Image forming apparatus

Abstract

To enable execution of processing of detecting a foreign substance such as sand attached onto an image carrier to reduce the influence of the foreign substance.SOLUTION: An image forming apparatus 100 has an optical sensor 60 and a control unit 201. The control unit 201 performs control to execute a toner supply operation to cause an image carrier 10 to carry, on its surface, a predetermined toner image formed by toner image forming means and supply a toner in the predetermined toner image to a contact member 16 in contact with the image carrier 10, on the basis of detection signals output from light receiving elements 62, 63 of the optical sensor 60 that have received reflected light after the start of rotation of the image carrier 10 for a print job and before an initial image forming area in the print job reaches a detection position.SELECTED DRAWING: Figure 12

Description

[Technical Field]

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

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

[0003] Such image forming apparatuses may be equipped with a function for detecting abnormalities on image carriers such as photosensitive drums and intermediate transfer belts and suppressing the occurrence of image defects associated with the abnormalities. An example of an abnormality on an image carrier may be a foreign object that has entered the image forming apparatus. If a foreign object enters the image forming apparatus, the foreign object may adhere to the image carrier and scratch the image carrier, or the foreign object may be collected by a contact member that contacts the image carrier, causing damage to the contact member. A typical example of a contact member is a cleaning member that collects toner from the image carrier.

[0004] Image forming devices are installed in various air-conditioning environments. For example, in some environments, strong ceiling fans are used to cool the room, blowing wind into the image forming device. This can cause foreign matter such as dust and sand (grit, sand particles) to enter the image forming device. When an image forming device is placed in a strong wind environment with blowing sand, fine sand particles have adhered to the intermediate transfer belt and photosensitive drum inside the image forming device. Therefore, measures to deal with foreign matter such as sand are required.

[0005] Patent Document 1 discloses technology related to control when foreign matter (specifically, paper such as a label or part of a paper) adheres to the intermediate transfer belt. In the technology described in Patent Document 1, when foreign matter is detected on the intermediate transfer belt, the operation of the intermediate transfer belt is stopped to prevent damage to the cleaning member. Patent Document 1 also describes methods for detecting foreign matter, such as a method of determining whether the amount of current between the rollers that sandwich the intermediate transfer belt falls within a predetermined range, and a method of detecting the amount of light reflected from the intermediate transfer belt and determining whether the amount of reflected light falls within a predetermined range. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-151348 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the above-mentioned conventional techniques have the following problems.

[0008] For example, in a strong wind environment where sand or other foreign matter is blowing around, foreign matter such as sand may adhere to an image carrier such as an intermediate transfer belt or a photosensitive drum while the operation of an image forming apparatus is stopped. In such a situation, if a configuration that stops the operation of the image forming apparatus when a foreign matter is detected, as in the above-mentioned conventional technology, the foreign matter would be detected when the image forming apparatus starts operating, causing the operation of the image forming apparatus to be stopped, which may cause inconvenience to the user. Therefore, it is desirable to be able to continue the operation of the image forming apparatus without causing inconvenience to the user when a foreign matter such as sand is detected.

[0009] SUMMARY OF THE INVENTION It is therefore an object of the present invention to make it possible to detect foreign matter such as sand adhering to an image carrier and to execute processing to reduce the influence of the foreign matter. [Means for solving the problem]

[0010] The above object is achieved by an image forming apparatus according to the present invention. In summary, according to one aspect of the present invention, an image forming apparatus includes a toner image forming means for forming a toner image, a rotatable image carrier for carrying the toner image formed by the toner image forming means on its surface, a contact member for contacting the surface of the image carrier, a light emitting element for irradiating light onto the surface of the image carrier, and a light receiving element for receiving light reflected from the light emitting element onto the surface of the image carrier and outputting a detection signal according to the amount of received light, an optical sensor for receiving the reflected light at a detection position in the moving direction of the surface of the image carrier, and a control unit capable of controlling the toner image forming means, and the toner image forming apparatus is capable of performing a toner image forming process on one or more recording materials in response to a single start instruction. In an image forming apparatus that executes a print job including transferring toner images carried on image forming areas on the surface of the image carrier, the control unit controls the image carrier to carry a predetermined toner image formed by the toner image forming means on the surface of the image carrier and to supply toner of the predetermined toner image to the contact member based on a detection signal output by the light receiving element upon receiving the reflected light after the image carrier has started to rotate for the print job but before the first image forming area in the print job reaches the detection position. [Effects of the Invention]

[0011] According to the present invention, it is possible to detect foreign matter such as sand adhering to an image carrier and to execute processing to reduce the influence of the foreign matter. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Figure 2] FIG. 2 is a block diagram showing a control configuration of the image forming apparatus. [Figure 3] FIG. 10 is a top view for explaining the arrangement of the optical sensors. [Figure 4] FIG. 2 is a schematic cross-sectional view for explaining the configuration of an optical sensor. [Figure 5]10 is a graph showing a detected waveform when light reflected from the intermediate transfer belt is detected by an optical sensor. FIG. [Figure 6] 10 is a graph showing a detected waveform when light reflected from a toner patch is detected by an optical sensor. FIG. [Figure 7] 10 is a graph showing a waveform detected when diffused light reflected from sand on the intermediate transfer belt is detected by an optical sensor. FIG. [Figure 8] 10 is a graph showing a waveform detected when specularly reflected light from sand on the intermediate transfer belt is detected by an optical sensor. FIG. [Figure 9] 10 is a graph showing a waveform detected when an optical sensor detects specularly reflected light from an intermediate transfer belt having sand attached to almost the entire surface thereof; FIG. [Figure 10] 10 is a graph showing a waveform detected when an optical sensor detects diffused light from an intermediate transfer belt having sand attached to almost the entire surface thereof; FIG. [Figure 11] 1 is a schematic diagram illustrating an example of a usage environment of an image forming apparatus in which sand adheres to substantially the entire surface of an intermediate transfer belt. [Figure 12] FIG. 2 is a flowchart of control in the first embodiment. [Figure 13] 10A and 10B are schematic diagrams illustrating an example of a supply toner image in a toner supply operation. [Figure 14] FIG. 10 is a timing chart illustrating an example of an operation when a toner supply operation is not executed in the control of the first embodiment. [Figure 15] FIG. 10 is a timing chart illustrating an example of an operation when a toner supply operation is executed in the control of the first embodiment. [Figure 16] 10A and 10B are schematic diagrams illustrating other examples of supplied toner images in the toner supplying operation. [Figure 17] 10 is a graph showing a change in the detected waveform of specularly reflected light when foreign matter on the intermediate transfer belt is collected by a contact member. FIG. [Figure 18] 10 is a graph showing a change in the detected waveform of diffusely reflected light when foreign matter on the intermediate transfer belt is collected by a contact member. [Figure 19] FIG. 10 is a flowchart of control of Modification 1. [Figure 20] FIG. 10 is a flowchart of control in Modification 2. [Figure 21] FIG. 10 is a schematic cross-sectional view showing another example of the configuration of an image forming apparatus. [Figure 22] 10 is a graph showing detected waveforms of specularly reflected light and diffusely reflected light for explaining threshold values in Example 2. FIG. [Figure 23] FIG. 10 is a block diagram showing a control configuration of another example of an image forming apparatus. [Figure 24] FIG. 10 is a timing chart for explaining the operation under the control of the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the examples may be changed as appropriate depending on the configuration of the apparatus to which the invention is applied and various conditions. In other words, the scope of the present invention is not limited to the following examples.

[0014] [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 laser beam printer that employs an intermediate transfer system and is capable of forming a full-color image on a sheet-shaped recording material P using an electrophotographic system. The image forming apparatus 100 forms an image on the recording material P based on signals (information) input from an external device connected to the image forming apparatus 100, such as an image reading device or a host computer such as a personal computer.

[0015] Image forming apparatus 100 has four image forming units Sa, Sb, Sc, and Sd as multiple image forming units (stations) inside (inside) housing (exterior cover) 120 of apparatus main body 110. Image forming units Sa, Sb, Sc, and Sd form images using toner of each color: yellow (Y), magenta (M), cyan (C), and black (K). 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).

[0016] The configuration of each image forming unit S is essentially the same except for the color of toner used. Elements having the same or corresponding functions or configurations provided for each color may be generally described by omitting the suffixes a, b, c, and d indicating that the element is for one of the colors. For convenience, the magnitude (high / low) of voltage or potential (or potential difference) refers to the magnitude (high / low) when compared in absolute value unless otherwise specified. In addition, since paper is primarily used as the recording material P in the image forming apparatus 100, the recording material P may sometimes be referred to as paper, but the recording material P also includes materials other than paper and materials containing materials other than paper.

[0017] 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.

[0018] The photosensitive drum 1, which is a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) serving as a first image carrier that carries a toner image, is driven to rotate at a predetermined peripheral speed (process speed) in the direction of arrow R1 in FIG. 1 (counterclockwise direction) by a driving force transmitted from a drive motor provided in a drive unit 90 (FIG. 2) serving as a driving means. In this embodiment, the photosensitive drum 1 is driven to rotate at a peripheral speed of 200 mm / sec. When a print job is started by a DC controller (control circuit unit) 200 (described later) receiving an image signal, the photosensitive drum 1 begins to be driven to rotate.

[0019] The surface (outer periphery) of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential (dark potential Vd) of a predetermined polarity (negative in this embodiment) by a charging roller 2, which is a roller-type charging member serving as charging means. The charging roller 2 is disposed in contact with the surface of the photosensitive drum 1 and is pressed against the photosensitive drum 1 with a predetermined pressure. The charging roller 2 is rotated in accordance with the rotation of the photosensitive drum 1. During charging, a charging voltage (charging bias), which is a DC voltage of the same polarity (negative in this embodiment) as the charging polarity of the photosensitive drum 1, is applied to the charging roller 2 by a charging power source (high-voltage power source) 24 ( FIG. 2 ) serving as charging voltage application means (charging voltage application unit).

[0020] The surface of the rotating photosensitive drum 1, which has been charged, is scanned and exposed by an exposure device (laser scanner unit) 3 as exposure means in accordance with an image signal, and an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 1 (surface of the photosensitive drum 1). For example, when a full-color image is formed, each of the photosensitive drums 1a, 1b, 1c, and 1d is exposed by exposure devices 3a, 3b, 3c, and 3d in accordance with image signals of color component images corresponding to each image forming station S. As a result, electrostatic latent images corresponding to the yellow, magenta, cyan, and black color component images of the target color image are formed on each of the photosensitive drums 1a, 1b, 1c, and 1d.

[0021] The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by a developing device (developing unit) 4 as a developing means, which supplies toner as a developer, and forms a toner image (toner image, developer image) on the photosensitive drum 1. The developing device 4 includes a developer container 41 that contains toner, which is a non-magnetic single-component 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. During development, the developing roller 42 is rotated by a driving force transmitted from a drive motor provided in a driving unit 90 (FIG. 2) as a driving means. In this embodiment, the developing roller 42 is rotated at a peripheral speed of 300 mm / sec in a rotational direction such that the surface of the developing roller 42 moves in the same direction as the surface of the photosensitive drum 1 at the contact point between the photosensitive drum 1 and the developing roller 42. By rotating the developing roller 42 at 1.5 times the speed of the photosensitive drum 1 in this manner, stable development can be achieved. The developing roller 42 carries the toner contained in the developer container 41 and transports the toner to a development position, which is the contact portion (opposing portion) between the photosensitive drum 1 and the developing roller 42. During development, a development voltage (developing 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 developing roller 42 by a development power supply (high-voltage power supply) 25 ( FIG. 2 ) serving as a development 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 deposits toner charged to the same polarity (negative in this embodiment) as the charging polarity of the photosensitive drum 1 by the charging roller 2 onto a portion (image portion) of the photosensitive drum 1 where the potential has decreased due to exposure (reverse development method). However, the present invention can also be applied to an image forming apparatus that performs development using toner charged to the polarity opposite to the charging polarity of the photosensitive drum 1.

[0022] In this embodiment, the image forming apparatus 100 has a developer contact / separation mechanism 80 ( FIG. 2 ) for contacting and separating the developing roller 42 with and from the photosensitive drum 1. In this embodiment, when the image forming apparatus 100 is stopped, the developer contact / separation mechanism 80 separates the developing roller 42 from the photosensitive drum 1. During development, the developer contact / separation mechanism 80 contacts the developing roller 42 with the photosensitive drum 1. In this embodiment, the developer 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 developer contact / separation mechanism 80 is configured to move (rotate) the developer container 41 against the biasing force of the pressure spring, thereby separating the developing roller 42 from the photosensitive drum 1. The developer contact / separation mechanism 80 is also configured to allow the developer container 41 to move (rotate) due to the biasing force of the pressure spring, thereby allowing the developing roller 42 to contact the photosensitive drum 1. The developing contact / separation mechanism 80 is driven by a driving force transmitted from a driving motor provided in a driving unit 90 (FIG. 2) serving as a driving means. The developing roller 42 is driven to rotate when brought into contact with the photosensitive drum 1, and stops rotating when separated from the photosensitive drum 1.

[0023] In this embodiment, the rotation speed of the developing roller 42 is set so that the solid density (maximum image density) of yellow, magenta, cyan, and black is 1.5 for A4 size GF-C081 paper manufactured by Canon Inc. The solid density was measured using a handheld densitometer eXact manufactured by X-rite Corporation.

[0024] 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 ) 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 becomes −200 V. 2 In this embodiment, a developing voltage of −350 V is applied to the developing roller 42 during development.

[0025] 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.

[0026] Opposing the four photosensitive drums 1 is an intermediate transfer belt 10, an intermediate transfer body formed of a rotatable endless belt, which serves as a second image carrier for carrying a toner image. The intermediate transfer belt 10 is tensioned by three axes of multiple tension rollers: first, second, and third tension rollers 11, 12, and 13. The first tension roller 11, together with the third tension roller 13, forms the surface of the intermediate transfer belt 10 onto which the toner image is transferred. The second tension roller 12 functions as a tension roller that applies a predetermined tension to the intermediate transfer belt 10. The third tension roller 13 functions as a drive roller that transmits driving force to the intermediate transfer belt 10 and also functions as an opposing roller (opposing member, opposing electrode) for 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) when the third tension roller 13 is rotationally driven by a driving force transmitted from a drive motor provided in a drive unit 90 (FIG. 2) serving as a drive means. The intermediate transfer belt 10 is rotationally driven at a peripheral speed (approximately 200 mm / sec) corresponding to the peripheral speed of the photosensitive drum 1. The first and second tension rollers 11 and 12 are driven to rotate in accordance with the rotation of the intermediate transfer belt 10. Primary transfer rollers 6a, 6b, 6c, and 6d, which are roller-type primary transfer members serving as primary transfer means, are arranged on the inner peripheral surface of the intermediate transfer belt 10 in correspondence with 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 the contact portion between the photosensitive drum 1 and the intermediate transfer belt 10. The primary transfer roller 6 is rotated in accordance with the rotation of the intermediate transfer belt 10.

