Fixing device and image forming apparatus

Abstract

To provide a fixing device that can reduce a start-up time of the fixing device from when a heat generation unit starts heat generation until when a fixing member reaches a target temperature, and can effectively prevent unnecessary temperature rise such as temperature rise at ends and abnormal temperature rise, and an image forming apparatus.SOLUTION: A fixing device 1 comprises: a heat generation unit 36 that includes a first heating element 361 having a positive temperature coefficient, and a second heating element 362 having a temperature coefficient smaller than the first heating element or a negative temperature coefficient; and a fixing member (31) that conveys a sheet P heated by heat generated by the heat generation unit 36. The first heating element 361 and the second heating element 362 are electrically connected in series to each other. At normal temperature, a resistance value of the first heating element 361 is smaller than a resistance value of the second heating element 362. When the heat generation unit 36 generates heat, under a predetermined temperature rise condition, the resistance value of the first heating element 361 becomes larger than the resistance value of the second heating element 362.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a fixing device and an image forming apparatus such as a copier, a multifunction machine, a printer, or a facsimile machine. [Background technology]

[0002] 2. Description of the Related Art In an image forming apparatus, a fixing device that heats a fixing member (for example, a fixing belt) using a heating element having a positive temperature coefficient (hereinafter, sometimes referred to as a PTC heater) has been conventionally known (see, for example, Patent Document 1).

[0003] PTC heaters are useful heating elements that effectively prevent unnecessary temperature rises by utilizing the sudden rise in resistance at the Curie point (temperature). When the Curie point is exceeded, the resistance at the point where the Curie point is exceeded increases, and the amount of current decreases. This makes it possible to suppress unnecessary temperature rises in the PTC heater.

[0004] For example, the PTC heater effectively prevents end temperature rise, in which the temperature of an end region of the fixing belt other than the region through which the small-sized sheet passes (the region from which heat is absorbed by the sheet) when the small-sized sheet, which is a sheet that is smaller than the maximum-sized sheet in the width direction along the sheet surface perpendicular to the conveying direction of the sheet such as recording paper, passes through the fixing belt, becomes higher than the temperature of the passing region by a predetermined temperature or more. In addition, the PTC heater effectively prevents abnormal temperature rise, in which the temperature becomes abnormally high due to unintended temperature control (for example, because power supply to the heat generating unit is not stopped even when the detected temperature exceeds the target temperature). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-212132 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, if the Curie point of the PTC heater is set low in order to prevent unnecessary temperature rise, the resistance value of the PTC heater rises when the fixing device is started up (warmed up), suppressing the temperature rise of the fixing member. As a result, the components of the fixing device, including fixing members other than the PTC heater (e.g., fixing belt), are not heated promptly, and the start-up time of the fixing device from when the PTC heater starts to generate heat until the fixing members reach the target temperature becomes long.

[0007] In this regard, Patent Document 1 does not disclose anything about solving the problem of the long start-up time of the fixing device.

[0008] Therefore, the present disclosure aims to provide a fixing device that heats a fixing member using a heating element having a positive temperature coefficient, which can shorten the start-up time of the fixing device from when the heating section starts to generate heat until the fixing member reaches a target temperature, and which can effectively prevent unnecessary temperature increases such as end temperature increases and abnormal temperature increases, as well as provide a fixing device and image forming apparatus. [Means for solving the problem]

[0009] In order to solve the above problem, the fixing device disclosed herein comprises a heating section including a first heating element having a positive temperature coefficient and a second heating element having a temperature coefficient smaller than that of the first heating element or a negative temperature coefficient, and a fixing member that transports a sheet in a heated state by heat generated by the heating section, wherein the first heating element and the second heating element are electrically connected in series, and at room temperature the resistance value of the first heating element is smaller than the resistance value of the second heating element, and when the heating section generates heat, the resistance value of the first heating element is greater than the resistance value of the second heating element under specified temperature rise conditions.

[0010] The image forming apparatus according to the present disclosure is characterized by including the fixing device according to the present disclosure. Effect of the Invention

[0011] According to the present disclosure, it is possible to shorten the start-up time of the fixing device from when the heat generating part starts generating heat until the fixing member reaches the target temperature, and it is also possible to effectively prevent unnecessary temperature increases such as end temperature increases and abnormal temperature increases. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic cross-sectional view showing a configuration of an image forming apparatus including a fixing device according to an embodiment of the present invention. [Figure 2A] 2 is a perspective view showing a main part of a fixing device in the image forming apparatus shown in FIG. [Figure 2B] FIG. 2B is a cross-sectional view taken along line AA shown in FIG. 2A. [Diagram 3] FIG. 2 is a plan view illustrating a heating portion of the fixing device according to the first embodiment. [Figure 4] FIG. 4 is an electrical circuit diagram showing an equivalent circuit of a PTC heater and a second heater in the heat generating portion. [Figure 5A] 1 is a table showing resistance values, current values, voltage values, and power values ​​relative to temperature changes of a heat generating portion. [Figure 5B] 1 is a graph showing resistance values ​​versus temperature changes of a heat generating portion. [Figure 5C] 1 is a graph showing power values ​​versus temperature changes of a heat generating portion. [Figure 6A] 11 is a graph showing power line density versus temperature change of a heat generating portion. [Figure 6B] 1 is a graph showing power line density versus temperature change of a heat generating portion. [Figure 7] FIG. 11 is a perspective view showing a temperature detection unit of a fixing device according to a second embodiment. [Figure 8] FIG. 11 is a block diagram showing a control configuration for controlling the fixing temperature of a fixing device according to a second embodiment. [Figure 9] 13 is a graph showing the power line density versus temperature change of a heat generating portion when pulse width modulation control is performed as power control and the duty ratio is set to a value smaller than 1 during end portion temperature rise. [Figure 10]FIG. 11 is a plan view illustrating a heating portion of a fixing device according to a third embodiment. [Figure 11] FIG. 11 is a block diagram showing a control configuration for controlling the fixing temperature of a fixing device according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals. The names and functions of the components are also the same. Therefore, detailed description thereof will not be repeated.

[0014] FIG. 1 is a schematic cross-sectional view showing the configuration of an image forming apparatus 100 including a fixing device 1 according to the present embodiment.

[0015] The image forming device 100 is a multifunction device having a copy function, a scanner function, a facsimile function, and a printer function, and transmits an image of an original document read by the image reading device 130 to the outside, and forms an image of an original document read by the image reading device 130 or an image received from the outside on a sheet such as recording paper in color or monochrome.

