Image-forming device

Abstract

This image-forming device is configured to include a control unit capable of, on the basis of a detection signal outputted by a light receiving element upon reception of reflected light, performing control so as to execute deposit removal processing for removing deposits on the surface of an image carrier, after the rear end of an image-forming area on the surface of the image carrier, in which a toner image that is to be transferred to a preceding recording material can be formed, has passed through the detection position of an optical sensor, and until the front end of the image-forming area on the surface of the image carrier, in which a toner image that is to be transferred to a next recording material can be formed, reaches the detection position during the execution of the print job.

Description

Image forming device

[0001] The present invention relates to an image forming apparatus such as a printer, a copying machine, a facsimile machine, or a multifunction machine having a plurality of functions of these machines, which uses an electrophotographic method or an electrostatic recording method.

[0002] In conventional image forming devices such as electrophotographic printers, an electrostatic latent image is formed on a photoreceptor, and toner, a color material charged to the electrostatic latent image, is supplied to the electrostatic latent image and developed to form a toner image on the photoreceptor. This toner image is transferred to a recording material such as paper directly or via an intermediate transfer member, and then fixed to form an image on the recording material. A photosensitive drum, which is a drum-shaped photoreceptor, is widely used as the photoreceptor. An intermediate transfer belt, which is an endless belt, is widely used as the intermediate transfer member.

[0003] Such image forming apparatuses may be equipped with a function for detecting abnormalities on the photosensitive drum or intermediate transfer belt, which are image carriers, and suppressing the occurrence of image defects associated with the abnormalities. Possible abnormalities on the photosensitive drum or intermediate transfer belt include, for example, condensation inside the image forming apparatus. When condensation occurs inside the image forming apparatus and water droplets from the condensation adhere to the photosensitive drum or intermediate transfer belt, the following problems may occur. For example, a low-density image may be printed due to fluctuations in the surface potential of the photosensitive drum. Furthermore, water droplets may collect toner adhering to a cleaning member or toner charging member for cleaning the surface of the photosensitive drum or intermediate transfer belt, and the toner may be transferred to a recording material such as paper, resulting in image defects.

[0004] Image forming apparatuses are installed in various air-conditioning environments, and the indoor environment can change significantly when the air-conditioning function is activated. Because the image forming apparatus is nearly sealed by an exterior cover, the internal temperature of the image forming apparatus changes with a certain time lag relative to changes in the indoor environment. Therefore, when the heating function is activated in a cold indoor environment, the temperature inside the image forming apparatus remains low despite the rise in the indoor temperature. For example, when the paper feed tray or cartridge tray is opened or when a fan for cooling IC chips such as motor drivers installed inside the image forming apparatus is activated, warm air from the room may enter the image forming apparatus, causing condensation.

[0005] Japanese Patent Laid-Open Publication No. 2021-026192 proposes a configuration in which a temperature and humidity sensor installed inside an image forming apparatus detects temperature and humidity prior to image formation, and if the detected temperature and humidity indicates that condensation may have formed inside the image forming apparatus, an operation is performed to determine whether condensation has occurred. In the configuration described in Japanese Patent Laid-Open Publication No. 2021-026192, a toner patch is formed to detect the condensation state, and the density of the toner patch is detected by a density detection means. If the density is lower than a predetermined density, it is determined that condensation has occurred, and a condensation recovery mode is executed.

[0006] In the configuration of JP 2021-026192 A, a temperature and humidity sensor located inside the image forming apparatus detects a condition that is suspected of causing condensation prior to image formation. However, for example, if condensation occurs when air from an air conditioning function flows directly into the image forming apparatus and comes into contact with low-temperature components inside the image forming apparatus, the following problem occurs. For example, if air flows into the image forming apparatus from the paper discharge port of the image forming apparatus due to air blown from the ceiling, such as a ceiling fan, during a print job, warm water vapor generated from recording materials such as paper that have passed through the fixing device may flow back into the image forming apparatus during the print job, causing significant localized condensation.

[0007] In addition, in the configuration of JP 2021-026192 A, a temperature and humidity sensor detects temperature and humidity prior to image formation, and if the detected temperature and humidity indicate a condensation state, a toner patch is formed to determine whether or not condensation has occurred. If it is determined that condensation has not occurred, normal image formation is performed. This can result in unnecessary toner consumption and downtime due to the formation of the toner patch, potentially impairing usability.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to suppress image defects caused by condensation or the like during a print job.

[0009] The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image forming apparatus comprising: toner image forming means for forming a toner image; a rotatable image carrier for carrying the toner image formed by the toner image forming means on its surface; transfer means for transferring the toner image formed on the surface of the image carrier onto a recording material; a light-emitting element for irradiating light onto the surface of the image carrier; and an optical sensor for detecting the reflected light at a detection position in the moving direction of the surface of the image carrier, the optical sensor including a light-emitting element for irradiating light from the light-emitting element onto the surface of the image carrier and receiving the reflected light to output a detection signal according to the amount of received light, the optical sensor forming a print image on one or more recording materials in response to a single start instruction, and discharging the toner image formed on one or more recording materials through a recording material discharge port. The image forming apparatus executes a print job in which a number of recording materials are discharged from inside the apparatus to outside the apparatus, and the image forming apparatus has a control unit capable of controlling the apparatus to execute an adhesion removal process to remove adhesions from the surface of the image carrier based on a detection signal output by the light receiving element upon receiving the reflected light during the period from when the rear end in the movement direction of the image forming area on the surface of the image carrier, on which a toner image to be transferred to a preceding recording material can be formed, passes the detection position until the front end in the movement direction of the image forming area on the surface of the image carrier, on which a toner image to be transferred to a next recording material can be formed, reaches the detection position.

[0010] According to another aspect of the present invention, there is provided a printing apparatus including a toner image forming means for forming a toner image, a rotatable image carrier that carries on its surface the toner image formed by the toner image forming means, a drive section that drives the image carrier to rotate, a transfer means that transfers the toner image formed on the surface of the image carrier to a recording material, a light-emitting element that irradiates light onto the surface of the image carrier, and a light-receiving element that irradiates light from the light-emitting element onto the surface of the image carrier, receives reflected light, and outputs a detection signal according to the amount of received light, and an optical sensor that detects the reflected light at a detection position in the moving direction of the surface of the image carrier, and in response to a single start instruction, forms a print image on one or more recording materials, and ejects the one or more recording materials from inside the apparatus to outside the apparatus through a recording material ejection port. In an image forming apparatus that executes a print job to be discharged, when a numerical value related to a detection signal output by the light receiving element after receiving the reflected light after the trailing end in the movement direction of the image forming area on the surface of the image carrier where a toner image to be transferred to the last recording material of the print job can be formed passes the detection position during execution of the print job, the image forming apparatus has a control unit that is capable of controlling the drive unit so that the time from when the trailing end in the movement direction of the image forming area on the surface of the image carrier where a toner image to be transferred to the last recording material can be formed passes the detection position to when the rotation of the image carrier stops is longer than when the numerical value related to the detection signal does not satisfy the predetermined condition.

[0011] According to the present invention, it is possible to suppress image defects caused by condensation or the like during a print job.

[0012] FIG. 1 is a schematic cross-sectional view of an image forming apparatus.

[0013] FIG. 2 is a block diagram showing the control configuration of the image forming apparatus.

[0014] FIG. 3 is a top view for explaining the arrangement of the optical sensors.

[0015] FIG. 4 is a schematic cross-sectional view for explaining the configuration of the optical sensor.

[0016] FIG. 5 is a graph showing a detected waveform when the reflected light from the intermediate transfer belt is detected by an optical sensor.

[0017] FIG. 6 is a graph showing a detected waveform when the reflected light from the toner patch is detected by an optical sensor.

[0018] FIG. 7 is a timing chart showing an outline of an example of the operation during a print job.

[0019] FIG. 8 is a graph showing a waveform detected when the optical sensor detects reflected light from the intermediate transfer belt in a state where water droplets adhere to the surface of the intermediate transfer belt due to condensation.

[0020] FIG. 9 is a schematic diagram showing an example of the conditions under which condensation occurs inside an image forming apparatus.

[0021] FIG. 10 is a graph for explaining the change in the surface potential of the photosensitive drum depending on whether or not condensation occurs.

[0022] FIG. 11 is a timing chart showing an outline of an example of operation during idling.

[0023] FIG. 12 is a flowchart showing an example of the operation of a print job.

[0024] FIG. 13 is a flowchart showing another example of the operation of a print job.

[0025] FIG. 14 is a timing chart showing an outline of another example of the operation during a print job.

[0026] FIG. 15 is a timing chart showing an outline of another example of the operation during a print job.

[0027] FIG. 16 is a schematic cross-sectional view of another example of an image forming apparatus.

[0028] FIG. 17 is a timing chart showing another example of the operation during the idling operation.

[0029] FIG. 18 is a flowchart showing another example of the operation of a print job.

[0030] FIG. 19 is a graph showing a detected waveform when diffused light reflected from sand on the intermediate transfer belt is detected by an optical sensor.

[0031] FIG. 20 is a graph showing a detected waveform when specularly reflected light from sand on the intermediate transfer belt is detected by an optical sensor.

[0032] FIG. 21 is a flowchart showing another example of the operation of a print job.

[0033] FIG. 22 is a flowchart showing another example of the operation of a print job.

[0034] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the examples may be changed as appropriate depending on the configuration and various conditions of the apparatus to which the invention is applied, and the scope of the invention is not intended to be limited to the following examples. [Example 1] 1. Overall configuration and operation of the image forming apparatus

[0035] 1 is a schematic cross-sectional view of an image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a tandem laser beam printer that employs an intermediate transfer system and is capable of forming a full-color image on a sheet-shaped recording material P using an electrophotographic system. The image forming apparatus 100 forms an image on the recording material P based on signals (information) input from an external device connected to the image forming apparatus 100, such as an image reading device or a host computer such as a personal computer.

[0036] Image forming apparatus 100 has four image forming units Sa, Sb, Sc, and Sd as multiple image forming units (stations) inside (inside) a housing (exterior cover) 120 of apparatus main body 110. Image forming units Sa, Sb, Sc, and Sd form images using toner of each color: yellow (Y), magenta (M), cyan (C), and black (K), respectively. These four image forming units Sa, Sb, Sc, and Sd are arranged in a line at regular intervals in a direction intersecting the vertical direction (approximately horizontal in this embodiment).

[0037] The configuration of each image forming unit S is essentially the same except for the color of toner used. Elements having the same or corresponding functions or configurations provided for each color may be generally described by omitting the suffixes a, b, c, and d indicating that the element is for one of the colors. For convenience, the magnitude (high / low) of voltage or potential (or potential difference) refers to the magnitude (high / low) when compared in absolute value unless otherwise specified. Because paper is primarily used as the recording material P in the image forming apparatus 100, the recording material P is sometimes referred to as paper, but the term "recording material P" also includes materials other than paper and materials containing materials other than paper.

[0038] In this embodiment, the image forming unit S is configured to include photosensitive drums 1 (1a, 1b, 1c, 1d), charging rollers 2 (2a, 2b, 2c, 2d), developing devices 4 (4a, 4b, 4c, 4d), drum cleaning devices 5 (5a, 5b, 5c, 5d), etc., which will be described later.

[0039] The photosensitive drum 1, which is a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) serving as a first image carrier for carrying a toner image, is rotationally driven at a predetermined peripheral speed (process speed) in the direction of arrow R1 in FIG. 1 (counterclockwise direction) by a driving force transmitted from a drive motor provided in a drive unit 90 (FIG. 2) serving as a driving means. In this embodiment, the photosensitive drum 1 is rotationally driven at a peripheral speed of 200 mm / sec. When a print job is started by a DC controller 200 serving as a control unit (described later) receiving an image signal, the rotational driving of the photosensitive drum 1 is started.

[0040] The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential (dark potential Vd) of a predetermined polarity (negative in this embodiment) by a charging roller 2, which is a roller-type charging member serving as charging means. The charging roller 2 is disposed in contact with the surface of the photosensitive drum 1 and is pressed against the photosensitive drum 1 with a predetermined pressure. The charging roller 2 is rotated in accordance with the rotation of the photosensitive drum 1. During charging, a charging voltage (charging bias), which is a DC voltage of the same polarity (negative in this embodiment) as the charging polarity of the photosensitive drum 1, is applied to the charging roller 2 by a charging power source (high-voltage power source) 24 ( FIG. 2 ) serving as charging voltage application means (charging voltage application unit).

[0041] The surface of the rotating photosensitive drum 1 that has been charged is scanned and exposed in accordance with an image signal by an exposure device (laser scanner unit) 3 serving as exposure means, and an electrostatic latent image (electrostatic image) of a color component corresponding to each image forming station S is formed on the photosensitive drum 1. For example, when a full-color image is formed, each of the photosensitive drums 1a, 1b, 1c, and 1d is exposed by exposure devices 3a, 3b, 3c, and 3d in accordance with an image signal of a color component corresponding to each image forming station S. As a result, electrostatic latent images corresponding to the yellow, magenta, cyan, and black color component images of the target color image are formed on each of the photosensitive drums 1a, 1b, 1c, and 1d.

[0042] The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by a developing device (developing unit) 4 serving as a developing means, which supplies toner as a developer, thereby forming a toner image (toner image, developer image) on the photosensitive drum 1. The developing device 4 includes a developer container 41 containing toner, which is a non-magnetic single-component developer, and a developing roller 42 serving as a developing member (developer carrier). During development, the developing roller 42 is brought into contact with the surface of the photosensitive drum 1. During development, the developing roller 42 is rotated by a driving force transmitted from a drive motor provided in a driving unit 90 ( FIG. 2 ) serving as a driving means. In this embodiment, the developing roller 42 is rotated at a peripheral speed of 300 mm / sec in a rotational direction such that the surface of the developing roller 42 moves in the same direction as the surface of the photosensitive drum 1 at the contact point between the photosensitive drum 1 and the developing roller 42. By rotating the developing roller 42 at 1.5 times the speed of the photosensitive drum 1 in this manner, stable development can be achieved. The developing roller 42 carries the toner contained in the developer container 41 and transports the toner to a development position where the photosensitive drum 1 and the developing roller 42 contact each other. During development, a development voltage (developing bias), which is a DC voltage having the same polarity (negative in this embodiment) as the charging polarity of the photosensitive drum 1, is applied to the developing roller 42 by a development power supply (high-voltage power supply) 25 ( FIG. 2 ) serving as a development voltage application unit (developing voltage application unit). In this embodiment, the normal charging polarity of the toner carried by the developing roller 42 is negative. In this embodiment, the developing device 4 deposits toner charged to the same polarity (negative in this embodiment) as the charging polarity of the photosensitive drum 1 by the charging roller 2 onto portions (image areas) of the photosensitive drum 1 where the potential has decreased due to exposure (reverse development method). However, the present invention can also be applied to image forming apparatuses that perform development using toner charged to the polarity opposite to the charging polarity of the photosensitive drum 1.

