JP2010190968A - Image-forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image-forming device which detects a malfunction in an optical discharging element, without a new component arranged on the periphery of a photoreceptor, to quickly execute a necessary procedure such as warning. <P>SOLUTION: The current flowing from a charging roller 12a to a photosensitive drum 11a is detected with a direct current-measuring circuit 106, and the life or abnormality of an optical discharging element 112a is detected, and then an alarm is issued to a user. When the optical discharging element 112a is determined to be abnormal, image-forming jobs remaining after that are increasingly dropped in productivity and finished for the present. Then, an image-forming device 100 is shifted to a standby mode, and whether a degenerated mode is to be executed is determined by the user through an operation panel 203. The degenerated mode makes the image-forming device 100 usable for the present, even in a pre-exposure-lacked state, by decreasing productivity and forming an image under image-forming conditions which assume that there is no pre-exposure. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus provided with a photostatic element that erases an electrostatic image by uniformly exposing the surface of a photoreceptor before charging, and more specifically, the function of the photostatic element is suddenly impaired during continuous image formation. Concerning the control of the case.

  An image in which a photostatic element is disposed between the toner image transfer portion and the charging member so as to face the photoconductor, and the photostatic element uniformly exposes the surface of the photoconductor before charging to erase the previous electrostatic image. A forming apparatus has been put into practical use (Patent Document 1).

  The light neutralizing element irradiates the photosensitive layer of the photosensitive member with light at an exposure density higher than the exposure density at the time of writing an electrostatic image, generates a large amount of charge carriers in the photosensitive layer, and uses a charging member. Discharge the charged potential.

  However, in recent years, as a result of increasing the rotational speed of the photoreceptor (so-called process speed), there have been cases where charge carriers generated by exposure using a photostatic element are transported to a charging position and the charging potential is lowered.

  For this reason, the exposure amount of the light neutralization element is adjusted to the minimum level necessary for static elimination to reduce the number of charge carriers that are generated by the static elimination exposure and carried to the charging position (Patent Document 2).

  At the same time, the DC voltage applied to the charging member in order to charge the photosensitive member is increased several percent to 10% from the required charging potential, and the charging potential that will be damaged by the charge carriers carried to the charging position in advance. (Patent Document 3).

JP-A-11-133825 Japanese Patent Laid-Open No. 2003-307979 JP 2001-142365 A Japanese Patent Laid-Open No. 06-006536

  During continuous image formation, the exposure amount of the light neutralizing element may suddenly decrease due to toner adhesion or lamp burnout in the light neutralizing element.

  At this time, as described above, if the DC voltage applied to the charging member is increased more than the necessary charging potential, the charging potential is increased as it is in the portion after the output of the light neutralizing element is reduced ( FIG. 7). As a result, it has been found that unnecessary developer (reversal toner, magnetic carrier) is likely to adhere to the portion after the exposure amount of the photosensitive member has decreased. Since the neutralization by the light neutralization element does not function normally, the influence of the previous electrostatic image is exerted on the charged potential distribution of the charged photosensitive member, and the ghost image may be defective. There may be a difference in the density of the output image before and after the exposure amount decreases.

  Therefore, as shown in Patent Document 3, it is proposed to arrange a potential sensor downstream of the charging member, measure the potential of the photosensitive member, and warn of a malfunction of the photostatic element when the potential suddenly rises. It was done.

  However, it is not economical to arrange a potential sensor for the purpose of only warning the malfunction of the photostatic element on a photoconductor that is not originally equipped with a potential sensor. Since the diameter of the photoconductor has been reduced and a large number of components are mounted around the photoconductor without any gaps, it is difficult to place a relatively large potential sensor.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of detecting a malfunction of a photostatic element and promptly issuing a warning without arranging new parts around a photoreceptor.

  The image forming apparatus of the present invention exposes the photosensitive member, developing means for developing an electrostatic image formed on the surface of the photosensitive member into a toner image, and the surface after the toner image is transferred to a transfer medium. And a charging member that contacts the surface that has been discharged by the light discharging element, and a charging bias is applied to the charging member to form the electrostatic image to charge the photoconductor. And a power source to be used. A current detecting means for detecting a direct current flowing through the photosensitive member by the charging bias; and an abnormality of the light static eliminating element is determined based on a decrease in the current detected by the current detecting means. Warning issuing means for issuing an abnormality of the means.

  In the image forming apparatus of the present invention, the potential increase on the surface of the photoconductor due to the malfunction of the photostatic element is determined by the decrease in the current flowing through the photoconductor when a charging bias is applied. This is because the amount of current necessary for charging the surface of the photoreceptor after the charge removal is larger than the amount of current required for charging the surface of the photoreceptor whose charge removal is insufficient (FIG. 8).

  Therefore, it is possible to promptly issue a warning by detecting a malfunction of the light neutralizing element without arranging a new part such as a potential sensor around the photoreceptor.

It is explanatory drawing of a structure of the image forming apparatus of 1st Embodiment. It is explanatory drawing of a structure of an image formation part. It is explanatory drawing of the photosensitive layer of a photosensitive drum. It is explanatory drawing of a structure of an optical static elimination element. It is explanatory drawing of the assembly structure of the light guide of an optical static elimination element. It is explanatory drawing of control of the charging voltage applied to a charging roller. It is explanatory drawing of the relationship between the photosensitive drum electric potential of a charging roller position, and the amount of pre-exposure. It is explanatory drawing of the relationship between the direct current value which flows through a charging roller, and the amount of pre-exposure. It is explanatory drawing of the relationship between the amount of pre-exposure and fog removal contrast. FIG. 3 is a block diagram of each unit related to the control of the first embodiment. 3 is a flowchart of control according to the first embodiment. It is a time chart of a normal mode. It is a time chart of a degeneration mode. It is a block diagram of each unit regarding control of Example 2. 6 is a flowchart of control according to the second embodiment. It is a flowchart of control which adjusts the amount of pre-exposure.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention can be implemented in another embodiment in which a part or all of the configuration of the embodiment is replaced with the alternative configuration as long as a warning or the like is detected by detecting a change in the current flowing through the transfer member.

  Therefore, the present invention can also be implemented in an image forming apparatus that uses a recording material as a transfer medium, that is, an image forming apparatus that directly transfers a toner image formed on a photosensitive member to a recording material.

  In the present embodiment, only main parts related to toner image formation / transfer will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, a composite machine, in addition to necessary equipment, equipment, and a housing structure. It can be implemented in various applications such as a machine.

  In addition, about the general matter of the image forming apparatus shown by patent documents 1-4, illustration is abbreviate | omitted and the overlapping description is abbreviate | omitted.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of the configuration of the image forming apparatus according to the first embodiment, and FIG. 2 is an explanatory diagram of the configuration of the image forming unit.

  As shown in FIG. 1, the image forming apparatus 100 is a tandem intermediate transfer type full color printer in which image forming portions Pa, Pb, Pc, and Pd are arranged along an intermediate transfer belt 31.

