Image forming apparatus

When jam occurs in one of a tandem conveyance path and bypass conveyance path, a sheet is automatically discharged from the conveyance path where no jam has occurred. A sheet retained at the upstream side with respect to a first fixing device in a sheet conveying direction is automatically discharged to the outside of an image forming apparatus by using the conveyance path where no jam has occurred. After the automatic discharging of the sheet is completed, a user is prompted to remove the jammed sheet.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus which uses electrophotography, and more particularly to an image forming apparatus such as a copying machine, a printer, or a facsimile device.

2. Description of the Related Art

An image forming apparatus discussed in Japanese Patent Application Laid-Open No. 2006-91330 includes two fixing devices installed in a conveying direction of a sheet. This image forming apparatus includes first and second conveyance paths respectively prepared as sheet conveyance paths to pass the sheet through the two fixing devices and to pass the sheet through only one of the fixing devices.

In the image forming apparatus, when jam (conveying abnormality) occurs, the burden of jam handling imposed on a user is reduced by automatically discharging a sheet (which is not in a jammed state) retained in the apparatus to the outside of the image forming apparatus. More specifically, when jam occurs in a paper feeding unit or the like other than the fixing device, a sheet retained in the first conveyance path is preferentially discharged, and then a sheet retained in the second conveyance path is discharged. Subsequently, the user carries out jam handling, in other words, removes jammed paper from the apparatus.

The aforementioned process is performed because the image forming apparatus employs a configuration in which the sheet is discharged to the outside of the image forming apparatus via a juncture position of the first and second conveyance paths. In other words, the process is performed in order to prevent jamming of the sheets respectively retained in the first and second conveyance paths at the juncture position.

However, in the image forming apparatus discussed in Japanese Patent Application Laid-Open No. 2006-91330, a solution is yet to be found to the occurrence of jam in one of the first and second conveyance paths, and hence there is room for improvement. In other words, when jam occurs in one of the first and second conveyance paths, the burden of jam handling imposed on the user needs to be reduced.

SUMMARY OF THE INVENTION

The present invention is directed to an image forming apparatus which can reduce the burden of jam handling imposed on a user when jam occurs in one of first and second paths.

DESCRIPTION OF THE EMBODIMENTS

Referring toFIG. 1, an image forming apparatus100of a first exemplary embodiment of the present invention will be described. Hereinafter, members having a configuration and performing an operation similar to previously cited members are denoted by similar reference numerals to omit description as occasion demands.

The image forming apparatus illustrated inFIG. 1includes first to fourth image forming units Pa to Pd disposed in parallel to function as image forming devices, and toner images of different colors are formed through latent-image forming, developing and transferring processes.

The image forming units Pa to Pd respectively include photosensitive drums3ato3dwhich function as image bearing members for exclusive use, and form toner images of respective colors to be charged to negative polarities on the photosensitive drums3ato3d. An intermediate transfer belt130is installed as an intermediate transfer member adjacent to the photosensitive drums3ato3d. The toner images of the respective colors formed on the photosensitive drums3ato3dare primary-transferred onto the intermediate transfer belt130, and then transferred onto a sheet P by a secondary transfer unit T2. In the sheet P to which the toner images have been transferred, the toner images are fixed by heat and pressure applied from fixing units9aand9b, and then discharged as fixed images to the outside of the image forming apparatus100. Drum chargers2ato2d, developing devices1ato1d, primary-transfer chargers24ato24d, and cleaners4ato4dare respectively disposed on outer peripheries of the photosensitive drums3ato3d. A light source device and a polygon mirror (not shown) are installed in an upper part of the image forming apparatus100.

The rotating polygon mirror performs scanning with a laser beam emitted from the light source device. Then, a reflection mirror deflects a light flux of the laser beam, and an fθ lens converges the light flux on meridian lines of the photosensitive drums3ato3dto perform exposure, thereby forming latent images on the photosensitive drums3ato3daccording to an image signal.

