JP5847760B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method for forming an image by electrophotography.

  In an electrophotographic image forming apparatus such as a printer or a copying machine, a charging process for uniformly charging a photosensitive drum, an exposure process for forming an electrostatic latent image by exposing the charged photosensitive drum, an electrostatic latent The image is developed through a series of processes including a development process for forming a visible image by attaching toner to the image, a transfer process for transferring the visible image to paper, and a fixing process for fusing and fixing the visible image transferred to the paper. Form.

  In this type of image forming apparatus, a developing roller for developing the electrostatic latent image is disposed opposite to the image bearing surface of the photosensitive drum on which the electrostatic latent image is formed. A toner as a developer is carried on the surface of the developing roller. When developing the electrostatic latent image, a developing electric field is generated between the developer carrying surface of the developing roller and the image carrying surface of the photosensitive drum, and the toner adheres to the electrostatic latent image by the action of the developing electric field. .

  The rotation axis of the photosensitive drum and the rotation axis of the developing roller are arranged in parallel so that the distance between the image carrying surface and the developer carrying surface facing each other does not fluctuate due to the rotation of the photosensitive drum and the rotation of the developing roller. Is done. However, in an actually assembled image forming apparatus, the rotating shaft of the photosensitive drum and the rotating shaft of the developing roller are arranged within a predetermined tolerance. In other words, strictly speaking, in the main scanning direction of the photosensitive drum after assembly, for example, the rotating shaft of the photosensitive drum and the rotating shaft of the developing roller are close to each other on one end side, and the rotating shaft of the photosensitive drum is on the other end side. A state in which the rotating shaft of the developing roller is separated can occur.

  When a constant potential difference is applied between the image carrying surface and the developer carrying surface to generate a developing electric field, the strength of the developing electric field is small at a position where the distance between the image carrying surface and the developer carrying surface is large. As a result, the density of the visible image is reduced. Further, at a position where the distance between the image carrying surface and the developer carrying surface is small, the intensity of the developing electric field becomes large and the density of the visible image becomes high. That is, in the main scanning direction, if the distance between the rotating shaft of the photosensitive drum and the rotating shaft of the developing roller differs depending on the position, a difference in the amount of toner adhesion occurs depending on the position in the main scanning direction. Becomes density unevenness in the visible image and deteriorates the image quality. In order to avoid such density unevenness, the above tolerance is managed as an extremely small value.

  In order to alleviate the above-described tolerance, for example, Japanese Patent Application Laid-Open No. H11-260260 discloses that when a process cartridge including drum peripheral members such as a photosensitive drum and a developing roller is assembled, the photosensitive drum and the developing in the main scanning direction are developed. A technique for storing a distribution of distances between rollers and performing image formation according to the stored information is disclosed. In this technique, in accordance with stored information, in the portion where the distance between the photosensitive drum and the developing roller is short, the intensity of the light beam applied to the image bearing surface during the exposure is reduced, and the photosensitive drum and The intensity of the light beam can be increased at a position far from the developing roller.

JP 2005-316073 A

  In the technique disclosed in Patent Document 1, the developer carrying surface can be configured to be completely parallel to the rotating shaft of the developing roller, and the distance between the photosensitive drum and the developing roller is not changed at all after assembly. If it is assumed that this is not the case, it can be said that the technology can suppress the occurrence of density unevenness.

  However, the developer carrying surface of the actually produced developing roller is not completely parallel to the rotation axis of the developing roller, and warpage of about several tens of μm occurs. Due to such warping, when the developing roller rotates, an axial runout occurs in which the developer carrying surface approaches or separates from the image carrying surface. As a result, the distance between the image bearing surface and the developer bearing surface varies with the rotation of the photosensitive drum and the rotation of the developing roller.

  Further, the rotational speed of the photosensitive drum and the rotational speed of the developing roller are not necessarily the same, and the circumferential length of the photosensitive drum and the circumferential length of the developing roller are not necessarily in a constant multiple relationship. That is, the distance between the image carrying surface and the developer carrying surface varies every time the photosensitive drum rotates even at the same position on the image carrying surface. In such an image forming apparatus in which the distance between the image bearing surface and the developer bearing surface sequentially varies, when the technique disclosed in Patent Document 1 is applied, the distance between the image bearing surface and the developer bearing surface is determined. A situation occurs in which the intensity of the light beam is increased despite the small distance, and a situation in which the intensity of the light beam is reduced despite the large distance between the image carrying surface and the developer carrying surface. That is, density unevenness may be further deteriorated by applying the technique disclosed in Patent Document 1.

  The present invention has been made in view of such a problem of the prior art, and can suppress density unevenness of a visible image due to a change in the distance between the image carrying surface and the developer carrying surface. An object is to provide an image forming apparatus and an image forming method capable of improving the image quality of the entire image.

