JP2007101615A - Sheet conveying device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet conveying device with a configuration capable of preventing failure such as the occurrence of an abnormal image by preventing dew condensation from occurring. <P>SOLUTION: The sheet conveying device for ejecting a sheet on which a toner image has been fixed by heat/pressure by using a heating member and a pressure member arranged to be opposed to each other in a conveying path for the sheet on which the toner image is carried is provided with: a curved part 201A at a part of a sheet guide part for guiding the sheet on which the toner image has been fixed to an ejection part; and a sheet cooling part 204 at the curved part 201A. The sheet moving on the curved part 201A is cooled by moving while coming into contact with the curved part 201A by making its moving speed higher on a downstream side than on an upstream side in a conveying direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus, and more particularly to a configuration for preventing heat generated in a fixing process from affecting dew condensation on a peripheral portion and a sheet.

  In an image forming apparatus such as a copying machine, printer, or facsimile machine, an electrostatic latent image formed on a latent image carrier is subjected to a visible image processing in a development process, and then the visible image is used as one of recording media. An electrostatic transfer is performed on a sheet such as a certain recording paper, and the transferred visible image is obtained, for example, by heating and fixing to obtain a copy or a recorded product.

One of the components used for fixing is a heating roller and pressure roller that are opposed to each other across the sheet conveyance path, and heat and pressure are applied to the toner image in the process of nipping and conveying the sheet by both rollers. There is a configuration using a heat roller fixing system in which fixing is performed.
In recent years, the heat roller fixing method has advantages such as high heat efficiency and high speed, high heat transfer efficiency and stable fixing efficiency, and simple structure due to its use as a sheet conveyance medium. It has come to be used frequently.

The sheet after fixing is discharged to a discharge tray or the like by a sheet conveying device having a discharge roller disposed in the vicinity of the heating roller and the pressure roller.
The toner image is melted and permeated by the action of heat and pressure, and is fixed to the sheet through a curing process due to a decrease in temperature. However, the sheet after fixing is often extremely hot, and may reach a temperature exceeding 100 ° C., for example. For this reason, when continuous fixing operations are performed, when a new fixed sheet is stacked on the sheets stacked on the paper discharge tray, the toner has not yet been cooled and cured. The image may be rubbed due to the rubbing of the image, or the toner that has been cooled and cured by heat accumulation may be remelted on the stacked sheets, which may cause the toner image to peel off.

  Conventionally, in order to prevent the occurrence of such image defects, a heat pipe is used for a belt used as a conveyance member for a sheet conveyed after fixing or for a conveyance unit facing a roller for conveying a sheet. A configuration has been proposed in which the toner on the sheet is cooled by heat radiation through a heat pipe (for example, Patent Documents 1 and 2).

JP 2004-279542 A (paragraph “0045” column) JP 04-26005 (paragraph "0011" column)

  However, since the configuration disclosed in the above-mentioned patent document is intended for the entire surface where the sheet such as the belt or the conveying member contacts and moves, the cooling is required in the case of a relatively large sheet conveying path structure. This is effective in that the area can be secured, but there are the following problems when a configuration that achieves downsizing, which has been increasingly demanded in recent years, is targeted.

  Along with the miniaturization, the length of the conveyance path from the fixing device to the discharge section such as the sheet discharge tray becomes shorter, and it becomes difficult not only to secure a space for installing a conventional cooling mechanism within this range. For example, in a case where the length of the height direction is reduced by curving the middle of the conveyance path to reduce the size of the apparatus, the fixing device and the sheet discharge tray are brought close to each other. There is a possibility that the toner image after fixing cannot be sufficiently cooled and cured because the distance is shortened.

  In particular, in a device intended for full-color image formation where the component mounting density is significantly higher than the number of component parts during monochrome image formation, the conveyance path to the sheet discharge section after fixing is the installation space for other component parts. In some cases, the space for providing the sheet cooling unit cannot be secured due to the fact that the sheet is likely to be restricted.

On the other hand, not only the sheet conveyance mechanism but also a detection unit such as a passage sensor for monitoring the sheet conveyance state may be disposed around the fixing device.
In the case of a configuration including such a detection means, a forced cooling air flow may be generated using a cooling fan or the like in order to avoid the cooling unit not being provided. Since the hot air is caused to flow, the flow of hot air also occurs in the portion where the detection means is arranged in a state where the conveyance path length is short, and the detection error in the detection means may become prominent.

  In addition, if a cooling mechanism is provided, especially when a means with high heat dissipation efficiency such as a heat pipe is used, the heat pipe and the conveyance path in contact with the heat pipe depending on the temperature and humidity around the heat pipe are used. Condensation may occur on the component. When condensation occurs, water droplets may adhere to the sheet moving on the conveyance path.

  If water droplets adhere to the sheet, the moisture content on the surface where the water droplets have adhered changes, causing curling or adverse effects on the charging characteristics during image formation at the next stage when duplex copying is performed. Or the toner image may be blurred.

