Abstract:
The present invention relates to a fixing apparatus which radiates rays to a detection object and which detects the rays returned from the detection object to obtain a temperature signal. The apparatus specifies a radiant ratio of the surface of the detection object using at least one of accumulated image forming times, detection position, and radiation deterioration, corrects the detected temperature signal based on the specified radiant ratio of the surface of the detection object to produce temperature data, and controls a power to be supplied to a heating mechanism which raises temperature of the detection object based on the produced temperature data.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates particularly to a fixing apparatus which is usable in image forming apparatuses such as a copying apparatus and a printer apparatus in an electrophotographic system using a thermally melting developer and which fixes a developer to an output object.  
         [0003]     2. Description of the Related Art  
         [0004]     A fixing apparatus incorporated in an image forming apparatus using an electrophotographic process applies heat to a toner (developer) positioned on an output object, that is, a recording material to soften the toner, and applies pressure to the toner to fix the toner to the recording material. In recent years, induction heating has been broadly utilized as a heating system capable of reducing a time from when power supply is started until temperature reaches a fixable temperature at which the toner softens, that is, a heating time.  
         [0005]     However, in the fixing apparatus using the induction heating, it is difficult to correctly detect the temperature of a heat roller (heating member) for fixing the toner to the recording material.  
         [0006]     There have been many proposals in order to improve these respects.  
         [0007]     For example, it has been described in Japanese Patent Application Laid-Open No. 2003-229242 that an apparatus (fixing apparatus) for heating a heating object member by the induction heating has an optical system and a mirror for guiding infrared rays radiated from a heating object member to infrared-ray detection means, and power supplied to heating means for heating the heating object member is controlled based on the detected infrared rays.  
         [0008]     For example, it has been described in Japanese Patent Application Laid-Open No. 2003-57987 that in a fixing apparatus comprising a temperature detection device which detects the infrared rays emitted from a fixing roller to thereby speculate and detect the temperature of the fixing roller, infrared-ray emission of the fixing roller in a wavelength region detectable by the temperature detection device is set to be not more than the infrared-ray emission of the toner in the wavelength region, and an infrared-ray detection member has a film member which absorbs the infrared rays.  
         [0009]     For example, it has been proposed in Japanese Patent Application Laid-Open No. 2003-57989 that in an apparatus for controlling a surface temperature of a heating/fixing rotary member for a fixing apparatus, comprising: a temperature detection device; and contact state switching means capable of switching a contact state between the temperature detection device and the heating/fixing rotary member, the contact state and non-contact state of surface temperature detection means be switched.  
         [0010]     However, the proposal of any of the above-described documents relates to contact temperature detection means. Response of the contact temperature detection means differs from that of a non-contact temperature sensor. Therefore, detected temperature includes a time lag. Therefore, it is difficult to correctly manage fixing temperature of the heat roller. A sliding surface of a detection surface of the contact temperature detection means is deteriorated with life of the heat roller (increase of the number of image formed/fixed sheets). Therefore, the response of the sensor accompanying deterioration of radiation of the infrared rays is deteriorated, and a detected temperature becomes incorrect (wrong detection). As to the infrared-ray radiation, the deterioration differs depending on individual places on the surface of the roller. Therefore, when correction coefficient is equal, the detected temperature includes an error.  
       BRIEF SUMMARY OF THE INVENTION  
       [0011]     An object of the present invention is to provide a fixing apparatus capable of correctly detecting temperature of a heating object over a long term, and stably fixing a toner to a recording material in a constant condition range.  
         [0012]     According to the present invention, there is provided a heating apparatus comprising:  
         [0013]     a heating member to which energy is supplied to generate heat and to thereby heat a recording material and a developer;  
         [0014]     a plurality of heating mechanisms which supply the energy to the heating member and which are disposed in association with a longitudinal direction of the heating member and which selectively allow the heating member to generate the heat in accordance with temperature distribution of the heating member in the longitudinal direction;  
         [0015]     a surface state maintaining mechanism which maintains infrared-ray quantity on the surface of the heating member in a predetermined range; and  
         [0016]     a plurality of temperature detection mechanisms including a plurality of radiated heat detection sections which detect the radiated heat reflected from the heating member without contacting the heating member and a plurality of temperature detection sections which detect ambient temperature of the radiated heat detection section, the plurality of temperature detection mechanisms being disposed using a region in which the heating member generates the heat as a unit.  
         [0017]     Moreover, according to the present invention, there is provided a fixing apparatus comprising:  
         [0018]     a heating member to which a magnetic field is supplied to generate heat and to thereby heat a recording material and a developer;  
         [0019]     a plurality of first and second coil members which supply the magnetic field to the heating member to generate induction heat and which are disposed in a longitudinal direction of the heating member and which are capable of independently supplying the magnetic field;  
         [0020]     a surface state maintaining mechanism which maintains infrared-ray quantity on the surface of the heating member in a predetermined range;  
         [0021]     a plurality of temperature detection mechanisms including a plurality of radiated heat detection sections which detect the radiated heat reflected from the heating member without contacting the heating member and a plurality of temperature detection sections which detect ambient temperature of the radiated heat detection section, the plurality of temperature detection mechanisms being disposed using a region in which the heating member generates the heat as a unit; and  
         [0022]     a pressure supplying member which is brought into contact with the heating member in a predetermined position and which fixes the developer to the recording material passed between the pressure supplying member and the heating member.  
