Abstract:
An ink jet printing apparatus includes a plurality of heads for discharging liquids used for plural types of prints each exhibiting a different attribute. Further the apparatus includes a control apparatus for adjusting and controlling a timing of a preliminary discharge for maintaining a discharge not contributing to records by said plurality of heads, per attribute of the liquids to be discharged in such a manner that droplets of the liquids exhibiting the same attribute are discharged to the same position.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink jet printing apparatus including a unit for recovering a function of a nozzle defined as an ink discharge member of an ink jet head for printing a print image by jetting ink liquid droplets. 
     2. Related Background Art 
     In recent years, a resolution of an ink jet printing apparatus has increasingly been enhanced. The resolution, which was hitherto on the order of 180 dpi, increases up to 360 dpi and further to 600 dpi more than three times as high as the above. The resolution is thus increased, which turns ink liquid droplets into much finer liquid droplets and further enhances a density of a nozzle arrangement. With this higher resolution, a variety of control operations and works have been implemented with respect to nozzle members defined as ink discharging portions of the ink jet printing apparatus in order to obtain a discharge stability. For example, when the printing ceases for a long period of time, a nozzle surface is capped so as not to unnecessarily evaporate the water content from an ink liquid in the nozzle member. This prevents the ink from being unable to be discharged due to an increase in viscosity of the ink liquid in the nozzle member and a composite factor such as a fixation of the ink adhered to the periphery of the nozzle, an adhesion of dusts and the increased viscosity of the ink in the nozzle member. Further, there is conducted an operation of sucking the ink liquid within the nozzle. A first purpose of this operation is to forcibly remove the ink liquid of which the viscosity increases at the nozzle if the ink jet printing apparatus has been in an unused state for a long time. A second purpose of the operation described above is to remove bubbles existing inside the ink liquid in the nozzle member. Moreover, the nozzle surface is exposed directly to the atmospheric air during the printing process, and therefore the viscosity of the ink liquid increases on the nozzle surface. Then, a discharge resistance rises due to the ink layer having the increased viscosity, with the result that the liquid droplets can not be discharged with a stability. Further, for obviating an increased concentration of a color ink liquid due to the increased viscosity of the ink, the ink is discharged when starting the print and during the printing, thereby obtaining the stable discharge (which operation is referred to as a preliminary discharge). A variety of nozzle recovering operations based on the method described above have hitherto been carried out, however, particularly a preliminary discharging method of discharging the ink liquid droplets into a cap for the preliminary discharge at an interval of a fixed time by way of the nozzle recovering operation during the printing, is conceived as a quite important nozzle recovering method. In a serial ink jet printing apparatus having a plurality of nozzle rows consisting of a comparatively small number of printing nozzles, e.g., approximately 128 nozzles, the preliminary discharge involves the use of a method of carrying out the preliminary discharge by moving a carriage mounted with the nozzles to a predetermined preliminary discharge position. Further, in a high-speed full-multi printing apparatus including a plurality of nozzle rows consisting of a comparatively large number of printing nozzles, e.g., approximately 5200 nozzles, with respect to an electrostatic absorption carrier in which the carrier apparatus of the printing apparatus uses a belt etc., or an air suction adsorbing method, or an intermediate transfer body system using a drum and a transfer body system, there is taken a method of effecting the preliminary discharge on a belt used for the electrostatic adsorption carrier or in an arbitrary position or a random position on the drum used in the transfer body system. 
