JP2016062007A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve energy saving and maintain stable fixing performance.SOLUTION: There is provided a fixing device 12 including a fixing belt 38, a pressure roller 30, heating means 56 for heating the fixing belt 38, and temperature detection means 34 for detecting the temperature of the fixing belt 38, where the heating means 56 has heating areas divided into plurality over the width of a sheet P and is installed on the upstream of a fixing nip part N and the temperature detection means 34 is installed on the downstream of the heating means 56 and on the upstream of the fixing nip part N; the fixing device 12 further includes heating control means 37 for controlling the heating means 56 so that the temperature of the fixing belt 38 in contact with an image area becomes a fixing temperature and the temperature of the fixing belt 38 in contact with a non-image area becomes a temperature lower than the fixing temperature, and on the basis of a result of the detection of the temperature detection means 34, when the temperature of the fixing belt 38 in contact with the image area is less than a predetermined temperature, adjusting a power to be supplied to the heating means 56.SELECTED DRAWING: Figure 5

Description

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

  Various image forming apparatuses using an electrophotographic system have been devised as image forming apparatuses such as copying machines, facsimile machines, printers, or their combined machines, and are well known in the art. In the image forming process, an electrostatic latent image is formed on the surface of a photosensitive drum as an image carrier, and the electrostatic latent image on the photosensitive drum is developed with a toner or the like as a developer to be visualized. The developed image is transferred onto a recording material (also referred to as paper, recording paper, or recording medium) such as paper or an OHP sheet by a transfer device to carry the image, and unfixed on the recording material by a fixing device using heat and pressure This is established by the process of fixing the toner image.

  Various types of fixing devices have been proposed. For example, a heat roller type fixing device has a nip between a fixing roller and a pressure roller heated by a heating means such as a halogen heater or an induction heating coil. The toner is melted and fixed by heat and pressure by forming a portion and passing a recording material carrying an image through the nip portion.

  In recent years, market demands for energy saving and high speed have been increasing for image forming apparatuses, and belt type and film type fixing devices are often used as fixing devices for realizing energy saving.

  For example, Patent Document 1 discloses that an endless sheet-shaped fixing belt to be heated, a nip forming member disposed inside the fixing belt, and a pressure contact between the fixing belt and the nip forming member. Disclosed is a fixing device including a rotatable pressure roller having a contact portion serving as a fixing nip, and a heater lamp for heating the fixing belt disposed inside the fixing belt and away from the fixing nip. Has been.

  In recent years, with belt type fixing devices, further warm-up time (time required from room temperature to a predetermined printable temperature (reload temperature) such as when the power is turned on) and first print time (after receiving a print request, It is desired to shorten the time required for the printing operation after the printing preparation and the paper discharge to be completed.

  Further, for example, Patent Document 2 discloses a fixing device for surf fixing (film fixing) using a ceramic heater. According to this method, the heat capacity and size can be reduced as compared with the belt-type fixing device, the rise time can be shortened, and the preheating power can be reduced.

  In addition, as a temperature control of the fixing member in the fixing device, there is known a configuration in which a temperature detecting unit that detects the temperature of the fixing member is provided and a heating unit that heats the fixing member is controlled based on the detection by the temperature detecting unit. It has been.

  For example, in Patent Document 3, the temperature of the heat source is determined based on the detection results of the first temperature detection unit installed downstream of the fixing nip unit and the second temperature detection unit detecting the temperature of the heat source installed in the fixing nip unit. A controlled heating device is disclosed. Further, in Patent Document 4, a planar heater is disposed outside the fixing nip, and a temperature detecting unit is disposed between the heating position of the heater and the fixing nip portion to detect the temperature of the fixing belt. A fixing device to be controlled is disclosed.

  In the fixing device disclosed in Patent Document 4, energy saving is achieved by using a planar heater and performing appropriate temperature control based on the detection result of the temperature detection means installed between the heating position of the heater and the fixing nip portion. However, there was still room for further energy conservation.

  Further, in the conventional fixing device, the control temperature of each heating area is determined as the same image even if the image of each area on the recording material is different. Therefore, the control temperature of the heating area is determined so that sufficient fixing is possible in the area on the recording material that requires the most fixing energy. For this reason, in the area on the recording material in the image area that does not require fixing energy, the recording material and the toner are excessively heated, and energy is consumed.

  Further, if the amount of heat supplied to the fixing member is reduced due to deterioration of the heating means, there is a risk of causing a fixing failure.

  Therefore, the present invention achieves energy saving by performing heating in accordance with the image area, and stable fixing by controlling the power supplied to the heating unit in accordance with the change in the amount of heat supplied from the heating unit to the fixing member. An object of the present invention is to provide a fixing device capable of maintaining the performance.