[0043] In this embodiment, the image forming apparatus 100 has a contact / separation mechanism 80 ( FIG. 2 ) for contacting and separating the developing roller 42 with and from the photosensitive drum 1. In this embodiment, when the image forming apparatus 100 is stopped, the contact / separation mechanism 80 separates the developing roller 42 from the photosensitive drum 1. During development, the contact / separation mechanism 80 contacts the developing roller 42 with the photosensitive drum 1. In this embodiment, the developing container 41 is configured to be swingable, and is biased in a direction toward contact with the photosensitive drum 1 by a pressure spring, which is a biasing member serving as a biasing means. The contact / separation mechanism 80 moves (rotates) the developing container 41 against the biasing force of the pressure spring, thereby separating the developing roller 42 from the photosensitive drum 1. The contact / separation mechanism 80 also allows the developing container 41 to move (rotate) due to the biasing force of the pressure spring, thereby allowing the developing roller 42 to contact the photosensitive drum 1. The contact / separation mechanism 80 is driven by a driving force transmitted from a driving motor provided in a driving unit 90 (FIG. 2) serving as a driving means. The developing roller 42 is driven to rotate when it is brought into contact with the photosensitive drum 1, and stops rotating when it is separated from the photosensitive drum 1.

[0044] In this embodiment, the rotation speed of the developing roller 42 is set so that the solid density (maximum image density) of yellow, magenta, cyan, and black is 1.5 for A4 size GF-C081 paper manufactured by Canon Inc. The solid density was measured using a handheld densitometer eXact manufactured by X-rite Corporation.

[0045] In this embodiment, a charging voltage of −1000 V is applied to the charging roller 2 during charging, and the surface of the photosensitive drum 1 is uniformly charged to a surface potential (dark potential Vd) of −600 V. In this embodiment, the exposure amount (laser light amount: μJ / cm2) of the exposure device 3 is set so that the surface potential (light potential VL) of the photosensitive drum 1 after exposure by the exposure device 3 is −200 V. In this embodiment, a development voltage of −350 V is applied to the development roller 42 during development.

[0046] In this embodiment, the charging roller 2, the exposure device 3, the developing device 4, etc. of each image forming station S constitute a toner image forming means for forming a toner image.

[0047] Opposing the four photosensitive drums 1 is an intermediate transfer belt 10, an intermediate transfer body formed of a rotatable endless belt, which serves as a second image carrier carrying a toner image. The intermediate transfer belt 10 is tensioned by three axes of a plurality of tension rollers: first, second, and third tension rollers 11, 12, and 13. The first tension roller 11, together with the third tension roller 13, forms the surface of the intermediate transfer belt 10 onto which the toner image is transferred. The second tension roller 12 functions as a tension roller that applies a predetermined tension to the intermediate transfer belt 10. The third tension roller 13 functions as a drive roller that transmits driving force to the intermediate transfer belt 10 and also functions as an opposing roller for a secondary transfer roller 20 (described later). A total tension of 60 N is applied to the intermediate transfer belt 10 by the second tension roller 12. The intermediate transfer belt 10 rotates (circulates or moves circulatingly) in the direction of arrow R2 in FIG. 1 (clockwise direction) when the third tension roller 13 is rotationally driven by a driving force transmitted from a drive motor provided in a drive unit 90 (FIG. 2) serving as a drive means. The intermediate transfer belt 10 is rotationally driven at a peripheral speed (approximately 200 mm / sec) corresponding to the peripheral speed of the photosensitive drum 1. The first and second tension rollers 11 and 12 are driven to rotate in accordance with the rotation of the intermediate transfer belt 10. Primary transfer rollers 6a, 6b, 6c, and 6d, which are roller-type primary transfer members serving as primary transfer means, are arranged on the inner peripheral surface of the intermediate transfer belt 10 in correspondence with each of the photosensitive drums 1a, 1b, 1c, and 1d. The primary transfer roller 6 comes into contact with the inner peripheral surface of the intermediate transfer belt 10 and presses the intermediate transfer belt 10 against the photosensitive drum 1, thereby forming a primary transfer portion (primary transfer nip) N1, which is the contact portion between the photosensitive drum 1 and the intermediate transfer belt 10. The primary transfer roller 6 is rotated in accordance with the rotation of the intermediate transfer belt 10.

[0048] At the primary transfer portion N1, the toner image formed on the photosensitive drum 1 is transferred (primary transfer) by the action of the primary transfer roller 6 onto the rotating intermediate transfer belt 10, which serves as a transfer receiving member. During the primary transfer, a primary transfer voltage (primary transfer bias), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the primary transfer roller 6 by a primary transfer power supply (high-voltage power supply) 23, which serves as a primary transfer voltage application means (primary transfer voltage application portion). In this embodiment, a primary transfer voltage of +500 V is applied to the primary transfer roller 6 during the primary transfer. For example, when forming a full-color image, toner images of yellow, magenta, cyan, and black formed on the four photosensitive drums 1a, 1b, 1c, and 1d are sequentially transferred onto the intermediate transfer belt 10 in a superimposed state. As a result, four-color toner images corresponding to the desired color image are formed on the intermediate transfer belt 10. In this embodiment, the primary transfer power supply 23 is a common power supply capable of applying a positive or negative voltage to the four primary transfer rollers 6a, 6b, 6c, and 6d. The primary transfer power supply 23 is capable of outputting a positive voltage in the range of +100V to +2000V (where "to" indicates a range that includes the numerical values ​​before and after the range), and a negative voltage in the range of -200V to -2000V. In this embodiment, a configuration is described in which a voltage is applied to multiple primary transfer rollers 6 from a common primary transfer power supply 23, but the present invention is not limited to such a configuration. The present invention can also be applied to a configuration in which multiple primary transfer power supplies are provided corresponding to each primary transfer roller 6.

[0049] In this embodiment, the intermediate transfer belt 10 is an endless belt (film) consisting of two layers: a base layer and a surface layer. The base layer is a 70 μm thick layer formed from a polyethylene naphthalate resin with a quaternary ammonium salt, an ionic conductive agent acting as an electrical resistance adjuster, dispersed therein, and has an elastic modulus of 2000 MPa. In this embodiment, the base layer of the intermediate transfer belt 10 is formed by blow molding. However, other molding methods include centrifugal molding, tube extrusion, inflation molding, extrusion molding, and cylindrical extrusion molding. The surface layer is formed on the outer peripheral surface of the base layer, which is the outer peripheral side of the intermediate transfer belt 10. The surface layer is a 3 μm thick layer formed from a material in which antimony-doped zinc oxide, an electrical resistance adjuster, is dispersed in an acrylic resin base material, and polytetrafluoroethylene (PTFE) particles are added as a solid lubricant. Methods for forming the surface layer include, for example, dip coating, spray coating, flow coating, shower coating, roll coating, spin coating, and ring coating. In the intermediate transfer belt 10 of this example, the base layer obtained by blow molding was fitted onto the outer periphery of a cylindrical mold, the edges were sealed, and the mold was then immersed in a container filled with a surface layer liquid, and the mold was then pulled up so that the relative speed between the liquid level of the curable composition and the base layer was constant, thereby forming a coating film made of the surface layer liquid on the surface of the base layer.

[0050] In this example, the volume resistivity of the intermediate transfer belt 10 is 1×10 Ω·cm. The volume resistivity of the intermediate transfer belt 10 was measured using a Mitsubishi Chemical Corporation Hiresta-UP (MCP-HT450) connected to a UR probe (model MCP-HTP12) at an applied voltage of 100 V for a measurement time of 10 seconds. The environment of the measurement chamber for measuring the volume resistivity of the intermediate transfer belt 10 was set to a temperature of 23°C and a humidity (relative humidity) of 50%, and the volume resistivity of the intermediate transfer belt 10 was measured after leaving it in the measurement chamber for 4 hours. In this example, the glossiness of the surface (outer peripheral surface) of the intermediate transfer belt 10 was 75. The glossiness of the surface of the intermediate transfer belt 10 was measured using a Horiba, Ltd. handheld glossmeter IG-320. In this example, the peripheral length of the intermediate transfer belt 10 was 800 mm.

[0051] In this embodiment, the primary transfer roller 6 is a roller with an outer diameter of 11 mm, which is made by covering a nickel-plated steel rod with an outer diameter of 5 mm with a foamed sponge body mainly composed of NBR and epichlorohydrin rubber, the volume resistivity of which is adjusted to 105 Ω·cm and a thickness of 3 mm. In this embodiment, the rubber hardness of the foamed sponge body constituting the primary transfer roller 6 was 20° when measured with an Asker hardness tester type C under a load of 500 g.

[0052] A secondary transfer roller 20, a roller-type secondary transfer member serving as a secondary transfer means, is disposed on the outer peripheral surface of the intermediate transfer belt 10, facing the third tension roller 13. The secondary transfer roller 20 contacts the outer peripheral surface of the intermediate transfer belt 10 and is pressed with a pressure of 50 N against the third tension roller 13, which is disposed opposite the secondary transfer roller 20 across the intermediate transfer belt 10. This causes the secondary transfer roller 20 to form a secondary transfer portion (secondary transfer nip) N2, which is the contact portion between the intermediate transfer belt 10 and the secondary transfer roller 20. The secondary transfer roller 20 is rotated in accordance with the rotation of the intermediate transfer belt 10. The toner image formed on the intermediate transfer belt 10 is transferred (secondary transfer) at the secondary transfer portion N2 onto a recording material P, which is being conveyed while being sandwiched between the intermediate transfer belt 10 and the secondary transfer roller 20. During the secondary transfer, a secondary transfer voltage (secondary transfer bias), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the secondary transfer roller 20 by a secondary transfer power supply 21 serving as a secondary transfer voltage application unit (secondary transfer voltage application unit). The application of voltage from the secondary transfer power supply (high-voltage power supply) 21 causes a current to flow from the secondary transfer roller 20 to the third tension roller 13. As a result, the toner image carried on the intermediate transfer belt 10 is secondarily transferred to the recording material P at the secondary transfer section N2. During the secondary transfer, the voltage applied to the secondary transfer roller 20 by the secondary transfer power supply 21 is controlled so that a constant current flows from the secondary transfer roller 20 to the third tension roller 13 via the intermediate transfer belt 10. The magnitude of the current required for the secondary transfer is predetermined based on the installation environment (ambient environment) of the image forming apparatus 100 and the type of recording material P. In this embodiment, the secondary transfer power supply 21 is capable of outputting a voltage in the range of +100 V to +4000 V. The third tension roller 13 is electrically grounded (connected to ground potential). A recording material (transfer material, recording medium, media) P such as paper or an OHP sheet is stored in a cassette 51 serving as a recording material storage unit.This recording material P is sent out from a cassette 51 by a feeding roller 50 or the like as a feeding member, and is transported to the secondary transfer section N2 by a pair of registration rollers 52 as a transporting member in synchronization with the toner image on the intermediate transfer belt 10.

[0053] In this embodiment, the secondary transfer roller 20 is a roller with an outer diameter of 18 mm, which is made by covering a nickel-plated steel rod with an outer diameter of 8 mm with a foam sponge body made mainly of NBR and epichlorohydrin rubber, the foam sponge body having a volume resistivity of 108 Ω·cm and a thickness of 5 mm. In this embodiment, the rubber hardness of the foam sponge body constituting the secondary transfer roller 20 was 30° when measured with an Asker hardness tester type C under a load of 500 g.

[0054] The recording material P onto which the toner image has been transferred is conveyed to a fixing device 30 serving as a fixing unit. The fixing device 30 includes a fixing roller 31 incorporating a heater 33 as a heat source, and a pressure roller 32 that is in pressure contact with the fixing roller 31. The fixing device 30 applies heat and pressure to the recording material P bearing the unfixed toner image in a fixing section (fixing nip) where the fixing roller 31 and the pressure roller 32 abut against each other, thereby fixing (melting and solidifying) the toner image onto the recording material P. For example, when forming a full-color image, four color toner images on the recording material P are melted and mixed and fixed onto the recording material P. The recording material P on which the toner image has been fixed and a print image has been formed is discharged (output) to the outside of the housing 120 of the apparatus main body 110 (outside the machine) through a paper discharge outlet (recording material discharge outlet) 130, which is an opening formed in the housing 120 of the apparatus main body 110. The recording material P is loaded on a tray 70 provided on the upper part of the housing 120 of the apparatus main body 110 .

[0055] On the other hand, toner remaining on the surface of the photosensitive drum 1 after the primary transfer (primary transfer residual toner) is removed from the surface of the photosensitive drum 1 and collected by a drum cleaning device 5 serving as a photosensitive body cleaning means. The drum cleaning device 5 has a cleaning blade 71 serving as a cleaning member arranged in contact with the surface of the photosensitive drum 1, and a cleaning container 72 that stores the primary transfer residual toner removed from the surface of the photosensitive drum 1 by the cleaning blade 71. The drum cleaning device 5 scrapes the primary transfer residual toner from the surface of the rotating photosensitive drum 1 with the cleaning blade 71 and stores it in the cleaning container 72.

[0056] Furthermore, toner remaining on the surface of the intermediate transfer belt 10 after the secondary transfer (secondary transfer residual toner) is charged to a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) by a conductive brush 16 serving as a toner charging member. This toner then moves to the photosensitive drum 1 at the primary transfer portion N1, for example, the primary transfer portion N1a, which is the most upstream in the rotation direction (surface movement direction) of the intermediate transfer belt 10, and is collected by a drum cleaning device 5. When cleaning the intermediate transfer belt 10, a conductive brush voltage (conductive brush bias), which is a DC voltage opposite to the normal charging polarity of the toner (positive polarity in this embodiment), is applied to the conductive brush 16 by a conductive brush power supply (high-voltage power supply) 17 serving as a cleaning voltage application means (cleaning voltage application unit). In this way, in this embodiment, deposits such as secondary transfer residual toner remaining on the intermediate transfer belt 10 after the secondary transfer are removed from the intermediate transfer belt 10 using the conductive brush 16. In this embodiment, the conductive brush 16 is made of conductive pile yarns primarily composed of conductive nylon, with a density of 200 F / mm², a pile length of 5 mm, three pile rows, and a yarn resistance of 10¹⁰Ω. The conductive brush 16 contacts the outer peripheral surface of the intermediate transfer belt 10. The conductive brush 16 is positioned downstream of the secondary transfer unit N2 and upstream of the primary transfer unit N1 (the most upstream primary transfer unit N1a) in the rotational direction of the intermediate transfer belt 10. In this embodiment, the conductive brush 16 is pressed against the third tension roller 13, which is positioned opposite the conductive brush 16 across the intermediate transfer belt 10, so that the conductive pile yarns penetrate the intermediate transfer belt 10 by 1 mm or more. In this embodiment, the conductive brush power supply 17 is capable of outputting a voltage ranging from +100 V to +4000 V.

[0057] The image forming apparatus 100 of this embodiment can form a full-color print image by the above-described operation. The image forming apparatus 100 of this embodiment can also form a monochrome print image using only one desired image forming unit S, or can form a multicolor print image using only some of the multiple image forming units S.

[0058] In this embodiment, in each image forming station S, the photosensitive drum 1, the charging roller 2 as a process means acting on the photosensitive drum 1, the developing device 4, and the drum cleaning device 5 are integrated to form a process cartridge 7 (7a, 7b, 7c, 7d). The process cartridge 7 is detachable from the main body 110 of the image forming apparatus 100 via mounting means such as a mounting guide and a positioning member provided in the main body 110 of the image forming apparatus 100. In this embodiment, the main body 110 of the image forming apparatus 100 is the portion excluding the process cartridges 7.

