Image forming apparatus

Abstract

To provide an image forming apparatus that suppresses color shift in a sub-scanning direction caused by a change in frictional force of a primary transfer part due to a change in the amount of toner supplied to the primary transfer part.SOLUTION: The image forming apparatus includes an image forming portion (5) including an intermediary transfer belt (8) and a photosensitive drum (1) and configured to transfer a toner image from the photosensitive drum onto the intermediary transfer belt, a drum driving source (62) configured to drive the photosensitive drum, and a print ratio acquiring portion (200) configured to acquire print ratio information indicating a print ratio per unit area of the toner image formed by the image forming portion. And a control means (104) for adjusting the rotational speed difference between the photoreceptor drum and the transfer belt by controlling the drum driving source.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Conventional electrophotographic image forming devices, such as laser printers and copiers, employ an intermediate transfer method in which a toner image formed on a photosensitive drum is first transferred to an intermediate transfer belt, and then secondarily transferred to a recording material. During the image formation process of such image forming devices, the amount of toner present between the photosensitive drum and the intermediate transfer belt (the primary transfer section) varies depending on the image being printed. When the amount of toner changes, the frictional force acting on the primary transfer section changes, which in turn changes the rotational speed of the photosensitive drum and the intermediate transfer belt. If the speed of the photosensitive drum and the intermediate transfer belt fluctuates during image formation, the overlapping position of each color in the sub-scanning direction fluctuates, resulting in color misregistration.

[0003] To solve this problem, Patent Document 1 forms a toner image within the printing area and an additional toner image outside the printing area so that the amount of toner between the photosensitive drum and the intermediate transfer belt is equal to or greater than a predetermined amount. This keeps the amount of toner between the image carrier and the intermediate transfer body at a constant level and reduces color misregistration. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-164950 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the method of Patent Document 1, a toner image is formed outside the printing area, and therefore a toner image that is not placed on the recording material is formed outside the printing area, requiring extra toner and resulting in a large amount of toner consumption.

[0006] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide an image forming apparatus that suitably reduces color misregistration in the sub-scanning direction without consuming excess toner. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention has the following configuration: That is, an image forming apparatus includes a transfer belt onto which toner images of multiple colors are transferred in a superimposed manner, an image forming unit having a photosensitive drum and transferring the toner image on the photosensitive drum to the transfer belt, a drum drive source that drives the photosensitive drum, a print rate acquisition unit that acquires print rate information that indicates the print rate per unit area of ​​the toner image formed by the image forming unit, and control means that adjusts the difference in rotation speed between the photosensitive drum and the transfer belt by controlling the drum drive source based on the print rate information acquired by the print rate acquisition unit.

[0008] In order to achieve the above object, the present invention has the following configuration: an image forming apparatus including a transfer belt onto which toner images of multiple colors are transferred in a superimposed manner, an image forming unit having a photosensitive drum and transferring the toner image on the photosensitive drum to the transfer belt, a drum drive source that drives the photosensitive drum, a feature amount acquisition unit that acquires feature amount information that indicates feature amounts related to color shifts in images formed by the image forming unit, and control means that adjusts the difference in rotational speed between the photosensitive drum and the transfer belt by controlling the drum drive source based on the feature amount information acquired by the feature amount acquisition unit. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an image forming apparatus that can reduce color misregistration in the sub-scanning direction that varies depending on the printing rate without consuming excess toner. [Brief explanation of the drawings]

[0010] [Figure 1] Schematic cross-sectional view of an image forming apparatus [Figure 2] Block diagram showing the control system [Figure 3] A diagram illustrating the relationship between the printing rate and the amount of color misalignment in the sub-scanning direction. [Figure 4] Flowchart showing drum driving speed adjustment control in the first embodiment [Figure 5] Flowchart showing drum driving speed adjustment control in the second embodiment [Figure 6] Flowchart showing drum driving speed adjustment control in the third embodiment DETAILED DESCRIPTION OF THE INVENTION

[0011] [Example 1] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the components described in the embodiments are merely examples, and unless otherwise specified, the scope of the present invention is not intended to be limited to only those components.

