JP2019159312A - Heating device, fixing device, and image forming apparatus - Google Patents

Abstract

To accurately detect a change in resistance (change in current) of a plurality of resistance heating elements of a planar heating body to precisely detect the presence/absence of abnormality (presence/absence of disconnection) in the resistance heating elements.SOLUTION: A heating device comprises: resistance heating elements 361 to 368 that are connected in parallel; power supply means (410); current detection means 430; voltage detection means 450; and a control unit 400 as current control means that controls a current flowing in the resistance heating elements on the basis of results of detection performed by the current detection means and voltage detection means. The control unit 400 starts supply of power to the resistance heating elements, and subsequently executes detection with the current detection means 430 in a state where the waveform of an AC current of the supplied power continues in the same waveform for a predetermined time or more, which is required for detection of current and voltage performed by the current detection means and voltage detection means.SELECTED DRAWING: Figure 6B

Description

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

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 having a low heat capacity is heated by a planar heating element composed of a base material and a resistance heating element. In this planar heating element, a plurality of resistance heating elements are arranged on a base material arranged in the width direction of the fixing belt, and these resistance heating elements are electrically connected in parallel. Thus, the temperature rise of the non-sheet passing portion when small size paper is passed is suppressed (Patent Document 1). By using a PTC heater having a positive temperature coefficient for the resistance heating element, it is possible to further suppress the temperature rise of the non-sheet passing portion and save energy.

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

However, if the length of the resistance heating elements is shortened and the number of the heaters is increased in order to further suppress the temperature rise of the non-sheet passing portion, it is difficult to attach temperature detection sensors to all of them in terms of space and cost. . Therefore, for example, if the temperature detection sensor is attached only to one resistance heating element in the center in the longitudinal direction, if the resistance heating element is disconnected, the current of the other resistance heating element may continue to increase, and temperature control may become impossible. .

Therefore, in the technique of Patent Document 1, the resistance value of the resistance heating element sandwiched in the short direction between the two electrodes is detected, and when the resistance value becomes larger than a predetermined value due to the disconnection of the resistance heating element, power feeding is performed. (Alternating current) is stopped. In this technique, the resistance value R of the resistance heating element is calculated by measuring the voltage value E between two electrodes and dividing the voltage value E by the current value I flowing between the electrodes (R = V / I). Here, the general method for detecting the interelectrode current value I is detected by converting the alternating current into a voltage value after rectifying the alternating current.

However, since the power control of the resistance heating element is also performed by phase control in Patent Document 1, there is a problem that the detection accuracy of the current value during the phase control is significantly reduced. In addition, the resistance value of the resistance heating element changes according to the temperature change caused by the power supply, and the current value also changes. For this reason, there is a difficult problem of determining at which timing current value the presence / absence of abnormality (disconnection of resistance heating element) regardless of power control.

The present invention has been made in view of such problems, and an object thereof is to accurately detect a resistance change (current change) of a resistance heating element.

In order to solve the above-mentioned problems, a heating device of the present invention includes a resistance heating element that is arranged in plural along the longitudinal direction of a base material and is electrically connected in parallel to each other, and a power supply that supplies power to the resistance heating element. A current detection means for detecting a current flowing through the resistance heating element, a voltage detection means for detecting a voltage applied to the resistance heating element, and a detection result of the current detection means and the voltage detection means. And a current control means for controlling a current flowing through the resistance heating element, after the power supply to the resistance heating element is started, the waveform of the alternating current supplied to the resistance heating element is the current detection The detection by the current detection means is executed in a state where the same waveform continues for a predetermined time required for the current detection by the means.

According to the present invention, after the power supply to the resistance heating element is started, the waveform of the alternating current supplied to the resistance heating element continues in the same waveform for a predetermined time or more necessary for detection of current and voltage. Since the current detection by the current detection means is executed, the resistance change (current change) of the resistance heating element can be detected with high accuracy.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. 1 is a principle diagram of an image forming apparatus according to an embodiment of the present invention. 1 is a cross-sectional view of a first fixing device according to an embodiment of the present invention. FIG. 4 is a cross-sectional view of a second fixing device according to an embodiment of the present invention. FIG. 6 is a cross-sectional view of a third fixing device according to an embodiment of the present invention. FIG. 6 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 arrangement | sequence state of each resistance heating element of the planar heating element which provided the electrode at both ends. (A)-(c) is a top view which shows the arrangement | sequence state of each resistance heating element of the planar heating element which provided the electrode at one end. (A)-(c) is a top view which shows the arrangement | sequence state of each resistance heating element of the meandering pattern which provided the electrode at both ends. (A)-(c) is a top view which shows the arrangement | sequence state of each resistance heating element of the meandering pattern which provided the electrode in one end. It is a figure which shows a heating apparatus, an electric power supply circuit, and a control part. (A) is a figure which shows the change of the temperature and current of a resistance heating element, (b) is a figure which shows the change of the voltage waveform by duty control, (c) is a figure which shows the voltage-current correlation of a resistance heating element. is there. It is a flowchart which shows the basic control operation | movement of the heating apparatus by an electric current detection means. It is a flowchart which shows the detailed control operation | movement of the heating apparatus by an electric current detection means. It is a flowchart which shows the control operation of the heating apparatus by a temperature detection sensor.

