JP2013103464A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the amount of ink consumed in maintenance.SOLUTION: An image forming apparatus includes: a plurality of heads for ejecting liquid; maintenance units corresponding to the plurality of heads, respectively, and for carrying out maintenance of the heads while consuming liquid; and a control unit for controlling the maintenance units to carry out maintenance to only heads as maintenance objects whose printable areas exist within a predetermined range, out of the plurality of heads.

Description

  The present invention relates to an image forming apparatus.

  As an image forming apparatus, an ink jet printer that prints an image on a medium (for example, paper) by ejecting ink (a kind of liquid) from a nozzle of a head is known. In such a printer, when clogging occurs in some of the plurality of nozzles in the head, missing dots are generated in the formed image, causing deterioration in image quality. Therefore, there is known a head maintenance (for example, cleaning) so that each nozzle is not clogged (for example, see Patent Document 1). By regularly performing such maintenance, it is possible to prevent nozzle clogging.

JP 2002-225255 A

  During maintenance, ink is sucked and discharged. These inks are discharged from the head as maintenance ink. That is, ink is consumed for maintenance. In particular, when a plurality of heads are provided in the printer, there is a problem in that the amount of ink consumed for maintenance increases when periodic maintenance is performed on all the heads.

  An object of the present invention is to reduce the amount of liquid consumed for maintenance.

  A main invention for achieving the above object is a plurality of heads that discharge liquid, a maintenance unit corresponding to each of the plurality of heads, a maintenance unit that performs maintenance that consumes the liquid, and the plurality of heads An image forming apparatus comprising: a control unit that causes the maintenance unit to perform the maintenance periodically only for a maintenance target head that has a printable range within a predetermined range among the heads. It is.

  Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

1 is a schematic sectional view of a printer 1. 2 is a block diagram of the printer 1. FIG. It is the schematic which shows the structure of a head. It is the figure which expanded and showed the head 31A of FIG. 4 is a cross-sectional view for explaining an internal structure of a head 31. FIG. It is the schematic diagram which showed the raster line formed in each pass in the case of printing by 4 passes. It is a schematic diagram for demonstrating the movement of a head. FIG. 8 is an explanatory diagram of processing by a printer driver. FIG. 6 is an explanatory diagram showing a configuration of a nozzle inspection unit 90. FIG. 6 is a diagram showing an example of arrangement of a cleaning unit 70. FIG. 3 is a conceptual diagram showing a configuration of a cleaning unit 70. It is explanatory drawing about a use head and an unused head. It is a flowchart which shows the flow of a maintenance process.

  At least the following matters will become clear from the description of the present specification and the accompanying drawings.

A plurality of heads for discharging liquid, a maintenance unit corresponding to each of the plurality of heads, a maintenance unit for performing maintenance that consumes the liquid, and a printable range by the heads among the plurality of heads is predetermined. An image forming apparatus including the control unit that causes the maintenance unit to perform the maintenance periodically only for the maintenance target heads within the range becomes clear.
According to such an image forming apparatus, since a head that is not used for printing is not regularly maintained, the amount of liquid consumed for the maintenance can be reduced.

In this image forming apparatus, the plurality of heads may be arranged in a crossing direction that intersects a medium transport direction, and the predetermined range may be a width of the medium in the crossing direction.
According to such an image forming apparatus, the maintenance target head can be easily determined.

In this image forming apparatus, the plurality of heads are arranged in a crossing direction that intersects with the conveyance direction of the medium, and the predetermined range may be a maximum value of the length in the crossing direction in a print job. Good.
According to such an image forming apparatus, the amount of liquid consumed for maintenance can be further reduced.

  In this image forming apparatus, the control unit determines the maintenance target head from the plurality of heads when the medium is set, and the maintenance target head every time a predetermined period elapses after printing is started. However, the maintenance unit may perform the maintenance.

  In this image forming apparatus, the control unit determines the maintenance target head from the plurality of heads at the start of printing, and applies the maintenance target head to the maintenance target head every time a predetermined period elapses from the start of printing. The maintenance unit may perform the maintenance.

In this image forming apparatus, each head includes an inspection unit that performs nozzle inspection to determine whether or not there is a defective nozzle in each head, and the control unit performs the maintenance on the maintenance target head, and then performs the maintenance. The nozzle is inspected by the inspection unit for the head of the maintenance, and the maintenance target head performs the maintenance again when it is determined that there is a defective nozzle in the nozzle inspection, For unused heads other than the maintenance target head, it is desirable not to immediately perform the maintenance even when it is determined in the nozzle inspection that there is a defective nozzle.
According to such an image forming apparatus, when a defective nozzle is detected for the maintenance target head, the defective nozzle can be recovered by performing maintenance again. In addition, for unused heads, the amount of liquid consumption can be reduced by not performing maintenance immediately even if a defective nozzle is detected. Therefore, it is possible to optimally cope with the detection result of the defective nozzle.

In this image forming apparatus, the image forming apparatus further includes a holding unit that holds missing presence information indicating that it is determined that the unused head includes a defective nozzle in the nozzle inspection, and the control unit includes the holding unit. And the maintenance unit causes the unused head to perform the maintenance when the missing information is held and the time from when the missing information is held in the holding unit exceeds a threshold. desirable.
According to such an image forming apparatus, it is possible to prevent the defective nozzles of the unused heads from becoming unrecoverable.

In this image forming apparatus, it is preferable that the missing information is information prepared for each of the plurality of heads.
According to such an image forming apparatus, it is possible to reduce the amount of liquid consumed during maintenance of unused heads.

In such an image forming apparatus, the maintenance may be any one of cleaning, flushing, and wiping, or a combination thereof.
According to such an image forming apparatus, the amount of liquid consumed by maintenance can be reduced.

  In the following embodiments, a lateral ink jet printer (hereinafter also referred to as a printer 1) will be described as an example of the image forming apparatus.

=== First Embodiment ===
<Regarding the configuration example of the printer 1>
A configuration example of the printer 1 will be described with reference to FIGS. FIG. 1 is a schematic sectional view of the printer 1. FIG. 2 is a block diagram of the printer 1. FIG. 3 is a schematic diagram showing the configuration of the head. In the following description, when referring to “up and down direction” and “left and right direction”, the direction indicated by the arrow in FIG. 1 is used as a reference. In addition, the “front-rear direction” refers to a direction orthogonal to the paper surface in FIG. FIG. 3 is a view of the head viewed from above the carriage 42 through the carriage 42.
In the present embodiment, a description will be given using roll paper 2 (continuous paper) as a medium on which the printer 1 forms an image.

