JP5289023B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus.

  In recent years, multifunction devices equipped with all output terminals such as copiers, printers, and fax machines have been accepted in the market. As such an output terminal, an electrophotographic image forming apparatus is widely used. In addition, it is desired to extend the life of the apparatus body as the machine speed increases. In addition, from the viewpoint of ecology, it is also required to eliminate waste, that is, reduce consumables, extend the life of consumables, and improve reliability.

  On the other hand, black-and-white machines have been mainstream in the past, but colorization of manuscripts or output files is also progressing in offices. Therefore, in order to reduce TCO (total cost required for the user), a color image forming apparatus in which the cost of the apparatus main body and the running cost are equivalent to those of a monochrome machine is desired.

  Under such circumstances, a color image is formed by providing a plurality of photosensitive drums which are drum-type electrophotographic photosensitive members, and sequentially transferring toner images of different colors formed on the respective photosensitive drums to the transfer target. So-called tandem image forming apparatuses are becoming mainstream.

  2. Description of the Related Art In an image forming apparatus that forms an image using an electrostatic latent image as an intermediate medium, a charging roller system that uses a relatively low voltage and that can be easily downsized is widely used. A charging roller, which is a charging member used in this charging roller system, is provided with an elastic body layer and a protective layer on the surface of the elastic layer on the outer peripheral surface of a metal shaft. Then, the protective layer is in contact with the photosensitive drum, and a DC voltage (Vdc) alone or a voltage (Vdc + Vac) obtained by superimposing an AC voltage and a DC voltage is applied to a metal shaft from a high voltage power source.

  Some tandem image forming apparatuses use an intermediate transfer member or a recording material carrier as an image carrier for conveying an image transferred from a photosensitive member. That is, as a tandem image forming apparatus, a toner image formed on the surface of a photosensitive drum is multiplex-transferred onto an intermediate transfer belt, which is a belt-shaped intermediate transfer member, and the toner image on the intermediate transfer belt is transferred to paper. There is an image forming apparatus that repeats a process of transferring to a main recording material. Further, as the tandem image forming apparatus, there is an image forming apparatus that repeats a process of directly transferring a toner image formed on the surface of a photosensitive drum onto a recording material carried on a conveyance belt that is a belt-like recording material carrier. is there.

  In a tandem type image forming apparatus, when a black and white image is output, a photosensitive drum for forming a toner image other than black is also driven in order to prevent a sliding scratch with the intermediate transfer belt or the conveyance belt. . However, in this configuration, for example, when a cleaning blade is used for cleaning the photosensitive drum, the photosensitive drum that is not related to image formation can be scraped by rubbing, the life thereof is shortened, and the user who outputs many black and white images Will increase TCO.

  Therefore, there is an image forming apparatus having a monochrome image output mode for outputting a monochrome image and a color image output mode for outputting a color image as follows. That is, in the black and white image output mode, the transfer device is separated from the photosensitive drum for forming a toner image other than black, and its driving is stopped. In the color image output mode, the transfer device is brought into contact with a photosensitive drum for forming a toner image other than black together with a photosensitive drum for forming a black toner image. According to this configuration, even a user who outputs a large number of black and white images can extend the life of the photosensitive drum for forming a toner image other than black, which helps to reduce TCO.

Patent Document 1 discloses a technique for detecting the film thickness of a photoreceptor from a current flowing through a charging member.
JP-A-5-223513

  In an image forming apparatus that separates the transfer device from the photosensitive drum for forming a toner image other than black when outputting a black and white image, a color image is output immediately after the output of the black and white image. In some cases, the transfer belt or the conveyance belt is brought into contact with the belt while rotating. This is from the viewpoint of improving image productivity.

  However, the photosensitive drum generally has a shorter life than the intermediate transfer belt or the conveyance belt, and its replacement frequency is high. Therefore, there is a high risk that the photosensitive drum is attached to the apparatus main body in a state where it cannot be properly rotated.

  For example, in a state where the coupling is caught or the photosensitive drum does not rotate by rotating only the shaft, the photosensitive drum may not be able to rotate and may stop. In such a state, if the intermediate transfer belt or the conveyance belt is driven while being brought into contact with the photosensitive drum, the photosensitive drum is rubbed by the intermediate transfer belt or the conveyance belt, thereby causing an image defect.

  As a method for detecting that the photosensitive drum is rotating, a method for measuring the Doppler effect by a laser or the like can be considered.

In addition, a method of detecting that the photosensitive drum is rotating by detecting that the charged region has reached the measurement position by using a means for measuring the surface potential of the photosensitive drum has been implemented. However, these techniques, such as for necessary to provide a special detection means, easily lead to cost increase, and spaces need easily.

  There is also a method for detecting that the photosensitive drum is rotating by detecting the amount of current flowing through a transfer roller, which is a primary transfer member for transferring the toner image from the photosensitive drum to the intermediate transfer member. However, when the primary transfer roller is brought into contact with the photosensitive drum from a state separated from the photosensitive drum, it cannot be used as a means for confirming that the photosensitive drum is rotating.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of controlling whether to continue driving input to a photoconductor according to the rotation state of the photoconductor with a simple configuration.

  Another object of the present invention is to provide an image forming apparatus capable of controlling whether or not the contact operation between the photoconductor and the image carrier can be executed according to the rotation state of the photoconductor with a simple configuration. It is.

The above object is achieved by the image forming apparatus according to the present invention. In summary , the present invention includes a first photosensitive member that can rotate, a first image forming unit that forms an image on the first photosensitive member, a second photosensitive member that can rotate, A charging member that charges the second photosensitive member, a second image forming unit that forms an image on the second photosensitive member, a driving unit that rotationally drives the second photosensitive member, and the charging member An application unit that applies a voltage to the member, a detection unit that detects a current flowing through the charging member, and an image formed on the first photoconductor and an image formed on the second photoconductor are recorded. An intermediate transfer belt transported to a transfer position on the material, a first posture in which the intermediate transfer belt is in contact with the first photoconductor and is separated from the second photoconductor, and the intermediate transfer belt is in the first position. The intermediate transfer belt is in a second posture in contact with one photoconductor and the second photoconductor. A contact / separation mechanism capable of switching the posture, and a first image forming unit that performs image formation in a state in which the intermediate transfer belt is in the first posture and rotation of the second photoconductor is stopped. And the second image forming mode in which the first image forming unit and the second image forming unit perform image formation while the intermediate transfer belt is in the second posture. Control means, and when the control means shifts from image formation in the first image formation mode to image formation in the second image formation mode, the intermediate transfer belt and the first photosensitive member. When the current detected by the detection means is within a predetermined range when the drive means is driven and a predetermined voltage is applied to the charging member in a state where the body is maintained, the first transfer of the intermediate transfer belt is performed. One attitude To execute the switching of the al to the second position, said detected by the detecting means current is an image forming apparatus and controls to stop the image forming when it is outside the predetermined range.

  According to the present invention, it is possible to control whether or not to continue driving input to the photoconductor according to the rotation state of the photoconductor with a simple configuration. In addition, according to the present invention, it is possible to control whether or not the contact operation between the photoconductor and the image carrier can be performed according to the rotation state of the photoconductor with a simple configuration.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
1. Overall Configuration and Operation of Image Forming Apparatus FIGS. 1 and 2 show a schematic configuration of an embodiment of an image forming apparatus according to the present invention. The image forming apparatus 101 according to the present exemplary embodiment is a color laser printer using a transfer type electrophotographic process, a contact charging method, and a reversal developing method and having a maximum sheet passing size of A3. The image forming apparatus 101 is a recording material, for example, paper, an OHP sheet, or the like according to image information from an external host device such as a personal computer or an image reading apparatus that is communicably connected to the image forming apparatus main body (apparatus main body). A color image can be formed and output. Information indicating whether or not the image forming apparatus 101 is ready to output is transmitted to the external host device, and is displayed as a message on the display unit of the external host device so as to be recognizable to the user.

