JP2006071803A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming apparatus and an image forming method surely correcting curling of a recording medium. <P>SOLUTION: The image forming apparatus is provided with an idle paper passing mode having recording paper P pass through a fixing apparatus 32 before image formation by an image forming part 50 or after fixing by toner in the fixing apparatus 32. Curling of the recording paper P is surely corrected with the idle paper passing mode. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus and an image forming method.

  In the image forming apparatus, an image is formed on a recording medium such as recording paper by an image forming material such as toner, and the recording medium may be curled due to various factors. A recording medium having a large curl remains curled even in a state where it is discharged to a discharge tray or the like, so that the accommodation property is deteriorated.

  In order to correct the curl of the recording medium, various methods and structures have been conventionally proposed. For example, Patent Document 1 describes a printing apparatus having a correction unit that corrects curl by a curved portion when a sheet after a print pattern is fixed passes.

However, even if curl correction is performed by a correction means having such a curved portion, the effect may not be sufficient, and a large curl may remain on the recording medium.
Japanese Patent Laid-Open No. 11-2224012

  In view of the above facts, an object of the present invention is to obtain an image forming apparatus and an image forming method capable of more reliably correcting curling of a recording medium.

  According to the first aspect of the present invention, an image forming unit that forms an image by adhering an image forming material to a recording medium, and the recording medium on which the image is formed by the image forming unit is conveyed and sandwiched on the recording medium. A fixing unit for fixing the image forming material, and at least one of before the image formation by the image forming unit or after the fixing of the image forming material by the fixing unit, the recording medium is nipped by the fixing unit and conveyed. A paper passing mode.

  In this image forming apparatus, an image forming material is adhered to a recording medium in an image forming unit. The image forming material can be fixed to the recording medium while the fixing unit conveys the recording medium while pinching it.

  In this image forming apparatus, at least before image formation by the image forming unit (hereinafter simply referred to as “before image formation”) or after fixing of the image forming material by the fixing unit (hereinafter simply referred to as “after fixing”). On the other hand, there is an empty paper passing mode in which the recording medium is conveyed while being sandwiched between fixing units. By performing this empty paper passing mode, the curl of the recording medium can be corrected more reliably.

  According to a second aspect of the present invention, in the first aspect of the present invention, the image forming apparatus further includes a reverse conveyance unit that reverses and conveys the recording medium on which the image forming material is fixed by the fixing unit to the image forming unit. Features.

  Therefore, it is possible to form and fix images on both sides of the recording medium. And against the recording medium on which images are formed on both sides. The curl can be corrected more reliably.

  3. The image forming apparatus according to claim 1 or 2, wherein, for example, a so-called image generated after image recording on a recording medium (especially thick paper) is performed when an empty paper feeding mode is performed before fixing as described in claim 9. Curling can be effectively corrected.

  In the empty paper passing mode before fixing, the thickness of the recording medium is equal to or greater than a predetermined value as described in claim 10, and the basis weight of the recording medium is equal to or greater than a predetermined value as described in claim 11. In this case, it is considered that image curling is likely to occur. In addition, when the recording medium is a specific size as described in claim 12, it is assumed that the thickness of the recording medium is equal to or greater than a predetermined value or the basis weight is equal to or greater than a predetermined value, and the empty paper passing mode before fixing is performed. May be.

  Further, as the fixing unit, for example, as described in claim 3, when the thermal recording unit fixes the image forming material by heating the pre-recording medium, the image forming material is recorded with a simple configuration. It can be reliably fixed on the medium.

  In this configuration, if the empty sheet passing mode is performed before image formation as described in claim 13, so-called side curl of the recording medium (particularly plain paper) can be effectively suppressed.

  In the empty paper feeding mode before image formation, the basis weight of the recording medium is equal to or less than a predetermined value when the thickness of the recording medium is equal to or less than a predetermined value as described in claim 14. In such cases, it is considered that side curl is likely to occur. Further, as described in claim 4, the image forming apparatus includes a resistance measuring unit that measures an electric resistance value of the recording medium before image formation by the image forming unit. In addition, if the electrical resistance value is greater than or equal to a predetermined value, the moisture content of the recording medium is also greater than or equal to the predetermined value, and side curl is likely to occur. It is preferable.

  As described above, by performing the curl correction only when the conditions of the recording medium where the curl is likely to occur are satisfied, compared with the case where the curl correction is uniformly performed on all the recording media, Productivity can be increased.

  Further, as described in claim 5, when the fixing unit is capable of changing the amount of heating to the recording medium at least in the empty paper passing mode, the heating is more suitable for curl correction, which is different from that at the time of fixing. Can curl as a quantity. Also, it is possible to set conditions suitable for fixing at the time of fixing.

  The heating amount from the fixing unit to the recording medium can be changed, for example, in the empty paper passing mode by passing the fixing unit at a conveyance speed different from that during fixing, or the temperature of the fixing unit itself can be changed. It may be said. In this configuration, as described in claim 6, temperature detecting means for detecting the temperature of the fixing unit may be provided.

  In the configuration in which the temperature of the fixing unit is detected by the temperature detecting unit, the timing of performing the empty sheet passing in the empty sheet passing mode based on the temperature of the fixing unit detected by the temperature detecting unit, as described in claim 17. By controlling this, it is possible to wait until the temperature suitable for curl correction is reached at the fixing unit and perform the empty paper passing mode.