[0059] The image forming apparatus 100 is also provided with an optical sensor 60 that is used when performing correction control to correct color misregistration and density of images formed by the image forming apparatus 100 and when detecting condensation. The optical sensor 60 is disposed at a position (detection position) D downstream of the primary transfer unit N1 (the most downstream primary transfer unit N1d) and upstream of the secondary transfer unit N2 in the rotation direction of the intermediate transfer belt 10 so as to detect the surface (outer peripheral surface) of the intermediate transfer belt 10 and the toner thereon. In this embodiment, the optical sensor 60 is disposed at a position facing the first tension roller 11 across the intermediate transfer belt 10. The optical sensor 60 will be described in detail later.

[0060] The above-described operations are repeated when performing continuous printing to form print images continuously on a plurality of recording materials P. When the image forming apparatus 100 of this embodiment continuously forms print images on a plurality of A4 sheets of paper, for example, it performs continuous printing by leaving a gap (paper gap) of 50 mm between the rear end of the previous sheet and the front end of the next sheet. 2. Control Configuration

[0061] Next, a description will be given of the control configuration of the image forming apparatus 100 in this embodiment. Fig. 2 is a block diagram showing an outline of the control configuration for controlling the operation of the image forming apparatus 100 in this embodiment.

[0062] The external device 300 issues a print command (start instruction and various setting information) to the controller 210, which is a conversion unit serving as a conversion means provided inside the image forming apparatus 100, and transmits image data of the print image to the controller 210. In this embodiment, the external device 300 is a personal computer (PC) that is a host computer. The controller 210 receives RGB or CMYK image data from the external device 300 and converts it into CMYK exposure data (image signals) according to a mode specified by the external device 300. In this embodiment, the exposure data converted at this time is 600 dpi. In addition to the type and size of paper, the modes specified by the external device 300 include a mode related to image quality and a mode for changing the number of lines in the dither matrix.

[0063] The controller 210 transfers the converted exposure data to an exposure control device 203 as exposure control means provided in a DC controller 200, which is a control unit as control means provided inside the image forming apparatus 100. The exposure control device 203 controls the exposure device 3 in accordance with instructions from a CPU 201, which will be described later. In the image forming apparatus 100 of this embodiment, halftone density is controlled by adjusting the on / off area of ​​the exposure data. When the CPU 201 receives a print command from the controller 210, it starts a print job.

[0064] The DC controller 200 includes a CPU (arithmetic processing unit) 201 as an arithmetic processing unit, and a memory (storage unit) 202 including a ROM, RAM, etc. as a storage unit. The DC controller 200 controls the operation of each unit of the image forming apparatus 100 by causing the CPU 201 to execute processing in accordance with programs and data previously stored in the memory 202. The DC controller 200 (CPU 201) controls, for example, the charging power supply 24, the developing power supply 25, the exposure control device 203 (exposure device 3), the primary transfer power supply 23, the secondary transfer power supply 21, the drive unit 90, the contact / separation mechanism 80, etc., to form an electrostatic latent image, transfer the developed toner image, and perform other operations to form an image. The DC controller 200 (CPU 201) is also connected to an operation unit 150 provided in the image forming apparatus 100. The operation unit 150 is configured to have a display unit that displays information under the control of the DC controller 200 (CPU 201), an input unit that inputs information to the DC controller 200 (CPU 201) based on operations by an operator such as a user or a service representative, etc. The operation unit 150 may be configured to have a touch panel that functions as both a display means and an input means.

[0065] The DC controller 200 (CPU 201) also receives signals from the optical sensor 60, which are used when executing correction control to correct color misregistration and density of images formed in the image forming apparatus 100 and when detecting condensation. For example, in the correction control, the optical sensor 60 detects the amount of light reflected from a test pattern (a toner image for detection) formed on the outer peripheral surface of the intermediate transfer belt 10 at a position opposite the optical sensor 60. The output of a detection signal indicating the detection result of the amount of reflected light by the optical sensor 60 ranges from 0 V to 3.3 V. In this embodiment, the optical sensor 60 is configured so that the output of the detection signal increases as the amount of light received by the first and second light-receiving elements 62 and 63 (described later) increases. The DC controller 200 (CPU 201) performs calculations using the detection results from the optical sensor 60 to perform density correction and color misregistration correction. In this embodiment, the density correction control method involves creating a correction curve for an image signal that achieves a desired density curve based on the detection results of a test pattern for density detection (a density control correction pattern). In this embodiment, the color misregistration correction control method involves correcting the image formation timing for each color based on the detection results of a test pattern (registration correction pattern) for detecting the amount of color misregistration. The color misregistration correction control and density correction control are performed when the execution conditions are met, which are set in advance according to predetermined changes in temperature and humidity, the number of prints (number of sheets passed), etc. Condensation detection will be described in detail later.

[0066] In this embodiment, the primary transfer power supply 23 is shared by the four image forming units S as described above. Although not shown in the figure, the charging power supply 24, the developing power supply 25, and the contact / separation mechanism 80 are provided independently for each image forming unit S. The charging power supply 24, the developing power supply 25, and the contact / separation mechanism 80 may each be shared by at least some of the image forming units S. The drive unit 90 includes a drive motor as a drive source and drive transmission members. The drive unit 90 includes drive motors for driving components such as the photosensitive drum 1, the developing roller 42 of the developing device 4, the intermediate transfer belt 10 (third tension roller 13), and the contact / separation mechanism 80. The drive motors for driving these components may be provided independently, or a common drive motor may be used to drive at least some of these components. The drive motors for driving the components for each color may be provided independently, or a common drive motor may be used to drive at least some of the components for each color. In this embodiment, the photosensitive drum 1 and the developing roller 42 of the developing device 4 in each image forming station S can be rotated and stopped independently.

[0067] Here, a print job (print operation, print sequence, image forming operation, image forming sequence) is a series of operations initiated by a single start command to form and output an image on one or more recording materials P. A print job generally includes an image forming process, a pre-rotation process, a paper-to-paper interval process when forming images on multiple recording materials P, and a post-rotation process. The image forming process is a period during which an electrostatic latent image of the image to be actually formed and output on the recording materials P is formed, a toner image is formed, and the toner image is first transferred, second transferred, and fixed. This period is referred to as image formation time. More specifically, the timing of image formation varies depending on the positions where the charging, exposure, development, first transfer, second transfer, and fixing processes are performed. The pre-rotation process is a period during which preparatory operations are performed before the image forming process, from when a start command is input until the actual start of image formation. The paper-to-paper interval process is a period corresponding to the interval between recording materials P when image formation is performed continuously on multiple recording materials P (during continuous printing). The post-rotation process is a period in which a tidying operation (preparatory operation) is performed after the image forming process. The non-image forming period is a period other than the image forming period, and includes the pre-rotation process, the sheet interval process, the post-rotation process, and the pre-multiple rotation process, which is a preparatory operation when the image forming apparatus 100 is turned on or when it returns from a sleep state. 3. Optical Sensor

[0068] Next, the configuration of the optical sensor 60 will be described. Fig. 3 is a top view of the intermediate transfer belt 10 near the optical sensors 60 (60F, 60R). Note that with respect to the image forming apparatus 100 and its components, the front side of the paper in Fig. 1 (the lower side in Fig. 3) is the front side, and the back side of the paper in Fig. 1 (the upper side in Fig. 3) is the rear side.

[0069] In this embodiment, the image forming apparatus 100 is provided with a front optical sensor 60F and a rear optical sensor 60R as optical sensors 60. In the width direction, which is approximately perpendicular to the direction of movement of the surface of the intermediate transfer belt 10, the front optical sensor 60F is located forward of the center, and the rear optical sensor 60R is located rear of the center. The optical sensors 60 (60F, 60R) are held by a holding member 65 made of electrically grounded sheet metal. The holding member 65 is supported on the rotation shaft of the first tension roller 11 so that the distance between the intermediate transfer belt 10 and the optical sensors 60 (60F, 60R) is always constant regardless of the inclination of the first tension roller 11. In this embodiment, the optical sensors 60 (60F, 60R) are positioned so that the distance from the intermediate transfer belt 10 is 3 mm.

[0070] In this embodiment, the front optical sensor 60F and the rear optical sensor 60R have substantially the same configuration, so we will explain the front optical sensor 60F as a representative (F and R indicating the front or rear optical sensor 60 will be omitted as appropriate).

[0071] FIG. 4 is a cross-sectional view illustrating the configuration of the optical sensor 60. The optical sensor 60 includes a light-emitting element 61, a first light-receiving element 62, a second light-receiving element 63, and a holder 64. The light-emitting element 61 is configured as an LED or the like. The first light-receiving element 62 and the second light-receiving element 63 are each configured as a phototransistor or the like. In this embodiment, the light-emitting element 61 emits infrared light, which is irradiated onto the surface of the intermediate transfer belt 10 or a test pattern formed on the surface of the intermediate transfer belt 10. Light reflected from the surface of the intermediate transfer belt 10 or the test pattern formed on the surface of the intermediate transfer belt 10 is received by the first and second light-receiving elements 62 and 63. In this embodiment, the light-emitting element 61 is a light-emitting element that emits infrared light with a peak wavelength of 800 nm, and the first and second light-receiving elements 62 and 63 are light-receiving elements whose light-receiving sensitivity peaks at a wavelength of 800 nm.

[0072] 4, the normal line G is approximately perpendicular to the surface of the intermediate transfer belt 10. The light-emitting element 61 is disposed at an angle of 15° with respect to the normal line G. The holder 64 adjusts the shape of the light guide path so that the spot diameter when infrared light is irradiated from the light-emitting element 61 onto the intermediate transfer belt 10 is 2 mm. The first light-receiving element 62 is disposed at an angle of 15° with respect to the normal line G, and receives infrared light that is specularly reflected and diffusely reflected from the surface of the intermediate transfer belt 10 and the test pattern. The second light-receiving element 63 is disposed at an angle of 45° with respect to the normal line G, and receives infrared light that is diffusely reflected from the surface of the intermediate transfer belt 10 and the test pattern. 4. Waveform of Light Reflected from the Surface of the Intermediate Transfer Belt Detected by the Optical Sensor

[0073] Next, we will explain the waveform (detection waveform) of the detection signal (detection output) that indicates the detection result when the optical sensor 60 detects reflected light from the surface of the intermediate transfer belt 10. Here, we will explain the detection waveform acquired by the front optical sensor 60F, but the same tendency is observed in the detection waveform acquired by the rear optical sensor 60R (the same applies below to the detection signals of the optical sensors 60R and 60F). Furthermore, the letters F and R indicating the front or rear optical sensor 60 will be omitted as appropriate.

[0074] FIG. 5 is a graph showing the detected waveforms when the first and second light receiving elements 62 and 63 detect light reflected from the surface of the intermediate transfer belt 10. Note that FIG. 5 shows the detected waveforms when no condensation occurs inside the image forming apparatus 100. (a) in FIG. 5 is the detected waveform showing the detection result (specular reflection and diffuse reflection) by the first light receiving element 62, and (b) in FIG. 5 is the detected waveform showing the detection result (diffuse reflection) by the second light receiving element 63. The light emitting element 61 is driven in section (i) in FIG. 5. As a result of detecting the reflected light in this section (i), the detected result by the first light receiving element 62 is approximately 3.0 V, but the detected result by the second light receiving element 63 is lower. In other words, in section (i), the amount of reflected light detected by the second light receiving element 63 is lower than the amount of reflected light detected by the first light receiving element 62. This is because most of the light reflected from the intermediate transfer belt 10 is specular reflection. In this embodiment, the amount of light emitted by the light-emitting element 61 and the light-receiving sensitivity of the first light-receiving element 62 are adjusted so that when the first light-receiving element 62 detects light reflected from the intermediate transfer belt 10, the detection result by the first light-receiving element 62 is approximately 3.0 V. In this embodiment, the optical sensor 60 is configured so that the greater the amount of light received by the first light-receiving element 62, the greater the output of the detection signal indicating the detection result of the first light-receiving element 62. In section (ii) in Figure 5, the intermediate transfer belt 10 is rotating, and it can be seen that the amount of reflected light detected by the first and second light-receiving elements 62, 63 varies depending on the surface properties of the intermediate transfer belt 10. 5. Waveform of reflected light from the toner patch detected by the optical sensor

[0075] Next, we will explain the waveform (detection waveform) of the detection signal (detection output) that indicates the detection result when the optical sensor 60 detects reflected light from the toner patch (detection toner image that constitutes the test pattern) on the intermediate transfer belt 10.

[0076] 6 is a graph showing, as an example, detected waveforms when the first and second light receiving elements 62 and 63 detect reflected light from a solid yellow toner patch 10 mm long in the rotation direction of the intermediate transfer belt 10. Graph (a) in FIG. 6 is a detected waveform showing the detection result (specularly reflected light and diffusely reflected light) by the first light receiving element 62, and graph (b) in FIG. 6 is a detected waveform showing the detection result (diffusely reflected light) by the second light receiving element 63.

[0077] First, the detection waveform ((a) in FIG. 6) by the first light receiving element 62 will be described. In the section where reflected light from the intermediate transfer belt 10 is detected, the first light receiving element 62 receives a large amount of specularly reflected light, so the detection result by the first light receiving element 62 is approximately 3.0 V. However, in the section where the toner patch is detected, the detection result by the first light receiving element 62 drops significantly to approximately 0.6 V. This is because the reflected light from the toner patch is mainly diffusely reflected light, so in the section where the toner patch is detected, the amount of reflected light that reaches the first light receiving element 62 is less than in the section where reflected light from the intermediate transfer belt 10 is detected.

[0078] Next, the detection waveform ((b) in FIG. 6) by the second light receiving element 63 will be described. The second light receiving element 63 hardly detects the light reflected from the intermediate transfer belt 10, but detects a lot of the light reflected from the toner patch, and the detection result by the second light receiving element 63 is approximately 3.0 V. In this embodiment, the light receiving sensitivity of the second light receiving element 63 is adjusted so that when the second light receiving element 63 detects the light reflected from the toner patch, the detection result by the second light receiving element 63 is approximately 3.0 V. In this embodiment, the optical sensor 60 is configured so that the greater the amount of light received by the second light receiving element 63, the greater the output of the detection signal indicating the detection result of the second light receiving element 63. 6. Detection of Reflected Light from the Surface of the Intermediate Transfer Belt During a Print Job 6-1. Overview of Operations During a Print Job

[0079] Next, a description will be given of an operation in this embodiment in which the optical sensor 60 is driven during a print job to detect reflected light from the surface (base) of the intermediate transfer belt 10. As an example, a description will be given of a detection operation in which the front optical sensor 60F is used.