  In order to achieve this object, a fixing device according to the present invention includes a fixing member that rotates in contact with an unfixed image, a pressure member that forms a fixing nip portion between the fixing member, and the fixing member. In a fixing device comprising a heating means for heating and a temperature detecting means for detecting the temperature of the fixing member, and fixing the recording material carrying an unfixed image through the fixing nip portion, the heating means comprises: A heating region divided into a plurality of longitudinal directions perpendicular to the recording material conveyance direction, and disposed upstream of the fixing nip portion in the rotation direction of the fixing member; The heating member is disposed downstream of the heating means and upstream of the fixing nip portion, and each heating area is controlled in accordance with image information formed on the recording material, so that the temperature of the fixing member in contact with the image area is The heating means is controlled so that the temperature of the fixing member that contacts the non-image area is lower than the fixing temperature, and the image area is set based on the detection result of the temperature detection means. When the temperature of the fixing member that comes into contact is less than a predetermined temperature, a heating control unit that adjusts the power supplied to the heating unit is provided.

  According to the present invention, energy is saved by performing heating in accordance with the image area, and stable control is achieved by controlling the power supplied to the heating unit according to the change in the amount of heat supplied from the heating unit to the fixing member. Fixing performance can be maintained.

1 is a schematic diagram illustrating an embodiment of an image forming apparatus. FIG. 3 is a schematic diagram illustrating a basic configuration example (1) of the fixing device. FIG. 3 is an explanatory diagram schematically adding a state of heat radiation from a fixing belt in the fixing device shown in FIG. 2. FIG. 6 is a schematic diagram illustrating a basic configuration example (2) of the fixing device. 1 is a schematic diagram illustrating an embodiment of a fixing device according to the present invention. It is a schematic diagram which shows the structural example of a heating means. It is a schematic diagram which shows the example of arrangement | positioning of a heating means. It is explanatory drawing which shows an example of the image formation pattern which consists of an image area | region and a non-image area | region. It is explanatory drawing which shows the other example of the image formation pattern which consists of an image area | region and a non-image area | region. 6 is a graph showing an example of temperature control of a fixing belt corresponding to an image area and a non-image area. FIG. 6 is an explanatory diagram schematically adding a state of heat radiation from the fixing belt in the fixing device shown in FIG. 5. 6 is a graph showing a relationship between a fixing belt position before and after passing through a heating unit and a fixing belt temperature (front surface / back surface). 5 is a graph showing an example of temperature control of a fixing belt corresponding to an image area and a non-image area, and also shows a temperature when the amount of generated heat is reduced. FIG. 3 is an explanatory view showing a fixing device in which a contact-type temperature detecting unit and a biasing unit are installed on the inner peripheral side of the fixing belt. FIG. 4 is an explanatory diagram showing a fixing device in which a contact-type temperature detecting unit and a cleaning unit are installed on the inner peripheral side of the fixing belt. FIG. 3 is an explanatory view showing a fixing device provided with a temperature detecting means on the surface side of the fixing belt. It is explanatory drawing which shows the fixing device provided with the temperature detection means for every divided heating area. It is explanatory drawing which shows the fixing device provided with the thermopile array with respect to the divided heating area | region.

  Hereinafter, a configuration according to the present invention will be described in detail based on the embodiment shown in FIGS.

  The fixing device according to the present embodiment forms a fixing nip portion (fixing nip portion N) between a fixing member (fixing belt 38) that rotates in contact with an unfixed image (toner image T) and the fixing member. A pressure member (pressure roller 30) for heating, a heating means (heating means 56) for heating the fixing member, and a temperature detection means (temperature detection means 34) for detecting the temperature of the fixing member. In the fixing device (fixing device 12, FIG. 5) for fixing the recording material (paper P) carrying the recording medium through the fixing nip portion, the heating means is divided into a plurality of longitudinal directions perpendicular to the recording material conveyance direction. In addition to having a heating area, it is installed upstream of the fixing nip portion in the rotation direction of the fixing member, and the temperature detection means is installed downstream of the heating means and upstream of the fixing nip portion in the rotation direction of the fixing member, and is on the recording material. Formed image Each heating area is controlled according to information, and the temperature of the fixing member that contacts the image area becomes the fixing temperature (first target temperature, FIG. 10), and the temperature of the fixing member that contacts the non-image area is higher than the fixing temperature. The heating unit is controlled so that the temperature becomes a lower temperature (second target temperature, FIG. 10), and the temperature of the fixing member contacting the image area is less than the predetermined temperature based on the detection result of the temperature detection unit. In this case, a heating control means (heating control means 37) for adjusting the power supplied to the heating means is provided. In addition, the code | symbol in embodiment and the example of application are shown in a parenthesis.

(Image forming device)
FIG. 1 is a schematic configuration diagram illustrating the overall configuration of an embodiment of an image forming apparatus according to the present invention. The outline and operation of the internal configuration of the image forming apparatus will be described with reference to FIG.

  As shown in FIG. 1, the image forming apparatus 1 includes a paper feeding unit 4, a registration roller pair 6, a photosensitive drum 8 as an image carrier, a transfer unit 10, a fixing device 12, and the like. .

  The paper feeding means 4 feeds the paper P as a recording material stored in a stacked state and the paper P stored in the paper feeding tray 14 one by one in order from the top. It has a roller 16 and the like. The paper P sent out by the paper supply roller 16 is temporarily stopped by the registration roller pair 6, and after the misalignment is corrected, it is formed on the photosensitive drum 8 at a timing synchronized with the rotation of the photosensitive drum 8. The toner image is sent to the transfer portion 11 by the registration roller pair 6 at a timing when the leading end of the toner image coincides with a predetermined position at the leading end of the sheet P in the transport direction.

