JP2010128457A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which the rotation or vibration of a developing roller is not directly transmitted to an image carrier to prevent image irregularity due to the vibration of the image carrier arising from the rotation or vibration of the developing roller and which can correct image density even when a gap distance between the image carrier and the developing roller fluctuates. <P>SOLUTION: In the image forming apparatus 100 including a photoreceptor drum 1, a charger 2, an exposure device 3, and a developing cartridge 4 applying a prescribed developing bias to the developing roller 5 to visualize an electrostatic latent image on the surface of the photoreceptor drum 1 with a developer on the developing roller 5, wherein the developing roller 5 is disposed facing the photoreceptor drum 1 with a prescribed gap to form an image by an electrophotographic system, the image forming apparatus includes an optical sensor 11 detecting the gap distance between the developing roller 5 and the photoreceptor drum 1, and adjusts effective developing potential in response to the magnitude of the gap distance between the developing roller 5 and the photoreceptor drum 1 detected by the optical sensor 11. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an electrophotographic image forming apparatus that supplies toner to an image carrier on which an electrostatic latent image is formed, such as a copying machine, a printer, a facsimile machine, and the like.

  Conventionally, in an electrophotographic image forming apparatus, an electrostatic latent image is formed on the surface of an image carrier, and the electrostatic latent image on the surface of the image carrier is developed with a developer to form a toner image on the surface of the image carrier. Then, the toner image is transferred from the image carrier to the recording paper, and the recording paper is heated and pressurized to fix the toner image on the recording paper. Further, since residual toner and residual charge remain on the surface of the image carrier, the residual toner is removed by a cleaning device, and the residual charge is removed by a static eliminator.

  By the way, as a general developer for developing an electrostatic latent image on an image carrier, there are a one-component developer composed only of toner and a two-component developer composed of a mixture of toner and carrier. Since the one-component developer does not use a carrier, there is an advantage that a stirring mechanism for uniformly mixing the toner and the carrier becomes unnecessary, and the configuration of the developing device is simplified. For this reason, it is often used in small image forming apparatuses.

  In the non-contact developing method using a one-component developer, a thin layer of one-component developer (toner) is formed on the peripheral surface of the developing roller, and this thin layer is separated from the image carrier by a predetermined distance as the developing roller rotates. Then, the toner is conveyed to the opposite development position, a development bias is applied, and the electrostatic latent image on the surface of the image carrier is developed with toner.

  In such an image forming apparatus, when the distance (development gap) between the image carrier and the developing roller varies for each developing cartridge as the developing device, the toner supplied from the developing roller to the image carrier is Since it affects the amount, it is important how to stabilize the image density without being influenced by the change in the distance (development gap) between the image carrier and the developing roller.

  As a conventional technique, as a method of stabilizing the image density, the developing roller is pressed against the image carrier through a distance holding means such as a roller to secure a distance (development gap) between the image carrier and the developing roller. In general, there is disclosed a method for detecting a developing gap between an image carrier and a developing roller secured by a gap holding means such as a roller and correcting the image density according to the detection result (patent) Reference 1).

As another technique, a test patch image formed on an image carrier is detected by an image density sensor, and the image density is corrected by adjusting the amplitude of the DC component and AC component of the developing bias from the detection result. It is disclosed (see Patent Document 2).
JP-A-5-72880 JP 2004-233704 A

  However, in the above-described system in which the developing roller is pressed against the image carrier via a roller in order to keep the image carrier and the developing roller at a predetermined interval, the image carrier which is a part that regulates the development gap due to long-term use. There is a problem that the developing gap changes due to the toner scattered on the contact surface of the body with the roller and the roller itself sticking or the roller itself is worn.

  Furthermore, since the method of stabilizing the image density against this change uses a roller, the rotation and vibration of the developing roller are directly imaged by pressing the developing roller against the image carrier through the roller. This is one of the major causes of vibration of the image carrier transmitted to the carrier. Accordingly, even if the distance between the image carrier and the developing roller is detected and the image density is corrected, there is a problem that image unevenness occurs due to vibration of the image carrier.

  Further, in the conventional method of stabilizing the image density, when a test patch image is detected and the image density is corrected based on the detection result, a number of adjustment steps may be periodically performed for stabilization. is necessary. Therefore, there is a problem that toner is consumed by the test patch formation, and operations not related to the image formation are integrated into the life of the image carrier and the developing cartridge.

  The present invention has been made in view of the above-described conventional problems. Even when the distance between the image carrier and the developing roller varies for each developing cartridge, the developing cartridge is mounted in the image forming apparatus. Another object of the present invention is to provide an image forming apparatus capable of correcting the image density without consuming extra toner.

  The configuration of the image forming apparatus according to the present invention for solving the above problems is as follows.

  The present invention includes an image carrier on which an electrostatic latent image is formed, a charging unit that charges the surface of the image carrier, an exposure unit that exposes the image carrier to form an electrostatic latent image, and a peripheral surface. Development in which a developing roller carrying a developer thin layer is provided, a predetermined developing bias is applied to the developing roller, and the electrostatic latent image on the surface of the image carrier is visualized in a non-contact manner by the developer on the developing roller. In the image forming apparatus for forming an image by electrophotography, the developing roller is made to face the image carrier at a predetermined interval by the developing means, and the interval between the developing roller and the image carrier A distance sensor for detecting a distance is provided, and an effective developing potential is adjusted in accordance with a distance between the developing roller and the image carrier detected by the distance sensor, that is, a so-called developing gap size. Is

  According to the present invention, the developing unit is configured such that the developing roller is disposed at a position facing the image carrier at a predetermined interval by contacting the frame of the image forming apparatus and the frame of the developing unit. It is preferable to do.

