JP2014178635A - Fixing device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of fixing images even when a heat quantity deprived by paper such as cardboard is large, and an image forming apparatus using the fixing device.SOLUTION: A fixing device comprises temperature control sensors 11 and 12 that detect a temperature of a fixing belt 1 to perform temperature control of the fixing belt. In use conditions in which a change in temperature occurs out of a heat supply range of a heat source 3 that is controlled to be turned on by the temperature control sensors 11 and 12 (conditions in which offset area occurs), a fixing device determines a heat quantity supplied from the heat source 3 with predetermined conditions other than conditions based on temperature information obtained from the temperature control sensors 11 and 12, for example, determines a heat quantity with the predetermined conditions to prevent offset (both cold offset and hot offset).

Description

  The present invention relates to a fixing device used in an image forming apparatus such as a copying machine, a facsimile machine, a printer, and a multifunction machine of these, and a fixing device that includes an endless fixing member and a pressure member to perform a fixing process, and the fixing device. The present invention relates to a mounted image forming apparatus.

  In recent years, market demands for energy saving and high speed have been increasing for image forming apparatuses such as printers and copiers. In an image forming apparatus, an unfixed toner image is transferred to a recording material sheet, printing paper, photosensitive paper, electrostatic recording paper, etc. by an image transfer method or a direct method by an image forming process such as electrophotographic recording, electrostatic recording, and magnetic recording. Formed on recording material. As a fixing device for fixing an unfixed toner image, a contact heating method fixing device such as a heat roller method, a film heating method, and an electromagnetic induction heating method is widely used.

  As examples of such a fixing device, a belt-type fixing device (for example, see Patent Document 1) and a surf fixing (film fixing) fixing device (for example, see Patent Document 2) using a ceramic heater are known.

  In the belt-type fixing device, as a first problem in recent years, further warm-up time (time required from normal temperature to a predetermined printable temperature (reload temperature) such as when the power is turned on) and first print time (printing) After receiving the request, it is desired to shorten the time until the printing operation is performed after the print preparation and the paper discharge is completed. As a second problem, the number of sheets passed per unit time increases and the required heat amount increases as the speed of the image forming apparatus increases, so that the amount of heat is insufficient particularly at the beginning of continuous printing (so-called temperature drop). Is a problem.

  As a method for solving the first problem, surf fixing using a ceramic heater has been proposed, and this method enables a reduction in heat capacity and a reduction in size as compared with a belt-type fixing device. However, in this method, since only the nip portion is locally heated, the other portions are not heated. Therefore, there is a problem that the belt is in the coldest state at the entrance of the sheet or the like of the nip, and a fixing defect is likely to occur. In particular, in a high-speed machine (because the rotation of the belt is fast and the heat radiation of the belt outside the nip portion increases), there is a third problem that fixing failure is more likely to occur.

  In order to solve the first to third problems as described above, in the configuration using an endless belt, it is possible to warm the whole belt, to shorten the first print time from the heating standby time, and There has been proposed a fixing device that solves the shortage of heat at the time of high-speed rotation and can obtain good fixability even when mounted on a high-production image forming apparatus (see, for example, Patent Document 3).

  FIG. 1 is a schematic view of a fixing device described in Patent Document 3. A pipe-shaped metal heat conductor 2 is fixed inside the endless belt 1 as a fixing belt so as to be able to guide the movement of the endless belt 1, and the metal heat conductor 2 is formed by a heat source 3 in the metal heat conductor 2. The endless belt 1 is heated via Further, a pressure roller 4 that forms a nip portion N in contact with the metal heat conductor 2 via the endless belt 1 is provided, and the endless belt 1 is moved in the circumferential direction so as to rotate as the pressure roller 4 rotates. Let With this configuration, it is possible to warm the entire endless belt constituting the fixing device, to shorten the first print time from the heating standby time, and to solve the shortage of heat during high-speed rotation. Yes. In the figure, 4a is a metal roller constituting the pressure roller 4, and 4b is an elastic layer.

