JP2007017612A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the lowering of cooling efficiency inside an image forming apparatus when performing double-sided printing. <P>SOLUTION: The image forming apparatus 10 is provided with a cooling fan 42 for cooling the inside of the apparatus by sending air from the side of the first conveying path 15 for forming an image on paper P to the side of the second conveying path 70 for reversing a sheet from a front surface to a back surface between the first conveying path 15 and the second conveying path 70. When it takes predetermined time or longer until finishing the development of the data of the image formed on the back surface of the paper P, the paper P is made to stand by at the first standby position X1 on a more upstream side in a conveying direction than a position opposed to the cooling fan 42 on the second conveying path 70 so that sent air from the cooling fan 42 may not be kept interrupted by the paper P. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention blows air from the first conveyance path side to the second conveyance path side to cool the inside of the apparatus between a first conveyance path for forming an image on a sheet and a second conveyance path for reversing the sheet. The present invention relates to an image forming apparatus provided with means.

  In an image forming apparatus using an electrophotographic system or an inkjet system, a cooling fan (air blowing unit) that exhausts air from the inside of the apparatus and cools the inside of the apparatus is provided on the back side of the apparatus body so that the exhaust from the inside of the apparatus is on the user side. Is not suitable for.

However, when a double-sided conveyance unit for reversing the front and back sides of a sheet with an image formed on the front side is added to the back of the apparatus main body, the first conveyance path for forming an image on the sheet and the inside of the double-sided conveyance unit Since the cooling fan is interposed between the second conveyance path passing through the sheet, if it takes time to develop the data of the image formed on the back side of the sheet, the sheet waiting inside the duplex conveyance unit As a result, the exhaust from the cooling fan is blocked for a long time, and the cooling efficiency inside the apparatus is reduced (for example, see Patent Document 1).
Japanese Patent Laid-Open No. 11-296053

  The present invention has been made in consideration of the above facts, and the second conveyance from the first conveyance path side between the first conveyance path for forming an image on the sheet and the second conveyance path for reversing the front and back of the sheet. In an image forming apparatus provided with a blowing unit that blows air to the road side and cools the inside of the apparatus, a decrease in cooling efficiency inside the apparatus when performing double-sided printing is suppressed.

  The image forming apparatus according to claim 1, a sheet storage unit that stores a sheet, a first transport path that extends from the sheet storage unit to the outside of the apparatus, and a first transport unit that transports the sheet in the first transport path; An image forming unit that forms an image on a sheet that is conveyed on the first conveying path by the first conveying unit; and the first conveying unit that branches from the image forming unit on the first conveying path from the downstream side in the conveying direction. A second conveyance path that merges upstream of the image forming unit with respect to the conveyance direction, and a second conveyance that conveys the sheet from the second conveyance path to the first conveyance path with the trailing edge at the top and reverses the front and back. And a blower unit provided between the first conveyance path and the second conveyance path, for blowing air from the first conveyance path side to the second conveyance path side to cool the inside of the apparatus, and the image forming means Image formation on the back side of the sheet can be started An image forming apparatus comprising: a first control unit that controls the second conveyance unit so that the sheet waits in the second conveyance path, wherein the first control unit is configured to transfer the sheet to the second conveyance unit. When the standby time for waiting in the conveyance path becomes longer than a predetermined time, the second sheet is set so that the sheet stands by at a first standby position upstream in the conveyance direction from a position facing the air blowing unit in the second conveyance path. The conveyance means is controlled.

  In the image forming apparatus according to the first aspect, the sheet is accommodated in the sheet accommodating portion, and the first conveyance path extends from the sheet accommodating portion to the outside of the apparatus. In the first conveying path, the sheet is conveyed by the first conveying unit, and an image is formed on the conveyed sheet by the image forming unit.

  Further, the second conveyance path branches from the image forming unit of the first conveyance path from the downstream side in the conveyance direction, and merges from the image forming unit of the first conveyance path to the upstream side of the conveyance direction. The sheet is transported from the second transport path to the first transport path by the second transport means with the trailing edge as the head. As a result, the sheet is turned upside down and conveyed in the first conveying path, and an image is formed on the back surface of the sheet by the image forming means.

  In addition, air blowing means is provided between the first conveyance path and the second conveyance path. This blowing means cools the inside of the apparatus by sending air from the first conveyance path side to the second conveyance path side.

  In addition, after the image is formed on the front surface of the sheet, until the image formation on the back surface of the sheet can be started, the second transport unit is controlled by the first control unit, and the sheet is transported to the second transport path. It is supposed to wait at.

  Here, when the standby time for the sheet to wait in the second conveyance path is longer than the predetermined time, the sheet is at the first standby position on the upstream side in the conveyance direction from the position facing the air blowing unit of the second conveyance path. The second transport unit is controlled by the first control unit so as to wait.

  Accordingly, it is possible to prevent the air blown from the air blowing unit from being continuously blocked by the sheet in the second conveyance path for a long time, and thus it is possible to suppress a decrease in the cooling effect inside the apparatus.

  An image forming apparatus according to a second aspect of the present invention is the image forming apparatus according to the first aspect, wherein the first control unit is configured such that the sheet is once opposed to the air blowing unit in the second conveyance path. The second transport unit is controlled so that the second transport unit is transported to the second standby position on the downstream side in the transport direction, and when the standby time becomes longer than the predetermined time, the second standby unit is reversely fed from the second standby position to the first standby position. It is characterized by doing.

  In the image forming apparatus according to claim 2, the second conveyance unit is controlled by the first control unit, and the sheet is temporarily placed in the second standby on the downstream side in the conveyance direction from the position facing the air blowing unit in the second conveyance path. Then, when the standby time at the second standby position becomes longer than a predetermined time, it is fed back from the second standby position to the first standby position.

  Thereby, it can prevent that the ventilation from a ventilation means continues being interrupted by the sheet | seat in a 2nd conveyance path for a long time, and can suppress the fall of the cooling effect inside an apparatus. Further, when the waiting time of the sheet on the second conveying path is short, the conveying distance from the standby position of the sheet on the second conveying path to the first conveying path is shortened, and image formation on the back surface of the sheet is started. Since the time required until printing is shortened, double-sided printing can be accelerated.

