JP2023180795A - Image forming device - Google Patents

Abstract

To provide an image formation device which can detect an abnormality of a static eliminator, with a simple configuration, the static eliminator radiating erase light before transfer in an intermediate transfer system using a two-component developer.SOLUTION: An image formation device includes: a plurality of image formation units having an image carrier body, a charge device, an exposure device, and a developer; an intermediate transfer belt; a primary transfer member; a secondary transfer member; a static eliminator; an image concentration sensor; and a control unit. The image concentration sensor detects concentration of a toner image primarily transferred on an intermediate transfer belt. The control unit controls a development DC voltage applied on the development carrier and output of erase light before transfer of the static eliminator. The control unit forms a reference image with the output of the erase light before transfer changed in plural stages and determines an abnormality of the static eliminator on the basis of at least one of concentration of a reference image detected by the image concentration sensor and a situation of generation of an image defect in the reference image.SELECTED DRAWING: Figure 7

Description

The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, a multifunction machine thereof, etc. equipped with an image carrier, and particularly relates to an intermediate transfer type image forming apparatus using a two-component developer containing a toner and a carrier. .

In an image forming apparatus, an electrostatic latent image formed on an image bearing member such as a photoreceptor is developed by a developing device and visualized as a toner image. As one of such developing devices, a two-component developing method using a two-component developer containing a magnetic carrier and a toner is adopted. In the two-component reversal development system, the photoreceptor and toner are charged with the same polarity, and the carrier is charged with the opposite polarity. The potential of the photoreceptor corresponding to the white background portion of the image is set in a direction that electrostatically attracts carriers. However, since the magnetic force of the developing roller is usually greater, the carrier circulates within the developing device without leaving the developing roller.

Incidentally, the surface potential of a photoreceptor varies due to environmental changes and the like. When the surface potential of the photoreceptor increases, carriers move to the surface of the photoreceptor, so-called white area carrier development, which occurs more easily. Furthermore, when the toner charge amount increases due to changes in the environment, the development potential difference is increased to ensure image density. If this development potential difference becomes too large, charges will be injected into the carrier, and the carrier will be charged to the same polarity as the toner. Then, when the toner is developed on the electrostatic latent image formed on the photoreceptor, the carrier is also developed together with the toner, which is what is called image area carrier development.

On the other hand, intermediate transfer type image forming apparatuses are widely used in which a toner image that is primarily transferred from a photoreceptor onto an intermediate transfer belt is secondarily transferred to a recording medium such as paper. In such an intermediate transfer type image forming apparatus, when carrier development occurs in a white background area, the carrier developed on the photoreceptor is transferred to the intermediate transfer belt. When an image formed on a photoreceptor in an image forming unit downstream of the intermediate transfer belt is transferred to the intermediate transfer belt at the primary transfer nip, if carriers attached to the intermediate transfer belt in the upstream image forming unit intervene, This carrier forms a gap between the photoreceptor and the intermediate transfer belt. As a result, the toner around the carrier cannot move onto the intermediate transfer belt, causing a phenomenon called "white spots" in which part of the image appears white. Further, when image area carrier development occurs, the carrier developed on the photoreceptor forms a gap between the photoreceptor and the intermediate transfer belt during primary transfer. As a result, the toner around the carrier cannot move onto the intermediate transfer belt, which also causes "white spots."

In particular, when using an amorphous silicon photoreceptor having an amorphous silicon layer with a high dielectric constant as a photosensitive layer and applying a developing voltage in which an alternating current voltage is superimposed on a direct current voltage, the developing current tends to flow, so that carrier development occurs in the white background area. and image area carrier development are likely to occur. Furthermore, when a hard resin belt is used as the intermediate transfer belt, white streaks are more likely to occur.

Therefore, various methods have been proposed for suppressing carrier development. For example, in Patent Document 1, a magnetic brush on a developing roller is removed toward the most downstream position in the rotational direction of the developing roller at the portion in contact with the photoreceptor drum. An image forming apparatus is disclosed that includes a static eliminator that irradiates electric light. In this image forming apparatus, the downstream part of the development area is irradiated with static eliminating light (pre-transfer erase light) to bring the surface potential of the white background area closer to the development potential, thereby weakening the electric field in the white background area that develops the carrier on the white background area, and Suppresses development.

Japanese Patent Application Publication No. 2018-185451

According to the method disclosed in Patent Document 1, as the output of the pre-transfer erase light is increased, the effect of suppressing white spots becomes higher. However, there is a problem in that if an abnormality occurs in the static eliminator that irradiates the pre-transfer erase light, a sufficient effect of suppressing white spots cannot be obtained.

In view of the above-mentioned problems, an object of the present invention is to provide an image forming apparatus that can detect abnormalities in a static eliminator that irradiates pre-transfer erase light with a simple configuration in an intermediate transfer method using a two-component developer. do.

In order to achieve the above object, a first configuration of the present invention includes a plurality of image forming sections including an image carrier, a charging device, an exposure device, and a developing device, an intermediate transfer belt, and a primary transfer member. The image forming apparatus includes a secondary transfer member, a static eliminator, an image density sensor, and a control section. A photosensitive layer is formed on the surface of the image carrier. The charging device charges the surface of the image carrier to a predetermined surface potential. The exposure device forms an electrostatic latent image in which the charge is attenuated by irradiating light onto the image carrier charged by the charging device. The developing device includes a developer carrier that carries a two-component developer containing a magnetic carrier and toner, and the developer carrier has a static image formed on the surface of the image carrier in a development area facing the image carrier. The electrolatent image is developed into a toner image. The intermediate transfer belt is endless and is disposed adjacent to the image forming section, and the toner image formed on the surface of the image carrier is primarily transferred to the outer peripheral surface. The primary transfer member contacts the inner peripheral surface of the intermediate transfer belt at a position facing the image carrier to form a primary transfer nip between the image carrier and the intermediate transfer belt. The toner image formed on the surface of the intermediate transfer belt is primarily transferred. The secondary transfer member secondary transfers the toner image that has been primarily transferred onto the intermediate transfer belt onto a recording medium. The static eliminator irradiates a region of the image carrier from the development region to the primary transfer nip with pre-transfer erase light. The image density sensor detects the density of the toner image primarily transferred onto the intermediate transfer belt. The control unit controls the development DC voltage applied to the developer carrier and the output of the pre-transfer erase light of the static eliminator. The control unit forms a reference image by changing the output of the pre-transfer erase light in a plurality of stages, and based on at least one of the density of the reference image detected by the image density sensor and the occurrence of image defects in the reference image. Determine whether there is an abnormality in the static eliminator.

According to the first configuration of the present invention, an abnormality in the static eliminator is determined based on at least one of the density of the reference image formed by changing the output of the pre-transfer erase light in multiple stages and the occurrence of image defects in the reference image. Determine. Thereby, the presence or absence of an abnormality in the static eliminator can be detected with high precision using a simple method.

