JP5330584B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus able to efficiently restrict paper from being curved and stacked, by restricting curl only in a case where paper may be curved and stacked. <P>SOLUTION: The image forming apparatus comprises: fixing means for heating paper conveyed from transfer means, in order to melt and fixes a toner image transferred to paper; ejecting means for ejecting the paper heated by the fixing means, onto a paper ejection tray; raising and lowering means 61 and 62 for moving the paper ejection tray upward and downward; paper detecting means for detecting the size of paper for image formation; and paper ejection tray adjusting means 8 for moving the paper ejection tray upward and downward by the raising and lowering means based on the size of the paper detected by the paper detecting means. In the paper ejection tray, its height is adjustable in many steps. <P>COPYRIGHT: (C)2013,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile machine, and more particularly to an image forming apparatus that can suppress curling stacking due to curling of paper after printing.

  2. Description of the Related Art Conventionally, electrophotographic image forming apparatuses are widely used in printer apparatuses, copiers, facsimile apparatuses, and the like. In general, an electrophotographic image forming apparatus forms a latent image of a document image on a photosensitive drum, attaches toner to the latent image to visualize it as a toner image, and then transfers the toner image onto a sheet. Finally, an image is formed on the sheet by an image forming process in which the sheet is heated to melt and fix the transferred toner image. In the fixing step in the image forming process, the sheet onto which the toner image is transferred is sandwiched and conveyed by a fixing roller having a heater and a pressure roller that presses the fixing roller with a predetermined pressing force. Thus, heat is applied to the toner image by the fixing roller. Since the moisture on the printing surface of the paper evaporates due to the applied heat, the moisture amount differs between the printing surface and the back surface of the paper, and the paper is curled with the printing surface inside. When the curled paper is discharged to the paper discharge tray, there is a high possibility that a curled stack in which the paper curls on the paper discharge tray is generated.

  In order to suppress the curl generated on the paper, a method has been developed in which heat is also applied to the back surface of the paper so that the moisture content on the back surface is approximately equal to the moisture content on the printing surface. For example, in Japanese Patent Laid-Open No. 05-216361, a mechanism for double-sided printing is used to allow white paper to be printed on the back surface even in single-sided printing, and moisture on the back surface is evaporated in the fixing step in the back surface image forming process. Thus, a method for suppressing curling has been developed by balancing the moisture content of the front and back surfaces.

JP 05-216361 A

  However, in the above method, in the case of single-sided printing, the printing process on the dummy back side is performed after the printing side printing process is completed only for heating the back side of the paper with a fixing roller equipped with a heater. Since the paper reversal process and the re-fixing process are increased as compared with the printing process, the time required for printing increases. Increasing the number of printing steps in order to suppress curling until the paper curling stack is difficult to occur is not preferable from the viewpoint of increasing the efficiency of the printing process.

  The present invention has been conceived under the circumstances described above, and is an image that can efficiently suppress the curling stack of sheets by suppressing curling only when the curling stack of sheets is likely to occur. The object is to provide a forming apparatus.

  In order to solve the above problems, the present invention takes the following technical means.

  The image forming apparatus provided by the first solving means of the present invention includes a paper supply means for supplying paper, a photosensitive drum for forming a toner image of an image to be imaged, and the toner image on the paper. In order to transfer the toner image to the photosensitive drum, the transfer unit presses the sheet supplied from the sheet supply unit to the photosensitive drum, and the transfer unit transfers the toner image transferred to the sheet from the transfer unit. A fixing means for heating the paper; a discharging means for discharging the paper heated by the fixing means to a paper discharge tray; a temperature detecting means for detecting the temperature of the fixing means; and a temperature detected by the temperature detecting means. And a discharge speed control means for changing the discharge speed of the paper to the paper discharge tray by the discharge means so as to increase the paper discharge speed as the temperature is higher.

  The image forming apparatus provided by the second solving means of the present invention includes a paper supply means for supplying paper, a photosensitive drum for forming a toner image of an image to be imaged, and the toner image on the paper. In order to transfer the toner image to the photosensitive drum, the transfer unit presses the sheet supplied from the sheet supply unit to the photosensitive drum, and the transfer unit transfers the toner image transferred to the sheet from the transfer unit. A fixing means for heating the paper; a discharging means for discharging the paper heated by the fixing means to a paper discharge tray; and a discharge direction switching means provided at a discharge port of the paper discharge tray for switching the paper discharge direction. A temperature detecting means for detecting the temperature of the fixing means, and when the temperature detected by the temperature detecting means is lower than a predetermined temperature, the discharge direction is set to a normal discharge direction, A discharge direction control means for setting the discharge direction to a predetermined discharge direction closer to the discharge tray than the normal discharge direction when the temperature detected by the temperature detection means is equal to or higher than the predetermined temperature; Is further provided.

  The image forming apparatus provided by the third solving means of the present invention includes a paper supply means for supplying paper, a photosensitive drum for forming a toner image of an image to be imaged, and the toner image on the paper. In order to transfer the toner image to the photosensitive drum, the transfer unit presses the sheet supplied from the sheet supply unit to the photosensitive drum, and the transfer unit transfers the toner image transferred to the sheet from the transfer unit. The fixing means for heating the paper, the discharging means for discharging the paper heated by the fixing means to the paper discharge tray, and the paper discharge tray can be adjusted in multiple stages, and the paper discharge tray is moved up and down. A lifting / lowering means for moving the paper, a paper detection means for detecting the size of the paper on which the image is to be formed, and the lifting / lowering means to raise the discharge tray based on the paper size detected by the paper detection means. Further comprising a paper discharge tray adjustment means for moving the.

  According to a fourth aspect of the present invention, there is provided an image forming apparatus comprising: a paper supply means for supplying paper; a photosensitive drum for forming a toner image of an image to be imaged; In order to transfer the toner image to the photosensitive drum, the transfer unit presses the sheet supplied from the sheet supply unit to the photosensitive drum, and the transfer unit transfers the toner image transferred to the sheet from the transfer unit. An image forming apparatus comprising: a fixing unit that heats a sheet; a discharge unit that discharges the sheet heated by the fixing unit to a discharge tray; and a sheet reversing unit that reverses the sheet heated by the fixing unit. A paper setting unit that sets a size of a sheet on which an image is formed, a determination unit that determines whether or not the paper size set by the paper setting unit satisfies a predetermined condition, A second discriminating unit that discriminates whether or not an image is formed on one side of the sheet supplied from the sheet supply unit; and the size of the sheet is the predetermined condition when the sheet is imaged on one side When satisfying the condition, the sheet heated by the fixing unit is reversed by the sheet reversing unit, heated by the fixing unit, and then discharged to the sheet discharge tray by the discharging unit, and the sheet is image-formed on one side. If the size of the sheet does not satisfy the predetermined condition, the image forming control unit further discharges the sheet heated by the fixing unit to the discharge tray by the discharge unit.

  An image forming apparatus provided by a fifth solving means of the present invention comprises a paper supply means for supplying paper, a photosensitive drum for forming a toner image of an image to be imaged, and the toner image on paper. In order to transfer the toner image to the photosensitive drum, the transfer unit presses the sheet supplied from the sheet supply unit to the photosensitive drum, and the transfer unit transfers the toner image transferred to the sheet from the transfer unit. An image forming apparatus comprising: a fixing unit that heats a sheet; a discharge unit that discharges the sheet heated by the fixing unit to a discharge tray; and a sheet reversing unit that reverses the sheet heated by the fixing unit. The print information creating means for creating print information, the paper setting means for setting the size of paper to be printed, and the paper size set by the paper setting means satisfy a predetermined condition. Determining means for determining whether or not a sheet is image-formed on one side from the print information, and when the sheet is image-formed on one side and the size of the paper is When a predetermined condition is satisfied, a print information changing unit that reverses the sheet heated by the fixing unit by the sheet reversing unit, heats the sheet by the fixing unit, and then discharges the sheet to the discharge tray by the discharge unit; When the image is formed on one side of the sheet and the size of the sheet does not satisfy the predetermined condition, the print information changing unit causes the sheet heated by the fixing unit to be discharged to the discharge tray by the discharge unit. A higher-level device.