Hereinafter, a heating device according to an embodiment of the present invention, a fixing device using the heating device, and an image forming apparatus (laser printer) 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 duplicate description thereof is simplified or omitted as appropriate. Further, dimensions, materials, shapes, relative arrangements, and the like in the description of each component are examples, and the scope of the present invention is not limited to these unless otherwise specified.

In the following embodiments, “recording medium” is 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, prepreg sheets obtained by impregnating carbon fibers with a resin in advance.

A medium to which a developer or ink can be attached, a recording paper, and a recording sheet are all included in the “recording medium”. In addition to plain paper, “paper” includes cardboard, postcard, envelope, 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 that an image having a meaning such as a character or a figure is imparted to the medium, but also an image having no meaning such as a pattern is imparted to the medium. Also means.

(Laser printer configuration)
FIG. 1A is a configuration diagram schematically showing a configuration of a color laser printer 100 as an embodiment of an image forming apparatus including a heating device or a fixing device 300 of the present invention. FIG. 1B 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 units. These process units form an image with developers of black (K), yellow (Y), magenta (M), and cyan (C) corresponding to the color separation components of the color image.

The process units 1K, 1Y, 1M, and 1C have the same configuration except that they have toner bottles 6K, 6Y, 6M, and 6C containing unused toners of different colors. Therefore, the configuration of one process unit 1K will be described below, and description of the other process units 1Y, 1M, 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 eliminating 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 development means for performing visible image processing of the electrostatic latent image formed on the image carrier. 5K etc. The process unit 1K is detachably attached to the main body of the laser printer 100 so that consumable parts can be replaced at the same time.

The exposure device 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 irradiate the image carrier 2K by reflecting the laser beam Lb from the laser diode by the mirror 7a based on the writing scan according to the image information, that is, based on the image data.

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

The intermediate transfer belt 16 circulates while being stretched over the primary transfer rollers 19K, 19Y, 19M, and 19C, the driving roller 18, and the driven roller 17. The secondary transfer roller 20 is disposed so as to face the driving roller 18 and contact the intermediate transfer belt 16. If 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 that combines these images.

The belt cleaning device 21 is installed on the downstream side of the secondary transfer roller 20 in the traveling direction of the intermediate transfer belt 16. A cleaning backup roller is provided on the opposite side of the belt cleaning device 21 with respect to the intermediate transfer belt 16.

A paper feeding device 200 having a tray on which the paper P is stacked is installed below the laser printer 100. The sheet feeding device 200 constitutes a recording medium supply unit, and can store a large number of sheets P as recording media in a bundle, and includes a sheet feeding roller 60 and a roller pair 210 as a conveying means for the sheet P. It is unitized with. The paper feeding device 200 can be inserted into and removed from the main body of the laser printer 100 in order to replenish paper. The paper feed roller 60 and the roller pair 210 are disposed above the paper feeding device 200, and convey the uppermost paper P of the paper feeding device 200 toward the paper feeding path 32.

The registration roller pair 250 as a separating and conveying means is disposed 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. By 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 in the conveyance direction of the registration roller pair 250, and the registration sensor 31 detects the passage of the leading edge of the sheet. When a predetermined time elapses after the registration sensor 31 detects the passage of the leading edge of the sheet, the sheet is abutted against the registration roller pair 250 and temporarily stops.

At the downstream end of the sheet feeding device 200, a conveyance roller 240 for conveying the sheet conveyed rightward 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 composed of a pair of upper and lower rollers. The roller pair 210 can be FRR separation type or FR separation type. In the FRR separation system, a separation roller (return roller) to which a fixed amount of torque is applied in the counter-feeding direction via a torque limiter by a drive shaft is brought into pressure contact with the feeding 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 is brought into pressure contact with a feeding roller via a torque limiter, and a sheet is separated at a nip between the rollers.

In this embodiment, the roller pair 210 is configured by the FRR separation method. That is, the roller pair 210 includes an upper feeding roller 220 that conveys the paper into the machine, and a lower separation roller 230 that is given a driving force by a drive shaft via a torque limiter in the opposite direction to the feeding roller 220. It consists of

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

The sheet P on which the slack is formed at the leading end against the registration roller pair 250 is aligned with the timing at which the toner image formed on the intermediate transfer belt 16 is suitably transferred, and the secondary transfer roller 20 and the driving roller. 18 to the secondary transfer nip (transfer nip N in FIG. 1B). The fed paper P is electrostatically transferred to the desired transfer position with high accuracy by the toner image formed on the intermediate transfer belt 16 by the bias applied at the secondary transfer nip. ing.

