Abstract:
An ink jet recording apparatus includes: a print head having an ink discharge port for discharging ink toward a recording medium, thereby performing printing on the recording medium; a recording medium thickness setting unit setting a thickness of the recording medium; a droplet amount setting unit setting an ink droplet amount depending on the recording medium thickness; and a droplet amount control unit controlling an amount of an ink droplet to be discharged from the ink discharge port to the set ink droplet amount.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims priority from Japanese Patent Application No. 2006-27903 filed Feb. 6, 2006, the entire content of which is incorporated herein by reference. 
   TECHNICAL FIELD 
   The invention relates to a method of controlling an ink jet recording apparatus and an ink jet recording apparatus. 
   BACKGROUND 
   There is known an ink jet printer that repeats recording operation and feeding operation to thereby form an image on the recording medium. In the recording operation, ink is discharged toward a recording medium while a head for discharging ink is reciprocated in the main scanning direction. In the feeding operation, the recording medium is fed in the sub scanning direction. 
   A plurality of nozzles or ink discharge ports are formed in the head. The nozzles are for discharging ink in the feeding direction of the recording medium. Ink is discharged toward the recording medium from the nozzles. 
   Jpn. Pat. Appln. Laid-Open Publication No. 2003-72055 discloses an ink jet recording device that maintains constant the interval between the head and surface of the recording medium facing the head in order to prevent displacement of ink droplet impact point on the recording medium, which will occur since the recording medium is moved at a predetermined speed. 
   Further, Jpn. Pat. Appln. Laid-Open Publication No. 2002-96528 discloses an ink jet recording apparatus that detects the changeable interval between the head and platen and performs predetermined processing such as changing the ink droplets discharge timing to thereby obtain a satisfactory image. 
   SUMMARY 
   However, the apparatus of Jpn. Pat. Appln. Laid-Open Publication No. 2003-72055 has disadvantages in that a mechanism for maintaining constant the interval between the head and surface of the recording medium becomes complicated to result in higher cost. Further, in the case where a plain paper is used as the recording medium, adhesion of ink causes the paper to swell to cause cockling (phenomenon in which the paper surface undulates) with the result that the paper is brought into contact with the head to cause ink stain on the image or damage to the head. 
   Further, a user can arbitrarily adjust the head gap in the case of the apparatus of Jpn. Pat. Appln. Laid-Open Publication No. 2002-96528. However, in the case where a large head gap is set, if the size of ink droplets discharged from the ink discharge ports is relatively small, ink becomes a mist state and the ink may fly in various directions, resulting in a variation in the ink droplet impact point. The ink head is reciprocated in the main scanning direction while the recording medium is moved in the sub scanning direction, so that the air existing between the head and recording medium moves in a complex manner. In particular, a technique for discharging a very small ink droplet with an ink amount of about 1 pl (picoliter) has recently been developed to improve image quality, and the ink may fly by the air flow. 
     FIG. 1  is a view schematically showing the positional relationship between the head and plain paper placed on the platen. In this case, the head discharges ink while moving from the left to right of the illustration. In the case where the amount of ink to be discharged is relatively large, ink reaches the printing surface, depicting the trajectory as represented by b. On the other hand, in the case where the amount of ink to be discharged is relatively small, discharged ink reaches the printing surface, depicting the trajectory as represented by a or c due to complex movement of air around the head, which is caused by the reciprocating motion of the head and movement of the printing paper, resulting in a variation in the ink droplet impact point. 
   In view of the foregoing, it is an object of the invention to provide a method of controlling an ink jet recording apparatus by appropriately controlling the ink amounts of the discharged ink droplets and an ink jet recording apparatus that can appropriately control the ink amounts of the discharged ink droplets. 
   In order to attain the above and other objects, the invention provides an ink jet recording apparatus, including: a print head having an ink discharge port for discharging ink toward a recording medium, thereby performing printing on the recording medium; a recording medium thickness setting unit setting a thickness of the recording medium; a droplet amount setting unit setting an ink droplet amount depending on the recording medium thickness; and a droplet amount control unit controlling an amount of an ink droplet to be discharged from the ink discharge port to the set ink droplet amount. 
   According to another aspect, the invention provides a method for controlling an ink jet recording apparatus having a print head formed with an ink discharge port for discharging ink toward a recording medium and a controller controlling an ink amount of an ink droplet to be discharged from the ink discharge port, the method including: setting thickness of the recording medium; and setting an ink droplet amount depending on the recording medium thickness, the controller controlling the ink amount of an ink droplet to be discharged from the ink discharge port to the set ink droplet amount. 
