Inkjet recording device

Abstract

While transporting multiple sheets of paper in succession and forming a color image on each sheet, the ink ejection width is narrowed to match the width of the paper if the paper width is insufficient, while image formation is carried out as planned for paper that is wide enough. [Solution] The control unit 38 of the inkjet recording device 10 sets a print queue for each line head 15Y to 15M, indicating a queue of print jobs to form a color image on the paper P, and executes the print jobs according to the print queue. If the width of the paper is narrower than the width of the paper used in the print job before execution, the control unit 38 sets paper width information in the print queue of each line head in association with the print job before execution, and performs a masking process to narrow the color image of the print job before execution in the paper width direction based on the paper width information set in the print queue of each line head.

Description

Technical Field

[0001] The present invention relates to an inkjet recording apparatus that forms a color image on a sheet by ejecting ink droplets of each color from a plurality of line heads onto the sheet, and particularly relates to a technique for narrowing the width of ink ejection according to the width of the sheet.

Background Art

[0002] As an inkjet recording apparatus, there is one that arranges a plurality of line heads at intervals along the conveyance direction of a sheet conveyed by a conveyance belt, and sequentially ejects ink droplets of each color from each line head onto the conveyed sheet to form a color image on the sheet.

[0003] Further, in the image forming apparatus described in Patent Document 1, an edge of a sheet is detected by an image sensor, and based on the detected edge, a positional deviation in the main scanning direction (width direction) of the sheet is recognized. Before ejecting ink droplets from the line head, mask processing is performed on the image data based on the recognized positional deviation.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, in the configuration in which a plurality of line heads are arranged at intervals along the conveyance direction of a sheet conveyed by a conveyance belt as described above, there may be a case where a plurality of sheets are continuously conveyed, and ink droplets are sequentially ejected onto each sheet by each line head to form respective color images on each sheet.

[0006] On the other hand, if the paper width is narrow and the color image extends beyond the width of the paper, it is necessary to apply a mask to the color image to narrow the ink droplet ejection range of each line head in the width direction of the paper.

[0007] However, when multiple sheets of paper are transported in succession as described above, and ink droplets are sequentially ejected onto each sheet by each line head to form a color image on each sheet, if the ink droplet ejection range of all line heads is narrowed in the width direction of the paper at the same time, an inconvenience occurs in some sheets of paper where the width of the color image becomes narrower, even if the color image does not extend beyond the width of the paper. For this reason, it is necessary to apply a masking process to the color image on each sheet of paper.

[0008] Patent Document 1 recognizes the misalignment of the paper in the width direction and applies a mask to the image data based on the recognized misalignment before the ink droplets are ejected from the line head. However, it does not apply a mask to the image data for each individual sheet of paper, nor does it suggest doing so.

[0009] Therefore, the present invention has been made in view of the above circumstances, and aims to transport multiple sheets of paper in succession and form a color image on each sheet, while narrowing the ink ejection width to match the paper width for sheets that are too narrow, and forming images as planned for sheets that are wide enough. [Means for solving the problem]

[0010] An inkjet recording apparatus according to one aspect of the present invention comprises: a transport belt for transporting paper; a plurality of line heads arranged at intervals along the transport direction of the paper, which sequentially eject ink droplets of predetermined colors onto the paper to form a color image; a paper width sensor positioned upstream of each line head in the transport direction of the paper for detecting the width of the paper; a print queue for each line head indicating a queue for at least one print job to form the color image on the paper, executing the print job according to the print queue; and, if the paper width detected by the paper width sensor is determined to be narrower than the width of the paper used in the print job, a control unit which sets width information indicating the detected paper width in the print queue of each line head, corresponding to the print queue before the execution, and performs a masking process to narrow the color image corresponding to the print queue before the execution to the width indicated by the width information in the paper width direction, based on the width information set in the print queue of each line head. [Effects of the Invention]

[0011] According to the present invention, when multiple sheets of paper are transported in succession and a color image is formed on each sheet, the ink ejection width can be narrowed to match the width of the paper for sheets that are too narrow, while images can be formed as planned on sheets that are wide enough. [Brief explanation of the drawing]

[0012] [Figure 1] This is a cross-sectional view showing an inkjet recording apparatus according to one embodiment of the present invention. [Figure 2] This is a block diagram showing the internal configuration of the inkjet recording device according to this embodiment. [Figure 3]This schematic diagram illustrates the process of sequentially executing the first, second, third, and fourth print jobs according to the print queue, continuously transporting the first to fourth sheets of paper by a conveyor belt, and sequentially ejecting ink droplets of each color onto each sheet of paper by each line head, thereby forming the color images of the first to fourth print jobs on each sheet. [Figure 4] This flowchart shows the control procedure for setting paper width information for each line head in the print queue of the line head, in association with the print job before execution. [Figure 5A] This flowchart shows the control procedure for masking the color image of the print job before execution, narrowing it in the width direction of the paper, for each line head. [Figure 5B] This flowchart shows the control procedure following Figure 5A. [Modes for carrying out the invention]

[0013] The following describes an inkjet recording apparatus according to one embodiment of the present invention. Figure 1 is a cross-sectional view showing an inkjet recording apparatus according to one embodiment of the present invention. As shown in Figure 1, the inkjet recording apparatus 10 includes an image reading unit 11, an image forming unit 12, a paper feeding unit 14, a transport unit 15, and a transport unit 16, etc.