[0012] <Image forming device> FIG. 1 shows an electrophotographic image forming apparatus 100 that forms multicolor images. Process stations (process cartridges) 5Y, 5M, 5C, and 5K are detachable image forming units. The four process stations 5Y, 5M, 5C, and 5K have the same structure but use different toner colors. The YMCK suffixes at the end of the reference numbers indicate the toner colors: yellow, magenta, cyan, and black (K). The YMCK suffixes will be omitted hereafter except when describing specific process stations. The toner container 23 is a container for holding toner. The photosensitive drum 1 is an image carrier that carries an electrostatic latent image or a toner image. The charging roller 2 uniformly charges the surface of the photosensitive drum 1. The exposure device 7 scans the surface of the photosensitive drum 1 with laser light corresponding to input image data, forming an electrostatic latent image corresponding to the image data on the surface of the photosensitive drum 1. The exposure device 7 is a narrowly defined image forming unit that forms the electrostatic latent image. The developing roller 3 develops the electrostatic latent image by adhering toner held in a toner container 23 to the electrostatic latent image, thereby forming a toner image. The primary transfer roller 6 transfers the toner image carried on the photosensitive drum 1 to the intermediate transfer belt 8. At a nip portion (secondary transfer position) formed by the secondary transfer roller 11 and the intermediate transfer belt 8, the multi-color toner image formed on the intermediate transfer belt 8 is secondarily transferred to the sheet P. The intermediate transfer belt 8 is stretched between a drive roller 9 and an opposing roller 10, and is rotated in the direction of arrow A by the drive roller 9. The primary transfer roller 6, opposing roller 10, and secondary transfer roller 11 rotate in conjunction with the rotation of the intermediate transfer belt 8.

[0013] A portion of the visible image is not transferred to the sheet P at the secondary transfer position and remains on the intermediate transfer belt 8. Since this visible image remaining on the belt is unnecessary, it is removed by a cleaning operation. In the cleaning operation, the unnecessary visible image is transported by the intermediate transfer belt 8 to the cleaning blade 21, scraped off by the cleaning blade 21, and collected in the waste toner container 22, thereby removing the visible image.

[0014] In this embodiment, in order to transfer almost all of the toner image carried on the photosensitive drum 1 to the intermediate transfer belt 8, the rotation speed of the photosensitive drum 1 is slower than the rotation speed of the intermediate transfer belt 8. Specifically, the photosensitive drum 1 is driven 2% slower than the intermediate transfer belt 8. This makes it possible to reduce the amount of toner (residual toner) remaining on the photosensitive drum 1 during primary transfer. For this reason, in this embodiment, a cleaning mechanism such as a cleaning blade for collecting residual toner on the photosensitive drum 1 is not provided.

[0015] The paper feed unit 12 sends the sheet P stored in the paper feed cassette 13 to a pair of conveying rollers 15 by a paper feed roller 14. The pair of conveying rollers 15 sends the sheet P to a pair of registration rollers 16. The pair of registration rollers 16 conveys the sheet P so that the leading edge of the sheet P reaches the secondary transfer position at the same time that the toner image conveyed by the intermediate transfer belt 8 arrives at the nip position with the secondary transfer roller 11.

[0016] The sheet P sandwiched between the intermediate transfer belt 8 and the secondary transfer roller 11 is sent to the fixing device 17. The fixing device 17 includes a fixing roller 18 and a pressure roller 19 for pressing against the fixing roller 18. The fixing roller 18 and pressure roller 19 of the fixing device 17 are arranged so that they can be rotated in the direction of the arrow by a fixing motor 61, which will be described later. The fixing roller 18 incorporates a fixing heater 30 and a temperature sensor 31 that measures the temperature of the fixing heater 30. The toner image is fixed to the sheet P by heating and pressurizing the sheet P. After image formation is complete, the sheet P is sent to the paper discharge rollers 20, which then discharge the sheet to the paper discharge tray 90.

[0017] <Control System> FIG. 2 illustrates a control system for controlling the image forming apparatus 100. The printer control unit 101 includes a CPU 104, a ROM (read-only memory), and a RAM (random access memory), all of which are not shown, and controls various units included in the image forming apparatus 100. The ROM stores a control program. The CPU 104 is connected to an image forming unit 110, a drive unit 111, and a sensor unit 112. The image forming unit 110 includes a fuser 17, an exposure device 7, a process station 5, and the like. The drive unit 111 is a drive circuit that drives a paper feed motor 60, a fuser motor 61, a drum drive motor 62, and an intermediate transfer belt drive motor 63 in accordance with instructions from the CPU 104. The paper feed motor 60 drives the paper feed roller 14, the pair of transport rollers 15, and the pair of registration rollers 16. The fuser motor 61 drives the fuser roller 18, the pressure roller 19, and the paper discharge roller 20. The drum drive motor 62 is a drum drive source that drives the photosensitive drum 1, the charging roller 2, and the developing roller 3. The intermediate transfer belt drive motor 63 drives the drive roller 9 .

