Abstract:
Ink jet recording in both color and monochromatically uses a recording apparatus having a recording head with ink discharge openings for discharging ink onto a recording medium, wherein the ink discharge openings correspond respectively to black ink and a plurality of non-black inks of colors that become black when mixed, and also having a carriage for moving the recording head relative to the recording medium. Monochromatic recording is performed by alternately recording on the recording medium black dots formed by the black ink and black dots formed by mixing the plurality of non-black inks while moving the recording head relative to the recording medium.

Description:
This application is a division of application Ser. No. 07/608,631 filed Nov. 6, 1990, now U.S. Pat. No. 5,220,342 which is a continuation of application Ser. No. 07/464,698 filed Jan. 16, 1990, now abandoned, which is a continuation of application Ser. No. 07/342,966 filed Apr. 25, 1989, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an ink jet recording method for a recording device equipped with a head having a plurality of nozzles corresponding to the respective ink colors of detractive color mixing of color recording to be used, for example, in color ink jet recording device. 
     2. Related Background Art 
     FIG. 1 is a schematic upper view of an example of an ink jet recording device in general, FIG. 2 is a block diagram showing its control system. 
     In FIG. 1, numeral  1  is a platen which rotates at predetermined steps for sub-scanning during recording with a recording medium (not shown) wound therearound. Numeral  2  is a line feed motor which transmits rotation to the rotational shaft of the platen  1  through a gear  3 .  4  is an ink Jet recording head (hereinafter called “head”) mounted freely slidable on a guide bar (not shown) arranged in parallel to the platen  1 , and is provided with a plurality of discharge openings  5  for discharging ink as droplets. Numeral  6  is a belt for moving the head  5  reciprocally in the longitudinal direction of the platen  1 . Numerals  7  and  8  are pulleys arranged at the both ends of the belt  6 , and numeral  9  a carriage motor for rotating the pulley  8 . 
     Numeral  10  is a paper sensor for detecting the presence of a recording medium arranged in the vicinity of the surface of the platen  1 , numeral  11  an encoder sensor mounted on the head  4 , and numeral  12  a linear encoder fixedly arranged in parallel to the platen  1  and also opposed to the encoder sensor  11 . Numeral  13  is a home position sensor for detecting that the head  4  is in the home position, numeral  14  is a cap which is used when restoring poor discharge including non-discharge, numeral  15  a motor which is the driving source for progressing forward and backward the cap  14  with respect to the head, and numeral  16  a cap sensor for detecting that the cap  14  is mounted on the head  4 . 
     In the above constitution, when the recording medium is mounted on the platen  1 , it is detected by the paper sensor  10  to be made in a recordable state. When the recording start button is pushed the carriage is moved, and the head  4  after being set at the home position, moves following the printing format of the recording device, and permits ink droplets to fly following the recording data from the discharge openings. The head  4  is subjected to main scanning, driven by the belt  6  with the motor  9  as the driving source. Every time when one line of main scanning is completed, the motor  2  is driven to rotate the platen  1 . 
     For preventing clogging of the discharge openings of the head  4 , the cap  14  is covered over the head  4  periodically or if necessary. This state is detected by the cap sensor  16 , and recording actuation is intermitted by this detection. The restoration actuation comprises absorbing the ink within the nozzles from outside of the nozzles by an absorbing mechanism (not shown) communicated to the cap  14 , thereby removing foreign matters, etc. within the nozzles. By doing so, subsequent defective recording will be cancelled. 
     Next, the constitution of the control system shown in FIG. 2 is to be described. 
     CPU  20  constitutes the main body of control, to which a group of switches  21  (arranged on the operational panel) are connected through an input and output interface (not shown), a DC servo reversing circuit  22  for driving the carriage motor  9 , a stepping motor driving circuit  23  for driving the line feed motor  2 , a head driver  24  for driving the recording head  4  based on the recording data, a group of various sensors  25 , the encoder sensor  11  and the home position sensor  13 . 
