Patent Description:
An image printed by an inkjet printer which is an image forming apparatus is formed by a large number of ink dots arranged in an array, discharged from a nozzle array. The position where an ink dot is formed (i.e., dot formation position), which is the position where the ink lands on a printing medium, may deviate from the target position. In such a case, an image printed on the recording medium such as a paper sheet is not clear. In particular, some inkjet printers include a plurality of carriages arranged in a sub-scanning direction, and each of the carriages carries one or more liquid discharge heads. In such an inkjet printer, if the carriages are not accurately positioned at the respective designed positions, the dot formation positions are misaligned among the carriages. As a result, an image printed by these carriages is not clear. Accordingly, the carriages are positioned at the designed positions in the inkjet printer with delicate adjustment. For example, the use of a jig can keep variations in positioning accuracy within a certain range but cannot reduce the positioning variations to zero.

A method known in the art for adjusting the dot formation positions in the sub-scanning direction in inkjet printers is adjusting the conveyance distance of the recording medium. However, in an inkjet printer that performs printing with a plurality of carriages arranged side by side in the sub-scanning direction, the method of adjusting the conveyance distance of the recording medium is not effective. Since a conveyance mechanism to convey a recording medium is common among the carriages, the adjustment result is reflected in the dot formation positions of ink discharged from all the carriages. For this reason, the dot formation positions of ink discharged from a carriage that does not require adjustment are adversely affected, and the landing positions of ink deviate. In this case, the dot formation positions cannot be adjusted by adjusting the conveyance distance of the recording medium.

There are known approaches for providing an image forming apparatus that can easily reduce reading unevenness in a scanning direction and a method for white adjustment. For example, according to <CIT>, an image sensor is attached to an inkjet head unit that has a width matching a medium width, and the voltages applied to liquid discharge heads are adjusted based on the result of image capturing received from the image sensor.

However, the technique disclosed in <CIT> is not effective for a case where the landing positions of ink deviate in the sub-scanning direction in a serial inkjet printer including a plurality of carriages arranged in the sub-scanning direction, driven individually. Specifically, when the voltages applied to the liquid discharge heads are adjusted, the adjustment can be made in the main scanning direction in which the carriages perform scanning, but the adjustment cannot be made in the sub-scanning direction in which the recording medium is conveyed. As a result, the deviations in landing positions of ink in the sub-scanning direction cannot be eliminated.

<CIT> discloses an image formation device and a word correction method capable of suppressing reading unevenness relative to a scanning direction.

<CIT> discloses a printing apparatus including a plurality of printing units along one guide can read test patterns printed with a plurality of types of conveying amount of a recording medium and determine a conveying amount based on the reading result.

<CIT> discloses a liquid discharge device for eliminating misalignment of drawing due to variation in assembly between carriages.

In view of the foregoing, an object of the present disclosure is to provide an image forming apparatus, an image forming system, an image forming method, and a program that can eliminate deviations in landing positions of ink caused by variations in installation positions of a plurality of carriages arranged in the sub-scanning direction.

An embodiment provides a serial image forming apparatus including a plurality of carriages each of which carries a liquid discharge head. The image forming apparatus includes an acquisition unit, an identifying unit, a discharge control unit, and a movement control unit. The acquisition unit acquires divided print data divided from print data. The divided print data has an extended size extended in a direction corresponding to a conveyance direction of a recording medium from a size corresponding to a length of a nozzle array of the liquid discharge head in the conveyance direction. The identifying unit identifies, for the liquid discharge head of a particular carriage of the plurality of carriages, a shifted data portion from the divided print data acquired by the acquisition unit. The shifted data portion has a size corresponding to the length of the nozzle array and is shifted by a number of pixels corresponding to an amount of deviation from a target installation position of the particular carriage in the conveyance direction. The discharge control unit controls the liquid discharge head to discharge ink to the recording medium using the shifted data portion identified by the identifying unit. The movement control unit controls the particular carriage
to move in a main scanning direction based on the shifted data portion identified by the identifying unit.

According to another embodiment, an image forming system includes the image forming apparatus described above and a dividing unit to divide, from the print data, the divided print data.

Another embodiment provides a method for forming an image by a serial image forming apparatus including a plurality of carriages each of which carries a liquid discharge head. The method includes acquiring divided print data divided from print data. The divided print data has an extended size extended in a direction corresponding to a conveyance direction of a recording medium from a size corresponding to a length of a nozzle array of the liquid discharge head in the conveyance direction. The method further includes identifying, for the liquid discharge head of a particular carriage of the plurality of carriages, from the divided print data, a shifted data portion having a size corresponding to the length of the nozzle array and being shifted by a number of pixels corresponding to an amount of deviation from a target installation position of the particular carriage in the conveyance direction; controlling the liquid discharge head to discharge ink to the recording medium using the shifted data portion; and controlling the particular carriage to move in the main scanning direction based on the shifted data portion.

Another embodiment provides a carrier medium carrying computer readable codes which, when executed by a computer system, cause the computer system to carry out the method described above.

