JP5583544B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus that fix a developer on a recording material.

  2. Description of the Related Art An electrophotographic image forming apparatus includes a fixing device that fixes toner onto a sheet after transferring toner as a developer onto the sheet as a recording material. In a conventional fixing device, a pressure roller is usually pressed against a heating roller.

  Recently, image forming apparatuses have been improved in various parts in order to meet the needs for high-speed image formation (printing). In the fixing device, in order to give a heat amount necessary for fixing the toner to the sheet conveyed at high speed, an improvement is made to increase the nip length of the fixing nip portion. For example, Patent Document 1 discloses a cylindrical heating roller made of a heat conductive material, an endless belt disposed on the outer periphery of the heating roller, longer than the outer periphery of the heating roller, and conveying the recording medium to the heating roller. A tension roller that is disposed on the downstream side in the direction and on which the endless belt is suspended, and a pressure roller that presses against the heating roller via the endless belt and forms a nip portion with the endless belt. A fixing device is disclosed. In this fixing device, an example is disclosed in which a peeling roller is provided in contact with a pressure roller (see FIG. 2). In this configuration, the fixing nip portion is from the portion where the heating roller and the pressure roller abut to the portion where the tension roller and the pressure roller abut. Therefore, in addition to the pressure caused by the sandwiching between the heating roller and the pressure roller, pressure can also be applied to the recording paper from the endless belt, so that the fixing performance is improved.

JP 2005-128337 A

  In the fixing device described in FIG. 2 of Patent Document 1, the heating roller is rotated by a driving force from a driving source, and the tension roller is driven by the heating roller. In such a configuration, when a rotation delay occurs in the tension roller due to slipping or the like, the endless belt is bent and floats at the fixing nip portion, and thus fixing failure may occur.

  In addition, when an excessive rotation delay occurs in the tension roller, a large speed difference is generated between the tension roller that sandwiches the paper and the pressure roller, and an image shift in which the toner transferred to the paper is shifted may occur.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a fixing device capable of reliably fixing a developer on a recording material without causing defective fixing and image displacement, and an image forming apparatus including the fixing device. And

  The fixing device according to the present invention includes a fixing belt, a fixing roller, a peeling roller, a pressure roller, a plurality of gears, and a driving unit, and a fixing nip portion on a recording material conveyed through a conveying path. To fix the developer. The fixing belt is endless. The fixing roller is installed along the conveyance path, and suspends the fixing belt together with the peeling roller. The peeling roller peels the recording material from the fixing belt. The pressure roller is in pressure contact with the fixing roller and the peeling roller via the fixing belt, forms a fixing nip portion with the fixing belt, and conveys the recording material together with the fixing belt. The plurality of gears are connected to the rotation shafts of the fixing roller, the peeling roller, and the pressure roller, and are engaged so that the rotation directions of the fixing roller, the peeling roller, and the pressure roller are opposite to each other. The driving means drives a plurality of gears.

  In this configuration, by setting the gear ratio of the plurality of gears so that the fixing roller, the peeling roller, and the pressure roller rotate at a predetermined peripheral speed ratio, the peripheral speed of the peeling roller is higher than the peripheral speed of the fixing roller. It does not occur that the fixing belt floats at the fixing nip portion due to excessive slowing, and that the peripheral speed of the peeling roller and the peripheral speed of the fixing roller are not excessively slowed. Therefore, it is possible to prevent the occurrence of fixing failure and image shift, and the developer can be reliably fixed on the recording material.

  In the above invention, the fixing device includes a first one-way clutch and a second one-way clutch. The first one-way clutch contacts and separates the rotating shaft of the peeling roller and a gear that rotates the peeling roller. The second one-way clutch contacts and separates the rotation shaft of the fixing roller and the gear that rotates the fixing roller.

  In this configuration, when the peripheral speed of the fixing roller and the peeling roller exceeds a certain speed, the first one-way clutch and the second one-way clutch are disengaged, so that the fixing roller and the peeling roller are driven by the pressure roller that is the driving roller. . In addition, when the peripheral speed of the fixing roller and the peeling roller is equal to or lower than a predetermined speed, the first one-way clutch and the second one-way clutch are engaged. Driven in conjunction.