[0018] The sensor unit 112 is connected to the registration sensor 25 and the discharge sensor 26 , and outputs detection signals output by the registration sensor 25 and the discharge sensor 26 to the CPU 104 .

[0019] The controller 102 converts the color space of image data and instructs the printer control unit 101 to print. The controller 102 is connected to the host computer 103 via a network, a printer cable, or the like. The controller 102 receives image information and print commands from the host computer 103. The controller 102 analyzes the image information, converts it into bitmap data, and transmits the bitmap data to the printer control unit 101 in synchronization with the TOP signal transmitted from the printer control unit 101. After analyzing and converting the image information into bitmap data, the controller 102 transmits printing information to the print control unit 101, which relates to the unit area on which toner is applied relative to the image size. The print control unit 101 sends the received printing information to the printing rate acquisition unit 200, which calculates the printing rate of the image to be formed. The drum drive speed adjustment unit 201 determines the speed at which the drive unit 111 drives the drum drive motor 62, using a method described below.

[0020] Printer control unit 101 may be realized by CPU 104 executing a control program. Some or all of the functions of printer control unit 101 may be realized by an application specific integrated circuit (ASIC). Some or all of the functions handled by CPU 104 may also be realized by hardware such as an ASIC or FPGA. FPGA is an abbreviation for field programmable gate array.

[0021] <Relationship between printing rate and sub-scanning color misalignment> The relationship between print rate and color misregistration will be explained using Figure 3. Figures 3(a) and 3(b) show the transition of sub-scanning color misregistration from the leading edge to the trailing edge of sheet P when two images with different print rates are printed without adjusting the drum drive speed in this embodiment. For images with a low print rate (approximately 0.5%), the sub-scanning color misregistration does not fluctuate much from the leading edge to the trailing edge of the paper, and the color misregistration amount stabilizes at about 50 μm. On the other hand, when the print rate increases to about 5%, the sub-scanning color misregistration amount fluctuates from the leading edge to the trailing edge of the paper, fluctuating by about 200 μm between sheets.

[0022] In this embodiment, this variation in sub-scanning color misregistration is influenced by variations in the frictional force acting on the primary transfer section where the photosensitive drum 1 and intermediate transfer belt 8 contact each other. It is known that the frictional resistance acting on the primary transfer section varies greatly depending on the presence or absence of toner. High frictional resistance occurs particularly when there is no toner before printing begins. Therefore, before printing, the intermediate transfer belt 8 is pulled backward in the transport direction by the photosensitive drum 1. When a toner image formed by process cartridge 5Y enters the primary transfer section under such conditions, the frictional resistance decreases, reducing the tension on the intermediate transfer belt 8, causing the intermediate transfer belt to advance slightly in the transport direction (slip). This causes the toner image formed by process cartridge 5Y to arrive slightly earlier than the images formed by other process stations, resulting in sub-scanning color misregistration. Because this phenomenon occurs at the primary transfer section of each process cartridge, process cartridge 5Y experiences slippage three times, 5M experiences slippage twice, and 5C experiences slippage once before the toner image reaches the primary transfer section of process cartridge 5K. Therefore, process cartridge 5Y is most affected by slippage.

[0023] The relationship between the print rate and the amount of sub-scanning color misregistration for process cartridge 5Y is shown in Figure 3(c). When the print rate is low (less than 0.5%), there is almost no sub-scanning color misregistration due to slippage, and the lower limit is determined by the amount of sub-scanning color misregistration due to other factors (for example, drum eccentricity). Furthermore, when the print rate exceeds 5%, the slippage that occurs at the primary transfer section saturates, and the amount of sub-scanning color misregistration no longer worsens.

[0024] Even when the printing rate is around 5%, sub-scanning color misalignment can be reduced by adjusting the drum drive speed, which will be described later. Figure 3(d) shows the amount of sub-scanning color misalignment when the drum drive speed adjustment control, which will be described later, is implemented. The amount of sub-scanning color misalignment, which was around 200 μm before the countermeasure, can be improved to around 50 to 100 μm by implementing this adjustment control.

