Image forming apparatus and image forming method

An image forming apparatus includes an image carrier, a transfer roller, a transfer roller position detector and a controller. The transfer roller includes a concaved portion formed on a circumferential surface thereof with the concaved portion having a width in the circumferential direction larger than a width of a transfer nip formation area formed between the image carrier and the transfer roller in the circumferential direction. The transfer roller includes an elastic member disposed on the circumferential surface thereof. The transfer roller position detector is configured and arranged to detect a rotational position of the transfer roller. The controller is configured to stop rotation of the transfer roller in a state in which the concaved portion is located at the transfer nip formation area on the basis of the rotational position of the transfer roller.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No. 2009-160668 filed on Jul. 7, 2009. The entire disclosure of Japanese Patent Application No. 2009-160668 is hereby incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to an electro photographic type image forming apparatus and an image forming method to transfer a toner image onto access transfer material such as paper, and to form an image onto the transfer material using a transfer roller having an elastic member on its circumferential surface.

2. Related Art

In the related art, as an electro photographic type image forming apparatus, the image forming apparatus is suggested in which a transfer material gripping member is installed on a transfer roller, and a leading edge of the transfer material is pinched by the gripping member and transfers the toner image of the image carrier to the transfer material such as paper (for example, refer to JP-A-2000-508280). With the image forming apparatus, it is possible to reliably separate the transfer material from the image carrier after the transferring operation completed.

Additionally, another image forming apparatus is suggested in which a transfer roller having an elastic member on the surface thereof presses onto the image carrier to form a transfer nip, and a toner image of the image carrier is transferred onto the transfer material by applying a transfer bias to the transfer roller (for example, JP-A-2009-36943).

SUMMARY

In the image forming apparatus described in JP-A-2009-36943, the transfer roller press-contacts the image carrier constantly. Therefore, the long-term pressure between the transfer roller and the image carrier causes the elastic member of the transfer roller to be deformed. When the elastic member of the transfer roller is deformed, banding or defects in the image are caused in the deformed portion, and the quality of the image is degraded.

An advantage of some aspects of the invention is to provide the image forming apparatus and the image forming method capable of performing a better image transfer and reliably separating the transfer material from the transfer roller.

According to one aspect of invention, there is provided an image forming apparatus and the image forming method. An elastic member is installed in the circumferential surface of the transfer roller having a concaved portion, along with which a transfer nip formation area is formed where the transfer roller is pressed against the image carrier when the image is transferred. In this case, the width of the concaved portion is larger than the width of the transfer nip formation area in the circumferential direction of the transfer roller. The transfer roller is stopped when the concaved portion is in the transfer nip formation area, so as not to have contact between the transfer roller and the image carrier when the image is not transferred. Thus, the transfer nip is not formed in the transfer nip formation area between the transfer roller and the image carrier when the image forming operation of the image forming apparatus is not performed. Accordingly, the elastic member of the transfer roller is not twisted, even when the image forming apparatus is not operated for a long time. Thus, the image defect and the occurrence of the banding caused by the twisting of the elastic member are suppressed effectively and a higher quality image can be obtained.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention will now be described in terms of the explanatory embodiment with reference to the accompanying drawings.

FIG. 1is a schematic and partial diagram showing the image forming apparatus according to the first embodiment of the invention.

The image forming apparatus1of the first embodiment forms an image using a liquid developer including toner particles and transfer liquid. As shown inFIG. 1, the image forming apparatus1includes photosensitive bodies2Y,2M,2C and2K arranged horizontally, or in tandem nearly horizontally. Here,2Y is a yellow photosensitive body,2M is a magenta photosensitive body,2C is a cyan photosensitive body and2K is a black photosensitive body. As used herein, other parts of the image forming apparatus are provided with the letters Y, M, C and K at the end of reference numbers to respectively indicate the corresponding colors of yellow, magenta, cyan and black.

