Patent Publication Number: US-10766254-B2

Title: Liquid discharge apparatus, liquid discharge system, and liquid discharge method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2018-051784, filed on Mar. 19, 2018, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a liquid discharge system, a liquid discharge apparatus, and a liquid discharge method. 
     Description of the Related Art 
     When an image with a high-resolution setting is printed by a conventional serial inkjet printer, a technique of multi-pass printing is used to perform a rendering process to divide an original image into pieces of image data corresponding to respective scans, and complete an image by performing a plurality of scans. In this technique, an upper limit is imposed on the drive frequency of an inkjet recording head. Therefore, the speed at which the recording head is carried decreases as the resolution of an image to be formed increases. 
     To perform high-speed printing, there is a technique of thinning out dots (reducing the number of dots or decimation) to increase the head drive frequency. 
     SUMMARY 
     According to an embodiment of this disclosure, a liquid discharge apparatus includes a liquid discharge head configured to discharge liquid onto an object in accordance with a discharge cycle signal, image data, and a drive waveform; and a carriage on which the liquid discharge head is mounted. The carriage is configured to scan the object in a predetermined direction. The liquid discharge apparatus further includes circuitry configured to output pattern data for decimating the discharge cycle signal, the image data, and the drive waveform in accordance with a number of scans performed by the carriage to form a line of an image. The circuitry is configured to decimate the discharge cycle signal in accordance with the pattern data. 
     Another embodiment provides a liquid discharge apparatus that includes the liquid discharge head and the carriage described above. The liquid discharge apparatus further includes circuitry configured to receive pattern data for decimating the discharge cycle signal, the image data, and the drive waveform in accordance with a number of scans performed by the carriage to form a line of an image. The circuitry is configured to decimate the discharge cycle signal in accordance with the pattern data. 
     In yet another embodiment, a liquid discharge system includes one of the above-described liquid discharge apparatuses. 
     Yet another embodiment provides a method for discharging liquid onto an object with a liquid discharge head mounted on a carriage that scans the object in a predetermined direction. The method includes discharging the liquid onto the object in accordance with a discharge cycle signal, image data, and a drive waveform; outputting pattern data for decimating the discharge cycle signal, the image data, and the drive waveform in accordance with a number of scans performed by the carriage to form a line of an image; and decimating the discharge cycle signal in accordance with the pattern data. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a block diagram illustrating an example of a general arrangement of a liquid discharge system according to an embodiment; 
         FIG. 2  is a view illustrating a general arrangement of a serial inkjet recording apparatus; 
         FIGS. 3A and 3B  are views of an example of an ink head of the inkjet recording apparatus illustrated in  FIG. 2 ; 
         FIG. 4  is a view of an example of an internal structure of a carriage for the ink head illustrated in  FIGS. 3A and 3B ; 
         FIG. 5  is a block diagram illustrating an example configuration of system blocks of the liquid discharge system; 
         FIG. 6  is a diagram illustrating a rendering process performed by a rendering unit according to an embodiment; 
         FIGS. 7A and 7B  are diagrams illustrating generating of a discharge cycle signal by a discharge cycle signal generation unit according to an embodiment; 
         FIGS. 8A and 8B  are diagrams illustrating an example of a decimation process in a decimation controller; 
         FIG. 9  is a diagram illustrating an example operation of a carriage controller; 
         FIGS. 10A and 10B  are comparative diagrams illustrating the differences between an operation in which invalid data is not decimated in divided images, and an operation in which invalid data is decimated in the divided images; 
         FIG. 11  is a graph and a chart illustrating a method of controlling cooling fans; and 
         FIG. 12  is a diagram illustrating an example of a liquid discharge apparatus according to Embodiment 2. The accompanying drawings are intended to depict embodiments of the present invention and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     
    
    
     DETAILED DESCRIPTION 
     In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve similar results. 
     Although the embodiments are described with technical limitations with reference to the attached drawings, such description is not intended to limit the scope of the disclosure and all of the components or elements described in the embodiments of this disclosure are not necessarily indispensable. 
     Referring now to the drawings, embodiments of the present disclosure are described below. In the drawings for explaining the following embodiments, the same reference codes are allocated to elements (members or components) having the same function or shape and redundant descriptions thereof are omitted below. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     The following is a detailed description of liquid discharge systems, liquid discharge apparatuses, and liquid discharge methods as embodiments of this disclosure. 
