Image forming apparatus, control method, and control program

Abstract

This suppresses variations in the peripheral velocity fluctuation period in each image carrier. [Solution] The system comprises an image carrier 41 on which toner images of each color are individually formed corresponding to multiple colors, a belt B facing each of the image carriers of each color arranged along the transport direction, an image carrier drive unit 411, 412 that individually drives each of the image carriers of each color, and a belt drive unit 463, 464 that transports the belt, a speed fluctuation period detection means 11 that detects the peripheral speed fluctuation period of each of the image carriers of each color, and an image carrier drive control unit 12 that adjusts the rotation speed of each of the image carriers of each color in order to reduce the difference in peripheral speed fluctuation periods of each of the image carriers of each color.

Description

[[Technical Field]]

[0001] The present disclosure relates to an image forming apparatus, a control method, and a control program. [[Background Art]]

[0002] A so-called tandem-type image forming apparatus in which drums for respective colors corresponding to a plurality of colors are arranged side by side in the conveying direction of a belt has been conventionally used. In this image forming apparatus, it is necessary to transfer toner images formed on the drums of respective colors onto the belt side in an overlapping manner at appropriate timing. For this reason, the drums of respective colors need to be rotated synchronously. On the other hand, drums are consumable parts that are more prone to deterioration than other components, and are generally replaced when deteriorated. For this reason, compared to drum holding units assembled on the premise that they are not removed, eccentricity due to clearance error is more likely to occur in the drum holding unit. This eccentricity has been a cause of periodic speed fluctuation on the outer circumference of the drum even when the drum maintains constant-speed rotation. Hereinafter, the speed fluctuation occurring on the outer circumference of the drum is referred to as outer circumferential speed fluctuation.

[0003] Fig. 9 is a diagram showing outer circumferential speed fluctuation, where the horizontal axis represents time and the vertical axis represents numerical values corresponding to the speed of the outer circumference of the drum. A solid line L3 and a dotted line L4 show a case where the phases of periodic outer circumferential speed fluctuation are shifted by half a period. The outer circumferential speed fluctuation in an eccentric drum forms a pattern that repeats increases and decreases with one rotation of the drum as one period. The phases of outer circumferential speed fluctuation in the drums of respective colors can vary, albeit to varying degrees. As shown in Fig. 9, when a half-period phase shift occurs between two drums, the speed difference between the outer circumferences becomes maximum, resulting in increased color misregistration, which can degrade the image quality of a formed image.

[0004] Accordingly, in the image forming apparatus disclosed in Patent Document 1, adjustment has been performed in which the phase of outer circumferential speed fluctuation of each drum is detected, and each drum is rotated to match the phases of outer circumferential speed fluctuation. [[Prior Art Documents]] [[Patent Documents]]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 09-146329 [Overview of the project] [Problems that the invention aims to solve]

[0006] The drum transfers toner by creating a slight speed difference between itself and the belt at their closest proximity. For this reason, the drum is coated with a lubricant on its outer surface to reduce electrostatic restraint with the belt and maintain rotation at the target speed. On the other hand, prolonged use can lead to deterioration or depletion of the lubricant, increasing the restraining force on the drum from the belt and causing a change in the period of fluctuation of the outer circumference speed of the drum. As a result, even when the phase of the peripheral speed fluctuations of each color drum was matched, the speed varied due to the mismatch in periods, and the degradation of image quality due to color shift could not be suppressed.

[0007] The objective of this disclosure is to improve the image quality of the formed image. [Means for solving the problem]

[0008] To solve the above problems, This disclosure relates to an image forming apparatus, An image carrier in which toner images of each color are individually formed to correspond to multiple colors, A belt is positioned opposite each of the image carriers of each color, which are arranged in the transport direction, and transfers the superimposed toner images of each color onto a recording medium. An image carrier drive unit that drives each of the aforementioned colored image carriers individually, The system includes a belt drive unit that transports the aforementioned belt, A velocity fluctuation period detection means for detecting the peripheral velocity fluctuation period in the image carrier of each color, The system includes an image carrier drive control unit that adjusts the rotation speed of each colored image carrier so that the difference in peripheral velocity fluctuation periods of each colored image carrier falls within a predetermined range.

[0009] Furthermore, this disclosure relates to a control method for an image forming apparatus, A control method for an image forming apparatus comprising: an image carrier on which toner images of each color are individually formed corresponding to multiple colors; a belt positioned opposite the image carriers of each color arranged along the transport direction, which transfers a superimposed toner image of the toner images of each color onto a recording medium; an image carrier drive unit for individually driving the image carriers of each color; a belt drive unit for transporting the belt; and a speed fluctuation period detection means for detecting the peripheral speed fluctuation period of the image carriers of each color, wherein The system is configured to adjust the rotation speed of each colored image carrier so that the difference in the peripheral velocity fluctuation period of each colored image carrier falls within a predetermined range.

[0010] Furthermore, this disclosure relates to a control program, A computer controls an image forming apparatus having an image carrier on which toner images of each color are individually formed corresponding to multiple colors; a belt positioned opposite each of the image carriers of each color arranged along the transport direction, which transfers the superimposed toner images of each color onto a recording medium; an image carrier drive unit that individually drives each of the image carriers of each color; a belt drive unit that transports the belt; and a speed fluctuation period detection means that detects the peripheral speed fluctuation period of each of the image carriers of each color. The system is configured to function as an image carrier drive control unit that adjusts the rotation speed of each colored image carrier so that the difference in peripheral velocity fluctuation periods of each colored image carrier falls within a predetermined range. [Effects of the Invention]

[0011] According to this disclosure, it is possible to improve the image quality of the formed image. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows a schematic configuration of the image forming apparatus according to this embodiment. [Figure 2] This is a functional block diagram showing the control structure of the image forming apparatus according to this embodiment. [Figure 3]FIG. 1 is a diagram illustrating a schematic configuration of a lubricant applying mechanism. [Figure 4] FIG. 2 is a circuit block diagram related to control of drive rollers that feed drums of respective colors and a belt in an image forming apparatus. [Figure 5] FIG. 3 is a view of the belt, the color registration sensor, and the determination mark for color registration correction as seen from the left side of the paper plane of FIG. 1. [Figure 6] FIG. 4 is an enlarged view, viewed from the same line of sight as FIG. 5, of a determination mark for color registration correction formed in a non-image forming area of the belt. [Figure 7] FIG. 5 is a view of a speed fluctuation detection pattern for detecting a peripheral speed fluctuation period in each color drum formed on the belt, as seen from the left side of the paper plane of FIG. 1. [Figure 8] FIG. 6 is a diagram illustrating an example of drum peripheral speed fluctuation plotted with the horizontal axis representing time and the vertical axis representing detection time intervals of each bar-shaped pattern of detection data. [Figure 9] FIG. 7 is a diagram illustrating peripheral speed fluctuations in two drums where a difference in peripheral speed fluctuation periods is within a predetermined range or the periods match, but a difference in phase occurs. [Figure 10] FIG. 8 is a flowchart illustrating drum drive control including rotation speed adjustment for reducing a fluctuation difference in peripheral speed fluctuation periods among respective color drums. DETAILED DESCRIPTION OF EMBODIMENTS

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0014] [Overall Configuration of Image Forming Apparatus] An image forming apparatus 1 according to the present embodiment is a tandem-type color image forming apparatus that forms a color image on a sheet serving as a recording medium by an electrophotographic method. The image forming apparatus 1 forms an image based on image data obtained by reading an image from a document or image data received from an external device. As shown in Figure 1, the image forming apparatus 1 comprises an automatic document transport unit 2, a scanner unit 3, an image forming unit 4, and a paper feeding unit 5. Furthermore, as shown in Figure 2, the image forming apparatus 1 includes a storage unit 6, an operation display unit 7, a control unit 10, and color resist sensors 101 to 104.

