Patent Publication Number: US-11654700-B2

Title: Printer and method for printing

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2019-148323, filed on Aug. 13, 2019, in the Japan Patent Office and Japanese Patent Application No. 2020-125716, filed on Jul. 22, 2020, in the Japan Patent Office, the entire disclosures of which are hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     Aspects of the present disclosure relate to a printer and a method for printing. 
     Related Art 
     A printer moves a carriage mounting a head that discharges a liquid to print an image. If a skew occurs during a conveyance of a sheet such as a web in the printer, an image position deviates from an edge of a sheet in a width direction. 
     The printer using a cut sheet includes a sensor to detect a position of the sheet in the width direction. The printer measures the position of a first sheet in the width direction conveyed a present time. Further, the printer adjusts a position of an image formation of a second sheet conveyed next time. 
     SUMMARY 
     In an aspect of this disclosure, a printer includes a printing device to print an image on a sheet, a carriage mounting the printing device, the carriage to scan in a main-scanning direction, a detector on the carriage, the detector to detect a presence and an absence of the sheet, and circuitry to detect an edge position of the sheet in the main-scanning direction based on a detection result by the detector while the printing device prints a first scan of the image on the sheet, adjust a print start position at which the printing device starts printing a second scan of the image on the sheet based on the edge position detected in the first scan, and control the printing device to print the second scan of the image from the print start position. 
     In another aspect of this disclosure, a method for printing an image on a sheet is provided, the method includes scanning a printing position in a main-scanning direction to print a first scan of the image on the sheet, detecting an edge position of the sheet in the main-scanning direction during the scanning, adjusting a print start position to start printing a second scan of the image on the sheet based on the edge position, and scanning the printing position to print the second scan of the image on the sheet from the print start position. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The aforementioned and other aspects, features, and advantages of the present disclosure will be better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG.  1    is a schematic side view of a configuration of an example of a printer as a liquid discharge apparatus according to a first embodiment of the present disclosure; 
         FIG.  2    is a schematic plan view of the liquid discharge apparatus of  FIG.  1   ; 
         FIG.  3    is a schematic perspective view of a portion of the liquid discharge apparatus according to the first embodiment of the present disclosure; 
         FIG.  4    is a schematic plan view of a head of the liquid discharge apparatus according to the first embodiment of the present disclosure; 
         FIG.  5    is a block diagram of a controller of the liquid discharge apparatus according to the first embodiment of the present disclosure; 
         FIG.  6    is a block diagram of a part related to a control of an image position adjustment by a sheet edge position of a sheet according to the first embodiment of the present disclosure; 
         FIG.  7    is a schematic plan view of the sheet illustrating an adjustment of the print start position (image-formation start position) according to the first embodiment of the present disclosure; 
         FIG.  8    is a plan view of the sheet illustrating the adjustment of the print start position when the print start position is adjusted in scan units; and 
         FIG.  9    is a flowchart of control of a print operation by a controller. 
     
    
    
     The accompanying drawings are intended to depict embodiments of the present disclosure 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 have the same function, 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. 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. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, embodiments of the present disclosure are described below. A printer as a liquid discharge apparatus according to a first embodiment of the present disclosure is described with reference to  FIGS.  1  to  4   . 
       FIG.  1    is a cross-sectional side view of the printer  1  according to an embodiment of the present disclosure.  FIG.  2    is a plan view of the printer  1  of  FIG.  1   .  FIG.  3    is a perspective view of a main part of the printer  1 .  FIG.  4    is a schematic plan view of a bed of the printer  1  according to the first embodiment of the present disclosure. 
     The printer  1  is a serial-type inkjet recording apparatus as a liquid discharge apparatus. The printer  1  includes a printing device  10  and a conveyor  20  in an apparatus body  100 . The printing device  10  prints on a sheet  2  such as a roll paper, a continuous sheet, for example. The conveyor  20  conveys the sheet  2 . 
     Further, the printer  1  includes a roll feeder  30  and a roll winder  40  outside the apparatus body  100 . The roll feeder  30  accommodates a feeding roll  3  in which the sheet  2  is wound in a roll shape and feeds the sheet  2  to the printing device  10 . 
