Fixing device and image forming apparatus including the same

A fixing device includes a pressuring member, a fixing frame, a pressuring frame, a pressure changing part, a rotation detecting part and a rotation transmitting part. The pressuring member forms a fixing nip with a fixing member. The fixing frame supports the fixing member. The pressuring frame supports the pressuring member. The pressure changing part changes fixing nip pressure. The rotation transmitting part transmits rotation of the pressuring member to the rotation detecting part. The fixing frame is turnably supported around a fulcrum part provided on the pressuring frame. The pressure changing part turns the fixing frame around the fulcrum part. The rotation transmitting part has a first rotating body and a second rotating body. The first rotating body is provided on a rotation shaft of the pressuring member. The second rotating body is engaged with the first rotating body and rotatably supported around the fulcrum part.

INCORPORATION BY REFERENCE

This application is based on and claims the benefit of priority from Japanese Patent Application No. 2016-052187 filed on Mar. 16, 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 fixing device.

An electrophotographic type image forming apparatus is provided with a fixing device including a pressuring roller which comes into pressure contact with a fixing roller which is to be heated. The fixing device includes a pressure changing part which changes pressure at a fixing nip formed between the pressuring roller and the fixing roller. The pressure changing part changes the pressure at the fixing nip by turning a fixing roller supporting frame around an axis.

The fixing device further includes a rotation detecting part which detects rotation of the pressuring roller via a plurality of gears. The rotation detecting part detects rotation of the fixing roller by detecting the rotation of the pressuring roller. Thereby, the fixing roller can be prevented from being heated locally in a state where the rotation of the fixing roller is stopped.

A driving force transmitting device which transmits driving force to the fixing roller has been known although not a mechanism which transmits rotation force from the pressuring roller to the rotation detecting device. An example of the driving force transmitting device has a driven gear fixed to the fixing roller and a fixing roller driving gear which is rotatably supported by a side frame to which a fixing unit (the fixing device) is fixedly attached. In the driving force transmitting device, a rotating shaft (a pin) of the fixing roller driving gear is engaged with an engagement part formed in the fixing unit. By engaging the pin with the engagement part, the fixing roller driving gear and the driven gear are engaged with each other at a predetermined position.

SUMMARY

In accordance with an aspect of the present disclosure, a fixing device includes a fixing member, a pressuring member, a fixing frame, a pressuring frame, a pressure changing part, a rotation detecting part and a rotation transmitting part. The fixing member is heated by a heat source. The pressuring member forms a fixing nip with the fixing member. The fixing frame rotatably supports the fixing member. The pressuring frame rotatably supports the pressuring member. The pressure changing part changes pressure at the fixing nip. The rotation detecting part detect rotation of the pressuring member. The rotation transmitting part transmits the rotation of the pressuring member to the rotation detecting part. The fixing frame is supported so as to be turnable around a fulcrum part provided on the pressuring frame. The pressure changing part turns the fixing frame around the fulcrum part to change the pressure at the fixing nip. The rotation transmitting part has a first rotating body and a second rotating body. The first rotating body is provided on a rotation shaft of the pressuring member. The second rotating body is engaged with the first rotating body and supported so as to be rotatable around the fulcrum part.

In accordance with an aspect of the present disclosure, an image forming apparatus includes an image forming part and a fixing device. The image forming part transfers a toner image on a sheet. The fixing device described above 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 printer1that is an image forming apparatus will be described.FIG. 1is a sectional view schematically showing an internal structure of the printer1.

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 body2so as to be detachably inserted in the front and rear direction. In the sheet feeding cassette3, the sheets S (a bundle of sheets) are stored. 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 image forming part11and the fixing device12are disposed on a middle portion of the conveying path15. The ejecting part13is disposed on a downstream side end portion of the conveying path15. The control device14totally controls the printer1. Below the conveying path15, an inversion path16along which the sheet S is conveyed at a duplex printing is formed.

The sheet feeding part10feeds the sheet S stored in the sheet feeding cassette3toward the conveying path15one by one. The image forming part11transfers a toner image on the sheet S. The image forming part11has a toner container20, a drum unit21and an optical scanning device22.

The toner container20contains a toner (a developer) of black color, for example. The drum unit21has a photosensitive drum23, a charging device24, a developing device25, a transferring roller26and a cleaning device27. The charging device24, the developing device25, the transferring roller26and the cleaning device27are disposed around the photosensitive drum23in the order of transferring process. The transferring roller26comes into pressure contact with the photosensitive drum23from the lower side to form a transferring nip26a. The fixing device12has a pressuring roller32which forms a fixing nip N with a fixing belt31, as described later in detail.