  In the image forming unit Pd, a yellow toner image is formed on the photosensitive drum 11 d and is primarily transferred to the intermediate transfer belt 31. In the image forming unit Pc, a magenta toner image is formed on the photosensitive drum 11 c and is primarily transferred to the yellow toner image on the intermediate transfer belt 31. In the image forming portions Pb and Pa, a cyan toner image and a black toner image are formed on the photosensitive drums 11b and 11a, respectively, and are sequentially primary-transferred on the intermediate transfer belt 31 in the same manner.

  The four-color toner images primarily transferred to the intermediate transfer belt 31 are transported to the secondary transfer portion Te and collectively transferred to the recording material P. The recording material P on which the four-color toner images are secondarily transferred is heated and pressed by the fixing device 40 to fix the toner images on the surface, and then discharged to the outside of the image forming apparatus 100.

  The separating devices 23a and 23b separate the recording material P drawn from the recording material cassettes 21a and 21b by the pickup rollers 22a and 22b one by one and send them to the registration roller 25.

  The registration roller 25 receives and waits for the recording material P in a stopped state, and sends the recording material P to the secondary transfer portion Te in synchronization with the toner image on the intermediate transfer belt 31.

  The belt cleaning device 37 slides the cleaning blade against the intermediate transfer belt 31 to remove the transfer residual toner remaining on the intermediate transfer belt 31 through the secondary transfer portion Te.

  The fixing device 40 presses the pressure roller 41b against the fixing roller 41a provided with the heater 41c to form a heating nip. The recording material P is heated and pressurized in the process of being nipped and conveyed by the heating nip, melts the toner image, and fixes the full-color image on the surface.

  An intermediate transfer belt 31, which is an example of a transfer medium, is supported around a tension roller 33, a driving roller 36, and a counter roller 34, and is driven by a driving roller 36 connected to a pulse motor (not shown) to be 300 mm / mm. It rotates in the direction of arrow B at a peripheral speed of sec. The intermediate transfer belt 31 uses polyimide having a thickness of 100 μm, and has a width of 330 mm in the thrust direction and a circumferential length of 700 mm at the secondary transfer portion Te. The material of the intermediate transfer belt 31 may be PET [polyethylene terephthalate] or PVdF [polyvinylidene fluoride].

  The control unit 103 includes a control board and a motor drive board for controlling the operation of the mechanism in each unit of the image forming apparatus. The environmental sensor 105 is arranged so that the environmental temperature and humidity around the apparatus can be accurately measured without being affected by the fixing unit 40 serving as a heat source in the apparatus, and the control unit 103 outputs the output of the environmental sensor 105. Various controls are performed based on the above.

  The image forming portions Pa, Pb, Pc, and Pd are substantially the same except that the color of the toner used in the developing devices 14a, 14b, 14c, and 14d is different from black, cyan, magenta, and yellow. Hereinafter, the black image forming portion Pa will be described, and the other image forming portions Pb, Pc, and Pd will be described by replacing “a” at the end of the reference numerals with “b”, “c”, and “d”.

  As shown in FIG. 2, the image forming unit Pa includes a charging roller 12a, an exposure device 13a, a developing device 14a, a primary transfer roller 35a, a photostatic element 112a, and a cleaning device 15a around the photosensitive drum 11a.

  The photosensitive drum 11a, which is an example of a photosensitive member, has a negatively charged photosensitive layer, and is rotated in the direction of the arrow R1 at a process speed of 300 mm / sec by receiving a driving force from a driving motor (not shown). To do.

  A charging roller 12a, which is an example of a charging member, is driven to rotate in contact with the photosensitive drum 11a, and a vibration voltage obtained by superimposing an AC voltage on a DC voltage is applied from a power source D3, which is an example of a power source. As a result, the surface of the photosensitive drum 11a is charged to a uniform negative potential.

  An exposure apparatus 13a, which is an example of an exposure apparatus, scans a scanning beam image data obtained by developing a black separated color image with a rotating mirror and scans the surface of the charged photosensitive drum 11a with a static image. Write an image.

  The developing device 14a, which is an example of a developing unit, stirs and charges the two-component developer, and supports the photosensitive drum 11a around the fixed magnetic pole 14j on the developing sleeve 14s that rotates counterclockwise, and rubs the photosensitive drum 11a. Let By applying an oscillating voltage obtained by superimposing an AC voltage to a negative DC voltage from the power supply D4, the toner charged to the electrostatic image of the photosensitive drum 11a having a positive polarity relative to the developing sleeve 14s is negatively charged. The electrostatic image is reversed and developed.

  The two-component developer is constituted by mixing a magnetic carrier having an average particle diameter of 50 μm, a nonmagnetic toner having an average particle diameter of 6 μm, and a predetermined external additive, and the weight ratio of the nonmagnetic toner is 5%. Since the magnetic carrier has iron oxide as a main component and is hard and has a large particle size, a DC voltage of the oscillating voltage is set so as to avoid transfer to the photosensitive drum 11a.

  The primary transfer roller 35 a presses the intermediate transfer belt 31 to form a primary transfer portion Ta between the photosensitive drum 11 a and the intermediate transfer belt 31. By applying a positive DC voltage from the power source D1 to the primary transfer roller 35a, the negative toner image carried on the photosensitive drum 11a is primarily transferred to the intermediate transfer belt 31 passing through the primary transfer portion Ta. .

  The primary transfer roller 35a is a metal member obtained by plating a steel material such as sulfur free cutting steel with zinc or the like, or a part or the whole of a metal member such as aluminum or stainless steel with a conductive polyurethane sponge layer. . The primary transfer roller 35a is a urethane sponge roller that is formed to have a diameter of 16 mm by disposing an elastic layer of 4 mm on the surface of a core metal having a diameter of 8 mm, and has a resistance value of 5 × 10 7 Ω when a voltage of 1 kV is applied.

  At the time of primary transfer in a standard environment where the temperature / humidity is 23 ° C./60%, a current of 40 μA is applied to the core of the primary transfer roller 35a. is doing.

  The cleaning device 15a employs a counter blade method, and slides the cleaning blade 110a against the photosensitive drum 11a to remove residual toner remaining on the surface of the photosensitive drum 11a after passing through the primary transfer portion Ta. The cleaning device 15a includes a cleaning blade 110a that is held by the cleaning container 109a and is in contact with the surface of the photosensitive drum 11a, and a screw 111a that transports transfer residual toner in the longitudinal direction in the cleaning container 109a.

  The cleaning blade 110a is an elastic blade made of urethane rubber having a thickness of 3 mm and having a free length of 8 mm, and comes into contact with the photosensitive drum 11a with a linear pressure of about 0.35 N / cm.

  By the way, there is a case where a ghost image is formed when a halftone image as seen in a highlight portion of an image is copied after continuously copying clear and bright images. A ghost image is a problem that an image pattern copied last time appears in an image that should originally be a uniform halftone image.

  At the time of writing the electrostatic image, for example, image exposure is performed on the surface of the photosensitive member charged to −500V, and the potential of the exposed portion is lowered to about −100V. At the time of development, toner is attached to the exposed portion due to a potential difference from the non-exposed portion and developed, and in the subsequent transfer, the recording material charged positively comes into contact with the photoreceptor. For this reason, after the transfer, the surface potential of the photoreceptor changes as a whole in the positive direction, and the potential of the exposed portion exceeds -100V and becomes -50V.

