Image forming apparatus

Abstract

To reduce the likelihood of the generation of abnormal images such as an unsharp image and a blurred image.SOLUTION: When the time exceeding a predetermined time A elapses from the completion of the previous printing operation, an image forming apparatus executes, before starting a printing operation, a detection mode (process control) for detecting the image density of a toner image for detection carried on an intermediate transfer belt 8 (or photoreceptor drum 1Y) with an image density detection sensor 98, and when the image density is reduced by more than a predetermined value B from an image density detected in the previously executed detection mode, executes a control mode (moisture removal mode) for performing idle driving of the photoreceptor drum 1Y.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to an image forming apparatus such as a copier, printer, facsimile, or a combination device thereof. [Background technology]

[0002] Conventionally, in image forming apparatuses such as copiers and printers, there is a known technique for detecting the image density of a detection toner image formed on the surface of a photoreceptor (photoreceptor drum) or intermediate transfer material (intermediate transfer belt), and executing a control mode to reduce the occurrence of abnormal images based on the detection result (see, for example, Patent Document 1).

[0003] On the other hand, Patent Document 1 discloses a technique for reducing the problem of the surface of the photoreceptor drum deteriorating due to discharge products. This technique involves detecting the image density of a detection toner pattern (detection toner image) formed on the surface of the photoreceptor drum, and when it is determined that the degree of deterioration of the photoreceptor drum due to discharge products is severe based on the detection results, a large amount of toner is deposited on the surface of the photoreceptor drum. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Conventional image forming machines sometimes produced abnormal images such as blurred or streaky images when the photoreceptor (photoreceptor drum) had film on its surface, causing the printing process to start with a high moisture content in the photoreceptor.

[0005] This invention was made to solve the problems described above, and aims to provide an image forming apparatus that is less likely to produce abnormal images such as blurred or streaky images. [Means for solving the problem]

[0006] The image forming apparatus in this invention comprises a photoreceptor on which a toner image is carried, and an image density detection means for detecting the image density of a detection toner image carried on the surface of the photoreceptor or an intermediate transfer body on which the toner image carried on the photoreceptor is transferred. If a predetermined time has elapsed since the completion of the previous printing operation, before the printing operation is started, a detection mode is executed in which the image density detection means detects the image density of the detection toner image carried on the photoreceptor or the intermediate transfer body, and if the image density is In relation to the previous printing operation mentioned above, the one before In the detection mode that has been executed, if the image density detected is lower than a predetermined value, a control mode is executed in which the photoreceptor is driven without power. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an image forming apparatus that is less likely to produce abnormal images such as blurred or smudged images. [Brief explanation of the drawing]

[0008] [Figure 1] This is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention. [Figure 2] This is a diagram showing a magnified view of a portion of the image-making section. [Figure 3] This is a schematic diagram showing the intermediate transfer belt and its vicinity. [Figure 4] This flowchart shows an example of the control when executing the moisture removal mode. [Figure 5] This flowchart shows the control when performing a moisture removal mode as a variation. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments for carrying out this invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations will be simplified or omitted as appropriate.

[0010] First, the overall configuration and operation of the image forming apparatus 100 will be explained using Figures 1 and 2. Figure 1 is a schematic diagram showing a printer as an image forming apparatus, and Figure 2 is an enlarged view showing a part of its image-forming section. As shown in Figure 1, an intermediate transfer belt 8, which serves as a central transfer body, is installed in the center of the image forming apparatus body 100. Opposite the intermediate transfer belt 8, image forming units 6Y, 6M, 6C, and 6K corresponding to each color (yellow, magenta, cyan, and black) are arranged side by side. Furthermore, an operation display panel 95 is installed on the exterior of the main body 100 of the image forming apparatus, which displays information related to the printing operation (image forming operation) and allows for operation.

[0011] Referring to Figure 2, the image-forming unit 6Y corresponding to yellow consists of a photoreceptor drum 1Y as the photoreceptor, and a charging device 4Y, a developing device 5Y, a cleaning device 2Y, a static elimination device (not shown), etc., arranged around the photoreceptor drum 1Y. The image-forming process (charging process, exposure process, developing process, transfer process, cleaning process, static elimination process) is then performed on the photoreceptor drum 1Y to form a yellow image on the photoreceptor drum 1Y.

[0012] Furthermore, the other three image units, 6M, 6C, and 6K, have almost the same configuration as the yellow-compatible image unit 6Y, except for the color of the toner used, and each forms an image corresponding to its respective toner color. Below, we will omit explanations of the other three image units, 6M, 6C, and 6K, and only explain the yellow-compatible image unit 6Y.

[0013] Referring to Figure 2, the photoreceptor drum 1Y, which acts as the photoreceptor, is driven to rotate counterclockwise by a main motor (not shown). Then, at the position of the charging device 4Y, the surface of the photoreceptor drum 1Y is uniformly charged (this is the charging process). Specifically, the charging device 4Y in this embodiment is a charging roller, to which a DC voltage is applied as a charging bias from the power supply 93. Thereafter, the surface of the photosensitive drum 1Y reaches the irradiation position of the laser beam L emitted from the exposure device 7, and an electrostatic latent image corresponding to yellow is formed by exposure scanning in the width direction (the direction perpendicular to the paper surface in FIGS. 1 and 2, which is the main scanning direction) at this position (this is the exposure step).