[0015] [Automatic document transport unit and scanner unit] The automatic document transport unit 2 includes a tray for placing the document D, a mechanism for transporting the document D along a transport path, and transport rollers, etc. The scanner unit 3 is equipped with an optical system including a light source and a reflector. The scanner unit 3 illuminates the original document D being transported along the transport path or placed on the platen glass with the light source, receives the reflected light, and performs scanning. The scanner unit 3 also converts the image read by the received reflected light into an electrical signal and outputs it to the control unit 10.

[0016] [Image Forming Unit] The image forming unit 4 comprises individual image forming units Y, M, C, and K corresponding to four colors, a belt B, and a fixing device 110. Each imaging unit Y, M, C, and K forms yellow, magenta, cyan, and black toner images on its respective image carrier drum 41. Then, each drum 41 first transfers the toner images of each color, Y, M, C, and K, formed on its outer surface to the belt B. The configuration and operation of each image-forming unit Y, M, C, and K are, in principle, identical. Therefore, the configuration and the series of image-forming operations performed by the image-forming unit 4 will be explained below, using the image-forming unit Y of the yellow image as an example.

[0017] The drum 41 is a photoreceptor drum made of an organic photoreceptor, in which a photosensitive layer made of a resin containing an organic photoconductor is formed on the outer surface of a cylindrical metal substrate. The drum 41 is driven to rotate counterclockwise in Figure 1. Examples of resins that make up the photosensitive layer include polycarbonate resin, silicone resin, polystyrene resin, acrylic resin, methacrylic resin, etc. Furthermore, the resin that makes up the photosensitive layer may also be epoxy resin, polyurethane resin, vinyl chloride resin, melamine resin, etc.

[0018] The charging device 42 uses a charging charger to charge the photosensitive layer of the drum 41 to a certain potential. The exposure apparatus 43 exposes the non-image area of ​​the drum 41 based on the image data Dy from the control unit 10. As a result, the charge in the exposed area is removed, and an electrostatic latent image is formed in the image area of ​​the drum 41. The developing device 44 supplies toner, which is a developer, onto the electrostatic latent image formed on the drum 41, forming a yellow toner image on the drum 41.

[0019] The primary transfer roller (primary transfer section) 45 transfers the yellow toner image formed on the drum 41 to the belt B. Similarly, the other imaging units M, C, and K also transfer magenta, cyan, and black toner images to belt B. This creates superimposed toner images of each color (Y, M, C, and K) on belt B.

[0020] Belt B is an intermediate transfer belt consisting of a semiconducting endless belt. Belt B is suspended by a plurality of rollers, including a drive roller 462, and is conveyed clockwise in Figure 1 as the rollers rotate. Belt B is brought into close proximity to or in contact with each of the opposing drums 41 by the primary transfer rollers 45. A transfer current corresponding to the applied voltage flows through each of the primary transfer rollers 45. As a result, each toner image developed on the surface of each drum 41 is sequentially transferred to belt B by each primary transfer roller 45.

[0021] The secondary transfer device (secondary transfer unit) 46 has a secondary transfer roller 461 and a drive roller 462 that rotates the belt B. The secondary transfer device 46 secondary transfers the toner image that has been primary transferred to the belt B to the paper P. The secondary transfer roller 461 is pressed against the belt B, and the drive roller 462 is one of a plurality of rollers that wind the belt B. The secondary transfer device 46 forms a transfer nip through which the paper P passes using the pair of secondary transfer rollers 461 and drive roller 462. The toner image on the belt B is secondary transferred at the transfer nip to the paper P that has been transported from the paper trays 51-53 of the paper feeding unit 5.

[0022] The secondary transfer roller 461 is supported by an actuator (not shown) that separates it from the belt B and the drive roller 462. The belt B may have a judgment mark 109 for color resist correction and a speed fluctuation detection pattern 121 formed on it by the image forming unit 4. In this case, the secondary transfer roller 461 is separated from the belt B by the actuator to prevent the judgment mark 109, etc., from being transferred from the belt B.

[0023] A residual toner cleaning device 47 is provided on the downstream side in the rotational direction of the transfer position of the drum 41 to the belt B. This cleaning device 47 removes residual toner, paper dust, and other residues remaining on the surface of the drum 41 after primary transfer. The cleaning device 47 brings a flat or sheet-shaped cleaning blade, made of an elastic material such as polyurethane rubber, into contact with the drum 41. The cleaning device 47 employs a so-called blade cleaning method.

[0024] Furthermore, a residual toner cleaning device 48 is provided on the downstream side in the transport direction at the transfer position on belt B. This cleaning device 48 removes any residue remaining on belt B after secondary transfer.

[0025] As shown in Figure 3, a lubricant application mechanism 49 is positioned downstream in the conveying direction from the transfer position of the drum 41 to the belt B, and in front of the cleaning device 47. The lubricant application mechanism 49 is a lubricant application means for applying lubricant to the drum 41. The lubricant application mechanism 49 includes a brush roller 491, a solid lubricant 492, and a brush cleaning member 493. The brush roller 491 rotates under motor drive, contacting both the solid lubricant 492 and the drum 41. This allows the brush roller 491 to supply lubricant particles scraped from the solid lubricant 492 to the drum 41 for spread and coating.

[0026] The solid lubricant 492 is selected from materials that, when applied, reduce the surface energy and thereby reduce the adhesion between the drum 41 and the belt B. Examples include fatty acid metal salts, fluororesins, or mixtures thereof. Fatty acid metal salts are particularly preferred. Linear hydrocarbons are preferred as the fatty acid of the fatty acid metal salt. For example, myristic acid, palmitic acid, stearic acid, oleic acid, etc. are preferred, with stearic acid being even more preferred. Examples of metals include lithium, magnesium, calcium, strontium, zinc, cadmium, aluminum, cerium, titanium, and iron. Among these, zinc stearate, magnesium stearate, aluminum stearate, and iron stearate are preferred.

[0027] The brush cleaning member 493 is positioned in contact with the brush roller 491. The brush cleaning member 493 collects the toner recovered by the brush roller 491 from the drum 41 before it reaches the solid lubricant 492.

[0028] [Fusing device] The fuser unit 110 has a pair of fuser rollers 111 and performs a fixing process to fix the toner image transferred to the paper P. The pair of fuser rollers 111 form a fixing nip through which the paper P passes between the pair of rollers. In the fixing nip, the fuser unit 110 heats and pressurizes the paper P on which the toner image has been transferred to fix the image to the paper P. The image forming unit 4 heats and pressurizes the paper P on which the toner images of each color have been secondarily transferred by the fixing unit 110, and then discharges it outside the machine by passing it through a predetermined transport path.