  According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, the fixing unit can change a clamping force to the recording medium at least in the empty paper passing mode. It is characterized by.

  In this way, by changing the pinching force to the recording medium between the fixing time and the empty paper passing mode, the curling force can be corrected as a pinching force more suitable for curling correction.

  According to an eighth aspect of the present invention, in the first aspect of the first to seventh aspects of the present invention, a recording medium accommodating portion for accommodating a recording medium before image formation, and a recording medium in the recording medium accommodating portion Control means for storing at least one of a first elapsed time since the image was stored and a second elapsed time since the last image formation, and controlling the image forming unit and the fixing unit based on the storage result; It is characterized by having.

  Thus, by controlling the image forming unit and the fixing unit based on at least one of the first elapsed time and the second elapsed time, the state (for example, moisture content) of the recording medium is predicted, and control corresponding to this is performed. Can be done. Note that this control includes adjusting whether or not the empty sheet passing mode is performed, or adjusting the time and the heating amount from the fixing unit to the recording medium when the empty sheet passing mode is performed.

  According to the invention of claim 18, an image forming portion that forms an image by attaching an image forming material to a recording medium, and the recording medium on which the image is formed by the image forming portion is conveyed and held on the recording medium. A fixing roll for fixing the image forming material, a first discharge unit from which the recording medium on which the image forming material has been fixed is discharged, and conveying the recording medium from the fixing roll to the first discharge unit, A transport roll that can be reversed in a direction opposite to the transport direction; and a second discharge unit that discharges the recording medium transported by the reverse rotation of the transport roll, and transports the recording medium when the transport roll is reversed. The path is curved toward the non-image forming surface side of the recording medium.

  According to a nineteenth aspect of the present invention, an image forming unit that forms an image by attaching an image forming material to a recording medium, and a recording medium on which the image is formed by the image forming unit are conveyed and held on the recording medium. A fixing roll for fixing the image forming material, a first discharge unit from which the recording medium on which the image forming material has been fixed is discharged, and conveying the recording medium from the fixing roll to the first discharge unit, A transport roll that can be reversed in a direction opposite to the transport direction; and a second discharge unit that discharges the recording medium transported by the reverse rotation of the transport roll, and transports the recording medium when the transport roll is reversed. The direction is located closer to the non-image forming surface than the holding tangent of the transport roll.

  According to the invention of claim 20, an image forming unit for forming an image by attaching an image forming material to a recording medium, and a recording medium on which the image is formed by the image forming unit are conveyed and sandwiched on the recording medium. A fixing roll for fixing the image forming material, a first discharge unit from which the recording medium on which the image forming material has been fixed is discharged, and conveying the recording medium from the fixing roll to the first discharge unit, A transport roll that can be reversed in a direction opposite to the transport direction; and a second discharge unit that discharges the recording medium transported by the reverse rotation of the transport roll, and transports the recording medium when the transport roll is reversed. The path is curved in a direction opposite to the conveyance path of the recording medium from the fixing roll to the conveyance roll.

  21. The recording medium in which an image is formed in the image forming section and the image forming material is fixed by the fixing roll is transported by the transport roll and discharged to the first discharge section. be able to. Further, by reversing the transport roll, the recording medium can be reversed and discharged to the second discharge unit.

  In any of the configurations described in claims 18 to 20, when the recording medium is reversed and discharged to the second discharge portion by the reverse rotation of the transport roll, the recording medium is curved toward the non-image forming surface side. Will be. Thereby, the side curl of the recording medium can be reliably corrected.

  Since the present invention has the above-described configuration, the curling of the recording medium can be corrected more reliably.

  FIG. 1 shows an image forming apparatus 12 according to the first embodiment of the present invention.

  A paper feed tray 16 that is detachable from the housing 14 is disposed at the lower part of the housing 14 of the image forming apparatus 12, and the recording paper P stacked in the paper feed tray 16 is sequentially taken out by a pickup roll 18. Can be transported. The paper feed tray 16 is provided with a size detection sensor 17 so that the size of the stored recording paper P can be detected.

  A transport roll 20 is disposed at a predetermined position in the housing 14 and constitutes a transport path 22 for transporting the recording paper P. Further, guide members 24 are arranged on both sides of the conveyance path 22, and the recording paper P is guided along the conveyance path 22. In the following, the terms “upstream” and “downstream” simply mean upstream and downstream in the transport direction, respectively.

  In the middle of the conveyance path 22, the photosensitive drum 26 is disposed so as to contact the recording paper P, and rotates while being in contact with the recording paper P. The surface of the photosensitive drum 26 is charged by a charging device (not shown), and then an exposure device 28 irradiates a laser beam corresponding to image information to form an electrostatic latent image. The electrostatic latent image is developed (visualized) by supplying toner from the developing device 30. At the contact portion with the recording paper P, the photosensitive drum 26 is in close contact with the recording paper P by sandwiching the recording paper P with the transfer roll 29. As a result, the toner image on the photosensitive drum 26 is transferred to the recording paper P, and an image is formed on the recording paper P. The image forming unit 50 of the present invention is configured including the photosensitive drum 26, the exposure device 28, the developing device 30, and the like.

