JP2004191966A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image of high image quality having neither image defect nor unevenness in print quality such as gloss by performing exact temperature control of a fixing member 20 independently of variation in input voltage or variation of resistance value of a fixing heater even when a fixing belt with an elastic layer is used as the fixing member 20. <P>SOLUTION: After start of power delivery to a fixing heater 16, a fixing device predicts maximum power supply to the fixing heater 16 according to rise time of temperature sensed by a main thermistor 18 or a sub-thermistor 19, and corrects output power according to the maximum power supply at the time of output of power necessary for stable operation of the fixing device 12. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a fixing device and an image forming device.

  More specifically, for example, the present invention relates to an image forming apparatus such as an electrophotographic copying machine, a printer, and a facsimile, and a fixing device used therein.

  2. Description of the Related Art In recent years, colorization in image forming apparatuses such as printers and copiers has been advanced. As an electrophotographic color image forming apparatus, a plurality of photosensitive drums are arranged in a row according to each color, and a color image is formed by sequentially superimposing toner images of each color formed on each photosensitive drum on a transfer medium. A so-called in-line type image forming apparatus has been proposed.

  As a fixing device used in such a color image forming apparatus, a heat roller fixing method having an elastic layer on a fixing member is well known. In the heat roller type fixing method having an elastic layer, the heat capacity of the heat roller itself becomes large, and the time (warm-up time) required for raising the temperature of the fixing roller to a temperature suitable for fixing the toner image is increased. There was a problem that it was long. This not only makes the user wait unnecessarily, but is also not preferable from the viewpoint of power consumption. Further, the cost of the fixing device has been expensive.

  As a fixing device having a short warm-up time, a fixing device of a belt fixing type often used for a black and white printer is well known. FIG. 14 shows a schematic configuration model diagram of an example of such a belt fixing device.

  Reference numeral 201 denotes the overall reference number of the belt fixing device of the present embodiment. Reference numeral 202 denotes a fixing belt unit, which is a heater holder 207 having a substantially semi-circular cross section in cross section, a fixing heater 204 fixedly disposed on the lower surface of the heater holder 207 along the length of the heater holder (perpendicular to the drawing), An assembly comprising an endless belt-shaped (cylindrical) thin-layer fixing belt 203 loosely fitted to a heater holder 207 provided therewith.

  Reference numeral 205 denotes an elastic pressure roller, and both ends of the metal core are rotatably supported between side plates of the fixing device.

  The fixing belt unit 202 is arranged on the upper side of the elastic pressure roller 205 in parallel with the pressure roller 205 with the fixing heater 204 facing downward, and a predetermined pressing force is applied to both ends of the heater holder 207 by urging means (not shown). Is pressed down. As a result, the lower surface of the fixing heater 204 is pressed against the upper surface of the elastic pressure roller 205 with the fixing belt 203 interposed therebetween against the elasticity of the pressure roller, thereby forming a fixing nip portion 206 having a predetermined width.

  The elastic pressure roller 205 is driven to rotate at a predetermined peripheral speed in a counterclockwise direction indicated by an arrow by a drive mechanism (not shown). Due to the rotational drive of the elastic pressure roller 205, a rotational force acts on the fixing belt 203 in the fixing nip portion 206 by the frictional force between the elastic pressure roller 205 and the outer surface of the fixing belt 203, and the fixing belt 203 has an inner peripheral surface. The outer periphery of the heater holder 207 is driven to rotate in the clockwise direction of the arrow at a peripheral speed substantially corresponding to the peripheral speed of the elastic pressure roller 205 while sliding in close contact with the lower surface of the fixing heater 204 in the fixing nip portion 206.

  The fixing belt 203 is, for example, an endless belt made of a heat-resistant resin having a thickness of about 50 μm, and a release layer (such as a fluorine coating resin) having a thickness of 10 μm is formed on the surface thereof. Further, in order to reduce the heat capacity of the fixing belt 203, no elastic layer is used for the fixing belt 203.

  The fixing heater 204 has a resistance heating element formed on a ceramic substrate. A temperature detecting unit 209 is brought into contact with the fixing heater 204, the temperature of the fixing heater 204 is detected, and power supplied to the fixing heater 204 is controlled by a control unit (not shown) so that the temperature of the fixing heater 204 becomes a desired temperature. And temperature control is performed.

  When the elastic pressure roller 205 is driven to rotate, the fixing belt 203 is driven to rotate, and the fixing heater 204 rises to a predetermined temperature and the temperature is controlled, the recording material P carrying the unfixed toner image t is transferred to the fixing nip. It is introduced between a fixing belt 203 and an elastic pressure roller 205. The unfixed toner image carrying surface of the recording material P comes into close contact with the outer surface of the fixing belt 203 and is conveyed by nipping the fixing nip 206 together with the fixing belt 203. In the nipping and conveying process, the heat of the fixing heater 204 is applied to the recording material P via the fixing belt 203, and the pressing force of the fixing nip portion 206 causes the unfixed toner image t to remain on the recording material P permanently. The image is fixed by heat and pressure as a fixed image. The recording material P passes through the fixing nip 206 and is discharged with a curvature separated from the surface of the fixing belt 203.

  In the fixing device 201 having such a configuration, since the heat capacity of the fixing belt 203 is extremely small, after the power is supplied to the fixing heater 204, the fixing nip 206 is heated to a temperature at which the toner image can be fixed in a short time. It is possible to warm.

  However, when the belt fixing device 201 using the fixing belt 203 without such an elastic layer is used as a fixing device of a color image forming apparatus, the fixing belt 203 serving as a fixing member has no elastic layer. The surface of the fixing belt 203 cannot follow the unevenness of the surface of the recording material P, the unevenness due to the presence or absence of the toner layer, and the unevenness of the toner layer itself. I will. Heat is transmitted well from the fixing belt 203 to the convex portion that makes good contact with the fixing belt 203, and heat from the fixing belt 203 is less likely to transmit to the concave portion that does not make good contact with the fixing belt 203. As described above, the toner layer reflects the difference in the melting state due to the unevenness, thereby affecting the image after fixing.

  In particular, in the case of a color image, since toner images of a plurality of colors are superimposed and mixed and used, the unevenness of the toner layer is larger than that of a black and white image, and when the fixing belt 203 has no elastic layer, the gloss of the image after fixing is high. The unevenness increases and the image quality deteriorates. Further, when the recording material P is an OHP sheet, when the image after fixing is projected, light scattering occurs due to the non-uniform appearance of the image after fixing microscopically. It causes a decline.

  Further, if silicone oil or the like is applied to the fixing belt 203 having no elastic layer and silicon oil or the like so that heat is transmitted evenly and well to the irregularities of the recording material P and the unfixed toner image t, the cost increases and the fixing speed increases. There was a problem that the post-image and the recording material P became sticky with oil.

  Therefore, a fixing device that constitutes a low-cost color-on-demand fixing device by using a fixing belt having an elastic layer in the belt fixing device has been proposed (for example, see Patent Document 1).

  FIG. 15 is a schematic configuration diagram of a belt fixing device using a fixing belt 203 having an elastic layer as a fixing member. Components and parts common to those in the apparatus of FIG. 14 are denoted by the same reference numerals, and description thereof will not be repeated.

  When this fixing device is used, the thermal response of the fixing belt 203 is poor due to the small thermal conductivity of the silicone rubber layer used for the elastic layer of the fixing belt 203, and the sleeve temperature follows the temperature of the fixing heater 204. It is accompanied by a large delay. Further, the difference between the temperature of the fixing heater 204 and the temperature of the fixing belt 203 is as large as several tens of degrees Celsius even in a steady state, and the difference between the temperature during idling and the time during sheet feeding is greatly different. Therefore, it was very difficult to control the temperature of the fixing belt.

Therefore, instead of the fixing heater unit as in the apparatus in FIG. 14, the temperature detecting unit 209 is disposed on the surface or the inner surface of the fixing belt 203 as in the apparatus in FIG. , PID control (P: Proportional-proportional, I: Integral-integral, D: Differential-differential) or the like to control the temperature of the fixing heater 204 to control the temperature of the fixing belt. By using such a configuration, the temperature of the fixing belt 203 can be controlled with higher accuracy.
JP-A-11-15303

However, in this fixing device,
1) Since the thermal conductivity of the silicone rubber layer used for the elastic layer of the fixing belt 203 is low and there are many members from the fixing heater 204 to the surface of the fixing belt, the temperature of the fixing belt increases after the fixing heater 204 is energized. Until then, so-called poor thermal response.

  2) There is a delay in the detection timing of the fixing nip due to the position of the temperature detecting unit 209 for detecting the temperature of the fixing belt 203 being far from the fixing nip 206.

  The dead time (time lag) due to the two reasons is relatively large. Feedback control represented by PID control is realized by detecting a change in the control amount and adding an operation amount corresponding to the control amount. It takes time to reach the appropriate temperature. Therefore, overshoot and undershoot are likely to occur, and large hunting (temperature ripple) is likely to occur.

This problem is particularly relevant for a. Immediately after startup, b. It is remarkable at the start of paper passing, and as a countermeasure for these problems,
a. When starting the fixing device, the fixing device has two or more power levels of a first power level for quickly raising the temperature of the fixing device and a second power level for stabilizing the temperature of the fixing device, and has a predetermined power level. Method of shifting to feedback control after setting the time to the required power value in consideration of the heat storage condition of the fixing device b. When the power supplied to the fixing heater 16 is corrected to a predetermined value and supplied without performing the PID control for a certain period of time in accordance with the entry timing of the recording material P at the start of sheet feeding, the thermal It has been found that a method of correcting the power to a substantially necessary power value in consideration of the characteristics and the heat storage condition of the fixing device is very effective.

  In the case of performing the above control, the predetermined power value of the second power level at the time of startup and the predetermined power value to be corrected at the start of sheet feeding are respectively used for stabilizing the temperature of the fixing device at the startup time at the target temperature. And the power value required when the paper is passed. If the predetermined power value is significantly different from the required power value, the temperature deviates from the target temperature, and the temperature ripple increases.

  In the present fixing device, wave number control or phase control is used as power output control, and the power is controlled not in a form of how many watts but in what percentage of the maximum supply power (full power). In other words, the power value required for the temperature control must be controlled in the form of a percentage of the maximum supply power.

  On the other hand, the maximum supply power varies due to variations in the input voltage to the fixing heater 204 and variations in the resistance value of the fixing heater 204. Table 1 shows variations in voltage, resistance, and power in the present fixing device within a 120 V range. Here, the range of the input voltage is 85 to 110% of the rated voltage, and the variation of the resistance is ± 7%.

  At this time, the variation of the maximum power supplied to the fixing heater 204 has about twice the variation from 747 W to 1441 W. Here, in performing the control of a or b described above, the maximum supply power is 1107 W, which is the central value, and when outputting 30% as the predetermined power, 332 W is output. On the other hand, when the lower limit of the power is 747 W, the predetermined power is 224 W, and when the power is 1441 W, the predetermined power is 432 W. In some cases, a large temperature ripple occurs when a predetermined power is input.

  Specifically, at the upper and lower limits of the maximum supply power, the temperature ripple is about 12 ° C., and in the in-line type electrophotographic color image forming apparatus used for the test, the gloss of the printed matter output is about one color. 7 and about 11 in the case of the secondary color, resulting in a decrease in image quality (Table 2). In addition, depending on a recording material or an image pattern, a large temperature variation causes a problem that a fixing defect such as a hot offset or a deterioration of fixing property occurs.

  When the maximum power supply is large, the overshoot at the time of startup becomes excessively large, and when used repeatedly, the operation at a higher temperature is repeated, thereby causing a problem that the life of the fixing device is shortened. . In addition, excessive overshoot causes a large loss from the viewpoint of power consumption and wastes unnecessary power consumption.

  Here, the description has been made assuming that the resistance of the fixing heater 204 is 13.0Ω in a 120V zone. However, in a region where the rated voltage is 127V, when a fixing heater having the same resistance value is used, the variation up to 110% and the resistance value In consideration of the variation, it is necessary to consider the maximum supply power to the fixing heater 204 up to 1614W.

  Further, when considering the use in the 100V area, the maximum supply power to the fixing heater 204 needs to be considered up to 519W in consideration of the variation of the rated voltage up to 85% of 100V and the variation of the resistance value.

  Summing up the above, the variation in the maximum power supply to the fixing heater 204 is about three times from 519 W to 1614 W.

  In this case, the temperature control becomes more unstable for the same reason, further lowering the image quality due to the fluctuation of gloss, and depending on the recording material and image pattern, further fixing defects such as hot offset and deterioration of fixing property are further caused. The problem of worsening occurs. Further, when the maximum supply power is large, the overshoot at the time of startup is further increased, and the operation at a higher temperature is repeated with repeated use, thereby further shortening the life of the fixing device, and There is a problem that power consumption is further increased.