  When the fixing roller and the peeling roller are driven by the pressure roller, the one-way clutch is activated if excessive rotation delay occurs in the fixing roller or the peeling roller due to slipping on the fixing roller or the peeling roller. Then, the fixing roller, the peeling roller, and the pressure roller are driven in conjunction with each other. For this reason, an excessive rotation delay of the fixing roller and the peeling roller does not occur with respect to the pressure roller, and it is possible to prevent a fixing defect and an image shift.

  In addition, when the fixing roller, the peeling roller, and the pressure roller are driven by a plurality of gears and the slippage of the fixing roller and the peeling roller is reduced, the fixing roller and the peeling roller have the same peripheral speed as the pressure roller. In such a case, the one-way clutch is disengaged, and the fixing roller and the peeling roller are driven by the pressure roller. Thereby, it is possible to reduce the load on the gear for rotating the fixing roller and the load on the fixing roller and to prevent wear. The same applies to the peeling roller. Therefore, the developer can be reliably fixed on the recording material.

  In the fixing device according to the invention, the plurality of gears are gear ratios for rotating the rollers at a peripheral speed ratio satisfying a relationship of the peripheral speed Vk of the pressure roller> the peripheral speed Vh of the peeling roller> the peripheral speed Vt of the fixing roller. Is set to

  In this configuration, the peeling roller installed on the downstream side in the conveyance direction of the recording material has a higher peripheral speed than the fixing roller, so that the fixing belt does not bend at the fixing nip portion, and the fixing belt is surely floated. Can be prevented. Further, since the circumferential speed Vk of the pressure roller is set to be faster than the circumferential speed Vh of the peeling roller and the circumferential speed Vt of the fixing roller, according to the change in the circumferential speed of the fixing roller and the peeling roller, The one-way clutch can be securely connected and separated. Therefore, the developer can be reliably fixed on the recording material.

  In the above invention, the fixing device includes a heating roller. The heating roller includes a cored bar part and a heating source for heating the cored bar part, and suspends the fixing belt by the cored bar part upstream of the fixing roller in the conveying direction of the fixing belt to heat the fixing belt.

  In this configuration, the heating roller does not include an elastic layer, and the fixing belt is suspended from the cored bar portion of the heating roller. Therefore, the heating roller has a small heat capacity, and can heat the cored bar portion and the fixing belt with less energy and a short time. Further, by adopting a fixing belt having a small heat capacity and rotating it at high speed, the heat transfer characteristics to the fixing nip portion can be improved. Therefore, the fixing process can be performed in a short time after activation.

  The image forming apparatus of the present invention includes the fixing device of the present invention and an image forming unit. The image forming unit forms an image by transferring the developer to a recording material conveyed to the fixing device.

  In this configuration, the image formed on the recording material by the image forming unit is stably and surely fixed by the fixing device, so that a high-quality image can be formed without causing fixing failure or image displacement.

  According to the present invention, fixing failure and image displacement do not occur, and the developer can be reliably fixed on the recording material.

1 is a configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a transparent diagram illustrating a configuration of a fixing device according to an exemplary embodiment of the present invention. It is a block diagram which shows the positional relationship of a fixing roller, a peeling roller, a pressure roller, and a some gear. 4 is a table showing sizes, peripheral speeds, and the like of a fixing roller, a peeling roller, a pressure roller, and a plurality of gears.

  As shown in FIG. 1, an image forming apparatus 100 includes a first image forming unit 1 that forms a yellow toner image, a second image forming unit 2 that forms a magenta toner image, and a third image forming unit that forms a cyan toner image. 3 and a tandem type color image forming apparatus including a fourth image forming unit 4 for forming a black toner image. Hereinafter, a general term for the four image forming units included in the image forming apparatus 100 is referred to as an image forming unit group 5.

