JP2015230348A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus, in which a sufficient space where separation means for separating a transfer material from an image carrier is to be disposed to oppose to the image carrier can be secured in a periphery of the image carrier when it is required to dispose writing means closer to the image carrier, and rubbing on an image can be prevented.SOLUTION: The image forming apparatus includes: a photoreceptor drum 1; a charging roller 2 for charging the photoreceptor drum 1; an optical writing device 3 disposed to oppose to the photoreceptor drum, which writes a latent image on the photoreceptor drum 1; a developing device 4 for developing the latent image by using a toner; a transfer roller 11 for transferring the toner image from the photoreceptor drum 1 onto a recording sheet P; and a cleaning device 5 for cleaning the photoreceptor drum 1. A conveyance path of the recording sheet P is configured in such a manner that a direction where the recording sheet P is conveyed toward a transfer nip, and a direction where the recording sheet P is discharged from the transfer nip, make an angle of less than 180° on a side where the transfer roller 11 is disposed.

Description

  The present invention relates to an image forming apparatus.

  As an image forming apparatus such as a copying machine or a printer, an apparatus using a light emitting diode (LED) array in an optical writing apparatus (hereinafter referred to as “LED system”) is known, such as Patent Document 1. In the LED method, the size of the optical writing device is smaller than that using a laser diode (LD) in the optical writing device (hereinafter referred to as “LD method”), so that the device size can be reduced. . In addition, the LED system can simplify the mechanism of the apparatus compared to the LD system. For this reason, the LED method is often used in the direct transfer type image forming apparatus that is widely used in low-priced products.

  Since the emission of LED has variations in wavelength and amplitude, the focal point cannot be reduced and the energy density cannot be increased. For this reason, in the LED system, it is necessary to arrange an optical writing device as writing means close to the photosensitive drum.

  FIG. 4 shows a schematic configuration around the photosensitive drum of a conventional machine by direct transfer using the LED method. A charging roller 202, an optical writing device 203, a developing device 204, a transfer roller 211, a cleaning device 241, and the like are arranged in order with respect to the rotation direction of the photosensitive drum 201 (arrow A in the drawing). A transfer nip is formed by the transfer roller 211 being pressed against the photosensitive drum 201. In the LED system, the optical writing device 203 as writing means needs to be arranged close to the photosensitive drum 201. Therefore, as shown in FIG. 4, the optical writing device 203 is disposed between the charging roller 202 and the developing device 204 so as to face the photosensitive drum 201. In order to arrange the optical writing device 203, a gap of about 10 mm is required between the charging roller 202 and the developing device 204.

  FIG. 5 shows a schematic configuration around a photosensitive drum of a general image forming apparatus by direct transfer using the LD method. Since the LD emits light with relatively little variation in wavelength and amplitude and has the same phase, the focal point can be made extremely small and the energy density can be increased. In the LD method, the energy density of the laser beam can be increased, so that the optical writing device can be arranged at a position away from the photosensitive member. It is sufficient if there is a gap of about 3 mm between the charging roller 102 and the developing device 104 for securing the optical path of the laser beam.

  The LED method requires a wider gap between the charging roller 202 and the developing device 204 than the LD method. As shown in FIG. 4, when the position of the developing device 204 is moved toward the transfer roller 211 to widen the space between the charging roller 202 and the developing device 204, the position of the transfer roller 11 is also moved toward the cleaning device 205. There is a need to. As a result, the space between the transfer roller 211 and the cleaning device 205 becomes narrow, so that a space for disposing the separation claw cannot be secured between the transfer roller 211 and the cleaning device 205. If the separation claw cannot be arranged, there is a problem that the separation property for separating the recording paper P from the photosensitive drum 201 becomes insufficient and thin paper or the like cannot be separated.

