Fixing device and image forming apparatus including the same

A fixing device includes a fixing member, a pressuring member, a deforming part, an approach guide and a guide adjusting part. The fixing member is rotatable and heated by a heat source. The pressuring member is rotatable and forms a fixing nip between the fixing member and the pressuring member. The deforming part deforms the fixing nip. The approach guide guides a sheet to the fixing nip. The guide adjusting part moves the approach guide to a position corresponding to the fixing nip after deformation, as the deforming part deforms the fixing nip.

INCORPORATION BY REFERENCE

This application is based on and claims the benefit of priority from Japanese Patent application No. 2016-068404 filed on Mar. 30, 2016, which is incorporated by reference in its entirety.

BACKGROUND

The present disclosure relates to a fixing device which fixes a toner image on a sheet and an image forming apparatus including the same.

An electrophotographic type image forming apparatus includes a fixing device which fixes a toner image transferred on a sheet, such as a paper, on the sheet.

An example of the fixing device includes a pressuring roller which comes into pressure contact with an endless fixing belt which is heated. A pressing pad comes in contact with an inner circumferential face of the fixing belt to press the fixing belt to the pressuring roller. The pressing pad is made of material having a high elastic coefficient. Pressing force of the pressing pad to the pressuring roller is higher at a downstream side than at an upstream side in a movement direction of the fixing belt. By rotating the fixing belt with large curvature at an exit of a pressure contact area, the sheet can be separated from the fixing belt adequately.

Another example of the fixing device includes a pair of upper and lower approach guides which guides the sheet to a fixing nip. Each approach guide is fixed to a frame of the fixing device.

SUMMARY

In accordance with an aspect of the present disclosure, a fixing device includes a fixing member, a pressuring member, a deforming part, an approach guide and a guide adjusting part. The fixing member is rotatable and heated by a heat source. The pressuring member is rotatable and forms a fixing nip between the fixing member and the pressuring member. The deforming part deforms the fixing nip. The approach guide guides a sheet to the fixing nip. The guide adjusting part moves the approach guide to a position corresponding to the fixing nip after deformation, as the deforming part deforms the fixing nip.

In accordance with an aspect of the present disclosure, an image forming apparatus includes an image forming part and the fixing device. The image forming part transfers a toner image on a sheet. The fixing device fixes the toner image on the sheet.

DETAILED DESCRIPTION

Hereinafter, with reference to the attached drawings, a preferable embodiment of the present disclosure will be described. The following description is based on directions shown in each figure.

With reference toFIG. 1, a printer1as an image forming apparatus according to a first embodiment will be described.FIG. 1is a sectional view schematically showing an inner structure of the printer1. In the following description, “a conveying direction” shows a conveying direction in which a sheet S is conveyed. In addition, “an upstream”, “a downstream” and other similar descriptions respectively show “an upstream” side, “a downstream” side and other similar concept in the conveying direction.

The printer1includes an apparatus main body2, a sheet feeding cassette3and an ejection tray4. The sheet feeding cassette3is provided in a lower portion of the apparatus main body2and stores the sheets S (a bundle of sheets S). The ejection tray4is formed on an upper face of the apparatus main body2.

The printer1further includes a sheet feeding part10, an image forming part11, a fixing device12, an ejecting part13and a control device14. The sheet feeding part10is disposed on an upstream side end portion of a conveying path15extending from the sheet feeding cassette3to the ejection tray4. The sheet feeding part10feeds the sheet S stored in the sheet feeding cassette3toward the conveying path15one by one. The image forming part11is disposed on a middle portion of the conveying path15. The fixing device12is disposed closer to the downstream side of the conveying path15than the image forming part11. The ejecting part13is disposed on a downstream side end portion of the conveying path15. The control device14totally controls the printer1.

The image forming part11has a drum unit21which forms a toner image using a toner (a developer) supplied from a toner container20. The drum unit21develops a latent image formed by an exposure of an optical scanning device22into the toner image. The image forming part11(the drum unit21) transfers the toner image on the sheet S conveyed along the conveying path15. The fixing device12fixes the toner image on the sheet S. The sheet S having the toner image is ejected by the ejecting part13on the ejection tray4.

Next, with reference toFIGS. 2 to 8, the fixing device12will be described.FIG. 2is a sectional view taken along a line II-II ofFIG. 1.FIG. 3is a sectional view taken along a line of III-III ofFIG. 2.FIG. 4is a bottom view showing a first pressing pad42of the fixing device12.FIG. 5is a bottom view showing a second pressing pad43of the fixing device12.FIG. 6is a sectional view taken along a line VI-VI ofFIG. 2.FIG. 7is a sectional view showing a state where an approach guide35is turned to a second position P2from a state shown inFIG. 6.FIG. 8is a block diagram showing a control system of the printer1.

As shown inFIG. 2andFIG. 3, the fixing device12has a fixing belt30, a pressuring roller31, a fixing driving part32, an induction heating (IH) heater33, a deforming part34, an approach guide35and a guide adjusting part36(refer toFIG. 6). The fixing device12employs a so-called sliding belt type.

The fixing belt30as a fixing member has flexibility, and is formed into an endless shape. The fixing belt30is formed into a cylindrical shape elongated in the left and right direction (a direction of a rotation axis). The fixing belt30is supported by the fixing frame (not shown) so as to be capable of rotating (circulating). The fixing belt30is formed by laminating a substrate layer, an elastic layer and a releasing layer in the order from an inner side (they are not shown). The substrate layer is made of polyimide resin mixed with nickel or metal powder, for example. The elastic layer is made of silicon rubber, for example. The releasing layer is made of fluororesin, for example.