  If this phenomenon is repeated, the potential difference is not eliminated even by the negative charge of the photosensitive drum that is performed before the exposure. Therefore, the surface potential is shifted in the positive direction only at that portion, and a dark toner image is formed. May be.

  In order to prevent such a ghost, exposure before charging (pre-exposure) using a photostatic element is effective. The pre-exposure generally uses an array light source in which LEDs are aligned in the longitudinal direction of the photoconductor, and uses the same wavelength region as the main sensitivity wavelength region of the photoconductor in order to completely remove charges. (Patent Documents 1 and 2).

  However, when pre-exposure is applied to the photoreceptor, a phenomenon called dark decay occurs in which the surface potential of the photoreceptor decreases after passing through the charging member.

  In other words, there are amorphous amorphous silicon photoconductors and organic photoconductors as photoconductors, but the organic photoconductor is coated with a conductive base material, a charge generation layer coated thereon, and further thereon. The charge transport layer is provided to form a layer structure.

  In the photosensitive layer irradiated with light, photocarriers generated in the charge generation layer (charges having a polarity opposite to the charging polarity of the drum) move through the charge transport layer and move toward the drum surface. As a result, a charged dark portion potential portion and a bright portion potential portion where the charged potential is canceled are generated, and an electrostatic image is formed on the photosensitive member.

  At this time, in the photosensitive member irradiated with the pre-exposure, the photocarrier generated from the charge generation layer moves to the surface of the photosensitive layer, and the surface potential of the photosensitive member is leveled. However, since it takes time to move the photo carrier, it takes time until the potential on the surface of the photoreceptor is stabilized.

  It is considered that the dark decay phenomenon occurs when the surface of the state where the potential is not stable passes through the charging member in the cycle until the surface potential of the photoreceptor becomes stable. The phenomenon of dark decay is considered to be a phenomenon in which there are residual photocarriers that move in the photosensitive layer after being charged, and the charged potential is attenuated by the photocarriers.

  Therefore, under conditions where no pre-exposure or image exposure is applied, no photocarrying and residual photocarriers that move in the photosensitive layer are generated, and no dark decay occurs.

  When pre-exposure is irradiated due to the phenomenon of dark decay, the potential decreases after passing through the charging member, so that the surface potential of the photoreceptor on the surface facing the developing sleeve is uncertain because it reaches the developing device. Become. Due to the dark decay phenomenon, the fog removal contrast Vback, which is the difference between the potential of the developing sleeve and the potential of the dark portion of the photosensitive member, becomes uncertain.

  Here, if the fog removal contrast Vback is insufficient, the negatively charged toner adheres to the white background portion of the image and a fogging image defect occurs. On the other hand, when the fog removal contrast Vback is excessive, a phenomenon that the magnetic carrier is discharged from the developing sleeve to the surface of the photosensitive member (referred to as “carrying”) or a phenomenon that the toner whose charge is reversed is discharged to the white background portion of the image occurs. There are things to do.

  Therefore, in order to compensate for the uncertainty of the charging potential generated by dark decay, the system disclosed in Patent Document 3 is provided with a potential sensor for measuring the surface potential of the photosensitive member between the charging member and the developing device. is doing. However, the potential sensor can be deployed if the system has a large diameter of the photoconductor, but there is no space for deployment in a small system where the outer diameter of the photoconductor is Φ30 mm or less.

  For this reason, the control unit 103 predicts the fluctuation of the charging potential of the photosensitive drum 11a caused by dark decay based on the output of the environment sensor 105, and controls the additional amount of the DC voltage applied to the charging roller 12a. Yes. This is because the problem of carry-on and fogging described above can be avoided if the amount of dark attenuation can be controlled to about ± 10V.

<Photosensitive drum>
FIG. 3 is an explanatory diagram of the photosensitive layer of the photosensitive drum.

  As shown in FIG. 3, the photoconductor drum 11a is an organic photoconductor formed by laminating an undercoat layer B, a charge generation layer C, and a charge transport layer D in this order on a support A for an electrophotographic photoconductor. is there.

  The support A can be used without particular limitation as long as it has conductivity and does not affect the measurement of hardness. For example, a metal or alloy such as aluminum, copper, chromium, nickel, zinc and stainless steel formed into a drum shape can be used.

  The undercoat layer B is used for improving adhesion of the photosensitive layer, improving coating properties, protecting the support, coating defects on the support, improving charge injection from the support, or protecting the photosensitive layer from electrical breakdown. Formed for. An ethylene-acrylic acid copolymer is dissolved in a suitable solvent and coated on a support. The thickness of the undercoat layer B is preferably 0.1 to 2 μm.

  In the case of forming a laminated photosensitive layer in which the charge generation layer C and the charge transport layer D are functionally separated and laminated, the charge generation layer C and the charge transport layer D are laminated on the undercoat layer B in this order.

  As the charge generation material used for the charge generation layer C, a phthalocyanine compound capable of increasing sensitivity in order to realize high image quality was used.

  The charge generating material is dispersed together with 0.3 to 4 times the amount of binder resin and solvent using a method such as a homogenizer, ultrasonic dispersion, ball mill, vibration ball mill, sand mill, attritor and roll mill. Then, the charge generation layer C is formed by applying the dispersion onto the undercoat layer and drying it. The film thickness of the charge generation layer C is preferably 5 μm or less, and particularly preferably in the range of 0.1 to 2 μm.

  In the charge transport layer D, poly-N-vinylcarbazole as a charge transport material is dispersed / dissolved in a solvent together with a suitable binder resin, and the solution is applied onto the charge generation layer C and dried using the method described above. Thus, a thickness of 29 μm was formed. As for the mixing ratio of the charge transport material and the binder resin, when the total weight of both is 100, the weight of the charge transport material is preferably 20 to 90, more preferably 30 to 80. If the amount of the charge transporting material is less than that, the charge transporting ability is lowered, and problems such as a decrease in sensitivity and an increase in residual potential occur. The film thickness of the charge transport layer D in the multilayer photoreceptor having a protective layer (not shown) is preferably 1 to 50 μm, more preferably 3 to 30 μm. The protective layer can be formed by polymerizing or crosslinking a hole transporting compound having a chain polymerizable functional group.

  Examples of the binder resin include polymers and copolymers of vinyl compounds such as styrene, vinyl acetate, vinyl chloride, acrylic acid ester, methacrylic acid ester, vinylidene fluoride, and trifluoroethylene. There are also polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, polycarbonate, polyester, polysulfone, polyphenylene oxide, polyurethane, cellulose resin, phenol resin, melamine resin, silicon resin, and epoxy resin.

  Other materials for the undercoat layer B include polyvinyl alcohol, poly-N-vinylimidazole, polyethylene oxide, ethyl cellulose, casein, polyamide, N-methoxymethylated 6 nylon, copolymer nylon, glue, gelatin and the like.

  Other materials for the charge generation layer C include selenium-tellurium, pyrylium, and thiapyrylium dyes. Further, there are various central metals and crystal systems, more specifically, phthalocyanine compounds having crystal types such as α, β, γ, ε, and X type. Examples include anthanthrone pigments, dibenzpyrenequinone pigments, pyranthrone pigments, trisazo pigments, disazo pigments, monoazo pigments, indigo pigments, quinacridone pigments, asymmetric quinocyanine pigments, quinocyanine, and amorphous silicon. The charge generation layer C may be formed on the undercoat layer B by using a vapor deposition method or the like using a film composed of a single composition of the charge generation material.

