SHEET CONVEYING APPARATUS AND IMAGE FORMING APPARATUS

Abstract

Provided is a sheet conveying apparatus which can improve rippling of a sheet. The sheet conveying apparatus which conveys the sheet includes an electromagnetic hysteresis brake 131 which is configured to apply a tension force in a conveying direction of the sheet and a controller 500C which performs control on the electromagnetic hysteresis brake 131 to vary a load. The controller 500C performs control on the load of the electromagnetic hysteresis brake 131 according to information relating to the sheet.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet conveying apparatus which conveys a sheet and suppresses rippling or curls of the sheet, and an image forming apparatus which includes the sheet conveying apparatus.

2. Description of the Related Art

In the related art, an image forming apparatus which employs an electrophotographic system develops a latent image formed on a photosensitive drum serving as an image bearing member so as to be a visible image, and then transfers the visible image (a toner image) onto the sheet using an electrostatic force. Next, the toner image on the sheet is fixed by heat and pressure, and an image is recorded on the sheet.

As for a fixing apparatus of such an image forming apparatus, a heat roller fixation system is employed. In the heat roller fixation system, a fixing roller is kept in a predetermined temperature using a heat source such as a heater provided therein, an elastic pressure roller comes in press contact with the fixing roller to form a nip portion. Further, the toner image is fixed onto the sheet in the nip portion.

However, in a heat fixing process of the fixing apparatus, since the heat and the pressure is applied to the sheet with the toner image transferred thereon, moisture is evaporated from the inside of the sheet in process of passing through the nip portion of the fixing apparatus or after passing through the nip portion of the fixing apparatus. At this time, a humidity of the sheet is changed due to the heat and a stress is applied on the sheet due to the pressure. Therefore, a phenomenon called curls to bend the sheet or a phenomenon called rippling to make the sheet waved is generated.

Herein, it is considered that sheet paper which is most commonly used as a sheet is observed at a fiber level. The sheet is formed of short fibrous tissues which are intertwined, and moisture is contained in the fibrous tissue or between the fibrous tissues. Furthermore, there occurs an equilibrium state in a state where the fibrous tissue and water are combined by hydrogen bonding, so that the sheet has smoothness.

However, when the heat and the pressure are applied in the fixing process, the fibrous tissues are sheared. In this state, when the heat is added to evaporate the moisture, the hydrogen bonding occurs between the fibrous tissues once more and the sheet is deformed. When the sheet is left as it is, the sheet absorbs moisture from the surroundings, the hydrogen bonding between the fibrous tissues is torn off again and returns to the original state. However, when the moisture is not absorbed between some fibrous tissues of the sheet, the deformation of the sheet is kept on. As deformation patterns, there are the curls and the rippling as described above. The curls are generated by an extension difference between the front and back surfaces of the sheet, and the rippling is generated by the extension difference in the center portion and the end portion of the sheet.

As described above, one of the factors that cause the rippling on the end portion of the sheet lies in a process when the sheet passes through the nip portion of the fixing apparatus. For example, in the case of the fixing apparatus which includes a wide nip portion such as a belt fixing system, a conveying speed in the nip portion is set to be high for the end portion rather than the center portion in the width direction perpendicular to the conveying direction of the sheet in order to prevent wrinkles of the sheet when the sheet passes through the nip portion. Therefore, in a case where a pulling operation is exerted on the sheet, the end portion of the sheet is extended in the conveying direction compared to a portion near the center portion after passing through the nip portion, thereby generating the rippling in the end portion of the sheet.

Further, as described above, one of the factors that cause the rippling in the end portion of the sheet lies in a process after the sheet passes through the nip portion of the fixing apparatus. In a state where the sheets are stacked as a sheet bundle, the end portion of each sheet is in contact with the air, so that moisture frequently goes in and out. When the heat is added to the sheet in the fixing process, the moisture inside the sheet is evaporated, and then the end portion of the sheet rapidly absorbs the moisture, the end portion of the sheet is finally extended in the conveying direction compared to a portion near the center portion, thereby generating the rippling in the end portion of the sheet.

Therefore, there is proposed a technology of correcting the deformation of the sheet described above in the related art. U.S. Pat. No. 7,840,173 discloses a sheet conveying apparatus in which two decurl portions are disposed, and the decurl portions include a plurality of roller groups to correct the curls of the sheet. Then, while the sheet is nipped and conveyed by the roller groups included in the decurl portion, the curls of the sheet are corrected.

However, a technology disclosed in U.S. Pat. No. 7,840,173 can correct the curls to make the sheet bent among the deformations of the sheet described above, but it is difficult to sufficiently correct the rippling of the sheet caused by a difference in extension occurring between the center portion and the end portion of the sheet.

Further, a deformation level of the sheet is different according to a basis weight, a type, an image density, an environmental humidity, and the like. For this reason, the deformation level is not sufficiently improved only by passing the sheet through the decurl portion as described above.

Therefore, the invention is to further develop the technology in the related art, and it is desirable to provide a sheet conveying apparatus which can improve the rippling of the sheet.

Further, it is also desirable to provide a sheet conveying apparatus which can improve the rippling of the sheet even under different conditions such as the basis weight, the type, the image density, and the environmental humidity.

SUMMARY OF THE INVENTION

It is desirable to provide the following configurations.

A sheet conveying apparatus conveys a sheet with an image formed thereon by an image forming portion, and includes a load portion which is configured to apply a tension force in a conveying direction to the sheet and a load controller which performs control on the load portion to vary a load thereof. The load controller performs control on the load portion to vary the load thereof according to information relating to the sheet.

Further, an image forming apparatus includes an image forming portion which forms a toner image, a fixing portion which heats and fixes the toner image formed on a sheet by the image forming portion, a load portion which applies a tension force in a conveying direction to the sheet passed through the fixing portion, and a load controller which performs control on the load portion to vary a load. The load controller performs control the load of the load portion according to information relating to the sheet.

Further, a sheet conveying apparatus which conveys a sheet includes a load portion which applies a tension force of a conveying direction to the sheet and a load controller which performs control on the load portion to vary a load. The load controller performs control on the load portion to apply a load on the sheet according to information relating to the sheet which is input to the load controller.

According to the invention, since the tension force in the conveying direction is applied on the sheet, even when a difference in extension occurs between the center portion and the end portion of the sheet, it is possible to reduce the difference and to improve rippling of the sheet.

Furthermore, even in a case where the conditions such as a basis weight, a type, an image density, an environmental humidity are different, it is possible to apply the tension force on the sheet according to the conditions, and thus the rippling of the sheet can be more effectively improved.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a sheet rippling correction apparatus according to a first embodiment;

FIG. 2 is a cross-sectional view illustrating an electrophotographic printer according to the first embodiment;

FIG. 3 is a cross-sectional view illustrating a sheet humidifying apparatus according to the first embodiment;

FIG. 4 is a diagram illustrating the outline of the sheet humidifying apparatus according to the first embodiment;

FIG. 5 is a block diagram illustrating control of the electrophotographic printer, the sheet humidifying apparatus, and the sheet pulling and conveying apparatus according to the first embodiment;

FIG. 6 is a flowchart illustrating control of the sheet pulling and conveying apparatus according to the first embodiment;

FIG. 7A is a cross-sectional view illustrating the sheet pulling and conveying apparatus according to the first embodiment;

FIG. 7B is a cross-sectional view illustrating the sheet pulling and conveying apparatus according to the first embodiment;

FIG. 8 is a perspective view illustrating the sheet pulling and conveying apparatus according to the first embodiment;

FIG. 9 is a top view illustrating the sheet pulling and conveying apparatus according to the first embodiment;

FIG. 10 is a diagram illustrating the outline of the shape of a sheet P;

FIG. 11 is a graph illustrating a relation between an exciting current of a load portion and a brake torque according to the first embodiment;

FIG. 12A is a table listing states of a sheet obtained by experiments according to the first embodiment;

FIG. 12B is a table listing states of a sheet obtained by experiments according to the first embodiment;

FIG. 12C is a table listing states of a sheet obtained by experiments according to the first embodiment;

FIG. 13A is a table listing states of a sheet obtained by experiments according to the first embodiment;