     In the constitution shown in FIG. 2, CPU  20  performs the following operational actuation corresponding to the operational input performed by the switch group  21  provided on the operational panel (not shown). More specifically, by referring to the input from the encoder sensor  11  and the home position sensor  13 , the driving control of the carriage motor  9  is conducted through the DC servo reversing circuit  22 , and also the driving control of the line feed motor  2  through the stepping motor driving circuit  23 , whereby the recording data D is output to the head driver  24  and the recording head  4  is driven with the head driver  24 . Also, control of other mechanisms is conducted corresponding to the inputs from another group of sensors  25 . 
     Under such constitution, recording actuation is commenced by pushing down of the print switch among the switch group  21 , and the line feed motor is driven several steps on confirmation of the presence of recording paper by the paper sensor  10 , whereby the platen  1  is rotated and the recording paper set at the recording start position. Subsequently, the carriage motor  9  is driven to move the recording head  4  in a reciprocating manner, and the line feed motor  2  is driven as synchronized therewith to deliver the recording paper line by line. During such actuation, driving signals corresponding to the recording data are applied from the head driver  24  on the recording head  4  to drive the recording head  4 , whereby ink is discharged as droplets through the discharge openings of the nozzles  5  to effect recording of letters, images, etc. 
     FIG. 3 is a schematic front view of the head  4  in FIG.  1 . 
     As shown in FIG. 3, four discharge openings  41 ,  42 ,  43  and  44  are arranged at predetermined intervals on the same line. To the openings  41  to  44  the ink of cyan (C), magenta (M), yellow (Y) and black (BK) are sequentially supplied. At the respective ink path communicated with the discharge opening energy generating members generating energy for discharging ink are mounted, which may comprise piezoelectric elements, etc. (not shown), and by applying predetermined voltages to the piezoelectric element, ink is discharged through the openings as droplets. To each of the openings  41  to  44  a pressure chamber the shape of a pipe (not shown) is individually communicated, and each pressure chamber is communicated, through a vinyl pipe, etc., to an ink tank containing the color ink corresponding to that opening. 
     In this case, as shown in FIG. 4, for the input signal, first a voltage Vrev of negative polarity is generated for a time period T1, which voltage is applied on the piezoelectric element to expand the pressure chamber. Next, a positive voltage Vop is generated for a time period T2, which is applied on the piezoelectric element to reduce the pressure chamber, thereby discharging the ink as the droplets. Further, the application voltage is gradually reduced over a time period T3, thereby effecting restoration actuation of the nozzle diameter. By setting suitably the levels of the voltages Vrev, Vop, the ink discharging amount (namely the recording dot diameter) can be varied. The minimum time interval for ink discharging is made, for example, the maximum 3 kHz of 333 μs. Full color recording can be effected by the presence of respective driving of the energy generating member provided corresponding to ink path communicated discharge openings  41  to  44 , control of the ink discharging amount, etc. Also, if the recording data D is letter data, recording of letter is also possible. 
     However, in such ink jet recording method of the prior art, which may be suitable for full color image by driving the energy generating member of the ink path corresponding respectively to the four colors, although printing only by black is necessary for recording of letter recording, the energy generating members in the ink path of other color are to be controlled, whereby no high speed printing could be performed. For example, in the case of performing recording one letter by 12 (dot)×7 (dot), if superfluous time other than recording is disregarded, when driven at 3 kHz, about 36 letters (3000/(12×7)=36) can be recorded per second, which however cannot be said to be high speed printing, thus not satisfying the demand. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an ink jet recording method which performs color recording and monochromatic recording comprises the steps of providing a recording apparatus having a recording head with ink discharge openings for discharging ink onto a recording medium, wherein the ink discharge openings correspond respectively to black ink and a plurality of non-black inks of colors that become black when mixed, and means for moving the recording head relative to the recording medium, and performing the monochromatic recording by alternately recording on the recording medium black dots formed by the black ink and black dots formed by mixing the plurality of non-black inks while moving the recording head relative to the recording medium. 
