Patent Publication Number: US-2011076043-A1

Title: Fixing device

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is based upon and claims the benefit of priority from: U.S. provisional application 61/246,491, filed on Sep. 28, 2009; U.S. provisional application 61/246,485, filed on Sep. 28, 2009; and U.S. provisional application 61/246,495, filed on Sep. 28, 2009; the entire contents all of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to a technique to detect the temperature of an induction heated belt surface in a non-contact manner. 
     BACKGROUND 
     Hitherto, with an energy-saving technique, reduction in heat capacity of a heating target member and quick temperature rising by induction heating or the like are possible. 
     In a fixing device of a system in which a belt is heated by induction heating, a structure is known in which a non-contact type thermostat detects the temperature of a surface of the belt on the side of contact with a sheet. 
     In the structure using the non-contact type thermostat, there is a case where a gap between the thermostat and the belt is not stably maintained, and this is a problem in stabilizing the performance of the thermostat. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an image forming apparatus. 
         FIG. 2  is a view showing an example of an auxiliary heat generating member. 
         FIG. 3  is a sectional view showing a structure of an auxiliary heat generating member  6 ′ in a second embodiment. 
         FIG. 4  is a sectional view showing a schematic structure of an auxiliary heat generating member  6 ″ in a third embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to embodiments, a fixing device includes a belt, a roller, a support member, a coil, an auxiliary heat generation member, and a temperature sensor. 
     The belt is a belt having an endless shape. 
     The nip forming member is arranged inside the belt. 
     The roller forms a nip with the belt. 
     The support member supports the belt interposed between the member and the roller. 
     The coil generates a magnetic field for inducing current in the belt. 
     The auxiliary heat generation member generates heat with the current induced by the magnetic field in the loop of the belt. 
     The temperature sensor is opposed to the auxiliary heat generation member with the belt interposed between the element and the auxiliary heat generation member and detects the temperature of an outer peripheral surface of the belt. 
     Hereinafter, embodiments will be described with reference to the drawings. 
     First Embodiment 
     First, a first embodiment will be described. 
       FIG. 1  is a view showing a schematic structure of a fixing device of a first embodiment. 
     As shown in  FIG. 1 , a fixing device according to First Embodiment includes a belt  1 , a nip forming member (support member)  2 , a roller  3 , a coil  4 , a temperature sensor  5 , a thermostat  7 , an auxiliary heat generation member  6  and a thermostat  7 . 
     The belt  1  is an endless belt. 
     The belt  1  has a multi-layer structure in which at least a release layer and a heat generating layer are laminated from the side of contact with a sheet which is an object of a fixing process. It is needless to say that an elastic layer can be provided between the release layer and the heat generating layer. 
     Here, for example, PFA (polytetrafluoroethylene) is adopted as the release layer, and for example, Ni is used as the heat generating layer. Of course, nonmagnetic metal (stainless, silver, copper, aluminum, etc.) can also be used as the heat generating layer. 
     The nip forming member  2  is arranged inside the belt  1 . 
     The nip forming member  2  is made of, for example, a heat-resistant silicone sponge or silicone rubber. In the first embodiment, although a roller shape rotating around a rotation center axis  2   p  is adopted as the nip forming member  2 , a non-rotating fixed member can also be adopted. 
     The roller  3  nips the belt  1  in cooperation with the nip forming member  2  and forms a nip. 
     The coil  4  heats the belt  1  by induction heating. 
     The thermostat  7  is arranged to be opposite to apart of the auxiliary heat generating member through the belt  1 , and detects the temperature of the outer peripheral surface of the belt  1  in a non-contact manner. 
     As the thermostat  7 , for example, a thermopile type non-contact temperature detection element or a non-contact thermistor can be adopted so that a friction load is not applied to the surface of the belt  1 . The thermostat  7  is arranged so that at least a part thereof is positioned above the belt  1 . 
     The temperature detection element  5  is arranged at a side of the belt  1 . In the first embodiment, the nip forming member  2  and the roller  3  are arranged horizontally. By this, while the size of the fixing device in height direction is not enlarged, and it is avoided that heat is excessively applied to the temperature detection element  5 , the temperature detection element  5  can detect the temperature of the surface of the belt  1 . 
     The auxiliary heat generating member  6  is arranged inside the belt  1 . The auxiliary heat generating member  6  includes a conductive material, and generates Joule heat by induction heating of the coil  4 . 
     Besides, the auxiliary heat generating member  6  is formed to have an arc shape along the inner peripheral surface of the belt  1 , and at lease one end (here, an upper end) in the peripheral direction of the belt  1  extends to a non-opposite area A 2  which is not opposite to the coil  4 . 