FIG. 13B is a table listing states of a sheet obtained by experiments according to the first embodiment;

FIG. 13C is a table listing states of a sheet obtained by experiments according to the first embodiment;

FIG. 14A is a table listing states of a sheet obtained by experiments according to the first embodiment;

FIG. 14B is a table listing states of a sheet obtained by experiments according to the first embodiment;

FIG. 15A is a table listing states of a sheet obtained by experiments according to the first embodiment;

FIG. 15B is a table listing states of a sheet obtained by experiments according to the first embodiment;

FIG. 16A is a table listing setting values under various conditions of a sheet tension force according to the first embodiment;

FIG. 16B is a table listing setting values under various conditions of the sheet tension force according to the first embodiment;

FIG. 17 is a top view illustrating a sheet pulling and conveying apparatus according to a second embodiment;

FIG. 18 is a flowchart illustrating control of the sheet pulling and conveying apparatus according to the second embodiment; and

FIG. 19 is a cross-sectional view illustrating a sheet rippling correction apparatus according to another embodiment.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, exemplary embodiments of the invention will be described in detail with reference to the drawings. However, dimension, material, shape, and relative arrangement of components described in the following embodiments may be appropriately changed according to the configuration or various conditions of the apparatus to which the invention pertains. Therefore, there is no purpose of limiting the scope of the invention only to these embodiments, if not otherwise specified.

First Embodiment

An image forming apparatus according to the embodiment will be described using FIGS. 1 to 14C.

<Image Forming Apparatus>

FIG. 2 is a cross-sectional view schematically illustrating a color electrophotographic printer 500 as an example of the image forming apparatus which is taken along a conveying direction of a sheet. Herein, the color electrophotographic printer will be simply referred to as a “printer”.

The sheet is used to form a toner image thereon. Specific examples of the sheet include plain paper, a resin sheet-like medium as a substitute for the plain paper, thick paper, a medium used for an overhead projector, and the like.

The printer illustrated in FIG. 2 includes an image forming portion 510 of each color of Y (yellow), M (magenta), C (cyan), and Bk (black). The image forming portion 510 of each color is used to form a toner image of each color on the sheet. The image forming portion 510 of each color includes process portions as follows; an electrophotographic photoconductor (photosensitive drum) 511 serving as an image bearing member which carries an electrostatic latent image on the surface in correspondence with each color of Y, M, C, and K, a charging roller 512, a laser scanner 513, and a development device 514. The photosensitive drum 511 is charged by the charging roller 512 in advance. Then, the photosensitive drum 511 is exposed to light by the laser scanner 513 and forms a latent image. The latent image is a toner image developed by the development device 514 and becomes a visible image.

In a primary transfer portion which is formed by the photosensitive drum 511 and a primary transfer roller 515, the respective toner images formed and carried on the surfaces of the photosensitive drums 511 are primarily transferred onto an intermediate transfer belt 531 by the primary transfer roller 515 in a sequentially superimposed manner.

On the other hand, the sheet P is fed out of a sheet cassette 520 one by one and then sent to a registration roller pair 523. The registration roller pair 523 once stops the sheet P, and corrects skew feeding in a case where the sheet is fed on the skew. Then, the registration roller pair 523 sends the sheet to a secondary transfer portion between the intermediate transfer belt 531 and a secondary transfer roller 535 in synchronization with the toner images on the intermediate transfer belt 531. The color toner images on the intermediate transfer belt are secondarily transferred onto the sheet P in a lump by the secondary transfer roller 535 which is a transfer member for example.

Then, as described above, the sheet with the image (the toner image) formed thereon by the image forming portion is conveyed to a fixing apparatus 100. In the fixing apparatus (a fixing portion) 100, the sheet is nipped in a fixing nip portion and the unfixed toner image is applied with heat and pressure, so that the toner image is fixed on the sheet. After passing through the fixing apparatus 100, the sheet is sent to a sheet rippling correction apparatus 201 by a main discharge roller 540 to correct rippling by the sheet rippling correction apparatus 201, and then discharged onto a discharge tray 565.

<Fixing Apparatus>

Herein, the fixing apparatus will be described. As illustrated in FIG. 2, the fixing apparatus 100 includes a fixing roller 110 serving as a heating rotating member and a pressure roller 111 serving as a pressure rotating member. The fixing roller 110 applies heat (which is generated by a halogen heater (not illustrated) therein) to the toner T on the sheet P while conveying the sheet P in corporation with the pressure roller 111. The fixing roller 110, for example, includes the halogen heater which is built in a metal core made of a cylindrical aluminum tube having an outer diameter of 56 mm and an inner diameter of 50 mm. On the surface of the metal core, for example, an elastic layer made of silicon rubber having a thickness of 2 mm and a hardness (Asker C) of 45° is coated and the surface of the elastic layer is coated with a PFA or PTFE heat-resistant toner parting layer.

The pressure roller 111 conveys the sheet P in cooperation with the fixing roller 110. The pressure roller 111 also includes, for example, a metal core made of a cylindrical aluminum tube having an outer diameter of 56 mm and an inner diameter of 50 mm. On the surface of the metal core, for example, an elastic layer made of silicon rubber having a thickness of 2 mm and a hardness (Asker C) of 45° is coated and the surface of the elastic layer is coated with a PFA or PTFE heat-resistant toner parting layer.

A fixing nip N illustrated in FIG. 2 is formed by the fixing roller 110 and the pressure roller 111. The inventors have been performed experiment in which the sheet P is conveyed at a conveying speed of 300 to 500 mm/sec based on conditions as follows: a setting temperature of the surface of the fixing roller 110 is 180° C., a setting temperature of the surface of the pressure roller 111 is 100° C., an environmental temperature of 23° C., and an environmental humidity of 50%. Then, the sheet P heated and pressed in the fixing nip N is further applied with heat from the fixing roller 110 which has a temperature higher than that of the pressure roller 111, and the fibrous tissue on the upper side of the sheet P is extended further more than on the lower side thereof. As a result, curls in the lower direction (hereinafter, referred to as lower curls) are generated. Further, the fibrous tissue of the end portion in a width direction perpendicular to a conveying direction of the sheet is extended in the conveying direction further more than the center portion, and thus the length of the conveying direction of the sheet becomes different in the end portion and the center portion. As a result, the rippling is generated in the end portion of the sheet.

<Controller>

As information relating to the sheet, basis weight information of the sheet P in the sheet cassette 520 is input by a user through an operation panel (operation portion) 570, and the information is sent to a CPU and a memory which included in a controller 500C in the image forming apparatus illustrated in FIG. 5.

Herein, as information relating to the sheet which can be input from the operation panel, the basis weight is given as an example in the embodiment, but the invention is not limited thereto. Besides the basis weight, for example, information of types of the sheet (plain paper, coated paper, embossing paper, thin paper, recycled paper, and the like), size information, and the like are used. The information thus input relating to the sheet is sent to the controller (load controller) 500C as described above.

Further, image density information of the toner image on the sheet P formed by the image forming portion 510 is sent to the CPU and the memory which are included in the controller (the load controller) 500C in the image forming apparatus illustrated in FIG. 5.

Further, a temperature and a humidity in the image forming apparatus 500 are detected by an environment sensor 500D which is provided over the sheet cassette 520 in the image forming apparatus 500, and the temperature information and the humidity information are sent to the CPU and the memory which are included in the controller 500C. The environment sensor 500D serves as a humidity detection portion which detects environmental humidity.

Herein, the controlling configuration of the entire apparatus will be described using FIG. 5. FIG. 5 is a block diagram illustrating the entire control relation between the image forming apparatus 500 and the sheet rippling correction apparatus 201. The controller 500C of the image forming apparatus 500 and a controller 201C of the sheet rippling correction apparatus 201 each are a computer system which includes a CPU and a memory and further includes, while not illustrated, a calculation unit, an I/O port, a communication interface, a driving circuit, and the like.

The controls of the respective controllers described above are performed by predetermined programs, when executed by the respective CPUs, which are stored in the memory. Further, the respective controllers described above are connected to each other through a communication portion COM, and can exchange the information. In addition, the blocks not directly associated to the description of the invention are not illustrated in the drawing.

