JP2009258524A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which is configured to prevent erroneous detection of the optical sensor by preventing an optical sensor from getting dirty, and accordingly, is capable of accurately adjusting image quality. <P>SOLUTION: The image forming apparatus 10 includes a photoreceptor 3, a paper conveying path S and an optical sensor unit 100. An electrostatic latent image is formed on the surface of the photoreceptor 3. The paper conveying path S is formed by paper conveying guides 22 and 24 disposed so as to convey a recording medium to the photoreceptor 3. The optical sensor unit 100 includes the optical sensor 110, a casing 120 and an opening/closing member 130. The optical sensor 110 detects the density of the reference toner image formed on the surface of the photoreceptor 3. The casing 120 is configured to store the optical sensor 110, and includes a light emitting port 113 for securing the light emission path of the optical sensor 110 and a light receiving port 114 for securing the light receiving path of the optical sensor 110. The opening/closing member 130 is configured to cover the light emitting port 113 and the light receiving port 114 of the casing 120. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image in an electrophotographic process, such as a copying machine, a printer, and a facsimile machine.

  A photoreceptor used in an image forming apparatus that forms an image by an electrophotographic process, such as a copying machine or a laser printer, causes fluctuations in surface potential due to environmental changes such as temperature. In addition, mechanical stress such as contact with the cleaning blade accumulates due to repetition of the electrophotographic process, and the photosensitive member undergoes film reduction in which the film pressure of the photosensitive layer on the surface decreases due to wear, and the surface potential decreases.

  On the other hand, since the developer used in the electrophotographic process is powder, the electrical characteristics are easily affected by changes in humidity. For example, when the humidity decreases, the electrical resistance value increases due to a decrease in the moisture content, and development The charge amount of the toner contained in the agent increases. Further, the developer is subjected to mechanical stress due to stirring in the developing device, and this also causes a change in electrical characteristics.

  Such changes in the surface potential of the photoconductor and changes in the electrical characteristics of the developer due to changes in the environment and changes over time cause changes in the density of the image formed by the electrophotographic process and cause deterioration in image quality. .

Therefore, the conventional image forming apparatus includes an optical sensor that detects the density of the toner image on the surface of the photoreceptor, and controls the process conditions of the electrophotographic process based on the detection result of the density of the toner image by the optical sensor. There is something. For example, a plurality of rectangular reference toner images called toner patches are formed on the surface of a photoreceptor under different process conditions, and a grid of charging chargers is formed based on the result of density detection by an optical sensor for each of the plurality of toner patches. An image forming apparatus that controls process conditions by changing a voltage, a developing bias, a driving voltage for laser exposure, and the like has been proposed (for example, see Patent Document 1).
Japanese Patent Application Laid-Open No. 07-120989

  However, the conventional image forming apparatus in which the optical sensor is arranged as described above has the following problems.

  That is, as in Patent Document 1, when an optical sensor is disposed in the vicinity of a cleaning unit that scrapes and collects the residual toner after transfer from the photoreceptor, the residual toner adheres to the optical sensor, and the optical sensor is contaminated by the optical sensor. False detection may occur and affect image quality adjustment. Further, there is no cover for preventing the optical sensor from being soiled.

  To solve this problem, there is a method of cleaning the optical sensor by a service person during maintenance, but the service person cannot always go out and clean.

  An object of the present invention is to provide an image forming apparatus capable of preventing an optical sensor from being erroneously detected by preventing contamination of the optical sensor and performing an accurate image quality adjustment.

  The image forming apparatus of the present invention includes an image carrier, a conveyance path, and an optical sensor unit. An electrostatic latent image is formed on the surface of the image carrier. The transport path is formed by a transport guide arranged to transport the recording medium to the image carrier. The optical sensor unit includes an optical sensor, a casing, and an opening / closing member. The optical sensor detects the density of the reference toner image formed on the surface of the image carrier. The casing houses the optical sensor, and is provided with a light emitting port for securing the light emitting path of the optical sensor and a light receiving port for securing the light receiving path of the optical sensor. The opening / closing member covers the light emitting port and the light receiving port of the casing.

  The optical sensor unit in the image forming apparatus of the present invention is disposed in the vicinity of the conveyance path with the opening / closing member facing the conveyance path. The opening / closing member closes when a part or all of the opening / closing member protrudes into the conveyance path and the conveyed recording medium contacts the opening / closing member.