  In the image forming apparatus provided by the first solving means of the present invention, when the sheet passes through the fixing device and the sheet is at a predetermined temperature or higher, the sheet is conveyed after the trailing end of the sheet has passed the sheet discharge sensor. The rotation speed of the rollers and discharge rollers is set to a predetermined high speed so that the paper reaches the paper discharge tray before curling occurs on the paper. Can be suppressed.

  In the image forming apparatus provided by the second solving means of the present invention, when the sheet passes through the fixing device, if the sheet is at a temperature or higher, the discharge direction of the sheet is set downward. Is high and curling is likely to occur, it is possible to appropriately suppress curling stacking of sheets.

  In the image forming apparatus provided by the third solving means of the present invention, a round stack of sheets is formed according to the width and length of the sheet, the temperature and humidity inside the image forming apparatus, and the stacking amount of the discharge tray. Since the position and shape of the paper discharge tray are changed so as not to occur, it is possible to appropriately suppress the curling stack of paper when curling occurs.

  In the image forming apparatus provided by the fourth and fifth solving means of the present invention, when the size of the paper detected by the paper detecting means during single-sided printing satisfies the predetermined condition, the image forming apparatus is heated by the fixing means. The paper is reversed by the paper reversing means, heated by the fixing means, and then discharged to the paper discharge tray by the discharge means. Therefore, if the condition of the size of the paper that is likely to cause the rounded stack of paper is set as the predetermined condition in the previous period, the front and back surfaces of the paper are heated by the fixing unit when the rounded stack of paper is likely to occur. Therefore, curling stack can be suppressed. In addition, when the rounded stack of sheets is difficult to occur, the fixing unit does not heat the back side of the paper (the side on which the image is not formed), so the image forming operation is performed only for heating the back side of the paper. It can be omitted, and curling stacking of sheets can be efficiently suppressed.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

1 is a diagram for explaining an embodiment of an image forming apparatus according to the present invention. 1 is a diagram for explaining a first embodiment of an image forming apparatus according to the present invention. FIG. It is a figure which shows the change of the temperature of a fixing roller. 6 is a flowchart illustrating a part of a processing procedure of print processing according to the first embodiment. 6 is a flowchart illustrating a part of a processing procedure of print processing according to the first embodiment. It is a figure for demonstrating 5th Embodiment of the image forming apparatus which concerns on this invention. 10 is a flowchart illustrating a part of a processing procedure of print processing according to the second embodiment. 10 is a flowchart illustrating a part of a processing procedure of print processing according to the second embodiment. It is a figure for demonstrating 3rd Embodiment of the image forming apparatus which concerns on this invention. It is an example of the table which has set up the raising amount of the raising / lowering shaft. 6 is a flowchart showing a processing procedure of drive control for changing the position and shape of a paper discharge tray. It is a figure which shows an example of the data structure of the printing information input. FIG. 5 is a diagram for explaining a relationship between the size of a sheet S and the likelihood of a rounded stack. 14 is a flowchart illustrating a processing procedure of print processing according to a fourth embodiment. It is a figure for demonstrating the method to change printing information. FIG. 6 is a diagram for explaining a relationship between the amount of sheets S stacked on a sheet discharge tray and the likelihood of a rounded stack. 14 is a flowchart illustrating a processing procedure of print processing according to a fifth embodiment. It is a figure for demonstrating the method to change printing information.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram for explaining an embodiment of an image forming apparatus according to the present invention, taking as an example a printer connected to a personal computer for printing.

  The image forming apparatus 1 includes a photosensitive drum 21, a charging roller 22, an exposure device 23, a developing device 24, a transfer roller 25, a cleaner 26, a fixing device 3, a branch guide 41, a paper discharge roller 42, conveyance rollers 43 and 44, conveyance. A roller 5, a paper discharge tray 6, a paper feed cassette 7, a control device 8, and an operation panel 9 are provided.

  In this image forming apparatus 1, the photosensitive drum 21 is charged to a predetermined voltage level by the charging roller 22 (charging process), and the photosensitive drum 21 is exposed by the exposure device 23 based on the image data (image data to be formed). Then, a latent image is formed (latent image forming step). Toner is attached to the latent image formed on the photosensitive drum 21 by the developing device 24 to be visualized (toner image formation) (developing step), and transfer. An image is formed on the sheet by an image forming process that includes pressing the sheet S against the toner image on the photosensitive drum 21 by the roller 25 and transferring the toner image to the sheet S (transfer process).

  Accordingly, the charging roller 22, the exposure device 23, the developing device 24, and the transfer roller 25 are arranged in this order around the photosensitive drum 21, and the charging roller 22, the exposing device 23, and the developing roller are synchronized with the rotation of the photosensitive drum 21. By sequentially operating the device 24 and the transfer roller 25, an image is formed on the paper S supplied from the paper feed cassette 7 during one rotation of the photosensitive drum 21.

  The photosensitive drum 21 on which the toner image has been transferred returns to the position of the charging roller 22 after the toner remaining on the drum peripheral surface is removed by the cleaner 26 (cleaning process). Formation will begin.

  On the other hand, paper S is supplied from the paper feed tray 7 in synchronization with the rotation of the photosensitive drum 21, and in the case of single-sided printing, the paper S is discharged to the paper discharge tray 6 through the single-sided printing path R1. .

  The paper feed cassette 7 stores and stacks the paper S. The paper S is picked up one by one by the transport roller 71 and fed to the single-sided printing path R1 by the transport roller 44. A partition (not shown) that can move according to the size of the paper S to be stored is provided inside the paper feed cassette 7. Further, a sensor for detecting the size of the paper S accommodated by the position of the partition and a sensor for detecting the presence or absence of the paper S of each size are provided inside the paper feed cassette 7. . In FIG. 1, these sensors are collectively referred to as a paper sensor 72 for simplification. Information on the size of the paper S and the presence / absence of the paper S detected by the paper sensor 72 is output to the control device 8. Instead of detecting the size of the paper S at the partition position, the size of the paper S is detected depending on which of the plurality of paper feed cassettes 7 prepared according to the paper size is set. May be.

  A fixing device 3 and a conveying roller 5 are provided in this order on the downstream side of the photosensitive drum 21 on the single-sided printing path R1. The sheet S on which the image is formed is conveyed to the fixing device 3, and after the toner image is melted and fixed by the fixing device 3 (fixing process), a paper discharge tray provided on the upper surface of the image forming apparatus 1 by the conveying roller 5. 6 is conveyed. A paper discharge roller 42 is provided at the upper discharge port of the image forming apparatus 1, and the paper transported by the transport roller 5 is discharged to the paper discharge tray 6 by the paper discharge roller 42 (discharge process).

  The fixing device 3 fixes the toner image transferred to the paper S by applying heat and pressure. The fixing device 3 includes a fixing roller 31 having a heater for applying heat, and a predetermined amount for the fixing roller 31. There is provided a pressure roller 32 that presses with a pressing force of.

  The image forming apparatus 1 also has a double-sided printing function. Specifically, a branch guide 41 is provided in the vicinity of the paper discharge roller 42, and a double-sided printing path R2 that returns from the branch guide 41 to the conveying roller 44 on the single-sided printing path R1 is provided. In double-sided printing, the image forming apparatus 1 feeds the paper S on which single-sided printing has been performed to the double-sided printing path R2 by the discharge roller 42 and the branch guide 41, and the conveying roller 44 by the conveying roller 43 on the double-sided printing path R2. Then, the image is also formed on the back surface by returning to the single-sided printing path R1. After the image is formed on the back surface, the toner image on the back surface is melted and fixed by the fixing device 3 and discharged to the paper discharge tray 6 by the transport roller 5 and the paper discharge roller 42 as in the case of single-sided printing.

  In the case of normal single-sided printing, as described above, the paper S passes through the single-sided printing path R1 and an image is formed by the photosensitive drum 21 and the transfer roller 25. After fixing processing is performed by the fixing device 3, The paper passes through the lower side of the branch guide 41 and is discharged to the paper discharge tray 6 by the paper discharge roller 42. On the other hand, in the case of duplex printing, the printed paper S is drawn so as to pass above the branch guide 41 due to the reverse rotation of the discharge roller 42 after its rear end portion has passed through the branch guide 41. The sheet S passes through the double-sided printing path R2 and is returned again to the single-sided printing path R1 by the transport roller 44 (reversing step). The branch guide 41, the paper discharge roller 42, and the transport rollers 43 and 44 for performing the reversing process are collectively referred to as a reversing mechanism. Since the sheet S returned to the single-sided printing path R1 by the reversal process is reversed, the printing is performed on the back side when the paper S passes through the single-sided printing path R1 again.