  An object of the present invention is to allow efficient cooling of a sheet even with a short conveying path length in view of the problem in conveying a fixed sheet in the conventional sheet conveying apparatus, particularly a downsized apparatus. Another object of the present invention is to provide a sheet conveying apparatus and an image forming apparatus having a configuration capable of preventing remelting of toner.

  Another object of the present invention is to provide a sheet conveying apparatus and an image forming apparatus having a configuration capable of preventing problems such as occurrence of abnormal images without causing condensation even when the conveying path length is short. is there.

  In order to achieve this object, according to the first aspect of the present invention, a toner image is fixed by heat and pressure by using a heating member and a pressure member that are arranged opposite to each other in a conveyance path of a sheet carrying the toner image. In the sheet conveying apparatus for discharging the sheet after being fed, a sheet guide unit that guides the fixed sheet toward the discharge unit is provided, and the sheet guide unit extends from the sheet introduction side to the discharge unit. A curved part is formed in the middle, a sheet cooling part is provided in the curved part, and the sheet moving through the sheet guide part moves at a moving speed on the downstream side in the transport direction corresponding to the discharge side rather than on the upstream side in the transport direction. The sheet cooling unit is cooled while being brought into contact with the curved portion of the sheet guide unit by being accelerated and tensioned.

  The invention according to claim 2 is characterized in that the sheet cooling section is configured to be in surface contact with the tensioned sheet.

  The invention according to claim 3 is characterized in that the sheet cooling portion is provided with a metal heat pipe capable of dissipating heat of the sheet.

  The invention according to claim 4 is characterized in that the heat pipe provided in the sheet cooling section is configured to be forcibly cooled.

  The invention according to claim 5 is characterized in that the heat pipe is provided in contact with the sheet guide portion.

  The invention according to claim 6 is characterized in that the heat pipe is provided at least upstream in the sheet conveying direction from the introduction side to the discharge portion in the sheet guide portion.

  The invention according to claim 7 is characterized in that a curved shape of the curved portion of the sheet guide portion is set with reference to the same center as the heat pipe.

  The invention according to claim 8 is characterized in that the curved portion is configured to prevent the toner from adhering to the side of the sheet that contacts the surface to be fixed.

  The invention described in claim 9 is characterized in that a coating layer of fluororesin is used as a configuration for preventing the toner from adhering.

  The invention described in claim 10 is characterized in that a portion other than the position in contact with the heat pipe in the sheet guide portion is made of resin.

  The invention according to claim 11 is characterized in that the heat pipe is elastically pressed against the sheet guide portion.

  The invention according to claim 12 is characterized in that the heat pipe is integrated with the sheet guide by using an adhesive having thermal conductivity.

  The invention according to claim 13 is characterized in that the heat pipe is integrated with the metal portion of the sheet guide portion by brazing.

  According to a fourteenth aspect of the present invention, there is provided sheet conveyance for discharging a sheet on which a toner image has been fixed by heat and pressure, using a heating member and a pressure member that are disposed opposite to each other in a conveyance path of a sheet carrying a toner image. In the apparatus, the apparatus includes a sheet guide portion that guides the fixed sheet toward the discharge portion, and the sheet guide portion is curved with a sheet cooling portion on the way from the sheet introduction side to the discharge portion. A heat pipe capable of transferring heat between the sheet guide portion and the sheet located at the upstream side of the sheet conveyance direction and the forced cooling means thereof are used as the sheet cooling portion. The heat pipe is characterized in that a cooling function form corresponding to a heat radiation state can be changed by controlling the forced cooling means.

  The invention according to claim 15 is characterized in that the cooling function configuration can be changed according to the humidity in the sheet guide portion.

  According to a sixteenth aspect of the present invention, the change in the cooling mode function is performed by connecting a humidity detecting means and / or a temperature detecting means for detecting humidity at the sheet guide portion on the input side, and operating the forced cooling means on the output side. This is performed by a control unit to which a drive unit for setting the state is connected, and the control unit stops the means used for the forced cooling when the humidity is equal to or higher than a predetermined value and / or lower than a predetermined temperature. It is characterized by.

  The invention described in claim 17 is characterized in that the control unit sets an operation state of the heat pipe with respect to the forcing means in accordance with a sheet conveyance mode.

  According to an eighteenth aspect of the present invention, the control unit continues the operation of the forced cooling means until the conveyance is completed when a sheet conveyance mode for double-sided continuous printing is selected in the sheet conveyance mode. However, the forced cooling means is stopped in cases other than continuous duplex printing.

  According to a nineteenth aspect of the present invention, the sheet conveying apparatus according to any one of the first to eighteenth aspects is used in an image forming apparatus.

  The invention according to claim 20 is characterized in that the sheet conveying device is arranged behind a fixing device used for image fixing.

  According to a twenty-first aspect of the present invention, the fixing device and the sheet discharge portion are arranged close to each other by positioning a curved portion in the middle of the sheet guide portion.

  According to invention of Claim 1 and 2, the curved part provided in the sheet | seat guide part is made into a sheet | seat cooling part, and it can move, contacting, when a sheet | seat is tense with respect to a curved part. In the invention described in claim 2, since the surface can be contacted with the sheet cooling portion, the configuration is such that the curved portion is provided in the sheet guide portion and the fixing portion and the discharge portion are close to each other. However, it becomes possible to increase the cooling efficiency of the sheet.

