Image forming apparatus

Abstract

This disclosure relates to an image forming apparatus. An image forming apparatus capable of forming images in monochrome and multiple colors includes a first image forming unit, a second image forming unit, and a control unit. The image forming unit includes a rotatable image carrier member, a rotatable developing member that contacts the image carrier member to supply developer to its surface, and a developing member that supplies developer to the developing member. The control unit switches between an image forming operation that forms an image on the surface of the image carrier member and a cleaning operation that removes deposits from the surface of the image carrier member using the developing member by controlling the voltage applied to the developing member and the voltage applied to the developing member.

Description

Technical Field

[0001] This invention relates to an image forming apparatus. Background Technology

[0002] Electrophotographic image forming apparatuses form images by developing an electrostatic latent image formed on the surface of a photosensitive drum, which serves as an image carrier, using a developer located on a developer carrier member. A known configuration of a contact developing system is in which developing, during image formation, is performed simultaneously with the developer carrier member contacting the image carrier member. In this contact developing system configuration, a developing roller having an elastic layer on the outer peripheral surface of a rotating shaft member is generally used as the developer carrier member.

[0003] Additionally, an image forming apparatus known as a so-called image carrier component cleaner-free system (hereinafter also referred to as "cleaner-free system") is known, in which no cleaning components are provided to remove and collect toner residues on the image carrier component, so as to reduce the size of the image forming apparatus and reduce costs by reducing the number of components.

[0004] In a cleaner-less image forming apparatus, untransferred toner and atomized toner enter between the photosensitive drum and the charging roller. Therefore, the toner pressed between the photosensitive drum and the charging roller may fuse to the photosensitive drum. Since the fused toner interferes with exposure, blank spots may appear in the image. Furthermore, when the fused portion is continuous in the circumferential direction of the photosensitive drum, image defects such as white streaks appear.

[0005] In cleaner-less systems, it is necessary to collect toner not used for image formation, such as untransferred toner and atomized toner, in the developing unit. However, toner fused to the photosensitive drum cannot be removed and recovered unless strong force is applied in the developing unit. Typically, the developing roller is covered by a toner layer, but by exposing the surface of the developing roller from the toner layer, the photosensitive drum can be more strongly rubbed and the toner present on the photosensitive drum can be removed.

[0006] Furthermore, products using an intermediate transfer belt as the intermediate transfer medium have been put into practical use as image forming apparatuses. In such image forming apparatuses using an intermediate transfer belt, the toner image formed on the photosensitive drum is first transferred to the intermediate transfer belt in a single transfer by a primary transfer unit. Next, a secondary transfer unit transfers the toner image on the intermediate transfer belt a second time onto the transfer material. Then, the toner image on the transfer material is fixed using a fixing device.

[0007] In the case of a color image forming apparatus, the processing cartridges are arranged outside the intermediate transfer belt, for example, sequentially representing yellow, magenta, cyan, and black from the upstream side along the rotational movement direction of the intermediate transfer belt. The processing cartridge includes a photosensitive drum, a charging unit surrounding the photosensitive drum, an exposure unit, and a developing unit. A primary transfer unit performing one transfer is arranged at the position of each photosensitive drum facing each processing cartridge, with the intermediate transfer belt interposed therebetween.

[0008] Furthermore, to improve the durability of the image forming apparatus, a method is used where the photosensitive drum and developing rollers only contact each other when necessary and separate when not needed. Using this method, in monochrome image forming mode for forming monochrome images (monochrome printing), only the black developing roller contacts the photosensitive drum, while the developing rollers for colors other than black are separated from the photosensitive drum. This state of the developing rollers is called single contact. Simultaneously, during full-color printing, the state where all developing rollers are in contact with the photosensitive drum is called full contact. Additionally, the state where all developing rollers are separated from the photosensitive drum outside of printing operations is called full separation. This developing-separation type image forming apparatus can undergo a cycle of state transitions between full separation, full contact, single contact, and full separation depending on the printing state.

[0009] In the image forming operation, a preprocessing operation (hereinafter referred to as the pre-rotation sequence) is performed to start the driving source and supply high voltage, corresponding to the start of image forming, followed by a developing contact, and then a developing separation is performed after image forming is complete. Afterwards, a postprocessing operation (hereinafter referred to as the post-rotation sequence) is performed to stop the high voltage supply and stop the driving source, thus completing a series of image forming operations.

[0010] When such an image forming apparatus performs a printing job in which full-color printing and monochrome printing are mixed, a post-rotation sequence and a pre-rotation sequence are required each time a transition from full-color printing to monochrome printing or from monochrome printing to full-color printing is made, thereby extending the time to complete the printing job.

[0011] Regarding the issue of adhesion on the photosensitive drum, Japanese Patent Application Publication No. 2021-124604 describes the scraping and removal of deposits on the surface of the photosensitive drum using a developing roller.

[0012] In addition, regarding the issue of extended completion time for printing jobs that combine full-color and monochrome printing, Japanese Patent Application Publication No. 2003-345101 discloses a method that switches between developing and separating operations without stopping the printing operation, thereby shortening the image formation time and suppressing unnecessary use of the processing cartridge, thus reducing performance degradation. Summary of the Invention

[0013] However, in the configuration described in the above document, for example, when switching from full-color printing to monochrome printing, since the image formation operation is completed in monochrome printing after the developing roller switches from a fully contact state to a single contact state, the scraping operation is only performed on black.

[0014] The present invention was made in view of the above problems, and the object of the present invention is to efficiently clean the toner on the photosensitive drum with a developing roller in an image forming apparatus capable of performing full-color printing and monochrome printing without a cleaner system.

[0015] The present invention provides an image forming apparatus, comprising a first image forming unit corresponding to a first color and a second image forming unit corresponding to a second color other than the first color.

[0016] The first image forming unit includes: a rotatable first image carrier member, the surface of which is exposed to light to form an electrostatic latent image on the surface of the first image carrier member; a rotatable first developing member, which contacts the first image carrier member to supply developer to the surface of the first image carrier member and rotates at a speed different from the rotational speed of the first image carrier member; and a first developer supply member, which supplies developer to the surface of the first developing member.

[0017] The second image forming unit includes: a rotatable second image carrier member, the surface of which is exposed to light to form an electrostatic latent image on the surface of the second image carrier member; a rotatable second developing member, which contacts the second image carrier member to supply developer to the surface of the second image carrier member and rotates at a speed different from the rotational speed of the second image carrier member; and a second developer supply member, which supplies developer to the surface of the second developing member.

