Image forming apparatus

An image forming apparatus includes: a photosensitive drum; a light guide plate that irradiates, onto the photosensitive drum, light incoming through an end thereof by emitting the light from an irradiation end surface thereof; a static elimination light source that is disposed near the end of the light guide plate and emits the light into the light guide plate; and a blocking wall that is disposed between the light guide plate and the photosensitive drum to cover the irradiation end surface, and restricts the light emitted from the irradiation end surface non-uniformly in a longitudinal direction of the light guide plate. Of the light emitted from the irradiation end surface, portions emitted from end regions located around ends of the light guide plate are less restricted by the blocking wall than a portion emitted from a region other than the end regions of the light guide plate.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an image forming apparatus that performs static elimination on a photosensitive drum using light.

Description of the Background Art

It is conventional to eliminate static from a photosensitive drum by irradiating the photosensitive drum with light from a static elimination lamp in image forming apparatuses such as copiers, facsimile machines, printers, and multifunction peripherals. An image forming apparatus includes, for example, an image forming unit (image former), a transfer device, and a fixing device as an image forming mechanism. The image forming unit forms a toner image. The toner image formed is transferred onto paper. The fixing device fixes the transferred toner image to the paper. The paper having the image formed thereon is ejected out of the image forming apparatus.

The image forming unit has a photosensitive drum, a development device, and the like. An electrostatic latent image is formed on the photosensitive drum and developed into a toner image, and the toner image is transferred from the photosensitive drum onto paper. After the toner image has been transferred onto the paper, the photosensitive drum is irradiated with light (static elimination light) from a static elimination lamp to reduce the potential of the photosensitive drum. Thus, static is eliminated from the photosensitive drum, so that a next electrostatic latent image can be formed thereon.

Preferably, a static elimination device including the static elimination lamp performs the static elimination using light having a uniform dose distribution by uniformly irradiating static elimination light onto the photosensitive drum, so that image degradation can be prevented or reduced. Various techniques have been disclosed regarding such a static elimination device.

For example, Japanese Unexamined Patent Application Publication No. 2001-042715 discloses an image forming apparatus including a light path restriction member that restricts static elimination light emitted by a static elimination lamp from being irradiated onto ends of a photosensitive drum.

For another example, Japanese Unexamined Patent Application Publication No. 2017-181878 discloses a static elimination device including: a light source; a light guide member having an end surface (one end surface) that receives incoming light from the light source and an end surface (opposite end surface) opposite to the one end surface; a reflective member that causes the light emitted from the opposite end surface of the light guide member to re-enter the light guide member; and a holding member that holds an opposite end surface-ward end of the light guide member. The light guide member includes, on a surface thereof located away from an image bearing member, a reflective portion that extends in an axial direction and reflects the light incoming through the one end surface. The light guide member also includes a light emission surface which faces the image bearing member and from which the light reflected by the reflective portion is emitted toward the image bearing member. The light guide member has a static elimination region where the light emitted from the light emission surface is irradiated onto the image bearing member and a light-blocking region where the holding member blocks the light emitted from the light emission surface. The static elimination region and the light-blocking region are adjacent to each other in the axial direction. The reflective portion continuously spans across the static elimination region and at least a portion of the light-blocking region.

The image forming apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2001-042715 and the static elimination device disclosed in Japanese Unexamined Patent Application Publication No. 2017-181878 are aimed at uniform static elimination on the photosensitive drum (image bearing member) and reduction of image degradation. Other than the inventions disclosed in Japanese Unexamined Patent Application Publication No. 2001-042715 and Japanese Unexamined Patent Application Publication No. 2017-181878, inventions aimed at uniform static elimination on photosensitive drums have been proposed.

However, the conventional image forming apparatus and the conventional static elimination device described above are not sufficient in terms of uniform static elimination, and an image forming apparatus that achieves higher performance has been desired. In the case of a recent less-expensive model of image forming apparatus including a charging roller, in particular, a light guide plate having a Fresnel pitch is used with a single light source provided at one end thereof, in terms of cost reduction. However, it is difficult to apply such a light guide plate having a Fresnel pitch to the invention disclosed in Japanese Unexamined Patent Application Publication No. 2001-042715. It is possible to apply a light guide plate having a Fresnel pitch to the invention disclosed in Japanese Unexamined Patent Application Publication No. 2017-181878. However, it is difficult to achieve a uniform dose distribution on the image bearing member, and therefore chargeability of the image bearing member tends to be non-uniform in portions around ends thereof.

The present invention has been made in view of the circumstances described above, and an object thereof is to provide an image forming apparatus that achieves cost reduction, static elimination on a photosensitive drum with light having a uniform dose distribution, and prevention or reduction of image degradation.

SUMMARY OF THE INVENTION

An image forming apparatus according to an embodiment of the present invention includes: a photosensitive drum; a light guide plate that is disposed with a longitudinal direction thereof being substantially parallel to an axial direction of the photosensitive drum and that irradiates, onto the photosensitive drum, static elimination light incoming through an end thereof by emitting the static elimination light from an irradiation end surface thereof, the irradiation end surface of the light guide plate being a surface facing the photosensitive drum; a light source that emits the static elimination light into the light guide plate, the light source being disposed in the vicinity of the end of the light guide plate; and a blocking member that restricts the static elimination light emitted from the irradiation end surface in a non-uniform manner in the longitudinal direction of the light guide plate, the blocking member being disposed between the light guide plate and the photosensitive drum, and covering the irradiation end surface, wherein the static elimination light emitted from the irradiation end surface includes static elimination light emitted from end regions located around ends of the light guide plate and static elimination light emitted to a central region being a region other than the end regions of the light guide plate, and the static elimination light emitted from the end regions is less restricted by the blocking member than the static elimination light emitted from the central region.