In order to achieve the above object, the present invention employs the following technical means. In other words, the image forming apparatus according to the present invention includes an image carrier, an exposure device, a developer carrier, an electric field generation unit, an interval detection unit, an interval prediction unit, and a correction unit. The image carrier includes an image carrying surface on which an electrostatic latent image is formed. The exposure device irradiates the image bearing surface with a light beam to form an electrostatic latent image on the image bearing surface. The developer carrying member is disposed to face the image carrying surface and includes a developer carrying surface that carries a developer that develops the electrostatic latent image formed on the image carrying surface. The electric field generation unit applies a development electric field for developing the electrostatic latent image formed on the image carrying surface to the developer carrying body by superimposing an AC voltage and a DC voltage, whereby the image carrying surface and the developer are applied. It forms between the carrying surfaces. The interval detection unit detects the interval between the image carrying surface and the developer carrying surface based on the magnitude of the AC current that flows as the AC voltage is applied . The interval prediction unit includes a detection result of the interval detection unit during one rotation of the developer carrying surface with the rotation of the developer carrying member, a time required for one rotation of the developer carrying surface, Based on the moving speed, an interval between the image carrying surface and the developer carrying surface when the light beam irradiation position on the image carrying surface moves to a position facing the developer carrying body is predicted. The correction unit corrects the intensity of the light beam irradiated by the exposure unit in accordance with the interval between the image carrying surface and the developer carrying surface predicted by the interval prediction unit .

  According to this image forming apparatus, it is possible to appropriately adjust the intensity of a light beam that forms an electrostatic latent image on an image bearing surface even under a situation in which axial deflection occurs when the developing roller rotates. it can. As a result, it is possible to suppress the density unevenness of the visible image due to the variation in the distance between the image carrying surface and the developer carrying surface, and it is possible to improve the image quality of the entire image.

On the other hand, from another viewpoint, the present invention forms an electrostatic latent image on the image bearing surface by irradiating the image bearing surface of the image bearing member with a light beam, and develops the image carrier so as to face the image bearing surface. It is also possible to provide an image forming method for developing the electrostatic latent image formed on the image carrying surface with the developer carried on the developer carrying surface of the agent carrying body. That is, in the image forming method according to the present invention, first, a developing electric field for developing the electrostatic latent image formed on the image carrying surface is applied with the AC voltage and the DC voltage superimposed on the developer carrying member. The distance between the image bearing surface and the developer bearing surface is generated based on the magnitude of the AC current that is generated between the image bearing surface and the developer bearing surface and flows along with the application of the AC voltage . Information indicating the fluctuation state is acquired. Next, information indicating the fluctuation state during one rotation of the developer carrying surface as the developer carrying member rotates, the time required for one rotation of the developer carrying surface, the moving speed of the image carrying surface, Based on the above, the distance between the image carrying surface and the developer carrying surface when the irradiation position of the light beam on the image carrying surface moves to a position facing the developer carrying body is predicted. Then, the intensity of the light beam applied to the image carrying surface is corrected according to the predicted interval between the image carrying surface and the developer carrying surface.

  According to the present invention, it is possible to suppress the density unevenness of the visible image due to the variation in the distance between the image carrying surface and the developer carrying surface, and it is possible to improve the image quality of the entire image.

1 is a schematic configuration diagram showing the overall configuration of a multifunction machine according to an embodiment of the present invention. The figure which shows the hardware constitutions of the multifunctional device in one Embodiment of this invention. 1 is a functional block diagram showing a multifunction machine according to an embodiment of the present invention. 1 is a schematic configuration diagram illustrating an example of an interval detection configuration included in a multifunction peripheral according to an embodiment of the present invention. The figure which shows an example of the space | interval detection in one Embodiment of this invention. The flowchart which shows an example of the light beam intensity correction | amendment procedure which the compound machine in one Embodiment of this invention implements

  Hereinafter, an embodiment of the present invention will be described in more detail with reference to the drawings. In the following, the present invention is embodied as a digital multifunction machine.

  FIG. 1 is a schematic configuration diagram illustrating an example of the overall configuration of a digital multifunction peripheral according to the present embodiment. As shown in FIG. 1, the multifunction peripheral 100 includes a main body 101 including an image reading unit 120 and an image forming unit 140, and a platen cover 102 attached above the main body 101. An original table 103 made of a transparent plate such as contact glass is provided on the upper surface of the main body 101, and the original table 103 is opened and closed by a platen cover 102. Further, the platen cover 102 includes a document conveying device 110. An operation panel 161 is provided on the front surface of the multifunction device 100 so that the user can give the multifunction device 100 a start of copying and other instructions, and can confirm the state and settings of the multifunction device 100.