  A resistance value sensor 46 that detects the electrical resistance value of the recording paper P is disposed on the upstream side of the transfer roll 29. As the resistance value sensor 46, for example, a sensor or the like that measures a current value that actually flows can be applied by applying a voltage by bringing electrodes into contact with two points of the recording paper P, but is not limited thereto. Note that since there is generally a one-to-one relationship between the moisture content of the recording paper P and the resistance value, the moisture content of the recording paper P is indirectly detected by detecting the resistance value of the recording paper P in this way. You can know the rate.

  A fixing device 32 is disposed on the downstream side of the photosensitive drum 26. Of the two rolls constituting the fixing device 32, at least the roll contacting the image forming surface of the recording paper P is a heating roll 32H provided with a heater 33 (see FIG. 3 and the like) inside, and the other roll is pressurized. The roll is 32N. Then, the recording paper P is rotated by sandwiching the recording paper P by these two rolls, whereby the recording paper P is heated and the toner constituting the toner image of the recording paper P is fixed to the recording paper P.

  A first discharge roll 34 </ b> A is disposed on the downstream side of the fixing device 32, and discharges the recording paper P to a first discharge tray 36 </ b> A provided at the top of the housing 14. Further, the first discharge roll 34A can be reversed in the direction opposite to the direction in which the recording paper P is conveyed to the first discharge tray 36A. The recording paper P is sent to the reversing unit 38 attached. A switching member 55 for switching the conveyance direction of the recording paper P is provided downstream of the fixing device 32.

  A scanner 54 is provided above the casing 14 so that image information formed on a sheet or the like can be read.

  A switching member 56 is provided in the reversing unit 38 in the vicinity of the housing 14, and a predetermined reversing path 44 is constituted by a reversing roll 40 and a reversing guide member 42 in the center. On the opposite side of the reversing unit 38 from the housing 14, a second discharge roll 34 </ b> B for nipping and conveying the recording paper P and a second discharge tray 36 </ b> B for discharging the recording paper P are provided. The recording paper P is sent to either the reverse path 44 or the second discharge roll 34B by the switching member 56.

  The recording paper P that has passed through the reversing path 44 is joined to the transport path 22 from the upstream side of the transport roll 20. In this state, the photosensitive drum 26 comes into contact with the surface (non-image forming surface) opposite to the image forming surface on which the image is formed before reversal, so that the image can be formed on both surfaces of the recording paper P. On the other hand, the recording paper P sent to the second discharge roll 34B is discharged to the second discharge tray.

  As shown in FIG. 2, signals from the size detection sensor 17 and the resistance value sensor 46 are sent to the control device 52, and based on the signals, the control device 52 picks up the roll 18, the transport roll 20, and the image forming unit 50. The fixing device 32, the first discharge roll 34A, the second discharge roll 34B, the switching members 55 and 56, and the like are controlled. In particular, the present invention has an empty paper passing mode in which the recording paper P is passed through the fixing device 32 before image formation by the image forming unit 50 or after toner fixing by the fixing device 32. The control device 52 performs overall control of the image forming apparatus 12 including mode control.

  Next, the process of forming an image on the recording paper P by the image forming apparatus 12 of the present embodiment and the operation thereof will be described.

  First, a case where an image is formed on the plain paper P1 as the recording paper P will be described with reference to FIGS. In the following drawings, a part of the configuration of the image forming apparatus is omitted or simplified.

  The plain paper P1 is a thin paper compared to a thick paper P2 described later. In general, as the recording paper P becomes thinner or softer (basis weight becomes smaller), the side curl tends to increase. Further, the side curl is considered to be greatly affected by the moisture content of the plain paper P1. For example, in the graph shown in FIG. 22, it can be seen that the smaller the basis weight (although there is some variation), the greater the anti-image curl, that is, the curl toward the non-image forming surface side. It can also be seen that the higher the moisture content, the greater the anti-image curl. This anti-image curl is a curl toward the non-image forming surface, and includes the above-mentioned side curl in a broad sense.

  The plain paper P1 taken out from the paper feed tray 16 by the pickup roll 18 is conveyed by the conveyance roll 20 and the resistance value of the plain paper P1 is detected by the resistance value sensor 46 before the image forming unit 50 forms an image. .

  When this resistance value is equal to or greater than a predetermined value, the moisture content of the plain paper P1 is also equal to or greater than the predetermined value, and it is considered that so-called side curl is likely to occur on the plain paper P1. Therefore, in this case, the control device 52 performs the empty sheet passing mode before the image forming unit 50 forms an image. That is, as shown in FIG. 3, the image forming unit 50 passes the paper without forming an image on one side, passes through the fixing device 32 (empty paper), and heats the plain paper P1. By this heating, a part of the water content of the plain paper P1 evaporates and the moisture content decreases.

  Thereafter, the first discharge roll 34A is reversed with the first discharge roll 34A once holding the plain paper P1, and the plain paper P1 is fed again into the transport path 22 through the reverse path 44 as shown in FIG. Thereafter, the resistance value of the plain paper P1 is measured in the same manner, and if it exceeds the predetermined value, the empty paper passing mode is performed. However, in general, the water content of the plain paper P1 can be reduced to such an extent that curling can be suppressed in the single paper passing mode.

