JP2008003430A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus designed such that even if dew condensation occurs on a conveyance guide or a conveyance roller disposed downstream of a fixing apparatus as a result of the installation of the image forming apparatus in a low temperature place, image failure arising during both-side printing is prevented without adding a fan, a duct, and so on. <P>SOLUTION: When both-sided printing is designated and the temperature and humidity of the interior of the body 1 of the apparatus and the temperature of a fixing section 7, detected by an apparatus interior temperature humidity sensor 33 and fixing temperature sensor 34 prior to the start of an image forming operation, are within the range of conditions for causing dew condensation, which are recorded in a ROM 32, paper with an image formed on one side of it is once stopped before the paper is switched back on the downstream side of the fixing section 7, and the switch back operation is started after a predetermined time elapses. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine and a printer, and more particularly to an image forming apparatus capable of forming images on both sides of a sheet.

  2. Description of the Related Art Conventionally, image forming apparatuses such as copiers and printers that can print an image on both sides of a sheet are known. An image forming apparatus having such a double-sided printing function has an image on one side. There is a configuration in which the printed paper is reversed downstream of the fixing device and conveyed to the double-sided conveyance path, sent again to the image forming unit via the double-sided conveyance path, and an image is printed on the remaining one side. .

  By the way, in an image forming apparatus using an electrophotographic system, it is generally composed of a fixing roller that has a heater inside and is driven to rotate, and a pressure roller that is driven to rotate while being in pressure contact with the fixing roller. A fixing device that melts and fixes the toner to the sheet material by sandwiching the sheet material with the toner between the fixing roller and the pressure roller and applying heat and pressure is used. In the case where water is contained, the water contained in the paper is evaporated by being heated at the time of image fixing, and is discharged from the fixing device as water vapor.

  Here, when the image forming apparatus is installed at a low temperature, the water vapor discharged from the fixing device as described above is cooled by a conveyance guide or a conveyance roller provided on the downstream side of the fixing device in the sheet conveyance direction. Condensation may occur, and in such a case, the paper may get wet due to the condensed water droplets, which may cause trouble in transporting the paper such as jam and skew. In particular, in an image forming apparatus having a double-sided printing function as described above, a sheet wetted by water droplets during double-sided printing is re-conveyed to the image forming unit, which may cause image defects.

In view of this, a method for preventing condensation on the downstream side of the sheet conveying direction of the fixing device has been proposed. For example, in Patent Document 1, a duct connected to the duct portion of the suction device is arranged along the fixing device. By installing the suction fan provided in the suction device, the hot air generated in the fixing device is blown through the duct to the conveyance guide provided downstream in the paper conveyance direction of the fixing device, and provided downstream of the fixing device. An image forming apparatus that prevents condensation on the transport guide is disclosed.
JP 2001-34147 A

  However, since the image forming apparatus described in Patent Document 1 requires a space for installing a suction fan and a duct, it is not preferable to install these from the viewpoint of miniaturization of the image forming apparatus. From the viewpoint of power consumption, it is desirable that these are not installed.

  In view of the above problems, the present invention provides a fan, a duct, and the like separately even when the image forming apparatus is installed at a low temperature and condensation occurs on a conveyance guide or a conveyance roller provided downstream of the fixing device. An object of the present invention is to provide an image forming apparatus capable of preventing image defects during double-sided printing.

  In order to achieve the above object, the present invention provides a sheet feeding unit for stacking sheets, a discharge unit provided above the sheet feeding unit, a sheet conveyance path connecting the discharge unit and the sheet feeding unit, An image forming unit, a fixing unit, and a switchback roller, which are sequentially arranged from the upstream side in the sheet conveying direction along the sheet conveying path, and the sheet switched back by the switchback roller are conveyed again upstream of the image forming unit. A double-sided printing transport path, and a control unit that controls the transport of paper inside the apparatus, and executes a single-sided printing mode for forming an image on one side of the paper and a double-sided printing mode for forming an image on both sides of the paper In a possible image forming apparatus, there is provided a dew condition detecting unit that detects whether or not the inside of the apparatus is in a dew generation condition, and the control unit is provided with the dew condition detecting unit before executing the duplex printing mode. What if the condensation condition is detected, the switchback roller temporarily stop the paper before the switch back operation by, it is characterized by resuming the switchback operation after a predetermined time has elapsed.