  As shown in FIGS. 1 and 2, the printer 1 according to this embodiment includes a conveyance unit 20, a feeding unit 10, a platen 29, and a conveyance path along which the conveyance unit 20 conveys the roll paper 2. And a winding unit 80. Furthermore, the printer 1 includes a head unit 30, a carriage unit 40, a cleaning unit 70, a nozzle inspection unit 90, a controller 60 that controls these units and the like to control the operation as the printer 1, a detector group 50, ,have.

  The feeding unit 10 feeds the roll paper 2 to the transport unit 20. The feeding unit 10 includes a winding shaft 18 around which the roll paper 2 is wound and rotatably supported, a relay roller 19 for winding the roll paper 2 fed from the winding shaft 18 and guiding the roll paper 2 to the transport unit 20; have.

  The transport unit 20 transports the roll paper 2 sent by the feeding unit 10 along a preset transport path. As shown in FIG. 1, the transport unit 20 includes a relay roller 21 that is positioned horizontally to the right of the relay roller 19, a relay roller 22 that is positioned obliquely downward to the right when viewed from the relay roller 21, and the relay roller 22. The first transport roller 23 located on the upper right side when viewed from the upstream side (upstream side when viewed from the platen 29 in the direction in which the roll paper 2 is transported), and the right side (the roll paper 2 is viewed from the first transport roller 23). In the direction of conveyance, the second conveyance roller 24 located on the downstream side as viewed from the platen 29, the reverse roller 25 positioned vertically downward as viewed from the second conveyance roller 24, and the right side as viewed from the reverse roller 25. And a delivery roller 27 located above the relay roller 26 as viewed from the relay roller 26.

The relay roller 21 is a roller that winds the roll paper 2 sent from the relay roller 19 from the left side and loosens it downward.
The relay roller 22 is a roller that winds the roll paper 2 sent from the relay roller 21 from the left side and conveys it obliquely upward to the right.

  The first transport roller 23 includes a first drive roller 23a driven by a motor (not shown), and a first driven roller 23b arranged to face the first drive roller 23a with the roll paper 2 interposed therebetween. have. The first transport roller 23 is a roller that pulls up the roll paper 2 slacked downward and transports it to the printing region R facing the platen 29. The first transport roller 23 is configured to temporarily stop transport during a period in which image formation is performed on a portion of the roll paper 2 on the print region R (that is, as described later, the head is By ejecting ink to the corresponding portion of the roll paper 2 that is stopped while moving in the left-right direction and the front-rear direction, an image for one page is formed on the portion). In addition, when the first driven roller 23b rotates as the first drive roller 23a rotates by the drive control of the controller 60, the transport amount of the roll paper 2 positioned on the platen 29 (the length of the portion of the roll paper) Is adjusted).

  As described above, the transport unit 20 has a mechanism for transporting the portion of the roll paper 2 wound between the relay rollers 21 and 22 and the first transport roller 23 by slacking it downward. The slackness of the roll paper 2 is monitored by the controller 60 based on a detection signal from a slack detection sensor (not shown). Specifically, when a portion of the roll paper 2 slackened between the relay rollers 21 and 22 and the first transport roller 23 is detected by the slack detection sensor, a tension of an appropriate magnitude is applied to the portion. Therefore, the transport unit 20 can transport the roll paper 2 in a relaxed state. On the other hand, when the portion of the roll paper 2 that has been loosened is not detected by the slack detection sensor, an excessive amount of tension is applied to the portion, and therefore the transport of the roll paper 2 by the transport unit 20 is temporarily performed. And the tension is adjusted to an appropriate level.

  The second transport roller 24 includes a second drive roller 24a driven by a motor (not shown), and a second driven roller 24b disposed so as to face the second drive roller 24a with the roll paper 2 interposed therebetween. have. The second transport roller 24 is a roller that transports the portion of the roll paper 2 on which the image has been formed by the head unit 30 in the horizontal right direction along the support surface of the platen 29 and then transports it vertically downward. Thereby, the conveyance direction of the roll paper 2 is changed. The second driven roller 24b rotates as the second drive roller 24a is driven to rotate by the drive control of the controller 60, whereby a predetermined amount given to the portion of the roll paper 2 located on the platen 29 is obtained. Tension is adjusted.

The reversing roller 25 is a roller that wraps the roll paper 2 sent from the second conveying roller 24 from the upper left side and conveys it diagonally upward to the right.
The relay roller 26 is a roller that winds the roll paper 2 sent from the reversing roller 25 from the lower left side and conveys it upward.
The feed roller 27 is configured to wind the roll paper 2 sent from the relay roller 26 from the lower left side and send it to the take-up unit 80.

  The platen 29 supports the part of the roll paper 2 located in the printing region R on the conveyance path and heats the part. As shown in FIG. 1, the platen 29 is provided in correspondence with the printing region R on the conveyance path, and in a region along the conveyance path between the first conveyance roller 23 and the second conveyance roller 24. Has been placed.

  As described above, the roll paper 2 moves sequentially through the rollers, whereby a transport path for transporting the roll paper 2 is formed. Note that the roll paper 2 is intermittently conveyed along the conveyance path in units of areas corresponding to the print area R by the conveyance unit 20 (that is, one page worth of the roll paper 2 on the print area R). Every time an image is formed is intermittently conveyed).

The head unit 30 is for ejecting ink as an example of a liquid onto a portion of the roll paper 2 that has been fed into the printing region R on the transport path (on the platen 29) by the transport unit 20. The head unit 30 has eight heads 31 having the same configuration. These eight heads 31 are arranged in a staggered manner in the carriage 42 as shown in FIG. In the following description, the eight heads 31 are 31A to 31H in order from the rear side in the column direction.
Details of the configuration of the head 31 will be described later.

  The carriage unit 40 is for moving each head (heads 31 </ b> A to 31 </ b> H) of the head unit 30. The carriage unit 40 is supported by a carriage guide rail 41 (indicated by a two-dot chain line in FIG. 1) extending in the transport direction (left-right direction) and reciprocally movable along the carriage guide rail 41 in the transport direction (left-right direction). A carriage 42 and a motor (not shown).

  The carriage 42 is configured to move in the transport direction (left-right direction) integrally with each head by driving a motor (not shown). The carriage 42 is provided with a head guide rail (not shown) extending in the row direction (front-rear direction). Each head is driven in the row direction (front-rear direction) along the head guide rail by driving the motor. Configured to move to.

The cleaning unit 70 (corresponding to a maintenance unit) is for cleaning each head of the head unit 30 (a kind of maintenance). The cleaning unit 70 is provided at a home position (hereinafter referred to as HP; see FIG. 1), and performs cleaning by sucking ink from the nozzles of the head.
Details of the cleaning unit 70 will be described later.

