JP2012145700A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of suitably changing the conveyance interval of a recording medium and preventing the excessive temperature rise in a non-sheet passing region of a fixing belt without lowering the productivity of the recording medium on which a toner image is fixed while suppressing the increase in cost of a fixing device.SOLUTION: The paper passing interval of a storage medium P for conveying to a fixing nip part is changed based on the comparison results between a detection value of an edge temperature sensor 27 and a predetermined threshold value. In addition, the edge temperature sensor 27 detects the temperature at the edge of a fixing belt 21 prior to starting of image formation operation of an image forming job based on the command of the image forming job and the change timing of the paper passing interval of the storage medium P to the fixing nip part is determined based on the detection results. The change timing of the paper passing interval may be determined based on the time elapsed after completion of the previous image forming job.

Description

  The present invention relates to an image forming apparatus such as a fax machine, a printer, or a copier provided with a fixing device.

  Conventionally, as this type of image forming apparatus, the surface of the photoconductor as an image carrier is uniformly charged, and an electrostatic latent image is formed by irradiating the charged photoconductor with an exposure pattern based on print data. An electrophotographic image forming apparatus that forms a toner image by applying toner to an electrostatic latent image on a photosensitive member and developing it is known. The toner image on the photosensitive member is transferred to a recording medium such as paper (transfer paper) and then fixed on the recording medium by being melted and fixed by applying pressure and heat by a fixing device.

  In recent years, the use of electrophotographic image forming apparatuses has become widespread, and has come to cope with various changes in types and sizes of recording media such as paper (transfer paper, sheets). In the fixing device used in the image forming apparatus corresponding to the recording media of various sizes as described above, the temperature of the non-sheet passing region where the recording medium on the surface of the fixing member does not pass when the small size recording medium is passed. Tends to rise. When such a temperature rise in the non-sheet passing region occurs, the fixing member is damaged by the heat, or a difference in the linear expansion of the diameter of the fixing member occurs due to a temperature deviation in the axial direction of the fixing member). There is a risk that the transport quality of the recording medium will be reduced. In addition, there are problems such as deviation in glossiness and occurrence of hot offset when changing from a small size recording medium to a large size recording medium.

  In Patent Document 1, a toner image is recorded by passing a recording medium such as paper (transfer paper, sheet) carrying a toner image between a fixing roller having a built-in heater and a pressure roller in pressure contact with the fixing roller. A fixing device for fixing to a medium, wherein a first heater having a light distribution corresponding to a small-size recording medium and a second heater having a light distribution corresponding to the other end are provided in a sheet passing range. What was divided and installed in is disclosed. In this fixing device, the temperature of the fixing member surface can be controlled by the first heater when the small-size sheet is passed, so that the temperature rise in the non-sheet passing region can be suppressed. However, the number of heaters increases and the fixing device becomes larger. As a result, the heat capacity (power consumption) increases due to an increase in cost and expansion of the fixing device.

  In addition, under the background of energy saving in recent years, development of an energy-saving type fixing device in which heat transfer efficiency from a heat source to a fixing member is increased. In such an energy-saving type fixing device, the amount of heat diffusion in the width direction of the fixing member is reduced, and the temperature rise in the non-sheet passing region where the recording medium does not pass is remarkable. For excessive temperature rise in the non-sheet passing area, the sheet passing interval, which is the interval for transporting the recording medium, is lengthened to suppress the supply of heat to the fixing member and to the sheet passing area of the fixing member and the pressure member. Measures to diffuse heat are generally adopted. The switching of the sheet passing interval is performed based on the maximum temperature of the non-sheet passing region, for example. Although the position of the highest temperature in the non-sheet passing area varies depending on the size of the transfer paper, in order to suppress an increase in cost, based on the temperature detection result of the end temperature sensor provided at an arbitrary position in the width direction end of the fixing member, A configuration for predicting the maximum temperature in the non-sheet passing region has been proposed. The rate of temperature rise differs between the position of the highest temperature in the non-sheet passing area and the temperature detection position of the end temperature sensor, and the position of the highest temperature has higher sensitivity. That is, the temperature rise rate is higher at the highest temperature position than at the temperature detection position of the end temperature sensor. For this reason, in the energy-saving type fixing device in which the temperature rise in the non-sheet passing region is remarkable, the threshold value of the edge temperature sensor output that defines the timing for changing the sheet passing interval is set to be low. However, if the threshold value of the edge temperature sensor output is set to a low value, the temperature of the edge temperature is increased due to the overshoot of the temperature change at the start of printing even though the temperature rise in the non-sheet passing area does not occur before the sheet passing. There exists a subject that a sensor will detect temperature more than a threshold value and will change productivity and reduce productivity.

  The present invention has been made in view of the above problems, and an object of the present invention is to convey a recording medium without reducing the productivity of the recording medium on which the toner image is fixed while suppressing an increase in the cost of the fixing device. It is an object of the present invention to provide an image forming apparatus capable of appropriately changing the interval and preventing an excessive temperature rise in a recording medium non-passage area of a fixing member.

