JP2013156446A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a composition capable of suppressing a toner consumption amount, and preventing a cleaning blade from curling.SOLUTION: A toner band is supplied to a contact part of a cleaning blade at a normal frequency when a setting value of a primary transfer current is below a predetermined threshold. On the other hand, the toner band is supplied to the contact part of the cleaning blade at a bit higher frequency than the normal frequency when the setting value of the primary transfer current is the predetermined threshold or larger. Thus, when the transfer current is low, and a generation amount of a discharge product is low, resulting in the cleaning blade hardly likely to be curled, a toner consumption amount is suppressed by decreasing the frequency of supplying the toner band. On the other hand, when the transfer current is high, and the generation amount of the discharge product is large, resulting in the cleaning blade likely to be curled, the toner band is supplied more frequently to prevent the cleaning blade from curling.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and more particularly to a configuration having a cleaning blade that contacts an image carrier such as a photosensitive drum or an intermediate transfer body.

  2. Description of the Related Art As an electrophotographic image forming apparatus, an apparatus that forms an image by transferring a toner image onto a recording sheet via an image carrier such as a photoreceptor or an intermediate transfer body on which a toner image is formed is widely used. . After the transfer, the toner remains on the surface of the image carrier. As a method for removing the residual toner on the image carrier, a cleaning blade made of a resin member having a plate-like elasticity is used. In cleaning using a cleaning blade, the edge portion of the blade end surface is brought into contact with the surface of the rotating image carrier to sweep away residual toner.

  Here, if the frictional force at the contact portion is high, such as insufficient toner supplied to the contact portion between the cleaning blade and the image carrier, the cleaning blade is likely to be turned up. When the cleaning blade is turned over, the toner is easy to slip through, so that the cleaning blade cannot be sufficiently cleaned.

  In order to prevent such cleaning blade turning, a configuration is known in which toner is supplied to the contact portion between the image carrier and the cleaning blade separately from the residual toner (see Patent Documents 1 and 2).

JP-A-60-194484 JP-A-11-109819

  As a factor that the cleaning blade turns over, there is an influence of a transfer bias applied when the toner image is transferred. For example, a toner image formed on an image carrier is electrostatically transferred to an intermediate transfer member or a recording material by a bias applied to a transfer unit. Here, since the amount of current that flows when the toner image is transferred is affected by the environment and the like, the setting of the transfer bias is usually changed in consideration of the environment and the like. At this time, as the transfer bias increases, the amount of discharge products adhering to the image carrier increases, and the frictional force increases at the contact portion between the image carrier and the cleaning blade. As a result, the cleaning blade tends to chatter or turn over.

  In order to prevent the cleaning blade from being turned over against the above-described factors, the toner may be supplied to the contact portion with high frequency. However, if the toner supply frequency is constantly increased, the toner consumption increases. As a result, the running cost increases and the waste toner container replacement cycle increases.

  In view of such circumstances, the present invention was invented to realize a configuration capable of suppressing the turning-up of the cleaning blade while suppressing toner consumption.

  The present invention relates to an image carrier that carries a toner image, a toner image forming unit that forms a toner image on the surface of the image carrier, and a toner image formed on the image carrier by applying a transfer bias. In an image forming apparatus comprising transfer means for transferring the image to another image carrier, and a cleaning blade that abuts on the surface of the image carrier, a predetermined portion is provided at a contact portion between the cleaning blade and the image carrier. A toner supply mode for supplying a toner image can be executed, the transfer bias is set according to a predetermined condition, and the first transfer bias is set to a frequency higher than the frequency when the set transfer bias is the first transfer bias. An image forming apparatus comprising: a control unit that determines a frequency of executing the toner supply mode so that the frequency of the second transfer bias is higher than that of the second transfer bias. Located in.

  According to the present invention, since the frequency of executing the toner supply mode is determined based on the set transfer bias, the execution frequency of the toner supply mode is increased when the generation amount of the discharge product is large, and the generation amount is reduced. When the number is small, the execution frequency of the toner supply mode can be lowered. As a result, when the generation amount of the discharge product is large and the cleaning blade is likely to be turned over, the frequency of supplying the toner can be increased to suppress the turning of the cleaning blade. On the other hand, when the generation amount of the discharge product is small and the cleaning blade is hardly turned over, the toner consumption frequency can be reduced by reducing the frequency of supplying the toner.

1 is a schematic cross-sectional configuration diagram of an image forming apparatus according to a first embodiment of the present invention. FIG. 3 is a schematic configuration diagram illustrating a part of an image forming unit in detail. FIG. 3 is a schematic configuration diagram illustrating the details of the fixing device extracted. FIG. 3 is a plan view of the fixing device. FIG. 4 is a diagram illustrating an ATVC control table of a primary transfer bias according to the first embodiment. 6 is a flowchart for determining a toner supply mode according to the first embodiment. FIG. 6 is a diagram illustrating a table of transfer current thresholds for dividing the frequency of executing the toner supply mode according to the first embodiment. FIG. 10 is a table showing a process speed threshold table for dividing the frequency of executing the toner supply mode according to the second embodiment of the present invention. 9 is a flowchart for determining a toner supply mode according to a second embodiment. FIG. 5 is a schematic cross-sectional configuration diagram of an image forming apparatus according to a third embodiment of the present invention. The schematic block diagram which extracts and shows the contact / separation mechanism in detail. 10 is a flowchart for determining a toner supply mode according to a third embodiment.

<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS. First, a schematic configuration of the image forming apparatus according to the present exemplary embodiment will be described with reference to FIGS.

[Image forming apparatus]
FIG. 1 shows a schematic cross-sectional configuration of the image forming apparatus of the present embodiment. The image forming apparatus 100 is a full-color electrophotographic image forming apparatus using an intermediate transfer system having four photosensitive drums.

  The image forming apparatus 100 includes first, second, third, and fourth image forming units (process units) Sa, Sb, Sc, and Sd as a plurality of image forming units. The image forming portions Sa, Sb, Sc, and Sd are for forming colors of yellow, magenta, cyan, and black, respectively.

  In the present embodiment, the configuration of each of the image forming units Sa to Sd is substantially the same except that the color of the toner used is different. Therefore, in the following, unless there is a particular distinction, the subscripts a, b, c, and d given to the reference numerals in the drawing are omitted to indicate that they are elements provided for any color, and are summarized Explained.

  The image forming unit S includes a photosensitive drum 1 as an image carrier. Around the photosensitive drum 1, a charging roller 2 as a primary charging unit, a laser scanner 3 as an exposure unit, a developing device 4 as a developing unit, a drum cleaner 6 as a drum cleaning unit, and the like rotate the photosensitive drum 1. They are sequentially arranged along the direction. In this embodiment, when the photosensitive drum 1 is an image carrier, the charging roller 2, the laser scanner 3, and the developing device 4 constitute a toner image forming unit. Further, adjacent to the photosensitive drums 1a to 1d of the image forming portions Sa to Sd, a belt body that can be moved around, that is, an intermediate transfer belt 51 as another image carrier or an intermediate transfer body is disposed. In this embodiment, when the intermediate transfer belt 51 is an image carrier, the photosensitive drum 1, the charging roller 2, the laser scanner 3, the developing device 4, and a primary transfer roller 53 described later constitute a toner image forming unit.

