Patent Publication Number: US-6209986-B1

Title: Inkjet printers

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an inkjet printer for outputting plotting data prepared in a host computer to paper. 
     Inkjet printers have been known in the art wherein an image output region corresponding to one page of the paper is divided into a plurality of bands, and the image information to be outputted is written to a bit map memory in raster data form for each band, and the image data in the bit map memory is used to control the ink discharge from nozzles of the inkjet head to output the image on long sized paper for each band. 
     In the preparation of the image, there is a limit to the length that the inkjet printer can plot in one operation because of a limitation coordinates to be handled in the application at the host computer side. For example, if the axis has coordinates up to 32767, in a printer with a resolution of 360 dpi, 32767×(25.4/360)=2311 mm is the longest length that can be handled. 
     Under these circumstances, a method may be used wherein the data is sectioned into certain block lengths and plotted with upper portion margin and a lower portion margin of zero, so that the next plotting is continuous with the present plotting, which effectively permits longer plotting. 
     In this case, as shown in FIG.  4 (A), the sectioned data is regarded as data coupled with the number of nozzles of an inkjet head  14 . A final image  30  of the first page (1st sheet) coincides with a discharge nozzle region D of the inkjet head  14 . Accordingly, in this condition, if the paper is carried in the forward direction by a portion of width of the inkjet head  14 , the band image of the second page (2nd sheet) can be made continuous with the final band image  30  of the first page with the zero margin. 
     However, as shown in FIG.  4 (B), in case the sectioned data is not coincident with the number of nozzles of the inkjet head  14 , the undischarge nozzle region X of the inkjet head  14  is not coincided with the final band image  30  on the first page. For this reason, when the plotting of the second page is to be made, where the paper is carried in the forward direction by the head width portion of the inkjet head  14 , a white stripe of the undischarged nozzle region X portion is formed between the final image  30  on the first page and the first band image on the second page, which causes the discontinuation of the next plotting. 
     Normally, when plotting image is to be prepared at the host computer side, an operator is not required to be conscious of the number of nozzles of the plotting head of the printer. Furthermore, the application at the host computer side corresponds to a variety of printers in many cases, and since there is a possibility that the number of nozzles of the inkjet is variable among the printers, there is a problem in that the preparation of data matched with the printers is difficult. 
     The present invention has an object of solving the foregoing problems. 
     SUMMARY OF THE INVENTION 
     The present invention is constructed in such a way that a certain data segmented to a certain block length is subjected to a band plotting with an upper portion margin and a lower portion margin of zero, and the resulting band plotting is made to be continuous with the next plotting, and as a result, in case of performing a longer plotting, it can prevent the generation of a white stripe at the splice between the final band image of the previous plotting and the band image of the next plotting. 
     The inkjet printer segments an image output region of one page portion into a plurality of bands, and stores an image to be outputted in a bit map memory in the mode of a raster data for each band, and the image stored in the bit map memory is outputted to each band by discharging the ink from the nozzles of the inkjet head onto the long size paper. A CPU determines the number of the nozzles counting from the first nozzle that discharges the ink out of the total number of the nozzles of the inkjet head, and feeds inversely the plotting paper by only a distance portion corresponding to the number of the undischarged nozzles, or an amount corresponding to the backlash portion of the number of the undischarged nozzles and the paper carrying mechanism. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flow chart showing an operation of the present invention. 
     FIG. 2 is a block diagram of an inkjet printer. 
     FIG. 3 is an explanation drawing showing an entire image to be outputted by the inkjet printer. 
     FIG. 4 is an explanation drawing of conventional arts. 
     FIG. 4A represents sectioned data of an entire image that is coincident with the number of nozzles of an inkjet head. 
     FIG. 4B represents sectioned data that is not coincident with the number of nozzles of an inkjet head. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The mode of an embodiment of the present invention will be described in details by referring to the attached figures. 