A side sectional view showing the internal configuration of an image forming apparatus 100 according to a first embodiment of the present invention An enlarged view showing the configuration around the image forming section Pd in FIG. 1 A diagram showing the configuration around the photoreceptor drum 1d in the image forming section Pd. A diagram showing a state in which a magnetic brush B is formed in the opposing portion of the photosensitive drum 1d and the developing roller 33. Plan view (FIG. 5(a)) and side view (FIG. 5(b)) of the static eliminator 50 A block diagram showing an example of a control path of the image forming apparatus 100 Graph showing the relationship between pre-transfer erase light output and halftone image density A diagram showing a reference image P1 of a horizontal line pattern. A diagram showing a reference image P2 of a solid pattern. Flowchart showing an example of abnormality detection control of the static eliminator 50 executed in the image forming apparatus 100 of the first embodiment An enlarged view showing the configuration around an image forming section Pa of an image forming apparatus 100 according to a second embodiment of the present invention Flowchart showing an example of abnormality detection control of the static eliminator 50 executed in the image forming apparatus 100 of the second embodiment A diagram showing a modification including a CIS 81 that reads a toner image formed on the intermediate transfer belt 8

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing the internal structure of an image forming apparatus 100 according to a first embodiment of the present invention. Four image forming sections Pa, Pb, Pc, and Pd are arranged in the main body of the image forming apparatus 100 (here, a color multifunction peripheral) in order from the upstream side in the transport direction (left side in FIG. 1). These image forming sections Pa to Pd are provided corresponding to images of four different colors (yellow, cyan, magenta, and black), and are formed into yellow, cyan, and magenta by each charging, exposure, development, and transfer process. and black images are sequentially formed.

These image forming units Pa to Pd are provided with photosensitive drums (image carriers) 1a, 1b, 1c, and 1d that carry visible images (toner images) of each color. Furthermore, in FIG. 1, an intermediate transfer belt (intermediate transfer body) 8 that rotates counterclockwise is provided adjacent to each of the image forming stations Pa to Pd. The toner images formed on these photoreceptor drums 1a to 1d are sequentially primarily transferred and superimposed onto an intermediate transfer belt 8 that moves while contacting each of the photoreceptor drums 1a to 1d. Thereafter, the toner image primarily transferred onto the intermediate transfer belt 8 is secondarily transferred onto a transfer paper P, which is an example of a recording medium, by a secondary transfer roller 9. Furthermore, the transfer paper P on which the toner image has been secondarily transferred is discharged from the main body of the image forming apparatus 100 after the toner image is fixed in the fixing section 13 . An image forming process is performed on each of the photoreceptor drums 1a to 1d while rotating the photoreceptor drums 1a to 1d clockwise in FIG.

The transfer paper P onto which the toner image is secondarily transferred is housed in a paper cassette 16 disposed at the bottom of the main body of the image forming apparatus 100 . Transfer paper P is conveyed to the nip portion between secondary transfer roller 9 and drive roller 11 of intermediate transfer belt 8 via paper feed roller 12a and registration roller pair 12b. A dielectric resin sheet is used for the intermediate transfer belt 8, and a seamless belt is mainly used. Further, a blade-shaped belt cleaner 20 for removing toner and the like remaining on the surface of the intermediate transfer belt 8 is arranged downstream of the secondary transfer roller 9.

When image data is input from a host device such as a personal computer, first, the main motor 40 (see FIG. 6) rotates the photosensitive drums 1a to 1d. Then, the surfaces of the photoreceptor drums 1a to 1d are uniformly charged by the charging devices 2a to 2d. Next, the exposure device 5 irradiates light according to the image data to form electrostatic latent images on each of the photosensitive drums 1a to 1d according to the image data. Each of the developing devices 3a to 3d is filled with a predetermined amount of two-component developer containing yellow, cyan, magenta, and black toner. Note that when the ratio of toner in the two-component developer filled in each developing device 3a to 3d falls below a specified value due to the formation of a toner image, which will be described later, the toner is removed from each developing device 3a to 3d from the toner container 4a to 4d. Toner is replenished. The toner in this developer is supplied onto the photoreceptor drums 1a to 1d by the developing devices 3a to 3d and electrostatically adheres thereto. As a result, a toner image corresponding to the electrostatic latent image formed by exposure from the exposure device 5 is formed.

Then, an electric field is applied by the primary transfer rollers 6a to 6d between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d at a predetermined transfer voltage. As a result, the yellow, cyan, magenta, and black toner images on the photoreceptor drums 1a to 1d are primarily transferred onto the intermediate transfer belt 8. These images are formed with predetermined positional relationships. Thereafter, in preparation for the subsequent formation of a new electrostatic latent image, toner and the like remaining on the surfaces of the photoreceptor drums 1a to 1d after the primary transfer are removed by cleaning devices 7a to 7d.

The intermediate transfer belt 8 is stretched between a driven roller 10 on the upstream side and a drive roller 11 on the downstream side. When the intermediate transfer belt 8 starts rotating counterclockwise with the rotation of the drive roller 11 by the belt drive motor 41 (see FIG. 6), the transfer paper P is transferred from the registration roller pair 12b to the drive roller 11 at a predetermined timing. The toner image on the intermediate transfer belt 8 is transferred to a nip portion (secondary transfer nip portion) with a secondary transfer roller 9 provided adjacent thereto, and the toner image on the intermediate transfer belt 8 is secondarily transferred onto the transfer paper P. The transfer paper P on which the toner image has been secondarily transferred is conveyed to the fixing section 13.

The transfer paper P conveyed to the fixing section 13 is heated and pressurized by a pair of fixing rollers 13a to fix the toner image on the surface of the transfer paper P, forming a predetermined full-color image. The transfer paper P on which a full-color image has been formed is sorted in the conveyance direction by a branching section 14 branching into multiple directions, and is sent as it is (or after being sent to the double-sided conveyance path 18 and images are formed on both sides) to a discharge roller. The paper is discharged onto the discharge tray 17 by the pair 15.

An image reading section 21 is arranged above the discharge tray 17, and a document conveying device 22 is attached to the upper surface of the image reading section 21. The image reading unit 21 includes a scanning optical system equipped with a scanner lamp that illuminates the original during copying, a mirror that changes the optical path of the reflected light from the original, and a condenser lens that collects the reflected light from the original to form an image. , and a CCD sensor (none of which is shown) that converts imaged image light into an electrical signal, and reads an original image and converts it into image data. The document conveyance device 22 automatically conveys a sheet-like document to the reading position of the image reading section 21 .

An image density sensor 25 is arranged at a position downstream of the image forming section 1d and facing the intermediate transfer belt 8. As the image density sensor 25, an optical sensor is generally used that includes a light emitting element such as an LED and a light receiving element such as a photodiode. When measuring the amount of toner adhering on the intermediate transfer belt 8, when measuring light is irradiated from a light emitting element to each reference image formed on the intermediate transfer belt 8, the measuring light includes light reflected by the toner and the belt surface. The light is reflected by the light and enters the light receiving element.

The reflected light from the toner and belt surfaces includes specularly reflected light and diffusely reflected light. The specularly reflected light and the diffusely reflected light are separated by a polarization separation prism, and then enter separate light receiving elements. Each light receiving element photoelectrically converts the received specularly reflected light and diffusely reflected light and outputs an output signal to the control section 90 (see FIG. 6). Then, the amount of toner is detected from the change in the characteristics of the output signals of specularly reflected light and diffusely reflected light, and density correction (calibration) is performed by comparing it with a predetermined reference density and adjusting the characteristic value of the developing voltage. be exposed.

