JP5998113B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet.

  2. Description of the Related Art Conventionally, an apparatus described in Patent Document 1 is known as an image forming apparatus that forms an image on a sheet. In the apparatus, a fan and a duct are provided to cool the conveyance motor and the guide member that are heated in the apparatus main body of the image forming apparatus. The air flow generated by the fan is blown to the guide member from the opening opened in the duct. Further, the air flow is guided by the guide surface of the duct and guided to the transport motor.

JP 2000-304395 A

  In the technique described in Patent Document 1, when an air flow is blown from a duct to a conveyance motor or a guide member that is a cooling target, surrounding air may be involved and an unnecessary air flow may occur. As a result, there is a problem that foreign matters such as toner and dust adhere to the cooling target.

  The present invention has been made in view of the above problems, and provides an image forming apparatus that suppresses foreign air from flowing into the detection sensor when the detection sensor is cooled by an air flow. Objective.

An image forming apparatus according to an aspect of the present invention includes a sheet conveyance path in which a sheet is conveyed in a predetermined conveyance direction, a sheet conveyance path disposed opposite to the sheet conveyance path, rotationally driven about an axis, and a toner on a circumferential surface A photosensitive drum that carries an image, and a conveyance belt that is disposed to face the photosensitive drum across the sheet conveyance path, is driven to rotate, and forms a nip portion with the photosensitive drum; And a transfer unit that transfers the toner image onto the sheet so as to pass through the nip portion, and is disposed downstream of the nip portion in the conveyance direction, and the toner image is transferred to the sheet. A fixing unit that performs a fixing process on the sheet and a fixing unit that is disposed on the opposite side of the photosensitive drum from the transfer unit with a predetermined gap from the transfer unit. The transport unit that transports the sheet into the sheet transport path upstream of the nip portion in the transport direction, and the transport so as to face the transfer unit in a cross-sectional view that intersects the axial direction of the photosensitive drum. A detection sensor disposed in the unit and performing a predetermined detection operation; and the gap between the transfer unit and the transport unit along the axial direction , disposed on one end side in the axial direction of the transport unit. and cooling air flow generating unit for flowing air stream, the being the gap thus formed between the transfer unit and the transfer unit, and the cooling air path for guiding the cooling air flow towards said detection sensor , One that is interposed along the axial direction in the gap between the transfer unit and the transport unit, and intersects the axial direction from the periphery of the transfer unit It characterized by having a a shielding member for shielding an air stream flowing toward the cooling air passage along.

  According to this configuration, the sheet conveyed through the sheet conveyance path is subjected to a fixing process in the fixing unit after the toner image is transferred in the nip unit. The detection sensor is disposed in the transport unit so as to face the transfer unit. Then, the cooling air flow generated by the air flow generation unit flows between the transfer unit and the transport unit, and reaches the detection sensor while being guided to the cooling air passage. For this reason, it is suppressed that the temperature of a detection sensor rises, and it is prevented that the malfunction of a detection sensor arises. On the other hand, when the cooling airflow flows between the transfer unit and the transport unit from the airflow generator, the peripheral airflow easily flows from the gap between the transfer unit and the transport unit. In particular, since the toner easily moves around the transfer unit, when the toner flows into the cooling air passage, the detection sensor is contaminated with the toner, and the detection accuracy is lowered. Even in such a case, according to the above configuration, the shielding member is interposed in the gap between the transfer unit and the transport unit along the axial direction. The shielding member shields the airflow that flows from the periphery of the transfer unit toward the cooling air passage along the direction intersecting the axial direction. For this reason, the detection sensor is stably cooled by the cooling air flow, and foreign substances such as toner are prevented from adhering to the detection sensor.

  In the above configuration, the shielding member is preferably an elastic member that is compressed and disposed between the transfer unit and the transport unit.

  According to this configuration, the shielding member, which is an elastic member, is disposed between the transfer unit and the transport unit so as to be compressed, thereby further preventing an air flow from flowing into the cooling air passage from the periphery of the transfer unit. Is done.

  In the above configuration, the transfer unit includes a notch formed so as to expose a part of the transport unit to the sheet transport path side downstream of the transport belt in the transport direction, and the detection sensor Preferably, the sheet sensor is disposed in the conveyance unit so as to face the notch portion and detects the sheet conveyed from the nip portion via the notch portion.

  According to this configuration, the sheet sensor is disposed to face the sheet conveyance path on the downstream side in the conveyance direction with respect to the conveyance belt. When the sheet subjected to the fixing process passes through the nip portion again, the heat of the sheet is transmitted to the sheet sensor, and the temperature of the sheet sensor is likely to rise. Even in such a case, since the sheet sensor is cooled by the cooling airflow, the sheet sensor stably detects that the sheet has been carried out from the nip portion.