[0029] [Drum drive unit and belt drive unit] Figure 4 is a circuit block diagram related to the control of the drive rollers 462 that feed the drums 41 of each color and belt B in the image forming apparatus 1. Note that the configurations related to the control of each drum 41 in the image forming sections Y, M, C, and K are all the same, and only one set is shown in Figure 4, with the others omitted.

[0030] As shown in Figure 4, a drum drive motor 411 that rotates the drum 41 is controllably connected to the control unit 10. The drum 41 is connected to the drive shaft of the drum drive motor 411 via a transmission mechanism 412 that includes a reduction gear. The drum drive motor 411 and the transmission mechanism 412 constitute the drum drive unit as the image carrier drive unit, and their operation is controlled by the control unit 10.

[0031] Furthermore, a belt drive motor 463 that rotates the drive roller 462 is controllably connected to the control unit 10. The drive shaft of the belt drive motor 463 is connected to the drive roller 462 via a transmission mechanism 464 including a reduction gear. The belt drive motor 463 and the transmission mechanism 464 constitute the belt drive unit, and their operation is controlled by the control unit 10.

[0032] Both the drum drive motor 411 and the belt drive motor 463 are DC brushless motors. The control unit 10 individually transmits PWM signals as command values ​​to each drive motor 411 and 463 to control their speed and torque. PWM is an abbreviation for PulseWidthModulation. Each drive motor 411 and 463 is driven based on the command received from the control unit 10, and this drive rotates the drum 41 or the drive roller 462.

[0033] Both the drum drive motor 411 and the belt drive motor 463 output a predetermined number of FG pulse signals to the control unit 10 at regular intervals per rotation. In addition, each drive motor 411 and 463 is equipped with an origin sensor 414 and 466 that outputs an origin signal at a predetermined axis angle defined as the origin of the output shaft. The origin sensors 414 and 466 output once for each rotation of the output shaft of the drive motor 411 and 463.

[0034] Furthermore, encoders 413 and 465 are attached to the drum 41 and drive roller 462 as phase sensors to detect a predetermined phase. The encoders 413 and 465 output pulse signals at regular intervals according to their respective rotations. The control unit 10 performs feedback control of each drive motor 411, 463 based on the FG pulse signal and the encoder pulse signal. Note that the drive motors 411 and 463 may be other motors whose operating amount and rotational speed can be controlled. Also, the rotational amount of the drive motors 411 and 463 may utilize other well-known configurations in which the amount of rotation and rotational angle can be detected.

[0035] [Paper feed section] The paper feeding unit 5 is comprised of multiple paper trays 51 to 53, each containing a different type of paper P. The paper feeding unit 5 feeds the paper P to the image forming unit 4 via a predetermined transport path.

[0036] [Operation display] The operation display unit 7 is composed of, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit 71 and an operation unit 72. The display unit 71 of the operation display unit 7 may utilize an organic EL display. The display unit 71 displays various operation screens, the operating status of each function, etc., according to the display control signals input from the control unit 10. It also accepts touch operations from the user and outputs operation signals to the control unit 10. The operation unit 72 is equipped with various operation keys such as a numeric keypad and a start key, and accepts various input operations from the user and outputs operation signals to the control unit 10. The user can operate the operation display unit 7 to make settings related to image formation, such as image quality settings, magnification settings, application settings, output settings, and paper settings. The user can also operate the operation display unit 7 to give instructions for paper transport and stop the device. The display unit 71 and the operation unit 72 may be configured as separate and independent components.

[0037] [Color Resist Sensor] Figure 5 shows belt B and color resist sensors 101-104 as viewed from the left side of Figure 1. Hereafter, color resist sensors 101-104 will be abbreviated as sensors 101-104. The symbol S indicates the main scanning direction, which is perpendicular to the conveying direction of belt B, and F indicates the sub-scanning direction, which is along the conveying direction of belt B. In Figure 5, belt B is transported to the upper side of the paper.

[0038] Sensors 101-104 are positioned upstream of the cleaning device 48 in the transport path of belt B, as shown in Figure 1. Furthermore, sensors 101-104 are arranged in a line along the main scanning direction S, as shown in Figure 5. Sensors 101, 102 and sensors 103, 104 are positioned opposite each other at both ends of the main scanning direction S of belt B. Sensors 101, 102 and sensors 103, 104 are positioned opposite the non-image forming regions Bn located on both sides of the image forming region Bw of belt B.

[0039] Figure 5 illustrates a case where rows of judgment marks 109Y to 109K for color resist correction are formed on the passage lines of sensors 101 and 104. However, the judgment marks 109 may be in one row or multiple rows, and may be formed at any of the detection positions of sensors 101 to 104. In the following description, when judgment marks 109Y to 109K are not distinguished by color, they will be referred to simply as judgment marks 109. The judgment marks 109Y to 109K are each formed in a line of three, spaced uniformly along the sub-scanning direction. Note that there may be one judgment mark 109Y to 109K, or two or more of them.

[0040] Sensors 101-104 are also used to read the speed fluctuation detection pattern 121 for detecting the outer speed fluctuation period of each color drum 41, as described later. For this purpose, four sensors 101-104 are provided. However, if the sole purpose is to read the judgment mark 109 for color resist correction, one or more sensors 101-104 are sufficient. Alternatively, the judgment marks 109Y to 109K may be divided into four columns according to color and formed at the respective reading positions of sensors 101 to 104.

[0041] Figure 6 is an enlarged view of the determination marks 109K and 109C formed in the non-image-forming region Bn by the image-forming unit 4, viewed from the same line of sight as in Figure 5. The judgment marks 109K,C for color resist correction consist of a rod-shaped first judgment section 107K,C and a second judgment section 108K,C. Although not shown in Figure 6, the judgment marks 109M,Y also consist of a first judgment section and a second judgment section. Furthermore, in the following description, when the first determination unit 107K,C is not distinguished by color, it will be referred to as the first determination unit 107. Similarly, when the second determination unit 108K,C is not distinguished by color, it will be referred to as the second determination unit 108.

[0042] As shown in Figure 6, the first determination unit 107 is strip-shaped and parallel to the main scanning direction S. The second determination unit 108 is strip-shaped and aligned with the diagonal direction formed by combining the main scanning direction S and the sub-scanning direction F. When belt B is transported at a specified speed, the first determination unit 107 and the second determination unit 108 are detected sequentially, for example, by the sensor 101. Let t1 be the elapsed time from detection by the first determination unit 107 to detection by the second determination unit 108. In this case, if there is a deviation in the main scanning direction S at the determination mark 109, the elapsed time t1 will increase or decrease compared to when the determination mark 109 is in the correct position. Then, depending on whether the elapsed time t1 increases or decreases, it is possible to determine whether the deviation at the determination mark 109 is in one direction or the other of the main scanning direction S. Furthermore, the amount of deviation in the main scanning direction S can be determined by the length of the elapsed time t1.

[0043] Furthermore, by detecting the first determination units 107 of the two determination marks 109, which are arranged in the sub-scanning direction and are of different colors, the deviation of the sub-scanning direction F for each color can be determined. In Figure 6, determination marks 109K and 109C are shown as examples, but the same applies to other colors.

