Fixing device and image forming apparatus

A fixing device is disclosed, including: a fixing rotative body, a heat source, and a control part. The control part conducts a printing temperature control which varies an ON ratio per unit time of the heat source based on a detection result of the temperature detecting part to maintain a printing target temperature in a printing state, conducts a waiting temperature control which performs an ON/OFF control based on the detection result of the temperature detecting part to maintain a waiting target temperature in a waiting state after a printing operation ends, and conducts a forcible ON control which forcibly turns on the heat source for a predetermined time before starting the ON/OFF control when the detection result of the temperature detecting part after the printing operation ends is lower than the waiting target temperature.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a fixing device and an image forming apparatus including the fixing device, such as a copier, a printer, or the like using an electro-photographic technology.

2. Description of the Related Art

Conventionally, for example, in an image forming apparatus using an electro-photographic scheme, a toner image is formed on an image carrier, and the toner image is transferred onto a recording medium. After the toner image is transferred, the recording medium is carried to a fixing device, and is heated and pressed by the fixing device, so as to fix the toner image on the recording medium and then eject the recording medium.

In general, as illustrated inFIG. 1, in the fixing device, a fixing belt52is set around a fixing roller53and a heating roller54internally having a heat source55, and the fixing belt52is clipped and pressed by the fixing roller53and a pressure roller51. A paper sheet (recording medium)59is passed through between nip parts of the fixing roller53and the pressure roller51. An entry guide57is provided to guide the paper sheet59to the nip parts at an upstream side above the nip parts formed by the fixing roller53and the pressure roller51, and an output guide58for guiding the paper sheet59from the nip parts to be ejected is provided at a downstream side. That is, the fixing roller53rotates in a direction of an arrow A1and the fixing belt52moves in a direction of an arrow A2. In this case, the pressure roller51contacting and pressing the fixing roller53through the fixing belt52rotates in a direction of an arrow A3. The paper sheet59passes through the nip parts by being guided by the entry guide57in accordance with a direction of an arrow B, and is carried out from the nip parts by being guided by the output guide58.

In the fixing device, it is required to assure a capability of stably fixing an image while maintaining a target heating temperature. Conventionally, a technology has been used to control turning on and off the heat source (heater)55for heating the heating roller54based on a temperature of the fixing belt52detected by a temperature detecting part56. In detail, in a case in which a temperature detected by the temperature detecting part56is lower than a target control temperature being a predetermined value, a duty of turning on electricity for the heat source (heater)55is set to be 100% and the heat source (heater)55is turned on. In a case in which the temperature detected by the temperature detecting part56is higher than the predetermined value, the duty of turning on electricity for the heat source (heater)55is set to be 0% and the heat source (heater)55is turned off. The above-described temperature control scheme is called an on/off control scheme which is disclosed by Japanese Patent No. 3746913.

In the fixing device applying the on/off control scheme, a temperature ripple with respect to a target control temperature becomes greater. Accordingly, Japanese Laid-open Patent Application No. 60-163102 discloses a PID (Proportional, Integral, and Derivative) control for optimizing multiple parameters depending on deviations of a detected temperature and the target control temperature by combining a control algorithm with proportions, integrals, and derivatives. In the PID control, the duty of turning on electricity to a heater (heat source) varies in a range of 0% through 100%.

On the other hand, an object of Japanese Laid-open Patent Application No. 2008-122757 is to make the temperature ripple smaller and stably shorten a rising time. A control technology is disclosed to vary the duty of turning on electricity to be a value calculated by using a detection result of the temperature detecting part based on a predetermined algorithm.

As described in Japanese Laid-open Patent Application No. 2008-122757, in a fixing device using the PID control alone, the temperature ripple becomes smaller. However, since the PID control frequently turns on and off the heater (heat source) even in a waiting state, energy consumption becomes greater than that of the on/off control.

On the contrary, in a case of switching from the on/off control to the PID control after printing, an overshoot becomes greater due to a temperature inside the fixing part after printing, and it takes time to assure the capability of fixing an output image.

In the above-described conventional fixing device, it is difficult to suppress the overshoot when moving to the waiting state after printing, without making the temperature ripple greater.

SUMMARY OF THE INVENTION

The present invention solves or reduces one or more of the above problems.