         [0023]     Furthermore, according to the present invention, there is provided a temperature control method comprising:  
         [0024]     radiating rays to a detection object, and detecting the rays returned from the detection object to obtain a temperature signal;  
         [0025]     specifying a radiant ratio of the surface of the detection object using at least one of accumulated image forming times, detection position, and radiation deterioration;  
         [0026]     correcting the detected temperature signal based on the specified radiant ratio of the surface of the detection object to produce temperature data; and  
         [0027]     controlling a power to be supplied to a heating mechanism which raises temperature of the detection object based on the produced temperature data.  
         [0028]     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0029]     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
         [0030]      FIG. 1  is a schematic drawing showing one example of a fixing apparatus to which an embodiment of the present invention is applied;  
         [0031]      FIG. 2  is a schematic diagram showing an example of a heating apparatus incorporated in the fixing apparatus shown in  FIG. 1 ;  
         [0032]      FIG. 3  is a schematic diagram showing another example of the heating apparatus shown in  FIG. 2 ;  
         [0033]      FIG. 4  is a schematic diagram showing one example of a driving circuit (temperature control circuit) which operates the fixing apparatus shown in  FIGS. 1 and 2  (or  3 );  
         [0034]      FIG. 5  is a schematic diagram showing one example in which temperature of a heat roller of the fixing apparatus shown in  FIGS. 1 and 2  is set by the driving circuit shown in  FIG. 4 ;  
         [0035]      FIG. 6  is a schematic diagram showing one example of display shown in a display section in a step of setting the temperature, shown in  FIG. 7 ;  
         [0036]      FIG. 7  is a schematic diagram showing another example in which the temperature of the heat roller of the fixing apparatus shown in  FIGS. 1 and 2  is set by the driving circuit shown in  FIG. 4 ; and  
         [0037]      FIG. 8  is a schematic diagram showing a relation between the totaled number of passed sheets and the radiant ratio of the surface of the heat roller in the fixing apparatus shown in  FIGS. 1 and 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0038]     An embodiment of the present invention will be described hereinafter with reference to the drawings.  
         [0039]      FIG. 1  shows a fixing apparatus to be incorporated in image forming apparatuses such as a copying apparatus and a printer apparatus for fixing a thermally melting developer to a sheet-like output medium to obtain a hard copy, that is, a printing output.  
         [0040]     The fixing apparatus has been broadly utilized for fixing a toner (developer) to the sheet-like output medium to obtain the printing output. Examples of the sheet-like output medium include paper, resin sheet and the like. The developer (toner) is electrostatically held by the sheet-like output medium. The fixing apparatus applies heat to the toner and the sheet-like output medium to soften the toner, and applies a predetermined pressure in such a manner as to fix the toner to the medium.  
         [0041]     A fixing apparatus  1  has a heat roller  3 , a press roller  5 , and a heating device  7  of an induction heating system. Axial lines of the heat roller  3  and the press roller  5  are parallel to each other.  
         [0042]     The pressure is supplied to the press roller  5  by a pressurizing mechanism (spring and roller holding structure)  9 , and accordingly the press roller is pressed onto the heat roller  3 . Various known structures are usable in the spring and roller holding structure as long as the press roller  5  can be pressed onto the heat roller  3  with a predetermined pressure.  
         [0043]     An outer peripheral portion of the press roller  5  deforms based on the pressure supplied from the pressurizing mechanism  9 . A deformed region is referred to as the nip N. The nip N has a predetermined width which is a length of an outer peripheral surface of the rollers  3  and  5 . An outer diameter and material of the press roller  5 , pressure during the pressing onto the heat roller  3 , outer diameter and hardness of the heat roller  3  and the like are appropriately set in such a manner that the width of the nip N falls in a constant range.  
         [0044]     A claw  11  is disposed in a predetermined position defined on a downstream side from the nip N along an outer periphery of the heat roller  3  during rotation of the heat roller. The claw  11  is used for releasing (peeling) a sheet (sheet-like medium) S from adhesion between the sheet S and the surface of the heat roller  3  caused by curving (of the sheet S) on the side of the surface of the heat roller. The adhesion is caused by curl of the sheet S itself by fusion bonding of the surface of the heat roller  3  to the toner on the sheet S, or application of the heat.  
         [0045]     A plurality of claws  11  may be disposed while associated with intensity of the fusion bonding of the sheet S to the surface of the heat roller  3  or degree of curvature of the sheet S on the side of the roller surface, that is, peelability. The claw  11  may be omitted in a case where the peelability (of the sheet S) is high. The claw  11  may be disposed on the outer periphery of the press roller  5  in a positional relation similar to that with respect to the heat roller  3 .  
         [0046]     A cleaning roller  13  and/or an oil (coat) roller  15  is disposed in a predetermined position around either or both of the heat roller  3  and the press roller  5 . The cleaning roller  13  is used in removing a toner, dust (especially particulates generated from the sheet S) and the like sometimes sticking to the surfaces of the heat roller  3  and the press roller  5 . The oil (coat) roller  15  prevents the toner from being fixed to the surfaces of the heat roller  3  and the press roller  5  and/or supplies oil to the surface of the corresponding roller for a purpose of enhancing the peelability of the sheet S described above. The oil is, for example, preferably silicone based.  