[0044] Let t2 be the elapsed time from detection by the first determination unit 107K to detection by the first determination unit 107C. If there is a misalignment of the sub-scanning direction F between the two determination marks 109, the elapsed time t2 will increase or decrease compared to when the two determination marks 109 are in the correct position. Based on whether the elapsed time t2 increases or decreases, it is possible to determine whether the misalignment is in one or the other direction of the sub-scanning direction F between each determination mark 109. Furthermore, the amount of misalignment in the sub-scanning direction F can be identified by the magnitude of the timing difference of the elapsed time t2 relative to the correct value.

[0045] As mentioned above, it is also possible to form judgment marks 109 for each of the Y, M, C, and K colors and detect them individually with each of the sensors 101 to 104. In this case, the amount of deviation for each color in the sub-scanning direction F can be determined by the magnitude of the difference in the timing detected by the first judgment unit 107 at each of the sensors 101 to 104. The shift for each color in the main scanning direction S is the same as described above.

[0046] [Control system for image forming apparatus] The storage unit 6 is composed of an HDD (Hard Disk Drive) or non-volatile semiconductor memory, etc. As shown in Figure 2, the storage unit 6 stores various programs such as the control program 61, image data used for image formation, setting information, and other various data.

[0047] The communication interface 120 consists of components such as a NIC (Network Interface Card) and a modem, and is used to send and receive data between PCs and peripheral devices.

[0048] The control unit 10 is comprised of a CPU, RAM, ROM, etc. The CPU loads various programs stored in the ROM and storage unit 6 into the RAM. In this way, the CPU comprehensively controls the automatic document transport unit 2, scanner unit 3, image forming unit 4, paper feeding unit 5, storage unit 6, operation display unit 7, etc. For example, the control unit 10 performs various image processing on image data acquired from an external PC or the like via the scanner unit 3 or the communication interface 120. Furthermore, the control unit 10 outputs the YMCK image data Dy, Dm, Dc, and Dk generated by the image processing to the image forming unit 4. The control unit 10 also controls the operation of the image forming unit 4 to form an image on the paper P.

[0049] Furthermore, the control unit 10 realizes the functional configurations shown in Figure 2 by the CPU executing the control program 61. Specifically, the control unit 10 functions as a detection processing unit 11, a drum drive control unit 12 as an image carrier drive control unit, an exposure control unit 13, a resist processing unit 14, and a notification processing unit 15. Each of these functional configurations will now be explained.

[0050] [Detection Processing Unit] The detection processing unit 11 performs control to detect the outer peripheral speed fluctuation period in the drums 41 of each color (Y, M, C, K). The detection processing unit 11 functions as a speed fluctuation period detection means in cooperation with the image forming unit 4 and sensors 101 to 104. As mentioned above, the drum 41 may experience peripheral velocity fluctuations at a frequency that matches the rotation period due to eccentricity or other causes. Furthermore, the peripheral velocity fluctuation period of the drum 41 may change due to changes over time in the electrostatic restraint force with belt B, etc.

[0051] The detection processing unit 11 detects periodic fluctuations in the outer circumference speed and their period for each colored drum 41 by the following control and processing. Figure 7 is a view from the left side of Figure 1 of the speed fluctuation detection pattern 121 for detecting the outer circumference speed fluctuation period in each colored drum 41 formed on belt B.

[0052] The detection processing unit 11 controls the image forming units Y, M, C, and K to form velocity fluctuation detection patterns 121 of each color in the non-image forming region Bn of the belt B. The velocity fluctuation detection pattern 121 consists of rod-shaped patterns arranged in the sub-scanning direction along the main scanning direction S. During the formation of the rod-shaped pattern, laser exposure is performed on each drum 41 at a constant angular interval at the target rotation speed during image formation, based on the output of the encoder 413. The electrostatic latent image of the rod-shaped pattern is formed for at least one rotation of the drum 41, and more preferably for multiple rotations. After the drum 41 is developed, a speed variation detection pattern 121 in the form of a rod shape is transferred to the belt B at intervals based on the speed variation at the outer circumference of the drum 41. The rod-shaped patterns are originally formed at uniform intervals in the sub-scanning direction, but if there is a fluctuation in the outer peripheral speed of the drum 41, they are transferred to the belt B at intervals corresponding to the fluctuation. The detection processing unit 11 transports belt B at a constant speed and causes each of the sensors 101 to 104 to read the speed fluctuation detection pattern 121 for each color.

[0053] The time intervals at which each sensor 101 to 104 detects the bar-shaped pattern of the speed fluctuation detection pattern 121 are determined, and the data arranged in order is stored in the storage unit 6. This sequence of time intervals becomes the detection data for the outer circumference speed fluctuations of each colored drum 41. Figure 8 is a diagram showing an example of peripheral velocity fluctuation in the drum 41, with time on the horizontal axis and the detection time interval of a bar-shaped pattern on the vertical axis. The detection time interval of the bar-shaped pattern is a value proportional to the velocity of the drum's outer circumference. Therefore, changes in the values ​​of the detection time interval of a series of bar-shaped patterns indicate fluctuations in the peripheral velocity of the drum 41. In Figure 8, the symbol L1 represents the case where there is a fluctuation in the outer circumferential velocity fluctuation period, while the symbol L2 represents the case where there is no fluctuation in the outer circumferential velocity fluctuation period for comparison. Figure 8 shows the case where the outer circumferential velocity fluctuation period in drum 41 is shortened by the restraining force on belt B. The detection processing unit 11 obtains a maximum value E1 and a minimum value E2 from the detection data of the outer circumference speed fluctuation in the drum 41, and calculates the outer circumference speed fluctuation period from the time interval between these values.

[0054] [Drum drive control unit] The drum drive control unit 12 adjusts the rotational speed of each drum 41 of each color so that the difference in the outer circumference speed fluctuation period of each drum 41 is within a predetermined range. More preferably, the drum drive control unit 12 makes the outer circumference speed fluctuation periods of each drum 41 of each color equal. The above predetermined range may be arbitrarily set from an input unit such as the operation unit 72. For example, the drum drive control unit 12 may adjust the values ​​of the other drums 41 to be closer to the outer circumference speed fluctuation period of one drum 41 as a reference, so that the difference in the outer circumference speed fluctuation periods of the drums 41 of each color falls within a predetermined range. Alternatively, the peripheral speed fluctuation period of all drums 41 may be approximated to the period at the target rotational speed during image formation of the drum 41, and adjusted so that the difference in peripheral speed fluctuation periods of each color drum 41 is within a predetermined range. The period of peripheral velocity fluctuation in drum 41 can be adjusted by increasing or decreasing the rotational speed of drum 41. Increasing the rotational speed of drum 41 shortens the period of peripheral velocity fluctuation in drum 41. Decreasing the rotational speed of drum 41 lengthens the period of peripheral velocity fluctuation in drum 41.

[0055] The rotational speed of drum 41 is adjusted by either (1) or (2) below. (1) The drum drive control unit 12 calculates the ratio fc / fv of the outer peripheral speed fluctuation period fc at each drum 41 to the period fv at the target rotational speed of the drum 41. The drum drive control unit 12 then multiplies the calculated ratio fc / fv by the current rotational speed of the drum 41. This brings the outer peripheral speed fluctuation period at each drum 41 closer to the period at the target rotational speed of the drum 41 during image formation, so that the difference in the outer peripheral speed fluctuation periods of each color drum 41 is within a predetermined range. The drum drive control unit 12 may also multiply the current rotational speed of the drum 41 by a value obtained by further multiplying the calculated ratio fc / fv by a coefficient.

