Patent Publication Number: US-7212761-B2

Title: Fuser and temperature control method

Description:
The present application is a Continuation of U.S. application Ser. No. 10/805,420, filed Mar. 22, 2004, now U.S. Pat. No. 7,079,782 the entire contents of which is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a fixing apparatus installed in image forming apparatuses, copiers, and printers where an image is formed on a transfer material by an electrophotographic process, for fusing and fixing a development agent placed on the transfer material to it. 
   2. Description of the Related Art 
   In copiers and printers using an electron process, it is known that a toner image formed on a photoconductive drum is transferred onto a transfer material and thereafter the toner image is fused in a fixing apparatus having a heating roller and a pressurizing roller and fixed onto the transfer material. 
   At this time, for controlling the temperature of the heating roller, a method of detecting the surface temperature of the heating roller by a detecting element, which is arranged in contact with the surface of the heating roller, has been known. However, the contact-type temperature detecting element slides on the surface of the heating roller, so that it may degrade the surface, thereby shortening the life of the heating roller. When the surface is degraded, the sensitivity of the detecting element decreases, with the result that wrong temperature may be detected. 
   Also another method has been known which uses a temperature detecting element for detecting the temperature of a heating roller without being in contact with the heating roller by sensing infrared rays emitted from the heating roller. 
   However, the emission rate of infrared rays from a heating roller detected by the non contact temperature detecting element differs between the life-start time and the life-end time since the surface of the heating roller is gradually degraded while being in contact with a transfer material holding toner thereon. Since the degradation of the surface of the heating roller varies depending upon the type and size of a transfer material to be fed, the infrared ray emission rate varies in the longitudinal direction of the roller. To describe more specifically, since infrared ray emission rate changes, the time for the temperature detected by the non-contact temperature-detecting element to reach a predetermined temperature delays. 
   For example, Japanese Patent Application KOKAI Nos. 2001-242743 or 2000-259033 discloses a fixing apparatus in which the temperature of a heating roller is detected by a temperature-detecting element in contact with a non-paper-feeding area and a non-contact temperature-detecting element for detecting the temperature of a paper-feeding area. However, a time lag is produced since the sensitivity differs between the contact-type temperature detector and the non-contact temperature detector. Hence, it has been difficult to accurately detect the temperature of a heating roller. 
   Furthermore, Japanese Patent Application KOKAI No. 2000-227732 discloses a fixing apparatus in which the radiation emission rate from a heating roller installed therein is detected by a radiation-detecting unit. However, since the radiation-detecting device is installed in a fixing apparatus where toner and paper dust are scattered, wrong detection may occur due to smudges. To solve this, it is effective to provide not only cleaning means to the temperature detecting element but also cleaning means to the radiation detecting unit; however they increase cost. In addition, the infrared ray emission rate varies depending upon how significantly stained on the surface of the heating roller. 
   Furthermore, in Japanese Patent Application KOKAI No. 2001-34109 discloses a technique for correcting temperature based on the difference between the temperature detected by an infrared detecting member for detecting the amount of infrared rays and the temperature detected by surface temperature detecting means which includes a thermistor for correcting the temperature of the infrared detecting member. 
   In this way, in the case where a non-contact temperature-detecting element is used, when infrared ray radiation rate changes, the temperature of the heating roller cannot be sensed accurately. Since heating means for heating the heating roller control heat generation depending upon the surface temperature of the heating roller inaccurately detected, the heating roller is not controlled at a proper temperature. 
   BRIEF SUMMARY OF THE INVENTION 
   According to an aspect of the present invention, there is provided a fixing apparatus comprising: 
   a heating roller a surface of which is formed of a conductive material; 
   a heating unit which heats the heating roller; 
   a temperature detecting mechanism having one or more non-contact temperature detecting units which are arranged in non-contact with the surface of the heating roller and which detect the surface temperature of the heating roller by sensing infrared rays emitted from the heating roller; and 
   a correction circuit which corrects information as to the surface temperature of the heating roller output from the non-contact temperature detecting unit(s) based on a predetermined correction coefficient. 
   According to another aspect of the present invention, there is provided a method of controlling temperature comprising: 
   detecting the temperature of a heating roller by use of a non-contact temperature-detecting unit; 
   correcting the detected temperature based on a predetermined correction coefficient when the temperature detected by the non-contact temperature detecting unit falls within a temperature correction range. 
