Image forming apparatus

Abstract

To suppress the occurrence of such a malfunction that a detection pattern cannot be normally detected by a detection device.SOLUTION: A first detection mode in which a detection pattern TP formed in a non-image region N of an intermediate transfer belt 8 by imaging units 6Y, 6M, 6C, 6K is detected by optical sensors 95A, 95B on the basis of a prescribed imaging condition in the time of image formation and a second detection mode in which the detection pattern TP formed in the non-image region N of the intermediate transfer belt 8 by the imaging units 6Y, 6M, 6C, 6K is detected by the optical sensors 95A, 95B on the basis of an imaging condition that has the higher image density than the prescribed imaging condition in the time of non-image formation are switched on the basis of a prescribed condition.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] This invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multi-function machine thereof.

Background Art

[0002] Conventionally, in an image forming apparatus such as a copying machine or a printer, a detection pattern (test pattern) is formed in a non-image area of an image carrier such as an intermediate transfer belt, and based on the result of detecting the detection pattern with a detection device (TM sensor), a technique for adjusting imaging conditions (process control) is known (see, for example, Patent Document 1).

[0003] Specifically, in Patent Document 1, during image formation (printing), a test pattern (detection pattern) is formed in non-image areas at both ends in the width direction of an intermediate transfer belt (image carrier) separately from the image to be formed in the image area, and the test pattern is optically detected with a TM sensor (detection device). Then, based on the detection result of the TM sensor, process control such as the writing timing of an exposure device and toner density control is performed.

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a conventional image forming apparatus, when the image density of a detection pattern formed in a non-image area of an image carrier decreases, the detection pattern may not be normally detected by the detection device. And in such a case, the imaging conditions could not be properly adjusted.

[0005] This invention is made to solve the above-described problems, and an object thereof is to provide an image forming apparatus in which a defect that the detection pattern cannot be normally detected by the detection device hardly occurs.

Means for Solving the Problems

[0006] The image forming apparatus according to the present invention includes an image carrier, an image forming unit that forms a desired toner image in an image area on the surface of the image carrier based on predetermined image forming conditions during image formation, and a detection device that can detect a detection pattern as a toner image formed in a non-image area on the surface of the image carrier by the image forming unit. During image formation, based on the predetermined image forming conditions, the detection pattern formed in the non-image area of the image carrier by the image forming unit is detected by the detection device in a first detection mode. During non-image formation, based on image forming conditions in which the image density is higher than the predetermined image forming conditions, the detection pattern formed in the non-image area of the image carrier by the image forming unit is detected by the detection device in a second detection mode, and the first detection mode and the second detection mode are switched based on predetermined conditions. The first detection mode is executed at a predetermined timing during image formation in normal times. When the image density of the detection pattern detected by the detection device is equal to or higher than a predetermined value, based on the detection result detected by the detection device in the first detection mode, the image formation conditions during the image formation are adjusted. When the image density of the detection pattern detected by the detection device is lower than the predetermined value, the second detection mode is executed, and based on the detection result detected by the detection device in the second detection mode, the image formation conditions during the image formation are adjusted. is provided.

Advantages of the Invention

[0007] According to the present invention, it is possible to provide an image forming apparatus in which a defect that the detection device cannot normally detect the detection pattern hardly occurs.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Best Mode for Carrying Out the Invention

[0009] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals, and the redundant description will be appropriately simplified or omitted.

[0010] First, with reference to FIGS. 1 and 2, the overall configuration and operation of the image forming apparatus 100 will be described. FIG. 1 is a configuration diagram showing a printer as an image forming apparatus, and FIG. 2 is an enlarged view showing a part of its image forming unit. As shown in FIG. 1, in the center of the image forming apparatus main body 100, an intermediate transfer belt 8 (intermediate transfer member) as an image carrier is installed. Further, image forming units 6Y, 6M, 6C, 6K (photosensitive drums 1Y, 1M, 1C, 1K) corresponding to each color (yellow, magenta, cyan, black) are arranged side by side so as to face the intermediate transfer belt 8. Note that an operation display panel 110 (information acquisition means) for displaying information related to a printing operation (image forming operation) and performing operations is installed on the exterior of the image forming apparatus main body 100.

[0011] Referring to FIG. 2, the image forming unit 6Y corresponding to yellow is composed of a photosensitive drum 1Y, a charging device 4Y, a developing device 5Y, a cleaning device 2Y, a lubricant supply device 3, a charge removing device (not shown), etc., arranged around the photosensitive drum 1Y (photosensitive member). Then, on the photosensitive drum 1Y, an image forming process (charging process, exposure process, developing process, transfer process, cleaning process, charge removing process) is performed, and a yellow image is formed on the photosensitive drum 1Y.

[0012] Note that the other three image forming units 6M, 6C, and 6K have substantially the same configuration as the image forming unit 6Y corresponding to yellow, except that the color of the toner used is different, and images corresponding to their respective toner colors are formed. Hereinafter, the description of the other three image forming units 6M, 6C, and 6K will be appropriately omitted, and only the description of the image forming unit 6Y corresponding to yellow will be given.