  An image reading unit 120 is provided below the document table 103. The image reading unit 120 reads an image of a document with the scanning optical system 121 and generates digital data (image data) of the image. The document can be placed on the document table 103 or the document transport device 110. The scanning optical system 121 includes a first carriage 122, a second carriage 123, and a condenser lens 124. The first carriage 122 is provided with a linear light source 131 and a mirror 132, and the second carriage 123 is provided with mirrors 133 and 134. The light source 131 illuminates the document. The mirrors 132, 133, and 134 guide reflected light from the document to the condenser lens 124, and the condenser lens 124 forms an optical image on the light receiving surface of the line image sensor 125.

  In the scanning optical system 121, the first carriage 122 and the second carriage 123 are provided so as to reciprocate in the sub-scanning direction 135. By moving the first carriage 122 and the second carriage 123 in the sub-scanning direction 135, the image of the document placed on the document table 103 can be read by the image sensor 125. When reading an image of a document set on the document conveying device 110, the image reading unit 120 temporarily stops the first carriage 122 and the second carriage 123 according to the image reading position, and passes the image reading position. Are read by the image sensor 125. The image sensor 125 generates document image data from the light image incident on the light receiving surface. The generated image data can be printed on a sheet (transfer object) in the image forming unit 140. The generated image data can also be transmitted to other devices through a network via a network interface (not shown) or the like.

  The image forming unit 140 prints image data obtained by the image reading unit 120 or image data received from another device through the network on a sheet. The image forming unit 140 includes a photosensitive drum 141 that is an image carrier. The photosensitive drum 141 rotates in one direction at a constant speed. Around the photosensitive drum 141, a charger 142, an exposure unit 143, a developing unit 144, and a cleaning unit 145 are arranged in this order from the upstream side in the rotation direction. The charger 142 uniformly charges the surface (image carrying surface) of the photosensitive drum 141. The exposure device 143 irradiates the uniformly charged surface of the photosensitive drum 141 with a light beam according to the image data to form an electrostatic latent image on the photosensitive drum 141. For example, the exposure unit 143 includes a laser diode and a polygon mirror that are light sources. The light source modulates the intensity of the emitted light beam in accordance with image data (image signal) input from the outside. The polygon mirror deflects the light beam emitted from the light source, and scans the light beam on the photosensitive drum 141 in the main scanning direction. The developing device 144 attaches toner as a developer to the electrostatic latent image, and forms a toner image as a visible image on the photosensitive drum 141. The developing device 144 includes a developing roller 144 a that faces the surface of the photosensitive drum 141 over the entire main scanning direction of the photosensitive drum 141. A gap is provided between the developing roller 144a and the photosensitive drum 141, and the toner carried on the surface (developer carrying surface) of the developing roller 144a is between the developer carrying surface and the image carrying surface. It adheres to the electrostatic latent image by the action of the generated developing electric field. The cleaning unit 145 cleans the surface of the photosensitive drum 141 by removing waste toner remaining on the surface of the photosensitive drum 141 after the transfer from the photosensitive drum 141. These processes are performed in series by the rotation of the photosensitive drum 141.

  The image forming unit 140 feeds paper from the manual feed tray 151, the paper feed cassettes 152, 153, and 154 to the transfer unit between the photosensitive drum 141 and the transfer roller 146. Various sizes of paper can be placed or stored in the manual feed tray 151 and the paper feed cassettes 152, 153, and 154. The image forming unit 140 selects a sheet specified by the user or a sheet corresponding to the automatically detected document size, and feeds the selected sheet from the manual feed tray 151 or the cassettes 152, 153, and 154 by the feeding roller 155. . The fed paper is transported to the transfer section by transport rollers 156 and registration rollers 157. The sheet on which the toner image is transferred is conveyed to the fixing device 148 by the conveyance belt 147. The fixing device 148 has a fixing roller 158 and a pressure roller 159 with a built-in heater, and fixes the toner image on the sheet by heat and pressing force. The image forming unit 140 discharges the sheet that has passed through the fixing device 148 to the discharge tray 149.

  Although not particularly limited, the present embodiment is configured such that the charge amount on the surface of the photosensitive drum 141 irradiated with the exposure light decreases. The developing roller 144a carrying the toner is given a potential between the potential of the non-exposed area where the light beam is not irradiated on the photosensitive drum 141 and the potential of the exposed area where the light beam is irradiated. Further, the toner is charged with the same polarity as the charged polarity of the photosensitive drum 141, and the toner adheres to the exposed area by an electric field generated between the exposed area of the photosensitive drum 141 and the developing roller 144a. To do. Further, the transfer roller 146 is given a potential having a polarity opposite to that of the photosensitive drum 141 (a polarity opposite to that of the toner), and the toner attached to the exposure region is transferred onto the sheet.

