JP2018092020A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that prevents the occurrence of temperature unevenness and buckling failure of a fixing belt, and prevents rubbing between the fixing belt and a nip forming unit.SOLUTION: A fixing device comprises: an endless belt that has flexibility; a pressure member that is provided on the outside of the belt and is opposed to the belt; a nip forming unit that is provided on the inside of the belt and forms a fixing nip between the belt and the pressure member; a heat source that heats the belt; and a temperature detection part that detects the temperature of the belt. The heat source generates heat in a lighting condition where a temperature detected by the temperature detection part does not reach a first predetermined temperature, and the fixing device starts rotation of the belt at the time point at which the temperature detected reaches a second predetermined temperature.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a fixing device and an image forming apparatus including the fixing device.

  In recent years, there has been a strong market demand for energy saving and high speed for image forming apparatuses such as copiers, printers, facsimiles, and multifunction machines having at least two of these functions.

  Among the image forming apparatuses, the fixing device has a large amount of power consumption and a large room for energy saving. Therefore, various proposals have been made. For example, in Patent Document 1, the film is thin and flexible with a low heat capacity. A nip forming unit is fixedly arranged inside the endless belt (in the loop), and a fixing nip is formed between the belt and the pressure rotator by the contact pressure between the nip forming unit and the pressure rotator. A fixing device is known.

  In the fixing device having such a configuration, the belt width direction (paper width direction) is used in order to prevent excessive temperature rise at the end of the belt when passing small size paper while supporting recording materials of various sizes. ), A plurality of halogen heaters (radiation type heat sources) having different light distributions are provided inside the belt, and heat is moved in the longitudinal direction of the belt on the surface of the nip forming member constituting the nip forming unit facing the belt. Patent Document 2 discloses covering with a heat transfer auxiliary member.

  In the fixing device having the thin endless belt described above, the fixing belt is directly heated by a radiant heat source such as a halogen heater. It is heated and the temperature rises rapidly. On the other hand, the portion of the fixing belt that is not opposed to the heater is not heated directly by the heater, so the temperature remains relatively low. When the thin belt is partially and locally heated as described above, a temperature difference may occur in the circumferential direction or the longitudinal direction of the fixing belt. Such a temperature difference becomes a “temperature spot” in the circumferential direction of the fixing belt. If a temperature spot with a large temperature difference occurs, the fixing is caused by the local thermal expansion of the fixing belt (difference in expansion from other locations). There is a risk of distortion on the surface of the belt. Further, if the distortion exceeds the yield stress of the fixing belt, buckling failure (kink) may occur in the fixing belt. Particularly in a film-like fixing belt, since the temperature rise is steep, the actual belt temperature may be increased more than necessary even if the heating is controlled according to the detection of the belt temperature. When distortion occurs on the surface of the fixing belt, a good fixing nip is not formed, and an image with a deteriorated quality is formed.

  Further, in the fixing device having the above configuration, the belt rotates between the pressure rotator and the nip forming unit at the fixing nip and rotates, and is guided by flanges arranged at both ends except for the fixing nip so as to run. Therefore, securing a stable running property of the belt is also a problem. In particular, when the diameter of the belt is reduced in order to reduce the size of the fixing device, there is a situation in which the durability of the belt is lowered due to friction with the inner periphery of the belt at the circumferential entrance and exit of the nip forming unit during rotation. If the fixing belt is rotated in a low temperature state, the rubbing resistance at the fixing nip is large, and the fluctuation of the locus of the traveling belt is large.

  It is an object of the present invention to provide a fixing device in which temperature spots and buckling failure do not occur in the fixing belt, and the fixing belt and the nip forming unit do not rub.

  The problem is that an endless belt having flexibility, a pressure member provided outside the belt, facing the belt, and provided inside the belt, the belt and the pressure member A nip forming unit that forms a fixing nip therebetween, a heat source that heats the belt, and a temperature detector that detects the temperature of the belt, and the temperature detected by the temperature detector is a first predetermined temperature This is solved by a fixing device that starts the rotation of the belt when the heat source generates heat under the lighting condition that does not reach, and the detected temperature reaches the second predetermined temperature.

  In the present invention, the heat source is heated as a lighting condition in which the target temperature is a first predetermined temperature that does not cause a temperature difference in the circumferential direction and the longitudinal direction of the belt so as to cause temperature spots and kinks, and the belt reaches the second predetermined temperature. Since the rotation of the belt is started when it reaches, the belt and the nip forming unit are not rubbed.

