Image forming apparatus

Abstract

To suppress image defect caused by dew condensation or the like in a print job.SOLUTION: An image forming apparatus 100 has a control part 200 which can control so as to execute deposited material removal processing for removing deposited materials on the surface of an image carrier 10 on the basis of a detection signal outputted when a light receiving element 62 receives reflection light by the time a front edge of an image formation area of the surface of the image carrier 10 on which a toner image to be transferred to the next recording material P can be formed reaches a detection position D since an end edge of the image formation area of the surface of the image carrier 10 on which a toner image to be transferred to a preceding recording medium P can be formed passes through the detection position D of an optical sensor 60 during execution of the print job.SELECTED DRAWING: Figure 12

Description

[Technical field]

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

[0002] Conventionally, in an image forming apparatus such as a printer using an electrophotographic method, an electrostatic latent image is formed on a photoreceptor, and toner, which is a color material charged, is supplied to the electrostatic latent image and developed to form a toner image on the photoreceptor. This toner image is transferred directly or via an intermediate transfer body to a recording material such as paper, and fixed to form an image on the recording material. A photoreceptor drum, which is a drum-type photoreceptor, is widely used as the photoreceptor. Also, an intermediate transfer belt, which is an endless belt, is widely used as the intermediate transfer body.

[0003] Such an image forming apparatus may have a function of detecting an abnormality on the photosensitive drum or intermediate transfer belt, which is an image carrier, and suppressing the occurrence of image defects due to the abnormality. An abnormality on the photosensitive drum or intermediate transfer belt may be, for example, caused by condensation inside the image forming apparatus. When condensation occurs inside the image forming apparatus and water droplets due to the condensation adhere to the photosensitive drum or intermediate transfer belt, the following problems may occur. For example, an image with low density may be printed due to fluctuations in the surface potential of the photosensitive drum. In addition, water droplets may collect toner adhered to a cleaning member or a 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, causing image defects.

[0004] Image forming apparatuses are installed in various air-conditioning environments, and the indoor environment may change significantly when the air-conditioning function is activated. Since the image forming apparatus is almost sealed by an exterior cover, the internal temperature of the image forming apparatus changes with a certain time lag in response to the change 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 in relation to 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 a motor driver arranged inside the image forming apparatus is activated, warm air from the room may enter the image forming apparatus, causing condensation.

[0005] Patent Document 1 proposes a configuration in which a temperature and humidity sensor installed inside the image forming device detects temperature and humidity before image formation, and if condensation inside the image forming device is suspected from the detected temperature and humidity, an operation is performed to determine whether or not condensation has occurred. In the configuration described in Patent Document 1, a toner patch is formed to detect the condensation state, and the density of this toner patch is detected by a density detection means, and if the density is lower than a predetermined density, it is determined that condensation has occurred, and a condensation recovery mode is executed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-026192 Summary of the Invention [Problem to be solved by the invention]

[0007] In the configuration of Patent Document 1, a temperature and humidity sensor arranged inside the image forming apparatus detects a state where condensation is suspected prior to image formation. However, for example, 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, when 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 material such as paper that has passed through the fixing device flows back into the image forming apparatus during the print job, causing noticeable condensation locally.

[0008] In addition, in the configuration of Patent Document 1, the temperature and humidity are detected by a temperature and humidity sensor prior to image formation, and if the detected temperature and humidity indicate a suspected condensation state, a toner patch is formed to determine whether or not condensation has occurred. If it is determined that there is no condensation, a normal image formation operation is performed. This may result in unnecessary toner consumption and downtime due to the formation of the toner patch, which may impair usability.

[0009] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to suppress image deterioration caused by condensation or the like during a print job. [Means for solving the problem]

[0010] 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: 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, 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, and an optical sensor for detecting the reflected light at a detection position in the moving direction of the surface of the image carrier, and forming a print image on one or more recording materials in response to one start instruction, and transferring the toner image formed on the surface of the image carrier to a recording material 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 machine to outside the machine, and the image forming apparatus is characterized in that, during the execution of the print job, a control unit is provided that is capable of controlling the execution of 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, 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.

[0011] 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 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, 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, and an optical sensor for detecting the reflected light at a detection position in the moving direction of the surface of the image carrier, and forming a print image on one or more recording materials in response to one start instruction, and discharging the one or more recording materials from inside the machine to outside the machine through a recording material discharge port. The image forming apparatus is characterized in that it has a control unit capable of controlling the drive unit so that, when a numerical value relating 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 on which a toner image to be transferred to the last recording material of the print job is formed passes the detection position during execution of the print job, the time from when the trailing 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 last recording material is formed passes the detection position to when the rotation of the image carrier stops is longer than when the numerical value relating to the detection signal does not satisfy the specified condition. Effect of the Invention

[0012] According to the present invention, it is possible to suppress image defects caused by condensation or the like during a print job. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Diagram 2] FIG. 2 is a block diagram showing a control configuration of the image forming apparatus. [Diagram 3] FIG. 4 is a top view for explaining the arrangement of optical sensors. [Figure 4]FIG. 2 is a schematic cross-sectional view for explaining a configuration of an optical sensor. [Diagram 5] 10 is a graph showing a detection waveform when reflected light from the intermediate transfer belt is detected by an optical sensor. [Figure 6] 10 is a graph showing a detected waveform when reflected light from a toner patch is detected by an optical sensor. FIG. [Figure 7] FIG. 4 is a timing chart showing an overview of an example of an operation during a print job. [Figure 8] 11 is a graph showing a detected waveform when an optical sensor detects reflected light from an intermediate transfer belt in a state where water droplets are attached to the surface of the intermediate transfer belt due to condensation. [Figure 9] FIG. 2 is a schematic diagram showing an example of a condition in which condensation occurs inside an image forming apparatus; [Figure 10] 5 is a graph illustrating a change in surface potential of a photosensitive drum depending on the presence or absence of condensation. FIG. [Figure 11] FIG. 11 is a timing chart showing an outline of an example of an operation during idling. [Figure 12] FIG. 11 is a flowchart illustrating an example of an operation of a print job. [Figure 13] FIG. 10 is a flowchart illustrating another example of the operation of a print job. [Figure 14] FIG. 11 is a timing chart outlining another example of operations during a print job. [Figure 15] FIG. 11 is a timing chart outlining another example of operations during a print job. [Figure 16] FIG. 11 is a schematic cross-sectional view of another example of an image forming apparatus. [Figure 17] FIG. 11 is a timing chart showing another example of the operation during the idling operation. [Figure 18] FIG. 10 is a flowchart illustrating another example of the operation of a print job. [Figure 19] 11 is a graph showing a detection waveform when diffusely reflected light from sand on the intermediate transfer belt is detected by an optical sensor. FIG. [Figure 20]11 is a graph showing a detection waveform when regular reflection light from sand on the intermediate transfer belt is detected by an optical sensor. FIG. [Figure 21] FIG. 10 is a flowchart illustrating another example of the operation of a print job. [Figure 22] FIG. 10 is a flowchart illustrating another example of the operation of a print job. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] 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 embodiments may be changed as appropriate depending on the configuration of the apparatus to which the invention is applied and various conditions, and the scope of the invention is not limited to the following embodiments.

[0015] [Example 1] 1. Overall configuration and operation of the image forming apparatus 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 type laser beam printer employing an intermediate transfer system that 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 a signal (information) input from an external device connected to the image forming apparatus 100, for example, an image reading device or a host computer such as a personal computer.

[0016] Image forming apparatus 100 has four image forming units Sa, Sb, Sc, and Sd as a plurality of image forming units (stations) inside (inside) housing (exterior cover) 120 of device 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).

[0017] The configuration of each image forming unit S is substantially 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 a voltage or potential (or potential difference) refers to the magnitude (high / low) when compared in absolute value unless otherwise specified. In the image forming apparatus 100, since paper is mainly used as the recording material P, the recording material P may be referred to as paper, but the recording material P may also include materials other than paper or materials including materials other than paper.

[0018] 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.

[0019] 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 driving motor provided in a driving 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 drive of the photosensitive drum 1 is started.

[0020] 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 the 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 toward the photosensitive drum 1 with a predetermined pressing force. The charging roller 2 rotates 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 section).

[0021] The surface of the rotating photosensitive drum 1 that has been charged is scanned and exposed by an exposure device (laser scanner unit) 3 as an exposure means in response to an image signal, and an electrostatic latent image (electrostatic image) of a color component corresponding to each image forming section 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 the exposure devices 3a, 3b, 3c, and 3d in response to an image signal of a color component corresponding to each image forming section 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.

[0022] The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by supplying toner as a developer by a developing device (developing unit) 4 as a developing means, and a toner image (toner image, developer image) is formed on the photosensitive drum 1. The developing device 4 has a developing container 41 that contains toner, which is a non-magnetic one-component developer as a developer, and a developing roller 42 as a developing member (developer carrier). During development, the developing roller 42 is brought into contact with the surface of the photosensitive drum 1. Also, during development, the developing roller 42 is rotationally driven by a driving force transmitted from a driving motor provided in a driving unit 90 (FIG. 2) as a driving means. In this embodiment, the developing roller 42 is rotationally driven at a circumferential speed of 300 mm / sec in a rotation direction in which the surface of the developing roller 42 moves in the same direction as the surface of the photosensitive drum 1 at the contact portion between the photosensitive drum 1 and the developing roller 42. In this way, by rotating the developing roller 42 at 1.5 times the speed of the photosensitive drum 1, development can be stably performed. The developing roller 42 carries the toner contained in the developing container 41 and conveys the toner to a developing position where the photosensitive drum 1 and the developing roller 42 are in contact with each other. During development, a developing 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 developing power source (high voltage power source) 25 (FIG. 2) as a developing voltage application means (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 attaches the toner charged to the same polarity (negative in this embodiment) as the charging polarity of the photosensitive drum 1 by the charging roller 2 to a portion (image portion) on the photosensitive drum 1 where the potential has been reduced by exposure (reverse development method). However, the present invention can also be applied to an image forming apparatus which performs development using toner charged to the polarity opposite to the charging polarity of the photosensitive drum 1.

[0023] 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 respect to 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 in which the developing roller 42 contacts the photosensitive drum 1 by a pressure spring, which is a biasing member serving as a biasing means. The contact / separation mechanism 80 is configured to move (rotate) 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 is configured to allow the developing container 41 to move (rotate) by 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) as a driving means. The developing roller 42 is rotationally driven when brought into contact with the photosensitive drum 1, and stops rotating when separated from the photosensitive drum 1.