  FIG. 2 is a hardware configuration diagram of a control system in the multifunction machine. The multifunction peripheral 100 according to the present embodiment includes a CPU (Central Processing Unit) 201, a RAM (Random Access Memory) 202, a ROM (Read Only Memory) 203, an HDD (Hard Disk Drive) 204, an original conveying device 110, and an image reading unit 120. A driver 205 corresponding to each drive unit in the image forming unit 140 is connected via an internal bus 206. The ROM 203, the HDD 204, and the like store programs, and the CPU 201 controls the multifunction peripheral 100 in accordance with instructions from the control program. For example, the CPU 201 uses the RAM 202 as a work area, and controls the operation of each driving unit by exchanging data and commands with the driver 205. The HDD 204 is also used to store image data obtained by the image reading unit 120 and image data received from other devices via a network.

  An operation panel 161 and various sensors 207 are also connected to the internal bus 206. The operation panel 161 receives a user operation and supplies a signal based on the operation to the CPU 201. Moreover, the operation panel 161 displays an operation screen on the display with which the operation panel 161 is provided according to the control signal from CPU201. The sensor 207 includes various sensors such as an open / close detection sensor for the platen cover 102, a document detection sensor on the document table 103, a temperature sensor for the fixing device 148, and a detection sensor for the conveyed paper or document.

  FIG. 3 is a functional block diagram of a portion related to formation of an electrostatic latent image in the multifunction machine of the present embodiment. As illustrated in FIG. 3, the multifunction peripheral 100 includes an interval detection unit 301, an interval prediction unit 302, and a correction unit 303. In FIG. 3, the developing roller 144 a and the photosensitive drum 141 to which the developing electric field is applied by the electric field generating unit 306 are illustrated as the electric field applying target unit 304.

  The interval detector 301 detects an interval between the image carrying surface of the photosensitive drum 141 and the developer carrying surface of the developing roller 144a. Although not particularly limited, in the present embodiment, the interval detection unit 301 includes the image bearing surface of the photosensitive drum 141 and the developing roller based on the developing electric field generation signal applied to the developing roller 144a in order to generate the above-described developing electric field. The distance between the developer carrying surface 144a is detected.

  In this example, the electric field generation unit 306 applies a development electric field generation signal to the development roller 144a. The electric field generation unit 306 includes an AC voltage source that outputs an AC signal (AC voltage) and a DC voltage source that outputs a DC signal (DC voltage). The electric field generation unit 306 applies a development electric field generation signal obtained by superimposing the AC voltage generated by the AC voltage source to the DC voltage generated by the DC voltage source to the developing roller 144a. The DC component in the development electric field generation signal has a function of moving the toner from the developer carrying surface of the developing roller 144a to the exposure area on the image carrying surface of the photosensitive drum 141. In addition, the AC component causes toner to flow back and forth between the developer carrying surface of the developing roller 144a and the image carrying surface of the photoconductive drum 141, thereby reducing density unevenness and improving image quality compared to the case where only the DC component is present. Have the effect of

  For example, when the distance between the image bearing surface of the photosensitive drum 141 and the developer bearing surface of the developing roller 144a is constant, the AC current when the developing electric field generation signal is applied is constant. On the other hand, when the distance between the image carrying surface of the photosensitive drum 141 and the developer carrying surface of the developing roller 144a becomes narrow, the capacitance of the capacitor formed by the image carrying surface and the developer carrying surface increases. Therefore, the impedance between the image carrying surface and the developer carrying surface is reduced, and the AC current is increased. Further, when the distance between the image carrying surface of the photosensitive drum 141 and the developer carrying surface of the developing roller 144a is increased, the capacitance of the capacitor formed by the image carrying surface and the developer carrying surface is reduced. As a result, the impedance between the image carrying surface and the developer carrying surface increases and the AC current decreases. Therefore, a change in the distance between the image carrying surface and the developer carrying surface can be detected as a change in the AC current value when the electric field generation signal is applied.

  As described above, the developer carrying surface of the developing roller 144a is not completely parallel to the rotation axis of the developing roller 144a, and a warp of about several tens of μm occurs. On the other hand, the surface of the photosensitive drum 141 carries an electrostatic latent image and needs to transfer the electrostatic latent image to a transfer target. Therefore, the surface of the photosensitive drum 141 is extremely accurate with respect to the rotation axis of the photosensitive drum 141. It is configured in a parallel state. Therefore, when both the photosensitive drum 141 and the developing roller 144a rotate, the change in the distance between the image carrying surface and the developer carrying surface is mainly due to axial deflection (development of the developer carrying surface) when the developing roller 144a rotates. Will occur. In other words, the fluctuation of the interval between the image carrying surface and the developer carrying surface periodically occurs between a narrow interval and a wide interval with the rotation of the developing roller 144a.

