JP2022183257A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control electric power of a resistance heating element properly on target.

SOLUTION: An image formation device has an exterior member (a lateral face cover 101) opening and closing when mounting and demounting a fixation device 300, and the fixation device comprises: resistance heating elements (PTC elements 361-368); temperature detection means (temperature sensors TH1 and TH2) that detect the temperature of the resistance heating elements; electric power control means (an electric power control unit 400) that controls electric power of the resistance heating elements; and mounting/demounting/exchange detection means 460 that detects whether the resistance heating elements are mounted/demounted, and exchanged. When the mounting/demounting/exchange detection means is caused to activate by the opening/closing of the exterior member, the mounting/demounting/exchange detection means is configured to detect the mounting/demounting/exchange of the resistance heating elements, the electric power control means supplies an electric power duty 100% to the resistance heating elements as a prescribed adjustment-purpose electric power duty continuously without interruption over a prescribed supply period before the use of the resistance heating elements; acquires the electric power of the resistance heating elements and a temperature change of the resistance heating elements detected by the temperature detection means while supplying the adjustment-purpose electric power duty; and adjusts the electric power duty during use of the resistance heating elements in accordance with the electric power and the temperature change.

SELECTED DRAWING: Figure 6D

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present invention relates to an image forming apparatus.

Various types of fixing devices are known for use in electrophotographic image forming apparatuses. One of them is a type in which a thin fixing belt with a low heat capacity is heated by a heating device composed of a substrate and a resistance heating element. This heating device has a resistance heating element disposed on a base material arranged in the width direction of the fixing belt (see, for example, Patent Documents 1 and 2).

A resistance heating element is generally formed by printing a heating pattern of a resistance heating material on the surface of a substrate such as a ceramic substrate by screen printing. In addition to variations in the resistance of the resistive heating material itself, variations in the line width and thickness of the heating pattern produced by screen printing also cause variations in the resistance. For this reason, the resistance heating element is characterized by large variations in the total resistance value.

In particular, the thinner the line width of the heating pattern and the thinner the thickness, the greater the variation in the total resistance value, which may make it difficult to properly control the power of the resistance heating element. If electric power cannot be properly controlled in a fixing device using a resistance heating element, the temperature change of the thin fixing belt becomes large, resulting in poor fixation of printed toner on paper and image peeling.

Some resistance heating elements have a characteristic that the resistance value changes depending on the temperature (such as a PTC heater). When such a resistance heating element is used, it is necessary to record information on changes in resistance value with respect to temperature changes in a non-volatile memory or the like, and to control power according to changes in resistance value. Therefore, when the fixing unit is replaced with a new unit, the temperature resistance characteristics of the resistance heating element (change in resistance value with respect to temperature change) must be rerecorded in a non-volatile memory or the like. becomes difficult.

The invention described in Patent Document (Japanese Patent Application Laid-Open No. 2018-25743) uses the rate of change of the resistance value of the heating resistor when power is supplied to the heating resistor (time rate of change of the resistance value) for state determination. That is, the rate of change in resistance value is used as a trigger for judging an abnormal state such as a change in resistance value due to an increase in temperature at the end portion due to continuous printing of small sizes or a change in resistance value due to disconnection of the heating element. However, in the invention described in Patent Document (Japanese Patent Application Laid-Open No. 2018-25743), variations in electric power (heater output) due to variations in temperature resistance characteristics of resistance heating elements are not taken into consideration.

The present invention has been made in view of such problems, and the electric power of the resistance heating element can be properly controlled as intended, regardless of variations in resistance temperature characteristics (change in resistance value with respect to temperature change) of the resistance heating element. intended to

In order to solve the above-described problems, an image forming apparatus according to the present invention is an image forming apparatus having a fixing device detachably mounted, which has an exterior member that opens and closes when the fixing device is attached and detached, and the fixing device includes a resistor. A heating element, temperature detection means for detecting the temperature of the resistance heating element, power control means for controlling power of the resistance heating element, and attachment/detachment replacement detection for detecting whether or not the resistance heating element has been removed or replaced. means for activating the attachment/detachment replacement detection means by opening/closing the exterior member, and when the attachment/detachment replacement detection means detects the attachment/detachment/replacement of the resistance heating element, the power control means controls the use of the resistance heating element. A power duty of 100% is continuously supplied to the resistance heating element as a predetermined power duty for adjustment over a predetermined supply period without interruption, and while the power duty for adjustment is being supplied, the resistor The electric power of the heating element and the temperature change of the resistance heating element detected by the temperature detection means are obtained, and the power duty of the resistance heating element during use is adjusted according to the electric power and the temperature change. do.

According to the image forming apparatus of the present invention, even if the fixing unit is replaced with a new unit, the electric power of the resistance heating element can be appropriately controlled as intended regardless of variations in the resistance value of the resistance heating element.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention; FIG. 1 is a principle diagram of an image forming apparatus according to an embodiment of the present invention; FIG. 4 is a plan view showing a method of attaching and detaching the fixing device 300; FIG. 1 is a cross-sectional view of a first fixing device according to an embodiment of the invention; FIG. FIG. 4 is a cross-sectional view of a second fixing device according to an embodiment of the invention; FIG. 5 is a cross-sectional view of a third fixing device according to an embodiment of the invention; FIG. 5 is a cross-sectional view of a fourth fixing device according to an embodiment of the invention; It is the top view (a) and sectional drawing (b) of the resistance heating element which provided the electrode in one end. 1 is a plan view of a resistance heating element in which resistance elements are arranged in parallel and electrodes are provided at both ends; FIG. 1 is a plan view of a resistance heating element in which resistance elements are arranged in parallel and an electrode is provided at one end; FIG. FIG. 3 shows a heating device, a power supply circuit and a power controller; (a) is a diagram showing changes in temperature and current of the resistance heating element, (b) is a diagram showing changes in voltage waveform due to duty control, and (c) is a diagram showing the voltage-current correlation of the resistance heating element. be. 4 is a flow chart showing a basic control operation of the heating device by means of current detection means; 4 is a flow chart showing a detailed control operation of the heating device by means of current detection means. 4 is a flow chart showing a control operation of a heating device by a temperature sensor; 5 is a flowchart showing the operation (diagnosis mode) of the power control section after detecting attachment/detachment of the fixing unit; FIG. 4 is a diagram showing temperature resistance characteristics of a heat generating member;

A heating device used in an embodiment of the present invention, and a fixing device and an image forming apparatus (laser printer) using the heating device will be described below with reference to the drawings. A laser printer is an example of an image forming apparatus, and the image forming apparatus is not limited to a laser printer. That is, the image forming apparatus can be configured as a copier, a facsimile machine, a printer, a printing machine, or an inkjet recording apparatus, or a multifunction machine combining at least two of these.

The same or corresponding parts in each figure are denoted by the same reference numerals, and redundant description thereof will be appropriately simplified or omitted. Also, the dimensions, materials, shapes, relative positions, and the like in the description of each component are examples, and are not intended to limit the scope of the present invention unless otherwise specified.