Each of the charging sections3Y,3M,3C and3K is installed around the photosensitive bodies2Y,2M,2C and2K, respectively. Exposure sections4Y,4M,4C and4K which are the image writing sections, developing sections5Y,5M,5C and5K, first transfer sections6Y,6M,6C and6K, and the photosensitive bodies cleaning sections7Y,7M,7C and7K are installed in this order in the rotational direction α of the photosensitive bodies2Y,2M,2C and2K from each of the charging sections3Y,3M,3C and3K.

Also, the image forming apparatus1includes a transfer belt, more specifically, an endless shaped intermediate transfer belt8. The intermediate transfer belt8preferably constitutes an image carrier of the first embodiment. The intermediate transfer belt8is positioned above each of the photosensitive bodies2Y,2M,2C and2K. The intermediate transfer belt8is press-contacted to each of the photosensitive bodies2Y,2M,2C and2K with a first transfer section6Y,6M,6C and6K, respectively.

Although it is not shown in the drawings, the intermediate transfer belt8is preferably formed by 3 layered structure which is made by a relatively soft elastic belt, including a flexible substrate for example resin, an elastic layer, for example, rubber layer, formed on the surface of the substrate, and an outer layer formed on the surface of the elastic layer. As an embodiment of the intermediate transfer belt8, for example, the intermediate transfer belt disclosed in JP-A-2009-36943 can be employed. The description of the intermediate transfer belt described in JP-A-2009-36943 is omitted because the intermediate transfer belt can be understood from the description therein. Of course, the intermediate transfer belt8is not limited to the belt described in JP-A-2009-36943. The intermediate transfer belt8is located tightly between the intermediate transfer belt driving roller9and the intermediate transfer belt tension roller10. The intermediate transfer belt driving roller9is driven by the intermediate transfer belt driving motor (not shown). The intermediate transfer belt8is rotated in a rotational moving direction β, in a tensioned state.

Also, the location order of the photosensitive bodies corresponding to each of the colors Y, M, C and K is not limited toFIG. 1and may be arranged arbitrarily.

A second transfer section11which is a transfer apparatus, is installed on the intermediate transfer belt driving roller9side of the intermediate transfer belt8. The second transfer section11includes a second transfer roller12and a second transfer cleaning section13.

As shown inFIG. 1andFIG. 2A, the second transfer roller12includes a substrate having a concaved portion14which is formed on the peripheral (circumferential) surface of the substrate12aand extending to the axial direction of second transfer roller12. The second transfer roller12further includes an elastic member12bwhich is formed with a sheet type elastic layer, for example, rubber which is wound on the peripheral surface of a circular section of the substrate12a, except for the concaved portion14. In this case, both ends of the elastic member12bare fixed on the side walls of the concaved portion14though it is not shown in the drawings. Also, the length of the elastic member12bwhich is located on the circular shaped outer peripheral surface of the second transfer roller12as measured in a circumferential direction of the transfer roller12is set to be longer than a maximum size of a transfer material19used in the image forming apparatus1as measured in a moving direction of the transfer material19. A resist layer is formed with the elastic member12bon the peripheral surface of the circular section of the second transfer roller12. As the elastic member12b, an elastic material which is used in an elastic layer known in the related art such as the intermediate transfer belt of the image forming apparatus, can be used (for example, the elastic layer such as urethane of the intermediate transfer belt8as described in JP-A-2009-36943).

Further, the elastic member12bof the second transfer roller12is press-contacted to the intermediate transfer belt8by bias force of a bias member like spring, not shown in the drawings. Accordingly, the second transfer nip11ais formed in a transfer nip formation area between the intermediate transfer belt8and the elastic member12bof the second transfer roller12, as shown inFIG. 1. At this time, the intermediate transfer belt driving roller9functions as a backup roller against the pressure of the second transfer roller12.