  In the present invention, it is preferable to use the developing bias voltage of the developing roller or the exposure amount of the exposing means for adjusting the effective developing potential.

  In the present invention, it is preferable that the image carrier is formed of a transparent member, and the distance sensor is disposed on the back side of the peripheral surface of the image carrier facing the developing roller.

  In the present invention, it is preferable to use a one-component developer as the developer.

  According to the present invention, an image carrier on which an electrostatic latent image is formed, a charging unit that charges the surface of the image carrier, an exposure unit that exposes the image carrier to form an electrostatic latent image, and a peripheral unit. Provided with a developing roller carrying a thin developer layer on the surface, a predetermined developing bias is applied to the developing roller, and the electrostatic latent image on the surface of the image carrier is visualized in a non-contact manner by the developer on the developing roller. An image forming apparatus that forms an image by an electrophotographic method with a developing unit (e.g., a developing cartridge) configured to cause the developing roller to face the image carrier at a predetermined interval by the developing unit. A distance sensor for detecting a distance between the roller and the image carrier, and an effective developing potential is set according to a distance between the developing roller and the image carrier detected by the distance sensor, that is, a so-called development gap. For example, even when the developing gap varies when the developing cartridge is mounted in the image forming apparatus, the developing cartridge or the like can be developed by correcting the image density without consuming excessive toner. It is possible to provide an image forming apparatus capable of realizing stable image output while suppressing variations in image density for each unit.

  According to the invention, the developing unit is configured such that the developing roller is opposed to the image carrier at a predetermined interval by contacting the frame of the image forming apparatus and the frame of the developing unit. With this arrangement, when the image forming operation is executed, the development gap does not change due to the ingress of scattered toner even during long-term use, and the rotation and vibration of the developing roller are directly transmitted to the image carrier. Therefore, image unevenness due to the vibration of the image carrier caused by the rotation and vibration of the developing roller can be prevented.

  Further, according to the present invention, the developing bias voltage of the developing roller or the exposure amount of the exposure unit is used to adjust the effective development potential, so that the image density is corrected and each development unit such as a development cartridge is adjusted. Thus, it is possible to provide an image forming apparatus capable of realizing stable image output while suppressing variations in image density.

  According to the invention, the image carrier is formed of a transparent member, and the distance sensor is disposed on the back side of the peripheral surface of the image carrier that faces the developing roller. Since it is not necessary to provide a space for installing the distance sensor around the carrier, it is possible to save the space of the image forming apparatus.

  According to the present invention, the use of a one-component developer as the developer eliminates the need for an agitation mechanism for agitating the developer and simplifies the configuration of the developing device, thereby reducing the size of the image forming apparatus. be able to.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best embodiment of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is an explanatory diagram showing the configuration of the image forming unit of the image forming apparatus according to the first embodiment of the present invention.

  In the first embodiment, as shown in FIG. 1, a photosensitive drum (image carrier) 1 on which an electrostatic latent image is formed, a charger (charging means) 2 for charging the surface of the photosensitive drum 1, a photosensitive drum An exposure device (exposure means) 3 that exposes the body drum 1 to form an electrostatic latent image and a developing roller 5 that carries a thin developer layer on its peripheral surface, and a predetermined developing bias is applied to the developing roller 5. And a developing cartridge (developing means) 4 for visualizing the electrostatic latent image on the surface of the photosensitive drum 1 in a non-contact manner with the developer on the developing roller 5. The developing roller 5 is moved by the developing cartridge 4 to the photosensitive drum 1. In an image forming apparatus 100 that forms an image by an electrophotographic method so as to face each other at a predetermined interval, an optical sensor (distance sensor) 11 that detects a distance between the developing roller 5 and the photosensitive drum 1 is provided. By sensor 11 Depending on the size of the gap distance of the developing roller 5 and the photosensitive drum 1 that issued, it is characterized in adjusting the effective development potential.

  The photoconductive drum 1 is provided with a surface layer of a photoconductive material on the outer periphery of a conductive substrate, and the conductive substrate is grounded and is configured to rotate in the direction of arrow A in FIG. The surface of the photosensitive drum 1 is uniformly charged by a charger 2.

  The exposure device 3 forms an electrostatic latent image on the surface of the photosensitive drum 1 by irradiating a beam of light such as laser light or LED light based on the input image signal.

  In the developing cartridge 4, the developing roller 5 is arranged to face the photosensitive drum 1 at a predetermined interval. The developing cartridge 4 contains toner as a one-component developer. The toner accommodated in the developing cartridge 4 is formed as a thin toner layer on the peripheral surface of the developing roller 5, is carried by the developing roller 5, and is a direction along the rotation direction of the opposing photosensitive drum 1. It is rotated and conveyed in the direction of arrow B.

