JP4655874B2 - Fixing apparatus and image forming apparatus using the same - Google Patents

Description

  The present invention relates to a printer, a copy, which forms an image by forming a toner image using an electrophotographic system, an electrostatic recording system, etc., and finally transferring the toner image as an unfixed toner image to a sheet-like material and then fixing it. The present invention relates to a fixing device used in an image forming apparatus such as an image forming apparatus or a multifunction peripheral, and in particular, a fixing device having a peeling member installed in the vicinity of a peripheral surface of a heating roll and an image forming apparatus using the same. It is about improvement.

  In the image forming apparatus as described above, as the fixing device, a heating roll and a pressure roll that are press-contacted so as to form a nip portion (for fixing) through which a sheet carrying an unfixed toner image is passed, There is one that uses a fixing device that has a peeling member that is installed in a state where the leading end is close to the peripheral surface of the heating roll and peels the sheet after passing through the nip portion from the heating roll (Patent Document 1).

  In this type of fixing device, the heating roll is generally a cylindrical roll, and the roll is connected to the inner peripheral surface side by energizing a heating source such as a halogen heater installed inside the hollow of the roll. Those that are configured to be heated from above are often used. Further, from the viewpoint of ensuring that the paper discharged from the nip portion between the heating roll and the pressure roll at the time of fixing is peeled off from the heating roll, the separation member has a distance between the tip portion and the heating roll. It is said that it needs to be held so that it is 1 mm or less.

JP 58-7167 A

  However, such a fixing device generally has a warm-up operation for heating the heating roll to a predetermined temperature (final fixing temperature) in a short time by abrupt heating by a heating source at a time such as when the power is turned on. However, there are the following problems by performing such a heating operation.

That is, when a rapid heating such as a warm-up operation is performed, a rapid temperature difference is likely to occur between the inner peripheral surface side and the outer peripheral surface side of the heating roll. When the sharp temperature difference region including the neighboring site is strongly heated by the heating source than other portions occurs, the corresponding area is more likely to be deformed by thermal expansion than the other sites. As a result, the peeling member installed in a state of being close to the outer peripheral surface of the heating roll and the heating roll are brought closer to each other or are in complete contact with each other.

  And when such a state is reached, the toner or the like adhering to the heating roll may be transferred and adhered to the peeling member in an abnormally close or complete contact with the heating roll, or There is a problem that the toner or the like adhering to the peeling member side is transferred and adhered to the fixing target paper side during the peeling. Moreover, there exists a problem that the outer peripheral surface of a heating roll will be damaged because the front-end | tip part of a peeling member contacts a heating roll.

  By the way, a measure to make the heating state uniform by rotating the heating roll during warm-up can be considered. However, in this case, the heat-up heat is transmitted to the pressure roll member that rotates while being pressed against the heated heating roll, so that the time required for warm-up becomes longer. For this reason, this measure cannot be an appropriate measure under the current situation where shortening during warm-up is required.

  The present invention has been made in view of the above problems, and when heating operation such as during warm-up is performed without extending the time required for warm-up operation of the heating roll, Occurrence of an abnormal approach or complete contact with the leading end of the peeling member can be prevented, so that transfer of toner or the like to the peeling member or transfer from the peeling member to the sheet at the time of fixing can be prevented. Furthermore, the present invention provides a fixing device that can prevent the occurrence of problems such as damage to a heating roll due to contact with a peeling member, and an image forming apparatus using the same.

  The fixing device of the present invention is configured to be in pressure contact with a rotating cylindrical heating roll, a heating source that is installed inside the heating roll and heats the heating roll from the inner peripheral surface side by energization, and the heating roll. A pressure member that forms a nip portion that allows a sheet-like material carrying an unfixed toner image to pass therethrough and a pressure member that is installed in a state where the tip portion is close to the outer peripheral surface of the heating roll and passes through the nip portion. A fixing device having a peeling member for peeling a subsequent sheet-like material from the heating roll, and maintaining a state where the tip of the peeling member is displaced to a separated position separated from the outer peripheral surface of the heating roll, and While the sheet-like material carrying the unfixed toner image starts to be discharged from the nip portion and finishes passing, the peeling member closes to the outer peripheral surface of the heating roll. In which it characterized in that a displacement device to keep a state of being displaced location.

  Here, the time when the displacement device keeps the state where the leading end portion of the peeling member is displaced to the separated position is the time when the sheet material to be fixed does not pass through the nip portion between the heating roll and the pressure member. However, it is desirable that the timing includes at least the timing of performing the warm-up operation of the heating roll.

  The displacement device includes, for example, a displacement driving unit that operates to displace the distal end portion of the peeling member between the separation position and the peeling position, and the heating roll when the sheet-like object enters the nip portion. Alternatively, a position change detecting unit that detects a position change of the pressure member is provided, and the displacement driving unit performs an operation of displacing the tip end portion of the peeling member to the peeling position based on the detection result of the position change detecting unit. Configured.

  In this case, the displacement drive unit has a mechanical configuration and is driven by using the power generated by the detection operation of the position change detection unit, or is driven by an electric signal or the like. It may be a thing. The position change detection unit may be of a system that can detect a position change with a mechanical configuration, or may be of a system that can detect a position change optically or electrically. Further, transmission of the detection result of the position change detection unit to the displacement drive unit may be performed by mechanical motion transmission (for example, a link mechanism or the like) or by electrical signal transmission. May be.

  In such a configuration, the position change of the heating roll or the pressure member does not occur during the time when the sheet-like material does not enter the nip portion, including when the heating roll warms up. Since there is no detection result, the displacement drive unit does not operate, and the distal end portion of the peeling member is kept in a state of being displaced to a separated position separated from the outer peripheral surface of the heating roll. On the other hand, when the sheet-like material enters the nip portion, the position change of the heating roll or the pressure member occurs due to the presence of the paper, and this position change is detected by the position change detection unit. Based on the detection result, the displacement driving unit is operated, and the tip end portion of the peeling member is kept displaced to the peeling position.

  In addition, the displacement device includes a displacement driving unit that operates to displace the distal end portion of the peeling member between the separation position and the peeling position, and the heating roll when the sheet-like object enters the nip portion. Alternatively, a temperature change detection unit that detects a temperature change of the pressure member is provided, and the displacement driving unit performs an operation of displacing the tip end portion of the peeling member to the peeling position based on the detection result of the temperature change detection unit. It may be configured as follows.

  In this case, the temperature change detection unit may be set so as to detect the surface temperature immediately after passing through the nip portion of the heating roll or the pressure member as much as possible. Further, the temperature change at this time is a change on the temperature lowering side in particular, and it is preferable to detect a predetermined amount of temperature decrease from a predetermined reference temperature.

  In this case, when the heating roll warms up, when the sheet-like material does not enter the nip portion, the temperature change of the heating roll or the pressure member does not occur and the temperature change detection unit Since there is no result of detecting the temperature change, the displacement driving unit does not operate, and the tip end portion of the peeling member is kept in a state of being displaced to a separated position separated from the outer peripheral surface of the heating roll. On the other hand, when the sheet-like material enters the nip portion, the paper roll is deprived of heat, causing a temperature change of the heating roll or the pressure member, and this temperature change is detected by the temperature change detection unit. Therefore, the displacement driving unit is operated based on the detection result, and the distal end portion of the peeling member is kept in the state of being displaced to the peeling position.

  Furthermore, the displacement device includes a displacement drive unit that operates to displace the tip of the peeling member between the separation position and the peeling position, and a conveyance passing position before the sheet-like material enters the nip part. A transfer passage position detection unit for detecting the movement, and based on a detection result of the transfer passage position detection unit, the displacement driving unit is configured to execute an operation of displacing the tip of the peeling member to the peeling position. But you can.