     In the present specification, the liquid discharge apparatus includes a liquid discharge head or a liquid discharge device (unit) and drives the liquid discharge head to discharge liquid. The term “liquid discharge apparatus” used here includes, in addition to apparatuses to discharge liquid to materials to which the liquid can adhere, apparatuses to discharge the liquid into gas (air) or liquid. 
     The liquid discharge apparatus may include at least one of devices to feed, convey, and discharge the material to which liquid can adhere. The liquid discharge apparatus may further include at least one of a pretreatment apparatus and a post-processing apparatus. 
     As the liquid discharge apparatuses, for example, there are image forming apparatuses to discharge ink onto sheets to form images and three-dimensional fabricating apparatuses to discharge molding liquid to a powder layer in which powder is molded into a layer-like shape, so as to form three-dimensional fabricated objects. 
     The “liquid discharge apparatus” is not limited to an apparatus to discharge liquid to visualize meaningful images, such as letters or figures. For example, the liquid discharge apparatus may be an apparatus to form meaningless images, such as meaningless patterns, or fabricate meaningless three-dimensional images. 
     The above-mentioned term “material to which liquid can adhere” represents a material which liquid can, at least temporarily, adhere to and solidify thereon, or a material into which liquid permeates. Examples of “material to which liquid can adhere” include paper sheets, recording media such as recording sheet, recording sheets, film, and cloth; electronic components such as electronic substrates and piezoelectric elements; and media such as powder layers, organ models, and testing cells. The term “material to which liquid can adhere” includes any material to which liquid adheres, unless particularly limited. 
     The above-mentioned “material to which liquid adheres” may be any material, such as paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, ceramics, or the like, as long as liquid can temporarily adhere. 
     Further, the term “liquid” includes any liquid having a viscosity or a surface tension that can be discharged from the head. The “liquid” is not limited to a particular liquid and may be any liquid having a viscosity or a surface tension to be discharged from a head. However, preferably, the viscosity of the liquid is not greater than 30 mPa·s under ordinary temperature and ordinary pressure or by heating or cooling. Examples of the liquid include a solution, a suspension, or an emulsion including, for example, a solvent, such as water or an organic solvent, a colorant, such as dye or pigment, a functional material, such as a polymerizable compound, a resin, a surfactant, a biocompatible material, such as DNA, amino acid, protein, or calcium, and an edible material, such as a natural colorant. Such a solution, a suspension, or an emulsion can be used for, e.g., inkjet ink, surface treatment liquid, a liquid for forming components of electronic element or light-emitting element or a resist pattern of electronic circuit, or a material solution for three-dimensional fabrication. 
     The “liquid discharge apparatus” may be an apparatus in which the liquid discharge head and a material to which liquid can adhere move relatively to each other. However, the liquid discharge apparatus is not limited to such an apparatus. For example, the liquid discharge apparatus may be a serial head apparatus that moves the liquid discharge head or a line head apparatus that does not move the liquid discharge head. 
     Examples of the liquid discharge apparatus further include a treatment liquid coating apparatus to discharge a treatment liquid to a sheet to coat the sheet with the treatment liquid to reform the sheet surface and an injection granulation apparatus to discharge a composition liquid including a raw material dispersed in a solution from a nozzle to mold particles of the raw material. 
     The terms “image formation”, “print”, “printing”, and the like used in this specification are synonymous. 
     Further, “resolution” used in this specification represents the resolution set in the print settings. 
     In the description below, a serial type inkjet recording apparatus will be described as an example of “an apparatus that discharges liquid (a liquid discharge apparatus)”. In the serial type inkjet recording apparatus described below, an inkjet recording head is equivalent to a “liquid discharge head”. 
     In the description below, a serial inkjet recording apparatus will be described as an example of “an apparatus that discharges liquid (a liquid discharge apparatus)”. In the serial inkjet recording apparatus described below, an inkjet recording head is equivalent to a “liquid discharge head”. 