     The preliminary discharge explained above presents no problem in terms of a re-usability, a disposal processing property, a preserving property and an intra-appliance dangerousness when the preliminary discharge is executed using the liquids exhibiting the same attributes, e.g., the inks of the same color stuff, the same concentration and the same chemical characteristic. However, in the case of simultaneously using the liquids having different attributes, for instance, when enhancing an image quality by use of the above liquid and a printability enhancing liquid classified as one kind of color stuff reactive substances, there might arise an inconvenience in the preliminary discharge described above. Herein, the enhancement of the printability implies an enhancement of image qualities such as a density, a saturation, a degree of sharpness of an end portion and a dot diameter etc., an enhancement of a fixing property of the ink, and an enhancement of a weatherability such as a water resistance and a light resistance, i.e., an image preserving property. Further, the term “insoluble” implies such a:phenomenon that the anion radical contain in a dye within the ink and the cation radical of a cation substance which is contained in the printability enhancing liquid, cause interaction ion-wise enough to produce ion-coupling, and the color stuff (dye) uniformly solved in the ink is separated from the solution. Note that according to the present invention, even if all the dyes in the ink are not necessarily dissolved, there are obtained effects such as enhancements of the density, the character quality and the fixing property. Moreover, the term “agglutination” is used having the same meaning as the term “insoluble” when the-color stuff used in the ink is an aqueous dye containing, e.g., the anion radical. Further, if the color stuff used in the ink is a pigment, a pigment dispersant or the pigment surface and the cation radical of the cation substance which is contained in the printability enhancing liquid, cause ion-wise interaction, with the result that the pigment is brought into a dispersing destruction including an enlargement of a particle-size of the pigment. Normally, with the agglutination described above, the viscosity of the ink increases. 
     In the full-multi printing apparatus using the printability enhancing liquid exhibiting the performance explained above, when effecting the preliminary discharge onto the carrier belt in order to ensure a discharge reliability of the printing head, and if the printing heads for respective colors including the printing head for discharging the printability enhancing liquid onto the carrier belt execute the preliminary discharges in proper positions on the carrier belt, the ink dyes become insoluble due to the printability enhancing liquid and the ink dye as well, and a coagulation thereof occurs on the carrier belt. In general, when the coagulation described above occurs on the carrier belt, there declines a cleaning property of an ink cleaning apparatus for removing the inks on the carrier belt to prevent the inks from being transferred on the next printing paper. The decline of the cleaning property is that there decreases a quantity of the inks adsorbed to the cleaner for removing the inks adhered onto the carrier belt, and there grows a possibility of the inks being adhered to the next printing paper. Further, the adhesion of the inks onto the carrier belt, especially when the electrostatic adsorption carrier is carried out, might cause changes in dielectric constant and on volume resistivity, which in turn leads to a change in a paper adsorbing force. The change in the adsorbing force of the carrier belt changes a condition under which cockling thereof occurs, with the result that a floating quantity of the printing paper above the carrier belt varies. If the paper floating quantity increases, the printing paper is brought into contact with the printing head, which might cause a paper jam. This is considered inappropriate as the printing system. 
     Moreover, in a printing apparatus having an ink circulating system, a system for recovering only the liquids assuming the same color, composed of the same color stuff and having the same concentration is, not in an economic aspect, required to be structured when in the printing process or in a discharge portion protecting state. 
     Further, in the high-speed printing system required to execute the preliminary discharge onto the intermediate transfer body or the printing paper carrier member for maintaining the ink discharge portion, there arises a necessity for changing the cleaning materials for the preliminarily-discharged member, depending upon cleaning properties of the various inks. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to obviate the problems described above. 
     To accomplish this object, according to a first aspect of the present invention, an ink jet printing apparatus including a plurality of heads for discharging liquids used for plural types of prints each exhibiting a different attribute, comprises a control unit for adjusting and controlling a timing of a preliminary discharge for maintaining a discharge not contributing to records by the plurality of heads, per attribute of the liquids to be discharged in such a manner that droplets of the liquids exhibiting the same attribute are discharged to the same position. 
     According to a second aspect of the invention, in the ink jet printing apparatus according to the first aspect, the liquids exhibiting the different attributes are an ink containing a coloring agent, and a liquid, not containing the coloring agent, for enhancing a quality of an image formed by the ink. 