[0027] At the primary transfer portion N1, the toner image formed on the photosensitive drum 1 is transferred (primary transfer) onto the rotating intermediate transfer belt 10 (the surface of the intermediate transfer belt 10) as a transfer target by the action of the primary transfer roller 6. 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 charge polarity of the toner, is applied to the primary transfer roller 6 by a primary transfer power supply (high-voltage power supply) 23 serving as a primary transfer voltage application means (primary transfer voltage application portion). In this embodiment, a primary transfer voltage of +500 V is applied to the primary transfer roller 6 during the primary transfer. For example, when forming a full-color image, toner images of yellow, magenta, cyan, and black formed on the four photosensitive drums 1a, 1b, 1c, and 1d are sequentially transferred onto the intermediate transfer belt 10 so as to be superimposed on top of each other. As a result, four-color toner images corresponding to the desired color image are formed on the intermediate transfer belt 10. In this embodiment, the primary transfer power supply 23 is a common power supply capable of applying a positive or negative voltage to the four primary transfer rollers 6a, 6b, 6c, and 6d. The primary transfer power supply 23 is capable of outputting a positive voltage in the range of +100V to +2000V (where "to" indicates a range that includes the numerical values before and after it), and a negative voltage in the range of -200V to -2000V. In this embodiment, a configuration in which a voltage is applied to multiple primary transfer rollers 6 from a common primary transfer power supply 23 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 multiple primary transfer power supplies are provided corresponding to each primary transfer roller 6.

[0028] In this embodiment, the intermediate transfer belt 10 is an endless belt (film) consisting of two layers: a base layer and a surface layer. The base layer is a 70 μm thick layer formed from a polyethylene naphthalate resin with a quaternary ammonium salt, an ionic conductive agent acting as an electrical resistance adjuster, dispersed therein. The layer has an elastic modulus of 2000 MPa. In this embodiment, the base layer of the intermediate transfer belt 10 is formed by blow molding. However, other molding methods include centrifugal molding, tube extrusion, inflation molding, extrusion molding, and cylindrical extrusion molding. The surface layer is formed on the outer peripheral surface of the intermediate transfer belt 10. The surface layer is a 3 μm thick layer formed from an acrylic resin base material with antimony-doped zinc oxide dispersed therein as an electrical resistance adjuster and polytetrafluoroethylene (PTFE) particles added as a solid lubricant. 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 present embodiment, the intermediate transfer belt 10 was prepared by fitting the base layer obtained by blow molding onto the outer periphery of a cylindrical mold, sealing the edges, and then immersing the mold in a container filled with a surface layer liquid. The mold was then pulled up so that the relative speed between the liquid level of the curable composition and the base layer was constant, thereby forming a coating film made of the surface layer liquid on the surface of the base layer.

[0029] In this embodiment, the volume resistivity of the intermediate transfer belt 10 is 1×10 10 The volume resistivity of the intermediate transfer belt 10 is Ω·cm. The volume resistivity of the intermediate transfer belt 10 was measured using a Mitsubishi Chemical Corporation Hiresta-UP (MCP-HT450) connected to a UR probe (model MCP-HTP12) at an applied voltage of 100 V for a measurement time of 10 seconds. The environment of the measurement chamber for measuring the volume resistivity of the intermediate transfer belt 10 was set to a temperature of 23°C and a humidity (relative humidity) of 50%, and the volume resistivity of the intermediate transfer belt 10 was measured after leaving it in the measurement chamber for 4 hours. In this example, the glossiness of the surface (outer surface) of the intermediate transfer belt 10 was 75. The glossiness of the surface of the intermediate transfer belt 10 was measured using a Horiba, Ltd. IG-320 handheld glossmeter. In this example, the peripheral length of the intermediate transfer belt 10 was 800 mm, and the width in a direction approximately perpendicular to the direction of movement (rotation) of the surface of the intermediate transfer belt 10 was 250 mm.

[0030] 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 The roller has an outer diameter of 11 mm and is covered with a foamed sponge body whose main components are NBR and epichlorohydrin rubber, and whose resistance is adjusted to 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 measured using an Asker hardness tester type C, and was found to be 20° under a load of 500 g (4.9 N).

[0031] A secondary transfer roller 20, which is a roller-type secondary transfer member serving as a secondary transfer means, is disposed on the outer peripheral surface of the intermediate transfer belt 10 at a position facing the third tension roller 13. The secondary transfer roller 20 contacts the outer peripheral surface of the intermediate transfer belt 10 and is pressed with a pressure of 50 N against the third tension roller 13, which is disposed at a position facing the secondary transfer roller 20 across the intermediate transfer belt 10. This causes the secondary transfer roller 20 to form a secondary transfer portion (secondary transfer nip) N2, which is the contact portion between the intermediate transfer belt 10 and the secondary transfer roller 20. The secondary transfer roller 20 is rotated in accordance with the rotation of the intermediate transfer belt 10. At the secondary transfer portion N2, the toner image formed on the intermediate transfer belt 10 is transferred (secondary transfer) onto a recording material P, which is being conveyed while being sandwiched between the intermediate transfer belt 10 and the secondary transfer roller 20. During the secondary transfer, a secondary transfer voltage (secondary transfer bias), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the secondary transfer roller 20 by a secondary transfer power supply 21 serving as a secondary transfer voltage application means (secondary transfer voltage application unit). The application of voltage from the secondary transfer power supply (high-voltage power supply) 21 causes a current to flow from the secondary transfer roller 20 to the third tension roller 13. As a result, the toner image carried on the intermediate transfer belt 10 is secondarily transferred to the recording material P at the secondary transfer section N2. During the secondary transfer, the voltage applied to the secondary transfer roller 20 by the secondary transfer power supply 21 is controlled so that a constant current flows from the secondary transfer roller 20 to the third tension roller 13 via the intermediate transfer belt 10. The magnitude of the current required for the secondary transfer is predetermined based on the installation environment (ambient environment) of the image forming apparatus 100 and the type of recording material P. In this embodiment, the secondary transfer power supply 21 is capable of outputting a voltage in the range of +100 V to +4000 V. The third tension roller 13 is electrically grounded (connected to ground potential). A recording material (transfer material, recording medium, media) P such as paper or an OHP sheet is stored in a cassette 51 serving as a recording material storage unit.The recording material P is fed from a cassette 51 by a feeding roller 50 or the like as a feeding member, and is transported to the secondary transfer section N2 by a pair of registration rollers 52 as a transporting member in synchronization with the toner image on the intermediate transfer belt 10.

[0032] 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 The roller has an outer diameter of 18 mm and is covered with a foamed sponge body composed mainly 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° when subjected to a load of 500 g (4.9 N), as measured using an Asker hardness tester type C. The length of the secondary transfer roller 20 in the direction of its rotation axis is equal to the length (width) in the width direction, which is approximately perpendicular to the moving direction of the surface of the intermediate transfer belt 10.

[0033] The recording material P onto which the toner image has been transferred is conveyed to a fixing device 30 serving 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 applies heat and pressure to the recording material P bearing the unfixed toner image in a fixing section (fixing nip) where the fixing roller 31 and the pressure roller 32 abut against each other, thereby fixing (melting and solidifying) the toner image onto the recording material P. For example, when 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 of the housing 120 of the apparatus main body 110 (outside the machine) through a paper discharge outlet (recording material discharge outlet) 130, which is an opening formed in the housing 120 of the apparatus main body 110. The recording material P is loaded on a tray 70 provided on the upper part of the housing 120 of the apparatus main body 110 .

[0034] On the other hand, toner remaining on the surface of the photosensitive drum 1 after the primary transfer (primary transfer residual toner) is removed from the surface of the photosensitive drum 1 and collected by a drum cleaning device 5 serving as a photosensitive body cleaning means. The drum cleaning device 5 has a cleaning blade 71 serving as a cleaning member (cleaning member) arranged in contact with the surface of the photosensitive drum 1, and a cleaning container 72 that stores the primary transfer residual toner removed from the surface of the photosensitive drum 1. The drum cleaning device 5 uses the cleaning blade 71 to scrape the primary transfer residual toner from the surface of the rotating photosensitive drum 1 and stores it in the cleaning container 72. The length of the cleaning blade 71 in the longitudinal direction is equal to the length of the photosensitive drum 1 in the direction of the rotation axis.

[0035] Furthermore, the toner remaining on the surface of the intermediate transfer belt 10 after the secondary transfer (secondary transfer residual toner) is charged to a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) by the conductive brush 16 serving as a toner charging member. This toner then moves to the photosensitive drum 1 at the primary transfer portion N1, for example, the primary transfer portion N1a located at the most upstream position in the moving 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 supply (high-voltage power supply) 17 serving as cleaning voltage application means (cleaning voltage application unit). Thus, in this embodiment, deposits such as secondary transfer residual toner remaining on the intermediate transfer belt 10 after the secondary transfer are removed from the intermediate transfer belt 10 using the conductive brush 16. In this embodiment, the conductive brush 16 has a density of 200 F / mm 2 , pile length 5mm, pile row 3 rows, raw yarn resistance 10 10The conductive brush 16 is made of conductive pile yarns whose main component is 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 downstream of the secondary transfer portion N2 and upstream of the primary transfer portion N1 (the most upstream primary transfer portion N1a) in the moving direction of the surface of the intermediate transfer belt 10. In this embodiment, the conductive brush 16 is pressed against a third tension roller 13 disposed opposite 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 supply 17 is capable of outputting a voltage in the range of +100V to +4000V. The longitudinal length of the conductive brush 16 is equal to the width of the intermediate transfer belt 10.

[0036] The image forming apparatus 100 of this embodiment can form a full-color print image by the above-described operation. The image forming apparatus 100 of this embodiment can also form a monochrome print image using only one desired image forming unit S, or form a multicolor print image using only some of the multiple image forming units S.

[0037] In this embodiment, in each image forming station S, the photosensitive drum 1, the charging roller 2 as a process means acting on the photosensitive drum 1, the developing device 4, and the drum cleaning device 5 are integrated to form a process cartridge 7 (7a, 7b, 7c, 7d). The process cartridge 7 is detachable from the main body 110 of the image forming apparatus 100 via mounting means such as a mounting guide and a positioning member provided in the main body 110 of the image forming apparatus 100. In this embodiment, the main body 110 of the image forming apparatus 100 is the portion excluding the process cartridges 7 from the image forming apparatus 100.

[0038] The image forming apparatus 100 is also provided with an optical sensor 60 that is used when performing correction control to correct color shifts and density of images formed in the image forming apparatus 100 and when detecting foreign matter such as sand on the intermediate transfer belt 10. 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 that is downstream of the primary transfer unit N1 (the most downstream primary transfer unit N1d) and upstream of the secondary transfer unit N2 in the moving direction of the surface 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. Details of the optical sensor 60 will be described later.

[0039] The above-described operations are repeated when performing continuous printing to form print images continuously on a plurality of recording materials P. When forming print images continuously on a plurality of A4 sheets of paper, for example, the image forming apparatus 100 of this embodiment performs continuous printing with a gap (paper gap) of 50 mm between the rear end of the previous sheet and the front end of the next sheet.

[0040] 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.

[0041] 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 conversion means provided inside the image forming apparatus 100, and transmits image data of the print image to the controller 210. In this embodiment, the external device 300 is a personal computer (PC) that is a host computer. The controller 210 receives RGB or CMYK image data from the external device 300 and converts it into CMYK exposure data (image signals) according to a mode specified by the external device 300. In this embodiment, the exposure data converted at this time is 600 dpi. In addition to the type and size of paper, the modes specified by the external device 300 include a mode related to image quality and a mode for changing the number of lines in the dither matrix.

[0042] The controller 210 transfers the converted exposure data to an exposure control device 203, which serves as exposure control means, provided in a DC controller (control circuit unit) 200 provided inside the image forming apparatus 100. The exposure control device 203 controls the exposure device 3 in accordance with instructions from a CPU 201, which will be described later. In the image forming apparatus 100 of this embodiment, halftone density is controlled by adjusting the on / off area of the exposure data. When the CPU 201 receives a print command from the controller 210, it starts a print job.

[0043] The DC controller 200 includes a CPU 201 as a control unit (arithmetic processing unit) and a memory 202 including a ROM, RAM, nonvolatile memory, etc. as a storage unit (storage unit). The DC controller 200 controls the operation of each unit of the image forming apparatus 100 by executing processing in accordance with programs and data stored in advance in the memory 202 using 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 conductive brush power supply 17, the drive unit 90, the developing contact / separation mechanism 80, etc., to form an electrostatic latent image, transfer the developed toner image, and perform other operations to form an image. The DC controller 200 (CPU 201) is also connected to an operation unit 150 provided in the image forming apparatus 100. The operation unit 150 is configured to have a display unit that displays information under the control of the DC controller 200 (CPU 201), an input unit that inputs information to the DC controller 200 (CPU 201) based on operations by an operator such as a user or a service representative, etc. The operation unit 150 may be configured to have a touch panel that functions as both a display means and an input means.

[0044] The DC controller 200 (CPU 201) also receives signals from the optical sensor 60, which is used when executing correction control to correct image color shift and density, and when detecting foreign matter such as sand on the intermediate transfer belt 10. For example, in the correction control, the optical sensor 60 detects the amount of light reflected from a test pattern (detection toner image) formed on the intermediate transfer belt 10 at a position opposite the optical sensor 60. The detection output (detection signal) indicating the detection result of the amount of reflected light by the optical sensor 60 is, for example, 0 V to 3.3 V. In this embodiment, the optical sensor 60 is configured so that the detection outputs of the first and second light receiving elements 62 and 63, which will be described later, increase as the amount of light received by these elements increases. The DC controller 200 (CPU 201) performs calculations using the detection results from the optical sensor 60 to correct density and color shift. In this embodiment, the density correction control method involves creating an image signal correction curve that will obtain the desired density curve based on the detection results of a test pattern for density detection (density control correction pattern). Also, 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 for detecting the amount of color misregistration (registration correction pattern). The color misregistration correction control and density correction control are performed when the execution conditions are met, with pre-set execution conditions corresponding to predetermined temperature and humidity changes, the number of prints (number of sheets passed), etc. Detection of foreign matter such as sand on the intermediate transfer belt 10 will be described later.

[0045] In this embodiment, the primary transfer power supply 23 is shared by the four image forming units S as described above. Although not shown, the charging power supply 24, the developing power supply 25, and the developing contact-separation mechanism 80 are provided independently for each image forming unit S. The charging power supply 24, the developing power supply 25, and the developing contact-separation mechanism 80 may each be shared by at least some of the image forming units S. The drive unit 90 includes a drive motor as a drive source and drive transmission members. The drive unit 90 includes drive motors for driving components such as the photosensitive drum 1, the developing roller 42 of the developing device 4, the intermediate transfer belt 10 (third tension roller 13), and the developing contact-separation mechanism 80. The drive motors for driving these components may be provided independently, or a common drive motor may be used to drive at least some of these components. The drive motors for driving the components for each color may be provided independently, or a common drive motor may be used to drive at least some of the components for each color. In this embodiment, 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.