[0016] An original transport device 110 that is supported so as to be freely opened and closed is provided above the image reading device 130. The original transport device 110 transports one or more originals one by one in sequence. The image reading device 130 scans a scanning optical system 130b to read an original placed on an original placement table 130a, or reads an original transported by the original transport device 110 to generate image data.

[0017] The image forming apparatus 100 includes a fixing device 1, a developing device 2, a photoconductor drum 3, a drum cleaning device 4, a charger 5, an intermediate transfer belt device 7, a secondary transfer device 11, an optical scanning device 12, and a paper feed section .

[0018] The image forming apparatus 100 handles image data corresponding to color images using the colors black (K), cyan (C), magenta (M), and yellow (Y), or monochrome images using a single color (e.g., black). The image forming apparatus 100 is provided with four developing devices 2, four photoconductor drums 3, four drum cleaning devices 4, and four chargers 5 for forming four types of toner images, and four image stations Pa, Pb, Pc, and Pd are configured corresponding to black, cyan, magenta, and yellow, respectively.

[0019] The optical scanning device 12 exposes the surface of the photoreceptor drum 3 to light to form an electrostatic latent image. The developing device 2 develops the electrostatic latent image on the surface of the photoreceptor drum 3 to form a toner image on the surface of the photoreceptor drum 3. The drum cleaning device 4 removes and collects residual toner on the surface of the photoreceptor drum 3. The charger 5 uniformly charges the surface of the photoreceptor drum 3 to a predetermined potential. Through the series of operations described above, a toner image of each color is formed on the surface of each photoreceptor drum 3.

[0020] The intermediate transfer belt device 7 includes an intermediate transfer roller 6, an endless intermediate transfer belt 71, an intermediate transfer driving roller 72, an intermediate transfer driven roller 73, and a cleaning device 9. Four intermediate transfer rollers 6 are provided inside the intermediate transfer belt 71 so as to form four types of toner images corresponding to the respective colors. The intermediate transfer rollers 6 transfer the toner images of the respective colors formed on the surfaces of the photosensitive drums 3 onto the intermediate transfer belt 71 which moves in a circulating manner.

[0021] The intermediate transfer belt 71 is stretched around an intermediate transfer drive roller 72 and an intermediate transfer driven roller 73. In the image forming apparatus 100, the toner images of each color formed on the surface of each photoconductor drum 3 are sequentially transferred and superimposed to form a color toner image on the surface of the intermediate transfer belt 71. The cleaning device 9 removes and collects waste toner remaining on the surface of the intermediate transfer belt 71 without being transferred to the sheet P.

[0022] The secondary transfer device 11 pinches and conveys a sheet P conveyed through the sheet conveying path 21 to a transfer nip portion TN between the secondary transfer roller 11a and the intermediate transfer belt 71. When the sheet P passes through the transfer nip portion TN, the toner image on the surface of the intermediate transfer belt 71 is transferred to the sheet P, and the sheet P is conveyed to the fixing device 1.

[0023] The fixing device 1 includes a fixing belt 31 (one example of a fixing member) that rotates about an axis, and a pressure roller 32. The fixing device 1 sandwiches a sheet P, onto which a toner image has been transferred, in a fixing nip portion FN between the fixing belt 31 and the pressure roller 32, and applies heat and pressure to the sheet P, thereby fixing the toner image onto the sheet P. Although not shown in FIG. 1, the fixing device 1 also includes components other than the fixing belt 31 and the pressure roller 32. Details of the fixing device 1 will be described later.

[0024] The paper feed section 18 includes a paper feed cassette for stacking sheets used for image formation, and is provided below the optical scanning device 12. The sheet P is pulled out of the paper feed section 18 by a pickup roller 16 and conveyed to a sheet conveying path 21. The sheet P conveyed to the sheet conveying path 21 passes through the secondary transfer device 11 and the fixing device 1, and is discharged to a discharge tray 19 by a discharge roller 17.

[0025] A conveying roller 13, a registration roller 14, and a discharge roller 17 are arranged in the sheet conveying path 21. The conveying roller 13 promotes the conveying of the sheet P. The registration roller 14 conveys the sheet P at a speed equal to the process speed for forming an image on the sheet P. The registration roller 14 is provided between the paper feed section 18 and the secondary transfer device 11, and adjusts the conveying timing of the sheet P so that the toner image is transferred to the sheet P by the secondary transfer device 11. For example, the registration roller 14 stops the sheet P conveyed from the paper feed section 18 in a state where the sheet P is sandwiched, and starts conveying the sheet P at a constant speed in synchronization with the secondary transfer device 11.

[0026] When an image is formed on the back side of the sheet P in addition to the front side, the conveying direction of the sheet P is changed by the discharge rollers 17, and the sheet P is conveyed to the reversing conveying path 22. In the reversing conveying path 22, the sheet P is guided to the registration rollers 14 in a state in which the sheet P is reversed by the reversing conveying rollers 15. The image forming apparatus 100 forms an image on the back side of the sheet P guided to the registration rollers 14 in the same manner as on the front side, and discharges the sheet P to the discharge tray 19.

[0027] Fig. 2A is a perspective view showing a main part of the fixing device 1 in the image forming apparatus 100 shown in Fig. 1. Fig. 2B is a cross-sectional view taken along the line AA shown in Fig. 2A.

[0028] The fixing device 1 further includes a support member 33 provided inside the fixing belt 31, a fixing pad 34 (abutment member), a sliding sheet 35, and a heat generating section 36 (heater section).

[0029] The fixing belt 31 is an endless (annular) flexible belt. The fixing belt 31 is rotatable about a rotation axis α (see FIG. 2A) along a direction perpendicular to the conveying direction S of the sheet P.

[0030] The fixing belt 31 may be, for example, a belt having a predetermined thickness (for example, about 30 μm to 100 μm) of metal such as nickel or a polyimide (PI) base on which an elastic layer (for example, a silicone rubber layer) having a predetermined thickness (for example, about 100 μm to 300 μm) is formed, and a release layer (for example, a fluororesin layer) having a thickness (for example, about 20 μm to 30 μm) is further formed thereon, specifically, a belt having a PFA tube on the silicone rubber layer, or a belt having a fluororesin coating. In this example, the fixing belt 31 is a belt having a total thickness of 300 μm, with silicone rubber provided on a nickel base having a thickness of 40 μm, and a PFA tube provided on the silicone rubber layer. The inner diameter of the fixing belt 31 is 30 mm in this example. However, the present invention is not limited to these specific dimensions.

