Image forming device

Abstract

To execute flushing at appropriate timing in a case of performing flushing via a flushing opening formed on a conveyor belt.SOLUTION: A conveyor belt 2 includes plural sets of flushing openings 31 and a belt home position hole 32. A discharge timing control unit specifies an interval of a detection timing of the belt home position hole 32 by an image sensor 29 for each detection timing, specifies a reference interval from the specified interval L for the plurality of detection timings, generates a flushing timing corresponding to the detection timing of the belt home position hole 32 when the belt home position hole 32 is detected in a detection period of the prescribed length including the reference timing after the reference interval from the detection timing Td of the belt home position hole 32, and causes a print engine to execute flushing at the flushing timing.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] In inkjet recording devices such as inkjet printers, the ink may thicken due to drying, causing the nozzles of the recording head to become clogged. Therefore, flushing is performed to eject and discard the thickened ink. In some image forming devices, holes or slits are provided in the conveyor belt, and ink is ejected through the holes or slits to perform flushing (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-113690 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-062887 Summary of the Invention [Problem to be solved by the invention]

[0004] When flushing is performed by ejecting ink from a nozzle through an opening as described above, it is necessary to identify the timing at which the opening is positioned directly below the nozzle in the transport direction (sub-scanning direction) during the rotation of the transport belt.

[0005] For example, a belt home position hole is provided in the conveying belt, and the timing at which the opening is located directly below the nozzle is determined based on the detection timing of the belt home position hole at a predetermined position, the relative distance (known) between the belt home position hole in the conveying direction and the opening corresponding to the nozzle, the relative distance (known) between the detection position of the belt home position hole in the conveying direction and the nozzle, and the linear speed (known) of the conveying belt.

[0006] When the timing at which the opening is positioned directly below the nozzle is identified in this way, foreign matter such as a piece of paper that is attached at a position other than the belt home position hole may be falsely detected as the belt home position hole, or the belt home position hole may not be detected due to foreign matter that is attached at the position of the belt home position hole. In such cases, flushing may not be performed at the appropriate time, and ink may be ejected onto the conveyor belt.

[0007] The present invention has been made in consideration of the above problems, and aims to provide an image forming device that performs flushing at an appropriate timing when flushing is performed through a flushing opening formed in a conveying belt. [Means for solving the problem]

[0008] The image forming apparatus according to the present invention includes a conveyor belt for conveying a print sheet, a print engine having a plurality of nozzles arranged in a main scanning direction and for ejecting ink from the nozzles onto the print sheet, and a discharge timing control unit for controlling ink discharge timing of the print engine. The conveyor belt includes a plurality of sets of flushing openings and a belt home position hole, and the discharge timing control unit (a) determines, for each timing at which the belt home position hole is detected by a sensor installed at a predetermined position, an interval between the timing at which the belt home position hole is detected and the timing at which the belt home position hole was last detected, (b) determines a reference interval from the intervals determined for the plurality of timings, and (c) when the belt home position hole is detected within a predetermined detection period that includes the reference interval after the timing at which the belt home position hole is detected, generates flushing timing for the nozzles that should perform flushing corresponding to the detection timing of the belt home position hole, and causes the print engine to perform flushing of the nozzles at the flushing timing. [Effects of the Invention]

[0009] According to the present invention, an image forming apparatus can be obtained that performs flushing at an appropriate timing when flushing is performed through a flushing opening formed in a conveyor belt.

[0010] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a side view illustrating the mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of the image forming apparatus shown in FIG. [Figure 3] FIG. 3 is a diagram showing an example of the conveyor belt 2 in FIG. [Figure 4] FIG. 4 is a block diagram showing the electrical configuration of the image forming apparatus 10 according to the embodiment of the present invention. [Figure 5] FIG. 5 is a diagram illustrating the reference interval Lbase of the detection timing of the belt home position hole 32 in FIG. 3, and the detection period of the belt home position hole 32 based on the reference interval Lbase. [Figure 6] FIG. 6 is a diagram for explaining determination of the reference interval Lbase when false detection of the belt home position hole 32 in FIG. 3 occurs. [Figure 7] FIG. 7 is a diagram for explaining a process to be performed when false detection of the belt home position hole 32 in FIG. 3 occurs. [Figure 8] FIG. 8 is a diagram for explaining a process to be performed when the belt home position hole 32 in FIG. 3 is not detected. [Figure 9] FIG. 9 is a diagram for explaining the process when the belt home position hole 32 in FIG. 3 is not detected consecutively. [Figure 10] FIG. 10 is a diagram for explaining the details of the detection of the belt home position hole 32 in FIG. [Figure 11] FIG. 11 is a flowchart (1 / 2) illustrating the operation of the image forming apparatus 10 shown in FIGS. [Figure 12] FIG. 12 is a flowchart (2 / 2) illustrating the operation of the image forming apparatus 10 shown in FIGS. [Figure 13] FIG. 13 is a flowchart illustrating the details of the reference interval determination process (step S14) in FIG. [Figure 14] FIG. 14 is a flowchart illustrating the timing notification determination process (step S10) in FIG. 11 in detail. [Figure 15] FIG. 15 is a flowchart illustrating the details of the forced timing notification determination process (step S18) in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] Fig. 1 is a side view illustrating the mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention, and Fig. 2 is a plan view of the image forming apparatus shown in Fig. 1.

