JP2006098998A - Heating device, control method of heating device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heating device whose first printing time can be shortened by enabling temperature control over a heater in standby mode by switching a temperature detection part between normal temperature control time and standby temperature control time. <P>SOLUTION: The heating device which heats a recording material carrying an image at a nip part formed by a 1st fixing member and a 2nd fixing member abutting against the 1st fixing member while holding and conveying it is equipped with a heat source which is arranged on an internal surface side of the 1st fixing member nearby the nip part to heat the 1st fixing member, a 1st temperature detection part which is arranged not in contact with the heat source and detects the temperature of the 1st fixing member, a 2nd temperature detection part which is arranged in contact with the heat source and detects the temperature of the heat source, and a control part which controls the temperature of the heat source based upon a detection result of the 1st temperature detection part or 2nd temperature detection part. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heating device that heats a recording material carrying an image by nipping and conveying it at a nip formed by a first fixing member and a second fixing member, a method for controlling the heating device, and an image forming device equipped with the heating device It relates to the device.

  Specifically, a recording material (paper, printing paper, transfer material sheet, OHT sheet, etc.) using toner made of heat-meltable resin or the like by an appropriate image forming process unit such as electrophotography, electrostatic recording, and magnetic recording. A toner image heating apparatus and a control of the heating apparatus in which a non-fixed toner image formed and supported on the surface of glossy paper, glossy film, etc. is heat-fixed as a permanently fixed image on the surface of the recording material carrying the image. The present invention relates to a method and an image forming apparatus such as a laser beam printer and a facsimile equipped with the heating device. In particular, the present invention relates to an on-demand heating apparatus that is suitable for use in a color image forming apparatus and has a low cost and a short rise time (so-called warm-up time).

  In recent years, colorization has progressed in image forming apparatuses such as printers and copiers.

  As a heating device used in such a color image forming apparatus, a heat roller type fixing device having an elastic layer on a fixing member is well known. An example of a heating device using a fixing roller having such an elastic layer is shown in FIG.

  In this heating device, the fixing roller 101 is rotated in the direction of the arrow, and the contact nip portion (fixing nip) N of the two heating rollers including the fixing roller 101 and the pressure roller 102 adjusted to a predetermined fixing temperature. The recording material P on which the unfixed toner image t is placed can pass through.

  When the unfixed toner image t passes through the nip portion N, it is heated and pressed by the fixing roller 101 and the pressure roller 102 and fixed on the recording material P as a completed image (permanently fixed image).

  Each of the rollers 101 and 102 includes a halogen heater H at the center, and the radiant energy generated from the halogen heater H is absorbed by the aluminum cores 101a and 102a inside each roller and heated. The thermistors 103 and 104 are arranged in elastic contact with the surfaces of the rollers 101 and 102, respectively, and power is supplied to the halogen heater H of the rollers 101 and 102 based on the temperature detected by the thermistors 103 and 104. Is controlled to adjust the temperature.

  Elastic layers 101b and 102b made of silicone rubber having a thickness of 2 mm are provided around the aluminum cores 101a and 102a of the rollers 101 and 102, respectively. PFA (tetrafluoroethylene / perfluoroalkyl ether copolymer / tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin), FEP (tetrafluoroethylene / hexafluoropropylene copolymer) to prevent paper dust and the like from sticking Coating layers 101c and 102c are formed of a resin having good releasability and heat resistance, such as coalescence / tetrafluoroethylene / hexafluoropropylene copolymer resin).

  The reason why the elastic layer 101b is provided on the side of the fixing roller 101, which is a fixing member in contact with the unfixed toner t, in the fixing nip portion N is to fix the toner image surface as uniformly as possible.

  By providing the elastic layer 101b on the fixing roller 101 side, when the toner image t passes through the fixing nip portion N, the elastic layer 101b is deformed along the toner layer, so that the toner that is unevenly placed on the image. However, it is encased in the elastic layer 101b and heated uniformly to achieve uniform fixing.

  The image fixed uniformly in this way has no gloss unevenness, and has a feature that the light transmittance of the image is excellent particularly when fixing an OHT (transparent sheet for an overhead projector).

  However, in the heat roller type heating device having such an elastic layer, the heat capacity of the heat roller itself increases, and the time required to raise the temperature of the fixing roller 101 to a temperature suitable for toner image fixing. There was a problem that (warm-up time) was long. Further, the cost of the fixing member is also expensive.

  On the other hand, as an inexpensive heating device having a short warm-up time, a film fixing type heating device used in a black and white printer or the like is well known. An example of such a film heating apparatus is shown in FIG.

  In this heating apparatus, a fixing nip N is formed by sandwiching a thin fixing film 111 between a heater 112 fixedly supported by a support member 115 and an elastic pressure roller 114, and the fixing film 111 is attached to the heater 112. The recording material P carrying the toner image t is nipped and conveyed between the fixing film 111 and the pressure roller 114 in the fixing nip portion, and is moved from the heater 112 via the fixing film 111. In this configuration, the toner image on the recording material is heated by heat. The unfixed toner image t on the recording material P receives heat and pressure when passing through the fixing nip portion N, and is fixed on the recording material P as a completed fixed image (permanently fixed image).

  The fixing film 111 is an endless film made of a heat-resistant resin having a thickness of about 50 μm, for example, and a release layer (such as a fluororesin coating layer) having a thickness of about 10 μm is formed on the surface. A resistance heating element is formed on a substrate. The temperature detection means 113 is brought into contact with the heater 112, the temperature of the heater 112 is detected, and the temperature is controlled by a control means (not shown) so that the temperature of the heater 112 becomes a desired temperature.