The developing devices1ato1dare filled with predetermined amounts of cyan, magenta, yellow, and black toners as developers by a feeding device (not shown). The developing devices1ato1drespectively develop the latent images on the photosensitive drums3ato3dto be visible as cyan, magenta, yellow, and black toner images.

The intermediate transfer belt130that functions as an image forming device is supported by a driving roller13, a secondary transfer inner roller4, and a tension roller15. The tension roller15is biased by a spring member (not shown), and predetermined tension is applied to the intermediate transfer belt. The intermediate transfer belt130is rotated and driven in an arrow direction by the driving roller13at a peripheral velocity nearly equal to those of the photosensitive drums3ato3c. The image forming apparatus100of the exemplary embodiment has a process speed of 80 mm/seconds, and can form eighty images of A4 sizes a minute.

The yellow toner image of a first color on the photosensitive drum3ais primary-transferred to an outer peripheral surface of the intermediate transfer belt130by an electric field and pressure generated by a primary transfer bias applied to the intermediate transfer belt130during passage through a nip between the photosensitive drum3aand the intermediate transfer belt130.

Similarly hereinafter, the magenta toner image of a second color, the cyan toner image of a third color, and the black toner image of a fourth color are sequentially superimposed to be transferred onto the intermediate transfer belt130, thereby forming a synthetic color image corresponding to a target color image.

A secondary transfer roller11is disposed in a position facing the secondary transfer inner roller14borne in parallel to the intermediate transfer belt130. The secondary transfer roller11is in contact with a bottom surface of the intermediate transfer belt130. A secondary transfer voltage source Ec applies to the secondary transfer roller11a secondary transfer bias of a polarity opposite to a toner charged polarity. In the exemplary embodiment, a secondary transfer voltage is +2 kv.

After arrival of the synthetic color image at the secondary transfer unit T2in which the intermediate transfer belt130and the secondary transfer roller11come into contact with each other, the synthetic color image is secondary-transferred to the sheet P as a sheet conveyed from a paper feed cassette10aor10bserving as a sheet containing device through a registration roller12and a transfer front guide constituting a sheet conveying mechanism. The image forming apparatus100of the exemplary embodiment is configured to continuously feed a plurality of sheets P from the paper feed cassette10aor10bto the secondary transfer unit T2.

An electrostatic force generated by application of the secondary transfer voltage to the secondary transfer roller11enables transfer of the synthetic color image from the intermediate transfer belt130to the sheet P.

The photosensitive drums3ato3dwhich has completed primary transfer are subjected to cleaning to remove transfer residual toners by the cleaners4ato4d, and then made ready for next latent image formation. The toners and other foreign objects left on the intermediate transfer belt130are removed by a cleaning blade19disposed to come into contact with a surface of the intermediate transfer belt130.

Various image forming devices described above concerning formation of the toner images on the sheet constitute toner image forming devices.

The sheet P that have received the toner images is guided through a tandem conveyance path71sequentially to a first fixing device9afunctioning as a first image heating device and a second fixing device9bfunctioning as a second image heating device. The toner images on the sheet P are fixed receiving heat and pressure, and then discharged as output articles via a paper discharge conveyance path79to a discharge portion73located outside the image forming apparatus100.

The sheet P heated by the first and second fixing devices9aand9bcan be conveyed, in place of being conveyed toward the discharge portion73, to a two-sided conveyance path75to be conveyed again to the secondary transfer unit T2. In addition, in the exemplary embodiment, through a bypass conveyance path72as a second path, the sheet P heated by the first fixing device9a(one of the heating devices) can be conveyed to the discharge portion73and the two-sided conveyance path75without passing through the second fixing device9b(another heating device). Switching between the tandem conveyance path71and the bypass conveyance path72is performed by a flapper69. The tandem conveyance path71and the bypass conveyance path72are combined together at a juncture position before reaching the discharge portion.

