JP7562238B2 - Heating device, fixing device and image forming apparatus - Google Patents

Description

The present invention relates to a heating device having multiple resistive heating elements, a fixing device, and an image forming apparatus.

Various types of fixing devices are known for use in electrophotographic image forming apparatuses. One type uses a planar heater composed of a substrate and a resistance heating element to heat a thin fixing belt with low heat capacity. This planar heater has multiple resistance heating elements arranged on a substrate arranged in the width direction of the fixing belt, and these resistance heating elements are electrically connected in parallel. This is intended to suppress temperature rise in non-paper passing areas when small-sized paper is passed through (Patent Documents 1 and 2). By using a PTC heater with a positive temperature coefficient as the resistance heating element, it is possible to further suppress temperature rise in non-paper passing areas and achieve energy conservation.

As mentioned above, when multiple resistive heating elements are connected in parallel, even if one of the resistive heating elements breaks, current will continue to flow through the other resistive heating elements. If a temperature detection sensor such as a thermistor is provided in the heating area of each resistive heating element, the temperature of the resistive heating elements can be controlled individually, so abnormal temperature increases in the resistive heating elements will not occur.

However, attaching temperature detection sensors to all of them would be costly. Therefore, if a temperature detection sensor is attached to only one resistive heating element in the center of the longitudinal direction, for example, if that resistive heating element breaks, the current in the other resistive heating elements may continue to increase, making it impossible to control the temperature.

The present invention was made in consideration of these problems, and aims to provide a heating device, fixing device, and image forming device that can control the temperature of multiple resistive heating elements of a planar heater using as few temperature detection sensors as possible, and prevent abnormal temperature increases.

In order to solve the above problem, the heating device of the present invention is characterized by having a plurality of resistive heating elements arranged along the longitudinal direction of a substrate and electrically connected in parallel to each other, a power control means for supplying power to the plurality of resistive heating elements, a first temperature detection means for detecting the temperature of a first resistive heating element which is one of the plurality of resistive heating elements, a second temperature detection means for detecting the temperature of a second resistive heating element which is another one of the plurality of resistive heating elements, and a control means for controlling the amount of power of the power control means based on the detection result of the first temperature detection means so that the temperature of the plurality of resistive heating elements becomes a first predetermined temperature, and for cutting off the supply of power from the power control means to the plurality of resistive heating elements when the second temperature detection means detects a second predetermined temperature.

According to the present invention, even if the first resistive heating element is broken and the first temperature detection means is unable to control the temperature of the multiple resistive heating elements, the power supply to each resistive heating element is cut off when the second temperature detection means detects a second predetermined temperature, thereby preventing an abnormal temperature rise in each resistive heating element.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating the principle 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. 11 is a cross-sectional view of a third fixing device according to an embodiment of the present invention. FIG. 11 is a cross-sectional view of a fourth fixing device according to an embodiment of the present invention. 1A to 1C are plan views showing the arrangement of each resistive heating element of a sheet heating element having electrodes on both ends. 1A to 1C are plan views showing the arrangement of each resistive heating element of a sheet heating element having an electrode at one end. FIG. 2 is a diagram showing a heating device, a power control circuit, and a control unit. 4 is a flowchart showing a control operation of the heating device.

Below, a heating device according to an embodiment of the present invention, and a fixing device and an image forming device (laser printer) using said heating device will be described with reference to the drawings. Note that in each drawing, the same or corresponding parts are given the same reference numerals, and duplicated explanations will be appropriately simplified or omitted. Furthermore, the dimensions, materials, shapes, relative positions, etc. in the explanations of each component are merely examples, and are not intended to limit the scope of this invention unless specifically stated otherwise.

In the following embodiment, the "recording medium" will be described as "paper", but the "recording medium" is not limited to paper. The "recording medium" includes not only paper, but also overhead projector sheets, fabric, metal sheets, plastic films, and prepreg sheets made of carbon fibers pre-impregnated with resin.

"Recording media" includes all media onto which developer or ink can be attached, recording paper, and recording sheets. In addition to plain paper, "paper" also includes cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, etc.

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

(Laser printer configuration)
Fig. 1A is a schematic diagram showing the configuration of a color laser printer 100 as one embodiment of an image forming apparatus including a heating device or fixing device 300 of the present invention. Fig. 1B shows a simplified diagram of the principle of the laser printer 100.

The color laser printer 100 is equipped with four process units 1K, 1Y, 1M, and 1C as image forming means. These process units form images using developers of the colors black (K), yellow (Y), magenta (M), and cyan (C), which correspond to the color separation components of a color image.

