Patent Publication Number: US-7588317-B2

Title: Printing apparatus, printhead, and driving method therefor

Description:
FIELD OF THE INVENTION 
     This invention relates to a printing apparatus, printhead, and driving method therefor. More particularly, this invention relates to driving of a printhead having at least first type printing elements and second type printing elements which require different application powers in order to obtain a desired printing characteristic. 
     An inkjet printhead according to this invention can be applied to a general printing apparatus, and also to apparatuses such as a copying machine, a facsimile apparatus having a communication system, and a wordprocessor having a printing unit. Further, this invention can be applied to an industrial printing apparatus multifunctionally combined with various processing apparatuses. 
     BACKGROUND OF THE INVENTION 
     The arrangement of a printhead used in an inkjet printing apparatus which prints information (e.g., a desired character and image) on a sheet-like print medium (e.g., paper or a film) is disclosed in, for example, Japanese Patent Publication Laid-Open No. 2002-374163. According to this publication, a printing element formed from a heating element (heater), a driver for driving the printing element, and a logic circuit for selectively driving the driver in accordance with image data are formed on a silicon substrate. 
     Color inkjet printers using a thermal inkjet technique of discharging ink by heat energy are achieving higher resolutions year after year. Particularly in the printhead of the inkjet printer, the layout density of orifices (nozzles) for discharging ink increases from 600 orifices to 1,200 orifices per inch. 
     The amount of discharge ink droplet which forms each pixel tends to decrease year after year in order to reduce graininess in the gradation of a monochrome image and at middle to low-density portions on a color photographic image. Especially in a printhead which discharges color ink, the amount of discharge ink droplet was about 15 pl a few years ago, but has decreased to 5 pl or 2 pl recently. 
     However, the following problem occurs when a printhead which prints a high-resolution image by small ink droplets is adopted. That is, when a high-resolution color graphic image or photographic image is printed, a high-resolution, high-quality image is printed to meet the user&#39;s need if a printhead discharging a small droplet is employed. To the contrary, in image printing of a color graph on a spreadsheet or the like that does not require high resolution, the use of small ink droplets increases the scan count, and it becomes difficult to meet demands for high-speed printing. 
     In order to solve this problem, countermeasures must be taken to increase the number of orifices laid out on one array and increase a printable area where printing is done by one scan or to increase the orifice layout density and enable printing a high-resolution image by one scan. 
     For example, Japanese Patent Publication Laid-Open No. 2002-79672 discloses a printhead in which orifice arrays are staggered and laid out on the two sides of a common ink supply port (common liquid chamber). This enables the layout density of orifice arrays to become double, compared to that of a single array. Even if the ink droplet is downsized, the printing speed does not decrease. 
     A printhead having the highest orifice layout density has 1,200 orifices per inch, and the mainstream of the discharge ink droplet amount is 2 pl. However, in order to meet demands for higher image qualities, the discharge ink droplet amount must be reduced to 1 pl or less. Moreover, in order to maintain the same printing speed, the number (common supply number) of orifices must be increased. However, if the number of orifices of the printhead is simply increased, the printhead becomes large, which is disadvantageous in cost and size. 
     In order to decrease the discharge ink droplet amount to 1 pl or less and maintain the printing speed for higher image qualities, the orifice layout density must be double or more the current maximum layout density (1,200 orifices per inch). Note that when orifices are staggered and laid out on the two sides of the ink supply port, the layout density on one side suffices to be 1,200 orifices per inch. 
     If the orifice layout density is further increased (to 2,400 orifices (1,200 orifices on one side) per inch), it becomes difficult to ensure the necessary width of a partition which separates adjacent nozzles, and the necessary width of an ink channel which greatly influences discharge performance. To solve this problem, there is proposed an arrangement in which orifices laid out on each array are staggered by changing the distance from the common liquid chamber. 
     When orifices on one array are staggered, the distance from the common liquid chamber to the orifice changes. In this case, in order to attain the same orifice discharge performance between orifices having the different distances, it is considered effective to optimize, in accordance with the position, the shape and size of each electrothermal transducer (heater) for generating heat energy. However, when the shape and size of the heater are changed, driving energy applied to the heater must be adjusted in accordance with the shape. 