Here, an operation of the printer1will be described. The control device14executes the following image forming operation based on an input image date.

The charging device24charges a surface of the photosensitive drum23. The optical scanning device22exposes the photosensitive drum23based on the image data (refer to a dashed arrow inFIG. 1). The developing device25develops a latent image on the photosensitive drum23into a toner image. On the other hand, the sheet S is conveyed from the sheet feeding cassette3to the conveying path15. The toner image is transferred on the sheet S passing through the transferring nip26a. The fixing device12presses and heats the sheet S passing through the fixing nip N to fix the toner image on the sheet S. After the fixing processing, the sheet S is ejected by the ejecting part13on the ejection tray4.

Next, with reference toFIGS. 2 to 7, the fixing device12will be described.FIG. 2is a perspective view showing the fixing device12.FIG. 3is a III-III sectional view ofFIG. 1.FIG. 4is a IV-IV sectional view ofFIG. 3.FIG. 5is a perspective view showing a left side portion of the fixing device12.FIG. 6is a perspective view showing a vicinity around a left fulcrum pin46of the fixing device12.FIG. 7is a perspective view showing a left pressuring frame41and the others of the fixing device12.

As shown inFIGS. 2 and 3, the fixing device12includes a device frame30, a fixing belt31, a pressuring roller32, an induction heating (IH) heater33, a pressure changing part34, a rotation detecting part35and a rotation transmitting part36. The fixing device12employs a so-called sliding belt type.

As shown inFIG. 2, the device frame30has a case30aand a cover30b, and is formed into a substantially rectangular parallelepiped shape elongated in the left and right direction. On the case30a, a part of the conveying path15which introduces the sheet S to the fixing nip N is formed. The details of the device frame30will be described later.

As shown inFIGS. 3 and 4, the fixing belt31that is a fixing member has flexibility, and is formed into an endless shape. The fixing belt31is formed into a cylindrical shape elongated in the left and right direction (a direction of a rotation axis). The fixing belt31is supported by the device frame30so as to be capable of rotating (circulating). The fixing belt31is formed by laminating a substrate layer, an elastic layer and a releasing layer in the order from the inner side (they are not shown). The substrate layer is made of polyimide resin mixed with metal powder, for example. The elastic layer is made of silicon rubber, for example. The releasing layer is made of fluororesin, for example.

In an inner hollow space of the fixing belt31, a pressing member37is non-rotatably disposed. The pressing member37presses the fixing belt31on the pressuring roller32. On both ends of the fixing belt31in the left and right direction (the direction of the rotation axis), a pair of left and right caps38is attached. Between an inner circumferential face of each cap38and an outer circumferential face of the fixing belt31, an annular elastic member38ais interposed. Both left and right end portions of the above described pressing member37penetrate through the pair of left and right caps38.

The pressuring roller32that is a pressuring member is formed into a cylindrical shape elongated in the left and right direction. The pressuring roller32is supported by the device frame30so as to be rotatable around an axis. The pressuring roller32comes into pressure contact with the fixing belt31from the lower side of the fixing belt31. Between the fixing belt31and the pressuring roller32, the fixing nip N is formed. The pressuring roller32is formed by laminating an elastic layer32band the others on an outer circumferential face of a cylindrical core material32a. The core material32athat is a rotation shaft is made of metal, such as stainless steel and aluminum, for example. The elastic layer32bis made of silicon rubber or silicon sponge, for example. On an outer circumferential face of the elastic layer32a, a releasing layer (fluororesin, not shown) is laminated.

To a left end portion of the core material32a, a first gear60connected to a fixing driving motor39is fixedly attached (refer toFIG. 3). The fixing driving motor39drives the pressuring roller32via the first gear60to rotate it around the rotation shaft.

The IH heater33that is a heat source is disposed on an upper side (an opposing side to the fixing nip N) of the fixing belt31. The IH heater33generates magnetic field to heat the fixing belt31.

As shown inFIGS. 5 to 7, the device frame30has a fixing frame40and a pressuring frame41. The fixing frame40and the pressuring frame41are formed by sheet metal working, for instance. Both left and right ends of the fixing frame40and the pressuring frame41are covered with the covers30b(refer toFIG. 2).

The fixing fame40supports the fixing belt31via the pressing member37so as to be rotatable (refer toFIG. 3). In detail, both left and right ends of the pressing member37are fixedly attached to a pair of left and right fixing side plates42of the fixing frame40. The fixing belt31is configured to be capable of circulating around the pressing member37.