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

The process unit 1K has an image carrier 2K (e.g., a photosensitive drum), a drum cleaning device 3K, and a charge removal device. The process unit 1K further has a charging device 4K as a charging means for uniformly charging the surface of the image carrier, and a developing device 5K as a developing means for performing visible image processing of the electrostatic latent image formed on the image carrier. The process unit 1K is detachably attached to the main body of the laser printer 100, and consumable parts can be replaced at the same time.

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

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

The intermediate transfer belt 16 is adapted to circulate around the primary transfer rollers 19K, 19Y, 19M, and 19C, the drive roller 18, and the driven roller 17. The secondary transfer roller 20 is disposed opposite the drive roller 18 and in contact with the intermediate transfer belt 16. If the image carriers 2K, 2Y, 2M, and 2C are the first image carriers for each color, then the intermediate transfer belt 16 is the second image carrier that combines these 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. In addition, a cleaning backup roller is installed on the opposite side of the intermediate transfer belt 16 from the belt cleaning device 21.

A paper feeder 200 having a tray for stacking paper P is installed below the laser printer 100. This paper feeder 200 constitutes the recording medium supply section, and can store a large number of sheets of paper P as a recording medium in a bundle, and is unitized with a paper feed roller 60 and a roller pair 210 as a means for transporting paper P. The paper feeder 200 can be inserted and removed from the main body of the laser printer 100 for the purpose of replenishing paper, etc. The paper feed roller 60 and the roller pair 210 are located above the paper feeder 200, and transport the topmost paper P of the paper feeder 200 toward the paper feed path 32.

The pair of registration rollers 250, which serve as a separation and transport means, are disposed immediately upstream of the secondary transfer roller 20 in the transport direction, and can temporarily stop the paper P fed from the paper feed device 200. This temporary stop creates slack in the leading edge of the paper P, correcting any skew in the paper P.

A registration sensor 31 is disposed immediately upstream of the registration roller pair 250 in the conveying direction, and this registration sensor 31 detects the passage of the leading edge of the paper. After the registration sensor 31 detects the passage of the leading edge of the paper, when a predetermined time has elapsed, the paper is abutted against the registration roller pair 250 and temporarily stopped.

At the downstream end of the paper feeder 200, a transport roller 240 is provided to transport the paper transported to the right from the roller pair 210 upward. As shown in FIG. 1A, the transport roller 240 transports the paper upward toward the registration roller pair 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 type, a separation roller (return roller) to which a certain amount of torque is applied in the counter-feed direction by the drive shaft via a torque limiter is pressed against the feed roller to separate the paper at the nip between the rollers. In the FR separation type, a separation roller (friction roller) supported on a fixed shaft is pressed against the feed roller via a torque limiter to separate the paper at the nip between the rollers.

In this embodiment, the roller pair 210 is configured using the FRR separation method. That is, the roller pair 210 is configured with an upper feed roller 220 that transports 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 feed roller 220.

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

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

The post-transfer transport 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 transport path 33. The fixing device 300 includes a fixing belt 310 that includes 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 other configurations of the fixing device 300 are also possible, as shown in Figures 2B to 2D, which will be described later.

The post-fixing transport path 35 is disposed above the fixing device 300, and at the upper end of the post-fixing transport path 35, it branches into a paper discharge path 36 and a reversing transport path 41. A switching member 42 is disposed at this branching point, and the switching member 42 is adapted to swing around its swing shaft 42a. In addition, a pair of paper discharge rollers 37 is disposed near the open end of the paper discharge path 36.

The reverse transport path 41 merges with the paper feed path 32 at the other end opposite the branching point. A pair of reverse transport rollers 43 is provided midway along the reverse transport path 41. The paper output tray 44 is installed on the top of the laser printer 100, forming a concave shape facing inward of the laser printer 100.

The powder container 10 (e.g., a toner container) is disposed between the transfer device 15 and the paper feed device 200. The powder container 10 is removably attached to the main body of the laser printer 100.

The laser printer 100 of this embodiment requires a certain distance between the paper feed roller 60 and the secondary transfer roller 20 due to the transfer paper transport. The powder container 10 is installed in the dead space created by this distance, making the entire laser printer smaller.

The transfer cover 8 is installed on top of the paper feed device 200, directly in front of the paper feed device 200 in the direction in which it is pulled out. By opening this transfer cover 8, the inside of the laser printer 100 can be inspected. The transfer cover 8 is equipped with a manual feed roller 45 for manual paper feed, and a manual feed tray 46 for manual paper feed.