1 is a schematic cross-sectional configuration diagram illustrating an embodiment of a fixing device. It is a perspective view which shows the basic composition of a nip formation unit. It is a figure which shows roughly the layout of the laser displacement meter at the time of measuring the belt locus | trajectory during rotation. It is a figure which shows the belt locus | trajectory obtained from the measurement result. FIG. 3 is an enlarged view near a fixing nip. 5 is a graph showing a relationship between a belt temperature of a fixing belt and a belt displacement amount. 6 is a flowchart showing heating control of the fixing belt. 5 is a graph showing an example of a relationship between a heater lighting rate, a lighting time, and a fixing belt temperature. It is a graph which shows an example of the temperature rising characteristic by the applied voltage of a ceramic heater. FIG. 10A is a graph showing an example of a temperature rise profile when the end heater temperature rise is changed according to the temperature of the fixing belt at the start of the operation of the fixing device. FIG. FIG. 10b shows a case where the operation starts from a state where the temperature is higher than that in the cold state. It is a graph which shows that the amount of displacement of a belt track increases relatively when the belt linear velocity is high. 1 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic sectional view showing a fixing device 20 according to an embodiment of the present invention. The fixing device 20 includes an endless fixing belt 21 that is a thin and flexible cylindrical fixing member, and a pressure roller 22 that is a pressure member that abuts from the outer peripheral side of the fixing belt 21. ing. The fixing belt 21 is heated by radiant heat of halogen heaters 23A and 23B (hereinafter also referred to as first halogen heater 23A and second halogen heater 23B) as a plurality of fixing heat sources arranged inside (in the loop). The halogen heater represents a radiant heat source as a fixing heat source which is a main heat source.

  Further, a nip forming member 24 that forms a fixing nip N with the pressure roller 22 via the fixing belt 21 and a stay member 25 (support member) that supports the nip forming member 24 are arranged inside the fixing belt 21. Has been. The nip forming member 24 arranged across the width direction of the fixing belt 21 is fixedly supported by the stay member 25, thereby preventing the nip forming member 24 from being bent by the pressure from the pressure roller 22, A uniform nip width is obtained over the axial direction (longitudinal direction) of the pressure roller 22. The nip forming member 24 is a heat-resistant member having high mechanical strength and a heat-resistant temperature of 200 ° C. or more, particularly heat-resistant resins such as polyimide (PI) resin, polyether ether ketone (PEEK) resin, and reinforced them with glass fiber. Is made up of. This prevents deformation of the nip forming member 24 due to heat in the toner fixing temperature range, ensures a stable fixing nip state, and stabilizes the output image quality. The stay member 25 and the halogen heaters 23A and 23B are fixedly held at both ends in the longitudinal direction by a side plate of the fixing device 20 or a separately provided holder.

  A heat transfer auxiliary member 27, also referred to as a soaking member, that facilitates heat transfer in the longitudinal direction of the fixing belt is disposed so as to cover the surface of the nip forming member 24 that faces the inner peripheral surface of the fixing belt 21. In addition, heat is prevented from staying in the end region of the fixing belt 21 when passing small-size paper, and the heat is positively moved in the width direction of the fixing belt 21, that is, in the longitudinal direction of the heat transfer auxiliary member 27. Thus, temperature non-uniformity in the longitudinal direction is eliminated. Therefore, the heat transfer auxiliary member 27 is made of a material having high thermal conductivity that enables heat transfer in a short time, such as copper (398 W / mk) or aluminum (236 W / mk). In the depiction in FIG. 2, the surface of the heat transfer assisting member 27 that faces the inner peripheral surface of the fixing belt 21 is a surface that directly contacts the fixing belt 21 and is a nip forming surface that is formed in a flat shape. However, it may be a concave shape or other shapes. When the nip forming surface has a concave shape, the discharge direction of the leading edge of the recording paper is closer to the pressure roller, and the separation is improved and the occurrence of jam is suppressed. Here, in addition to plain paper, the recording material includes thick paper, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, and the like.