     According to a third aspect of the invention, in the ink jet printing apparatus according to the second aspect of the invention, the head is of a serial scan type, the printing apparatus provides one of areas exceeding a printing range with a preliminary discharge position for the ink and the other area with a preliminary discharge position for the image quality enhancing liquid, and the control unit performs control in such a manner that the liquids are discharged to the corresponding positions. 
     According to a fourth aspect of the invention, in the ink jet printing apparatus according to the second aspect of the invention, the head is of a serial scan type, the printing apparatus provides one of areas exceeding a printing range with a preliminary discharge position for the ink and a preliminary discharge position for the image quality enhancing liquid, which is disposed adjacently to the preliminary discharge position for the ink, and the control unit controls a discharge timing in such a manner that the liquids are preliminarily discharged to the corresponding positions. 
     According to a fifth aspect of the invention, in the ink jet printing apparatus according to the second aspect of the invention, the head is of a serial scan type, the printing apparatus provides one of areas exceeding a printing range with a preliminary discharge position for the ink, and a discharge timing is controlled so that the ink is preliminarily discharged to the preliminary discharge position for the ink, and the image quality enhancing liquid is preliminarily discharged onto a recording medium. 
     According to a sixth aspect of the invention, in the ink jet printing apparatus according to the second aspect of the invention, the head is of a full-line type, the printing apparatus includes a carrier belt for carrying the recording medium, and the control unit performs control of preliminarily discharging the ink onto the carrier belt and-preliminarily discharging the image quality enhancing liquid onto the recording medium. 
     According to a seventh aspect of the invention, in the ink jet printing apparatus according to the sixth aspect, a unit for making the liquid discharging position coincident with each other includes a sensor for detecting an upper end of paper, a head-to-head delay counter for counting a carrier distance to a printing head with a sensor signal serving as a trigger, a paper position counter actuated with a counter signal serving as a trigger, a head-to-head delay counter for counting a carrier distance to a next printing head, a comparing circuit for comparing a signal of the paper position counter with a signal of a printing area designation register and outputting a printing signal, and a comparing circuit for comparing the signal of the paper position counter with a signal of a preliminary discharge area designation register and outputting a preliminary discharge signal. 
     According to an eighth aspect of the invention, the ink jet printing apparatus according to the sixth aspect of the invention further comprises a cleaning unit for cleaning the ink discharged onto the carrier belt. 
     According to a ninth aspect of the invention, in the ink jet printing apparatus according to the second aspect of the invention, the head is of the full-line type, the recording apparatus includes a carrier belt for carrying the recording medium, and the control unit performs control of preliminarily discharging of the image quality enhancing liquid to a first position on the carrier belt, and preliminarily discharging of the ink to a second position adjacent to the first position with a spacing therebetween. 
     According to a tenth aspect of the invention, the ink jet printing apparatus according to the seventh aspect of the invention further comprises a cleaning unit for cleaning the ink discharged onto the record carrier belt, the cleaning unit having a circumferential length corresponding to a distance containing a width of the first position, a width of the second position, and an adjacent spacing between the first and second positions. 
     According to an eleventh aspect of the invention, in the ink jet printing apparatus according to the first aspect of the invention, a recording unit for printing a printed material includes an electrothermal converting element for generating an energy for discharging the ink. 
     According to a twelfth aspect of the invention, in the ink jet printing apparatus according to the eleventh aspect of the invention, the ink is discharged out of a discharge port by utilizing layer boiling occurred in the ink with the thermal energy applied by the electrothermal converting element. 
     The constructions given above make it feasible to improve a re-usability of the inks and to maintain the cleaning function of the cleaning member for a carrier medium or a transfer medium, and to thus enhance the easiness of processing the disposal inks. Further, it is possible to reduce the costs for the ink jet printing apparatus and to hold the performance thereof. 
     These together with other objects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. 