  In this configuration, since the optical sensor unit is disposed in the vicinity of the conveyance path with the opening / closing member facing the conveyance path, the opening / closing member is located at a position where it can contact the recording medium. Further, since the opening / closing member is closed by the contact of the recording medium, the paper dust generated by the conveyance of the recording medium and the floating toner by the transfer adhere to the light emitting port and the light receiving port of the casing, and the light emitting path and the light receiving path of the optical sensor are blocked. Shielding can be prevented.

  In this configuration, the opening / closing member is preferably opened when the rear end of the recording medium passes through the opening / closing member.

  In this configuration, since the opening / closing member is open while the recording medium does not pass through the opening / closing member, the density of the toner image on the surface of the image carrier can be detected by the optical sensor without being blocked by the opening / closing member. Therefore, image quality adjustment can be performed based on the detection result of the toner image.

  Further, it is preferable that the optical sensor unit is disposed within the width of the minimum width recording medium among a plurality of sizes of recording media that can be conveyed.

  In this configuration, the opening / closing member that covers the optical sensor can be closed not only by the recording medium having the maximum width but also by all the recording media that are conveyed.

  Further, it is preferable that the opening / closing member is provided with a rib on the surface facing the conveyance path when closed.

  In this configuration, it is possible to reduce the conveyance noise generated while the recording medium passes through the opening / closing member, and the opening / closing member can be easily closed when the conveyed recording medium contacts the rib.

  In addition, it is preferable that the holding force with the open / close member opened is smaller than the pressing force for conveying the recording medium.

  In this configuration, the opening / closing member can be closed by the recording medium without the recording medium being jammed or the leading end of the recording medium being curled.

  In addition, the optical sensor unit is preferably arranged on the opposite side of the image carrier with the conveyance path interposed therebetween.

  In this configuration, it is necessary to dispose a plurality of units such as a charging unit, a developing unit, a cleaning unit, and a static elimination lamp, which are indispensable for the image forming process, on the image carrier side across the conveyance path. Arranging the sensor unit reduces design freedom. For this reason, it is possible to reduce the size of the image forming apparatus by arranging the optical sensor unit on the opposite side of the image carrier with the conveyance path having a relatively high degree of freedom.

  In this configuration, the image forming apparatus of the present invention further includes an openable / closable door cover for removing the jammed recording medium on the opposite side of the image carrier across the conveyance path, and the optical sensor unit is attached to the door cover. Preferably it is arranged.

  In this configuration, when the conveyed recording medium is jammed at a transfer position other than on the optical sensor unit, the opening / closing member is in an open state. The toner adheres to the optical sensor and becomes dirty. However, when a jam occurs, by opening the jam release door cover to which the optical sensor unit is attached from the main body of the image forming apparatus, paper dust and toner at the time of jam do not adhere to the optical sensor and become dirty.

  In addition, the opening / closing member is positioned in a position where the upstream end of the opening / closing member in the conveyance direction of the recording medium does not protrude into the conveyance path from the surface facing the conveyance path of the conveyance guide, and the opening / closing member in the conveyance direction of the recording medium It is preferable that the downstream end is located at a position protruding from the surface facing the conveyance path of the conveyance guide into the conveyance path.

  In this configuration, since the recording medium to be conveyed does not come into contact with the upstream end of the recording medium in the conveyance direction of the opening / closing member, it is possible to prevent the recording medium from being jammed or the recording medium tip from being broken. In addition, since the recording medium to be conveyed contacts the downstream end of the opening / closing member in the conveying direction of the recording medium, the opening / closing member can be closed by the recording medium.

  Furthermore, the conveyance guide is preferably provided with a guide rib on the surface facing the conveyance path.

  In this configuration, since the conveyance direction can be changed so that the recording medium to be conveyed approaches the optical sensor unit, the opening / closing member can be easily closed.

  In addition, when the opening / closing member is in the open state, the upstream end of the opening / closing member in the conveyance direction of the recording medium is positioned so as not to protrude into the conveyance path from the surface facing the conveyance path of the guide rib. It is preferable that the end is located at a position protruding from the surface of the guide rib facing the conveyance path to the conveyance path.

  In this configuration, since the recording medium to be conveyed does not come into contact with the upstream end of the recording medium in the conveyance direction of the opening / closing member, it is possible to prevent the recording medium from being jammed or the recording medium tip from being broken. In addition, since the recording medium to be conveyed contacts the downstream end of the opening / closing member in the conveying direction of the recording medium, the opening / closing member can be closed by the recording medium.