In the following embodiments, the "recording medium" is described as "paper", but the "recording medium" is not limited to paper (paper). The "recording medium" includes not only paper but also OHP sheets, fabrics, metal sheets, plastic films, or prepreg sheets in which carbon fibers are previously impregnated with resin.

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

In addition, the term "image formation" used in the following description refers not only to imparting meaningful images, such as characters and figures, to a medium, but also to imparting meaningless images, such as patterns, to a medium. also means

(Configuration of laser printer)
FIG. 1A is a configuration diagram schematically showing the configuration of a color laser printer as one embodiment of an image forming apparatus 100 having a heating device or fixing device 300 used in the embodiment of the present invention. FIG. 1B also shows a simplified illustration of the principle of the color laser printer.

The image forming apparatus 100 includes four process units 1K, 1Y, 1M and 1C as image forming means. These process units form images 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 they have toner bottles 6K, 6Y, 6M and 6C containing unused toner of different colors. Therefore, the configuration of one process unit 1K will be described below, and the description of the other process units 1Y, 1M, and 1C will be omitted.

The process unit 1K has an image carrier 2K (for example, a photosensitive drum), a drum cleaning device 3K, and a neutralizer. 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 developing means for performing visible image processing on the electrostatic latent image formed on the image carrier. It has 5K and so on. The process unit 1K is detachably attached to the main body of the image forming apparatus 100, and consumable parts can be replaced at the same time.

The exposure device 7 is arranged above each of the process units 1K, 1Y, 1M, and 1C installed in this image forming apparatus 100 . The exposure device 7 is configured to perform write scanning according to image information, that is, to irradiate the image carrier 2K with laser light L from a laser diode reflected by a mirror 7a based on image data.

The transfer device 15 is arranged below each of 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 19K, 19Y, 19M and 19C are arranged in contact with the intermediate transfer belt 16 so as to face the respective image carriers 2K, 2Y, 2M and 2C.

The intermediate transfer belt 16 circulates while being stretched over primary transfer rollers 19K, 19Y, 19M, 19C, a driving roller 18, and a driven roller 17. As shown in FIG. The secondary transfer roller 20 is arranged in contact with the intermediate transfer belt 16 so as to face the drive roller 18 . If the image carriers 2K, 2Y, 2M, and 2C are the first image carriers of each color, the intermediate transfer belt 16 is the second image carrier that synthesizes those images.

The belt cleaning device 21 is installed downstream of the secondary transfer roller 20 in the running direction of the intermediate transfer belt 16 . 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 device 200 having a tray for stacking sheets P is installed below the image forming apparatus 100 . The paper feeder 200 constitutes a recording medium supply section, and can accommodate a large number of sheets P as a recording medium in a bundle. unitized with.

The paper feeding device 200 is detachable from the main body of the image forming apparatus 100 in order to replenish paper and the like. The paper feed roller 60 and the roller pair 210 are arranged above the paper feeder 200 so as to convey the uppermost paper P of the paper feeder 200 toward the paper feed path 32 .

A pair of registration rollers 250 as a separating and conveying unit is arranged immediately upstream in the conveying direction of the secondary transfer roller 20 and can temporarily stop the paper P fed from the paper feeding device 200 . Due to this temporary stop, slack is formed on the leading end side of the paper P, and the skew of the paper P is corrected.

A registration sensor 31 is disposed immediately upstream of the registration roller pair 250 in the conveying direction, and the registration sensor 31 detects the passage of the leading edge of the sheet. After the registration sensor 31 detects the passage of the leading edge of the paper, when a predetermined period of time elapses, the paper hits the pair of registration rollers 250 and temporarily stops.

At the downstream end of the paper feeder 200, a transport roller 240 is arranged for upwardly transporting the paper transported from the roller pair 210 to the right side. As shown in FIG. 1A, the transport rollers 240 transport the paper upward toward the pair of registration rollers 250 .

The roller pair 210 is composed of a pair of upper and lower rollers. The roller pair 210 can be of the FRR separation type or the FR separation type. In the FRR separation method, a separation roller (return roller) to which a constant amount of torque is applied in the direction opposite to the paper feed direction by a drive shaft via a torque limiter is brought into pressure contact with the feed roller to separate the paper at the nip between the rollers. In the FR separation method, a separation roller (friction roller) supported by a fixed shaft via a torque limiter is brought into pressure contact with a feed roller to separate the paper at the nip between the rollers.

In this embodiment, the roller pair 210 is constructed by the FRR separation method. That is, the roller pair 210 consists of an upper feed roller 220 that conveys the paper into the machine and a lower separation roller 230 that is driven by a drive shaft through a torque limiter in the direction opposite to the feed roller 220. consists of

The separating roller 230 is biased toward the feeding roller 220 by biasing means such as a spring. The feeding roller 60 rotates to the left in FIG. 1A by transmitting the driving force of the feeding roller 220 through the clutch means.

The paper P, which has been bumped against the pair of registration rollers 250 and has slack at its leading edge, is transferred to the secondary transfer roller 20 and the drive roller in time with the timing at which the toner image formed on the intermediate transfer belt 16 is suitably transferred. 18 (transfer nip N in FIG. 1B). Then, the toner image formed on the intermediate transfer belt 16 is electrostatically transferred to the desired transfer position with high precision by the bias applied at the secondary transfer nip. ing.

The post-transfer conveying path 33 is arranged above the secondary transfer nip between the secondary transfer roller 20 and the driving roller 18 . The fixing device 300 is installed near the upper end of the post-transfer conveying path 33 . The fixing device 300 includes a fixing belt 310 containing a heating device, and a pressure roller 320 as a pressure member that rotates while contacting the fixing belt 310 with a predetermined pressure. Note that the fixing device 300 may have other configurations as shown in FIGS. 2B to 2D, which will be described later.

The post-fixing transport path 35 is disposed above the fixing device 300 , and branches into a paper discharge path 36 and a reversing transport path 41 at the upper end of the post-fixing transport path 35 . A switching member 42 is arranged at this branched portion, and the switching member 42 swings around a swing shaft 42a. A paper discharge roller pair 37 is arranged near the opening end of the paper discharge path 36 .

The reverse transport path 41 joins the paper feed path 32 at the other end opposite to the branched portion. A reverse conveying roller pair 43 is arranged in the middle of the reverse conveying path 41 . The discharge tray 44 is installed on the upper portion of the image forming apparatus 100 so as to form a concave shape toward the inside of the image forming apparatus 100 .

A powder container 10 (for example, a toner container) is arranged between the transfer device 15 and the paper feeding device 200 . The powder container 10 is detachably attached to the main body of the image forming apparatus 100 .

The image forming apparatus 100 of the present embodiment requires a predetermined distance from the paper feed roller 60 to the secondary transfer roller 20 due to transfer paper transport. Then, the powder container 10 is installed in the dead space generated at this distance to reduce the size of the laser printer as a whole.

The transfer cover 8 is installed above the paper feeding device 200 and in front of the paper feeding device 200 in the pull-out direction. By opening the transfer cover 8, the inside of the image forming apparatus 100 can be inspected. The transfer cover 8 is provided with a manual paper feeding roller 45 for manual paper feeding and a manual paper feeding tray 46 for manual paper feeding.