  Temperature sensors 29A and 29B, which are temperature detection units for detecting the belt temperature, are provided at appropriate positions on the outer peripheral side of the fixing belt 21, for example, positions facing the halogen heaters 23A and 23B. A separation member 41 that separates the paper P from the fixing belt 21 is disposed on the downstream side in the transport direction. Further, as is well known, a releasable pressure means for pressing the pressure roller 22 to the fixing belt 21 is provided.

  In order to achieve a low heat capacity, the endless fixing belt 21 which is thin and small in diameter like a film is composed of a base material on the inner peripheral side made of a metal material such as nickel or SUS, or a resin material such as polyimide, and a PFA. It is constituted by a release layer on the outer peripheral side formed of (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) or PTFE (polytetrafluoroethylene). An elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber may be interposed between the base material and the release layer. When the thickness of the elastic layer is about 100 μm, when the unfixed toner is crushed and fixed, minute irregularities on the belt surface can be absorbed by the elastic deformation of the elastic layer, and uneven gloss can be avoided. From the viewpoint of reducing the heat capacity, the fixing belt 21 is set to a thickness of 1 mm or less and a diameter of 20 to 40 mm as a whole. The thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are set in a range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm. In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is preferably 0.2 mm or less, more preferably 0.16 mm or less, and the diameter is 30 mm. The following is desirable.

  The stay member 25 having a T-shaped cross section has an upright portion 25a that is upright on the side opposite to the fixing nip N side, and is arranged so that halogen heaters 23A and 23B as main heat sources are separated by the upright portion 25a. One of the halogen heaters 23A and 23B has a heat generating portion at a longitudinal center portion corresponding to a small size paper, and the other has a heat generating portion at both longitudinal end portions corresponding to a large size paper. By arranging the two halogen heaters 23A and 23B apart from each other by the stay member 25 having a T-shaped cross section, the problem of mutual heating of the heaters can be avoided as compared with a conventional fixing device in which a plurality of halogen heaters are juxtaposed. , Heating efficiency can be increased. The halogen heaters 23 </ b> A and 23 </ b> B are configured to generate heat by being output controlled by a power supply unit provided in a printer main body of the image forming apparatus described later. The output control is performed by a temperature provided on the outer periphery of the fixing belt 21. This is performed based on the temperature detection result of the belt surface by the sensors 29A and 29B. By such heater output control, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature.

  Reflecting members 28A and 28B are disposed between the stay member 25 and the halogen heaters 23A and 23B. Accordingly, the heating efficiency of the halogen heaters 23A and 23B with respect to the fixing belt 21 can be increased, and wasteful energy consumption due to the stay member 25 being heated by the radiant heat from the halogen heaters 23A and 23B can be suppressed. The same effect can be obtained by performing heat insulation or mirror treatment on the surface of the stay member 25 instead of providing the reflecting members 28A and 28B.

  The pressure roller 22 includes a cored bar, an elastic layer made of foamable silicone rubber or fluororubber provided on the surface of the cored bar, and a release layer made of PFA, PTFE, etc. provided on the surface of the elastic layer. It is configured. At a location where the pressure roller 22 is pressed against the fixing belt 21 by a pressing means such as a spring and is pressed against the fixing belt 21, the elastic layer of the pressure roller 22 is crushed to form a fixing nip N having a predetermined width. The The pressure roller 22 is rotationally driven by a driving source such as a motor provided in the printer main body. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 through the fixing nip N, and the fixing belt 21 is driven to rotate. The fixing belt 21 is sandwiched and rotated at the fixing nip N, and travels while being guided by side plate flanges disposed at both ends except for the fixing nip N.

  In the present embodiment, the pressure roller 22 is a solid roller, but may be a hollow roller. In that case, a heat source such as a halogen heater may be disposed inside the pressure roller 22. The elastic layer may be solid rubber, but if there is no heat source inside the pressure roller, sponge rubber may be used. Sponge rubber is more preferable because heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away.

  FIG. 2 is a perspective view showing a basic configuration of the nip forming unit. As shown in FIG. 2, the nip forming unit includes a nip forming member 24, a stay member 25, and a heat transfer assisting member 27. In the nip forming unit, the surface of the nip forming member 24 opposite to the fixing nip N side is integrated with the plane of the stay member 25 on the fixing nip N side. At this time, uneven shapes such as bosses and pins may be formed on the respective surfaces, and these may be fitted in a shape-constrained manner. The heat transfer assisting member 27 is fitted and integrated so as to cover the surface of the substantially rectangular parallelepiped nip forming member 24 facing the inner peripheral surface of the fixing belt 21. The heat transfer assisting member 27 and the nip forming member 24 may be integrated with each other by providing a claw or the like, but may be bonded or the like.