  Further, since the optical writing device 203 is disposed facing the photosensitive drum 201, the positions of the developing device 204 and the cleaning device 205 that are also disposed facing the photosensitive drum 201 are closer to each other. . As shown in FIG. 4, the direction in which the recording paper P is conveyed toward the transfer nip (arrow B in the figure) and the direction in which the recording paper P that has passed through the transfer nip is discharged (arrow C in the figure) These are tangential directions of the photosensitive drum 201 at the contact point between the photosensitive drum 201 and the transfer roller 211. That is, the direction in which the recording paper P is conveyed to the transfer nip and the direction in which the recording paper P is discharged from the transfer nip are horizontal (angle A0 in the figure is 180 °). In order to prevent the direction (arrow B in the figure) in which the recording paper P is conveyed toward the transfer nip from interfering with the developing device 204, it is necessary to dispose them both to some extent. The direction in which the recording paper P is conveyed toward the transfer nip (arrow B in the figure) and the direction in which the recording paper P is discharged from the transfer nip (arrow C in the figure) when the developing device 204 is arranged to some extent are It approaches the cleaning device 105. As a result, the recording paper P that has passed through the transfer nip is likely to come into contact with the cleaning device 105, and there is also a problem that the image surface of the recording paper P is rubbed and an image defect is likely to occur.

  The present invention has been made in view of the above background, and an object of the present invention is to provide separation means for separating a transfer material from an image carrier when the writing means needs to be arranged close to the image carrier. To provide an image forming apparatus capable of securing a sufficient space around the image bearing member to be disposed so as to face the body and preventing image rubbing.

  An image carrier that carries and rotates a toner image; a charging unit that charges the image carrier; a writing unit that is disposed opposite to the image carrier and writes a latent image on the image carrier; And developing means for developing the latent image using toner to form a toner image, and a transfer nip is formed on the image carrier by contacting the toner image, and the toner image is sandwiched between the image carrier and the transfer nip. In the image forming apparatus including a transfer unit that transfers onto a transfer material and a cleaning unit that cleans the image carrier, a direction in which the transfer material is conveyed toward the transfer nip, and the transfer material is in the transfer nip. The transfer material conveyance path is configured such that the direction of discharge from the transfer device forms an angle of less than 180 ° on the side where the transfer means is disposed.

  When the writing means is disposed opposite to the image carrier, a sufficient space is provided around the image carrier so that the separating means for separating the transfer material from the image carrier is disposed opposite the image carrier. As well as image blurring.

1 is a schematic configuration diagram of a printer according to an embodiment. FIG. 2 is a schematic configuration diagram around a photosensitive drum in the printer. FIG. 4 is a diagram illustrating a positional relationship between the periphery of the photosensitive drum and a recording paper conveyance path. FIG. 3 is a schematic configuration diagram of the periphery of a photosensitive drum of a conventional machine that is directly transferred by an LED method. FIG. 2 is a schematic configuration diagram of a periphery of a photosensitive drum of a general image forming apparatus by direct transfer using an LD method.

  Hereinafter, an embodiment in which the present invention is applied to an electrophotographic laser beam printer will be described. First, the overall configuration and operation of the printer will be described.

FIG. 1 is a schematic configuration diagram illustrating a configuration of a printer 20 according to the present embodiment.
As shown in FIG. 1, the printer 20 includes a process cartridge 10 including a photosensitive drum 1 as an image carrier at a substantially central portion of the machine frame. The photoreceptor drum is, for example, a negatively charged organic photoreceptor having a diameter of 30 mm, and has a photoreceptor layer (not shown) on an aluminum drum base (not shown). Below the process cartridge 10, there is provided a transfer roller 11 for transferring a toner image formed on the photosensitive drum 1 formed by the process cartridge 10 onto a recording sheet as a transfer material. A sheet cassette 12 serving as a sheet material storage unit for storing and storing sheets as recording media for transferring a toner image on the photosensitive drum 1 is sequentially placed under the machine frame, and sheets are sequentially supplied from the sheet cassette 12. A paper feed roller 13 is provided for feeding to a transfer portion between the photoreceptor 1 and the transfer roller 11. Further, on the left side of the process cartridge 10 in the drawing, a fixing device 15 for fixing the toner image on the recording paper is provided. Further, a manual feed tray 100 as a paper placement device is provided on the right side of the process cartridge 10 in the drawing.