  In FIG. 1, a primary transfer belt (endless belt) 6 is disposed above the image forming unit group 5. The primary transfer belt 6 is stretched around a support roller 61 and a primary transfer belt drive roller 62, is stretched in a loop shape, and rotates in a direction indicated by an arrow R. The primary transfer belt 6 is formed of a resin such as polyimide or polyamide containing an electron conductive material and formed into a thin film.

  The image forming unit group 5 is arranged in the order of the first image forming unit 1, the second image forming unit 2, the third image forming unit 3, and the fourth image forming unit 4 in the direction of the arrow R along the primary transfer belt 6. Has been placed.

  On the inner peripheral side of the primary transfer belt 6, primary transfer rollers 71, 72, 73, 74 for transferring the single color toner images formed by the image forming unit group 5 onto the primary transfer belt 6 are arranged. The primary transfer rollers 71, 72, 73, 74 stretch the primary transfer belt 6, and the photosensitive drums 161, 162, 163 provided in the image forming unit group 5 with the primary transfer belt 6 interposed therebetween, respectively. 164. The single color toner images respectively formed by the image forming unit group 5 are sequentially transferred (primary transfer) so as to be superimposed on the primary transfer belt 6 to form one color toner image. The primary transfer belt 6, which is an image carrier, conveys the primarily transferred toner image to a position (secondary transfer position) where the primary transfer belt driving roller 62 and the secondary transfer unit 51 face each other. Hereinafter, in the primary transfer belt 6, the support roller 61 side is referred to as an upstream side, and the primary transfer belt drive roller 62 side is referred to as a downstream side.

  A secondary transfer unit 51 is disposed at a secondary transfer position facing the primary transfer belt driving roller 62 with the primary transfer belt 6 interposed therebetween. The color toner image formed on the primary transfer belt 6 is transferred onto a sheet (recording material) P by electrostatic force at a secondary transfer position where the primary transfer belt driving roller 62 and the secondary transfer unit 51 face each other.

  A primary transfer belt cleaning unit 10 for cleaning the surface of the primary transfer belt 6 is installed at a position facing the support roller 61 across the primary transfer belt 6. The primary transfer belt cleaning unit 10 includes a belt cleaning brush 11 and a belt cleaning blade 12 that are arranged so as to contact the primary transfer belt 6. The toner remaining in the toner is removed.

  In FIG. 1, a tray 14 for storing paper P is disposed below the image forming unit group 5. The paper P in the tray 14 is moved by the arrow Y until the secondary transfer unit 51 is opposed to the primary transfer belt 6 by the plurality of paper feed roller pairs 131 to 134 arranged in the conveyance path 130. The paper P is transported in the transport direction shown, and the color toner image on the primary transfer belt 6 is secondarily transferred onto the paper P at the secondary transfer position.

  The sheet P on which the color toner image is secondarily transferred is conveyed to the fixing device 15. Then, the color toner image is fixed on the paper P by the fixing device 15, and the paper P is discharged from the image forming apparatus 100 by the paper discharge roller pair 135.

  Next, a specific configuration of the fixing device 15 according to the embodiment of the present invention will be described. FIG. 2 shows the overall configuration of the fixing device 15.

  The fixing device 15 includes a fixing belt 21, a fixing roller 22, a peeling roller 23, a heating roller 24, a pressure roller 25, a first lever 26, a second lever 27, a third lever 28, The first spring 29 is a first biasing means, the second spring 30 is a second biasing means, and the third spring 31 is a third biasing means. The fixing device 15 includes a first temperature sensor 32 and a second temperature sensor 33. Further, the fixing device 15 includes paper guides 151 to 153. The fixing device 15 includes a control unit 20.

  The fixing belt 21 is endless and is suspended by a fixing roller 22, a peeling roller 23, and a heating roller 24. As shown in FIG. 2, the fixing belt 21 has a triangular shape with rounded corners.

  The fixing belt 21 is thin in order to reduce the heat capacity. The thickness of the fixing belt 21 is, for example, 150 μm to 500 μm.