     To adjust the driving energy, it is considered to change, in accordance with the heater shape, a signal for determining the time during which electric energy is applied to the heater. In this case, however, the number of signal lines increases. In a general inkjet printhead, this leads to an increase in the number of terminals which connect the printhead to the apparatus main body since signals from the printing apparatus main body are supplied through these signal lines 
     Also, the printing apparatus main body does not have a sufficient margin for the number of signal lines in a cable for supplying signals to the printhead. Hence, the printing apparatus main body must be modified to increase the number of signals supplied via the cable and increase the number of ASIC ports in order to output the signals. 
     These changes undesirably increase the size and cost of an inkjet printing apparatus of which reduction of size and cost is strongly demanded. 
     This problem is not limited to only a thermal inkjet printhead but common to all printheads having at least two types of printing elements which require different application electric energies (powers) in order to obtain a desired printing characteristic. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is conceived as a response to the above-described disadvantages of the conventional art. 
     For example, a printing apparatus according to the present invention is capable of driving different types of printing elements arranged in a printhead by proper powers without increasing the number of signal lines between the printhead and the apparatus main body, complicating the circuit configuration, or decreasing the printing speed. 
     According to one aspect of the present invention, preferably, there is provided a printhead having a substrate including at least first type printing elements and second type printing elements, comprising: a time-division driving circuit, provided on the substrate, which selects a block to time-divisionally drive the first and second type printing elements in corresponding first and second periods; and a common signal line, provided on the substrate, which supplies, to the first and second type printing elements, enable signals for designating different driving periods in the first and second periods. 
     In accordance with the invention as described above, a printing apparatus which prints with a printhead having at least the first type printing elements and second type printing elements, generates time-division signals representing the first and second periods corresponding to the first and second type printing elements, and supplies, to the first and second type printing elements via a common signal line, enable signals for designating different driving periods in the first and second periods. 
     By supplying signals representing different energization periods via a common signal line for supplying a signal for designating the energization period, appropriate powers can be applied to at least the two types of printing elements which require different application powers in order to attain a desired printing characteristic. 
     Hence, different types of printing elements arranged in the printhead can be driven by proper powers without increasing the number of signal lines between the printhead and the apparatus main body, complicating the circuit configuration, and decreasing the printing speed. As a result, a desired printing characteristic can be obtained by printing elements of either type. 
     The first and second type printing elements may have energy generating elements of different shapes. As the layout pattern, for example, the first and second type printing elements may be staggered. 
     The first and second type printing elements may be laid out on the same substrate at a density of 1,200 printing elements or more per inch in a predetermined direction. 
     Each printing element may comprise an orifice which discharges ink, and an energy generating element which is arranged in correspondence with the orifice, and may print by the inkjet method. In this case, the energy generating element may be an electrothermal transducer. 
     According to another aspect of the present invention, preferably, there is provided a printing apparatus which prints with a printhead having at least first type printing elements and second type printing elements, comprising: a signal generating circuit which generates time-division signals representing first and second periods corresponding to the first and second type printing elements; and a driving circuit which supplies, to the first and second type printing elements by using a common signal line, enable signals for designating different driving periods in the first and second periods. 
     Note that the time-division signal suffices to be a signal for dividing the first and second printing elements into a plurality of blocks for each type and driving each block by time division. 
     According to still another aspect of the present invention, preferably, there is provided a method of driving a printhead having at least first type printing elements and second type printing elements, comprising: a signal generating step of generating time-division signals representing first and second periods corresponding to the first and second type printing elements; and a driving step of supplying, to the first and second type printing elements via a common signal line, enable signals for designating different driving periods in the first and second periods. 
     The invention is particularly advantageous since signals representing different energization periods are supplied via a common signal line for supplying a signal for designating the energization period, and hence appropriate powers are applied to at least the two types of printing elements which require different application powers in order to obtain a desired printing characteristic. 
     Different types of printing elements arranged in the printhead can be driven by proper powers without increasing the number of signal lines between the printhead and the apparatus main body, complicating the circuit configuration, and decreasing the printing speed. In this manner, a desired printing characteristic can be achieved by printing elements of either type. 
     Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1A  is an enlarged schematic view showing some orifices and some electrothermal transducers on the second printing element substrate according to an embodiment of the present invention; 
         FIG. 1B  is a timing chart showing a signal associated with driving of the electrothermal transducer in  FIG. 1A ; 
         FIG. 2  is a perspective view showing a printing cartridge according to the embodiment of the present invention; 
         FIG. 3  is an exploded perspective view showing the structure of a printhead shown in  FIG. 2 ; 
         FIG. 4  is a partially cutaway perspective view showing the arrangement of a printing element substrate according to the embodiment of the present invention; 
         FIG. 5  is a partially cutaway perspective view showing the arrangement of another printing element substrate according to the embodiment of the present invention; 
         FIG. 6  is a block diagram showing the circuit of the second printing element substrate according to the embodiment of the present invention; 
         FIG. 7  is a timing chart showing a signal according to a modification; 
         FIG. 8  is a schematic view showing an inkjet printing apparatus which mounts the printhead cartridge shown in  FIG. 2 ; and 
         FIG. 9  is a block diagram showing the control configuration of the inkjet printing apparatus shown in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. 
     Note that building elements described in the following embodiment are merely illustrative, and do not limit the scope of the present invention. 
     In this specification, the terms “print” and “printing” not only include the formation of significant information such as characters and graphics, but also broadly include the formation of images, figures, patterns, and the like on a print medium, or the processing of the medium, regardless of whether they are significant or insignificant and whether they are so visualized as to be visually perceivable by humans. 
     Also, the term “print medium” not only includes a paper sheet used in common printing apparatuses, but also broadly includes materials, such as cloth, a plastic film, a metal plate, glass, ceramics, wood, and leather, capable of accepting ink. 
     Furthermore, the term “ink” (to be also referred to as a “liquid” hereinafter) should be extensively interpreted similar to the definition of “print” described above. That is, “ink” includes a liquid which, when applied onto a print medium, can form images, figures, patterns, and the like, can process the print medium, and can process ink (e.g., can solidify or insolubilize a coloring agent contained in ink applied to the print medium). 
     (Arrangement of Printhead Cartridge) 
       FIGS. 2 to 5  are perspective views for explaining a printhead cartridge, inkjet printhead, and ink tank which are used in an inkjet printing apparatus according to the embodiment of the present invention. 
     The inkjet printhead (to be simply referred to as a printhead hereinafter) is one building element of the printhead cartridge. As shown in  FIG. 2 , a printhead cartridge  1000  comprises a printhead  1001 , and an ink tank  1900  which is detachable from the printhead  1001  and supplies ink to the printhead  1001 . The printhead  1001  discharges ink, which is supplied from the ink tank  1900 , from orifices in accordance with printing information, and prints a character, image, or the like on a print medium. 
     The printhead cartridge  1000  is detachable from the carriage of the printing apparatus. The printhead cartridge  1000  is electrically connected to the carriage via the connection terminal of the carriage. Further, the printhead cartridge  1000  is fixed and supported at a predetermined position by the positioning unit of the carriage. The ink tank  1900  has tanks for black ink, cyan ink, magenta ink, and yellow ink. Each tank of the ink tank  1900  is detachable from the printhead  1001 , and each tank can be independently exchanged. This arrangement contributes to reducing the running cost of a printing operation of the printing apparatus. 
     The printhead  1001  adopts a method of printing using a heating element (heater) as an electrothermal transducer which generates heat energy in order to generate film boiling in ink in accordance with an electrical signal. 
     As shown in  FIGS. 2 and 3 , the printhead  1001  comprises a printing element unit  1002  which prints a character, image, or the like on a print medium such as print paper, and an ink supply unit  1003  which supplies ink to the printing element unit  1002 . Moreover, the printhead  1001  comprises a tank holder  2000  which detachably holds the ink tank  1900  for supplying ink to the ink supply unit  1003 . 
     The printing element unit  1002 , ink supply unit  1003 , and tank holder  2000  of the printhead  1001  will be explained in detail. 
     As shown in  FIG. 3 , the printing element unit  1002  has a printing element substrate  1100 , printing element substrate  1101 , first plate  1200 , electric wiring tape  1300 , electric contact substrate  2200 , and second plate  1400 . Ink supply ports  1201  and  1201   a  are formed in the first plate  1200 . 
     The ink supply unit  1003  has an ink supply member  1500 , a channel forming member  1600 , a joint rubber  2300 , filters  1700 , and seal rubbers  1800 . 