[0080] FIG. 7 is a timing chart showing the operation of each part during a print job in this embodiment. As an example, FIG. 7 shows the operation of each part when a print job for continuously printing three A4 sheets of paper (hereinafter, simply referred to as a "three-sheet print job") is executed. FIG. 7 also shows the rotational drive timing of the photosensitive drum 1, the rotational drive timing of the intermediate transfer belt 10, the timing when the developing roller 42 contacts or separates from the photosensitive drum 1, the drive timing of the exposure device 3 for image formation, the drive timing of the optical sensor 60 (the light-emitting element 61), and the sampling timing, which is the data acquisition period for calculating and processing the detection results of the first light-receiving element 62. In this embodiment, the photosensitive drums 1a, 1b, 1c, and 1d rotate and stop synchronously. Furthermore, in this embodiment, when the photosensitive drum 1 is rotating during a print job, the charging roller 2 is substantially always charging the surface of the photosensitive drum 1, except during the idling operation described below. The operation according to the timing chart in FIG. 7 is controlled by the DC controller 200. In this embodiment, the operation of a print job in full color mode will be described as an example, but the same effect as in this embodiment can be obtained in a print job in monochrome mode.

[0081] When a print job is started, first, the photosensitive drums 1a, 1b, 1c, and 1d and the intermediate transfer belt 10 start to be rotated, and then the developing roller 42 is brought into contact with the photosensitive drum 1. The timing of the contact of the developing roller 42 with the photosensitive drum 1 is adjusted so that the developing roller 42 comes into contact with the photosensitive drum 1 after the surface of the photosensitive drum 1 charged by the charging roller 2 has reached the development position (the contact point between the photosensitive drum 1 and the developing roller 42). The developing rollers 42a, 42b, 42c, and 42d come into contact with the corresponding photosensitive drums 1a, 1b, 1c, and 1d at the same timing.

[0082] Next, after the developing roller 42 is brought into contact with the photosensitive drum 1, image formation (exposure by the exposure device 3) is performed. In FIG. 7, image formation is ON corresponding to the length of the A4 paper in the transport direction. This indicates that, during this section, each photosensitive drum 1a, 1b, 1c, and 1d is exposed by each exposure device 3a, 3b, 3c, and 3d in accordance with an image signal, as described above. FIG. 7 shows the timing of image formation at the yellow image forming station Sa as a representative example. The timing of image formation at the magenta, cyan, and black image forming stations Sb, Sc, and Sd is slightly delayed in accordance with the movement of the intermediate transfer belt 10. As a result, electrostatic latent images corresponding to the yellow, magenta, cyan, and black color component images of the target color image are formed on each photosensitive drum 1a, 1b, 1c, and 1d. This electrostatic latent image is developed at the development position by the supply of toner by the developing rollers 42a, 42b, 42c, and 42d, forming toner images of yellow, magenta, cyan, and black on the photosensitive drums 1a, 1b, 1c, and 1d. The toner images formed on the photosensitive drums 1a, 1b, 1c, and 1d are sequentially transferred onto the same image forming area (area where a toner image can be formed) on the intermediate transfer belt 10 so as to be superimposed on each other. This sequentially forms predetermined images on the intermediate transfer belt 10 to be transferred to each recording material P (three A4 sheets in the example shown in FIG. 3). As described above, in this embodiment, in continuous printing in which print images are formed consecutively on multiple A4 sheets, the gap (paper gap) between the trailing edge of the previous sheet and the leading edge of the next sheet is 50 mm. For simplicity, in this embodiment, the size of the image forming area on the intermediate transfer belt 10 is assumed to be substantially the same as the size of the recording material P. Therefore, in continuous printing in which print images are formed continuously on multiple A4 sheets of paper, the gap (paper spacing) between the rear end of the previous image forming area and the front end of the next image forming area on the intermediate transfer belt 10 is 50 mm. However, the size of the image forming area on the intermediate transfer belt 10 may be smaller than the size of the recording material P (a margin is generated at least on the front and rear ends of the recording material P in the conveyance direction and on one and the other ends of the recording material P in the width direction substantially perpendicular to the conveyance direction).In addition, the size of the image forming area on the intermediate transfer belt 10 may be larger than the size of the recording material P (the image forming area extends beyond the recording material P at least at one of the leading and trailing ends in the rotation direction of the intermediate transfer belt 10 and one and other ends in the width direction).

[0083] In this embodiment, the optical sensor 60 is driven during a print job to detect light reflected from the surface of the intermediate transfer belt 10. In this embodiment, the first light receiving element 62 detects light regularly reflected from the surface of the intermediate transfer belt 10. 6-2. Timing for detecting light reflected from the surface of the intermediate transfer belt during a print job

[0084] The timing of sampling the detection result by the first light receiving element 62 in this embodiment will be described.

[0085] In this embodiment, the DC controller 200 samples the detection results of the first light receiving element 62 during sampling periods (1), (2), (3), and (4) in Fig. 7 during a print job. In this embodiment, the DC controller 200 samples the detection results of the first light receiving element 62 at 0.1 mm intervals in terms of the surface movement distance of the intermediate transfer belt 10 during each of the sampling periods. Sampling period (1) in Fig. 7 extends from the time when the optical sensor 60 is driven and the light emitting element 61 is turned on to the time when the leading edge of the image forming area (herein also referred to as the "first image forming area") on the intermediate transfer belt 10, where an image to be transferred to the first recording material P is formed, reaches detection position D of the optical sensor 60 (the position of the spot of light emitted by the light emitting element 61 in the rotation direction of the intermediate transfer belt 10). 7 is the period from when the rear end of the image forming area of ​​the first sheet on the intermediate transfer belt 10 passes the detection position D of the optical sensor 60 to when the leading edge of the image forming area of ​​the second sheet on the intermediate transfer belt 10 reaches the detection position D of the optical sensor 60. Similarly, sampling period (3) in FIG. 7 is the period from when the rear end of the image forming area of ​​the second sheet on the intermediate transfer belt 10 passes the detection position D of the optical sensor 60 to when the leading edge of the image forming area of ​​the third sheet on the intermediate transfer belt 10 reaches the detection position D of the optical sensor 60. Sampling period (4) in FIG. 7 is the period from when the rear end of the image forming area of ​​the third sheet on the intermediate transfer belt 10 passes the detection position D of the optical sensor 60 to when the drive of the intermediate transfer belt 10 is turned off.

[0086] As described above, in this embodiment, the DC controller 200 samples the detection result by the first light receiving element 62 at a timing that avoids the timing when the image formation area on the intermediate transfer belt 10 passes through the detection position D of the optical sensor 60. This is to accurately detect the amount of light reflected from the surface of the intermediate transfer belt 10 without being affected by the toner image on the intermediate transfer belt 10.

[0087] 7 shows an example of a print job for three sheets, but if a print job for four or more sheets is performed, the sampling section between the rear end of the image forming area for the nth sheet on the intermediate transfer belt 10 and the front end of the image forming area for the n+1th sheet can be increased, similar to the above sampling sections (2) and (3). 6-3. Detection results of reflected light from the surface of the intermediate transfer belt when there is no condensation

[0088] Next, we will explain the results of an experiment that investigated the relationship between the number of prints, the detection results by the first light receiving element 62, and the print images when no condensation has occurred inside the image forming apparatus 100. Under normal conditions when no condensation has occurred inside the image forming apparatus 100, the detection waveform when the optical sensor 60 detects reflected light from the surface of the intermediate transfer belt 10 is as explained using Figure 5.

[0089] Table 1 shows the relationship between the detection results by the first light receiving element 62 and the confirmation results of the printed image when a 50-sheet print job was performed using paper with a moisture content of 9.0 wt% as the recording material P in an environment with a temperature of 30°C and a humidity (relative humidity) of 80%.

[0090] In Table 1, the detection results by the first light-receiving element 62 represent an average value for every five sheets. Here, the average value of the detection results by the first light-receiving element 62 for every five sheets was calculated from 100 sampling results (sampling data) for each number of prints. That is, in this embodiment, the DC controller 200 calculates the average value of the detection results (sampling data) of the amount of light reflected from the surface of the intermediate transfer belt 10 while the intermediate transfer belt 10 rotates 10 mm for each number of prints (sampling interval). The sampling timing for the first sheet is the timing until the leading edge of the image formation area on the intermediate transfer belt 10 reaches the detection position D of the optical sensor 60, which corresponds to sampling interval (1) in FIG. 7 . The sampling timings for the second through 49th sheets correspond to sampling intervals (2) or (3) in FIG. 7 , which are sampling intervals between the trailing edge of the image formation area on the intermediate transfer belt 10 for each number of prints and the leading edge of the next image formation area on the intermediate transfer belt 10. The timing for the 50th sheet is the timing when the rear end of the image forming area for the 50th sheet on the intermediate transfer belt 10 passes the detection position D of the optical sensor 60, and corresponds to sampling section (4) in FIG.

[0091] In addition, the print images were repeated in a set of five sheets, in the following order: one text image, one halftone image with a density of 0.8, one solid image, and two solid white images. The image confirmation results are summarized and displayed as the number of prints at the time when the first text image of the set of five was printed. For example, the confirmation results for the first text image, the second halftone image, and the third solid image are displayed in the column for the first sheet.

[0092] In Table 1, the image quality levels are indicated by alphabetical notation in the columns for text, halftone, solid, and other defects. "A" indicates no problems at all. "B" indicates slight image defects, with text showing slight blurring, halftone and solid images showing image densities lower than the reference density, and other defects showing slight toner contamination. In the following explanation, image densities lower than the reference density will be referred to as "low density." "C" indicates clear image defects, with text showing clear blurring, halftone and solid images showing clear low density, and other defects showing toner contamination. In Table 1, the column for the 50th sheet is marked "no data" because there are no image quality confirmation results.

[0093]

[0094] As shown in Table 1, under normal conditions where no condensation occurs inside the image forming apparatus 100, the amount of light reflected from the intermediate transfer belt 10 is generally constant, so the average value of the detection result by the first light receiving element 62 is around 3.0 V at any timing.

[0095] Furthermore, as shown in Table 1, there were no problems with the image quality for any number of prints. 6-4. Detected waveform of reflected light from the surface of the intermediate transfer belt when condensation is present

[0096] Next, we will explain the detection waveform when the optical sensor 60 detects reflected light from the surface of the intermediate transfer belt 10 when water droplets adhere to the surface of the intermediate transfer belt 10 due to condensation occurring inside the image forming apparatus 100.

[0097] 8 is a graph showing a detection waveform obtained when the first light receiving element 62 detects light reflected from the surface of the intermediate transfer belt 10 in a state in which water droplets adhere to the surface of the intermediate transfer belt 10 due to condensation occurring inside the image forming apparatus 100. The light emitting element 61 is driven in section (i) in FIG. 8, and the intermediate transfer belt 10 is rotationally driven in section (ii). The amount of light emitted by the light emitting element 61 and the light receiving sensitivity of the first light receiving element 62 are set to the same as when the detection waveform obtained in the absence of condensation shown in FIG. 5 is obtained.

[0098] 5A, when no water film due to condensation has formed on the surface of the intermediate transfer belt 10, the average value of the detection result by the first light receiving element 62 is approximately 3.0 V. In contrast, in the detection waveform of FIG. 8A, when a water film due to condensation has formed on the surface of the intermediate transfer belt 10, the average value of the detection result by the first light receiving element 62 is approximately 2.5 V. This is because the amount of reflected light reaching the first light receiving element 62 is reduced due to absorption of the irradiated light by water droplets, a decrease in reflectance, a change in refractive index, etc.

[0099] Furthermore, when comparing the detection waveform of (a) in Figure 5 with the detection waveform of Figure 8, the detection waveform of Figure 8 has a larger deviation in the detection result by the first light-receiving element 62 in section (ii) than the detection waveform of (a) in Figure 5. This is because there is unevenness in the adhesion of water droplets to the surface of the intermediate transfer belt 10. Furthermore, the detection pattern of the rotation period of the intermediate transfer belt 10 seen in the detection waveform of (a) in Figure 5 is not seen in the detection waveform of Figure 8. This is because the amount of reflected light changes due to uneven adhesion of water droplets, making it difficult to detect the surface condition of the intermediate transfer belt 10.

[0100] In this way, the amount of light reflected from the surface of the intermediate transfer belt 10 detected by the first light receiving element 62 decreases due to water droplets (water film) that have adhered to the surface of the intermediate transfer belt 10 due to condensation. Fig. 8 shows an example of the detection result when water droplets have adhered to the surface of the intermediate transfer belt 10. According to the studies of the present inventors, the average amount of light reflected from the surface of the intermediate transfer belt 10 (detection result by the first light receiving element 62) tends to decrease as the amount of water droplets adhering to the surface of the intermediate transfer belt 10 increases, and the deviation of the amount of light reflected (detection result by the first light receiving element 62) tends to increase.

[0101] Here, detection of the condensation state using the optical sensor 60 in this embodiment is particularly effective when the surface gloss of the intermediate transfer belt 10 is relatively high or when there is little gloss unevenness. Specifically, the surface gloss of the intermediate transfer belt 10 is preferably 60 or higher, more preferably 80 or higher. The surface gloss of the intermediate transfer belt 10 may be 100. Furthermore, the deviation of the gloss unevenness from the average value is preferably 30% or less, more preferably 20% or less. In this embodiment, as described above, the surface gloss of the intermediate transfer belt 10 is 75. Furthermore, as described above, the surface gloss of the intermediate transfer belt 10 can be measured using a commercially available measuring device, such as the IG-320 handheld gloss meter from Horiba, Ltd. In order to distinguish between reflected light from the surface of the intermediate transfer belt 10 and reflected light from water droplets adhering to the surface of the intermediate transfer belt 10, it is desirable for the surface gloss of the intermediate transfer belt 10 to have little gloss unevenness, because this makes it easier for differences in reflected light to occur. Examples of coating methods for the surface layer of the intermediate transfer belt 10 having such a high gloss and minimal unevenness include dip coating and ring coating. 6-5. Detection results of reflected light from the surface of the intermediate transfer belt when condensation is present

[0102] Next, we will explain the results (relationships between the number of prints, the detection results by the first light-receiving element 62, and the print images) of an experiment similar to the experiment that obtained the results in Table 1 when condensation did not occur, but was conducted under conditions where condensation did occur. Here, the experiment was conducted under conditions where air was blown from the ceiling by a ceiling fan, which was the condition under which condensation would occur inside the image forming apparatus 100.

[0103] 9 is a diagram showing the positional relationship between the image forming apparatus 100 and the ceiling fan in this experiment. The image forming apparatus 100 shown in FIG. 9 has the same configuration as the image forming apparatus 100 of this embodiment shown in FIG. 1. In this experiment, a ceiling fan was installed directly above the paper discharge port 130 of the image forming apparatus 100, and a print job was performed under conditions in which the air blown from the ceiling fan had a wind speed of 1.5 m / s near the paper discharge port 130 of the image forming apparatus 100. The other conditions in this experiment were substantially the same as those in the experiment in which the results in Table 1 were obtained.

[0104] Table 2 summarizes the results of this experiment in the same way as Table 1. The alphabets in the columns for text, halftone, solid, and other defects in Table 2 have the same meanings as in Table 1.

[0105]

[0106] From Table 2, it can be seen that the average value of the detection results by the first light-receiving element 62 tends to decrease as the number of prints increases. This is due to the following reason. That is, water vapor generated from the paper that has passed through the fixing device 30 is pushed back into the interior of the image forming apparatus 100 by the wind from the ceiling fan that enters through the paper discharge outlet 130 of the image forming apparatus 100. Then, when this water vapor pushed back into the interior of the image forming apparatus 100 comes into contact with the intermediate transfer belt 10, condensation occurs, and as a result, the amount of reflected light detected by the first light-receiving element 62 decreases, as described with reference to FIG. 8 .