[0013] Referring to FIG. 2, the photosensitive drum 1Y as a photoreceptor is rotationally driven counterclockwise by the main motor. Then, at the position of the charging device 4Y, the surface of the photosensitive drum 1Y is uniformly charged (charging process). Specifically, a predetermined charging bias (about -600V) is applied from the charging power supply 91 controlled by the control unit 90 to the charging device 4Y (charging roller). Thereafter, the surface of the photosensitive drum 1Y reaches the irradiation position of the laser beam L (exposure light) 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 (exposure process). At this time, the exposure amount of the exposure device 7 controlled by the control unit 90 is 100%, and a latent image potential (surface potential) of about 0 to -100V is formed on the surface of the photosensitive drum 1Y (the portion where the electrostatic latent image is formed).

[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 (developing process). Specifically, a predetermined developing bias (about -500V) is applied from the developing power supply 92 controlled by the control unit 90 to the developing device 5Y (developing roller 51Y). Thereafter, the surface of the photosensitive drum 1Y reaches the position facing the intermediate transfer belt 8 and the primary transfer roller 9Y, 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 (primary transfer process). At this time, a small amount of untransferred toner remains on the photosensitive drum 1Y.

[0015] Thereafter, the surface of the photoreceptor drum 1Y reaches the position facing the cleaning device 2Y, and at this position, the untransferred toner remaining on the photoreceptor drum 1Y is collected into the cleaning device 2Y by the cleaning blade 2a (this is the cleaning process). Here, inside the cleaning device 2Y, a lubricant supply device 3 (a lubricant supply device for the photoreceptor), which consists of a lubricant supply roller 3a, a solid lubricant 3b, a compression spring 3c, etc., is installed. Then, the lubricant is scraped off little by little from the solid lubricant 3b by the lubricant supply roller 3a that rotates in the clockwise direction in Fig. 2, and the lubricant is supplied to the surface of the photoreceptor drum 1Y by the lubricant supply roller 3a. Finally, the surface of the photoreceptor drum 1Y reaches the position facing the charge elimination device (not shown), and at this position, the residual potential on the photoreceptor drum 1 is removed. In this way, a series of image forming processes performed on the photoreceptor drum 1Y are completed.

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

[0017] Here, the intermediate transfer belt 8 as the intermediate transfer member is stretched and supported by a plurality of roller members 16 to 22, 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. The four primary transfer rollers 9Y, 9M, 9C, and 9K sandwich the intermediate transfer belt 8 between the photosensitive drums 1Y, 1M, 1C, and 1K respectively to form a primary transfer nip. Then, a transfer voltage (primary transfer bias) with a polarity opposite to that 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. In this way, the toner images of each color on the photosensitive 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 position opposite to the secondary transfer belt 72 (and the secondary transfer roller 70) as a transfer member. At this position, the secondary transfer opposing roller 22 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.

[0019] 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. Furthermore, the intermediate transfer belt 8 reaches the position of the intermediate transfer lubricant supply device 30. And at this position, a lubricant is supplied to the surface of the intermediate transfer belt 8. In this way, a series of transfer processes performed on the intermediate transfer belt 8 are completed.

[0020] Here, referring to FIG. 1, the sheet P conveyed to the position of the secondary transfer nip as a transfer nip is conveyed from the paper feeding device 26 disposed below the apparatus main body 100 via the paper feeding roller 27, the registration roller pair 28, and the like. Specifically, in the sheet feeding device 26, a plurality of sheets P such as transfer paper are stacked and stored. When the sheet feeding roller 27 is rotationally driven counterclockwise in FIG. 1, the top sheet P is fed toward the nip between the rollers of the registration roller pair 28 via the first conveyance path K1.

[0021] The sheet P conveyed to the registration roller pair 28 (conveyance roller pair) temporarily stops at the position of the roller nip of the registration roller pair 28 where the rotational drive has stopped. Then, in synchronization with the color image on the intermediate transfer belt 8, the registration roller pair 28 is rotationally driven, and the sheet P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the sheet P. In this way, the registration roller pair 28 functions as a conveyance means for conveying the sheet P toward the transfer nip (secondary transfer nip). Further, the registration roller pair 28 is rotationally driven by a motor (not shown) controlled by the control unit 90.

[0022] Thereafter, the sheet P onto which the color image has been transferred at the position of the secondary transfer nip is conveyed by the secondary transfer belt 72, separated from the secondary transfer belt 72, and then conveyed to the position of the fixing device 50 by the conveyance belt 60. And at this position, the color image transferred onto the surface is fixed onto the sheet P by the heat and pressure of the fixing belt and the pressure roller (this is the fixing process). Thereafter, the sheet P is discharged outside the apparatus by the discharge roller pair via the second conveyance path K2. The sheet P discharged outside the apparatus by the discharge roller pair is sequentially stacked on the stack portion as an output image. In this way, a series of image forming operations (printing operations) in the image forming apparatus are completed.

[0023] Next, with reference to FIG. 2, the configuration and operation of the developing device 5Y in the image forming unit will be described in more detail. The developing device 5Y includes a developing roller 51Y facing the photosensitive drum 1Y, a doctor blade 52Y facing the developing roller 51Y, two conveying screws 55Y disposed in the developer storage section, a density detection sensor 56Y for detecting the toner density in the developer, and the like. The developing roller 51Y is composed of a magnet fixed inside and a sleeve rotating around the magnet. In the developer storage section, a two-component developer G composed of a carrier and toner is stored.

