JP2012003011A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation apparatus capable of reliably reducing a sheet-curl in any cross-fiber direction of a sheet relative to a feeding direction, and stably reducing it over a long period of time.SOLUTION: An image formation apparatus provided with a fixing unit for fixing toner images transferred onto a recording sheet includes a sheet-curl correction unit which is arranged downstream of the fixing unit in a sheet-feeding direction, holds both ends of a sheet in a direction perpendicular to the sheet feeding direction and feeding the sheet while providing it with force in the sheet feeding direction and outward of the sheet in a direction perpendicular to the sheet feeding direction.

Description

  The present invention relates to an image forming apparatus, and more particularly to a technique for suppressing paper curl that occurs when a toner image is fixed on a paper by heating and pressing.

  An electrophotographic image forming apparatus forms an electrostatic latent image on a photosensitive member by laser scanning, attaches powder toner to the electrostatic latent image by a developing means, and transfers the toner image directly to a sheet. Alternatively, the toner image is transferred onto a sheet via an intermediate transfer member, and the toner image on the sheet is melted and fixed on the sheet with heat and pressure by a fixing unit.

  In the fixing unit, a pressure roller is pressed against a heated heating belt or heating roller to form a nip portion that sandwiches the paper, and pressure and heat are applied to the toner on the paper while the paper is conveyed. Here, when the paper is thinly absorbing moisture and there is a temperature difference between the heating roller and the pressure roller of the fixing unit, the paper curls.

  In addition to the appearance of the curl being deteriorated, the curl may deteriorate the alignment of the paper on the paper discharge tray and further increase the jam rate on the conveyance path. Therefore, it is desirable that the curl after fixing is as small as possible.

  For example, Patent Document 1 discloses a configuration in which the paper is tensioned by a pair of rollers disposed after the fixing unit to reduce curl. Further, for example, in Patent Document 2, a pair of rollers disposed after the fixing unit is tapered to generate a component force in a direction perpendicular to the paper transport direction, and the paper is transported by pulling the paper. A configuration for reducing curling in a direction perpendicular to the direction is disclosed.

  The curl direction of the paper changes depending on the arrangement of the fibers, and the curl is likely to occur in the width direction of the fibers. Therefore, it is necessary to apply tension in the width direction of the fibers. However, depending on the type of paper, the width direction of the fiber may be the long side direction or the short side direction of the paper, and the paper direction when set in the image forming apparatus is also left to the user. There are many cases. Therefore, the direction of the fiber cannot be specified. Therefore, as in the invention of Patent Document 1, even if tension is applied only in the conveying direction, curling cannot always be reduced.

  The invention of Patent Document 2 tries to solve the problem with respect to the invention of Patent Document 1, but the following another problem occurs. The component force generated by the difference in diameter of the roller such as a taper is generated by deforming the sheet by the velocity component in the width direction of the sheet. Since this speed is very slow, the amount of deformation is very small, and gradually increases after the paper is sandwiched between the rollers. For this reason, if the paper is warm after fixing, and if the moisture content of the paper is high, the paper will not be able to give enough force due to stress relaxation. Does not generate excessive force. On the other hand, slippage always occurs in one roller between the tapered rollers, so that the wear of the roller is great and the effect is reduced when used for a long period of time. Further, for example, when the printing rates of the left and right images are different in the paper width direction, an unbalance of the conveyance force occurs, which causes a paper skew.

  Therefore, in view of the above-described circumstances, the present invention can reliably reduce curl regardless of the width direction of the fiber of the paper with respect to the conveyance direction, and further reduce curl stably for a long period of time. An object of the present invention is to provide an image forming apparatus that can perform the above-described process.

  An image forming apparatus according to the present invention is an image forming apparatus including a fixing unit that fixes a toner image transferred onto a recording sheet, and is disposed downstream of the fixing unit in the sheet conveying direction and perpendicular to the sheet conveying direction. And a paper curl correction unit that conveys the paper while applying a force in a direction perpendicular to the paper conveyance direction and to the outside of the paper.

