Method for controlling image forming apparatus, image forming apparatus

Abstract

To properly correct a time interval of ejection of ink in an inkjet recording device in accordance with a pulse interval of a rotary encoder.SOLUTION: A processor 81 measures a pulse interval for each rotational phase of a rotary encoder 6 (S101). Further, the processor 81 cumulatively records, in a recording device, the pulse interval or a measured value which is a moving average deviation of the pulse intervals, associating the pulse interval or the measured value with the rotational phase, every time when the pulse intervals are measured (S105). Further, the processor 81 derives a reference value which is a representative value of the measured value corresponding to a plurality of cycle numbers predetermined for each rotational phase (S106). Further the processor 81 derives a correction value of the time interval of ejection of ink in an inkjet recording device in accordance with a difference between a new measured value and the reference value corresponding to the rotational phase which is common with the new measured value, every time when the new measured value is obtained (S201).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a control method for an image forming apparatus having a conveyor belt for conveying a sheet, and to an image forming apparatus. [Background technology]

[0002] An inkjet image forming apparatus includes an inkjet recording device that forms an image on a sheet by ejecting ink onto the sheet being transported. The image forming apparatus may include a transport belt that transports the sheet. The transport belt is rotatably supported by a plurality of support rollers.

[0003] The rotation speed of the conveyor belt varies due to various fluctuation factors, such as uneven rotation of a drive motor, or a load that the conveyor belt receives from the sheet when the sheet reaches the conveyor belt.

[0004] Fluctuations in the rotation speed of the conveyor belt result in fluctuations in the conveying speed of the sheet, and when the inkjet recording apparatus ejects ink at a predetermined reference interval in a case where the conveying speed of the sheet fluctuates, image distortion occurs.

[0005] Therefore, the image forming apparatus may include a rotary encoder attached to the support roller (see, for example, Patent Document 1). In this case, a pulse interval, which is the time interval between pulses output by the rotary encoder, is measured. Furthermore, the time interval of ink ejection of the inkjet recording device is corrected according to the difference between the pulse interval and the reference interval. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2008-132707 A Summary of the Invention [Problem to be solved by the invention]

[0007] The plurality of support rollers that support the conveyor belt include a drive roller and a driven roller. The drive roller is rotated by the drive motor. The driven roller rotates in accordance with the rotation of the conveyor belt.

[0008] The driven roller is an example of a rotating body that rotates in conjunction with the conveyor belt. Factors that cause fluctuations in the rotation speed of the driven roller include a load on the conveyor belt, factors related to the drive motor and the drive roller, and factors related to the driven roller.

[0009] For example, fluctuation factors related to the driven roller include the eccentric state of the rotation shaft of the driven roller, or vibration of the driven roller.

[0010] However, the fluctuation factors related to the driven roller do not affect the rotation speed of the conveyor belt, i.e., the fluctuation factors related to the driven roller do not affect the conveying speed of the sheet.

[0011] In addition, the rotary encoder may be attached to the driven roller. In this case, the pulse interval of the rotary encoder may fluctuate due to a cause unrelated to the conveying speed of the sheet. As a result, the time interval of ink ejection of the inkjet recording device may be erroneously corrected.

[0012] An object of the present invention is to provide a control method for an image forming device and an image forming device that can correctly correct the time interval of ink ejection of an inkjet recording device in accordance with the pulse interval of a rotary encoder when the rotary encoder is attached to a rotating body that rotates in conjunction with a conveying belt. [Means for solving the problem]

[0013] A control method for an image forming apparatus according to one aspect of the present invention is a method for controlling an image forming apparatus including a conveyor belt, an inkjet recording device, a rotating body, and a rotary encoder. The conveyor belt is an endless belt that is driven to rotate and convey a sheet. The inkjet recording device forms an image on the sheet by ejecting ink onto the sheet conveyed by the conveyor belt. The rotating body rotates in conjunction with the conveyor belt. The rotary encoder outputs a pulse every time the rotating body rotates by a predetermined unit angle. The control method includes a processor timing a pulse interval that is a time interval between the pulses output from the rotary encoder for each rotation phase of the rotary encoder. The control method further includes the processor accumulating and recording a timing value that is the pulse interval or a moving average value of the pulse interval in a storage device in association with the rotation phase every time the pulse interval is timed. The control method further includes the processor deriving a reference value that is a representative value of the timing value for a predetermined number of cycles for each rotation phase. The control method further includes the processor deriving, each time a new clock value is obtained, a correction value for the time interval of the ink ejection of the ink jet recording device in accordance with a difference between the new clock value and the reference value corresponding to the rotation phase common to the new clock values.The control method further includes the processor correcting the time interval of the ink ejection of the ink jet recording device in accordance with the correction value.