  In the above configuration, the transfer unit includes a guide portion that guides the sheet detached from the conveyance belt in the conveyance direction, the notch portion is formed in the guide portion, and the shielding member includes: It is desirable to interpose between the guide part and the transport unit.

  According to this configuration, the notch portion can be formed using the guide portion that guides the sheet detached from the conveyance belt, and the shielding member is interposed between the guide portion and the conveyance unit. Can do.

  In the above configuration, it is preferable that the detection sensor is a density sensor that is disposed in the conveyance unit so as to face the conveyance belt and detects a density of a detection toner image formed on the conveyance belt.

  According to this configuration, the density of the detection toner image can be detected using the back side of the conveyance belt with respect to the sheet conveyance path. Further, since the concentration sensor is cooled by the cooling air flow, the concentration is stably detected. Further, even when the toner of the detection toner image rises from the conveyance belt, the toner is prevented from adhering to the density sensor by the cooling air flow.

  In the above-described configuration, it is desirable to further include a partition member protruding from the transport unit along the axial direction and defining a part of the cooling air passage.

  According to this configuration, the flow of the cooling air flow in the axial direction is promoted by the partition member.

  In the above configuration, a plurality of the detection sensors are arranged at different positions in the transport direction, and the partition member functions to divide the cooling airflow flowing in from the airflow generation unit toward the plurality of sensors. It is desirable to have.

  According to this configuration, the cooling airflow can be guided toward the plurality of detection sensors by the partition member.

  In the above configuration, it is desirable that the partition member has a function of positioning the electrical wiring extended from the detection sensor.

  According to this configuration, the electrical wiring of the detection sensor can be positioned using the partition member.

  According to the present invention, there is provided an image forming apparatus in which when the detection sensor is cooled by an air flow, ambient air flows in and foreign matter is prevented from adhering to the detection sensor.

1 is a perspective view of an image forming apparatus according to an embodiment of the present invention. 1 is an internal cross-sectional view of an image forming apparatus according to an embodiment of the present invention. 1 is an enlarged cross-sectional view of a part of an image forming apparatus according to an embodiment of the present invention. It is sectional drawing which expanded a part of FIG. 3 further. FIG. 3 is a perspective view of a transport unit of the image forming apparatus according to the embodiment of the invention. FIG. 6 is a perspective view of a state where a transfer unit is removed from the transport unit of FIG. 5. FIG. 6 is a perspective view of a state where a front standing wall is removed from the transport unit of FIG. 5. FIG. 6 is a perspective view of a state where a transfer unit and a front standing wall are removed from the transport unit according to the embodiment of the invention. It is the perspective view which expanded the periphery of the airflow generation part of the conveyance unit which concerns on embodiment of this invention. It is a perspective view which shows the flow of the air in the cooling air path which concerns on embodiment of this invention. It is a side view which shows the flow of the air in the cooling air path which concerns on embodiment of this invention.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 schematically shows an internal structure of image forming apparatus 1 shown in FIG. In FIG. 2, the upper housing 22 of FIG. 1 does not appear. The image forming apparatus 1 shown in FIGS. 1 and 2 is a so-called monochrome printer, but in other embodiments, the image forming apparatus is a color printer, a facsimile machine, a multifunction machine having these functions, or a toner image. Other devices for forming the sheet may be used. Note that the terms used in the following description, such as “up”, “down”, “front”, “rear”, “left” and “right”, are merely for the purpose of clarifying the description. There is no limitation on the principle of the image forming apparatus. In the following description, the term “sheet” means copy paper, coated paper, OHP sheet, cardboard, postcard, tracing paper, other sheet material subjected to image forming processing, or any processing other than image forming processing. Means the sheet material to receive.

  The image forming apparatus 1 includes a main housing 2 having a substantially rectangular parallelepiped shape. The main housing 2 connects a substantially rectangular parallelepiped lower housing 21, a substantially rectangular parallelepiped upper housing 22 disposed above the lower housing 21, and the lower housing 21 and the upper housing 22. And a connecting housing 23. The connection housing 23 extends along the right edge and the back edge of the main housing 2. The sheet subjected to the printing process is discharged into a discharge space 24 surrounded by the lower casing 21, the upper casing 22, and the connecting casing 23.

  The operation unit 221 protruding in the front direction of the upper housing 22 includes, for example, an LCD touch panel 222. The operation unit 221 is formed so as to be able to input information related to the image forming process. For example, the user can input the number of sheets to be printed, the print density, and the like through the LCD touch panel 222. Housed in the upper housing 22 are mainly an apparatus for reading an image of a document and an electronic circuit that controls the entire image forming apparatus 1.