  Further, in order to reduce the heat capacity of the fixing film 111, the fixing film 111 is not provided with an elastic layer. In the heating device having such a configuration, the heat capacity of the fixing film 111 is extremely small. Therefore, after the power is supplied to the heater 112, the temperature of the fixing nip portion N is raised to a temperature capable of fixing the toner image in a short time. It is possible.

  However, when a film heating device using the fixing film 111 not provided with an elastic layer is used as a heating device of a color image forming apparatus, unevenness due to the presence or absence of the surface of the recording material P or the toner layer, unevenness of the toner itself, etc. The surface of the fixing film 111 cannot follow, and there is a difference in heat applied from the fixing film between the convex portion and the concave portion. That is, there is a problem that heat is well transmitted from the fixing film at the convex portion that is in good contact with the fixing film, and heat from the fixing film is less transmitted at the concave portion than the convex portion.

  Further, in a color image, since a plurality of color toner layers are mixed and used in combination, the unevenness of the toner layer is larger than that of a black and white image, and when the fixing film as a fixing member does not have an elastic layer, the gloss of the fixed image is increased. When the unevenness becomes large and the image quality is deteriorated, or when the recording material is OHT, there is a problem that the image quality is lowered due to poor transparency when a fixed image is projected.

As a conventional technique, Patent Document 1 proposes a heating device that constitutes a low-cost color on-demand heating device by using a fixing belt (fixing film) having an elastic layer in a film heating device.
Japanese Patent Laid-Open No. 11-15303 (Patent No. 3051085)

  In a color on-demand heating device using a fixing belt (fixing film) having an elastic layer, a first mode is provided by providing a standby mode in which the heating device is preheated by pre-heating the fixing device before stopping the fixing operation. Time can be shortened.

  However, the thermal conductivity of silicone rubber or the like used for the elastic layer of the fixing belt is not so high, and since many members enter between the surface of the fixing belt and the temperature detection part of the heater, the responsiveness is poor, It is difficult to control the temperature of the surface of the fixing belt by the temperature detection unit of the heater. In particular, it is difficult for the temperature detection unit on the back of the heater to detect that the recording material has passed through the heating device and took the heat of the surface of the fixing belt to reduce the temperature of the surface of the fixing belt. There is a problem that it takes too much.

  Therefore, a method for controlling the temperature by controlling the heater by moving the arrangement of the temperature detection unit to the inner surface or surface of the fixing belt other than the heater unit and detecting the temperature of the fixing belt itself has been attempted. If measurement is performed in the standby mode that is stopped in this state, the temperature of the heater itself cannot be detected, and the heater may overheat. When the temperature of the heater is excessively high, there is a problem that the member holding the heater is melted or the elastic layer of the fixing belt is damaged by heat and deformed.

  The present invention has been made in view of the above problems, and in a color on-demand heating apparatus, the temperature of the heater can be controlled in the standby mode by switching the temperature detection unit during normal temperature control and standby temperature control. It is another object of the present invention to provide a heating apparatus and a control method thereof that can shorten the first print time, and an image forming apparatus equipped with the heating apparatus.

  Alternatively, it is an object of the present invention to provide a heating device, a control method thereof, and an image forming apparatus equipped with the heating device, which can prevent deformation of the elastic layer of the fixing belt and occurrence of problems associated therewith.

  In order to achieve any of the above objects, a heating apparatus and an image forming apparatus according to the present invention mainly have the following configuration.

That is, a heating device that heats a recording material carrying an image while nipping and conveying it at a nip formed by a first fixing member and a second fixing member that contacts the first fixing member.
A heat source disposed at a position near the nip portion on the inner surface side of the first fixing member for heating the first fixing member;
A first temperature detecting means disposed at a position not in contact with the heat source and detecting the temperature of the first fixing member;
A second temperature detecting means arranged in contact with the heat source and detecting the temperature of the heat source;
Control means for controlling the temperature of the heat source based on detection results by the first temperature detection means and the second temperature detection means.

  Alternatively, an image forming apparatus equipped with the above-described heating device has the following configuration.

That is, an image forming apparatus that forms an output image on a recording material by an electrophotographic method is as follows.
Means for generating a toner image on the recording material;
And a heating device for fixing the generated toner image on the recording material as the output image.

  According to the present invention, in the temperature control of the heating device, by switching the temperature detection means during normal temperature control and standby temperature control, the rise time in the color on-demand heating device can be shortened without overheating the heater. Is possible.

  Alternatively, it is possible to prevent the deformation of the elastic layer of the fixing belt and the accompanying generation of glossy streaks in the image, and to shorten the rise time in the color on-demand heating device without excessive heating of the heater.

  Embodiments of the present invention will be described below with reference to the drawings.

[Embodiment 1]
(1) Configuration of Image Forming Apparatus FIG. 1 is a diagram showing a schematic configuration of a color image forming apparatus according to an embodiment of the present invention. The color image forming apparatus can obtain a full color image by superposing four color toner images of yellow (Y), cyan (C), magenta (M), and black (K) using an electrophotographic system. .

  Y, C, M, and K are four process cartridges that form yellow, cyan, magenta, and black color toner images, respectively, arranged in the order of Y, C, M, and K from the bottom to the top. Each of the process cartridges Y, C, M, and K includes a photosensitive drum 1 as an image carrier, a charging roller 2 as a charging unit, a developing unit 3 for developing an electrostatic latent image, and a cleaning of the photosensitive drum. A so-called all-in-one cartridge in which the means 4 and the like are collected in one container is used. Yellow toner is used for the developing means 3 of the yellow process cartridge Y, cyan toner is used for the developing means 3 of the cyan process cartridge C, magenta toner is used for the developing means 3 of the magenta process cartridge M, and black process cartridge K is used. The developing means 3 is filled with black toner.

  An optical system 5 that forms an electrostatic latent image by exposing the photosensitive drum 1 is provided corresponding to the four color process cartridges Y, C, M, and K. As the optical system 5, a laser scanning exposure optical system is used.