  In this technique, the endless belt is directly heated, so that energy saving is high, and it is possible to further shorten the first print time from the heating standby time. However, as the heat capacity of the fixing member is reduced, the side effect that the temperature of the fixing member is likely to fluctuate with respect to disturbance has occurred. Since the heat capacity is small, the temperature is affected by the airflow in the image forming apparatus and the configuration of the pressure R (for example, the heat capacity increases on the side where the gear is present. As a result, the heat capacity increases). The decrease is likely to occur, and the temperature rise is delayed on the side where the gear of the pressure member is present at the time of start-up.

  Such a side effect also affects the case where printing paper passes during normal printing. For example, since the ratio of the amount of heat taken by the paper to the amount of heat of the fixing member has increased, it is necessary to perform highly accurate fixing control so that the amount of heat necessary for passing the paper is appropriately output from a heating source.

  By improving the temperature control of the fixing member, countermeasures against this problem were taken, and the problem was solved in the area where the temperature control can be performed (temperature detection range of the temperature sensor). A new problem has occurred.

  For example, when the temperature control position of the fixing member is outside the sheet passing area and the sheet passes in a heating area other than the temperature control position of the fixing member, a significant offset occurs in the sheet passing area. Since the temperature control position of the fixing member is outside the sheet passing area, the fixing member only operates at a constant temperature, and the amount of heat supplied from the heating source is reduced. On the other hand, when the paper passes within the heating area, the same amount of heat as that in the normal fixing operation is required in the paper passing area. As a result, the amount of heat is insufficient in the above region, and a cold offset occurs.

  Conventionally, the offset did not occur in such a mode because the heat capacity of the fixing member was large, and the fixing property could be secured at the end of the sheet even under the use conditions as described above. However, due to the low heat capacity of the fixing member, the problem that an offset occurs when printing paper passes outside the temperature detection range of the temperature control sensor becomes significant.

  In order to take a fundamental countermeasure against this problem, for example, one heating source and a temperature control sensor are brought to the center of the heating source in the sheet passing width direction. However, when only one heating source is used, the temperature rise at the end of the sheet passing range at the time of small-size sheet passing is remarkable, and the productivity cannot be maintained high. Further, with only one heater, necessary electric power cannot be secured from the viewpoint of flicker / harmonic for fixing. For this reason, the means for using one heating source is not effective in practical use, and cannot be adopted particularly in an image forming apparatus with high productivity.

  When a plurality of heating sources are provided, it is necessary to always arrange a temperature sensor in the paper passing area in various paper sizes used in the market. However, if this is attempted, the number of temperature sensors increases, which increases costs and makes it difficult to secure a layout space in the image forming apparatus. Instead of providing a plurality of temperature sensors, it is also possible to appropriately change the longitudinal position of the temperature sensor depending on, for example, the sheet passing size. However, it is necessary to provide a mechanism for operating the temperature sensor, which also increases the cost and increases the size of the image forming apparatus, and is difficult to adopt as a countermeasure.

  On the other hand, as a viewpoint from the fixing control side, for this problem, there can be considered a means of performing paper passing while promoting heat storage with a gap between papers. However, even when that means is used, for example, when the paper thickness is thick, the amount of heat taken away by the paper increases with respect to the heat capacity of the fixing member. Even if an offset occurs and the sheet is passed after storing heat with a gap between the sheets, it is not a countermeasure. Although it is possible to simply increase the set temperature during paper feeding, depending on the smoothness of the paper, it is not only possible to secure fixing properties in areas where the amount of heat is insufficient, but also to increase the temperature. As a result, the fixing unit has excessive heat and shortens the durable life of each member.

  The present invention has been made to solve the above-described technical problem, and makes it possible to fix an image even when a sheet of paper or the like takes a large amount of heat.

  The fixing device of the present invention includes a rotatable fixing member, a heat source for heating the fixing member, a pressure member that forms a nip with the fixing member, and a nip that faces the pressure member inside the fixing member. And a temperature control means for detecting the temperature of the fixing member and controlling the temperature of the fixing member, and the temperature outside the heat supply range of the heating source controlled by the temperature control means. In use conditions where the change occurs, the amount of heat supplied from the heating source is determined under a predetermined condition other than the condition of the temperature information obtained from the temperature control sensor.

