JP2019105836A - Heater, fixing device, and image forming apparatus - Google Patents

Abstract

To control the temperature of a plurality of resistance heating elements of a planar heating body with a smallest possible number of temperature detection means (temperature detection sensors), and prevent an abnormal increase in temperature.SOLUTION: A heater of the present invention comprises: resistance heating elements 361 to 368 that are arranged in plurality in the longitudinal direction of a substrate 350 and electrically connected in parallel to each other; power control means (AC power supply 410 and triac 420) that supplies power to the resistance heating elements; a first temperature detection sensor TH1 that detects the temperature of the first resistance heating element 364; a second temperature detection sensor TH2 that detects the temperature of the second resistance heating element 368; and control means (control unit 400) that controls the power control means such that the temperature of the resistance heating elements becomes a predetermined temperature on the basis of a result of detection performed by the first temperature detection sensor TH1, and blocks the supply of power when the second temperature detection sensor TH2 detects an abnormal temperature.SELECTED DRAWING: Figure 4

Description

The present invention relates to a heating device having a plurality of resistance heating elements, a fixing device, and an image forming apparatus.

Various types of fixing devices used in electrophotographic image forming apparatuses are known. One of them is a type in which a thin fixing belt of low heat capacity is heated by a planar heating member composed of a base material and a resistance heating element. In this planar heating body, a plurality of resistance heating elements are disposed on a base material disposed in the width direction of the fixing belt, and these resistance heating elements are electrically connected in parallel. In this way, the temperature rise of the non-sheet-passing portion when passing a small size sheet is suppressed (Patent Documents 1 and 2). By using a PTC heater having a positive temperature coefficient for the resistance heating element, it is possible to save energy by further suppressing the temperature rise in the non-sheet-passing portion.

As described above, when a plurality of resistance heating elements are connected in parallel, current continues to flow through the other resistance heating elements even if any one resistance heating element is disconnected. If a temperature detection sensor such as a thermistor is disposed in the heating region of each resistance heating element, the temperature of the resistance heating element can be individually controlled, so that the abnormal temperature rise of the resistance heating element does not occur.

However, it is expensive to attach a temperature detection sensor to all of them. Therefore, for example, if the temperature detection sensor is attached to only one resistance heating element at the center in the longitudinal direction, the current of the other resistance heating elements may continue to increase and temperature control may become impossible if the resistance heating element is broken. .

The present invention has been made in view of such problems, and a heating device and a fixing device capable of preventing an abnormal temperature rise by controlling the temperature of a plurality of resistance heating elements of a planar heating body with as few temperature detection sensors as possible. And providing an image forming apparatus.

In order to solve the above-mentioned subject, a heating device of the present invention supplies electric power to a plurality of resistance heating elements disposed in parallel along the longitudinal direction of the substrate and electrically connected to each other in parallel, and the plurality of resistance heating elements Power control means, first temperature detection means for detecting the temperature of a first resistance heating element which is one of the plurality of resistance heating elements, and second resistance heat generation which is another one of the plurality of resistance heating elements Power of the power control means such that the temperature of the plurality of resistance heating elements becomes a first predetermined temperature based on a second temperature detection means for detecting the temperature of the body and a detection result of the first temperature detection means Control means for controlling the amount and interrupting the supply of power from the power control means to the plurality of resistance heating elements when the second temperature detection means detects a second predetermined temperature I assume.

According to the present invention, even if the first resistance heating element is disconnected and the temperature control of the plurality of resistance heating elements by the first temperature detection means becomes impossible, the second temperature detection means detects the second predetermined temperature. Since the supply of power to each resistance heating element is shut off, abnormal temperature rise of each resistance heating element can be prevented.

FIG. 1 is a schematic view of an image forming apparatus according to an embodiment of the present invention. FIG. 1 is a principle view of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a first fixing device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a second fixing device according to an embodiment of the present invention. FIG. 7 is a cross-sectional view of a third fixing device according to an embodiment of the present invention. FIG. 7 is a cross-sectional view of a fourth fixing device according to an embodiment of the present invention. (A)-(c) is a top view which shows the arrayed state of each resistance heating element of the planar heating element which provided the electrode in the both ends. (A)-(c) is a top view which shows the arrayed state of each resistance heating element of the planar heating element which provided the electrode in one end. It is a figure showing a heating device, a power control circuit, and a control part. It is a flow chart which shows control operation of a heating device.

Hereinafter, a heating device according to an embodiment of the present invention, and a fixing device and an image forming apparatus (laser printer) using the heating device will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the redundant description thereof will be appropriately simplified or omitted. Further, dimensions, materials, shapes, relative arrangements and the like in the description of each component are only examples, and the scope of the present invention is not limited to them unless specifically described.

In the following embodiments, “recording medium” will be described as “paper”, but “recording medium” is not limited to paper (paper). The “recording medium” includes not only paper (paper) but also OHP sheets, fabrics, metal sheets, plastic films, or prepreg sheets in which a carbon fiber is impregnated with a resin in advance.

The media, recording paper, and recording sheets, to which the developer and the ink can be attached, are all included in the "recording medium". In addition to plain paper, "paper" also includes thick paper, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, and the like.

In addition, “image formation” used in the following description means not only the addition of an image having a meaning such as characters and figures to a medium, but also the addition of an image having no meaning such as a pattern to a medium Also mean.

