Image forming apparatus

A fixing unit 8 is fitted with a rail 28 along which a rail guide provided inside an image forming apparatus can slide. This allows the fixing unit 8 to be extracted out of the image forming apparatus. When the fixing unit 8 is extracted out of the image forming apparatus, a transferring body separating member 26, which has thus far been prevented from rotating by the rail 28, is made to rotate by the force applied by a tension spring 27. An end portion of the transferring body separating member 26 presses a transfer roller bracket 24 and thereby moves a transfer roller 17. Thus, the transfer roller 17 is separated from a photoconductor drum 2.

This application is based on Japanese Patent Application No. 2005-171783 filed on Jun. 13, 2005, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus such as a digital copier or laser printer, and more particularly to a jam disposal mechanism that allows a paper jam to be disposed of from the side of a fixing unit.

2. Description of Related Art

The construction of a conventional image forming apparatus is shown inFIG. 8. Reference numeral100represents an image forming apparatus, which is here assumed to be a digital multifunctional product, for example. When the image forming apparatus100performs a copying operation, in an image forming section P arranged above a conveying belt9inside the cabinet of the multifunctional product, steps of charging, exposure, development, and transferring are performed to form a predetermined image based on original image data read by an image reading section6.

In the image forming section P, a photoconductor drum2for carrying a visible image (toner image) is arranged. The toner image formed on the photoconductor drum2is transferred to a sheet (recording medium)7carried and conveyed by a transfer belt9that moves adjacently to the image forming section P. The transferred toner image is then fixed on the sheet7in a fixing unit8, and is then ejected out of the cabinet of the apparatus. While the photoconductor drum2is rotated clockwise (in the direction indicated by arrow A) as viewed inFIG. 8, an image forming process is performed with respect to the photoconductor drum2.

Next, the image forming section P will be described in detail. The photoconductor drum2is arranged so as to be freely rotatable. Around and above the photoconductor drum2, there are provided: a charger3for electrically charging the photoconductor drum2, an exposure unit4for exposing the photoconductor drum2to light representing image information; a developer unit5for forming a toner image on the photoconductor drum2; and a cleaning section10for removing developing agent (toner) that remains on the photoconductor drum2.

The surface of the photoconductor drum2is first electrically charged uniformly by the charger3, and is then exposed to light by the exposure unit4so that an electrostatic latent image according to an image signal is formed on the photoconductor drum2. The developer unit5is loaded with a predetermined amount of toner by a toner container11. This toner is fed by the developer unit5onto the photoconductor drum2so as to be electrostatic ally adhered to the surface thereof, on which a toner image is thus formed according to the electrostatic latent image formed through the exposure by the exposure unit4.

The sheet7to which the toner image is transferred is housed in a sheet housing section12, which is composed of a plurality of paper feed cassettes12a,12b, and12cand a stack bypass (hand-feed tray)12dprovided above them. The sheet is fed via paper feed rollers13and resist rollers14onto the conveying belt9so as to be conveyed into position on the photoconductor drum2. The paper feed cassettes12a,12b, and12care detachably attached to the apparatus cabinet1.

The conveying belt9is hung around and between a drive roller15, disposed downstream, and a follower roller16, disposed upstream. When the conveying belt9starts to rotate counter-clockwise, the sheet7is conveyed via the resist rollers14onto the conveying belt9. At this time, an image write signal turns on, so that an image is formed on the photoconductor drum2with predetermined timing.

Under the photoconductor drum2, a transfer roller17is arranged to which a predetermined transfer voltage is applied. At the nip between the photoconductor drum2and the transfer roller17, the toner image on the photoconductor drum2is transferred to the sheet7. The sheet7is held on the conveying belt9by electrostatic attraction. The conveying belt9is formed of a dielectric resin sheet, and is built as an endless or seamless belt by joining together opposite ends of such a sheet.

