Fixing device and image forming system using the same

Abstract

To suppress wasteful cooling which does not contribute to cooling of a medium and to secure fixing performance when fixing an unfixed image on the medium by heating and cooling belt type conveying fixing means, as compared with the case where the conveying fixing means is cooled continuously.SOLUTION: A fixing device comprises: heating fixing means 1 having a heating source 1a; belt type conveying fixing means 2 which is provided stretched around the heating fixing means 1 so as to be capable of circulating and conveys a medium S while being in contact with an image surface of the medium S; pressing fixing means 3 which is pressed so as to form a fixing area FA between itself and the heating fixing means 1; cooling means 4 which is provided so as to be in contact with a reverse side of a medium conveyance area of the conveying fixing means 2 at a more downstream side in the conveyance direction of the medium S than the fixing area FA in the conveying fixing means 2 and cools the conveying fixing means 2; and switching means 5 which performs switching between a contact state and a non-contact state of the conveying fixing means 2 with the cooling means 4 depending on a passing state of the medium S at a cooling area CA of the cooling means 4.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fixing device and an image forming system using the same. [Background technology]

[0002] Conventionally, fixing devices of this type are already known, for example, as described in Patent Documents 1 to 3. Patent document 1 discloses a gloss-imparting device that has a cooling mode in which an endless belt is cooled by a heat sink and a non-cooling mode in which the endless belt is not cooled by a heat sink, and that operates in the non-cooling mode during start-up operations. Patent document 2 discloses an embodiment in which a fixing device having a heat sink is provided with a belt drive device that temporarily stops or slows down a belt member after the trailing end of a recording material passes through the fixing nip area, and returns the belt member to its original state before the leading end of the succeeding recording material reaches the fixing nip area. Patent document 3 discloses a fixing device that is equipped with a gloss treatment mode in which a cooling means cools a recording medium, on which an unfixed toner image has been fixed, to a predetermined temperature range while the recording medium is in contact with the fixing belt, thereby glossing the image forming surface, and also has a temperature adjustment mode in which the temperature of the cooling means is adjusted in the start-up state and / or standby state. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-181337 A (Form for carrying out the invention, FIG. 2) [Patent Document 2] JP 2007-163787 A (Best Mode for Carrying Out the Invention, FIG. 4) [Patent Document 3] JP 2006-243444 A (Best Mode for Carrying Out the Invention, FIG. 4) Summary of the Invention [Problem to be solved by the invention]

[0004] The technical problem that the present invention aims to solve is to provide a fixing device and an image forming system using the same that, when fixing an unfixed image on a medium by heating and cooling a belt-shaped conveying and fixing means, suppresses unnecessary cooling that does not contribute to cooling of the medium and ensures fixing performance, compared to when the conveying and fixing means is continuously cooled. [Means for solving the problem]

[0005] The first technical feature of the present invention is a fixing device that heats and pressurizes a medium on which an unfixed image is held, and then cools it to fix the unfixed image, comprising: a heating and fixing means having a heat source; a belt-shaped transporting and fixing means that is stretched across the heating and fixing means and is circulatable, and that transports the medium in contact with the image surface of the medium; a pressure fixing means that is arranged opposite the heating and fixing means across the transporting and fixing means, and is pressurized to form a fixing area between the heating and fixing means; a cooling means that is arranged in contact with the back surface of the media transport area of ​​the transporting and fixing means downstream of the fixing area in the transporting direction of the medium, of the transporting and fixing means, and that cools the transporting and fixing means; and a switching means that switches the transporting and fixing means and the cooling means between contact and non-contact depending on the state of the medium passing through the cooling area of ​​the cooling means.

[0006] A second technical feature of the present invention is a fixing device having the first technical feature, characterized in that the switching means switches the conveying and fixing means and the cooling means to a non-contact state while the medium does not pass through a cooling area of ​​the conveying and fixing means cooled by the cooling means. A third technical feature of the present invention is a fixing device having the second technical feature, characterized in that the switching means switches the cooling means to a contact state before the leading end of the medium in the transport direction reaches the entrance of the cooling area, and switches the cooling means to a non-contact state when the trailing end of the medium in the transport direction reaches the exit of the cooling area. A fourth technical feature of the present invention is a fixing device having the second technical feature, characterized in that the switching means switches the cooling means to a non-contact state under the condition that the medium is cooled to a predetermined temperature before the trailing end of the medium in the transport direction reaches an exit of the cooling area.

[0007] A fifth technical feature of the present invention is a fixing device having the first technical feature, characterized in that the switching means includes a moving mechanism that moves the cooling means relative to the conveying and fixing means. A sixth technical feature of the present invention is a fixing device having the fifth technical feature, characterized in that the moving mechanism supports the cooling means so that the cooling means can be oscillated, with an end portion on the exit or entrance side of the cooling area of ​​the cooling means as a oscillating point, and oscillates the cooling means between a contact position where the cooling means contacts the conveying and fixing means and a retracted position where the cooling means is retracted from the conveying and fixing means. A seventh technical feature of the present invention is a fixing device having the fifth technical feature, characterized in that the fixing device further comprises a positioning means provided on the back side of the media transporting area of ​​the transporting and fixing means, which maintains the surface posture of the media transporting area of ​​the transporting and fixing means when all or part of the cooling means is retracted from the contact position with the back side of the transporting and fixing means.

[0008] An eighth technical feature of the present invention is a fixing device having the first technical feature, characterized in that the switching means includes a moving mechanism that moves the conveying and fixing means relative to the cooling means. A ninth technical feature of the present invention is a fixing device having the eighth technical feature, characterized in that the moving mechanism is provided on the back side of the media transport area of ​​the transporting and fixing means other than the cooling area, and is equipped with a pushing-up means for pushing up the media transport area portion of the transporting and fixing means in a direction away from the cooling means.

[0009] A tenth technical feature of the present invention is a fixing device having the first technical feature, characterized in that the fixing device further comprises an opposing rotation means that is arranged opposite an entrance to a cooling area of ​​the cooling means across the conveying and fixing means and rotates following the conveying and fixing means. An eleventh technical feature of the present invention is a fixing device having the tenth technical feature, characterized in that the fixing device further comprises a plurality of opposing rotating means arranged opposite an entrance of the cooling area of ​​the cooling means and a location different from the entrance, across the conveying and fixing means, and rotating in accordance with the conveying and fixing means. A twelfth technical feature of the present invention is a fixing device having the ninth technical feature, characterized in that the fixing device further comprises one or more opposing rotation means arranged opposite an entrance to a cooling area of ​​the cooling means across the conveying and fixing means, or arranged opposite an entrance to the cooling area and a location different from the entrance, and rotating in accordance with the conveying and fixing means, and part or all of the opposing rotation means move in conjunction with the push-up means.

[0010] A thirteenth technical feature of the present invention is a fixing device having the first technical feature, characterized in that the switching means has a position detection means for detecting the position of the leading or trailing end in the transport direction of the medium upstream of the fixing area in the transport direction of the medium, and determines the position of the leading or trailing end in the transport direction of the medium transported by the transporting and fixing means based on the detection result of the position detection means, and switches between the contact and non-contact state of the cooling means. A fourteenth technical feature of the present invention is a fixing device having the thirteenth technical feature, characterized in that when the position detection means detects the rear end position of the medium in the transport direction, the switching means switches the cooling means to a non-contact state when the rear end of the medium reaches an outlet of the cooling area based on the detection result. A fifteenth technical feature of the present invention is a fixing device having the thirteenth technical feature, characterized in that when the position detection means detects the leading edge position of the medium in the transport direction, the switching means switches the cooling means to a contact state before the leading edge of the medium reaches an entrance of the cooling area based on the detection result.

[0011] A 16th technical feature of the present invention is a fixing device having the first technical feature, characterized in that the switching means has a discrimination means for discriminating the distance between the trailing end of the preceding medium in the transport direction and the leading end of the following medium in the transport direction, and does not execute the switching operation between contact and non-contact of the cooling means under the condition that the distance discriminated by the discrimination means is less than the length of the cooling area. A 17th technical feature of the present invention is an image forming system comprising an image creating means for creating an unfixed image on a medium, and a fixing device having any of the 1st to 16th technical features for fixing the unfixed image held on the medium. Effect of the Invention