     Embodiment 1 
       FIG. 1  is a block diagram illustrating an example of a general configuration of a liquid discharge system according to the present embodiment. A liquid discharge system  1  illustrated in  FIG. 1  includes a personal computer (PC)  100  and a serial inkjet recording apparatus  200 . The PC  100  is a terminal including computer components such as a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM). In the PC  100 , the CPU loads basic software and applications from the ROM or a hard disk drive (HDD) into the RAM and executes the basic software and applications, in response to an activation instruction from an operating unit. Image processing is then performed with the functions thus implemented. Further, the PC  100  instructs the serial inkjet recording apparatus  200  to perform printing, via a communication interface, and outputs print data. The image processing in the PC  100  and the print data to be output to the serial inkjet recording apparatus  200  will be described later. 
       FIG. 2  is a view plan illustrating a general arrangement of the serial inkjet recording apparatus  200 .  FIG. 2  schematically illustrates the general arrangement of the serial inkjet recording apparatus  200 . 
     Inkjet recording heads (hereinafter referred to simply as “ink heads”)  202  of the respective colors are mounted on a carriage  201 . The ink heads  202  discharge inks (liquids) of the respective colors such as monochrome and color inks as ink droplets (liquid droplets).  FIG. 2  illustrates an example in which four-color ink heads that discharge inks of the respective colors of Y (yellow), M (magenta), C (cyan), and Bk (black) are arranged. Each ink head  202  has a nozzle face on which a large number of discharge nozzles are arranged, and causes each discharge nozzle to discharge ink droplets. 
     The carriage  201  is supported by a guide rod  203  to reciprocate in the direction indicated by arrow A (hereinafter “main scanning direction A”) in  FIG. 2 . Driven by a main scanning motor  204  (a carriage motor), the carriage  201  reciprocates for scanning in the main scanning direction A as a timing belt  207  supported by a driving shaft  205  and a driven shaft  206  rotates. The carriage  201  is provided with an encoder sensor  208 . The position of the carriage  201  in the main scanning direction A is detected by the encoder sensor  208  reading a linear scale  209  (an encoder sheet) extending in the direction of movement of the carriage  201 . 
     A platen  221  is disposed at a position facing the nozzle faces of the ink heads  202 . While being attracted by the platen  221 , a recording sheet  222  to which liquid can adhere is sent in the direction indicated by arrow B (hereinafter “sub-scanning direction B”) by a conveyance mechanism hidden behind the recording sheet  222 . 
     Accordingly, the serial inkjet recording apparatus  200  illustrated in  FIG. 2  alternately repeats scanning of the carriage  201  in the main scanning direction A and conveyance of the recording sheet  222  in the sub-scanning direction B. In that process, the serial inkjet recording apparatus  200  discharges ink droplets onto the recording sheet  222 , thereby forming an image with dots of ink droplets on the recording sheet  222 . 
       FIGS. 3A and 3B  are views of an example of the ink head  202 .  FIG. 3A  illustrates an example of the discharge nozzle arrangement on the nozzle face (also referred to as the nozzle plate) of the ink head  202 .  FIG. 3B  illustrates an exploded view of the ink head  202 . 
       FIG. 3A  illustrates discharge nozzles  312  arranged in a staggered pattern on a nozzle plate  311  (the nozzle face). As an example, the discharge nozzles  312  are arranged in two columns and 64 rows. Such a large number of discharge nozzles  312  arranged in a staggered pattern meets high-resolution image formation. 
     Next, the structure of the ink head  202  is described with reference to  FIG. 3B . Note that, in  FIG. 3B , the number of the discharge nozzles  312 , the number of pressure chambers  322 , the number of restrictors  332 , the number of piezoelectric elements  363 , and the like are reduced for ease of understanding of principal components of the ink head  202 . 
     The ink head  202  includes the nozzle plate  311 , a pressure chamber plate  321 , a restrictor plate  331 , a diaphragm plate  341 , a rigid plate  351 , and a piezoelectric element group  361 . 
     The nozzle plate  311  is the plate in which the discharge nozzles  312  are formed and has the nozzle face. Formed in the pressure chamber plate  321  are pressure chambers  322 . Formed in the restrictor plate  331  are the restrictors  332 . The restrictors  332  connect a common ink channel  352  to the pressure chambers  322  and controls the flow rate of the ink to be supplied into the pressure chambers  322 . Formed in the diaphragm plate  341  are diaphragms  342  and filters  343 . The pressure chamber plate  321 , the restrictor plate  331 , and the diaphragm plate  341  are sequentially stacked, positioned, and joined to each other, to form a channel substrate. The channel substrate is joined to the rigid plate  351 , and the filters  343  are made to face the opening of the common ink channel  352 . The upper open end of an ink introduction pipe  353  is connected to the common ink channel  352  of the rigid plate  351 , and the lower open end of the ink introduction pipe  353  is connected to the ink tank of the corresponding color. 