  According to the third aspect of the present invention, since the heat pipe is provided in the cooling section, the toner is accelerated and cooled and the ambient temperature is prevented from decreasing the heat radiation efficiency even when the transport path length in the transport section is short. Can be prevented from rising.

  According to the fourth aspect of the present invention, since the heat pipe can be forcibly cooled, it is possible to prevent the cooling efficiency from being lowered.

  According to the fifth aspect of the present invention, since the heat pipe is in contact with the sheet guide portion, the heat radiation effect can be enhanced through the wide conveyance path in which the area in contact with the sheet and the area in contact with the atmosphere are wide. It becomes possible.

  According to the sixth aspect of the present invention, since the heat pipe is provided at least on the upstream side of the sheet conveyance rear side from the introduction side to the discharge portion in the sheet guide portion, the heat drop rate with respect to the sheet in the high temperature state after fixing is reduced. It is possible to enhance the cooling and curing of the toner.

According to the seventh aspect of the present invention, the curved portion of the seat guide portion has a curved shape based on the same center as that of the heat pipe, and thus exhibits a shape that curves along the outer peripheral surface of the heat pipe. Accordingly, since the opposing relationship between the outer peripheral surface of the heat pipe and the curved portion is made uniform and the temperature distribution does not vary, the contact with the fixing surface of the sheet can be achieved efficiently. In the invention according to claim 14, since the fluororesin coating layer is provided as the configuration, the sheet is smoothly moved and the fluororesin is used. By using non-adhesiveness, it is possible to prevent the toner from rubbing and adhering to the metal portion on which the sheet moves.

  According to the invention described in claim 10, since the sheet guide portion other than the metal portion with which the heat pipe contacts is made of resin, it is possible to prevent condensation due to the occurrence of a temperature gradient when the sheet guide portion is made of metal over the entire area. It becomes possible.

  According to the eleventh aspect of the present invention, since the heat pipe is in elastic contact with the sheet guide member, it is possible to increase the contact rate and prevent the cooling efficiency from being lowered.

  According to the invention described in claims 12 and 13, since the heat pipe is integrated with the sheet guide portion by means that does not lower the thermal conductivity, it is possible to prevent the cooling efficiency from being lowered. In particular, in the invention described in claim 12, the integration work is simplified by using an adhesive having good thermal conductivity, and in the invention described in claim 13, the integration strength is ensured by brazing. It becomes possible.

  According to the fourteenth and fifteenth aspects of the present invention, since the heat pipe can change the cooling function form, it is possible to optimize the cooling state and the condensation prevention state for the sheet. In particular, in the invention according to the twentieth aspect, since the cooling function form can be changed according to the humidity in the sheet conveyance path, generation of water droplets due to condensation of water vapor can be reliably prevented.

  According to a sixteenth aspect of the present invention, the control unit used for deflecting the cooling function configuration of the heat pump is used for the forced cooling when the humidity is equal to or higher than a predetermined value and / or lower than a predetermined temperature. Since the means can be stopped, the evaporation of water droplets is promoted by stopping the cooling and raising the temperature when the humidity is high, and at the low temperature, the water droplets are prevented from being generated due to overcooling. It is possible to prevent the occurrence of abnormal images by preventing the sheet charging characteristics from changing.

  According to the seventeenth aspect of the present invention, drive control for the forcing means of the heat pipe can be performed according to the sheet conveyance mode, so that when the continuous sheet conveyance is started, the ambient temperature is low and condensation occurs. It is possible to prevent the occurrence of condensation due to a decrease in temperature by stopping the cooling operation by the heat pipe at the start of easy conveyance.

  According to the invention described in claim 18, when the sheet conveyance mode for double-sided continuous printing is selected in the sheet conveyance mode, the operation of the forced cooling means is continued until the conveyance is completed. Since the forced cooling means is stopped in cases other than continuous printing, the cooling efficiency can be improved even when the printing interval until the printing on the second surface performed after the printing on the first surface is shortened during the double-sided continuous printing. Thus, the cooling and curing of the toner can be promoted.

  According to the nineteenth and twentieth aspects of the present invention, even when a conveyance unit having a short conveyance path length of the sheet after fixing is used, image loss due to remelting of the toner or the like is prevented without reducing the cooling efficiency. In addition, it is possible to prevent condensation, and it is possible to prevent the occurrence of abnormal images due to changes in the charging characteristics of the sheet.

  According to the twenty-first aspect of the present invention, even when the fixing device and the sheet discharge portion are arranged close to each other by providing a curved portion in the middle of the sheet guide portion, the sheet cooling portion is connected to the curved portion of the sheet guide portion. The sheet is tensioned and brought into contact with this portion, whereby the toner can be efficiently cooled, and the length of the sheet conveyance path can be shortened to reduce the size of the apparatus.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to examples.