[0014] The paper feeding unit 14 is equipped with a paper feeding cassette 21. The paper feeding cassette 21 is provided with a paper feeding roller 22, which pulls out the paper P contained in the paper feeding cassette 21 and transports it to the transport path 25 of the transport unit 15.

[0015] The transport unit 15 includes a transport path 25 for transporting paper P from the paper feed unit 14, transport rollers 26 provided at appropriate locations on each transport path 25, 28, a registration roller 27 for correcting the diagonal feeding of paper P and sending the paper P to the transport unit 16, a transport path 28 for transporting paper P that has been transported through the transport unit 16, and an discharge roller 32 for discharging paper P that has been transported through the transport path 28 to the discharge tray 31.

[0016] The conveying unit 16 includes a driving roller 8, a driven roller 9, a tension roller 5, and a conveyor belt 6. The conveyor belt 6 is an endless belt and is stretched over the driving roller 8, the driven roller 9, and the tension roller 5. The driving roller 8 is a roller that is rotationally driven counterclockwise by a motor (for example, a stepping motor). When the driving roller 8 is rotationally driven, the conveyor belt 6 moves circumferentially counterclockwise, and the driven roller 9 and the tension roller 5 are rotationally driven passively counterclockwise.

[0017] The sheet P is guided through the resist roller 27 to the conveyor belt 6 of the conveying unit 16 and is conveyed in the conveying direction A by the conveyor belt 6.

[0018] The tension roller 5 is a roller for appropriately maintaining the tension of the conveyor belt 6. The suction roller 7 contacts the conveyor belt 6 and electrostatically adsorbs the sheet P to the conveyor belt 6 by charging the conveyor belt 6.

[0019] In addition, the image reading unit 11 has, for example, a contact image sensor (CIS) as an imaging element that optically reads the image of the document M. When a plurality of documents M are placed on the document tray 1, these documents M are sequentially pulled out from the document tray 1 and conveyed, and the image of each document M is read by the imaging element, and each document M is sequentially discharged to the discharge tray 2 and stacked. For each image of each document M, the output of the imaging element is converted into image data indicating the image of the document M.

[0020] The image forming unit 12 inputs image data indicating the image of the original document M, and forms the image of the original document M indicated by the image data on the paper P by an inkjet method. The image forming unit 12 has respective line heads 15Y, 15B, 15C, 15M that eject ink droplets of four colors (yellow, black, cyan, and magenta). Each of the line heads 15Y, 15B, 15C, 15M ejects ink droplets of each color onto the paper P being conveyed by the conveyance belt 6 of the conveyance unit 4 and applies them to form a color image on the paper P.

[0021] After the image of the original document is formed on the paper P by the image forming unit 12, the paper P is discharged to the discharge tray 31 through the discharge roller 32 via the conveyance path 28.

[0022] Also, between the registration roller 27 and each of the line heads 15Y, 15B, 15C, 15M, a paper width sensor 33 and a paper leading edge sensor 34 for detecting the width of the paper P are sequentially arranged from the upstream side in the conveyance direction A of the paper P. The paper width sensor 33 is, for example, a CIS extending in the width direction of the paper P, and detects the leading edge and both side edges of the paper P illuminated by a light source 33A provided below the paper width sensor 33. The paper leading edge sensor 34 is an optical sensor including, for example, a light emitting element that irradiates light onto the paper P and a light receiving element that receives the light reflected by the paper P, and detects the leading edge of the paper P. Both side ends of the paper width sensor 33 are located outside the maximum width of the paper P printable by the inkjet recording apparatus 10 in the width direction of the paper P orthogonal to the conveyance direction A of the paper P. The paper width sensor 33 has the width direction as the main scanning direction.

[0023] FIG. 2 is a block diagram showing the internal configuration of the inkjet recording apparatus 10. As shown in FIG. 2, the inkjet recording apparatus 10 includes an image reading unit 11, an image forming unit 12, a paper feeding unit 14, a conveyance unit 15, a conveyance unit 16, a paper width sensor 3, a paper leading edge sensor 34, a storage unit 35, a communication unit 36, and a control unit 37. These components are capable of transmitting and receiving data or signals to and from each other through a bus.

[0024] The memory unit 35 is a large-capacity storage device such as an SSD (Solid State Drive) or HDD (Hard Disk Drive) that stores various application programs and various types of data.

[0025] The communication unit 36 ​​is a communication interface equipped with a communication module such as a LAN chip. This communication unit 36 ​​is connected to an external terminal device (not shown) via a network (such as an intranet) N and performs data communication with the external terminal device.

[0026] The control unit 37 consists of a processor, RAM (Random Access Memory), and ROM (Read Only Memory). The processor is, for example, a CPU (Central Processing Unit), ASIC, or MPU (Micro Processing Unit). The control unit 37 functions as a control unit 38 when the control program stored in the ROM or storage unit 35 is executed by the processor.