As shown inFIG. 2, on both ends of the fixing belt30in the left and right direction, a pair of left and right caps37is attached. Each cap37is formed into a cylindrical shape having a closed bottom. Between an inner circumferential face of each cap37and an outer circumferential face of the fixing belt30, an annular elastic member37ais interposed. Around an outer circumferential face of each cap37, a connecting gear37bis formed. At a center of the bottom face (each of left and right end faces) of each cap37, a circular through hole37cis formed.

At the right side of the fixing belt30, a rotation detecting mechanism38is provided. The rotation detecting mechanism38has a transmitting gear38a, a rotating pulse plate38band a rotation detecting sensor38c. The transmitting gear38ais meshed with the connecting gear37bof the right cap37to transmit rotation of the fixing belt30to the rotating pulse plate38b. The rotating pulse plate38bhas a plurality of light-shielding pieces (not shown) aligned in a circumferential direction at equal intervals. The rotation detecting sensor38cis a photo-interrupter having a light emitting part and a light receiving part which oppose to each other on both sides of the rotating pulse plate38b. The rotation detecting sensor38ctransmits light receiving information changing depending on rotation of the rotating pulse plate38bto the control device14. One or more rotation detecting sensor38cmay be provided so as to detect rotation of at least one of the pair of left and right caps37.

As shown inFIG. 2andFIG. 3, the pressuring roller31as a pressuring member is formed into a cylindrical shape elongated in the left and right direction. The pressuring roller31is supported by the fixing frame so as to be rotatable. The pressuring roller31comes into pressure contact with the fixing belt30from the lower side of the fixing belt30. Between the fixing belt30and the pressuring roller31, a fixing nip N is formed. The pressuring roller31is formed by laminating an elastic layer31bon an outer circumferential face of a core material31a, for example. The core material31ais made of metal, such as stainless steel and aluminum, for example. To a right end portion of the core material31a, a driving gear31cis fixed. The elastic layer31bis made of silicon rubber or silicon sponge, for example. On an outer circumferential face of the elastic layer31b, a releasing layer (fluororesin or the like, not shown) is laminated.

As shown inFIG. 2, the fixing driving part32has a fixing drive motor32aand a drive intermediate gear32b. The fixing drive motor32ais connected to the driving gear31cvia the drive intermediate gear32b. The fixing drive motor32adrives the pressuring roller31to rotate it around a rotation axis.

As shown inFIG. 2andFIG. 3, the IH heater33as a heat source is disposed at the upper side of the fixing belt30(an opposing side to the fixing nip N). The IH heater33generates magnetic field to heat the fixing belt30.

The deforming part34is provided in order to press the fixing belt30to the pressuring roller31. The deforming part34is configured to deform a shape of the fixing nip N. The deforming part34has a supporting stay40, a switching adjusting part41, two pressing pads42and43, a switching detecting mechanism44and a belt guide45.

The supporting stay40as a supporting member extends in an inner space of the fixing belt30in the left and right direction. Both left and right end portions of the supporting stay40are loosely fitted in the through holes37cof the pair of left and right caps37. The both left and right end portions of the supporting stay40protrude outside from the inner space of the fixing belt30, and are supported by the fixing frame. A middle portion of the supporting stay40in the left and right direction has a sectional view of a substantially U-shape whose lower side is opened (refer toFIG. 3). Under the supporting stay40, a rotation space SP is formed. On an upper face of the supporting stay40, the arc-shaped belt guide45as a guide member is fixed (refer toFIG. 3). An outer circumferential face of the belt guide45is coming into contact with the inner circumferential face30aof the fixing belt30.

As shown inFIG. 2, the switching adjusting part41as a nip adjusting part has a switching rotation shaft46, a switching motor47and a switching gear train48. The switching rotation shaft46extends in the inner space of the fixing belt30in the left and right direction. To the both left and right end portions of the supporting stay40(the both left and right end portions outside of the caps37), a pair of bearing parts46ais provided. The switching rotation shaft46is supported between the pair of bearing parts46a. Thereby, the switching rotation shaft46is supported by the supporting stay40via the pair of bearing parts46ato be rotatable in the rotation space SP around a rotation axis. A right end portion of the switching rotation shaft46penetrates the bearing part46aand protrudes rightward from the supporting stay40. The switching motor47is connected to the switching rotation shaft46via the switching gear train48. The switching motor47is a geared motor, for example, and rotates the switching rotation shaft46around the rotation axis (refer to a dashed arrow inFIG. 3).

As shown inFIG. 2andFIG. 6, the switching gear train48has a switching drive gear48aand a switching intermediate gear48b. The switching drive gear48ais a so-called spur gear, and fixed to the right end portion of the switching rotation shaft46. The switching intermediate gear48bis a so-called stepped gear, and rotatably supported by the fixing frame. A small diameter gear of the switching intermediate gear48bis meshed with the switching drive gear48a. A large diameter gear of the switching intermediate gear48bis meshed with a pinion gear47afixed to an output shaft of the switching motor47. The switching gear train48transmits drive force (rotation force) of the switching motor47to the switching rotation shaft46.

The two pressing pads42and43as pressing members are each made of heat-resistant resin, such as liquid crystal polymer, and formed into a substantially rectangular parallelepiped shape elongated in the left and right direction. As shown inFIG. 2andFIG. 3, the two pressing pads42and43oppose to each other and fixed to the switching rotation shaft46. One pressing pad42is provided at a position where it is turned at 180 degrees around the switching rotation shaft46from the other pressing pad43. The two pressing pads42and43respectively have pressure contact faces42aand43awhich are configured to come into contact with the inner circumferential face30aof the fixing belt30.