[0107] Furthermore, as shown in Table 2, no problems occurred with the character images up to the 41st sheet, but the characters began to fade on the 46th sheet.

[0108] Furthermore, as shown in Table 2, slight density loss was observed in halftone images from the 16th sheet onwards, and significant density loss was observed from the 36th sheet onwards. This was because condensation inside the image forming apparatus 100 also caused condensation on the surface of the photosensitive drum 1, changing the surface potential of the photosensitive drum 1.

[0109] Here, a description will be given of the phenomenon in which the density of a halftone image is reduced due to a change in the surface potential of the photosensitive drum 1. FIG.

[0110] FIG. 10A shows the surface potential of the photosensitive drum 1 under normal conditions in which no condensation occurs inside the image forming apparatus 100. The dark potential Vd is the surface potential of the photosensitive drum 1 after being charged by the charging roller 2. Immediately after the surface of the photosensitive drum 1 passes the charging position (roughly the contact point between the photosensitive drum 1 and the charging roller 2) where the charging voltage is applied by the charging roller 2 (before it reaches the exposure position by the exposure device 3), the surface potential of the photosensitive drum 1 is uniformly charged to the dark potential Vd. Thereafter, the surface of the photosensitive drum 1 is exposed by the exposure device 3 at the exposure position in accordance with an image signal. As a result, the surface potential of the portion of the surface of the photosensitive drum 1 exposed by the exposure device 3 (image portion) becomes the light potential VL. A development voltage Vdc is applied to the developing roller 42, and the toner on the developing roller 42 moves to and adheres to the surface of the photosensitive drum 1 due to the development contrast Vc, which is the potential difference between the development voltage (potential of the developing roller 42) Vdc and the light potential VL. Furthermore, the back contrast Vb, which is the potential difference between the dark potential Vd and the development voltage Vdc, affects so-called fogging, which is the movement of toner from the development roller 42 to the portion of the photosensitive drum 1 at the dark potential Vd (non-image portion). The smaller the back contrast Vb, the greater the amount of toner that causes fogging. Therefore, when forming a halftone image, the smaller the back contrast Vb, the higher the density of the halftone image.

[0111] FIG. 10B shows the surface potential of the photosensitive drum 1 when condensation occurs on the surface of the photosensitive drum 1. Condensation on the surface of the photosensitive drum 1 occurs when moisture from condensation on the surface of the intermediate transfer belt 10 transfers to the surface of the photosensitive drum 1 or when air blown from a ceiling fan entering through the paper discharge port 130 of the image forming apparatus 100 directly contacts the surface of the photosensitive drum 1. Normally, the surface of the photosensitive drum 1 is charged by the charging roller 2 through a discharge current from the charging roller 2 to the photosensitive drum 1. Such discharge occurs in at least one of the minute gaps formed between the charging roller 2 and the photosensitive drum 1, upstream and downstream of the contact point between the charging roller 2 and the photosensitive drum 1 in the rotational direction of the photosensitive drum 1. However, when condensation occurs on the surface of the photosensitive drum 1, in addition to the discharge current, a direct current flows from the charging roller 2 to the photosensitive drum 1 at the contact point between the charging roller 2 and the photosensitive drum 1. As a result, the dark potential Vd', which is the surface potential of the photosensitive drum 1 immediately after passing the charging position (roughly the contact point between the photosensitive drum 1 and the charging roller 2) when condensation is present, becomes higher than the dark potential Vd when there is no condensation. Accordingly, the light potential VL' when there is condensation also becomes higher than the light potential VL when there is no condensation, and the development contrast Vc' when there is condensation becomes lower than the development contrast Vc when there is no condensation. As a result, the movement of toner on the developing roller 42 to the photosensitive drum 1 decreases, resulting in a low density halftone image.

[0112] Furthermore, as shown in Table 2, slight density loss was observed in solid images from the 31st sheet onward, and significant density loss was observed from the 41st sheet onward. The density loss in solid images, as described above, is due to a decrease in the development contrast Vc', as shown in FIG. 10B, which reduces the amount of toner movement from the development roller 42 to the photosensitive drum 1. In other words, if the amount of toner movement from the development roller 42 to the photosensitive drum 1 at the development contrast Vc is 100%, the amount of movement at the development contrast Vc' is less than 100%. Furthermore, as shown in FIGS. 10A and 10B, the primary transfer contrast Vt' in the presence of condensation increases as the light-area potential VL' increases, compared to the primary transfer contrast Vt, which is the potential difference between the light-area potential VL and the primary transfer voltage Vt1 in the absence of condensation. This increases the discharge current generated between the photosensitive drum 1 and the intermediate transfer belt 10. As a result, due to a reversal of the charge polarity of the toner on the intermediate transfer belt 10, the toner that was primarily transferred onto the intermediate transfer belt 10 returns to the photosensitive drum 1, a so-called retransfer occurs, resulting in a low density solid image.

[0113] Furthermore, as shown in Table 2, in addition to low density in halftone images and solid images, image defects were observed on the 26th and 36th sheets, where toner stains were caused by a mixture of yellow, magenta, cyan, and black toners. This occurs when toner adhering to the conductive brush 16 is absorbed by water droplets on the intermediate transfer belt 10 and transferred from the intermediate transfer belt 10 to the paper. Once an image defect due to toner stains occurs, the amount of toner adhering to the conductive brush 16 decreases, and subsequent printing causes toner adhesion to the conductive brush 16 to increase again. This results in the problem occurring randomly in the latter half of a print job. 6-6. Recovery Process

[0114] In this embodiment, the image forming apparatus 100 detects the amount of light reflected from the surface of the intermediate transfer belt 10 using the optical sensor 60 during a print job, as described above. If the image forming apparatus 100 determines that condensation has occurred inside the apparatus based on the detection results, as described below, it executes a condensation removal process to eliminate the condensation (remove moisture) before image defects caused by the condensation occur. The condensation removal process is an example of an adhesion removal process that removes adhesions (moisture in this embodiment) from the surface of the intermediate transfer belt 10 as a recovery process from an abnormal state on the intermediate transfer belt 10. In this embodiment, the condensation removal process is executed by interrupting image formation in the print job. The image forming apparatus 100 then resumes image formation for the print job after sufficiently removing moisture from the photosensitive drum 1 and the intermediate transfer belt 10 through the condensation removal process. Under the experimental conditions that yielded the results in Table 2, it was found that the condensation removal process could be executed by temporarily suspending printing after printing the 11th sheet without printing the 12th sheet (also referred to as "interrupting the print job"). Therefore, in this embodiment, based on the results of Table 2, the image forming apparatus 100 interrupts the print job and executes the condensation removal process when the average value of the detection result by the first light receiving element 62 drops to 2.8 V.

[0115] Here, obtaining the detection result (detection signal) from the optical sensor 60 and controlling the execution of a predetermined process such as condensation removal is also referred to as simply detecting (determining) the condensation state. The same applies to detecting foreign matter such as sand, which will be described later.

[0116] 11 is a timing chart showing an outline of the operation of each part during the condensation removal process in this embodiment. The operation according to the timing chart in FIG.

[0117] In this embodiment, the condensation removal process involves rotating the photosensitive drums 1a, 1b, 1c, and 1d and the intermediate transfer belt 10 for a predetermined time (also referred to as "idle rotation operation" here). In this embodiment, the predetermined time t for which the idle rotation operation continues is set to 15 seconds.

[0118] Here, during the idling operation, it is preferable to keep the developing roller 42 separated from the photosensitive drum 1 in order to prevent moisture adhering to the surface of the photosensitive drum 1 from transferring to the developing roller 42 and the developing device 4. When the developing roller 42 is separated from the photosensitive drum 1 during the idling operation, the developing roller 42 does not need to rotate and a developing voltage does not need to be applied to the developing roller 42 during the idling operation. In this embodiment, during the idling operation, the developing roller 42 is separated from the photosensitive drum 1, the rotation of the developing roller 42 is stopped, and a developing voltage is not applied to the developing roller 42. However, for example, if the image forming apparatus 100 is not provided with a mechanism for separating the developing roller 42 from the photosensitive drum 1, the developing roller 42 may be configured to rotate in contact with the photosensitive drum 1 during the idling operation.

[0119] In this embodiment, a charging voltage is not applied to the charging roller 2 during the idling operation. However, a charging bias similar to that used during image formation may be applied to the charging roller 2 during the idling operation. In a configuration in which the idling operation is performed while the developing roller 42 is in contact with the photosensitive drum 1, a developing voltage similar to that used during image formation may be applied to the developing roller 42. In this embodiment, the intermediate transfer belt 10 is in contact with each photosensitive drum 1a, 1b, 1c, and 1d during the idling operation. However, if the image forming apparatus 100 is provided with a belt contact / separation mechanism capable of separating the intermediate transfer belt 10 from at least one photosensitive drum 1, the intermediate transfer belt 10 may be separated from at least one photosensitive drum 1 during the idling operation. In this embodiment, a primary transfer voltage is not applied to the primary transfer roller 6 during the idling operation. However, a primary transfer voltage similar to that used during image formation may be applied to the primary transfer roller 6 during the idling operation. In this embodiment, during the idling operation, the secondary transfer voltage is not applied to the secondary transfer roller 20. However, during the idling operation, the secondary transfer voltage may be applied to the secondary transfer roller 20 in the same manner as during image formation, for example.

[0120] In an experiment conducted under the same conditions as the experiment that yielded the results in Table 2, after printing the 11th sheet, the print job was interrupted and idle rotation was performed for 15 seconds. Then, after the idle rotation, printing of the 12th and subsequent sheets was resumed (also referred to as "resuming the print job"). As a result, there was no slight density loss in the halftone image, and the detection result by the first light-receiving element 62 on the 16th sheet was 3.1 V. This was because the water droplets on the intermediate transfer belt 10 disappeared, causing the light emitted by the light-emitting element 61 to reflect off the surface of the intermediate transfer belt 10. The water droplets on the intermediate transfer belt 10 disappeared due to the idle rotation because they adhered to the conductive brush 16 and secondary transfer roller 20, were removed from the intermediate transfer belt 10, and some of the water droplets further evaporated. It is believed that the water droplets on the photosensitive drum 1 also disappeared at this time, thereby suppressing image defects. The reason why the water droplets on the photosensitive drum 1 disappear during the idle rotation is thought to be that the moisture on the photosensitive drum 1 transfers onto the intermediate transfer belt 10, and the water droplets on the intermediate transfer belt 10 are removed in the same manner as described above, or some of the water droplets evaporate. It is also thought that some of the water droplets on the photosensitive drum 1 are also removed by the drum cleaning device 5 during the idle rotation.

[0121] In this embodiment, the idle rotation operation was performed for 15 seconds, but the duration of the idle rotation operation is not limited to this. The duration of the idle rotation operation may be set appropriately taking into consideration the expected amount of water droplets and the time required to remove them. The duration of the idle rotation operation is not limited to this, but may be, for example, approximately 5 seconds to 1 minute. In other words, the duration of the idle rotation operation is not limited to this, but may be, for example, the time required for the intermediate transfer belt 10 to rotate approximately 1 to 20 times. In this embodiment, the peripheral length of the intermediate transfer belt 10 is 800 mm, the peripheral speed of the intermediate transfer belt 10 is approximately 200 mm / sec, and the time required for the intermediate transfer belt 10 to rotate once is approximately 4 seconds.

[0122] Furthermore, the deterioration in the detection results by the first light receiving element 62 and the timing of image defects occurring as the number of prints increases shown in Table 2 are just examples, and these change depending on the setting conditions such as the installation position and wind speed of the ceiling fan. The timing and degree of image defects also change depending on the configuration of the image forming apparatus 100, for example, the setting value of the surface potential of the photosensitive drum 1, the electrical resistance value of the intermediate transfer belt 10, and the adhesive force between the toner and these components. Therefore, depending on the characteristics of the image forming apparatus 100, etc., the print job can be interrupted based on the detection results by the first light receiving element 62, and the intermediate transfer belt 10 can be made to idle. 7. Control Procedure

[0123] 12 is a flowchart showing an outline of the operation of the image forming apparatus 100, including the operation of detecting the condensation state and the condensation removal process in this embodiment. The operation according to the flowchart in FIG.

[0124] When a print job is instructed by the controller 210, the DC controller 200 starts a print job for n sheets (S11). Next, the DC controller 200 determines whether the average value R of the detection results by the first light-receiving element 62 is equal to or less than 2.8 V, assuming that the average value R crosses the threshold value at a predetermined timing (sampling intervals (1) to (4)) described with reference to FIG. 7 (S12). When the average value R of the detection results by the first light-receiving element 62 is equal to or less than 2.8 V, this is an example of a case where the numerical value (voltage in this embodiment) related to the detection signal output by the light-receiving element (first light-receiving element 62 in this embodiment) of the optical sensor 60 receives reflected light and outputs it satisfies a predetermined condition. If the DC controller 200 determines in S12 that the average value R of the detection results by the first light-receiving element 62 is equal to or less than 2.8 V, it interrupts the print job and performs an idling operation (S13). The DC controller 200 then determines whether the time t since the start of the idling operation has elapsed a predetermined time, 15 seconds in this embodiment (S14). If the DC controller 200 determines in S14 that the time t has not elapsed, it continues the idling operation (S13). If the DC controller 200 determines in S14 that the time t has elapsed is 15 seconds, it ends the idling operation, resumes the print job (S15), and repeats the determination in S12. On the other hand, if the DC controller 200 determines in S12 that the average value R of the detection results by the first light-receiving element 62 is greater than 2.8 V, it determines whether all printing of the print job has been completed (S16). If the DC controller 200 determines in S16 that all printing of the print job has been completed, it ends the print job (S17). On the other hand, if the DC controller 200 determines in S16 that all printing of the print job has not been completed, it continues the print job (S18) and repeats the determination in S12. effect

[0125] As described above, in this embodiment, the optical sensor 60 is driven during a print job, the first light-receiving element 62 detects reflected light from the surface of the intermediate transfer belt 10, and the transition of the average value of the detection results is monitored. In particular, in this embodiment, whether the average value of the detection results by the first light-receiving element 62 falls below a predetermined threshold during the print job is monitored. This makes it possible to determine the state of condensation on the surface of the intermediate transfer belt 10 and the surface of the photosensitive drum 1. In this embodiment, if the average value of the detection results by the first light-receiving element 62 falls below the threshold, it is determined that condensation has occurred on the surface of the intermediate transfer belt 10 and the surface of the photosensitive drum 1. In this case, the print job is interrupted before an image defect occurs, and the photosensitive drums 1a, 1b, 1c, and 1d and the intermediate transfer belt 10 are rotated in an idle rotation operation. This removes water droplets adhering to the photosensitive drums 1 and the intermediate transfer belt 10, thereby maintaining good image quality throughout the print job, even in a situation where wind from a ceiling fan flows into the interior of the image forming apparatus 100 and condensation would occur. That is, according to this embodiment, it is possible to suppress the occurrence of image defects caused by water droplets adhering to the photosensitive drum 1 or the intermediate transfer belt 10 during a print job.