  According to the present invention, in the image forming apparatus having the above configuration, in the double-sided printing mode, the control unit is configured to detect a dew condition before the paper is stopped before the switchback operation and before the predetermined time elapses. The switchback operation is resumed when the temperature inside the main body exceeds a predetermined temperature.

  According to the present invention, in the image forming apparatus having the above-described configuration, a sheet feeding unit for stacking sheets, a discharge unit provided above the sheet feeding unit, and a sheet conveyance path connecting the discharge unit and the sheet feeding unit And an image forming unit, a fixing unit, and a switchback roller, which are sequentially arranged along the paper transport path from the upstream side in the paper transport direction, and the paper switched back by the switchback roller to the upstream side of the image forming unit. A single-sided printing mode for forming an image on one side of the paper, and a double-sided printing mode for forming an image on both sides of the paper. In the image forming apparatus capable of executing the dew condition, a dew condition detecting unit that detects whether or not the inside of the apparatus is in a dew generation condition is provided, and the control unit includes the dew condition before the duplex printing mode is executed. When the dew condensation condition is detected by the detection means, the paper is temporarily stopped before the switchback operation by the switchback roller, and the switchback operation is resumed when the temperature inside the apparatus becomes a predetermined temperature or more. It is a feature.

  According to the present invention, in the image forming apparatus having the above-described configuration, the dew condensation condition is determined based on a temperature of a fixing unit, and the dew condensation condition detecting unit is a fixing temperature sensor.

  According to the present invention, in the image forming apparatus having the above-described configuration, the dew condensation condition is determined based on temperature and humidity in the apparatus main body, and the dew condition detection unit is an in-machine temperature and humidity sensor.

  According to the first configuration of the present invention, when an image forming operation is performed under the dew condensation condition, when an image is formed on one side of the sheet, moisture contained in the sheet evaporates and dew condensation occurs in the apparatus main body. The paper may get wet due to condensed water droplets, but by temporarily stopping the paper before the switchback operation and starting the switchback operation after a predetermined time has elapsed, the temperature inside the device body during the paper stop time The moisture in the apparatus main body can be removed by the rising, and the moisture of the paper can be evaporated even when the paper is wetted by the condensed water droplets, so that it is possible to prevent image defects due to the wetness of the paper.

  According to the second configuration of the present invention, in the image forming apparatus having the first configuration, if the temperature in the apparatus main body is equal to or higher than a predetermined temperature, the moisture in the apparatus main body is removed by the temperature increase in the apparatus main body. Since it can be removed, wetting of the paper can be prevented and image defects due to wetting of the paper can be prevented. In such a case, the switchback operation starts even if the predetermined time has not elapsed. Therefore, the time required for the image forming operation can be shortened.

  According to the third configuration of the present invention, the apparatus main body is configured such that the paper is temporarily stopped before the switchback operation, and the switchback operation is started when the temperature in the apparatus main body is equal to or higher than a predetermined temperature. Since the water in the apparatus main body can be surely removed by the temperature rise inside, the paper can be prevented from getting wet, and the image defect due to the paper getting wet can be more effectively prevented.

  According to the fourth configuration of the present invention, in the image forming apparatus having any one of the first to third configurations, the dew condensation condition is determined based on the temperature of the fixing unit, and the dew condition sensor is used as a dew condition sensor. Because it is possible to accurately determine whether or not it is a cold start, if the duplex printing mode is specified at the cold start where condensation tends to occur, the paper is surely stopped before the switchback operation. Image defects due to paper wetting can be prevented.

  According to the fifth configuration of the present invention, in the image forming apparatus having any one of the first to third configurations, the dew condensation condition is determined based on the temperature and humidity in the apparatus main body, and the dew condition is detected in the apparatus. By using the temperature / humidity sensor, it is possible to determine whether to temporarily stop the paper before the switchback operation according to the usage environment such as temperature and humidity when using the device. Image defects can be prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, the overall configuration of the image forming apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram illustrating the overall configuration of an image forming apparatus according to the present invention, and the right side is illustrated as the front side of the image forming apparatus. Here, in this embodiment, a printer is illustrated as an example of an image forming apparatus. However, it goes without saying that the present invention can be applied to a copying machine other than a printer, for example, a copying machine.