  The intermediate transfer belt 51 is wound around a driving roller 52, a steering roller 55, a secondary transfer inner roller 56, and an upstream regulating roller 58 as a plurality of support members. The steering roller 55 also has a function of applying a tension force for tensioning the intermediate transfer belt 51, and both ends of the steering roller 55 are attached in a substantially left direction in FIG. 1 by a spring biasing means (not shown). It is energized. The intermediate transfer belt 51 is rotated in the direction of the arrow in the figure by the driving force transmitted by the driving roller 52 as belt driving means.

  Primary transfer rollers 53 a to 53 d as transfer means (primary transfer members) are arranged at positions facing the respective photosensitive drums 1 a to 1 d on the inner peripheral surface side of the intermediate transfer belt 51. The primary transfer rollers 53 a to 53 d are urged toward the photosensitive drums 1 a to 1 d via the intermediate transfer belt 51. That is, the primary transfer rollers 53a to 53d press the intermediate transfer belt 51 against the photosensitive drums 1a to 1d, respectively. Then, primary transfer portions (primary transfer nips) N1a to N1d where the photosensitive drums 1a to 1d and the intermediate transfer belt 51 come into contact are formed.

  Further, a secondary transfer outer roller 57 as a transfer means (secondary transfer member) is disposed at a position facing the secondary transfer inner roller 56 on the outer peripheral surface side of the intermediate transfer belt 51. The secondary transfer outer roller 57 contacts the outer peripheral surface of the intermediate transfer belt 51 to form a secondary transfer portion (secondary transfer nip) N2.

  The images on the photosensitive drums 1a to 1d formed by the respective image forming units Sa to Sd are sequentially multiplex-transferred onto the intermediate transfer belt 51 that moves and passes adjacent to the photosensitive drums 1a to 1d. Thereafter, the image transferred onto the intermediate transfer belt 51 is further transferred to a recording material P (other image carrier) such as paper in the secondary transfer portion N2.

  FIG. 2 is a schematic diagram showing the image forming unit S in more detail. Further description will be made with reference to FIG. 2 as well. The photosensitive drum 1 is rotatably supported by the image forming apparatus main body. The photosensitive drum 1 is a cylindrical electrophotographic photosensitive member that basically includes a conductive substrate 11 such as aluminum and a photoconductive layer 12 formed on the outer periphery thereof. The photosensitive drum 1 has a support shaft 13 at the center thereof. The photosensitive drum 1 is rotationally driven about a support shaft 13 in the direction of an arrow R1 by a driving unit (not shown). In the present embodiment, the charging polarity of the photosensitive drum 1 is negative.

  Above the photosensitive drum 1 in the figure, a charging roller 2 as a primary charging means is disposed. The charging roller 2 is in contact with the surface of the photosensitive drum 1 and uniformly charges the surface of the photosensitive drum 1 to a predetermined polarity and potential. The charging roller 2 includes a conductive core 21 disposed in the center, a low resistance conductive layer 22 formed on the outer periphery thereof, and a medium resistance conductive layer 23, and is configured in a roller shape as a whole. Yes. The charging roller 2 is disposed in parallel with the photosensitive drum 1 while both ends of the cored bar 21 are rotatably supported by bearing members (not shown). The bearing members at both ends are urged toward the photosensitive drum 1 by pressing means (not shown). As a result, the charging roller 2 is pressed against the surface of the photosensitive drum 1 with a predetermined pressing force. The charging roller 2 is driven to rotate in the direction indicated by the arrow R2 as the photosensitive drum 1 rotates in the direction indicated by the arrow R1. A charging bias voltage is applied to the charging roller 2 by a charging bias power source 24 as a charging bias output unit. Thereby, the surface of the photosensitive drum 1 is uniformly charged by contact.

  A laser scanner 3 is disposed on the downstream side of the charging roller 2 in the rotation direction of the photosensitive drum 1. The laser scanner 3 scans the laser beam based on the image information while turning it on / off, and exposes the photosensitive drum 1. As a result, an electrostatic image (latent image) corresponding to the image information is formed on the photosensitive drum 1.

  A developing device 4 is arranged on the downstream side of the laser scanner 3 in the rotation direction of the photosensitive drum 1. The developing device 4 includes a developing container 41 that contains a two-component developer including non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as a developer. A developing sleeve 42 as a developer carrying member is rotatably installed in an opening of the developing container 41 facing the photosensitive drum 1. In the developing sleeve 42, a magnet roller 43 as a magnetic field generating unit is fixedly disposed so as not to rotate with respect to the rotation of the developing sleeve 42. The two-component developer is carried on the developing sleeve 42 by the magnetic field formed by the magnet roller 43. Further, a regulating blade 44 as a developer regulating member that regulates the two-component developer carried on the developing sleeve 42 and thins it is installed at a position below the developing sleeve 42 in the drawing. The developing container 41 is divided into a developing chamber 45 and an agitating chamber 46, and a replenishing chamber 47 containing replenishing toner is provided in the upper portion of the drawing.

  A thin layer of the two-component developer on the developing sleeve 42 is conveyed to a developing area facing the photosensitive drum 1 as the developing sleeve 42 rotates. The two-component developer on the developing sleeve 42 rises in the developing region by the magnetic force of the developing main pole of the magnet roller 43 located in the developing region, and a magnetic brush for the two-component developer is formed. The surface of the photosensitive drum 1 is rubbed by the magnetic brush, and a developing bias voltage is applied to the developing sleeve 42 by a developing bias power source 48 as a developing bias output means. Thereby, the toner adhering to the carrier constituting the ears of the magnetic brush adheres to the exposed portion of the electrostatic image on the photosensitive drum 1 to form a toner image. In the present embodiment, a toner image is formed on the photosensitive drum 1 by reversal development in which toner charged to the same polarity as the charging polarity of the photosensitive drum 1 is attached to a portion of the photosensitive drum 1 where the charge is attenuated by exposure. .