(Configuration of laser printer)
FIG. 1A is a block diagram schematically showing the configuration of a color laser printer 100 as an embodiment of an image forming apparatus provided with a heating device or fixing device 300 of the present invention. FIG. 1B also illustrates the principle of the laser printer 100 in a simplified manner.

The color laser printer 100 includes four process units 1K, 1Y, 1M and 1C as image forming means. These process units form an image with developers of respective colors of black (K), yellow (Y), magenta (M) and cyan (C) corresponding to color separation components of a color image.

Each of the process units 1K, 1Y, 1M, and 1C has the same configuration except that it has toner bottles 6K, 6Y, 6M, and 6C containing different colors of unused toner. Therefore, the configuration of one process unit 1K will be described below, and the descriptions of the other process units 1Y, 1M, and 1C will be omitted.

The process unit 1K includes an image carrier 2K (for example, a photosensitive drum), a drum cleaning device 3K, and a charge removing device. The process unit 1K further includes a charging device 4K as charging means for uniformly charging the surface of the image carrier, and a developing device as a developing means for performing visible image processing of the electrostatic latent image formed on the image carrier. It has 5K and so on. The process unit 1K is detachably mounted to the main body of the laser printer 100, and consumable parts can be replaced simultaneously.

The exposure unit 7 is disposed above the process units 1K, 1Y, 1M, and 1C installed in the laser printer 100. The exposure unit 7 is configured to perform writing scanning according to image information, that is, to reflect the laser light Lb from the laser diode by the mirror 7a based on the image data and to irradiate the image carrier 2K.

The transfer device 15 is disposed below the process units 1K, 1Y, 1M, and 1C in this embodiment. This transfer device 15 corresponds to the transfer means TM of FIG. 1B. The primary transfer rollers 19 K, 19 Y, 19 M, 19 C are disposed in contact with the intermediate transfer belt 16 so as to face the image carriers 2 K, 2 Y, 2 M, 2 C.

The intermediate transfer belt 16 circulates in a state of being wound around the respective primary transfer rollers 19 K, 19 Y, 19 M, 19 C, the driving roller 18 and the driven roller 17. The secondary transfer roller 20 is disposed opposite to the drive roller 18 and in contact with the intermediate transfer belt 16. When the image carriers 2K, 2Y, 2M, and 2C are the first image carriers of the respective colors, the intermediate transfer belt 16 is a second image carrier obtained by combining those images.

The belt cleaning device 21 is disposed downstream of the secondary transfer roller 20 in the traveling direction of the intermediate transfer belt 16. In addition, a cleaning backup roller is installed on the opposite side of the intermediate transfer belt 16 to the belt cleaning device 21.

A sheet feeding apparatus 200 having a tray for stacking sheets P is installed below the laser printer 100. The sheet feeding apparatus 200 constitutes a recording medium supply unit, and can store a large number of sheets P as a recording medium in a bundle, and the sheet feeding roller 60 or the roller pair 210 as a conveyance unit of the sheet P. Are united with The sheet feeding device 200 can be inserted into and removed from the main body of the laser printer 100 for the purpose of supplying sheets. The sheet feeding roller 60 and the roller pair 210 are disposed above the sheet feeding device 200, and convey the uppermost sheet P of the sheet feeding device 200 toward the sheet feeding path 32.

The pair of registration rollers 250 as separating and conveying means is disposed immediately upstream of the secondary transfer roller 20 in the conveying direction, and can temporarily stop the sheet P fed from the sheet feeding device 200. By this temporary stop, slack is formed on the leading end side of the sheet P, and the skew (skew) of the sheet P is corrected.

A registration sensor 31 is disposed immediately upstream of the registration roller pair 250 in the conveyance direction, and the registration sensor 31 detects passage of the leading end of the sheet. After the registration sensor 31 detects the passage of the leading end of the sheet, when a predetermined time elapses, the sheet is abutted against the pair of registration rollers 250 and is temporarily stopped.

At the downstream end of the sheet feeding device 200, a conveyance roller 240 for conveying the sheet conveyed to the right from the roller pair 210 upward is disposed. As shown in FIG. 1A, the conveyance roller 240 conveys the sheet toward the upper registration roller pair 250.

The roller pair 210 is configured by a pair of upper and lower rollers. The roller pair 210 can be an FRR separation system or an FR separation system. In the FRR separation method, a separation roller (return roller) to which a fixed amount of torque is applied in the reverse sheet feeding direction via a torque limiter by a drive shaft is brought into pressure contact with the feeding roller to separate sheets at the nip between the rollers. In the FR separation method, a separation roller (friction roller) supported on a fixed shaft is brought into pressure contact with a feed roller via a torque limiter to separate sheets at a nip between the rollers.

In this embodiment, the roller pair 210 is configured in the FRR separation system. That is, the roller pair 210 includes an upper feed roller 220 for transporting the sheet into the machine, and a lower separation roller 230 to which driving force is applied by a drive shaft via a torque limiter in the opposite direction to the feed roller 220. It consists of

The separation roller 230 is biased toward the feed roller 220 by biasing means such as a spring. The sheet feeding roller 60 is configured to rotate leftward in FIG. 1A by transmitting the driving force of the sheet feeding roller 220 through the clutch means.