[0018] The image forming apparatus also includes:

[0019] The control unit is configured to control the developing voltage applied to the first developing member and the second developing member, and the supply voltage applied to the first developer supply member and the second developer supply member. The control unit is capable of performing image forming operations, namely, forming a developer image on the surface of the first image carrier member by supplying developer from the first developing member to an electrostatic latent image formed on the surface of the first image carrier member, and forming a developer image on the surface of the second image carrier member by supplying developer from the second developing member to an electrostatic latent image formed on the surface of the second image carrier member; and cleaning operations other than the image forming operations, wherein deposits already attached to the surface of the image carrier member are removed by the developing member through the cleaning operations.

[0020] The image forming operation includes a first image forming operation that forms an image using only a first image forming unit and a second image forming operation that forms an image using a first image forming unit and a second image forming unit;

[0021] The first image forming unit can move the first developing member between a contact state in which the first developing member and the first image carrier member are in contact with each other and a separation state in which the first developing member and the first image carrier member are separated from each other; the second image forming unit can move the second developing member between a contact state in which the second developing member and the second image carrier member are in contact with each other and a separation state in which the second developing member and the second image carrier member are separated from each other, and performs image forming and cleaning operations in the contact state; and

[0022] The control unit is configured to perform control to execute a cleaning operation after the second image forming operation in the event of switching from the second image forming operation to the first image forming operation;

[0023] Execution control to perform cleaning operations in the first and second image forming units without causing the second developing member in the second image forming unit, which is in contact with the second image carrier member, to transition to a separated state; and

[0024] The control is executed to switch the second developing member to a separated state in the second image forming unit after the cleaning operation, and to perform the first image forming operation in the first image forming unit.

[0025] According to the present invention, in an image forming apparatus with a cleaner-free system capable of performing full-color and monochrome printing, the toner on the photosensitive drum can be cleaned efficiently using a developing roller.

[0026] Further features of the invention will become clear from the following description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0027] Figure 1 This is a block diagram used to explain the color image forming apparatus of Embodiment 1;

[0028] Figure 2 The development separation in Example 1 was explained;

[0029] Figure 3A and Figure 3B An example of a developing roller used in an image forming apparatus according to Embodiment 1 is shown;

[0030] Figure 4 This is a standard development and separation timing diagram;

[0031] Figure 5The state transition between developing contact and separation in Example 1 is explained;

[0032] Figure 6 The potential relationship in the scraping operation in Example 1 is explained;

[0033] Figures 7A to 7C The state of the surface of the developing roller during the scraping operation in Example 1 is explained;

[0034] Figure 8 This is a timing diagram of the scraping process after the image is formed in Example 1;

[0035] Figure 9 This is a timing diagram of the scraping process when switching from full color to monochrome in the comparative example;

[0036] Figure 10 This is a timing diagram of the scraping process when switching from full color to monochrome in Example 1;

[0037] Figure 11 This is a timing diagram of the scraping process when switching from monochrome to full color in the comparative example;

[0038] Figure 12 This is a timing diagram of the scraping process when switching from monochrome to full color in Example 1;

[0039] Figure 13 This is a timing diagram of the scraping process when switching from monochrome to full color in Example 2; and

[0040] Figure 14 This is a block diagram illustrating an example of a control system for an image forming apparatus. Detailed Implementation

[0041] Preferred embodiments of the present invention will now be described in detail by way of example with reference to the accompanying drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the following embodiments should be appropriately varied depending on the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless otherwise specifically stated, the scope of the invention is not intended to be limited.

[0042] Example 1

[0043] Reference Figure 1 The overall configuration and image forming operation of the electrophotographic image forming apparatus (hereinafter referred to as the image forming apparatus) according to Embodiment 1 of the present invention are described. Figure 1 This is a schematic cross-sectional view showing a schematic configuration of an image forming apparatus 100 according to an embodiment of the present invention.

[0044] In this embodiment, four color image forming stations S (SY, SM, SC, and SK) for yellow, magenta, cyan, and black are provided as image forming units in a sequential arrangement from left to right in the figure. Each image forming station is an electrophotographic image forming mechanism with the same configuration, except for the color of the developer (hereinafter referred to as toner) 90 contained in each developing apparatus. In the following description, when it is necessary to distinguish colors, any one of the symbols Y (yellow), M (magenta), C (cyan), and K (black) will be added to the reference numerals. These symbols are omitted if it is not necessary to distinguish colors. The plurality of image forming stations S correspond to the image forming station SK (first image forming unit) corresponding to black as the first color and to the stations corresponding to colors other than the first color (yellow, magenta, and cyan). Monochrome printing of an image formed using only the first color is a first image forming operation. Full-color printing of an image formed using all colors, including the first color, is a second image forming operation.

[0045] Each image forming station has a photosensitive drum 1 as an image carrier, a charging roller 2 as a charging component, a developing unit 4, and a primary transfer device 51 as its main components. The primary transfer device 51 faces the photosensitive drum 1, with an intermediate transfer belt 53 positioned between them as an intermediate transfer component. The exposure device 3 can be shared by all image forming stations, or it can be provided for each image forming station.

[0046] In this embodiment, the photosensitive drum 1, charging roller 2, and developing device 4 are integrated into a processing cartridge 8 and configured to be detachably attachable to the main body of the image forming apparatus (the portion of the image forming apparatus 100 excluding the processing cartridge 8). However, the processing cartridge in this invention may include at least the photosensitive drum 1 and the developing device 4, and may be configured to be detachably attachable to the apparatus body as a whole. Furthermore, the developing device 4 may be configured separately to be independently detachably attachable to either the apparatus body or the processing cartridge 8. Additionally, the photosensitive drum 1 and the developing device 4 may be fastened to the main body of the image forming apparatus to eliminate the need for user replacement.

[0047] The photosensitive drum 1 is a rotatable cylindrical photosensitive component that rotates about the axis of the cylinder in the direction of the arrow (counterclockwise in the figure). In this embodiment, the outer peripheral surface of the photosensitive drum 1 is driven to rotate at a speed of 180 mm / sec.

[0048] The surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. In this embodiment, the charging roller 2 is a conductive roller with a conductive rubber layer provided on a metal core, and it is mounted by contacting the photosensitive drum 1, which is connected in parallel under a predetermined pressure, so as to rotate with the rotation of the photosensitive drum 1. A charging voltage can be applied to the charging roller 2 from the power supply device 67 (power supply component). In this embodiment, the photosensitive drum 1 is charged by applying a DC voltage of -1150V to the charging roller 2. At this time, the surface potential of the photosensitive drum 1 is approximately -500V.

