JP2009192720A - Fixing device and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of rapidly following up change of a target temperature and reducing temperature ripple, and an image forming apparatus using the same. <P>SOLUTION: The fixing device includes a fixing belt 60 having a heating heater 62H, a pressure roller 63 coming into contact with the fixing belt 60 to form a fixing nip N between the fixing belt and the pressure roller, a thermistor 65 detecting temperature of the fixing belt 60, and a control part 66 controlling heating amount of the heating heater 62H based on the target temperature set as a target when controlling the heating amount of the heating heater 62H and detection temperature that is a result of detection by the thermistor 65, and fixes a toner image on paper with heat and pressure by making the paper pass through the fixing nip N. In the fixing device, the control means 66 switches a control condition among at the rising time, at the printing initial time, at the time when the target temperature is not changed in the midst of printing, and at the time when a predetermined number of sheets are printed after the target temperature is changed in the midst of printing. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing device that fixes a toner image on a recording medium to the recording medium by heat and pressure, and an image forming apparatus including the fixing device.

  2. Description of the Related Art Conventionally, an image forming apparatus using dry toner is provided with a heat fixing device that fixes an unfixed toner image formed on a sheet serving as a recording medium on the sheet by heating and pressing. The thermal fixing device includes a fixing member having a surface endlessly moved and having a heating means such as a heater, and a pressure member that has a surface endlessly moved and contacts the fixing member to form a fixing nip with the fixing member. The fixing operation is realized by passing the sheet through the fixing nip. In order to fix a toner image onto a sheet without impairing image quality in such a thermal fixing device, it is necessary to keep the temperature of a fixing member that supplies heat to the toner image at a fixing nip constant at a target temperature. . If the temperature is too high or too low than the target, there is a risk of inducing an image failure called offset or fixing failure. Therefore, it is important to maintain the temperature of the fixing member at a temperature suitable for fixing.

  As a method for controlling the temperature of the fixing member of the fixing device, a fixing temperature detecting means for detecting the temperature of the fixing member is provided, and heating is performed based on the detected temperature of the fixing temperature detecting means and a target temperature that is a target for temperature control. There is one that determines the heating amount of the means and controls the operation amount (heater duty) to the heating means. Usually, the target temperature is a desired temperature at a detection position determined so that the temperature at the fixing nip of the fixing member becomes a temperature suitable for fixing.

  On-off control and table control are known as operation amount control for the heating means of the fixing member. In the on / off control, when the detected temperature falls below the target temperature, the operation to the heating unit is turned on (energization is performed at a heater duty of 100%), and when the detected temperature exceeds the target temperature, the operation to the heating unit is turned off. However, this on / off control can be used for temperature control during standby because of a large temperature ripple, but is difficult to use for temperature control during printing. Table control prepares a table that defines the amount of operation to the heating means against the difference (deviation) between the target temperature and the detected temperature, and the difference from the previous detected temperature, and temperature control is based on that table. Is to do. In the table control, it is necessary to prepare and switch a plurality of tables in accordance with situations such as warm-up operation, standby operation, and printing operation. However, in table control, the capacity of the control unit must be increased in order to determine the heater duty for each table, and the number of evaluations for determining the heater duty in accordance with each table increases.

  Also known are PID control that performs P (Proportion) control, I (Integral) control, D (Differential) control, and the like. PID control consists of a proportional operation that produces an output proportional to the difference (deviation) between the target temperature and the detected temperature, an integral operation that produces an output proportional to the integral of the deviation, and a differential that produces an output proportional to the differential of the deviation. The operation amount to the heating means is determined by combining the operations. For example, the fixing devices described in Patent Documents 1 and 2 calculate and output the operation amount to the heating unit by PID control so that the detected temperature becomes the target temperature. In this PID control, the amount of operation to the heating means is calculated and output so that the detected temperature becomes the target temperature, and control to reduce the deviation between the target temperature and the detected temperature is performed. Can be maintained at a temperature close to the target temperature.

JP 2002-296554 A JP 2007-178968 A

  Incidentally, in the fixing device, the target temperature may be changed during printing for the following reason. When a large number of sheets are continuously printed, the temperature at the end portion in the axial direction of the fixing member tends to increase. As the number of continuous prints on a sheet having a small axial length increases, the temperature rise at the axial end of the fixing member becomes more conspicuous. In the axially central portion of the fixing member, which is a paper passing area where the fixing member and the paper are in contact with each other, the amount of heat supplied to the fixing member is consumed by the paper, whereas the fixing member and the paper are not in contact with each other. This is because there is no sheet that consumes heat supplied to the fixing member at the axial end of the fixing member, which is the area. An increase in the temperature at the axial end of the fixing member may deteriorate the fixing member such as a fixing belt and cause a fixing failure. Therefore, when the axial end of the fixing member exceeds a predetermined temperature, the target temperature is lowered within a range where the temperature at the fixing nip is a temperature suitable for fixing.