The sheet7having the toner image transferred thereto is separated from the conveying belt9, and is conveyed to the fixing unit8. On the other hand, after the transfer of the toner image, the photoconductor drum2is cleaned by the cleaning section10so that the toner that remains on the surface of the photoconductor drum2is removed in preparation for the subsequent formation of a new electrostatic latent image. Conveyed from the conveying belt9to the fixing unit8, the sheet7is then heated and pressed by a pair of fixing rollers8aand8bso that the toner image is fixed on the surface of the sheet7to form a predetermined image. Having the image formed thereon, the sheet7then passes via pairs of conveying rollers18and19, and is then ejected by a pair of ejection rollers20onto an ejected paper tray21.

Although not illustrated, a charge removing device for removing the residual electric charge on the surface of the photoconductor drum2is provided on the downstream side of the cleaning section10. Reference numeral22represents a cover provided on a side face of the apparatus cabinet1. The cover22is so built as to be freely openable and closable in the direction indicated by arrow B about a pivot23. Opening this cover22allows simple maintenance work, such as removable of a paper jam.

In the image forming apparatus constructed as described above, if the sheet7is stuck in the middle of image formation and causes a paper jam, for example, extracting the fixing unit8out of the apparatus cabinet1parallel to the paper conveying direction (that is, leftward inFIG. 8) makes it possible to dispose of the paper jam. Inconveniently, however, doing so involves pulling out the sheet7held between the photoconductor drum2and the transfer roller17, and this may cause various problems, such as the sheet7breaking, or the unfixed toner splashing and soiling the interior of the apparatus.

To overcome this inconvenience, for example, JP-A-2002-72819 proposes an intermediary-transfer-type image forming apparatus wherein at least a secondary transferring member and fixing means are held with a holding member and wherein this holding member is so built as to be freely extractable in a direction that points away from the image forming apparatus and that coincides with the paper ejection direction. Certainly, this makes it possible to remove a jammed sheet without breaking it or soiling the interior and exterior of the apparatus with unfixed toner.

With the technique disclosed in JP-A-2002-72819 mentioned above, however, it is necessary to provide a holding member for holding at least the fixing unit8and the transfer roller17. In this case, for the holding member to be able to hold the fixing unit8and the transfer roller17, the holding member itself needs to be considerably large. Disadvantageously, this unduly increases the size and cost of the image forming apparatus. Moreover, to dispose of a paper jam, it is necessary to extract the holding member along with the fixing unit8and the transfer roller17it holds. Disadvantageously, this requires a wider work space than extracting the fixing unit8alone.

SUMMARY OF THE INVENTION

In view of the conventionally experienced inconveniences and disadvantages mentioned above, it is an object of the present invention to provide a compactly and simply constructed image forming apparatus that allows jam disposal with a minimum work space, without breakage of the jammed sheet, and without splashing of unfixed toner.

To achieve the above object, according to the present invention, an image forming apparatus is provided with: an image carrying body; a transferring body for transferring a toner image formed on the image carrying body to a sheet; first force applying means for keeping the transferring body in pressed contact with the image carrying body at a predetermined angle; a fixing unit for fixing the toner image transferred to the sheet by the transferring body, the fixing unit being so arranged as to be extractable substantially parallel to a paper conveying direction in order to allow jam disposal; and a transferring body separating member that, as the fixing unit is extracted, selectively takes one of a first position where the transferring body separating member separates the transferring body from the image carrying body against the force applied by the first force applying means and a second position where the transferring body separating member keeps the transferring body in pressed contact with the image carrying body.

With this construction, on the occasion of jam disposal, as the fixing unit is extracted, the transferring body is separated from the image carrying body, and thus the jammed sheet is prevented from being forcibly pulled out. This allows jam disposal without breakage of the jammed sheet, and without splashing of toner and hence without soiling of the interior and exterior of the apparatus. Moreover, this jam disposal mechanism does not require a large component. This helps avoid increasing the size of the apparatus, and allows jam disposal without requiring a wide work space.

According to the present invention, in the image forming apparatus described above, the transferring body separating member separates the transferring body from the image carrying body in a direction substantially opposite to the direction in which the first force applying means applies the force.

