Patent Publication Number: US-7593679-B2

Title: Heat recycling image forming apparatus

Description:
PRIORITY STATEMENT 
   This application claims priority upon Japanese Patent Application No. 2004-079532, filed on Mar. 19, 2004, the disclosure of which is incorporated herein in its entirety by reference. 
   BACKGROUND OF THE PRESENT INVENTION 
   There is a global demand to reduce energy consumption of image forming apparatuses. Some conventional image forming apparatuses have been designed to reuse the heat that is generated during the image formation. 
   Specifically, Japanese Patent Application Laid-Open No. H05-19654 and Japanese Patent Application Laid-Open No. 2000-338803 disclose image forming apparatuses that use a heat pipe to reuse the heat generated during the image formation for image fixation. These image forming apparatuses include a heat sink, which is positioned downstream of the section where the recording medium is heated to a melting point of toner to fuse toner images onto the recording medium. Moreover, a radiator is positioned upstream of the section where the heat fusion is performed. 
   These apparatuses have been designed so that the heat sink of the heat pipe absorbs the heat from the recording medium that has passed through the heat fusion section, and the radiator of the heat pipe releases the absorbed heat onto another recording medium as the another recording medium passes through the heat fusion section. This design allows thermal energy obtained from both the toner image fixing operation and the post-fixed recording medium to be transferred onto the recording medium prior to fixing of toner images. By absorbing the heat from the toner fixated images and the recording medium after passing through the heat fusion section, incidence of an offset (smearing) on the recording medium can be reduced if not prevented. On the other hand, preliminary heating of the unfixed toner images and the recording medium by the radiator before reaching the heat fusion section reduces heat energy required for fusing the toner images in the heat fusion section. Thus, the reuse of heat for the image fixing process for preliminary heating reduces the energy consumption. 
   However, the heat pipe in the conventional technology was originally designed to ensure efficient heat transfer from the heat sink to the radiator using elements that have extremely high thermal-conductivity. Moreover, heat transfer by thermal conduction causes heat to be transferred from a higher-temperature location toward a lower-temperature location, but not from the lower-temperature location to the higher-temperature location. Accordingly, when the heat pipe is used, the temperature of the heat sink can not rise higher than the temperature of the radiator. Moreover, the temperature of the heat fusion section increases to its upper limit during the toner fixation process, reaching a higher temperature than that of the heat sink of the heat pipe. As such, the radiator cannot be positioned in the heat fusion section, because the heat fusion section has a temperature that is higher than that of the heat sink. Therefore, the reuse of waste heat by the heat pipe for the toner fixing operation can be applied only to the preheating operation, in which the temperature of the recording medium with unfixed toner images is raised to a particular level; but not to the heating operation that occurs in the heat fusion section. 
   The typically close proximity of the preheating unit (radiator) and the heat fusion section causes heat to be transferred from the heat fusion section to the radiator by air conduction, raising the temperature of the radiator. As the temperature of the radiator rises and a temperature differential between the radiator and the heat sink becomes smaller, heat cannot be transferred from the heat sink to the radiator. On the other hand, if the radiator is positioned away from the heat fusion section, to avoid convection heating by the heat fusion section, then there is less efficient reuse of heat since the recording medium releases heat between the radiator and the heat fusion section. 
   Japanese Patent Application Laid-Open Publication No. 2001-42672 discloses an image forming apparatus that use Peltier elements to cool the surfaces of a conveying belt and a recording medium on a conveying belt downstream of the heat fusion region. In this conventional image forming apparatus, the heating member is positioned upstream from the heat fusion region in order to come into contact with the conveying belt. It is possible for this image forming apparatus to preheat the conveying belt by heat from the heating member. However, this heating member uses fans, heat sinks, and the like which release large amounts of heat into the air; and is an inefficient use of heat even when used as an auxiliary heating unit. 
   SUMMARY 
   At least one embodiment of the present invention can solve at least one of the problems described above regarding the conventional technology. 