   According to another aspect, the invention provides a storage medium storing a set of program instructions executable on a data processing device for controlling an ink jet recording apparatus having a print head formed with an ink discharge port for discharging ink toward a recording medium and a controller controlling an ink amount of an ink droplet to be discharged from the ink discharge port, the instructions including: setting thickness of the recording medium; and setting an ink droplet amount depending on the recording medium thickness, the controller controlling the ink amount of an ink droplet to be discharged from the ink discharge port to the set ink droplet amount. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
       FIG. 1  is a view schematically showing a state where ink droplets are discharged toward the recording medium from the head; 
       FIG. 2  is a block diagram showing an electrical configuration of a personal computer and a printer according to an embodiment of the present invention; 
       FIG. 3  is a view showing a printer property setting window displayed on a display unit; 
       FIGS. 4(   a ) and  4 ( b ) are conceptual views showing the positional relationship between a paper placed on a platen and a head, wherein  FIG. 4(   a ) shows a case where a plain thin paper is used while  FIG. 4(   b ) shows a case where a thin glossy paper is used; 
       FIGS. 5(   a ) and  5 ( b ) are conceptual views showing the positional relationship between a paper placed on the platen and head, wherein  FIG. 5(   a ) shows a case where the head is shifted to a lower position while  FIG. 5(   b ) shows a case where the head is shifted to a higher level; 
       FIGS. 6(   a ) and  6 ( b ) are conceptual views showing the positional relationship between a paper placed on the platen and head, wherein  FIG. 6(   a ) shows a case where a thin glossy paper is used while  FIG. 6(   b ) shows a case where a thin plain paper is used; 
       FIG. 7  shows an example of a droplet amount table for a normal gap that stores the ink droplet amount that changes in association with the paper thickness and the paper type and an example of another droplet amount table for a large gap that stores the ink droplet size that does not change irrespective of the paper thickness and the paper type; and 
       FIG. 8  is a flowchart showing processing executed in the PC of  FIG. 2 . 
   

   DETAILED DESCRIPTION 
   A method of controlling an ink jet recording apparatus and an ink jet recording apparatus according to an embodiment of the invention will be described while referring to the accompanying drawings wherein like parts and components are designated by the same reference numerals to avoid duplicating description. 
     FIG. 2  is a block diagram showing an electrical configuration of a personal computer (hereinafter, referred to merely as “PC”)  10  and a printer  20  connected to the PC  10 . The PC  10  functions as an image processor for controlling the printer  20  to serve as an ink jet recording apparatus. 
   The PC  10  includes a CPU  11 , an ROM  12 , an RAM  13 , a hard disk drive (hereinafter, referred to as “HDD”)  14 , an operation section  15 , an LCD (Liquid Crystal Display)  16  serving as a display unit, and a printer interface (hereinafter, referred to as “I/F”)  17 . These components are connected to each other by a bus  18 . 
   The CPU  11  is a calculation unit. The CPU  11  executes programs stored in the ROM  12 , RAM  13 , and HDD  14 . The ROM  12  is a read-only memory that stores a basic program such as a boot program. 
   The RAM  13  is a rewritable memory. The RAM  13  stores data that needs to be temporarily stored in processing performed by the CPU  11 . When an application program or printer driver stored in the HDD  14  is executed, the application or driver is transferred to the RAM  13 . 
   The HDD  14  is a rewritable memory. The HDD  14  includes an OS memory  14   a  that stores an operating system executed on the PC  10 , a droplet amount table memory  14   b  that stores droplet amount tables T 1  and T 2  shown in  FIG. 7  that are referred to when a printer driver performs halftone processing, a printer driver memory  14   c  that stores the printer driver, and an image data memory  14   d  that stores image data. 
   The printer driver includes a program whose flowchart will be described with reference to  FIG. 8 . The printer driver may be originally stored in a data recording medium, such as a CD-ROM, and is stored in the HDD  14  from the data recording medium. Or, the printer driver may be downloaded to the HDD  14  from a network such as the Internet. 