  The image forming apparatus according to claim 3, a sheet storage unit that stores a sheet, a first transport path that extends from the sheet storage unit to the outside of the apparatus, and a first transport unit that transports the sheet in the first transport path; An image forming unit that forms an image on a sheet that is conveyed on the first conveying path by the first conveying unit; and the first conveying unit that branches from the image forming unit on the first conveying path from the downstream side in the conveying direction. A second conveyance path that merges upstream of the image forming unit with respect to the conveyance direction, and a second conveyance that conveys the sheet from the second conveyance path to the first conveyance path with the trailing edge at the top and reverses the front and back. And a blower unit provided between the first conveyance path and the second conveyance path, for blowing air from the first conveyance path side to the second conveyance path side to cool the inside of the apparatus, and the image forming means Image formation on the back side of the sheet can be started An image forming apparatus comprising: a second control unit configured to control the second transport unit so that the sheet stands by in the second transport path, wherein the second control unit is configured such that the sheet is the second transport unit. To wait at a first standby position on the upstream side in the transport direction from a position facing the air blowing means on the transport path or at a second standby position on the downstream side in the transport direction from a position facing the air blowing means on the second transport path, The second conveying means is controlled.

  In the image forming apparatus according to claim 3, the second conveying unit is controlled by the second control unit, and the first standby position on the upstream side in the conveying direction from the position where the sheet faces the blowing unit in the second conveying path or It waits in the 2nd standby position of the conveyance direction downstream from the position facing the ventilation means of a 2nd conveyance path.

  This improves the cooling effect inside the apparatus so that the air from the blowing means is not blocked by the sheet in the second conveyance path, or the conveyance distance from the standby position in the second conveyance path to the first conveyance path It is possible to shorten the time required to start image formation on the back side of the sheet, speed up double-sided printing, and the like.

  An image forming apparatus according to a fourth aspect of the present invention is the image forming apparatus according to the third aspect, wherein when the high speed mode giving priority to a print speed is selected, the second control unit has the sheet in the second state. When the standard speed mode that waits at the standby position and does not give priority to the printing speed is selected, the second conveying unit is controlled so that the sheet waits at the first standby position.

  In the image forming apparatus according to claim 4, when the second conveyance unit is controlled by the second control unit and the high-speed mode giving priority to the printing speed is selected, the sheet stands by at the second standby position, When the standard speed mode that does not give priority to the print speed is selected, the sheet stands by at the first standby position.

  In other words, when the required printing speed is higher than the image quality, the distance from the standby position in the second conveyance path to the first conveyance path is shortened until image formation on the back side of the sheet is started. When the required time is shortened and the image quality requirement is higher than the printing speed, the air from the air blowing means is not blocked by the sheet in the second conveyance path to improve the cooling effect inside the apparatus, and image formation Stabilize the operation of the means.

  The image forming apparatus according to claim 5 is the image forming apparatus according to claim 3, wherein the second control unit has a predetermined amount of image data capacity formed on the back surface of the sheet by the image forming unit. If it is less than the sheet, the sheet waits at the second standby position, and if the volume of image data formed on the back surface of the sheet by the image forming means is a predetermined amount or more, the sheet waits at the first standby position. Thus, the second conveying means is controlled.

  The image forming apparatus according to claim 5, wherein the second transport unit is controlled by the second control unit, and the amount of image data formed on the back surface of the sheet by the image forming unit is less than a predetermined amount. Waits at the second standby position, and when the amount of data of the image formed on the back surface of the sheet by the image forming means is a predetermined amount or more, the sheet waits at the first standby position.

  That is, when the amount of image data formed on the back side of the sheet by the image forming unit is small, the waiting time of the sheet in the second conveyance path is shortened, and during this short time, the air is blown from the blowing unit. Even if it is blocked, the cooling effect inside the apparatus does not decrease so much, so that the time required for starting the image formation on the back surface of the sheet is shortened by waiting the sheet at the second standby position. In addition, when there is a lot of image data formed on the back side of the sheet by the image forming unit, the waiting time of the sheet in the second conveyance path becomes long, and during this long time, the air from the blowing unit is blocked. If the operation is continued, the cooling effect inside the apparatus is greatly reduced. Therefore, the sheet is kept waiting at the first standby position so that the air from the air blowing means is not blocked for a long time.

  Thus, when the image data formed on the back surface of the sheet is developed quickly by the image forming unit, the sheet can be conveyed to the first conveying path without being delayed. Further, when the development of the image data formed on the back side of the sheet by the image forming unit is slow, the conveyance of the sheet to the first conveyance path is somewhat delayed, but the delay time is the time required for the development of the image data. It is short compared with, and it is not so much a problem. The effect of being able to suppress a decrease in the cooling effect inside the apparatus is greater than that.

  The image forming apparatus according to claim 6 is the image forming apparatus according to claim 3, wherein the second control unit is configured such that the image formed on the back surface of the sheet by the image forming unit is a single color. Waits at the second standby position, and when the image formed by the image forming unit on the back side of the sheet is multicolored, the second conveying unit is controlled so that the sheet stands by at the first standby position. It is characterized by that.

  In the image forming apparatus according to claim 6, when the second conveying unit is controlled by the second control unit and the image formed on the back surface of the sheet by the image forming unit is monochromatic, the sheet waits at the second standby position. When the image formed by the image forming unit on the back side of the sheet is multicolored, the sheet stands by at the first standby position.

  That is, when the image formed on the back side of the sheet by the image forming unit is a single color, the image data capacity is small, and the waiting time of the sheet in the second conveyance path is shortened. Since the cooling effect inside the apparatus does not decrease so much even if the airflow is blocked, the sheet is made to wait at the second standby position, and the time required until image formation on the back surface of the sheet is started is shortened. In addition, when the image formed by the image forming unit on the back side of the sheet is multicolored, the image data has a large capacity, and the waiting time of the sheet in the second conveyance path becomes long. During this long time, the blowing unit If the ventilation from the air continues to be blocked, the cooling effect inside the apparatus is greatly reduced. Therefore, the sheet is kept waiting at the first standby position so that the air from the blowing means is not blocked for a long time.

  Thus, when the image data formed on the back surface of the sheet is developed quickly by the image forming unit, the sheet can be conveyed to the first conveying path without being delayed. Further, when the development of the image data formed on the back surface of the sheet by the image forming means is slow, although the sheet is somewhat delayed in transporting to the first transport path, it is possible to suppress a decrease in the cooling effect inside the apparatus, and the image Image formation by the forming means can be stabilized.

  The image forming apparatus according to claim 7 is the image forming apparatus according to claim 3, wherein when the sheet size is less than a predetermined size, the second control unit causes the sheet to be in the second standby state. The second conveying means is controlled so that the sheet waits at the first standby position when the sheet waits at the position and the size of the sheet is equal to or larger than a predetermined size.

  In the image forming apparatus according to claim 7, when the second conveying unit is controlled by the second control unit and the sheet size is less than a predetermined size, the sheet waits at the second standby position, When the size of the sheet is equal to or larger than the predetermined size, the sheet stands by at the first standby position.