[0014] The image forming apparatus 10 according to this embodiment is a device such as a printer, a copier, a facsimile machine, or a multifunction machine, and in this embodiment is equipped with a line-head inkjet color printing mechanism.

[0015] The image forming apparatus 10 shown in FIG. 1 includes a print engine 10a and a sheet transport unit 10b. The print engine 10a physically prints an image to be printed on a print sheet (such as print paper). An ink cartridge is detachably attached to the print engine 10a, and the print engine 10a performs printing using ink supplied from the ink cartridge. The sheet transport unit 10b transports the print sheet to the print engine 10a.

[0016] In this embodiment, print engine 10a is equipped with line-head type inkjet recording units 1a to 1d corresponding to four ink colors: cyan, magenta, yellow, and black, and ink is ejected onto a print sheet by inkjet recording units 1a to 1d.

[0017] As shown in Figure 2, in this embodiment, each of the inkjet recording units 1a, 1b, 1c, and 1d has one or more (three in this example) head units 11. These head units 11 are arranged along the main scanning direction and are detachable from the device body. The head unit 11 (i.e., each of the inkjet recording units 1a, 1b, 1c, and 1d) has multiple nozzles arranged in the main scanning direction, and ejects ink from the nozzles onto a print sheet.

[0018] In this embodiment, the sheet conveying section 10b includes a circular conveying belt 2 arranged opposite the print engine 10a to convey the print sheet, a drive roller 3, a driven roller 4, and a tension roller 4a around which the conveying belt 2 is suspended, an adsorption roller 5 that nips the print sheet together with the conveying belt 2, a downstream conveying belt 6, and a dryer 7.

[0019] A drive roller 3, a driven roller 4, and a tension roller 4a rotate the conveyor belt 2. The print sheet 101 conveyed from a paper feed cassette 20 (described later) is nipped by an attraction roller 5, and the nipped print sheet 101 is conveyed by the conveyor belt 2 to the printing positions of the inkjet recording units 1a-1d in order, where an image of each color is printed by the inkjet recording units 1a-1d. The sheet sensor 2a detects the passage of the print sheet, and the current position of the print sheet on the conveyance path is determined based on the detection timing. The image is then printed at the appropriate position on the print sheet. After printing, the print sheet is discharged to a discharge tray 10c or the like by a subsequent conveyor belt 6. At this time, a dryer 7 dries the print sheet on which the ink has been discharged.

[0020] 3 is a diagram showing an example of the conveyor belt 2 in FIG. 1. The conveyor belt 2 is provided with a plurality of flushing openings 31. For example, as shown in FIG. 3, a plurality of flushing openings 31 are formed in the conveyor belt 2, and the flushing openings 31 are formed in at least two rows (two rows in FIG. 3) along the main scanning direction. In other words, there are flushing openings 31 arranged at different positions in the conveying direction. Furthermore, the plurality of flushing openings 31 are arranged so as to cover the entire range of the plurality of nozzles arranged in the inkjet recording units 1a to 1d in the main scanning direction (that is, so that there are no missing portions).

[0021] In addition, in the area other than the flushing opening 31, a belt home position hole 32 (described later) is provided ahead of the leading flushing opening 31 in the conveying direction, and sheet suction holes 33 are arranged approximately uniformly at a predetermined density.

[0022] 1, ink receiving units 8a to 8d are provided below the head unit 11 of the inkjet recording units 1a to 1d. Flushing (e.g., line flushing) for each nozzle of each of the inkjet recording units 1a, 1b, 1c, and 1d is performed when one of the flushing openings 31 is located directly below the head unit 11 of the inkjet recording units 1a, 1b, 1c, and 1d, and the ink ejected from the nozzles during flushing is received by the corresponding ink receiving unit 8a, 8b, 8c, and 8d through the flushing opening 31 and is then collected in a waste ink tank.

[0023] The sheet suction units 9 are arranged along the sheet transport path at a location other than the ink receiving units 8a to 8d. A negative pressure is applied to the sheet suction units 9, causing the print sheet to adhere to the transport belt 2 through the sheet suction holes. A negative pressure lower than that applied to the sheet suction units 9 is applied to the ink receiving units 8a to 8d.

[0024] Furthermore, the sheet transport unit 10b is equipped with a paper feed cassette 20 as a paper feed source. The paper feed cassette 20 stores print sheets 101, and a lift plate 21 pushes the print sheets 101 upward to abut against a pickup roller 22. The print sheets 101 placed in the paper feed cassette 20 are picked up one by one from above by the pickup roller 22 onto a paper feed roller 23. The paper feed roller 23 is a roller that transports the print sheets 101 fed from the paper feed cassette 20 by the pickup roller 22 onto a transport path one by one.