[0014] Thereafter, the surface of the photosensitive drum 1Y reaches the position facing the developing device 5Y, and the electrostatic latent image is developed at this position to form a yellow toner image (this is the developing step). Thereafter, the surface of the photosensitive drum 1Y reaches the position facing the intermediate transfer belt 8 and the primary transfer roller 9Y (transfer position), and the toner image formed on the surface of the photosensitive drum 1 is primarily transferred to the surface of the intermediate transfer belt 8 at this position (this is the primary transfer step). At this time, a small amount of untransferred toner remains on the photosensitive drum 1Y.

[0015] Thereafter, the surface of the photosensitive drum 1Y reaches the position facing the cleaning device 2Y, and the untransferred toner remaining on the photosensitive drum 1Y is collected into the cleaning device 2Y by the cleaning blade 2a and the cleaning brush 2b (this is the cleaning step). Finally, the surface of the photosensitive drum 1Y reaches the position facing the charge removal device (not shown), and the residual potential on the photosensitive drum 1 is removed at this position. Thus, a series of image forming processes performed on the photosensitive drum 1Y is completed.

[0016] Note that the above-described image forming process is also performed in the same manner as in the yellow image forming unit 6Y in the other image forming units 6M, 6C, and 6K. That is, the laser beam L based on the image information is irradiated onto the photosensitive drums 1M, 1C, and 1K of the respective image forming units 6M, 6C, and 6K from the exposure device 7 disposed above the image forming unit. Specifically, the exposure device 7 emits the laser beam L from a light source, scans the laser beam L with a polygon mirror driven to rotate, and irradiates it onto the photosensitive drum through a plurality of optical elements. After that, the toner images of each color formed on the photoreceptor drums 1M, 1C, and 1K through the development process by each developing device 5M, 5C, and 5K are superposed on the intermediate transfer belt 8 and primarily transferred. Thus, a color image is formed on the intermediate transfer belt 8.

[0017] Here, the intermediate transfer belt 8 is stretched and supported by a plurality of roller members 16 to 21, and is endlessly moved in the direction of the arrow in FIG. 3 by the rotational drive of one roller member (drive roller 16) by a drive motor (not shown). The four primary transfer rollers 9Y, 9M, 9C, and 9K sandwich the intermediate transfer belt 8 between the photoreceptor drums 1Y, 1M, 1C, and 1K, respectively, to form a primary transfer nip. Then, a transfer voltage (primary transfer bias) having a polarity opposite to the polarity of the toner is applied to the primary transfer rollers 9Y, 9M, 9C, and 9K. Then, the intermediate transfer belt 8 travels in the direction of the arrow and sequentially passes through the primary transfer nips of the primary transfer rollers 9Y, 9M, 9C, and 9K. Thus, the toner images of each color on the photoreceptor drums 1Y, 1M, 1C, and 1K are superposed and primarily transferred onto the surface of the intermediate transfer belt 8 (this is the primary transfer process).

[0018] After that, the intermediate transfer belt 8 on which the toner images of each color are superposed and primarily transferred reaches the opposing position (transfer position) with the secondary transfer belt 72 (and the secondary transfer roller 70) as a transfer device. At this position, the secondary transfer opposing roller 21 sandwiches the intermediate transfer belt 8 and the secondary transfer belt 72 between it and the secondary transfer roller 70 to form a secondary transfer nip (transfer nip). Then, the four-color toner image formed on the intermediate transfer belt 8 is secondarily transferred onto a sheet P such as paper conveyed to the position of this secondary transfer nip (this is the secondary transfer process). At this time, untransferred toner that has not been transferred to the sheet P remains on the intermediate transfer belt 8. After that, the intermediate transfer belt 8 reaches the position of the intermediate transfer cleaning device 10. And at this position, deposits such as untransferred toner adhering to the surface of the intermediate transfer belt 8 are removed. Thus, a series of transfer processes performed on the intermediate transfer belt 8 is completed.

[0019] Referring to Figure 1, the sheet P that is transported to the position of the secondary transfer nip, which serves as the transfer nip, is transported from the paper feed device 26 located below the main body of the device 100, via the paper feed roller 27 and the pair of registration rollers 28, etc. More specifically, the paper feeder 26 stores multiple sheets P of paper or the like stacked together. When the paper feed roller 27 is driven to rotate counterclockwise in Figure 1, the top sheet P is fed through the transport path K1 towards the space between the register rollers 28.

[0020] The sheet P, transported by the register roller pair 28 (conveyor roller pair), temporarily stops at the position of the roller nip of the register roller pair 28, where the rotational drive has been stopped. Then, in time with the color image on the intermediate transfer belt 8, the register roller pair 28 is driven to rotate, and the sheet P is transported toward the secondary transfer nip. In this way, the desired color image is transferred onto the sheet P.

[0021] Subsequently, the sheet P onto which the color image has been transferred at the secondary transfer nip is transported by the secondary transfer belt 72, and after being separated from the secondary transfer belt 72, it is transported to the fixing device 50 by the transport belt 60. At this position, the color image transferred to the surface is fixed onto the sheet P by heat and pressure from the fixing belt and pressure rollers (this is the fixing process). Subsequently, the sheet P is discharged from the device via the transport path K2 by the paper discharge roller pair. The sheet P discharged from the device by the paper discharge roller pair is sequentially stacked on the stacking section as output images. Thus, the series of image forming operations (printing operations) in the image forming apparatus is completed.

[0022] Next, Figure 2 will provide a more detailed explanation of the configuration and operation of the developing device 5Y in the image-making section. The developing device 5Y consists of a developing roller 51Y as a developer carrier facing the photoreceptor drum 1Y, a doctor blade 52Y facing the developing roller 51Y, two transport screws 55Y arranged in the developer storage section, a toner concentration detection sensor 56Y as a toner concentration detection means for detecting the toner concentration of the developer G, etc. The developing roller 51Y (developer carrier) consists of a magnet fixed inside and a sleeve that rotates around the magnet. The developer storage section contains the developer G (two-component developer) consisting of a carrier and toner.