  The fixing roller 22 includes a rotating shaft 221, a cored bar 222, and an elastic layer 223. The rotation shaft 221 extends from both ends of the fixing roller 22. The cored bar 222 is a hollow cylinder formed of a metal such as iron (Fe) or aluminum (Al). The elastic layer 223 is formed of a material such as urethane sponge or silicon rubber, and is provided around the cored bar portion 222. The fixing roller 22 sandwiches the sheet (recording material) P together with the pressure roller 25 via the fixing belt 21.

  The peeling roller 23 includes a rotating shaft 231 and a cored bar portion 232. The rotating shaft 231 extends from both ends of the peeling roller 23. The peeling roller 23 peels the paper P on which the toner (developer) is fixed from the fixing belt 21.

  The heating roller 24 is installed upstream of the fixing roller 22 in the rotation direction of the fixing belt 21. The heating roller 24 includes a rotating shaft 241, a heating source 242, and a cored bar portion 243. The rotating shaft 241 extends from both ends of the heating roller 24. The heating roller 24 heats the cored bar portion 243 by the heating source 242. A heating wire or a halogen lamp (heater lamp) is used as the heating source 242 and is installed at the center of the heating roller 24 in order to heat the cored bar 243 evenly. The core metal part 243 is a hollow cylinder formed of a metal such as iron (Fe) or aluminum (Al), has a thickness of 0.4 mm to 1.2 mm, and has a small heat capacity. The heating roller 24 suspends the fixing belt 21 at the cored bar 243 and heats the fixing belt 21. The first temperature sensor 32 measures the surface temperature of the heating roller 24. The control unit 20 controls the heat generation amount of the heating source 242 by turning on / off the heating source 242 or adjusting the heat generation amount according to the surface temperature of the heating roller 24 measured by the first temperature sensor 32. .

  The pressure roller 25 includes a rotating shaft 251, a heat source 252, a cored bar 253, and an elastic layer 254. The rotating shaft 251 extends from both ends of the pressure roller 25. The pressure roller 25 heats the cored bar part 253 by the heating source 252. A heating wire or a halogen lamp (heater lamp) is used as the heating source 252, and is installed at the center of the heating roller 24 in order to heat the cored bar 253 and the elastic layer 254 evenly. The core metal part 253 is a hollow cylinder formed of a metal such as iron (Fe) or aluminum (Al). The elastic layer 254 is formed of a material such as urethane sponge or silicon rubber, and is provided around the cored bar portion 253.

  The pressure roller 25 is in pressure contact with the fixing roller 22 and the peeling roller 23 via the fixing belt 21, and forms a fixing nip portion 215 with the fixing belt 21. The fixing nip 215 extends from a portion where the fixing roller 22 and the pressure roller 25 abut via the fixing belt 21 to a portion where the peeling roller 23 and the pressure roller 25 abut via the fixing belt 21. The pressure roller 25 fixes the toner on the paper P at the fixing nip 215. The second temperature sensor 33 measures the surface temperature of the pressure roller 25. The control unit 20 controls the heat generation amount of the heating source 252 by turning on / off the heating source 252 or adjusting the heat generation amount according to the surface temperature of the pressure roller 25 measured by the second temperature sensor 33. To do. At the fixing nip 215, heat and pressure are applied to the paper P to which the toner has been transferred, and the toner is fixed on the paper P.

  In the present invention, the surface of the pressure roller 25 (elastic layer 254) is heated by the heating source 252. Thereby, the fixing performance of the fixing device 15 can be improved.

  The first lever 26 (26A, 26B) is installed on both sides of the fixing roller 22 and the peeling roller 23. The rotation shaft 221 of the fixing roller 22 and the rotation shaft 231 of the peeling roller 23 are rotatably fixed to the first lever 26 at a predetermined interval. The first lever 26 is rotatable about the rotation shaft 221 of the fixing roller 22 as a fulcrum 261.

  One end of the first spring 29 is fixed to an end of the first lever 26 opposite to the fulcrum 261, that is, a point 262 opposite to the first fulcrum 261 across the peeling roller 23. The other end of the first spring 29 is fixed to the point 283 of the third lever 28. The first spring 29 constantly urges the first lever 26 with a predetermined force. The first lever 26 rotates around the fulcrum 261 in the direction approaching the pressure roller 25, and the peeling roller 23 is Then, it is pressed against the pressure roller 25 via the fixing belt 21.