   The printer  20  includes a print head  24 , a platen  34 , a head moving mechanism (not shown), and a recording paper conveying mechanism (not shown). The platen  34  is fixedly provided in the housing (not shown) of the printer  20 . The head moving mechanism moves the print head  24  in a main scanning direction relative to the platen  34 . The recording paper conveying mechanism conveys a recording paper on the platen  34  in a sub scanning direction that is perpendicular to the main scanning direction. The print head  24  includes: a plurality of nozzles  26  for ejecting ink droplets in a direction toward the platen  34 ; and an actuator  28  for actuating the nozzles  26  to eject ink droplets therefrom. The printer  20  further includes a gap adjustment section  22 , a driver  30 , and a droplet amount controller  32 . The gap adjustment section  22  adjusts the gap (head gap) between the print head  24  and the platen  34 . The driver  30  generates a drive signal of a waveform for driving the actuator  28 . The droplet amount controller  32  controls the driver  30  to change the waveform of the drive signal, thereby controlling the ink amounts of the ink droplets. 
   Various setting items made in the printer driver processing will next be described with reference to  FIG. 3 .  FIG. 3  shows a property setting window  28  displayed on the LCD  16  when a user selects print property setting in the printer driver processing. 
   Displayed on the property setting window  28  are a paper type/thickness selection box  28   a  for selecting the type and thickness of a printing paper which is a recording medium on which an image is printed, a paper size setting box  28   b  for selecting the size of a printing paper, a resolution setting box  28   c  for setting the resolution of an image to be printed, and a number-of-sets setting box  28   d  for setting the number of sets to be printed. 
   The paper type/thickness selection box  28   a  has a display area for displaying a selected paper type/thickness and an icon (a down-facing triangle) at the right end of the display area. When a user operates a mouse to point a cursor to the icon and clicks the mouse, a pull-down menu is displayed as also shown in  FIG. 3 . Then, when the user moves the cursor to any item on the displayed pull-down menu, the item indicated by the cursor is selected. 
   In the present embodiment, as the type/thickness of a printing paper, the user can select either thin plain paper, thick plain paper, thin glossy paper, or thick glossy paper. Similarly, the paper size setting box  28   b  has a display area for displaying a selected paper size and an icon for expanding a pull-down menu for item selection. The user can select the print paper size among A4, B5, postcard, and envelope. 
   The resolution setting box  28   c  has also an area for displaying a selected resolution and an icon for expanding a pull-down menu for item selection. The user can select either high-resolution or low-resolution. High-resolution is, e.g., 1200×1200 dpi, and low resolution is, e.g., 600×600 dpi. The ink droplet amount, that is, the amount of ink used to form each ink droplet differs depending on the selected resolution. 
   The number-of-sets setting box  28   d  has an area for displaying the determined number of sets by a numeric value. On the right side of this area, an increment icon (an up-facing triangle) for incrementing the numerical value and a decrement icon (down-facing triangle) for decrementing the numerical value are arranged vertically. When the user operates a mouse to move a cursor to these icons and click the mouse, the number of sets to be printed can be set. As a matter of course, a numerical keypad can be used to directly input the number of sets. 
   Next, the interval between the print head  24  and the surface of the recording paper will be described with reference to  FIGS. 4(   a ) and  4 ( b ).  FIGS. 4(   a ) and  4 ( b ) show the case where the interval between the upper surface of the platen  34  and lower surface of the print head  24  where the nozzles  26  are formed is set to G. In the case where a thin plain paper is selected as a printing paper, as shown in  FIG. 4(   a ), the interval between the upper surface (printing surface) of the thin plain paper and the print head  24  becomes A which is a value obtained by subtracting the thickness of the thin plain paper from the interval G. 
   In the case where a thin glossy paper is selected as a printing paper, when the thin glossy paper is placed on the upper surface of the platen  34 , as shown in  FIG. 4(   b ), the interval between the upper surface (printing surface) of the thin glossy paper and the print head  24  becomes B which is a value obtained by subtracting the thickness of the thin glossy paper from the interval G. 
   In general, the thickness of the thin plain paper is about 90 μm (micrometer) and thickness of the thin glossy paper is 225 μm, so that the interval A is larger than the interval B. Accordingly, when printing is performed on the thin plain paper, the interval between the print head lower surface and printing surface becomes comparatively large. Air moves in this large gap between the head and the printing paper, and therefore the ink droplet impact point varies for small-size ink droplets. In the case where the printing paper is an envelope, the thickness thereof is 210 to 260 μm, and therefore the interval between the print head  24  and printing surface becomes comparatively small. 