With this construction, the transferring body separating member allows the transferring body to move only in a predetermined direction. Thus, the introduction of the jam disposal mechanism does not impose an undue burden on the image forming apparatus.

According to the present invention, in the image forming apparatus described above, the transferring body separating member is coupled to a second force applying means that applies to the transferring body a force that causes the transferring body to tend to move apart from the image carrying body, and the force applied by the second force applying means is stronger than the force applied by the first force applying means. Here, as the fixing unit is extracted, the second force applying means makes the transferring body separating member move into the first position.

With this construction, it is possible to realize a simply constructed jam disposal mechanism by the use of force applying means.

According to the present invention, in the image forming apparatus described above, the transferring body separating member is so supported as to be rotatable about an axis parallel to the rotation axis of the transferring body. Here, the transferring body separating member is coupled to a second force applying means that applies to the transferring body separating member a force that causes the transferring body separating member to tend to move to the first position, and the force applied by the second force applying means is so set that, when the transferring body separating member moves to the first position, the moment of the force that the second force applying means applies to the transferring body separating member is greater than the moment of the force that the first force applying means applies to the transferring body separating member. As the fixing unit is extracted, the force applied by the second force applying means makes the transferring body separating member rotate to move into the first position.

With this construction, the transferring body separating member can be rotated with the force applying means. Thus, it is possible to realize a simply constructed jam disposal mechanism.

According to the present invention, in the image forming apparatus described above, the fixing unit is fitted with a rail that allows the fixing unit to be extracted. Here, when the fixing unit is not extracted, the transferring body separating member makes contact with an end of the rail so as to be held in the second position and, when the fixing unit is extracted, the transferring body separating member loses contact with the end of the rail so as to move to the first position.

With this construction, the jam disposal mechanism in which the transferring body separating member is operated as the fixing unit is extracted can be built by sharing an existing component. This helps minimize the increase in the number of components, and helps give the apparatus a simple construction.

According to the present invention, the image forming apparatus described above is further provided with: driving means for driving the transferring body separating member; detecting means for detecting whether or not the fixing unit is extracted; and a control section for controlling the driving means based on a detection signal from the detecting means. Here, based on the detection signal, the control section places the transferring body separating member selectively in one of the first and second positions.

With this construction, it is possible to realize a jam disposal mechanism in which the transferring body separating member can be operated electrically.

According to the present invention, in the image forming apparatus described above, the transferring body separating member moves to the first position while pressing part of a bracket portion supporting the transferring body.

With this construction, it is possible to provide the jam disposal mechanism without imposing an undue burden on the image forming apparatus. Moreover, it is possible to exploit an existing component and thereby to avoid an undue increase in the number of components.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. First, the image forming apparatus of a first embodiment of the invention will be described. It should be noted that such parts as are found also in the conventional image forming apparatus100(seeFIG. 8) are identified with common reference numerals, and no description thereof will be repeated unless necessary.

FIG. 1is a schematic perspective view showing the relationship among the photoconductor drum (image carrying body)2, the transfer roller (transferring body)17, and the fixing unit8in the image forming apparatus of a first embodiment of the present invention. InFIG. 1, the fixing unit8is housed inside the image forming apparatus. As shown inFIG. 1, the fixing unit8is arranged at a predetermined distance from the photoconductor drum2and the transfer roller17. Moreover, to allow the fixing unit8to be extracted out of the image forming apparatus in a direction that is substantially parallel to the paper conveying direction, the fixing unit8is fitted with a rail28. The rail28is so supported as to be slid able along a rail guide (unillustrated) provided inside the image forming apparatus.

FIG. 2is a front view of part Q indicated by a broken-line circle inFIG. 1, as seen in the direction of the transfer roller17. The photoconductor drum2and the transfer roller17are arranged perpendicular to the plane of the figure. The transfer roller17is supported on a transfer roller bracket24. To this transfer roller bracket24, a force is applied by a transfer spring (for example, a compression spring, serving as first force applying means)25. This keeps the transfer roller17pressed onto the photoconductor drum2at a predetermined angle.