  In each of the process cartridges Y, C, M, and K, the optical system 5 performs scanning exposure based on the image data on the photosensitive drum 1 that is uniformly charged by the charging unit 2. An electrostatic latent image corresponding to the scanning exposure image is formed on the surface. By setting the developing bias applied to the developing roller of the developing means 3 from a bias power source (not shown) to an appropriate value between the charged potential and the latent image (exposed rear) potential, the toner charged to a negative polarity Is selectively attached to the electrostatic latent image on the photosensitive drum 1 and developed.

  That is, a yellow toner image is formed on the photosensitive drum 1 of the yellow process cartridge Y, a cyan toner image is formed on the photosensitive drum 1 of the cyan process cartridge C, and a magenta toner is applied on the photosensitive drum 1 of the magenta process cartridge M. A black toner image is formed on the photosensitive drum 1 of the black process cartridge K, respectively.

  The monochromatic toner images developed and formed on the photosensitive drums 1 of the process cartridges Y, C, M, and K are on the intermediate transfer member 6 that rotates at a substantially constant speed in synchronization with the rotation of the photosensitive drums 1. In this way, a full color toner image is synthesized and formed on the intermediate transfer body 6 by being superimposed and sequentially transferred in a predetermined alignment state.

  In the present embodiment, an endless intermediate transfer belt is used as the intermediate transfer member 6, and is suspended and stretched around three rollers: a driving roller 7, a secondary transfer roller facing roller 14, and a tension roller 8. Yes, driven by the drive roller 7.

  A primary transfer roller 9 is used as a primary transfer unit of the toner image from the photosensitive drum 1 of each process cartridge Y, C, M, and K to the intermediate transfer belt 6. By applying a primary transfer bias having a polarity opposite to that of toner from a bias power source (not shown) to the primary transfer roller 9, the intermediate transfer belt 6 is placed on the photosensitive drum 1 of each process cartridge Y, C, M, K. In contrast, the toner image is primarily transferred.

  After the primary transfer from the photosensitive drum 1 to the intermediate transfer belt 6 in each of the process cartridges Y, C, M, and K, the toner remaining as a transfer residue on the photosensitive drum 1 is removed by the cleaning unit 4. In the present embodiment, blade cleaning using a urethane blade is used as the cleaning means 4.

  The above process is performed in the process cartridges Y, C, M, and K for each color of yellow, cyan, magenta, and black in synchronization with the rotation of the intermediate transfer belt 6, and the primary transfer toner for each color is transferred onto the intermediate transfer belt 6. The images are formed one after another. At the time of image formation of only a single color (monochrome mode), the above process is performed only for the target color.

  On the other hand, the transfer material P set in the transfer material cassette 10 serving as a transfer material supply unit is fed by the feed roller 11 and suspended by the registration roller 12 around the secondary transfer roller facing roller 14 at a predetermined control timing. The intermediate transfer belt 6 is conveyed to a nip portion between the intermediate transfer belt 6 and the secondary transfer roller 13 as a secondary transfer unit.

  The primary transfer toner image formed on the intermediate transfer belt 6 is collectively transferred onto the transfer material P by a bias having a polarity opposite to that of a toner applied from a bias application unit (not shown) to a secondary transfer roller 13 as a secondary transfer unit. Transcribed.

  The secondary transfer residual toner remaining on the intermediate transfer belt 6 after the secondary transfer is removed by the intermediate transfer belt cleaning means 15. In this embodiment, similar to the cleaning unit 4 for the photosensitive drum 1, the intermediate transfer member is cleaned with a urethane blade.

  The toner image secondarily transferred onto the transfer material P is melted and fixed on the transfer material P by passing through a heating device F as fixing means, and is sent out to a discharge tray 32 through a discharge path 31. It becomes an output image of the image forming apparatus.

(2) Configuration of Heating Device FIG. 2 is a diagram showing a schematic configuration of the heating device F. The heating device F of the present embodiment is a heating device of a fixing belt heating method and a pressurizing rotating body driving method.

1) Overall Configuration of Heating Device The fixing belt 20 as a first fixing member is a cylindrical (endless belt-like) member in which an elastic layer is provided on a belt-like member. The fixing belt 20 will be described in detail in section 3) described later.

  Reference numeral 22 denotes a pressure roller as a second fixing member. Reference numeral 17 denotes a heater holder having a heat resistance and rigidity having a substantially semicircular arc shape in cross section. Reference numeral 16 denotes a fixing heater as a heat source, which is disposed on the lower surface of the heater holder 17 along the length of the holder 17. is there. The fixing belt 20 is loosely fitted on the heater holder 17. In this embodiment, the fixing heater 16 is a ceramic heater which will be described in detail in section 2).

  The heater holder 17 is formed of a liquid crystal polymer resin having high heat resistance, plays a role of holding the fixing heater 16 and guiding the fixing belt 20. In the present embodiment, Zenite 7755 (trade name) manufactured by DuPont is used as the liquid crystal polymer. The maximum usable temperature of Zenite 7755 is about 270 ° C.

  The pressure roller 22 is configured by forming a silicone rubber layer having a thickness of about 3 mm on a stainless steel core by injection molding and coating a PFA resin tube having a thickness of about 40 μm thereon. The pressure roller 22 is disposed such that both ends of the core bar are rotatably supported by bearings between a side plate (not shown) and a front side plate of the apparatus frame 24. On the upper side of the pressure roller 22, the heating assembly including the heater 16, the heater holder 17, the fixing belt 20, and the like is disposed in parallel with the pressure roller 22 with the heater 16 side facing downward. Is urged in the axial direction of the pressure roller 22 by a force of 98 N (10 kgf) on one side and a total pressure of 196 N (20 kgf) by a pressing mechanism (not shown), and the fixing belt 16 is passed through the fixing belt 20. A fixing nip portion N having a predetermined width required for heat fixing is formed by pressing the elastic layer of the pressure roller 22 against the elasticity of the elastic layer with a predetermined pressing force. The pressurizing mechanism has a pressure releasing mechanism (pressure adjusting means), and has a configuration in which the pressurizing is released and the transfer material P can be easily removed at the time of jam processing or the like.