[0012] According to a first technical feature of the present invention, when fixing an unfixed image on a medium by heating and cooling a belt-shaped conveying and fixing means, it is possible to suppress unnecessary cooling that does not contribute to cooling of the medium and ensure fixing performance, compared to the case where the conveying and fixing means is continuously cooled. According to the second technical feature of the present invention, in a situation where cooling of the medium is not required, the cooling operation of the conveying and fixing means by the cooling means can be omitted. According to the third technical feature of the present invention, in a state where the medium passes through the cooling area of ​​the cooling means, the cooling operation of the conveying and fixing means can be performed by the cooling means. According to a fourth technical feature of the present invention, even if the medium does not completely pass through the cooling area of ​​the cooling means, if the temperature of the medium is sufficiently cooled, the cooling operation of the conveying and fixing means by the cooling means can be omitted. According to the fifth technical feature of the present invention, the cooling means can be easily switched between contact and non-contact by moving the cooling means relative to the conveying and fixing means. According to the sixth technical feature of the present invention, the cooling means can be switched between contact and non-contact with the conveying and fixing means with a simple configuration as a switching means, compared to when the entire cooling means is switched between contact and non-contact with the conveying and fixing means. According to the seventh technical feature of the present invention, even if a method is adopted in which the cooling means is moved relative to the transporting and fixing means, the surface attitude of the medium transport area of ​​the transporting and fixing means can be maintained without change. According to the eighth technical feature of the present invention, the conveying and fixing means is moved relative to the cooling means, so that the cooling means can be easily switched between contact and non-contact. According to the ninth technical feature of the present invention, the conveying and fixing means can be moved relative to the cooling means with a simple configuration as the switching means. According to the tenth technical feature of the present invention, the medium transported onto the transporting and fixing means can be appropriately brought into close contact with the cooling area of ​​the cooling means, compared to a case in which the counter rotating means is not used. According to the eleventh technical feature of the present invention, the medium transported onto the transporting and fixing means can be brought into closer contact with the cooling area of ​​the cooling means more appropriately than in the case where one counter rotating means is provided at the entrance to the cooling area of ​​the cooling means. According to the twelfth technical feature of the present invention, even in an embodiment in which the counter rotation means is provided in the cooling area of ​​the cooling means, the pushing-up means can push up the conveying and fixing means without the counter rotation means getting in the way. According to a thirteenth technical feature of the present invention, by utilizing a position detection means for detecting the transport position of the medium, it is possible to easily grasp the timing for switching the cooling means to a contact or non-contact state by the switching means. According to the fourteenth technical feature of the present invention, by utilizing a position detection means for detecting the transport position of the medium, it is possible to easily switch the cooling means to a non-contact state. According to the fifteenth technical feature of the present invention, by utilizing a position detection means for detecting the transport position of the medium, it is possible to easily realize switching of the cooling means to the contact state. According to the sixteenth technical feature of the present invention, when the distance between the preceding medium and the following medium is equal to or less than the length of the cooling region of the cooling means, the switching operation by the switching means can be omitted. According to the 17th technical feature of the present invention, when fixing an unfixed image on a medium by heating and cooling a belt-shaped conveying and fixing means, it is possible to construct an image forming system including a fixing device that can suppress unnecessary cooling that does not contribute to cooling of the medium and ensure fixing performance, compared to when the conveying and fixing means is continuously cooled. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1A is an explanatory diagram showing an overview of an embodiment of an image forming system incorporating a fixing device to which the present invention is applied; FIG. 1B is an explanatory diagram showing a representative embodiment of the switching means shown in FIG. 1A; and FIG. 1C is an explanatory diagram showing another representative embodiment of the switching means shown in FIG. [Diagram 2] FIG. 1 is an explanatory diagram showing an overall configuration of an image forming system according to a first embodiment. [Diagram 3] FIG. 4 is an explanatory diagram illustrating a main part of a second fixing unit according to the first embodiment. [Figure 4] (a) is an explanatory diagram showing special paper for photo images as an example of a medium, (b) is an explanatory diagram showing the state after a toner image has been fixed to the special medium, and (c) is an explanatory diagram showing the state after a toner image has been fixed to ordinary paper as an example of a medium. [Diagram 5] FIG. 1 is an explanatory diagram showing the main parts of the contact / separation mechanism used in embodiment 1, where (a) shows a state in which the cooler is arranged in a contact position with respect to the transport / fixing belt, and (b) shows a state in which the cooler is arranged in a non-contact position with respect to the transport / fixing belt. [Figure 6] 4 is an explanatory diagram showing a control system for the second fixing unit and its peripheral parts according to the first embodiment. FIG. [Figure 7] 5 is a flowchart showing a process of connecting and disconnecting a cooler used in the first embodiment. [Figure 8](a) is an explanatory diagram showing the arrangement of the cooler just before the medium enters the cooling area of ​​the second fixer, and (b) is an explanatory diagram showing the arrangement of the cooler just after the medium has passed through the cooling area of ​​the second fixer. [Figure 9] (a) is an explanatory diagram showing a schematic diagram of a state in which multiple media are transported to the second fixing device with a predetermined page gap LPG, (b) is an explanatory diagram showing an example of the contact and separation operation of the cooler when LPG>LCA (the length of the cooling area along the media transport direction of the second fixing device), and (c) is an explanatory diagram showing an example of the contact and separation operation of the cooler when LPG≦LCA. [Figure 10] FIG. 11 is an explanatory diagram showing a main part of a second fixing unit according to a first modified embodiment. [Figure 11] FIG. 1A is an explanatory diagram showing the function of a positioning roll in the first modified embodiment, and FIG. 1B is an explanatory diagram showing a secondary problem when no positioning roll is used. [Figure 12] FIG. 11 is an explanatory diagram showing a main part of a second fixing unit according to the second embodiment. [Figure 13] FIG. 1 is an explanatory diagram showing the main parts of the contact / separation mechanism used in embodiment 1, where (a) shows the state in which the transport / fixing belt is placed in a contact position with respect to the cooler, and (b) shows the state in which the transport / fixing belt is placed in a non-contact position with respect to the cooler. [Figure 14] (a) is an explanatory diagram showing the position of the transporting and fixing belt just before the medium enters the cooling area of ​​the second fixing device, and (b) is an explanatory diagram showing the position of the transporting and fixing belt just after the medium has passed through the cooling area of ​​the second fixing device. [Figure 15] FIG. 11 is an explanatory diagram showing a main part of a second fixing unit according to the third embodiment. [Figure 16] 13 is a flowchart showing a process of connecting and disconnecting a cooler used in the third embodiment. [Figure 17] (a) is an explanatory diagram showing the state in which the back surface temperature of the media is measured by a temperature sensor when the leading edge of the media passes halfway (D) through the cooling area of ​​the second fixing unit, (b) is an explanatory diagram showing an example of the retraction operation of the cooler performed when the temperature Td measured by the temperature sensor is below a predetermined allowable temperature Tth, and (c) is an explanatory diagram showing an example of the retraction operation of the cooler performed when Td>Tth. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Overview of the embodiment FIG. 1(a) shows an outline of an embodiment of an image forming system including a fixing device to which the present invention is applied. In the figure, the image forming system includes an image forming means 11 that forms an unfixed image G on a medium S, and a fixing device 10 that fixes the unfixed image G held on the medium S. The fixing device 10 is a fixing device that heats and pressurizes the medium S on which an unfixed image G is held, and then cools it to fix the unfixed image G, and is equipped with a heating and fixing means 1 having a heat source 1a, a belt-like conveying and fixing means 2 that is stretched across the heating and fixing means 1 and is circulatable, and conveys the medium S in contact with the image surface of the medium S, a pressure fixing means 3 that is arranged opposite the heating and fixing means 1 across the conveying and fixing means 2 and is pressurized to form a fixing area FA between it and the heating and fixing means 1, a cooling means 4 that is arranged in contact with the back surface of the medium conveying area of ​​the conveying and fixing means 2 downstream of the fixing area FA in the conveying direction of the medium S on the conveying and fixing means 2, and cools the conveying and fixing means 2, and a switching means 5 that switches the conveying and fixing means 2 and the cooling means 4 between contact and non-contact depending on the passing state of the medium S in the cooling area CA of the cooling means 4.

[0015] In such technical means, the fixing device 10 of the present embodiment may be incorporated into an image forming apparatus including an image creating means 11 that creates an unfixed image G, or may be incorporated into a post-processing device separate from the image forming apparatus, and configured as an image forming system consisting of multiple units. Moreover, the heat fixing means 1 includes, for example, a heat fixing roll. The heat source 1a may be either built-in or external. Furthermore, the transport fixing means 2 includes a fixing belt. In this example, in order to obtain a high-gloss image such as a photographic image, it is preferable that the fixing belt is an endless film made of, for example, a thermosetting polyimide resin, on whose surface a highly smooth coating layer made of fluororubber, silicone rubber or the like is formed. Furthermore, the pressure fixing means 3 may be in the form of a roll or a belt, as long as it is pressed so as to form a fixing area FA between it and the heat fixing means 1. The cooling means 4 may be any means that cools by contacting the rear surface of the medium transport area of ​​the transporting and fixing means 2. A heat dissipation means that dissipates absorbed heat, such as a heat sink, is mainly used. The switching means 5 may be any means that uses the passage state of the medium S in the cooling area CA of the cooling means 4 as a criterion for switching the cooling means 4 to a contact state or a non-contact state with the transporting and fixing means 2.

[0016] Next, a typical or preferred embodiment of the fixing device according to the present embodiment will be described. First, a representative embodiment of the switching means 5 is to switch the conveying and fixing means 2 and the cooling means 4 to a non-contact state while the medium S is not passing through the cooling area CA of the conveying and fixing means 2 by the cooling means 4. This is based on the fact that the cooling of the medium S is performed in the cooling area CA by the cooling means 4, not in the entire medium conveying area of ​​the conveying and fixing means 2. In other words, since cooling of the medium S is not required while the medium S is not passing through the cooling area CA, omitting the cooling operation of the conveying and fixing means 2 by the cooling means 4 during this time does not affect the cooling process of the medium S at all.

[0017] Therefore, a preferred embodiment of the switching means 5 is one in which the cooling means 4 is switched to a contact state before the leading edge of the medium S in the transport direction reaches the entrance (upstream starting point) of the cooling area CA, and the cooling means 4 is switched to a non-contact state when the trailing edge of the medium S in the transport direction reaches the exit (downstream end point) of the cooling area CA. In this example, the cooling means 4 performs a cooling operation of the transport / fixing means 2 while the medium S passes through the cooling area CA of the cooling means 4. In addition, the cooling effect on the medium S depends on characteristic information (thickness, thermal conductivity, etc.) of the medium S. For this reason, it is possible that the medium S will be cooled to a predetermined temperature (allowable cooling temperature) before it has passed through the cooling area CA by the cooling means 4.

[0018] A preferred embodiment of the switching means 5 suitable for such a case is one in which the cooling means 4 is switched to a non-contact state under conditions in which the medium S is cooled to a predetermined temperature before the trailing end of the medium S in the transport direction reaches the exit of the cooling area CA. In this example, it is necessary to determine whether the medium S passing through the cooling area CA has been sufficiently cooled along the way. At this time, a temperature detection means (not shown) may be provided to measure the temperature of the medium S (for example, the temperature of the back side of the medium S that is not in contact with the transport and fixing means 2) along the way in the transport direction of the medium S in the cooling area CA. Then, based on a detection signal from the temperature detection means, it is determined whether the temperature of the medium S has reached the allowable cooling temperature, and the state of the cooling means 4 is switched by the switching means 5.