[0126] Modifications of the present embodiment will be described below. 9-1. Modifications of the method for detecting the condensation state and the condensation removal process

[0127] In this embodiment, the DC controller 200 is configured to execute the idle rotation operation for a predetermined time, but the present invention is not limited to this configuration. For example, the DC controller 200 may be configured to adjust the execution time of the idle rotation operation according to the rate of fluctuation of the average value of the first light-receiving element 62 during a print job (such as the amount of fluctuation per unit time or the amount of fluctuation per unit number of prints). In this case, for example, the DC controller 200 can control the execution time of the idle rotation operation to increase the faster the rate of fluctuation of the average value of the first light-receiving element 62 during a print job.

[0128] Furthermore, the condensation removal process is not limited to idling. For example, the image forming apparatus 100 may be stopped for a predetermined time until the water droplets on the photosensitive drums 1 and the intermediate transfer belt 10 evaporate and the condensation is sufficiently eliminated, as in this embodiment. Stopping the image forming apparatus 100 means stopping at least the photosensitive drums 1a, 1b, 1c, and 1d, the intermediate transfer belt 10, and components acting on these (such as the charging roller 2 and the developing roller 42). Therefore, for example, fans serving as air blowers for drawing in or exhausting air inside or outside the image forming apparatus 100, heaters serving as heating devices, and control devices may be operating. In this case, the general operation of the image forming apparatus 100 is similar to that described using the flowchart of FIG. 12 , except that the print job is interrupted in S13 and then the image forming apparatus 100 is stopped.

[0129] Furthermore, during the idling operation for dew condensation removal or while the image forming apparatus 100 is stopped, it is possible to heat a heating unit such as a heater in the fixing device 30 to raise the temperature inside the image forming apparatus 100 and promote evaporation of water droplets resulting from condensation. The heating unit is not limited to the heater in the fixing device 30, and may be, for example, a heater provided for heating any location in the image forming apparatus 100, such as the photosensitive drum 1, or a heater provided specifically for eliminating condensation. Furthermore, during the idling operation for dew condensation removal or while the image forming apparatus 100 is stopped, it is possible to promote discharge of moisture resulting from evaporation of water droplets to the outside of the apparatus by, for example, using a fan as a blower that draws in or exhausts air inside or outside the image forming apparatus 100.

[0130] Furthermore, in this embodiment, the print job was interrupted to perform the condensation removal process (idle rotation in this embodiment), but the condensation removal process may also be performed after a series of prints (image formation) in the print job is completed. In this case, for example, under the same conditions as the experiment that produced the results in Table 2, in a 20-sheet print job, only slight density loss occurred in halftone images, but no noticeable image defects occurred in other images. Furthermore, in the next print job, good images can be obtained because the condensation has been removed. In this way, performing the condensation removal process when the print job is completed has the advantage of minimizing image defects without causing downtime (a period during which images cannot be output) during the print job.

[0131] FIG. 13 is a flowchart outlining the operation of the image forming apparatus 100, including the condensation detection operation and condensation removal process in this case. The operation according to the flowchart in FIG. 13 is controlled by the DC controller 200. When a print job is instructed by the controller 210, the DC controller 200 starts a print job for n sheets (S21). Next, the DC controller 200 determines whether all printing of the print job is complete (S22). If the DC controller 200 determines in S22 that all printing of the print job is complete, it determines whether the average value R of the detection results by the first light-receiving element 62 during the sampling period (4) described with reference to FIG. 7 is 2.8 V or less (S23). If the DC controller 200 determines in S23 that the average value R of the detection results by the first light-receiving element 62 is 2.8 V or less, it performs an idling operation when ending the print job, and then performs a normal post-rotation process to end the print job (S24). In other words, in this case, when the print job is ended, the time from when the trailing edge of the image forming area of ​​the final page on the intermediate transfer belt 10 passes detection position D to when the rotation of the intermediate transfer belt 10 stops is longer than when only the normal post-rotation process is performed. Also, if the DC controller 200 determines in S23 that the average value R of the detection results by the first light-receiving element 62 is greater than 2.8 V, it ends the print job by performing the normal post-rotation process without performing the idling operation. Note that if the operation of the image forming apparatus 100 is stopped as a condensation removal process when a print job is ended, the DC controller 200 can postpone (prohibit) the start of the next print job until a predetermined stop time has elapsed, even if a command for the next print job has been issued.

[0132] The DC controller 200 may also be configured to select whether to interrupt a print job and perform the condensation removal process or to perform the condensation removal process when the print job is terminated. For example, at the start of a print job, the DC controller 200 can determine, based on image data received by the controller 210, whether to form a predetermined image (e.g., a halftone image) that may cause low density during the print job. The DC controller 200 can then control the operation of FIG. 13 (to perform the condensation removal process when the print job is terminated) if there is no such image, and the operation of FIG. 12 (to interrupt the print job and perform the condensation removal process) if there is a such image. Note that, when the DC controller 200 performs the operation of FIG. 12 and detects condensation, it may determine whether to interrupt the print job and perform the condensation removal process or to perform the condensation removal process when the print job is terminated, depending on whether a predetermined image (e.g., a halftone image) that may cause low density is subsequently formed. The halftone image is not limited to the one used in the experimental example described above. For example, the halftone image may have a toner coverage (area ratio of the image area) of approximately 20% to 80% when the toner coverage (area ratio of the image area) of a solid image is 100%. Furthermore, for example, the DC controller 200 may select whether to interrupt the print job and perform the condensation removal process, or to perform the condensation removal process when the print job is completed, depending on the number of prints in the print job. In this case, for example, if the number of prints in the print job is equal to or greater than a predetermined number, the print job may be interrupted and the condensation removal process may be performed, or if the number of prints is less than the predetermined number, the condensation removal process may be performed when the print job is completed. The same selection as above may also be made based on the number of remaining prints at the time condensation is detected.

[0133] In this embodiment, the detection result of the first light receiving element 62 for the amount of light reflected from the surface of the intermediate transfer belt 10 when no water droplets are present on the intermediate transfer belt 10 is assumed to be approximately 3.0 V. However, the output of the first light receiving element 62 may vary depending on, for example, the light emission amount of the light emitting element 61, the sensitivity setting of the first light receiving element 62, and contamination of the light emitting element 61 or the first light receiving element 62. Therefore, the detection result of the amount of light reflected from the surface of the intermediate transfer belt 10 by the first light receiving element 62 at the start of a print job does not necessarily have to be approximately 3.0 V. Furthermore, for example, the DC controller 200 acquires an average value of the detection results of the amount of light reflected from the surface of the intermediate transfer belt 10 by the first light receiving element 62 at the start of a print job and stores this average value in the memory 202 as an initial value. The initial value of the detection result by the first light receiving element 62 at the start of a print job may be, for example, the value acquired in the aforementioned sampling interval (1). The DC controller 200 can determine whether condensation has occurred based on the amount of change from the initial value of the detection result by the first light-receiving element 62 during the print job. In this case, for example, 0.2 V, which corresponds to the difference between the initial value of 3.0 V and the threshold value of 2.8 V in this embodiment, can be used as a threshold value. Condensation can be determined when the amount of change is equal to or greater than this threshold. Alternatively, condensation can be determined based on the ratio of the amount of change in the detection result by the first light-receiving element 62 to the initial value or maximum value. For example, condensation can be determined when the average value of the detection result by the first light-receiving element 62 drops by just under 10% (e.g., 7%) from the initial value or maximum value. In this way, the degree of decrease (amount of change, e.g., difference or percentage) of the average value of the detection result by the first light-receiving element 62 during the print job from the initial value at the start of the print job can be monitored. This can also achieve the same effect as this embodiment.

[0134] In this embodiment, the average value of 100 sampling results (sampling data) was calculated as the detection result by the first light-receiving element 62, and the change in the average value was used as a means for determining the condensation state. However, the number of sampling points used as the average value is not limited to the number used in this embodiment and can be set appropriately depending on the desired accuracy of determining the condensation state, etc. Also, deviation can be used instead of the average value as a means for determining the condensation state. As an example, the following formula (1) is a formula for calculating the deviation, where xi is the i-th detection signal, μ is the average value, and n is the number of sampling points, which is 100 in this embodiment.

[0135] Determining the condensation state based on the deviation has the advantage that, when water droplets adhering to the intermediate transfer belt 10 are sparse, the value may change more sensitively than by calculating the average value. For example, when the calculated deviation is equal to or greater than a predetermined threshold, it can be determined that condensation has occurred. It is also possible to use both the average value and the deviation. For example, when the average value is equal to or less than a predetermined threshold value (or the amount of change in the average value is equal to or greater than a predetermined threshold value) and the deviation is equal to or greater than a predetermined threshold value, it can be determined that condensation has occurred. 9-2. Modified examples of the timing for detecting condensation

[0136] FIG. 14 is a timing chart showing an overview of the operation of each unit during a print job in one modified example. The operation according to the timing chart of FIG. 14 is controlled by the DC controller 200. For example, when sufficient time is required for the light-emitting element 61 to start up, the optical sensor 60 may be driven prior to driving the intermediate transfer belt 10, as shown in FIG. 14. In this case, for example, in consideration of the start-up time of the light-emitting element 61, image formation may be started so that condensation can be detected in the aforementioned sampling intervals (1), (2), (3), and (4). In other respects, the operation according to the timing chart of FIG. 14 is substantially the same as the operation according to the timing chart of FIG. 7.

[0137] FIG. 15 is a timing chart illustrating an overview of the operation of each component during a print job in another modified example. The operation according to the timing chart in FIG. 15 is controlled by the DC controller 200. Condensation caused by the wind from a ceiling fan is caused by water vapor generated from paper passing through the fixing device 30, so the likelihood of water droplets adhering to the intermediate transfer belt 10 during image formation on the first sheet is low. In light of this, for example, as shown in FIG. 15 , acquisition of detection results by the first light-receiving element 62 may begin from sampling interval (2) between the rear end of the image formation area for the first sheet and the front end of the image area for the second sheet on the intermediate transfer belt 10. That is, in the example of FIG. 15 , detection results by the first light-receiving element 62 are acquired during sampling intervals (2), (3), and (4). In this case, for example, if the average value of the detection results by the first light-receiving element 62 during sampling intervals (2), (3), and (4) is equal to or less than a predetermined threshold, it can be determined that condensation has occurred. Alternatively, as described above, the average value of the detection results by the first light-receiving element 62 in sampling period (2) can be used as an initial value, and the state of condensation can be determined based on the amount of change from this initial value in the average value of the detection results in sampling periods (3) and (4). By starting detection from sampling period (2), it becomes possible to form an image without waiting for the light-emitting element 61 to start up. In other respects, the operation according to the timing chart of FIG. 15 is substantially the same as the operation according to the timing chart of FIG. 7 described above.

[0138] In this embodiment, the optical sensor 60 was driven and its detection results were sampled in sampling section (4) to determine the condensation state when a print job was completed. This allows for a condensation removal process to be performed as necessary when a print job is completed, thereby reducing the impact of condensation when the next print job is started. However, the present invention is not limited to this. It is not necessary to sample the detection results of the optical sensor 60 in sampling section (4), or even to drive the optical sensor 60. Even in this case, the impact of condensation on the print job can be reduced based on the detection results of the optical sensor 60 in sampling section (2) or (3), or even sampling section (1). Furthermore, in this embodiment, the detection results of the optical sensor 60 were sampled in all inter-sheet regions on the intermediate transfer belt 10, as in sampling section (2) or (3). This allows for a more rapid assessment of the progress of condensation. However, the present invention is not limited to this. For example, sampling of the detection results of the optical sensor 60 in the inter-sheet region every predetermined number of sheets may be performed in sampling section (2) or (3), or the like. Alternatively, the detection results of the optical sensor 60 may be sampled in only a portion of the inter-sheet region. In this case, if possible in relation to the start-up of the optical sensor 60, the driving (light emission) of the optical sensor 60 may be stopped between the paper intervals where the detection results of the optical sensor 60 are sampled.

[0139] In this embodiment, the image forming apparatus 100 drives the optical sensor 60 and samples the detection results of the optical sensor 60 to determine the condensation state for all print jobs. However, the present invention is not limited to this. The image forming apparatus 100 may be capable of executing print jobs by switching between a detection mode (first mode) in which the optical sensor 60 determines the condensation state and a normal mode (second mode) in which the optical sensor 60 does not. The method for determining the condensation state using the optical sensor 60 in the detection mode may be the same as in this embodiment. For example, the control unit 200 can switch between the detection mode and the normal mode before starting a print job or during execution of a print job depending on the environment. Here, the environment may be at least one of the temperature and humidity inside or outside the image forming apparatus 100, but is preferably at least one of the temperature and humidity outside the image forming apparatus 100. As an example, the control unit 200 acquires the environmental detection results from an environmental sensor (not shown) provided in the image forming apparatus 100. Based on the environmental detection results, the control unit 200 can control the image forming apparatus 100 to execute the print job in the detection mode when the temperature outside the image forming apparatus 100 is 30°C or higher, preferably when the temperature is 30°C or higher and the humidity (relative humidity) is 80% or higher. The control unit 200 can also control the image forming apparatus 100 to execute the print job in the normal mode when the temperature is lower than 30°C, preferably when the temperature is lower than 30°C and the humidity (relative humidity) is lower than 80%. According to the method described in this embodiment, the condensation state can be determined using the optical sensor 60 within a period equivalent to the inter-sheet process during execution of the print job. Therefore, the duration of the inter-sheet process and the post-rotation process is substantially the same between the detection mode and the normal mode, provided that conditions other than the mode switching conditions are substantially the same, except when the inter-sheet process and the post-rotation process are extended by the condensation removal process. 9-3. Modified Configuration of the Image Forming Apparatus

[0140] In this embodiment, the image forming apparatus 100 is configured to remove adhering matter, such as secondary transfer residual toner, remaining on the intermediate transfer belt 10 after secondary transfer using a conductive brush 16, but the present invention is not limited to such a configuration. FIG. 16 is a schematic cross-sectional view of a modified image forming apparatus. In the image forming apparatus of FIG. 16, elements having the same or corresponding functions or configurations as those of the image forming apparatus of FIG. 1 are designated by the same reference numerals as those of the image forming apparatus of FIG. 1, and detailed descriptions thereof will be omitted. The image forming apparatus 100 of FIG. 16 includes a belt cleaning device 18 as an intermediate transfer member cleaning means, located on the outer peripheral surface of the intermediate transfer belt 10, facing the third tension roller 13. The belt cleaning device 18 includes a cleaning blade 73 as a cleaning member disposed in contact with the surface of the intermediate transfer belt 10, and a cleaning container 74 that contains adhering matter, such as secondary transfer residual toner, removed from the surface of the intermediate transfer belt 10 by the cleaning blade 73. The belt cleaning device 18 uses a cleaning blade 73 to scrape off adhering matter such as secondary transfer residual toner from the surface of the rotating intermediate transfer belt 10, and collects the adhering matter in a cleaning container 74. The present invention can also be applied to an image forming apparatus 100 having such a configuration. 9-4. Modifications related to reflected light to be detected

[0141] In this embodiment, condensation detection was performed based on the detection results from the first light-receiving element 62 of the optical sensor 60. This is because the light emitted by the light-emitting element 61 is mainly reflected as specular light by the intermediate transfer belt 10. However, for example, if the surface of the intermediate transfer belt 10 has a low gloss or if the intermediate transfer belt 10 has a color with a white component, the light may be mainly reflected as diffuse light rather than specular light by the intermediate transfer belt 10. In this case, condensation detection can also be performed based on the detection results from the second light-receiving element 63. Furthermore, the detection results from the second light-receiving element 63 can also be used when foreign matter other than water droplets, such as sand (sand dust) or toner that is not normally present outside the image formation area, is expected to adhere to the intermediate transfer belt 10 (see Example 3).