  A pressing cover 223 disposed on the upper housing 22 is used for pressing the document. The presser cover 223 is attached to the upper housing 22 so as to be rotatable up and down. The user rotates the holding cover 223 upward to place the document on the upper housing 22. Thereafter, the user can operate the operation unit 221 to read an image of the document on a device provided in the upper housing 22.

  A manual feed tray 240 is disposed on the right side surface of the lower housing 21. The manual feed tray 240 can be rotated up and down on the upper end 240B side with the lower end 240A (FIG. 2) as a fulcrum. The user can place a sheet on the manual feed tray 240 when the manual feed tray 240 is rotated downward and the manual feed tray 240 is in a position protruding to the right of the lower housing 21. The sheet on the manual feed tray 240 is drawn into the lower housing 21 based on an instruction input by the user through the operation unit 221, is subjected to image forming processing, and is discharged into the discharge space 24.

  With reference to FIG. 2, the image forming apparatus 1 includes a cassette 110, a paper feeding unit 11, a second paper feeding roller 114, an intermediate roller 115, a registration roller pair 116, and an image forming unit 120. The paper feed unit 11 includes a pickup roller 112 and a first paper feed roller 113. The sheet feeding unit 11 sends the sheet P to the sheet conveyance path PP. The sheet conveyance path PP is disposed so as to pass from the sheet feeding unit 11 through a transfer nip TP (nip unit) disposed in the image forming unit 120 via the intermediate roller pair 115 and the registration roller pair 116. It is a transport path. The sheet P is conveyed in the conveyance direction from the lower side to the upper side along the sheet conveyance path PP.

  The cassette 110 accommodates the sheet P inside. The cassette 110 can be pulled out from the lower housing 21 in the front direction (the front side in FIG. 2). The sheet P accommodated in the cassette 110 is sent upward in the lower housing 21. Thereafter, the sheet P is subjected to an image forming process in the lower housing 21 based on an instruction input by the user through the operation unit 221, and is discharged to the discharge space 24. The cassette 110 includes a lift plate 111 that supports the sheet P. The lift plate 111 is inclined so as to push up the leading edge of the sheet P upward.

  The pickup roller 112 is disposed on the leading edge of the sheet P pushed upward by the lift plate 111. When the pickup roller 112 rotates, the sheet P is pulled out from the cassette 110.

  The first paper feed roller 113 is disposed downstream of the pickup roller 112 in the sheet conveyance direction. The first paper feed roller 113 sends the sheet P further downstream. The second paper feed roller 114 is disposed inside the manual feed tray 240. The second paper feed roller 114 pulls the sheet P on the manual feed tray 240 into the lower housing 21. The user can selectively use the sheet P stored in the cassette 110 or the sheet P placed on the manual feed tray 240.

  The intermediate roller pair 115 is disposed downstream of the first paper feed roller 113 and the second paper feed roller 114 in the sheet conveyance direction. The intermediate roller pair 115 conveys the sheet P sent out by the first paper feed roller 113 and the second paper feed roller 114 further downstream.

  The registration roller pair 116 defines the position of the sheet in a direction orthogonal to the sheet conveyance direction. Thereby, the position of the image formed on the sheet P is adjusted. The registration roller pair 116 conveys the sheet P to the image forming unit 120 in accordance with the timing at which the toner image is transferred to the sheet P in the image forming unit 120. The registration roller pair 116 has a function of correcting skew (skew) of the sheet P. The registration roller pair 116 includes a driven roller 116A and a registration roller 116B (FIG. 3).

  Referring to FIG. 2, the image forming unit 120 includes a photosensitive drum 121, a charger 122, an exposure device 123, a developing device 124, a toner container 125, a transfer roller 126, a conveyance belt 180, and a cleaning. Device 127.

  The photosensitive drum 121 is disposed to face the sheet conveyance path PP and is driven to rotate about an axis. The photosensitive drum 121 has a cylindrical shape. The photosensitive drum 121 has an electrostatic latent image formed on its peripheral surface and carries a toner image corresponding to the electrostatic latent image.

  The charger 122 is applied with a predetermined voltage and charges the peripheral surface of the photosensitive drum 121 substantially uniformly. The exposure device 123 irradiates the peripheral surface of the photosensitive drum 121 charged by the charger 122 with laser light. The laser light is emitted in accordance with image data output from an external device (not shown) such as a personal computer that is communicably connected to the image forming apparatus 1. As a result, an electrostatic latent image corresponding to the image data is formed on the peripheral surface of the photosensitive drum 121.