     Other objects and advantages of the present invention will become apparent during the following discussion in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view showing a construction of an ink jet printing apparatus; 
     FIG. 2 is a block diagram showing a control apparatus of the printing apparatus; 
     FIG. 3 is a diagram showing a printing paper supplying apparatus; 
     FIG. 4 is a diagram showing a carrier apparatus; 
     FIG. 5 is a block diagram showing a data creating unit; 
     FIG. 6 is a timing chart; 
     FIG. 7 is a timing chart continued from the timing chart in FIG. 6; and 
     FIG. 8 is a view illustrating another embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will hereinafter be described with reference to the accompanying drawings. 
     FIG. 1 is a view illustrating a construction of a typical ink jet printing apparatus. Referring to FIG. 1, a printing paper supplying apparatus is constructed as follows. Sheets of printing paper  101  defined as printing mediums are stacked in a paper feeding cassette  100 . 
     A pick-up roller  102  is rotated in this state, and the first printing paper  101  is thereby carried to a printing unit. Actuation of a sheet carrying unit of a carrier apparatus is started simultaneously with the printing paper pick-up process described above. A carrier drive energy is given upon rotations of a driving motor  111 . 
     The driving motor  111  is classified as a pulse motor of which a rotating speed and a rotational quantity are open-controllable. The driving motor  111  can be precisely controlled by a phase signal transmitted from a carrier control apparatus. With the rotations of the driving motor  111 , a rotational energy is transmitted to a driving roller  112  and a carrying roller  104 , and a carrier belt  105  starts rotating with the rotations of the two rollers  112 ,  104 . Therefore, a carrying velocity of the carrier belt  105  can be easily controlled by controlling the rotating speed of the driving motor  111 . 
     Further, in order to prevent a slippage between the two rollers  112 ,  104  and the carrier belt  105  by giving a fixed tension to the carrier belt  105 , a belt flexure preventing roller  110  pressed by a belt flexure preventing spring  109  acts on the carrier belt  105 . Moreover, a high voltage is applied to an electric supply roller  127  for supplying the carrier belt  105  with a static electricity for electrostatically adsorbing the printing paper  101  to the carrier belt  105 . 
     With the operation described above, there is also performed an operation of moving the printing head to a printing position. The respective printing heads are attached to a head unit  126  defined as a printing apparatus, and the head unit  126  is movable in a vertical direction  121 . Further, a nozzle unit  117  of each printing head is capped with a cap  118  when in a non-printing state, and a cap unit  130  is movable in a bilateral direction  116 . 
     Upon a start of the print, the head unit  126  temporarily rises, and the cap unit  130  is moved right and left, thereby uncapping the cap  118 . Thereafter, the head unit  126  descends down to the printing position. FIG. 1 shows a state where the printing head unit  126  is lowered down to the printable position. 
     Referring again to FIG. 1, what is illustrated therein is the head unit  126  mounted with five types of printing heads arranged sequentially from the right side in FIG. 1 such as a fifth head  125  for a yellow print, a fourth head  124  for a print in magenta, a third head  123  for a print in cyan, a second head  122  for a print in black, and a first head  19  for a printability enhancing liquid. 
     Furthermore, the printing head includes an ink supply tube  120  serving as an ink flow path for supplying the ink, and a disposal ink tube for disposing of the disposal ink. The ink supply tube  120  for the printing serves to supply the ink toward the printing heads from a sub-tank  107 . Furthermore, the ink used for recovering a function of the printing head is discharged toward the sub-tank  107  via the cap  118  from the nozzle unit  117  of the printing head. A tube for connecting the nozzle unit  117  to the sub-tank  107  is an ink supply recovery tube  106 . 
     The sub-tank  107  is disposed for obtaining a fixed liquid level difference with respect to a nozzle surface which is required in the ink jet printing apparatus, and an ink tank  108  serves as an ink supplying apparatus, wherein a portion therebetween is connected by a tube. 