  At the position of the photosensitive drum 1 facing the developing roller 5, the electrostatic latent image on the surface of the photosensitive drum 1 is developed in a non-contact manner with the toner supplied by the developing roller 5 and visualized as a toner image. The toner image is transferred to the recording paper 10 by the transfer roller 6, and then is transferred to the fixing device 7 and is heated and melted to be fixed on the recording paper 10.

  The toner remaining on the surface of the photosensitive drum 1 without being transferred to the recording paper 10 after the transfer from the photosensitive drum 1 to the recording paper 10 is removed and collected by the cleaner device 9. Thereafter, the charge remaining on the surface of the photosensitive drum 1 is uniformly discharged by the charge removing lamp 8. In this way, a series of image forming processes is completed.

  Here, the developing cartridge 4 according to the present embodiment will be described in detail with reference to the drawings. FIG. 2 is an explanatory diagram showing the configuration of the developing cartridge constituting the image forming apparatus of the present embodiment.

  As shown in FIG. 2, the developing cartridge 4 contains toner as a one-component developer. The toner is conveyed to the vicinity of the toner supply roller 20 while being agitated by the rotation of the toner conveying member 21 disposed inside the developing cartridge 4, and is conveyed toward the developing roller 5 by the toner supply roller 20. ing.

  Specifically, the developing cartridge 4 has an opening 4 a at a portion facing the photosensitive drum 1. Inside the developing cartridge 4, the developing roller 5 is disposed in parallel to the photosensitive drum 1 in a state of facing the photosensitive drum 1 in the opening 4 a. A toner supply roller 20 is disposed in parallel with the developing roller 5 in contact with the developing roller 5. Further, a toner conveying member 21 is arranged substantially horizontally adjacent to the toner supply roller 20.

  A toner layer regulating member 19 for regulating the layer thickness of the developer (toner) adhering to the surface of the developing roller 5 is disposed on the outer peripheral portion of the developing roller 5.

  The toner supply roller 20 is configured to rotate in the same rotational direction (arrow C direction) as the developing roller 5 while being in pressure contact with the developing roller 5. In other words, at the portion where the toner supply roller 20 and the developing roller 5 face each other, the rollers are rotated so that the moving directions of the roller surfaces are opposite to each other. The toner conveying member 21 is configured to rotate in a direction (arrow D direction) opposite to the rotation direction of the toner supply roller 20.

  In addition, a voltage is applied to the toner supply roller 20 from a bias power source (not shown), and the voltage is a direction in which the toner is electrically pushed toward the developing roller 5, for example, a negative polarity toner. A large bias voltage is applied to the side.

  The toner that is frictionally charged by the toner supply roller 20 and is supplied to the developing roller 5 by the bias voltage is conveyed to a position where the toner layer regulating member 19 contacts by the rotation operation of the developing roller 5. The toner carried on the developing roller 5 is regulated to a predetermined charge amount and thickness by a toner layer regulating member 19 and then is opposed to the developing region (the photosensitive drum 1 on which the electrostatic latent image is formed). To the development step.

  Undeveloped toner on the developing roller 5 that has not been used in the developing process is returned to the developing cartridge 4 by the rotation of the developing roller 5. At this time, the uncharged toner is charged with the remaining developer toner on the developing roller 5 by the charge neutralizing member 22 installed in front of the toner supply roller 20, and the toner supply roller 20 and the developing roller 5 are pressed against each other. It is peeled off and collected. Then, the toner is again agitated and conveyed by the toner supply roller 20 and the toner conveying member 21 and reused.

  The photosensitive drum 1 is conveyed at a peripheral speed Va (for example, 117 mm / s) in a direction indicated by an arrow in FIG. 1 with a translucent conductive substrate grounded and a surface potential charged to, for example, −700 V.

  The developing roller 5 is composed of a conductive elastic roller made of conductive urethane rubber to which a conductive agent such as carbon black is added on the surface of a cylindrical member of φ12, or a cylindrical roller made of an aluminum material. It rotates in the B direction at a peripheral speed Vb (for example, 225 mm / s). A voltage of E1 (for example, −600 V) is applied to the developing roller 5 by a developing bias power source through a shaft of a conductive support (stainless steel, conductive resin, etc.) (not shown).

  The toner supply roller 20 is made of urethane foam that serves as both toner agitation and toner removal after development, and rotates in the direction of arrow C at a peripheral speed Vc (eg, 133 mm / s). A voltage of E2 (for example, −650 V) is applied to the toner supply roller 20 by a supply bias power source via a shaft of a conductive support (not shown) such as stainless steel or conductive resin.

  The non-magnetic one-component toner that has been negatively precharged by the toner supply roller 20 and has moved to the surface of the developing roller 5 is conveyed to a position where the toner layer regulating member 19 contacts with the rotation of the developing roller 5.

  The toner layer regulating member 19 is a conductive (stainless steel, phosphor bronze, conductive resin, etc.) plate member having a thickness of 0.1 mm, and is in contact with the developing roller 5 at a linear pressure of 15 to 30 gf / cm. A voltage of E3 (for example, −650 V) is applied to the toner layer regulating member 19 by a bias power source (not shown).

  The toner layer on the developing roller 5 is developed to face the photosensitive drum 1 in a non-contact manner by rotating the developing roller 5 after the toner adhesion amount and the toner charge amount are regulated to a predetermined amount by the toner layer regulating member 19. It is transported to the area and has a mechanism for flying and developing the toner.