<Sheet Rippling Correction Apparatus>

Next, as the sheet conveying apparatus which conveys a sheet passed through the fixing portion, the sheet rippling correction apparatus 201 will be described using FIG. 1. FIG. 1 is a cross-sectional view illustrating the entire sheet rippling correction apparatus 201. The sheet P on which a toner image is fixed by heating and pressurizing the toner image by the fixing apparatus 100 is sent to an input roller pair 207 (in a direction of arrow A in FIG. 1) of the sheet rippling correction apparatus 201 by the main discharge roller 540. Further, after the conveying direction is changed by a conveying guide 208 to the vertical direction (a direction of arrow B in FIG. 1), the sheet is sent to a sheet humidifying apparatus 202 serving as a moisture applying apparatus. Herein, the sheet P is humidified by a humidifying roller pair 220 and 230 and a humidifying roller pair 221 and 231.

The sheet P discharged out of the sheet humidifying apparatus 202 is successively sent to the sheet pulling and conveying apparatus (the sheet conveying apparatus) 101. After being humidified at a predetermined humidity or more by the sheet humidifying apparatus 202, the sheet P passes through the sheet pulling and conveying apparatus 101, so that the center portion in the width direction perpendicular to the conveying direction of the sheet is extended further more than the end portion. Therefore, a difference in length between the end portion of the width direction of the sheet and the center portion of the conveying direction of the sheet is reduced, and thus the rippling is improved. After the sheet P passes through the sheet pulling and conveying apparatus 101, the conveying direction is changed by a conveying guide 209 to a direction of arrow C in FIG. 1, and then discharged to the outside of the sheet rippling correction apparatus 201 by a discharge roller pair 210 and is stacked on the discharge tray 565.

In FIG. 1, a reservoir 204 contains humidification liquid LQ1 used for humidifying the sheet P. The humidification liquid LQ1 contained in the reservoir 204 is supplied in a direction of arrow D in FIG. 1 by a pump 206 through a water pipe 205 toward a water tank 240 which is provided in the sheet humidifying apparatus 202. Humidification liquid LQ2 is supplied into the water tank 240. The humidification liquid LQ1 and LQ2 contains water as a main component.

<Sheet Humidifying Apparatus>

Next, the sheet humidifying apparatus 202 in the sheet rippling correction apparatus will be described using FIGS. 3 and 4. FIG. 3 is a cross-sectional view illustrating the entire sheet humidifying apparatus 202, and FIG. 4 is a diagram illustrating the outline of the sheet humidifying apparatus 202.

The sheet P sent in the same direction of arrow B in FIG. 3 as that of arrow B in FIG. 1 is introduced into an inlet guide 250 and sent to the nip portion of a first humidifying roller pair 220 and 230, and is transferred by the humidification liquid LQ2 and humidified. Next, the sheet P is further humidified by transferring the humidification liquid LQ2 again onto the surface in process of passing through the nip portion of a second humidifying roller pair 221 and 231.

Next, the sheet P passed through the nip portion of the second humidifying roller pair 221 and 231 passes through a conveying roller pair 222 and 232 and sent to the sheet pulling and conveying apparatus 101 through a humidifying portion discharge guide 251.

The respective humidifying rollers of the first humidifying roller pair 220 and 230 and the second humidifying roller pair 221 and 231 are all elastic rollers in which a solid rubber layer containing NBR and silicon as main components is formed in the surface of a shaft core made of a metal rigid body such as stainless steel.

Water feeding rollers 223, 224, 225, 233, 234, and 235 sequentially supply the humidification liquid LQ2 in the water tank 240 to the respective humidifying rollers of the first humidifying roller pair 220 and 230 and the second humidifying roller pair 221 and 231. The water feeding rollers 223, 224, 225, 233, 234, and 235 are the elastic rollers in which a material of which the surface has hydrophilicity to hold water on the surface of the shaft core made of the metal rigid body such as the stainless steel; for example, a solid rubber layer containing NBR as a main component is formed on the surface of the shaft core. As the solid rubber layer, a metal or a hydrophilic-processed resin may be used.

The water feeding roller 223 comes into contact with both the humidifying roller 220 and the humidifying roller 221 among the respective humidifying rollers of the first humidifying roller pair 220 and 230 and the second humidifying roller pair 221 and 231. Further, since the water feeding roller 224 comes into contact with the water feeding roller 223 and the water feeding roller 225 comes into contact with the water feeding roller 224, a water path is formed from the inside of the water tank 240 toward the humidifying roller 220 and the humidifying roller 221.

The water feeding roller 233 comes into contact with both the humidifying roller 230 and the humidifying roller 231 among the respective humidifying rollers of the first humidifying roller pair 220 and 230 and the second humidifying roller pair 221 and 231. Further, since the water feeding roller 234 comes into contact with the water feeding roller 233 and the water feeding roller 235 comes into contact with the water feeding roller 234, a water path is formed from the inside of the water tank 240 toward the humidifying roller 230 and the humidifying roller 231.

Regulating rollers 226 and 236 are configured to regulate a water amount to be supplied to the respective humidifying rollers of the first humidifying roller pair 220 and 230 and the second humidifying roller pair 221 and 231. The regulating rollers 226 and 236 are rollers which are subjected to coating treatment with nickel, chrome, or the like on the surface of the shaft core made of the metal rigid body such as the stainless steel.

The regulating roller 226 comes into contact with the water feeding roller 224, and the regulating roller 236 comes into contact with the water feeding roller 234 so as to suppress the amount of the humidification liquid held on the surface of each solid rubber layer and to regulate the amount of water to be supplied to the sheet P. In other words, the regulating rollers 226 and 236 come into press contact with the solid rubber layers of the water feeding rollers 224 and 234 to cause deformation, and squeeze the humidification liquid contained in the surface. Therefore, the sheet P is humidified at an optimal humidity, and thus the extending effect is accelerated by the above-mentioned sheet pulling and conveying apparatus 101.

As illustrated in FIG. 3, the respective rollers of the first humidifying roller pair 220 and 230 and the second humidifying roller pair 221 and 231, the water feeding rollers 223, 224, 225, 233, 234, and 235, the regulating rollers 226 and 236, and the conveying roller pair 222 and 232 are bisymmetrically arranged with the sheet P interposed therebetween and each rotate in the respective directions of arrows. Therefore, both faces of the sheet P are uniformly humidified with water.

Among the above-mentioned rollers, the end portions of the humidifying rollers 230 and 231 and the conveying roller 232 disposed on the left side with respect to the sheet P are respectively fixed to driving gears 260, 261, and 262 as illustrated in FIG. 4 and a rotation driving force is transferred by driving motors (not illustrated). The other rollers are rotatably driven by a driving force transferred from the respective surfaces of the humidifying rollers 230 and 231 and the conveying roller 232.

By supplying moisture to the sheet using the humidifying roller pair which humidifies the above-mentioned sheet P, water content can be increased up to a level required for accelerating the extension according to a tension load on the center portion in the width direction of the sheet P by the sheet pulling and conveying apparatus 101.

<Sheet Pulling and Conveying Apparatus>

Next, the sheet pulling and conveying apparatus 101 in the sheet rippling correction apparatus will be described using FIGS. 7A to 9. FIGS. 7A and 7B are cross-sectional views illustrating the sheet pulling and conveying apparatus, FIG. 8 is a perspective view illustrating the sheet pulling and conveying apparatus, and FIG. 9 is a top view illustrating the sheet pulling and conveying apparatus.

The sheet pulling and conveying apparatus 101 conveys the sheet P while nipping the sheet P using a first roller A104 and a first roller B105 which are included in a first roller pair illustrated in FIGS. 7A and 7B, and a second roller A106 and a second roller B107 which are included in a second roller pair on the downstream in the conveying direction of the first roller pair. The sheet pulling and conveying apparatus 101 applies a tension force to the sheet P in order to extend the center portion of the width direction of the sheet to the conveying direction while nipping and conveying the sheet. Then, the sheet P is guided between a discharge upper guide 117 and a discharge lower guide 118, and discharged to the outside of the sheet pulling and conveying apparatus 101.