[0025] The transport rollers 27 are rollers that transport the print sheet 101 on a predetermined transport path. When the transported print sheet 101 is detected by the resist sensor 28a, the resist rollers 28 temporarily stop the print sheet 101 and transport the print sheet 101 to the print engine 10a (specifically, to the nip position between the attraction roller 5 and the transport belt 2) at the secondary paper feed timing. The secondary paper feed timing is specified by the control unit 81, which will be described later, so that an image is formed at a specified position on the print sheet 101.

[0026] Furthermore, an image sensor 29 is provided above the conveyor belt 2. The image sensor 29 is an optical sensor, for example, a line sensor (here, two CISs (Contact Image Sensors)) arranged along the main scanning direction. Also, a reference plate 29a of a predetermined color (a color different from the surface color of the conveyor belt 2) is arranged below the image sensor 29 and the conveyor belt 2. The image sensor 29 irradiates light onto the conveyor belt 2 using, for example, an LED, and detects the reflected light with each light-receiving element such as a photodiode, thereby identifying the color of each position within a predetermined range in the main scanning direction (here, the belt position detection area, belt home position hole detection area, and sheet outline detection area in FIG. 3).

[0027] The belt position detection area is an area for detecting the displacement of the conveying belt 2 in the main scanning direction, and is set so that both end edges of the conveying belt 2 are included in the belt position detection area even if the conveying belt 2 is displaced in the main scanning direction.

[0028] The belt home position hole detection area is an area for detecting the belt home position hole 32, and is set so that the belt home position hole 32 is included in the belt home position hole detection area even if the conveying belt 2 is displaced in the main scanning direction.

[0029] The sheet outer shape detection area is an area for detecting the outer shape of the print sheet 101 on the conveyor belt 2, and is set so that the print sheet 101 is included in the sheet outer shape detection area even if the conveyor belt 2 is displaced in the main scanning direction.

[0030] The belt home position hole 32 is detected based on an image (specifically, a belt home position hole detection area) captured by the image sensor 29. The (image of) the belt home position hole 32 is detected by the image sensor 29 in a color (the color of the reference plate 29a) different from the (image of) the surface of the conveyor belt 2, and the position of the (image of) the belt home position hole 32 is identified.

[0031] As shown in FIG. 3, the width of the inkjet recording units 1a, 1b, 1c, and 1d (i.e., the width of the nozzle array) is equal to or greater than the width of the print sheet 101, and the width of the array of flushing openings 31 is equal to or greater than the width of the inkjet recording units 1a, 1b, 1c, and 1d (i.e., the width of the nozzle array).

[0032] Fig. 4 is a block diagram showing the electrical configuration of image forming apparatus 10 according to an embodiment of the present invention. As shown in Fig. 4, image forming apparatus 10 includes a printing device 71 having the mechanical configuration shown in Figs. 1 and 2, as well as an operation panel 72, a storage device 73, an image reading device 74, and a processing unit 75.

[0033] The operation panel 72 is arranged on the surface of the housing of the image forming device 10 and is equipped with a display device 72a such as an LCD display and an input device 72b such as hard keys or a touch panel, and displays various messages to the user on the display device 72a and accepts user operations on the input device 72b.

[0034] The storage device 73 is a non-volatile storage device (such as a flash memory or a hard disk drive) that stores data, programs, and the like required for controlling the image forming apparatus 10.

[0035] The image reading device 74 is equipped with a platen glass and an automatic document feeder, and optically reads the image of a document placed on the platen glass or a document transported by the automatic document feeder, and generates image data of that image.

[0036] The arithmetic processing device 75 includes a computer that operates according to a program, an ASIC (Application Specific Integrated Circuit) that executes predetermined operations, and the like, and operates as various processing units. The computer includes a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and the like, and operates as various processing units (together with the ASIC as necessary) by loading a program stored in the ROM, storage device 73, etc. into the RAM and executing it on the CPU.

[0037] Here, the arithmetic processing unit 75 operates as a control unit 81 and an image processing unit 82 .

[0038] The control unit 81 controls the printing device 71 (print engine 10a, sheet conveying unit 10b, etc.) to execute a print job requested by a user. In this embodiment, the control unit 81 causes the image processing unit 82 to execute predetermined image processing, and controls the print engine 10a (head unit 11) to eject ink to form a print image on a print sheet. The image processing unit 82 executes predetermined image processing such as RIP (Raster Image Processing), color conversion, and halftoning on the image data of the image to be printed on the print sheet.

[0039] The control unit 81 causes the printing device 71 to print an image specified by the user. Specifically, the control unit 81 causes the print engine 10a to print a user's original image based on print image data specified by the user. The control unit 81 causes the print engine 10a to eject ink when printing the user's original image.

[0040] The control unit 81 also includes a discharge timing control unit 81a that controls the ink discharge timing of the print engine 10a. The discharge timing control unit 81a causes the print engine 10a to discharge ink from each nozzle at one of the flushing timings corresponding to each nozzle of the print engine 10a. This flushing is performed to discard ink that has thickened in the nozzles.