  Around the photosensitive drum 8, in the rotation direction indicated by the arrows, a charging roller 18 as a charging unit, a mirror 20 constituting a part of an exposure unit (not shown), a developing unit 22 including a developing roller 22a, A transfer unit 10 and a cleaning unit 24 including a cleaning blade 24a are disposed. Between the charging roller 18 and the developing means 22, exposure light Lb is irradiated to the exposure unit 26 on the photosensitive drum 8 via the mirror 20 and scanned.

  In this image forming apparatus 1, when the photosensitive drum 8 starts to rotate, the surface of the photosensitive drum 8 is uniformly charged by the charging roller 18, and the exposure light Lb is irradiated and scanned on the exposure unit 26 based on the image information. Thus, an electrostatic latent image corresponding to the image to be created is formed. The electrostatic latent image is moved to the developing means 22 by the rotation of the photosensitive drum 8, where toner is supplied to be visualized to form a toner image. The toner image formed on the photosensitive drum 8 is transferred onto the paper P that has entered the transfer portion 11 at a predetermined timing by applying a transfer bias by the transfer means 10.

  The paper P carrying the toner image is conveyed toward the fixing device 12, fixed by the fixing device 12, and then discharged and stacked on a paper discharge tray (not shown). The configuration of the fixing device 12 will be described later.

  Next, the residual toner remaining on the photosensitive drum 8 without being transferred at the transfer portion 11 reaches the cleaning means 24 as the photosensitive drum 8 rotates, and while passing through the cleaning means 24, the cleaning blade 24a. Is scraped off and cleaned. Thereafter, the residual potential on the photosensitive drum 8 is removed by a neutralizing unit (not shown), and is prepared for the next image forming process.

(Fixing device)
[Prerequisite configuration]
Next, a fixing device provided in the image forming apparatus will be described. Prior to the description of the fixing device according to the present invention, a configuration (conventional configuration) which is a premise of the fixing device according to the present invention will be described with reference to FIG.

  The fixing device 90 shown in FIG. 2 includes a pressure roller 91 and a fixing belt 92 so that the fixing belt 92 is directly heated from the inner peripheral side by a heating means 93 (ceramic heater, thermal head, etc.). It has become. The sheet P carrying the toner image T is conveyed to the fixing nip N of the fixing device 90 and the fixing operation is performed at the fixing nip N.

  The fixing belt 92 is an endless belt or a film using a metal or a resin material. The surface layer of the fixing belt 92 has a release layer, and has a release property so that toner does not adhere. There may be an elastic layer between the base material of the fixing belt 92 and the release layer. When there is no elastic layer, the heat capacity is reduced and the fixability is improved, but when the unfixed image is crushed and fixed, minute irregularities on the surface of the belt are transferred to the image and the image has a crusty skin shape. There arises a problem that uneven gloss (skin skin image) remains. In order to improve this, it is necessary to provide, for example, a silicone rubber layer of 100 [μm] or more as the elastic layer. Due to the deformation of the silicone rubber layer, fine irregularities are absorbed and the skin image is improved.

  A support member 96 (stay) for supporting the fixing nip portion N is provided inside the fixing belt 92 to prevent the nip forming member 97 that receives pressure from the pressure roller 91 from being bent and to have a uniform nip in the axial direction. The width is obtained.

  The pressure roller 91 has an elastic rubber layer on the core and a release layer on the surface. The pressure roller 91 is rotated by a driving force transmitted from a driving source such as a motor through a gear. The pressure roller 91 is pressed against the fixing belt 92 by a spring or the like, and has a predetermined nip width when the elastic rubber layer is crushed and deformed.

  The pressure roller 91 may be a hollow roller, and the pressure roller 91 may have a heating source such as a halogen heater. The elastic rubber layer may be solid rubber, but when there is no heater inside the pressure roller 91, sponge rubber may be used. Sponge rubber is more desirable because it increases heat insulation and makes it difficult for the fixing belt to lose heat.

  The fixing belt 92 rotates along with the pressure roller 91. In the fixing device 90 shown in FIG. 2, the pressure roller 91 rotates and the driving force is transmitted to the fixing belt 92 at the fixing nip portion N, whereby the fixing belt 92 rotates. The fixing belt 92 is sandwiched and rotated at the fixing nip portion N, and travels while being guided by holding members (flanges) at both ends except for the fixing nip portion N.

  In the fixing device 90, the first temperature detecting means 94 disposed on the inner peripheral surface of the fixing belt 92 downstream of the fixing nip N and the second temperature detecting means 95 installed in the vicinity of the heating means 93. Based on this temperature detection, the temperatures of the fixing belt 92 and the heating means 93 are appropriately controlled. With such a fixing device 90, it is possible to realize a fixing device that is low in cost and quick in warm-up.

  FIG. 3 is an explanatory view schematically showing the state of heat radiation from the surface of the fixing belt 92 in the fixing device 90 shown in FIG.