[0142] As described above, in this embodiment, the image forming apparatus 100 includes toner image forming means (such as the charging roller 2, the exposure device 3, and the developing device 4) that form a toner image, a rotatable image carrier (intermediate transfer belt) 10 that carries on its surface the toner image formed by the toner image forming means, transfer means (such as the secondary transfer roller 20) that transfers the toner image formed on the surface of the image carrier 10 to a recording material P, and an optical sensor 60 that includes a light-emitting element 61 that emits light toward the surface of the image carrier 10, and light-receiving elements 62 and 63 (in this embodiment, the first light-receiving element 62) that emit light from the light-emitting element 61 toward the surface of the image carrier 10, receive the reflected light, and output a detection signal according to the amount of received light, and detects the reflected light at a detection position D in the movement direction of the surface of the image carrier 10. In response to a single start instruction, the image forming apparatus 100 executes a print job in which a print image is formed on one or more recording materials P and the one or more recording materials P are discharged from the inside of the apparatus to the outside of the apparatus through the recording material discharge port (paper discharge port) 130. In this embodiment, the image forming apparatus 100 includes a control unit (DC controller) 200 that can perform control to perform an adhesion removal process (condensation removal process) to remove adhesions (condensation) from the surface of the image carrier 10 during execution of a print job, based on a detection signal output by the light receiving element 62 upon receiving the reflected light during the period from when the trailing edge, in the movement direction, of the image forming area on the surface of the image carrier 10, on which a toner image to be transferred to a preceding recording material P can be formed, passes the detection position D until the leading edge, in the movement direction, of the image forming area on the surface of the image carrier 10, on which a toner image to be transferred to a next recording material P can be formed, reaches the detection position D. In this embodiment, the control unit 200 controls the drive unit 90 that rotates the image carrier 10 to perform an idling operation, in which the image carrier 10 rotates without forming a toner image on the surface of the image carrier 10, as the adhesion removal process. In this embodiment, the control unit 200 controls the drive unit 90 to perform the idling operation for a predetermined period of time. However, the control unit 200 can also control the drive unit 90 that drives the rotation of the image carrier 10 so as to maintain the rotation of the image carrier 10 in a stopped state for a predetermined time as the adhering matter removal process. In this embodiment, the control unit 200 executes the adhering matter removal process by interrupting the formation of a toner image on the surface of the image carrier 10 in the print job.However, the control unit 200 can also execute the deposit removal process after all toner images have been formed on the surface of the image carrier 10 in the print job.

[0143] In this embodiment, the control unit 200 can further perform the above control based on a detection signal output by the light-receiving element 62 after receiving the reflected light after the trailing edge, in the movement direction, of the image forming area on the surface of the image carrier 10, on which a toner image to be transferred to the last recording material P of the print job can be formed, passes the detection position D during execution of a print job. In this embodiment, the control unit 200 can further perform the above control based on a detection signal output by the light-receiving element 62 after receiving the reflected light before the leading edge, in the movement direction, of the image forming area on the surface of the image carrier 10, on which a toner image to be transferred to the first recording material P of the print job can be formed, reaches the detection position D during execution of a print job. In other words, in this embodiment, the control unit 200 can perform the above control based on a detection signal output by the light-receiving element 62 after receiving the reflected light, when an area other than the image forming area on the surface of the image carrier 10, on which a toner image to be transferred to the recording material P in the print job can be formed, passes the detection position D during execution of a print job. In other words, in this embodiment, during the execution of a print job, when the rear end in the movement direction of the image forming area on the surface of the image carrier 10, where the toner image to be transferred to the last recording material P of the print job can be formed, passes through the detection position D and the numerical value related to the detection signal output by the light receiving element 62 after receiving the reflected light, satisfies a predetermined condition, the control unit 200 can control the drive unit 90 so that the time from when the rear end in the movement direction of the image forming area on the surface of the image carrier 10, where the toner image to be transferred to the last recording material P can be formed, passes through the detection position D to when the rotation of the image carrier 10 stops is longer than when the numerical value related to the detection signal does not satisfy the predetermined condition.

[0144] The control unit 200 can perform the above control when the numerical value related to the detection signal output by the light-receiving element 62 after receiving the reflected light crosses a predetermined threshold. In this embodiment, the control unit 200 performs the above control based on the average value of the numerical value related to the detection signal output by the light-receiving element 62 after receiving the reflected light. In this embodiment, the control unit 200 performs the above control when the amount of reflected light indicated by the average value is equal to or less than a predetermined threshold. However, the control unit 200 can also perform the above control based on the deviation of the detection signal output by the light-receiving element 62 after receiving the reflected light. In this case, the control unit 200 can perform the above control when the deviation is equal to or greater than a predetermined threshold. Furthermore, the control unit 200 can also perform the above control based on the amount of change between a first average value of the numerical value related to the detection signal output by the light-receiving element 62 after receiving the reflected light and a second average value of the numerical value related to the detection signal output by the light-receiving element 62 after receiving the reflected light, which is obtained after the first average value, during execution of a print job. In this case, the control unit 200 can perform the above control when the amount of change in the second average value relative to the first average value is equal to or greater than a predetermined threshold. The control unit 200 can also change the time of the deposit removal process based on the rate of change in the value of the detection signal output by the light-receiving element 62 after receiving the reflected light during the print job. In this embodiment, the light-receiving element 62 mainly receives specularly reflected light as the reflected light. In this embodiment, the deposit is moisture adhering to the surface of the image carrier 10. However, a light-receiving element (second light-receiving element) 63 that mainly receives diffusely reflected light as the reflected light may also be used to detect moisture adhering to the surface of the image carrier 10. In addition, in this embodiment, the image forming apparatus 100 has, as image carriers, a photosensitive member 1 which is a first image carrier, and an intermediate transfer member 10 which is a second image carrier that transports the toner image primarily transferred from the photosensitive member 1 to a recording material P for secondary transfer, and the optical sensor 60 irradiates light onto the surface of the intermediate transfer member 10 and detects the reflected light.

[0145] According to this embodiment, it is possible to suppress image degradation caused by condensation on the surface of the intermediate transfer belt 10 during a print job.

[0146] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are assigned the same reference numerals as those of embodiment 1, and detailed descriptions thereof will be omitted.

[0147] In the first embodiment, the idle rotation of the intermediate transfer belt 10 was performed for a predetermined time of 15 seconds based on a fluctuation in the average value of the detection result by the first light receiving element 62 due to the previously obtained idle rotation. In contrast, in the present embodiment, the optical sensor 60 is driven during the idle rotation of the intermediate transfer belt 10, and the idle rotation is terminated based on the detection result by the first light receiving element 62.

[0148] 17 is a timing chart showing an outline of the operation of each part during idling in this embodiment. The operation according to the timing chart in FIG.

[0149] In this embodiment, the print job is interrupted in response to the detection result from the first light receiving element 62, and the developing roller 42 is separated from the photosensitive drum 1. Note that the photosensitive drum 1 and the intermediate transfer belt 10 continue to rotate. The optical sensor 60 is driven and sampling is started at the timing when the position corresponding to the timing when the developing roller 42 is separated from the photosensitive drum 1 reaches the optical sensor 60. This is to accurately detect the amount of light reflected from the surface of the intermediate transfer belt 10 without being affected by toner that has moved from the developing roller 42 onto the intermediate transfer belt 10 via the photosensitive drum 1.

[0150] In this embodiment, as in the first embodiment, the DC controller 200 samples the detection results of the first light receiving element 62 at 0.1 mm intervals in terms of the surface movement distance of the intermediate transfer belt 10 and calculates the average value of 100 sampled data points. That is, the DC controller 200 calculates the average value of the detection results (sampled data) of the amount of light reflected from the surface of the intermediate transfer belt 10 while the intermediate transfer belt 10 rotates 10 mm. In this embodiment, the DC controller 200 obtains the average value of the 10 mm sampled data over 800 mm, which is one rotation of the intermediate transfer belt 10, during idling. Then, when all of the average values ​​are greater than 3.0 V, the DC controller 200 determines that the condensation state has been resolved and resumes the print job.

[0151] 18 is a flowchart showing an outline of the operation of the image forming apparatus 100, including the operation of detecting the condensation state and the condensation removal process in this embodiment. The operation according to the flowchart in FIG.

[0152] When a print job is instructed by the controller 210, the DC controller 200 starts a print job for n sheets (S31). Next, the DC controller 200 determines whether the average value R of the detection results by the first light-receiving element 62 is 2.8 V or less at a predetermined timing (sampling periods (1) to (4)) described with reference to FIG. 7 (S32). If the DC controller 200 determines in S32 that the average value R of the detection results by the first light-receiving element 62 is 2.8 V or less, it interrupts the print job and performs an idling operation (S33). Then, the DC controller 200 determines whether the average value R of the detection results by the first light-receiving element 62 during the idling operation is 3.0 V or less (S34). If the DC controller 200 determines in S34 that the average value R of the detection results by the first light-receiving element 62 is greater than 3.0 V, it ends the idling operation, resumes the print job (S35), and repeats the determination in S32. On the other hand, if the DC controller 200 determines in S34 that the average value R of the detection results by the first light-receiving element 62 is 3.0 V or less, it determines whether the time t since the start of the idling operation has elapsed a predetermined time, 15 seconds in this embodiment (S36). If the DC controller 200 determines in S36 that the time t has not elapsed, it continues the idling operation (S33). If the DC controller 200 determines in S36 that the time t has elapsed is 15 seconds, it ends the idling operation, resumes the print job (S35), and repeats the determination in S32. This allows the idling operation to be terminated, assuming that moisture has been sufficiently removed from the surface of the intermediate transfer belt 10, even if the average value R is no longer 3.0 V or less due to a change in the state of the intermediate transfer belt 10 caused by factors other than moisture. If the DC controller 200 determines in S32 that the average value R of the detection results by the first light receiving element 62 is greater than 2.8 V, it determines whether all printing of the print job has been completed (S37). If the DC controller 200 determines in S37 that all printing of the print job has been completed, it ends the print job (S38).On the other hand, if the DC controller 200 determines in S37 that all printing of the print job has not been completed, it continues the print job (S39) and makes the determination in S32 again.

[0153] The average value used in S34 is the average value of sampling data acquired at 100 points at 0.1 mm intervals along the surface movement distance of the intermediate transfer belt 10, and the average value for each of the 100 points may be monitored to determine whether it is equal to or less than 3.0 V. Alternatively, the moving average of the first light receiving element 62 during idling operation may be used.

[0154] Furthermore, in this embodiment, the print job is restarted when the average value of the detection results by the first light-receiving element 62 becomes greater than 3.0 V over one revolution of the intermediate transfer belt 10, but the trigger for restarting the print job is not limited to this. For example, the trigger does not necessarily have to be when the detection results by the first light-receiving element 62 exceed a predetermined value over one revolution of the intermediate transfer belt 10, and may be set appropriately taking into account the number of prints remaining in the print job, the sensitivity of the image forming apparatus 100 to image defects, the acceptable range of image quality, etc. The print job can be restarted when it is detected that at least a portion of the intermediate transfer belt 10 in the rotational direction has sufficiently recovered from condensation.

[0155] Furthermore, in this embodiment, it is possible to appropriately make modifications similar to those described in the modification example of embodiment 1. For example, the idling operation can be performed when a print job is completed, and the idling operation can be terminated based on the detection result of the first light receiving element 62 during the idling operation.

[0156] Thus, in this embodiment, the control unit 200 controls the drive unit 90 to terminate the idling operation based on the detection signal output by the light receiving element 62 upon receiving reflected light while the idling operation is being performed.

[0157] As described above, in this embodiment, by performing the above-described operations, water droplets on the surface of the intermediate transfer belt 10 can be more reliably removed in the condensation removal process. Furthermore, if the condensation can be removed early, the idle rotation operation can be quickly terminated, thereby shortening downtime. Therefore, according to this embodiment, the occurrence of image defects due to condensation can be more efficiently and reliably suppressed. [Embodiment 3]

[0158] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are assigned the same reference numerals as those of embodiment 1, and detailed descriptions thereof will be omitted.

[0159] In the first and second embodiments, the optical sensor 60 is used to detect water droplets due to condensation on the intermediate transfer belt 10, but the optical sensor 60 can also detect things other than water droplets. For example, if foreign matter such as sand enters the image forming apparatus 100 during a print job and gradually accumulates on the intermediate transfer belt 10, the optical sensor 60 can detect this. In this embodiment, the detection of sand on the intermediate transfer belt 10 will be described.

[0160] FIG. 19 is a graph showing the waveform detected by the second light-receiving element 63 when sand is present on the intermediate transfer belt 10 and passes the position of the optical sensor 60. The light-emitting element 61 is driven during section (i) in FIG. 19 . As shown in FIG. 19 , the light reflected from the surface of the intermediate transfer belt 10 is primarily specular, so the amount of light received by the second light-receiving element 63, which receives diffusely reflected light, is small. On the other hand, the light reflected from the sand is primarily diffusely reflected, so the amount of light received by the second light-receiving element 63 increases when the sand passes the detection position D of the optical sensor 60. Taking advantage of this tendency, for example, as shown in FIG. 19 , a threshold value can be set in advance to satisfy a predetermined condition. When a detection signal (detection output) exceeding (crossing) the threshold value is obtained, it can be determined that a foreign object such as sand is present on the intermediate transfer belt 10 (i.e., an abnormality on the intermediate transfer belt 10).

[0161] Diffusely reflected light can also be received by the first light-receiving element 62. Figure 20 shows a detection waveform obtained when sand on the intermediate transfer belt 10, the same as in Figure 19, is detected by the first light-receiving element 62. When sand passes through detection position D of the optical sensor 60, the amount of specularly reflected light from the surface of the intermediate transfer belt 10 decreases, thereby reducing the amount of light received by the first light-receiving element 62. Taking advantage of this tendency, for example, as shown in Figure 19, a threshold value can be set in advance to satisfy a predetermined condition. When a detection signal (detection output) is obtained that falls below (crosses) the threshold value, it can be determined that sand or other foreign matter is present on the intermediate transfer belt 10 (an abnormality on the intermediate transfer belt 10).

[0162] When foreign matter on the intermediate transfer belt 10 is detected as described above, the DC controller 200 can control at least one of the operation unit 150 and the external device 300 to execute a notification process to notify an operator such as a user of the detection. Specifically, when foreign matter on the intermediate transfer belt 10 is detected, the DC controller 200 controls the operation unit 150 or the external device 300 to output a signal to notify the operator such as a user of information regarding the adhesion of foreign matter to the surface of the intermediate transfer belt 10. The information notified by the notification process may simply notify the operator such as a user of the presence of foreign matter on the intermediate transfer belt 10, or may prompt the user to perform maintenance (e.g., cleaning) or replacement of the intermediate transfer belt 10. In addition to executing the notification process, the DC controller 200 can also control the image forming apparatus 100 to stop (prohibit) operation (printing) until a predetermined process (e.g., cleaning or replacement) is performed by the operator such as a user. The DC controller 200 can control the image forming apparatus 100 so that it can resume operation (printing) when predetermined information is input by an operator such as a user from at least one of the operation unit 150 or the external device 300, or when replacement of the intermediate transfer belt 10 or a unit including it is detected by a mechanism that detects that the intermediate transfer belt 10 has been replaced.