[0024] 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 paper GF-C081 made by Canon Inc. The solid density was measured using a handheld densitometer eXact made by X-rite Inc.

[0025] 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 area potential Vd) of −600 V. In this embodiment, the exposure amount (laser light amount: μJ / cm 2 ) of the exposure device 3 is adjusted so that the surface potential (light area potential VL) of the photosensitive drum 1 after exposure by the exposure device 3 is −200 V. 2 In this embodiment, a developing voltage of −350 V is applied to the developing roller 42 during development.

[0026] In this embodiment, the charging roller 2, the exposure device 3, the developing device 4, etc. of each image forming section S constitute a toner image forming means for forming a toner image.

[0027] Opposing the four photosensitive drums 1, an intermediate transfer belt 10, which is an intermediate transfer body formed of a rotatable endless belt as a second image carrier that carries a toner image, is arranged. The intermediate transfer belt 10 is stretched around three axes of first, second, and third tension rollers 11, 12, and 13 as a plurality of tension rollers. The first tension roller 11, together with the third tension roller 13, forms a surface onto which the toner image of the intermediate transfer belt 10 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 a driving force to the intermediate transfer belt 10, and also functions as an opposing roller of the 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) as the third tension roller 13 is rotated by a driving force transmitted from a driving motor provided in a driving unit 90 (FIG. 2) as a driving means. The intermediate transfer belt 10 is rotated at a circumferential speed (about 200 mm / sec) corresponding to the circumferential speed of the photosensitive drum 1. The first and second tension rollers 11 and 12 are rotated 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 as primary transfer means, are arranged on the inner circumferential surface side of the intermediate transfer belt 10 in correspondence with the photosensitive drums 1a, 1b, 1c, and 1d, respectively. The primary transfer roller 6 comes into contact with the inner circumferential surface of the intermediate transfer belt 10 and presses the intermediate transfer belt 10 toward the photosensitive drum 1, thereby forming a primary transfer portion (primary transfer nip) N1 which is a 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.

[0028] The toner image formed on the photosensitive drum 1 is transferred (primary transfer) onto the rotating intermediate transfer belt 10 as a transfer target by the action of the primary transfer roller 6 in the primary transfer section N1. 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 source (high voltage power source) 23 as a primary transfer voltage application means (primary transfer voltage application section). In this embodiment, a primary transfer voltage of +500V is applied to the primary transfer roller 6 during the primary transfer. For example, when a full-color image is formed, the toner images of each color of yellow, magenta, cyan, and black formed on the four photosensitive drums 1a, 1b, 1c, and 1d are transferred in sequence onto the intermediate transfer belt 10 so as to be superimposed on each other. As a result, four-color toner images corresponding to the target 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 "-" indicates a range including the numerical values ​​before and after the range), and is capable of outputting a negative voltage in the range of -200V to -2000V. In this embodiment, a configuration in which a voltage is applied from a common primary transfer power supply 23 to a plurality of primary transfer rollers 6 will be described, but the present invention is not limited to such a configuration. The present invention can also be applied to a configuration in which a plurality of primary transfer power supplies are provided corresponding to the respective primary transfer rollers 6.

[0029] Here, in this embodiment, the intermediate transfer belt 10 is configured as 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 of a material in which a quaternary ammonium salt, an ion conductive agent serving as an electrical resistance regulator, is dispersed in a polyethylene naphthalate resin, 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, but molding methods other than blow molding 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 surface side of the intermediate transfer belt 10. The surface layer is a layer having a thickness of 3 μm, formed of a material in which antimony-doped zinc oxide as an electrical resistance regulator is dispersed in an acrylic resin as a base material, and polytetrafluoroethylene (PTFE) particles as a solid lubricant are added. Examples of methods for forming the surface layer include dip coating, spray coating, flow coating, shower coating, roll coating, spin coating, and ring coating. In the intermediate transfer belt 10 of this embodiment, the base layer obtained by blow molding is fitted to the outer periphery of a cylindrical mold, the ends are sealed, and the mold is immersed in a container filled with a surface layer liquid, and the intermediate transfer belt 10 is pulled up so that the relative speed between the liquid level of the curable composition and the base layer is constant, thereby forming a coating film made of the surface layer liquid on the surface of the base layer.

[0030] In this embodiment, the volume resistivity of the intermediate transfer belt 10 is 1×10 10 The resistivity is Ω·cm. The volume resistivity of the intermediate transfer belt 10 was measured by connecting a UR probe (model MCP-HTP12) to a Hiresta-UP (MCP-HT450) manufactured by Mitsubishi Chemical Corporation, applying a voltage of 100 V, and measuring for 10 seconds. The environment of the measurement room in which the volume resistivity of the intermediate transfer belt 10 was measured 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 it was left in the measurement room for 4 hours. In this embodiment, 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 with a handy glossmeter IG-320 manufactured by Horiba, Ltd. In this embodiment, the peripheral length of the intermediate transfer belt 10 was 800 mm.

[0031] In this embodiment, the primary transfer roller 6 is made of a nickel-plated steel rod having an outer diameter of 5 mm and a volume resistivity of 10 5 It is a roller with an outer diameter of 11 mm, covered with a foamed sponge body mainly composed of NBR and epichlorohydrin rubber, adjusted to a resistance of 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 a load of 500 g was applied, when measured using an Asker hardness tester type C.

[0032] A secondary transfer roller 20, which is a roller-type secondary transfer member serving as a secondary transfer means, is disposed at a position facing the third tension roller 13 on the outer peripheral surface side of the intermediate transfer belt 10. The secondary transfer roller 20 contacts the outer peripheral surface of the intermediate transfer belt 10 and is pressed against the third tension roller 13 disposed at a position facing the secondary transfer roller 20 via the intermediate transfer belt 10 with a pressure of 50 N. As a result, the secondary transfer roller 20 forms a secondary transfer portion (secondary transfer nip) N2, which is a 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) onto a recording material P serving as a transfer target, which is conveyed while being sandwiched between the intermediate transfer belt 10 and the secondary transfer roller 20, at the secondary transfer portion N2. During the secondary transfer, a secondary transfer voltage (secondary transfer bias), which is a DC voltage of the polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment), is applied to the secondary transfer roller 20 by a secondary transfer power source 21 as a secondary transfer voltage application means (secondary transfer voltage application unit). When a voltage is applied from the secondary transfer power source (high voltage power source) 21, a current flows 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 from the secondary transfer power source 21 to the secondary transfer roller 20 is controlled so that the current flowing from the secondary transfer roller 20 to the third tension roller 13 via the intermediate transfer belt 10 is constant. The magnitude of the current for performing the secondary transfer is determined in advance depending on the installation environment (ambient environment) of the image forming apparatus 100 and the type of the recording material P. In this embodiment, the secondary transfer power source 21 can output a voltage in the range of +100 V to +4000 V. The third tension roller 13 is electrically grounded (connected to a 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 section.The recording material P is sent out from a cassette 51 by a feeding roller 50 as a feeding member, and is transported to a secondary transfer portion N2 by a pair of registration rollers 52 as a transport member in synchronization with the toner image on the intermediate transfer belt 10.

[0033] In this embodiment, the secondary transfer roller 20 is made of a nickel-plated steel rod having an outer diameter of 8 mm and a volume resistivity of 10 8 It is a roller with an outer diameter of 18 mm, covered with a foamed sponge body mainly composed of NBR and epichlorohydrin rubber, adjusted to a resistance of Ω·cm and a thickness of 5 mm. In this embodiment, the rubber hardness of the foamed sponge body constituting the secondary transfer roller 20 was 30° under a load of 500 g when measured using an Asker hardness tester type C.

[0034] The recording material P onto which the toner image has been transferred is conveyed to a fixing device 30 as a fixing means. The fixing device 30 has 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 heats and presses the recording material P carrying the unfixed toner image in a fixing section (fixing nip) which is a contact section between the fixing roller 31 and the pressure roller 32, and fixes (melts and adheres) the toner image onto the recording material P. For example, when a full-color image is formed, 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 (outside the machine) of the housing 120 of the device main body 110 through a paper discharge port (recording material discharge port) 130 as an opening formed in the housing 120 of the device main body 110. The recording material P is loaded on a tray 70 provided on the upper part of a housing 120 of the apparatus main body 110 .

[0035] Meanwhile, 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 contains 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 off the surface of the rotating photosensitive drum 1 with the cleaning blade 71, and contains it in the cleaning container 72.

[0036] In addition, the toner (secondary transfer residual toner) remaining on the surface of the intermediate transfer belt 10 after the secondary transfer is charged to a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) by the conductive brush 16 as a toner charging member. Then, this toner moves to the photosensitive drum 1 at the primary transfer portion N1, for example, the primary transfer portion N1a at the most upstream in the rotation direction (movement direction of the surface) of the intermediate transfer belt 10, and is collected by the 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 source (high voltage power source) 17 as a cleaning voltage application means (cleaning voltage application portion). Thus, in this embodiment, the 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 by using the conductive brush 16. In this embodiment, the conductive brush 16 has a density of 200 F / mm 2 , pile length is 5mm, pile rows are 3 rows, raw yarn resistance is 10 10The conductive brush 16 is made of conductive pile yarns mainly composed of Ω conductive nylon. The conductive brush 16 is in contact with the outer peripheral surface of the intermediate transfer belt 10. The conductive brush 16 is disposed at a position downstream of the secondary transfer portion N2 and upstream of the primary transfer portion N1 (the most upstream primary transfer portion N1a) in the rotation direction of the intermediate transfer belt 10. In this embodiment, the conductive brush 16 is pressed against the third tension roller 13 disposed at a position facing the conductive brush 16 across the intermediate transfer belt 10 so that the conductive pile yarns penetrate into the intermediate transfer belt 10 by 1 mm or more. In this embodiment, the conductive brush power source 17 is capable of outputting a voltage in the range of +100V to +4000V.

[0037] The image forming apparatus 100 of this embodiment can form a full-color print image by the above-mentioned 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 form a multi-color print image using only some of the multiple image forming units S.

[0038] In this embodiment, in each image forming section 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 device body 110 of the image forming apparatus 100 via mounting means such as a mounting guide and a positioning member provided in the device body 110 of the image forming apparatus 100. In this embodiment, the device body 110 is the portion of the image forming apparatus 100 excluding the process cartridges 7.

[0039] The image forming apparatus 100 is also provided with an optical sensor 60 that is used when performing correction control to correct color shift and density of an image formed in the image forming apparatus 100 and when detecting a condensation state. The optical sensor 60 is disposed so as to detect the surface (outer peripheral surface) of the intermediate transfer belt 10 and the toner thereon at a position (detection position) D downstream of the primary transfer portion N1 (the most downstream primary transfer portion N1d) and upstream of the secondary transfer portion N2 in the rotation direction of the intermediate transfer belt 10. 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.