[0014] According to another aspect of the present invention, there is provided an image forming apparatus including the conveyor belt, the inkjet recording device, the rotating body, and the rotary encoder, and further including a processor for implementing the control method. Effect of the Invention

[0015] According to the present invention, it is possible to provide a control method for an image forming apparatus and an image forming apparatus that can correctly correct the time interval of ink ejection of an inkjet recording device in accordance with the pulse interval of a rotary encoder attached to a rotating body that rotates in conjunction with a conveying belt. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing the configuration of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is a block diagram showing the configuration of a control device in the image forming apparatus according to the embodiment. [Diagram 3] FIG. 3 is a diagram showing a configuration of a rotary encoder in the image forming apparatus according to the embodiment. [Figure 4] FIG. 4 is a flowchart showing an example of a procedure of pre-correction processing in the image forming apparatus according to the embodiment. [Diagram 5] FIG. 5 is a diagram showing an example of the configuration of the timing data and the reference data in the image forming apparatus according to the embodiment. [Figure 6] FIG. 6 is a flowchart showing an example of a procedure for interval correction control in the image forming apparatus according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the following embodiment is an example of the present invention, and is not intended to limit the technical scope of the present invention.

[0018] [Configuration of image forming apparatus 10] The image forming apparatus 10 according to the embodiment executes a print process for forming an image on a sheet 9.

[0019] As shown in FIG. 1, an image forming apparatus 10 includes a main body 1, a sheet storage unit 2, a sheet transport device 3, an inkjet recording device 4, a heater 5, and a control device 8.

[0020] The main body 1 is a housing. The sheet storage unit 2, the sheet transport device 3, the inkjet recording device 4, the heater 5, and the control device 8 are accommodated in the main body 1.

[0021] The sheet storage unit 2 is capable of storing a plurality of sheets 9. The sheet transport device 3 sends out the sheet 9 in the sheet storage unit 2 to a transport path 30 in the main body 1, and further transports the sheet 9 along the transport path 30.

[0022] The sheet conveying device 3 includes a sheet supplying device 31, a plurality of pairs of conveying rollers 32, a first belt conveying device 33, and a second belt conveying device .

[0023] The sheet supply device 31 feeds the sheets 9 in the sheet storage unit 2 one by one to the conveying path 30. A plurality of pairs of conveying rollers 32 convey the sheets 9 fed by the sheet supply device 31 along the conveying path 30, and further discharge the sheets 9 on which images have been formed from an outlet 30a of the conveying path 30.

[0024] A connecting unit (not shown) is connected to the main body 1. The connecting unit receives and accumulates the sheets 9 after image formation, which are discharged from the discharge port 30a of the conveying path 30.

[0025] The first belt transport device 33 is disposed at a print position in the transport path 30. The first belt transport device 33 takes over transport of the sheet 9 from some of the plurality of transport roller pairs 32 at the print position.

[0026] Further, the first belt conveying device 33 conveys the sheet 9 to a drying position in the conveying path 30. The drying position is a position in the conveying path 30 subsequent to the printing position.

[0027] The first belt conveyor device 33 includes an endless conveyor belt 331, a plurality of support rollers 332 and 333, and a drive motor 334. The plurality of support rollers 332 and 333 support the conveyor belt 331 so as to be rotatable.

[0028] The conveyor belt 331 is rotated by a drive motor 334. The conveyor belt 331 conveys the sheet 9 with the sheet 9 placed on its upper surface.

[0029] The second belt conveying device 34 takes over the conveyance of the sheet 9 from the first belt conveying device 33. Furthermore, the second belt conveying device 34 conveys the sheet 9 from the drying position in the conveying path 30 to a further subsequent stage.

[0030] The inkjet recording device 4 forms an image on the sheet 9 by ejecting ink onto the sheet 9 conveyed by the conveyor belt 331 of the first belt conveyor device 33 .

