JP2010169998A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that can discharge a sheet without incurring deterioration in loading property. <P>SOLUTION: An air blowing opening 35 is provided below a discharge roller 30 and the air form a fan 33 is blown on the sheet that is discharged from the discharge roller 30 from this air blowing opening. Then, a control section controls the fan 33 so that the amount of blown air is a prescribed amount when the air is blown toward a leading edge portion of the sheet when the sheet is discharged and increasing the amount of blown air to be more than a prescribed amount after the leading edge portion of the sheet is discharged. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to sheet discharge speed control when discharging a sheet to a sheet stacking unit.

  2. Description of the Related Art Conventionally, in image forming apparatuses such as printers, facsimiles, copiers, and multifunction printers, a sheet discharging unit discharges a sheet on which an image is formed by a sheet discharging unit and stacks the sheet on a sheet stacking unit provided below the sheet discharging unit. Equipment.

  In such an image forming apparatus, when an image is formed on a sheet, the toner image is formed on the photosensitive drum, the toner image is transferred onto the sheet, and then the toner image is fixed on the sheet by the fixing unit. I try to let them. Then, after fixing the toner image on the sheet in this way, the sheet is discharged from the sheet discharge port to the stacking tray as the sheet stacking portion by the discharge roller provided in the sheet discharge device. When the sheets are discharged to the stacking tray in this way, the sheets are stacked on the stacking tray while the toner image is solidified by cooling by natural heat radiation.

  By the way, in recent years, electrophotographic full-color image forming apparatuses have become widespread, and in addition to the output to a transparent resin sheet for an overhead projector, an output to a newly colored resin sheet as a water-resistant output medium has been achieved. It is starting to be demanded.

  Here, also in the image formation on the sheet formed of the resin, the toner image formed on the photosensitive drum is transferred to the sheet, and then the toner image is heated in the fixing unit, similarly to the normal paper. To fix. Note that when fixing a toner image on a sheet, a larger amount of heat is required for fixing the toner image than for normal paper, so the conveyance speed at the fixing unit is slower than that for normal paper, and the unit By securing the amount of heat applied to the sheet per hour, fixing properties are obtained.

  However, depending on the installation environment of the main body of the image forming apparatus, natural heat radiation may not be in time until a sheet given a large amount of heat for fixing a toner image is discharged onto the stacking tray. In this case, the toner image formed on the sheet may not be hardened and may stick to the previously stacked sheet.

  Note that, when a large amount of heat is applied to the resin sheet, the rigidity is remarkably lowered and the smoothness of the surface is high, so that the adhesiveness with the previously stacked sheet is higher than that of the paper. For this reason, when natural heat radiation is not in time, when the sheet is discharged, the downstream end portion in the sheet discharge direction is bent downward, and the downstream end in the discharge direction is placed on the stacking tray 24 as shown in FIG. Immediately after reaching, the downstream end of the sheet S in the discharge direction may be rounded.

  Further, although the downstream end portion in the discharge direction does not round, curl may occur at the downstream end portion in the discharge direction of the sheet S as shown in FIG. Further, when the downstream end of the sheet in the discharge direction is bent downward, it sticks to the previously stacked sheet, and thereafter, the sheet S1 previously stacked as shown in FIG. Due to the close contact, the sheet S may buckle in the middle of discharge and may cause jam due to poor discharge.

  Therefore, conventionally, in order to prevent the sheets from buckling during the discharge, the stacking tray 24 is loosened to be close to the discharge port to reduce the downward deflection of the sheets, and the sheets can be sufficiently cooled by natural heat dissipation. In addition, the discharge speed is slowed and the discharge interval is widened.

  However, when such a measure is taken, the number of sheets that can be stacked decreases as the stacking tray becomes slanted. Further, in order to prevent the stacked sheets from sticking, it is necessary to make an extremely large discharge interval, and the productivity is remarkably lowered as compared with normal paper output.

  For this reason, conventionally, a blower port is provided near the discharge port, and the sheet is cooled at the same time as the downstream end portion in the discharge direction is lifted by blowing so that the downstream end portion in the sheet discharge direction does not hang down. This prevents the sheets from sticking to each other at the time of discharge and the sticking between the stacked sheets (see Patent Document 1).