  In the image forming apparatus, the paper curl correcting unit includes a driving roller as one pair of rollers for sandwiching the paper, and the pair of rollers provided corresponding to both ends of the paper, and the driving roller. And a drive shaft that is driven faster than the angular velocity of the drive roller corresponding to the paper conveyance speed of the fixing unit, and is provided on the drive roller. And a cam mechanism that generates a force for moving the driving roller in a direction perpendicular to the paper transport direction and toward the outside of the paper depending on a rotation angle difference with the driving shaft.

  Further, in the above image forming apparatus, a plurality of paper curl correction units are arranged according to the corresponding paper width of the image forming apparatus, and each unit has pressing load changing means capable of changing the pressing load on the correction roller, The pressing load changing means reduces the pressing load of a sheet curl correction unit having a correction roller located inside the correction roller that sandwiches both ends of the sheet according to the sheet width of the conveyed sheet. May be.

  In the above image forming apparatus, the torque limiter capable of adjusting the rotational drive of the drive source, the curl predicting means for predicting the curl of the paper, the pressing load changing means and the torque limiter based on the prediction result of the curl predicting means. And a control means for controlling.

  In the above image forming apparatus, a first temperature detection unit that measures the temperature of the heating unit included in the fixing unit, a second temperature detection unit that measures the temperature of the pressure unit included in the fixing unit, A paper thickness detecting means for measuring the paper thickness on the paper conveyance path upstream of the fixing unit, and a moisture content detecting means for detecting the moisture content of the paper. The curl of the paper may be predicted based on the information.

  In the above image forming apparatus, the paper curl correction unit may be disposed in a unit case of the fixing unit.

  According to the present invention, in the image forming apparatus, curling can be reliably reduced regardless of the width direction of the fiber of the paper with respect to the conveyance direction, and curling can be stably reduced for a long period of time. It becomes possible.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. 1 is a main part configuration diagram (a configuration diagram of a roller unit) of an image forming apparatus according to an embodiment of the present invention; 1 is a main part configuration diagram of an image forming apparatus according to an embodiment of the present invention (a configuration diagram of a roller unit: a side view). 1 is an internal configuration diagram (a configuration diagram of a storage unit) of an image forming apparatus according to an embodiment of the present invention. It is explanatory drawing of the operation | movement which makes tensile force act in the paper width direction in embodiment of this invention. It is the flowchart which showed change operation of pressing force and drive torque based on curl prediction in the embodiment of the present invention. It is explanatory drawing of the relationship between the input of a curl prediction means in embodiment of this invention, and an output.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 1 arranges each color developing unit on a transfer belt 2 as an intermediate transfer member, forms a color image with toner on the transfer belt 2, and forms the color image on a sheet conveyed from a sheet cassette 4. Then, the toner is melted and fixed by heat and pressure in the fixing unit 6 to form a color image.

  There are four types of developing units: a K developing unit 501 having black toner, a C developing unit 502 having cyan toner, an M developing unit 503 having magenta toner, and a Y developing unit 504 having yellow toner. The developing unit includes a toner hopper 53 that stores toner, a developing roller 52 that forms a toner layer and contacts the photosensitive drum 54 with the toner, a drum cleaner 57 that cleans the photosensitive drum 54, and a charger that charges the photosensitive drum 54. 55, an exposure unit 56 for writing an electrostatic latent image on the photosensitive drum 54.

  The transfer belt 2 is stretched around a plurality of rollers and is conveyed by a belt driving roller 3. The belt cleaner 91 removes residual toner on the transfer belt 2. The primary transfer roller 58 is disposed inside the transfer belt 2 so as to face the photoconductive drum 54.

  The paper transport path 8 is connected to the secondary transfer roller 7 and the transfer from the paper cassette 4 on which the paper is accumulated, through the pick roller 9, the separation roller 11, the paper moisture content detection means 70, the paper thickness detection means 71, and the registration roller 69. The paper passes between the belts 2, reaches the fixing unit 6 from the conveyance belt 81, and is discharged onto a paper discharge tray (not shown) by a paper discharge roller 68.