[0031] The heater 5 heats the ink on the sheet 9 transported by the second belt transport device 34. In this way, the heater 5 dries the ink on the sheet 9.

[0032] The control device 8 executes various data processing and controls the image forming device 10 .

[0033] 2, the control device 8 includes a CPU (Central Processing Unit) 81 and peripheral devices of the CPU 81. The peripheral devices include a RAM (Random Access Memory) 82, a secondary storage device 83, a signal interface 84, and the like.

[0034] The secondary storage device 83 is a computer-readable non-volatile storage device. The secondary storage device 83 can store and update the computer programs and various data. For example, one or both of a flash memory and a hard disk drive are adopted as the secondary storage device 83.

[0035] The signal interface 84 converts signals output by various sensors into digital data, and transmits the converted digital data to the CPU 81. Furthermore, the signal interface 84 converts control commands output by the CPU 81 into control signals, and transmits the control signals to the devices to be controlled.

[0036] The control device 8 further includes a communication device 85. The communication device 85 is capable of communicating with another information processing device such as a host device. The host device transmits a print job to the image forming apparatus 10. The CPU 81 communicates with the information processing device through the communication device 85.

[0037] The CPU 81 is a processor that executes various types of data processing and control by executing computer programs. The RAM 82 is a computer-readable volatile storage device. The RAM 82 temporarily stores the computer programs executed by the CPU 81 and data that is output and referenced in the course of the CPU 81 executing various types of processing.

[0038] The CPU 81 includes a plurality of processing modules that are realized by executing the computer programs, including a main processing unit 8a, a transport control unit 8b, and a print control unit 8c.

[0039] The main processing unit 8a executes control to start various processes in response to an operation on an operating device (not shown) or in response to reception of data from another device. Furthermore, the main processing unit 8a also executes control of a display device (not shown).

[0040] The conveyance control unit 8b controls the sheet conveying device 3. In this way, the conveyance control unit 8b controls the sending out of the sheet 9 from the sheet storage unit 2 and the conveyance of the sheet 9. The print control unit 8c causes the inkjet recording device 4 to execute the print process in synchronization with the conveyance of the sheet 9 by the sheet conveying device 3.

[0041] In the first belt conveying device 33, the rotation speed of the conveyor belt 331 varies due to various fluctuation factors. For example, the fluctuation factors include uneven rotation of the drive motor 334, or a load that the conveyor belt 331 receives from the sheet 9 when the sheet 9 reaches the conveyor belt 331.

[0042] Fluctuations in the rotation speed of the conveyor belt 331 appear as fluctuations in the conveying speed of the sheet 9. When the conveying speed of the sheet 9 fluctuates, if the inkjet recording device 4 ejects ink at a predetermined reference interval, image distortion occurs.

[0043] Therefore, the image forming apparatus 10 includes a rotary encoder 6 attached to one of the plurality of support rollers 332, 333. A pulse interval, which is a time interval between pulses output by the rotary encoder 6, is measured. The time interval between ink ejection of the inkjet recording device 4 is corrected based on the pulse interval.

[0044] Meanwhile, the plurality of support rollers 332, 333 that support the conveyor belt 331 include a drive roller 332 and a driven roller 333. The drive roller 332 is rotated by a drive motor 334.

[0045] The driving roller 332 rotates the conveyor belt 331. That is, the driving motor 334 drives and rotates the conveyor belt 331 via the driving roller 332. The driven roller 333 rotates in accordance with the rotation of the conveyor belt 331.

[0046] The driven roller 333 is an example of a rotating body that rotates in conjunction with the conveyor belt 331. Factors that cause fluctuations in the rotation speed of the driven roller 333 include a load on the conveyor belt 331, and fluctuation factors related to the drive motor 334 and the drive roller 332. Furthermore, factors that cause fluctuations in the rotation speed of the driven roller 333 also include fluctuation factors related to the driven roller.

[0047] For example, fluctuation factors related to the driven roller 333 include the eccentric state of the rotation shaft 333a of the driven roller 333, vibration of the driven roller 333, and the like.

[0048] However, the fluctuation factors related to the driven roller 333 do not affect the rotation speed of the conveyor belt 331. In other words, the fluctuation factors related to the driven roller 333 do not affect the conveying speed of the sheet 9.