[0027] The control unit 38 comprehensively controls the inkjet recording device 10. The control unit 38 is connected to the image reading unit 11, image forming unit 12, paper feeding unit 14, transport unit 15, transport unit 16, paper width sensor 33, paper leading edge sensor 34, storage unit 35, and communication unit 36, and controls the operation of these components and transmits and receives signals or data between them.

[0028] The control unit 38 functions as a processing unit that performs various processes necessary for image formation by the inkjet recording device 10.

[0029] Furthermore, the control unit 38 determines the detection timing of the leading edge of the paper P based on the detection output of the paper width sensor 33. As the paper P is transported, when both ends of the paper P reach the detection position of the paper width sensor 33, it detects the positions of both ends of the paper P using a known method based on the detection output of the paper width sensor 33 (for example, detecting the outermost two positions where the paper width sensor 33 was able to read the image of the paper P in the main scanning direction).

[0030] Furthermore, the control unit 38 determines the detection timing of the leading edge of the paper P based on the detection output of the light-receiving element of the leading edge sensor 34.

[0031] Furthermore, the conveyor belt 6 corresponds to the conveyor belt in the claims, each line head 15Y, 15B, 15C, and 15M corresponds to each line head in the claims, the paper width sensor 33 corresponds to the paper width sensor in the claims, and the control unit 38 corresponds to the control unit in the claims.

[0032] In an inkjet recording device 10 with this configuration, the control unit 38 executes a print job when, for example, a print job transmitted from an external terminal device is received by the communication unit 36. The print job includes printing conditions such as paper size and image data of each color (print target data) indicating a color image. The control unit 38 converts the image data of each color of the print job into raster data, drives and controls the motor that rotates the drive roller 8 of the transport unit 16 to transport the paper P by the transport belt 6, and controls each line head 15Y, 15B, 15C, 15M based on the raster data of each color related to the print job, so that each line head 15Y, 15B, 15C, 15M ejects ink droplets onto the paper P on the transport belt 6, thereby forming the color image of the print job on the paper P and executing the print job.

[0033] Furthermore, the control unit 38 of the inkjet recording device 10 sets the ink ejection at each line head 15Y, 15B, 15C, and 15M to perform image formation of the print data included in the print job, and sets a print queue that indicates a waiting line for ink ejection for each job in order to execute multiple print jobs consecutively. The control unit 38 executes the print jobs by ejecting ink according to the print queue.

[0034] Figure 3 is a schematic diagram illustrating the process of sequentially executing the first print job J1, second print job J2, third print job J3, and fourth print job J4 according to the print queue, continuously transporting the first to fourth sheets of paper P by the transport belt 6, and sequentially ejecting ink droplets of each color onto each sheet of paper P by the line heads 15Y, 15B, 15C, and 15M, thereby forming the color images of the first to fourth print jobs J1 to J4 on each sheet of paper P.

[0035] Figure 3 shows an example in which the paper width sensor 33 sequentially detects the width of the first to fourth sheets of paper P upstream of each line head 15Y, 15B, 15C, and 15M in the paper transport direction A. The detection points for the widths of the first to fourth sheets of paper P are denoted as th1, th2, th3, and th4.

[0036] Furthermore, the paper leading edge sensor 34 sequentially detects the leading edges of the first to fourth sheets of paper P. The detection points for the leading edges of the first to fourth sheets of paper P are denoted as ts1, ts2, ts3, and ts4. Since the paper leading edge sensor 34 is located downstream of the paper width sensor 33 in the paper P transport direction A, each detection point ts1, ts2, ts3, and ts4 is delayed in time compared to each detection point th1, th2, th3, and th4.

[0037] Furthermore, since the paper width sensor 33 and the paper leading edge sensor 34 are located upstream of the line heads 15Y, 15B, 15C, and 15M of the image forming unit 12 in the transport direction A of the paper P, the paper P is in a blank state when its leading edge reaches the detection position of the paper width sensor 33 and the detection position of the paper leading edge sensor 34 in the transport direction A.

[0038] Here, when the control unit 38 forms a color image on the paper P by executing the first print job J1, for example, it starts ejecting ink droplets from each line head 15Y, 15B, 15C, and 15M for the print job corresponding to the paper P at each timing when the leading edge of the paper P reaches each line head 15Y, 15B, 15C, and 15M.

[0039] Under the control of the control unit 38, the paper P is transported by the registration roller 27, passes the detection position of the leading edge of the paper P by the paper leading edge sensor 34, and is transported by the transport belt 6. Here, the distances from the detection position of the paper leading edge sensor 34 to each line head 15Y, 15B, 15C, and 15M are known, and the transport distance of the paper P corresponds to the rotation angle of the motor that rotates the drive roller 8 of the transport belt 6. Based on these distances and rotation angles, the control unit 38 calculates the rotation angle of the motor of the drive roller 8 required to transport the paper P by the respective distance from the detection position of the leading edge of the paper P.