  The developing device 124 supplies toner to the peripheral surface of the photosensitive drum 121 on which the electrostatic latent image is formed. The toner container 125 supplies toner to the developing device 124. The toner container 125 supplies toner to the developing device 124 sequentially or as necessary. When the developing device 124 supplies toner to the photosensitive drum 121, the electrostatic latent image formed on the peripheral surface of the photosensitive drum 121 is developed (visualized). As a result, a toner image is formed on the peripheral surface of the photosensitive drum 121. The developing device includes a developing roller 124A (FIG. 3) that carries toner on its peripheral surface. The developing roller 124A is disposed to face the photosensitive drum 121 at the developing position. The developing roller 124 </ b> A is rotated and supplies toner to the photosensitive drum 121.

  The transfer roller 126 is disposed to face the peripheral surface of the photoconductive drum 121. The transfer roller 126 contacts the inner peripheral surface of the conveyance belt 180 and presses the conveyance belt 180 against the photosensitive drum 121. A transfer bias is applied to the transfer roller 126 from a bias application unit (not shown).

  The conveyance belt 180 is disposed to face the photosensitive drum 121 with the sheet conveyance path PP interposed therebetween. The conveyor belt 180 is an endless belt. The conveyor belt 180 is driven to form a transfer nip TP with the photosensitive drum 121. The conveyance belt 180 carries the sheet P on its surface and conveys the sheet P so that the sheet P passes through the transfer nip TP. The conveyor belt 180 transmits a rotational driving force to the transfer roller 126 via the inner peripheral surface. The conveyance belt 180 is stretched by a stretching roller 182 and a driving roller 181 on the upstream side and the downstream side in the sheet conveyance direction from the transfer roller 126. The driving roller 181 receives a rotational driving force from a driving unit (not shown) and rotates the conveyor belt 180. The transfer roller 126 and the stretching roller 182 rotate along with the conveyance belt 180 and rotate at the same speed as the conveyance belt 180. When the sheet P passes through the transfer nip TP, the toner image formed on the peripheral surface of the photosensitive drum 121 is transferred to the sheet P.

  The cleaning device 127 removes the toner remaining on the peripheral surface of the photosensitive drum 121 after the toner image is transferred to the sheet P. The peripheral surface of the photosensitive drum 121 cleaned by the cleaning device 127 passes again below the charger 122 and is uniformly charged. Thereafter, the above-described toner image is newly formed.

  The image forming apparatus 1 further includes a fixing device 130 (FIG. 2) (fixing unit) disposed downstream of the image forming unit 120 (transfer nip TP) in the transport direction. The fixing device 130 performs a fixing process on the sheet P on which the toner image is transferred. The fixing device 130 includes a heating roller 131 that melts the toner on the sheet P, and a pressure roller 132 that causes the sheet P to adhere to the heating roller 131. When the sheet P passes between the heating roller 131 and the pressure roller 132, the toner image is fixed on the sheet P.

  The image forming apparatus 1 further includes an upper conveyance roller pair 133 disposed downstream of the fixing device 130 and a discharge roller pair 134 disposed downstream of the upper conveyance roller pair 133. The sheet P is discharged from the lower housing 21 by the upper conveyance roller pair 133 and the discharge roller pair 134. The sheets P discharged from the lower housing 21 are stacked on the upper wall 210.

  Next, the transfer unit 180M and the transport unit 1M according to the present embodiment will be described with reference to FIGS. 3 to 9 in addition to FIG. FIG. 3 is an enlarged cross-sectional view of a part of the image forming apparatus 1 of FIG. FIG. 3 is an enlarged cross-sectional view of the periphery of the photosensitive drum 121 and the conveyance belt 180. FIG. 4 is a cross-sectional view in which a part of FIG. 3 is further enlarged. In FIG. 4, the photosensitive drum 121 does not appear. FIG. 5 is a perspective view of the transport unit 1M and the transfer unit 180M of the image forming apparatus 1 according to the present embodiment. FIG. 6 is a perspective view of a state where the transfer unit 180M is removed from the transport unit 1M of FIG. FIG. 7 is a perspective view of the transport unit 1M of FIG. 5 with the front standing wall 1MF removed. FIG. 8 is a perspective view of the transfer unit 1M with the transfer unit 180M and the front standing wall 1MF removed. Further, FIG. 9 is an enlarged perspective view of the periphery of the sirocco fan 50 of the transport unit 1M.