(side cover)
FIG. 1C is a plan view showing how the fixing device 300 is attached and detached. The fixing device 300 of the image forming apparatus 100 may be replaced due to the end of its life, failure, or other errors.

As shown in FIG. 1C, a side cover 101 as an openable and closable exterior member is provided on the side surface of the main body of the image forming apparatus 100 for maintenance and the like. When the fixing device 300 is attached or detached, the side cover 101 is opened and the fixing device 300 is slid in the direction of the arrow (outward).

In the case of the image forming apparatus 100 in which the user purchases and replaces the fixing device 300 by himself/herself, the fixing device 300 generally includes a new product detection mechanism. When the fixing device 300 is replaced by the user, the new product detection mechanism resets the life counter when the image forming apparatus 100 detects that the fixing device 300 is new, and automatically continues the image forming apparatus 100. can be used

A current fuse or a thermal fuse is generally used for new product detection of the image forming apparatus 100 . That is, when a replacement part is replaced with a new one, a current fuse or a temperature fuse is mounted inside the replacement part so that the image forming apparatus 100 can detect that the replacement part is new.

When the main body of the image forming apparatus 100 detects that the current fuse or the thermal fuse is connected (unblown), it recognizes it as a new product and resets the number-of-printed counter (PM counter). That is, PM counter processing is executed in new product detection.

Following this PM counter processing, the current fuse or thermal fuse is melted by energization and heating. After that, the image forming apparatus 100 recognizes the replacement part as an obsolete part because the fuse of the replacement part is already blown and does not conduct. By installing a current fuse or a thermal fuse in the fixing device 300, when the fixing device 300 is replaced with a new one, the new replacement is detected by the new product detection operation on the main body side of the image forming apparatus 100. Supply of the power duty for adjustment is automatically started in step S15 of FIG. 6D.

In this embodiment, the attachment/detachment replacement detection means 460 is arranged adjacent to the opening/closing axis of the side cover 101 of FIG. 1C. When the fixing device 300 is attached to or removed from the main body of the image forming apparatus 100, the side cover 101 is always opened and closed. Therefore, the activation (ON/OFF) of the attachment/detachment replacement detection means 460 is used as a trigger signal for starting the new product detection operation using the current fuse or thermal fuse.

When the heat-generating member 360 of the fixing device 300 is disconnected, the entire fixing device 300 is replaced with a new one as described above, and only the heat-generating member 360 is replaced with a new heat-generating member 360 . In this case, replacement of the heat-generating member 360 is normally performed by a serviceman, not by a user.

Also in the case of replacement by the serviceman, by providing an attachment/detachment replacement detecting means for detecting whether or not the heat generating member 360 has been attached/detached/replaced, the power duty for adjustment can be supplied in the same manner as in the replacement of the fixing device 300 with a new product. Can be started automatically. The attachment/detachment replacement detection means can be configured, for example, by arranging a new product detection contact between the folder 340 and the heat generating member 360 in FIG. 2A.

That is, by removing the disconnected old heat generating member 360 from the folder 340 and then attaching the new heat generating member 360, the new product detection contact is opened and closed. By detecting the opening/closing operation of the new product detection contact on the main body side of the image forming apparatus 100, it is recognized that the heat generating member 360 has been replaced with a new product.

(laser printer operation)
Next, the basic operation of the laser printer according to this 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 section of the image forming apparatus 100, as shown in FIG. 1A. Then, the paper feed roller 60 separates only the uppermost paper sheet from the stack of paper sheets P stacked on the paper feeder 200 and feeds it to the paper feed path 32 .

When the leading edge of the paper P sent out by the paper feed roller 60 and the roller pair 210 reaches the nip of the registration roller pair 250, it becomes slack and waits in that state. Then, the optimum timing (synchronization) for transferring the toner image formed on the intermediate transfer belt 16 to the paper P is obtained, and the tip skew of the paper P is corrected.

In the case of manual paper feeding, the stack of paper stacked on the manual feed tray 46 passes through a part of the reversing conveyance path 41 one by one from the uppermost paper by the manual paper feed roller 45 and is nipped by the registration roller pair 250 . transported to. The subsequent operations are the same as those for paper feeding from the paper feeding device 200 .

Here, as for 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 exposing device 7 irradiates the surface of the image carrier 2K with the laser light L based on the image data.

On the surface of the image carrier 2K irradiated with the laser beam L, the potential of the irradiated portion is lowered to form an electrostatic latent image. The developing device 5K has a developer carrier that carries a developer containing toner, and the unused black toner supplied from the toner bottle 6K is passed through the developer carrier to form an electrostatic latent image. is transferred to the surface portion of the image carrier 2K.

The image carrier 2K to which the toner has been transferred forms (develops) a black toner image on its surface. Then, the toner image formed on the image carrier 2K is transferred to the intermediate transfer belt 16. FIG.

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 transported to and collected by the waste toner conveying means to the waste toner storage section in the process unit 1K. Further, the static elimination device eliminates residual charges on the image carrier 2K from which the residual toner has been removed by the cleaning device 3K.

In the process units 1Y, 1M, and 1C of each color, toner images are similarly formed on the image carriers 2Y, 2M, and 2C, and transferred to the intermediate transfer belt 16 so that the toner images of each color are superimposed.

The intermediate transfer belt 16 onto which the toner images of the respective colors are transferred so as to overlap each other travels to the secondary transfer nip between the secondary transfer roller 20 and the driving roller 18 . On the other hand, the pair of registration rollers 250 sandwiches the sheet of paper that abuts against them and rotates at a predetermined timing. The sheet is conveyed to the secondary transfer nip of the secondary transfer roller 20 . In this manner, the toner image on the intermediate transfer belt 16 is transferred onto the paper P sent out by the registration roller pair 250 .

The paper P onto which the toner image has been transferred is transported to the fixing device 300 through the post-transfer transport 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 on the sheet P by applying heat and pressure. The paper P on which the toner image is fixed is sent from the fixing device 300 to the transport path 35 after fixing.

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

Next, the case of double-sided printing will be described. As in the case of single-sided printing, the fixing device 300 feeds the paper P to the paper discharge path 36 . When double-sided printing is performed, the pair of paper discharge rollers 37 conveys a portion of the paper P to the outside of the image forming apparatus 100 by rotational driving.

When the trailing edge of the paper P passes through the paper discharge path 36, the switching member 42 swings around the swing shaft 42a as indicated by the dotted line in FIG. do. Almost at the same time as the upper end of the post-fixing transport path 35 is closed, the paper discharge roller pair 37 rotates in a direction opposite to the direction in which the paper P is transported out of the image forming apparatus 100 , and sends the paper P to the reverse transport path 41 . .

The sheet P sent out to the reverse transport path 41 reaches the registration roller pair 250 via the reverse transport roller pair 43 . Then, the registration roller pair 250 finds the optimum timing (synchronization) for transferring the toner image formed on the intermediate transfer belt 16 to the toner image untransferred surface of the paper P, and feeds the paper P to the secondary transfer nip.