FIG. 2 is an enlarged view showing the structure around the image forming section Pd in FIG. FIG. 3 is a diagram showing the configuration around the photosensitive drum 1d in the image forming section Pd. Note that in the following explanation, the image forming section Pd in FIG. 1 will be exemplified, but since the image forming sections Pa to Pc have basically the same configuration, the explanation will be omitted.

Around and below the rotatably arranged photoreceptor drum 1d, a charging device 2d that charges the photoreceptor drum 1d, an exposure device 5 (see FIG. 1) that exposes image information to the photoreceptor drum 1d, A developing device 3d that forms a toner image on the photosensitive drum 1d and a cleaning device 7d that removes developer (toner) etc. remaining on the photosensitive drum 1d are provided. Further, a primary transfer roller 6d is arranged between the developing device 3d and the cleaning device 7d with the intermediate transfer belt 8 interposed therebetween.

The photosensitive drum 1d includes a conductive base 19a and a photosensitive layer 19b formed on the surface of the conductive base 19a. In this embodiment, an amorphous silicon layer is laminated as a photosensitive layer 19b on the surface of a cylindrical conductive substrate 19a made of aluminum.

The charging device 2d includes a charging roller 27 that contacts the photoreceptor drum 1d to uniformly charge the surface of the drum, and a charging cleaning brush 29 that cleans the charging roller 27. Note that a charged cleaning roller may be used instead of the charged cleaning brush 29. A predetermined DC voltage and AC voltage are applied to the charging roller 27 by a charging voltage power source 52 . Then, the charging device 2d makes the surface potential V0 of the photosensitive drum 1d higher than the developing DC voltage Vdc of the developing roller 33, which will be described later, and the potential difference (white background potential difference) V0 with the developing DC voltage Vdc of the developing roller 33. -Vdc is charged to a predetermined value (for example, 150V or less).

The developing device 3d is made of resin and contains two agitating conveyance screws 30, a developing roller (developer carrier) 33, a regulating blade 35, and a two-component developer containing a magnetic carrier and a non-magnetic toner. It has a developing container 36.

The developing roller 33 includes a cylindrical non-magnetic developing sleeve 33a that rotates counterclockwise in FIG. 3, and a magnet 33b that is non-rotatably fixed inside the developing sleeve 33a and has a plurality of magnetic poles. There is. In this embodiment, the magnetic poles of the magnet 33b include a regulation pole (not shown) consisting of an N pole, a transport pole (not shown) consisting of an S pole, a main pole 34 consisting of an N pole, and a separation pole consisting of an N pole. (not shown), etc.

A developing voltage, which is a developing DC voltage Vdc and a developing AC voltage Vac superimposed on the developing DC voltage Vdc, is applied to the developing roller 33 by a developing voltage power source 53 . Further, a regulating blade 35 is attached to the developing container 36 along the axial direction of the developing roller 33 (direction perpendicular to the paper surface of FIG. 2). A slight gap (regulating gap) is provided between the tip of the regulating blade 35 and the outer peripheral surface of the developing roller 33.

FIG. 4 is a diagram showing a state in which a magnetic brush B is formed at a portion where the photoreceptor drum 1d and the developing roller 33 face each other. The developer is conveyed to the developing roller 33 while being stirred by the stirring conveyance screw 30 . Then, as shown in FIG. 4, a magnetic brush B made of magnetic carrier C and toner T is formed on the developing roller 33. The magnetic brush B on the developing roller 33 passes through the regulating blade 35 by the rotation of the developing roller 33, and is conveyed to a portion (developing region R) where the developing roller 33 and the photoreceptor drum 1d face each other. Since the developing roller 33 is applied with the developing DC voltage Vdc and the developing AC voltage Vac, the toner T is transferred from the developing roller 33 to the photoreceptor drum 1d due to the potential difference with the surface potential of the photoreceptor drum 1d (image area potential VL). The electrostatic latent image (exposed area) on the photoreceptor drum 1d is developed.

The cleaning device 7d includes a cleaning blade (cleaning member) 37 and a recovery screw 39. The cleaning blade 37 is fixed in contact with the photoreceptor drum 1d, and cleans toner and the like remaining on the surface of the photoreceptor drum 1d. The residual toner removed from the surface of the photoreceptor drum 1d by the cleaning blade 37 is discharged to the outside of the cleaning device 5d as the recovery screw 39 rotates.

A predetermined primary transfer voltage having a polarity opposite to that of the toner T is applied to the primary transfer roller 6d by a transfer voltage power source 54 (see FIG. 3).

The intermediate transfer belt 8 is formed of a resin belt that does not have an elastic layer such as TPU (thermoplastic polyurethane). The material of the intermediate transfer belt 8 is thermoplastic resin such as PC (polycarbonate), PVDF (polyvinylidene fluoride), PA (polyamide), acrylic, nylon, etc., and thermosetting resin such as PI (polyimide). , PAI (polyamideimide), and the like. Further, whether it is a thermoplastic resin or a thermosetting resin, it is also possible to use a resin whose surface is coated with an acrylic coating or the like. Further, in order to impart electrical conductivity to the intermediate transfer belt 8, an ion conductive agent or an electronic conductive agent is added to the resin material.

A static eliminator 50 that irradiates erase light (pre-transfer erase light) onto the surface of the photoreceptor drum 1d is arranged above the developing device 3d. As shown in FIG. 5, the static eliminator 50 includes a plurality of LED chips 50b mounted at predetermined intervals on a substrate 50a. One static eliminator 50 is provided for each of the photoreceptor drums 1a to 1d.

As shown in FIG. 2, the static eliminator 50 of the image forming section Pd is attached to, for example, the cleaning device 5c of the adjacent image forming section Pc. Note that the static eliminator 50 of the image forming section Pd may be attached to the upper part of the developing device 3d.

The static eliminator 50 is arranged so as to irradiate pre-transfer erase light toward an area from the development area where the magnetic brush B of the development roller 33 is in contact with the photoreceptor drum 1d to the primary transfer nip. By the pre-transfer erase light of the static eliminator 50, the unexposed area (white background area) on the surface of the photoreceptor drum 1d is neutralized so that the developing DC voltage Vdc of the developing roller 33 is lower than that and the potential is higher than a predetermined potential (for example, 150 V). be done.

Next, a control path of the image forming apparatus 100 of the present invention will be explained. FIG. 6 is a block diagram showing an example of a control path used in the image forming apparatus 100 of the present invention. Note that when using the image forming apparatus 100, various controls are performed on each part of the apparatus, so the control path for the entire image forming apparatus 100 becomes complicated. Therefore, the portions of the control path that are necessary for implementing the present invention will be mainly explained here.

The control unit 90 includes a CPU (Central Processing Unit) 91 as a central processing unit, a ROM (Read Only Memory) 92 that is a read-only storage unit, a RAM (Random Access Memory) 93 that is a readable and writable storage unit, and a temporary A temporary storage unit 94 that stores image data, etc., a counter 95 that cumulatively counts the number of printed sheets, and a counter 95 that sends control signals to each device in the image forming apparatus 100 and receives input signals from the operation unit 70. At least a plurality of (in this case, two) I/Fs (interfaces) 96 are provided. Further, the control unit 90 can be placed at any location inside the main body of the image forming apparatus 100.