   According to a further aspect of the present invention, there is provided a fixing apparatus comprising: 
   a heating roller a surface of which is formed of a conductive material; 
   a heating unit which heats the heating roller; 
   a temperature detecting mechanism including a temperature detecting unit and a signal output section; 
   the temperature detecting unit which is arranged in non-contact with the surface of the heating roller and detects the surface temperature of the heating roller by sensing infrared rays emitted from the heating roller; and 
   in which the signal output section which is arranged at a predetermined site rarely affected by infrared rays emitted from the heating roller and which converts the information as to the surface temperature of the heating roller from the temperature detecting unit into an electric signal. 
   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 DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. 
       FIG. 1  is a schematic view explaining the structure of a fixing apparatus to which a first embodiment of the present invention can be applied; 
       FIG. 2  is a block diagram explaining the control system of the fixing apparatus shown in  FIG. 1 ; 
       FIG. 3  is graph showing a method of controlling temperature applicable to a fixing apparatus according to the present invention; 
       FIG. 4  is a reference table explaining how to obtain a correction coefficient used in a temperature controlling method applicable to a fixing apparatus according to the present invention; 
       FIG. 5  is a graph showing the temperature versus the warming-up time of the charger shown in  FIG. 1 ; 
       FIG. 6  is a flowchart explaining the operation of the fixing apparatus shown in  FIG. 1 ; 
       FIG. 7  is a schematic view of an example of a moving mechanism for moving the temperature detecting mechanism; 
       FIG. 8  is a schematic side view of the moving mechanism shown in  FIG. 7 ; 
       FIG. 9  is a schematic view showing another moving mechanism for moving the temperature detecting mechanism shown in  FIG. 1 ; 
       FIG. 10  is a schematic figure of a fixing apparatus according to a second embodiment; and 
       FIG. 11  is a schematic view of the fixing apparatus shown in  FIG. 10 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An example of a fixing apparatus to which an embodiment of the present invention can be applied will be explained with reference to the accompanying drawing. 
   (First Embodiment) 
     FIG. 1  shows a fixing apparatus to which an embodiment of the present invention can be applied. 
   As shown in  FIG. 1 , a fixing apparatus  1  has a heating roller  2 , pressurizing roller  3 , pressurizing spring  4 , separation nail  5 , cleaning roller  6 , heat-induction unit  7 , temperature detecting mechanism  8  and thermostat  9 . 
   The heating roller  2  has a surface formed of an conductive member composed of iron, stainless steel, nickel, or an alloy of aluminum and stainless steel. 
   The pressurizing roller  3  is an elastic roller formed of a rotation axis having a predetermined diameter covered with a silicon rubber or fluorine rubber of a predetermined thickness. 
   The pressurizing spring  4  applies a predetermined pressure to the axis of the heating roller  2  such that the pressuring roller  3  is maintained in posture almost in parallel to the axis of the heating roller  2 . On the other hand, the pressurizing spring  4  can be maintained in parallel to the heating roller  2  since predetermined pressure is applied to the pressurizing spring  4  from both ends of the pressurizing roller  3  via a pressurizing support bracket  4   a  for supporting the axis of the pressurizing roller  3 . 
   By virtue of this, a nip of a predetermined width is formed between the heating roller  2  and pressurizing roller  3 . 
   The heating roller  2  is rotated in a direction indicated by the arrow, CW, at substantially a constant rate by a fixing apparatus motor  32 , which will be explained later with reference to  FIG. 2 , or a main motor  33  for rotating a photoconductive drum  34  shown in the same figure. The pressurizing roller  3 , since it is in contact with the heating roller  2  by means of the pressurizing spring  4 , is rotated in a reverse direction of the rotation direction of the heating roller  2  at a position in contact with the heating roller  2  when the heating roller  2  is rotated. 
   The separation nail  5  is set around the heating roller  2  and at a predetermined position which is specified by being downstream of the nip at which the heating roller  2  and the pressurizing roller  3  are in contact with each other, in the rotation direction of the heating roller  2  and in the proximity of the nip. The separation nail  5  plays a role of separating a paper sheet P passing through the nip from the heating roller  2 . Note that the present invention is not limited to this embodiment. For example, when a large amount of developing agent is used for forming a color image on a paper sheet by fusing, it is difficult to separate the paper sheet from the heating roller. Therefore, in such a case, a plurality of separation nails  5  may be provided, whereas a separation nail may not be provided when a paper is easily separated. 
   The cleaning roller  6  removes debris such as toner or paper dust coming off on the surface of the heating roller  2 . 