  FIG. 9 is a diagram illustrating a configuration of a sheet discharge unit of such a conventional image forming apparatus. In this image forming apparatus, the blower port 35 is provided near the discharge port 36, and the sheet S discharged by the discharge roller 30 is lifted by the air blown from the blower port 35, and at the same time, the discharged sheet S is removed. I'm trying to cool it down.

JP 2001-122490 A

  By the way, in such a conventional image forming apparatus, as shown in FIG. 9, when the blower port 35 is provided near the discharge port 36, the discharge roller 30 is beside the blower port. The discharge roller 30 is cooled. When the discharge roller 30 is thus cooled, the toner image is cooled by the nip portion of the discharge roller 30 with which the toner image on the sheet contacts when being discharged by the discharge roller 30. For this reason, a roller mark as shown in FIG. 10 is generated on the discharged sheet, and the image quality is remarkably deteriorated.

  Here, for example, as shown in FIG. 11, if the air blowing port 35 is provided below the discharge roller 30, the discharge roller 30 can be prevented from being cooled by the air blowing. However, if the air outlet is separated from the discharge roller 30, the discharge roller 30 obstructs the air blowing, and the downstream end portion in the discharge direction of the sheet discharged from the discharge roller 30 is as shown in FIG. It hangs down.

  In this state, most of the blown air escapes from the opening H, and it becomes difficult to lift the sheet S without obtaining the necessary wind pressure, and also due to the wind around the discharge roller 30 Then, the sheet S is cooled while being hung. As a result, the toner image becomes solid in this state, and curls as shown in FIG. 11B remain on the discharged sheet, so that the stackability of the sheet S is deteriorated. As described above, if the air blowing port 35 is provided below the discharge roller 30, the discharge roller 30 can be prevented from being cooled by the air blowing, but the stackability of the sheets S is deteriorated.

  For example, as shown in FIG. 12, if the discharge roller 30 has a length extending over the entire width direction orthogonal to the sheet conveying direction, generation of roller marks can be prevented. However, when the discharge roller 30 is configured in this way, the air outlet cannot be provided near the discharge roller 30 as shown in FIG. 9, so that the downstream end of the sheet discharge direction is prevented from dripping as described above. I can't.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that can discharge sheets without deteriorating stackability.

  The present invention provides an image forming apparatus that discharges a sheet to a sheet stacking unit by a discharge unit, and is provided below the discharge unit and blows air toward the sheet discharged by the discharge unit, and the blow port A blower that blows the air blown out from the sheet, and when discharging the sheet by the discharger, when blowing the wind toward the downstream end in the sheet discharge direction, a predetermined amount of air is sent and the downstream end in the sheet discharge direction passes After that, a control unit that controls the blowing unit so as to increase the blowing amount from the predetermined amount is provided.

  As in the present invention, when the sheet is discharged, when the downstream end portion in the sheet discharge direction is discharged, the blowing amount is set to a predetermined amount, and after the downstream end portion in the sheet discharging direction is discharged, the blowing amount is set to a predetermined amount. By increasing the number, the sheet can be discharged without deteriorating the stackability.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is an overall configuration diagram of a color laser printer which is an example of an image forming apparatus according to an embodiment of the present invention.

  In FIG. 1, reference numeral 100 denotes a color laser printer, and 100A denotes a color laser printer main body (hereinafter referred to as a printer main body). The printer main body 100A is provided with an image forming unit 101 for forming an image on a sheet. Further, the printer main body 100A is provided with a sheet feeding unit 16, a transfer unit 103, a fixing unit 20, and a sheet discharge unit 41.

  Here, the image forming unit 101 is arranged in the vertical direction, and carries a toner image of four colors of yellow, magenta, cyan, and black, and is a photosensitive drum that is an image carrier that is driven to rotate counterclockwise. 1 (1a to 1d). Further, around the photosensitive drum 1, the charging device 2 (2a to 2d), the scanner unit 3 (3a to 3d), the developing device 4 (4a to 4d), and the cleaning device 6 (6a to 6d) are arranged along the rotation direction. ) Etc. are arranged.

