JP2008164902A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which decreases the ambient temperature of a passage sensor without an increase in size or decrease in processing speed even in the case where a passage sensor is located on an air path along which heated air due to heat exhaustion by the fixing unit blows. <P>SOLUTION: The image forming apparatus 100 comprises: a fixing device 7 that thermally fixes an unfixed toner image, transferred to the surface of recording paper to be conveyed; a filler 95 swung as the recording paper passes; a sensor body 96 disposed on the air path along which heated air flows as a result of heat exhaustion by the fixing device, and used for detecting whether the filler 95 has swung or not; and a shield cover 97 enclosing the sensor body 96, thereby shielding the sensor body 96 from heated air flowing through the air path. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus including a fixing unit that thermally fixes an unfixed toner image transferred onto a recording sheet.

  An image forming apparatus used in a copying machine, a printer, a facsimile, and a multifunction machine having at least two of these functions performs selective exposure according to image information on the surface of a uniformly charged photosensitive drum. Then, a latent image is formed, the formed electrostatic latent image is developed to form a toner image, and the toner image is transferred to a recording sheet to form an image. The recording sheet is discharged to a discharge tray after an unfixed toner image is fixed by the fixing unit. Generally, the fixing unit melts and fixes the unfixed toner on the recording sheet by pressing a heating roller containing a heat source such as a halogen heater against the recording sheet.

  The discharge sensor detects the passage of the recording sheet at a predetermined detection position downstream of the fixing unit in order to rotate the discharge roller for discharging the recording sheet on which the toner image is fixed in the fixing unit to the discharge tray. Is detected. In addition, in order to timing the operation of a switchback mechanism that switches back the recording paper and sends it to the reverse conveyance path so that an image is formed on the other side of the recording paper on which the image is formed on one side, a predetermined downstream side of the fixing unit is operated. The switchback sensor detects the passage of the recording paper at the detection position. Such a passage sensor that detects the passage of the recording paper, such as a paper discharge sensor or a switchback sensor, is generally composed of an optical sensor such as a photo interrupter for checking whether or not the filler is oscillated as the recording paper passes. The sensor body is used for detection.

  On the other hand, when the heated surface of the heating roller comes into pressure contact with the recording paper, a part of heat is radiated through the recording paper. However, since the heating roller has a length in the longitudinal direction that is equal to or greater than the maximum width of the recording paper that can be conveyed, the heat in the area where the recording paper is not pressed, that is, the non-sheet passing area is not radiated through the recording paper. . Therefore, a larger amount of exhaust heat is released from the non-sheet passing area of the heating roller than the sheet passing area. In the case of an image forming apparatus in which the recording paper is conveyed upward from the fixing unit, that is, the recording paper is discharged from above the fixing unit, the fixing is performed when the narrow recording paper is continuously pressed. Due to the heat generated by the exhaust heat of the part, the temperature in the apparatus above the non-sheet passing region of the heating roller rises, and various devices such as a passage sensor are affected, and there is a possibility that improper operation processing is performed. If the ambient temperature exceeds a predetermined operation guarantee temperature, the passage sensor cannot obtain operation guarantee.

Thus, for example, Patent Document 1 discloses providing a fan that forcibly exhausts hot air above the fixing unit in the longitudinal direction. However, the provision of such a fan is contrary to the demand for miniaturization because the apparatus becomes large due to layout restrictions and the like. Therefore, an air path that leads from above the fixing unit to the outside of the apparatus is often provided, and hot air is often released by natural convection due to a temperature gradient. In this case, for example, in Japanese Patent Application Laid-Open No. H11-228688, taking into account the variation in operation due to the temperature change of the switchback sensor, the conveyance speed is made slower than the normal speed only during the period when the recording paper passes the detection position of the switchback sensor. Control is disclosed.
JP 2002-62771 A JP-A-8-314203

  However, when the control is performed as disclosed in Patent Document 2, the reversal processing speed decreases. Further, when the same control is performed on the paper discharge sensor, there is a problem that the image forming processing speed is reduced.

  The present invention has been made in view of such problems, and even when a passage sensor is located on an air path through which hot air due to exhaust heat of the fixing unit flows, without increasing the size or reducing the processing speed, An object of the present invention is to provide an image forming apparatus capable of lowering the ambient temperature of a passage sensor.