Here, the developer used in this embodiment will be described.
The developer used in the developing cartridge 4 is a non-magnetic one-component toner which is a one-component developer, and is a fine particle toner whose average volume particle diameter is classified to 7 to 10 μm.

  As a method for producing such fine particles, a so-called pulverization method is generally used in which a resin, a colorant or the like is melt-kneaded and then pulverized and classified. In addition, a toner manufacturing method called a wet method has been proposed. In this wet method, a monomer (monomer) in which a colorant or an additive is dispersed in an aqueous medium in the presence of a dispersion stabilizer. There are a suspension polymerization method, an emulsion polymerization method, a phase inversion emulsification method and the like for polymerization.

  In addition, the binder resin material used for the toner is, for example, selected from the group of styrene resin, vinyl chloride resin, phenol resin, epoxy resin, polyester resin, polyether polyol resin, polyurethane resin, or polyvinyl butyral resin. Species or two or more may be used.

  The binder resin material may be one in which crystalline waxes or incompatible substances are finely dispersed in advance from the synthesis stage. However, among the binder resin materials described above, the polyester resin or the polyether polyol resin is excellent in thermal properties such as resin elasticity, and therefore it is desirable to use them for the binder resin material.

  The colorant used in the toner is not particularly limited as long as it is a variety of dyes and pigments that have been used as toner materials so far, and is organic or inorganic as shown below. Various dyes and pigments can be used. That is, examples of the black colorant include carbon black, copper oxide, manganese dioxide, aniline black, activated carbon, nonmagnetic ferrite, magnetic ferrite, and magnetite.

  In the toner for developing the electrostatic latent image, components such as magnetic powder such as magnetite, hematite or various ferrites, an anti-offset agent, or a charge control agent can be blended as necessary in addition to the above materials.

  The offset preventive agent used for the purpose of improving the fixing property of the toner is not particularly limited as long as it has been used as a toner material so far, and the following can be used. For example, petroleum wax such as paraffin wax, oxidized paraffin wax or microcrystalline wax, mineral wax such as montan wax, animal and plant wax such as beeswax or carnauba wax, or polyolefin wax (polyethylene or And synthetic waxes such as oxidized polyolefin wax or Fischer-Tropsch wax. These offset inhibitors may be used alone or in combination of two or more.

  As the charge control agent, various substances from low molecular compounds to high molecular compounds can be used. For example, a quaternary ammonium salt compound, a nigrosine compound, an organometallic complex, a chelate compound, and a monomer having an amino group are homopolymerized. Alternatively, copolymerized polymer compounds and the like can be mentioned. In addition, inorganic fine powders such as silica fine powder and titanium oxide fine powder are suitably used as the external additive or fluidizing agent added for the purpose of charge adjustment and surface resistance adjustment. These inorganic fine powders are made of silicone varnish, various modified silicone varnishes, silicone oil, various modified silicone oils, silane coupling agents, silane coupling agents having functional groups, and other organosilicons for hydrophobicity and chargeability control. It may be treated with a treating agent such as a compound. Moreover, 1 type, or 2 or more types chosen from the processing agent mentioned above may be used.

Next, a characteristic configuration of the image forming apparatus 100 of the present embodiment will be described with reference to the drawings.
FIG. 3 is a plan view showing an installed state of the photosensitive drum and the developing cartridge constituting the image forming apparatus of the present embodiment, and FIG. 4 shows an installed state of a distance sensor for detecting the installed state of the photosensitive drum and the developing cartridge. It is explanatory drawing shown.

  As shown in FIG. 3, the photosensitive drum 1 is positioned on the frame 12 of the image forming apparatus 100 by the rotation shaft 18 of the photosensitive drum 1. Further, when the developing cartridge 4 is attached to the image forming apparatus 100, the frame 12 of the image forming apparatus 100 and the frame 41 of the developing cartridge 4 are in contact with each other at the contact portion 12a without any gap, so that the developing roller 5 and the photosensitive roller 4 are photosensitive. An interval distance (hereinafter referred to as “development gap”) G of the body drum 1 is maintained at a predetermined interval.

  In the non-contact developing method in which the photosensitive drum 1 on which the electrostatic latent image is formed and the developing roller 5 for developing the electrostatic latent image by attaching toner to the electrostatic latent image are arranged at a predetermined distance, the photosensitive drum 1 Due to the electric field strength between the developing roller 5 and the developing roller 5, the force that causes the toner to fly from the developing roller 5 changes, and the developed density changes. This electric field strength is determined by the potential difference between the photosensitive drum 1 and the developing roller 5 and the developing gap G.

  That is, when the potential difference between the photosensitive drum 1 and the developing roller 5 is constant, if the developing gap G increases, the electric field strength decreases and the developing amount of toner to be developed decreases. On the other hand, if the development gap G is small, the electric field strength increases, and the development amount of the developed toner increases.

  Between the photosensitive drum 1 and the developing roller 5, an optical sensor 11 for detecting the distance of the developing gap G is disposed. As shown in FIG. 4, the optical sensor 11 includes a light emitting unit 11a and a light receiving unit 11b. The light emitting unit 11 a and the light receiving unit 11 b are arranged to face each other so as to sandwich the developing gap G in a direction perpendicular to the developing gap G between the photosensitive drum 1 and the developing roller 5.