     The piezoelectric element group  361  constructed of a large number of piezoelectric elements  363  arranged on a piezoelectric element supporting substrate  362  is inserted through an opening  354  in the rigid plate  351 , and the free ends of the respective piezoelectric elements  363  are bonded and secured to the diaphragms  342 . Thus, the ink head  202  is formed. 
     Electrode pads  364  for connecting to a drive control board  30  (see  FIG. 4 ) are provided on the piezoelectric element supporting substrate  362  and are electrically connected to the drive control board  30  by soldering. A piezoelectric element driving integrated circuit (IC)  365  that applies a drive waveform to the piezoelectric elements  363  in accordance with the command value of an image data signal serially transmitted from the drive control board  30  is also mounted on the piezoelectric element supporting substrate  362 . 
     Note that the piezoelectric element driving IC  365  and each piezoelectric element  363  are electrically connected by a copper foil pattern  366 . Meanwhile, piezoelectric element connecting electrode pads  367  are designed to electrically connect the piezoelectric elements  363  to the copper foil pattern  366 , and bonding the piezoelectric elements  363  to the piezoelectric element supporting substrate  362 . 
     As the ink head  202  has such a structure, ink droplets are discharged from the discharge nozzles  312  in accordance with the driving states of the piezoelectric elements  363  corresponding to the respective discharge nozzles  312 . There are two kinds of driving states, which are driving and micro vibration driving, and ink droplets are discharged by driving. 
       FIG. 4  is a view of an example of the internal structure of the carriage  201 . The carriage  201  includes the drive control board  30 , the ink heads  202 , cables  211 , and cooling fans  212 . Here, the cooling fans  212  are an example of a “cooling device”. 
     The ink heads  202  discharge ink droplets onto the recording sheet  222  in accordance with the command values of a drive waveform signal and an image data signal transmitted from the drive control board  30  through the cables  211 . Although  FIG. 4  illustrates an example in which two ink heads  202  are mounted on the carriage  201 , the other ink heads  202  are not illustrated in  FIG. 4 . Further, the arrangement and the number of the ink heads  202  are not limited to those illustrated in  FIG. 4 . 
     The cooling fans  212 , head cooling fins  213 , and a substrate cooling fin  214  take away the heat generated as the ink heads  202  are driven. 
       FIG. 5  is a block diagram illustrating an example of system configuration of the liquid discharge system  1 .  FIG. 5  illustrates primarily the system blocks between a PC board  10 , a main controller board  20 , and the drive control board  30 . The drive control board  30  is mounted on the carriage  201 . Note that the mounting positions of the respective blocks in the main controller board  20  and the drive control board  30  are not limited to those illustrated in  FIG. 5 . For example, a part or all of the drive control board  30  may be mounted on the main body of the serial inkjet recording apparatus  200  outside the carriage  201 . 
     A routing information protocol (RIP)  11  is formed as a functional unit as software installed in the PC  100  is implemented. The RIP  11  performs image processing in accordance with a color profile and user&#39;s setting, and issues a printing instruction to the main controller board  20 . A rendering unit  12  is a functional module of the RIP  11 , divides a print image into pieces of image data corresponding to respective scans in accordance with the print settings, and outputs information about a decimation pattern. The rendering unit  12  is equivalent to a “dividing unit” and a “pattern data output unit”. The information about the decimation pattern is equivalent to “pattern data”. The information about the decimation pattern will be hereinafter referred to as the “decimation pattern”. 
     An operation panel  230  is a user interface of the serial inkjet recording apparatus  200 . The operation panel  230  includes an operating unit and a display unit. 
     A system controller  21  controls the entire printer system. For example, the system controller  21  receives print information from the RIP  11 , in accordance with a printing instruction transmitted from the RIP  11 , and performs printing by controlling the respective components. In this embodiment, the system controller  21  receives information such as the resolution set in the print settings, image data, and the decimation pattern from the rendering unit  12 , controls the respective components in accordance with the information, and performs printing. 