  The image forming apparatus 101 of the present embodiment is a so-called quadruple tandem drum type image forming apparatus. That is, the image forming apparatus 101 has a plurality of process cartridges 8, and each process cartridge 8 once multiplex-transfers a toner image continuously to a movable intermediate transfer body 91. After that, the toner image is collectively transferred from the intermediate transfer member 91 to the recording material S to form a color image. In this embodiment, four process cartridges 8 are arranged in order of yellow, magenta, cyan, and black in series in the moving direction of the intermediate transfer member 91. This will be described in more detail below.

  The image forming apparatus 101 according to the present exemplary embodiment includes, as a plurality of image forming units, first, yellow, and magenta (M), cyan (C), and black (Bk) color images. Second, third, and fourth image forming units PY, PM, PC, and PBk are included. The four image forming units PY, PM, PC, and PBk have the same configuration except for the color of the developer to be used. The subscripts Y, M, C, and Bk that indicate the presence are omitted, and will be described collectively.

  For example, the overall operation when a four-color image is formed will be described. According to a signal from an external host device that is communicably connected to the image forming apparatus 101, an image signal that has been color-separated is generated. In response to this signal, toner images of the respective colors are formed in the process cartridges 8Y, 8M, 8C, and 8BK of the image forming units PY, PM, PC, and PBk.

  In each of the process cartridges 8Y, 8M, 8C, and 8Bk, a rotatable drum type electrophotographic photosensitive member (photosensitive member) having an organic material photosensitive layer on a conductive support as an image carrier, that is, the photosensitive drum 1 is provided. Then, charging is performed by a charging roller 2 which is a charging member as a charging unit. The uniformly charged surface is scanned and exposed by an image exposure device (laser beam scanner) 3 as an image exposure unit, thereby forming an electrostatic latent image (electrostatic image) on the photosensitive drum 1. A toner image is formed on the photosensitive drum 1 by supplying toner as a developer to the electrostatic latent image by the developing device 4 as a developing unit. The toner images of the respective colors formed on the respective photosensitive drums 1 are sequentially transferred (primary transfer) on the intermediate transfer belt 91 that is an endless belt-like intermediate transfer body in each primary transfer portion d. A primary transfer roller 92 that is a primary transfer member as a primary transfer unit is provided on the inner peripheral surface side of the intermediate transfer belt 91 so as to face each photosensitive drum 1. By the action of the primary transfer roller 92, the toner image is transferred from the photosensitive drum 1 to the intermediate transfer belt 91 (primary transfer). The color toner image formed on the intermediate transfer belt 91 is conveyed to the secondary transfer portion N where the intermediate transfer belt 91 and the secondary transfer roller 10 as a secondary transfer member as a secondary transfer unit face each other. The recording material S thus transferred is collectively transferred (secondary transfer). Next, the recording material S onto which the toner image has been transferred is conveyed to a fixing device 13 as a fixing unit, where the toner image is fixed and then discharged outside the apparatus. In this embodiment, the fixing device 13 applies heat and pressure to the recording material S by a pair of fixing rollers to melt and fix the toner image on the recording material S.

2. Configuration and Operation of Each Element of Image Forming Unit Next, each element of each image forming unit P will be described in more detail with reference to FIGS. Hereinafter, when it is necessary to particularly distinguish each element included in each image forming unit P, for example, the first, second, third, and fourth photosensitive drums 1PY, 1PM, 1PC, and 1Bk are respectively “ It is described as “first”, “second”, “third”, “fourth”.

  The process cartridge 8 includes a drum-type electrophotographic photosensitive member (photosensitive member) that can rotate as an image carrier, that is, a photosensitive drum 1. In this embodiment, the photosensitive drum 1 is an organic photoconductor (OPC) drum, and its outer diameter is 30 mm. As shown in FIG. 4, the photosensitive drum 1 is coated with a photosensitive layer 1b made of an organic photoconductive layer (OPC) on the outer peripheral surface of a drum base 1a made of a conductive material such as aluminum which is electrically grounded. Is formed. In this embodiment, OPC has a negative charging characteristic. The photosensitive layer 1b is composed of four layers of an undercoat layer (CPL) 1b1, an injection blocking layer (UCL) 1b2, a charge generation layer (CGL) 1b3, and a charge transport layer (CTL) 1b4.

  The photosensitive layer 1b is usually an insulator, and has a feature that it becomes a conductor when irradiated with light of a specific wavelength. This is because holes (electron pairs) are generated in the charge generation layer 1b3 by light irradiation, and they become a charge flow charge. The charge generation layer 1b3 is made of a phthalocyanine compound having a thickness of 0.2 μm, and the charge transport layer 1b4 is made of a polycarbonate in which a hydrazone compound having a thickness of about 25 μm is dispersed. The photosensitive drum 1 is rotationally driven in the direction of the arrow R1 (counterclockwise) by a photosensitive member driving means 19 (DC brushless motor) at a process speed (peripheral speed) of 250 mm / sec around the center support shaft.

  The process cartridge 8 includes a charging roller 2 that is a contact-type charging device as charging means. The charging roller 2 is a contact charging member formed in a roller shape. The charging roller 2 is a member for uniformly charging the surface (outer peripheral surface) of the photosensitive drum 1 to a predetermined polarity and potential.

  As shown in FIG. 4, the charging roller 2 is configured by covering the outer peripheral surface of a metal cored bar 2a with an elastic layer 2b, a resistance layer 2c, and a surface layer 2d. Both ends of the metal core 2a in the longitudinal direction are rotatably held by bearing members. In this embodiment, the charging roller 2 has a length of 320 mm in the longitudinal direction (rotational axis direction). The bearing member is urged toward the photosensitive drum 1 by a pressing spring (compression spring) 2e as an urging member. Thus, the charging roller 2 is pressed against the surface of the photosensitive drum 1 with a predetermined pressing force, and forms a charging portion (charging nip portion) a between the surface of the photosensitive drum 1. The charging roller 2 is driven to rotate as the photosensitive drum 1 rotates.

  A charging voltage (charging bias) is applied to the charging roller 2 by a charging power source (high voltage power source) V1 serving as a charging voltage applying unit (bias applying unit). Connected to the charging power source V1 is an ammeter V2 as current detecting means for detecting a DC component of a current (charging current) flowing from the charging roller 2 to the photosensitive drum 1 when a charging voltage is applied. The detection result of the direct current component of the charging current by the ammeter V2 is input to the CPU 50 as the control means. The CPU 50 instructs the drive unit 19 of the photosensitive drum 1 and the drive unit 20 (FIG. 1) of the intermediate transfer belt 91 to drive and stop, and also instructs the output value of the charging power source V1 and the output and stop. It is configured to be able to.

  An oscillating voltage obtained by superimposing a DC voltage and an alternating voltage is applied as a charging voltage to the metal core 2 a of the charging roller 2. As a result, the surface of the rotating photosensitive drum 1 is uniformly and uniformly charged to a predetermined polarity and potential.

  In this embodiment, an oscillating voltage in which a DC voltage of −600 V, a frequency = 1500 Hz, a peak-to-peak voltage Vpp = 1400 V, and a sinusoidal AC voltage are superimposed is applied to the charging roller 2 during image formation. As a result, the peripheral surface of the photosensitive drum 1 is uniformly contact-charged to −600 V (dark part potential Vd).

  A charging roller cleaning member 2 f is provided for the charging roller 2. In the present embodiment, the charging roller cleaning member 2f is a flexible cleaning film. The cleaning film 2f is disposed in parallel to the longitudinal direction (rotation axis direction) of the charging roller 2 by the support member 2g, and is disposed so as to form a contact nip with the charging roller 2 on the surface near the free end. As a result, the surface layer of the charging roller 2 is rubbed with the cleaning film 2f, and attached contaminants (fine toner, external additives, etc.) on the surface layer of the charging roller 2 are removed.