  When the resistance value of the plain paper P1 is equal to or less than a predetermined value, image formation by the image forming unit 50 and toner fixing by the fixing device 32 are sequentially performed as shown in FIG. At this time, since the plain paper P1 is so-called preheated by empty paper, it can be fixed even if the temperature (fixing output) of the fixing device 32 is low.

  When an image is formed only on one side of the plain paper P1, the first discharge roll 34A is rotated forward to discharge the plain paper P1 to the first discharge tray 36A. In the case of forming an image on both sides of the plain paper P1, the first discharge roll 34A is reversed with the plain paper P1 being sandwiched, and the plain paper P1 is sent again to the transport path 22 through the reverse path 44, and the plain paper P1. An image may be formed on the non-image forming surface.

  Since the discharged plain paper P1 is suppressed from generating side curls, the storage capacity in the first discharge tray 36A is increased. Further, in the plain paper P1 in which the side curl is generated, the peelability from the photosensitive drum 26 is deteriorated particularly when the image is formed on both sides, and the end of the plain paper P1 comes into contact with the guide member 24. However, in this embodiment, such a paper jam can also be prevented.

  In the above description, the moisture content predicted from the resistance value of the plain paper P1 is used as a judgment material for determining whether or not the empty paper passing mode is performed on the plain paper P1, but the judgment material is not limited to this. Table 1 shows various judgment materials that can be used, the relationship between ON (execution) and OFF (non-execution) of the empty paper passing mode, and the productivity in each case. This “productivity” refers to the number of recording sheets P that can form an image per unit time (here, per minute) and discharge it to the first discharge tray 36A.

  For example, when the moisture content of the recording paper P can be directly measured, the execution / non-execution of the empty paper passing mode may be determined based on the moisture content. In the case of general plain paper P1, side curl can be effectively suppressed by performing the empty paper passing mode when the moisture content is 7 to 8% or more.

Further, when the thickness or basis weight of the plain paper P1 is equal to or less than a predetermined value, it is considered that side curl is likely to occur. In these cases, the empty paper passing mode may be performed. In the case of general plain paper, when the thickness is about 80 μm or less, or when the basis weight is 64 g / m ² or less, side curl is likely to occur (or the side curl becomes larger). The empty paper passing mode before image formation may be performed.

  Even when any of the above judgment materials is used, the productivity when the empty paper passing mode is performed is 20 ppm. Although this is lower than the productivity (30 ppm) when the empty paper passing mode is not performed, it is possible to maintain high productivity. In particular, as in the present invention, in the configuration in which execution / non-execution of the empty paper passing mode is determined for each plain paper P1 in units of one sheet, the empty paper passing mode is uniformly applied to all the plain papers P1. In comparison, a reduction in productivity can be suppressed.

  Next, a case where an image is formed on the thick paper P2 as the recording paper P will be described with reference to FIGS. The thick paper P2 is thicker than the plain paper P1, and side curl is difficult to occur, but so-called image curl after toner adhesion is likely to occur. More specifically, the image curl of the thick paper P2 occurs due to heat applied when passing through the fixing device 32, the thick paper P2 being curved along the shape of the transport path 22, and the like. The image curl tends to increase as the hardness of the thick paper P2 becomes harder or thicker.

  The thick paper P2 is also taken out from the paper feed tray 16 by the pickup roll 18 as in the case of the plain paper P1, but in this embodiment, the size detection sensor 17 (see FIG. 1) detects the size at the time of taking out. Then, in the case of a specific size, the recording paper P is regarded as a thick paper P2. Specifically, as shown in Table 2, when the size of the recording paper P is a postcard size / envelope size, the recording paper P is considered to be a thick paper P2, and when it is not a specific size, The paper P1 is considered (in the case where the recording paper P is considered to be the plain paper P1, the empty paper mode before image formation is performed as necessary as described above).

  For the thick paper P2, first, as shown in FIG. 6, after image formation by the image forming unit 50 and fixing by the fixing device 32, the thick paper P2 is moved to the reverse path 44 by reverse rotation of the first discharge roll 34A. Then, as shown in FIG. Here, when image formation is performed only on one side of the thick paper P2, an empty paper passing mode is performed as shown in FIG. That is, image formation by the image forming unit 50 is not performed, and the image curl of the thick paper P2 is corrected by passing through the fixing device 32 (empty paper). When image formation is performed also on the back surface of the thick paper P2, after the first image formation and fixing, the thick paper P2 passes through the reversing path 44 by reversing the first discharge roll 34A, and is sent again to the conveying path 22 to be reversed. Image formation and fixing are performed on the thick cardboard P2. Thereafter, the empty paper passing mode is performed.

  After the empty paper passing mode, the first discharge roll 34A is rotated forward to discharge the thick paper P2 to the first discharge tray 36A. Since the discharged cardboard P2 has its image curl corrected, the capacity in the first discharge tray 36A is increased.

  Note that the material for determining whether or not to perform the empty paper passing mode on the thick paper P2 is not limited to the above-described size. Table 2 above shows various judgment materials that can be used, the relationship between on (execution) and off (non-execution) of the empty paper passing mode, and the productivity in each case.

For example, when the thickness or basis weight of the recording paper P is a predetermined value or more, the recording paper P can be regarded as the thick paper P2, and image curl is likely to occur (or image curl becomes larger). In this case, the empty paper passing mode may be performed. In general, when the thickness is about 180 μm or more, or when the basis weight is 100 g / m ² or less, image curl is likely to occur. In these cases, an empty paper passing mode after fixing may be performed.