[0046] Here, a print job (print operation, print sequence, image forming operation, image forming sequence) is a series of operations that starts with a single start command and forms and outputs an image on one or more recording materials P. A print job generally includes an image forming process, a pre-rotation process, a paper-to-paper interval process when forming images on multiple recording materials P, and a post-rotation process. The image forming process is a period during which an electrostatic latent image of the image to be actually formed and output on the recording material P is formed, a toner image is formed, and the toner image is first transferred, second transferred, and fixed. This period is referred to as the image formation time. More specifically, the timing of the image formation time varies depending on the positions where the charging, exposure, development, first transfer, second transfer, and fixing processes are performed. The pre-rotation process is a period during which preparatory operations are performed before the image forming process, from when a start command is input until the actual start of image formation. The paper-to-paper interval process is a period corresponding to the interval between recording materials P when image formation is performed continuously on multiple recording materials P (during continuous printing). The post-rotation process is a period in which a rearrangement operation (preparatory operation) is performed after the image forming process. The non-image forming period is a period other than the image forming period, and includes the pre-rotation process, the sheet interval process, the post-rotation process, and the pre-multiple rotation process, which is a preparatory operation when the image forming apparatus 100 is turned on or when the image forming apparatus 100 returns from a sleep state.

[0047] 3. Optical Sensor Next, the configuration of the optical sensor 60 will be described. Fig. 3 is a schematic top view of a unit including the intermediate transfer belt 10 near the optical sensors 60 (60F, 60R). Note that with respect to the image forming apparatus 100 and its elements, the front side of the paper in Fig. 1 (the lower side in Fig. 3) is referred to as the front side, and the back side of the paper in Fig. 1 (the upper side in Fig. 3) is referred to as the rear side. Also, with respect to the image forming apparatus 100 and its elements, the up and down direction refers to the up and down of the direction of gravity (the vertical direction), but does not mean just directly above or just below, and also includes the above and below of a horizontal plane passing through the element or position of interest.

[0048] In this embodiment, the image forming apparatus 100 is provided with a front optical sensor 60F and a rear optical sensor 60R as optical sensors 60. In the width direction, which is approximately perpendicular to the 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 rearward 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 on the rotation shaft of the first tension roller 11 so that the distance between the intermediate transfer belt 10 and the optical sensors 60 (60F, 60R) is always constant regardless of the inclination of the first tension roller 11. In this embodiment, the optical sensors 60 (60F, 60R) are disposed so that the distance between them and the intermediate transfer belt 10 is 3 mm.

[0049] In this embodiment, the front optical sensor 60F and the rear optical sensor 60R have substantially the same configuration, so we will explain the front optical sensor 60F as a representative (F and R indicating the front or rear optical sensor 60 will be omitted as appropriate).

[0050] FIG. 4 is a schematic cross-sectional view illustrating the configuration of the optical sensor 60. The optical sensor 60 includes a light-emitting element 61, a first light-receiving element 62, a second light-receiving element 63, and a holder 64. The light-emitting element 61 is configured with an LED or the like. The first light-receiving element 62 and the second light-receiving element 63 are each configured with a phototransistor or the like. In this embodiment, the light-emitting element 61 emits infrared light, which is irradiated onto the surface of the intermediate transfer belt 10 or a test pattern formed on the intermediate transfer belt 10. Reflected light from the surface of the intermediate transfer belt 10 or the test pattern formed on the intermediate transfer belt 10 is received by the first and second light-receiving elements 62 and 63. In this embodiment, the light-emitting element 61 is a light-emitting element that emits infrared light with a peak at a wavelength of 800 nm, and the first and second light-receiving elements 62 and 63 are light-receiving elements whose light-receiving sensitivity peaks at a wavelength of 800 nm.

[0051] Normal line G in FIG. 4 is approximately perpendicular to the surface of the intermediate transfer belt 10. The light-emitting element 61 is disposed at an angle of 15° with respect to normal line G. The holder 64 adjusts the shape of the light guide path so that the spot diameter when infrared light is irradiated from the light-emitting element 61 onto the intermediate transfer belt 10 is 2 mm. The first light-receiving element 62 is disposed at an angle of 15° with respect to normal line G and receives infrared light that is specularly reflected and diffusely reflected from the surface of the intermediate transfer belt 10 and the test pattern. The second light-receiving element 63 is disposed at an angle of 45° with respect to normal line G and receives infrared light that is diffusely reflected from the surface of the intermediate transfer belt 10 and the test pattern.

[0052] 4. Waveform of reflected light from the surface of the intermediate transfer belt detected by the optical sensor Next, we will explain the waveform of the detection output (detection waveform) that shows the detection result when the optical sensor 60 detects reflected light from the surface of the intermediate transfer belt 10. Here, we will explain the detection waveform acquired by the front optical sensor 60F, but the same tendency is observed in the detection waveform acquired by the rear optical sensor 60R (the same applies below to the detection waveforms of the optical sensors 60F and 60R). Furthermore, F and R, which indicate the front or rear optical sensor 60, will be omitted as appropriate.

[0053] FIG. 5 is a graph showing the detected waveforms when the first and second light receiving elements 62 and 63 detect light reflected from the surface of the intermediate transfer belt 10. Note that FIG. 5 shows the detected waveforms when no foreign matter, such as sand, is attached to the intermediate transfer belt 10. (a) in FIG. 5 is the detected waveform showing the detection result (specularly reflected light and diffusely reflected light) by the first light receiving element 62, and (b) in FIG. 5 is the detected waveform showing the detection result (diffusely reflected light) by the second light receiving element 63. The light emitting element 61 is driven in section (i) in FIG. 5. As a result of detecting the reflected light in this section (i), the detected output of the first light receiving element 62 is approximately 3.0 V, but the detected output of the second light receiving element 63 is lower. In other words, in section (i), the amount of reflected light detected by the second light receiving element 63 is lower than the amount of reflected light detected by the first light receiving element 62. This is because most of the light reflected from the surface of the intermediate transfer belt 10 is specularly reflected. In this embodiment, the amount of light emitted by the light-emitting element 61 and the light-receiving sensitivity of the first light-receiving element 62 are adjusted so that when the first light-receiving element 62 detects light reflected from the surface of the intermediate transfer belt 10, the detection output of the first light-receiving element 62 is approximately 3.0 V. In this embodiment, the optical sensor 60 is configured so that the detection output of the first light-receiving element 62 increases as the amount of light received by the first light-receiving element 62 increases. In section (ii) in Figure 5, it can be seen that the intermediate transfer belt 10 is rotating, and the amount of reflected light detected by the first and second light-receiving elements 62, 63 varies depending on the surface properties of the intermediate transfer belt 10.

[0054] 5. Waveform of reflected light from a toner patch detected by an optical sensor Next, we will explain the detection output waveform (detection waveform) that shows the detection result when the optical sensor 60 (here, the front optical sensor 60F) detects reflected light from the toner patch (the detection toner image that constitutes the test pattern) on the intermediate transfer belt 10.

[0055] 6 is a graph showing, as an example, the detection waveforms when the first and second light receiving elements 62 and 63 detect reflected light from a solid yellow toner patch 10 mm long in the moving direction on the surface of the intermediate transfer belt 10. (a) in FIG. 6 is the 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 the detection waveform showing the detection result (diffuse reflection light) by the second light receiving element 63.

[0056] First, the detection waveform of the first light receiving element 62 ((a) in FIG. 6) will be described. In the section where reflected light from the surface of the intermediate transfer belt 10 is detected, the first light receiving element 62 receives a large amount of specularly reflected light, and the detection output of the first light receiving element 62 is approximately 3.0 V. However, in the section where the toner patch is detected, the detection output of the first light receiving element 62 drops significantly to approximately 0.6 V. This is because the light reflected from the toner patch is mainly diffusely reflected light, and therefore the amount of reflected light reaching the first light receiving element 62 in the section where the toner patch is detected is less than in the section where reflected light from the surface of the intermediate transfer belt 10 is detected.

[0057] Next, the detection waveform of the second light receiving element 63 ((b) in FIG. 6) will be described. The second light receiving element 63 hardly detects light reflected from the surface of the intermediate transfer belt 10, but detects a large amount of light reflected from the toner patch, and the detection output of the second light receiving element 63 is approximately 3.0 V. In this embodiment, the light receiving sensitivity of the second light receiving element 63 is adjusted so that when the second light receiving element 63 detects light reflected from the toner patch, the detection output of the second light receiving element 63 becomes approximately 3.0 V. In this embodiment, the optical sensor 60 is configured so that the detection output of the second light receiving element 63 increases as the amount of light received by the second light receiving element 63 increases.

[0058] 6. Outline of the effects of foreign matter intrusion and countermeasures It is expected that image forming apparatus 100 will be used in a variety of environments. Therefore, in some cases, image forming apparatus 100 may be used in an environment where foreign objects are likely to enter the interior of the apparatus. For example, in a windy environment where a ceiling fan is in use and sand (sand dust, sandy dirt) is blowing around, foreign objects such as sand may enter the interior of image forming apparatus 100 due to the wind and adhere to various components. Foreign objects such as sand may be carried by the wind and enter the interior of image forming apparatus 100, for example, from paper discharge port 130 of image forming apparatus 100 or from openings for ventilation by fans (not shown), such as an exhaust fan or an intake fan.

[0059] If sand or other foreign matter gets inside the image forming apparatus 100, the sand or other foreign matter may adhere to the photosensitive drum 1 (the outer peripheral surface of the photosensitive drum 1) or the intermediate transfer belt 10 (the outer peripheral surface of the intermediate transfer belt 10). For example, if sand or other foreign matter adheres to the intermediate transfer belt 10, the surface of the intermediate transfer belt 10 may be scratched. Since the intermediate transfer belt 10 transports the toner image to the transfer material P, scratches on the surface of the intermediate transfer belt 10 may affect the image formed by the image forming apparatus 100. Furthermore, the image forming apparatus 100 has many contact members that come into contact with the outer peripheral surface of the intermediate transfer belt 10. Specifically, in this embodiment, the secondary transfer roller 20, the conductive brush 16, and the photosensitive drum 1 come into contact with the outer peripheral surface of the intermediate transfer belt 10. Therefore, if foreign matter such as sand adheres to the intermediate transfer belt 10, the foreign matter may move from the intermediate transfer belt 10 to a contact member, causing scratches on the contact member, or the surface of the intermediate transfer belt 10 may be scratched due to friction between the contact member and the intermediate transfer belt 10 caused by the foreign matter. Thus, if foreign matter such as sand adheres to the intermediate transfer belt 10, it may cause damage to the intermediate transfer belt 10 or the contact member that contacts the intermediate transfer belt 10. Note that, as a contact member that contacts the intermediate transfer belt 10, the photosensitive drum 1 may have foreign matter such as sand adhered to it from the intermediate transfer belt 10, and may also have foreign matter such as sand adhere directly to the photosensitive drum 1. As with the intermediate transfer belt 10, if foreign matter such as sand adheres to the photosensitive drum 1, it may cause damage to the photosensitive drum 1 or the contact member that contacts the photosensitive drum 1.

[0060] As described above, for example, in a windy environment where sand or other foreign matter is blowing around, foreign matter such as sand may adhere to the intermediate transfer belt 10 or the photosensitive drum 1 while the image forming apparatus 100 is stopped. In this case, if a configuration is used in which the operation of the image forming apparatus 100 is stopped when foreign matter such as sand is detected, the foreign matter would be detected when the image forming apparatus 100 starts operating, causing the operation of the image forming apparatus 100 to be stopped, which may inconvenience the user. Therefore, it is desirable to be able to continue the operation of the image forming apparatus 100 without causing inconvenience to the user when foreign matter such as sand is detected. In other words, it is desirable to be able to detect the adhesion of foreign matter such as sand on the intermediate transfer belt 10 or the photosensitive drum 1, perform processing to reduce the impact of the adhesion of the foreign matter as quickly as possible, and then continue the operation of the image forming apparatus 100.

[0061] Therefore, in this embodiment, the optical sensor 60 is used to determine whether or not foreign matter such as sand is present on the intermediate transfer belt 10. If it is determined that foreign matter is present, a process is quickly performed to reduce the impact of the foreign matter, allowing the image forming apparatus 100 to continue operating. The process of reducing the impact of foreign matter such as sand is performed by a toner supply operation (toner purge) that supplies toner to contact members to which foreign matter may be attached. This toner supply operation dilutes (or covers) foreign matter such as sand adhering to the contact members with toner, thereby preventing scratches on the contact members or the intermediate transfer belt 10. Furthermore, this toner supply operation washes away (washes away) foreign matter such as sand adhering to the contact members with toner, thereby removing at least some of the foreign matter from the contact members before it can scratch the contact members or the intermediate transfer belt 10.

[0062] Here, sand will be mainly used as an example of foreign matter that may adhere to the intermediate transfer belt 10, but the foreign matter is not limited to sand and may be any foreign matter that would not normally be present on the intermediate transfer belt 10.

[0063] Also, here, obtaining the detection result by the optical sensor 60 and performing the process for executing the toner supply operation is also referred to as simply detecting foreign matter (sand, etc.) or determining whether or not foreign matter (sand, etc.) is present. In other words, it is not necessarily necessary to actually detect or determine that the foreign matter is a specific foreign matter such as sand.

[0064] 7.Detection of foreign objects using optical sensors Next, detection of foreign matter using the optical sensor 60 will be described.

[0065] First, we will explain the detection waveform of the optical sensor 60 when foreign matter such as sand adheres locally to the intermediate transfer belt 10. When sand adheres to the intermediate transfer belt 10, the detection waveforms indicating the amount of light received by the first light receiving element 62 and the second light receiving element 63 are as shown in Figures 7 and 8. Specifically, Figures 7 and 8 show the results when sand with an average particle size of 5 μm is scattered only in a 1.5 cm square area on the intermediate transfer belt 10 so that it passes through detection position D of the optical sensor 60 (here, the front optical sensor 60F).

[0066] 7 is a graph showing the detection waveform of the second light receiving element 63 when sand is present on the intermediate transfer belt 10 and passes the detection position D of the optical sensor 60. The light emitting element 61 is driven in section (i) in FIG. 7. As shown in FIG. 7, the light reflected 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 light reflected from the sand is mainly diffusely reflected light, so the amount of light received by the second light receiving element 63 increases when the sand passes the detection position D of the optical sensor 60.

[0067] Diffusely reflected light can also be received by the first light receiving element 62. Fig. 8 shows a detection waveform when sand on the intermediate transfer belt 10, the same as in Fig. 7, is detected by the first light receiving element 62. When the sand passes 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 light received by the first light receiving element 62 decreases compared to when it is receiving reflected light from the surface of the intermediate transfer belt 10.