[0019] A typical example of the configuration of the switching means 5 is a mode including a moving mechanism that moves the cooling means 4 relative to the conveying and fixing means 2. This moving mechanism includes any mode in which the cooling means 4 is moved to a non-contact position while remaining partially in contact with the conveying and fixing means 2, or the cooling means 4 is moved entirely to a non-contact position. 1(b), a preferred embodiment of the movement mechanism is one in which the cooling means 4 is supported so as to be able to swing, with the end of the cooling area CA of the cooling means 4 on the exit side or the entrance side as the swing point, and the cooling means 4 is swung between a contact position where it comes into contact with the conveying and fixing means 2 and a retracted position where it retracts from the conveying and fixing means 2. This example is preferable from the viewpoint of stabilizing the switching operation with a simpler configuration than an embodiment in which the entire cooling means 4 is moved linearly in parallel with respect to the conveying and fixing means 2 to switch between contact and non-contact. Furthermore, when the cooling means 4 is retracted from the conveying and fixing means 2 to the retracted position, a gap is generated between the conveying and fixing means 2 and the cooling means 4, and there is a concern that part of the media conveying area of ​​the conveying and fixing means 2 may drop in the retracted direction. From the viewpoint of effectively solving this type of secondary problem, it is preferable to provide a positioning means 8 on the back side of the media conveying area of ​​the conveying and fixing means 2, as shown in Fig. 1(b). This positioning means 8 may be disposed so as to maintain the surface orientation of the media conveying area of ​​the conveying and fixing means 2 when all or part of the cooling means 4 is retracted from the contact position with the back side of the conveying and fixing means 2.

[0020] 1(c), there is a typical example of the switching means 5, which includes a moving mechanism for moving the conveying and fixing means 2 relative to the cooling means 4. This moving mechanism may move the entire conveying and fixing means 2 to a non-contact state relative to the cooling means 4, but from the viewpoint of maintaining the trajectory of the outlet or inlet of the medium conveying flow area of ​​the conveying and fixing means 2, a preferred embodiment is one in which a part of the conveying and fixing means 2 is kept in contact and the remaining part is moved to a non-contact state. A preferred embodiment of this type of moving mechanism is to provide a push-up means 9 on the back side of the media transport area of ​​the transporting and fixing means 2, other than the cooling area CA, and to use this push-up means 9 to push up the media transport area portion of the transporting and fixing means 2 in a direction away from the cooling means 4. In this example, the push-up means 9 may be in contact with the conveying and fixing means 2 before being pushed up, or may not be in contact with the conveying and fixing means 2. In addition, in the case where the push-up means 9 is in contact with the conveying and fixing means 2 before being pushed up, the push-up means 9 can also serve as the positioning means 8 described above.

[0021] From the viewpoint of ensuring the cooling effect of the cooling means 4, it is preferable that the medium S transported by the transporting and fixing means 2 is disposed in close proximity to the cooling area CA of the cooling means 4. From this viewpoint, a preferred embodiment has an opposing rotation means 6 (specifically, 6a) that is disposed opposite the entrance to the cooling area CA of the cooling means 4 across the conveying and fixing means 2 and rotates following the conveying and fixing means 2, as shown in Figures 1(a) to (c). An even more preferred embodiment includes an embodiment in which a plurality of opposing rotating means 6 (specifically 6a, 6b) are arranged opposite the entrance of the cooling area CA of the cooling means 4 and a location other than the entrance (the exit in this example) across the conveying and fixing means 2, as shown in Figures 1(a) to (c), and rotate following the conveying and fixing means 2. In addition, in an embodiment in which the switching means 5 includes the push-up means 9 as a moving mechanism, as shown by the imaginary line in Fig. 1(c), a part or all of the counter rotating means 6 (6a, 6b) is preferably moved in conjunction with the push-up means 9. This embodiment is effective in keeping the conveying / fixing means 2 out of contact with the cooling means 4 as the push-up means 9 moves.

[0022] Furthermore, from the viewpoint of properly grasping the switching timing by the switching means 5, it is preferable that the switching means 5 has a position detection means 7 for detecting the position of the leading or trailing end in the transport direction of the medium S upstream of the fixing area FA in the transport direction of the medium S, as shown in Figure 1(a), and determines the position of the leading or trailing end in the transport direction of the medium S transported by the transporting and fixing means 2 based on the detection result of the position detection means 7, and switches between the contact or non-contact state of the cooling means 4. In this example, when the position detection means 7 detects the rear end position of the medium S in the transport direction, the switching means 5 switches the cooling means 4 to a non-contact state based on the detection result when the rear end of the medium S reaches the exit of the cooling area CA. In addition, when the position detection means 7 detects the leading edge position of the medium S in the transport direction, the switching means 5 switches the cooling means 4 to a contact state based on the detection result at a point before the leading edge of the medium S reaches the entrance of the cooling area CA.

[0023] Furthermore, the switching operation of the switching means 5 is performed depending on the transport position of the medium S, but if the distance between the multiple media S (the distance between the rear end of the preceding medium S and the front end of the following medium S) is short, there is a possibility that cooling of the media S will be insufficient. From this viewpoint, a preferred embodiment of the switching means 5 is one having a discrimination means (not shown) that discriminates the distance between the rear end in the transport direction of the preceding medium and the front end in the transport direction of the following medium, and does not execute the contact / non-contact switching operation of the cooling means 4 under conditions where the distance discriminated by this discrimination means is equal to or less than the length of the cooling area CA.

[0024] Hereinafter, the present invention will be described in more detail based on the embodiments shown in the accompanying drawings. First embodiment FIG. 2 shows the overall configuration of the image forming system according to the first embodiment. -Overall configuration of image forming system- In the same figure, the image forming system 15 has an apparatus main body 16 equipped with an image forming unit capable of forming color images, and a post-processing device 50 is attached to the upper part of the apparatus main body 16 as an optional device, while a multi-tiered media supply container 81 (81a, 81b) for supplying media such as paper is housed in the lower part of the apparatus main body 16 and can be pulled out.

[0025] -Image forming unit- The image forming unit used in this embodiment employs, for example, an electrophotographic system, and has a so-called tandem configuration in which image forming sections 20 (20a-20d) of four colors, yellow (Y color), magenta (M color), cyan (C color), and black (K color), are arranged in parallel with respect to a belt-shaped intermediate transfer body 30. Therefore, the toner images of each color formed in each image forming section 20 (20a-20d) are, for example, sequentially primarily transferred onto the intermediate transfer body 30 to be multiplexed, and the multiplexed toner images are transferred collectively onto the medium transported from the medium supply container 81 and fixed. Note that the color arrangement of the four color image forming sections 20 is not limited to this order, and may be in another order.

[0026] The image forming section 20 (20a to 20d) in this embodiment is composed of a photoconductor 21 as an image carrier that forms and holds each color component toner image, a charger 22 such as a charging roll that charges the photoconductor 21, an exposure device 23 such as a laser scanner that forms a latent image on the charged photoconductor 21, a developer 24 that visualizes the electrostatic latent image on the photoconductor 21, a primary transfer device 25 consisting of, for example, a primary transfer roll that primarily transfers the toner image on the photoconductor 21 onto the intermediate transfer body 30, a photoconductor cleaner 26 that cleans residual toner remaining on the photoconductor 21, and a charge remover 27 that removes residual charge on the photoconductor 21. The exposure device 23 in this embodiment is configured to expose the entire four-color image forming section 20 (20a to 20d) by a single exposure device.

[0027] The intermediate transfer body 30 is stretched around a number of tension rolls. For example, tension roll 31 serves as a drive roll for circulating and transporting the intermediate transfer body 30, and tension roll 32 is disposed opposite to tension roll 31 as a backup roll for a secondary transfer device 33, which is, for example, a secondary transfer roll. Furthermore, at a position opposite to tension roll 31 of the intermediate transfer body 30, an intermediate transfer body cleaner 34 for removing residual toner on the intermediate transfer body 30 is disposed. Furthermore, within the device main body 16, four color toner boxes 35 are provided above the intermediate transfer body 30 to supply toner corresponding to each of the developing devices 24 in each image forming section 20, and toner corresponding to each color is supplied to the developing devices 24 via a transport path not shown.

[0028] Furthermore, the medium transport system 80 in this embodiment is configured as follows. The medium sent out by the pickup roll 82 from each medium supply container 81 is separated by the action of the feed roll 83 and the retard roll 84, and only one medium is transported to the downstream transport path. In addition, in the transport path, there are provided an alignment roll 85 that positions and aligns the medium transported from the medium supply container 81 before it enters the secondary transfer device 33, and a first fixer 40 that fixes the unfixed toner image transferred onto the medium by the secondary transfer device 33. In addition, a switching member 86 is provided downstream of the first fixer 40, and by switching this switching member 86, the medium that has left the first fixer 40 can be switched to a two-way path between the post-processing device 50 side and the first discharge receiver 87 side that accommodates the medium that is directly discharged from the device main body 16. Although two medium supply containers 81a and 81b for storing media of different sizes are shown as medium supply container 81, the present invention is not limited to this, and three or more medium supply containers may be provided, or only one medium supply container may be provided. Also, a manual feeder (not shown) may be provided to guide the medium to the transport path.

[0029] The first fixing device 40 of this embodiment is, for example, as follows: The first fixing device 40 includes a heat fixing roll 41 having an internal heat source such as a halogen lamp (not shown), and a pressure fixing roll 42 that is disposed opposite the heat fixing roll 41 and sandwiches and transports the medium in a fixing area formed between the heat fixing roll 41 and the pressure fixing roll 42. Therefore, when the medium carrying the unfixed toner image passes through the fixing area of ​​the first fuser 40, the unfixed toner image on the medium is fixed onto the medium by heat and pressure. In this example, the first fixing device 40 is a pair of rolls using a heating and pressurizing method, but the present invention is not limited to this. A pressure pad is disposed opposite the heating and fixing roll, and a pressure belt that rolls with the heating and fixing roll is interposed between the heating and fixing roll and the pressure pad. The medium is sandwiched in the fixing area formed between the heating and fixing roll and the pressure belt, and heating and pressurizing the medium to be fixed can be selected as appropriate.