  Other materials for the charge transport layer D include heterocyclic compounds such as polystyrylanthracene and polymer compounds having condensed polycyclic aromatics, and heterocyclic compounds such as pyrazoline, imidazole, oxazole, triazole, and carbazole. There are low-molecular compounds such as triarylalkane derivatives such as triphenylmethane, triarylamine derivatives such as triphenylamine, phenylenediamine derivatives, N-phenylcarbazole derivatives, stilbene derivatives, and hydrazone derivatives.

  The photoconductive drum 11a may be an amorphous silicon photoconductor that can have a long life, or an electron beam curable photoconductor that is cured by an electron beam instead of being cured by heat.

<Optical neutralization element>
FIG. 4 is an explanatory diagram of the configuration of the optical static elimination element, and FIG. 5 is an explanatory diagram of the assembly structure of the light guide of the optical static elimination element.

  As shown in FIG. 2, the light neutralizing element 112a is disposed upstream of the cleaning blade 110a in the rotation direction of the photosensitive drum 11a.

  If the printing operation is continuously performed for several cycles after the image forming apparatus 100 is started up, the electrostatic image formed in the previous cycle may remain thin in the next cycle, and a so-called latent image ghost may appear. The latent image ghost is conspicuous when a solid black image is formed in a white background in the first cycle (one page) and a uniform halftone image is formed in the second cycle (second page).

  Immediately after starting up the image forming apparatus 100, the sensitivity of the surface of the photosensitive drum 11a is very high. In the first cycle, the sensitivity is reduced only in the solid black portion exposed to the photosensitive drum 11a, and the portions other than the solid black are sensitive. Remains high. In this state, when the electrostatic image of the second cycle is written, the portion of the surface of the photosensitive drum 11a where the sensitivity has been lowered appears in the uniform halftone image of the second cycle. In this way, the fact that a thin image corresponding to the electrostatic image written in the previous cycle appears in the next cycle is called a latent image ghost. The electrostatic image written in the previous cycle is gradually eliminated if it is naturally left in the air. However, when the peripheral speed of the photosensitive drum 11a is increased as in the image forming apparatus 100, the electrostatic image in the next cycle is overwritten before the electrostatic image written in the previous cycle is naturally relaxed. Therefore, a latent image ghost is generated with higher contrast.

  Therefore, in the image forming apparatus 100, in order to prevent the latent image ghost, the surface of the photosensitive drum 11a is uniformly exposed by using the light neutralizing element 112a to eliminate the electrostatic image, and the electrostatic image written in the previous cycle is eliminated. ing.

  The light neutralizing element 112a pre-exposes the surface of the photosensitive drum 11a to uniformly neutralize the surface of the photosensitive drum before image formation, and removes a latent image ghost on the photosensitive drum 1.

  As shown in FIG. 4, the light neutralizing element 112 a irradiates light from an LED lamp 503 disposed at the end of the light guide 501, leaks from the side surface of the light guide 501, and pre-exposes the surface of the photosensitive drum 11 a. The light guide 501 is disposed along the longitudinal direction of the photosensitive drum 11a at a distance of 4 mm facing the photosensitive drum 11a in order to neutralize the surface of the photosensitive drum 11a after the transfer process. In FIG. 4, portions other than the photosensitive drum 11a and the light guide 501 are not shown.

The light neutralizing element 112a has a spectrum of the LED lamp 503 having a peak at 400 to 800 nm. By adjusting the current applied to the LED lamp 503, the light quantity on the surface of the photosensitive drum 11a is changed from 5 μW / inch ² to 30 μW / inch ^2. It is possible to control within the range.

  An LED lamp 503, which is a light source of the light neutralizing element 112a, is mounted on the image forming apparatus main body, while a light guide 501, which is a light irradiation member of the light neutralizing element 112a, is mounted on a process cartridge on which the photosensitive drum 11a is mounted. . For this reason, the light guide 501 is replaced together with the replacement of the process cartridge, but the LED lamp 503 is not replaced.

  The LED lamp 503 is mounted on the outer side in the longitudinal direction of the static elimination width (region) of the photosensitive drum 1 on the outer side of the image forming apparatus side plate (image forming apparatus main body). The LED lamp 503 makes output light incident on the end surface 506 of the light guide 501 from a direction parallel to the longitudinal direction of the light guide 501. A light shielding measure (not shown) is taken around the LED lamp 503 so that the light from the LED lamp 503 does not unnecessarily expose the end of the photosensitive drum 11a.

  For the light guide 501, a resin (acrylic, polycarbonate, polystyrene, or the like) with excellent light transmittance, glass, or the like is used. A plurality of V-shaped notches 502 are provided in the longitudinal direction of the surface of the light guide 501 as opposed to the photosensitive drum 11a as uneven portions related to reflection.

  By the step 502, light incident from the end of the light guide 501 as indicated by an arrow C is irradiated in a direction perpendicular to the longitudinal direction of the light guide 501 (in the direction of arrow D). Irradiation light is irradiated as “charge removal light” on the surface of the photosensitive drum 11a with a predetermined charge removal width (exposure width).

  The depth of the step 502 is made deeper and wider as it gets farther from the LED lamp 503 so that the surface of the photosensitive drum 11a is irradiated with the uniform amount of light in the longitudinal direction. The step 502 is larger in size according to the position in the longitudinal direction of the light guide 501, that is, as the distance from the end surface 506 of the light guide 501 on which the LED lamp 503 is disposed increases.

  The number of steps 502 may be arbitrary and may be one. Further, the cross-sectional shape of the step 502 need not be V-shaped, and can be other shapes such as a U-shape or an I-shape. The inclination of the step 502 with respect to the axial direction is also arbitrary.

  Further, here, one LED lamp 503 is provided at a position facing one end face of the light guide 501, but when the amount of light is insufficient, one LED lamp 503 is measured at each position facing the both end faces of the light guide. Two may be provided. In that case, the center of the light guide is deepest (larger) so that the exposure dose distribution in the longitudinal direction of the photosensitive drum 1a is uniform.

  As shown in FIG. 5, actually, the light guide 501 itself is covered with a white resin case 504 as a reflective cover in order to increase the utilization efficiency of the output light of the LED lamp 503. The resin case 504 has an opening in the longitudinal direction facing the photosensitive drum 1a, and has an opening 507 corresponding to the end face 506 on which light from the LED lamp (503: FIG. 4) is incident. Note that a highly reflective color (white, silver, etc.) may be applied to the surface of the light guide 501 excluding the emission region, or a reflective film may be provided. As shown in FIG. 2, the resin case 504 is attached to a process cartridge including the photosensitive drum 11a so as to be positioned at a predetermined rotational position of the photosensitive drum 11a.

  When the “light guide type” is used as the light neutralizing element 112a, the light amount ripple (shake width) on the surface of the photosensitive drum 11a is small and uniform compared to the case where the “chip array type” in which a plurality of LEDs are arranged is used. Pre-exposure (static elimination) is possible. In addition, the light static elimination element 112a can be arranged at low cost with small size and light weight and power saving. As a result, image defects such as horizontal streaks and positive ghosts generated in a halftone image can be prevented without impairing the design freedom of the image forming apparatus main body, and a good image can be obtained.