According to the embodiments of the present disclosure, deviations in landing positions of ink caused by variations in installation positions of a plurality of carriages arranged in the sub-scanning direction can be eliminated.

Referring now to the drawings, descriptions are given in detail below of an image forming apparatus, an image forming system, an image forming method, and a program for causing a computer system to perform the image forming method according to embodiments of the present disclosure with reference to the drawings.

Terms used in this disclosure are defined as described below. "Computer software," which may be referred to simply as "software" in the following description, is defined as a program related to operation of a computer or any information that is used in processing performed by a computer and equivalent to a program. "Application software," which may be referred to simply as an "application," is a generic name for any software used to perform certain processing. By contrast, an "operating system (OS)" is software for controlling a computer to allow, for example, application software to use computer resources. An "OS" controls basic operations of the computer, such as input and output of data, management of hardware resources such as a memory and a hard disk, and processes to be performed.

"Application software" operates by utilizing functions provided by an OS. A "program" is a set of instructions for causing a computer to perform processing to generate a certain result. Information that is not a direct command to a computer is not referred to as a program itself. However, information that defines processing performed by a program is similar in nature to a program and thus is interpreted as equivalent to a program. For example, a data structure, which is a logical structure of data represented by an interrelation between data elements, is interpreted as equivalent to a program.

<FIG> is a schematic diagram illustrating a configuration of an image forming apparatus of an image forming system according to the present embodiment. A description is given of a schematic configuration of an image forming system <NUM> according to the present embodiment with reference to <FIG>.

As illustrated in <FIG>, the image forming system <NUM> includes an image forming apparatus <NUM> and a personal computer (PC) <NUM>.

The image forming apparatus <NUM> is a serial image forming apparatus that includes a plurality of carriages. The mage forming apparatus <NUM> discharges ink from liquid discharge heads carried by the carriages, so as to form an image on a recording medium such as a paper sheet. As illustrated in <FIG>, the image forming apparatus <NUM> includes carriages 15U and 15D.

The carriage 15U reciprocates in a main scanning direction indicated by arrow A1 in <FIG>, perpendicular to a sub-scanning direction indicated by arrow B in <FIG>, in which a recording medium P is conveyed. By so doing, the carriage 15U changes the landing positions of ink discharged from a liquid discharge head 16U mounted on the carriage 15U. The carriage 15U carries one or more liquid discharge heads 16U. The carriage 15U is disposed upstream from the carriage 15D in the sub-scanning direction.

As will be described later, the liquid discharge head 16U includes a nozzle array including a plurality of nozzles for discharging ink, arranged in the sub-scanning direction.

The carriage 15D reciprocates in the main scanning direction, indicated by arrow A2 in <FIG>, perpendicular to the sub-scanning direction, indicated by arrow B in <FIG>, in which the recording medium P is conveyed. By so doing, the carriage 15D changes the landing positions of ink discharged from a liquid discharge head 16D mounted on the carriage 15D. The carriage 15D carries one or more liquid discharge heads 16D. The carriage 15D is disposed downstream from the carriage 15U in the sub-scanning direction.

The liquid discharge head 16U of the carriage 15U and the liquid discharge head 16D of the carriage 15D may discharge different inks from each other. For example, the liquid discharge head 16U may form an image with color inks such as cyan (C), magenta (M), yellow (Y), and black (K) inks, and the liquid discharge head 16D may form an image with a spot color ink such as a white ink, a metallic color ink, or a fluorescent color ink. Alternatively, one of the liquid discharge head 16U and the liquid discharge head 16D may discharge one or more achromatic inks and the other may discharge one or more chromatic inks.

Although the image forming system <NUM> illustrated in <FIG> includes two carriages, i.e., the carriage 15U and the carriage 15D, the number of the carriages is not limited thereto, and the image forming system <NUM> may include three or more carriages.

The PC <NUM> is an information processing apparatus that transmits, to the image forming apparatus <NUM>, print data to be subjected to printing. In the present embodiment, the PC <NUM> divides the print data into pieces of data corresponding to the liquid discharge head 16U of the carriage 15U and the liquid discharge head 16D of the carriage 15D, respectively, and transmits the divided pieces of data to the image forming apparatus <NUM>. In this disclosure, the data obtained by dividing the print data by the image forming apparatus <NUM> may be referred to as "divided print data.

The information processing apparatus that transmits print data to the image forming apparatus <NUM> is not limited to the PC <NUM> but may be, for example, a smartphone, a tablet communication terminal, or a workstation.

<FIG> is a block diagram illustrating a hardware configuration of the image forming apparatus according to the present embodiment. A description is given of a hardware configuration of the image forming apparatus <NUM> according to the present embodiment with reference to <FIG>.

As illustrated in <FIG>, the image forming apparatus <NUM> includes a controller <NUM>, a control panel <NUM>, a sensor <NUM>, head drivers 140U and 140D, main scanning motors 17U and 17D, a sub-scanning motor <NUM>, and a conveyance roller <NUM>.

