1. Field of the Invention
This invention relates to an inkjet printer and a recording heads unit, especially an inkjet printer and a recording heads unit having a structure capable of equalizing color tone of an image.
2. Description of Related Art
As a recording terminal connected to a word processor, a personal computer or the like, various kinds of printers such as a dot impact printer, an inkjet printer, a laser printer, a thermoelectric printer, a dye sublimation printer or the like have been developed. Among all, the inkjet printer has been a mainstream of a printer since it has advantages such as, recording images can be done more quietly, more easily, more inexpensively and the like than printers of the other methods.
In the inkjet printer, recording heads comprising lots of nozzles are placed. The inkjet printer jets ink as minute liquid drops from each nozzle at the recording heads toward a recording medium for recording images. The inkjet printer these days carries four arrayed recording heads on a carriage for spraying ink of each process color of yellow (Y), magenta (M), cyan (C) and black (K). By moving the carriage over the recording medium (back-and-forth movement), the inkjet printer is capable of recording a full-colored image easily.
Incidentally, when the carriage makes the back-and-forth movement over the recording medium, since the order of each recording head is fixed, the order of each recording head along a moving direction of the carriage differs between forth movement and back movement. In this case, in an image recording area, ink color piling order in an area corresponding to the forth movement is opposite to the order in an area corresponding to the back movement. As a result, color tone on a recording-finished image alternately changes at each area and thereby it causes degradation of image quality.
To solve this problem, there is a method of repeating the operation of followings: while the carriage moves over the recording medium, certain ink colors are formed whereas the rest of ink colors are not formed on each dot, and at the second or later movement, other ink colors are formed on the dot, which already has the certain ink colors formed thereon (formed by the carriage movement until the last time) (for example, refer to Japanese Patent Application Publication (Unexamined) No. Tokukai-Hei 5-278232). With this method, it is possible to locate pixels having different ink color piling order next to each other, and thereby it is possible to inhibit color tone change on a recording-finished image.
However, with the above-mentioned method, since it is necessary to form a dot by not piling the same color ink thereon but piling other color thereon, high-leveled technique such as controlling ink color piling order from each nozzle among recording head for jetting different ink colors from each other, is required. Consequently, a complicated control structure is required.