JP5197264B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus.

  Conventionally, as an electrophotographic image forming apparatus, there are, for example, an electrophotographic copying machine, an electrophotographic printer (such as an LED printer and a laser beam printer), and an electrophotographic facsimile apparatus.

  In this type of image forming apparatus, the surface of the electrophotographic photosensitive member is uniformly charged by a charging device, and the charged photosensitive drum surface is exposed by an image exposure device to form an electrostatic latent image. The electrophotographic photoreceptor is rotatable in a drum type or an endless belt type, and is driven to rotate at a predetermined speed. Hereinafter, the electrophotographic photoreceptor is referred to as a photosensitive drum or a drum.

  The electrostatic latent image is visualized with a developer (hereinafter referred to as toner) by a developing device to form a toner image, and the toner image is transferred to a transfer material by a transfer device. Thereafter, the toner image is fixed on the transfer material as a fixed image by the fixing device and output. The transfer drum remaining on the surface of the photosensitive drum after the transfer of the toner image onto the transfer material is removed by a cleaning device to prepare for the next image forming operation.

  In recent years, as a charging device, a contact charging type device is mounted on many image forming apparatuses, and most of them are a roller charging type in which a conductive roller is used as a contact charging member and a voltage is applied thereto. There are a direct current method in which only a direct current voltage is applied as a charging voltage, and an alternating current method in which an alternating current voltage is superimposed on the direct current voltage.

  The AC superposition method has an advantage that the surface of the photosensitive drum can be uniformly charged. On the other hand, since a discharge is generated in a minute gap between the contact charging member and the photosensitive drum, the surface of the photosensitive drum is damaged, the wear amount of the photosensitive drum is increased, and the life of the photosensitive drum is shortened.

  On the other hand, the direct current method has less damage to the photosensitive drum because the energy of discharge generated in the minute gap between the contact charging member and the photosensitive drum is smaller than the alternating current superposition method. Long life can be achieved. Therefore, from the viewpoint of extending the life of the photosensitive drum, it is desirable to charge the photosensitive drum by a direct current method.

  However, particularly when the photosensitive drum is charged by the direct current method, there are the following problems.

  The surface potential on the surface of the photosensitive drum after image formation is nonuniform according to the formed image pattern. Even if the next charging is performed in this state, it cannot be uniformly charged depending on the previous formed image, and as a result, the surface potential of the photosensitive drum becomes non-uniform when the image is exposed next time by an image exposure apparatus such as a laser. Sometimes. That is, when a halftone image is formed after a pattern having a high contrast is formed, a so-called “ghost image” in which the previous image pattern appears during the halftone may occur.

  Therefore, the photosensitive drum surface is irradiated with a pre-charging exposure device having a light source such as an LED uniformly (entire exposure) and exposed to light on the surface of the photosensitive drum in the previous image formation and a non-image. Equalize the dark potential of the part. This makes it possible to uniformly charge at the next charging and eliminates the generation of ghost images. In order to eliminate the generation of a ghost image, it is better to use a larger amount of light for the pre-charging exposure apparatus.

However, if the pre-charging exposure device uniformly irradiates the surface of the photosensitive drum and sufficiently equalizes the potential on the photosensitive drum, the transfer residue on the photosensitive drum that has not been transferred to the transfer material in the transfer process. There was a problem that the toner was scattered. This may occur in an image forming apparatus that performs pre-charge exposure before the cleaning process. The toner image is formed on the electrostatic latent image formed on the surface of the photosensitive drum by the image exposure device. Transfer residual toner on the photosensitive drum that has not been transferred to the transfer material by the transfer process also remains on the electrostatic latent image. If the electrostatic latent image is leveled sufficiently uniformly by the pre-charging exposure apparatus, the adhesion between the toner and the photosensitive drum is weakened, and the image of the transfer residual toner may be destroyed and the toner may be scattered. Therefore, in order to prevent toner scattering, it is better to use a smaller light amount for the pre-charging exposure apparatus.

  Further, Patent Document 1 reports a problem that the light amount of the pre-charging exposure apparatus decreases due to the long-time use of the pre-charging exposure apparatus. If the light amount of the pre-charging exposure apparatus decreases, the history of the previous formed image cannot be completely erased, and a ghost image may be generated.

  Therefore, in order to achieve both suppression of ghost image generation and prevention of toner scattering, charging is performed according to pre-charge exposure devices such as LEDs, photosensitive drum film thickness, photosensitive drum sensitivity manufacturing variations, and usage changes. It is necessary to adjust the light amount of the pre-exposure device to an optimum light amount.

  Conventionally, the control of the light amount of the pre-charge exposure apparatus is performed based on the relationship between the photosensitive drum surface potential detected by the surface potential detection means and the current applied to the charging means, as described in Patent Document 1. It was. Since the photosensitive drum surface potential detecting means can directly measure the photosensitive drum surface potential, the light amount of the pre-charging exposure apparatus can be adjusted to obtain a desired photosensitive drum surface potential.

Further, in Patent Document 2, the photosensitive drum film thickness (photosensitive layer film thickness) is estimated from the current value that flows through the charging member by applying a detection bias to the charging member, and the light amount of the pre-charge exposure device is determined by the sensitivity of the photosensitive member. It was changed according to the drum film thickness. In this method, when the photosensitive drum film thickness is thick, the light amount of the pre-charging exposure apparatus is adjusted to be small, and the photosensitive drum film thickness is adjusted to be large as the image forming apparatus is used.
Japanese Patent Laid-Open No. 11-174755 JP 2004-334063 A

  However, the surface potential detecting means is expensive, and there remains a problem in providing a cheaper image forming apparatus.