The two pressing pads42and43are rotatable around the switching rotation shaft46. The switching motor47is configured to be capable of keeping a position (a posture) of each of the pressing pads42and43. A selected one of the two pressing pads42and43makes the downward pressure contact face42a(or43a) come into pressure contact with the inner circumferential face30aof the fixing belt30. Thereby, the fixing nip N is formed between the fixing belt30and the pressuring roller31.

As shown inFIG. 4andFIG. 5, the pressure contact faces42aand43aof the two pressing pads42and43are each formed such that its width is gradually widened from a center portion toward both end portions in the left and right direction (a direction of the switching rotation shaft46). The pressure contact faces42aand43aof the two pressing pads42and43are different from each other. “A width”, “a nip width” and other similar descriptions show a length of the fixing nip N in a rotation direction (or a conveying direction) of the fixing belt30. Hereinafter, for convenience of explanation, one pressing pad42is also called as a first pressing pad42and the other pressing pad43is also called as a second pressing pad43. In addition, the fixing nip N1formed by the first pressing pad42is also called as a first fixing nip N1and the fixing nip N formed by the second pressing pad43is also called as a second fixing nip N2. Furthermore, in a description in common to the two fixing nips N1and N2, a reference “N” is only shown.

The first pressing pad42(the pressure contact face42a) is formed such that a difference in the width between the both left and right end portions and the center portion in the left and right direction is larger than that of the second pressing pad43(the pressure contact face43a) (G1>G2). A width of the center portion of the pressure contact face42ain the left and right direction is narrower than a width of the center portion of the pressure contact face43ain the left and right direction. That is, the pressure contact face42anarrows at the center portion in the left and right direction more largely than the pressure contact face43a. Accordingly, a ratio of the nip width of the both left and right end portions to the nip width of the center portion in the left and right direction is larger at the fixing nip N1than at the fixing nip N2.

A sliding sheet made of fluororesin may be fixed on the pressure contact faces42aand43aof the pressing pads42and43. In addition, the inner circumferential face30aof the fixing belt30may be coated with coating material made of polyimide, polyamide-imide or polytetrafluoroethylene (PTFE).

As shown inFIG. 2, the switching detecting mechanism44has a switching pulse plate44aand a switching detecting sensor44b. The switching pulse plate44ais fixed to the right end portion of the switching rotation shaft46, and rotates together with the switching rotation shaft46. The switching pulse plate44ahas a plurality of light-shielding pieces (not shown) aligned in a circumferential direction at equal intervals. The switching detecting sensor44bis a photo-interrupter having a light emitting part and a light receiving part which oppose to each other on both sides of the switching pulse plate44a. The switching detecting sensor44btransmits light receiving information changing depending on rotation of the switching pulse plate44ato the control device14. The switching detecting mechanism44detects which one of the two pressing pads42and43comes into contact with the inner circumferential face30aof the fixing belt30.

As shown inFIG. 6andFIG. 7, the approach guide35is provided closer to the upstream side than the fixing nip N on a side of the pressuring roller31. The approach guide35guides the sheet S to the fixing nip N. The approach guide35has a guide shaft35aextending in the left and right direction and a plurality of guide plates35bfixed to the guide shaft35a.FIGS. 6 and 7each show one of the guide plates35b. The guide shaft35ais rotatably supported by the fixing frame. Each guide plate35bis formed into a substantially plate shape. Each guide plate35bis extended from the guide shaft35atoward the fixing nip N.

The approach guide35is turnable around the guide shaft35a. The approach guide35is turnable between a first position P1(refer toFIG. 6) where the approach guide35corresponds to the first fixing nip N1and a second position P2(refer toFIG. 7) where the approach guide35corresponds to the second fixing nip N2. The approach guide35turned to the first position P1directs a distal end of each guide plate35btoward a side of the fixing belt30. The second position P2is set to be lower than the first position P1(refer toFIG. 7).

The guide adjusting part36is provided in order to transmit rotation force from the switching adjusting part41to the approach guide35and to turn the approach guide35corresponding to deformation of the fixing nip N. The guide adjusting part36has a guide gear train50and a pair of left and right adjusting cams51.FIGS. 6 and 7show one of the adjusting cams51.

The guide gear train50as a drive transmitting part has a guide intermediate gear50aand a guide drive gear50b. The guide intermediate gear50ais a so-called spur gear, and rotatably supported by the fixing frame. The guide intermediate gear50ais meshed with the pinion gear47aof the switching motor47. The guide drive gear50bis a so-called spur gear, and fixed to an adjusting shaft50cextending in the left and right direction. The guide drive gear50bis meshed with the guide intermediate gear50a. Accordingly, the guide intermediate gear50aand the guide drive gear50bare driven by the switching motor47to be rotated. Both left and right end portions of the adjusting shaft50care rotatably supported by the fixing frame.

A gear ratio of the switching gear train48(the gears48aand48b) to the guide gear train50(the gears50aand50b) is set such that a rotation angle of the switching rotation shaft46is equal to a rotation angle of each adjusting cam51.