[0049] Furthermore, the rotary encoder 6 may be attached to the driven roller 333. In this embodiment as well, the rotary encoder 6 is attached to the rotation shaft 333a of the driven roller 333 (see FIG. 3).

[0050] 3, the rotary encoder 6 includes a pulse plate 61 and a detection sensor 62. The pulse plate 61 is connected to a rotation shaft 333a of the driven roller 333. As a result, the pulse plate 61 and the rotation shaft 333a of the driven roller 333 are integrally formed.

[0051] A plurality of marks 61a are formed at a constant pitch along the circumferential direction of the pulse plate 61. Each of the marks 61a is a thin line or a slit formed on the surface of the pulse plate 61.

[0052] The detection sensor 62 detects each of the marks 61a at a predetermined position. For example, the detection sensor 62 is a photosensor, a capacitance sensor, etc. The detection sensor 62 outputs a pulse every time it detects a mark 61a.

[0053] The position of each of the marks 61a corresponds to the rotation phase of the rotary encoder 6. The rotation phase of the rotary encoder 6 can also be said to be the rotation phase of the driven roller 333.

[0054] Every time the pulse plate 61 and the driven roller 333 rotate by a predetermined unit angle, one of the multiple marks 61a is detected by the detection sensor 62. When the number of marks 61a is (N+1), the unit angle is 180 / N (degrees).

[0055] Therefore, the rotary encoder 6 outputs a pulse every time the driven roller 333 rotates by the predetermined unit phase.

[0056] When the rotary encoder 6 is attached to the driven roller 333, the pulse interval of the rotary encoder 6 may fluctuate due to factors unrelated to the transport speed of the sheet 9. As a result, the time interval of ink ejection of the inkjet recording device 4 may be erroneously corrected.

[0057] If the time intervals for ink ejection from the inkjet recording device 4 are erroneously corrected, image distortion occurs.

[0058] The plurality of processing modules in the CPU 81 further includes a pre-processing unit 8d (see FIG. 2). The pre-processing unit 8d executes pre-correction processing, which will be described later. By executing the pre-correction processing, a reference value V2, which will be described later, is derived (see FIG. 4).

[0059] Furthermore, the print control unit 8c uses the reference value V2 to correct the time interval of ink ejection of the inkjet recording device 4 (see FIG. 4). This makes it possible to correctly correct the time interval of ink ejection of the inkjet recording device 4 in accordance with the pulse interval of the rotary encoder 6.

[0060] [Pre-correction processing] An example of the procedure of the pre-correction process will be described below with reference to the flowchart shown in FIG.

[0061] The pre-processing unit 8d executes the pre-correction process when the drive motor 334 operates. In the following description, S101, S102, ... represent identification codes of a plurality of steps in the pre-correction process.

[0062] In the pre-correction processing, the pre-processing unit 8d first executes the process of step S101. In the following description, the time interval of the pulses output from the rotary encoder 6 is referred to as a pulse interval IP1.

[0063] <Process S101> In step S101, the pre-processing unit 8d measures a pulse interval IP1 from when one of the pulses is output to when the next of the pulses is output from the rotary encoder 6. After that, the pre-processing unit 8d shifts the process to step S102.

[0064] <Process S102> In step S102, the preprocessing unit 8d updates the phase number i, and advances the process to step S103.

[0065] The phase number i is a number that identifies the rotational phase of the rotary encoder 6. For example, when the unit angle is 180 / N (degrees), the phase number i is any one of 1 to N. It can also be said that the phase number i is a number that identifies the rotational phase of the driven roller 333.

[0066] When the original phase number i is any one of 1 to (N-1), the pre-processing unit 8d updates the phase number i by adding 1 to the original phase number i. When the original phase number i is N, the pre-processing unit 8d updates the phase number i to 1.

[0067] Therefore, the phase number i is updated to 1 every time the driven roller 333 rotates once.

[0068] <Process S103> In step S103, the preprocessing unit 8d determines whether the updated phase number i is 1 or not.

[0069] When the pre-processing unit 8d determines that the updated phase number i is 1, the pre-processing unit 8d shifts the process to step S104. On the other hand, when the pre-processing unit 8d determines that the updated phase number i is 1, the pre-processing unit 8d shifts the process to step S105.