  Even when any of the above judgment materials is used, the productivity when the empty paper passing mode is performed is 20 ppm as in the case where the empty paper passing mode is performed on the plain paper P1 before image formation. It has become. Although this is lower than the productivity (30 ppm) when the empty paper passing mode is not performed, it is possible to maintain high productivity. In particular, in the configuration in which execution / non-execution of the empty paper passing mode is determined in units of one sheet for the plain paper P1 as in the present invention, the empty paper passing mode is uniformly applied to all the plain papers P1. Compared with, it is possible to suppress a decrease in productivity.

  In the above description, the heating amount and clamping force of the recording paper P in the empty paper passing mode are set according to the predicted curl amount (predicted curling amount) of the recording paper P, or at the time of fixing and the empty paper passing mode. If it can be changed according to time, fixing and curl correction can be performed under optimum conditions required for each, which is preferable.

  Table 3 shows an example of changing the temperature of the heating roll 32H (HR temperature), the conveyance speed of the recording paper P, and the nipping load according to the predicted curl amount of the recording paper P.

  For example, when the predicted curl amount is large, the temperature of the heating roll 32H of the fixing device 32 is also relatively high. Conversely, when the predicted curl amount is small, the temperature of the heating roll 32H is relatively low. This temperature adjustment can be performed, for example, by changing the energization amount to the heater 33 in the heating roll 32H.

  In this configuration, as shown in FIG. 9, there is a time difference ΔT until the temperature of the heating roll 32H reaches the set temperature in the empty paper passing mode from the set temperature during fixing. Therefore, as shown in FIG. 10, a temperature sensor 58 for detecting the temperature of the heating roll 32H of the fixing device 32 is provided, and the paper supply timing of the reverse feed roll 40F is adjusted by the control device 52 so that the heating roll 32H is empty. It is preferable to perform control so that the recording paper P reaches the fixing device 32 when the set temperature in the paper passing mode is reached.

  In addition, the amount of heat transferred from the fixing device 32 to the recording paper P can be adjusted as a result by changing the conveyance speed of the recording paper P. In this configuration, a so-called DC motor is preferably used as a drive motor for driving the roller of the fixing device 32. FIG. 11 shows changes in the conveyance speed when a DC motor and a stepping motor are used as the drive motor. In the configuration using the stepping motor, there is a deviation of the phase angle from when the conveyance speed change signal is received until the conveyance speed actually reaches a new value. On the other hand, in the configuration using a DC motor, this shift is short, and the transfer speed can be changed quickly in a short time, so that it is possible to cope with a sudden change in the transfer speed. For example, the conveyance speed can be changed from the middle of the first sheet of recording paper P to suppress or correct curling during the image formation of the first sheet.

  Further, in the above, as shown in FIG. 12, for example, the pressure roll 32N of the fixing device 32 is supported by the swing arm 60 so as to be swingable, and the clamping force for the recording paper P is set to the predicted curl amount by switching the clutch 62. In response, or in the empty paper passing mode, it may be different between the fixing time and the fixing time.

  Further, it is determined whether or not to perform the empty paper passing mode for the recording paper P, and in the case of performing the empty paper passing mode, how much the heating amount and the clamping force to the recording paper P are set. The adjustment is preferably performed in consideration of, for example, the elapsed time since the last image formation and the elapsed time after the recording paper P is stored in the paper feed tray 16.

  That is, as shown in FIG. 13, the time interval of the print signal from the previous image formation (previous job) to the next image formation is monitored. If this time is long, for example, the recording paper P is air It can be considered that the moisture content is increased by absorbing more of the moisture therein. Also, as shown in FIG. 14, the moisture content of the recording paper P becomes high even when the time from the paper feed tray 16 containing the recording paper P mounted on the housing 14 to the print signal is long. It is thought that there is. Moreover, in the paper feed tray 16, the moisture content of the recording paper P located at the end (upper and lower ends) in the stacking direction is higher than that of the recording paper P located in the middle. Conceivable.

  Therefore, in these cases, the processing shown in Table 4 is performed.

  As a specific measuring method of “time” in Table 4, for example, in the case shown in FIG. 13, the image forming end signal is stored in the control device 52, and the next image forming start is started from the previous image forming end signal. Measure the time to signal. In the case shown in FIG. 14, the attachment / detachment signal at the previous attachment / detachment is stored in the controller 52 by the attachment / detachment sensor of the paper feed tray 16, and the time from the attachment / detachment signal to the image formation start signal is measured.

  As shown in Table 4, when the time is in the range of 1 to 10 minutes, for example, the conveyance speed is relatively increased, the set temperature of the heating roll 32H is also increased, and the clamping force is also increased. Then, an empty sheet passing mode is performed on a predetermined number (for example, five sheets) of recording sheets P. On the other hand, when this time is in the range of 30 min or more, for example, the conveyance speed is relatively slow, the set temperature of the heating roll 32H is lowered, and the clamping force is also lowered.

  In addition to this, the temperature and humidity around the image forming apparatus 12 may be detected by a sensor, and the above control may be performed in consideration of these values.