The controller <NUM> includes a central processing unit (CPU) <NUM>, a read only memory (ROM) <NUM>, a random access memory (RAM) <NUM>, a non-volatile RAM (NVRAM) <NUM>, an application specific integrated circuit (ASIC) <NUM>, print controllers 106U and 106D, main scanning motor drivers 107U and 107D, an input and output (I/O) interface <NUM>, a communication interface <NUM>, and a sub-scanning motor driver <NUM>.

The CPU <NUM> is a processor that controls the entire operation of the image forming apparatus <NUM>. The ROM <NUM> is a non-volatile storage device that stores fixed data such as programs to be executed by the CPU <NUM>. The RAM <NUM> is a volatile storage device that serves as a work area for processing executed by the CPU <NUM>. Further, the RAM <NUM> temporarily stores data such as image data.

The NVRAM <NUM> is a non-volatile storage device that retains data and programs even when the power supply of the image forming apparatus <NUM> is off.

The ASIC <NUM> is an integrated circuit that executes various kinds of signal processing on image data, image processing such as rearrangement, and processing on other input and output signals for controlling the entire operation of the image forming apparatus <NUM>.

The print controller 106U is a control circuit that controls the discharge operation of the liquid discharge head 16U via the head driver 140U under the control of the CPU <NUM>. The print controller 106U transfers data for driving the liquid discharge head 16U to the head driver 140U. For example, the print controller 106U transfers image data as serial data to the head driver 140U. Further, the print controller 106U outputs, for example, a transfer clock, a latch signal, and a control signal used for transferring the image data to the head driver 140U. The head driver 140U selectively applies, based on the serially-input image data corresponding to one line of print data to be printed by the liquid discharge head 16U, driving pulses to pressure generators of the liquid discharge head 16U. The driving pulses represent a drive waveform received from the print controller 106U. In so doing, the head driver 140U drives the liquid discharge head 16U to discharge ink. The image data is based on the divided print data divided by the PC <NUM> described above, and will be described in detail later.

The print controller 106D is a control circuit that controls the discharge operation of the liquid discharge head 16D via the head driver 140D under the control of the CPU <NUM>. The print controller 106D transfers data for driving the liquid discharge head 16D to the head driver 140D. For example, the print controller 106D transfers image data as serial data to the head driver 140D. Further, the print controller 106U outputs, for example, a transfer clock, a latch signal, and a control signal used for transferring the image data, to the head driver 140D. The head driver 140D selectively applies, based on the serially-input image data corresponding to one line of print data to be printed by the liquid discharge head 16D, driving pulses to pressure generators of the liquid discharge head 16D. The driving pulses represent a drive waveform received from the print controller 106D. In so doing, the head driver 140U drives the liquid discharge head 16D to discharge ink. The image data is based on the divided print data divided by the PC <NUM> described above, and will be described in detail later.

The main scanning motor driver 107U is a driving circuit that controls the operation of the main scanning motor 17U under the control of the CPU <NUM>. The main scanning motor 17U moves the carriage 15U in the main scanning direction under the control of the main scanning motor driver 107U.

The main scanning motor driver 107D is a driving circuit that controls the operation of the main scanning motor 17D under the control of the CPU <NUM>. The main scanning motor 17D moves the carriage 15D in the main scanning direction under the control of the main scanning motor driver 107D.

The I/O interface <NUM> is an interface circuit used to obtain the data from the sensor <NUM> and extract the data used to control elements and units of the image forming apparatus <NUM>. The sensor <NUM> is, for example, an optical sensor that reads a printed image on the recording medium P or a temperature sensor that detects the temperature of a heater in printing.

The communication interface <NUM> is an interface circuit that transmits and receives data and signals to and from the PC <NUM>. Specifically, the communication interface <NUM> transmits and receives data and signals to and from the PC <NUM> via a cable or a network. In a configuration where the communication interface <NUM> communicates with the PC <NUM> via a network, the communication interface <NUM> complies with, for example, Transmission Control Protocol (TCP)/Internet Protocol (IP).

The print data (divided print data) stored in a reception buffer of the communication interface <NUM> is analyzed by the CPU <NUM> and subjected to processing (e.g., image processing and data rearrangement) executed by the ASIC <NUM>. The processed pieces of data are transferred, as discharge data, to the head driver 140U and the head driver 140D by the print controller 106U and the print controller 106D, respectively.

The sub-scanning motor driver <NUM> is a driving circuit that controls the operation of the sub-scanning motor <NUM> under the control of the CPU <NUM>. The sub-scanning motor <NUM> rotates the conveyance roller <NUM> under the control of the sub-scanning motor driver <NUM> so as to convey the recording medium P in the sub-scanning direction. The conveyance roller <NUM> rotates, driven by the sub-scanning motor <NUM>, and conveys the recording medium P in the sub-scanning direction along a conveyance passage.

The control panel <NUM> is a device such as a touch panel for inputting and outputting various kinds of information.