  The winding unit 80 is for winding the roll paper 2 (image-formed roll paper) sent by the transport unit 20. This take-up unit 80 is fed from the relay roller 81 that is rotatably supported and a relay roller 81 for winding the roll paper 2 sent from the feed roller 27 from the upper left side and conveying it obliquely downward to the right. And a take-up drive shaft 82 for taking up the roll paper 2.

The nozzle inspection unit 90 (corresponding to an inspection unit) is for automatically detecting whether or not ink is ejected from the nozzles of each head of the head unit 30 (the presence or absence of a nozzle with defective ejection).
Details of the nozzle inspection unit 90 will be described later.

  The controller 60 (corresponding to a control unit) is a control unit for controlling the printer 1. As shown in FIG. 2, the controller 60 includes an interface unit 61, a CPU 62, a memory 63, a unit control circuit 64, and a timer 65. The interface unit 61 is for transmitting and receiving data between the host computer 110 as an external device and the printer 1. Note that data received by the printer 1 from the host computer 110 includes print data, command data, and the like.

  The CPU 62 is an arithmetic processing unit for controlling the entire printer 1. The memory 63 is for securing an area for storing a program of the CPU 62, a work area, and the like. The CPU 62 controls each unit by a unit control circuit 64 according to a program stored in the memory 63.

  The memory 63 has a register (not shown) and the like, and holds information (nozzle missing flag to be described later) indicating an inspection result by the nozzle inspection unit 90. That is, the memory 63 corresponds to a holding unit.

  The timer 65 measures time (elapsed time) by, for example, counting the number of pulses of the internal clock having a fixed period. In the present embodiment, the time after the ejection failure nozzle is detected in the nozzle inspection is measured. Note that the count value of the timer 65 returns to an initial value (for example, zero) by reset.

  The detector group 50 is for monitoring the situation in the printer 1. For example, the detector group 50 is attached to a transport roller and used for control such as transport of the roll paper 2. And a linear encoder for detecting the position of the carriage 42 (or head 31) in the transport direction (left-right direction). In this embodiment, a paper width detection sensor (not shown) that detects the length of the roll paper 2 in the row direction (that is, the paper width) is provided in the carriage 42, for example, and the roll paper 2 is provided in the transport path of the printer 1. Is set, the paper width in the row direction of the roll paper 2 can be detected.

<About the configuration of the head>
As described above, the head unit 30 of the printer 1 has eight heads 31 (31A to 31H). These heads have the same configuration. Therefore, the configuration of the head will be described using one of the heads (here, the head 31A).

FIG. 4 is an enlarged view of the head 31A of FIG.
As shown in FIG. 4, n (for example, 180) nozzles are provided on the lower surface of the head 31A for each of the four colors of ink (for each color). That is, the head 31A has 180 nozzles for discharging cyan ink, nozzles for discharging magenta ink, nozzles for discharging yellow ink, and nozzles for discharging black ink (180 × 4 in total). = 1720)). The 180 nozzles are arranged in a row along the row direction (front-rear direction), forming a cyan nozzle row C, a magenta nozzle row M, a yellow nozzle row Y, and a black nozzle row K. .

  FIG. 5 is a cross-sectional view for explaining an example of the internal structure of the head 31. In the drawing, a cross section of a portion corresponding to two nozzles adjacent in the transport direction is shown. The head 31 includes a drive unit 32, a case 33 for housing the drive unit 32, and a flow path unit 34 attached to the case 33.

  The drive unit 32 includes a piezo element group composed of a plurality of piezo elements 321, a fixed plate 323 to which the piezo element group is fixed, and a flexible cable 324 for supplying power to each piezo element 321. Each piezo element 321 is attached to the fixed plate 323 in a so-called cantilever state. The fixed plate 323 is a plate-like member having rigidity capable of receiving a reaction force from the piezo element 321. The flexible cable 324 is a flexible sheet-like wiring board, and is electrically connected to the piezo element 321 on the side surface of the fixed end opposite to the fixed plate 323. On the surface of the flexible cable 324, a head controller HC, which is a control IC for controlling driving of the piezo element 321 and the like, is mounted.

  The case 33 has a rectangular parallelepiped block-like outer shape having a storage empty portion 331 in which the drive unit 32 can be stored. The flow path unit 34 is joined to the front end surface of the case 33. The housing empty portion 331 has a size that allows the drive unit 32 to be fitted exactly. The case 33 is also formed with an ink supply pipe 332 for supplying ink from a corresponding ink cartridge (not shown) to the flow path unit 34.

  The flow path unit 34 includes a flow path forming substrate 35, a nozzle plate 36, and an elastic plate 37. The flow path forming substrate 35 is laminated and integrated so that the flow path forming substrate 35 is sandwiched between the nozzle plate 36 and the elastic plate 37. Constructed. The nozzle plate 36 is a thin plate made of stainless steel on which nozzles (Nz) are formed.

  In the flow path forming substrate 35, a plurality of empty portions to be the pressure chambers 351 and the ink supply ports 352 are formed corresponding to the respective nozzles Nz. The reservoir 353 is a liquid storage chamber for supplying the ink stored in the ink cartridge to each pressure chamber 351 and communicates with the other end of the corresponding pressure chamber 351 through the ink supply port 352. The ink supplied from the ink cartridge is introduced into the reservoir 353 through the ink supply pipe 332.

  The drive unit 32 is inserted into the housing empty portion 331 with the free end portion of the piezo element 321 facing the flow path unit 34, and the distal end surface of the free end portion is bonded to the corresponding island portion 373. Further, the back surface of the fixed plate 323 is bonded to the inner wall surface of the case 33 that partitions the housing empty portion 331. When a drive signal is supplied to the piezo element 321 via the flexible cable 324 in this stored state, the piezo element 321 expands and contracts to expand and contract the volume of the pressure chamber 351. Due to such a change in the volume of the pressure chamber 351, pressure fluctuation occurs in the ink in the pressure chamber 351. Then, ink droplets can be ejected from the corresponding nozzles Nz by utilizing the variation in the ink pressure.

<Operation example of printer 1>
As described above, the printer 1 according to the present embodiment is provided with eight heads 31 (31A to 31H) having nozzle rows in which nozzles are arranged in the row direction (front-rear direction). Then, the controller 60 ejects ink from the nozzles while moving each of these heads in the transport direction (left-right direction), and forms a raster line along the transport direction (left-right direction). The image of one page is formed on the portion of the roll paper 2.

  Here, the controller 60 according to the present embodiment executes printing of a plurality of passes (two passes, four passes, etc.). That is, in order to increase the resolution of the image in the column direction, printing is performed by slightly changing the position of each head in the column direction for each pass. As an image forming method, for example, known interlace (microweave) printing is executed.

  This will be described more specifically with reference to FIG. FIG. 6 is a schematic diagram showing raster lines formed in each pass in a case of printing in 4 passes.