  FIG. 1 is a schematic diagram showing an example of an image forming apparatus using a process cartridge according to an embodiment of the present invention. The image forming apparatus shown in FIG. 1 is a color printer that can form a full-color image using a tandem method. is there. In the present invention, not only the printer shown in FIG. 1 but also a copying machine, a facsimile machine, a printing machine or the like is included as an image forming apparatus.

In FIG. 1, the image forming apparatus 120 includes the following apparatuses.
Image forming devices 121Y, 121C, 121M, and 121K that form images of respective colors according to the original image, transfer devices 122 that are disposed to face the image forming devices 121Y, 121C, 121M, and 121K, and the respective image forming devices A paper feed cassette 124A provided in a manual feed tray 123, a feeding roller 123A, and a paper feeding device 124 as sheet feeding means for feeding a recording sheet to a transfer area where the devices 121Y, 121C, 121M, 121K and the transfer device 122 face each other. A registration roller 133 that supplies the recording sheet conveyed from the manual feed tray 123 or the paper feed cassette 124A in accordance with the image forming timing of the image forming apparatuses 121Y, 121C, 121M, and 121K, and the sheet after transfer in the transfer region Fixing device 1 for fixing a recording sheet corresponding to a sheet-like medium It is 0.

  The fixing device 110 uses a heating roller 110A and a pressure roller 110B, which can face each other across the conveyance path of the recording sheet, to melt and soften the image by the action of heat and pressure, and to penetrate the image on the recording sheet. A heat roller fixing method for fixing a toner image is used.

The transfer device 122 uses a belt 122A (hereinafter referred to as a transfer belt) that is wound around a plurality of rollers as a transfer body, and applies a transfer bias to a position facing the photosensitive drum in each image forming device. The transfer bias means 122Y, 122C, 122M, and 122K are arranged so as to apply a transfer bias having a polarity opposite to that of the toner, thereby sequentially superimposing and transferring the toner images formed by the respective image forming devices.
In the transfer device 122, a secondary transfer bias unit 122F for collectively transferring the toner images superimposed and transferred onto the transfer belt 122A to the recording sheet is disposed on the recording sheet conveyance path.

The image forming apparatus 120 has a larger heat capacity than that of paper such as plain paper generally used for copying, 90 K paper such as an OHP sheet, card, postcard, thick paper equivalent to a basis weight of about 100 g / m ₂ or more, and an envelope. Any so-called special sheet can be used as the recording sheet.

In FIG. 1, each of the image forming apparatuses 121Y, 121C, 121M, and 121K develops colors of yellow, cyan, magenta, and black, respectively, and uses the same toner color, but has the same configuration. The configuration of the image forming device 121K will be described as a representative of the image forming devices 121Y, 121C, 121M, and 121K.
The image forming device 121K includes a photosensitive drum 125K as an electrostatic latent image carrier, a charging device 127K, a developing device 126K, and a cleaning device 128K that are sequentially arranged along the rotation direction of the photosensitive drum 125K. A configuration is used in which an electrostatic latent image is formed between the device 127K and the developing device 126M according to image information corresponding to the color separated by the writing light 129K from the writing device 129. In addition to the drum shape, the electrostatic latent image carrier may have a belt shape. Image forming devices arranged around these photosensitive drums, in other words, image forming devices are collectively stored in a process cartridge having a unit structure including a housing.
In the image forming apparatus 120 shown in FIG. 1, since the transfer device 122 extends obliquely, the space occupied by the transfer device 122 in the horizontal direction can be reduced.

In the image forming apparatus 120 having the above configuration, image formation is performed based on the following steps and conditions. In the following description, an image forming apparatus that forms an image using the black toner denoted by reference numeral 121K on behalf of each image forming apparatus will be described, but the same applies to other image forming apparatuses. Preface.
At the time of image formation, the photosensitive drum 125K is rotationally driven by a main motor (not shown), is neutralized by an AC bias (DC component is zero) applied to the charging device 127K, and its surface potential is set to a reference potential of about −50V. Is done.
Next, the photosensitive drum 125K is uniformly charged to a potential substantially equal to the DC component by applying a DC bias superimposed with an AC bias to the charging device 127K, and the surface potential thereof is approximately −500 V to −700 V (target). The charging potential is determined by a process control unit).

  When the photosensitive drum 125K is uniformly charged, a writing process is executed. An image to be written is written for forming an electrostatic latent image using a writing device 129 in accordance with digital image information from a controller unit (not shown). That is, in the writing device 129, laser light from a laser light source that emits light based on a laser diode light emission signal binarized for each color corresponding to digital image information is converted into a cylinder lens (not shown), a polygon motor 129A, A photosensitive drum that carries an image for each color via the fθ lens 129B, the first to third mirrors, and the WTL lens. In this case, for convenience, the photosensitive drum 125K is irradiated with the irradiated portion. The surface potential on the surface of the photosensitive drum becomes approximately −50 V, and an electrostatic latent image corresponding to the image information is formed.

  The electrostatic latent image formed on the photosensitive drum 125K is subjected to visible image processing using a toner having a color complementary to the color separation color by the developing device 126K. In the developing process, an AC bias is applied to the developing sleeve. The toner (Q / M: -20 to -30 μC / g) is developed only in the image portion where the potential is lowered by the irradiation of the writing light by applying DC: −300 V to −500 V with the superimposed toner, and the toner image Is formed.