The hardware configuration of the image forming apparatus <NUM> is not limited to that illustrated in <FIG>. The image forming apparatus <NUM> does not necessarily include all the components illustrated in <FIG> or may include some other components.

<FIG> is a block diagram illustrating a hardware configuration of the PC according to the present embodiment. A description is given below of the hardware configuration of the PC <NUM> according to the present embodiment with reference to <FIG>.

As illustrated in <FIG>, the PC <NUM> includes a CPU <NUM>, a ROM <NUM>, a RAM <NUM>, an auxiliary memory <NUM>, a media drive <NUM>, a display <NUM>, a network interface <NUM>, a keyboard <NUM>, a mouse <NUM>, and a digital versatile disc (DVD) drive <NUM>.

The CPU <NUM> is a processor that controls the entire operation of the PC <NUM>. The ROM <NUM> is a non-volatile storage device that stores programs to be executed by the PC <NUM>. The RAM <NUM> is a volatile storage device that serves as a work area for the CPU <NUM>.

The auxiliary memory <NUM> is a storage device such as a hard disk drive (HDD) or a solid state drive (SSD) that stores various kinds of data including print data and programs.

The media drive <NUM> controls reading and writing of data to and from a recording medium <NUM> such as a flash memory under the control of the CPU <NUM>.

The display <NUM> is a display device that includes, for example, a liquid crystal display or an organic electro-luminescence (EL) display on which various kinds of information such as a cursor, a menu, a window, characters, and images are displayed.

The network interface <NUM> is an interface for data communication with the image forming apparatus <NUM> via a network. The network interface <NUM> is, for example, a network interface card (NIC) that supports ETHERNET and establishes communications in compliance with TCP/IP.

The keyboard <NUM> is an input device used for selecting characters, numbers, or various instructions, and for moving a cursor, for example. The mouse <NUM> is an input device for selecting and executing various instructions, selecting an object to be processed, and moving a cursor, for example.

The DVD drive <NUM> controls reading and writing of various kinds of data from and to a DVD <NUM> that is a removable storage medium. The DVD <NUM> is, for example, a DVD-ROM or a DVD-recordable (DVD-R).

The CPU <NUM>, the ROM <NUM>, the RAM <NUM>, the auxiliary memory <NUM>, the media drive <NUM>, the display <NUM>, the network interface <NUM>, the keyboard <NUM>, the mouse <NUM>, and the DVD drive <NUM> are connected to one another to communicate with each other, via a bus line <NUM> such as an address bus or a data bus.

The hardware configuration of the PC <NUM> is not limited to that illustrated in <FIG>. The PC <NUM> does not necessarily include all the components illustrated in <FIG> or may include other components.

<FIG> is a block diagram illustrating a functional configuration of the image forming system according to the present embodiment. <FIG> are diagrams each illustrating an operation of the image forming apparatus in a case where the landing positions of ink do not deviate in the sub-scanning direction of the liquid discharge heads. <FIG> are diagrams each illustrating an operation of the image forming apparatus in a case where the landing positions of ink deviate in the sub-scanning direction of the liquid discharge heads. A description is given of the functional configuration and an operation of the image forming system <NUM> according to the present embodiment with reference to <FIG>.

As illustrated in <FIG>, the PC <NUM> includes a communication unit <NUM>, a dividing unit <NUM>, and a print data transmission unit <NUM>.

The communication unit <NUM> is a functional unit for performing data communication with the image forming apparatus <NUM>. The communication unit <NUM> is implemented by the network interface <NUM> illustrated in <FIG>.

The dividing unit <NUM> is a functional unit that divides the print data to be subjected to printing, into a plurality of divided print data. The dividing unit <NUM> divides the print data into divided print data to be allocated to the nozzle array of the liquid discharge head 16U of the carriage 15U and the nozzle array of the liquid discharge head 16D of the carriage 15D.

Descriptions are given of a nozzle configuration of the liquid discharge head 16D and the divided print data to be allocated to the liquid discharge head 16D with reference to <FIG>. The liquid discharge head 16D herein is the representative of the liquid discharge heads 16D and 16U. The liquid discharge head 16D includes, for example, <NUM> nozzles such as nozzles N1 to N100 illustrated in <FIG>. In <FIG>, the direction from bottom to top is the sub-scanning direction (indicated by arrow B). As illustrated in <FIG>, the nozzles N1 to N100 are arranged in the sub-scanning direction. Although the nozzles N1 to N100 are arranged in a zigzag shape in the sub-scanning direction in <FIG>, the nozzle arrangement is not limited thereto. For example, the nozzles N1 to N100 may be linearly arranged in the sub-scanning direction.