     An image data memory  22  is a memory for temporarily storing image data transmitted from the rendering unit  12 . 
     A memory controller  23  stores image data in the image data memory  22 . The memory controller  23  also reads image data from the image data memory  22  and outputs the image data to a decimation controller  25  (or an image data decimation controller). 
     A discharge cycle signal generation unit  24  includes a register that sets the decimation pattern transmitted from the rendering unit  12 , and a register that sets a resolution. The discharge cycle signal generation unit  24  generates a discharge cycle signal using an output signal from the encoder sensor  208  in accordance with the decimation pattern and the resolution set in the respective registers, and outputs the generated discharge cycle signal to a drive waveform generation unit  32 . 
     The decimation controller  25  thins out image data output from the memory controller  23  in accordance with the decimation pattern. In response to an output of a discharge cycle signal from the discharge cycle signal generation unit  24  to the drive waveform generation unit  32 , the memory controller  23  reads image data from the image data memory  22  and outputs the image data and the decimation pattern set in a register to the decimation controller  25 . In accordance with the decimation pattern, the decimation controller  25  thins out the image data that has been output together with the decimation pattern. Note that, in a case where the decimation pattern indicates no decimation, the decimation controller  25  does not thin the image data. The decimation controller  25  outputs the corresponding image data signal to the ink head  202 . The image data signal is masked data that specifies the size (such as large droplets, medium droplets, or small droplets) of the ink droplets in the valid data of the image. 
     A carriage controller  26  includes a register that sets the decimation pattern transmitted from the rendering unit  12 , and a register that sets a resolution. The carriage controller  26  controls the main scanning motor  204  in accordance with the decimation pattern and the resolution set in the respective registers. The position of the carriage  201  is calculated in accordance with an output signal from the encoder sensor  208 . 
     A drive waveform data memory  31  stores the drive waveform corresponding to the ink head  202 . 
     In response to an input of a discharge cycle signal output from the discharge cycle signal generation unit  24 , the drive waveform generation unit  32  outputs a drive waveform read from the drive waveform data memory  31  as drive waveform data to a digital-to-analog (D/A) converter  33  (represented as “DAC  33 ” in  FIG. 5 ). 
     The D/A converter  33  converts the drive waveform data into an analog signal. A voltage amplifier  34  (an operational amplifier) amplifies the voltage of the analog signal output from the D/A converter  33 . A current amplifier  35  amplifies the current of the driving waveform voltage output from the voltage amplifier  34  (the operational amplifier), and supplies the drive waveform subjected to the current amplification to each piezoelectric element  363  (see  FIG. 3B ) in the ink head  202 . 
     A thermistor  41  detects heat generated in the ink head  202 . A cooling fan controller  36  (a cooling controller) controls the cooling fans  212  in accordance with the temperature detected by the thermistor  41 . 
     Rendering Process 
     In a case where the resolution set in the print settings is as high as 1200 dpi, the distance between the dots of ink droplets formed on the recording sheet  222  (see  FIG. 2 ) is short. Therefore, adjacent ink droplets merge. To prevent such merging, adjacent dots are formed in a plurality of scans on the sheet to gain, with the time lags, the time for drying the adjacent ink droplets. 
     In accordance with an instruction from the RIP  11 , the rendering unit  12  performs a rendering process to divide the image to be printed into pieces of image data corresponding to the respective scans. 
       FIG. 6  is a diagram illustrating a rendering process to be performed by the rendering unit  12 . An original image M 1  illustrated in  FIG. 6  is a two-dimensional image of an image with a high resolution (1200 dpi, for example). Each dot d represents one dot that is printed at intervals of 1200 dpi in the main scanning direction A. In a case where the original image M 1  is a solid image, the data of the respective dots is all valid data, and, if thinning is performed on this data, image quality becomes lower. The same effect can be achieved in a case where a part of the valid data is invalid data as in a case where the original image is not a solid image. However, for ease of explanation, all data of dots in the original image M 1  is valid in the description below. 