[0049] The exposure device 3, acting as an exposure unit, acquires an image signal from the control unit 65 and scans the surface of the photosensitive drum 1 with a laser beam corresponding to the image signal. Therefore, an electrostatic latent image corresponding to the image signal is formed on the charged photosensitive drum 1. The image signal can be acquired from an external information processing device 900. The control unit 65 can be, for example, an information processing device, such as a control circuit having computing resources such as a processor and memory.

[0050] The developing apparatus 4 supplies toner 90 to the electrostatic latent image on the photosensitive drum 1 to visualize the latent image as a toner image (developer image). The developing apparatus 4 is provided to enable contact and separation with the photosensitive drum 1 via a contact / separation mechanism 48. Figure 2 An example of a black image forming station is shown. The developing unit 4K can be in a contact state (indicated by the solid line 4K(a)) and a separated state (indicated by the dashed line 4K(b)). The developing unit 4 only contacts (developing contacts) the photosensitive drum 1 during image formation. As a contact / separation mechanism 48, for example, a mechanism can be used such that the positional relationship between the developing unit 4 and the photosensitive drum 1 is changed by pushing the receiving portion disposed at the developing unit 4 by a moving member, wherein the moving member is driven by a drive source to move or rotate in parallel, and such that the positional relationship between the photosensitive drum 1 and the developing roller 42 is changed from a contact state to a separated state or from a separated state to a contact state. However, the structure of the contact / separation mechanism 48 is not limited to this.

[0051] The developing apparatus 4 is equipped with a rotatable developing roller 42 as a developing component, a toner supply roller 43 as a developer supply component, and an adjusting doctor blade 44 as a developer adjusting component. The toner supply roller 43 is an elastic sponge roller with foam formed on the outer periphery of a conductive core. The toner supply roller 43 is mounted to contact the developing roller 42 with a predetermined penetration amount. The toner 90 supplied by the toner supply roller 43 and held by the developing roller 42 is adjusted in thickness by the adjusting doctor blade 44 to form a thin layer for developing. Here, the adjusting doctor blade 44 has the function of adjusting the layer thickness of the toner 90 on the developing roller 42, and also functions as a developer charging component that imparts a predetermined charge to the toner 90 on the developing roller 42.

[0052] The power supply device 67 is configured to function as a developing voltage application unit 671 that applies a developing voltage to the developing roller 42 included in the developing apparatus 4, a supply voltage application unit 672 that applies a supply voltage to the toner supply roller 43, and an adjusting voltage application unit 673 that applies an adjusting voltage to the adjusting doctor blade 44. The power supply device 67 can be provided separately as a charging power supply for the charging roller and a developing power supply for the developing apparatus. In that case, the charging power supply and the developing power supply can be considered together as a power supply component. Furthermore, the developing power supply for the developing roller and the power supply for the toner supply roller can be separate. In that case, the charging power supply, the developing power supply, and the supply power supply can be considered together as a power supply component. Additionally, the power supply device 67 can be used for voltage application during image transfer, or it can provide separate transfer power supplies. In this embodiment, the power supply device 67 changes the voltage applied to each component under the control of the control unit 65. Figure 14 This is a block diagram illustrating an example of a control system based on control unit 65. The diagram shows an example in which power supply device 67, in addition to the developing voltage application unit 671, supply voltage application unit 672, and regulating voltage application unit 673, also functions as a charging voltage application unit 674 and a transfer voltage application unit 675.

[0053] The developing roller 42 is driven to rotate in the direction of the arrow in the figure (clockwise), such that the direction of movement of its surface is the same as the direction of movement of the photosensitive drum 1. The developing roller 42 can rotate at a different speed than the photosensitive drum 1. In this embodiment, the developing roller 42 is driven to rotate such that the surface of the developing roller 42 moves at a higher speed than the surface of the photosensitive drum 1 in order to obtain an appropriate image density. In addition, the developing apparatus 4 is pressed against the photosensitive drum 1 by a force-applying member (not shown), resulting in the developing roller 42 being pressed against the photosensitive drum 1. The surface of the developing roller 42 is thus deformed to form a developing gap (developing unit), thereby enabling stable development to be performed in a stable contact state.

[0054] An example of the surface shape of the developing roller 42 is shown in Figure 3A and Figure 3B As shown in the image. Figure 3A As shown, the developing roller 42 of this embodiment has a base layer 422 and a surface layer 423 formed on the outer periphery of the shaft 421. Figure 3BThis is an enlarged cross-sectional view of the developing roller gap portion, in which the developing roller 42 is in contact with the photosensitive drum 1. The surface layer 423 of the developing roller 42 has a structure in which coarse particles 423b are dispersed in a surface bonding resin 423a. As a result, a plurality of irregularities are formed on the surface of the surface layer 423, including a plurality of recesses and a plurality of protrusions for toner delivery. The ten-point average roughness Rzjis of the protrusions is greater than the volume average particle size of the toner 90. In this embodiment, the volume average particle size of the toner 90 is 7 μm, and the Rzjis of the surface layer 423 is 10 μm. A suitable Rzjis range for the surface layer of the developing roller is approximately 8 μm to 30 μm.

[0055] The toner image formed on the photosensitive drum 1 is electrostatically transferred to the intermediate transfer belt 53 by a primary transfer device 51, which is one of the transfer components. A full-color toner image is formed by sequentially superimposing and transferring toner images of corresponding colors onto the intermediate transfer belt 53.

[0056] A full-color toner image is transferred onto the recording material P, which is the transfer target, using a secondary transfer device 52, a transfer component different from the primary transfer device 51. Afterwards, the toner image on the recording material is pressed and heated by a fixing device 6 to fix the image onto the recording material P. Finally, the recording material P is discharged as a product with the image formed thereon.

[0057] A cleaning device 7 is installed downstream of the secondary transfer device 52 in the moving direction of the intermediate transfer belt 53 to remove and collect the toner 90 remaining on the intermediate transfer belt 53.

[0058] The intermediate transfer belt 53 is tensioned by three rollers: a tension roller 58, a drive roller 57, and a counter-roller 59 (secondary transfer counter-roller). The tension roller 58 applies tension to the intermediate transfer belt 53 by moving about its rotation axis. The drive roller 57 transmits rotational drive to the intermediate transfer belt 53. The counter-roller 59 is positioned facing the secondary transfer roller 56 and is driven to rotate while holding the intermediate transfer belt 53. The secondary transfer device 52 consists of the secondary transfer roller 56 and the counter-roller 59.