  In this case, the transport passage position detection unit is not particularly limited as long as it can detect the transport passage position before the sheet-like material enters the nip portion. Further, the displacement driving unit is configured to start the operation of displacing the leading end portion of the peeling member to the peeling position immediately after obtaining the conveyance passing position information of the sheet-like material detected by the conveyance passing position detecting unit. Alternatively, the required time from the detection of the position information to immediately before being introduced into the nip portion of the sheet-like material is estimated and calculated, and after the required time has elapsed, the tip of the peeling member is displaced to the peeling position. You may comprise so that operation | movement may be started.

  When configured in this way, the displacement drive unit often does not operate during the period when the sheet-like material does not enter the nip part, including when the heating roll warms up, and the tip of the peeling member is It is kept in a state of being displaced to a separated position separated from the outer peripheral surface of the heating roll. On the other hand, at the time immediately before the sheet-like material enters the nip portion, the displacement drive is activated based on the detection information of the transport passage position detecting portion at the latest, and the leading end portion of the peeling member is displaced to the peeling position. Kept.

  Further, the image forming apparatus of the present invention includes an image forming apparatus that forms a toner image based on image information and finally transfers the toner image as an unfixed toner image to a sheet-like material, and an unfixed toner transferred by the image forming apparatus. The image forming apparatus includes a fixing device that fixes a toner image by passing a sheet-like material carrying an image and applying heat and pressure, and uses any one of the fixing devices configured as described above as the fixing device. Is. The image forming apparatus is generally intended to form a color image, but may be an image forming apparatus that forms only a single color (mainly black and white) image.

  According to the fixing device of the present invention, the leading end portion of the peeling member is displaced to the separated position separated from the outer peripheral surface of the heating roll by the peeling member displacement device, and the unfixed toner image is While the sheet-like material to be carried begins to be discharged from at least the nip between the heating roll and the pressure member and then finishes passing, the tip of the peeling member is displaced to the peeling position close to the outer peripheral surface of the heating roll. It will be kept in the state. As a result, at least during the warm-up of the heating roll, the tip of the peeling member is displaced to a spaced position separated from the outer peripheral surface of the heating roll. There is no possibility that the deforming heating roll and the tip of the peeling member will be abnormally approached or contacted completely.

  Therefore, when the heating operation such as during warm-up is performed without extending the time required for the warm-up operation of the heating roll, the phenomenon of abnormal approach or complete contact between the heating roll and the tip of the peeling member occurs. As a result, the transfer of toner etc. from the heating roll to the peeling member and the transfer adhesion of toner etc. from the peeling member to the sheet at the time of fixing, the heating roll by contact of the peeling member The occurrence of various problems such as damage can be prevented.

  Further, according to the image forming apparatus of the present invention, by using the fixing device as described above, it is possible to start the image forming operation while avoiding the extension of the time required for the warm-up operation of the heating roll, Good and stable image without the risk of transfer adhesion of toner or the like from the peeling member of the fixing device to the sheet material to be fixed in the image formation after the warm-up, or damage to the heating roll due to the contact of the peeling member Formation can be performed.

[Embodiment 1]
FIG. 1 shows a main part of an image forming apparatus and a fixing device according to Embodiment 1 of the present invention.

  The image forming apparatus 1 constitutes a color printer using, for example, an electrophotographic system. The printer 1 includes a color image forming unit 10 that forms a toner image T in a main body 2 and transfers the toner image T to a sheet P, and a sheet P that carries an unfixed toner image T transferred by the image forming unit 10. The fixing device 20A for fixing the toner image T by passing the toner and the paper transport device 30 for supplying the paper P to the image forming unit 10 or transporting it to a predetermined part are appropriately distributed and installed. It is configured. In FIG. 1, reference numeral 3 denotes a system controller that comprehensively controls the operation of the entire printer.

  The color image forming unit 10 includes a photosensitive drum 11 as an image carrier, a charging roll 12 as a charging unit disposed around the photosensitive drum 11, a laser scanning device (ROS) 13 as an image exposure unit, a developing unit. A developing device 14, a primary transfer roll 15 as a primary transfer means, an intermediate transfer belt 16 as an intermediate transfer body, and a secondary transfer roll 17 as a secondary transfer means. Incidentally, the image forming unit 10 is of a type that forms a black and white image, but preferably an image forming unit that can form a color image is adopted.

  The photosensitive drum 11 is formed by forming a photosensitive layer made of an organic photosensitive material or the like on the peripheral surface of a conductive drum that is rotatably supported. When an image forming operation (printing) is performed, a driving device (not shown) drives the photosensitive drum 11 in the direction of the arrow. It is driven to rotate at a predetermined speed. Then, the peripheral surface of the photosensitive drum 11 is uniformly charged by the charging roll of the image forming device 12, and then the laser beam light modulated based on the image information from the laser scanning device 13 is applied to the charged surface. By performing scanning exposure, electrostatic latent images of predetermined color components are sequentially formed. The laser scanning device 13 operates based on an image signal for each color component obtained after predetermined processing is performed in an image processing device (not shown) installed in the main body 2 on image information appropriately input from the outside.

  Subsequently, the electrostatic latent image on the photosensitive drum 11 is developed with a predetermined color developer (toner) supplied from the developing device 14 to be a single color (unfixed) toner image. The developing device 14 includes four developing units each having a four-color developer (toner) dedicated to yellow (Y), magenta (M), cyan (C), and black (K). Mounted at equal intervals on the peripheral surface of the frame, and during development, the rotating frame is rotated by a predetermined angle so that the developing device for storing the toner of the color to be developed is sequentially developed to the developing area facing the photosensitive drum 11. A so-called rotary developing device is used. As a result, when the color image forming unit 10 forms a full color image formed by superimposing the four color toner images, the four developing devices of the developing device 14 are moved to the developing regions, respectively. As a result, the toner images of the four colors are sequentially formed on the photosensitive drum 11.

  The toner image formed on the photosensitive drum 11 in this manner is electrostatically primary transferred by the primary transfer roll 15 onto the intermediate transfer belt 16 that rotates while being in contact with the photosensitive drum 11. The intermediate transfer belt 16 is composed of an endless belt capable of electrostatically carrying a toner image, and is driven around a plurality of support rolls with a predetermined tension to rotate in the direction of the arrow. Yes. In the case of forming a full-color image, the four color toner images on the photosensitive drum are superimposed on the intermediate transfer belt 16. The peripheral surface of the photosensitive drum 11 after the primary transfer is cleaned by removing unnecessary materials such as residual toner and paper dust attached to the peripheral surface by a cleaning device (not shown).

  Thereafter, the toner image primarily transferred to the intermediate transfer belt 16 is transferred to the secondary transfer roll on the paper P supplied at a predetermined timing toward the secondary transfer position between the intermediate transfer belt 16 and the secondary transfer roll 17. 17 is electrostatically (collectively) secondary transferred. The secondary transfer roll 17 is supported so as to be able to come into contact with and separate from the intermediate transfer belt 16 and is in contact with the intermediate transfer belt 16 only at the time of performing the secondary transfer, and at other times the intermediate transfer belt 16. It is set to be in a state of being separated from. After the secondary transfer, the outer peripheral surface of the intermediate transfer belt 20 is cleaned by removing unnecessary materials such as residual toner and paper dust attached to the peripheral surface by a cleaning device (not shown).

  The paper P is accommodated in the paper feed cassette 31, and is sent one by one from the paper feed cassette 31 by the feed device 32 including a pick-up roll, a feed roll, and a retard roll, and then a plurality of transport roll pairs 33 and guides. It is conveyed to the resist roll pair 34 through the member. Thereafter, the sheet P is supplied toward the secondary transfer position (between the intermediate transfer belt 16 and the secondary transfer roll 17) by the resist roll pair 34 in anticipation of the transfer timing of the toner image. The paper P on which the unfixed toner image T has been transferred at the secondary transfer position is then transported toward the fixing device 20A while being guided by the paper transport member 19, and subjected to a fixing process.