[0023] The developing apparatus 5Y, configured in this way, operates as follows: The sleeve of the developing roller 51Y rotates in the direction of the arrow in Figure 2. The developer G, which is supported on the developing roller 51Y by the magnetic field formed by the magnet, moves along the developing roller 51Y as the sleeve rotates. Here, the developer G in the developing device 5Y is adjusted so that the proportion of toner in the developer G (toner concentration) is within a predetermined range. Specifically, when a low toner density is detected by the toner density detection sensor 56Y (toner density detection means) installed in the developing device 5Y, new toner is supplied from the toner container 58 into the developing device 5Y by the rotational drive of the replenishment roller 59 (installed inside the toner container 58) by the toner replenishment device 94 so that the toner density falls within a predetermined range. Subsequently, the toner supplied from the toner container 58 into the developer container is mixed and agitated with the developer G by two transport screws 55Y, circulating between the two isolated developer containers (movement in the direction perpendicular to the paper plane in Figure 2). The toner in the developer G is then attracted to the carrier by triboelectric charging and, together with the carrier, is supported on the developer roller 51Y by the magnetic force formed on the roller 51Y.

[0024] The developer G supported on the developing roller 51Y is transported in the direction of the arrow in Figure 2 to the position of the doctor blade 52Y. At this position, the amount of developer G on the developing roller 51Y is adjusted to the appropriate level, and then it is transported to the position opposite the photoreceptor drum 1Y (the developing area). Then, the toner is attracted to the latent image formed on the photoreceptor drum 1Y by the electric field formed in the developing area. After that, the developer G remaining on the developing roller 51Y reaches above the developer storage section as the sleeve rotates, and at this position it is detached from the developing roller 51Y. The electric field formed in the developing region is created by the developing bias applied to the developing roller 51Y by the developing power supply 97, and the surface potential (latent image potential) formed on the surface of the photoreceptor drum 1Y by the charging process and the exposure process. Furthermore, the toner container 58 is detachably (replaceable) installed in the developing unit 5Y (image forming apparatus 100). When the new toner contained inside the toner container 58 is depleted, it is removed from the developing unit 5Y (image forming apparatus 100) and replaced with a new one.

[0025] Next, the intermediate transfer belt device in this embodiment will be described in detail using Figure 3 and other figures. Referring to Figure 3, the intermediate transfer belt device consists of an intermediate transfer belt 8 as an intermediate transfer body, four primary transfer rollers 9Y, 9M, 9C, and 9K as four transfer devices, a drive roller 16, a driven roller 17, a pre-transfer roller 18, a tension roller 19, a cleaning opposing roller 20, an intermediate transfer cleaning device 10, a secondary transfer opposing roller 21, a secondary transfer device 69, and so on. The intermediate transfer belt 8, acting as an intermediate transfer body, contacts four photoreceptor drums 1Y, 1M, 1C, and 1K, each carrying a toner image of a different color, to form a primary transfer nip. The intermediate transfer belt 8 is stretched and supported primarily by six roller members (a drive roller 16, a driven roller 17, a pre-transfer roller 18, a tension roller 19, a cleaning opposing roller 20, and a secondary transfer opposing roller 21).

[0026] In this embodiment, the intermediate transfer belt 8 (intermediate transfer member) is formed of a single layer or multiple layers of PVDF (polyvinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), etc., in which a conductive material such as carbon black is dispersed. The intermediate transfer belt 8 has a volume resistivity of 10 6 ~10 13 Ωcm and a surface resistivity on the back side of the belt of 10 7 ~10 13 Ωcm. Also, the intermediate transfer belt 8 is set to have a thickness in the range of 20 to 200 μm. In this embodiment, the thickness of the intermediate transfer belt 8 is about 60 μm and the volume resistivity is about 10 9 Ωcm. Incidentally, if necessary, a release layer can also be coated on the surface of the intermediate transfer belt 8. At that time, as the material used for the coating, fluororesins such as ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (polyvinylidene fluoride), PEA (perfluoroalkoxyfluororesin), FEP (ethylene tetrafluoride-hexafluoropropylene copolymer), PVF (polyvinyl fluoride), etc. can be used, but it is not limited thereto.

[0027] The primary transfer rollers 9Y, 9M, 9C, 9K are each in contact with the corresponding photoreceptor drums 1Y, 1M, 1C, 1K via the intermediate transfer belt 8. Specifically, the yellow transfer roller 9Y is in contact with the yellow photoreceptor drum 1Y via the intermediate transfer belt 8, the magenta transfer roller 9M is in contact with the magenta photoreceptor drum 1M via the intermediate transfer belt 8, the cyan transfer roller 9C is in contact with the cyan photoreceptor drum 1C via the intermediate transfer belt 8, and the black transfer roller 9K is in contact with the black photoreceptor drum 1K via the intermediate transfer belt 8. The primary transfer rollers 9Y, 9M, 9C, 9K are each elastic rollers having a conductive sponge layer formed on a core metal, and have a volume resistance of 10 6 ~10 12 Ω (preferably, 10 7 ~10 9It is adjusted to fall within the range of Ω. The primary transfer rollers 9Y, 9M, 9C, and 9K configured in this way are a transfer device that transfers the toner image supported on the surface of the photoreceptor drums 1Y, 1M, 1C, and 1K (photoreceptors) to the intermediate transfer belt 8 (intermediate transfer body).