  In order to achieve the above object, an image forming apparatus according to claim 1 is configured to thermally fix an unfixed toner image transferred onto a conveyed recording sheet, and to swing as the recording sheet passes. A swinging member, a sensor that is located on an air path through which hot air due to exhaust heat of the fixing unit flows, detects whether the swinging member swings, and surrounds the sensor, and from the hot air that flows through the air path, And a shielding cover that shields the sensor.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the shielding cover is made of a heat resistant resin.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the sensor is disposed so as to be separated from the conveyance reference of the recording paper to be conveyed in the width direction of the recording paper. It is a feature.

  An image forming apparatus according to a fourth aspect is the image forming apparatus according to any one of the first to third aspects, wherein the space between the side walls of the exterior chassis of the apparatus is in the width direction of the recording paper to be conveyed. A stay that is connected and positioned above the fixing unit, the sensor is attached to a vertical piece of the stay, and the shielding cover has a space between the sensor and a lower side and a side of the sensor. It is characterized by covering.

  The image forming apparatus according to claim 5, in the image forming apparatus according to claim 4, extends horizontally from a vertical piece of the stay or a lower portion of the vertical piece of the stay in a direction opposite to the sensor mounting side. An opening is formed in the horizontal piece to form part of the air path.

  The image forming apparatus according to claim 6 is the image forming apparatus according to claim 5, wherein the shielding cover is attached by extending a portion covering a lower part of the sensor and adhering to a lower surface of the horizontal piece of the stay. It is characterized by being able to.

  According to the image forming apparatus of the first aspect, air whose temperature has been raised by the exhaust heat of the fixing unit, that is, hot air, flows in the air path where the sensor for detecting the presence or absence of the swing of the swing member is located. However, since the shielding cover surrounds the sensor and shields the sensor from the hot air flowing through the air path, the sensor is isolated from the hot air flowing through the air path and no direct hot air flows in. Therefore, compared with the case where a shielding cover is not provided, the ambient temperature of the sensor can be lowered, and it becomes possible to set the sensor operation guarantee temperature or lower. Therefore, the sensor can reliably detect the presence or absence of the swinging member, and the operation process associated with the passage of the recording paper can be performed satisfactorily without a decrease in the conveyance speed. In addition, since the object can be achieved only by adding a shielding cover, a layout change such as providing a fan is not required, so that the apparatus is not increased in size. Note that that the sensor is positioned on the air path means that hot air flowing through the air path flows directly into the sensor when the shielding cover is not provided. In addition, the shielding cover shielding the sensor from the air path means that the hot air flowing through the air path is almost prevented from flowing directly into the sensor. It does not exclude that the liquid flows into the sensor.

  According to the image forming apparatus of the second aspect, the shielding cover is made of a heat resistant resin. Therefore, since the shielding cover is not melted and deformed by the hot air flowing through the air path, the sensor can be reliably shielded from the hot air flowing through the air path for a long period of time. The heat-resistant resin means a resin having heat resistance against a temperature exceeding the temperature of hot air flowing in the vicinity of a sensor assumed by use of the image forming apparatus. Further, since the shielding cover is made of a resin, it is possible to select an appropriate material having characteristics such as heat resistance and heat insulation as necessary, and the molding process is facilitated.

  According to the image forming apparatus of the third aspect, the sensor is arranged so as to be separated from the conveyance reference of the recording sheet to be conveyed in the width direction of the recording sheet. When the recording paper with a narrow width does not pass through the fixing unit, that is, when hot air that has become hotter due to exhaust heat generated from the non-sheet passing area flows toward the sensor located on the air path, and therefore does not have a shielding cover In such a case, the ambient temperature of such a sensor becomes higher. Therefore, it is necessary to lower the ambient temperature of the sensor, and it is significant to provide a shielding cover. It should be noted that the sensor is disposed apart from the conveyance reference of the recording paper to be conveyed in the width direction. For example, when the recording paper is conveyed with the center reference as the fixing unit, the sensor is centered in the width direction of the recording paper. When the recording paper is transported with reference to the right edge, the sensor is placed near the left edge in the width direction of the recording paper, that is, near the left edge. Means.