[0059] In this embodiment, an image carrier component cleaner-free system is employed, wherein the developing unit 4 collects the toner 90 that has not been transferred and remains on the surface of the photosensitive drum 1, without requiring a dedicated cleaner for the photosensitive drum 1. Until the surface of the photosensitive drum 1 has passed through the position facing the primary transfer device 51 (primary transfer position) and reached the contact position with the charging roller 2 (charging position), no component contacts the surface of the photosensitive drum 1. Therefore, when the developing roller 42 of the developing unit 4 contacts the photosensitive drum 1, the developing unit 4 can collect the toner 90 remaining on the photosensitive drum 1 after image formation. When employing this cleaner-free system, it is also preferable to use a non-magnetic single-component developer as the toner 90. However, the above configuration is not limited to achieving the effects of the present invention.

[0060] Next, a summary of the image formation process in this embodiment will be described. During image formation, -300V is applied to the developing roller 42. A voltage of -400V is applied to the adjusting doctor blade 44, and -400V is also applied to the toner supply roller 43. Since the toner 90 of the present invention has a negative charging polarity, the toner is readily supplied from the toner supply roller 43 to the developing roller 42.

[0061] In the photosensitive drum 1, the surface potential of the image printing section where the toner image is formed is on the normal charging polarity side of the toner 90, and its absolute value is controlled to be lower than the voltage applied to the developing roller 42. Simultaneously, in the image non-printing section where no toner image is formed, the surface potential is controlled to a drum potential of -500V. As a result, the toner, charged by the potential difference with the developing roller 42, is developed in the image printing section.

[0062] The toner image developed on the photosensitive drum is transferred to the intermediate transfer belt 53 at the primary transfer section formed by the primary transfer device 51. However, toners with low charge and toners with polarity opposite to normal charge are not transferred and protrude between the charging roller 2 and the photosensitive drum 1. Furthermore, atomized toner also protrudes into the charging roller 2 in the same manner. As a result, the toner is stressed and deformed between the charging roller 2 and the photosensitive drum 1, and may adhere to the photosensitive drum 1 as an adhering substance. In the portions of the photosensitive drum where toner adheres, the transferability during the next image formation is reduced, making it more likely that untransferred toner will appear. Consequently, deposits grow on the photosensitive drum.

[0063] Because the laser beam emitted from the exposure device 3 is blocked at the fusion portion on the photosensitive drum, the surface potential of the photosensitive drum 1 does not reach the predetermined potential, and the image density at the solid printing portion becomes low. In particular, white stripes will appear on the image where the fusion material is continuous in the rotational direction of the photosensitive drum. Therefore, it is necessary to remove the toner remaining on the photosensitive drum.

[0064] Figure 4The timing of image formation in a comparative example, hypothesized from a conventional example, is shown. The latent images (Y latent image, M latent image, C latent image, and K latent image) of yellow (Y), magenta (M), cyan (C), and black (K) are shown in two phases: a period during which the image (latent image) is formed (ON) and a period during which the image (latent image) is not formed (OFF). Furthermore, regarding the contact and separation of the developing apparatus for each color (Y developing, M developing, C developing, and K developing), the upper side shows the contact state, the lower side shows the separation state, and the transition time between the two states is also shown. Additionally, the primary transfer of each color is indicated by the transfer period (ON) and the non-transfer period (OFF). Furthermore, the secondary transfer to the recording medium (recording material P) is shown in two phases: a transfer period (ON) and a non-transfer period (OFF).

[0065] First, when an image forming start signal is input to the image forming apparatus 100, the intermediate transfer belt 53 and the photosensitive drums 1Y, 1M, 1C, and 1K begin to rotate. Then, the charging rollers 2Y, 2M, 2C, and 2K apply a DC voltage to charge the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K to a desired negative polarity charging potential.

[0066] Then, the exposure device 3 radiates laser light based on the image information to begin forming an electrostatic latent image on the photosensitive drums 1Y, 1M, 1C, and 1K (on the image-bearing components). This is Figure 4 The image formation ON timing for each color latent image is as follows (t41 for yellow Y). In this embodiment, the electrostatic latent images are formed in the order of yellow latent image, magenta latent image, cyan latent image, and black latent image (t42 for yellow Y).

[0067] Then, the developing units 4Y, 4M, 4C, and 4K come into contact with the photosensitive drums 1Y, 1M, 1C, and 1K on which electrostatic latent images have already formed. This indicates that... Figure 4 Each color in the process reaches a contact state during development. As a result, toner is supplied, making the electrostatic latent image visible and forming a toner image on the photosensitive drums 1Y, 1M, 1C, and 1K. At this time, the developing units 4Y, 4M, 4C, and 4K, starting from the upstream side of the rotation direction of the intermediate transfer belt 53, contact the photosensitive drums 1Y, 1M, 1C, and 1K in the order of magenta M, cyan C, and black K, immediately before image formation (toner image formation). That is, as... Figure 4 As shown, a contact state is established and toner image formation is performed in order from the upstream side to the downstream side.

[0068] Furthermore, the developing units 4Y, 4M, 4C, and 4K are separated in the order of 4Y from the upstream side to 4K from the downstream side, and the toner image is formed. In the case of monochrome printing, the state transition is performed by the contact / separation mechanism 48, so that only the black K developing unit 4K enters the developing contact state with the photosensitive drum 1K.

[0069] Figure 5 An example of the state transition between developing contact and developing separation in this embodiment is shown. The image forming apparatus 100 can take three states: "completely separated," "completely in contact," and "single contact." Completely separated is a state other than image forming, in which all developing rollers are separated. Completely in contact is a state in full-color printing where all developing rollers are in contact during image forming. Monochrome contact is a state in monochrome printing where only black K is in contact during image forming. In this embodiment, these three states transition from complete contact to single contact, from single contact to complete separation, and from complete separation to complete contact again, as indicated by the arrows in the figure. The state transitions in this embodiment are as described above, but the invention is not limited thereto. Configurations that allow transitions from complete contact to complete separation, from complete separation to single contact, and from single contact to complete contact, etc., are also applicable.

[0070] Subsequently, the toner image formed on the photosensitive drums 1Y, 1M, 1C, and 1K is electrostatically transferred to the intermediate transfer belt 53 via primary transfer devices 51Y, 51M, 51C, and 51K (indicating...). Figure 4 One transfer of each color in the process (ON).

[0071] The intermediate transfer belt 53 is a resin ring belt that contacts the photosensitive drums 1Y, 1M, 1C, and 1K. The intermediate transfer belt 53 is driven by a drive motor 80 that rotates the drive roller 57. Figure 1 The intermediate transfer belt 53 rotates clockwise. As the intermediate transfer belt 53 rotates with the photosensitive drums 1Y, 1M, 1C, and 1K according to the image forming operation, voltage is applied to the primary transfer devices 51Y, 51M, 51C, and 51K, thereby sequentially transferring the monochrome toner image onto the intermediate transfer belt 53 (primary transfer). Untransferred toner remaining on the photosensitive element is collected by the developing devices 4Y, 4M, 4C, and 4K.