According to this configuration, the static elimination light emitted from the irradiation end surface is irradiated onto the photosensitive drum after being restricted by the blocking member. Portions of the static elimination light emitted from end regions located around ends of the light guide plate are less restricted by the blocking member than a portion emitted to a central region being a region other than the end regions of the light guide plate. According to this configuration, the static elimination light irradiated onto the photosensitive drum achieves a more uniform dose distribution throughout a length of the photosensitive drum in the axial direction (longitudinal direction) of the photosensitive drum. This reduces non-uniformity in chargeability of the photosensitive drum and image unevenness that can occur during image formation.

In the image forming apparatus described above, the blocking member may be a blocking wall having a height that varies according to locations in the longitudinal direction, and being disposed substantially parallel to the axial direction of the photosensitive drum between the light source and the photosensitive drum, and the blocking wall may restrict the static elimination light emitted from the irradiation end surface by blocking the static elimination light.

According to this configuration, the blocking wall restricts the static elimination light emitted from the irradiation end surface. Thus, it is possible to restrict the static elimination light more reliably with a simple configuration.

In the image forming apparatus described above, the height of the blocking wall may be higher in a portion corresponding to the central region than in portions corresponding to the end regions.

According to this configuration, the degree of the restriction on the static elimination light emitted from the irradiation end surface is higher in the central region than in the end regions. Thus, the static elimination light irradiated onto the photosensitive drum achieves a more uniform dose distribution throughout the length of the photosensitive drum in the axial direction (longitudinal direction) of the photosensitive drum. This reduces non-uniformity in chargeability of the photosensitive drum and image unevenness that can occur during image formation.

In the image forming apparatus described above, the blocking wall may be stair-like and have a plurality of levels of height, and boundaries between the different levels of height may be vertical.

This configuration makes it possible to accurately set the restriction on the static elimination light to a desired degree for each of the regions that are different in the height of the blocking wall. It is therefore possible to achieve a desired dose distribution throughout the length of the photosensitive drum in the axial direction (longitudinal direction) of the photosensitive drum.

In the image forming apparatus described above, the end regions may not be provided with the blocking wall.

The structure according to this configuration that eliminates the need for the blocking wall in the end regions allows for a reduction in cost for manufacturing the blocking wall. Since the end regions are not provided with the blocking wall, the static elimination light in these regions can be efficiently used, avoiding a waste of the static elimination light, and thus reducing power consumption.

The image forming apparatus described above may further include a housing that accommodates the light guide plate therein, the housing having an opening in a side thereof facing the photosensitive drum. In this configuration, the blocking wall may be provided on an edge of the opening of the housing, the blocking wall may not be provided around ends of the housing, and the edge of the opening may have grooves around the ends of the housing to widen the opening.

According to this configuration, the opening is widened at ends of the edge, thereby reducing the restriction on the static elimination light. It is therefore possible to use the static elimination light efficiently. Since the opening is widened by forming the grooves in the housing, a common housing may be used for different models by forming grooves as necessary. The use of the common housing for different models allows for mass production of the housing, achieving cost reduction.

In the image forming apparatus described above, the blocking wall may be provided with a reflective member on a surface thereof facing the irradiation end surface, and the reflective member diffusely reflects light.

According to this configuration, a portion of the static elimination light emitted from the irradiation end surface is diffusely reflected by the reflective member, and the resulting scattered light is reflected off the irradiation end surface and re-emitted from the irradiation end surface. Repetition of such light emission from the irradiation end surface reduces non-uniformity in light emitted from the irradiation end surface that can occur in a light guide plate having a Fresnel pitch. Thus, it is possible to reduce occurrence of a defect such as a fringe pattern in an image formed.

In the image forming apparatus described above, the height of the blocking wall may be at a highest level in a location corresponding to a dose peak in a dose distribution of the static elimination light irradiated onto the photosensitive drum from the light source without the blocking wall, and the height of the blocking wall may be determined according to the dose distribution.

According to this configuration, it is possible to achieve an optimal height of the blocking wall. Thus, the static elimination light irradiated onto the photosensitive drum achieves a more uniform dose distribution throughout the length of the photosensitive drum in the axial direction (longitudinal direction) of the photosensitive drum. This reduces non-uniformity in chargeability of the photosensitive drum and image unevenness that can occur during image formation.

According to the present invention, it is possible to provide an image forming apparatus that achieves cost reduction, static elimination on a photosensitive drum with light having a uniform dose distribution, and prevention or reduction of image degradation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following describes Embodiment 1 of the present invention in detail with reference to the accompanying drawings.FIG. 1is a schematic cross-sectional view of an image forming apparatus100according to Embodiment 1 of the present invention.

The image forming apparatus100according to Embodiment 1 is an electrophotographic image forming apparatus, and includes an image reader1, an image former3disposed under the image reader1, and a paper feeder2disposed under the image former3as illustrated inFIG. 1.

The image reader1includes a document table11including transparent glass, an automatic document feeder (ADF)12that automatically feeds a document onto the document table11, and a document image reader13that scans and reads an image of the document placed on the document table11. The image former3is provided in an image forming apparatus main body110. The image former3includes a photosensitive drum30(image bearing member) and various constituent elements disposed around the photosensitive drum30for performing an electrophotographic process.

The image former3includes the photosensitive drum30, a charger31, an exposure device32, a developing device33, a transfer device50, a static eliminator34, and a cleaner55.

The charger31, the exposure device32, the developing device33, the transfer device50, the static eliminator34, and the cleaner55are provided around the photosensitive drum30in the stated order.