     In accordance with another aspect of the invention, an ink jet recording apparatus which performs color recording and monochromatic recording comprises a recording head having ink discharge openings for discharging ink onto a recording medium, wherein the ink discharge openings correspond respectively to black ink and a plurality of non-black inks of colors that become black when mixed and wherein the recording head performs monochromatic recording by alternately recording on the recording medium black dots formed by the black ink and black dots formed by mixing the plurality of non-black inks, and moving means for moving the recording head relative to the recording medium during the monochromatic recording. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2, respectively, show an example of an ink jet recording apparatus and a block diagram showing its control system; 
     FIG. 3 is a front view of a nozzle unit of a head  4  shown in FIG. 1, 
     FIG. 4 is a drive signal waveform chart for ink injection of the discharge opening of head shown in FIG.  3 . 
     FIG. 5 is a view showing a first recording method according to the present invention, 
     FIG. 6 is a view showing a second recording method according to the present invention, and 
     FIG. 7 is a block diagram showing a carriage motor control system necessary for realizing the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention enables high speed monochromatic recording to accomplish the above object by making the main scanning speed during monochromatic recording faster than during color recording and performing monochromatic recording by having alternately the black of single color and the black formed by mixing the three colors of cyan, magenta and yellow recorded on a recording medium. 
     Also, by making black and the black by mixing of three colors recorded alternately in the main scanning direction and the sub-scanning direction on the opposed recording medium relative to the minimum recording pitch, it becomes possible to further enhance recording quality of monochromatic recording. 
     Further, by making the ink discharging amount of the ink for three color mixing from each discharge opening, smaller than that of the single black, the recording dot diameter of two kinds of the ink can be balanced, for example made uniform to improve recording quality. 
     In the present invention, by making the main scanning speed in monochromatic recording faster than during color recording and performing recording by using alternately black and the black by mixing of three colors, recording is effected as if black ink were alternately being discharged from two different discharge openings, whereby high speed monochromatic recording becomes possible with the maximum driving frequency of the head being the same. 
     Further, by recording the single color black and the black by mixing of three colors alternately in the main scanning direction and the sub-scanning direction, arrangement of dot size can be done with good balance, and by making the ink discharging amount through each discharge opening by three color mixing smaller, the dot diameters can be balanced, for example made uniform, whereby both can contribute to improvement of recording quality. 
     The present invention will be described in detail below with reference to FIGS. 5 to  7 . 
     FIG. 7 is a block diagram of a carriage motor control system necessary for realizing the present invention and FIGS. 5 and 6 are views showing first and second recording methods of the present invention. 
     In FIG. 7, the control system includes an F/V converter  31  for frequency-voltage converting an FG signal output from an encoder sensor  11 , a reference voltage generator  32  for generating two types of reference voltage Vref on the basis of a signal from a CPU  20 , a comparator for comparing the reference voltage Vref and the output from the F/V converter  31 , a power amplifier  34  for power-amplifying the output from the comparator  33 , and a normal/reverse rotation circuit  35  for directly supplying the output from the power amplifier  34  to a carriage motor  9  or for, when an instruction is supplied from the CPU  20 , supplying the output from the power amplifier  34  to the carriage motor  9  so that the carriage motor  9  is rotated in a reverse direction. 
     In the arrangement shown in FIG. 7, a rotational speed of the carriage motor  9 , i.e. a moving speed of a head  4  is detected by the encoder sensor  11 , and is fed back to the F/V converter  31 . An F/V-converted signal is compared with the reference voltage Vref by the comparator  33 . The reference voltage Vref is designated by the CPU  20  so that it becomes higher in a black-and-white recording mode than in a color recording mode. The comparator  33  outputs the difference between the output from the F/V converter  31  and the reference voltage Vref, and this voltage difference is power-amplified. The amplified voltage is applied to the carriage motor  9  to rotate it. The carriage motor  9  is rotated to minimize the output from the comparator  33 , and its rotational speed is fed back through the encoder sensor  11 , thus performing DC servo control. 
     When the reference voltage Vref is high, since the output from the comparator  33  is increased, the rotational speed of the carriage motor  9  is increased, and the head  4  is moved at a high speed. Therefore, in the black-and-white recording mode, the moving speed of the head  4 , i.e. a main scanning speed is increased as compared to the color recording mode. Since the head  4  reciprocates along a platen  1 , the normal/reverse rotation circuit  35  functions every time the head  4  reaches a main scanning moving limit, thus reversing the carriage motor. 