  Japanese Patent Application Laid-Open No. 2004-151561 shows a method of switching control gains at the initial stage and thereafter in each section between papers and between papers, and also shows an example of changing the target temperature between paper passing and papers. However, the responsiveness of the fixing temperature detection means is highly responsive in order to switch the control gain in the initial stage between the paper passing part and the paper and thereafter, or to switch the target temperature between the paper passing part and the paper, The system must have a low printing speed and a high thermal response of the fixing device. Therefore, in the system shown in Patent Document 1, in the case of a system in which the responsiveness of the fixing temperature detecting means is low, the printing speed is high, and the thermal responsiveness of the English deposition apparatus is low, the actual temperature is higher than the target temperature However, there is a risk that temperature ripples such as overshoots that fall off and undershoots that fall below are increased.

  Patent Document 2 shows an example in which when the target temperature of the fixing member is lowered, the target temperature is changed into a ramp shape instead of a step shape by setting the target temperature in a plurality of stages. By adopting such a configuration, a configuration is shown in which the temperature followability is increased to prevent undershoot. However, the target temperature is lowered in a ramp shape over time, so that the axial end temperature of the fixing member is reduced. There is a possibility that it is not possible to cope with a condition where the target temperature needs to be lowered immediately, such as when the temperature rises.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a fixing device that can quickly follow a target temperature change and reduce temperature ripple, and an image forming apparatus using the same. Is to provide.

請求項５の発明は、請求項１、２、３又は４の定着装置において、上記定着部材は、複数の張架部材に張架される定着ベルトであることを特徴とするものである。
請求項６の発明は、像担持体と、該像担持体上に潜像を形成する潜像形成手段と、該像担持体上の潜像を現像しトナー像を形成する現像手段と、該像担持体上のトナー像を転写材上に転写する転写手段と、該転写手段により転写材に転写されたトナー像を定着する定着手段とを備える画像形成装置において、上記定着手段として、請求項１、２、３、４又は５の定着装置を用いることを特徴とするものである。
請求項１乃至５の定着装置において、立ち上げ動作時には、室温から大きな偏差のある目標温度に向けて高い応答性で昇温することが求められる。また、印字初期動作には、目標温度に速やかに近づき、温度の振動的な挙動を減衰させることが求められる。目標温度変更無しの印字動作時には、目標温度近くにきた条件で目標温度周辺を維持しつつ、且つ温度リップルを低減させることが求められる。印字中の目標温度変更から所定枚数の印字動作までは、目標温度に速やかに追従させる必要があり、且つ温度リップルを低減させることが求められる。定着装置の制御部は、これらの各動作の要求に対して適正な制御条件に切り替えて温度制御を行う。例えば、ＰＩＤ制御による温度制御では、数１式で示される定数の比例ゲインＫＰ、積分ゲインＫＩ、微分ゲインＫＤを上記４種類の動作に応じて設定することで、加熱手段の加熱量を制御している。これにより、立ち上げ時及び印字中において、定着部材の温度を目標温度変化に速やかに追従させ、温度リップルを低減させる。 In order to achieve the above object, the invention of claim 1 is characterized in that the surface of the fixing member is moved endlessly and has heating means, and the surface of the fixing member is moved endlessly and comes into contact with the fixing member to fix between the fixing member. The pressure member forming the nip, the fixing temperature detecting means for detecting the temperature of the fixing member, the target temperature for controlling the heating amount of the heating means, and the detection result of the fixing temperature detecting means. Control means for controlling the heating amount of the heating means on the basis of the detected temperature, allowing the recording medium to pass through the fixing nip, and fixing the toner image on the recording medium to the recording medium by heat and pressure. In the fixing device, the control means controls at the time of start-up, at the time of initial printing, when the target temperature is not changed during printing, and when a predetermined number of sheets are printed from when the target temperature is changed during printing. Features switching conditions Is shall.
According to a second aspect of the present invention, in the fixing device of the first aspect, the control means uses the detected temperature and the target temperature to set the detected temperature at the detection position of the fixing member as the target temperature. A calculation output means for calculating and outputting a suitable heating amount is provided, and the heating amount of the heating means is controlled based on the output value of the calculation output means.
According to a third aspect of the present invention, in the fixing device according to the second aspect, the calculation output means performs calculation output by PID control.
According to a fourth aspect of the present invention, in the fixing device according to the third aspect, the control unit changes the constants KP (proportional gain), KI (integral gain), and KD (differential gain) expressed by equation (1). Is characterized by switching.