Then, the secondary transfer roller 20 and the drive roller 18 transfer the toner image to the toner image untransferred surface (back surface) of the paper P when the paper P passes through the secondary transfer nip. Then, the paper P onto which the toner image has been transferred is transported to the fixing device 300 through the post-transfer transport path 33 .

The fixing device 300 fixes the unfixed toner image on the back surface of the paper P by sandwiching the conveyed paper P between the fixing belt 310 and the pressure roller 320 and applying heat and pressure. In this way, the paper P having the toner images fixed on both sides thereof is fed from the fixing device 300 to the transport path 35 after fixing.

The switching member 42 is in a position where the vicinity of the upper end of the post-fixing transport path 35 is open as indicated by the solid line in FIG. 1A at the timing when the paper P is sent out from the fixing device 300 . Then, the paper P delivered from the fixing device 300 is delivered to the paper discharge path 36 via the fixing transportation path. The paper discharge roller pair 37 pinches the paper P sent to the paper discharge path 36, rotates, and discharges the paper P to the paper discharge tray 44, thereby completing double-sided printing.

After the toner image on the intermediate transfer belt 16 is transferred to the paper P, residual toner remains on the intermediate transfer belt 16 . A belt cleaning device 21 removes this 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 conveying means and collected in the powder container 10 .

(fixing device)
Next, the heating device and first to fourth fixing devices 300 used in the embodiment of the present invention will be further described below. The heating device used in this embodiment is for heating the fixing belt 310 of the fixing device 300 .

The first fixing device, as shown in FIG. 2A, 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) having an outer diameter of 25 mm and a thickness of 40 to 120 μm.

As 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 increase durability and ensure release properties. An elastic layer made of rubber or the like having a thickness of 50 to 500 μm may be provided between the substrate and the release layer.

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

The pressure roller 320 has an outer diameter of 25 mm, for example, and includes a solid iron core 321, an elastic layer 322 formed on the surface of the core 321, and a release layer formed on the outer side of the elastic layer 322. 323. The elastic layer 322 is made of silicone rubber and has a thickness of 3.5 mm, for example. In order to improve the releasability of the elastic layer 322, it is desirable to form a releasing layer 323 of a fluorine resin layer having a thickness of about 40 μm, for example. A pressure roller 320 is pressed against the fixing belt 310 by an urging means.

A stay 330 and a folder 340 are arranged in the axial direction inside the fixing belt 310 . The stay 330 is made of a 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 and stably forms the fixing nip SN.

The folder 340 is for holding the substrate 350 of the heating device and is supported by the stay 330 . The folder 340 is preferably made of a heat-resistant resin with low thermal conductivity, such as LCP, which reduces heat transfer to the folder 340 to efficiently heat the fuser belt 310 .

The shape of the folder 340 is such that it supports only two locations near both ends of the substrate 350 in the width direction in order to avoid contact with the high-temperature portion of the substrate 350 . As a result, the amount of heat flowing to folder 340 can be further reduced, and fixing belt 310 can be efficiently heated.

(Heating Device) The heating device has a heating member 360 composed of a resistance heating element. As shown in FIG. 3A, the heat-generating member 360 is formed on a base material 350 that is an elongated thin metal plate member coated with an insulating material.

Low-cost aluminum, stainless steel, or the like is preferable as the material of the base material 350 . The base material 350 is not limited to being made of metal, and can be made of ceramics such as alumina and aluminum nitride, or non-metallic materials such as glass and mica that are excellent in heat resistance and insulation.

In order to improve the heat uniformity of the heating device and improve the image quality, the substrate 350 may be made of a material with high thermal conductivity, such as copper, graphite, or graphene. In this embodiment, an alumina substrate having a short width of 8 mm, a long width of 270 mm, and a thickness of 1.0 mm is used.

Specifically, the heat-generating member 360 in FIG. 3A is formed in parallel two rows in the longitudinal direction of the base material 350 in a straight line. One ends of the two rows of heat-generating members 360 are connected to power supply electrodes 360c and 360d via power supply lines 369a and 369c with small resistance values formed in the longitudinal direction on one end side of the base material 350, respectively. . The electrodes 360c, 360d are connected to power supply means including an AC power supply 410 as shown in FIG.

The other end of the heat-generating member 360 is connected to the other end of the base material 350 by folding it toward the opposite side of the base material 350 in the longitudinal direction via a power supply line 369b having a small resistance value formed in the short direction. It is The heat-generating member 360, the electrodes 360c and 360d, and the power supply lines 369a to 369c are formed with a predetermined line width and thickness by screen printing.

The material of the heat-generating member 360 can be formed by applying a paste prepared by mixing silver (Ag), silver-palladium (AgPd), glass powder, or the like by screen printing or the like, followed by firing. The resistance value of the heat generating member 360 can be, for example, 10Ω at room temperature. The resistance material of the heat generating member 360 may also be silver alloy (AgPt), ruthenium oxide (RuO2), or the like.

A thin overcoat layer or insulating layer 370 covers the surfaces of the heat generating member 360 and the power supply lines 369a to 369c. The insulating layer 370 ensures the slidability of the fixing belt 310 and also ensures insulation between the fixing belt 310, the heat generating member 360, and the power supply lines 369a to 369c.

As the material of the insulating layer 370, heat-resistant glass having a thickness of 75 μm, for example, can be used. The heat-generating member 360 heats the fixing belt 310 in contact with the insulating layer 370 side by heat transfer to increase the temperature thereof, and heats and fixes an unfixed image on the paper P conveyed to the fixing nip SN.

(Heat-Generating Member Using PTC Elements) The heat-generating member 360, as shown in FIGS. It can also be configured by connecting in parallel. In this case, if the total resistance value of the heating member 360 is 10Ω, the resistance value of each of the PTC elements 361 to 368 is as large as 80Ω.

In order to gain this large resistance value, it is necessary to make the line width of the PTC elements 361 to 368 as thin and thin as possible to increase the number of meandering. However, if this is the case, variations in the line width and thickness of the PTC elements 361 to 368 increase, and there is a problem that the resistance value of the heat generating member 360 varies greatly. The embodiment of the present invention is particularly effective against such large variations in the resistance value of the heat generating member 360 .

The PTC element is made of a material having a positive temperature coefficient of resistance, and has the characteristic that the resistance value increases as the temperature T rises (current I decreases and the heater output decreases). A temperature coefficient of resistance (TCR) is, for example, 1500 PPM (parts per million)
can be The temperature resistance coefficient can be stored in a memory of the power control unit 400, which will be described later.

The PTC elements 361 to 368 in FIGS. 3B and 3C are arranged linearly and at regular intervals in the longitudinal direction of the substrate 350 . On both sides of the PTC elements 361 to 368 in the short direction, feed lines 360a and 360b having a small resistance are arranged linearly parallel to each other, and both ends of the PTC elements 361 to 368 are connected to the feed lines 360a and 360b. It is A power supply means including an AC power supply 410 is connected to electrodes 360c and 360d formed at one end of each of the power supply lines 360a and 360b, as shown in FIG.