  As can be understood from the above description, in the present embodiment, whether or not to perform the empty paper feeding mode is considered in consideration of not only the type of the recording paper P but also the environment and conditions at the time of image formation. Can individually control the heating amount and clamping force of the recording paper P, and the number of recording papers P that perform the empty paper passing mode, thereby achieving more reliable curl correction and high image formation productivity. Both can be achieved. In addition, since it is not necessary to change various conditions required for fixing, the fixing property is not deteriorated.

  Further, in the present embodiment, the curl correction of the recording paper P can be effectively performed only by adding control for performing the empty sheet passing mode in the image forming apparatus including the fixing device 32 and the reversing unit. . Since the addition of a new member and a big change of a structure are not accompanied, this invention can be comprised at low cost.

  FIG. 15 shows an image forming apparatus 112 according to the second embodiment of the present invention. In the following, the same components and members as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the image forming apparatus 112 of the second embodiment, the reversing unit 38 of the first embodiment is not provided, and the second discharge tray 36 </ b> B is directly attached to the housing 14. A second discharge roll 34B is attached to the housing 14.

  The second discharge tray 36B is rotated around a rotation shaft (not shown), and the discharge angle θ (inclination angle from the horizontal plane) can be changed. For example, the sheet discharge angle θ is 0 degree at the position indicated by the two-dot chain line in FIG. 15 and about 30 degrees at the position indicated by the solid line.

  In this image forming apparatus 112, the conveyance path 116 of the recording medium P after the reverse rotation of the first conveyance roll 34A has a curvature on the non-image forming surface side (non-image side) (that is, the image forming surface side, FIG. 15, the relative positions of the first transport roll 34 </ b> A and the second transport roll 34 </ b> B are determined so as to protrude downward.

  Therefore, in the image forming apparatus 112 according to the second embodiment, it is of course possible to discharge the recording paper P, on which the toner has been fixed by the fixing device 32, to the first discharge tray 36A without reversing the first discharge roll 34A. However, the first discharge roll 34A can be reversed, and the recording paper P can be sandwiched and conveyed by the second discharge roll 34B and discharged to the second discharge tray 36B. In the latter case, since the conveyance path 116 of the recording paper P has a curvature on the non-image forming surface side, the side curl of the recording paper P is corrected, and the recording paper P on the second discharge tray 36B is corrected. Capacity is also improved.

  Further, the second discharge tray 36 </ b> B is rotated around the rotation shaft 114 to change the discharge angle θ, thereby improving the accommodation performance.

  In the image forming apparatus 112 of the second embodiment, as a material for determining whether or not to perform curl correction with the curvature of the conveyance path 116 set to the non-image forming surface side, the moisture content of the recording paper P is the same as in the first embodiment. The rate, thickness, basis weight, ambient temperature / humidity, time elapsed since the last image formation, time elapsed since the paper feed tray 16 was mounted on the housing 14, and the like can be used.

  For example, as shown in Table 5, when the thickness of the recording paper P is relatively thick, the basis weight of the recording paper P is relatively large, or the ambient humidity (installation humidity) where the image forming apparatus 112 is installed ) Is relatively high, the discharge angle θ of the second discharge tray 36 may be set to 30 degrees to correct the side curl of the recording paper P.

  In the second embodiment, the configuration for correcting the side curl of the recording paper P using the discharge path from the first discharge roll 34A to the second discharge roll 34B is not limited to the above-described configuration, and for example, is shown below. The structure of each modification may be sufficient.

  In the example shown in FIG. 16, the conveyance path 116 constituted by the first discharge roll 34A and the second discharge roll 34B is a non-image forming surface than the tangent L1 when the recording paper P is sandwiched by the first discharge roll 34A. Located on the side.

  In the example shown in FIG. 17, the curvature of the conveyance path 116 (the direction in which the recording paper P is curved) is opposite to the curvature of the path from the heating roll 32H and the pressure roll 32N of the fixing device 32 to the first discharge roll 34A. It is supposed to be oriented.

  16 and FIG. 17, as a result, the side curl of the recording paper P is corrected in the transport path 116, and the storage capacity of the recording paper P in the second discharge tray 36B is improved. .

  FIG. 18 shows an image forming apparatus 212 according to the third embodiment of the present invention. In the second embodiment, an image forming apparatus that does not include the reversing unit 38 is described. However, in the third embodiment, the reversing unit 238 is provided.

  The reversing unit 238 has substantially the same configuration as the reversing unit 38 of the first embodiment, but the reversing unit 238 is provided with a second discharge roll 34B and a second discharge tray 36B similar to those of the second embodiment. It has been.

  As described above, even in the image forming apparatus 212 including the reversing unit 238, the side curl of the recording paper P is effectively corrected in the conveyance path 214 configured by the first discharge roll 34A and the reversal auxiliary roll 37. It can be set as the structure to do. By providing a configuration for correcting the side curl in the reversing unit 238, it is not necessary to provide a configuration for correcting the curl in the main body of the image forming apparatus 212, and the cost can be reduced.

  In place of the reversing unit 238, as shown in FIG. 19, a so-called finisher 240 (sometimes referred to as a sorter or a high capacity unit) is provided with a second discharge roll 34B and a second discharge tray 36B, so 214 may be configured. In the finisher 240, a plurality of second discharge trays 36B are provided in the vertical direction, and more recording paper P can be accommodated as compared with a configuration having only one second discharge tray 36B. Further, if necessary, a plurality of recording papers P can be classified (sorted, stacked, etc.) and stored. Even when the transport path 214 is configured in the finisher 240, it is not necessary to provide a configuration for curl correction in the main body of the image forming apparatus 212, so that the cost can be reduced.