         [0047]     Non-contact temperature detection means (temperature detection mechanism)  17  and safety device  19  are disposed in predetermined positions in the vicinity of either or both of the heat roller  3  and the press roller  5 . The temperature detection mechanism  17  and the safety device  19  are disposed in the positions which are not influenced by a magnetic flux (line of magnetic force) generated from the heating device  7 . The temperature detection mechanism  17  detects the temperature of the surface of the heat roller  3 . The temperature detection mechanism  17  is a temperature sensor (non-contact), for example, of a thermopile type. The temperature detection mechanism  17  may include, for example, a thermistor of a contact type. At least two temperature detection mechanisms  17  are disposed at a predetermined interval in a longitudinal direction of the heat roller  3 .  
         [0048]     The temperature detection mechanism  17  is disposed, for example, on an arbitrary surface including an axis of the heat roller  3  when viewed in a peripheral direction (direction of a plane crossing the axis at right angles) of the heat roller  3 . The temperature detection mechanism  17  may be disposed in an arbitrary position, for example, in the vicinity of the nip N (upstream of a rotation direction of the heat roller  3 ) or the heating device  7  (space between the heating device  7  and the heat roller  3 ), when viewed from the peripheral direction (direction of the plane crossing the axis at right angles) of the heat roller  3 . The temperature detection mechanism  17  is capable of detecting, for example, the temperature of the space between the heat roller  3  and the heating device  7  and the temperature around the heat roller  3  in the vicinity of the nip N, that is, temperatures in a plurality of positions in the peripheral direction of the heat roller  3 , when viewed in the peripheral direction (direction of the plane crossing the axis at right angles) of the heat roller  3 . The safety device  19  is, for example, a thermostat. The thermostat  19  stops an operation of the heating device  7 , that is, an output of an induced current in a case where the temperature of the surface of the heat roller  3  rises at a temperature which has not been expected. The rise of the temperature of the surface of the heat roller  3  at the unexpected temperature is caused, for example, by abnormality (burnout/damage) of the temperature detection mechanism  17 .  
         [0049]     The heat roller  3  has a metal conductive layer  3   a  which generates heat by eddy current generated by the magnetic field (line of magnetic force) supplied by the heating device  7 , and is formed, for example, into a tube or rod shape. The heat roller  3  is rotated in an arrow direction centering on an inherent axial line (not shown) by a rotating force supplied by a motor (not shown) or a power transmission mechanism. The outer peripheral surface of the heat roller  3  is moved at a predetermined speed [mm/second] (the heat roller  3  is rotated at a predetermined rotation number, and the speed at which the outer peripheral surface is moved can therefore be obtained from the rotation number). An elastic layer and/or a mold release layer capable of reducing a remaining toner.  
         [0050]     The press roller  5  is brought into contact with the outer periphery of the heat roller  3  via the nip N. Therefore, when the heat roller is rotated, the press roller is rotated in an arrow direction at the predetermined rotation number. The outer peripheral surface of the press roller  5  is moved at a predetermined movement speed [mm/second].  
         [0051]     The heating device  7  has a coil  21  which supplies a magnetic field having a predetermined intensity to the metal conductive layer  3   a  of the heat roller  3 . The coil  21  is wound around a core  23  formed of a magnetic material by the predetermined number of windings, and is formed into a predetermined shape. The coil  21  (heating device  7 ) may be disposed inside the heat roller  3 , when the heat roller  3  is tubular (hollow).  
         [0052]     As shown in  FIG. 2 , the coil  21  is divided, for example, into three along the longitudinal direction of the heat roller  3 . Cores are disposed for coils, although not described in detail. When the coil  21  is divided into three, the coil positioned in a middle of heat roller  3  in the longitudinal direction is formed to be electrically equivalent to two coils position in opposite ends. When the coil  21  is divided into three, the coil positioned in the middle of the heat roller  3  in the longitudinal direction is referred to as a first coil  21 - 1 . The coils positioned on opposite sides (end portions of the roller  3  in the longitudinal direction) of the first coil  21 - 1  with respect to the longitudinal direction of the heat roller  3  are referred to as second coils  21 - 2 . When one of the second coils is identified, they are referred to as a first end coil  21 - 2   a,  second end coil  21 - 2   b.  The first end coil  21 - 2   a  of the second coil is electrically connected to the second end coil  21 - 2   b  in series. The coils other than the first coil  21 - 1  are operated under the same control.  
         [0053]     A size of the first coil  21 - 1  is defined in such a manner that a length of the sheet in contact with the heat roller  3  can be heated in a case where the sheet S is a sheet having an at least A4 size and a short side of the sheet S is conveyed in a direction crossing a conveying direction of the sheet S at right angles during the conveying. When a region (width) of the sheet S contacting the heat roller is small as compared with the length of the heat roller  3 , power can be supplied only to the middle (first) coil  21 - 1  in such a manner that the only region corresponding to the contact width of the sheet S can be heated. Since the coil  21  is divided into the middle (first) coil  21 - 1  and the opposite end (second) coils  21 - 2 , a temperature distribution of the heat roller  3  in the longitudinal direction can be uniformed.  