The pair of left and right adjusting cams51is fixed to the both left and right end portions of the adjusting shaft50c. Each adjusting cam51rotates around the adjusting shaft50ctogether with the guide drive gear50b. The above described guide gear train50transmits the rotation force of the switching adjusting part41(the switching motor47) to each adjusting cam51. Around an outer circumferential face of each adjusting cam51, a first cam face51aand a second cam face51bare formed. The first cam face51aand the second cam face51bare respectively formed around one half and the other half of the outer circumferential face of each adjusting cam51. The first cam face51aand the second cam face51bare formed into curved faces having curvatures different from each other. The first cam face51ahas a curvature smaller (a radius of curvature larger) than that of the second cam face51b.

Each adjusting cam51is provided in contact with the approach guide35. In a state where the first cam face51aof each adjusting cam51comes into contact with each guide plate35b, the approach guide35is turned to the first position P1(refer toFIG. 6). On the other hand, in a state where the second cam face51bof each adjusting cam51comes into contact with each guide plate35b, the approach guide35is turned to the second position (refer toFIG. 7). That is, each adjusting cam51is provided in order to turn the approach guide35corresponding to the deformation of the fixing nip N (N1, N2).

The printer1includes an operation panel60(refer toFIG. 8) through which a user performs an input operation. The user inputs a size or a type of the sheet S through the operation panel60or an external terminal (not shown) connected to the printer1. The printer1includes a power source (not shown) which supplies power to each devices and the others, and a cooling fan (not shown) which introduces outside air into the inside of the apparatus main body2. The power source and the cooling fan are each provided with a temperature/humidity sensor61(refer toFIG. 8) which detects environment temperature or environment humidity.

The above described control device14has an arithmetic processing part (not shown) executing an arithmetic processing according to a program stored in a storage part (not shown). As shown inFIG. 8, the fixing drive motor32a, the IH heater33, the rotation detecting sensor38c, the switching motor47, the switching detecting sensor44b, the operation panel60and the temperature/humidity sensor61(each device and the others) are electrically connect to the control device14. Each device and the others are adequately controlled by the control device14. Another device (not shown) performing the image forming operation is also electrically connected to the control device14and controlled.

Next, an operation of the deforming part34of the fixing device12will be described.

Information showing the size and the type of the sheet S, which are input by the user through the operation panel60or the external terminal, is transmitted to the control device14. The control device14controls the switching adjusting part41(the switching motor47) on the basis of the type of the sheet S passing through the fixing nip N (switching control). The switching adjusting part41rotates the two pressing pads42and43around the switching rotation shaft46to switch the pressing pads42and43so as to make either one of them come into pressure contact with the inner circumferential face30aof the fixing belt30. That is, the switching adjusting part41deforms the fixing nip N.

For instance, when the sheet S which is easy to be crinkled, such as an envelope and a thin paper, is subjected to the fixing processing, the control device14controls the switching adjusting part41to make the first pressing pad42come into pressure contact with the inner circumferential face30aof the fixing belt30. In detail, the control device14receives an output signal (a detection result) output from the switching detecting sensor44b, and recognizes that either of the two pressing pads42or43comes into contact with the inner circumferential face30aof the fixing belt30. The control device14controls the switching adjusting part41on the basis of the detection result of the switching detecting mechanism44(the switching detecting sensor44b).

As shown inFIG. 6, when the first pressing pad42comes into pressure contact with the inner circumferential face30aof the fixing belt30, the control device14controls the switching adjusting part41to keep the state (not to drive the switching motor47). In this case, the guide adjusting part36makes the first cam face51aof each adjusting cam51come into contact with a lower face of the guide plates35b. That is, the approach guide35has been already turned to the first position P1.

On the other hand, as shown inFIG. 7, when the second pressing pad43comes into pressure contact with the inner circumferential face30aof the fixing belt30, the guide adjusting part36makes the second cam face51bof each adjusting cam51come into contact with the lower faces of the guide plates35b. That is, the second nip N2is formed, and the approach guide35is kept in a state where it is turned to the second position P2.

In this case, the switching motor47is controlled by the control device14to rotate the switching rotation shaft46by a predetermined angle (for example, 180 degrees). The switching motor4rotates the switching rotation shaft46until the first pressing pad42comes into contact with the inner circumferential face30aof the fixing belt30. Thereby, the fixing nip N is switched from the second fixing nip N2to the first fixing nip N1(refer toFIG. 6). In addition, at the same time of the rotation of the switching rotation shaft46, the switching motor47rotates the guide gear train50and each adjusting cam51. For instance, when the switching motor47rotates the switching rotation shaft46by 180 degrees, each adjusting cam51is also rotated by 180 degrees. Accordingly, each guide plate35bof the approach guide35slides relative to each adjusting cam51from the second cam face51bto the first cam face51a. Thereby, the approach guide35is turned from the second position P2to the first position P1(refer toFIG. 6).

As described above, as the deforming part34deforms the fixing nip N from the second fixing nip N2to the first fixing nip N1, the guide adjusting part36makes the approach guide35turn to the first position P1where the approach guide35corresponds to the first fixing nip N1after the deformation. The storage part of the control device14previously stores (sets) information showing a rotation angle of the switching rotation shaft46used for switching the two pressing pads42and43. The control device14recognizes the rotation angle of the switching rotation shaft46on the basis of the detection result of the switching detecting sensor44b. The control device14calculates a rotation angle of the switching motor47using the information stored in the storage part and the detection result of the switching detecting censor44b. The switching motor47(the switching rotation shaft46) may be rotated in the clockwise direction or the counterclockwise direction inFIG. 6andFIG. 7.