As illustrated in FIG. 8, the first roller A104, the first roller B105, the second roller A106, and the second roller B107 have elastic rubbers 104b, 105b, 106b, and 107b such as silicon, NBR, and EPDM. The elastic rubbers 104b, 105b, 106b, and 107b are formed on the surfaces of roller shafts 104a, 105a, 106a, and 107a made of a high rigidity material such as stainless steel and iron. Herein, all the outer diameters φ of the elastic rubbers 104b, 105b, 106b, and 107b are set to 20 mm. Further, as illustrated in FIG. 8, the elastic rubbers 105b and 107b of the first roller B105 and the second roller B107 are formed in a region corresponding to the length L1 of the center portion in the width direction of the sheet so as to be uniformly disposed with respect to a sheet passing center. In other words, the outer diameters of the first roller B105 and the second roller B107 are provided such that the center region in the width direction perpendicular to the conveying direction of the sheet has an outer diameter larger than that of the end region. Herein, the sheet passing center is a position of the center in the width direction as a reference when the sheet is conveyed. The length L1 is shorter than the length of the sheet P in the width direction which may become a problem causing the rippling illustrated in FIG. 10. Herein, the length L1 is set to 100 mm (L1=100 mm).

Further, a conveying upper guide 114 and a conveying lower guide 115 serving as guide members to guide the sheet are provided between nip portions of the first roller pair and the second roller pair, and the distance between the nip portions is set to 25 mm.

The first roller A104 and the second roller A106 are provided such that both ends of the roller shafts 104a and 106a are supported to an upper plate 119 through gears (not illustrated).

The first roller B105 is provided such that both ends of the roller shaft 105a are supported to a first pressure plate 113 through a gear (not illustrated). The first pressure plate 113 is rotatably supported to a lower plate 120 through a first rotation shaft (not illustrated), and the bottom surface is urged by a first pressure spring 109. Therefore, the first roller B105 is pressurized to the first roller A104, so that the nip portion is formed.

The second roller B107 is provided such that both ends of the roller shaft 107a are supported to a second pressure plate 112 through a gear (not illustrated). The second pressure plate 112 is rotatably supported to the lower plate 120 through a second rotation shaft 122, and the bottom surface is urged by a second pressure spring 108. Therefore, the second roller B107 is pressurized to the second roller A106, so that the nip portion is formed.

A reflective light type of sheet sensor 103 is disposed in an entrance lower guide 121 to detect whether the sheet P is arrived at.

FIG. 9 is a top view for describing the driving of the first roller A104 and the second roller A106.

In the drawing, the CPU is a controller which controls the operations of an electromagnetic clutch CL serving as a clutch portion (driving controller) and a driving motor M serving as a driving portion.

As illustrated in FIG. 9, the driving gear 104G1 is held and fixed on one end of the first roller A104. The first roller A104 is rotated by receiving a rotation driving force through driving transmission gears 123, 124, and 125 and a clutch gear CLG from a motor gear MG of the driving motor M serving as a driving source (the driving portion). The first roller B105 pressurized by the first roller A104 is rotatably driven according to the rotation of the first roller A104.

The driving gear 106G is held and fixed on one end of the second roller A106. The second roller A106 is rotated by receiving a rotation driving force through driving transmission gears 126, 127, 128, and 129 from the motor gear MG of the driving motor M serving as the driving source (the driving portion). The second roller B107 pressurized by the second roller A106 is rotatably driven according to the rotation of the second roller A106.

The clutch gear CLG is fixed on the electromagnetic clutch CL. While the electromagnetic clutch CL is powered on, the driving force between the clutch gear CLG and the driving transmission gear 124 is transferred through a clutch shaft 132, and the first roller A104 rotates. On the other hand, when the electromagnetic clutch CL is not powered on, the driving force between the clutch gear CLG and the driving transmission gear 124 is not transferred, the driving force of the driving motor M is not transferred to the driving gear 104G, and thus the first roller A104 does not rotate.

Further, the driving gear 104G2 is fixed on the other end of the first roller A104. The driving gear 104G2 is connected to a load portion 131 such as an electromagnetic powder brake and an electromagnetic hysteresis brake through a driving transmission gear 130.

The load portion 131 applies a tension force to the sheet in the conveying direction, and can change a brake torque according to an exciting current value. In addition, in the following description, the electromagnetic hysteresis brake (electromagnetic brake) will be exemplified as the load portion. FIG. 11 illustrates a relation between an exciting current of the electromagnetic hysteresis brake used in the embodiment and the brake torque. As illustrated in FIG. 11, the exciting current and the brake torque are proportional to each other, and the electromagnetic hysteresis brake can be varied to be a predetermined brake torque by changing the exciting current as needed.

As described in the following, the transmission of a driving force to the first roller pair is disconnected at a timing point when the sheet P is arrived at the nip portion of the second roller pair. After the transmission of the driving force to the first roller pair is disconnected, the first roller pair generates a load on the conveyance of the sheet P by the second roller pair. Therefore, when the sheet P is nipped between the first roller pair and the second roller pair, the sheet P is conveyed while a tension force (a tension force in the conveying direction of the sheet) is generated in the sheet P conveyed by the second roller pair. Then, the tension force loaded on the sheet P is also changed according to a magnitude of the brake torque generated by the load portion 131.

In the embodiment, when the brake torque is 100%, the tension force loaded on the sheet is set to be 8 kgf. In the embodiment, when the tension force becomes 8 kgf or more, the load is increased, so that the roller slips over the sheet in the nip portion of the second roller pair (106 and 107).

FIG. 6 illustrates a flowchart relating to driving control according to the embodiment, and FIG. 5 illustrates a block diagram relating to the driving control according to the embodiment. FIGS. 7A and 7B illustrate front cross-sectional views of the sheet pulling and conveying apparatus 101 for describing the driving control according to the embodiment. FIG. 7A is the front cross-sectional view during a period of time from 0 to X msec after the sheet sensor is turned on, and FIG. 7B is the front cross-sectional view at the time of X msec after the sheet sensor is turned on.

When a sheet passing job signal is input to the CPU (the controller) (S6-1), the basis weight, the type, the image density, and the humidity information are confirmed as information relating to the sheet (S6-2). Then, the exciting current is set such that the brake torque necessary for the electromagnetic hysteresis brake 131 serving as the load portion becomes a brake torque corresponding to a predetermined sheet tension force according to the information relating to the above sheet (S6-3). The predetermined sheet tension force according to the information relating to the sheet will be described below in detail.

Then, the driving motor M is powered on (S6-4), and the current also starts to flow to the electromagnetic hysteresis brake 131 (S6-5). At the same time, the electromagnetic clutch CL is powered on and the sheet starts to be passed (S6-6). As a result, the driving force of the driving motor M is transferred to the driving gears 104G1 and 106G through the driving transmission gear, so that the first roller A104 and the second roller A106 are rotated.

Then, the sheet P is guided to the entrance lower guide 121 in the sheet pulling and conveying apparatus 101, and when an ON signal of the sheet sensor 103 is confirmed (S6-7), the electromagnetic clutch CL is powered off after X msec (S6-8). When the electromagnetic clutch CL is powered off, the driving force to the first roller A104 is released. The value of time X is a time taken until the leading end of the sheet P is just interposed in the nip portion of the second roller pair after the sheet sensor 103 is turned on, and a conveying speed of the sheet P and a distance from the sheet sensor 103 to the nip portion of the second roller pair are determined. Herein, since the conveying speed of the sheet P is set to 300 mm/s, and a distance from the sheet sensor 103 to the nip portion of the second roller pair is set to 45 mm, time X is set to 160 msec.

As illustrated in FIG. 7A, since the electromagnetic clutch CL comes to be the ON state during a period of time from 0 to X msec after the sheet sensor is turned on, the driving force is transferred to the first roller A104, and the sheet P is conveyed by the driving of the first roller A104. On the other hand, as illustrated in FIG. 7B, the leading end of the sheet P is just arrived at the nip portion of the second roller pair at the time point of X msec after the sheet sensor is turned on, and the sheet P is conveyed by the driving force of the second roller A106. At the same time, since the electromagnetic clutch CL comes to be the OFF state and the driving force is not transferred to the first roller A104, the first roller pair is rotatably driven to the sheet conveyed by the second roller pair.