  According to the image forming apparatus of the fourth aspect, the side wall of the exterior chassis of the apparatus is connected in the width direction of the recording sheet to be conveyed, and the stay is located above the fixing unit. It is attached to the vertical piece. Therefore, the sensor attached to the vertical piece of the stay is positioned above the fixing unit. Therefore, by using the rising airflow due to the temperature gradient, it is possible to form an air path for releasing hot air due to exhaust heat from the fixing unit to the outside of the apparatus without providing a fan or a duct. The sensor will be located. Therefore, the shielding cover covers the lower side and the side of the sensor, so that the sensor is isolated from the hot air flowing upward in the air path and no direct hot air flows in, so that the ambient temperature of the sensor can be lowered. Furthermore, since there is a vertical piece of stay on the sensor mounting side, hot air does not flow from this side. In addition, it is preferable to cover with a shielding cover, a stay, or another member so that hot air does not flow in from the side opposite to the sensor mounting side or from above. Further, the shielding cover provides a space between the sensor and covers it. For this reason, the air present in this space exhibits a heat insulating function, so that the ambient temperature of the sensor can be further lowered.

  According to the image forming apparatus of the fifth aspect, the opening is formed in the vertical piece of the stay or the horizontal piece extending horizontally from the lower part of the vertical piece of the stay in the direction opposite to the sensor mounting side, Part. Therefore, compared to the case where no openings are formed in the vertical and horizontal pieces of the stay, there are more air paths to release hot air due to exhaust heat from the fixing unit, so heat can be radiated more smoothly and the sensor ambient temperature can be increased. Can be reduced.

  According to the image forming apparatus of the sixth aspect, the shielding cover is attached by extending a portion covering the lower side of the sensor and bonding it to the lower surface of the horizontal piece of the stay. Therefore, the lower part of the sensor can be completely covered with the shielding cover, so that hot air can be prevented from flowing directly into the sensor from the lower part, and the ambient temperature of the sensor can be further lowered.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. A copy / facsimile multifunction peripheral 100 equipped with an image forming apparatus according to an embodiment of the present invention has a built-in image forming apparatus for forming an image on a recording sheet, as shown in FIG. A main body 110, a reading table 120 functioning as a flatbed scanner for reading an image of an original, and an operation panel 130 for inputting start of image reading and image formation.

  As shown in FIG. 2 partially showing a schematic cross-sectional view, the main body 110 is provided with a paper feed cassette 101 for sequentially supplying recording paper for recording images on the bottom of the apparatus. An image forming unit 102 is disposed above the cassette 101, and a paper discharge tray 103 is disposed above the image forming unit 102. A conveyance path 104 for conveying recording paper from the paper feed cassette 101 to the paper discharge tray 103 extends upward from one end side of the paper feed cassette 101 to the image forming unit 102 and further extends upward. Then, it is formed so as to bend in the horizontal direction and lead to the paper discharge tray 103.

  Further, the main body 110 is provided with a switchback mechanism 105 that switches back the recording paper conveyed through the conveyance path 104 between the image forming unit 102 and the paper discharge tray 103. A reverse conveyance path 106 is formed so that the recording paper switched back by the switchback mechanism 105 joins the conveyance path 104. As described above, in the main body 110, when an image is recorded on the other side of the recording sheet on which the image is recorded on one side by the image forming unit 102, the switchback mechanism 105 passes the reverse conveyance path 106. An image is recorded by the image forming unit 102 on the other surface of the conveyed recording paper.

  The paper feed cassette 101 has a box shape that can store recording paper of various sizes, and is provided at the bottom of the apparatus so that it can be pulled out, so that it can be loaded with recording paper as required. The recording paper stored in the paper feed cassette 101 is always positioned at the paper feed position at one end of the uppermost paper by the guide 101a. A paper feed mechanism 101b including a pickup roller, a reverse roller, and a separation pad is provided at the paper feed position, and the recording paper is fed into the transport path 104 one by one.

  The image forming unit 102 includes a charging device 2, an LED head 3, a developing device 4, a transfer roller 5, and a cleaning device 6 disposed around the photosensitive drum 1, and a conveyance path 104 on the downstream side of the photosensitive drum 1. And a fixing device 7 disposed in the space.

  The photosensitive drum 1 is rotated at a predetermined speed by a motor, and the surface thereof is charged to a constant voltage by the charging device 2. The charging device 2 is a non-contact corona charging method called a so-called scorotron charger, in which a discharge wire is disposed substantially at the center of a casing electrode forming a half space, and a grid electrode is provided on the photosensitive drum 1 side. The corona discharge is generated by applying a predetermined voltage to the discharge wire, and the amount of ions generated by the corona discharge is controlled by the grid electrode. The charging device 2 may employ another charging device such as a contact roller charging method instead of the non-contact corona charging method.