[0040] The above-described operations are repeated when performing continuous printing to continuously form print images 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 of paper.

[0041] 2. Control configuration 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.

[0042] 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 a 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 signal) 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 of a dither matrix.

[0043] 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 according to instructions from a CPU 201, which will be described later. In the image forming apparatus 100 of this embodiment, the 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.

[0044] The DC controller 200 includes a CPU (arithmetic processing unit) 201 as an arithmetic processing unit, a memory (storage unit) 202 including a ROM, a RAM, etc. as a storage unit. The DC controller 200 controls the operation of each unit of the image forming apparatus 100 by executing processing according to programs and data stored in advance in the memory 202 in the CPU 201. 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 driving unit 90, the contact / separation mechanism 80, etc., and performs the formation of an electrostatic latent image, the transfer of a developed toner image, etc., 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 includes 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 the operation of an operator such as a user or a service representative, etc. The operation unit 150 may include a touch panel that functions as both a display means and an input means.

[0045] The DC controller 200 (CPU 201) also performs a process of receiving a signal from the optical sensor 60, which is used when performing correction control for correcting color shift and density of an image formed in the image forming apparatus 100 and when detecting a condensation state. For example, in the above correction control, the optical sensor 60 detects the amount of reflected light from a test pattern (toner image for detection) formed on the outer circumferential surface of the intermediate transfer belt 10 at a position facing 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 is 0V to 3.3V. 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 result by the optical sensor 60 to perform density correction and color shift correction. In this embodiment, as a method of density correction control, a correction curve of an image signal is created so that a desired density curve can be obtained based on the detection result of a test pattern for density detection (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. The detection of the condensation state will be described in detail later.

[0046] In this embodiment, the primary transfer power source 23 is shared by the four image forming units S as described above. In this embodiment, the charging power source 24, the developing power source 25, and the contact / separation mechanism 80 are provided independently for each image forming unit S, although not shown. The charging power source 24, the developing power source 25, and the contact / separation mechanism 80 may 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 a drive transmission member. The drive unit 90 includes a drive motor for driving the photosensitive drum 1, the developing roller 42 of the developing device 4, the intermediate transfer belt 10 (the third tension roller 13), the contact / separation mechanism 80, and the like. The drive motors for driving each of these members may be provided independently, or the drive motors for driving at least some of these members may be shared. The drive motors for driving the members for each color may be provided independently, or the drive motors for driving at least some of the members for each color may be shared. In this embodiment, in each image forming station S, the photosensitive drum 1 and the developing roller 42 of the developing device 4 can be rotated and stopped independently.

[0047] Here, a print job (print operation, print sequence, image forming operation, image forming sequence) is a series of operations that are started by one start instruction and form and output an image on one or more recording materials P. A print job generally has an image forming process, a pre-rotation process, a 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 an image that is actually formed on a recording material P and output is formed, a toner image is formed, and the toner image is primarily transferred, secondary transferred, and fixed, and the image forming time refers to this period. More specifically, the timing of the image forming time differs depending on the position where each process of charging, exposure, development, primary transfer, secondary transfer, and fixing is performed. The pre-rotation process is a period during which a preparatory operation is performed before the image forming process from when a start instruction is input until the image formation actually starts. The paper-interval process is a period corresponding to the period between recording materials P when image formation is continuously performed 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 above-mentioned pre-rotation process, the sheet interval process, the post-rotation process, and further the pre-multiple rotation process which is a preparatory operation when the image forming apparatus 100 is turned on or when the image forming apparatus 100 returns from a sleep state.

[0048] 3.Optical Sensor 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.

[0049] In this embodiment, the image forming apparatus 100 is provided with a front optical sensor 60F and a rear optical sensor 60R as the optical sensor 60. In the width direction, which is substantially perpendicular to the moving direction of the surface of the intermediate transfer belt 10, the front optical sensor 60F is disposed forward of the center, and the rear optical sensor 60R is disposed rear of the center. The optical sensors 60 (60F, 60R) are held by a holding member 65 made of an electrically grounded metal plate. The holding member 65 is supported by the rotating shaft of the first tension roller 11, and the distance between the intermediate transfer belt 10 and the optical sensor 60 (60F, 60R) is always constant with respect to the inclination of the first tension roller 11. In this embodiment, the optical sensor 60 (60F, 60R) is disposed so that the distance between the intermediate transfer belt 10 and the optical sensor 60 (60F, 60R) is 3 mm.

[0050] In this embodiment, the front optical sensor 60F and the rear optical sensor 60R have substantially the same configuration, so the front optical sensor 60F will be described as a representative (F and R indicating the front or rear optical sensor 60 will be omitted as appropriate).

[0051] FIG. 4 is a cross-sectional view for explaining the configuration of the optical sensor 60. The optical sensor 60 is configured with a light-emitting element 61, a first light-receiving element 62, a second light-receiving element 63, a holder 64, and the like. The light-emitting element 61 is configured with an LED, and the first light-receiving element 62 and the second light-receiving element 63 are each configured with a phototransistor, and 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. Then, reflected light 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, a light-emitting element that emits infrared light with a peak wavelength of 800 nm is used as the light-emitting element 61, and a light-receiving element whose light-receiving sensitivity is peaked at a wavelength of 800 nm is used as the first and second light-receiving elements 62 and 63.

[0052] 4 is substantially perpendicular to the surface of the intermediate transfer belt 10. The light emitting element 61 is disposed at an inclination of 15° with respect to the normal line G. The shape of the light guide path is adjusted by the holder 64 so that the spot diameter when infrared light is irradiated from the light emitting element 61 to the intermediate transfer belt 10 is 2 mm. The first light receiving element 62 is disposed at an inclination 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 inclination 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.

[0053] 4. Waveform of reflected light from the surface of the intermediate transfer belt detected by the optical sensor Next, a description will be given of the waveform (detection waveform) of the detection signal (detection output) showing the detection result when the optical sensor 60 detects reflected light from the surface of the intermediate transfer belt 10. Here, the detection waveform acquired by the front optical sensor 60F will be described, but the same tendency can be seen 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). Also, F and R indicating the front or rear optical sensor 60 will be omitted as appropriate.

[0054] FIG. 5 is a graph showing the detection waveforms when the first and second light receiving elements 62 and 63 detect the reflected light from the surface of the intermediate transfer belt 10. FIG. 5 shows the detection waveforms when no condensation occurs inside the image forming apparatus 100. (a) in FIG. 5 is a detection waveform showing the detection result (specular reflection light and diffuse reflection light) by the first light receiving element 62, and (b) in FIG. 5 is a detection waveform showing the detection result (diffuse reflection light) by the second light receiving element 63. The light emitting element 61 is driven in the section (i) in FIG. 5, and as a result of detecting the reflected light in this section (i), the detection result by the first light receiving element 62 is about 3.0 V, but the detection result by the second light receiving element 63 is lower than this. That is, in the section (i), the reflected light amount detected by the second light receiving element 63 is lower than the reflected light amount detected by the first light receiving element 62. This is because most of the reflected light 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 the detection result by the first light receiving element 62 is about 3.0 V when the first light receiving element 62 detects the reflected light from the intermediate transfer belt 10. In this embodiment, the optical sensor 60 is configured so that the output of the detection signal indicating the detection result of the first light receiving element 62 increases as the amount of light received by the first light receiving element 62 increases. In the section (ii) in FIG. 5, the intermediate transfer belt 10 rotates, and it can be seen that the amount of reflected light detected by the first and second light receiving elements 62 and 63 varies depending on the surface properties of the intermediate transfer belt 10.

[0055] 5. Waveform of reflected light from a toner patch detected by an optical sensor Next, a description will be given of the waveform (detection waveform) of the detection signal (detection output) indicating the detection result when the optical sensor 60 detects reflected light from a toner patch (a toner image for detection that constitutes a test pattern) on the intermediate transfer belt 10.

[0056] Fig. 6 is a graph showing, as an example, detection waveforms when reflected light from a solid yellow toner patch having a length of 10 mm in the rotation direction of the intermediate transfer belt 10 is detected by the first and second light receiving elements 62, 63. (a) in Fig. 6 is a detection waveform showing the detection result (specular reflection light and diffuse reflection light) by the first light receiving element 62, and (b) in Fig. 6 is a detection waveform showing the detection result (diffuse reflection light) by the second light receiving element 63.

[0057] 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 lot of specularly reflected light, so the detection result by the first light receiving element 62 is about 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 about 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.

[0058] Next, the detection waveform by the second light receiving element 63 ((b) in FIG. 6) will be described. The second light receiving element 63 hardly detects reflected light from the intermediate transfer belt 10, but detects a lot of reflected light from the toner patch, and the detection result by the second light receiving element 63 is about 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 reflected light from the toner patch, the detection result by the second light receiving element 63 is about 3.0 V. In this embodiment, the optical sensor 60 is configured so that the output of the detection signal indicating the detection result of the second light receiving element 63 becomes larger as the amount of light received by the second light receiving element 63 becomes larger.

[0059] 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 Next, a description will be given of an operation of driving the optical sensor 60 during a print job in this embodiment and detecting reflected light from the surface (base) of the intermediate transfer belt 10. As an example, a detection operation using the front optical sensor 60F will be described.

[0060] FIG. 7 is a timing chart showing an outline of the operation of each part during a print job in this embodiment. FIG. 7 shows an outline of the operation of each part when a print job for continuously printing three sheets of A4 paper (here, simply referred to as a "three-sheet print job") is executed as an example. FIG. 7 shows the rotation drive timing of the photosensitive drum 1, the rotation 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 emission timing of the light emitting element 61), and the sampling timing which is a data acquisition period for calculating and processing the detection result by the first light receiving element 62. In this embodiment, the photosensitive drums 1a, 1b, 1c, and 1d rotate and stop synchronously. In this embodiment, the surface of the photosensitive drum 1 is substantially always charged by the charging roller 2 when the photosensitive drum 1 is rotating during a print job, except during an idling operation to be described later. 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 effects as in this embodiment can be obtained in a print job in monochrome mode.

[0061] 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 reaches the development position (the contact portion between the photosensitive drum 1 and the developing roller 42). Also, 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.