  Concave portions 24a and 24b as stepped portions are formed at both ends in the longitudinal direction of the nip forming member 24, and an end heater 26a as an end heat source different from the main heat source (fixing heat source) is formed at these locations. , 26b are housed and attached together and used to heat both ends of a Nobi size paper width larger than the maximum standard size. As the end heater, a contact heat transfer type heat source that is a resistance heating element such as a ceramic heater is generally used.

  The surface of the heat transfer auxiliary member 27 that faces the inner peripheral surface of the fixing belt 21 is configured as a belt sliding contact surface 27a. However, the nip forming member 24 substantially becomes a nip forming surface in terms of mechanical strength. This is a surface 24c facing the pressure roller 22.

  As described above, in the present embodiment, the end heaters 26 a and 26 b are integrally provided on the nip forming member 24 necessary for forming the fixing nip, so that the end heaters 26 a and 26 b are provided on the fixing belt 21. It can be placed inside with space saving. Further, the surfaces of the end heaters 26a and 26b facing the inner surface of the fixing belt 21 are configured to be located at the same height (on the same plane) as the surface of the nip forming member 24 facing the fixing belt 21. The sufficient pressure applied by the pressure roller 22 can be applied via the heat transfer auxiliary member 27. As a result, the fixing belt 21 is in intimate contact with the end heaters 26a and 26b, and stable belt running is possible. Further, the fixing belt 21 and the end heaters 26a and 26b are in contact with each other with a sufficient contact pressure, and good heating is maintained.

  By the way, in the fixing device 20 of the present embodiment, as described above, the fixing belt 21 is sandwiched and rotated by the fixing nip N, and other than the fixing nip N, it is guided by the side plate flanges disposed at both ends and travels. Thus, it has been confirmed that when the temperature of the fixing belt 21 changes, the running track of the belt changes. FIG. 3 schematically shows the layout of the measuring instrument when the belt trajectory during rotation is measured. A high-speed, high-precision laser displacement meter L-KG3000 manufactured by Keyence was used as a measuring device, and the amount of displacement of the belt outer circumference with respect to the temperature of the fixing belt was measured. The belt trajectory obtained from the measurement result by the laser displacement meter is shown in FIG. In the figure, 21a (solid line) is a belt locus when the paper is passed at a target control temperature, 21b is a belt locus when the belt temperature is low, and 21c is a belt locus when the belt temperature is high. Even if the belt temperature changes, there is no significant displacement near the exit of the fixing nip N, and it has been found that the amount of displacement near the entrance of the fixing nip N is absorbed as it advances through the fixing nip N.

  FIG. 5 is an enlarged view of the vicinity of the fixing nip N. FIG. In the belt locus 21a when the sheet is passed at the target fixing temperature, the inner periphery of the fixing belt and the nip forming unit (the heat transfer assisting member 27 in the drawing) do not rub except for the nip width. However, in the belt trajectory 21b when the belt temperature is low, the rigidity of the belt itself is increased due to the low belt temperature and tends to be close to a perfect circle. Then, the inner periphery of the belt may rub against the nip forming unit.

  FIG. 6 shows the relationship between the belt temperature of the fixing belt and the amount of belt displacement. Here, the “+ (plus)” side of the displacement is the displacement toward the heat transfer assisting member 27 side (belt inner circumference side), and the “− (minus)” side is the belt outer circumference side, as can be seen from FIG. It is displacement to. In the temperature range of the fixing belt practical for the fixing process, it is found that the displacement is almost linear, and the displacement is about 0.3 mm per 50 deg.

  A lubricant such as fluorine grease is interposed between the surface of the heat transfer auxiliary member 27 and the inner peripheral surface of the fixing belt 21 to improve the slidability, but lubrication is performed in a region other than the fixing nip N such as a nip inlet. Since there is no mechanism for positively holding the agent, if the fixing belt 21 rotates in a low temperature state, it will come into contact with the heat transfer assisting member 27 and cause wear, resulting in shortening the life of the fixing device. ing. Therefore, in order to avoid such a situation, heating and rotation of the fixing belt 21 are controlled. If the inner periphery of the fixing belt 21 and the heat transfer assisting member 27 do not contact at a portion other than the fixing nip N, the life of the fixing device can be increased.