[0025] <Drum drive speed adjustment control> The operation of the drum drive speed adjustment unit 201 of this embodiment will be described using the flowchart of Figure 4. When a print instruction is received from the host computer 103 to the controller 102, the controller 102 sends print information to the print control unit 101 along with an instruction to execute printing.

[0026] Upon receiving the print instruction, the print control unit 101 starts drum drive speed adjustment control S400. In S401, the print control unit 101 acquires the print rate R by the print rate acquisition unit 200 using the print information received from the controller 102. Here, the print rate R is calculated by adding together the areas of the toner images formed by the YMCK process cartridges relative to the area (unit area) of the sheet P to be printed, calculated from 0% to 100%. Therefore, in this embodiment, the value of R is 0% to 400%.

[0027] In S402 to S404, the print control unit 101 determines the drum drive speed using the printing rate R via the drum drive speed adjustment unit 201. In S402, the drum drive speed adjustment unit 201 determines whether the printing rate R is equal to or greater than a predetermined threshold value Th. In this embodiment, the threshold value Th is set to 3.5%, which is the printing rate at which sub-scanning color misregistration begins to exceed 150 μm. If it is determined in S402 that the printing rate R is less than the threshold value Th, the drum drive speed adjustment unit 201 sets the drum drive speed to the nominal design value in S403. Here, the drum drive speed is set to a speed 2% slower than the intermediate transfer belt drive speed. This increases the toner transfer efficiency in the primary transfer unit.

[0028] If the printing rate R is equal to or greater than the threshold value Th in S402, the drum drive speed adjustment unit 201 sets the drum drive speed in S404 to a speed closer to the intermediate transfer belt drive speed than in S403. Here, the drum drive speed is set to a speed 0.5% slower than the intermediate transfer belt drive speed. This significantly improves the amount of color misregistration in the sub-scanning direction, as shown in Figure 3(d). Note that it is known that performing S404 slightly reduces the toner transfer efficiency at the primary transfer unit. The small amount of residual toner that was not transferred adheres to the charging roller 2, but the amount is so small that it does not adversely affect the image.

[0029] In the first embodiment, a method for reducing color misregistration in the sub-scanning direction by adjusting the drum drive speed according to image coverage information has been described. This makes it possible to print with stable image quality with reduced color misregistration, regardless of the print image density (print coverage). While this embodiment determines whether or not to adjust the drum drive speed by setting a threshold value Th for the print coverage, it is also possible to use a method in which the drum drive speed is determined in stages using the print coverage as an input, or a method in which the drum drive speed is determined using a linear equation for the print coverage.

[0030] Furthermore, instead of adjusting the drum driving speed, the same effect can be obtained by lowering the speeds of the paper feed motor 60, the fixing motor 61, and the intermediate transfer belt 63 so that they approach the drum driving speed.

[0031] [Example 2] In the second embodiment, a countermeasure will be described for the case where the drum drive speed adjustment control described in the first embodiment causes a decrease in the efficiency of toner transfer from the photosensitive drum 1 to the intermediate transfer belt 8 during primary transfer, resulting in a large amount of residual toner remaining on the photosensitive drum 1. The configuration diagram of the second embodiment is the same as that shown in FIGS. 1 and 2 described in the first embodiment, and therefore a description thereof will be omitted. Note that the charging roller cleaning control described below is executed by the printer control unit 101.

[0032] <Charging roller cleaning control> If primary transfer continues with the photosensitive drum 1 and intermediate transfer belt 8 driven at approximately the same speed due to the drum drive speed adjustment control of the first embodiment, the residual toner may accumulate on the charging roller 2 via the photosensitive drum 1. If the charging roller 2 becomes contaminated with toner, the photosensitive drum 1 will gradually become non-uniformly charged, which may lead to image defects such as uneven image density.

[0033] Therefore, in this embodiment, the amount N of dirt on the charging roller 2 is estimated by performing the drum drive speed adjustment control, and the charging roller cleaning operation is performed when the amount N of dirt reaches a certain level or more, thereby preventing image damage.