         [0054]     In the image forming apparatus using the fixing apparatus, when the toner is passed through the nip N, that is, a fixing point together with the sheet S, the toner is heated by the heat supplied from the heat roller  3  to soften (the toner is electrostatically positioned on the sheet S as an image to be fixed onto the sheet S). The softened toner receives a predetermined pressure from the heat roller  3  and the press roller  5  in the nip N. By the above-described steps, the toner, that is, an image to be output is fixed onto the sheet S.  
         [0055]     Next, a “position” in which the temperature detection mechanism  17  is to be disposed will be described.  
         [0056]     The temperature detection mechanism (temperature sensor of the thermopile type)  17  is disposed in association with three divided individual coil spaces with respect to the longitudinal direction of the heat roller  3  shown, for example, in  FIG. 2 . As to the thermopile type temperature sensor  17 , at least two sensors are disposed between the first coil  21 - 1  and the first end coil  21 - 2   a  and between the first coil  21 - 1  and the second end coil  21 - 2   b  in a projected state along the axis of the heat roller  3 . As to the thermopile type temperature sensor  17 , preferably three sensors are disposed in a region most heated by the first (middle) coil  21 - 1 , and regions most heated by the second coils  21 - 2   a  and  21 - 2   b  with respect to the longitudinal direction of the heat roller  3 . Adding the above-described two sensors, five sensors are disposed in total. More thermopile type temperature sensors  17  may be prepared with respect to the longitudinal direction of the heat roller  3 . For example, as shown in  FIG. 3 , when the second coils  21 - 2  are formed to be long in such a manner as to cover the opposite ends of the heat roller  3 , another coil is disposed in each of the opposite ends of the second coils  21 - 2 . Adding the above-described five sensors, seven sensors are disposed.  
         [0057]     The thermopile type temperature sensors  17  are positioned in the divided regions on the side of the heat roller  3 , when the sheet S is passed through the nip N in a display by a plane (the same direction as that of  FIG. 1 ) crossing the axis of the heat roller  3 , that is, in a state in which the sensors are viewed in the same direction as that of  FIG. 1 . Since the thermopile type temperature sensors  17  are arranged in the above-described positions, the temperature of the space between any of the first coil  21 - 1 , first end coil  21 - 2   a,  and second end coil  21 - 2   b  and the surface of the heat roller  3  is detectable. Furthermore, since the thermopile type temperature sensors  17  are arranged in the above-described positions, the temperature of the surface of the heat roller  3  in the vicinity of the nip N is detectable.  
         [0058]      FIG. 4  shows one example of a driving circuit (temperature control circuit) which operates the fixing apparatus shown in  FIGS. 1 and 2 .  
         [0059]     The middle coil  21 - 1  and the end coil  21 - 2  (the first end coil  21 - 2   a  and the second end coil  21 - 2   b  connected in series are treated as one coil) of the heating device  7  are connected in parallel with capacitors  31   a,    31   b  for resonance. A set of the first coil  21 - 1  and the capacitor  31   a,  and a set of the second coil  21 - 2  and the capacitor  31   b  are connected to switching elements  32   a ,  32   b.  In the individual switching elements  32   a,    32   b,  for example, an insulated gate bipolar transistor (IGBT) capable of supplying a current, for example, of about 100 amperes (A), an electric field transistor (MOS-FET) and the like are usable.  
         [0060]     A first inverter circuit  33   a  is defined by the middle (first) coil  21 - 1 , capacitor  31   a,  and switching element  32   a,  and a second inverter circuit  33   b  is defined by the end (second) coil  21 - 2 , capacitor  31   b , and switching element  32   b.    
         [0061]     A direct current which is rectified by a rectification circuit  34  and whose ripple content is smoothed into a predetermined magnitude is supplied to the individual inverter circuits  33   a,    33   b.  The rectification circuit  34  is connected to a commercial alternating-current power supply. A transformer  35  capable of detecting all power consumption by the heating device  7  (first coil  21 - 1 , second coil  21 - 2 ) is disposed in a stage previous to the rectification circuit  34 .  
         [0062]     Control terminals of the switching elements  32   a ,  32   b  are connected to driving circuits  36   a,    36   b  which turn on the individual switching elements at predetermined timings. Each of the driving circuits  36   a ,  36   b  applies a predetermined driving voltage to the control terminal of the corresponding switching element. An operation timing of the driving circuit  36   a  or  36   b , that is, a timing at which the driving voltage is applied to the control terminal of the corresponding switching element  32   a  or  32   b  from the driving circuit  36   a  or  36   b  is instructed by a control circuit  37   a  or  37   b.  The control circuits  37   a ,  37   b  instruct a frequency in a range, for example, of 20 to 60 kHz to the driving circuits  36   a ,  36   b.  When the driving voltages having predetermined frequencies are supplied from the driving circuits  36   a,    36   b,  the inverter circuits  33   a,    33   b  defined including the switching elements  32   a,    32   b  are repeatedly turned on in accordance with the supplied frequencies. When the inverter circuits  33   a,    33   b  are repeatedly turned on in accordance with the supplied frequencies, currents having predetermined magnitudes are supplied to the first coil  21 - 1  and second coil  21 - 2  in the inverter circuits  33   a,    33   b.  The magnitude of the current is defined in accordance with the magnitude of the heat to be generated by the heat roller  3 . In other words, the magnitude of the heat generated by the heat roller  3  depends on the frequency instructed from the control circuits  37   a,    37   b.    