     (Printing Element Substrate) 
       FIG. 4  is a partially cutaway perspective view for explaining the arrangement of the printing element substrate  1100 . 
     The printing element substrate  1100  is used to discharge black ink. A plurality of electrothermal transducers  1103  which generate heat energy in order to discharge ink, and electric wires of Al or the like which supply power to the electrothermal transducers  1103  are formed on one surface of an Si substrate  1110  having about 0.5 to 1 mm in thickness. On the printing element substrate  1100 , a plurality of ink channels (not shown) and a plurality of orifices  1107  are formed in correspondence with the electrothermal transducers  1103  by a photolithographic process. The ink channels communicate with a common liquid chamber  1112  having an ink supply port  1102  for supplying ink. The printing element substrate  1100  is bonded and fixed to the first plate  1200 . 
     As shown in  FIG. 3 , the second plate  1400  having openings is bonded and fixed to the first plate  1200 . The electric wiring tape  1300  is so held as to be electrically connected to the printing element substrate  1100  via the second plate  1400 . An electrical signal for discharging ink is applied from the electric wiring tape  1300  to the printing element substrate  1100 . The electric wiring tape  1300  has an electric wiring portion corresponding to the printing element substrate  1100 . The electric contact substrate  2200  has an external signal input terminal  1301  which is arranged in correspondence with the electric wiring portion and receives an electrical signal from the printing apparatus. The external signal input terminal  1301  is positioned and fixed on the rear surface of the ink supply member  1500 . 
     On the printing element substrate  1100 , the electrothermal transducers  1103  are staggered on respective arrays on the two sides of the ink supply port  1102 . Electrodes  1104  for supplying power to electric wires are arrayed on two sides outside the electrothermal transducers (heaters)  1103 . Bumps  1105  of Au or the like are formed on the electrodes  1104 . On the Si substrate  1110 , the orifices  1107  and an ink channel wall  1106  which forms an ink channel corresponding to each electrothermal transducer  1103  are formed from a resin material by a photolithographic process, forming an orifice group  1108 . 
       FIG. 5  is a partially cutaway perspective view for explaining the arrangement of the printing element substrate  1101 . The printing element substrate  1101  is used to discharge color inks of three colors. In the printing element substrate  1101 , three common liquid chambers  1112  having ink supply ports  1102  are formed parallel to each other. The electrothermal transducers  1103  and ink orifices  1107  are formed on the two sides of each ink supply port  1102 . 
     In  FIG. 5 , the electrothermal transducers  1103  and ink orifices  1107  on the two sides of the ink supply port  1102  are respectively arranged linearly. In practice, the electrothermal transducers  1103  and ink orifices  1107  are staggered to increase the orifice density, which will be described later. 
     On the printing element substrate  1101 , similar to the printing element substrate  1100 , ink supply ports  1102 , electrothermal transducers  1103 , electric wires, electrodes  1104 , and the like are formed on an Si substrate  1110 . Ink channels and ink orifices  1107  are formed from a resin material on the Si substrate  1110  by a photolithographic process. On the printing element substrate  1101 , similar to the printing element substrate  1100 , bumps  1105  of Au or the like are formed on the electrodes  1104  for supplying power to electric wires. 
     As shown in  FIG. 3 , the printhead  1001  is completed by coupling the printing element unit  1002  to the ink supply unit  1003  and coupling the resultant structure to the tank holder  2000 . 
     (Operation of Printhead Cartridge) 
     As described above, the tanks of the ink tank  1900  respectively store inks of corresponding colors. Each tank of the ink tank  1900  has an ink supply port (not shown) for supplying ink to the printhead  1001 . When the ink tank  1900  is mounted on the printhead  1001 , each ink supply port press-contacts a corresponding filter  1700  formed at the joint of the printhead  1001 . Then, ink in each tank is supplied from the ink supply port to the printing element substrate  1100  via a corresponding ink supply path  1501  of the printhead  1001  and the first plate  1200 . 
     Ink supplied to the printing element substrate  1100  is supplied into a bubbling chamber positioned at the end of each ink channel having the electrothermal transducer  1103  and orifice  1107 . Finally, the ink is discharged as an ink droplet toward a print medium by heat energy applied from the electrothermal transducer  1103 . 
