Patent Description:
In an electrophotographic type image forming apparatus, a developing nip area is formed between a developing roller of a developing device and a photosensitive drum, and a transferring nip area is formed between a transferring roller and the photosensitive drum. An electrostatic latent image formed on the photosensitive drum is developed into a toner image at the developing nip area, and the developed toner image is transferred from the photosensitive drum to a sheet at the transferring nip area. The sheet is conveyed along a predetermined conveying direction and guided to the transferring nip area by a guide member. On the conveying path on the upstream side of the transferring nip area in the sheet conveying direction or in the vicinity of the conveying path, a developer (a toner) scattered from the developing device tends to accumulate.

Therefore, in order to prevent the toner from entering between the developing device and the guide member, a gap between the guide member and the developing device may be blocked by a blocking member such as a sponge.

On the other hand, in the image forming apparatus, a process unit in which the developing device and the photosensitive drum are unitized may be detachably supported by the apparatus main body. The process unit is detached from the apparatus main body by being turned upward around a rotation axis along the horizontal direction and then pulled out along a direction orthogonal to the rotation axis. The above-described blocking member also serves to prevent the toner accumulated on the upper surface of the guide member from falling when the process unit is turned.

In a case where the blocking member is provided, when the leading end of the sheet guided along the guide member comes into contact with the photosensitive drum, a closed space is formed by the developing device, the blocking member, the guide member, the sheet, and the photosensitive drum. When the sheet moves in accordance with the rotation of the photosensitive drum, the volume of the space changes by the amount of the movement of the sheet, and an air flow is generated in the space, and the position of the toner image formed on the photosensitive drum is shifted, resulting in the generation of image defects, such as transverse stripes.

Therefore, the guide member described in Patent document <NUM> is provided with a rib at the tip end portion, and a gap through the rib is formed between the conveyed sheet and the tip end portion. As a result, the change in the volume of the space can be reduced when the sheet moves in accordance with the rotation of the photosensitive drum.

Moreover,<CIT> discloses an image forming apparatus which has a guide part that forms a conveyance path for a sheet to be conveyed from a paper feeding part to an image carrier. A channel is formed between a developing device and the guide part. The channel has an opening/closing member that can open/close the channel.

However, in the guide member described in the above-described patent document, since a gap is opened between the guide member and the sheet, there is a case where an air flow flowing through the gap to the conveying path is generated. Then, there is a problem that the scattered toner flows into the conveying path by the air flow. In such a situation where the problem that occurs when the blocking member is provided is not sufficiently solved, it is preferable not to provide the blocking member so as not to form the above-described closed space. However, in the case where the blocking member is not provided, there is a problem that the toner accumulated on the upper surface of the guide member falls when the process unit is turned.

In view of the above circumstances, it is an object of the present invention to provide an image forming apparatus capable of suppressing the generation of air flow when the sheet enters the transferring nip area and preventing the toner from falling when the process unit is turned.

In order to solve the above problems, an image forming apparatus according to the present invention includes a process unit which is configured to be turned upward around a turning shaft and then detached from an apparatus main body, wherein the process unit includes: a photosensitive drum rotating in a predetermined rotating direction; a developing device which faces a surface of the photosensitive drum to form a developing nip area; a guide member which comes into contact with an upper surface of a sheet and guides the sheet to a downstream side of the developing nip area in the rotating direction; and a seal member supported between the developing device and the guide member in a turnable manner, wherein the seal member opens a gap between the developing device and the guide member in a state where the process unit is attached to the apparatus main body, and when the process unit is turned upward when detached from the apparatus body, the seal member is turned to close the gap between the developing device and the guide member.

According to the present invention, since the seal member is turned to a posture for opening the gap between the guide member and the developing device and a posture for blocking the toner accumulated on the guide member, with the turning of the process unit, it becomes possible to suppress the air flow generated when the sheet is conveyed to the transferring nip area and to prevent the toner accumulated on the guide member from falling.

Hereinafter, with reference to the attached drawings, an image forming apparatus according to the present invention will be described.

First, with reference to <FIG>, the entire structure of the image forming apparatus will be described. <FIG> is a side view schematically showing the inner structure of the image forming apparatus. Hereinafter, the left side of the paper on which <FIG> is drawn is referred to as the front side of the image forming apparatus. Reference numerals Fr, Rr, L, and R in each drawing indicate the front, rear, left, and right sides of the image forming apparatus.