  According to the present invention, a sheet is taken away like a thick sheet by using a sheet passing condition that a specified amount of heat is supplied from a heating source regardless of the detection result of the temperature of the fixing member by the temperature sensor during the sheet passing. Even when the amount of heat is large, the image can be fixed.

Explanatory drawing showing an example of a conventional fixing device Sectional drawing which shows Embodiment 1 of the fixing apparatus of this invention Explanatory drawing which shows the structure of the fixing device of Embodiment 1 in the longitudinal direction. FIG. 3 is an explanatory diagram illustrating a relationship between a configuration in a longitudinal direction of the fixing device according to the first exemplary embodiment and a sheet width to be passed. Explanatory drawing which shows the fixing device of another embodiment of the present invention (configuration using a plurality of heaters) Explanatory drawing which shows one Embodiment of a light-shielding member Schematic diagram for explaining the configuration of an image forming apparatus using a fixing device according to the present invention.

Embodiment 1 of the fixing device of the present invention will be described below with reference to the drawings.
<Embodiment 1>
FIG. 2 is a cross-sectional view showing the configuration of an embodiment of the fixing device according to the present invention.
The fixing device has a pressure rotator (pressure roller 4 in the case of FIG. 2) and the fixing belt 1, and the fixing belt 1 is directly heated from the inner peripheral side by a heat source 3 (halogen heater in the example of FIG. 2). The At this time, in the fixing belt 1 of FIG. 2, there is a nip forming member 6 that forms a nip with the pressure roller 4 opposed via the fixing belt 1, and directly (or a sliding sheet (not shown) on the inner surface of the fixing belt. (Indirectly through). The heat source 3 may be the illustrated halogen heater, but may be IH, a resistance heating element, a carbon heater, or the like.

  Although the shape of the nip portion is flat in FIG. 2, it may be a concave shape or other shapes. (When the nip shape is concave, the discharge direction of the leading edge of the recording paper is closer to the pressure roller and the separation is improved, so that jamming is suppressed.)

  The fixing belt 1 is a metal belt such as nickel or SUS or an endless belt (or film) using a resin material such as polyimide. The surface layer of the belt has a release layer such as a PFA or PTFE layer, and has a release property so that toner does not adhere. There may be an elastic layer formed of a silicone rubber layer or the like between the belt substrate and the PFA or PTFE layer. When there is no silicone rubber layer, the heat capacity is reduced and the fixability is improved, but when the unfixed image is crushed and fixed, minute irregularities on the belt surface are transferred to the image, and the image has a crusty skin shape. There arises a problem that the gloss unevenness (zudder skin image) remains. In order to improve this, it is necessary to provide a silicone rubber layer of 100 [μm] or more. Due to the deformation of the silicone rubber layer, fine irregularities are absorbed and the skin image is improved.

  A support member 7 (stay) for supporting the nip portion is provided inside the fixing belt 1 to prevent the nip forming member 6 that receives pressure from the pressure roller from being bent and to obtain a uniform nip width in the axial direction. I am doing so. The support member 7 is held and fixed to the holding member 8 (flange) at both ends and positioned. Further, the reflection member 9 is provided between the heat source 3 and the support member 7, and wasteful energy consumption due to the support member 7 being heated by radiant heat from the heat source 3 or the like is suppressed. Here, the same effect can be obtained even if the surface of the support member 7 is heat-insulated or mirror-finished instead of having the reflecting member 9.