Referring toFIGS. 1 and 3, a method for conveying the sheet in each conveyance path and each paper feed cassette will be described. The tandem conveyance path71, the bypass conveyance path72, the two-sided conveyance path75, a before-fixing conveyance path76, a before-registration conveyance path77, and a paper discharge conveyance path79respectively include conveying rollers81c,81d,81j,81h,81g, and81idisposed to function as sheet conveying mechanisms. The paper feed cassettes10aand10brespectively include conveying rollers81fand81kdisposed to function as sheet conveying mechanisms. The conveying rollers81c,81d,81j,81h,81g,81i,81f, and81kare rotated and driven by conveying motors80c,80d,80j,80h,80g,80i,80f, and80k. Each rotating conveying roller comes into contact with the sheet P, thereby conveying the sheet P in each conveyance path and each paper feed cassette.

FIG. 1illustrates a state where front doors90aand90bcovering a front of the image forming apparatus100are both opened by about 120°, while image formation is performed when the doors90aand90bare closed. The doors90aand90brespectively include door sensors91aand91bdisposed to detect opened/closed states. When at least one of the doors90aand90bis open, the image formation is stopped. When jam occurs, by opening the doors90aand90b, the user can access the conveyance path of the sheet P, the first fixing device9a, the second fixing device9bor the like to carry out jam handling (removal of the jammed sheet from the apparatus).

The jam means abnormality in conveying the sheet, in other words, a situation or a phenomenon where conveyance of the sheet, i.e., an image forming job, needs to be interrupted due to inappropriate conveyance of the recoding material through the conveyance path. Thus, the occurrence of jam necessitates removal of all the sheets retained in the image forming apparatus. After removable of all the retained sheets from the image forming apparatus, the interrupted image forming job can be resumed.

As illustrated inFIG. 2, a controller141is disposed to control an operation of the image forming apparatus100. The controller141that functions as a controller includes a CPU and a ROM for storing a control program, and controls operations of the image forming units Pa to Pd, the fixing motors80aand80b, the power sources Ea to Ec, and the conveying motors80cto80jbased on information from sheet detection sensors74ato74m, thermistors THa and THb, and an operation unit143. The sheet detection sensors74ato74m, the thermistors THa and THb, the operation unit153, the fixing motors80aand80b, the power sources Ea and Eb, and the conveying motors80cto80jwill be described below.

Next, referring toFIG. 3, the first and second fixing devices9aand9bemployed by the embodiment will be described in detail.

The first and second fixing devices9aand9bare arrayed in series on the conveying path of the sheet P.

The first and second fixing devices9aand9bare similar in hardware configuration except for temperature control described below. Hence, subscripts to discriminate both from each other are omitted and configurations of the first and second fixing devices9aand9bwill be described.

Each of the first and second fixing devices9aand9bincludes a fixing roller51and a pressure roller52rotatably disposed to make a pair. The first and second fixing devices9aand9bare pressurized to form fixing nips, i.e., first and second nips, for passing the sheet P.

The fixing roller51of the present exemplary embodiment is configured in such a manner that a silicon rubber elastic layer having a thickness of 4 mm is placed on an Fe cylindrical core metal having an outer diameter of φ72 mm and an uppermost part is covered with a PFA tube having a thickness of 30 μm as a discrete layer.

The pressure roller52is configured in such a manner that a silicon rubber elastic layer having a thickness of 2.0 mm is placed on an Fe cylindrical core metal having an outer diameter of φ76 mm and an uppermost part is covered with a PFA tube having a thickness of 30 μm as a discrete layer. The pressure roller52is pressurized to the fixing roller51at total pressure of about 50 kgf, and driven and rotated by the pressure roller52driven by the fixing motor80. In the fixing device of the exemplary embodiment, a fixing nip width is about 10 mm during pressurization.

A heater53such as a halogen heater is disposed in the fixing roller51. Based on temperature information of the thermistor TH for detecting a temperature of the fixing roller51, the controller141adjusts power supplied from the power source E to the heater53to maintain the fixing roller51at a predetermined temperature.

Though not disposed in the exemplary embodiment, a similar heater may be installed in the pressure roller52.