  The photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by a charging roller 2 and then receives an image exposure L by an image exposure device 3 as image exposure means. In this embodiment, the image exposure apparatus 3 as an image exposure unit outputs a laser beam modulated in accordance with a color separation / imaging exposure optical system of a color original image and a time-series electric digital pixel signal of image information. It has a scanning exposure system by laser scanning. The image exposure device 3 forms electrostatic latent images of color components corresponding to the image forming portions PY, PM, PC, and PBk of the target color image on the photosensitive drums 1Y, 1M, 1C, and 1Bk.

  In this embodiment, a laser beam scanner 3 using a semiconductor laser is used as the image exposure device 3 as image exposure means. The laser beam scanner 3 outputs a laser beam modulated in accordance with an image signal sent from the external host device to the image forming apparatus 101 side, and performs laser scanning exposure on the uniformly charged surface of the rotating photosensitive drum 1. (Image exposure). By this laser scanning exposure, the potential of the portion irradiated with the laser light L on the photosensitive drum 1 is lowered, so that an electrostatic latent image corresponding to the scanned and exposed image information is formed on the rotating photosensitive drum 1. Is done. In this embodiment, the exposed portion potential Vl is −150V. The irradiation position of the image exposure L on the photosensitive drum 1 is the exposure part b.

  The electrostatic latent image formed on the photosensitive drum 1 is developed with toner by a developing device 4 as developing means. In this embodiment, the developing device 4 is a two-component contact developing device (two-component magnetic brush developing device). The developing device 4 includes a developing container (developing device main body) 40, a developing sleeve 41 as a developer carrying member having a magnet roller fixedly disposed therein, a developer regulating blade 42 as a developer regulating member, and the inside of the developing container 40. Developer agitating members 43, 44, etc. disposed on the bottom side. In the developing container 40, a two-component developer (developer) 46, which is mainly a mixture of resin toner particles (toner) and magnetic carrier particles (carrier), is accommodated. The developing sleeve 41 is rotatably disposed in the developing container 40 with a part of its outer peripheral surface exposed to the outside.

  A developer regulating blade 42 is opposed to the developing sleeve 41 with a predetermined gap, and a thin developer layer is formed on the developing sleeve 41 as the developing sleeve 41 rotates in the direction indicated by the arrow R2 (counterclockwise). Form. In this embodiment, the developing sleeve 41 is disposed opposite to the photosensitive drum 1 so that the closest distance (S-Dgap) to the photosensitive drum 1 is maintained at 350 μm. A facing portion between the photosensitive drum 1 and the developing sleeve 41 is a developing portion c. The developing sleeve 41 is rotationally driven so that the surface of the developing sleeve 41 moves in the direction opposite to the traveling direction of the surface of the photosensitive drum 1 in the developing portion c.

  The developer thin layer on the developing sleeve 41 comes into contact with the surface of the photosensitive drum 1 at the developing portion c and rubs the photosensitive drum 1 appropriately. A predetermined developing voltage (developing bias) is applied to the developing sleeve 41 from a developing power source (high voltage power source) as a developing voltage applying unit (bias applying unit). In the present embodiment, the developing voltage applied to the developing sleeve 41 is an AC voltage in which a DC voltage (Vdc) and an AC voltage (Vac) are superimposed. More specifically, the vibration voltage is obtained by superimposing Vdc of −400 V and Vac of 1500 Vpp and frequency = 12 kHz.

  The toner in the developer coated as a thin layer on the rotating developing sleeve 41 and conveyed to the developing section c is selectively selected corresponding to the electrostatic latent image formed on the photosensitive drum 1 by the electric field by the developing voltage. Adhere to. Thereby, the electrostatic latent image on the photosensitive drum 1 is developed as a toner image. In this embodiment, the toner adheres to the exposed bright portion on the photosensitive drum 1 and the electrostatic latent image is reversely developed.

  The developer thin layer on the developing sleeve 41 that has passed through the developing portion c is returned to the developer reservoir in the developing container 40 as the developing sleeve 41 continues to rotate. In the developing device 4, stirring screws 43 and 44 are provided as developer stirring members. The agitating screws 43 and 44 rotate in synchronization with the rotation of the developing sleeve 41, and have a function of agitating and mixing the supplied toner with a carrier to give the toner a predetermined charged charge. Further, the agitating screws 43 and 44 respectively convey the developer in the opposite direction in the longitudinal direction, and supply the developer to the developing sleeve 41. At the same time, the agitating screws 43 and 44 have a function of transporting the developer whose toner density (ratio of toner in the developer) has been reduced by the developing process to the toner replenishing section and circulating the developer in the developing container 40. Have.

A sensor 45 that detects a change in the magnetic permeability of the developer and detects the toner concentration in the developer is provided on the upstream side wall surface of the stirring screw 44 of the developing device 4. A toner supply opening 47 is provided slightly downstream. After performing the developing operation, the developer is carried to the detection unit of the sensor 45, where the toner density is detected. Depending on the detection result, the toner replenishing screw 51 provided in the developer replenishing container (toner replenishing unit) 5 connected to the developing device 4 is appropriately rotated from the toner replenishing unit 5 through the toner replenishing opening 47 of the developing device 4. Toner is supplied. Thereby, the toner concentration in the developer is kept constant. The replenished toner is conveyed by the agitating screw 44, mixed with the carrier, given a suitable charge, and then carried to the vicinity of the developing sleeve 41. A thin layer is formed on the developing sleeve 41 for development. The In this example, a negatively chargeable toner having an average particle diameter of 5.5 μm was used as the toner, and a magnetic carrier having a saturation magnetization of 205 emu / cm ³ and an average particle diameter of 35 μm was used as the carrier. In this embodiment, toner and carrier mixed at a weight ratio of 8:92 were used as the developer.

  Toner remaining on the photosensitive drum 1 without being transferred to the intermediate transfer belt 91 in the primary transfer portion d (transfer residual toner) is removed from the photosensitive drum 1 by a cleaning device 7 as a photosensitive member cleaning means. The cleaning device 7 removes the transfer residual toner on the photosensitive drum 1 by a cleaning blade 7 a as a cleaning member provided in contact with the photosensitive drum 1. The photosensitive drum 1 whose surface has been cleaned is subjected to the next image forming process. As a material of the cleaning blade 7a, a urethane rubber material is widely used.

  In this embodiment, the image exposure device 3 and the developing device 4 constitute an image forming unit that forms an image on the photosensitive drum 1 charged by the charging roller 2.

  In this embodiment, the photosensitive drum 1 and the charging roller 2, the developing device 4 and the cleaning device 7 as process means acting on the photosensitive drum 1 are integrally formed into a cartridge and can be attached to and detached from the apparatus main body. The process cartridge 8 is configured. In the present embodiment, each process cartridge 8 has a memory tag (not shown), which can be detected when the process cartridge 8 is replaced with respect to the apparatus main body.

3. Intermediate transfer belt unit An intermediate transfer unit 9 as a transfer device is provided so as to face each photosensitive drum 1 of each image forming portion P. In the intermediate transfer unit 9, an intermediate transfer belt 91, which is an endless belt-like intermediate transfer member as an image carrier that conveys an image transferred from the photosensitive drum 1, includes a drive roller 94, a tension roller 95, and a secondary transfer counter roller. 96 is stretched with a predetermined tension. The intermediate transfer belt 91 is driven by the conveyance body driving means 20 (DC brushless motor) and rotates (circulates) in the direction of the arrow R3 (clockwise) at a process speed (circumferential speed) of 250 mm / sec. It is assumed that the carrier drive means 20 is operating normally by a drive current or the like.