[0028] The drive roller 16 is positioned downstream of the intermediate transfer belt in the direction of travel relative to the four photoreceptor drums (photoreceptors), and is positioned so as to contact the inner surface of the intermediate transfer belt 8 when the intermediate transfer belt 8 is wrapped around it at a winding angle of approximately 120 degrees. The drive roller 16 is rotated clockwise in Figure 3 by a drive motor (not shown) controlled by the control unit 90. As a result, the intermediate transfer belt 8 travels in a predetermined direction (clockwise in Figure 3).

[0029] The driven roller 17 is positioned upstream of the intermediate transfer belt 8 in the direction of travel relative to the four photoreceptor drums, and is positioned so as to contact the inner surface of the intermediate transfer belt 8 when the intermediate transfer belt 8 is wrapped around it at a winding angle of approximately 180 degrees. The portion of the intermediate transfer belt 8 from the driven roller 17 to the drive roller 16 is set to be approximately horizontal. The driven roller 17 rotates in a clockwise direction as the intermediate transfer belt 8 travels, as shown in Figure 3.

[0030] The tension roller 19 is in contact with the outer circumferential surface of the intermediate transfer belt 8. The pre-transfer roller 18, the cleaning opposing roller 20, and the secondary transfer opposing roller 21 are in contact with the inner circumferential surface of the intermediate transfer belt 8. Between the secondary transfer opposing roller 21 and the tension roller 19, an intermediate transfer cleaning device 10 (cleaning blade) is installed so as to contact the cleaning opposing roller 20 via an intermediate transfer belt 8.

[0031] Referring to Figure 3, the secondary transfer opposing roller 21 is in contact with the secondary transfer roller 70 via the intermediate transfer belt 8 and the secondary transfer belt 72. The secondary transfer opposing roller 21 has a cylindrical core made of stainless steel or the like, with a volume resistance of 10 on its outer surface. 7 ~108 An elastic layer 83 (with a thickness of approximately 5 mm) is formed from NBR rubber with a hardness of approximately Ω and a hardness (JIS-A hardness) of approximately 48 to 58 degrees.

[0032] Next, the secondary transfer apparatus 69, which serves as a transfer device, will be described in detail using Figure 3. Referring to Figure 3, the secondary transfer device 69 consists of a secondary transfer belt 72, a secondary transfer roller 70, a separation roller 71, a secondary transfer blade 73 (cleaning blade), etc. The secondary transfer device 69 is a transfer device that transfers the toner image supported on the surface of the intermediate transfer belt 8, which acts as an intermediate transfer body, to the sheet P. The secondary transfer roller 70 and the secondary transfer belt 72 function as transfer members that transfer the toner image supported on the intermediate transfer belt 8 to the sheet P, which is transported to a transfer nip (secondary transfer nip) formed between them and the intermediate transfer belt 8 (intermediate transfer body).

[0033] The secondary transfer belt 72 is an endless belt stretched and supported by a plurality of roller members (secondary transfer rollers 70 and separation rollers 71), and is made of substantially the same material as the intermediate transfer belt 8. The secondary transfer belt 72 contacts the intermediate transfer belt 8, which acts as an intermediate transfer body, to form a secondary transfer nip (transfer nip), and also conveys the sheet P that is sent out from the secondary transfer nip.

[0034] The secondary transfer roller 70 forms a secondary transfer nip by sandwiching the intermediate transfer belt 8 and the secondary transfer belt 72 between it and the secondary transfer opposing roller 21. The secondary transfer roller 70 has an elastic layer formed (coated) on a hollow core made of stainless steel, aluminum, etc., with a hardness (Asker C hardness) of about 40 to 50 degrees. The elastic layer of the secondary transfer roller 70 can be formed in a solid or foamed sponge form by dispersing conductive fillers such as carbon in a rubber material such as polyurethane, EPDM, or silicone, or by incorporating an ionic conductive material. In this embodiment, the elastic layer has a volume resistance of 10 to suppress the concentration of the transfer current. 6.5 ~10 7.5 It is set to approximately Ω.

[0035] Furthermore, in this embodiment, the secondary transfer roller 70 is electrically connected to a power supply unit (not shown), and a secondary transfer bias (high voltage) consisting of a superimposed DC component and an AC component is applied from the power supply unit. This secondary transfer bias applied to the secondary transfer roller 70 is for secondary transfer of the toner image carried on the surface of the intermediate transfer belt 8 (primary transfer) to the sheet P that is transported to the secondary transfer nip, and consists of a DC voltage with a polarity different from the polarity of the toner (positive polarity in this embodiment) and an AC voltage with a peak-to-peak voltage of about 4 to 10 kV superimposed. As a result, the toner carried on the toner-carrying surface (outer peripheral surface) of the intermediate transfer belt 8 is electrostatically moved from the secondary transfer opposing roller 21 side toward the secondary transfer device 69 side by the secondary transfer electric field. In this embodiment, the secondary transfer bias is applied to the secondary transfer roller 70 as the transfer member. However, the secondary transfer bias can also be applied to the secondary transfer opposing roller 21 as the transfer opposing member, or it can be applied to both the secondary transfer roller 70 and the secondary transfer opposing roller 21, respectively. However, when applying the DC component of the secondary transfer bias to the secondary transfer opposing roller 21, a DC voltage with the same polarity as the toner (negative polarity) will be applied.

[0036] Furthermore, the secondary transfer roller 70 is driven to rotate counterclockwise in Figure 3 by a drive motor (not shown) controlled by the control unit 90, causing the secondary transfer belt 72 to rotate (travel) counterclockwise in Figure 3, and the separation roller 71 to rotate counterclockwise in Figure 3.