  Referring to FIGS. 4 and 5, image forming apparatus 1 includes transfer unit 180M. The transfer unit 180M is a unit in which the transport belt 180, the driving roller 181, the stretching roller 182, and the transfer roller 126 are integrally supported. The transfer unit 180M has a function of transporting the sheet P so that the sheet P passes through the transfer nip TP and transferring the toner image to the sheet P. The transfer unit 180M is mounted on a transport unit 1M described later.

  Referring to FIGS. 4, 7, and 9, transfer unit 180 </ b> M includes guide portion 183. The guide unit 183 extends along the front-rear direction (the axial direction of the photosensitive drum 121) above the drive roller 181 in the transfer unit 180M. The guide unit 183 has a function of guiding the sheet P detached from the transport belt 180 in the transport direction. The guide part 183 includes a guide rib 183G and a notch part 184 (FIG. 7).

  The guide ribs 183G are a plurality of ribs arranged at intervals in the front-rear direction in the guide portion 183. The sheet P is guided toward the fixing device 130 along the guide rib 183G. The notch 184 is a recess formed at the center in the front-rear direction of the guide 183. The notch 184 is formed on the downstream side in the transport direction from the transport belt 180 so as to expose a part of the transport unit 1M described later to the sheet transport path PP side.

  Further, the image forming apparatus 1 includes a transport unit 1M. The transport unit 1M is disposed on the right wall 2R (FIGS. 1 and 2) side of the main housing 2. The transport unit 1M is arranged with a predetermined gap with respect to the transfer unit 180M on the opposite side of the photosensitive drum 121 (right side of the transfer unit 180M) as viewed from the transfer unit 180M. The transport unit 1M is arranged along the front-rear and up-down directions at the right end of the main housing 2. The right wall 2R of the main housing 2 is provided in the transport unit 1M. The transport unit 1M transports the sheet P on which the fixing process has been performed to the sheet transport path PP on the upstream side in the transport direction from the transfer nip TP. The transport unit 1M includes a reverse transport path RP, a first transport roller pair 141, a second transport roller pair 142, a reverse guide unit 145, and a front standing wall 1MF.

  The reverse conveyance path RP is a conveyance path through which the sheet P is conveyed again toward the transfer nip TP. The first transport roller pair 141 and the second transport roller pair 142 are disposed at appropriate positions on the reverse transport path RP and transport the sheet P. As shown in FIGS. 2, 4, and 5, the reverse guide portion 145 is a guide wall that defines the right side portion of the reverse conveyance path RP above the transfer unit 180 </ b> M. Further, as shown in FIG. 5, the front standing wall 1MF is a wall portion erected so as to face leftward in the front portion of the transport unit 1M.

  Referring to FIG. 2, the sheet P that has been subjected to the fixing process in the fixing device 130 is conveyed upward by the upper conveying roller pair 133. At this time, during double-sided printing in which an image is also formed on the back side of the sheet P, the switching guide 135 is rotated to switch the conveyance direction of the sheet P to the right side. As a result, the sheet P is carried into the reverse conveyance path RP by the reverse carry-in roller 136. Referring to FIG. 4, the sheet P conveyed further downward (arrow D <b> 41 in FIG. 4) on the reverse conveyance path RP is moved by the first conveyance roller pair 141 and the second conveyance roller pair 142 to the arrow in FIG. 4. It is further conveyed as shown in D42. Then, in the sheet conveyance path PP, the sheet P is conveyed again into the sheet conveyance path PP in the conveyance junction MP on the upstream side of the transfer nip TP. When the sheet P is conveyed again to the transfer nip TP by the registration roller pair 116 and the conveyance belt 180, the toner image is transferred to the back surface of the sheet P.

  As shown in FIG. 4, the transfer unit 180 </ b> M is supported by the transport unit 1 </ b> M by a tension spring (not shown) in such a posture that the upper end portion is inclined to the right side. Specifically, a pair of tension springs (not shown) disposed at both ends in the front-rear direction of the transfer unit 180M, which are upper ends of the transfer unit 180M, are formed at both ends in the front-rear direction of the transport unit 1M. Is attached to the support portion 146 (FIG. 8). The lower part of the transfer unit 180M is supported by a bracket 1MB (FIG. 8) extending in the front-rear direction in the transport unit 1M. At this time, a gap is formed between the transfer unit 180M and the transport unit 1M, and a later-described cooling air passage AP (FIG. 4) is formed.

  As illustrated in FIG. 4, a driven roller 116 </ b> A that is a roller on the right side of the registration roller pair 116 is rotatably supported by the transport unit 1 </ b> M. When the transfer unit 180M is attached to the transport unit 1M, the stretching roller 182 is disposed above the driven roller 116A.