In an aspect of this disclosure, there is provided a fixing device including a fixing rotative body configured to fix a toner image onto a recording medium by melting the toner image; a heat source configured to heat the fixing rotative body; a control part configured to control the heat source; and a temperature detecting part configured to detect a temperature of the fixing rotative body; wherein the control part is configured to conduct a printing temperature control which varies an ON ratio per unit time of the heat source based on a detection result of the temperature detecting part to maintain a printing target temperature in a printing state, to conduct a waiting temperature control which performs an ON/OFF control based on the detection result of the temperature detecting part to maintain a waiting target temperature in a waiting state after a printing operation ends, and to conduct a forcible ON control which forcibly turns on the heat source for a predetermined time before starting the ON/OFF control when the detection result of the temperature detecting part after the printing operation ends is lower than the waiting target temperature.

Moreover, an image forming apparatus is configured to include the fixing device.

In another aspect of this disclosure, there is provided a fixing device including a fixing rotative body configured to fix a toner image onto a recording medium by melting the toner image; a heat source configured to heat the fixing rotative body; a control part configured to control the heat source; and a temperature detecting part configured to detect a temperature of the fixing rotative body; wherein the control part is configured to conduct a printing temperature control which varies an ON ratio per unit time of the heat source based on a detection result of the temperature detecting part to maintain a printing target temperature in a printing state, to conduct a waiting temperature control which performs an ON/OFF control based on the detection result of the temperature detecting part to maintain a waiting target temperature in a waiting state after a printing operation ends, to conduct a rotation control which rotates the fixing rotative body for a predetermined time without turning on the heat source, and to conduct a forcible ON control which forcibly turns on the heat source for a predetermined time before starting the ON/OFF control when the detection result of the temperature detecting part after stopping a rotation of the fixing rotative body is lower than the waiting target temperature.

Moreover, an image forming apparatus is configured to include the fixing device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A configuration of an image forming apparatus will be described with reference toFIG. 2andFIG. 3.FIG. 2is a schematic diagram illustrating the configuration of the image forming apparatus according to an embodiment.FIG. 3is a schematic diagram illustrating a fixing device according to the embodiment.

A transfer belt device18is arranged at a center in the image forming apparatus100. Imaging devices22K for black,22Y for yellow,22M for magenta, and22C for cyan, which are filled with toner, are arranged at a top surface of the transfer belt device18. In each of the imaging devices22K,22Y,22M, and22C, a photoreceptor19, a charging roller20, and a developing roller21are integrally arranged. The transfer belt device18includes a pair of support rollers25and26, and an intermediate transfer belt27being set around the support rollers25and26. One of the support rollers25and26functions as a driving roller, and a driving motor (not shown) is connected to a rotation shaft of the driving roller. When the driving motor is driven, the intermediate transfer belt27is rotated in a state in which the intermediate transfer belt27is set around the support rollers25and26.

An exposure part23is arranged at an upper side of the imaging devices22K,22Y,22M, and22C. A fixing device15and a sheet ejection part24are arranged downstream of the transfer belt device18(at a left side in the image forming apparatus100inFIG. 2). A sheet stock part16and a sheet feeding part17are arranged to stock and feed paper sheets9as recording media (inFIG. 3) at a bottom of the image forming part100.

In this configuration, the charging roller20uniformly charges a surface of the photoreceptor19for each of the imaging devices22K,22Y,22M, and22C. Next, information of images and letters supplied by a personal computer and an image scanner is exposed at a dot unit by the exposure part23, and an electrostatic latent image is formed on the surface of each of the photoreceptors19. After that, the electrostatic latent image is developed by toner supplied by the developing roller21and is visualized as a toner image on each of the photoreceptors19.

While a toner image is being formed, the paper sheet9being a recording medium is conveyed from the sheet stock part16to the transfer belt device18, and sequentially contacts to each of the photoreceptors19of the imaging devices22K,22Y,22M, and22C. Then, toner images for respective colors formed on the photoreceptors19are superposed onto the paper sheet9. That is, a toner image of four colors is formed on the paper sheet9. The paper sheet9on which the toner image is formed is conveyed from the transfer belt device18to the fixing device15, and the toner image is fixed on the paper sheet9. The paper sheet9is ejected outside the image forming apparatus100via the sheet ejection part24.