[0040] The control unit 38 sequentially detects the leading edges of the first to fourth sheets of paper P that have been transported by the registration roller 27, based on the detection output of the light-receiving element of the paper leading edge sensor 34. The control unit 38 detects the rotation angle of the motor of the transport belt 6 from the detection points ts1, ts2, ts3, and ts4 of each leading edge, and determines the timing when the motor's rotation angle reaches the rotation angle corresponding to each of the above-mentioned separation distances. When the control unit 38 determines the timing when the leading edges of the first to fourth sheets of paper P have reached each of the line heads 15Y, 15B, 15C, and 15M, it starts ejecting ink droplets for image formation of the first print job J1 from each of the line heads 15Y, 15B, 15C, and 15M at each timing. As a result, ink droplets of each color are ejected and applied to the first to fourth sheets of paper P, and images of each respective color are formed on each sheet of paper P.

[0041] Furthermore, based on the detection output of the paper width sensor 33, the control unit 38 detects both sides of the first to fourth sheets of paper P in the width direction, and sequentially determines the width of the first to fourth sheets of paper P at the detection points th1, th2, th3, and th4 for each side edge.

[0042] Each time the width of the first to fourth sheets of paper P is determined, the control unit 38 compares the width of the paper P with the width of the paper size indicated by the print job applied to the paper P (the size in the width direction). If the determined width of the paper P is narrower than the width of the paper size indicated by the print job, it performs a masking process on the color image of the print job to narrow the color image in the width direction of the paper P. If the determined width of the paper P matches or is wider than the width of the paper size indicated by the print job, it does not perform the masking process. This masking process is, for example, a process in which, for each color raster data that makes up the color image as print data related to the print job, each pixel in the area on both sides in the width direction of the image indicated by the raster data is replaced with a white pixel (a pixel consisting of a predetermined pixel value to prohibit ejection), thereby narrowing the image formed by ink ejection in the width direction of the paper P to the detected width of the paper P. The control unit 38 sets, for example, the pixel regions in the image that make up the width of the paper size indicated by the print job, which are outside the width direction of the determined blank paper P, as the side regions to be replaced with white pixels.

[0043] The control unit 38 controls each line head 15Y, 15B, 15C, and 15M based on the raster data of each color that has been masked, narrowing the ink droplet ejection range in the width direction of the paper P by each line head 15Y, 15B, 15C, and 15M, and causing each line head 15Y, 15B, 15C, and 15M to eject their respective ink droplets onto the paper P on the conveyor belt 6, thereby forming a color image on the paper P. As a result, the color image is formed without extending beyond the edges of the paper P. Furthermore, the ink droplets ejected by each line head 15Y, 15B, 15C, and 15M do not extend beyond the edges of the paper P and contaminate the conveyor belt 6 or other components.

[0044] By controlling the paper in this way, when the paper width sensor 33 detects the positions of both edges of a blank sheet of paper P, the control unit 38 determines the width of the paper P based on the detected positions of both edges. If the determined width of the paper P is narrower than the width of the paper size indicated by the print job, a masking process is applied to the raster data of each color related to the print job so that the color image is formed without extending beyond the edges of the paper P.

[0045] However, when multiple print jobs are executed consecutively, and each paper P corresponding to each job is transported in succession, and ink droplets are sequentially ejected onto each paper P by line heads 15Y, 15B, 15C, and 15M, if masking is applied simultaneously to the raster data of each color related to all print jobs, then for paper P with a width greater than the width of the paper size indicated by the print job, even if the image does not extend beyond the width of the paper P, the width of the image may be narrowed, and image formation may not occur properly.

[0046] For example, in the example shown in Figure 3, at the point in time when the control unit 38 determines that the width of the paper P corresponding to the third print job J3 is narrower than the width of the paper size indicated by the print job (referred to here as detection point th3), the first sheet of paper P corresponding to the first print job J1 has already passed through the first to third line heads 15Y, 15B, and 15C, and is currently passing through the fourth line head 15M. Therefore, the yellow, black, and cyan images of the first print job J1 have already been formed on the first sheet of paper P, and the magenta image of the first print job J1 is in the process of being formed.

[0047] Furthermore, at the time of the above determination, the second sheet of paper P corresponding to the second print job J2 has passed the first line head 15Y, is passing the second and third line heads 15B and 15C, and has not yet reached the fourth line head 15M. Therefore, the yellow image of the second print job J2 has already been formed on the second sheet of paper P, the black and cyan images of the second print job J2 are in the process of being formed, and the magenta image of the second print job J2 has not yet been formed.

[0048] Furthermore, the third sheet of paper P, corresponding to the third print job J3, has not yet reached the respective line heads 15Y, 15B, 15C, and 15M. Therefore, the third sheet of paper P is blank, as the yellow, black, cyan, and magenta images for the third print job J3 have not yet been formed.

[0049] Similarly, the fourth sheet of paper P corresponding to the fourth print job J4 is blank, as the lineheads 15Y, 15B, 15C, and 15M have not yet reached the yellow, black, cyan, and magenta images for the fourth print job J4.