[0037] The separation roller 71 is positioned downstream of the secondary transfer nip in the conveying direction of the sheet P. The sheet P, which is sent out from the secondary transfer nip, is conveyed along the secondary transfer belt 72 which runs counterclockwise as shown in Figure 3, and then, at the position of the separation roller 71, is separated from the secondary transfer belt 72 by the secondary transfer belt 72, which has a curved surface formed along the outer circumference of the separation roller 71 (curvature separation). In this embodiment, the secondary transfer belt 72 is tensioned by two roller members, the secondary transfer roller 70 and the separation roller 71. However, it is also possible to configure the system to tension and support the secondary transfer belt 72 with three or more roller members. The secondary transfer blade 73 contacts the surface of the secondary transfer belt 72 to remove foreign matter such as toner and paper dust adhering to the surface of the secondary transfer belt 72. The secondary transfer blade 73 is pressed against the secondary transfer roller 70 via the secondary transfer belt 72 so as to contact the secondary transfer roller 70 in a counter-direction relative to the direction of travel of the secondary transfer belt 72.

[0038] In this embodiment, a separation mechanism 80 is provided to separate the intermediate transfer belt 8 downward from the transfer position (the position shown in Figure 3) so that a primary transfer nip (transfer nip) is not formed for transferring the toner image from the photoreceptor drum 1Y (photoreceptor) to the intermediate transfer belt 8 (intermediate transfer body). Such a separation mechanism 80 can be, for example, a cam mechanism consisting of a biasing member that biases the primary transfer roller 9Y upward (in the direction of pressing it against the photoreceptor drum 1Y via the intermediate transfer belt 8) and a cam that pushes the primary transfer roller 9Y downward against the biasing force of the biasing member. Furthermore, such a separation mechanism 80 can be provided for each of the four colors (yellow, magenta, cyan, and black), or multiple color mechanisms can be provided together.

[0039] The configuration and operation of the image forming apparatus 100, which are characteristic of this embodiment, will be described in detail below. Referring to Figures 2 and 3, the image forming apparatus 100 in this embodiment is provided with an image density detection sensor 98, which is an image density detection means for detecting the image density of a detection toner image supported on the surface of the intermediate transfer belt 8 (an intermediate transfer body on which the toner image supported on the photoreceptor drum 1Y is transferred).

[0040] This image density detection sensor 98 (image density detection means) is an optical sensor that optically detects the image density of the toner image (image) formed on the intermediate transfer belt 8. Specifically, the image density detection sensor 98 is a reflective optical sensor consisting of a light-emitting element and a light-receiving element. Light emitted from the light-emitting element is projected onto the surface of the intermediate transfer belt 8, and the light reflected from that surface is received by the light-receiving element. Then, the output of the image density detection sensor 98 (light-receiving element) changes according to the density (height) of the toner image, and the image density is determined from the output value. The image density detection sensor 98 is located downstream of the four photoreceptor drums 1Y, 1M, 1C, and 1K (primary transfer nip) and upstream of the secondary transfer device 69 (secondary transfer nip). Then, at a time separate from the normal printing operation (for example, during the warm-up before printing starts), the image formation process described above is performed to form a dummy toner image for detection (detection toner image) on the photoreceptor drum 1Y, and the image density of the detection toner image transferred from the photoreceptor drum 1Y onto the intermediate transfer belt 8 is detected by the image density detection sensor 98. As the detection toner image, for example, a solid vertical band image corresponding to one full rotation of the photoreceptor drum 1Y can be used. In addition, the detection toner image is formed to align with the widthwise position of the image density detection sensor 98 (for example, the center in the widthwise direction). Furthermore, the detection of the image density of the toner image for detection by this image density detection sensor 98 is performed separately for each of the four colors (yellow, magenta, cyan, and black).

[0041] In this embodiment, if a predetermined time A has elapsed since the completion of the previous printing operation (the one performed immediately prior to the printing operation to be performed this time), a detection mode (hereinafter referred to as "process control") is executed before the start of the printing operation (the current printing operation) in which the image density X1 of the detection toner image carried on the intermediate transfer belt 8 (intermediate transfer body) is detected by the image density detection sensor 98 (image density detection means). Then, if the image density X1 is lower than the image density X0 detected in the previously executed detection mode (the "process control" performed immediately prior to the previous printing operation) by a predetermined value B (when X0-X1>B), a control mode (hereinafter referred to as "moisture removal mode") is executed in which the photoreceptor drum 1Y (photoreceptor) is idled for a predetermined time (for example, 10 rotations). Conversely, if the current image density X1 is not lower than the previous image density X0 by a predetermined value B (i.e., X0-X1 ≤ B), the control mode ("moisture removal mode") is not activated, and the printing operation starts immediately.

[0042] Furthermore, when process control (detection mode) is executed, in addition to determining whether or not the moisture removal mode is necessary based on the detected image density, the image formation conditions (such as development bias, charging bias, and exposure amount of the exposure device 7) may also be adjusted. Furthermore, the image density data X0 and X1 detected by the image density detection sensor 98 are stored in the storage unit 91 of the control unit 90 each time they are detected, and are erased (overwritten) when they are no longer needed. Furthermore, the control unit 90 of the image forming apparatus 100 is equipped with a timer (not shown), which measures the time elapsed since the completion of the previous printing operation (idling time).