     The thermostat  7  is arranged to be opposite to the auxiliary heat generating member  6  in the non-opposite area A 2  through the belt  1 . As stated above, also when the non-contact thermostat  7  is adopted which is required to accurately maintain the distance to an object as a temperature detection object, the back side in an area where the temperature is detected by the thermostat  7  is guided by the auxiliary heat generating member  6 , so that fluttering or undulating in the portion of the belt  1  facing the thermostat  7  can be suppressed. As a result, the performance of the thermostat  7  can be stably exhibited. 
     Besides, the thermostat  7  is made opposite to the non-opposite area A 2  (area outside a heating target area A 1  of the coil  4 ) where the auxiliary heat generating member  6  is not opposite to the coil  4 . Thus, it is possible to reduce a possibility that the thermostat  7  receives the influence of a magnetic flux from the coil  4 . Besides, since the non-opposite area A 2  is continuous with the heating target area A 1 , when a phenomenon such as abnormal overheat occurs in the heating target area A 1 , the thermostat  7  can detect the abnormal overheat in the heating target area A 1  by the heat transmitted from the heating target area A 1  to the non-opposite area A 2 . 
     Besides, the non-opposite area A 2  of the auxiliary heat generating member  6  is provided on the upper end side of the auxiliary heat generating member  6 . 
     When consideration is given to the characteristic that heat transfers upward, in order to realize more accurate temperature detection, it is preferable to arrange the thermostat upward with respect to the belt to the extent possible. Accordingly, in the peripheral direction, “a direction in which the auxiliary heat generating member  6  is projected to a position not opposite to the coil  4 ” is upward. 
     Further, in the first embodiment, the auxiliary heat generating member  6  is projected from the coil  4  in at least one direction of directions parallel to a rotation axis  3   p.  The thermostat  7  is arranged to be opposite to the portion of the non-opposite area A 2  projecting from the coil  4  in the direction parallel to the rotation axis  3   p.    
     In the heat generating layer (conductive layer) of the belt  1 , reduction in heat capacity (reduction in thickness) is performed in order to enable quick temperature rising by induction heating. 
     Accordingly, the magnetic field generated by the coil  4  passes through the heat generating layer of the belt  1 , and reaches a heat generating layer  6   b  (the details will be described later) of the auxiliary heat generating member  6 . By this, Joule heat is generated in the belt  1  and the auxiliary heat generating member  6 , and the belt  1  is heated. 
     Besides, when the thermostat  7  is arranged as shown in the first embodiment, as compared with a structure in which a contact-type thermostat is arranged inside the belt, the size of the device can be greatly reduced. Besides, since the temperature of the surface of the belt  1  is measured in a non-contact manner, the outer peripheral surface of the belt  1  is not damaged. 
     Incidentally, it is not necessary that the non-opposite area A 2  is provided in the same range as the width of the auxiliary heat generating member  6  in the direction parallel to the rotation axis  3   p,  and the non-opposite area has only to be provided at least at a position opposite to the thermostat  7  (see  FIG. 2 ). 
     By this, the yield of material when the auxiliary heat generating member is formed can be improved, and this can contribute to reduction in cost. 
     As described above, according to the first embodiment, it becomes easy to stably maintain the gap between the outer peripheral surface of the belt  1  and the thermostat  7 . Besides, it becomes possible to detect abnormal heat generation of the auxiliary heat generating member  6 . 
     Second Embodiment 
     Next, a second embodiment will be described. 
     The second embodiment is a modified example of the first embodiment. Accordingly, a portion having the same function as a portion described in the first embodiment is denoted by the same reference numeral and its description will be omitted. 
     In the second embodiment, in order to enable quick temperature rising, a structure for reducing influence of temperature unevenness (gloss unevenness) in a thin belt is added. 
     The auxiliary heat generating member  6 ′ in the second embodiment has a structure as shown in  FIG. 3 . 
     The auxiliary heat generating member  6 ′ has a multi-layer structure in which a release layer  6   a,  a heat generating layer  6   b,  a soaking layer  6   c,  and a radiation prevention layer  6   d  are laminated from the inner surface side of the belt  1  toward the nip forming member  2 . 
     The release layer  6   a  is made of a material having a low friction coefficient and high heat resistance in order to maintain a gap with respect to the coil  4  and a gap with respect to the thermostat  7  when the belt  1  contacts with the auxiliary heat generating member  6 ′. 