  A primary transfer roller 53 is disposed below the photosensitive drum 1 on the downstream side of the developing device 4 in the rotational direction of the photosensitive drum 1 in the drawing. The primary transfer roller 53 includes a cored bar 531 and a conductive layer 532 formed in a cylindrical shape on the outer peripheral surface thereof. Both ends of the primary transfer roller 53 are urged toward the photosensitive drum 1 by a pressing member (not shown) such as a spring. As a result, the conductive layer 532 of the primary transfer roller 53 is pressed against the surface of the photosensitive drum 1 via the intermediate transfer belt 51 with a predetermined pressing force. Further, a primary transfer bias power source 54 as a primary transfer bias output means is connected to the cored bar 531. A primary transfer portion N1 is formed between the photosensitive drum 1 and the primary transfer roller 53. An intermediate transfer belt 51 is sandwiched between the primary transfer portion N1. The primary transfer roller 53 contacts the inner peripheral surface of the intermediate transfer belt 51 and rotates as the intermediate transfer belt 51 moves. At the time of image formation, the primary transfer roller 53 is supplied with a primary transfer bias power source 54 by a reverse polarity (second polarity) of the normal charging polarity of the toner (first polarity: negative polarity in the present embodiment). : Positive transfer in this embodiment) is applied. An electric field is formed between the primary transfer roller 53 and the photosensitive drum 1 in such a direction that the toner of the first polarity moves from the photosensitive drum 1 toward the intermediate transfer belt 51. As a result, the toner image on the photosensitive drum 1 is transferred (primary transfer) to the surface of the intermediate transfer belt 51. As the primary transfer bias voltage, a voltage corresponding to the primary transfer target current determined by the conditions of the image forming apparatus is set.

  Deposits such as toner (primary transfer residual toner) remaining on the surface of the photosensitive drum 1 after the primary transfer process are cleaned by the drum cleaner 6. The drum cleaner 6 includes a cleaning blade 61 as a drum cleaning member, a conveying screw 62, and a drum cleaner housing 63. The cleaning blade 61 is brought into contact with the photosensitive drum 1 at a predetermined angle and pressure by a pressurizing unit (not shown). As a result, the toner remaining on the surface of the photosensitive drum 1 is scraped off from the photosensitive drum 1 by the cleaning blade 61 and is collected in the drum cleaner housing 63. The collected toner or the like is transported by the transport screw 62 and discharged to a waste toner container (not shown).

  In FIG. 1, the intermediate transfer belt 51, primary transfer rollers 53a to 53d, secondary transfer inner roller 56, secondary transfer outer roller 57, intermediate transfer belt cleaner 59, etc. are shown below the photosensitive drums 1a to 1d in the drawing. The intermediate transfer unit 5 is configured. The secondary transfer inner roller 56 is electrically grounded. The secondary transfer inner roller 56 contacts the inner peripheral surface of the intermediate transfer belt 51 and rotates as the intermediate transfer belt 51 moves.

  For example, when a full-color image is formed, toner images of the respective colors are formed on the photosensitive drums 1a to 1d of the first to fourth image forming units Sa to Sd. The toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 51 by receiving a primary transfer bias from the primary transfer rollers 53 facing the photosensitive drums 1a to 1d with the intermediate transfer belt 51 interposed therebetween (primary transfer). ) This toner image is conveyed to the secondary transfer portion N2 as the intermediate transfer belt 51 rotates.

  Meanwhile, by this time, the recording material P is conveyed to the secondary transfer portion N2 by the recording material supply means 8. That is, in the recording material supply means 8, the recording material P taken out one by one by the pickup roller 82 from the cassette 81 as the recording material accommodation unit is conveyed to the secondary transfer unit N2 by the conveying roller 83 and the like.

  The toner image on the intermediate transfer belt 51 is transferred (secondary transfer) onto the recording material P by the constant voltage power source of the secondary transfer bias power source to the secondary transfer outer roller 57, and the toner is transferred to the secondary transfer portion N2. The recording material P to which the image has been transferred is conveyed to a fixing device 7 as a fixing unit.

  Further, deposits such as toner (secondary transfer residual toner) remaining on the outer peripheral surface of the intermediate transfer belt 51 after the secondary transfer process are removed and collected by the intermediate transfer belt cleaner 59. The intermediate transfer belt cleaner 59 has the same configuration as the drum cleaner 6. That is, the intermediate transfer belt cleaner 59 also has a cleaning blade 59 a having the same configuration as the cleaning blade 61. The cleaning blade 59a is in contact with the intermediate transfer belt 51 at a predetermined angle and pressure by a pressurizing unit (not shown).

  In the case of this embodiment, the cleaning blades 61 and 59a are made of rubber elastic material. For example, urethane rubber, silicon rubber, fluorine rubber, chloropyrene rubber, butadiene rubber, or the like can be used as the material. In particular, urethane rubber can be preferably used because it has superior wear characteristics compared to other rubbers. For example, the cleaning blades 61 and 59a are made by adhering a plate-like urethane rubber having a thickness of 1 to 3 mm and a JIS-A hardness of 60 to 80 ° on a sheet metal holder so that the free length is about 5 to 12 mm. is there. The photosensitive drum 1 or the intermediate transfer belt 51 is brought into contact with a load of about 49 to 490 mN.

  When the recording material P is conveyed to the fixing device 7 and passes through the recording material P, the recording material P is pressurized and heated at a substantially constant pressure and temperature from both the front and back surfaces. As a result, the unfixed toner image on the surface of the recording material P is melted and fixed on the recording material P. Thus, a full color image is formed on the recording material P.

  3 and 4 are schematic configuration model diagrams of the fixing device 7. The fixing device of the present embodiment is a heating device of a fixing belt heating method and a pressure rotating body driving method (tensionless type).

  Reference numeral 70 denotes a fixing belt, which is a cylindrical member (endless belt-like or sleeve-like) formed by providing an elastic layer on a belt-like member. Reference numeral 72 denotes a pressure roller. On the lower surface of the heater holder 97 disposed in the fixing belt 70, a fixing heater 96 is disposed along the length (rotational axis direction) of the fixing belt 70. The fixing belt 70 is fitted on the heater holder 97. On the upper side of the pressure roller 72, a fixing belt unit including a fixing heater 96, a heater holder 97, a fixing belt 70 and the like is arranged in parallel with the pressure roller 72 with the heater side facing downward. Then, both ends of the heater holder 97 are urged in the axial direction of the pressure roller 72 by a pressure mechanism (not shown), for example, with a force of 98 N (10 kgf) on one side and a total pressure of 196 N (20 kgf). Thereby, the downward surface of the fixing heater 96 is brought into pressure contact with the elastic layer of the pressure roller 72 via the fixing belt 70 with a predetermined pressing force, thereby forming a fixing nip portion.

  The entrance guide 73 guides the recording material so that the recording material P that has passed through the secondary transfer portion N2 is accurately guided to the fixing nip portion where the fixing belt 70 and the pressure roller 72 are in the fixing heater portion. Play a leading role. The pressure roller 72 is driven to rotate in the direction of the arrow. A rotational force acts on the cylindrical fixing belt 70 by the pressure frictional force at the fixing nip portion between the outer surface of the pressure roller 72 and the fixing belt 70 due to the rotational driving of the pressure roller 72. The fixing belt 70 is driven to rotate in the direction of the arrow around the outer circumference of the heater holder 97 while the inner surface of the fixing belt 70 slides in close contact with the downward surface of the fixing heater 96.