  Here, an example in which the light guide 501 is provided in the process cartridge has been described. However, the light guide may not be mounted on the process cartridge but may be provided on the image forming apparatus main body side. According to this aspect, since the light guide 501 is not mounted, the cost of the process cartridge can be reduced.

<Charging roller>
FIG. 6 is an explanatory diagram for controlling the charging voltage applied to the charging roller.

  As shown in FIG. 6, the charging roller 12a is formed by covering the outside of a shaft member (core metal 12e), which is a conductive support for applying a charging voltage, with an intermediate resistance elastic layer 12f. The charging roller 12a is a contact-type charging member that makes contact with the photosensitive drum 11a without making a gap by using the elasticity of the elastic layer 12f, and charges the photosensitive drum 11a with a relatively low voltage.

  In the shaft member (core metal 12e), a bearing portion and a voltage application electrode receiving portion at both ends and an elastic layer covering portion having an outer diameter of φ14 mm are integrally formed of metal.

The elastic layer 12f is composed of a conductive rubber having a thickness of 1 to 2 mm in which a conductive agent such as carbon black is dispersed and mixed. In order to prevent charging unevenness during image formation, the volume resistance value 10 ⁵ to 10. It is adjusted to ⁷ Ωcm.

Alternatively, the peripheral surface of the elastic layer covering portion of the conductive support is formed by injection molding an ABS resin containing an ion conductive polymer compound such as polyether ester amide and having a volume resistance of 10 ⁵ to 10 ⁷ Ωcm. You may coat | cover 0.5-1 mm on the top. A protective layer made of a thermoplastic resin composition in which conductive fine particles such as tin oxide are dispersed may be sequentially formed on the surface of the resistance adjustment layer thus formed.

  The power source D3 applies an oscillating voltage (bias voltage Vdc + Vac) obtained by superimposing an AC voltage having a frequency f on a DC voltage to the metal core 12e of the charging roller 12a. As a result, the peripheral surface of the rotating photosensitive drum 11a is charged to the potential of the bias voltage Vdc. The power source D3 includes a direct current (DC) power source 101 and an alternating current (AC) power source 102.

  The control unit 103 performs on / off control of the DC power supply 101 and the AC power supply 102 of the power supply D3 so as to apply a DC voltage, an AC voltage, or a superimposed voltage of both to the charging roller 12a. The control unit 103 also controls the DC voltage value applied from the DC power source 101 to the charging roller 12a and the peak-to-peak voltage value of the AC voltage applied from the AC power source 102 to the charging roller 12a.

  The AC current measurement circuit 104 inputs AC current value information formed by measuring the AC current value flowing through the charging roller 12 a via the photosensitive drum 11 a to the control unit 103.

  The environmental sensor 105 inputs environmental information formed by measuring the temperature and humidity of the environment in which the image forming apparatus (100) is installed to the control unit 103.

  Based on the AC current value information, the environmental information, and the like, the control unit 103 executes an appropriate peak-to-peak voltage value calculation / determination program for the charging roller 12a in the charging process of image formation.

<DC current measurement circuit>
7 is an explanatory diagram of the relationship between the photosensitive drum potential at the charging roller position and the pre-exposure amount, FIG. 8 is an explanatory diagram of the relationship between the DC current value flowing through the charging roller and the pre-exposure amount, and FIG. 9 is the pre-exposure amount and the fogging. It is explanatory drawing of the relationship with taking contrast.

  As shown in FIG. 2, the latent image ghost of the electrostatic image written in the previous cycle becomes thinner as the pre-exposure amount of the light neutralizing element 112a increases, and becomes thinner. The effect decreases and becomes darker. On the other hand, since the charged charge is consumed to cancel the pre-exposure carrier generated on the photosensitive layer of the photosensitive drum 11a by the pre-exposure of the photostatic element 112a, the larger the pre-exposure amount, the worse the charging performance. The smaller the is, the better the charging performance. From this point of view, it is desirable that the pre-exposure amount is set to a marginal exposure amount that can suppress the latent image ghost to an allowable level.

  However, the pre-exposure amount decreases with the life of the pre-exposure lamp as the total number of images formed increases and approaches the endurance life, and eventually turns off completely. As a result, the latent image ghost deteriorates as it approaches the endurance life.

  In order to solve this problem, it is conceivable to set a sufficiently large pre-exposure amount in advance in consideration of a decrease in the pre-exposure amount of the light neutralizing element 112a. However, since the charging performance deteriorates as the pre-exposure amount increases, this method may not provide a sufficient drum surface potential.

  Further, as described above, the control unit 103 presupposes a normal pre-exposure amount of the light neutralizing element 112a, and applies a DC voltage that predicts the dark attenuation amount of the photosensitive drum 11a based on the output of the environmental sensor 105 to the charging roller 12a. Is applied. For this reason, if the light static elimination element 112a is excessively soiled or does not light up after reaching the end of its life, the prediction is wrong and the DC voltage applied to the charging roller 12a becomes inappropriate.

  That is, as the dark decay is lost, the surface potential of the photosensitive member that has passed through the charging member increases, and the fog removal contrast Vback, which is the potential difference between the surface potential of the white background portion of the photosensitive member and the potential of the developing sleeve, is excessive. Become. In this case, transfer (carrying) of the magnetic carrier to the photosensitive drum 11a occurs, which may cause a secondary disaster such as an abnormal image, a scratch on the surface of the photosensitive member, or a missing cleaning blade.

  Therefore, a method has been considered in which a dedicated pre-exposure amount measuring sensor is provided inside the image forming apparatus main body, and the pre-exposure amount is controlled based on sensor information from the pre-exposure amount measuring sensor. However, the pre-exposure amount measuring sensor is not desirable in view of equipment cost and size restrictions around the photosensitive drum 11a.

  Therefore, in this embodiment, as shown in FIG. 6, the current flowing from the charging roller 12a to the photosensitive drum 11a is detected by the DC current measuring circuit 106, and the life or abnormality of the photostatic element 112a is detected to warn the user. To emit. When the pre-exposure amount decreases, the surface potential of the photosensitive drum 11a increases in the negative direction, so that the amount of negative charge to be supplied from the charging roller 12a to the photosensitive drum 11a for charging to a predetermined negative potential is small. For this reason, if it is detected that the direct current flowing through the charging roller 12a to which a predetermined charging bias is applied is decreased, it can be determined that the pre-exposure amount of the photostatic element 112a has decreased.

  In order to detect a direct current flowing between the photosensitive drum 11a and the charging roller 12a, the rotating shaft of the photosensitive drum 11a is disconnected from the ground potential, and a direct current is generated between the rotating shaft of the photosensitive drum 11a and the ground potential. A measurement circuit 106 is arranged. The DC current measurement circuit 106 includes a fixed resistor that extracts a DC current that flows to the ground potential via the photosensitive drum 11a from the charging roller 12a to which a charging bias in which a DC voltage and an AC voltage are superimposed is applied. In addition, a capacitor that bypasses an alternating current due to the alternating voltage applied to the charging roller 12a, and a direct current voltage generated at both ends of the fixed resistor are amplified and converted to an analog voltage of 0 to 5V and output to the control unit 103. Circuit.