[0062] 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 in the transport direction of the A4 paper. This indicates that in this section, each of the photosensitive drums 1a, 1b, 1c, and 1d is exposed by each of the exposure devices 3a, 3b, 3c, and 3d according to the image signal as described above. FIG. 7 shows the timing of image formation in the yellow image forming unit Sa as a representative, and the timing of image formation in the magenta, cyan, and black image forming units 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 of the photosensitive drums 1a, 1b, 1c, and 1d. This electrostatic latent image is developed by supplying toner by the developing rollers 42a, 42b, 42c, and 42d at the developing position, and a toner image of each color of yellow, magenta, cyan, and black is formed on each of the photosensitive drums 1a, 1b, 1c, and 1d. The toner images formed on each of the photosensitive drums 1a, 1b, 1c, and 1d are transferred in sequence so as to be superimposed on the same image forming area (area where a toner image can be formed) on the intermediate transfer belt 10. As a result, a predetermined image to be transferred to each recording material P (three sheets of A4 paper in the example of FIG. 3) is formed in sequence on the intermediate transfer belt 10. As described above, in this embodiment, in continuous printing in which print images are formed continuously on multiple A4 sheets, the interval (paper interval) 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 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 interval (paper gap) between the rear end of the previous image forming area on the intermediate transfer belt 10 and the front end of the next image forming area 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 transport direction and on one and the other ends of the recording material P in the width direction approximately perpendicular to the transport 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 the other ends in the width direction).

[0063] 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. Also, in this embodiment, the first light receiving element 62 detects specularly reflected light from the surface of the intermediate transfer belt 10.

[0064] 6-2. Timing of detecting reflected light from the surface of the intermediate transfer belt during a print job The sampling timing of the detection result by the first light receiving element 62 in this embodiment will be described.

[0065] In this embodiment, the DC controller 200 samples the detection results by the first light receiving element 62 in sampling sections (1), (2), (3), and (4) in FIG. 7 during a print job. In addition, in this embodiment, the DC controller 200 samples the detection results by the first light receiving element 62 at intervals of 0.1 mm when viewed in terms of the surface movement distance of the intermediate transfer belt 10 in each of the above sampling sections. The sampling section (1) in FIG. 7 is set to be from the timing when the light emitting element 61 is turned on by driving the optical sensor 60 to the timing when the leading edge of the image forming area (here, also referred to as the "first image forming area") on the intermediate transfer belt 10 where the image to be transferred to the first recording material P is formed reaches the detection position D of the optical sensor 60 (the position of the spot of the light irradiated by the light emitting element 61 in the rotation direction of the intermediate transfer belt 10). 7 is from the timing 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 the timing 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 section (3) in FIG. 7 is from the timing 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 the timing 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 section (4) in FIG. 7 is from the timing 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 the timing when the drive of the intermediate transfer belt 10 is turned off.

[0066] 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 forming 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 reflected light from the surface of the intermediate transfer belt 10 without being affected by the toner image on the intermediate transfer belt 10.

[0067] Note that FIG. 7 shows an example of a print job for three sheets, but if a print job for four or more sheets is performed, it is sufficient to increase 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, similar to the sampling sections (2) and (3) described above.

[0068] 6-3. Detection results of reflected light from the surface of the intermediate transfer belt when there is no condensation Next, a description will be given of the results of an experiment that examines the relationship between the number of prints, the detection result by the first light receiving element 62, and the print image when no condensation occurs inside the image forming apparatus 100. Under normal conditions when no condensation occurs 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 described with reference to FIG.

[0069] 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 print job of 50 sheets was performed using paper with a moisture content of 9.0 wt% as the recording material P in an environment of a temperature of 30°C and a humidity (relative humidity) of 80%.

[0070] In Table 1, the detection result by the first light receiving element 62 indicates an average value for every 5 sheets. Here, the average value of the detection result by the first light receiving element 62 for every 5 sheets was obtained from 100 sampling results (sampling data) for each number of prints. That is, in this embodiment, the DC controller 200 obtains an average value of the detection results (sampling data) of the amount of reflected light from the surface of the intermediate transfer belt 10 while the intermediate transfer belt 10 rotates by 10 mm for each number of prints (sampling section). The sampling timing for the first sheet is the timing until the leading edge of the image forming area of ​​the first sheet on the intermediate transfer belt 10 reaches the detection position D of the optical sensor 60, and corresponds to the sampling section (1) in FIG. 7. The sampling timings for the second to 49th sheets are the timings corresponding to the sampling sections (2) or (3) in FIG. 7, and are sampling sections between the trailing edge of the image forming area of ​​each number of prints on the intermediate transfer belt 10 and the leading edge of the next image forming area. 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 the sampling section (4) in FIG.

[0071] Here, the print images were repeated in a set of five sheets in the following order: one character image, one halftone image with a density of 0.8, one solid image, and two solid white sheets. The image confirmation results are shown as the number of prints at the time when the character image, which is the first print in the set of five, is printed. For example, the confirmation results of the first character image, the second halftone image, and the third solid image are shown in the column for the first sheet.

[0072] In Table 1, the image quality level is indicated by alphabetical notation in the columns for text, halftone, solid, and other defects. "A" indicates no problem at all. "B" indicates slight image defects, and for text, it indicates slight fading, for halftone and solid, it indicates image density lower than the standard density, and for other defects, it indicates slight toner staining. In the following explanation, image density lower than the standard density is referred to as "low density". "C" indicates clear image defects, and for text, it indicates clear fading, for halftone and solid, it indicates clear low density, and for other defects, it indicates toner staining. In Table 1, the column for the 50th sheet has "no data" because there is no image quality check result.

[0073] [Table 1]

[0074] As shown in Table 1, under normal conditions where no condensation is occurring inside the image forming apparatus 100, the amount of light reflected from the intermediate transfer belt 10 is roughly constant, so that the average value of the detection result by the first light receiving element 62 is around 3.0 V at any given time.

[0075] Also, as shown in Table 1, there were no problems with image quality for any number of prints.

[0076] 6-4. Detected waveform of reflected light from the surface of the intermediate transfer belt when condensation is present Next, we will explain the detection waveform when the optical sensor 60 detects reflected light from the surface of the intermediate transfer belt 10 in a case where condensation occurs inside the image forming apparatus 100 and water droplets adhere to the surface of the intermediate transfer belt 10.

[0077] Fig. 8 is a graph showing a detection waveform when the first light receiving element 62 detects reflected light from the surface of the intermediate transfer belt 10 in a state where water droplets are attached 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 in the absence of condensation shown in Fig. 5 was obtained.

[0078] In the detection waveform of (a) in Fig. 5 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 about 3.0 V. In contrast, in the detection waveform of Fig. 8 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 about 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.

[0079] Furthermore, when comparing the detection waveform in (a) of FIG. 5 with the detection waveform in FIG. 8, the detection waveform in FIG. 8 has a larger deviation in the detection result by the first light receiving element 62 in section (ii) than the detection waveform in (a) of FIG. 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 in (a) of FIG. 5 is not seen in the detection waveform in FIG. 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.

[0080] 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 is reduced by 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 a detection result when water droplets have adhered to the surface of the intermediate transfer belt 10. According to the study by the present inventors, the more water droplets that adhere to the surface of the intermediate transfer belt 10, the lower the average value of the amount of light reflected from the surface of the intermediate transfer belt 10 (detection result by the first light receiving element 62) becomes, and the deviation of the amount of reflected light (detection result by the first light receiving element 62) tends to become larger.

[0081] Here, the 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 more, more preferably 80 or more. The surface gloss of the intermediate transfer belt 10 may be 100. Moreover, 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. Moreover, as described above, the surface gloss of the intermediate transfer belt 10 can be measured by a commercially available measuring device, for example, a handy gloss meter IG-320 by Horiba, Ltd. In order to distinguish between the reflected light from the surface of the intermediate transfer belt 10 and the reflected light from water droplets attached to the surface of the intermediate transfer belt 10, it is preferable that the surface gloss unevenness of the intermediate transfer belt 10 is less because it is easier for a difference in reflected light to occur. Examples of a coating method for the surface layer of the intermediate transfer belt 10 having such a high gloss and minimal unevenness include dip coating and ring coating.

[0082] 6-5. Detection results of reflected light from the surface of the intermediate transfer belt when condensation is present Next, the results of an experiment similar to the experiment that gave the results in Table 1 when condensation did not occur, but conducted under conditions where condensation did occur (relationships between the number of prints, the detection results by the first light receiving element 62, and the print images) will be described. Here, the experiment was conducted under conditions where a ceiling fan was blowing air from the ceiling, which was the condition for condensation to occur inside the image forming apparatus 100.

[0083] Fig. 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.

[0084] 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.

[0085] [Table 2]

[0086] From Table 2, it can be seen that the average value of the detection result by the first light receiving element 62 tends to decrease as the number of printed sheets increases. This is for 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 port 130 of the image forming apparatus 100. Then, the water vapor pushed back into the interior of the image forming apparatus 100 comes into contact with the intermediate transfer belt 10, causing condensation, 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.

[0087] Furthermore, as shown in Table 2, no problems occurred with the text images up to the 41st sheet, but by the 46th sheet, the text had become faint.

[0088] Furthermore, as shown in Table 2, slight density loss was observed in the halftone image from the 16th sheet onwards, and significant density loss was observed from the 36th sheet onwards. This is because condensation inside the image forming apparatus 100 also caused condensation on the surface of the photosensitive drum 1, causing a change in the surface potential of the photosensitive drum 1.

[0089] Here, a description will be given of the phenomenon in which a density reduction in a halftone image occurs due to a change in the surface potential of the photosensitive drum 1. FIG.

[0090] FIG. 10(a) shows the surface potential of the photosensitive drum 1 under normal conditions where no condensation occurs inside the image forming apparatus 100. The dark area 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 through the charging position (roughly the contact portion between the photosensitive drum 1 and the charging roller 2) by the charging roller 2 to which a charging voltage is applied (before reaching the exposure position by the exposure device 3), the surface potential of the photosensitive drum 1 is uniformly charged to the dark area potential Vd. Thereafter, the surface of the photosensitive drum 1 is exposed by the exposure device 3 according to an image signal at the exposure position. As a result, the surface potential of the portion (image portion) of the surface of the photosensitive drum 1 exposed by the exposure device 3 becomes the light area potential VL. In addition, a development voltage Vdc is applied to the developing roller 42, and the toner on the developing roller 42 moves to the surface of the photosensitive drum 1 and adheres thereto due to a development contrast Vc, which is the potential difference between the development voltage (potential of the developing roller 42) Vdc and the light area potential VL. In addition, the back contrast Vb, which is the potential difference between the dark potential Vd and the developing voltage Vdc, affects so-called fogging, which is the movement of toner from the developing roller 42 to the portion (non-image portion) of the photosensitive drum 1 at the dark potential Vd. 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 denser the halftone image tends to be.