According to a fifth aspect of the present invention, in the fixing device according to the first, second, third, or fourth aspect, the fixing member is a fixing belt stretched around a plurality of stretch members.
According to a sixth aspect of the present invention, there is provided an image carrier, a latent image forming unit for forming a latent image on the image carrier, a developing unit for developing the latent image on the image carrier to form a toner image, An image forming apparatus comprising: a transfer unit that transfers a toner image on an image carrier onto a transfer material; and a fixing unit that fixes the toner image transferred to the transfer material by the transfer unit. 1, 2, 3, 4 or 5 fixing devices are used.
In the fixing device according to any one of claims 1 to 5, during the start-up operation, it is required to raise the temperature with high responsiveness toward a target temperature having a large deviation from room temperature. The initial printing operation is required to quickly approach the target temperature and attenuate the vibrational behavior of the temperature. At the time of printing operation without changing the target temperature, it is required to reduce the temperature ripple while maintaining the vicinity of the target temperature under the condition that the temperature is close to the target temperature. From the change in the target temperature during printing to the printing operation for a predetermined number of sheets, it is necessary to quickly follow the target temperature and it is required to reduce the temperature ripple. The control unit of the fixing device performs temperature control by switching to an appropriate control condition in response to the request for each of these operations. For example, in temperature control based on PID control, the heating amount of the heating unit is controlled by setting the constant proportional gain KP, integral gain KI, and differential gain KD shown in Equation 1 according to the above four types of operations. ing. As a result, the temperature of the fixing member quickly follows the target temperature change during start-up and printing, and temperature ripple is reduced.

  According to the present invention, there is an excellent effect that it is possible to provide a fixing device that can quickly follow a target temperature change and reduce temperature ripple, and an image forming apparatus using the same.

  Hereinafter, an embodiment in which the present invention is applied to a printer as an image forming apparatus will be described. First, the configuration and operation of the printer according to this embodiment will be described. FIG. 1 is a schematic configuration diagram showing the overall configuration of the printer according to the present embodiment. The printer includes a drum-shaped photosensitive member 1 as an image carrier that rotates in the direction of arrow A in the drawing. Around the photoconductor 1, a scorotron charging device 2 as a charging means for uniformly charging the surface of the photoconductor 1, and the surface of the charged photoconductor 1 is exposed with exposure light R to form an electrostatic latent image. An exposure device (ROS) 3 as a latent image forming means, a developing device 4 as a developing means for developing toner by attaching toner to the electrostatic latent image, and a toner image on the photoreceptor 1 obtained by development as a recording medium. Transfer device 5 as a transfer means for transferring onto the sheet P of paper, a cleaning device 8 as a cleaning means for cleaning the transfer residual toner on the surface of the photoreceptor 1, and a charge eliminating device 9 for removing residual charges on the surface of the photoreceptor 1. Are arranged in this order. Further, a fixing device 6 as a fixing unit is disposed downstream of the transfer device 5 in the sheet conveyance direction. A sheet tray 7 for storing a plurality of sheets P in a stacked manner is disposed below the photoreceptor 1.

  In the printer having the above-described configuration, first, an original image signal read from a document by an image reading unit (not shown) or an original image signal created by an external computer (not shown) is input to an image processing unit (not shown) to obtain an appropriate image. Processing is performed. The input image signal obtained in this way is input to the exposure apparatus 3 to modulate the exposure light R. The exposure light R modulated by the input image signal is raster-irradiated on the surface of the photoconductor 1 uniformly charged by the scorotron charging device 2. When the exposure light R is irradiated on the surface of the photoconductor 1 by raster irradiation, an electrostatic latent image corresponding to the input image signal is formed on the photoconductor 1. The electrostatic latent image formed on the photoreceptor 1 is developed with toner by the developing device 4 to form a toner image on the photoreceptor 1. The toner image formed on the photoconductor 1 is conveyed toward a transfer device 5 disposed facing the photoconductor 1 as the photoconductor 1 rotates in the direction of arrow A. On the other hand, the paper P stored in the paper tray 7 is conveyed toward the transfer nip portion between the photoconductor 1 and the transfer device 5, and the toner image on the photoconductor 1 is transferred onto the paper P by the transfer device 5. Is done. The toner image transferred onto the paper P is conveyed and fixed by the fixing device 6 to obtain a desired image. Deposits such as transfer residual toner remaining on the surface of the photoreceptor 1 after the transfer of the toner image to the paper P is cleaned by the cleaning device 8. Further, the residual charge on the surface of the photosensitive member 1 is removed by the static eliminator 9, and one image forming operation is completed.