As shown inFIG. 2B, a straight width w1of the concaved portion14in the peripheral (circumferential) direction of the second transfer roller (the transfer material19moving direction on the second transfer nip11aposition) is set wider than width w2in the same direction of the transfer nip formation area where the second transfer nip11ais formed (w1>w2). Hereinafter, a measurement method of the nip width w2will be described. First of all, two liquid curable silicon rubbers for the template are coated on the portion where the nip is formed for the measurement of the second transfer roller12. Next, the two liquid curable silicon rubbers of the second transfer roller12are pressed to the belt driving roller9of the second transfer roller12with a constant pressure, which forms a concaved portion with the two liquid curable silicon rubbers. As the two liquid curable silicon rubbers, EXAFINE (injection type; available from GC Corporation) can be used in this embodiment. Further, after curing the two liquid curable silicon rubbers, the width of the nip forming section which is the thin film portion of the concaved portion is measured using the vernier calipers. The width of the measured nip forming section is the nip width w2.

Further, the transfer bias is applied to the second transfer roller12. During the image forming operation, the second transfer roller12is rotated in the rotational direction β, and at the same time the transfer bias is applied when the second transfer roller12is moved to the moving direction β of the intermediate transfer belt8, so that the toner image which is transferred to the intermediate transfer belt8with the transfer nip11ais transferred to the transfer material like paper.

The gripper15which is a gripping member to pinch the transfer material, the gripper support member16which is an access receiving member receiving the gripper and seated by the gripper15, and a separating click17which is a member for separating the transfer material, are installed in the concaved portion14. Although not shown in the drawings, the gripper15is installed in a predetermined number along the axial direction of the second transfer roller12, and each gripper15is formed in a shape of the teeth of a comb. Also, the gripper support member16is installed on the corresponding position of each gripper15and the separating click17is installed between the comb teeth, and at the outside of the comb teeth, which is located at both ends of the gripper15.

Further, the image forming apparatus1has a gate roller18which transports the transfer material toward the second transfer nip11a. Also, the gate roller18supplies the transfer material19to the second transfer nip11aat such a timing that the toner image which is transported by the second transfer belt8is secondarily transferred at the second transfer section11.

The gripper15is rotated toward the gripper support member16just before the concaved portion14reaches to the second transfer nip11a, so that the gripper15pinches the leading edge19aof the transfer material19, which is transported toward the direction of the transportation direction δ from the gate roller18, with the gripper support member16. In the state in which the gripper15pinches the leading edge19aof the transfer material19, the toner image which is carried on the intermediate transfer belt8, is transferred onto the transfer material19at the second transfer nip11a. Further, in the state in which the gripper15pinches the leading edge19aof the transfer material19, the transfer material19which is passed through the second transfer nip11a, is reliably separated from the intermediate transfer belt8forming the second transfer nip11a. Then, the leading edge19aof the transfer material19is released rotating toward the separating direction from the gripper support member16. Also, before and after the release of the transfer material19by the gripper15, each separating click17is projected to its projection position. Accordingly, the back surface of the leading edge of the transfer material19(the opposite surface of the toner image transfer surface of the transfer material) is projected from each separating click17. In this way, the transfer material19is separated from the transfer roller12. Then, each separating click17returns within the concaved portion14. Each operation of the gripper15and the separating click17is controlled by the gripper control cam and the separating click control cam which are not shown in the drawings, by the rotation of the second transfer roller12.

As shown in theFIG. 3B, the intermediate transfer belt driving roller9and the second transfer roller12are rotated by one common intermediate transfer belt/second transfer roller driving motor20. In other words, the driving force of the intermediate transfer belt/second transfer roller driving motor20is delivered to the intermediate transfer belt driving roller9, so that the intermediate transfer belt driving roller9is rotated counterclockwise in an arrow when viewed in a direction shown inFIG. 3A. Further, the driving force of the intermediate transfer belt/second transfer roller driving motor20is delivered to the second transfer roller12through the intermediate gear21, which is installed on the shaft9aof the intermediate transfer belt driving roller9to be integrally rotatable with the shaft9a, and the second transfer roller driving gear22, which is installed on shaft12cof the second transfer roller12to be integrally rotatable with the shaft12c. Accordingly, the second transfer roller12is rotated clockwise in the direction γ when viewed in a direction inFIG. 3A.