To achieve the above object, the invention of claim 1 comprises a toner image forming means for forming a toner image on a recording medium, and a fixing device for fixing the toner image on the recording medium, wherein the fixing device comprises: An image forming apparatus comprising: an endless fixing member that is movable on the surface; a pressure member that is rotatably driven so as to face the fixing member; and a heat source that generates heat for heating the fixing nip portion. Comparing the detected value of the end temperature detecting means with a preset threshold value, the end temperature detecting means for detecting the temperature of the end in the width direction intersecting the moving direction of the surface of the fixing member And a control unit that changes a conveyance interval of the storage medium conveyed to the fixing nip portion, and the control unit starts an image forming operation of the image forming job based on an instruction of the image forming job. Before, before The temperature of the end of the fixing member is detected by the end temperature detecting means, and the change timing of the conveyance interval of the storage medium to the fixing nip is determined based on the detection result. It is.
According to a second aspect of the present invention, there is provided a toner image forming means for forming a toner image on a recording medium, and a fixing device for fixing the toner image on the recording medium. An image forming apparatus comprising: a fixing member having a shape; a pressure member that is rotatably driven so as to face the fixing member; and a heat source that generates heat for heating the fixing nip portion. Based on the comparison result between the end temperature detecting means for detecting the temperature of the end in the width direction intersecting the moving direction of the surface of the member, and the detection value of the end temperature detecting means and a preset threshold value, Control means for changing the conveyance interval of the storage medium to be conveyed to the nip portion, and the control means before the image forming operation of the image forming job is started based on the command of the image forming job. Forming job Based on the time elapsed since After the completion, it is characterized in that to determine the change timing of the transport distance of the storage medium to the fixing nip portion.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the control unit changes the threshold value based on a target temperature heated by the heat source.
According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the control unit changes the threshold based on a thickness of the recording medium.
According to a fifth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the control unit changes the threshold based on a toner consumption amount in the image forming unit.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the fixing member is a flexible member, and the fixing device is connected to the additional member via the fixing member. A pressure receiving member that receives pressure from the pressure member is provided.

According to the present invention, the fixing member is controlled by changing the conveyance interval of the storage medium conveyed to the fixing nip portion based on the comparison result between the detection value of the end temperature detection means and a preset threshold value. Excessive temperature rise in the non-passing area of the recording medium is suppressed. Then, before starting the image forming operation of the image forming job based on the command of the image forming job, control is performed so as to determine the change timing of the conveyance interval of the storage medium to the fixing nip portion. For example, the temperature of the end of the fixing member is detected by the end temperature detecting means before the image forming operation of the image forming job is started, and the storage medium is stored in the fixing nip portion based on the detection result. The change timing of the conveyance interval is determined. Alternatively, before starting the image forming operation of the image forming job, the timing for changing the conveyance interval of the storage medium to the fixing nip portion is determined based on the time elapsed after the end of the previous image forming job. If it is likely that overshooting of the temperature of the fixing member will occur due to the determination of the change timing of the conveyance interval as described above, the end of the fixing member by the end temperature detecting means may occur. Based on the temperature detection result and the time elapsed since the end of the previous image forming job, control can be performed so as not to change the storage medium conveyance interval. Accordingly, it is possible to prevent the conveyance interval of the storage medium from being changed based on erroneous detection of a temperature increase in the non-passage area of the recording medium due to the overshoot of the fixing member temperature at the start of the image forming operation. On the other hand, if the time has not elapsed since the previous image forming operation and there is no risk of overshooting of the fixing member temperature, the temperature at the temperature detection position of the end temperature detection means in the recording medium non-passing area is The image forming operation starts from a high state. In this case, the change in the conveyance interval of the storage medium is continued based on the detection result of the temperature of the end of the fixing member by the end temperature detecting means and the time elapsed since the end of the previous image forming job. Can be controlled. Thus, regardless of the elapsed time from the previous image forming operation, it is possible to detect the temperature rise in the recording medium non-passing area with high accuracy without being affected by the overshoot at the start of the image forming operation. Therefore, it is possible to appropriately perform control for changing the conveyance interval of the storage medium based on the comparison result between the detected value of the temperature of the recording medium non-passing area and the threshold, and excessive temperature in the recording medium non-passing area of the fixing member. The rise can be prevented.
In addition, since there is no need to provide a plurality of temperature detection means corresponding to each position where the maximum temperature is generated in the recording medium non-passage area that changes according to the size of the recording medium, an increase in the cost of the fixing device can be suppressed. . In addition, since the conveyance interval of the storage medium is not changed unnecessarily, the productivity of the recording medium on which the toner image is fixed does not decrease.

1 is a schematic configuration diagram of an image forming apparatus including a fixing device according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram illustrating a configuration example of a fixing device of the image forming apparatus. FIG. 3 is a diagram of the inside of the fixing device as viewed from above, and is an explanatory diagram showing a sheet passing area and a non-sheet passing area in the fixing belt. The graph which shows an example of each time transition of the temperature of the maximum temperature of a non-sheet passing area | region, and the temperature of the temperature detection position of an edge part temperature sensor. FIG. 3 is a block diagram illustrating an example of a main part of a control system that controls the fixing device according to the exemplary embodiment. 6 is a graph showing a temperature transition when the sheet passing interval is changed in accordance with the output of the end temperature sensor in the fixing device of the present embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an image forming apparatus including a fixing device according to an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment is a tandem type color printer. Four bottles 102Y, 102M, 102C, and 102K corresponding to the respective colors (yellow, magenta, cyan, and black) are detachably (replaceable) installed in the bottle housing portion 101 above the image forming apparatus main body 1. ing. An intermediate transfer unit 85 is disposed below the bottle housing portion 101. Image forming portions 4Y, 4M, 4C, and 4K corresponding to the respective colors (yellow, magenta, cyan, and black) are arranged in parallel so as to face an intermediate transfer belt 78 as an intermediate transfer member of the intermediate transfer unit 85. . These image forming units 4Y, 4M, 4C, and 4K and an intermediate transfer unit 85, as well as an exposure unit 3 described later, first transfer bias rollers 79Y, 79M, 79C, and 79K, a secondary transfer backup roller 82, and a secondary transfer roller 89 Etc. constitute toner image forming means for forming a toner image on the recording medium P.

  In each of the image forming units 4Y, 4M, 4C, and 4K, photosensitive drums 5Y, 5M, 5C, and 5K are disposed as image carriers. In addition, around each of the photosensitive drums 5Y, 5M, 5C, and 5K, a charging unit 75 as a charging unit, a developing unit 76 as a developing unit, a cleaning unit 77 as an image carrier cleaning unit, and a neutralizing unit, respectively. The static elimination part (not shown) etc. of this are arrange | positioned. Then, an image forming process (charging process, exposure process, developing process, transfer process, cleaning process) is performed on each of the photosensitive drums 5Y, 5M, 5C, and 5K. Each color image (toner image) is formed on 5K.