[0163] Furthermore, when foreign matter is detected on the intermediate transfer belt 10 as described above, the DC controller 200 may control the intermediate transfer belt 10 to execute a foreign matter removal process to remove foreign matter from the intermediate transfer belt 10 as a recovery process from an abnormality on the intermediate transfer belt 10. The foreign matter removal process is an example of an adhesion removal process for removing adhesions (such as sand in this embodiment) from the surface of the intermediate transfer belt 10 as a recovery process from an abnormal state on the intermediate transfer belt 10. The foreign matter removal process may be executed, for example, by interrupting a print job based on the detection result by the optical sensor 60 during the print job. Alternatively, the foreign matter removal process may be executed when the print job is terminated based on the detection result by the optical sensor 60 during the print job. An example of the foreign matter removal process is the idling operation similar to that in Examples 1 and 2. This allows foreign matter on the intermediate transfer belt 10 to be removed by the conductive brush 16 ( FIG. 1 ) or the belt cleaning device ( FIG. 16 ). The idling operation as the foreign matter removal process can be executed for a predetermined time (e.g., 15 seconds) similar to the idling operation in Example 1. Alternatively, the idling operation as the foreign matter removal process can be terminated when it is determined that the foreign matter has been removed based on the detection result by the optical sensor 60, as in the second embodiment. In this case, the idling operation as the foreign matter removal process can be terminated when the detection result by the second light receiving element 63 no longer exceeds the predetermined threshold (or the detection result by the first light receiving element 62 no longer falls below the predetermined threshold).

[0164] 21 is a flowchart showing an outline of the operation of the image forming apparatus 100 in this embodiment, including the operation of detecting and notifying foreign matter on the intermediate transfer belt 10. The operation according to the flowchart in FIG. 21 is controlled by the DC controller 200.

[0165] When a print job is instructed by the controller 210, the DC controller 200 starts a print job for n sheets (S41). Next, the DC controller 200 determines whether the detection result by the second light-receiving element 63 exceeds a predetermined threshold at a predetermined timing (sampling intervals (1) to (4)) described with reference to FIG. 7 (S42). If the DC controller 200 determines in S42 that the detection result by the second light-receiving element 63 exceeds the predetermined threshold, it interrupts the print job, executes a notification process in the operation unit 150 or the external device 300 (S43), and stops operation of the image forming apparatus 100 (S44). On the other hand, if the DC controller 200 determines in S42 that the detection result by the second light-receiving element 62 is equal to or less than the predetermined threshold, it determines whether all printing of the print job has been completed (S45). If the DC controller 200 determines in S45 that all printing of the print job has been completed, it ends the print job (S46). On the other hand, if the DC controller 200 determines in S45 that all printing of the print job has not been completed, it continues the print job (S47) and makes the determination in S42 again.

[0166] 22 is a flowchart showing an outline of the operation of the image forming apparatus 100 in this embodiment, including the operation of detecting foreign matter on the intermediate transfer belt 10 and the foreign matter removal process. The operation according to the flowchart in FIG. 22 is controlled by the DC controller 200. Here, a case where a print job is interrupted to perform the foreign matter removal process is taken as an example.

[0167] 22 and 21, the processes of S41, S42, and S45 are the same, and therefore will not be described again. In this example, if the DC controller 200 determines in S42 that the detection result by the second light-receiving element 63 exceeds a predetermined threshold, it interrupts the print job and executes an idling operation as a foreign matter removal process (S48). After the idling operation as a foreign matter removal process is completed, the DC controller 200 resumes the print job and performs the determination of S42 again.

[0168] As described above, the DC controller 200 may determine in S42 whether the detection result by the first light receiving element 63 is below a predetermined threshold, and if so, execute a notification process or a foreign matter removal process. As described above, the foreign matter removal process may be executed when the print job is completed. The foreign matter is not limited to sand, but may be any adhering matter, such as toner, that is not normally present outside the image forming area (non-image forming area).

[0169] As described above, when foreign matter such as sand or toner adheres to the surface of the intermediate transfer belt 10, it is possible to determine whether there is an abnormality on the surface of the intermediate transfer belt 10 by comparing the detection result from the first light receiving element 62 or the second light receiving element 63 with the preset threshold value for each element. By performing determination using a threshold value in this manner, it is possible to detect the occurrence of image defects that are difficult to prevent by simply detecting the adhesion of water droplets, or signs of damage to the intermediate transfer belt 10 or members that come into contact with it.

[0170] The detection of condensation described in the first and second embodiments and the detection of foreign matter described in this embodiment can both be performed in parallel. For example, in addition to the average value and the amount of change in the detection results from the first light receiving element 62, a determination is made based on the threshold value of the detection results from the second light receiving element 63, and if either of these satisfies the predetermined conditions described above, it can be determined that there is an abnormality on the intermediate transfer belt 10. This makes it possible to prevent image defects from occurring.

[0171] As described above, in this embodiment, the light receiving element 63 mainly receives diffusely reflected light as reflected light. In this embodiment, the control unit 200 can control the light receiving element 62 to execute a foreign matter removal process (foreign matter removal process) or a notification process when a numerical value related to the detection signal output by the light receiving element 63 after receiving the reflected light exceeds a threshold value. However, the light receiving element 62 may mainly receive specularly reflected light as reflected light. In this case, the control unit 200 can control the light receiving element 62 to execute a foreign matter removal process (foreign matter removal process) or a notification process when the amount of reflected light indicated by the detection signal output by the light receiving element 62 after receiving the reflected light falls below a predetermined threshold value. In this embodiment, the image carriers include the photosensitive element 1 as a first image carrier and the intermediate transfer element 10 as a second image carrier that transports the toner image primarily transferred from the photosensitive element 1 to the recording material P for secondary transfer. The optical sensor 60 irradiates light toward the surface of the intermediate transfer element 10 and detects the reflected light.

[0172] As described above, according to this embodiment, it is possible to suppress image defects caused by the adhesion of foreign matter such as sand to the surface of the intermediate transfer belt 10 during a print job.

[0173] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

[0174] In the above-described embodiment, the optical sensor detects the light reflected from the surface of the intermediate transfer belt, which is the image carrier (second image carrier), to detect the presence of condensation or foreign matter. However, the present invention is not limited to this embodiment. The optical sensor may also detect the light reflected from the surface of the photosensitive drum, which is the image carrier (first image carrier), to detect the presence of condensation or foreign matter. Alternatively, both of these detections may be performed.

[0175] In the above-described embodiment, the image forming apparatus is capable of forming full-color images, but the present invention is not limited to this. The present invention can also be applied to an image forming apparatus that is capable of forming only monochrome (black and white or monochromatic) images.

[0176] Furthermore, the photosensitive member is not limited to a drum-shaped member (photosensitive drum), but may be, for example, an endless belt-shaped member (photosensitive belt), etc. Furthermore, the intermediate transfer member is not limited to an endless belt, but may be, for example, an intermediate transfer drum that is stretched around a frame and has a drum-like shape.

[0177] Furthermore, in the above-described embodiment, the developing member contacts the photosensitive member to perform development, but it may also be disposed opposite the photosensitive member without contacting it to perform development.

[0178] In the above-described embodiment, the image forming apparatus has a cleaning device for cleaning the surface of the photosensitive member, but the image forming apparatus may have a configuration that does not have a special cleaning device for cleaning the surface of the photosensitive member. In this case, the residual toner on the photosensitive member may be collected by the developing device.

[0179] In the above embodiment, the operation when the front optical sensor 60F is used has been described as an example. However, the present invention is not limited to this, and the rear optical sensor 60R may also be used. Furthermore, both the front optical sensor 60F and the rear optical sensor 60R may also be used. In this case, for example, if condensation is detected by either one of the optical sensors 60 or if condensation is detected by both optical sensors 60, the recovery process may be executed. The same applies to the detection of foreign matter such as sand. Furthermore, the number of optical sensors capable of detecting reflected light from the surface of the image carrier provided in the image forming apparatus is not limited to two, but may be one, three, or more.

[0180] According to the present invention, there is provided an image forming apparatus that forms an image on a recording material using an electrophotographic method or an electrostatic recording method.

[0181] The present invention is not limited to the above-described embodiments, and various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to apprise the public of the scope of the present invention.

[0182] This application claims priority based on Japanese Patent Application No. 2023-159284, filed on September 22, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. An image forming apparatus having a toner image forming means for forming a toner image, a rotatable image carrier for carrying on its surface the toner image formed by the toner image forming means, a transfer means for transferring the toner image formed on the surface of the image carrier to a recording material, and an optical sensor including a light emitting element for irradiating light toward the surface of the image carrier and a light receiving element for irradiating light from the light emitting element toward the surface of the image carrier, receiving reflected light and outputting a detection signal according to the amount of received light, the optical sensor detecting the reflected light at a detection position in the moving direction of the surface of the image carrier, the image forming apparatus executing a print job in which a print image is formed on one or more recording materials in response to a single start instruction, and the one or more recording materials are discharged from inside the machine to outside the machine through a recording material discharge port, An image forming device having a control unit capable of controlling, during execution of a print job, to perform an adhesion removal process to remove adhesions from the surface of the image carrier based on a detection signal output by the light receiving element after receiving the reflected light, between the time when the rear end in the movement direction of the image forming area on the surface of the image carrier, on which a toner image to be transferred to a preceding recording material is formed, passes the detection position and the time when the leading end in the movement direction of the image forming area on the surface of the image carrier, on which a toner image to be transferred to a next recording material is formed, reaches the detection position.

2. An image forming apparatus as described in claim 1, wherein the control unit controls a drive unit that drives the image carrier to rotate so as to perform an idling operation in which the image carrier rotates without forming a toner image on the surface of the image carrier as the adhesion removal process.

3. The image forming apparatus according to claim 2, wherein the control section controls the drive section so as to perform the idling operation for a predetermined period of time.

4. An image forming apparatus as described in claim 2, wherein the control unit controls the drive unit to terminate the idling operation based on a detection signal output by the light receiving element when it receives the reflected light while the idling operation is being performed.

5. An image forming apparatus as described in claim 1, wherein the control unit controls a drive unit that rotates the image carrier so as to maintain the rotation of the image carrier in a stopped state for a predetermined period of time as the adhesion removal process.

6. The image forming apparatus according to claim 1, wherein the control unit executes the deposit removal process by interrupting the formation of a toner image on the surface of the image carrier during a print job.

7. The image forming apparatus according to claim 1, wherein the control section executes the deposit removal process after formation of all toner images on the surface of the image carrier in a print job has been completed.

8. The image forming apparatus of claim 1, wherein the control unit is further capable of performing the control during execution of a print job based on a detection signal output by the light receiving element after receiving the reflected light and outputting after the rear end in the movement direction of the image forming area on the surface of the image carrier on which a toner image to be transferred to the final recording material of the print job can be formed has passed the detection position.

9. An image forming apparatus as described in claim 1, wherein the control unit is further capable of performing the control during execution of a print job based on a detection signal output by the light receiving element upon receiving the reflected light before the leading edge in the movement direction of the image forming area on the surface of the image carrier on which a toner image to be transferred to the first recording material of the print job can be formed reaches the detection position.

10. An image forming apparatus having a toner image forming means for forming a toner image, a rotatable image carrier carrying on its surface the toner image formed by the toner image forming means, a drive section for driving the image carrier to rotate, a transfer means for transferring the toner image formed on the surface of the image carrier to a recording material, and an optical sensor having a light-emitting element for irradiating light toward the surface of the image carrier and a light-receiving element for irradiating light from the light-emitting element toward the surface of the image carrier, receiving reflected light and outputting a detection signal according to the amount of received light, the optical sensor detecting the reflected light at a detection position in the moving direction of the surface of the image carrier, the image forming apparatus executing a print job in which a print image is formed on one or more recording materials in response to a single start instruction and the one or more recording materials are discharged from inside the machine to outside the machine through a recording material discharge port, an image forming apparatus having a control unit capable of controlling the drive unit so that, when a numerical value related to a detection signal output by the light receiving element after receiving the reflected light after the trailing end in the movement direction of an image forming area on the surface of the image carrier on which a toner image to be transferred to a last recording material of the print job is formed passes the detection position during execution of a print job, the time from when the trailing end in the movement direction of an image forming area on the surface of the image carrier on which a toner image to be transferred to the last recording material of the print job passes the detection position to when rotation of the image carrier stops is longer than when the numerical value related to the detection signal does not satisfy the specified condition.

11. An image forming apparatus according to any one of claims 1 to 10, wherein the control unit performs the control when a numerical value relating to a detection signal output by the light receiving element upon receiving the reflected light crosses a predetermined threshold value.

12. An image forming apparatus according to any one of claims 1 to 10, wherein the control section performs the control based on an average value of a numerical value related to a detection signal output by the light receiving element upon receiving the reflected light.

13. The image forming apparatus according to claim 12, wherein the control section performs the control when the amount of reflected light indicated by the average value is equal to or less than a predetermined threshold value.

14. An image forming apparatus according to any one of claims 1 to 10, wherein the control section performs the control based on a deviation in a detection signal output by the light receiving element upon receiving the reflected light.

15. The image forming apparatus according to claim 14, wherein the control section performs the control when the deviation is equal to or greater than a predetermined threshold value.

16. An image forming apparatus as claimed in any one of claims 1 to 9, wherein the control unit performs the control based on the amount of change in a second average value of a numerical value relating to a detection signal output by the light receiving element after receiving the reflected light, which is obtained after the first average value, relative to a first average value of a numerical value relating to a detection signal output by the light receiving element after receiving the reflected light, during execution of a print job.

17. The image forming apparatus according to claim 16, wherein the control section performs the control when an amount of change in the second average value from the first average value is equal to or greater than a predetermined threshold value.

18. An image forming apparatus as claimed in any one of claims 1 to 9, wherein the control unit changes the time of the adhesion removal process based on the rate of change in a numerical value relating to the detection signal output by the light receiving element upon receiving the reflected light during a print job.

19. An image forming apparatus according to any one of claims 1 to 10, wherein the light receiving element mainly receives specularly reflected light as the reflected light.

20. The image forming apparatus according to claim 19, wherein the adhering matter is moisture adhering to the surface of the image carrier.

21. An image forming apparatus according to any one of claims 1 to 10, wherein the light receiving element receives mainly diffusely reflected light as the reflected light.

22. The image forming apparatus according to claim 21, wherein the adhering matter is sand adhering to the surface of the image bearing member.

23. An image forming apparatus as described in any one of claims 1 to 10, having as the image carriers a photosensitive member which is a first image carrier, and an intermediate transfer member which is a second image carrier that transports the toner image primarily transferred from the photosensitive member for secondary transfer onto a recording material, and the optical sensor irradiates light toward the surface of the intermediate transfer member and detects the reflected light.

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