  The toner image formed on the photosensitive drum 1 enters a primary transfer portion (primary transfer nip portion) d that is a facing portion between the photosensitive drum 1 and the intermediate transfer belt 91. In the primary transfer portion d, a primary transfer roller 92 that is a primary transfer member as a primary transfer unit is in contact with the back side of the intermediate transfer belt 91. In order to enable primary transfer voltage (primary transfer bias) to be independently applied to the primary transfer roller 92 by each image forming portion P, primary transfer as primary transfer voltage applying means (bias applying means) is provided. A voltage power supply 93 is connected.

  The intermediate transfer belt unit 9 has a contact / separation mechanism 14 as switching means for switching the contact state or separation state between the photosensitive member and the transfer device. In this embodiment, the contact / separation mechanism 14 applies pressure to the photosensitive drums 1P, 1M, and 1C of the primary transfer rollers 92Y, 92M, and 92C in the first, second, and third image forming units PY, PM, and PC. And release of pressurization is performed by an instruction from the CPU 50. The contact / separation mechanism 14 is configured to be able to push the bearing portions of the primary transfer rollers 92Y, 92M, and 92C toward the photosensitive drums 1Y, 1M, and 1C.

When the intermediate transfer belt 91 is separated from the photosensitive drum 1, the contact / separation mechanism 14 moves the tension roller 95 by a predetermined amount h by the moving unit 15 (FIG. 2: first posture). In this case, by abutting and separating mechanism 14 in conjunction with the tension roller 95 is operated, the first to third image forming portions PY, PM, in PC (second image forming unit), the first to third primary transfer rollers 92Y, 92M, 92C are separated first to third photosensitive drums 1Y, 1M, from 1C (second photosensitive member). Further, at this time, the fourth image forming portion PBk (first image forming unit) in the intermediate transfer belt 91 is not separated structure from the photosensitive drum 1Bk (first photosensitive member). Therefore, even if the contact / separation mechanism 14 is moved by the transfer position maintaining roller 110 provided on the back side of the intermediate transfer belt 91 between the third image forming unit PC and the fourth image forming unit PBk. The position of the primary transfer roller 92Bk No. 4 is hardly changed. Further, when the intermediate transfer belt 91 is brought into contact with the photosensitive drum 1, the tension roller 95 is moved by the moving unit 15 in the opposite direction to the case where it is separated from the above. As a result, the contact / separation mechanism 14 operates in conjunction with the tension roller 95 to direct the first to third primary transfer rollers 92Y, 92M, and 92C toward the first to third photosensitive drums 1Y, 1M, and 1C. And pressurize (FIG. 1: second posture).

  The toner image formed on the intermediate transfer belt 91 is collectively transferred (secondary transfer) to the recording material S by a secondary transfer roller 10 as a secondary transfer unit. The recording material S is supplied from a recording material feeding means (not shown) and is sent to the secondary transfer portion N by a paper feed roller 12 as a conveying means at a predetermined timing.

  The secondary transfer residual toner remaining on the intermediate transfer belt 91 after the secondary transfer is cleaned by a cleaning blade 11a which is a cleaning member provided in the intermediate transfer belt cleaner 11 as an intermediate transfer body cleaning unit. The image forming process.

The material of the intermediate transfer belt 91 is preferably a resin-based or rubber belt containing a metal core, or a belt made of resin and rubber. In addition, the intermediate transfer belt 91 having an elastic layer may be used in consideration of image improvement such as improvement of toner scattering and voids. In this example, a resin belt in which carbon was dispersed in PI (polyimide) and the volume resistivity was controlled to the order of 10 ⁸ Ωcm was used. In this embodiment, the intermediate transfer belt 91 has a thickness of 80 μm, a width (a length in a direction substantially perpendicular to the moving direction) of 320 mm, and an entire circumference of 900 mm.

In this embodiment, the primary transfer roller 92 is made of a conductive sponge. In this embodiment, the primary transfer roller 92 has an electric resistance of 10 ⁶ Ω or less, an outer diameter of 16 mm, and a length in the longitudinal direction (rotation axis direction) of 315 mm.

4). Monochrome image output mode (first image formation mode)
In the image forming apparatus 101 according to the present exemplary embodiment, at the time of activation, the intermediate transfer belt 91 is separated from the first to third photosensitive drums 1Y, 1M, and 1C and is in a stopped state. When a request for forming only a black and white image is made from the external host to the CPU 50, the intermediate transfer belt 91 is not brought into contact with the first to third photosensitive drums 1Y, 1M, and 1C. The first to third photosensitive drums 1Y, 1M, and 1C are not driven. Then, the black toner image formed on the fourth photosensitive drum 1Bk is transferred (primary transfer) to the intermediate transfer belt 91.

  In this embodiment, a voltage of +500 V was applied as the primary transfer voltage in consideration of transfer efficiency for the toner transferred to the exposed portion (exposed portion potential Vl: −150 V).

5. Color image output mode (second image formation mode)
When a request to form only a color image is made from the external host to the CPU 50, the first to third photosensitive drums 1Y, 1M, and 1C and the intermediate transfer belt 91 are placed in a state where they are stationary. Make contact. Then, after the contact is completed, the first to fourth photosensitive drums 1Y, 1M, 1C, 1Bk and the intermediate transfer belt 91 are driven.

  First, a toner image of the first color (yellow) formed on the first photosensitive drum 1Y is transferred to the intermediate transfer belt 91. Thereafter, the toner images of the second color (magenta), the third color (cyan), and the fourth color (black) respectively formed on the second, third, and fourth photosensitive drums 1M, 1C, and 1Bk are sequentially intermediated. Multiple transfer is performed on the transfer belt 91. After the image forming process is completed, the contact / separation mechanism 14 separates the first to third photosensitive drums 1Y, 1M, 1C and the intermediate transfer belt 91 from each other. The same applies to the case where the image forming process is completed in the color image formation in the color black mixed mode described below.

  In this embodiment, in consideration of the transfer efficiency with respect to the toner transferred to the exposed portion (exposed portion potential Vl: −150 V), a voltage of +500 V is applied to all the first to fourth colors as the primary transfer voltage.

6). Mixed Color / Black Mode The request made from the external host to the CPU 50 is to perform both monochrome image formation and color image formation. When shifting from monochrome image output to color image output, the following is performed. To do. That is, in this case, first, driving of the first to third photosensitive drums 1Y, 1M, and 1C is started, and then the intermediate transfer belt 91 is rotated while rotating the first to third photosensitive drums 1Y, 1M, and 1C. Are brought into contact with the first to third photosensitive drums 1Y, 1M, and 1C.

  At this time, the following detection is performed at the timing when the CPU 50 instructs the first to third photosensitive drums 1Y, 1M, and 1C to start driving.

7). Detection of rotation of the photosensitive drum when the photosensitive drum and the intermediate transfer belt are in contact One of the objects of this embodiment is to reliably rotate the photosensitive drum 1 when the primary transfer roller 92 is brought into contact with the intermediate transfer belt 92 from a separated state. Is to effectively prevent the occurrence of sliding scratches on the photosensitive drum.

The DC component IDC of the charging current flowing from the charging roller 2 to the photosensitive drum 1 when a charging voltage is applied from the charging power source V1 to the charging roller 2 is the potential of the surface of the photosensitive drum 1 regardless of the type of the charging roller 2 or the like. The amount of change depends on the film thickness of the photosensitive layer and the rotation speed (FIGS. 5 and 6). When the potential of the surface of the photoreceptor is increased from 0 to Vd (dark part potential) or decreased from Vd to 0, the IDC sets the thickness of the photosensitive layer to d, the relative dielectric constant ε, and the dielectric constant in vacuum. If ε0 is L, the effective charging width of the charging roller 2 is L, and the process speed is vp, it is expressed by the following relational expression (1).
| IDC | = | ε · ε0 · L · vp · Vd / d | (Formula 1)

  Here, since ε, ε0, and L can be regarded as constants, if three of the four items are known, the other can be determined. In addition, even if the thickness of the photosensitive layer is unknown even if the change in potential is unknown, if the IDC becomes a substantially constant value, the rotational speed (process speed) settles at a constant value. Can be determined.