  A method for estimating the film thickness of the photosensitive drum from the current value flowing through the charging member by applying a detection bias to the charging member and adjusting the light amount of the pre-charge exposure apparatus according to the film thickness is as follows: A certain effect can be obtained for variations in thickness and photosensitive characteristics. However, it has been difficult to adjust the light quantity of the pre-charge exposure apparatus by predicting variations in the production of the pre-charge exposure apparatus or changes in the light quantity associated with long-term use. Therefore, it has been demanded that the variation in the light amount of the pre-charging exposure apparatus in manufacturing be adjusted more strictly before shipping. However, if the light quantity is adjusted strictly, there is a problem that the production efficiency is lowered and a lot of cost is required. Further, there has been a problem that a ghost image is generated with long-term use or when the user defaces the pre-charge exposure apparatus and the light amount of the pre-charge exposure apparatus decreases. Furthermore, when the contact charging member varies or the resistance value varies depending on the use environment, the charging current value is deviated and high detection accuracy may not be obtained.

  Therefore, in order to provide an image forming apparatus that is cheaper and can prevent toner scattering without generating a ghost image, it is required not to use the photosensitive drum surface potential detecting means. Also, depending on the pre-charge exposure device such as LED, photosensitive drum film thickness, photosensitive drum sensitivity manufacturing variations, individual charging member variations, pre-charging exposure device at the time of use, photosensitive drum, charging member Therefore, it is required to adjust the light amount of the pre-charging exposure apparatus to an optimum light amount.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image that can prevent toner scattering while maintaining good image quality without using surface potential detection means, thus being cheaper and without generating a ghost image over a long period of time. It is to provide a forming apparatus.

In order to achieve the above object, a typical configuration of an image forming apparatus according to the present invention includes a rotatable electrophotographic photosensitive member, and a contact charging member that contacts the photosensitive member and charges the surface of the photosensitive member. And a charging current detection device that detects a value of a current flowing through the contact charging member, and a pre-charging exposure device that exposes the surface of the photoconductor to remove residual charges before charging by the contact charging member. The forming apparatus includes a standard exposure device that exposes the surface of the photoconductor adjusted to a predetermined light amount, and applies a predetermined voltage to the contact charging member during non-image formation. The first surface that flows to the contact charging member when the surface of the surface of the photoconductor exposed by turning on the standard exposure device without turning on the pre-charge exposure device is charged with the contact charging member again. The current value of The pre-exposure device is turned on without the standard exposure device being turned on for the photosensitive member that is charged by applying a predetermined voltage to the contact charging member during non-image formation and detected by a flow detection device. the region of the surface of the photosensitive member was exposed by, upon re-charged by the contact charging member, to detect a second current flowing through the contact charging member in the charging current detecting device, the first And a controller that determines a light amount of the pre-charging exposure apparatus during image formation based on a current value and the second current value.

  According to the present invention, it is possible to appropriately and optimally determine the light amount of the pre-charging exposure apparatus during image formation without using the surface potential detection means. Therefore, a cheaper image forming apparatus can be provided. In addition, an image forming apparatus that suppresses ghosting and maintains good image quality without causing toner scattering is provided regardless of variations in the electrophotographic photosensitive member, contact charging member, and pre-charge exposure apparatus, and usage conditions. can do.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings.

[First Embodiment]
(1) Image Forming Unit FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the first embodiment of the present invention.

The image forming apparatus according to the present embodiment performs a series of image forming processes of charging, exposure, development, transfer, and cleaning on a rotating or rotating (rotatable) electrophotographic photosensitive member to perform a transfer material. An electrophotographic printer for forming an image on the printer.

  That is, an image corresponding to an electrical image signal input from the external host device 200 such as a personal computer to the control means (engine controller) 101 of the image forming apparatus 100 is formed on a transfer material (recording medium). The control unit 101 exchanges various types of information with the external host device 200, and comprehensively controls the operation of the image forming apparatus according to a predetermined control program and a reference table. The transfer material is, for example, a recording sheet, an OHP sheet, or a cloth. The transfer material may be an intermediate transfer member such as an intermediate transfer drum or an intermediate transfer belt.

  Here, as a process means for executing the series of image forming processes, a contact charging member 3 that is a charging means for charging a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 2 that is driven to rotate is used. including. Further, the image exposure apparatus 1 is an image exposure unit that forms an electrostatic latent image by exposing the surface of the charged photosensitive drum 2 to image exposure. Furthermore, a developing device 4 that is a developing unit that develops the electrostatic latent image with a developer to visualize it as a developer image (toner image), a transfer device 6 that is a transfer unit that transfers the toner image to a transfer material, A cleaning device 5 is included as cleaning means for cleaning the photosensitive drum 2 after transfer.

  Among these members constituting the process means, at least some of the members can be configured as a process cartridge 10 that can be attached to and detached from the image forming apparatus main body. In the process cartridge 10 of this embodiment, the photosensitive drum 2, the contact charging member 3, the developing device 4, and the cleaning device 5 are collectively unitized. FIG. 2 is an enlarged view of a portion of the process cartridge 10 in FIG. These components are assembled in a predetermined mutual relationship within the cartridge. The process cartridge 10 is inserted into and attached to a predetermined part in the main body of the image forming apparatus in a predetermined manner, and conversely, can be removed from the main body of the apparatus. In addition, the process cartridge 10 includes a storage unit 9 that stores various information related to the process cartridge. The control means 101 exchanges various information with the storage means 9.

  The photosensitive drum 2 is driven to rotate at a predetermined peripheral speed (process speed) in the clockwise direction of the arrow R1.

  The contact charging member 3 is a member that contacts the surface of the photosensitive drum 2 and charges the surface of the photoreceptor. In the present embodiment, the contact charging member 3 is a conductive roller disposed in contact with the photosensitive drum 2, and rotates in the counterclockwise direction indicated by an arrow R 3 following the rotation of the photosensitive drum 2. By applying a predetermined charging voltage (DC voltage) from the power supply unit 31 to the contact charging member 3, the surface of the rotating photosensitive drum 2 is uniformly charged to a predetermined polarity / potential (dark portion potential).