  In the image forming apparatus shown in FIG. 1, a sheet feeding unit 2 such as a sheet feeding cassette for storing stacked sheets P is provided at the lower part of the apparatus main body 1. On the front side of the paper feeding unit 2, separation feeding means 3 for feeding the stacked paper P one by one from the uppermost paper is provided. A paper transport path R1 for transporting the paper fed from the paper feed unit 2 to the rear of the apparatus main body 1 is formed at the upper part of the separating and feeding means 3, and the paper is transported along the paper transport path R1. A reversing roller 4, a registration roller pair 5, an image forming unit 6, and a fixing unit 7 are arranged in order from the upstream in the transport direction.

  The image forming unit 6 is provided with a photosensitive drum 8 which is an electrophotographic photosensitive member. Around the photosensitive drum 8, a charging unit 9 for charging the photosensitive drum 8 and the photosensitive drum 8 are provided. Developing means 10 for developing the electrostatic latent image formed on the photosensitive drum 8, transfer means 11 for transferring the toner image on the photosensitive drum 8 to a sheet, and cleaning for removing residual toner remaining on the surface of the photosensitive drum 8. Means 12 are provided.

  Further, a scanner unit 13 that irradiates information light based on input image information onto the photosensitive drum 8 is disposed above the photosensitive drum 8. The fixing unit 7 includes a fixing roller 14 having a built-in heat source such as a halogen lamp, and a pressure roller 15 that presses against the fixing roller 14 and forms a nip through which a sheet passes.

  A downstream end portion of the paper transport path R1 is provided with a paper discharge path R2 that transports the paper after image fixing upward and discharges it to the discharge tray 16 so as to be continuous therewith, and the paper discharge path R2 A conveying roller pair 17 is disposed along the discharge path, and a discharge roller pair 18 is disposed at the downstream end of the sheet discharge path R2. In addition, the transport roller pair 17 also serves as a switchback roller when performing double-sided printing, and a sheet switched back by the transport roller pair 17 at the upstream end of the paper discharge path R2 is continuous. A double-sided printing conveyance path R3 is provided for conveying the image to the image forming unit 6 again.

  The double-sided printing conveyance path R3 extends downward from the apparatus main body 1 and further to the front side, and its downstream end is formed so as to merge with the paper conveyance path R1 upstream of the reverse roller 4. A duplex transport roller pair 19, 20, 21, and 22 is arranged in this order from the upstream in the sheet transport direction along the duplex printing transport path R3.

  Regarding the image forming operation by the image forming apparatus configured as described above, first, the operation during single-sided printing (single-sided printing mode) will be described. When the start of image formation is input by the user, information light based on image information is irradiated from the scanner unit 13 onto the photosensitive drum 8 whose surface has been charged by the charging unit 9. An electrostatic latent image is formed.

  The electrostatic latent image is developed by the developing unit 10 to form a toner image on the photosensitive drum 8. At this time, the sheet P fed one by one from the sheet feeding unit 2 by the separation feeding unit 3 and conveyed by the reversing roller 4 is synchronized with the formation of the toner image by the registration roller pair 5 in the image forming unit 6. The toner image formed on the photosensitive drum 8 is transferred to the paper P by the transfer unit 11.

  The sheet P on which the toner image has been transferred is conveyed to the fixing unit 7 along the sheet conveyance path R1, and is heated and pressed by the fixing roller 14 and the pressure roller 15 so that the toner image is applied to the surface of the sheet P. It is fixed. The paper on which the image is formed is transported from the paper transport path R1 to the paper discharge path R2, and is discharged to the discharge tray 16 by the transport roller pair 17 and the discharge roller pair 18. Note that the toner remaining on the surface of the photosensitive drum 8 after the transfer is removed by the cleaning means 12.