The image forming apparatus <NUM> includes an apparatus main body <NUM> having an approximately rectangular parallelepiped hollow part. On the top plate of the apparatus main body <NUM>, a vertical rear wall <NUM> and a discharge tray <NUM> inclined upwardly from the lower end of the rear wall <NUM> are formed. An opening is formed on the top plate in front of the discharge tray <NUM>. The opening is opened and closed by an upper cover <NUM>. When the opening is opened by the upper cover <NUM>, the hollow part of the apparatus main body <NUM> is exposed through the opening. A sheet discharge port <NUM> is formed on the upper portion of the rear wall <NUM>.

In the lower portion of the front plate of the apparatus main body <NUM>, a manual sheet feeding port <NUM> is formed. Further, a manual sheet feeding tray <NUM> is supported on the front plate of the apparatus main body <NUM> in a rotatable manner around a fulcrum below the manual sheet feeding port <NUM>. An opening is formed in the front plate above the manual sheet feeding port <NUM>. The opening is opened and closed by a front cover <NUM>. When the opening is opened by the front cover <NUM>, the hollow part of the apparatus main body <NUM> is exposed through the opening.

In the hollow part of the apparatus main body <NUM>, a sheet feeding cassette <NUM>, a sheet feeding part <NUM>, an image forming part <NUM>, and a fixing device <NUM> are housed. Further, a main conveying path <NUM>, an inversion path <NUM>, and a manual sheet feeding path <NUM> along which the sheet is conveyed are formed in the apparatus main body <NUM>.

The sheet feeding cassette <NUM> is housed in the lower portion of the hollow part, and is detachable along the front-and-rear direction through the opening formed in the front plate of the apparatus main body <NUM>. The sheet feeding cassette <NUM> includes a placement plate <NUM> on which the sheet S is placed, and a retard roller <NUM>. The placement plate <NUM> is supported on the bottom plate of the sheet feeding cassette <NUM> so as to be turnable upward and downward around the rear end portion. The retard roller <NUM> is disposed in front of the placement plate <NUM>.

The sheet feeding part <NUM> is disposed above the front end portion of the sheet feeding cassette <NUM>, and includes a pickup roller <NUM> and a feed roller <NUM> arranged in front of the pickup roller <NUM>. The pickup roller <NUM> is rotated in contact with the sheet S placed on the placement plate <NUM> turned upward, and sends the sheet S forward. The feed roller <NUM> comes into contact with the retard roller <NUM> to form a separation nip area between them.

The image forming part <NUM> is disposed above the sheet feeding cassette <NUM>, and includes a photosensitive drum <NUM>, a charger <NUM>, a developing device <NUM>, a transferring roller <NUM>, a cleaning device <NUM>, and an exposure device <NUM>. The photosensitive drum <NUM> is supported so as to be rotatable in the counterclockwise direction of <FIG>. The charger <NUM>, the developing device <NUM>, the transferring roller <NUM>, and the cleaning device <NUM> are arranged in order along the rotating direction of the photosensitive drum <NUM> around the photosensitive drum <NUM>. In this example, the charger <NUM> is disposed above the photosensitive drum <NUM>, the developing device <NUM> is disposed on the front side pf the photosensitive drum <NUM>, the transferring roller <NUM> is disposed below the photosensitive drum <NUM>, and the cleaning device <NUM> is disposed on the rear side of the photosensitive drum <NUM>.

The developing device <NUM> includes a developing housing <NUM>, two agitating members <NUM>, and a developing roller <NUM>. The two agitating members <NUM> are housed in the developing housing <NUM> to agitate the developer. The developing roller <NUM> is arranged to face the photosensitive drum <NUM> through the opening of the developing housing <NUM>, and forms a developing nip area between the developing roller <NUM> and the photosensitive drum <NUM>. At the developing nip area, the toner moves from the developing roller <NUM> to the photosensitive drum <NUM>. A toner container <NUM> is detachably connected to the developing housing <NUM>.

The transferring roller <NUM> faces the photosensitive drum <NUM> from below and forms a transferring nip area between the photosensitive drum <NUM> and the transferring roller <NUM>.