  Reference numerals 18 and 19 denote two thermistors, main and sub, as first and second temperature detecting means. The main thermistor 18 as the first temperature detecting means is disposed in non-contact with the fixing heater 16 that is a heat source. In the present embodiment, the main thermistor 18 is provided so as to elastically contact the inner surface of the fixing belt 20 above the heater holder 17. The temperature of the inner surface of the fixing belt 20 is detected. The sub-thermistor 19 as the second temperature detecting means is disposed in contact with the back surface of the fixing heater 16 as a heat source, and detects the temperature of the back surface of the fixing heater.

  In the main thermistor 18, a thermistor element is attached to the tip of a stainless steel arm 25 fixedly supported by the heater holder 17, and the movement of the inner surface of the fixing belt 20 becomes unstable due to the elastic swing of the arm 25. Even in this state, the thermistor element is always kept in contact with the inner surface of the fixing belt 20.

  FIG. 3 is a perspective view showing the positional relationship among the fixing heater 16, the main thermistor 18, and the sub-thermistor 19 in the heating apparatus of the present embodiment. The main thermistor 18 is disposed near the longitudinal center of the fixing belt 20 and the fixing heater 16, and is disposed so as to contact the inner surface of the fixing belt 20. The sub thermistor 19 is disposed so as to contact the back surface of the fixing heater 16 in the vicinity of the longitudinal end portion at a position 90 mm from the longitudinal center.

  In the present embodiment, as the transfer material P, A4-sized regular paper (longitudinal width 210 mm) and A5-sized regular paper (longitudinal width 145 mm) can be passed on the basis of the center. The gist of the present invention is not limited to the size of the standard paper.

  In FIG. 3, the main thermistor 18 is arranged in the vicinity of the longitudinal center portion, while the sub-thermistor 19 is arranged at a position 90 mm from the longitudinal center, that is, at a position outside the A5 size paper and inside the A4 size paper. When the temperature of the sub-thermistor 19 is monitored to prevent the temperature rise at the end when small size paper such as A5 size paper is continuously fed, and the temperature reaches a certain level In addition, the sheet feeding is stopped and the heating device is idly rotated, so that the temperature rise at the end portion is alleviated and then the feeding of the next sheet is started.

  The main thermistor 18 and the sub-thermistor 19 are connected to a control circuit unit (CPU) 21 (FIG. 2), and the control circuit unit 21 detects the temperature of the fixing heater 16 based on the outputs of the main thermistor 18 and the sub-thermistor 19. The adjustment control content is determined, and energization to the fixing heater 16 is controlled by the heater drive circuit unit 28 (FIG. 4).

  Reference numerals 23 and 26 denote an entrance guide and a fixing paper discharge roller assembled to the apparatus frame 24. The entrance guide 23 serves to guide the transfer material so that the transfer material P that has passed through the secondary transfer nip is accurately guided to the fixing nip portion N. The entrance guide 23 of the present embodiment is made of polyphenylene sulfide (PPS) resin.

  The pressure roller 22 is rotationally driven in a counterclockwise direction indicated by an arrow at a predetermined peripheral speed by a motor (M) that functions as a driving unit. A rotational force acts on the cylindrical fixing belt 20 by the pressure frictional force at the fixing nip portion N between the outer surface of the pressure roller 22 and the fixing belt 20 due to the rotational driving of the pressure roller 22, and the fixing belt 20 has its inner surface. While the side is in close contact with the downward surface of the fixing heater 16 and slides, the outer circumference of the heater holder 17 is rotated following the clockwise direction of the arrow. Grease is applied to the inner surface of the fixing belt 20, and the slidability between the heater holder 17 and the inner surface of the fixing belt 20 is ensured.

  The pressure roller 22 is rotationally driven, and accordingly, the cylindrical fixing belt 20 is driven and rotated, and the fixing heater 16 is energized. The fixing heater 16 is heated to rise to a predetermined temperature and the temperature is adjusted. In this state, the transfer material P carrying an unfixed toner image is introduced between the fixing belt 20 and the pressure roller 22 in the fixing nip portion N while being guided along the entrance guide 23. The toner image carrying surface side of the transfer material P is in close contact with the outer surface of the fixing belt 20, and the fixing nip portion N is nipped and conveyed together with the fixing belt 20. In this nipping and conveying process, heat from the fixing heater 16 is applied to the transfer material P via the fixing belt 20, and an unfixed toner image on the transfer material P is heated and pressurized on the transfer material P to be melted and fixed. . The recording material P that has passed through the fixing nip N is separated from the fixing belt 20 by the curvature, and is discharged by the fixing discharge roller 26.

2) Configuration of Fixing Heater 16 In this embodiment, the fixing heater 16 as a heat source is made of aluminum nitride as a substrate and coated with polyimide on the surface. The back side is a ceramic with a resistance heating element formed on a substrate by applying a conductive paste containing silver / palladium alloy into a film with a uniform thickness by screen printing and then applying a glass coating with pressure-resistant glass. A heater is used.

  4A and 4B are diagrams showing the structure of an example of a ceramic heater, in which FIG. 4A is a front view, FIG. 4B is a partially broken back view, and FIG. 4C is an enlarged cross-sectional view.

  The fixing heater 16 is supported by being fixed to the heater holder 17 with the surface side exposed downward.