[0024] The developing device 5Y configured as described above operates as follows. The sleeve of the developing roller 51Y rotates in the direction of the arrow in FIG. 2. Then, the developer G carried on the developing roller 51Y by the magnetic field formed by the magnet moves on the developing roller 51Y as the sleeve rotates. Here, the developer G in the developing device 5Y is adjusted so that the ratio (toner density) of the toner in the developer G is within a predetermined range. Specifically, when a state where the toner density is low is detected by the toner density sensor installed in the developing device 5Y, new toner is replenished from the toner container 58 into the developing device 5Y so that the toner density is within the predetermined range (a toner replenishing device not shown is controlled). After that, the toner replenished from the toner container 58 into the developer storage section is circulated through the two isolated developer storage sections while being mixed and agitated with the developer G by the two conveying screws 55Y (a movement in the direction perpendicular to the plane of FIG. 2). Then, the toner in the developer G is adsorbed to the carrier by frictional charging with the carrier and is carried onto the developing roller 51Y together with the carrier by the magnetic force formed on the developing roller 51Y.

[0025] The developer G carried on the developing roller 51Y is conveyed in the direction of the arrow in FIG. 2 and reaches the position of the doctor blade 52Y. Then, after the amount of the developer G on the developing roller 51Y is optimized at this position, it is conveyed to the facing position with the photosensitive drum 1Y (which is the developing area). Then, toner is adsorbed onto the latent image formed on the photosensitive drum 1Y by the electric field (the potential difference between the developing bias and the latent image potential) formed in the developing area. After that, the developer G remaining on the developing roller 51Y reaches above the developer housing portion as the sleeve rotates and is detached from the developing roller 51Y at this position. Note that the toner container 58 is detachably (replaceably) installed with respect to the developing device 5Y (image forming apparatus 100). And when the new toner accommodated therein becomes empty, the toner container 58 is removed from the developing device 5Y (image forming apparatus 100) and replaced with a new one.

[0026] Next, with reference to FIG. 3 and the like, the intermediate transfer belt device in the present embodiment will be described in detail. Referring to FIG. 3, the intermediate transfer belt device includes an intermediate transfer belt 8 (intermediate transfer member) as an image carrier, four primary transfer rollers 9Y, 9M, 9C, 9K, a driving roller 16, a driven roller 17, a pre-transfer roller 18, a tension roller 19, a cleaning opposing roller 20, a lubricant opposing roller 21, an intermediate transfer cleaning device 10, an intermediate transfer lubricant supply device 30, a secondary transfer opposing roller 22 as a transfer opposing member, a secondary transfer device 69, and the like. The intermediate transfer belt 8 as an image carrier forms a primary transfer nip in contact with four photosensitive drums 1Y, 1M, 1C, 1K that respectively carry toner images of each color. The intermediate transfer belt 8 is mainly stretched and supported by seven roller members (the driving roller 16, the driven roller 17, the pre-transfer roller 18, the tension roller 19, the cleaning opposing roller 20, the lubricant opposing roller 21, the secondary transfer opposing roller 22).

[0027] In this embodiment, the intermediate transfer belt 8 is formed by a single layer or multiple layers of PVDF (polyvinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), etc., with a conductive material such as carbon black dispersed therein. The intermediate transfer belt 8 has a volume resistivity of 10 6 ~10 13 Ω·cm, and the surface resistivity on the back side of the belt is adjusted to be in the range of 10 7 ~10 13 Ω·cm. 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 Ω·cm. Note that, if necessary, a release layer can also be coated on the surface of the intermediate transfer belt 8. In that case, as the material used for the coating, fluororesins such as ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (polyvinylidene fluoride), PEA (perfluoroalkoxyfluororesin), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PVF (polyvinyl fluoride), etc. can be used, but it is not limited thereto.

[0028] 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 with a conductive sponge layer formed on a core metal, having a volume resistance of 10 6 ~10 12 Ω (preferably, 10 7 ~10 9It is adjusted so as to be in the range of (Ω).

[0029] The driving roller 16 is arranged to contact the inner peripheral surface of the intermediate transfer belt 8 in a state where the intermediate transfer belt 8 is wound around it at a winding angle of about 120 degrees at a position downstream in the running direction of the intermediate transfer belt with respect to the four photoreceptor drums. The driving roller 16 is rotationally driven in the clockwise direction in FIG. 3 by a driving motor (not shown) controlled by the control unit 90. Thereby, the intermediate transfer belt 8 travels in a predetermined running direction (the clockwise direction in FIG. 3).

[0030] The driven roller 17 is arranged to contact the inner peripheral surface of the intermediate transfer belt 8 in a state where the intermediate transfer belt 8 is wound around it at a winding angle of about 180 degrees at a position upstream in the running direction of the intermediate transfer belt with respect to the four photoreceptor drums. In the intermediate transfer belt 8, the portion from the driven roller 17 to the driving roller 16 is set to be substantially horizontal. The driven roller 17 is driven to rotate followingly in the clockwise direction in FIG. 3 as the intermediate transfer belt 8 runs.