  Next, the fixing device 6 will be described in detail. FIG. 2 is a configuration diagram illustrating a configuration of the fixing device according to the present exemplary embodiment. As shown in FIG. 2, in the fixing device 6, a fixing belt 60 as a fixing member is stretched between a fixing roller 61 and a heating roller 62 as a heating unit. The fixing roller 61 is rotationally driven by a drive source (not shown), and the fixing belt 60 moves endlessly in the direction of arrow B in the figure, whereby the heating roller 62 is driven to rotate. In order to give an appropriate predetermined tension to the fixing belt 60, the heating roller 62 is urged in a direction to be separated from the fixing roller 61 by an urging means (not shown) such as a spring. Further, a pressure roller 63 is disposed as a pressure member that forms a fixing nip N in contact with the fixing roller 61 with the fixing belt 60 interposed therebetween at a position facing the fixing roller 61. The pressure roller 63 is rotationally driven in the direction of arrow C in the figure by a drive source identical to that of the fixing roller 61 via a gear (not shown) and pressurizes the fixing roller 61 with an appropriate pressing force by an urging means (not shown). . Further, the fixing device 6 is provided with a guide member 64 and the like for guiding the sheet toward the fixing nip N. A thermistor 65 that is a fixing temperature detecting means for detecting the surface temperature of the fixing belt 60 is disposed in the vicinity of the stretched portion of the fixing belt 60 between the fixing roller 61 and the heating roller 62.

  The fixing belt 60 includes, for example, a base layer made of polyimide resin or the like, an elastic layer made of silicon rubber provided on the base layer, and tetrafluoroethylene / perfluoroalkyl vinyl ether provided on the elastic layer. A multilayer structure belt having a polymer (FPA), a surface layer made of a fluororesin such as PFA (perfluoroalkoxy fluororesin) or polytetrafluoroethylene (PFTE) can be used. The fixing roller 61 and the pressure roller 63 include a metal cored bar, an elastic layer formed of silicon rubber provided on the surface of the cored bar, and a surface layer formed of a fluororesin laminated on the surface of the elastic layer. It is configured. In this way, the fixing roller 61 having the elastic layer and the pressure roller 63 are in pressure contact with each other via the fixing belt 60, so that the fixing nip portion N that is a contact portion between the fixing belt 60 and the pressure roller 63 is compared. Can be formed widely. The heating roller 62 includes a cored bar portion made of metal and a surface layer made of a fluororesin or the like. As the material of the cored bar portion of the heating roller 62, a material having a small specific heat and a large thermal conductivity is preferably used. Further, the core portion of the heating roller 62 is formed in a hollow shape, and a heater 62H as a heating means is built in the core. The heating roller 62 is heated by the heater 62H, and the fixing belt 61 stretched between the fixing roller 61 and the heating roller 62 is heated.

  The fixing device 6 is provided with a control unit 66 that is a control means for controlling the temperature at the fixing nip N to a temperature suitable for fixing. The controller 66 controls the operation amount of the heater 62H based on the detection result of the thermistor 67 and the target temperature that is a target for the control. Here, the target temperature is a desired temperature at a detection position by the thermistor 65 that is determined such that the temperature at the fixing nip N is a temperature suitable for fixing.

  FIG. 3 is a block diagram of a control unit that performs power supply control to the heater. As shown in FIG. 3, the detection output from the thermistor 65 is transmitted to the control unit 66. And the data of the detection output and target temperature which the control part 66 received are transmitted from the control part 66 to the operation amount calculating part 67 as a calculation output means. The operation amount calculation unit 67 outputs a calculation result for determining the heating amount of the heater 62 </ b> H to the control unit 66 based on the received detection output and the target temperature. Data based on the calculation result is transmitted to a PWM drive circuit (not shown) that controls power supply to the heater 62H, and an operation amount (heater duty) to be a heating amount of the heater 62H is determined.