  The photosensitive drums 5Y, 5M, 5C, and 5K are rotationally driven in a clockwise direction in FIG. 1 by a drive motor (not shown). Then, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are uniformly charged at the position of the charging unit 75 (charging process). Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the irradiation position of the laser light L emitted from the exposure unit 3 as an exposure unit, and electrostatic scanning corresponding to each color is performed by exposure scanning at this position. A latent image is formed (exposure process). The surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K on which the electrostatic latent image is formed reach a position facing the developing device 76, and the electrostatic latent image is developed at this position, so that each color toner image is developed. Formed (development process). The surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K on which the toner images are formed reach positions facing the intermediate transfer belt 78 and the first transfer bias rollers 79Y, 79M, 79C, and 79K as primary transfer means, At this position, the toner images on the photosensitive drums 5Y, 5M, 5C, and 5K are transferred onto the intermediate transfer belt 78 (primary transfer process). At this time, a small amount of untransferred toner remains on the photosensitive drums 5Y, 5M, 5C, and 5K. Thereafter, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach a position facing the cleaning unit 77, and untransferred toner remaining on the photoconductive drums 5Y, 5M, 5C, and 5K is removed at this position. It is mechanically recovered by a cleaning blade 77 (cleaning process). Finally, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach a position facing a neutralization unit (not shown), and the residual potential on the photoconductive drums 5Y, 5M, 5C, and 5K is removed at this position. The Thus, a series of image forming processes performed on the photosensitive drums 5Y, 5M, 5C, and 5K is completed. The toner images of the respective colors formed on the photosensitive drums through the development process are transferred onto the intermediate transfer belt 78 in an overlapping manner. As a result, a color image is formed on the intermediate transfer belt 78.

  The intermediate transfer unit 85 includes an intermediate transfer belt 78, four primary transfer bias rollers 79Y, 79M, 79C, and 79K, a secondary transfer backup roller 82, a cleaning backup roller 83, a tension roller 84, and an intermediate transfer member cleaning unit. The transfer cleaning unit 80 and the like are included. The intermediate transfer belt 78 is stretched and supported by the three rollers 82 to 84 and is endlessly moved in the direction of the arrow in FIG. The four primary transfer bias rollers 79Y, 79M, 79C, and 79K sandwich the intermediate transfer belt 78 with the photosensitive drums 5Y, 5M, 5C, and 5K, respectively, thereby forming primary transfer nips. Then, a transfer bias reverse to the polarity of the toner is applied to the primary transfer bias rollers 79Y, 79M, 79C, and 79K. The intermediate transfer belt 78 travels in the direction of the arrow and sequentially passes through the primary transfer nips of the primary transfer bias rollers 79Y, 79M, 79C, and 79K. In this way, the toner images of the respective colors on the photosensitive drums 5Y, 5M, 5C, and 5K are primarily transferred while being superimposed on the intermediate transfer belt 78. The intermediate transfer belt 78 on which the toner images of the respective colors are transferred in a superimposed manner reaches a position facing the secondary transfer roller 89. At this position, the secondary transfer backup roller 82 sandwiches the intermediate transfer belt 78 between the secondary transfer roller 89 and forms a secondary transfer nip. The four-color toner images formed on the intermediate transfer belt 78 are transferred onto a recording medium P such as paper (transfer paper) conveyed to the position of the secondary transfer nip. At this time, untransferred toner that has not been transferred to the recording medium P remains on the intermediate transfer belt 78. Thereafter, the intermediate transfer belt 78 reaches the position of the intermediate transfer cleaning unit 80. At this position, the untransferred toner on the intermediate transfer belt 78 is collected. Thus, a series of transfer processes performed on the intermediate transfer belt 78 is completed.

  The recording medium P transported to the position of the secondary transfer nip is transported from the paper feed unit 12 disposed below the image forming apparatus main body 1 via the paper feed roller 97, the registration roller pair 98, and the like. Is. Specifically, a plurality of recording media P such as paper (transfer paper) are stored in the paper supply unit 12 in an overlapping manner. When the paper feed roller 97 is rotationally driven in the counterclockwise direction in FIG. 1, the uppermost recording medium P is fed between the rollers of the registration roller pair 98. The recording medium P conveyed to the registration roller pair 98 is temporarily stopped at the position of the roller nip of the registration roller pair 98 that has stopped rotating. Then, the registration roller pair 98 is rotationally driven in synchronization with the color image on the intermediate transfer belt 78, and the recording medium P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the recording medium P. Thereafter, the recording medium P on which the color image is transferred at the position of the secondary transfer nip is conveyed to a fixing position by the fixing device 20. At this position, the color image transferred from the photosensitive drum is fixed on the recording medium P by heat and pressure generated by the fixing belt 21 and the pressure roller 31. Thereafter, the recording medium P is discharged out of the apparatus through a pair of paper discharge rollers 99. The recording medium P discharged out of the apparatus by the discharge roller pair 99 is sequentially stacked on the stack unit 100 as an output image. Thus, a series of image forming processes in the image forming apparatus 1 is completed.

  FIG. 2 is a schematic configuration diagram illustrating a configuration example of the fixing device 20 installed in the image forming apparatus 1. As shown in FIG. 2, the fixing device 20 includes a fixing belt 21 as an endless fixing member that can move on the surface, a pressure roller 31 that is a pressure rotating member that can be driven to rotate as a pressure member, and a fixing belt 21. And a pressure receiving member that receives pressure from the pressure roller 31 via the.