     In the construction discussed above, the printing paper, when fed out of the.paper feeding cassette  100 , is brought into close contact with the carrier belt  105  by a close-fitting roller  115 . At this time, the carrier belt  105  remains in a charged state by the electric supply roller  127 , and hence the printing paper  101  is adsorbed to the carrier belt  105 . The printing paper  101  carried in the above state passes through under a TOF sensor  103 . At this moment, the print controlling apparatus is actuated. Let L 1  be a distance between the printability enhancing liquid printing head  119  and the TOF sensor  103 , and, after counting an elapse of the time required for the carrier belt  105  to move the distance L 1  from the moment when the printing paper  101  passes under the TOF sensor  103 , the printability enhancing liquid printing head  119  starts printing. Similarly, let Ln (n=2 to 5) be an interval between the printing heads, and each of the printing heads starts printing after the printing paper  101  has been carried a distance given by L 1 +ΣLm(m=2 to 5) after the TOF sensors  103  has made a TOF confirmation of the printing paper  101 . Herein, when m=2, it indicates a case of the black ink printing head, and, when m=5, it indicates a case of the yellow ink printing head. 
     The carrier belt  105  reaches a de-electrifying roller  128  and is thereby de-electrified, and hence the printing paper  101  printed by the procedures described above becomes easily separable from the carrier belt  105 . The printing paper  101  is thus separated due to a curvature of the driving roller  111  and discharged by a sheet discharge roller  114  into a discharged sheet tray  113 . In the construction explained above, the second printing paper  101  as a next sheet of printing paper, upon detecting a rear end of the printing paper  101  by the TOF sensor  103 , is picked up by the pick-up roller  102  and carried by the carrier apparatus to the printing apparatus, in which the sheet  101  is printed. 
     Given therefore between the first and second sheets of printing paper is a spacing corresponding to a moving distance of the carrier belt till an upper end of the second sheet is detected by the TOF sensor  103  since the pick-up roller has picked up the second printing paper after the lower end of the first printing paper passed under the TOF sensor  103 . Accordingly, the print control apparatus of each printing head is capable of confirming an image printing position from an upper or lower end signal of the sheet which is transmitted from the TOF sensor  103  and from a rotational quantity of the driving motor  111 , and further capable of distinguishing the first printing paper from the second printing paper. 
     As shown in FIG. 1, the printability enhancing liquid printing head  119  is disposed most upstream of the start-of-print position, and four types of printing heads using dye inks are disposed downstream thereof. In the above-described construction of the printing head, a printability enhancing liquid used by the printability enhancing liquid printing head  119  is substantially colorless clear and transparent, and a result of the printing is discriminated with a difficulty even when coated over the printing paper as compared with the dye inks used by other printing heads. Therefore, the printability enhancing liquid is preliminarily discharged to an arbitrary position on the printing paper in the process of its being carried by the carrier belt, which therefore involves a means for ensuring a nozzle discharging reliability. Further, each of the printing heads using other dye inks preliminarily discharges the ink between the first and second sheets of printing paper, whereby the nozzle discharging reliability can be ensured. Namely, only the preliminarily discharged dye inks exist on the printing belt, and a cleaning roller  129  defined as a cleaning apparatus becomes possible of its being constructed of an ink absorbing member for cleaning only the dye inks. 
     FIG. 2 is a block diagram showing a control unit of the printing apparatus. A position A of the carrier apparatus illustrated in FIG. 4 is connected to a position A shown in FIG.  2 . Further, the printing paper supplying apparatus is shown in FIG.  3 . 
     Shown herein is a diagram of a construction of mechanism in which the attention is paid to the preliminary discharge when in the printing process. As shown in FIG. 3, the printing paper supplying apparatus is constructed so that a paper feeding timing generation circuit  215  gives a timing at which the pick-up roller is rotated in order to pick up the printing paper out of the paper feeding cassette at the start of the printing. A paper feeding driving apparatus  214  rotates a pick-up motor  213  at this timing. 
     Further, for simultaneously driving the carrier belt, as shown in FIG. 4, a carrier driving timing circuit  202  generates a pulse driven with a fixed period, and this pulse is transmitted to a carrier apparatus driving apparatus  201 , in which a rotary force of a pulse motor  200  for rotating the carrier belt is generated. At this time, a feeding quantity of the carrier belt is set 1/n or n-times a raster resolution of the printing paper. 