  A nozzle row (nozzles) of the head 31 (for example, the head 31A) is shown on the left side of FIG. 6, and ink is ejected from the nozzles while the head 31 (nozzle row) moves in the transport direction, thereby causing a raster. A line is formed. The position in the row direction of the head 31 (nozzle row) shown in the figure is the position in the first pass, and if the head 31 (nozzle row) moves in the transport direction while maintaining this position, one pass The printing of the eyes is executed, and the three raster lines shown in the figure (raster line L1 written as pass 1 at the right end) are formed.

  Next, when the head 31 (nozzle row) moves in the row direction, and the head 31 (nozzle row) moves in the transport direction while maintaining the moved position, the second pass printing is executed, and FIG. 2 are formed (raster line L2 written as pass 2 at the right end). Since interlace (microweave) printing is employed, the raster line L2 adjacent to the raster line L1 is formed by ink ejected from a nozzle different from the nozzle from which the ink forming the raster line L1 is ejected. Will be. Therefore, the moving distance of the head 31 (nozzle row) in the row direction is not a quarter of the distance between nozzles (eg, 1/180 inch) (1/180 × 1/4 = 1/720 inch), The distance is larger than this (hereinafter, this distance is referred to as distance d).

  Thereafter, by performing the same operation, the third pass and the fourth pass are printed, and the remaining raster lines shown in the figure (raster line L3 written as pass 3 and pass 4 on the right end) are displayed. , L4). Thus, by forming raster lines in four passes, the resolution of the image in the column direction can be made four times (= 720 ÷ 180).

  In the present embodiment, so-called bidirectional printing is performed. That is, the movement direction of the head 31 (nozzle row) when the first pass and the third pass printing are performed is different from the movement direction of the head 31 (nozzle row) when the second pass, the fourth pass and the second print are performed. The reverse direction (detailed later).

  In the following, an image forming operation (in other words, an ink ejection operation) of the printer 1 will be described as an operation example of the printer 1, but the case of FIG. In the description, FIG. 6 is also referred to as needed).

<Example of Image Forming Operation of Printer 1>
Here, a printing operation example of the printer 1 will be described with reference to FIGS. 6 and 7. FIG. 7 is a schematic diagram for explaining the movement of the head. Before explaining the printing operation, first, FIG. 7 will be described.

  FIG. 7 shows how the head moves during the printing process (that is, a series of processes related to image formation). The head unit 30 of the printer 1 has eight heads 31 (heads 31A to 31H). Since these eight heads 31 are all provided on the carriage 42, they move in the same direction relative to the roll paper 2. Here, in order to make the description easy to understand, the description is made on the assumption that the number of heads 31 (and nozzle rows) is one instead of a plurality.

For convenience, the head is represented by a circle (there is a large circle and a small circle in the figure, but there is no meaning in distinguishing both), and the movement of the head is represented by an arrow. Here, the arrow pointing in the left-right direction in the figure indicates the movement of the head in the transport direction, and the arrow pointing in the vertical direction indicates the movement of the head in the row direction. In addition, each arrow is provided with a reference numeral S1 to S10, which is a step number used in the description of the subsequent printing process.
Further, there are step numbers to which pass 1 to pass 4 are attached, and these step numbers represent steps in which an image forming operation is executed by ejecting ink.

  Hereinafter, the printing process will be described with reference to FIGS. The printing process is realized mainly by the controller 60. In particular, in the present embodiment, it is realized by the CPU 62 processing a program stored in the memory 63. And this program is comprised from the code | cord | chord for performing the various operation | movement demonstrated below.

  When the above-described intermittent roll paper 2 is transported and the roll paper 2 is stopped, a printing process for forming an image for one page on the portion of the roll paper 2 on the printing region R is started.

  First, the controller 60 moves the carriage 42 (that is, each head) in the forward direction from the HP position (the direction from the upstream side to the downstream side in the direction in which the roll paper 2 is conveyed) (step S1). Note that the position where the carriage 42 arrives by the movement of step S1 (the position before starting step 2 described later) is also referred to as the origin position.

  The controller 60 performs the first pass printing by causing the head to eject ink while continuing the movement of the head 31 in the forward direction (step S2). As a result, the raster line L1 (raster line of pass 1) shown in FIG. 6 is formed.

  When the head reaches the first folding position, the controller 60 moves the head in the column direction (step S3). In the present embodiment, the head is moved by the distance d.

  Thereafter, the controller 60 performs the second pass printing by causing the head to eject ink while moving the head in the backward direction (the direction from the downstream side to the upstream side in the direction in which the roll paper 2 is conveyed). (Step S4). As a result, the raster line L2 (pass 2 raster line) shown in FIG. 6 is formed.

  When the head reaches the second folding position, the controller 60 moves the head in the column direction (step S5). In the present embodiment, the head is moved by the distance d.

  Next, the controller 60 further performs the same processing as the processing from step S2 to step S4 (step S6 to step S8). In this process, the raster line L3 (raster line of pass 3) shown in FIG. 6 by the third pass printing (step S6) is changed to the raster line shown in FIG. 6 by the fourth pass printing (step S8). L4 (raster line of pass 4) is formed respectively. The controller 60 returns the position of the head in the row direction (step S9). That is, the head is moved by a distance 3d in the direction opposite to the direction in which the head has moved in steps S3, S5, and S7.

  Then, the controller 60 moves the head to the HP position (step S10), and ends the printing process for forming an image for one page. In this embodiment, image formation for one page is performed in four passes. However, the present invention is not limited to this. For example, image formation for one page may be performed in two passes.

<Outline of processing by printer driver>
As described above, the printing process starts when print data is transmitted from the host computer 110 connected to the printer 1. The print data is created by processing by the printer driver. Hereinafter, processing by the printer driver will be described with reference to FIG. FIG. 8 is an explanatory diagram of processing by the printer driver.

  The printer driver receives image data from the application program, converts it into print data in a format that can be interpreted by the printer 1, and outputs the print data to the printer. When converting image data from an application program into print data, the printer driver performs resolution conversion processing, color conversion processing, halftone processing, rasterization processing, command addition processing, and the like.

  The resolution conversion process is a process for converting image data (text data, image data, etc.) output from an application program into a resolution (print resolution) for printing on paper. For example, when the print resolution is specified as 720 × 720 dpi, the vector format image data received from the application program is converted into bitmap format image data with a resolution of 720 × 720 dpi. Note that each pixel data of the image data after the resolution conversion process is multi-gradation (for example, 256 gradations) RGB data represented by an RGB color space. This gradation value is determined based on RGB image data.

  The color conversion process is a process for converting RGB data into CMYK color space data. The CMYK color space is a color space corresponding to the ink (color) used in the printer 1. In other words, the printer driver creates CMYK system plane image data based on the RGB data. For example, when the ink to be used is four colors of CMYK, image data of the CMYK plane is created.