  The charging device 2 is for uniformly charging the surface of the photosensitive drum, and the scanner unit 3 is for irradiating a laser beam based on image information to form an electrostatic latent image on the photosensitive drum. It is. The scanner unit 3 irradiates the photosensitive drum 1 by irradiating image light corresponding to an image signal to a polygon mirror 9 (9a to 9d) rotated at high speed by a scanner motor (not shown) by a laser diode (not shown). Scan.

  The developing device 4 is for making yellow, magenta, cyan, and black toners adhere to the electrostatic latent image to be visualized as a toner image. The cleaning device 6 is a toner remaining on the surface of the photosensitive drum after transfer. It is for removing.

  In FIG. 1, reference numeral 7 (7a to 7d) denotes a process cartridge in which the photosensitive drum 1, the charging device 2, the developing device 4, and the cleaning device 6 are integrally formed into a cartridge, and the process cartridge 7 is perpendicular to the printer main body 100A. In the direction, it is mounted interchangeably.

  Further, 12 (12a to 12d) is a transfer roller provided in the transfer unit 103, which will be described later, and provided inside the transfer conveyance belt 11 for conveying the sheet. At the same time, the transfer conveyance belt 11 is sandwiched.

  The transfer roller 12 is connected to a power supply for transfer bias (not shown), and a positive charge is applied from the transfer roller 12 to the sheet via the transfer conveyance belt 11. By applying the transfer bias in this way, the negative color toner images on the photoconductive drum are sequentially transferred to the sheet in contact with the photoconductive drum 1 while being held on the transfer conveyance belt 11, so that multicolor An image is formed.

  The sheet feeding unit 16 stores a plurality of sheets S, and feeds out the sheets S stored in a sheet feeding cassette 17 loaded on the bottom of the printer main body by a pickup roller 18 which is a sheet feeding roller. When the image is formed, the sheets S stored in the paper feed cassette 17 are separated and fed one by one by the pickup roller 18, and then conveyed to the transfer unit 103 by the registration roller pair 19 at a predetermined timing. The

  The transfer unit 103 includes a transfer conveyance belt 11 disposed to face the photosensitive drum 1. The transfer conveyance belt 11 electrostatically attracts the sheet to the outer peripheral surface facing the photosensitive drum 1 and circulates and moves so as to bring the sheet into contact with the photosensitive drum 1. Then, the sheet S is conveyed to the transfer position by the transfer conveyance belt 11 by being electrostatically attracted to the transfer conveyance belt 11 that circulates and moves the toner image on the photosensitive drum 1.

  Next, an image forming operation of the color laser printer 100 configured as described above will be described.

  First, when the surface of the photosensitive drum 1 uniformly charged by the charging device 2 is scanned with a laser beam corresponding to the image information irradiated from the scanner unit 3, a latent image is formed on the surface of the photosensitive drum. Is done. Further, the latent image is developed by the developing device 4, whereby toner images of four colors of yellow, magenta, cyan, and black are formed on the surface of the photosensitive drum.

  In parallel with the toner image forming operation, the sheets S accommodated in the paper feed cassette 17 are picked up by the pickup roller 18 and separated and fed one by one. Thereafter, the sheet S fed from the sheet feeding cassette 17 is guided to the stopped registration roller pair 19 to correct skewing, and then synchronized with the image forming operation by the registration roller pair 19. It is conveyed to the transfer unit 103. The sheet S thus transported to the transfer unit 103 is attracted to the transfer transport belt 11 and transported to a transfer portion where the photosensitive drum 1 and the transfer transport belt 11 are in pressure contact.

  Next, the toner image of each color on the photosensitive drum is formed on the sheet by the action of the transfer roller 12 disposed in each transfer unit and applied with a voltage having a polarity opposite to that of the toner. The images are superimposed and transferred sequentially. The sheet S on which the four color toner images are transferred in this way is separated from the transfer conveyance belt 11 and conveyed to the fixing unit 20.

  Next, after the fixing toner image is transferred, the sheet S conveyed to the fixing unit 20 is pressed and heated when it passes through the fixing nip between the heating roller 21 and the pressure roller 22 in the fixing unit 20. Then, a full-color print image is fixed on the sheet as a permanent image. Next, the sheet S on which the full-color print image is fixed as a permanent image in this way is conveyed by the conveyance roller pair 23 and then is stacked by the discharge roller 30 from the discharge port 42 as a stacking tray 24 that is a sheet stacking portion below. The paper is stacked.