  The image forming apparatus according to the present invention prevents the optical sensor from being soiled by preventing the optical sensor from being erroneously detected, and can perform accurate image quality adjustment.

  Hereinafter, an image forming apparatus according to the best embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention.

  The image forming apparatus 10 records and outputs the image data from the externally connected device when the externally connected device such as a personal computer is connected as well as the recording output of the image read by the image reading device.

  In the image forming apparatus 10, each process unit responsible for each function of the image forming process is disposed around a photosensitive member (image carrier) 3. Around the photoreceptor 3, a charging unit 5, an optical scanning unit 11, a developing unit 2, a transfer unit 6, a cleaning unit 4, a static elimination lamp 12 and the like are sequentially arranged.

  The charging unit 5 uniformly charges the surface of the photoreceptor 3. The optical scanning unit 11 exposes and scans the uniformly charged photoreceptor 3 to write an electrostatic latent image. The developing unit 2 visualizes the electrostatic latent image written by the optical scanning unit 11 with the developer supplied from the developer supply container 7. The transfer means 6 transfers the image visualized on the photoreceptor 3 onto a sheet (recording medium). The cleaning unit 4 can remove the developer remaining on the photoconductor 3 and record a new image on the photoconductor 3. The neutralizing lamp 12 removes the charge on the surface of the photoreceptor 3.

  A registration roller 14 that guides the sheet to the transfer position at a predetermined timing is disposed on the upstream side of the transfer position located between the photoreceptor 3 and the transfer unit 6 on the sheet transport path S. On the other hand, on the downstream side of the transfer position on the paper transport path S, a fixing device 8 for fixing the unfixed developer image attached on the paper on the paper is disposed.

  Under the image forming apparatus 10, a paper supply tray 94 that is housed in the main body of the image forming apparatus 10 is disposed, and the uppermost sheet stored in the paper supply tray 94 is separated in the vicinity of the paper supply tray 94. Then, a pickup roller 16 is disposed to guide the sheet to the sheet conveyance path.

  The paper supply tray 94 is a paper storage tray for storing paper. The paper stored in the paper supply tray 94 is separated one by one and supplied to the image forming unit. The sheets separated and supplied one by one from the sheet supply tray 94 by the pickup roller 16 are timed with the operation of the image forming process performed around the photoreceptor 3 by the registration rollers 14 on the sheet conveyance path S, and transferred. Sequentially supplied to the transfer position between the means 6 and the photoreceptor 3. At this transfer position, the developer image formed on the photoreceptor 3 is transferred onto the sheet by the transfer voltage of the transfer means 6. Note that the paper supply to the paper supply tray 94 is performed by pulling out the paper supply tray 94 from the front of the image forming apparatus 10.

  On the lower surface of the image forming apparatus 10, paper fed from a paper feeding apparatus having a multi-stage paper feeding tray prepared as a peripheral device and a paper feeding apparatus capable of storing a large amount of paper is received as an image forming unit. Paper receiving openings 17a to 17c for sequentially supplying the paper are provided.

  The sheet that has passed the transfer position is guided to the fixing device 8. In the fixing device 8, the sheet having the image transferred thereon is sequentially received, and the unfixed developed image transferred onto the sheet by heat and pressure is fixed by the fixing roller 81 and the pressure roller 82. The sheet on which the image is recorded is further conveyed to the downstream side of the sheet conveying path S by the conveying roller 25 and guided to the switching gate 9.

  The optical sensor unit 100 according to the present invention is provided between the registration roller 14 and the transfer unit 6 on the opposite side of the photoconductor 3 with the paper transport path S interposed therebetween.

  FIG. 2 is a diagram illustrating an arrangement position of the optical sensor unit in the image forming apparatus according to the embodiment of the present invention.

  FIG. 2 is a view from the back of FIG. The optical sensor unit 100 is provided between the registration roller 14 and the transfer position between the photosensitive member 3 and the charging unit 6. Further, the opening / closing member 130 is directed toward the sheet conveying path S, and a part of the opening / closing member 130 is protruded into the sheet conveying path S. This position is a position where the toner pattern formed on the photoconductor 3 for image quality adjustment can be read during image quality adjustment. Note that the entire opening / closing member 130 may be protruded into the sheet conveyance path S. The position of the optical sensor unit 100 is not limited to this, and is a position where the toner pattern formed on the photosensitive member 3 for image quality adjustment can be read, and the opening / closing member 130 is moved by the conveyed paper. Any position that can be closed is acceptable. The optical sensor unit 100 is attached to the paper transport guide 24 to determine the position of the paper transporting the paper transport guide 24 and the opening / closing member 130, and the opening / closing member 130 covers the light emitting port 113 and the light receiving port 114 by the paper. be able to. However, the present invention is not limited to this, and any position may be used as long as the opening / closing member 130 can cover the light emitting port 113 and the light receiving port 114.