  The pressure roller 72 is rotationally driven, and accordingly, the cylindrical fixing belt 70 is driven and rotated, and the fixing heater 96 is energized. The fixing heater 96 is heated to a predetermined temperature, and the temperature is adjusted. It will be in the state. In this state, the recording material P carrying the unfixed toner image t is introduced between the fixing belt 70 and the pressure roller 72 in the fixing nip portion while being guided by the entrance guide 73. Then, the toner image carrying surface side of the recording material P is in close contact with the outer surface of the fixing belt 70 in the fixing nip portion, and the fixing nip portion is nipped and conveyed together with the fixing belt 70. At this time, heat of the fixing heater 96 is applied to the recording material P via the fixing belt 70, and the unfixed toner image t on the recording material P is heated and pressurized on the recording material P to be melted and fixed. The recording material P that has passed through the fixing nip is separated from the fixing belt 70 by the curvature, and is discharged by the fixing discharge roller 76.

  Next, a description will be given of the temperature rise of the non-sheet passing portion and the throughput reduction control for suppressing the temperature rise when a small size paper having a small width is continuously fixed. In the temperature distribution of the fixing belt in the width direction when small-size paper is continuously fixed, heat transfer occurs from the non-sheet passing portion to the low temperature portion of the sheet passing portion, and the temperature rises at the end of the sheet passing. As a result, an abnormal image called hot offset is generated due to overheating. Therefore, by reducing the productivity, that is, by increasing the interval between the images (toner images) formed continuously (intermediate paper), Throughput reduction control is performed to suppress the temperature rise in the paper passing section. Note that the interval between papers is an interval between images continuously formed by an image forming job other than a predetermined toner image which is a toner band described later.

  In FIG. 4, 99 and 98 are thermistors as temperature detecting means. The main thermistor 99 as temperature detecting means is disposed at the center of the fixing heater, which is a heating element, and is in contact with the back surface of the fixing heater in this embodiment, and detects the temperature of the back surface of the fixing heater.

  The thermistor 98 is in elastic contact with the inner surface of the fixing belt 70 above the heater holder 97 and detects the temperature of the inner surface of the fixing belt 70. This thermistor is attached at a position of, for example, 144.1 mm from the center of the heater holder, and is located inside A4 (148.5 mm) and outside LTR (139.7 mm) in the central reference conveyance of the paper.

  The outputs of the main thermistor 99 and the thermistor 98 are respectively connected to a control circuit unit (CPU) 71 via an A / D converter. The control circuit unit 71 determines the temperature control contents of the fixing heater 96 based on the outputs of the main thermistor 99 and the thermistor 98, and supplies the fixing heater 96 with the heater driving circuit unit 78 as a power supply unit (heating means). Control energization.

  When continuously fixing small-size paper having a smaller width than the thermistor 98 is positioned at the time of image formation, the temperature of the non-sheet passing area rises. At this time, the thermistor 98 as temperature detecting means detects the temperature of the inner surface of the fixing belt 70. When the thermistor 98 detects a certain temperature, in order to suppress the temperature rise in the non-sheet passing area, the thermistor 98 stands by in a rotating state in which no sheet is passed until the temperature reaches a predetermined temperature or lower. Then, when the thermistor 98 becomes below a certain temperature, the paper feeding is resumed. By increasing the sheet interval by throughput reduction control, the time during which no transfer residual toner is generated is increased for the same number of sheets to be passed. In the image forming apparatus according to the present embodiment, the process speed is normally 160 mm / sec and 25 PPM (Paper Par Mine). On the other hand, when the throughput down control is operated, although it varies depending on the paper width, for example, when LTR (139.7 mm) is continuously fed, the throughput decreases to 12 PPM.

[Toner supply mode]
In the present embodiment, in order to prevent the cleaning blades 61 and 59a from being turned over, toner supply is performed because toner is interposed as a lubricant at the contact portions between the cleaning blades 61 and 59a, the photosensitive drums 1a to 1d, and the intermediate transfer belt 51. Run the mode. That is, the image forming apparatus 100 includes a control unit C that is a control unit that controls an image forming operation. The controller C executes a toner supply mode in which a predetermined toner image (toner band) is supplied to a contact portion between the cleaning blade 59a and the intermediate transfer belt 51 or a contact portion between the cleaning blade 61 and the photosensitive drum 1. Is possible.

  When supplying the toner band to the contact portion between the cleaning blade 59 a and the intermediate transfer belt 51, the toner band formed in any one of the image forming units S is transferred to the intermediate transfer belt 51. Then, at the secondary transfer portion N2, for example, by applying a bias in the reverse direction to the normal direction to the secondary transfer outer roller 57, the toner band is not transferred to the secondary transfer portion N2, but directed toward the cleaning blade 59a. And is supplied to the contact portion.

  On the other hand, when the toner band is supplied to the contact portion between the cleaning blade 61 and the photosensitive drum 1, the toner band formed in the image forming unit S where the photosensitive drum 1 exists is transferred to the intermediate transfer belt 51 without cleaning. Transport toward the blade 61. At this time, in the primary transfer portion N1, for example, a bias in the reverse direction to the normal direction is applied to the primary transfer roller 53 so that the toner band is not transferred by the intermediate transfer belt 51. Then, the toner band is supplied to the contact portion.

  In the present embodiment, the toner supply mode refers to a mode for supplying a toner band to one or both of them. Such a toner supply mode is executed at the time of non-image formation in which image formation based on the image formation job is not performed, such as a post-rotation operation performed between the sheets or after the end of the image formation job. In the case where both of the above are executed, for example, either one is executed between predetermined papers, and then the other is executed between subsequent papers or sequentially executed in a post-rotation.

  More specifically, the toner band is a maximum density image (solid image) having a length in the sub-scanning direction of the entire width in the main scanning direction of 1 mm or 2 mm. Such a toner band is supplied to the contact portion between the cleaning blade and the photosensitive drum or the intermediate transfer belt in the interruption sequence between sheets or the post-rotation sequence. For example, when an image forming number set as described below is reached, an interrupt sequence between sheets is supplied. If not, the image forming operation is terminated by a normal post-rotation sequence without being supplied.

  In the present embodiment, the frequency of execution of such a toner supply mode is changed depending on whether or not the cleaning blade is likely to be turned over as follows. That is, the control unit C sets the primary transfer bias to be applied to the primary transfer unit N1, which is one of the factors that cause the cleaning blade to be easily turned over, according to a predetermined condition, and sets the set primary transfer. The frequency of executing the toner supply mode is determined based on the bias. Specifically, the toner supply mode is set so that the frequency when the set transfer bias is the second transfer bias higher than the first transfer bias is higher than the frequency when the set transfer bias is the first transfer bias. Determine how often to execute.

  When the transfer bias (current value) at each of the primary transfer portions N1a to N1d of yellow, magenta, cyan, and black is large, the generation amount of discharge products increases. Then, the amount of discharge product attached to the surface of the photosensitive drum 1 or the intermediate transfer belt 51 is increased, and the frictional force of the contact portion between the cleaning blades 61 and 59a and the photosensitive drum 1 or the intermediate transfer belt 51 is increased. Blade chattering and turning are likely to occur.