[0091] 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 due to condensation on the surface of the intermediate transfer belt 10 transfers to the surface of the photosensitive drum 1, or when air 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 charge of the photosensitive drum 1 by the charging roller 2 is formed by a discharge current from the charging roller 2 to the photosensitive drum 1. Such a discharge occurs in at least one of the minute gaps formed between the charging roller 2 and the photosensitive drum 1 on the upstream side and downstream side of the contact portion between the charging roller 2 and the photosensitive drum 1 in the rotation 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 current flows directly from the charging roller 2 to the photosensitive drum 1 at the contact portion 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 smaller 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 low density of the halftone image.

[0092] Also, as shown in Table 2, slight density deficiency was observed in the solid image from the 31st sheet, and significant density deficiency was observed from the 41st sheet onwards. The density deficiency of the solid image is caused by the decrease in the development contrast Vc' as shown in FIG. 10(b), which reduces the movement of the toner on the development roller 42 to the photosensitive drum 1, as described above. In other words, when the amount of movement of the toner on 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%. Also, as shown in FIGS. 10(a) and 10(b), the primary transfer contrast Vt' when condensation is present is increased by the increase in the light area potential VL', compared to the primary transfer contrast Vt, which is the potential difference between the light area potential VL and the primary transfer voltage Vt1 when there is no 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 phenomenon known as retransfer, resulting in a low density solid image.

[0093] 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 occurred due to a mixture of yellow, magenta, cyan, and black toners. This occurs when the 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 the 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.

[0094] 6-6.Recovery process In this embodiment, the image forming apparatus 100 detects the amount of reflected light from the surface of the intermediate transfer belt 10 by the optical sensor 60 during a print job as described above. Then, when the image forming apparatus 100 determines that condensation has occurred inside the apparatus based on the detection result, as described later, it executes a condensation removal process to eliminate the condensation state (remove moisture) before an image defect caused by the condensation occurs. The condensation removal process is an example of an attachment removal process that removes attachments (moisture in this embodiment) on 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. Then, the image forming apparatus 100 resumes image formation for the print job after sufficiently removing moisture on the photosensitive drum 1 and the intermediate transfer belt 10 by the condensation removal process. Under the conditions of the experiment that gave the results in Table 2, it is found that after the eleventh sheet is printed, the printing is temporarily stopped without printing the twelfth sheet (also referred to as "interrupting the print job" here), and the condensation removal process is executed. Therefore, in this embodiment, based on the results in 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.

[0095] In this case, obtaining the detection result (detection signal) by the optical sensor 60 and controlling to execute a predetermined process such as dew condensation removal process is also referred to as simply detecting (determining) the dew condensation state. The same applies to detecting foreign matter such as sand, which will be described later.

[0096] 11 is a timing chart showing an overview of the operation of each part during the condensation removal process in this embodiment. The operation according to the timing chart in FIG.

[0097] In this embodiment, as the condensation removal process, an operation of rotating each of 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) is performed. In this embodiment, the predetermined time t for which the idle rotation operation continues is set to 15 seconds.

[0098] Here, during the idling operation, it is preferable to separate the developing roller 42 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 the developing voltage does not need to be applied to the developing roller 42 during the idling operation. In this embodiment, the developing roller 42 is separated from the photosensitive drum 1 during the idling operation, the rotation of the developing roller 42 is stopped, and the developing voltage is not applied to the developing roller 42. However, for example, in a case where 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.

[0099] In this embodiment, the charging voltage is not applied to the charging roller 2 during the idling operation. However, the charging bias may be applied to the charging roller 2 during the idling operation, for example, in the same manner as in the image formation. In this case, in a configuration in which the idling operation is performed with the developing roller 42 in contact with the photosensitive drum 1, the developing voltage may be applied to the developing roller 42, for example, in the same manner as in the image formation. In addition, in this embodiment, the intermediate transfer belt 10 is in contact with each of the photosensitive drums 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 addition, in this embodiment, the primary transfer voltage is not applied to the primary transfer roller 6 during the idling operation. However, the primary transfer voltage may be applied to the primary transfer roller 6 during the idling operation, for example, in the same manner as in the image formation. In this embodiment, the secondary transfer voltage is not applied to the secondary transfer roller 20 during the idling operation. However, the secondary transfer voltage may be applied to the secondary transfer roller 20 during the idling operation, for example, in the same manner as during image formation.

[0100] In an experiment under the same conditions as the experiment that gave the results in Table 2, after printing the 11th sheet, the print job was interrupted and an idle rotation operation was performed for 15 seconds. Then, after the idle rotation operation, printing of the 12th sheet and after was resumed (here, it is also called "resuming the print job"). As a result, there was no slight low density of the halftone image, and the detection result of the first light receiving element 62 on the 16th sheet was 3.1 V. This is because the water droplets on the intermediate transfer belt 10 disappeared, and the light emitted by the light emitting element 61 was reflected on the surface of the intermediate transfer belt 10. The water droplets on the intermediate transfer belt 10 disappeared due to the idle rotation operation because the water droplets on the intermediate transfer belt 10 adhered to the conductive brush 16 and the secondary transfer roller 20, and were removed from the intermediate transfer belt 10, and further some of the water droplets evaporated. At this time, it is considered that the water droplets on the photosensitive drum 1 also disappeared in the same way, which suppressed the image defect. It is believed that the reason why the water droplets on the photosensitive drum 1 disappear during the idling operation is 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 believed that some of the water droplets on the photosensitive drum 1 are also removed by the drum cleaning device 5 during the idling operation.

[0101] In this embodiment, the idle rotation operation is performed for 15 seconds, but the execution time of the idle rotation operation is not limited to this. The execution time of the idle rotation operation may be set appropriately in consideration of the expected amount of water droplets and the time required to remove the water droplets. The execution time of the idle rotation operation is not limited to this, but can be, for example, about 5 seconds to 1 minute. In other words, the execution time of the idle rotation operation is not limited to this, but can be, for example, the time it takes the intermediate transfer belt 10 to make about 1 to 20 revolutions. 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 about 200 mm / sec, and the time it takes the intermediate transfer belt 10 to make one revolution is about 4 seconds.

[0102] Moreover, the deterioration of the detection result by the first light receiving element 62 and the timing of occurrence of image defects with an increase in the number of printed sheets 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 occurrence 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 members. Therefore, the print job may be interrupted and the intermediate transfer belt 10 may be idled based on the detection result by the first light receiving element 62 depending on the characteristics of the image forming apparatus 100.

[0103] 7. Control Procedure 12 is a flow chart showing an outline of the operation of the image forming apparatus 100 including the dew condensation detection operation and the dew condensation removal process in this embodiment.

[0104] 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 judges whether the average value R of the detection result by the first light receiving element 62 is 2.8V or less as a case where the average value R crosses the threshold value at a predetermined timing (sampling section (1) to (4)) described with reference to FIG. 7 (S12). When the average value R of the detection result by the first light receiving element 62 is 2.8V or less, this is an example of a case where a numerical value (voltage in this embodiment) related to a detection signal output by a light receiving element (first light receiving element 62 in this embodiment) of the optical sensor 60 receiving reflected light satisfies a predetermined condition. When the DC controller 200 judges in S12 that the average value R of the detection result by the first light receiving element 62 is 2.8V or less, it interrupts the print job and executes an idling operation (S13). Thereafter, the DC controller 200 judges whether or not the time t from the start of the idling operation has passed a predetermined time, 15 seconds in this embodiment (S14). If the DC controller 200 judges in S14 that the time t has not passed 15 seconds, it continues to execute the idling operation (S13). If the DC controller 200 judges in S14 that the time t has passed 15 seconds, it ends the idling operation, resumes the print job (S15), and performs the judgment of S12 again. On the other hand, if the DC controller 200 judges in S12 that the average value R of the detection result by the first light receiving element 62 is greater than 2.8 V, it judges whether or not all printing of the print job has been completed (S16). If the DC controller 200 judges 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 performs the determination in S12 again.

[0105] 8. Effects As described above, in this embodiment, the optical sensor 60 is driven during a print job, the first light receiving element 62 detects the reflected light from the surface of the intermediate transfer belt 10, and the transition of the average value of the detection result is monitored. In particular, in this embodiment, whether or not the average value of the detection result by the first light receiving element 62 becomes equal to or less than a predetermined threshold value during the print job is monitored. This makes it possible to determine the condensation state on the surface of the intermediate transfer belt 10 and further the surface of the photosensitive drum 1. In this embodiment, when the average value of the detection result by the first light receiving element 62 becomes equal to or less than the threshold value, it is determined that condensation has occurred on the surface of the intermediate transfer belt 10 and further the surface of the photosensitive drum 1. In this embodiment, in this case, the print job is interrupted before an image defect occurs, and an idling operation is performed to rotate each of the photosensitive drums 1a, 1b, 1c, and 1d and the intermediate transfer belt 10. As a result, even in a state in which wind from a ceiling fan flows into the interior of the image forming apparatus 100 and condensation occurs, water droplets attached to the photosensitive drum 1 and the intermediate transfer belt 10 can be removed, and good image quality can be maintained throughout the print job. 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 intermediate transfer belt 10 during a print job.

[0106] 9. Variations A modification of this embodiment will be described below.

[0107] 9-1. Method for detecting condensation and modified condensation removal process In this embodiment, the DC controller 200 is configured to execute the idling operation for a preset time, but the present invention is not limited to such a configuration. For example, the DC controller 200 may be configured to adjust the execution time of the idling operation according to the rate of change of the average value of the first light receiving element 62 during a print job (the amount of change per unit time, the amount of change per unit number of prints, etc.). In this case, for example, the DC controller 200 can control so that the execution time of the idling operation is increased as the rate of change of the average value of the first light receiving element 62 during a print job increases.

[0108] In addition, the dew condensation removal process is not limited to the idling operation. For example, the image forming apparatus 100 may be stopped for a predetermined time until the water droplets on the photosensitive drum 1 and the intermediate transfer belt 10 evaporate and the dew condensation state 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 the members acting on them (such as the charging roller 2 and the developing roller 42). Therefore, for example, a fan as a blowing means for sucking or exhausting air inside and outside the image forming apparatus 100, a heater as a heating means, a control means, and the like may be operating. The outline of the operation of the image forming apparatus 100 in this case is the same as that described using the flow chart of FIG. 12, but in S13, the image forming apparatus 100 is stopped after the print job is interrupted.