The post-transfer conveyance path 33 is disposed above the secondary transfer nip between 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 including a heating device, and a pressure roller 320 as a pressure member that rotates while contacting 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 branches to a paper discharge path 36 and a reverse conveyance path 41 at the upper end of the post-fixation conveyance path 35. A switching member 42 is disposed at this branching portion, and the switching member 42 swings about its swing shaft 42a. A pair of paper discharge rollers 37 is disposed in the vicinity of the opening end of the paper discharge path 36.

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

The powder container 10 (for example, toner container) is disposed between the transfer device 15 and the paper 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 paper feed roller 60 to the secondary transfer roller 20 due to transfer paper conveyance. And the powder container 10 is installed in the dead space produced in this distance, and size reduction of the whole laser printer is aimed at.

The transfer cover 8 is installed in front of the paper feeding device 200 in the drawing direction above the paper feeding device 200. By opening the transfer cover 8, the inside of the laser printer 100 can be inspected. The transfer cover 8 is provided with a manual feed roller 45 for manual feed and a manual tray 46 for manual feed.

Note that the laser printer of this embodiment is an example of an image forming apparatus, and the image forming apparatus is not limited to a laser printer. In other words, the image forming apparatus can be configured as any one of a copying machine, a facsimile machine, a printer, a printing machine, and an ink jet recording apparatus, or as a complex machine that combines at least two of these.

(Laser printer operation)
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 performing single-sided printing will be described. As shown in FIG. 1A, the paper feed roller 60 is rotated by a paper feed signal from the control unit of the laser printer 100. Then, the paper feed roller 60 separates only the uppermost paper of the bundled paper P stacked on the paper feeding device 200 and sends 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 forms a slack and waits in that state. Then, an optimal timing (synchronization) for transferring the toner image formed on the intermediate transfer belt 16 to the paper P is achieved, and the leading edge skew of the paper P is corrected.

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

Here, regarding the image forming operation, one process unit 1K will be described, and 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 device 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 beam Lb, the potential of the irradiated portion is lowered to form an electrostatic latent image. The developing device 5K includes 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 via the developer carrier. The 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 the surface thereof. Then, the toner image formed on the image carrier 2K 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 and collected by a waste toner transport unit to a waste toner storage unit in the process unit 1K. Further, the static eliminator neutralizes the residual charge of 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 for the respective colors, toner images are similarly formed on the image carriers 2Y, 2M, and 2C, and transferred to the intermediate transfer belt 16 so that the respective color toner images are overlapped.

The intermediate transfer belt 16 to 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 drive roller 18. On the other hand, the registration roller pair 250 sandwiches and rotates the paper abutted on it at a predetermined timing, and matches the timing at which the toner image formed by superimposing and transferring on the intermediate transfer belt 16 is suitably transferred, It 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 to the paper P sent out by the registration roller pair 250.

The paper P on which the toner image has been transferred is conveyed to the fixing device 300 through the post-transfer conveyance path 33. The paper 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 paper P by heating and pressing. The paper P on which the toner image is fixed is sent out from the fixing device 300 to the post-fixing conveyance path 35.

The switching member 42 is in a position where the vicinity of the upper end of the post-fixing conveyance path 35 is opened as shown by the solid line in FIG. 1A at the timing when the sheet P is sent out from the fixing device 300. The paper P sent out from the fixing device 300 is sent out to the paper discharge path 36 via the post-fixing conveyance path 35. The paper discharge roller pair 37 sandwiches the paper P sent to the paper discharge path 36 and rotates to discharge the paper P to the paper discharge tray 44, thereby completing single-sided printing.

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

When the rear end of the paper P passes through the paper discharge path 36, the switching member 42 swings about the swing shaft 42a as shown by the dotted line in FIG. 1A, and closes the upper end of the post-fixing transport path 35. To do. Almost simultaneously with the closing of the upper end of the post-fixing conveyance path 35, the paper discharge roller pair 37 rotates in a direction opposite to the direction in which the paper P is conveyed out of the laser printer 100, and sends the paper P to the reverse conveyance path 41.

The sheet P sent out to the reverse conveyance path 41 reaches the registration roller pair 250 through the reverse conveyance roller pair 43. Then, the registration roller pair 250 feeds the paper 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-transfer surface of the paper P.

The secondary transfer roller 20 and the driving roller 18 transfer the toner image to the toner image non-transfer surface (back surface) of the paper P when the paper P passes through the secondary transfer nip. Then, the paper P on which the toner image is transferred is conveyed to the fixing device 300 through the post-transfer conveyance 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 heating and pressing the paper P. In this way, the paper P on which the toner images are fixed on both the front and back sides is sent out from the fixing device 300 to the post-fixing conveyance path 35.