     FIGS. 5(   a ) and  5 ( b ) are views showing the case where the vertical position of the head is changed. In this embodiment, the vertical position of the print head  24  is controlled by the gap adjustment section  22 . 
     FIG. 5(   a ) shows a case where the head  24  is shifted to a lower position (gap position  1 ). In this case, the interval between the print head lower surface and printing surface of the thin plain paper becomes C.  FIG. 5(   b ) shows a case where the print head  24  is shifted to a higher position (gap position  2 ). In this case, the interval between the head lower surface and printing surface of the thin plain paper becomes D. The interval D is larger than the interval C. 
   As is the case with  FIGS. 4(   a ) and  4 ( b ),  FIGS. 6(   a ) and  6 ( b ) compare a case where the thin glossy paper is used and case where the thin plain paper is used. Cockling of a small degree occurs in the glossy paper. Cockling of a larger degree occurs in the plain paper in comparison with the glossy paper. Therefore, the interval between the head  24  and thin plain paper needs to be set larger.  FIG. 6(   a ) shows a state where a thin glossy paper is placed on the platen  34  and the interval between the head lower surface and printing surface is set to E.  FIG. 6(   b ) shows a state where a thin plain paper is placed on the platen  34  and the interval between the head lower surface and printing surface is set to F which is a value obtained when cockling does not occur. As shown in dotted curves in  FIG. 6(   b ), cockling easily occurs in the plain paper due to absorption of ink into the paper, so that the head  24  needs to be shifted to a higher position. 
   It is noted that the interval (head gap) between the head lower surface and platen upper surface can be set to either one of a normal gap of 1.4 mm and a large gap of 2 mm. 
   A plurality of pairs of droplet amount tables T 1  and T 2  for setting the ink droplet amounts are stored in the droplet amount table memory  14   b . A pair of droplet amount tables T 1  and T 2  is stored for each resolution.  FIG. 7  shows an example of the pair of droplet amount tables T 1  and T 2  for the resolution of 1200×1200 dpi. One pair of droplet amount tables T 1  and T 2  for each resolution include a droplet amount table T 1  for the normal head gap of 1.4 mm and another droplet amount table T 2  for the large head gap of 2 mm. 
   In the droplet amount table T 1 , the “distance between head and print surface” is a value obtained by subtracting the paper thickness from the normal gap of 1.4 mm between the head  24  and the platen  34 . 
   In the present embodiment, three ink droplet sizes: small-dot, middle-dot, and large-dot are used to perform printing in so-called halftone processing. As shown in  FIG. 7 , the droplet amount table T 1  for the normal gap stores therein twelve values of ink droplet amounts for the three ink droplet sizes in association with the four pairs of the thickness and the type of the printing papers. 
   For example, as apparent from  FIG. 7 , 3 pl (small-dot), 5 pl (middle-dot), and 10 pl (large-dot) are set for the thin plain paper, while 1.5 pl (small-dot), 3 pl (middle-dot), and 10 pl (large-dot) are set for the thick glossy paper. As to the large-dot, the ink droplet amount is set to the same largest value (10 pl) for all of the thin plain, thick plain, thin glossy, and thick glossy papers. As to the middle-dot and small-dot, the ink droplet size is set larger for the thinner papers, and is set larger for the plain papers than for the glossy papers. 
   To the contrary, in the droplet amount table T 2  for the large gap, the ink droplet amount of the largest value of 10 pl that is used for the large-dot in the droplet amount table T 2  for the normal gap is set for all of the ink droplet sizes of small-dot, middle-dot, and large-dot irrespective of the thickness and type of the printing papers. 
   Next, processing executed by the printer driver will be described with reference to  FIG. 8 . 
     FIG. 8  is a flowchart showing the processing executed by the printer driver. 
   The printer driver firstly displays the printer property window shown in  FIG. 3  to allow a user to set paper thickness, paper type, paper size, and resolution (S 10 ). 
   Then, color conversion processing is performed for an image to be printed (S 20 ). In this color conversion processing, RGB (Red, Green, Blue) values constituting an input image are converted into CMYK values (Cyan, Magenta, Yellow, Black) for printing. Although detailed description is omitted here, before the color conversion processing, an optimum profile for a selected paper type is selected and, based on the selected profile, profile conversion is performed for the image data. 
   Then, whether the head gap should be the normal gap or the large gap is determined based on the paper thickness, paper type, and paper size that have been set in S 10  (S 30 ). 