Reference numeral26represents a transferring body separating member, the use of which facilitates jam disposal in the image forming apparatus. The transferring body separating member26has a shaft26aparallel to the shaft17aof the transfer roller17, and is rotatable about the shaft26a. As shown inFIG. 2, the transferring body separating member26is fitted, under the shaft26a, with a tension spring (serving as second force applying means)27, of which the other end is fixed. Thus, to the transferring body separating member26, a force is applied that causes it to tend to move rightward in the figure.

So long as the fixing unit8is housed inside the image forming apparatus, however, the rail28provided on the fixing unit8keeps contact with the transferring body separating member26, and thereby prevents the transferring body separating member26from rotating. Thus, irrespective of the force applied by the tension spring27, the transferring body separating member26remains unmovable, and an end portion26bof the transferring body separating member26is kept apart from the transfer roller bracket24.

Next, the operation of the transferring body separating member26when the fixing unit8is extracted out of the image forming apparatus will be described.FIG. 3is a schematic perspective view showing the relationship among the photoconductor drum2, the transfer roller17and the fixing unit8when the fixing unit8is extracted out of the image forming apparatus. Here, the fixing unit8has been extracted in the direction indicated by arrow C shown inFIG. 3. When the fixing unit8is extracted out of the image forming apparatus, the transferring body separating member26operates as shown inFIG. 4.

FIG. 4is a front view of part R indicated by a broken-line ellipse inFIG. 3, as seen in the direction of the axis of the transfer roller17. As a result of the fixing unit8being extracted out of the image forming apparatus, the rail28moves rightward (in the direction indicated by arrow C) in the figure. Now, the transferring body separating member26is liberated from the restriction of movement by the rail28. Thus, the force applied by the tension spring27causes the transferring body separating member26to rotate in the direction indicated by arrow D in the figure about the shaft26a. As the transferring body separating member26rotates, an end portion26bthereof hits the transfer roller bracket24and then moves it in a direction (the direction indicated by arrow E in the figure) substantially opposite to the direction in which the transfer spring25applies the force to the transfer roller bracket24.

Here, since the transfer roller bracket24receives the force applied by the transfer spring25, the force applied by the tension spring27needs to be so set that, when the transferring body separating member26rotates, the moment of the force that the tension spring27applies to the transferring body separating member26is greater than the moment of the force that the transfer spring25applies to the transferring body separating member26.

In the construction described above, when the fixing unit8is extracted out of the image forming apparatus, the photoconductor drum2and the transfer roller17are located at a predetermined distance from each other. Thus, when a paper jam is disposed of with the fixing unit8extracted, the jammed sheet is prevented from being pulled out while it is held between the photoconductor drum2and the transfer roller17. In this way, it is possible to dispose of a paper jam without breaking the jammed sheet, and without splashing the unfixed toner developed on the sheet by the transfer roller17and hence without soiling the interior of the apparatus etc.

On the other hand, when the fixing unit8is housed back inside the image forming apparatus, the transferring body separating member26is pushed by the rail28so as to be rotated, in the direction opposite to arrow D inFIG. 4, out of contact with the transfer roller bracket24. Since the transfer roller bracket24receives the force applied by the transfer spring25, it is pushed up in the direction (opposite to the direction indicated by arrow E inFIG. 4) in which it receives the applied force. This brings the transfer roller17back into contact with the photoconductor drum2, restoring the state before the fixing unit8is extracted.

In this embodiment, as the transferring body separating member26rotates, the transfer roller17is brought apart from the photoconductor drum2. This, however, is not meant as any limitation, and many modifications and variations are possible within the object of the present invention. For example, the transfer roller17may be brought apart form the photoconductor drum2without rotating the transferring body separating member26. Specifically, the image forming apparatus may be constructed, for example, as follows.