  Therefore, the rotational speed of the photosensitive drum 1 can be detected by monitoring the DC component IDC of the charging current that flows to the area of the photosensitive drum 1 that has been neutralized by an image exposure apparatus, a static elimination exposure apparatus, a static elimination charger, or the like. It becomes possible. As a result, in addition to detecting the rotation / stop of the photosensitive drum 1, if the film thickness of the photosensitive layer can be grasped in advance for the change in potential of the surface of the photosensitive drum 1, the rotational speed is stable. Can also be detected. That is, the rotation state of the photosensitive drum 1 can be detected.

  Here, in this embodiment, the IDC measuring means is provided between the charging power source V 1 and the charging roller 2. However, the current flowing from the charging roller 2 to the photosensitive drum 1 flows from the photosensitive drum 1 toward the ground, and the current flowing from the photosensitive drum 1 toward the ground can be measured.

  Note that, when the absolute value of the DC voltage applied to the charging roller 2 is increased, the DC component of the measured charging current increases and is easy to detect. However, if a voltage higher than the fog removal bias is applied to the charging roller 2 without applying a voltage to the developing sleeve 41, the carrier adheres to the photosensitive drum 1 when the two-component developing method is used. End up. Here, the fog removing bias refers to a difference between a DC voltage applied to the charging roller 2 and a DC voltage applied to the developing sleeve 41 during image formation.

  Carrier adhesion can be avoided by applying a DC voltage to the developing sleeve 41 and controlling so as not to create a potential difference with the potential on the photosensitive drum 1. However, when the photosensitive drum 1 is suddenly stopped when the rotation of the photosensitive drum 1 is unstable, carrier adhesion occurs, which is not preferable.

  Therefore, when detecting the rotation of the photosensitive drum 1, it is desirable to apply a DC voltage that does not cause carrier adhesion to the charging roller 2 and not to apply a voltage to the developing sleeve 41.

  As a result of the measurement, when the current value falls within a range in which an error is added to the predicted current value calculated from the equation (1), it is determined that the rotation of the photosensitive drum 1 has become stable. If the current value does not fit, the following can be considered.

(1) When the measured current value exceeds the predicted value (i) The rotation speed is fast (ii) The film thickness of the photosensitive layer is thinner than expected (changed to another photosensitive drum)
(Iii) Abnormality of high voltage circuit (iv) Leak generation (2) When measured current value is lower than expected value (i) Slow rotation speed (ii) Film thickness of photosensitive layer is thicker than expected (another photosensitivity) Was replaced with a drum)
(Iii) Abnormality of the high voltage circuit (3) When the current value hardly flows (special case of (2) above)
(Ii) Not rotating (ii) Abnormal high voltage circuit (iii) The photosensitive member is not neutralized (iv) The charging roller is missing (v) There is no photosensitive drum

  Here, the abnormality of the high voltage circuit and the occurrence of leakage can be separately detected as errors on the high voltage substrate side. When the charging roller 2 is removed, the absence of the photosensitive drum 1 can be detected by detecting the presence or absence of the process cartridge 8. When the photosensitive drum 1 is not neutralized, the image forming exposure apparatus is not operating normally. In these cases, an appropriate error message is displayed, and the driving of the photosensitive drum 1 and the intermediate transfer belt 91 (or the conveyance belt: see Example 2) is stopped to deal with it.

  Further, when the thickness of the photosensitive layer is suddenly changed after the photosensitive drum 1 is replaced with another photosensitive drum 1, it is difficult to distinguish from the fact that the rotational speed of the photosensitive drum 1 is changed. Using a means for detecting the change of the process cartridge 8 by a memory tag or the like, it is detected that the photosensitive drum 1 has been replaced, or the film thickness of the photosensitive layer is calculated from the current that is flowing, and the value is used. It can be considered to control thereafter. In these cases, the driving of the photosensitive drum 1 does not necessarily have to be stopped, but may be configured to stop.

  Hereinafter, detection of driving of the photosensitive drum 1 in this embodiment will be described with reference to the flowchart of FIG.

  In the case of transition from monochrome image output to color image output, the fourth photosensitive drum 1Bk and the intermediate transfer belt 91 are driven, and the first to third photosensitive drums 1Y, 1M, and 1C are stopped (S101). .

  The first to third photosensitive drums 1Y, 1M, and 1C are turned on (S102). At this time, the rotation of the driving means of the first to third photosensitive drums 1Y, 1M, 1C and the intermediate transfer belt 91 is detected by a driving current or the like (S103). If not rotating normally, the CPU 50 outputs a signal for displaying an error in the driving system to the external host side to stop driving (S104).

  The CPU 50 applies a voltage (rotation detection voltage) for detecting the rotation of the photosensitive drum 1 from the charging power source V1 to the charging roller 2 and starts the charging process of the photosensitive drum 1 (S105). The AC voltage component (AC bias) of the rotation detection voltage is set to a voltage (peak-to-peak voltage) at which charging failure does not occur, for example, 1400 Vpp, based on a detection value of an environmental sensor (not shown) included in the image forming apparatus 101. To do. The DC voltage component (DC bias) of the rotation detection voltage is set to the same value as the fog removal bias set based on the detection value of the environmental sensor, for example, -200V.

  Then, the CPU 50 measures the direct current component of the charging current value flowing from the charging roller 2 to the photosensitive drum 1 detected by the ammeter V2 (S106). In this embodiment, the sampling period is 4 ms.

As a result of the measurement, when the DC component of the charging current (hereinafter referred to as “measured current value”) falls within the range obtained by adding an error to the current value calculated from the following equation (2), the CPU 50 detects the photosensitive drum. It is determined that 1 is rotating stably (S107).
| IDC | = | ε · ε0 · L · vp · Vd / d | ≈10 μA (Expression 2)
(However, ε = 2.5
ε0 = 8.854 × 10 ⁻¹² F / m
L = 320mm
vp = 250mm / s
Vd = -200V
d = 31 μm (new photosensitive drum), 15 μm (guaranteed film thickness lower limit))

In this embodiment, the CPU 50 determines that the rotation of the photosensitive drum 1 is stabilized in the following case in a new photosensitive drum (film thickness: 31 μm). That is, the total surface exposed neutralization region comes into a charging position a by the image exposure device 3, the rotation start 300ms later, it is 8 times when the measured current value continuously subsided 10 .mu.A ± 1 .mu.A. In this case, the CPU 50 starts the contact operation between the first to third photosensitive drums 1Y, 1M, 1C and the intermediate transfer belt 91 (S107). Then, after the abutting operation is completed, the CPU 50 changes the DC component of the charging voltage applied from the charging power source V1 to the charging roller 2 to a value (−600 V) at the time of image formation, and starts image formation.

  On the other hand, the CPU 50 performs the following operation when the measured current value exceeds twice (50 μA) the amount of current flowing through the photosensitive drum (film thickness 15 μm) that is the lower limit of the guaranteed photosensitive film thickness of the photosensitive layer twice. . That is, in this case, the CPU 50 outputs a signal for displaying an error relating to the high voltage circuit to the external host side, and drives the first to fourth photosensitive drums 1Y, 1M, 1C, 1Bk and the intermediate transfer belt 91. Stop (S108, S110).