     By the above rendering process, the rendering unit  12  divides the original image M 1  into pieces of image data (divided images m 1 , m 2 , . . . ) of the respective scans as illustrated in  FIG. 6 . The number of divided images m 1 , m 2 , . . . varies depending on the intervals at which the valid data is printed in the scan. For ease of explanation of the principles,  FIG. 6  illustrates the original image M 1  that has 8-dot data in the main scanning direction A. As for the divided images m 1 , m 2 , . . . , four divided images m 1 , m 2 , m 3 , and m 4  are illustrated as the divided images obtained in a case where the original image M 1  is formed by repeating scanning in the main scanning direction A four times (or through four passes). The four divided images m 1 , m 2 , m 3 , and m 4  are an example of divided images in such a combination that no adjacent dots are printed in the same pass. The combination is specified by the RIP  11  or the like, and the rendering unit  12  selectively performs the dividing. 
     The respective divided images m 1 , m 2 , m 3 , and m 4  are the image data respectively corresponding to first, second, third, and fourth scans scan 1 , scan 2 , scan 3 , and scan 4 , which are in the order of scanning in the same area (the same area in a certain row). To clearly indicate in which pass each dot is printed, scan numbers “1”, “2”, “3”, and “4” are given in the dots indicating the valid data in the respective divided images m 1 , m 2 , m 3 , and m 4 , for ease of explanation. In each of the divided images m 1 , m 2 , m 3 , and m 4 , the dots without any scan number are invalid data added by the rendering unit  12 . The invalid data is data not to be printed as dots, and a signal for micro vibration driving is output to the ink heads  202  so that no ink is discharged during the periods of the invalid data. 
     As described above, the divided images m 1 , m 2 , m 3 , and m 4  are formed with valid data for discharging ink droplets and invalid data for discharging no ink droplets. Through the four passes, the valid data of the respective divided images m 1 , m 2 , m 3 , and m 4  is sequentially formed on the sheet surface, and the image corresponding to the original image M 1  is formed on the sheet surface.  FIG. 6  also presents an image in which all the dots are printed on the sheet so that the relationship between the respective dots in the image on the sheet and the divided images m 1 , m 2 , m 3 , and m 4 , which are used to form the dots, becomes obvious. Scan numbers indicating the sequence in dot formation are given to the respective dots. 
     The rendering unit  12  further outputs a decimation pattern of a rendering pattern to which the invalid data is added for each of the divided images m 1 , m 2 , m 3 , and m 4 . The decimation pattern is a pattern indicating the position of the invalid data in the rendering pattern. In this example, the valid data of the divided images to be used in the respective scans scan 1 , scan 2 , scan 3 , and scan 4  is arranged as illustrated in  FIG. 6 . Therefore, the respective decimation patterns of scans scan 1 , scan 2 , scan 3 , and scan 4  are “0x88”, “0x22”, “0x44”, “0x11”, respectively. Note that each decimation pattern is in hexadecimal representation. 
     These decimation patterns, the image data of the respective divided images, and the resolution set in the print settings are transmitted from the rendering unit  12  to the system controller  21 . 
     Generation of Discharge Cycle Signal 
       FIGS. 7A and 7B  are diagrams illustrating generation of a discharge cycle signal by the discharge cycle signal generation unit  24 . The discharge cycle signal generation unit  24  generates the discharge cycle signal using an output signal from the encoder sensor  208 , in accordance with the decimation pattern and the resolution set in the registers.  FIGS. 7A and 7B  illustrate discharge cycle signals with the resolution of 1200 dpi without decimation ( FIG. 7A ) and with decimation ( FIG. 7B ). In each of  FIGS. 7A and 7B , a timing chart illustrates an example of output signals from the linear scale  209  and the encoder sensor  208 , and a discharge cycle signal generated by the discharge cycle signal generation unit  24 . The linear scale  209  is compatible with a pattern cycle corresponding to 300 dpi, for example. 
     In the case without any decimation pattern illustrated in  FIG. 7A , to generate a discharge cycle signal of 1200 dpi, the discharge cycle signal generation unit  24  generates a discharge cycle signal illustrated in  FIG. 7A  from an output signal from the encoder sensor  208 . The ink heads  202  perform driving for discharge (such as driving to discharge large droplets, or micro vibration driving) at the timing of each rise. 