  The control unit 103 detects the output of the DC current measuring circuit 106 and determines the state of the potential of the photosensitive drum 11a after passing through the light neutralizing element 112a and before reaching the charging roller 12a, that is, the lighting state of the light neutralizing element 112a. To do. When the control unit 103, which is an example of a warning issuing unit, determines an abnormality of the light neutralizing element based on a decrease in the current detected by the direct current measuring circuit 106, which is an example of the current detecting unit, the abnormality of the light neutralizing unit is detected. Is announced.

As shown in FIG. 7 with reference to FIG. 2, when the pre-exposure amount of the photostatic element 112a increases, the surface potential of the photosensitive drum 11a that reaches the charging roller 12a decreases. On the other hand, when the pre-exposure light amount of the light neutralizing element 112a becomes 12 μW / inch ² or less, the surface potential of the photosensitive drum 11a in contact with the charging roller 12a gradually increases as the pre-exposure amount decreases.

As shown in FIG. 8 with reference to FIG. 2, as the surface potential of the photosensitive drum 11a increases, the direct current flowing through the charging roller 12a to which an equal charging bias is applied decreases. When the pre-exposure light amount of the photostatic element 112a is 12 μW / inch ² or less, the direct current flowing between the charging roller 12a and the photosensitive drum 11a during charging decreases as the pre-exposure amount decreases.

  FIG. 9 shows a calculation of the potential difference between the developing sleeve 14s and the photosensitive drum 11a when the surface of the charged photosensitive drum 11a reaches the developing position with the DC voltage Vdc of the developing bias applied to the developing sleeve 14s being a fixed value. FIG.

  As shown in FIG. 9 with reference to FIG. 2, when the pre-exposure amount of the light neutralizing element 112a decreases, the fog removal contrast Vback in the developing device 14a increases. Since the surface potential of the photosensitive drum 11a charged by the charging roller 12a to which an equal charging bias is applied increases, the difference voltage (= fogging contrast Vback) from the DC voltage applied to the developing sleeve 14s increases by nearly 50V. .

  For this reason, when the pre-exposure amount of the light neutralizing element 112a becomes excessively low, the fog removal contrast Vback is increased, and the magnetic carrier (+) of the two-component developer is easily transferred from the developing sleeve 14s to the photosensitive drum 11a. When magnetic carriers having a large particle diameter are mixed in an image, a defective image called a carry image is obtained. Further, since the minority reversal toner (+) carried on the developing sleeve 14s adheres to the white background portion of the image, a fogging image defect is likely to occur.

  That is, the charged potential of the photosensitive drum 11a that has been attenuated by the pre-exposure of the photostatic element 112a is increased by the amount that is not attenuated by the abnormality of the photostatic element 112a. As a result, the fog removal contrast Vback, which is the difference between the charging potential and the DC voltage Vdc, increases on the opposing surface of the developing sleeve 14s and the photosensitive drum 11a. The large fog removal contrast Vback may cause the magnetic carrier to move from the developing sleeve 14 s to the photosensitive drum 11 a, and cause damage to the photosensitive drum 11 a or chipping of the cleaning blade.

  Further, the effect of leveling the surface potential of the photosensitive drum 11a after the primary transfer, which is an important role of the photostatic element 112a, that is, the effect of eliminating the remaining electrostatic image formed in the previous image formation is lost. For this reason, charging is performed in a state where the potential unevenness caused by the electrostatic image formed in the previous image formation is left, and a weak charging unevenness is formed on the charging surface, so that the density unevenness ( (Ghost image) is likely to occur.

  Therefore, in the following embodiment, in order to prevent the occurrence of a carry-on image, a change in the pre-exposure amount of the light neutralizing element 112a is detected by the direct current measuring circuit 106. The DC current flowing from the charging roller 12a to the photosensitive drum 11a is always detected, and the lighting state of the light neutralizing element 112a is estimated from the detected current value, and the abnormal state is detected quickly.

<Example 1>
FIG. 10 is a block diagram of each unit related to the control of the first embodiment, FIG. 11 is a flowchart of the control of the first embodiment, FIG. 12 is a time chart of the normal mode, and FIG.

  As shown in FIG. 11 with reference to FIG. 10, when the image formation is started (S11), the control unit 103 reads the output of the direct current measurement circuit 106 at the timing between images, and the direct current necessary for charging Current is measured (S12).

  The reason for measuring the direct current at the timing between images is that the potential after the primary transfer is stable because of the white background, and that productivity is not lowered.

  That is, since various electrostatic images are written in the previous image formation at the position of the image, the potential when passing through the primary transfer portion is, for example, about −300 V in the white background portion (unexposed portion), The potential of the black image (exposed portion) is about −50V. For this reason, when the direct current is measured at the position of the image, the measurement result is different depending on whether it is a white background or a black image in the previous image formation, and the abnormality of the light neutralizing element 112a is accurately determined. become unable.

  In the first embodiment, the image interval (between sheets) is 30 mm, and the rotational speed of the photosensitive drum 11a is 300 mm / sec. Therefore, the image interval passage time is 100 msec. If it is 100 msec, sampling at intervals of 8 msec can be performed 10 times and sufficient measurement accuracy can be ensured. Therefore, it is not necessary to increase the image interval (paper interval) and reduce productivity in order to measure DC current.

  If the previous imaging conditions at the position where the direct current is measured can be fixed, the above-described error can be avoided even if the direct current is measured at the position of the previous image.

  The control unit 103 calculates a difference ΔIdc by subtracting the measured DC current from the previously measured DC current stored in the memory 202 (S13).

  If the difference ΔIdc is ΔIdc <5 μA (YES in S14), the control unit 103 assumes that there is no abnormality in the light neutralizing element 112a and continues the normal image forming operation (S17).

  However, if ΔIdc ≧ 5 μA (NO in S14), the control unit 103 indicates that the LED lamp of the light discharging element 112a has reached the end of its life or that the light discharging element 112a has become dirty due to sudden toner scattering. Display above. Further, it is determined that a report to the service person is necessary, and a warning requesting service support is transmitted to the service station via the network (S15).

  At this time, if the remaining image forming job is continued with the abnormality of the light neutralizing element 112a left unattended, as described above, the fog removal contrast Vback may increase and a defective image may be output. . However, it is not preferable to wait for the image forming apparatus 100 to return with one image forming job being interrupted.

  Therefore, when the abnormality of the light neutralizing element 112a is determined, for the remaining image forming jobs thereafter, the image interval is greatly expanded, and image formation is executed at every other timing in normal image formation. At this time, the DC voltage applied to the charging roller 12a is temporarily reduced by 50V in order to cancel the increase in the fog removal contrast Vback. Then, at the stage where the image forming job is completed, the image forming apparatus 100 is brought into the standby mode, and the user is made to select whether or not to execute the degenerate mode (S16) through the operation panel 203.

  In the reduction mode (S16), the image forming apparatus 100 is used for the time being even in a state where there is no pre-exposure by causing image formation under reduced image productivity under the precondition that there is no pre-exposure. enable.