  The paper P on which the toner image T has been fixed by passing through the fixing device 20A is discharged from the fixing device 20A, and then is directly discharged onto the discharge tray 36 by the discharge roller pair 35. This completes the basic printing operation. Note that, when an image is formed with the above four color toner images in this print, a full color image is finally obtained.

  Next, the fixing device 20A in the printer 1 will be described.

  As shown in FIG. 2 and the like, the fixing device 20A has a heating roll 22 installed so as to be rotationally driven inside a main body 21, and a sheet carrying the unfixed toner image T in pressure contact with the heating roll 22. A pressure roll 23 installed so as to form a fixing nip portion N that allows P to pass therethrough, and a release sheet 25 that peels the paper P after passing through the fixing nip portion N from the heating roll 22 are mainly installed. ing. In FIG. 2 and the like, reference numeral 29A denotes a paper introduction guide plate on the inlet side of the fixing nip N, and 29B denotes a paper discharge guide plate on the outlet side of the fixing nip N.

  The heating roll 22 is made of a core metal formed in a relatively thin cylindrical shape with a metal such as aluminum or stainless steel, and a releasable material such as tetrafluoroethylene or PFA formed on the outer peripheral surface of the core metal. One halogen heater 24 as a heating source is installed at a substantially central position inside the roll (the hollow portion of the cored bar). Further, the heating roll 22 is rotationally driven at a predetermined speed in the arrow direction A by receiving the rotational power of a rotational driving device (not shown).

  In the heating roll 22, detection information from a temperature sensor 26 that measures the roll surface temperature is transmitted to the fixing unit controller 27, and the fixing unit controller 27 energizes the halogen heater 24 based on a predetermined control program. By controlling the energization operation 28 (ON / OFF control), the roll inner peripheral surface 22b is heated so as to be maintained at a predetermined temperature (fixing temperature, standby temperature, etc.). The fixing unit controller 27 is connected to the system controller 3 (FIG. 1), and necessary control and information exchange are performed.

  The pressure roll 23 includes a cored bar formed of a metal such as stainless steel and aluminum, a heat resistant elastic layer made of silicone rubber or the like formed on the outer peripheral surface of the cored bar, and the elastic layer. Is formed of a release layer made of a release material such as tetrafluoroethylene or PFA. The pressure roll 23 is supported so as to be brought into pressure contact with the heating roll 22 that is rotationally driven by a pressure mechanism (not shown) at a predetermined pressure.

  As shown in FIG. 2 and FIG. 3, the release sheet 25 is obtained by holding a rectangular sheet base material made of stainless steel with a holder (not shown) from one long side thereof. Further, the release sheet 25 is entirely retracted to the downstream side in the rotation direction of the heating roll 22 from the outlet of the nip portion N, and the longitudinal (long side) direction of the sheet base material is the position of the heating roll 22 at that position. The front end portion 25a, which is a free end not held by the holder, is brought close to the outer peripheral surface 22a of the heating roll 22 with a predetermined gap d (about 200 to 500 μm) while facing each other along the axial direction. It is installed in a state (FIG. 4).

  In the fixing device 20A, as shown in FIGS. 2 to 4, the leading end portion 25a of the release sheet 25 is maintained in the state of being displaced to the separation position R separated from the outer peripheral surface 22a of the heating roll 22, and is not yet determined. While the paper P carrying the contact toner image T starts to be discharged from at least the nip portion N between the heating roll 22 and the pressure roll 23 and then passes through, the leading end 25a is peeled close to the outer peripheral surface of the heating roll 22. A release sheet displacing device 4 </ b> A that keeps the state displaced to the position S is provided.

  In this example, as the release sheet displacement device 4A, a displacement drive unit 40A that operates to passively displace the leading end 25a of the release sheet 25 between the separation position R and the release position S described above, and the paper P is a nip. A position change detection unit 50A that detects a change in position of the pressure roll 23 when entering the portion N is provided, and based on the detection result of the position change detection unit 50A, the displacement drive unit 40A moves the leading end 25a of the release sheet. A configuration in which an operation of displacing to the peeling position S is executed is applied.

  The displacement drive unit 40A includes a swing frame 41 that swings so that the release sheet 25 is attached to one end and the leading end 25a of the release sheet is displaced between the separation position R and the release position S, and the swing frame. 41 is rotatably connected to an end opposite to the end to which the release sheet 25 is attached via a support shaft 42a so that the swing frame 41 swings in a predetermined direction (B, C). And a drive arm 42 that operates in the same manner.

  Of these, the swing frame 41 is supported by a support frame 43 configured as a part of the apparatus main body 21 so as to be swingable in the arrow directions B and C via a support shaft 42a. The drive arm 42 in the displacement drive unit 40A is used in combination as a link arm that constitutes a part of the position change detection unit 50A described later, and is linked to the operation of the position change detection unit 50A as will be described later. (Specifically, it is displaced in the arrow directions D and E).

  On the other hand, the position change detection unit 50A is attached to a support frame 51 whose one end is configured as, for example, a part of the apparatus main body 21 via a support shaft 51a so as to be swingable. It comprises a swing detection frame 52 that supports the shaft 23a of the pressure roll 23 and swings with a change in the position of the shaft 23a (a change in position caused by the presence or absence of the paper P in the fixing nip N).

  The swing detection frame 52 is disposed so as to support the pressure roll shaft 23a from the side opposite to the side where the heating roll 22 is located, and the pressure roll 23 (the shaft 23a of the pressure roll 23a depending on the presence or absence of the paper P in the nip portion N). ) Is attached so as to swing in the directions of arrows G and H in conjunction with the state of displacement in the direction of approaching and separating from the heating roll 22. Further, the other end of the swing detection frame 52 is rotatably connected to the drive arm 42 in the displacement drive unit 40A and the support shaft 52a.

  The swing detection frame 52 may be a swing frame of a pressure mechanism (not shown) in which the pressure roll 23 is brought into pressure contact with the heating roll 22 with a predetermined pressure, in addition to a dedicated one. Good. The swing detection frame 52 is installed on the pressure roll 23 side so that the pressure roll 23 can be displaced so as to be in a state of being in pressure contact with the heating roll 22 under the pressure applied by the pressure mechanism described above. This is because it is supported. For this reason, when the heating roll 22 is supported so as to be displaceable, the swing detection frame 52 is provided so as to support the shaft of the heating roll 22 and the like, and is configured to detect a change in the position of the shaft. It is also possible to do.

  Therefore, the release sheet displacement device 4A has a configuration in which the displacement drive unit 40A (the drive arm 42) and the position change detection unit 50A (the swing detection frame 52) are mechanically connected by the link mechanism.

  In addition, the release sheet displacement device 4A is used before the sheet P to be fixed enters the fixing nip portion N and at the time after passing through the nip portion N and completely discharged (when no paper is passed). The leading end portion 25a of the release sheet 25 is maintained in a state of being displaced to a separation position S separated from the outer peripheral surface of the heating roll 22 by a predetermined distance t (about 1 to 2 mm) (FIGS. 2 and 4), and its fixing nip portion When the sheet P to be fixed enters and passes through N (when the sheet passes), the position of the pressure roll 23 changes as the sheet P intervenes in the fixing nip N as will be described later. By utilizing this, the tip 25a of the release sheet 25 is set so as to be displaced in the release position R (FIG. 3).

  Further, in this release sheet displacement device 4A, when the leading end portion 25a of the release sheet 25 is displaced to the release position R, the release sheet 25a is reliably stopped at the release position by a stopper (not shown). Further, in the release sheet displacement device 4A, the displacement drive unit 40A or the like is based on the displacement amount at which the leading end 25a of the release sheet 25 is displaced between the release position R and the separation position S (separation distance: t−d). The dimension shape and displacement amount of the swing detection frame 52 of the position change detection unit 50A are set as appropriate.

  Next, the operation of the fixing device 20A provided with such a release sheet displacement device 4A will be described.