[0072] Next, the operation of suppressing the growth of deposits on the photosensitive drum 1 will be described. Figure 6 This shows each voltage during image formation. The horizontal axis indicates the passage of time. The vertical axis indicates the voltage.

[0073] Right now:

[0074] The voltage applied to the developing roller 42: -300V (indicated by the solid line); and

[0075] The voltage applied to the toner supply roller 43 is -400V (indicated by the dashed line between t61 and t62).

[0076] Therefore, the voltage difference between the toner supply roller 43 and the developing roller 42 applied during image formation is -100V. Furthermore, in this embodiment, since the normal charging polarity of the toner is negative, the potential difference formed as the driving force for supplying toner from the toner supply roller 43 to the developing roller 42 is as follows:

[0077] Potential difference: +100V.

[0078] When the image forming operation on the intermediate transfer belt 53 is completed in each print job, the control unit 65 changes the voltage applied to the toner supply roller 43 from -400V during image forming to -350V (indicated by the dotted line between t62 and t63) and rotates the toner supply roller for a predetermined time. As a result, the potential difference changes from 100V to 50V, the pressure of the toner from the toner supply roller 43 to the developing roller 42 becomes weaker than during image forming, and the amount of toner on the developing roller becomes less than the amount during image forming. Hereinafter, this control, which, apart from the image forming operation, makes the potential difference less than the potential difference during image forming and causes the developing roller 42 and the photosensitive drum 1 to rotate in contact with each other, is referred to as the scraping operation.

[0079] Summary Figure 6 As shown, the voltage applied to the developing roller 42 rises to -300V at time t61 and remains thereafter until time t63. The voltage applied to the toner supply roller 43 rises to -400V at time t61 and remains thereafter until time t62. The potential difference during this image forming operation is 100V. At time t62, the voltage applied to the toner supply roller 43 becomes -350V and remains thereafter until time t63. The potential difference during this scraping operation is 50V.

[0080] When the voltage applied to the toner supply roller 43 during image formation is on the supply side (applied voltage difference > 0), as in this embodiment, where the voltage applied to the toner supply roller 43 during the scraping operation is closer to the voltage applied to the developing roller 42 than the voltage applied during image formation, it is difficult to supply toner to the developing roller 42, and the amount supplied is reduced. As a result, the amount of toner on the developing roller 42 is reduced, and the surface irregularities of the developing roller 42 tend to come into direct contact with the photosensitive drum 1.

[0081] For example, when the voltage applied to the toner supply roller 43 changes from -400V to -350V, the toner dosage on the developing roller 42 decreases, causing a portion of the developing roller surface 423 to become exposed from the toner coating on the developing roller 42 after passing through the adjusting doctor blade 44.

[0082] Figure 7A The appearance of the developing roller surface 423 is shown when the voltage applied to the toner supply roller 43 is -400V. Figure 6 During the image formation operation. Figure 7B The developing roller surface 423 is shown when the voltage applied to the toner supply roller 43 is -350V. Figure 6 During the scraping operation. Figure 7B The image shows the state before the molten material X immediately adjacent to the photosensitive drum 1 is scraped off from the portion exposed by the toner coating on the protrusion of the developing roller surface (indicated as exposed portion Z in the figure). Additionally, Figure 7C This shows the state immediately following the scraping away of most of the molten material X from the exposed portion Z.

[0083] Here, when the circumferential speed of the developing roller 42 is V1 and the circumferential speed of the photosensitive drum 1 is V2, there is a difference in circumferential speed between V1 and V2, and in this embodiment, V1 > V2. Therefore, since the portion of the developing roller surface exposed from the toner coating contacts the photosensitive drum 1 and rotates with it at a different circumferential speed, the molten material on the photosensitive drum 1 can be scraped off. That is, the scraping operation means cleaning the surface of the photosensitive drum 1 by scraping off the molten material, and therefore can also be described as a cleaning operation.

[0084] By setting the voltage applied to the toner supply roller 43 during scraping to -250V and generating a potential difference of -50V, the potential relationship allows the toner to return from the developing roller 42 to the supply roller 43 side.

[0085] Furthermore, when the normal charge polarity of the toner is on the positive side, a corresponding voltage can be applied. For example, the voltage applied to the developing roller 42 during image formation can be changed to +300V, the voltage applied to the toner supply roller 43 can be changed to +400V, and the voltage applied to the toner supply roller 43 during scraping can be changed to +350V.

[0086] The completion of the image forming operation on the intermediate transfer belt 53 signifies the timing at which the trailing edge of the image from each image forming station is transferred to the intermediate transfer belt 53. In this embodiment, the scraping operation is executed sequentially, starting from the upstream image forming station that first completes image forming. To simplify control, the scraping operation can be started simultaneously in all Y, M, C, and K image forming stations. In this case, the timing for transitioning to the scraping operation is when the trailing edge of the image from the downstream image forming station K is transferred to the intermediate transfer belt 53.

[0087] Scraping operation during full-color printing

[0088] Figure 8The timing of the scraping operation in each image forming station is shown. The voltage applied to the developing roller 42, the voltage applied to the toner supply roller 43 during image forming, and the voltage applied to the toner supply roller 43 during scraping are shown.

[0089] The latent images of each color (Y latent image, M latent image, C latent image, and K latent image) are shown in two phases: a period during which an image (latent image) is formed (ON) and a period during which no image (latent image) is formed (OFF). Furthermore, the developing voltage applied to the developing roller 42 for each color (-300V in this embodiment) is shown in two phases: a period during which voltage is applied (ON) and a period during which voltage is not applied (OFF). Additionally, the supply voltage applied to the supply roller 43 for each color is shown in three phases: a period during which -400V is applied during image formation (ON), a period during which -350V is applied during scraping (ON), and a period during which no voltage is applied (OFF). Furthermore, regarding the contact and separation of the developing apparatus for each color (Y developing, M developing, C developing, and K developing), the upper side shows the contact state, the lower side shows the separation state, and the transition time between the two states is also shown. Additionally, in this figure, the scraping operation period in the contact state is shaded.