  In other words, if image formation is performed while ignoring the photosensitive drum carry or ghost image, the image will develop into a serious image defect. It is desirable to wait for maintenance. However, it is not preferable to prohibit the use of the image forming apparatus 100 when the service person cannot respond immediately after reporting or when the user is in a hurry to output.

  Therefore, even when the control unit 103 determines that the light neutralization element 112a is abnormal, the control unit 103 does not completely stop the image forming operation and can shift to the degeneration mode (S16), and can shift to the degeneration mode. The user is notified (S15).

  When the user attaches importance to output, the control unit 103 immediately shifts to the reduction mode because the shift to the reduction mode is permitted through the operation panel 203 (S16).

  In the operation panel 203, the basic setting is set to allow the transition to the degradation mode, and the transition to the degradation mode is performed unless the user performs an operation to prohibit the transition to the degradation mode (S16). ). This is because the degeneration mode has little effect on image problems and the life of the photosensitive drum except for reducing productivity.

  However, of course, if it can be determined that there are many adverse effects of the transition to the degradation mode, it is possible to set so that the transition to the degradation mode is not performed until the user gives an instruction.

Now, the degeneration mode involves the following change of image forming conditions (S16).
(1) The number of pre-rotations at the start of image formation is increased by one, and the entire exposure is performed by the exposure apparatus. This avoids a drum ghost that is particularly likely to occur in the first image due to the high sensitivity of the photosensitive layer.
(2) The DC voltage of the charging bias is reduced. As a result, the fog removal contrast Vback is returned to a normal value to avoid adhesion of the magnetic carrier to the photosensitive drum and image defects.

  As shown in FIG. 12, if the light neutralizing element 112a is normal, after receiving the image forming job, the light neutralizing element 112a is turned on and five pre-rotations are executed. During the pre-rotation, charging bias and development bias are started, transfer voltage is automatically set, and image formation is started. In the normal mode, the DC voltage of the charging bias is −700 V in anticipation of attenuation due to pre-exposure.

  As shown in FIG. 13, in the degeneration mode, after receiving an image forming job, the light neutralization element 112a is not turned on, and six pre-rotations, which is one more than usual, are executed prior to continuous image formation. . In addition to the normal operation during the pre-rotation, the entire exposure of the photosensitive drum 11a is performed once by the exposure devices 13a, 13b, 13c, and 13d. The DC voltage of the charging bias is −650 V, which is −50 V lower than when there is pre-exposure.

  In the normal mode, -700 V is applied as the DC voltage of the charging bias, while in the degeneration mode, the dark attenuation amount of the photosensitive drum due to the pre-exposure in the normal mode is expected to be 50 V, and the charging potential is- It is lowered to 650V. The power supply D3 is instructed by the control unit 103 to change the charging high voltage setting, and the charging high voltage is set low by the expected amount of attenuation due to pre-exposure.

  That is, when the photosensitive drum 11a starts rotating prior to continuous image formation, in the normal mode, application of the DC voltage of the charging bias is started about 3 to 7 turns from the start of rotation, and the potential of the photosensitive drum 11a is in a stable state. The image formation starts after waiting for the image to be held.

  On the other hand, in the degenerate mode, the pre-rotation time is extended by one turn of the photosensitive drum 11a prior to continuous image formation. Then, for the added pre-rotation, the charging bias is applied and the entire exposure by the exposure device 13a is performed to remove potential unevenness and sensitivity unevenness remaining on the entire surface of the photosensitive drum 11a. Then, by performing overall exposure by the exposure device 13a to remove potential unevenness and sensitivity unevenness, it is possible to suppress the generation of a ghost image even if the residual charge removal effect by the pre-exposure is lost.

  Here, since the exposure amount by the exposure device 13a is smaller than the exposure amount of the light static elimination element 112a without scanning, in order to ensure the necessary neutralization effect, the exposure amount of the exposure device 13a is set to a normal black level. It is desirable to raise it higher than when exposing the image.

  Subsequent continuous image formation and post-rotation operations are performed in exactly the same sequence as in the normal mode in the degenerate mode. For this reason, the demerit when the mode is shifted to the degeneration mode is that the pre-rotation time is increased by one rotation of the photosensitive drum 11a, and the productivity is lost accordingly. Table 1 shows the effect of the degeneration mode.

  Table 1 shows the experimental results of comparing the photosensitive drum potential at the charging position, the fog removal contrast Vback, and the presence / absence of an image defect by changing the DC voltage of the charging bias in a plurality of stages without turning on the light neutralizing element 112a.

  As shown in Table 1, according to the control of the first embodiment, it is possible to accurately detect an abnormal state of pre-exposure with a direct current flowing through the charging roller along with charging and to promptly issue a warning. In addition, it is possible to continue the image forming operation without causing an image defect by the degeneration mode, instead of completely stopping the image forming apparatus even when the pre-exposure is abnormal.

<Example 2>
FIG. 14 is a block diagram of each unit related to the control of the second embodiment, FIG. 15 is a flowchart of the control of the first embodiment, and FIG. 16 is a flowchart of the control for adjusting the pre-exposure amount.

  In Example 1, when the difference ΔIdc between the previous measured value and the current measured value of the direct current accompanying charging became 5 μA or more, it was immediately determined that the photostatic element 112a was abnormal, and the transition to the degenerate mode was promoted. .

  In the second embodiment, when the difference ΔIdc between the previous measured value and the current measured value of the direct current accompanying charging becomes 5 μA or more, the operation of the light neutralizing element 112a is checked for the time being. Encourage transition to degraded mode only when possible. When the function of the light neutralizing element 112a can be recovered, the function is recovered and the normal mode is continued.

  Since the measurement of the direct current accompanying charging in the second embodiment and the control for comparing the measured values to determine the transition to the degenerate mode are the same as in the first embodiment, the steps common to FIG. Common reference numerals are assigned and redundant explanations are omitted.

  As shown in FIG. 14, the element current measuring circuit 209 measures the current flowing through the photostatic element 112a. The pre-exposure amount control circuit 208 controls the current flowing through the light neutralization element 112a to change the exposure output of the light neutralization element 112a.

  As shown in FIG. 15 with reference to FIG. 14, when the image formation is started (S11), the control unit 103 causes the direct current flowing through the charging roller 12a by the direct current measurement circuit 106 at the timing of the previous image interval. Is measured (S12).

  The control unit 103 calculates the difference ΔIdc between the previous measurement value and the current measurement value stored in the memory 202 (S13), and if the difference ΔIdc is less than 5 μA (YES in S14), the normal mode (FIG. 12). The image formation is continued (S17).

  However, if the difference ΔIdc is 5 μA or more (NO in S14), the control unit 103 activates the element current measurement circuit 209 to detect whether or not a current is flowing through the light static elimination element 112a (S21).

  When no current is flowing through the light neutralizing element 112a (NO in S22), the control unit 103 enlarges the image interval to finish the rest of the image forming job, and waits for the image forming apparatus in the degeneracy mode permission waiting state. (S15). Thereafter, the reduction mode is executed with the user's permission (S16).

  On the other hand, when a current is flowing through the light neutralization element 112a (YES in S22), the control unit 103 adjusts the exposure output of the light neutralization element 112a after expanding the image interval and finishing the rest of the image forming job. Is executed (S23).