  The pressure roller 31 is provided so as to face the fixing belt 21 and is pressed against the outer peripheral surface of the fixing belt 21 by a pressing means such as a spring or a leaf spring (not shown). The pressure roller 31 has, for example, a diameter of 25 to 30 mm and an elastic layer formed on a hollow or solid cored bar. The elastic layer of the pressure roller 31 is formed of a material such as foamable silicone rubber, silicone rubber, or fluorine rubber, for example. A thin release layer made of a resin such as PFA (tetrafluoroethylene bar fluoroalkyl vinyl ether copolymer) or PTFE (tetrafluoroethylene) can also be provided on the surface layer of the elastic layer. The pressure roller 31 is in pressure contact with the fixing belt 21 to form a desired fixing nip portion between both members. The pressure roller 31 is provided with a gear that meshes with the drive gear of the drive mechanism, and the pressure roller 31 is rotationally driven in the direction of the arrow (clockwise). In addition, both ends of the pressure roller 31 in the width direction are rotatably supported on the side plate of the fixing device 20 via bearings. In the case of a pressure roller using a hollow cored bar, a heat source such as a halogen heater (halogen lamp) can be provided inside the cored bar.

  The pressure receiving member receives pressure from the pressure roller 31 and presses the fixing belt 21 and the pressure roller 31 to form a fixing nip portion. The pressure receiving member includes a nip forming member 22 facing the inner peripheral surface of the fixing belt 21 and a support stay 23 as a supporting member for supporting the nip forming member 22 from the side opposite to the fixing nip portion. The nip forming member 22 is constituted by a member obtained by winding a fluororubber or the like with a sheet made of PTFE (tetrafluoroethylene) resin, for example. Further, the support stay 23 also functions as a reinforcing member that increases the strength of the pressure receiving member.

  A pressure receiving member including the nip forming member 22 and the support stay 23 is disposed inside the fixing belt 21 together with a heat conduction pipe 24 as a heat transfer member and a heater 25 as a heat source.

  The fixing belt 21 is a thin and flexible endless belt, and rotates (runs) in an arrow direction (counterclockwise direction) in the drawing. The fixing belt 21 is formed by sequentially laminating an elastic layer and a release layer on a base material, and the entire thickness thereof is set to a predetermined thickness (for example, 1 mm) or less. The base material of the fixing belt 21 has a layer thickness of 20 to 70 μm, for example, and is formed of a metal material such as nickel or stainless steel or a resin material such as polyimide.

  The elastic layer of the fixing belt 21 has a layer thickness of 100 to 300 μm, for example, and is formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber. By providing the elastic layer, minute irregularities on the surface of the fixing belt 21 in the fixing nip portion are not formed, and heat is uniformly transmitted to the toner image T on the recording medium P, so that generation of a scum skin image is suppressed.

  The release layer of the fixing belt 21 has a layer thickness of 5 to 50 μm, for example, and includes PFA (tetrafluoroethylene / fluorofluorovinylvinylether copolymer) resin, PTFE (tetrafluoroethylene) resin, polyimide, and polyether. It is formed of a material such as imide or PES (polyether sulfide). By providing the release layer, releasability (peelability) for the toner T (toner image) is ensured. The diameter of the fixing belt 21 is set within a range of 15 to 120 mm, for example. In the present embodiment, the diameter of the fixing belt 21 is set to 30 mm.

  Inside the fixing belt 21 (inner peripheral surface side), a heater 25, a support stay 23, and the like are fixed. The fixing belt 21 is pressed by the support stay 23 to form a fixing nip portion with the pressure roller 31. Further, it is desirable to apply a black heat resistant coating that easily absorbs radiant heat from the heater 25 on the inner peripheral surface of the fixing belt 21.

  The heat conduction pipe 24 is provided so as to be in contact with the inner peripheral surface of the fixing belt 21 and transmits heat of the heater 25 to the fixing belt 21. The heat conduction pipe 24 is made of, for example, a base material such as SUS or Ni, and the shape in a cross section perpendicular to the axis extending in the longitudinal direction (width direction) has a C-shaped arc shape. The end of the heat conduction pipe 24 on the pressure roller side is formed so as to accommodate the nip forming member 22, and the support stay 23 supports the nip forming member 22 through the end of the heat conduction pipe 24. It is configured as follows. Note that it is desirable to apply a fluorine-based sliding coating to the outer peripheral surface of the heat conducting pipe 24 in contact with the fixing belt 21.

  The heater 25 is a heat source that generates heat for heating the fixing nip portion. In this embodiment, an infrared heater composed of a halogen heater (halogen lamp) is used as the heater 25, but an infrared heater such as a carbon heater may be used. Further, both ends of the heater 25 are fixed to the side plate of the fixing device 20, and the output of the heater 25 is controlled by a power supply unit or a controller of the main body of the image forming apparatus 1. The fixing belt 21 is heated by the radiant heat from the heater 25, and heat is applied to the toner image T on the recording medium P from the surface of the heated fixing belt 21.

  The output control of the heater 25 is performed, for example, by arranging a temperature sensor such as a thermopile facing the surface (outer peripheral surface) of the fixing belt 21 and detecting the belt surface temperature by the temperature sensor. Further, the output control of the heater 25 is performed by bringing a temperature sensor such as a contact type thermistor into contact with the inner peripheral surface of the fixing belt 21 in a region inside the fixing belt 21 where light from the heater 25 is blocked by the support stay 23. You may arrange | position so that it may carry out based on the temperature detection result of the temperature sensor. By such output control of the heater 25, the temperature (fixing temperature) of the fixing belt 21 can be set to a desired target temperature. Further, by directly heating the fixing belt 21 with the heater 25, the heat capacity can be reduced, and further warm-up can be shortened and energy can be saved.

  In the fixing device 20 having the above configuration, when the heater 25 generates heat, the heat conduction pipe 24 is heated, and heat is transmitted to the fixing belt 21 in contact with the heat conduction pipe 24. In order to efficiently transfer heat from the heat conduction pipe 24 to the fixing belt 21, contact between the heat conduction pipe 24 and the fixing belt 21 is important. When the heat conduction pipe 24 and the fixing belt 21 are not in contact with each other locally, they are insulated by the air layer, and the heat supply to the fixing belt 21 is insufficient, so that further heating is required, leading to a reduction in energy saving. Moreover, since the heat conduction pipe 24 is overheated, the durability of the coating film on the surface is also affected. Therefore, the shape of the heat conduction pipe 24 is an important factor that determines energy saving and durability.