The ROM 92 stores data that will not be changed while the image forming apparatus 100 is in use, such as programs for controlling the image forming apparatus 100 and numerical values necessary for control. The RAM 93 stores necessary data generated during control of the image forming apparatus 100, data temporarily required for controlling the image forming apparatus 100, and the like.

Further, the control unit 90 transmits control signals from the CPU 91 to each part and device in the image forming apparatus 100 through the I/F 96. Further, signals and input signals indicating the status of each part and device are transmitted to the CPU 91 through the I/F 96. The parts and devices controlled by the control section 90 include, for example, image forming sections Pa to Pd, exposure device 5, secondary transfer roller 9, main motor 40, belt drive motor 41, voltage control circuit 51, and image input section 60. , the operation unit 70, and the like.

The image input unit 60 is a receiving unit that receives image data transmitted from a personal computer or the like to the image forming apparatus 100. The image signal input from the image input section 60 is converted into a digital signal and then sent to the temporary storage section 94 via the I/F 96.

The voltage control circuit 51 is connected to a charging voltage power source 52, a developing voltage power source 53, and a transfer voltage power source 54, and operates each of these power sources based on an output signal from the control section 90. In response to a control signal from the voltage control circuit 51, the charging voltage power source 52 applies a charging voltage to the charging rollers 27 in the charging devices 2a to 2d. A developing voltage power source 53 applies a developing voltage obtained by superimposing a developing DC voltage Vdc and a developing AC voltage Vac to the developing rollers 33 in the developing devices 3a to 3d. A transfer voltage power supply 54 applies predetermined primary transfer voltages and secondary transfer voltages to the primary transfer rollers 6a to 6d and the secondary transfer roller 9, respectively.

The charging voltage applied to the charging roller 27 from the charging voltage power source 52 is preferably a DC voltage. When the charging voltage is a DC voltage, the amount of discharge from the charging roller 27 to the photoreceptor drums 1a to 1d is smaller than when the charging voltage is a superimposed voltage of DC voltage and AC voltage, and the amount of discharge from the photoreceptor drums 1a to 1d is smaller. The amount of wear on the photosensitive layer 19b can be reduced.

The operation unit 70 is provided with a liquid crystal display unit 71 and an LED 72 that indicates various states.The user operates the stop/clear button on the operation unit 70 to stop image formation, and operates the reset button to resume image formation. Various settings of the forming apparatus 100 are set to default states. The liquid crystal display section 71 shows the status of the image forming apparatus 100, the image forming status, and the number of copies to be printed. Various settings of the image forming apparatus 100 are performed from a printer driver of a personal computer.

Next, the control of the pre-transfer erase light of the static eliminator 50 and the primary transfer current applied to the primary transfer rollers 6a to 6d, which are the characteristic parts of the present invention, will be explained. In the image forming apparatus 100 that uses amorphous silicon photoreceptors as the photoreceptor drums 1a to 1d and uses two-component development type developing devices 3a to 3d, since the resistance of the photosensitive layer 19b is low, current flows to the magnetic brush in the development area. easy. Therefore, charge injection into the carrier and charge injection into the photoreceptor drums 1a to 1d through the magnetic brush are likely to occur. In particular, in a system that uses a developing voltage in which an alternating current voltage is superimposed on a direct current voltage, a magnetic brush (developing) current tends to flow, and the above-mentioned charge injection phenomenon becomes noticeable.

Therefore, in the present invention, by controlling the pre-transfer erase light, white spots that occur on an image due to carrier development are suppressed. Hereinafter, the white mark occurrence patterns and the white mark suppression mechanism for each occurrence pattern will be described in detail.

[1. About the pattern of white markings]
(1-1. White pattern caused by carrier development on white background)
When carrier development occurs in a white area at a certain image forming section (for example, image forming section Pa), no white spot occurs at the image forming section Pa, but the carrier developed on the photoreceptor drum 1a is transferred to the intermediate transfer belt 8. If the carrier moves, the carrier gets caught between the photoreceptor drum 1b and the intermediate transfer belt 8 when a downstream image forming unit (for example, image forming unit Pb) attempts to primarily transfer the toner, and the toner around the carrier moves. inhibit. As a result, white spots (white spots) occur in the toner color (cyan) portion on the downstream side. In this case, the white streaks in the black portion of the most downstream image forming portion Pd are most degraded. Further, white marks caused by carrier development on the white background are likely to occur in halftone patterns, horizontal line patterns, vertical line patterns, checker (lattice) patterns, and the like.

(1-2. White streaks caused by image area carrier development)
For example, in reversal development, if the white background part potential V0 of the photoreceptor drums 1a to 1d is +250V, the image part (after exposure) potential VL=+20V, the development DC voltage Vdc=+180V, and the development AC voltage Vpp=1100V, the image part When developing, charge injection occurs into the carrier and the photoreceptor drums 1a to 1d. In particular, when amorphous silicon photoreceptors with low resistance are used as the photoreceptor drums 1a to 1d and a carrier with low resistance is used, this charge injection is likely to occur. When charge injection occurs, the image area potential changes in a direction approaching the developing DC voltage, and the charge polarity of the carrier also changes to the same polarity as the toner. As a result, the carrier is developed in the image areas of the photoreceptor drums 1a to 1d similarly to the toner (image area carrier development).

Then, the carrier developed in the image area is transferred to the intermediate transfer belt 8 made of resin, and by being interposed between the photoreceptor drums 1a to 1d and the intermediate transfer belt 8, the toner around the carrier is removed from the photoreceptor drums 1a to 1d. 1d to the intermediate transfer belt 8 becomes difficult. As a result, white spots (white spots) occur around the carrier. White streaks due to image area carrier development are likely to occur in solid patterns where the potential difference between the white background area and the image area is the largest.

Note that the contact state between the photoreceptor drums 1a to 1d and the intermediate transfer belt 8 around the carrier attached to the drum is different depending on whether the intermediate transfer belt 8 is a resin belt or an elastic belt. The situation of occurrence is different. More specifically, when the intermediate transfer belt 8 is an elastic belt, the intermediate transfer belt 8 deforms along the carrier, so the toner around the carrier can also move, and white spots are less likely to occur.

(1-3. White spots caused by carrier development on the edge of the image)
When carrier is developed on the edge portions (white background portions) of a halftone pattern, horizontal line pattern, vertical line pattern, checker pattern, etc., movement of surrounding toner is inhibited during primary transfer to the intermediate transfer belt 8. As a result, white spots (white spots) occur around the carrier. In this case, the charged polarity of the carrier is opposite to that of the toner (negative polarity).

[2. Regarding the suppression mechanism of white markings]
As a method for improving the above-mentioned white spots, before the primary transfer from the photoreceptor drums 1a to 1d to the intermediate transfer belt 8, the surfaces of the photoreceptor drums 1a to 1d are irradiated with pre-transfer erase light by the static eliminator 50. We found that this was effective. The mechanism for suppressing white markings will be explained below.

(2-1. Suppression of white spots caused by carrier development on white background area by pre-transfer erase light)
As described above, for example, when white background carrier development occurs at the image forming section Pa, white streaks occur at the image forming sections Pb to Pd on the downstream side of the image forming section Pa. Therefore, by improving the primary transferability of toner images in the downstream image forming portions Pb to Pd, it is possible to suppress the occurrence of white spots caused by carrier development in the white background area.