As shown inFIG. 7, the pressuring frame41supports the pressuring roller32so as to be rotatable. A pair of left and right pressuring side plates43of the pressuring fame41each are formed into a substantially L shape in the side view. Each pressuring sideplate43has a vertical plate43velongated in the vertical direction and a horizontal plate43hextending forward from a lower portion of the vertical plate43v. Each horizontal plate43hhas a positioning hole44(a positioning part) to which a bearing45is fixedly attached. Each positioning hole44is recessed downward from an upper edge of the horizontal plate43h. The pair of left and right positioning holes44support the core material32a(the rotating shaft) of the pressuring roller32via the bearings45.

On the vertical plate43vof each pressuring side plate43, a fulcrum pin46that is a fulcrum part is provided. The pair of left and right fulcrum pins46is protruded outward (in a direction separating from each other) from the pair of left and right vertical plates43v.

As shown inFIG. 6, each fulcrum pin46penetrates through a rear lower portion of each fixing side plate42of the fixing frame40. Thereby, the fixing frame40is rotatably (turnably) supported by the pair of left and right fulcrum pins46. Around each fulcrumpin46, a restriction plate47is fitted. Each fulcrum pin46penetrates through a loose hole (not shown) formed in the restriction plate47. The pair of left and right restriction plates47is fixedly attached (fastened with screws) to the fixing side plates42of the fixing frame40. The pair of left and right restriction plates47restricts the fixing frame40supported by each fulcrum pin46from being moved in the left and right direction (the direction of the rotation axis). Thereby, the fixing frame40can be rotated around each fulcrum pin46without displacing in the direction of the rotation axis. Accordingly, positioning precision of the fixing belt31is improved so that the fixing nip N can be suitably formed.

As shown inFIGS. 5 and 6, each fixing side plate42of the fixing frame40has an arm part41aextending forward. Between each arm part41aand the apparatus main body2, a coil spring48is interposed. The pair of left and right coil springs48biases the fixing frame40toward a side of the pressuring roller32. The fixing belt31is biased by the coil springs48to be moved to a contact position where the fixing belt31comes into pressure contact with the pressuring roller32. In this state, the fixing nip N where is set at a predetermined pressure is formed.

The pressure changing part34is configured to adjust biasing force of the coil springs48so as to change the pressure at the fixing nip N. The pressure changing part34has a pair of left and right eccentric cams (not shown), a rotation connecting shaft50and a pair of left and right activating parts51.FIGS. 5 to 7show the left side portion of the pressure changing part34.

The pair of left and right eccentric cams is fixed to the rotation connecting shaft50, and rotates around the rotation connecting shaft50. Each of the eccentric cam is formed to have a change in distance from a circumferential cam face to a rotation center. To a left end portion of the rotation connecting shaft50, a pressure changing gear52connected to a motor (not shown) is fixedly attached. On driving the motor, each eccentric cam (the rotation connecting shaft50) is rotated. The motor is electrically connected to the control device14to be controlled to be driven.

Each activating part51is configured to be relatively slid on the circumferential cam face of each eccentric cam. Each activating part51is moved upward and downward as each eccentric cam is rotated. When each activating part51is moved upward, each arm part41aof the fixing frame40is moved upward against biasing force of the coil spring48. Thereby, the fixing belt31is kept at a state where the fixing belt31is moved to a release position where a pressure contact state against the pressuring roller32is set to be capable of releasing. On the other hand, when each activating part51is moved downward, each arm part41ais biased by each coil spring48to be moved downward. Thereby, the fixing belt31is kept at another state where the fixing belt31is moved to a contact position where the fixing belt31is set to be capable of coming into pressure contact with the pressuring roller32. That is, the fixing belt31(the fixing frame40) is configured to be turnable between the contact position and the release position. The pressure changing part34changes the pressure at the fixing nip N by rotating (turning) the fixing frame40around the fulcrum pins46. The control device14moves the fixing belt4to the release position when the fixing processing (the image forming processing) is stopped.

As shown inFIGS. 5 to 7, the rotation detecting part35is provided on the left pressuring side plate43of the pressuring frame41. The rotation detecting part35has a pulse plate53and a rotation detecting sensor54.

The pulse plate53is rotatably supported by the vertical plate43vof the left pressuring side plate43. The pulse plate53is positioned on a lower rear side of the fulcrum pin46. The pulse plate53has a plurality of light-shielding pieces53aextending in a direction parallel to a rotation axis of the pule plate53and arranged in a circumferential direction at equal intervals. The pulse plate53is formed into a substantially cap shape with each light-shielding piece53aextending rightward (refer toFIG. 3). On a left face of the pulse plate53, a transmitting gear55is fixedly attached. The transmitting gear55is positioned on the same rotation axis as the rotation axis of the pulse plate53.