     The roll winder  40  accommodates a winding roll  4  in which the sheet  2 , onto which an image is printed by the printing device  10 , is wound. The sheet  2  is wound in the roll shape in the winding roll  4 . 
     The printing device  10  reciprocally movably holds and guides a carriage  105  in a main-scanning direction indicated by arrow “X” by a guide  102  attached to a stay  103  bridged across a left-side plate  101 A and a right-side plate  101 B. The main-scanning direction X is also referred to as a “first direction.” The main-scanning direction X is also referred to as a “width direction” of the sheet  2 . The carriage  105  is fitted to the guide  102  so that a fitting portion  105   a  formed on a back side of the carriage  105  is movably fitted to the guide  102 . Thus, the carriage  105  reciprocally moves (scans) along the guide  102  in the main-scanning direction X (first direction). 
     The carriage  105  mounts three liquid discharge devices  110  ( 110 A to  110 C) as print devices. Each of the three liquid discharge devices  110  includes a liquid discharge head  111  as a liquid discharger and a sub tank  112  that supplies a liquid to the liquid discharge head  111 . Hereinafter, the “liquid discharge head” is simply referred to as the “head.” The liquid discharge device  110  includes the head  111  and the sub tank  112  formed as a single body. 
     Thus, the carriage  105  moves a printing position at which the head  111  discharges the liquid onto the sheet  2  in the main-scanning direction X. 
     As illustrated in  FIG.  4   , the head  111  includes a nozzle array in which a plurality of nozzles  111   a  to discharge a liquid is arrayed. 
     Thus, the three heads  111 A to  111 C are arranged at different positions in a staggered manner (see  FIG.  4   ) in a conveyance direction of the sheet  2  (sub-scanning direction Y) as a second direction that intersects the main-scanning direction X as the first direction (width direction of the sheet  2 ). The conveyance direction (sub-scanning direction) indicated by arrow “Y” in  FIG.  2   . 
     In  FIG.  4   , a part of the nozzle  111   a  in one of the head  111  is overlapped with a part of the nozzle  111   a  in another head  111  at a joint between the heads  111 . 
     Further, the carriage  105  mounts a sheet detector  601  to detect a presence and an absence of the sheet  2 . 
     Further, the printer  1  includes a linear encoder sheet  161  and a linear encoder  160 . The linear encoder sheet  161  is stretched along the main-scanning direction X. The linear encoder  160  includes an encoder sensor  162  to read the linear encoder sheet  161  to detect a position of the carriage  105 . 
     The printer  1  includes a cartridge holder  121  detachably attach a plurality of main tanks  120  (liquid cartridges) containing liquids of respective colors on one end of the apparatus body  100 . The cartridge holder  121  includes a liquid feed pump, etc., to supply liquid of the respective colors from the main tanks  120  to the heads  111  of the liquid discharge devices  110  via supply tubes  123  of respective colors. The main tanks  120  are detachably attached to the cartridge holder  121 . 
     The conveyor  20  includes a conveyance roller  201  and a counter roller  202  as a conveyor on an upstream side of the printing device  10  in a sub-scanning direction of the sheet  2  indicated by arrow “Y” in  FIG.  2   . The conveyor  20  sandwiches the sheet  2  between the conveyance roller  201  and the counter roller  202  to convey the sheet to the printing device  10 . The sub-scanning direction Y is also referred to as a “conveyance direction.” 
     The conveyor  20  includes a platen  203  and a suction mechanism  204  (see  FIG.  1   ). The platen  203  faces the head  111  to guide the sheet  2 . The suction mechanism  204  attracts the sheet  2  through suction holes  203   a  of the platen  203 . Although only a portion of the suction holes  203   a  is illustrated in  FIG.  2   , the platen  203  includes suction holes  203   a  formed all over an entire surface of the platen  203 . 