  When the developing cartridge 4 is newly replaced or is removed from the image forming apparatus 100 and reattached for maintenance, the photosensitive drum 1 and the developing roller 5 are stopped prior to image formation. Then, the development gap G in the center in the longitudinal direction (axial direction) of the photosensitive drum 1 is detected.

Here, detection of the development gap G in the image forming apparatus 100 will be described with reference to the drawings.
FIG. 5 is a block diagram showing an electrical configuration for detecting the development gap in the image forming apparatus of this embodiment, and FIG. 6 is a graph showing the relationship between the value of the development gap and the value of the development bias.

  In the image forming apparatus 100, as shown in FIG. 5, the received light amount development gap conversion that converts the received light amount received by the optical sensor 11 and the light receiving unit 11b of the optical sensor 11 into a developing gap G (interval distance). A processing unit 13, a developing bias calculator 14 that determines a developing bias voltage value according to the developing gap G, and a developing bias control that controls the developing roller 5 to apply the developing bias voltage determined by the developing bias calculator 14 to the developing roller 5. Part 15 is provided.

  When detecting the developing gap G between the photosensitive drum 1 and the developing roller 5, as shown in FIG. 4, light is emitted from the light emitting portion 11 a of the optical sensor 11 toward the developing gap G, and the developing gap G is set. The light that has passed is received by the light receiving portion 11 b of the optical sensor 11.

  Then, as shown in FIG. 5, the amount of light passing through the light receiving unit 11 b of the optical sensor 11 is converted into a development gap G by the received light amount development gap conversion processing unit 13. With respect to the converted value of the development gap G, the development bias voltage value is set so that the image density set in advance in the development bias calculator 14 becomes an appropriate value (for example, optical density ID = 1.4). And the development bias voltage determined by the development bias controller 15 is controlled to be applied.

  As shown in FIG. 6, the development bias is determined based on the relationship between the development gap G and the development bias, and the development bias control unit 15 controls to apply the determined development bias voltage.

  For example, when the development gap is 150 μm, the development bias is corrected to −450 V, when the development gap is 200 μm, it is corrected to −600 V, and when the development gap is 250 μm, it is corrected to −750 V. An image forming operation is performed with the corrected correction developing bias.

  It should be noted that the light emitting portion 11a and the light receiving portion 11b are directed to the distance between the peripheral surface of the non-image area portion not carrying toner and the photosensitive drum 1, that is, toward the developing gap G, at both ends of the developing roller 5. It may be arranged on one side or both sides of the end, and the development gap G may be detected as described above during the rotation before image formation prior to image formation.

Next, the relationship between the development gap G and the image density will be described with reference to a graph.
FIG. 7 is a graph showing the relationship between the developing gap G and the image density when the DC bias voltage applied to the developing roller in the image forming apparatus of this embodiment is changed.

  As shown in FIG. 7, the image density tends to decrease as the development gap G increases. In the same development gap, the image density increases as the DC development bias increases.

  For this reason, according to the detected value of the development gap G, if the development gap G is large on the basis of the data set in advance in the development bias calculation unit 14, the development bias is corrected in the direction of increasing the development gap. When G is small, the developing bias is corrected to be lowered, and the developing bias controller 15 controls the developing bias applied at the time of image formation.

  In the present exemplary embodiment, the image forming apparatus 100 uses a developing method in which a DC developing bias voltage is applied to the developing bias, but the developing method applies a DC bias and an AC bias to the developing bias in a superimposed manner. Also good. In this case, the image density is corrected by adjusting the DC bias voltage and the frequency of the AC bias voltage according to the size of the developing gap G to be detected.

  As described above, according to the first embodiment, the optical sensor 11 that detects the distance between the photosensitive drum 1 and the developing roller 5, that is, the developing gap G, is provided, and the received light amount developing gap conversion process is performed. Since the effective development potential is adjusted according to the development gap G by the development unit 13, the development bias calculation unit 14, and the development bias control unit 15, even if the development gap G varies from one device to another, the image forming apparatus performs development. When the cartridge is mounted, by creating a toner patch, the image density can be corrected without excessive consumption of toner, and variations in image density can be suppressed.

  Further, according to the present embodiment, when the developing cartridge 4 is mounted on the image forming apparatus 100, the frame 12 of the image forming apparatus 100 and the frame 41 of the developing cartridge 4 abut on the abutting portion 12a without any gap. Thus, when the image forming operation is performed, the development gap G does not change due to the ingress of scattered toner even during long-term use, and the rotation and vibration of the developing roller 5 are directly transmitted to the photosensitive drum 1. The image unevenness due to the vibration of the photosensitive drum 1 due to the rotation and vibration of the developing roller 5 can be prevented.

(Second Embodiment)
Next, a second embodiment according to the present invention will be described with reference to the drawings.
FIG. 8 is a graph showing the relationship between the exposure amount and the photosensitive drum surface potential of the image forming apparatus according to the second embodiment of the present invention, and FIG. 9 shows the electrical configuration for detecting the development gap in the image forming apparatus. FIG. 10 is a graph showing the relationship between the development gap value and the exposure value.