  The optical sensor unit 100 is disposed on the opposite side of the photoreceptor 3 with the paper transport path S interposed therebetween. This is because a plurality of units such as the charging unit 5, the developing device 2, the cleaning unit 4, and the charge removal lamp 12 that are indispensable for the image forming process are arranged in the region on the photoconductor 3 side with the sheet conveyance path S interposed therebetween. Further, it is necessary to dispose the optical sensor unit 100 in that region, which reduces the degree of freedom in design. For this reason, the optical sensor unit 100 is arranged in a region opposite to the photosensitive member 3 with the sheet conveyance path S interposed therebetween, which has a relatively high degree of freedom in arrangement. By arranging the optical sensor unit 100 at this position, the image forming apparatus 10 can be downsized.

  The sheet conveyance guides 22 and 24 are provided with guide ribs 26 and 28, respectively. By providing the guide ribs 26, 28, the opening / closing member 130 can be reliably closed by changing the paper transport direction so that the fed paper approaches the opening / closing member 130.

  The optical sensor unit 100 is located at a position where the upstream end of the opening / closing member 130 in the sheet conveying direction does not protrude into the sheet conveying path S from the surface facing the sheet conveying path S of the guide rib 28 when the opening / closing member 130 is open. The downstream end of the member 130 in the sheet conveyance direction is disposed so as to be located at a position protruding from the surface of the guide rib 28 facing the sheet conveyance path S to the sheet conveyance path S. This is because when the upstream end of the opening / closing member 130 in the sheet conveyance direction is positioned below the guide rib 28, the conveyed sheet does not contact the side surface of the opening / closing member 130, and a paper jam or a paper break at the leading edge of the sheet occurs. It is because it can prevent. At the same time, the conveyed sheet contacts the downstream end of the opening / closing member 130 in the sheet conveying direction, so that the opening / closing member 130 can be closed.

  The paper conveyance guides 22 and 24 do not have to be provided with guide ribs. In this case, in the optical sensor unit 100, the upstream end of the opening / closing member 130 in the sheet conveying direction protrudes from the surface of the sheet conveying guide 24 facing the sheet conveying path S to the sheet conveying path S when the opening / closing member 130 is open. The opening / closing member 130 is disposed such that the downstream end of the opening / closing member 130 in the sheet conveyance direction protrudes from the surface of the sheet conveyance guide 24 facing the sheet conveyance path S to the sheet conveyance path S.

  FIG. 3 is a diagram showing a part of the configuration of the optical sensor unit in the image forming apparatus according to the embodiment of the present invention.

  The optical sensor substrate unit 102 is a constituent part of the optical sensor unit 100. The optical sensor substrate unit 102 includes an optical sensor 110 and a casing 120.

  The optical sensor 110 includes a light emitting sensor 111 and a light receiving sensor 112. The optical sensor 110 is housed in a resin casing 120. In the casing 120, a light emitting port 113 for securing a light emitting path for light emitted from the light emitting sensor 111 and a light receiving port 114 for securing a light receiving path for light received by the light receiving sensor 112 are provided. The optical sensor 110 and the casing 120 are generally commercially available.

  The optical sensor 110 irradiates the photosensitive member 3 with light from the light emitting sensor 111, receives the reflected light from the photosensitive member 3 with the light receiving sensor 112, and detects the density of the reference toner image formed on the surface of the photosensitive member 3.

  FIG. 4 is a diagram showing a part of the configuration of the optical sensor unit in the image forming apparatus according to the embodiment of the present invention.

  The opening / closing member unit 104 is a constituent part of the optical sensor unit 100. The opening / closing member unit 104 includes an opening / closing member 130, a spring 142, and an opening / closing member mounting plate 150.

  The opening / closing member 130 is provided with a rib 132 on the surface facing the sheet conveyance path S when closed, which contacts the sheet. By providing the ribs 132, it is possible to reduce the conveyance noise during the conveyance of the paper, and when the conveyed paper contacts the ribs 132, the opening / closing member 130 is reliably closed.