  In the present embodiment, the image exposure apparatus 1 is a laser scanner including a laser / polygon mirror / lens system. Laser light modulated in accordance with the image signal is scanned out from the image exposure apparatus 1 and reflected by the mirror 11 with respect to the photosensitive drum 2. As a result, the surface of the photosensitive drum uniformly charged by the contact charging member 3 is subjected to laser scanning exposure. By this exposure, the surface potential of the exposed portion on the surface of the photosensitive drum is attenuated to the bright portion potential, and an electrostatic latent image corresponding to the image exposure pattern is formed on the surface of the photosensitive drum with electrostatic contrast with the dark portion potential.

  The developing device 4 includes a developer container 40 containing the developer T, a developer carrier 41 that carries and conveys the developer, and a developer layer thickness regulating member 42 that regulates the developer coating on the developer carrier. have. In this embodiment, magnetic monocomponent toner is used as the developer T. The developer carrier 41 is disposed to face the photosensitive drum 2 in a non-contact manner with a predetermined gap. When the photosensitive drum 2 rotates in the R1 direction, the developer carrier 41 rotates in the counterclockwise direction indicated by an arrow R2 with a predetermined peripheral speed ratio. The developer T conveyed by the rotating developer carrier 41 is regulated to a desired layer thickness by the developer layer thickness regulating member 42 and conveyed to the development position facing the photosensitive drum 2. A predetermined developing voltage is applied to the developer carrier 41 from the power supply unit 43. As a result, the electrostatic latent image formed on the surface of the photosensitive drum 2 is visualized as a toner image (reverse development or normal development).

  On the other hand, the transfer material 7 stored in the paper feed cassette 71 is separated and fed by the paper feed roller 72 and conveyed to the registration roller 73 in synchronization with the formation of the latent image on the photosensitive drum 2. The transfer material 7 is conveyed to a transfer device 6 composed of a transfer roller by a registration roller 73 in synchronization with the leading edge of the toner image formed on the photosensitive drum 2, and the transfer device 6 and the photosensitive drum 2 are contacted. The toner enters the transfer nip, which is a contact portion, and is nipped and conveyed. While the transfer material 7 is nipped and conveyed through the transfer nip portion, a predetermined transfer voltage (a voltage having a predetermined potential opposite to the toner charging polarity) is applied to the transfer device 6. As a result, the toner image formed on the surface of the photosensitive drum is sequentially electrostatically transferred onto the surface of the transfer material 7.

  The transfer material 7 exiting the transfer nip is separated from the surface of the photosensitive drum 2 and introduced into the fixing device 8 by the conveying device 14. The fixing device 8 is, for example, a heat roller type fixing device, and the transfer material 7 is nipped and conveyed at the fixing nip portion, whereby an unfixed toner image is fixed on the transfer material as a fixed image by heat and pressure. Then, the image-fixed transfer material 7 is discharged to the outside of the apparatus.

  Further, the transfer residual toner remaining on the photosensitive drum 2 after the transfer material is separated is removed by the cleaning device 5 using the cleaning blade 5a formed of an elastic blade. The photosensitive drum 2 whose surface is cleaned by the cleaning device 5 is repeatedly used for image formation.

  Pre-charging exposure comprising an LED (LED exposure device), a halogen lamp, etc., downstream of the transfer device 6 in the rotation direction of the photosensitive drum 2 and upstream of the cleaning device 5 in the rotation direction of the photosensitive drum 2 (before the cleaning process). A device 12 is arranged. The pre-charging exposure device 12 exposes the entire surface of the photosensitive drum before charging by the contact charging member 3 to remove residual charges (electrical memory), so that the surface of the photosensitive member that has become nonuniform due to the previous formed image is removed. This is a pre-charge exposure apparatus for leveling the potential.

(2) Operation Sequence of Image Forming Apparatus FIG. 3 is an operation sequence diagram of the image forming apparatus.

  a. Pre-multi-rotation process: a starting operation period (starting operation period, warming period) of the image forming apparatus. When the main power switch is turned on, a main motor (not shown) of the apparatus is driven to rotate the photosensitive drum 2 to execute a preparatory operation for a predetermined process device.

  b. Pre-rotation step: This is a period during which the pre-printing operation is executed. This pre-rotation process is executed following the pre-multi-rotation process when a print signal is input during the pre-multi-rotation process. When the print signal is not input, the drive of the main motor is temporarily stopped after the previous multi-rotation process is completed, and the rotation of the photosensitive drum 2 is stopped. The image forming apparatus is in a standby (standby) state until the print signal is input. Kept. When the print signal is input, the main motor is driven again, the photosensitive drum 2 rotates, and the pre-rotation process is executed.

  c. Printing process (image forming process, image forming process): When a predetermined pre-rotation process is completed, an image forming process for the rotating photosensitive drum 2 is subsequently performed. As a result, the toner image formed on the surface of the photosensitive drum is transferred to a transfer material, and the fixing process of the toner image by the fixing device is performed, and the image formed product is printed out. In the case of the continuous printing (continuous printing) mode, the above printing process is repeated for a predetermined set number of prints.

  d. Inter-sheet process: Transfer material in the transfer nip portion after the trailing edge of one transfer material passes through the transfer nip in the continuous printing mode and before the leading edge of the next transfer material reaches the transfer nip. This is a non-sheet passing state period.

  e. Post-rotation process: This is a period in which the photosensitive drum 2 is driven to rotate by continuing to drive the main motor for a while after the last transfer material printing process is completed, and a predetermined post-operation is executed.

  f. Standby: When the predetermined post-rotation process is completed, the drive of the main motor is stopped, the rotation of the photosensitive drum 2 is stopped, and the image forming apparatus is kept in a standby state until the next print start signal is input.

  In the case of only one print, the image forming apparatus goes into a standby state after the post-rotation process after the printing is completed. When a print start signal is input in the standby state, the image forming apparatus proceeds to a pre-rotation process.