  That is, when the sheet size is small, the image data volume is small, and the waiting time of the sheet in the second conveyance path is shortened. During this short time, even if the blowing from the blowing unit is blocked, the inside of the apparatus Since the cooling effect does not decrease so much, the sheet is made to wait at the second standby position, and the time required until image formation on the back surface of the sheet is started is shortened. Further, when the sheet size is large, the amount of image data is large, and the waiting time of the sheet in the second conveyance path becomes long. During this long time, if the blowing from the blowing means continues to be blocked, Since the cooling effect is greatly reduced, the sheet is made to wait at the first standby position so that the air blown from the blowing means is not blocked for a long time.

  Thus, when the image data formed on the back surface of the sheet is developed quickly by the image forming unit, the sheet can be conveyed to the first conveying path without being delayed. Further, when the development of the image data formed on the back surface of the sheet by the image forming means is slow, although the sheet is somewhat delayed in transporting to the first transport path, it is possible to suppress a decrease in the cooling effect inside the apparatus, and the image Image formation by the forming means can be stabilized.

  An image forming apparatus according to an eighth aspect is the image forming apparatus according to the third aspect, wherein the second control unit waits at the second standby position when the number of prints is less than a predetermined number. When the number of printed sheets is equal to or greater than a predetermined number, the second conveying unit is controlled so that the sheet waits at the first standby position.

  In the image forming apparatus according to claim 8, when the second conveying unit is controlled by the second control unit and the number of printed sheets is less than the predetermined number, the sheet stands by at the second standby position, and the number of printed sheets is If the number is greater than the predetermined number, the sheet waits at the first standby position.

  In other words, when the number of prints is small, the temperature of the image forming unit for image formation is short, so that the temperature inside the apparatus does not increase so much. The time required until image formation is started is shortened. When the number of prints is large, the image forming means continuously forms an image for a long time, so that the temperature rise inside the apparatus becomes large. Make sure that the airflow is not blocked for a long time.

  As a result, the printing speed can be increased when the temperature rise inside the apparatus is small, and the cooling effect inside the apparatus can be improved when the temperature rise inside the apparatus is large.

  The image forming apparatus according to claim 9 is the image forming apparatus according to claim 3, further comprising an environmental temperature detecting unit that detects an environmental temperature of the apparatus, and the second control unit is configured to detect the environmental temperature. When the environmental temperature detected by the means is lower than the predetermined temperature, the sheet stands by at the second standby position, and when the environmental temperature detected by the environmental temperature detection means is equal to or higher than the predetermined temperature, the sheet is The second conveying means is controlled to wait at a standby position.

  In the image forming apparatus according to claim 9, when the second conveyance unit is controlled by the second control unit and the environmental temperature of the apparatus detected by the environmental temperature detection unit is lower than the predetermined temperature, the sheet is 2 Waits at the standby position, and when the environmental temperature of the apparatus detected by the environmental temperature detection means is equal to or higher than a predetermined temperature, the sheet stands by at the first standby position.

  That is, when the environmental temperature of the apparatus is low, the temperature rise inside the apparatus does not increase so much. Therefore, the time required for the sheet to wait at the second standby position and image formation on the back side of the sheet is started. Shorten. Further, when the environmental temperature of the apparatus is high, the temperature inside the apparatus increases, so that the sheet is kept waiting at the first standby position, and the air from the blowing unit is continuously continued for a long time by the sheet in the second conveyance path. And keep it unobstructed.

  As a result, the printing speed can be increased when the temperature rise inside the apparatus is small, and the cooling effect inside the apparatus can be improved when the temperature rise inside the apparatus is large.

  The image forming apparatus according to claim 10 is the image forming apparatus according to claim 3, wherein the image forming unit is provided facing the first conveyance path and carries a toner image. And the toner image carried on the image carrier with the first conveyance path interposed therebetween is transferred to the sheet conveyed on the first conveyance path by the first conveyance unit. And a fixing unit provided on the downstream side in the conveyance direction from the transfer unit and fixing the toner image transferred onto the sheet to the sheet. The second control means detects the temperature of the fixing means when the temperature of the fixing means detected by the fixing temperature detection means is lower than a predetermined temperature. And wait until the fixing temperature is detected. If the temperature of the fixing unit detected by is equal to or greater than the predetermined temperature, so that the sheet waits at the first waiting position, and controls the second conveying means.

  The image forming apparatus according to claim 10, wherein the image carrier is provided facing the first conveyance path, the transfer unit is opposed to the image carrier with the first conveyance path in between, and the transfer unit is Then, the toner image carried on the image carrier is transferred to the sheet conveyed by the first conveying means. Further, a fixing unit is provided on the downstream side in the transport direction from the image carrier and the transfer unit in the first transport path, and the toner image transferred to the sheet is fixed by the fixing unit.

  Here, the temperature of the fixing unit is detected by the fixing temperature detecting unit, and when the temperature of the fixing unit detected by the fixing temperature detecting unit is lower than a predetermined temperature, the sheet waits at the second standby position, When the temperature of the fixing unit detected by the fixing unit is equal to or higher than a predetermined temperature, the second conveying unit is controlled by the second control unit so that the sheet stands by at the first standby position.

  That is, when the temperature of the fixing unit is low, the temperature rise inside the apparatus does not increase so much. Therefore, the time required for the sheet to wait at the second standby position and image formation on the back side of the sheet is started. Shorten. Further, when the temperature of the fixing unit is high, the temperature inside the apparatus increases, and the temperature difference between the position where the sheet of the fixing unit passes and the position where the sheet does not pass increases. However, the sheet is not continuously blocked by the sheet in the second conveyance path for a long time, thereby suppressing a decrease in the cooling effect inside the apparatus and suppressing an increase in the temperature difference in the fixing unit.

  Since the present invention has the above-described configuration, the apparatus blows air from the first conveyance path side to the second conveyance path side between the first conveyance path for forming an image on the sheet and the second conveyance path for reversing the front and back of the sheet. In an image forming apparatus provided with a blowing means for cooling the inside, it is possible to suppress a decrease in cooling efficiency inside the apparatus when performing double-sided printing. In addition, when the temperature rise inside the apparatus is small, double-sided printing can be speeded up.

  Next, embodiments of the present invention will be described with reference to the drawings.