The PTC elements 361 to 368 and feeder lines 360a and 360b are also covered with a thin insulating layer 370, like the serial heat generating member 360 (FIG. 3A). This insulating layer 370 can be made of, for example, heat-resistant glass with a thickness of 75 μm. The insulating layer 370 insulates and protects the PTC elements 361 to 368 and the power supply lines 360a and 360b, and maintains slidability with the fixing belt 310. FIG.

The PTC elements 361 to 368 can be formed by coating the substrate 350 with a paste prepared by, for example, silver palladium (AgPd) or glass powder by screen printing or the like, and then firing the substrate 350. can. In this embodiment, the resistance value of each of the PTC elements 361 to 368 is set to 80Ω at room temperature (the total resistance value is 10Ω).

As for the materials of the PTC elements 361 to 368, a silver alloy (AgPt) or ruthenium oxide (RuO ₂ ) resistance material may be used in addition to the materials described above. The power supply lines 360a and 360b and the electrodes 360c and 360d can be made of silver (Ag) or silver palladium (AgPd) by screen printing or the like.

The insulating layer 370 side of the PTC elements 361 to 368 is heated by contact with the fixing belt 310, the temperature of the fixing belt 310 is increased by heat transfer, and the unfixed image conveyed to the fixing nip SN is heated and fixed.

As shown in FIG. 3B(a), the PTC elements 361 to 368 are divided into eight in the longitudinal direction and electrically connected in parallel. Although the PTC elements 361 to 368 are rectangular in FIG. 3B(a), it is also possible to turn the firing pattern of the PTC elements 361 to 368 into a meandering shape in order to obtain a desired output (resistance value). be.

By using the PTC elements 361 to 368, when the temperature of the PTC elements in the non-paper-passing area rises due to small-size paper passing, the temperature resistance dependence of the resistance heating element as shown in FIG. , the amount of heat generated by the PTC element is reduced, and the temperature rise can be suppressed. Due to this feature, for example, when printing on paper narrower than the full width of the PTC elements 361 to 368 (for example, within the width of the PTC elements 363 to 366), the PTC elements 361, 362, 367, and 368 outside the paper width heat the paper. The temperature rises because it is not deprived. Then, the resistance values of these PTC elements 361, 362, 367 and 368 increase.

Since the voltage applied to the PTC elements 361 to 368 is constant, the outputs of the PTC elements 361, 362, 367, and 368 outside the paper width are relatively lowered, suppressing the edge temperature rise. When the PTC elements 361 to 368 are electrically connected in series, the only way to suppress the temperature rise of the resistance heating element outside the paper width in continuous printing is to reduce the printing speed. By electrically connecting the PTC elements 361 to 368 in parallel, it is possible to suppress the temperature rise in the non-paper passing portion while maintaining the printing speed.

The arrangement of the PTC elements 361 to 368 is not limited to the state shown in FIG. 3B(a). In FIG. 3B(a), since there are gaps extending in the width direction between the PTC elements 361 to 368, the amount of heat generated in the gaps is reduced, which tends to cause uneven fixing. Therefore, in FIGS. 3B(b) and (c), the ends of the PTC elements 361 to 368 are overlapped with each other in the longitudinal direction.

In FIG. 3B(b), the ends of the PTC elements 361 to 368 are formed with L-shaped notches to form stepped portions, and the stepped portions are overlapped with the stepped portions of the ends of the adjacent resistance heating elements. In FIG. 3B(c), the ends of the PTC elements 361 to 368 are formed with inclined portions by oblique cutouts, and the inclined portions are overlapped with the inclined portions of the ends of the adjacent resistance heating elements. By overlapping the ends of the PTC elements 361 to 368 with each other in this way, it is possible to suppress the influence of a decrease in the amount of heat generated in the gaps between the resistance heating elements.

The electrodes 360c and 360d may be arranged on both ends of the PTC elements 361 to 368, or may be arranged on one side of the PTC elements 361 to 368 as shown in FIGS. 3B(a) to 3B(c). By arranging the electrodes 360c and 360d on one side in this way, it is possible to save space in the longitudinal direction.

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

As shown in FIG. 4, the first temperature sensor TH1 and the second temperature sensor TH2 are arranged so as to be pressed against the back side of the substrate 350 by a spring. The first temperature sensor TH1 is for temperature control and the second temperature sensor TH2 is for safety compensation. Both of the two temperature sensors TH1 and TH2 can be composed of contact-type thermistors with a thermal time constant of less than 1 second.

The first temperature sensor TH1 for temperature control is arranged in the heating area of the PTC element 364 (fourth from the left end) as the first resistance heating element in the central area in the longitudinal direction within the minimum sheet passing width. The second temperature sensor TH2 for safety compensation is located in the heating area of the PTC element 368 (8th from the left end) (or the PTC element 361 (1st from the left end)) as the second resistance heating element at the end in the longitudinal direction. are placed.

Both of the two temperature sensors TH1 and TH2 are arranged within the regions of the PTC elements 364 and 368 avoiding the gap between the resistive heating elements where the amount of heat generated decreases. This improves the temperature controllability, and also facilitates disconnection detection when disconnection occurs in some of the resistance heating elements.

Note that the first temperature sensor TH1 may be arranged in the heating region of any one of the PTC elements 363, 365, and 366. Further, the second temperature sensor TH2 can be arranged in the heating region of the second PTC element 362 or the seventh PTC element 367 from the left end as long as it is in the longitudinal end region. does not need to be placed in

(Power Supply Circuit) FIG. 4 shows a power supply circuit for supplying power to the heating device. The heat-generating member 360 of the heating device here uses the PTC elements 361-368 of FIGS. 3B and 3C. A power supply circuit for supplying power to the heat generating member 360 or the PTC elements 361 to 368 is shown below the heating device.

This power supply circuit is composed of a power control section 400 as power control means, an AC power supply 410 , a triac 420 , a current detection means 430 , a heater relay 440 and a voltage detection means 450 . An AC power supply 410, a current transformer CT of current detection means 430, a triac 420, and a heater relay 440 are arranged in series between electrodes 360c and 360d. A voltage detection means 450 is arranged between the electrodes 360c and 360d.

Temperatures T ₄ and T ₈ detected by the first temperature sensor TH1 and the second temperature sensor TH2 are input to the power control section 400 . Based on the temperature _T4 obtained from the first temperature sensor TH1, the power control unit 400 duty-controls the current supplied to the electrodes 360c and 360d by the triac 420 so that each of the PTC elements 361 to 368 reaches a predetermined target temperature. do.

Specifically, the triac 420 duty-controls the current flowing through the heat-generating member 360 with a duty ratio corresponding to the temperature difference between the current temperature _T4 of the first temperature sensor TH1 and the target temperature. At a duty ratio of 0%, the current becomes zero, and at a duty ratio of 100%, the current becomes maximum.

FIG. 5(b) exemplifies the voltage conversion value Viac of the supply current at 100% duty and 75% duty. It can be seen that in the 75% duty control, the voltage conversion value Viac largely fluctuates in a predetermined cycle.