[0030] -Example of post-processing device configuration- 2, post-processing device 50 of the present embodiment is provided in the middle of medium transport path 51, and includes second fixer 60 that makes the toner image surface of the medium highly glossy, and cutter 70 that cuts the medium that has passed through second fixer 60. In the present embodiment, second discharge receiver 88 is provided downstream of post-processing device 50 to accommodate media that have passed through cutter 70.

[0031] -Basic configuration of the second fixing unit- The second fixing unit 60 has the same basic configuration as the fixing device 10 shown in FIG. That is, as shown in Figures 2 and 3, the second fixing device 60 comprises a heating fixing roll 61 as a heating fixing means, a transporting fixing belt 62 as a transporting fixing means that is circulated around the heating fixing roll 61 and transports the medium S in contact with the image surface of the medium S, a pressure fixing roll 63 as a pressure fixing means that is arranged opposite the heating fixing roll 61 across the transporting fixing belt 62 and is pressurized to form a fixing area FA between the heating fixing roll and the transporting fixing belt 62, and a cooler 64 as a cooling means that is arranged in contact with the back surface of the media transporting area SA of the transporting fixing belt 62 downstream of the fixing area FA of the transporting fixing belt 62 in the transporting direction of the medium S and cools the transporting fixing belt 62.

[0032] <Heat fixing roll> The heat fixing roll 61 has a configuration in which a release layer (not shown) made of a PFA tube or the like is formed around a highly thermally conductive metal core 61a, and a heat source 65 such as a halogen lamp is provided inside the core 61a, and the heat source 65 controls heating so that the surface of the heat fixing roll 61 reaches a predetermined temperature. In this embodiment, the heat fixing roll 61 is rotated by a drive motor 69 (see FIG. 6), and the conveying and fixing belt 62 is rotated circulatoryly by the heat fixing roll 61.

[0033] <Conveyor and fixing belt> The conveying and fixing belt 62 is formed by forming a highly smooth coating layer of fluororubber, silicone rubber, etc. on the surface of an endless film made of, for example, a thermosetting polyimide resin. The conveying and fixing belt 62 is stretched around a heat fixing roll 61, a peeling roll 67, and a steering roll 68, and can be circulated by the rotation of the heat fixing roll 61. Here, the peeling roll 67 rotates following the movement of the transport-fixing belt 62, and the transport-fixing belt 62 is wound around the peeling roll 67 while being tensioned, so that the direction of movement of the transport-fixing belt 62 is suddenly changed. Therefore, the medium S on the transport-fixing belt 62 is naturally peeled off from the transport-fixing belt 62 at the position of the peeling roll 67 due to the rigidity of the medium S itself. In addition, the steering roll 68 is designed to constantly tension the transport-fixing belt 62 itself. The steering roll 68 maintains the tension by pressing the transport-fixing belt 62 outward, and corrects the deviation that occurs when the transport-fixing belt 62 moves in a circular motion (the phenomenon in which the transport-fixing belt 62 moves toward one end of the steering roll 68). The base material and the covering layer of the conveying / fixing belt 62 are selected to have an appropriate thickness to maintain mechanical strength and to effectively utilize thermal energy. For example, a covering layer of about 35 μm is formed on a base material of about 75 μm.

[0034] <Pressure fixing roll> On the other hand, the pressure fixing roll 63 has a highly thermally conductive metal core 63a coated with an elastic layer 63b such as silicone rubber, and a release layer (not shown) similar to the release layer of the heat fixing roll 61 is formed on the surface of the elastic layer 63b. In the present embodiment, a heat source 66 such as a halogen lamp is also provided inside the core 63a of the pressure fixing roll 63, and heating is controlled so that the surface of the pressure fixing roll 63 reaches a predetermined temperature. Therefore, the medium S transported to the second fixing device 60 is heated and pressurized in the fixing area FA between the heat fixing roll 61 and the pressure fixing roll 63 with the toner image surface in contact with the transport fixing belt 62.

[0035] <Cooler> In this embodiment, the cooler 64 is provided in contact with the back surface of the transport-fixing belt 62 between the heat-fixing roll 61 and the peeling roll 67 (corresponding to the medium transport area SA). The cooler 64 contacts a part of the medium transport area SA of the transport-fixing belt 62, and this contact area is the cooling area CA. In other words, the cooler 64 cools the transport-fixing belt 62 by absorbing heat from the transport-fixing belt 62 in the cooling area CA. Therefore, the medium S transported in close contact with the transport-fixing belt 62 is cooled. The cooler 64 in this embodiment corresponds to a so-called heat sink. The cooler 64 is composed of a fin member 64a provided with a number of heat dissipation fins extending in a direction substantially perpendicular to the surface along the conveying / fixing belt 62, and a cover 64b having a rectangular cross section and shaped like a cylinder that is provided to cover the fin member 64a. The cooler 64 is designed to forcibly dissipate heat from the fin member 64a by blowing air into the cooler 64 using an air blower (not shown). In addition, the cooler 64 is provided with a temperature sensor 641 (see FIG. 6), for example, on a part of the fin member 64a, and based on the detection result of the temperature sensor 641, an air blower (not shown) is turned on and off or the strength of the air volume is adjusted.

[0036] <Second fixing unit peripheral structure> Furthermore, in this example, an entrance guide member 52 that guides the medium S to the entrance of the second fixing device 60 is provided near the entrance of the second fixing device 60, and a position sensor 53 that detects the position of the leading or trailing end of the medium S passing through the transport path 51 is provided. Further, an exit guide member 54 that guides the medium S discharged from the exit of the second fixing device 60 is provided near the exit of the second fixing device 60, and a transport roll 55 is provided downstream of this exit guide member.

[0037] <Selection of media> Normally, to obtain a high-gloss image like a photographic image, it is preferable to use a special paper as shown in Fig. 4(a) as the medium S. As shown in the figure, the special paper has a moisture-proof layer L2 on both sides of a base layer L1, and further has an image-receiving layer L3 on the recording surface (toner image forming surface) side. The moisture-proof layer L2 is made of a resin with no air permeability such as polyethylene, and a thickness of about several μm is sufficient to obtain the moisture-proof effect of the base layer L1. The image-receiving layer L3 is mainly composed of a thermoplastic resin such as polyester with a melting temperature of about 130° C., and has a layer thickness of 5 to 20 μm, preferably about 10 μm. On the other hand, the base layer L1 is composed mainly of cellulose, and has the same composition as plain paper, but it is also possible to use a dedicated base layer L1 with a different composition. Therefore, like photographic paper used in silver halide photography, by providing moisture-proof layers L2 on both sides of the base layer L1 and further providing an image-receiving layer L3 similar to the toner material, it is possible to eliminate air permeability and prevent problems such as the base layer L1 absorbing moisture in a high humidity environment, causing stretching and curling, or the toner image being stretched and cracking, etc. Also, the toner image is fused together with the image-receiving layer L3 by the image-receiving layer L3, and by applying pressure, the toner image is well embedded in the image-receiving layer L3, making it possible to obtain a smooth print surface.

[0038] When the second fixer 60 uses such special paper in the photo print mode, the toner image becomes embedded in the image receiving layer L3 as shown in Fig. 4(b). At this time, the surface properties of the transport / fixing belt 62 of the second fixer 60 are transferred, and the surface of the image receiving layer L3 and the surface of the toner image become substantially uniform, resulting in a glossy image. Meanwhile, Fig. 4(c) shows a state in which the toner image is fixed only by the first fixer 40 onto plain paper as the medium S in the plain paper print mode. In this case, the toner image is placed on the base layer L1, and the toner image protrudes from the image surface, resulting in an image with poor gloss.

[0039] -Characteristic configuration of the second fixing unit- <Necessity for a contact mechanism> In this embodiment, the second fixing device 60 includes a contact / separation mechanism 100 as a switching unit for switching the cooler 64 between contact with the conveying / fixing belt 62 and non-contact with the conveying / fixing belt 62. Here, assuming that the contact / separation mechanism 100 is not provided, the cooler 64 always maintains contact with the back surface of the transport fixing belt 62. At this time, the medium S that has passed through the fixing area FA between the heat fixing roll 61 and the pressure fixing roll 63 moves in close contact with the transport fixing belt 62, and is cooled only while passing through the cooling area CA of the media transport area SA of the transport fixing belt 62 where the cooler 64 contacts. Therefore, if the cooler 64 performs a cooling operation when the medium S has not passed through the cooling area CA, it will end up cooling only the transport fixing belt 62, not the medium S. Then, the temperature of the transport fixing belt 62 will be unnecessarily lowered, and a lot of power will be required for heating when the transport fixing belt 62 is heated again by the heat fixing roll 61. In other words, the power required for the cooling operation of only the transport fixing belt 62, which does not contribute to cooling the medium S, will be wasted. In this example, while the medium S is not passing through the cooling area CA of the transport-fixing belt 62 cooled by the cooler 64, the transport-fixing belt 62 and the cooler 64 are switched to a non-contact state, thereby aiming to reduce waste of power.

[0040] <Example of contact / separation mechanism configuration> In this example, as shown in Figures 5(a) and (b), the contact / separation mechanism 100 depends on the passage state of the medium S through the cooling area CA of the cooler 64, determines the period when the medium S does not pass through the cooling area CA, and moves the cooler 64 from the contact position to the retracted position. First, the contact / separation mechanism 100 has a swing shaft 101 at an end portion on the outlet (downstream end point B) side of the cooling area CA of the cooler 64, and supports the cooler 64 so that it can swing around the swing shaft 101 as a swing point. The contact / separation mechanism 100 swings the cooler 64 between a contact position where it comes into contact with the transport-fixing belt 62 and a retreat position where it retreats in a direction away from the transport-fixing belt 62. 5(a) and 5(b), the contact / separation mechanism 100 is provided with a variable mechanism 102 that changes the end position of the entrance (upstream starting point A) side of the cooling area CA of the cooler 64 in the direction of oscillation and rotation. In this example, the variable mechanism 102 includes an eccentric cam 104 rotated by a drive motor 103, cam followers 105 rotatably provided on both sides of the entrance side of the cooling area CA of the cooler 64 in the width direction and abutting on the cam surface of the eccentric cam 104, and a biasing spring 106 provided at a corner of the cooler 64 on the free rotation end side diagonally opposite to the oscillation shaft 101 and serving as a biasing means for biasing the cooler 64 toward the conveying / fixing belt 62 side.