  The fixing belt 21 is sandwiched between the pressure member 11 and the nip forming member 22. When the pressure member 11 is rotated by a driving source (not shown), the fixing belt 21 is also rotated by the reaction force of the frictional force. If this frictional force is small, the fixing belt 21 slips, and heat is not diffused by rotation, so that heat is locally supplied, which causes ignition. Further, the transportability of the recording medium P is lowered, and a deviation occurs in the amount of heat supplied, resulting in image quality abnormalities such as poor fixing and gloss deviation. As described above, in order to efficiently transfer heat from the heat conduction pipe 24 to the fixing belt 21, contact between the heat conduction pipe 24 and the fixing belt 21 is important. As the rotational load increases, slip problems arise.

  Therefore, in this embodiment, in order to prevent the fixing belt 21 from slipping, grease is applied to the inner surface of the fixing belt 21 to reduce the frictional resistance. Further, the frictional resistance is reduced by coating the inner surface of the fixing belt 21 and the outer surface of the heat conduction pipe 24 with a low sliding coating film. The load when the fixing belt 21 is rotated in the tangential direction is preferably 2000 g or less.

  In the fixing device 20 configured as described above, the recording medium P on which an image is formed by the toner T is fixed by the pressure of the pressure member 11 and the heat of the fixing belt 21 at the fixing nip portion. The fixing belt 21 whose temperature has been lowered by the fixing operation is heated again by the heater 25, and ON / OFF control of the heater 25 is performed so as to be stabilized at the target temperature.

  In this embodiment, an infrared heater 25 such as a halogen heater is used as a heat source. However, if the structure can heat the upstream side of the fixing nip portion of the heat conduction pipe 24 in the recording medium conveyance direction, induction heating is used. Further, heating means such as a resistance heating element may be used.

  The fixing device 20 includes a belt fixing method (a method in which a belt wound around a fixing roller and a heating roller and a pressure roller are in contact with each other), a roller / roller fixing method (a fixing roller and a pressure). It is also possible to use a method in which the rollers are in contact with each other. Further, from the viewpoint of energy saving, it is desirable that each roller has a small diameter and a thin wall.

  FIG. 3 is a view of the inside of the fixing device 20 according to the present embodiment as viewed from above, and shows a sheet passing area (recording medium passing area) and a non-sheet passing area (recording medium non-passing area) in the fixing belt 21. FIG. In the fixing device 20 of the present embodiment, the heater 25 incorporated in the fixing belt 21 includes a central heater 25 a that heats the central portion of the fixing belt 21 in the width direction by the partial heat generating portion 25 a ′, and the width direction of the fixing belt 21. The end heaters 25b are used to heat the both end portions of each of the two end portions with a partial heat generating portion 25b ′. Further, as temperature detecting means for detecting the temperature of the fixing belt 21, a central temperature sensor 26 as central part temperature detecting means for detecting the temperature of the central part in the width direction of the fixing belt 21, and an end in the width direction of the fixing belt 21. And an end temperature sensor 27 as end temperature detecting means for detecting the temperature of the section. The fixing device 20 of the present embodiment employs a twin heater system that controls the central heater 25a and the end heater 25b, respectively. When a large-size sheet is passed, both the central heater 25a and the end heater 25b are lit. When a small size is passed, only the central heater 25a is turned on to control the temperature.

  Note that the sheet passing area in the drawing is such that the A4 size recording medium P, which is frequently used among small sizes, is conveyed in the longitudinal direction (vertical direction) (hereinafter referred to as “A4 portrait passing sheet”). In this case, the area where the recording medium P faces is shown. Further, the non-sheet passing area in the figure indicates an area where the recording medium P does not face in the case of A4 vertical sheet passing. The heater length Lc of the central heater 25a is set based on A4 longitudinal paper or LT longitudinal paper, which is frequently used even in a small size, in order to prevent deterioration in fixing property due to temperature sag at the heater end. , A4 longitudinal paper or LT longitudinal paper is set slightly longer. Here, the LT longitudinal paper is a paper that conveys the letter-size recording medium P in the longitudinal direction (longitudinal direction).

  The central heater 25 a is controlled according to the output of the central temperature sensor 26, and the end heater 25 b is controlled according to the output of the end temperature sensor 27. The edge temperature sensor 27 also has a function of detecting a temperature rise in the non-sheet passing area. In the present embodiment, a non-contact type thermopile is used for the central temperature sensor 26, and a non-contact type thermistor is used for the end temperature sensor 27.

  Further, when the small size paper is passed, only the central heater 25a is turned on, and the temperature of the heater portion that is slightly longer than the paper size is highest in the non-paper passing area as shown in the figure. If a temperature sensor is provided in the maximum temperature portion, an excessive temperature rise can be directly detected. However, a temperature sensor is provided for each paper size, which causes an increase in cost. Therefore, in the present embodiment, the correlation between the maximum temperature in the non-sheet passing area and the temperature detected by the end temperature sensor 27 is measured in advance, and the temperature in the non-sheet passing area is determined from the detected temperature of the end temperature sensor 27. By predicting and detecting the rise, the rise in cost is suppressed. When the end temperature sensor 27 detects an excessive temperature rise in the non-sheet passing region, the sheet passing interval is lengthened, the supply of heat to the fixing belt 21 is suppressed, and the sheet passing through the fixing belt 21 and the pressure roller 31 is performed. A method of diffusing heat in the region is generally adopted.