FIGS. 5A and 5Bare schematic front views showing the construction of and around the transferring body separating member26in the image forming apparatus of a second embodiment of the present invention, as seen in the direction of the axis of the transfer roller17,FIG. 5Ashowing a state in which the fixing unit8(seeFIG. 1) is not extracted out of the image forming apparatus andFIG. 5Bshowing a state in which the fixing unit8is extracted out of the image forming apparatus. In other respects, the construction here is the same as in the first embodiment, and therefore no overlapping description will be repeated.

The transferring body separating member26is fitted with a tension spring27, of which the other end is fixed to the image forming apparatus. The tension spring27applies to the transferring body separating member26a force that causes it to tend to move in a direction substantially opposite to the direction in which the transfer spring25applies the force to the transfer roller bracket24. The force applied by the tension spring27is set to be stronger than the force applied by the tension spring27. Also in this embodiment, however, as in the first embodiment, when the fixing unit8is not extracted out of the fixing unit8, the transferring body separating member26is prevented from moving by, for example, a rail28fitted to the fixing unit8. Thus, the end portion26bof the transferring body separating member26is kept apart from the transfer roller bracket24.

When the fixing unit8is extracted out of the image forming apparatus, the transferring body separating member26is liberated from the state locked by the rail28. Thus, the force applied by the tension spring27causes the transferring body separating member26to move in the direction indicated by arrow F inFIG. 5B. The end portion26bof the transferring body separating member26then hits the transfer roller bracket24and then moves it down in the direction indicated by arrow E in the figure. In this way, the transfer roller17can be brought apart from the photoconductor drum2.

In this embodiment, the transferring body separating member26is provided with a movement distance limiting mechanism29. The movement distance limiting mechanism29is composed of a limiting hole29aand a pin29bfixed to the apparatus. The movement distance limiting mechanism29serves to limit to a predetermined distance the movement distance of the transferring body separating member26, which is pulled by the force applied by the tension spring27.

The rail28, which is fitted to the fixing unit8, is shaped, in an end portion28athereof that makes contact with the transferring body separating member26, to have a predetermined slope. Thus, when the fixing unit8is housed back inside the image forming apparatus, the transferring body separating member26is pushed up along the slope of the end portion28aof the rail28so as to be brought out of contact with the transfer roller bracket24. Since the transfer roller bracket24receives the force applied by the transfer spring25, it is pushed up in the direction (opposite to the direction indicated by arrow E inFIG. 5B) in which it receives the applied force. This brings the transfer roller17back into contact with the photoconductor drum2, restoring the state before the fixing unit8is extracted.

In the embodiments described above, as a member that prevents the movement of the transferring body separating member26when the fixing unit8is housed inside the image forming apparatus, a rail28is used that is fitted to the fixing unit8. This, however, is not meant as any limitation. In the embodiments described above, as force applying means fitted to the transferring body separating member26, a tension spring is used. This, however, is not meant as any limitation. For example, a compression spring, a twist coil spring, or the like may be used instead.

The transferring body separating member26and the tension spring27may be provided at both ends of the transfer roller17, or at one end thereof. Providing the transferring body separating member26and the transfer roller17at one end, however, leads to a poor balance when the transfer roller17is brought apart from the photoconductor drum2. This imposes an undue burden on the transfer spring25or the like that applies the force to the transfer roller17, and may cause failure of the apparatus. Thus, it is preferable that the transferring body separating member26and the transfer roller17be provided at both ends.

In the first and second embodiments described above, the transfer roller17is brought apart from the photoconductor drum2by designing the transferring body separating member26to be movable by force applying means. It is however possible to adopt any other construction within the object of the present invention. For example, it is possible to adopt a construction as described below.

FIG. 6is a schematic front view showing the construction of and around the transferring body separating member26in the image forming apparatus of a third embodiment of the present invention, as seen in the direction of the axis of the transfer roller17. In this figure, the fixing unit8is housed inside the image forming apparatus. In other respects, the construction here is the same as in the first embodiment, and therefore no overlapping description will be repeated.