  Next, the operation during double-sided printing (double-sided printing mode) will be described. When the user inputs the start of double-sided image formation, first, an image is formed on the surface of the paper in the same way as during single-sided printing described above. The toner remaining on the surface of the photosensitive drum 8 is removed by the cleaning unit 12 and the photosensitive drum 8 is charged again by the charging unit 9. The paper on which single-sided printing has been completed is discharged from the paper transport path R1 through the paper discharge path R2 to the discharge tray 16. However, in the case of duplex printing, the paper is transported when the trailing edge of the paper enters the paper discharge path R2. The rotation directions of the roller pair 17 and the discharge roller pair 18 are reversed, and the sheet is pulled back into the apparatus main body 1. The pulled paper is not returned to the paper transport path R1, but is transported to the duplex printing transport path R3.

  Then, the sheet transported to the duplex printing transport path R3 is changed downstream in the transport direction downstream of the duplex transport roller pair 19 and further transported by the duplex transport roller pairs 20, 21, and 22. After returning to the upstream side of the reversing roller 4 in the sheet conveyance path R1 and forming an image on the remaining back surface in the same manner as in the above-described single-sided printing, the sheet is transferred to the discharge tray 16 via the sheet conveyance path R1 and the sheet discharge path R2. Discharged.

  Next, the configuration of the control system and the like of the image forming apparatus according to the present invention will be described with reference to FIG. FIG. 2 is a block diagram showing the configuration of the control system of the image forming apparatus according to the present invention. The image forming apparatus 1 includes a main body control unit 30. The main body control unit 30 includes an interface 31, a ROM 32, an in-machine temperature / humidity sensor 33, a fixing temperature sensor 34, an image forming control circuit 35, and a fixing control circuit. 36 and a motor control circuit 37 are connected.

  The interface 31 performs data transmission / reception with a host device such as a personal computer (not shown), for example, and the ROM 32 operates as a program for operating the image forming unit 6 and the fixing unit 7 to perform image formation, which will be described later. As described above, during double-sided printing, the dew condensation condition used for determining whether or not to temporarily stop the paper before switchback and the start condition of the switchback operation of the temporarily stopped paper are stored.

  Here, the dew condensation condition means that when an image forming operation is performed under the condition, the moisture contained in the paper used for image formation is discharged from the fixing unit 7 as water vapor in the apparatus main body 1. In this embodiment, the temperature is determined based on the temperature and humidity in the apparatus main body 1 and the temperature of the fixing unit 7, and the apparatus main body 1 is in a predetermined temperature and humidity range. The case where the temperature of the fixing unit 7 is less than 60 ° C. is defined as the dew condensation condition. Note that the temperature and humidity in the apparatus main body 1 and the temperature of the fixing unit 7 set as the dew condensation conditions can be changed as appropriate.

  The in-machine temperature / humidity sensor 33 and the fixing temperature sensor 34 are used as a dew condition detecting unit for detecting the dew condition. The in-machine temperature / humidity sensor 33 detects the temperature and humidity in the apparatus main body 1. The fixing temperature sensor 34 detects the temperature of the fixing unit 7, and each detection result is output to the main body control unit 30 as needed. The image formation control circuit 35 and the fixing control circuit 36 operate the image forming unit 6 and the fixing unit 7 in accordance with output signals from the main body control unit 30, respectively.

  The motor control circuit 37 drives the paper transport motor 38 based on the output signal from the main body control unit 30, and the paper transport motor 38 is driven to drive the registration roller pair 5 and the discharge roller pair 18 (FIG. 1). And a sheet conveying roller such as the conveying roller pair 17 is rotated to convey the sheet to the image forming unit 6 and the fixing unit 7, and the sheet on which the image is formed is discharged to the discharge tray 16. Further, at the time of duplex printing, the sheet is switched back downstream of the fixing unit 7 and conveyed again to the image forming apparatus 6 and the fixing unit 7.

  The main body control unit 30 outputs control signals to various control circuits based on the image data received via the interface 31. When data is input from the interface 31, the program stored in the ROM 32 is stored. Accordingly, control signals are output to the image forming control circuit 35, the fixing control circuit 36, and the motor control circuit 37, and the image forming operation is performed by controlling the respective components such as the image forming unit 6, the fixing unit 7 and the paper conveying motor 38. Execute.