  In order to create a temperature difference between a portion where an image is present and a portion where an image is not present using a heating means 93 installed on the back surface of the fixing belt 92 as in the fixing device 90 shown in FIG. 2, the temperature of the fixing belt 92 is rapidly increased. For this purpose, it is necessary to reduce the width of the heat generating part and increase the heat flux.

  However, in the fixing device 90 shown in FIG. 2, in order to stably supply heat from the heating unit 93 to the fixing belt 92, the width of the heat generating portion of the heating unit 93 is set to the same width as the nip width. In the configuration as shown in FIG. 2, it is difficult to control the energization to the heating means 93 in accordance with the image information to reduce the heating of the portion without the image.

  The heating means 93 is installed in the fixing nip portion N. In the case of a color machine, about 100 μm of a silicone rubber layer is required as described above in order to prevent fixing defects such as distorted skin. This silicone layer has a low thermal conductivity. Therefore, even if the belt surface temperature is controlled using the second temperature detection means 95 installed in the vicinity of the heating means 93, the heating result is reflected after passing through the nip. Therefore, in the fixing device shown in FIG. 2, the first temperature detection means 94 is installed at a position away from the heating means 93, and the belt temperature is controlled based on the detection result.

  When the first temperature detecting means 94 is installed as in the fixing device 90 shown in FIG. 2, as shown in FIG. 3, the first temperature detecting means 94 from the heating position, or the first temperature detecting means 94 to the fixing nip. Since the distance to the portion N becomes long, the influence of heat radiation and thermal diffusion increases from the heating to the fixing nip portion N. For this reason, when heating is performed according to image information, it is difficult to maintain a predetermined region at a necessary temperature due to temperature decrease or diffusion due to heat radiation. Furthermore, if the temperature is raised in consideration of heat dissipation and diffusion, extra power is consumed in addition to the power required for fixing.

  On the other hand, for example, in the fixing device 90 shown in FIG. 4, since the distance from the heating position to the fixing nip portion N is short, the above-described heat dissipation and thermal diffusion hardly occur, and it is suitable for heating according to image information. It can be said that it was a configuration. However, if the amount of heat generation decreases due to deterioration of the heating element of the heating means 93, it becomes difficult to supply the necessary amount of heat to the image area. Reference numeral 98 denotes a heater holder and 99 denotes a fixing roller.

[Configuration of Fixing Device]
One embodiment of the fixing device according to the present invention is shown in FIG. As shown in FIG. 5, the fixing device 12 includes a fixing belt 38 (fixing member), a pressure roller 30 (pressure member), a heating unit 56, and a pressure roller 40 (pressure member).

  The fixing belt 38 rotates in contact with the unfixed image, and the pressure roller 30 is disposed so as to be able to press a part of the fixing belt 38, and forms a fixing nip portion N between the fixing belt 38 and the fixing belt 38. In the fixing device 12, the paper P carrying the toner image T is inserted into the fixing nip portion N to perform heating and fixing.

  The leading end of the paper P inserted through the fixing nip N is separated by a separation means (not shown) such as a separation plate and a separation claw disposed on the fixing belt 38 side and / or the pressure roller 30 side, and is sent to the next process. Discharged. Note that the separation plate, the separation claw, and the like are preferably in a non-contact state with a minute gap from the fixing belt 38 and the pressure roller 30 because of the influence on the image quality.

  The fixing belt 38 may include a base body 38a, an elastic layer 38b coated on the surface of the base body 38a, and a release layer 38c coated on the surface of the elastic layer 38c. The fixing belt 38 is preferably an endless seamless belt.

  The substrate 38a can be, for example, a SUS substrate having an outer diameter of 40 mm and a thickness of 40 μm, but is not limited thereto, and may be a metal substrate made of polyimide (PI) resin, iron, nickel, or the like. The elastic layer 38b is made of, for example, silicone rubber having a layer thickness of about 100 μm. Fluorine rubber, foamable silicone rubber, or the like can be used.

  The release layer 38c has a layer thickness of about 5 to 50 μm, PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer resin), polyimide, polyetherimide, PES (polyether sulfide), PTFE (polytetrafluoro). Ethylene) and the like can be used. By forming the release layer 38c, it is possible to enhance the durability and secure the release property.

  The pressure roller 30 can be configured to include a cored bar 30a and an elastic layer 30b coated on the surface of the cored bar 30a. The pressure roller 30 is pressed against the fixing belt 38 by an urging means (not shown).

  The cored bar 30a can be a thin cylindrical body made of a metal material such as iron having an outer diameter of 40 mm and a thickness of 2 mm, for example, and a heat source such as a heater is fixed inside the cylindrical body. Good. For example, a halogen heater or a carbon heater can be used as the heater. The elastic layer 30b can be made of, for example, silicone rubber and has a thickness of 5 mm. It is preferable to form a fluororesin layer having a thickness of about 40 μm on the surface of the elastic layer 30b in order to improve the releasability.

  A belt support member 61 is provided on the inner peripheral side of the fixing belt 38, and a nip forming member 60 is installed at the fixing nip portion N. The belt support member 61 and the nip forming member 60 are connected to a side plate of a fixing device (not shown) and support the fixing belt 38.