[0050] As shown in Figure 3, if the third sheet of paper P is narrower than the width of the paper size indicated by the third print job, applying a mask to the raster data showing the magenta image in the process of forming the first print job J1 will narrow the width of the magenta image from a certain point, even if the magenta image of the first print job J1 does not extend beyond the width of the paper P. Similarly, applying a mask to the raster data showing the black and cyan images in the process of forming the second print job J2 will narrow the width of the black and cyan images from a certain point, even if the black and cyan images of the second print job J2 do not extend beyond the width of the paper P. Furthermore, applying a mask to the raster data showing the magenta image before the formation of the second print job J2 will narrow the width of the magenta image from a certain point, even if the magenta image of the second print job J2 does not extend beyond the width of the paper P.

[0051] Furthermore, if the fourth sheet of paper P corresponding to the fourth print job J4 has a width greater than or equal to the width of the paper size indicated by the fourth print job, applying a mask to the raster data of each color before the formation of the fourth print job J4 will narrow the width of the color image of the fourth print job J4.

[0052] Therefore, for each type of paper P, it is necessary to control whether or not to apply mask processing to the raster data of each color related to each print job.

[0053] In this embodiment, the control unit 38 determines the width of the blank paper P based on the positions of both edges of the blank paper P detected by the paper width sensor 33. If the width of the paper P is narrower than the width of the paper size indicated by the print job to be executed applied to the paper P, the control unit 38 sets width information indicating the determined width of the paper P in the print queue of each line head 15Y, 15B, 15C, and 15M, corresponding to the print queue of the print job to be executed. Then, based on the width information of the paper P set in the print queue of each line head 15Y, 15B, 15C, and 15M, the control unit 38 performs a masking process to narrow the color image corresponding to the print queue of the print job to the width indicated by the width information of the paper P in the width direction.

[0054] For example, as shown in Figure 3, if the control unit 38 determines that the third blank sheet of paper P is narrower than the width of the paper size indicated by the third print job, at the time of this determination th3, it sets the width information of the third sheet of paper P in the print queue associated with the unexecuted third print job J3 applied to the third sheet of paper P in the print queue of each line head 15Y, 15B, 15C, and 15M. Then, based on the width information of the third sheet of paper P set in the print queue of each line head 15Y, 15B, 15C, and 15M, the control unit 38 performs a masking process on the raster data of each color related to the unexecuted third print job J3 to narrow the color image of the third print job J3 in the width direction of the paper P.

[0055] In this case, the control unit 38 does not set the width information for the third sheet of paper P in association with the first print job J1, second print job J2, and fourth print job 4 applied to the first, second, and fourth sheets of paper P in the print queue of each line head 15Y, 15B, 15C, and 15M. Therefore, mask processing is not performed on the raster data of each color related to the first print job J1, second print job J2, and fourth print job 4 applied to the first, second, and fourth sheets of paper P.

[0056] Therefore, if the image of each color represented by the raster data for each color related to the print job does not extend beyond the width of the paper P, the width of the image of each color will not be narrowed. In other words, when transporting multiple sheets of paper P in succession and forming a color image on each sheet of paper P based on a respective print job, the ink ejection width is narrowed to match the width of the paper P for sheets of paper P that are not wide enough for color image formation, while image formation can be performed as planned for sheets of paper P that are wide enough.

[0057] Next, when the width of the paper P determined as described above is narrower than the width of the paper size indicated by the print job, the control procedure for setting the width information of the paper P in the print queue of each line head 15Y, 15B, 15C, and 15M in association with the print job to be executed will be explained with reference to the flowchart shown in Figure 4.

[0058] When the control unit 38 detects the positions of both sides of a blank sheet of paper P using the paper width sensor 33, it determines the width of the paper P based on the positions of both sides of the paper P (S101), and determines whether the width of the paper P is narrower than the width of the paper size indicated by the print job to be executed before the paper P is applied (S102).

[0059] For example, in the example shown in Figure 3, when the paper width sensor 33 detects the positions of both edges of the first blank sheet of paper P, the control unit 38 determines the width of the first sheet of paper P (S101) and determines that the width of the first sheet of paper P is not narrower than the width of the paper size indicated by the first print job J1 that is to be executed and applied to the first sheet of paper P (S102 "No"). Similarly, when the paper width sensor 33 detects the positions of both edges of the second and fourth blank sheets of paper P, the control unit 38 determines the widths of the second and fourth sheets of paper P (S101) and determines that the widths of the second and fourth sheets of paper P are not narrower than the widths of the respective paper sizes indicated by the second print job J2 and fourth print job J4 that are to be executed and applied to the second and fourth sheets of paper P (S102 "No").

[0060] Furthermore, when the paper width sensor 33 detects the positions of both ends of the third blank sheet of paper P, the control unit 38 determines the width of the third sheet of paper P (S101) and determines that the width of the third sheet of paper P is narrower than the width of the paper size indicated by the third print job J3 that is applied to the third sheet of paper P before execution (S102 "Yes").