  As shown in FIGS. 1 to 3, the image forming apparatus 10 includes an image forming apparatus main body 12 and a duplex conveying unit 50 added to the image forming apparatus main body 12. The image forming apparatus main body 12 includes paper feed trays 13 and 14 that store the paper P, a paper feed roll 20 that vertically conveys the paper P from the paper feed tray 13 to the image forming unit 16, a registration roll 21, and a paper feed tray 14. A paper feed roll 23 and a transport roll 25 that vertically transport the paper P to the image forming unit 16 are provided. The paper feed roll 20 is disposed at the downstream end in the transport direction of the paper feed tray 13 and rotates in contact with the paper P set at the top of the paper feed tray 13 to feed the top paper P. It is sent out from the tray 14 to the first conveyance path 15 extending upward. The registration roll 21 is disposed in the first conveyance path 15 and temporarily stops the paper P sent out from the paper feed tray 13 by the paper feed roll 20 to correct the conveyance posture, and then the image forming unit. 16 to carry vertically. The paper feed roll 23 is disposed at the downstream end of the paper feed tray 14 in the transport direction, rotates in contact with the paper P set on the top of the paper feed tray 14, and removes the top paper P. It sends out to the 1st conveyance path 15. The transport roll 25 is disposed in the first transport path 15, and vertically transports the paper P sent from the paper feed tray 14 by the paper feed roll 23 to the image forming unit 16.

  The image forming unit 16 includes a photosensitive drum 22 that rotates counterclockwise in the figure (in the direction of arrow A), a charging roll 24 that is sequentially disposed around the photosensitive drum 22 in the direction of arrow A in the figure, and exposure. A device 26, a developing device 28, a transfer roll 30, and a cleaning device 32 are provided. The charging roll 24 rotates in contact with the photosensitive drum 22 to uniformly charge the photosensitive drum 22.

  The exposure device 26 uses a known exposure method such as an optical scanning method for scanning light in the axial direction of the photosensitive drum 22 or a line exposure method for exposing the photosensitive drum 22 in a line shape. An electrostatic latent image is formed on the image 22 based on the image data.

  Further, the developing device 28 rotatably supports the developing roll 28A that rotates opposite to the photosensitive drum 22 and the developing roll 28A, and the two-component developer composed of toner and carrier or the one-component developer composed only of toner. Is provided with a developing housing 28 </ b> B and a stirring mechanism 28 </ b> C. In the developing device 28, the toner accommodated in the developing housing 28B is agitated by the agitating mechanism 28C and adsorbed and held on the developing roll 28A. Then, a developing bias is applied to the developing roll 28A, and the toner moves from the developing roll 28A onto the electrostatic latent image on the photosensitive drum 28. Thereby, the electrostatic latent image on the photosensitive drum 22 is visualized (developed).

  The transfer roll 30 is in contact with the photosensitive drum 22 across the conveyance path of the paper P, and a bias having a polarity opposite to that of the toner is applied to the transfer roll 30, so that the paper P is transferred from the photosensitive drum 22. The toner image is transferred to the surface. Further, the cleaning device 32 brings the blade into contact with the photosensitive drum 22 to remove the residual toner on the photosensitive member 22.

  A fixing device 34 is disposed on the downstream side in the transport direction of the image forming unit 16. The fixing device 34 includes a heating roll 34A that is in contact with the transfer surface of the paper P, and a pressure roll 34B that is pressed against the heating roll 34A across the conveyance path of the paper P, so that the toner image is transferred. The toner sheet is fixed on the sheet P by the pressed sheet P being pressurized and heated by the heating roll 34A and the pressure roll 34B.

  A discharge roll 36 is disposed on the downstream side in the transport direction of the fixing device 34, and a discharge tray 38 is formed on the upper surface of the casing 11 of the image forming apparatus main body 12. P is discharged to the discharge tray 38 by the discharge roll 36.

  A cooling fan 42 is disposed on the back surface (right side in the drawing) of the image forming apparatus main body 12 so as to face the first conveyance path 15, and exhaust air (not shown) is disposed at a position facing the cooling fan 42 of the housing 11. Mouth is provided. The cooling fan 42 blows and exhausts air from the inside of the apparatus to the back side to cool the inside of the apparatus.

  Further, a reversing conveyance path 40 extending to the back surface (right side in the drawing) of the image forming apparatus main body 12 branches from between the fixing device 34 and the discharge 36 roll in the first conveyance path 15. Between the transport roll 25 and the transport roll 21, a reverse transport path 41 extending from the rear surface of the apparatus is joined.

  Further, a double-sided conveyance unit 50 can be added to the back surface (right side in the figure) of the image forming apparatus main body 12. The double-sided conveyance unit 50 includes a double-sided conveyance unit main body 60 mounted on the back surface of the image forming apparatus main body 12, conveyance rollers 62, 63, and 64, and a reversal conveyance path 41 from the reversal conveyance path 40 of the image forming apparatus main body 12. A reversing conveyance path 66 is provided that extends to the rear. The transport rolls 62, 63, 64 are disposed along the second transport path 66. The entire reversing conveyance paths 40, 66, and 41 are referred to as a second conveyance path 70.

  Before the sheet P conveyed to the duplex conveying unit 50, the toner image is transferred at the nip portion N and the toner image is fixed by the fixing device 34, and the leading end side is once placed on the discharge tray 38 by the discharge roller 36. Is discharged. Then, when the rear end of the sheet P passes through the branch point between the first conveyance path 15 and the reversing conveyance path 40, the discharge roll 36 rotates reversely, and a conveyance path switching mechanism (not shown) By closing the one conveyance path 15 and opening the reversal conveyance path 40, the reversal conveyance path 40 is passed to the duplex conveyance unit 50.

  Then, the sheet P conveyed to the duplex conveying unit 50 is conveyed from the second conveying path 66 to the reversing conveying path 41 with the rear end at the top by the conveying rolls 62, 63, 64, and the reversing conveying path 41. To the first transport path 15. In this state, the paper P is turned upside down and passes through the nip portion N with the front surface on which the image is formed facing the transfer roll 30 side and the back surface on which the image is not formed faces the photosensitive drum 22 side. .

Here, the conveyance of the paper P is controlled by the control unit 100. Hereinafter, first to seventh embodiments of a method for controlling the conveyance of the paper P during double-sided printing by the control unit 100 will be described with reference to the flowcharts of FIGS. 4 to 11.
[First embodiment]
As shown in the flowchart of FIG. 4, when a double-sided print job is received, the processing routine is started, and the process proceeds to step 1. In step 1, the negative determination is repeated until the development of the image data is completed. In step 2, the paper feed roll 20, or the paper feed roll 23, and the transport roll 25 are driven to feed paper P from the paper feed cassette 13 or the paper feed cassette 14.