Note that the laser printer of this embodiment is an example of an image forming device, and the image forming device is not limited to a laser printer. In other words, the image forming device can be configured as any one of a copier, facsimile, printer, printing machine, and inkjet recording device, or as a multifunction device that combines at least two or more of these.

(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. As shown in Fig. 1A, the paper feed roller 60 rotates in response to a paper feed signal from the control unit of the laser printer 100. The paper feed roller 60 then separates only the topmost sheet of the stack of sheets P loaded in the paper feed 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, the toner image formed on the intermediate transfer belt 16 is transferred to the paper P at the optimal timing (synchronization), and the leading edge skew of the paper P is corrected.

When feeding paper manually, a stack of paper sheets stacked on the manual feed tray 46 is transported one by one, starting from the topmost sheet, through a part of the inverted transport path 41 by the manual feed roller 45 to the nip of the registration roller pair 250. The subsequent operation is the same as when feeding paper from the paper feed device 200.

Here, the image forming operation will be explained for one process unit, 1K, and the explanation for 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 laser light Lb based on the image data.

When the surface of the image carrier 2K is irradiated with the laser light Lb, the potential of the irradiated portion decreases, forming an electrostatic latent image. The developing device 5K has a developer carrier that carries a developer containing toner, and transfers unused black toner supplied from the toner bottle 6K via the developer carrier to the surface portion of the image carrier 2K on which the electrostatic latent image has been formed. The image carrier 2K to which the toner has been transferred forms (develops) a black toner image on its surface. The toner image formed on the image carrier 2K is then 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 by a waste toner transport means to a waste toner storage section in the process unit 1K for collection. In addition, the charge removal device removes residual charge from 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 each color, toner images are formed on the image carriers 2Y, 2M, and 2C in the same manner, and the toner images of each color are transferred to the intermediate transfer belt 16 so that they are superimposed.

The intermediate transfer belt 16, on which the toner images of each color have been transferred so as to overlap, travels to the secondary transfer nip between the secondary transfer roller 20 and the drive roller 18. Meanwhile, the pair of registration rollers 250 rotates, nipping the paper that is abutted against them at a predetermined timing, and transports the paper to the secondary transfer nip of the secondary transfer roller 20 in time with the timing at which the toner images formed by superimposing and transferring onto the intermediate transfer belt 16 are appropriately transferred. In this way, the toner image on the intermediate transfer belt 16 is transferred to the paper P sent out by the pair of registration rollers 250.

The paper P with the toner image transferred thereto is transported through post-transfer transport path 33 to fixing device 300. The paper P transported to fixing device 300 is then sandwiched between fixing belt 310 and pressure roller 320, where the unfixed toner image is fixed to the paper P by applying heat and pressure. The paper P with the fused toner image is sent from fixing device 300 to post-fixing transport path 35.

When the paper P is sent out from the fixing device 300, the switching member 42 is in a position that opens the vicinity of the upper end of the post-fixing transport path 35, as shown by the solid line in FIG. 1A. The paper P sent out from the fixing device 300 is then sent out to the paper discharge path 36 via the post-fixing transport path 35. The paper discharge roller pair 37 pinches the paper P sent out to the paper discharge path 36 and rotates to discharge the paper onto the paper discharge tray 44, 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 sends the paper P to the paper discharge path 36. Then, when performing double-sided printing, the pair of paper discharge rollers 37 are driven to rotate to transport a portion of the paper P outside the laser printer 100.

Then, 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. Almost simultaneously with the closing of the upper end of the post-fixing transport path 35, the pair of paper discharge rollers 37 rotates in the direction opposite to the direction in which the paper P is transported out of the laser printer 100, and sends the paper P to the reverse transport path 41.

The paper P sent to the reverse transport path 41 passes through the reverse transport roller pair 43 and reaches the registration roller pair 250. The registration roller pair 250 then determines the optimal timing (synchronization) for transferring the toner image formed on the intermediate transfer belt 16 to the non-transferred surface of the paper P, and sends 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 non-transferred side (reverse side) of the paper P as the paper P passes through the secondary transfer nip. The paper P with the transferred toner image is then transported to the fixing device 300 via the post-transfer transport path 33.