The toner images of the respective colors that have been subjected to the visible image processing in the development process are transferred to a recording sheet that is fed out with registration timing set by a registration roller 133. The recording sheet is transferred to a roller before reaching the transfer belt 122A. The sheet is biased electrostatically to the transfer belt 122A by application of a suction bias by the sheet suction bias means configured as described above.
The transfer belt 122A is separated from the photosensitive drum by applying a bias having a polarity opposite to that of the toner by the transfer bias means 122Y, 122C, 122M, and 122BK provided in the transfer device 122 at a position facing the photosensitive drum in each image forming device. The toner image is electrostatically transferred and the superimposed toner image is collectively transferred to the recording sheet by the secondary transfer bias unit 122F.

The recording sheet that has undergone the transfer process for each color is separated from the transfer belt 122A by a driving roller of the transfer belt unit (indicated by reference numeral 122A1 in FIG. 1 for convenience), conveyed toward the fixing device 110, and added to the fixing belt 110. By passing through a fixing nip composed of a pressure roller, the toner image is fixed on the recording sheet and discharged to the paper discharge tray 132.
The image forming apparatus 120 shown in FIG. 1 can perform not only image formation on one side of a recording sheet discharged after fixing but also image formation on both sides. The recording sheet after fixing is conveyed to the reverse circulation path RP, and is fed toward the registration roller 133 by a feeding roller RP1 located at the end of the circulation path and serving also as a sheet feeding from the manual feed tray 123. Switching of the recording sheet conveyance path during image formation on one side and both sides is performed by a conveyance path switching claw RP2 disposed behind the fixing device 110.

  The conveyance path switching claw RP2 is provided in a conveyance unit used as a sheet conveyance apparatus, which will be described later, and switches the conveyance path according to the sheet conveyance form.

  The physical properties including the above-described charging potential are not limited to the above values, and can of course be changed according to color, density, and the like. In FIG. 1, reference numerals T1 to T4 denote toner supply tanks used in the developing device.

2 is an external view of the sheet conveying apparatus 200, and FIG. 3 is a cross-sectional view in side view for explaining the main part of the sheet conveying apparatus shown in FIG.
In the present exemplary embodiment, the conveyance unit configuring the sheet conveyance apparatus 200 has a unit configuration, and only this part can be attached to and detached from the image forming apparatus 120.

  The sheet conveyance device 200 can change the conveyance direction of a recording sheet discharged from the fixing device 110 in a substantially upward state toward a discharge tray 132 (see FIG. 1) extended in a substantially horizontal direction. A sheet guide part 201 as a path is provided.

2 and 3, a swingable conveyance path switching claw RP2 capable of switching the conveyance direction between the sheet discharge tray 132 side and the reverse conveyance path RP side is provided above the sheet guide portion 201. At a position adjacent to the conveyance path switching claw RP2, a reverse guide portion 202 (see FIG. 2) having a recording sheet conveyance surface directed toward the reverse conveyance path RP (see FIG. 1) is provided.
In FIG. 2, the reverse guide unit 202 is provided with a roller 203 positioned on the driven side among the reverse rollers for guiding the recording sheet whose transport path is switched to the reverse transport path RP.

In the conveyance path formed by the sheet guide unit 201, a cooling unit for the recording sheet to be conveyed is provided in part.
As the sheet cooling unit, a curved portion 201A located at a recording sheet conveyance direction changing portion in the sheet guide unit 201 is used. As shown in FIG. 3, the curved portion 201A has a fixing surface of the recording sheet, that is, a fixing surface of the recording sheet. The heat pipe 204 is disposed in contact with the opposite side of the surface facing the toner carrying surface. In FIG. 3, reference numeral 205 indicates a paper discharge roller for feeding a recording sheet that moves on the sheet guide unit 201 to the paper discharge tray 132.

  The curved portion 201A in the sheet guide portion 201 is made of aluminum, aluminum alloy, brass, or a metal member having high thermal conductivity, which has good thermal conductivity, and a heat-resistant resin is used for portions other than this portion. ing. Thus, unlike the case where the entire sheet guide is made of metal, the temperature decrease range due to the expansion of the heat radiation area via the heat pipe 204 does not increase, and the surrounding atmosphere is increased when the temperature decrease range increases. Condensation due to temperature drop can be suppressed.

  The curved portion 201A is provided in the vicinity of the sheet passing sensor S1 that detects the passage of the recording sheet, as shown in FIG. 4, on the upstream side in the conveyance direction of the recording sheet in the sheet guide portion 201. The L-shaped locking portion provided is hooked on a fitting portion 201B formed on the sheet guide portion 201, thereby constituting a part of the recording sheet conveyance surface in the sheet guide portion 201. Note that a plurality of bending portions 201A can be provided in addition to one place on the upstream side in the conveyance direction of the recording sheet depending on the form of the sheet guide portion 201, that is, the conveyance path length and the conveyance conversion shape. Further, as described above, the sheet passing sensor S1 uses an optical sensor provided at an opening provided at the center in the longitudinal direction of the sheet guide portion 201, as indicated by reference numeral L1 in FIG.