The switching member 42 is in a position where the vicinity of the upper end of the post-fixing conveyance path 35 is opened as shown by the solid line in FIG. 1A at the timing when the sheet P is sent out from the fixing device 300. The paper P sent out from the fixing device 300 is sent out to the paper discharge path 36 via the fixing conveyance path. The paper discharge roller pair 37 sandwiches the paper P sent to the paper discharge path 36, rotates and discharges it 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 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 transported to the powder container 10 by the waste toner transport 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 FIGS. 3A (a) and 4, a base 350 in which an elongated metal thin plate member is covered with an insulating material, and disposed on the base 350. The heating member 360 is provided.

The heat generating member 360 includes a plurality of resistance heat generating elements 361 to 368 arranged linearly and at equal intervals in the longitudinal direction of the base material 350. Feeding lines 360a and 360b having small resistance values are linearly arranged in parallel with each other on both sides in the short direction of the resistance heating elements 361 to 368, and both ends of the resistance heating elements 361 to 368 are connected to the feeding lines 360a and 360b. Is connected. And the electric power supply means containing the alternating current power supply 410 is connected to the electrodes 360c and 360d formed in each one end part of the feeder lines 360a and 360b as shown in FIG.

The heating device of the present embodiment includes a first temperature detection sensor TH1 and a second temperature detection sensor TH2 as temperature detection means for detecting the temperature of the resistance heating element. The temperature detection sensors TH1 and TH2 can be composed of, for example, a thermistor.

As shown in FIG. 4, the first temperature detection sensor TH <b> 1 and the second temperature detection sensor TH <b> 2 are arranged so as to be crimped to the back side of the base material 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. Both of the two temperature detection sensors TH1 and TH2 can be configured by a contact type thermistor having a thermal time constant of less than 1 second.

The first temperature detection sensor TH1 for temperature control is arranged in the heating region of the resistance heating element 364 (fourth from the left end) as the first resistance heating element in the central region in the longitudinal direction within the minimum sheet passing width. The second temperature detection sensor TH2 for safety compensation has a resistance heating element 368 (8th from the left end) (or resistance heating element 361 (first from the left end)) as the second resistance heating element at the end in the longitudinal direction. Located 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 that avoids the gap between the resistance heating elements where the amount of heat generation is reduced. As a result, the temperature controllability is improved, and it is easy to detect disconnection when disconnection occurs in some resistance heating elements.

The first temperature detection sensor TH1 may be arranged in any heating region of the resistance heating elements 363, 365, and 366. Further, the second temperature detection sensor TH2 can be arranged in the heating region of the second resistance heating element 362 or the seventh resistance heating element 367 from the left end as long as it is the end region in the longitudinal direction. It is not necessary to arrange at the extreme end.

A power supply circuit as power supply means for supplying power to the resistance heating elements 361 to 368 is shown below the heating device of FIG. This power supply circuit includes a control unit 400 as current control means, an AC power supply 410, a triac 420, a current detection means 430, and a heater relay 440. The AC power supply 410, the current transformer CT of the current detection means 430, the triac 42, and the heater relay 440 are arranged in series between the electrodes 360c and 360d.

The temperatures T ₄ and T ₈ detected by the first temperature sensor TH 1 and the second temperature sensor TH 2 are input to the control unit 400. 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 target temperature, a duty control electrode 360c, the supply current to 360d by the triac 420 To do.

Specifically, the current duty ratio corresponding to the temperature difference the temperature T ₄ and the target temperature of the first temperature sensor TH1, duty control of the current triac 420 flows through the resistance heating element 361-368. The current becomes zero when the duty ratio is 0%, and the current becomes maximum when the duty ratio is 100%. FIG. 5B illustrates the voltage conversion value Viac of the supply current at 100% duty and 75% duty. In the 75% duty control, it can be seen that the voltage conversion value Viac fluctuates greatly in a predetermined cycle.

The control unit 400 can be configured by 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 due to the paper passing (heat transfer to the paper) is generated. Therefore, not only the temperature T ₄ obtained from the first temperature sensor TH1 but also the heat removal is considered. By controlling the supply current, the temperature of the fixing belt 310 can be controlled to a desired temperature.

The current detection means 430 detects the sum of the current values flowing through the resistance heating elements 361 to 368. That is, the 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.

Here, when any one of the resistance heating elements 361 to 368 fails or is disconnected, the current value read by the control unit 400 decreases. In particular, when the resistance heating element 364 detected by the first temperature sensor TH1 fails or is disconnected, the temperature control function by the control unit 400 is lost, regardless of the temperatures of the other resistance heating elements 361 to 363 and 365 to 368. A situation occurs in which power is continuously supplied to the electrodes 360c and 360d by the triac 420 at a duty ratio of 100%.

Therefore, in the present embodiment, when the current obtained by the current detection unit 430 becomes less than a predetermined threshold current, the heater relay 440 is turned off to interrupt the current flowing through the electrodes 360c and 360d. Specifically, the amount of current flowing through the resistance heating elements 361 to 368 is detected by the current detection unit 430 using the voltage conversion value Viac converted by the current transformer CT.