[0068] By utilizing the tendency of the detection results of the optical sensor 60 to detect foreign matter such as sand, it is possible to detect foreign matter on the intermediate transfer belt 10. For example, as shown in FIG. 7, a threshold value is set in advance as a case where a predetermined condition is satisfied, and when a detection output from the second light receiving element 63 exceeds (crosses or exceeds) the threshold value, it can be determined that a foreign matter exists on the intermediate transfer belt 10 (an abnormality on the intermediate transfer belt 10). Also, as shown in FIG. 8, a threshold value is set in advance as a case where a predetermined condition is satisfied, and when a detection output from the first light receiving element 62 falls below (crosses or exceeds) the threshold value, it can be determined that a foreign matter exists on the intermediate transfer belt 10 (an abnormality on the intermediate transfer belt 10).

[0069] As described above, for example, in a strong wind environment where sand and the like are blowing around, foreign matter such as sand may adhere to the intermediate transfer belt 10 while the image forming apparatus 100 is stopped.

[0070] Therefore, in this embodiment, immediately after the image forming apparatus 100 (intermediate transfer belt 10) starts operating, the optical sensor 60 detects reflected light from the intermediate transfer belt 10. This makes it possible to detect foreign matter such as sand adhering to the intermediate transfer belt 10 while the image forming apparatus 100 is stopped.

[0071] However, in a situation where foreign matter such as sand adheres to the intermediate transfer belt 10 while the image forming apparatus 100 is stopped, a relatively large amount of foreign matter such as sand may adhere to a wide area on the intermediate transfer belt 10, causing the foreign matter to be continuously present on the intermediate transfer belt 10. For this reason, it may be difficult to detect foreign matter based on the difference in the detection result (whether or not the difference crosses the threshold value corresponding to the difference) when the foreign matter passes through the detection position D of the optical sensor 60 within one revolution of the intermediate transfer belt 10, or the foreign matter may be constantly detected.

[0072] To explain further, when foreign matter such as sand adheres to the intermediate transfer belt 10, the foreign matter may adhere to substantially the entire surface of the intermediate transfer belt 10. When foreign matter adheres to substantially the entire surface of the intermediate transfer belt 10, the detection waveform will not have a peak as shown in FIGS. 7 and 8, but will have an overall deviation in the detection result due to the adhesion of the foreign matter. For example, FIGS. 9 and 10 are graphs showing the detection waveform of the optical sensor 60 (here, the front optical sensor 60F) when foreign matter adheres to substantially the entire surface of the intermediate transfer belt 10. FIG. 9 shows the detection waveform of the amount of specularly reflected light by the first light receiving element 62, and FIG. 10 shows the detection waveform of the amount of diffusely reflected light by the second light receiving element 63. 9 and 10 respectively show a detection waveform when no foreign matter is attached to the intermediate transfer belt 10 immediately before the image forming apparatus 100 (intermediate transfer belt 10) stops operating, and a detection waveform immediately after the image forming apparatus 100 (intermediate transfer belt 10) starts operating after foreign matter has attached to almost the entire surface of the intermediate transfer belt 10. In other words, Figures 9 and 10 show changes in the detection waveform when foreign matter such as sand attaches (accumulates) to almost the entire surface of the intermediate transfer belt 10 while the image forming apparatus 100 (intermediate transfer belt 10) is stopped operating.

[0073] The following usage environment of the image forming apparatus 100 is assumed as a case where foreign matter such as sand adheres to substantially the entire surface of the intermediate transfer belt 10. For example, as shown in FIG. 11, this is an environment where a strong wind is blowing from above the image forming apparatus 100 by a ceiling fan, and sand (sand dust, sand particles) is present in the air. If the image forming apparatus 100 is installed in such a usage environment, the wind may cause sand to enter the interior of the image forming apparatus 100, resulting in sand adhering to substantially the entire surface of the intermediate transfer belt 10. Assuming such a usage environment, adhesion of sand to the intermediate transfer belt 10 was confirmed under the following conditions. Sand with an average particle size of 5 μm was used at a concentration of 100 mg / m 3 The image forming apparatus 100 was installed in a space where a wind speed of 4 m / s was blown from above the image forming apparatus 100 for 5 hours, and then the wind was stopped and the apparatus was left for 20 hours. For example, under these conditions, it was confirmed that sand that had entered the interior of the image forming apparatus 100 was deposited on almost the entire surface of the intermediate transfer belt 10. Note that these wind strengths and concentrations are only an example of the conditions under which it was confirmed that foreign matter such as sand adhered to almost the entire surface of the intermediate transfer belt 10, and the conditions are not limited to these.

[0074] In this way, when foreign matter adheres to substantially the entire surface of the intermediate transfer belt 10, it may be difficult to detect the foreign matter during the rotation of the intermediate transfer belt 10 (within one rotation). For example, in the case of the detection waveforms shown in Figures 7 and 8, a peak due to the foreign matter is formed, and the presence of the foreign matter can be determined based on the difference in the detection output between the peak and the detection output before and after the peak. However, in the case of the detection waveforms immediately after the start of operation of the image forming apparatus 100 (intermediate transfer belt 10) shown in Figures 9 and 10, the peak due to the foreign matter does not appear clearly, so it is difficult to obtain the difference in the detection output between the peak and the detection output before and after the peak, making it difficult to determine whether or not foreign matter is attached.

[0075] Therefore, in this embodiment, the optical sensor 60 detects reflected light from the intermediate transfer belt 10 immediately before the previous stop of operation of the image forming apparatus 100 (intermediate transfer belt 10) and immediately after the current start of operation of the image forming apparatus 100 (intermediate transfer belt 10). If a difference of a certain amount or more is observed between the two detection results, it is determined that foreign matter is present on the intermediate transfer belt 10. Immediately before the stop of operation of the image forming apparatus 100, substantially no foreign matter is attached to the intermediate transfer belt 10. This is because the foreign matter is collected by a contact member that contacts the intermediate transfer belt 10, etc. By comparing the detection waveform immediately before the stop of operation of the image forming apparatus 100 (intermediate transfer belt 10) without any foreign matter attached to the intermediate transfer belt 10 with the detection waveform immediately after the next start of operation of the image forming apparatus 100 (intermediate transfer belt 10), it is possible to detect the attachment of foreign matter to the intermediate transfer belt 10 during the stop of operation of the image forming apparatus 100 (intermediate transfer belt 10). Here, the period immediately before the image forming apparatus 100, specifically the intermediate transfer belt 10, stops operating is also simply referred to as "immediately before operation stops." This period immediately before operation stops is typically during the post-rotation process. Here, the period immediately after the image forming apparatus 100, specifically the intermediate transfer belt 10, starts operating is also simply referred to as "immediately after operation starts." This period immediately after operation starts is typically during the pre-rotation process or the pre-multiple-rotation process. Here, the period while the image forming apparatus 100, specifically the intermediate transfer belt 10, is stopped is also simply referred to as "during operation stop." This period while operation is stopped is typically when the image forming apparatus 100 is in a sleep state or a power-off state.

[0076] Typically, if no foreign matter enters the image forming apparatus 100, the state inside the image forming apparatus 100 remains unchanged between immediately before the previous shutdown and immediately after the current startup. Therefore, in this case, the surface state (reflected light intensity) of the intermediate transfer belt 10 remains substantially the same immediately before the previous shutdown and immediately after the current startup. On the other hand, for example, in an environment where strong winds are blowing continuously and sand is blown about, sand may be carried by the wind into the image forming apparatus 100 and then adhere to and accumulate on the intermediate transfer belt 10. If such accumulation of foreign matter on the intermediate transfer belt 10 occurs during a shutdown, the surface state (reflected light intensity) of the intermediate transfer belt 10 differs between immediately before the previous shutdown and immediately after the current startup, resulting in a difference in the detection output of the optical sensor 60. Therefore, it is effective to detect foreign matter on the intermediate transfer belt 10 based on the difference in the amount of reflected light from the intermediate transfer belt 10 between immediately before the previous shutdown and immediately after the current startup. Furthermore, foreign matter such as sand that gets inside the image forming apparatus 100 accumulates on the intermediate transfer belt 10 while the apparatus is stopped, increasing in amount. Therefore, if the operation is stopped for a long time, the amount of foreign matter adhering (accumulating) increases, so it is particularly effective to detect foreign matter on the intermediate transfer belt 10 based on the difference in the amount of reflected light from the intermediate transfer belt 10 immediately before the previous operation was stopped and immediately after the current operation is started.

[0077] When it is detected that sand or other foreign matter is attached to the intermediate transfer belt 10, it is likely that sand or other foreign matter is also attached to the photosensitive drum 1 in the same manner.

[0078] Here, foreign matter detection using the optical sensor 60 according to the present invention is particularly effective when the surface gloss of the intermediate transfer belt 10 is relatively high or when there is little gloss unevenness. Specifically, the surface gloss of the intermediate transfer belt 10 is preferably 60 or higher, more preferably 80 or higher. The surface gloss of the intermediate transfer belt 10 may be 100. Furthermore, the deviation of the gloss unevenness from the average value is preferably 30% or less, more preferably 20% or less. In this embodiment, as described above, the surface gloss of the intermediate transfer belt 10 is 75. Furthermore, as described above, the surface gloss of the intermediate transfer belt 10 can be measured using a commercially available measuring device, such as the IG-320 handheld gloss meter from Horiba, Ltd. In order to distinguish between reflected light from the surface of the intermediate transfer belt 10 and reflected light from foreign matter attached to the surface of the intermediate transfer belt 10, it is desirable for the surface gloss of the intermediate transfer belt 10 to have little gloss unevenness, because this makes it easier for differences in reflected light to occur. Examples of 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.

[0079] 8. Control of foreign object detection and toner supply operations Next, the control of the foreign matter detection operation and the toner supply operation in this embodiment will be described with reference to the flowchart of FIG.

[0080] First, when starting a print job, the CPU 201 reads from the memory 202 the thresholds A and B that were determined by executing the processes of S106 and S107 (described later) immediately before the previous operation stop (S101). The details of determining the thresholds A and B in S106 and S107 will be described later.

[0081] Next, immediately after starting operation (during the pre-rotation step or the pre-multiple-rotation step), the CPU 201 acquires the detected light amount A2 of the first light receiving element 62 and the detected light amount B2 of the second light receiving element 63, and stores them in the memory 202 (S102). The detected light amount A2 of the first light receiving element 62 is the average value of the sampling results of the detection output of the first light receiving element 62. Also, the detected light amount B2 of the second light receiving element 63 is the average value of the sampling results of the detection output of the second light receiving element 63.

[0082] The detected light amounts A2 and B2 will now be described in more detail. In this embodiment, in order to more accurately compare the surface conditions of the intermediate transfer belt 10 before and after the adhesion of foreign matter and determine the presence or absence of foreign matter, the sampling intervals of the detection outputs of the first light receiving element 62 and the second light receiving element 63 are shortened. Specifically, the detection outputs of the first light receiving element 62 and the second light receiving element 63 are sampled at 0.1 mm intervals along the movement distance of the surface of the intermediate transfer belt 10. This sampling interval is preferably 0.01 mm or more and 0.2 mm or less. In this embodiment, this sampling interval is the same as the sampling interval (e.g., 0.1 mm) used when detecting reflected light from the toner patch, but a different sampling interval may also be used. In this embodiment, the detection of reflected light from the intermediate transfer belt 10 immediately after the start of operation is performed for a maximum period from the start of rotation of the intermediate transfer belt 10 until the intermediate transfer belt 10 has completed one rotation. However, if foreign matter can be detected early in S103 (described later), the detection of reflected light from the intermediate transfer belt 10 immediately after the start of this operation may be completed in a period shorter than the period for one rotation of the intermediate transfer belt 10. During the sampling in S102, the CPU 201 calculates the average values of the detection outputs of the 10 sampling points as the detected light amounts A2 and B2, and stores them in the memory 202.

[0083] Each time the CPU 201 stores the average values of the detection outputs of the 10 sampling points as detected light amounts A2 and B2 in the memory 202, it compares the detected light amounts A2 and B2 with the thresholds A and B read in S101 (S103). If there is a timing in S103 where the detected light amount A2 is equal to or less than threshold A and the detected light amount B2 is equal to or greater than threshold B, the CPU 201 executes a toner supply operation (S104). This is because it can be determined that a foreign object is present on the intermediate transfer belt 10 that passed through detection position D at that timing. The CPU 201 then executes image formation (S105). For convenience, FIG. 12 shows an example in which a foreign object is detected early, and sequentially describes the detection of reflected light from the intermediate transfer belt 10 immediately after the start of operation (S102), the determination of whether a toner supply operation is necessary (S103), the toner supply operation (S104), and image formation (S105). However, in this embodiment, the timing of the toner supply operation is changed depending on the timing at which a foreign object is detected between the start of rotation of the intermediate transfer belt 10 and the completion of one full rotation of the intermediate transfer belt 10 at the longest. In this embodiment, if a foreign object is detected after a predetermined timing during detection of reflected light from the intermediate transfer belt 10 (such as the timing at which preparation for image formation on the first sheet is completed), the toner supply operation is performed in the interval between image formation on the first and second sheets (see FIG. 15). On the other hand, if there is no timing in S103 when the detected light amount A2 is equal to or less than threshold A and the detected light amount B2 is equal to or greater than threshold B, the CPU 201 does not perform the toner supply operation and performs image formation as usual (S105). This is because it can be determined that no foreign object is present on the intermediate transfer belt 10.

[0084] In this embodiment, the toner supply operation is executed when both the detected light amounts A2 and B2 satisfy a predetermined condition. For example, when the amount of foreign matter is small and the fluctuations in the amount of specularly reflected light and the amount of diffusely reflected light are small, it is possible that the threshold condition is satisfied due to the variation in only one of the detected light amounts A2 and B2. Therefore, in this embodiment, if only one of the detected light amounts A2 and B2 satisfies the predetermined condition, the amount of foreign matter is considered to be small and the toner supply operation is not executed. In other words, by determining whether or not foreign matter is present based on whether both the detected light amounts A2 and B2 satisfy the predetermined condition, the accuracy of foreign matter detection can be improved. This allows the toner supply operation to be avoided when it is not necessary, thereby reducing toner consumption and shortening control time.

[0085] The toner supply operation (toner purge) in S104 will be further described. In this embodiment, during the toner supply operation, as shown in FIG. 13, a band-shaped toner image (toner band) extending in the width direction of the intermediate transfer belt 10 is formed on the intermediate transfer belt 10 using toner of each color, yellow, magenta, cyan, and black. The predetermined toner image formed on the intermediate transfer belt 10 during the toner supply operation is also referred to as a "supply toner image," and the toner constituting the supply toner image is also referred to as "supply toner." In this embodiment, the length of each supply toner image in the moving direction of the surface of the intermediate transfer belt 10 is 10 mm, and the length in the width direction of the intermediate transfer belt 10 covers substantially the entire width of the intermediate transfer belt 10. In this embodiment, the density of each supply toner image is a solid density. Here, "substantially the entire width direction of the intermediate transfer belt 10" refers to substantially the entire area (image forming area) in the width direction of the intermediate transfer belt 10 to which toner can be supplied. In this embodiment, the width of this area is 230 mm, which is approximately the same as the width of the area in the direction of the rotation axis of the photosensitive drum 1, which corresponds to the width direction of the intermediate transfer belt 10, in which the developing roller 42 can supply toner onto the photosensitive drum 1.