  FIG. 4 is a graph showing time transitions of the maximum temperature in the non-sheet passing region of the fixing belt 21 and the temperature detected by the end temperature sensor. In the figure, L1 represents the time transition of the detected temperature of the end temperature sensor in the conventional fixing device, and L2 represents the time transition of the detected temperature of the end temperature sensor in the energy saving type fixing device 20 employed in this embodiment. Is shown. Also, L3 in the figure represents the time transition of the temperature of the highest temperature portion of the non-sheet passing area in the conventional fixing device, and L4 represents the non-sheet passing area in the energy saving type fixing device 20 employed in the present embodiment. The time transition of the temperature of the highest temperature part is shown.

  As shown in FIG. 4, in the case of the energy saving type fixing device 20 of the present embodiment, the amount of heat diffusion in the width direction of the fixing belt 21 decreases, and the temperature rise in the non-sheet passing region becomes significant. Further, the rate of temperature rise differs between the highest temperature portion in the non-sheet passing region and the temperature detection position of the end temperature sensor 27, and the highest temperature portion has higher sensitivity. That is, the temperature rises more easily in the highest temperature part of the non-sheet passing region. Therefore, even if the conventional fixing device and the energy-saving type fixing device 20 of the present embodiment have the same maximum temperature T1 in the non-sheet-passing region, the detected temperature of the end temperature sensor 27 is the case of the conventional fixing device. In the case of the energy saving type fixing device 20 of the present embodiment, T3, which is different from each other. Therefore, the threshold for the output of the end temperature sensor 27 used for determining the timing for changing the sheet passing interval is smaller in the energy saving type fixing device 20.

  FIG. 5 is a block diagram illustrating an example of a main part of a control system that controls the fixing device of the present embodiment. The controller 200 as a control means includes a CPU, a RAM, a ROM, and the like, and includes an intermediate transfer unit 85 including the exposure unit 3, the image forming units 4Y, 4M, 4C, and 4K, the rotation driving unit of the intermediate transfer belt 78, and the like. Are connected to a recording medium transport unit 201 for driving the paper feed roller 97, the registration roller pair 98, and the like, a communication interface unit 202 for communicating with an external host computer device, and the like. The controller 200 is connected to the heaters 25 a and 25 b of the fixing device 20, the temperature sensors 26 and 27, and the pressure roller driving unit 28 that drives the rotation of the pressure roller 31. The controller 200 receives a print job (image forming job) command or image data from an external host computer device or the like via the communication interface unit 202, and executes a control program incorporated in advance, thereby executing the recording medium P. An image forming operation for forming and outputting a color image is controlled.

  The controller 200 performs the following control on the fixing device 20 by executing a control program incorporated in advance. For example, the controller 200 controls to change the sheet passing interval, which is the conveyance interval of the storage medium P conveyed to the fixing nip portion, based on the comparison result between the detection value of the end temperature sensor 27 and a preset threshold value. To do. Further, the controller 200 detects the temperature of the end of the fixing belt 21 by the end temperature sensor 27 before starting the image forming operation of the image forming job based on the command of the image forming job (print job). Then, based on the detection result, the change timing of the sheet passing interval of the storage medium P to the fixing nip portion is determined. Further, the controller 200 stores the image data in the fixing nip portion based on the time elapsed since the end of the previous image forming job before starting the image forming operation of the image forming job based on the command of the image forming job. The change timing of the sheet passing interval of the medium P can also be determined. Further, the controller 200 changes the threshold based on the target temperature of the fixing belt 21 heated by the heater 25, changes the threshold based on the thickness of the recording medium P that is an image formation target, The threshold value can be controlled based on the toner consumption amount in the units 4Y, 4M, 4C, and 4K.

  FIG. 6 is a graph showing a temperature transition when the sheet passing interval is changed in accordance with the output of the end temperature sensor in the fixing device 20 of the present embodiment. In the figure, L5 indicates the time transition of the temperature detected by the end temperature sensor 27, and L6 indicates the time transition of the temperature of the maximum temperature portion in the non-sheet passing region. Further, L7 in the figure is a threshold for the output of the end temperature sensor 27 used for determining the timing for changing the sheet passing interval. When the output of the edge temperature sensor 27 is equal to or greater than the threshold value L7, the sheet passing interval is lengthened, and when the output of the edge temperature sensor 27 is smaller than the threshold value L7, the sheet passing interval is shortened (initial default state). ) In this way, by changing the sheet passing interval based on the output of the edge temperature sensor 27 and the threshold value L7, as shown in FIG. 7, the temperature transition L6 of the highest temperature portion in the non-sheet passing area is below an arbitrary temperature. Can be controlled.

  In the case of the energy saving type fixing device 20 employed in the present embodiment, the threshold value for the output of the edge temperature sensor 27 used when determining the timing for changing the sheet passing interval as described above is the conventional one. It is set lower than the fixing device (see FIG. 4). When the threshold value is low, as shown in the area A in FIG. 6, the end portion due to overshoot at the start of the image forming operation is generated even though the temperature rise of the non-sheet passing area does not occur before the sheet passing. The temperature sensor 27 detects a temperature equal to or higher than the threshold value, and increases the paper passing interval, thereby reducing productivity.

  Therefore, in this embodiment, non-sheet passing due to overshoot at the start of the image forming operation is controlled by delaying the determination timing of whether or not to change the sheet passing interval based on the temperature detection result of the end temperature sensor 27. This prevents false detection of temperature rise in the area and suppresses the decrease in productivity. In addition, when the image forming operation is started from a state where the maximum temperature portion of the non-sheet passing region and the detected temperature of the end temperature sensor 27 are high after continuous sheet passing, the sheet passing based on the temperature detection result of the end temperature sensor 27 is performed. The temperature rise in the non-sheet passing area is continuously detected without delaying the timing for determining whether or not to change the interval. Specifically, when the output of the end temperature sensor 27 after receiving the image forming job command and before starting the image forming operation is smaller than a predetermined reference value set in advance, the end temperature sensor Control is performed so as to delay the determination timing of whether or not to change the sheet passing interval based on the temperature detection result of 27. Further, when the output of the edge temperature sensor 27 before the start of the image forming operation is equal to or greater than the predetermined reference value, the timing for determining whether or not it is necessary to change the sheet passing interval based on the temperature detection result of the edge temperature sensor 27 is delayed. Control not to. For example, if the output of the edge temperature sensor 27 before the start of the image forming operation is less than the threshold value of the edge temperature sensor output for changing the sheet passing interval, the sheet passing interval is changed after the first page has passed through the fixing device 20. If it is equal to or greater than the above threshold, control is performed so as not to delay the timing for determining whether or not to change the sheet passing interval. By controlling as described above, it is possible to detect the temperature increase in the non-sheet passing area with high accuracy, and to suppress the decrease in the productivity of the printed recording medium P and the shortening of the member life.