[0041] FIG. 5 is a diagram illustrating the reference interval Lbase of the detection timing of the belt home position hole 32 in FIG. 3, and the detection period of the belt home position hole 32 based on the reference interval Lbase.

[0042] Also, as shown in FIG. 5, for a nozzle that should be flushed, the ejection timing control unit 81a generates a flushing timing Tf for that nozzle from the timing Td at which the belt home position hole 32 is detected by the image sensor 29 installed at a predetermined position, and causes the print engine 10a to perform flushing of that nozzle at that flushing timing Tf.

[0043] For example, for each nozzle, a delay dt from the detection timing Td of the belt home position hole 32 to the flushing timing Tf is derived and set in advance, and the flushing timing Tf is derived from the detection timing Td based on the delay dt. Note that the delay dt is specified based on the relative distance (known) between the belt home position hole 32 in the conveying direction and the flushing opening 31 corresponding to the nozzle, the relative distance (known) between the image sensor 29 and the nozzle in the conveying direction, etc.

[0044] Before generating the flushing timing Tf (during the reference interval setting period in Figure 5), the ejection timing control unit 81a (a) determines the interval L(i) (i = 1, 2, ...) between the detection timing Td of the belt home position hole 32 and the previous detection timing Td for each timing Td at which the belt home position hole 32 is detected, and (b) determines the reference interval Lbase from the multiple (N, here three) intervals L(n), L(n-1), L(n-2) determined for the multiple timings Td.

[0045] In this embodiment, the ejection timing control unit 81a (a) determines whether the difference between the maximum and minimum values ​​of the intervals L(n-2), L(n-1), and L(n) determined for the most recent multiple timings (N times, here 3 times) is less than or equal to a predetermined threshold value THb, and (b) if the difference is less than or equal to the predetermined threshold value THb, sets the average value of the intervals determined for the multiple timings (here, (L(n-2) + L(n-1) + L(n)) / 3) to the reference interval Lbase.

[0046] FIG. 6 is a diagram illustrating how the reference interval Lbase is determined when a false detection of the belt home position hole 32 occurs in FIG. 3. For example, if a foreign object such as a piece of paper of the same color as the belt home position hole 32 adheres to the belt home position hole detection area (a location other than the belt home position hole 32), a false detection of the belt home position hole 32 occurs, as shown in FIG. 6. When a false detection of the belt home position hole 32 occurs, the difference described above increases. Therefore, if the difference is not equal to or less than the predetermined threshold THb, the ejection timing control unit 81a determines that a false detection of the belt home position hole 32 has occurred, derives the difference described above repeatedly at each detection timing Td until the difference becomes equal to or less than the predetermined threshold THb, and determines whether the difference is equal to or less than the predetermined threshold THb. When the difference becomes equal to or less than the predetermined threshold THb, the ejection timing control unit 81a sets the reference interval Lbase as described above and generates the flushing timing Tf after the reference interval Lbase is set (the flushing execution period in FIG. 6).

[0047] Then, after determining the reference interval Lbase, if the belt home position hole 32 is detected during a detection period that includes the detection timing Td of the belt home position hole 32 and the reference timing after the reference interval Lbase, the ejection timing control unit 81a generates a flushing timing Tf corresponding to the detection timing of the belt home position hole 32. In this embodiment, as shown in Fig. 5, the detection period is set to a period from a timing that is earlier than the reference timing (Td + Lbase) by the tolerance THi to a timing that is later than the reference timing (Td + Lbase) by the tolerance THi. Note that the tolerance THi is set so that ink passes through the flushing opening 31 even if the flushing timing Tf is deviated by the tolerance THi.

[0048] FIG. 7 is a diagram for explaining a process to be performed when false detection of the belt home position hole 32 in FIG. 3 occurs.

[0049] On the other hand, for example, as shown in FIG. 7, if the belt home position hole 32 is detected outside the above-mentioned detection period, the ejection timing control unit 81a determines that the detection is a false detection and does not generate the flushing timing Tf corresponding to the detection timing Td.

[0050] FIG. 8 is a diagram for explaining a process to be performed when the belt home position hole 32 in FIG. 3 is not detected.

[0051] On the other hand, if a foreign object such as a piece of paper that is the same color as the surface color of the conveyor belt 2 adheres to the belt home position hole 32, non-detection of the belt home position hole 32 (the belt home position hole 32 is not detected during the detection period) occurs, as shown in Figure 8. When non-detection of the belt home position hole 32 occurs, the ejection timing control unit 81a identifies the non-detection at the end of the detection period and generates flushing timing Tf corresponding to that point. In this case, the ejection timing control unit 81a may not generate flushing timing Tf corresponding to the end of the detection period.

[0052] In addition, in the case of no detection, as shown in Figure 8, the ejection timing control unit 81a sets the next detection period (from the point that is time Lbase-THi x 2 after the end of the detection period to the point that is time Lbase after the end of the detection period) to a timing that is earlier than the timing after the reference interval Lbase from the end of the detection period by the time width from the above-mentioned reference timing to the end of the detection period (i.e., the above-mentioned tolerance width THi) as the next reference timing.