  The second lever 27 (27A, 27B) is installed on both sides of the fixing roller 22 and the heating roller 24. The rotation shaft 221 of the fixing roller 22 and the rotation shaft 241 of the heating roller 24 are rotatably fixed to the second lever 27 with a predetermined interval. The second lever 27 is rotatable about the rotation shaft 221 of the fixing roller 22 as a fulcrum 271.

  One end of the second spring 30 is fixed to an end portion of the second lever 27 opposite to the fulcrum 271, that is, a point 272 opposite to the second fulcrum 271 across the heating roller 24. The other end of the second spring 30 is fixed to a point 101 on the main body of the image forming apparatus 100. The second spring 30 constantly urges the second lever 27 with a predetermined force. The second lever 27 rotates in a direction away from the peeling roller 23 with the fulcrum 271 as a center point. The fixing belt 21 is stretched.

  The third lever 28 (28A, 28B) is installed on both sides of the pressure roller 25. A rotation shaft 251 of the pressure roller 25 is fixed to the third lever 28 so as to be rotatable. The third lever 28 is rotatable with a point separated from the pressure roller 25 by a predetermined distance (a point below the rotating shaft 251 in FIG. 2) as a third fulcrum 281.

  One end of the third spring 31 is fixed to an end of the third lever 28 opposite to the fulcrum 281, that is, a point 282 opposite to the third fulcrum 281 across the pressure roller 25. The other end of the third spring 31 is fixed to a point 411 of the fixing portion 41 installed in the vicinity of the paper guide 152. The third spring 31 constantly urges the third lever 28 with a predetermined force, the third lever 28 rotates in a direction approaching the fixing roller with the fulcrum 281 as a center point, and the pressure roller 25 is It is pressed against the fixing roller 22 via the fixing belt 21.

  The paper guides 151 to 153 regulate the transport direction of the paper P.

  Next, as shown in FIG. 3, the fixing device 15 includes a plurality of gears (gears) and a DC motor 200 as a driving unit between the fixing roller 22, the peeling roller 23, and the pressure roller 25. The drive mechanism 150 is provided. The DC motor 200 is controlled by the control unit 20. The driving mechanism 150 drives the fixing roller 22, the peeling roller 23, and the pressure roller 25 in conjunction with each other by a plurality of gears when the peripheral speed of the fixing roller 22 and the peeling roller 23 is equal to or lower than a predetermined speed. In addition, when the fixing roller 22 and the peeling roller 23 exceed a certain speed, the driving mechanism 150 does not drive the fixing roller 22 and the peeling roller 23 with a plurality of gears, and the fixing roller 22 and the peeling roller 23 are the pressure roller 25. Follow.

  In the driving mechanism 150, the gears rotate the respective rollers at a peripheral speed ratio that satisfies the relationship of the peripheral speed Vk of the pressure roller 25> the peripheral speed Vh of the peeling roller 23> the peripheral speed Vt of the fixing roller 22. Is set to

  The detailed configuration of the drive mechanism 150 will be described below. FIG. 3 shows an arrangement example of each gear of the drive mechanism 150. FIG. 4 shows an example of the size, rotation direction, peripheral speed ratio, number of rotations per unit time, roller diameter, and roller peripheral speed of each gear.

  In FIG. 3, a plurality of teeth are provided around each gear, but the illustration is omitted. In addition, as shown in FIG. 4, the module of the gear of each gear is m = 1.

  The fixing roller 22 is connected to the fixing R gear 220. The peeling roller 23 is connected to the peeling R gear 230. The heating roller 24 is not connected to a gear. The pressure roller 25 is connected to the pressure R gear 250.