The fixing device 300 clamps the transported paper P between the fixing belt 310 and the pressure roller 320, and applies heat and pressure to fix the unfixed toner image to the back side of the paper P. In this way, the paper P with the toner images fixed on both sides is sent from the fixing device 300 to the post-fixing transport path 35.

When the paper P is sent out from the fixing device 300, the switching member 42 is in a position that opens the vicinity of the upper end of the post-fixing transport path 35, as shown by the solid line in FIG. 1A. The paper P sent out from the fixing device 300 is then sent out to the paper discharge path 36 via the fixing transport path. The paper discharge roller pair 37 clamps the paper P sent out to the paper discharge path 36, rotates, and discharges the paper to the paper discharge tray 44, 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. The belt cleaning device 21 removes this residual toner from the intermediate transfer belt 16. The toner removed from the intermediate transfer belt 16 is transported by the waste toner transport means to the powder container 10 and collected in the powder container 10.

(Fixing device)
Next, the heating device according to the embodiment of the present invention and the first to fourth fixing devices 300 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 element, and has a base material 350 made of an elongated thin metal plate member covered with an insulating material, and a heat generating member 360 disposed on the base material 350, as shown in Fig. 3A(a) and Fig. 4.

The heat generating member 360 is composed of a number of resistance heating elements 361-368 arranged linearly and at equal intervals in the longitudinal direction of the substrate 350. Low resistance power supply lines 360a, 360b are arranged linearly and parallel to each other on both sides of the short side of each resistance heating element 361-368, and both ends of each resistance heating element 361-368 are connected to these power supply lines 360a, 360b. Power control means is connected to electrodes 360c, 360d formed on one end of each of the power supply lines 360a, 360b, as shown in FIG. 4.

The heating device of this embodiment has a first temperature detection sensor (first temperature detection means) TH1 and a second temperature detection sensor (second temperature detection means) TH2 as temperature detection means for detecting the temperature of the resistive heating element. These temperature detection sensors TH1 and TH2 can be configured, for example, with a thermistor.

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

The first temperature detection sensor TH1 for temperature control is arranged in the heating area of the resistive heating element 364 (fourth from the left end) as the first resistive heating element in the longitudinal central region within the minimum paper passing width. The second temperature detection sensor TH2 for safety compensation is arranged in the heating area of the resistive heating element 368 (eighth from the left end) (or resistive heating element 361 (first from the left end)) as the second resistive heating element at the longitudinal extreme end.

The two temperature detection sensors TH1 and TH2 are both positioned within the area of the resistive heating elements 364 and 368, avoiding the gaps between the resistive heating elements where a drop in heat generation occurs. This improves temperature controllability and also makes it easier to detect disconnections in some of the resistive heating elements.

The first temperature detection sensor TH1 may be placed in the heating region of any of the resistive heating elements 363, 365, and 366. The second temperature detection sensor TH2 may be placed in the second resistive heating element 362 from the left end or the seventh resistive heating element 367, as long as it is in the longitudinal end region, and does not necessarily have to be placed at the longitudinal end.

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

The temperatures _T4 and _T8 detected by the first and second temperature sensors TH1 and TH2 are input to a control unit 400 serving as a control means. Based on the temperature _T4 obtained from the first temperature sensor TH1, the control unit 400 controls the amount of power supplied to the electrodes 360c and 360d by the triac 420 so that the respective resistance heating elements 361 to 368 reach predetermined temperatures.

The control unit 400 can be configured with a microcomputer including a CPU, ROM, RAM, an I/O interface, etc. When paper is passed through the fixing nip SN, heat is removed (heat transferred to the paper) by the paper passing through, so the temperature of the fixing belt 310 can be controlled to a desired temperature by controlling the amount of power supply taking into consideration not only the temperature _T4 obtained from the first temperature sensor TH1 but also the removed heat.

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

A release layer made of fluororesin such as PFA or PTFE and having a thickness of 5 to 50 μm is formed on the outermost surface of the fixing belt 310 to improve durability and ensure releasability. An elastic layer made of rubber or the like and having a thickness of 50 to 500 μm may be provided between the base and the release layer.

The base material of the fixing belt 310 is not limited to polyimide, and may be a heat-resistant resin such as PEEK or a metal base material such as nickel (Ni) or SUS. The inner 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, for example, 25 mm and is composed of a solid iron core 321, an elastic layer 322 formed on the surface of the core 321, and a release layer 323 formed on the outside of the elastic layer 322. The elastic layer 322 is made of silicone rubber and has a thickness of, for example, 3.5 mm. To improve the release properties of 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, for example, about 40 μm. The pressure roller 320 is pressed against the fixing belt 310 by a biasing 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 ends are supported by both side plates of the heating device. The stay 330 reliably receives the pressing force of the pressure roller 320 to stably form the fixing nip SN.