The charger31uniformly charges a surface of the photosensitive drum30to a predetermined potential through application of a direct-current (DC) voltage. The charger31includes a charging roller31aand a charger cleaning roller31b. Only a direct-current voltage component excluding an alternating-current voltage component is applied to the charging roller31a. The charging roller31apassively rotates in accompaniment to rotation (surface movement) of the photosensitive drum30while in contact with the surface of the photosensitive drum30. The charger cleaning roller31bcleans a surface of the charging roller31a. The charger cleaning roller31bpassively rotates in accompaniment to rotation (surface movement) of the charging roller31awhile in contact with the surface of the charging roller31a.

The exposure device32emits image writing light modulated based on image data from a laser light source32atoward the photosensitive drum30. More specifically, the exposure device32(laser light source32a) irradiates the surface of the photosensitive drum30rotating and being uniformly charged to the predetermined potential with the image writing light while scanning the image writing light in a main scanning direction. Thus, the exposure device32can write a latent image (electrostatic latent image) on the photosensitive drum30.

The developing device33makes visible the latent image formed on the photosensitive drum30with a toner. The developing device33causes a charged toner to adhere to the latent image formed on the photosensitive drum30by the exposure device32. By thus making visible the latent image on the photosensitive drum30, the developing device33can develop the latent image into a toner image.

The transfer device50electrostatically transfers the toner image formed on the photosensitive drum30onto paper P such as image transfer paper. The transfer device50includes a transfer roller51(transfer member). The transfer roller51passively rotates in accompaniment to the rotation (surface movement) of the photosensitive drum30while in contact with the surface of the photosensitive drum30. A transfer bias (voltage) is applied to the transfer roller51.

The static eliminator34eliminates residual potential remaining on the photosensitive drum30after the image transfer. The static eliminator34is located downstream of the transfer device50and upstream of the charger31in a rotation direction of the photosensitive drum30. In the present example, the static eliminator34is disposed between the transfer device50and the cleaner55. The static eliminator34eliminates residual potential remaining on the photosensitive drum30by irradiating the surface of the photosensitive drum30with light (static elimination light), as described in detail below.

The cleaner55removes residual toner remaining on the photosensitive drum30after the image transfer without being transferred by the transfer device50. The residual toner removed by the cleaner55is collected in a waste toner collection container (not shown) disposed between a front cabinet of the image forming apparatus100and the image former3.

As illustrated inFIG. 1, the image former3includes a fixing device38. After the toner image has been transferred onto the paper P by the transfer device50, the fixing device38fixes the toner image to the paper P through heating. The fixing device38includes a heating roller39and a fixing roller40. The heating roller39is heated to a predetermined fixing temperature. The fixing roller40is pressed against the heating roller39at a predetermined fixing pressure. Thus, the fixing device38can fuse the toner image on the paper P using the heat from the heating roller39and fix the toner image to the paper P using the fixing pressure of the fixing roller40exerted on the heating roller39.

The image forming apparatus100further includes the paper feeder2and a transporter4. The paper feeder2includes a paper feed cassette21and a manual paper feed tray22as a plurality of paper feed devices. The image forming apparatus100selects one paper feed device from the paper feed cassette21and the manual paper feed tray22. Furthermore, the image forming apparatus100separately transports the paper P to the transporter4one sheet at a time using a pickup roller23for the selected paper feed device. The transporter4includes a registration roller20, an ejection roller25, and a transport roller26. The registration roller20transports, in a transport direction Y, the paper P sent thereto from the paper feeder2toward a transfer nip N. The registration roller20stays at rest before the paper P is sent thereto. The registration roller20is driven to start rotating such that the electrostatic latent image on the photosensitive drum30and an image formation area (area other than a void (margin) area) of the paper P coincide when the paper P abuts the transfer nip N.

The image forming apparatus100includes transport paths S1and S2, an inverting transport path S3, and a catch tray24. Through the transport paths S1and S2, the paper P is transported from the paper feeder2to the image former3, and the paper P having the toner image fixed thereto is transported to the catch tray24. The inverting transport path S3is used for duplex printing. After the paper P having the toner image printed on a front side thereof has turned around at the ejection roller25, the inverting transport path S3guides the paper P back to the registration roller20with the front and back sides of the paper P inverted. Thus, the image forming apparatus100can form a toner image on the back side of the paper P as well as on the front side in duplex printing. Transport rollers for transporting the paper P are disposed in appropriate positions in the vicinity of the transport paths S1and S2, and the inverting transport path S3.

The image forming apparatus100according to Embodiment 1 has pre-transfer paper guides60and61between the registration roller20and the transfer nip N. The pre-transfer paper guide60, which guides a printing side of the paper P, is held by the developing device33. Note here that “the pre-transfer paper guide60being held by the developing device33” encompasses both a configuration in which a housing of the developing device33itself is used as the pre-transfer paper guide60and a configuration in which the pre-transfer paper guide60being a separate member is supported on the housing of the developing device33. As a result of the pre-transfer paper guide60being held by the developing device33, the positional accuracy between the photosensitive drum30and a tip of the pre-transfer paper guide60increases, reducing streaks and banding that can occur due to impact. The pre-transfer paper guide60being held by the developing device33also contributes to a reduction in size of the image forming apparatus100.

In the case where the housing of the developing device33itself is used as the pre-transfer paper guide60, the pre-transfer paper guide60is made from a resin (for example, polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) resin), which is the same material as the housing of the developing device33. Likewise, in the case where the pre-transfer paper guide being a separate member is supported on the housing of the developing device33, the pre-transfer paper guide60is preferably made from a resin. In the present embodiment, the pre-transfer paper guide60is made from a resin.

The following describes the static eliminator34in detail with reference to the drawings.FIG. 2is an enlarged schematic cross-sectional view for illustrating an arrangement of the photosensitive drum30and the static eliminator34in the image forming apparatus100according to Embodiment 1 of the present invention.FIG. 3is a schematic view of the static eliminator34as seen in a direction from the photosensitive drum30to the static eliminator34in the image forming apparatus100according to Embodiment 1 of the present invention.