     The conveyor  20  includes a conveyance guide  205  on an entrance side (right-side in  FIG.  1   ) of the conveyor  20 . The conveyance guide  205  guides, to the printing device  10 , the sheet  2  fed from the feeding roll  3 . The conveyor  20  further includes a conveyance guide  206  on an exit side (left-side in  FIG.  1   ) of the conveyor  20 . The conveyance guide  206  guides, to the winding roll  4 , the sheet  2  on which an image is printed by the printing device  10 . 
     The printer  1  includes a maintenance unit  150  to maintain and recover a discharge function the head  111 . The maintenance unit  150  is disposed on one side (right-side in  FIGS.  2  and  3   ) of the printer  1  in the main-scanning direction X of the carriage  105 . 
     The maintenance unit  150  includes, for example, a cap  151  to cap a nozzle surface of the head  111  and a wiper  152  including a web  153  to wipe the nozzle surface of the head  111 . 
     In the printer  1 , the conveyance roller  201  and the counter roller  202  conveys the sheet  2  in the sub-scanning direction Y (conveyance direction) while the sheet  2  is attracted to the platen  203 . 
     Therefore, for example, the printer  1  drives the head  111  in accordance with print signals while moving the carriage  105  in the main-scanning direction X to discharge a liquid of a desired color onto the sheet  2  stopped to print one line. Then, the printer  1  repeatedly feeds the sheet  2  by a predetermined distance and then prints next line of the image. The above-described operations of feeding and printing are repeated to form a desired image on the sheet  2 , and then the sheet  2  is ejected to the winding roll  4  to perform single-pass printing. The printer  1  repeatedly scans the carriage  105  and conveys the sheet  2  for a plurality of times to print one line to perform multi-pass printing. 
       FIG.  5    is a block diagram of an example of a controller  500  of the printer  1  according to an embodiment of the present disclosure. 
     As illustrated in  FIG.  7   , the controller  500  includes a main controller  500 A that includes a central processing unit (CPU)  501 , a read-only memory (ROM)  502 , and a random access memory (RAM)  503 . The CPU  501  administrates the control of the entire printer  1 . The ROM  502  stores fixed data, such as various programs including programs executed by the CPU  501 , and the RAM  503  temporarily stores image data and other data. The main controller  500 A also serves as a control unit to control the printer in the first embodiment of the present disclosure. 
     The controller  500  further includes a non-volatile random-access memory (NVRAM)  504  and an image processor  505 . The NVRAM  504  is a rewritable memory capable of retaining data even when an apparatus (printer  1 ) is powered off. The image processor  505  processes various signals on image data, performs sorting or other image processing, and processes input and output signals to control the entire apparatus (printer  1 ). 
     The controller  500  includes a data transfer to drive and control the head  111 , a head drive controller  508  including a drive signal generator, and a head driver (driver IC)  509  to drive the head  111  on the carriage  105 . 
     The controller  500  includes a motor driver  510  that drives a main-scanning motor  551  that moves and scans the carriage  105 , a sub-scanning motor  552  that drives the conveyance roller  201 , and a maintenance motor  553  that moves (elevates) the caps  151  and drives a suction device of the maintenance unit  150 . 
     The controller  500  also includes a wiping controller  520  that drives the wiper  152 . 
     The controller  500  includes an I/O unit  513 . The I/O unit  513  acquires information from a detection output of sheet detector  601 , and various types of sensors mounted on the apparatus (printer  1 ) such as a temperature sensor. The I/O unit  513  also extracts data for controlling the apparatus (printer  1 ) and uses extracted data to control the apparatus (printer  1 ). 
     Further, the controller  500  is connected to an operation panel  514  to input and display information necessary to operate the apparatus (printer  1 ). 
     The controller  500  further includes a host interface (I/F)  506  to transmit and receive data and signals to and from, e.g., a printer driver  591  of a host  590 . The controller  500  uses the I/F  506  to receive the data and signal from the printer driver  591  of the host  590  such as an information processing device such as a personal computer, an image reading device, or an imaging device via a cable or a network. 