     (Arrangement of Inkjet Printing Apparatus) 
     An inkjet printing apparatus (to be referred to as a printing apparatus hereinafter) which can mount the cartridge type printhead  1001  will be explained. 
       FIG. 8  is a schematic view showing an example of the arrangement of the printing apparatus which can mount a printhead according to the present invention. 
     In this printing apparatus, the printhead cartridge  1000  shown in  FIG. 2  is positioned and exchangeably mounted on a carriage  102 . The carriage  102  has an electrical connection portion for transmitting a driving signal or the like to each discharge portion via the external signal input terminal  1301  of the printhead cartridge  1000 . 
     The carriage  102  is reciprocally guided and supported along a guide shaft  103  which extends in the scan direction of the carriage  102  and is arranged in the apparatus main body. The carriage  102  is connected to a carriage belt  107 . When the driving force of a driving motor  104  is transmitted to the carriage belt  107  via pulleys  105  and  106 , the carriage  102  moves along the guide shaft  103 . The carriage  102  comprises a linear encoder  130  for detecting the moving position of the carriage  102 . 
     A recovery unit  138  which performs a recovery operation of the printhead  1001  is arranged near the home position in the carriage moving direction. 
     Printing media  108  such as print sheets or thin plastic plates are separated and fed one by one from an auto sheet feeder (ASF)  132  by rotating pickup rollers  131  by a sheet feed motor  135  via a gear. By rotation of a conveyance roller  109 , the printing medium  108  is conveyed through a position (printing position) facing to the orifice surface of the printhead cartridge  1000 . A sensor  133  which detects the fed printing medium  108  is arranged near the conveyance roller  109 . 
     Note that the carriage scan direction is also called the main scan direction, and the printing medium conveyance direction is also called the sub-scan direction. 
     The printhead cartridge  1000  is mounted on the carriage  102  so that the array direction of orifices at each discharge portion is perpendicular or diagonal to the scan direction of the carriage  102 . Ink droplets are discharged from orifice arrays to print. 
     The printing apparatus comprises power supply means, and signal supply means for supplying a driving signal for driving the printing element and other signals to the printhead cartridge. 
       FIG. 9  is a block diagram showing the configuration of the control circuit of the printing apparatus. 
     In  FIG. 9 , reference numeral  1700  denotes an interface which inputs printing data;  1701 , an MPU;  1702 , a ROM which stores a control program to be executed by the MPU  1701 ;  1703 , a DRAM which saves various data (the above-described printing data, a printing signal supplied to the printhead, and the like); and  1704 , a gate array (G.A.) which supplies and controls printing data to the printhead  1001 . 
     The gate array  1704  also controls data transfer between the interface  1700 , the MPU  1701 , and the DRAM  1703 . 
     The carriage motor  104  moves the carriage  102  to which the printhead  1001  is mounted. Reference numeral  1709  denotes a conveyance motor which conveys a printing medium;  1705 , a head driver which drives the printhead  1001 ;  1706  and  1707 , motor drivers which drive the conveyance motor  1709  and the carriage motor  104 , respectively. 
     The operation of the above control configuration will be explained. When printing data is input to the interface  1700 , it is converted into a printing signal between the gate array  1704  and the MPU  1701 . The motor drivers  1706  and  1707  are driven, and at the same time the printhead  1001  is driven in accordance with the printing signal supplied to the head driver  1705 , thereby printing. 
     The MPU  1701  generates control signals in order to drive and control the printhead  1001 . The control signals include a block selection signal for time-divisionally driving the printing elements of the printhead  1001 , and a heat enable signal (ENB) for determining the driving period of the printing element. These control signals are supplied to the printhead  1001  via the head driver  1705 . The block selection signal is supplied to the printhead  1001  together with the printing signal via the same signal line. Details of these signals will be described later. 
     (Driving of Printing Element) 
     The printing element substrate  1101  of the printhead and a method of driving the printing element of the printhead will be described in detail with reference to  FIGS. 1A ,  1 B,  6 , and  7 . 
       FIG. 1A  is an enlarged schematic view showing some orifices and some electrothermal transducers for one ink supply port in the printing element substrate  1101 . The printing element substrate  1101  is designed so that orifices are laid out at a density of 2,400 orifices per inch for each ink and the ink droplet amount discharged from each orifice is about 1 pl. 