  A power feeding connector 27 is attached to the first and second electrode portions c and d of the fixing heater 16. Power is supplied from the heater drive circuit section 28 to the first and second electrode sections c and d via the power supply connector 27, so that the resistance heating element layer b generates heat and the fixing heater 16 quickly rises in temperature. . The heater drive circuit unit 28 is controlled by a control circuit unit (CPU) 21.

  In normal use, the rotation of the fixing belt 20 starts as the pressure roller 22 starts rotating, and the temperature of the inner surface of the fixing belt 20 increases as the temperature of the fixing heater 16 increases. The energization of the fixing heater 16 is controlled, and the input power is controlled so that the inner surface temperature of the fixing belt 20, that is, the detected temperature of the main thermistor 18 becomes 195 ° C.

3) Fixing belt 20
FIG. 5 shows a cross section of the fixing belt 20 used in this embodiment. As the base layer 20a, a SUS belt is used in which a SUS base tube is formed into a seamless belt shape having a thickness of 30 μm by drawing. An elastic layer 20b and a release layer 20c are formed on the SUS belt 20a.

  Here, a fixing rubber 20 is formed by forming a silicone rubber layer 250 μm as an elastic layer by a ring coating method and then covering a PFA resin tube having a thickness of 30 μm as a release layer. By providing a fluororesin layer on the surface of the fixing belt 20, the surface releasability is improved, and the offset phenomenon that occurs when the toner once adheres to the surface of the fixing belt 20 and moves to the transfer material P again is prevented. can do.

Further, when the fluororesin layer on the surface of the fixing belt 20 is a PFA tube, a uniform fluororesin layer can be formed more easily.
(3) Temperature control The temperature control will be described next. In the present embodiment, the temperature control is roughly divided into the following three control patterns.

1. Startup temperature control 1. 2. Constant temperature control Standby temperature control The startup temperature control is a temperature control that heats the target temperature from a temperature lower than the target temperature. The constant temperature control is a temperature control that keeps the recording material at the target temperature while the paper is being fed. The standby temperature control is temperature control for maintaining a predetermined temperature even when the rotation of the fixing device is stopped in order to increase the rise time of the fixing device during a printing operation.

  Here, the detected value of the main thermistor 18 is used as the target temperature in order to detect the fixing belt temperature during paper passing. The reason why the detection value of the sub-thermistor 19 is insufficient is that the thermal conductivity of silicone rubber or the like used for the elastic layer of the fixing belt is not so high, and between the surface of the fixing belt and the temperature detection means of the heater. Since many members are included, the responsiveness is poor, and it is difficult to control the temperature of the fixing belt surface by the temperature detection means of the heater. In particular, it is difficult for the temperature detection means on the back side of the fixing heater 16 to detect that the recording material has passed through the heating device and took the heat of the fixing belt surface to reduce the temperature of the fixing belt surface. It is inappropriate because it takes too much time.

  On the other hand, in the configuration of the heating device of the present embodiment, there is a problem that if the standby temperature control is performed using the detection value of the main thermistor 18, the fixing heater 16 may be overheated. This is because if the fixing heater 16 is heated while the rotation of the heating device is stopped, the fixing belt 20 is also stopped, so that heat is not easily transmitted to the main thermistor 18.

  In this embodiment, standby temperature control is performed using the detection value of the sub-thermistor 19. FIG. 6 shows the temperature on the back side of the fixing heater when the standby temperature control is performed with the detection value of the main thermistor 18 and with the detection value of the sub-thermistor 19. When the detection value of the main thermistor 18 is used, the fixing heater 16 overheats, whereas when the detection value of the sub-thermistor 19 is used, the fixing heater 16 does not overheat.

  In this embodiment, the target temperature is controlled to a target temperature of 195 ° C. by the main thermistor 18, and the standby temperature is controlled to 130 ° C. by the sub-thermistor 19. Hereinafter, the flow of each temperature control is shown in the flowchart of FIG.

  First, in step S710, the CPU 21 determines whether or not standby temperature control is to be performed. If standby temperature control is not to be performed (S710—NO), the process proceeds to step S730.

  On the other hand, when performing standby temperature control (S710-YES), the process proceeds to step S720, and standby temperature control is performed in which the heating device is heated in advance in order to shorten the rise time of the fixing device.

  This standby temperature adjustment control (S720) is a characteristic part of the embodiment of the present invention. This temperature control is a control mode in which the heating device is preheated in order to shorten the rise time of the fixing device when a print signal is received. At the time of standby temperature control, the detection value of the sub-thermistor 19 disposed in contact with the back of the fixing heater is used as temperature detection means. During standby temperature control, PID control is performed so that the detection value of the sub-thermistor is 130 ° C.

  FIG. 8 is a diagram illustrating the relationship between the rise times when the standby temperature control is performed and when the standby temperature control is not performed. When standby temperature control is performed, the time to reach the target temperature is 7 seconds, whereas when standby temperature control is not performed, the time to reach the target temperature is 12 seconds. By performing this control, since the fixing device is preheated, the rise time is shortened, and the first print time is improved during the standby temperature control.

  Next, in step S730, a print signal (print signal) is received, and the process proceeds to startup temperature control (S740). In the start-up temperature control, the target temperature is set to a predetermined target value, and the temperature control is performed so that the target temperature is reached.

  In the start-up temperature control (S740), the fixing motor starts to rotate when a print signal (print signal) is received, and power is turned on with a detection value of the main thermistor 18 as a target temperature of 195 ° C. In the present embodiment, the input power is 800 W.

  When the detected value of the main thermistor 18 reaches 175 ° C., which is 20 ° C. lower than the target temperature, the temperature control is switched to PID control so that temperature overshoot does not occur. Even if the target temperature is reached, the PID control is continued to keep the temperature constant, and the process proceeds to steady temperature control.