  First, a normal fixing operation will be described. At the time of fixing, the unfixed toner image T is transferred on the image forming unit 10 side to the fixing nip portion N between the heating roll 22 and the pressure roll 23 heated to the fixing temperature and rotating in the arrow direction A. The paper P is introduced while being guided by the paper introduction guide plate 29A on the entrance side (FIGS. 1 and 2). Since it is heated and pressurized when passing through the fixing nip N, the unfixed toner image T is fused and fixed on the paper P.

  As shown in FIG. 2 and the like, the paper P discharged from the fixing nip portion N after the completion of fixing is peeled off from the heating roll 22 by itself or by the peeling action of the peeling sheet 26, and then the paper discharge guide plate 29B on the outlet side. Is discharged to the outside of the fixing device main body 21. As a result, the fixing process ends.

  At the time when the fixing operation is executed, the position of the pressure roll 23 is particularly at the point before the sheet P carrying the unfixed toner image T enters the fixing nip N as shown in FIG. Since there is no change, the release sheet displacing device 4A is not particularly operated, and the tip 25a of the release sheet 25 is kept displaced to the separation position S as initially set. Thereby, the front-end | tip part 25a of the peeling sheet 25 is maintained in the state spaced apart from the outer peripheral surface of the heating roll 22 more than the separation distance d of the peeling position R (by a difference (td) more) (FIG. 4). .

  Thereafter, when the paper P carrying the unfixed toner image T enters the fixing nip portion N (including the time when the paper P enters and passes through), the paper P intervenes in the fixing nip portion N as shown in FIG. By doing so, the pressure roll 23 is slightly displaced in the direction away from the heating roll 22 against the urging force of the pressure mechanism (dotted arrow direction J: downward in this example).

  As a result, the position of the shaft 23a of the pressure roll 23 slightly changes in the arrow direction J. Therefore, the swing detection frame 52 of the position change detection unit 50A that supports the shaft 23a uses the support shaft 51a as a fulcrum in the arrow direction H. Rocks. Then, using this as a trigger, the drive arm 42 of the displacement drive unit 40A connected to the swing detection frame 52 is displaced in the arrow direction E, and further, the swing arm 41 connected to the drive arm 43 is supported. It swings in the arrow direction C with the shaft 43a as a fulcrum. As a result, the release sheet 25 swings in the arrow direction C together with the swing arm 41, and stops when the leading end portion 25a reaches the release position R (by the stopper (not shown)). In this way, the release sheet 25 is in a state where it can exert its release action.

  Therefore, the sheet P carrying the unfixed toner image T that has entered the fixing nip N is displaced to the peeling position R when the leading edge Pa is discharged from the nip N. Therefore, the peeling sheet 25 is peeled off from the heating roll 22 by receiving the peeling action.

  Further, when the sheet P carrying the unfixed toner image T is completely discharged from the fixing nip portion N after the fixing is completed, the sheet P having a thickness at the fixing nip portion N does not intervene. 23 is displaced so as to return to the direction in which it is pressed against the heating roll 22 (dotted arrow direction K: upward in this example).

  As a result, the position of the shaft 23a of the pressure roll 23 slightly changes in the arrow direction K, so that the swing detection frame 52 of the position change detection unit 50A that supports the shaft 23a uses the support shaft 51a as a fulcrum as the arrow direction G. Rocks. Then, as a trigger, the drive arm 42 of the displacement drive unit 40A connected to the swing detection frame 52 is displaced in the arrow direction D, and the swing arm 41 connected to the drive arm 42 is further supported by the support shaft. It swings in the arrow direction B with 42a as a fulcrum. As a result, the release sheet 25 swings in the arrow direction B together with the swing arm 41, and stops swinging when the leading end 25a reaches the separation position S. In this way, the release sheet 25 is kept away from the outer peripheral surface of the heating roll 22 (FIG. 2).

  Next, a warm-up operation of the heating roll 22 performed when the power of the fixing device 20A (actually the printer 1 main body) is turned on will be described.

  When the power is turned on, for example, warm-up power is supplied from the power supply device 28 to the halogen heater 24 of the heating roll 22 by the control operation of the fixing unit controller 27. At this time, the heating roll 22 is in a state where the rotation is stopped, and the pressure roll 23 is in a state where the rotation is stopped and pressed against the heating roll 22.

  The energization of the halogen heater 24 causes the halogen heater 24 to generate heat strongly and radiate strong radiant heat toward the entire area of the inner peripheral surface of the roll. Therefore, the heating roll 22 is rapidly heated from the inner peripheral surface side. become. Thereby, the heating roll 22 is heated to a temperature (threshold temperature) slightly exceeding a predetermined temperature (fixing temperature) in a relatively short time. The roll temperature at this time is detected by the temperature sensor 26. And when it is heated to this threshold temperature, the warm-up is completed. After the warm-up is completed, the heating roll 22 is controlled so as to be maintained at the fixing temperature, so that the fixing operation can be performed.

  And at the time of this warm-up, the heating roll 22 is heated rapidly, and is deformed by a little thermal expansion.

  However, in the fixing device 20A, as described above, when the sheet P is not interposed in the fixing nip portion N by the release sheet displacement device 4A (when the sheet is not passed), the leading end portion 25a of the release sheet is positioned at the release position. Since it is displaced to the separation position S farther away from the outer peripheral surface of the heating roll 22 than R (FIG. 2), the heated heating roll 22 and the leading end portion 25a of the release sheet are abnormally approached or completely contacted. The phenomenon does not occur.

  As a result, the occurrence of a phenomenon of abnormal approach or complete contact between the outer peripheral surface of the heating roll 22 and the leading end portion 25a of the release sheet 25 is prevented during warm-up. It is also possible to prevent the transfer adhesion of toner and the like from the roll 22 to the release sheet 25 and the transfer and adhesion of toner and the like from the release sheet 25 to the paper P at the time of fixing. Occurrence of damage to the peripheral surface of the heating roll 22 is also prevented.

  Further, due to the effect at the time of warming up of the fixing device 20A, it becomes possible for the printer 1 to start the first printing operation after the warming up of the heating roll 22 at the same timing as before. Further, in the printing operation after the warm-up, it is possible to perform a good and stable printing operation without occurrence of transfer adhesion of toner or the like from the release sheet 25 of the fixing device 20A to the paper P to be fixed.

[Embodiment 2]
FIG. 5 shows a part of the printer (fixing device) according to Embodiment 2 of the present invention.

  The fixing device 20B in this printer has the same configuration as the fixing device 20A in the printer 1 of the first embodiment, except that the release sheet displacement device 4B having a different configuration is applied instead of the above-described release sheet displacement device 4A. Is. For this reason, in FIG. 5 etc., the same code | symbol is attached | subjected with respect to the printer 1 which concerns on Embodiment 1, and the fixing device 20A, and the description about the common component is required below. It is omitted except in some cases (the same applies to the following embodiments).

  The release sheet displacement device 4B in the fixing device 20B includes a displacement drive unit 40B that operates to actively displace the leading end portion 25a of the release sheet 25 between the separation position R and the release position S, and the sheet P is a fixing nip portion. N is provided with a temperature change detection unit 60 that detects a temperature change of the pressure roll 23 when entering N, and the displacement drive unit 40B is based on the detection result of the temperature change detection unit 60. An operation of displacing the distal end portion 25a to the peeling position R is performed.

  The displacement drive unit 40B is the opposite side of the swing frame 41 (including its support frame 43) similar to the displacement drive unit 40A in Embodiment 1 and the end of the swing frame 41 to which the release sheet 25 is attached. And a drive arm 45 of a solenoid device 44 that is pivotally connected to the end of the shaft through a support shaft 42a and operates to swing the swing frame 41 in a predetermined direction (B, C). ing. The solenoid device 44 moves the drive arm 45 forward and backward in the arrow directions M and L (operation in the protruding direction and operation in the retracting direction) so that the drive arm 45 swings the swing frame 41 in the arrow directions B and C. Is attached. Further, the solenoid device 44 is connected to the fixing unit controller 27, and operates according to a control signal from the fixing unit controller 27 based on detection information of a temperature sensor (61) described later (advancing / retracting operation of the drive arm 45). It has become.