  The printing process of c is the time of image formation, and the pre-multi-rotation process of a, the pre-rotation process of b, the paper gap process of d, and the post-rotation process of e are non-image formation (non-image formation). Note that the image formation in the pre-charge exposure device 12 is a time when pre-exposure is performed on an area of the photosensitive drum 2 where a toner image will be formed. The image formation in the image exposure apparatus 1 (standard exposure apparatus) is a time when image exposure is performed on the area of the photosensitive drum 2 where a toner image will be formed.

(3) Control of Pre-Charge Exposure Device 12 FIG. 4 is a block diagram of a control system of the pre-charge exposure device 12.

  As described above, the contact charging member 3 is disposed in contact with the photosensitive drum 2. The photosensitive drum 2 has at least two kinds of light emitted from an image exposure apparatus 1 that forms an electrostatic latent image using a laser or the like as a light source and light emitted from a pre-charging exposure apparatus 12 that uses an LED or the like as a light source. The light from the light source can be irradiated. In this embodiment, a laser exposure apparatus is used as the image exposure apparatus 1, and an LED exposure apparatus is used as the pre-charge exposure apparatus. The image exposure apparatus 1 performs light intensity correction (APC = Automatic Power Control). Therefore, a desired amount of light can be output stably over a long period of time.

  The contact charging member 3 is connected to a power supply unit 31 that applies a DC voltage as a charging voltage. The control device 101 is provided with a charging current detection device 32 (charging current detection means) that detects a current flowing through the contact charging member 3. In addition, a pre-exposure light amount control means (a pre-exposure light amount control device that variably controls the light amount of the pre-charge exposure device 12) 33 for controlling the output of the pre-charge exposure device 12 based on the result of the charging current detection device 32 is disposed. The amount of light of the pre-exposure device 12 is controlled.

  In this embodiment, the pre-exposure light quantity control means 33 makes the light quantity variable by changing the current (voltage) input to the pre-charge exposure apparatus 12. The light amount variable means of the pre-charging exposure apparatus 12 is not limited to this, and may be performed by pulse width modulation (PWM) control or the like.

  As a light source of the pre-charging exposure apparatus 12, an LED, a halogen lamp, or the like can be used. Although the light source to be used is not particularly limited, it is preferable to use an LED from the viewpoint of low driving voltage and easy downsizing of the apparatus. In this embodiment, the LED is used.

  It is necessary to set the light amount of the pre-charge exposure device 12 to a light amount that does not generate a ghost image and does not cause toner scattering.

  Here, generation of a ghost image will be described. The surface potential on the surface of the photosensitive drum after image formation is nonuniform according to the formed image. Even if the next charging is performed in this state, it may not be uniformly charged depending on the previous formed image, and the photosensitive drum surface potential at the next exposure by the image exposure apparatus 1 may become non-uniform. A ghost image is generated. Therefore, it is necessary to make the surface potential of the photosensitive drum 2 more uniform by the pre-charge exposure device 12 before charging.

  A ghost image is likely to occur in an image subjected to image exposure next time after an image having a high contrast is formed on a photosensitive drum. That is, the ghost image is generated by calculating the difference between the bright portion potential and the dark portion potential on the surface of the photosensitive drum when the image exposure is performed by the image exposure device 1 that forms an electrostatic latent image by the pre-charge exposure device 12 until the next charging. It is important to make it as small as possible.

  In other words, in a system equipped with the pre-charge exposure device 12, the light portion potential on the surface of the photosensitive drum when exposed by the image exposure device 1 and the light portion potential on the surface of the photosensitive drum when the entire surface is exposed by the pre-charge exposure device 12. Is an important parameter for ghost image generation.

Next, toner scattering will be described. If the surface of the photosensitive drum is uniformly irradiated with a larger exposure amount by the pre-charge exposure device 12 and the potential of the surface of the photosensitive drum is sufficiently equalized, residual toner that has not been transferred in the transfer process will be scattered. May arise. This may occur in an image forming apparatus that performs pre-charge exposure before the cleaning process as in the present embodiment. The toner image formed on the photosensitive drum is formed on the electrostatic latent image formed by the image exposure apparatus 1. The transfer residual toner on the photosensitive drum that has not been transferred to the transfer material 7 by the transfer process also remains on the electrostatic latent image. If the electrostatic latent image is leveled sufficiently uniformly by the pre-charge exposure device 12, the adhesion between the toner and the photosensitive drum is weakened, the toner image remaining on the electrostatic latent image is destroyed, and the toner is exposed to light. It may scatter from the drum. In other words, the occurrence of toner scattering is the difference between the bright portion potential on the surface of the photosensitive drum when exposed by the image exposure device 1 that forms an electrostatic latent image and the dark portion potential when the image is not exposed. It is important not to make it too small.

  In other words, in the image forming apparatus provided with the pre-charging exposure device 12 between the transfer unit and the cleaning unit, the above matters are important parameters for toner scattering. That is, the relationship between the bright part potential on the surface of the photosensitive drum when exposed by the image exposure apparatus 1 and the bright part potential on the surface of the photosensitive drum when exposed entirely by the pre-charging exposure apparatus 12 is an important parameter.

  Here, the charging current detection will be described. While applying a DC voltage to the contact charging member 3 and charging the photosensitive drum surface to a predetermined charging potential (dark portion potential), the image exposure apparatus 1 does not emit light (lights on), and only the pre-charging exposure apparatus 12 emits light. Change to light up (light up). The charging current detector 32 detects the charging current value when the exposed area of the photosensitive drum 2 is charged again by the contact charging member 3.

  FIG. 5 shows the relationship between the light amount (lx · s) of the pre-charging exposure apparatus 12 and the charging current value Ic (μA) as the second current value at this time. Here, the charging potential (dark portion potential) on the surface of the photosensitive drum by the contact charging member 3 is set to −600V.