[0086] In this embodiment, the toner supply operation involves the same steps as in image formation: charging, exposure, development, and primary transfer, to form a supply toner image on the intermediate transfer belt 10. That is, in this embodiment, the toner supply operation involves forming a supply toner image over substantially the entire image forming area on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1, and then transferring the supply toner image to the intermediate transfer belt 10. This results in a supply toner image over substantially the entire image forming area on the intermediate transfer belt 10 in the width direction of the intermediate transfer belt 10. Here, the entire image forming area on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1 and the entire image forming area on the intermediate transfer belt 10 in the width direction of the intermediate transfer belt 10 are collectively referred to as "substantially the entire width of the image forming area." When the supply toner image formed on the photosensitive drum 1 is transferred to the intermediate transfer belt 10, a portion of the supply toner image is supplied to the cleaning blade 71 as residual toner. Furthermore, a portion of the supply toner image transferred to the intermediate transfer belt 10 is supplied to the secondary transfer roller 20, and another portion is supplied to the conductive brush 16. The supplied toner supplied to the conductive brush 16 is then collected in the same manner as the secondary transfer residual toner described above. That is, the supplied toner is charged by the conductive brush 16, moves to the photosensitive drum 1 (for example, the photosensitive drum 1a located most upstream in the moving direction of the surface of the intermediate transfer belt 10), and is collected by the drum cleaning device 5. During this process, foreign matter such as sand adhering to each contact member is diluted (or covered) with the supplied toner, thereby preventing damage to the contact members and the intermediate transfer belt 10. Furthermore, during this process, foreign matter such as sand adhering to each contact member is washed away (swept away) with the supplied toner, and at least some of the foreign matter such as sand can be removed from the contact members together with the supplied toner.

[0087] The reason for supplying toner to substantially the entire width of the image forming area is as follows: Foreign matter such as sand is unlikely to adhere to only specific portions of the intermediate transfer belt 10 in the width direction of the intermediate transfer belt 10. Similarly, foreign matter such as sand is unlikely to adhere to only specific portions of the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1. Therefore, by supplying toner to substantially the entire width of the image forming area, toner can be supplied to the contact members that come into contact with the intermediate transfer belt 10 or the photosensitive drum 1 over substantially the entire width of the image forming area. This makes it possible to dilute (or cover) foreign matter adhering to the contact members with toner, or to wash away (push away) foreign matter that has come into contact with the contact members over substantially the entire width of the image forming area.

[0088] The CPU 201 acquires the detected light amount A1 of the first light receiving element 62 and the detected light amount B1 of the second light receiving element 63 immediately before stopping operation (during the post-rotation process) after completing formation of the last image in S105, and stores them in the memory 202 (S106). The detected light amount A1 of the first light receiving element 62 is the average value of the sampling results of the detection output of the first light receiving element 62. The detected light amount B1 of the second light receiving element 63 is the average value of the sampling results of the detection output of the second light receiving element 63. Here, "immediately before stopping operation" refers, more specifically, to after the image formation area of the last image in the print job on the intermediate transfer belt 10 has passed the detection position D of the optical sensor 60. Thereafter, the CPU 201 determines the threshold values A and B, stores (updates) the information on the threshold values A and B in the memory 202 (S107), and stops (ends) operation of the image forming apparatus 100.

[0089] The acquisition of the detected light amounts A1 and B1 and the determination of the thresholds A and B in S106 and S107 will be further described. First, in S106, immediately before stopping operation at the end of the print job, the CPU 201 acquires the detection outputs of the first light receiving element 62 and the second light receiving element 63 over a period corresponding to one revolution of the intermediate transfer belt 10 and stores the detected light amounts A1 and B1 in the memory 202. Also, in S106, the CPU 201 calculates the average values of the detection outputs of the first light receiving element 62 and the second light receiving element 63 acquired during one revolution of the intermediate transfer belt 10 as the detected light amounts A1 and B1, respectively, and stores the average values in the memory 202. In this embodiment, the sampling interval at this time is also set to 0.1 mm intervals in the moving distance of the surface of the intermediate transfer belt 10, as described above. Next, in S107, the CPU 201 sets the thresholds A and B. The CPU 201 sets the threshold value A based on the detected light amount A1 and the threshold value B based on the detected light amount B1, separately. As described above, the threshold value A is a threshold value for comparison with the detected light amount A2, and the threshold value B is a threshold value for comparison with the detected light amount B2. Specifically, in this embodiment, the threshold value A is set to 0.9 times the detected light amount A1, and the threshold value B is set to 1.1 times the detected light amount B1. These 0.9 times and 1.1 times correspond to a predetermined difference (difference) in the amount of light reflected from the intermediate transfer belt 10 immediately before the previous operation was stopped and immediately after the current operation was started, respectively, for determining whether or not a toner supply operation is required.

[0090] In this embodiment, threshold value A is set to 0.9 times the detected light amount A1, and threshold value B is set to 1.1 times the detected light amount B1, but threshold values A and B are not limited to these values. For example, the detection waveform may differ depending on the color of the intermediate transfer belt 10, or the susceptibility of the intermediate transfer belt 10 to scratches by foreign matter may differ depending on its hardness. Therefore, it is possible to set the threshold values appropriately depending on the detection waveform and the foreign matter to be detected.

[0091] Furthermore, if information (threshold values A and B in this embodiment) regarding the detection result of light reflected from the intermediate transfer belt 10 immediately before the previous operation was stopped has not been acquired, typically, the following can be done, for example, during the first operation of the image forming apparatus 100. In this case, image formation (S105) can be performed without detecting light reflected from the intermediate transfer belt 10 immediately after the start of operation (S102), determining whether or not a foreign object is present (S103), and performing the toner supply operation (S104). In this case, the foreign object detection operation of Modified Example 2, which will be described later, may be performed.

[0092] Further, the detection of reflected light from the intermediate transfer belt 10 immediately after the start of operation and immediately before the stop of operation is performed when the toner patch (toner image for detection) on the intermediate transfer belt 10 has not passed the detection position D.

[0093] FIGS. 14 and 15 are timing charts outlining the operation of each component during a print job in this embodiment. FIGS. 14 and 15 illustrate an example of a print job in which three A4 sheets are continuously printed. FIG. 14 illustrates an example in which it is determined that no foreign matter is present on the intermediate transfer belt 10 and the toner supply operation is not performed, while FIG. 15 illustrates an example in which it is determined that a foreign matter is present on the intermediate transfer belt 10 and the toner supply operation is performed. FIGS. 14 and 15 also illustrate the rotational drive timing of the intermediate transfer belt 10, the timing at which the developing roller 42 contacts or separates from the photosensitive drum 1, the drive timing of the exposure device 3 for image formation or toner supply operation, the drive timing of the optical sensor 60 (the light-emitting element 61 emits light), and the sampling timing, which is the data acquisition period for calculating and processing the detection results of the first light-receiving element 62 and the second light-receiving element 63. In this embodiment, the photosensitive drums 1a, 1b, 1c, and 1d rotate and stop in synchronization with the intermediate transfer belt 10. In this embodiment, when the photosensitive drum 1 is rotating during a print job, the surface of the photosensitive drum 1 is substantially always charged by the charging roller 2. Also, Fig. 15 shows an example of a case where a toner supply operation is performed between the first and second image formations in accordance with the timing of foreign matter detection while detecting reflected light from the intermediate transfer belt 10 immediately after the start of operation. The operations in accordance with the timing charts in Figs. 14 and 15 are controlled by the CPU 201.

[0094] As shown in FIGS. 14 and 15, sampling of the detection outputs of the first light receiving element 62 and the second light receiving element 63 is performed immediately after the start of operation and immediately before the stop of operation (operations of S102 and S106 in FIG. 12, respectively). Furthermore, detected light amounts A2 and B2 are calculated for every 10 sampling points of the detection outputs of the first light receiving element 62 and the second light receiving element 63 immediately after the start of operation, and compared with threshold values A and B based on the detection outputs of the first light receiving element 62 and the second light receiving element 63 immediately before the previous stop of operation. This determines whether a toner supply operation is required. In this embodiment, after the drive of the intermediate transfer belt 10 (and the photosensitive drum 1) is started, sampling of the detection outputs of the first light receiving element 62 and the second light receiving element 63 is started immediately after the start of operation, while the developing roller 42 is separated from the photosensitive drum 1. In this embodiment, sampling of the detection outputs of the first light receiving element 62 and the second light receiving element 63 immediately after the start of operation is started substantially simultaneously with the start of drive of the intermediate transfer belt 10. After image formation is completed and the developing roller 42 is separated from the photosensitive drum 1, sampling of the detection outputs of the first light receiving element 62 and the second light receiving element 63 immediately before the operation is stopped is performed. As soon as this sampling is completed, drive of the intermediate transfer belt 10 is stopped, and the operation of the image forming apparatus 100 is terminated. In this embodiment, drive of the intermediate transfer belt 10 is stopped substantially simultaneously with the completion of sampling of the detection outputs of the first light receiving element 62 and the second light receiving element 63 immediately before the operation is stopped. In this embodiment, the optical sensor 60 is driven only for the period required to sample the detection outputs of the first light receiving element 62 and the second light receiving element 63, taking into account the start-up time of the light-emitting element 61, etc. However, for example, the optical sensor 60 may be driven constantly during operation of the image forming apparatus 100 (intermediate transfer belt 10). 14, it is determined that no foreign matter is present on the intermediate transfer belt 10, so the toner supply operation is not performed. On the other hand, in the example of FIG. 15, it is determined that foreign matter is present on the intermediate transfer belt 10, so the toner supply operation is performed. In the example of FIG. 15, as described above, the toner supply operation is performed in the interval between sheets after the completion of image formation on the first sheet and before the start of image formation on the second sheet. After the toner supply operation is performed, image formation is performed as usual.

[0095] In the example of FIG. 15, the toner supply operation is performed between the image formation of the first sheet and the image formation of the second sheet, but it may be performed at other timings. For example, if foreign matter is detected early as described with reference to FIG. 12, the toner supply operation may be performed before the image formation of the first sheet. Furthermore, in a print job in which one image is formed or a print job in which continuous image formation is performed for a predetermined number of sheets or less (e.g., five sheets or less), the toner supply operation may be performed after all images of the print job are completed. From the viewpoint of quickly reducing the influence of foreign matter, the number of images formed before the toner supply operation is performed from the start of operation of image forming apparatus 100 is appropriately about 10 sheets or less, preferably five sheets or less, more preferably three sheets or less, and most preferably one sheet or less. Alternatively, the first image formation may always be started after determining whether or not a toner supply operation is required.

[0096] In this embodiment, the supply toner image formed on the intermediate transfer belt 10 during the toner supply operation has a uniform amount of supply toner across substantially the entire width of the intermediate transfer belt 10. However, the pattern of the supply toner image is not limited to this. For example, there may be a case where wind is more likely to enter the interior of the image forming apparatus 100 from only one side of the width of the intermediate transfer belt 10 (the front-to-rear direction of the image forming apparatus 100), and the side where wind is more likely to enter tends to have more foreign matter such as sand adhere to it. In this case, if foreign matter tends to adhere across the width of the intermediate transfer belt 10, the amount of supply toner may be increased on the side with more foreign matter adherence than on the side with less foreign matter adherence. For example, as shown in FIG. 16 , the length of each color supply toner image in the direction of movement on the surface of the intermediate transfer belt 10 can be changed depending on the position across the width of the intermediate transfer belt 10, thereby changing the amount of supply toner across the width of the intermediate transfer belt 10. In the example shown in FIG. 16 , the length of each supply toner image of each color in the moving direction of the surface of the intermediate transfer belt 10 increases from one end (front side) to the other end (rear side) in the width direction of the intermediate transfer belt 10. Also, for example, the amount of supply toner in the width direction of the intermediate transfer belt 10 can be changed by changing the density of the supply toner image depending on the position in the width direction of the intermediate transfer belt 10. For example, supply toner images of each color may be formed in which the density of the supply toner image increases from one end (front side) to the other end (rear side) in the width direction of the intermediate transfer belt 10. Both the shape and density of the supply toner image may be changed depending on the position in the width direction of the intermediate transfer belt 10. Furthermore, the supply toner image is not limited to one whose shape and density change continuously in the width direction of the intermediate transfer belt 10 as described above, but may also change in a stepwise manner in the width direction of the intermediate transfer belt 10 (for example, between the front half and the rear half). The supply toner image may be composed of a plurality of discontinuous toner images in the width direction of the intermediate transfer belt 10.

[0097] In this embodiment, the density of the supplied toner image is a solid density, but the density of the supplied toner image is not limited to this and can be set appropriately depending on the tendency of foreign matter adhering to the intermediate transfer belt 10 and the amount of such foreign matter adhering.

[0098] Furthermore, in this embodiment, the detection results of both the first light receiving element 62 and the second light receiving element 63 are used, but it is also possible to use only one of these detection results. Furthermore, in this embodiment, when the detection results of both the first light receiving element 62 and the second light receiving element 63 are used, the toner supply operation is executed if both the detected light amounts A2 and B2 satisfy a predetermined condition. However, it is also possible to execute the toner supply operation if only one (or a specific one) of the detected light amounts A2 and B2 satisfies a predetermined condition.

[0099] Although the above description has focused primarily on the front optical sensor 60F, the control of this embodiment can be performed using either the front optical sensor 60F or the rear optical sensor 60R. The control of this embodiment can be performed using only one of the front optical sensor 60F and the rear optical sensor 60R, or both. For example, when both the front optical sensor 60F and the rear optical sensor 60R are used, the toner supply operation can be performed even when it is determined that a foreign object is present only on one side of the intermediate transfer belt 10 in the width direction. In this case, for example, the amount of toner supplied to the half of the intermediate transfer belt 10 in the width direction on the side where the foreign object is determined to be present can be increased compared to the amount of toner supplied to the other half. For example, the amount of toner supplied to the intermediate transfer belt 10 in the width direction can be changed by changing the pattern (shape, density) of the supplied toner image as described above in accordance with the detection results of the front optical sensor 60F and the rear optical sensor 60R.

[0100] In this embodiment, a threshold value is set based on the detection result of the light reflected from the intermediate transfer belt 10 in a state where it can be evaluated that there is substantially no foreign matter attached, and the presence or absence of foreign matter is determined based on whether the detection result exceeds (crosses) the threshold value. However, the present invention is not limited to this configuration. It is sufficient to determine the difference between the detection result of the light reflected from the intermediate transfer belt 10 in a state where it can be evaluated that there is substantially no foreign matter attached and the detection result of the light reflected from the intermediate transfer belt 10 in a state where there is foreign matter attached. Therefore, the presence or absence of foreign matter may be determined by directly calculating the difference between the two detection results and determining whether the difference exceeds (crosses) a predetermined threshold value. In this case, the ratio of the two detection results may be compared with the threshold value, rather than the difference between the two detection results themselves. For example, the presence of foreign matter can be determined when the amount of specular reflection light (detection output) decreases by more than 10% or when the amount of diffuse reflection light (detection output) increases by more than 10%.