  This color conversion processing is performed based on a table in which gradation values of RGB data are associated with gradation values of CMYK data corresponding to the ink to be used. This table is called a color conversion lookup table (LUT). Note that the pixel data after the color conversion processing is data of 256 gradations expressed by a CMYK color space.

  The halftone process is a process for converting high gradation number data into gradation number data that can be formed by a printer. By this halftone processing, data indicating 256 gradations is converted into 1-bit data indicating 2 gradations or 2-bit data indicating 4 gradations. In the image data after halftone processing, 1-bit or 2-bit pixel data corresponds to each pixel, and this pixel data indicates the dot formation status (the presence / absence of dots, the size of dots) in each pixel. Become data. For example, in the case of 2 bits (4 gradations), no dot corresponding to the dot gradation value [00], formation of a small dot corresponding to the dot gradation value [01], and medium corresponding to the dot gradation value [10] It is converted into four stages like dot formation and large dot formation corresponding to the dot gradation value [11]. After that, after the dot creation rate is determined for each dot size, pixel data is created so that the printer 1 forms the dots in a dispersed manner using a dither method, γ correction, error diffusion method, or the like. .

  The rasterizing process rearranges the pixel data arranged in a matrix for each pixel data in the order of data to be transferred to the printer 1. For example, the pixel data is rearranged according to the arrangement order of the nozzles of each head.

The command addition process is a process for adding data indicating a command corresponding to the printing method to the rasterized data. Examples of commands include a conveyance command, a suction command, and a carriage movement command.
The print data created through these processes is transmitted to the printer 1 by the printer driver.

<About the nozzle inspection unit>
FIG. 9 is an explanatory diagram showing an example of the configuration of the nozzle inspection unit 90. The nozzle inspection unit 90 includes a detection electrode 91, a high voltage power supply unit 92, a first limiting resistor 93, a second limiting resistor 94, a detecting capacitor 95, an amplifier 96, a detection control unit 97, and a smoothing capacitor. 98 and a voltage detection unit 99. The nozzle plate 36 of the head 31 is connected to the ground and has a ground potential, and functions as a part of the nozzle inspection unit 90.

  The detection electrode 91 is formed of a metal wire in a spider web shape. When this detection electrode 91 is set to a high potential, it becomes a high potential not only in the area of the metal wire in the form of a spider web but also in a wide range.

  The high-voltage power supply unit 92 is a power supply that brings the detection electrode 91 to a predetermined potential. The high-voltage power supply unit of the present embodiment is constituted by a DC power supply of about 600V to 1000V.

  The first limiting resistor 93 and the second limiting resistor 94 are disposed between the high-voltage power supply unit 92 and the detection electrode 91, and control a current flowing between the high-voltage power supply unit 92 and the detection electrode 91. The first limiting resistor 93 and the second limiting resistor 94 of the present embodiment have the same resistance value (for example, 1.6 MΩ).

  The detection capacitor 95 is an element for extracting a potential change component of the detection electrode 91. One end of the detection capacitor 95 is connected to the detection electrode 91, and the other end is connected to the amplifier 96. The bias component (DC component) of the detection electrode 91 is removed by the detection capacitor 95. The capacitance of the detection capacitor 95 is 4700 pF, for example.

  The amplifier 96 amplifies the signal on the other end side of the detection capacitor 95. The amplifier 96 of this embodiment has an amplification factor of 4000 times. Thereby, a detection signal whose potential changes at about 3 V can be obtained from the amplifier 96.

  The detection control unit 97 controls the nozzle inspection unit 90 and determines whether each nozzle is clogged based on the detection signal output from the amplifier 96.

  The smoothing capacitor 98 suppresses a rapid change in potential. One end of the smoothing capacitor 98 is connected to the first limiting resistor 94 and the second limiting resistor 95, and the other end is connected to the ground. The capacity of the smoothing capacitor 98 is, for example, 0.1 μF.

  The voltage detection unit 99 detects whether or not the detection electrode 91 is at a predetermined voltage. The voltage detection unit 99 includes a first resistor 99a and a second resistor 99b that form a voltage dividing circuit. The first resistor 99a and the second resistor 99b are connected in series, one end of the first resistor 99a is at the same potential as the detection electrode 91, and the second resistor 99b is connected to the ground. When the controller 60 detects the potential between the first resistor 99a and the second resistor 99b, it can be detected whether or not the detection electrode 91 is at a predetermined voltage. In the present embodiment, the first resistor 99a has a resistance value of 6 MΩ, and the second resistor 99b has a resistance value of 33 kΩ.

Next, the operation of nozzle inspection by the nozzle inspection unit 90 will be described.
When ink is ejected from the nozzle (Nz) formed on the nozzle plate 36, the potential of the detection electrode 91 changes. This potential change is detected by the detection capacitor 95 and the amplifier 96, and the detection signal is detected by the detection control unit. 97 is output. If the nozzle is clogged, ink is not ejected, so the potential of the detection electrode 91 does not change and no voltage change appears in the detection signal.
By detecting this difference in voltage change, it is possible to determine whether or not ink has been ejected from the nozzle.

  In this embodiment, the nozzle inspection is performed by detecting the voltage change of the detection electrode 91. However, the nozzle inspection method is not limited to this, and the nozzle inspection may be performed by other methods. . In the following description, the fact that there are nozzles that do not eject ink due to clogging or the like (nozzles with defective ejection) is also referred to as nozzle omission.

<About the cleaning unit>
The cleaning unit 70 of the printer 1 of the present embodiment performs cleaning (a type of maintenance) by sucking ink. As shown in FIG. 1, the cleaning unit 70 is provided at a position where the head faces when the carriage 42 is positioned at the home position (HP). The cleaning unit 70 performs a cleaning process (ink suction) for eliminating the ejection failure of the head unit 30.

  FIG. 10 is a diagram illustrating an arrangement example of the cleaning unit 70. The cleaning unit 70 of the present embodiment includes a pair of head caps 73 corresponding to two adjacent heads among the heads 31A to 31H arranged in a staggered manner. The pair of head caps 73 are provided on the lifting platform 72. That is, when the lifting platform 72 is moved up and down by a lifting mechanism (not shown), the pair of head caps 73 are also moved up and down accordingly. The left head cap 73 in the figure corresponds to the heads in the left column in the figure (head 31A, head 31C, head 31E, head 31G), and the right head cap 73 in the figure corresponds to the right side in the figure. This corresponds to the heads in the row (head 31B, head 31D, head 31F, head 31H). By moving the carriage 42 in the row direction and the transport direction and disposing the target head on the head cap 73, the two heads can be cleaned.