  When forming an image, the surface of the photosensitive drum 54 is charged by the charger 55, and light corresponding to the image is applied by the exposure device 56 to drop the potential on the photosensitive drum 54. The portion reaches the developing roller 52 by the rotation of the photosensitive drum 54, and when it comes into contact with the toner layer, the charged toner adheres to the image position. The toner image on the photosensitive drum 54 is transferred onto the transfer belt 2 at a portion where the primary transfer roller 58 presses the transfer belt 2.

  The toner image on the photosensitive drum 54 of each developing unit is transferred onto the transfer belt 2 to form a color toner image. Then, the toner image is transferred onto the sheet conveyed by the secondary transfer roller 7 by the conveyance of the transfer belt 2. The sheet on which the toner image has been transferred is conveyed to the fixing unit 6 by the conveying belt 81, and the toner is melted and fixed by heat and pressure from the heating roller 61 and the pressure roller 62, thereby forming a color image. After that, the roller pair is sandwiched between the driving roller 81 and the driven roller 91 which are roller pairs, and the roller pair is provided with a tensile force in the conveying direction and a tensile force in the paper width direction by a roller unit arranged at the end in the paper width direction. To reduce.

  A configuration for curling reduction will be described. FIG. 2 is a main part configuration diagram (a configuration diagram of a roller unit) of the image forming apparatus according to the embodiment of the present invention. In the image forming apparatus of this embodiment, two roller units are arranged so as to correspond to two types of paper widths (for example, 210 mm width for A4 and 294 mm width for A3). FIG. 3 is a side view of FIG. 2 as viewed from the direction of arrow A, and the sheet conveyance direction is the direction of arrow a.

  The first roller unit 801 corresponds to a wide sheet, and the second roller unit 802 corresponds to a narrow sheet. Although it is possible to configure the first roller unit 801 to correspond to a narrow sheet and the second roller unit 802 to correspond to a narrow sheet, it is more effective to pull the entire sheet width. Therefore, the former configuration is preferable.

  The roller pair includes a driving roller 81 and a driven roller 91. The drive roller 81 is supported by the drive shaft 86 so as to be rotatable and movable in the axial direction, and rubber or the like is used to increase the coefficient of friction with the paper. The cam 83 is fixed to the drive roller 81, and the pin 84 is fixed to the drive shaft 86. The end of the return spring 82 is fixed to the drive shaft 86 by a stopper 85, pushes the drive roller 81 in the direction b in the figure, and gives the drive roller 81 a rotational force in the direction of the arrow d in the figure, thereby The pin 84 is pressed against the end face 831 parallel to the.

  The drive shaft 86 is given rotational torque by a drive source 88 such as a motor via a torque limiter 87. The driven roller 91 is rotatably held by the holder 93 via the driven shaft 92. The pressure spring 94 presses the retainer 93 and presses the driven roller 91 against the drive roller 81.

  The first eccentric cam 95 is connected to the first cam operating shaft 96 and is rotated by the first cam drive mechanism 97 to change the pressing force of the pressure spring 94. The second eccentric cam 98 is connected to the second cam operating shaft 99 and is rotated by the second cam drive mechanism 100, and the pressing force of the pressure spring of the second roller unit 802 via the slide mechanism 101. To change.

  The control means 110 includes a storage means 111 that stores information on the type of paper (coated paper, plain paper, etc.) inserted into the paper cassette 4 and paper width, a paper moisture content detection means 70, and a paper thickness detection. Data of the means 71, the first temperature detecting means 75 for detecting the surface temperature of the heating roller 61, and the second temperature detecting means 76 for measuring the surface temperature of the pressure roller 62 are input.

  FIG. 4 shows an internal configuration diagram of the storage unit 111. The storage unit 111 includes an interface circuit 124, a storage element 122, and an arithmetic unit 123 that controls them. An operation panel 120 of the image forming apparatus and a user personal computer 121 are connected to the interface circuit 124. The user inputs information on the paper type (for example, plain paper or coated paper) and the paper width (for example, A4 or A3) from the operation panel 120 or the personal computer 121. This information is stored in the storage element 122, and the information is output to the control means 110 during printing.