  FIG. 20 shows an image forming apparatus 312 according to the fourth embodiment of the present invention. The image forming apparatus 312 includes a reversing unit 328 that is substantially the same as that of the third embodiment, but the auxiliary transport roll 242 is provided in the reversing unit 238, which is different from the reversing unit 138 of the second embodiment. Is different.

  In general, as the first discharge roll 34A and the second discharge roll 24B, a roll 241 with corrugation as shown in FIG. 21A is often used in order to improve accommodation. However, if the recording paper P in a wavy state with a roll having corrugation is nipped and conveyed, the recording paper P is stretched straight in a wavy state, which causes wrinkles.

  In contrast, as shown in FIG. 21B, in the present embodiment, a roll without corrugation is used as the auxiliary transport roll 242. Thereby, it is possible to prevent the recording paper P from being wrinkled.

  In the second to fourth embodiments, the image forming apparatus having the second conveyance roll 34B and the second discharge tray 36B has been described as an example. However, in these configurations, the image forming surface is in a lower side (so-called “so-called”). The sheet can be discharged to the second discharge tray 36B by face-down).

  In the second to fourth embodiments, since the second discharge tray 36B is located on the side of the casing 14 and can be arranged so as to be located on the user side of the image forming apparatus. The paper P can be easily taken out. Furthermore, it is easy to provide a space for arranging the scanner 54 above the first discharge tray 36A. In other words, even when the scanner 54 is provided, the second discharge tray 36 </ b> B can be provided to secure the discharge space for the recording paper P.

  In each embodiment of the present invention, the means for detecting the type, thickness, basis weight, etc. of the recording paper P is not limited to the above. For example, ultrasonic waves may be applied to the recording paper P from an ultrasonic measurement device, the return speed may be monitored, or the paper quality and properties of the recording paper P may be detected by an optical sensor (media sensor). In general, an external device such as a personal computer is often connected to the image forming apparatus, but the type of the recording paper P may be determined based on an input from the external device.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to a first embodiment of the present invention. 1 is a block diagram of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a conveyance path, a reverse path, and the vicinity thereof in the image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a conveyance path, a reverse path, and the vicinity thereof in the image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a conveyance path, a reverse path, and the vicinity thereof in the image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a conveyance path, a reverse path, and the vicinity thereof in the image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a conveyance path, a reverse path, and the vicinity thereof in the image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a conveyance path, a reverse path, and the vicinity thereof in the image forming apparatus according to the first embodiment of the present invention. 6 is a graph schematically showing a relationship between a recording paper feed timing and a temperature of a heating roll of a fixing device. FIG. 6 is a schematic diagram illustrating a conveyance path, a reverse path, and the vicinity thereof in an image forming apparatus according to a modification of the first embodiment of the present invention. It is a graph which shows roughly the timing of the change of the actual conveyance speed with respect to the conveyance speed change signal with a DC motor and a stepping motor. FIG. 6 is a schematic diagram illustrating a conveyance path, a reverse path, and the vicinity thereof in an image forming apparatus according to a modification of the first embodiment of the present invention. It is explanatory drawing which shows the case where the curl correction based on the time interval of the front and back print signals is performed. FIG. 9 is an explanatory diagram illustrating a case where curl correction is performed based on a time from mounting of a paper feed cassette to a print signal. It is the schematic which shows the structure of the image forming apparatus of 2nd Embodiment of this invention. It is the schematic which shows the structure of the image forming apparatus of the modification of 2nd Embodiment of this invention. It is the schematic which shows the structure of the image forming apparatus of the modification of 2nd Embodiment of this invention. It is the schematic which shows the structure of the image forming apparatus of 3rd Embodiment of this invention. It is the schematic which shows the structure of the image forming apparatus of the modification of 3rd Embodiment of this invention. It is the schematic which shows the structure of the image forming apparatus of 4th Embodiment of this invention. It is the schematic which shows a discharge roll, (A) shows the discharge roll with which the corrugation was attached, (B) shows the discharge roll of this invention without corrugation. 4 is a graph showing the relationship between the basis weight and curl amount of a recording sheet classified according to the moisture content.

Explanation of symbols

DESCRIPTION OF SYMBOLS 12 Image forming apparatus 14 Case 16 Paper feed tray 17 Size detection sensor 18 Pickup roll 20 Conveyance roll 22 Conveyance path 24 Guide member 24B Discharge roll 26 Photosensitive drum 28 Exposure apparatus 29 Transfer roll 30 Developing apparatus 32N Pressure roll 32H Heating roll 32 fixing device 33 heater 34A first discharge roll 34B second discharge roll 36A first discharge tray 36B second discharge tray 38 reverse unit 40 reverse roll 40F reverse feed roll 42 reverse guide member 44 reverse path 46 resistance value sensor 50 image forming unit 52 Control Device 54 Scanner 56 Switching Member 58 Temperature Sensor 60 Swing Arm 62 Clutch 112 Image Forming Device 114 Rotating Shaft 116 Conveyance Path 138 Reversing Unit 212 Image Forming 212 Image Forming Device 238 Reversing Unit 240 Fini Shah 242 auxiliary conveyance rolls 312 image forming apparatus 328 reversing unit P recording paper P1 plain paper P2 thick θ paper discharge angle L2 tangent