When being rotatably driven, the first roller A104 is connected to the load portion 131 through the driving gear 104G2 and the driving transmission gear 130, so that a torque load is generated in order to rotate the first roller A104 of which the driving force is released. As a result, in FIG. 7B, the sheet P is conveyed while a tension force in the conveying direction of the sheet is generated on the sheet P between the first roller pair and the second roller pair. In the embodiment, the load torque (the brake torque) of the load portion (the electromagnetic hysteresis brake) 131 is set such that the tension force applied on the sheet P becomes a predetermined tension force based on information relating to the sheet such as the sheet type, the image density, and the humidity information.

Further, in the embodiment, as illustrated in FIG. 8, the nip portion between the first roller pair and the second roller pair is formed in a region corresponding to the length L1 (100 mm here) of the center portion in the width direction of the sheet so as to be uniformly disposed with respect to a sheet passing center. With this configuration, only the center portion in the width direction of the sheet P between the first roller pair and the second roller pair is applied with the predetermined tension force over a range from the leading end of the trailing end. Herein, the description has been made about that the tension force of the conveying direction applied to the sheet is only to the center portion in the width direction, but the invention is not limited thereto. The tension force of the conveying direction applied to the sheet may be set to be large in the center area in the width direction compared to the end areas such that a difference in extension between the center portion and the end portions in the width direction comes to be reduced.

Then, it is determined whether the job is ended (S6-9), and in a case where the job is ended, the flow from S6-2 is repeatedly performed based on the basis weight, the type, the image density, and the humidity information of the next job which is subsequently input. When the job is ended, the driving motor M and the electromagnetic hysteresis brake 131 are turned off and the sheet passing is ended (S6-10), and then the job is ended (S6-11).

The curls generated in the sheet P illustrated in FIG. 10, a feature of the rippling shape in the end portion, and a measurement method will be described. The rippling is measured in a state where the sheet P is placed on a measurement plate 700. Herein, the length of the end portion of the sheet P in the conveying direction is set to L edge [mm], and the length of the center portion is set to L center [mm].

Further, an upper side or a lower side of the sheet P illustrated in FIG. 10, that is, bend shapes Pwave generated in the end portions in the width direction perpendicular to the conveying direction are referred to as an end portion rippling, and one of these bend shapes having a maximum gap X max on the measurement plate 700 is a target for evaluating a rippling amount.

The inventors have been performs experiments for confirming effects of the sheet pulling and conveying apparatus 101 in the embodiment, and the exemplary results are shown in FIGS. 12A to 15. Specifically, the length L edge [mm] of the end portion, the length L center [mm] of the center portion, and a maximum rippling amount X max [mm] of the sheet P were measured under various conditions.

A usual environment (a temperature of 23° C. and a humidity of 50%) was set as a basic experiment condition in this experiment, and the density of the toner image fixed on the sheet was set to be less than 50% of the toner density. Further, in a case where the sheet passed through the sheet humidifying apparatus 202 of the embodiment under the above basic experiment condition, the sheet humidity immediately after the passing was set to 7% or more.

The inventors measured the humidity contained in the sheet in the embodiment using the sheet P immediately after the sheet P passed through the sheet rippling correction apparatus 201 and discharged onto the discharge tray 565. Herein, a microwave type of sheet humidity measuring meter was used.

Further, herein, a condition for the achievement of rippling correction was set to a case where a maximum rippling amount of the sheet was lowered down to 1.0 mm or less.

FIGS. 12A to 12C show the results obtained when the plain paper having a basis weight of 81 gsm as information relating to the sheet besides the basic experiment condition is passed. FIG. 12A shows the case of one image forming apparatus (no sheet passing in the sheet rippling correction apparatus), and FIGS. 12B and 12C show a case where the sheet is passed in the sheet rippling correction apparatus 201. The sheet tension force of FIG. 12B was set to 1 kgf, and the sheet tension force of FIG. 12C was set to 3 kgf.

In the case of FIG. 12A (no tension force), an extension amount of the length of the end portion of the sheet was 0.6 mm, an extension amount of the length of the center portion of the sheet was 0.0 mm, and the maximum rippling amount was 3.3 mm.

Compared to the case of no tension force, the case of the tension force has obtained the following results.

In a case where FIG. 12B (a tension force of 1 kgf), the extension amount of the length of the end portion of the sheet was 0.6 mm, the extension amount of the length of the center portion of the sheet was 0.3 mm, and the maximum rippling amount was 1.7 mm. In contrast, in the case of FIG. 12C (a sheet tension force of 3 kgf), the extension amounts of the lengths of the end and center portions of the sheet were 0.6 mm, and the maximum rippling amount was 1.0 mm.

Therefore, in the basic experiment condition, it can be known that in the case of the plain paper having a basis weight of 81 gsm, there was a difference between the extension amounts of the center portion of the sheet under the sheet tension forces of 1 kgf and 3 kgf. When the sheet tension force was 3 kgf or more, a difference in length of the end portion and the center portion was able to be made to 0 mm, and the maximum amount of the sheet rippling was able to be improved from 3.3 mm of FIG. 12A to 1.0 mm of FIG. 12C. In addition, in FIGS. 12B and 12C, the humidity of the sheet was 8.0%.

FIGS. 13A to 13C show the results obtained when the thick paper having a basis weight of 157 gsm as information relating to the sheet besides the basic experiment condition is passed. FIG. 13A shows the case of one image forming apparatus (no sheet passing in the sheet rippling correction apparatus), and FIGS. 13B and 13C show a case where the sheet is passed in the sheet rippling correction apparatus 201. The sheet tension force of FIG. 13B was set to 3 kgf, and the sheet tension force of FIG. 13C was set to 4 kgf.

In the case of FIG. 13A (no tension force), an extension amount of the length of the end portion of the sheet was 0.5 mm, an extension amount of the length of the center portion of the sheet was 0.0 mm, and the maximum rippling amount was 2.5 mm.

Compared to the case of no tension force, the case of the tension force has obtained the following results.

In a case where FIG. 13B (a tension force of 3 kgf), the extension amount of the length of the end portion of the sheet was 0.5 mm, the extension amount of the length of the center portion of the sheet was 0.3 mm, and the maximum rippling amount was 1.7 mm. In contrast, in the case of FIG. 13C (a sheet tension force of 4 kgf), the extension amounts of the lengths of the end and center portions of the sheet both were 0.5 mm, and the maximum rippling amount was 1.0 mm.

Therefore, in the basic experiment condition, when the sheet tension force was 4 kgf or more in the case of the thick paper having a basis weight of 157 gsm, a difference in length of the end portion and the center portion was able to be made to 0 mm. Further, the maximum amount of the sheet rippling was able to be improved from 2.5 mm of FIG. 13A to 1.0 mm of FIG. 13C. As in the case of the thick paper illustrated in FIGS. 13A to 13C, when the basis weight of the sheet is increased, the sheet thickness becomes thick, so that a higher sheet tension force is required compared to the plain paper illustrated in FIGS. 12A to 12C. In addition, in FIGS. 13B and 13C, the humidity of the sheet was 7.7%.

FIGS. 14A and 14B show the results obtained when a sheet density less than 50% in the basic experiment condition is set to 50% or more as information relating to the sheet, and a thick paper having a basis weight of 157 gsm, on which an image is fixed at a high image density (the sheet density equal to or more than 50%), is passed.

FIGS. 14A and 14B show a case where the sheet is passed in the sheet rippling correction apparatus 201. The sheet tension force of FIG. 14A was set to 4 kgf, and the sheet tension force of FIG. 14B was set to 5 kgf.

In the case of FIG. 14A (a tension force of 4 kgf), the extension amount of the length of the end portion of the sheet was 0.5 mm, the extension amount of the length of the center portion of the sheet was 0.3 mm, and the maximum amount of the rippling was 1.7 mm. In contrast, in the case of FIG. 14B (a sheet tension force of 5 kgf), the extension amounts of the lengths of the end and center portions of the sheet both were 0.5 mm, and the maximum amount of the rippling was 1.0 mm.

Therefore, in the high image density (the sheet density equal to or more than 50%), when the sheet tension force was 5 kgf or more in the case of the thick paper having a basis weight of 157 gsm, a difference in length of the center portion of the sheet was able to be made to 0 mm, and the maximum amount of the sheet rippling was able to be improved to 1.0 mm.