  Next, the control conditions of the controller 66 that controls the temperature of the fixing belt 60 will be described in detail. FIG. 4 is a characteristic diagram illustrating temperature control of the fixing belt. As shown in FIG. 4, the control unit 66 controls the control condition 1 when the fixing device 6 is started up, the control condition 2 when printing is started (up to M printed sheets), and when the target temperature is not changed during printing (printed sheet number M + 1). The control condition 3 is set for the first and subsequent sheets (the section without the target temperature change), and the control condition 4 is set when the predetermined number of sheets is printed after the target temperature is changed (the section from the target temperature change to the predetermined number of printed sheets P). Switching control conditions. In this embodiment, the target temperature is changed at the initial printing (a predetermined time before the start of printing N sheets) and when a predetermined number of sheets is passed.

The manipulated variable calculation unit 67 according to the present embodiment uses a PID compensator that performs PID control. FIG. 5 is a control gain table used in the operation amount calculation unit according to the present embodiment. In this embodiment, the operation amount to the heater 62H is calculated based on the following equation 1 and PID control according to the control gain table shown in FIG. In the control condition 1, since it is required to increase the temperature with high responsiveness toward the target temperature having a large deviation from the room temperature during the start-up operation, the proportional gain KP and the integral gain KI are set large, and the differential gain KD is set to Set smaller. Under the control condition 2, since it is required to quickly approach the target temperature and attenuate the vibrational behavior of the temperature during the initial printing operation, the proportional gain KP and the differential gain KD are set large, and the integral gain KI is decreased. Set. In the control condition 3, in the printing operation without changing the target temperature, it is necessary to reduce the temperature ripple such as the overshoot and undershoot of the temperature while maintaining the vicinity of the target temperature under the condition that is close to the target temperature by the control condition 2. Therefore, the control gain is set smaller. Since the integral operation may cause a reverse action around the target temperature, the integral gain KI is set to 0, and the proportional gain KP and the differential gain KD are set. In the control condition 4, it is necessary to promptly follow the target temperature in the printing operation of the predetermined number of printed sheets P from the change of the target temperature during printing, and in order to reduce temperature ripples such as temperature overshoot and undershoot, The gain KP is set large and the differential gain KD is set to a small value. Further, in order to approach the target temperature without deviation, the integral gain KI is also set to a small value.

  As described above, the control unit of the fixing device according to the present embodiment is characterized in that four control conditions are prepared and switched at startup and printing. When the target temperature decreases during printing, even if the control condition 3 is maintained as it is, the temperature of the fixing belt does not follow and the control that follows the target temperature cannot be realized. This is because the control condition 3 is suitable for following the target temperature with a small temperature ripple at the target temperature that has already been reached, but not suitable for following the target temperature change.

  FIG. 6 is a characteristic diagram showing temperature transitions of the fixing belt and the pressure roller when the control conditions are switched during printing under the PID control shown in FIG. FIG. 7 is a characteristic diagram showing the temperature transition of the fixing belt and the pressure roller during startup under the PID control shown in FIG. FIG. 8 is a characteristic diagram showing the temperature transition of the fixing belt and the pressure roller when the control condition is not switched during printing. Under the PID control shown in FIG. 6, when the target temperature is lowered during continuous printing of a large number of sheets, the temperature control is performed by switching from the control condition 3 to the control condition 4, and therefore the temperature of the fixing belt (detection value of the thermistor). It can be seen that almost follows the target temperature without undershooting. As a result, even when the target temperature has to be lowered immediately, such as when the temperature of the end portion of the fixing belt 60 has increased, the target temperature can be quickly followed. Further, under the PID control shown in FIG. 7, the start-up operation under the control condition 1 can realize a rapid temperature increase and a small overshoot of the fixing belt. On the other hand, as shown in FIG. 8, when the control condition 3 is maintained as it is even if the target temperature is changed, the temperature of the fixing belt does not follow and decrease even if the target temperature decreases. It can be seen that control to follow the target temperature is not possible.