  FIG. 2 is a diagram for explaining the first embodiment of the image forming apparatus according to the present invention. In the figure, only characteristic portions different from the image forming apparatus 1 shown in FIG. 1 are left, and common portions are appropriately omitted. The ease with which the sheet S curls depends on the amount of heat applied by the fixing device 3. Therefore, the generation of the rounded stack is further suppressed according to the amount of heat applied.

  The image forming apparatus 1 </ b> B shown in the figure is provided with a temperature sensor 33 and a paper discharge sensor 34 in the fixing device 3 ′, and the rotational speed of the transport roller 5 and the paper discharge roller 42 is controlled by the control device 8. 1 is different from the image forming apparatus 1 shown in FIG.

  The temperature sensor 33 detects the temperature of the fixing roller 31 and outputs the detected temperature information to the control device 8. In the present embodiment, the temperature sensor 33 has a thermistor (not shown) and outputs a voltage proportional to the temperature rise. The control device 8 determines the temperature of the fixing roller 31 based on the voltage input from the temperature sensor 33.

  FIG. 3 is a diagram illustrating a change in the temperature of the fixing roller 31. The temperature of the fixing roller 31 is controlled within a target control temperature range and changes within the control temperature range. The sheet S that has passed through the fixing device 3 when the temperature of the fixing roller 31 is high is likely to curl and rounded stacks are likely to occur. In this embodiment, when the temperature T detected by the temperature sensor 33 is equal to or higher than the predetermined temperature Tt, it is determined that there is a high possibility that the curled stack will occur, and before the curl occurs on the paper S that has passed through the fixing device 3. In order to reach the paper discharge tray 6, the conveyance speed of the paper S is increased. Note that the temperature Tt varies depending on the diameter, rotation speed, and the like of the fixing roller 31, and therefore it is necessary to determine an appropriate value by experiment.

  The paper discharge sensor 34 detects the paper S sent out by the fixing roller 31 and the pressure roller 32, and outputs detection information of the paper S to the control device 8. In the present embodiment, the paper discharge sensor 34 has a photo sensor (not shown). When the photo sensor detects the paper S, a high level voltage is output, and when the photo sensor does not detect the paper S, A low level voltage is output. The control device 8 determines that the trailing edge of the paper S has passed through the paper discharge sensor 34 because the voltage input from the paper discharge sensor 34 has changed from a high level to a low level.

  The transport roller 5 and the discharge roller 42 are driven by a drive motor that is different from the drive motor that drives the fixing roller 31 and the pressure roller 32. The transport speed of the paper S by the transport roller 5 and the discharge roller 42 is determined by the fixing roller. The speed can be changed to a predetermined speed faster than the discharge speed of the paper S by the pressure roller 31 and the pressure roller 32. Although omitted in FIG. 2, a plurality of conveyance rollers are also arranged between the conveyance roller 5 and the discharge roller 42, and these conveyance rollers are also driven by the same drive motor as the conveyance roller 5 and the discharge roller 42. Driven.

  When the temperature T detected by the temperature sensor 33 is equal to or higher than the predetermined temperature Tt when the paper S passes through the fixing device 3, the control device 8, after the trailing edge of the paper S passes through the paper discharge sensor 34, The drive motor is controlled so as to increase the rotational speeds of the transport roller 5 and the discharge roller 42.

  First, the transport roller 71 is driven to take out the paper S from the paper feed cassette 7 (S10-1), and waits until the temperature of the fixing roller 31 falls within the target control temperature range (S10-2). When the temperature of the fixing roller 31 falls within the target control temperature range (S10-2: YES), a toner image based on the bitmap is transferred to the first surface of the paper S (S10-3), and the toner is fixed by the fixing device 3 The image is fixed (S10-4).

  The temperature of the fixing roller 31 when the sheet S passes through the fixing device 3 is detected, and it is determined whether or not the temperature T is equal to or higher than a predetermined temperature Tt (S10-5). When the temperature T is lower than the temperature Tt (S10-5: NO), the transport roller 5 and the discharge roller 42 are driven at a normal rotation speed, so that the paper S is transported and discharged at a normal speed. On the other hand, if the temperature T is equal to or higher than the temperature Tt (S10-5: YES), it is determined whether or not the trailing edge of the paper S has passed through the paper discharge sensor 34 (S10-6). Until the trailing edge of the paper S passes the paper discharge sensor 34 (S10-6: NO), the paper S is conveyed at a normal speed. When the trailing edge of the sheet S passes the sheet discharge sensor 34 (S10-6: YES), the rotation speeds of the transport roller 5 and the discharge roller 42 are changed to a predetermined high speed, and the sheet S is transported and discharged at a high speed. (S10-7).

  In the present embodiment, when the temperature T detected by the temperature sensor 33 is equal to or higher than the predetermined temperature Tt when the paper S passes through the fixing device 3, the rear end of the paper S passes through the paper discharge sensor 34. Then, the rotation speeds of the transport roller 5 and the discharge roller 42 are set to a predetermined high speed so as to reach the paper discharge tray 6 before the paper S is curled. Therefore, when the temperature of the fixing roller 31 is high and curling is likely to occur, it is possible to appropriately suppress the curled stack of sheets.

  In the present embodiment, when the temperature T detected by the temperature sensor 33 is equal to or higher than the predetermined temperature Tt, the conveyance speed of the paper S is changed to a predetermined high speed. However, the present invention is not limited to this. For example, the conveyance speed of the paper S may be increased according to the detected temperature.

  In the present embodiment, the curving stack is suppressed by changing the conveyance speed based on the temperature T detected by the temperature sensor 33. However, the curling stack may be suppressed by another method. For example, the curling stack may be suppressed by changing the angle at which the paper S is discharged from the discharge port.

  FIG. 6 is a view for explaining a second embodiment of the image forming apparatus according to the present invention. In the figure, only characteristic portions different from the image forming apparatus 1 shown in FIG. 1 are left, and common portions are appropriately omitted.

  1C differs from the image forming apparatus 1 shown in FIG. 1 in that a temperature sensor 33 is provided in the fixing device 3 ″ and a separator 67 is provided in the discharge port. Since this is the same as that of the first embodiment (see FIG. 2), description thereof is omitted.

  The separator 67 is provided between the discharge roller 42 and the discharge port, and switches the discharge direction of the paper S. The separator 67 switches the discharge direction between the upward direction and the downward direction according to a switching signal from the control device 8. When the discharge direction is downward, the time until the leading edge of the discharged paper S reaches the paper discharge tray 6 is shortened. Therefore, the angle δ ′ formed by the paper S and the paper discharge tray 6 is the upward direction of the discharge direction. It becomes smaller than the angle δ in the case. Therefore, it is possible to prevent the paper S from being rounded and stuck.

  When the temperature T detected by the temperature sensor 33 when the sheet S passes through the fixing device 3 is equal to or higher than the predetermined temperature Tt, the control device 8 switches the separator 67 so that the discharge direction is downward. On the other hand, when the detected temperature T is lower than the predetermined temperature Tt, the separator 67 is switched so that the discharge direction is the upward direction.

  FIG. 7 is a flowchart showing the processing procedure of step S10 in FIG. 4 among the processing procedures of the printing processing in the present embodiment. This processing procedure is a processing procedure after the print data for one page is bitmap-developed when the simplex printing process is performed based on the paper width W and the paper length L. Steps S10-1 to S10-5 are the same as those in the flowchart of FIG.

  When the temperature T of the fixing roller 31 when the sheet S passes through the fixing device 3 is lower than the temperature Tt (S10-5: NO), the discharge direction is set to the upward direction (S10-11). That is, the separator 67 is switched when the discharge direction is the downward direction, and the separator 67 is not switched when the discharge direction is the upward direction. On the other hand, when the temperature T is equal to or higher than the temperature Tt (S10-5: YES), the discharge direction is the downward direction (S10-12). That is, the separator 67 is switched when the discharge direction is the upward direction, and the separator 67 is not switched when the discharge direction is the downward direction.