In the exemplary embodiment, the fixing devices9aand9bare both roller-type fixing devices. However, one or both of fixing members facing each other may be belt-type fixing devices in which endless belts and pressure members form fixing nips. In the exemplary embodiment, the fixing devices9aand9bsimilar in configuration are used. However, fixing devices different from each other in configuration, for example, a roller-type fixing device and a belt-type fixing device, or a combination of roller-type fixing devices different in configuration, or a combination of belt-type fixing devices different in configuration, may be used.

In the image forming apparatus100, a cardboard mode for forming an image on a cardboard (150 g/m2or more) and a plain paper mode for forming an image on plain paper (less than 150 g/m2) are executable. The user can select one of the cardboard mode and the plain paper mode by operating the operation unit143illustrated inFIG. 7.

When the cardboard mode is selected, a sheet P which is a cardboard is conveyed from the paper feed cassette10ato the secondary transfer unit T2, and a synthetic color toner image is secondary-transferred from the intermediate transfer belt130to the sheet P. Subsequently, the sheet P is conveyed to the first fixing device9ato heat the synthetic color toner image. The sheet P which has passed through the first fixing device9ais guided to the tandem conveyance path71by the flapper60located in a position A indicated by a solid line inFIG. 3, and conveyed to the discharge portion73after the synthetic toner image is heated again by the second fixing device9b. In order to form an image on the backside of the sheet P, the sheet P which has passed through the second fixing device9bis conveyed to the two-sided conveyance path75.

On the other hand, when the plain paper mode is selected, a synthetic color toner image is secondary-transferred by the secondary transfer unit T2from the paper feed cassette10bto a sheet P which is plain paper. Then, the sheet P is guided to the bypass conveyance path72by the flapper60located in a position B indicated by a broken line inFIG. 3, and conveyed to the discharge portion73bypassing the second fixing device9b. In the plain paper mode, as in the case of the cardboard mode, in order to form an image on the backside of the sheet P, the sheet P is conveyed through the bypass conveyance path72to the two-sided conveyance path75.

Referring to Table 1 below, temperature control of the fixing rollers51aand51bof the first and second fixing devices9aand9bin both of the aforementioned modes will be described.

As illustrated in Table 1, when the cardboard mode is executed, power distribution to the heaters is controlled so that the fixing rollers51aand51bof the first and second fixing devices can both be set at 180°. On the other hand, when the plain paper mode is executed, the fixing roller51aof the first fixing device9ais controlled to be at 180°, while the fixing roller51bof the second fixing device9bwhich makes no contribution to fixing is controlled to be at a temperature lower than that in the cardboard mode. In the exemplary embodiment, in the plain paper mode, power distribution to the heater is controlled so that the fixing roller51bof the second fixing device9bcan be set to 150°.

Thus, the two fixing devices9aand9band the bypass conveyance path72are provided so that an amount of heat applied to the sheet P can be controlled. Accordingly, various sheets P can be dealt with.

Next, a method for detecting the sheet P in the fixing device and the conveyance path will be described.

In the exemplary embodiment, as illustrated inFIG. 3, each of the tandem conveyance path71and the bypass conveyance path72includes two sheet detection sensors as detecting devices. In the tandem conveyance path71, one sheet detection sensor74bis disposed in the conveyance path, and another sheet detection sensor74cis disposed in a discharge port of the fixing device9b. In the bypass conveyance path72, two sheet detection sensors74dand74eare disposed.

The fixing devices9aand9brespectively include sheet detection sensors74aand74bin discharge ports. The sheet detection sensor74ais provided in the discharge port of the fixing device9a, the sheet detection sensor74bis provided in the discharge port of the fixing device9b, and sheet detection sensors74fand74mare provided in a paper feeding unit78. A sheet detection sensor74gis provided in the before-registration conveyance path77, a sheet detection sensor74his provided in the before-fixing conveyance path76, and sheet detection sensors74j,74kand74lare provided in the two-sided conveyance path75.