The folder 340 is for holding the base material 350 of the heating device and is supported by the stay 330. The folder 340 is preferably formed from a heat-resistant resin with low thermal conductivity such as LCP, which reduces heat transfer to the folder 340 and allows the fixing belt 310 to be heated efficiently.

The shape of the folder 340 is such that it supports only two points near both ends of the substrate 350 in the short direction to avoid contact with the high-temperature parts of the substrate 350. This further reduces the amount of heat flowing to the folder 340, allowing the fixing belt 310 to be heated efficiently.

The resistive heating elements 361-368 and the power supply lines 360a, 360b are covered with a thin insulating layer 370. This insulating layer 370 can be made of heat-resistant glass with a thickness of, for example, 75 μm. The insulating layer 370 insulates and protects the resistive heating elements 361-368 and the power supply lines 360a, 360b, and maintains sliding properties with the fixing belt 310, as described below.

The substrate 350 is preferably made of low-cost materials such as aluminum or stainless steel. The substrate 350 is not limited to metal, and can be made of ceramics such as alumina or aluminum nitride, or non-metallic materials with excellent heat resistance and insulation such as glass or mica. To improve the thermal uniformity of the heating device and enhance 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 with a short side width of 8 mm, a long side width of 270 mm, and a thickness of 1.0 mm is used.

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

In addition to the above-mentioned materials, resistance materials such as silver alloy (AgPt) and ruthenium oxide (RuO ₂ ) may be used for the materials of the resistance heating elements 361 to 368. The materials of the power supply lines 360a, 360b and the electrodes 360c, 360d can be formed by screen printing or the like using silver (Ag) or silver palladium (AgPd).

The insulating layer 370 side of the resistive heating elements 361-368 comes into contact with the fixing belt 310 and heats it, increasing the temperature of the fixing belt 310 through heat transfer, and heating and fixing the unfixed image transported to the fixing nip SN.

As shown in FIG. 3A(a), the resistive heating elements 361-368 are divided into eight parts in the longitudinal direction, and each part is electrically connected in parallel. To obtain the desired output (resistance value), each resistive heating element 361-368 can be configured with a folded meandering firing pattern. In the illustrated example, the resistive heating elements 361-368 are configured with a meandering pattern in which a thin wire is folded twice to complete one and a half round trips.

By adjusting the materials and thermal conductivities of the substrate 350 and the resistive heating elements 361-368, the fixing nip SN can be heated not only by the resistive heating elements 361-368 but also through the substrate 350. For this reason, it is desirable to use a material with high thermal conductivity, such as aluminum nitride, for the material of the substrate 350.

Gaps are formed between the resistive heating elements 361-368 to ensure insulation. If the gaps are too large, uneven fixing occurs due to a decrease in the amount of heat generated in the gaps. Conversely, if the gaps are too small, insulation is not possible and a short circuit occurs between the resistive heating elements 361-368.

Therefore, the size of the gap is preferably 0.3 mm to 1 mm, and more preferably 0.4 mm to 0.7 mm. As described above, by heating the fixing nip SN through the substrate 350, it is possible to suppress uneven fixing caused by the gaps between the resistance heating elements 361 to 368.

The resistive heating elements 361-368 can also be made of a material with PTC (positive temperature coefficient of resistance) characteristics, as shown in FIG. 5(a). A material with PTC characteristics has a characteristic that the resistance value increases when the temperature T increases (the current I decreases and the heater output decreases). The temperature coefficient of resistance (TCR) can be, for example, 1500 PPM (parts per million). The temperature coefficient of resistance can be stored in the memory of the control unit 400.

Due to this feature, for example, when printing on paper narrower than the overall width of the resistive heating elements 361-368 (for example, within the width of the resistive heating elements 363-366), the temperature of the resistive heating elements 361, 362, 367, and 368 outside the paper width rises because the heat is not absorbed by the paper. This causes the resistance values of the resistive heating elements 361, 362, 367, and 368 to rise.

Since the voltage applied to the resistive heating elements 361-368 is constant, the output of the resistive heating elements 361, 362, 367, 368 outside the paper width is relatively lower, suppressing the rise in temperature at the ends. If the resistive heating elements 361-368 are electrically connected in series, the only way to suppress the temperature rise of the resistive heating elements outside the paper width during continuous printing is to slow down the printing speed. By electrically connecting the resistive heating elements 361-368 in parallel, it is possible to suppress the temperature rise in non-paper passing areas while maintaining the printing speed.