  The temperature change detection unit 60 includes a temperature sensor 61 arranged so as to detect the surface temperature in the vicinity of the exit side of the fixing nip N of the pressure roll 23. The temperature sensor 61 is connected to the fixing unit controller 27 and receives the detection result (electric signal).

  In this release sheet displacement device 4B, the detection result (converted to temperature) input from the temperature sensor 61 is compared with a preset threshold value in the fixing unit controller 27, and the temperature of the detection result is fixed during the fixing operation. When the temperature falls below the threshold value, a control operation for transmitting a control signal for causing the solenoid device 44 to project the drive arm 45 in the arrow direction M is executed. On the other hand, when the detected temperature is equal to or higher than the threshold, a control signal for operation for retracting the drive arm 45 in the arrow direction L is transmitted to the solenoid device 44. The threshold value at this time is set to a temperature lower by about 40 ° C. than the surface temperature of the heating roll 22 detected by the temperature sensor 26, for example.

  As described above, in the release sheet displacement device 4B, the displacement drive unit 40B and the temperature change detection unit 60 are configured separately, and the displacement drive unit 40B has a configuration based on detection information obtained from the temperature change detection unit 60. The operation is controlled.

  In addition, the release sheet displacement device 4B is used before the sheet P to be fixed enters the fixing nip portion N and at the time after passing through the nip portion N and completely discharged (when no paper is passed). Usually, the surface temperature of the pressure roll 23 is set so that the front end portion 25a of the release sheet 25 is displaced to the separation position S because there is no large temperature change (temperature decrease) compared to when the paper is passed. (FIGS. 4 and 5).

  Further, in this release sheet displacement device 4B, the tip 25a of the release sheet 25 is moved with respect to the swing amount of the swing frame 41 of the displacement drive unit 40B and the movement of the drive arm 45 based on the release position R and the separation position S. The amount and the like are set as appropriate.

  Next, the operation of the fixing device 20B provided with such a release sheet displacement device 4B will be described.

  First, the fixing operation of the unfixed toner image T onto the paper P by the fixing device 20B is performed in the same manner as the fixing device 20A in the first embodiment.

  Next, the operation of the release sheet displacement device 4B at the time when the fixing operation is executed will be described.

  First, as shown in FIG. 5, at the time before the paper P carrying the unfixed toner image T enters the fixing nip portion N, the surface temperature of the pressure roll 23 changes so as to be significantly reduced. Therefore, the release sheet displacing device 4B is not particularly operated, and the leading end portion 25a of the release sheet 25 is kept in the displaced position S as initially set. Thereby, the front-end | tip part 25a of the peeling sheet 25 is kept in the state spaced apart from the outer peripheral surface of the heating roll 22 more than the separation distance d of the peeling position R (by a difference (td) more) (FIG. 4,). FIG. 5).

  Thereafter, when the paper P carrying the unfixed toner image T enters the fixing nip portion N (including the time when the paper P enters and passes through), the paper P intervenes in the fixing nip portion N as shown in FIG. As a result, a large amount of heat from the pressure roll 23 is taken (absorbed) to the paper P side, and the temperature of the roll surface rapidly decreases.

  At this time, when it is determined that the detection result (temperature) of the temperature sensor 61 that detects the surface temperature of the pressure roll 23 is lower than the above-described threshold value, the control signal transmitted from the fixing unit controller 27 is used. The solenoid device 44 performs an operation of projecting the drive arm 45 in the arrow direction M. As a result, the swing arm 41 connected to the drive arm 45 swings in the arrow direction C with the support shaft 43a as a fulcrum. As a result, the release sheet 25 swings in the arrow direction C together with the swing arm 41, and stops when the leading end 25a reaches the release position R (FIG. 6). In this way, the release sheet 25 is in a state where it can exert its release action.

  Therefore, the sheet P carrying the unfixed toner image T that has entered the fixing nip N is displaced to the peeling position R when the leading edge Pa is discharged from the nip N. Therefore, the peeling sheet 25 is peeled off from the heating roll 22 by receiving the peeling action.

  When the sheet P carrying the unfixed toner image T is completely discharged from the fixing nip portion N after the fixing is completed, the sheet P does not intervene in the fixing nip portion N. Will begin to rise again.

  At this time, when it is determined that the detection result (temperature) of the temperature sensor 61 that detects the surface temperature of the pressure roll 23 has reached a temperature equal to or higher than the above-described threshold, a control signal transmitted from the fixing unit controller 27 is used. The solenoid device 44 performs an operation of retracting the drive arm 45 in the arrow direction L. Thus, the swing arm 41 connected to the drive arm 45 swings in the arrow direction B with the support shaft 43a as a fulcrum. As a result, the release sheet 25 swings in the arrow direction B together with the swing arm 41, and the tip 25a is displaced to the release position R and stops. In this way, the release sheet 25 is kept away from the outer peripheral surface of the heating roll 22 (FIG. 5).

  Subsequently, regarding the warm-up operation of the heating roll 22, when the power is turned on, for example, power for warm-up is supplied from the power supply device 28 to the halogen heater 24 by the control operation of the fixing unit controller 27B. As in the case of the first embodiment, the heating roll 22 is warmed up. And at the time of this warm-up, there is a high possibility that the heating roll 22 is rapidly heated and deformed due to thermal expansion.

  However, in the fixing device 20B, when the sheet P is not interposed in the fixing nip portion N (during non-passage), the leading end portion 25a of the release sheet is moved to the release position as described above by the release sheet displacement device 4B. Since it is displaced to the separation position S farther away from the outer peripheral surface of the heating roll 22 than R (FIG. 5), the heated heating roll 22 and the leading end portion 25a of the release sheet are abnormally approached or completely in contact with each other. The phenomenon does not occur. As a result, the same effect as that of the first embodiment can be obtained by the fixing device 20B. The same effect as that of the first embodiment can also be obtained for the printer 1 using the fixing device 20B.

[Embodiment 3]
FIG. 7 shows a part of the printer (fixing device) according to Embodiment 3 of the present invention.

  The fixing device 20C in the printer is changed by applying a release sheet displacement device 4C having a different configuration in place of the release sheet displacement devices 4A and 4B described above. It has the same configuration as 20B.

  The release sheet displacement device 4C in the fixing device 20C includes a displacement drive unit 40B that operates to actively displace the leading end portion 25a of the release sheet 25 between the separation position R and the release position S, and the sheet P is a nip portion N. A position change detection unit 50B that detects a change in the position of the pressure roll 23 when entering the roll, and based on the detection result of the position change detection unit 50B, the displacement drive unit 40B removes the leading end 25a of the release sheet from the release position. The operation of displacing to S is executed. The displacement drive unit 40B is the same as the solenoid drive type displacement drive unit 40B in the second embodiment described above.

  The position change detection unit 50B has one end of the position change detection unit 50A according to the first embodiment attached to a support frame 55 so as to be swingable in the arrow directions G and H via a support shaft 55a. Is attached to the other end portion of the swinging pressure frame 56 that supports the shaft 23a of the pressure roll 23 at different sites, and the frame 56 is fixed to a predetermined pressure (fixing) in the arrow direction k. The pressure spring 57 is urged by the pressing force required at the nip portion N, and the position change of the pressure spring 57 is generated via the swing pressure frame 56 depending on the presence or absence of the paper P in the fixing nip portion N. It is composed of a pressure fluctuation detection sensor 58 for detecting a (position change). As the swinging pressure frame 56 and the pressure spring 57, those constituting a pressure mechanism for applying pressure to the pressure roll 23 can be used. The pressure fluctuation detection sensor 58 is configured using, for example, a pressure contact element or the like. The pressure fluctuation detection sensor 58 is connected to the fixing unit controller 27 and inputs the detection result (electric signal).