  In FIG. 1, reference numeral 51 denotes sheet attribute detection means provided on the upstream side of the registration roller pair 19 in the sheet conveyance direction. When the sheet S is stopped by the registration roller pair 19, the sheet attribute detection unit 51 detects the sheet attribute, in the present embodiment, whether the sheet is made of resin.

  Reference numeral 50 denotes an environmental temperature detection unit provided on the upper portion of the sheet feeding unit 16. The environmental temperature detection unit 50 detects the temperature of the environment where the printer main body 100A is installed. Reference numeral 60 denotes a control unit that controls the printer main body 100A. The control unit 60 controls an image forming operation and a fan blowing operation described later based on signals from the environmental temperature detection unit 50 and the sheet attribute detection unit 51. To do.

  FIG. 2 is a diagram illustrating the configuration of the sheet discharge unit 41. As shown in FIG. 2, it is detected that the leading edge of the sheet has arrived from the fixing nip between the heating roller 21 and the pressure roller 22 in the vicinity of the conveyance roller pair 23 that sandwiches and conveys the sheet that has passed through the fixing unit 20. A detection flag 23f is provided.

  Further, a full load detection flag 40 that functions as a detection unit that detects the sheet stacking amount on the stacking tray is rotatably provided downstream of the discharge roller 30 in the sheet discharge direction. Then, the position of the full load detection flag 40 is detected by a full load detection sensor 61 shown in FIG. 3 to be described later, thereby detecting that the sheets on the stacking tray are full.

  The full load detection flag 40 has a center of rotation above the discharge roller 30. When the sheet S is discharged, the full load detection flag 40 contacts the sheet S from above and presses the sheet. The full load detection flag 40 is in contact with an upstream end portion (hereinafter referred to as a rear end portion) in the sheet discharge direction after being stacked on the stacking tray, and suppresses lifting of the rear end portion of the sheet, thereby preventing the rear end of the sheet. This prevents the portion from blocking the discharge port 42 and the air blowing port 35.

  Further, a blower space G formed by the bottom surface of the stacking tray 24 and the duct member 34 is formed below the stacking tray 24. Outside air is sent to the downstream side of the blower space G in the sheet conveyance (discharge) direction. A fan 33 for taking in and blowing air is provided.

  When the fan 33, which is a blowing means, rotates, the outside air passes through a louver 33a provided on the exterior of the printer body, and dust and the like are removed by a filter (not shown) installed inside the printer 33. Inhaled into the ventilation space. Thereafter, the outside air sucked in by the fan 33 proceeds in the direction of the arrow in the air blowing space, is reversed below the discharge roller 30, and blows out along the stacking tray 24 from the air blowing port 35 provided below the discharge roller 30. Is done.

  FIG. 3 is a block diagram of the control unit 60 of the color laser printer 100 for controlling the sheet discharge unit 41. The control unit 60 includes a detection flag 23f, an environmental temperature detection unit 50, a sheet attribute detection unit 51, a full load. A signal from the detection sensor 61 is input. The control unit 60 drives the counter 52 based on the signal from the detection flag 23f, and controls the driving of the fan 33 based on the signal from the environmental temperature detection means 50 and the like.

  In the present embodiment, when it is determined from the detection result of the sheet attribute detection means 51 that the sheet being conveyed is made of resin, the sheet reaching the conveyance roller pair 23 is detected after the fixing process. When the flag 23f is detected, the drive of the fan 33 is controlled. For example, if the fan 33 is in a blowing state, as shown in the timing chart of FIG. 4, the fan 33 is temporarily stopped, and at the same time, counting by the counter 52 is started to calculate the sheet conveyance distance from the conveyance roller pair 23.

  Then, after the downstream end of the sheet in the sheet discharge direction (hereinafter referred to as the leading end) reaches the stacking tray 24, the fan air flow shown in FIG. 4 is a predetermined air flow based on the count value of the counter 52. A control signal for driving the fan 33 is output so that the initial air blowing amount is obtained.

  Here, with respect to the fan air flow rate, a control mode is selected so as to perform optimal control based on the detection results of the sheet attribute detection means 51 and the environmental temperature detection means 50. That is, the control unit 60 identifies the attribute of the sheet being conveyed from the detection result of the sheet attribute detection unit 51, and when the sheet is made of resin, first, the control of temporarily stopping the fan 33 already described. Select.