  FIG. 11 is a conceptual diagram showing an example of the configuration of the cleaning unit 70. FIG. 11 shows a portion corresponding to one head of the pair of head caps 73. As shown in FIG. 11, the cleaning unit 70 includes a head cap 73, a hose 74, and a suction pump 75.

  In the head cap 73, the internal space is partitioned into four suction chambers 73a. When the head cap 73 is raised, the head cap 73 comes into close contact with the lower surface of the head 31. At this time, each of the four suction chambers 73a has a closed space covering the corresponding nozzle row of the four nozzle rows. Form. That is, the head cap 73 is raised so as to seal the lower surface (nozzle surface) of the head 31.

  The suction pump 75 has two small rollers 75a in the vicinity of the peripheral edge thereof, and a hose 74 is wound around the two small rollers 75a. Then, when the suction pump 75 is driven by a motor (not shown) and rotates in the direction of the arrow, the air in the hose 74 is pushed by the small roller 75a, thereby exhausting in the closed space in the head cap 73. ing. When exhaust is performed in the closed space, the closed space becomes negative pressure, and ink is sucked from the nozzles of the head 31. The sucked ink is discharged through a hose 74 to a waste ink discharge unit (not shown). In this way, nozzle clogging is prevented or recovered from nozzle clogging.

  In the present embodiment, the number of head caps 73 of the cleaning unit 70 is two. However, the number of head caps 73 is not limited to this, and it is sufficient that each of the plurality of heads 31 can be cleaned. For example, the number of head caps 73 may be one. Alternatively, eight head caps 73 may be provided corresponding to all eight heads 31. In this case, the head cap 73 can exhibit the following functions without the suction pump 75 being operated. That is, when the printer 1 does not perform printing (and when the carriage 42 is located at the home position), the head cap 73 rises and comes into close contact with the lower surface of the head 31. This suppresses evaporation of ink from the nozzles (in other words, ink drying). That is, the head cap 73 can seal the lower surface (nozzle surface) of the head 31 during a printing pause so as to exhibit a function as a lid that suppresses ink evaporation.

  By regularly cleaning the head by the cleaning unit 70 described above, nozzle clogging can be prevented. Here, “regular” refers to, for example, every time a certain period of time has elapsed since printing was started, or every time a pass is performed a predetermined number of times (every time a predetermined page is printed). However, when a plurality of heads are provided as in the printer 1 of the present embodiment, if the regular cleaning is performed on all the heads, the amount of ink consumed by the cleaning increases. In the present embodiment, as described below, the amount of ink consumed for cleaning is reduced.

<About used head and unused head>
When a plurality of heads are provided as in the printer 1 of the present embodiment, all of the plurality of heads may not be used during printing.

  FIG. 12 is an explanatory diagram of the used head and the unused head. The figure shows the position (origin position) of the carriage 42 (each head) when the first pass (pass 1) is performed. That is, after this, the carriage 42 (each head) moves 3d to the downstream side and upstream side in the transport direction and forward in the front-rear direction by the pass, and printing for one page is performed (see FIG. 7). ).

  In FIG. 12, the symbol “a” indicates the maximum print width that can be printed by the eight heads 31 (that is, the printable range by the eight heads 31). The symbol b indicates the width (paper width) of the roll paper 2 to be printed. The roll paper 2 is set so that one end in the row direction is positioned at the rear end (reference position) in the row direction of the maximum print width a. Further, it is assumed that when the carriage 42 is at the origin position, the # 1 nozzle of the head 31A is located at the reference position in the drawing. The length of each nozzle row of the head 31 (length in the row direction) is L. Since the carriage 42 moves 3d to the front side in the column direction during printing of one page, for example, the printable range (the range in the column direction) of the four heads 31A to 31D (heads indicated by oblique lines) is the reference position. To 4L + 3d.

  In FIG. 12, the paper width b of the roll paper 2 set in the printer 1 is smaller than the maximum printing width a. In this case, printing is not performed in a range wider than the paper width b of the roll paper 2. As shown in the drawing, when the carriage 42 is located at the origin, the nozzle length 4L of the heads 31A to 31D is equal to the paper width b of the roll paper 2 (4L = b). That is, there are four heads 31 </ b> A to 31 </ b> D that can print within the range of the paper width b of the roll paper 2. That is, when printing on the roll paper 2 in the figure, the four heads 31E to H are not used, and only the four heads 31A to 31D are used. In the following description, the heads used for printing such as the heads 31A to 31D are referred to as used heads (corresponding to maintenance target heads), and the heads not used for printing such as the heads 31E to 31H are not yet used. Called the used head. In addition, when even one nozzle is used in printing (4 passes) of one page among a plurality of nozzles of the head, it is assumed that the head is a used head.

  If printing is continuously performed on the roll paper 2 and the above-described cleaning is periodically performed on all the heads, a large amount of ink is discharged for cleaning. That is, more ink is discarded without being used for printing. In addition, about the head (unused head) which is not used for printing, since the possibility of nozzle clogging is low, and even if clogged, it is not used for printing on the roll paper 2, it is formed on the roll paper 2. There is no deterioration in the image quality.

  Therefore, in this embodiment, the used head (maintenance target head) is periodically cleaned, and the unused head is not periodically cleaned. In this way, the amount of ink consumed by cleaning is reduced. However, if there are defective ejection nozzles in the unused head, leaving them as they are, there is a risk that the defects will not be recovered even if maintenance such as cleaning is performed. Therefore, after the used heads are cleaned, the nozzles of all the heads are inspected. When there are defective ejection nozzles in the unused heads, the unused heads are cleaned when the time after the failure is detected exceeds a threshold value. (It will be described later).

<About maintenance processing>
FIG. 13 is a flowchart showing the flow of maintenance processing in the present embodiment. The following description will be given with reference to FIG.

  First, when the roll paper 2 is set in the printer 1, the controller 60 detects the paper width b of the roll paper 2 by a paper width detection sensor (not shown), and the paper width b (length in the row direction) of the roll paper 2. Accordingly, the head to be used in the head unit 30 is selected (determined) (S101). For example, in the case of FIG. 12, as described above, the four heads 31A to 31D are used heads (maintenance target heads), and the four heads 31E to 31H are unused heads. Then, the printing process (image forming operation) as described above is started (S102). In the present embodiment, the paper width b of the roll paper 2 is detected by a paper width detection sensor (not shown), but the present invention is not limited to this. For example, a guide rail (not shown) that is movable in the row direction and guides the conveyance of the roll paper 2 may be provided, and the paper width b of the roll paper 2 may be detected at the position of the guide rail (position in the row direction). . Further, for example, in the user interface in the host computer 110, the paper width of the roll paper 2 may be set according to the type (size) of the roll paper 2 selected by the user.