As illustrated inFIGS. 2 and 3, the static eliminator34includes a static elimination light source34a, a light guide plate34b, and a housing34caccommodating the light guide plate34b. The housing34chas an opening34din a side thereof facing the photosensitive drum30. The light guide plate34bherein has a configuration having a Fresnel pitch and is disposed substantially parallel to the photosensitive drum30. Specifically, a longitudinal direction of the light guide plate34bis substantially parallel to a rotation axis30aof the photosensitive drum30. Note that the photosensitive drum30and the light guide plate34beach have a shape that is elongate in a direction perpendicular to the plane inFIG. 2.

As in the case of the light guide plate34b, a longitudinal direction of the housing34cis substantially parallel to the rotation axis30a(axial direction) of the photosensitive drum30since the housing34caccommodates the light guide plate34b. The static elimination light source34ais disposed in the vicinity of one end of the light guide plate34b. As described above, the housing34chas the opening34din the side thereof facing the photosensitive drum30. Note that a blocking wall36is provided on an edge35of the opening34d. The blocking wall36has a height that varies according to locations in the longitudinal direction of the photosensitive drum30. That is, the blocking wall36is disposed between the light guide plate34band the photosensitive drum30. Thus, as described in detail below, the blocking wall36closes the opening34d, and light L emitted from the light guide plate34bis irradiated onto the photosensitive drum30after being restricted in a non-uniform manner in the longitudinal direction of the light guide plate34b. Since the photosensitive drum30rotates in the rotation direction D, the entirety of the outer circumferential surface of the photosensitive drum30is irradiated with the light L.

The static elimination light source34aemits the light L toward the light guide plate34b. The static elimination light source34ais, for example, a light-emitting element such as a light-emitting diode (LED). The light L, which is static elimination light emitted from the static elimination light source34a, enters the light guide plate34bthrough an end surface of the light guide plate34b. The light L that has entered the light guide plate34bis then emitted toward the photosensitive drum30from an irradiation end surface34efacing the opening34dof the housing34c. The light L emitted from the irradiation end surface34epasses through the opening34dto reach the photosensitive drum30. The blocking wall36herein is disposed between the light guide plate34band the photosensitive drum30so as to cover the irradiation end surface34e, and thus the light L emitted from the irradiation end surface34eis irradiated onto the photosensitive drum30after being restricted by the blocking wall36.

Note that in order to irradiate the photosensitive drum30throughout a length thereof in the longitudinal direction with the light emitted from the light guide plate34b, the light guide plate34b(irradiation end surface34e) has a length in the longitudinal direction on par with (substantially equal to) the longitudinal length of the photosensitive drum30, the light guide plate34band the photosensitive drum30are opposed to each other, and the light L is emitted toward the photosensitive drum30from the entirety of the irradiation end surface34e. Since the light L is emitted toward the photosensitive drum30from the irradiation end surface34eof the light guide plate34bas described above, the light L inFIG. 3is emitted from the irradiation end surface34ein a direction perpendicular to the plane inFIG. 3, which in other words is in a direction away from the plane inFIG. 3.

As a result of the light L emitted by the static elimination light source34abeing irradiated onto the photosensitive drum30through the light guide plate34b, residual potential remaining on the photosensitive drum30is eliminated. Note that it is preferable that the static elimination on the photosensitive drum30be uniform. Non-uniform static elimination can adversely affect image formation and degrade the resulting image. It is therefore preferable that the dose distribution of the light L (static elimination light) on the photosensitive drum30be uniform.

As illustrated inFIG. 3the blocking wall36has a height that varies according to locations. Specifically, regions R1and R2are not provided with the blocking wall36. That is, the blocking wall36has a height of “0” in the regions R1and R2. The blocking wall36has a height of h1in regions R31and R33, and a height of h2in a region R32out of a region R3provided with the blocking wall36. The height satisfies the relationship represented by h1<h2.

That is, the blocking wall36has a plurality of levels of height, and is therefore stair-like. Boundaries between the regions that are different in the height of the blocking wall36are vertical. Specifically, the boundary between the regions R1and R31, the boundary between the regions R31and R32, the boundary between the regions R32and R33, and the boundary between the regions R33and R2each extend in a vertical direction. Note here that the regions R1and R2are end regions located around ends of the light guide plate34b. Since the photosensitive drum30and the light guide plate34bhave substantially the same length and are opposed to each other as described above, the photosensitive drum30has equivalent regions corresponding to those of the light guide plate34b. That is, the regions R1and the R2can be described as end regions located at ends of the photosensitive drum30. Likewise, the region R3(regions R31, R32, and R33) can be described as a central region, which is a region other than the end regions at the ends of the photosensitive drum30.

As described above, the light L emitted from the irradiation end surface34eto be irradiated onto the photosensitive drum30is restricted by the blocking wall36while passing through the opening34d. The degree of the restriction has a proportionate relationship to the height of the blocking wall36. Specifically, the degree of the restriction is lower in the regions R1and R2where the height of the blocking wall36is “0” than in the regions R31and R33where the height of the blocking wall36is h1. The degree of the restriction is lower in the regions R1and R2than in the region R32where the height of the blocking wall36is h2. The degree of the restriction is lower in the regions R31and R33where the height of the blocking wall36is h1than in the region R32where the height of the blocking wall36is h2.