   The heat-induction unit  7  is arranged outside the heating roller  2  and has at least one heating coil (magnetizing coil), which applies a predetermined magnetic field to the heating roller  2  when a predetermined electric power is supplied. When the predetermined electric power is supplied from a magnetizing circuit  22  to the heating coil, the heating roller  2  is heated to a predetermined temperature. 
   The temperature detecting mechanism  8  is arranged in no contact with the surface of the heating roller  2  for detecting the temperature of the outer surface of the heating roller  2 . To explain more specifically, the temperature detecting mechanism  8  is arranged downstream of the position of the heat-induction unit  7  in the rotation direction of the heating roller  2  and arranged upstream of the nip portion, and plays a role of detecting the surface temperature of the heating roller  2  heated by the heat-induction unit  7 . 
   The thermostat  9  senses abnormal heating, a phenomena where the surface temperature of the heating roller  2  abnormally increases. When heat is abnormally generated, the thermostat  9  shuts off the power to be supplied to the heating coil of the heat-induction unit  7 . It is preferable that at least one thermostat  9  is arranged near the surface of the heating roller  2 . 
   Around the pressurizing roller  3 , a separation nail (not shown) for separating a paper sheet P from the pressurizing roller  3  and a cleaning roller (not shown) for removing toner deposited on the circumference surface of the pressurizing roller  3  may be provided. 
   When a paper sheet P holding toner T thereon passes through the nip portion formed between the heating roller  2  and the pressurizing roller  3 , the toner T is molten and pressed onto the sheet P to fix an image on the paper. 
     FIG. 2  shows a block diagram explaining the control system of the fixing apparatus shown in  FIG. 1  and also shows a schematic view of the fixing apparatus as seen from the arrow R. 
   As shown in  FIG. 2 , the heat-induction unit  7  includes induction heating coils  7 A,  7 B and  7 C. The heating coils  7 A is arranged along the axial direction of the heating roller  2  so as to face the center portion thereof and applies a magnetic field to the center portion. Coils  7 B and  7 C are arranged along the axial direction of the heating roller  2  so as to face the lateral portions thereof to apply magnetic fields to the both lateral portions. 
   The temperature detecting mechanism  8  includes a plurality of non-contact temperature detecting elements, for example,  8   a ,  8   b ,  8   c ,  8   d , and  8   e , which are arranged along the longitudinal direction of the heating roller  2 . For example, the non-contact temperature detecting element  8   a  is arranged so as to face the coil  7 A; the non-contact temperature detecting element  8   b  is arranged so as to face the coil  7 B. The non-contact temperature detecting element  8   c  is arranged so as to face the coil  7 C. The non-contact temperature detecting element  8   d  is arranged so as to face the joint between the coil  7 A and the coil  7 B. The non-contact temperature detecting element  8   e  is arranged so as to face the joint between the coil  7 A and the coil  7 C. 
   In this way, it is preferable that the temperature detecting elements  8  be arranged so as to face the centers of the coils and the joints of adjacent coils of the induction-heating unit  7 . More specifically, the number of coils (CX) arranged in the heat-induction unit  7  and the number (SY) of non-contact temperature detecting elements arranged in the temperature detector mechanism  8  preferably satisfy the following equation:
 
 SY= 2 CX− 1.
 
   The non-contact temperature detecting elements  8   a  to  8   e , each may have an infrared-ray sensing section for converting infrared radiation energy from the heating roller  2  into electric power and a temperature signal circuit board for converting the electric power from the infrared-ray sensing section to an electric signal. As the infrared-ray sensing section, a thermopile generating electromotive force due to, for example, the Seebeck effect, an infrared ray sensor for sensing a temperature change due to the pyroelectric effect may be used. 
   As shown in  FIG. 2 , a main CPU  20  is connected directly or indirectly to an IH controller  21 , an excitation (magnetization) circuit  22 , temperature detecting circuit  23 , a temperature correcting circuit  24 , a motor driving circuit  25 , a counter  26 , a display section  27 , a timer  28 , RAM  29 , ROM  30 , and NVRAM  31 . 
   The main CPU  20  integrally controls the fusing/fixing operation of the fixing apparatus  1 . 
   The IH controller  21  outputs a driving signal to the excitation circuit  22  to allow the heat-induction unit  7  to supply a predetermined electric power. More specifically, the IH controller  21  controls the temperature of the heating roller  2  so as to be set at a temperature required for fusing/fixing based on the temperature information of the heating roller  2  output from the temperature detecting circuit  23 , directly or via the temperature correcting circuit  24 . Note that, as shown in this embodiment, in the case where a temperature detecting mechanism including a plurality of temperature detecting units capable of detecting a plurality of sites of the heating roller is used, it is preferable that the temperature detecting units are arranged both upstream and downstream of the nip so as to ensure a temperature difference (ripple) between the upstream site and downstream sites falls within a predetermined range. 