  In addition, the CPU 50 has a measured current value between twice the amount of current flowing through the photosensitive drum at the guaranteed minimum film thickness of the photosensitive layer and the amount of current flowing through the new photosensitive drum (9 to 50 μA), and the film of the photosensitive layer. When the value predicted from the thickness is exceeded, the following operation is performed. That is, in this case, the CPU 50 outputs a signal for displaying a drive system error to the external host side, and stops driving the first to fourth photosensitive drums 1Y, 1M, 1C, 1Bk and the intermediate transfer belt 91. (S109, S111).

  The CPU 50 also has unstable rotation of the photosensitive drum 1 when the measured current value is between the lower limit of the error range due to variations in the ammeter V2 and the amount of current flowing through the new photosensitive drum (1 to 9 μA). The following operation is performed. That is, in this case, the CPU 50 outputs a signal for displaying a drive system error to the external host side, and stops driving the first to fourth photosensitive drums 1Y, 1M, 1C, 1Bk and the intermediate transfer belt 91. (S109, S111).

  Further, when the measured current value is less than the upper limit (1 μA) of the error range due to the variation of the ammeter V2, the CPU 50 determines that the photosensitive drum 1 is not rotating or the charge removal is not functioning. Perform the action. That is, the CPU 50 outputs a signal for displaying an error of the drive system or the image exposure apparatus 3 to the external host side, and drives the first to fourth photosensitive drums 1Y, 1M, 1C, 1Bk and the intermediate transfer belt 91. Is stopped (S112).

  As described above, the image forming apparatus 101 according to the present exemplary embodiment is charged by the photosensitive member 1, the charging member 2 that charges the photosensitive member 1, the voltage applying unit V1 that applies a voltage to the charging member 2, and the charging member 2. Image forming means 3 and 4 for forming an image on the photoreceptor 1. The image forming apparatus 101 according to the present exemplary embodiment includes a current detection unit V2 that detects a current that flows when a predetermined voltage is applied to the charging member 2 when starting an image forming process. In one embodiment, the image forming apparatus 101 according to the present exemplary embodiment includes a control unit that controls whether to continue driving input to the photosensitive member 1 based on the output of the current detection unit V2. In this embodiment, the CPU 50 has the function of this control means. As a result, when the current detected by the current detection means V2 is within the predetermined current range, the control means 50 can continue the drive input to the photoreceptor 1 and start the image forming process. On the other hand, when the current detected by the current detection means V2 is outside the predetermined current range, the control means 50 can interrupt the drive input to the photoreceptor 1 and stop the image forming process.

  The image forming apparatus 101 according to the present exemplary embodiment includes an image carrier (intermediate transfer member) 91 that conveys an image transferred from the photosensitive member 1, and a state in which driving is input to the photosensitive member 1 and the image carrier 91. And a contact means (contact / separation mechanism) 14 for contacting the photoconductor 1 and the image transport body 91. In one embodiment, the image forming apparatus 101 according to the present exemplary embodiment includes a control unit that controls whether or not the contact operation by the contact unit 14 can be performed based on the output of the current detection unit V2. . In this embodiment, the CPU 50 has the function of this control means. Thereby, when the current detected by the current detection means V2 is within the predetermined current range, the control means 50 can start the image forming process by executing the contact operation by the contact means 14. On the other hand, when the current detected by the current detection means V2 is outside the predetermined current range, the control means 50 can stop the image forming process without causing the contact means 14 to perform the contact operation. After the image forming process is completed, the contact means 14 can separate the photoconductor 1 and the image carrier 91 from each other.

  By performing the above control, the intermediate transfer belt 91 can be brought into contact with the first to third photosensitive drums 1Y, 1M, and 1C in a stable state. Can be effectively prevented.

  As described above, according to this embodiment, even when the intermediate transfer belt 91 is brought into contact with the photosensitive drum 1 from a state separated from the photosensitive drum 1, it can be detected that the photosensitive drum 1 is rotated with a simple configuration. Further, it is possible to effectively prevent the occurrence of sliding scratches on the photosensitive drum 1. That is, according to the present embodiment, it is possible to control whether or not the drive input to the photosensitive drum 1 can be continued according to the rotation state of the photosensitive drum 1 with a simple configuration. Further, according to the present embodiment, it is possible to control whether or not the contact operation between the photosensitive drum 1 and the intermediate transfer belt 91 can be performed according to the rotation state of the photosensitive drum 1 with a simple configuration.

Example 2
Next, another embodiment of the present invention will be described. In this embodiment, elements having the same or equivalent functions and configurations as those of the above-described embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

1. Overall Configuration and Operation of Image Forming Apparatus FIGS. 8 and 9 show a schematic configuration of an embodiment of an image forming apparatus according to the present invention. The image forming apparatus 102 according to the present exemplary embodiment is a color laser printer that uses a transfer type electrophotographic process, a contact charging method, and a reversal development method and has a maximum sheet passing size of A3. The image forming apparatus 102 is a recording material, for example, a sheet, an OHP sheet, or the like according to image information from an external host device such as a personal computer or an image reading apparatus that is communicably connected to the image forming apparatus main body (apparatus main body). A color image can be formed and output. Information indicating whether or not the image forming apparatus 102 is ready to output is transmitted to the external host device, and displayed as a message on the display unit of the external host device so that the user can recognize it.

  The image forming apparatus 102 according to the present exemplary embodiment is a so-called four-tandem drum type image forming apparatus. In other words, the image forming apparatus 102 has a plurality of process cartridges 8, and each process cartridge 8 continuously multiplex-transfers toner images onto a recording material S conveyed by a movable recording material carrier 91 ′. To form a color image. In this embodiment, four process cartridges 8 are arranged in order of yellow, magenta, cyan, and black in series in the moving direction of the recording material carrier 91 '. This will be described in more detail below.

  The image forming apparatus 102 according to the present exemplary embodiment includes a first image forming unit configured to form yellow (Y), magenta (M), cyan (C), and black (Bk) images as a plurality of image forming units. Second, third, and fourth image forming units PY, PM, PC, and PBk are included. The four image forming units PY, PM, PC, and PBk have the same configuration except for the color of the developer to be used. The subscripts Y, M, C, and Bk that indicate the presence are omitted, and will be described collectively.

  For example, the overall operation when a four-color image is formed will be described. According to a signal from an external host device communicably connected to the image forming apparatus 102, a color-separated image signal is generated. In response to this signal, toner images of the respective colors are formed in the process cartridges 8Y, 8M, 8C, and 8BK of the image forming units PY, PM, PC, and PBk.

  In each of the process cartridges 8Y, 8M, 8C, and 8Bk, the rotatable photosensitive drum 1 as an image carrier is charged by a charging roller 2 that is a charging member as a charging unit. The uniformly charged surface is scanned and exposed by an image exposure device (laser beam scanner) 3 as an image exposure unit, thereby forming an electrostatic latent image (electrostatic image) on the photosensitive drum 1. A toner image is formed on the photosensitive drum 1 by supplying toner as a developer to the electrostatic latent image by the developing device 4 as a developing unit. The toner images of the respective colors formed on the respective photosensitive drums 1 are sequentially superimposed and transferred onto the recording material S on the conveyance belt 91 ′, which is an endless belt-like recording material carrier, at each transfer portion d. A transfer roller 92 ′, which is a transfer member serving as a transfer unit, is provided on the inner peripheral surface side of the transport belt 91 ′ so as to face each photosensitive drum 1. The toner image is transferred from 1 to the recording material S on the conveying belt 91 ′. Then, the recording material S to which the toner image is transferred is conveyed to a fixing device 13 as fixing means, where the toner image is fixed and then discharged outside the apparatus. In this embodiment, the fixing device 13 applies heat and pressure to the recording material S by a pair of fixing rollers to melt and fix the toner image on the recording material S.

