying ink discharge nozzles with reduced nozzle diameters in high density allows the number of gradients to be increased without losing resolution as described above, but indiscriminately increasing the density of nozzles does not necessarily mean that high image quality can be realized. The reason is that an excessively high density array of nozzles leads to adjacent ink dots on the recording medium overlapping unnecessarily, which may cause the ink dots to blur. Such blurring causes deterioration in image quality. Also, the ink-jet method has a phenomena called ink shifting, and there is a problem in that this ink shifting becomes more pronounced as the density of the nozzles is increased and the resolution is raised. Consequently, this ink shifting leads to deterioration in image quality.
{circle around (3)} An arrangement may be conceived wherein adjacent nozzles do not simultaneously discharge ink such that ink is not overlapped in the same main scan of the recording head, thereby reducing image deterioration due to the blurring and ink shifting described above in problem {circle around (2)}. For example, in the event that there are 256 nozzles, each nozzles rests intermittently, so that 128 nozzles are driven to record the image with each scan. With such an arrangement, in the event that a solid image is recorded, the printing duty of one main scan of the recording head is 50%, so the printing concentration of one main scan of the recording head deteriorates. On the other hand, an arrangement may be conceived wherein the recording head performs two main scans to avoid deterioration of the printing concentration, but this would make the recording time longer.
{circle around (4)} In the event of using concentration ink, a recording head and ink cartridge are provided for each ink to be
Kanome Osamu
Shibata Tsuyoshi
Tomida Yoshinori
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Thinh
LandOfFree
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