     The CPU  501  of the controller  500  reads out and analyzes print data in a reception buffer included in the I/F  506 , performs necessary image processing, data rearrangement processing, and the like by the image processor  505 , and transfers the image data from the head drive controller  508  to the head driver  509 . 
     The head drive controller  508  transfers the above-described image data as serial data and also outputs a transfer clock, a latch signal, and a control signal, for example, necessary for transfer of the image data and confirmation of the transfer to the head driver  509 . 
     The head drive controller  508  includes the drive signal generator including a digital-to-analog (D/A) converter to perform digital-to-analog (D/A) conversion of pattern data of drive pulse stored in the ROM  502 , a voltage amplifier, a current amplifier, and the like. The head drive controller  508  generates a drive waveform including one drive pulse or a plurality of drive pulses and output to the head driver  509 . 
     In accordance with serially-inputted image data corresponding to one line recorded by the head  111 , the head driver  509  selects the drive pulses of a driving waveform transmitted from the head drive controller  508  and applies the selected drive pulses to the pressure generator to drive the head  111 . Thus, the head driver  509  drives the head  111 . At the time of driving the head  111 , the head driver  509  selects a part or all of the drive pulses forming the driving waveform or a part or all of waveform elements forming the drive pulse. Thus, the head  111  can selectively discharge dots of different sizes, e.g., large droplets, medium droplets, and small droplets. 
       FIG.  6    is a block diagram of a part related to a control of an image position adjustment by an edge position of the sheet according to the first embodiment of the present disclosure. 
     The controller  500  includes a carriage position detector  602 , a sheet edge position detector  603 , a sheet edge position storage  604 , and a print controller  605 . 
     The sheet detector  601  detects presence or absence of the sheet  2 . 
     The carriage position detector  602  detects a position of the carriage  105  (carriage position) obtained from a detection output from the linear encoder  160 . 
     The sheet edge position detector  603  detects an edge of the sheet  2  (sheet edge) in the width direction of the sheet  2  (main-scanning direction X) from a transition state of the detection output of the sheet detector  601 . The sheet edge position detector  603  further detects, as the sheet edge position, the carriage position detected by the carriage position detector  602  when the sheet edge is detected. The sheet edge position detector  603  stores data of the detected sheet edge position in the sheet edge position storage  604 . The “data of the sheet edge position” is also referred to as “sheet edge position data” or “edge position data.” 
     The sheet edge position detector  603  sets, a position at which the detection output from the sheet detector  601  changes from an absence of the sheet  2  to a presence of the sheet  2 , to one of the sheet edge position (right edge position, for example) when the carriage  105  moves from a home position toward the sheet  2 . The home position is set as a position at which the head  111  is capped with the cap  151  of the maintenance unit  150 . 
     Similarly, the sheet edge position detector  603  sets, a position at which the detection output of the sheet detector  601  changes from the presence of the sheet  2  to the absence of the sheet  2 , to another of the sheet edge position (left edge position, for example) when the carriage  105  moves from the home position to in the direction from the home position toward the sheet  2  side. 
     The sheet edge position detector  603  detects the sheet edge position for each scan in the print operation of the image. The sheet edge position detector  603  rewrites the sheet edge position data stored in the sheet edge position storage  604  to data of a latest sheet edge position for each time the sheet edge position detector  603  detects the sheet edge position. The “print operation” is an operation of discharging a liquid by the head  111  while moving the carriage  105 . 
     If a first scan and second scan of the carriage  105  is performed without discharging the liquid, and the liquid is discharged from a third scan of the carriage  105 , the third scan of the carriage is defined as “the first scan” in which the controller  500  detect the sheet edge position in the main-scanning direction X based on a detection result by the sheet edge position detector  603  while the printing device  10  prints a first scan of the image on the sheet  2 . 
     The print controller  605  processes the image data, drives the printing mechanism  606 , and controls a print operation to print on the sheet  2 . The print controller  605  controls to adjust an image-formation start position (print start position) for the print operation of a next image based on a final sheet edge position obtained by the print operation of a current image. The print mechanism  606  includes the head drive controller  508 , the head driver  509 , the heads  111 , the motor driver  510 , for example, to print an image on the sheet  2 . 