The fixing device <NUM> is disposed on the rear side of the image forming part <NUM>, and includes a fixing roller and a pressing roller.

The main conveying path <NUM> is formed so as to curve upward from the separation nip area, extend rearward substantially horizontally through the transferring nip area and the fixing device <NUM>, and curve upward from the fixing device <NUM> toward the discharge port <NUM>. A direction along the main conveying path <NUM> is defined as a conveying direction of the sheet S, and the upstream side and the downstream side in the following description indicate the upstream side and the downstream side in the conveying direction of the sheet S. The inversion path <NUM> branches from the main conveying path <NUM> on the downstream side of the fixing device <NUM>, and merges with the main conveying path <NUM> on the downstream side of the separation nip area. The manual sheet feeding path <NUM> merges with the main conveying path <NUM> on the downstream side of the separation nip area from the manual sheet feeding port <NUM>.

On the main conveying path <NUM>, an intermediate rollers pair <NUM>, a registration rollers pair <NUM>, a switchback path <NUM>, and a discharge rollers pair <NUM> are provided in order from the upstream side. The intermediate rollers pair <NUM> is disposed on the downstream side of the junction of the inversion path <NUM>, the manual sheet feeding path <NUM> and the main conveying path <NUM>. The registration rollers pair <NUM> is disposed between the intermediate rollers pair <NUM> and the transferring nip area. The switchback path <NUM> is disposed on the downstream side of the fixing device <NUM>. The discharge rollers pair <NUM> is disposed inside the discharge port <NUM>.

The main conveying path <NUM> from the registration rollers pair <NUM> to the transferring nip area is formed between an upper guide member <NUM> and a lower guide member <NUM> below the developing device <NUM> along a substantially horizontal direction from the front side to the rear side. The upper guide member <NUM> is supported by the developing housing <NUM> of the developing device <NUM>, and the lower guide member <NUM> is supported by the apparatus main body <NUM>.

The upper guide member <NUM> has a width corresponding to the maximum size of the sheet and a predetermined length along the conveying direction. The lower surface of the upper guide member <NUM> is formed to be planner and is curved in an upward arc shape along the conveying direction.

The photosensitive drum <NUM>, the charger <NUM>, the developing device <NUM>, the cleaning device <NUM>, the toner container <NUM> and the upper guide member <NUM> are unitized as a process unit P. As described above, the charger <NUM> is disposed above the photosensitive drum <NUM>, the developing device <NUM> and the upper guide member <NUM> are disposed in front of the photosensitive drum <NUM>, and the cleaning device <NUM> is disposed on the rear side of the photosensitive drum <NUM>. The process unit P has an end portion on the side of the cleaning device <NUM>. The process unit P is positioned at a predetermined position with respect to the apparatus main body <NUM>, and the end portion of the process unit P is turnably supported by a turning shaft <NUM> extending along the horizontal direction. That is, when the process unit P is attached at the predetermined position, the photosensitive drum <NUM> faces the transferring roller <NUM> to form the transferring nip area, and the upper guide member <NUM> faces the lower guide member <NUM> to form the main conveying path. Attachment/detachment of the process unit P will be described later.

A seal member <NUM> is provided in a gap G between the developing device <NUM> and the upper guide member <NUM>. The seal member <NUM> will be described with reference to <FIG>. <FIG> is a perspective view showing the seal member, <FIG> is a side view showing the seal member attached to the developing device, and <FIG> is a perspective view showing the end portion of the seal member attached to the developing device.

As shown in <FIG>, the seal member <NUM> includes a shaft member <NUM>, a sheet body <NUM> supported by the shaft member <NUM> in a cantilever manner, weights <NUM> provided at the left and right ends of the shaft member <NUM>, and bosses <NUM> protruding from the outer surfaces of the weights <NUM>.

The shaft member <NUM> is an elongated member having a rectangular cross section, and has a length longer than the maximum width of the sheet S. A plurality of fixing pieces 93a having the same thickness as that of the shaft member <NUM> protrude from the rear surface of the shaft member <NUM> at predetermined intervals in the left-and-right direction. The sheet body <NUM> has a rectangular shape long in the left-and-right direction, and is made of flexible material. The front end portion of the sheet body <NUM> is fixed to the lower surfaces of the shaft member <NUM> and the fixing pieces 93a by adhesion or the like.