   In an image forming apparatus according to an embodiment of the present invention, a recording medium with a toner image is heated in a heat fusion region to fix the toner image on the recording medium. The image forming apparatus includes a heat pump that includes a heat absorbing unit that absorbs heat from one or both of the recording medium and the toner image in a region that is different from the heat fusion region; and a heat radiating unit that release the heat, which is absorbed by the heat absorbing unit, to heat a recording medium with a toner image in the heat fusion region. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of an image forming apparatus according to an embodiment of the present invention; 
       FIG. 2  is a schematic of an image forming device, according to an embodiment of the present invention; 
       FIG. 3A  is a transverse sectional view of a first example of a heat pump, according to an embodiment of the present invention; 
       FIG. 3B  is a top view of the first example of a heat pump; 
       FIG. 4  is a transverse sectional view of a second example of a heat pump, according to an embodiment of the present invention; 
       FIG. 5  is a schematic of an image forming device, according to an embodiment of the present invention; and 
       FIG. 6  is a schematic of an image forming device, according to an embodiment of the present invention. 
   

   The accompanying drawings are intended to depict example embodiments of the present invention and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
   DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
   Example embodiments of the present invention will be described below with reference to the accompanying drawings. Other embodiments not explicitly called out below, for brevity, nonetheless are contemplated. Included in the following text is a description of a powder-toner image developing electro-photographic copier (hereinafter, “copier”), according to an embodiment of the present invention. Such a copier can be described as a type of image forming apparatus. 
     FIG. 1  is a block diagram of a copier, according to an embodiment of the present invention. The copier has a main body that includes a printer section  100 , a sheet feeding unit  200 , an image scanning unit  300 , and a document conveying unit  400 . The image scanning unit  300  is located above the printer section  100 . The document conveying unit  400  includes an automatic document feeder (ADF) is located above the image scanning unit  300 . Moreover, the copier includes a control unit (not shown) that controls the operations of various units of the copier. 
   The image scanning unit  300  includes an image reading sensor  36  to read image information from documents positioned on an exposure glass  32  and send the read image information to the control unit. Based on the image information that is received from the image scanning unit  300 , the control unit controls a laser, an LED and the like (not shown) positioned in an irradiating device  21  that irradiates a writing laser beam L onto photosensitive drums  40 Bk,  40 Y,  40 M, and  40 C. Through this irradiation, latent electrostatic images are formed on the surfaces of the photosensitive drums  40 Bk,  40 Y,  40 M, and  40 C and the latent images are developed into respective toner images through an image developing process. 
   In addition to the irradiating device  21 , the printer section  100  has a primary image transferring device  62 , a secondary image transferring device  22 , a toner image fixing device  25 , a sheet discharging device, and a toner feeder (not shown). 
   The sheet feeding unit  200  has media bank  43  into which a plurality of sheet feeding cassettes  44  are inserted; a plurality of sheet feeding rollers  42  that extract sheets of a recording medium P (e.g., paper) from any one of the sheet feeding cassettes  44 ; a plurality of sheet separating rollers  45  that separate the sheets of the recording media P and feed each sheet sequentially to a sheet feeding path  46 . Sheet conveying rollers  47  feed the recording media P to a sheet feeding path  48  of the printer section  100 . In addition to the sheet feeding unit  200 , manual sheet feeding is possible using a manual sheet feeding tray  51 , that is located on the side of the image forming apparatus, into which the recording Media P separated sheet-by-sheet by a sheet separating roller  52 . A resist roller  49  discharges, e.g., the recording media P one sheet at a time, from any one of the sheet feeding cassettes  44  or the manual sheet feeding tray  51 , and sends the recording media P to a secondary image transferring nip positioned between an intermediate image transferring belt  10  that is an intermediate image transferring member, and the secondary image transferring device  22 . 
   When taking copies of color documents, the color document is set on a document stand  30  of the document conveying unit  400 , or the document conveying unit  400  is opened and the document is set on the exposure glass  32  of the image scanning unit  300 . Then, upon operating a START key (not shown), the document that is set at the document conveying unit  400  is conveyed onto the exposure glass  32 , and the image scanning unit  300  is activated. If, on the other hand, a document is manually placed on the exposure glass  32  and the START key is operated, the image scanning unit  300  is activated immediately to move a primary scanning member  33  and a secondary scanning member  34 . 
   Light is emitted from a light source at the primary scanning member  33 , light reflects off the surface of the document, and is further reflected towards the secondary scanning member  34 . A mirror at the secondary scanning member  34  reflects the light through an imaging lens  35  onto an image reading sensor  36  that reads the image information. 