  The paper moisture content detection means 70 is, for example, a humidity sensor having a measurement unit in the vicinity of the paper surface. The correlation between the humidity in the vicinity of the paper surface and the moisture content is obtained in advance, and the moisture content of the paper is obtained from the detected humidity. The correlation between the moisture content and the humidity is obtained by previously conditioning the paper in an environment where the relative humidity is changed, measuring the moisture content of the paper, and measuring the surface humidity with a sensor. As shown in FIG. 1, the sheet thickness detection means 71 includes a thickness detection drive roller 72, a detection roller 73 pressed by a spring or the like, and a displacement sensor 74 that measures the vertical displacement of the detection roller 73. When the paper is transported between the thickness detection drive roller 72 and the detection roller 73, the detection roller 73 is lifted by the thickness of the paper, so the thickness of the paper is obtained by the displacement. The first temperature detection means 75 and the second temperature detection means 76 are thermistors or the like.

  In FIG. 2, in order to deal with a wide sheet, the first roller unit 801 rotates the first eccentric cam 95 to push the driven roller 91 against the driving roller 81 so that the sheet is pulled in the width direction. . In the case of a narrow sheet, the second eccentric cam 98 is rotated so that the driven roller 91 of the second roller unit 802 is pressed. At this time, the load on the first roller unit may or may not be released. Such an operation is performed by the control unit 110 controlling the rotation angles of the first cam drive mechanism 97 and the second cam drive mechanism 100 based on the sheet width information in the storage unit 111.

  With reference to FIG. 5 (a diagram showing one side of the first roller unit 801), an operation for applying a tensile force in the paper width direction will be described. The paper 40 is nipped between the heating roller 61 and the pressure roller 62 (FIG. 1) of the fixing unit and conveyed in the direction of arrow a. And it is sandwiched and conveyed between the driving roller 81 and the driven roller 91 (FIG. 2) of the roller pair. The drive source 88 rotates the drive shaft 86 in the arrow c direction via the torque limiter 87.

  The conveyance speed of the paper 40 by the fixing unit is set slower than the speed when the driving source 88 rotates the driving roller 81 to convey the paper 40. This setting is performed at the time of design, and the peripheral speed is calculated from the rotational speed, gear ratio, and roller diameter of the motor that is the drive source, and the peripheral speed is set as the paper conveyance speed. Therefore, the angular velocity of the drive shaft 86 becomes faster than the angular velocity of the drive roller 81, and the pin 84 pushes the slope of the cam 83 in the direction of arrow e with a force corresponding to the set torque of the torque limiter 88. The force in this direction becomes a force for pulling the paper in the transport direction, and reduces curling in the transport direction. Then, the force in the direction of arrow e generates a component force in the direction of arrow f due to the slope of the cam 83, and pushes the drive roller 81 in the direction of arrow f. The force in this direction pulls the paper in the width direction and reduces curling that occurs in the width direction.

  After the sheet 40 passes through the roller pair, the driving roller 81 is pushed in the direction of arrow b and rotated in the direction of arrow d by the force of the return spring 82, and the pin 84 as shown in FIG. Return to the initial state of touching.

  The control unit 110 is also a curl prediction unit, and includes paper type information in the storage unit 111, water content information in the paper moisture content detection unit 70, paper thickness information in the paper thickness detection unit 71, and first temperature detection. The curling of the sheet is predicted from the surface temperature information of the heating roller 61 of the means 75 and the surface temperature information of the pressure roller 62 of the second temperature detecting means 76.

  The curl changes depending on the type of paper (coated paper, plain paper), moisture content, thickness, surface temperature of the heating roller 61, and temperature difference between the heating roller 61 and the pressure roller 62. The curl of plain paper is larger than that of coated paper, the moisture content is higher, the thickness is thinner, the surface temperature of the heating roller 61 is higher, and the temperature difference between the heating roller 61 and the pressure roller 62 is larger. The correlation between the information and the curl is obtained in advance, and the control unit 110 predicts the curl from the acquired information based on the correlation. Then, the rotation angle of the first cam drive mechanism 97 or the second cam drive mechanism 100 is controlled according to the predicted curl amount, the pressing force of the driven roller 91 against the drive roller 81 is changed, and the torque is further increased. The drive torque of the limiter 87 is changed.