  The pressure roller 4 is provided with an elastic layer 4b made of elastic rubber on a cored bar 4a, and a release layer (PFA or PTFE layer) is provided on the surface in order to obtain releasability. The pressure roller 4 is rotated by a driving force transmitted through a gear from a driving source such as a motor provided in the image forming apparatus. The pressure roller 4 is pressed against the fixing belt 1 by a spring or the like, and has a predetermined nip width when the elastic layer 4b is crushed and deformed. The pressure roller 4 may be a hollow roller, and the pressure roller 4 may have a heating source such as a halogen heater. The elastic layer 4b may be solid rubber, but if there is no heater inside the pressure roller 4, sponge rubber may be used. Sponge rubber is more desirable because it increases heat insulation and makes it difficult for the fixing belt to lose heat.

  The fixing belt 1 is rotated by the pressure roller 4. In the case of FIG. 2, the pressure roller 4 is rotated by a driving source (not shown), and the driving force is transmitted to the belt at the nip portion N, whereby the fixing belt 1 is rotated. The fixing belt 1 is sandwiched at the nip portion N and can be rotated, and travels while being guided by the holding member 8 (flange) at both ends other than the nip portion. With such a configuration, it is possible to realize a fixing device that is inexpensive and has a fast warm-up.

  In the configuration of FIG. 2, an example in which there are two halogen heaters as the heat source 3 is shown. In the figure, 4a is a core of the pressure roller 4, 4b is an elastic layer, 6 is a nip forming member inside the fixing belt 1, 7 is a supporting member, 9 is a reflecting member, 10 is a light shielding member, and N is a nip portion. .

The configuration of this fixing device will be described in more detail with reference to FIG.
FIG. 3 shows the positional relationship between the heating width of the heat source 3 installed in the longitudinal direction of the fixing belt 1 formed of an endless belt constituting the fixing sleeve and the temperature sensor as the temperature control means at each location in the configuration of FIG. FIG. 3 is a schematic diagram when the image is viewed from the lower direction in FIG. 2.

  The central region of the fixing belt 1 is heated by the central heater 3a, and the temperature is detected by the central temperature control sensor 11, and the temperature is controlled. The end region of the fixing belt 1 is heated by the end heater 3b, the temperature is detected by the end temperature control sensor 12, and the temperature is controlled. That is, the temperature is controlled by lighting control of the heaters 3a and 3b. By adopting such a configuration, a fixing device is configured. Although the illustration of the temperature control device is omitted, the end temperature control sensor itself may incorporate the control device.

  Here, when the paper P having the paper width as shown in FIG. 4 is passed, there is a problem that the temperature control position of the fixing belt 1 protrudes outside the paper passing area. That is, the contribution to the paper temperature by the edge heater 3b cannot be clearly detected at the edge side portion in the paper passing direction of the paper whose temperature is detected by the edge temperature control sensor 12. It is easy to operate just to maintain a constant temperature. Accordingly, the amount of heat supplied from the end heater 3b is reduced. On the other hand, since the paper P also passes through the heating area of the end heater 3b, the same amount of heat as in the normal fixing operation is required in the paper passing area. As a result, the amount of heat is insufficient in the above-described protruding region, and fixing defects are likely to occur.

In this embodiment, when the paper P having such a size is passed, regardless of the temperature detection result of the fixing belt 1 by the end temperature control sensor 12, the end heater 3b defines the fixing belt 1. Supply an amount of heat. The amount of heat to be supplied is determined so as to be an appropriate amount of heat depending on the environmental temperature, environmental humidity, paper temperature, and paper thickness. For example, the amount of heat supplied may be defined by a conversion formula with environmental temperature, environmental humidity, paper temperature, etc. as variables for each paper thickness, or the amount of heat necessary for fixing is measured in advance. They may be stored in the image forming apparatus as a table, and the necessary amount of heat may be obtained as appropriate. That is, in a use condition in which a temperature change occurs outside the heat supply range controlled by the temperature control sensors 11 and 12 that are temperature control means, the amount of heat supplied from the heaters 3a and 3b is obtained from the temperature information obtained from the temperature control sensor. It is determined under predetermined conditions other than the conditions.

  That is, the amount of heat supplied from the heat source 3 is determined by conditions other than the temperature information obtained from the temperature control sensors 11 and 12. In the case of use conditions where the temperature control position of the heat source 3 is outside the sheet passing area and the paper P passes through the heating area other than the temperature control position of the heating source, the temperature control of the heat source 3 occurs. And supply the specified amount of heat that would be needed. Thereby, even when the paper is passed within the heating width other than the control position related to heating, the fixability can be ensured.