     In the decimation patterns (“0x88”, “0x22”, “0x44”, and “0x11”) illustrated in  FIG. 7B , the decimation controller  25  outputs image data generated by decimating the invalid data from the respective divided images m 1 , m 2 , m 3 , and m 4  in accordance with the respective decimation patterns. Accordingly, the discharge cycle signal generation unit  24  generates discharge cycle signals corresponding to the respective decimation patterns. In  FIG. 7B , the discharge cycle signals indicated by combinations of a solid line and a dashed line are equivalent to the discharge cycle signal illustrated in  FIG. 7A . The discharge cycle signals indicated only by the solid lines are the discharge cycle signals subjected to decimation performed in accordance with the respective decimation patterns. As the discharge cycle signals are decimated in this manner and the discharge timing is shifted for each scan, discharge driving can be performed only with valid data in each scan. 
     Decimation Process 
     In response to an output of a discharge cycle signal generated by the discharge cycle signal generation unit  24 , the memory controller  23  reads image data divided for the respective scans from the image data memory  22  at the output timing of the discharge cycle signal, and transfers the discharge cycle signal, together with the decimation pattern used in generating the discharge cycle signal, to the decimation controller  25 . 
       FIGS. 8A and 8B  are diagrams illustrating an example of a decimation process in the decimation controller  25 . As illustrated in  FIG. 8A , image data subjected to rendering is a rendering pattern in which eight dots in the main scanning direction A are completed through four passes (the scans scan 1 , scan 2 , scan 3 , and scan 4 ) in this example. Accordingly, the respective decimation patterns are expressed as “0x88”, “0x22”, “0x44”, and “0x11”. The decimation controller  25  periodically decimates the invalid data (added invalid data) from the image data (the divided images m 1 , m 2 , m 3 , and m 4 ) sequentially read at the predetermined timings from the image data memory  22 , in accordance with the respective decimation patterns. The dots indicated by dashed lines in  FIG. 8A  represent the dots from which data is decimated. 
     Specifically, as illustrated in  FIG. 8A , the decimation controller  25  performs decimation on rendered image data, in accordance with the respective decimation patterns. In this example, the decimation patterns are designed to decimate the valid data, which is ¾ of the divided images m 1 , m 2 , m 3 , and m 4 . Therefore, all the invalid data added by the rendering unit  12  are decimated at this point, and only the valid data forming the original image M 1  remains. 
     A decimation process using other decimation patterns is now described.  FIG. 8A  illustrates an example of decimation patterns with which the decimation controller  25  decimates the invalid data, which is ¾ of the divided images m 1 , m 2 , m 3 , and m 4 , but some other decimation patterns may be used. Some other decimation patterns such as 2/4 or ¼ decimation patterns may be used, as long as the decimation controller  25  decimates the invalid data in accordance with the decimation patterns. For example, other optimum patterns may be output depending on the resolution set in the print settings, the sequence in image formation, and the like. 
       FIG. 8B  illustrates an example of decimation in a case where eight dots are completed in two passes (the scans scan 1  and scan 2 ). In  FIG. 8B , the respective decimation patterns are expressed as “0xAA” and “0x55”. As illustrated in  FIG. 8B , in the case of two passes, dot printing is performed every other dot, and an image is completed through two scans. Decimation is performed in accordance with the decimation patterns for the respective passes, and the invalid data represented by the dots indicated by dashed lines in  FIG. 8B  is decimated. 
     Carriage Control 
       FIG. 9  is a diagram illustrating an example operation of the carriage controller  26 . The carriage controller  26  selects the carriage speed corresponding to the resolution and the decimation pattern from a speed correspondence table illustrated in  FIG. 9 , and changes the speed of the carriage  201 . As illustrated in  FIG. 9 , even if the resolution is high, the speed of the carriage  201  is higher in a case where decimation is performed than in a case where no decimation is performed. For example, when image formation with a resolution of 1200 dpi is performed without decimation, the speed of the carriage  201  is only 200 mm/s. However, when the same image formation is performed with ½ decimation (corresponding to  FIG. 8B ), the speed increases to 400 mm/s. When the same image formation is performed with ¾ decimation (corresponding to  FIG. 8A ), the speed is as high as 800 mm/s. That is, high-speed printing can be performed with a high resolution. Furthermore, the valid data is not decimated. Accordingly, degradation of image quality can be prevented. The same applies to a case where image formation with a resolution of 600 dpi is performed. 