[0031] The fixing pad 34 is made of, for example, synthetic resin, and is formed in a long plate shape extending in a width direction W (the direction of the rotation axis of the fixing belt 31) along the sheet surface perpendicular to the conveying direction S of the sheet P being conveyed, and a sliding sheet 35 is provided between the fixing pad 34 and the fixing belt 31. The fixing pad 34 is preferably made of a heat-resistant resin material, and for example, a heat-resistant resin material such as liquid crystal polymer (LCP) or PEEK (polyether ether ketone) can be used. The length of the fixing pad 34 is approximately equal to the length of the fixing belt 31 in the width direction W.

[0032] The support member 33 supports the fixing pad 34 while pressing the sliding sheet 35 against the inner circumferential surface of the fixing belt 31. That is, the support member 33 is a member that supports the fixing pad 34 and the sliding sheet 35 while pressing them against the inner circumferential surface of the fixing belt 31. The support member 33 has a substantially L-shaped cross section and has a long plate-shaped fixed portion 33a to which the fixing pad 34 is fixed, and a long plate-shaped standing portion 33b standing from an end of the fixed portion 33a. Both ends of the support member 33 in the width direction W are fixed to a fixing frame (not shown).

[0033] The fixing pad 34 is provided with a heat generating section 36 that heats the fixing belt 31. The heat generating section 36 includes a first heat generating element 361 and a second heat generating element 362. The first heat generating element 361 and the second heat generating element 362 extend in the width direction W, and are arranged side by side on a heater substrate 363 (substrate) in a short side direction T that is aligned with the transport direction. The detailed configuration of the heat generating section 36 will be described later.

[0034] The fixing belt 31 is heated to a predetermined fixing temperature (for example, 180° C.) by the heat generating unit 36. The fixing pad 34, the sliding sheet 35, the fixing belt 31, and the like that may be affected by the heat from the heat generating unit 36 ​​are heat resistant.

[0035] The pressure roller 32 is disposed at a position facing the fixing pad 34 with the fixing belt 31 interposed therebetween. The pressure roller 32 rotates about a rotation axis parallel to the rotation axis α of the fixing belt 31, and extends parallel to the fixing belt 31. The pressure roller 32 presses the fixing belt 31 toward the fixing pad 34 to form a fixing nip FN (see FIG. 2A) between the pressure roller 32 and the fixing belt 31. The pressure roller 32 can be configured, for example, as a roller member in which the surface of a cylindrical core material made of a metal such as aluminum is covered with an elastic material such as rubber. The outer diameter of the pressure roller 32 is not limited to this, but is set to 30 mm in this example.

[0036] A driving force from a driving source (not shown) such as a motor is transmitted to the pressure roller 32 via a drive transmission mechanism (not shown) such as gears. The pressure roller 32 is driven to rotate by receiving the driving force from the driving source. As the pressure roller 32 is driven to rotate, the fixing belt 31 is driven to rotate in a second rotation direction M2 opposite to the first rotation direction M1 of the pressure roller 32. In other words, the pressure roller 32 forms a fixing nip portion FN by contacting with the surface 31a of the fixing belt 31, and transmits a driving force to the fixing belt 31 via the fixing nip portion FN, thereby rotating the fixing belt 31.

[0037] The sliding sheet 35 is provided so as to be in sliding contact with the inner circumferential surface of the fixing belt 31. The fixing pad 34 is supported by a support member 33. The sliding sheet 35 is fixed to the fixing pad 34 on the side facing the fixing belt 31. The fixing belt 31 slides against the sliding sheet 35 as the pressure roller 32 is driven to rotate. A lubricant may be applied to the sliding sheet 35 to reduce frictional force with the fixing belt 31.

[0038] (First embodiment) FIG. 3 is a plan view illustrating the heat generating section 36 in the fixing device 1 according to the first embodiment.

[0039] The fixing device 1 includes a heat generating section 36 that heats a fixing member (in this example, the fixing belt 31). The heat generating section 36 includes a first heat generating element 361 and a second heat generating element 362.

[0040] The first heating element 361 has a positive temperature coefficient. That is, the temperature coefficient of the first heating element 361 is a positive temperature coefficient regardless of the temperature change of the heating section 36. The first heating element 361 is a self-temperature controllable element whose resistance value increases when the Curie point is exceeded, and a representative example is a PTC (Positive Temperature Coefficient) heater. In this example, the first heating element 361 is a PTC heater. The Curie point of the first heating element 361 can be exemplified as about 200°C. The resistance value Rp of the PTC heater can be appropriately adjusted by the thickness, width, length, material, etc. of the PTC heater. For the PTC heater, a material whose heat quantity undergoes a phase transition when the Curie point is exceeded, such as barium titanate, can be suitably used.

[0041] The second heating element 362 has a smaller temperature coefficient or a more negative temperature coefficient (in this example, the second heating element 362 has a negative temperature coefficient) than the first heating element 361. That is, the temperature coefficient of the second heating element 362 is a smaller temperature coefficient than the positive temperature coefficient of the first heating element 361 or a more negative temperature coefficient, regardless of the temperature change of the heating section 36.

[0042] The second heating element 362 may be any heating element having a temperature coefficient that is smaller than the positive temperature coefficient of the first heating element 361 or is a negative temperature coefficient, and examples of the second heating element 362 include lamp-type heaters such as lamp heaters that have been widely used in the past, and planar heaters such as ceramic heaters. In this example, the second heating element 362 is a ceramic heater. For example, the second heating element 362 may be selected from known materials such as conductive carbon, silver-palladium (PdAg), and Ni alloy.

[0043] Further, the second heating element 362 may have a resistance value Rn that is constant or approximately constant (for example, within a range of about ±10% of the median resistance value at each temperature) regardless of temperature changes.

[0044] 2B, the first heating element 361 and the second heating element 362 are fixed on the upstream side and the downstream side in the transport direction S, respectively, on the same surface of the heater substrate 363. The heater substrate 363 is provided in the fixing pad 34 with the first heating element 361 and the second heating element 362 facing the fixing nip portion FN.