2. Configuration and operation of each element of the image forming unit The CPU 50 instructs the driving unit 20 ′ of the conveyance belt 91 ′ as a conveyance unit driving unit to drive and stop instead of the driving unit 20 of the intermediate transfer belt 91. Except for this, the configuration is substantially the same as in the first embodiment.

3. Transport Unit A transport unit 9 ′ serving as a transfer device is provided so as to face each photosensitive drum 1 of each image forming unit P. In the transport unit 9 ′, a transport belt 91 ′, which is an endless belt-shaped recording material carrier, is wound around the drive roller 94 and the tension roller 95 with a predetermined tension. The conveyor belt 91 'is driven by the conveyor driving means 20' (DC brushless motor) and rotates (circulates) in the direction of the arrow R4 at a process speed (circumferential speed) of 250 mm / sec. It is assumed that the carrier drive means 20 ′ is operating normally by a drive current or the like.

  In the image forming apparatus 102 of this embodiment, the toner image is directly transferred from each photosensitive drum 1 to the recording material S. In the transfer part d, a transfer roller 92 ', which is a transfer member as a transfer means, is in contact with the back side of the conveyance belt 91'. To the transfer roller 92 ′, a transfer voltage power source 93 serving as a transfer voltage applying unit (bias applying unit) is connected to each image forming unit P so that a transfer voltage (transfer bias) can be applied independently.

  The conveyance belt unit 9 ′ includes a contact / separation mechanism 14 ′ as a switching unit that switches a contact state or a separation state between the photosensitive member and the transfer device. In the present embodiment, the contact / separation mechanism 14 'adds the first to third primary transfer rollers 92'Y, 92'M, 92'C to the first to third photosensitive drums 1Y, 1M, 1C. Pressure and release of pressurization are performed according to instructions from the CPU 50. The contact / separation mechanism 14 'is configured to be able to push the bearing portions of the transfer rollers 92'Y, 92'M, 92'C toward the photosensitive drums 1Y, 1M, 1C.

  When the conveying belt 91 ′ is separated from the photosensitive drum 1, the contact / separation mechanism 14 ′ moves the tension roller 95 by a predetermined amount h by the moving unit 15 (FIG. 9). At this time, the contact / separation mechanism 14 ′ operates in conjunction with the tension roller 95, so that the first to third transfer rollers 92 ′ Y, 92 ′ M, and 92 ′ C are the first to third photosensitive rollers. Separated from the drums 1Y, 1M, 1C. In this embodiment, in the fourth image forming portion PBk, the transfer roller 92 'is not separated from the photosensitive drum 1Bk. Therefore, even if the contact / separation mechanism 14 ′ is moved between the third image forming unit PC and the fourth image forming unit PBk by the transfer position maintaining roller 110 provided on the back side of the transport belt 91 ′. The position of the fourth transfer roller 92′Bk is hardly changed. Further, when the conveying belt 91 ′ is brought into contact with the photosensitive drum 1, the tension roller 95 is moved by the moving unit 15 in the opposite direction to the case where it is separated from the above. As a result, the contact / separation mechanism 14 ′ operates in conjunction with the tension roller 95, and the first to third transfer rollers 92′Y, 92′M, and 92′C are moved to the first to third photosensitive drums 1Y, 1Y, Pressure is applied toward 1M and 1C (FIG. 7).

4). Black-and-white image output mode In the image forming apparatus 102 of the present embodiment, at the time of activation, the conveyance belt 91 ′ is separated from the first to third photosensitive drums 1 Y, 1 M, and 1 C and is in a stopped state. . When a request for forming only a monochrome image is made from the external host to the CPU 50, the conveying belt 91 'is not brought into contact with the first to third photosensitive drums 1Y, 1M, 1C, The first to third photosensitive drums 1Y, 1M, and 1C are not driven. Then, the black toner image formed on the fourth photosensitive drum 1Bk is transferred to the recording material S conveyed by the conveyance belt 91 ′.

  In this embodiment, in consideration of the transfer efficiency with respect to the toner transferred to the exposed portion (exposed portion potential Vl: −150 V), a voltage of +3000 V was applied as the transfer voltage.

5. Color Image Output Mode When a request for forming only a color image is made from the external host to the CPU 50, the first to third photosensitive drums 1Y, 1M, and 1C and the conveyor belt 91 ′ are stationary. The contact is made in the state. Then, after the contact is completed, the first to fourth photosensitive drums 1Y, 1M, 1C, 1Bk and the conveyance belt 91 ′ are driven.

  First, a toner image of the first color (yellow) formed on the first photosensitive drum 1Y is transferred to the recording material S on the conveyance belt 91 '. Thereafter, the second color (magenta), third color (cyan), and fourth color (black) toner images respectively formed on the second, third, and fourth photosensitive drums 1M, 1C, and 1Bk are sequentially conveyed. Multiple transfer is performed on the recording material S on the belt 91 '. After the image forming process is completed, the contact / separation mechanism 14 'separates the first to third photosensitive drums 1Y, 1M, 1C and the transport belt 91'. The same applies to the case where the image forming process is completed in the color image formation in the color black mixed mode described below.

  In this embodiment, considering the transfer efficiency for the toner transferred to the exposure portion (exposure portion potential Vl: −150V), the transfer voltage is a voltage of the first color + 3000V, the second color + 3500V, the third color 4000V, the fourth color + 4500V. Applied.

6). Mixed Color / Black Mode The request made from the external host to the CPU 50 is to perform both monochrome image formation and color image formation. When shifting from monochrome image output to color image output, the following is performed. To do. In other words, in this case, first, the driving of the first to third photosensitive drums 1Y, 1M, and 1C is started, and then the first to third photosensitive drums 1Y, 1M, and 1C are rotated while the conveyance belt 91 ′ is rotated. Are brought into contact with the first to third photosensitive drums 1Y, 1M, and 1C.

  At this time, the following detection is performed at the timing when the CPU 50 instructs the first to third photosensitive drums 1Y, 1M, and 1C to start driving.

7). Detection of rotation of the photosensitive drum at the time of contact between the photosensitive drum and the conveyor belt Hereinafter, detection of driving of the photosensitive drum 1 in this embodiment will be described with reference to a flowchart shown in FIG.

  In the case of transition from monochrome image output to color image output, the fourth photosensitive drum 1Bk and the conveyance belt 91 ′ are driven, and the first to third photosensitive drums 1Y, 1M, and 1C are stopped (S201). .

  The first to third photosensitive drums 1Y, 1M, and 1C are turned on (S202). At this time, the rotation of the driving means for the first to third photosensitive drums 1Y, 1M, 1C and the conveyance belt 91 'is detected by a driving current or the like (S203). If not rotating normally, the CPU 50 outputs a signal for displaying an error in the driving system to the external host side to stop driving (S204).

  The CPU 50 applies a voltage (rotation detection voltage) for detecting the rotation of the photosensitive drum 1 from the charging power source V1 to the charging roller 2 and starts the charging process of the photosensitive drum 1 (S205). The AC voltage component (AC bias) of the rotation detection voltage is set to a voltage (peak-to-peak voltage) at which charging failure does not occur, for example, 1400 Vpp, based on a detection value of an environmental sensor (not shown) included in the image forming apparatus 102. To do. The DC voltage component (DC bias) of the rotation detection voltage is set to the same value as the fog removal bias set based on the detection value of the environmental sensor, for example, -200V.

  Then, the CPU 50 measures the direct current component of the charging current value flowing from the charging roller 2 to the photosensitive drum 1 detected by the ammeter V2 (S206). In this embodiment, the sampling period is 4 ms.