  The control unit 103 transmits a command for optimizing the pre-exposure amount to the pre-exposure amount control circuit 208, and controls the pre-exposure amount control circuit 208 based on the measurement result by the direct current measurement circuit 106 to thereby control the light neutralization element 112a. The pre-exposure amount is adjusted (S23).

  The control unit 103 also determines whether or not correction up to a necessary pre-exposure amount is possible in accordance with the change in exposure output (S24).

  When it is determined that the pre-exposure amount can be corrected (YES in S24), the control unit 103 executes the pre-exposure amount correction (S25) and permits image formation in the normal mode (FIG. 12) ( S17). However, when it is determined that the pre-exposure amount cannot be corrected (NO in S24), the image forming apparatus is put on standby in a permission mode of the degeneration mode (S15). The change contents of the degeneration mode are the same as those in the first embodiment.

  Here, the control (S23) for adjusting the pre-exposure amount of the light neutralizing element 112a is executed according to the flowchart of FIG.

  As shown in FIG. 16 with reference to FIG. 14, when it is determined that the pre-exposure light amount needs to be changed due to the current flowing through the light neutralization element 112 a (YES in S 22), the control unit 103 determines the pre-exposure amount. The shortage is calculated (S23-1).

  The control unit 103 switches the pre-exposure amount in two stages by the pre-exposure amount control circuit 208, and re-measures the direct current Idc using the direct current measurement circuit 106 at each pre-exposure amount. Regarding the switching of the pre-exposure amount, it is preferable to shift the pre-exposure amount in two steps, that is, a pre-exposure amount that is sufficiently larger than the pre-exposure amount that is normally used and a sufficiently small pre-exposure amount.

In Example 2, the normal pre-exposure amount setting is set before exposure aimed approximately 15μW / inch ^2, pre-exposure of remeasurement switching to two stages, respectively 10 .mu.W / inch ² and 30μW / Inch ² is set. The control unit 103 calculates each constant of the light quantity correction formula 1 using the measurement result of the direct current Idc.
Y = αX + β: Light quantity correction formula 1

  That is, the amount of light before switching to two steps is L1 and L2, and the measured values of the direct current at the respective pre-exposure amounts are Idc1 and Idc2. Constants α and β are calculated by substituting L1, L2, Idc1, and Idc2 into the light amount correction equation 1, respectively.

  Then, the previous light quantity L-det corresponding to the measurement value Idc-int at the time of initialization stored in the memory 202 is calculated by the light quantity correction formula 1 (S23-1). Subsequently, a pre-exposure amount L-det is set in the pre-exposure amount control circuit 208 to cause the light neutralizing element 112a to perform pre-exposure. Then, the direct current measurement circuit 106 measures again the measured value Idc-det of the direct current flowing through the charging roller 12a at the pre-exposed position. Next, a difference ΔIdc-int between the measurement value Idc-int at the time of initialization and the measurement value Idc-det at the pre-exposure amount L-det is calculated (S23-2).

  If the difference ΔIdc-int is less than 5 μA (YES in S24-1), the control unit 103 determines that the pre-exposure amount can be controlled to an appropriate output and sets the pre-exposure amount L-det (S25).

  If the difference ΔIdc-int is 5 μA or more (NO in S24-1), the control unit 103 determines that the pre-exposure amount cannot be corrected by hardware (S24-2), and enters the degeneration mode. Migration is executed (S15).

  According to the control of the second embodiment, it is possible to detect an abnormality in the pre-exposure by measuring the direct current flowing from the charging roller 12a to the photosensitive drum 11a in the abnormal state of the pre-exposure. In the control of the second embodiment, it can also be determined whether or not the pre-exposure abnormality is irreparable, so that the transition to the degenerate mode is suppressed to the limit, and image formation in the normal mode is possible as much as possible. It can be done as long as possible.

  In addition, when the pre-exposure is abnormal, the main body is not stopped, but an image forming operation in the degenerate mode is possible, and the secondary disaster described above can be prevented while preventing the occurrence of abnormal images.

<Example 3>
The degeneration mode is not limited to the procedure and control contents described in the first and second embodiments.

  In the third embodiment, the control for dealing with the abnormality of the light neutralizing element 112a is the same as the first and second embodiments in that the DC voltage output to the charging roller 12a is lowered to return the fog removal contrast Vback to the normal level. is there. However, without waiting for selection by the user, continuous image formation is continued as it is while increasing the image interval and reducing the productivity.

  An image forming apparatus that performs pre-exposure between a transfer unit and a charging member to erase the remainder of the previous electrostatic image.

11a Photosensitive drum 12a Charging roller 13a Exposure device 14a Developing device 15a Cleaning device 35a Primary transfer roller 100 Image forming device 101 DC power source 102 AC power source 103 Control unit 105 Environmental sensor 106 DC current measuring circuit 112a Photostatic device 203 Operation panel 208 Pre-exposure Quantity control circuit 209 Element current measurement circuit 501 Light guide 503 LED lamps D1, D2, D3, D4 Power supply Ta Primary transfer section

Claims (8)

A photoconductor, a developing unit that develops an electrostatic image formed on the surface of the photoconductor into a toner image, and a photostatic element that exposes the surface after the toner image is transferred to a transfer medium to remove static electricity. An image comprising: a charging member in contact with the surface neutralized by the light neutralizing element; and a power source for charging the photosensitive member by applying a charging bias to the charging member to form the electrostatic image. In the forming device,
Current detecting means for detecting a direct current flowing through the photosensitive member by the charging bias;
An image forming apparatus comprising: a warning issuing unit that issues an abnormality of the optical charge removal unit when an abnormality of the photostatic discharge unit is determined based on a decrease in current detected by the current detection unit. .   Control means for enabling control of a degenerate mode for coping with the abnormality of the light static elimination element when the abnormality of the light static elimination element is determined based on a decrease in the current detected by the current detection means The image forming apparatus according to claim 1.   The warning issuing means compares the previous current value detected by the current detecting means at the rotational position of the photoconductor corresponding to the image interval of continuous image formation with the current value, thereby reducing the current. The image forming apparatus according to claim 2, wherein:   4. The image forming apparatus according to claim 2, wherein the control in the degeneration mode includes control for reducing a DC voltage output from the power source to the charging member.   3. The control of the degeneration mode includes a control for adjusting an exposure amount of the photostatic element by increasing an exposure amount of the photostatic element and re-measurement of a current by the current detection unit. 5. The image forming apparatus according to any one of items 4 to 4. An exposure device that exposes the surface of the photoreceptor charged using the charging member to form the electrostatic image;
6. The image according to any one of claims 2 to 5, wherein the control in the degeneration mode includes a control for discharging the surface by exposing the surface using the exposure apparatus prior to the start of continuous image formation. Forming equipment.   3. The control in the degeneration mode includes control for allowing a user to select to perform continuous image formation by reducing productivity in a state in which a warning is displayed and continuous image formation is waited. 7. The image forming apparatus according to any one of claims 6 to 6.   When determining that the current detected by the current detection unit is decreased, the control unit waits for the next continuous image formation after increasing the image interval and ending the rest of the continuous image formation. The image forming apparatus according to claim 7.

Images