  Next, the environmental temperature in which the printer main body 100A is installed is detected by the environmental temperature detection means 50, and one of the low temperature environment control mode, the normal temperature environment control mode, and the high temperature environment control mode is selected according to the environmental temperature.

  For example, when the environmental temperature is less than 20 ° C., the low temperature environment control mode is selected. In this mode, when the count value of the counter 52 reaches T1, that is, after the leading edge of the sheet reaches the stacking tray 24, the sheet discharged from the discharge roller 30 as shown in the control table of FIG. Therefore, air is not blown to the sheet front end. That is, the fan air flow rate is set to 0% of the predetermined maximum air flow rate.

  Here, after the sheet leading edge reaches the stacking tray 24 in this way, the sheet leading edge is not excessively cooled by preventing air from being blown to the sheet leading edge. It can be prevented from hardening in the curled state.

  Further, when the count value of the counter 52 reaches T2, that is, when the rear end portion of the sheet passes through the air blowing port 35, the fan air blowing amount is set to 33% of the predetermined maximum air volume. Here, in a low temperature environment of 20 ° C. or less, the sheet cooling effect by natural heat dissipation is considerably large. For this reason, if the fan air flow rate is 33% of the maximum air flow rate at the rear end portion of the sheet, the sheet can be sufficiently cooled, and sheet discharge failure and sticking can be prevented. .

  When the environmental temperature is 20 ° C. or higher and lower than 27 ° C., the normal temperature environmental control mode is selected. In the case of this mode, as shown in FIG. 5, with respect to the sheet discharged from the discharge roller 30, air is blown so that the fan air blowing amount is 33% of the maximum air amount at the sheet leading end. Here, by blowing air so that the fan air blowing amount is 33% of the maximum air flow at the sheet front end portion as described above, the sheet front end portion is not excessively cooled and can be prevented from being hardened in a curled state. .

  Further, at the rear end portion of the seat, the fan air flow rate is set to 66% of the maximum air flow rate. Here, since the cooling effect of the sheet by natural heat dissipation is large even in a normal temperature environment of 20 ° C. or more and less than 27 ° C., if the fan air flow rate is set to 66% of the maximum air flow rate at the sheet rear end, the sheet discharge Defects and sticking can be prevented.

  When the environmental temperature is 27 ° C. or higher, the high temperature environmental control mode is selected. In the case of this mode, as shown in FIG. 5, with respect to the sheet discharged from the discharge roller 30, air is blown so that the fan air blowing amount is 50% of the maximum air volume at the sheet leading end.

  Here, in a high temperature environment, by blowing air so that the fan air blowing amount is 50% of the maximum air volume at the sheet front end portion in this way, the sheet front end portion is not excessively cooled and is solidified in a curled state. Can be prevented. Further, at the rear end portion of the seat, the fan air flow rate is set to 100% of the maximum air flow rate. Here, since the sheet cooling effect due to natural heat radiation is slight in a high temperature environment of 27 ° C. or more, the sheet discharge is performed by setting the fan air flow rate to the maximum air flow rate (100%) at the rear end of the sheet. Defects and sticking can be prevented.

  Next, in the color laser printer 100 formed as described above, the air blowing operation control when discharging the A4 size sheet will be described with reference to the flowchart shown in FIG.

  First, the control unit 60 determines from the detection result of the sheet attribute detection means 51 whether the conveyed sheet is made of resin (S100). When it is determined that the sheet is made of resin (Y in S100), when a detection signal is input from the detection flag 23f that detects the leading edge of the sheet S, the control mode for the resin sheet is performed. Is selected (S101).

  Next, it is determined whether the environmental temperature is less than 20 ° C. based on the environmental temperature information from the environmental temperature detecting means 50 (S102). Here, when the environmental temperature is lower than 20 ° C. (Y in S102), the low temperature environmental control mode is selected (S103). When this mode is selected, when the detection signal of the detection flag 23f is received and the fan 33 is blowing air toward the stacking tray 24, as shown in the timing chart of FIG. Stop it once. At the same time, the counter 52 starts counting in order to calculate the sheet conveyance distance from the conveyance roller pair 23.