[0031] The tension roller 19 contacts the outer peripheral surface of the intermediate transfer belt 8. The pre-transfer roller 18, the cleaning opposing roller 20, the lubricant opposing roller 21, and the secondary transfer opposing roller 22 contact the inner peripheral surface of the intermediate transfer belt 8. An intermediate transfer cleaning device 10 (cleaning blade) is installed between the secondary transfer opposing roller 22 and the lubricant opposing roller 21 so as to contact the cleaning opposing roller 20 via the intermediate transfer belt 8. An intermediate transfer lubricant supply device 30 (lubricant supply device) is installed between the cleaning opposing roller 20 and the tension roller 19 so as to contact the lubricant opposing roller 21 via the intermediate transfer belt 8. Similar to the lubricant supply device 3 for the photoreceptor drum, the intermediate transfer lubricant supply device 30 is composed of a lubricant supply roller, a solid lubricant, a compression spring, etc. Then, the lubricant is scraped off little by little from the solid lubricant by the lubricant supply roller rotating in the counterclockwise direction in FIG. 3, and the lubricant is supplied to the surface of the intermediate transfer belt 8 by the lubricant supply roller.

[0032] Referring to FIG. 3, the secondary transfer opposing roller 22 as the transfer opposing member is in contact with the secondary transfer roller 70 (transfer member) via the intermediate transfer belt 8 and the secondary transfer belt 72. The secondary transfer opposing roller 22 has a volume resistance of 10 7 ~10 8 Ω or so and is formed with an elastic layer 83 (layer thickness is about 5 mm) made of NBR rubber having a hardness (JIS - A hardness) of about 48 to 58 degrees on the outer peripheral surface of a cylindrical core metal made of stainless steel or the like.

[0033] Next, the secondary transfer device 69 will be described in detail with reference to FIG. 3. Referring to FIG. 3, the secondary transfer device 69 is composed 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 roller 70 and the secondary transfer belt 72 function as transfer members for transferring the toner image carried on the intermediate transfer belt 8 to the sheet P conveyed to the transfer nip (secondary transfer nip) formed between them and the intermediate transfer belt 8 (image carrier).

[0034] The secondary transfer belt 72 is an endless belt stretched and supported by a plurality of roller members (the secondary transfer roller 70 and the separation roller 71), and is formed of substantially the same material as the intermediate transfer belt 8. The secondary transfer belt 72 contacts the intermediate transfer belt 8 as the image carrier to form a secondary transfer nip (transfer nip), and conveys the sheet P sent out from the secondary transfer nip.

[0035] 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 counter roller 22. The secondary transfer roller 70 is formed (coated) with an elastic layer having a hardness (Asker C hardness) of about 40 to 50 degrees on a hollow core made of stainless steel, aluminum, etc. The elastic layer of the secondary transfer roller 70 can be formed in a solid or foamed sponge shape by dispersing a conductive filler such as carbon in a rubber material such as polyurethane, EPDM, or silicone, or by containing an ionic conductive material. In the present embodiment, the elastic layer has a volume resistance of 10 6.5 ~10 7.5 Ω or so to suppress the concentration of the transfer current.

[0036] Also, in the present embodiment, the secondary transfer roller 70 is electrically connected to a secondary transfer power source (not shown), and a secondary transfer bias (high voltage) in which a DC component and an AC component are superimposed is applied from the secondary transfer power source. The secondary transfer bias applied to the secondary transfer roller 70 is for secondarily transferring the toner image carried (primarily transferred) on the surface of the intermediate transfer belt 8 to the sheet P conveyed to the secondary transfer nip. As a result, the toner carried on the toner-carrying surface (outer peripheral surface) of the intermediate transfer belt 8 electrostatically moves from the side of the secondary transfer counter roller 22 toward the secondary transfer device 69 side by the secondary transfer electric field. In the present embodiment, the secondary transfer bias is applied to the secondary transfer roller 70 as a transfer member, but the secondary transfer bias can also be applied to the secondary transfer counter roller 22 as a transfer counter member, or the secondary transfer bias can be applied to both the secondary transfer roller 70 and the secondary transfer counter roller 22. However, when applying a DC component of the secondary transfer bias to the secondary transfer counter roller 22, a DC voltage of the same polarity as the toner (negative polarity) is applied.

[0037] Further, the secondary transfer roller 70 (transfer member) is rotationally driven counterclockwise in FIG. 3 by a drive motor (not shown) controlled by the control unit 90 to rotate (travel) the secondary transfer belt 72 counterclockwise in FIG. 3 and to rotationally drive the separation roller 71 to rotate idly counterclockwise in FIG. 3.

[0038] The separation roller 71 is disposed at a position on the downstream side in the conveyance direction of the sheet P with respect to the secondary transfer nip. The sheet P sent out from the secondary transfer nip is conveyed along the secondary transfer belt 72 traveling counterclockwise in FIG. 3 and then separated (separated by curvature) from the secondary transfer belt 72 by the secondary transfer belt 72 having a curved surface formed along the outer periphery of the separation roller 71 at the position of the separation roller 71. In this embodiment, the secondary transfer belt 72 is configured to be stretched by two roller members, i.e., the secondary transfer roller 70 and the separation roller 71. However, the secondary transfer belt 72 may also be configured to be stretched and supported by three or more roller members. The secondary transfer blade 73 abuts against the surface of the secondary transfer belt 72 to remove foreign matters 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 abut against the secondary transfer belt 72 in the counter direction with respect to the traveling direction of the secondary transfer belt 72.