  The curved portion 201 </ b> A has a curved shape with the same center as that of the heat pipe 204 as a reference, and is curved along the outer peripheral surface of the heat pipe 204. As a result, the opposing relationship between the outer peripheral surface of the heat pipe 204 and the curved portion 201A is made uniform and the temperature distribution does not vary, so that heat can be efficiently transmitted toward the heat radiating side. In the present embodiment, a stainless steel sheet metal member is used for the bending portion 201A, and a spring portion having a shape for holding the heat pipe 204 on the back side of the bending portion 201A, that is, a so-called elastic piece portion is provided in the bending portion 201A. The outer peripheral surface of the heat pipe 204 is pressed against the back surface of the heat pipe 204.

  On the other hand, a member for preventing adhesion of toner is provided on the surface of the curved portion 201A that faces the fixing surface of the recording sheet. In this embodiment, a coating layer (not shown) of fluororesin is provided. Yes. As a result, the frictional resistance against the recording sheet moving through the curved portion 201A is reduced, and the transfer of the toner located on the fixing surface is prevented to prevent image rubbing.

As shown in FIG. 5, the installation structure of the heat pipe 204 with respect to the bending portion 201 </ b> A includes a compression spring 206 between the position facing the bending portion 201 </ b> A and the stationary portion of the sheet conveying apparatus 200 in the circumferential direction of the heat pipe 204. The heat pipe 204 is integrated with the back surface of the bending portion 201A using a heat conductive adhesive as shown by reference sign SL in FIG. There is a configuration in which the heat pipe 204 is integrated with the back surface of the curved portion 201A by brazing using a metal braze.
In these installation structures, since the area of the contact portion between the heat pipe 204 and the back surface of the curved portion 201 is larger than the case where only the outer periphery of the heat pipe 204 itself contacts, the heat conduction efficiency is improved. be able to.

In the present embodiment, the recording sheet moving through the sheet conveying apparatus 200 is conveyed with different speeds on the upstream side in the conveying direction and on the downstream side in the conveying direction. That is, the nipping / conveying speed by the discharge roller 205 provided on the sheet conveying apparatus 200 side is increased with respect to the nipping / conveying speed of the recording sheet set by the heating roller 110A and the pressure roller 110B provided in the fixing device 110. It has become.
As a result, when the leading end of the recording sheet is nipped by the paper discharge roller 205, the recording sheet is tensioned (expanded) in the sheet guide portion 201 by being applied at a higher speed than before. For this reason, it will be in the state pressed strongly with respect to the sheet | seat guide part 201, and heat transfer from a recording sheet will be performed favorably by obtaining this state also with respect to the curved part 201A.

  On the other hand, the heat pipe 204 is forcibly cooled rather than naturally cooled. FIG. 7 is a plan view of the sheet conveying apparatus 200. In FIG. 7, the heat pipe 204 has an end portion located in a heat exhaust duct 207 provided inside the sheet conveying apparatus 200. Is provided with a heat sink 204A and has a large contact area with outside air flowing through the exhaust heat duct 207.

  A cooling fan 208, which is a forced cooling means for the heat pipe 204, is disposed at one end in the longitudinal direction of the exhaust heat duct 207, and the operation state of the cooling fan 208 is controlled by a control unit described later. Yes.

FIG. 8 is a block diagram illustrating a configuration of a control unit for controlling the cooling function form using the heat pipe 204 in the present embodiment. In FIG. 8, the control unit 300 includes a control unit that executes an image forming sequence. The operation panel 301, temperature detection means 302, and humidity detection means 303 are connected to the input side, and the drive unit 304 of the cooling fan 208 is connected to the output side.
The operation panel 301 is used to input a recording sheet conveyance mode. For example, the number of copies and an image forming format such as one side or both sides are input. As shown in FIG. 8, the temperature detection unit 302 is arranged upstream of the recording sheet conveyance direction to detect the ambient temperature in the sheet conveyance path, similarly to the sheet passing sensor S <b> 1, and the humidity sensor 303 Similar to the temperature detection sensor 302, it detects the humidity in the sheet conveyance path.

In this embodiment, as in a large apparatus that can take a long conveyance path, even if the temperature drop due to the heat pipe is significant, the temperature change is balanced by using the conveyance path length and a predetermined temperature difference with respect to room temperature. Unlike the configuration in which the fixing device 110 settles down, the fixing device 110 and the paper discharge tray 132 come close to each other, and the so-called transport path length between them is shortened so that the size of the device is reduced. In this case, the conveyance path is prevented from being overcooled during cooling using a heat pipe, and the generation of water droplets caused by condensation of water vapor generated by the overcooling is prevented.
For this reason, the controller 300 stops the cooling fan 208 and actively cools the heat pipe 204 when the temperature is such that the amount of water vapor generated from the recording sheet increases and / or when the atmospheric humidity is high. There is no such thing. In other words, the cooling fan 208 is stopped when the amount of water evaporated from the recording sheet increases or when the humidity is the same as that of the recording sheet.