  The conveyance unit 1M includes a sheet detection sensor 51 (detection sensor), a density detection sensor 52 (detection sensor), and a sirocco fan 50 (air flow generation unit). The sheet detection sensor 51 and the density detection sensor 52 are arranged in the transport unit 1M so as to face the transfer unit 180M in a cross-sectional view intersecting the axial direction of the photosensitive drum 121, and execute a predetermined detection operation.

  The sheet detection sensor 51 is disposed in the transport unit 1M so as to face the notch 184 of the transfer unit 180M. As shown in FIG. 8, the sheet detection sensor 51 is disposed below and to the left of the reversing guide portion 145 and in the central portion in the front-rear direction of the transport unit 1M. The sheet detection sensor 51 detects the leading end portion or the trailing end portion of the sheet P conveyed in the conveying direction from the transfer nip TP through the notch 184. The detection information of the sheet P by the sheet detection sensor 51 is used for adjusting the feeding timing of the subsequent sheet P by the registration roller pair 116.

  3, 4, and 8, the density detection sensor 52 is disposed in the transport unit 1 </ b> M so as to face the transport belt 180 of the transfer unit 180 </ b> M. In FIG. 5, the transfer unit 180 </ b> M is attached to the transport unit 1 </ b> M, and the density detection sensor 52 is disposed on the back side of the transport belt 180, so the density detection sensor 52 does not appear. Further, as shown in FIG. 8, the density detection sensor 52 is disposed below and behind the sheet detection sensor 51. The density detection sensor 52 detects the density of the toner image for density detection that is transferred from the photosensitive drum 121 to the transport belt 180 and formed on the transport belt 180. Therefore, the density of the density detection toner image can be detected using the back side of the conveyance belt 180 with respect to the sheet conveyance path PP. The density information detected by the density detection sensor 52 is used for adjusting the amount of toner to be replenished to the developing device 124 and adjusting the developing bias applied to the developing roller 124A.

  The sirocco fan 50 is arranged inside the front standing wall 1MF (FIG. 5). That is, with reference to FIG. 7 and FIG. 9, the sirocco fan 50 is disposed at the front end of the transport unit 1M. The sirocco fan 50 causes a cooling air flow to flow between the transfer unit 180M and the transport unit 1M along the axial direction of the photosensitive drum 121 toward the rear. The sirocco fan 50 includes an outlet 50A (FIG. 9). The outlet 50A is opened rearward. The cooling airflow is blown out from the blowout port 50A.

  As described above, a predetermined gap is formed between the transfer unit 180M and the transport unit 1M. The gap functions as a cooling air path AP shown in FIG. In other words, the cooling air passage AP is formed between the transfer unit 180M and the transport unit 1M, and guides the cooling air flow toward the sheet detection sensor 51 and the density detection sensor 52.

  When double-sided printing is performed on the sheet P, the sheet P that has been heated by passing through the fixing device 30 is conveyed through the reverse conveyance path RP, and then again passes through the transfer nip TP. When the sheet P carried out from the transfer nip TP is conveyed along the guide portion 183 of the transfer unit 180M, the heat of the sheet P is transmitted to the sheet detection sensor 51 via the notch portion 184. Alternatively, the heat of the sheet P is transmitted to the back side of the transfer unit 180M via the transport belt 180, and the density detection sensor 52 is warmed. When the temperature of the sheet detection sensor 51 and the density detection sensor 52 rises, the detection accuracy may be lowered, or malfunction of each sensor may be caused. Even in such a case, in the present embodiment, since the sheet detection sensor 51 is cooled by the cooling airflow, the temperature increase of the sheet detection sensor 51 is suppressed. As a result, the sheet detection sensor 51 stably detects that the sheet P has been unloaded from the transfer nip TP. Further, since the concentration detection sensor 52 is cooled by the cooling air flow, the concentration is detected stably. Further, even when the toner of the density detection toner image rises from the conveyance belt 180, the toner is prevented from adhering to the density detection sensor 52 by the cooling air flow.

  On the other hand, when a strong cooling airflow flows from the sirocco fan 50 into the cooling air passage AP, a new airflow is caused around the transfer unit 180M by the cooling airflow. Specifically, as indicated by an arrow AF1 in FIG. 3, an air flow flows into the gap AT (FIG. 4) between the upper end of the transfer unit 180M and the transport unit 1M while passing from the transfer nip TP to above the transfer unit 180M. Becomes easier to flow in. In the transfer nip TP, toner may be scattered when the toner image on the photosensitive drum 121 is transferred onto the sheet P by discharge. As shown in FIG. 3, in the present embodiment, a cleaning device 127 that collects toner from the photosensitive drum 121 is disposed above the transfer nip TP. Accordingly, when the air flow indicated by the arrow AF1 in FIG. 4 includes scattered toner, the toner flowing in from the gap AT adheres to the sheet detection sensor 51 and the density detection sensor 52. As a result, malfunctions of the sheet detection sensor 51 and the density detection sensor 52 may occur.