  FIG. 6 is a flow for changing the pressing force and the driving torque based on the curl prediction according to the embodiment of the present invention. The state where the apparatus is turned on is started, and the pressing force of the driven roller 91 and the driving torque of the torque limiter 87 are set to the initial state (step S1). When there is a print instruction (step S2 / YES), the control unit 110 acquires the paper type, moisture content, paper thickness, surface temperature of the heating roller 61, and temperature difference information between the heating roller 61 and the pressure roller 62, and the correlation equation. The amount of curl is calculated from (step S3).

  Next, the necessary pressing force and driving torque are calculated from the calculated curl amount (step S4). In this method, for a certain curl amount, a pressing force and a driving torque that can reduce the curl to an allowable value are obtained through experiments, and a correlation formula is created and calculated based on the correlation equation. Next, the present value of the pressing force and the driving torque is compared with the calculated pressing force and the driving torque, and the increase amount or the decrease amount is calculated (step S5). The control means 110 instructs the first cam drive mechanism 97 or the second cam drive mechanism 100 on the rotation angle corresponding to the pressing force, and further instructs the drive torque of the torque limiter 87 (step S6).

  Thereafter, printing is performed (step S7). When the number of prints in the first print instruction is reached (step S8 / YES), the return pressing force and drive torque are returned to the initial state after the start, and the print instruction is waited (step S1). . If the number of printed sheets has not been reached (step S8 / NO), the process returns to curl calculation (step S3).

  According to the embodiment, it is possible to reduce curl regardless of the fiber direction of the paper. Moreover, in order to reduce curl reliably, a larger tensile force is required, and the minimum is 5N, preferably 10N or more. Therefore, the pressing force of the driven roller 91 against the driving roller 81 is preferably 10 N or more when the friction coefficient between the driving roller 81 and the sheet is 1.0, and 20 N or more to prevent slippage. As described above, when the sheet and the driving roller 81 are slipped with a large pressing force, the conveyance becomes unstable and the driving roller 81 is worn heavily. In the configuration of this embodiment, however, slipping is caused by the torque limiter 88. In addition, the wear of the drive roller 81 is small, curling can be stably reduced for a long period of time, and the conveyance becomes unstable due to the slip, and the paper is not skewed.

  On the other hand, when the heated paper after the fixing unit and the moisture content of the paper are high, if a tensile force is applied, stress relaxation occurs, and the paper stretches by about 0.5% at the maximum. When the paper width is 210 mm, the elongation is about 1 mm, and therefore a stroke that can give a tensile force to the elongation is necessary. In the present embodiment, the angular velocity of the drive shaft 86 of the drive roller 81 can be increased by several percent or more with respect to the paper conveyance speed. Since the cam 83 converts the angular velocity difference into a displacement in the width direction and generates a pulling force, a sufficient stroke in the width direction can be secured, and the curl can be reliably reduced without being affected by the stress relaxation of the paper. Further, since the angular velocity difference can be made large, it is possible to generate a sufficient pulling force in the width direction immediately after the roller pair is nipped, and curl can be reduced over the entire sheet conveyance direction.

  Further, it is possible to apply a pulling force to the entire width of the paper, whether the paper is narrow or wide, and the curling can be surely reduced. Further, when it is determined that the curl is small, the pressing force of the roller pair is reduced, and further the torque of the torque limiter is reduced. As a result, the wear of the roller pair can be reduced, and the curl can be stably reduced for a long period of time.

  Even if the user of the image forming apparatus neglects to input the type (thickness) of the sheet, the apparatus detects the sheet thickness, so that the curl can be removed reliably. On the other hand, the installation environment of the image forming apparatus or the environment in the apparatus has a correlation with the moisture content of the paper, but for example, the moisture content of the paper immediately after opening is low and does not necessarily match. Therefore, curling can be reliably predicted by measuring the moisture content of the paper.

  The curl prediction accuracy is improved and not only can the curl be surely removed, but also the minimum pressing force of the roller pair and the torque of the torque limiter are sufficient, so the roller pair is less worn and the curl can be stably reduced for a long period of time.