[0061] If the control unit 38 determines that the width of the blank third sheet of paper P is narrower than the width of the paper size indicated by the third print job J3 that is not yet executed and applied to the third sheet of paper P (S102 "Yes"), at the time of this determination th3, it sets width information indicating the width of the third sheet of paper P for the print queue associated with the third print job J3 that is not yet executed in the print queues of each line head 15Y, 15B, 15C, and 15M (S103).

[0062] Furthermore, the control unit 38 determined that for the first, second, and fourth blank sheets of paper P, the width of the paper P was not narrower than the width of the paper size indicated by the print job applied to the paper P before execution (S102 "No"), so S103 was not performed at the respective determination times th1, th2, and th4.

[0063] Next, the control procedures for masking the color image of the print job before execution in the width direction of the paper P, for each line head 15Y, 15B, 15C, and 15M, will be explained with reference to the flowcharts shown in Figures 5A and 5B. Note that when the control procedures in the flowcharts shown in Figures 5A and 5B are being performed, the control procedures in the flowchart shown in Figure 4 are repeatedly performed.

[0064] The control unit 38 identifies the print job to be ejected, in the example shown in Figure 3, the first print job J1, based on the print queues of each line head 15Y, 15B, 15C, and 15M (S201), and determines whether there is a print queue corresponding to another print job that is earlier in the sequence than the print queue corresponding to the identified print job (S202).

[0065] In the example shown in Figure 3, if the first print job J1 is the first print job in the print queue of each line head 15Y, 15B, 15C, and 15M, and is subject to the determination by S202, then there is no previous print job. Therefore, the control unit 38 determines, based on the print queue of each line head 15Y, 15B, 15C, and 15M, that there is no previous print job for the first print job J1 (S202 "No"). Then, based on the detection output of the paper width sensor 33, the control unit 38 determines at point th1 the width of the first sheet of paper P on which the color image of the first print job J1 is formed, whether or not the width information of the paper P is set in association with the selected first print job J1 in the print queue of each line head 15Y, 15B, 15C, and 15M (S203).

[0066] As described above, since the paper width P of the first, second, and fourth sheets is not narrow, width information indicating the paper width P is not set for the print queues corresponding to the first print job J1, second print job J2, and fourth print job J4 before execution in each linehead 15Y, 15B, 15C, and 15M.

[0067] The control unit 38 determines that the print queues corresponding to the first print job J1 for each line head 15Y, 15B, 15C, and 15M do not have width information for the paper P set (S203 "No"). It converts the image data of each color representing the color image of the print queue corresponding to the first print job J1 into raster data of each color, and stores and sets the raster data of each color in the buffer memory of each line head 15Y, 15B, 15C, and 15M (S204). At the timing when the leading edge of the first sheet of paper P reaches each line head 15Y, 15B, 15C, and 15M, it starts the ink droplet ejection operation of each line head 15Y, 15B, 15C, and 15M based on the raster data of each color (S205).

[0068] Therefore, when executing the first print job J1 according to the print queue, that is, when ejecting ink from the print queue corresponding to the first print job J1, the image data of each color representing the color image of the first print job J1 is converted into raster data of each color, and the raster data of each color is stored and set in the buffer memory of each line head 15Y, 15B, 15C, and 15M, respectively.

[0069] Furthermore, if the width of the first sheet of paper P is narrower than the width of the paper size indicated by the first print job J1 that is applied to the first sheet of paper P before execution (S102 "Yes"), then width information indicating the width of the first sheet of paper P may be set in the print queue of each line head 15Y, 15B, 15C, 15M in association with the first print job J1 that is applied before execution (S103). In this case, the control unit 38 determines, based on the print queue, that there is no print job immediately preceding the first print job J1 (202 "No"), and at the time th1, when it determines the width of the first sheet of paper P on which the color image of the selected first print job J1 will be formed based on the detection output of the paper width sensor 33, it determines that the width information of the first sheet of paper P has been set in the print queue corresponding to the first print job J1 at each line head 15Y, 15B, 15C, and 15M (S203 "Yes"), converts the image data of each color representing the color image of the first print job J1 into raster data of each color (S206), and applies the above masking process to the raster data of each color related to the first print job J1 based on the width information of the first sheet of paper P, and sets the raster data of each color (S207). Then, at the timing when the leading edge of the first sheet of paper P reaches each line head 15Y, 15B, 15C, and 15M, the control unit 38 starts the ink droplet ejection operation of each line head 15Y, 15B, 15C, and 15M based on the raster data of each color (S205).

[0070] Next, the control unit 38 identifies the next print job to be ink ejected, the second print job J2 in the example shown in Figure 3, based on the print queues of each line head 15Y, 15B, 15C, and 15M (S201), and determines whether there is a print queue corresponding to another print job that is earlier in the sequence than the print queue corresponding to the identified print job (S202). In this example, the control unit 38 determines that there is a first print job J1 that is one position earlier than the second print job J2 (S202 "Yes"). In this case, at the time th2 when the control unit 38 determines the width of the second sheet of paper P for the selected second print job J2 based on the detection output of the paper width sensor 33, it determines whether the paper width information has been set in the print queue corresponding to the second print job J2 at each line head 15Y, 15B, 15C, and 15M (S208).