[0043] This type of control is necessary because, as the photoreceptor drum 1Y has been used for a while, and filming (a phenomenon in which toner resin components, etc., adheres to the surface of the photoreceptor drum 1Y) occurs, if the time between the end of the previous printing operation and the start of a new printing operation (the waiting time) becomes long, the amount of moisture absorbed by the photoreceptor drum 1Y increases. If a new printing operation is started with such a high amount of moisture absorbed by the photoreceptor drum 1Y, abnormal images such as blurred or streaky images will occur in the printed image. Normally, as the time between the start of a new print operation (idle time) increases, the amount of toner charge decreases, so the image density X1 detected by process control before the print operation should be higher than the previous image density X0. However, if the current image density X1 is lower than the previous image density X0, it can be determined that, as described above, the amount of moisture absorbed by the photoreceptor drum 1Y has increased, making it difficult for the image to adhere to the drum surface. In this embodiment, the aforementioned "predetermined value B" is set as a margin to confirm such a determination. Furthermore, when the amount of moisture absorbed by the photoreceptor drum 1Y becomes high, the photoreceptor drum 1Y is driven without image formation (rotating without image formation), which removes the absorbed moisture from the photoreceptor drum 1Y and reduces its absorbed moisture content.

[0044] In this embodiment, the moisture removal mode (control mode) is performed with a charge bias applied to the charging device 4Y and a development bias applied to the developing roller 51Y (developer carrier). Specifically, in the moisture removal mode, the photoreceptor drum 1Y is idle-driven with the same charging bias applied from the power supply 93 to the charging device 4Y as during normal printing, and the same developing bias applied from the developing power supply 97 to the developing roller 51Y as during normal printing. It is preferable that other image-forming components such as the developing device 5Y, charging device 4Y, and cleaning device 2Y are also idle-driven at this time. By implementing this type of control, problems such as the surface of the photoreceptor drum 1Y becoming soiled or damaged with toner during moisture removal mode are reduced.

[0045] As described above, in this embodiment, before the printing operation, the degree of moisture absorption of the photoreceptor drum 1Y is determined based on the image density detection result of the toner image detection sensor 98, and if it is determined that the amount of moisture absorption is high, a moisture removal mode is executed to reduce the amount of moisture absorption. Therefore, it is possible to reduce the occurrence of abnormal images such as blurry or smudged images.

[0046] In this embodiment, process control (detection mode) is performed only if a predetermined time A has elapsed since the completion of the previous printing operation (the one performed previously in relation to the printing operation to be performed this time). This is because, if the time until a new print operation is started (the waiting time) is short, even if the filming of the photoreceptor drum 1Y is progressing, the amount of moisture absorbed by the photoreceptor drum 1Y will not increase significantly. Also, if the aforementioned "specified time A" is set too short, process control (detection mode) will be performed frequently, resulting in wasted toner consumption and unnecessary delays before printing can begin. Conversely, if the aforementioned "specified time A" is set to be too long, the moisture removal mode will be less likely to be executed when it is truly needed. Taking these factors into consideration, "specified time A" is set to an appropriate value.

[0047] In this embodiment, the image density of the detection toner image supported on the surface of the intermediate transfer belt 8 (intermediate transfer body) is detected by the image density detection sensor 98 (image density detection means), and the necessity of the moisture removal mode (control mode) is determined based on the detection result. Alternatively, the image density of the detection toner image supported on the surface of the photoreceptor drum 1Y (photoreceptor) can be detected by an image density detection sensor 99 (see Figure 2) as an image density detection means, and the necessity of the moisture removal mode (control mode) can be determined based on the detection result. In other words, if a predetermined time A has elapsed since the end of the previous printing operation, a detection mode (process control) is executed before the start of the printing operation, in which the image density X1 of the detection toner image carried on the photoreceptor drum 1Y is detected by the image density detection sensor 99. If the image density X1 is lower than the image density X0 detected in the previous detection mode (process control) by a predetermined value B, a control mode (moisture removal mode) is executed, which drives the photoreceptor drum 1Y without moving it. The image density sensor 99 for the photoreceptor used in this case is an optical sensor, similar to the image density sensor 98 for the intermediate transfer body shown in Figure 3. The image density sensor 99 for the photoreceptor is installed downstream of the developing device 5Y and upstream of the primary transfer roller 9Y, facing the photoreceptor drum 1Y, as shown in Figure 2.

[0048] In this embodiment, before the printing operation starts and after the control mode (moisture removal mode) has been executed, the detection mode (process control) is executed again. If the image density X2 is lower than the image density X1 detected in the detection mode (process control) executed before the control mode (moisture removal mode) is executed by a second predetermined value C (when X1-X2>C), the control mode (moisture removal mode) is executed again. In contrast, if the current image density X2 is not lower than the previous image density X1 by a predetermined value C (when X1-X2 ≤ C), the control mode (moisture removal mode) is not performed again, and the printing operation starts immediately. Furthermore, since the process control performed at this time is not significantly longer than the previous one, the predetermined value C mentioned above is set to be smaller than the previous predetermined value B (B>C>0).

[0049] Thus, if it is determined that no improvement in image density was observed after the previous moisture removal mode, it is assumed that the amount of moisture absorbed by the photoreceptor drum 1Y has not been sufficiently reduced. By executing the moisture removal mode again, the amount of absorbed moisture can be sufficiently reduced, thereby reducing the occurrence of abnormal images such as blurred or streaky images. Furthermore, in this embodiment, the control is configured to repeatedly execute the moisture removal mode if it is determined that no improvement in image density was observed in the previous moisture removal mode. As a result, the effect of reducing the occurrence of abnormal images such as blurred or streaky images is further enhanced.