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

Even when the triac 420 sets the duty ratio to 0%, the power supply can be stopped in the same manner, but the heater relay 440 is turned off in order to reliably cut off the current. When the temperature T ₈ detected by the second temperature sensor TH2 exceeds the predetermined threshold value, the heater relay 440 can be turned off to substantially cut off the current flowing through the electrodes 360c and 360d. It is.

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

On the outermost surface layer of the fixing belt 310, a release layer having a thickness of 5 to 50 μm is formed with a fluorine-based resin such as PFA or PTFE in order to enhance durability and secure 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.

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

Inside the fixing belt 310, a stay 330 and a folder 340 are disposed in the axial direction. 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 base material 350 of the heating device, and is supported by the stay 330. The folder 340 can be preferably formed of a heat-resistant resin having a low thermal conductivity such as LCP, whereby heat transfer to the folder 340 is reduced and the fixing belt 310 can be efficiently heated.

In order to avoid contact with the high temperature part of the base material 350, the folder 340 has a shape that supports only two locations near both ends in the short direction of the base material 350. Thereby, the amount of heat flowing to the folder 340 can be further reduced and the fixing belt 310 can be efficiently heated.

The resistance heating elements 361 to 368 and the feed lines 360a and 360b are covered with a thin insulating layer 370. The insulating layer 370 can be made of heat resistant glass having a thickness of 75 μm, for example. Insulating layer 370 insulates and protects resistance heating elements 361-368 and feed lines 360a, 360b, and maintains slidability with fixing belt 310 as will be described later.

As the material of the substrate 350, low-cost aluminum, stainless steel, or the like is preferable. The substrate 350 is not limited to a metal, but can be made of a ceramic such as alumina or aluminum nitride, or a non-metallic material having excellent heat resistance and insulation properties such as glass or mica. In order to improve the thermal uniformity of the heating device and improve the image quality, the base material 350 may be made of a material having a 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.

The resistance heating elements 361 to 368 are formed by, for example, applying a paste prepared by silver palladium (AgPd) or glass powder to the base material 350 by screen printing or the like, and then firing the base material 350. Can do. In this embodiment, the resistance value of the resistance heating elements 361 to 368 is 80Ω at room temperature.

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

The insulating layer 370 side of the resistance heating elements 361 to 368 comes into contact with the fixing belt 310 and heats, 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. 3A (a), the resistance heating elements 361 to 368 are divided into eight in the longitudinal direction and are electrically connected in parallel. Each of the resistance heating elements 361 to 368 in FIG. 3A (a) is formed of a strip-shaped planar heating element. However, in order to obtain a desired output (resistance value), the windings meander as shown in FIGS. 3C and 3D. You may comprise by the shape-like baking pattern. In FIG. 3C and FIG. 3D, the resistance heating elements 361 to 368 are configured by a one-and-a-half-turn bending pattern in which the narrow line is folded twice.

The base material 350 and the resistance heating elements 361 to 368 can heat the fixing nip SN not only through the resistance heating elements 361 to 368 but also through the base material 350 by adjusting the respective materials and thermal conductivity. For this reason, the material of the base material 350 is desirably a material having high thermal conductivity such as aluminum nitride.

A gap is formed between the resistance heating elements 361 to 368 to ensure insulation. If the gap is too large, uneven fixing due to a decrease in the amount of heat generated in the gap occurs. On the contrary, if the gap is too small, 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. Note that, as described above, the fixing nip SN is heated via the substrate 350, so that fixing unevenness due to the gap between the resistance heating elements 361 to 368 can be suppressed.

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

With this feature, for example, when printing paper that is narrower than the entire 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, and 368 outside the paper width are printed on paper. The temperature rises because it is not deprived of heat. Then, the resistance values of the resistance heating elements 361, 362, 367, and 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, and 368 outside the paper width are relatively lowered, and the end temperature rise is suppressed. When the resistance heating elements 361 to 368 are electrically connected in series, there is no method other than reducing the printing speed in order to suppress the temperature rise of the resistance heating elements outside the paper width in continuous printing. By electrically connecting the resistance heating elements 361 to 368 in parallel, an increase in the temperature of the non-sheet passing portion can be suppressed while maintaining the printing speed.

The arrangement of the resistance heating elements 361 to 368 is not limited to the state shown in FIG. In FIG. 3A (a), since there is a gap that continues in the short direction between the resistance heating elements 361 to 368, a decrease in the amount of heat generation occurs in the gap portion, thereby easily causing uneven fixing. Therefore, in FIGS. 3A (b) and 3 (c), the ends of the resistance heating elements 361 to 368 are overlapped with each other in the longitudinal direction.