         [0063]     The heat generated from the heat roller  3  is detected for each position of the temperature detection mechanism  17  in the longitudinal direction of the heat roller  3  by the non-contact temperature detection means, that is, the temperature detection mechanism  17 . Temperature information of an arbitrary position of the heat roller  3  in the longitudinal direction detected by the temperature detection mechanism  17  is input into a temperature control CPU  38 . When a structure of the temperature detection mechanism  17  separately requires an ASIC section, a temperature detection circuit is disposed between the mechanism and the temperature control CPU  38 . When a contact type temperature sensor (not shown) is disposed besides or inside the temperature detection mechanism  17 , its output signal (temperature data) is also input into the temperature control CPU  38 .  
         [0064]     The temperature control CPU  38  specifies an inverter circuit to be turned on and the frequency to be supplied referring to temperature information input from each temperature detection mechanism  17  and quantity of heat required in the heat roller  3  and/or the temperature distribution in the longitudinal direction of the heat roller  3 .  
         [0065]     The specified frequencies are input into the driving circuits  36   a ,  36   b  via the control circuits  37   a ,  37   b.  The driving voltage having the frequency specified by the temperature control CPU  38  is supplied to the control terminal of the corresponding switching element  32   a,    32   b  from the driving circuit  36   a,    36   b . Therefore, the quantity of heat required for the heat roller  3  and/or the temperature distribution in the longitudinal direction of the heat roller  3  are optimized based on the size of the sheet to be fixed.  
         [0066]     In the fixing apparatus shown in  FIGS. 1 and 2  and the driving circuit shown in  FIG. 4 , an example in which two (sets of) coils are disposed has been described, but the number of (the sets of) the coils may be arbitrarily set, and three (sets) or more may be disposed. The temperature detection mechanisms  17  are preferably increased in accordance with the number of the coils. As to at least the number of the coils required, the number of the sets of the coils is added to the number of the coils.  
         [0067]      FIG. 5  shows an example in which the temperature of the heat roller of the fixing apparatus shown in  FIGS. 1 and 2  is set by the driving circuit shown in  FIG. 4 .  
         [0068]     When an image forming apparatus (not shown) is started, all temperature sensors  17  are turned on. Moreover, the power having a predetermined frequency is supplied to all the first and second coils (S 1 ).  
         [0069]     Self temperature data and roller temperature detection signal (infrared-ray detection value) are output from ambient temperature detection sections (not shown) of the individual temperature sensors  17  and thermopile sections (not shown). It is to be noted that when a contact type thermistor is disposed (in each temperature sensor  17 ), an output of the contact type thermistor is usable in the detection of self temperature (S 2 ).  
         [0070]     A detected temperature signal indicating the temperature of the surface of the heat roller  3  corresponding to the position of each temperature sensor  17  is obtained from self temperature data output from each temperature sensor  17  and roller temperature detection signal (infrared-ray detected value) (S 3 ).  
         [0071]     It is judged by the temperature control CPU  38  whether or not the temperature of the surface has reached reference temperature concerning all regions in the longitudinal direction (axial direction, i.e., main scanning direction) of the heat roller  3  based on the detected temperature signal. It is also judged whether or not the temperature has reached the reference temperature concerning the peripheral direction of the heat roller  3 . An order in which the temperature data (detection signal) is output can be arbitrarily set. It is also possible to set a latching timing on the side of the temperature control CPU  38  (S 4 ).  
         [0072]     When it is detected that the temperature of the surface of the heat roller  3  has reached the reference temperature in step S 4  (S 4 -Yes), it is judged by the temperature control CPU  38  whether or not a difference between the temperature in the region where the temperature is raised by the first coil  21 - 1  and that in the region where the temperature is raised by the second coil  21 - 2  is in a predetermined range so that the temperature immediately before the nip N between the heat roller  3  and the press roller  5  reaches a target temperature in all the regions of a main scanning direction. If necessary, temperature unevenness (ripple) in the peripheral direction of the heat roller  3  is also judged (S 5 ).  
         [0073]     When the temperature difference on the surface of the heat roller  3  is within the predetermined range in the step S 5  (S 5 -Yes), it is checked whether or not printing (output) is reserved (S 6 ).  
         [0074]     When the printing (output) is not reserved in the step S 6  (S 6 -No), “standby routine” is executed (S 7 ), and “standby control routine” for holding the temperature of the surface of the heat roller  3  at “standby temperature” is executed (S 8 ).  
         [0075]     When the printing (output) is reserved in the step S 6  (S 6 -Yes), the sheet S to which a toner image has been transferred is supplied to the nip N between the heat roller  3  and the press roller  5  subsequently to “printing operation (image forming step)”, and “fixing step” of fixing the toner to the sheet S starts (S 9 ).  
         [0076]     When it is detected in the step S 4  that the temperature of the surface of the heat roller  3  does not rise at the reference temperature (S 4 -No), “temperature raising routine (warming-up)” is executed. That is, the power having the predetermined frequency is continuously supplied to all the coils (S 10 ).  