As shown inFIG. 1, a photo sensor23and a cam24for the photo sensor23are installed at the end of the second transfer roller12. The photo sensor23is the second transfer roller position detector (corresponding to the transfer roller position detector) for detecting the rotational position of the second transfer roller12. The cam24for photo sensor23is located near the photo sensor23. The cam24for the photo sensor23has a circular plate having a notch24a, and is integrally installed to the second transfer roller12so as to be rotatable with the shaft12cof the second transfer roller12. Those which are well known in the related art can be used for the photo sensor23and the cam24for the photo sensor23. Also, the photo sensor23detects the rotational position of the notch24aof the cam24, so that it detects the position of the second transfer roller12to output the second transfer roller position signal (ON signal) having a pulse shape.

In this case, the concaved portion14is integrally installed to be rotatable with the second transfer roller12, so that relative position between the rotational position of the second transfer roller12and the rotational position of the concaved portion14is not changed, and both rotational positions are determined at once. Accordingly, the second transfer roller position signal which is output by the photo sensor23is the signal of the position of the concaved portion14, and the photo sensor23and the cam24constitute the position detector of the concaved portion14which detects the rotational position of the concaved portion14. In this case, when the photo sensor23outputs one of the second transfer roller position signals (ON signal), the second transfer roller position signal maintains an OFF signal until it newly detects the position of the concaved portion14and outputs the next second transfer roller position signals (ON signal).

As shown inFIG. 2A, the center of a notch detector23aof the photo sensor23is arranged on the imaginary straight line ε which connects the center of the rotational shaft9aof the intermediate transfer belt driving roller9to the center of the rotational shaft12cof the second transfer roller12, so that it is attached on the apparatus body, for example. Also, the circumferential center of the notch24ais arranged on the imaginary straight line ζ which connects the circumferential center of the concaved portion14to the center of the rotational shaft12c. Accordingly, the concaved portion14is positioned on the second transfer nip11awhen the notch detector23aof the photo sensor23detects the notch24aand outputs the second transfer roller position signal (ON signal).

As shown inFIGS. 3A and 3B, the partial circular shape outer surface25aof the contact member25having a fan-shape substantially on the side of the second transfer roller12is integrally installed on the rotational shaft12cto be rotatable with the second transfer roller12at a position corresponding to the concaved portion14. A circular shape contact member26on the side of the intermediate transfer belt8is installed on the rotational shaft9aof the intermediate transfer belt driving roller9to be unmovable to the axial direction of the rotational shaft9aand relatively rotatable with respect to the rotational shaft9a. When the concaved portion14is positioned on the second transfer nip11a, the partial circular shape outer surface25aof the contact member25on the side of the second transfer roller12is contacted with the outer surface26aof the contact member26on the side of the intermediate transfer belt8and both rotational shafts9a,12care positioned so as not to approach each other or so as not to substantially approach each other. Accordingly, when the concaved portion14is positioned at the transfer nip formation area as shown inFIG. 3A, the second transfer roller12(more specifically, the elastic member12b) is not contacted with the intermediate transfer belt8by providing the contact members25and26. Moreover, since the concaved portion14with width w1is set larger than the second transfer nip11awith a width of w2, the second transfer roller12can be reliably prevented from contacting the intermediate transfer belt8at the transfer nip formation area.

As shown inFIGS. 4A and 4B, when the concaved portion14is separated from the transfer nip formation area, the partial shaped outer surface25aof the contact member25on the side of the second transfer roller12and the outer surface26aof the contact member26on the side of the intermediate transfer belt8are separated. Accordingly, the elastic member12bof the second transfer roller12contacts the intermediate transfer belt8which is wound around the intermediate transfer belt driving roller9, and the second transfer nip11ais formed in the transfer nip formation area.

The second transfer roller cleaning section13removes the liquid developer which is attached on the elastic member12bof the second transfer roller12with a cleaning member, such as a cleaning blade. The liquid developer which is removed by the cleaning member is returned to the liquid developer carrier.