  In the above embodiment, the roller unit is arranged in the case of the fixing unit 6 so that the roller unit and the pressure roller 62 can be arranged close to each other, and a tensile force can be applied in a state where the paper temperature is high. It is possible. Furthermore, since it is inside the case, the heat released from the heating roller 61 can be held, so that it is possible to prevent the temperature of the sheet from being lowered between the heating roller 61 and the pressure roller 62 to the roller unit.

  The higher the temperature of the paper, the higher the effect of reducing the curl. According to this embodiment, the condition that the curl becomes large such that the water content of the paper is high and the temperature difference between the heating roller 61 and the pressure roller 62 is large. But curl can be reliably reduced. Since the curl reduction effect is great, the pressing force of the driven roller 91 against the driving roller 81 and the driving torque of the torque limiter 87 can be lowered, the life of the roller pair can be extended, and the driving source 88 Small size and low power consumption can be achieved. In the present embodiment, the fixing unit 6 includes the heating roller 61 and the pressure roller 62, but the same effect can be expected even if one of them is a belt or both are belts.

  As described in the above embodiment, the present invention provides a latent image forming apparatus that forms a latent image on a photoreceptor, a developing device that attaches toner to the latent image, and a toner image on the photoreceptor is transferred to a sheet. A transfer device that transports the paper, a fixing unit that melts and fixes the toner image on the paper (consisting of a heating roller (or heating belt) and a pressure roller (or pressure belt)), In an electrophotographic image forming apparatus having a roller unit, a roller unit disposed on the downstream side of the fixing unit in the sheet conveyance direction includes a roller pair that sandwiches and conveys at least both ends in the sheet width direction, and one of the roller pairs is driven. A driving shaft of the driving roller that supports the driving roller so as to be movable in an axial direction, the driving roller is connected to a cam mechanism, and the cam mechanism is rotated at an angle of rotation between the driving roller and the driving shaft. difference Therefore, a force for moving the drive roller toward the outside in the paper width direction is generated, and the drive shaft is driven by an angular velocity of the drive roller corresponding to the paper conveyance speed of the fixing unit via a torque limiter from the drive source. Driven fast.

  The roller pair sandwiches the end in the sheet width direction, and sets the angular speed of the drive shaft so that the sheet conveying speed of the driving roller is faster than the sheet conveying speed of the fixing unit. When the sheet reaches the roller pair, an angular velocity difference is generated between the drive roller and the drive shaft, and a force by the torque set by the torque limiter acts on the cam mechanism. The cam mechanism converts a rotational force into an axial force and applies an axial force to the drive roller. As a result, the driving roller pulls the sheet in the transport direction and also in the width direction.

  In order to reduce curling, it is necessary to pull the paper in the curling direction. Curling by the fixing unit mainly occurs in the width direction of the paper fiber, but it cannot be specified whether the width direction of the fiber is parallel or perpendicular to the paper transport direction. According to this configuration, it is possible to reduce curl regardless of the fiber direction of the paper. Furthermore, a greater tensile force is required to reliably reduce curl. Therefore, in order to reduce the curl, it is necessary to increase the pressing force of the driving roller of the roller pair. However, if slip is caused by the large pressing force, the conveyance becomes unstable and the roller wears severely. Also, since the heated paper after the fixing unit and the moisture content of the paper is high, stress relaxation occurs, so the roller pair needs a sufficient stroke in the width direction to give a tensile force even if the paper is deformed. It is. In this configuration, there is no slip by using the torque limiter, and the angular velocity of the drive shaft of the drive roller can be made faster than the conveyance speed of the paper. Since the angular velocity difference is converted into a displacement in the width direction by the cam and a tensile force is generated, a sufficient stroke in the width direction can be secured, and the curl can be reliably reduced without being affected by the stress relaxation of the paper. Further, since the angular velocity difference can be made large, it is possible to generate a sufficient tensile force in the width direction immediately after the roller pair is nipped, and curl can be reduced over the entire conveyance direction of the paper. Further, since there is no slip, the conveyance can be stabilized and the wear can be reduced, so that a larger pressing force can be applied and the torque setting of the torque limiter can be increased to give a large pulling force to the paper.

  The present invention further includes a pressing load changing device in which a plurality of roller units are arranged according to the corresponding paper width of the image forming apparatus, and the pressing load can be changed for each roller unit. The pressing load of the roller unit having the roller pair positioned inside is reduced with respect to the pressing load of the roller unit that sandwiches the outermost end portion between the left and right roller pairs in accordance with the sheet width.