  In the present embodiment, a shielding sponge 60 (shielding member) is disposed in order to solve the above problems. The shielding sponge 60 is interposed in the gap between the transfer unit 180M and the transport unit 1M along the axial direction (sheet width direction) of the photosensitive drum 121, and intersects the axial direction from the periphery of the transfer unit 180M. The airflow flowing toward the cooling air passage AP along the direction is shielded. In the present embodiment, the shielding sponge 60 is a sponge material (elastic member) that is compressed between the transfer unit 180M and the transport unit 1M.

  Referring to FIG. 6, a pair of shielding sponges 60 are arranged on transport unit 1 </ b> M so as to sandwich sheet detection sensor 51. The shielding sponge 60 is a prismatic sponge material extending in the front-rear direction. When the transfer unit 180M is mounted on the transport unit 1M, as shown in FIG. 4, the shielding sponge 60 is interposed between the guide portion 183 of the transfer unit 180M and the transport unit 1M in a compressed state.

  As a result, the gap located above the density detection sensor 52 and in front of and behind the sheet detection sensor 51 is sealed, and the flow of air from the periphery of the transfer unit 180M to the cooling air path AP is suppressed. Further, since the upper part of the cooling air passage AP is defined by the shielding sponge 60, the cooling air flow blown out from the blowout port 50A is linearly guided toward the rear. As a result, the sheet detection sensor 51 and the density detection sensor 52 are stably cooled by the cooling air flow, and foreign substances such as toner are prevented from adhering to the sheet detection sensor 51 and the density detection sensor 52. The shielding sponge 60 is disposed between the transfer unit 180M and the transport unit 1M so as to be further prevented from flowing an air flow from the periphery of the transfer unit 180M into the cooling air passage AP. Further, according to the above configuration, the notch portion 184 can be formed by using the guide portion 183 that guides the sheet P detached from the conveyance belt 180, and the guide portion 183, the conveyance unit 1M, A shielding sponge 60 can be interposed between the two.

  10 and 11 are a perspective view and a side view showing the flow of the cooling air flow in the cooling air passage AP between the transfer unit 180M and the transport unit 1M.

  In the present embodiment, a reversing guide portion 145 is disposed along the vertical direction on the right side of the shielding sponge 60. Therefore, by arranging the shielding sponge 60 between the transfer unit 180M and the transport unit 1M, it is possible to prevent the air flow (arrow AF2 in FIG. 10) generated in the sheet transport path PP from flowing into the cooling air path AP. Is done.

  In the present embodiment, the transport unit 1M further includes a partition wall member 61 and a left wall portion 62 (FIG. 10). The left wall portion 62 is a wall portion facing leftward below the shielding sponge 60 in the transport unit 1M.

  The partition member 61 is a plate-like member protruding from the left wall 62 of the transport unit 1M along the axial direction of the photosensitive drum 121. The partition member 61 is extended in the front-rear direction with a predetermined height in the left-right direction. The partition member 61 defines a part of the cooling air passage AP. For this reason, the partition member 61 promotes the flow of the cooling airflow in the axial direction.

  As described above, the sheet detection sensor 51 and the density detection sensor 52 are arranged at different positions in the sheet conveyance direction (vertical direction). The partition wall member 61 is disposed between the sheet detection sensor 51 and the density detection sensor 52 in the vertical direction. For this reason, as shown in FIGS. 10 and 11, the cooling air flow that has flowed into the cooling air passage AP from the outlet 50A of the sirocco fan 50 is separated from the first cooling air flow AP1 on the upper side by the partition wall member 61. It is divided into the second cooling air flow AP2 on the lower side. The first cooling air flow AP <b> 1 is guided to the sheet detection sensor 51. Further, the second cooling air flow AP <b> 2 is guided to the concentration detection sensor 52. As a result, the cooling airflow can be guided toward the plurality of detection sensors. Therefore, the sheet detection sensor 51 and the density detection sensor 52 are stably cooled.

  Furthermore, in the present embodiment, the partition wall member 61 has a function of positioning the electrical wiring extended from the sheet detection sensor 51 and the density detection sensor 52. In other words, electrical wires extending from the sheet detection sensor 51 and the density detection sensor 52 and routed to an electrical board (not shown) of the transport unit 1M are arranged along the partition wall member 61. Therefore, the electrical wiring of the sheet detection sensor 51 and the density detection sensor 52 can be positioned using the partition wall member 61 that guides the cooling air flow.