White spots caused by carrier development are particularly noticeable in images where the electrostatic latent image has many boundaries (edges) between areas where the surface potential is V0 (white area) and areas where the surface potential is VL (image area). Occur. This is because the transferability of the edge portion is originally weak. Therefore, by performing optical charge removal before transfer using pre-transfer erase light, the potential of V0 is lowered and the potential difference between V0 and VL is reduced, thereby improving primary transfer properties. As a result, it is possible to control the occurrence of white spots.

Note that if the white pattern caused by the carrier development on the white background area is not eliminated by optical charge removal before transfer using the pre-transfer erase light, the white background area potential difference (V0-Vdc) of the upstream image forming area Pa is lowered and the white background area carrier development is performed. There are ways to suppress it. However, with this method, care must be taken because image fogging at the image forming portion Pa may worsen.

(2-2. Suppression of white spots caused by image area carrier development by pre-transfer erase light)
When image area carrier development occurs, charge is injected into the carrier, which is originally of negative polarity, and becomes positive. In a state where charges are injected into the carrier, charge is naturally injected into the photoreceptor drums 1a to 1d as well. Charge injection into the photoreceptor drums 1a to 1d acts in the direction of bringing the surface potential of the photoreceptor drums 1a to 1d closer to the developing DC voltage Vdc (+180V), so the image area potential VL (+20V) is lowered by the carrier contact. This means that only the portion that is

As a result, a potential difference occurs in the image portion potential VL between the portion where charge injection has occurred and the surrounding portion thereof. The potential difference on the photoreceptor drums 1a to 1d generates a wraparound electric field in that portion, and the toner on the photoreceptor drums 1a to 1d is held on the photoreceptor drums 1a to 1d by the force of this strong wraparound electric field. Even when the toner image in the portion where charge injection has occurred reaches the primary transfer portion, this wraparound electric field obstructs the movement of the toner, resulting in white spots.

Here, even in a solid image, the toner actually covers about 70 to 80% of the surface of the photoreceptor drums 1a to 1d, and the toner melts and spreads during the fixing process, covering the surface of the paper. Cover. Therefore, when the pre-transfer erase light is irradiated by the static eliminator 50, the pre-transfer erase light can sufficiently reach the surfaces of the photoreceptor drums 1a to 1d even in solid image areas.

When the pre-transfer erase light is irradiated to a portion where the surface potential has increased due to charge injection (a portion in contact with carriers), the image portion potential VL of that portion decreases and becomes equal to the surrounding potential. As a result, the toner is no longer electrically bound, and the toner around the carrier also moves easily to the intermediate transfer belt 8. Thereby, white spots caused by carrier development in the image area can be eliminated by irradiating the pre-transfer erase light. However, if the irradiated erase light is too strong, the electrical toner holding power of the photoreceptor drums 1a to 1d becomes too small, resulting in increased toner scattering at the edge portions of character images.

(2-3. Suppression of white spots caused by carrier development on edge portions by pre-transfer erase light)
Carrier development on the edge portion of the image occurs due to the edge potential difference (V0 - VL), so if V0 is lowered by pre-transfer erase, the adhesion of the toner to the photoreceptor drums 1a to 1d will be reduced, and white spots will be reduced. Eliminate. Further, in this case, by lowering the white background potential difference (V0-Vdc), it is possible to improve the white pattern while maintaining the image density to some extent.

(2-4. Verification of white pattern suppression effect by pre-transfer erase light)
The image density and occurrence of white spots were verified when the developing DC voltage and the output of the pre-transfer erase light were varied. The test method was to investigate the relationship between the developing DC voltage, the output of the pre-transfer erase light of the static eliminator 50, and the image density, white spots, and toner scattering using a testing machine as shown in FIG.

The image forming conditions were that the printing speed (process speed) was 70 sheets/min, and the developing roller 33 had a developing sleeve 33a with an outer diameter of 20 mm and a blasted outer peripheral surface and a ten-point average roughness (JIS) of 5 to 10 μm. used. For the regulation blade 35, a magnetic blade made of stainless steel (SUS430) with a thickness of 1.5 mm was used, and the distance (regulation gap) between the regulation blade 35 and the developing roller 33 was set to 0.5±0.03 mm. A developing voltage in which a DC voltage of 80 to 250 V (determined by Vdc calibration) and an AC voltage with a peak-to-peak value (Vpp) of 500 to 1400 V (determined by Vac calibration) was superimposed was applied to the developing roller 33. The surface potential (white background part potential) V0 of the photosensitive drums 1a to 1d was set to 150 to 320V (white background part potential difference: fixed at V0-Vdc=70V), and the image part potential VL was set to 20V.

The photoreceptor drums 1a to 1d are made of amorphous silicon (a-Si) photoreceptors with a dielectric constant of 11, and the peripheral speed ratio of the developing roller 33 to the photoreceptor drums 1a to 1d is 1.8 (trail rotation at the opposing position). The distance between the photoreceptor drums 1a to 1d and the developing roller 33 (DS distance) was set to 0.375±0.025 mm. Further, the surface potential (bright potential) of the photoreceptor drums 1a to 1d was set to 160 to 350V (determined by Vdc calibration, Vo-Vdc=70V), and the image area potential (dark potential) was set to 20V. A resin belt without an elastic layer was used as the intermediate transfer belt 8.

The static eliminator 50 used was one in which an LED 50b (R8C/2C, manufactured by EVERLIGHT) that emits erase light with a wavelength of 640 nm was mounted on a substrate 50a.

(Evaluation method for image density and white streaks)
The standard size of the white mark is about 1.5 mm in width and 0.5 mm in height. Therefore, the state of the white pattern was detected using a 6 cm wide solid image. The state of the white streak was determined by measuring the density of the reference image at a pitch of 0.7 mm using an image density sensor 25 (spot diameter φ3 mm). Then, if the image density decreased below the threshold value, or if the density decreased within a certain width, it was determined that a white mark had occurred.

The evaluation criteria were as follows: ○ indicates that the image density reached the target density, and × indicates that the image density did not meet the target density. When the number of white markings was zero, it was marked as ○, when one or two were recognized, it was marked as △, and when three or more were recognized, it was marked as ×. The evaluation results are shown in Table 1 together with the input current of the pre-transfer erase light.

As shown in Table 1, when the image density is ensured and no white streaks occur (colored areas), the margin (tolerance) of the developing DC voltage Vdc increases as the output of the pre-transfer erase light is increased. ) can be seen to expand.

[3. Regarding abnormality detection of static eliminator 50]
If an abnormality such as a failure or dirt occurs in the static eliminator 50 that irradiates the pre-transfer erase light, the output of the pre-transfer erase light cannot be maintained, and the occurrence of white spots cannot be sufficiently suppressed. Therefore, in this embodiment, abnormality detection control for detecting an abnormality in the static eliminator 50 is made executable.

(3-1. Detection of abnormality in static eliminator 50 based on image density of reference image)
FIG. 7 is a graph showing the relationship between the output of the pre-transfer erase light and the halftone image density. As shown in Figure 7, when halftone images with a printing rate of 30% (○ data series), 40% (△ data series), and 50% (◇ data series) are used as image patterns, the erase before transfer is Since the surface potential changes before and after light irradiation, the image density also changes.