     The heat generating layer  6   b  is formed of a metal layer which can be induction heated. Incidentally, a magnetic shunt metal having a Curie point of about 230° C. may be adopted as the heat generating layer  6   b  so that the heat generating layer  6   b  does not abnormally generate heat. 
     The soaking layer  6   c  is arranged in order to prevent temperature fluctuation in the direction of the rotation axis  3   p  of the belt from occurring by passing of a sheet (small size sheet such as a B5 sheet) having a small size in the direction parallel to the rotation axis  3   p.  A material having high heat conductivity such as, for example, copper or aluminum can be adopted as the soaking layer  6   c.  Besides, a functional material such as a heat pipe can be adopted as the soaking layer  6   c.    
     The width of the soaking layer  6   c  in the direction of the rotation axis  3   p  of the roller  3  is narrower than the width of the coil  4  in the direction of the rotation axis  3   p  of the roller  3 , and is wider than the width of a maximum size sheet conveyed by the roller  3  in the direction of the rotation axis  3   p  of the roller  3 . 
     When the width of the soaking layer  6   c  is excessively wide, since heat generated in the heat generating layer  6   b  is significantly absorbed by the soaking layer  6   c,  the width is set to become necessary and sufficient for a fixing process of a sheet as a fixing object. 
     Besides, the width of the heat generating layer  6   b  in the direction of the rotation axis  3   p  of the roller  3  is wider than the width of the coil  4  in the direction of the rotation axis  3   p  of the roller  3 . Besides, the width of the heat generating layer  6   b  in the direction of the rotation axis  3   p  of the roller  3  can be made wider than the width, in the direction of the rotation axis  3   p,  of an area of the belt  1  where the temperature reaches a specified fixing temperature at the time of a fixing process. 
     Incidentally, here, although the description is made on the example of the multi-layer structure in which the release layer  6   a,  the heat generating layer  6   b,  the soaking layer  6   c  and the radiation prevention layer  6   d  are laminated in this order, it is needless to say that the multi-layer structure may be such that the release layer  6   a,  the soaking layer  6   c,  the heat generating layer  6   b  and the radiation prevention layer  6   d  are laminated in this order. 
     As described above, according to the second embodiment, the occurrence of temperature unevenness in the auxiliary heat generating member  6 ′ can be suppressed, and reduction in picture quality (gloss unevenness) due to the temperature unevenness of a belt period can be prevented. 
     Third Embodiment 
     Next, a third embodiment will be described. 
     The third embodiment is a modified example of the first and the second embodiments. Accordingly, a portion having the same function as a portion described in the first and the embodiments is denoted by the same reference numeral and its description will be omitted. 
       FIG. 4  is a sectional view showing a schematic structural view of an auxiliary heat generating member  6 ″ in the third embodiment. 
     As shown in  FIG. 4 , in the auxiliary heat generating member  6 ″ in the third embodiment, in addition to the object of protecting a soaking layer  6   c ′, a radiation prevention layer  6   d ′ prevents heat from being radiated to a nip forming member  2  from the auxiliary heat generating member  6 ″. 
     The radiation prevention layer  6   d ′ has a heat conductivity lower than that of either one (here, the soaking layer  6   c ′) of the heat generating layer  6   b  and the soaking layer  6   c ′, which is closer to the nip forming member  2 . 
     By this, it is possible to prevent that heat generated in the heat generating layer  6   b  escapes to the nip forming member  2 . As a result, the heat generated in the heat generating layer  6   b  can be efficiently transmitted to the belt  1 . 
     Besides, a surface  6   d′a  of the radiation prevention layer  6   d ′ on the belt side has a color having higher lightness than that of a surface  6   c′a , on the nip forming member  2  side, of either one (here, the soaking layer  6   c ′) of the heat generating layer  6   b  and the soaking layer  6   c ′, which is closer to the nip forming member  2 . For example, the surface  6   d′a  can be made white, and the surface  6   c′a  can be made black. 
     By this, it is possible to suppress that heat generated in the heat generating layer  6   b  of the auxiliary heat generating member  6 ″ is transferred to the nip forming member  2  side, and the belt  1  can be efficiently heated. 
     Incidentally, it is needless to say that not only the techniques described in the first to the third embodiments are individually adopted, but also they can be arbitrarily combined with each other and can be adopted. 
     As described above in detail, according to the technique disclosed in the specification, it is possible to provide the technique to stably maintain the gap between the induction heated belt and the non-contact thermostat to detect the temperature of the belt surface. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of invention. Indeed, the novel apparatus and methods described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the apparatus and methods described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.