[0109] Also, during the idling operation as the condensation removal process or while the image forming apparatus 100 is stopped, for example, a heating means such as a heater of the fixing device 30 is heated to raise the temperature inside the image forming apparatus 100, thereby facilitating the evaporation of water droplets generated by condensation. The heating means is not limited to the heater of the fixing device 30, and may be, for example, a heater provided to heat any part of the image forming apparatus 100 such as the photosensitive drum 1, or a heater provided specially to eliminate the condensation state. Also, during the idling operation as the condensation removal process or while the image forming apparatus 100 is stopped, for example, a fan serving as a blowing means for sucking or exhausting air inside and outside the image forming apparatus 100 may be used to suck or exhaust air, thereby facilitating the discharge of moisture generated by the evaporation of water droplets to the outside of the apparatus.

[0110] In addition, in this embodiment, the print job is interrupted to perform the condensation removal process (idle rotation in this embodiment), but the condensation removal process may 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 in which the results in Table 2 were obtained, in the case of a print job of 20 sheets, only a slight density loss occurs in halftone images, but no noticeable image defects occur in other images. In addition, in the next print job, since the condensation has been removed, a good image can be obtained. In this way, by performing the condensation removal process when the print job is ended, there is an advantage that the occurrence of image defects can be suppressed to a minor one without causing downtime (a period during which images cannot be output) during the print job.

[0111] FIG. 13 is a flow chart showing an outline of the operation of the image forming apparatus 100 including the dew condensation state detection operation and the dew condensation removal process in this case. The operation according to the flow chart in FIG. 13 is controlled by the DC controller 200. When the print job is instructed by the controller 210, the DC controller 200 starts a print job of n sheets (S21). Next, the DC controller 200 judges whether or not all printing of the print job is completed (S22). If the DC controller 200 judges in S22 that all printing of the print job is completed, it judges whether or not the average value R of the detection result by the first light receiving element 62 is 2.8 V or less in the sampling section (4) described with reference to FIG. 7 (S23). If the DC controller 200 judges in S23 that the average value R of the detection result by the first light receiving element 62 is 2.8 V or less, it executes an idling operation when finishing the print job, and then executes a normal post-rotation process to finish the print job (S24). That is, in this case, when the print job is ended, the time from when the rear end of the image forming area of ​​the last page on the intermediate transfer belt 10 passes the detection position D until the rotation of the intermediate transfer belt 10 stops is longer than when only the normal post-rotation process is performed. Also, when 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, when the operation of the image forming apparatus 100 is stopped as a condensation removal process when the print job is ended, the DC controller 200 may postpone (prohibit) the start of the next print job until a predetermined stop time has elapsed, even if the next print job is instructed.

[0112] The DC controller 200 may be configured to select whether to interrupt the print job and execute the condensation removal process, or to execute the condensation removal process when the print job is ended. For example, the DC controller 200 can determine whether to form a predetermined image (e.g., a halftone image) that may cause low density during the print job based on the image data received by the controller 210 at the start of the print job. If there is no corresponding image, the DC controller 200 can control to execute the operation of FIG. 13 (execute the condensation removal process when the print job is ended), and if there is a corresponding image, to execute the operation of FIG. 12 (interrupt the print job and execute the condensation removal process). Note that, at the point of time when the DC controller 200 detects the condensation state by executing the operation of FIG. 12, it may determine whether to interrupt the print job and execute the condensation removal process, or to execute the condensation removal process when the print job is ended, depending on whether to form a predetermined image (e.g., a halftone image) that may cause low density thereafter. The halftone image is not limited to the one used in the above-mentioned experimental example, and may be, for example, an image in which the toner amount (area ratio of the image portion) is about 20% to 80% when the toner amount (area ratio of the image portion) of a solid image is 100%. Also, 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 ended, 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 a predetermined number or more, the print job may be interrupted and the condensation removal process may be performed, and if the number of prints is less than the predetermined number, the condensation removal process may be performed when the print job is ended. The same selection as above may be made based on the remaining number of prints at the time when the condensation state is detected.

[0113] In the present embodiment, the detection result of the reflected light amount from the surface of the intermediate transfer belt 10 by the first light receiving element 62 when no water droplets are attached on the intermediate transfer belt 10 is described as about 3.0 V. However, the output of the first light receiving element 62 obtained may vary depending on, for example, the amount of light emitted by the light emitting element 61, the sensitivity setting of the first light receiving element 62, and dirt on the light emitting element 61 and the first light receiving element 62. Therefore, the detection result of the reflected light amount 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 about 3.0 V. Also, for example, the DC controller 200 obtains an average value of the detection results of the reflected light amount 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 the average value in the memory 202 as an initial value. As the initial value of the detection result by the first light receiving element 62 at the start of a print job, for example, the value obtained in the above-mentioned sampling section (1) can be used. The DC controller 200 can determine whether or not 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, is set as a threshold, and when the amount of change is equal to or greater than the threshold value, it can be determined that condensation has occurred. Alternatively, it may be determined whether or not condensation has occurred 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, it can be determined that condensation has occurred when the average value of the detection result by the first light receiving element 62 has decreased by slightly less than 10% (for example, 7%) from the initial value or maximum value. In this way, it may be possible to monitor the degree of decrease (amount of change, for example, difference or ratio) 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. This can also provide the same effect as this embodiment.

[0114] 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 in this embodiment, and may be set appropriately depending on the desired accuracy of determining the condensation state. Also, deviation may 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.

[0115]

number

[0116] 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 with greater sensitivity than by calculating the average value. For example, when the calculated deviation is equal to or greater than a predetermined threshold value, it can be determined that the condensation state exists. 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 the condensation state exists.

[0117] 9-2. Modification of the timing for detecting condensation FIG. 14 is a timing chart showing an overview of the operation of each part 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 it is necessary to allow sufficient start-up time for the light-emitting element 61, 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 can be started so that the condensation state can be detected in the above-mentioned sampling sections (1), (2), (3), and (4). Other points of the operation according to the timing chart of FIG. 14 are substantially the same as the operation according to the timing chart of FIG. 7.

[0118] FIG. 15 is a timing chart showing an outline of the operation of each part 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 of a ceiling fan occurs due to water vapor generated from paper that has passed through the fixing device 30, so there is a low possibility that water droplets will adhere to the intermediate transfer belt 10 during image formation of the first sheet. In view of this, for example, as shown in FIG. 15, acquisition of the detection result by the first light receiving element 62 may be started from a sampling section (2) between the rear end of the image formation area of ​​the first sheet on the intermediate transfer belt 10 and the front end of the image area of ​​the second sheet. That is, in the example of FIG. 15, the detection result by the first light receiving element 62 is acquired in the sampling sections (2), (3), and (4). In this case, for example, it can be determined that there is condensation when the average value of the detection results by the first light receiving element 62 in the sampling sections (2), (3), and (4) is equal to or less than a predetermined threshold value. Alternatively, as described above, the average value of the detection results by the first light receiving element 62 in the sampling period (2) can be set as an initial value, and the state of condensation can be determined based on the amount of change from the initial value in the average value of the detection results in the sampling periods (3) and (4). By starting detection from the sampling period (2), it becomes possible to form an image without waiting for the start-up of the light emitting element 61. Other points of the operation according to the timing chart of FIG. 15 are substantially the same as those according to the timing chart of FIG. 7 described above.

[0119] In this embodiment, in order to determine the condensation state when the print job is ended, the optical sensor 60 is driven and the detection result is sampled in the sampling section (4). This makes it possible to execute a condensation removal process when the print job is ended as necessary, and to suppress the influence of condensation when the next print job is started. However, the present invention is not limited to this, and it is not necessary to sample the detection result of the optical sensor 60 in the sampling section (4), and further to drive the optical sensor 60. Even in this case, it is possible to suppress the influence of condensation in the print job based on the detection result of the optical sensor 60 in the sampling section (2) or (3), and further, the sampling section (1). Furthermore, in this embodiment, the detection result of the optical sensor 60 is sampled in all the paper-to-paper regions on the intermediate transfer belt 10, as in the sampling section (2) or (3). This makes it possible to grasp the progress of condensation more quickly. However, the present invention is not limited to this, and for example, the detection results of the optical sensor 60 may be sampled in a part of the inter-sheet region, such as sampling the detection results of the optical sensor 60 in the inter-sheet region for every predetermined number of sheets, as the sampling section (2) or (3). In this case, if possible in relation to the rise of the optical sensor 60, the drive (light emission) of the optical sensor 60 may be stopped in the inter-sheet region where the detection results of the optical sensor 60 are sampled.

[0120] In this embodiment, the image forming apparatus 100 drives the optical sensor 60 to sample the detection result of the optical sensor 60 in order to determine the dew condensation state using the optical sensor 60 in all print jobs. However, the present invention is not limited to this. The image forming apparatus 100 may be capable of executing a print job by switching between a detection mode (first mode) in which the dew condensation state is determined using the optical sensor 60 and a normal mode (second mode) in which the dew condensation state is not determined. The method of determining the dew condensation state using the optical sensor 60 in the detection mode may be the same as that of this embodiment. For example, the control unit 200 can switch between the detection mode and the normal mode before the start of a print job or during the execution of a print job according to 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 detection result of the environment by an environment sensor (not shown) provided in the image forming apparatus 100. Then, the control unit 200 can control the image forming apparatus 100 to execute the print job in the detection mode based on the result of the detection of the environment, 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. Then, the control unit 200 can 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 determination of the condensation state using the optical sensor 60 can be performed within a period equivalent to the inter-sheet process during the execution of the print job. Therefore, except for the case where the period of the inter-sheet process or the post-rotation process is extended by the condensation removal process, if the conditions other than the conditions regarding the mode switching are substantially the same, the length of the period of the inter-sheet process or the post-rotation process is substantially the same in the detection mode and the normal mode.

[0121] 9-3. Modifications of the configuration of the image forming apparatus In this embodiment, the image forming apparatus 100 is configured to remove the secondary transfer residual toner and other deposits remaining on the intermediate transfer belt 10 after the secondary transfer using the conductive brush 16, but the present invention is not limited to such a configuration. FIG. 16 is a schematic cross-sectional view of an image forming apparatus of one modified example. 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 given the same reference numerals as those of the image forming apparatus of FIG. 1, and detailed explanations are omitted. The image forming apparatus 100 of FIG. 16 has a belt cleaning device 18 as an intermediate transfer body cleaning means at a position facing the third tension roller 13 on the outer circumferential surface side of the intermediate transfer belt 10. The belt cleaning device 18 has a cleaning blade 73 as a cleaning member arranged in contact with the surface of the intermediate transfer belt 10, and a cleaning container 74 that contains deposits 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 scrapes off adhering matter such as secondary transfer residual toner from the surface of the rotating intermediate transfer belt 10 using a cleaning blade 73, and stores 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.