  The plurality of gears of the driving mechanism 150 are driven by a motor 200 that is a driving means. A pinion 201 is connected to the rotation shaft of the motor 200. A fixing input gear 202 and a pressure fulcrum gear 203 are installed between the pinion 201 and the pressure R gear 250. The pinion 201, the fixing input gear 202, the pressure fulcrum gear 203, and the pressure R gear 250 are engaged in this order. In FIG. 3, the pinion 201 is rotated counterclockwise by the motor 200 (shown as CCW (counter clockwise) in FIG. 4). Accordingly, the fixing input gear 202 rotates clockwise (indicated as CW (clockwise) in FIG. 4; the same applies hereinafter), and the pressing fulcrum gear 203 rotates counterclockwise to apply pressure. The R gear 250 (pressure roller 25) is driven clockwise.

  Further, between the pressure fulcrum gear 203 and the fixing R gear 220, an idle C1 gear 204, an idle C2 gear 205, and an idle C3 gear 206 are installed. The pressure fulcrum gear 203, the idle C1 gear 204, the idle C2 gear 205, the idle C3 gear 206, and the fixing R gear 220 are engaged in this order. In FIG. 3, when the pressure fulcrum gear 203 rotates counterclockwise, the idle C1 gear 204 rotates clockwise, the idle C2 gear 205 rotates counterclockwise, and the idle C3 gear 206 rotates clockwise. The fixing R gear 220 rotates counterclockwise. As a result, the fixing roller 22 is driven counterclockwise.

  Further, an idle D1 gear 207, an idle D2 gear 208, and an idle D3 gear 209 are installed between the fixing R gear 220 and the peeling R gear 230. The fixing R gear 220, the idle D1 gear 207, the idle D2 gear 208, the idle D3 gear 209, and the peeling R gear 230 are engaged in this order. In FIG. 3, when the fixing R gear 220 rotates counterclockwise, the idle D1 gear 207 rotates clockwise, the idle D2 gear 208 rotates counterclockwise, and the idle D3 gear 209 rotates clockwise. The fixing R gear 220 rotates counterclockwise. As a result, the fixing roller 22 is driven counterclockwise.

  As described above, the plurality of gears of the drive mechanism 150 are connected to the rotation shafts of the fixing roller 22, the peeling roller 23, and the pressure roller 25, and the fixing roller 22, the peeling roller 23, the pressure roller 25, Engage so that the direction of rotation is opposite. Therefore, even when the fixing roller 22, the peeling roller 23, and the pressure roller 25 are driven by the driving mechanism 150, as shown in FIG. 2, the sheet P moves along the conveyance path 130 from upstream to downstream, that is, Then, the toner is conveyed from the fixing roller 22 toward the peeling roller 23.

  The fixing R gear 220 connected to the fixing roller 22 includes a one-way clutch 225 that is a first one-way clutch that contacts and separates the rotating shaft 221 and the gear 224. Further, the peeling R gear 230 connected to the peeling roller 23 includes a one-way clutch 235 that is a second one-way clutch that contacts and separates the rotary shaft 231 and the gear 234. In the fixing device 15, when the fixing roller 22 and the peeling roller 23 can rotate at a peripheral speed equal to or higher than a constant speed, the one-way clutches 225 and 235 are disengaged and are not driven by a plurality of gears of the driving mechanism 150. The fixing roller 22 and the peeling roller 23 are driven by the pressure roller 25. As a result, it is possible to prevent wear of the fixing belt 21, the fixing roller 22, and the peeling roller 23, and an increase in the load on the fixing R gear 220 and the peeling R gear 230.

  FIG. 4 shows the peripheral speed ratio when the peripheral speed of the pressure roller 25 is 1. The peripheral speed of each gear and the radius of each gear when the motor 200 rotates at 12.02 rps are as shown in FIG.

  As shown in FIG. 4, the diameter of each roller is 50 mm for the pressure roller 25, 35 mm for the fixing roller 22, and 15 mm for the peeling roller 23. As described above, when the motor 200 rotates at 12.02 rps, the peripheral speed Vk of the pressure roller 25 is 325 mm / s, the peripheral speed Vt of the fixing roller 22 is 316.49 mm / s (= Vt0), and The peripheral speed Vh of the peeling roller 23 is 322.38 mm / s (= Vh0). That is, the peripheral speed ratio of each roller satisfies the relationship of Vk> Vh> Vt. The peripheral speed ratio Vt / Vk of the fixing roller 22 and the pressure roller 25 is 97.38%, and the peripheral speed ratio Vt / Vk of the peeling roller 23 and the pressure roller 25 is 99.19%.