  For this reason, in the present embodiment, when the primary transfer bias is large, the frequency of supplying the toner band to the cleaning blade, that is, the frequency of executing the toner supply mode, is more frequent than when the primary transfer bias is small. Have a lot. Next, the setting of the primary transfer bias that serves as a reference for determining the execution frequency of the toner supply mode will be described.

[Primary transfer bias setting]
In the present embodiment, the primary transfer bias (primary transfer current value) is determined based on the temperature and humidity where the apparatus main body is placed, and the film thickness amount of the conductive layer (photoconductive layer 12) of the photosensitive drum 1. Thickness). As the characteristics of the toner, the charge amount of the toner varies depending on the difference in temperature and humidity. Therefore, the transfer current required for transferring the toner image on the photosensitive drum to the intermediate transfer belt differs. In this embodiment, the reference for setting the transfer current is the relative humidity. For this reason, an environmental sensor H capable of prescribing temperature and humidity is installed as an environmental detection means in the apparatus main body. A signal detected by the environmental sensor H is sent to the control unit C, and the control unit C calculates the relative humidity in the apparatus main body. The control unit C sets the relative humidity as a predetermined condition for setting the primary transfer bias.

  Further, when the film thickness of the conductive layer of the photosensitive drum 1 is different even at the same temperature and humidity, an optimal transfer current value is set according to the film thickness. This is because the conductive layer of the photosensitive drum 1 is scraped as the number of uses increases, and the electrostatic capacity of the photosensitive drum 1 changes, so that the setting of the current value is increased as the conductive layer is scraped to maintain transfer efficiency. This is because. In this embodiment, the thickness detection means for detecting the thickness of the conductive layer is a current detection sensor 24a (FIG. 2) that detects the amount of current when a DC bias is applied to the charging roller 2 from the charging bias power supply 24. . The signal detected by the current detection sensor 24a is sent to the control unit C, and the control unit C compares the detected charging DC current value with the initial current value to calculate the thickness of the conductive layer.

  FIG. 5 is a primary transfer current table set with respect to the relative humidity in the apparatus main body and the amount of abrasion of the conductive layer of the photosensitive drum 1 according to the present embodiment. Since the toner used in the apparatus of the present embodiment has a different charge amount with respect to the relative humidity, a primary transfer current value corresponding to the relative humidity detected by the environmental sensor H provided in the main body is set. In this embodiment, the primary transfer current value is set corresponding to each of the three categories of low humidity, normal humidity, and high humidity. In the environment between sections, the primary transfer current value is calculated by linear interpolation.

  In addition, the thickness of the conductive layer of the photosensitive drum 1 is initially 29 μm. As the number of uses increases, the conductive layer is shaved due to the influence of a cleaning blade or the like. When the remaining film thickness is less than 15 μm, the function as the photosensitive drum cannot be sufficiently maintained. Therefore, the remaining film thickness of the conductive layer is set to 15 μm as the life of the photosensitive drum. In the table of FIG. 5, the transfer current value at the thickness of the conductive layer between 29 μm and 15 μm is obtained by linear interpolation.

[Determination of toner supply mode execution frequency]
Next, a sequence for determining the execution frequency of the toner supply mode in this embodiment will be described with reference to FIGS. In the present embodiment, the execution frequency of the toner supply mode is determined based on the flow shown in FIG. 6 in consideration of the environment in which the apparatus is placed and the transfer current value. First, the control unit C sets the primary transfer current set value (set transfer bias) of at least one color among the set values of the primary transfer current of each color set according to the apparatus conditions to a predetermined threshold value. It is determined whether or not this is the case (S1). When the first transfer bias is lower than the predetermined threshold value, the toner supply mode is executed at the first frequency (S2). When the second transfer bias is equal to or higher than a predetermined threshold, the toner supply mode is executed at a second frequency that is higher than the first frequency (S3).

  The predetermined threshold value is set to an optimum value according to the environment where the cleaning blade is placed and the transfer current value, and has a threshold value table shown in FIG. Since the cleaning blade is soft in a high temperature and high humidity environment due to the nature of rubber, turning and chatter are more likely to occur than in a low temperature and low humidity environment. For this reason, even when the frequency of supplying the toner band is the same, there is a high possibility of turning over even with a small transfer current in a high temperature and high humidity environment. Therefore, in this embodiment, as shown in FIG. 7, a threshold value is set for each environment.

  As an example, the aforementioned threshold value is 20 μA in a normal temperature and normal humidity environment. The transfer current to be set varies depending on the film thickness of the conductive layer accompanying the use of the photosensitive drum 1 as described above, and may have both set values of the threshold value of 20 μA or more. For example, when the transfer current value is set to 25 μA, the toner band supply condition A is applied, in which the execution frequency of the toner supply mode is slightly high.

  On the other hand, when the transfer current value is set to be less than 20 μA, the toner band supply condition B, which is a normal frequency that is lower than the toner band supply condition A in execution frequency, is applied. Each toner band supply condition is determined by experiment. For example, in the toner band supply condition A, the toner band supply mode is executed every 75 image formation sheets, and in the toner band supply condition B, the toner band supply mode is executed every 100 image formation sheets. The number of images formed is accumulated by a counter included in the apparatus main body.

  For example, when the toner band is supplied to the contact portion between the cleaning blade 59a and the intermediate transfer belt 51 under the toner band supply condition A, the A4 size is rotated after the total number of image formation reaches 75 sheets, or between sheets. 1 mm width of black toner band is supplied. At this time, the secondary transfer bias is a weak bias having the same polarity as the toner so that the supplied toner band is not transferred to the secondary transfer roller. In this embodiment, the voltage is controlled to be −100 V. However, when the bias value of the same polarity is large, the toner with the reversed polarity is attracted to the roller surface, and the recording material is stained during image formation. It is desirable that the bias be weak.

  As described above, since the frequency of executing the toner supply mode is determined based on the set primary transfer current, the execution frequency of the toner supply mode is increased when the generated amount of discharge products is large, and the generated amount When the amount of toner is small, the execution frequency of the toner supply mode can be lowered. That is, when the set current is high, a lot of discharge products are generated, and a lot of discharge products adhere to the surfaces of the photosensitive drum 1 and the intermediate transfer belt 51. For this reason, in this case, the frequency of supplying the toner band is increased to prevent the frictional force of the contact portion with the cleaning blade from increasing. As a result, even when the amount of discharge products is large and the cleaning blade is easily turned over, the cleaning blade can be turned up.

  On the other hand, when the set current is low, the generation of discharge products is small, and the discharge products adhering to the surfaces of the photosensitive drum 1 and the intermediate transfer belt 51 are also reduced. For this reason, in this case, the toner consumption can be suppressed by reducing the frequency of supplying the toner band.