Further, as shown inFIG. 1, the image forming apparatus1has a first air flow generator27, a second air flow generator28, a transfer material transporter29, a third air flow generator30and an image fixing section31. The first air flow generator27blows air toward the leading edge19aof the transfer material19which is released from the pinch of the gripper15as indicated by the arrow. Accordingly, it is prevented that the leading edge19aof the transfer material19is moved with the intermediate transfer belt8simultaneously. Also, the second air flow generator28suctions the air as indicated by the arrow so that the back surface of the transfer material19is drawn and separated from the second transfer roller12. Accordingly, the transfer material19is drawn by the suction air generated by the second air flow generator28and the transfer material is transported to a transfer material transporter29.

The transfer material transporter29has a transfer material transport belt29ahaving a plurality of holes and rotating in arrow direction in endless shape, and a suction member29b. When the transfer material19is transported to the transfer material transporter29, the transfer material19is drawn by air suction of the suction member29b, and transported toward the third air flow generator30by the transfer material transport belt29a. The third air flow generator30suctions air as indicated by the direction of the arrow. By air suction of the third air flow generator30, the back surface of the transfer material19which is separated from the second transfer roller12is drawn toward the third air flow generator30. Accordingly, the transfer material19is drawn and guided to the third air flow generator30, and the transfer material19moves toward the image fixing section31due to the rotational force of the transfer material transport belt29a. So, the toner image of the transfer material19is heated, pressed and fixed by the image fixing section31.

FIG. 5is a block diagram showing a control for the intermediate transfer belt/second transfer roller driving motor20of the image forming apparatus1of first embodiment of the invention.

As shown inFIG. 5, the intermediate transfer belt/second transfer roller driving motor20of the first embodiment are controlled by an electronic controller32of the image forming apparatus1. In this case, the controller32controls the operation of the intermediate transfer belt/second transfer roller driving motor20on the basis of the second transfer roller position signal (the concaved portion position signal; ON signal) from the photo sensor23and the image forming operation finish signal (ON signal) from an image forming operation finish signal output section33so as to control the rotation of the intermediate transfer belt8and the second transfer roller12. Therefore, the controller32controls the rotational position of the second transfer roller12(the rotational position of the concaved portion14) on the basis of the second transfer roller position signal (ON signal) and the image forming operation finish signal (ON signal).

Next, the description will be made regarding the sequence control in the first embodiment which controls the rotation of the second transfer roller12on the basis of the image forming operation finish signal and the rotational position of the concaved portion14of the second transfer roller12.FIG. 6is an explanatory view showing the sequence control for an intermediate transfer belt and a second transfer roller driving motor of a first embodiment.FIG. 7is a flow chart showing the image forming operation until the intermediate transfer belt/second transfer roller driving motor20is turned off according to the first embodiment.

As shown inFIG. 6andFIG. 7, controller32sets the image forming apparatus1to normal image forming mode, when the image forming signal10is input by a user operating the operation button. Thus, the normal image forming operation is started by the image forming apparatus1. Accordingly, the intermediate transfer belt/second transfer roller driving motor20is driven (ON). When the image forming operation is finished by the image forming apparatus1, the image forming operation finish signal is output from the image forming operation finish signal output section33to the controller32. After the image forming operation finish signal is output, when the concaved portion14is detected by the second transfer roller position detector initially, the second transfer roller position signal (ON signal) is output from the photo sensor23to the controller32. When the second transfer roller position signal (ON signal) is input to the controller32, the rotation of the intermediate transfer belt/second transfer roller driving motor20is stopped (OFF). As described above, in the state that the rotation of the intermediate transfer belt/second transfer roller driving motor20is stopped, the concaved portion14of the second transfer roller12is located at the transfer nip formation area, and the elastic member12bof the second transfer roller12is not in contact with the intermediate transfer belt8, as shown inFIGS. 3A and 3B.

Regarding the other constitution and other image forming operation of the image forming apparatus1in the first embodiment, these are the same as in the conventional related art image forming apparatus using a liquid developer, so the description thereof will be omitted.