[0050] In this embodiment, if the detection mode (process control) and the control mode (moisture removal mode) are repeatedly performed a predetermined number of times N before the printing operation starts, the execution of subsequent detection modes (process control) and control modes (moisture removal mode) is interrupted, and a notification is issued indicating that there is an abnormality in the image forming apparatus. As explained earlier, in this embodiment, if it is determined that the previous moisture removal mode did not improve the image density, the control system repeatedly executes the moisture removal mode again. However, if such control is repeated beyond a limit, it is considered that there is a malfunction in the device (either the moisture absorbed by the photoreceptor drum 1Y cannot be removed, or there is a malfunction due to other factors). Furthermore, if such control is repeated indefinitely, printing will never be possible. Therefore, in this embodiment, an upper limit N (for example, 5 times) is set for the number of times the moisture removal mode is repeated, and the moisture removal mode is not executed beyond this limit. Instead, the operation display panel 95 (see Figure 1) displays a message indicating that there is a malfunction in the device and that maintenance by a service technician is required. It is preferable that, for users who prioritize printing even when the above-mentioned abnormal image occurs, the user can operate the operation display panel 95 to select when to start printing.

[0051] In this embodiment, when the moisture removal mode (control mode) is executed, the control unit 90 controls the intermediate transfer belt 8 (intermediate transfer body) to be separated from the transfer position by the separation mechanism 80, which was previously explained using Figure 3. By implementing this control, the problem of the intermediate transfer belt 8 sliding against the photoreceptor drum 1Y, which is driven without moisture in the moisture removal mode, and causing unnecessary wear is suppressed.

[0052] Below, using Figure 4, we will explain an example of the control when executing the moisture removal mode (control mode). As shown in Figure 4, first, when a command for a desired print job (print operation) is input by the user operating the operation display panel 95 (step S1), it is determined whether the elapsed time (idle time) since the end of the previous print job is longer than a predetermined time A (step S2). If it is determined that the elapsed time (idle time) is shorter than the predetermined time A, the print operation is started immediately (step S9). In response to this, in step S2, if it is determined that the elapsed time (standing time) is longer than the predetermined time A, process control (detection mode) is executed to detect the image density X1 (step S3), and it is determined whether the difference (X0-X1) with the image density X0 detected previously and stored in the memory unit 91 exceeds the predetermined value B (step S4). If it is determined that the difference (X0-X1) does not exceed the predetermined value B, it is assumed that there is almost no change in the moisture content of the photoreceptor drum 1Y (and therefore no abnormal images are generated), and the printing operation is started as is (step S9). In response to this, if it is determined in step S4 that the difference (X0-X1) exceeds a predetermined value B, the moisture removal mode (control mode) is executed (step S5) because the amount of moisture absorbed by the photoreceptor drum 1Y is considered to be high (and abnormal images will occur). After that, the process control (detection mode) is executed again to detect the image density X2 (step S6), and it is determined whether the difference (X1-X2) with the previous image density X1 detected in step S3 exceeds a predetermined value C (step S7). If it is determined that the difference (X1-X2) does not exceed the predetermined value C, the moisture absorbed by the photoreceptor drum 1Y is considered to have been sufficiently removed (and abnormal images will not occur), and the printing operation is started as is (step S9). In response to this, if it is determined in step S7 that the difference (X1-X2) exceeds a predetermined value B, it is determined that the moisture absorbed by the photoreceptor drum 1Y has not been sufficiently removed (resulting in the occurrence of an abnormal image), and the flow from step S5 onward is repeated. At this time, it is determined whether the number of executions of process control (and moisture removal mode) has exceeded a predetermined number N (upper limit) (step S8), and if it has exceeded the predetermined number N, a warning such as an abnormality is displayed on the operation display panel 95 (step S10).

[0053] <Variation> In the modified image forming apparatus 100, if the control mode (moisture removal mode) is repeatedly performed before the printing operation starts, the toner concentration W1 of the developer G in the developing apparatus 5Y is detected by the toner concentration detection sensor 56Y (toner concentration detection means) before the control mode (moisture removal mode) is started. If the toner concentration W1 is lower than the toner concentration W0 detected by the toner concentration detection sensor 56Y before the start of the previous control mode (moisture removal mode) by a predetermined value D (when W0-W1>D), the control unit 90 controls the apparatus to replenish toner in the developing apparatus 5Y using the toner replenishment device 94 (see Figure 2). Specifically, referring to the flowchart shown in Figure 5, in this modified example, unlike that in Figure 4, after the determination in step S4, the toner concentration of the developer G in the developing device 26 is detected (step S20), and after the moisture removal mode is executed in step S5, it is determined whether the moisture removal mode has been executed two or more times (step S21). As a result, if the moisture removal mode has been executed two or more times, it is determined whether the difference in toner concentration before and after (W0-W1) exceeds a predetermined value D (step S22). If the difference (W0-W1) exceeds the predetermined value D, a predetermined amount of toner is replenished (step S23), and if the difference (W0-W1) does not exceed the predetermined value D, the flow from step S6 onwards is performed as is. By performing this type of control, even if the amount of toner charge in the developer G inside the developer unit 5Y decreases due to being left unattended, and toner scattering occurs from the developer unit 5Y during the moisture removal mode, causing the toner concentration of the developer G to decrease, toner is replenished to the developer G, thus maintaining a toner concentration of the developer G above a predetermined value.

[0054] As described above, the image forming apparatus 100 in this embodiment is provided with a photoreceptor drum 1Y (photoreceptor) on which a toner image is carried, and an image density detection sensor 98 (image density detection means) that detects the image density of a detection toner image carried on the surface of an intermediate transfer belt 8 (or photoreceptor drum 1Y) to which the toner image carried on the photoreceptor drum 1Y is transferred. If a time exceeding a predetermined time A has elapsed since the completion of the previous printing operation, a detection mode (process control) is executed before the start of the printing operation, in which the image density of the detection toner image carried on the intermediate transfer belt 8 (or photoreceptor drum 1Y) is detected by the image density detection sensor 98. If the image density is lower than the image density detected in the previously executed detection mode by a predetermined value B, a control mode (moisture removal mode) is executed to drive the photoreceptor drum 1Y without moving it. This makes it less likely for abnormal images such as blurry or smudged images to occur.