  The LED head 3 is a so-called self-luminous printer head in which LED arrays are arranged in parallel for the number of recording pixels and light emitted from the LED array is imaged on the surface of the photosensitive drum 1 by a selfoc lens array. The surface of the photosensitive drum 1 is selectively exposed to the body drum 1 based on the image information, and an electrostatic latent image is formed on the surface. The surface of the photosensitive drum 1 charged by the charging device 2 is attenuated by being exposed by the LED head 3, and an electrostatic latent image is formed by a potential difference from the unexposed portion. As the image information, for example, an image of a document read by the reading table 130 functioning as a flatbed scanner is transmitted to the LED head 3 as an electric signal. As the exposure device, a scanning optical system using a semiconductor laser in addition to the LED head 3 may be employed.

  The developing device 4 includes a supply roller, a development roller, and a toner container. The toner in the toner container is developed through the supply roller due to a difference in bias voltage applied to the supply roller and the development roller from an electric circuit (not shown). A toner layer is formed on the surface of the developing roller. The developing roller on which the toner layer is formed is rotated at a position close to the photosensitive drum 1, and the toner on the developing roller moves to the photosensitive drum 1 due to a potential difference from the electrostatic latent image on the photosensitive drum 1. A toner image is formed on the surface of the photosensitive drum 1 based on the electrostatic latent image. Such a developing device 4 is an example, and selection of magnetic toner or non-magnetic toner, selection of contact development method or non-contact development method, and the like are arbitrary.

  The transfer roller 5 is a roller made of EPDM foam or urethane sponge, and is pressed against the photosensitive drum 1 at a position opposed to the conveyance path 104 so that a bias voltage is applied from an application circuit (not shown). Yes. The recording sheet supplied from the sheet feeding cassette 101 via the conveyance path 104 is nipped by the photosensitive drum 1 and the transfer roller 5 and a bias voltage is applied, so that a toner image formed on the surface of the photosensitive drum 1 is formed. Transferred to recording paper.

  The cleaning device 6 includes a cleaning blade, and removes and collects toner and paper dust remaining on the surface of the photosensitive drum 1. The cleaning blade is pressed against the surface of the photosensitive drum 1 after transfer and a constant voltage is applied from an electric circuit (not shown), thereby removing toner and paper dust remaining on the surface of the photosensitive drum 1 and electrostatic latent. Erase the image. Waste toner and paper dust scraped off by the cleaning blade are conveyed to the front side of the apparatus by a screw or the like and accumulated in a waste toner collection container (not shown).

  As shown in FIG. 3, the fixing device 7 includes a heating roller 71 and a pressure roller 72 that are respectively disposed at positions opposed to the conveyance path 104, and is not fixed on a recording sheet conveyed through the conveyance path 104. A fixing unit that heat-fixes the toner image on the recording medium. The heating roller 71 is a hollow roller made of aluminum or the like, and a heat source 73 such as a halogen heater that generates heat by power supply from a power supply circuit (not shown) is disposed in the inner space thereof, and the surface is maintained at a predetermined temperature. . The heating roller 71 is driven to rotate at a predetermined peripheral speed by a motor (not shown). The pressure roller 72 is rotatably supported by the bearing and is pressed against the heating roller 71 with a predetermined pressing force. The pressure roller 72 is rotated by the rotation of the heating roller 71. When the recording sheet on which the unfixed toner image is transferred is nipped and conveyed between the pressure contact portions of the heating roller 71 and the pressure roller 72, the toner is melted by the heat of the heating roller 71 and pressed by the pressure contact portion. The toner image is fixed by heat. A toner image is formed on a recording sheet by the image forming unit 102 configured as described above.

  The heating roller 71 is installed and accommodated in a first fixing housing 74 having a long box shape made of resin together with a cleaning roller for cleaning the surface of the heating roller 71, a temperature sensor for measuring the surface temperature of the heating roller 71, and the like. ing. The pressure roller 72 is installed and accommodated in a second fixing housing 75 made of a resin-like long box that is pivotally supported with respect to the first fixing housing 74.