   The excitation circuit  22  supplies to a predetermined amount of power to coils  7 A to  7 C in response to the magnetization signal output from the IH controller  21 . By supply a predetermined amount of power, each of the coils  7 A to  7 C generates predetermined magnetic flux serving as “heating power”. The “heating power” is defined as the magnitude of magnetic flux which permits the heating roller  2  to generate spiral current and which is determined by the magnitude of electric power supplied to each of the coils  7 A to  7 C. For example, when a paper sheet passes through the center portion of the heating roller  2 , a predetermined electric power is generated for magnetizing the coil  7 A. On the other hand, when a paper sheet passes through the center portion and the lateral portions of the heating roller  2 , a predetermined amount of power, for example, 1,300 W, is generated to magnetize the coils  7 A to  7 C. 
   The temperature detecting circuit  23  is connected to non-contact temperature detecting elements  8   a  to  8   e  and outputs a temperature detection signal, which is temperature information of the heating roller  2  detected. In this embodiment, the following explanation will be made by designating the temperature information of the heating roller  2  detected by the non-contact temperature detecting element  8   a  as a temperature detection signal SG 1 . Note that the temperature detecting circuit  23  can output temperature detection signals SG 2 , SG 3 , SG 4  and SG 5 , which are temperature information respectively obtained by other non-contact temperature detecting elements  8   b  to  8   e.    
   The temperature correcting circuit  24  is connected to a RAM  24   a  which stores a predetermined correction coefficient, which will be described later, a ROM  24   b  which is an operation area in which a correction operation is performed based on the temperature detection signal SG 1 . The temperature correcting circuit  24  carries out temperature correction and outputs a correction value CV 1  obtained through calculation performed from the correction coefficient and the temperature detection signal SG 1 . 
   The motor driving circuit  25  is connected to a fusion motor  32  for rotating the heating roller  2  or may be connected to a main motor  33  for rotating a photoconductive drum  34 . 
   The counter  26  counts the rotation number of the heating roller  2  rotated by the fusion motor  32 , the rotation number of the photoconductive drum  34  rotated by the main motor  33 , or the number CN of paper sheets on which an image is to be fused and fixed, that is the number of paper sheets passing through the space between the heating roller  2  and pressurizing roller  3 . The counter  26  may count the number of paper sheets P 1  which pass through the space between both rollers  2  and  3  in contact with the center axial portion separately from the number of paper sheets P 2  in contact with the entire surface including the center and lateral axial portions. 
   The display section  27  displays a serviceman inspection mode which informs that it is time for cleaning and exchanging the heating roller  2  and for cleaning for the temperature detecting mechanism  8 . 
   The timer  28  detects the elapsed time ET from the power is turned on. For example, W/UT 1 , W/UT 2 , W/UT 3  requiring for warming-up can be detected. The RAM  29  temporarily stores predetermined information detected by the counter  26  and the timer  28 . The ROM  30  stores an initial program and fixed information. 
   NVRAM  31  stores the number of fixation paper sheets counted by the counter  26  and the rotation number of the heating roller  2  or the rotation number of the photoconductive drum  34 . These numbers are stored while renewing and the stored numbers will not disappear when the power is turned off. The number CN of the fixation paper sheets includes the count numbers CNP 1  and CNP 1  corresponding to paper sheets P 1  and P 2 . 
   Next, correction operation of temperature carried out by the temperature correcting circuit  24  will be explained. 
   A method how to correct the temperature by a fixing apparatus according to the present invention will be explained with reference to  FIG. 3 . 
   As shown in  FIG. 3 , the lateral axis shows the count number CN of the fixation sheets counted by the counter  26  and the longitudinal axis shows the temperature detected by the non-contact temperature detecting element  8   a , represented by the detected-temperature signal SG 1 . 
   Curve α shows a change of the detected-temperature signal, SG 1  with an increase of the sheet number of the fixation papers (count number CN) when power E 1  is supplied to coils  7 A to  7 C of the heat-induction unit  7  as heating power, in order to heat the heating roller  2  to a predetermined temperature Ti. As shown by Curve α, the non-contact detecting element  8   a  (temperature detecting mechanism  8 ) detects temperature information T 2  by infrared rays emitted from the heating roller  2  which is heated to a predetermined temperature T 1  when power E 1  is supplied to the induction-heating unit  7 , and outputs the detection temperature signal SG 1  including the temperature information T 2 , to the IH controller  21 , until reaching, for example, the count number CN 1 . 