As illustrated inFIG. 3, the fixing device15includes a fixing belt2which is driven and rotated by being set around at least two rollers: a fixing roller3as a fixing member and a heating roller4as a heating member, and a pressure roller1as a pressure member for contacting and pressing a surface of the fixing belt2. In addition, the heating roller4includes a heat source5. Thus, the fixing roller3, the heating roller4, and the fixing belt2can be collectively called a fixing rotative body50. The fixing rotative body50may include a pressure roller. A temperature of the fixing rotative body50(the surface of the fixing belt2in this case) is detected by a temperature detecting part6.

The pressure roller1is formed by a core member1aand a coating layer1bfor coating the core member1a. For example, the core member1ais a carbon steel core having a 4.5 mm thickness and a 23 mm diameter. The coating layer1bincludes a silicon rubber thickness layer, and a PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer resin) layer. The silicon rubber thick layer is 3.5 mm in thickness, and the PFA layer is 30 μm in thickness. The pressure roller1presses the paper sheet9to the fixing belt2, rotates in a direction of an arrow a driven by a gear (not shown), and the fixing belt2is driven and rotated by a driving force of the pressure roller1.

For example, the fixing belt2is formed of a three layer structure of polyimide, silicon rubber, and PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer resin). Furthermore, in detail, in order to improving an image quality of the toner image and realizing stability of the image quality, a silicone rubber layer having 150 μm thickness as an elastic layer is provided with a surface of a polyimide substrate being an endless belt having 70 μm in thickness and 45 mm in a diameter φ. To ensure ease of releasing toner, the PFA of 30 μm thickness is further formed on the silicon rubber provided with the polyimide substrate. The fixing belt2is supported by the fixing roller3and the heating roller4.

The fixing roller3is arranged at a position facing the pressure roller1through the fixing belt2, and forms a nip part for fixing a toner image10formed on the paper sheet9. The heating roller4is a hollow member made of aluminum, iron, or the like, and is arranged to rotatably support the fixing belt2. In addition, the fixing belt2can be stable and conveyed by being rotated at least 100° with respect to the heating roller4.

As described above, the heat source5is arranged inside the heating roller4. For example, the heat source5can be a halogen heater. The halogen heater is connected to a control substrate which forms a control part30with a harness. Therefore, the heat source5is controlled by the control part30, and supplies thermal energy necessary to fix the toner image10onto the paper sheet9. For example, the control part30includes a micro-computer.

Moreover, for control of the heat source5by the control part30, the temperature detecting part6is arranged on the heating roller4to face the fixing belt2. The heat source5formed by the halogen heater is controlled based on the temperature detected by the temperature detecting part6. It should be noted that a contact type thermistor is used for the temperature detecting part6. Advantageously, by applying the contact type thermistor, an inexpensive configuration can be realized.

Moreover, by arranging the temperature detecting part6on the heating roller4, it is possible to avoid contacting the paper sheet9. Accordingly, it is possible to reduce damage and malfunctions, and to ensure the temperature detecting part6contacts the fixing belt2. Therefore, it is possible to reduce a temperature error caused by unstable contact, and to improve stability of image quality.

An entry guide7is provided at an upstream side above the nip part, which is formed by the pressure roller1and the fixing roller3which are contacting the paper sheet9, in a sheet conveyance direction (a moving direction of the fixing belt2). The paper sheet9is guided to the nip part by the entry guide7. By guiding the paper sheet9to the nip part between the pressure roller1and the fixing roller3with the entry guide7, movement of the paper sheet9can be stable, and the paper sheet9can be steadily conveyed. An output guide8is arranged at the downstream side below the nip part in the sheet conveyance direction (the moving direction of the fixing belt2).

As illustrated inFIG. 4, in the image forming apparatus100, there are a printing state (a printing operation)4aand a waiting state4b, and a target temperature31is controlled to be different in the printing state4aand in the waiting state4b. With respect to the target temperature31, based on a detected temperature of the fixing belt2by the temperature detecting part6, a duty of the heat source5is controlled by PID (Proportional, Integral, and Derivative) control81in the printing state4a, and by an ON/OFF control83in the waiting state4b.

The PID control81is a control combining P (Proportional), I (Integral), and D (Derivative), and optimizes multiple parameters depending on a deviation between a target value and a current value. In this case, an ON ratio of the heat source5for a unit time is varied based on a detection result of the temperature detecting part6so as to maintain the target temperature31in the printing state4a.