  FIG. 4 is a diagram illustrating an example of a more specific configuration of the interval detection unit 301 and the electric field generation unit 306. In this example, the electric field generation unit 306 includes an AC voltage source 401, a high voltage generation transformer 402, and a DC voltage source 403. The AC voltage source 401 is connected to the primary side of the high-voltage generation transformer 402, and an electric field application target portion 304 to which a developing electric field is applied is connected to one end of the secondary side of the high-voltage generation transformer 402. A DC voltage source 403 is connected to the other end of the secondary side of the high-voltage generating transformer 402.

  The AC voltage supplied from the AC voltage source 401 is boosted by the high-voltage generating transformer 402 and applied to the developing roller 144 a that configures the electric field application target portion 304. A DC voltage supplied from a DC voltage source is also applied to the developing roller 144a. That is, the boosted AC voltage and DC voltage are applied to the developing roller 144a in a superimposed manner.

  In addition, the interval detection unit 301 includes an AC current extraction capacitor 404 and a detection unit 405 that outputs a voltage corresponding to the magnitude of the AC current. In this example, one end of the capacitor 404 is connected between the DC voltage source 403 and the high voltage generation transformer 402, and a configuration in which the detection unit 405 can detect the magnitude of the AC current flowing on the secondary side of the high voltage generation transformer 402. It has become. The detection unit 405 includes, for example, a rectifier circuit and a smoothing circuit, and converts an AC current flowing through the secondary side of the high-voltage generation transformer 402 extracted via the capacitor 404 into a DC current. Then, the detection unit 405 outputs a voltage corresponding to the magnitude of the DC current to the interval prediction unit 302.

  FIG. 5 is a diagram schematically illustrating the voltage output by the detection unit 405. In FIG. 5, the horizontal axis corresponds to time, and the vertical axis corresponds to the output voltage. A state where the output voltage is large corresponds to a state where the distance between the image carrying surface and the developer carrying surface is narrow, and a state where the output voltage is small corresponds to a state where the distance between the image carrying surface and the developer carrying surface is wide.

  As shown in FIG. 5, the interval between the image carrying surface and the developer carrying surface varies periodically between a narrow interval and a wide interval. In FIG. 5, a time t0 corresponding to one cycle corresponds to a time required for one rotation of the developer carrying surface with the rotation of the developing roller 144a.

  Based on the detection result of the interval detection unit 301, the interval prediction unit 302 performs image holding when the position on the image holding surface irradiated with the light beam by the exposure unit 143 moves to a position facing the developer carrier. The distance between the surface and the developer carrying surface is predicted. In the present embodiment, the change in the distance between the image carrying surface and the developer carrying surface on the image carrying surface becomes one cycle while the developing roller 144a makes one rotation, and the image carrying surface and the developer carrying are carried out. Predict the distance between the faces.

  That is, the interval predicting unit 302 determines that the image carrying surface and the developer carrying surface are based on the time t0 required for the developer carrying surface to rotate once with the rotation of the developing roller 144a and the moving speed Vd of the image carrying surface. Predict the distance between the faces.

  Assuming that the time required for the position on the image bearing surface irradiated with the light beam from the exposure device 143 at the start of exposure to move to a position facing the developing roller 144 a as the photosensitive drum 141 rotates is t 1. During the time t1, the developing roller 144a moves by (t1 / t0) rotation. Therefore, by specifying the interval between the image carrying surface and the developer carrying surface in a state in which the developing roller 144a has been moved by (t1 / t0) rotation from the state of the developing roller 144a at the start of exposure, the light is exposed by the exposure unit 143. The distance between the image carrying surface and the developer carrying surface when the position on the image carrying surface irradiated with the beam moves to a position facing the developer carrying body can be predicted.

  For example, if the developing roller 144a is in the state of time P in FIG. 5 at the start of exposure, the position on the image bearing surface to which the light beam is irradiated at the start of exposure changes with the rotation of the photosensitive drum 141. When the developing roller 144a is moved to a position opposite to 144a, the developing roller 144a is in a state at time Q when the time t1 has elapsed from time P in FIG. 5 (a state where the developing roller 144a has rotated (t1 / t0)). Further, when the time t0 further elapses from this state, the developing roller 144a rotates once, so that the interval between the image carrying surface and the developer carrying surface is the same as the interval at time Q. That is, when the position on the image bearing surface irradiated with the light beam at the start of exposure moves to a position facing the developing roller 144a as the photosensitive drum 141 rotates, the image bearing surface and the developer at the time Q are moved. After that, the interval between the image carrying surface and the developer carrying surface is the same as the interval between the image carrying surface and the developer carrying surface at time Q every time t0 elapses. become. Therefore, on the image bearing surface irradiated with the light beam, the interval variation between the image bearing surface and the developer bearing surface shown in FIG. 5 varies at each circumferential distance (t0 × Vd) on the image bearing surface. It will occur periodically.