  The execution frequency of the toner supply mode described above is determined using the threshold value of the set current. However, the frequency corresponding to each set current may be set finely. In short, the frequency may be set so as to increase as the current value increases. The frequency may be determined by a secondary transfer current applied to the secondary transfer portion N2 in addition to the primary transfer current. Similarly, when the secondary transfer current is used, the relationship between the secondary transfer current value set in consideration of the environment and the frequency is obtained in advance. And it sets so that frequency may become so high that an electric current value becomes high.

<Second Embodiment>
A second embodiment of the present invention will be described with reference to FIGS. Note that the configuration of the image forming apparatus of the present embodiment is the same as that of the image forming apparatus of the first embodiment. In the first embodiment described above, the frequency of the toner supply mode is determined by determining whether the primary transfer current value set based on the environment of the apparatus main body is equal to or greater than a predetermined threshold value. In this embodiment, in addition to this, the frequency of the toner supply mode is determined in consideration of the length between sheets. In other words, since toner is not supplied between images that are continuously formed (between sheets), if the length between the sheets increases, the contact between the cleaning blade and the photosensitive drum or the intermediate transfer belt may occur. Increases frictional force. For this reason, chattering and turning of the cleaning blade are likely to occur. Here, when the throughput reduction control is executed, the gap between the sheets becomes long, and therefore the cleaning blade is likely to be turned over. Therefore, in this embodiment, the frequency of the toner supply mode is determined in consideration of the length between sheets.

  Therefore, in this embodiment, as shown in FIG. 8, the process speed of the image forming apparatus is used as a predetermined threshold value for determining the frequency of the toner supply mode. That is, the length between sheets is controlled in terms of process speed (PPM). The threshold value is set for each environment. The control flow at this time is shown in FIG.

  As shown in FIG. 9, it is determined whether or not the process speed is equal to or lower than a predetermined threshold value (S21). When the process speed is the first interval larger than the predetermined threshold value, the toner supply mode is executed at the first frequency (S22). For example, when it is not the throughput down control, the toner band is supplied under the toner band supply condition B which is a normal frequency.

  On the other hand, when the process speed is equal to or smaller than the predetermined threshold value in S21 and the second interval is longer than the first interval, the same determination as in the first embodiment is performed. That is, with reference to FIG. 7, the primary transfer current value among the primary transfer current values of the respective colors set based on the environment of the apparatus main body is equal to or greater than a predetermined threshold value. Judgment is made (S23). When it is lower than the predetermined threshold value, the toner supply mode is executed at a second frequency that is higher than the first frequency (S24). When the predetermined threshold value is exceeded, the toner supply mode is executed at a third frequency that is higher than the second frequency (S25).

  That is, even when the throughput down control is executed, if the set value of the transfer current is low, the toner band is supplied under the toner band supply condition A that is slightly more frequent. Further, when the throughput reduction control is executed and the set value of the transfer current is high, the toner band is supplied under the high-frequency toner band supply condition C. For example, toner supply is performed every 50 sheets for image formation in toner band supply condition C, every 75 sheets for image formation in toner band supply condition A, and every 100 sheets for image formation in toner band supply condition B. Run the mode.

  In this embodiment, since the execution frequency of the toner supply mode is determined in consideration of the length between sheets, the cleaning blade can be prevented from turning over more optimally and the toner consumption can be suppressed. It is done. Other configurations and operations are the same as those in the first embodiment.

<Third Embodiment>
A third embodiment of the present invention will be described with reference to FIGS. In the image forming apparatus 100A of this embodiment, a contact / separation mechanism 1000 for the primary transfer roller 53 is added to the image forming apparatus of the first embodiment. About another structure, it is the same as that of 1st Embodiment. In the present embodiment, the contact / separation mechanism 1000 can switch between a full color mode (second image forming mode) and a black (Bk) single color mode (first image forming mode).

  In the image forming apparatus of the tandem type intermediate transfer system as in the present embodiment, the photosensitive drum 1 rotates in contact with the intermediate transfer belt 51, so that the primary transfer pressure, the cleaning blade, the friction with the intermediate transfer belt 51, etc. Causes scratches and scrapes on the surface. For this reason, the yellow, magenta, and cyan photosensitive drums 1a to 1c may have a short life due to scratches and scrapes even though the frequency of forming a full-color image is small. Therefore, it is not preferable that the yellow, magenta, and cyan photosensitive drums 1a to 1c and the intermediate transfer belt 51 that are not in use are always rotated in contact with each other when an image is formed in the black monochrome mode.

  Therefore, in order to prevent the photosensitive drum from being scraped and scratched, in the black monochrome mode, the intermediate transfer belt 51 is separated from the photosensitive drums 1a to 1c that are not used except black. Accordingly, it is possible to prevent the short life of the yellow, magenta, and cyan photosensitive drums 1a to 1c even in a usage environment that is less frequently used than the black monochrome mode. In the normal state, to shorten the start-up time of the black monochrome mode, the main unit is in a standby state, or after the image formation is completed, the black monochrome mode is the default, and the contact / separation mechanism is used for full-color mode image formation. It is switched by 1000.

  The position indicated by the solid line in FIG. 10 is the full color mode, and the position indicated by the broken line is the black monochrome mode. FIG. 11A shows the state of the contact / separation mechanism 1000 in the full color mode, and FIG. 11B shows the state of the contact / separation mechanism 1000 in the black monochrome mode. As shown in FIG. 10, the contact / separation mechanism 1000 uses the primary transfer rollers 53 a to 53 c, which are any one of the plurality of primary transfer rollers 53 a to 53 d, as the intermediate transfer belt 51. Bring to and away from each other.

  In the black monochrome mode which is the first image forming mode, the primary transfer rollers 53a to 53c, which are any transfer means, are separated from the intermediate transfer belt 51, and the intermediate transfer belt 51 is further separated from the photosensitive drums 1a to 1c. . Then, image formation is performed without applying a primary transfer bias to the primary transfer rollers 53a to 53c. That is, the black toner image formed on the photosensitive drum 1d is transferred to the intermediate transfer belt 51 by applying a primary transfer bias only to the primary transfer roller 53d.

  In the full color mode which is the second image forming mode, the primary transfer rollers 53a to 53c, which are any transfer means, are brought into contact with the intermediate transfer belt 51, and the intermediate transfer belt 51 is further brought into contact with the photosensitive drums 1a to 1c. Let Then, a primary transfer bias is applied to the primary transfer rollers 53a to 53d, which are all transfer units, to form an image. That is, the toner images of the respective colors formed on the photosensitive drums 1 a to 1 d are transferred to the intermediate transfer belt 51 by applying a primary transfer bias to the primary transfer rollers 53 a to 53 d, respectively.