  In step S750, after reaching the target value, steady temperature control is performed so as to maintain the temperature at which the recording material passes through the paper at a predetermined target value.

  The constant room temperature adjustment control (S750) is a control mode in which PID control is performed so that the detected value of the main thermistor is 195 ° C. while the recording material is passing, following the start-up temperature adjustment control, and the recording material is discharged. After completion, the fixing motor is stopped. When it is desired to reduce power consumption while the image forming apparatus is stopped, the output of the fixing heater 16 is turned off after the recording material is passed. Further, when the next first print time is advanced, the control can be switched so as to shift to the standby temperature control.

  Then, when printing of all the print data is finished, the printing is finished (S760).

(Modification of Embodiment 1)
In the description of the above-described embodiment, it has been described that the standby temperature adjustment control performs the PID control, but it is not necessarily limited to the PID control control. For example, as a modification of the first embodiment, control for turning on / off the input power may be performed based on the detection value of the sub-thermistor 19.

  The electric power supplied to the fixing heater 16 is controlled to be on / off so as to be kept within a certain temperature range. When the detection value of the sub-thermistor 19 reaches 130 ° C, the temperature control output is turned off (the heat source is turned off), and when the detection value decreases to 120 ° C, the heat source is driven so that the temperature control output is 40%. The temperature control in the standby mode can also be performed by performing control (on / off control) by switching the heat source on or off.

  FIG. 9 shows, as a modified example in the first embodiment, a comparison result between the detection value of the sub-thermistor 19 when the on-off control is performed and the detection value of the sub-thermistor 19 when the PID control is performed with 130 ° C. as the target value. .

  Compared with the case of PID control, the fluctuation range of the detected temperature of the sub-thermistor 19 in the on / off control is larger. However, unlike temperature control during printing, temperature control during standby does not require accurate temperature control, and thus temperature control can be simplified. By performing on / off control, there is no need to set complicated PID gain setting values, temperature control during standby mode can be performed even with a simpler temperature control method, and the first printout time can be shortened. Become.

  As described above, according to the present embodiment, by switching the thermistor, which is the temperature detecting means to be used, during normal temperature adjustment and standby temperature adjustment, the color heater can be turned on without overheating the fixing heater. The rise time in the demand heating device can be shortened.

  Alternatively, by maintaining the predetermined temperature, it is possible to reliably raise the temperature immediately after starting from the standby mode to the fixing temperature.

  Alternatively, by maintaining the heater temperature at a predetermined temperature, it is possible to prevent the heater from being excessively heated during the standby mode, and the first print time can be shortened.

[Embodiment 2]
Next, a second embodiment according to the present invention will be described. Here, the overall configuration of the image forming apparatus is the same as that of FIG. The feature of this embodiment is that the heating device has a pressure mechanism for adjusting the contact pressure between the heating sleeve and the pressure roller, and realizes a preheating mode.

  In the case of a color on-demand fixing device employing a fixing belt heating method, the elastic layer of the fixing belt made of silicone rubber or the like may be deformed after a long-term stoppage. As a result, the rotation of the fixing belt may become unstable during subsequent use, or the pressure state of the deformed portion may change and a belt-like glossy spot may appear in the output image. The deformation of the elastic layer of the fixing belt is considered to occur by the following mechanism.

  First, immediately after the printing is finished, the driving is stopped while the fixing belt and the pressure roller are kept in a high temperature state due to residual heat, but the pressure is continuously applied to the nip portion. Then, the elastic layer of the fixing belt memorizes the shape in the nip (planar shape), which is different from the original shape of the fixing belt, and the shape in which the elastic layer is crushed by pressure and the thickness is reduced, The aforementioned deformation occurs. Thereafter, the temperature of the nip portion decreases with the stop time and eventually reaches room temperature, but the deformation once stored in shape remains without being erased.

  Particularly in recent years, the operation speed of the apparatus has been increased, and accordingly, the speed of the recording material passing through the fixing apparatus has also been increased. In other words, it is necessary to further improve the fixing ability, so the operating temperature and pressure are set higher, the nip width is set wider (large deformation), and the thermal conductivity of the elastic layer (rubber layer) of the sleeve Measures such as increasing the

  However, all of these conditions are such that the deformation of the elastic layer of the fixing belt is more likely to deteriorate. In order to prevent the above problem, the heating device in the present embodiment has a mechanism for automatically releasing the applied pressure, and the deformation can be prevented by releasing the applied pressure.

  FIG. 10 shows the configuration of the heating device in the present embodiment. The pressure mechanism includes a pressure spring 51, a pressure plate 52, and a fixed fulcrum 55 provided on the frame portion. The pressure plate 52 plays the role of lever and transmits the restoring force received by the spring portion (power point) to the contact portion 56 with the guide member that is the point of action. In the figure, reference numeral 54 denotes a rotating cam for releasing the applied pressure, which can be rotated in the direction of the arrow about the rotating shaft 53 by a drive control mechanism not shown. FIG. 10 shows a pressure state. When the 180 ° cam rotates from here, the pressure plate 52 is lifted upward, and the pressure applied to the pressure roller 22 of the heating unit 20 is released. It becomes. Further, it can be switched to the original pressurized state by rotating the rotary cam 54 by 180 °.

  The pressure is released by the pressurizing mechanism while the heating device is stopped. The pressure mechanism is controlled so as to return to the pressure contact state before the printing operation.

  The temperature control in this embodiment will be described. In the present embodiment, temperature control is roughly divided into the following three control patterns.