[0071] If the control unit 38 determines that the paper width information for paper P has not been set in the print queue corresponding to the second print job J2 at each line head 15Y, 15B, 15C, 15M (S208 "No"), it determines for each line head 15Y, 15B, 15C, 15M whether or not ink ejection for the first print job J1 that preceded the second print job J2 has been completed (S209).

[0072] In the state shown in Figure 3, at point th2, when the width of the second sheet of paper P for the second print job J2 is determined based on the detection output of the paper width sensor 33, the previous first print job J1 has not yet finished at each line head 15Y, 15B, 15C, and 15M.

[0073] The control unit 38 determines that the previous first print job J1 has not finished at each line head 15Y, 15B, 15C, and 15 (S209 "No"), and since the ejection of ink droplets of each color related to the first print job J1 has not finished, it converts the image data of the second print job J2 in the print queue of each line head 15Y, 15B, 15C, and 15 into raster data at the timing when the ejection of ink droplets at that line head is finished, and stores and sets each raster data in the buffer memory of each line head 15Y, 15B, 15C, and 15M respectively (S210).

[0074] Furthermore, if the control unit 38 determines that the previous first print job J1 has finished in at least one of the line heads 15Y, 15B, 15C, and 15 (S209 "Yes"), the ejection of ink droplets for the first print job J1 by at least one of those line heads has already finished. Therefore, at the above time th2, the control unit 38 immediately converts the image data of the second print job J2 in the print queue of that line head into raster data and quickly sets the raster data (S211).

[0075] Then, at the timing when the leading edge of the second sheet of paper P reaches each line head 15Y, 15B, 15C, and 15M, the control unit 38 starts the ink droplet ejection operation of each line head 15Y, 15B, 15C, and 15M based on the raster data of each color (S205).

[0076] Next, the control unit 38 identifies the next print job to be targeted for ink ejection, the third print job J3 in the example shown in Figure 3, based on the print queues of each line head 15Y, 15B, 15C, and 15M (S201), and determines whether there is a print queue corresponding to another print job that is ahead of the print queue corresponding to the identified print job (S202). In this example, the control unit 38 determines that there is a second print job J2 that is one position ahead of the third print job J3 (S202 "Yes"). At the point th3, when the width of the third sheet of paper P for the third print job J3 is determined based on the detection output of the paper width sensor 33, the control unit 38 determines whether the width information of paper P has been set in the print queue corresponding to the third print job J3 for each line head 15Y, 15B, 15C, and 15M (S208).

[0077] In this example, the control unit 38 determines that the paper width information for the selected third print job J3 has been set in the print queue for each line head 15Y, 15B, 15C, and 15M (S208 "Yes"). The control unit 38 then determines for each line head 15Y, 15B, 15C, and 15M whether the second print job J2, which preceded the third print job J3, has finished (S212).

[0078] In the state shown in Figure 3, at point th3, when the width of the third sheet of paper P for the third print job J3 is determined based on the detection output of the paper width sensor 33, the previous second print job J2 has finished at line head 15Y, while the previous second print job J2 has not finished at the other line heads 15B, 15C, and 15M.

[0079] The control unit 38 determines that the previous second print job J2 has finished at the line head 15Y (S212 "Yes"), and since the ejection of ink droplets for the second print job J2 by ​​the line head 15Y has already finished, it immediately converts the image data of the third print job J3 in the print queue of the line head 15Y into raster data at the above time th3 (S213), immediately applies a mask process to the raster data based on the width information of the third sheet of paper P, and quickly stores and sets the raster data in the buffer memory of the line head 15Y (S214).

[0080] Furthermore, the control unit 38 determines that the previous second print job J2 has not been completed at each of the other line heads 15B, 15C, and 15M (S212 "No"). Since the ejection of ink droplets for the second print job J2 by ​​each of the other line heads 15B, 15C, and 15M has not been completed, the control unit 38 converts the image data of the third print job J3 in the print queue of each line head 15B, 15C, and 15M into raster data at the timing when the ejection of ink droplets for the second print job J2 by ​​the line head is completed (S215). Based on the width information of the third sheet of paper P, the control unit 38 sequentially applies mask processing to the black, cyan, and magenta raster data and stores and sets the black, cyan, and magenta raster data in the buffer memory of each of the other line heads 15B, 15C, and 15M respectively (S216).

[0081] Then, at the timing when the leading edge of the third sheet of paper P reaches each line head 15Y, 15B, 15C, and 15M, the control unit 38 starts the ink droplet ejection operation of each line head 15Y, 15B, 15C, and 15M based on the raster data of each color (S205).

[0082] Furthermore, based on the print queues of each line head 15Y, 15B, 15C, and 15M, the control unit 38 identifies the next print job to be targeted for ink ejection, in the example shown in Figure 3, the fourth print job J4 (S201), and determines whether there is a print queue corresponding to another print job that is ahead of the print queue corresponding to the identified print job (S202). In this example, the control unit 38 determines that there is a third print job J3 that is one position ahead of the fourth print job J4 (S202 "Yes"). At the point th4 in which the width of the fourth sheet of paper P for the fourth print job J4 is determined based on the detection output of the paper width sensor 33, the control unit 38 determines whether the paper width information for P has been set in the print queues corresponding to the fourth print job J4 for each line head 15Y, 15B, 15C, and 15M (S208).