  Next, in step 3, a negative determination is made until the paper P is detected by the sensor 72 (see FIGS. 1 to 3) disposed between the paper feed roll 20 and the registration roll 21 in the first transport path 15. If it is repeated and affirmed, it proceeds to Step 4. In step 4, the negative determination is repeated until a predetermined time t <b> 0 elapses after the paper P is detected by the sensor 72 in step 3. Here, the predetermined time t0 is slightly longer than the time during which the paper P is transported from the detection position of the paper P by the sensor 72 to the registration roll 21, and the paper P is once at the nip portion of the registration roll 21. Stopped. In step 5, the registration roll 21 is driven to convey the paper P to the nip portion N, and the toner image is transferred to the paper P.

  Next, in step 6, after rotating the registration roll 21 by a predetermined amount, the driving is stopped, and the rear end portion of the paper P is conveyed to the paper discharge roll 36 and stopped. Next, in step 7, the transport path switching mechanism is operated, the first transport path 15 is closed at the branch point between the first transport path 15 and the second transport path 70, and the second transport path 70 is opened. Next, in step 8, the paper discharge roll 36 is rotated in the reverse direction to drive the conveyance rolls 62, 63, 64 of the double-sided conveyance unit 50, so that the paper P is conveyed in the second conveyance path 70 with the trailing edge as the head. To do. The rear end portion of the paper P becomes the tail when the paper P is transported by the first transport path 15 to form an image on the front surface, and is formed from the second transport path 70 to form the image on the back surface. This is a portion that becomes the head when it is transported to one transport path 15.

  Next, in step 9, negative determination is repeated until the paper P is detected by the sensor 74 (see FIG. 2) disposed between the transport roll 62 and the transport roll 63 in the second transport path 70. Then, the process proceeds to step 10. In Step 10, after the paper discharge roll 36 and the transport rolls 62, 63, 64 are rotated by a predetermined amount, the driving is stopped, and the paper P is transported to the second standby position X2 and stopped (see FIG. 2). Here, the second standby position X2 is a position where the trailing edge of the paper P is slightly upstream in the transport direction from the point where the second transport path 70 joins the first transport path 15 and faces the cooling fan 42. When the sheet P is further on the downstream side in the transport direction and the sheet P stops at the second standby position X2, the air blowing from the cooling fan 42 is blocked by the sheet P.

  Next, the process proceeds to step 11 shown in the flowchart of FIG. 5. In step 9, it is determined whether or not a predetermined time t1 has elapsed since the sheet P was detected by the sensor 74. If the determination is affirmative, step 12 is denied. Then, the process proceeds to step 14. In step 12, the transport rollers 62, 63, and 64 are reversely rotated by a predetermined amount to transport the paper P to the first standby position X1 and stop (see FIG. 3).

  Here, in the first standby position X1, the rear end portion of the paper P is on the upstream side in the transport direction from the position facing the cooling fan 42 of the second transport path 70, and the paper P is at the first standby position X1. When stopped, the air from the cooling fan 42 is not blocked by the paper P.

  Next, in step 13, the negative determination is repeated until the development of the image data is completed. On the other hand, in step 14, the negative determination is repeated until the development of the image data is completed, the process returns to step 11, and if affirmed, the process proceeds to step 15.

  In step 15, the transport rollers 62, 63, 64 are rotated forward, and the paper P is transported from the second transport path 70 to the first transport path 15. Next, in step 16, the negative determination is repeated until the paper P is detected by the sensor 72. In step 17, the transport path switching mechanism is operated, the first transport path 15 is opened at the branch point between the first transport path 15 and the second transport path 70, and the second transport path 70 is closed.

  Next, in step 18, the negative determination is repeated until a predetermined time t <b> 0 elapses after the paper P is detected by the sensor 72 in step 16. In step 19, the registration roll 21 is driven and the paper P is transported through the first transport path 15, and an image is formed on the back surface of the paper P and discharged. Then, the processing routine ends.

  In other words, in the present embodiment, when the time for which the paper P waits in the second transport path 70 becomes long, the paper P reaches the second upstream side in the transport direction from the position facing the cooling fan 42 of the second transport path 70. 1 Waits at the standby position X1. Accordingly, it is possible to prevent the air blown from the cooling fan 42 from being continuously blocked by the paper P in the second conveyance path 70 for a long time, and it is possible to suppress a decrease in the cooling effect inside the apparatus.

Further, the paper P is once transported from the position facing the cooling fan 42 of the second transport path 70 to the second standby position X2 on the downstream side in the transport direction, and then the standby time at the second standby position X2 is longer than a predetermined time. When it becomes longer, the vehicle moves backward from the second standby position X2 to the first standby position X1. As a result, when the standby time of the paper P in the second transport path 70 is short, the transport distance from the standby position of the paper P in the second transport path 70 to the first transport path 15 becomes short, and the paper P Since the time required to start image formation on the back side can be shortened, double-sided printing can be speeded up.
[Second Embodiment]
When a duplex printing job is received, steps 1 to 10 shown in the flowchart of FIG. 4 described above are executed, and then the process proceeds to step 100 shown in the flowchart of FIG. In step 100, it is determined whether the print mode selected by the user is a high-speed mode in which the print speed is prioritized over the image quality or a standard speed mode in which the image quality is prioritized over the print speed. If there is, the process proceeds to step 101, and if it is the high speed mode, the process proceeds to step 103.

  In step 101, it is determined whether or not a predetermined time t1 has elapsed since the paper P was detected by the sensor 74 in step 9, and if affirmative, the process proceeds to step 102, and if negative, the process proceeds to step 104. In step 102, the transport rollers 62, 63, and 64 are reversely rotated by a predetermined amount to transport and stop the paper P to the first standby position X1 (see FIG. 3).

  Next, in step 103, the negative determination is repeated until the development of the image data is completed. On the other hand, in step 104, the negative determination is repeated until the development of the image data is completed, the process returns to step 101, and if affirmed, the process proceeds to step 105.

  In step 105, the transport rollers 62, 63, 64 are rotated forward, and the paper P is transported from the second transport path 70 to the first transport path 15. Next, in step 106, the negative determination is repeated until the paper P is detected by the sensor 72. In step 107, the transport path switching mechanism is operated, the first transport path 15 is opened at the branch point between the first transport path 15 and the second transport path 70, and the second transport path 70 is closed.

  Next, in step 108, the negative determination is repeated until the predetermined time t0 elapses after the paper P is detected by the sensor 72 in step 106. When the determination is affirmative, the routine proceeds to step 109. In step 109, the registration roll 21 is driven to transport the paper P through the first transport path 15, and an image is formed on the back surface of the paper P and discharged. Then, the processing routine ends.