  In this release sheet displacement device 4C, the fixing unit 27 compares the detection result (result converted to the magnitude of pressure fluctuation) input from the pressure fluctuation detection sensor 58 with a preset threshold value. When the pressure fluctuation exceeds a threshold value, a control operation is performed to transmit a control signal for operation that causes the drive arm 45 to protrude in the arrow direction M to the solenoid device 44. Has been. On the other hand, when the detected pressure fluctuation is equal to or smaller than the threshold, the solenoid apparatus 44 is configured to transmit a control signal for operation to retract the drive arm 45 in the arrow direction L.

  As described above, in the release sheet displacement device 4C, the displacement drive unit 40B and the pressure fluctuation detection sensor 58 are configured separately, and based on the detection information obtained from the pressure fluctuation detection sensor 58, the displacement drive unit 40B. The operation is controlled.

  In addition, the release sheet displacement device 4C is used before the sheet P to be fixed enters the fixing nip portion N and at the time after passing through the nip portion N and completely discharged (when no paper is passed). Usually, since the position of the pressure roll 23 does not change significantly against the applied pressure, the front end portion 25a of the release sheet 25 is set so as to be kept in the displaced position S ( 4 and 7). Furthermore, in this release sheet displacement device 4C, the tip 25a of the release sheet 25 is moved with respect to the swing amount of the swing frame 41 of the displacement drive unit 40B and the movement of the drive arm 45 with reference to the release position R and the separation position S. The amount and the like are set as appropriate.

  Next, the operation of the fixing device 20C provided with such a release sheet displacement device 4C will be described.

  First, the fixing operation of the unfixed toner image T onto the paper P by the fixing device 20C is performed in the same manner as in the case of the fixing device 20A in the first embodiment.

  Next, the operation of the release sheet displacement device 4C at the time when the fixing operation is executed will be described.

  First, as shown in FIG. 7, before the paper P carrying the unfixed toner image T enters the fixing nip portion N, the position of the pressure roll 23 may change so as to be greatly lowered. Therefore, the release sheet displacing device 4C is not particularly operated, and the leading end portion 25a of the release sheet 25 is kept in the displaced position S as initially set. Thereby, the front-end | tip part 25a of the peeling sheet 25 is kept in the state spaced apart from the outer peripheral surface of the heating roll 22 more than the separation distance d of the peeling position R (by a difference (td) more) (FIG. 4,). FIG. 7).

  Thereafter, when the paper P carrying the unfixed toner image T enters the fixing nip portion N (including the time when the paper P enters and passes through), the paper P intervenes in the fixing nip portion N as shown in FIG. By doing so, the pressure roll 23 is slightly away from the heating roll 22 against the urging force of the pressure mechanism (the pressure applied by the pressure spring 57) (dotted arrow direction J: downward in this example). Displace.

  As a result, the position of the shaft 23a of the pressure roll 23 is slightly changed in the arrow direction J. Therefore, the swinging pressure frame 56 of the position change detecting unit 50B that supports the shaft 23a has the support shaft 55a as a fulcrum as the arrow direction. Swing to H. Since the pressure spring 57 is contracted by the downward swing of the swing pressure frame 56, the pressure change at that time is detected by the pressure fluctuation detection sensor 58, and the detection result (the magnitude of the pressure change). Is determined to be larger than the above-described threshold value, the solenoid device 44 performs an operation of causing the drive arm 45 to protrude in the arrow direction M in accordance with a control signal transmitted from the fixing unit controller 27. As a result, the swing arm 41 connected to the drive arm 45 swings in the arrow direction C with the support shaft 43a as a fulcrum. As a result, the release sheet 25 swings in the arrow direction C together with the swing arm 41, and stops when the leading end 25a reaches the release position R (FIG. 8). In this way, the release sheet 25 is in a state where it can exert its release action.

  Therefore, the sheet P carrying the unfixed toner image T that has entered the fixing nip N is displaced to the peeling position R when the leading edge Pa is discharged from the nip N. Therefore, the peeling sheet 25 is peeled off from the heating roll 22 by receiving the peeling action.

  Further, when the sheet P carrying the unfixed toner image T is completely discharged from the fixing nip portion N after the fixing is completed, the sheet P does not intervene in the fixing nip portion N. Return to position.

  At this time, when it is determined that the detection result (pressure change magnitude) of the pressure fluctuation detection sensor 58 for detecting the magnitude of pressure fluctuation due to the position change of the pressure roll 23 has become smaller than the above threshold value. In response to the control signal transmitted from the fixing unit controller 27, the solenoid device 44 performs an operation of retracting the drive arm 45 in the arrow direction L. Thus, the swing arm 41 connected to the drive arm 45 swings in the arrow direction B with the support shaft 43a as a fulcrum. As a result, the release sheet 25 swings in the arrow direction B together with the swing arm 41, and the tip 25a is displaced to the release position R and stops. In this way, the release sheet 25 is kept away from the outer peripheral surface of the heating roll 22 (FIG. 7).

  Subsequently, regarding the warm-up operation of the heating roll 22, in the fixing device 20C, when the sheet P is not interposed in the fixing nip portion N by the release sheet displacement device 4C (when the sheet is not passed), As described above, the leading end portion 25a of the release sheet is displaced to the separation position S farther from the outer peripheral surface of the heating roll 22 than the release position R (FIG. 7). For this reason, a phenomenon in which the heat-deformed heating roll 22 and the leading end portion 25a of the release sheet approach abnormally or completely does not occur. As a result, the same effect as that of the first embodiment can be obtained by the fixing device 20B. The same effect as that of the first embodiment can also be obtained for the printer 1 using the fixing device 20B.

[Embodiment 4]
FIG. 9 shows a part of the printer (secondary transfer unit and fixing device) according to Embodiment 4 of the present invention.

  The fixing device 20D in this printer has the same configuration as the fixing device 20A in the printer 1 of the first embodiment, except that the release sheet displacement device 4D having a different configuration is applied instead of the above-described release sheet displacement device 4A. Is.

  The release sheet displacement device 4D in the fixing device 20D has a displacement driving unit 40A that operates to passively displace the leading end 25a of the release sheet 25 between the separation position R and the release position S, and the sheet P is fixed. A conveyance passage position detection unit 70A that detects a conveyance passage position before entering the nip portion N is provided, and the displacement driving unit 40A peels off the leading end portion 25a of the release sheet based on the detection result of the conveyance passage position detection unit 70A. An operation of displacing to the position S is executed. The displacement drive unit 40A is the same as the machine-type displacement drive unit 40A in the first embodiment described above. Reference numeral 18 in FIG. 9 and the like denotes a backup roll that supports the intermediate transfer belt 16 at the secondary transfer position.

  The transport passage position detector 70A enters the fixing nip portion N by regarding the contact / separation operation of the secondary transfer roll 17 in the image forming unit 10 of the printer body 2 as the passage timing and non-passage timing of the secondary transfer position of the paper P. This is to detect the transport passage position of the paper P before the printing. In this example, as the transport passage position detection unit 70A, for example, a support frame 71 installed between the fixing device 20D and the secondary transfer unit is swingably attached via a support shaft 71a, and the secondary transfer unit side The shaft 17a of the secondary transfer roll 17 is rotatably connected to one end of the roller, and the driving frame 42 of the displacement driving unit 40A is rotated by the support shaft 72a to the opposite end (fixing device side). A configuration composed of a swing detection arm 72 freely connected was applied.

  This swing detection arm 72 is linked to the contact / separation operation in the arrow directions Q1 and Q2 during the secondary transfer of the secondary transfer roll 17, and the end side connected to the drive frame 42 is in the direction of the arrow with the support shaft 71a as a fulcrum. G and H are attached so as to swing.

  Accordingly, the release sheet displacement device 4D has a configuration in which the displacement drive unit 40A (the drive arm 42) and the transport passage position detection unit 70A (the swing detection arm 72) are mechanically connected by a link mechanism. .