[0041] According to the contact / separation mechanism 100 of this example, when the cooler 64 is set at a contact position where it contacts the transport-fixing belt 62, as shown in Fig. 5(a), for example, the eccentric cam 104 is rotated counterclockwise by the drive motor 103, and the small diameter portion r1 of the eccentric cam 104 is brought into contact with the cam follower 105 by the biasing force of the biasing spring 106. Then, the cooler 64 swings toward the transport-fixing belt 62 with the swing shaft 101 as a swing point, and is disposed at a predetermined contact position. On the other hand, when the cooler 64 is to be retreated to the retreat position, as shown in Fig. 5(b), the eccentric cam 104 is rotated clockwise by the drive motor 103, and the large diameter portion r2 of the eccentric cam 104 is brought into contact with the cam follower 105 against the biasing force of the biasing spring 106. Then, the cooler 64 swings in a direction away from the conveying-fixing belt 62 with the swing shaft 101 as a swing point, and is disposed at a predetermined retreat position.

[0042] <Close transportability of media> In this embodiment, from the viewpoint of ensuring the cooling effect of the cooler 64, as shown in FIG. 3, the medium S transported by the transport-fixing belt 62 is arranged in close proximity to the cooling area CA of the cooler 64. In this example, an entrance-side opposing roll 131 serving as an opposing rotation means is provided at a location on the surface side of the transport-fixing belt 62 corresponding to the entrance (upstream starting point A) of the cooling area CA of the cooler 64. The entrance-side opposing roll 131 is disposed in contact with the transport-fixing belt 62 and rotates following the transport-fixing belt 62. Further, an outlet-side opposed roll 132 serving as an opposed rotating means is provided at a position on the surface side of the transport-fixing belt 62 corresponding to the outlet (downstream end point B) of the cooling area CA of the cooler 64. The outlet-side opposed roll 132 is disposed in contact with the transport-fixing belt 62 and rotates following the transport-fixing belt 62. In this example, it is necessary to provide the entrance-side opposed roll 131 at a location corresponding to the entrance of the cooling area CA. As a result, the medium S transported on the transport-fixing belt 62 is drawn in by the entrance-side opposed roll 131 so as to come into close contact with the transport-fixing belt 62 at the entrance of the cooling area CA. On the other hand, the exit side opposed roll 132, together with the entrance side opposed roll 131, is effective in bringing the medium S into close contact with the transport-fixing belt 62 at two locations, one before and one after the other, in the transport direction of the medium S. However, although the exit side opposed roll 132 is provided at a location corresponding to the exit of the cooling area CA, the present invention is not limited thereto, and the exit side opposed roll 132 may be provided upstream of the exit of the cooling area CA.

[0043] -Control system for the second fixing unit- In this example, the control system of the second fixing unit 60 has a control device 150 configured with a microcomputer including various processors, as shown in Fig. 6. The term "processor" here refers to a processor in a broad sense, and includes a general-purpose processor (e.g., CPU: Central Processing Unit, etc.) and a dedicated processor (e.g., GPU: Graphics Processing Unit, ASIC: Application Specific Integrated Circuit, FPGA: Field Programmable Gate Array, programmable logic device, etc.). An operation panel 151 of the image forming system 15 is connected to this control device 150. This operation panel 151 is provided with a start switch for starting an image forming process on the medium S, a mode switch for specifying an image forming mode such as single-sided printing, double-sided printing, high-definition printing, and a medium type designation section for designating the medium type to be used, and the like. Furthermore, a program (e.g., see FIG. 7) related to the contact / separation process of the cooler 64 is pre-installed in the ROM serving as a storage device of the control device 150. Various detectors such as a position sensor 53 and a temperature sensor 641 are also connected to the control device 150. Furthermore, various control targets (the drive motor 69, the heat sources 65 and 66, the drive motor 103 of the contact / separation mechanism 100, etc.) are also connected to the control device 150. The processor of the control device 150 receives instruction signals from an operation panel 151 and detection signals from various detectors, executes the above-mentioned programs, and sends appropriate control signals to each controlled object.

[0044] -Cutting device- In this embodiment, the cutting device 70 is capable of cutting the sides of the medium, for example, to produce a borderless print. For this reason, as shown in FIG. 2, the cutting device 70 includes a slitter 71 for cutting the medium in the width direction, a plurality of circular cutters 72 (72a, 72b) for cutting the medium in the feed direction length, and a plurality of transport rolls 73, 74 for transporting the medium. The slitter 71 has a number of blades corresponding to the number of cuts required in the axial direction, and cuts the medium in the feed direction while transporting it. In addition, the circular cutter 72 cuts the medium by temporarily stopping the transport of the medium and moving the rolling cutter of the upper blade along the lower blade. Note that the circular cutter 72 may be, for example, a roller cutter provided in the axial direction, and cut the medium while transporting it. Furthermore, the cutting device 70 does not only have the function of cutting the medium into multiple sheets (for example, four sheets), but can also print one L-size image on a postcard-sized medium (100 x 150 mm) and finish the print without borders using the cutting device 70. Furthermore, by combining printing four images on an A4-sized medium with printing one image each on any number of postcard-sized media, any number of L-size digital camera photos can be obtained. Furthermore, by making the widthwise position of the blade of the slitter 71 variable, it is possible to cut into various sizes, such as four pieces, six pieces, or eight pieces.

[0045] -Basic operation of image forming system- Next, the basic operation of such an image forming system will be described. 2, the multiple toner images formed on intermediate transfer body 30 by multiplexing the toner images of each color by each image forming unit 20 (20a to 20d) are transferred collectively onto the medium sent out from medium supply container 81 by secondary transfer device 33. The transferred unfixed toner image is fixed by first fixer 40, and then guided by switching member 86 to second discharge receiver 88 via first discharge receiver 87 or post-processing device 50.

[0046] In this embodiment, the medium transport direction is switched by the switching member 86 as follows. That is, in the plain paper print mode (low gloss print) in which a normal image is formed, after fixing by the first fixing device 40, the medium is discharged to the first discharge receiver 87 by the switching member 86. On the other hand, in the photo print mode (high gloss print) in which a high gloss image such as a photographic image is formed, after fixing by the first fixing device 40, the medium is transported to the second fixing device 60 side by the switching member 86, and after further fixing by the second fixing device 60, the medium is discharged to the second discharge receiver 88 via the cutting device 70. In particular, the cutting device 70 may be used when borderless prints such as photographic images are preferred, and when cutting is not particularly required, the medium may be discharged to the second discharge receiver 88 without cutting.

[0047] Normally, to obtain a high gloss image like a photographic image, it is preferable to use a special paper as the medium S as shown in FIG. In photo print mode, when such special paper is used and fixing is performed by the second fixing device 60, the toner image becomes embedded in the image receiving layer L3 as shown in Fig. 4(b). At this time, the surface properties of the transport fixing belt 62 of the second fixing device 60 are transferred, and the surface of the image receiving layer L3 and the surface of the toner image become substantially uniform, resulting in a glossy image.

[0048] - Fixing action by the second fixing device - The fixing action by the second fixing device 60 is performed as follows. 3, the medium S that has been guided to the post-processing device 50 via the first fixing device 40 is about to enter the second fixing device 60. In this state, in the second fixing device 60, the heat fixing roll 61 and the pressure fixing roll 63 have been heated to a temperature at which fixing is possible by the heat sources 65 and 66, respectively, and the transport fixing belt 62 is in a state of circular rotation in association with the driving rotation of the heat fixing roll 61. Furthermore, the cooler 64 is set at a contact position with the rear surface of the transport / fixing belt 62, on the condition that the leading edge of the medium S has passed a predetermined reference position C. The cooler 64 is then in a standby state in which it will perform a cooling operation by driving the air blower. In this state, the medium S undergoes a heating and pressure fixing process in the fixing area FA of the second fixing device 60, is transported by the transport fixing belt 62, is cooled by the cooler 64, and is then discharged from the second fixing device 60. For this reason, by using the special paper shown in FIG. 4 as the medium S and going through a series of fixing processes including heating and pressurizing followed by cooling, it is possible to obtain a highly glossy image like a photographic image.

[0049] - Cooler connection and disconnection processing - In the process of performing the fixing process of the second fixing device 60 described above, the second fixing device 60 performs a contact / separation operation of the cooler 64 in parallel. This process of connecting and disconnecting the cooler is performed, for example, according to the flowchart shown in FIG. First, as shown in Fig. 6, the control device 150 detects whether or not the leading edge of the medium S has passed position P of the position sensor 53. When the leading edge of the medium S passes position P of the position sensor 53, the control device 150 starts the counting operation of the timer counter using the detection result as a trigger. Then, the control device 150 determines whether or not the leading edge of the medium S has passed a predetermined reference position C in front of the cooling area CA of the cooler 64. This reference position C serves as a reference for moving the cooler 64 from the retracted position to the contact position, and is appropriately selected based on the timing at which the movement of the cooler 64 to the contact position is completed before the medium S reaches the entrance of the cooling area CA by the cooler 64. In this example, the timing when the leading edge of the medium S passes the reference position C is determined using the count value of a timer counter triggered by the detection output of the position sensor 53. However, this is not limited to this, and if the position P of the position sensor 53 is selected to be the reference position C, it is also possible to directly perform the setting operation to the contact position of the cooler 64 using the detection output of the position sensor 53.