     Referring to FIGS. 2 to  4 , it is assumed that the raster resolution and a driving pulse phase of the carrier belt show a one-to-one-correspondence. Namely, the mechanism is that when a phase of the pulse motor  200  is advanced by one, the carrier belt moves by one raster of the print image. When the printing paper is carried to the printing apparatus, the print control apparatus starts operating, and, to begin with, the upper end of the paper is detected by the TOF sensor  203 . 
     With this signal serving as a trigger, there starts an operation of a paper position counter  206  of each printing head which is. provided in a counter unit  204 . With a trigger of the TOF sensor  203 , there begins an operation of a head-to-head delay counter (L 1 )  205  for counting a carrier distance from the TOF sensor to the printability enhancing liquid printing head. The carrier distance is measured by counting the number of carrier driving timing pulses. Herein, the printability enhancing liquid printing head is referred to as a first head, the black ink printing head is termed a second head, and other heads are likewise referred to as a third head, a fourth head and a fifth head. 
     The head-to-head delay counter (L 1 )  205  is cleared when a counter value becomes 0 from L 1 , and outputs a trigger signal to a next output port. Then, the head-to-head delay counter (L 1 )  205  stops operating until the trigger signal is again inputted thereto. The carrier apparatus is therefore in such a state that the upper end of the printing paper passes under the TOF sensor  203  and thereafter the printing paper moves a distance L 1 , in which state the upper end of the printing paper comes just under the first head. At this time, the head-to-head delay counter (L 1 )  205  effects a start trigger upon a head-to-head delay counter (L 2 ) as well as on a paper position counter ( 1 )  206  conceived as a second counter, and then halts. 
     Incidentally, when an area extending from the upper end of the printing paper down to the lower end thereof is expressed by the number of rasters, the upper end of the sheet is expressed as a first raster, the lower end of the sheet is an M-th raster, and a distance up to the upper end of the next printing paper is an N-th raster. Herein, a start-of-print raster position of the printing area excluding upper and lower end margins of the paper, is referred to as an H-th raster position, and a final raster position of the sheet is termed an F-th raster position. 
     A printing area designation register  207  shown in FIG. 2 is stored with a H-th raster value and an F-th raster value. When a value of the paper position counter ( 1 )  206  is between “H” and “F”, the output signal is asserted in a comparing circuit  209  but is negated in cases other than,this. Namely, a state where this signal is asserted indicates an execution of the printing. Hence, this signal (which will be hereinafter referred to as a heat window signal) turns out to be a print command signal within a data creating unit  211 . Further, similarly a value of a first head preliminary discharge area designation register is set. This setting process is implemented for printing the data excluding the printing data in order to ensure a discharge stability of the nozzle within the printing head. A preliminary discharge area can be set in an arbitrary position in an arbitrary area ranging from the first raster to the N-th raster. Supposing that the preliminary discharge start position is referred to as an h-th raster position and a preliminary discharge end position is termed an f-th raster position, it is judged by using the paper position counter whether or not the present raster position is in the preliminary discharge area. 
     In the case of the first head, if the paper position counter ( 1 )  206  exists between “h” and “f” of the first head preliminary discharge area designation register  208 , a preliminary discharge signal is asserted from the comparing circuit  209 . For the duration of the assertion of this signal (which is hereinafter referred to as a preliminary discharge window signal), there is performed the control of executing the preliminary discharge. In the case of the first head  212 , the ink to be used is the printability enhancing liquid of which the color is transparent or as close as transparent, and therefore a printed result can not be recognized even when the preliminary discharge is effected on the printing paper, with the result that the values “h” and “f” of the preliminary discharge positions are assumed to be on the printing paper, and the preliminary discharge is executed on the printing paper. 