     In the following embodiment of the present invention, the reference voltage Vref in the black-and-white (monotone) recording mode is set to be double that in the color recording mode, so that the main scanning speed of the head  4  is doubled. 
     A recording method according to the present invention will now be described. 
     In FIG. 5, white circles represent dots recorded by ink drops of black ink BK, and black circles represent dots recorded in black obtained by mixing three subtractive primary colors of cyan (C), magenta (M) and yellow (Y). Small points represent non-recorded points of 7×12 dots. A character formed by white and black circles is an English letter “E”, and a horizontal arrow indicates a main scanning direction. 
     An interval between adjacent recorded dots is about 0.15 mm, and a maximum drive frequency f of a recording head is set to be 3 kHz. Conventionally, a recording head performs main scan at 0.45 m/s, while in this embodiment, the recording head performs main scan and recording at 0.9 m/s (double or twice the conventional speed) in a black character recording mode. Odd-numbered columns in the main scanning direction are recorded in an ink color of black ink BK, and even-numbered columns are recorded in black obtained by mixing three colors C, M and Y. Thus, a conventional character recording speed is about 36 cps, while in this embodiment, the character recording speed is 71 cps or about double the conventional speed. 
     When the black ink BK and black obtained by mixing three colors are used, it must be determined that recording data is monotone (black-and-white) data or color tone data. For example, a switch can be arranged in a sensor group  25 , and is operated in accordance with a data content. According to the operation content of the switch, the above determination can be performed by the CPU  20 . Alternatively, a command can be transmitted in a data transmission mode to discriminate black-and-white data from color data. Furthermore, black-and-white or color data can be automatically discriminated by an arithmetic operation of the CPU  20  in the recording apparatus. 
     A second recording method of the present invention will now be described with reference to FIG.  6 . 
     In this embodiment, in addition to the first recording method of the above embodiment, a black BK and a black obtained by mixing three colors are alternately recorded on a surface of a recording medium. In this manner, the black BK and the black obtained by mixing three colors are alternately recorded in a main scanning direction (row direction) and a subscanning direction (column direction), so that two kinds of black can be distributed to be well balanced, and recording can be made without impairing character recording quality due to a small difference between the two types of black. 
     Since the black obatained by mixing three colors is formed by flying ink drops at three different positions to an identical position with respect to a recorded dot of the black BK, an amount of ink becomes three times the black ink BK, and a recording dot size is increased, thus degrading character quality. Ink injection amounts from C, M, and Y nozzles are preferably controlled to be smaller than that of the black BK so that a recording dot system (or optical reflection density) of black obtained by mixing three colors is same as that of the black BK. 
     In the above embodiment, a head comprising four discharge openings C, M, Y and BK is used. A head unit having a plurality of such heads may be used. 
     In addition, the present invention can be applied to an apparatus having plural heads disposed in proximity to each other which are provided with a single or plural discharge opening for C, M, Y and BK. 
     Also, the so called head can be one capable of moving relative to the apparatus, and can be one in which discharge openings are provided over one line relative to the member to be recorded. 
     The carriage motor  9  comprises a DC (direct current) motor to perform DC servo control. In place of the DC motor, a stepping motor may be used. An array of discharge openings of each color is set to be perpendicular to the above embodiment, and the main scanning direction is set to in the rotating direction of the platen  1 , so that a so-called rotary drum system may be employed. 
     In the above embodiment, the main scanning speed is doubled. However, the present invention is not limited to this embodiment, and a speed corresponding to an operation capacity of a mechanism can be set. 
     As can be apparent from the description, according to the present invention, the main scanning speed in the black-and-white recording mode is set to be higher than that in the color recording mode, and a black itself and a black obtained by mixing three colors are alternately recorded on a recording medium to perform monotone or black-and-white recording. Thus, a recording speed in a black-and-white recording mode using a color head can be increased. 
     Two types of black are alternately recorded in the main scanning and subscanning directions, thus improving character quality. 
     Ink injection amounts from the discharge openings for mixing three colors are decreased to uniform a recording dot system with balance and to improve recording quality.