[0053] Fig. 9 is a diagram for explaining the process when the belt home position hole 32 is not detected consecutively in Fig. 3. Note that Fig. 9 shows an example where no detection occurs twice consecutively, but the same process (described later) is also executed if no detection occurs three or more consecutive times.

[0054] For example, as shown in FIG. 9, if the belt home position hole 32 is not detected by the end of the detection period consecutively, the discharge timing control unit 81a repeatedly sets the next detection period to a timing that is earlier than the timing after the reference interval Lbase from the end of the detection period by the allowable width THi (i.e., the time width from the reference timing to the end of the detection period) as the next reference timing.

[0055] Here, a detailed description will be given of the detection of the belt home position hole 32. Fig. 10 is a diagram for explaining the details of the detection of the belt home position hole 32 in Fig. 3.

[0056] The ejection timing control unit 81a (a) repeatedly attempts to detect the left and right edges of an object in the image obtained by the image sensor 29, line by line; (b) if the left and right edges were not detected in the previous line but are detected in the current line, the position of the current line in the sub-scanning direction is set to the leading edge coordinate F_POS; and if the left and right edges were detected in the previous line but are not detected in the current line, the position of the current line in the sub-scanning direction is set to the trailing edge coordinate R_POS. In addition, the ejection timing control unit 81a (c) identifies the minimum value of the left edge coordinate LE_POS and the maximum value of the right edge coordinate RE_POS in the main scanning direction for the section from the leading edge coordinate to the trailing edge coordinate in the sub-scanning direction, determines the difference between the maximum and minimum values ​​as the main scanning direction size of the object, and determines the difference between the leading edge coordinate and the trailing edge coordinate as the sub-scanning direction size of the object, and (d) detects the object as the belt home position hole 32 if the main scanning direction size and the sub-scanning direction size are each within a predetermined range, and does not detect the object as the belt home position hole 32 if at least one of the main scanning direction size and the sub-scanning direction size is not within the predetermined range.

[0057] The left and right edges are defined as points where there is a change in pixel value that exceeds a predetermined threshold, and the edge closest to the origin in the main scanning direction is defined as the left edge, and the edge farthest from the origin is defined as the right edge. For example, as shown in Figure 10, the boundary between an object pixel PXobj and a background pixel PXbg is detected as the left or right edge.

[0058] Specifically, if the main scanning direction size is equal to or greater than the main scanning direction lower limit value EDG_HL and less than the main scanning direction upper limit value EDG_HH, and if the sub-scanning direction size is equal to or greater than the sub-scanning direction lower limit value EDG_VL and less than the sub-scanning direction upper limit value EDG_VH, the above-mentioned object is detected as the belt home position hole 32; otherwise, the above-mentioned object is not detected as the belt home position hole 32.

[0059] Next, the operation of the image forming apparatus will be described.

[0060] When printing an image, the ejection timing control unit 81a controls the print engine 10a to eject ink onto the print sheet from the nozzles of the inkjet recording units 1a, 1b, 1c, and 1d at the ink ejection timing for pixels in the image to which ink should be ejected.

[0061] Furthermore, the ejection timing control unit 81a determines the reference interval Lbase of the belt home position hole 32 before flushing, then repeatedly generates flushing timing based on the reference interval Lbase, and executes flushing at one of the flushing timings according to predetermined flushing conditions (such as the passage of a predetermined length of non-use time of the image forming apparatus 10). At this time, the ejection timing control unit 81a selects the nozzles to be flushed (some or all of the nozzles) and performs flushing for the selected nozzles. Specifically, when the image sensor 29 detects the belt home position hole 32 while the conveyor belt 2 is rotating, the ejection timing control unit 81a identifies the flushing opening 31 corresponding to the selected nozzle, and determines the flushing timing for each selected nozzle based on the relative position of the identified flushing opening 31-i with respect to the belt home position hole 32, etc. Then, when the flushing timing arrives for each nozzle, the ejection timing control unit 81a ejects ink to perform flushing.

[0062] Specifically, the ejection timing control unit 81a operates as follows.

[0063] 11 and 12 are flowcharts illustrating the operation of the image forming apparatus 10 shown in FIGS.

[0064] When the image forming apparatus 10 is started up or a printing operation is started, the ejection timing control unit 81a initializes the counters edg_cnt, L, and hp_cnt to zero, and also initializes the flags line_flushing_en and nondet_flag to False (step S1).

[0065] Here, the counter edg_cnt counts the number of lines including edges, the counter L counts the number of lines at the interval L, and the counter hp_cnt counts the number of times the belt home position hole 32 is detected. The flag line_flushing_en indicates whether the determination of the reference interval Lbase has been completed and the flushing execution period has started, and the flag nondet_flag indicates whether forced flushing timing due to non-detection has been generated. The flag nondet_flag is reset to False when normal flushing timing based on the detection of the belt home position hole 32 is generated.

[0066] The control unit 81 rotates the conveyor belt 2, and also controls the sheet conveying unit 10b to convey the print sheet 101 as necessary.