  As shown in FIG. 2, the recording paper is conveyed from the paper feed cassette 101 along the conveyance path 104 to the image forming unit 102, and after the image is formed by the image forming unit 102, the recording paper is transferred to the paper discharge tray 103. Discharged. As shown in FIG. 3, the conveyance path 104 extends substantially upward from the paper feed cassette 101 to the image forming unit 102. In the middle of the conveyance path 104, conveyance rollers 80 for conveying the recording paper in a nip are appropriately provided. Is provided. The conveying roller 80 is rotated by a rotational force transmitted from a motor (not shown) to the roller shaft. A conveyance driven roller 81 is disposed at a position opposite to the conveyance path 104 of the conveyance roller 80, the roller surface being in pressure contact with the rotation of the conveyance roller 80 and rotating. With such a conveyance path 104, a reverse C path is formed from the paper feed cassette 101 to the paper discharge tray 103.

  The switchback mechanism 105 is disposed in the conveyance path 104 between the image forming unit 102 and the paper discharge tray 103, switches back the recording paper conveyed through the conveyance path 104, and feeds it to the reverse conveyance path 106. . The switchback mechanism 105 is disposed at the end of the conveyance path 104 and rotates in both forward and reverse directions. The discharge roller 82 is positioned opposite to the conveyance roller 104 with the conveyance path 104 interposed therebetween. A paper discharge driven roller 83 that rotates following the rotation, and a diverting claw 84 that is provided at a branch point between the transport path 104 and the reverse transport path 106 and switches the transport path of the recording paper.

  The paper discharge roller 82 is rotated by a rotational force transmitted from a motor (not shown) to a roller shaft, and conveys the recording paper with the paper discharge driven roller 83 facing the nip. The paper discharge roller 82 normally rotates in the forward direction (counterclockwise direction), and discharges the recording paper that has passed through the image forming unit 102 to a discharge tray 103 provided outside. On the other hand, when the surface of the recording sheet that has passed through the image forming unit 102 is reversed and supplied to the image forming unit 102 again, such as when performing double-sided image formation, the trailing edge of the recording sheet is the discharge roller 82. When the paper is transported to a predetermined position near the position, the paper discharge roller 82 rotates in the reverse direction (clockwise direction), switches the recording paper transport direction, and transports it toward the reverse transport path 106.

  A turning pawl 84 is provided at a branch point between the conveyance path 104 and the reverse conveyance path 106 to switch the conveyance path of the recording paper. When the recording paper is conveyed from the image forming unit 102 to the paper discharge roller 82 side, the reverse conveyance path 106 is blocked by the leading end, and when the recording paper is fed from the paper discharge roller 82 side to the reverse conveyance path 106. Operates so as to block the conveyance path 104 by the tip.

  The reverse conveyance path 106 is extended so as to rejoin the conveyance path 104 on the upstream side of the paper feed cassette 101 from the branch point of the conveyance path 104 provided with the deflection pawl 84 substantially downward. In the middle of this, a conveyance roller 80 for nipping and conveying the recording paper and a driven conveyance rotor 81 are provided as appropriate so as to face each other.

  The conveyance path 104 on the downstream side of the fixing device 7 and the reverse conveyance path 106 near the branch point from the conveyance path 104 are respectively a lower guide member 90, an upper guide member 91, and an integrally molded product of synthetic resin such as ABS. An intermediate guide member 92 is formed. The lower curved surface of the lower guide member 90 constitutes the lower curved surface of the conveyance path 104, and a conveyance roller 80 and a paper discharge roller 82 are disposed. The upper guide member 91 has a lower curved surface that constitutes an upper curved surface of the conveyance path 104 downstream of the branch point and an upper curved surface of the reverse conveyance path 106, and is provided with a discharge driven roller 83. Yes. The intermediate guide member 92 has a lower curved surface that forms an upper right curved surface of the conveyance path 104 upstream of the branch point and a lower curved surface of the reverse conveyance path 106, and a conveyance driven roller 81 is provided. ing. The upper guide member 91 and the intermediate guide member 92 are fixed by screws (not shown) or the like, but are provided to be rotatable with respect to the lower guide member 90 in order to release the nip between the rollers. Further, the right curved surface of the second fixing housing 75 of the fixing device 7 forms a part of the left curved surface of the reverse conveyance path 106 and is formed so as to be smoothly connected to the upper curved surface of the intermediate guide member 92. In addition, a part of the reverse conveyance path 106 is formed by facing the left curved surface of the side cover 93. Although not shown, the three guide members 90, 91, 92 are formed with a large number of openings penetrating in the vertical direction.