[0090] and Figure 4 The same applies; the developing contacts begin in the order of yellow (Y), magenta (M), cyan (C), and black (K) (for yellow (Y), it's t81). Once the developing contacts are complete, the image formation operation begins. Figure 8 The timing for image formation ON of the latent image and the timing for image formation ON of the developing roller voltage for each color are specified; for yellow (Y), it is t82). The voltage applied to the toner supply roller 43 for each color is also set during the image formation of the corresponding color. Subsequently, by supplying toner to the formed latent image, the Y image, M image, C image, and K image (toner image) are formed sequentially.

[0091] After image formation for each color is complete, the voltage applied to the corresponding toner supply roller 43 is changed from -400V to -350V (t83 for yellow Y). As a result, a scraping operation begins sequentially in the image forming station S. After a predetermined scraping time, the voltages of the developing roller 42 and the toner supply roller 43 are turned off, and the scraping operation ends. Afterward, development separation is performed, and the printing end operation begins and ends.

[0092] Scraping operation during the switch from full color to monochrome in the comparative example.

[0093] Next, the scraping operation based on a comparative example assumed from the prior art will be described when full-color printing and monochrome printing are mixed. Figure 9 The timing for switching from full-color printing to monochrome printing is shown.

[0094] During the full-color period, after the contact of the developing roller 42 has begun (t91 for yellow Y), latent image formation is turned on (ON), the voltage applied to the developing roller 42 is turned on (ON), and the voltage applied to the toner supply roller 43 is the value at which image formation occurs (t92 for yellow Y). When latent image formation is turned off (OFF), the voltage applied to the developing roller 42 and toner supply roller 43 for yellow Y, magenta M, and cyan C is turned off (OFF) (cyan C is indicated by symbol A1), and the developing rollers 42Y, 42M, and 42C are separated from the photosensitive drums 1Y, 1M, and 1C, respectively (indicated by symbols A2 and t93 for cyan C).

[0095] Simultaneously, for black, the voltage applied to the developing roller 42 remains ON, and the voltage applied to the toner supply roller 43 also remains at the value during image formation. Furthermore, the developing roller 42K maintains contact with the photosensitive drum 1K. As a result, after full-color printing is completed, it is possible to switch to a monochrome printing operable state and continue printing (monochrome latent image formation is indicated by symbol A3) without requiring a complete separation to stop the high-voltage supply or a printing operation accompanied by post-processing. This is consistent with... Figure 5 The transition from full contact (full color) to single contact (monochrome) corresponds to the state change. Subsequently, after image formation is performed in the single contact state, the voltage of the toner supply roller 43K for black K is changed to the voltage during scraping (indicated by symbol A4), and the scraping operation is performed (indicated by symbol A5).

[0096] According to the timing diagram above, even with a mix of full-color and monochrome printing, the image formation speed will not decrease significantly. Furthermore, since the processing cartridges used for yellow (Y), magenta (M), and cyan (C) will not be used beyond what is required, performance degradation of the processing cartridges can be reduced.

[0097] However, in Figure 9 In the comparative example shown, the developing apparatus for yellow (Y), magenta (M), and cyan (C) is separated from the photosensitive drum 1, and no scraping operation is performed at the end of full-color printing. Therefore, the scraping operation after the image forming operation is only performed in black (K). When such a printing job continues, the scraping operation for yellow (Y), magenta (M), and cyan (C) is not performed, so the molten material adheres to the photosensitive drum 1.

[0098] The scraping operation during the switch from full color to monochrome in this embodiment

[0099] Therefore, in this invention, as Figure 10As shown, a scraping operation is performed when switching from full-color printing to monochrome printing. Specifically, during the full-color printing period, after the developing roller 42 begins to contact (t101 for yellow Y), latent image formation is turned on (ON), the voltage applied to the developing roller 42 is turned on (ON), and the voltage applied to the toner supply roller 43 becomes the value at the time of image formation (t102 for yellow Y). When the image formation for each color is complete, the voltage applied to the toner supply roller 43 shifts to the value at the time of the scraping operation, while maintaining the voltage applied to the developing roller 42 when image formation is on (ON). As a result, a scraping operation is performed through the developing roller 42, which is in contact. As an example, for cyan C, the end of image formation (latent image) is indicated by reference numeral B1, the point at which the voltage of the toner supply roller 43 is changed for the scraping operation is indicated by reference numeral B2, and the execution of the scraping operation is indicated by reference numeral B3.

[0100] After full-color printing, for yellow (Y), magenta (M), and cyan (C), the voltage applied to the developing roller 42 and the voltage applied to the toner supply roller 43 are turned off, and the developing rollers 42Y, 42M, and 42C are separated from the photosensitive drums 1Y, 1M, and 1C (for cyan C, it is t103). Simultaneously, for black (K), the voltage of the developing roller 42K is maintained, and the voltage of the toner supply roller 43K returns to the value at the time of image formation. As a result, monochrome printing of black (K) can be performed. After the image of black (K) is formed, a scraping operation is performed on black (K), and the processing in the figure ends. Based on the above operations, when switching from full-color to monochrome, a scraping operation is performed on each color, thus efficiently suppressing fusion.

[0101] exist Figure 10 In the example, during the switch from full-color printing to monochrome printing, the scraping operation for black (K) is performed within the same timeframe as for yellow (Y), magenta (M), and cyan (C) (indicated by reference numeral B4). However, for black (K), the scraping operation is performed during monochrome printing after the switch (indicated by reference numeral B5), thus shortening the scraping time during the switch.

[0102] Scraping operation during the switch from monochrome to full color in the comparative example.

[0103] Next, Figure 11 The timing for switching from monochrome printing to full-color printing is shown in a comparative example based on prior art assumptions. First, during the monochrome printing period, the voltage of the developing roller 42K for black K and the voltage of the toner supply roller 43K are turned on (ON) (t111), and only the developing roller 42K and the photosensitive drum 1K are in contact (single contact).

[0104] Subsequently, in order to switch to full-color printing, the developing rollers 42Y, 42M, and 42C contact the photosensitive drums 1Y, 1M, and 1C (t112 for yellow Y). This corresponds to the following situation, in Figure 5 In the state transitions shown, after starting from the single-contact state (the state where the developing roller 42K contacts the photosensitive drum 1K), the developing roller 42K reaches a fully separated state (indicated by reference numeral C1) once it separates from the photosensitive drum 1K, and then transitions to the fully contact state (the state where the developing rollers 42Y, 42M, 42C, and 42K are in contact with the photosensitive drums 1Y, 1M, 1C, and 1K). Therefore, the time to switch from monochrome printing to full-color printing is longer than the time to switch from full-color printing to monochrome printing. In full-color printing, after the image is formed, a scraping operation is performed in yellow (Y), magenta (M), cyan (C), and black (K).