       FIGS. 10A and 10B  are comparative diagrams illustrating the differences between an operation in which invalid data is not decimated in divided images m 1 , m 2 , . . . , and an operation in which invalid data is decimated in the divided images m 1 , m 2 , . . . . Note that the periods given reference character “micro” in  FIGS. 10A and 10B  are the micro vibration periods of invalid data. The periods given reference character “large” are the driving periods during which large droplets are discharged. 
     In  FIGS. 10A and 10B , in the case where no decimation is performed, driving needs to be performed four times for each discharge action. Therefore, the speed of the carriage  201  is low. In the case where decimation is performed, the micro vibration driving for invalid data can be eliminated. Accordingly, the carriage  201  operates at a higher speed. 
     Normally, to increase the speed of a carriage, the maximum drive frequency of the ink heads needs to be made higher. This requires a very difficult technique, which leads to higher costs. In this embodiment, on the other hand, the invalid data in divided images is decimated, and the number of times a discharge cycle signal is output is reduced accordingly. Thus, the number of times of driving is only once for one discharge action, thereby enabling increases in the speed of the carriage (four times as high in this example) without any increase in the maximum drive frequency of the ink heads. As a result, productivity also increases. 
     As described above, this embodiment can attain a high head drive frequency without a decrease in resolution. 
       FIG. 11  is a graph and a chart illustrating a method of controlling the cooling fans  212 . As illustrated in the graph in  FIG. 11 , as the drive frequency increases, the heat generated by the carriage  201  increases. It is known that, as the drive frequency increases, the amount of heat generated by the ink heads  202  and the drive control board  30  increases. This is because the electric current flowing per unit time increases. An approach to inhibit heat generation is keeping the drive cycle as is. 
     In a structure in which speed is not increased but is maintained, performing the decimation described above is advantageous in lowering the drive frequency and accordingly reducing the amount of heat generated. As the amount of heat generation decreases, the apparatus can be made compact. Normally, fins (see  FIG. 4 ) for radiating heat, such as the head cooling fins  213  and the substrate cooling fins  214 , are provided in each ink head and the drive control board. Further, the fins are cooled by the cooling fans  212 . Since the amount of heat generated is large, such components are larger in size, increasing the cost. 
     The table in  FIG. 11  illustrates the relationship between the decimation patterns and the power consumption by the cooling fans. As illustrated in  FIG. 11 , adopting the decimation described above can suppress heat generation and accordingly reduce the power consumption by the cooling fans. Further, the size of the fins and the like can be reduced, and the component costs and the like can be lowered. 
     Further, when the cooling fan controller  36  switches the driving of the cooling fans  212  in accordance with the decimation patterns, the power consumption can be reduced as illustrated in the table in  FIG. 11 . 
     Although the description above concerns an example in which an image is formed through a plurality of scans in the main scanning direction, the example is used for explaining principles of this disclosure. Alternatively, aspects of this disclosure can adopt to any appropriate method in which an image is formed in one of scanning the main scanning direction and scanning in the sub-scanning direction or combination thereof. 
     Embodiment 2 
       FIG. 12  is a block diagram illustrating an example of a liquid discharge apparatus according to Embodiment 2.  FIG. 12  illustrates an example of system configuration of a serial inkjet recording apparatus  200  as an example of a liquid discharge apparatus.  FIG. 12  differs from  FIG. 5  in that the RIP  11  and the rendering unit  12  are mounted on the main controller board  20 . That is, the serial inkjet recording apparatus  200  illustrated in  FIG. 12  can perform a rendering process and the like on a printed image. The functions of the other components, the flow of signals, and the like are substantially the same as those of Embodiment 1, and redundant descriptions are omitted. The liquid discharge apparatus according to Embodiment 2 can achieve the same effects as the effects of the liquid discharge system according to Embodiment 1. 
     The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention. Any one of the above-described operations may be performed in various other ways, for example, in an order different from the one described above. 
     Each of the functions of the described embodiments may be implemented by one or more processing circuits or circuitry. Processing circuitry includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application specific integrated circuit (ASIC), digital signal processor (DSP), field programmable gate array (FPGA) and conventional circuit components arranged to perform the recited functions.