1. Start-up temperature control 2. Constant temperature control 3. Standby temperature control Start-up temperature control is a temperature control that heats the target temperature from a temperature lower than the target temperature. Is in a pressurized state. The constant temperature control is temperature control that keeps the recording material at the target temperature while the paper is being fed. Similarly, the heating device is in a pressurized state by the pressurizing mechanism. The standby temperature control is a temperature control for maintaining a predetermined temperature even when the rotation of the fixing device is stopped in order to increase the rise time of the fixing device during a printing operation. ing.

  Here, the detected value of the main thermistor 18 is used as the target temperature in order to detect the fixing belt temperature during paper passing. The reason why the detection value of the sub-thermistor 19 is insufficient is that the thermal conductivity of silicone rubber or the like used for the elastic layer of the fixing belt is not so high, and between the surface of the fixing belt and the temperature detection means of the heater. Since many members are included, the responsiveness is poor, and it is difficult to control the temperature of the fixing belt surface by the temperature detection means of the heater.

  On the other hand, in the configuration of the heating device of the present embodiment, if the standby temperature control is performed using the detected value of the main thermistor 18, there is a problem that the heater is excessively heated. This is because if the fixing heater 16 is heated while the rotation of the heating device is stopped, the fixing belt 20 is also stopped, so that heat is not easily transmitted to the main thermistor 18. Furthermore, since the pressure is released by the pressurization mechanism, the apparent heat capacity is smaller than in the pressurized state, so even if a small amount of power is applied, the heater temperature reacts excessively and overheats, making control difficult. .

  Therefore, in this embodiment, standby temperature control is performed using the detection value of the sub-thermistor 19. When the standby temperature adjustment control is performed using the detection value of the main thermistor 18, the heater is excessively heated. On the other hand, when the detection value of the sub-thermistor 19 is used, the heater is not excessively heated.

  In this embodiment, the target temperature is controlled to 195 ° C. by the main thermistor 18, and the standby temperature is controlled to 130 ° C. by the sub-thermistor 19.

  Hereinafter, standby temperature control in the preheating mode will be described. Since the startup temperature control and the steady temperature control are the same as those in the first embodiment, description thereof will be omitted.

  Standby temperature control is a control mode in which the heating device is preheated in order to shorten the rise time of the heating device when a print signal is received. At that time, deformation of the heating sleeve is prevented by reducing the applied pressure by a pressure release mechanism (pressure adjusting means).

  During standby temperature control, the detection value of the sub-thermistor 19 disposed in contact with the back of the fixing heater 16 is used as temperature detection means. At the time of standby temperature control, PID control is performed so that the detection value of the sub-thermistor 19 becomes 130 ° C. When a print signal is received, the pressure release mechanism (pressure adjusting means) is operated to return to a normal pressure, and then the operation proceeds to start-up temperature control. The time required for operating the pressure release mechanism (pressure adjusting means) to return to the normal pressure is 1 second.

  FIG. 11 is a diagram showing the relationship between the rise time when the standby temperature control is performed and when it is not performed in the present embodiment. When standby control is performed, it takes 9 seconds to reach the target temperature, whereas when standby temperature control is not performed, it takes 13 seconds. By performing this control, the rise time is shortened and the first print time is shortened. improves.

  As described above, according to this embodiment, the elastic layer of the fixing belt is prevented from being deformed and the resulting image gloss streaks are prevented, and the rise in the color-on-demand heating apparatus is prevented without excessive heating of the heater. It becomes possible to shorten the time.

[Embodiment 3]
Next, Embodiment 3 according to the present invention will be described. Here, the overall configuration of the image forming apparatus is the same as that of FIG. FIG. 12 shows the configuration of the heating device in this embodiment. The difference from the first and second embodiments is that, in the first and second embodiments, the main thermistor 18 detects the temperature on the inner surface of the fixing belt, whereas in this embodiment, the temperature of the surface of the fixing belt 20 is detected. This is because the non-contact type main thermistor 18b that can be used is used.

  In the present embodiment, since the surface temperature of the fixing belt 20 can be directly measured, it is possible to control the temperature of the surface of the heating sleeve with higher accuracy than in the first embodiment.

  However, since the disposition of the main thermistor 18b as the temperature detecting means and the disposition of the fixing heater portion 16 are farther from the case of the first and second embodiments, the temperature control of the surface of the fixing belt 20 can be accurately performed. The temperature of the fixing heater 16 itself cannot be detected. Therefore, when the rotation is stopped and the standby temperature control is performed by the main thermistor 18b, the fixing heater 16 surely overheats, the member holding the fixing heater 16 melts, or the elastic layer of the fixing belt 20 However, there is a problem that a problem such as deformation due to heat damage occurs. In the present embodiment, the above-described problem is avoided by performing standby control using the sub-thermistor 19.

  In this embodiment, the target temperature is controlled to 180 ° C. by the main thermistor 18b, and the standby temperature is controlled to 130 ° C. by the sub-thermistor. Hereinafter, each temperature control will be described.

  Hereinafter, temperature control during standby mode, which is a feature of the present invention, will be described. Since the startup temperature control and the steady temperature control are the same as those in the first embodiment, description thereof will be omitted.

  The standby temperature control is a control mode in which the heating device is preheated in order to shorten the rise time of the fixing device when a print signal is received. During standby temperature control, the detection value of the sub-thermistor 19 disposed in contact with the back of the fixing heater 16 is used as temperature detection means. During standby temperature control, PID control is performed so that the detection value of the sub-thermistor is 130 ° C.

  As described above, according to the present embodiment, even if the main thermistor 18b is arranged at a position away from the fixing heater 16 by switching the thermistor that is the temperature detecting means at the time of normal temperature control and standby temperature control. It is possible to shorten the rise time in the color on-demand heating device without overheating the fixing heater 16.