  Next, after the leading edge of the sheet S is conveyed by the discharge roller 30 and the full load detection flag 40 as a pressing member is lifted by the upper surface of the sheet, the leading edge of the sheet S is in the posture as shown in FIG. To reach the loading tray 24. Even after the leading edge of the sheet reaches the stacking tray 24 in this way, no air is blown to the leading edge of the sheet discharged from the discharge roller 30 until the count value by the counter 52 reaches T1. Like that.

  Here, when the air is not blown to the leading end of the sheet, the leading end of the sheet S that has reached the stacking tray 24 is rounded by receiving the frictional force from the stacking tray 24. However, in the present embodiment, since the sheet S receives the load of the full load detection flag 40 or the downward pressing force F1 by the urging means (not shown), the leading end portion of the sheet S swells further upward (flexure). Is not regulated, and no further rounding occurs.

  Further, even after the leading edge of the sheet S reaches the stacking tray 24, the sheet is corrected so as to follow the surface shape of the stacking tray by the load of the full load detection flag 40, so as shown in FIG. There is no curling at the tip. In other words, when the leading edge of the sheet S reaches the stacking tray 24, the sheet S receives the force of F1 by the full load detection flag 40, and thereafter moves along the stacking tray 24 without curling the leading edge. Go.

  Next, after the leading edge of the sheet reaches the stacking tray 24, when the count value of the counter described above reaches a value T1 corresponding to the length of 1/3 of the A4 size at the sheet conveyance distance shown in FIG. A fan control signal corresponding to the initial air flow rate is output from the control unit 60. In this case, since the environmental temperature is less than 20 ° C. and the low-temperature environment control mode is selected, the sheet discharged from the discharge roller 30 is not blown to the front end of the sheet.

  Thereafter, when the count value of the counter reaches a value T2 corresponding to 2/3 length of the A4 size in the transport distance of the discharged sheet, as shown in FIG. The air is blown so that it becomes%. At this time, as shown in FIG. 7B, the angle formed between the discharged sheet S and the stacking tray 24 is sufficiently small, so that it remains on the sheet even if the amount of air flow is increased. Curling does not occur.

  If the environmental temperature is 20 ° C. or higher (N in S102), it is next determined from the environmental temperature information from the environmental temperature detecting means 50 whether the environmental temperature is 27 ° C. or higher (S105). Here, when the environmental temperature is less than 27 ° C. (N in S105), the room temperature environmental control mode is selected (S106), and the count value of the counter reaches the value T1 after the sheet leading edge reaches the stacking tray 24. When it reaches, a fan control signal corresponding to the initial air flow rate is output from the control unit 60. In this case, with respect to the sheet discharged from the discharge roller 30, air is blown so that the fan air blowing amount is 33% of the maximum air amount at the front end of the sheet.

  Note that when the sheet S is discharged by about 1/3 of the total length (about 100 mm in the present embodiment), the leading edge of the sheet is in contact with the stacking tray 24. At this time, there is no gap corresponding to the opening H shown in FIG. 11A described above, and the full load detection flag 40 urges the sheet S from above.

  For this reason, even when the fan 33 is rotated at a low speed of 33% of the maximum air volume, the air volume that escapes is small and exceeds the force that the sheet S adheres to the previously stacked sheet. The wind pressure can be obtained, and the sheet S can be prevented from buckling during discharge.

  Thereafter, when the count value of the counter reaches a value T2 corresponding to the length of 2/3 of the A4 size in the transport distance of the discharged sheet, the fan air flow rate is 66, which is the maximum air flow rate as shown in FIG. The air is blown so that it becomes%.

  If the environmental temperature is 27 ° C. or higher (Y in S105), the high temperature environmental control mode is selected (S107), and the count value of the counter reaches the value T1 after the sheet leading edge reaches the stacking tray 24. Then, a fan control signal corresponding to the initial air flow rate is output from the control unit 60. In this case, with respect to the sheet discharged from the discharge roller 30, the fan is blown so that the fan blow amount is 50% of the maximum air amount at the leading end of the sheet.