[Contact / separation mechanism]
As shown in FIG. 11, the contact / separation mechanism 1000 includes a rotation support frame 109, an arm 107, a slider 101, a cam 102, and the like. The pin 108 fixed to the rotation support frame 109 is driven up and down by the arm 107. The slider 101 is movable in the left-right direction in the figure by guiding a long groove 105G to a pin 105 fixed to the apparatus main body. The spring 104 urges and moves the slider 101 in the right direction in the drawing to a position where the roller 103 fixed to the slider 101 contacts the cam 102. The cam 102 is rotationally driven by the motor M1 via the speed reduction mechanism 111.

  As shown in FIG. 11A, in the full color mode, the cam 102 moves to a position where the spring 104 is pressed and contracted, and the slider 101 is moved in the left direction in the figure. Then, the pin 106 fixed to the arm 107 descends along the long groove 106G, and the arm 107 rotates counterclockwise in the drawing around the pin 107G to push up the pin 108.

  On the other hand, as shown in FIG. 11B, in the black monochrome mode, the cam 102 moves to a position where the spring 104 extends, and the slider 101 biased by the spring 104 moves to the right in the drawing. Then, the pin 106 fixed to the arm 107 is raised along the long groove 106G, and the pin 108 is lowered by rotating the arm 107 clockwise around the pin 107G. The pin 108 is guided in the vertical direction in the figure by a guide (not shown), and is urged downward in the figure by a spring (not shown) so as to contact the end of the arm 107. Then, the pin 108 is moved in the vertical direction following the rotation of the arm 107.

  In the full color mode shown by the solid line in FIG. 10, the contact / separation mechanism 1000 in FIG. 11A rotates the arm 107 with the pin 107G as a fulcrum, and rotates the rotation support frame 109 fixed to the pin 108 upward. Move. The primary transfer rollers 53a, 53b, 53c supported by the rotation support frame 109 are lifted by the rotation of the rotation support frame 109 to push up the intermediate transfer belt 51, and the intermediate transfer belt 51 is moved to the photosensitive drum 1a. Press against 1b, 1c. Thereby, the primary transfer portions (nip portions) N1a, N1b, N1c, and N1d are formed. In the full color mode, a full color image using a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image formed on the photosensitive drums 1a, 1b, 1c, and 1d is formed on the intermediate transfer belt 51, and the recording material. Transferred to P.

  On the other hand, in the black monochromatic mode shown by the broken line in FIG. 10, the contact / separation mechanism 1000 rotates the arm 107 about the pin 107G as a fulcrum and rotates fixed to the pin 108, as shown in FIG. The support frame 109 is rotated downward. The primary transfer rollers 53a, 53b, 53c supported by the rotation support frame 109 are lowered by the rotation of the rotation support frame 109, and the intermediate transfer belt 51 is separated from the photosensitive drums 1a, 1b, 1c. Let In the black monochrome mode, a monochrome image using the black toner image formed on the photosensitive drum 1 d is formed on the intermediate transfer belt 51 and transferred to the recording material P.

  In the image forming apparatus as described above, the discharge product formed on the intermediate transfer belt in the full-color mode is larger in yellow, magenta, and cyan than in the black monochrome mode. For this reason, the chatter and turning of the cleaning blades 61 and 59a are more likely to occur in the full color mode. Therefore, in the present embodiment, the execution frequency of the toner supply mode is higher in the full color mode than in the black single color mode.

  FIG. 12 is a flow using the cleaning band supply sequence of the present embodiment. As shown in FIG. 12, the control unit C determines whether the image is formed in the full color mode or the black monochrome mode (S31). In either case, the same flow as in the second embodiment is performed. That is, it is determined from FIG. 8 whether the process speed is equal to or lower than a predetermined threshold value (S32-1, S32-2). After that, it is determined whether one of the primary transfer current setting values for each color determined based on the environment of the apparatus main body in FIG. 7 is equal to or greater than a predetermined threshold value (S33-). 1, S33-2).

  In the full color mode, the execution frequency of the toner supply mode is determined as follows. First, when the process speed is larger than the predetermined threshold value, the toner supply mode is executed at the first frequency (S34-1). That is, the toner band is supplied under the toner band supply condition B which is a normal frequency.

  On the other hand, when the process speed is equal to or lower than a predetermined threshold and the primary transfer current value of any of the primary transfer current values of each color is lower than the predetermined threshold, the first frequency is exceeded. The toner supply mode is executed at a second frequency that is high (S35-1). That is, the toner band is supplied under the toner band supply condition A that is slightly more frequent. When one of the primary transfer current values of each color is equal to or greater than a predetermined threshold value, the toner supply mode is executed at a third frequency that is higher than the second frequency. (S36-1). That is, the toner band is supplied under the high-frequency toner band supply condition C. For example, toner supply is performed every 50 sheets for image formation in toner band supply condition C, every 75 sheets for image formation in toner band supply condition A, and every 100 sheets for image formation in toner band supply condition B. Run the mode.

  On the other hand, in the case of the black monochrome mode, the execution frequency of the toner supply mode is determined as follows. In the black monochrome mode, the frequency is lower than the first frequency, which is the normal frequency, under all conditions. First, when the process speed is larger than the predetermined threshold value, the toner supply mode is executed at the fourth frequency (S34-2). That is, the toner band is supplied under the toner band supply condition E that is infrequent.

  On the other hand, when the process speed is equal to or lower than the predetermined threshold value and any of the primary transfer current values of the respective colors is lower than the predetermined threshold value, the fourth frequency is exceeded. The toner supply mode is executed at a fifth frequency that is high (S35-2). That is, the toner band is supplied under the toner band supply condition D that is slightly less frequent. When one of the primary transfer current values of each color is equal to or greater than a predetermined threshold value, the toner supply mode is executed at a sixth frequency that is higher than the fifth frequency. (S36-2). That is, the toner band is supplied under the toner band supply condition F slightly less frequently than the normal frequency. For example, in the toner band supply condition F, toner is supplied every 150 sheets, in the toner band supply condition D, every 200 images are formed, and in the toner band supply condition E, every 300 images are formed. Run the mode.

  In the case of the present embodiment, as described above, the optimum toner band that varies depending on the difference in the total amount of discharge products due to the difference in the number of primary transfer portions, the difference in process speed with different paper lengths, and the difference in transfer current value. Supplying. Therefore, it is possible to prevent the cleaning blade from turning over more optimally without consuming more toner than necessary. Other configurations and operations are the same as those of the second embodiment described above.

<Other embodiments>
In the second embodiment described above, the execution frequency of the toner supply mode is determined based on the process speed and the set value of the transfer current value. However, the execution frequency of the toner supply mode may be determined only based on the process speed. In the third embodiment described above, the execution frequency of the toner supply mode is determined by the process speed, the set value of the transfer current value, and the image formation mode. However, the execution frequency of the toner supply mode is determined only by the image formation mode. You may do it. That is, the execution frequency may be determined only in the full color mode or the single color mode. Further, the execution frequency of the toner supply mode may be determined based on the process speed and the image formation mode, or the execution frequency of the toner supply mode may be determined based on the set value of the transfer current value and the image formation mode.