   When the head gap is the normal gap, whether the paper type selected in S 10  is a plain paper or not is further determined (S 40 ). 
   In the case where the plain paper has been selected (S 40 : Yes), whether the paper thickness selected in S 10  is thin or thick is determined (S 50 ). 
   The halftone processing is then performed (S 60 ). That is, the size of each CMYK ink droplet for each pixel is set to either one of: small, middle, large, and none through a dither method or an error diffusion method. The ink amount for the ink droplet of the determined size is set based on the thickness of the plain paper while referring to the ink droplet amount table T 1  for the normal gap shown in  FIG. 7 . 
   On the other hand, in the case where not the plain paper but the glossy paper has been selected (S 40 : No), whether the paper thickness selected in S 10  is thin or thick is determined (S 70 ). Then, the halftone processing is performed to set the size of each CMYK ink droplet for each pixel to either small, middle, large, or none, and to set the ink amount for the ink droplet of the determined size based on the thickness of the glossy paper with reference to the ink droplet amount table T 1  for the normal gap (S 80 ). 
   On the other hand, when the head gap is the large gap, the halftone processing is performed and the largest droplet amount of 10 pl is set for all of the small, middle, and large ink droplets with reference to the ink droplet amount table T 2  for the large gap (S 90 ). So, in the case where the interval between the nozzles  26  and the surface of the recording medium becomes large, the ink droplet amount can be prevented from being set smaller than 10 pl. This keeps the ink droplet impact point on the recording medium constant and prevents image distortion which will be caused by displacement of the ink droplet impact point, thereby achieving clear and high-quality image printing. 
   After the setting has been made in the halftone processing in S 60 , S 80 , or S 90 , the setting data is output to the printer  20  (S 100 ). In the printer  20 , the gap adjustment section  22  sets the head gap to the gap (normal or large) determined in S 30 , and the droplet amount controller  32  controls the driver  30  to drive the actuator  28  to actuate the head  24  to eject ink droplets of the determined sizes with the determined ink droplet amounts. 
   As described above, when the paper type and the paper thickness have been set, the printer driver sets the ink droplet amount depending on the set paper thickness and paper type. Thus, in the case where the thin plain paper is selected, the interval between the head  24  and surface of the printing paper placed on the platen  34  is large. The problem accompanied by the cockling will not occur. By setting the ink droplet amount comparatively large, it is possible to prevent a variation in the ink droplet impact point. 
   Further, in the case where a thick glossy paper is selected, the interval between the head  24  and surface of the printing paper placed on the platen  34  is small. Cockling of a small degree occurs on the glossy paper. So, even though the ink droplet amount is set comparatively small, variation in the ink droplet impact point can be prevented, thereby achieving the high-quality image printing. 
   While the invention has been described in detail with reference to the embodiment thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention. 
   For example, in the above embodiment, settings of the ink droplet amounts are made on the printer driver on the PC  10  side. However, the printer  20  may be modified to have the electrical configuration the same as those shown in  FIG. 2  and to perform settings of the ink droplet amounts in the same manner as described above with reference to  FIG. 8 . For example, the printer  20  may be modified so as to be capable of receiving a data storing medium directly attached thereto, and of printing image data stored in the data recording medium. 
   The printer  20  may be modified to print only on a single type of recording paper. For example, the printer  20  may be modified to print only on plain paper. In such a case, it is sufficient that the user selects only the thickness of the printing paper. The paper type/thickness selection box  28   a  on the printer property window of  FIG. 3  is modified to select only the thickness of the printing paper. The ink droplet amount table T 1  for the normal gap shown in  FIG. 7  is modified to include rows only for the plain paper. In  FIG. 8 , the process of S 40 , S 70 , and S 80  may be omitted, and the process of S 60  is modified to perform the halftone processing and to set the droplet amounts for the small, middle, and large ink droplets based on the thickness of the printing paper. 
   The paper size is set by the user on the display window in the above embodiment. Alternatively, the printer  20  may be provided with a paper feeding apparatus for feeding a paper by using a guide plate. The user can adjust the guide plate to the size of the paper stacked. In such a case, the adjusted position of the guide plate may be detected to identify the paper type. For example, the printer  20  may determine that the stacked papers are plain papers or glossy papers when the A4 size is detected, and may determine that the stacked papers are envelops when the envelop size is detected.