     Next, an overview of a print position adjustment (image-formation position adjustment) in the first embodiment of the present disclosure is described with reference to  FIGS.  7  and  8   .  FIG.  7    is a plan view of the sheet  2  illustrating the print position adjustment.  FIG.  8    is a plan view of the sheet  2  illustrating the print position adjustment when the print start position is adjusted in scan units. 
     As illustrated in  FIG.  7   , it is assumed that images G 1  and G 2  are sequentially printed on the sheet  2 . The images G 1  and G 2  are printed by four scans of the carriage  105  (first scan C 1  to fourth scan C 4 ). 
     The image G 2  (another image) is separated from the image G 1  in the sub-scanning direction Y so that a space is formed between the image G 1  and G 2  in the sheet  2 . 
     Then, the sheet edge position detector  603  detects a right-edge position R and a left-edge position L of the sheet  2  for each scan of the carriage  105  from the first scan C 1  to the fourth scan C 4 . Further, the sheet edge position detector  603  updates (rewrites) a stored value of the sheet edge position to the detected (latest) value of the sheet edge position in the sheet edge position storage  604  for each time the sheet edge position detector  603  detects the sheet edge positions. 
     For example, in the first scan C 1  of the image G 1 , the controller  500  determines the print position of the image G 1  based on the right-edge position R detected by the sheet edge position detector  603  when the sheet  2  is set to a print position of the printer  1 . The controller  500  may determine the print position of the image G 1  based on a home position of the carriage  105  in the first scan C 1  of the image G 1 . Then, the controller  500  starts printing the image G 1  on the sheet  2 . 
     The “home position” of carriage  105  is determined by a sensor on an apparatus body of the printer  1  that detects a position of the carriage  105  when the carriage  105  is at a standby position before start printing the image. The home position of the carriage  105  may be determined by a position of the carriage  105  moved a predetermined distance from a position at which the carriage  105  contacts a side plate of the apparatus body of the printer  1 . 
     At the time of printing, the sheet edge position detector  603  detects the right-edge position R and the left-edge position L of the sheet  2  in the first scan C 1  and stores the right-edge position data R and the left-edge position data L in the sheet edge position storage  604  as the last (latest) sheet edge position detected last by the sheet edge position detector  603 . 
     Next, the controller  500  prints the image G 1  by the second scan C 2 , and the sheet edge position detector  603  detects the sheet edge position of the sheet  2 , updates (rewrite) the stored value of sheet edge position to the detected (latest) value of the sheet edge position, and stores the detected (latest) value of the sheet edge position in the sheet edge position storage  604 . 
     Similarly, in each of the third scan C 3  and the fourth scan C 4 , the sheet edge position detector  603  detects the sheet edge positions of the sheet  2 , updates (rewrites) the stored value of the sheet edge position to the detected (latest) value of sheet edge position in the sheet edge position storage  604 , stores the detected (latest) value of the sheet edge position in the sheet edge position storage  604 . 
     Thus, the sheet edge position detector  603  updates (rewrites) and stores the data of sheet edge position detected in the fourth scan C 4  in the sheet edge position storage  604  as the most upstream of the sheet edge position (the last sheet edge position of the image G 1 ) in the conveyance direction (sub-scanning direction Y) of the sheet  2 . The sheet edge position of the sheet  2  is detected in the main-scanning direction X (width direction of the sheet  2 ). 
     Thus, the sheet edge position detector  603  detects the sheet edge position of the sheet  2  in the width direction (main-scanning direction X) from the detection result of the sheet detector  601  for each scan of the carriage  105  during the print operation to print the image on the sheet  2 . The sheet edge position detector  603  further stores the sheet edge position data of the detected sheet edge position while updating (rewriting) the sheet edge position data. 
     Then, the controller  500  adjusts the print position (image-forming position) of the image G 2  (another image) based on the most upstream side of the sheet edge position (last sheet edge position) updated (rewritten) and stored in the fourth scan C 4  of the image G 1  when the controller  500  starts printing the next image G 2 . The last sheet edge position is the latest sheet edge position detected last by the sheet edge position detector  603 . 