  Thereafter, when the count value of the counter of the control unit reaches a value T2 corresponding to 2/3 of the A4 size in the conveyed distance of the discharged sheet, the fan air blowing amount is maximum as shown in FIG. Air is blown so that the air volume becomes 100%. Here, although the sheet cooling effect due to natural heat dissipation is slight in a high temperature environment of 27 ° C. or higher, sheet discharge failure and sticking are prevented by setting the fan air flow rate to the maximum air volume (100%). be able to. As a result, the sheets can be discharged without deteriorating the stackability.

  As described above, in the present embodiment, the position when the wind is blown toward the leading edge of the sheet according to the sheet attribute detected by the sheet attribute detecting unit 51 and the environmental temperature detected by the environmental temperature detecting unit 50. The amount of air to be quantified and increased is changed.

  After the image is formed in this way, when discharging the fixed sheet, when the front end of the sheet is discharged, the blowing amount is set to a predetermined amount, and after the leading end of the sheet is discharged, the blowing amount is set to a predetermined amount. By increasing the number of sheets, the sheet can be discharged without deteriorating the stackability.

  In this embodiment, the paper size is A4 and the control mode is divided into three according to the environmental temperature. However, the setting should be determined according to the main body configuration of the image forming apparatus. It is not limited to setting the form.

1 is an overall configuration diagram of a color laser printer that is an example of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a diagram illustrating a configuration of a sheet discharge unit provided in the color laser printer. FIG. 3 is a control block diagram for controlling a sheet discharge unit of the color laser printer. 6 is a timing chart showing control of a fan provided in the sheet discharge unit. Control table for the fan. The flowchart explaining control of the said fan. The figure explaining the sheet discharge operation | movement of the said sheet discharge part. FIG. 10 is a diagram for explaining a problem in discharging a sheet of a conventional image forming apparatus. FIG. 10 is a schematic diagram illustrating a sheet discharge unit of another conventional image forming apparatus. FIG. 10 is a schematic diagram illustrating an image forming surface of a sheet discharged by a sheet discharge unit of another conventional image forming apparatus. FIG. 6 is a diagram for explaining a problem in discharging a sheet in another conventional image forming apparatus. The figure which shows the conventional discharge roller pair which a roller trace does not appear.

24 Stack tray 30 Discharge roller 33 Fan 35 Blower port 40 Full load detection flag 41 Sheet discharge unit 42 Discharge port 50 Environmental temperature detection unit 51 Sheet attribute detection unit 60 Control unit 100 Color laser printer 100A Color laser printer body 101 Image forming unit G Space S sheet

Claims (7)

In the image forming apparatus for discharging the fixed sheet to the sheet stacking unit by the discharge unit after the image formation,
An air outlet that is provided below the discharge means and blows out air toward the sheet discharged by the discharge means;
Air blowing means for blowing air blown from the air blowing port;
When discharging the sheet by the discharging means, when blowing air toward the downstream end portion in the sheet discharging direction, the blowing amount is set to a predetermined amount, and after passing the downstream end portion in the sheet discharging direction, the blowing amount is set to the predetermined amount. A control unit for controlling the air blowing means to increase more than,
An image forming apparatus comprising:   2. The image forming apparatus according to claim 1, wherein the control unit increases an air blowing amount after the downstream end of the discharged sheet comes into contact with a stacking tray or a sheet stacked on the stacking tray. Attribute detection means for detecting the attribute of the sheet,
2. The control unit according to claim 1, wherein the predetermined amount when the air is blown toward the downstream end portion in the sheet discharge direction and the amount of air to be increased are changed according to the attribute of the sheet detected by the attribute detecting unit. Or the image forming apparatus according to 2; Equipped with environmental temperature detection means for detecting environmental temperature,
2. The control unit according to claim 1, wherein the control unit changes a predetermined amount when the air is blown toward the downstream end portion in the sheet discharge direction and an air flow amount to be increased according to the environmental temperature detected by the environmental temperature detection unit. 4. The image forming apparatus according to any one of items 1 to 3.   5. The image forming apparatus according to claim 1, further comprising a pressing member that presses against the sheet discharged from the discharging unit from above.   6. The image forming apparatus according to claim 5, wherein lifting of the upstream end in the sheet discharge direction stacked on the stacking tray is suppressed by the pressing member.   The image forming apparatus according to claim 5, wherein the pressing member is a full load detection flag for detecting a sheet stacking amount on a stacking tray.

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