   However, as the heating roller  2  comes closer to the end of the life which means that exchange/cleaning of the heating roller  2  is required, the infrared radiation rate of the heating roller  2  decreases or the temperature detecting mechanism  8  (non-contact temperature detecting element  8   a ) gets dirty. As a result, as shown by Curve α, the detection temperature that is, the detection temperature signal SG 1 , gradually decreases. In other words, despite the fact that constant power E 1  is supplied to the heat-induction unit  7 , that is, the same heating power, is supplied to the heating roller  2 , the temperature detected by the temperature detecting mechanism  8  (non-contact temperature detecting element  8   a ) in the beginning differs from that detected by the end of the life. 
   A temperature correction method according to the present invention is characterized in that, while the temperature difference, that is, the detection temperature signal SG 1 , falls within a range of temperature information T 2  to T 3  (temperature correction range), temperature correction is performed, and when the temperature difference reaches the detection temperature information T 3  (cleaning/exchange range), the cleaning of the temperature detecting mechanism  8  or the cleaning/exchange of the heating roller  2  is instructed. 
   The correction coefficient (β 1 , β 2 , β 3 ) may be defined in accordance with a predetermined table indicating the difference of temperature detection signal SG 1  defined depending upon the count number of fixation sheets, in the conditions where constant power E 1  is supplied to the heat-induction unit  7 , as shown in  FIG. 3 . More specifically, in this embodiment, the table shown in  FIG. 4  may be used. 
   As shown in  FIG. 4 , the temperature correcting circuit  24  outputs, to the IH controller  21 , the correction value CV 1  which is obtained by adding, a correction coefficient (β 1 , β 2 , β 3 ), that is, correction temperature, to the detected temperature signal SG 1  output from the temperature detecting circuit  23  as the detected temperature of the heating roller  2 . Note that, when the correction temperature is performed based on the correction coefficient (β 1 , β 2 , β 3 ) shown in  FIG. 4 , the temperature of the heating roller  2  after the correction avoids being lower than the real temperature of the heating roller  2  shown in  FIG. 3 . As a result, it is possible to prevent detecting the temperature of the heating roller at a value lower than the real temperature of the heating roller  2 , thereby preventing outputting a larger power to the heat-induction unit  7 . 
   Next, an example how to warming up a fixing apparatus of the present invention will be explained. 
     FIG. 5  shows time versus temperature during the warming-up process. 
   As shown in  FIG. 5 , the lateral axis shows warming-up time W/UT measured by a timer  28 . The left longitudinal axis shows a predetermined surface temperature of the heating roller  2  and the right longitudinal axis shows the detected temperature signal SG 1 , that is, the temperature detected by the temperature detecting mechanism  8 . The temperature detecting mechanism  8  detects the temperature of the heating roller  2  by sensing infrared rays emitted therefrom to obtain the detected temperature (for example, T 2  or T 3 ), which therefore does not coincide with the temperature of the heating roller  2  shown on the left longitudinal axis. Needless to say, the detected temperature is information as to the temperature of the heating roller obtained after a predetermined arithmetic calculation is applied. 
   Curve γ shows a temperature change with time during the warming-up process where the heating roller  2  is warmed up to a predetermined temperature, 180° C. In this embodiment, the time periods for first, second, third warming-up for a fixing apparatus are set up as shown by Curve γ. The first warming-up time W/UT 1  is the time period required for generating heat from the heating roller  2 , at, for example, 160° C., which is lower by a predetermined value than the predetermined temperature, 180° C. The second warming-up time, W/UT 2 , is a time point at which the heating roller  2  has reached the predetermined temperature 180° C., more specifically, the time period including a predetermined allowance of time after the time the heating roller  2  has reached the predetermined temperature, 180° C. The third warming-up time W/UT 3  is the time when a correction time has passed after the-second warming-up time W/UT 2 , in other words, the time at which the warming-up is completed. 