The exemplary embodiment uses a sheet detection sensor which converts presence of a sheet P into an electric signal to detect the material. In this sensor, a flag is pressed by deadweight of the conveyed sheet P and an optical axis of a transmissive photointerrupter sensor is blocked to shield light. The main body controller141manages sheet presence information from all the sheet detection sensors of the image forming apparatus100to determine the occurrence of jam. More specifically, if there is deviation from an ON-OFF chart calculated from a set size and a conveying speed in the conveying direction of the sheet P for a fixed period of time or more, the occurrence of jam is determined. In other words, delay jam is determined when a leading edge of sheet does not turn ON the sheet detection sensor at an ON-timing. Similarly, retention jam is determined when a trailing edge of sheet does not turn OFF the sheet detection sensor at an OFF-timing. For example, when winding jam occurs at the discharge port of the second fixing device9b, the sheet detection sensor74cis not turned ON at a predetermined timing, and hence the main body controller141determines delay jam.

Upon detecting jam in the tandem conveyance path71or the bypass conveyance path72, the main body controller141immediately controls the conveying motor80cor80dto stop the conveying operation of the sheet on the conveyance path where the jam has occurred. Subsequently, the main body controller141switches the flapper69to automatically discharge the sheet on a side upstream of a branching position70of the tandem conveyance path71and the bypass conveyance path72in the conveying direction of the sheet, and then stops the operation of the image forming apparatus100. The main body controller141displays (informs) the occurrence of jam, its occurrence position, and its processing method on a display unit142functioning as an informing device to prompt the user to carry out jam handling. Referring to a flowchart below, a procedure of the automatic discharge operation will be described in detail.

Referring to a flowchart ofFIG. 4, the automatic discharge operation at the time of the occurrence of jam which is a gist of the present invention will be described. Operations of all the devices in the apparatus in the flowchart are controlled, determined or executed by the main body controller141.

First, in step S1, at the time of completion of temperature control of the fixing devices9aand9bor an image forming preparation operation such as toner stirring operations in the developing devices1ato1d, a standby state is set to wait for image formation. In step S2, when an operation such as pressing of a copy button is performed to start an image forming operation, the main body controller141starts the image forming operations of the aforementioned image forming units Pa to Pd. The main body controller141adjusts, according to a mode selected by the user, outputs of the power sources Ea and Eb so that the fixing rollers51aand51bof the fixing devices9aand9bcan be set to the temperatures illustrated in Table 1. Further, the main body controller141controls rotations of the conveying rollers81cand81dof the tandem and bypass conveyance paths71and72according to the selected mode.

In other words, when the “cardboard mode” is selected, the conveying roller81cof the tandem conveyance path71is rotated, while rotation of the conveying roller81dof the bypass conveyance path72is stopped. On the other hand, when the “plain paper mode” is selected, rotation of the conveying roller81cof the tandem conveyance path71is stopped, while the conveying roller81dof the bypass conveyance path72is rotated. Even if the “plain paper mode” is selected, the fixing roller51bof the second fixing device9bis rotated to maintain a predetermined temperature.

Conveyance of the sheet P from the paper feed cassette10aor10bis started in synchronization with timing of conveying the synthetic color toner image from the intermediate transfer belt130to the secondary-transfer unit T2.

In step S3, from this point of time, the main body controller141obtains detection information from all the sheet detection sensors in the image forming apparatus100to monitor an occurrence of jam of the sheet P. When the image forming operation is finished without any jam, and all sheets P having images formed thereon are discharged to the discharge portion73, in step S13, processing in the flowchart is completed.

If jam occurs, in step S4, the main body controller141determines whether there is any sheet P in the branching position70where the path branches into the tandem conveyance path71and the bypass conveyance path72(refer toFIG. 3). More specifically, the main body controller141makes the determination based on history of a detection signal from the sheet detection sensor74aset in the discharge port of the fixing device9a. In the exemplary embodiment, a distance of a sheet conveyance path from the sheet detection sensor74ato the branching position70is 38 mm, and a conveying speed is 380 mm/second, and hence it takes 0.1 second for the sheet P to pass therebetween. Thus, the main body controller141determines that there is a sheet P in the branching position70if 0.1 second or more has passed after switching of the detection signal from the recording detection sensor74ato an “ON signal” or if 0.1 second is yet to pass after switching to an “OFF signal”. If the main body controller141determines that there is a sheet Pin the branching position70, an automatic discharge operation of a residual sheet P is inhibited, and hence the process proceeds to step S10.