[0070] <Process S104> In step S104, the preprocessing unit 8d updates the cycle number j, and advances the process to step S105.

[0071] The cycle number j is a number that is updated within a range of 1 to M every time the driven roller 333 rotates once. M is a predetermined number of cycles. For example, M is an integer equal to or greater than 20 and less than 50. It can also be said that M is a predetermined number of rotations of the driven roller 333.

[0072] When the original cycle number j is any one of 1 to (M-1), the pre-processing unit 8d updates the cycle number j by adding 1 to the original cycle number j. When the original cycle number j is M, the pre-processing unit 8d updates the cycle number j to 1.

[0073] <Process S105> In step S105, pre-processing unit 8d records clock value V1 in secondary storage device 83. Clock value V1 is the pulse interval IP1 or a moving average value of pulse interval IP1 clocked in step S101. Thereafter, pre-processing unit 8d shifts the process to step S106.

[0074] In this embodiment, pre-processing unit 8d derives an exponential moving average of the pulse interval IP1 measured in step S101 as a measured value V1. Furthermore, pre-processing unit 8d records the derived measured value V1 in secondary storage device 83. The exponential moving average is an example of a moving average.

[0075] When the time count value V1 is a moving average of the pulse interval IP1, excessive changes in the time count value V1 caused by electrical noise occurring in the pulses are suppressed. In addition, by employing a process for deriving an exponential moving average of the pulse interval IP1, the memory capacity required for temporarily storing the pulse interval IP1 can be reduced. Note that the time count value V1 may be a weighted moving average of the pulse interval IP1.

[0076] As shown in FIG. 5, the preprocessing unit 8d accumulates and records in the secondary storage device 83 the clock values ​​V1 for at least the most recent predetermined number M of cycles for each phase number i through the process in step S105.

[0077] Therefore, a data area capable of recording at least N×M clock values ​​V1 is secured in the secondary storage device 83 as a storage area for the clock data D1 (see FIG. 5).

[0078] In the following description, the clock value V1 corresponding to the combination of phase number i and cycle number j is represented as V1(i,j).

[0079] In step S105, the preprocessing unit 8d records the clock value V1(i,j) in the storage area of ​​the secondary storage device 83 for the clock data D1.

[0080] <Process S106> In step S106, the preprocessing unit 8d derives a reference value V2(i) corresponding to the phase number i.

[0081] The reference value V2(i) is a representative value of the clock values ​​V1(i,1) to V1(i,M) of phase number i for a predetermined number M of cycles.

[0082] The pre-processing unit 8d associates the derived reference value V2(i) with the phase number i and records it in the secondary storage device 83 (see FIG. 5). As a result, the reference data D2 including the reference value V2 for each rotation phase of the rotary encoder 6 is recorded in the secondary storage device 83 (see FIG. 5).

[0083] In this embodiment, the preprocessing unit 8d derives the average value of the timing values ​​V1(i,1) to V1(i,M) of phase number i for a predetermined number M of cycles as the reference value V2(i).

[0084] Note that preprocessing unit 8d may derive a median or mode value of M clock values ​​V1(i,1) to V1(i,M) as reference value V2(i).

[0085] Furthermore, pre-processing unit 8d may derive, as reference value V2(i), an average value of the remaining part of M clock values ​​V1(i,1) to V1(i,M) after excluding some that satisfy a predetermined exclusion condition.

[0086] For example, the exclusion condition includes a first exclusion condition and a second exclusion condition. The first exclusion condition is that a predetermined number of values, counting from the maximum, are among M clock values ​​V1(i,1) to V1(i,M). The second exclusion condition is that a predetermined number of values, counting from the minimum, are among M clock values ​​V1(i,1) to V1(i,M).

[0087] Pre-processing unit 8d derives reference value V2(i) and then records reference value V2(i) in secondary storage device 83, and then transitions the process to step S101. As a result, each time rotary encoder 6 outputs the pulse, the processes of steps S101 to S106 are executed.

[0088] As described above, the pre-processing unit 8d measures the pulse interval IP1 for each rotation phase of the rotary encoder 6 (see step S101 in FIG. 4). As described above, the phase number i is a number that identifies the rotation phase.

[0089] Furthermore, each time a pulse interval IP1 is measured, the preprocessing unit 8d accumulates and records in the secondary storage device 83 a measured value V1 corresponding to the measured pulse interval IP1 in association with the rotation phase (see step S105 in FIG. 4 and FIG. 5).