[0105] At this point, if no scraping operation is performed when switching from monochrome to full-color printing, the possibility of drum fusion in the black K layer increases. Conversely, if a scraping operation is performed during switching to reduce drum fusion, the timing of the black K layer's development separation needs to be delayed, further extending the switching time.

[0106] The scraping operation during the switch from monochrome to full color in this embodiment

[0107] Therefore, in this embodiment, as Figure 12 As shown, when switching from monochrome printing to full-color printing, the black K image forming station performs a short-duration scraping operation (reference numeral D1) with little or no impact on the switching time. Here, in the case of full-color printing, re-transfer of the images from the upstream Y, M, and C image forming stations may occur in the black K image forming station SK (a phenomenon where a portion of the previously transferred image is re-transferred to the photosensitive drum when transferring the toner for the next color). However, in the case of monochrome printing, the black K image forming station is unaffected by this re-transfer, thus shortening the scraping operation time.

[0108] In this embodiment, the scraping operation time is set to 1.5 seconds during the switchover operation from full-color printing to monochrome printing. Furthermore, the scraping operation time is set to 0.5 seconds during the switchover operation from monochrome printing to full-color printing. However, the time for each scraping operation is not limited to these values. For example, instead of setting the scraping time to a fixed value, it can be varied according to the print quantity, print pattern, environment, etc. Additionally, the predetermined switchover time A from full-color printing to monochrome printing is 1.0 second, the predetermined switchover time B from monochrome printing to full-color printing is 2.5 seconds, and the developing contact and separation times are each 1.0 second.

[0109] Table 1 shows a comparison between this embodiment and a comparative example. In the comparative example, "No Scratching" indicates the time (seconds) required without scraping and the state of the drum's fusion. "Scratching" indicates the time (seconds) required with scraping and the state of the drum's fusion. Regarding the state of the drum's fusion, "X" indicates fused (NG), and "O" indicates no fusion (OK). Different fusion states for black and other colors are indicated separately. Each time mentioned herein is merely an example.

[0110] [Table 1]

[0111]

[0112]

[0113] (1) In the comparative example, switch from full color to monochrome.

[0114] In the case of "no scratching" after full-color printing, the switching time is a predetermined time A (1.0 second). In this case, the transition from the fully contact state to the single contact state can be performed without going through the fully separated state and without scratching, so the required time is relatively short. However, since no scratching is performed after full-color printing, but only after monochrome printing is black K scratching performed, blistering occurs for every color other than black.

[0115] Meanwhile, in the case of "scraping" after full-color printing, the switching time requirement is a total of 4.5 seconds, including the contact (1.0 second), scraping (1.5 seconds), and separation (1.0 second) of the developing roller 42 after full-color printing, plus a predetermined time A. In this case, the fusion is removed at all photosensitive drums.

[0116] (2) In this embodiment, switching from full color to monochrome

[0117] In this embodiment, after full-color printing, a scraping operation is performed without separating the corresponding color developing roller 42, and then switching to monochrome printing is initiated. Therefore, the required time is the sum of the predetermined time A (1.0 second) and the scraping time (1.5 seconds), which is 2.5 seconds. Compared to the "no scraping" case in (1), the switching time is extended by 1.5 seconds, but the drum fusion for each color can be removed. Furthermore, compared to the "with scraping" case in (1), the effect of removing the drum fusion is the same, and the required time can be shortened by 2.0 seconds.

[0118] In summary, when switching from full-color printing to monochrome printing, in the comparative example in (1), if the predetermined switching time A remains unchanged, drum fusion occurs in yellow (Y), magenta (M), and cyan (C). To reduce drum fusion, a developing contact needs to be performed again to perform the scraping operation, which results in a longer switching time. Meanwhile, in this embodiment in (2), a switching time longer than the required switching time A for the scraping time is required, but under the condition that drum fusion does not occur, the switching can be performed in a shorter time than in the conventional example.

[0119] (3) In the comparative example, switch from monochrome to full color.

[0120] In the case of "no scratching" after monochrome printing, the switchover time requires a predetermined time B (2.5 seconds) longer than predetermined time A because a complete separation state is required. Furthermore, since no scratching is performed after monochrome printing, the possibility of fusion on the black K drum increases. Meanwhile, in the case of "scraping" after monochrome printing, the switchover time, in addition to the predetermined time B, also requires the black K scratching time (1.5 seconds), for a total of 3.5 seconds. In this case, fusion is removed from all photosensitive drums.

[0121] (4) In this embodiment, switching from monochrome to full color

[0122] In this embodiment, the required time is the sum of the predetermined time B (2.5 seconds) and the scraping time (0.5 seconds), which is 3.0 seconds, and the switching time is the same as in the "no scraping" case in (2). This is because the scraping operation is performed in parallel at the end of the required time. Furthermore, compared to the "with scraping" case in (2), the effect of removing the fused drum is the same, and the required time can be shortened by 1.5 seconds.

[0123] In summary, when switching from monochrome printing to full-color printing, in the conventional example where the predetermined switching time B remains unchanged in (3), drum fusion occurs in black K. To reduce drum fusion, a scraping operation is performed, thus requiring a delayed development separation, resulting in a prolonged switching time. In contrast, in this embodiment in (4), the scraping operation is performed within the switching operation time, allowing the switching to be performed in the same time as in the conventional example and suppressing the occurrence of drum fusion.

[0124] By doing so, when full-color and monochrome printing are mixed, the switching operation can be performed efficiently while the scraping operation is being performed. In this embodiment, a mechanism that can be implemented independently in each processing cartridge is used for developing contact / separation, but a configuration of contact / separation mechanism 48 that separates from black K can be obtained by using yellow Y, magenta M, and cyan C together.

[0125] According to this embodiment, in an image forming apparatus with a cleaner-free system where the developing roller 42 and the photosensitive drum 1 can contact and separate from each other, the scraping operation to remove deposits from the surface of the photosensitive drum via the developing roller can be performed during switching operations from full-color printing to monochrome printing and from monochrome printing to full-color printing. Therefore, during the cleaning operation of the photosensitive drum 1, unnecessary contact time between the photosensitive drum 1 and the developing roller 42 can be reduced, and the switching operation can be performed efficiently.

[0126] Example 2

[0127] Will use Figure 13 Explanation of Example 2. When comparing this example with Example 1, the difference lies in the scraping operation during the switching operation from monochrome printing to full-color printing. Since the configuration and operation of this device are mostly the same as those in Example 1 described above, the following description focuses on the differences from Example 1.