  The amount of heat supplied also depends on the heat storage state as a unit of the fixing device. In passing paper after mass printing, the amount of heat required for fixing is small, while in passing paper from a state where the fixing device is cooled, the amount of heat required for fixing is large. Therefore, the heat storage state of the fixing unit may be determined by a temperature sensor installed in the image forming apparatus or in the fixing device, and the supplied heat amount may be changed as appropriate. Further, when a non-contact temperature sensor is used as the temperature sensor, there is a type that detects the temperature by measuring the ambient temperature as the non-contact temperature sensor. In that case, the heat storage state of the fixing unit may be determined using the ambient temperature of the non-contact temperature sensor.

If it is difficult to determine the heat storage state of the fixing unit by the temperature control sensors 11 and 12 as described above, the amount of heat supplied may be appropriately changed by the following method as another means.
(1) The paper passing time in the previous job and the elapsed time from the end of the previous job can be used. The longer the sheet passing time for the previous job, the more heat is stored in the fixing device. Further, as the elapsed time from the end of the previous job is shorter, the fixing device enters the next job while the heat is stored. In this case, the amount of heat necessary for fixing is not changed, but the amount of heat supplied is reduced.
(2) Also, the number of sheets to be passed or the passing time before the specified time before the next job is used. The heat storage state of the fixing unit is determined based on how much paper is passed within the specified time immediately before.
(3) It is also possible to use the number of sheets that have been passed so far, or the passing time. The heat storage state of the fixing unit is determined based on how much paper is passed that day.

  For example, in the case of a fixing device having a two-heater configuration as shown in FIG. 2, the central temperature control sensor 11 for controlling the temperature of the central heater 3a is installed in the sheet passing area. In this case, the central temperature control sensor 11 performs temperature control as in the past, and the supplied heat amount is appropriately changed while monitoring, so that the image formation at that time is performed rather than supplying the specified amount by the end temperature control sensor 12. According to the situation, the fixing operation can be realized with a more appropriate amount of heat. Therefore, for example, it is also an effective means to appropriately define the amount of heat supplied to the heater (lighting duty) with reference to the amount of heat supplied (lighting duty) of the central heater 3a.

  For example, when the same lighting duty is output by the end heater 3b with respect to the lighting duty of the central heater 3a, the amount of heat that can be secured is investigated in advance, and the end for securing the same heat amount as the central heater. Just find the heater lighting duty. With that alone, the amount of heat supplied to the end heater can be controlled appropriately in accordance with the usage status of the image forming apparatus. For example, in order to ensure the same amount of heat (to keep the fixing sleep surface temperature constant), the end heater needs a lighting duty 1.2 times that of the central heater, and the like. By always ensuring a lighting duty 1.2 times that of the central heater, it is possible to secure the heat amount and the fixing property of the sheet edge by means other than the output of the edge temperature control sensor. When reflecting actual control, the effect of soft start / soft stop and lighting duty is 100%, so the upper limit is 100%. It becomes.

  Further, when this embodiment is used, offset (both cold offset and hot offset) can be prevented. However, since the specified heat amount is supplied, the temperature rises in the non-sheet passing region. For this reason, when continuously passing paper, it is necessary to pass the paper while dissipating heat with a gap between the papers, which has been conventionally taken as a countermeasure for increasing the end temperature. As a specific means for spacing the paper, for example, the output value of the temperature sensor that detects the temperature in the corresponding region (edge temperature control sensor in FIG. 3) is used. There is a means to delay the time until image formation and to leave a gap between papers. Alternatively, if there is a temperature sensor installed in the non-sheet passing region and for detecting the temperature of the pressure roller, the output value may be used. In addition, as a means for spacing between sheets, a control may be used that does not perform control based on the temperature detection result, for example, a gap between sheets after a specified time from the start of sheet passing. As is well known, cold offset occurs when the amount of heat is insufficient, and hot offset occurs when the amount of heat is excessive.