  Further, a paper discharge sensor 94 is provided as a passage sensor for detecting whether or not the leading edge of the recording paper transported at a predetermined detection position on the transport path 104 upstream from the paper discharge roller 82 and downstream from the fixing device 7 is detected. Yes. The paper discharge sensor 94 detects a paper discharge filler 95 that is a swinging member that swings as the leading end of the recording paper transported through the transport path 104 at the detection position, and whether or not the paper discharge filler 95 is swinging. The paper discharge sensor main body 96 is included. Since the conveyance reference is the center reference in the width direction of the recording paper and it is necessary to detect all the recording papers that can be processed, the discharge filler 95 is provided so that the recording papers of all sizes to be conveyed can be detected. Although not shown in detail, a long bar-like arm provided with a leading end protruding in the conveyance path 104 at a substantially central position in the width direction of the recording sheet in the conveyance path 104, that is, a direction orthogonal to the conveyance direction of the recording sheet, and a rear end of the arm Is formed of a long rotating shaft fixed to one end portion and a light shielding portion which is fixed to the other end portion of the rotating shaft and blocks light from the light emitting element of the paper discharge sensor main body 96. The rotation shaft is rotatably supported by a bearing provided on the lower guide member 90. The paper discharge sensor main body 96 is a light-shielding photointerrupter (optical sensor) in which a light emitting element and a light receiving element are arranged to face each other with a gap. The paper discharge filler 95 stands up when there is no recording paper at the detection position, and the light path between the light emitting element and the light receiving element is shielded by the light shielding portion, and the paper discharge sensor main body 96 outputs an off signal. When the recording paper passes through the detection position, the leading edge of the recording paper presses the arm of the paper discharge filler and the paper discharge filler rotates and tilts, so that the light shielding portion rotates and the light shielding is released. Outputs an on signal. After a predetermined time has elapsed since the paper discharge sensor 94 outputs an ON signal for detecting the leading edge of the recording paper, the paper discharge roller 82 is rotated in the forward direction to discharge the recording paper toward the paper discharge tray 103. .

  Although not shown, a switchback as a passage sensor that detects whether or not the trailing edge of the recording sheet conveyed at a predetermined detection position in the conveyance path 104 upstream from the paper discharge roller 92 and downstream from the fixing device 7 is detected. A sensor is also provided. The switchback sensor is configured in the same manner as the paper discharge sensor, and after a predetermined time has elapsed since the switchback sensor outputs a signal for detecting the trailing edge of the recording paper, the paper discharge roller 82 is rotated in the reverse direction to change the state. The counter pawl 84 is operated so as to block the conveyance path 104 by the tip, and the recording sheet is fed toward the reverse conveyance path 106. Further, the conveyance roller 80 disposed in the reverse conveyance path 106 is rotated to rejoin the recording paper to the conveyance path 104.

  As shown in FIG. 4, a schematic perspective view partially showing the appearance of the frame of the main body 110 is formed between the side walls 111 and 112 on both front and rear sides of the exterior chassis constituting the exterior portion of the frame of the main body 110 ( There are provided a first stay 113 and a second stay 114 which are connected over the width direction of the recording paper to be conveyed. As shown in FIG. 3 to be referred to, the fixing unit 7 is held on the vertical piece of the first stay 113 by a pin or the like. The second stay 114 is provided in parallel above the first stay 113, and the lower guide member 90 is placed on the upper surface of the upper horizontal piece 114a. In this way, the lower guide member 90 is disposed at a predetermined position above the fixing device 7. The second stay 114 includes a vertical piece 114b extending vertically downward from the left end of the upper horizontal piece 114a and a lower horizontal piece 114c extending horizontally leftward from the lower end of the vertical piece 114b. As long members having substantially the same cross section. Both the first stay 113 and the second stay 114 are formed by molding a thin plate metal such as SECC or stainless steel.

  A discharge sensor main body 96 is attached to the vertical piece 114b of the second stay 114 as shown in FIG. The paper discharge sensor main body 96 is disposed at a predetermined position on the right side of the vertical piece 114b so that the light emitting element and the light receiving element can block the optical path between them by the light shielding portion of the paper discharge filler 95. Yes. Although not shown, the signal line from the paper discharge sensor main body 96 is disposed on the left side of the vertical piece 114b.