   Upon receiving image information from the scanner units, the image forming apparatus performs laser-writing, or implements the developing process by forming toner images on the photosensitive drums  40 . The image forming apparatus then operates one of the resist rollers  49  to feed the recording media P of a size appropriate for the image information. 
   Concurrently, a driving motor (not shown) rotates one of a plurality of supporting rollers  14 ,  15 , and  16 ; and the other two supporting rollers can be subordinately driven to rotate the intermediate image transferring belt  10 . At the same time, each of the individual image forming units  18  act in unison to rotate the photosensitive drum  40 , and form each single-color image of black, yellow, magenta, and cyan on the photosensitive drum  40 . As the intermediate image transferring belt  10  is moved, each of the single-color images is sequentially transferred and a composite color image is formed on the intermediate image transferring belt  10 . 
   One of the sheet feeding rollers  42  of the sheet feeding unit  200  is selectively rotated, and recording media P from one of the sheet feeding cassettes  44  is extracted and fed one-by-one, by the sheet separating roller  45 , to the sheet feeding path  46 . Each sheet of recording media P is guided on the sheet feeding path  45  within the printer section  100  by sheet conveying rollers  47 , and stops moving upon hitting the resist roller  49 . Or, the sheet feeding roller  50  rotates to extract recording media P from the manual sheet feeding tray  51 , the sheet separating roller  52  separates recording media P one-by-one into the sheet feeding path  53 , and the flow of manually fed recording sheet is stopped by hitting against the resist roller  49 . 
   Then, the resist roller  49  rotates to align with the composite color image on the intermediate image transferring belt  10 , and recording media P is fed into the secondary image transferring nip, which is a member formed by the contact of the intermediate image transferring belt  10  and the secondary image transferring rollers  23 . The composite color image is transferred onto the recording media P by the effects of an electrical field for image transfer and contact pressure in the nip. 
   The recording media P, upon which the composite color image has been transferred, is then sent to a toner image fixing device  25  by a sheet conveying belt  24  of the secondary image fixing device  25 ; and after fixing the toner image by an application of pressure and heat through the pressure roller  4  at the toner image fixing device  25 , the recording media P is and discharged by an discharging roller  56  onto a discharge tray  57 . 
     FIG. 2  is a schematic of the toner image fixing device  25 , according to an embodiment of the present invention. The toner image fixing device  25  includes a toner image fixing belt  2  that is made of a heat-resistant material; and this toner image fixing belt  2  is supported by four supporting rollers  5 . Inside this toner image fixing belt  2 , there is a heat pump  1  that includes a heating member  1 H that heats the recording media P, and a heat sink  1 C that is a cooling member; both of which come into contact with the toner image fixing belt  2 . 
   A heat fusion region  6  is formed at a location where the heating member  1 H and the toner image fixing belt  2  come into contact; and a cooling region  7  is formed at a location where the heat sink  1 C and the toner fixation belt come into contact. The heat fusing region  6  and the cooling region  7  are adjacent so as to occupy substantially the same location. An arrow A indicates a direction in which the recording media P is transported; as such, the heat sink  1 C can be described as being located downstream from the heating member  1 H. An arrow H in the heat pump  1  indicates a direction in which heat is transferred inside the heat pump. The pressure roller  4  presses against the toner image fixing belt  2 , which is sandwiched between the pressure roller  4  and the heating member  1 H and the heat sink  1 C of the heat pump  1 . 
   When a recording media P that carries an unfixed toner image enters the toner image fixing device  25 , the recording media P is pressed between the heating member  1 H and the pressure roller  4  in the heat fusion region  6 ; then heat is applied to the recording media P by the heating member  1 H so that the toner image fuses on the recording media P. After passing through the heat fusion region  6 , the recording media P is pressed and conveyed to the cooling region  7  by the toner image fixing belt  2  and the pressure roller  4 . The recording media P carrying fused toner is pressed between the heat sink  1 C and the pressure roller  4 ; then some heat is absorbed from the recording media P by the heat sink  1 C to cure and fix the toner images on the recording media P. The heat absorbed by the heat sink  1 C is transferred to heating member  1 H, where the heat is reused. 
   In  FIG. 2 , the heating member  1 H and the heat sink  1 C adjacent to each other to form a single nip above the pressure roller  4 . 