FIG. 2 is a diagram showing a schematic configuration around the photosensitive drum in the printer.
As shown in FIG. 2, a charging roller 2 as a charging unit and an optical writing device as an optical writing unit are arranged around the photosensitive drum 1 in order with respect to the rotation direction of the photosensitive drum 1 (arrow A in the figure). 3. A developing device 4 as a developing means, a separation claw 40 as a transfer material separating means, a cleaning device 5 as a cleaning means, and the like are arranged. The photosensitive drum 1, the charging roller 2, the optical writing device 3, the developing device 4, and the cleaning device 5 disposed around the photosensitive drum 1 are supported by a common support as a process cartridge 10, and are attached to the printer main body. It can be attached and detached as a unit. The developing device 4 has a predetermined layer thickness of a rotatable developing sleeve 4a disposed to face the photosensitive drum 1 with a predetermined gap (about 300 μm), and a developer such as toner on the developing sleeve 4a. A regulation blade 4b and the like are provided. The transfer roller 11 is disposed opposite to the photosensitive drum 1 and forms a transfer nip by being pressed against the surface of the photosensitive drum 1 with a predetermined pressing force. The cleaning device 5 has a cleaning blade 5a.

Next, an image forming operation by the image forming apparatus will be described.
In FIG. 2, when image information is input from a host computer (not shown), the photosensitive drum 1 is driven at a predetermined peripheral speed (for example, 180 mm / sec) in the direction of arrow A (clockwise) by driving a main motor (not shown). ), And the surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. When LED light emitted from an LED array (not shown), which is a plurality of light emitting elements in the optical writing device 3, hits the photosensitive drum 1 based on the image data, the potential of the exposed portion on the photosensitive drum 1 is changed. The electrostatic latent image is formed by lowering. Then, it was charged to the same polarity as the charging polarity (negative polarity) of the photosensitive drum 1 by the developing sleeve 4a of the developing device 4 to which the developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 1 was applied. A developer such as toner is attached to the electrostatic latent image formed on the photosensitive drum 1 and is reversely developed (visualized) as a toner image. The plurality of light emitting elements in the optical writing device 3 are not limited to the LED array, but may be anything as long as they need to be arranged close to the photosensitive drum 1. For example, a plurality of organic EL elements may be used.

  In FIG. 1, the recording paper P is separated and conveyed one by one from the paper feed cassette 12 by the paper feed roller 13 or from the manual feed tray 100 by the manual paper feed roller 17, and is stopped by hitting the registration roller 14. It is done. Then, the recording paper P that has stopped against the registration roller 14 is sent to the transfer nip in accordance with the timing of toner image formation of the process cartridge 10.

  For example, a transfer bias in which an AC component is superimposed on a DC component is applied to the transfer roller 11 from a transfer bias power source (not shown). An electrostatic force is generated between the photosensitive drum 1 and the transfer roller 11 by the transfer roller 11 to which a transfer bias having a polarity opposite to that of the toner (positive polarity) is applied, and the electrostatic force is conveyed to the transfer nip by the electrostatic force. A toner image on the photosensitive drum 1 is transferred to the recording paper P. The recording paper P onto which the toner image has been transferred is separated from the photosensitive drum 1 and conveyed to the fixing device 15.

Next, the arrangement of components in the vicinity of the transfer nip around the photosensitive drum, which is a feature of the present invention, will be described in detail.
In FIG. 2, the position of the transfer roller 11 with respect to the photosensitive drum 1 is determined so that the separation claw 40 can be disposed between the transfer roller 11 and the cleaning device 5 around the photosensitive drum. The separation claw 40 is disposed to face the photosensitive drum 1. Further, as indicated by an arrow B in the drawing, a conveyance path for conveying the recording paper P to the transfer nip is configured so that the recording paper P hits the surface of the photosensitive drum 1.

  By providing the separation claw 40, the recording paper P on which the toner image is transferred can be effectively separated from the photosensitive drum 1. As a method of separating the recording paper P from the photosensitive drum 1, a method of providing a conductive brush to which a bias voltage is applied and bringing it into contact with the recording paper P is also conceivable. In this method, the recording sheet P is separated from the photosensitive drum 1 by removing the charge of the recording sheet P attached to the photosensitive drum 1 by electrostatic force with a charging brush. However, in this method, when the recording paper P is a thin paper having a basis weight or less (for example, having a thickness of about 52 gsm) or when the recording paper P is curled, the recording paper P is exposed to light. There is a possibility that it cannot be separated from the body drum 1 well. By providing the separation claw 40, the recording paper P can be reliably separated from the photosensitive drum 1 even in such a case.