In FIG. 3A (b), stepped portions formed by L-shaped notches are formed at the ends of the resistance heating elements 361 to 368, and the stepped portions are overlapped with the stepped portions at the ends of the adjacent resistance heating elements. . 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 are overlapped with the inclined portions at the end portions of the adjacent resistance heating elements. Thus, by making the ends of the resistance heating elements 361 to 368 overlap each other, it is possible to suppress the influence of a decrease in the amount of heat generated in the gap between the resistance heating elements.

Further, the electrodes 360c and 360d are arranged at both ends of the resistance heating elements 361 to 368, and on one side of the resistance heating elements 361 to 368 as shown in FIGS. 3B (a) to (c) and 3D (a) to (c). It is also possible to arrange. Thus, space saving in the longitudinal direction can be achieved by arranging the electrodes 360c and 360d on one side.

(Fixing operation)
In FIG. 2A, when the sheet P is passed from the direction of the arrow toward the fixing nip SN, the sheet P is heated between the fixing belt 310 and the pressure roller 320 and the toner image is fixed on the sheet P. At this time, the fixing belt 310 is heated by heat from the heat generating member 360 while sliding with 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, when only the first temperature detection sensor TH1 is disposed, only the resistance heating element 364 in which the first temperature detection sensor TH1 is disposed is partially disconnected. When power feeding is interrupted, the temperature of the resistance heating element 364 does not rise. For this reason, when the resistance heating element 364 is set to a constant temperature by temperature control, an excessively high current is continuously supplied to other normal resistance heating elements 361 to 363 and 365 to 368, and an abnormally high temperature is generated.

Therefore, in the present embodiment, the second temperature detection sensor TH2 is disposed in the heating region of the resistance heating element 368 at the end. The second temperature sensor TH2 is a temperature T ₈ of the resistance heating element 368 detects, when the temperature T ₈ is abnormally high temperature as described above, the electrode 360c, the control unit 400 so as to cut off the supply current to 360d triac 420 is controlled. In addition, even when the second temperature detection sensor TH2 itself becomes the predetermined temperature T _N or less (T ₈ <T _N ) due to disconnection, the control unit 400 controls the triac 420 so as to cut off the supply current to the electrodes 360c and 360d. To do.

(Other Embodiments of Fixing Device)
The fixing device 300 is not limited to the first fixing device in FIG. 2A. Hereinafter, the second to fourth fixing devices will be described 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 of the pressure roller 320, and heats the fixing belt 310 between the pressure roller 390 and the heating device.

The heating device described above is disposed 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 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 increase the circumferential contact length with the fixing belt 310 instead of omitting the above-described pressing roller 390, this heating device can change the cross section of the base material 350 and the insulating layer 370 in accordance with the curvature of the fixing belt 310. It is formed in an arc shape. The heat generating member 360 is disposed at the center of the arc-shaped base material 350. The rest is 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, a nip forming member 332 and a stay 333 made of a metal channel material are arranged on the opposite side of the pressure roller 320 from the fixing belt 310 so that the nip forming member 332 and the stay 333 are included. A pressure belt 334 is disposed so as to be able to go around. Then, the sheet P is passed through the fixing nip SN between the pressure belt 334 and the pressure roller 320 and heated and fixed. The rest is the same as the first fixing device of 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, as indicated by a broken line in FIG. 2A. The fixing belt 310 may be disposed so as to be pressure-bonded to the inner peripheral surface (downstream inner peripheral surface of the resistance heating element 368) by an urging means. Increasing the number of resistance heating elements makes it difficult to secure the space for installing the temperature detection sensor. However, by arranging the second temperature detection sensor TH2 as described above, the difficulty in securing the space can be alleviated. The second temperature detection sensor TH2 for safety compensation is disposed not only for the resistance heating element 368 but also for each heating region of the other resistance heating elements 361 to 363 and 365 to 367 including the inner peripheral surface of the fixing belt 310. May be.

(Abnormality detection)
Here, the operation of abnormality detection by the control unit 400 will be described with reference to the flowcharts of FIGS. 6A to 6C. FIG. 6A is a flowchart of the basic control operation of the heating device. In step S1, the heater relay 440 is confirmed to be turned on by a start-up signal from the heating device or the fixing device 300. The voltage conversion value Viac converted by the current transformer CT of the current detection unit 430 is read into the control unit 400. This reading timing is immediately after the start-up of the fixing device 300.

Immediately after the start of the start-up, specifically, after a predetermined time T [ms] has elapsed since the heater relay 440 was turned on, as in step S2. That is, because of the characteristics of the circuit of the current detection means 430, a predetermined time is required until the current value is converted into the voltage value by the current transformer CT and stable current detection can be performed.

Therefore, after a predetermined time T [ms] has elapsed, the current detection permission OK (Yes) in step S3 is received, and in step S4, the current detection, that is, the voltage conversion value Viac is read into the control unit 400. Considering the influence of noise picked up during current detection during this reading, the number of current detection samplings is set to multiple times within a specified period, and the maximum and minimum extreme values are excluded from the detected multiple current values. It is desirable to do. If the current detection permission is No in step S3, the flow ends.