  Further, in the release sheet displacement device 4D, the secondary transfer roll 17 is separated from the intermediate transfer belt 16 (supported by the backup roll 18), and the sheet P to be fixed enters the fixing nip portion N. Before and after the sheet is completely discharged after passing through the nip portion N (when no paper is passed), the leading end portion 25a of the release sheet 25 is separated from the outer peripheral surface of the heating roll 22 by a predetermined distance t. While being displaced to the separation position S (FIGS. 9 and 4), on the other hand, the secondary transfer roll 17 is in contact with the intermediate transfer belt 16, and the sheet P to be fixed is fixed to the fixing nip portion N. Is set so that the leading end 25a of the release sheet 25 is displaced to the release position R at the time when the sheet enters and passes (at the time of paper passing) (FIG. 10).

  Next, the operation of the fixing device 20D provided with such a release sheet displacement device 4D will be described.

  First, the fixing operation of the unfixed toner image T onto the paper P by the fixing device 20D is performed in the same manner as in the case of the fixing device 20A in the first embodiment.

  Next, the operation of the release sheet displacement device 4D at the time when the fixing operation is executed will be described.

  First, as shown in FIG. 9, when the secondary transfer roll 17 is in a state of being separated from the intermediate transfer belt 16, the secondary transfer roll 17 is moved in the direction of the arrow Q <b> 1, so that the transport passage position is detected. The swing detection arm 72 in the portion 70A is in a state of swinging in the arrow direction G about the support shaft 71a. As a result, the drive arm 42 in the displacement drive unit 40A connected to the swing detection arm 72 is displaced in the arrow direction D, so that the swing arm 41 swings in the arrow direction B about the support shaft 43a. As a result, the leading end portion 25a of the release sheet 25 attached to the swing arm 41 is displaced to the separation position S separated from the heating roll 22 (FIG. 9).

  That is, before the sheet P is supplied to the secondary transfer position and before entering the fixing nip portion N, the secondary transfer roll 17 is not displaced, so that the release sheet displacement device 4D is also particularly operated. Instead, the tip 25a of the release sheet 25 is kept in the displaced position S as initially set.

  Thereafter, when the secondary transfer time comes and the secondary transfer roll 17 is in contact with the intermediate transfer belt 16, the secondary transfer roll 17 is moved in the direction of the arrow Q2, and therefore the conveyance pass. The swing detection arm 72 in the position detector 70A swings in the arrow direction H about the support shaft 71a.

  As a result, the drive arm 42 in the displacement drive unit 40A is displaced in the arrow direction E, so that the swing arm 41 swings in the arrow direction C around the support shaft 43a. The tip 25a of the attached release sheet 25 is displaced to the release position R close to the heating roll 22 (FIG. 10). In this way, the release sheet 25 is in a state where it can exert its release action. At this time, the sheet P is supplied to the secondary transfer position to perform secondary transfer of the toner image, and the sheet P carrying the unfixed toner image is conveyed toward the fixing nip portion N of the fixing device 20D. Has been introduced.

  Therefore, the sheet P carrying the unfixed toner image T that has entered the fixing nip N is displaced to the peeling position R when the leading edge Pa is discharged from the nip N. Therefore, the peeling sheet 25 is peeled off from the heating roll 22 by receiving the peeling action. Note that the secondary transfer roll 17 is in contact with the intermediate transfer belt 16 at least until the paper P to be fixed passes through the fixing nip N of the fixing device.

  Further, after the fixing is completed and the sheet P carrying the unfixed toner image T is completely discharged from the fixing nip portion N, the secondary transfer roll 17 moves in the arrow direction Q1 and is separated from the intermediate transfer belt 16. In this state, the swing detection arm 72 in the transport passage position detector 70A swings in the arrow direction G about the support shaft 71a.

  As a result, the drive arm 42 in the displacement drive unit 40A connected to the swing detection arm 72 is displaced in the arrow direction D, so that the swing arm 41 swings in the arrow direction B about the support shaft 43a. As a result, the leading end portion 25 a of the release sheet 25 attached to the swing arm 41 is displaced to the separation position S separated from the heating roll 22. In this way, the release sheet 25 is kept away from the outer peripheral surface of the heating roll 22 (FIG. 9).

  Subsequently, regarding the warm-up operation of the heating roll 22, in this fixing device 20D, since the secondary transfer roll 17 is in the separated position by the release sheet displacement device 4D at the time of such warm-up, the release sheet as described above. The distal end portion 25a of the heating roller 22 is also maintained in a state of being displaced to a separation position S away from the outer peripheral surface of the heating roll 22 (FIG. 9). For this reason, a phenomenon in which the heat-deformed heating roll 22 and the leading end 25a of the release sheet approach abnormally or completely does not occur. As a result, the same effect as that of the first embodiment can be obtained by the fixing device 20B. The same effect as that of the first embodiment can also be obtained for the printer 1 using the fixing device 20B.

[Embodiment 5]
FIG. 11 shows a part (secondary transfer unit and fixing device) of a printer according to Embodiment 5 of the present invention.

  The fixing device 20E in this printer has the same configuration as the fixing device 20D in the printer 1 of the fourth embodiment, except that the release sheet displacement device 4E having a different configuration is applied instead of the above-described release sheet displacement device 4D. Is.

  The release sheet displacement device 4E in the fixing device 20E includes a displacement driving unit 40B that operates to actively displace the leading end 25a of the release sheet 25 between the separation position R and the release position S, and the sheet P is a fixing nip part. A transport passage position detection unit 70B that detects a transport passage position before entering N, and based on the detection result of the transport passage position detection unit 70B, the displacement driving unit 40B removes the leading end 25a of the release sheet from the release position S. It is comprised so that the operation | movement displaced to may be performed. The displacement drive unit 40B is the same as the solenoid drive type displacement drive unit 40B in the second embodiment described above.

  The transport passage position detector 70B detects the transport passage position of the paper P by detecting the passage of the paper P at a predetermined position before reaching the fixing device 20E. In this example, the conveyance passage position detection unit 70B includes, for example, a sheet passage detection sensor 75 that detects the passage of the sheet P (the front end portion Pa) conveyed from the secondary transfer unit to the fixing device 20E. The thing was applied. The paper passage detection sensor 75 is connected to the fixing unit controller 27 and inputs the detection result (electric signal).

  In the release sheet displacement device 4E, when the detection result (result of detecting the passage of the leading edge of the paper) input from the paper passage detection sensor 75 is obtained in the fixing unit controller 27, the drive arm 45 is connected to the solenoid device 44. Is configured to execute a control operation for transmitting an operation control signal for projecting the lens in the arrow direction M. On the other hand, when the detection result from the paper passage detection sensor 75 is not inputted, a control signal for operation for retracting the drive arm 45 in the arrow direction L is transmitted to the solenoid device 44. At this time, the drive arm 45 is allowed to protrude in the arrow direction M, and at least the time required for the fixing target sheet P to completely pass through the fixing nip N after reaching the sheet passing detection sensor 75 is secured. Is set as follows.

  As described above, the release sheet displacement device 4E has a configuration in which the displacement drive unit 40B and the transport passage position detection unit 70B are independent, and the operation of the displacement drive unit 40B is controlled based on detection information obtained therefrom. It is the composition which becomes.

  Further, the release sheet displacement device 4E is completely discharged before the sheet P to be fixed reaches the conveyance passage position detection unit 70B and before entering the fixing nip N and through the nip N. At the time after this (when paper is not passed), the leading end 25a of the release sheet 25 is set so as to be displaced to the separation position S (FIGS. 4 and 11).

  Further, in this release sheet displacement device 4E, the leading end portion 25a of the release sheet 25 is moved with respect to the swing amount of the swing frame 41 of the displacement drive unit 40B and the movement of the drive arm 45 based on the release position R and the separation position S. The amount and the like are set as appropriate.

  Next, the operation of the fixing device 20E provided with such a release sheet displacement device 4E will be described.