  On the other hand, there is a method of dividing the resistance value of the fixing heater 204 in accordance with the rated voltage of each region of the heater. In this case, not only the cost and the management cost of the fixing heater are increased, but also the If the product is used in a different destination area across regions, or when a different destination is mistakenly made, not only is there a concern that users will be dissatisfied with the above-mentioned problems, but as a result, There is a concern that service costs will increase.

  Here, even if the heaters are sorted out as described above, the problem in the upper and lower limits of the maximum supply power in each region in the first place cannot be solved. In other words, there are areas where the power supply is very unstable in the area where the fixing device is used, and the range of the input power may be significantly different from the rated voltage.In such a case, the same problem will eventually occur. Become.

  The present invention has been made in view of the above problems, and even when a fixing belt having an elastic layer is used as a fixing member, the fixing member is not affected by variations in input voltage and resistance values of the fixing heater. It is an object of the present invention to solve the following problems by performing accurate temperature control.

  1) A fixing device capable of obtaining a high-quality image with no image defects and no print quality unevenness such as gloss regardless of a variation in an input voltage and a variation in a resistance value of a fixing heater, and an image equipped with the fixing device Provision of forming equipment.

  2) To provide a fixing device having high durability and a long service life irrespective of variation in input voltage and variation in resistance value of a fixing heater, and an image forming apparatus equipped with the fixing device.

  3) To provide a fixing device which consumes low power regardless of a variation in input voltage and a variation in resistance value of a fixing heater, and an image forming apparatus equipped with the fixing device.

  4) By providing the same fixing device even in regions having different rated voltages, it is possible to reduce costs and service costs.

  The present invention is a fixing device and an image forming apparatus having the following configurations.

(1) At least a heating body, a power supply unit for supplying power to the heating body, at least one or more temperature detecting means, a first rotating body that moves together with the recording material, and a pressure contact portion with the recording material. And a second rotating body that conveys the recording material, and feedback-controls the power supplied from the power supply unit to the heating body based on the temperature detected by the temperature detecting unit. In the fixing device, the temperature of the first rotating body is controlled by doing so, and the recording material carrying the image is nipped and conveyed and heated by the pressing portion.
The power required for heating supplied to the heating element is corrected by a predetermined power substantially equal to a power value required for stable operation of the fixing device,
When the predetermined power is output, the power supply to the heating element is controlled based on the maximum power supply value to the fixing device.

(2) an endless first rotating body;
A second rotator pressed against the first rotator, wherein the second rotator causes the recording material bearing the image to be nipped and conveyed by the pressed portions of the first and second rotators;
Temperature increasing means for increasing the temperature of a local portion of the first rotating body by receiving power supply;
Temperature detection means for detecting the temperature at a position different from the pressure contact portion with respect to the rotation direction of the first rotating body,
Based on the temperature detected by the temperature detecting means, the first control means for performing feedback control of the power supplied to the temperature increasing means,
Setting means for variably setting a set value corresponding to electric power to be supplied to the temperature increasing means, based on a temperature increase rate detected by the temperature detecting means when energized at a predetermined energization amount;
When the fixing device is started up, in the vicinity of the timing when the temperature detected by the temperature detecting means reaches the target temperature or in the vicinity of the timing when the recording material enters the pressure contact portion, the electric power according to the set value set by the setting means. And a second control means for temporarily supplying the temperature control means to the temperature increasing means.

  (3) In the first rotating body, when the moving speed of the outer periphery of the rotating body is V, the length from the press contact portion to the temperature detection position is a, and the outer circumferential length of the first rotating body is L, The fixing device according to (2), wherein the time t during which the two control means is performed is represented by t ≦ (a + L) / V.

  (4) The temperature raising means includes a heater which is provided in the vicinity of the pressure contact portion and generates heat when energized, or a coil which generates an eddy current in the first rotating body by generating a magnetic field when energized. The fixing device according to (2) or (3).

  (5) A nonvolatile memory for storing a value corresponding to a temperature increasing rate detected by the temperature detecting means when the predetermined amount of current is supplied, and a set value set by the setting means. The fixing device according to (2) or (3).

  (6) An image forming apparatus for forming an image on a recording material and fixing the image on the recording material using the fixing device according to any one of (1) to (5).

  (7) Further, there is provided first determining means for determining the degree of heat storage of the fixing device, wherein the setting means determines the result of the determination by the first determining means, and detects the temperature when a predetermined amount of power is supplied. The fixing device according to (2) or (3), wherein a set value corresponding to electric power to be supplied to the temperature increasing unit is variably set based on the temperature increasing speed detected by the unit.

  (8) Further, there is provided a second judging means for judging the type of the recording material, wherein the setting means determines the judgment result by the second judging means and the temperature detecting means when energizing with a predetermined energizing amount. The fixing device according to (2) or (3), wherein a set value according to the power to be supplied to the temperature increasing unit is variably set based on the temperature increasing speed detected by the fixing device.

(9) an endless first rotating body;
A second rotator pressed against the first rotator, wherein the second rotator causes the recording material bearing the image to be nipped and conveyed by the pressed portions of the first and second rotators;
Temperature increasing means for increasing the temperature of a local portion of the first rotating body by receiving power supply;
A first temperature detection unit that detects a temperature at a position different from the pressure contact portion with respect to a rotation direction of the first rotating body,
Second temperature detecting means provided near the pressure contact portion,
Based on the temperature detected by the first temperature detecting means, first control means for feedback controlling the power supplied to the temperature increasing means,
Setting means for variably setting a set value corresponding to electric power to be supplied to the temperature increasing means based on a temperature increasing rate detected by the second temperature detecting means when energized at a predetermined energizing amount,
When the fixing device is started up, in the vicinity of the timing when the temperature detected by the temperature detecting means reaches the target temperature or in the vicinity of the timing when the recording material enters the pressure contact portion, the electric power according to the set value set by the setting means. And a second control means for temporarily supplying the temperature control means to the temperature increasing means.

  (10) In the first rotating body, when the moving speed of the outer periphery of the rotating body is V, the length from the press contact portion to the temperature detection position is a, and the outer circumferential length of the first rotating body is L, The fixing device according to (9), wherein the time t during which the two control means is performed is represented by t ≦ (a + L) / V.

  (11) The temperature raising means includes a heater which is provided in the vicinity of the pressure contact portion and generates heat when energized, or a coil which generates an eddy current in the first rotating body by generating a magnetic field when energized. (9) or (10).

  (12) The fixing device according to (9) or (10), further including a nonvolatile memory that stores a set value set by the setting unit.

  (13) An image forming apparatus for forming an image on a recording material and fixing the image on the recording material using the fixing device described in any one of (9) to (12).

  (14) Further, the image forming apparatus further includes first determining means for determining the degree of heat storage of the fixing device, wherein the setting means determines a result of the determination by the first determining means and detects the temperature when a predetermined amount of power is supplied. The fixing device according to (9) or (10), wherein a set value corresponding to power to be supplied to the temperature increasing unit is variably set based on a temperature increasing speed detected by the unit.

  (15) Further, there is provided a second determination means for determining the type of the recording material, wherein the setting means determines a result of the determination by the second determination means and the temperature detection means when a predetermined amount of power is supplied. The fixing device according to (9) or (10), wherein a set value corresponding to electric power to be supplied to the temperature increasing means is variably set based on the temperature increasing speed detected by the fixing device.

  According to the invention of (1), accurate temperature control of the fixing member is performed irrespective of the variation of the input voltage and the variation of the resistance value of the fixing heater (heating body). It is possible to obtain a high-quality image without printing quality unevenness, and to provide a fixing device with low power consumption, high durability and long life.

  Even when a fixing belt having an elastic layer is used as the fixing member, the temperature of the fixing member is controlled accurately regardless of the variation in the input voltage and the variation in the resistance value of the fixing heater, so that there is no image defect. Achieving high-quality images without print quality unevenness such as gloss, high durability and long life, low power consumption, and providing the same fixing device in regions with different rated voltages Thus, cost reduction and service cost reduction can be achieved.

  According to the invention of (2), accurate temperature control of the fixing member is performed irrespective of the variation of the input voltage and the variation of the resistance value of the fixing heater (heating body). It is possible to obtain a high-quality image without printing quality unevenness, and to provide a fixing device with low power consumption, high durability and long life.

  According to the invention of (3), further accurate temperature control of the fixing member is performed irrespective of the variation of the input voltage and the variation of the resistance value of the fixing heater (heating body). Thus, it is possible to obtain a high-quality image with no uneven printing quality, and to provide a fixing device with low power consumption, high durability and long life.

  According to the invention of (4), the present invention can be applied to a fixing device having an on-demand property, regardless of a variation in input voltage or a variation in resistance value of a fixing heater (heating body). Performs accurate temperature control of the fixing member.As a result, it is possible to obtain a high-quality image with no image defects and no print quality unevenness such as gloss, and a fixing device with low power consumption, high durability and high life. Can be provided.

  According to the invention of (5), accurate temperature control of the fixing member is performed irrespective of the variation of the input voltage and the variation of the resistance value of the fixing heater. It is possible to provide a fixing device that can obtain a high-quality image with no power consumption, low power consumption, high durability, and long life. Further, stable temperature control can be maintained before and after the power supply is turned off.

  According to the invention of (6), it is possible to provide an image forming apparatus provided with a fixing device having the effect of any of the above-mentioned inventions (1) to (5).

  According to the invention of (7), regardless of the variation of the input voltage and the variation of the resistance value of the fixing heater, and furthermore, regardless of the heat storage condition of the fixing device, the fixing member can be accurately positioned even when the recording material enters. By performing temperature control, as a result, it is possible to obtain a high-quality image with no image defects and no printing quality unevenness such as gloss, and it is possible to provide a fixing device with low power consumption, high durability and a long life. .

  According to the invention of (8), the accurate temperature of the fixing member can be maintained even when the recording material enters, irrespective of the variation of the input voltage or the variation of the resistance value of the fixing heater and irrespective of the type of the recording material. As a result, it is possible to obtain a high-quality image with no image defects and no print quality unevenness such as gloss, and to provide a fixing device with low power consumption, high durability and long life.

  According to the invention of (9), accurate temperature control of the fixing member is performed regardless of the variation in the input voltage or the variation in the resistance value of the fixing heater and regardless of the recording material even when the recording material enters. As a result, it is possible to obtain a high-quality image with no image defects and no print quality unevenness such as gloss, and to provide a fixing device with low power consumption, high durability and long life.

  According to the invention of (10), further accurate temperature control of the fixing member is performed irrespective of the variation of the input voltage and the variation of the resistance value of the fixing heater (heating body). Thus, it is possible to obtain a high-quality image with no uneven printing quality, and to provide a fixing device with low power consumption, high durability and long life.

  According to the invention of (11), the present invention can be applied to a fixing device having an on-demand property, regardless of the variation of the input voltage and the variation of the resistance value of the fixing heater (heating body). Performs accurate temperature control of the fixing member.As a result, it is possible to obtain a high-quality image with no image defects and no print quality unevenness such as gloss, and a fixing device with low power consumption, high durability and high life. Can be provided.

  According to the invention of (12), accurate temperature control of the fixing member is performed irrespective of the variation of the input voltage and the variation of the resistance value of the fixing heater. It is possible to provide a fixing device that can obtain a high-quality image with no power consumption, low power consumption, high durability, and long life. Further, stable temperature control can be maintained before and after the power supply is turned off.

  According to the invention of (13), it is possible to provide an image forming apparatus provided with a fixing device having the effects of any of the above-mentioned inventions (9) to (12).

  According to the invention of (14), regardless of the variation of the input voltage and the variation of the resistance value of the fixing heater, and furthermore, regardless of the heat storage state of the fixing device, the fixing member can be accurately positioned even when the recording material enters. By performing temperature control, as a result, it is possible to obtain a high-quality image with no image defects and no printing quality unevenness such as gloss, and it is possible to provide a fixing device with low power consumption, high durability and a long life. .

  According to the invention of (15), the temperature control of the fixing member can be accurately performed even when the recording material enters, irrespective of the variation of the input voltage and the variation of the resistance value of the fixing heater, and regardless of the type of the recording material. As a result, it is possible to obtain a high-quality image having no image defects and no print quality unevenness such as gloss, and to provide a fixing device with low power consumption, high durability and long life.

  An embodiment of the present invention will be described. Preferred embodiments of the present invention will be illustratively described in detail below with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment should be appropriately changed depending on the configuration of the apparatus to which the invention is applied and various conditions. Is not limited to the following examples.

(1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration diagram showing a color image forming apparatus according to Embodiment 1 of the present invention. The image forming apparatus of the present embodiment is a tandem type full color printer of an electrophotographic system.

  The image forming apparatus includes an image forming unit 1Y for forming a yellow image, an image forming unit 1M for forming a magenta image, an image forming unit 1C for forming a cyan image, and a black image. It has four image forming units (image forming units) of the image forming unit 1Bk to be formed, and these four image forming units are arranged in a line at a fixed interval.