Each of the two weights <NUM> has a rectangular parallelepiped shape long in the upper-and-lower direction, and is made of material such as resin. The right and left end surfaces of the shaft member <NUM> are fixed to the upper portion of the inner surfaces of the weights <NUM>, and the weights <NUM> extend downward from the shaft member <NUM>. The boss <NUM> protrudes from the upper portion of the outer surface of each weight <NUM>.

As shown in <FIG>, the seal member <NUM> is disposed as close as possible to the photosensitive drum <NUM> with a posture in which the sheet body <NUM> extends forward on the opposite side to the photosensitive drum <NUM>. Both bosses <NUM> (see <FIG>) are rotatably supported by shaft supporting portions 61a (see <FIG>) formed on the lower surface of the developing housing <NUM>. The left and right weights <NUM> are accommodated in notches 81a (see <FIG>) formed in the upper guide member <NUM>.

The seal member <NUM> is supported by the weights <NUM> such that the sheet body <NUM> is kept in a substantially horizontal posture. Specifically, the weight of the weights <NUM> is set such that the sheet body <NUM> is kept in a substantially horizontal posture where a force in which the fixing piece 93a and the sheet body <NUM> rotate the shaft member <NUM> in the counterclockwise direction of <FIG> is balanced by the force in which the weights <NUM> rotates the shaft member <NUM> in the clockwise direction of <FIG>. The posture of the seal member <NUM> is referred to as an equilibrium posture.

In such a state that the seal member <NUM> is supported in the equilibrium posture, the tip end portion of the sheet body <NUM> is separated upward from the upper guide member <NUM>. That is, when the process unit P is attached to the apparatus main body <NUM>, a gap G is formed between the developing housing <NUM> of the developing device <NUM> and the upper guide member <NUM>.

Next, an image forming operation will be described. First, the charger <NUM> charges the photosensitive drum <NUM>, and the exposure device <NUM> exposes the photosensitive drum <NUM> based on image data. Thus, an electrostatic latent image is carried on the photosensitive drum <NUM>. The developing device <NUM> develops the electrostatic latent image into a toner image. On the other hand, the sheet S placed on the placement plate <NUM> of the sheet feeding cassette <NUM> is fed by the pickup roller <NUM>, and after being separated at the separation nip area, is conveyed to the main conveying path <NUM>. Thereafter, the sheet S is conveyed by the intermediate rollers pair <NUM>, and after the conveying timing is adjusted by the registration rollers pair <NUM>, the sheet S is conveyed to the transferring nip area.

The upper surface of the sheet S passed through the registration rollers pair <NUM> is conveyed along the lower surface of the upper guide member <NUM>, and guided from the upper guide member <NUM> to the photosensitive drum <NUM> along the curved direction of the lower surface of the upper guide member <NUM>. At this time, the leading end of the sheet S comes into contact with the surface of the photosensitive drum <NUM> from the upstream side in the rotating direction of the photosensitive drum <NUM>, and enters the transferring nip area as the photosensitive drum <NUM> rotates.

At the transferring nip area, the toner image carried on the photosensitive drum <NUM> is transferred to the sheet S. Thereafter, the sheet S is conveyed to the fixing device <NUM>. The fixing device <NUM> fixes the toner image to the sheet. The sheet on which the toner image is fixed is conveyed along the main conveying path <NUM> toward the discharge port <NUM>, discharged through the discharge port <NUM> by the discharge rollers pair <NUM>, and stacked on the discharge tray <NUM>. The toner remaining on the photosensitive drum <NUM> after the toner image is transferred to the sheet is removed by the cleaning device <NUM>.

Next, one example of the process unit P detaching method will be described with reference to <FIG> and <FIG>. <FIG> are side views schematically explaining the image forming apparatus in which the process unit is turned. <FIG> is a side view showing the seal member when the process unit is turned.

When the process unit P is detached from the apparatus main body <NUM>, as shown in <FIG>, the upper cover <NUM> is turned to open the hollow part of the apparatus main body <NUM>. Then, the toner container <NUM> (see <FIG>) is detached from the developing device <NUM> and pulled out through the opening of the top plate of the apparatus main body <NUM>. Next, as shown in FIG. 6B, the front cover <NUM> is turned to open the hollow part, and the process unit P is turned upward around the turning shaft <NUM>. The turning angle is <NUM> degrees, for example.