  In this embodiment, when the sheet S passes through the fixing device 3 and the temperature T detected by the temperature sensor 33 is equal to or higher than the predetermined temperature Tt, the discharge direction of the sheet S is set downward. Therefore, when the temperature of the fixing roller 31 is high and curling is likely to occur, it is possible to appropriately suppress the curled stack of sheets.

  When the temperature T detected by the temperature sensor 33 is equal to or higher than the predetermined temperature Tt by combining the first embodiment and the second embodiment, the discharge direction of the paper S is set to the downward direction, and the paper S The conveyance speed may be a predetermined high speed. Further, when the temperature T detected by the temperature sensor 33 is equal to or higher than the predetermined temperature Tt, the discharge direction of the paper S is set to the downward direction, and the conveyance speed of the paper S is increased according to the detected temperature T. Also good.

  FIG. 9 is a view for explaining a third embodiment of the image forming apparatus according to the present invention. This figure is an enlarged view of the periphery of the paper discharge tray, which is a characteristic part different from the image forming apparatus 1 shown in FIG.

  In the image forming apparatus 1A shown in FIG. 1, the discharge tray 6 is changed to a deformable discharge tray 6 ′, a first lifting shaft 61, a second lifting shaft 62 for deforming the discharge tray 6 ′, The image forming apparatus 1 is different from the image forming apparatus 1 shown in FIG. 1 in that the drive motors 63 and 64 are provided and the load sensor 65 and the temperature / humidity sensor 66 are provided.

  The paper discharge tray 6 'has a first panel 6'a, a second panel 6'b, and a third panel 6'c. The first panel 6'a is a panel corresponding to a position where the leading edge of the printed paper S discharged from the discharge port contacts, and the leading edge of the discharged paper S is the position of the panel of the stacked paper S. Abut. The second panel 6′b is a panel that is rotatably supported at the distal end portion (the right end portion in FIG. 9) in the discharge direction of the first panel 6′a. The third panel 6′c is a panel that connects the image forming apparatus 1A and the first panel 6′a. The third panel 6′c is rotatably supported by the image forming apparatus 1A at the lower part of the discharge port, and has a leading end (first) in the discharge direction. The right end of the three panels 6'c is connected to the left end of the first panel 6'a so as to be rotatable.

  The first elevating shaft 61 is disposed at a position to press the back surface (the lower surface in FIG. 9) of the first panel 6′a, and the first panel 6′a is moved up and down to be connected to the discharge port. The distance is changed.

  When the first panel 6′a is at the basic position (when the paper discharge tray 6 ′ is at the position indicated by the broken line in FIG. 9), the leading edge of the paper S discharged from the discharge port contacts the paper discharge tray 6 ′. The angle γ formed by the sheet S and the sheet discharge tray 6 ′ when in contact with each other becomes large, and rounded stacks are likely to occur. On the other hand, when the first panel 6′a is at a high position (when the paper discharge tray 6 ′ is at the position indicated by the solid line in FIG. 9), the leading edge of the paper S discharged from the discharge port is the paper discharge tray 6 ′. The angle γ ′ formed by the paper S and the paper discharge tray 6 ′ when abutting on the sheet becomes small, and the rounded stack is unlikely to occur. Therefore, in the present embodiment, when a rounded stack is likely to occur due to the paper width W and the paper length L of the paper S, the rounded stack is less likely to occur by setting the first panel 6'a to a higher position. I have to.

  The second elevating shaft 62 is disposed at a position that presses the back surface (the lower surface in FIG. 9) of the second panel 6′b, and moves the second panel 6′b up and down to move the first panel 6′b. The angle formed between the panel 6′a and the second panel 6′b is changed.

  When the first panel 6'a is at a high position, the inclination of the third panel 6'c is increased, and the paper S is curled. Unevenness may occur in the shape of the sheets S stacked on the sheet. If paper discharge is continued in a state in which the shape of the paper S is undulated, the contact load between the leading edge of the paper S discharged from the discharge port and the undulation increases, and a rounded stack may occur. Therefore, in the present embodiment, when the sheet length L of the sheet S is large, the angle formed by the first panel 6′a and the second panel 6′b is decreased to change the shape of the discharge tray 6 ′ to the curl of the sheet S. By approaching the shape, the occurrence of undulation of the shape of the stacked paper S is suppressed.

  The drive motors 63 and 64 drive the first elevating shaft 61 and the second elevating shaft 62, respectively, and are controlled by the control device 8. Note that other drive components such as a solenoid may be used instead of the drive motor.

  The stacking amount sensor 65 detects the stacking amount of the sheets S stacked on the paper discharge tray 6 ′. The load amount sensor 65 detects the load amount when the leading end of the detection lever 65a is lifted by the stacked sheets S. In the present embodiment, an unillustrated shielding plate provided at the base end portion of the detection lever 65a blocks an unillustrated photosensor, whereby the output voltage of the photosensor changes, and this output voltage is output to the control device 8. . Note that the load amount sensor 65 is not limited to this, and may be one that detects the load amount by another method.

  When a large amount of paper S is stacked on the paper discharge tray 6 ′, the distance between the discharge port and the stacked paper S is short, and curling stacking is unlikely to occur (see FIG. 16). Therefore, in this case, even if the position of the first panel 6′a is lowered to some extent, the rounded stack is unlikely to occur. In order to further stack the sheets S, it is necessary to lower the position of the first panel 6'a. Therefore, in the present embodiment, the position of the first panel 6′a is lowered according to the stacking amount of the sheets S detected by the stacking amount sensor 65. The second elevating shaft 62 is lowered in conjunction with the first elevating shaft 61 so as not to change the angle formed by the first panel 6′a and the second panel 6′b.

  The temperature / humidity sensor 66 is provided inside the image forming apparatus 1 </ b> A and detects the internal temperature and humidity, and outputs information on the detected temperature and humidity to the control device 8.

  When the temperature inside the image forming apparatus 1A is high, the temperature of the fixing device 3 changes slightly higher than the control temperature, so that the heat applied to the sheet S from the fixing device 3 increases. Accordingly, the curl generated on the paper S increases. Further, when the humidity inside the image forming apparatus 1A is high, the moisture content of the sheet S increases, so that the difference in moisture content between the surface heated by the fixing device 3 and the back surface becomes large. Accordingly, the curl generated on the paper S increases. Therefore, in the present embodiment, when the temperature and humidity inside the image forming apparatus 1A are high, the first panel 6′a is corrected to a higher position in order to suppress the rounded stack.

  FIG. 10 is an example of a table in which the rising amounts of the first lifting shaft 61 and the second lifting shaft 62 are set. The first elevating shaft 61 and the second elevating shaft 62 move up and down in accordance with the values set in the table, thereby changing the position and shape of the paper discharge tray 6 ′. When both the rising amounts are zero, the paper discharge tray 6 ′ has a basic shape at the basic position (indicated by a broken line in FIG. 9).

  FIG. 10A is a table in which the amount of increase according to the paper width and the paper length is set. When the paper width W is small or when the paper length L is large, the amount of ascending of the first elevating shaft 61 is set to be larger. Further, when the paper length L is larger than the predetermined value, the rising amount of the second lifting shaft 62 is set to be smaller than the rising amount of the first lifting shaft 61. As a result, the angle formed by the first panel 6′a and the second panel 6′b is reduced, and the occurrence of undulations in the shape of the stacked sheets S is suppressed.

  FIG. 10B is a table in which a correction amount of an increase amount for performing correction according to the temperature and humidity inside the image forming apparatus is set. When the inside of the image forming apparatus is hot and humid, the amount of correction is set so that the rising amounts of both the lifting shafts 61 and 62 are larger, and when the temperature is low and low humidity, the rising amounts of both the lifting shafts 61 and 62 are smaller. ing.

  FIG. 10C is a table in which a correction amount of the ascending amount for correcting according to the stacking amount of the paper discharge tray 6 ′ is set. In the present embodiment, the load sensor 65 outputs a high voltage when the load is small, and outputs a low voltage when the load is large. When the output voltage from the load sensor 65 is 4.5 V or more, the load is small and there is no need to correct the increase amount, so that the correction amount is set to zero. When the output voltage is 1.5V to 4.5V, a correction amount corresponding to the output voltage is set, and when the output voltage increases by 0.5V, the increase amount is set to decrease by 5 mm. When the output voltage is 1.5 V or less, the amount of increase is set to be zero. In this case, the paper discharge tray 6 ′ is positioned at the basic position (see the broken paper discharge tray 6 ′ in FIG. 9).