In another case, when the sheet S which is hard to be crinkled, such as a plain paper and a thick paper, is subjected to the fixing processing, the control device14switches and controls the switching adjusting part41such that the second pressing pad43comes into pressure contact with the inner circumferential face30aof the fixing belt30. Thereby, the second fixing nip N2is formed, and the approach guide35is turned to the second position P2(refer toFIG. 7). The switching control has the same procedure as the above thin paper case, and its detailed description is omitted.

After that, the control device14executes the image forming processing as described above. The fixing drive motor32ais controlled by the control device14to rotate the pressuring roller31. The fixing belt30is driven by the pressuring roller31to be rotated. The rotation detecting sensor38cdetects the rotation of the rotating pulse plate38b. The control device14receives the detection result of the rotation detecting sensor38c, and then drives the IH heater33. The IH heater33heats the fixing belt30. The fixing device12presses and heats the sheet S passing through the fixing nip N to fix the toner image on the sheet S (the fixing processing). If the rotation detecting sensor38cdoes not detect the rotation of the rotating pulse plate38b(the fixing belt30), the control device14does not drive the IH heater33and displays an error message on the operation panel60or the like.

As described above, depending on the type of the sheet S, either one of the first pressing pad42or the second pressing pad43is selected. That is, depending on the type of the sheet S, the nip width can be changed. Thereby, even in the case where the sheet S which is easy to crinkled, such as an envelope and a thin paper, is subjected to the fixing processing, the sheet S can be prevented from being crinkled.

According to the fixing device12of the first embodiment as described above, the guide adjusting part36turns (moves) the approach guide35corresponding to the fixing nip N (N1or N2) deformed by the deforming part34. In addition, the movement of the approach guide35by the guide adjusting part36is linked with the deformation of the fixing nip N by the deforming part34. Thereby, the approach guide35can be turned to a position suitable for the shape of the fixing nip N so that the sheet S can be guided to the fixing nip N smoothly.

In addition, according to the fixing device12of the first embodiment, the switching adjusting part41makes one selected from the two pressing pads42and43come into pressure contact with the inner circumferential face30aof the fixing belt30. The nip width is changeable by switching the pressing pads42and43. Because the fixing nips N1and N2each have the nip width which is wider at the both end portions than the center portion in the left and right direction, force for conveying the sheet S (conveying force) is larger at the both end portions than at the center portion in the left and right direction. Thereby, the sheet S is conveyed while extending in the left and right direction and, therefore, can be prevented from being crinkled. Accordingly, it becomes possible to form the fixing nip N where the sheet S can be conveyed appropriately, the toner image can be fixed on the sheet S appropriately and the sheet S is hard to be crinkled.

Furthermore, force for rotating each of the pressing pads42and43(rotation force) is transmitted to the approach guide35via the guide adjusting part36to turn the approach guide35. That is, the switching adjusting part41is used in common as a drive source which rotates each of the pressing pads42and43and turns the approach guide35. Thereby, the deformation of the fixing nip N and the movement of the approach guide35can be linked with each other by a simple configuration.

Furthermore, according to the fixing device12of the first embodiment, the approach guide35slides relative to each of the cam faces51aand51bof each adjusting cam51to be turned to a position (P1or P2) corresponding to the fixing nip N (N1or N2) after the deformation. In this way, use of a cam mechanism in the guide adjusting part36can appropriately link the deformation of the fixing nip N with the movement of the approach guide35.

The fixing device12of the first embodiment is provided with the two pressing pads42and43. However, the present disclosure is not limited to the number of the pressing pad. For instance, two or more pressing pads may be provided. In this case, in order to correspond to change in the number of the pressing pad (the number of the deformed shape of the fixing nip N), each adjusting cam51of the guide adjusting part36may have two or more cam faces so as to turn the approach guide35to two or more positions. Furthermore, in the first embodiment, the two pressing pads42and43are fixed to one switching rotation shaft46and rotatably supported around the switching rotation shaft46. However, the present disclosure is not limited to the embodiment. For instance, a plurality of pressing pads may be lineally moved upward and downward.

Next, with reference toFIGS. 9 to 14, the fixing device16of a second embodiment will be described.FIG. 9is a sectional view schematically showing the fixing device16of the second embodiment.FIG. 10is a sectional view taken along a line X-X ofFIG. 9.FIG. 11is a schematic view showing a top face and a side face of a part of a deforming part70(in a standard state).FIG. 12is a schematic view showing the top face and the side face of the part of the deforming part70(in a center pressure decreased state).FIG. 13is a sectional view taken along a line XIII-XIII ofFIG. 9.FIG. 14is a sectional view showing a state where the approach guide35is turned to the first position P1from a state shown inFIG. 13. In the following description, the same configurations as the fixing device12of the first embodiment are shown with the same reference numbers as the first embodiment, and their description is omitted.

As shown inFIG. 9andFIG. 10, the fixing device16of the second embodiment includes a deforming part70different from the deforming part34of the fixing device12of the first embodiment. The deforming part70has a supporting stay71, a pressing member72, a pressing adjusting part73and an angle detecting mechanism74.

The pressing member72is made of heat-resistant resin, such as liquid crystal polymer, for example, and extends in the inner space of the fixing belt30in the left and right direction. The pressing member72has a pressing pad75and a base material76fixed on an upper face of the pressing pad75. The pressing pad75is formed into a substantially rectangular parallelepiped shape elongated in the left and right direction. The base material76is formed into a substantially plate shape elongated in the left and right direction. An upper face of the base material76is fixed on a lower face of the supporting stay71. The pressing pad75has a pressure contact face77which comes into pressure contact with the inner circumferential face30aof the fixing belt30. The pressure contact face77forms a lower face of the pressing pad75.