     Similarly, the sheet edge position detector  603  detects the sheet edge positions of the sheet  2  in the fifth scan C 5  to the eighth scan C 8  of the image G 2 , and the sheet edge position detector  603  updates (rewrites) the sheet edge position data stored in the sheet edge position storage  604  to the data of detected (latest) sheet edge position and stores the data of detected (latest) sheet edge position in the sheet edge position storage  604 . 
     If the image G 1  includes two scans of the first scan C 1  and the second scan C 2  without the third scan C 3  and the fourth scan C 4 , the image G 2  (another scan) starts from a third scan C 3 . 
     Similarly, the controller  500  adjusts the print start position (image-forming start position) at a time of printing next image based on the sheet edge position of a last scan of the current image. 
     The print start position of the first scan C 1  in the image G 1  is, for example, a left end of the first scan C 1  when the printing is performed from left to right in  FIG.  7   . 
     The controller  500  does not adjust the print position for each scan when printing the same image (one continuous image) because the print start position (image-formation start position) of a unit image (one continuous image) corresponding to each scan may be displaced that cause deterioration in print quality as illustrated in  FIG.  8   . Thus, the controller  500  (circuitry) detects the sheet edge position by the sheet edge position detector  603  for each scan of the carriage  105  while stop adjusting the print start position for each scan of the carriage  105  during printing one continuous image on the sheet  2 . 
       FIG.  9    is a flowchart of a control of the print operation of the controller  500  is described with reference to a flowchart illustrated in  FIG.  9   . 
     First, when a print start instruction is received (step S 0 ), the controller  500  determines whether the sheet  2  is conveyed after a last detection of the sheet edge position (step S 1 ). Hereinafter, steps S 0  and S 1  are simply referred to as “S 0 ” and “S 1 ”, respectively. 
     The sheet edge position detector  603  detects the sheet edge position of the sheet  2  when the sheet  2  is conveyed after the last detection of the sheet edge position (S 2 ). 
     The controller  500  may convey the sheet  2  described in following examples of conveyance processes (1) to (3) after printing the image G 1  and before printing the image G 2  in an example illustrated in  FIG.  7   . In the above case, the controller  500  detects the sheet edge position of the sheet  2  by the sheet edge position detector  603  before start printing the image G 2 . Then, the controller  500  adjusts the image-formation start position (print start position) of the image G 2  based on the detected sheet edge position by the sheet edge position detector  603 . 
     Example of Conveyance of the Sheet  2   
     (1) A conveyance of the sheet during the sheet  2  is set (loaded) in the printer  1 . 
     (2) A conveyance during detection and storing of the right-edge position R of the sheet  2  in the next scan (print scan) while performing a dummy discharge operation. 
     The controller  500  drives the head  111  to perform the “dummy discharge operation” that discharge the liquid that does not contribute the image formation on the sheet  2  to maintain the head  111 . Here, the sheet edge position detector  603  always updates (rewrites) the right-end position R of the sheet  2  (does not perform an image shift) and holds the updated (rewritten) right-edge position even when the power is turned off. 
     (3) A conveyance of the sheet  2  after the final detection of the right-edge position R and before start of printing process when the following at least one of conveyance processes (a) to (d) is executed. 
     (a) Manual feed (the user feeds the sheets  2  as many sheets as the user desires). 
     (b) Test feed (the sheet  2  is fed to check whether a temperature setting is appropriate). 
     (c) A conveyance to cut the sheet  2  at a manual cutting position. 
     (d) A conveyance to dry the sheet  2  after printing (including printing an adjustment chart). 
     Contrary, the controller  500  starts image formation of the first image (S 3 ) when the sheet  2  is not conveyed after the last detection of the sheet edge position in step S 1 . At the time of starting S 3 , the controller  500  refers to the last detection of the sheet edge position (S 4 ) and adjusts the image-formation start position (print start position) (S 5 ). 