  The image forming apparatus may handle various paper sizes. In order to reduce curl, it is desirable to apply a pulling force to the end of the paper. However, if the left and right positions of the roller pair are aligned with the widest sheet, the end of the sheet may not be clamped by the roller pair in the case of a narrow sheet. Therefore, a plurality of roller units are arranged so as to be compatible with various paper widths. In the case of the widest paper, in order to apply a tensile force to the entire paper width, it is necessary to increase the pulling force of the outer roller unit than the inner roller unit. Therefore, the pressing load of the roller unit located inside is reduced, the pulling force is reduced and the outside pulling force is increased, so that the curl can be reduced over the entire width of the sheet.

  In the present invention, the roller unit is disposed in the unit case of the fixing unit. In order to reduce the curl by applying a pulling force to the paper, it is effective that the temperature of the paper is high. By placing a roller unit that applies tensile force to the paper in the unit case of the fixing unit, the roller unit can be placed immediately after the heating roller or heating belt, and the tensile force acts on the paper at a high paper temperature. It becomes possible. Furthermore, it is possible to maintain the surrounding environment at a high temperature, to prevent a decrease in the temperature of the paper, and to reduce curl more effectively.

  Further, according to the present invention, the set torque can be controlled by the torque limiter, and the pressing load of the roller pair and the set torque of the torque limiter are changed based on the prediction of the curl predicting means for predicting the curl of the sheet. The curl predicting unit, for example, information on the thickness and type of paper (information on whether it is coated paper, high-quality paper, or recycled paper) and setting information that is used when the paper is supplied to the image forming apparatus This is a means for calculating the magnitude of curl based on information from a temperature / humidity sensor provided in the image forming apparatus.

  FIG. 7 shows the relationship between the input and output of the curl prediction means. The thickness and type of the paper are input from the operation panel (or the user's personal computer) of the main body. As the paper type, “coated paper”, “recycled paper”, and “quality paper” are selected from the keys on the operation panel, and the curl predicting means correlates f1, f2, and f3 according to the paper type (in the example of FIG. 7). 3 types, but not limited to this number). Alternatively, one correlation equation and coefficients corresponding to the temperature, humidity, and paper thickness of the correlation equation may be provided as a table. The paper thickness can be selected from “thick paper”, “plain paper”, and “thin paper” on the operation panel, and the curl predicting means has a numerical value (T1 to T9) corresponding thereto as a table. Temperature and humidity are measured values input from the temperature and humidity sensor. The curl prediction means calculates the curl amount from the correlation equations f1, f2, f3 corresponding to the paper type and the input data. Further, the setting of the torque limiter is changed according to the calculated value so that the setting of the pressing load of the roller pair can be changed. For example, when the paper is thick, the curl is small, and it is not necessary to apply a pulling force with the roller pair. Such a condition is predicted by the curl prediction means, the pressing force of the roller pair is lowered, and further the torque of the torque limiter is lowered. As a result, the wear of the roller pair can be reduced, and the curl can be stably reduced for a long period of time.

  Further, the present invention provides a first temperature detection means for measuring the temperature of the heating roller or the heating belt, a second temperature detection means for measuring the temperature of the pressure roller or the pressure belt, and upstream of the fixing unit. A sheet thickness detecting unit that measures the sheet thickness on the side conveyance path, and a moisture content detecting unit that detects the moisture content of the sheet. The curl predicting means uses the data of the paper thickness detecting means for the paper thickness, and uses the data of the first temperature detecting means, the second temperature detecting means, and the moisture content detecting means for detecting the moisture content of the paper. And the curl is calculated using the correlation equation corresponding to those inputs.