  The controller 60 determines whether or not a predetermined period has elapsed since the start of printing (S103). If the predetermined period has not elapsed (NO in S103), step S103 is performed again. If it is determined that the predetermined period has elapsed (YES in S103), it is determined whether a nozzle omission flag is set and the count value of the timer 65 is greater than the threshold (S104). Initially, both the nozzle omission flag and the timer 65 are in the initial state (no nozzle omission flag is raised and the count value of the timer 65 is zero), so NO is determined in step S104, and only for the heads used (heads 31A to 31D). Thus, the cleaning unit 70 performs cleaning (S105). Then, after the cleaning of the heads in use, the nozzle inspection unit 90 performs nozzle inspection (nozzle check) on all eight heads 31 (heads 31A to 31H) of the head unit 30 (S106). If nozzle missing (no defective ejection) is found in all the heads in the nozzle inspection (NO in S107), the process returns to step S102 to start (restart) printing. On the other hand, when it is determined in the nozzle inspection that there is a missing nozzle, it is determined whether or not the head with the missing nozzle is a used head (heads 31A to 31D) (S108). If the head with nozzle omission is a used head (YES in S108), it is determined whether the number of times of cleaning is smaller than a predetermined number n (n is an integer of 2 or more, for example, 3). At first, since the number of times of cleaning is one, it is determined YES (YES in S109), the process returns to step S105, and the used head is cleaned again.

  If it is determined in step S108 that the head with nozzle missing is a head other than the used head (that is, an unused head) (NO in S108), for example, a register missing in the memory 63 indicates a nozzle missing flag (with missing). (Corresponding to information) is set up (S110). Then, the timer 65 starts counting (S111), and the process returns to step S102. That is, if there is a missing nozzle in an unused nozzle, the printing process is performed immediately without performing the cleaning immediately. Thereafter, when a predetermined period has elapsed (YES in S103), the determination in step S104 is performed. Here again, if the nozzle omission flag is set and the count value of the timer 65 is not larger than the threshold value, step S105 for cleaning only the used head is performed. On the other hand, if it is determined in step S104 that the nozzle missing flag is set and the count value of the timer 65 is greater than the threshold value (YES in S104), the controller 60 cleans the cleaning unit 70 for all heads. (S112). Thereafter, the nozzle inspection unit 90 performs nozzle inspection for all the heads (S113), and determines whether or not each head has a missing nozzle (nozzle inspection) (S114).

  As a result of the nozzle inspection, if it is determined that there is no nozzle missing in all the heads (NO in S114), the controller 60 initializes the nozzle missing flag and the count value of the timer 65 (S115), and returns to step S102. If it is determined that there is a missing nozzle (YES in S114), it is determined whether the head with the missing nozzle is a working head (S116). If the head is used (YES in S116), the nozzle omission flag and the count value of the timer 65 are initialized (S117), and the process returns to step S105 to clean the used head.

  Further, if the head with nozzle missing is an unused head in step S116 (NO in S116), and if it is determined in step S109 that the number of times of cleaning is n times (for example, 3 times) or more (in S109). NO), for example, an error is displayed on the display unit or the like of the host computer 110 (S118).

  Thus, in this embodiment, periodic cleaning is performed only for the heads (head 31A to head 31D) used for printing on the roll paper 2, and for the heads (head 31E to head 31H) not used for printing, Regular cleaning is not performed. By doing so, the amount of ink consumed for cleaning can be reduced without affecting the image quality of the printed image on the roll paper 2.

  In the present embodiment, after the used heads are cleaned, the nozzle inspection of all the heads is performed. If there is a missing nozzle in the used head, cleaning is performed again to recover the missing nozzle. On the other hand, if there is a missing nozzle in the unused head, there is no effect on printing, so the nozzle missing flag is set immediately without cleaning and the timer 65 starts counting to continue printing. Yes. In this way, it is possible to take an optimum response to the case where nozzle missing is detected. However, if there is a missing nozzle in the unused head, if it is left as it is, the missing nozzle may not be recovered by cleaning or the like. Therefore, if the count value of the timer 65 exceeds the threshold value, the unused head is cleaned. Like to do. As a result, it is possible to prevent the head with missing nozzles from becoming unrecoverable.

  In the present embodiment, the head to be used is selected according to the paper width of the roll paper 2. Since the paper width of the roll paper 2 can be easily detected by a sensor or the like, the head to be used can be easily determined from a plurality of heads.

  In the present embodiment, if the nozzle inspection in step S106 results in a nozzle missing in the unused head, a nozzle missing flag is set for the unused head (four heads in the present embodiment) in step S110. However, a nozzle omission flag may be prepared for each head. If nozzle missing is detected in a certain head among the unused heads, a nozzle missing flag is set only for the certain head, and the used head and the certain head are cleaned in step S112. May be performed. In this way, the number of heads that are cleaned in step S112 can be reduced, and the amount of ink consumed in maintenance can be further reduced.

=== Second Embodiment ===
In the second embodiment, the method of selecting the head to be used is different from that in the first embodiment. Note that the configuration of the printer and the printing operation are the same as those in the first embodiment, and a description thereof will be omitted.

  In the second embodiment, a head that can be printed within the range of the maximum value in the column direction in the print job is a use head (maintenance target head). Note that the print job is a job for causing the printer 1 to print a printed matter having contents corresponding to the print data.

  For example, for the roll paper 2 having a paper width b in FIG. 12, the maximum width of the print job in print data received from the host computer 110 (the maximum value in the column direction length from the reference position) is half of the paper width b (for example, In the case of the range in the upper half in the figure, the heads used are two heads 31A and 31B. That is, regardless of the range of the paper width b of the roll paper 2, the heads 31C to 31H that are not actually used for printing are unused heads. The maintenance process is the same as that in the first embodiment. However, in the first embodiment, the head to be used is selected according to the paper width when the roll paper 2 is set, but in the second embodiment, printing is started at the start of printing (more specifically, after receiving print data). The head to be used is selected according to the job.

  Thus, by determining the head to be used according to the print job, the amount of ink consumed for maintenance can be further reduced.

=== Other Embodiments ===
The above-described embodiment is mainly described with respect to the liquid discharge apparatus, but also includes disclosure of a liquid discharge method and the like. The above-described embodiments are for facilitating understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

<About liquid ejection device>
In the above-described embodiment, an ink jet printer is described as an example of an image forming apparatus. However, the image forming apparatus is not limited to the ink jet printer, and discharges fluids other than ink (liquid, liquid in which particles of functional material are dispersed, fluid such as gel). It can also be embodied in a device. For example, color filter manufacturing apparatus, dyeing apparatus, fine processing apparatus, semiconductor manufacturing apparatus, surface processing apparatus, three-dimensional modeling machine, gas vaporizer, organic EL manufacturing apparatus (especially polymer EL manufacturing apparatus), display manufacturing apparatus, film formation You may apply the technique similar to the above-mentioned embodiment to the various apparatuses which applied inkjet technology, such as an apparatus and a DNA chip manufacturing apparatus. These methods and manufacturing methods are also within the scope of application.