Claims (20)

An image forming unit that forms an image by attaching an image forming material to a recording medium;
A fixing unit for fixing the image forming material on the recording medium by conveying while sandwiching the recording medium on which the image is formed in the image forming unit;
With
An empty paper passing mode in which the recording medium is conveyed while being pinched by the fixing unit at least one of before the image formation by the image forming unit or after the fixing of the image forming material by the fixing unit
An image forming apparatus comprising: A reversing conveyance unit for reversing and conveying the recording medium on which the image forming material is fixed in the fixing unit to the image forming unit;
The image forming apparatus according to claim 1, further comprising:   The image forming apparatus according to claim 1, wherein the fixing unit is a thermal fixing unit that heats a recording medium and fixes an image forming material. Resistance measuring means for measuring an electric resistance value of a recording medium before image formation by the image forming unit;
The image forming apparatus according to claim 1, further comprising:   5. The image forming apparatus according to claim 2, wherein the fixing unit is capable of changing a heating amount to the recording medium at least in the empty paper passing mode. The fixing unit can change its temperature,
Temperature detecting means for detecting the temperature of the fixing unit;
The image forming apparatus according to claim 2, further comprising:   The image forming apparatus according to claim 1, wherein the fixing unit is configured to be able to change a holding force with respect to a recording medium at least in the empty paper passing mode. A recording medium storage unit for storing a recording medium before image formation;
At least one of a first elapsed time since the recording medium was stored in the recording medium storage unit and a second elapsed time from the previous image formation is stored, and the image forming unit and the fixing are based on the storage result Control means for controlling the unit,
The image forming apparatus according to claim 1, further comprising: An image forming method for forming an image on a recording medium using the image forming apparatus according to claim 1,
An image forming method, wherein the empty sheet passing mode is performed after fixing of the image forming material by the fixing unit.   The image forming method according to claim 9, wherein the empty paper passing mode is performed when a thickness of the recording medium is equal to or greater than a predetermined value.   The image forming method according to claim 9, wherein the empty paper passing mode is performed when a basis weight of the recording medium is equal to or greater than a predetermined value.   The image forming method according to claim 9, wherein the empty sheet passing mode is performed when a recording medium has a specific size. An image forming method for forming an image on a recording medium using the image forming apparatus according to claim 2,
An image forming method, wherein the empty sheet passing mode is performed before an image is formed on a recording medium by the image forming unit.   The image forming method according to claim 13, wherein the empty paper passing mode is performed when the thickness of the recording medium is equal to or less than a predetermined value.   The image forming method according to claim 13, wherein the empty paper passing mode is performed when a basis weight of the recording medium is a predetermined value or less. The image forming method according to claim 13, wherein an image is formed on a recording medium using the image forming apparatus according to claim 4.
An image forming method, wherein the empty paper passing mode is performed when the electrical resistance value is equal to or greater than a predetermined value. The image forming method according to claim 13, wherein an image is formed on a recording medium using the image forming apparatus according to claim 6.
An image forming method, comprising: controlling a timing of performing empty paper passing in the empty paper passing mode based on the temperature of the fixing unit detected by the temperature detecting unit. An image forming unit that forms an image by attaching an image forming material to a recording medium;
A fixing roll for fixing the image forming material on the recording medium by conveying while sandwiching the recording medium on which the image is formed in the image forming unit;
A first discharge unit for discharging the recording medium on which the image forming material is fixed as described above;
A transport roll that transports the recording medium from the fixing roll to the first discharge unit, and that can be reversed in a direction opposite to the transport direction;
A second discharge unit for discharging the recording medium conveyed by the reverse rotation of the conveyance roll;
With
An image forming apparatus, wherein a conveyance path of a recording medium when the conveyance roll is reversed is curved toward a non-image forming surface side of the recording medium. An image forming unit that forms an image by attaching an image forming material to a recording medium;
A fixing roll for fixing the image forming material on the recording medium by conveying while sandwiching the recording medium on which the image is formed in the image forming unit;
A first discharge unit for discharging the recording medium on which the image forming material is fixed as described above;
A transport roll that transports the recording medium from the fixing roll to the first discharge unit, and that can be reversed in a direction opposite to the transport direction;
A second discharge unit for discharging the recording medium conveyed by the reverse rotation of the conveyance roll;
With
An image forming apparatus, wherein a conveyance direction of a recording medium when the conveyance roll is reversed is positioned closer to a non-image forming surface than a pinching tangent of the conveyance roll. An image forming unit that forms an image by attaching an image forming material to a recording medium;
A fixing roll for fixing the image forming material on the recording medium by conveying while sandwiching the recording medium on which the image is formed in the image forming unit;
A first discharge unit for discharging the recording medium on which the image forming material is fixed as described above;
A transport roll that transports the recording medium from the fixing roll to the first discharge unit, and that can be reversed in a direction opposite to the transport direction;
A second discharge unit for discharging the recording medium conveyed by the reverse rotation of the conveyance roll;
With
An image forming apparatus, wherein a conveyance path of a recording medium when the conveyance roll is reversed is curved in a direction opposite to a conveyance path of a recording medium from the fixing roll to the conveyance roll.

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