  The pressing roller 40 may have a configuration in which an outer diameter is 15 mm to 20 mm, and includes a cored bar 40b and an elastic layer 40a covered on the surface thereof. The core metal 40b can be made of, for example, an iron core metal, and the elastic layer 40a can be made of, for example, silicone rubber. Moreover, you may form the fluororesin layer for improving mold release property on the surface of the elastic layer 40a.

  The pressing roller 40 is pressed against the fixing belt 38 by an urging unit (not shown). The pressing roller 40 can maintain the contact between the heating unit 56 and the fixing belt 38 to realize stable heating.

  The pressure roller 30 and the pressure roller 40 are pivotally supported so as to be rotatable in the longitudinal direction of a casing (not shown) of the fixing device 12, and driving means and the like for each roller (not shown) are fixedly held on the casing.

  A heating unit 56 is provided on the inner peripheral side of the fixing belt 38. The heating unit 56 is attached to the stay-like member 59 and is disposed at a position where it can contact the inner periphery of the fixing belt 38. The heating means 56 is a planar heating element such as a thermal heater in which a resistance heating element is formed. The heating unit 56 is connected to the power supply unit 39 and is supplied with electric power from the power supply unit 39.

  The configuration of the planar heating element is not particularly limited. For example, as shown in FIG. 6, resistance heating in which conductive particles are dispersed in a heat-resistant resin on an insulating base material 57. And a heating element 58 which is a body. The width of the heating element 58 is preferably as narrow as about 3 mm, for example.

  As shown in FIG. 7, the heating unit 56 includes a plurality of (seven in this embodiment) heating units 56 a to 56 g arranged in the width direction of the paper P, and each heating unit 56 a to 56 g has a heating element 58. And forming a heating region. Each heating part 56a-56g can control heating independently, and can heat the fixing belt 38 each independently.

  The heating means 56 is desirably installed in the vicinity of the upstream of the fixing nip N. Thereby, the influence of heat radiation from the fixing belt 38 to the fixing nip portion N can be reduced. Furthermore, the fixing belt 38 can be conveyed to the fixing nip portion N in a state where heat from the back surface (also referred to as the inner peripheral surface) is transmitted to the front surface, and heating according to the image becomes possible. In the example shown in FIG. 5, the heating unit 56 is disposed approximately 90 ° upstream from the fixing nip N in the rotation direction.

  The temperature detector 34 detects the temperature of the inner or outer peripheral surface of the fixing belt 38 upstream of the fixing nip N of the fixing belt 38 and downstream of the heating unit 56. The temperature detection unit 34 is, for example, a thermistor. In the example of FIG. 5, the temperature of the inner peripheral surface of the fixing belt 38 that is provided on the inner peripheral side is detected.

  It is also preferable to provide a heating temperature detection means 36 in the vicinity of the heating means 56 and detect the temperature of the heating means 56. The heating temperature detection means 36 is a thermistor, for example.

  The heating control unit 37 controls the power supply unit 39 based on the detection information of the temperature detection unit 34 and controls the amount of power supplied from the power supply unit 39 to the heating unit 56. Further, when the heating temperature detection means 36 is provided, the power supply unit 39 is controlled based on the detection information of the temperature detection means 34 and the heating temperature detection means 36. The heating control means 37 is composed of a microcomputer having a CPU, ROM, RAM, I / O interface and the like.

  The heating unit 56 may be configured to use an external heating unit such as electromagnetic induction heating provided on the outer peripheral side of the fixing belt 38 and heating the fixing belt 38 from the outer peripheral side.

[Heating control]
In the fixing device 12 according to the present embodiment, the heating control unit 37 changes the heating rate of the heating unit 56 based on image information (image data) for forming an image on the paper P, so that the heating unit unit is heated. Control heating. That is, the image information is divided into an image area and a non-image area, and when the unfixed toner image T on the paper P is fixed on the paper P, the image area is fixed at a required fixing temperature, and the non-image area is fixed. The temperature is lower than that. Thus, it is possible to realize energy saving by controlling the heating element 58 according to the image information.

  8A shows an image formation pattern in which an image area a, a non-image area b, and an image area c exist on the paper P in order from the leading end side in the transport direction, and FIG. In addition, an image forming pattern in which an image area a and a non-image area b exist in order from the leading end side in the transport direction Y is shown. Here, fixing is required in the image area a and the image area c, but fixing is not necessary in the non-image area b because there is no toner to be fixed.

  When image information of the above pattern is input to the heating control unit 37 from an image processing apparatus (not shown), the heating control unit 37 causes the temperature of the part of the fixing belt 38 corresponding to the non-image region b to be in the image regions a and c. The heating unit 56 is controlled to be lower than the temperature of the corresponding fixing belt 38. Note that “corresponding to an image region or a non-image region” means a position where the fixing belt 38 is in close contact, and is hereinafter also expressed as close contact as appropriate.

  In other words, the power corresponding to the fixing temperature is supplied to the entire area of the heating unit 56 at the part corresponding to the image area a, and the supplied power is reduced at the part corresponding to the non-image area b. Further, in the case of FIG. 8A, electric power at which the fixing temperature is obtained again is supplied to the portion corresponding to the image region c.