[Other embodiments]
Note that an object of the present invention is to supply a storage medium storing software program codes for realizing the functions of the above-described embodiments to a control unit of an image forming apparatus or a heating apparatus, and a computer (or CPU or CPU) of the control unit. Needless to say, this can also be achieved when the MPU) reads and executes the program code stored in the storage medium. The storage of the program code is not limited to the client computer, and can be stored in a computer functioning as a server, for example.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention.

  As a storage medium for supplying the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a DVD, a magnetic tape, a nonvolatile memory card, a ROM, or the like is used. it can.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (operating system) operating on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.

  Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that the CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

  The thermistor that is the temperature detection means to be used is switched between the normal temperature control and the standby temperature control by the control provided by the program provided by the present embodiment and the computer-readable storage medium storing the program, and the fixing heater It is possible to shorten the rise time in the color on-demand heating apparatus without excessively increasing the temperature.

  Alternatively, it is possible to prevent the deformation of the elastic layer of the fixing belt and the accompanying occurrence of glossy streaks in the image, and to shorten the rise time in the color on-demand heating device without excessive heating of the heater. .

1 is a diagram illustrating a schematic configuration of a color image forming apparatus according to Embodiment 1. FIG. It is a figure which shows schematic structure of the heating apparatus F concerning Embodiment 1. FIG. 3 is a perspective view showing a positional relationship among a fixing heater 16, a main thermistor 18, and a sub-thermistor 19 in the heating device. FIG. It is a figure which illustrates the structure of a ceramic heater. FIG. 3 is a diagram illustrating a cross section of a fixing belt. It is a figure which shows a comparison with the case where standby temperature control is performed with the detection value of the main thermistor 18, and when the detection value of the sub thermistor 19 is performed. Flow chart of temperature control in the first embodiment It is a figure which shows the relationship of the rise time when the standby temperature control is performed and when the standby temperature control is not performed. As a modified example of Embodiment 1, it is a figure which shows the comparison result of the detection value of the sub thermistor 19 at the time of performing on-off control, and the detection value of the sub thermistor 19 at the time of performing PID control by making 130 degreeC into a target value. It is a figure which shows the structure of the heating apparatus in Embodiment 2. FIG. In Embodiment 2, it is a figure which shows the relationship of the rise time when not performing standby temperature control control. It is a figure which shows the heating apparatus structure in Embodiment 3. It is a figure which shows the structure of the fixing apparatus of a heat roller system as a prior art example. It is a figure which shows the structure of the fixing apparatus of a film fixing system as a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging means 3 Developing means 4 Cleaning means 5 Optical system 6 Intermediate transfer body 16 Fixing heater 17 Heater holder 18 Main thermistor 19 Sub thermistor 20 Fixing belt 22 Pressure roller

Claims (11)

In a heating device that heats a recording material carrying an image while nipping and conveying it at a nip formed by a first fixing member and a second fixing member that contacts the first fixing member,
A heat source disposed at a position near the nip portion on the inner surface side of the first fixing member for heating the first fixing member;
A first temperature detecting means disposed at a position not in contact with the heat source and detecting the temperature of the first fixing member;
A second temperature detecting means arranged in contact with the heat source and detecting the temperature of the heat source;
And a control unit that controls the temperature of the heat source based on a detection result by the first temperature detection unit or the second temperature detection unit. The control means controls the temperature of the heat source based on the detection result of the first temperature detection means during conveyance of the recording material, and based on the detection result of the second temperature detection means during preheating when the recording material is not conveyed. The heating apparatus according to claim 1, wherein the temperature of the heat source is controlled. 3. The heating apparatus according to claim 1, wherein the first fixing member in contact with the image surface of the recording material is provided with an elastic layer and a release layer on a belt-like member. The heating apparatus according to claim 1 or 2, wherein the heat source uses a ceramic heater formed by forming a resistance heating element on a ceramic substrate. The said control means controls the temperature of the said heat source by PID control based on the detection result of a said 2nd temperature detection means at the time of the preheating which does not convey the said recording material. Heating device. 5. The control unit according to claim 1, wherein the control unit controls the temperature by switching the heat source on or off based on a detection result of the second temperature detection unit during preheating without conveying the recording material. A heating apparatus according to the above. Pressure adjusting means for adjusting the pressure generated by the contact between the first fixing member and the second fixing member;
7. The pressure adjusting means according to claim 1, wherein the pressure generated by the contact is released during preheating when the recording material is not transported, and the pressure generated by the contact is returned when the recording material is transported. A heating apparatus according to the above. The first temperature detecting means is disposed at a position in contact with the inner surface of the first fixing member, detects the inner surface temperature of the first fixing member, or is not in contact with the surface of the first fixing member. The heating apparatus according to any one of claims 1 to 7, wherein the heating apparatus is disposed at a position and detects a surface temperature of the first fixing member. An image forming apparatus for forming an output image on a recording material by an electrophotographic method,
Means for generating a toner image on the recording material;
An image forming apparatus comprising: the heating device according to claim 1, wherein the generated toner image is fixed on the recording material as the output image. In a control method of a heating device that heats a recording material carrying an image while nipping and conveying it at a nip formed by a first fixing member and a second fixing member that contacts the first fixing member,
Setting a target temperature of a heat source disposed at a position near the nip portion on the inner surface side of the first fixing member in order to heat the first fixing member;
First temperature detection means that is disposed in a non-contact position with the heat source and detects the temperature of the first fixing member, or second temperature detection means that is disposed in contact with the heat source and detects the temperature of the heat source. And a control step of controlling the temperature of the heat source to the target temperature based on a detection result by the heating device. The control step controls the temperature of the heat source based on the detection result of the first temperature detection means during conveyance of the recording material, and based on the detection result of the second temperature detection means during preheating when the recording material is not conveyed. The method for controlling a heating apparatus according to claim 10, wherein the temperature of the heat source is controlled.

Images