   The temperature sensing circuit  23  outputs the temperature information T 2  as the temperature detection signal SG 1  when the temperature of the heating roller  2  is 180° C. The temperature information T 3  is lower than the temperature information T 2 , as indicated on the right longitudinal axis and preferably lower than the temperature (160° C.) of the first warming-up time W/UT 1 . In this embodiment, the temperature information T 3  is defined as the temperature at which exchange or cleaning of the unit is instructed in the exchange/cleaning cycle (PM cycle), if the temperature does not reach T 3  even after the first warming-up time W/UT 1  has passed. Furthermore, the temperature correction according to this embodiment is preferably performed during the warming up and preferably the temperature information T 3  is not near 160° C. This is because when temperature correction is carried out by reducing the temperature of the heating roller by the fusing/fixing operation, the fusing/fixing control may be confused. 
   Referring to the flowchart shown in  FIG. 6 , how to operate the fixing apparatus of the present invention will be explained. 
   As shown in  FIG. 6 , when the fixing apparatus is turned on (S 1 ) to supply the power to the temperature detecting mechanism  8 , warming up is initiated (S 2 ). The IH controller  21  supplies a magnetization signal to the excitation circuit  22 . When a predetermined amount of power is supplied to the heat-induction unit  7 , the temperature of the heating roller rises. 
   When the first warming-up time W/UT 1  is measured by a timer  28  (S 3 —YES), whether the temperature detection signal SG 1  output from the temperature sensing circuit  23  is equal to or greater than the temperature information T 3  or not is determined (S 4 ). 
   When the temperature detection signal SG 1  is greater than the temperature information T 3  (S 4 —YES), the second warming-up time W/UT 2  is further measured by the timer  28  (S 5 —YES) and thereafter whether the temperature detection signal SG 1  is equal to or greater than the temperature information T 2  or not is determined (S 6 ). 
   When the temperature detection signal SG 1  is lower than the temperature information T 2  (S 6 —NO), the temperature is corrected (S 7 ) in the manner mentioned above. More specifically, a predetermined correction is performed depending upon the count number of fixation paper sheets counted by the counter  26 . When the count number CN is smaller than the count number CN 4  (S 8 —YES), a correction value CV 1  (correction coefficient varied depending upon the count number CN is added to the temperature detection signal SG 1 ), as shown in  FIG. 4 , is output from the temperature correcting circuit  24  (S 9 ). 
   Whether the output correction value CV 1  is equal to or greater than the temperature information T 2  or not is determined (S 10 ). When the correction value CV 1  is the temperature information T 2  or more (S 10 —YES), the warming up is terminated (S 11 ). When a printing instruction (fixing instruction) is given (S 12 —YES), the fixing operation is started (S 13 ) and the number of fixation paper sheets counted by the counter  26  is renewed (S 14 ). The count number renewed is stored in NVRAM  31  whose memory will not be erased even if the power is turned off. When the printing instruction is not given (S 12 —NO), the heating roller is maintained at a predetermined temperature as the stand-by state (S 15 ). 
   On the other hand, in Step S 10 , when the correction value CV 1  is lower than the temperature information T 2  (S 10 —NO), the warming-up operation is carried out until a predetermined time passes. More specifically, when time does not reach the third warming-up time W/UT 3  (S 16 —NO), the operation goes back to step S 6  where, whether or not the temperature detection signal SG 1  is equal to or greater than the temperature information T 2  is determined (S 6 ). 
   When the time reaches the third warming-up time W/UT 3  (S 16 —YES) or when the temperature detection signal SG 1  is lower than the temperature information T 3  in Step S 4  (S 4 —NO), or when the count number CN is equal to or greater than CN 4  in step S 8  (S 8 —NO), the warming-up process is terminated and then the power to be supplied to the heat-induction unit  7  is stopped (S 17 ), and then the serviceman inspection mode is displayed on the display section  27  to inform that the heating roller  2  must be exchanged and the temperature detecting mechanism  8  must be cleaned (S 18 ). 
   The correction coefficient is not limited to the example shown in  FIG. 4 . The correction coefficient may be a predetermined value which is determined depending upon the material, thickness or size of an image recording medium to be fed, or a feeding speed of the medium, the rotation number of the heating roller  2  and the rotation number of the photoconductive drum  33  counted by the counter  26 . 
   The temperature detecting mechanism  8  containing five non-contact temperature detecting elements,  8   a ,  8   b ,  8   c ,  8   d , and  8   e , has been explained. The present invention is not limited to this. The temperature detecting mechanism  8  may contain at least one non-contact temperature-detecting element of  8   a  and  8   b.    
   Furthermore, as means for generating heat from the heating roller  2 , a heat-induction unit  7  is mentioned. However, the present invention is not limited to this. A lamp may be arranged within the heating roller  2 . 