  Note that the numerical values in the table shown in FIG. 10 are only examples, and the diameter of the fixing roller 31, the rotation speed, the amount of heat applied, the size of each panel 6 ′ a, 6 ′ b, 6 ′ c of the paper discharge tray 6 ′, stacking Since it varies depending on the configuration of the quantity sensor 65, an appropriate value must be determined by experiment.

  FIG. 11 is a flowchart showing a processing procedure of drive control of the drive motors 63 and 64, which is performed by the control device 8 in order to change the position and shape of the discharge tray 6 ′.

  First, it is determined whether or not a printing process is being performed (S41). If printing is not in progress (S41: NO), reception of print information is awaited (S42). When print information is received (S42: YES), it is determined whether or not the paper width W is 150 mm or less (S43).

  When the paper width W is 150 mm or less (S43: YES), it is determined whether or not the paper length L is larger than 150 mm and smaller than 365 mm (S44). When the paper length L is 150 mm or less, 35 mm is set as the lift amount H1 of the first lift shaft, and 35 mm is set as the lift amount H2 of the second lift shaft (S45). When the paper length L is larger than 150 mm and smaller than 365 mm, 40 mm is set as the rising amount H1 of the first lifting shaft, and 40 mm is set as the lifting amount H2 of the second lifting shaft (S46). When the paper length L is 365 mm or more, 40 mm is set as the lift amount H1 of the first lift shaft, and 35 mm is set as the lift amount H2 of the second lift shaft (S45). The paper width W and the paper length L of the paper S are referred to from the paper size data (see FIG. 12) of the received print information.

  When the paper width W is larger than 150 mm (S43: NO), it is determined whether or not the paper length L is 200 mm or less (S48). When the paper length L is 200 mm or less (S48: YES), 30 mm is set as the lift amount H1 of the first lift shaft, and 30 mm is set as the lift amount H2 of the second lift shaft (S49). When the paper length L is greater than 200 mm (S48: NO), 35 mm is set as the lift amount H1 of the first lift shaft, and 30 mm is set as the lift amount H2 of the second lift shaft (S50).

  Next, the temperature and humidity inside the image forming apparatus 1A are detected by the temperature / humidity sensor 66 (S51), and the environment inside the image forming apparatus 1A is determined based on the detected temperature and humidity (S52). When the environment is LL (a low temperature and low humidity state where the temperature is 15 degrees or less and the humidity is 40% or less), 3 mm is reduced from the rising amount H1 of the first lifting shaft and the rising amount H2 of the second lifting shaft (S53). When the environment is NN (normal state of temperature 16 to 25 degrees, humidity 41% to 64%), the lift amount H1 of the first lift shaft and the lift amount H2 of the second lift shaft are not corrected (S54). When the environment is HH (high temperature and high humidity state with a temperature of 26 ° C. or higher and a humidity of 65% or higher), 3 mm is added to the lift amount H1 of the first lift shaft and the lift amount H2 of the second lift shaft (S55).

  Next, it is determined whether or not the voltage E input from the load sensor 65 is larger than 1.5V and smaller than 4.5V (S56). The voltage E is always output from the load sensor 65 to the control device 8. When the voltage E is 1.5 V or less, the lift amount H1 of the first lift shaft and the lift amount H2 of the second lift shaft are set to zero (S57). When the voltage E is larger than 1.5V and smaller than 4.5V, the rising amount H1 of the first lifting shaft and the rising amount H2 of the second lifting shaft are reduced by {10 × (4.5−E)} mm. . For example, when E is 3V, 15 mm is reduced. When the voltage E is 4.5 V or more, the rising amount H1 of the first lifting shaft and the rising amount H2 of the second lifting shaft are not corrected (S59).

  As described above, the lift amount H1 of the first lift shaft and the lift amount H2 of the second lift shaft are determined, and in order to drive the first lift shaft 61 and the second lift shaft 62, the drive motor 63 and 64 is driven (S60).

  If it is determined in step S41 that the printing process is being performed (S41: YES), the first elevating shaft 61 and the second elevating shaft 62 are moved according to the change in the stacking amount of the paper discharge tray 6 ′ during printing. Since it is driven, the process proceeds to step 56.

  In the present embodiment, the round stack of the sheets S does not occur according to the sheet width W and the sheet length L of the sheets S, the temperature and humidity inside the image forming apparatus 1A, and the stacking amount of the sheet discharge tray 6 ′. In addition, the position and shape of the paper discharge tray 6 ′ are changed. Therefore, when curling occurs, it is possible to appropriately suppress the curling stack of sheets.

  In the third embodiment, the sheet width W and the sheet length L of the sheet S, the temperature and humidity inside the image forming apparatus 1A, and the stacking amount of the sheet discharge tray 6 ′ are set. Although the position and shape are changed, it is not limited to using all these conditions. For example, when the sheet S is changed only in accordance with the sheet width W and the sheet length L, the temperature / humidity sensor 66 and the load sensor 65 need not be provided. Further, in addition to the paper width W and the paper length L of the paper S, it may be changed according to conditions such as the thickness and type of the paper S.

  In the fourth embodiment, in the single-sided printing in the image forming apparatus 1 of FIG. 1, when a predetermined condition is satisfied, an image is formed on the surface of the paper S and is not immediately discharged to the paper discharge tray 6, but double-sided printing is performed. By returning to the single-sided printing path R1 through the path R2, passing through the fixing device 3 again, and then discharging it to the paper discharge tray 6, the occurrence of curling is suppressed.

  The control device 8 controls single-sided printing and double-sided printing in the image forming apparatus 1, but also controls printing processing for suppressing the occurrence of curling in single-sided printing. The control device 8 changes the setting based on the print information input from the personal computer 10 and controls the print data of the print information to be printed on the paper S.

  FIG. 12 is a diagram illustrating an example of a data structure of print information input from the personal computer 10. The print information includes print method data, paper size data, and print data for each page. The printing method data is information indicating whether the printing data is printed by single-sided printing or double-sided printing. The paper size data is information on the size of the paper S to be printed, and includes the paper length L that is the length of the paper S in the transport direction and the paper width W that is the length in the direction orthogonal to the transport direction. .

  When the printing method data input from the personal computer 10 indicates double-sided printing, the control device 8 performs control so that the printing data is double-sided printed on the paper S. On the other hand, even when the printing method data indicates single-sided printing, control is performed to perform double-sided printing in order to suppress curling according to the paper length L and the paper width W, which are paper size data.

  FIG. 13 is a diagram for explaining the relationship between the size of the paper S and the ease of occurrence of the rounded stack, and shows a state in which the leading edge of the paper S discharged from the discharge port reaches the paper discharge tray 6. . FIG. 13A shows a case where the paper length L is relatively long. After the leading edge of the sheet reaches the sheet discharge tray 6, the sheet S is continuously pushed from the rear by the discharge roller 42, so that a rounded stack is likely to occur. FIG. 13B shows the case where the paper length L is relatively short. When the leading edge of the paper reaches the paper discharge tray 6, the trailing edge of the paper S is going to pass through the discharge port and descend to the paper discharge tray 6, so that the rounded stack is unlikely to occur.

  FIG. 13C shows the case where the paper width W is relatively narrow. Since the sheet S is easily broken and the air resistance received from below is small, the angle α formed between the sheet S and the sheet discharge tray 6 when the leading edge of the sheet reaches the sheet discharge tray 6 is increased, and a rounded stack is likely to occur. When the paper width W is narrow, since the heat consumed by the paper S passing through the fixing device 3 is small, the temperature of the fixing device 3 changes slightly higher than the control temperature. Therefore, the paper S is better dried than the case where the paper width W is wide, so that the curl becomes large and a rounded stack is likely to occur. FIG. 3D shows the case where the paper width W is relatively wide. Since the sheet S is not easily broken and the amount of air received from below is large, the angle α ′ formed between the sheet S and the sheet discharge tray 6 when the leading edge of the sheet reaches the sheet discharge tray 6 is small, and the rounded stack is not easily generated.