As a result of the measurement, when the measured current value falls within a range in which an error is added to the current value calculated from the equation (2) shown in the first embodiment, the photosensitive drum 1 rotates stably. (S207). In this embodiment, the CPU 50 determines that the rotation of the photosensitive drum 1 is stabilized in the following case in a new photosensitive drum (film thickness: 31 μm). That is, the total surface exposed neutralization region comes into a charging position a by the image exposure device 3, the rotation start 300ms later, it is 8 times when the measured current value continuously subsided 10 .mu.A ± 1 .mu.A. In this case, the CPU 50 starts the contact operation between the first to third photosensitive drums 1Y, 1M, 1C and the transport belt 91 ′ (S207). Then, after the abutting operation is completed, the CPU 50 changes the DC component of the charging voltage applied from the charging power source V1 to the charging roller 2 to a value (−600 V) at the time of image formation, and starts image formation.

  On the other hand, the CPU 50 performs the following operation when the measured current value exceeds twice (50 μA) the amount of current flowing through the photosensitive drum (film thickness 15 μm) that is the lower limit of the guaranteed photosensitive film thickness of the photosensitive layer twice. . That is, in this case, the CPU 50 outputs a signal for displaying an error related to the high voltage circuit to the external host side, and drives the first to fourth photosensitive drums 1Y, 1M, 1C, 1Bk and the conveyance belt 91 ′. Stop (S208, S210).

  In addition, the CPU 50 has a measured current value between twice the amount of current flowing through the photosensitive drum at the guaranteed minimum film thickness of the photosensitive layer and the amount of current flowing through the new photosensitive drum (9 to 50 μA), and the film of the photosensitive layer. When the value predicted from the thickness is exceeded, the following operation is performed. That is, in this case, the CPU 50 outputs a signal for displaying a drive system error to the external host side, and stops driving the first to fourth photosensitive drums 1Y, 1M, 1C, 1Bk and the conveying belt 91 ′. (S209, S211).

  The CPU 50 also has unstable rotation of the photosensitive drum 1 when the measured current value is between the lower limit of the error range due to variations in the ammeter V2 and the amount of current flowing through the new photosensitive drum (1 to 9 μA). The following operation is performed. That is, in this case, the CPU 50 outputs a signal for displaying a drive system error to the external host side, and stops driving the first to fourth photosensitive drums 1Y, 1M, 1C, 1Bk and the conveying belt 91 ′. (S209, S211).

  Further, when the measured current value is less than the upper limit (1 μA) of the error range due to the variation of the ammeter V2, the CPU 50 determines that the photosensitive drum 1 is not rotating or the charge removal is not functioning. Perform the action. That is, the CPU 50 outputs a signal for displaying an error of the drive system or the image exposure apparatus 3 to the external host side, and drives the first to fourth photosensitive drums 1Y, 1M, 1C, 1Bk and the conveyance belt 91 ′. Is stopped (S212).

  By performing the above control, the conveyance belt 91 'can be brought into contact with the first to third photosensitive drums 1Y, 1M, and 1C in a stable state. Can be effectively prevented.

  As described above, according to the present embodiment, it is possible to detect that the photosensitive drum 1 is rotating with a simple configuration even when the conveyance belt 91 ′ is brought into contact with the photosensitive belt 1 from a state separated from the photosensitive drum 1. Further, it is possible to effectively prevent the occurrence of sliding scratches on the photosensitive drum 1. That is, according to the present embodiment, it is possible to control whether or not the drive input to the photosensitive drum 1 can be continued according to the rotation state of the photosensitive drum 1 with a simple configuration. Further, according to this embodiment, it is possible to control whether or not the contact operation between the photosensitive drum 1 and the conveyance belt 91 ′ can be performed according to the rotation state of the photosensitive drum 1 with a simple configuration.

Others While the present invention has been described with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

  In the above-described embodiment, the fourth photosensitive drum 1Bk is not separated from the intermediate transfer belt 91 or the conveyance belt 91 ′. However, the present invention is effectively applied to a configuration in which the fourth photosensitive drum 1Bk is separated. be able to. The present invention can also be effectively applied to a configuration in which the photosensitive drums 1Y, 1M, 1C, and 1Bk are independently separated. In the above-described embodiment, the present invention is applied to the four-tandem drum type image forming apparatus, but any number of image carriers may be used. Further, although the voltage applied to the charging roller 2 is the one in which the direct current component and the alternating current component are superimposed, only the direct current component may be applied. Further, the contact charging member is not limited to the roller in the above-described embodiment, and may be, for example, a brush-like member.

1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention (when an intermediate transfer belt is in contact). 1 is a schematic cross-sectional view of an embodiment (when an intermediate transfer belt is separated) of an image forming apparatus according to the present invention. 2 is a schematic cross-sectional view showing in more detail a configuration around a photosensitive drum in an embodiment of the image forming apparatus according to the present invention. FIG. 1 is a schematic cross-sectional view of a photosensitive drum and a charging roller in an embodiment of an image forming apparatus according to the present invention. It is a graph which shows the relationship between the direct-current component of a photosensitive layer film thickness and charging current. It is a graph which shows the relationship between the process speed and the direct current component of charging current. FIG. 6 is a flowchart illustrating an example of control for detecting rotation of the photosensitive drum when the photosensitive drum and the intermediate transfer belt are in contact with each other according to the present invention. It is a schematic block diagram of the other Example (at the time of conveyance belt contact) of the image forming apparatus which concerns on this invention. It is a schematic block diagram of the other Example (at the time of conveyance belt separation) of the image forming apparatus which concerns on this invention. It is a flowchart figure which shows an example of control of the rotation detection of the photosensitive drum at the time of contact | abutting with the photosensitive drum and conveyance belt according to this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Image exposure apparatus 4 Developing apparatus 8 Process cartridge 9 Intermediate transfer unit 9 'Conveyance unit 14 Primary transfer roller contact / separation mechanism 14' Transfer roller contact / separation mechanism 19 Photosensitive drum driving means 20 Intermediate Transfer belt driving means 20 'Conveying belt driving means 50 CPU
91 Intermediate transfer belt 91 'Conveying belt 92 Primary transfer roller 92' Transfer roller V1 Charging power supply V2 Ammeter

Claims (2)

Comprising a rotatable first photosensitive member, a first image forming unit for forming an image on the first photosensitive member,
A second photosensitive member rotatable, said second and a charging member for charging the photosensitive member, the second image forming unit for forming an image on a second photosensitive member,
Drive means for rotationally driving the second photoconductor;
Applying means for applying a voltage to the charging member;
Detecting means for detecting a current flowing through the charging member;
An intermediate transfer belt for conveying the position for transferring the image formed on the second photosensitive member on the image formed on the first photosensitive member onto a recording material,
Wherein a first position in which the intermediate transfer belt is separated from the abutment to and said second photoreceptor to said first photoconductor, the intermediate transfer belt said first photoconductor and said second photoconductor A contact / separation mechanism capable of switching the position of the intermediate transfer belt to the second position to be contacted ;
A first image forming mode for forming an image in the first image forming unit in a state in which the intermediate transfer belt is in the first posture and the rotation of the second photoconductor is stopped; and Control means for switching and executing the first image forming unit and the second image forming mode in which image formation is performed in the second image forming unit in the state of the second posture;
The control means keeps driving of the intermediate transfer belt and the first photosensitive member when shifting from image formation in the first image formation mode to image formation in the second image formation mode. When the current detected by the detecting means when the driving means is driven and a predetermined voltage is applied to the charging member is within a predetermined range, the intermediate transfer belt is changed from the first posture to the second posture. An image forming apparatus , wherein switching is executed, and control is performed to stop image formation when the current detected by the detection unit is outside a predetermined range .   When the current detected by the detection unit is out of a predetermined range, the control unit does not switch the intermediate transfer belt from the first posture to the second posture, and the first photoconductor. The image forming apparatus according to claim 1, wherein driving of the second photosensitive member and the intermediate transfer belt is stopped.

Images