[0039] Hereinafter, the configuration and operation of the image forming apparatus 100, which are characteristic in this embodiment, will be described in detail. As described above with reference to FIGS. 1 to 3 and the like, the image forming apparatus 100 in this embodiment is provided with an intermediate transfer belt 8 (intermediate transfer member) as an image carrier, and image forming units 6Y, 6M, 6C, and 6K. Referring to FIG. 4(A), the image forming units 6Y, 6M, 6C, and 6K are for forming a desired toner image TG (which is a color image in this embodiment) in an image area M on the surface of the intermediate transfer belt 8 (image carrier) based on predetermined image forming conditions during image formation (printing). Further, as described above, in the present embodiment, the image forming units 6Y, 6M, 6C, and 6K include a plurality of photosensitive drums 1Y, 1M, 1C, 1K (photosensitive members) arranged side by side so as to face the intermediate transfer belt 8 as an intermediate transfer member, a plurality of charging devices (4Y) for charging the plurality of photosensitive drums 1Y, 1M, 1C, 1K respectively, an exposure device 7 for forming a latent image on the surface of each of the plurality of photosensitive drums 1Y, 1M, 1C, 1K, and a plurality of developing devices (5Y) for developing the latent image formed on the surface of each of the plurality of photosensitive drums 1Y, 1M, 1C, 1K.

[0040] Note that the above-described "image forming conditions" are at least one of the developing bias supplied from the developing power source 92 to the developing device (in the present embodiment, the developing roller of the developing device for each color), the toner concentration of the developer G stored in the developing device, the charging bias supplied from the charging power source 91 to the charging device (in the present embodiment, the charging roller of the charging device for each color), the exposure amount in the exposure device 7, and the exposure timing in the exposure device 7. Also, in the present specification and the like, the "image area M" is the maximum range in the width direction of the intermediate transfer belt 8 (image carrier) that can be transferred onto the sheet P and on which an image can be formed. Further, in the present specification and the like, the "non-image area N" is the range in the width direction of the intermediate transfer belt 8 (image carrier) outside the area of the "image area M".

[0041] Here, referring to FIGS. 1, 3, 4, etc., the image forming apparatus 100 in the present embodiment is provided with optical sensors 95A and 95B as detection devices capable of detecting a detection pattern TP as a toner image formed in the non-image area N (see FIG. 4) on the surface of the intermediate transfer belt 8 (image carrier) by the image forming units 6Y, 6M, 6C, and 6K. Specifically, the detection pattern TP is a plurality of rectangular patterns formed at intervals over the entire circumferential direction in the non-image areas N at both ends in the width direction of the intermediate transfer belt 8 (image carrier). Specifically, at a predetermined timing, a plurality of rectangular patterns (detection pattern TP) are formed in a circumferential shape at equal intervals with respect to the running direction of the intermediate transfer belt 8 indicated by the white arrow in FIG. 4. Note that the image forming units 6Y, 6M, 6C, and 6K are set to have a length in the width direction such that they can form toner images (detection patterns TP) even in the non-image area N of the intermediate transfer belt 8 (set to a length including the non-image area N).

[0042] Then, the two optical sensors 95A and 95B as detection devices are arranged to face the non-image areas N at both ends in the width direction of the intermediate transfer belt 8 (image carrier). Specifically, in the present embodiment, the optical sensors 95A and 95B are arranged downstream of the four image forming units 6Y, 6M, 6C, and 6K (downstream in the running direction of the intermediate transfer belt 8) and upstream of the secondary transfer nip. Then, by optically detecting the detection pattern TP with the two optical sensors 95A and 95B, it is possible to grasp the image density of the detection pattern TP, the presence and degree of color misregistration of the four colors, etc. And based on the detection results, the developing power supply 92, charging power supply 91, and exposure device 7 are controlled by the control unit 90 so that they are properly corrected, and the developing bias, toner density, charging bias, exposure amount, and exposure timing of each color are adjusted.

[0043] Also, by optically detecting the detection pattern TP with the two optical sensors 95A and 95B, it is also possible to grasp the image density deviation in the width direction, the running speed uniformity and skew of the intermediate transfer belt 8, etc. And based on the detection results, the control unit 90 adjusts the deviation in the width direction of the developing gap, adjusts the driving speed of the driving roller 16, or adjusts the inclination of the central axis of the driven roller 17 so that they are optimized. In addition, in the present embodiment, apart from the two optical sensors 95A and 95B as detection devices, a density detection sensor 94 (second optical sensor) for detecting the image density of the image TG and the background portion (the portion where no image is formed) formed in the image area M of the intermediate transfer belt 8 is disposed at a position in the width direction sandwiched between the two optical sensors 95A and 95B. Then, based on the detection result by this density detection sensor 94, it is determined whether the image density of the image TG is appropriate, whether the background portion is dirty, and so on. And based on the determination, the image formation conditions are adjusted as necessary.