  For these reasons, when the paper length L is shorter than the predetermined paper length Lt, or when the paper width W is larger than the predetermined paper width Wt, curling stacks are unlikely to occur, and curling need not be suppressed. I can judge. Since the paper length Lt and the paper width Wt vary depending on the diameter of the fixing roller 31, the rotational speed, the amount of heat applied, and the like, it is necessary to determine appropriate values through experiments.

  In this embodiment, when the paper length L is equal to or greater than the predetermined paper length Lt and the paper width W is equal to or smaller than the predetermined paper width Wt, the back surface is used to suppress curling even if single-sided printing is specified. Double-sided printing (hereinafter, referred to as “curl-suppressing printing”) is performed on white paper.

  The control device 8 creates a print image based on the print data input from the personal computer 10 and outputs it to the exposure unit 23. Specifically, in the case of normal single-sided printing, a print image in which print data for one page is expanded into a bitmap is created and output to the exposure unit 23, and all print data input from the personal computer 10 is output to this print data. Process. When performing double-sided printing, print data for two pages is expanded into a bitmap for the first side and a bitmap for the second side. When performing curl-suppressing printing, print data for one page is developed into a bitmap for the first side, and a blank bitmap is created in the bitmap for the second side.

  When performing double-sided printing or curl suppression printing, the control device 8 performs a reversing operation using the branch guide 41 and the discharge roller 42. That is, after the sheet S passes through the single-sided printing path R1 and is printed on the first side, the front and back are reversed and returned to the single-sided printing path R1 again. The sheet S passes through the single-sided printing path R <b> 1 and is printed on the second side, and then is discharged to the discharge tray 6 by the discharge roller 42. Accordingly, when curl suppression printing is performed, a print image based on the print data is printed on the first surface of the paper S, and a blank image is printed on the second surface.

  The control device 8 determines whether or not the paper S designated by the paper size data input from the personal computer 10 is in the paper feed cassette 7. Specifically, it is determined whether the information on the size of the paper S input from the paper sensor 72 matches the paper size data input from the personal computer 10 and whether the paper S is in the paper feed cassette 7. to decide. If there is a designated paper S, the printing process is performed. If there is no designated paper S, the personal computer 10 is notified that there is no designated paper S.

  The operation panel 9 is provided with operation buttons for changing various settings of the image forming apparatus 1. The pressing signal of the operation button is input to the control device 8, and the control device 8 changes the corresponding setting.

  Next, the processing procedure will be described with reference to the flowchart shown in FIG.

  FIG. 14 shows a processing procedure of print processing that is performed when the control device 8 receives print data, and is started when print information is received from the personal computer 10.

  First, it is determined whether or not the designated paper S is in the paper feed cassette 7 (S1). If there is no sheet (S1: NO), the personal computer 10 is notified that there is no designated sheet (S2), and the process is terminated. If there is a designated sheet (S1: YES), it is determined whether single-sided printing is designated (S3). That is, it is determined whether or not the printing method data input from the personal computer 10 indicates single-sided printing. If duplex printing is designated (S3: NO), duplex printing processing (S4 to S6) is performed.

  In the double-sided printing process, two pages of print data are bitmap-developed from print data input from the personal computer 10 (S4). Next, the conveyance roller 71 is driven to take out the paper S from the paper feed cassette 7, and a toner image based on the bitmap for the first surface is transferred to the first surface of the paper S. It is fixed. Next, the reversing mechanism is driven to invert the sheet S, the toner image based on the second-surface bitmap is transferred to the second surface, the toner image is fixed by the fixing device 3, and the sheet S is discharged. (S5). It is determined whether or not all print data of the print data has been printed (S6). If there is print data that has not been printed (S6: NO), the process returns to step S4, and if all print data has been printed (S6: NO). In S6: YES, the process is terminated.

  If single-sided printing is designated in step S3 (S3: YES), it is determined whether to perform single-sided printing processing or curl suppression printing processing based on the paper length L and paper width W of the designated paper. The It is determined whether or not the designated paper width W is equal to or smaller than the predetermined paper width Wt (S7). If the designated paper width W is larger than the predetermined paper width Wt (S7: NO), a round stack is generated. Since it is difficult to perform, single-sided printing processing (S9 to S11) is performed. If the designated paper width W is less than or equal to the predetermined paper width Wt (S7: YES), it is determined whether or not the designated paper length L is greater than or equal to the predetermined paper length Lt (S8). When the designated paper length L is smaller than the predetermined paper length Lt (S8: NO), it is difficult for the round stack to occur, so single-sided printing processing (S9 to S11) is performed, and the designated paper length L is the predetermined paper length L. When it is equal to or longer than the paper length Lt (S8: YES), curl suppression printing processing (S12 to S15) is performed.

  That is, only when the designated paper width W is equal to or smaller than the predetermined paper width Wt and the designated paper length L is equal to or larger than the predetermined paper length Lt, it is determined that the rounded stack is likely to occur, and curling is suppressed. Printing processing (S12 to S15) is performed, otherwise single-sided printing processing (S9 to S11) is performed.

  In the single-sided printing process, the print data for one page is developed from the print data input from the personal computer 10 (S9), the transport roller 71 is driven, the paper S is taken out from the paper feed cassette 7, and the bitmap is printed. Is transferred to the first surface of the sheet S, the toner image is fixed by the fixing device 3, and the sheet S is discharged (S10). It is determined whether or not all the print data of the print data has been printed (S11). If there is print data that has not been printed (S11: NO), the process returns to step S9, and if all the print data has been printed (S11: NO) In S11: YES, the process is terminated.

  In the curl suppression printing process, print data for one page is developed into a bitmap for the first surface from the print data input from the personal computer 10 (S12). Next, a blank bitmap is created as a bitmap for the second side (S13). Thereafter, the same process as the double-sided printing process is performed.

  Next, the operation of the image forming apparatus 1 will be described.

  In this embodiment, when single-sided printing is designated, the curl suppression printing process is performed only when the paper width W is equal to or smaller than the predetermined paper width Wt and the paper length L is equal to or larger than the predetermined paper length Lt. Otherwise, normal single-sided printing is performed. Therefore, curl suppression printing processing is performed only when paper curl stacks are likely to occur, and normal single-sided printing processing with fewer steps is performed when paper curl stacks are difficult to occur. Stack can be suppressed.

  In the fourth embodiment, in the curl suppression printing process, a blank bitmap is created and printed on the second surface of the paper S. However, the present invention is not limited to this. Since the purpose is to apply heat to the second surface by the fixing device 3, the charging roller 22, the exposure device 23, and the developing device 24 are not driven when passing through the single-side printing path R1 again, and the photosensitive drum. The sheet S may be transported by the photosensitive drum 21 and the transfer roller 25 without forming a toner image on the sheet 21. Further, a curl-suppressing printing path R3 (see the broken line arrow R3 in FIG. 1) for guiding the paper S on which the first side is printed from the double-sided printing path R2 directly to the fixing unit 3 is provided, and the fixing unit is applied to the second side Only 3 may be allowed to pass.

  In the first embodiment, the control device 8 determines whether or not to perform the curl suppression printing process based on the printing information input from the personal computer 10 and performs the curl suppression printing process different from the double-sided printing process. However, the present invention is not limited to this. For example, the personal computer 10 may determine whether to perform the curl-suppressing printing process, change the print information, and output the print information to the control device 8.

  FIG. 15 is a diagram for explaining a method of changing print information on the personal computer 10. FIG. 15A shows print information before the change, which is the same as that shown in FIG. FIG. 15B shows the print information after the change when it is determined from the paper size data in the print information of FIG. This determination is made by the CPU of the personal computer 10 from the sheet length L and the sheet width W of the sheet S. In the print information of FIG. 15B, the printing method data is changed from single-sided printing to double-sided printing in order to perform curl suppression printing processing, and blank page print data is inserted after the print data of each page. When the print information after this change is input, the control device 8 performs double-sided printing processing. Thereby, the curl suppression printing process is performed without the control device 8 making a determination.

  Further, in changing the print information, instead of inserting blank page print data after the print data of each page, the charging roller 22, the exposure unit 23, and the development unit 24 are used when passing the single-sided printing path R1 again. You may make it add the data which designates performing control which does not function.