On the other hand, if there is no sheet P in the branching position70, in step S5, the main body controller141checks a jam-occurrence position of the sheet P. If the jam-occurrence position is in any one of the sheet detection sensors74band74cof the tandem conveyance path71or the sheet detection sensors74dand74eof the bypass conveyance path72, the process proceeds to step S6to automatically discharge the sheet retained in the apparatus.

On the other hand, if jam occurs in a position other than the aforementioned position, i.e., one of the paper feeding unit78, the before-registration conveyance path77, the before-fixing conveyance path76, the fixing device9a, the paper discharge conveyance path79, and the two-sided conveyance path75, a sheet P left on a side upstream of the jam-occurrence position cannot be automatically discharged, and hence no automatic discharging is carried out. In other words, when jam occurs in any one of the sheet detection sensors74f,74g,74h,74a,74i,74j,74k,74l, and74m, no automatic discharge operation is performed. Thus, in this case, the process advances to step S10. The main body controller141immediately controls rotations of all the conveying motors in the image forming apparatus100to stop rotations of the conveying rollers and displays the jam-occurrence position and its processing method on the display unit142functioning as the informing device to stand by. In other words, the main body controller141interrupts the image forming job to inform the user about jam handling. The jam handling may also be informed to a host computer connected to the image forming apparatus via a network. In other words, the controller141functioning also as the informing device may be configured to perform overall control so that information contents can be displayed on a monitor connected to the host computer.

If the jam-occurrence position is in one of the tandem and bypass conveyance paths71and72, in step S6, in order to perform automatic discharging, the main body controller141controls the conveying motor to stop rotation of the conveying roller in the conveyance path where the jam has occurred, and then switches the flapper69.

For example, when the sheet P conveyed to the fixing device9bis wound on the fixing roller during execution of the cardboard mode and the jam occurs, delay jam of the sheet detection sensor74cis determined. In this case, a jam-occurrence position is within the tandem conveyance path71. Then, the main body controller141issues a stop signal to the conveying motor80cand the fixing motor80bto stop rotation of the conveying roller81cin the tandem conveyance path71. The main body controller141switches the flapper69to feed the sheet P to the bypass conveyance path72, and rotates the conveying roller81din the bypass conveyance path72.

As a result, the sheet left in the bypass conveyance path72is discharged to the discharge portion73outside the image forming apparatus.

Similarly, when jam occurs in the bypass conveyance path72during execution of the plain paper mode, the main body controller141issues a stop signal to the conveying motor80dto stop rotation of the conveying roller81din the bypass conveyance path72. Then, the main body controller141switches the flapper69to feed the sheet P to the tandem conveyance path72, and rotates the conveying roller81cin the tandem conveyance path71.

As a result, the sheet left in the tandem conveyance path71is discharged to the discharge portion73outside the image forming apparatus.

If a sheet P is determined to be present on a conveyance path upstream of the branching position70in step S7, in step S8, the main body controller141controls the conveying motor to feed the residual sheet P to the discharge portion73via the bypass conveyance path72, thereby performing an automatic discharge operation. When the sheet P is present on the conveyance path upstream of the branching position at the time of the occurrence of jam, the main body controller141obtains ON signals from the sheet detection sensors74a,74f,74g,74h,74j,74k,74l, and74minstalled in the fixing device9a, the before-fixing device conveyance path76, the before-registration conveyance path77, the paper feeding unit78, and the two-sided conveyance path75.

In this case, when sheets P are left in all the sheet detection sensors74a,74f,74g,74h,74j,74k,74m, and74n, the main body controller141only needs to control the conveying and fixing motors so that all the conveying and fixing rollers in the apparatus can rotate. However, if sheets P are left only in the sheet detection sensors74aand74hof the fixing device9aand the before-fixing conveyance path76, the main body controller141is not required to operate all the conveying and fixing motors. In this case, the main body controller141selectively operates only the fixing motor80afor rotating the fixing roller51aof the fixing device9a, the conveying motor80hfor rotating the conveying roller81hof the before-fixing conveyance path76, and the conveying motors80dand80inecessary for conveying the residual sheet P to the discharge portion73. Thus, the main body controller141performs control to operate only the conveying and fixing rollers necessary for conveying the residual sheet of the most upstream side when jam occurs, thereby executing an automatic discharge operation.