[0044] Here, in the present embodiment, as shown in FIG. 4(A), normally, during image formation (during printing), a first detection mode is executed in which a detection pattern TP formed in the non-image area N of the intermediate transfer belt 8 (image carrier) by the image forming units 6Y, 6M, 6C, and 6K is detected by the optical sensors 95A and 95B (detection devices) based on predetermined image formation conditions. And as shown in FIG. 4(B), during non-image formation (in the present embodiment, after a series of image formation operations are completed (after printing)), based on image formation conditions in which the image density is higher than the predetermined image formation conditions (image formation conditions during printing), a second detection mode in which the detection pattern TP formed in the non-image area N of the intermediate transfer belt 8 by the image forming units 6Y, 6M, 6C, and 6K is detected by the optical sensors 95A and 95B (detection devices) and the above-described first detection mode are switched based on predetermined conditions. That is, in the intermediate transfer belt 8, a first detection mode in which the detection pattern TP carried in the non-image area N is detected by the optical sensors 95A and 95B while carrying the image TG to be transferred to the sheet P in the image area M, and a second detection mode in which the detection pattern TP carried in the non-image area N is detected by the optical sensors 95A and 95B without forming the image TG in the image area M are configured to be switched based on predetermined conditions. In addition, in the present embodiment, the second detection mode is executed by performing an image formation operation without the conveyance of the sheet P after a series of printing is completed (after the image formation operation is completed).

[0045] Specifically, during normal operation, the first detection mode is executed at a predetermined timing during image formation (for example, for each predetermined number of printed sheets, at regular intervals, when a change in the environment (temperature and humidity) exceeds a predetermined range, etc.). When the image density of the detection pattern TP detected by the optical sensors 95A and 95B (detection devices) is equal to or higher than a predetermined value A, the image formation conditions (during printing) are adjusted based on the detection results detected by the optical sensors 95A and 95B in the first detection mode. On the other hand, when the image density of the detection pattern TP detected by the optical sensors 95A and 95B is lower than the predetermined value A, the second detection mode is executed, and the image formation conditions (during printing) are adjusted based on the detection results detected by the optical sensors 95A and 95B in the second detection mode. In this embodiment, as the detection result detected by the detection device, the average of the detection results respectively detected by the two optical sensors 95A and 95B can be used.

[0046] Specifically, referring to FIG. 5, the magnitude of the output voltage (sensor output voltage) of the optical sensors 95A and 95B is related to the magnitude of the image density (the lower the output voltage, the higher the image density). And those with an output voltage equal to or lower than the threshold value Vx (those with an image density equal to or higher than the predetermined value A) are determined to be the portions of the rectangular pattern in the detection pattern TP. However, due to surface deterioration of the intermediate transfer belt 8 or the like, as shown in FIG. 5(A), under the image formation conditions during printing, if the image density of the detection pattern TP does not become sufficiently high and the output voltage exceeds the threshold value Vx, sufficient detection of the detection pattern TP cannot be performed. In this embodiment, in such a state, without adjusting the image formation conditions by the first detection mode, the image formation conditions are changed so that the image density becomes high after printing, and as shown in FIG. 5(B), the image density of the detection pattern TP is made sufficiently high and the output voltage becomes equal to or lower than the threshold value Vx, and the detection of the detection pattern TP (second detection mode) is executed. In this embodiment, during the first detection mode, the developing bias is set to about -500 V, the charging bias is set to about -600 V, and the exposure amount of the exposure device 7 is set to about 100%. On the other hand, during the second detection mode, the developing bias is changed to about -700 V, the charging bias is changed to about -800 V, and the exposure amount of the exposure device 7 is changed to about 150%.

[0047] By controlling in this way, even if the image density of the detection pattern TP formed in the non-image area N of the intermediate transfer belt 8 decreases and the detection pattern TP cannot be normally detected by the optical sensors 95A and 95B as it is, the second detection mode can be executed after the printing is completed to appropriately adjust the image forming conditions.

[0048] The following is a further supplementary explanation. Since the detection pattern TP is a toner image formed in the non-image area N that does not involve the transfer (secondary transfer) to the sheet P, sufficient image density may not be obtained due to multiple factors even when imaging is performed under the image forming conditions during printing. For example, when the amount of developer G sucked up onto the developing roller 51Y is not uniform between the central portion in the width direction and the end portion in the width direction and the deviation is large, the developing bias and the toner density are adjusted so that sufficient image density is maintained in the image area M. Therefore, the image density may extremely decrease in the non-image area. In particular, when the developer G is deteriorated over time, such a phenomenon becomes prominent. Also, in the primary transfer process, the nip pressure at the end portion in the width direction of the primary transfer nip may be low, resulting in a decrease in the image density of the non-image area N. In such a case, since the image on the sheet P is normal and not abnormal in the image area M, the decrease in the image density in the non-image area N is not recognized by the user. However, the image density of the detection pattern TP formed on the intermediate transfer belt 8 may decrease and it is highly likely that it cannot be detected by the optical sensors 95A and 95B.