  At this time, the actual supplied power is input so as to preliminarily heat the portion before the image area enters the nip portion, as indicated by the hatched portion in the figure. The preheating area s1 is an area that is necessary because the heating length in the circumferential direction of the heating means 56 and the heating element 58 itself require a temperature raising time. The preheating region s1 is desirably as small as possible from the viewpoint of energy saving.

  FIG. 9A shows an image forming pattern in which an image region c and a non-image region d exist on the paper P in the paper width direction X orthogonal to the transport direction Y. FIG. 9B shows an image forming pattern in which an image area e and a non-image area f exist in the paper width direction X, but an image area g exists on the leading end side in the transport direction Y. Yes. That is, a part of the non-image area f is an image area g.

  In the case of FIG. 9A, the heating control unit 37 heats so that the temperature of the portion of the fixing belt 38 corresponding to the non-image area d is lower than the temperature of the portion of the fixing belt 38 corresponding to the image area c. The heating area of the means 56 is controlled.

  Further, in the case of FIG. 9B, the heating control means 37 has the fixing belt 38 in which the temperature of the portion of the fixing belt 38 corresponding to the non-image area (the overlapping portion of f and h) corresponds to the image areas e and g. The heating area of the heating means 56 is controlled so as to be lower than the temperature of the part.

  That is, the power corresponding to the fixing temperature is supplied to the heating unit 56 at the part corresponding to the image area, and the supplied power is reduced at the part corresponding to the non-image area. Also in this case, the preheating region s1 is necessary.

  At this time, the heating control unit 37 performs feed forward control on the heating unit 56 to supply the heating element 58 with electric power determined in advance so as to reach a predetermined temperature.

  As a control in this case, the power supply may be completely stopped (off) at a portion corresponding to the non-image area. However, if the temperature is excessively lowered, the rise to the fixing temperature in the next image area is caused. It may not be in time.

  For this reason, as shown in FIG. 10, in the part corresponding to the non-image area, the second target temperature is lower than the first target temperature (fixing temperature) corresponding to the image area, but higher than the room temperature by a predetermined temperature. It is desirable to control so as to keep the fixing member temperature.

  In this way, power is also supplied to the portion corresponding to the non-image area, but the supplied power is reduced. That is, since the supply power in the region P ′ is smaller than the supply power in the region P in FIG. 10, it is possible to save energy.

  In this way, the heating control unit 37 controls the heat generation area divided into a plurality of parts, and heats the image area on which the toner image T is transferred to the fixing temperature according to the position of the toner image T on the paper P. The non-image area where the toner image T is not transferred is set to a temperature lower than the fixing temperature.

  Here, as described above, the temperature detecting unit 34 detects the temperature of the inner peripheral surface or the outer peripheral surface of the fixing belt 38 upstream of the fixing nip portion N of the fixing belt 38 and downstream of the heating unit 56. doing.

  FIG. 11 is an explanatory diagram schematically showing a state of heat radiation from the fixing belt 38 in the fixing device 12 shown in FIG. In addition, a part is shown in a simplified manner. As shown in FIG. 11, the heating unit 56 is installed at a position other than the fixing nip N, and the temperature detection unit 34 is installed in a narrow area downstream of the heating unit 56 and upstream of the fixing nip N. Thus, the influence of heat radiation from the fixing belt 38 can be reduced, and the heating control is performed based on the detected temperature of the fixing belt 38 detected near the fixing nip portion N, regardless of the ambient temperature. The amount of heat required for fixing can be accurately supplied to the image.

  Further, as shown in FIG. 11, since the heating means 56 is provided approximately 90 ° upstream from the fixing nip N, the distance from the heating means 56 to the fixing nip N is short, and the outside of the image area after the heating is performed. The heat diffusion to the image area is suppressed, the heat supply necessary only for the image area can be achieved, and energy saving can be achieved.

  FIG. 12 shows the relationship between the belt temperature and the belt temperature before and after passing through the heating position by the heating means 56 (heating element 58) when the fixing belt 38 is heated at the position where the temperature detecting means 34 shown in FIG. It is a graph, Comprising: The surface temperature of the fixing belt 38 and a back surface temperature are shown. Moreover, the heating means 56 and the press roller 40 are typically added.

  As shown in FIG. 12, since the back surface temperature of the fixing belt 38 is in contact with the heating unit 56, the temperature rapidly increases in the vicinity of the contact surface. On the other hand, the temperature of the surface temperature becomes maximum at a position away from the heating means 56 on the downstream side due to a delay in thermal response.

  For this reason, in the configuration in which the heating unit 56 is provided on the inner peripheral side of the fixing belt 38 and the fixing belt 38 is heated from the back surface, the temperature detecting unit 34 considers the thermal response characteristics of the fixing belt 38 and the heating performance of the heating unit 56. Thus, it is preferable to install the heater 56 at a position where heat from the fixing belt 38 is transmitted from the back surface to the front surface. In other words, the temperature detecting unit 34 is installed at a position where the inner and outer peripheral temperatures of the fixing belt 38 become substantially equal after heating by the heating unit 56, and detects the temperature of the fixing belt 38 at the position. It is preferable to do.