[0034] Furthermore, when the charging roller cleaning operation is performed, the printing operation is interrupted, which has the adverse effect of reducing printing productivity. For this reason, in this embodiment, whether or not to perform the drum drive speed adjustment control can be specified in the print instruction from the controller 102. The controller 102 may determine whether or not to enable the drum drive speed adjustment control according to a user specification, or may determine whether or not to enable the drum drive speed adjustment control by detecting from the content of the printed image that the image is one in which color shift is not a problem (for example, office documents).

[0035] Next, the operation of the drum driving speed adjusting unit 201 and the charging roller cleaning control performed by the printer control unit 101 in this embodiment will be described with reference to the flowchart of FIG.

[0036] Upon receiving the print instruction, the print control unit 101 starts drum drive speed adjustment control S500. In S501, the print control unit 101 determines whether or not to adjust the drum drive speed using the valid / invalid information for the drum drive speed adjustment control received from the controller 102. If the designation is invalid in S501, the process proceeds to S504, where the drum drive speed is set to the nominal design value and printing is started. If the designation is valid in S501, the drum drive speed adjustment control is performed in S502 to S505. S502 to S505 are the same as S401 to S404 described with reference to FIG. 4 in the first embodiment, and therefore a description thereof will be omitted.

[0037] After adjusting the drum drive speed in S505, the printer control unit 101 starts the charge roller cleaning control S510 (FIG. 5B). In S511, the printer control unit 101 clears the current charge roller contamination amount N to 0 and waits for the start of image formation in S512. If the printer control unit 101 detects that image formation has been completed in S512, it checks in S513 whether there are any print instructions received from the controller 102. If it determines in S513 that there are still print instructions remaining and printing needs to continue, the printer control unit 101 increases the contamination amount N by ΔN in S514. ΔN is designed to be a value proportional to the amount of residual toner remaining in the primary transfer unit during image formation. In this embodiment, ΔN = sheet P area × average print rate R × coefficient K. The coefficient K is determined based on the speed changed by adjusting the drum drive speed. When the intermediate transfer belt drive speed is -0.5%, K = 0.001. For example, if the sheet area is A4 paper (210 mm x 296 mm), the average printing rate R=0.05, and the coefficient K=0.001, then ΔN=3.108.

[0038] In S515, the printer control unit 101 determines whether the updated amount of dirt N is equal to or greater than the threshold value Tn. If the amount of dirt N is less than the threshold value Tn, the process returns to S512 and waits for the next image formation. If the amount of dirt N is equal to or greater than the threshold value Tn, the charge roller cleaning operation of S516 to S518 is started. Here, the threshold value Tn is designed to be a value smaller than the amount of dirt N at the timing when image defects caused by dirt on the charge roller 2 occur, and in this embodiment, Tn=50. If the above-mentioned images with ΔN=3.108 are printed continuously, the charge roller cleaning operation will start when 16 sheets have been printed.

[0039] The printer control unit 101 temporarily suspends the printing operation in S516 and then starts the charge roller cleaning operation in S517. The charge roller cleaning operation performed by the printer control unit 101 is as follows. First, a cleaning bias is applied to the charge roller 2 and the primary transfer roller 6, respectively, and the photosensitive drum 1, charge roller 2, and intermediate transfer belt 8 are rotated to transfer the residual toner from the charge roller 2 to the photosensitive drum 1. Then, the exposure device 7 exposes the surface of the photosensitive drum 1 on which the residual toner is carried to laser light. This causes the residual toner to be transferred from the photosensitive drum 1 to the intermediate transfer belt 8 at the primary transfer section. The residual toner transferred to the intermediate transfer belt 8 is scraped off the surface of the intermediate transfer belt 8 by the cleaning blade 21 shown in FIG. 1 and collected in the waste toner container 22, completing the cleaning of the charge roller 1.

[0040] When the charging roller cleaning operation is complete, the printer control unit 101 proceeds to S518, resumes the interrupted printing operation, and returns to S511 to clear the amount of dirt N to 0. The printer control unit 101 repeats the processes of S511 to S518, and when it determines in S513 that there are no subsequent print instructions and that printing has ended, it performs the charging roller cleaning operation in S519 and ends the charging roller cleaning control S510.

[0041] In the above, in the second embodiment, a countermeasure was described for the case where charging roller contamination becomes a problem due to the effect of reducing the difference in rotation speed between the photosensitive drum and the intermediate transfer belt in order to reduce color misregistration. According to the second embodiment, the photosensitive drum speed is increased, and the degree of contamination of the charging roller is estimated from the number of sheets printed and the print rate, and cleaning control is performed before the contamination affects the printed image. As a result, printing control that achieves both color misregistration and image quality can be performed. Furthermore, if slight color misregistration is not a problem and productivity is to be prioritized, printing can be performed without reducing productivity by disabling the drum drive speed adjustment control.