[0045] The fixing member (31) fixes the toner on the sheet P while transporting the sheet P in a state heated by the heat generated by the heat generating section 36. The fixing member is a fixing belt 31 in this example, but may be a roller member such as a heating roller or a fixing roller in addition to a belt member such as the fixing belt 31.

[0046] In this embodiment, the first heating element 361 and the second heating element 362 are electrically connected in series. At room temperature, the resistance value Rp of the first heating element 361 is smaller than the resistance value Rn of the second heating element 362. Here, "room temperature" refers to a natural temperature after the heating section 36 has not generated heat for a long period of time, and means that the heating section 36 is at the same or approximately the same temperature as the ambient temperature (room temperature) of the fixing device 1. The room temperature can be, for example, about 15°C to 30°C.

[0047] <At room temperature (when starting up)> When power is supplied to the first heating element 361 and the second heating element 362 in this room temperature state, since the first heating element 361 and the second heating element 362 are electrically connected in series in the heating section 36, power is first concentrated on the second heating element 362, whose resistance value Rn is greater than the resistance value Rp of the first heating element 361, and the temperature gradient of the second heating element 362 can be made steeper than that of the first heating element 361. This makes it possible to shorten the start-up time of the fixing device from when the heating section 36 starts to generate heat until the fixing member (31) reaches the target temperature.

[0048] In the past, in order to shorten the warm-up time of a fixing device, the power may be set to supply a larger power to the heating unit than is required to fix the toner to the sheet. In this case, when fixing the toner to the sheet, the power supplied to the heating unit must be reduced by power control to the heating unit to be lower than the power at the time of start-up, which may cause concerns about the effect of electromagnetic interference (EMI) on other devices, such as flicker noise.

[0049] In this regard, in the present embodiment, the start-up time of the fixing device from when the heat generating section 36 starts to generate heat until the fixing member (31) reaches the target temperature can be shortened, and the power supplied to the heat generating section 36 when fixing the toner to the sheet P is autonomously reduced. As a result, when fixing the toner to the sheet P, it is not necessary to reduce the power supplied to the heat generating section 36 to less than the power at start-up by controlling the power for the heat generating section 36, and this makes it possible to effectively prevent electromagnetic interference to other equipment.

[0050] <Immediately after warm-up is complete> Next, as the temperature of the heating section 36 increases from the start of heat generation of the heating section 36, the resistance value Rp of the first heating element 361, which has a positive temperature coefficient, increases. Then, since the first heating element 361 and the second heating element 362 are electrically connected in series in the heating section 36, the amount of power supplied to the second heating element 362 decreases. Therefore, the ratio of power supply from the first heating element 361 to the second heating element 362 can be increased, and this can improve the contribution rate of the second heating element 362 to heating the fixing member (31).

[0051] <Job in progress> Next, when a print job is executed in the image forming apparatus 100, the resistance value Rn of the second heating element 362 corresponds to the heat temperature of the second heating element 362. Then, since the first heating element 361 and the second heating element 362 are electrically connected in series in the heating section 36, the power supply ratio between the first heating element 361 and the second heating element 362 corresponds to the resistance value Rn of the second heating element 362. For example, it is possible to balance the power supply ratio between the first heating element 361 and the second heating element 362. This allows both the first heating element 361 and the second heating element 362 to contribute to heating the fixing member (31).

[0052] <Unnecessary temperature rise> In this embodiment, when the heat generating section 36 generates heat, the resistance value Rp of the first heat generating element 361 becomes larger than the resistance value Rn of the second heat generating element 362 under a predetermined temperature rise condition. Here, examples of the predetermined temperature rise condition include an end temperature rise condition and an abnormal temperature rise condition. Here, the term "end temperature rise" refers to a state in which the temperature (average temperature) of the end regions γa and γb other than the passing region β (region where heat is absorbed by the sheet P) of the small size sheet (P) in the fixing member (31) when the small size sheet (P) is a sheet P with a size smaller than the maximum size sheet P in the width direction W of the sheet P passes through the fixing member (31) becomes higher than the temperature (average temperature) of the passing region β by a predetermined temperature or more. In addition, the term "abnormal temperature rise" refers to a state in which the temperature becomes abnormally high due to unintended temperature control, for example, not stopping the power supply to the heat generating section 36 even when the detected temperature exceeds the target temperature.

[0053] In this way, when the heating section 36 generates heat, the resistance value Rp of the first heating element 361 becomes greater than the resistance value Rn of the second heating element 362 under specified temperature rise conditions, so that the amount of power supplied to the first heating element 361 can be reduced in the event of unnecessary temperature rise such as end temperature rise or abnormal temperature rise, thereby mitigating unnecessary temperature rise.

[0054] For example, when the predetermined temperature rise condition is an end temperature rise condition, the resistance values ​​R1, R3 of the end regions γa, γb of ​​the first heating element 361 become higher than the resistance value R2 of the passage region β as the number of passing sheets P increases, so that the amount of power supplied to the first heating element 361 can be suppressed in the end regions γa, γb by the positive temperature coefficient (PTC). This allows power to be supplied mainly to the passage region β. In detail, the power supplied to the end regions γa, γb of ​​the first heating element 361 can be made smaller than the power supplied to the passage region β, and the resistance value Rp of the first heating element 361 increases overall, so that the power supply ratio of the second heating element 362 to the first heating element 361 can be reduced. This allows the heating unit 36 ​​to suppress heating to the end regions γa, γb of ​​the fixing member (31) while including the second heating element 362.

[0055] Furthermore, when the specified temperature rise condition is an abnormal temperature rise condition, as the temperature of the first heating element 361 increases, the resistance value Rp of the first heating element 361 increases overall, thereby making it possible to reduce the overall amount of power supplied to the first heating element 361 and the second heating element 362.

[0056] In this embodiment, the first heating element 361 has an elongated shape that is long in the width direction W of the sheet P. The first heating element 361 has a common applied voltage from the center to both ends in the longitudinal direction L along the width direction W. In other words, the first heating element 361 is supplied (applied) with power (voltage) from both ends in the short side direction along the conveyance direction S. In this example, the first heating element 361 is sandwiched between a pair of first electrodes (361a, 361b) extending in the long side direction L in the short side direction T.

[0057] By doing this, even if the temperature in any region in the longitudinal direction L of the first heating element 361 becomes higher than in other regions, the resistance value (R1, R3) of the region with the higher temperature will autonomously increase more than the other regions, thereby making it possible to autonomously suppress heat generation in the region with the higher temperature.