<FIG> illustrates a part of a pixel configuration of the print data. In <FIG>, numbers are assigned to the pixel rows each extending in the main scanning direction (lateral direction in <FIG>) in the print data for convenience of description. In <FIG>, a print data portion PP is a part of the print data corresponding to <NUM> pixel rows (e.g., pixel rows <NUM> to <NUM>). Using the print data portion PP, the liquid discharge head 16D discharges ink in a discharge operation in certain scanning in the main scanning direction performed by the carriage 15D. In other words, the liquid discharge head 16D discharges ink from the nozzles N1, N2,. and N100 based on data portions corresponding to the pixel rows <NUM>, <NUM>,. and <NUM>, respectively. In the subsequent scanning by the carriage 15D, the liquid discharge head 16D discharges ink from the nozzles N1, N2,. , and N100 based on data portions corresponding to the pixel rows <NUM>, <NUM>,. , and <NUM>, respectively. The liquid discharge head 16D repeats such an operation until an image is formed for the entire print data. The liquid discharge head 16U disposed upstream from the liquid discharge head 16D in the sub-scanning direction operates in a manner similar to that of the liquid discharge head 16D described above.

The pixel configuration of the print data according to the present embodiment is not limited to that illustrated in <FIG>, and another pixel configuration may be used. In addition, the number of nozzles is not limited to <NUM> as illustrated in <FIG>.

With the operation described above, when the landing positions of ink discharged by the liquid discharge head 16D of the carriage 15D overlap, without deviations, with the landing positions of the ink discharged by the liquid discharge head 16U of the carriage 15U (disposed upstream from the carriage 15D in the sub-scanning direction) in the sub-scanning direction, a desired clear image is printed on the recording medium P. In other words, ideally, the divided print data can be obtained by dividing, with the dividing unit <NUM>, the print data into data portions each corresponding to <NUM> pixel rows, like the print data portion PP illustrated in <FIG>. The print data portion PP is ideal divided print data for a case where the installation positions of the carriages 15U and 15D in the sub-scanning direction are not deviated from the target installation positions. However, in an image forming apparatus including a plurality of carriages (e.g., the carriages 15U and 15D) like the image forming apparatus <NUM> according to the present embodiment, if the carriages are not accurately positioned at the respective designed positions, the dot formation positions are misaligned among the carriages. As a result, an image printed by these carriages is not clear. Assume that the carriage 15D is installed at a position deviated downstream in the sub-scanning direction from the target installation position by three nozzles of the liquid discharge head 16D. In such a case, when the liquid discharge head 16D discharges ink based on the data portion of the print data corresponding to the pixel rows <NUM> to <NUM> as illustrated in <FIG>, an image printed on the recording medium P is deviated downstream by three pixels. In this case, the image printed by the liquid discharge head 16D overlaps the image printed by the liquid discharge head 16U at a position deviated by three pixels, and the printed image is not clear.

To address such an inconvenience, in the present embodiment, the amount of deviation in installation position of the carriage 15D in the sub-scanning direction from the target installation position is grasped in advance, and the liquid discharge head 16D is controlled to discharge ink based on the divided print data in which the amount of deviation is taken into account. For example, assume that the installation position of the carriage 15D carrying the liquid discharge head 16D illustrated in <FIG> is deviated downstream in the sub-scanning direction by three nozzles of the liquid discharge head 16D as described above. In this case, the liquid discharge head 16D discharges ink based on a print data portion PPa (serving as a shifted data portion) illustrated in <FIG>, which is shifted downstream in the sub-scanning direction by three pixels, from the print data portion PP (i.e., ideal divided print data) illustrated in <FIG>. In other words, the liquid discharge head 16D discharges ink from the nozzles N1, N2,. , and N100 based on data portions corresponding to the pixel rows <NUM>, <NUM>,. , and <NUM>, respectively. In the subsequent scanning of the carriage 15D, the liquid discharge head 16D discharges ink from the nozzles N1, N2,. , and N100 based on data portions corresponding to the pixel rows <NUM>, <NUM>,. , and <NUM>, respectively. The liquid discharge head 16D repeats such an operation until an image is formed for the entire print data.

In this way, the liquid discharge head 16D discharges ink based on the shifted data portion that is shifted by the number of pixels in the print data corresponding to the amount of deviation in installation position of the carriage 15D in the sub-scanning direction. As a result, the landing positions of ink discharged by the liquid discharge head 16D of the carriage 15D match the landing positions of ink discharged by the liquid discharge head 16U of the carriage 15U in the sub-scanning direction, so as to print a desired clear image on the recording medium P.