In other words, in the present embodiment, when the printing speed is required by the user rather than the image quality, the conveyance distance from the standby position in the second conveyance path 70 to the first conveyance path 15 is shortened to reduce the back surface of the paper P. If the image quality is required rather than the printing speed by the user, the time from the start of image formation to the image is reduced, and the air from the cooling fan 42 is blown on the paper P in the second conveyance path 70 for a long time. The effect of cooling the inside of the apparatus is improved so as not to keep blocking, and the operation of the image forming unit 16 is stabilized.
[Third embodiment]
When a duplex print job is received, steps 1 to 10 shown in the flowchart of FIG. 4 are executed, and then the process proceeds to step 200 shown in the flowchart of FIG. In step 200, it is determined whether the image formed on the back surface of the paper P is multicolor or single color. If it is multicolor, the process proceeds to step 201, and if it is single color, the process proceeds to step 202.

  In step 201, the transport rollers 62, 63, and 64 are rotated in reverse by a predetermined amount to transport the paper P to the first standby position X1 and stop (see FIG. 3). Next, in step 202, the negative determination is repeated until the development of the image data is completed.

  In step 203, the transport rollers 62, 63, 64 are rotated forward and the paper P is transported from the second transport path 70 to the first transport path 15. Next, in step 204, the negative determination is repeated until the paper P is detected by the sensor 72. If the determination is affirmative, the process proceeds to step 205. In step 205, the transport path switching mechanism is operated, the first transport path 15 is opened at the branch point between the first transport path 15 and the second transport path 70, and the second transport path 70 is closed.

  Next, in step 206, the negative determination is repeated until the predetermined time t0 elapses after the paper P is detected by the sensor 72 in step 204. If the determination is affirmative, the process proceeds to step 207. In step 207, the registration roll 21 is driven and the paper P is transported through the first transport path 15, and an image is formed on the back surface of the paper P and discharged. Then, the processing routine ends.

  That is, when the image formed on the back surface of the paper P by the image forming unit 16 is monochromatic, the image data capacity is small, and the waiting time of the paper P in the second transport path 70 is shortened. Since the cooling effect inside the apparatus does not deteriorate so much even if the air from the cooling fan 42 is blocked, the paper P is kept waiting at the second standby position X2 until image formation on the back surface of the paper P is started. Reduce the time required for. If the image formed on the back side of the paper P by the image forming unit 16 is multicolored, the amount of image data is large, and the standby time of the paper P in the second conveyance path 70 becomes long. When the air from the cooling fan 42 continues to be blocked, the cooling effect inside the apparatus is greatly reduced. Therefore, the paper P is kept waiting at the first standby position X1, and the air from the cooling fan 42 is continuously blocked for a long time. Do not.

As a result, when the image data formed on the back surface of the paper P by the image forming unit 16 is rapidly developed, the paper P can be transported to the first transport path 15 without being delayed. In addition, when the development of the image data formed on the back surface of the paper P by the image forming unit 16 is slow, although the paper P is transported to the first transport path 15 somewhat, the cooling effect inside the apparatus is reduced. The image formation by the image forming unit 16 can be stabilized.
[Fourth embodiment]
When a duplex print job is received, steps 1 to 10 shown in the flowchart of FIG. 4 are executed, and then the process proceeds to step 300 shown in the flowchart of FIG. In step 300, it is determined whether or not the size of the paper P is equal to or larger than a predetermined size. If the result is affirmative, the process proceeds to step 301. If the result is negative, the process proceeds to step 302.

  In step 301, the transport rollers 62, 63, and 64 are reversely rotated by a predetermined amount, and the paper P is transported to the first standby position X1 and stopped (see FIG. 3). Next, in step 302, the negative determination is repeated until the development of the image data is completed.

  In step 303, the transport rollers 62, 63 and 64 are rotated forward, and the paper P is transported from the second transport path 70 to the first transport path 15. Next, in step 304, negative determination is repeated until the paper P is detected by the sensor 72, and if affirmed, the process proceeds to step 305. In step 305, the transport path switching mechanism is operated to open the first transport path 15 at the branch point between the first transport path 15 and the second transport path 70 and close the second transport path 70.

  Next, in step 306, the negative determination is repeated until the predetermined time t0 elapses after the paper P is detected by the sensor 72 in step 304. If the determination is affirmative, the process proceeds to step 307. In step 307, the registration roll 21 is driven and the paper P is transported through the first transport path 15, and an image is formed on the back surface of the paper P and discharged. Then, the processing routine ends.

  That is, when the size of the paper P is small, the image data capacity is small, and the standby time of the paper P in the second transport path 70 is shortened. During this short time, the air from the cooling fan 42 is blocked. However, since the cooling effect inside the apparatus does not decrease so much, the paper P is put on standby at the second standby position X2, and the time required until image formation on the back surface of the paper P is started is shortened. Further, when the size of the paper P is large, the amount of image data is large, and the waiting time of the paper P in the second transport path 70 becomes long. During this long time, the air blowing from the cooling fan 42 continues to be blocked. Since the cooling effect inside the apparatus is greatly reduced, the paper P is kept waiting at the first standby position X1 so that the air blown from the cooling fan 42 is not blocked for a long time.

As a result, when the image data formed on the back surface of the paper P by the image forming hand 16 is rapidly developed, the paper P can be transported to the first transport path 15 without delay. In addition, when the development of the image data formed on the back surface of the paper P by the image forming hand 16 is slow, although the transport of the paper P to the first transport path 15 is somewhat delayed, the cooling effect inside the apparatus is reduced. The image formation by the image forming unit 16 can be stabilized.
[Fifth Embodiment]
When a duplex print job is received, steps 1 to 10 shown in the flowchart of FIG. 4 described above are executed, and then the process proceeds to step 400 shown in the flowchart of FIG. In step 400, it is determined whether the number of prints is N or more. If the result is affirmative, the process proceeds to step 401, and if the result is negative, the process proceeds to step 402.

  In step 401, the transport rolls 62, 63, and 64 are reversely rotated by a predetermined amount to transport the paper P to the first standby position X1 and stop (see FIG. 3). Next, in step 402, the negative determination is repeated until the development of the image data is completed.

  In step 403, the transport rollers 62, 63, 64 are rotated forward and the paper P is transported from the second transport path 70 to the first transport path 15. Next, in step 404, the negative determination is repeated until the paper P is detected by the sensor 72. If the determination is affirmative, the process proceeds to step 405. In step 405, the transport path switching mechanism is operated, the first transport path 15 is opened at the branch point between the first transport path 15 and the second transport path 70, and the second transport path 70 is closed.