  First, in the configuration of the fixing device according to the present embodiment, since the fixing belt 21 is directly heated by the halogen heaters 23A and 23B, which are radiant heat sources, the heating of the fixing belt 21 is opposed to the halogen heaters 23A and 23B. The surface (inner peripheral surface) is partially heated by the heater. As a result, a temperature difference occurs in the circumferential direction and the longitudinal direction (width direction) of the fixing belt 21, and such a temperature difference causes “temperature spots” in the circumferential direction of the fixing belt. If this occurs, the surface of the fixing belt may be distorted due to a difference in the amount of local thermal expansion of the fixing belt. Further, if the distortion exceeds the yield stress of the fixing belt, buckling failure (kink) may occur in the fixing belt. When distortion occurs on the surface of the fixing belt, a good fixing nip is not formed, and an image with deteriorated quality is formed.

  In the present embodiment, the halogen heaters 23A and 23B are turned on at a low lighting rate, and “a temperature at which a temperature difference does not occur in the circumferential direction or the longitudinal direction of the fixing belt 21 enough to cause temperature spots or kinks” (“first predetermined It is possible to avoid the occurrence of temperature spots and buckling fractures (kinks) by raising the temperature while controlling the temperature below (referred to as “temperature”).

  In FIG. 7, under the lighting condition where the fixing belt does not reach the first predetermined temperature, the halogen heater 23A (small size paper) or the halogen heaters 23A and 23B (large size paper) is heated and fixed at a low lighting rate. The belt 21 is heated (step 1). While the fixing belt 21 is heated until it approaches the first predetermined temperature, “the inner periphery of the fixing belt 21 and the heat transfer assisting member 27 do not come into contact with each other except the fixing nip N (the rigidity of the belt is Since it becomes the second predetermined temperature (second predetermined temperature <first predetermined temperature), it is determined whether or not the temperature detected by the temperature sensors 29A and 29B is higher than the second predetermined temperature. After the determination (step 2) and the fixing belt 21 reaches the second predetermined temperature, the fixing belt 21 is rotated at a predetermined rotational speed (step 3). After the rotation of the fixing belt 21 is started, the fixing belt 21 is heated at a higher lighting rate (predetermined lighting rate) (step 4). When the fixing belt 21 reaches the first predetermined temperature, the image forming preparation is completed or the warm-up operation is completed.

  FIG. 8 is a graph showing an example of the relationship between the heater lighting rate, lighting time, and fixing belt temperature. When lighting is performed at a lighting rate of 10% every 50 [msec], a gentle temperature rise curve (solid line) is shown, and control can be performed so that temperature spots do not occur. On the other hand, when the lighting rate is set to 30%, a rapid temperature rise curve (dotted line) is obtained, temperature control becomes difficult, and temperature spots and buckling failure (kink) may occur. Therefore, in the temperature rise control in the “heating at a low lighting rate” stage in the flow of FIG. 7, a method of repeating a very low lighting rate in a short time is effective.

  Note that as described above, the more uniform the fixing belt 21 is, the less likely it is that temperature spots and buckling breaks (kinks) occur. Therefore, when passing large-size paper, the halogen heaters 23A and 23B are reduced. When lighting at the lighting rate, the belt temperature is detected by the corresponding temperature sensors 29A and 29B, and the lighting rates of the halogen heaters 23A and 23B are individually controlled, so that the temperature of the entire fixing belt 21 is uniform. It is desirable to raise the temperature to a second predetermined temperature in the state. However, even in this case, it is necessary to control the temperature below the first predetermined temperature that does not cause temperature spots and buckling fracture (kinks).

  Further, in the present embodiment, end heaters 26a and 26b, which are contact heat transfer type heat sources, are provided in order to heat both ends of the nobi size paper width larger than the maximum standard size. A ceramic heater, which is a contact heat transfer type heat source, has a substantially linear temperature rise characteristic with respect to an applied voltage, and hardly causes overshoot like a halogen heater. FIG. 9 shows the temperature rise characteristics of the ceramic heater when 100 [V], 80 [V], and 60 [V] are respectively applied. It can be seen that the calorific value is proportional to the square of the applied voltage. In order to gradually raise the temperature of the fixing belt by the halogen heaters 23A and 23B, it is necessary to repeat a low lighting rate in a short time as shown in FIG. 8, but the end heaters 26a and 26b which are ceramic heaters are applied with an applied voltage. The rate of temperature rise can be controlled.