         [0077]     When the temperature difference of the surface of the heat roller  3  is larger than a predetermined magnitude in the step S 5  (there is a ripple, i.e., temperature unevenness) (S 5 -No), it is checked whether or not a time until the temperature of the region where the temperature is raised by one of the coils reaches the reference temperature is within a defined time (S 11 ).  
         [0078]     It is detected in the step S 11  that the time until the temperature of the region where the temperature is raised by one of the coils reaches the reference temperature is within the defined time although there is temperature unevenness in the temperature of the surface of the heat roller  3  (S 11 -No). In this case, the “temperature raising routine (warming-up)” of the step S 10  is executed. In this case, the power having the predetermined frequency is supplied to the coil capable of heating the region where the temperature of the surface of the heat roller  3  is low.  
         [0079]     In the step S 11 , the time until the temperature of the region where the temperature is raised by one of the coils on the surface of the heat roller  3  reaches the reference temperature exceeds the defined time (the temperature does not rise within the defined time) (S 11 -Yes). In this case, it is judged “the surface of the heat roller  3  is deteriorated”. In this case, in a display section of the image forming apparatus, for example, as shown in  FIG. 6 , a message urging maintenance such as “heat roller change/temperature sensor cleaning” is displayed (S 12 ).  
         [0080]     It is to be noted that when “standby routine” is set in the step S 7 , the temperature of the surface of the heat roller  3  is maintained at a first standby temperature which can be restored at a temperature at which printing-out is possible in a predetermined time for a constant time even in a case where reservation for the printing (output) is input in the step S 6 . When the temperature of the surface of the heat roller  3  is maintained at the first standby temperature, in the same manner as in the step S 5 , the powers having the predetermined frequencies are continuously supplied independently or simultaneously to the first and second coils in such a manner that temperature unevenness (ripple) is within a predetermined range in the longitudinal direction of the heat roller  3 . It is to be noted that the powers may be non-continuously supplied to the individual coils based on the output of the temperature sensor  17  (the supplying of the powers to all the coils is sometimes stopped with a change of the frequency of the supplied power in order to prevent the temperature of the surface of the heat roller  3  from being raised at first standby temperature).  
         [0081]     When the reservation for the printing (output) is input in the step S 6 , and “fixing step” is executed in the step S 9 , the coil to which the power is supplied, the time for which the power is supplied, or the frequency of the power is sometimes changed in accordance with the size of the sheet S. For example, when the length (width) of the image forming region is shorter than that of the heat roller  3 , the time for which the power is supplied to the second (end) coil  21 - 2  is set to be short as compared with the time for which the power is supplied to the first (middle) coil  21 - 1 . The time for which the power is supplied to the individual coils is set to be constant, and the frequency to be supplied may be changed for each coil (a case where level of interference sound generated depending on the difference of the frequency is in a predetermined range).  
         [0082]     On the other hand, when larger heat is absorbed at a fixing time as compared with a usual sheet S, the powers supplied to the arbitrary/all coils are increased based on the outputs of the individual temperature sensors  17  (the frequency is changed). For example, when the toners corresponding to a plurality of colors decomposed based on subtractive primaries are in a stacked state, or when an output medium (sheet S) is thick, a target defined temperature of the heat roller  3  differs especially with respect to the size of the output medium, medium type, and output medium thickness. For example, when the output medium is thick, the target defined temperature is raised. The power supplied to the arbitrary coil is controlled in such a manner that the temperature of the heat roller  3  is a target temperature with respect to temperature drop or temperature ripple.  
         [0083]     Additionally, it has been known that the surface of the heat roller  3  wears and/or deteriorates depending on the totaled size of the supplied output medium, and the type or thickness of the output medium, and radiant ratio fluctuates in the arbitrary position in the main scanning direction. For example, as shown in  FIG. 8 , when the number of passed sheets reaches about twenty thousand sheets, the radiant ratio drops by about 10% as compared with an initial state. It is to be noted that this deterioration ratio also depends on the type of the passed sheet (output medium) S. Therefore, as described later, infrared-ray quantity from the heat roller  3  and intensity (emission ratio) of rays (for detection) radiated from the temperature sensor  17  are changed.  
         [0084]     When the radiant ratio changes in this manner, and even when the actual temperature of the heat roller  3  is equal in the main scanning direction, a detection result (temperature data) output from the temperature sensor  17  is the temperature that differs with each position in the main scanning direction of the heat roller  3 . It is to be noted that the radiant ratio can be arbitrarily set in accordance with one or a plurality of sets of fixing size, image output times (fixed sheet number), roller rotation number and the like. Needless to say, the deterioration ratio (radiant ratio) may be set, for example, based on a counter value held by a counter  138  connected to the CPU  38  (or a storage section defined as firmware of the CPU  38 ), that is, the image forming times.  
         [0085]     Therefore, the cleaning roller  13  contains an abrasive for polishing the surface of the heat roller  3  beforehand, and the radiant ratio of the heat roller  3  is preferably uniformed. A heat-resistant temperature of the abrasive is preferably 200° C. or more, and, for example, colloidal silica, diamond (slurry), alumina (aluminum oxide), cerium oxide, zirconia (zirconium oxide), ceramics, nickel and the like are usable. It is to be noted that the abrasive may be mixed in the oil supplied to the heat roller  3  by the oil roller  15 . The color or resistance to water/oil is not especially restricted.  