[0056] (2) The drum drive control unit 12 compares the outer peripheral speed fluctuation period fc of each drum 41 with the period fv at the target rotational speed when the drum 41 is forming an image. Then, if the outer circumference speed fluctuation period fc of each drum 41 is short, the current rotational speed of the drum 41 is reduced by a specified value or by a specified ratio. Furthermore, if the outer circumference speed fluctuation period fc of each drum 41 is long, the current rotational speed of the drum 41 will be increased by a specified value or by a specified ratio. These measures allow the difference in the outer circumference speed fluctuation period of each colored drum 41 to be adjusted to fall within a predetermined range.

[0057] The drum drive control unit 12 may perform a rough adjustment of the rotational speed of the drum 41 without relying on the magnitude of the difference between the period fc and the period fv, as in (2). Alternatively, the drum drive control unit 12 may perform (2) first and then fine-tune the rotation speed of the drum 41 using (1).

[0058] Regardless of whether the drum drive control unit 12 performs (1) or (2), it is preferable that the detection processing unit 11 detects the outer circumference speed fluctuation period of each drum 41 again after the adjustment. In that case, if the difference in the outer circumference speed fluctuation periods of the drums 41 of each color does not fall within a predetermined range, the rotation speed of some or all of the drums 41 is readjusted.

[0059] Furthermore, when the drum drive control unit 12 adjusts the rotational speed of the drum 41, it sets a command value for the encoder 413 and monitors the encoder 413 while performing the adjustment. In particular, in the case of adjustment (1), the drum drive control unit 12 adjusts the rotational speed of the drum 41 by feedback control based on the output of the encoder 413.

[0060] Furthermore, the drum drive control unit 12 adjusts the difference in peripheral speed fluctuation periods of each colored drum 41 to be within a predetermined range, and then performs phase alignment of the peripheral speed fluctuation periods of each colored drum 41. Figure 9 is a diagram showing the peripheral speed fluctuations of two drums 41 where the difference in peripheral speed fluctuation periods between the two drums 41 is within a predetermined range or coincides, but there is a phase difference. In this example, the peripheral speed fluctuation of one drum 41 is shown in diagram L3, and the peripheral speed fluctuation of the other drum 41 is shown in diagram L4. There is a half-period phase difference between diagram L3 and diagram L4. A tolerance value is set for the phase difference, and if it exceeds the tolerance value, the drum drive control unit 12 performs phase adjustment.

[0061] The drum drive control unit 12 determines the maximum and minimum values ​​of the peripheral speed fluctuations in the drum 41 and determines their phases. The phases of the maximum and minimum values ​​can be obtained by recording the output of the encoder 413 when forming the speed fluctuation detection pattern 121. The drum drive control unit 12 identifies the phases of the peripheral speed fluctuations that occurred at the maximum and minimum values ​​by comparing them with the recorded output of the encoder 413. Furthermore, once the phases of the maximum and minimum values ​​are identified, the drum drive control unit 12 can also determine the phases of the nodes or antinodes in the peripheral speed fluctuations of the drum 41. Therefore, the drum drive control unit 12 can determine the phase of the nodes or antinodes of each color drum 41 and calculate the phase difference between them.

[0062] If the phase of any of the drums 41 is advanced, the rotation of the drum drive motor 411 is temporarily stopped or reduced before returning to its original speed. This allows the phase to be delayed. If the phase of any of the drums 41 is lagging, the drum drive motor 411 is temporarily accelerated to return to its original speed. This allows the phase to be advanced.

[0063] [Exposure Control Unit] The exposure control unit 13 controls the timing of laser writing during image formation for each color exposure device 43. The drum 41 has a target rotation speed set to a specified value during image formation. The exposure control unit 13, in principle, determines the operating timing of the exposure apparatus 43 in accordance with the specified value of the target rotation speed.

[0064] When the drum drive control unit 12 adjusts the rotational speed to keep the difference in the outer peripheral speed fluctuation period of each drum 41 within a predetermined range, the operating timing of the exposure device 43 also needs to be adjusted. This is because the time it takes for the image to travel from the exposure position on the outer surface of the exposure device 43 to the transfer position on the belt B varies depending on the rotation speed of the drum 41. Therefore, the exposure control unit 13 calculates a new arrival time based on the time the drum 41 reaches the target rotational speed during image formation and the rate of increase or decrease of the rotational speed of the drum 41. The exposure control unit 13 adjusts the operating timing of the exposure apparatus 43 based on the increase or decrease in the new arrival time relative to the original arrival time. In this case, the increase or decrease in the arrival time based on the rotational speed adjustment to keep the difference in the outer circumference speed fluctuation period of the drum 41 within a predetermined range is called the "first timing adjustment value".

[0065] Furthermore, as mentioned above, the drum drive control unit 12 performs phase alignment of the outer peripheral speed fluctuation period in the drum 41. The exposure control unit 13 also needs to adjust the operating timing of the exposure device 43 in relation to this phase alignment. The exposure control unit 13 obtains the amount of phase adjustment due to the phase alignment of the drum 41 from the drum drive control unit 12. The exposure control unit 13 then calculates the adjustment time based on the ratio of the adjustment amount to the phase of one cycle of the outer peripheral speed fluctuation period of the drum 41 and the outer peripheral speed fluctuation period. In this case, the adjustment time based on the phase alignment of drum 41 is referred to as the "second timing adjustment value".

[0066] The exposure control unit 13 adjusts the writing timing using first and second timing adjustment values ​​in conjunction with the rotation speed adjustment and phase alignment to match the peripheral speed fluctuation period.

[0067] [Resistance Processing] The resist processing unit 14 performs resist processing after the drum drive control unit 12 adjusts the rotational speed to bring the difference in the outer peripheral speed fluctuation period of each drum 41 within a predetermined range. This resist processing is preferably performed after the rotational speed adjustment of each drum 41 and after the laser writing timing adjustment by the exposure control unit 13. After each of the above adjustments, the resist processing unit 14 controls the image forming unit 4 for each color to form the determination marks 109 shown in Figure 5 in the non-image forming area Bn of the belt B. Then, based on the detection by sensors 101 and 104, the resist processing unit 14 detects the color misalignment in the main scanning direction and sub-scanning direction for each of the Y, M, C, and K colors.

[0068] The resist processing unit 14 detects the amount of color shift in the main scanning direction S and sub-scanning direction F for each color based on the elapsed times t1 and t2 described above. Furthermore, the resist processing unit 14 reduces the amount of color shift by controlling the laser in the exposure apparatus 43 for each color. The resist processing unit 14 reduces the color shift in the sub-scanning direction F by adjusting the axis angle of the drum 41 where laser writing is started. The resist processing unit 14 reduces color shift in the main scanning direction S by adjusting the laser emission start timing for each laser scan.