The power control unit 400 can be configured with a microcomputer including a CPU, ROM, RAM, I/O interface, and the like. When the paper is passed through the fixing nip SN, heat _removal (heat transferred to the paper) is generated due to the passage of the paper. The temperature of the fixing belt 310 can be controlled to a desired temperature by controlling the supply current with the .

Current detection means 430 detects the sum of current values flowing through heat generating member 360 . That is, the power control unit 400 reads the magnitude of the current flowing between the electrodes 360c and 360d via the voltage generated in the secondary resistance of the current transformer CT. Also, the voltage detection means 450 detects a voltage value E between the electrodes 360c and 360d of the heat generating member 360, and the power control section 400 reads the voltage E. FIG. Then, the resistance value R (=E/I) of the heat generating member 360 is calculated from the current value I and the voltage value E in the power control unit 400 .

Here, if any one of the PTC elements 361 to 368 fails or disconnects, the current value read by the power control unit 400 decreases. In particular, if the PTC element 364 whose temperature is detected by the first temperature sensor TH1 fails or is disconnected, the temperature control function of the power control unit 400 is lost. Then, regardless of the temperatures of the other PTC elements 361-363 and 365-368, power is continuously supplied from the triac 420 to the electrodes 360c and 360d at a duty ratio of 100%.

Therefore, in this embodiment, when the current obtained by the current detection means 430 becomes less than a predetermined threshold current, the heater relay 440 is turned off to cut off the current flowing through the electrodes 360c and 360d. Specifically, the amount of current flowing through the PTC elements 361 to 368 is detected by the current detecting means 430 as a voltage conversion value Viac obtained by voltage conversion by the current transformer CT.

The converted voltage value Viac is compared with a predetermined threshold voltage Vith stored in advance in the power control unit 400 . As a result, when Viac<Vith, that is, when the amount of current to the PTC elements 361 to 368 falls below a predetermined threshold current, the heater relay 440 is turned OFF to stop power supply to the PTC elements 361 to 368. do.

The power supply can be similarly stopped by setting the duty ratio to 0% by the triac 420, but the heater relay 440 is turned off to reliably cut off the current. When the temperature _T8 detected by the second temperature sensor TH2 exceeds a predetermined threshold, the heater relay 440 can be turned OFF to substantially cut off the current flowing through the electrodes 360c and 360d. is.

(fixing operation)
In FIG. 2A, when the paper P is passed through the fixing nip SN in the direction of the arrow, the paper P is heated between the fixing belt 310 and the pressure roller 320, and the toner image is fixed on the paper P. As shown in FIG. At this time, the fixing belt 310 is heated by the heat from the heat generating member 360 while sliding on the insulating layer 370 of the heat generating member 360 .

In the temperature control of the heat-generating member 360 for setting the fixing belt 310 to a predetermined temperature, if only the first temperature sensor TH1 is arranged, only the PTC element 364 in which the first temperature sensor TH1 is arranged is partially disconnected, and power is cut off. Then, the temperature of the PTC element 364 does not rise. Therefore, in an attempt to keep the PTC element 364 at a constant temperature by temperature control, the other normal PTC elements 361 to 363 and 365 to 368 continue to be supplied with an excessive current, resulting in an abnormally high temperature.

Therefore, in this embodiment, the second temperature sensor TH2 is arranged in the heating area of the PTC element 368 at the end. This second temperature sensor TH2 detects the temperature _T8 of the PTC element 368, and when the temperature _T8 reaches the above-described abnormally high temperature, the power control unit 400 causes the triac 420 to cut off the supply current to the electrodes 360c and 360d. to control. Also, when the temperature of the second temperature sensor TH2 itself falls below a predetermined temperature T _N (T ₈ <T _N ) due to disconnection, the power control unit 400 controls the triac 420 so as to cut off the supply current to the electrodes 360c and 360d. do.

(Another Embodiment 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 side opposite to the pressure roller 320, and the fixing belt 310 is sandwiched and heated between the pressure roller 390 and the heating device.

The above-described heating device is arranged inside the fixing belt 310 . An auxiliary stay 331 is attached to one side of the stay 330, and a nip forming member 332 is attached to the other side. The heating device is held by this auxiliary stay 331 . The nip forming member 332 contacts the pressure roller 320 via the fixing belt 310 to form a fixing nip SN.

As shown in FIG. 2C, the third fixing device has a heating device inside the fixing belt 310 . In this heating device, instead of omitting the pressure roller 390 described above, the length of contact with the fixing belt 310 in the circumferential direction is lengthened. It is formed in an arc shape. The heat-generating member 360 is arranged in the center of the arc-shaped base material 350 . Others are the same as the second fixing device of FIG. 2B.

The fourth fixing device, as shown in FIG. 2D, is divided into a heating nip HN and a fixing nip SN. That is, a nip forming member 332 and a stay 333 made of a metal channel member are arranged on the opposite side of the pressure roller 320 from the fixing belt 310 so as to enclose the nip forming member 332 and the stay 333 . A pressure belt 334 is arranged so as to be rotatable. Then, the paper 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 in FIG. 2A.

Further, the second temperature sensor TH2 for safety compensation, as indicated by the dashed line in FIG. 310 (the inner peripheral surface on the downstream side of the PTC element 368) may be arranged so as to be crimped by an urging means. If the number of resistance heating elements is increased, it becomes difficult to secure the installation space for the temperature sensors. Further, the second temperature sensor TH2 for safety compensation may be arranged not only for the PTC element 368 but also for each heating area of the other PTC elements 361 to 363 and 365 to 367 including the inner peripheral surface of the fixing belt 310. .

(abnormality detection)
Here, the operation of abnormality detection by power control unit 400 will be described with reference to the flow charts of FIGS. 6A to 6C. FIG. 6A is a flow chart of the basic control operation of the heating device. In step S1, it is confirmed that the heater relay 440 is turned on by the start-up start signal of the heating device or the fixing device 300. FIG. A voltage conversion value Viac obtained by voltage conversion by the current transformer CT of the current detection means 430 is read into the power control section 400 . The timing of this reading is immediately after the start-up of fixing device 300 is started.

Immediately after the start-up is preferably performed after a predetermined time T [ms] has passed since the ON operation of the heater relay 440, as in step S2 in detail. That is, due to the characteristics of the circuit of the current detection means 430, it takes a predetermined time until the current value is converted into a voltage value by the current transformer CT and the current can be stably detected.

Therefore, after a predetermined time T [ms] has passed, the current detection permission OK (Yes) is received in step S3, and the current detection, ie, the voltage conversion value Viac is read into the power control unit 400 in step S4. Considering the influence of noise picked up during current detection during this reading, the number of sampling times for current detection is set multiple times in a predetermined period, and aggregation processing such as excluding the maximum and minimum extreme values among the multiple detected current values. It is desirable to If the current detection permission is No in step S3, the flow ends.

When the current value is sampled and detected a plurality of times during a predetermined period at startup, current detection accuracy is best when the duty ratio is 100%, as shown in FIG. 5(b). For example, when the duty ratio is 75%, the current value decreases at regular intervals, and in this relationship, the current detection period cannot be set too long, and the effect of noise is accordingly increased. On the other hand, detection at a duty ratio of 100% at the time of start-up also leads to determination of the presence or absence of an abnormality before the start of paper feeding, and has the effect of being able to prevent the occurrence of defective fixing (defective printing). be.