  In the second embodiment, in the image forming apparatus 100 according to the first embodiment, the photosensitive member uniformly charged by the charger 2 by changing the exposure amount irradiated from the exposure device 3 to the photosensitive drum 1. The surface potential of the exposed portion of the drum 1 is changed as shown in FIG.

  That is, if the exposure amount from the exposure device 3 is increased, the amount of decrease in the surface potential of the photosensitive drum 1 is increased. Conversely, if the exposure amount from the exposure device 3 is decreased, the surface potential of the photosensitive drum 1 is increased. Reduce the amount of decrease. Thereby, even when the developing gap G varies from device to device, the electric field strength between the photosensitive drum 1 and the developing roller 5 can be made constant.

  When the developing cartridge 4 is newly replaced or when it is once removed from the image forming apparatus 100 and reattached for maintenance, as in the first embodiment, as shown in FIG. 9 to detect the developing gap G, and as shown in FIG. 9, the received light amount received by the light receiving unit 11b of the optical sensor 11 is converted into the developing gap G by the received light amount developing gap conversion processing unit 13. With respect to the converted value of the development gap G, the exposure amount is determined so that the image density preset in the exposure amount calculation unit 16 becomes an appropriate value (for example, optical density ID = 1.4). Then, the exposure amount control unit 17 performs control so that exposure is performed with the exposure amount determined.

  As shown in FIG. 10, the exposure amount is determined from the relationship between the development gap G and the exposure amount. In the exposure amount control unit 17, the voltage or current for supplying the determined exposure amount to the laser or LED of the exposure apparatus 3 is determined. By controlling, the exposure amount at the time of image formation is controlled.

  For example, when the development gap is 150 μm, the exposure amount is corrected to 0.2 μJ / cm 2, when the development gap is 200 μm, it is corrected to 0.3 μJ / cm 2, and when the development gap is 250 μm, the exposure amount is corrected. Correct to 0.4 μJ / cm 2. An image forming operation is performed with the corrected exposure amount.

  It should be noted that the light emitting portion 11a and the light receiving portion 11b are directed to the distance between the peripheral surface of the non-image area portion not carrying toner and the photosensitive drum 1, that is, toward the developing gap G, at both ends of the developing roller 5. It may be arranged on one side or both sides of the end, and the development gap G may be detected as described above during the rotation before image formation prior to image formation.

  Since it is configured as described above, according to the second embodiment, the optical sensor 11 that detects the distance between the photosensitive drum 1 and the developing roller 5, that is, the developing gap G, is provided, and the received light amount developing gap converting process is performed. Since the exposure amount is adjusted according to the development gap G by the unit 13, the exposure amount calculation unit 16, and the exposure amount control unit 17, even when the development gap G varies from device to device, the image forming apparatus includes a developing cartridge. When the toner image is mounted, by creating a toner patch, the image density can be corrected without excessive consumption of toner, and variations in image density can be suppressed.

(Third embodiment)
Next, a third embodiment according to the present invention will be described with reference to the drawings.
FIG. 11 is an explanatory diagram showing the configuration of the image forming unit of the image forming apparatus according to the third embodiment of the present invention, and FIG. 12 is a distance for detecting the installation state of the photosensitive drum and the developing cartridge constituting the image forming apparatus. FIG. 13 is a block diagram showing an electrical configuration for detecting a development gap in the image forming apparatus.

  In the third embodiment, as shown in FIGS. 11 and 12, in the image forming apparatus 300, instead of the photosensitive drum 1 and the optical sensor 11 according to the first embodiment, the photosensitive drum 301 is made of a transparent member. The laser sensor (distance sensor) 312 is provided inside the photosensitive drum 301.

  Note that the image forming apparatus 300 according to the third embodiment has the same basic configuration and functions as those of the image forming apparatus 100 according to the first embodiment, and those having the same configurations and functions are denoted by the same reference numerals. Thus, the description is omitted.

  The photosensitive drum 301 is made of a transparent material, and a transparent electrode layer made of a transparent conductive material is formed on the outer surface of the transparent substrate as an electrode layer. The transport layers are sequentially stacked.

  As a material for the light-transmitting substrate, a polymer compound having a light-transmitting property such as acrylic resin, methacrylic resin, and polycarbonate can be widely used.

  The material of the translucent electrode layer may be a vapor-deposited thin film of metal such as copper, brass, silver, gold, aluminum or palladium, a vapor-deposited film of ITO (In, Sn compound), or a transparent conductive fine powder such as ITO. A coating layer of a transparent resin binder dispersion can be used.

  As the charge generation material in the charge generation layer, organic pigments such as phthalocyanine, azo compound, quinacridone, polycyclic quinone, and perylene, and organic dyes such as thiapyrylium salt and squarylium salt are used.

  In the charge generation layer, an electron accepting material as a chemical sensitizer, for example, cyano compounds such as tetracyanoethylene, 7,7,8,8-tetracyanoquinodimethane, quinones such as anthraquinone and p-benzoquinone, Nitro compounds such as 2,4,7-trinitrofluorenone and 2,4,5,7-tetranitrofluorenone, or dyes such as xanthene dyes, thiazine dyes and triphenylmethane dyes as optical sensitizers. It may be added.