  Therefore, by determining the voltage applied to the end heaters 26a and 26b, the end heaters 26a and 26b can reach the second predetermined temperature in accordance with the timing when the fixing belt 21 reaches the second predetermined temperature. It becomes possible. Therefore, when fixing Nobi size paper, it is difficult to heat the halogen heaters 23A and 23B by simultaneously lighting the end heaters 26a and 26b in addition to the halogen heaters 23A and 23B when the temperature is raised to the second predetermined temperature. The vicinity of the fixing nip N of the fixing belt 21, particularly the end of the belt can also be heated, and control can be performed so that the temperature is uniform over the entire circumference of the fixing belt 21. However, even in this case, it is necessary to control the temperature below the first predetermined temperature that does not cause temperature spots and buckling fracture (kinks).

  In addition, because of the linear temperature rise characteristics of the ceramic heater with respect to the applied voltage, the optimum application to the end heaters 26a and 26b based on the result of detecting the belt temperature by the temperature sensors 29A and 29B when the halogen heaters 23A and 23B are turned on. The voltage can be estimated. FIG. 10a shows a temperature increase curve of the fixing belt when the fixing device starts operation from the cold time (and therefore when the halogen heater lighting control is started), and FIG. 10b shows a temperature higher than that at the cold time after passing the paper. A temperature increase curve when the fixing device starts operation from a high state is shown. When the temperature of the fixing belt 21 at the start of operation is equal to or lower than the second predetermined temperature, the end heaters 26a and 26b are also turned on at the same time so that the halogen heaters 23A and 23B are difficult to heat, and the fixing nip N of the fixing belt 21 The vicinity can also be heated. Here, by determining the voltage applied to the end heaters 26a and 26b according to the belt temperature at the start of the operation, the determined voltage is detected by the temperature sensors 29A and 29B facing the halogen heaters 23A and 23B. If the temperature is applied to the end heaters 26a and 26b until the temperature rises to the second predetermined temperature, the entire circumference and width of the fixing belt 21 can be uniformly raised to the second predetermined temperature.

  As described above, the belt trajectory varies depending on the temperature of the fixing belt 21. When the belt trajectory during rotation is measured with the laser displacement meter layout shown in FIG. It was also revealed that the amount of displacement increased relatively (FIG. 11). Therefore, in order to reduce the fluctuation amount of the belt trajectory of the fixing belt 21, the belt linear velocity is set low until reaching the reload temperature (predetermined predetermined temperature) after reaching the second predetermined temperature. It is also effective.

  In this embodiment, the temperature of the fixing belt is detected by a plurality of temperature sensors. However, if there is a deviation in the temperature detected by both sensors, the halogen corresponding to the belt portion that has reached the second predetermined temperature first. The belt portion corresponding to the other halogen heater reaches the second predetermined temperature while keeping the temperature of the belt portion near the second predetermined temperature by further lowering or turning off the lighting rate of the voltage applied to the heater. Wait to do. Then, the rotation of the fixing belt is started when the temperature detected by each temperature sensor reaches the second predetermined temperature. At this time, the applied voltage of the end heater is controlled based on the higher detected temperature when an image forming start command is issued from the image forming apparatus.

  Finally, an image forming apparatus according to an embodiment of the present invention will be described. FIG. 12 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention, in which the above-described fixing device is mounted. The image forming apparatus 1 is a color laser printer. In the center of the printer body, four image forming units 4Y, 4C, 4M, and 4K are provided side by side along the extending direction of the intermediate transfer belt 30. Yes. Each of the image forming units 4Y, 4C, 4M, and 4K stores developers of different colors of yellow (Y), cyan (C), magenta (M), and black (K) corresponding to the color separation components of the color image. Other than that, the configuration is the same.

  Specifically, each of the image forming units 4Y, 4C, 4M, and 4K constituting the image station includes a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoconductor 5, and A developing device 7 for supplying toner to the surface of the photoreceptor 5 and a cleaning device 8 for cleaning the surface of the photoreceptor 5 are provided. In FIG. 12, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4 </ b> K are assigned color codes, and the other image forming units 4 </ b> Y, 4 </ b> C, and 4 </ b> M The reference numerals are omitted.