  Next, the operation of the fixing device 15 will be described.

(1) Basic state (completely driven state)
In the fixing device 15, the fixing roller 22 and the peeling roller 23 are normally driven by the pressure roller 25, and the fixing roller 22 and the peeling roller 23 rotate at the same speed as the pressure roller 25. At this time, the one-way clutches 225 and 235 are disengaged and are not driven by a plurality of gears of the driving mechanism 150, and the fixing roller 22 and the peeling roller 23 are completely driven by the pressure roller 25. . The pressure roller 25 is driven by the DC motor 200 of the drive mechanism 150 and a plurality of gears.

  In this state, there is no floating due to the deflection of the fixing belt 21 in the fixing nip portion 215, or there is little or no speed difference between the rollers that pinch the paper P, so that no fixing failure or image displacement occurs.

(2) Decrease in peripheral speed of fixing roller and peeling roller (transition to drive state)
In the fixing device 15, when the fixing roller 22 and the peeling roller 23 slip and the amount of slip increases, the peripheral speed of the fixing roller 22 and the peeling roller 23 gradually decreases. As described above, when the rotation delay between the fixing roller 22 and the peeling roller 23 increases, problems such as image misalignment occur. Therefore, in the fixing device 15, when the peripheral speed Vh of the peeling roller 23 is equal to or lower than Vh0 (= 322.38 mm / s), the one-way clutch 225 is engaged (actuated), and the rotating shaft 231 and the gear 234 are connected. Therefore, the peeling roller 23 is driven by the DC motor 200 of the driving mechanism 150 and a plurality of gears. Similarly, in the fixing device 15, when the peripheral speed Vt of the fixing roller 22 is equal to or lower than Vt 0 (= 316.49 mm / s), the one-way clutch 235 is engaged (actuated), and the rotating shaft 221 and the gear 224 are connected. Therefore, the fixing roller 22 is driven by the DC motor 200 of the driving mechanism 150 and a plurality of gears. The pressure roller 25 is continuously driven by the DC motor 200 of the drive mechanism 150 and a plurality of gears.

  When the one-way clutches 225 and 235 are engaged, the peripheral speeds of the rollers are in a relationship of Vk> Vh> Vt as described above.

  In this state, the peeling roller 23 has a higher peripheral speed than the fixing roller 22, so that no floating occurs due to the deflection of the fixing belt 21 in the fixing nip 215. Further, since the fixing roller 22, the peeling roller 23, and the pressure roller 25 are driven by the driving mechanism 150, the peripheral speed ratio is constant and is not set to a speed difference that causes an image shift. Accordingly, no image shift occurs.

(3) Increase in the peripheral speed of the fixing roller and peeling roller (transition to the fully driven state)
In the fixing device 15, when the slippage of the fixing roller 22 and the peeling roller 23 decreases, the fixing roller 22 and the peeling roller 23 are driven by the pressure roller 25, and the peripheral speed Vt of the fixing roller 22 and the peeling roller 23 are peeled off. The circumferential speed Vh of the roller 23 gradually increases.

  When the peripheral speed Vt of the fixing roller 22 exceeds Vt0 (= 316.49 mm / s), the rotational speed of the rotating shaft 221 of the fixing R gear 220 is higher than that of the gear 224. At this time, the one-way clutch 225 is disengaged and the rotating shaft 221 and the gear 224 are disconnected, so that the fixing roller 22 is completely driven by the pressure roller 25.

  Similarly, when the peripheral speed Vh of the peeling roller 23 exceeds Vh0 (= 322.38 mm / s), the rotational speed of the rotating shaft 231 of the peeling R gear 230 is higher than that of the gear 234. At this time, the one-way clutch 235 is disengaged and the rotating shaft 231 and the gear 234 are separated, so that the peeling roller 23 is completely driven by the pressure roller 25.

  When the peripheral speed of the fixing roller 22 and the peeling roller 23 is further increased, the fixing roller 22 rotates at the same speed as the pressure roller 25.