[0122] 9-4.Modifications regarding reflected light to be detected In this embodiment, the dew condensation state is detected based on the detection result by 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 regular reflection light by the intermediate transfer belt 10. However, for example, when the surface of the intermediate transfer belt 10 has a low glossiness or when the intermediate transfer belt 10 has a color with a white component, the above-mentioned light may be mainly reflected as diffuse reflection light instead of regular reflection light by the intermediate transfer belt 10. In this case, it is also possible to detect the dew condensation state based on the detection result by the second light receiving element 63. In addition, the detection result by the second light receiving element 63 can be used in cases where it is assumed that sand (sand dust, sand particles) or toner that does not exist outside the image forming area is attached to the intermediate transfer belt 10 as foreign matter other than water droplets (see Example 3).

[0123] Thus, in this embodiment, the image forming apparatus 100 has a toner image forming means (such as the charging roller 2, the exposure device 3, and the developing device 4) that forms 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, a 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 irradiates light toward the surface of the image carrier 10, and light-receiving elements 62 and 63 (in this embodiment, a first light-receiving element 62) that irradiate light from the light-emitting element 61 toward the surface of the image carrier 10, receive the reflected light reflected, and output a detection signal according to the amount of received light, and detects the reflected light at a detection position D in the moving direction of the surface of the image carrier 10. In response to one 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 inside the machine to outside the machine through a recording material discharge port (paper discharge port) 130. In this embodiment, the image forming apparatus 100 has a control unit (DC controller) 200 capable of performing control so as to perform an adhesion removal process (condensation removal process) for removing adhesions (condensation) on the surface of the image carrier 10 based on a detection signal output by the light receiving element 62 receiving the reflected light during the period from when the rear end in the above-mentioned movement direction of the image forming area on the surface of the image carrier 10 on which the toner image to be transferred to the preceding recording material P can be formed passes through the detection position D until the front end in the above-mentioned movement direction of the image forming area on the surface of the image carrier 10 on which the toner image to be transferred to the 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 so as to perform an idling operation for rotating the image carrier 10 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 so as to perform the idling operation for rotating the image carrier 10 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 adhesion removal process. In this embodiment, the control unit 200 executes the adhesion removal process by interrupting the formation of a toner image on the surface of the image carrier 10 in a print job.However, the control unit 200 can also execute the deposit removal process after the formation of all toner images on the surface of the image carrier 10 in a print job is completed.

[0124] 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 the rear end in the movement direction of the image forming area on the surface of the image carrier 10 on which the toner image to be transferred to the last recording material P of the print job can be formed passes the detection position D during the 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 end in the movement direction of the image forming area on the surface of the image carrier 10 on which the toner image to be transferred to the first recording material P of the print job can be formed reaches the detection position D during the 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 the toner image to be transferred to the recording material P in the print job can be formed passes the detection position D during the execution of a print job. In other words, in this embodiment, when a print job is being executed and the rear end in the above-mentioned movement direction of the image forming area on the surface of the image carrier 10 on which the toner image to be transferred to the last recording material P of the print job is to be formed passes through the detection position D, and the numerical value related to the detection signal output by the light receiving element 62 upon 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 above-mentioned movement direction of the image forming area on the surface of the image carrier 10 on which the toner image to be transferred to the last recording material P is to be formed passes through the detection position D until 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.

[0125] 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 reflected light amount 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 more than a predetermined threshold. The control unit 200 can also perform the above control based on the amount of change in 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 acquired after the first average value, relative to 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, during the execution of a print job. In this case, the control unit 200 can perform the above control when the amount of change of the second average value relative to the first average value is equal to or greater than a predetermined threshold value. The control unit 200 can also change the time of the adherent removal process based on the speed of change of a numerical value related to the detection signal output by the light receiving element 62 upon receiving the reflected light during a print job. In this embodiment, the light receiving element 62 mainly receives regular reflected light as the reflected light. In this embodiment, the adherent is moisture adhered to the surface of the image carrier 10. However, a light receiving element (second light receiving element) 63 that mainly receives diffuse reflected light as the reflected light may be used to detect moisture adhered to the surface of the image carrier 10. Furthermore, 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 for secondary transfer onto a recording material P, and an optical sensor 60 irradiates light onto the surface of the intermediate transfer member 10 and detects the reflected light.

[0126] According to this embodiment, it is possible to suppress image deterioration caused by condensation on the surface of the intermediate transfer belt 10 during a print job.

[0127] [Example 2] 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 given the same reference numerals as those of embodiment 1, and detailed explanations are omitted.

[0128] In the first embodiment, the idling operation of the intermediate transfer belt 10 is 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 idling operation, which is obtained in advance. In contrast, in the present embodiment, the optical sensor 60 is driven during the idling operation of the intermediate transfer belt 10, and the idling operation is ended based on the detection result by the first light receiving element 62.

[0129] 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.

[0130] In this embodiment, the print job is interrupted and the developing roller 42 is separated from the photosensitive drum 1 in response to the detection result by the first light receiving element 62. 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 in accordance with the timing at which the position corresponding to the timing at which the developing roller 42 is separated from the photosensitive drum 1 reaches the optical sensor 60. This is to accurately detect the amount of reflected light from the surface of the intermediate transfer belt 10 without being affected by the toner that has moved from the developing roller 42 onto the intermediate transfer belt 10 via the photosensitive drum 1.

[0131] In this embodiment, similarly to the first embodiment, the DC controller 200 samples the detection results by 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 the sampling data for 100 points. That is, the DC controller 200 obtains the average value of the detection results (sampling data) of the amount of reflected light from the surface of the intermediate transfer belt 10 while the intermediate transfer belt 10 rotates by 10 mm. In this embodiment, the DC controller 200 obtains the average value of the sampling for the above 10 mm over 800 mm, which is one rotation of the intermediate transfer belt 10, during the idling operation. Then, when all the average values ​​are greater than 3.0 V, the DC controller 200 determines that the condensation state has been eliminated and resumes the print job.

[0132] 18 is a flow chart showing an outline of the operation of the image forming apparatus 100 including the dew condensation detection operation and the dew condensation removal process in this embodiment.

[0133] 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 judges whether the average value R of the detection result by the first light receiving element 62 is 2.8 V or less at a predetermined timing (sampling section (1) to (4)) described with reference to FIG. 7 (S32). If the DC controller 200 judges in S32 that the average value R of the detection result by the first light receiving element 62 is 2.8 V or less, it interrupts the print job and executes an idling operation (S33). Then, the DC controller 200 judges whether the average value R of the detection result by the first light receiving element 62 during the idling operation is 3.0 V or less (S34). If the DC controller 200 judges in S34 that the average value R of the detection result by the first light receiving element 62 is greater than 3.0 V, it ends the idling operation, resumes the print job (S35), and performs the judgment in S32 again. On the other hand, if the DC controller 200 determines in S34 that the average value R of the detection result by the first light receiving element 62 is 3.0V or less, it determines whether or not the time t from the start of the idling operation has passed a predetermined time, 15 seconds in this embodiment (S36). If the DC controller 200 determines in S36 that the time t has not passed 15 seconds, it continues to perform the idling operation (S33). If the DC controller 200 determines in S36 that the time t has passed 15 seconds, it ends the idling operation, resumes the print job (S35), and performs the determination in S32 again. As a result, even if the average value R is no longer 3.0V or less due to a change in the state of the intermediate transfer belt 10 caused by a factor other than moisture, it is possible to end the idling operation by determining that moisture on the surface of the intermediate transfer belt 10 has been sufficiently removed. Furthermore, 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 or not 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 performs the determination in S32 again.

[0134] 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 may be used.

[0135] In this embodiment, the print job is restarted when the average value of the detection result 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 the detection result by the first light receiving element 62 exceeding a predetermined value over one revolution of the intermediate transfer belt 10, and may be set appropriately in consideration of the number of prints remaining in the print job, the sensitivity of the image forming apparatus 100 to the occurrence of 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 area in the rotation direction of the intermediate transfer belt 10 has sufficiently recovered from the condensation state.

[0136] Also 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 by the first light receiving element 62 during the idling operation.

[0137] As described above, in this embodiment, the control unit 200 controls the drive unit 90 to end the idling operation based on the detection signal output by the light receiving element 62 upon receiving reflected light during the idling operation.

[0138] As described above, in this embodiment, by performing the above-mentioned 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 idling operation can be quickly terminated to shorten downtime. Therefore, according to this embodiment, the occurrence of image defects due to condensation can be more efficiently and reliably suppressed.

[0139] [Example 3] 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 given the same reference numerals as those of embodiment 1, and detailed explanations are omitted.

[0140] In the first and second embodiments, the optical sensor 60 is used to detect water droplets caused by condensation on the intermediate transfer belt 10, but the optical sensor 60 can also detect things other than water droplets. For example, if a foreign object such as sand enters the interior of 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.

[0141] FIG. 19 is a graph showing a detection waveform 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 in the section (i) in FIG. 19. As shown in FIG. 19, the reflected light from the surface of the intermediate transfer belt 10 is mainly specularly reflected light, 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 reflected light from the sand is mainly diffusely reflected light, so the amount of light received by the second light receiving element 63 increases at the timing when the sand passes the detection position D of the optical sensor 60. By utilizing this tendency, for example, as shown in FIG. 19, a threshold value is set in advance as a case where a predetermined condition is satisfied, and when a detection signal (detection output) that exceeds (crosses) the threshold value is obtained, it is possible to determine that a foreign object such as sand is present on the intermediate transfer belt 10 (anomaly on the intermediate transfer belt 10).

[0142] Also, the diffusely reflected light can be received by the first light receiving element 62. FIG. 20 shows a detection waveform when the sand on the intermediate transfer belt 10, which is the same as that in FIG. 19, is detected by the first light receiving element 62. When the sand passes through the detection position D of the optical sensor 60, the amount of specularly reflected light from the surface of the intermediate transfer belt 10 decreases, and the amount of received light detected by the first light receiving element 62 decreases accordingly. By utilizing this tendency, for example, as shown in FIG. 19, a threshold value is set in advance as a case where a predetermined condition is satisfied, and when a detection signal (detection output) that falls below (crosses) the threshold value is obtained, it is possible to determine that a foreign object such as sand is present on the intermediate transfer belt 10 (anomaly on the intermediate transfer belt 10).