  When the space between the transfer roller 11 and the cleaning device 5 is widened, the space between the transfer roller 11 and the developing device 4 is narrowed. For this reason, when the recording paper P is conveyed toward the transfer nip from the tangential direction of the photosensitive drum 1 at the contact point between the photosensitive drum 1 and the transfer roller 11 as in the prior art, the conveying path (arrow D in the figure). ) Interferes with the developing device 4. By conveying the recording paper P so as to hit the surface of the photosensitive drum 1, the conveyance path can be prevented from interfering with the developing device 4.

  In general, the recording paper P that has passed through the transfer nip is discharged in the tangential direction of the photosensitive drum 1 at the contact point between the photosensitive drum 1 and the transfer roller 11. By transporting the recording paper P so as to hit the surface of the photosensitive drum 1, an angle formed between the direction in which the recording paper P is transported to the transfer nip and the direction in which the recording paper P is discharged from the transfer nip (the angle in the figure). A) can be made smaller than that of the conventional machine (angle A0 in the figure). As a result, the conveyance path of the recording paper P discharged from the transfer nip in the tangential direction of the photosensitive drum 1 is separated from the cleaning device 5, so that the recording paper P on which the toner image is formed comes into contact with the cleaning device 5. The occurrence of rubbing can be prevented.

  When the transfer roller 11 is used as the transfer means, it is natural that the recording paper P that has passed through the transfer nip is discharged in the tangential direction of the photosensitive drum 1. For this reason, in the present embodiment, the recording paper P is transported so as to hit the surface of the photosensitive drum 1 and the recording paper P is transported in a tangential direction from the transfer nip so that the recording paper P is transported. ing. Conversely, the conveyance path of the recording paper P may be configured so that the recording paper P is conveyed from the tangential direction of the photosensitive drum 1 to the transfer nip and discharged from a direction other than the tangential direction of the photosensitive drum 1. Good. In this configuration, instead of the transfer roller 11, for example, a suction belt type may be used as the transfer unit.

  In order to prevent the image surface of the recording paper P on which the toner image is formed from coming into contact with the cleaning device 5, a method of arranging a spur on the lower surface of the cleaning device 5 is also conceivable. However, when the space between the transport path 42 and the cleaning device 5 is narrow, the distance between the spur and the transport path 42 is short, so that the recording paper P passes between the spur and the transport path 42. There is a risk of spurs. Further, in order to surely avoid the recording paper P coming into contact with the cleaning device 5, it is necessary to use a large number of spurs, which is disadvantageous in terms of cost.

  As shown in FIG. 3, a depression may be provided in a portion of the conveyance path 42 located below the cleaning apparatus 5 so that the distance between the cleaning apparatus 5 and the conveyance path 42 is sufficiently large. Generally, since the conveyance speed in the fixing process is slower than the conveyance speed in the transfer process, curling may occur on the recording paper P between the transfer nip and the fixing device 15. By providing the depression in the transport path 42, the curl generated on the recording paper P can be absorbed by the depression, so that the occurrence of image rubbing due to the recording paper P coming into contact with the cleaning device 5 can be prevented more reliably. be able to.