The control part30includes a printing state control for varying the ON ratio of the heat source5for the unit time based on the detection result of the temperature detecting part6so as to maintain the target temperature31in the printing state4a, and a waiting state control for conducting the ON/OFF control83based on the detection result of the temperature detecting part6so as to maintain the target temperature31in the waiting state4bafter a printing operation ends.

Accordingly, during the printing operation, the multiple parameters are optimized by the PID control81being variable control depending on the deviation of a detected temperature and the target temperature31by combining P (Proportional), I (Integral), and D (Derivative), and the duty of the heat source5is controlled. By this control, it is possible to reduce a temperature ripple and to improve stability of the image quality. It should be noted that the variable control is not limited to the PID control81but may be any one of a PI control, an I-PD control, I-P control, and a PI-D control. The PI control is a simplified type of the PID control (=Proportional+Integral+Derivative) and is a control combining Proportional and Integral (Proportional+Integral). The I-PD control is a proportional derivative precedence type control, the I-P control is an integral proportional control, and the PI-D control is a derivative precedence type control.

As illustrated inFIG. 4, an overshoot4din a temperature waveform4c, which is detected by the temperature detecting part6becomes greater when switching the PID control81in the printing state4ato the ON/OFF control83in the waiting state4bafter the printing operation. The PID control81supplies heat to the nip part by turning on the heat source5. During the printing operation, the paper sheet9absorbs the heat. However, after the printing operation, the heat remains on the nip part. Also, during the printing operation, both the pressure roller1and the fixing roller3are rotated to convey the paper sheet9as the recording medium. However, these rotations of the pressure roller1and the fixing roller3are stopped when the printing operation ends. After the rotations are stopped, heat transferred by the rotation in the printing operation is retained in the fixing rotative body50. Since the above-described control is performed to ensure the capability of fixing the toner image onto the paper sheet9as the recording medium, the heat remains in the fixing rotative body50even if the heat source5is not lighted (is not in an ON state), and a temperature waveform does not become stable. Therefore, an amount of the overshoot4dis varied depending on the number of printed sheets, a printing temperature, a thickness and type of the paper sheet9, and a print mode.

In the PID control81, the temperature is always detected, an arithmetic operation is performed by using the detected temperature and the target temperature31, and the duty of the heat source5is determined. Advantageously, the temperature ripple can be reduced. However, since the heat source5is frequently turned on and off to maintain a constant temperature, a great amount of energy is consumed. Accordingly, although this operation of turning on and off the heat source5is adequate for ensuring the capability of fixing the toner image, in the printing state4a, the operation is inadequate in the waiting state4b. Thus, in the waiting state4b, the ON/OFF control83is conducted to turn on the heat source5when the temperature is lower than the target temperature31, and to turn off the heat source5when the temperature is higher than the target temperature31. Therefore, it is possible to reduce energy consumption.

In this case, a change of the control is performed simultaneously when the printing state4ais transferred to the waiting state4b. However, there is a problem in which the overshoot4din the temperature waveform4cbecomes greater when the change of the control is performed. This problem is caused in a first case in which the target temperature31in the printing state4ais higher than the target temperature31in the waiting state4band in a second case in which the target temperature31in the printing state4ais lower than the target temperature31in the waiting state4b. Hereinafter, the target temperature31in the printing state4ais called a printing temperature, and the target temperature31in the waiting state4bis called a waiting temperature. The second case will be briefly described.

First, the printing temperature is set for each of print modes for respective paper types and paper grammage. Since energy necessary to fix the toner image10onto the paper sheet9is different for each paper type, the printing temperature is set to be different for each paper type to apply appropriate energy, so as to print an image with a stable quality.

As one example of the print modes, a thin paper mode is applied to the paper sheet9having the paper grammage of 60 g/m2to 65 g/m2, and the printing temperature is 150° C. for the thin paper mode. A regular paper mode is applied to the paper sheet9having the paper grammage of 66 g/m2to 74 g/m2, and the printing temperature is 160° C. for the regular paper mode. A middle thickness mode is applied to the paper sheet9having the paper grammage of 75 g/m2to 90 g/m2, and the printing temperature is 170° C. for the middle thickness mode. Also, the waiting temperature is 160° C. so that time required to change from the waiting state4bto the printing state4ais made to be shorter. Accordingly, the first case in which the printing temperature is higher than the waiting temperature corresponds to the printing operation in the middle thickness mode. In this case, the printing temperature is 170° C. and the waiting temperature is 160° C. Thus, the printing temperature is higher than the waiting temperature. The second case in which the printing temperature is lower than the waiting temperature corresponds to the printing operation in the thin paper mode. In this case, the printing temperature is 150° C. and the waiting temperature is 160° C. Thus, the printing temperature is lower than the waiting temperature.