[0058] Incidentally, as in the configuration described in Patent Document 1, the PTC heater (first heating element) and the resistance heater (second heating element) are supplied (applied) with power (voltage) from both ends in the short side direction (the voltage applied from the center to both ends in the long side direction is the same), and in a configuration in which they are electrically connected in series in the conveying direction, the resistance heater is particularly susceptible to variations in resistance value at each point in the long side direction. For example, when the resistance heater is applied by a method such as printing, the film thickness of the resistance heater is likely to become uneven, which in turn is likely to cause variations in the resistance value within the surface.

[0059] Furthermore, in such a configuration, if the resistance heater has a negative temperature coefficient, even if the temperature in any region in the longitudinal direction L of the heat generating part becomes higher than in other regions and the resistance value of the region where the temperature of the PTC heater is higher rises autonomously higher than the resistance value of the other regions, a current will flow in the short direction between the PTC heater and the resistance heater in the region where the temperature of the heat generating part is higher. This cancels out the positive temperature coefficient (temperature characteristic) in the region where the temperature of the PTC heater is higher, and it is therefore not possible to reliably suppress unnecessary temperature rises.

[0060] In this regard, in the present embodiment, the second heating element 362 has an elongated shape that is long in the width direction W of the sheet P. The second heating element 362 has a common applied voltage from the center to both ends in the short side direction T along the conveying direction S. In other words, the second heating element 362 is supplied (applied) with power (voltage) from both ends in the longitudinal direction L. In this example, the second heating element 362 is sandwiched between a pair of second electrodes (362a, 362b) that extend in the short side direction T in the longitudinal direction L.

[0061] This allows power (voltage) to be supplied (applied) to the second heating element 362 from both ends in the longitudinal direction L. This makes it possible to reduce the effect of variations in resistance value at various points in the longitudinal direction L on the second heating element 362. Note that for the first heating element 361, the applied voltage is the same from the center to both ends in the longitudinal direction L along the width direction W, but even if there is an in-plane variation in resistance value, the effect of the in-plane variation in resistance value is small because the variation in resistance value Rn with respect to temperature is large.

[0062] In this embodiment, the first heating element 361, to which a common voltage is applied from the center to both ends in the longitudinal direction L along the width direction W, and the second heating element 362, to which a common voltage is applied from the center to both ends in the lateral direction T along the conveying direction S, are electrically connected in series. Therefore, when the second heating element 362 has a negative temperature coefficient, there is an advantage as follows. That is, even if the temperature in any one of the regions (γa, γb) in the longitudinal direction L of the heating section 36 becomes higher than that in the other region (β) and the resistance value (R1, R3) of the region (γa, γb) where the temperature of the first heating element 361 is higher autonomously increases higher than the resistance value (R2) of the other region (β), no current flows in the lateral direction T between the first heating element 361 and the second heating element 362 in the region (γa, γb) where the temperature of the heating section 36 is higher. This prevents the positive temperature coefficient (temperature characteristic) from being cancelled out in the region (γa, γb) where the temperature of the first heating element 361 becomes high, and ultimately makes it possible to reliably suppress unnecessary temperature rise.

[0063] In the present embodiment, the predetermined temperature rise condition is an end portion temperature rise condition.

[0064] In this way, the first heating element 361 can effectively prevent end temperature rise, in which the temperature of the end regions γa, γb other than the passage region β of the small size sheet (P) becomes higher than the temperature of the passage region β by a predetermined temperature or more.

[0065] The predetermined temperature rise condition may be an end temperature rise condition, which effectively prevents the first heating element 361 from abnormally increasing in temperature due to unintended temperature control.

[0066] In this embodiment, the heat generating section 36 has a first terminal electrode 364 for supplying power to the first heat generating element 361 and a second terminal electrode 365 for supplying power to the second heat generating element 362 provided only at one of both ends in the longitudinal direction L along the width direction W of the heat generating section 36 (the left end in the example shown in Figure 3).

[0067] By doing this, compared to the case where a first terminal electrode 364 and a second terminal electrode 365 are provided at both end portions, respectively, a single connector can be connected to the first terminal electrode 364 and the second terminal electrode 365, thereby saving on connectors.

[0068] In detail, one first electrode 361a of the pair of first electrodes (361a, 361b) is electrically connected to the first terminal electrode 364. The other first electrode 361b of the pair of first electrodes (361a, 361b) and one second electrode 362a of the pair of second electrodes (362a, 362b) are electrically connected to each other. The other second electrode 362b of the pair of second electrodes (362a, 362b) is electrically connected to the second terminal electrode 365. This allows power to be supplied to the first heating element 361 and the second heating element 362 between the first terminal electrode 364 and the second terminal electrode 365.

[0069] (Example) In the following description of the embodiment, the first heating element 361 is referred to as a PTC heater (361), and the second heating element 362 is referred to as a second heater (362).

[0070] <At room temperature (when starting up)> -PTC heater- As shown in FIG. 3, the PTC heater (361) has a pair of first electrodes (361a, 361b) provided at both ends in the short direction T. Therefore, for the sake of convenience, the entire area in the long direction L is divided into three areas: one end area γa, a passing area β, and the other end area γb. The resistance value R1 of the end area γa, the resistance value R2 of the passing area β, and the resistance value R3 of the end area γb are all set to 6 Ω at room temperature (20° C. in this example).

[0071] Here, the end region γa, the passing region β, and the end region γb are connected in parallel in the form of an equivalent circuit, so that the combined resistance value Rp of the resistance values ​​(R1, R2, R3) of the regions (γa, β, γb) between the pair of first electrodes (361a, 361b) of the PTC heater (361) is 2 [Ω].

[0072] FIG. 4 is an electric circuit diagram showing an equivalent circuit of the PTC heater (361) and the second heater (362) in the heat generating part 36. FIG. 5A is a chart showing the resistance value, the current value, the voltage value, and the power value with respect to the temperature change of the heat generating part 36. FIG. 5B and FIG. 5C are graphs showing the resistance value and the power value with respect to the temperature change of the heat generating part 36, respectively. FIG. 6A and FIG. 6B are a chart and a graph showing the power line density with respect to the temperature change of the heat generating part 36, respectively. In FIG. 6A and FIG. 6B, PmR2 [W / mm] and PmR1 [W / mm] respectively represent the power line density of the passing region β and one end region γa of the PTC heater (361). Here, the power line density of the other end region γb is substantially the same as the power line density PmR1 of one end region γa, and is therefore represented by the power line density PmR1 of one end region γa. In addition, PmRn [W / mm] represents the power line density of the second heater (362), Pm main [W / mm] represents the sum of the power line density PmR2 of the passing area β of the PTC heater (361) and the power line density PmRn of the second heater (362), and Pm sub [W / mm] represents the sum of the power line density PmR1 of one end area γa of the PTC heater (361) and the power line density PmRn of the second heater (362).