  In the fixing device 20 of the above-described embodiment, whether or not to delay the determination timing of whether or not to change the sheet passing interval based on the temperature detection result of the end temperature sensor 27 depends on the previous image forming job (print job). You may control based on the time which passed after completion | finish of. In this case, since the control is based on the elapsed time, the detection accuracy of the temperature rise in the non-sheet-passing area is lower than the control based on the output of the end temperature sensor 27 and the reference value. Considering the detection error of the head temperature sensor 27 and the like, it is superior to the above embodiment in terms of control safety. The reference time for the elapsed time when controlling whether to delay the determination timing of whether or not to change the sheet passing interval is set to 5 seconds, for example.

  Further, in the fixing device 20 of the above embodiment, when the target temperature of the fixing belt 21 is changed, the maximum temperature portion in the non-sheet passing region and the detected temperature of the end temperature sensor 27 also change. The temperature rising speed is different between the temperature detection positions of the part and the end temperature sensor 27, and the highest temperature part has higher sensitivity. For this reason, a detection error occurs in the temperature rise in the non-sheet passing region, and there is a possibility that the productivity is lowered and the member life is shortened. Therefore, control may be performed so as to change the threshold for the output of the end temperature sensor 27 that changes the sheet passing interval in accordance with the target temperature of the fixing belt 21. With this control, even when the target temperature is changed, a temperature rise in the non-sheet passing region can be detected with high accuracy, and a reduction in productivity and a reduction in member life can be suppressed.

  Further, in the fixing device 20 of the above-described embodiment, when the thickness of the recording medium P (hereinafter referred to as “paper thickness”) is changed, the amount of heat taken away from the fixing belt 21 by the recording medium P changes. The amount of heat that needs to be supplied to will also vary. For this reason, the temperature at the maximum temperature portion in the non-sheet passing area and the temperature detection position of the end temperature sensor 27 change, and a detection error occurs in the temperature rise in the non-sheet passing area, resulting in a decrease in productivity and a shortened member life. There is a fear. Therefore, control may be performed so as to change the threshold value for the output of the edge temperature sensor 27 that changes the sheet passing interval in accordance with the paper thickness used for the image forming job. With this control, even when the paper thickness changes, a temperature rise in the non-sheet passing region can be detected with high accuracy, and a reduction in productivity and a reduction in member life can be suppressed.

  Further, in the fixing device 20 of the above embodiment, when the image density (printing density) to which the toner is attached changes, the amount of heat taken from the fixing belt 21 by the recording medium P to which the toner image is transferred changes. The amount of heat that needs to be supplied to the fixing belt 21 also changes. For this reason, the temperature at the maximum temperature portion in the non-sheet passing area and the temperature detection position of the end temperature sensor 27 change, and a detection error occurs in the temperature rise in the non-sheet passing area, resulting in a decrease in productivity and a shortened member life. There is a fear. Therefore, the threshold value for the output of the edge temperature sensor 27 for changing the sheet passing interval may be changed in accordance with the toner consumption that increases or decreases depending on the image density. With this control, even when the image density (toner consumption) changes, a temperature rise in the non-sheet passing area can be detected with high accuracy, and a reduction in productivity and a reduction in member life can be suppressed.