   The heat pump  1  will now be described in more detail. The heat pump  1  transfers heat from the lower temperature heat sink  1 C to a higher temperature heating member  1 H. The heat pump  1  transfers heat just as a water pump moves water from a lower place to a higher place. 
   A heat pump is a more energy-efficient heating unit than, e.g., a conventional electrical resistance heater. And, when the heat sink has a lower temperature than the heating member, and especially when the temperature differential between the heat sink and the heating member is small, the efficiency of heat transfer becomes higher. While toner image fixing operations are being performed steadily, the heat sink  1 C can maintain higher efficiency, compared with places other than the toner image fixing device  25 , because large amounts of heat flow from the toner images and recording medium P to the heat sink  1 C of the heat pump  1 . 
   On the topic of heat differentials, in the toner image fixing device  25  of  FIG. 2 , there can be a circumstance in which there is substantially no difference (if not none at all) between the temperature of the heat sink, which has a small amount of heat, and the temperature of the area outside the heat sink when the toner image fixing device  25  starts up. It is therefore difficult to raise the temperature to the level required for toner image fixing even if there is heat transfer to the heating member. In this situation, an auxiliary heating unit (not shown) can be provided. The auxiliary heating unit can be positioned at the heat sink side or the heating member side, or both sides; but a quicker response can be expected if the auxiliary heating unit is placed at the heating member side. 
   The types of heat pumps used for the transfer of heat in copiers include common mechanical compression type heat pumps used e.g., in household refrigerators and air conditioners; chemical types such as absorption types and adsorption types; magnetic refrigeration types, or acoustic types. There are some heat pumps that use Peltier elements. Theoretically, any heat pump can be used in an image forming apparatus. But among these heat pumps, Peltier elements can be advantageous due to their suitability for miniaturization and on-demand operation. 
     FIG. 3A  is a transverse sectional view of a first example of a heat pump that uses Peltier elements, according to an embodiment of the present invention.  FIG. 3B  is a schematic of a top view of the heat pump shown in  FIG. 3A . 
   In  FIG. 3A  and  FIG. 3B , the Peltier element is configured from semiconductors  71  and junctions  72 . There are two types of semiconductors  71 : N-type semiconductors  71 N and P-type semiconductors  71 P. As illustrated in  FIG. 3B , the two types of semiconductors are arranged in an alternating pattern, with an insulating member  74  sandwiched between each semiconductor  71 . An electrical current flows serially through the semiconductors  71  via junctions  72  on the heat sink side (hereinafter “heat sink junctions  72 C”) and junctions  72  on the heating member side (hereinafter “heating member junctions  72 H”). 
   Bismuth-tellurium, for example, can be used as the semiconductor material of the semiconductors  71 . Alloys, e.g., zinc-antimony or sodium-cobalt oxide, can also be used as a semiconductor material that can operate at higher temperatures than bismuth-tellurium. The junctions  72  can be sheets of a metal having high electrical conductivity, e.g., copper, aluminum and the like. A difference between the heat sink junctions  72 C and the heating member junctions  72 H is the direction of electrical current is reversed. 
   As illustrated in  FIG. 3A , by applying the electrical current, a heat-conducting member  73  becomes the heating member  73 H, and a heat-conducting member  73  becomes the heat sink  73 C. In other words, when the electrical current flows from the P-type semiconductor  71 P to the metallic sheet (heating member junction  72 H), and then from the metallic sheet (heating member junction  72 H) to the N-type semiconductor  71 N, the heating member junction  72 H causes the heating member  73 H to radiate heat. On the other hand, when electrical current flows from the N-type semiconductor  71 N to the metallic sheet (heat sink junction  72 C), and then from the metallic sheet (heat sink junction  72 C) to the P-type semiconductor  71 P, the heat sink junction  72 C causes the heat sink  73 C to absorb heat. 
   The heat-conducting members (heat sink  73 C and heating member  73 H) are positioned adjacent to the junctions (heat sink junction  72 C and heating member junction  72 H) of the Peltier elements (N-type semiconductors  71 N and P-type semiconductors  71 P). The heating member  73 H guides the heat absorbed by the Peltier element  71 P into the heat fusion region  6 ; while the heat sink  73 C guides the heat from the cooling region  7  into the Peltier element  71 N. The heat-conducting materials have high heat conductivity; and, unlike the heat pump, transfers heat passively. As high-conductivity materials, not only copper, aluminum, and the like, but also, e.g., ceramics with high heat conductivity may be used. Alternatively, a heat pipe may be embedded into the heat conducting members. 