  Here, in the present embodiment, when duplex printing is designated, the temperature and humidity in the apparatus main body 1 detected by the in-machine temperature and humidity sensor 33 and the fixing temperature sensor 34 before the start of the image forming operation, and the fixing unit 7. The temperature is compared with the condensation condition recorded in the ROM 32, and when the condensation condition is detected, the sheet on which the image is formed on one side is temporarily stopped before switching back downstream of the fixing unit 7 for a predetermined time. The switchback operation is started after the passage, and the ROM 32 stores a stop time of the paper P as a start condition of the switchback operation. The stop time of the paper P can be changed as appropriate according to the specifications of the apparatus main body 1. However, if the stop time is too long, the user may misidentify as a paper jam. For this reason, it is preferable to set the stop time of the paper P within 3 minutes at the longest.

  FIG. 3 is a flowchart showing the operation of the image forming apparatus according to the first embodiment of the present invention. With reference to FIGS. 1 and 2, the image recording process will be described according to the steps in FIG.

  First, when image formation is started by the user (step S1), it is determined whether or not the double-sided printing mode is set (step S2), and when the single-sided printing mode is designated instead of the double-sided printing mode. The image forming operation is immediately started, and the paper P fed from the paper feeding unit 2 is transported to the image forming unit 6 and the fixing unit 7 on the paper transporting path R1 and received via the interface 31. Based on the above, an image is formed on one side of the paper P (step S3), conveyed on the paper discharge path R2 by the conveyance roller pair 17, and discharged to the discharge tray 16 by the discharge roller pair 18 (step S10).

  On the other hand, when the duplex printing mode is designated in step S2, the main body control unit 30 detects the apparatus detected by the in-machine temperature / humidity sensor 33 and the fixing temperature sensor 34, which are dew condensation condition detection means, before the image forming operation is started. The temperature and humidity in the main body 1 and the temperature of the fixing unit 7 are compared with the set values of the temperature and humidity in the apparatus main body 1 and the temperature of the fixing unit 7 stored in the ROM 32 as the dew condensation conditions (step S4). Is within the range of the dew condensation condition (step S5).

  When the determination as to whether or not the dew condensation condition is satisfied, the main body control unit 30 starts an image forming operation. Here, at least one of the temperature and humidity in the apparatus main body 1 and the temperature of the fixing unit 7 is the dew condensation condition. If it is within the range, after the image is formed on one side of the paper as in the single-sided printing mode (step S6), the paper P is moved to its position before the switchback operation by the transport roller pair 17 is started. Is temporarily stopped (step S7).

  Then, the main body control unit 30 stops the paper P according to the stop time stored in the ROM 32, and after a predetermined time has passed, outputs a control signal to the motor control circuit 37 to reverse the transport roller pair 17 and start the switchback operation. (Step S8). The switched-back paper P is transported on the duplex printing transport path R3 by the duplex transport roller pairs 19 to 22, transported again to the image forming unit 6 and the fixing unit 7, and received through the interface 31. Based on the above, an image is formed on the back surface of the paper P (step S9), conveyed by the conveying roller pair 17, and discharged to the discharge tray 16 by the discharge roller pair 18 (step S10).

  On the other hand, in step S5, when neither the temperature / humidity in the apparatus main body 1 nor the temperature of the fixing unit 7 is within the range of the set value set as the dew condensation condition, it is applied to one side of the sheet in the same manner as in the single-sided printing mode. After the image is formed (step S11), the paper P is immediately switched back by the conveying roller pair 17 (step S12), and an image is formed on the back surface of the paper P (step S9). 16 (step S10).

  As described above, by temporarily stopping the sheet P before the switchback operation and starting the switchback operation after a predetermined time has elapsed, an image is formed on one side of the sheet when the image forming operation is performed under the dew condensation condition. In this case, moisture contained in the paper evaporates in the fixing unit 7 and is condensed in the apparatus main body 1. The paper may get wet by the condensed water droplets. Since the moisture in the apparatus main body 1 can be removed by removing the moisture of the printed paper or by the temperature rise in the apparatus main body 1, image defects due to the wetness of the paper can be prevented.

  Next, a second embodiment of the present invention will be described. In this embodiment, the overall configuration of the apparatus main body 1 is the same as that shown in FIG. 1 shown in the first embodiment, and the control system is also the same as that shown in FIG. 2 shown in the first embodiment. To do.