  Below the image forming units 4Y, 4C, 4M, and 4K, an exposure device 9 that exposes the surface of the photoreceptor 5 is disposed. The exposure device 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each photoconductor 5 with laser light based on image data.

  A transfer device 3 is disposed above the image forming units 4Y, 4C, 4M, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as a transfer body, four primary transfer rollers 31 as primary transfer means, and a secondary transfer roller 36 as secondary transfer means. Further, the transfer device 3 includes a secondary transfer backup roller 32, a cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35.

  The intermediate transfer belt 30 is an endless belt and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, when the secondary transfer backup roller 32 is driven to rotate, the intermediate transfer belt 30 runs (rotates) in the direction indicated by the arrow in the figure.

  Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. In addition, each primary transfer roller 31 is connected to a power source of a printer main body, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to each primary transfer roller 31. .

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Similarly to the primary transfer roller 31, the secondary transfer roller 36 is also connected to the power source of the printer main body, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It has come to be.

  The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30.

  A bottle container 2 is provided in the upper part of the printer main body, and four toner bottles 2Y, 2C, 2M, and 2K containing replenishing toner are detachably attached to the bottle container 2. As is well known, a replenishment path is provided between each toner bottle 2Y, 2C, 2M, 2K and each developing device 7, and each development from each toner bottle 2Y, 2C, 2M, 2K is performed via this replenishment path. The toner is supplied to the device 7.

  On the other hand, a lower portion of the printer main body is provided with a paper feed tray 10 that stores paper P as a recording material, a paper feed roller 11 that carries the paper P out of the paper feed tray 10, and the like. As is well known, a manual paper feed mechanism may be provided.

  In the printer main body, a transport path R is provided for discharging the paper P from the paper feed tray 10 through the secondary transfer nip to the outside of the apparatus. In the transport path R, a pair of registration rollers 12 serving as transport means for transporting the paper P to the secondary transfer nip is disposed upstream of the position of the secondary transfer roller 36 in the paper transport direction.

  Further, the fixing device 20 described in detail above is disposed downstream of the position of the secondary transfer roller 36 in the paper conveyance direction, and fixes the unfixed image transferred onto the paper P. Further, a pair of paper discharge rollers 13 for discharging the paper to the outside of the apparatus is provided downstream of the fixing device 20 in the paper conveyance direction of the conveyance path R. In addition, a paper discharge tray 14 for stocking paper discharged outside the apparatus is provided on the upper surface of the printer main body.

  The basic operation of the printer according to this embodiment is as follows. When the image forming operation is started, the photoconductors 5 in the image forming units 4Y, 4C, 4M, and 4K are rotationally driven clockwise in the drawing, and the surface of each photoconductor 5 is set to a predetermined polarity by the charging device 6. Uniformly charged. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9 to form an electrostatic latent image on the surface of each photoconductor 5. At this time, the image information to be exposed on each photoconductor 5 is single-color image information obtained by separating a desired full-color image into color information of yellow, cyan, magenta, and black. In this way, toner is supplied to each electrostatic latent image formed on each photoconductor 5 by each developing device 7, whereby the electrostatic latent image is visualized (visualized) as a toner image. .

  When the image forming operation is started, the secondary transfer backup roller 32 is driven to rotate counterclockwise in the figure, and the intermediate transfer belt 30 is caused to run in the direction indicated by the arrow in the figure. Then, a constant voltage or a constant current controlled voltage having a polarity opposite to the charging polarity of the toner is applied to each primary transfer roller 31. As a result, a transfer electric field is formed in the primary transfer nip between each primary transfer roller 31 and each photoconductor 5.

  Thereafter, when each color toner image on the photoconductor 5 reaches the primary transfer nip as each photoconductor 5 rotates, the toner image on each photoconductor 5 is formed by the transfer electric field formed in the primary transfer nip. The images are sequentially superimposed and transferred onto the intermediate transfer belt 30. Thus, a full color toner image is carried on the surface of the intermediate transfer belt 30. Further, the toner on each photoconductor 5 that could not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Thereafter, the surface of each photoconductor 5 is neutralized, and the surface potential is initialized.