   When using a metallic heat conducting material for the heat conducting members, consideration should be given to an electrical insulating material that is positioned between the heat conducting members and the junctions, so as to avoid any contact with the junction that could result in a short circuit. The insulating member  74  is positioned between the heat sink  73 C and the heating member  73 H, and between the semiconductors  71 N and  71 P to deter a short circuit between the N-type semiconductor  71 N and the P-type semiconductor  71 P. Furthermore, the insulating member  74  also insulates against heat transfer to reduce heat conduction between the heating member and heat sink. 
   The heating member  73 H can be equipped with an auxiliary heater  75  that is activated when sufficient heat cannot be absorbed at the heat sink due to a low temperature, for example, the low temperature when the toner fixation device has just been activated. Electrical resistance heaters, e.g., ceramic heaters and the like, are suitable for the auxiliary heater  75 . 
   At the heating member junction  72 H of the Peltier element, Joule heat is added to the heat conducted from the heat sink junction  72 C to reach a temperature (about 200-300 degrees centigrade) at which toner images can be fixed. Some commercially available Peltier elements have an upper temperature limit at the heating member junction of about 80 degrees centigrade because the Peltier elements are joined with a reflow-solder that has a low fusing temperature. But some materials that can be used for the semiconductors  71 N and  71 P can reach a temperature of about 150 to 200 degrees centigrade, (e.g., bismuth-tellurium materials), and others over 200 degrees centigrade (e.g., zinc-antimony materials, sodium-cobalt materials, etc.) 
   The configuration of the heat pump  1  using Peltier elements is not limited to the configurations illustrated in both  FIG. 3A  (transverse sectional view) and  FIG. 3B  (top view). Any heat pump configuration may be used provided that heat is absorbed and released using the Peltier effect. 
     FIG. 4  is a transverse sectional view of a second example of a heat pump, according to an embodiment of the present invention. In  FIG. 3A  and  FIG. 3B  the semiconductors  71 N and  71 P and the insulating members  74  have a rectangular block shape, but in  FIG. 4  the semiconductors  71 N and  71 P and the insulating members  74  have a shape resembling the letter “n”. The relative positions and roles of each component in  FIG. 4  are the same as  FIG. 3A  and  FIG. 3B , so an explanation is omitted. In  FIG. 4 , the heating member junction  72 H and the heat sink junction  72 C are attached at the feet of the n-shaped semiconductors  71 N and  71 P and the insulating members  74 . 
   Comparing  FIGS. 3A and 3B  with  FIG. 4 , instead of placing the heat conducting elements  73 C and  73 H on both sides of the row of semiconductors  71 N and  71 P and insulating members  74 , the heat conducting elements  73 C and  73 H are placed underneath the feet of the n-shaped semiconductors  71 N and  71 P and insulating members  74 , reduces the cubic volume needed for the heat conducting members  73 C and  73 H. 
   A decrease in cubic volume of the heat conducting members  73 C and  73 H reduces heat capacity of the heat conducting members  73 C and  73 H which reduces a start-up time of the heat pump  1 . But since a purpose of the heat conducting members  73 C and  73 H can be to homogenize the temperature at the heat fusion region  6  and the cooling region  7 , consideration should be given against making the heat conducting members  73 C and  73 H extremely small if this purpose is to be adequately served. Where the heat conducting members  73 C and  73 H in  FIG. 4  are not made extremely small, they nevertheless can be made, e.g., smaller than the heat conducting members  73 C and  73 H of  FIGS. 3A and 3B . 
   The transfer of heat using Peltier elements is not limited to a single row, as in the heat pumps of  FIG. 3A ,  FIG. 3B , and  FIG. 4 ; and it is acceptable to position multiple rows of Peltier elements that are configured to incrementally move heat from the heat sink to the heating member. In this multiple row configuration, heat conducting members made, e.g., of copper, aluminum and the like, are positioned between Peltier elements the multiple rows. Compared to single row heat transfer, multiple row heat transfer can transfer heat between a heat sink and a heating member that has a relatively larger temperature differential. Furthermore, reducing the temperature differential in front of and behind the first row of Peltier elements reduces the danger of damage to the Peltier elements and surrounding members due to thermal stress. 