         [0086]     For example, particle diameters of the abrasives are as follows:  
                                                           colloidal silica   0.02 to 0.05   (μm);           diamond (slurry)   0.2 to 8   (μm);           aluminum oxide (alumina)   0.05 to 5   (μm); and           cerium oxide   0.01 to 4   (μm).                      
 
         [0087]     It is to be noted that in a case where a predetermined time elapses from when the surface of the heat roller  3  is maintained at the first standby temperature, or a predetermined time elapses after the “fixing step” of the step S 9  ends, the surface of the heat roller  3  is maintained at a second standby temperature at which power consumption is smaller than that at the first standby temperature. The second standby temperature is a temperature at which the temperature of the heat roller  3  can be reset at a temperature at which the “fixing step” is executable within a defined time in a case where the powers are supplied to the individual coils at a time when the printing (output) is instructed. Needless to say, the powers to be supplied to the individual coils are controlled based on the temperature or the temperature signal of the heat roller  3  output from the temperature sensor  17 .  
         [0088]      FIG. 7  shows another example in which the temperature of the heat roller of the fixing apparatus shown in  FIGS. 1 and 2  is set by the driving circuit shown in  FIG. 4 .  
         [0089]     When an image forming apparatus (not shown) is started, all temperature sensors  17  are turned on. Moreover, the power having a predetermined frequency is supplied to all the first and second coils (S 101 ).  
         [0090]     Self temperature data and roller temperature detection signal (infrared-ray detection value) are output from ambient temperature detection sections (not shown) of the individual temperature sensors  17  and thermopile sections (not shown). It is to be noted that when a contact type thermistor is disposed (in each temperature sensor  17 ), an output of the contact type thermistor is usable in the detection of the self temperature (S 102 ).  
         [0091]     A detected temperature signal indicating the temperature of the surface of the heat roller  3  corresponding to the position of each temperature sensor  17  is obtained from self temperature data output from each temperature sensor  17  and roller temperature detection signal (infrared-ray detected value) (S 103 ).  
         [0092]     It is judged by the temperature control CPU  38  whether or not the surface has reached the reference temperature concerning all regions in the longitudinal direction (axial direction, i.e., main scanning direction) of the heat roller  3  based on the detected temperature signal. It is also judged whether or not the temperature has reached the reference temperature concerning the peripheral direction of the heat roller  3 . An order in which the temperature data (detection signal) is output can be arbitrarily set. It is also possible to set a latching timing on the side of the temperature control CPU  38  (S 104 ).  
         [0093]     When it is detected that the temperature of the surface of the heat roller  3  has reached the reference temperature in step S 104  (S 104 -Yes), it is judged by the temperature control CPU  38  whether or not a difference between the temperature in the region where the temperature is raised by the first coil  21 - 1  and that in the region where the temperature is raised by the second coil  21 - 2  is in a predetermined range. If necessary, temperature unevenness, that is, ripple in the peripheral direction of the heat roller  3  is also judged (S 105 ).  
         [0094]     When the temperature difference on the surface of the heat roller  3  is within the predetermined range in the step S 105  (S 105 -Yes), it is checked whether or not printing (output) is reserved (S 106 ).  
         [0095]     When the printing (output) is not reserved in the step S 106  (S 106 -No), “standby routine” is executed (S 107 ), and “standby control routine” for holding the surface of the heat roller  3  at the “standby temperature” is executed (S 108 ).  
         [0096]     When the printing (output) is reserved in the step S 106  (S 106 -Yes), the sheet S to which a toner image has been transferred is supplied to the nip N between the heat roller  3  and the press roller  5  subsequently to the “printing operation (image forming step)”, and the “fixing step” of fixing the toner to the sheet S starts (S 109 ).  
         [0097]     When it is detected in the step S 104  that the temperature of the surface of the heat roller  3  does not rise at the reference temperature (S 104 -No), the “temperature raising routine (warming-up)” is executed. That is, the power having the predetermined frequency is continuously supplied to all the coils (S 110 ).  
         [0098]     When the temperature difference of the surface of the heat roller  3  is larger than a predetermined magnitude in the step S 105 , that is, there is a ripple (temperature unevenness) (S 105 -No), it is checked whether or not a time until the temperature of the region where the temperature is raised by one of the coils reaches the reference temperature is within a defined time (S 111 ).  
         [0099]     It is detected in the step S 111  that the time until the temperature of the region where the temperature is raised by one of the coils reaches the reference temperature is within the defined time although there is the temperature unevenness in the temperature of the surface of the heat roller  3  (S 111 -No). In this case, the “temperature raising routine (warming-up)” of the step S 110  is executed. In this case, the power having the predetermined frequency is supplied to the coil capable of heating the region where the temperature of the surface of the heat roller  3  is low. At this time, the temperature data (roller temperature, infrared-ray detection value) output from the individual temperature sensors  17  differs with each sensor. The infrared-ray emission ratio from the heat roller  3  also fluctuates in accordance with the position of the heat roller  3  in the main scanning direction. Therefore, the intensity (emission ratio) of the ray (for detection) radiated toward the heat roller  3  from the thermopile section (not shown) of the temperature sensor  17  is changed based on the relation between the passed sheet number and the drop of the radiant ratio shown in  FIG. 8 .  