  In the lower part of the image forming apparatus, the paper feed roller 11 starts to rotate, and the paper P is sent out from the paper feed tray 10 to the transport path R. The sheet P sent to the conveyance path R is timed by the registration roller 12 and is sent to the secondary transfer nip between the secondary transfer roller 36 and the secondary transfer backup roller 32. At this time, a transfer voltage having a polarity opposite to the toner charge polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field in the secondary transfer nip.

  Thereafter, when the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip as the intermediate transfer belt 30 rotates, the toner image on the intermediate transfer belt 30 is generated by the transfer electric field formed in the nip. Are collectively transferred onto the paper P. At this time, the residual toner on the intermediate transfer belt 30 that could not be transferred onto the paper P is removed by the belt cleaning device 35, and the removed toner is conveyed to a waste toner container placed in the printer body. To be recovered.

  Thereafter, the paper P is conveyed to the fixing device 20, and the toner image on the paper P is fixed to the paper P by the fixing device 20. Then, the paper P is discharged out of the apparatus by the paper discharge roller 13 and stocked on the paper discharge tray 14.

  The above description is an image forming operation when a full-color image is formed on a sheet. A single color image can be formed using any one of the four image forming units 4Y, 4C, 4M, and 4K. Two or three image forming units can be used to form a two-color or three-color image.

  The present invention has been described based on the embodiments. The present invention is not limited to the embodiments, and can be appropriately changed within the scope of the present invention. The image forming apparatus provided with the fixing device of the present invention is not limited to a copying machine or a printer, but may be a facsimile machine or a multifunction machine having a plurality of functions.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Bottle accommodating part 2C, 2K, 2M, 2Y Toner bottle 3 Transfer apparatus 4C, 4K, 4M, 4Y Image forming part 5 Photoconductor 6 Charging apparatus 7 Developing apparatus 8 Cleaning apparatus 9 Exposure apparatus 10 Paper feed tray 11 Paper feed roller 12 Registration roller 13 Paper discharge roller 14 Paper discharge tray 20 Fixing device 21 Fixing belt 22 Pressure roller 23A, 23B Halogen heater 24 Nip forming member 24a, 24b Recess 24c Surface 25 Stay member 25A First member 25B Second member 25a Standing portion 26a, 26b End heater 27 Heat transfer assisting member 27a Nip forming surface 28A, 28B Reflecting member 29A, 29B Temperature sensor (temperature detection unit)
30 Intermediate transfer belt 31 Primary transfer roller 32 Secondary transfer backup roller 33 Cleaning backup roller 34 Tension roller 35 Belt cleaning device 36 Secondary transfer roller 41 Separating member N Fixing nip P Paper α β Irradiation angle

JP 2010-32631 A Japanese Patent Laid-Open No. 2006-145961

Claims (6)

An endless belt having flexibility;
A pressure member provided outside the belt and facing the belt;
A nip forming unit provided inside the belt and forming a fixing nip between the belt and the pressure member;
A heat source for heating the belt;
A temperature detection unit that detects the temperature of the belt, the heat source generates heat under a lighting condition in which the temperature detected by the temperature detection unit does not reach a first predetermined temperature, and the detected temperature is a second The fixing device starts rotating the belt when a predetermined temperature is reached.   The heat source is a plurality of radiant heat sources having different light distributions in the longitudinal direction, and each of the plurality of radiant heat sources is lit so as to reach a uniform temperature until the belt reaches the second predetermined temperature. The fixing device according to claim 1, wherein the fixing device is controlled under conditions.   The nip forming unit includes a nip forming member and a heat transfer assisting member disposed so as to cover a surface of the nip forming member facing the inner peripheral surface of the belt. A plurality of contact heat transfer type heat sources provided at both ends in the longitudinal direction of the surface facing the heat transfer assisting member and respectively heating the end portions in the width direction of the belt. 3. The fixing device according to claim 1, wherein the lighting condition is determined by a temperature of the belt at a start of lighting control of the heat source which is a radiation type heat source.   The lighting condition is controlled so that the contact heat transfer type heat source also reaches the second predetermined temperature in accordance with a timing at which the belt reaches the second predetermined temperature by the radiation type heat source. The fixing device according to 3.   5. The fixing device according to claim 1, wherein the belt has a plurality of linear rotation speeds and rotates the belt at a low rotation linear speed at least until reaching a reload temperature.   An image forming apparatus comprising the fixing device according to claim 1.

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