[0101] 9. Effect of toner supply operation Next, the effect of the toner supply operation will be further explained by comparing this embodiment with a comparative example. After the image forming apparatus 100 is placed under conditions where the sand described above adheres to substantially the entire surface of the intermediate transfer belt 10, the toner supply operation is performed in this embodiment, but not in the comparative example.

[0102] When sand adheres to the intermediate transfer belt 10, the detection waveforms of the first light-receiving element 62 and the second light-receiving element 63 change as shown in FIGS. 9 and 10. If the intermediate transfer belt 10 continues to operate, the sand is collected by the contact member during one rotation of the intermediate transfer belt 10. Therefore, the detection waveforms of the first light-receiving element 62 and the second light-receiving element 63 during the second rotation of the intermediate transfer belt 10 change with each rotation of the intermediate transfer belt 10, as shown in FIGS. 17 and 18. Here, FIG. 17 is a graph showing the detection waveform of the amount of specularly reflected light by the first light-receiving element 62, and FIG. 18 is a graph showing the detection waveform of the amount of diffusely reflected light by the second light-receiving element 63. Because the sand is collected by the contact member, the detection result by the optical sensor 60 returns to its original state, with virtually no foreign matter attached, within several rotations of the intermediate transfer belt 10 (e.g., two to five rotations). However, the sand remains collected on the contact member.

[0103] Therefore, in this embodiment, a toner supply operation is performed to dilute (or cover) the foreign matter adhering to the contact member with toner, thereby protecting the contact member and the intermediate transfer belt 10. In addition, the foreign matter collected by the contact member is washed away (swept away) with toner, and finally, the foreign matter is collected together with the toner by the drum cleaning device 5.

[0104] However, when the toner supply operation is not performed as in the comparative example, foreign matter remains attached to the contact members for a longer period of time, potentially resulting in problems caused by the foreign matter. For example, if foreign matter adheres to the conductive brush 16, the foreign matter between the conductive brush 16 and the intermediate transfer belt 10 may rub against the intermediate transfer belt 10, scratching the intermediate transfer belt 10. This may result in poor toner transfer performance at the scratched portion of the intermediate transfer belt 10, leading to image defects such as blank areas due to transfer failure at the scratched portion. Furthermore, if the intermediate transfer belt 10 is scratched in the form of vertical stripes (stripe-like stripes along the movement direction of the surface of the intermediate transfer belt 10), this may result in image defects such as blank areas. Furthermore, foreign matter such as sand adhering to the conductive brush 16 may inhibit the toner from being charged by the conductive brush 16, potentially resulting in poor cleaning. Table 1 shows the problems caused by the adhesion of foreign matter described above, including problems that occur when foreign matter adheres to other contact members. The drum cleaning member in Table 1 corresponds to the cleaning blade 71 described above. The belt cleaning members in Table 1 correspond to belt cleaning blade 73 and the like in the case where image forming apparatus 100 is provided with belt cleaning device 18 as in the configuration shown in FIG. 21, which will be described later.

[0105] [Table 1]

[0106] As shown in Table 1, in the comparative example in which the toner supply operation is not performed, there is a possibility that image defects will occur. In contrast, in this embodiment, the toner supply operation is performed by the control described above, so that the occurrence of such image defects can be suppressed.

[0107] In a case where multiple photosensitive drums 1 are provided, as in the image forming apparatus 100 of this embodiment, if foreign matter such as sand adheres to the intermediate transfer belt 10, it is likely that the foreign matter will also adhere to all of the photosensitive drums 1. Therefore, when performing the toner supply operation, it is preferable to form the supply toner on all of the photosensitive drums 1 as in this embodiment, but this is not limited to this. For example, in a configuration in which the influence of foreign matter adhering to the conductive brush 16 or the belt cleaning member is greater than the influence of foreign matter adhering to the drum cleaning member, it is possible to form a supply toner image on at least one of the multiple photosensitive drums 1.

[0108] The image forming apparatus 100 may also be configured to perform a secondary transfer roller cleaning operation that returns toner adhering to the secondary transfer roller 20 to the intermediate transfer belt 10 and collects it. In the secondary transfer cleaning operation, a voltage of the normal charging polarity of the toner is applied to the secondary transfer roller 20, or a voltage of the same polarity as the normal charging polarity of the toner and a voltage of the opposite polarity are alternately applied to the secondary transfer roller 20. This makes it easier for foreign matter such as sand adhering to the secondary transfer roller 20 to return to the intermediate transfer belt 10 along with the toner adhering to the secondary transfer roller 20, thereby more quickly removing the foreign matter from the secondary transfer roller 20. The foreign matter such as sand returned to the intermediate transfer belt 10 from the secondary transfer roller 20 is collected by the drum cleaning device 5 together with the toner by the action of the conductive brush 16. Alternatively, if the image forming apparatus 100 is provided with a belt cleaning device 18 (FIG. 21), as described below, the foreign matter such as sand returned to the intermediate transfer belt 10 from the secondary transfer roller 20 is collected by the belt cleaning device 18. The secondary transfer roller cleaning operation can be performed at any timing when an area other than the image forming area (non-image forming area) in the moving direction of the surface of the intermediate transfer belt 10 passes through the secondary transfer portion N2. Alternatively, when the toner supply operation is performed, the secondary transfer roller cleaning operation may be performed immediately before the subsequent image forming area reaches the secondary transfer portion N2.

[0109] Thus, in this embodiment, the image forming apparatus 100 comprises a toner image forming means (such as a charging roller 2, an exposure device 3, and a 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 contact member (such as a conductive brush 16) that contacts the surface of the image carrier 10, an optical sensor 60 that receives the reflected light at a detection position D in the direction of movement of the surface of the image carrier 10, and light receiving elements 62 and 63 that emit light from the light emitting element 61 toward the surface of the image carrier 10 and output a detection signal according to the amount of light received, and receives the reflected light, and a control unit (CPU) 201 that can control the toner image forming means, and executes a print job that includes transferring the toner images carried in the image forming areas on the surface of the image carrier 10 to one or more recording materials P in response to a single start instruction. In this embodiment, the control unit 201 controls the image carrier 10 to carry a predetermined toner image (supply toner image) formed by the toner image forming means on the surface of the image carrier 10 and to supply the toner of the predetermined toner image to the contact member 16, based on the detection signal output by the light receiving elements 62 and 63 upon receiving the reflected light after the image carrier 10 has started to rotate for the print job and before the first image forming area in the print job has reached the detection position D. In this embodiment, the control unit 201 controls to execute the toner supply operation based on a first detection signal (corresponding to the detected light amounts A1 and B1) output by the light receiving elements 62 and 63 after receiving the reflected light before the rotation of the image carrier 10 for the previous print job has stopped and after the last image forming area in the previous print job has passed the detection position D, and a second detection signal (corresponding to the detected light amounts A2 and B2) output by the light receiving elements 62 and 63 after the rotation of the image carrier 10 has started for the current print job and before the first image forming area in the current print job has reached the detection position D. In this embodiment, the second detection signal is a detection signal output by the light receiving elements 62 and 63 after receiving the reflected light during the first rotation of the image carrier 10 after the rotation of the image carrier 10 has started for the current print job.

[0110] In this embodiment, the control unit 201 controls not to execute the toner supply operation when the difference between the numerical value related to the first detection signal and the numerical value related to the second detection signal is a first value, but to execute the toner supply operation when the difference is a second value greater than the first value. In this embodiment, the control unit 201 controls based on the average value of the numerical values related to the detection signals output by the light-receiving elements 62 and 63 after receiving the reflected light. When executing the toner supply operation, the control unit 201 can also control the image carrier 10 to carry the predetermined toner image on its surface before a toner image is carried on the first image forming area in the print job. When executing the toner supply operation, the control unit 201 can also control the image carrier 10 to carry the predetermined toner image on its surface between the previous image forming area and the next image forming area in the print job. The contact members include a member for cleaning the surface of the image carrier 10 (the conductive brush 16, the belt cleaning blade 73), and a member for transferring a toner image from the image carrier 10 to the recording material P (the secondary transfer roller 20). In this embodiment, when the toner supply operation is performed, the control unit 201 controls the image carrier 10 to carry the predetermined toner image over substantially the entire area of the surface of the image carrier 10 that can carry a toner image in the width direction that is substantially perpendicular to the direction of movement of the surface of the image carrier 10. When the toner supply operation is performed, the control unit 201 can control the image carrier 10 to carry the predetermined toner image having different lengths in the direction of movement of the surface of the image carrier 10 between a first position in the width direction and a second position different from the first position. In addition, when performing a toner supply operation, the control unit 201 can control the image carrier 10 to carry on its surface the specified toner image having different densities at a first position in the width direction and a second position different from the first position.

[0111] In this embodiment, the image carrier 10 is an intermediate transfer member onto which a toner image is transferred from another image carrier (photosensitive drum) 1 that carries a toner image formed by a toner image forming unit on its surface. The present embodiment also includes a plurality of other image carriers 1a-1d, and the control unit 201, when executing a toner supply operation, controls the plurality of other image carriers 1a-1d to carry the predetermined toner image, and transfers the predetermined toner image from the plurality of other image carriers 1a-1d to the image carrier 10, so that the predetermined toner image is carried on the surface of the image carrier 10. The light receiving element 62 mainly receives specularly reflected light as the reflected light, and the light receiving element 63 mainly receives diffusely reflected light as the reflected light. The optical sensor 60 may also include, as light receiving elements, a light receiving element 62 that mainly receives specularly reflected light as the reflected light, and a light receiving element 63 that mainly receives diffusely reflected light as the reflected light.

[0112] As described above, according to this embodiment, it is possible to detect foreign matter such as sand adhering to the intermediate transfer belt 10 and execute processing to reduce the influence of the foreign matter. Therefore, it is possible to continue the operation of the image forming apparatus 100 after reducing the influence of the foreign matter such as sand.

[0113] 10. Variations Next, several modifications of this embodiment will be described. Note that in each modification, the description of the same configuration and operation as in the first embodiment will be omitted as appropriate.

[0114] <Variation 1> In the first embodiment, foreign matter detection is performed based on the detection results of the reflected light from the intermediate transfer belt 10 immediately before the operation is stopped and immediately after the operation is started, but the present invention is not limited to this embodiment. For example, the reference threshold value may be determined when the image forming apparatus 100 is first operated.

[0115] Fig. 19 is a flowchart for explaining the control of the foreign matter detection operation and the toner supply operation in this case. Fig. 19(a) is a flowchart for explaining the process of determining the reference threshold value at the first operation of the image forming apparatus 100 (when a new image forming apparatus 100 is first turned on). Fig. 19(b) is a flowchart for explaining the process at the second or subsequent operation of the image forming apparatus 100.

[0116] 19(a), during the initial operation of the image forming apparatus 100, the CPU 201 stores, in the memory 202, for example, the average values of the detection outputs of the first light receiving element 62 and the second light receiving element 63 during the first rotation of the intermediate transfer belt 10 (corresponding to one rotation of the intermediate transfer belt 10) as detected light amounts A0 and B0 (S201). The CPU 201 also sets threshold values A0' and B0' based on the acquired detected light amounts A0 and B0, and stores them in the memory 202 (S202). For example, the threshold value A0' can be set to 0.9 times the detected light amount A0, and the threshold value B0' can be set to 1.1 times the detected light amount B0.

[0117] As shown in FIG. 19B, when the image forming apparatus 100 subsequently starts a print job, the CPU 201 reads from the memory 202 the threshold values A0′ and B0′ determined during the initial operation of the image forming apparatus 100 (S301). The CPU 201 then stores the average values of ten sampling points of the detection outputs of the first light receiving element 62 and the second light receiving element 63 immediately after the start of operation as detected light amounts A2 and B2, respectively (S302). The CPU 201 then compares the detected light amounts A2 and B2 with the threshold values A0′ and B0′, respectively, to determine whether a foreign object is present on the intermediate transfer belt 10 (S303). Based on the determination result in S303, the toner supply operation is performed in S304, and the image formation is performed in S305. These processes are similar to the processes in S104 and S105 of FIG. 12 in the first embodiment.

[0118] The first operation of the image forming apparatus 100 is, for example, the initial adjustment operation when a new image forming apparatus 100 equipped with a new intermediate transfer belt 10 is first turned on. When a print job is executed following this initial adjustment operation, the process of FIG. 19(a) is followed by the process of FIG. 19(b).

[0119] 19A, the thresholds A0' and B0' are determined based on the reflected light from one circumference of the intermediate transfer belt 10 during the initial operation of the image forming apparatus 100. However, the rotation of the intermediate transfer belt 10 for detecting the reflected light is not limited to the first rotation. The thresholds A0' and B0' may be determined based on the detection result of the reflected light from any rotation of the intermediate transfer belt 10 from the second rotation onward during the initial operation of the image forming apparatus 100, for example, immediately before the operation is stopped. In this case, even if foreign matter is attached to the intermediate transfer belt 10 before the initial operation of the image forming apparatus 100, the reference thresholds can be determined after the foreign matter is removed from the intermediate transfer belt 10.

[0120] As described above, in this modification, the control unit 201 controls to execute the toner supply operation based on the first detection signal (corresponding to the detected light amounts A0 and B0) output by the light receiving elements 62 and 63 upon receiving reflected light during the first rotation of the image carrier 10, and the second detection signal (corresponding to the detected light amounts A2 and B2) output by the light receiving elements 62 and 63 upon receiving reflected light after the start of rotation of the image carrier 10 for the current print job and before the first image formation area on the surface of the image carrier 10 for the current print job reaches the detection position D. In this modification, the first detection signal is the detection signal output by the light receiving elements 62 and 63 upon receiving the reflected light during the first revolution of the image carrier 10 after the start of rotation of the image carrier 10 during the first rotation of the image carrier 10. In addition, in this embodiment, the second detection signal is a detection signal output by the light receiving elements 62 and 63 upon receiving reflected light during the first rotation of the image carrier 10 after the start of rotation of the image carrier 10 for the current print job.