  Photosensitive drums 2a, 2b, 2c, and 2d are installed in the image forming units 1Y, 1M, 1C, and 1Bk, respectively. Around the photosensitive drums 2a, 2b, 2c, 2d, charging rollers 3a, 3b, 3c, 3d, developing devices 4a, 4b, 4c, 4d, transfer rollers 5a, 5b, 5c, 5d, a drum cleaning device 6a, Exposure devices 7a, 7b, 7c, and 7d are provided above the charging rollers 3a, 3b, 3c, and 3d and the developing devices 4a, 4b, 4c, and 4d, respectively. I have. The developing devices 4a, 4b, 4c, and 4d store yellow toner, magenta toner, cyan toner, and black toner, respectively.

  An endless belt-shaped intermediate transfer member 40 as a transfer medium is in contact with each primary transfer portion N of each of the photosensitive drums 2a, 2b, 2c, and 2d of the image forming portions 1Y, 1M, 1C, and 1Bk. The intermediate transfer belt 40 is stretched between a drive roller 41, a support roller 42, and a secondary transfer opposing roller 43, and is rotated (moved) in the direction of the arrow (clockwise) by the drive of the drive roller 41.

  The transfer rollers 5a, 5b, 5c, 5d for primary transfer are in contact with the photosensitive drums 2a, 2b, 2c, 2d via the intermediate transfer belt 40 at the respective primary transfer nips N.

  The secondary transfer opposing roller 43 contacts the secondary transfer roller 44 via the intermediate transfer belt 40 to form a secondary transfer portion M. The secondary transfer roller 44 is provided so as to be able to freely contact and separate from the intermediate transfer belt 40.

  A belt cleaning device 45 that removes and collects untransferred toner remaining on the surface of the intermediate transfer belt 40 is provided near the drive roller 41 outside the intermediate transfer belt 40.

  Further, a fixing device 12 is provided downstream of the secondary transfer unit M in the transport direction of the recording material P.

  Further, an environment sensor 50 and a media sensor 51 are installed in the image forming apparatus.

  When an image forming operation start signal (print start signal) is issued, each of the photosensitive drums 2a, 2b, 2c, and 2d of the image forming units 1Y, 1M, 1C, and 1Bk, which are driven to rotate at a predetermined process speed, is charged with a charging roller. In this embodiment, the negative electrodes 3a, 3b, 3c, and 3d uniformly charge.

  The exposure devices 7a, 7b, 7c and 7d convert the input color-separated image signals into optical signals at a laser output unit (not shown), and convert the converted optical signals into laser beams. Scanning exposure is performed on each of the charged photosensitive drums 2a, 2b, 2c, and 2d to form an electrostatic latent image.

  First, the yellow toner is charged on the surface of the photosensitive member by the developing device 4a to which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 2a is applied onto the photosensitive drum 2a on which the electrostatic latent image is formed. The electrostatic latent image is visualized by electrostatic attraction according to the electric potential, and is used as a developed image. This yellow toner image is primarily transferred onto the rotating intermediate transfer belt 40 by the transfer roller 5a to which a primary transfer bias (a polarity opposite to that of the toner (positive polarity)) is applied at the primary transfer portion N. Is done. The intermediate transfer belt 40 to which the yellow toner image has been transferred is rotated toward the image forming unit 1M.

  In the image forming section 1M, the magenta toner image formed on the photosensitive drum 2b in the same manner as described above is superimposed on the yellow toner image on the intermediate transfer belt 40, and is transferred by the primary transfer section N. Is done.

  Thereafter, the cyan and black toner images formed by the photosensitive drums 2c and 2d of the image forming units 1C and 1Bk are respectively primary-colored on the yellow and magenta toner images superimposedly transferred on the intermediate transfer belt 40. A full-color toner image is formed on the intermediate transfer belt 40 by superimposing sequentially at the transfer portion N.

  Then, the recording material (transfer material) P is conveyed to the secondary transfer unit M by the registration roller 46 at the timing when the leading end of the full-color toner image on the intermediate transfer belt 40 is moved to the secondary transfer unit M. A full-color toner image is secondarily transferred to the recording material P by the secondary transfer roller 44 to which a secondary transfer bias (a polarity opposite to that of the toner (positive polarity)) is applied. The recording material P on which the full-color toner image has been formed is conveyed to the fixing device 12, where the full-color toner image is heated and pressed at the fixing nip between the fixing belt 20 and the pressure roller 22 to melt on the surface of the recording material P. After fixing, the sheet is discharged to the outside, and becomes an output image of the image forming apparatus. Then, a series of image forming operations ends.

  Note that the image forming apparatus has an environment sensor 50, and biases and fixing conditions of charging, development, primary transfer, and secondary transfer are changed according to an atmosphere environment (temperature, humidity) in the image forming apparatus. It has a possible configuration, and is used for adjusting the density of a toner image formed on the recording material P and for achieving optimal transfer and fixing conditions. Further, the image forming apparatus has a media sensor 51, and by determining the recording material P, the transfer bias and the fixing condition can be changed according to the recording material. Is used to achieve optimal transfer and fixing conditions.

  At the time of the primary transfer, the primary transfer residual toner remaining on the photosensitive drums 2a, 2b, 2c, and 2d is removed and recovered by the drum cleaning devices 6a, 6b, 6c, and 6d. Further, the secondary transfer residual toner remaining on the intermediate transfer belt 40 after the secondary transfer is removed and collected by the belt cleaning device 45.

(2) Fixing device 12
FIG. 2 is a schematic model diagram of the fixing device 12 in the present embodiment. The fixing device 12 of the present embodiment is a heating device of a fixing belt heating system and a rotating body driving system for tension (tensionless type).

1) Overall Configuration of Apparatus 12 A fixing belt 20 as a first rotating body (first fixing member) has a cylindrical shape (endless belt shape, sleeve shape) in which an elastic layer is provided on a belt-shaped member. It is a member. The fixing belt 20 will be described in detail in section 6) below.

  Reference numeral 22 denotes a pressure roller as a second rotating body (second fixing member). Reference numeral 17 denotes a heater holder having a heat resistance and rigidity of a substantially semicircular trough-shaped cross section as a heating element holding member. Reference numeral 16 denotes a fixing heater as a heating element (heat source). It is arranged along. The fixing belt 20 is loosely fitted to the heater holder 17. In the present embodiment, the fixing heater 16 is a ceramic heater as described in detail in the section 2) described later.

  The heater holder 17 is formed of a liquid crystal polymer resin having high heat resistance, and serves to hold the fixing heater 16 and guide the fixing belt 20. In this example, Zenit 7755 (trade name) manufactured by DuPont was used as the liquid crystal polymer. The maximum usable temperature of Zenite 7755 is about 270 ° C.

  The pressure roller 22 is formed by forming a silicone rubber layer having a thickness of about 3 mm on a stainless steel core by injection molding, and coating a PFA resin tube having a thickness of about 40 μm thereon. The pressure roller 22 is disposed so that both ends of the cored bar are rotatably held between the inner and outer side plates (not shown) of the apparatus frame 24 by bearings. A fixing belt unit including the fixing heater 16, the heater holder 17, the fixing belt 20, and the like is disposed above the pressure roller 22 in parallel with the pressure roller 22 with the heater 16 facing downward. Is urged in the axial direction of the pressure roller 22 by a pressure mechanism (not shown) with a force of 98 N (10 kgf) on one side and a total pressure of 196 N (20 kgf) so that the downward surface of the fixing heater 16 is interposed via the fixing belt 20. The elastic layer of the pressure roller 22 is pressed against the elastic layer with a predetermined pressing force against the elasticity of the elastic layer to form a fixing nip portion 27 having a predetermined width required for heat fixing. The pressurizing mechanism has a pressure release mechanism, and is configured to release the pressurization at the time of jam clearance or the like and to easily remove the recording material P.

  Reference numerals 18 and 19 denote main and sub thermistors as first and second temperature detecting means. The main thermistor 18 as the first temperature detecting means is disposed in non-contact with the fixing heater 16 which is a heating element, and in this embodiment, is elastically brought into contact with the inner surface of the fixing belt 20 above the heater holder 17 to fix the image. The temperature of the inner surface of the belt 20 is detected. The sub thermistor 19 as the second temperature detecting means is disposed at a position closer to the fixing heater 16 which is a heat source than the main thermistor 18, and in this embodiment, is in contact with the back surface of the fixing heater 16. Detect temperature.

  The main thermistor 18 has a thermistor element attached to the tip of a stainless steel arm 25 fixedly supported by the heater holder 17, and the arm 25 elastically swings, so that the inner surface of the fixing belt 20 becomes unstable. In this case, the thermistor element is always kept in contact with the inner surface of the fixing belt 20.

  FIG. 3 is a perspective model diagram showing a positional relationship between the fixing heater 16, the main thermistor 18, and the sub thermistor 19 in the fixing device of the present embodiment. The main thermistor 18 is arranged near the longitudinal center of the fixing belt 20, and the sub thermistor 19 is arranged near the end of the fixing heater 16. The main thermistor 18 is arranged so as to contact the inner surface of the fixing belt 20 and the back surface of the fixing heater 16, respectively.

  The outputs of the main thermistor 18 and the sub thermistor 19 are connected to a control circuit unit (CPU) 21 via A / D converters 64 and 65, respectively. The content of the temperature control of the fixing heater 16 is determined based on the above, and the power supply to the fixing heater 16 is controlled by the heater drive circuit unit 28 (FIGS. 2 and 4) as a power supply unit (heating unit).

  Reference numerals 23 and 26 denote an entrance guide and a fixing / discharge roller mounted on the apparatus frame 24. The entrance guide 23 is provided so that the recording material P, which has passed through the secondary transfer nip, is accurately guided to a fixing nip 27 which is a pressure contact portion between the fixing belt 20 and the pressure roller 22 in the fixing heater 16. Play the role of leading. The entrance guide 23 of the present embodiment is made of polyphenylene sulfide (PPS) resin.

  The pressure roller 22 is driven to rotate at a predetermined peripheral speed in the direction of the arrow by a driving means (not shown). A rotational force acts on the cylindrical fixing belt 20 by the frictional contact between the outer surface of the pressure roller 22 and the fixing belt 20 at the fixing nip 27 due to the rotation of the pressing roller 22, and the fixing belt 20 is rotated. The inner surface of the heater holder 17 is driven to rotate in the direction shown by the arrow while sliding in close contact with the downward surface of the fixing heater 16. Grease is applied to the inner surface of the fixing belt 20 to ensure slidability between the heater holder 17 and the inner surface of the fixing belt 20.

  The pressure roller 22 is driven to rotate, whereby the cylindrical fixing belt 20 is driven to rotate, and power is supplied to the fixing heater 16, and the temperature of the fixing heater 16 rises to a predetermined temperature. In the adjusted state, the recording material P carrying the unfixed toner image is guided and introduced along the entrance guide 23 between the fixing belt 20 and the pressure roller 22 of the fixing nip portion 27, and is introduced. At this time, the toner image carrying surface side of the recording material P is in close contact with the outer surface of the fixing belt 20, and the fixing nip portion 27 is nipped and transported together with the fixing belt 20. In the nipping and conveying process, the heat of the fixing heater 16 is applied to the recording material P via the fixing belt 20, and the unfixed toner image t on the recording material P is heated and pressed onto the recording material P to be fused and fixed. You. The recording material P that has passed through the fixing nip 27 is separated from the fixing belt 20 by a curvature, and is discharged by a fixing discharge roller 26.

2) Main thermistor 18
As shown in FIGS. 2 and 3, the main thermistor 18 is arranged near the longitudinal center of the fixing belt 20, and is arranged so as to contact the inner surface of the fixing belt 20. The main thermistor 18 is used as means for detecting the temperature of the fixing belt 20 which is closer to the temperature of the fixing nip. Therefore, in normal operation, the temperature is controlled so that the detected temperature of the main thermistor 18 becomes the target temperature.

3) Sub thermistor 19
As shown in FIG. 3, the sub thermistor 19 is disposed near an end of the fixing heater 16 and is arranged so as to contact the back surface of the fixing heater 16. The sub thermistor 19 serves as a safety device that detects the temperature of the fixing heater 16 as a heating element and monitors the temperature of the fixing heater so as not to exceed a predetermined temperature.
Further, the sub-thermistor 19 monitors the overshoot of the temperature of the fixing heater 16 at the time of startup and the temperature rise of the end portion. For example, by raising the temperature of the end portion, the temperature of the end portion of the fixing heater 20 becomes a predetermined temperature. If it exceeds, it is used for determining to perform control such as lowering the throughput so that the end portion temperature rise does not deteriorate further.

4) Fixing heater 16
In the present embodiment, the fixing heater 16 as a heat source is configured to apply a conductive paste containing a silver-palladium alloy on a substrate of aluminum nitride in a film having a uniform thickness by a screen printing method, thereby forming a resistance heating element. A ceramic heater, which is formed and coated with a pressure-resistant glass, is used.