  First, the fixing operation of the unfixed toner image T onto the paper P by the fixing device 20E is performed in the same manner as in the case of the fixing device 20D in the fourth embodiment.

  Next, the operation of the release sheet displacement device 4E at the time when the fixing operation is executed will be described.

  First, as shown in FIG. 11, no detection signal is obtained from the paper passage detection sensor 75 before the paper P carrying the unfixed toner image after the secondary transfer passes through the paper passage detection sensor 75. Therefore, the release sheet displacing device 4E is not particularly operated, and the leading end portion 25a of the release sheet 25 is kept in the state of being displaced to the separation position S separated from the heating roll 22 as described above.

  Thereafter, when the paper P carrying the unfixed toner image after the secondary transfer reaches the paper passage detection sensor 75 and the passage thereof is detected, the solenoid device 44 is driven by the control signal transmitted from the fixing unit controller 27. An operation of projecting the arm 45 in the arrow direction M is performed.

  As a result, the swing arm 41 connected to the drive arm 45 swings in the arrow direction C with the support shaft 43a as a fulcrum. As a result, the release sheet 25 swings in the arrow direction C together with the swing arm 41, and stops when the leading end 25a reaches the release position R (FIG. 12). In this way, the release sheet 25 is in a state where it can exert its release action. At this time, the paper P to be fixed that has passed through the paper passage detection sensor 75 is introduced into the fixing nip N of the fixing device 20E.

  Therefore, the sheet P carrying the unfixed toner image T that has entered the fixing nip N is displaced to the peeling position R when the leading edge Pa is discharged from the nip N. Therefore, the peeling sheet 25 is peeled off from the heating roll 22 by receiving the peeling action.

  Further, after the fixing is completed and the sheet P carrying the unfixed toner image T is completely discharged from the fixing nip N, when a predetermined time elapses from when the detection signal of the sheet passage detection sensor 75 is obtained, the fixing unit In accordance with a control signal transmitted from the controller 27, the solenoid device 44 performs an operation of retracting the drive arm 45 in the arrow direction L. Thereby, as described above, the release sheet 25 is maintained in a state of being displaced to the separation position S away from the outer peripheral surface of the heating roll 22 by the release sheet displacement device 4E (FIG. 11).

  Subsequently, regarding the warm-up operation of the heating roll 22, in the fixing device 20E, the paper passage detection sensor 75 does not detect the passage of the paper by the release sheet displacement device 4E during the warm-up. As described above, the leading end portion 25a of the release sheet is also maintained in a state of being displaced to the separation position S away from the outer peripheral surface of the heating roll 22 (FIG. 11). For this reason, a phenomenon in which the heat-deformed heating roll 22 and the leading end 25a of the release sheet approach abnormally or completely does not occur. As a result, the same effect as that of the first embodiment can be obtained by the fixing device 20B. In addition, the same effect as that of the fourth embodiment (1) can be obtained for the printer 1 using the fixing device 20B.

[Other embodiments]
In the first and third embodiments, the case where the position change detecting unit 40 is configured to detect the position change of the pressure roll 23 is exemplified, but in addition, the position change of the heating roll 22 can be detected. In this case, it is possible to employ a position change detection unit configured to detect the position change of the heating roll 22 without needing to be described in detail.

  Moreover, in Embodiment 2, although the case where the thing of the structure which detects the temperature change of the heating roll 22 was employ | adopted as the temperature change detection part 60 was illustrated, when the temperature change of the heating roll 22 can be detected in addition to this. Needless to say, it is also possible to employ a temperature change detection unit configured to detect a temperature change of the heating roll 22.

  In the fifth embodiment, the case where the sheet P passing position detection unit 70 (passing position detection sensor 75) is installed in the sheet conveyance path between the secondary transfer position and the fixing device is illustrated. In addition, for example, it is possible to employ a configuration in which the passage position detection unit 70 is installed in the paper transport path on the near side (upstream side in the paper transport direction) from the secondary transfer position.

FIG. 2 is a schematic explanatory diagram illustrating main parts of an image forming apparatus (printer) and a fixing device according to Embodiment 1 (2 to 5). FIG. 3 is a schematic explanatory diagram illustrating a main part of the fixing device according to Embodiment 1 (an operation state of the release sheet displacement device when not passing paper). FIG. 3 is an explanatory diagram showing an operation state of the release sheet displacement device when the fixing device of FIG. It is explanatory drawing which shows the structure and state of the peeling position and separation | spacing position of a peeling sheet. FIG. 10 is a schematic explanatory diagram illustrating a main part of the fixing device according to Embodiment 2 (an operating state of the release sheet displacement device when not passing paper). FIG. 6 is an explanatory diagram illustrating an operation state of the release sheet displacement device when the fixing device illustrated in FIG. FIG. 10 is a schematic explanatory diagram illustrating a main part of the fixing device according to Embodiment 3 (an operating state of the release sheet displacement device when paper is not passed). It is explanatory drawing which shows the operation state of the peeling sheet displacement apparatus at the time of paper passing of the fixing device of FIG. FIG. 10 is a schematic explanatory diagram illustrating a main part of the fixing device according to Embodiment 4 (an operation state of the release sheet displacement device when paper is not passed). FIG. 10 is an explanatory diagram illustrating an operation state of the release sheet displacement device when the fixing device illustrated in FIG. 9 passes (arrives). FIG. 10 is a schematic explanatory diagram illustrating a main part of the fixing device according to Embodiment 5 (an operating state of the release sheet displacement device when not passing paper). FIG. 12 is an explanatory diagram illustrating an operation state of the release sheet displacement device when the fixing device illustrated in FIG. 11 passes (arrives).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Printer (image forming apparatus), 4A, 4B, 4C, 4D, 4E ... Release sheet displacement device, 10 ... Image forming unit (image forming device), 20A, 20B, 20C, 20D, 20E ... Fixing device, 22 ... Heating roll, 22a ... outer peripheral surface, 22b ... inner peripheral surface, 23 ... pressure roll (pressure member), 24 ... halogen heater (heating source), 25 ... release sheet (release member), 25a ... tip, 40A, 40B ... Displacement drive unit, 50A, 50B ... Position change detection unit, 60 ... Temperature change detection unit, 70A, 70B ... Conveyance passing position detection unit, T ... Unfixed toner image, P ... Paper (sheet-like material), N ... Nip part, S ... separation position, R ... peeling position.

Claims (2)

A rotating cylindrical heating roll;
A heating source that is installed inside the hollow of the heating roll and heats the heating roll from the inner peripheral surface side by energization;
A pressure member that is placed in pressure contact with the heating roll and forms a nip that allows a sheet-like material carrying an unfixed toner image to pass through;
A fixing device having a peeling member that is installed in a state in which a tip portion is close to the outer peripheral surface of the heating roll and peels the sheet-like material after passing through the nip portion from the heating roll;
While keeping the leading end portion of the peeling member displaced to a separation position separated from the outer peripheral surface of the heating roll, the sheet-like object carrying the unfixed toner image starts to be discharged from at least the nip portion and passes through. setting a displacement device while the keeping the tip of the peeling member in the state of being displaced to the release position close to the outer circumferential surface of the heating roll ending,
The displacement device is:
A displacement drive unit that operates to displace the leading end of the peeling member between the separation position and the peeling position, and a change in position of the heating roll or the pressure member when the sheet-like material enters the nip portion. A position change detection unit for detecting
A fixing device, wherein the displacement driving unit is configured to perform an operation of displacing a tip end portion of the peeling member to a peeling position based on a detection result of the position change detection unit . An image forming device that forms a toner image based on image information and finally transfers the toner image as an unfixed toner image to a sheet-like material, and a sheet-like material that carries the unfixed toner image transferred by the image forming device is passed through. A fixing device that fixes the toner image by heating and pressurizing,
An image forming apparatus using the fixing device according to claim 1 as the fixing device.

Images