   In this embodiment, the temperature detection signal SG 1  output from the temperature detecting circuit  23  has been explained. However, temperature correction can be performed as to the temperature detection signals SG 2 , SG 3 , SG 4 , and SG 5 , which are temperature information based on other non-contact temperature detecting elements  8   b  to  8   e.    
   Next, a moving mechanism for moving the temperature detecting mechanism  8  will be explained. 
   As shown in  FIG. 7 , the non-contact temperature detecting elements  8   a  and  8   b  constituting the temperature detecting mechanism  8  may be arranged movably by the moving mechanism  800  in the axial direction S. 
   The movable mechanism  800  has a lope-form moving mechanism  800 A, which is moved in the axial direction S by a motor (not shown). The moving mechanism  800 A holds the non-contact temperature detecting elements  8   a  and  8   b  at different phases along the rotation direction of the heating roller  2 , as shown in  FIG. 8 . The non-contact temperature detecting elements  8   a  and  8   b  are preferably arranged in the same distance apart from the surface of the heating roller  2 . The moving mechanism  800 A is not limited to a lope-form. A belt-form and a rack-and-pinion form may be employed. 
   The moving mechanism  800  moves non-contact temperature detecting elements  8   a  and  8   b  to predetermined detection positions near the surface of the heating roller  2  when heat is generated from the heating roller  2  by the fusing/fixing operation and moves them back to a standby area  810  formed at one end of the moving mechanism  800  in the axial direction. The stand-by area  810  may be separated, by a dustproof wall  810   a  formed near the heating roller, from the heating roller  2 , around which toner and dust are scattered by the fixing operation. Furthermore, at a predetermined position of the stand-by area  810 , a temperature-detecting element cleaning mechanism  810   b  may be provided for cleaning the non-contact temperature detecting elements  8   a  and  8   b  moved to the stand-by area  810 . 
   As shown in  FIG. 9 , the temperature detecting mechanism  8  may be provided movably by the moving mechanism  850  in the direction of the arrow Q, which is perpendicular to the axial direction S of the heating roller  2 . 
   The moving mechanism  850  has moving means, which is constituted of a drive shaft having a spiral cut formed therein and a temperature-detecting mechanism holding member engaged with the spiral cut and movably formed along the axial direction of the drive shaft. The non-contact temperature detecting elements  8   a  to  8   e  of the temperature detecting mechanism  8  are arranged such that they are respectively arranged at the predetermined temperature detection positions of the temperature detecting mechanism holding member when the heating roller  2  generates heat by the fusing/fixing operation. In operations other than fusing/fixing, the non-contact temperature detecting elements  8   a  and  8   b  are moved in the direction of the arrow Q and placed in the stand-by area  860 . In the stand-by area  860 , a dustproof wall  860   a  and the temperature detecting element cleaning mechanism  860   b  may be provided similarly in the stand-by area  810 . 
   As described, in the present invention employing a non-contact temperature detecting mechanism, since it is possible to prevent a sliding trace from being formed on the surface of the heating roller  2  unlike the case of using the contact-type temperature detecting mechanism. Therefore, the life of the heating roller  2  can be extended. 
   Since the detected temperature is corrected by the correction coefficient previously set, the temperature of the heating roller can be quickly increased. As a result, the warming-up time can be reduced. Furthermore, it is possible to prevent the corrected temperature of the heating roller  2  from decreasing the predetermined temperature of the heating roller  2 . As a result, the heat-generation efficiency can be improved. 
   The temperature detecting mechanism  8 , when the sensitivity of the mechanism deteriorates due to smudge, is cleaned by the serviceman inspection mode or the temperature-detecting element cleaning mechanisms  810   b  and  860   b . Therefore, the life of the mechanism  8  is extended and the deterioration of temperature detection characteristics can be prevented. In addition, it is possible to prevent the temperature detecting mechanism  8  from detecting the wrong temperature, thereby preventing trouble in temperature control of the heating roller performed based on the temperature detected. 
   (Second Embodiment) 
   Next, referring to  FIGS. 10 and 11 , the second embodiment will be explained. With respect to the structural elements shown in  FIGS. 10 and 11 , like reference numerals are used to designate like structural elements corresponding to those like in the first embodiment and any further explanation is omitted for brevity&#39;s sake. 
     FIG. 10  shows an example of a fixing apparatus to which a second embodiment is applied. 
   As shown in  FIG. 10 , a fixing apparatus  101  has a temperature detecting mechanism  40 . The temperature detecting mechanism  40  is provided in no contact with the surface of the heating roller  2  and has an infrared-ray sensing unit  41  which converts infrared radiation energy from the heating roller  2  to electric power and a temperature signal circuit board  42  which converts the electric power from the infrared-ray sensing unit  41  into an electric signal. 