  In the present embodiment, the interval predicting unit 302 displays information indicating the variation state of the interval between the image carrying surface and the developer carrying surface as shown in FIG. It is acquired from the interval detection unit 301 during the initialization operation performed when returning from the power mode to the normal mode, and the information is retained. Based on this information, the interval predicting unit 302 determines the image bearing surface and developer when the light beam irradiation position at the start of exposure moves to a position facing the developing roller 144a as the photosensitive drum 141 rotates. Predict the distance between the bearing surface. For example, the interval prediction unit 302 changes the interval between the held image carrying surface and the developer carrying surface based on the voltage input from the interval detection unit 301 when an image formation instruction is input. In the information indicating the state, the state of the developing roller 144a is grasped (for example, the state at the time P).

  Further, the interval prediction unit 302 periodically determines the interval between the image carrying surface and the developer carrying surface based on the information indicating the variation state of the interval between the image carrying surface and the developer carrying surface. Predict the state of fluctuation. As described above, on the image bearing surface, the circumferential distance (t0 × Vd) on the image bearing surface is one cycle, and within this distance, the distance between the image bearing surface and the developer bearing surface is the development distance. It fluctuates corresponding to one rotation of the roller 144a. Therefore, the fluctuation state corresponding to one period of the interval between the image carrying surface and the developer carrying surface as shown in FIG. 5 is associated with the circumferential distance (t0 × Vd) on the image carrying surface. Thus, it is possible to predict the distance between the image carrying surface and the developer carrying surface when each position on the image carrying surface moves to a position facing the developing roller 144a as the photosensitive drum 141 rotates. it can.

  The time t0 required for the developer carrying surface to make one rotation with the rotation of the developing roller 144a and the moving speed Vd of the image carrying surface may be registered in the interval prediction unit 302 in advance. When acquiring information indicating the fluctuation state of the interval between the surface and the developer carrying surface, a configuration that is appropriately measured may be used.

  The interval predicting unit 302 predicts the photosensitive drum 141 based on the state of the developing roller 144a grasped as described above and the state of the periodic fluctuation of the interval between the image carrying surface and the developer carrying surface. The distance between the image bearing surface and the developer bearing surface on the image bearing surface is input to the correction unit 303.

  Note that the fluctuation state of the gap between the image carrying surface and the developer carrying surface is, for example, when the photosensitive drum 141 or the developing roller 144a is pulled out by the user forcibly pulling out the paper that has jammed in the paper transport path. It does not change greatly unless it is forcibly rotated by an external force. For this reason, the interval predicting unit 302 does not acquire the fluctuation state of the interval between the image carrying surface and the developer carrying surface every time the initialization operation is performed, but the interval between the image carrying surface and the developer carrying surface. The configuration may be such that, when an operation that changes the fluctuation state is performed, the fluctuation state of the interval between the image carrying surface and the developer carrying surface is acquired.

  The correction unit 303 corrects the intensity of the light beam emitted by the exposure unit 143 according to the interval between the image carrying surface and the developer carrying surface predicted by the interval prediction unit 302. For example, when the distance between the image carrying surface of the photosensitive drum 141 and the developer carrying surface of the developing roller 144a becomes narrow, the intensity of the developing electric field that appears between the image carrying surface and the developer carrying surface increases. For this reason, the amount of toner adhering from the developer carrying surface to the exposed area of the image carrying surface increases, and the density of the toner transferred from the image carrying surface of the photosensitive drum 141 to the sheet to be transferred increases. In order to avoid such an increase in toner density, the light beam intensity is decreased in accordance with the timing at which the distance between the image carrying surface and the developer carrying surface becomes narrow, and the exposure area from the developer carrying surface to the image carrying surface is reduced. It is only necessary to suppress an increase in the amount of toner adhering to the surface.

  On the other hand, when the distance between the image carrying surface of the photosensitive drum 141 and the developer carrying surface of the developing roller 144a is widened, the intensity of the developing electric field appearing between the image carrying surface and the developer carrying surface is reduced. For this reason, the amount of toner adhering from the developer carrying surface to the exposure area of the image carrying surface is reduced, and the density of the toner transferred from the image carrying surface of the photosensitive drum 141 to the sheet is lowered. In order to avoid such a decrease in toner density, the intensity of the light beam is increased in accordance with the timing at which the interval between the image carrying surface and the developer carrying surface becomes wide, and the exposure from the developer carrying surface to the image carrying surface is performed. What is necessary is just to suppress that the amount of toner adhering to the region is reduced.