  FIGS. 4A and 4B are structural model diagrams of an example of such a ceramic heater. FIG. 4A is a partially cutaway surface model diagram, FIG. 4B is a rear model diagram, and FIG. 4C is an enlarged cross-sectional model diagram.

The fixing heater 16
a. A horizontally long aluminum nitride substrate a whose longitudinal direction is the direction perpendicular to the paper passing direction,
b. A 10 μm thick conductive paste containing a silver-palladium (Ag / Pd) alloy, which is applied in a linear or band shape by screen printing on the surface side of the aluminum nitride substrate a along its length and generates heat when a current flows. Resistance heating element layer b having a width of about 1 to 5 mm,
c. As a power supply pattern for the resistance heating element layer b, first and second electrode portions c and d and extended electric circuit portions e and f are also formed on the surface side of the aluminum nitride substrate a by screen printing of silver paste or the like. ,
d. In order to protect the resistance heating element layer b and the extended electric circuit portions e and f and to secure insulation, the thin film having a thickness of about 10 μm, which can withstand rubbing with the fixing belt 20, is formed thereon. Glass coat g,
e. Sub thermistor 19 provided on the back side of aluminum nitride substrate a
Etc.

  The fixing heater 16 is fixedly supported by a heater holder 17 with its front side exposed downward.

  A power supply connector 30 is mounted on the first and second electrode portions c and d of the fixing heater 16. When power is supplied from the heater drive circuit section 28 to the first and second electrode sections c and d via the power supply connector 30 described above, the resistance heating element layer b generates heat, and the fixing heater 16 quickly rises in temperature. . The heater drive circuit 28 is controlled by the control circuit (CPU) 21.

  In normal use, the driven rotation of the fixing belt 20 starts with the rotation of the pressure roller 22, and the temperature of the inner surface of the fixing belt 20 increases with the temperature of the fixing heater 16. The power supply to the fixing heater 16 is controlled by PID control, and the input power is controlled so that the inner surface temperature of the fixing belt 20, that is, the detected temperature of the main thermistor 18 becomes 190 ° C.

5) Fixing heater drive circuit section 28
FIG. 5 is a block diagram of a control circuit unit (CPU) 21 as a temperature control unit of the fixing unit and a fixing heater driving circuit unit 28. The power supply electrode sections cd of the fixing heater 16 are connected to the fixing heater drive circuit section 28 via a power supply connector (not shown).

  In the fixing heater drive circuit unit 28, reference numeral 60 denotes an AC power supply, 61 denotes a triac, 62 denotes a zero-cross generation circuit, and 21 denotes a control circuit unit (CPU). The triac 61 is controlled by the control circuit unit 21. The triac 61 turns on and off the heating resistor layer b of the fixing heater 16.

  The AC power supply 60 sends a zero cross signal to the control circuit section 21 via the zero cross detection circuit 62. The control circuit 21 controls the triac 61 based on the zero cross signal. In this way, when the heating resistor layer b of the fixing heater 16 is energized from the fixing heater driving circuit section 28, the entire temperature of the fixing heater 16 rapidly rises.

  The outputs of the main thermistor 18 for detecting the temperature of the fixing belt 20 and the sub thermistor 19 for detecting the temperature of the fixing heater 16 are taken into the control circuit (CPU) 21 via A / D converters 64 and 65, respectively.

  The control circuit unit 21 controls the heater power by controlling the power supplied to the fixing heater 16 by controlling the AC voltage applied to the fixing heater 16 by the triac 61 based on the temperature information of the fixing heater 16 from the main thermistor 18 by controlling the phase and wave number. Control is performed so that the temperature is maintained at a predetermined control target temperature (set temperature).

  That is, the temperatures of the main thermistor 18 and the sub thermistor 19 are monitored as voltage values by the control circuit section 21 so that the temperature of the fixing belt 20 is maintained at a predetermined set temperature and the fixing heater 16 is controlled. The power supply to the fixing heater 16 is controlled so as to be driven within a predetermined temperature.

  PID control is used as a typical temperature control method. As a power control method, there are a wave number control, a phase control, and the like. Here, the phase control will be described.

  That is, the control circuit unit 21 detects the temperature of the main thermistor 18 every 2 μsec, and determines the amount of power supply to the fixing heater 16 by PID control so as to control the temperature to a desired temperature in the control circuit unit 21. For example, in order to specify the power in 5% steps, generally, an energization angle of 5% is used for one half-wave of an AC waveform supplied from a power supply. The energization angle is obtained as a timing at which the triac 61 is turned on when the zero-cross signal is detected by the zero-cross generation circuit 62.

6) Fixing belt 20
In this embodiment, the fixing belt 20 is a cylindrical (endless belt-shaped) member in which an elastic layer is provided on a belt-shaped member.
Specifically, a silicone rubber layer (elastic layer) having a thickness of about 300 μm is formed on a cylindrical endless belt (belt base material) having a thickness of 30 μm by SUS by a ring coating method, and then a thickness of 30 μm is formed. Of the PFA resin tube (outermost surface layer). When the heat capacity of the fixing belt 20 formed in such a configuration was measured, it was 12.2 × 10 ⁻² J / cm ² · ° C. (heat capacity per 1 cm ^{2 of the} fixing belt).

a. Resin such as polyimide can be used for the base layer of the fixing belt 20, but a metal such as SUS or nickel has a thermal conductivity of about 10 times as large as that of polyimide and higher on-demand property than polyimide. Therefore, in this embodiment, SUS which is a metal is used for the base layer of the fixing belt 20.

b. Elastic Layer of Fixing Belt As the elastic layer of the fixing belt 20, a rubber layer having a relatively high thermal conductivity is used. This is to obtain a higher on-demand property. The material used in this example has a specific heat of about 12.2 × 10 ⁻¹ J / g · ° C.

c. Release Layer of Fixing Belt By providing a fluororesin layer on the surface of the fixing belt 20, the releasability of the surface is improved, and the toner once adheres to the surface of the fixing belt 20 and moves to the recording material P again. Can be prevented from occurring in the offset phenomenon. Further, by forming the fluororesin layer on the surface of the fixing belt 20 as a PFA tube, it is possible to more easily form a uniform fluororesin layer.

d. Heat Capacity of Fixing Belt Generally, when the heat capacity of the fixing belt 20 increases, the temperature rise becomes slow, and the on-demand property is impaired. For example, depending on the configuration of the fixing device, the heat capacity of the fixing belt 20 needs to be about 4.2 J / cm ² · ° C. or less when assuming a rise within one minute without standby temperature control. I know.

In the present embodiment, at the time of startup from a room temperature state, an electric power of about 1000 W is applied to the fixing heater 16, and the fixing belt 20 is designed to rise to 190 ° C. within 20 seconds. For the silicone rubber layer, a material having a specific heat of about 12.2 × 10 ⁻¹ J / g · ° C. is used. At this time, the thickness of the silicone rubber must be 500 μm or less, and the heat capacity of the fixing belt 20 is It needs to be about 18.9 × 10 ⁻² J / cm ² · ° C. or less. On the other hand, if the temperature is set to 4.2 × 10 ⁻² J / cm ² · ° C. or less, the rubber layer of the fixing belt 20 becomes extremely thin, and the elastic layer becomes poor in terms of image quality such as OHT permeability and gloss unevenness. It becomes equivalent to an on-demand fixing device having no image.

In this embodiment, the thickness of the silicone rubber necessary for obtaining a high-quality image such as OHT transparency and gloss setting was 200 μm or more. The heat capacity at this time was 8.8 × 10 ⁻² J / cm ² · ° C.

In other words, the heat capacity of the fixing belt 20 in the configuration of the fixing device similar to the present embodiment is generally from 4.2 × 10 ⁻² J / cm ² · ° C. to 4.2 J / cm ² · ° C. or less. . Among them, a fixing with a heat capacity of 8.8 × 10 ⁻² J / cm ² · ° C. or more and 18.9 × 10 ⁻² J / cm ² · ° C. or less can achieve both on-demand performance and high image quality. A belt was used.

(3) Method of Predicting Maximum Supply Power Input to Fixing Device In the present embodiment, the maximum supply power value to fixing heater 16 according to the rise time of the detected temperature of main thermistor 18 after the current supply to fixing heater 16 is started. , And when the power value required for stable operation of the fixing device is output, the output power is corrected according to the maximum supply power value, so that the overshoot can be performed regardless of the variation of the input voltage or the variation of the resistance value of the fixing heater 16. / Prevents undershoot and performs stable temperature control even at startup or at the start of paper passing. The above control is performed by the control circuit unit (CPU) 21.

  In the present embodiment, as a method of estimating the maximum supply power input to the fixing device, full power (100%) is supplied during startup temperature control, and the temperature rise time of the fixing heater 16 as a heating element is determined by using a sub-thermistor. By measuring from the 19 detected temperatures, the maximum supply power is predicted. Specifically, the time T (msec) required for the detected temperature of the sub thermistor 19 to rise from 150 ° C. to 210 ° C. during the rising temperature control is measured, and the expected maximum supply power E (W) is calculated as follows. (1) is calculated.

E = 2000−0.76 × T + 0.00010 × T2 (1)
The prediction formula used here is optimized in the fixing device having the configuration described in this embodiment, and should be appropriately changed according to the configuration of the device to which the invention is applied and various conditions. . It goes without saying that the temperature varies depending on the temperature range in which the time of the rising rise curve is measured.

In other words, as the relationship between the time of the rise curve and the input power,
E = α + β × T + λ × T2 (2)
In the fixing device having the configuration described in the present embodiment, when the relationship between the heating time required for the detection temperature of the sub thermistor 19 to rise from 150 ° C. to 210 ° C. and the input power is shown, Since the case where a coefficient is taken as in equation (1) matches well, such a prediction equation is used. Further, a simple coefficient was used to reduce the load on the control circuit unit (CPU) 21. It is not always necessary to use a second-order polynomial in the prediction equation. Depending on the configuration of the fixing device, the second-order term may be omitted, a higher-order term may be used, or an equation of another form may be used. You may use it.

  FIG. 5 shows the result of comparison between the above-mentioned prediction formula and actual measurement values. The time required for the detection temperature of the sub thermistor 19 to rise from 150 ° C. to 210 ° C. is determined by A / D converting the output of the thermistor in the in-line type electrophotographic color image forming apparatus used for the test. Measured. On the other hand, the actually supplied power was measured by A / D converting the output of the power value via the YOKOGAWA WT200 DIGITAL POWER METER with the Keyence PC temperature recorder NR250 and taking it into the PC.

  As shown in FIG. 5, the measured value and the prediction formula agree well, and it is understood that the maximum supply power can be accurately obtained by using this embodiment.

  In the present embodiment, the prediction of the maximum supply power using the rising temperature control is performed when the detected temperature of the sub thermistor 19 exceeds the measurement range before the rising temperature control. Before the temperature increase, if the detected temperature of the sub thermistor 19 is 140 ° C. or higher, the predicted value is not updated.

FIG. 16 is a flowchart illustrating a method of estimating the maximum supply power input to the fixing device according to the present exemplary embodiment. By using the detected temperature of the sub thermistor in this way, the maximum supply power can be accurately obtained.
In the present embodiment, the temperature range for measuring the time of the rising rise curve has been described assuming that the detected temperature of the sub thermistor 19 is from 150 ° C. to 210 ° C. This range is determined from the following conditions.

1) Low temperature lower limit of temperature range-The lower limit is the initial temperature of the sub thermistor, which is at least higher than the operating temperature environment.-When the low temperature side is used, the rising curve is too steep to increase the error in power estimation.-Operating temperature Affected by the environment and the heat storage state of the fixing device (correction may be required in some cases)
2) Regarding the high temperature upper limit of the temperature range-The upper limit is the maximum drive temperature at startup.-The higher the upper limit, the longer the measurement time of the rise curve, and the slower the reflection of the power forecast. As the temperature range for measuring the time of the curve, the detection temperature of the sub thermistor 19 was used as the most preferable condition from 150 ° C. to 210 ° C. From the above conditions, it is preferable to use a temperature range of 70 ° C. or more and 230 ° C. or less for the temperature range of the rising curve, but it is not always necessary to use the temperature within the range.

(4) Temperature Control of the Fixing Device In this embodiment, the temperature of the fixing belt is detected by bringing the main thermistor 18 into contact with the inner surface of the fixing belt 20, and the input power of the fixing heater 16 is controlled by feedback control such as PID control. Temperature control is performed based on the method of controlling the temperature.

  On the other hand, at the time of starting the fixing device and at the time of starting the sheet feeding, the following control is performed in order to further improve the temperature control accuracy and prevent overshoot / undershoot. The details are described below.

1) Temperature Control at Startup In this embodiment, in order to start up quickly and without excessive overshoot, an area where feedback control is prohibited during start-up temperature control is provided. By performing power control using the level, stable temperature control is performed without causing overshoot.

  In the present embodiment, as the plurality of power levels, the power supplied to the fixing heater 16 includes a first power level for promptly raising the fixing device temperature, an overshoot is prevented, and the fixing device temperature is stabilized. Is switched at a predetermined timing during the startup temperature control.