     The preliminary discharge positions of other-heads are set between the M-th raster and the N-th raster. With this setting, the preliminary discharge is effected between the first printing paper and the second printing paper. A data creating unit  211  creates the printing data and generates a driving signal. In the case of the first head  212 , the data creating unit (for the first head)  211  executes inside the printing data processing. 
     FIG. 5 is a diagram illustrating an internal configuration of the data creating unit. In the data creating unit, a data input apparatus  210  inputs the printing data to a shift register  219 , synchronizing with a clock. At a point of time when the data for one raster are inputted to the shift register  219 , a content of the shift register  219  is transferred to a shift register  221  in accordance with a carrier driving timing pulse. Based herein.on the carrier driving timing pulse signal, the printing data are created, and a liquid droplet discharge driving signal is generated. 
     Liquid droplet discharge control  218  and printing data transfer control  220  are started based on a logical ADD of a logical multiply  216  of the carrier driving timing pulse and a heat window, and of a logical multiply  224  of the carrier driving timing pulse and a preliminary discharge window. The driving pulse signal etc. is generated in the liquid droplet discharge control  218 . In the printing data transfer control  220 , a shift clock is transmitted to the shift register  221 . In the shift register  221 , the printing data are serially transmitted synchronizing with the shift register. Further, a data selection  223  implies a selection circuit, and preliminary discharge data  224  is selected in a state where a signal of the logical multiply of the carrier driving timing pulse and the preliminary discharge window is asserted. In states other than the above-mentioned state, the printing data are selected. The preliminary discharge data  224  for controlling discharge data when in the preliminary discharging process normally shows a full-nozzle print, and the preliminary discharge indicates all the nozzles to discharge the inks. Accordingly, a position of the preliminary discharge window in terms of carrying the paper is controlled, whereby the preliminary discharge can be done in any portions in the same circuit. 
     FIG. 6 is a timing chart. A position B in a timing chart shown in FIG. 7 is connected to a position B in FIG.  6 . 
     When starting the printing, a paper feeding timing signal  301  for feeding the printing paper is asserted in the printing apparatus. Further, at the same time, an actuation of a carrier driving timing pulse  302  is started. 
     The printing paper adsorbed onto the carrier belt passes through a sense point of the TOF sensor for detecting the upper end of the printing paper. The printing paper remains at the sense point of the TOF sensor, during which the TOF sensor continues to assert the TOF signal. A value of the head-to-head delay counter (L 1 ) is preset at a rising end of the TOF sensor. The delay counter (L 1 ) counts  303  the number of the paper carrier timing pulses required for moving a distance from the TOF sensor to the first head, and stops  309  the operation when the upper end of the printing paper arrives at just under the nozzle of the first head. The paper position counter ( 1 ) starts operating, wherein a stop timing  309  of the head-to-head delay counter (L 1 ) serves as a trigger. The paper position counter ( 1 ) is preset before counting the number of paper carrier timing pulses necessary for moving a distance to the next printing paper, and continues a countdown till the counter value becomes 0. 
     For the printing, the heat window is asserted after a paper carrying time at  304  has elapsed since a timing  309  at which the paper position counter ( 1 ) starts operating, and the preliminary discharge window is asserted after a paper carrying time at  305  has elapsed since the timing  309  at which the paper position counter ( 1 ) starts operating and is negated after counting an arbitrary number of preliminary discharge pulses. 
     In the case of the first head, the position for implementing the preliminary discharge is on the printing paper, and the discharge data becomes data taking a logical ADD of the printing data and the preliminary discharge data. The printing by the first head is negated at a timing  307  when an arbitrary margin at the lower end of the paper. Referring to FIG. 6, oblique lines  308  indicate that the printing data itself is printed, and a part  306  indicates that the logical ADD data of the printing data and the preliminary discharge data are printed. 
     The head-to-head delay counter (L 1 ) of the second head starts operating upon reaching a stop timing  309  of the head-to-head delay counter (L 1 ). The head-to-head delay counter (L 2 ) has the same function as that of the head-to-head delay counter (L 1 ) described above, and stops operating when counting a distance between the first and second heads. 