  In the present embodiment, the paper P that has been temporarily stopped before the switchback operation during double-sided printing is characterized in that the switchback operation is started if the temperature inside the apparatus main body 1 is equal to or higher than a predetermined temperature. The ROM 32 stores a set value of the temperature inside the apparatus main body 1 used for determining whether to start the switchback operation. Note that the set value of the temperature in the apparatus main body 1 as the start condition of the switchback operation can be changed as appropriate according to the specifications of the apparatus main body 1, but at least not to cause image formation defects. Until then, the temperature of the apparatus main body 1 must be set to a temperature at which the moisture of the wet paper can be blown off by the water droplets condensed or the water inside the apparatus main body 1 can be removed.

  FIG. 4 is a flowchart showing the operation of the image forming apparatus according to the second embodiment of the present invention. With reference to FIGS. 1 and 2, the image recording process will be described according to the steps in FIG. As in the first embodiment, when image formation is started by the user (step S1), it is determined whether the double-sided printing mode is set (step S2), and the single-sided printing mode is designated. The image forming operation is immediately started, and an image is formed on one side of the paper P (step S3) and discharged to the discharge tray 16 (step S12).

  On the other hand, when the double-sided printing mode is designated, the main body control unit 30 determines the temperature and humidity in the apparatus main body 1 and the temperature of the fixing unit 7 detected by the dew condition detection unit before starting the image forming operation. (Step S4), and determines whether these values are within the range of the condensation condition (step S5). When the determination is completed, the main body control unit 30 starts the image forming operation. Here, when at least one of the temperature and humidity in the apparatus main body 1 or the temperature of the fixing unit 7 is within the set value range set as the dew condensation condition, an image is formed on one side of the paper P (step S6). ), The paper P is temporarily stopped at that position before the switchback operation by the conveying roller pair 17 (step S7).

  Here, in this embodiment, once the paper P is stopped, the main body control unit 30 compares the temperature in the apparatus main body 1 detected by the in-machine temperature / humidity sensor 33 with the set value stored in the ROM 32 (step S31). S8), it is determined whether the temperature in the apparatus body 1 is equal to or higher than a predetermined temperature (step S9). If the temperature in the apparatus main body 1 is lower than the predetermined temperature, the process returns to step S8, and the temperature in the apparatus main body 1 is again compared with the set value after a predetermined time has elapsed. And when the temperature in the apparatus main body 1 is more than predetermined temperature, a switchback operation is started (step S10).

  The switched-back paper P is conveyed again to the image forming unit 6 and the fixing unit 7, and an image is formed on the back surface of the paper P (step S11), and discharged to the discharge tray 16 (step S12). On the other hand, in step S5, if neither the temperature / humidity in the apparatus main body 1 nor the temperature of the fixing unit 7 is within the set value range set as the dew condensation condition, an image is formed on one side of the paper P ( In step S13, the paper P is immediately switched back by the conveying roller pair 17 (step S14), an image is formed on the back surface of the paper P (step S11), and is discharged to the discharge tray 16 (step S12).

  As described above, the sheet P is temporarily stopped before the switchback operation, and the switchback operation is started when the temperature in the apparatus main body 1 is equal to or higher than the predetermined temperature. When this is done, when an image is formed on one side of the paper, the moisture contained in the paper evaporates in the fixing unit 7 and condenses in the apparatus main body 1. Since moisture can be removed, wetting of the paper can be prevented, and image defects due to wetting of the paper can be prevented.

  Next, a third embodiment of the present invention will be described. In this embodiment, the overall configuration of the apparatus main body 1 is the same as that shown in FIG. 1 shown in the first embodiment, and the control system is also the same as that shown in FIG. 2 shown in the first embodiment. To do.

  In the present embodiment, when the paper P once stopped before the switchback operation during double-sided printing has a temperature in the apparatus main body 1 equal to or higher than a predetermined temperature even after a predetermined time has elapsed or before the predetermined time has elapsed. Is characterized in that the switchback operation is started, and the ROM 32 sets the stop time of the paper P and the temperature inside the apparatus main body 1 used to determine whether or not to start the switchback operation. The value is stored. Note that the set time of the stop time of the paper P and the temperature in the apparatus main body 1 can be appropriately changed according to the specifications of the apparatus main body 1 as in the first and second embodiments.