The sheet P which has been abutted against the registration roller pair 250 and has a slack formed at the leading end is synchronized with the timing at which the toner image formed on the intermediate transfer belt 16 is suitably transferred. 18 to the secondary transfer nip (transfer nip N in FIG. 1B). Then, in the discharged sheet P, the toner image formed on the intermediate transfer belt 16 is electrostatically transferred to a desired transfer position with high accuracy by the bias applied in the secondary transfer nip. ing.

The post-transfer conveyance path 33 is disposed above the secondary transfer nip of the secondary transfer roller 20 and the drive roller 18. The fixing device 300 is installed near the upper end of the post-transfer conveyance path 33. The fixing device 300 includes a fixing belt 310 containing a heating device, and a pressure roller 320 as a pressing member that rotates while being in contact with the fixing belt 310 with a predetermined pressure. The fixing device 300 may have other configurations as shown in FIGS. 2B to 2D described later.

The post-fixing conveyance path 35 is disposed above the fixing device 300, and is branched into the paper discharge path 36 and the reverse conveyance path 41 at the upper end of the post-fixing conveyance path 35. The switching member 42 is disposed at this branch portion, and the switching member 42 is pivoted about the pivot shaft 42a. In the vicinity of the opening end of the paper discharge path 36, a paper discharge roller pair 37 is disposed.

The reverse conveying path 41 joins the sheet feeding path 32 at the other end opposite to the branching portion. Further, in the middle of the reverse conveyance path 41, a reverse conveyance roller pair 43 is disposed. The paper discharge tray 44 is installed on the top of the laser printer 100 so as to form a concave shape in the inward direction of the laser printer 100.

The powder container 10 (for example, a toner container) is disposed between the transfer device 15 and the sheet feeding device 200. The powder container 10 is detachably attached to the main body of the laser printer 100.

The laser printer 100 according to the present embodiment requires a predetermined distance from the sheet feeding roller 60 to the secondary transfer roller 20 according to the relationship of transfer sheet conveyance. And the powder container 10 is installed in the dead space which arose in this distance, and the miniaturization of the whole laser printer is achieved.

The transfer cover 8 is disposed on the upper side of the sheet feeding device 200 and in front of the sheet feeding device 200 in the pulling direction. Then, by opening the transfer cover 8, the inside of the laser printer 100 can be checked. The transfer cover 8 is provided with a manual paper feed roller 45 for manual paper feed and a manual paper feed tray 46 for manual paper feed.

Note that the laser printer of the present embodiment is an example of an image forming apparatus, and the image forming apparatus is not limited to the laser printer. That is, the image forming apparatus may be configured as a multifunction machine in which any one of a copying machine, a facsimile, a printer, a printing machine, and an ink jet recording apparatus, or at least two of them are combined.

(Operation of laser printer)
Next, the basic operation of the laser printer according to the present embodiment will be described below with reference to FIG. 1A. First, the case of single-sided printing will be described. The paper feed roller 60 is rotated by a paper feed signal from the control unit of the laser printer 100 as shown in FIG. 1A. Then, the sheet feeding roller 60 separates only the uppermost sheet of the bundle of sheets P stacked on the sheet feeding device 200 and sends it to the sheet feeding path 32.

When the leading edge of the sheet P fed by the sheet feeding roller 60 and the roller pair 210 reaches the nip of the registration roller pair 250, the sheet P forms a slack and stands by in that state. Then, the optimum timing (synchronization) for transferring the toner image formed on the intermediate transfer belt 16 to the sheet P is achieved, and the leading edge skew of the sheet P is corrected.

In the case of manual feeding, a bundle of sheets stacked on the manual feed tray 46 passes a part of the reverse conveying path 41 by the manual feed roller 45 one by one from the uppermost sheet, and the nip of the registration roller pair 250 It is transported to. The subsequent operation is the same as the sheet feeding from the sheet feeding device 200.

Here, with regard to the image forming operation, one process unit 1K will be described, and the description of the other process units 1Y, 1M, and 1C will be omitted. First, the charging device 4K uniformly charges the surface of the image carrier 2K to a high potential. Then, the exposure unit 7 irradiates the surface of the image carrier 2K with the laser beam Lb based on the image data.

On the surface of the image carrier 2K irradiated with the laser light Lb, the potential of the irradiated part is lowered to form an electrostatic latent image. The developing device 5K has a developer carrier that carries a developer containing toner, and an electrostatic latent image is formed on the unused black toner supplied from the toner bottle 6K through the developer carrier. It is transferred to the surface portion of the image carrier 2K. The image carrier 2K to which the toner is transferred forms (develops) a black toner image on the surface thereof. Then, the toner image formed on the image carrier 2 K is transferred to the intermediate transfer belt 16.

The drum cleaning device 3K removes residual toner adhering to the surface of the image carrier 2K after the intermediate transfer process. The removed residual toner is sent to and collected by the waste toner storage unit in the process unit 1K by the waste toner conveyance means. Further, the charge removing device removes the residual charge of the image carrier 2K from which the residual toner has been removed by the cleaning device 3K.

Similarly, in the process units 1Y, 1M, and 1C of the respective colors, toner images are formed on the image carriers 2Y, 2M, and 2C, and transferred onto the intermediate transfer belt 16 so that the respective color toner images overlap.