     In order to lay out orifices at a high density of 1,200 per inch on each side of the ink supply port in the printing element substrate  1101 , orifices on the each side are laid out not in a straight line but in a staggered shape. On the printing element substrate  1101 , electrothermal transducers  400 A and  400 B which generate heat energy to be applied to ink are formed around corresponding orifices  100 A and  100 B. In addition, the shape of the electrothermal transducer is changed in accordance with the distance from an ink supply port  500 . 
     More specifically, the electrothermal transducer  400 B (to be referred to as a B type electrothermal transducer hereinafter) close to the ink supply port  500  is elongated in a direction perpendicular to the ink supply port. To the contrary, the electrothermal transducer  400 A (to be referred to as an A type electrothermal transducer hereinafter) distant from the ink supply port has almost the square shape. As for the width of the ink channel which communicates with the ink supply port  500 , a width  800  of an ink channel  300 A extending to the distant orifice  100 A (to be referred to as an A type orifice hereinafter) is set to only a width  801  of an elongated heater (B type electrothermal transducer) at most. Since ink is supplied from the ink supply port  500  to the distant orifice  100 A, the resistance of the entire ink channel  300 A is high, and performance degrades in terms of the repetitive discharge speed of droplets. To prevent this, according to the embodiment, the electrothermal transducer  400 A is shaped into almost the square by decreasing the aspect ratio from that of the electrothermal transducer  400 B close to the ink supply port  500 . This design changes the relationship between the orifice shape and the electrothermal transducer. With this design, the ink discharge performance can improve, and a 1-pl droplet can be more stably discharged regardless of the distance from the ink supply port to the printing element. 
     The shape of the electrothermal transducer will be examined. When the aspect ratio of the electrothermal transducer decreases and its shape comes close to the square, the ineffective bubbling area (area which is formed owing to a low temperature around the printing element and does not contribute to the bubbling pressure) of the electrothermal transducer (printing element) relatively shrinks. In addition, as for the bubbling power efficiency on the discharge side, the back flow resistance (flow resistance between the ink supply port and the printing element) greatly increases because the channel is longer than that of a printing element close to the ink supply port. Hence, variations between staggered printing elements can be suppressed by decreasing the area of the electrothermal transducer  400 A distant from the ink supply port  500 . In other words, according to the embodiment, the area of the electrothermal transducer of a printing element (A type printing element) distant from the ink supply port is decreased, and the electrothermal transducer is shaped into the square. With this design, the discharge performance of the A type printing element is made to coincide with that of a printing element (B type printing element) close to the ink supply port. 
     The areas and ink channel widths of the two types of electrothermal transducers will be further explained with reference to  FIG. 1A . 
     First and second orifice groups  900  and  901  each including a plurality of orifices for discharging a 1-pl ink droplet are respectively arranged on the two sides of the ink supply port  500 . Each orifice group includes two orifice arrays, i.e., an array of A type orifices  100 A and an array of B type orifices  100 B which are parallel in the longitudinal direction (to be referred to as an array direction hereinafter) of the ink supply port  500 . In each orifice group, the A type orifices  100 A and B type orifices  100 B are staggered from each other in the array direction. The distance between two adjacent orifices in the array direction is set to 1/1200 inches. The two orifice groups  900  and  901  are shifted by only 1/2400 inches in the array direction. In this manner, the layout density of orifices for each ink is set to 2,400 orifices per inch on the printing element substrate  1101 . 
     In each orifice group ( 900  or  901 ), the electrothermal transducers  400 A and  400 B which are arranged in correspondence with the A and B type orifices  100 A and  100 B communicate with the ink supply port  500  via the corresponding ink channels  300 A and  300 B. The width  800  of the ink channel  300 A corresponding to the A type orifice  100 A is limited by the width  801  of the B type electrothermal transducer  400 B, and is set only almost equal to or smaller than the width  801 . For proper discharge, when orifices are to be laid out at a high density of 1,200 orifices or more per inch in consideration of a small space which is necessary between the electrothermal transducer and the partition, orifices are laid out more desirably in a staggered shape than in a straight line while considering the shape of the electrothermal transducer. 