  Further, in the configuration in which the external heating means for heating the heating means 56 from the outer peripheral side of the fixing belt 38 is provided and the fixing belt 38 is heated from the front surface, the temperature distribution on the front surface / back surface shown in FIG. . That is, the surface temperature of the fixing belt 38 is higher in the vicinity of the heating unit 56, and the temperature is lower as it is closer to the fixing nip portion N. For this reason, in order to accurately control the temperature in front of the fixing nip portion N, the temperature detecting means 34 is installed at a position close to the fixing nip portion N so that the temperatures of the back surface and the front surface of the fixing belt 38 are substantially equal. Is preferred.

  By the way, as described with reference to FIG. 10, in the fixing device 12 according to the present embodiment, the first target temperature is set in the portion corresponding to the image area, and the second target temperature is set in the portion corresponding to the non-image area. The feed forward control is performed so as to maintain the fixing member temperature. However, the heating element 58 is a resistance heating element. One target temperature may not be reached.

  FIG. 13 is a graph showing the temperature of the fixing belt 38 as a dotted line when the temperature does not reach the first target temperature even if the temperature is controlled due to the deterioration of the heating element 58 in the graph shown in FIG. As described above, when the predetermined power is supplied and the initial desired heat generation amount is not obtained due to deterioration of the heating element 58 or the like, the desired fixing temperature is not reached and the fixing performance is deteriorated.

  Therefore, in the fixing device 12 according to the present embodiment, the heating control unit 37 is configured such that the detection result of the temperature detection unit 34 installed downstream of the heating unit 56 and in front of the fixing nip N is equal to or lower than a predetermined temperature. For example, when the temperature is lower than the first target temperature by a predetermined temperature or more, by increasing the electric power supplied to the heating element 58 according to the decrease, the heating element 58 is initially desired due to deterioration or the like. Even when the amount of heat generated is not reached, stable fixing properties are maintained. At this time, when the heating temperature detection means 36 is provided, the detection result of the heating temperature detection means 36 may be used together.

  As described above, according to the fixing device 12 according to this embodiment, energy is saved by performing heating according to the image area, and heating is performed according to a change in the amount of heat supplied from the heating unit 56 to the fixing belt 38. By controlling the power supplied to the means 56, stable fixing performance can be maintained.

  Specifically, the fixing belt 38 is directly heated by using a heating unit 56 that is contact-type and divided for each heating area and can be controlled independently, and an appropriate amount of heat is applied to the image area according to the image formed on the recording material. By supplying, it is possible to suppress the supply of heat to the non-image area to save energy, and to shorten the first print time from the heating standby time.

  Further, even when the heating element 58 of the heating means 56 deteriorates with time and the amount of supplied heat is reduced, this is detected by the temperature detection means installed downstream of the heating means 56 and upstream of the fixing nip N. By adjusting the power supplied to the heating means 56 in accordance with the detection result of 34, the occurrence of fixing failure due to a decrease in the amount of heat supplied to the fixing belt 38 is prevented, and the amount of heat generated changes due to deterioration of the heating element 58 or the like. Even in this case, the calorific value can always be kept constant and stable fixing properties can be maintained.

  Next, a preferred installation example of the temperature detection means 34 will be described. FIG. 14 shows an example of the fixing device 12 in which the contact-type temperature detection means 34 is installed on the inner peripheral side of the fixing belt 38.

  In the fixing device 12 described so far, when the fixing belt 38 rotates, the fixing belt 38 rotates along with the pressure roller 30. However, the presence of the pressing roller 40 causes the fixing belt between the pressing roller 40 and the fixing nip portion N to be rotated. 38 is pulled, and the belt shape in front of the fixing nip portion N is not circular, but as shown by a solid line in FIG. The behavior of changes.

  Since the behavior of the fixing belt 38 changes in this way, when the temperature detecting means 34 is disposed on the inner peripheral side of the fixing belt 38, the temperature detection is performed in order to maintain the contact between the temperature detecting means 34 and the fixing belt 38. It is preferable that the means 34 is urged toward the belt inner peripheral side. As an urging means for urging the temperature detecting means 34 toward the inner peripheral side of the fixing belt 38, for example, a leaf spring 70 can be used as shown in FIG.

  By using a variable biasing means such as a leaf spring 70 to bias the temperature detection means 34 from the inner peripheral side of the fixing belt 38 to the outer side, belt deformation occurs during rotation. Even if it exists, sufficient contact can be maintained.

  Further, when the contact-type temperature detecting means 34 is installed on the inner peripheral side of the fixing belt 38, it is also preferable to install a cleaning means for removing wear powder and the like. FIG. 15 shows an example of the fixing device 12 in which a contact-type temperature detection unit 34 and a scraper 71 as a cleaning unit are installed on the inner peripheral side of the fixing belt 38.

  In the fixing device 12 described so far, the fixing belt 38 rotates while the inner peripheral surface thereof is in contact with the heating unit 56, so that the inner peripheral surface of the fixing belt 38 is rubbed by the heating unit 56 and the inner peripheral surface of the fixing belt 38 is rubbed. Wear powder is generated from the surface. If the wear powder adheres to the contact-type temperature detection means 34, there is a risk of erroneous detection.