[0090] Furthermore, pre-processing unit 8d derives a reference value V2(i) for each rotation phase (see step S106 in FIG. 4). As described above, reference value V2(i) is a representative value of clock values ​​V1(i,1) to V1(i,M) for a predetermined number of cycles M.

[0091] [Spacing correction control] The print control unit 8c executes interval correction control when causing the inkjet recording device 4 to execute the print process (see FIG. 6).

[0092] Hereinafter, a new clock value V1(i,j) obtained each time the rotary encoder 6 outputs a pulse will be referred to as a new clock value VI1. Also, a reference value V2(i) corresponding to the rotation phase common to the new clock value VI1 will be referred to as a corresponding reference value VI2 (see formula (1)).

[0093]

number

[0094] In the interval correction control, the print control unit 8c executes the process of step S201 and the process of step S202 shown in FIG.

[0095] The print control unit 8c executes the processes of steps S201 and S202 every time it causes the inkjet recording device 4 to eject ink. This adjusts the time until the inkjet recording device 4 next ejects ink.

[0096] <Process S201> In step S201, the print control unit 8c derives a correction value V3 according to the difference between the new clock value VI1 and the corresponding reference value VI2. The print control unit 8c derives a new correction value V3 every time a new clock value VI1 is obtained.

[0097] The correction value V3 is a value for correcting the time interval of ink ejection from the inkjet recording device 4.

[0098] For example, the print control unit 8c derives the correction value V3 by applying the new clock value VI1 and the corresponding reference value VI2 to the following formula (2). In formula (2), the reference value VS1 is a predetermined value. The reference value VS1 is a standard value of the pulse interval IP1.

[0099]

number

[0100] <Process S202> Furthermore, in step S202, the print control unit 8c corrects the time interval of ink ejection from the inkjet recording device 4 in accordance with the correction value V3.

[0101] For example, the print control unit 8c controls the inkjet recording device 4 so that the time interval between ink ejections becomes the corrected interval T1 derived by the following formula (3).

[0102]

number

[0103] In formula (3), the standard interval TS1 is the time interval of ink ejection corresponding to when the conveyor belt 331 of the first belt conveying device 33 rotates at a predetermined standard speed.

[0104] The pre-correction processing by the pre-processing unit 8d and the interval correction control by the print control unit 8c are an example of processing that realizes a control method of the image forming apparatus .

[0105] As described above, the fluctuation factors of the rotation speed of the driven roller 333 include fluctuation factors related to the driven roller 333. The fluctuation factors related to the driven roller 333 include the eccentric state of the rotation shaft 333a of the driven roller 333, the vibration of the driven roller 333, and the like.

[0106] The fluctuation in the rotation speed of the driven roller 333 caused by the driven roller 333 occurs periodically in the driven roller 333. That is, the fluctuation in the rotation speed of the driven roller 333 caused by the driven roller 333 appears repeatedly in each of the rotation phases of the driven roller 333.

[0107] On the other hand, fluctuations in the rotational speed of driven roller 333 that are not caused by driven roller 333 only appear with a low frequency in each of the rotational phases of driven roller 333. Therefore, fluctuations in the rotational speed of driven roller 333 that are not caused by driven roller 333 are reflected in only a small portion of the M clock values ​​V1(i,1) to V1(i,M) for each of the rotational phases.

[0108] In this embodiment, the reference value V2(i) for each rotation phase is, for example, an average value of the timing values ​​V1(i,1) to V1(i,M) for a predetermined number of cycles M for each rotation phase.

[0109] Therefore, the reference value V2(i) represents the fluctuation in the rotation speed of the driven roller 333 that is mainly caused by the driven roller 333. The fluctuation in the rotation speed represented by the reference value V2(i) has almost no effect on the rotation speed of the conveyor belt 331.

[0110] On the other hand, the new timing value V1(i,j) obtained for each rotation phase reflects both the fluctuation in the rotational speed of the driven roller 333 caused by the driven roller 333 and other fluctuations that affect the rotational speed of the conveying belt 331.

[0111] In this embodiment, the correction value V3 is a value based on the difference between the new clock value V1(i,j) and the reference value V2(i) corresponding to that clock value V1(i,j) (see equation (2)).