The main body controller141performs control so as to prevent overlapping of a sheet left in the tandem conveyance path71or the bypass conveyance path72used for automatic discharging, with a sheet left on the sheet conveying-direction on a side upstream of the fixing device9a(first nip, branching position) in the conveyance path used for automatic discharging. In other words, the main body controller141controls each conveying mechanism so that the sheet left in the conveyance path used for automatic discharging can be discharged prior to the sheet left on the upstream side of the fixing device9ain a sheet conveying direction.

At the time of the occurrence of jam, the intermediate transfer belt130bears a synthetic toner image. In order to prevent sticking of a toner on the sheet P, which is conveyed through the secondary transfer unit T2to the discharge portion73after the occurrence of jam, the main body controller141switches a voltage applied to the secondary transfer roller11when the jam occurs, to a voltage of a same polarity as that of the toner.

In the exemplary embodiment, a voltage of −1 KV is applied to the secondary transfer roller11during the automatic discharge operation.

An unfixed toner image on the sheet P left in the before-fixing conveyance path76is fixed (heated) by the fixing device9a, and hence the inside of the apparatus or user's hands are not stained even if the automatic discharge operation is carried out. So far, the jam in the tandem conveyance path71has been cited as an example. However, even if jam occurs in the bypass conveyance path72, automatic discharging can similarly be carried out by switching the flapper69to the tandem conveyance path71side.

In step S10, after completion of all the automatic discharge operations, the apparatus stops its operation, and displays the occurrence of jam and its handling method on the display unit142to inform the user about jam handling, and stands by. More specifically, for example, when jam occurs in the fixing device9b, the main body controller141performs control to display “open the front door to draw the fixing device9b, and remove jammed paper” on the display unit142, thereby prompting the user to remove the jammed paper.

The front doors90aand90bof the apparatus are always required to be opened so that the user can carry out work of drawing the fixing device9b. Thus, in step S11, the main body controller141investigates presence of jammed paper at the time of checking whether the front doors90aand90bhave been opened and then closed again, based on detection information from the door sensors91aand91billustrated inFIG. 1.

In this case, if a detection result which the main body controller141obtains from the sheet detection sensor74bof the fixing device9b, changes to an “OFF signal”, its means that the jammed paper has been removed, and hence the main body controller141determines that the jam handling has been completed and resets a jam error state. Then, in step S12, after an apparatus recovery operation such as a fixing device temperature readjustment is performed, the main body controller141resumes the interrupted image formation. The main body controller141returns to step S3at the time of restarting the conveyance of the sheet P to continue monitoring of an occurrence of jam again.

According to the aforementioned flowchart, the automatic discharge operation is executed at the time of the occurrence of jam, and the number of sheets to be removed from the apparatus by the user (operator) can be reduced to a minimum. As a result, usability can be improved.

Referring to a flowchart ofFIG. 5, an image forming apparatus according to a second exemplary embodiment of the present invention will be described. Description of items similar to those of the first exemplary embodiment is omitted, and members identical to previously cited members are denoted by identical reference numerals.

In the present exemplary embodiment, when the jam occurs in one of tandem and bypass conveyance paths71and72, after a sheet P left on a side upstream of a branching position70is automatically discharged, a dischargeable sheet P left in the conveyance path where the jam has occurred is also automatically discharged.

The image forming apparatus will be described by taking an example where there is a plurality of sheets P left within the tandem conveyance path71after the flowchart (step S8) of the first exemplary embodiment illustrated inFIG. 4is performed, and the sheets P are present on a side upstream of a jam-occurrence position in a sheet conveying direction.