The intermediate transfer belt 16 on which the toner images of the respective colors are transferred so as to overlap with each other travels to the secondary transfer nip of the secondary transfer roller 20 and the driving roller 18. On the other hand, the registration roller pair 250 nips and rotates the sheet abutted thereto at a predetermined timing, and in accordance with the timing at which the toner image formed by overlapping transfer on the intermediate transfer belt 16 is suitably transferred. The sheet is conveyed to the secondary transfer nip of the secondary transfer roller 20. Thus, the toner image on the intermediate transfer belt 16 is transferred onto the sheet P fed by the registration roller pair 250.

After transfer, the sheet P on which the toner image has been transferred is conveyed to the fixing device 300 through the conveyance path 33. Then, the sheet P conveyed to the fixing device 300 is sandwiched between the fixing belt 310 and the pressure roller 320, and the unfixed toner image is fixed to the sheet P by heating and pressing. The sheet P on which the toner image is fixed is fed from the fixing device 300 to the conveyance path 35 after being fixed.

The switching member 42 is at a position at which the vicinity of the upper end of the post-fixing conveyance path 35 is open as shown by the solid line in FIG. 1A at the timing when the sheet P is fed from the fixing device 300. Then, the sheet P sent from the fixing device 300 is sent to the sheet discharge path 36 via the conveyance path 35 after fixing. The sheet discharge roller pair 37 nips the sheet P fed to the sheet discharge path 36 and discharges the sheet P to the sheet discharge tray 44 by being rotationally driven, thereby completing single-sided printing.

Next, the case of performing double-sided printing will be described. As in the case of single-sided printing, the fixing device 300 sends the sheet P to the sheet discharge path 36. Then, when performing duplex printing, the discharge roller pair 37 conveys a part of the sheet P to the outside of the laser printer 100 by rotational driving.

Then, when the rear end of the sheet P passes the sheet discharge path 36, the switching member 42 pivots about the pivot shaft 42a as shown by the dotted line in FIG. 1A, and the upper end of the conveying path 35 is closed after fixing. Do. Almost simultaneously with the closing of the upper end of the conveyance path 35 after fixing, the discharge roller pair 37 rotates in the direction opposite to the direction in which the sheet P is conveyed out of the laser printer 100 and delivers the sheet P to the reverse conveyance path 41.

The sheet P fed to the reverse conveyance path 41 passes through the reverse conveyance roller pair 43 and reaches the registration roller pair 250. Then, the registration roller pair 250 delivers the sheet P to the secondary transfer nip at an optimal timing (synchronization) for transferring the toner image formed on the intermediate transfer belt 16 to the toner image non-transferred surface of the sheet P.

Then, the secondary transfer roller 20 and the drive roller 18 transfer the toner image to the toner image non-transferred surface (rear surface) of the sheet P when the sheet P passes through the secondary transfer nip. Then, the sheet P on which the toner image has been transferred is transported to the fixing device 300 through the transport path 33 after transfer.

The fixing device 300 fixes the unfixed toner image on the back surface of the sheet P by holding the sheet P conveyed by the fixing belt 310 and the pressure roller 320 and heating and pressing. Thus, the sheet P on which the toner image is fixed on both the front and back sides is sent out from the fixing device 300 to the conveyance path 35 after fixing.

The switching member 42 is at a position at which the vicinity of the upper end of the post-fixing conveyance path 35 is open as shown by the solid line in FIG. 1A at the timing when the sheet P is fed from the fixing device 300. Then, the sheet P delivered from the fixing device 300 is delivered to the paper discharge path 36 via the fixing transport path. The sheet discharge roller pair 37 nips the sheet P fed to the sheet discharge path 36, rotationally drives the sheet P, and discharges the sheet P to the sheet discharge tray 44, thereby completing double-sided printing.

After the toner image on the intermediate transfer belt 16 is transferred to the sheet P, residual toner adheres on the intermediate transfer belt 16. The belt cleaning device 21 removes the residual toner from the intermediate transfer belt 16. Further, the toner removed from the intermediate transfer belt 16 is conveyed to the powder container 10 by the waste toner conveyance means, and is collected in the powder container 10.

(Fixing device)
Next, the heating device and the first to fourth fixing devices 300 according to the embodiment of the present invention will be further described below. The heating device of this embodiment is for heating the fixing belt 310 of the fixing device 300. The heating device is composed of a planar heating body, and as shown in FIG. 3A (a) and FIG. 4, a base 350 in which an elongated thin metal plate member is coated with an insulating material, and The heating member 360 is provided.

The heat generating member 360 is composed of a plurality of resistance heating elements 361 to 368 arranged linearly and at equal intervals in the longitudinal direction of the base material 350. Feeding lines 360a and 360b of small resistance value are linearly disposed in parallel to each other on both sides in the width direction of each resistance heating element 361 to 368, and both ends of each resistance heating element 361 to 368 are connected to the feeding lines 360a and 360b. Is connected. The power control means is connected to the electrodes 360c and 360d formed at one end of each of the feed lines 360a and 360b as shown in FIG.

The heating device of the present embodiment has a first temperature detection sensor (first temperature detection means) TH1 and a second temperature detection sensor (second temperature detection means) TH2 as temperature detection means for detecting the temperature of the resistance heating element. . These temperature detection sensors TH1 and TH2 can be configured by thermistors, for example.