[0121] <Variation 2> In the first embodiment, foreign matter detection was performed based on the detection results of light reflected from the intermediate transfer belt 10 immediately before the operation was stopped and immediately after the operation was started. However, the present invention is not limited to this configuration. For example, foreign matter detection may be performed based on the detection results of light reflected from the intermediate transfer belt 10 during the first and second revolutions of the intermediate transfer belt 10 immediately after the operation was started. For example, if an abnormal termination operation is performed immediately before the operation was stopped due to a momentary interruption or the like, it may be impossible to acquire (store) the detection results of light reflected from the intermediate transfer belt 10 immediately before the operation was stopped. Even in such a case, if there is a difference of a certain amount or more between the amount of light reflected from the intermediate transfer belt 10 during the first and second revolutions of the intermediate transfer belt 10 immediately after the operation was started, it is possible that foreign matter was attached to the intermediate transfer belt 10 before the start of the current operation. In other words, the difference in the amount of light reflected from the intermediate transfer belt 10 during the first and second revolutions of the intermediate transfer belt 10 immediately after the start of the current operation may be due to foreign matter being collected by the contact member. Therefore, based on this difference, it is possible to execute the toner supply operation assuming that foreign matter has been collected by the contact member.

[0122] 20 is a flowchart for explaining the control of the foreign object detection operation and the toner supply operation in this case. When the CPU 201 starts a print job, immediately after the start of the operation, the CPU 201 stores the average values of the detection outputs of the first light receiving element 62 and the second light receiving element 63 for every 10 sampling points during the first rotation of the intermediate transfer belt 10 as detected light amounts A1' and B1' in the memory 202 (S401). Thereafter, the CPU 201 stores the average values of the detection outputs of the first light receiving element 62 and the second light receiving element 63 (for one rotation of the intermediate transfer belt 10) during the second rotation of the intermediate transfer belt 10 as detected light amounts A2 and B2 in the memory 202 (S402). The CPU 201 also sets threshold values A' and B' based on the detected light amounts A2 and B2 obtained during the second rotation of the intermediate transfer belt 10 and stores them in the memory 202 (S403). For example, the threshold value A1' can be 0.9 times the detected light amount A2, and the threshold value B1' can be 1.1 times the detected light amount B2. Then, the CPU 201 compares the detected light amounts A1' and B1' with the threshold values A' and B', respectively, and determines whether or not foreign matter was present on the intermediate transfer belt 10 during the first rotation of the intermediate transfer belt 10 (S404). Based on the determination result in S404, the toner supply operation is performed in S405, and the image formation is performed in S406, which are the same as the processes in S104 and S105 of FIG. 12 in the first embodiment.

[0123] In this modification, when comparing the detection results of reflected light from the intermediate transfer belt 10 during the first and second revolutions of the intermediate transfer belt 10 immediately after the start of operation, the detected light amounts A2 and B2 obtained during the second revolution of the intermediate transfer belt 10 are used as the reference for thresholds A' and B'. This is because during the second revolution of the intermediate transfer belt 10, foreign matter is collected by the contact member, reducing the amount of foreign matter adhering to the intermediate transfer belt 10. From this perspective, the detected light amounts obtained during the second and subsequent revolutions of the intermediate transfer belt 10 can be used as the reference for thresholds A' and B'. However, from the perspective of quickly determining thresholds A' and B', the detected light amounts obtained during the fifth or subsequent revolution of the intermediate transfer belt 10, preferably the third or subsequent revolution, and most preferably the second revolution, are used.

[0124] Furthermore, the foreign matter detection operation in this modified example is more effective when there is a clear difference in the amount of light reflected from the intermediate transfer belt 10 between the first and second revolutions of the intermediate transfer belt 10. FIG. 21 is a schematic cross-sectional view showing another example of the configuration of an image forming apparatus. In the image forming apparatus of FIG. 21, elements having the same or corresponding functions or configurations as those of the image forming apparatus of FIG. 1 are denoted by the same reference numerals. The image forming apparatus 100 of FIG. 21 includes a belt cleaning device 18 as an intermediate transfer member cleaning means, located on the outer peripheral surface of the intermediate transfer belt 10, facing the third tension roller 13. The belt cleaning device 18 includes a belt cleaning blade 73 as a cleaning member (cleaning member) disposed in contact with the surface of the intermediate transfer belt 10, and a cleaning container 74 that collects adhering matter, such as secondary transfer residual toner, removed from the surface of the intermediate transfer belt 10. The belt cleaning device 18 uses the belt cleaning blade 73 to scrape adhering matter, such as secondary transfer residual toner, from the surface of the rotating intermediate transfer belt 10 and collects the adhering matter in the cleaning container 74. The length of the belt cleaning blade 73 in the longitudinal direction is equal to the width of the intermediate transfer belt 10. In this way, when the image forming apparatus 100 is provided with the belt cleaning device 18, the difference in the amount of reflected light from the intermediate transfer belt 10 between the first and second revolutions of the intermediate transfer belt 10 becomes more apparent. This is because the belt cleaning blade 73 scrapes off and cleans the deposits on the intermediate transfer belt 10, so that the surface of the intermediate transfer belt 10 is cleaned during the first revolution of the intermediate transfer belt 10, and there is no foreign matter on the second revolution of the intermediate transfer belt 10. Therefore, the foreign matter detection operation of this modified example is particularly effective when the image forming apparatus 100 is provided with the belt cleaning device 18, as shown in FIG. 21 .

[0125] Furthermore, in the control of the first embodiment, if information (threshold value) regarding the reflected light from the intermediate transfer belt 10 immediately before the previous operation stop cannot be acquired, foreign matter detection according to this modified example may be performed.

[0126] As described above, in this modification, the control unit 201 controls to execute the toner supply operation based on the first detection signal (corresponding to the detected light amounts A1' and B1') output by the light receiving elements 62 and 63 upon receiving reflected light during the first rotation of the image carrier 10 after the start of rotation of the image carrier 10 for the current print job, and the second detection signal (corresponding to the detected light amounts A2 and B2) output by the light receiving elements 62 and 63 upon receiving reflected light after the light receiving elements 62 and 63 output the first detection signal but before the first image formation area on the surface of the image carrier 10 for the current print job reaches the detection position D. In this modification, the second detection signal is the detection signal output by the light receiving elements 62 and 63 upon receiving reflected light during the second rotation of the image carrier 10 after the start of rotation of the image carrier 10 for the current print job.

[0127] <Variation 3> In the first embodiment, the light reflected from the intermediate transfer belt 10 was detected and compared immediately before the operation was stopped and immediately after the operation was started. However, if there is substantially no accumulation of foreign matter such as sand on the intermediate transfer belt 10, foreign matter detection may be omitted. For example, the operation stop time of the image forming apparatus 100 may be measured, and foreign matter detection may be performed only if the operation stop time is equal to or longer than a predetermined time during which foreign matter such as sand may accumulate on the intermediate transfer belt 10. The predetermined time may be set appropriately depending on the configuration of the image forming apparatus 100, and may be, for example, 10 minutes to 1 hour. This allows the foreign matter detection operation to be omitted when it is not necessary.

[0128] The operation downtime of image forming apparatus 100 can be measured, for example, by storing the time when image forming apparatus 100 last stopped and comparing it with the current operation start time of image forming apparatus 100. Then, for example, in accordance with the flowchart of Fig. 12, the processes of S101 to S104 may be executed only if the operation downtime of image forming apparatus 100 is equal to or longer than a predetermined time.

[0129] [Example 2] Next, another embodiment of the present invention will be described. The basic configuration and operation of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are assigned the same reference numerals as those of embodiment 1, and detailed descriptions thereof will be omitted.

[0130] In this embodiment, a plurality of threshold values are set for the detection results from the first light receiving element 62 and the second light receiving element 63, respectively, and the amount of toner supplied is changed according to the amount of foreign matter attached.

[0131] The setting of thresholds in this embodiment will be described. In the first embodiment, a threshold A for the detection result by the first light receiving element 62 and a threshold B for the detection result by the second light receiving element 63 are set. In contrast, in this embodiment, a threshold C for the detection result by the first light receiving element 62 and a threshold D for the detection result by the second light receiving element 63 are further set.

[0132] Specifically, as shown in Fig. 22(a), for example, a value 10% lower than the average value of the detection output of the first light receiving element 62 immediately before the operation stopped is set as threshold A, and a value 20% lower than the average value is set as threshold C. Similarly, as shown in Fig. 22(b), for example, a value 10% higher than the average value of the detection output of the second light receiving element 63 immediately before the operation stopped is set as threshold B, and a value 20% higher than the average value is set as threshold D.

[0133] 22(a) and (b) show examples of the detection waveforms of the first light receiving element 62 and the second light receiving element 63 when sand is attached to multiple locations (sand 1, sand 2) on the intermediate transfer belt 10. Sand 1 and sand 2 are each attached to an area of 1.5 cm square on the intermediate transfer belt 10. Sand 2 has a larger amount of attached sand so that the attachment density is higher than that of sand 1.

[0134] As shown in FIGS. 22(a) and 22(b), if the detection results from the first light-receiving element 62 and the second light-receiving element 63 immediately after the start of operation exceed thresholds C and D, respectively, it can be determined that there was a time when the amount of foreign matter adhesion was high. In this embodiment, the amount of toner supplied in the toner supply operation is increased in this case. Specifically, for example, the length of the supply toner image of each solid color in the direction of movement on the surface of the intermediate transfer belt 10 is increased from 10 mm to 20 mm. It is also possible that either one of the detection results from the first light-receiving element 62 or the second light-receiving element 63 exceeds thresholds C or D. In this embodiment, it is also determined that there was a time when the amount of foreign matter adhesion was relatively high, and the amount of toner supplied in the supply operation is increased. Table 2 summarizes the relationship between the thresholds, detection results, and amount of toner supplied (the length of the supply toner image in the direction of movement on the surface of the intermediate transfer belt 10) in this embodiment.

[0135] [Table 2]

[0136] In this embodiment, particular attention is paid to the side with a large amount of foreign matter attached, and if either the detection results from the first light receiving element 62 or the second light receiving element 63 exceed threshold value A or threshold value B, the toner supply operation is performed, but this is not limited to such an embodiment. For example, a setting may be made such that the toner supply operation is not performed unless the detection results from the first light receiving element 62 or the second light receiving element 63 exceed threshold value C or threshold value D, respectively. In this case, for a specific type of foreign matter that is likely to be detected only by either the first light receiving element 62 or the second light receiving element 63, the amount of toner consumed by the toner supply operation can be reduced, allowing toner to be used efficiently.

[0137] In this embodiment, two thresholds are set for each of the detection results from the first light receiving element 62 and the second light receiving element 63, but the number of thresholds is not limited to this. For example, if it is desired to further increase the amount of toner supplied when a larger amount of foreign matter adheres, the threshold may be further increased. In this embodiment, the added threshold has a difference of 20% from the average detection output, but the value of the threshold is not limited to this. As described above, the threshold can be changed as appropriate depending on the color, hardness, etc. of the intermediate transfer belt 10.

[0138] Furthermore, as explained in the first embodiment, the control of this embodiment can be performed using either the front optical sensor 60F or the rear optical sensor 60R. The control of this embodiment may be performed using only one of the front optical sensor 60F and the rear optical sensor 60R, or may be performed using both.

[0139] Furthermore, for example, when the detection result of only one of the front optical sensor 60F and the rear optical sensor 60R exceeds threshold C or threshold D, the amount of supplied toner may be increased only on half of the width direction of the intermediate transfer belt 10 on the side where the threshold is exceeded. For example, the amount of supplied toner in the width direction of the intermediate transfer belt 10 can be changed by changing the pattern (shape, density) of the supplied toner image as described above according to the detection results of the front optical sensor 60F and the rear optical sensor 60R.

[0140] Alternatively, during the first rotation of the intermediate transfer belt 10, the area in the rotation direction of the intermediate transfer belt 10 where the foreign matter exists may be detected, and during the second rotation of the intermediate transfer belt 10, toner may be supplied to that area (the area on the intermediate transfer belt 10 where the foreign matter existed). The area in the rotation direction of the intermediate transfer belt 10 where the foreign matter exists may be detected, for example, based on the timing when a detection result exceeding a threshold value is obtained. Toner may be supplied as a toner supply operation, or may be performed in addition to and similar to a toner supply operation. This operation may also be performed on an area in the rotation direction of the intermediate transfer belt 10 when thresholds C and D are exceeded. This is because, for example, when a large amount of sand has accumulated on the intermediate transfer belt 10, exceeding thresholds C and D, it may not be possible to remove all of the foreign matter in one rotation (one rotation of the intermediate transfer belt 10). By performing this operation, damage to contact members caused by the foreign matter can be reduced by mixing the toner with the foreign matter. That is, for example, contact and rubbing between the foreign matter remaining on the intermediate transfer belt 10 and the photosensitive drum 1 can be reduced by interposing toner between the photosensitive drum 1 and the foreign matter, thereby reducing direct contact of the foreign matter with the photosensitive drum 1. Furthermore, by mixing the foreign matter with the toner, the foreign matter can be collected together with the toner, improving the collection efficiency of the foreign matter.

[0141] The foreign matter detection according to this embodiment may be applied to a modification of the first embodiment.

[0142] Thus, in this embodiment, the control unit 201 controls so that when the difference between the numerical value relating to the first detection signal (e.g., the detection signal just before operation stops) and the numerical value relating to the second detection signal (e.g., the detection signal just after operation starts) is a first value, the control unit 201 does not execute a toner supply operation, and when the difference is a second value greater than the first value, the control unit 201 executes a toner supply operation to cause a predetermined toner image (supplied toner image) of a first amount of toner to be carried on the surface of the image carrier 10, and when the difference is a third value greater than the second value, the control unit 201 executes a toner supply operation to cause the image carrier 10 to carry the predetermined toner image of a second amount of toner that is greater than the first amount of toner.

[0143] [Example 3] Next, another embodiment of the present invention will be described. The basic configuration and operation of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are assigned the same reference numerals as those of embodiment 1, and detailed descriptions thereof will be omitted.

[0144] In this embodiment, in order to make it difficult for foreign matter to adhere to the contact members that come into contact with the intermediate transfer belt 10, the number of contact members that come into contact with the intermediate transfer belt 10 is reduced when foreign matter is detected. This prevents the contact members and the intermediate transfer belt 10 from being damaged by foreign matter.

[0145] First, a case where this embodiment is applied to an image forming apparatus 100 equipped with a belt cleaning device 18 as shown in FIG. 21 will be described.

[0146] 23 is a block diagram showing an outline of a control configuration for controlling the operation of the image forming apparatus 100 in this embodiment. As shown in Fig. 23, in this embodiment, the image forming apparatus 100 has a primary transfer unit contact / separation mechanism 81 that brings the intermediate transfer belt 10 into contact with and separates it from the photosensitive drums 1a to 1d. In addition, in this embodiment, the image forming apparatus 100 has a secondary transfer unit contact / separation mechanism 82 that brings the secondary transfer roller 20 into contact with and separates it from the intermediate transfer belt 10.

[0147] 24 is a timing chart for explaining the control of the foreign matter detection operation and the toner supply operation in this embodiment. The timing chart in Fig. 24 shows an overview of the operation of each part of the image forming apparatus 100 during a print job, similar to the timing charts in Fig. 14 and Fig. 15, but Fig. 24 also shows the contact and separation states of the photosensitive drums 1a to 1d and the secondary transfer roller 20 with respect to the intermediate transfer belt 10 by the primary transfer unit contact and separation mechanism 81 and the secondary transfer unit contact and separation mechanism 82. The operations according to the timing chart in Fig. 24 are controlled by the CPU 201.