The arrangement of the resistive heating elements 361 to 368 is not limited to the state shown in FIG. 3A(a). In FIG. 3A(a), there are gaps between the resistive heating elements 361 to 368 that continue in the short direction. Also, in FIGS. 3A(b) and (c), the ends of the resistive heating elements 361 to 368 overlap each other in the long direction.

In FIG. 3A(b), a step is formed by an L-shaped notch at the end of the resistive heating elements 361-368, and the step is made to overlap the step at the end of the adjacent resistive heating element. In FIG. 3(c), an inclined portion is formed by an oblique notch at the end of the resistive heating elements 361-368, and the inclined portion overlaps the inclined portion at the end of the adjacent resistive heating element. By overlapping the ends of the resistive heating elements 361-368 in this way, the effect of a decrease in heat generation in the gaps between the resistive heating elements can be suppressed.

Also, the electrodes 360c and 360d can be arranged on both ends of the resistive heating elements 361 to 368, or on one side of the resistive heating elements 361 to 368 as shown in Figures 3B(a) to (c). By arranging the electrodes 360c and 360d on one side in this way, space can be saved in the longitudinal direction.

(Fixing Operation)
2A , when paper P is passed from the direction of the arrow toward the fixing nip SN, the paper P is heated between the fixing belt 310 and the pressure roller 320, and the toner image is fixed onto the paper P. At this time, the fixing belt 310 is heated by the heat from the heat generating member 360 while sliding against the insulating layer 370 of the heat generating member 360.

When controlling the temperature of the heat generating member 360 to bring the fixing belt 310 to a predetermined temperature, if only the first temperature detection sensor TH1 is arranged, and only the resistive heating element 364 in which the first temperature detection sensor TH1 is arranged is partially disconnected and the power supply is cut off, the temperature of the resistive heating element 364 will not rise. The same is true when the first temperature detection sensor TH1 and the second temperature detection sensor TH2 are arranged within the heating area of the same resistive heating element. For this reason, when trying to keep the resistive heating element 364 at a constant temperature (first predetermined temperature) through temperature control, more power than necessary continues to be supplied to the other normal resistive heating elements 361-363, 365-368, resulting in an abnormally high temperature.

Therefore, in this embodiment, the first temperature detection sensor TH1 and the second temperature detection sensor TH2 are arranged in the heating areas of different resistive heating elements 364, 368. As a result, even if only the resistive heating element 364 where the first temperature detection sensor TH1 is arranged is partially disconnected and the power supply is cut off, the second temperature detection sensor TH2 detects the abnormally high temperature of the other normal resistive heating element 368 as a predetermined temperature higher than the first predetermined temperature as the second predetermined temperature, so that the power supply can be safely cut off. For example, the second predetermined temperature is a temperature determined in advance by an experiment or the like, and is a temperature above which problems will occur if it rises any higher.

In particular, since the resistive heating element 368 is disposed at the end of the substrate 350 in the longitudinal direction, the second predetermined temperature can be easily detected early due to the influence of the end temperature rise. Therefore, the power supply can be cut off more safely than when the second temperature detection sensor TH2 is disposed at a resistive heating element other than the end in the longitudinal direction. The second temperature detection sensor TH2 can also detect a predetermined temperature (disconnection) that is lower than the first predetermined temperature of the resistive heating element 368 and cut off the power supply. For example, the temperature to be detected in this case is a temperature determined in advance by an experiment or the like, and is a temperature below which a problem would occur if it dropped any lower.

(Another embodiment of the fixing device)
The fixing device 300 is not limited to the first fixing device in Fig. 2A. The second to fourth fixing devices will be described below with reference to Fig. 2B to Fig. 2D. As shown in Fig. 2B, the second fixing device has a pressure roller 390 on the opposite side to the pressure roller 320, and heats the fixing belt 310 by sandwiching it between the pressure roller 390 and a 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 other side. The heating device is held by this auxiliary stay 331. The nip forming member 332 abuts against the pressure roller 320 via the fixing belt 310 to form the fixing nip SN.