     Next, the sheet edge position detector  603  detects the sheet edge position for each scan while performing the print operation of the image on the sheet  2 , updates (rewrites) the sheet edge position data stored in the sheet edge position storage  604  to the data of detected (latest) sheet edge position, and stores the data of detected (latest) sheet edge position in the sheet edge position storage  604  (S 6 ). 
     Then, the controller  500  starts forming image of a second image (S 7 ). At the time of start of image formation, the controller  500  refers to the last detection of the sheet edge position (S 8 ) and adjusts the image-formation start position (print start position) (S 9 ). Then, the controller  500  repeats the same print operation until the print operations is completed. The controller  500  proceeds to next process after completion of the print operation (S 10 ). 
     Thus, the printer  1  can adjust the print start position of the image on the sheet  2  even when a skew of the sheet  2  (web) is occurred during a conveyance of the sheet  2  (web) to print the image on the sheet  2  (web) such as the roll paper or the continuous sheet. Thus, the printer can improve the print quality. 
     When the printer  1  enters an energy-saving mode (mode that reduces power consumption), the controller  500  does not detect the sheet edge position that is unnecessary to hold an execution history of the conveyance operation to reduce a number of detection of sheet edge position to reduce the power consumption. 
     When the print operation is interrupted midway and the sheet  2  is conveyed, the controller  500  adjusts the image-formation start position (print start position) based on the sheet edge position that is last to be detected by the sheet edge position detector  603  during a previous printing operation. 
     Thus, the controller  500  (circuitry) adjusts the print start position at which the printing device  10  starts printing the second scan of the image on the sheet  2  based on a latest edge position detected based on a last detection result by the, the sheet edge position detector  603  while the printing device  10  prints the first scan of the image, when the sheet  2  is conveyed in a sub-scanning direction Y perpendicular to the main-scanning direction X after the printing device  10  interrupts printing the first scan of the image and before the printing device  10  starts printing the second scan of the image on the sheet  2 . 
     The above-described embodiments may be applied when the images G 1  and G 2  are separated by a predetermined distance (see  FIG.  7   ). For example, the above-described embodiments may be applied when the images G 1  and G 2  are printed by different printing jobs, or when the images G 1  and G 2  are separated by a distance that is visibly recognizable that the images G 1  and G 2  are separated even if the images G 1  and G 2  are printed by the same printing job. 
     The sheet is a web such as a roll paper or a continuous sheet in the above-described embodiments as an example. However, the sheet is not limited to the web. For example, the web may be a recording medium (object to be printed) such as a long sheet material, a wallpaper, a sheet for electronic circuit board, or the like other than the continuous body such as the roll paper or the continuous sheet. 
     In the present embodiments, a “liquid” discharged from the head is not particularly limited as long as the liquid has a viscosity and surface tension of degrees dischargeable from the 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 that contains, 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, or a surfactant, a biocompatible material, such as DNA, amino acid, protein, or calcium, or 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 solution, 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. 
     Examples of an energy source to generate energy to discharge liquid include a piezoelectric actuator (a laminated piezoelectric element or a thin-film piezoelectric element), a thermal actuator that employs a thermoelectric conversion element, such as a heating resistor, and an electrostatic actuator including a diaphragm and opposed electrodes. 
     The “liquid discharge apparatus” may include devices to feed, convey, and eject the material on which liquid can adhere. The liquid discharge apparatus may further include a pretreatment apparatus to coat a treatment liquid onto the material, and a post-treatment apparatus to coat a treatment liquid onto the material, onto which the liquid has been discharged. 
     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 arbitrary images, such as arbitrary patterns, or fabricate three-dimensional images. 
     The terms “image formation”, “recording”, “printing”, “image printing”, and “fabricating” used herein may be used synonymously with each other. 
     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. For example, the controller  500  as described above may be implemented by one or more processing circuits or circuitry. 
     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that, within the scope of the above teachings, the present disclosure may be practiced otherwise than as specifically described herein. With some embodiments having thus been described, it is obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the scope of the present disclosure and appended claims, and all such modifications are intended to be included within the scope of the present disclosure and appended claims.