With the turning of the process unit P, as shown in <FIG>, the seal member <NUM> is turned by its own weight in the counterclockwise direction of <FIG> with respect to the developing device <NUM>, and the tip end of the sheet body <NUM> comes into contact with the upper guide member <NUM>. At this time, the tip end of the sheet body <NUM> is slightly deformed along the upper surface of the upper guide member <NUM>, and the seal member <NUM> is slightly turned in the counterclockwise direction in <FIG> from the equilibrium posture. When the process unit P is turned, the weights <NUM> does not come into contact with the upper guide member <NUM>.

Thereafter, as shown in <FIG>, the process unit P is pulled out obliquely along the front and upper direction through the openings of the top plate and the front plate of the apparatus main body <NUM>. Thus, the process unit P is detached from the apparatus main body <NUM>.

With reference to <FIG>, as a comparative example, a case will be described, in which a blocking member <NUM> for blocking the gap G between the developing device <NUM> and the upper guide member <NUM> is provided. In this case, when the leading end of the sheet S comes into contact with the surface of the photosensitive drum <NUM>, a closed space X surrounded by the developing device <NUM> (the developing housing <NUM> and the developing roller <NUM>), the blocking member <NUM>, the upper guide member <NUM>, the sheet S and the photosensitive drum <NUM> is formed. When the leading end of the sheet S moves toward the transferring nip area as the photosensitive drum <NUM> is rotated, the volume of the space X changes (increases) by the amount of the movement Y. When the volume of the space X changes as described above, a downwardly air flow is generated in the space X, and the position of the toner image carried on the surface of the photosensitive drum <NUM> is shifted downward, resulting in image defects such as transverse stripes.

On the other hand, in the present embodiment, as described above, the gap G is opened between the developing device <NUM> and the upper guide member <NUM>, and the closed space as in the comparative example is not formed. Therefore, since the generation of air flow can be suppressed when the tip end of the sheet S moves toward the transferring nip area as the photosensitive drum <NUM> is rotated, so that no image defect is generated.

However, if the gap G is thus provided, the toner scattered through the gap G may be accumulated on the upper guide member <NUM>. Then, if the process unit P is turned upward when the process unit P is detached from the apparatus main body <NUM>, the toner T accumulated on the upper guide member <NUM> may fall through the gap G between the upper guide member <NUM> and the developing device <NUM>.

However, in the present embodiment, if the process unit P is turned when the process unit P is detached from the apparatus main body <NUM>, as shown in <FIG>, the tip end of the sheet body <NUM> of the seal member <NUM> comes into contact with the upper guide member <NUM>, so that the toner T accumulated on the upper guide member <NUM> is blocked by the sheet body <NUM>. Therefore, the toner accumulated on the upper guide member <NUM> can be prevented from falling.

Further, since the seal member <NUM> is rotated by its own weight to a posture of opening the gap between the upper guide member <NUM> and the developing device <NUM> and a posture of bringing the sheet body <NUM> into contact with the upper guide member <NUM> as the process unit P is turned, the configuration of rotating the seal member <NUM> becomes unnecessary.

Claim 1:
An image forming apparatus (<NUM>) including a process unit (P) which is configured to be turned upward around a turning shaft (<NUM>) and then detached from an apparatus main body (<NUM>), wherein
the process unit (P) includes:
a photosensitive drum (<NUM>) rotating in a predetermined rotating direction;
a developing device (<NUM>) which faces a surface of the photosensitive drum (<NUM>) to form a developing nip area;
a guide member (<NUM>) which comes into contact with an upper surface of a sheet and guides the sheet to a downstream side of the developing nip area in the rotating direction; and
a seal member (<NUM>) supported between the developing device (<NUM>) and the guide member (<NUM>) in a turnable manner, wherein
the seal member (<NUM>) opens a gap between the developing device (<NUM>) and the guide member (<NUM>) in a state where the process unit (P) is attached to the apparatus main body (<NUM>), and when the process unit (P) is turned upward when detached from the apparatus body (<NUM>), the seal member (<NUM>) is turned to close the gap between the developing device (<NUM>) and the guide member (<NUM>).