As shown in FIG. 4, the first temperature detection sensor TH1 and the second temperature detection sensor TH2 are disposed in such a manner as to be pressure-bonded to the back side of the base 350 by a spring. The first temperature detection sensor TH1 is for temperature control, and the second temperature detection sensor TH2 is for safety compensation. The two temperature detection sensors TH1 and TH2 can be configured by contact thermistors each having a thermal time constant of less than 1 second.

The temperature control first temperature detection sensor TH1 is disposed in the heating area of the resistance heating element 364 (fourth from the left end) as a first resistance heating element in the central longitudinal direction within the minimum sheet passing width. The second temperature detection sensor TH2 for safety compensation is a resistance heating element 368 (eight from the left end) (or resistance heating element 361 (first from the left end) as a second resistance heating element which is the longitudinal endmost part. It is arranged in the heating area.

The two temperature detection sensors TH1 and TH2 are both disposed in the region of the resistance heating elements 364 and 368, which avoids the gap between the resistance heating elements where the amount of heat reduction occurs. This improves the temperature controllability, and also makes it easier to detect a break when a break occurs in a part of the resistance heating element.

The first temperature detection sensor TH1 may be disposed in the heating region of any one of the resistance heating elements 363, 365, 366. The second temperature detection sensor TH2 may be disposed in the second resistance heating element 362 or the seventh resistance heating element 367 from the left end if it is in the longitudinal end area, and the second temperature detection sensor TH2 is not necessarily the longitudinal end There is no need to place in

Below the heating device of FIG. 4, a power control circuit as power control means for feeding (powering) the resistance heating elements 361 to 368 is shown. The power control circuit is composed of an AC power supply 410 and a triac 420. The AC power supply 410 and the triac 420 are connected in series between the electrodes 360c and 360d.

The temperatures T ₄ and T ₈ detected by the first temperature sensor TH1 and the second temperature sensor TH2 are input to the control unit 400 as control means. Control unit 400, based on the temperature T ₄ obtained from the first temperature sensor TH1, so that each resistive heating element 361 to 368 reaches a predetermined temperature, the electrode 360c, controls the supply power amount to the 360d by the triac 420 .

The control unit 400 can be configured by a microcomputer including a CPU, a ROM, a RAM, an I / O interface, and the like. When fed to the fixing nip SN, since heat removal caused by paper feeding (heat transfer amount to the paper) occurs, not only the temperature T ₄ obtained from the first temperature sensor TH1, also taking into account the heat removal amount By controlling the amount of supplied power, the temperature of fixing belt 310 can be controlled to a desired temperature.

As shown in FIG. 2A, the first fixing device is composed of a thin fixing belt 310 with a low heat capacity and a pressure roller 320. The fixing belt 310 has, for example, a cylindrical substrate made of polyimide (PI) and having an outer diameter of 25 mm and a thickness of 40 to 120 μm.

In the outermost layer of the fixing belt 310, a release layer having a thickness of 5 to 50 μm is formed of a fluorine-based resin such as PFA or PTFE in order to enhance the durability and ensure the releasability. An elastic layer made of rubber or the like with a thickness of 50 to 500 μm may be provided between the base and the release layer.

The base of the fixing belt 310 is not limited to polyimide, and may be a heat resistant resin such as PEEK, or a metal base such as nickel (Ni) or SUS. The inner circumferential surface of the fixing belt 310 may be coated with polyimide, PTFE or the like as a sliding layer.

The pressure roller 320 has, for example, an outer diameter of 25 mm, and is a solid iron core metal 321, an elastic layer 322 formed on the surface of the core metal 321, and a release layer formed on the outer side of the elastic layer 322. And H.323. The elastic layer 322 is formed of silicone rubber and has a thickness of, for example, 3.5 mm. In order to enhance the releasability of the surface of the elastic layer 322, it is desirable to form a release layer 323 of, for example, a fluororesin layer having a thickness of about 40 μm. The pressure roller 320 is in pressure contact with the fixing belt 310 by the urging means.

Inside the fixing belt 310, a stay 330 and a folder 340 are arranged in the axial direction. The stay 330 is made of metal channel material, and both end portions thereof are supported by both side plates of the heating device. The stay 330 reliably receives the pressing force of the pressure roller 320 to stably form the fixing nip SN.

The folder 340 is for holding the base 350 of the heating device and is supported by the stay 330. The folder 340 can be preferably formed of a low thermal conductive heat resistant resin such as LCP, thereby reducing heat transfer to the folder 340 and heating the fixing belt 310 efficiently.

In order to avoid contact with the high temperature portion of the base 350, the folder 340 is shaped so as to support only two places near both ends of the base 350 in the lateral direction. Thus, the amount of heat flowing to the folder 340 can be further reduced, and the fixing belt 310 can be efficiently heated.

The resistive heating elements 361 to 368 and the feed lines 360 a and 360 b are covered by a thin insulating layer 370. The insulating layer 370 can be made of, for example, heat-resistant glass having a thickness of 75 μm. The insulating layers 370 insulate and protect the resistance heating elements 361 to 368 and the feeders 360a and 360b, and maintain the slidability with the fixing belt 310 as described later.