However, when the dividing unit <NUM> divides the print data and allocates the print data portion PP illustrated in <FIG> (corresponding to the pixel rows <NUM> to <NUM> and serving as the divided print data) to the ink discharge of the liquid discharge head 16D as described above, the print data portion PP does not include the data portion corresponding to the pixel rows <NUM> to <NUM>. In this case, the ink discharge based on the print data portion PPa illustrated in <FIG> cannot be performed. To address such an inconvenience, in the present embodiment, the dividing unit <NUM> of the PC <NUM> divides the print data into data portions (divided print data) having margins at both ends in the direction corresponding to the sub-scanning direction so that the identifying unit <NUM> of the image forming apparatus <NUM> can identify, from the divided print data, a shifted data portion shifted by the number of pixels corresponding to the amount of deviation in installation position of the carriage 15D in the sub-scanning direction, as the data portion used for ink discharge. In other words, the dividing unit <NUM> divides the print data into not the data portions (divided print data) corresponding to the length of the nozzle array of the liquid discharge head 16D (in <FIG>, the length of the nozzle array corresponds to <NUM> pixel rows) but data portions (divided print data) having a size extended by a set number of pixels at each end in the direction corresponding to the sub-scanning direction. For example, assume that the maximum amount of deviation in installation position of the carriage 15D in the sub-scanning direction is equivalent to five nozzles (five pixels). In this case, in the example illustrated in <FIG>, the dividing unit <NUM> divides the print data not into the data portions each corresponding to <NUM> pixels, such as the data portion corresponding to the pixel rows <NUM> to <NUM> and the data portion corresponding to the pixel rows <NUM> to <NUM>, but into data portions each having a size extended by five pixels at both ends in the direction corresponding to the sub-scanning direction, such as a data portion corresponding to the pixel rows <NUM> to <NUM> and a data portion (divided print data) corresponding to the pixel rows <NUM> to <NUM>. Further assume that the carriage 15D is installed at a position deviated downstream in the sub-scanning direction from the designed position by three nozzles of the liquid discharge head 16D, as described above. In this case, when the image forming apparatus <NUM> receives the data portion corresponding to the pixel rows <NUM> to <NUM> as one of the divided print data, the image forming apparatus <NUM> can identify a data portion corresponding to the pixel row <NUM> to <NUM> from the divided print data and allocate the identified data portion to the liquid discharge head 16D.

The deviation in installation position of the carriage 15D in the sub-scanning direction may be considered as a deviation from a reference position, or a deviation relative to the installation position of the carriage 15U. The processing of dividing print data performed by the dividing unit <NUM> for coping with the deviation in installation position of the carriage 15D in the sub-scanning direction and the processing of identifying the data portion of the divided print data to be allocated to the liquid discharge head 16D can be applied to the carriage 15U and the liquid discharge head 16U.

Returning back to <FIG>, the description is continued below.

The print data transmission unit <NUM> is a functional unit that transmits the divided print data divided by the dividing unit <NUM> to the image forming apparatus <NUM> via the communication unit <NUM>.

The dividing unit <NUM> and the print data transmission unit <NUM> described above are implemented, for example, as the CPU <NUM> illustrated in <FIG> executes a program. Note that some or all of the functional units described above may be implemented by a hardware circuit (e.g., an integrated circuit) such as a field-programmable gate array (FPGA) or an ASIC, in place of software programs.

Each functional unit of the PC <NUM> illustrated in <FIG> is a conceptual representation of a function, and the functional configuration of the PC <NUM> is not limited to that illustrated in <FIG>. For example, a plurality of functional units of the PC <NUM> illustrated as independent units in <FIG> may be configured as a single functional unit. Further, functions provided by a single functional unit of the PC <NUM> illustrated in <FIG> may be divided and allocated to a plurality of functional units.

As illustrated in <FIG>, the image forming apparatus <NUM> includes a communication unit <NUM>, a print data acquisition unit (acquisition unit) <NUM>, an identifying unit <NUM>, a discharge control unit <NUM>, a movement control unit <NUM>, and a storage unit <NUM>.

The communication unit <NUM> is a functional unit that performs data communication with the PC <NUM>. The communication unit <NUM> is implemented by the communication interface <NUM> illustrated in <FIG>.

The storage unit <NUM> is a functional unit that stores in advance information indicating deviations in installation positions of the carriage 15U and the carriage 15D in the sub-scanning direction described above. The amount of deviation in installation positions of the carriage 15U and the carriage 15D in the sub-scanning direction may be obtained by, for example, printing a chart for checking deviations in advance and checking the deviation on the chart. Alternatively, the image forming apparatus <NUM> may include a scanner that reads the printed chart, and the amount of deviation may be automatically obtained based on read data obtained by the scanner. The information indicating the obtained amounts of deviation in installation positions of the carriage 15D and the carriage 15U in the sub-scanning direction is stored in the storage unit <NUM>. For obtaining the deviation in installation position of the carriage 15D in the sub-scanning direction relative to the installation position of the carriage 15U in the sub-scanning direction, only information indicating the deviation of the carriage 15D may be stored in the storage unit <NUM>. For obtaining the deviation in installation position of the carriage 15U in the sub-scanning direction relative to the installation position of the carriage 15D in the sub-scanning direction, only information indicating the deviation of the carriage 15U may be stored in the storage unit <NUM>. The storage unit <NUM> is implemented by the RAM <NUM> or the NVRAM <NUM> illustrated in <FIG>.

The print data acquisition unit <NUM> is a functional unit that acquires the divided print data from the PC <NUM> via the communication unit <NUM>.