  In the fourth embodiment, it is determined whether or not the curl suppression printing process is performed based on the sheet length L and the sheet width W of the sheet S, but the present invention is not limited to this. For example, the determination may be made based on either the paper length L or the paper width W of the paper S. The determination may be made based on the type of the paper S, or may be made based on any combination of the type of the paper S, the paper length L, and the paper width W.

  Further, it may be determined whether or not to perform the curl suppression printing process based on the number of printed sheets.

  FIG. 16 is a diagram for explaining the relationship between the amount of sheets S stacked on the sheet discharge tray 6 and the ease with which a rounded stack is generated. The leading edge of the sheet S discharged from the discharge port is the discharge tray 6. A state in which the paper S stacked on the paper has been reached is shown. FIG. 16A shows the case where the loading amount of the sheets S is small. In this case, since the distance from the discharge port to the stacked sheets S is long, the angle β formed by the discharged sheets S and the stacked sheets S becomes large, and rounded stacks are likely to occur. FIG. 16B shows the case where the amount of sheets S loaded is large. In this case, since the distance from the discharge port to the stacked sheets S is short, the angle β ′ formed by the discharged sheets S and the stacked sheets S is small, and the rounded stack is unlikely to occur.

  Accordingly, the number of printed sheets N is counted, and the amount of sheets S stacked on the paper discharge tray 6 is small until the predetermined number of printed sheets Nt is reached, so that the rounded stack is likely to occur, and after reaching the predetermined number of printed sheets Nt Since the amount of sheets S stacked on the discharge tray 6 is large, it can be determined that the rounded stack is unlikely to occur. The number of printed sheets Nt varies depending on the depth of the paper discharge tray 6, the diameter of the fixing roller 31, the rotational speed, the amount of heat to be applied, and the like, so an appropriate value must be determined by experiment.

  In the fifth embodiment of the image forming apparatus according to the present invention, a determination based on the number N of prints is added to the determination as to whether or not to perform curl suppression printing in the fourth embodiment. That is, when curl-suppressing printing is performed based on the determination based on the paper length L and the paper width W, the number of printed sheets N is counted, and curling-suppressing printing is performed for a predetermined number of printed sheets Nt or less. After exceeding Nt, normal single-sided printing is performed. The number of printed sheets N may be counted by the control device 8, or a counter may be provided at the discharge port to count the number of sheets actually discharged. In addition, a sensor for detecting the stacking amount of the paper discharge tray 6 may be provided so that the determination is based on the stacking amount instead of the number of printed sheets.

  FIG. 17 is a flowchart illustrating a processing procedure of print processing according to the fifth embodiment. The flowchart shown in the figure is different from the printing process in the fourth embodiment shown in FIG. 14 in that steps S32 to S34 are added. Steps S21 to S31 are the same as steps S1 to S11 in the flowchart shown in FIG.

  If YES in step S28, the number N of prints is initialized to zero (S32). Next, 1 is added to the number of printed sheets N (S33), and it is determined whether the number of printed sheets N is equal to or smaller than a predetermined number of printed sheets Nt (S34). When the number of printed sheets N is equal to or less than the predetermined number of printed sheets Nt (S34: YES), it is determined that a rounded stack is likely to occur, and curl suppression printing processing (S35 to S38) is performed. The curl suppression printing process (S35 to S38) is the same as steps S12 to S15 in the flowchart shown in FIG. 4, except that if NO in step S38, the process returns to step S33. That is, every time one sheet is printed, it is determined whether or not the number of printed sheets N is increased by 1 and is equal to or smaller than the number of printed sheets Nt. If the number of printed sheets N is greater than the predetermined number of printed sheets Nt (S34: NO), it is determined that the rounded stack is unlikely to occur, and single-sided printing processing (S29 to S31) is performed.

  In the present embodiment, since the determination based on the number N of printed sheets is made in addition to the determination based on the paper length L and the paper width W, the curl-suppressing printing process is performed with more limited cases where the paper is likely to be rounded and stacked. Is called. Therefore, it is possible to suppress the curling stack of sheets more efficiently.

  FIG. 18 is a diagram for explaining a method for changing print information when print information is changed by the personal computer 10 and then output to the control device 8 in the present embodiment. FIG. 18A shows print information before change, which is the same as that shown in FIG. FIG. 18B shows the print information after the change when it is determined from the paper size data in the print information of FIG. In the print information shown in FIG. 18B, the printing method data is changed from single-sided printing to double-sided printing as in FIG. 15B, and blank paper print data is inserted after the print data of each page. However, in FIG. 15B, blank page print data is inserted up to the last nth page, but in FIG. 18B, after blank page print data is inserted up to the Ntth page, printing method data indicating single-sided printing is displayed. Has been inserted. In the case of Nt ≧ n, blank paper print data is inserted up to the last nth page as in FIG. 15B.

  When the print information after this change is input, the control device 8 performs double-sided printing processing up to the Ntth page, and performs single-sided printing processing from the (Nt + 1) th page. Thereby, the control device 8 can perform the printing process according to the input print information without determining whether or not to perform the curl suppression printing process.

  In the above embodiment, the printer apparatus that prints print data input from a personal computer has been described. However, the present invention is not limited to this. The present invention can also be applied to a facsimile apparatus that prints print data that is input via a connected telephone line, a copier that prints print data read by a scanner, or a multi-function peripheral of these.

  The image forming apparatus according to the present invention is not limited to the above-described embodiment. The specific configuration of each part of the image forming apparatus according to the present invention can be varied in design in various ways.