As described above, according to the present embodiment, the sheet passing interval of the storage medium P conveyed to the fixing nip portion based on the comparison result between the detected value of the end temperature sensor 27 serving as the end temperature detecting means and a preset threshold value. By controlling so as to change the (conveyance interval), an excessive temperature rise in the non-sheet passing area (recording medium non-passing area) of the fixing belt 21 as the fixing member is suppressed. Then, before starting the image forming operation of the image forming job based on the command of the image forming job, control is performed so as to determine the change timing of the sheet passing interval of the storage medium P to the fixing nip portion. For example, the temperature of the end portion of the fixing belt 21 is detected by the end temperature sensor 27 before the image forming operation of the image forming job is started, and the storage medium to the fixing nip portion is determined based on the detection result. The timing for changing the P sheet passing interval is determined. Alternatively, before starting the image forming operation of the image forming job, the change timing of the sheet passing interval of the storage medium P to the fixing nip portion is determined based on the time elapsed after the end of the previous image forming job. . In the case where there is a possibility that overshoot of the temperature of the fixing belt 21 occurs due to the determination of the timing for changing the sheet passing interval, the fixing belt 21 by the end temperature sensor 27 may be generated. It is possible to control so as not to change the sheet passing interval of the storage medium P based on the detection result of the temperature at the end of the recording medium and the time elapsed since the end of the previous image forming job. Thereby, it is possible to prevent the sheet passing interval of the storage medium P from being changed based on the erroneous detection of the temperature rise in the non-sheet passing region due to the temperature overshoot of the fixing belt 21 at the start of the image forming operation. On the other hand, when the time has not elapsed since the previous image forming operation and there is no possibility of overshooting of the temperature of the fixing belt 21, the temperature at the temperature detection position of the end temperature sensor 27 in the non-sheet passing region is set. The image forming operation starts from a high state. In this case, the sheet passing interval of the storage medium P is changed based on the detection result of the temperature of the end of the fixing belt 21 by the end temperature sensor 27 and the time elapsed since the end of the previous image forming job. Can be controlled to continue. As a result, regardless of the elapsed time from the previous image forming operation, it is possible to detect the temperature rise in the non-sheet-passing region with high accuracy without being affected by the overshoot at the start of the image forming operation. Therefore, it is possible to appropriately perform the control of changing the sheet passing interval of the storage medium P based on the comparison result between the detected value of the temperature of the non-sheet passing area and the threshold value. Temperature rise can be prevented.
In addition, since it is not necessary to provide a plurality of temperature detecting means corresponding to each position where the maximum temperature is generated in the non-sheet passing region that changes according to the size of the recording medium P, it is possible to suppress an increase in the cost of the fixing device 20. it can. Further, since the paper passing interval of the storage medium P is not changed unnecessarily, the productivity of the recording medium P on which the toner image is fixed does not decrease.
Also, according to the present embodiment, the storage medium P is passed through the fixing nip portion based on the time elapsed since the end of the previous image forming job without using the temperature detection result of the end temperature sensor 27. In the case of determining the interval change timing, it is possible to avoid the risk of inappropriate determination of the sheet passing interval change timing due to erroneous detection of the edge temperature sensor 27.
Further, according to the present embodiment, the target of the fixing belt 21 is changed by changing the threshold value to be compared with the detected value of the end temperature sensor 27 based on the target temperature of the fixing belt 21 heated by the heater 25 as a heat source. Even when the temperature is changed, the temperature increase in the non-sheet passing region of the fixing belt 21 can be detected with high accuracy, and the decrease in productivity and the shortening of the member life can be suppressed.
According to the present embodiment, the fixing belt 21 is changed even when the paper thickness of the recording medium P is changed by changing the threshold value to be compared with the detection value of the end temperature sensor 27 based on the paper thickness of the recording medium P. The temperature rise in the non-sheet-passing area can be detected with high accuracy, and the decrease in productivity and the shortening of the member life can be suppressed.
In addition, according to the present embodiment, by changing the threshold based on the toner consumption amount in each of the image forming units 4Y, 4M, 4C, and 4K, the image density (printing density) to which the toner is attached changes. Even when the toner consumption changes, the temperature increase in the non-sheet passing region of the fixing belt 21 can be detected with high accuracy, and the decrease in productivity and the shortening of the member life can be suppressed.
Further, according to the present embodiment, the pressure receiving member (nip forming member 22, support stay 23) that receives pressure from the pressure roller 31 via the flexible fixing belt 21, and the fixing belt 21. By providing a heat conduction pipe 24 as a heat transfer member provided so as to be in contact with the inner peripheral surface and transferring the heat of the heater 25 to the fixing belt 21, between the fixing belt 21 and the pressure roller 31 as the pressure means. In addition, the fixing nip portion can be stably formed, and the heat of the heater 25 can be efficiently transmitted to the fixing belt 21.

  As mentioned above, although this invention was demonstrated based on suitable embodiment, this invention is not limited to what was demonstrated by the said embodiment, In the range which does not deviate from the summary, it can change variously.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 3 Exposure part 4Y, 4M, 4C, 4K Image forming part 20 Fixing apparatus 21 Fixing belt 22 Nip forming member 23 Support stay (reinforcing stay)
24 Heat conduction pipe 25 Heater 25a Central heater 25b End heater 26 Central temperature sensor 27 End temperature sensor 31 Pressure roller 78 Intermediate transfer belt 79Y, 79M, 79C, 79K First transfer bias roller 82 Secondary transfer backup roller 85 Intermediate Transfer unit 89 Secondary transfer roller 200 Controller 201 Recording medium transport unit 202 External communication interface T Toner P Recording medium (transfer paper)

JP-A-8-220932

Claims (6)

A toner image forming unit that forms a toner image on a recording medium; and a fixing device that fixes the toner image on the recording medium. The fixing device includes an endless fixing member that is movable on the surface; and the fixing member. An image forming apparatus having a pressure member that can be driven to rotate, and a heat source that generates heat to heat the fixing nip,
End temperature detecting means for detecting the temperature of the end in the width direction crossing the moving direction of the surface of the fixing member;
Control means for changing a conveyance interval of the storage medium conveyed to the fixing nip portion based on a comparison result between the detection value of the end temperature detection means and a preset threshold value;
The control unit detects the temperature of the end of the fixing member by the end temperature detecting unit before starting the image forming operation of the image forming job based on the command of the image forming job, and detects the detected temperature. An image forming apparatus that determines a change timing of a conveyance interval of a storage medium to the fixing nip portion based on a result. A toner image forming unit that forms a toner image on a recording medium; and a fixing device that fixes the toner image on the recording medium. The fixing device includes an endless fixing member that is movable on the surface; and the fixing member. An image forming apparatus having a pressure member that can be driven to rotate, and a heat source that generates heat to heat the fixing nip,
End temperature detecting means for detecting the temperature of the end in the width direction crossing the moving direction of the surface of the fixing member;
Control means for changing a conveyance interval of the storage medium conveyed to the fixing nip portion based on a comparison result between the detection value of the end temperature detection means and a preset threshold value;
The control means stores the image data in the fixing nip portion based on the time elapsed from the end of the previous image forming job before starting the image forming operation of the image forming job based on the image forming job command. An image forming apparatus that determines a change timing of a conveyance interval of a medium. The image forming apparatus according to claim 1 or 2,
The image forming apparatus, wherein the control unit changes the threshold based on a target temperature heated by the heat source. The image forming apparatus according to claim 1 or 2,
The image forming apparatus, wherein the control unit changes the threshold value based on a thickness of the recording medium. The image forming apparatus according to claim 1 or 2,
The image forming apparatus, wherein the control unit changes the threshold based on a toner consumption amount in the image forming unit. The image forming apparatus according to claim 1,
The fixing member is a flexible member,
The image forming apparatus, wherein the fixing device includes a pressure receiving member that receives pressure from the pressure member through the fixing member.

Images