[0042] [Example 3] In the third embodiment, a method for controlling the drum drive speed adjustment when images with high and low print rates are mixed, and adjustment of image forming conditions performed when adjusting the drum drive speed, will be described. The configuration diagram of the third embodiment is the same as that of the first embodiment shown in FIGS. 1 and 2, and therefore the description thereof will be omitted.

[0043] <What to do if the print rate changes during continuous printing> In this embodiment, a method for adjusting the drum drive speed when printing a job that includes a mixture of images with low and high coverage rates is described. When changing the drum drive speed during continuous printing, it is desirable to wait until all primary transfers of the images being printed are complete before changing the drum drive speed. In this embodiment, if it is necessary to change the drum drive speed during continuous printing, the image formation interval is widened to be equal to or greater than the distance from the latent image position of process cartridge 5Y to the primary transfer position of process cartridge 5K.

[0044] Changing the drum drive speed during continuous printing requires extending the image formation interval, reducing productivity. Therefore, in this embodiment, the conditions for switching the drum drive speed are changed to reduce the number of times the drum drive speed is changed. First, when a high-print-rate image is printed while continuously printing low-print-rate images, the color misregistration needs to be improved. Therefore, similar to the first embodiment, the drum drive speed is switched when the threshold value Th reaches 3.5% or higher. On the other hand, when the print rate changes from a high print rate to a low print rate, color misregistration does not worsen. Therefore, hysteresis is introduced so that the drum drive speed is not switched until the threshold value Th falls below 1.0%. This reduces the number of times the drum drive speed is switched. Furthermore, if information on multiple subsequent images is available in advance, the timing for switching the drum drive speed can be determined using print rate information for several sheets ahead, further reducing the number of times the drum drive speed is switched.

[0045] <Changing image formation conditions> When the distance between the position where the exposure device 7 forms the latent image and the primary transfer position is large relative to the rotational direction of the photosensitive drum 1, the transport time from the start of image formation until the leading edge of the image reaches the secondary transfer position varies significantly depending on the drum drive speed. Specifically, when the distance between the position where the exposure device 7 forms the latent image and the primary transfer position is 60 mm relative to the rotational direction of the photosensitive drum 1, the transport timing changes as follows: That is, when the drum drive speed is -2% of the intermediate transfer belt drive speed and -0.5% of the intermediate transfer belt drive speed, the transport timing to the secondary transfer position changes by approximately 0.9 mm. If adjusting the drum drive speed in this way affects image quality, image quality can be improved by changing the image formation conditions when the drum drive speed is adjusted. In this embodiment, the image formation conditions are changed so that the image writing timing is delayed by 0.9 mm when the drum drive speed is increased.

[0046] Changing the image forming conditions is not limited to adjusting the timing of image writing in the sub-scanning direction. For example, it is also possible to change the timing so as to advance the timing at which the leading edge of the paper reaches the secondary transfer position. Also, if the drum drive speed affects the amount of toner supplied from the developing roller 3, it is possible to improve image quality in terms of density by adjusting the bias applied to the developing roller 3.

[0047] <Flowchart of Example 3> The operation of the drum drive speed adjustment unit 201 of this embodiment and the drum drive speed adjustment control performed by the printer control unit 101 will be described using Figure 6. Upon receiving a print instruction, the print control unit 101 starts the drum drive speed adjustment control in S600. The drum drive speed adjustment control performed by the print control unit 101 in S601 to S603 and S605 is the same as S401 to S404 described in Figure 4 of the first embodiment, so a description thereof will be omitted.

[0048] If the printer control unit 101 sets the drum drive speed to the intermediate transfer belt drive speed -2% in S603, it sets the image formation condition C1 to match the selected drum drive speed in S604, and performs subsequent image formation. In this embodiment, as described above, the image formation condition C1 is the image write timing, and in S604, C1 is set to the design nominal timing. Furthermore, to optimize the drum speed switching frequency, it changes the threshold value Th used in S602 to Th1. In this embodiment, Th1 = 3.5%. If the printer control unit 101 sets the drum drive speed to the intermediate transfer belt drive speed -0.5% in S605, it sets the image formation condition C2 to match the selected drum drive speed in S606, and performs subsequent image formation. In S606, it sets the image formation condition C2, which is the image write timing, to a value 0.9 mm behind the design nominal timing. Furthermore, to optimize the drum drive speed switching frequency, it changes the threshold value Th used in S602 to Th2. In this embodiment, Th2 = 1.0%.