[0049] In particular, when the detection patterns TP are detected by the optical sensors 95A and 95B to grasp the color misregistration of four colors and perform control (color matching control) to correct the color misregistration, when the sensor outputs of the optical sensors 95A and 95B become equal to or lower than the threshold value Vx (see FIG. 5), the leading edge is recognized, and the timing is fed back to the exposure timing of the exposure apparatus 7. Considering a decrease in the image density of the detection pattern TP, a measure of setting the threshold value Vx higher in advance is also conceivable. However, since there may be cases where rubbing marks due to unit detachment or deformation (set) of the intermediate transfer belt 8 due to long-term storage at a high temperature occur on the base portion of the intermediate transfer belt 8, the threshold value Vx needs to be set to be lower than the base portion by a predetermined amount. In the present embodiment, the sensor outputs of the optical sensors 95A and 95B are adjusted so that the sensor output of the base portion of the intermediate transfer belt 8 becomes 4V, and the threshold value Vx of the pattern portion (image portion) is set to 1.3V. This threshold value Vx is set to 2.5V or less so as not to be affected by the variation of the base portion assuming the variation of the base portion due to rubbing or set of the base portion to be ±1.5V. Also, since the lower limit sensor output of the pattern portion is 0.1V, it is calculated from the intermediate value thereof. As shown in FIG. 5(A), the detection pattern TP (see FIG. 4(A)) formed during printing may not fall below the threshold value Vx of 1.3V due to the deviation of development or the like described above. In such a case, conventionally, since color matching control is difficult, printing has been continued using the exposure timing in the latest successful color matching control in the past assuming that the color matching control has failed. However, if the user determines that the color matching accuracy deteriorates due to temperature changes or the like and is unacceptable in terms of image quality, a service call will be made and maintenance will be performed by the service technician. However, many users dislike the downtime of the apparatus due to such maintenance. The decrease in the image density of such a detection pattern TP is caused by forming an image under the imaging conditions during printing, and it is a problem that can be solved by forming the detection pattern TP under imaging conditions where the image density increases at a timing different from that during printing. From this perspective, in the present embodiment, when a decrease in the image density of the detection pattern TP formed during printing occurs (when the first detection mode fails), after the printing is completed, adjustment control (second detection mode) using the detection pattern TP formed under high-image-density imaging conditions is performed.

[0050] Hereinafter, with reference to FIGS. 6 and 7, an example of control related to the first and second detection modes will be described. First, as shown in FIG. 6, when printing (image formation) is started, it is determined whether it is the timing to perform the first detection mode (step S1). That is, it is determined whether it is the timing to adjust imaging conditions such as color matching control. Such a timing is predetermined, for example, for each predetermined number of printed sheets as described above. And when it is the timing to perform the first detection mode, the first detection mode as described above with reference to FIG. 4(A) etc. is executed (step S2). Then, it is determined whether the image density of the detection pattern TP is equal to or higher than a predetermined value A (whether the sensor output is equal to or lower than the threshold value Vx) (step S3). That is, it is determined whether the first detection mode has been executed normally (succeeded). As a result, when the detection is successful, the imaging conditions are adjusted based on the detection result, and this flow ends. On the other hand, when the detection fails, a "first detection mode failure flag" is set in terms of control (step S4).

[0051] Then, as shown in FIG. 7, it is determined whether the "first detection mode failure flag" is set (step S10). As a result, when the "First Detection Mode Failure Flag" is set, it is determined whether the "Second Detection Mode Failure Flag" is set (step S11). As a result, when the "Second Detection Mode Failure Flag" is not set, after printing is completed, the second detection mode as described above with reference to FIG. 4(B) etc. is executed (step S12). Then, it is determined whether the image density of the detection pattern TP is equal to or greater than a predetermined value A (whether the sensor output is equal to or less than the threshold value Vx) (step S13). That is, it is determined whether the second detection mode has been executed normally (successfully). As a result, when the detection is successful, the imaging conditions are adjusted based on the detection result, and after clearing the "First Detection Mode Failure Flag" (step S15), this flow ends. On the other hand, when the detection fails, the "Second Detection Mode Failure Flag" is set under control (step S14), and the flow after step S15 is executed. Also, when the "First Detection Mode Failure Flag" is not set in step S10, or when the "Second Detection Mode Failure Flag" is set in step S11, the flow after step S15 is executed. Note that when the "Second Detection Mode Failure Flag" is set, printing is continued using the imaging conditions adjusted by the latest detection mode that was successful in the past. Then, the fact that it is such a state is displayed (notified) on the operation display panel 110 (see FIGS. 1 and 3), and the user is entrusted with the judgment regarding the necessity of a service call (maintenance).

[0052] As described above, the image forming apparatus 100 according to the present embodiment includes an intermediate transfer belt 8 (image carrier), image forming units 6Y, 6M, 6C, 6K that form a desired toner image TG in an image area M on the surface of the intermediate transfer belt 8 based on predetermined image forming conditions during image formation, and optical sensors 95A, 95B (detection devices) capable of detecting a detection pattern TP as a toner image formed in a non-image area N on the surface of the intermediate transfer belt 8 by the image forming units 6Y, 6M, 6C, 6K. During image formation, based on predetermined image forming conditions, a first detection mode in which the detection pattern TP formed in the non-image area N of the intermediate transfer belt 8 by the image forming units 6Y, 6M, 6C, 6K is detected by the optical sensors 95A, 95B, and during non-image formation, based on image forming conditions in which the image density is higher than the predetermined image forming conditions, a second detection mode in which the detection pattern TP formed in the non-image area N of the intermediate transfer belt 8 by the image forming units 6Y, 6M, 6C, 6K is detected by the optical sensors 95A, 95B are switched based on predetermined conditions. This makes it less likely that a problem will occur in which the detection pattern TP cannot be normally detected by the optical sensors 95A, 95B.