  Therefore, as shown in FIG. 15, erroneous detection is prevented by providing a cleaning means for removing wear powder such as a scraper 71 on the upstream side of the temperature detection means 34 so that the wear powder does not adhere to the temperature detection means 34. It becomes possible to do.

  The example in which the temperature detection unit 34 is installed on the inner peripheral side of the fixing belt 38 has been described so far, but the temperature detection unit 34 may be provided on the front side of the fixing belt 38. FIG. 16 shows an example of the fixing device 12 in which the temperature detecting means 34 is provided on the surface side of the fixing belt 38.

  When the temperature detecting means 34 is provided on the surface side of the fixing belt 38, if this is a contact type temperature detecting means, the fixing belt 38 is scratched due to wear and causes fixing failure. When installing 34, it is necessary to use a non-contact temperature detecting means.

  In the fixing device 12 described so far, in order to perform heating control independently for the image area, the heating unit 56 is divided into a plurality of heating units to form a heating area, and each has heating elements 58a to 58e. ing. FIG. 17 shows an example in which the heating means 56 has five heating elements 58a to 58e.

  In the heating control corresponding to the image area, as shown in FIG. 17, a total of five temperature detection means 34 are provided corresponding to the divided heating areas of the heating means 56, and correspond to each position. The temperature of the heating area is detected.

  Here, as shown in FIG. 18, the temperature detection means 34 may detect two or more divided heating regions, and may be provided with a predetermined number smaller than the number of heating regions. For example, by using a thermopile array as shown in FIG. 18 as the temperature detecting means 34, it is not necessary to install a temperature detecting means for each divided heating region, and the cost can be reduced.

  In the example of FIGS. 17 and 18, the temperature detecting means 34 is provided on the outer peripheral side of the fixing belt 38, but it may be provided on the inner peripheral side of the fixing belt 38 as described above. .

  The above-described embodiment is a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 4 Paper feed means 6 Registration roller pair 8 Photosensitive drum 10 Transfer means 11 Transfer part 12 Fixing device 14 Paper feed tray 16 Paper feed roller 18 Charging roller 20 Mirror 22 Development means 22a Development roller 24 Cleaning means 24a Cleaning blade 26 Exposure unit 30 Pressure roller 30a Core 30b Elastic layer 34 Temperature detection unit 36 Heating temperature detection unit 37 Heating control unit 38 Fixing belt 38a Base 38b Elastic layer 38c Release layer 39 Power supply unit 40 Pressing roller 40a Elastic layer 40b Core 56 heating means 56a to 56g heating section 57 base material 58 heating element 58a to 58e heating element 59 stay-like member 60 nip forming member 61 belt support member 70 leaf spring 71 scraper Lb exposure light N fixing nip P paper T toner image

JP 2004-286922 A Japanese Patent No. 2861280 JP 2006-98998 A JP 2012-159543 A

Claims (10)

A fixing member that rotates in contact with an unfixed image;
A pressure member that forms a fixing nip with the fixing member;
Heating means for heating the fixing member;
Temperature detecting means for detecting the temperature of the fixing member,
In a fixing device that fixes a recording material carrying an unfixed image through the fixing nip portion,
The heating means has a heating region divided into a plurality of longitudinal directions perpendicular to the recording material conveyance direction, and is installed upstream of the fixing nip portion in the rotation direction of the fixing member.
The temperature detecting means is installed downstream of the heating means and upstream of the fixing nip portion in the rotation direction of the fixing member,
Each heating area is controlled according to image information formed on the recording material, and the temperature of the fixing member in contact with the image area becomes the fixing temperature, and the temperature of the fixing member in contact with the non-image area is the fixing temperature. And controlling the heating means so that the temperature is lower than,
Fixing comprising heating control means for adjusting power supplied to the heating means when the temperature of the fixing member in contact with the image area is less than a predetermined temperature based on the detection result of the temperature detection means. apparatus.   2. The temperature detection unit detects the temperature of the fixing member at a position where the inner peripheral side and the outer peripheral side of the fixing member are substantially equal to each other after being heated by the heating unit. Fixing device. The heating means is provided on the inner peripheral side of the fixing member,
The fixing device according to claim 1, further comprising a pressing unit that presses the fixing member toward the heating unit from an outer peripheral side of the fixing member.   The fixing device according to claim 1, wherein the temperature detection unit is disposed in contact with an inner peripheral surface of the fixing member.   The fixing device according to claim 4, further comprising an urging unit that urges the temperature detection unit toward an inner peripheral surface side of the fixing member.   A cleaning means for removing abrasion powder generated from the fixing member is provided downstream of the position where the fixing member is heated by the heating means and upstream of the temperature detecting means. Item 6. The fixing device according to Item 4 or 5.   4. The fixing device according to claim 1, wherein the temperature detection unit is disposed on an outer peripheral side of the fixing member in a non-contact manner with the fixing member. 5.   The fixing device according to claim 1, wherein the temperature detecting unit is provided in each of the divided heating regions of the heating unit.   The temperature detecting means detects two or more heating areas of the divided heating areas of the heating means, and is provided with a predetermined number smaller than the number of heating areas. The fixing device according to any one of the above.   An image forming apparatus comprising the fixing device according to claim 1.