     A head-to-head delay counter (L 3 ) starts operating upon the halt of the head-to-head delay counter (L 2 ). The printing area remains unchanged without depending on the printing heads, and hence the upper end margin, the printing area and the lower end margin with respect to the second head, are the same as those of the first head. More specifically, referring to FIG. 6,  304  and  311  for determining an upper end margin quantity are the same. 
     The preliminary discharge position of the second head is, however, different from the first head. There has passed a time  312  after the heat window  2  is negated, and thereafter the lower end of the printing paper passes just under the nozzle of the second head. The preliminary discharge window  2  is asserted with a time delay  314  from a timing  313 . At this preliminary discharge timing, the printing paper does not exist just under the nozzle of the second head, and it follows that the preliminary discharge onto the carrier belt is carried out. 
     A preliminary discharge  315  at this time corresponds to data for the,preliminary discharge. As in the case of the printing control of the second head, a printing timing of a fifth head is after the stop of the operation of the delay counter (L 2 ), and, as shown in FIG. 7, after a time  316  has elapsed, a head-to-head delay counter (L 5 ) starts operating. 
     FIG. 8 shows another embodiment. Referring to FIG. 8, the numeral  405  represents a first head for discharging the printability enhancing liquid, and the numerals  406  through  409  designate second through fifth heads for discharging the dye inks. 
     A carrier belt  403  having the present construction is shown in a circle in a lower portion of the first head  405 . A configuration of a carrier belt cleaner  410  is illustrated in a circle in a right lower portion in FIG.  8 . Preliminary discharge receiving portions  401  for the printability enhancing liquid and preliminary discharge receiving portions  402  for the dye ink, are alternately disposed on a base member of the carrier belt  403 , and a period thereof is  404 . 
     On the other hand, the carrier belt cleaner  410  is a member brought into contact with the carrier belt  403  and so constructed as to absorb the preliminary discharge liquid. A circumferential length (3.13×cleaner&#39;s diameter  413 ) of the carrier belt cleaner  410  is coincident with a preliminary discharging portion period  404  on the base member of the carrier belt  403 . Further, the carrier belt is so structured as to be a multiple of integer of the preliminary discharge portion period. 
     According to the construction discussed above, the ink adhered to the preliminary discharge receiving portion (for the printability enhancing liquid)  401  and the ink adhered to the preliminary discharge receiving portion (for the dye ink)  402 , are respectively separated in terms of their areas and thus adhered to the cleaner portion (for the printability enhancing liquid)  412  of the carrier belt cleaner  410  and to the cleaner portion (for the dye ink)  411  thereof, whereby an optimal cleaning process can be executed without mixing the two kinds of ink liquids on the carrier belt cleaner  410 . 
     As discussed above, according to the present invention, the preliminary discharging positions are set the same per attribute of the ink. With this contrivance, as exemplified in the embodiment discussed above, the ion coupling of the anion radical and the cation radical on the carrier belt is prevented, thereby making it easier to recover the ink liquids on the carrier belt. 
     Note that the form of the recording head for discharging the ink and the printability enhancing liquid is not limited to the above-described full-line type and can be applied to a printer of such a type that the recording head is mounted on a carriage and performs the recording by effecting serial scans. The serial scan type printer can be constructed such that, for example, the preliminary discharge receiving member for the ink is disposed in one area, while the preliminary discharge receiving member for the printability enhancing liquid is disposed in the other area with the recording area interposed therebetween, and there is performed the control of respectively discharging the ink and the printability enhancing liquid. Further, as a matter of course, the preliminary discharge receiving member and the preliminary discharge receiving member for the printability enhancing liquid may be disposed adjacently in one area, and the preliminary discharges can be individually executed by controlling the discharge timing. Furthermore, the printability enhancing liquid may be preliminarily discharged onto the recording paper, and the ink may also be preliminarily discharged onto the ink preliminary discharge receiving member disposed in one area. 
     The many features and advantages of the invention are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.