Reducing the degree of the restriction on the light L to be emitted from the irradiation end surface34eby setting the height of the blocking wall36in the regions R1and R2to a lower level than in the region R3(regions R31, R32, and R33) as described above allows for irradiation of the photosensitive drum30with the light L achieving a more uniform dose distribution throughout the length of the photosensitive drum30in the longitudinal direction of the photosensitive drum30. The region R32where the height of the blocking wall36is at the highest level is a region including a portion of the photosensitive drum30to be irradiated with the largest dose of light if the light L is irradiated without the blocking wall36. Setting the height of the blocking wall36in the region R32to a highest level allows for irradiation of the photosensitive drum30with the light L achieving a more uniform dose distribution throughout the length of the photosensitive drum30in the longitudinal direction of the photosensitive drum30. Generally, the dose peak in dose distribution is located toward the end facing the static elimination light source34aaway from a center of the photosensitive drum30in the longitudinal direction.

In Embodiment 1, as described above, setting the degree of the restriction on the light L to be emitted from the irradiation end surface34eto a lower level in the regions R1and R2, which are the end regions located around the ends of the light guide plate34b, than in the other region, which is the region R3, allows for irradiation of the photosensitive drum30with the light L achieving a more uniform dose distribution throughout the length of the photosensitive drum30in the longitudinal direction of the photosensitive drum30. This reduces non-uniformity in chargeability of the photosensitive drum30and image unevenness that can occur during the image formation on the paper P. As described above, it is preferable to set the height of the blocking wall36to a highest level to increase the degree of the restriction in the region R32, which is a region including a portion of the photosensitive drum30to be irradiated with the largest dose of light if the light L is irradiated without the blocking wall36. This configuration allows for irradiation of the photosensitive drum30with the light L achieving a more uniform dose distribution throughout the length of the photosensitive drum30in the longitudinal direction of the photosensitive drum30, and thus reduces non-uniformity in chargeability of the photosensitive drum30and image unevenness that can occur during the image formation on the paper P.

In some cases, a common component is applied to different models of image forming apparatuses, because mass production of components and the like results in cost reduction. In a case where common components (for example, the static elimination light source34a, the light guide plate34b, and the housing34c) are applied to different models of image forming apparatuses, the dose distribution of the light L to be irradiated onto the photosensitive drum30can be different between the different models. However, non-uniformity in the dose distribution in each model can be reduced by employing the blocking wall36specific to the model. That is, the blocking wall36for each model is given a configuration specific to the model by changing the height, the regions different in height, and the like, while common components are used as the static elimination light source34a, the light guide plate34b, the housing34c, and the like, allowing for cost reduction through mass production of such components.

The following describes the static eliminator34of the image forming apparatus100according to Embodiment 1 using Example 1. Note that the following particularly describes the blocking wall36.

FIG. 4is a schematic view illustrating a configuration of a static eliminator34according to Example 1 of the present invention as seen in a direction from the photosensitive drum30to the static eliminator34.FIG. 5is a diagram showing dose distribution of light L irradiated onto a photosensitive drum30according to Example 1 of the present invention. Note that components that have the same function and operation as the components that have already been described are labelled using the same reference signs, and detailed description thereof is omitted.

As illustrated inFIG. 4, the static eliminator34of an image forming apparatus100according to Example 1 has a blocking wall36disposed on an edge35of a housing34c. Regions R101and R102, which are end regions located around ends of a light guide plate34b, are not provide with the blocking wall36on the edge35, whereas a region R103, which is a central region located between the regions R101and R102, is provided with the blocking wall36. The region R103is divided into regions R131, R132, and R133, where the blocking wall36has a height that varies from region to region. Note that the blocking wall36illustrated inFIG. 4has a different shape from the blocking wall36illustrated inFIG. 3. That is, the height of the blocking wall36progressively decreases in the order of the region R131, which is the closest region to the static elimination light source34a, the region R132, and the region R133.

InFIG. 5, the horizontal axis represents location in a longitudinal direction of the light guide plate34b, and the vertical axis represents dose of the light L irradiated onto the photosensitive drum30from each location in the longitudinal direction of the light guide plate34b. The light L irradiated onto the photosensitive drum30herein means light that is emitted out of the static eliminator34, which is specifically light that is emitted from an irradiation end surface34e, and then directly irradiated onto the photosensitive drum30through the opening34d.

A graph in a dashed line inFIG. 5represents dose distribution of the light L that was irradiated ono the photosensitive drum30in a configuration including no blocking wall36. A graph in a solid line represents dose distribution of the light L that was irradiated onto the photosensitive drum30in a configuration including the blocking wall36. As shown inFIG. 5, the blocking wall36has a height of 0.6 mm in a region (region R131) ranging from a location at a distance of 45 mm to a location at a distance of 100 mm from an end of the light guide plate34bfacing the static elimination light source34a, a height of 0.4 mm in a region (region R132) ranging from a location at a distance of 100 mm to a location at a distance of 150 mm from the end of the light guide plate34bfacing the static elimination light source34a, and a height of 0.3 mm in a region (region R133) ranging from a location at a distance of 150 mm to a location at a distance of 240 mm from the end of the light guide plate34bfacing the static elimination light source34a. Note that a region (region R101) ranging from a location at a distance of 0 mm to a location at a distance of 50 mm and a region (region R102) ranging from the location at a distance of 240 mm to a location at a distance of 330 mm from the end of the light guide plate34bfacing the static elimination light source34aare not provided with the blocking wall36. That is, the blocking wall36has a height of 0 mm in these regions.

As shown inFIG. 5, the configuration including no blocking wall36resulted in a non-uniform dose distribution that is uneven in the longitudinal direction. However,FIG. 5indicates that the blocking wall36reduced unevenness in dose distribution in the longitudinal direction and improved uniformity thereof. The height of the blocking wall36may be determined by obtaining dose distribution without the blocking wall36, setting the height of the blocking wall36to a highest level in a region including a location having a dose peak, and then setting the height of the blocking wall36in the other regions according to variation of the dose. Preferably, compared to the height of the blocking wall36in the end regions located around the ends of the light guide plate34b, the height of the blocking wall36is set to a higher level in a central region, which is a region other than the end regions and is located between the end regions.