Next, as illustrated inFIG. 5, the first case in which the printing temperature is higher than the waiting temperature will be described. In the printing state4a, heat is accumulated in the fixing rotative body50, and the overshoot4dbecomes greater. The overshoot4d-1is indicated by a dashed circle inFIG. 5. When the control is changed from the PID control81to the ON/OFF control83after the printing operation, the temperature is higher than the target temperature31. The heat source5as the heater is turned off and is in the waiting state4b. However, if the overshoot4d-1is greater, it takes time to reduce the temperature. If a print request is made, it is required to wait until the temperature is reduced, and the image forming apparatus100is an unavailable apparatus. Moreover, if the temperature becomes extremely high, components may be damaged, and life durations of components may be shorter due to repetitive occurrences of high temperature.

Accordingly, the fixing rotative body50is rotated in a certain time after the printing operation to transfer the heat. As illustrated inFIG. 5, a temperature waveform4c-1depicted by a dashed line including the great overshoot4d-1can be reduced to be a temperature waveform5cdepicted by a solid line. Instead of providing an additional component, the above-described method of rotating the fixing rotative body50inexpensively overcomes the above-described problem by a simple control operation. InFIG. 5, a rotation operation5fof the fixing rotative body50for reducing the overshoot4d-1is illustrated corresponding to the temperature waveform5c.

After the printing operation by the fixing rotative body50, a rotation time is set to be 5 sec. If an idle rotation time is set to be longer, the overshoot4d-1can be reduced. However, in a case in which a print amount is small and the heat has not accumulated, the temperature is greatly decreased. In this case, the rotation time is set so that the temperature of the fixing belt2can be reduced by 10° C. after 10 paper sheets are printed, with respect to a temperature difference 10° C. between 170° C. and 160° C., until the waiting temperature after printing in the middle thickness mode is reached. In this configuration, since the rotation time required to decrease the temperature of the fixing belt2by 10° C. is approximately 5 sec, the idle rotation time is set to be 5 sec.

Next, the second case in which the printing temperature is lower than the waiting temperature will be described with reference toFIG. 6. InFIG. 6, a temperature waveform4c-2including a great overshoot4d-2, which is depicted by a dashed line, appears in a case in which the heat source5is lighted (in an ON state) when the temperature is lower than the waiting temperature immediately after the control is changed. In this case, the heat source5retains the ON state until the temperature reaches the target temperature31. Thus, the great overshoot4d-2is caused. A duty portion6qin this case is illustrated corresponding to the great overshoot4d-2of the temperature waveform4c-2in a duty6pof the heat source5which is depicted corresponding to a temperature waveform6c.

As described above, in order to reduce the great overshoot4d-2, a rotation operation5fof the fixing rotative body50is performed. The temperature of the fixing belt2is lower than the target temperature31immediately after switching from the printing state to the waiting state. If the rotation is performed, each of the rollers4,3, and1is rotated in a state of the heat source5being turned on. Accordingly, the above-described operation is performed to release the heat and reduce the overshoot4d-2while receiving the heat. Elevation of the temperature is made to be slowed down. However, the great overshoot4d-2is caused after the rotation is stopped. During the rotation, the heat source5is controlled to be forcibly turned off (0%) independent of the temperature to perform an overshoot control. After successive printing, the temperature of the fixing roller3as the fixing member becomes a high temperature, and component service life duration becomes shorter. Even if a print request is made, the printing operation cannot be immediately started, and it takes time to start the printing operation.

Accordingly, between the PID control81for the printing state and the ON/OFF control83for the waiting state, a rapid elevation of the temperature is suppressed by turning off the heat source5and by conducting an idle operation. After that, the rotation is stopped, a turn-on time (an ON period) of the heat source5is determined based on an elevation gradient of the temperature in a state of stopping the rotation. Then, an ON control for forcibly turning on the heat source5during the determined turn-on time alone is provided between the PID control81and the ON/OFF control83. Therefore, it is possible to suppress the overshoot4d-2due to the ON/OFF control83.