As a material of the substrate 350, low cost aluminum, stainless steel or the like is preferable. The substrate 350 is not limited to metal, and may be made of ceramic such as alumina or aluminum nitride, or a non-metal material such as glass or mica excellent in heat resistance and insulation. In order to improve the thermal uniformity of the heating device and enhance the image quality, the substrate 350 may be made of a material having a high thermal conductivity such as copper, graphite, or graphene. In the present embodiment, an alumina base having a width of 8 mm, a width of 270 mm and a thickness of 1.0 mm is used.

The resistance heating elements 361 to 368 are formed, for example, by applying a paste prepared by mixing silver palladium (AgPd), glass powder, or the like to the substrate 350 by screen printing or the like, and then baking the substrate 350. Can. In the present embodiment, the resistance value of the resistance heating elements 361 to 368 is set to 80 Ω at normal temperature.

The materials of the resistance heating elements 361 to 368 may be silver alloy (AgPt) or ruthenium oxide (RuO ₂ ) resistance materials other than those described above. The materials of the feeders 360a and 360b and the electrodes 360c and 360d can be formed by screen printing or the like using silver (Ag) or silver palladium (AgPd).

The insulating layer 370 side of the resistance heating elements 361 to 368 contacts and heats the fixing belt 310, and the temperature of the fixing belt 310 is raised by heat transfer to heat and fix the unfixed image conveyed to the fixing nip SN.

As shown in FIG. 3A (a), the resistance heating elements 361 to 368 are divided into eight in the longitudinal direction and electrically connected in parallel. Each resistance heating element 361-368 can be comprised by the baking pattern of a return meander shape, in order to obtain a desired output (resistance value). In the illustrated example, the resistance heating elements 361 to 368 are configured by a bending pattern of one reciprocation half where the narrow line is folded twice.

The base material 350 and the resistance heating elements 361 to 368 can heat the fixing nip SN through the base material 350 as well as the resistance heating elements 361 to 368 by adjusting the respective materials and the thermal conductivity. Therefore, as a material of the substrate 350, a material having a high thermal conductivity such as aluminum nitride is desirable.

A gap is formed between the resistance heating elements 361 to 368 in order to ensure insulation. If the gap is too large, uneven fixing occurs due to a decrease in the amount of heat generation in the gap portion. On the contrary, if the gap is too small, it can not be insulated and a short circuit occurs between the resistance heating elements 361 to 368.

Therefore, the size of the gap is preferably 0.3 mm to 1 mm, and more preferably 0.4 mm to 0.7 mm. Incidentally, as described above, by heating the fixing nip SN through the base member 350, it is possible to suppress the fixing unevenness due to the gap between the resistance heating elements 361 to 368.

Further, as shown in FIG. 5A, the resistance heating elements 361 to 368 can also be made of a material having PTC (positive temperature coefficient of resistance) characteristics. The material having this PTC characteristic is characterized in that when the temperature T rises, the resistance value increases (the current I decreases and the heater output decreases). The temperature resistance coefficient (TCR = Temperature Coefficient of Resistance) can be, for example, 1500 PPM (parts per million). The temperature resistance coefficient can be stored in the memory of the control unit 400.

Due to this feature, for example, when printing a paper narrower than the full width of the resistance heating elements 361 to 368 (for example, within the width of the resistance heating elements 363 to 366), the resistance heating elements 361, 362, 367, 368 outside the paper width The temperature rises because it does not lose heat. Then, the resistance values of the resistance heating elements 361, 362, 367, 368 increase.

Since the voltage applied to the resistance heating elements 361 to 368 is constant, the outputs of the resistance heating elements 361, 362, 367, 368 outside the sheet width relatively decrease, and the temperature rise at the end is suppressed. When the resistance heating elements 361 to 368 are electrically connected in series, there is no way other than lowering the printing speed to suppress the temperature rise of the resistance heating element outside the paper width in continuous printing. By electrically connecting resistance heating elements 361 to 368 in parallel, it is possible to suppress the temperature rise of the non-sheet-passing portion while maintaining the printing speed.

The arrangement of the resistance heating elements 361 to 368 is not limited to the state shown in FIG. 3A (a). In FIG. 3A (a), there is a gap extending in the lateral direction between the resistance heating elements 361 to 368. Moreover, in FIG. 3A (b) and (c), the ends of the resistance heating elements 361 to 368 overlap each other in the longitudinal direction.

In FIG. 3A (b), a step formed by L-shaped notches is formed at the end of resistance heating element 361 to 368, and the step is overlapped with the step of the end of the adjacent resistance heating element. . In FIG. 3 (c), inclined portions are formed by oblique notches at the end portions of the resistance heating elements 361 to 368, and the inclined portions overlap the inclined portions of the end portions of the adjacent resistance heating elements. By overlapping the end portions of the resistance heating elements 361 to 368 with each other as described above, it is possible to suppress the influence of the decrease in the amount of heat generation in the gap between the resistance heating elements.

The electrodes 360c and 360d may be disposed on both ends of the resistance heating elements 361 to 368, or may be disposed on one side of the resistance heating elements 361 to 368 as shown in FIG. 3B (a) to (c). By arranging the electrodes 360c and 360d on one side in this manner, space saving in the longitudinal direction can be achieved.