Through the above, Example 1 has been described. However, the image forming apparatus100according to Embodiment 1 may have a configuration other than as described above. For example, the dose distribution also changes depending on the dose of the light L at the time when the light L is emitted from the static elimination light source34aand the angle of the light L emitted from the static elimination light source34a. It is therefore preferable to determine the configuration of the blocking wall36according to the dose distribution.

In a case where the longitudinal location of the peak of the dose distribution in the configuration including no blocking wall36is toward the end facing the static elimination light source34aaway from the longitudinal center of the light guide plate34b, for example, the blocking wall36may take any of the following first to third forms.

In the first form, the height of the blocking wall36is set to a highest level in a region corresponding to the peak and to a lower level in two regions having the region corresponding to the peak therebetween, and one of the two regions that is closer to the static elimination light source34ahas a smaller range than the other of the two regions that is farther from the static elimination light source34a.

In the second form, the height of the blocking wall36is set to a highest level in a region corresponding to the peak and to a lower level in two regions having the region corresponding to the peak therebetween, and each of the two regions is divided into a plurality of regions having a plurality of levels of height of the blocking wall36. Furthermore, the number of levels of height of the blocking wall36(the number of regions different in height) is smaller in one of the two regions that is closer to the static elimination light source34athan in the other of the two regions that is farther from the static elimination light source34a.

In the third form, the height of the blocking wall36is set to a highest level in a region corresponding to the peak and to a lower level in two regions having the region corresponding to the peak therebetween, and each of the two regions is divided into a plurality of regions having a plurality of levels of height of the blocking wall36. Furthermore, the range of each of the regions in the two regions is set so that the farther from the static elimination light source34athe region is, the larger the range thereof is. In this case, the two regions are other than regions respectively including the ends of the light guide plate34b. That is, the two regions are regions located inward of the regions (outermost regions) respectively including the ends of the light guide plate34b.

In a case where the longitudinal location of the peak of the dose distribution in the configuration including no blocking wall36is toward the end opposite to the static elimination light source34aaway from the longitudinal center of the light guide plate34b, for example, the blocking wall36may take any of forms respectively achieved through inversion of the first to third forms described above at the longitudinal center.

In a case where the longitudinal location of the peak of the dose distribution in the configuration including no blocking wall36is at the longitudinal center of the light guide plate34b, for example, the blocking wall36may take a form in which the height of the blocking wall36is set to a highest level in a region corresponding to the peak, the region corresponding to the peak is located at the longitudinal center, and the height of the blocking wall36in each of the other regions is set so that the farther from the longitudinal center the region is, the lower the height of the blocking wall36in the region is, and thus the blocking wall36has a symmetrical shape with respect to the longitudinal center.

The image forming apparatus100according to Embodiment 1 has been described above. However, the present invention is not limited to the configuration described above. For example, as described with reference toFIG. 3, the boundary between the regions R1and R31, the boundary between the regions R31and R32, the boundary between the regions R32and R33, and the boundary between the regions R33and R2each extend in the vertical direction in the configuration described above, but may alternatively each extend at an angle to the vertical direction.

FIG. 6is an enlarged schematic view of another form of the blocking wall36in the image forming apparatus100according to Embodiment 1 of the present invention. As illustrated inFIG. 6, the height of the blocking wall36may gradually change in an inclined manner according to longitudinal locations around a boundary B between regions different in height. Note that the blocking wall36is linearly inclined around the boundary B inFIG. 6, but the inclination may alternatively be in a curved line.

Preferably, the inside of the housing34cis white in order for the light L that has entered the light guide plate34bfrom the static elimination light source34ato be diffusely reflected. However, the inside of the housing34cis not limited to being white, and may alternatively be black. Alternatively, the inside of the housing34cmay be black and a portion thereof may be white. For example, at least portions of the inside of the housing34cthat are located around the ends of the light guide plate34bmay be white. This configuration promotes reflection of the light L, and thus improves uniformity of the light L to be irradiated onto the photosensitive drum30in the longitudinal direction.

The following describes an image forming apparatus according to Embodiment 2 of the present invention with reference to the drawings. Note that components that have the same function and operation as the components that have already been described are labelled using the same reference signs, and detailed description thereof is omitted.

FIG. 7is a schematic view of a static eliminator34as seen in a direction from a photosensitive drum30to the static eliminator34in an image forming apparatus100according to Embodiment 2 of the present invention. The static eliminator34in Embodiment 2 has the same configuration as the static eliminator34in Embodiment 1 except that an edge35of a housing34cin Embodiment 2 further has grooves37in portions thereof corresponding to ends of a light guide plate34b.

The edge35of the housing34cfurther includes the grooves37in the portions thereof corresponding to the ends of the light guide plate34bas illustrated inFIG. 7. That is, an opening34dis widened in these portions by, for example, cutting or otherwise processing the edge35. Specifically, the opening34dis widened by forming the groove37in a portion of the edge35in a region R201located around the end of the light guide plate34bfacing a static elimination light source34a. A region R202located around the other end of the light guide plate34bthat is farther from the static elimination light source34ais divided into regions R221and R222. The opening34dis also widened by forming the groove37in a portion of the edge35in the region R222closer to the other end of the light guide plate34b. This configuration reduces restriction on the light L to be emitted from an irradiation end surface34ein the regions R201and R222, and thus increases the dose of the light L to be emitted from the static eliminator34. That is, the thus formed grooves37widen the opening34d, reduce restriction on the light L to be emitted from the irradiation end surface34ein the regions R201and R222respectively located at the ends of the light guide plate34b, and thus increase the dose of the light L to be irradiated onto the photosensitive drum30.