  When the fixing unit includes a heating roller or a heating belt and a pressure roller or a pressure belt, the curl becomes larger with respect to the heating side as the temperature on the pressing side is lower and the temperature on the heating side is higher. . Therefore, the curl predicting means uses information of the first temperature detecting means for measuring the temperature of the heating roller or the heating belt and the second temperature detecting means for measuring the temperature of the pressure roller or the pressing belt. Also, curl changes depending on the thickness and moisture content of the paper, so that the paper thickness is measured on the transport path upstream of the fixing unit so that information can be obtained before the paper reaches the fixing unit. The curl is predicted using information by the detecting means and the moisture content detecting means for detecting the moisture content of the paper. In this configuration, even if the user of the image forming apparatus neglects to input the paper type, the apparatus detects the paper thickness, so that the curl can be removed reliably. On the other hand, the installation environment of the image forming apparatus or the environment in the apparatus has a correlation with the moisture content of the paper, but for example, the moisture content of the paper immediately after opening is low and does not necessarily match. Therefore, curling can be reliably predicted by measuring the moisture content of the paper. In addition, the accuracy of curl prediction is improved and not only can the curl be removed reliably, but the minimum required force of the roller pair and torque limiter torque are required, so there is little wear on the roller pair and stable curling can be achieved for a long period of time. Can be reduced.

  The above-described embodiment is a preferred embodiment of the present invention, and the scope of the present invention is not limited to the above-described embodiment alone, and various modifications are made without departing from the gist of the present invention. Implementation is possible.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Transfer belt 3 Belt drive roller 4 Paper cassette 6 Fixing unit 7 Transfer roller 8 Conveyance path 9 Pick roller 11 Separating roller 61 Heating roller 62 Pressure roller 63 Heater 68 Paper discharge roller 69 Registration roller 70 Paper moisture content detection Means 71 Paper thickness detection means 75 First temperature detection means 76 Second temperature detection means 81 Drive roller 82 Return spring 83 Cam 87 Torque limiter 88 Drive source 91 Followed roller 95 First eccentric cam 98 Second eccentricity Core cam 110 Control means 111 Storage means 801 First roller unit 802 Second roller unit

JP 2007-055793 A JP 2002-241021 A

Claims (6)

An image forming apparatus including a fixing unit for fixing a toner image transferred on a recording paper,
While being disposed downstream of the fixing unit in the sheet conveyance direction, sandwiching both ends of the sheet in a direction perpendicular to the sheet conveyance direction, and applying a force in a direction perpendicular to the sheet conveyance direction and the sheet conveyance direction toward the outside of the sheet An image forming apparatus comprising a paper curl correction unit for transporting paper. The paper curl correction unit is
A pair of rollers for sandwiching the paper, including a driving roller on one side, the pair of rollers provided corresponding to both ends of the paper;
A driving shaft that supports the driving roller so as to be movable in the axial direction, and that is driven faster than an angular velocity of the driving roller corresponding to a paper conveyance speed of the fixing unit by receiving a rotational drive of a driving source;
A cam mechanism that is provided on the drive roller and generates a force that moves the drive roller in a direction perpendicular to the paper transport direction and toward the outside of the paper by a rotational angle difference between the drive roller and the drive shaft;
The image forming apparatus according to claim 1, further comprising: The paper curl correction unit is
A plurality are arranged according to the corresponding paper width of the image forming apparatus,
A pressing load changing means capable of changing the pressing load on the correction roller for each unit;
The pressing load changing means reduces the pressing load of the sheet curl correction unit having the correction roller located inside the correction roller that sandwiches both ends of the sheet according to the sheet width of the conveyed sheet. The image forming apparatus according to claim 2, wherein: A torque limiter capable of adjusting the rotational drive of the drive source;
Curl prediction means for predicting curl of paper;
Control means for controlling the pressing load changing means and the torque limiter based on the prediction result of the curl prediction means;
The image forming apparatus according to claim 3, further comprising: First temperature detecting means for measuring the temperature of the heating means included in the fixing unit;
Second temperature detection means for measuring the temperature of the pressure means included in the fixing unit;
A sheet thickness detecting means for measuring the sheet thickness on the sheet conveyance path upstream from the fixing unit;
Moisture content detecting means for detecting the moisture content of the paper;
Have
The image forming apparatus according to claim 4, wherein the curl predicting unit predicts a curl of the sheet based on information of the detecting units.   The image forming apparatus according to claim 1, wherein the paper curl correction unit is disposed in a unit case of the fixing unit.

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