[0073] In the values ​​in the table shown in FIG. 5A, if the resistance value of one end region γa of the PTC heater (361) is R1, the resistance value of the passing region β of the PTC heater (361) is R2, the resistance value of the other end region γb of ​​the PTC heater (361) is R3, and the combined resistance value of each region (γa, β, γb) between a pair of first electrodes (361a, 361b) of the PTC heater (361) is Rp, then Rp=1 / (1 / R1+1 / R2+1 / R3).

[0074] If the voltage value applied to the heat generating unit 36 ​​is V [V], then the total current value I [A] flowing through the heat generating unit 36 ​​is I = V / R. If the voltage value of the PTC heater (361) is Vp [V], and the voltage value applied to the second heater (362) is Vn [V], then Vp = Rp x I, and Vn = Rn x I, respectively. If the current value flowing through the PTC heater (361) is Ip [A], and the current value flowing through the second heater (362) is In [A], then Ip = Vp / Rp, and In = Vn x Rn, respectively.

[0075] If the total power value supplied to the PTC heater (361) is Pp [W] and the power value supplied to the second heater (362) is Pn [W], then Pp = Vp × Ip and Pn = Vn × In, respectively. If the power value of the end region γa of the PTC heater (361) is PR1 [W], the power value of the passing region β is PR2 [W], and the power value of the end region γb is PR3 [W], then PR1 = Vp 2 / R1,PR2=Vp 2 / R2, PR3=Vp 2 If the total power value supplied to the heat generating portion 36 is P [W], then P=V×I.

[0076] -Second heater- As shown in FIG. 3, the second heater (362) has a pair of second electrodes (362a, 362b) provided at both ends in the longitudinal direction L, and the resistance value Rn between the pair of second electrodes (362a, 362b) of the second heater (362) was set to 8 Ω at room temperature.

[0077] At start-up, the power value Pn (800 W in this example) of the second heater (362) is set to be greater than the power value Pp (200 W in this example) of the PTC heater (361), and so the temperature of the second heater (362) is higher than the temperature of the PTC heater (361).

[0078] Therefore, the resistance value R of the heat generating portion 36 is 10 [Ω] (=Rp+Rn) at room temperature due to the series connection of the resistances of the PTC heater (361) and the second heater (362).

[0079] <Immediately after warm-up is complete> -PTC heater- Immediately after the warm-up was completed, the temperature of the portion of the fixing pad 34 corresponding to the PTC heater (361) was approximately 140° C. At this time, the resistance values ​​(R1, R2, R3) of the regions (γa, β, γb) between the pair of first electrodes (361a, 361b) of the PTC heater (361) were all 10 Ω, and the resistance value Rp was 3.3 Ω.

[0080] -Second heater- After the warm-up was completed, the temperature of the fixing pad 34 at the location corresponding to the second heater (362) was approximately 220° C. At this time, the resistance value Rn between the pair of second electrodes (362a, 362b) of the second heater (362) was 7 Ω.

[0081] During the warm-up, the power value Pn (655.6 [W] in this example) of the second heater (362) is set to be greater than the power value Pp (312.2 [W] in this example) of the PTC heater (361), and therefore the temperature of the second heater (362) is higher than the temperature of the PTC heater (361).

[0082] Immediately after the warm-up is completed, the temperature difference between the portion of the fixing pad 34 corresponding to the PTC heater (361) and the portion corresponding to the second heater (362) is relatively large, at about 80° C.; however, since the PTC heater (361) and the second heater (362) are formed on the same heater substrate 363, after a while they become the same or approximately the same temperature.

[0083] From start-up to the completion of warm-up (from when the heat generating unit 36 ​​starts to generate heat until the fixing belt 31 reaches the target temperature), it is preferable that the power ratio (proportion) of the power value Pn of the second heater (362) to the total power value (Pp+Pn) of the power value Pp of the PTC heater (361) (200 [W] to 312.2 [W] in this example) and the power value Pn of the second heater (362) (800 [W] to 655.6 [W] in this example) is 60% to 80%.

[0084] In this example, the ratio of the power value Pn of the second heater (362) to the total power value (Pp+Pn) is 80% at start-up and 68% immediately after the warm-up is completed.

[0085] <Job in progress> -PTC heater- During a job for the maximum size sheet P, the temperature of the portion of the fixing pad 34 corresponding to the PTC heater (361) was approximately 180°C, the resistance values ​​(R1, R2, R3) of each region (γa, β, γb) between a pair of first electrodes (361a, 361b) of the PTC heater (361) were all 20Ω, and the resistance value Rp was 6.7Ω.

[0086] -Second heater- During a job for a maximum-sized sheet P, the temperature of the fixing pad 34 at a location corresponding to the second heater (362) was approximately 180° C. At this time, the resistance value Rn between the pair of second electrodes (362a, 362b) of the second heater (362) was 8 Ω.

[0087] In a job for a maximum-size sheet P, it is preferable that the power ratio between the power value Pp of the PTC heater (361) (309.9 [W] in this example) and the power value Pn of the second heater (362) (371.9 [W] in this example) is the same or approximately the same (for example, a ratio of 40% to 60%). In this example, the power ratios of the power value Pp of the PTC heater (361) and the power value Pn of the second heater (362) to the total power value (Pp+Pn) are 45% and 55%, respectively.

[0088] <End temperature rising> -PTC heater- During the temperature rise at the end of the small size sheet (P), the temperature of the portion of the fixing pad 34 corresponding to the end regions γa and γb reached 240°C, and the temperature of the portion of the fixing pad 34 corresponding to the passing region β reached 180°C, so that the temperatures of the end regions γa and γb rose higher than the temperature of the passing region β. As a result, the resistance values ​​(R1, R3) of the end regions γa and γb, which are non-passing portions of the PTC heater (361), were both 100Ω, the resistance value (R2) of the passing region β was 20Ω, and the resistance value Rp was 14.3Ω.