  There are the following three types of photosensitive drums A, B, and C. That is, the photosensitive drums A and B (thickness: large A> B small) having different film thicknesses (thicknesses of the photosensitive layer) and the photosensitive drums A having substantially the same film thickness and different sensitivities are provided. C (sensitivity; large A> C small) was used.

  The charging current value Ic is a current that flows through the contact charging member 3 when the photosensitive drum 2 is lowered from the dark part potential to the bright part potential by exposure and the lowered bright part potential is charged again to the dark part potential by next charging.

  If the exposure is performed with a larger amount of light, and the amount of change from the dark part potential to the light part potential is large, the amount of discharge when the light is again charged from the light part potential to the dark part potential by the contact charging member next time increases. Flows.

  Therefore, the charging current value Ic has a positive correlation with the amount of change from the dark portion potential to the light portion potential when the photosensitive drum 2 is exposed, that is, the light portion potential on the surface of the photosensitive drum. Further, in the comparison of photosensitive drums having substantially the same sensitivity and different film thicknesses, the thinner the photosensitive drum film, the more the amount of change from the dark part potential to the light part potential is the same. In this case, a larger charging current value Ic is obtained. This is because the charging ability of the photosensitive drum varies depending on the film thickness of the photosensitive drum. In comparison of photosensitive drums having substantially the same film thickness and different sensitivities, if the amount of change in the dark portion potential from the dark portion potential is the same, when the contact charging member 3 is recharged, the charging current value Ic is substantially equal. Become.

  Even if the same experiment was performed using the image exposure apparatus 1 that forms an electrostatic latent image instead of the pre-charge exposure apparatus 12 while exposing the entire surface of the photosensitive drum with a predetermined light amount, A charging current Ico that is a first current value corresponding to the light portion potential flows. However, at this time, the pre-charge exposure device 12 is not turned on.

  From the above experimental results, the charging current value when the entire surface of the photosensitive drum 2 is exposed by one exposure means while applying a direct current voltage to the contact charging member 3 and the surface of the photosensitive drum 2 is uniformly charged, and the photosensitive drum 2 is charged again. Is strongly correlated with the light portion potential on the surface of the photosensitive drum.

  As described above, both the generation of the ghost image and the occurrence of the toner scattering are both the photosensitive drum bright portion potential when the entire surface is exposed by the image exposure device 1 and the photosensitive drum bright portion potential when the entire surface is exposed by the pre-charge exposure device 12. Is an important parameter.

  Here, the image exposure apparatus 1 is used as a standard exposure apparatus (standard exposure apparatus adjusted to a predetermined light amount). The charging current value Ico detected while exposing the entire surface of the photosensitive drum 2 to a predetermined light amount only by the image exposure apparatus 1 is set as a standard value of the charging current. If the charging current detection is used, the charging current value Ico (first current value) and the charging current value Ic (second current) detected while exposing the entire surface of the photosensitive drum 2 only by the pre-charging exposure device 12 are used. And the current value).

  Therefore, it is preferable to pay attention to the parameter [Ic / Ico] and control the light amount of the pre-charging exposure apparatus 12 so that [Ic / Ico] becomes a desired value.

  The parameter used here is the simplest parameter [Ic / Ico], but is not limited to this as long as it is a relational expression between Ic and Ico, such as a relational expression of a difference between the charging current value Ico and the charging current value Ic. It doesn't matter.

  Further, as described above, the magnitude of the charging current value Ic detected while exposing the entire surface of the photosensitive drum 2 using only the pre-charge exposure device 12 varies depending on the film thickness of the photosensitive drum. Furthermore, since the resistance of the contact charging member 3 also varies depending on individual variations, usage conditions, and usage environments, it affects the magnitude of the charging current value Ic. Therefore, it is not preferable to control the light amount of the pre-charging exposure apparatus 12 so that the charging current value Ic becomes a desired value.

  Therefore, the entire surface of the photosensitive drum 2 is exposed only by the image exposure apparatus 1 having a more stable light emission amount, and the pre-charge exposure apparatus 12 is set so that [Ic / Ico] becomes a desired value based on the detected charging current value Ico. Control the amount of light.

  That is, a standard exposure apparatus adjusted to a predetermined light amount is provided. In the present embodiment, the image exposure apparatus 1 is also used as this standard exposure apparatus. At the time of non-image formation, the photosensitive drum 2 charged by applying a predetermined DC voltage to the contact charging member 3 is turned on without exposing the pre-charge exposure device 12 to light, and the standard exposure device 1 is turned on. To expose. The detection result of the charging current detection device 32 when the region of the photoreceptor surface exposed by the standard exposure device 1 is charged again by the contact charging member 3 is defined as a first charging current value. Further, the photosensitive drum 2 charged with a predetermined DC voltage applied to the contact charging member 3 at the time of non-image formation is turned on by exposing the pre-charge exposure device 12 without turning on the standard light source 1. 2 is charged. The detection result of the charging current detection device 32 when the region of the surface of the photoreceptor exposed by the pre-charging exposure device 12 is charged again by the contact charging member 3 is set as a second charging current value. The control device 101 has a control mode for determining the light amount of the pre-charging exposure device 12 during image formation from the relationship between the first charging current value and the second charging current value.

  According to the above control mode, the light amount of the pre-charging exposure device 12 is controlled to a desired value with respect to the usage status / manufacturing variation of the photosensitive drum 2 and the usage status / manufacturing variation of the contact charging member 3. be able to.

  Further, even if the amount of light of the pre-charge exposure apparatus 12 varies due to manufacturing, by controlling the output so that [Ic / Ico] becomes a desired value with respect to the pre-charge exposure apparatus 12, pre-charge The light quantity of the exposure device 12 can be adjusted optimally.