However, even if the duty ratio is less than 100%, if a constant duty ratio continues for a predetermined period during the current detection period, it is possible to predict in advance the amount of drop in the current value due to duty control. Therefore, it is possible to detect the current even after the start-up, even when the temperature of the PTC elements 361 to 368 has risen to some extent.

Here, the target correlation of the current-voltage of the PTC elements 361 to 368 is indicated by the solid line in FIG. 5(c). Broken lines above and below the solid line are current-voltage correlations at the lower limit of resistance and the upper limit of resistance.

As described above, when the temperature of the PTC elements 361 to 368 rises to some extent, the temperature is stabilized, so the current-voltage correlation is linearly stabilized as shown in FIG. 5(c). Therefore, it becomes easier to detect the current Iac flowing through the PTC elements 361 to 368 in a stable state. Also in this case, it is desirable to detect the current value Iac flowing through the PTC elements 361 to 368 before starting to pass the paper, and to determine the presence or absence of an abnormality.

FIG. 6B further embodies step S4 (perform current detection) in FIG. 6A as steps S8 to S11. In addition, in the case of failure detection execution No in step S7, the flow is terminated.

If the failure detection is OK (Yes) in step S7, in step S8, the current detection means 430 detects Viac obtained by voltage-converting the current value Iac flowing between the electrodes 360c and 360d of the PTC elements 361 to 368, and Viac is detected. Read into the power control unit 400 . Then, in step S9, the voltage value Vac between the electrodes 360c and 360d is detected by the voltage detection means 450, and the voltage value Vac is read into the power control section 400. FIG.

Thereafter, in step S10, a failure threshold current Ith (failure threshold voltage Vith) is calculated, and in step S11, the voltage conversion value Viac is compared with the failure threshold voltage Vith. If the voltage conversion value Viac is greater than or equal to the failure threshold value Vith (Viac≧Vith), the flow ends.

On the other hand, when the detected voltage conversion value Viac is smaller than the failure threshold value Vith (Viac<Vith), it is determined that one of the PTC elements 361 to 368 is "failed", that is, "disconnected", and the heater relay 440 is turned off in step S12. At the same time, in step S13, an error is notified by an error display on the operation panel of the printer 100. FIG.

If the feeding roller 60 or the like stops rotating at the same time as the power supply is interrupted while the paper is being fed, a paper jam occurs. . For this reason, it is preferable to continue the operation with only an error notification, except when the partial disconnection of the PTC elements 361 to 368 has a particularly large impact on safety and printing by FAX reception.

Here, the voltage value Vac between the electrodes 360c and 360d is separately detected because, as shown in FIG. 5B, the voltage value Vac applied between the electrodes 360c and 360d causes a This is because the current value Iac is greatly affected. Therefore, it is necessary to correct the fault threshold current Ith (Vith) depending on the magnitude of the detected voltage value Vac.

Further, as shown by the dashed lines (lower limit of resistance, upper limit of resistance) in FIG. It fluctuates within a range of about 10%. In order to cope with these variations, it may be necessary to correct the failure threshold current Ith (Vith) by the voltage value Vac.

In this embodiment, the allowable variation threshold of the voltage value Vac without correction of the failure threshold current Ith (Vith) is set, for example, within a range of ±5%. Correction can be made. Specifically, this correction increases or decreases the failure threshold voltage Vith corresponding to the rate of change (%) of the voltage value Vac when comparing the voltage conversion value Viac with the failure threshold voltage Vith in step S11.

FIG. 6C is a flow chart showing the aforementioned control operation of the heating device by the first temperature sensor TH1 and the second temperature sensor TH2. In step S21 of FIG. 6C, the printer 100 is instructed to execute the print job.

Then, in step S22, the power control unit 400 starts supplying power from the AC power supply 410 to the PTC elements 361 to 368 of the heat generating member 360. FIG. Then, in step S23, the temperature _T4 of the PTC element 364 located in the central region of the heat generating member 360 is detected by the first temperature sensor TH1.

Next, in step S24, the triac 420 starts controlling the temperature of the heat generating member 360. FIG. Also, in step S25, the temperature _T8 of the PTC element 368 is detected by the second temperature sensor TH2.

Then, in step S26, it is determined whether or not the temperature T ₈ ≧T _N (T _N : a predetermined temperature).If T ₈ <T _N , it is determined that an abnormally low temperature has occurred (disconnection has occurred), and power is supplied to the heat generating member 360 in step S27. The triac 420 is controlled by the power control unit 400 so that the is substantially cut off. Then, in step S28, an error display is displayed on the operation panel of the printer 100. FIG. The triac 420 may also be controlled so that the power supply to the heat generating member 360 is cut off (OFF) also when the temperature _T8 of the second temperature sensor TH2 becomes abnormally high.

Further, if T ₈ ≧T _N , it is determined that abnormally low temperature does not occur, and the printing operation is started in step S29. In this manner, in addition to the flow charts of FIGS. 6A and 6B by the current detection means 430 described above, by operating the power control section 400 according to the flow chart of FIG. More safety.

(power duty for adjustment)
FIG. 6D is a flow chart showing the operation (diagnosis mode) of the power control section 400 as power control means after the fixing device 300 is replaced with a new device and this is detected. This diagnosis mode is a mode for appropriately controlling the electric power of the heat generating member 360 as intended, regardless of variations in resistance temperature characteristics of the heat generating member 360 when the fixing device 300 is replaced with a new one.

When the detachment/replacement detection unit 460 detects detachment/replacement of the fixing unit 1 in step S31, the adjustment power duty is supplied to the heating member 360 in step S32. The power duty for adjustment at this time is assumed to be 100%. At step S33, the temperature of the rear surface of the heat-generating member 360 is detected by temperature detecting means such as a thermistor.

Thereafter, the current and voltage of the heat generating member 360 are detected in step S34. From the current value I and the voltage value E detected in step S35, the resistance value R (=E/I) of the heat generating member 360 is calculated. The calculated resistance value R is associated with the temperature information of the heat generating member 360 and stored in the non-volatile memory within the power control unit 400 in step S36.

The flow from step S33 to step 36 is repeated several times until the supply period of the power duty for adjustment reaches the predetermined period T in step 37. FIG. As a result, the temperature-resistance value characteristic (temperature resistance characteristic) of the heat generating member 360 as shown in FIG. 7 is obtained (solid line a).

The predetermined period T takes a longer time than a normal start-up operation with a power duty of 100%, especially when the power duty is not 100% but a small ratio such as 20 to 50%. This is because when the power duty is small, the temperature of the heat generating member 360 rises slowly, so it takes a longer time until the current/voltage can be stably detected than when the power duty is 100%.