Further, as to how much paper space should be left, the time between papers (time until the next image formation) may be defined according to the following contents.
(1) When the temperature sensor that detects the temperature of the corresponding area has decreased to the fixing target temperature, the next image formation is started.
(2) When the temperature sensor that detects the temperature in the corresponding region has decreased to a temperature that is higher than the fixing target temperature by a specified value, the next image formation is started. Productivity can be secured.
(3) Regardless of the output of the temperature sensor that detects the temperature in the corresponding area, a predetermined time is always ensured between the sheets, and the sheet is passed at that timing. Here, the prescribed time may be appropriately changed depending on the environmental temperature and humidity, the unit heat storage state, and the like.

Although the above describes the operation during the fixing operation (passing through the printing paper), the method for defining the amount of heat from the heating source is applicable to other methods regardless of the temperature detection result of the temperature control sensor. can do. An example is shown below.
(1) Prevention of offset due to edge temperature drop at start-up As described above, if the longitudinal deviation occurs in the heat capacity due to the structure of the pressure member (or other structure around the fixing member), the heat capacity is large. On the side, a temperature drop occurs in the heating region other than the temperature control position. Therefore, it is possible to use means such as supplying a specified amount of heat from a heating source for a certain time regardless of the output result of the temperature control sensor. In this case, it is desirable to define the heating time by, for example, the environmental temperature or the power supply voltage.
(2) When the airflow flows more strongly than during normal use If the machine's internal temperature rises excessively, such as when performing large-scale printing, increase the fan speed (increase the flow rate) compared to normal operation. Is used as a means. In that case, since the cooling of the fixing device is also promoted, deviation is likely to occur in the longitudinal direction of the fixing member after the cooling. Even if the amount of heat is applied uniformly in the longitudinal direction thereafter, the previous deviation in the longitudinal direction remains as the temperature deviation of the fixing member. Then, an end offset occurs in the subsequent sheet passing at the end of the fixing member where the temperature is extremely cooled. In order to deal with such a problem, a means such as supplying a prescribed amount of heat from a heating source for a certain time can be used regardless of the output result of the temperature control sensor. In this case, it is desirable to define the heating time by, for example, the environmental temperature and the cooling time.

<Embodiment 2>
FIG. 5 is an explanatory diagram showing the configuration of the fixing device according to the second embodiment of the present invention. In this embodiment, the heat source 3 is composed of three halogen heaters. The third halogen heater is provided because the target paper size is different. Depending on the size of the paper to be passed, the paper passes through an area other than the part where the temperature control sensor is arranged. In this case, an offset occurs for the above-described reason, and this embodiment is an effective prevention means for this.

<Embodiment 3>
FIG. 6 is an explanatory view showing an embodiment of the light shielding member. The embodiment shown in FIG. 2 includes a light shielding member 10 as illustrated.

  The shape of the light shielding member 10 is a stepped shape as shown in the figure in which a light shielding area is provided in accordance with the width size of each sheet. The light shielding member 10 is arranged so as to rotate in a non-contact manner along the inner side of the fixing belt 1, and is rotated to a position corresponding to various paper widths to shield an area unnecessary for heating. As a result, even when transfer paper with a narrow paper width is continuously passed, the non-sheet passing area does not become overheated, and control such as reducing productivity is required to cancel the overheated area. There is no. Accordingly, the number of halogen heaters can have the same function as that of the three-piece configuration shown in FIG. 5 even in the two-piece configuration shown in FIG.

  In addition, although the number of heaters can be reduced, in the case of a unit aiming at further miniaturization, this stepped shape cannot be provided with an infinite number of steps due to space reasons. In that case, it is an effective offset countermeasure means even in a fixing device equipped with the light shielding member shown in FIG.