What has been described above is an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
An image carrier that carries and rotates a toner image; a charging unit that charges the image carrier; a writing unit that is disposed opposite to the image carrier and writes a latent image on the image carrier; And developing means for developing the latent image using toner to form a toner image, and a transfer nip is formed on the image carrier by contacting the toner image, and the toner image is sandwiched between the image carrier and the transfer nip. In the image forming apparatus including a transfer unit that transfers onto a transfer material and a cleaning unit that cleans the image carrier, a direction in which the transfer material is conveyed toward the transfer nip, and the transfer material is in the transfer nip. The transfer material conveyance path is configured so that the direction of discharge from the recording medium forms an angle of less than 180 ° on the side where the transfer means is disposed.
Conventionally, the direction in which the recording paper P is conveyed toward the transfer nip and the direction in which the recording paper P that has passed through the transfer nip is discharged are both the photosensitive drum 1 at the contact point between the photosensitive drum 1 and the transfer roller 11. Is the tangential direction. That is, the direction in which the recording paper P is conveyed to the transfer nip and the direction in which the recording paper P is discharged from the transfer nip are horizontal. In this configuration, when a light emitting element that requires the optical writing device 3 to be disposed to face the photosensitive drum 1 such as an LED array is used, the photosensitive drum 1 is equivalent to the amount of the optical writing device 3 disposed. Since the surrounding space is eliminated, the separation claw 40 cannot be disposed around the photosensitive drum 1. The direction in which the recording paper P is conveyed toward the transfer nip and the direction in which the recording paper P is discharged from the transfer nip are not horizontal (180 °) as in the prior art, but form an angle (less than 180 °). Thus, by configuring the conveyance path of the recording paper P, a space for disposing the separation claw 40 can be secured.
In addition, since the conveyance path in the direction in which the recording paper P is discharged from the transfer nip is separated from the cleaning device 5, the recording paper P on which the toner image is formed is prevented from coming into contact with the cleaning device 5. can do.

(Aspect B)
In aspect A,
The transfer material conveyance path is configured so that the direction in which the transfer material is conveyed toward the transfer nip is horizontal.
As a result, when the writing unit is disposed to face the image carrier, a sufficient space is provided for placing the separating unit for separating the transfer material from the image carrier to face the image carrier. While securing around the carrier, it is possible to prevent image rubbing.

(Aspect C)
In aspects A to B,
Transfer material separating means for contacting the image carrier and separating the transfer material from the image carrier is provided.
Thereby, the separation property of separating the recording paper P discharged from the transfer nip from the photosensitive drum 1 can be improved.

(Aspect D)
In aspects A to C,
A transfer path for transferring the transfer material discharged from the transfer nip toward a subsequent process is provided, and a recess is provided in a portion of the transfer path positioned below the cleaning unit.
Generally, since the conveyance speed in the fixing process is slower than the conveyance speed in the transfer process, curling may occur on the recording paper P between the transfer nip and the fixing device 15. By providing a dent in the portion of the transport path 42 located below the cleaning device 5, the curl generated in the recording paper P can be absorbed by the dent, so that the recording paper P comes into contact with the cleaning device 5. Generation of image blur can be prevented more reliably.

1 Photosensitive drum (image carrier)
2 Charging roller (charging means)
3 Optical writing device (writing means)
4 Developing device (Developing means)
4a Developing sleeve 4b Regulating blade 5 Cleaning device 5a Cleaning blade 10 Process cartridge 11 Transfer roller (transfer means)
15 Fixing device 40 Separation claw (transfer material separation means)
142 Conveyance path P Recording paper

JP 2014-002350 A

Claims (4)

An image carrier that carries a toner image and is driven to rotate;
Charging means for charging the image carrier;
A writing unit disposed opposite to the image carrier and writing a latent image on the image carrier;
Developing means for developing the latent image using toner to form a toner image;
A transfer means for contacting the image carrier to form a transfer nip and transferring the toner image from the image carrier onto a transfer material sandwiched in the transfer nip;
In an image forming apparatus comprising a cleaning means for cleaning the image carrier,
The transfer material is conveyed such that the direction in which the transfer material is conveyed toward the transfer nip and the direction in which the transfer material is discharged from the transfer nip form an angle of less than 180 ° with respect to the side where the transfer means is disposed. An image forming apparatus comprising a path. The image forming apparatus according to claim 1.
An image forming apparatus, wherein a transfer material conveyance path is configured such that a direction in which the transfer material is conveyed toward the transfer nip is horizontal. The image forming apparatus according to claim 1, wherein
An image forming apparatus comprising: a transfer material separating unit that contacts the image carrier and separates the transfer material from the image carrier. The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus, comprising: a conveyance path for conveying the transfer material discharged from the transfer nip toward a subsequent process, wherein a depression is provided in a portion of the conveyance path positioned below the cleaning unit.

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