     FIG. 2 is a block diagram showing a construction of an inkjet printer  4  to which a plotting method according to an embodiment of the present invention is applied. An interface  6  of the inkjet printer  4  is connected to a host computer  2  that outputs an image information such as a design drawing that is prepared using an input device not shown herein. This image is usually represented by vector data. 
     The inkjet printer  4  is constructed in such a way that printing and outputting are carried out by converting the vector data transmitted from the host computer  2  to raster data. The vector data transmitted from the host computer  2  is stored into a RAM  8  by means of the interface  6  provided with a FIFO buffering function. The CPU  10  analyses the data against the plotted vector data stored in the RAM  8  on the basis of a program stored in a ROM  12 , and segments the vector data contained in each band into a system (for example, vector) of an intermediate code by applying processing such as a segmentation processing with a preset band width, and sort processing and the like. 
     An image processor  16  applies a DDA processing sequentially to the image of the intermediate code system that is stored in the RAM  8 , and converts the image represented by intermetiate code into raster data which is stored in a bit map memory  18 . The raster data that is stored in the bit map memory  18  is sequentially fed to an inkjet head  14  through a data transmission circuit  20 , and the raster data is copied by a head transmission memory  22 . The inkjet head  14 , as shown in FIG. 3, is driven by a head drive unit  26  in a horizontal direction that crosses the vertical direction, and transfers reciprocatingly in the horizontal direction (X axis direction) against a paper  24 . On the other hand, the paper  24  is driven in a vertical direction (Y axis direction) by a paper drive unit  28 , and the image represented by the raster data is printed on a band on the paper  24  by the inkjet head  14 . 
     Next, an operation of the inkjet printer in long size plotting will be explained by referring to FIG.  1 . 
     The CPU  10  performs an analysis of the plotting data (step  1 ) that is stored in the RAM  8  on the basis of the program stored in the ROM  12 , and performs the plotting of one band portion (step  2 ). At this time, if the number of nozzles of the inkjet printer  14  is coincident with the number of data, as shown in FIG.  4 (A), a nozzle disposition region D of the inkjet head  14  is coincident with the band width of the band image  30  to be printed on the paper. However, if the number of nozzles of the inkjet head  14  is not coincident with the number of data, namely, in case less than all of the nozzles of the inkjet head  14  are used in the plotting of one band, as shown in FIG.  4 (B), the nozzle disposition region D of the inkjet head  14  is not coincident with the band width of the band image  30 . 
     Next, the CPU  10  determines whether or not the plotted band image is the final band (step  3 ). If it is not the final band, the paper  24  that corresponds to one band portion is carried in the forward direction, and the process returns to step  1 , and continues band plotting. When it is the final band, the CPU  10  computes (step  5 ) a value X by subtracting the number of the nozzles that actually discharge the ink from the total number of nozzles of the inkjet head  14 . This value X corresponds to the distance of the disposition region of the nozzles in the X axis direction which are not used in the band image of the inkjet head  14 . 
     The CPU  10  computes (step  6 ) a value L by adding a corrected value such as the backlash of the paper carrying mechanism to the distance corresponding to the value X. Then, the CPU  10  drives the paper drive unit  28  and carries the paper  24  by the amount corresponding to the value L in the reverse direction (step  7 ), and completes the plotting of one page portion. The end of the nozzle is cause to be below a base  30   a  of the final band image  30  by the inverse feeding of the paper in an amount corresponding to the value L of the paper  24 . 
     Accordingly, when the plotting of the second page starts, even if the paper  24  is carried in the X axis direction and in the forward direction by the head width, namely, the nozzle disposition region E, the starting end of the nozzle disposition region E of the inkjet head  14  adjoins the base  30   a  of the final band image  30  of the preceding page with a zero gap, and can plot the band image of the next frame (page) continuously without causing a gap with the band image  30  of the preceding frame. 
     The present invention has been constructed as described in the foregoing, and even if the plotting data is received from a general (application), long size plotting without the white stripe becomes feasible.