<Embodiment 4>
The configuration of the image forming apparatus using the fixing device according to the embodiment of the present invention described above will be described with reference to FIG.
The image forming apparatus shown in FIG. 7 is a color printer that uses a tandem system in which image forming units that form a plurality of color images are juxtaposed along the belt extending direction. However, the present invention is not limited to this method, and can be applied not only to a printer but also to a copying machine, a facsimile machine, and the like.

  In FIG. 6, an image forming apparatus 100 includes photosensitive drums 20Y, 20C, 20M as image carriers that can form images as images corresponding to colors separated into yellow, cyan, magenta, and black, respectively. A tandem structure with 20 Bk arranged side by side is adopted.

  The image forming apparatus 100 having the configuration illustrated in FIG. 7 includes the photosensitive drums 20Y to 20Bk. A primary transfer process is performed on an endless belt (intermediate transfer member: hereinafter referred to as a transfer belt) 110 in which the visible images formed on the respective photosensitive drums 20Y to 20Bk can move in the direction of the arrow A1 while facing each other. This is executed and each image is superimposed and transferred. Thereafter, the recording sheet S using a recording sheet or the like is batch-transferred by executing a secondary transfer process.

  Around each photosensitive drum, an apparatus for image forming processing is arranged according to the rotation of the photosensitive drum. Now, the photosensitive drum 20Bk that performs black image formation will be described. The charging device 30Bk, the developing device 40Bk, the primary transfer roller 12Bk, and the cleaning device 50Bk that perform image forming processing along the rotation direction of the photosensitive drum 20Bk are described. Has been placed. For the writing performed after charging, the optical writing device 80 is used.

  The superimposed transfer on the transfer belt 110 is performed in the process in which the transfer belt 110 moves in the A1 direction. The visible image formed on each of the photoconductive drums 20Y to 20Bk is transferred so as to be superimposed on the same position of the transfer belt 110. Therefore, the timing is shifted from the upstream side toward the downstream side in the A1 direction by voltage application by the primary transfer rollers 12Y to 12Bk arranged to face the respective photosensitive drums 20Y to 20Bk with the transfer belt 110 interposed therebetween. The photosensitive drums 20Y to 20Bk are arranged in this order from the upstream side in the A1 direction. Each of the photosensitive drums 20Y to 20Bk is provided in an image station for forming yellow, cyan, magenta, and black images.

  The image forming apparatus 100 includes four image stations that perform image forming processing for each color. The photoconductor drums 20Y to 20Bk are arranged to face each other and include a transfer belt unit 101 including a transfer belt 110 and primary transfer rollers 12Y to 12Bk. The image forming apparatus further includes a secondary transfer roller 5 that is disposed opposite to the transfer belt 110 and is a transfer roller that is driven by the transfer belt 110 and rotates along with the transfer belt 110. Then, an intermediate transfer belt cleaning device 13 that is disposed to face the transfer belt 110 and cleans the transfer belt 110 is provided. In addition, an optical writing device 80 is provided as an optical writing device arranged to face below the four image stations.

  The optical writing device 80 is equipped with a semiconductor laser as a light source, a coupling lens, an fθ lens, a toroidal lens, a folding mirror, a rotating polygon mirror as a deflecting means, and the like. Writing light Lb corresponding to each color is emitted to each of the photosensitive drums 20Y to 20Bk to form an electrostatic latent image on the photosensitive drums 20Y to 20Bk. In the figure, for convenience, reference numerals are given only to black image stations, but the same applies to other image stations.

  The image forming apparatus 100 includes a sheet feeding device 61 as a paper feeding cassette on which recording sheets S transported between the photosensitive drums 20Y to 20Bk and the transfer belt 110 are stacked. In addition, the transfer section between each of the photosensitive drums 20Y to 20Bk and the transfer belt 110 is fed at a predetermined timing in accordance with the toner image formation timing of the recording sheet S conveyed from the sheet feeding device 61. A registration roller pair 4 that is fed out toward the side is provided. A sensor (not shown) that detects that the leading edge of the recording sheet S has reached the registration roller pair 4 is provided.