[0049] The printer control unit 101 waits for the start of the first image formation in S607, and once image formation has started, acquires subsequent image information in S608. If subsequent image information is available, the printer control unit 101 proceeds to S609 and recalculates the printing rate R from the subsequent image information. In S610, the printer control unit 101 performs the same determination as in S602 to determine whether the next drum drive speed to be selected is different from the current drum drive speed. If it is determined in S610 that a change in the drum drive speed is not necessary, the printer control unit 101 proceeds to S607 and waits for the start of the next image formation. If it is determined in S610 that a change in the drum drive speed is necessary, the printer control unit 101 proceeds to S611 and widens the image formation interval so that the start timing of the next image formation occurs after the primary transfer of the previous image has ended. Once the image formation interval has been widened and it is possible to switch the drum drive speed, the printer control unit 101 returns to S602. As a result, the printer control unit 101 adjusts the drum drive speed and changes the image formation conditions in S603 to S606, and then waits for the start of the next image formation in S607. When there is no more next image information in S608, the printer control unit 101 ends the processing of this flowchart.

[0050] As described above, in the third embodiment, when images with different printing rates are printed consecutively, the drum drive speed adjustment control switches the drum speed, widens the image formation interval, and switches the image formation conditions.

[0051] In the first to third embodiments, information on the printing rate R was used to determine whether or not to execute adjustment control of the drum drive speed. However, the present invention is not limited to this. For example, another index (image feature amount information) that indicates the tendency of the amount of applied toner on an image may be used. In this case, the printing rate acquisition unit 200 in FIG. 2 is replaced with a feature amount acquisition unit that acquires feature amounts related to the color shift of the image, and a determination is made as to whether or not to execute adjustment control of the drum drive speed based on the feature amount information acquired by the feature amount acquisition unit. For example, machine learning may be used to learn the printed image information as input and the amount of color shift in the sub-scanning direction as output, thereby determining the amount of color shift in the sub-scanning direction from the image information, and then determining whether or not to execute adjustment control of the drum drive speed.

[0052] [Other embodiments] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program.The present invention can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0053] [Note] The disclosure of the present embodiment also includes the following configuration examples and method examples.

[0054] (Item 1) a transfer belt onto which multiple color toner images are transferred in a superimposed manner; an image forming unit having a photosensitive drum and transferring a toner image on the photosensitive drum to the transfer belt; a drum drive source that drives the photosensitive drum; a printing rate acquisition unit that acquires printing rate information indicating a printing rate per unit area of ​​a toner image formed by the image forming unit; a control unit that adjusts the difference in rotation speed between the photosensitive drum and the transfer belt by controlling the drum drive source based on the printing rate information acquired by the printing rate acquisition unit; An image forming apparatus comprising:

[0055] (Item 2) The image forming apparatus according to item 1, characterized in that the control unit adjusts the speed of the drum drive source so as to reduce the difference in rotation speed between the photosensitive drum and the transfer belt when the printing rate information acquired by the printing rate acquisition unit exceeds a threshold value.

[0056] (Item 3) The image forming apparatus according to item 1, characterized in that the control means adjusts the speed of the drum drive source so that the difference in rotational speed between the photosensitive drum and the transfer belt becomes smaller as the printing rate becomes higher.

[0057] (Item 4) The image forming apparatus according to any one of items 1 to 3, characterized in that the control unit adjusts the difference in rotational speed between the photosensitive drum and the transfer belt, and then performs cleaning control of the image forming unit according to the amount of dirt on the image forming unit estimated when the image forming unit performs image formation.

[0058] (Item 5) The image forming apparatus according to any one of items 1 to 4, characterized in that the control means determines whether or not to adjust the difference in rotational speed between the photosensitive drum and the transfer belt in accordance with instructions from a host computer.