[0067] During the rotation of the conveyor belt 2, the control unit 81 acquires the image (image data) captured by the image sensor 29, and the ejection timing control unit 81a selects each line of the image as a target line one by one in the sub-scanning direction. Then, the ejection timing control unit 81a executes the following process for the target line.

[0068] First, the ejection timing control unit 81a attempts to detect the left and right edges of the line of interest (step S2), and determines whether or not the left and right edges have been detected (step S3).

[0069] When the above-mentioned left edge and right edge are detected, the ejection timing control unit 81a identifies the coordinates of the detected left edge and right edge, and (a) if the above-mentioned left edge and right edge are not detected on the previous line, the ejection timing control unit 81a initially sets the coordinates as the minimum coordinate value of the left edge and the maximum coordinate value of the right edge, and (b) if the above-mentioned left edge and right edge are detected on the previous line, if the coordinate of the left edge is smaller than the minimum coordinate value of the left edge up to the previous time, the ejection timing control unit 81a updates the minimum coordinate value of the left edge with the coordinate of the left edge, otherwise, leaves the minimum coordinate value of the left edge as it is, and if the coordinate of the right edge is larger than the maximum coordinate value of the right edge up to the previous time, the ejection timing control unit 81a updates the maximum coordinate value of the right edge with the coordinate of the right edge, otherwise, leaves the maximum coordinate value of the right edge as it is (step S4).

[0070] Furthermore, when the above-mentioned left edge and right edge are detected, the ejection timing control unit 81a counts up the counter edg_cnt and the counter L by 1 (step S5).

[0071] On the other hand, if the above-mentioned left edge and right edge are not detected on the current line of interest, the ejection timing control unit 81a determines whether the counter edg_cnt is greater than 0 (i.e., whether the left and right edges are detected on the previous line) (step S6).

[0072] If the counter edg_cnt is greater than 0 (that is, if the left and right edges were detected on the previous line but not on the current target line, and the end of the object in the sub-scanning direction was detected), the ejection timing control unit 81a performs belt home position hole identification processing for the object (step S7) and determines whether or not the belt home position hole 32 was detected (step S8). Specifically, as described above, if the minimum left edge coordinate value and maximum right edge coordinate value for the object are within a predetermined range, the object is detected as the belt home position hole 32.

[0073] Then, if the belt home position hole 32 is detected, it is determined whether the flag line_flushing_en is True (i.e., whether the reference interval Lbase has been determined and the generation of flushing timing is permitted) (step S9).

[0074] If the flag line_flushing_en is True, the ejection timing control unit 81a determines whether to generate flushing timing Tf corresponding to the detected belt home position hole 32 and notify the print engine 10a (step S10).

[0075] If it is determined that the flushing timing Tf should be generated and notified to the print engine 10a, the ejection timing control unit 81a generates the flushing timing Tf corresponding to the nozzles to be flushed and notifies the print engine 10a (step S11).

[0076] After generating the flushing timing Tf and notifying the print engine 10a, the ejection timing control unit 81a resets the counter L and the counter edg_cnt to zero (steps S12 and S13).

[0077] On the other hand, in step S9, if the flag line_flushing_en is not True, the reference interval Lbase has not yet been determined, so the ejection timing control unit 81a determines whether the reference interval Lbase can be properly obtained as described below (step S14).

[0078] If it is determined that the reference interval Lbase is properly obtained, the ejection timing control unit 81a derives and sets the reference interval Lbase, and sets the flag line_flushing_en to True (step S15). Then, after setting the reference interval Lbase, the ejection timing control unit 81a resets the counter L and the counter edg_cnt to zero (steps S12 and S13).

[0079] On the other hand, if the counter edg_cnt is not greater than 0 in step S6 (i.e., the counter edg_cnt is 0 and no left or right edges have been detected on the previous line), the ejection timing control unit 81a counts up the counter L by 1 (step S16) because an object such as the belt home position hole 32 has not been detected.

[0080] In this way, the reference interval Lbase is set, the flushing timing is generated, etc. Furthermore, whether or not to forcibly generate the flushing timing when no detection occurs is determined as follows.

[0081] First, the ejection timing control unit 81a determines whether the flag line_flushing_en is True (i.e., whether the reference interval Lbase has been determined and the generation of flushing timing is permitted) (step S17), and if the flag line_flushing_en is True, determines whether non-detection of the belt home position hole 32 has been detected and whether a forced timing notification should be sent (step S18).

[0082] If it is determined that forced timing notification is to be performed, the ejection timing control unit 81a generates flushing timing Tf corresponding to the nozzles to be flushed and notifies the print engine 10a (step S19). After generating the flushing timing Tf and notifying the print engine 10a, the ejection timing control unit 81a resets the counter L to zero (step S20).

[0083] Here, if the flag line_flushing_en is not True, or if it is determined that the forced timing notification is not to be performed, the processes of steps S19 and S20 are skipped.

[0084] Then, the ejection timing control unit 81a determines whether the operation of the conveying belt 2 etc. has ended (whether the target line is the last line of the image obtained from the image sensor 29) (step S21), and if the operation has ended, ends the processing; if not, it sets the target line as the next line (step S22), returns to step S2, and performs the subsequent processing in the same way on the new target line.