FIG. 10 is a diagram for explaining the results of experiments conducted by the inventor regarding the temperature difference between the case where the heat pipe 204 is provided and the case where the heat pipe 204 is not provided.
In the same figure, when the heat pipe 204 is not provided, the temperature of the sheet guide portion 201 exceeds 80 ° C., but when the heat pipe 204 is provided, the temperature of the sheet guide portion 201 is 50 ° C. Thus, it can be seen that a temperature reduction of about 30 ° C. can be obtained by providing the heat pipe 204 in the curved portion 201A having the above-described configuration even with a short conveyance path length. Thus, unlike the case where the temperature drop is small, it is possible to prevent image rubbing and the like due to remelting of the toner.

  However, although the temperature reduction can be obtained by providing the heat pipe 204, if the temperature in the sheet guide portion 201 is too low, the water vapor around the sheet guide portion 201 may be condensed and condensed. When the water droplets adhere to the sheet guide portion 201 due to condensation as described above, when the water droplets adhere to the recording sheet, a transfer failure or the like occurs due to a change in charging characteristics due to the water droplets, and a defective image such as white spots or white streaks is obtained. Will be.

  In this embodiment, in order to prevent the occurrence of such a defective image, the recording sheet is transported in a temperature condition in which a large amount of water vapor is generated, that is, during a large amount of continuous transport in single-sided copying before double-sided copying, The driving of the cooling fan 208 is stopped when the atmospheric humidity is above a predetermined level.

Since the present embodiment is configured as described above, the operation of the control unit 300 will be described as follows based on the flowcharts of FIGS. 11 to 13.
FIG. 11 is a flowchart for controlling the operation state of the cooling fan 208 according to the sheet conveyance form and printing form as an example of the cooling function form change control. In the case shown in FIG. It is said.
In the figure, the control unit 300 determines whether double-sided continuous printing is performed based on information from the operation panel 301, stops the cooling fan 208 in cases other than double-sided continuous printing, and in the case of double-sided continuous printing. The cooling fan 208 is driven. This driving is continued until the duplex continuous printing job is completed (ST1 to ST4).

  With this procedure, during continuous duplex printing, even if the printing interval until printing on the second surface after printing on the first surface is shortened, the toner is cooled and cured without lowering the cooling efficiency. Can be promoted.

  On the other hand, FIG. 12 is a flowchart for controlling the cooling function configuration of the heat pipe 204 in accordance with the detected temperature. In FIG. 12, it is determined whether or not the image is being formed (ST10). In 302, the temperature in the vicinity of the sheet guide portion 201 is detected, and it is determined whether or not the detected temperature is 60 ° C. or higher (ST11). When the detected temperature is 60 ° C. or higher, the cooling fan 207 is driven, and when the detected temperature is lower than that temperature, the cooling fan 207 is stopped (ST12, 13). This prevents the occurrence of water droplets by preventing overcooling by the heat pipe 204 when the temperature is below a predetermined temperature, such as immediately after startup or after a state in which image formation for a long time is not performed. can do.

Moreover, the case where atmospheric humidity is detected and a cooling function form is controlled is shown by FIG.
In FIG. 13, it is determined whether or not the image is being formed (ST20), and the humidity in the vicinity of the sheet guide portion 201 is detected by the humidity detection sensor 303 at the time of image formation (ST21). If it is determined that the humidity exceeds 80% in the detection result, the cooling fan 207 is stopped and heated to evaporate water droplets attached to the sheet conveying unit 201 (ST22). If the humidity is less than 80%, the cooling fan 207 is driven to perform cooling using the heat pipe 204 (ST23).
Note that the temperature and humidity standards given in this embodiment are merely examples, and the values vary depending on the configuration and the like, so it is desirable to set optimum values each time.

1 is a schematic diagram illustrating an example of an image forming apparatus to which a sheet conveying apparatus according to an embodiment of the present invention is applied. FIG. 2 is an external view of a sheet conveying device provided in the image forming apparatus illustrated in FIG. 1. FIG. 3 is a side sectional view for explaining a main configuration of the sheet conveying apparatus illustrated in FIG. 2. FIG. 4 is a cross-sectional view corresponding to FIG. 3 illustrating an arrangement configuration of a paper passing sensor used in a main part of the sheet conveying apparatus illustrated in FIG. 3. FIG. 4 is a cross-sectional view corresponding to FIG. 3, illustrating another example of a heat pipe support structure in the sheet conveying apparatus illustrated in FIG. 3. It is a partial schematic diagram for demonstrating the other example regarding the support structure of the heat pipe shown in FIG. FIG. 4 is a schematic plan view of the sheet conveying apparatus illustrated in FIG. 3. It is a block diagram for demonstrating the structure of the control part used for the sheet conveying apparatus by a present Example. FIG. 4 is a cross-sectional view corresponding to FIG. 3 for explaining an arrangement configuration of temperature detection sensors used in the main part of the sheet conveying apparatus shown in FIG. 3. It is a diagram which shows the result of having compared the temperature change by the heat pipe used for the sheet conveying apparatus by a present Example, and the temperature change when there is no heat pipe. It is a flowchart for demonstrating one of the control content implemented by the control part shown in FIG. It is a flowchart for demonstrating another example of the control content implemented by the control part shown in FIG. It is a flowchart for demonstrating the other example of the control content implemented by the control part shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 110 Fixing apparatus 110A Heating roller 110B Pressure roller 120 Image forming apparatus 200 Sheet conveying apparatus 201 Sheet guide part 201A Curved part 204 Heat pipe 205 Paper discharge roller 300 Control part 301 Operation panel 302 Temperature detection sensor 303 Humidity detection sensor RP Reverse conveyance path RP2 transport path switching claw