   The infrared sensing unit  41  is provided in the close proximity of the surface of the heating roller  2 , for detecting the temperature of the heating roller  2  by sensing the infrared rays emitted from the heating roller  2 . As the infrared-ray sensing unit  41 , a thermopile which produces electromotive force due to, for example, the Seebeck effect, or an infrared-ray sensor for sensing a temperature change due to the pyroelectric effect. 
   The temperature signal circuit board  42  is provided at a place rarely affected by infrared rays emitted from the heating roller  2  or thermal convection, more specifically, outside the case of a fixing apparatus  101 . Alternatively, the temperature signal circuit board  42  is held in a case which can mitigate the effects of infrared rays and thermal convection or may be placed inside or outside the fixing apparatus  101 . 
     FIG. 11  shows a schematic view of the fixing apparatus shown in  FIG. 10  as seen from the arrow R and a temperature detecting mechanism  40 . 
   As shown in  FIG. 11 , the temperature detecting mechanism  40  has a plurality of infrared detecting elements  41 , more specifically, an infrared ray temperature detecting element  41   a  arranged so as to face a coil  7 A, an infrared ray temperature detecting element  41   b  arranged so as to face a coil  7 B, and an infrared ray temperature detecting element  41   c  arranged so as to face a coil  7 C. 
   The temperature signal circuit board  42  includes a temperature signal circuit board  42   a  connected to the infrared ray temperature detecting element  41   a , a temperature signal circuit board  42   b  connected to the infrared ray temperature detecting element  41   b , and a temperature signal circuit board  42   c  connected to the infrared ray temperature detecting element  41   c . These temperature signal circuit boards  42   a  to  42   c  are individually connected to the temperature detecting circuit  23  and individually output a data temperature signal. The temperature detecting circuit  23  outputs a temperature detection signal based on the data temperature signal. For example, the temperature signal circuit board  42   a  outputs a data temperature signal DG 1  based on the temperature information detected by the infrared detecting element unit  41   a , whereas the temperature detecting circuit  23  outputs a temperature detection signal SG 1  based on the data temperature signal DG 1 . Note that the temperature signal circuit boards  42   b ,  42   c  output the data temperature signals DG 2  and DG 3 , respectively, whereas the temperature sensing circuit  23  can output temperature detection signals SG 2  and SG 3  based on the data temperature signals DG 2  and DG 3 , respectively. The temperature detecting signals SG 1  to SG 3  can be targets for temperature correction similarly in the first embodiment. 
   As described, by arranging non-contact type infrared sensing unit  41  for detecting the temperature by sensing infrared rays in the proximity of the heating roller  2 , more accurate temperature information can be obtained and further the temperature detection characteristics can be improved. In addition, by arranging the temperature signal circuit board  42  at a site rarely affected by infrared rays, it is possible to prevent corruption of the temperature signal circuit board  42  and extend the life of the circuit board  42 . 
   The infrared sensing unit  41  includes a warm contact section whose temperature is increased by absorbing infrared rays, and a cold contact section whose temperature is not increased since it is covered with heat sink. By virtue of the difference in temperature between the warm contact section and the cold contact section, electromotive force may be generated due to the Seebeck effect. In this case, since the cold contact section is preferably not affected by infrared rays and thermal convection, it may be arranged at a site free from the infrared rays and thermal convention, for example, by being integrally formed with the temperature signal circuit board  42 . 
   The temperature detecting mechanism  40  has been explained which has three temperature detecting units and three temperature signal circuit boards. However, the present invention is not limited to this and may include at least one temperature detecting unit and temperature signal circuit board. 
   In this embodiment, the moving mechanisms  800  and  850  explained with reference to  FIGS. 7 to 9  may be applied. The moving mechanism  800  moves the infrared ray temperature detecting elements  41   a – 41   c  in the direction of the arrow S and places them at the stand-by area  810 . Furthermore, the moving mechanism  850  moves the infrared ray temperature detecting elements  41   a – 41   c  in the direction of the arrow Q to place them at the stand-by area  860 . 
   Furthermore, in the site in which the temperature signal conversion circuit board is arranged and which is rarely affected by infrared rays, an atmosphere temperature detecting mechanism for detecting the temperature of the atmosphere may be provided. 
   Based on the temperature detecting signal SG 1  output from the temperature detecting circuit  23 , temperature correction explained in the first embodiment may be carried out.