  In addition, it is possible to cope with a case where the light amount of the pre-charge exposure device 12 is reduced due to long-term use or when the user stains the pre-charge exposure device 12. That is, by detecting the standard value Ico of the charging current with the image exposure apparatus 1, the output of the pre-charging exposure apparatus 12 is increased so that [Ic / Ico] becomes a desired value, and a desired value is applied to the photosensitive drum 2. It can be exposed with a light amount. The image exposure apparatus 1 performs light amount correction and can control the light amount for a long time to a desired value. Therefore, by determining the light amount of the pre-charge exposure device 12 based on the image exposure apparatus 1 with a stable light amount, the light amount of the pre-charge exposure device 12 can be set to a desired light amount.

  Even if only the pre-charge exposure device 12 is used (only the charge current value Ic is used), the amount of light of the pre-charge exposure device 12 may change depending on the use situation, which is not successful. This is because when the charging current value Ic fluctuates, it is not known whether the fluctuation is a change due to the usage status of the photosensitive drum 2 or the charging member or a change due to the usage status of the pre-charging exposure apparatus 12.

  Then, the amount of light of the pre-charging exposure device 12 at the time of image formation can be determined appropriately and optimally without using the surface potential detection means. Therefore, a cheaper image forming apparatus can be provided.

The table in FIG. 6 shows that image formation is performed with [Ic / Ico] varied by changing the light amount of the pre-charge exposure device 12 while keeping the light amount of the image exposure device 1 constant at 3.0 [mJ · m ⁻² ]. This is the state of occurrence of ghost images and the state of occurrence of toner scattering. At this time, a predetermined DC voltage was applied to the contact charging member 3, and the charging potential (dark portion potential) of the photosensitive drum 2 was set to -600V.

  There are three types of photosensitive drums A, B, and C. That is, photosensitive drums A and B (thickness: large A> B small) having substantially the same sensitivity and different film thicknesses, and the film thicknesses are substantially equal in sensitivity. Photoconductor drums A and C (sensitivity; large A> C small) were used.

  The ghost images were: x: ghost generation, Δ: slight ghost generation, ◯: no ghost generation.

  As for toner scattering, x: occurrence of toner scattering, Δ: slight occurrence of toner scattering, ○: no occurrence of toner scattering.

When no ghost occurs, all of the photosensitive drums A, B, and C [Ic / Ico ≧ 0.46]
It became the result.

Further, no toner scattering occurs in all of the photosensitive drums A, B, and C [Ic / Ico ≦ 0.58].
It became the result.

Therefore, in order to prevent toner scattering without the occurrence of a ghost image,
[0.46 ≦ Ic / Ico ≦ 0.58]
The light amount of the pre-charging exposure apparatus 12 may be controlled so that

  Next, the light amount control of the pre-charging exposure apparatus 12 will be described. In the present embodiment, the control device 101 executes a sequence for determining the light amount E (n) of the pre-charging exposure device 12 during image formation during pre-multi rotation during non-image formation. The determination of the light amount E (n) of the pre-charge exposure device 12 at the time of image formation is not limited to this. For example, the non-image formation may be performed at the time of pre-rotation or post-rotation.

  First, a predetermined DC voltage is applied to the contact charging member 3 at the time of multiple pre-rotations during non-image formation, and the surface of the photosensitive drum 2 is charged to a predetermined charging potential (dark portion potential) while being exposed by the image exposure apparatus 1. Expose the entire drum surface. Then, the charging current detection device 32 detects the charging current value Ico when the exposure area of the photosensitive drum 2 is recharged by the contact charging member 3. At this time, the light amount of the image exposure apparatus 1 is most preferably the same as that at the time of image formation, but is not limited to this, and other light amounts may be used. An effective result can be obtained as long as a light amount that is within Ico ± 25% is used for the charging current value Ico when the photosensitive drum 2 is exposed with the same light amount as that during image formation.

  That is, the light quantity of the image exposure apparatus 1 as a standard exposure apparatus when acquiring the first charging current value is equal to the light quantity of the image exposure apparatus 1 that forms an electrostatic latent image at the time of image formation. The amount of light of the image exposure apparatus 1 that forms an electrostatic latent image at the time of formation is within ± 25%.

  Subsequently, after the image exposure apparatus 1 is turned off, the light quantity of the pre-charge exposure apparatus 12 is changed from E (1) to E (n) while charging the photosensitive drum surface to a predetermined charging potential (dark part potential). The entire surface of the photosensitive drum is exposed a plurality of times by the pre-charge exposure device 12 while being changed. Then, charging current values Ic (1) to Ic (n) when the exposed area on the surface of the photosensitive drum exposed by E (1) to E (n) is recharged by the contact charging member 3 are charged by the charging current detector 32. Detect and calculate [Ic (n) / Ico].

The calculated value is
[0.46 ≦ Ic (n) /Ico≦0.58]
Then, the light amount of the pre-charging exposure device 12 at the time of image formation is determined to be E (n).

  In this embodiment, [0.46 ≦ Ic (n) /Ico≦0.58] is set, but this value must be determined in advance according to the image forming apparatus.

  Here, the light amount E (n) of the pre-charge exposure device 12 at the time of image formation determined as described above is set smaller than the light amount of the image exposure device 1 that forms an electrostatic latent image on the surface of the photosensitive member at the time of image formation. I have to.

  Thereafter, the image forming apparatus turns off the pre-charging exposure apparatus 12 and turns off the DC voltage applied to the contact charging member 3, and enters the standby mode. When a print start signal is input in the standby state, the image forming apparatus proceeds to a pre-rotation process. The pre-rotation process is executed following the pre-multi-rotation process when a print signal is input during the pre-multi-rotation process.

  The control of the pre-charging exposure apparatus 12 is executed by the control means 101 in accordance with a predetermined control program and a reference table. FIG. 7 shows the control flow diagram.

  STEP 1: A predetermined DC voltage is applied to the contact charging member 3 from the power supply unit 31 to charge the surface of the rotating photosensitive drum 2 to a predetermined charging potential (dark portion potential).

  STEP 2: The entire surface of the photosensitive drum is exposed by the image exposure apparatus 1.

  STEP 3: The charging current detection device 32 detects the charging current value Ico when the exposure area of the photosensitive drum 2 is recharged by the contact charging member 3.