[0050] In this example, the control device 150 performs a setting operation to the contact position of the cooler 64 as shown in FIG. 8(a) at the timing when the leading edge of the medium S reaches the reference position C, in accordance with the procedure shown in FIG. 5(a). This setting operation to the contact position of the cooler 64 is completed before the medium S reaches the entrance of the cooling area CA of the cooler 64, so the entire area of ​​the medium S is cooled by the cooling action as it passes through the cooling area CA of the cooler 64. Thereafter, the cooled medium S passes through the cooling area CA of the transport fixing belt 62 and is discharged from the second fixing device 60. At this time, when the rear end of the medium S passes through the exit (downstream end point B) of the cooling area, the control device 150 recognizes the timing when the medium S has passed through the cooling area CA from the count value of the timer counter, and performs an evacuation operation of the cooler 64 to the evacuation position, as shown in Figure 8(b), in accordance with the procedure shown in Figure 5(b). In this way, while the medium S is being added to the cooling area CA of the cooler 64 of the transport-fixing belt 62, the cooler 64 is set to the contact position, while while the medium S is not passing through the cooling area CA, the cooler 64 is retracted to a retracted position where it is not in contact with the transport-fixing belt 62. This prevents the transport-fixing belt 62 from being unnecessarily cooled by the cooler 64, which is preferable in that it is possible to eliminate the wasteful energy required for cooling the cooler 64 and for heating the heating-fixing roll 61 and the pressure-fixing roll 63.

[0051] - Fixing process when transporting multiple sheets of media using the second fixing unit - As shown in Fig. 9(a), multiple media S (S1, S2, ...) of the same or different types are transported at a predetermined interval. In Fig. 9(a), LCA means the length of the cooling area CA of the cooler 64 along the transport direction of the media S, and LPG means the distance (so-called page gap) between the rear end of the preceding medium S1 and the front end of the following medium S2. At this time, under the condition that the page gap LPG exceeds the cooling area LCA, LPG>LCA (the condition that the page gap is secured to a certain extent), as shown in Fig. 9(b), the cooler 64 may be moved from the retracted position to the contact position at the timing tC(1), tC(2) ... when the leading end of each medium S (S1, S2 ...) passes through the reference position C. On the other hand, the cooler 64 may be retracted from the contact position to the retracted position at the timing tB(1), tB(2) ... when the trailing end of each medium S (S1, S2 ...) passes through the downstream end point B of the cooling area CA.

[0052] In contrast, when the page gap LPG is equal to or smaller than the cooling area LCA, i.e., LPG≦LCA (the page gap is shorter than the cooling area), if the method shown in Fig. 9(b) is applied, there is a high possibility that the actual cooling effect of the cooler 64 on the medium will be insufficient. For this reason, in the case of this example, as shown in Fig. 9(c), it is preferable that the cooler 64 is not moved in and out of contact with the medium, but is exceptionally left in the contact position at all times.

[0053] ◎Transformation form 1 FIG. 10 is an explanatory diagram showing a main part of the second fixing unit according to the first modified embodiment. In the figure, the basic configuration of the second fixing device is substantially the same as that of the first embodiment, but further, a positioning roll 140 is provided on the back surface of the transport-fixing belt 62 between the entrance (upstream starting point A) of the cooling area CA and the fixing area FA. This positioning roll 140 is disposed at a position that matches the surface posture (reference posture) of the transport-fixing belt 62 in the medium transport area SA when the cooler 64 is set at the contact position. Incidentally, the same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed description thereof will be omitted here.

[0054] Here, in the first embodiment, since there is no positioning roll 140, when the cooler 64 is retracted to a retracted position with respect to the conveying and fixing belt 62 with the swing shaft 101 as a swing point, as shown by the dotted line in FIG. 11(a), a gap is generated between the back surface of the conveying and fixing belt 62 and the cooler 64. At this time, as shown by the dotted line in FIG. 11(a), there is a risk that the conveying and fixing belt 62, which is no longer supported by the cooler 64, will drop vertically downward. At this time, as shown in FIG. 11(b), an elevation angle θ is generated between the posture (corresponding to the belt travel direction) of the conveying and fixing belt 62 located between the fixing area FA and the entrance (upstream starting point A) of the cooling area CA and the above-mentioned reference posture (corresponding to the medium discharge direction m passing through the fixing area FA), and when the following medium passes through the fixing area FA, the medium S is likely to peel off from the medium conveying surface of the conveying and fixing belt 62. In this case, there is a concern that the leading edge of the medium S may peel off, resulting in uneven gloss at the leading edge.

[0055] However, as shown in the first modified embodiment, if a positioning roll 140 is provided, the surface attitude of the transport / fixing belt 62 is maintained at the reference attitude, so that the above-mentioned problems are eliminated, which is preferable.

[0056] ◎Transformation form 2 In this embodiment, the contact / separation mechanism 100 of the cooler 64 is provided with a swing shaft 101 at the end on the exit (downstream end point B) side of the cooling area CA, but this is not limited thereto, and it is also possible to provide a swing shaft at the end on the entrance (upstream start point A) side of the cooling area CA to enable swinging. In this case, the surface posture of the transport / fixing belt 62 between the entrance of the cooling area CA and the fixing area FA is kept at the reference posture, so there is no need to provide a positioning roll as described above. However, there is a possibility that the surface posture of the transport-fixing belt 62 may change between the exit of the cooling area CA (downstream end point B) and the medium peeling point by the peeling roll 67 (corresponding to the exit of the medium transport area SA). In this case, from the viewpoint of maintaining a good contact state between the medium S and the transport-fixing belt 62 between the downstream end point B and the peeling roll 67, it is preferable to install the above-mentioned positioning roll in the area where the surface posture of the transport-fixing belt 62 may change.

[0057] ◎Embodiment 2 FIG. 12 is an explanatory diagram showing a main part of the second fixing unit according to the second embodiment. In the figure, the basic configuration of the second fixing device 60 is substantially the same as that of the first embodiment, but includes a contact / separation mechanism 100 different from that of the first embodiment. Note that the same components as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and detailed descriptions of those components will be omitted here. In embodiment 2, as shown in Figures 13(a) and (b), the contact / separation mechanism 100 depends on the passage state of the medium S through the cooling area CA of the cooler 64, determines the period when the medium S does not pass through the cooling area CA, and moves the transport / fixing belt 62 from the contact position to a retracted position relative to the fixedly positioned cooler 64. In this example, the contact / separation mechanism 100 includes a push-up roll 160 as a push-up means on the back surface of the media transport area SA of the transport-fixing belt 62 other than the cooling area CA, a connecting holder 165 that holds both end shaft portions of the push-up roll 160, and a variable mechanism 170 that changes the position of the connecting holder 165 along the thickness direction of the transport-fixing belt 62. The timing of the contact / separation operation of the transport / fixing belt 62 by the contact / separation mechanism 100 is substantially the same as the timing of the contact / separation operation of the cooler 64 shown in the first embodiment.

[0058] In this example, the push-up roll 160 is provided in contact with the rear surface of the transport fixing belt 62 located between the fixing area FA and the entrance (upstream starting point A) of the cooling area CA of the cooler 64. In addition, the connecting holder 165 has a holding frame 166 extending along the width direction of the conveying and fixing belt 62 above the conveying and fixing belt 62, and at both ends of this holding frame, a pair of holding arms 167 are provided that hang down outside both sides of the width direction of the conveying and fixing belt 62. In this example, the connecting holder 165 rotatably holds both ends of the push-up roll 160 between a pair of holding arms 167. Furthermore, the connecting holder 165 rotatably holds both ends of the entrance side opposing roll 131 between the pair of holding arms 167. Here, the push-up roll 160 and the entrance side opposing roll 131 are disposed so as to have a predetermined positional relationship with the transport / fixing belt 62 therebetween.

[0059] Furthermore, the variable mechanism 170 includes an eccentric cam 172 rotated by a drive motor 171, a cam follower 173 rotatably mounted on both sides of a pair of holding arms 167 of the connecting holder 165 and abutting against the cam surface of the eccentric cam 172, and a biasing spring 174 as a biasing means for biasing the lower end of the holding arm 167 of the connecting holder 165 toward the transport-fixing belt 62.

[0060] According to the contact / separation mechanism 100 of this embodiment, when the transport-fixing belt 62 is set at the contact position where it contacts the cooler 64, as shown in Fig. 14(a), for example, the drive motor 171 rotates the eccentric cam 172 in the clockwise direction, and the large diameter portion r2 of the eccentric cam 172 contacts the cam follower 173 against the biasing force of the biasing spring 174. Then, the variable mechanism 170 pushes the connection holder 165 downward, and accordingly, the push-up roll 160 and the inlet side opposing roll 131 are pushed downward. As a result, the transport-fixing belt 62, which has been pushed up by the push-up roll 160, returns to the contact position where it contacts the cooler 64. At this time, the conveying fixing belt 62 is also pushed down in conjunction with the downward pressing action of the entrance side opposing roll 131, and with the conveying fixing belt 62 in contact with the cooler 64, the entrance side opposing roll 131 abuts against the entrance (upstream starting point A) of the cooling area CA of the cooler 64 while sandwiching the conveying fixing belt 62 therebetween.

[0061] On the other hand, when the transport-fixing belt 62 is to be retracted from the contact position where it contacts the cooler 64 to the retracted position, as shown in FIG. 14B, the eccentric cam 172 is rotated counterclockwise by the drive motor 171, and the small diameter portion r1 of the eccentric cam 172 is brought into contact with the cam follower 173 by the urging force of the urging spring 174. Then, the connecting holder 165 is pushed upward by the urging force of the urging spring 174. Accordingly, the push-up roll 160 pushes up the transport-fixing belt 62. At this time, the inlet side opposing roll 131 is also pushed upward by the pushing-up operation of the connecting holder 165 while maintaining the relative positional relationship with the push-up roll 160. Therefore, the transport fixing belt 62 contacts the outlet (downstream end point B) of the cooling area CA of the cooler 64, and is retreated to a retreat position that is inclined obliquely with respect to the contact position with the cooler 64. There is no concern that the entrance side opposing roll 131 will get in the way during this retreat operation of the transport fixing belt 62.