As shown inFIG. 9, three pressure changing faces78are formed on a part (a partial area) of the pressure contact face77of the pressing pad75in the left and right direction (a direction of a rotation axis). The three pressure changing faces78are set at a center portion and both end portions of the pressure contact face77in the left and right direction at equal intervals.

As shown inFIG. 9andFIG. 10, the pressing adjusting part73as the nip adjusting part has a rotation shaft80, three eccentric cams81and a drive part82. The pressing adjusting part73is configured so as to be able to change pressing force applied on each pressure changing face78.

The rotation shaft80is supported between a pair of left and right bearing parts80aso as to be rotatable around an axis in the rotation space SP. A right end portion of the rotation shaft80penetrates through the bearing part80a, and protrudes rightward from the supporting stay71. The three eccentric cams81are disposed corresponding to the three pressure changing faces78of the pressing member72, and fixed to the rotation shaft80. Each eccentric cam81penetrates through the supporting stay71, and is rotatable in a state where each eccentric cam81is in pressure contact with the upper face (a sliding face79) of the base material76.

As shown inFIG. 10, each eccentric cam81is a disk-shaped cam whose distance from the rotation shaft80to a cam face83is not constant. Around the cam face83of each eccentric cam81, a first lower point portion831, a second lower point portion832, a first higher point portion833and a second higher point portion834are set in the counterclockwise direction inFIG. 10at equal intervals. A distance D1between the first lower point portion831and the rotation shaft80is equal to a distance D2between the second lower point portion832and the rotation shaft80. A distance D3between the first higher point portion833and the rotation shaft80is equal to a distance D4between the second higher point portion834and the rotation shaft80. The distances D3and D4are longer than the distances D1and D2. The distances D1and D2(the distances D3and D4) may be different from each other.

As shown inFIG. 11, the eccentric cams81disposed on both end sides of the fixing belt30in the left and right direction are fixed to the rotation shaft80in a posture in which they have the same phase. The eccentric cam81disposed in the center portion of the fixing belt30in the left and right direction has the same shape as that of the eccentric cams81disposed on the both end sides of the fixing belt30in the left and right direction, and is fixed to the rotation shaft80in a posture in which its phase is shifted by 90 degrees with respect to the eccentric cams81disposed on the both end sides of the fixing belt30in the left and right direction. Hereinafter, for convenience of explanation, the eccentric cams81disposed on the both end sides of the fixing belt30in the left and right direction (the both end sides in the direction of the rotation axis) are also called as “end cams81a”, and the eccentric cam81disposed on the center portion of the fixing belt30in the left and right direction (the center portion in the direction of the rotation axis) is also called as “a center cam81b”. Furthermore, in a description in common to the two cams81aand81b, a reference number “81” is only shown. In addition, the pressure changing faces78corresponding to the end cams81aare also called as “end pressure changing faces78a”, and the pressure changing face78corresponding to the center cam81bis also called as “a center pressure changing face78b”. Furthermore, in a description in common to the two pressure changing faces78aand78b, a reference number “78” is only shown.

As shown inFIG. 9, the drive part82has an adjusting motor84and an adjusting gear train85. The adjusting motor84is connected to the rotation shaft80via the adjusting gear train85. The adjusting motor84drives each eccentric cam81to rotate it around the rotation shaft80(refer to a dashed arrow inFIG. 10). The adjusting motor84is a geared motor, for example, and is configured to be capable of keeping a rotation position (a posture) of each eccentric cam81.

As shown inFIG. 9andFIG. 13, the adjusting gear train85has an adjusting drive gear85aand an adjusting intermediate gear85b. The adjusting drive gear85ais a so-called spur gear, and fixed to a right end portion of the rotation shaft80. The adjusting intermediate gear85bis a so-called stepped gear, and rotatably supported by a fixing frame (not shown). A small diameter gear of the adjusting intermediate gear85bis meshed with the adjusting drive gear85a. A large diameter gear of the adjusting intermediate gear85bis meshed with a pinion gear84afixed to an output shaft of the adjusting motor84. The adjusting gear train85transmits driving force (rotation force) of the adjusting motor84to the rotation shaft80.

The guide intermediate gear50aof the guide adjusting part36is meshed with the pinion gear84aof the adjusting motor84. Accordingly, the guide intermediate gear50aand the guide drive gear50bare driven by the adjusting motor84to be rotated. A gear ratio of the adjusting gear train85(the gears85aand85b) to the guide gear train50(the gears50aand50b) is set such that a rotation angle of the rotation shaft80is equal to a rotation angle of each adjusting cam51.

As shown inFIG. 9, the angle detecting mechanism74has an angle pulse plate74afixed to the right end portion of the rotation shaft80and an angle detecting sensor74bwhich detects rotation of the angle pulse plate74a. The angle detecting mechanism74transmits information showing a rotation angle of each eccentric cam81to the control device14. The angle detecting mechanism74has substantially the same configuration as the switching detecting mechanism44, and its description is omitted.

Next, an operation of the deforming part70will be described. The adjusting motor84is controlled by the control device14to rotate the three eccentric cams81which are in contact with the sliding face79of the pressing member72, around the rotation shaft80. In this way, the pressing adjusting part73changes the pressing force applied on a part (the three pressure changing faces78) of the pressure contact face77in the direction of the rotation axis to deform the fixing nip N. Each eccentric cam81is set such that either one of the point portions831to834comes into contact with the sliding face79.