  STEP 4: The exposure by the image exposure apparatus 1 is turned off.

  STEP 5: The entire surface of the photosensitive drum 2 is exposed by the pre-charging exposure device 12 with a light amount of E (n = 1) while a DC voltage is applied to the contact charging member 3.

  STEP 6: The charging current detection device 32 detects the charging current value Ic (1) when the exposure area of the photosensitive drum exposed by the pre-charging exposure device 12 with the light quantity of E (n = 1) is recharged by the contact charging member 3. To do.

  STEP 7, 8, 9: [Ic (n = 1) / Ico] is calculated by the pre-exposure light quantity control means 33, and it is determined whether [0.46 ≦ Ic (n = 1) /Ico≦0.58]. .

  If the determination is No, the process proceeds to STEP 8, the light amount of the pre-charging exposure device 12 is set to E (n + 1), the process returns to STEP 5 again, and the determination is repeated until the determination in STEP 7 becomes Yes.

  When the determination is YES in STEP 7, the process proceeds to STEP 9, and the pre-charging exposure light quantity at the time of image formation is determined to be E (n).

  STEP 10: The pre-charging exposure apparatus 12 and the power supply unit 31 are turned off, and then the image forming apparatus enters a standby state waiting for a print job (print signal). When the print job is received, the pre-charge exposure apparatus receives an E (n) light amount. To form an image.

  As an example, the relationship between the control current input to the pre-charge exposure device 12 and the light amount of the pre-charge exposure device 12 in the initial state of the image forming apparatus is 0.23 with respect to the input control current of 1.0 [mA]. [Lx · s] An image forming apparatus that changes will be described. A process cartridge including the above-described photosensitive drum A was mounted on this image forming apparatus.

  Here, by increasing the control current input to the pre-charge exposure apparatus 12 in steps, the light amounts E (1) to E (n) of the pre-charge exposure apparatus 12 are changed in stages.

  When both the image forming apparatus and the process cartridge are in the initial state, the control current input to the pre-charging exposure apparatus 12 is 5.3 [mA], and the light amount of the pre-charging exposure apparatus 12 at this time is 1.2 [lx・ S].

  After 10000 sheets are formed using this image forming apparatus and process cartridge, the control current input to the pre-charge exposure apparatus 12 is 7.8 [mA], and the light amount of the pre-charge exposure apparatus 12 at this time Was 1.6 [lx · s]. The relationship between the control current input to the pre-charge exposure device 12 and the light amount of the pre-charge exposure device 12 is 0.21 [lx · s] with respect to the input control current of 1.0 [mA]. It was.

  Note that since the optimum exposure light amount of the inter-charge exposure device 12 changes according to the number of image formations, the number of image formations is counted by the control means.

  The reason why the light amount of the pre-charge exposure device 12 has changed from 1.2 [lx · s] to 1.6 [lx · s] due to the use of the image forming apparatus is that the photosensitive characteristics of the photosensitive drum A have changed due to use. is there. Further, the relationship between the control current input to the pre-charge exposure device 12 and the amount of light of the pre-charge exposure device 12 has changed because the light source of the pre-charge exposure device 12 has become dirty or has been used for a long time before being charged. This is because the light emission amount of the light source of the exposure device 12 has decreased.

  In the image forming apparatus including the control sequence as in the present invention, the light amount of the pre-charging exposure apparatus can be appropriately controlled. However, if the pre-charge exposure device is controlled by a method that is not based on the conventional standard exposure device, it is not possible to obtain an appropriate light amount even if the light amount of the pre-charge exposure device is strictly adjusted before shipping. It was. This is because when the light source of the pre-charge exposure apparatus becomes dirty or the light emission amount of the light source of the pre-charge exposure apparatus 12 decreases, it is not possible to obtain an appropriate light amount.

  As described above, the image exposure apparatus 1 is configured such that a predetermined DC voltage is applied to the contact charging member 3 at the time of multiple rotations before non-image formation, and the photosensitive drum surface is charged to a predetermined charging potential (dark portion potential). Alternatively, the entire surface of the photosensitive drum is exposed with a standard exposure apparatus. The charging current value detected at this time is set as a charging current value Ico that is a first current value. Further, the charging current value obtained by exposing the entire surface of the photosensitive drum with the pre-charging exposure device 12 while changing the light amount of the pre-charging exposure device 12 stepwise from E (1) to E (n) is obtained as the second current value. The charging current values are Ic (1) to Ic (n). From the results of the charging current value Ico and the charging current values Ic (1) to Ic (n), image formation is possible regardless of the variations of the photosensitive drum 2, the contact charging member 3, and the pre-charging exposure device 12, and the usage conditions. The amount of light of the pre-charging exposure apparatus 12 at the time can be determined appropriately and optimally. As a result, it is possible to provide an image forming apparatus that suppresses ghosts and maintains good image quality while preventing toner scattering.

  In this embodiment, the pre-charging exposure apparatus is controlled so that the ratio between the charging current value Ico and the charging current value Ic falls within a predetermined range. However, the present invention is not limited to this, and other measures such as setting the difference between the charging current value Ico and the charging current value Ic within a predetermined range may be used.

[Second Embodiment]
A second embodiment of the present invention will be described. In the present embodiment, as shown in FIG. 8, a dedicated standard light source 13 (standard exposure apparatus) that is adjusted in advance to a predetermined light amount is provided separately from the image exposure apparatus 1. In the present embodiment, the standard light source 13 is the same as the image exposure apparatus 1 that forms an electrostatic latent image, and includes a laser, a polygon mirror, and a lens system. The laser light is reflected by the folding mirror 11 and then irradiated on the surface of the photosensitive drum 2. The intensity of the laser light is corrected, and a desired amount of light can be output stably over a long period of time.

  In the present embodiment, the standard light source 13 is a light source that outputs laser light, but is not particularly limited as long as it can stably output a desired light amount over a long period of time.