  The second power level is appropriately corrected to a required power value in consideration of the heat storage condition of the fixing device.

  Specifically, the following control is performed.

  In the present embodiment, “first startup power output (100% full output)” → “heat-up time detection (predicted maximum supply power)” → “corrected first startup power input” → “predetermined temperature detection” Start-up control is performed in the order of “corrected start-up second power input” → “corrected PID control”.

  First, a power correction method will be described.

The following correction formula was used for power correction.

  Here, 1050 W is used as the reference maximum supply power because it is a typical maximum supply power under use conditions. This criterion may be changed as appropriate.

  Table 3 shows the results of the above-described correction. For example, when the maximum supply power is 1050 W, the output power should be 50%, and when the maximum supply power is 750 W and 1500 W, respectively, 67.8% and 38.5% of the full power are output, respectively. By doing so, the same power is output as a result. Unless such correction is performed, 325 W and 750 W of power are output when the maximum supply power is 750 W and 1500 W, respectively. However, the output cannot be more than the full power (100%) which is the maximum supply power. In this case, the output is set to 100%.

  Shown here are the temperature control temperatures in the plain paper mode and the OHT mode. As described above, as the count number advances, that is, as the expected temperature of the pressure roller 22 increases, the temperature regulation temperature is reduced.

  As described above, by using the count value in accordance with the number of startups of the fixing device, the temperature of the pressure roller is accurately predicted regardless of the use state of the fixing device, and the temperature of the pressure roller is predicted. By selecting the temperature control temperature, it does not cause image defects that occur when the fixing temperature control temperature is inappropriate and does not cause wrapping of the recording material. And a high quality image without uneven printing quality can be obtained.

  As described above, by correcting the output power rate according to the expected maximum supply power, stable temperature control can be performed regardless of the variation in the maximum supply power. Therefore, by optimizing the control parameters such that the power control is optimized when the maximum supply power is 1050 W, the optimum control is performed by performing the above-described correction even in the case of other powers. Become.

  Next, the output timing of the first power up and the second power up will be described.

  After the output of the first power (100%), the correction of the first power is performed by measuring the time required for the detected temperature of the sub thermistor 19 to rise from 150 ° C. to 210 ° C., as described above. The method is performed at the time when the predicted value of the maximum supply power is determined. After the corrected start-up first power output, the timing for switching to the second power and the input time of the second power are set as shown in Table 4. For the powers other than those shown in the table, those obtained by linear interpolation from the powers shown in this table are used.

  The reason why the switching timing is changed according to the maximum supply power is as follows.

  When the maximum supply power is large, full power is supplied, and the temperature rise of the fixing heater 16 during the period until the estimation of the maximum supply power by the sub thermistor 19 is completed is large. Switch to second power. Accordingly, the input time of the second power is long.

  -When the maximum supply power is small, after the prediction of the maximum supply power is over, the output power ratio to be corrected cannot output 100% or more. Make it as long as possible. The input time of the second power is shortened accordingly.

  By doing so, temperature control with a small overshoot can be performed irrespective of variations in the maximum supply power.

2) Temperature control at the start of sheet feeding In this embodiment, the PID control is not performed for a certain period of time in accordance with the entry timing of the recording material P at the start of sheet feeding, and the power supplied to the fixing heater 16 is set to a predetermined value. When feeding the recording material P, the temperature is corrected to a substantially required power value in consideration of the thermal characteristics of the recording material P and the heat storage condition of the fixing device, so that the temperature detection has a dead time (time lag). Stable temperature control is performed without causing temperature fluctuation due to the entry of the recording material P.

  More specifically, the PID control is performed before and after the paper is fed, and the PID control is not performed for about 0.3 to 0.7 seconds before the recording material enters at the time of the start of the paper feeding, and the substantially required power value required for the paper feeding is not performed. And then shifted to PID control. For example, the power is about 500 W for plain paper passing immediately after startup from a room temperature state. That is, when the reference maximum supply power is 1050 W, the output is about 47.5%.

  The correction equation described above is similarly used for power correction. In other words, in a situation where about 500 W is required, when the maximum supply power is 750 W and 1500 W, respectively, about 66.5% and 33.25% of the full power are output, and as a result, the same power (500 W ) Is output. In this case as well, if the control parameters are optimized so that the power control is optimal when the maximum supply power is 1050 W, the optimum control is performed by correcting other power.

  In this embodiment, the predetermined power supply time of 0.7 seconds can be changed by the maximum supply power. This is because when the maximum supply power is large, the error in the predicted value is relatively large because the heating time is short, and when the maximum supply power is small, the heating time is long because the heating time is long. This is because the error in the predicted value increases due to the influence of the heat storage condition and the use environment. That is, in order to reduce the influence of the difference between the predicted value obtained by the prediction formula and the actual maximum supply power, when the maximum supply power is apart from the reference 1050 W, the input time of the predetermined power is slightly shortened. did. Specifically, when the maximum supply power is 1500 W or more or 700 W or less, the predetermined power supply time is set to about 0.3 seconds to about 0.5 seconds before the recording material enters at the start of sheet feeding.

3) Second power at start-up, predetermined power input time at start of sheet passing, second power at start-up, and predetermined power input time at start of sheet feed will be described.
As described above, at the time of starting the fixing device and at the time of starting the sheet feeding, the electric power for preventing the temperature fluctuation near the timing when the detected temperature of the thermistor reaches the target temperature or near the timing when the recording material enters the fixing nip 27. It is necessary to make the input for the following reasons.

  a. The thermal conductivity of the silicone rubber layer used for the elastic layer of the fixing belt 20 is small, and since there are many members from the fixing heater 16 to the surface of the fixing belt, the power is supplied to the fixing heater 16 until the fixing belt temperature rises. The poor thermal response.

  b. The detection timing of the fixing nip portion is delayed due to the position of the temperature detecting means 18 for detecting the temperature of the fixing belt 20 being apart from the fixing nip 27.

  Since the thermal response is poor until the temperature of the fixing belt rises as shown in a, the fixing belt warms up evenly at startup and when power is supplied at the start of paper passing, so that the fixing belt is rotated for approximately one rotation. It is desirable that a necessary electric power value is supplied during the minute rotation. Further, as shown in b, since there is a delay in the temperature detection timing of the fixing nip portion, at the time of startup or at the time of power supply at the time of starting paper feeding, a necessary power value is supplied for substantially the delay time. Is desirable.

  Therefore, as the moving speed of the outer periphery of the fixing belt 20, when the process speed is V, the length from the pressure contact portion to the temperature detection position is a, and the outer peripheral length of the fixing belt 20 is L, the temperature at startup is stabilized. The ideal supply time of the electric power required to stabilize the temperature behavior at the start of sheet passing is around (a + L) / V.

  On the other hand, when used in an actual machine, an error occurs between the required power value and the predicted power value due to the influence of the heat storage condition of the fixing device, the use environment, etc., and the variation in the members and configuration of the fixing device. There is. When an error occurs, the temperature adjustment temperature fluctuates as the power supply time is longer. In addition, there is a case where it is not possible to keep supplying power for a long time to start up early due to the restriction of the rising time. For this reason, it is desirable to use the actual power supply time shorter than the ideal power supply time.

  From these grounds, a more preferable time t as the required power supply time at the start-up or at the start of paper passing can be expressed by the following equation.

t ≦ (a + L) / V
In this embodiment, the process speed is 87 mm / sec, the length from the pressure contact portion to the temperature detection position is 20 mm, and the outer peripheral length of the fixing belt 20 is 77.6 mm, so that the power supply time is within 1.12 sec. Is a preferred time.

  Of course, the present invention can be applied without being limited to the above time.

4) PID Control In the present embodiment, the output power factor of the power controlled by the PID control is corrected according to the expected maximum supply power. The output power factor determined by the PID control is corrected using the above-described correction formula in the same manner.

  In the conventional fixing device, in the PID control, for example, when the detected temperature of the main thermistor is lower than 2 ° C. with respect to the target temperature, the output power ratio is controlled to increase by 2.5%. In the present embodiment, when the detected temperature of the main thermistor is lower than the target temperature by 2 ° C., the output power rates are 1.79% and 2.5% when the maximum supply power is 750 W, 1050 W and 1500 W, respectively. %, 3.57%. Accordingly, when the detected temperature of the main thermistor is lower than 2 ° C., the power is increased by about 26.25 W regardless of the maximum supplied power.

  In this case as well, if the control parameters are optimized so that the power control is optimal when the maximum supply power is 1050 W, the optimum control is performed by correcting other power.

  FIG. 17 shows a flowchart of temperature control of the fixing device based on the predicted maximum input power. As described above, by performing power control based on the predicted maximum input power, stable temperature control is performed irrespective of a change in the maximum input power due to a variation in the input voltage or a variation in the resistance value of the fixing heater 16. be able to.

(5) Experimental Results Using This Example Next, experimental results using this example are shown.

1) Experimental method Using the fixing device at room temperature, the state of the main / sub thermistor detection temperature and the power applied to the fixing heater 16 when one sheet is printed after startup is measured. The maximum supply power is 800 W, 880 W, and 1030 W, respectively. , 1190W and 1440W.

  The detected temperature of each thermistor is measured by A / D converting the output of the thermistor in the in-line type electrophotographic color image forming apparatus used for the test. On the other hand, the actually supplied power was measured by A / D converting the output of the power value via the YOKOGAWA WT200 DIGITAL POWER METER with the Keyence PC temperature recorder NR250 and taking it into the PC.

  The gloss of the image after fixing was measured using the following method. As a measuring device, a gloss meter PG-3D manufactured by Nippon Denshoku Industries Co., Ltd. was used, and the measurement was performed by a 75 ° specular gloss measuring method in JIS Z 8741. As the toner amount on the recording material, the toner amount of the solid image portion of so-called primary colors of Y, M, C, and BK is about 0.5 to 0.6 mg / cm2, and the so-called secondary colors of R, G, and B are used. Fixing was performed with the solid portion being about 1.0 to 1.2 mg / cm 2, and the gloss of the image after fixing was measured.

  When the maximum supply power is 800 W, 880 W, 1030 W, 1190 W, and 1440 W, respectively, as a durability test, 150 k sheets of two-sheet intermittent continuous printing are performed using the fixing device of the present embodiment. Of the drive roller was measured.

2) Experimental Results FIG. 6 shows a fixing device using this embodiment, when the maximum supply power is 800 W, 880 W, 1030 W, 1190 W, and 1440 W, respectively, when one sheet is printed after startup from the room temperature state. Shows the detected temperature of the main / sub thermistor.

  As described above, it can be seen that the main and sub thermistors are accurately started up in appropriate states within about 10 seconds regardless of the difference in the maximum supply power. Also, it can be seen that the temperature can be controlled with high accuracy during the paper passing. As a result, the gloss of the output printed matter had a fluctuation range of about 4 or less for a single color, and a fluctuation range of about 6 or less for a secondary color. Further, regardless of the recording material and the image pattern, there was no occurrence of fixing failure such as hot offset and deterioration of fixability.

  Further, the detected temperature of the sub thermistor 19 did not exceed 260 ° C. regardless of the difference in the maximum supply power. When the driving torque after the durability test was measured, it was about 24.5 to 31.3 N · cm (about 2.5 to 3.2 kgf · cm). At this time, no malfunction of the fixing device was observed.

(6) Comparative Example Control of a conventional fixing device as a comparative example will be described.

  In the conventional fixing device, after the “start-up power (100% full output)” is input, the detected temperature of the main thermistor 18 is a predetermined temperature (target temperature−38 ° C .: In this embodiment, the target temperature is 195 ° C. (195 ° C.−38 ° C. = 157 ° C.), the “predetermined power as the second power level” is fixed at 37.5% output for about 0.6 seconds, and then “PID control”. Migrated. In addition, in the case of plain paper passing immediately after startup from the room temperature state, PID control is not performed for about 0.3 to about 0.7 seconds before entering the recording material at the start of the passing of the sheet, and the necessary time for the passing of the sheet is not required. A power of about 47.5% was output as the predetermined power, which is a substantially required power value, and the power supplied to the fixing heater 16 was again controlled by the PID control.

1) Experimental method Since the experiment was performed in the same manner as in the experiment using this embodiment, the description is omitted here. However, the control in the conventional fixing device is as described above.

2) Experimental Results FIG. 7 shows the detected temperatures of the main and sub thermistors when one sheet is printed after startup from room temperature when the maximum supply power is 750 W, 1050 W, and 1440 W, respectively, in the conventional fixing device.

  As described above, when the maximum supply power is large, the rise is fast, but the temperature ripple remains large and does not converge, and the first sheet passes. In addition, during paper passing, the maximum supply power cannot be suppressed to a desired temperature ripple (about 7 ° C.) in all cases of 750 W, 1050 W, and 1440 W, and the maximum temperature is about 12 ° C. In the in-line type electrophotographic color image forming apparatus used in the test, the gloss of the output printed matter fluctuated by about 7 for a single color, and fluctuated by about 11 for a secondary color, thereby deteriorating the image quality. In addition, depending on a recording material or an image pattern, a large temperature variation causes a problem that a fixing defect such as a hot offset or a deterioration of fixing property occurs.