  There are round holes for inserting the shaft 140 on both sides of the opening / closing member 130, and the opening / closing member mounting plate 150 also has a round hole for inserting the shaft 140. The spring 142 is inserted into the shaft 140, and the shaft 140 is inserted into the round holes of the opening / closing member 130 and the opening / closing member mounting plate 150. To prevent the shaft 140 from coming off, there are E-ring grooves on both sides of the shaft 140, and the E-rings are fixed to the grooves. As a method of attaching the opening / closing member unit 104 to the optical sensor substrate unit 102, a screw or a claw on the opening / closing member attachment plate 150 is used.

  The opening / closing member 130 can be opened / closed with respect to the optical sensor substrate unit 102 with the shaft 140 as a fulcrum. The opening / closing member 130 is normally opened by a spring 142 attached to the opening / closing member unit 104, and the opening / closing member 130 is closed by applying a weak force to the opening / closing member 130. The holding force of the spring 142 is about 5 g or less, and the spring force is such that when the paper leading edge is conveyed while contacting the opening / closing member 130, the paper is normally conveyed without curling the paper jam or the paper leading edge. .

  The opening / closing member 130 is closed when the conveyed paper comes into contact, and opens when the trailing edge of the paper passes through the opening / closing member 130. While the sheet does not pass through the opening / closing member 130, that is, while the sheet is not being conveyed, the opening / closing member 130 is open, so that the optical sensor 110 is not shielded by the opening / closing member 130, and the surface of the photoreceptor 3. Therefore, the image quality adjustment can be performed based on the detection result of the toner image density.

  FIG. 5 is a diagram illustrating an arrangement position of the optical sensor unit in the image forming apparatus according to the embodiment of the present invention.

  The optical sensor unit 100 is disposed within the width of the minimum width paper P1 among the plural sizes of paper that can be transported. This means that the opening / closing member 130 can be closed by not only the maximum width sheet P2 but all sheets that can be transported, and the light emitting port 113 and the light receiving port 114 can be covered. There are A3, A4 length, B5 length, A5 length, etc. as the paper size to be transported. However, in the case where the transport of each paper is transported based on the center in the transport width direction, the optical sensor unit is attached to the center shaft 50. You may arrange | position so that the center of 100 may come.

  FIG. 6 is a diagram illustrating a state during sheet conveyance in the image forming apparatus according to the embodiment of the present invention.

  6 is a view as seen from the back of FIG. FIG. 6A is a diagram in which the paper P is passing through the registration roller 14. Thereafter, the paper P travels toward the opening / closing member 130 along the guide ribs 26 provided in the paper transport guide 22. Here, if the sheet P is weak, the sheet P moves toward the opening / closing member 130 along the guide rib 28.

  FIG. 6B is a view before the sheet P passes between the photosensitive member 3 and the transfer unit 6. The paper P passing between the paper transport guide 22 and the paper transport guide 24 is guided by the guide rib 26 and reaches the rib 132. The sheet P closes the opening / closing member 130 by the waist pressure, and covers the light emitting port 113 and the light receiving port 114. Since the opening / closing member 130 is held by the spring 142, the opening / closing member 130 opens when the paper P passes over the opening / closing member 130.

  FIG. 7 is a diagram showing the movement of the optical sensor unit accompanying the sheet passage in the image forming apparatus according to the embodiment of the present invention.

  FIG. 7A is a diagram illustrating a state of the optical sensor unit 100 before the paper P passes through. The opening / closing member 130 is open, and the toner patch formed on the surface of the photoreceptor 3 can be read.

  FIG. 7B is a diagram illustrating a state of the optical sensor unit 100 immediately before the paper P passes. Since the leading edge of the sheet P is above the upstream end of the opening / closing member 130 in the sheet conveying direction, the sheet jam caused by the sheet P coming into contact with the side surface of the opening / closing member 130 and the folding of the leading edge of the sheet P are prevented. be able to.

  FIG. 7C is a diagram illustrating a state where the paper P is pressing the rib 132. Since the opening / closing member 130 is only supported by a weak force by the spring 142, it can be easily closed by pressing the paper P.

  FIG. 7D is a diagram in which the paper P passes through the optical sensor unit 100. As described above, since the opening / closing member 130 is only supported by a weak force by the spring 142, the paper P is not curled by the opening / closing member 130.

  FIG. 7E is a diagram illustrating a state of the optical sensor unit 100 after the paper P has passed. When the paper P passes, the opening / closing member 130 is opened again, and the toner patch formed on the surface of the photoreceptor 3 can be read.