  Next, in step 406, the negative determination is repeated until the predetermined time t0 elapses after the paper P is detected by the sensor 72 in step 404. If the determination is affirmative, the process proceeds to step 407. In step 407, the registration roll 21 is driven and the paper P is transported through the first transport path 15, and an image is formed on the back surface of the paper P and discharged. Then, the processing routine ends.

  That is, when the number of prints is small, the time required for the image forming unit 16 to form an image is short, and the temperature inside the apparatus does not rise so much. Therefore, the paper P is put on standby at the second standby position X2, and the back surface of the paper P The time required until image formation is started is shortened. When the number of prints is large, the image forming unit 16 forms an image continuously for a long time, so that the temperature rise inside the apparatus increases. Therefore, the sheet P is kept waiting at the first standby position X1 and cooled. The air from the fan 42 should not be blocked for a long time.

As a result, the printing speed can be increased when the temperature rise inside the apparatus is small, and the cooling effect inside the apparatus can be improved when the temperature rise inside the apparatus is large.
[Sixth Embodiment]
When a duplex print job is received, Steps 1 to 10 shown in the flowchart of FIG. 4 are executed, and then the process proceeds to Step 500 shown in the flowchart of FIG. In step 500, it is determined whether or not the environmental temperature of the apparatus detected by the temperature sensor 78 (see FIGS. 1 to 3) installed on the upper part of the image forming apparatus main body 12 is equal to or higher than T1. Proceed to step 501;

  In step 501, the transport rollers 62, 63, and 64 are reversely rotated by a predetermined amount to transport the paper P to the first standby position X1 and stop (see FIG. 3). Next, in step 502, the negative determination is repeated until the development of the image data is completed, and if affirmative, the process proceeds to step 503.

  In step 503, the transport rollers 62, 63, 64 are rotated forward and the paper P is transported from the second transport path 70 to the first transport path 15. Next, in step 504, the negative determination is repeated until the paper P is detected by the sensor 72. If the determination is affirmative, the process proceeds to step 505. In step 505, the transport path switching mechanism is operated to open the first transport path 15 at the branch point between the first transport path 15 and the second transport path 70 and close the second transport path 70.

  Next, in step 506, the negative determination is repeated until the predetermined time t0 has elapsed after the paper P is detected by the sensor 72 in step 504. If the determination is affirmative, the process proceeds to step 507. In step 507, the registration roll 21 is driven and the paper P is transported through the first transport path 15, and an image is formed on the back surface of the paper P and discharged. Then, the processing routine ends.

  That is, when the environmental temperature of the apparatus is low, the temperature rise inside the apparatus does not increase so much, so that the paper P is waited at the second standby position X2 and image formation on the back surface of the paper P is started. Reduce the time required. Further, when the environmental temperature of the apparatus is high, the temperature rise inside the apparatus becomes large. Therefore, the sheet P is made to wait at the first standby position X1, and the air blown from the cooling fan 42 is conveyed to the sheet in the second conveyance path 70. Do not continue to be blocked by P for a long time.

As a result, the printing speed can be increased when the temperature rise inside the apparatus is small, and the cooling effect inside the apparatus can be improved when the temperature rise inside the apparatus is large.
[Seventh embodiment]
When a duplex printing job is received, steps 1 to 10 shown in the flowchart of FIG. 4 described above are executed, and then the process proceeds to step 600 shown in the flowchart of FIG. In step 600, it is determined whether or not the temperature of the surface of the heating roll 34A detected by the temperature sensor 76 (see FIGS. 1 to 3) such as a thermistor in contact with the surface of the heating roll 34A is equal to or higher than T2. If the determination is affirmative, the process proceeds to step 601, and if the determination is negative, the process proceeds to step 602.

  In step 601, the transport rollers 62, 63, and 64 are reversely rotated by a predetermined amount to transport the paper P to the first standby position X1 and stop (see FIG. 3). Next, in step 602, the negative determination is repeated until the development of the image data is completed, and if affirmed, the process proceeds to step 603.

  In step 603, the transport rollers 62, 63, 64 are rotated forward and the paper P is transported from the second transport path 70 to the first transport path 15. Next, in step 604, the negative determination is repeated until the paper P is detected by the sensor 72. If the determination is affirmative, the process proceeds to step 605. In step 605, the conveyance path switching mechanism is operated, the first conveyance path 15 is opened at the branch point between the first conveyance path 15 and the second conveyance path 70, and the second conveyance path 70 is closed.

  Next, in step 606, the negative determination is repeated until the predetermined time t0 has elapsed after the paper P is detected by the sensor 72 in step 604. In step 607, the registration roll 21 is driven and the paper P is transported through the first transport path 15, and an image is formed on the back surface of the paper P and discharged. Then, the processing routine ends.

  That is, when the temperature of the surface of the heating roll 34A is low, the temperature rise inside the apparatus does not increase so much, so that the sheet P is waited at the second standby position X2 and image formation on the back surface of the sheet P is started. Reduce the time required until Further, when the temperature of the surface of the heating roll 34A is high, the temperature rise inside the apparatus increases, and the temperature difference between the position of the heating roll 34A where the paper P passes and the position where the paper P does not pass increases. Therefore, the air blown by the cooling fan 42 is not continuously blocked by the paper P in the second conveyance path 70 for a long period of time, and the deterioration of the cooling effect inside the apparatus is suppressed, and the temperature difference in the heating roll 34A is suppressed. Suppresses the increase of

  As described above, in the first to seventh embodiments, the image forming apparatus according to the present invention has been described by taking an image forming apparatus using an electrophotographic method as an example. The present invention can also be applied to other image forming apparatuses.

  Further, the sheet is not limited to paper, and includes a substrate on which a display filter, a wiring pattern, and the like are formed.

  Further, it is not essential to convey the sheet to the second standby position before waiting at the first standby position, and the sheet may be stopped at the first standby position from the beginning.