[0085] In this way, flushing timing is generated when no detection occurs, as needed.

[0086] Here, the reference interval determination process (step S14) will be described in detail. Fig. 13 is a flowchart illustrating the reference interval determination process (step S14) in Fig. 11 in detail.

[0087] In the reference interval determination process (step S14), as shown in FIG. 13, the ejection timing control unit 81a first stores the current value of the counter L for measuring the interval between the belt home position holes 32 in a storage device such as RAM (step S41), and then counts up the counter hp_cnt, which counts the number of times the belt home position holes 32 are detected, by 1 (step S42).

[0088] Furthermore, the discharge timing control unit 81a determines whether the counter hp_cnt is greater than or equal to a predetermined value N (here, N=3) (step S43), and if the counter hp_cnt is greater than or equal to the predetermined value N, derives the difference between the maximum and minimum values ​​of the counter L values ​​(N stored values) when the belt home position hole 32 was detected the most recent N times (step S44).

[0089] Then, the ejection timing control unit 81a determines whether the difference is equal to or less than a predetermined threshold value TH_j (step S45), and if the difference is equal to or less than the predetermined threshold value TH_j, determines that the reference interval Lbase can be properly obtained from the value of the counter L when the belt home position hole 32 was detected the most recent N times (step S46).

[0090] On the other hand, if the difference is not less than the threshold value TH_j (step S45), and if the counter hp_cnt is not greater than N, the ejection timing control unit 81a determines that the reference interval Lbase can be properly obtained from the value of the counter L when the belt home position hole 32 was detected the most recent N times (step S47).

[0091] In this way, if there is little variation in the value of the counter L when the belt home position hole 32 is detected the most recent N times, it is determined that the reference interval Lbase is properly obtained.

[0092] Here, the timing notification determination process (step S10) will be described in detail. Fig. 14 is a flowchart illustrating the timing notification determination process (step S10) in Fig. 11 in detail.

[0093] In the timing notification determination process (step S10), as shown in FIG. 14, the ejection timing control unit 81a first determines whether or not a flag nondet_flag indicating whether or not a forced timing notification has been performed is False (step S51).

[0094] If the flag nondet_flag is False, the ejection timing control section 81a sets (Lbase-THi) to Lbase_min at the start of the detection period, and sets (Lbase+THi) to Lbase_max at the end of the detection period (step S52).

[0095] On the other hand, if the flag nondet_flag is not False, the ejection timing control unit 81a sets the start point Lbase_min of the detection period to (Lbase-THi×2) and sets the end point Lbase_max of the detection period to Lbase (step S53). In other words, if no detection is detected, it is estimated that the previous reset timing of the counter L is delayed by THi, so the detection period is advanced by THi.

[0096] Then, the ejection timing control unit 81a determines whether the current value of the counter L is equal to or greater than Lbase_min and equal to or less than Lbase_max (that is, whether the current time is within the detection period) (step S54).

[0097] If the current value of the counter L is greater than or equal to Lbase_min and less than or equal to Lbase_max, the ejection timing control unit 81a determines that the print sheet 101 is not being transported (step S55), and determines to generate and notify the flushing timing (step S56), and sets the flag nondet_flag to False (step S57).

[0098] On the other hand, if the current value of the counter L is greater than or equal to Lbase_min and not less than or equal to Lbase_max (step S54), or if the print sheet 101 is being transported (step S55), the ejection timing control unit 81a determines not to generate and notify the flushing timing (step S58).

[0099] In this way, if the belt home position hole 32 is detected during the detection period, the flushing timing is generated and notified, and if the belt home position hole 32 is detected during a period other than the detection period, the flushing timing is not generated and notified.

[0100] Here, the forced timing notification determination process (step S18) will be described in detail. Fig. 15 is a flowchart illustrating the forced timing notification determination process (step S18) in Fig. 12 in detail.

[0101] In the forced timing notification determination process (step S18), as shown in FIG. 15, the ejection timing control unit 81a first determines whether a flag nondet_flag indicating whether a forced timing notification has been issued is False (step S61).

[0102] If the flag nondet_flag is False, the ejection timing control unit 81a sets the upper limit value L_limit of the detection interval L to (Lbase+THi) (step S62). On the other hand, if the flag nondet_flag is not False, the ejection timing control unit 81a sets the upper limit value L_limit of the detection interval L to Lbase (step S63). Note that here, the upper limit value L_limit is the same as the end of the detection period described above.

[0103] Then, the ejection timing control unit 81a determines whether the current value of the counter L is the upper limit value L_limit (step S64).

[0104] If the current value of the counter L is the upper limit value L_limit, the ejection timing control unit 81a determines that the print sheet 101 is not being transported (step S65), and determines to generate and notify the flushing timing (step S66), and sets the flag nondet_flag to True (step S67).

[0105] On the other hand, if the current value of the counter L is not the upper limit value L_limit (step S64) or if the print sheet 101 is being transported (step S65), the ejection timing control unit 81a determines not to generate and notify the flushing timing (step S68).