Therefore, a change in the density of the halftone image when the pre-transfer erase light is changed can be detected as a change in the luminous efficiency of the static eliminator 50. Table 2 shows the relationship between pre-transfer erase light and image density when a 30% halftone image is printed using a normal unit and a faulty unit as the static eliminator 50.

When determining that the unit is normal when the density difference is within ±0.02 with respect to each reference density when the input current of the pre-transfer erase light is changed to off (0 mA), 5 mA, and 10 mA, the normal unit is Since it falls within the range of ±0.02, it is determined that there is no problem. On the other hand, since the concentration difference in the faulty unit exceeds ±0.02, it is determined that there is a problem. Note that here, the abnormality of the static eliminator 50 is determined based on the density difference with respect to the reference density when the pre-transfer erase light changes, but static eliminator 50 is determined based on the presence or absence of density change when the pre-transfer erase light changes An abnormality in the device 50 may also be determined. Specifically, in Table 2, in the faulty unit, even when the pre-transfer erase light is turned off and changed to 5 mA and 10 mA, the image density does not change from 0.35, so it is determined that there is a problem.

(3-2. Detection of abnormality in the static eliminator 50 based on the occurrence of white spots)
From the verification results shown in Table 1, in settings where the target image density is secured and no white spots occur (hatched areas), as the pre-transfer erase light is increased, the margin of the developing DC voltage Vdc ( It can be seen that the margin) increases. Furthermore, when the developing DC voltage Vdc is 160 to 170 V, no white spots occur when the input voltage of the pre-transfer erase light is 10 mA, but white spots occur when the input voltage of the pre-transfer erase light is 5 mA. That is, when a decrease in the light intensity of the pre-transfer erase light occurs at a predetermined developing DC voltage Vdc, the presence or absence of white spots and the level of occurrence change, so it is possible to determine whether or not there is an abnormality in the static eliminator 50 based on the presence or absence of white spots and the level of occurrence. can be determined.

The developing DC voltage Vdc for white mark detection is a development method in which white marks do not occur, which is detected by detecting white marks on a reference image formed by changing the developing DC voltage Vdc under the condition that the pre-transfer erase light is fixed. Use the lower limit value of DC voltage (lower limit voltage for white spot generation). For example, in determining the white spot occurrence level, the developing DC voltage Vdc for white spot detection is set to be equal to or higher than the white spot occurrence lower limit voltage when the pre-transfer erase light quantity is set to an appropriate value. In determining the presence or absence of a white mark, the pre-transfer erase light amount is set to be equal to or higher than the white mark generation lower limit voltage when the erase light amount is the desired erase light amount for failure determination.

Methods for detecting white marks include a method using the image density sensor 25 and a method using the image reading section 21. In the method using the image density sensor 25, a solid (solid) pattern reference image is primarily transferred onto the intermediate transfer belt 8, and the image density sensor 25 detects the image density of the reference image. Since the image density decreases in areas where white streaks occur, the white streaks can be detected. For example, by detecting the reference image formed by the output of the currently set pre-transfer erase light at a predetermined timing, it is possible to check whether a white mark has occurred.

In the method using the image reading section 21, a white mark can be detected by reading the reference image output on the transfer paper P with the image reading section 21 and analyzing the read image data. In this case, work by the user or service personnel is required. On the other hand, regarding the detection efficiency of white marks, with the method using the image density sensor 25, white marks can only be detected at the sensor position facing the reference image on the intermediate transfer belt 8; When capturing, the white pattern can be detected in the entire width direction of the image area, which increases the detection efficiency. As a method of detecting a white mark using the image reading unit 21, there is also a method of using a local density difference or area in an image pattern, or a product of a density difference and an area.

Tables 3 and 4 show the relationship between the pre-transfer erase light, image density, and white pattern when a reference image is printed using a normal unit and a faulty unit as the static eliminator 50. Table 3 uses a horizontal line pattern reference image P1, which is a 0.1 mm line image printed at 0.1 mm intervals as shown in FIG. 8, as the reference image, and Table 4 uses the reference image P1 as shown in FIG. A reference image P2 of a solid (solid) pattern is used.

As shown in Tables 3 and 4, no white spots were observed in the normal unit when the input current of the pre-transfer erase light was 10 mA, but white spots were observed in the faulty unit even when the input current was 10 mA. was recognized. This situation was the same when a half pattern was used as the reference image and when a solid (solid) pattern was used. On the other hand, as shown in Table 4, when a solid (solid) pattern was used as the reference image, there was no difference in image density between the normal unit and the failed unit. Therefore, abnormality detection of the static eliminator 50 based on the occurrence of white spots is effective when a solid (solid) pattern is used as the reference image.

FIG. 10 is a flowchart illustrating an example of abnormality detection control of the static eliminator 50 executed in the image forming apparatus 100 of the first embodiment. The execution procedure of the abnormality detection control will be explained along the steps of FIG. 10, with reference to FIGS. 1 to 9 as necessary. Execution timing of the abnormality detection control includes, for example, when the image forming apparatus 100 is powered on, when the image forming apparatus 100 returns from a power saving (sleep) mode, and when the cumulative number of printed sheets since the previous execution of the abnormality detection control reaches a predetermined number of sheets. It will be done.

First, the control unit 90 changes the pre-transfer erase light of the static eliminator 50 in multiple stages to form a reference image (halftone pattern) in the image forming units Pa to Pd (step S1). Specifically, as shown in Table 2, the output (input current) of the pre-transfer erase light is changed to 0 mA (off state), 5 mA, and 10 mA (on state) to form a reference image, and the intermediate transfer belt 8 Primary transfer to.

Next, the control unit 90 measures the image density of the reference image using the image density sensor 25 (step S2). Then, the measured density ID of the reference image is compared with the reference density IDs corresponding to each pre-transfer erase light stored in the ROM 92 (or RAM 93) in advance (step S3).

Next, the control unit 90 determines whether or not there is an image forming unit Pa to Pd in which the density difference IDs−ID between the density ID of the reference image and the reference density IDs is greater than or equal to a predetermined value (step S4). If there is an image forming part Pa to Pd whose IDs-ID is equal to or greater than a predetermined value (for example, ±0.02 or more) (Yes in step S4), the static eliminator 50 irradiates the pre-transfer erase light to the image forming part. An abnormality is notified (step S5). Specifically, a message urging inspection of the static eliminator 50 is displayed on the liquid crystal display section 71. If there are no image forming units Pa to Pd whose IDs-ID is equal to or greater than the predetermined value (No in step S4), the process ends.

According to the control example shown in FIG. 10, the density ID of the reference image formed by changing the output of the pre-transfer erase light in multiple stages is detected. Then, when the density difference IDs-ID between the detected density ID and the reference density IDs is greater than or equal to a predetermined value, it is determined that there is an abnormality in the static eliminator 50. Thereby, the presence or absence of an abnormality in the static eliminator 50 can be detected with high accuracy using a simple method.

Note that in the control example shown in FIG. 10, abnormality detection of the static eliminator 50 was explained based on the image density of the reference image, but as shown in Tables 3 and 4, the static eliminator 50 is It is also possible to detect abnormalities in In that case, either form a solid (solid) pattern or a halftone pattern image as a reference image and detect a decrease in image density with the image density sensor 25, or transfer the reference image output onto the transfer paper P to the image reading unit 21. The occurrence of a white mark can be detected using the local density difference or area in the image pattern, or the product of the density difference and area.