[0143] When the DC controller 200 detects a foreign object on the intermediate transfer belt 10 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 for notifying an operator such as a user of the detection. Specifically, when the DC controller 200 detects a foreign object on the intermediate transfer belt 10, the DC controller 200 controls to output a signal to the operation unit 150 or the external device 300 to notify an operator such as a user of information regarding the adhesion of the foreign object to the surface of the intermediate transfer belt 10. The information notified by the notification process may simply notify the presence of a foreign object on the intermediate transfer belt 10, or may prompt the user to perform maintenance (cleaning, etc.) or replacement of the intermediate transfer belt 10. In addition, the DC controller 200 can execute the notification process and control to stop (prohibit) the operation (printing) of the image forming apparatus 100 until a predetermined process (cleaning or replacement) is performed by an operator such as a user. The DC controller 200 can control the image forming apparatus 100 to resume operation (printing) when predetermined information is input by an operator such as a user through 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 the intermediate transfer belt 10 is detected by a mechanism that detects that the intermediate transfer belt 10 or a unit including the intermediate transfer belt has been replaced.

[0144] Furthermore, when the DC controller 200 detects a foreign object on the intermediate transfer belt 10 as described above, the DC controller 200 may control to execute a foreign object removal process for removing the foreign object on the intermediate transfer belt 10 as a recovery process from an abnormality on the intermediate transfer belt 10. The foreign object removal process is an example of an attachment removal process for removing attachments (such as sand in this embodiment) on the surface of the intermediate transfer belt 10 as a recovery process from an abnormal state on the intermediate transfer belt 10. The foreign object removal process is 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 object removal process may be executed when the print job is ended based on the detection result by the optical sensor 60 during the print job. The foreign object removal process may include an idling operation similar to that in the first and second embodiments. Thereby, the foreign object on the intermediate transfer belt 10 can be removed by the conductive brush 16 (FIG. 1) or the belt cleaning device (FIG. 16). The idling operation as the foreign object removal process can be executed for a predetermined time (for example, 15 seconds) set in advance, similar to the idling operation in the first embodiment. 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).

[0145] 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 a foreign object on the intermediate transfer belt 10. The operation according to the flowchart in FIG.

[0146] 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 judges whether or not the detection result by the second light receiving element 63 exceeds a predetermined threshold at a predetermined timing (sampling section (1) to (4)) described with reference to FIG. 7 (S42). When the DC controller 200 judges 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 the operation of the image forming apparatus 100 (S44). On the other hand, when the DC controller 200 judges in S42 that the detection result by the second light receiving element 62 is equal to or less than the predetermined threshold, it judges whether or not all printing of the print job has been completed (S45). When the DC controller 200 judges 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 performs the determination in S42 again.

[0147] Fig. 22 is a flowchart showing an outline of the operation of the image forming apparatus 100 including the operation of detecting foreign matter on the intermediate transfer belt 10 and the foreign matter removal process in this embodiment. 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.

[0148] In the flowchart of Fig. 22 and the flowchart of Fig. 21, the processes of S41, S42, and S45 are the same, so the description will be omitted. In this example, when 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 ends, the DC controller 200 resumes the print job and performs the determination of S42 again.

[0149] As described above, the DC controller 200 may determine in S42 whether the detection result by the first light receiving element 63 falls below a predetermined threshold, and execute a notification process or a foreign matter removal process when the detection result falls below the predetermined threshold. As described above, the foreign matter removal process may be executed when the print job is ended. The foreign matter is not limited to sand, and may be any attached matter such as toner that is not normally present outside the image forming area (non-image forming area).

[0150] As described above, when foreign matter such as sand or toner adheres to 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 by the first light receiving element 62 or the second light receiving element 63 with the preset threshold value for each element. By performing a determination using a set threshold value in this manner, it is possible to detect the occurrence of image defects that are difficult to suppress 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.

[0151] The detection of the condensation state 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 of the detection result by the first light receiving element 62 and the amount of change therein, a determination is made based on the threshold value of the detection result by the second light receiving element 63, and if either of them 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.

[0152] Thus, 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 perform an adhesion removal process (foreign matter removal process) or a notification process when a value related to a detection signal output by the light receiving element 63 after receiving 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 perform an adhesion 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 reflected light falls below a predetermined threshold value. In this embodiment, the image carrier includes the photoconductor 1 as a first image carrier and the intermediate transfer body 10 as a second image carrier that conveys the toner image transferred primarily from the photoconductor 1 to the recording material P for secondary transfer, and the optical sensor 60 irradiates light toward the surface of the intermediate transfer body 10 to detect the reflected light.

[0153] 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.

[0154] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-mentioned embodiments.

[0155] In the above embodiment, the optical sensor detects the reflected light from the surface of the intermediate transfer belt, which is the image carrier (second image carrier), to detect the condensation state or the adhesion of foreign matter, but the present invention is not limited to this embodiment. The optical sensor may detect the reflected light from the surface of the photosensitive drum, which is the image carrier (first image carrier), to detect the condensation state or the adhesion of foreign matter. In addition, both of these detections may be performed.

[0156] In the above embodiment, the image forming apparatus is capable of forming a full-color image, but the present invention is not limited to this embodiment. The present invention can also be applied to an image forming apparatus capable of forming only a monochrome (black and white or monochromatic) image.

[0157] In addition, the photosensitive member is not limited to a drum-shaped one (photosensitive drum), and may be, for example, an endless belt-shaped one (photosensitive belt), etc. In addition, the intermediate transfer member is not limited to an endless belt, and may be, for example, an intermediate transfer drum that is stretched around a frame and formed into a drum shape.

[0158] In the above embodiment, the developing member is in contact with the photosensitive member to perform development, but it may be disposed opposite the photosensitive member without contacting the photosensitive member to perform development.

[0159] In the above embodiment, the image forming apparatus has a cleaning device for cleaning the surface of the photoconductor, but the image forming apparatus may have a configuration that does not have a special cleaning device for cleaning the surface of the photoconductor. In this case, the residual toner on the photoconductor may be collected by the developing device.

[0160] In the above embodiment, the operation in the case where 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 be used. In addition, both the front optical sensor 60F and the rear optical sensor 60R may be used. In this case, for example, when a condensation state is detected by either one of the optical sensors 60, or when a condensation state is detected by both of the optical sensors 60, a recovery process can be executed. The same applies to the detection of foreign matter such as sand. In addition, 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, and may be one, or may be three or more. [Explanation of symbols]

[0161] 1 Photosensitive drum (first image carrier) 2. Charge roller 3. Exposure equipment 4. Developing device 10 Intermediate transfer belt (second image carrier) 42 Developing roller 60 Optical Sensor 200 DC controller (control unit)

Claims

1. a toner image forming means for forming a toner image; a rotatable image carrier that carries a toner image formed by the toner image forming means on its surface; a transfer means for transferring the toner image formed on the surface of the image carrier onto a recording material; an optical sensor including a light-emitting element that irradiates light toward the surface of the image carrier, and a light-receiving element that receives light reflected from the light-emitting element that irradiates light toward the surface of the image carrier and outputs a detection signal according to the amount of light received, the optical sensor detecting the reflected light at a detection position in the moving direction of the surface of the image carrier; having An image forming apparatus which executes 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 apparatus to outside the apparatus through a recording material discharge port, An image forming apparatus characterized in having a control unit capable of controlling, during execution of a print job, 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, 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. The image forming apparatus according to claim 1, characterized in that the control unit controls a drive unit that drives the image carrier to rotate so as to perform an idling operation of rotating the image carrier without forming a toner image on the surface of the image carrier as the adhesion removal process.

3. 3. The image forming apparatus according to claim 2, wherein the control unit controls the drive unit so that the idling operation is performed for a predetermined time.

4. The image forming apparatus according to 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 the light receiving element receives the reflected light while the idling operation is being performed.

5. The image forming apparatus according to claim 1 , wherein the control unit controls a drive unit that drives the image carrier to rotate 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. 2. 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. 2. The image forming apparatus according to claim 1, wherein the control unit executes the deposit removal process after all toner images have been formed on the surface of the image carrier in a print job.

8. The image forming apparatus according to claim 1, characterized in that 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 a detection signal 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 last recording material of the print job can be formed, has passed the detection position.

9. The image forming apparatus according to claim 1, characterized in that 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 when receiving the reflected light before 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 the first recording material of the print job can be formed reaches the detection position.

10. a toner image forming means for forming a toner image; a rotatable image carrier that carries a toner image formed by the toner image forming means on its surface; A drive unit that rotates and drives the image carrier; a transfer means for transferring the toner image formed on the surface of the image carrier onto a recording material; an optical sensor including a light-emitting element that irradiates light toward the surface of the image carrier, and a light-receiving element that receives light reflected from the light-emitting element that irradiates light toward the surface of the image carrier and outputs a detection signal according to the amount of light received, the optical sensor detecting the reflected light at a detection position in the moving direction of the surface of the image carrier; having An image forming apparatus which executes 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 apparatus to outside the apparatus through a recording material discharge port, an image forming apparatus comprising: a control unit capable of controlling the drive unit so that, when a numerical value relating 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 relating to the detection signal does not satisfy the specified condition.

11. 11. The image forming apparatus according to claim 1, wherein the control unit performs the control when a value related to a detection signal output by the light receiving element after receiving the reflected light crosses a predetermined threshold value.

12. 11. The image forming apparatus according to claim 1, wherein the control section performs the control based on an average value of a numerical value related to a detection signal outputted by the light receiving element upon receiving the reflected light.

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

14. 11. The image forming apparatus according to claim 1, wherein the control section performs the control based on a deviation of a detection signal outputted by the light receiving element upon receiving the reflected light.

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

16. The image forming apparatus according to any one of claims 1 to 9, characterized in that the control unit performs the control based on the amount of change in a second average value of a numerical value related 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 related to a detection signal output by the light receiving element after receiving the reflected light, during execution of a print job.

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

18. The image forming apparatus according to any one of claims 1 to 9, characterized in that the control unit changes the time of the adhesion removal process based on the speed of change in a numerical value related to the detection signal output by the light receiving element upon receiving the reflected light during a print job.

19. 11. The image forming apparatus according to claim 1, wherein the light receiving element receives mainly specularly reflected light as the reflected light.

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

21. 11. The image forming apparatus according to claim 1, wherein the light receiving element receives mainly diffusely reflected light as the reflected light.

22. 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. 11. The image forming apparatus according to claim 1, further comprising a photosensitive member as a first image carrier, and an intermediate transfer member as a second image carrier that transports a toner image transferred from the photosensitive member for secondary transfer onto a recording material, and the optical sensor irradiates light onto a surface of the intermediate transfer member and detects the reflected light.

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