Regarding the above embodiment, the following additional notes are disclosed.
(Supplementary Note 1) Paper supply means for supplying paper, a photosensitive drum for forming a toner image of an image to be imaged, and supplied from the paper supply means for transferring the toner image onto the paper A transfer unit that presses the sheet to be in contact with the photosensitive drum; a fixing unit that heats the sheet conveyed from the transfer unit to melt and fix the toner image transferred to the sheet; and a heating unit that heats the sheet. Based on the temperature detected by the temperature detecting means for detecting the temperature of the fixing means, the temperature detecting means for detecting the temperature of the fixing means, the higher the temperature, the faster the paper discharging speed. An image forming apparatus comprising: a discharge speed control unit that changes a discharge speed of the paper to the paper discharge tray by the discharge unit.
(Supplementary Note 2) When the temperature detected by the temperature detection means is lower than a predetermined temperature, the discharge speed control means sets the discharge speed of the discharge means to a normal discharge speed, and the temperature detection means The image forming apparatus according to appendix 1, wherein when the detected temperature is equal to or higher than the predetermined temperature, the discharge speed of the discharge unit is increased to a predetermined speed higher than the normal discharge speed.
(Supplementary Note 3) A discharge direction switching unit that is provided at a discharge port of the discharge tray and switches the discharge direction of the paper, a temperature detection unit that detects the temperature of the fixing unit, and a temperature detected by the temperature detection unit Is lower than a predetermined temperature, the discharge direction is set to a normal discharge direction, and when the temperature detected by the temperature detecting means is equal to or higher than the predetermined temperature, the discharge direction is set to the normal discharge direction. An image forming apparatus further comprising: a discharge direction control unit configured to set a predetermined discharge direction closer to the discharge tray.
(Supplementary Note 4) A discharge direction switching unit that is provided at a discharge port of the discharge tray and switches the discharge direction of the paper, a temperature detection unit that detects the temperature of the fixing unit, and a temperature detected by the temperature detection unit Is lower than a predetermined temperature, the discharge speed of the discharge means is set to a normal discharge speed, and when the temperature detected by the temperature detection means is equal to or higher than the predetermined temperature, the discharge speed of the discharge means is The discharge speed control means for raising the discharge speed to a predetermined speed higher than the normal discharge speed, and when the temperature detected by the temperature detection means is smaller than the predetermined temperature, the discharge direction is set to the normal discharge direction. When the temperature detected by the temperature detecting means is equal to or higher than the predetermined temperature, the discharge direction is set to a predetermined value that brings the discharge direction closer to the discharge tray than the normal discharge direction. Further comprising a discharging direction controlling means for setting the direction out, the image forming apparatus according to note 3.
(Supplementary Note 5) A paper supply means for supplying paper, a photosensitive drum for forming a toner image of an image to be imaged, and a paper supply means for transferring the toner image onto the paper. A transfer unit that presses the sheet to be in contact with the photosensitive drum; a fixing unit that heats the sheet conveyed from the transfer unit to melt and fix the toner image transferred to the sheet; and a heating unit that heats the sheet. A discharge unit that discharges the discharged sheet to a discharge tray; and a sheet detection unit that detects the size of the sheet on which an image is formed. The discharge tray is adjustable in height in multiple stages. Lifting means for moving the paper tray up and down and discharge tray adjusting means for moving the discharge tray up and down by the lifting means based on the size of the paper detected by the paper detection means. Comprising, an image forming apparatus.
(Supplementary Note 6) The paper discharge tray rotates to the first panel corresponding to the position where the front end of the paper discharged from the discharge port contacts, and the front end of the first panel in the paper discharge direction. A second panel supported so as to be able to move, and the lift means moves up and down the first panel in order to change the distance between the first panel and the outlet. And a second elevating means for moving the second panel up and down in order to change an angle formed by the first panel and the second panel, and the paper discharge tray adjusting means is configured to detect the paper. Based on the size of the paper detected by the means, the first panel and the second panel are moved up and down by the first lifting and lowering means, so that the position of the discharge tray and The image according to appendix 5, which changes its shape Forming apparatus.
(Additional remark 7) It further has a load amount detection means for detecting the load amount of the paper discharged to the discharge tray, and the discharge tray adjustment means has a load amount detected by the load amount detection means, The image forming apparatus according to appendix 5 or 6, wherein the position of the paper discharge tray is changed.
(Supplementary Note 8) A temperature / humidity detection unit that detects internal temperature and humidity is further provided, and the discharge tray adjustment unit is configured to detect the position of the discharge tray according to the temperature and humidity detected by the temperature / humidity detection unit. 8. The image forming apparatus according to any one of appendices 5 to 7, wherein:
(Supplementary Note 9) The paper detection means also detects the thickness of the paper, and the paper discharge tray adjustment means changes the position of the paper discharge tray according to the paper thickness detected by the paper detection means. The image forming apparatus according to any one of appendices 5 to 8.
(Supplementary Note 10) The paper detection means also detects the type of paper, and the paper discharge tray adjustment means changes the position of the paper discharge tray according to the paper type detected by the paper detection means. The image forming apparatus according to any one of appendices 5 to 9.
(Supplementary Note 11) A paper supply means for supplying paper, a photosensitive drum for forming a toner image of an image to be imaged, and a paper supply means for transferring the toner image onto the paper. A transfer unit that presses the sheet to be in contact with the photosensitive drum; a fixing unit that heats the sheet conveyed from the transfer unit to melt and fix the toner image transferred to the sheet; and a heating unit that heats the sheet. An image forming apparatus further comprising: a discharge unit that discharges the discharged paper to a discharge tray; and a paper reversing unit that reverses the paper heated by the fixing unit, and sets a size of the paper on which the image is formed A paper setting unit that determines whether the size of the paper set by the paper setting unit satisfies a predetermined condition, and the paper supplied from the paper supply unit is displayed on one side. A second discriminating unit that discriminates whether or not the sheet is formed; and a sheet heated by the fixing unit when the sheet is image-formed on one side and the size of the sheet satisfies the predetermined condition. Is reversed by the paper reversing means, heated by the fixing means, and then discharged by the discharge means to the paper discharge tray. When the paper is image-formed on one side, the size of the paper is the predetermined size. An image forming apparatus comprising: an image forming control unit that discharges the sheet heated by the fixing unit to the sheet discharge tray when the condition is not satisfied.
(Additional remark 12) The image formation control means is a white paper as a toner image to be imaged on the photosensitive drum when the paper is image-formed on one side and the size of the paper satisfies the predetermined condition. 12. The image forming apparatus according to claim 11, wherein the toner image is formed and the sheet reversed by the sheet reversing unit is pressed against the photosensitive drum by the transfer unit.
(Additional remark 13) It further has a paper number discrimination means for judging whether or not the number of sheets discharged to the paper discharge tray is equal to or less than a predetermined number, and the image formation control means forms the image on one side of the paper. In the case where the size of each sheet satisfies the predetermined condition, when the number of sheets is equal to or less than the predetermined number, the sheet heated by the fixing unit is reversed by the sheet reversing unit, After being heated by the fixing unit, the sheet is discharged to the discharge tray by the discharge unit. When the number of sheets is larger than the predetermined number, the sheet heated by the fixing unit is discharged by the discharge unit to the discharge tray. The image forming apparatus according to appendix 11 or 12, wherein
(Supplementary note 14) The image forming apparatus according to any one of supplementary notes 11 to 13, wherein the predetermined condition is that a paper length which is a length in a conveyance direction of the paper is a predetermined paper length or more.
(Supplementary note 15) The image formation according to any one of supplementary notes 11 to 13, wherein the predetermined condition is that a paper width, which is a length in a direction orthogonal to a conveyance direction of the paper, is equal to or less than a predetermined paper width. apparatus.
(Supplementary Note 16) The predetermined condition is that the length of the paper in the transport direction is equal to or longer than the predetermined paper length, and the paper width of the length in the direction orthogonal to the transport direction is predetermined. 14. The image forming apparatus according to any one of appendices 11 to 13, wherein the image forming apparatus is equal to or less than a sheet width.
(Supplementary Note 17) The paper detection means also detects the type of paper, and the image formation control means is when the paper is image-formed on one side and the size of each paper satisfies the predetermined condition. When the detected paper type is a predetermined type, the paper heated by the fixing means is reversed by the paper reversing means, heated by the fixing means, and then discharged by the discharge means. When the detected paper type is not the predetermined type, the paper heated by the fixing unit is discharged to the paper discharge tray by the discharge unit. Image forming apparatus.

1, 1A, 1B, 1C Image forming apparatus 21 Photosensitive drum 22 Charging roller 23 Exposure unit 24 Development unit 25 Transfer roller (transfer means)
26 Cleaner 3, 3 'Fixing device (fixing means)
31 Fixing roller 32 Pressure roller 33 Temperature sensor (temperature detection means)
34 Paper discharge sensor 41 Branch guide (paper reversing means)
42 Paper discharge roller (discharge means, paper reversing means)
43, 44 Conveyance roller (paper supply means)
5 Conveying roller (discharge means)
6, 6 'discharge tray 6'a first panel 6'b second panel 6'c third panel 61 first elevating shaft (elevating means, first elevating means)
62 Second lifting shaft (lifting means, second lifting means)
63, 64 Drive motor (lifting means)
65 Load sensor (load detection means)
65a Detection lever 66 Branch guide 67 Separator (discharge direction switching means)
7 Feed cassette 8 Control device (paper setting means, discrimination means, second discrimination means, image formation control means, paper number discrimination means, paper discharge tray adjustment means, discharge speed control means, discharge direction control means)
9 Operation panel 10 PC

Claims (2)

Paper supply means for supplying paper;
A photosensitive drum for forming a toner image of an image to be imaged;
Transfer means for pressing the paper supplied from the paper supply means against the photosensitive drum in order to transfer the toner image onto the paper;
Fixing means for heating the paper conveyed from the transfer means in order to melt and fix the toner image transferred to the paper;
A discharge means for discharging the paper heated by the fixing means to a discharge tray;
Elevating means for vertically moving the paper discharge tray;
Paper detection means for detecting the size of the paper on which the image is formed;
A discharge tray adjusting unit that moves the discharge tray up and down by the lifting unit based on the size of the sheet detected by the sheet detection unit;
With
The discharge tray can be adjusted in multiple stages in height ,
The paper discharge tray is rotatably supported by a first panel corresponding to a position where the front end of the paper discharged from the discharge port abuts and a front end portion of the first panel in the paper discharge direction. A second panel,
The elevating means includes first elevating means for moving the first panel up and down in order to change the distance between the first panel and the discharge port, the first panel, and the second panel. Second elevating means for moving the second panel up and down to change the angle formed by
The paper discharge tray adjusting means may be configured such that when the paper length detected by the paper detection means is the first length, the paper length is less than the second length than when the paper length is the second length. An image forming apparatus that causes the first lifting and lowering means to move the first panel and the second panel up and down so that an angle formed by one panel and the second panel is small. . A load amount detecting means for detecting a load amount of the paper discharged to the discharge tray;
The discharge tray adjusting means changes the position of the discharge tray according to the stacking amount detected by the stacking amount detecting means;
The image forming apparatus according to claim 1 .

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