  Moreover, although the lateral type printer has been described in the above-described embodiment, the present invention is not limited to this. For example, a printer (so-called line printer) that discharges ink from a head to a medium while conveying the medium in the conveyance direction may be used. In the case of a line printer, the cleaning unit is provided at a position away from the conveyance path (for example, a position away from the print area in a direction intersecting the medium conveyance direction), and the head is periodically moved to that position. To clean it. Also in this case, the amount of ink consumed by the cleaning can be reduced by preventing the heads not used for printing from being periodically cleaned.

<About ink>
Since the above-described embodiment is an embodiment of a printer, ink is ejected from the nozzles, but this ink may be water-based or oil-based. Further, the liquid ejected from the nozzle is not limited to ink. For example, liquids (including water) including metal materials, organic materials (especially polymer materials), magnetic materials, conductive materials, wiring materials, film-forming materials, electronic inks, processing liquids, gene solutions, etc. are ejected from nozzles. May be.

  In the above-described embodiment, four colors of ink (cyan, magenta, yellow, and black) are used in each head (the number of nozzle rows is four). It may be 3 colors or less, or 5 colors or more.

<Discharge method>
In the above-described embodiment, ink is ejected using a piezoelectric element (piezo element). However, the method for discharging the liquid is not limited to this. For example, other methods such as a method of generating bubbles in the nozzle by heat may be used.

<About the head>
In the above-described embodiment, the number of heads of the head unit 30 is eight (heads 31A to 31H), but may be plural (two or more). For example, four or nine or more. Note that the more heads that are not used for printing among the plurality of heads, the more remarkable is the effect of reducing the amount of ink consumed by regular cleaning. In the above-described embodiment, each head is arranged in a staggered manner, but the present invention is not limited to this. For example, a plurality of heads may be arranged linearly.

<Maintenance>
In the above-described embodiment, cleaning for sucking ink from the nozzles is performed as maintenance for each head, but the maintenance method is not limited to this. For example, you may perform the cleaning which discharges ink from a nozzle by pressurizing the ink flow path of a head. Further, maintenance other than cleaning may be performed. For example, flushing may be performed by ejecting ink from the nozzle by causing the piezo element 321 of the head to expand and contract based on a drive pulse included in the drive signal output from the unit control circuit 64. Or you may perform the wiping which wipes and cleans the ink drop and dust which adhered to the nozzle formation surface (lower surface of the nozzle plate 36). Furthermore, cleaning, flushing, and wiping may be performed in combination. As in the above-described embodiment, the amount of ink consumed for maintenance can be reduced by preventing the heads not used for printing from performing regular maintenance.

DESCRIPTION OF SYMBOLS 1 Printer, 2 roll paper, 10 Feeding unit, 18 winding axis, 19 Relay roller, 20 Transport unit, 21 Relay roller, 22 Relay roller, 23 1st transport roller, 23a 1st drive roller, 23b 1st driven roller, 24 second transport roller, 24a second drive roller, 24b second driven roller, 25 reverse roller, 26 relay roller, 27 delivery roller, 29 platen, 30 head unit, 31A to 31H head, 32 drive unit, 33 case, 34 Channel unit, 35 channel forming substrate, 36 nozzle plate, 37 elastic plate, 40 carriage unit, 41 guide rail, 42 carriage, 50 detector group, 60 controller, 61 interface unit, 62 CPU, 63 memory, 4 unit control circuit, 65 timer, 70 cleaning unit, 72 lifting platform, 73 head cap, 73a suction chamber, 74 hose, 75 suction pump, 75a small roller, 80 winding unit, 81 relay roller, 82 winding drive shaft, 90 nozzle inspection unit, 91 detection electrode, 92 high voltage power supply unit, 93 first limiting resistor, 94 second limiting resistor, 95 detecting capacitor, 96 amplifier, 97 detection control unit, 98 smoothing capacitor, 99 voltage detection unit, 110 Host computer, 321 piezo element, 323 fixing plate, 324 flexible cable, 331 storage space, 332 ink supply pipe, 351 pressure chamber, 352 supply port, 353 reservoir

Claims (9)

A plurality of heads for discharging liquid;
A maintenance unit corresponding to each of the plurality of heads, wherein the maintenance unit performs maintenance that consumes the liquid;
Of the plurality of heads, a control unit that causes the maintenance unit to perform the maintenance periodically only for a maintenance target head whose printable range is within a predetermined range;
An image forming apparatus comprising: The image forming apparatus according to claim 1,
The plurality of heads are arranged in an intersecting direction intersecting a medium transport direction,
The predetermined range is a width of the medium in the intersecting direction.
An image forming apparatus. The image forming apparatus according to claim 1,
The plurality of heads are arranged in a crossing direction that intersects a transport direction of the medium,
The predetermined range is a maximum value of the length in the intersecting direction in the print job.
An image forming apparatus. The image forming apparatus according to claim 1,
The control unit determines the maintenance target head from the plurality of heads when the medium is set, and the maintenance unit receives the maintenance target head from the maintenance unit head every time a predetermined period elapses after printing is started. To perform maintenance,
An image forming apparatus. The image forming apparatus according to claim 1,
The control unit determines the maintenance target head from the plurality of heads at the start of printing, and performs maintenance on the maintenance unit with respect to the maintenance target head every time a predetermined period elapses after printing is started. To do,
An image forming apparatus. An image forming apparatus according to claim 1,
Each head has an inspection unit that performs a nozzle inspection to determine whether or not there is a defective nozzle.
The control unit, after performing the maintenance on the maintenance target head, to let the inspection unit perform the nozzle inspection for the plurality of heads,
For the maintenance target head, if it is determined in the nozzle inspection that there is a defective nozzle, perform the maintenance again,
An image forming apparatus characterized in that the maintenance is not immediately performed on unused heads other than the maintenance target head even when it is determined in the nozzle inspection that there is a defective nozzle. The image forming apparatus according to claim 6,
A holding unit for holding missing presence information indicating that it is determined that there is a defective nozzle in the unused head in the nozzle inspection;
When the holding unit holds the missing information and the time after the missing information is held by the holding unit exceeds a threshold, the maintenance unit is configured to maintain the unused unit with respect to the unused head. To perform the maintenance,
An image forming apparatus. The image forming apparatus according to claim 7,
The missing information is information prepared for each of the plurality of heads.
An image forming apparatus. The image forming apparatus according to claim 1,
The maintenance is any one of cleaning, flushing, wiping, or a combination thereof.
An image forming apparatus.

Images