     In the embodiment, the areas of the two types of orifices  100 A and  100 B are set equal to 70 μm 2  in order to adjust ink droplet amounts discharged from all orifices to 1 pl. The size of the electrothermal transducer is designed to 10 μm wide×28 μm long for the B type electrothermal transducer  400 B and 14 μm wide×18 μm long for the A type electrothermal transducer  400 A. The area of the electrothermal transducer is 280 μm 2  for the B type and 252 μm 2  for the A type. By setting the area of the A type electrothermal transducer  400 A smaller than that of the B type electrothermal transducer  400 B, the effective area which actually contributes to discharge is adjusted to balance the discharge abilities of the two types of orifices. 
     As described above, in the embodiment, the two types of electrothermal transducers, which are laid out at positions at different distances from the ink supply port, are different in size. In order to drive the two types of electrothermal transducers at high speed, optimal energies corresponding to them must be supplied. 
     The printing element substrate is obtained by forming heating elements (heaters) as electrothermal transducers on a semiconductor substrate in the film forming process. Thus, the resistance difference between heating elements on the same substrate is substantially determined by the element shape (aspect ratio). Further, it is known that the temperature of the heating element is determined by energy per unit area. In the embodiment, the area of the A type electrothermal transducer  400 A is set smaller (downsized) than that of the B type electrothermal transducer  400 B, and the aspect ratio (the size in a direction in which the current flows is dominant) is also set smaller (formed into the square), i.e., the resistance is set lower. 
     Since the resistance value of the electrothermal transducer  100 A is different from that of the electrotheremal transducer  100 B, when driving pulses of the same width (time) are applied to these electrotheremal transducers, energy generated by an electrothermal transducer of either type becomes excessive or short, failing in normal discharge. More specifically, if a driving pulse appropriate for the A type electrothermal transducer is set, energy generated by the B type electrothermal transducer becomes excessive. To the contrary, if a driving pulse appropriate for the B type electrothermal transducer is set, energy generated by the A type electrothermal transducer becomes short. 
     To prevent this, the embodiment gives attention to the fact that the printing elements of the printhead are time-divisionally driven. The printhead is configured so that driving signals (ENB signals) of different widths are applied to the A and B types via a common driving signal line (ENB signal line) to properly drive the two types of electrothermal transducers having different shapes. 
       FIG. 1B  is a timing chart showing a signal supplied from the printing apparatus main body. 
     As shown in  FIG. 1B , all printing elements are driven divisionally at eight timings (time division count=8). In each of block periods serving as eight divided timings, electrothermal transducers of the same type are driven. In addition, the pulse width of the ENB signal which determines the driving period is changed in each block period in accordance with the shape (type) of the electrothermal transducer. 
     In  FIG. 1B , eight symbols (B 1 , A 1 , . . . , B 4 , and A 4 ) described in the block period (BLOCK) correspond to symbols on the right side of  FIG. 1A . That is, A type electrothermal transducers are driven in block periods with a prefix “A”, whereas B type electrothermal transducers are driven in block periods with a prefix “B”. By using a single ENB signal, proper energies (powers) can be applied to drive the two types of electrothermal transducers having different shapes. 
     In  FIG. 1B , the period during which the ENB signal is at low level in each of the eight divided block periods B 1 , A 1 , B 2 , A 2 , B 3 , A 3 , B 4 , and A 4  is a driving period during which power is applied to the electrothermal transducer. The interval between driving periods is an idle period during which the printing element is refilled with ink by the discharge amount. As shown in  FIG. 1B , in the embodiment, the start timings of the driving periods of the A and B type electrothermal transducers are set so that the durations of idle periods become almost equal to each other. 
     Signals LT, CLK, DATA, and ENB shown in  FIG. 1B  will be explained with reference to  FIG. 6  showing the internal circuit of the printing element substrate  1101 . 
       FIG. 6  is a block diagram showing a circuit configuration corresponding to one of the two orifice groups shown in  FIG. 1A . The circuit shown in  FIG. 6  corresponds to 320 orifices contained in one orifice group, and the number of orifices corresponding to one ink supply port is 640. 