  In each of the above-described embodiments, an example in which the present invention is applied to an intermediate transfer type image forming apparatus has been described. However, the present invention is also applicable to a direct transfer type image forming apparatus. That is, the present invention can also be applied to a configuration in which a toner image is directly transferred from a photosensitive drum as an image carrier to a recording material as another image carrier.

  1 (1a, 1b, 1c, 1d) ... photosensitive drum (image carrier), 2 (2a, 2b, 2c, 2d) ... charging roller, 3 (3a, 3b, 3c, 3d) ... Laser scanner, 4 (4a, 4b, 4c, 4d) ... developing device, 24a ... current detection sensor (thickness detection means), 51 ... intermediate transfer belt (intermediate transfer member, other image carrier) 53 (53a, 53b, 53c, 53d) ... primary transfer roller (transfer means), 59a, 61 ... cleaning blade, 100, 100A ... image forming apparatus, 1000 ... contact / separation mechanism, C: Control unit (control means), H: Environmental sensor (environment detection means)

Claims (10)

An image carrier for carrying a toner image;
Toner image forming means for forming a toner image on the surface of the image carrier;
Transfer means for transferring a toner image formed on the image carrier to another image carrier by applying a transfer bias;
In an image forming apparatus comprising a cleaning blade that contacts the surface of the image carrier,
A toner supply mode for supplying a predetermined toner image to a contact portion between the cleaning blade and the image carrier can be executed, the transfer bias is set according to a predetermined condition, and the set transfer bias is a first transfer bias. Control means for determining the frequency of executing the toner supply mode so that the frequency of the second transfer bias higher than the first transfer bias is higher than the frequency of the transfer bias. ,
An image forming apparatus. An image carrier for carrying a toner image;
Toner image forming means for forming a toner image on the surface of the image carrier;
An intermediate transfer member to which a toner image formed on the image carrier is transferred;
Transfer means for transferring a toner image formed on the image carrier to the intermediate transfer member by applying a transfer bias;
In an image forming apparatus comprising a cleaning blade that contacts the surface of the intermediate transfer member,
A toner supply mode for supplying a predetermined toner image to a contact portion between the cleaning blade and the intermediate transfer member can be executed, the transfer bias is set according to a predetermined condition, and the set transfer bias is a first transfer bias. Control means for determining the frequency of executing the toner supply mode so that the frequency of the second transfer bias higher than the first transfer bias is higher than the frequency of the transfer bias. ,
An image forming apparatus. Having an environment detection means for detecting the environment in the device body,
The predetermined condition is a relative humidity detected by the environment detection means.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The image carrier is a photosensitive drum having a conductive layer,
Having a thickness detecting means for detecting the thickness of the conductive layer;
The predetermined condition is the thickness of the conductive layer detected by the thickness detection means.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The control means executes the toner supply mode at a first frequency when the set transfer bias is the first transfer bias lower than a predetermined threshold value, and the control unit executes the toner supply mode at the first threshold value or more. In the case of the second transfer bias, the toner supply mode is executed at a second frequency that is higher than the first frequency.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The control means has an interval more than the first interval than the frequency when the interval between the toner images continuously formed on the image carrier other than the predetermined toner image is the first interval. Determining the frequency of executing the toner supply mode so that the frequency in the case of the long second interval is high;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. A plurality of the image carriers, an intermediate transfer belt to which toner images formed on the plurality of image carriers are transferred, and the intermediate transfer belt are pressed against the plurality of image carriers to apply the transfer bias. As a result, the plurality of transfer units that respectively transfer the toner images from the plurality of image carriers to the intermediate transfer belt, and any one of the plurality of transfer units are in contact with the intermediate transfer belt. A contact / separation mechanism for separating,
The control unit separates any one of the transfer units from the intermediate transfer belt and performs the image formation without applying a transfer bias to any of the transfer units. The toner supply mode is set so that the frequency of the second image forming mode in which any transfer unit is brought into contact with the intermediate transfer belt and image transfer is performed by applying a transfer bias to all the transfer units is increased. Determine how often to run,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. An image carrier for carrying a toner image;
Toner image forming means for forming a toner image on the surface of the image carrier;
In an image forming apparatus comprising a cleaning blade that contacts the surface of the image carrier,
A toner supply mode for supplying a predetermined toner image to a contact portion between the cleaning blade and the image carrier can be executed, and in addition to the predetermined toner image, a toner image continuously formed on the image carrier The frequency of executing the toner supply mode is determined so that the frequency when the interval is the second interval longer than the first interval is higher than the frequency when the interval is the first interval. Having control means to
An image forming apparatus. A plurality of image carriers each carrying a toner image;
A plurality of toner image forming units that respectively form toner images on the plurality of image carriers;
An intermediate transfer belt to which toner images respectively formed on the plurality of image carriers are transferred;
A plurality of transfer means for respectively transferring toner images from the plurality of image carriers to the intermediate transfer belt by pressing the intermediate transfer belt against the plurality of image carriers and applying a transfer bias;
A plurality of cleaning blades respectively contacting the surfaces of the plurality of image carriers;
An image forming apparatus comprising: a contact / separation mechanism that contacts / separates any of the plurality of transfer units with respect to the intermediate transfer belt;
A toner supply mode for supplying a predetermined toner image to a contact portion between the cleaning blade and the image carrier can be executed, and any one of the transfer units is separated from the intermediate transfer belt, and any of the transfer units More than the frequency of the first image forming mode in which image formation is performed without applying a transfer bias to the intermediate transfer belt, any one of the transfer units is brought into contact with the intermediate transfer belt, and the transfer bias is applied to all the transfer units. Control means for determining the frequency of executing the toner supply mode so that the frequency of the second image forming mode for performing image formation increases.
An image forming apparatus. A plurality of image carriers each carrying a toner image;
A plurality of toner image forming units that respectively form toner images on the plurality of image carriers;
An intermediate transfer belt to which toner images respectively formed on the plurality of image carriers are transferred;
A plurality of transfer means for respectively transferring toner images from the plurality of image carriers to the intermediate transfer belt by pressing the intermediate transfer belt against the plurality of image carriers and applying a transfer bias;
A cleaning blade in contact with the surface of the intermediate transfer belt;
An image forming apparatus comprising: a contact / separation mechanism that contacts / separates any of the plurality of transfer units with respect to the intermediate transfer belt;
A toner supply mode for supplying a predetermined toner image to a contact portion between the cleaning blade and the intermediate transfer belt can be executed, and any one of the transfer units is separated from the intermediate transfer belt, and any of the transfer units More than the frequency of the first image forming mode in which image formation is performed without applying a transfer bias to the intermediate transfer belt, any one of the transfer units is brought into contact with the intermediate transfer belt, and the transfer bias is applied to all the transfer units. Control means for determining the frequency of executing the toner supply mode so that the frequency of the second image forming mode for performing image formation increases.
An image forming apparatus.

Images