[0069] [Notification Processing Unit] The notification processing unit 15 performs notification processing according to the number of times the drum drive control unit 12 adjusts the rotation speed of each colored drum 41 to keep the difference in the outer peripheral speed fluctuation period within a predetermined range. The notification processing unit 15 counts the number of times the rotation speed of each colored drum 41 is adjusted to keep the difference in the outer circumference speed fluctuation period within a predetermined range. The adjustment of the rotation speed of the drum 41 may be repeated multiple times until the appropriate outer circumference speed fluctuation period is achieved. However, even in such cases, the notification processing unit 15 counts the time until the appropriate outer circumference speed fluctuation period is achieved as just one adjustment. The notification processing unit 15 stores the above count value in the storage unit 6 and monitors whether it reaches a predetermined threshold. When the count value reaches the threshold, the notification processing unit 15 notifies the user via the display unit 71 that a particular drum 41 is nearing the end of its lifespan. The content of the notification may also be an instruction to replace the drum 41. Furthermore, the notification process is not limited to the display unit 71; it may also be communicated via an audio output unit or a lamp. Furthermore, the threshold value for the count value used to execute the notification process may be arbitrarily set from the operation unit 72.

[0070] [Drum drive control] The drum drive control, which includes adjusting the rotational speed to keep the difference in the variation of the outer peripheral speed variation period in each color drum 41 within a predetermined range, will be explained based on the flowchart in Figure 10. This drum drive control is realized by the CPU of the control unit 10 executing the control program 61. Furthermore, this drum drive control realizes a suitable control method for the image forming apparatus 1. This drum drive control is performed when the image forming apparatus 1 is not running a print job, including when it is started up, or between pages of a print job.

[0071] The detection processing unit 11 starts each color drum 41 at the target rotation speed (S1). Furthermore, the detection processing unit 11 exposes and develops the speed variation detection pattern 121 for at least one rotation on each color drum 41. Then, it transfers the speed variation detection pattern 121 to the non-image forming region Bn of the belt B (S3).

[0072] Next, the detection processing unit 11 reads the speed fluctuation detection pattern 121 of belt B using sensors 101 to 104. The outer circumference speed fluctuation of each color drum is then detected from the spacing between each rod-shaped pattern of the speed fluctuation detection pattern 121. The detection processing unit 11 determines the phase of the nodes or antinodes of the periodic outer circumference speed fluctuation and detects the period of the outer circumference speed fluctuation (S5).

[0073] The drum drive control unit 12 compares the period of the outer circumference speed fluctuation in each colored drum 41 with the period of the target rotational speed (S7). The drum drive control unit 12 proceeds to step S9 if the difference between the outer circumference speed fluctuation period and the target rotational speed period of any of the drums 41 is greater than or equal to an allowable value. Furthermore, the drum drive control unit 12 proceeds to S19 if the difference between the outer circumference speed fluctuation period and the target rotational speed period for all drums 41 is within the allowable value.

[0074] In S9, if the drum drive control unit 12 determines that the outer circumference speed fluctuation period of the drum 41 is shorter than the target rotational speed period, it proceeds to S11. In S11, the drum drive control unit 12 reduces the rotational speed of the drum drive motor 411 by a predetermined amount. Then, the drum drive control unit 12 performs phase alignment of the outer circumference speed fluctuation period of the drum 41 whose rotational speed has been adjusted (S13). Phase alignment is performed using the phase of one of the predetermined drums 41 as a reference. Then, the drum drive control unit 12 returns the process to S3.

[0075] On the other hand, if in S9 the drum drive control unit 12 does not determine that the outer circumference speed fluctuation period of the drum 41 is shorter than the target rotational speed period, it proceeds to S15. In S15, the drum drive control unit 12 accelerates the rotational speed of the drum drive motor 411 by a predetermined amount. Then, the drum drive control unit 12 performs phase alignment of the outer circumference speed fluctuation period in the drum 41 whose rotational speed has been adjusted (S17). In this case as well, the phase alignment is performed based on the phase of one of the predetermined drums 41. Then, the drum drive control unit 12 returns the process to S3.

[0076] If processing returns from S13 or S17 to S3, the detection processing unit 11 again forms the speed fluctuation detection pattern 121 and detects the outer circumference speed fluctuation period (S5). Then, the drum drive control unit 12 re-determines whether the difference between the outer circumference speed fluctuation period and the period of the target rotational speed in each color drum 41 has fallen within a predetermined range due to the previous adjustment (S7). If the result does not fall within the specified range, the processes S9-S17 and S3-S7 are repeated.

[0077] Meanwhile, as processing progresses from S7 to S19, the notification processing unit 15 determines whether or not the drum drive control unit 12 has performed an adjustment of the rotation speed (S19). If the rotation speed is not adjusted, the process proceeds to S31. Furthermore, if the rotation speed is adjusted, the notification processing unit 15 increments the count value of the number of rotation speed adjustments by one (S21). In addition, the notification processing unit 15 determines whether the count value has reached a threshold (S23). If the count value has not reached the threshold, the process proceeds to S27. If the count value has reached the threshold, the notification processing unit 15 executes notification processing (S25).

[0078] In S27, the exposure control unit 13 adjusts the laser writing timing of the exposure apparatus 43 based on a first timing adjustment value derived from the rotation speed adjustment. Furthermore, the exposure control unit 13 adjusts the writing timing of the laser of the exposure apparatus 43 using a second timing adjustment value based on phase alignment.

[0079] Next, the resist processing unit 14 performs resist processing after adjusting the rotation speed (S29). That is, the resist processing unit 14 forms judgment marks 109 on the belt B for each color, and these marks are read by sensors 101 and 104. The resist processing unit 14 then detects the color misalignment in the main scanning direction S and sub-scanning direction F for each color based on the reading results of the determination marks 109 for each color. Furthermore, the resist processing unit 14 corrects color misalignment by controlling the timing of laser writing and emission of the exposure device 43 based on the detection results.

[0080] In S31, the control unit 10 waits in a state where image formation is possible (S31), and then terminates the drum drive control. In this state, when image data is acquired from the scanner unit 3 or the communication I / E 120, the control unit 10 performs image formation. Additionally, if drum drive control was performed between pages of a print job, image formation for the next page will resume.

[0081] [Technical effects of the embodiment] In the image forming apparatus 1, the detection processing unit 11 detects the outer peripheral speed fluctuation period of each color drum 41 in cooperation with the image forming unit 4 and sensors 101 to 104. Furthermore, the image forming apparatus 1's drum drive control unit 12 adjusts the rotation speed of the drums 41 in order to keep the difference in the outer peripheral speed fluctuation period of each color drum 41 within a predetermined range. As a result, the image forming apparatus 1 can suppress color shifts caused by differences in the peripheral speed fluctuation period of each color drum 41, thereby improving the image quality of the formed image.

[0082] Furthermore, the drum drive control unit 12 controls the drum drive units for each color to adjust the difference in the outer peripheral speed fluctuation period of each color drum 41 within a predetermined range. This enables the image forming apparatus 1 to quickly and smoothly adjust the difference in the outer peripheral speed fluctuation period of each color drum 41 within a predetermined range.