In FIGS. 14A and 14B, since an influence of the humidity permeating the sheet on the toner image is reduced in the case of a high density image (the sheet density equal to or more than 50%), the sheet tension force (compared to a low density image) is necessarily increased. In addition, in FIGS. 14B and 14C, the humidity of the sheet was 7.3%.

FIGS. 15A and 15B show the results obtained when a thick paper having a basis weight of 157 gsm is passed, in which the thick paper is fixed with a toner image under an environment of a low humidity less than 20% such as a humidity of about 5% and a high image density (the sheet density equal to or more than 50%). In addition, in the embodiment, the environment of a humidity less than 20% is referred to as a low humidity environment, and the environment of a humidity equal to or more than 20% is referred to as a usual environment.

FIGS. 15A and 15B show a case where the sheet is passed in the sheet rippling correction apparatus 201. The sheet tension force of FIG. 15A is set to 5 kgf, and the sheet tension force of FIG. 15B is set to 6 kgf.

In the case of FIG. 15A (a tension force of 5 kgf), the extension amount of the length of the end portion of the sheet was 0.5 mm, the extension amount of the length of the center portion of the sheet was 0.3 mm, and the maximum amount of the rippling was 1.7 mm. In contrast, in the case of FIG. 15B (a sheet tension force of 6 kgf), the extension amounts of the lengths of the end and center portions of the sheet both were 0.5 mm, and the maximum amount of the rippling was 1.0 mm.

Therefore, in the low humidity environment (a humidity less than 20%) and the high image density (the sheet density equal to or more than 50%), when the sheet tension force was 6 kgf or more in the case of the thick paper having a basis weight of 157 gsm, a difference in length of the center portion of the sheet was able to be made to 0 mm. Further, the maximum amount of the sheet rippling was able to be improved to 1.0 mm.

In FIGS. 15A and 15B, since the humidity permeating the sheet is reduced compared to that in the usual humidity environment in the case of the low humidity environment (the humidity less than 20%) and the high density image (the sheet density equal to more than 50%), the sheet tension force is necessarily increased. In addition, in FIGS. 15A and 15B, the humidity of the sheet was 7.0%.

In FIG. 16, the setting values of the sheet tension force in the embodiment which are obtained from the experiments under various conditions including the above experiments are listed. In the setting values of FIG. 16, as a result of repeatedly performing experiments according to various conditions, it was confirmed that the rippling amount in all the conditions was 1.0 mm or less.

In other words, FIG. 16A shows a case where the basis weight is less than 90 gsm, a case where the basis weight is 90 gsm or more, a case where the image density is less than 50%, and a case where the image density is 50% or more under the usual environment (a humidity equal to or more than 20%). Further, FIG. 16B shows a case where the basis weight is less than 90 gsm, a case where the basis weight is 90 gsm or more, a case where the image density is less than 50%, and a case where the image density is 50% or more under the low humidity environment (the humidity less than 20%).

For example, in a case where the image density is less than 50% under the usual environment (the humidity equal to or more than 20%), when the basis weight is different, the controller 500C serving as the load controller performs control as illustrated in FIG. 16A. In other words, the controller 500C causes the load portion 131 to apply a tension force (a first tension force) of 3 kgf as a first load on the sheet having a basis weight less than 90 gsm (a first basis weight). On the other hand, the controller causes the load portion 131 to apply a tension force (a second tension force) of 4 kgf larger than the first tension force as a second load larger than the first load on the sheet having a basis weight (a second basis weight) of 90 gsm or more, which is larger than the first basis weight. Therefore, the rippling of the sheet can be improved to be 1.0 mm or less. In addition, when a load applied on the sheet having a low basis weight by the load portion 131 is too large, there is a possibility to tear the sheet, so that it is undesirable.

Further, for example, in a case where the basis weight of the sheet is less than 90 gsm under the usual environment (the humidity equal to or more than 20%), when the image density is different, the controller 500C serving as the load controller performs control as illustrated in FIG. 16A. In other words, the controller 500C causes the load portion 131 to apply a tension force (a first tension force) of 3 kgf as a first load on the sheet having an image density less than 50% (a first density). On the other hand, the controller causes the load portion 131 to apply a tension force (a second tension force) of 4 kgf larger than the first tension force as a second load larger than the first load on the sheet having an image density (a second density) of 50% or more, which is larger than the first density. Therefore, the rippling of the sheet can be improved to be 1.0 mm or less.

Further, for example, in a case where the image density is less than 50% and the basis weight of the sheet is less than 90 gsm, when an environmental humidity is different, the controller 500C serving as the load controller performs control as illustrated in FIGS. 16A and 16B. In other words, the controller 500C causes the load portion 131 to apply a tension force (a first tension force) of 3 kgf as a first load on the sheet when the humidity is 20% or more (a first humidity). On the other hand, the controller causes the load portion 131 to apply a tension force (a second tension force) of 4 kgf larger than the first tension force as a second load larger than the first load on the sheet when the humidity is less than 20% (a second humidity) lower than the first humidity. Therefore, the rippling of the sheet can be improved to be 1.0 mm or less.

In the embodiment, when the sheet tension force is large, a load torque applied on the motors and the gears is increased and temperature and noises are increased, so that the sheet tension force is designed to be optimized under various conditions. In a humidity under the usual environment where the sheet is passed at a highest frequency, it is possible to significantly improve the rippling amount while lowering the brake torque when a plain paper (a basis weight less than 90 gsm) containing a low density image (the toner image less than 50%) is passed.

As described above, the sheet is coated with moisture to be humidified at a predetermined humidity or more and then passed in the sheet pulling and conveying apparatus where the center portion in the width direction of the sheet is extended in the conveying direction. Therefore, a difference in length in the conveying direction of the sheet in the center portion and the end portion in the width direction of the sheet is reduced, and thus the rippling can be improved.

Furthermore, it is possible to more effectively improve the rippling of the sheet by selecting (varying) the sheet tension force on extending according to information (the basis weight, the sheet type, the density, and the environmental humidity) relating to the sheet.

Second Embodiment

The configuration of the sheet pulling and conveying apparatus according to the embodiment will be described using FIGS. 17 to 19. FIG. 17 is a top view illustrating the sheet pulling and conveying apparatus 101 used in the embodiment. The embodiment is different from the first embodiment only in the sheet pulling and conveying apparatus 101, and thus the configurations overlapped with the first embodiment will not be repeated.

In the above-mentioned embodiment, as the load portion, the electromagnetic hysteresis brake (the electromagnetic brake) is exemplified in which the brake torque can be changed as the exciting current is changed. In this regard, as the load portion, the embodiment describes a configuration in which a plurality of torque limiters TL1 to TL3 is connected to the driving gear 104G2 of the first roller A104 through clutches CL2 to CL4. Then, the load controller performs control such that the clutches CL2 to CL4 are selectively connected or disconnected so as to vary a load torque (in the following description, by 1 kgf in a range of 3 kgf to 6 kgf) by the torque limiters TL1 to TL3. Hereinafter, the description will be made in detail.

As illustrated in FIG. 17, a first torque limiter TL1 is connected to the driving gear 104G2 of the first roller A104 through an electromagnetic clutch CL2, a clutch gear CLG2, and a torque limiter gear TLG1. Further, a third torque limiter TL3 is connected to the driving gear 104G2 of the first roller A104 through an electromagnetic clutch CL4, a clutch gear CLG4, and a torque limiter gear TLG3.

Furthermore, a second torque limiter TL2 is connected in series to the clutch gear CLG2 which is connected to the driving gear 104G2 of the first roller A104, through an electromagnetic clutch CL3, a clutch gear CLG3, and a torque limiter gear TLG2.

In the embodiment, the setting value of the first torque limiter TL1 is set to make the sheet tension force become 3 kgf. Further, the setting value of the second torque limiter TL2 is set to make the sheet tension force become 2 kgf. Further, the setting value of the third torque limiter TL3 is set to make the sheet tension force become 1 kgf.

With the above configuration, in a case where the electromagnetic clutches CL2, CL3, and CL4 are turned off, the connection of the respective torque limiters TL1, TL2, and TL3 to the driving gear 104G2 of the first roller A104 is released, and thus the tension force disappears.