In order to improve the detection accuracy of the temperature resistance characteristics of the heat-generating member 360, the temperature change of the heat-generating member 360 is controlled such that the temperature gradient during temperature rise is 70° C./second or less, taking into consideration the operating temperature range of the heat-generating member 360. Desirably, it should be set at 50° C./sec or less. Although the temperature gradient is not impossible even at a power duty of 100%, it can be easily achieved at a power duty of less than 100%. By continuing to supply the adjustment power duty of less than 100% at the temperature gradient for at least 1 second, preferably 2 seconds or more, the heating member 360 is heated to a predetermined operating temperature, for example, 200° C., preferably 180° C. Temperature can be raised.

Here, if the variation in power supply voltage is ±15% (85V to 115V for 100V system, 204V to 276V for 240V system) and the variation in resistance value of heat generating member 360 is ±10%, the power of heat generating member 360 is There is a possibility that it will be about 1.4 times larger at maximum than when there is no variation (when the power supply voltage varies by +15% and the resistance value of the heat generating member 360 varies by -10%).

When the power of the heat-generating member 360 is maximized in this way, the time required for the heat-generating member 360 to reach 180° C. is less than 2 seconds (temperature gradient>70° C./sec) at a power duty of 100%, and the temperature resistance characteristic is improved. Detection accuracy deteriorates. Therefore, it is preferable to set the power duty to less than 100% in consideration of the case where the power of the heat generating member 360 is maximized due to the variation.

If it is determined in step S37 that the predetermined period T has elapsed, the supply of the power duty for adjustment is terminated in the next step S38. Then, in step S39, the power duty during use of the heat generating member 360 is adjusted based on the temperature-resistance value characteristics. That is, when the resistance value characteristic with respect to the detected temperature is smaller than the design value of the heat generating member 360 (broken line c in FIG. 7), the design power (the amount of heat generated per unit time) is not enough even if the predetermined power duty is supplied. Since it cannot be obtained, the duty is increased from the planned power duty. This increasing rate corresponds to the amount of divergence between the solid line a and the dashed line c in FIG.

Conversely, if the resistance value characteristic with respect to the detected temperature is greater than the design value of the heat generating member 360 ((broken line b in FIG. 7), the design power (the amount of heat generated per unit time) is Therefore, the duty is reduced from the planned power duty.The ratio of this reduction corresponds to the amount of divergence between the solid line a and the broken line b in Fig. 7. The power duty is adjusted in this way. After that, in step S40, the diagnosis mode ends, and the printing operation, that is, the supply of the adjusted power duty to the heat generating member 360 is started.

When the printing operation is restarted after finishing the printing operation, unless the fixing device 300 is replaced, the resistance value R detected by the previous power duty for adjustment and stored in the nonvolatile memory is read out, and the resistance value R is read out. and based on the detection result of the voltage detection means 450, the power duty during use of the heat generating member 360 is adjusted. In this case, the adjustment power duty is not supplied to the heat generating member 360 .

In this manner, the temperature characteristic of the actual resistance value R of the heat generating member 360 is calculated, and the power duty is adjusted so as to obtain the desired power (the amount of heat generated), and then the power duty is supplied to the heat generating member 360. Therefore, the electric power of the heat-generating member 360 can be appropriately controlled as intended regardless of variations in the resistance value of the heat-generating member 360 .

Although the present invention has been described above based on the embodiments, it is needless to say that the present invention is not limited to the above embodiments and can be variously modified within the scope of the technical idea described in the claims. . For example, the heating device can be used for purposes other than the fixing device, such as a drying device. Besides the PTC element, other resistance heating elements such as a ceramic heater can be used as the resistance heating element. 3A(b), 3B(c) and 3B(b), and 3B(c), it is of course possible to interfit with each other in a concave-convex shape or a comb-tooth shape. Also, the number of PTC elements may be less than eight or nine or more. Furthermore, it is also possible to arrange the PTC elements in a plurality of rows in the lateral direction of the substrate 350 .

SN: Fixing nip HN: Heating nip L: Laser light P: Paper TM: Transfer means TH1: First temperature sensor TH2: Second temperature sensor 1K, 1Y, 1M, 1C: Process units
2K, 2Y, 2M, 2C: Image carrier 3K, 3Y, 3M, 3C: Drum cleaning device
4K, 4Y, 4M, 4C: charging device 5K, 5Y, 5M, 5C: developing device (imaging section)
6K, 6Y, 6M, 6C: toner bottle 7: exposure device 7a: mirror 8: transfer cover 10: powder container 15: transfer device 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: post-transfer transport path 35: post-fixing transport path 36: paper discharge path 37: paper discharge roller pair 41: Reverse transport path 42: Member 42a: Swing shaft 43: Reverse transport roller pair 44: Discharge tray 45, 60: Paper feed roller 46: Tray 100: Printer 101: Side cover 200: Paper feeder (recording medium supply unit )
210: Roller pair 220: Feeding roller 230: Separation roller 240: Conveying 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: Release layer 330, 333: stay 331: auxiliary stay 332: nip forming member 334: pressure belt 340: folder 350: base material 360: heating member 361-368: PTC element (resistance heating element)
360a, 360b: feeder 360c, 360d: electrode 370: insulating layer 390: pressure roller 400: electric power control section 410: AC power supply 420: triac 430: current detection means 440: heater relay 450: voltage detection means 460: attachment/detachment replacement detection means

JP 2015-194713 A JP 2016-18127 A JP 2018-25743 A

Claims (6)

In an image forming apparatus in which a fixing device is detachably mounted,
an exterior member that opens and closes when the fixing device is attached and detached;
The fixing device includes a resistance heating element, temperature detection means for detecting the temperature of the resistance heating element, power control means for controlling the electric power of the resistance heating element, and whether or not the resistance heating element has been removed or replaced. Equipped with attachment/detachment replacement detection means for detecting
activating the attachment/detachment replacement detection means by opening and closing the exterior member;
When the attachment/detachment replacement detection means detects attachment/detachment/replacement of the resistance heating element, the power control means sets a power duty of 100 as a predetermined power duty for adjustment to the resistance heating element before using the resistance heating element. % continuously without interruption over a given supply period,
While the power duty for adjustment is being supplied, the power of the resistance heating element and the temperature change of the resistance heating element detected by the temperature detection means are acquired, and the resistance is adjusted according to the power and the temperature change. An image forming apparatus characterized by adjusting a power duty when a heating element is used. 2. An image forming apparatus according to claim 1, wherein a temperature gradient of said resistance heating element is set to 70[deg.] C./second or less when said power duty for adjustment is supplied to said resistance heating element. 3. The image forming apparatus according to claim 1, wherein a change in resistance with respect to temperature of said resistance heating element is detected during said power duty supply period. 4. An image forming apparatus according to claim 3, wherein a change in resistance with respect to temperature of said resistance heating element is obtained by current detecting means and voltage detecting means connected to said resistance heating element. Information on the detected resistance change rate with respect to the temperature of the resistance heating element is stored in a non-volatile memory, and the resistance heating element is detected based on the stored information on the resistance change rate and the detection result of the voltage detection means. 5. The image forming apparatus according to claim 4, wherein the power duty during use is adjusted. 6. An image forming apparatus according to claim 1, wherein said resistance heating element has a plurality of resistance elements or PTC elements electrically connected in parallel.

Images