  Furthermore, when the maximum supply power was large, the overshoot was large, and when the maximum supply power was 1440 W, the detected temperature of the sub-thermistor 19 exceeded 290 ° C. When such driving is repeated, each member of the fixing device is thermally degraded. When the maximum supply power was 1440 W, the drive torque after the durability test was measured and found to be about 43.1 N · cm. At this time, slippage of the fixing belt may occur during driving of the fixing device depending on conditions.

(7) Discussion First, overshoot and temperature ripple will be described.

  The state of power control in the case of using the conventional fixing device and the case of using the fixing device of the present embodiment and performing the above-described experiment will be described below.

  FIG. 8 shows a fixing device using this embodiment, in which the maximum supply power is 800 W, 880 W, 1030 W, 1190 W, and 1440 W, respectively. This shows the power rate applied to the power supply.

  6 and 8, when the maximum supply power is large, it is considered that the overshooting does not occur excessively due to the early transition to the second power and the correction of the output power ratio. In addition, the power control has converged in about 10 seconds, and it is considered that the correction of the output power factor is working effectively. Further, even at the start of the sheet passing, the output power rate is hardly disturbed, and it is considered that the correction works effectively.

  As a comparative example, FIG. 9 shows a conventional fixing device in which the maximum power supply is 750 W, 1050 W, and 1440 W, respectively. Show.

  7 and 9, when a constant control is performed over a wide range of the maximum supply power, a very large overshoot occurs when the maximum supply power is large (1440 W) at startup. I understand. When the maximum supply power is 750 W and 1440 W, the predetermined power is optimized at 1050 W, and the required power value does not match. Therefore, the paper feed is started without converging the power control. It can be seen that the temperature is not stable. Furthermore, when the maximum power supply is 750 W and 1440 W during the paper passing, the predetermined power at the start of the paper passing does not coincide with the required power value. It is considered that the temperature of the fixing belt 20 is disordered.

  Next, the durability of the fixing member will be described.

  If the driving that the detected temperature of the sub thermistor 19 exceeds about 290 ° C. is repeated during startup as in the conventional example, a slip of the fixing belt 20 occurs due to an increase in torque due to thermal deterioration of the fixing device. As a result, the durability life of the fixing members such as the fixing belt 20 and the pressure roller 22 is shortened.

  Due to the slip of the fixing belt 20, the kinetic frictional force between the fixing belt 20 and components inside the fixing belt 20 including the fixing heater 16 exceeds the maximum static frictional force with the pressure roller 22 or the recording material P. Occurs when: The kinetic frictional force between the fixing belt 20 and components inside the belt such as the fixing heater 16 is greatly affected by the state of grease in particular, and when the amount is reduced by moving to an unnecessary portion of the grease, It is known that when the grease itself is deteriorated, the dynamic friction force increases. As the endurance of the fixing device advances, the amount of grease decreases or the grease deteriorates, so that the dynamic friction force increases. In particular, excessive high-temperature driving causes large damage to grease.

  The kinetic frictional force between the fixing belt 20 and components inside the fixing belt 20 such as the fixing heater 16 is the largest factor among the loads on the driving means when the fixing device is driven. That is, by measuring the driving torque of the fixing device, the ease with which the fixing belt 20 slips can be predicted.

  The driving torque in the initial state of the fixing device is about 14.7 N · cm, and it has been found that the slip of the fixing belt 20 may occur when the driving torque exceeds about 14.7 N · cm. I have.

  When the conventional fixing device was used, the driving torque after the durability test was about 43.12 N · cm, whereas when the fixing device in the present embodiment was used, the driving torque was about 24.5 to 31. .36 N · cm. At this time, in the fixing device of the conventional example, slippage of the fixing belt 20 occurred, but no problem was found in the fixing device of the present embodiment.

  As described above, since almost no overshoot of the surface temperature of the fixing belt 20 occurs at the time of startup, the durability life can be greatly extended without imposing an excessively high temperature drive.

  Here, the slip of the fixing belt 20 is taken as an example, which is a remarkable one in which the durable life is shortened. However, if the overshoot of the fixing device is large, an excessive load is imposed on each member in the fixing device. Therefore, it is needless to say that preventing the overshoot using this embodiment has the effect of extending the life of each member in the fixing device.

  Note that the correction power used here does not have to exactly match the required predetermined power, but may be substantially the same. This is because the temperature of the fixing belt 20 is controlled so as to approach the target temperature again by returning to the PID control after the predetermined power supply for a certain period of time. In other words, if the correction power does not exactly match the required predetermined power, the temperature of the fixing belt 20 goes away from the target temperature, but is controlled so as to come close again. It suffices if the temperature fluctuation at that time is within a desired temperature ripple. In experiments, the reference power was set to 1050 W, and it was shown that the present invention can be effectively applied in some cases where the maximum supply power is from 750 W to 1440 W. It goes without saying that it can be applied to a wider range.

(8) Conclusion As described above, in the present embodiment, the maximum supply power value to the fixing heater 16 is predicted according to the rise time of the temperature detected by the sub thermistor 19 after the energization of the fixing heater 16 is started, and the stable operation of the fixing device is performed. The output power is corrected in accordance with the maximum supply power value at the time of output of the power value necessary for the power supply, thereby preventing overshoot / undershoot regardless of the variation of the input voltage and the variation of the resistance value of the fixing heater 16, and starting up. Stable temperature control could be performed even at the time of paper feeding or at the start of paper passing.

  In the present embodiment, the maximum supply power value to the fixing heater 16 is predicted according to the rise time of the temperature detected by the main thermistor 18 after the energization of the fixing heater 16 is started, and the output of the power value necessary for stable operation of the fixing device is performed. Sometimes, by correcting the output power according to the maximum supply power value, overshoot / undershoot is prevented irrespective of the variation of the input voltage and the variation of the resistance value of the fixing heater 16, and at the time of startup and at the start of paper feeding. A method for performing stable temperature control will be described.

  In this embodiment, the general configuration and control of the fixing device are the same as in the first embodiment. However, as a method of estimating the maximum supply power input to the fixing device, the maximum supply power is predicted by measuring the temperature rise of the fixing belt 20 to be heated from the detected temperature of the main thermistor 18, and The difference is that the output power is corrected when the power value required for stable operation is output.

  The configuration of the image forming apparatus is the same as that of the first embodiment, and is as shown in FIG. The configuration of the fixing device is the same as that of the first embodiment, and is as shown in FIGS. 2 to 4, and redundant description will be omitted.

  In the present embodiment, as a method for estimating the maximum supply power input to the fixing device, the maximum supply power is predicted by measuring the temperature rise of the fixing belt 20 to be heated from the detected temperature of the main thermistor 18. . Specifically, the time T (msec) required for the detected temperature of the main thermistor 18 to rise from 90 ° C. to 130 ° C. is measured, and the expected maximum supply power E (W) is calculated by the following equation. calculate.

E = 3500−2.7 × T + 0.00067 × T2 (3)
FIG. 10 shows the result of comparison between the above-mentioned prediction formula and actual measurement values. As described above, the actual measurement value and the prediction formula agree well, and it is understood that the maximum supply power can be accurately determined by using the present embodiment.

  The prediction formula used here is optimized in the fixing device having the configuration described in this embodiment, and should be appropriately changed according to the configuration of the device to which the invention is applied and various conditions. . Of course, it depends on the temperature range in which the time of the rising rise curve is measured.

In other words, as the relationship between the time of the rise curve and the input power,
E = α + β × T + λ × T2 (2)
In the fixing device having the configuration described in this embodiment, when the relationship between the heating time required for the detected temperature of the main thermistor 19 to rise from 90 ° C. to 130 ° C. and the input power is indicated. Since the case where the coefficient is taken as in the equation (3) matches well, such a prediction equation is used. Further, a simple coefficient was used to reduce the load on the control circuit unit (CPU) 21. It is not always necessary to use a second-order polynomial in the prediction equation. Depending on the configuration of the fixing device, the second-order term may be omitted, a higher-order term may be used, or an equation of another form may be used. You may use it.

  In the fixing device of this configuration, when the maximum supply power is predicted using the detected temperature of the main thermistor 18, the temperature rise of the fixing heater 16 is measured as compared with the case where the detected temperature of the sub thermistor 19 is used. The temperature rise of the fixing belt 20 heated by the fixing heater 16 tends to be slightly affected by the state of the nip portion between the fixing heater 16 and the fixing belt 20. In comparison with the case where the temperature rise is detected, although the accuracy is slightly lowered due to the variation of the fixing device, there is an advantage that the sub thermistor 19 is not required. That is, the same effect can be obtained even in a fixing device including only a main thermistor without a sub thermistor.

  In the present embodiment, the estimation of the maximum supply power using the rising temperature control is not possible if the detected temperature of the main thermistor 18 exceeds the measurement range before the rising temperature control. Before the temperature increase, when the detected temperature of the main thermistor 18 is 80 ° C. or higher, the predicted value is not updated.

  FIG. 18 is a flowchart illustrating a method for estimating the maximum supply power input to the fixing device according to the present exemplary embodiment. By using the detected temperature of the sub thermistor in this way, the maximum supply power can be accurately obtained.

  In the present embodiment, the temperature range for measuring the time of the rising rise curve is described assuming that the detected temperature of the main thermistor 18 is from 90 ° C. to 130 ° C. This range is determined from the following conditions.

1) Regarding the lower limit of the low temperature range-The lower limit is the initial temperature of the sub-thermistor, which is at least higher than the operating temperature environment.-It is affected by the operating temperature environment and the heat storage state of the fixing device. )
2) Regarding the high temperature upper limit of the temperature range-The upper limit is the maximum drive temperature at startup.-The higher the upper limit, the longer the measurement time of the rise curve, and the slower the reflection of the power forecast. As the temperature range for measuring the time of the curve, the most preferable condition was used in which the detected temperature of the main thermistor 18 was from 90 ° C. to 130 ° C. From the above conditions, it is preferable to use a temperature range of 70 ° C. or more and 150 ° C. or less for the temperature range of the rising curve, but it is not always necessary to use the temperature within the range.

  The effect when this embodiment is used is basically the same as that of the first embodiment, and the same effect can be obtained.

  As described above, in the present embodiment, the maximum supply power value to the fixing heater 16 is predicted according to the rise time of the detected temperature of the main thermistor 18 after the energization of the fixing heater 16 is started, and the power value required for the stable operation of the fixing device is estimated. The output power is corrected in accordance with the maximum supply power value at the time of output, thereby preventing overshoot / undershoot irrespective of the variation of the input voltage or the variation of the resistance value of the fixing heater 16, and at the time of startup and at the start of paper feeding. Also, stable temperature control could be performed.

  In the present embodiment, when estimating the maximum power supply value to the fixing heater 16 according to the rise time of the detected temperature of the sub thermistor 19 or the main thermistor 18 after the energization of the fixing heater 16 is started, the heat storage condition of the fixing device In order to make the fixing device less likely to be affected by the above, the update of the measurement result is determined by the heat storage condition of the fixing device, and when the power value required for stable operation of the fixing device is output, the output power is corrected according to the maximum supply power value, and at a predetermined timing. By recording in the EEPROM, overshoot / undershoot is prevented regardless of the power supply OFF-ON, the variation of the input voltage, and the variation of the resistance value of the fixing heater 16, and even at the time of startup and at the start of paper feeding. A method for performing stable temperature control will be described.

  In this embodiment, the general configuration and control of the fixing device are the same as in the first and second embodiments. However, it is different in that when the maximum supply power input to the fixing device is predicted, the output power is corrected when the power value required for stable operation of the fixing device is output by using a predicted value in consideration of the heat storage condition of the fixing device. .

  The configuration of the image forming apparatus is the same as in the first and second embodiments, and is as shown in FIG. The configuration of the fixing device is the same as that of the first embodiment, and is as shown in FIGS. 2 to 4, and redundant description will be omitted.

  In this embodiment, the time T (msec) required for the detected temperature of the sub-thermistor 19 to rise from 150 ° C. to 210 ° C. is measured, and the expected maximum supply power E (W) is calculated by the following equation. Is calculated. However, the predicted value is updated only when the detected temperature of the sub thermistor 19 immediately before startup is 140 ° C. or lower, and the following cases are classified according to the detected temperature of the sub thermistor 19.

E = 0.00010 × T2−0.74 × T + 2000 (.about.70 ° C.)
・ ・ ・ ・ ・ (4)
E = 0.00010 × T2-0.78 × T + 2000 (70 to 140 ° C.)
・ ・ ・ ・ ・ (5)
As shown in FIG. 11, a prediction formula for the case where the detected temperature of the sub-thermistor 19 immediately before startup is less than 70 ° C., and a case where the detected temperature is 70 ° C. or more and less than 140 ° C. The results obtained by comparing the measured values at the respective maximum supply powers in the case of 110 ° C. and 110 ° C. are shown. From the heat storage condition of the fixing device, it can be seen that the accuracy of the predicted value is further improved due to the case classification.