For instance, as shown inFIG. 11, a state where the first lower point portion831of each end cam81aand the second lower point portion832of the center cam81bcome into contact with the sliding face79of the pressing member72(the base material76) is called as “a standard state”. If the rotation shaft80is rotated by 90 degrees, 180 degrees and 270 degrees in the clockwise direction from the standard state, each end cam81ais rotated to a state where the second lower point portion832, the first higher point portion833and the second higher point portion834come into contact with the sliding face79in the order. In this time, the center cam81bis rotated to a state where the first higher point portion833, the second higher point portion834and the first lower point portion831come into contact with the sliding face79in the order. Here, the state where the second lower point portion832of each end cam81aand the first higher point portion833of the center cam81bcome into contact with the sliding face79is called as “a center pressure increased state”, the state where the first higher point portion833of each end cam81aand the second higher point portion834of the center cam81bcome into contact with the sliding face79is called as “an entire area pressure increased state”, and the state where the second higher point portion834of each end cam81aand the first lower point portion831of the center cam81bcome into contact with the sliding face79is called as “a center pressure decreased state”. In addition, the fixing nips N formed under the standard state, the center pressure increased state, the entire area pressure increased state and the center pressure decreased state are respectively called as a standard nip N10(refer toFIG. 11), a center pressure increased nip (not shown), an entire area pressure increased nip (not shown) and a center pressure decreased nip N20(refer toFIG. 12). Furthermore, in a description in common to the nip N10and the nip N20, a reference “N” is only shown.

The pressing member72is elastically deformed in the width direction depending on force with which the pressing member72is pressed on the inner circumferential face30aof the fixing belt30. As shown inFIG. 11, in the standard state, a standard pressing force is applied on the three pressure changing faces78. Then, the pressing member72(the pressure contact face77) is pressed on the inner circumferential face30aof the fixing belt30with a substantially uniform pressure in the left and right direction. Thereby, the standard nip N10is formed so as to have substantially the same width in the left and right direction. In the entire area pressure increased state (not shown), the pressure contact face77is pressed on the inner circumferential face30aof the fixing belt30with a substantially uniform pressure, and the entire area pressure increased nip is formed so as to have substantially the same width, in the same way.

On the other hand, as shownFIG. 12, in the center pressure decreased state, the center pressure changing face78bis applied with a first pressing force and each end pressure changing face78ais applied with a second pressing force higher than the first pressing force. Then, the center portion of the pressing member72in the left and right direction is pressed on the inner circumferential face30aof the fixing belt30with a force lower than that applied on the both end portions of the pressing member72in the left and right direction. Thereby, the center pressure decreased nip N20is formed so as to have a nip width which is gradually widened from the center portion toward the both end portions in the left and right direction. That is, the center pressure decreased nip N20is narrowed at the center portion in the left and right direction. In the center pressure increased state (not shown), the width of the pressure contact face77and the nip width of the center pressure increased nip are widened at the center portions in the left and right direction.

Next, a pressure changing control by the deforming part70will be described. Each eccentric cam81is set in the standard state.

The control device14controls the pressing adjusting part73on the basis of the type of the sheet S passing through the fixing nip N (the pressure changing control). The storage part of the control device14previously stores information showing a rotation angle used for recognizing a contact position where each cam face83(the point portions831to834) comes into contact with the sliding face79. The control device14recognizes the rotation angle of each eccentric cam81(a state of each eccentric cam81) on the basis of a detection result of the angle detecting sensor74b, and controls the adjusting motor84. The control device14calculates a rotation angle of the adjusting motor84using the information stored in the storage part and the detection result of the angle detecting sensor74b. The pressing adjusting part73changes the contact position where the cam face83of each eccentric cam81comes into contact with the sliding face79of the pressing member72.

For instance, when the sheet S which is hard to be crinkled is subjected to the fixing processing, the control device14controls each eccentric cam81to rotate (switch) it to the standard state. That is, the control device14performs control for forming the standard nip N10(refer toFIG. 11andFIG. 13). Here, because each eccentric cam81has been already rotated to the standard state, the control device14does not drive the adjusting motor84. In addition, in this case, the guide adjusting part36makes the second cam face51bof each adjusting cam51come into contact with the lower face of the guide plate35b. That is, the approach guide35is turned to the second position P2.

Next, for instance, when the sheet S which is easy to be crinkled is subjected to the fixing processing, the control device14controls each eccentric cam81to rotate it to the center pressure decreased state and to form the center pressure decreased nip N20(refer toFIG. 12andFIG. 14). The adjusting motor84is controlled by the control device14to rotate the rotation shaft80by 270 degrees in the clockwise direction inFIG. 13(alternatively, by 90 degrees in the counterclockwise direction). Thereby, each eccentric cam81is turned to the center pressure decreased state from the standard state, and the center pressure decreased nip N20is formed (refer toFIG. 14). Each eccentric cam81may be rotated in the clockwise direction or in the counterclockwise direction inFIGS. 13 and 14.

At the same time of the rotation of the rotation shaft80, the adjusting motor84rotates the guide gear train50and each adjusting cam51. For instance, when the rotation shaft80is rotated by 270 degrees in the clockwise direction inFIG. 13, each adjusting cam51is also rotated by 270 degrees. Accordingly, each guide plates35bslides relative to the adjusting cam51from the second cam face51btoward the first cam face51a. Thereby, the approach guide35is turned from the second position P2to the first position P1(refer toFIG. 14).