  The image forming apparatus 100 includes a fixing device 120 as a roller fixing type fixing unit for fixing the toner image to the recording paper S on which the toner image is transferred. In addition, a paper discharge roller 71 that discharges the fixed recording paper S to the outside of the main body of the image forming apparatus 100, and a paper discharge roller 71 that is disposed on the upper portion of the main body of the image forming apparatus 100 and outside the main body of the image forming apparatus 100. A paper discharge tray 17 on which the discharged recording paper S is stacked is provided. Further, toner bottles 9Y to 9Bk filled with toners of yellow, cyan, magenta, and black are provided below the paper discharge tray 17.

  In addition to the transfer belt 110 and primary transfer rollers 12Y, 12C, 12M, and 12Bk, the transfer belt unit 101 includes a driving roller 72 and a driven roller 73 around which the transfer belt 110 is wound. The driven roller 73 also has a function as a tension urging unit for the transfer belt 110. For this reason, the driven roller 73 is provided with an urging unit using a spring or the like. Such a transfer belt unit 101, the primary transfer rollers 12Y to 12Bk, the secondary transfer roller 5, and the cleaning device 13 constitute a transfer device 70.

  The sheet feeding device 61 is disposed at the lower part of the main body of the image forming apparatus 100, and includes a feeding roller 31 as a paper feeding roller that contacts the upper surface of the uppermost recording paper S. The uppermost recording sheet S is fed toward the registration roller pair 4 when the feeding roller 31 is driven to rotate counterclockwise in the drawing.

  Although not shown in detail, the cleaning device 13 provided in the transfer device 70 has a cleaning brush and a cleaning blade disposed so as to face and contact the transfer belt 110. These clean the transfer belt 110 by scraping and removing foreign matters such as residual toner on the transfer belt 110 with a cleaning brush and a cleaning blade.

  The cleaning device 13 also has a discharge means (not shown) for carrying out and discarding the residual toner removed from the transfer belt 110.

  The present invention is not limited to the embodiments described above, and many variations are possible by those having ordinary knowledge in the art within the technical idea of the present invention.

DESCRIPTION OF SYMBOLS 1 Fixing belt 3a Central heater 3b End heater 3 Heat source 4 Pressure roller 4a Core metal 4b Elastic layer 6 Nip forming member 7 Support member 8 Holding member 9 Reflecting member 10 Light shielding member 11 Central temperature control sensor 12 End temperature control sensor 100 Image forming apparatus N Nip part

JP 2004-286922 A Japanese Patent No. 2861280 JP 2007-334205 A

Claims (8)

A rotatable fixing member;
A heating source for heating the fixing member;
A pressure member that forms a nip with the fixing member;
A nip forming member that faces the pressure member and forms a nip inside the fixing member;
Temperature control means for detecting the temperature of the fixing member and controlling the temperature of the fixing member;
In use conditions in which a temperature change occurs outside the heat supply range of the heating source controlled by the temperature control means, the amount of heat supplied from the heating source is determined in advance other than the temperature information condition obtained from the temperature control sensor. Determined by conditions,
A fixing device. The fixing device according to claim 1,
The use condition in which the temperature change occurs outside the heat supply range of the heating source is a position where the paper passing area is out of the control position by the temperature control means.
A fixing device. The fixing device according to claim 1 or 2,
When the temperature of the fixing member is excessively increased, the temperature is controlled by the temperature control means for controlling the temperature of the fixing member, and the paper is passed through while releasing heat between the sheets to be passed.
A fixing device. The fixing device according to any one of claims 1 to 3,
The amount of heat supplied by the heating source is changed according to the paper thickness of the paper to be passed.
A fixing device. The fixing device according to any one of claims 1 to 4,
Changing the amount of heat supplied by the heating source according to the environmental temperature;
A fixing device. The fixing device according to any one of claims 1 to 5,
Changing the amount of heat supplied by the heating source according to environmental humidity;
A fixing device. The fixing device according to any one of claims 1 to 6,
Changing the amount of heat supplied by the heating source according to the temperature of the paper;
A fixing device. An image forming apparatus using the fixing device according to claim 1.