(Fixing operation)
In FIG. 2A, when the sheet P is fed toward the fixing nip SN in the arrow direction, the sheet P is heated between the fixing belt 310 and the pressure roller 320 and the toner image is fixed to the sheet P. At this time, the fixing belt 310 is heated by the heat from the heat generating member 360 while sliding with the insulating layer 370 of the heat generating member 360.

When only the first temperature detection sensor TH1 is disposed in temperature control of the heat generating member 360 for bringing the fixing belt 310 to a predetermined temperature, only the resistance heating element 364 in which the first temperature detection sensor TH1 is disposed is partially disconnected. When the power supply is shut off, the temperature of the resistance heating element 364 does not rise. The same applies to the case where the first temperature detection sensor TH1 and the second temperature detection sensor TH2 are disposed in the same heating region of the resistance heating element. Therefore, in order to make the resistance heating element 364 constant temperature (first predetermined temperature) by temperature control, power supply more than necessary continues to other normal resistance heating elements 361-363, 365-368, and abnormally high temperature Occurs.

So, in this embodiment, 1st temperature detection sensor TH1 and 2nd temperature detection sensor TH2 are arrange | positioned to the heating area | region of different resistance heating element 364,368. As a result, even when only the resistance heating element 364 in which the first temperature detection sensor TH1 is disposed is partially disconnected and the power supply is interrupted, another normal resistance heating element can be detected by the second temperature detection sensor TH2. By detecting the abnormally high temperature of 368 as a second predetermined temperature which is a predetermined temperature higher than the first predetermined temperature, the power supply can be shut off safely. For example, the second predetermined temperature is a temperature obtained in advance by experiments or the like, and is a temperature that causes a problem if the temperature rises above it.

In particular, since the resistance heating element 368 is disposed at the longitudinal end of the substrate 350, it is easy to detect the second predetermined temperature early due to the influence of the end temperature rise. Therefore, the power supply can be cut off more safely than in the case where the second temperature detection sensor TH2 is disposed on the resistance heating element other than the longitudinal end. The second temperature detection sensor TH2 can also cut off the power supply by detecting a predetermined temperature (breakage) lower than the first predetermined temperature of the resistance heating element 368. For example, the temperature to be detected in this case is a temperature obtained in advance by experiments or the like, and is a temperature that causes a problem if the temperature is further lowered.

(Other Embodiments of Fixing Device)
The fixing device 300 is not limited to the first fixing device of FIG. 2A. The second to fourth fixing devices will be described below with reference to FIGS. 2B to 2D. As shown in FIG. 2B, the second fixing device has a pressure roller 390 on the opposite side to the pressure roller 320, and heats the fixing belt 310 between the pressure roller 390 and the heating device.

The above-described heating device is disposed inside the fixing belt 310. The auxiliary stay 331 is attached to one side of the stay 330, and the nip forming member 332 is attached to the opposite side. The heating device is held by the auxiliary stay 331. The nip forming member 332 is in contact with the pressure roller 320 via the fixing belt 310 to form a fixing nip SN.

In the third fixing device, as shown in FIG. 2C, a heating device is disposed inside the fixing belt 310. In order to lengthen the circumferential contact length with the fixing belt 310 instead of omitting the pressing roller 390 described above, this heating device conforms to the curvature of the fixing belt 310 and the cross sections of the base 350 and the insulating layer 370 It is formed in an arc shape. The heat generating member 360 is disposed at the center of the arc-shaped substrate 350. Others are the same as the second fixing device of FIG. 2B.

As shown in FIG. 2D, the fourth fixing device is divided into a heating nip HN and a fixing nip SN. That is, the nip forming member 332 and the stay 333 made of metal channel material are disposed on the opposite side of the pressure roller 320 to the fixing belt 310, and the nip forming member 332 and the stay 333 are included. The pressure belt 334 is disposed to be rotatable. Then, the sheet P is passed through the fixing nip SN between the pressure belt 334 and the pressure roller 320 to be heated and fixed. Others are the same as the first fixing device of FIG. 2A.

Further, as indicated by a broken line in FIG. 2A, the second temperature detection sensor TH2 for safety compensation is heated by a resistance heating element 368 different from the resistance heating element 366 detected by the first temperature detection sensor TH1 for temperature control. It may be arranged to be pressure-bonded to the inner peripheral surface of the fixing belt 310 (the inner peripheral surface on the downstream side of the resistance heating element 368). When the number of resistance heating elements is increased, it becomes difficult to secure a space for disposing the temperature detection sensor, but by disposing the second temperature sensor TH2 as described above, the difficulty of securing the space can be alleviated. In addition, the second temperature detection sensor TH2 for safety compensation is disposed not only for the resistance heating element 368 but also for each of the other resistance heating elements 361 to 363, 365 to 367 including the inner peripheral surface of the fixing belt 310. It is also good.

(flowchart)
FIG. 5 is a flowchart showing the control operation of the heating device performed by the control unit 400 described above. In step S1 of FIG. 5, the color laser printer 100 is instructed to execute a print job. Then, in step S2, the control unit 400 starts power feeding from the AC power supply 410 to the resistance heating elements 361 to 368 of the heating member 360. In step S3, the temperature T ₄ of the resistance heating element 364 located in the central region of the heat generating member 360 is detected by the first temperature sensor TH1.

