Patent Publication Number: US-7708379-B2

Title: Method and apparatus for driving printer head and image formation

Description:
This application claims the benefit of priority under 35 U.S.C. § 119(a) of Korean Patent Application No. 10-2004-0113700, filed on Dec. 28, 2004 in the Korean Intellectual Property Office, the entire disclosure of which is hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an image forming method and apparatus. More particularly, the present invention relates to a method and apparatus for driving printing elements of a printer head by analyzing the power necessary to print a page before printing, and driving the printing elements according to the analysis results. 
   2. Description of the Related Art 
   Generally, image forming equipment convert a document written by a user via an application program, or an image photographed with, for instance, a digital camera, into encoded data. The image forming equipment outputs the encoded data onto media, thereby making the document or image visible to the user. 
   Recently, image forming equipment having an array-head structure has been developed. In such image forming equipment, a printer head having the same length as the width of a medium onto which an image is to be printed is used to achieve high speed and high quality printing. To fascilitate high speed and high quality printing, the print head utilizes many printing elements to convey the image. 
   In the case of an inkjet printer, a printer head includes a plurality of nozzles. The nozzles convey ink onto a medium to print the image. For each nozzle to convey ink onto the medium, the nozzles must be supplied with power of a predetermined value. 
   Therefore, in the case of image forming equipment having an array-head structure, such as inkjet printers, power consumed to print an image greatly increases as the number of printing heads increase. An increase in print heads, in turn, requires a high-power power supply to accommodate the increased power consumption. Consequently, the size of the image forming equipment cannot be reduced due to the physical size of high-power power supplies. 
   SUMMARY OF THE INVENTION 
   The present invention provides a method and apparatus for driving a printer head having a plurality of printing elements to print an image with low power without reducing printing quality or speed. According to exemplary aspects of the present invention the printer head is driven using an analysis of printing power consumption before printing occurs. 
   According to an aspect of the present invention, there is provided a method for sequentially driving a plurality of printer head printing elements for printing an image onto a medium by dividing the printing elements into N driving groups. The method comprises calculating a number of driving groups among the N driving groups wherein at least a first predetermined number of printing elements are driven for each line of print. The method calculates a number of print lines wherein the calculated number of driving groups is at least that of a second predetermined number. The method then increases the number of N driving groups if the calculated print lines are at least that of a third predetermined number. 
   The printing elements may convey ink onto a medium to print an image. 
   In calculating the number of driving groups, the number of driving groups wherein at least the first predetermined number of printing elements are driven may be calculated so that a distance between adjacent printing elements, which are being simultaneously driven, is N times the distance between adjacent printing elements of the printer head. 
   The first predetermined number may be half the number of printing elements included in each of the driving groups, the second predetermined number may be 0.7 of the number of driving groups, and the third predetermined number may be set considering power supplied to the printer head. 
   According to another aspect of the present invention, there is provided an image forming apparatus for printing an image by sequentially driving a plurality of printer head printing elements of a printer head, the printing elements being divided into N driving groups. The image forming apparatus comprises a printer head having a plurality of printing elements and a data input unit for receiving image data of an image that is to be printed. The apparatus may further comprise a control unit for providing control signals to sequentially drive the printing elements by dividing the printing elements into the N driving groups according to the input image data, wherein an image can be printed by driving the printing elements according to the control signals. 
   The control unit may comprise a memory for storing image data and a line analyzer for reading image data from the memory and calculating a number of driving groups among the N driving groups wherein at least a first predetermined number of printing elements are driven for each line of print. The control unit may further comprise a page analyzer for calculating the number of print lines wherein the calculated number of driving groups are at least that of a second predetermined number. The control unit may also comprise a group determiner for increasing the number of N driving groups if the calculated number of print lines are at least that of a third predetermined number. 
   The printing elements may convey ink onto a medium to print an image. 
   The first predetermined number may be half the number of printing elements included in each of the driving groups, the second predetermined number may be 0.7 of the number of driving groups, and the third predetermined number may be set considering power supplied to the printer head. 
   The method can be embodied in a computer readable medium having stored thereon instructions for driving a printer head in accordance with aspects of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages of the present invention will become more readily apparent by the detailed description of exemplary embodiments thereof, with reference to the attached drawings, in which: 
       FIG. 1  illustrates a block diagram of an image forming apparatus according to an embodiment of the present invention; 
       FIG. 2  depicts a view for explaining a method of sequentially driving a plurality of printing elements, which are divided into 10 driving groups, according to an embodiment of the present invention; 
       FIG. 3  depicts a view for explaining a method of sequentially driving a plurality of printing elements, which are divided into 20 driving groups, according to an embodiment of the present invention; and 
       FIG. 4  shows a flow chart illustrating a method of driving a printer head according to an embodiment of the present invention. 
   