  FIG. 19 is a flowchart illustrating a method of estimating the maximum supply power input to the fixing device according to the present exemplary embodiment. By using the detected temperature of the sub thermistor in this way, the maximum supply power can be accurately obtained.

  Here, the detected temperature of the sub thermistor 19 immediately before startup is used, but other methods such as the main thermistor 18 may be used to consider the heat storage condition of the fixing device. Instead of the measurement of the heating time by the sub thermistor 19, the measurement of the heating time by the main thermistor may be used.

  In addition to such a method, it is more preferable to perform correction in consideration of, for example, a voltage drop of a power supply circuit in order to increase the accuracy of a predicted value. However, in practice, it is sufficient that the influence of ripple due to power variation is sufficiently small, and it is not always necessary to use the effect.

  In the present embodiment, by recording the data in the EEPROM at a predetermined timing, the effect can be obtained even when the power supply is turned off and on while the fixing device is sufficiently warmed (the predicted value is not updated). I did it. The recording timing to the EEPROM may be determined in consideration of the life of writing to the EEPROM, the variation of the actual maximum power supply due to the variation of the power supply used, and the influence of the update interval. In this embodiment, when the prediction value is updated three times, the data written once in the EEPROM is updated.

  The effect when this embodiment is used is basically the same as that of the first and second embodiments, and the same effect can be obtained. However, since the accuracy of the predicted value is improved, the influence of the ripple due to the error of the predicted value of the maximum supply power can be further reduced, and the effect can be obtained even when the power supply is turned off and on. There is.

  As described above, in the present embodiment, when estimating the maximum power supply value to the fixing heater 16 according to the rise time of the temperature detected by the sub thermistor or the main thermistor 18 after the energization of the fixing heater 16 is started, the heat storage of the fixing device In order to reduce the influence of the condition, the update of the measurement result is determined by the heat storage condition of the fixing device, the output power is corrected according to the maximum supply power value when the power value required for stable operation of the fixing device is output, The overshoot / undershoot is prevented regardless of the power supply OFF-ON, the variation of the input voltage, and the variation of the resistance value of the fixing heater 16 at the time of start-up or at the start of sheet feeding. In addition, stable temperature control could be performed.

  In this embodiment, the method of estimating the maximum supply power in this embodiment can be applied to a fixing device of a different type from the fixing devices described in the first, second, and third embodiments, and the same effect can be obtained. It indicates that.

  As a fixing device different from the fixing device described in this embodiment, a so-called induction heating type fixing device was used. FIG. 13 is a schematic model diagram of a fixing device of the electromagnetic induction heating type.

  The magnetic field generating means includes magnetic cores 62a, 62b, 62c and an exciting coil 63.

  The magnetic cores 62a, 62b, and 62c are members having high magnetic permeability, and are preferably made of a material used for a transformer core such as ferrite or permalloy, and more preferably, ferrite that has little loss even at 100 kHz or more.

  Reference numeral 67 denotes a high-frequency transmission circuit unit serving as a power supply unit (power supply unit), which can generate a high frequency of 20 kHz to 500 kHz by a switching power supply. The exciting coil 63 generates an alternating magnetic flux by an alternating current (high-frequency current) supplied from the power supply unit 67.

  Reference numerals 61a and 61b denote belt guide members of a substantially semi-arc-shaped trough-shaped cross section, each of which has an opening side facing each other to form a substantially cylindrical body, and a fixing belt (fixing sleeve) which is a cylindrical electromagnetically inductive heating belt on the outside. , First rotating body) 20 is loosely fitted to the outside. The belt guide member 61a holds a magnetic core 62a, 62b, 62c as a magnetic field generating means and an exciting coil 63 inside. Further, a sliding member 65 is provided inside the fixing belt 20 on the belt guide member 61 a on the side of the nip portion 27 facing the pressure roller 22.

  Reference numeral 64 denotes a horizontally long pressing rigid stay which is disposed in contact with the inner flat surface of the belt guide member 61b.

  Reference numeral 66 denotes an insulating member for insulating the magnetic cores 62a, 62b, and 62c and the exciting coil 63 from the rigid pressing stay 64.

  The pressing rigid stay 64 exerts a pressing force by a pressing mechanism (not shown). As a result, the sliding member 65 on the lower surface of the belt guide member 61a and the pressure roller 22 are pressed against each other with the fixing belt 20 interposed therebetween to form the fixing nip portion 27 having a predetermined width.

  The pressure roller 22 is driven to rotate in a counterclockwise direction indicated by an arrow by a driving unit (not shown). A rotational force acts on the fixing belt 20 by a frictional force between the pressing roller 22 and the outer surface of the fixing belt 20 due to the rotational driving of the pressing roller 22, and the inner surface of the fixing belt 20 slides at the fixing nip 27. While being in close contact with the lower surface of the pressure roller 65, the belt guide members 61a and 61b rotate in a clockwise direction indicated by an arrow at a peripheral speed substantially corresponding to the rotational peripheral speed of the pressure roller 22. In this case, in order to reduce the mutual sliding frictional force between the lower surface of the sliding member 65 and the inner surface of the fixing belt 20 in the fixing nip portion 27, the lower surface of the sliding member 65 of the fixing nip portion 27 and the inner surface of the fixing belt 20 are reduced. A lubricant such as heat-resistant grease can be interposed therebetween.

  The alternating magnetic flux guided to the magnetic cores 62a, 62b, and 62c is generated between the magnetic cores 62a and 62b and between the magnetic cores 62a and 62c by an electromagnetic induction heating layer as a heating element of the fixing belt 20. An eddy current is generated (not shown). This eddy current generates Joule heat (eddy current loss) in the electromagnetic induction heating layer due to the specific resistance of the electromagnetic induction heating layer in the fixing belt 20 described later. Here, the heating area is defined as an area where the heating value is Q / e or more, where Q is the maximum heating value. This is an area where a heat value required for fixing can be obtained.

  In the fixing device of the electromagnetic induction heating type shown in the present embodiment, the fixing belt 20 used here includes a heating layer (not shown) made of a metal belt or the like serving as a base layer of the fixing belt 20 having the electromagnetic induction heat generation. , An elastic layer (not shown) laminated on its outer surface, and a release layer (not shown) laminated on its outer surface. A primer layer (not shown) may be provided between each layer for adhesion between the heat generating layer and the elastic layer and for adhesion between the elastic layer and the release layer. In the fixing belt 20 having a substantially cylindrical shape, the heat generation layer is on the inner surface side, and the release layer is on the outer surface side. As described above, when the alternating magnetic flux acts on the heat generating layer, an eddy current is generated in the heat generating layer, and the heat generating layer generates heat. The heat heats the fixing nip portion 27 via the elastic layer and the release layer, and heats the recording material P as a material to be heated passed through the fixing nip portion 27, thereby performing the heat fixing of the toner image. .

  The temperature of the fixing belt 20 is controlled such that a predetermined temperature is maintained by controlling the current supply to the exciting coil 63 by the temperature control systems 21 and 67 including the main thermistor 18 and the sub thermistor 19 as temperature detecting means. Is adjusted. That is, the main thermistor 18 is a temperature detecting means for detecting the temperature of the fixing belt 20. In this embodiment, the main thermistor 18 is exposed to the heat generating region H on the inner surface of the fixing belt 20 on the outer surface of the belt guide member 61a. It is arranged. The main thermistor 18 contacts the inner surface of the fixing belt 20 and detects the temperature of the fixing belt 20. Temperature information of the fixing belt 20 measured by the main thermistor 18 is input to the control circuit CPU21. The control circuit CPU 21 controls the current supply from the power supply unit 67 to the exciting coil 63 based on the input temperature information, and adjusts the temperature of the fixing belt 20, that is, the temperature of the fixing nip 27 to a predetermined temperature.

  Thus, the fixing belt 20 is rotated, and the power is supplied from the power supply unit 67 to the excitation coil 63, so that the electromagnetic induction heat of the fixing belt 20 is generated as described above, and the fixing nip 27 rises to a predetermined temperature to control the temperature. In this state, the recording material P, on which the unfixed toner image t conveyed from the image forming unit is formed, has an image surface facing upward between the fixing belt 20 and the pressure roller 22 of the fixing nip portion 27, that is, is fixed. The fixing nip 27 is conveyed in such a manner that the image is brought into close contact with the outer surface of the fixing belt 20 in the fixing nip 27 and the fixing nip 27 is conveyed together with the fixing belt 20. In the process in which the recording material P is nipped and conveyed through the fixing nip portion 27 together with the fixing belt 20, the unfixed toner image t on the recording material P is heated and fixed by electromagnetic induction heating of the fixing belt 20. After passing through the fixing nip portion 27, the recording material P is separated from the outer surface of the fixing belt 20 and is discharged and conveyed. After passing through the fixing nip, the heat-fixed toner image on the recording material is cooled to become a permanent fixed image.

  Similarly, in the fixing device using the electromagnetic induction heating method described above, the temperature rise of the heated fixing belt 20 is measured from the detected temperature of the main thermistor 18 in contact with the fixing belt 20, so that the exciting coil 63 Of the maximum power supply to the system. Similarly to the fixing device described in the present embodiment, the time T (msec) required for the detected temperature of the main thermistor 18 to rise from 90 ° C. to 130 ° C. is assumed to be the maximum supply power E (W). Can be expressed by the following equation.

E = 1900−0.62 + 0.000086 × T2 (6)
FIG. 12 shows the result of comparison between the above-mentioned prediction formula and actual measurement values. As described above, even in a fixing device different from the fixing device described in the present embodiment, the measured value and the expected expression (6) are in good agreement, and by using the present embodiment, the maximum supply power can be determined with high accuracy. I understand.

  FIG. 20 is a flowchart illustrating a method for estimating the maximum supply power input to the fixing device according to the present exemplary embodiment. By using the detected temperature of the main thermistor in this manner, the maximum supply power can be obtained with high accuracy. Here, as in the second embodiment, as the temperature range for measuring the time of the rise and rise curve, the most preferable condition in which the detection temperature of the main thermistor 18 is 90 ° C. to 130 ° C. is used. However, it is preferable to use any temperature range of 70 ° C. or more and 150 ° C. or less as in the second embodiment, and it is not always necessary to use the temperature within the range.

  In this manner, the control power at the time of the temperature control can be corrected from the predicted value of the maximum supply power to the excitation coil 63.

  Of course, it is needless to say that the same effect can be obtained by the same principle even when a method different from the two types of fixing devices shown here is used.

  As described above, in the present embodiment, even when a so-called electromagnetic induction heating type fixing device is used as a fixing device different from the fixing devices described in the first, second and third embodiments, the maximum supply in the present embodiment is also possible. A power prediction method can be applied, and the maximum supply power value to the excitation coil 63 can be predicted, and the control power at the time of temperature control can be corrected from the predicted value. As a result, overshoot / undershoot can be prevented irrespective of the variation of the input voltage, and stable temperature control can be performed even at the time of startup or at the start of sheet passing.

<Others>
1) As described above, in each of the above-described embodiments, the process speed is 87 mm / sec, the print speed is 16 sheets / min, the temperature control temperature is 195 ° C. It was described as about 0.3 seconds to about 0.7 seconds (or about 0.5 seconds) before. However, depending on the type of recording material and the image quality of the image to be obtained, or depending on conditions such as obtaining better fixing properties, it may be better to set the process speed, print speed, and temperature control temperature differently. Can be Even in such a case, by applying the method of the present invention, it is possible to perform accurate temperature control with small temperature fluctuation, and the same effect can be obtained. At this time, it goes without saying that the value of the predetermined power to be corrected and the input time of the predetermined power are different depending on the process speed, the printing speed, and the regulated temperature. The same applies to the timing of switching to the second power after startup and the time for supplying the second power.

  2) In each of the above-described embodiments, the maximum supply power was predicted from the measured heating time using a prediction formula. This is used to refer to the maximum supply power using a simple control algorithm. Therefore, other methods, for example, the relationship between the heating time and the maximum supply power may be predicted using a table or the like experimentally obtained, and the same effect can be obtained.

3) In each of the above-described embodiments, the maximum power supply was estimated from the heating time measured by the main thermistor and the sub thermistor. This is because the present invention is applied to a simple configuration at a low cost without adding a complicated configuration and control by utilizing the functions of the image forming apparatus. Therefore, the current detection unit and the voltage detection unit may be actually provided in the fixing device to directly measure and correct the maximum supply power. In this case, since the time for measuring the maximum supply power is short, there is an advantage that it can be instantaneously reflected in the power control. The power supplied to the fixing heater 16 as the current I (A) or the voltage V (V) measured by the current detecting means or the voltage detecting means is E = I × V = I ² × R = V ² / R ... (7)
Is represented by When both the current detecting means and the voltage detecting means are provided, accurate power can be measured, so that the predetermined power can be accurately corrected. When only one of them is provided, the variation of the fixing heater 16 is about 7%, which is an error when the power value is calculated as it is from the equation (7), but the resistance value of the fixing heater is measured in advance. It is also possible to calculate by putting.