FIG. 11 is an enlarged view showing the configuration around the image forming section Pa of the image forming apparatus 100 according to the second embodiment of the present invention. In this embodiment, the static eliminator 50 that irradiates the photoreceptor drum 1b of the image forming section Pb (see FIG. 1) with pre-transfer erase light (broken line arrow in FIG. 11) transfers the electricity to the photoreceptor drum 1a of the image forming section Pa. The rear erase light (white arrow in FIG. 11) is irradiated. Similarly, the static eliminator 50 irradiates the photoreceptor drums 1c and 1d of the image forming sections Pc and Pd (see FIG. 1) with pre-transfer erase light, and the static eliminator 50 irradiates the photoreceptor drums 1b and 1c of the image forming sections Pb and Pc after transfer. Irradiates erase light. Further, a contamination prevention film 80 is disposed upstream of the static eliminator 50 that irradiates the photoreceptor drum 1a of the image forming section Pa with pre-transfer erase light. The configuration of other parts of the image forming apparatus 100 is similar to that of the first embodiment.

According to this configuration, the pre-transfer erase light can eliminate static electricity on the surface of the photoreceptor drum 1b (1c, 1d) before primary transfer, and the post-transfer erase light can eliminate static electricity on the surface of the photoreceptor drum 1a (1b, 1c) after the primary transfer. This static elimination can be performed by one static elimination device 50.

When one static eliminator 50 is used to eliminate static electricity after transfer on the upstream photosensitive drums 1a (1b, 1c) and before transfer on the downstream photosensitive drums 1b (1c, 1d), pre-transfer erase is performed. When the light output is adjusted, the post-transfer erase light output also changes. Therefore, the position of the static eliminator 50 can be adjusted in the moving direction of the intermediate transfer belt 8 (left-right direction in FIG. 11). As a result, for example, when the output of the pre-transfer erase light to the downstream photosensitive drums 1b (1c, 1d) is reduced, the static eliminator 50 can be moved closer to the upstream photosensitive drums 1a (1b, 1c). , it is possible to reduce the static elimination effect caused by the pre-transfer erase light without reducing the static neutralization effect caused by the post-transfer erase light irradiation.

Further, the static eliminator 50 (the static eliminator 50 on the left side in FIG. 11) that irradiates pre-transfer erase light onto the photoreceptor drum 1a is configured such that an air flow along the intermediate transfer belt 8 is connected between the developing roller 33 and the primary transfer roller 6a. (pre-transfer area) and tends to cause toner scattering. Therefore, in this embodiment, a flexible pollution prevention film 80 is disposed upstream of the static eliminator 50 with respect to the moving direction of the intermediate transfer belt 8.

The anti-staining film 80 has one end (base end) fixed to the entire length of the developing device 3 a in the longitudinal direction, and the other end (free end) in contact with the intermediate transfer belt 8 . Thereby, it is possible to suppress the flow of air into the pre-transfer area of the image forming portion Pa, and to suppress contamination of the static eliminator 50 due to toner scattering.

As in the second embodiment shown in FIG. 11, the same static eliminator 50 is used to eliminate static electricity after transfer from the upstream photosensitive drums 1a (1b, 1c) and from the downstream photosensitive drums 1b (1c, 1d). When static electricity removal is performed before transfer, if there is an abnormality in static electricity removal before transfer, the static electricity removal after transfer will also be affected. Specifically, if an abnormality occurs in the charge removal after transfer to the upstream photoreceptor drums 1a (1b, 1c), the static electricity formed this time on the upstream photoreceptor drums 1a (1b, 1c) The latent image is influenced by the electrostatic latent image formed one revolution before the drum. In other words, if a reference image such as a solid pattern or a halftone pattern is printed and the image density is measured every time the photoreceptor drums 1a to 1d are rotated, if an abnormality occurs in charge removal after transfer, the image density can be measured during the second revolution of the drum. In this case, the image density fluctuates, and further fluctuates in the third round.

Since there is a lot of toner scattering between the development area where static elimination is performed before transfer and the primary transfer nip, there is a possibility that the static elimination device 50 may be contaminated with toner. On the other hand, since there is little toner scattering between the primary transfer nip where charge is removed after transfer and the cleaning devices 7a to 7d, there is a low possibility that the charge remover 50 will be contaminated by toner. Therefore, if an abnormality in charge removal after transfer to the photoreceptor drums 1a (1b, 1c) on the upstream side is not detected, but an abnormality in charge removal before transfer to the photoreceptor drums 1b (1c, 1d) on the downstream side is detected. , there is a high possibility of toner contamination.

Therefore, image density fluctuations (first image density fluctuations) in response to changes in the input current of the pre-transfer erase light at the downstream image forming section Pb (Pc, Pd) and the upstream image forming section Pa (Pb, Pc) By detecting the image density fluctuation (second image density fluctuation) accompanying the rotational speed of the photoreceptor drums 1a (1b, 1c), it is possible to detect a failure of the static eliminator 50 with higher accuracy.

FIG. 12 is a flowchart illustrating an example of abnormality detection control of the static eliminator 50 executed in the image forming apparatus 100 of the second embodiment. The execution procedure of the abnormality detection control will be explained along the steps of FIG. 12, with reference to FIGS. 1 to 9 and 11 as necessary. The execution timing of the abnormality detection control is the same as that of the first embodiment shown in FIG.

First, the control unit 90 changes the pre-transfer erase light of the static eliminator 50 in multiple stages to form a reference image (halftone pattern) in the image forming units Pa to Pd (step S1). Specifically, as shown in Table 2, the output (input current) of the pre-transfer erase light is changed to 0 mA (off state), 5 mA, and 10 mA (on state) to form a reference image, and the intermediate transfer belt 8 Primary transfer to.

Here, in the image forming units Pa to Pc excluding the image forming unit Pd located on the most downstream side, the same standard is used for each rotation speed (first round, second round, etc.) of the photosensitive drums 1a to 1c. An image is formed and primarily transferred to the intermediate transfer belt 8.

Next, the control unit 90 measures the image density of the reference image using the image density sensor 25 (step S2). Then, the measured density ID of the reference image is compared with the reference density IDs corresponding to each pre-transfer erase light stored in the ROM 92 (or RAM 93) in advance (step S3).

Next, the control unit 90 determines whether or not there is an image forming unit Pa to Pd in which the density difference IDs−ID between the density ID of the reference image and the reference density IDs is greater than or equal to a predetermined value (step S4). If there are image forming units Pa to Pd whose IDs-ID is greater than or equal to a predetermined value (for example, ±0.02 or greater) (Yes in step S4), the upstream side of the image forming unit whose Ds-ID is greater than or equal to the predetermined value is In the image forming section located in the immediate vicinity, it is determined whether or not there is a variation in the density ID of the reference image due to the number of rotations of the photoreceptor drums 1a to 1c (step S5).

For example, when IDs-ID is equal to or greater than a predetermined value in the image forming section Pc, the density ID of the reference image according to the rotational speed of the photoreceptor drum 1b in the image forming section Pb located immediately upstream of the image forming section Pc Determine whether or not there is a change in .