     In  FIG. 6 , reference numeral  601  denotes a shift register which receives and holds, bit by bit in accordance with a clock signal (CLK), image data input as a printing signal (DATA) and a block selection signal for designating a block to be time-divisionally driven. Reference numeral  602  denotes a latch which temporarily latches a signal held by the shift register  601  at the input timing of a latch signal (LT) during driving of the electrothermal transducer. Reference numeral  603  denotes a 3 to 8 decoder which decodes a 3-bit block selection signal latched by the latch  602  into eight block signals. Reference numeral  604  denotes each AND circuit which performs AND-operation of the ENB signal, a block signal output from the 3 to 8 decoder  603 , and a signal which makes an electrothermal transducer correspond to a block and is supplied from one of matrix-wired lines. Reference numeral  605  denotes a switching element which drives a corresponding electrothermal transducer in accordance with an output from the AND circuit  604 . Reference symbol VH denotes a power supply terminal for supplying energy to the electrothermal transducer. Reference symbol GNDH denotes a GND terminal to which the electrothermal transducer is connected via the switching element. Reference symbol ENB denotes an ENB terminal for receiving an ENB signal supplied from the head driver  1705  of the printing apparatus main body, as described above. 
     A circuit which is arranged in the printing apparatus main body and generates the ENB signal can be implemented by various circuits, in addition to the above-described configuration. For example, a circuit can be adopted which changes the pulse width of an output signal by adjusting the timing when a counter which receives the clock signal (CLK) is reset. A circuit of another configuration is also available. 
     In this configuration, electrothermal transducers of the same type are driven at the same timing in eight time-division block periods in the order of B 1 , A 1 , B 2 , A 2 . B 3 , A 3 , B 4 , and A 4  on the printing element substrate. More specifically, the pulse width (driving period) of the ENB signal is changed between block periods (A 1 , A 2 , A 3 , and A 4 ) corresponding to A type electrothermal transducers and block periods (B 1 , B 2 , B 3 , and B 4 ) corresponding to B type electrothermal transducers. This setting optimizes electric energies (powers) applied to the two types of electrothermal transducers. 
     According to the above-described embodiment, appropriate powers can be applied to the two types of electrothermal transducers having different shapes without increasing the number of signal lines between the printhead and the apparatus main body, complicating the circuit configuration, and decreasing the printing speed. 
     &lt;Modification&gt; 
     In the above embodiment, the eight time-division block periods are equal to each other, but this does not limit the present invention. In a configuration in which the frequency of the clock CLK is increased to shorten the data transfer time, the duration of the driving period may be changed in accordance with the type of electrothermal transducer. 
     Similar to  FIG. 1B ,  FIG. 7  is a timing chart showing a signal associated with driving of the electrothermal transducer according to the modification. As shown in  FIG. 7 , the block periods B 1 , B 2 , B 3 , and B 4  are set shorter than the block periods A 1 , A 2 , A 3 , and A 4  in accordance with the duration of the driving period of each type of electrothermal transducer. As a result, the time of one cycle during which all electrothermal transducers are driven once is shortened. Also in this modification, the start timings of the driving periods of the A and B type electrothermal transducers are set so that the durations of idle periods become almost equal to each other. 
     Other Embodiment 
     In the above embodiment, electrothermal transducers respectively arranged in 320 orifices which are laid out at high density on one side of the ink supply port are divided into eight and time-divisionally driven. However, the number of orifices, the time division count, and the circuit configuration are not limited to the above-described ones, and the present invention can be applied to printing apparatuses having printheads of various specifications. 
     The present invention can also be applied to a printing apparatus which prints by a printing method other than the inkjet method as far as the printhead comprises at least two types of energy generating elements which require different application powers in order to obtain a desired printing characteristic. 
     For example, orifices (printing elements) may be linearly laid out, or the number of types of energy generating elements (electrothermal transducers) which require different application powers may be three or more. The mechanical structure is not limited to a serial type, and a print medium may be moved relatively to the printhead. 
     In addition, the form of the printing apparatus to which the present invention is applied is not limited to an integrated or separate image output terminal for an information processing device such as a computer. In addition, the printing apparatus may take the form of a copying apparatus combined with a reader, a facsimile apparatus having a transmission/reception function, or a multi-functional peripheral having these functions. 
     As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims. 
     CLAIM OF PRIORITY 
     This application claims priority from Japanese Patent Application No. 2005-106799 filed on Apr. 1, 2005, the entire contents of which are incorporated herein by reference.