As shown in FIG. 2C, the third fixing device has a heating device disposed inside the fixing belt 310. This heating device omits the pressure roller 390 described above, and instead forms the cross sections of the base material 350 and insulating layer 370 in an arc shape to match the curvature of the fixing belt 310 in order to increase the circumferential contact length with the fixing belt 310. The heat generating member 360 is disposed in the center of the arc-shaped base material 350. The rest is the same as the second fixing device in 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 material are arranged on the opposite side of the pressure roller 320 from the fixing belt 310, and the pressure belt 334 is arranged so that it can rotate around the nip forming member 332 and the stay 333. Paper P is then passed through the fixing nip SN between the pressure belt 334 and the pressure roller 320 to be heated and fixed. The rest is the same as the first fixing device in FIG. 2A.

The second temperature detection sensor TH2 for safety compensation may be arranged to be pressed by a biasing means against the inner surface of the fixing belt 310 (the inner surface downstream of the resistance heating element 368) that 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 shown by the dashed line in FIG. 2A. Increasing the number of resistance heating elements makes it difficult to secure the space for the temperature detection sensor, but arranging the second temperature detection sensor TH2 as described above can alleviate the difficulty of securing the space. The second temperature detection sensor TH2 for safety compensation may be arranged not only in the resistance heating element 368, but also in each of the other resistance heating elements 361-363 and 365-367, including the inner surface of the fixing belt 310.

(flowchart)
Fig. 5 is a flow chart showing the control operation of the heating device executed by the control unit 400. In step S1 of Fig. 5, execution of a print job is instructed to the color laser printer 100. Then, in step S2, the control unit 400 starts supplying power from the AC power source 410 to each of the resistance heating elements 361 to 368 of the heat-generating member 360. Then, in step S3, the first temperature detection sensor TH1 detects the temperature _T4 of the resistance heating element 364 located in the central region of the heat-generating member 360.

Next, in step S4, temperature control of heat-generating member 360 is started. In step S5, the second temperature sensor detects temperature _T8 of resistive heating element 368. In step S6, it is determined whether temperature _T8 ≦ _Ts ( _Ts : upper safe temperature limit) or not, and if _Ts < _T8 , an abnormal temperature has occurred, power supply to heat-generating member 360 is cut off (OFF), and an error message is displayed on the operation panel of color laser printer 100. If _T8 ≦ _Ts , no abnormal temperature has occurred, and printing operation is started in step S9.

The present invention has been described above based on an embodiment, but it goes without saying that the present invention is not limited to the embodiment and can be modified in various ways within the scope of the technical ideas described in the claims. For example, the heating device of the present invention can be used for applications other than fixing devices, such as drying devices. In addition, the overlapping shape of the resistive heating elements can of course be other than that shown in Figures 3A(b)(c) and 3B(b)(c), such as interlocking of uneven shapes or comb-tooth shapes. In addition, the number of resistive heating elements may be less than eight or more than nine. Furthermore, it is also possible to arrange the resistive heating elements in multiple rows in the short direction of the substrate 350.

SN: Fixing nip HN: Heating nip Lb: Laser light P: Paper TM: Transfer means TH1: First temperature detection sensor TH2: Second temperature detection sensor 361-368: Resistance heating element
1K, 1Y, 1M, 1C: Process unit 2K, 2Y, 2M, 2C: Image carrier
3K, 3Y, 3M, 3C: Drum cleaning device 4K, 4Y, 4M, 4C: Charging device
5K, 5Y, 5M, 5C: Developing 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: Reversing transport path 42: Member 42a: Oscillating shaft 43: Reversing transport roller pair 44: Paper discharge tray 45, 60: Paper feed roller 46: Tray 100: Color laser printer 200: Paper feed device (recording medium supply section)
210: Pair of rollers 220: Feeding roller 230: Separation roller 240: Conveying roller 250: Pair of registration rollers 300: Fixing device 310: Fixing belt 320: Pressure roller 321: Iron core 321: Core 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: Power supply line 360c, 360d: Electrodes 361 to 368: Resistance heating element 370: Insulating layer 390: Pressing roller 400: Control unit 410: AC power source 420: Triac

JP 2015-194713 A JP 2016-18127 A

Claims (17)