A determination of the turn-on time (ON period) of the heat source5between the PID control81and the ON/OFF control83will be described. The idle rotation is conducted to reduce the overshoot4d-2after the PID control81in the printing state4a. After that, an elevation gradient of the temperature of the fixing rotative body50, which indicates an elevation amount of the temperature per second in a state of stopping the fixing rotative body50, is measured, and a difference between the target temperature31and the detected temperature by the temperature detecting part6is determined. Accordingly, a control table as illustrated in the following table 1 is defined beforehand. Based on a relationship between the elevation gradient of the temperature and the difference between the target temperature31and the temperature detected by the temperature detecting part6, the turn-on time (ON period) of the heat source5is determined.

For example, if the elevation gradient is 5° C. in a range of −10° C./s to 10° C./s and the difference between the target temperature31and the detected temperature is −15° C. in a range of −20° C. to 20° C., the turn-on time (ON period) of the heat source5as the heater is determined to be 1 sec.

Also, as illustrated inFIG. 6, there is a case in which the target temperature31in the waiting state is sufficiently higher than the target temperature31in the printing state, the heat is not accumulated inside the fixing rotative body50since a few paper sheets9are printed, and the target temperature31in the waiting state is not achieved even without rotating the fixing rotative body50after the printing operation ends. In this case, it is not required to rotate the fixing rotative body50even after the printing operation ends. On the contrary, as illustrated inFIG. 5, depending on the paper type of the paper sheet9as the recording medium, there is a case in which the target temperature31in the waiting state4bis lower than the target temperature31in the printing state4a. Accordingly, after the printing operation ends, control is always conducted to rotate the fixing rotative body50. Therefore, it is possible to reduce the overshoot4c-1in the first case in which the target temperature31in the printing state4ais higher than the target temperature31in the waiting state4binFIG. 5, and it is also possible to reduce the overshoot4c-2in the second case in which the target temperature31in the printing state4ais lower than the target temperature31in the waiting state4binFIG. 6.

In the embodiment, in the printing state4a, the ON ratio per unit time can be varied for the heat source5based on the detection result of the temperature detecting part6. Thus, it is possible to reduce the temperature ripple. Also, in the waiting state4bafter the print operation ends, the heat source5is turned on when the detected temperature becomes lower than the target temperature31, and the heat source5is controlled not to be turned on when the detected temperature is higher than the target temperature31.

As described above, in the fixing device15according to the embodiment, it is possible to reduce the temperature ripple during the printing state4a. Also, the ON control controls the heat source5to turn on when the detected temperature becomes lower than the target temperature31in the waiting state4bafter the print operation ends, it is possible, and the ON/OFF control83controls the heat source5not to be turned on when the detected temperature is higher than the target temperature. Therefore, it is possible to reduce energy consumption. Moreover, when the ON/OFF control83begins, the detected temperature is higher than the target temperature31. By switching to the ON/OFF control83, it is possible to reduce unnecessarily turning on the heat source5, to decrease the energy consumption, and to reduce wear of components. Therefore, the service life duration of components becomes longer, and the overshoots4d-1and4d-2can be reduced.

Moreover, even in a case in which the printing temperature is higher than the waiting temperature, and even in a case in which the printing temperature is lower than the waiting temperature, the overshoots4d-1and4d-2can be stably reduced.

Any one of various control methods such as the PID control81and the like as the control for varying the ON ratio per unit time can be applied, so that the control part30can be realized without being complicated and can perform stable control. In a case of changing the target temperature31in the printing state4adepending on the paper type of the paper sheet9as the recording medium, a stable printing operation can be realized for the paper sheet9.

In the image forming apparatus100according to the embodiment, the overshoots4d-1and4d-2can be reduced when the printing state4ais transitioned to the waiting state4b, and the energy consumption can be decreased.

The image forming apparatus100according to the embodiment can be an electro-photographic copier, a laser beam printer, a facsimile, and the like. As the heat source5, other than the halogen heater, for example, induction heating or a ceramic heater may be used. The temperature detecting part6is not limited to a thermistor, and may be a device for detecting temperature using a thermocouple, infrared radiation, or the like. The temperature detecting part6can be a contact type or a non-contact type.

The present application is based on the Japanese Priority Patent Application No. 2010-018390 filed on Jan. 29, 2010, the entire contents of which are hereby incorporated by reference.