   Thus, an image forming apparatus can use the heat pump  1  as the heat exchange unit to reuse the heat generated during the toner image fixing process, and can use the heating member  1 H is used as the heating unit in the heat fusion region  6  of the toner image fixing device  25 . The use of the heating member  1 H can achieve, compared with a configuration to perform auxiliary heating, a reduction in the amount of heat dissipated during heat transfer that accompanies the movement of the recording medium P. This reuse of waste heat and reduction of heat dissipation can achieve a reduction of electrical power required for tone image fixing that can make greater energy conservation possible. 
   The use of the heat sink  1 C of the heat pump  1  to cool the heated recording medium P can more effectively use the waste heat generated during the toner image fixing operation and, unlike a copier that uses a heat pipe, can more effectively reduce (if not minimize) deterioration in cooling efficiency when the copier is continuously used. Such reduced deterioration in cooling efficiency can help to reduce the chances of (if not prevent) an occurrence of an offset (smearing) of a toner image caused by insufficient cooling. 
   Furthermore, the heat pump  1  can use the Peltier elements, which can achieve a size of the heat pump  1  that is smaller than the other types of heat pumps. Moreover, the heat pump  1  using the Peltier elements can have faster heat control response compared with other types of heat pumps, so the heating temperature can be precisely controlled. 
   The auxiliary heater  75  positioned adjacent to the heat pump  1  can compensate for insufficient heat supply at start-up, and can help to ensure a more stable toner image fixing operation. 
   Furthermore, in a configuration in which the heating member  1 H and the heat sink  1 C have been positioned adjacent to each other to form a single nip on the pressure rollers  4 , the amount of heat dissipated from the recording medium P and the toner image on the recording medium P can be reduced on the path from the heat fusion region  6  to the cooling region  7 . This configuration can increase the heat entering the heat sink  1 C of the heat pump  1  and can improve heat exchange efficiency, and can reduce the amount of heat dissipated from the surface of the recording medium P compared with the configuration in which the heating member  1 H and the heat sink  1 C have not been positioned adjacent to each other. 
   The preceding discussion has assumed an image forming apparatus that uses powder-toner image developing, but the present invention is not limited only to such image developing. For example, an embodiment of the present invention can be an image forming apparatus using liquid-toner image developing, where the liquid-toner is fixed by heating. 
     FIG. 5  illustrates an image forming device according to an embodiment of the present invention. In  FIG. 5 , the heating member  1 H and the heat sink  1 C have been positioned apart from each other, and the pressure roller  4  is pressing the toner image fixing belt  2  against the heating member  1 H and the heat sink  1 C at the two locations. The toner image fixing device  25  in  FIG. 5  has the same configuration as the toner image fixing device  25  in  FIG. 2 , except that the pressure roller  4  and the heat pump  1  are pressed against each other at two points, so the descriptions of the individual members are omitted. 
   In the toner image fixing device  25  illustrated in  FIG. 5 , since the heating member  1 H and the heat sink  1 C are positioned apart from each other so that the pressure roller  4  and the heat pump  1  press against each other at two locations it is possible to gain a wider space between the heat fusion region  6  and the cooling region  7 . If the pressure members (e.g., the four supporting rollers  5 ) have the roller shape illustrated in  FIG. 5 , then a wider nip space can be achieved between the toner image fixing belt  2  and the pressure roller  4 . Thus, the wider nip space can help to achieve a more stable toner image fixing operation. 
   Next,  FIG. 6  illustrates an image forming device according to an embodiment of the present invention. In  FIG. 6 , two different pressure rollers, namely a heat sink pressure roller  4 C and a heating member pressure roller  4 H, press against the toner image fixing belt  2  which, in turn, presses against the heat sink  1 C and the heating member  1 H. The toner image fixing device  25  illustrated in  FIG. 6  has the same configuration as the toner image fixing device  25  illustrated in  FIG. 3 , except that the toner image fixing belt  2  is pressed against the two pressure rollers  4 C and  4 H to respectively form the cooling region  7  and the heat fusion region  6 ; so the descriptions of the individual members are omitted. 