A substrate;
A plurality of resistive heating elements arranged in a longitudinal direction of the base material and electrically connected in parallel to each other;
power control means configured to supply power to the plurality of resistive heating elements;
a first temperature detection means that faces only a first resistance heating element among the plurality of resistance heating elements within a width in the longitudinal direction;
a second temperature detection means disposed so as to face only one second resistive heating element different from the first resistive heating element among the plurality of resistive heating elements within the width in the longitudinal direction, and not to face any resistive heating elements other than the second resistive heating element within the width in the longitudinal direction;
a control unit configured to control the supply of power from the power control means so that the plurality of resistance heating elements are heated so that the temperature detected by the first temperature detection means becomes a first predetermined temperature, based only on the result detected by the first temperature detection means, and to cut off the power supplied from the power control means to all of the plurality of resistance heating elements in response to detection that the plurality of resistance heating elements including the second resistance heating element are heated and that the temperature detected by the second temperature detection means has reached a second predetermined temperature;
having
a resistance heating element different from the first resistance heating element and the second resistance heating element is provided between the first resistance heating element and the second resistance heating element,
The temperature detection means for detecting the temperatures of the plurality of resistive heating elements are only two, the first temperature detection means and the second temperature detection means, and the second temperature detection means is disposed opposite the second resistive heating element which is the resistive heating element located at the end furthest in the longitudinal direction.
1. An image forming apparatus comprising: The image forming apparatus of claim 1, wherein the second temperature detection means is the same type of temperature detection means as the first temperature detection means. A substrate;
A plurality of resistive heating elements arranged in a longitudinal direction of the base material and electrically connected in parallel to each other;
a first temperature detection means that faces only a first resistance heating element among the plurality of resistance heating elements within a width in the longitudinal direction;
a second temperature detection means disposed so as to face only one second resistive heating element different from the first resistive heating element among the plurality of resistive heating elements within the width in the longitudinal direction, and not to face any resistive heating elements other than the second resistive heating element within the width in the longitudinal direction;
a first elastic member that generates a force to bias the first temperature detection means against the base material;
a resistance heating element different from the first resistance heating element and the second resistance heating element is provided between the first resistance heating element and the second resistance heating element,
the temperature detection means for detecting the temperatures of the plurality of resistive heating elements are only two, the first temperature detection means and the second temperature detection means, and the second temperature detection means is disposed opposite the second resistive heating element which is the resistive heating element located at the end furthest in the longitudinal direction;
an image forming apparatus characterized in that the multiple resistive heating elements are heated so that the temperature detected by the first temperature detection means becomes a first predetermined temperature based solely on the result detected by the first temperature detection means, and multiple resistive heating elements including the second resistive heating element are heated, and power supplied to all of the multiple resistive heating elements is cut off in response to detection that the temperature detected by the second temperature detection means has reached a second predetermined temperature. In the image forming apparatus of claim 1, the first temperature detection means is positioned above one of the plurality of resistive heating elements. The image forming apparatus of claim 1, wherein the second temperature detection means is disposed in an end region in the longitudinal direction of the substrate. The image forming apparatus of claim 1, wherein the plurality of resistive heating elements are made of a resistive material having a positive resistance temperature characteristic. The image forming apparatus of claim 1, wherein at least a portion of adjacent resistive heating elements of the plurality of resistive heating elements overlap each other in the longitudinal direction of the substrate. 2. The image forming apparatus according to claim 1, wherein the fixing device includes the base material and the plurality of resistance heating elements.
A pressurizing rotor;
a nip forming member that forms a fixing nip between the pressing rotor and the pressing rotor and fixes a developer onto a recording medium that has passed through the fixing nip;
A cylindrical belt member;
An image forming apparatus having In the image forming apparatus of claim 8, the multiple resistance heating elements are disposed inside the belt member, and the belt member rotates around the multiple resistance heating elements while being sandwiched between the nip forming member and the pressure rotating body in the fixing nip. An image forming apparatus characterized in that. The image forming apparatus of claim 8, characterized in that the heat of the belt member is transferred to the fixing nip via the pressure rotating body. The image forming apparatus of claim 1 further comprises an image forming member that forms an image with a developer, and a recording medium supplying section that supplies a recording medium to the image forming apparatus, and a fixing device having the base material and the multiple resistance heating elements fixes the image on the recording medium. In the image forming apparatus of claim 1, the first temperature detection means and the second temperature detection means are each a thermistor. The image forming apparatus of claim 1, wherein the plurality of resistive heating elements are divided into eight parts. The image forming apparatus of claim 1, wherein the plurality of resistive heating elements are formed in a folded meandering heating pattern. The image forming apparatus of claim 1, characterized in that the substrate is made of aluminum nitride. In the image forming apparatus of claim 1, the control unit is configured to control the power control means so as to heat all of the plurality of resistive heating elements. The image forming apparatus of claim 3 further comprises a second elastic member arranged to press the second temperature detection means against the substrate.