[0055] In this embodiment, the present invention was applied to an image forming apparatus 100 that uses a secondary transfer roller 70 and a secondary transfer belt 72 as a transfer device, and an intermediate transfer belt 8 as an intermediate transfer body. However, the present invention can also be applied to an image forming apparatus of the so-called direct transfer type, which does not have an intermediate transfer body such as an intermediate transfer belt or intermediate transfer drum, but has a photoreceptor drum (photoreceptor) on which a toner image developed by a developing device is formed, and a transfer device such as a transfer roller and a transfer belt for transferring the toner image on the photoreceptor drum to a sheet that is transported to the position of the photoreceptor drum. In that case, the image density detection means is capable of detecting the image density of the detection toner image formed on the surface of the photoreceptor (photoreceptor drum) (see image density detection sensor 99 in Figure 2). Also, in that case, when the control mode (moisture removal mode) is executed, the transfer device is separated by a separation mechanism (which separates the transfer device from the transfer position so that a transfer nip is not formed). Furthermore, in this embodiment, the present invention was applied to an image forming apparatus 100 that uses a secondary transfer roller 70 and a secondary transfer belt 72 as a transfer device. However, the application of the present invention is not limited to this, and the present invention can also be applied to an image forming apparatus that does not use a secondary transfer belt as a transfer device and uses only a secondary transfer roller. Furthermore, in this embodiment, the present invention was applied to an image forming apparatus 100 that forms a color image. However, the present invention can also be applied to an image forming apparatus that forms only a monochrome image. Furthermore, even in such cases, the same effects as those of this embodiment can be obtained.

[0056] It is clear that the present invention is not limited to this embodiment, and that this embodiment can be modified as appropriate within the scope of the technical concept of the present invention, in addition to what is suggested here. Furthermore, the number, position, shape, etc. of the constituent members are not limited to this embodiment, and can be set to a number, position, shape, etc. that is suitable for carrying out the present invention. [Explanation of symbols]

[0057] 1Y, 1M, 1C, 1K Photoconductor drum (photoconductor), 4Y charging device, 5Y developing machine, 8. Intermediate transfer belt (intermediate transfer body), 51Y Developing Roller (Developer Carrier), 56Y Toner density detection sensor (toner density detection means), 80 Separation mechanism, 94 Toner supply device, 98, 99 Image density detection sensor (image density detection means), 100 Image forming apparatus (image forming apparatus main unit). [Prior art documents] [Patent Documents]

[0058] [Patent Document 1] Japanese Patent Publication No. 2020-86303

Claims

1. A photoreceptor on which the toner image is carried, Image density detection means for detecting the image density of a detection toner image supported on the surface of the photoreceptor, or an intermediate transfer body on which a toner image supported on the photoreceptor is transferred, Equipped with, An image forming apparatus characterized in that, if a predetermined time has elapsed since the completion of the previous printing operation, a detection mode is executed before the start of the printing operation in which the image density of the detection toner image supported on the photoreceptor or the intermediate transfer medium is detected by the image density detection means, and if the image density is lower than a predetermined value compared to the image density detected in the detection mode executed one step earlier in relation to the previous printing operation, a control mode is executed in which the photoreceptor is driven without power.

2. The image forming apparatus according to claim 1, characterized in that, before the printing operation is started and after the control mode has been executed, the detection mode is executed again, and when the image density is lower than a second predetermined value compared to the image density detected in the detection mode executed before the control mode was executed, the control mode is executed again.

3. The image forming apparatus according to claim 2, characterized in that if the detection mode and the control mode are repeatedly performed a predetermined number of times before the printing operation is started, the execution of the detection mode and the control mode thereafter is interrupted, and the apparatus is notified that there is an abnormality.

4. A developing apparatus containing a developer consisting of toner and carrier, for developing a latent image formed on the surface of the photoreceptor, A toner supply device for supplying toner to the developing device, A toner concentration detection means for detecting the toner concentration of the developer contained inside the developing device, Equipped with, The image forming apparatus according to claim 2 or 3, characterized in that, if the control mode is repeated before the printing operation is started, the toner concentration is detected by the toner concentration detection means before the control mode is started, and if the toner concentration is lower than a predetermined value compared to the toner concentration detected by the toner concentration detection means before the previous start of the control mode, toner is supplied to the developing apparatus by the toner supply device.

5. A charging device that applies a charging bias to charge the surface of the photoreceptor, A developer carrier to which a development bias is applied to develop the latent image formed on the surface of the photoreceptor, Equipped with, The image forming apparatus according to any one of claims 1 to 4, characterized in that the control mode is performed when a charging bias is applied to the charging device and a developing bias is applied to the developer carrier.

6. To prevent the formation of a transfer nip for transferring the toner image from the photoreceptor to the intermediate transfer body or sheet, the intermediate transfer body or the transfer device for transferring the toner image supported on the surface of the photoreceptor to the sheet is provided with a separation mechanism for separating it from the transfer position. The image forming apparatus according to any one of claims 1 to 5, characterized in that when the control mode is executed, the intermediate transfer body or the transfer apparatus is separated by the separation mechanism.

7. The image forming apparatus according to any one of claims 1 to 6, characterized in that the control mode is performed regardless of ambient humidity and is for reducing the amount of moisture absorbed by the image carrier.

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