   By positioning the heat sink pressure roller  4 C at the cooling region  7  and the heating member pressure roller  4 H at the heat fusion region  6 , spacing the cooling region  7  and the heat fusion region  6  can achieve a nip space in a manner similar to the configuration in  FIG. 5 , albeit a nip space that is wider. Moreover, the provision of the separate pressure rollers, namely the pressure rollers  4 C and  4 H, facilitates the heating member pressure roller  4 H being used to promote high temperature conditions and the heat sink pressure roller  4 C being used to promote low temperature conditions. The configuration in which one pressure roller is maintained at a higher temperature and another pressure roller is maintained at a lower temperature can reduce energy consumption compared with the toner image fixing device  25  having the configuration in which a common pressure member is pressed against both the heating member  1 H and the heat sink  1 C. 
   It is acceptable to use a material that has relatively a higher thermal conductivity ratio for the surface of the heating member pressure roller  4 H and the heat sink pressure roller  4 C. The use of the material that has a higher thermal conductivity ratio on the heating member pressure roller  4 H allows the heating member pressure roller  4 H to be heated (via convection and/or radiant, etc., heating) by the heating member  1 H during the interval after a recording medium P has passed and before the following recording medium P enters the heat fusion region  6  (or, in other words, when no recording medium P is interposed between the heating pressure roller  4 H and the heating member  1 H). The recording medium P is heated from both the upper and lower sides by the heating member  1 H and the heating member pressure roller  4 H, which can help to reduce the chance of insufficient heating of toner. 
   On the other hand, the use of the material that has a relatively high thermal conductivity ratio on the heat sink pressure roller  4 C allows the heat sink pressure roller  4 C to be cooled (via convection and/or radiant, etc., heat absorption) by the heat sink  1 C during the interval when the recording medium P passes through the cooling region  7 . The cooling of the heat sink pressure roller  4 C permits a cooling of the next recording medium P from both the upper and lower sides. It becomes possible to more efficiently absorb heat from the recording medium P, and to reduce the amount of heat dissipated out of the toner image fixing device  25  as the recording medium P is moving. Moreover, the chances of there occurring an offset (smearing) due to insufficient cooling can be reduced if not prevented. 
   In  FIGS. 2 ,  5  and  6 , the heat sink  1 C is positioned so as to cool the heated recording medium P, but the position of the heat sink  1 C is not limited as such. Alternatively, the heat sink  1 C can be positioned outside of the cooling region. 
   In the image forming apparatus, the places where waste heat is generated is not limited to the recording medium P having a fixed toner image. Waste heat is generated in places other than in the toner image fixing process, e.g., at a driving source and the like. Accordingly, as an example of an alternative, it is acceptable to position the heat sink  1 C at a place where waste heat is generated to reuse the waste heat as toner image fixing heat. 
   Continuing as to the example alternative, e.g., the heat sink  1 C can be placed in close proximity to a heat-generating member that is outside the toner image fixing device, and the heating member  1 H can be placed in the auxiliary heating unit in order, e.g., to recycle waste heat that is generated outside of the toner image fixing device  25 . Furthermore, the placement of the heat sink  1 C near a heat-generating member outside the toner image fixing device  25  can help to deter a rise in temperature of surrounding members. The conventional methods of deterring such a rise in temperature include positioning the heat-generating members outside the external chassis of the image forming apparatus. The example alternative can permit members, that otherwise could not be placed near the toner image fixing device  25 , to be placed near the toner image fixing device  25 ; which can widen the range of selectable layouts within the image forming apparatus. 
   It can be difficult to use the example alternative as a heating unit at the heat fusion region  6  in a circumstance in which the amount of waste heat from members outside of the toner image fixing device  25  is smaller compared with the waste heat from the recording medium P after toner image fixing. In that circumstance, it is possible to use the example alternative as an auxiliary heating unit. 
   One or more of the above-discussed example embodiments of the present invention can reduce heat loss more effectively than conventional toner image fixing methods that use a heat pipe. One or more of the above-identified embodiments of the present invention can reduce energy required for toner image fixing, and/or can facilitate greater energy-saving. 
   The present invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications are intended to be included within the scope of the present invention.