  As described above, the fixing device 7 includes the heating roller 71 whose surface is maintained at a predetermined temperature by the heat source 73. Therefore, the heat in the vicinity of the fixing device 7 is warmed by the heat radiation from the heating roller 71 and becomes hot air, and the air flows upward due to the rising airflow due to the temperature gradient. A number of openings 114d are formed in the upper horizontal piece 114a of the second stay 114, and a number of openings (not shown) penetrating in the vertical direction are formed in the lower guide member 90 and the upper guide member 91. Thus, an air passage is formed through which hot air generated by the exhaust heat of the fixing device 7 flows upward and is released to the outside of the main body 110.

  However, as shown in FIGS. 3 and 5, the paper discharge sensor main body 96 is positioned on the air passage extending upward from the fixing device 7. In addition, the fixing device 7 and the paper discharge sensor main body 96 are close to each other, and high-temperature hot air flows into the paper discharge sensor main body 96. Therefore, in the present embodiment, the opening 114e is formed in the vertical piece 114b and the lower horizontal piece 114c of the second stay 114, and is used as a part of the air path. As a result, the number of air paths for releasing hot air due to the exhaust heat of the fixing device 7 is increased, so that heat can be radiated smoothly and the ambient temperature of the paper discharge sensor main body 96 can be lowered.

  By the way, since the heating roller 71 has a length in the longitudinal direction that is a recording sheet that can be transported, for example, the maximum width of A4 size, when a recording sheet having a narrow width such as A5 size is pressed, The heat in the area where the sheet is not pressed, that is, the non-sheet passing area is not radiated through the recording sheet. Therefore, more waste heat is released from the non-sheet passing area of the heating roller 71 than in the sheet passing area. Since the recording sheet is pressed against the heating roller 71 on the basis of the center, more exhaust heat is released from the vicinity of both ends in the longitudinal direction of the fixing device 7. Therefore, when the fixing device 7 continuously processes the narrow recording paper, high-temperature hot air flows out to the air path near the both ends in the longitudinal direction of the fixing device 7. On the other hand, the discharge sensor main body 96 is attached to the end portion of the second stay 114 in the longitudinal direction due to the routing of the harness or the like, so that the high-temperature hot air flows into the discharge sensor main body 96. Therefore, in order to further reduce the ambient temperature of the paper discharge sensor main body 96, in this embodiment, a shielding cover 97 surrounding the paper discharge sensor main body 96 is provided.

  As shown in FIG. 5, the shielding cover 97 provides a space between the discharge sensor main body 96 and covers the lower side and the side of the discharge sensor main body 96, and opens the upper side of the discharge sensor main body 96. It is surrounded by a U-shape. As shown also in FIG. 6, the shielding cover 97 extends horizontally from the horizontal piece 97 a covering the lower side of the paper discharge sensor main body 96 and from both side ends of the horizontal piece 97 a and covers both sides of the paper discharge sensor main body 96. A heat-resistant resin molded member such as a PC (polycarbonate) provided with two vertical pieces 97b. The shielding cover 97 has a part (a hatched part in FIG. 6) of the horizontal piece 97a which is a part extending from a part covering the lower side of the discharge sensor main body 96, and a double-sided tape or the like on the lower surface of the horizontal piece 114c of the second stay 114. It is attached by adhering. The shielding cover 97 has a protrusion formed at the upper end of the vertical piece 97b, and the protrusion is inserted into the positioning opening formed in the upper horizontal piece 114a of the second stay 114, thereby positioning. Done. A lower guide member 90 is located on the side opposite to the attachment surface side of the discharge sensor main body 96, and the shielding cover 97 extends between the vertical piece 114 b of the second stay 114 and the lower guide member 90. The paper discharge sensor main body 96 is enclosed. The shielding cover 97 is made of a heat-resistant resin such as PC, but a general resin such as ABS may be used when the ambient temperature does not become so high. In order to further suppress an increase in temperature in the space isolated by the shielding cover 97, it is more preferable to use a resin with excellent heat insulation (low thermal conductivity) for the shielding cover 97. Note that a cutout for avoiding interference of the filler 95 with the rotating shaft is formed in one vertical piece 97b of the shielding cover 97.