[0083] In this example, the control unit 38 determines that the paper width information for paper P has not been set in the print queue corresponding to the fourth print job J4 for each line head 15Y, 15B, 15C, and 15M (S208 "No"), and determines for each line head 15Y, 15B, 15C, and 15M whether the third print job J3, which preceded the fourth print job J4, has finished (S209).

[0084] The control unit 38 determines that the previous third print job J3 has not finished for any of the line heads 15Y, 15B, 15C, and 15 (S209 "No"), and since the ejection of ink droplets of each color related to the third print job J3 has not finished, it converts the image data of the fourth print job J4 in the print queue of each line head 15Y, 15B, 15C, and 15 into raster data at the time when the ejection of ink droplets from that line head is finished, and sets the raster data into the buffer memory (S210).

[0085] Then, at the timing when the leading edge of the fourth sheet of paper P reaches each line head 15Y, 15B, 15C, and 15M, the control unit 38 starts the ink droplet ejection operation of each line head 15Y, 15B, 15C, and 15M based on the raster data of each color (S205).

[0086] In this embodiment, if the width of a blank sheet of paper P is narrower than the width of the paper size indicated by the print job to be executed before the sheet of paper P is applied, the print queue of each line head 15Y, 15B, 15C, and 15M sets the width information of the sheet of paper P in association with the print job to be executed, and based on the width information of the sheet of paper P set in the print queue of each line head 15Y, 15B, 15C, and 15M, the masking process is performed to narrow the color image of the print job to be executed in the width direction of the sheet of paper P. As a result, the images of each color indicated by the raster data of each color related to another print job do not extend beyond the width direction of the sheet of paper P, but the width of the images of each color is not narrowed. In other words, according to this embodiment, when multiple sheets of paper P are transported in succession and each color image is formed on each sheet of paper P, the ink ejection width is narrowed to match the width of the sheet of paper P for sheets of paper P that are not wide enough, while image formation is performed as planned for sheets of paper P that are wide enough.

[0087] In the above embodiment, a CIS is used as an example of the paper width sensor 33. Since this paper width sensor 33 detects both edges of the paper P, it is preferable that it has a length that exceeds the width of the paper P, as described above, but it is also possible to use a paper width sensor 33 that is shorter than the width of the paper P. In this case, a mechanism is provided to move the paper width sensor 33 in the width direction of the paper P, and the paper width sensor 33 is moved in the width direction to detect one edge of the paper P, and the width of the paper P is calculated based on the distance the paper width sensor 33 is moved and the position of the one edge of the paper P detected by the paper width sensor 33.

[0088] Furthermore, the configurations and processes of the embodiments described above using Figures 1 to 5B are merely examples of the present invention, and the present invention is not intended to be limited to these configurations and processes. [Explanation of Symbols]

[0089] 10. Inkjet recording device 11 Image reading unit 12 Image forming unit 14 Paper feed section 15Y, 15B, 15C, 15M Line Head 16 Conveyor Unit 33. Paper width sensor 34. Paper tip sensor 35 Storage section 36 Communications Department 37 Control Unit 38 Control Unit

Claims

1. A conveyor belt for transporting paper, A plurality of line heads are arranged at intervals along the paper transport direction and sequentially eject ink droplets of predetermined colors onto the paper to form a color image, A paper width sensor is positioned upstream of each line head in the paper transport direction and detects the width of the paper. For each line head, a print queue is set up indicating a queue for at least one print job to form the color image on the paper, and the print job is executed according to the print queue. If the paper width sensor determines that the paper width is narrower than the paper width used in the print job, then for each line head, width information indicating the detected paper width is set in the print queue of the line head, corresponding to the print queue before the execution. An inkjet recording apparatus comprising: a control unit that performs a masking process on the color image corresponding to the print queue before execution, based on the width information set in the print queue of each line head, to narrow the width of the paper in the width direction to the width indicated by the width information.

2. The inkjet recording apparatus according to claim 1, wherein the control unit determines whether there is a print queue one step prior to the print queue before execution in the print queue of each line head, and if it determines that there is no print queue one step prior, it performs a masking process to narrow the color image corresponding to the print queue before execution in the width direction of the paper based on the width information set in the print queue of each line head.

3. The control unit, If it is determined that there is a print queue immediately preceding the print queue before the execution, then for each line head, it is determined whether the immediately preceding print queue in the print queue of the line head has finished. The inkjet recording apparatus according to claim 2, which, if it is determined that the previous print queue has not finished, performs a masking process to narrow the color image corresponding to the print queue before execution in the width direction of the paper, based on the width information set in the print queue before execution, when the previous print queue has finished.

4. The inkjet recording apparatus according to claim 3, wherein, if the control unit determines that the previous print queue has finished, at the timing of determining that the previous print queue has finished, it performs a masking process to narrow the color image corresponding to the print queue before execution in the width direction of the paper, based on the width information set for the print queue before execution.

Images