  As the binder resin, polyarylate, polyvinyl butyral, polycarbonate, polyester, polystyrene, polymethyl methacrylate, polyvinyl chloride, phenoxy, epoxy, silicone resin and the like are used. The thickness of the charge generation layer is 0.05 to 5 μm, preferably 0.08 to 1 μm.

  As the charge transport material in the charge transport layer, polymer compounds such as polyvinyl carbazole and polysilane, hydrazone compounds, pyrazoline compounds, oxadiazole compounds, stilbene compounds, triphenylmethane compounds, triphenylamine compounds, enamine compounds, etc. Molecular compounds are used.

  As the binder resin, polyarylate, polyvinyl butyral, polycarbonate, polyester, polystyrene, polymethyl methacrylate, polyvinyl chloride, phenoxy, epoxy, silicone resin and the like are used. The thickness of the charge transport layer is 5 to 50 μm, preferably 10 to 40 μm.

An antioxidant may be added as an additive to the charge generation layer or the charge transport layer.
As the antioxidant, vitamin E, hydroquinone, hindered amine, hindered phenol, paraphenylenediamine, arylalkane and derivatives thereof, organic sulfur compounds, organic phosphorus compounds, and the like are used.

  As shown in FIG. 12, the laser sensor 312 is disposed on the back surface side of the peripheral surface of the photosensitive drum 301 facing the developing roller 5. Specifically, the laser-type sensor 312 is a reflection-type sensor that receives reflected light of light emitted from the light-emitting unit at the light-receiving unit, and has the light-emitting unit and the light-receiving unit on the same surface and faces the developing roller 5. Are arranged to be.

  When the developing cartridge 4 is newly replaced or when it is once removed from the image forming apparatus 300 and reattached for maintenance, the photosensitive drum 301 and the developing roller 5 are stopped prior to image formation. Then, the development gap G in the center in the longitudinal direction (axial direction) of the photosensitive drum 301 is detected.

  Here, detection of the development gap G in the image forming apparatus 300 will be described with reference to the drawings.

  As shown in FIG. 13, the image forming apparatus 300 includes a laser sensor 312 that detects the development gap G, a development bias calculation unit 14 that determines a development bias voltage value according to the development gap G, and a development bias calculation unit. A developing bias control unit 15 that controls the developing bias voltage determined by 14 to be applied to the developing roller 5 is provided.

  When detecting the developing gap G between the photosensitive drum 301 and the developing roller 5, as shown in FIG. 12, the light emitting part of the laser sensor 312 transmits the transparent image carrier and irradiates the developing roller 5 with light. Then, the light reflected by the developing roller 5 is received by a light position detecting element disposed in the light receiving portion of the laser type sensor 12, and the developing gap G is detected.

  For the detected value of the development gap G, the development bias voltage value is determined from the relationship between the development gap value and the image density set in advance in the development bias calculation unit 14, and is determined in the development bias control unit 15. The image forming operation is performed with the developed bias voltage.

  The laser sensor 312 is disposed at one end or both sides of the developing roller 5 at one end or both sides of the developing roller 5 so as to face the roller peripheral surface of the non-image area portion that does not carry toner, before image formation. The detection of the development gap G may be performed as described above during the rotation operation.

  As another modified example, as shown in FIG. 14, instead of correcting the development bias, the exposure amount preset in the exposure amount calculation unit 16 with respect to the detected value of the development gap G is used. The exposure amount control unit 17 determines the exposure amount at the time of image formation by controlling the voltage and current supplied to the laser or LED of the exposure device 3 in the exposure amount control unit 17.

  The laser sensor 312 is disposed at one end or both sides of the developing roller 5 at one end or both sides of the developing roller 5 so as to face the roller peripheral surface of the non-image area portion that does not carry toner, before image formation. The detection of the development gap G may be performed as described above during the rotation operation.

  Since configured as described above, according to the third embodiment, in the image forming apparatus 300, instead of the photosensitive drum 1 and the optical sensor 11 according to the first embodiment, a photosensitive drum configured by a transparent member. 301 and a laser-type sensor 312 provided inside the photosensitive drum 301, and the effective developing potential is adjusted according to the developing gap G by the developing bias calculation unit 14 and the developing bias control unit 15, so that each device is different. Even when the development gap G varies, it is possible to correct the image density without consuming excessive toner by creating a toner patch when the development cartridge is mounted in the image forming apparatus. Variations can be suppressed.

  In addition, according to the present embodiment, by arranging the laser sensor 312 on the back surface side of the photosensitive drum 301, it is possible to save the space of the image forming apparatus 300.

Here, a conventional image forming apparatus will be specifically described as a comparative example of the above-described embodiment of the present invention.
In the conventional image forming apparatus 400, as shown in FIG. 15, a roller 423 having an outer diameter larger than that of the developing roller 5 is attached to both ends of the developing roller 5 so that the developing gap 5 is attached to the photosensitive drum 1 via the roller 423. The development gap G is held at a predetermined interval (for example, 200 μm). Since the photosensitive drum 1 and the developing cartridge 404 are in contact with each other via the roller 423, vibration generated when the developing roller 5 rotates is directly transmitted to the photosensitive drum 1, and image defects such as banding occur.