  As described above, according to the copier / facsimile multifunction peripheral 100, the shielding cover 97 surrounds the paper discharge sensor main body 96 and shields the paper discharge sensor main body 96 from the hot air flowing through the air path that discharges the exhaust heat of the fixing device 7. Therefore, the discharge sensor main body 96 is isolated from the hot air, and the hot air does not flow directly. Therefore, compared with the case where the shielding cover 97 is not provided, the ambient temperature of the paper discharge sensor main body 96 can be lowered. Furthermore, since the shielding cover 97 covers and covers the paper discharge sensor main body 96, the air present in this space exhibits a heat insulating function, and the ambient temperature of the paper discharge sensor main body 96 can be further lowered. . Although the shielding cover 97 surrounding the sheet discharge sensor main body 96 has been described above, the shielding cover surrounding the sensor main body of the switchback sensor is also provided in the same manner.

  Note that the configuration of the copy / facsimile multifunction peripheral 100 shown in this embodiment is merely one aspect of the image forming apparatus according to the present invention, and various modifications can be made without departing from the scope of the present invention. is there. For example, when the recording paper is conveyed to the fixing device 7 on the right end basis, a shielding cover surrounding the passage sensor located near the left end in the longitudinal direction of the fixing device 7 may be provided.

  Further, although the case where the paper discharge sensor main body 96 is a light-shielding photo interrupter has been described, it may be a reflection type photo interrupter, or may be a sensor of various types affected by heat in addition to the optical method. Good. The configuration of the filler 95 is not limited, and a configuration in which the detection light (optical path) is appropriately routed by a reflection mirror or the like may be used. Further, the passage sensor surrounded by the shielding cover is not limited to the paper discharge sensor or the switchback sensor, and may be a size sensor for detecting the size of the recording paper to be conveyed.

  Further, in the present embodiment, the mode in which the image forming apparatus is implemented as the copy / facsimile multifunction peripheral 100 has been described. However, the image reading apparatus is not limited to this, and a printer, a facsimile machine, a copier, and any of these multifunction peripherals. Etc. are applicable.

1 is a schematic perspective view showing an external appearance of a copy / facsimile multifunction peripheral 100 according to an embodiment of the present invention. 1 is a schematic longitudinal sectional view partially showing a main body 110 of a copy / facsimile multifunction peripheral 100. FIG. FIG. 2 is a schematic longitudinal sectional view showing an enlargement of the vicinity of a fixing device 7 of a main body 110. 2 is a schematic perspective view partially showing an appearance of a frame of a main body 110. FIG. It is a schematic perspective view of the attachment state of the shielding cover. It is a perspective view which shows the shielding cover 97. FIG.

Explanation of symbols

7 Fixing unit (fixing part)
95 Discharge filler (swing member)
96 Discharge sensor body (sensor)
97 Shield cover 100 Copy / facsimile multifunction peripheral (image forming device)
111 Front side wall 112 of exterior frame 112 Rear side wall 114 of exterior frame Second stay (stay)
114b Vertical piece 114c Lower horizontal piece (horizontal piece)
114e opening

Claims (6)

A fixing unit that thermally fixes an unfixed toner image transferred onto a recording sheet to be conveyed;
A swing member that swings as the recording paper passes;
A sensor that is located on an air path through which hot air due to exhaust heat of the fixing unit flows, and that detects whether or not the swinging member swings;
An image forming apparatus comprising: a shielding cover that surrounds the sensor and shields the sensor from hot air flowing through the air path.   The image forming apparatus according to claim 1, wherein the shielding cover is made of a heat resistant resin.   The image forming apparatus according to claim 1, wherein the sensor is arranged so as to be separated from a conveyance reference of the recording sheet to be conveyed in a width direction of the recording sheet. A stay located above the fixing unit, connecting between the side walls of the exterior chassis of the apparatus in the width direction of the recording paper conveyed;
The sensor is attached to a vertical piece of the stay,
The image forming apparatus according to claim 1, wherein the shielding cover provides a space between the sensor and covers a lower side and a side of the sensor.   An opening is formed in the vertical piece of the stay, or a horizontal piece extending horizontally from the lower part of the vertical piece of the stay in a direction opposite to the sensor mounting side, and is formed as a part of the air path. The image forming apparatus according to claim 4.   The image forming apparatus according to claim 5, wherein the shielding cover is attached by extending a portion covering a lower part of the sensor and adhering to a lower surface of the horizontal piece of the stay.

Images