If there is a change in the density ID of the reference image due to the number of rotations of the photoreceptor drum in the image forming unit located immediately upstream (Yes in step S5), the image forming unit whose IDs-ID is equal to or greater than the predetermined value is An abnormality in the static eliminator 50 that irradiates the pre-transfer erase light is notified (step S6). Specifically, a message urging inspection of the static eliminator 50 is displayed on the liquid crystal display section 71.

If there is no variation in the density ID of the reference image due to the number of rotations of the photosensitive drum in the image forming unit located immediately on the upstream side (No in step S5), there is a possibility that the static eliminator 50 can be recovered by cleaning alone. , IDs-ID is a predetermined value or more, and the image forming unit is notified of dirt on the static eliminator 50 that irradiates the pre-transfer erase light (step S7). Specifically, a message urging cleaning of the static eliminator 50 is displayed on the liquid crystal display section 71. If there are no image forming units Pa to Pd whose IDs-ID is equal to or greater than the predetermined value (No in step S4), the process ends.

According to the control example shown in FIG. 12, when there is an image forming unit where the density difference IDs-ID between the density ID of the reference image and the reference density IDs is equal to or greater than a predetermined value, the image forming unit located immediately upstream , it is determined whether or not there is a variation in the density ID of the reference image due to the number of rotations of the photoreceptor drum. Then, it is determined whether there is an abnormality in the static eliminator 50 or whether the static eliminator 50 is dirty, depending on whether the density ID of the reference image changes with the rotational speed of the photosensitive drum. Thereby, abnormality and presence or absence of dirt in the static eliminator 50 can be detected with high precision using a simple method.

In addition, the present invention is not limited to the above-mentioned embodiments, and various changes can be made without departing from the spirit of the present invention. For example, in each of the above embodiments, a color multifunction machine as shown in FIG. Although the occurrence of white spots is detected by analyzing image data, and whether or not there is an abnormality in the static eliminator 50 is determined based on the detection result, the present invention is not limited to this. The present invention is applicable not only to color multifunction machines but also to intermediate transfer type image forming apparatuses equipped with a two-component development type developing device, such as color printers and color copying machines.

For example, if the image forming apparatus 100 is a color printer that does not have the image reading section 21, as shown in FIG. A white mark can also be detected by transmitting the image data of the reference image read by the CIS 81 to the control unit 90 and analyzing it.

INDUSTRIAL APPLICABILITY The present invention can be used in an intermediate transfer type image forming apparatus that uses a two-component developer containing toner and carrier. By utilizing the present invention, it is possible to provide an image forming apparatus that can detect an abnormality in a static eliminator that irradiates pre-transfer erase light with a simple configuration in an intermediate transfer system using a two-component developer.

Pa~Pd Image forming section 1a~1d Photosensitive drum (image carrier)
2a-2d Charging device 3a-3d Developing device 5 Exposure device 6a-6d Primary transfer roller (primary transfer member)
8 Intermediate transfer belt 9 Secondary transfer roller (secondary transfer member)
21 Image reading unit 25 Image density sensor 33 Developing roller (developer carrier)
50 Static eliminator 80 Contamination prevention film 81 CIS (image reading unit)
90 control unit 100 image forming apparatus

Claims (9)

an image carrier having a photosensitive layer formed on its surface;
a charging device that charges the surface of the image carrier to a predetermined surface potential;
an exposure device that irradiates light onto the image carrier charged by the charging device to form an electrostatic latent image with attenuated charging;
the electrostatic charge formed on the surface of the image carrier in a development area where the developer carrier is located opposite to the image carrier; a developing device that develops the latent image into a toner image;
a plurality of image forming units having;
an endless intermediate transfer belt that is disposed adjacent to the image forming section and that primarily transfers the toner image formed on the surface of the image carrier to an outer peripheral surface;
A primary transfer nip portion is formed between the image bearing member and the intermediate transfer belt by contacting the inner peripheral surface of the intermediate transfer belt at a position facing the image bearing member, and the image bearing member is formed in the primary transfer nip portion. a primary transfer member that primarily transfers the toner image formed on the surface of the body to the intermediate transfer belt;
a secondary transfer member that secondarily transfers the toner image primarily transferred to the intermediate transfer belt onto a recording medium;
a static eliminator that irradiates pre-transfer erase light to an area from the development area to the primary transfer nip portion of the image carrier;
an image density sensor that detects the density of the toner image primarily transferred onto the intermediate transfer belt;
a control unit that controls the development DC voltage applied to the developer carrier and the output of the pre-transfer erase light of the static eliminator;
Equipped with
The control unit changes the output of the pre-transfer erase light in multiple stages to form a reference image, and controls the density of the reference image detected by the image density sensor and the occurrence of image defects in the reference image. An image forming apparatus characterized in that it is determined whether or not there is an abnormality in the static eliminator based on at least one of the factors. The reference image is a halftone image having a predetermined printing rate,
1 . The control unit determines that there is an abnormality in the static eliminator when a density difference between the density of the reference image detected by the image density sensor and the reference density is a predetermined value or more. The image forming apparatus described in . The reference image is a halftone image having a predetermined printing rate,
The image forming apparatus according to claim 1, wherein the control unit determines that there is an abnormality in the static eliminator when the density of the reference image detected by the image density sensor does not change. The reference image is a solid image or a halftone image having a predetermined printing rate,
2. The control unit according to claim 1, wherein the control unit detects the occurrence of an image defect based on a density change of the reference image detected by the image density sensor, and determines whether or not there is an abnormality in the static eliminator. The image forming apparatus described above. comprising an image reading unit that reads the toner image primarily transferred to the intermediate transfer belt or the image output on the recording medium;
2. The control unit detects the occurrence of an image defect by analyzing image data of the reference image read by the image reading unit, and determines whether or not there is an abnormality in the static eliminator. The image forming apparatus according to any one of claims 1 to 4. The plurality of image forming units are arranged along the moving direction of the intermediate transfer belt,
The static eliminator, which is disposed between two adjacent image forming units, irradiates the pre-transfer erase light onto the image bearing member of the image forming unit located on the downstream side, and also irradiates the image bearing member of the image forming unit located on the downstream side with the pre-transfer erase light. 5. The image forming apparatus according to claim 1, wherein the image bearing member of the image forming section is irradiated with post-transfer erase light for removing residual charges after primary transfer. The control unit includes:
a first image density variation that is a density variation of the reference image with respect to the output of the pre-transfer erase light in the image forming section on the downstream side to which the pre-transfer erase light is irradiated by the static eliminator;
a second image density fluctuation that is a density fluctuation of the reference image in accordance with the rotational speed of the image carrier in the image forming section on the upstream side where the post-transfer erase light is irradiated by the static eliminator;
7. The image forming apparatus according to claim 6, wherein the presence or absence of an abnormality in the static eliminator is determined by detecting. The control unit determines that there is an abnormality in the static eliminator when the first image density variation is equal to or greater than a predetermined value and there is the second image density variation,
8. The image forming apparatus according to claim 7, wherein when the first image density fluctuation is equal to or greater than a predetermined value and there is no second image density fluctuation, it is determined that the static eliminator is contaminated. The image according to any one of claims 1 to 4, wherein the image carrier has an amorphous silicon layer as the photosensitive layer, and the intermediate transfer belt is a resin belt without an elastic layer. Forming device.

Images