  As described above, in the fixing device 15, when the separation roller 23 slips and the peripheral speed becomes slower than the fixing roller 22, or when the peripheral speed of the fixing roller 22 or the separation roller 23 decreases excessively, the driving is performed. The pressure roller 25, the fixing roller 22, and the peeling roller 23 are driven by the mechanism 150 in conjunction with each other. As a result, there is no floating between the fixing roller 22 and the peeling roller 23 due to the deflection of the fixing belt 21 or an excessive speed difference between the rollers that pinch the paper P. Therefore, it is possible to prevent the occurrence of fixing failure and image shift.

  As described above, according to the fixing device according to the embodiment of the present invention, it is possible to stably perform the fixing process without causing fixing failure or image shift.

  In addition, since the image forming apparatus according to the embodiment of the present invention includes the fixing device configured as described above, the toner image formed on the sheet by the image forming unit is stably and reliably fixed. Therefore, it is possible to form a high quality image without causing fixing failure or image shift.

  In the above description, an example in which the fixing belt 21 is suspended by three rollers, that is, the fixing roller 22, the peeling roller 23, and the heating roller 24 has been described. However, the present invention is not limited to this, The structure of may be sufficient. For example, the fixing belt may be suspended by two rollers as in the configuration disclosed in Patent Document 1. Also in this case, similarly to the above description, each roller may be configured to be driven in conjunction with a plurality of gears and driving means.

  DESCRIPTION OF SYMBOLS 1-4 ... Image forming unit 5 ... Image forming unit group 6 ... Primary transfer belt 10 ... Primary transfer belt cleaning unit 14 ... Tray 15 ... Fixing device 21 ... Fixing belt 22 ... Fixing roller 23 ... Peeling roller 24 ... Heating roller 25 ... Pressure roller 26 ... 1st lever 27 ... 2nd lever 28 ... 3rd lever 29 ... 1st spring 30 ... 2nd spring 31 ... 3rd spring 32 ... 1st temperature sensor 33 ... 2nd temperature sensor 41 ... fixing | fixed part 51 ... secondary transfer unit 61 ... support roller 62 ... primary transfer belt drive rollers 71, 72, 73, 74 ... primary transfer roller 100 ... image forming apparatus 225, 235 ... one-way clutch

Claims (4)

A fixing device that fixes a developer on a recording material conveyed along a conveyance path at a fixing nip portion,
An endless fixing belt,
A fixing roller installed along the conveyance path and suspending the fixing belt;
A separation roller that is installed on the downstream side of the conveyance path from the fixing roller, suspends the fixing belt, and separates the recording material from the fixing belt;
A pressure roller that is in pressure contact with the fixing roller and the peeling roller via the fixing belt, forms the fixing nip portion with the fixing belt, and conveys the recording material together with the fixing belt;
The fixing roller, the peeling roller, and the pressure roller are coupled to the respective rotation shafts, and are engaged so that the rotation directions of the fixing roller, the peeling roller, and the pressure roller are opposite to each other. Multiple gears,
Drive means for driving the plurality of gears;
A first one-way clutch that contacts and separates a rotation shaft of the peeling roller and a gear that rotates the peeling roller;
And a second one-way clutch that contacts and separates a rotation shaft of the fixing roller and a gear that rotates the fixing roller . The plurality of gears are
The peripheral speed Vk of the pressure roller> the peripheral speed Vh of the peeling roller> the peripheral speed Vt of the fixing roller
The fixing device according to claim 1 , wherein the fixing device is set to a gear ratio for rotating each of the rollers at a peripheral speed ratio that satisfies the above relationship. A cored bar part and a heating source for heating the cored bar part are provided, the fixing belt is suspended by the cored bar part on the upstream side of the fixing roller in the rotation direction of the fixing belt, and the fixing belt is heated. the fixing device according to claim 1 or 2 including a heating roller. A fixing device according to any one of claims 1 to 3 ,
An image forming means for forming an image by transferring a developer to a recording material conveyed to the fixing device;
An image forming apparatus.

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