The identifying unit <NUM> is a functional unit that reads, from the storage unit <NUM>, the information indicating the deviations in installation positions of the carriage 15U and the carriage 15D in the sub-scanning direction, and identifies, from each divided print data acquired by the print data acquisition unit <NUM>, a shifted data portion shifted by the number of pixels corresponding to the deviation indicated by the information. With this function, the data portion used for ink discharge by the liquid discharge head 16U of the carriage 15U and the data portion used for ink discharge by the liquid discharge head 16D of the carriage 15D are obtained.

The discharge control unit <NUM> is a functional unit that controls the ink discharge by the liquid discharge head 16U using the data portion corresponding to the liquid discharge head 16U, identified by the identifying unit <NUM>, and controls the ink discharge by the liquid discharge head 16D using the data portion corresponding to the liquid discharge head 16D, identified by the identifying unit <NUM>. Specifically, the discharge control unit <NUM> controls the ink discharge by the liquid discharge head 16U via the print controller 106U (control circuit) and controls the ink discharge by the liquid discharge head 16D via the print controller 106D (control circuit).

The movement control unit <NUM> is a functional unit that controls the carriage 15U and the carriage 15D to move in the main scanning direction in accordance with the control of the ink discharge by the liquid discharge head 16U and the liquid discharge head 16D by the discharge control unit <NUM>. The movement control unit <NUM> controls the carriage 15U and the carriage 15D to move in the main scanning direction based on the data portions identified by the identifying unit <NUM>. Specifically, the movement control unit <NUM> controls the carriage 15U to move in the main scanning direction via the main scanning motor driver 107U and controls the carriage 15D to move in the main scanning direction via the main scanning motor driver 107D.

The print data acquisition unit <NUM>, the identifying unit <NUM>, the discharge control unit <NUM>, and the movement control unit <NUM> described above are implemented, for example, as the CPU <NUM> illustrated in <FIG> executes a program. Some or all of the functional units described above may be implemented by a hardware circuit (e.g., an integrated circuit) such as a FPGA or an ASIC, in place of software programs.

Each functional unit of the image forming apparatus <NUM> illustrated in <FIG> is a conceptual representation of a function, and the functional configuration of the image forming apparatus <NUM> is not limited to that illustrated in <FIG>. For example, a plurality of functional units of the image forming apparatus <NUM> illustrated as independent units in <FIG> may be configured as a single functional unit. Further, functions provided by a single functional unit of the image forming apparatus <NUM> illustrated in <FIG> may be divided and allocated to a plurality of functional units.

Some of the functional units of the image forming apparatus <NUM> may be implemented by the PC <NUM>, or some of the functional units of the PC <NUM> may be implemented by the image forming apparatus <NUM>.

For example, the processing of dividing print data performed by the dividing unit <NUM> of the PC <NUM> may be performed by the image forming apparatus <NUM>. Further, for example, the processing of identifying the data portion of the divided print data performed by the identifying unit <NUM> of the image forming apparatus <NUM> may be performed by the PC <NUM>.

<FIG> is a flowchart of an overall operation of the image forming system according to the present embodiment. A description is given of the overall operation executed by the image forming system <NUM> according to the present embodiment with reference to <FIG>.

The dividing unit <NUM> of the PC <NUM> divides the print data into divided print data to be allocated to the nozzle array of the liquid discharge head 16U of the carriage 15U and the nozzle array of the liquid discharge head 16D of the carriage 15D. At this time, the dividing unit <NUM> divides the print data into divided print data each having margins at both ends in the direction corresponding to the sub-scanning direction so that the image forming apparatus <NUM> can identify, from the divided print data, the shifted data portions shifted by the number of pixels corresponding to the amounts of deviation in installation positions of the carriage 15U and the carriage 15D in the sub-scanning direction, respectively. The shifted data portions thus identified are used for ink discharge. In other words, the dividing unit <NUM> divides the print data into the divided data portions (serving as the divided print data) each having the size extended from the size corresponding to the length of the nozzle array of the liquid discharge head 16D and the liquid discharge head 16U. The extended data size is extended by the set number of pixels at each end in the direction corresponding to the sub-scanning direction. Then, the process proceeds to step S12.

The print data transmission unit <NUM> of the PC <NUM> transmits the divided print data divided by the dividing unit <NUM> to the image forming apparatus <NUM> via the communication unit <NUM>. Then, the process proceeds to step S13.

The print data acquisition unit <NUM> of the image forming apparatus <NUM> acquires the divided print data from the PC <NUM> via the communication unit <NUM>. Then, the process proceeds to step S14.

The identifying unit <NUM> of the image forming apparatus <NUM> reads, from the storage unit <NUM>, the information indicating the deviation in installation positions of the carriage 15U and the carriage 15D in the sub-scanning direction. The identifying unit <NUM> then identifies, in each divided print data acquired by the print data acquisition unit <NUM>, the shifted data portions shifted by the number of pixels corresponding to the amount of deviation indicated by the information, as the data portions to be subjected to printing, used for discharging ink by the liquid discharge head 16U and the liquid discharge head 16D, respectively. With this operation, the data portion used for ink discharge by the liquid discharge head 16U of the carriage 15U and the data portion used for ink discharge by the liquid discharge head 16D of the carriage 15D are obtained. Then, the process proceeds to step S15.