In contrast, in a case where the electromagnetic clutch CL2 is turned on, the electromagnetic clutch CL3 is turned off, and the electromagnetic clutch CL4 is turned off, the first torque limiter TL1 is connected to the driving gear 104G2 of the first roller A104 by the electromagnetic clutch CL2. Therefore, the load torque (3 kgf) of the first torque limiter TL1 is applied to the first roller A104, and the sheet tension force becomes 3 kgf.

Further, in a case where the electromagnetic clutch CL2 is turned on, the electromagnetic clutch CL3 is turned off, and the electromagnetic clutch CL4 is turned on, the first torque limiter TL1 and the third torque limiter TL3 are connected to the driving gear 104G2 of the first roller A104 by the respective electromagnetic clutches CL2 and CL4. Therefore, the load torque (3 kgf) of the first torque limiter TL1 and the load torque (1 kgf) of the third torque limiter TL3 are applied to the first roller A104, and the sheet tension force becomes 4 kgf.

Similarly, in a case where the electromagnetic clutch CL2 is turned on, the electromagnetic clutch CL3 is turned on, and the electromagnetic clutch CL4 is turned off, the first torque limiter TL1 and the second torque limiter TL2 are connected to the driving gear 104G2 of the first roller A104 by the respective electromagnetic clutches CL2 and CL3. Therefore, the load torque (3 kgf) of the first torque limiter TL1 and the load torque (2 kgf) of the second torque limiter TL2 are applied to the first roller A104, and the sheet tension force becomes 5 kgf.

Similarly, in a case where the electromagnetic clutch CL2 is turned on, the electromagnetic clutch CL3 is turned on, and the electromagnetic clutch CL4 is turned on, all the torque limiters TL1, TL2, and TL3 are connected to the driving gear 104G2 of the first roller A104 by all the electromagnetic clutches CL2, CL3, and CL4. Therefore, the load torque (3 kgf) of the first torque limiter TL1, the load torque (2 kgf) of the second torque limiter TL2, and the load torque (1 kgf) of the third torque limiter TL3 are applied to the first roller A104, and the sheet tension force becomes 6 kgf.

With the above configurations and controls, it is possible to vary the sheet tension force by 1 kgf in a range of 3 to 6 kgf. The predetermined sheet tension force of the embodiment is set as listed in FIG. 16 similarly to the first embodiment.

FIG. 18 is a flowchart illustrating the control according to the embodiment. The description on the same portions of the control as those of the first embodiment illustrated in FIG. 6 will not be repeated.

When a sheet passing job signal is input to the CPU (the controller) (S18-1), the basis weight, the type, the image density, and the humidity information are confirmed as information relating to the sheet (S18-2). Then, ON/OFF of the electromagnetic clutches CL2, CL3, and CL4 are set such that the brake torque necessary for the torque limiters TL1, TL2, and TL3 serving as the load portion becomes a brake torque corresponding to a predetermined sheet tension force according to the information relating to the above sheet (S18-3). In addition, the predetermined sheet tension force according to the information relating to the sheet is the same as that of the first embodiment described above, and on the basis of the predetermined sheet tension force, the electromagnetic clutches CL2, CL3, and CL4 are controlled to be powered on/off as described above.

Then, the driving motor M is powered on (S18-4), the electromagnetic clutches CL2, CL3, and CL4 is powered on or off (S18-5). At the same time, the electromagnetic clutch CL is also powered on and the sheet starts to be passed (S18-6). As a result, the driving force of the driving motor M is transferred to the driving gears 104G1 and 106G through the driving transmission gear, so that the first roller A104 and the second roller A106 are rotated.

Then, the sheet P is guided to the entrance lower guide 121 in the sheet pulling and conveying apparatus 101, and when an ON signal of the sheet sensor 103 is confirmed (S18-7), the electromagnetic clutch CL is powered off after X msec (S18-8). When the electromagnetic clutch CL is powered off, similarly to the first embodiment, the tension force thus set is applied to the sheet, and the sheet is extended.

Further, even in the embodiment similarly to the first embodiment, as illustrated in FIG. 8, the nip portion between the first roller pair and the second roller pair is formed in a region corresponding to the length L1 (herein, a width of 100 mm) of the center portion in the width direction of the sheet so as to be uniformly disposed with respect to a sheet passing center. With this configuration, only the center portion in the width direction of the sheet P between the first roller pair and the second roller pair is applied with the predetermined tension force in the conveying direction over a range from the leading end of the trailing end.

Then, it is determined whether the job is ended (S18-9), and in a case where the job is ended, the flow from S18-2 is repeatedly performed based on the basis weight, the type, the image density, and the humidity information of the next job which is subsequently input. When the job is ended, the driving motor M and the electromagnetic clutches CL2, CL3, and CL4 are turned off and the sheet passing is ended (S18-10), and then the job is ended (S18-11).

Similarly to the first embodiment, the setting values of the sheet tension force in the embodiment are listed in FIG. 16. In the setting values of FIG. 16, as a result of repeatedly performing experiments according to various conditions, it was confirmed that the rippling amount in all the conditions was 1.0 mm or less similarly to the first embodiment.

As described above, the sheet is coated with moisture to be humidified at a predetermined humidity or more and then passed in the sheet pulling and conveying apparatus where the center portion in the width direction of the sheet is extended in the conveying direction. Therefore, a difference in length in the conveying direction of the sheet in the center portion and the end portion in the width direction of the sheet is reduced, and thus the rippling can be improved.

Furthermore, it is possible to more effectively improve the rippling of the sheet by selecting (varying) the sheet tension force on extending according to information (the basis weight, the type, the density, and the environmental humidity) relating to the sheet.

Other Embodiments

In addition, the various conditions such as the basis weight, the type, the image density, and the environmental humidity as information relating to the sheet according to the first and second embodiments are given as an example, and thus other setting values may be used for the method of setting the conditions. For example, as illustrated in FIG. 19, in the configurations in the first and second embodiments, a humidity detector 601 (for example, an infrared humidity measuring meter) which detects a humidity contained in the sheet is provided on the downstream side of the sheet humidifying apparatus 202 and on the upstream side of the sheet pulling and conveying apparatus 101. Then, the sheet tension force applied to the sheet may be changed according to a humidity of the sheet detected by the humidity detector. In this case, when the sheet contains a large amount of moisture, the tension force becomes small compared to the case of a less humidity.

Specifically, when the humidity of the sheet detected by the humidity detector 601 is a second humidity larger than a first humidity, the controller 500C sets the load portion 131 and the torque limiters TL1 to TL3 with the second load smaller than the first load and applies the second tension force smaller than the first tension force to the sheet.

Further, the setting value of the tension force may be changed by the type of sheet (coated paper, embossing paper, thin paper, recycled paper, and the like) in the various conditions.

Further, the invention may be configured to change the load on the sheet based on information relating to the sheet such as the information relating to at least one of the basis weight of sheet, the type of sheet, the environmental humidity, the humidity contained in the sheet, and the image density on the sheet.

In the embodiment, the description has been made about the method of inputting the basis weight of the sheet in the operation panel, but the invention is not limited thereto. For example, a device such as an ultrasonic sensor to detect the basis weight may be disposed on the conveying path of the sheet, and the load on the sheet may be changed based on a detection value of the device. Further, a device such as an optical sensor to detect the type of sheet may be disposed on the conveying path of the sheet, and the load on the sheet may be changed based on a detection value of the device.

In addition, in the above-mentioned embodiment, the printer has been exemplified as the image forming apparatus, but the invention is not limited thereto. For example, another image forming apparatus such as a copying machine and a facsimile machine, or a multifunction peripheral combined with the functions of these apparatus may be employed. Further, the image forming apparatus has been exemplified in which an intermediate transfer member is used, the toner images of the respective colors are transferred onto the intermediate transfer member in a sequentially superimposed manner, and the toner images carried on the intermediate transfer member are transferred in a lump, but the invention is not limited thereto. For example, an image forming apparatus may be employed in which a sheet bearing member is used, the toner images of the respective colors are transferred onto the sheet carried on the sheet bearing member in a sequentially superimposed manner. When the invention is applied to the sheet rippling correction apparatus used in these image forming apparatuses, the same advantages can be obtained.