Furthermore, a blocking wall36is provided in a region R203being a central region located between the regions R201and R202. The region R203is divided into regions R231, R232, and R233, where the blocking wall36has a height that varies from region to region.

Generally, the dose of the light L emitted from regions around the ends of the light guide plate34bis lower than the dose of the light L emitted from the other regions. The dose of the light L to be emitted can therefore be increased by forming the grooves37as described above, and thus widening the opening34din the portions around the ends of the light guide plate34b.

For example, the opening34dmay be widened by forming the grooves37in the edge35as described above to ensure a sufficient dose of the light L around the ends of the light guide plate34bin a case where the dose distribution of the light L on the photosensitive drum30obtained by providing the blocking wall36on the edge35is not sufficiently uniform throughout a length of the photosensitive drum30in a longitudinal direction of the photosensitive drum30. The thus widened opening34dallows for irradiation of the photosensitive drum30with the light L achieving a more uniform dose distribution throughout the length of the photosensitive drum30in the longitudinal direction of the photosensitive drum30, reducing non-uniformity in chargeability of the photosensitive drum30and image unevenness that can occur during image formation on paper P.

This configuration may also be applied to a case where common components are used in different models of image forming apparatuses. That is, in a case where the dose distribution of the light L obtained by employing a different blocking wall36for each of the models is not sufficiently uniform throughout the length of the photosensitive drum30in the longitudinal direction of the photosensitive drum30, the grooves37may be formed to ensure a sufficient dose of the light L at the ends, and thus to achieve a more uniform dose distribution throughout the length of the photosensitive drum30in the longitudinal direction of the photosensitive drum30. This eliminates the need for producing a different housing34cfor each model. That is, a common housing34ccan be used for different models by forming the grooves37, achieving cost reduction.

The following describes the static eliminator34of the image forming apparatus100according to Embodiment 2 using Example 2. Note that the following particularly describes a portion of a blocking wall36around an end of a light guide plate34bfacing a static elimination light source34a.

FIG. 8is a diagram showing dose distribution of light L irradiated onto a photosensitive drum30according to Example 2 of the present invention. Note thatFIG. 8shows the dose distribution in a range from a longitudinal location at a distance of 0 mm to a longitudinal location at a distance of 15 mm from the end of the light guide plate34bfacing the static elimination light source34a. This range is equivalent to the region R201inFIG. 7. The static eliminator34according to Example 2 is equivalent to the static eliminator34illustrated inFIG. 7.

InFIG. 8, the horizontal axis represents location in a longitudinal direction of the light guide plate34b, and the vertical axis represents dose of the light L irradiated onto the photosensitive drum30from each location in the longitudinal direction of the light guide plate34b. The light L irradiated onto the photosensitive drum30herein means light that is emitted out of the static eliminator34, which is specifically light that is emitted from an irradiation end surface34e, and then directly irradiated onto the photosensitive drum30through the opening34d.

A graph in a dashed line inFIG. 8represents dose distribution of the light L that was irradiated ono the photosensitive drum30without any grooves37in the edge35. A graph in a solid line represents dose distribution of the light L that was irradiated onto the photosensitive drum30with a groove37having a depth of 0.4 mm provided in a portion of the edge35in the range at 0 mm to 15 mm from the end facing the static elimination light source34a. That is, the groove37is in the range (region R201inFIG. 7) from the longitudinal location at a distance of 0 mm to the longitudinal location at a distance of 15 mm from the end facing the static elimination light source34a. As a result of the groove37having a depth of 0.4 mm being formed in the edge35, the edge35has a height of 0.4 mm relative to the groove37.

FIG. 8indicates that the formation of the groove37resulted in an increase in the dose. The increase in the dose of the light L irradiated onto the photosensitive drum30as a result of the formation of the groove37is approximately 1.5 times the dose in the case of a configuration having no groove37.

The following next describes a method for determining the height of the blocking wall36in each region and the depth of the grooves37with reference to the drawings.FIG. 9is a diagram showing dose distribution of the light L that was irradiated onto the photosensitive drum30without the blocking wall36and the grooves37for determining configurations of the blocking wall36and the grooves37in the image forming apparatus100according to Embodiment 2 of the present invention.FIG. 10is a schematic view of configurations of the blocking wall36and the grooves37determined based onFIG. 9.FIG. 11is a diagram showing dose distribution of the light L that was irradiated onto the photosensitive drum30after the blocking wall36and the grooves37illustrated inFIG. 10had been formed.

Note that inFIGS. 9 and 11, the horizontal axis represents location in the longitudinal direction of the light guide plate34b, and the vertical axis represents dose of the light L irradiated onto the photosensitive drum30from each location in the longitudinal direction of the light guide plate34b. The light L irradiated onto the photosensitive drum30herein means light that is emitted out of the static eliminator34, which is specifically light that is emitted from the irradiation end surface34e, and then directly irradiated onto the photosensitive drum30through the opening34d.

Preferably, the height of the blocking wall36in each region and the depth of the grooves37are determined in consideration of reducing deterioration of the photosensitive drum30due to light fatigue as well as achieving a more uniform dose distribution of the light L to be irradiated onto the photosensitive drum30. Note here that charging and static elimination on the photosensitive drum30are performed by causing charge transfer in an organic film in the photosensitive drum30through irradiation of the photosensitive drum30with light, and thus controlling the potential of the photosensitive drum30. The chargeability of the photosensitive drum30decreases as charging and static elimination are repeated on the photosensitive drum30. In particular, the higher the dose of the light L irradiated onto the photosensitive drum30is, the more the chargeability of the photosensitive drum30decreases. It is therefore preferable to irradiate the light L onto the photosensitive drum30in a dose that allows sufficient static elimination on the photosensitive drum30and that reduces the decrease in the chargeability to a greater extent.