The discharge control unit <NUM> of the image forming apparatus <NUM> controls the liquid discharge head 16U to discharge ink using the data portion corresponding to the liquid discharge head 16U, identified by the identifying unit <NUM>, and controls the liquid discharge head 16D to discharge ink using the data portion corresponding to the liquid discharge head 16D, identified by the identifying unit <NUM>. Thus, printing on the recording medium P is executed. At this time, the movement control unit <NUM> of the image forming apparatus <NUM> controls the carriage 15U and the carriage 15D to move in the main scanning direction in accordance with the control of the ink discharge from the liquid discharge head 16U and the liquid discharge head 16D by the discharge control unit <NUM>.

After the division of the print data in step S11, steps S12 to S15 are repeated until the printing of the entire print data is completed.

As described above, the image forming apparatus <NUM> according to the present embodiment is a serial image forming apparatus that includes a plurality of carriages each carrying one or more liquid discharge heads. The print data acquisition unit <NUM> acquires divided print data divided from the print data. Each divided print data is extended in the direction corresponding to the conveyance direction of the recording medium P from a data portion of the print data corresponding to the length of the nozzle array (arranged in the conveyance direction of the recording medium P) of the liquid discharge head 16D (or 16U). The identifying unit <NUM> identifies, from the divided print data acquired by the print data acquisition unit <NUM>, the shifted data portion shifted by the number of pixels corresponding to the amount of deviation in installation position of the carriage 15D (or 15U) in the conveyance direction, from the target installation position, as the data portion to be used for ink discharge by the liquid discharge head 16D (or 16U). The shifted data portion has the length corresponding to the length of the nozzle array. The discharge control unit <NUM> controls the liquid discharge head 16D (or 16U) to discharge ink to the recording medium P using the data portion identified by the identifying unit <NUM>. The movement control unit <NUM> controls the carriage 15D (or 15U) to move in the main scanning direction based on the data portion identified by the identifying unit <NUM>. More specifically, the divided print data acquired by the print data acquisition unit <NUM> is divided from the print data such that each divided print data is extended at each end in the direction corresponding to the conveyance direction of the recording medium P by the set number of pixels from the data portion of the print data corresponding to the length of the nozzle array. As a result, deviations in landing positions of ink caused by variations in installation positions of the carriages (for example, the carriages 15U and 15D) arranged in the sub-scanning direction (conveyance direction) can be eliminated.

Note that, in a case where at least a portion of the functional units of the image forming apparatus <NUM> and the PC <NUM> according to the above-described embodiments is implemented by execution of a computer program, the computer program is prestored in, for example, a ROM. Alternatively, computer programs executed by the image forming apparatus <NUM> and the PC <NUM> according to the above-described embodiments may be provided as a file in a format installable to or executable by a computer and stored in a computer-readable recording medium, such as a compact disc read only memory (CD-ROM), a flexible disk (FD), a compact disc recordable (CD-R), or a digital versatile disk (DVD). Alternatively, the computer programs executed by the image forming apparatus <NUM> and the PC <NUM> according to the above-described embodiments may be stored in a computer connected to a network, such as the Internet, and may be downloaded through the network. Alternatively, the computer programs executed by the image forming apparatus <NUM> and the PC <NUM> according to the above-described embodiments may be provided or distributed via a network such as the Internet. The computer programs to be executed by the image forming apparatus <NUM> and the PC <NUM> according to the above-described embodiments have module structure including at least one of the above-described functional units. Regarding the actual hardware related to the computer programs, the CPU reads and executes the computer programs from the above-mentioned storage device to load the computer programs onto the main memory to implement the above-described functional units.

Claim 1:
A serial image forming apparatus comprising:
a plurality of carriages (15D; 15U) each of which carries a liquid discharge head (16D; 16U);
an acquisition unit (<NUM>) configured to acquire divided print data divided from print data, the divided print data having an extended size extended in a direction corresponding to a conveyance direction of a recording medium from a size corresponding to a length of a nozzle array of the liquid discharge head (16D; 16U) in the conveyance direction,
characterised in that the image forming apparatus further comprises:
an identifying unit (<NUM>) configured to identify, for the liquid discharge head (16D; 16U) of a particular carriage (15D) of the plurality of carriages (15D; 15U), a shifted data portion from the divided print data acquired by the acquisition unit (<NUM>), the shifted data portion having a size corresponding to the length of the nozzle array and being shifted by a number of pixels corresponding to an amount of deviation from a target installation position of the particular carriage (15D) in the conveyance direction;
a discharge control unit (<NUM>) configured to control the liquid discharge head (16D; 16U) to discharge ink to the recording medium using the shifted data portion identified by the identifying unit (<NUM>); and
a movement control unit (<NUM>) configured to control the particular carriage (15D) to move in a main scanning direction based on the shifted data portion identified by the identifying unit (<NUM>), the main scanning direction being perpendicular to the conveyance direction.