[0106] In this way, if the belt home position hole 32 is not detected by the end of the detection period, the flushing timing is forcibly generated and notified.

[0107] As described above, according to the embodiment, the conveyor belt 2 includes a plurality of sets of flushing openings 31 and belt home position holes 32. The ejection timing control unit 81a (a) determines, for each timing Td at which the belt home position hole 32 is detected by the image sensor 29 installed at a predetermined position, the interval L between the timing Td at which the belt home position hole 32 is detected and the timing Td at which the belt home position hole 32 was previously detected, (b) determines a reference interval Lbase from the interval L determined for each of the plurality of timings Td, and (c) if the belt home position hole 32 is detected within a predetermined detection period that includes the reference timing after the reference interval Lbase from the timing Td at which the belt home position hole 32 is detected, generates a flushing timing Tf for the nozzles for which flushing should be performed, corresponding to the detection timing Td of the belt home position hole 32, and causes the print engine 10a to perform flushing of the nozzles at the flushing timing Tf.

[0108] As a result, when flushing is performed through the flushing openings 21 formed in the conveyor belt 2, the flushing is performed at an appropriate timing.

[0109] It should be noted that various changes and modifications to the above-described embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the subject matter and without diminishing its intended advantages. In other words, it is intended that such changes and modifications be included within the scope of the claims.

[0110] For example, in the above embodiment, instead of providing the above-mentioned belt home position hole 32 separately from the flushing opening 31, one of the flushing openings 31 at the front in the conveying direction may be used as the belt home position hole. [Industrial Applicability]

[0111] The present invention is applicable to, for example, an inkjet type image forming apparatus. [Explanation of symbols]

[0112] 10 Image forming device 29 Image Sensor 31 Flashing opening 32 Belt home position hole 81a Discharge timing control section

Claims

1. a conveyor belt for conveying a print sheet; a print engine having a plurality of nozzles arranged in a main scanning direction and ejecting ink from the nozzles onto the print sheet; an ejection timing control unit that controls the ink ejection timing of the print engine; the conveyor belt has a plurality of sets of flushing openings and belt home position holes; the ejection timing control unit (a) specifies an interval between the timing at which the belt home position hole is detected by a sensor installed at a predetermined position and the timing at which the belt home position hole was last detected, for each timing at which the belt home position hole is detected; (b) specifies a reference interval from the intervals specified for the plurality of timings; and (c) when the belt home position hole is detected within a predetermined length of detection period including the reference timing after the reference interval from the timing at which the belt home position hole is detected, generates flushing timing for the nozzles for which flushing should be performed, corresponding to the detection timing of the belt home position hole, and causes the print engine to perform flushing of the nozzles at the flushing timing. An image forming apparatus comprising:

2. The image forming apparatus according to claim 1, characterized in that the ejection timing control unit (a) determines whether the difference between the maximum and minimum values ​​of the intervals identified for the most recent plurality of timings is equal to or less than a predetermined threshold value, (b) if the difference is equal to or less than the predetermined threshold value, sets the average value of the intervals identified for the plurality of timings to the reference interval, (c) repeats this for each timing until the difference becomes equal to or less than the predetermined threshold value, and determines whether the difference is equal to or less than the predetermined threshold value, and (d) generates the flushing timing after the reference interval is set.

3. The image forming apparatus according to claim 1, characterized in that the ejection timing control unit (a) generates the flushing timing corresponding to the end of the detection period if the belt home position hole is not detected by the end of the detection period, and (b) sets the next detection period to a timing that is earlier than the timing after the reference interval from the end of the detection period by the time width from the reference timing to the end of the detection period as the next reference timing.

4. The image forming apparatus according to claim 1, characterized in that, if the belt home position hole is not detected by the end of the detection period consecutively, the ejection timing control unit repeatedly sets the next detection period to a timing that is earlier than the timing after the reference interval from the end of the detection period by the time width from the reference timing to the end of the detection period as the next reference timing.

5. The ejection timing control unit (a) repeatedly attempts to detect the left edge and the right edge of an object for each line in the image obtained by the sensor; (b) when the left edge and the right edge are not detected in the previous line and the left edge and the right edge are detected in the current line, the position of the current line is set to a leading edge coordinate in the sub-scanning direction; when the left edge and the right edge are detected in the previous line and the left edge and the right edge are not detected in the current line, the position of the current line is set to a trailing edge coordinate in the sub-scanning direction; and (c) calculates a division from the leading edge coordinate to the trailing edge coordinate in the sub-scanning direction. the difference between the leading edge coordinate and the trailing edge coordinate in the main scanning direction is determined; the difference between the maximum and minimum values ​​is determined as the main scanning direction size of the object; and the difference between the leading edge coordinate and the trailing edge coordinate is determined as the sub-scanning direction size of the object; and (d) if the main scanning direction size and the sub-scanning direction size are each within a predetermined range, the object is detected as the belt home position hole; and if at least one of the main scanning direction size and the sub-scanning direction size is not within the predetermined range, the object is not detected as the belt home position hole.

Images