[0083] Furthermore, the drum drive control unit 12 adjusts the rotational speed of the drum 41 so that the difference between the outer peripheral speed fluctuation period of the drum 41 and the period at the target rotational speed is within a predetermined range. This makes it possible to converge the rotational speed of the drum 41 after adjustment for each color to a speed that does not deviate from the target rotational speed. Consequently, it becomes possible to maintain the image forming apparatus 1 in a state close to the initially planned drive state, and good image formation becomes possible.

[0084] Furthermore, the drum drive control unit 12 monitors the peripheral speed fluctuation period of each color drum 41 detected by the detection processing unit 11. The drum drive control unit 12 then determines whether to increase or decrease the rotational speed of each color drum 41 and adjusts the difference in peripheral speed fluctuation periods of each color drum 41 within a predetermined range. In other words, the drum drive control unit 12 can easily and quickly adjust the difference in peripheral speed fluctuation periods of each color drum 41 within a predetermined range by increasing or decreasing the rotational speed of the drums 41.

[0085] The image forming apparatus 1 is equipped with a phase-detecting encoder 413 on each color drum 41. The drum drive control unit 12 sets a target value for the output of the encoder 413 and adjusts the rotation speed of each color drum by feedback control. Therefore, the image forming apparatus 1 can stably and accurately adjust the difference in the outer peripheral speed fluctuation period of each color drum 41 within a predetermined range.

[0086] Furthermore, the drum drive control unit 12 determines the target value from the difference in the outer circumference speed fluctuation period of each color drum 41 obtained from the detection processing unit 11. The difference in the outer circumference speed fluctuation period may be the difference between each color drum 41, or the difference between the outer circumference speed fluctuation period of each color drum 41 and the period of the target rotational speed of the drum 41. These features allow the target value of the encoder 413 to be set appropriately, and effectively adjust the difference in the outer peripheral speed fluctuation period of each color drum 41 within a predetermined range.

[0087] Furthermore, the drum drive control unit 12 adjusts the outer peripheral speed fluctuation period for each color drum and then aligns the phase of the said outer peripheral speed fluctuation period. As a result, each color drum 41 is driven with its outer peripheral speed fluctuation period and phase approximately in sync. Therefore, the image forming apparatus 1 can suppress color shifts caused by differences in the outer peripheral speed fluctuation period and phase of each color drum 41, thereby improving the image quality of the formed image.

[0088] Furthermore, the drum drive control unit 12 performs phase alignment of the peripheral speed fluctuation period based on the output of the encoder 413 of each color drum 41. This allows for more precise phase alignment of the peripheral speed fluctuation period in each color drum 41. Consequently, the image forming apparatus 1 can suppress color shifts caused by differences in peripheral speed fluctuation period and phase in each color drum 41, enabling further improvement in the image quality of the formed image.

[0089] Furthermore, the drum drive control unit 12 performs phase alignment by aligning the phases of nodes or antinodes in the periodic peripheral velocity fluctuations of the outer circumference of each color drum 41. As a result, the phase alignment of the peripheral velocity fluctuation periods in each color drum 41 is performed more appropriately. Consequently, the image forming apparatus 1 can suppress color shifts caused by differences in peripheral velocity fluctuation periods and phases in each color drum 41, enabling further improvement in the image quality of the formed image.

[0090] The image forming apparatus 1 has an exposure control unit 13 that adjusts the timing of laser writing for exposure in accordance with the adjustment of the rotation speed of the drum 41. Therefore, even when the rotation speed of the drum 41 is adjusted, laser writing is performed appropriately, and the formed image can be maintained at high quality. Furthermore, the exposure control unit 13 adjusts the laser writing timing in accordance with the phase alignment of the drum 41. As a result, laser writing is performed appropriately when the phase alignment of the drum 41 is performed, making it possible to maintain an even higher quality image of the formed image.

[0091] The image forming apparatus 1 has a resist processing unit 14 that performs color resist adjustment after the drum drive control unit 12 adjusts the rotation speed of the drum 41. As a result, the image forming apparatus 1 can perform color resist adjustment while suppressing the effects of fluctuations in the peripheral speed of each color drum 41 and fluctuations in the period of said peripheral speed fluctuations. Therefore, it is possible to perform color resist adjustment while suppressing color shifts caused by unique factors such as differences in the period of peripheral speed fluctuations of each drum 41. This makes it possible to improve the image quality of the formed image.

[0092] The image forming apparatus 1 has a notification processing unit 15 that performs notification processing when the rotation speed adjustment of each color drum 41 by the drum drive control unit 12 reaches a predetermined number of times. This makes it possible to inform the user that wear and deterioration of the drum 41 over time is expected. When the drum 41 is replaced, a new drum 41 that is less prone to fluctuations in the outer peripheral speed fluctuation period is used. As a result, it becomes possible to improve the image quality of the formed image.

[0093] Furthermore, the control unit 10 adjusts the rotational speed to bring the difference in the outer circumference speed fluctuation period of each drum 41 within a predetermined range, and then reconfirms the outer circumference speed fluctuation period of each drum 41. Therefore, the image forming apparatus 1 can readjust if the peripheral speed fluctuation period of each drum 41 is not sufficiently synchronized. This enables the image forming apparatus 1 to perform high-quality image formation under more appropriate conditions.

[0094] Furthermore, the drum drive control unit 12 adjusts the rotational speed to keep the difference in peripheral speed fluctuation periods of each color drum 41 within a predetermined range when the print job is not running or between pages. Therefore, the difference in peripheral speed fluctuation periods of each drum 41 can be adjusted within a predetermined range by utilizing the period when the image forming apparatus 1 is not performing image forming. This makes it possible to maintain high image quality while maintaining high operating efficiency of the image forming apparatus 1.

[0095] Furthermore, the image forming apparatus 1 has a lubricant application mechanism 49 attached to each color drum 41. This reduces the restraining force from the belt B on each drum 41. Therefore, the lubricant application mechanism 49 and adjustments can be made to keep the difference in the peripheral speed fluctuation period of each color drum 41 within a predetermined range. As a result, the image forming apparatus 1 can suppress variations in the peripheral speed fluctuation period of each color drum 41 over a long period of time.

[0096] [others] Embodiments of the present disclosure have been described above. However, the present disclosure is not limited to the embodiments described above. For example, in the embodiments, a component integrally formed from a single member may be replaced with a component divided into multiple members that are connected or fixed to each other. Also, a component formed by connecting multiple members may be replaced with a component integrally formed from a single member. Furthermore, details shown in the embodiments can be modified as appropriate without departing from the spirit of the disclosure.

[0097] For example, the determination marks 109 for color resist correction and the speed fluctuation detection pattern 121 are not limited to being formed on belt B. For example, these marks 109 and patterns 121 may be formed on the paper P and read by sensors placed along its transport path. Furthermore, the form of the judgment mark 109 for color resist correction and the speed fluctuation detection pattern 121 are examples only and are not limited thereto. Other forms of marks or patterns that can achieve the same functionality may also be used.

[0098] Furthermore, the phase of the outer perimeter velocity fluctuation period in each colored drum 41 is not limited to being determined by detecting the maximum and minimum values ​​of the outer perimeter velocity fluctuation. For example, the outer perimeter velocity fluctuation period in the drum 41 is largely due to eccentricity. Therefore, the phase at which the eccentricity is maximum or minimum may be measured in advance when assembling the drum 41, and the drum 41 may be marked to detect the phase of the outer perimeter velocity fluctuation period. Alternatively, the output of encoder 413, which indicates the phase at which the eccentricity is maximum or minimum, may be stored in the storage unit 6. In this case, the phase of the outer perimeter speed fluctuation period may be detected from the output of encoder 413.