         [0100]     The infrared-ray emission ratio of each temperature sensor  17  is set beforehand in such a manner as to increase in accordance with the deterioration or the surface of the heat roller  3  as compared with an initial stage. In this case, needless to say, a change (change ratio) of the radiant ratio is set beforehand in such a manner that an error of the detected temperature falls within a predetermined range. The emission quantity of infrared rays is determined based on deterioration ratio held, for example, in a counter  138  (or a storage section defined as firmware of the CPU  38 ) connected to the CPU  38 .  
         [0101]     In the step S 111 , the time until the temperature of the region where the temperature is raised by one of the coils on the surface of the heat roller  3  reaches the reference temperature exceeds the defined time (the temperature does not rise within the defined time) (S 111 -Yes). In this case, it is judged that “the surface of the heat roller  3  is deteriorated”. In this case, in a display section of the image forming apparatus, for example, as shown in  FIG. 6 , a message urging maintenance such as “heat roller change/temperature sensor cleaning” is displayed (S 112 ).  
         [0102]     It is to be noted that when “standby routine” is set in the step S 107 , the temperature of the surface of the heat roller  3  is maintained at a first standby temperature which can be restored at a temperature at which printing-out is possible in a predetermined time for a constant time even in a case where reservation for the printing (output) is input in the step S 106 . When the temperature of the surface of the heat roller  3  is maintained at the first standby temperature, in the same manner as in the step S 105 , the powers having the predetermined frequencies are continuously supplied independently or simultaneously to the first and second coils in such a manner that temperature unevenness (ripple) is within a predetermined range in the longitudinal direction of the heat roller  3 . It is to be noted that the powers may be non-continuously supplied to the individual coils based on the output of the temperature sensor  17  (the supplying of the powers to all the coils is sometimes stopped with a change of the frequency of the supplied power in order to prevent the temperature of the surface of the heat roller  3  from being raised at first standby temperature).  
         [0103]     When the reservation for the printing (output) is input in the step S 106 , and the “fixing step” is executed in the step S 109 , the coil to which the power is supplied, the time for which the power is supplied, or the frequency of the power is sometimes changed in accordance with the size of the sheet S. For example, when the length (width) of the image forming region is shorter than that of the heat roller  3 , the time for which the power is supplied to the second (end) coil  21 - 2  is set to be short as compared with the time for which the power is supplied to the first (middle) coil  21 - 1 . The time for which the power is supplied to the individual coils is set to be constant, and the frequency to be supplied may be changed for each coil (a case where level of interference sound generated depending on the difference of the frequency is in a predetermined range).  
         [0104]     On the other hand, when larger heat is absorbed at a fixing time as compared with a usual sheet S, the powers supplied to the arbitrary/all coils are increased based on the outputs of the individual temperature sensors  17  (the frequency is changed). For example, when the toners corresponding to a plurality of colors decomposed based on subtractive primaries are in a stacked state, or when an output medium (sheet S) is thick, a target defined temperature of the heat roller  3  differs especially with respect to the size of the output medium, medium type, and output medium thickness.  
         [0105]     Additionally, it has been known that the surface of the heat roller  3  wears and/or deteriorates depending on the totaled size of the supplied output medium, and the type or thickness of the output medium, and radiant ratio fluctuates in the arbitrary position in the main scanning direction. For example, as shown in  FIG. 8 , when the number of passed sheets reaches about twenty thousand sheets, the radiant ratio drops by about 10% as compared with an initial state. It is to be noted that this deterioration ratio also depends on the type of the passed sheet (output medium) S. Therefore, as described later, infrared-ray quantity from the heat roller  3  and intensity (emission ratio) of rays (for detection) radiated from the temperature sensor  17  are changed. The deterioration ratio increases, when a required thermal capacity accompanying the fixing operation is larger. Therefore, a converted value of the radiant ratio of the infrared rays from the heat roller  3  is changed based on the deterioration ratio.  
         [0106]     Thus, the converted value is corrected in a detection position of the infrared ray from the heat roller  3  by each temperature sensor  17 . Accordingly, the temperature difference of the heat roller  3  in the longitudinal direction (main scanning direction) is maintained to be substantially constant in the life regardless of the type, thickness, and size (main scanning direction length) of the output medium (sheet) S and the total number of passed (image formed) sheets.  
         [0107]     As described above, according to a method of setting the temperature of the heat roller of the fixing apparatus using the thermopile type temperature sensor of the present invention,  
         [0108]     a) friction or the like by contact with the temperature detection device is prevented from being caused in the fixed image;  
         [0109]     b) the ripple (temperature unevenness) of the temperature of the heat roller surface is reduced;  
         [0110]     c) the range of the controlled temperature is enhanced (temperature difference is reduced) in the temperature control for the heat roller using the induction heating;  
         [0111]     d) traces of temperature changes (ripples) are inhibited from being left (generated) in the fixed image; and  
         [0112]     e) a warming-up time can be reduced.  
         [0113]     Therefore, the power consumption is also reduced. A quality of the toner image formed on the output material can be enhanced. It is to be noted that in the embodiment of the present invention, an induction heating system has been described as an example of the heating mechanism for raising the temperature of the heat roller, but the heating mechanism is not especially restricted as long as the temperature of the heat roller in the longitudinal direction can be independently controlled.  
         [0114]     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general invention concept as defined by the appended claims and their equivalents.