[0053] In the present embodiment, the present invention is applied to the image forming apparatus 100 using a secondary transfer roller 70 and a secondary transfer belt 72 as transfer members and an intermediate transfer belt 8 (intermediate transfer body) as an image carrier. On the other hand, the present invention can also be applied to an apparatus that does not include an intermediate transfer body such as an intermediate transfer belt or an intermediate transfer drum, and includes a photosensitive drum (photosensitive member) as an image carrier on which a toner image developed by a developing device is formed, and a transfer roller (or a transfer belt) as a transfer member that forms a transfer nip in contact with the photosensitive drum and transfers the toner image on the photosensitive drum to a sheet conveyed to the transfer nip, that is, a so-called direct transfer type image forming apparatus. In addition, in the present embodiment, the present invention is applied to the image forming apparatus 100 using the secondary transfer roller 70 and the secondary transfer belt 72 as transfer members. However, the application of the present invention is not limited thereto, and the present invention can also be applied to an image forming apparatus in which only the secondary transfer roller is used without using the secondary transfer belt as the transfer member. Further, in the present embodiment, the present invention is applied to the image forming apparatus 100 that forms a color image. On the other hand, the present invention can also be applied to an image forming apparatus that forms only a monochrome image. And even in such cases, the same effects as those of the present embodiment can be obtained.

[0054] It should be noted that the present invention is not limited to the present embodiment, and it is obvious that the present embodiment can be appropriately changed in addition to what is suggested in the present embodiment within the scope of the technical idea of the present invention. Further, the number, position, shape, etc. of the above-described constituent members are not limited to the present embodiment, and can be set to appropriate numbers, positions, shapes, etc. suitable for implementing the present invention.

Explanation of Reference Numerals

[0055] 1Y, 1M, 1C, 1K photosensitive drum (photosensitive member), 4Y charging device, 5Y developing device, 6Y, 6M, 6C, 6K image forming unit, 7 exposure device, 8 intermediate transfer belt (image carrier, intermediate transfer member), 95A, 95B optical sensor (detection device), TG image (toner image), TP detection pattern.

Prior Art Documents

Patent Documents

[0056]

Patent Document 1

Claims

1. An image carrier, an image forming unit that forms a desired toner image in an image area on the surface of the image carrier based on predetermined image forming conditions during image formation, a detection device capable of detecting a detection pattern as a toner image formed in a non-image area on the surface of the image carrier by the image forming unit, comprising: a first detection mode in which, during image formation, based on the predetermined image forming conditions, the detection pattern formed in the non-image area of the image carrier by the image forming unit is detected by the detection device; a second detection mode in which, during non-image formation, based on image forming conditions in which the image density is higher than the predetermined image forming conditions, the detection pattern formed in the non-image area of the image carrier by the image forming unit is detected by the detection device; is switched based on predetermined conditions, normally, the first detection mode is executed at a predetermined timing during image formation, when the image density of the detection pattern detected by the detection device is equal to or higher than a predetermined value, based on the detection result detected by the detection device in the first detection mode, the image forming conditions during image formation are adjusted, when the image density of the detection pattern detected by the detection device is lower than the predetermined value, the second detection mode is executed, and based on the detection result detected by the detection device in the second detection mode, the image forming conditions during image formation are adjusted. An image forming apparatus characterized by this.

2. The image carrier is an intermediate transfer body, The image forming unit includes a plurality of photoreceptors arranged in parallel so as to face the intermediate transfer body, a plurality of charging devices that charge the plurality of photoreceptors, an exposure device that forms a latent image on the surface of each of the plurality of photoreceptors, and a plurality of developing devices that develop the latent images formed on the surface of each of the plurality of photoreceptors. The image forming apparatus according to claim 1, characterized by this.

3. The image forming conditions are at least one of a developing bias supplied to the developing device, a toner concentration of a developer accommodated in the developing device, a charging bias supplied to the charging device, an exposure amount in the exposure device, and an exposure timing in the exposure device. The image forming apparatus according to claim 2, characterized by this.

4. The detection pattern formed in the non-image area in the second detection mode is formed by being changed so that the image density becomes higher than that under the predetermined image forming conditions, with respect to the development bias supplied to the developing device, the charging bias supplied to the charging device, and the exposure amount in the exposure device. The image forming apparatus according to claim 2 or claim 3, characterized in that.

5. The image forming apparatus according to any one of claims 1 to 4, characterized in that it is after a series of image forming operations have ended when non-image is being formed.

6. The detection pattern is a plurality of rectangular patterns formed at intervals over the entire circumferential direction in the non-image areas at both ends in the width direction of the image carrier, The image forming apparatus according to any one of claims 1 to 5, characterized in that the detection device is two optical sensors respectively facing the non-image areas at both ends in the width direction of the image carrier.

Images