[0089] -Second heater- Furthermore, the resistance value Rn between the pair of second electrodes (362a, 362b) of the second heater (362) was 8 [Ω] during the paper passage.

[0090] At this time, the power values ​​(PR1, PR3) of the end regions γa, γb of ​​the PTC heater (361) (in this example, 41.1 [W], 41.1 [W], power linear density: 0.41 [W / mm], 0.41 [W / mm] (see FIGS. 6A and 6B)) and the power value Pn of the second heater (362) (161.1 [W] in this example) are smaller than the power value PR2 of the passing region β of the PTC heater (361) (205.5 [W] in this example, power linear density: 2.05 [W / mm] (see FIGS. 6A and 6B)), making it difficult for the heater to generate heat, and the heating of the fixing belt 31 (and thus the sheet P) is mainly provided by the heat generated by the power value PR2 of the passing region β of the PTC heater (361) (205.5 [W] in this example).

[0091] At this time, the resistance value Rp of the PTC heater (361) is 14.3 [Ω], and the resistance value Rn of the second heater (362) is 8 [Ω], which is the reverse of the magnitude relationship compared to the resistance value Rp of the PTC heater (361) at room temperature, which is 2 [Ω], and the resistance value Rn of the second heater (362) at room temperature, which is 8 [Ω].

[0092] Second embodiment Incidentally, the power required to be supplied to the heating section 36 in order to heat the fixing member (31) to an appropriate temperature depends on image formation conditions such as the basis weight of the sheet P, the size of the sheet P, and the conveying speed of the sheet P. Therefore, it is desirable to stabilize the image quality by accurately controlling the temperature of the fixing member (31) in accordance with the various image formation conditions.

[0093] In this respect, the second embodiment is different from the first embodiment in that power control for controlling the power supplied to the heat generating portion 36 is performed.

[0094] In the second embodiment, the configurations that are substantially the same as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

[0095] Fig. 7 is a perspective view showing a temperature detection unit 37 of the fixing device 1 according to the second embodiment. Fig. 8 is a block diagram showing a control configuration for controlling the fixing temperature of the fixing device 1 according to the second embodiment.

[0096] In this embodiment, the fixing device 1 includes a temperature detection section 37 that detects the temperature of the fixing member (31). In this example, the temperature detection section 37 includes a first temperature detection section 371 and a second temperature detection section 372. The first temperature detection section 371 is provided in a position facing the passing area β of the fixing belt 31 in a non-contact manner with the surface 31a of the fixing belt 31, and detects the temperature (surface temperature) of the passing area β of the fixing belt 31. The second temperature detection section 372 is provided in a position facing either one of the end areas γa and γb of ​​the fixing belt 31 (the other end area γb in this example) in a non-contact manner with the surface 31a of the fixing belt 31, and detects the temperature (surface temperature) of either one of the end areas (γb) of the fixing belt 31.

[0097] As shown in Fig. 8, the image forming apparatus 100 includes a control unit 40. The control unit 40 may be provided in the fixing device 1. The control unit 40 includes a processing unit 40a including a computer such as a CPU (Central Processing Unit), and a storage unit 40b including a non-volatile memory such as a ROM (Read Only Memory) and a volatile memory such as a RAM (Random Access Memory). The control unit 40 controls the operation of various components by the processing unit 40a loading a control program stored in advance in the ROM of the storage unit 40b onto the RAM of the storage unit 40b and executing the program.

[0098] The temperature detection unit 37 (371, 372) is electrically connected to an input system of the control unit 40. This allows the control unit 40 to detect the surface temperature of the fixing belt 31 based on a detection signal sent from the temperature detection unit 37.

[0099] The control unit 40 includes a temperature detection unit 41 and a power control unit 42. The temperature detection unit 41 detects the surface temperature (detected temperature) of the fixing belt 31 based on the detection result of the temperature detection unit 37 (371, 372) (based on a detection signal detected by the temperature detection unit 37 and sent from the temperature detection unit 37 (371, 372)). The power control unit 42 performs power control to control the power supplied to the heating unit 36 ​​so that the detected temperature of the fixing member (31) detected by the temperature detection unit 41 becomes a predetermined target temperature.

[0100] Representative examples of this power control include on-off control, which alternates between supplying and cutting off power, phase control, which controls the timing of power supply and cutting off for each half cycle of the power AC waveform, wave number control, which controls the presence or absence of each half wave of the power AC waveform, and pulse width modulation (PWM) control, which controls the duty ratio of the pulse width at a constant cycle of the power pulse waveform.

[0101] In this way, the temperature of the fixing member (31) can be precisely controlled in accordance with image formation conditions such as the basis weight of the sheet P, the size of the sheet P, and the conveying speed of the sheet P. As a result, the detected temperature detected by the temperature detection unit 37, which detects the temperature of the fixing member (31), can be precisely maintained at the target temperature, thereby ensuring stable image quality.

[0102] FIG. 9 is a graph showing the power line density versus temperature change of the heat generating portion 36 when pulse width modulation control is performed as the power control and the duty ratio is set to a value smaller than 1 during the end portion temperature rise.

[0103] Incidentally, the passing area β of the fixing member (31) through which the sheet P passes is heated by the passing area β of the first heating element 361 in addition to being heated by the second heating element 362. Meanwhile, during the end temperature rise, the sheet P passing through the fixing member (31) is a small-sized sheet, and therefore excessive power is likely to be supplied thereto.

[0104] Therefore, when fixing the toner on the small size sheet (P), i.e., during the edge temperature rise, the control unit 40 may perform power control to reduce the power (in this example, power control to reduce the duty ratio in pulse width modulation control) compared to when fixing the toner on the maximum size sheet P, as shown in Fig. 9. Here, the control unit 40 recognizes (detects) in advance the size of the sheet P using a size detection unit (size sensor) not shown.

[0105] By doing so, when the toner is fixed onto the small size sheet (P), that is, during the end temperature rise, it is possible to suppress the supply of excessive power.

[0106] Third embodiment Fig. 10 is a plan view showing a schematic diagram of a heat generating section 36 in the fixing device 1 according to the third embodiment. Fig. 11 is a block diagram showing a control configuration for controlling the fixing temperature of the fixing device 1 according to the third embodiment.