  For example, in the above-described example, the image carrying surface and developer carrying when the light beam irradiation position on the image carrying surface at the start of exposure moves to a position facing the developing roller 144a as the photosensitive drum 141 rotates. When the interval prediction unit 302 predicts that the relationship with the surface is the state at time Q in FIG. 5, the correction unit 303 determines the light beam intensity at the start of exposure between the image carrying surface and the developer carrying surface in the state. The intensity is corrected according to the interval (voltage value). Thereafter, the correction unit 303 increases or decreases the light beam intensity according to the state of periodic fluctuation of the interval between the image carrying surface and the developer carrying surface. In this case, the fluctuation amount (variation width) of the light beam intensity is the distance (voltage) between the image carrying surface and the developer carrying surface in the information indicating the fluctuation state of the gap between the image carrying surface and the developer carrying surface. Value).

  By performing the above correction and exposing with the intensity of the light beam corresponding to the distance between the image carrying surface and the developer carrying surface, density unevenness on the image carrying surface, particularly in the sub-scanning direction, is generated. Can be suppressed.

  Although not particularly limited, in the present embodiment, the image signal corresponding to the image data to be printed generated by the image signal generation unit 305 is input to the exposure unit 143 via the correction unit 303. . That is, an image signal in which the correction of the light beam intensity is reflected in the correction unit 303 is input to the exposure unit 143, and a light beam corresponding to the image signal in which the correction is reflected is directed from the exposure unit 143 toward the photosensitive drum 141. Irradiated. Here, the image signal is a signal for driving the light source of the exposure unit 143, and includes information specifying the intensity of the light beam. The correction amount of the light beam intensity is obtained, for example, by acquiring in advance a correspondence relationship between the output voltage of the detection unit 405 and the light beam intensity so that the luminance variation width becomes the smallest in a visible image having a specific density level. The correction unit 303 may be set.

  Note that the interval prediction unit 302 and the correction unit 303 can be realized by, for example, an electric circuit or a dedicated arithmetic circuit. It can also be realized as hardware including a processor and a memory such as a RAM and a ROM, and software stored in the memory and operating on the processor.

  FIG. 6 is a flowchart illustrating an example of a light beam intensity correction procedure performed by the multifunction peripheral 100. Note that this procedure is started, for example, when an image formation instruction is input in the multifunction peripheral 100 as a trigger. At this time, the image signal generation unit 305 generates an image signal corresponding to the image data. In addition, the electric field generation unit 306 applies the development electric field generation signal to the electric field application target unit 304 (here, the development roller 144a). As a result, a developing electric field is generated between the developer carrying surface of the developing roller 144a and the image carrying surface of the photosensitive drum 141.

  When the procedure starts, the correction unit 303 applies the image signal of one exposure resolution (the amount irradiated to one point on the image bearing surface) input from the image signal generation unit 305 on the image bearing surface of the photosensitive drum 141. The exposure position at is specified (step S601). Next, the correction unit 303 inquires of the interval prediction unit 302 about the expected interval between the image carrying surface and the developer carrying surface when the exposure position moves to a position facing the developing roller 144a. In response to the inquiry, the interval prediction unit 302 notifies the correction unit 303 of the interval predicted by the above-described method (step S602).

  Upon receiving the notification, the correction unit 303 determines whether or not the light beam intensity needs to be corrected (step S603). For example, when the prediction interval input from the interval prediction unit 302 is within a range specified in advance, the correction unit 303 determines that correction is not necessary (No in step S603). In this case, the correction unit 303 inputs the input image signal to the exposure unit 143 without correcting it. On the other hand, when the prediction interval input from the interval prediction unit 302 is larger than the range specified in advance, the correction unit 303 determines that correction for weakening the light beam intensity to the specified level is necessary. In addition, when the prediction interval input from the interval prediction unit 302 is smaller than the predesignated range, the correction unit 303 determines that correction for increasing the light beam intensity to the predesignated intensity is necessary (step S603 Yes). In this case, the correction unit 303 corrects the light beam intensity according to the determination on the input image signal, and inputs the correction to the exposure unit 143 (step S604).

  The above processing is performed for all the image signals constituting the image data (No in steps S605 and S601). When the processing is completed for all image signals, the procedure ends (step S605 Yes).

  As described above, in this multi-function machine 100, the intensity of the light beam that forms the electrostatic latent image on the image bearing surface is appropriately adjusted even under a situation in which the shaft shake occurs when the developing roller 144a rotates. Can be adjusted. As a result, it is possible to suppress the density unevenness of the visible image due to the variation in the distance between the image carrying surface and the developer carrying surface, and it is possible to improve the image quality of the entire image.

  Further, in the multi-function device 100, even when the distance between the image carrying surface and the developer carrying surface becomes different from the time of assembly due to wear of the image carrying surface accompanying use, etc., The intensity of the light beam that forms the electrostatic latent image can be adjusted appropriately.