The rotation detecting sensor54is a photo-interrupter having a light emitting part and a light receiving part (they are not shown) which oppose to each other on both sides of the pulse plate53(refer toFIG. 3). The rotation detecting sensor54is configured to detect rotation of the pulse plate53. The rotation detecting sensor54transmits light receiving information changing depending on the rotation of the pulse plate53to the control device14.

As shown inFIG. 5, the rotation transmitting part36is provided on the left pressuring side plate43of the pressuring frame41. The rotation transmitting part36has the above described first gear60and a second gear61. The first gear60and the second gear61are so-called spur gears.

As described above, the first gear60that is a first rotating body is provided on the core material32a(the rotation shaft) of the pressuring roller32. The second gear61that is a second rotating body is rotatably supported by the left fulcrum pin46. The second gear61is arranged so as to be meshed (engaged) with the transmitting gear55and the first gear60. That is, the pulse plate53is engaged with the second gear61via the transmitting gear55. As described above, the rotation transmitting part36transmits the rotation of the pressuring roller32to the rotation detecting part35(the pulse plate53). Thereby, the rotation detecting part35can detect the rotation of the pressuring roller32.

According to the fixing device12as described above, each fulcrum pin46supporting the second gear61is provided on the pressuring frame41supporting the pressuring roller (the first gear60). That is, the first gear60and the second gear61are provided on the same member (the pressuring frame41). Thereby, a distance D1between centers of the both gears60and61can be set with high precision (refer toFIGS. 5 and 6). Accordingly, the rotation force can be effectively transmitted from the pressuring roller32to the rotation detecting part35.

The fulcrum pin46is used as a member supporting the fixing frame40in addition to the second gear61. The fixing frame40and the second gear61are rotated around the same fulcrum (each fulcrum pin46). Thereby, a manufacturing cost can be reduced compared with a case where a rotation fulcrum of the fixing frame40and a rotation fulcrum of the second gear61are separately formed.

In addition, according to the fixing device12described above, the pressuring roller32(the both end portions of the core material32a) is supported by each positioning hole44and thus can be positioned to the pressuring frame41with high precision. Thereby, positioning precision of the first gear60and the second gear61can be improved.

In addition, according to the fixing device12described above, the pulse plate53is also provided on the same member (the pressuring frame41) in addition to the first gear60and the second gear61. Thereby, a distance D2between centers of the second gear61and the pulse plate53can be set with high precision (refer toFIGS. 5 and 6) so that the pulse plate53can be smoothly rotated.

The rotation transmitting part36of the fixing device12of the embodiment has two of the gears60and61; the present disclosure is not limited to the embodiment. For instance, the rotation transmitting part36may have three or more gears. In this case, each gear may be rotatably supported to the pressuring frame41(either one of the left and right pressuring side plates43).

The rotation transmitting part36of the fixing device12of the embodiment has the gears60and61; the present disclosure is not limited to the embodiment. For instance, the rotation transmitting part may have a plurality of gears adjacently and tightly arranged. Alternatively, the rotation transmitting part may have a plurality of pulleys engaged via a belt.

In the embodiment, the control device14totally controls the printer1; a dedicated control device which controls the fixing device12may be provided. In the embodiment, the IH heater33is employed as the heat source; the present disclosure is not limited to the embodiment. For instance, a halogen heater may be provided in the hollow inner space of the fixing belt31. Furthermore, in the embodiment, the fixing device12employs the sliding belt type; the present disclosure is not limited to the embodiment. For instance, a fixing roller having an elastic layer may be employed other than the fixing belt31.

Although each embodiment was described in a case where configurations of the disclosure are applied to the monochromatic printer1as an example, the configurations of the disclosure may be applied to a color printer, a copying machine, a facsimile or a multifunctional peripheral, other than the monochromatic printer1.

As another embodiment of the fixing device12of the embodiment, the fixing belt31and the pressuring roller32may be switched. In this case, the same effect as that of the present embodiment can be obtained. In another embodiment, the fixing belt31and the pressuring roller32maybe switched on the figures of the present embodiment.

While the above embodiments has been described with reference to one embodiment of the fixing device and the image forming apparatus including the fixing device according to the present disclosure. A technical scope of the disclosure is not to be restricted by the above embodiments. The components in the above embodiments may be suitably replaced with other components, or variously combined with the other components. The claims are not restricted by the description of the embodiment of the disclosure as mentioned above.