Claims (21)

In a sheet conveying apparatus that discharges a sheet after the toner image is fixed by heat and pressure using a heating member and a pressure member that are arranged opposite to each other in the conveyance path of the sheet carrying the toner image,
A sheet guide portion for guiding the fixed sheet toward the discharge portion;
The sheet guide part is formed with a curved part on the way from the sheet introduction side to the discharge part,
The curved portion is provided with a sheet cooling portion,
While the sheet moving in the sheet guide portion is in tension with an increased moving speed on the downstream side in the transport direction corresponding to the discharge side rather than on the upstream side in the transport direction, the sheet guide portion is in contact with the curved portion of the sheet guide portion. The sheet conveying apparatus is cooled by the sheet cooling unit.   The sheet conveying apparatus according to claim 1, wherein the sheet cooling unit is configured to be in surface contact with the tensioned sheet.   The sheet conveying apparatus according to claim 1, wherein the sheet cooling unit is provided with a metal heat pipe capable of dissipating heat of the sheet.   The sheet conveying apparatus according to claim 3, wherein the heat pipe provided in the sheet cooling unit is configured to be forcibly cooled.   The transport apparatus according to claim 3, wherein the heat pipe is provided in contact with the sheet guide portion.   The sheet conveying apparatus according to claim 3, wherein the heat pipe is provided at least on the upstream side in the sheet conveying direction from the introduction side to the discharge unit in the sheet guide unit.   The sheet conveying apparatus according to claim 1, wherein the curved portion of the sheet guide portion has a curved shape based on the same center as the heat pipe.   8. The sheet conveying apparatus according to claim 1, wherein the curved portion is configured to prevent toner from adhering to a side of the sheet that contacts the fixing surface.   The sheet conveying apparatus according to claim 8, wherein a coating layer of a fluororesin is used as a configuration for preventing adhesion of the toner.   The sheet conveying apparatus according to claim 2, wherein a portion other than a position in contact with the heat pipe in the sheet guide portion is made of resin.   The sheet conveying apparatus according to claim 2, wherein the heat pipe is configured to be elastically pressed against the sheet guide portion.   12. The sheet conveying apparatus according to claim 2, wherein the heat pipe is integrated with an adhesive having thermal conductivity with respect to the sheet guide.   The sheet conveying apparatus according to claim 2, wherein the heat pipe is integrated with a metal portion in the sheet guide portion by brazing. In a sheet conveying apparatus that discharges a sheet on which a toner image is fixed by heat and pressure using a heating member and a pressure member that are arranged opposite to each other in a conveyance path of a sheet carrying a toner image,
A sheet guide portion for guiding the fixed sheet toward the discharge portion;
The sheet guide portion is formed with a curved portion having a sheet cooling portion in the middle from the sheet introduction side to the discharge portion,
As the sheet cooling unit, a heat pipe that is located at least upstream of the sheet guide direction in the sheet conveyance direction and capable of transferring heat between the sheet and a forced cooling unit thereof is used.
The sheet conveying apparatus, wherein the heat pipe is capable of changing a cooling function form corresponding to a heat radiation state by controlling the forced cooling means.   The sheet conveying apparatus according to claim 14, wherein the cooling function form can be changed according to humidity in the sheet guide portion. The cooling mode function is changed by connecting a humidity detecting means and / or a temperature detecting means for detecting the humidity at the sheet guide section on the input side, and a driving section for setting the operation state of the forced cooling means on the output side. Done in the connected control unit,
16. The sheet conveying apparatus according to claim 14, wherein the control unit stops the means used for the forced cooling when the humidity is equal to or higher than a predetermined value and / or lower than a predetermined temperature.   The sheet conveying apparatus according to any one of claims 14 to 16, wherein in the control unit, an operation state with respect to a forcing unit of the heat pipe is set according to a sheet conveying form.   In the control unit, when the sheet conveyance mode for double-sided continuous printing is selected in the sheet conveyance mode, the operation of the forced cooling unit is continued until the conveyance is completed, and in the case other than double-sided continuous printing The sheet conveying apparatus according to claim 17, wherein the forced cooling unit is stopped.   An image forming apparatus using the sheet conveying device according to claim 1.   The image forming apparatus according to claim 19, wherein the sheet conveying device is disposed behind a fixing device used for image fixing. 21. The image forming apparatus according to claim 19, wherein the fixing device and the sheet discharge portion are arranged close to each other by positioning a curved portion in the middle of the sheet guide portion.

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