  The above-described embodiments do not limit the technical scope of the present invention, and various modifications and applications other than those already described are possible within the scope of the present invention. For example, in the above-described embodiment, as a particularly preferable mode, the interval detection unit 301 is configured by an electric circuit, but the configuration is not limited thereto. The interval detector 301 only needs to be able to detect the interval between the image carrying surface of the photosensitive drum 141 and the developer carrying surface of the developing roller 144a, and is not limited to an electrical detection method, and may employ any configuration. it can. For example, an optical detection method or a physical detection method may be employed.

  Further, in the above-described embodiment, the correction amount of the light beam intensity is set to three states designated in advance (no correction, the light beam intensity is increased by a predetermined amount, and the light beam intensity is decreased by a predetermined amount). However, the correction amount of the light beam intensity may be based on the correspondence between the density unevenness of the visible image at a specific density level and the distance between the image carrying surface and the developer carrying surface. You may employ | adopt the structure which is fluctuate | varied in multiple steps or steplessly according to the space | interval with an agent carrying surface.

  Furthermore, in the above-described embodiment, a single-color printing multifunction device has been described. However, the invention is not limited to a single-color device, and may be a multi-color (full-color) multifunction device. In this case, the above-described control may be performed for each color exposure device. In the flowchart shown in FIG. 6, the order of the steps can be changed as appropriate within the range where the equivalent action is achieved. In the above embodiment, the configuration in which the DC voltage and the AC voltage for generating the developing electric field are applied to the developing roller 144a has been described. Any configuration can be employed.

  In addition, in the above-described embodiment, the present invention is embodied as a digital multifunction peripheral. However, the present invention can be applied not only to a digital multifunction peripheral but also to an arbitrary image forming apparatus such as a printer or a copying machine. .

  According to the present invention, it is possible to suppress the density unevenness of the visible image due to the variation in the distance between the image carrying surface and the developer carrying surface, and to improve the image quality as a whole image. It is useful as an image forming method.

100 MFP (image forming device)
141 Photosensitive drum (image carrier)
143 Exposing device 144 Developing device 144a Developing roller (developer carrier)
301 Interval Detection Unit 302 Interval Prediction Unit 303 Correction Unit 401 AC Voltage Source 402 High Voltage Generation Transformer 403 DC Voltage Source 404 Capacitor (for AC Current Extraction)
405 detector

Claims (2)

An image bearing member having an image bearing surface on which an electrostatic latent image is formed;
An exposure unit that forms an electrostatic latent image on the image bearing surface by irradiating the image bearing surface with a light beam;
A developer carrying body disposed opposite to the image carrying surface and having a developer carrying surface carrying a developer for developing an electrostatic latent image formed on the image carrying surface;
A developing electric field for developing an electrostatic latent image formed on the image carrying surface is applied to the developer carrying body by superimposing an AC voltage and a DC voltage, whereby the image carrying surface and the developer carrying An electric field generator that is generated between the surface and
An interval detector that detects an interval between the image carrying surface and the developer carrying surface based on the magnitude of the AC current that flows along with the application of the AC voltage ;
The detection result of the interval detection unit during one rotation of the developer carrying surface with the rotation of the developer carrying member, the time required for one rotation of the developer carrying surface, Based on the moving speed, an interval between the image carrying surface and the developer carrying surface when the irradiation position of the light beam on the image carrying surface is moved to a position facing the developer carrying body is determined. An interval predictor for prediction;
A correction unit that corrects the intensity of the light beam emitted by the exposure unit in accordance with the interval between the image carrying surface and the developer carrying surface predicted by the interval prediction unit;
An image forming apparatus comprising: An electrostatic latent image is formed on the image bearing surface by irradiating the image bearing surface of the image bearing member with a light beam, and on the developer bearing surface of the developer bearing member disposed opposite to the image bearing surface. An image forming method for developing an electrostatic latent image formed on the image carrying surface by a carried developer,
A developing electric field for developing the electrostatic latent image formed on the image bearing surface is applied with the AC voltage and the DC voltage superimposed on the developer bearing member, whereby the image bearing surface and the developer bearing member are applied. Information indicating a variation state of a gap between the image bearing surface and the developer bearing surface based on the magnitude of an AC current generated between the image bearing surface and the AC current applied with the AC voltage. A step to obtain,
Information indicating the fluctuation state during one rotation of the developer carrying surface with the rotation of the developer carrying member, time required for one rotation of the developer carrying surface, and movement of the image carrying surface Based on the speed, an interval between the image carrying surface and the developer carrying surface when the irradiation position of the light beam on the image carrying surface moves to a position facing the developer carrying body is predicted. And steps to
Correcting the intensity of the light beam according to the predicted spacing between the image bearing surface and the developer bearing surface;
An image forming method comprising:

Images