As described above, according to the fixing device 6 according to the present embodiment, the control unit 66 prepares four types of control conditions during start-up operation and printing, and performs temperature control by switching to control conditions suitable for each operation. The target temperature change can be followed quickly and temperature ripple can be reduced.
In addition, the fixing device 6 according to the present embodiment is an operation amount calculation unit 67 that is a calculation output unit that calculates and outputs a heating amount suitable for setting the temperature detected at the detection position of the fixing belt 60 by the thermistor 65 as the target temperature. And the operation amount to the heater 62H is controlled based on the output value of the operation amount calculation unit 67. Therefore, the operation amount to the heater 62H can be easily determined.
In addition, the fixing device 6 according to the present embodiment uses the PID compensator as the calculation output unit, so that the detected temperature of the fixing belt 60 can be brought close to the target temperature, and appropriate control with little deviation can be performed. .
In addition, the fixing device according to the present embodiment can bring the detected temperature of the fixing belt 60 close to the target temperature by changing the constant of the mathematical formula used for PID control to switch the control condition, and is appropriate with little deviation. Control can be performed.
Further, the fixing device 6 according to the present embodiment can have a structure with a small heat capacity by using the fixing belt 60 as a fixing member, and can realize high responsiveness to temperature control.
In addition, since the printer that is the image forming apparatus according to the present embodiment includes the fixing device 6, it is possible to ensure good fixing quality.
Note that the present invention is not limited to the fixing belt that is the fixing member described in the present embodiment, and may have a configuration using a fixing roller having a heating unit as the fixing member, or another form. . Further, although the pressure roller as the pressure member is used, a belt member or other forms may be used. The heating heater as the heating means heats the fixing belt as a fixing member from the inside, but the position of the heating means may be one that heats the surface from the outside of the fixing member. Instead, other forms such as a pressure member may be provided.
Furthermore, in the present embodiment, a printer having one color toner has been described. However, the present invention can also be applied to a color image forming apparatus that forms a color image by superposing a plurality of color toners on a recording medium.

1 is a schematic configuration diagram illustrating the configuration of an entire printer according to an embodiment. FIG. 2 is a configuration diagram illustrating a configuration of a fixing device of the printer. The block diagram of the control part which performs the electric power supply control to the heater of the fixing device. FIG. 6 is a characteristic diagram illustrating temperature control of a fixing belt of the fixing device. A control gain table used in the control unit of the fixing device. FIG. 6 is a characteristic diagram showing temperature transitions of the fixing belt and the pressure roller when the control conditions are switched during printing. The characteristic view which shows the temperature transition of the fixing belt and pressure roller at the time of starting. FIG. 6 is a characteristic diagram showing temperature transitions of the fixing belt and the pressure roller when the control condition is not switched during printing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 6 Fixing device 60 Fixing belt 61 Fixing roller 62 Heating roller 63 Pressure roller 64 Guide member 65 Thermistor 66 Control part 67 Operation amount calculating part

Claims (6)

A fixing member whose surface moves endlessly and has a heating means;
A pressure member whose surface moves endlessly, contacts the fixing member, and forms a fixing nip with the fixing member;
Fixing temperature detecting means for detecting the temperature of the fixing member;
A control means for controlling the heating amount of the heating means based on a target temperature which is a target for controlling the heating amount of the heating means and a detection temperature which is a detection result of the fixing temperature detection means,
In a fixing device for passing a recording medium through the fixing nip and fixing a toner image on the recording medium to the recording medium by heat and pressure,
The control means switches the control conditions at the time of start-up, at the initial printing, when the target temperature is not changed during printing, and when the target temperature is changed during printing and when a predetermined number of sheets are printed. A fixing device characterized by the above. The fixing device according to claim 1.
The control means includes calculation output means for calculating and outputting a heating amount suitable for setting the detection temperature at the detection position of the fixing member as the target temperature, using the detection temperature and the target temperature, A fixing device that controls a heating amount of the heating unit based on an output value of a calculation output unit. The fixing device according to claim 2.
The fixing device characterized in that the calculation output means performs calculation output by PID control. The fixing device according to claim 3.
The fixing unit is characterized in that the control unit switches the control condition by changing constants KP (proportional gain), KI (integral gain), and KD (differential gain) expressed by the equation (1).

The fixing device according to claim 1, 2, 3 or 4.
The fixing device, wherein the fixing member is a fixing belt stretched around a plurality of stretching members. An image carrier, latent image forming means for forming a latent image on the image carrier, developing means for developing a latent image on the image carrier to form a toner image, and a toner image on the image carrier An image forming apparatus comprising: a transfer unit that transfers the toner image onto the transfer material; and a fixing unit that fixes the toner image transferred to the transfer material by the transfer unit.
An image forming apparatus using the fixing device of claim 1, 2, 3, 4 or 5 as the fixing means.

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