[0107] The third embodiment differs from the second embodiment in that the supply of the first power to the first heating element 361 and the supply of the second power to the second heating element 362 are controlled independently of each other.

[0108] In the third embodiment, the configurations that are substantially the same as those in the first and second embodiments are denoted by the same reference numerals, and the description thereof will be omitted.

[0109] In this embodiment, the heat generating section 36 has a first terminal electrode 364 and a second terminal electrode 365 provided at one of both ends in the longitudinal direction L (the left side in the example shown in FIG. 10), and a common terminal electrode 366 for supplying power to both the first heating element 361 and the second heating element 362 is provided at the other end of the heat generating section 36 in the longitudinal direction L (the right side in the example shown in FIG. 10).

[0110] In detail, one second electrode 362a of the pair of second electrodes (362a, 362b) is electrically connected to the common terminal electrode 366. This allows a first power to be supplied to the first heating element 361 between the first terminal electrode 364 and the common terminal electrode 366, and a second power to be supplied to the second heating element 362 between the second terminal electrode 365 and the common terminal electrode 366.

[0111] The control unit 40 includes a first power control unit 42a and a second power control unit 42b. The first power control unit 42a performs first power control on the first power supplied to the first terminal electrode 364 and the common terminal electrode 366. The second power control unit 42b performs second power control on the second power supplied to the second terminal electrode 365 and the common terminal electrode 366. The control unit 40 performs the first power control and the second power control independently.

[0112] Here, as with the power control of the second embodiment, the first power control and the second power control can typically include on-off control that alternates between supplying and cutting off power, phase control that controls the timing of power supply time and power cutting time for each half cycle of the power AC waveform, a wave number control method that controls the presence or absence of each half wave of the power AC waveform, and pulse width modulation (PWM) control that controls the duty ratio of the pulse width at a constant cycle of the power pulse waveform.

[0113] In this way, the supply of the first power to the first heating element 361 and the supply of the second power to the second heating element 362 can be controlled independently, and therefore, instead of or in addition to the independent control as in the first embodiment, it is possible to control the first power to the first heating element 361 and to control the second power to the second heating element 362. Therefore, the first power and the second power can be accurately supplied to the first heating element 361 and the second heating element 362, respectively, with an appropriate distribution.

[0114] The present disclosure is not limited to the above-described embodiments, and can be implemented in various other forms. Therefore, the embodiments are merely illustrative in all respects and should not be interpreted as being limited. The scope of the present disclosure is indicated by the claims, and is not restricted in any way by the text of the specification. Furthermore, all modifications and changes within the scope of the claims are within the scope of the present disclosure. [Explanation of symbols]

[0115] 1 Fixing device 100 Image forming device 31 Fixing belt 31a surface 32 Pressure roller 33 Support member 34 Fixing Pad 35 Sliding Sheet 36 Heating Part 361 First heating element 361a One of the first electrodes 361b the other first electrode 362 Second heating element 362a One of the second electrodes 362b The other second electrode 363 Heater Board 364 1st terminal electrode 365 2nd terminal electrode 366 Common terminal electrode 37 Temperature detection unit 371 First temperature detection unit 372 Second temperature detection unit 40 Control section 40a Processing section 40b Storage section 41 Temperature detection unit 42 Power Control Unit 42a First power control section 42b Second power control section FN Fixing nip L Longitudinal M1 First rotation direction M2 2nd rotation direction P-sheet S Transport direction T Short direction W Width direction α Rotation axis β passing area γa One end region γb other end region

Claims

1. a heat generating section including a first heat generating element having a positive temperature coefficient and a second heat generating element having a temperature coefficient smaller than that of the first heat generating element or a negative temperature coefficient; and a fixing member that conveys a sheet in a state heated by heat generated by the heat generating section; the first heating element and the second heating element are electrically connected in series; At room temperature, the resistance value of the first heating element is smaller than the resistance value of the second heating element, 2. A fixing device according to claim 1, wherein, when the heat generating portion generates heat, a resistance value of the first heat generating element is greater than a resistance value of the second heat generating element under a predetermined temperature rise condition.

2. 2. The fixing device according to claim 1, The fixing device is characterized in that the first heating element has an elongated shape that is long in the width direction along the sheet surface perpendicular to the conveying direction of the sheet, and a common voltage is applied from the center to both ends in the longitudinal direction along the width direction.

3. 3. The fixing device according to claim 2, The second heating element has an elongated shape that is long in the width direction along the sheet surface perpendicular to the transport direction of the sheet, and a fixing device characterized in that a common voltage is applied from the center to both ends in the short direction along the transport direction.

4. 2. The fixing device according to claim 1, The fixing device is characterized in that the specified temperature rise condition is an end temperature rise condition in which, when a small-size sheet, which is a sheet having a size smaller than the maximum size of the sheet in a width direction along the sheet surface perpendicular to the conveying direction of the sheet, is passed through the fixing member, the temperature of an end region of the fixing member other than the passing region of the small-size sheet becomes higher by a specified temperature or more than the temperature of the passing region.

5. 2. The fixing device according to claim 1, the first heating element and the second heating element are elongated in a width direction along a sheet surface perpendicular to a conveying direction of the sheet, A fixing device characterized in that the heat generating portion has a first terminal electrode for supplying power to the first heat generating element and a second terminal electrode for supplying power to the second heat generating element provided at only one of both ends in the longitudinal direction along the width direction of the heat generating portion.

6. 2. The fixing device according to claim 1, the first heating element and the second heating element are elongated in a width direction along a sheet surface perpendicular to a conveying direction of the sheet, the heat generating portion has a first terminal electrode for supplying power to the first heat generating element and a second terminal electrode for supplying power to the second heat generating element provided at either one of both ends in a longitudinal direction along the width direction of the heat generating portion, and a common terminal electrode for supplying power to both the first heat generating element and the second heat generating element provided at the other end of the both ends in the longitudinal direction of the heat generating portion; A fixing device characterized in that a first power control of a first power supplied to the first terminal electrode and the common terminal electrode, and a second power control of a second power supplied to the second terminal electrode and the common terminal electrode are performed independently.

7. 2. The fixing device according to claim 1, a temperature detection unit that detects the temperature of the fixing member, a heat generating unit that controls power supplied to the heat generating unit so that a temperature of the fixing member detected based on a detection result of the temperature detecting unit becomes a predetermined target temperature;

8. 8. An image forming apparatus comprising the fixing device according to claim 1.

Images