[0128] Figure 13 The timing for switching from monochrome printing to full-color printing is shown. Without image defects caused by impact upon contact with the developing roller 42, the contact of the yellow Y (reference numeral E2) begins after the separation operation of the black K (reference numeral E1) is completed, thus minimizing the switching operation time. In this case, if a scraping operation is performed during the switching operation, the switching time is extended.

[0129] Therefore, in this embodiment, as Figure 13 As shown, the scraping operation is performed in conjunction with the scraping operation after full-color printing, and is also performed during the switching operation after image formation in monochrome printing. That is, the time for the scraping operation after full-color printing is extended. Therefore, for black K, by performing the scraping operation in a concentrated manner after image formation in full-color printing, the deposits on the photosensitive drum surface can be removed without extending the switching time.

[0130] As described above, in this embodiment, since the scraping operation during the switch from monochrome printing to full-color printing is performed in a concentrated manner after full-color printing, the contact of the yellow Y after monochrome printing can be accelerated, and the switchover time can be shortened. Therefore, unnecessary contact time between the photosensitive drum and the developing roller can be reduced, and the switchover operation can be performed efficiently.

[0131] According to the present invention, when full-color printing and monochrome printing are mixed in an image forming apparatus in which the developing roller 42 and the photosensitive drum 1 can contact and separate from each other, the toner on the drum can be removed and the switching time can be shortened when a scraping operation is performed when switching from full-color printing to monochrome printing or from monochrome printing to full-color printing.

[0132] While the invention has been described with reference to exemplary embodiments, it should be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the appended claims should be given the broadest interpretation to cover all such modifications and equivalent structures and functions.

Claims

1. An image forming apparatus characterized by comprising: The image forming apparatus includes a first image forming unit corresponding to a first color and a second image forming unit corresponding to a second color other than the first color. The first image forming unit includes: a rotatable first image carrier member, the surface of which is exposed to light to form an electrostatic latent image on its surface; a rotatable first developing member, which contacts the first image carrier member to supply developer to its surface and rotates at a speed different from that of the first image carrier member; and a first developer supply member, which supplies developer to the surface of the first developing member. The second image forming unit includes: a rotatable second image carrier member, the surface of which is exposed to light to form an electrostatic latent image on its surface; a rotatable second developing member, which contacts the second image carrier member to supply developer to its surface and rotates at a speed different from that of the second image carrier member; and a second developer supply member, which supplies developer to the surface of the second developing member. The image forming apparatus further includes: A control unit is configured to control the developing voltage applied to the first developing member and the second developing member, and the supply voltage applied to the first developer supply member and the second developer supply member. The control unit is capable of performing an image forming operation by supplying developer from the first developing member to an electrostatic latent image formed on the surface of the first image carrier member, thereby forming a developer image on the surface of the first image carrier member, and by supplying developer from the second developing member to an electrostatic latent image formed on the surface of the second image carrier member, thereby forming a developer image on the surface of the second image carrier member. The control unit also performs a cleaning operation other than the image forming operation, wherein deposits already attached to the surface of the image carrier member are removed by the developing member during the cleaning operation. The image forming operation includes a first image forming operation that forms an image using only the first image forming unit and a second image forming operation that forms an image using both the first image forming unit and the second image forming unit; The first image forming unit is capable of moving the first developing member between a contact state in which the first developing member and the first image carrier member are in contact with each other and a separation state in which the first developing member and the first image carrier member are separated from each other; the second image forming unit is capable of moving the second developing member between a contact state in which the second developing member and the second image carrier member are in contact with each other and a separation state in which the second developing member and the second image carrier member are separated from each other; and the image forming operation and the cleaning operation are performed in the contact state; and The control unit is configured to perform control to execute the cleaning operation after the second image forming operation in the event of switching from the second image forming operation to the first image forming operation; Execution control to perform the cleaning operation in the first image forming unit and the second image forming unit without causing the second developing member in the second image forming unit, which is in contact with the second image carrier member, to change to a separated state; and The control is executed to switch the second developing member to a separated state in the second image forming unit after the cleaning operation, and to perform the first image forming operation in the first image forming unit.

2. The image forming apparatus according to claim 1, wherein The control unit is configured to, in the case of switching from the second image forming operation to the first image forming operation, make the cleaning operation in the first image forming unit shorter than the cleaning operation in the second image forming unit during the cleaning operation performed in the first image forming unit and the second image forming unit after the second image forming operation.

3. The image forming apparatus according to claim 1, wherein: The control unit is configured to, upon switching from the first image forming operation to the second image forming operation, perform a cleaning operation in the first image forming unit and then bring the second developing member in the second image forming unit into a contact state, perform the second image forming operation in both the first and second image forming units, without bringing the first developing member in the first image forming unit, which was in a contact state with the first image carrier member during the first image forming operation, into a separated state.

4. The image forming apparatus according to claim 3, wherein: The control unit is configured to perform a cleaning operation in both the first and second image forming units after the second image forming operation is performed, and in the first image forming unit, the cleaning operation performed when switching from the first image forming operation to the second image forming operation takes a shorter time than the cleaning operation performed after the second image forming operation.

5. The image forming apparatus according to claim 1, wherein: The control unit is configured to perform a cleaning operation in both the first and second image forming units after the second image forming operation, in the case of switching from the first image forming operation to the second image forming operation, and the cleaning operation in the first image forming unit takes longer than the cleaning operation in the second image forming unit.

6. The image forming apparatus according to claim 1, wherein: The positional relationship between the first developing member in the first image forming unit and the first image carrier member in the second image forming unit and the positional relationship between the second developing member in the second image forming unit and the second image carrier member are switched between: (i) a state in which the first developing member is in contact with the first image carrier member in the first image forming unit and the second developing member is in contact with the second image carrier member in the second image forming unit; (ii) a state in which only the first developing member in the first image forming unit is in contact with the first image carrier member; and (iii) a state in which the first developing member is separated from the first image carrier member in the first image forming unit and the second developing member is separated from the second image carrier member in the second image forming unit.

7. The image forming apparatus according to claim 1, further comprising: An intermediate transfer member, which is an annular belt, is used to transfer developer images formed in the first image forming unit and the second image forming unit to the intermediate transfer member while the intermediate transfer member is rotated. The first image forming unit is arranged downstream of the second image forming unit in the rotational direction of the intermediate transfer member.

8. The image forming apparatus according to claim 1, wherein: The cleaning operation is a scraping operation used to remove deposits that have adhered to the surfaces of the first and second image carriers due to the difference in circumferential velocity between the developing component and the image carrier component.

9. The image forming apparatus according to any one of claims 1 to 8, wherein: The first image forming operation is monochrome printing using the first color, and the second image forming operation is printing using multiple colors.

Images