  The image forming apparatus according to the embodiment of the present invention has been described above. However, the present invention is not limited to this, and for example, the following modified embodiment can be taken.

  (1) In the above embodiment, the sponge member is used as the shielding member interposed between the transfer unit 180M and the transport unit 1M. However, the present invention is not limited to this. The shielding member may be a film member that extends from one of the transfer unit 180M and the conveyance unit 1M toward the other and is disposed along the sheet width direction.

  (2) Further, in the above-described embodiment, the conveyance unit 1M has been described as including the sheet detection sensor 51 and the density detection sensor 52, but the present invention is not limited to this. The transport unit 1M may include other detection sensors. Further, another detection sensor may be arranged on the transfer unit 180M side so as to face the transport unit 1M.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 1M Conveyance unit 1MB Bracket 1MF Front standing wall 2 Main housing 2R Right wall 50 Sirocco fan (air flow generation part)
50A Air outlet 51 Sheet detection sensor (detection sensor)
52 Concentration detection sensor (detection sensor)
60 Shielding sponge (shielding member)
61 Partition member 62 Left wall 116 Registration roller pair 121 Photosensitive drum 122 Charger 124 Developing device 127 Cleaning device 130 Fixing device (fixing portion)
141 First Conveying Roller Pair 142 Second Conveying Roller Pair 145 Reversing Guide Unit 146 Supporting Unit 180 Conveying Belt 180M Transfer Unit Text 181 Driving Roller 182 Stretching Roller 183 Guide Unit 183G Guide Rib 184 Notch AP Cooling Air Path P Sheet PP Sheet Transport path RP Reverse transport path MP Transport junction

Claims (8)

A sheet conveyance path through which the sheet is conveyed in a predetermined conveyance direction;
A photosensitive drum disposed opposite to the sheet conveying path, driven to rotate about an axis, and carrying a toner image on a peripheral surface;
A conveyance belt is disposed opposite to the photosensitive drum across the sheet conveyance path, is driven to rotate, and forms a nip portion with the photosensitive drum, so that the sheet passes through the nip portion. A transfer unit that conveys the sheet and transfers the toner image to the sheet;
A fixing unit that is disposed downstream of the nip portion in the transport direction and performs a fixing process on the sheet on which the toner image is transferred;
On the opposite side of the photosensitive drum as viewed from the transfer unit, the sheet, which is disposed with a predetermined gap with respect to the transfer unit and has undergone the fixing process, is disposed upstream of the nip portion in the transport direction. A conveyance unit for carrying in the sheet conveyance path on the side;
A detection sensor that is disposed in the transport unit so as to face the transfer unit in a cross-sectional view that intersects the axial direction of the photosensitive drum, and performs a predetermined detection operation;
An air flow generating section that is disposed on one end side in the axial direction of the transport unit, and causes a cooling air flow to flow into the gap between the transfer unit and the transport unit along the axial direction;
Wherein is the gap thus formed between the transfer unit and the conveyance unit, and the cooling air path for guiding the cooling air flow towards said detection sensor,
An air flow that is interposed along the axial direction in the gap between the transfer unit and the transport unit, and flows from the periphery of the transfer unit toward the cooling air path along a direction intersecting the axial direction. A shielding member for shielding;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the shielding member is an elastic member that is compressed and disposed between the transfer unit and the transport unit. The transfer unit includes a notch formed so as to expose a part of the transport unit to the sheet transport path side downstream of the transport belt in the transport direction.
The detection sensor is a sheet sensor that is disposed in the conveyance unit so as to face the notch portion, and detects the sheet conveyed from the nip portion via the notch portion. Item 3. The image forming apparatus according to Item 1 or 2. The transfer unit includes a guide unit that guides the sheet detached from the transport belt in the transport direction,
The notch is formed in the guide part,
The image forming apparatus according to claim 3, wherein the shielding member is interposed between the guide unit and the transport unit.   The detection sensor is a density sensor that is disposed in the conveyance unit so as to face the conveyance belt and detects the density of a detection toner image formed on the conveyance belt. The image forming apparatus described in 1.   The image forming apparatus according to claim 1, further comprising a partition member protruding from the transport unit along the axial direction and defining a part of the cooling air passage. A plurality of the detection sensors are arranged at different positions in the transport direction,
The image forming apparatus according to claim 6, wherein the partition wall member has a function of diverting the cooling air flow introduced from the air flow generation unit toward the plurality of sensors.   The image forming apparatus according to claim 6, wherein the partition member has a function of positioning an electrical wiring extended from the detection sensor.