  Further, the installation position is not particularly limited as long as it can irradiate the photosensitive drum. However, it is preferable to arrange the installation position at a position where it is difficult for the user to touch and dirt.

  In the first embodiment, the image exposure apparatus 1 that performs image exposure is also used as a standard light source to expose the entire surface of the photosensitive drum with a predetermined light amount, and the exposure area on the surface of the photosensitive drum is recharged by the contact charging member 3. The charging current value at that time was defined as a first charging current value Ico. On the other hand, in the second embodiment, a standard light source 13 is provided separately from the image exposure apparatus 1, and the entire surface of the photosensitive drum is exposed with the standard light source 13, and the exposure area on the surface of the photosensitive drum contacts The charging current value when recharged by the charging member 3 was defined as a first charging current value Ico.

  At this time, the amount of light from the standard light source 13 is preferably equal to the amount of light output by the image exposure apparatus 1 that forms the electrostatic latent image during image formation. However, the present invention is not limited to this. good. An effective result is obtained as long as a light amount that is within Ico ± 25% is used with respect to the charging current value Ico when the photosensitive drum 2 is exposed with a light amount equal to the light amount of the image exposure apparatus 1 at the time of image formation.

  Since other configurations and controls are the same as those in the first embodiment, the same components are denoted by the same reference numerals, and detailed description thereof is omitted.

  Here, in the present invention, the electrophotographic photosensitive member 2 is not limited to the drum type, but may be a flexible endless belt type that is rotationally driven.

  The contact charging member 3 is not limited to a roller type, but may be of other forms such as a blade type or a brush type.

  The pre-charging exposure device 12 may be disposed so as to expose the entire surface of the photosensitive drum from the cleaning device 5 downstream in the rotational direction of the photosensitive drum 2 and upstream of the contact charging member 3 in the rotational direction of the photosensitive drum 2. Good. In this case, generation of a ghost image is prevented. Then, since the entire surface of the photoconductor after the transfer residual toner is removed by the cleaning device 5 is exposed by the pre-charging exposure device 12, there is no problem of toner scattering.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. FIG. 2 is an enlarged view of a process cartridge portion of FIG. 1. FIG. 3 is an operation sequence diagram of the image forming apparatus. FIG. 3 is a block diagram of a control system of a pre-charging exposure apparatus. The figure showing the relationship between the light quantity of a pre-charge exposure apparatus, and a charging current. Verification data of the ghost image occurrence status and toner scattering occurrence status. 7 is a flowchart of light amount control of the pre-charging exposure apparatus. FIG. 10 is a schematic configuration diagram of an image forming apparatus according to a second embodiment.

Explanation of symbols

1 .... Image exposure device 1 .... Photosensitive drum 3 .... Contact charging member 4 .... Developing device 5 .... Cleaning device 6 .... Transfer device 7 .... Transfer material 8 .... Fixer 9 ..Storage means, 10 ..Process cartridge, 11 ..Mirror, 12 ..Pre-charge exposure device, 13 ..Standard light source, 31 ..Power supply unit, 32 ..Charge current detection device, 33. Control means, 71..cassette, 72..feed roller, 73..registration roller, T..developer (toner)

Claims (8)

A rotatable electrophotographic photoconductor, a contact charging member that contacts the photoconductor to charge the surface of the photoconductor, a charging current detection device that detects a current value flowing through the contact charging member, and the contact charging In an image forming apparatus comprising: a pre-charge exposure device that exposes the surface of the photoreceptor before charging by a member to remove residual charges;
A standard exposure device that exposes the surface of the photoreceptor that is adjusted to a predetermined amount of light,
During non-image formation, the photosensitive member charged by applying a predetermined voltage to the contact charging member was exposed by turning on the standard exposure device without turning on the pre-charge exposure device. When the surface area of the photosensitive member is charged again by the contact charging member, a first current value flowing through the contact charging member is detected by a charging current detector, and a predetermined value is applied to the contact charging member during non-image formation. An area on the surface of the photoconductor exposed by turning on the pre-charge exposure device without turning on the standard exposure device with respect to the photoconductor charged by applying the voltage of the contact charging member. The second current value flowing through the contact charging member is detected by a charging current detection device when charged again at, and based on the first current value and the second current value, Control to determine the light quantity of the pre-charge exposure device An image forming apparatus wherein a location. The standard exposure device is not lit on the photosensitive member charged to a predetermined potential by the contact charging member, and the pre-charging exposure device is exposed a plurality of times with different light amounts, and is exposed with different light amounts. 2. The image according to claim 1, wherein a plurality of second current values flowing through the contact charging member are detected when the plurality of regions on the surface of the photoconductor are charged again with the contact charging member. Forming equipment.   2. The light amount of the pre-charging exposure apparatus at the time of image formation is determined based on a second current value such that a ratio with the first current value is within a predetermined range. Or the image forming apparatus according to 2; It said standard exposure apparatus, an image forming apparatus according to any one of claims 1 to 3, characterized in that a laser exposure apparatus for performing intensity correction. The pre-charge exposure apparatus, an image forming apparatus according to any one of claims 1 to 4, characterized in that an LED exposure device. The standard exposure apparatus is an image exposure apparatus that forms an electrostatic latent image on a surface of the photoconductor, and the image forming apparatus includes a developing device that develops the electrostatic latent image. The image forming apparatus according to any one of 1 to 5. The amount of light of the standard exposure device when acquiring the first current value is equal to the amount of light of an image exposure device that forms an electrostatic latent image during image formation, or forms an electrostatic latent image during image formation. the image forming apparatus according to any one of claims 1 to 6, characterized in that the light quantity ± is within 25% of the image exposure apparatus. Light quantity of the pre-charge exposure device at the time of image formation, any one of claims 1 to 7, characterized in that the surface of the photosensitive member during image formation is smaller than the light quantity of the image exposure device for forming an electrostatic latent image The image forming apparatus described in the item .