  FIG. 5 is a flowchart showing the operation of the image forming apparatus according to the third embodiment of the present invention. With reference to FIGS. 1 and 2, the image recording process will be described in accordance with the steps in FIG. As in the first embodiment, when image formation is started by the user (step S1), it is determined whether the double-sided printing mode is set (step S2), and the single-sided printing mode is designated. The image forming operation is immediately started, and an image is formed on one side of the paper P (step S3), and is discharged to the discharge tray 16 (step S13).

  On the other hand, when the double-sided printing mode is designated, the main body control unit 30 determines the temperature and humidity in the apparatus main body 1 and the temperature of the fixing unit 7 detected by the dew condition detection unit before starting the image forming operation. (Step S4), and determines whether these values are within the range of the condensation condition (step S5). When the determination is completed, the main body control unit 30 starts the image forming operation. Here, when at least one of the temperature and humidity in the apparatus main body 1 or the temperature of the fixing unit 7 is within the set value range set as the dew condensation condition, an image is formed on one side of the paper P (step S6). ), The paper P is temporarily stopped at that position before the switchback operation by the conveying roller pair 17 (step S7).

  Here, in the present embodiment, once the paper P is stopped, the main body control unit 30 determines whether or not a predetermined stop time has elapsed since the paper P was stopped (step S8) and recorded in the ROM 32. If the predetermined time has not elapsed, the main body control unit 30 then compares the temperature in the apparatus main body 1 detected by the in-machine temperature / humidity sensor 33 with the set value recorded in the ROM 32 (step S9). Then, it is determined whether the temperature in the apparatus main body 1 is equal to or higher than a predetermined temperature (step S10). If the temperature is higher than the predetermined temperature, a switchback operation is started (step S11). Returning to step S8, it is determined whether or not a predetermined time has elapsed since the sheet P stopped again.

  On the other hand, if a predetermined time has elapsed since the sheet P was stopped in step S8, the process proceeds to the next step as it is and a switchback operation is started (step S11). The switched-back paper P is conveyed again to the image forming unit 6 and the fixing unit 7, and an image is formed on the back surface of the paper P (step S12), and discharged to the discharge tray 16 (step S13). On the other hand, in step S5, if neither the temperature / humidity in the apparatus main body 1 nor the temperature of the fixing unit 7 is within the set value range set as the dew condensation condition, an image is formed on one side of the paper P ( In step S14, the paper P is immediately switched back by the conveying roller pair 17 (step S15), an image is formed on the back surface of the paper P (step S12), and discharged to the discharge tray 16 (step S13).

  As described above, by temporarily stopping the paper P before the switchback operation, when the image forming operation is performed under the dew condensation condition, the moisture contained in the paper is fixed when the image is formed on one side of the paper. The paper evaporates in the unit 7 and forms dew in the apparatus main body 1, and the paper may get wet due to the condensed water droplets. Since the moisture in the apparatus main body 1 can be removed by the temperature rise in 1, the image defect due to the wetness of the paper can be prevented. Further, when the temperature inside the apparatus becomes equal to or higher than a predetermined value, the switchback operation is started even if the predetermined time has not elapsed, so that the time required for the image forming operation can be shortened.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, a sheet on which one side is printed at the time of duplex printing. When P is once transported to the paper discharge path R2 and the trailing end enters the paper discharge path R2, the transport roller pair 17 is reversed to pull the paper P back into the apparatus main body 1 and to the duplex printing transport path R3. The transporting configuration has been described, but this may be a configuration in which a switchback path is separately provided in the apparatus main body 1 and the paper P is reversed by the switchback path and transported to the duplex printing transport path R3.

  In the above-described embodiment, the dew condensation condition is set based on the temperature and humidity in the apparatus main body 1 and the temperature of the fixing unit 7, and the apparatus temperature and humidity sensor 33 and the fixing temperature sensor 34 are used as the dew condition detection unit. Whether the temperature and humidity in the main body 1 is in the dew condensation condition or whether the temperature of the fixing unit 7 is in the dew condensation condition is determined by the OR condition. If any one of the conditions is met, the dew condensation condition is determined. In this case, only the temperature and humidity in the apparatus main body 1 may be used as a dew condensation condition, and only the in-machine temperature and humidity sensor 33 may be used as a dew condensation condition detection unit. Alternatively, only the temperature of the fixing unit 7 may be used as a dew condensation condition detection unit. Only the fixing temperature sensor 34 may be used.