Next, temperature control of the heat generating member 360 is started in step S4. The temperature T ₈ of the resistance heating element 368 is detected by the second temperature sensor in step S5. Then, in step S6, it is judged whether or not temperature T ₈ ≦ T _s (T _s : safe upper limit temperature), and if T _s <T ₈ the power supply to the heat generating member 360 is cut off (OFF) as abnormal temperature generation. An error display is shown on the operation panel of the color laser printer 100. If T ₈ ≦ T _s , no abnormal temperature is generated and the printing operation is started in step S 9.

As mentioned above, although this invention was demonstrated based on embodiment, this invention is not limited to the said embodiment, It can not be overemphasized that it can change variously within the range of the technical idea as described in a claim. . For example, the heating device of the present invention can be used for applications other than fixing devices such as drying devices. Of course, the form of the overlap of the resistance heating element may be other than that of FIG. 3A (b) (c) or FIG. 3B (b) (c), such as a concavo-convex shape or an interdigitated fitting. . Also, the number of resistance heating elements may be less than eight or nine or more. Furthermore, it is also possible to arrange the resistance heating elements in a plurality of rows in the lateral direction of the substrate 350.

SN: fixing nip HN: heating nip Lb: laser beam P: paper TM: transfer means TH1: first temperature detection sensor TH2: second temperature detection sensor 361-368: resistance heating element
1K, 1Y, 1M, 1C: Process unit 2K, 2Y, 2M, 2C: Image carrier
3K, 3Y, 3M, 3C: drum cleaning device 4K, 4Y, 4M, 4C: charging device
5K, 5Y, 5M, 5C: Developing devices (image forming units) 6K, 6Y, 6M, 6C: Toner bottles 7: Exposure devices 7a: Mirrors 8: Transfer covers 10: Powder containers 15: Transfer devices 16: Intermediate transfer Belt 17: driven roller 18: drive roller
19K, 19Y, 19M, 19C: primary transfer roller 20: secondary transfer roller 21: belt cleaning device 31: registration sensor 32: paper feed path 33: transport path after transfer 35: transport path after fixing 36: paper discharge path 37: Output roller pair 41: reverse conveyance path 42: member 42a: swing shaft 43: reverse conveyance roller pair 44: discharge tray 45, 60: paper feed roller 46: tray 100: color laser printer 200: paper feeding device ( Recording medium supply unit)
210: roller pair 220: feed roller 230: separation roller 240: conveyance roller 250: registration roller pair 300: fixing device 310: fixing belt 320: pressure roller 321: iron core metal 321: core metal 322: elastic layer 323: Releasing layer 330, 333: Stay 331: Auxiliary stay 332: Nip forming member 334: Pressure belt 340: Folder 350: Substrate 360: Heating member 360a, 360b: Feeding wire 360c, 360d: Electrode 361 to 368: Resistance heating Body 370: Insulating layer 390: Pressure roller 400: Control unit 410: AC power supply 420: Triac

JP, 2015-194713, A JP, 2016-18127, A

Claims (10)

A plurality of resistance heating elements disposed along the longitudinal direction of the substrate and electrically connected in parallel with one another;
Power control means for supplying power to the plurality of resistance heating elements;
First temperature detection means for detecting the temperature of a first resistance heating element which is one of the plurality of resistance heating elements;
Second temperature detection means for detecting the temperature of a second resistance heating element which is another one of the plurality of resistance heating elements;
The amount of power of the power control means is controlled based on the detection result of the first temperature detection means so that the temperatures of the plurality of resistance heating elements become a first predetermined temperature, and the second temperature detection means Control means for interrupting the supply of power from the power control means to the plurality of resistance heating elements when the second predetermined temperature is detected;
A heating device characterized by having.   2. A heating apparatus according to claim 1, wherein said first temperature detecting means detects a temperature of said resistance heating element disposed in a longitudinal central region of said substrate.   The heating device according to claim 1 or 2, wherein the second temperature detection means detects the temperature of the resistance heating element disposed in the longitudinal end region of the base material.   The heating apparatus according to any one of claims 1 to 3, wherein the plurality of resistance heating elements are made of a resistive material having positive temperature coefficient of resistance.   The heating apparatus according to any one of claims 1 to 4, wherein the plurality of resistance heating elements overlap each other in the longitudinal direction of the base material. In the fixing device for fixing the developer on the recording medium, the recording medium carrying the developer is passed through a fixing nip formed between a pressure member and a nip forming member.
A fixing device comprising a cylindrical belt member heated by the heating device according to claim 1 and transferring heat of the belt member to the fixing nip.   The fixing device according to claim 6, wherein the heating device is disposed inside the belt member, and the belt member circulates around the heating device in a state of being sandwiched by the fixing nip.   7. The fixing device according to claim 6, wherein the heat of the belt member is transmitted to the fixing nip through the pressure member.   The second temperature detection means of the heating device according to claim 1 is in contact with the inner circumferential surface of the belt member on the downstream side of the resistance heating element disposed in the longitudinal direction end region of the base material. The fixing device according to claim 6, characterized in that:   An image comprising: an image forming unit that forms an image with a developer; a recording medium supply unit that supplies a recording medium to the image forming unit; and the fixing device according to any one of claims 6 to 9. Forming device.