[0112] Therefore, the correction value V3 is a value that mainly reflects only the fluctuation that affects the rotation speed of the conveyor belt 331. In this embodiment, the time interval of ink ejection is corrected using such a correction value V3 (see formula (3)).

[0113] By adopting this embodiment, the time interval of ink ejection in the inkjet recording device 4 is correctly corrected in accordance with the pulse interval IP1 of the rotary encoder 6.

[0114] In this embodiment, the print control unit 8c executes the interval correction control at a period close to the standard interval TS1. Meanwhile, the preprocessing unit 8d derives the reference value V2 at a period close to the period represented by the reference value VS1. Here, the reference value V2 is not necessarily derived in synchronization with the period of the interval correction control.

[0115] Therefore, the print control unit 8c may correct the time interval of ink ejection after a new clock value V1(i,j) is generated and before a reference value V2(i) corresponding to the new clock value V1(i,j) is derived. In this case, the print control unit 8c derives a correction value V3 according to the difference between the new clock value V1(i,j) and the most recent reference value V2(i).

[0116] The most recent reference value V2(i) corresponds to the common rotation phase with the new clock value V1(i,j), i.e., the most recent reference value V2(i) corresponds to the common phase number i with the new clock value V1(i,j).

[0117] Furthermore, the most recent reference value V2(i) is derived just before a new reference value V2(i) is derived based on the new timing value V1(i,j).

[0118] Reference value V2(i) is not a value that changes significantly with each rotation of driven roller 333. Therefore, there is no particular problem if reference value V2(i) derived before reference value V2(i) corresponding to new timing value V1(i,j) is used to derive correction value V3. [Explanation of symbols]

[0119] 3: Sheet transport device 4: Inkjet recording device 6: Rotary Encoder 8: Control device 10: Image forming device 32: Transport roller pair 33: First belt conveyor 34: Second belt conveyor 81: CPU (processor) 331:Conveyor belt 332: Drive roller 333: Driven roller (rotating body) 333a : Rotating shaft 334: Drive motor

Claims

1. A method for controlling an image forming apparatus including: an endless conveyor belt that is driven to rotate and conveys a sheet; an inkjet recording device that forms an image on the sheet by ejecting ink onto the sheet conveyed by the conveyor belt; a rotating body that rotates in conjunction with the conveyor belt; and a rotary encoder that outputs a pulse each time the rotating body rotates by a predetermined unit angle, A processor measures a pulse interval, which is a time interval between the pulses output from the rotary encoder, for each rotation phase of the rotary encoder; the processor accumulates and records in a storage device a timed value that is the pulse interval or a moving average value of the pulse interval in association with the rotation phase each time the pulse interval is measured; The processor derives a reference value that is a representative value of the time measurement value for a predetermined number of cycles for each of the rotation phases; the processor derives a correction value for a time interval of ink ejection of the ink jet recording device according to a difference between the new clock value and the reference value corresponding to the rotation phase common to the new clock value each time the new clock value is obtained; and correcting a time interval of the ink ejection of the ink jet recording device in accordance with the correction value by the processor.

2. The method of controlling an image forming apparatus according to claim 1 , wherein the processor derives an exponential moving average of the pulse intervals as the time measurement value.

3. 3. The method of claim 1, wherein the processor derives an average value of the measured time values ​​for the plurality of cycles for each rotation phase as the reference value.

4. The control method for an image forming apparatus according to any one of claims 1 to 3, wherein the processor derives the correction value using a reference value that corresponds to the rotational phase common to the new clock value and that was derived before the new reference value was derived based on the new clock value.

5. an endless conveyor belt that is rotated and conveys a sheet; an inkjet recording device that forms an image on a sheet by ejecting ink onto the sheet being conveyed by the conveyor belt; A rotating body that rotates in conjunction with the conveyor belt; a rotary encoder that outputs a pulse every time the rotor rotates by a predetermined unit angle; An image forming apparatus comprising: a processor that realizes the method for controlling an image forming apparatus according to claim 1 .

6. a plurality of support rollers that rotatably support the conveyor belt; The plurality of support rollers include a drive roller that is rotated by a motor and a driven roller that rotates in response to the rotation of the conveyor belt, The image forming apparatus according to claim 5 , wherein the rotating body is the driven roller.

Images