Further, the sheet rippling correction apparatus which is freely detachable to the image forming apparatus has been exemplified in the embodiment described above, but the invention is not limited thereto. For example, the sheet rippling correction apparatus may be integrally formed with the image forming apparatus, and when the invention is applied to the sheet rippling correction apparatus, the same advantage can be obtained.

Further, the sheet rippling correction apparatus (sheet processing apparatus) as an optional external apparatus which is freely detachable to the image forming apparatus has been exemplified in the embodiment described above, but the invention is not limited thereto. For example, the sheet rippling correction apparatus may be integrally formed with the image forming apparatus, and when the invention is applied to the sheet rippling correction apparatus, the same advantage can be obtained as the entire image forming system. Further, the configuration that the operation of the sheet rippling correction apparatus is controlled by controlling the controller included in the sheet rippling correction apparatus using the controller included in the image forming apparatus has been exemplified, but the invention is not limited thereto. For example, only the image forming apparatus includes the controller, and the operation of the sheet rippling correction apparatus may be controlled by the controller included in the image forming apparatus. Even in such a configuration, the same advantage can be obtained.

Further, in the embodiment described above, the outer diameters of the first roller B105 and the second roller B107 are set such that one in the center area in the width direction perpendicular to the conveying direction of the sheet is larger than that in the end area, but the invention is not limited thereto. Any configuration may be employed as long as the tension force in the conveying direction is applied to the center area in the width direction. Specifically, any configuration may be employed as long as the outer diameter of at least one roller among the rollers included in the first roller pair and the second roller pair is provided to be larger than that of the center area in the width direction perpendicular to the conveying direction of the sheet.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2013-220889, filed Oct. 24, 2013, which is hereby incorporated by reference herein in its entirety.

Claims

1. A sheet conveying apparatus which conveys a sheet with an image formed thereon by an image forming portion, comprising:

a load portion which is configured to apply a tension force in a conveying direction to the sheet; and

a load controller which performs control on the load portion to vary a load thereof,

wherein the load controller performs control on the load portion to vary the load thereof according to information relating to the sheet.

2. The sheet conveying apparatus according to claim 1, further comprising:

a first roller pair which includes a first roller A and a first roller B,

wherein the first roller B comes in press contact with the first roller A to form a nip portion, and nips and conveys the sheet; and

a second roller pair which includes a second roller A and a second roller B and is positioned on a downstream side in the conveying direction of the first roller pair,

wherein the second roller B comes in press contact with the second roller A to form a nip portion, and nips and conveys the sheet,

wherein an outer diameter of at least one of the first roller A, the first roller B, the second roller A, and the second roller B in a center area in the width direction perpendicular to the conveying direction of the sheet is larger than that in an end portion, and

wherein the load portion applies a load onto a rotation of the first roller pair.

3. The sheet conveying apparatus according to claim 1,

wherein the load portion includes an electromagnetic brake of which the brake torque is changed by changing an exciting current, and

wherein the load controller performs control on the load portion to vary the load by changing a current value excited in the load portion.

4. The sheet conveying apparatus according to claim 1,

wherein the load portion includes a plurality of torque limiters and a plurality of clutches which connects or disconnects the torque limiters, and

wherein the load controller performs control such that the clutches are selectively connected or disconnected to cause the torque limiters to vary the load.

5. The sheet conveying apparatus according to claim 1,

wherein the information relating to the sheet is information relating to at least one of a basis weight, a type of the sheet, an environmental humidity, a humidity contained in the sheet, and an image density on the sheet.

6. The sheet conveying apparatus according to claim 1,

wherein the information relating to the sheet is input by an operation portion which is provided in the image forming portion.

7. The sheet conveying apparatus according to claim 1,

wherein when a basis weight of the sheet is a first basis weight, the load controller sets the load portion to be a first load, and

wherein when the basis weight of the sheet is a second basis weight larger than the first basis weight, the load controller sets the load portion to be a second load larger than the first load.

8. The sheet conveying apparatus according to claim 1,

wherein when an image density on the sheet is a first density, the load controller sets the load portion to be a first load, and

wherein when the image density on the sheet is a second density larger than the first density, the load controller sets the load portion to be a second load larger than the first load.

9. The sheet conveying apparatus according to claim 1, further comprising

a humidity detection portion which detects an environmental humidity,

wherein when the environmental humidity detected by the humidity detection portion is a first humidity, the load controller sets the load portion to be a first load, and

wherein when the environmental humidity detected by the humidity detection portion is a second humidity lower than the first humidity, the load controller sets the load portion to be a second load larger than the first load.

10. The sheet conveying apparatus according to claim 1, further comprising

a moisture applying apparatus which applies moisture to the sheet on an upstream side in the conveying direction of the sheet from the load portion,

wherein the load controller sets the load portion to be a first load on the sheet of the first humidity, and

wherein the load controller sets the load portion to be a second load smaller than the first load on the sheet of which the humidity is a second humidity larger than the first humidity.

11. An image forming apparatus comprising:

an image forming portion which forms a toner image;

a fixing portion which heats and fixes the toner image formed on a sheet by the image forming portion;

a load portion which applies a tension force in a conveying direction to the sheet passed through the fixing portion; and

a load controller which performs control on the load portion to vary a load,

wherein the load controller performs control the load of the load portion according to information relating to the sheet.

12. The image forming apparatus according to claim 11, further comprising:

a first roller pair which includes a first roller A and a first roller B,

wherein the first roller B comes in press contact with the first roller A to form a nip portion, and nips and conveys the sheet; and

a second roller pair which includes a second roller A and a second roller B and is positioned on a downstream side in the conveying direction of the first roller pair,

wherein the second roller B comes in press contact with the second roller A to form a nip portion, and nips and conveys the sheet,

wherein an outer diameter of at least one of the first roller A, the first roller B, the second roller A, and the second roller B in a center area in the width direction perpendicular to the conveying direction of the sheet is larger than that in an end portion, and

wherein the load portion applies a load onto a rotation of the first roller pair.

13. The image forming apparatus according to claim 11, wherein

wherein the load portion includes an electromagnetic brake of which the brake torque is changed by changing an exciting current, and

wherein the load controller performs control on the load portion to vary the load by changing a current value excited in the load portion.

14. The image forming apparatus according to claim 11, wherein

wherein the load portion includes a plurality of torque limiters and a plurality of clutches which connects or disconnects the torque limiters, and

wherein the load controller performs control such that the clutches are selectively connected or disconnected to cause the torque limiters to vary the load.

15. The image forming apparatus according to claim 11, wherein

wherein the information relating to the sheet is information relating to at least one of a basis weight, a type of the sheet, an environmental humidity, a humidity contained in the sheet, and an image density on the sheet.

16. The image forming apparatus according to claim 15, further comprising

an operation portion,

wherein the information relating to the sheet is input by the operation portion.

17. The image forming apparatus according to claim 11, wherein

wherein when a basis weight of the sheet is a first basis weight, the load controller sets the load portion to be a first load, and

wherein when the basis weight of the sheet is a second basis weight larger than the first basis weight, the load controller sets the load portion to be a second load larger than the first load.

18. The image forming apparatus according to claim 11, wherein

wherein when an image density on the sheet is a first density, the load controller sets the load portion to be a first load, and

wherein when the image density on the sheet is a second density larger than the first density, the load controller sets the load portion to be a second load larger than the first load.

19. The image forming apparatus according to claim 11, further comprising

a humidity detection portion which detects an environmental humidity,

wherein when the environmental humidity detected by the humidity detection portion is a first humidity, the load controller sets the load portion to be a first load, and

wherein when the environmental humidity detected by the humidity detection portion is a second humidity lower than the first humidity, the load controller sets the load portion to be a second load larger than the first load.

20. The image forming apparatus according to claim 11, further comprising

a moisture applying apparatus which applies moisture to the sheet on an upstream side in the conveying direction of the sheet from the load portion,

wherein the load controller sets the load portion to be a first load on the sheet of the first humidity, and

wherein the load controller sets the load portion to be a second load smaller than the first load on the sheet of which the humidity is a second humidity larger than the first humidity.