[0099] Furthermore, while an encoder 413 is given as an example of a phase sensor for detecting the phase of the drum 41, it is not limited to this. Any well-known sensor capable of detecting the rotation angle and amount of rotation of the drum 41 can be used as the phase sensor. [Explanation of Symbols]

[0100] 1. Image forming apparatus 4 Image forming unit 6 Memory section 7 Operation display section 10 Control Unit 11. Detection processing unit (speed fluctuation period detection means) 12. Drum drive control unit (image carrier drive control unit) 13 Exposure Control Unit 14. Resist Processing Unit 15. Notification Processing Unit 41 Drum (image carrier) 411 Drum drive motor (image carrier drive unit) 412 Transmission mechanism (image carrier drive unit) 413 Encoder (Phase Sensor) 463 Belt-driven motor (belt drive unit) 464 Transmission mechanism (belt drive unit) 465 Encoder 49. Lubricant application mechanism (lubricant application means) 491 Brush Roller 492 Solid lubricant 493 Brush cleaning component 61 Control Program 71 Display section 72 Operation section 101-104 Color Resist Sensor 107,107K,107C First judgment section 108,108K,108C Second judgment section 109, 109Y, 109M, 109C, 109K - Marks for Judgment 121 Speed ​​fluctuation detection patterns B Belt Bn Non-image forming area Bw Image Formation Region E1 Maximum value E2 local minimum F Sub-scanning direction P paper S Main scanning direction

Claims

1. An image carrier in which toner images of each color are individually formed to correspond to multiple colors, A belt is positioned opposite each of the image carriers of each color, which are arranged in the transport direction, and transfers the superimposed toner images of each color onto a recording medium. An image carrier drive unit that drives each of the aforementioned colored image carriers individually, The system includes a belt drive unit that transports the aforementioned belt, A velocity fluctuation period detection means for detecting the peripheral velocity fluctuation period in the image carrier of each color, The system includes an image carrier drive control unit that adjusts the rotational speed of each colored image carrier so that the difference in peripheral velocity fluctuation periods of each colored image carrier falls within a predetermined range. Image forming apparatus.

2. The image carrier drive control unit controls the image carrier drive unit for each color to adjust the difference in peripheral velocity fluctuation periods of each color image carrier to within a predetermined range. The image forming apparatus according to claim 1.

3. The image carrier drive control unit adjusts the rotation speed of each colored image carrier so that the difference between the peripheral velocity fluctuation period of each colored image carrier and the period at the target rotation speed during image formation of the image carrier is within a predetermined range. The image forming apparatus according to claim 1.

4. The image carrier drive control unit is, After adjusting the rotational speed of each colored image carrier to adjust the difference in peripheral velocity fluctuation periods between them to within a predetermined range, the phases of these peripheral velocity fluctuation periods are aligned. The image forming apparatus according to claim 1.

5. A phase sensor is provided to detect the phase of each colored image carrier. The image carrier drive control unit performs phase alignment of the peripheral velocity fluctuation period in each color image carrier based on the output of the phase sensor of each color image carrier. The image forming apparatus according to claim 4.

6. The image carrier drive control unit performs phase alignment of the peripheral velocity fluctuation periods in each color image carrier by aligning the phases of the nodes or antinodes in the periodic peripheral velocity fluctuations in each color image carrier. The image forming apparatus according to claim 4.

7. The exposure control unit adjusts the writing timing of the laser used to expose each colored image carrier in accordance with the adjustment of the rotation speed of each colored image carrier performed by the image carrier drive control unit to keep the difference in peripheral velocity fluctuation periods of each colored image carrier within a predetermined range. The image forming apparatus according to claim 1.

8. The image carrier drive control unit adjusts the rotation speed of each colored image carrier to keep the difference in peripheral velocity fluctuation periods between each colored image carrier within a predetermined range, and then confirms the peripheral velocity fluctuation period of each colored image carrier using the velocity fluctuation period detection means. The image forming apparatus according to claim 1.

9. The image carrier drive control unit has a resist processing unit that performs color resist adjustment after adjusting the rotation speed of each color image carrier in order to bring the difference in peripheral velocity fluctuation periods of each color image carrier within a predetermined range. The image forming apparatus according to claim 1.

10. A phase sensor is provided to detect the phase of each colored image carrier. The image carrier drive control unit sets a target value detected by the phase sensor and, through feedback control, adjusts the rotation speed of each colored image carrier to keep the difference in peripheral velocity fluctuation periods between each colored image carrier within a predetermined range. The image forming apparatus according to claim 1.

11. The image carrier drive control unit determines the target value from the difference in peripheral velocity fluctuation periods of each colored image carrier detected by the velocity fluctuation period detection means. The image forming apparatus according to claim 10.

12. The image carrier drive control unit monitors the peripheral velocity fluctuation period of each colored image carrier detected by the velocity fluctuation period detection means, determines an increase or decrease in the rotational speed of each colored image carrier, and adjusts the difference in peripheral velocity fluctuation periods of each colored image carrier to within a predetermined range. The image forming apparatus according to claim 1.

13. The image carrier drive control unit adjusts the rotation speed of each colored image carrier to keep the difference in peripheral velocity fluctuation periods between each colored image carrier within a predetermined range, either when the print job is not running or between pages. The image forming apparatus according to claim 1.

14. Each of the aforementioned colored image carriers has a lubricant application means attached to it. The image forming apparatus according to claim 1.

15. The image carrier drive control unit counts the number of times it adjusts the rotation speed of each colored image carrier to keep the difference in peripheral velocity fluctuation periods between each colored image carrier within a predetermined range, and a notification processing unit executes a notification process when the predetermined number of adjustments is reached. The image forming apparatus according to claim 1.

16. A control method for an image forming apparatus comprising: an image carrier on which toner images of each color are individually formed corresponding to multiple colors; a belt positioned opposite the image carriers of each color arranged along the transport direction, which transfers a superimposed toner image of the toner images of each color onto a recording medium; an image carrier drive unit for individually driving the image carriers of each color; a belt drive unit for transporting the belt; and a speed fluctuation period detection means for detecting the peripheral speed fluctuation period of the image carriers of each color, wherein The rotation speed of each colored image carrier is adjusted so that the difference in peripheral velocity fluctuation periods between each colored image carrier falls within a predetermined range. A method for controlling an image forming apparatus.

17. A computer controls an image forming apparatus having an image carrier on which toner images of each color are individually formed corresponding to multiple colors; a belt positioned opposite each of the image carriers of each color arranged along the transport direction, which transfers the superimposed toner images of each color onto a recording medium; an image carrier drive unit that individually drives each of the image carriers of each color; a belt drive unit that transports the belt; and a speed fluctuation period detection means that detects the peripheral speed fluctuation period of each of the image carriers of each color. A control program that functions as an image carrier drive control unit, adjusting the rotation speed of each colored image carrier so that the difference in peripheral velocity fluctuation periods of each colored image carrier falls within a predetermined range.

Images