The sampling of the current detection needs to be performed in a state where the current waveform of the AC power source 410 continues with the same waveform for a predetermined time or more necessary for high-precision detection of current and voltage. The predetermined time required for high-precision detection of the current and voltage is at least 100 msec or more, preferably 200 msec or more.

When the current value is sampled and detected a plurality of times during a predetermined period at the time of startup, as shown in FIG. 5B, the current detection accuracy is best detected when the duty ratio is 100%. That is, the current detection accuracy is best when the same waveform in the full lighting state in which the waveform of the alternating current is formed only in the ON section with a duty ratio of 100% is continued for a predetermined time or more. For example, when the duty ratio is 75%, the current value decreases at a constant interval, and the current detection period cannot be made very long due to this relationship, and the current is more susceptible to noise. On the other hand, detection with a duty ratio of 100% at the time of start-up also leads to determination of whether or not there is an abnormality before the start of paper feeding, and it is possible to prevent the occurrence of fixing failure (printing failure). is there.

However, even if the duty ratio is less than 100%, if the same waveform continues for a predetermined period at a constant duty ratio during the current detection period, the amount of decrease in the current value due to duty control can be predicted in advance. For this reason, even after the start-up, even when the temperature of the resistance heating elements 361 to 368 has risen to some extent, current detection can be performed as long as the same waveform continues at a constant duty ratio. .

Here, the target correlation of the current-voltage of the resistance heating elements 361 to 368 is shown by a solid line in FIG. The broken lines above and below the solid line indicate the current-voltage correlation at the lower limit of resistance and the upper limit of resistance.

As described above, since the temperature is stabilized when the temperature of the resistance heating elements 361 to 368 is raised to some extent, the current-voltage correlation is stabilized linearly as shown in FIG. For this reason, it becomes easy to detect the current Iac flowing through the resistance heating elements 361 to 368 in a stable state. In this case as well, it is desirable to detect the current value Iac flowing through the resistance heating elements 361 to 368 before starting the sheet passing and determine whether there is an abnormality.

FIG. 6B is a more specific example of step S4 (execution of current detection) in FIG. 6A as in steps S8 to S11. In the case of failure detection execution No in step S7, the flow ends.

In the case of executing failure detection OK (Yes) in step S7, in step S8, Viac obtained by converting the voltage value of the current value Iac flowing between the electrodes 360c and 360d of the resistance heating elements 361 to 368 is detected by the current detection unit 430, and the Viac Is read into the control unit 400. 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 control unit 400.

Thereafter, a failure threshold current Ith (failure threshold voltage Vith) is calculated in step S10, and the voltage conversion value Viac is compared with the failure threshold voltage Vith in step S11. When the voltage conversion value Viac is equal to or greater than 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 “failure”, that is, “disconnected” occurs in any of the resistance heating elements 361 to 368, and the heater relay 440 is turned off in step S12. At the same time, the error is notified by an error display on the operation panel of the color laser printer 100 in step S13.

Note that if the rotation of the paper feed roller 60 or the like is stopped at the same time as the power supply is cut off during paper passing, a paper jam occurs. On the other hand, if the rotation of the paper feed roller 60 or the like is continued, the occurrence of fixing failure increases. . For this reason, it is desirable to continue the operation only with the error notification except when the influence of the partial disconnection of the resistance heating elements 361 to 368 is particularly large such as safety and printing by FAX reception.

Here, the voltage value Vac between the electrodes 360c and 360d is separately detected because the voltage value Vac applied between the electrodes 360c and 360d flows between the electrodes 360c and 360d as shown in FIG. This is because the current value Iac is greatly affected. For this reason, depending on the magnitude of the detected voltage value Vac, it is necessary to correct the failure threshold current Ith (Vith).

5C, the total resistance value between the electrodes 360c and 360d of the resistance heating elements 361 to 368 is also ± depending on the manufacturing variation of the resistance heating elements 361 to 368. It fluctuates in the range of about 5 to 10%. In order to cope with these variations, it may be necessary to correct Ith (Vith) of the failure threshold current by the voltage value Vac.

In the present embodiment, the allowable variation threshold value of the voltage value Vac without correction of the failure threshold current Ith (Vith) is, for example, within a range of ± 5%, and when the failure threshold current Ith (Vith) exceeds ± 5%, Corrections can be made. Specifically, when the voltage conversion value Viac is compared with the failure threshold voltage Vith in the step S11, the correction increases or decreases the failure threshold voltage Vith in accordance with the variation rate (%) of the voltage value Vac.

FIG. 6C is a flowchart showing the above-described control operation of the heating device by the first temperature detection sensor TH1 and the second temperature detection sensor TH2. In step S14 of FIG. 6C, the color laser printer 100 is instructed to execute a print job.