   Throughout the drawings, like reference numbers should be understood to refer to like elements, features, and structures. 
   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. 
     FIG. 1  illustrates a block diagram of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus includes a data input unit  100 , a control unit  110 , and a printer head  120 . The control unit  110  includes a control signal generator  130 , a memory  140 , a line analyzer  150 , a page analyzer  160 , and a group determiner  170 . 
   The data input unit  100  receives image data to be printed from a source such as a personal computer (PC), a digital camera, or a personal digital assistant (PDA). 
   The control unit  110  generates control signals to control operation of printer head  120  according to the input image data obtained from data input unit  100 . Printer head  120  receives control signals from control unit  110  and drives a plurality of printing elements to print an image. Printer head  120  may be an inkjet printer having a plurality of nozzles which convey ink. In the case of a piezoelectric inkjet printer, each nozzle conveys ink using a piezoelectric element, or in the case of a thermal inkjet printer, a heater. 
   The operations of control unit  110  will be described in more detail with reference to  FIG. 4 . 
   Image data input from data input unit  100  is stored in memory  140  in page units at step  400 . Power consumption is high when simultaneously driving all printing elements in order to print only one print line of a page. Thus, the image forming apparatus can be configured to partially print one print line by dividing the printer head printing elements into a plurality of driving groups, then sequentially driving each group.  FIG. 2  depicts a view to facilitate explanation of an embodiment of a method of sequentially driving a plurality of nozzles of an inkjet printer. In the example illustrated by  FIG. 2 , the nozzles are divided into 10 driving groups. Referring to  FIG. 2 , the exemplary printer has 60 nozzles, which are divided into 10 driving groups, each driving group having 6 nozzles. A first print line, Line 1, is printed by driving the nozzles to sequentially convey ink. The remaining second, third, and fourth print lines, Line 2, Line 3, and Line 4, are printed in the same way and result in a total of four print lines. 
   Line analyzer  150  reads the image data of a page from memory  140  and determines the number of driving groups to be simultaneously driven when the input image data is printed according to each print line. At step  410 , the driving groups include at least a preset number n of printing elements. The preset number n may be half the total number of printing elements included in a single driving group. 
   The operation of step  410  will be described with reference to  FIG. 2 . Regarding the first print line, Line 1, line analyzer  150  determines how many nozzles among the 6 nozzles included in the first driving group  200  that need to be driven in order to print the image data. Also, line analyzer  150  determines how may nozzles need to be driven in the remaining second through tenth driving groups. Then, line analyzer  150  determines the number of surplus driving groups in which three or more printing elements are to be driven. The line analyzer  150  repeats the same operations listed above for the remaining second through fourth print lines, Line 2, Line 3, and Line 4, to determine the number of surplus driving groups in which three or more printing elements are to be driven for each of the second through fourth print lines, Line 2, Line 3, and Line 4. 
   Page analyzer  160  receives the number of surplus driving groups of each first through fourth print lines, Line 1, Line 2, Line 3, and Line 4, output from line analyzer  150 . At step  420 , page analyzer  160  calculates the number of surplus print lines among the first through fourth print lines, Line 1, Line 2, Line 3, and Line 4, in which the number of surplus driving groups is a preset number m or more. The preset number m may be 0.7 of the number of driving groups to sequentially print one line. 
   The operation of step  420  will be described with reference to  FIG. 2 . For example, it is assumed that the number of surplus driving groups of the first print line, Line 1, is 6; the number of surplus driving groups of the second print line, Line 2, is 8; the number of surplus driving groups of the third print line, Line 3, is 9; and the number of surplus driving groups of the fourth print line, Line 4, is 7. The preset number m is 7. Then, page analyzer  160  calculates the number of surplus print lines having not less than 7 surplus driving groups as 3. 
   The group determiner  170  receives the number of surplus print lines output from page analyzer  160  and, at step  430 , determines whether the input number of surplus print lines is not less than a preset number x. If the input number of surplus print lines is not less than the preset number x, the number of driving groups is increased at step  440 . The preset number x may be determined in consideration of the characteristics of power supply for printer head  120 , such as continuity of current and efficiency. Alternatively, the preset number x can be arbitrarily set and the power supply designed to match the preset value. 
   If the number of driving groups is increased at step  430 , the time taken to print one line will also increase. Thus, frequency of the printer head  120  should be adjusted accordingly. 
     FIG. 3  depicts another view to facilitate explanation of an embodiment of a method of sequentially driving a plurality of nozzles. In the example illustrated by  FIG. 3 , the nozzles are divided into 20 driving groups. The driving groups are doubled in the embodiment illustrated by  FIG. 3  as compared to the embodiment illustrated by  FIG. 2 . Therefore, using the method illustrated in  FIG. 3 , a total of four print lines, Line 1, Line 2, Line 3, and Line 4, can be printed by driving the nozzles to sequentially convey ink from a first group  300  of nozzles. A total of 60 nozzles are divided into 20 driving groups, each driving group including 3 nozzles. When the nozzles are driven as illustrated in  FIG. 3 , approximately 50% less power is consumed compared to the power consumed when driving the nozzles as illustrated by  FIG. 2 . Since the time required in printing a single print line doubles when the number of driving groups are doubled, as illustrated in  FIG. 3 , the frequency of printer head  120  utilization may be reduced by 50% compared to the embodiment illustrated in  FIG. 2 . 
   The control signal generator  130  provides control signals to control operations of printer head  120  depending on the number of driving groups input from group determiner  170 . Printer head  120  drives the printing head according to control signals received and prints an image, as shown at step  450 . 
   As described above, it is possible to print using less power without reducing printing quality or speed by controlling the driving of the printer head using analyzed printing consumption power before printing. In addition, the overall size of the image forming apparatus can be reduced because a low-power power supply may be used. 
   Aspects of the present invention can also be embodied in a computer readable medium having stored thereon instructions for carrying out the invention. A computer readable medium is any data storage device that can store data and can thereafter be read by a computer system. Examples of a computer readable medium include, but are not limited to, read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, and carrier waves for data transmission. The computer readable medium can also be distributed over network coupled computer systems so that the computer readable instructions are stored and executed in a distributed fashion. Also, functional programs, codes, and code segments for accomplishing the present invention can be easily construed by programmers skilled in the art to which the present invention pertains. 
   While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.