1 is a side view schematically showing an image forming apparatus main body according to an embodiment of the present invention. FIG. 2 is a side view illustrating an outline of an image forming apparatus main body and a duplex conveyance unit according to an embodiment of the present invention. FIG. 2 is a side view illustrating an outline of an image forming apparatus main body and a duplex conveyance unit according to an embodiment of the present invention. 4 is a flowchart for explaining a first embodiment of a sheet conveyance control method in the image forming apparatus of FIGS. 1 to 3; 4 is a flowchart for explaining a first embodiment of a sheet conveyance control method in the image forming apparatus of FIGS. 1 to 3; 4 is a flowchart for explaining a second embodiment of a sheet conveyance control method in the image forming apparatus of FIGS. 1 to 3; 6 is a flowchart for explaining a third embodiment of a sheet conveyance control method in the image forming apparatus of FIGS. 1 to 3; 10 is a flowchart for explaining a fourth embodiment of a sheet conveyance control method in the image forming apparatus of FIGS. 1 to 3; 10 is a flowchart for explaining a fifth embodiment of a paper conveyance control method in the image forming apparatus of FIGS. 1 to 3; 10 is a flowchart for explaining a sixth embodiment of a paper conveyance control method in the image forming apparatus of FIGS. 1 to 3; 10 is a flowchart for explaining a seventh embodiment of a sheet conveyance control method in the image forming apparatus of FIGS. 1 to 3;

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 13 Paper feed tray (sheet accommodating part)
14 Paper feed tray (sheet storage)
15 First transport path 16 Image forming unit (image forming means)
20 Paper feed roll (first transport means)
21 resist roll (first conveying means)
23 Paper feed roll (first transport means)
25 Transport roll (first transport means)
42 Cooling fan (air blowing means)
62 Conveying roll (second conveying means)
63 Conveying roll (second conveying means)
64 Conveying roll (second conveying means)
70 Second transport path 76 Temperature sensor (fixing temperature detection means)
78 Temperature sensor (environmental temperature detection means)
100 control unit (first control means, second control means)
P Paper (sheet)

Claims (10)

A sheet accommodating portion for accommodating the sheet;
A first conveyance path extending from the sheet storage unit to the outside of the apparatus;
First conveying means for conveying a sheet in the first conveying path;
Image forming means for forming an image on a sheet conveyed on the first conveying path by the first conveying means;
A second transport path that branches from the downstream side in the transport direction from the image forming unit of the first transport path and joins the upstream side in the transport direction from the image forming unit of the first transport path;
A second conveying means for conveying the sheet from the second conveying path to the first conveying path with the rear end side as the head and turning the sheet upside down;
A blower unit provided between the first conveyance path and the second conveyance path, for blowing air from the first conveyance path side to the second conveyance path side to cool the inside of the apparatus;
First control means for controlling the second conveying means so that the sheet waits in the second conveying path until image formation on the back surface of the sheet can be started by the image forming means;
An image forming apparatus comprising:
When the waiting time for the sheet to stand by in the second conveyance path is longer than a predetermined time, the first control unit is configured to move the sheet upstream of the position in the conveyance direction from the position facing the air blowing unit in the second conveyance path. An image forming apparatus, wherein the second conveying unit is controlled to stand by at one standby position.   The first control means, once the sheet is conveyed to a second standby position on the downstream side in the conveyance direction from a position facing the air blowing means of the second conveyance path, and when the standby time becomes longer than the predetermined time, 2. The image forming apparatus according to claim 1, wherein the second transport unit is controlled so as to be fed back from the second standby position to the first standby position. A sheet accommodating portion for accommodating the sheet;
A first conveyance path extending out of the apparatus from the sheet storage unit;
First conveying means for conveying a sheet in the first conveying path;
Image forming means for forming an image on a sheet conveyed on the first conveying path by the first conveying means;
A second transport path that branches from the downstream side in the transport direction from the image forming unit of the first transport path and joins the upstream side in the transport direction from the image forming unit of the first transport path;
A second conveying means for conveying the sheet from the second conveying path to the first conveying path with the rear end side as the head and turning the sheet upside down;
A blower unit provided between the first conveyance path and the second conveyance path, for blowing air from the first conveyance path side to the second conveyance path side to cool the inside of the apparatus;
Second control means for controlling the second conveying means so that the sheet waits in the second conveying path until image formation on the back surface of the sheet by the image forming means can be started;
An image forming apparatus comprising:
The second control unit is configured such that the sheet is transported in a transport direction from a first standby position on the upstream side in the transport direction from a position facing the air blowing unit in the second transport path or a position facing the air blower in the second transport path. An image forming apparatus, wherein the second transport unit is controlled to stand by at a second standby position on the downstream side.   When the high-speed mode giving priority to the print speed is selected, the second control unit waits at the second standby position, and when the standard speed mode not giving priority to the print speed is selected, the sheet is The image forming apparatus according to claim 3, wherein the second conveying unit is controlled to stand by at a first standby position.   The second control unit waits at the second standby position when the volume of image data formed on the back side of the sheet by the image forming unit is less than a predetermined amount, and the image forming unit is on the back side of the sheet. 4. The image formation according to claim 3, wherein when the volume of image data to be formed is a predetermined amount or more, the second conveying unit is controlled so that the sheet stands by at the first standby position. apparatus.   When the image formed by the image forming unit on the back side of the sheet is a single color, the second control unit waits at the second standby position, and the image forming unit forms many images on the back side of the sheet. 4. The image forming apparatus according to claim 3, wherein when the color is set, the second conveying unit is controlled so that the sheet waits at the first standby position. 5.   The second control means waits at the second standby position when the sheet size is less than a predetermined size, and when the sheet size is equal to or larger than the predetermined size, the sheet waits at the first standby mode. The image forming apparatus according to claim 3, wherein the second conveying unit is controlled to stand by at a position.   The second control unit waits at the second standby position when the number of prints is less than the predetermined number, and waits at the first standby position when the number of prints is equal to or greater than the predetermined number. The image forming apparatus according to claim 3, wherein the second conveying unit is controlled. Having environmental temperature detection means for detecting the environmental temperature of the device;
When the environmental temperature detected by the environmental temperature detecting means is less than a predetermined temperature, the second control means waits at the second standby position, and the environmental temperature detected by the environmental temperature detecting means is predetermined. The image forming apparatus according to claim 3, wherein when the temperature is equal to or higher than the temperature, the second conveying unit is controlled so that the sheet stands by at the first standby position. The image forming means is
An image carrier that is provided facing the first conveyance path and carries a toner image;
A transfer that faces the image carrier with the first conveyance path in between and transfers a toner image carried on the image carrier onto a sheet conveyed on the first conveyance path by the first conveyance unit. Means,
A fixing unit provided on the downstream side in the conveyance direction from the image carrier and the transfer unit in the first conveyance path, and fixes the toner image transferred to the sheet to the sheet;
With
A fixing temperature detecting means for detecting the temperature of the fixing means;
The second control unit waits at the second standby position when the temperature of the fixing unit detected by the fixing temperature detecting unit is lower than a predetermined temperature, and the second control unit detects the fixing unit detected by the fixing temperature detecting unit. 4. The image forming apparatus according to claim 3, wherein when the temperature of the fixing unit is equal to or higher than a predetermined temperature, the second conveying unit is controlled so that the sheet stands by at the first standby position.

Images