The sheet P left on the side upstream of the jam-occurrence position and on the side downstream of a branching position70is first conveyed (moved back) in a reverse direction to be fed to a fixing device9aon the upstream side of the branching position70. Then, in step S9ofFIG. 5, a flapper69is switched to convey the sheet P forward through the bypass conveyance path72, thereby automatically discharging the sheet P.

The processing will be described by using the example cited in the first exemplary embodiment again. When winding jam occurs in a discharge port of a fixing device9b(delay jam in a position of a sheet detection sensor74c), conveyance in the tandem conveyance path71is first stopped to discharge the sheet P on the side upstream of the branching position70. Then, a main body controller141controls a conveying motor80c, a fixing motor80aand the flapper69to feed an undamaged sheet P left on a sheet detection sensor74bto the bypass conveyance path72in a switch-back manner, thereby enabling automatic discharging.

Thus, regarding the occurrence of jam in the tandem conveyance path71, for example, when the jam occurs in the fixing device9b, a sheet P can be automatically discharged from the tandem conveyance path71in addition to the sheet P left on the upstream side of the branching position. This configuration requires a user only to handle the jam in the fixing device9b, thus jam handling time can greatly shortened.

Referring toFIG. 6, an image forming apparatus according to a third exemplary embodiment of the present invention will be described. Description of items similar to those of the first and second exemplary embodiments is omitted, and members identical to previously cited members are denoted by identical reference numerals.

The third exemplary embodiment is different from the first exemplary embodiment illustrated inFIG. 1in that the image forming apparatus includes a bypass conveyance path72bypassing a first fixing device9a.

With this configuration, as in the case of the first and second exemplary embodiments, using a conveyance path where no jam occurs at the time of an occurrence of jam in one of tandem and bypass conveyance paths71and72, a sheet P left in the apparatus can be automatically discharged.

Recording materials P discharged to a discharge portion73by an automatic discharge operation all pass through a second fixing device9b, and hence the inside of the apparatus or user's hands are not stained by an unfixed toner image.

Even in the sectional configuration of the third exemplary embodiment illustrated inFIG. 6, as in the case of the first and second exemplary embodiments, recovery time after jam handling can be shortened, thus usability can be improved.

In each of the first to third exemplary embodiments, the color printer has been cited as the image forming apparatus. However, the image forming apparatus is not limited to the color printer. For example, a copying machine, a facsimile machine or the like may be used as an image forming apparatus. Each of the first to third exemplary embodiments has been described by way of the tandem fixing system where the two fixing devices are arrayed in series on the conveyance path as a plurality of fixing devices. However, the image forming apparatus may include three or more fixing devices.

Each of the first to third exemplary embodiments employs the configuration where the bypass conveyance path bypassing one of the two fixing devices merges onto the tandem conveyance path. However, the configuration is not limited to this type. The present invention can similarly be applied to the following configuration. More specifically, a tandem conveyance path passing through two fixing devices and a single conveyance path passing through only one of the two fixing devices may be provided, and a sheet may be conveyed and discharged through these two conveyance paths to the outside of the image forming apparatus without merging the two conveyance paths together on the downstream side in the sheet conveying direction. In this case, the discharge portion73is disposed in each of the tandem and single conveyance paths, and the sheet is directly discharged through the tandem conveyance path or the single conveyance path to the outside of the image forming apparatus.

As in the case of an image forming apparatus according to another exemplary embodiment of the present invention illustrated inFIG. 8, the present invention can be applied to an image forming apparatus which includes a conveyance path92passing through a first fixing device9abut bypassing a second fixing device9band a conveyance path93passing through the second fixing device9bbut bypassing the first fixing device9a.

Thus, by employing the configuration of the exemplary embodiment, the number of jammed sheets handled by a user can be decreased as much as possible, and the time and labor of jam handling imposed on the user can be reduced. As a result, the time necessary for the jam handling by the user can be shortened as much as possible, and a highly usable image forming apparatus can be provided. In other words, an interrupted image forming job can be recovered early.

This application claims priority from Japanese Patent Application No. 2008-289999 filed Nov. 12, 2008, which is hereby incorporated by reference herein in its entirety.