  Further, the scattered toner enters between the photosensitive drum 1 and the roller 423 by using for a long time, and is fixed to the surface of the photosensitive drum 1 or the surface of the roller 423. Due to the fixing toner, the development gap G is enlarged by about 50 to 100 μm from the initial value, and the image density is reduced by 0.2 to 0.4.

  On the other hand, in the embodiment according to the present invention described above, as shown in FIG. 3, the developing roller 5 and the photosensitive member are brought into contact with each other without the gap between the frame 12 of the image forming apparatus 100 and the frame 41 of the developing cartridge 4. The distance between the drums 1, that is, the development gap G is maintained at a predetermined distance.

  Accordingly, when the image forming operation is executed, the contact portion 12a that holds the development gap G at a predetermined interval is in contact with the frame 41 of the developing cartridge 4 without any gap, and development due to intrusion of scattered toner even during long-term use. Does not cause gap changes.

  Further, since the developing cartridge 4 and the photosensitive drum 1 are not in direct contact with each other, the rotation and vibration of the developing roller 5 are not directly transmitted to the photosensitive drum 1 and are caused by the rotation and vibration of the developing roller 5. Image unevenness due to vibration of the photosensitive drum 1 can be prevented.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. Embodiments obtained by appropriately combining the disclosed technical means are also included in the technical scope of the present invention.

  For example, in the above-described embodiment, the present invention is applied to a color image forming apparatus (multifunction machine, printer, etc.), but before transferring a toner image transferred to an intermediate transfer member (intermediate transfer belt). The present invention can also be applied to a monochrome image forming apparatus provided with a charging unit.

FIG. 2 is an explanatory diagram illustrating a configuration of an image forming unit of the image forming apparatus according to the first embodiment of the present invention. FIG. 3 is an explanatory diagram illustrating a configuration of a developing cartridge that constitutes the image forming apparatus according to the exemplary embodiment. FIG. 2 is a plan view showing an installed state of a photosensitive drum and a developing cartridge constituting the image forming apparatus. It is explanatory drawing which shows the installation state of the distance sensor which detects the installation state of the said photoreceptor drum and a developing cartridge. FIG. 2 is a block diagram illustrating an electrical configuration for detecting a development gap in the image forming apparatus. It is a graph which shows the relationship between the value of the said development gap, and the value of development bias. 3 is a graph showing a relationship between a developing gap G and an image density when a DC bias voltage applied to a developing roller in the image forming apparatus is changed. 6 is a graph showing a relationship between an exposure amount and a photosensitive drum surface potential of an image forming apparatus according to a second embodiment of the present invention. FIG. 2 is a block diagram illustrating an electrical configuration for detecting a development gap in the image forming apparatus. It is a graph which shows the relationship between the value of the said development gap, and the value of exposure amount. It is explanatory drawing which shows the structure of the image formation part of the image forming apparatus which concerns on 3rd Embodiment of this invention. FIG. 3 is an explanatory diagram illustrating an installation state of a distance sensor that detects an installation state of a photosensitive drum and a developing cartridge that constitute the image forming apparatus. FIG. 2 is a block diagram illustrating an electrical configuration for detecting a development gap in the image forming apparatus. FIG. 10 is a block diagram illustrating an electrical configuration for detecting a development gap as a modification of the third embodiment. It is explanatory drawing which shows the structure of the image forming part of the conventional image forming apparatus.

Explanation of symbols

1,301 Photosensitive drum (image carrier)
2 Charger (charging means)
3 Exposure equipment (exposure means)
4 Developer cartridge (Developer)
5 Developing roller 11 Optical sensor (distance sensor)
11a Light emitting unit 11b Light receiving unit 12 Frame 12a Abutting unit 13 Light reception amount development gap conversion processing unit 14 Development bias calculation unit 15 Development bias control unit 16 Exposure amount calculation unit 17 Exposure amount control unit 41 Frame 100, 300 Image forming apparatus 312 Laser Type sensor (distance sensor)
G Development gap

Claims (5)

An image carrier on which an electrostatic latent image is formed, a charging unit that charges the surface of the image carrier, an exposure unit that exposes the image carrier to form an electrostatic latent image, and a thin developer layer on the peripheral surface And a developing means for applying a predetermined developing bias to the developing roller and visualizing the electrostatic latent image on the surface of the image carrier in a non-contact manner with a developer on the developing roller. ,
In the image forming apparatus for forming an image by an electrophotographic method by causing the developing unit to face the image carrier at a predetermined interval by the developing unit,
A distance sensor for detecting a distance between the developing roller and the image carrier;
An image forming apparatus, wherein an effective developing potential is adjusted in accordance with a distance distance between the developing roller and the image carrier detected by the distance sensor.   2. The developing device according to claim 1, wherein the developing roller is disposed at a position facing the image carrier at a predetermined interval by contacting a frame of the image forming apparatus and a frame of the developing device. The image forming apparatus according to 1.   The image forming apparatus according to claim 1, wherein a developing bias voltage of the developing roller or an exposure amount of the exposure unit is used for adjusting the effective developing potential. The image carrier is composed of a transparent member,
4. The image forming apparatus according to claim 1, wherein the distance sensor is disposed on a back surface side of a peripheral surface of the image bearing member facing the developing roller. 5.   The image forming apparatus according to claim 1, wherein a single-component developer is used as the developer.

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