[0062] Third embodiment FIG. 15 is an explanatory diagram showing a main part of the second fixing unit according to the third embodiment. In the figure, the basic configuration of the second fixing device 60 is substantially the same as that of the first embodiment, but has been further improved in consideration of the situation in which the cooling effect of the medium S has already been obtained even if the medium S is in the middle of passing through the cooling area CA of the cooler 64. Note that the same components as those of the first embodiment are given the same reference numerals, and detailed description thereof will be omitted here. -Example of the contact mechanism- In the present embodiment, the contact / separation mechanism 100 is configured to allow the cooler 64 to swing, similarly to the first embodiment, and causes the cooler 64 to swing between a contact position and a retracted position with respect to the transport / fixing belt 62. In this embodiment, the timing at which the cooler 64 moves from the contact position to the retracted position is the same as in the first embodiment. However, the timing at which the cooler 64 moves from the retracted position to the contact position is different from that in embodiment 1. That is, in this embodiment, the temperature of the medium S passing through the cooling area CA of the cooler 64 is measured, and the timing at which the cooler 64 moves is made different based on the temperature information depending on whether the degree of cooling of the medium S is already sufficient or not.

[0063] In this example, a temperature sensor 180 is separately provided to measure the temperature of the back surface of the medium S opposite the image bearing surface (corresponding to the top surface of the medium S in FIG. 15) while the medium S is being transported in close contact with the transport-fixing belt 62 and passing through the cooling area CA of the cooler 64. This temperature sensor 180 is disposed above the transport-fixing belt 62 in a position not in contact with the medium S transported along the transport-fixing belt 62. For example, a radiation thermometer or the like is used as the non-contact type temperature sensor 180. Furthermore, the temperature sensor 180 measures the temperature Td of the leading end of the medium S passing through the midpoint D, which is the center position of the cooling area CA of the cooler 64 of the transport-fixing belt 62 in the medium transport direction.

[0064] In this example, the temperature sensor 180 measures the temperature of the rear surface of the medium S, and does not measure the temperature of the front surface (image bearing surface) of the medium S. For this reason, the temperature distribution in the thickness direction of the medium S varies depending on the thickness and physical properties of the medium S, and it is expected that the rear surface temperature of the medium S may be high depending on the type of the medium S. However, when the temperature of the rear surface of the medium S reaches or falls below the target temperature (allowable cooling temperature) Tth, it is easily inferred that the temperature of the surface of the medium S that is in direct contact with the cooling area CA of the cooler 64 is below the allowable cooling temperature. Furthermore, when Td≦Tth (for example, 60° C.), it is understood that the cooling process is completed when the medium S passes the intermediate point D. In this case, it is presumed that the cooling process for the medium S is completed when the rear end of the medium S passes the intermediate point D. In this state, there is no need to continue the cooling process until the medium S leaves the cooling area CA. For this reason, in this example, when the condition Td≦Tth (e.g., 60°C) is satisfied, a method is adopted in which an evacuation operation is initiated to retract the cooler 64 from the contact position to the evacuation position when the rear end of the medium S passes through the midpoint D of the cooling area CA. However, when the condition is Td>Tth (e.g., 60°C), as in embodiment 1, a method is adopted in which an evacuation operation is initiated to evacuate the cooler 64 from the contact position to the evacuation position when the rear end of the medium S passes the exit (downstream end point B) of the cooling area CA.

[0065] - Cooler connection and disconnection processing - The connecting / disconnecting process of the cooler is performed according to the flow chart shown in FIG. 16, for example. First, the control device 150 detects whether or not the leading edge of the medium S has passed position P of the position sensor 53. When the leading edge of the medium S passes position P of the position sensor 53, the control device 150 starts the counting operation of a timer counter using the detection result as a trigger. Then, the control device 150 determines whether or not the leading edge of the medium S has passed a predetermined reference position C in front of the cooling area CA of the cooler 64. This reference position C is the reference for moving the cooler 64, which is in the retracted position, to the contact position, and is selected in the same manner as in the first embodiment. In this example, the timing at which the leading edge of the medium S passes the reference position C is determined using the count value of a timer counter that is triggered by the detection output of the position sensor 53 .

[0066] In this example, when the leading edge of the medium S reaches the reference position C, the control device 150 performs a setting operation to the contact position of the cooler 64, as shown in FIG. 8(a), in accordance with the procedure shown in FIG. 5(a), as in the first embodiment. Since the setting operation of the medium S to the contact position of the cooler 64 is completed before the medium S reaches the entrance of the cooling area CA of the cooler 64, the entire area of ​​the medium S is cooled by the cooling action as it passes through the cooling area CA of the cooler 64.

[0067] Thereafter, as shown in FIG. 17(a), when the leading edge of the medium S reaches the midpoint D of the cooling area CA, the control device 150 determines from the count value of the timer counter that this is the timing when the leading edge of the medium S has passed the midpoint D, and measures the temperature Td of the backside of the leading edge of the medium S using the temperature sensor 180. At this time, the control device 150 compares the temperature Td measured by the temperature sensor 180 with a permissible cooling temperature Tth (for example, 60° C.), which is a predetermined target temperature. Then, when the control device 150 determines that the condition Td≦Tth is satisfied, as shown in FIG. 17(b), at the timing when the rear end of the medium S passes the midpoint D of the cooling area CA, it starts an evacuation operation to evacuate the cooler 64 from the contact position to the evacuation position. On the other hand, when the control device 150 is in the condition of Td>Tth (e.g., 60°C), as shown in Figure 17(c), when the rear end of the medium S passes the exit (downstream end point B) of the cooling area CA, it initiates an evacuation operation to retract the cooler 64 from the contact position to the evacuation position.

[0068] Thus, in this embodiment, the second fixing device 60 exerts substantially the same action as in the first embodiment, and also exerts the following unique action. Specifically, when the medium S is subjected to a sufficient cooling action while passing through the cooling area CA of the cooler 64, that is, when the medium S has reached a sufficiently cooled state, an evacuation operation is adopted in which the cooler 64 is evacuated to the evacuation position before the medium S passes through the cooling area CA. This makes it possible to avoid the waste of cooling energy that is not required for cooling the medium S being used only for cooling the transport-fixing belt 62. In this embodiment, the temperature measurement point by the temperature sensor 180 is the midpoint D of the cooling area CA, but this midpoint D is not limited to the central position of the cooling area CA in the media transport direction, and the midpoint D may be appropriately selected from the areas before and after the central position of the cooling area CA in the media transport direction. In this embodiment, the approaching / separating mechanism 100 used is substantially the same as that in the first embodiment, but it is also possible to use a mechanism substantially the same as that in the second embodiment.

[0069] (Additional Note) (((1))) A fixing device that heats and pressurizes a medium carrying an unfixed image, and then cools the medium to fix the unfixed image, A heat fixing means having a heat source; a belt-shaped conveying and fixing means that is stretched around the heat fixing means and is circulable, and that conveys the medium while contacting the image surface of the medium; a pressure fixing means arranged opposite to the heat fixing means with the conveying and fixing means interposed therebetween, and applying pressure to the heat fixing means so as to form a fixing area between the heat fixing means and the pressure fixing means; a cooling unit that is provided on the downstream side of the fixing area of ​​the conveying and fixing unit in the conveying direction of the medium and in contact with a rear surface of the medium conveying area of ​​the conveying and fixing unit, the cooling unit cooling the conveying and fixing unit; a switching means for switching between a contact state and a non-contact state between the conveying and fixing means and the cooling means depending on a passing state of the medium through a cooling area of ​​the cooling means; A fixing device comprising: (((2))) In the fixing device according to (((1)), The fixing device is characterized in that the switching means switches the conveying and fixing means and the cooling means to a non-contact state while the medium does not pass through a region of the conveying and fixing means cooled by the cooling means. (((3))) In the fixing device according to (((1))) or (((2)), The fixing device is characterized in that the switching means switches the cooling means to a contact state before the leading end of the medium in the transport direction reaches the entrance of the cooling area, and switches the cooling means to a non-contact state when the trailing end of the medium in the transport direction reaches the exit of the cooling area. (((4))) In the fixing device according to (((1))) or (((2)), The fixing device is characterized in that the switching means switches the cooling means to a non-contact state under conditions where the medium is cooled to a predetermined temperature before the trailing end of the medium in the transport direction reaches the exit of the cooling area. (((5))) In the fixing device according to any one of ((1)) to ((4)), The fixing device according to claim 1, wherein the switching means includes a moving mechanism for moving the cooling means relative to the conveying and fixing means. (((6))) In the fixing device according to (((5))), The fixing device is characterized in that the moving mechanism supports the cooling means so that it can be swung, with the exit or entrance end of the cooling area of ​​the cooling means as a swing point, and swings the cooling means between a contact position where it contacts the conveying and fixing means and a retracted position where it is retracted from the conveying and fixing means. (((7))) In the fixing device according to (((5))), A fixing device characterized by having a positioning means provided on the back side of the media transport area of ​​the transporting and fixing means, which maintains the surface posture of the media transport area of ​​the transporting and fixing means when all or part of the cooling means is retracted from a contact position with the back side of the transporting and fixing means. (((8))) In the fixing device according to any one of ((1)) to ((4)), The fixing device according to claim 1, wherein the switching means includes a moving mechanism for moving the conveying and fixing means relative to the cooling means. (((9))) In the fixing device according to (((8))), The fixing device is characterized in that the moving mechanism is provided on the back side of the media transport area of ​​the transporting and fixing means other than the cooling area, and is equipped with a pushing-up means that pushes up the media transport area portion of the transporting and fixing means in a direction away from the cooling means. (((10))) In the fixing device according to any one of (((1))) to (((9))), a fixing device comprising: a counter rotating means arranged opposite an entrance to a cooling area of ​​the cooling means across the conveying and fixing means, the counter rotating means rotating following the conveying and fixing means. (((11))) In the fixing device according to (((10))), A fixing device characterized by comprising a plurality of opposing rotating means arranged opposite the entrance of the cooling area of ​​the cooling means and at a location different from the entrance, across the conveying and fixing means, and rotating in accordance with the conveying and fixing means. (((12))) In the fixing device according to (((9))), one or more opposing rotation means arranged to face an inlet of a cooling area of ​​the cooling means across the conveying and fixing means, or arranged to face an inlet of the cooling area and a location different from the inlet, and rotating following the conveying and fixing means; A fixing device according to claim 1, wherein a part or all of said counter rotating means moves in conjunction with said push-up means. (((13))) In the fixing device according to any one of ((1))) to (((12)), The switching means has a position detection means for detecting the position of the leading or trailing end of the medium in the transport direction upstream of the fixing area in the transport direction of the medium, and determines the position of the leading or trailing end in the transport direction of the medium transported by the transporting and fixing means based on the detection result of the position detection means, and switches the cooling means between contact and non-contact states. (((14))) In the fixing device according to (((13))), The fixing device is characterized in that when the position detection means detects the trailing end position of the medium in the transport direction, the switching means switches the cooling means to a non-contact state when the trailing end of the medium reaches an outlet of the cooling area based on the detection result. (((15))) In the fixing device according to (((13))), The fixing device is characterized in that when the position detection means detects the leading edge position of the medium in the transport direction, the switching means switches the cooling means to a contact state based on the detection result at a point before the leading edge of the medium reaches the entrance of the cooling area. (((16))) In the fixing device according to any one of (((1))) to (((15))), The fixing device is characterized in that the switching means has a discrimination means for discriminating the distance between the rear end of the preceding medium in the transport direction and the front end of the following medium in the transport direction, and does not execute the contact / non-contact switching operation of the cooling means when the distance discriminated by the discrimination means is less than the length of the cooling area. (((17))) an imaging means for producing an unfused image on the medium; A fixing device according to any one of ((1))) to (((16))) that fixes an unfixed image held on a medium; An image forming system comprising:

[0070] According to the fixing device of (((1))), when fixing an unfixed image on a medium by heating and cooling the belt-shaped conveying and fixing means, it is possible to suppress unnecessary cooling that does not contribute to cooling of the medium and ensure fixing performance, compared to the case where the conveying and fixing means is continuously cooled. According to the fixing device of (((2))), in a situation where cooling of the medium is not required, the cooling operation of the conveying and fixing means by the cooling means can be omitted. According to the fixing device of (((3))), when the medium passes through the cooling area of ​​the cooling device, the cooling operation of the conveying and fixing device can be performed by the cooling device. According to the fixing device of (((4))), even if the medium does not completely pass through the cooling area of ​​the cooling means, if the temperature of the medium is sufficiently cooled, the cooling operation of the conveying and fixing means by the cooling means can be omitted. According to the fixing device of (((5))), the cooling means can be easily switched between contact and non-contact by moving the cooling means relative to the conveying and fixing means. According to the fixing device of (((6))), the cooling means can be switched between contact and non-contact with the conveying and fixing means with a simple configuration as a switching means, compared to when the entire cooling means is switched between contact and non-contact with the conveying and fixing means. According to the fixing device of (((7))), even if a method is adopted in which the cooling means is moved relative to the conveying and fixing means, the surface attitude of the medium conveying area of ​​the conveying and fixing means can be maintained without change. According to the fixing device of (((8))), the conveying and fixing means can be moved relative to the cooling means, so that the cooling means can be easily switched between contact and non-contact. According to the fixing device of (((9))), the conveying and fixing means can be moved relative to the cooling means with a simple configuration as the switching means. According to the fixing device of (((10))), the medium transported onto the transport and fixing means can be appropriately brought into intimate contact with the cooling area of ​​the cooling means, compared to a case in which the counter rotating means is not used. According to the fixing device of (((11))), the medium transported onto the transporting and fixing means can be brought into closer contact with the cooling area of ​​the cooling means more appropriately than in the case where one opposing rotating means is provided at the entrance to the cooling area of ​​the cooling means. According to the fixing device of (((12))), even in an embodiment in which the opposing rotation means is provided in the cooling area of ​​the cooling means, the pushing-up means can push up the conveying and fixing means without the opposing rotation means getting in the way. According to the fixing device of (((13))), by utilizing a position detection means for detecting the transport position of the medium, it is possible to easily grasp the timing at which the switching means switches the cooling means between contact and non-contact states. According to the fixing device of (((14))), by utilizing a position detection device that detects the transport position of the medium, it is possible to easily switch the cooling device to a non-contact state. According to the fixing device of (((15))), by using a position detection means for detecting the transport position of the medium, it is possible to easily switch the cooling means to a contact state. According to the fixing device of (((16))), when the distance between the preceding medium and the succeeding medium is equal to or less than the length of the cooling area of ​​the cooling means, the switching operation by the switching means can be omitted. According to the image forming system relating to (((17))), when fixing an unfixed image on a medium by heating and cooling the belt-shaped transporting and fixing means, it is possible to construct an image forming system including a fixing device that can suppress unnecessary cooling that does not contribute to cooling of the medium and ensure fixing performance, compared to the case where the transporting and fixing means is continuously cooled. [Explanation of symbols]

[0071] 1...heat fixing means, 2...transport fixing means, 3...pressure fixing means, 4...cooling means, 5...switching means, 6 (6a, 6b)...opposite rotation means, 7...position detection means, 8...positioning means, 9...push-up means, 10...fixing device, 11...imaging means, CA...cooling area, FA...fixing area, G...unfixed image, S...medium

Claims

1. A fixing device that heats and pressurizes a medium carrying an unfixed image, and then cools the medium to fix the unfixed image, A heat fixing means having a heat source; a belt-shaped conveying and fixing means that is stretched around the heat fixing means and is circulable, and that conveys the medium while contacting the image surface of the medium; a pressure fixing means arranged opposite to the heat fixing means with the conveying and fixing means interposed therebetween, and applying pressure to the heat fixing means so as to form a fixing area between the heat fixing means and the pressure fixing means; a cooling unit that is provided on the downstream side of the fixing area of ​​the conveying and fixing unit in the conveying direction of the medium and in contact with a rear surface of the medium conveying area of ​​the conveying and fixing unit, the cooling unit cooling the conveying and fixing unit; a switching means for switching between a contact state and a non-contact state between the conveying and fixing means and the cooling means depending on a passing state of the medium through a cooling area of ​​the cooling means; A fixing device comprising:

2. 2. The fixing device according to claim 1, The fixing device is characterized in that the switching means switches the conveying and fixing means and the cooling means to a non-contact state while the medium does not pass through a region of the conveying and fixing means cooled by the cooling means.

3. 3. The fixing device according to claim 2, The fixing device is characterized in that the switching means switches the cooling means to a contact state before the leading end of the medium in the transport direction reaches the entrance of the cooling area, and switches the cooling means to a non-contact state when the trailing end of the medium in the transport direction reaches the exit of the cooling area.

4. 3. The fixing device according to claim 2, The fixing device is characterized in that the switching means switches the cooling means to a non-contact state under conditions where the medium is cooled to a predetermined temperature before the trailing end of the medium in the transport direction reaches the exit of the cooling area.

5. 2. The fixing device according to claim 1, The fixing device according to claim 1, wherein the switching means includes a moving mechanism for moving the cooling means relative to the conveying and fixing means.

6. 6. The fixing device according to claim 5, The fixing device is characterized in that the moving mechanism supports the cooling means so that it can be swung, with the exit or entrance end of the cooling area of ​​the cooling means as a swing point, and swings the cooling means between a contact position where it contacts the conveying and fixing means and a retracted position where it is retracted from the conveying and fixing means.

7. 6. The fixing device according to claim 5, A fixing device characterized by having a positioning means provided on the back side of the media transport area of ​​the transporting and fixing means, which maintains the surface posture of the media transport area of ​​the transporting and fixing means when all or part of the cooling means is retracted from a contact position with the back side of the transporting and fixing means.

8. 2. The fixing device according to claim 1, The fixing device according to claim 1, wherein the switching means includes a moving mechanism for moving the conveying and fixing means relative to the cooling means.

9. 9. The fixing device according to claim 8, The fixing device is characterized in that the moving mechanism is provided on the back side of the media transport area of ​​the transporting and fixing means other than the cooling area, and is equipped with a pushing-up means that pushes up the media transport area portion of the transporting and fixing means in a direction away from the cooling means.

10. 2. The fixing device according to claim 1, a fixing device comprising: a counter rotating means arranged opposite an entrance to a cooling area of ​​the cooling means across the conveying and fixing means, the counter rotating means rotating following the conveying and fixing means.

11. 11. The fixing device according to claim 10, A fixing device characterized by comprising a plurality of opposing rotating means arranged opposite the entrance of the cooling area of ​​the cooling means and at a location different from the entrance, across the conveying and fixing means, and rotating in accordance with the conveying and fixing means.

12. 10. The fixing device according to claim 9, one or more opposing rotation means arranged to face an inlet of a cooling area of ​​the cooling means across the conveying and fixing means, or arranged to face an inlet of the cooling area and a location different from the inlet, and rotating following the conveying and fixing means; A fixing device according to claim 1, wherein a part or all of said counter rotating means moves in conjunction with said push-up means.

13. 2. The fixing device according to claim 1, The switching means has a position detection means for detecting the position of the leading or trailing end of the medium in the transport direction upstream of the fixing area in the transport direction of the medium, and determines the position of the leading or trailing end in the transport direction of the medium transported by the transporting and fixing means based on the detection result of the position detection means, and switches the cooling means between contact and non-contact states.

14. 14. The fixing device according to claim 13, The fixing device is characterized in that when the position detection means detects the trailing end position of the medium in the transport direction, the switching means switches the cooling means to a non-contact state when the trailing end of the medium reaches an outlet of the cooling area based on the detection result.

15. 14. The fixing device according to claim 13, The fixing device is characterized in that when the position detection means detects the leading edge position of the medium in the transport direction, the switching means switches the cooling means to a contact state based on the detection result at a point before the leading edge of the medium reaches the entrance of the cooling area.

16. 2. The fixing device according to claim 1, The fixing device is characterized in that the switching means has a discrimination means for discriminating the distance between the rear end of the preceding medium in the transport direction and the front end of the following medium in the transport direction, and does not execute the contact / non-contact switching operation of the cooling means when the distance discriminated by the discrimination means is less than the length of the cooling area.

17. an imaging means for producing an unfused image on the medium; The fixing device according to claim 1 , which fixes an unfixed image held on a medium; An image forming system comprising:

Images