  FIG. 8 is a diagram in which the door cover unit is moved in the image forming apparatus according to the embodiment of the present invention.

  FIG. 8 is a view from the back of FIG. The image forming apparatus 10 is provided with a door cover 42. The transfer means 6 and the optical sensor unit 100 are attached to the door cover 42. The door cover 42 is an openable / closable member provided to remove the retained paper when the paper jam occurs and the paper stays on the paper transport path S.

  When a paper jam occurs, if the paper is on the optical sensor unit 100, the opening / closing member 130 is closed, so that paper dust and toner do not adhere to the optical sensor 110. However, when the conveyed paper is jammed at a transfer position other than on the optical sensor unit 100, for example, the opening / closing member 130 is in an open state. Or toner adheres to the optical sensor 110 and becomes dirty. When a jam occurs, the paper cover and the toner at the time of jam do not adhere to the optical sensor 110 and become dirty by opening the door cover 42 to which the optical sensor unit 100 is attached from the image forming apparatus 10.

  Finally, the description of the above-described embodiment is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a diagram illustrating an arrangement position of an optical sensor unit in an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a diagram illustrating a part of the configuration of an optical sensor unit in the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a diagram illustrating a part of the configuration of an optical sensor unit in the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a diagram illustrating an arrangement position of an optical sensor unit in an image forming apparatus according to an embodiment of the present invention. FIG. 4 is a diagram illustrating a state during sheet conveyance in the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a diagram illustrating the movement of the optical sensor unit accompanying the sheet passage in the image forming apparatus according to the embodiment of the present invention. FIG. 5 is a diagram showing a door cover unit moved in the image forming apparatus according to the embodiment of the present invention.

Explanation of symbols

S-paper transport path 3-photosensitive member 10-image forming apparatus 22, 24-paper transport guide 26, 28-guide rib 42-door cover 100-optical sensor unit 110-optical sensor 113-light emitting port 114-light receiving port 120-casing 130-Opening / closing member 132-Rib

Claims (10)

An image carrier on which an electrostatic latent image is formed on the surface;
A conveyance path formed by a conveyance guide arranged to guide the recording medium to the image carrier;
An optical sensor for detecting the density of a reference toner image formed on the surface of the image carrier, a light emitting port for housing the optical sensor and securing a light emitting path for the optical sensor, and a light receiving path for the optical sensor. An optical sensor unit having a casing provided with a light receiving opening for securing, and an opening / closing member covering the light emitting opening and the light receiving opening of the casing;
With
The optical sensor unit is disposed in the vicinity of the transport path with the opening / closing member facing the transport path,
The open / close member is an image forming apparatus in which a part or all of the open / close member protrudes into the conveyance path, and the recording medium transported closes by contacting the open / close member.   The image forming apparatus according to claim 1, wherein the opening / closing member opens when a rear end of the recording medium passes through the opening / closing member.   The image forming apparatus according to claim 1, wherein the optical sensor unit is disposed within a width of a recording medium having a minimum width among a plurality of sizes of recording media that can be conveyed.   The image forming apparatus according to claim 1, wherein the opening / closing member is provided with a rib on a surface facing the conveyance path when the opening / closing member is closed.   The image forming apparatus according to claim 1, wherein a holding force of the open / close member in an open state is smaller than a pressing force for conveying the recording medium.   The image forming apparatus according to claim 1, wherein the optical sensor unit is disposed on the opposite side of the image carrier with the conveyance path interposed therebetween. Further comprising an openable / closable door cover for removing the jammed recording medium on the opposite side of the image carrier across the conveyance path,
The image forming apparatus according to claim 6, wherein the optical sensor unit is disposed on the door cover.   In the open state, the opening / closing member is located at a position where the upstream end of the opening / closing member in the conveyance direction of the recording medium does not protrude into the conveyance path from the surface of the conveyance guide facing the conveyance path. 8. The image forming apparatus according to claim 1, wherein a downstream end of the medium in the conveyance direction is located at a position protruding from the surface of the conveyance guide facing the conveyance path to the conveyance path.   The image forming apparatus according to claim 1, wherein the conveyance guide is provided with a guide rib on a surface facing the conveyance path.   In the open state, the opening / closing member is located at a position where an upstream end of the opening / closing member in the conveyance direction of the recording medium does not protrude from the surface of the guide rib facing the conveyance path, and the recording medium of the opening / closing member The image forming apparatus according to claim 9, wherein a downstream end of the guide rib is located at a position protruding from a surface of the guide rib facing the transport path to the transport path.

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