That is, it is preferable to set the height of the blocking wall36in each region and the depth of the grooves37so as to obtain a more uniform dose distribution of the light L on the photosensitive drum30for sufficient static elimination and reduce deterioration of the photosensitive drum30due to light fatigue.

In order to determine the height of the blocking wall36in each region and the depth of the grooves37, the dose distribution of the light L is obtained first by irradiating the light L onto the photosensitive drum30without the blocking wall36and the grooves37in the edge35as illustrated inFIG. 9. Note here that inFIG. 9, a maximum dose refers to a maximum amount of light in an allowable light fatigue range, and a minimum dose refers to a minimum amount of light necessary to perform sufficient static elimination. Note that the maximum dose and the minimum dose vary from model to model, and are therefore determined in advance by performing measurements for each model of the image forming apparatus100. A value intermediate between the maximum dose and the minimum dose is determined as a reference dose.

A range where the dose is substantially equal to the reference dose inFIG. 9does not need to be provided with the blocking wall36and is to only have the edge35. Ranges where the dose is higher than the reference dose inFIG. 9are to be provided with the blocking wall36on the edge35, and the height of the blocking wall36in these ranges is varied depending on the dose in each region. Ranges where the dose is lower than the reference dose inFIG. 9are to be provided with the grooves37in the edge35.

Specifically, in the housing34c, regions RO1and RO2, which are end regions located at the ends of the light guide plate34b, are to be provided with the grooves37in the edge35, and a region RC of a central region, which is a region other than the end regions, is to be provided with the blocking wall36and a region RS of the central region is to only have the edge35, as illustrated inFIG. 10. The blocking wall36in the region RC may have a plurality of levels of height depending on the dose shown inFIG. 9. In the present example, the blocking wall36has three levels of height.

The light L that is irradiated onto the photosensitive drum30after forming the blocking wall36and the grooves37having configurations illustrated inFIG. 10in the housing34chas a dose distribution as shown inFIG. 11. As shown inFIG. 11, the dose of the light L irradiated onto the photosensitive drum30from the regions RC and RS is substantially equal to the reference dose, and the dose of the light L from the regions RO1and RO2is slightly lower than the reference dose but is close to the reference dose. The configuration described above, in which the regions RO1are RO2are provided with the grooves37in the edge35, the region RC is provided with the blocking wall36having three levels of height on the edge35, and the region RS only has the edge35, allows for a more uniform dose distribution of the light L irradiated onto the photosensitive drum30, sufficient static elimination, and a reduction in deterioration of the photosensitive drum30due to light fatigue.

The following describes an image forming apparatus according to Embodiment 3 of the present invention with reference to the drawings. Note that components that have the same function and operation as the components that have already been described are labelled using the same reference signs, and detailed description thereof is omitted.

FIG. 12is a schematic cross-sectional view of a static eliminator34in an image forming apparatus100according to Embodiment 3 of the present invention. Embodiment 3 has the same configuration as Embodiment 1 except that a blocking wall36in Embodiment 3 is provided with a reflective member36aon a side thereof facing a light guide plate34b.

The blocking wall36is provided with the reflective member36afor diffusely reflecting light on the side thereof facing an irradiation end surface34eas illustrated inFIG. 12. As a result, light L emitted from a static elimination light source34aenters the light guide plate34b, is emitted from the irradiation end surface34eof the light guide plate34b, and is then diffusely reflected by the reflective member36awhile being restricted by the blocking wall36. The light L diffusely reflected by the reflective member36abecomes incident on the irradiation end surface34ein a scattered manner. The light L incident on the irradiation end surface34eafter having been reflected by the reflective member36ais then reflected by the irradiation end surface34eand emitted from the irradiation end surface34e. As described above, a portion of the light L emitted from the irradiation end surface34eis diffusely reflected by the reflective member36a, and the resulting scattered light is reflected off the irradiation end surface34eand re-emitted from the irradiation end surface34e. Repetition of this cycle allows for a reduction in bright spot unevenness. As a result, it is possible to reduce non-uniform charging on the photosensitive drum30and to reduce occurrence of a defect in an image to be formed.

The bright spot unevenness as used herein refers to light being distributed in a non-uniform manner in the longitudinal direction after having been emitted from the light guide plate34bwith a Fresnel pitch due to distribution on a Fresnel surface. The bright spot unevenness can make the chargeability of the photosensitive drum30non-uniform and cause occurrence of a fringe pattern in an image formed on paper P. However, as a result of providing the reflective member36a, it is possible to reduce the bright spot unevenness and to reduce occurrence of such a defect.

Note that the reflective member36amay have the same shape as the blocking wall36and may be a white member. Since it is preferable that the light L be diffusely reflected by the reflective member36a, the reflective member36apreferably has a rough surface rather than a glossy and smooth surface.

The reflective member36amay be provided also on portions of the edge35that do not have the blocking wall36. In this case, the edge35may be provided with the reflective member36adirectly on a side thereof facing the light guide plate34b. The reflective member36amay extend over the entire length of an opening34dand may be provided on either the side of the edge35or the side of the blocking wall36facing the light guide plate34b. Alternatively or additionally, the reflective member36amay be provided on an inner surface of the housing34cwhere the light guide plate34bis disposed. This configuration allows the light L to be further reflected, thereby reducing bright spot unevenness, reducing non-uniform charging on the photosensitive drum30, and reducing occurrence of a defect in an image to be formed.

The present invention is not limited to the embodiments described above and may be embodied in other specific forms. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting the invention described herein. Scope of the present invention is indicated by the appended claims rather than by the foregoing description. All modifications and changes that come within the meaning and range of equivalency of the claims are intended to be embraced within their scope.