  In FIG. 2, the input from the user is input from the outside of the personal computer or the like through the interface 31. However, the present invention is not limited to this, and the input may be performed using an operation panel or the like provided in the apparatus main body 1. I do not care. Further, the present invention is not limited to a monochrome printer, but can be applied to a color printer using a plurality of color toners such as black, cyan, magenta, and yellow, and a monochrome and color copier.

    The present invention can be used for an image forming apparatus such as a copying machine and a printer, and in particular, can be used for an image forming apparatus capable of forming an image on both sides of a sheet.

FIG. 1 is a schematic configuration diagram showing an overall configuration of an image forming apparatus according to the present invention. FIG. 2 is a block diagram illustrating a configuration of a control system and the like of the image forming apparatus according to the present invention. These are flowcharts showing the operation of the image forming apparatus according to the first embodiment. These are flowcharts showing the operation of the image forming apparatus according to the second embodiment. These are flowcharts showing the operation of the image forming apparatus according to the third embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Paper feed part 6 Image forming part 7 Fixing part 16 Discharge tray (discharge part)
17 Conveying roller pair 18 Discharging roller pair 19, 20, 21, 22 Duplex conveying roller pair 30 Main body control unit (control means)
31 Interface 33 In-machine temperature / humidity sensor 34 Fixing temperature sensor 35 Image formation control circuit 36 Fixing control circuit 37 Motor control circuit 38 Paper transport motor R1 Paper transport path R2 Paper discharge path R3 Duplex printing transport path P Paper

Claims (5)

A sheet feeding unit for stacking sheets, a discharge unit provided above the sheet feeding unit, a sheet conveyance path connecting the discharge unit and the sheet supply unit, and upstream in the sheet conveyance direction along the sheet conveyance path An image forming unit, a fixing unit, and a switchback roller arranged in order from the side, a double-sided printing conveyance path for reconveying the paper switched back by the switchback roller to the upstream side of the image forming unit, and the paper inside the apparatus An image forming apparatus capable of executing a single-sided printing mode for forming an image on one side of a sheet and a double-sided printing mode for forming an image on both sides of a sheet.
A dew condition detecting unit that detects whether or not the inside of the apparatus is in a dew generation condition; and the control unit detects the dew condition by the dew condition detecting unit before executing the duplex printing mode. In the image forming apparatus, the sheet is temporarily stopped before the switchback operation by the switchback roller, and the switchback operation is resumed after a predetermined time has elapsed.   In the double-sided printing mode, the control unit detects that the dew condition is detected and the sheet is stopped before the switchback operation. The image forming apparatus according to claim 1, wherein the switchback operation is resumed. A sheet feeding unit for stacking sheets, a discharge unit provided above the sheet feeding unit, a sheet conveyance path connecting the discharge unit and the sheet supply unit, and upstream in the sheet conveyance direction along the sheet conveyance path An image forming unit, a fixing unit, and a switchback roller arranged in order from the side, a double-sided printing conveyance path for reconveying the paper switched back by the switchback roller to the upstream side of the image forming unit, and the paper inside the apparatus An image forming apparatus capable of executing a single-sided printing mode for forming an image on one side of a sheet and a double-sided printing mode for forming an image on both sides of a sheet.
A dew condition detecting unit that detects whether or not the inside of the apparatus is in a dew generation condition; and the control unit detects the dew condition by the dew condition detecting unit before executing the duplex printing mode. In the image forming apparatus, the sheet is temporarily stopped before the switchback operation by the switchback roller, and the switchback operation is resumed when the temperature in the apparatus main body becomes equal to or higher than a predetermined temperature.   The image forming apparatus according to claim 1, wherein the dew condensation condition is determined based on a temperature of the fixing unit, and the dew condition detection unit is a fixing temperature sensor.   The image according to any one of claims 1 to 3, wherein the dew condensation condition is determined based on temperature and humidity in the apparatus main body, and the dew condition detection unit is an in-machine temperature and humidity sensor. Forming equipment.

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