The transferring body separating member26is fitted with a first gear30, and the first gear30is fitted, via a second gear31, to a third gear32, which is fitted to the output spindle of a stepping motor (serving as driving means)33. When the fixing unit8is not extracted out of the image forming apparatus, the rail28, which is fitted to the fixing unit8, remains in contact with a pressure sensor (serving as detecting means)34. The stepping motor33and the pressure sensor34are connected to the control section35of the image forming apparatus.

In the image forming apparatus constructed as described above, jam disposal is performed according to the flow chart shown inFIG. 7. Now, with reference toFIG. 7, the jam disposal operation of the third embodiment will be described. At the start of jam disposal, when the fixing unit8is extracted (step S1), the pressure sensor34moves apart from the rail28. Thus, the pressure sensor34turns off, and this allows detection of the extraction of the fixing unit8(step S2).

According to a detection signal from the pressure sensor34, the control section35instructs the stepping motor33to rotate the transferring body separating member26by a predetermined among counter-clockwise (step S3). As the transferring body separating member26rotates, the transfer roller bracket24is pressed down in a direction substantially opposite to the direction in which the transfer spring25applies the force to the transfer roller bracket24. This causes the transfer roller17to be separated from the photoconductor drum2.

On the other hand, on completion of jam disposal, when the fixing unit8is housed back inside the image forming apparatus (step S4), the rail28is brought back into contact with the pressure sensor34, and thus the pressure sensor34turns on. This allows detection of the fixing unit8being housed inside the image forming apparatus (step S5). Then, according to a detection signal from the pressure sensor34, the control section35instructs the stepping motor33to rotate the transferring body separating member26to rotate clockwise by a predetermined amount (step S6). This brings the transfer roller17back into contact with the photoconductor drum2.

In this embodiment, the transferring body separating member26is driven by the use of the stepping motor33and the gears30to32. This, however, is not meant as any limitation. For example, it is also possible to adopt a construction in which the transferring body separating member26is driven by the use of, for example, a solenoid (serving as driving means). Instead of electrically driving the transferring body separating member26as in this embodiment, it is also possible to adopt a construction in which a rack is formed on the rail28fitted to the fixing unit8so that the transferring body separating member26is driven as a result of a gear30fitted thereto being rotated to follow the movement of the rack moving along with the fixing unit8.

All the embodiments described above adopt a construction in which the transferring body separating member26presses the transfer roller bracket24to move the transfer roller17. This, however, is not meant as any limitation. The transfer roller17has only to be moved as the transferring body separating member26moves, and, to achieve this, it is also possible to adopt a construction in which any part other than the transfer roller bracket24is pressed to move the transfer roller17.

The direction in which the transferring body separating member26moves the transfer roller17apart from the photoconductor drum2is not limited to the direction specifically mentioned in connection with the embodiments described above. Since, however, the transfer roller17is so restricted as to make contact with the photoconductor drum at a predetermined angle, it is preferable that, as in the embodiments, the transfer roller17be moved in a direction substantially opposite to the direction in which the transfer spring25applies the force to the transfer roller bracket24.

According to the present invention, an image forming apparatus provided with an image carrying body that carries image light shone thereat by exposing means, a transferring body that transfers a toner image formed on the image carrying body to a sheet, and a fixing unit that fixes on the sheet the image transferred thereto by the transferring body, wherein the fixing unit is extractable substantially parallel to the paper conveying direction to allow jam disposal is further provided with a transferring body separating member that, as the fixing unit is extracted, separates the transferring body from the image carrying body.

Thus, jam disposal can be performed without breaking a sheet and without splashing unfixed toner on a sheet.

By rotatably building the transferring body separating member, it is possible to simply construct the jam disposal mechanism.

The transferring body separating member may be driven by force applying means, or may be driven electrically by the use of a motor or the like.

Moreover, the jam disposal mechanism constructed as described can be built by sharing part of the components conventionally existing in an image forming apparatus. Thus, according to the present invention, an image forming apparatus can be built with a reduced number of components and with a simple construction.