[0148] As shown in FIG. 24, immediately after the start of operation, the detection outputs of the first light receiving element 62 and the second light receiving element 63 are sampled. If foreign matter is detected at this time, the drive of the intermediate transfer belt 10 is stopped. When the drive of the intermediate transfer belt 10 is stopped, the photosensitive drums 1a-1d and the secondary transfer roller 20, which serve as contact members in contact with the intermediate transfer belt 10, are separated from the intermediate transfer belt 10. Note that although the contact and separation timings of the primary transfer portion N1 and the secondary transfer portion N2 are shown together in FIG. 24, the contact and separation timings of the primary transfer portion N1 and the secondary transfer portion N2 may be the same or different. When this separation is completed, the drive of the intermediate transfer belt 10 is resumed. As a result, with the photosensitive drums 1a-1d and the secondary transfer roller 20, which serve as contact members, separated from the intermediate transfer belt 10, the belt cleaning device 18 (belt cleaning blade 73) collects foreign matter from the surface of the intermediate transfer belt 10. This allows the photosensitive drums 1a to 1d and the secondary transfer roller 20, which serve as contact members, to come into contact with the intermediate transfer belt 10 from which foreign matter has been removed. At this time, it is preferable to rotate the intermediate transfer belt 10 at least one revolution. However, as described in the first embodiment, typically, the intermediate transfer belt 10 returns to a state in which there is substantially no foreign matter attached thereto within several revolutions (for example, two to five revolutions) of the intermediate transfer belt 10. Therefore, the number of revolutions of the intermediate transfer belt 10 at this time is often sufficient if it is five revolutions or less, preferably three revolutions or less, and more preferably two revolutions or less.

[0149] Thereafter, the photosensitive drums 1a to 1d and the secondary transfer roller 20, which serve as contact members, are brought into contact with the intermediate transfer belt 10 again. After that, a toner supply operation is performed. This is to prevent damage to the belt cleaning blade 73 or the intermediate transfer belt 10 by supplying toner to the belt cleaning blade 73 to dilute (cover) foreign matter with the toner or by washing away (pushing away) the foreign matter. Then, image formation is performed. Furthermore, just before the operation is stopped, the detection outputs of the first light receiving element 62 and the second light receiving element 63 are sampled, and the operation of the image forming apparatus 100 is terminated.

[0150] In this way, by separating the photosensitive drums 1a to 1d and the secondary transfer roller 20 from the intermediate transfer belt 10, it is possible to prevent foreign matter from adhering to contact members other than the belt cleaning blade 73, thereby minimizing the effects of foreign matter.

[0151] Note that when this embodiment is applied to the image forming apparatus 100 shown in FIG. 1, the operation of the image forming apparatus 100 is similar to that described above. However, contact members required to collect foreign matter on the intermediate transfer belt 10 are not separated from the intermediate transfer belt 10. For example, in the configuration of FIG. 1, among the contact members that contact the intermediate transfer belt 10, namely the secondary transfer roller 20, the conductive brush 16, and the photosensitive drums 1a to 1d, the conductive brush 16 and at least one photosensitive drum 1 (e.g., the photosensitive drum 1a located most upstream in the moving direction of the surface of the intermediate transfer belt 10) are kept in contact with the intermediate transfer belt 10 to collect foreign matter. As a result, when the drive of the intermediate transfer belt 10 is resumed, the foreign matter is charged by the conductive brush 16, transferred to the photosensitive drum 1, and collected by the drum cleaning device 5. Furthermore, toner is supplied to the conductive brush 16 and cleaning blade 71 that collected the foreign matter in a toner supply operation.

[0152] In this embodiment, the intermediate transfer belt 10 is stopped temporarily when a foreign object is detected in order to minimize contact between the contact member and the foreign object, but the present invention is not limited to this. For example, when a foreign object is detected, the intermediate transfer belt 10 may be allowed to continue rotating while the contact member is separated from the intermediate transfer belt 10. In this case, the contact time of the contact member with the intermediate transfer belt 10 is reduced by separating the contact member, but the rotation of the intermediate transfer belt 10 is not stopped, so the time required for the operation to reduce the influence of the foreign object can be shortened.

[0153] As described above, in this embodiment, the image forming apparatus 1 has a contact member (such as a belt cleaning blade 73 or a conductive brush 16) that contacts the image carrier (intermediate transfer belt) 10, another contact member (such as a secondary transfer roller 20) that contacts the surface of the image carrier 10, and a contact-separation mechanism (such as a secondary transfer contact-separation mechanism 82) that can separate the surface of the image carrier 10 from the other contact member 20. When performing a toner supply operation, the control unit 201 controls the contact-separation mechanism 82 to separate the surface of the image carrier 10 from the other contact member 20, rotate the image carrier 10 in a state in which the surface of the image carrier 10 is separated from the other contact member 20, and then causes the contact-separation mechanism 82 to contact the surface of the image carrier 10 with the other contact member 20, and then performs a toner supply operation to supply toner of a predetermined toner image (supply toner image) to the contact member 16 and the other contact member 20. The contact member is a member for cleaning the surface of the image carrier 10 (belt cleaning blade 73, conductive brush 16), etc., and another contact member is a member for transferring a toner image from the image carrier 10 to a recording material P (secondary transfer roller 20), another image carrier (photosensitive drum 1) that carries on its surface a toner image formed by a toner image forming means, etc.

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

[0155] In the above-described embodiment, the toner supply operation involves the steps of charging, exposing, and developing, similar to normal image formation, to form a supply toner image (toner band) on the photoconductor. Alternatively, the exposure step may be omitted, and toner may be supplied from the developing member to the photoconductor by using the potential difference between the surface potential of the photoconductor and the potential of the developing member at the development position, to form a supply toner image (toner band) on the photoconductor. For example, toner may be supplied from a developing member to which a development voltage is applied to the surface of an uncharged photoconductor.

[0156] Furthermore, the supplied toner is not limited to toner charged to the normal charging polarity, which adheres to a portion of the photoconductor where the surface potential is higher than the normal charging polarity of the toner relative to the potential of the developing member at the development position. The supplied toner may also be toner charged to the opposite polarity to the normal charging polarity, which adheres to a portion of the photoconductor where the surface potential is higher than the normal charging polarity of the toner relative to the potential of the developing member at the development position. In this case, for example, the supplied toner can be transferred to the intermediate transfer belt by applying a voltage of the normal charging polarity of the toner to the primary transfer roller.

[0157] Furthermore, in the above-described embodiment, the image forming device is provided with two optical sensors, but the number of optical sensors is not limited to two, and may be one, or three or more.

[0158] In the above-described embodiment, the optical sensor detects foreign matter by detecting light reflected from the surface of the intermediate transfer belt, which is the image carrier (second image carrier), but the present invention is not limited to this embodiment. Foreign matter may also be detected by detecting light reflected from the surface of the photosensitive drum, which is the image carrier (first image carrier), using the optical sensor. Furthermore, both of these detection methods may be performed.

[0159] In the above-described embodiment, the image forming apparatus is capable of forming full-color images, but the present invention is not limited to this. The present invention can also be applied to an image forming apparatus that is capable of forming only monochrome (black and white or monochromatic) images.

[0160] Furthermore, the photosensitive member is not limited to a drum-shaped member (photosensitive drum), but may be, for example, an endless belt-shaped member (photosensitive belt), etc. Furthermore, the intermediate transfer member is not limited to an endless belt, but may be, for example, an intermediate transfer drum that is stretched around a frame and formed into a drum-shaped member.

[0161] Furthermore, in the above-described embodiment, the developing member contacts the photosensitive member to perform development, but it may also be disposed opposite the photosensitive member without contacting it to perform development.

[0162] In the above-described embodiment, the image forming apparatus has a cleaning device for cleaning the surface of the photosensitive member, but the image forming apparatus may have a configuration that does not have a special cleaning device for cleaning the surface of the photosensitive member. In this case, the residual toner on the photosensitive member may be collected by the developing device. [Explanation of symbols]

[0163] 1 Photosensitive drum (first image carrier) 2 Charging roller 3 Exposure equipment 4. Developing device 5. Drum cleaning device 10 Intermediate transfer belt (second image carrier) 16 Conductive brush 18 Belt cleaning device 20 Secondary transfer roller 60 Optical Sensor 201 CPU (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 contact member that contacts the surface of the image carrier; 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 corresponding to the amount of light received, the optical sensor receiving the reflected light at a detection position in the moving direction of the surface of the image carrier; a control unit capable of controlling the toner image forming means; and 1. An image forming apparatus that executes a print job including transferring toner images respectively carried in image forming areas on a surface of an image carrier onto one or more recording materials in response to a single start instruction, and a control unit that controls the control unit to execute a toner supply operation to carry a predetermined toner image formed by the toner image forming means on the surface of the image carrier and supply toner of the predetermined toner image to the contact member, based on a detection signal output by the light receiving element upon receiving the reflected light after the rotation of the image carrier for the print job has started and before the first image forming area in the print job has reached the detection position.

2. 2. The image forming apparatus according to claim 1, wherein the control unit controls the toner supply operation based on a first detection signal output by the light receiving element after receiving the reflected light before rotation of the image carrier for the previous print job has stopped and after the last image forming area in the previous print job has passed the detection position, and a second detection signal output by the light receiving element after rotation of the image carrier for the current print job has started and before the first image forming area in the current print job has reached the detection position.

3. 3. The image forming apparatus according to claim 2, wherein the second detection signal is a detection signal output by the light receiving element upon receiving the reflected light during the first rotation of the image carrier after the start of rotation of the image carrier for the current print job.

4. The image forming apparatus of claim 1, wherein the control unit controls the toner supply operation based on a first detection signal output by the light receiving element upon receiving the reflected light during the first rotation of the image carrier, and a second detection signal output by the light receiving element upon receiving the reflected light after the start of rotation of the image carrier for the current print job and before the first image forming area in the current print job reaches the detection position.

5. 5. The image forming apparatus according to claim 4, wherein the first detection signal is a detection signal output by the light receiving element upon receiving the reflected light during the first revolution of the image carrier after the start of rotation of the image carrier.

6. 5. The image forming apparatus according to claim 4, wherein the second detection signal is a detection signal output by the light receiving element upon receiving the reflected light during the first rotation of the image carrier after the start of rotation of the image carrier for the current print job.

7. 2. The image forming apparatus according to claim 1, wherein the control unit controls the toner supply operation based on a first detection signal output by the light receiving element after receiving the reflected light during the first rotation of the image carrier after the start of rotation of the image carrier for the current print job, and a second detection signal output by the light receiving element after receiving the reflected light after the light receiving element outputs the first detection signal but before the first image forming area for the current print job reaches the detection position.

8. 8. The image forming apparatus according to claim 7, wherein the second detection signal is a detection signal output by the light receiving element upon receiving the reflected light during the second rotation of the image carrier after the start of rotation of the image carrier for the current print job.

9. The image forming apparatus according to any one of claims 2 to 8, characterized in that the control unit controls the toner supply operation not to be performed when the difference between the numerical value relating to the first detection signal and the numerical value relating to the second detection signal is a first value, and controls the toner supply operation to be performed when the difference is a second value greater than the first value.

10. The image forming apparatus of any one of claims 2 to 8, characterized in that the control unit controls the toner supply operation not to be performed when the difference between the numerical value related to the first detection signal and the numerical value related to the second detection signal is a first value, the control unit controls the toner supply operation to carry the specified toner image of a first amount of toner on the surface of the image carrier when the difference is a second value greater than the first value, and the control unit controls the toner supply operation to carry the specified toner image of a second amount of toner greater than the first amount on the surface of the image carrier when the difference is a third value greater than the second value.

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

12. 9. The image forming apparatus according to claim 1, wherein the control unit controls the image carrier to carry the predetermined toner image on its surface before a toner image is carried in the first image forming area in the print job when the toner supply operation is performed.

13. The image forming apparatus according to any one of claims 1 to 8, characterized in that, when executing the toner supply operation, the control unit controls the image carrier to carry the specified toner image in an area on the surface of the image carrier between the preceding image forming area and the next image forming area in the print job.

14. 9. The image forming apparatus according to claim 1, wherein the contact member is a member for cleaning the surface of the image carrier.

15. 9. The image forming apparatus according to claim 1, wherein the contact member is a member for transferring a toner image from the image carrier to a recording material.

16. Another contact member that contacts the surface of the image carrier; a contact / separation mechanism capable of separating the surface of the image carrier from the other contact member; and 9. The image forming apparatus according to claim 1, wherein, when executing the toner supply operation, the control unit controls the contact mechanism to separate the surface of the image carrier from the other contact member, rotate the image carrier while the surface of the image carrier is separated from the other contact member, and then controls the contact mechanism to bring the surface of the image carrier into contact with the other contact member, and then executes the toner supply operation to supply toner of the specified toner image to the contact member and the other contact member.

17. 17. The image forming apparatus according to claim 16, wherein the contact member is a member for cleaning the surface of the image carrier.

18. 17. The image forming apparatus according to claim 16, wherein the other contact member is a member for transferring a toner image from the image carrier to a recording material.

19. the other contact member is another image carrier that carries a toner image formed by the toner image forming means on its surface, 17. The image forming apparatus according to claim 16, wherein the image carrier is an intermediate transfer member onto which a toner image is transferred from the other image carrier.

20. The image forming apparatus according to any one of claims 1 to 8, characterized in that, when performing the toner supply operation, the control unit controls the specified toner image to be carried over substantially the entire area of the surface of the image carrier that is capable of carrying a toner image in a width direction that is substantially perpendicular to the direction of movement of the surface of the image carrier.

21. The image forming apparatus according to claim 20, characterized in that, when performing the toner supply operation, the control unit controls the image carrier to carry on its surface the specified toner image having different lengths in the direction of movement of the surface of the image carrier at a first position in the width direction and a second position different from the first position.

22. The image forming apparatus according to claim 20, characterized in that, when performing the toner supply operation, the control unit controls the image carrier to carry the specified toner image having different densities at a first position in the width direction and a second position different from the first position on the surface of the image carrier.

23. 9. The image forming apparatus according to claim 1, wherein the image carrier is an intermediate transfer member onto which a toner image is transferred from another image carrier that carries a toner image formed by the toner image forming means on its surface.

24. a plurality of the other image carriers; 24. The image forming apparatus according to claim 23, wherein the control unit, when executing the toner supply operation, controls each of the plurality of other image carriers to carry the predetermined toner image, and transfers the predetermined toner image from the plurality of other image carriers to the image carrier, thereby carrying the predetermined toner image on the surface of the image carrier.

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

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

27. 9. The image forming apparatus according to claim 1, wherein the optical sensor includes, as the light receiving element, a light receiving element that receives mainly specularly reflected light as the reflected light, and a light receiving element that receives mainly diffusely reflected light as the reflected light.

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