After that, the control device14executes the image forming processing by the image forming part11and the others. In the above description about the pressure changing control, as an example, the standard nip N10is formed when the sheet S, such as a plain paper and a thick paper, is subjected to the fixing processing. However, the present disclosure is not limited to the above example. For instance, the control device14may perform the pressure changing controls different between a thick paper and a plain paper (which is thinner than the thick paper and thicker than a thin paper). That is, the control device14may perform the pressure changing control to form the standard nip N10(refer toFIG. 11) when the thick paper is subjected to the fixing processing and to form the entire area pressure increased nip (to switch each eccentric cam81to the entire area pressure increased state) when the plain paper is subjected to the fixing processing. A procedure of the pressure changing control is the same as the above case of the thin paper, and its description is omitted. Alternatively, depending on the type of the sheet S, the control device14may perform the pressure changing control to form the center pressure increased nip (to switch each eccentric cam81to the center pressure increased state). In this case, each adjusting cam51of the guide adjusting part36may have two or more cam faces in order to correspond to the two or more changes in shape of the fixing nip N and to turn the approach guide35to two or more positions appropriately.

According to the fixing device16of the second embodiment as described above, the pressing adjusting part73adjusts (increases or decreases) the pressing force applied on the inner circumferential face30aof the fixing belt30by a part (each pressure changing face78) of the pressure contact face77in the left and right direction. Increasing and decreasing of the pressing force changes (increases or decreases) the nip width of the fixing nip N. Accordingly, it becomes possible to form the fixing nip N where the sheet S can be conveyed appropriately, the toner image can be fixed on the sheet S appropriately and the sheet S is hard to be crinkled. In addition, the center pressure decreased nip N20has the nip width which is wider at the both end portions than at the center portion in the left and right direction. Thus, the force for conveying the sheet S (the conveying force) is larger at the both end portions than at the center portion in the left and right direction. Thereby, the sheet S is conveyed while extending in the left and right direction and, therefore, can be prevented from being crinkled.

The guide adjusting part36transmits the rotation force from the pressing adjusting part73to the approach guide35and turns the approach guide35by linking with the deformation of the fixing nip N. The force for rotating each eccentric cam81(the rotation force) is transmitted to the approach guide35via the guide adjusting part36and turns the approach guide35. That is, the pressing adjusting part73is used in common as a drive source which rotates each eccentric cam81and turns the approach guide35. Thereby, the deformation of the fixing nip N and the turning of the approach guide35can be linked by a simple configuration.

The fixing device16of the second embodiment is provided with the three eccentric cams81. However, the present disclosure is not limited to the number of the eccentric cam81. One or more eccentric cams81may be provided. For instance, a single eccentric cam81may come into contact with the center portion of the pressing member72in the left and right direction. Alternatively, four or more eccentric cams81may come into contact with the pressing member72. In addition, the three eccentric cams81each has the same shape in the embodiment. However, the present disclosure is not limited to the embodiment. For instance, each end cam81amay be formed such that the pressing force applied on the pressure changing face78is larger.

Next, the fixing devices12and16of modified examples of the first and second embodiments will be described. In the flowing description, the same configuration as the fixing devices12and16of the first and second embodiments is shown with the same reference number as the first and second embodiments, and its description is omitted.

Under a high temperature and high humidity environment, because of increase in a moisture content of the sheet S, sheet conveying failure may easily occur or the sheet S may be easy to be crinkled. Thus, the fixing devices12and16of the modified examples are configured to change the fixing nip N depending on the environment condition.

The control device14controls the switching adjusting part41(or the pressing adjusting part73) on the basis of a detection result of the temperature/humidity sensor61(refer toFIG. 8). In detail, when a humidity detected by the temperature/humidity sensor61is higher than a predetermined humidity, the control device14switches and controls the switching adjusting part41(or the pressing adjusting part73) to form the first fixing nip N1(or the center pressure decreased nip N20). Thereby, even in a case of the sheet S which has a large moisture content and is easy to be crinkled, the sheet S can be subjected to the fixing processing without being crinkled. The predetermined humidity to be a reference for performing the above switching control is previously stored (set) in the storage part of the control device14.

The control device14may perform the switching control on the basis of a temperature detected by the temperature/humidity sensor61, instead of the humidity detected by the temperature/humidity sensor61. That is, the control device14is set to control the switching adjusting part41(or the pressing adjusting part73) on the basis of at least one of the environment temperature and the environment humidity.

In the fixing device12of the first embodiment, the switching gear train48and the guide gear train50are rotated by the switching motor47. As with this, in the fixing device16of the second embodiment, the adjusting gear train85and the guide gear train50are rotated by the adjusting motor84. Instead of these configurations, for instance, a dedicated drive motor which rotates each adjusting cam51via the guide gear train50may be provided separately. In this case, the control device14may drive the switching motor47(or the adjusting motor84) synchronously with the drive motor.

In the first and second embodiments, the control device14controls the printer1totally. However, the present disclosure is not limited to the control device14. For instance, a dedicated control part which controls the fixing devices12and16may be separately provided. In addition, in the first and second embodiments, the IH heater33is used as the heat source. However, the present disclosure is not limited to the embodiments. For instance, a heat source such as a halogen heater may be disposed in the inner space of the fixing belt30.

The first and second embodiments were described in a case where configurations of the disclosure are applied to the monochromatic printer1as an example. However, the configurations of the disclosure may be applied to a color printer, a copying machine, a facsimile, a multifunctional peripheral or the like, other than the monochromatic printer1.

While the present disclosure has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present disclosure.