Then, in step S <b> 15, power supply from the AC power supply 410 to the resistance heating elements 361 to 368 of the heat generating member 360 is started by the control unit 400. In step S16, the first temperature detection sensor TH1 detects the temperature T ₄ of the resistance heating element 364 located in the central region of the heat generating member 360.

Next, temperature control of the heat generating member 360 by the triac 420 is started in step S17. The temperature T ₈ of the resistance heating element 368 is detected by the second temperature sensor TH2 in step S18.

In step S19, it is determined whether or not the temperature T ₈ ≧ T _N (T _N : predetermined temperature). If T ₈ <T _N , an abnormally low temperature is generated (disconnection occurs), and in step S20, power is supplied to the heat generating member 360. The triac 420 is controlled by the control unit 400 so that is substantially blocked. In step S21, an error display is displayed on the operation panel of the color laser printer 100. Even if the temperature T ₈ of the second temperature sensor TH2 becomes abnormally high temperature, it may be controlled triac 420 to be likewise power is cut off to the heating member 360 (OFF).

If T ₈ ≧ _TN , no abnormal low temperature is generated, and the printing operation is started in step S22. In this way, in addition to the flow charts of FIGS. 6A and 6B by the current detection means 430 described above, the control unit 400 is operated by the flow chart of FIG. 6C by the second temperature detection sensor TH2, so that the heating device or the fixing device 300 can be operated. More safety.

As mentioned above, although this invention was demonstrated based on embodiment, it cannot be overemphasized that this invention is not limited to the said embodiment, and can be variously changed 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 the fixing device such as a drying device. Further, the resistance heating element may be overlapped with other shapes than those shown in FIGS. 3A (b) (c) and FIGS. 3B (b) (c), such as concavo-convex shapes and interdigitated shapes. . The number of resistance heating elements may be less than 8 or 9 or more. Furthermore, the resistance heating elements can be arranged in a plurality of rows in the short direction of the base material 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: Development device (image forming unit) 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: driving 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 conveyance path 35: post-fixation conveyance path 36: paper discharge path 37: Paper discharge roller pair 41: Reverse conveyance path 42: Member 42a: Swing shaft 43: Reverse conveyance roller pair 44: Paper 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: Feeding roller 230: Separation roller 240: Conveying roller 250: Registration roller pair 300: Fixing device 310: Fixing belt 320: Pressure roller 321: Iron cored bar 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: Heat generating member 360a, 360b: Feed line 360c, 360d: Electrodes 361-368: Resistance heating element 370: Insulation Layer 390: Pressing roller 400: Control unit 410: AC power supply 420: Triac 430: Current detection means 440: Heater relay 450: Voltage detection means

Japanese Patent Laying-Open No. 2015-227917

Claims (11)

A plurality of resistance heating elements that are arranged along the longitudinal direction of the substrate and electrically connected to each other in parallel;
Power supply means for supplying power to the resistance heating element;
Current detection means for detecting a current flowing through the resistance heating element;
Voltage detection means for detecting a voltage applied to the resistance heating element;
In a heating apparatus having current control means for controlling a current flowing through the resistance heating element based on detection results of the current detection means and the voltage detection means,
After the power supply to the resistance heating element is started, the waveform of the alternating current supplied to the resistance heating element remains in the same waveform for a predetermined time necessary for detection of the current by the current detection means. A heating device that performs detection by a current detection means.   The heating apparatus according to claim 1, wherein the same waveform is a full lighting state in which an alternating current waveform is formed only in an ON section.   3. The heating device according to claim 1, wherein the current control unit cuts off a current flowing through the resistance heating element when a value detected by the current detection unit is smaller than a predetermined threshold current.   The heating apparatus according to claim 3, wherein the current control means corrects the magnitude of the threshold current based on a detection result of the voltage detection means.   The heating device includes a temperature detection sensor that detects a temperature of at least one resistance heating element of the plurality of resistance heating elements, and detects the AC current supplied from the current control unit to the resistance heating element. 5. The heating device according to claim 2, wherein the heating device is configured to be capable of phase control based on a detection result of the sensor, and the detection by the current detection unit is performed before the phase control is performed.   6. The heating apparatus according to claim 2, wherein the resistance heating element has a positive resistance temperature coefficient. In a fixing device for fixing the developer to the recording medium by passing the recording medium carrying the developer 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 transmitting heat of the belt member to the fixing nip.   When the value detected by the current detection means is smaller than a predetermined threshold current, the current control means cuts off the current flowing through the resistance heating element before the recording medium passes through the fixing nip. The fixing device according to claim 7.   9. The fixing device according to claim 5, wherein the heating device is disposed inside the belt member and circulates around the heating device in a state where the belt member is sandwiched between the fixing nips.   9. The fixing device according to claim 7, wherein heat of the belt member is transmitted to the fixing nip through the pressure member.   An image having 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 claim 7. Forming equipment.

Images