  4) In each of the above-described embodiments, a case has been described in which PID control is basically used as power control for performing temperature control. This is used as a control method that quickly approaches the target temperature and is strong against disturbance. Therefore, temperature control can be performed by using P control, PI control, or other feedback control, and the same effect can be obtained.

5) In each of the above-described embodiments, the fixing belt 20 has a heat capacity of at least 4.2 × 10 ⁻² J / cm ² · ° C. or more and 4.2 J / cm ² · ° C. Explained. This is because when the heat capacity of the fixing belt 20 is equal to or higher than 4.2 × 10 ⁻² J / cm ² · ° C., the temperature of the temperature detecting portion of the main thermistor 18 is close to the temperature of the fixing nip position. When the heat capacity of the fixing belt 20 is 4.2 J / cm ² · ° C. or less, it is more effective to correct the power in accordance with the entry timing of the recording material P because the response is good. Therefore, when the heat capacity of the fixing belt 20 is equal to or higher than 4.2 × 10 ⁻² J / cm ² · ° C. and 4.2 J / cm ² · ° C., the exceptional effect is obtained by applying the present invention. For this reason, the present invention can be applied to a fixing device having a fixing belt having a heat capacity outside the range, and the same effect can be obtained.

  6) In each of the above-described embodiments, as a method for predicting the maximum supply power input to the fixing device, full power (100%) is supplied during the temperature control during startup, and detected by the main thermistor 18 or the sub thermistor 19. The method of measuring the heating rate to be performed has been described. This is to ensure higher on-demand performance by using full power. Therefore, the present invention can be applied to a method of supplying power of 75%, 50%, or the like, and measuring the temperature rising rate detected by the main thermistor 18 or the sub thermistor 19, and the same effect can be obtained. can get.

  7) In the fourth embodiment, the case where the temperature rising rate detected by the main thermistor 18 in the heat generation region H is detected has been described. This is to prevent the accuracy from slightly lowering due to the variation in the fixing device as compared with the case where the heating rate detected by the sub thermistor 19 is used outside the heating region H, for example. Therefore, by measuring the heating rate using the sub thermistor 19 outside the heat generation region H, the maximum supply power can be predicted, and the same effect can be obtained.

  8) Also, the fixing device in which the fixing belt 20 is provided with the elastic layer has been described. This is because a fixing device provided with an elastic layer was used because a higher color image quality can be obtained, and the present invention is applied to a fixing device having a fixing belt without an elastic layer such as a metal belt. And the same effect can be obtained.

  9) The fixing device using a ceramic heater having a resistance heating element formed on a ceramic substrate as a heating element and the fixing device using an electromagnetic induction heating method have been described. This is because it is used as a heating element of a low-cost on-demand fixing device for color, and is also used for a fixing device using a halogen lamp as a heating member or a fixing device using an electromagnetic induction heating method in a form different from the illustrated example. The same effect can be obtained.

  10) The first and second fixing members for forming the fixing nip are not limited to the fixing belt and the pressure roller of the embodiment. It is also possible to provide an apparatus in which both the first and second fixing members are provided with a heating element (heat source).

  11) The heating element does not necessarily have to be located in the fixing nip 27. For example, the heat source may be disposed at a position upstream of the fixing nip portion 27 in the fixing belt moving direction.

  12) The fixing device of the embodiment is a driving device for a rotary body for pressurization, but may be a device of a type in which a driving roller is provided on the inner peripheral surface of an endless fixing belt and the fixing belt is driven while applying tension.

  13) In the present invention, the fixing device includes not only a fixing device that heat-fixes an unfixed image on a recording material as a permanent image, but also an image heating device that tentatively fixes an unfixed image on a recording material, and a recording device that carries an image. An image heating apparatus for improving the image surface properties such as gloss by reheating the material is also included.

  14) The image forming method of the image forming apparatus is not limited to the electrophotographic method, and may be an electrostatic recording method, a magnetic recording method, or the like, or may be a transfer method or a direct method.

  Although various examples and embodiments of the present invention have been shown and described, those skilled in the art will appreciate that the spirit and scope of the present invention is not limited to the specific description and figures herein. It will be appreciated that various modifications and changes are set forth which are all set forth in the following claims.

Schematic configuration diagram of a color image forming apparatus according to an embodiment of the present invention. Sectional schematic view of a fixing device according to the first or second embodiment of the present invention. FIG. 4 is a perspective model view showing a positional relationship among a fixing heater, a main thermistor, and a sub thermistor in the first to third embodiments of the present invention. Schematic configuration of ceramic heater as heating element 4 is a graph showing the relationship between the sub-thermistor heating rate and the supplied power when the fixing device according to the first embodiment of the present invention is used. FIG. 4 is a graph of a detected temperature change of the main / sub thermistor when the startup temperature control is performed using the fixing device according to the first embodiment of the present invention. Graph of detected temperature change of main / sub thermistor when startup temperature control is performed using conventional fixing device FIG. 6 is a graph of a change in output power factor when the temperature is controlled by using the fixing device according to the first embodiment of the present invention. Graph of change in output power rate when startup temperature control is performed using a conventional fixing device 7 is a graph showing the relationship between the main thermistor heating rate and the supplied power when the fixing device according to the second embodiment of the present invention is used. Graph showing the relationship between the main thermistor heating rate and applied power when the present invention is applied to a fixing device of an electromagnetic induction heating type 7 is a graph showing the relationship between the sub-thermistor heating rate and the supplied power when the fixing device according to the third embodiment of the present invention is used. Cross-sectional schematic diagram of an electromagnetic induction heating type fixing device Sectional schematic diagram of a conventional belt fixing type fixing device Cross-sectional schematic diagram of a fixing device using a thermistor of a fixing belt inner surface contact type in a conventional belt fixing method. Flowchart of a method for estimating the maximum supply power input to the fixing device according to the first embodiment of the present invention 5 is a flowchart illustrating a method for controlling the temperature of the fixing device according to the first embodiment of the present invention. Flowchart of a method for estimating the maximum power supplied to the fixing device according to the second embodiment of the present invention Flowchart of a method for estimating the maximum power supplied to the fixing device according to the third embodiment of the present invention 4 is a flowchart illustrating a method for estimating a maximum supply power input to a fixing device according to a fourth embodiment of the present invention.

Explanation of reference numerals

1M, 1C, 1Y, 1Bk Image forming units 2a, 2b, 2c, 2d Photosensitive drums 3a, 3b, 3c, 3d Charging rollers 4a, 4b, 4c, 4d Developing devices 5a, 5b, 5c, 5d Transfer rollers 6a, 6b, 6c, 6d Drum cleaning device 12 Fixing device 16 Ceramic heater (heating body)
18 Main thermistor (first temperature detecting means)
19 Sub thermistor (first temperature detecting means)
20 Fixing belt (first rotating body)
21 CPU (power control unit)
22 Pressure roller (second rotating body)
28 Power supply (power supply unit)
Reference Signs List 40 intermediate transfer belt 44 secondary transfer roller 45 belt cleaning device 46 registration roller 50 environment sensor 51 media sensor P recording material N (primary) transfer unit M (secondary) transfer unit t toner

Claims (15)

At least a heating element, a power supply unit for supplying electric power to the heating element, at least one or more temperature detecting means, a first rotating element that moves together with the recording material, and a pressure contact part with the recording material are formed. And a second rotating body that conveys the recording material, and by feedback-controlling the power supplied from the power supply unit to the heating body based on the temperature detected by the temperature detecting unit. In a fixing device that controls the temperature of the first rotating body, and heats the recording material holding the image in the press-contact portion while nipping and conveying the recording material.
The power required for heating supplied to the heating element is corrected by a predetermined power substantially equal to a power value required for stable operation of the fixing device,
When the predetermined power is output, the power supply to the heating element is controlled based on the maximum power supply value to the fixing device. An endless first rotating body,
A second rotator pressed against the first rotator, wherein the second rotator causes the recording material bearing the image to be nipped and conveyed by the pressed portions of the first and second rotators;
Temperature increasing means for increasing the temperature of a local portion of the first rotating body by receiving power supply;
Temperature detection means for detecting the temperature at a position different from the pressure contact portion with respect to the rotation direction of the first rotating body,
Based on the temperature detected by the temperature detecting means, the first control means for performing feedback control of the power supplied to the temperature increasing means,
Setting means for variably setting a set value corresponding to electric power to be supplied to the temperature increasing means, based on a temperature increase rate detected by the temperature detecting means when energized at a predetermined energization amount;
When the fixing device is started up, in the vicinity of the timing when the temperature detected by the temperature detecting means reaches the target temperature or in the vicinity of the timing when the recording material enters the pressure contact portion, the electric power according to the set value set by the setting means. And a second control means for temporarily supplying the temperature control means to the temperature increasing means.   In the first rotating body, V is the moving speed of the outer circumference of the rotating body, a is the length from the pressure contact portion to the temperature detection position, and L is the outer circumferential length of the first rotating body. 3. The fixing device according to claim 2, wherein the time t in which is performed is represented by t ≦ (a + L) / V.   The said temperature rise means is provided near the pressure contact part, It has the heater which produces | generates heat by energization, or has a coil which generates an eddy current in the said 1st rotating body by generating a magnetic field by energization. Item 4. The fixing device according to item 2 or 3.   A non-volatile memory for storing a value corresponding to a temperature rising rate detected by the temperature detecting means when the predetermined amount of current is supplied, and a set value set by the setting means. 4. The fixing device according to 2 or 3.   An image forming apparatus for forming an image on a recording material and fixing the image on the recording material using the fixing device according to any one of claims 1 to 5.   Further, the image forming apparatus further includes first determining means for determining a heat storage condition of the fixing device, wherein the setting means detects a result of the determination by the first determining means and detects the temperature by the temperature detecting means when a predetermined amount of power is supplied. 4. The fixing device according to claim 2, wherein a set value corresponding to power to be supplied to the temperature raising unit is variably set based on the temperature rising speed.   The apparatus further includes a second determination unit configured to determine a type of the recording material, wherein the setting unit detects a result of the determination by the second determination unit and detects the temperature by the temperature detection unit when a predetermined amount of power is supplied. The fixing device according to claim 2, wherein a set value corresponding to power to be supplied to the temperature increasing unit is variably set based on the temperature increasing speed. An endless first rotating body,
A second rotator pressed against the first rotator, wherein the second rotator causes the recording material bearing the image to be nipped and conveyed by the pressed portions of the first and second rotators;
Temperature increasing means for increasing the temperature of a local portion of the first rotating body by receiving power supply;
A first temperature detection unit that detects a temperature at a position different from the pressure contact portion with respect to a rotation direction of the first rotating body,
Second temperature detecting means provided near the pressure contact portion,
Based on the temperature detected by the first temperature detecting means, first control means for feedback controlling the power supplied to the temperature increasing means,
Setting means for variably setting a set value corresponding to electric power to be supplied to the temperature increasing means based on a temperature increasing rate detected by the second temperature detecting means when energized at a predetermined energizing amount,
When the fixing device is started up, in the vicinity of the timing when the temperature detected by the temperature detecting means reaches the target temperature or in the vicinity of the timing when the recording material enters the pressure contact portion, the electric power according to the set value set by the setting means. And a second control means for temporarily supplying the temperature control means to the temperature increasing means.   In the first rotating body, V is the moving speed of the outer circumference of the rotating body, a is the length from the pressure contact portion to the temperature detection position, and L is the outer circumferential length of the first rotating body. 10. The fixing device according to claim 9, wherein a time t in which is performed is represented by t ≦ (a + L) / V.   The said temperature rise means is provided near the pressure contact part, It has the heater which produces | generates heat by energization, or has a coil which generates an eddy current in the said 1st rotating body by generating a magnetic field by energization. Item 11. The fixing device according to item 9 or 10.   The fixing device according to claim 9, further comprising a non-volatile memory that stores a set value set by the setting unit.   An image forming apparatus for forming an image on a recording material and fixing the image on the recording material using the fixing device according to any one of claims 9 to 12.   Further, the image forming apparatus further includes first determining means for determining a heat storage condition of the fixing device, wherein the setting means detects a result of the determination by the first determining means and detects the temperature by the temperature detecting means when a predetermined amount of power is supplied. The fixing device according to claim 9, wherein a setting value corresponding to power to be supplied to the temperature increasing unit is variably set based on the temperature increasing speed.   The apparatus further includes a second determination unit configured to determine a type of the recording material, wherein the setting unit detects a result of the determination by the second determination unit and detects the temperature by the temperature detection unit when a predetermined amount of power is supplied. 11. The fixing device according to claim 9, wherein a setting value corresponding to electric power to be supplied to the temperature increasing unit is variably set based on the temperature increasing speed.

Images