[0059] (Item 6) The image forming apparatus according to any one of items 1 to 5, characterized in that when a change in the printing rate acquired by the printing rate acquisition unit exceeds a threshold value during continuous printing, the control unit adjusts the difference in rotation speed between the photosensitive drum and the transfer belt by controlling the drum drive source after providing an interval for forming images in the image forming unit.

[0060] (Item 7) The image forming apparatus according to any one of items 1 to 6, characterized in that the control means performs control to adjust the difference in rotational speed between the photosensitive drum and the transfer belt, and also performs control to change image forming conditions.

[0061] (Item 8) a transfer belt onto which multiple color toner images are transferred in a superimposed manner; an image forming unit having a photosensitive drum and transferring a toner image on the photosensitive drum to the transfer belt; a drum drive source that drives the photosensitive drum; a feature amount acquiring unit that acquires feature amount information indicating feature amounts related to color misalignment of an image formed by the image forming unit; a control unit that adjusts the difference in rotation speed between the photosensitive drum and the transfer belt by controlling the drum drive source based on the feature information acquired by the feature acquisition unit; An image forming apparatus comprising: [Explanation of symbols]

[0062] 1 Photosensitive drum 2 Charging roller 3 Developing roller 7 Exposure equipment 8 Intermediate transfer belt 9 Drive roller 10 opposing roller 11 Secondary transfer roller 12 Paper feed unit 13 Paper cassette 18 Fuser roller 19 Pressure roller 20 Paper ejection roller 21 Cleaning blade 22 Waste toner container 23 Toner container 25 Cash register sensor 26 Emission sensor 30 Fixing heater 31 Temperature Sensor 60 Paper feed motor 61 Fuser motor 62 Drum drive motor 63 Intermediate transfer belt drive motor 90 Paper output tray 100 Image forming device 101 Printer control unit 102 Controller 103 Host Computer 110 Image forming unit 111 Drive unit 112 Sensor unit 200 Print rate acquisition section 201 Drum drive speed adjustment unit

Claims

1. a transfer belt onto which multiple color toner images are transferred in a superimposed manner; an image forming unit having a photosensitive drum and transferring a toner image on the photosensitive drum to the transfer belt; a drum drive source that drives the photosensitive drum; a printing rate acquisition unit that acquires printing rate information indicating a printing rate per unit area of ​​a toner image formed by the image forming unit; a control unit that adjusts the difference in rotation speed between the photosensitive drum and the transfer belt by controlling the drum drive source based on the printing rate information acquired by the printing rate acquisition unit; An image forming apparatus comprising:

2. The image forming apparatus according to claim 1, characterized in that, when the printing rate information acquired by the printing rate acquisition unit exceeds a threshold value, the control means adjusts the speed of the drum drive source so that the difference in rotational speed between the photosensitive drum and the transfer belt is reduced.

3. 2. The image forming apparatus according to claim 1, wherein the control means adjusts the speed of the drum drive source so that the difference in rotation speed between the photosensitive drum and the transfer belt becomes smaller as the printing rate increases.

4. The image forming apparatus according to claim 1, characterized in that the control means performs cleaning control of the image forming unit in accordance with the amount of dirt on the image forming unit estimated when the image forming unit performs image formation while performing control to adjust the rotational speed difference between the photosensitive drum and the transfer belt.

5. 2. The image forming apparatus according to claim 1, wherein the control means determines whether or not to adjust the difference in rotational speed between the photosensitive drum and the transfer belt in accordance with an instruction from a host computer.

6. 2. The image forming apparatus according to claim 1, wherein, when the printing rate acquired by the printing rate acquisition unit changes during continuous printing, the control unit adjusts the difference in rotation speed between the photosensitive drum and the transfer belt by controlling the drum drive source after leaving an interval between forming images in the image forming unit.

7. 2. The image forming apparatus according to claim 1, wherein the control means executes control to adjust the difference in rotation speed between the photosensitive drum and the transfer belt, and also executes control to change image forming conditions.

8. a transfer belt onto which multiple color toner images are transferred in a superimposed manner; an image forming unit having a photosensitive drum and transferring a toner image on the photosensitive drum to the transfer belt; a drum drive source that drives the photosensitive drum; a feature amount acquiring unit that acquires feature amount information indicating feature amounts related to color misalignment of an image formed by the image forming unit; a control unit that adjusts the difference in rotation speed between the photosensitive drum and the transfer belt by controlling the drum drive source based on the feature information acquired by the feature acquisition unit; An image forming apparatus comprising:

Images