In the image forming apparatus1of the first embodiment, the sheet shaped elastic member12bis installed on the peripheral surface of the second transfer roller12having the concaved portion14, and along with this, when the image forming operation is activated, the elastic member12bis contacted and pressed to the intermediate transfer belt8to form the second transfer nip11ain the transfer nip formation area. In this case, width w1in the peripheral direction of the concaved portion14of the second transfer roller12is set to be larger than width w2in the same direction of the transfer nip formation area where the second transfer nip11ais formed (w1>w2). Further, when the image forming operation is not performed and the intermediate transfer belt/second transfer roller driving motor20is not driven, the second transfer roller12is stopped in a state in which the concaved portion14is placed in the transfer nip formation area so that the elastic member12bis not in contact with the intermediate transfer belt8. Thus, when the image forming apparatus1is not performing the image forming operation, the second transfer nip11ais not formed between the intermediate transfer belt8and the second transfer roller12. Accordingly, the twist occurrence can be suppressed in the elastic layer of the intermediate transfer belt8and the elastic member12bof the second transfer roller12, even though the second transfer belt8and the second transfer roller12is not driven for a long time. Also, the twist occurrence can be suppressed in the elastic member12bof the second transfer roller12, even though the second transfer belt8and the second transfer roller12are not driven for a long time. Accordingly, the image defect and/or banding which is caused by the twisting of the elastic member12bof the second transfer roller12can be controlled effectively, whereby a good image quality can be obtained.

When the second transfer roller12is not rotated, the concaved portion14is positioned in the transfer nip formation area, so that the second transfer roller12can always stop in a constant position. Thus, when the next image forming operation is driven, the rotational position of the second transfer roller12can be controlled easily, so that the positioning between the rotational position of the second transfer roller12and the transported transfer material19can be accomplished easily.

Also, in the state in which the leading edge19aof the transfer material19is pinched by the gripper15, the transfer material19passes the second transfer nip11a, so that the transfer material19can be separated easily from the intermediate transfer belt8after the second transfer.

Further, the intermediate transfer belt8has an elastic layer, so that the transfer efficiency can be raised even though the transfer material19has high surface roughness. The twist occurrence can be suppressed in the elastic layer of the second transfer belt8and the elastic member12bof the second transfer roller12, because the second transfer nip11ais not formed even though the second transfer belt8and the second transfer roller12are not driven for a long time.

Second Embodiment

Referring now toFIGS. 8A,8B,9A,9B,10,11A and11B, an image forming apparatus and method in accordance with a second embodiment will now be explained. In view of the similarity between the first and second embodiments, the parts of the second embodiment that are identical to the parts of the first embodiment will be given the same reference numerals as the parts of the first embodiment. Moreover, the descriptions of the parts of the second embodiment that are identical to the parts of the first embodiment may be omitted for the sake of brevity.

FIG. 8Ais a partial view showing the image forming apparatus of the second embodiment of the invention and is the same partial view asFIG. 3A, andFIG. 8Bis an explanatory drawing viewed in the direction indicated by the arrow VIIIB ofFIG. 8A.FIG. 9Ais a view showing the second embodiment and is the same partial view asFIG. 4A, andFIG. 9Bis an explanatory drawing viewed in the direction indicated by the arrow IXB ofFIG. 9A.

The second embodiment differs from the first embodiment in that, as shown inFIGS. 8A,8B,9A, and9B, each of the intermediate transfer belt driving roller9and the second transfer roller12is rotated by the individual intermediate transfer belt driving motor34(one example of the image carrier driving source of the present invention) and the second transfer roller driving motor35(one example of the transfer roller driving source of the present invention) respectively. In other words, the driving force of the intermediate transfer belt driving motor34is delivered to the intermediate transfer belt driving roller9, so that the intermediate transfer belt driving roller9rotates counterclockwise as indicated by the direction of the arrow when viewed in the direction inFIG. 8AandFIG. 9A. Additionally, the driving force of the second transfer roller driving motor35is delivered to the rotational shaft12cof the second transfer roller12, so that the second transfer roller12rotates clockwise as indicated arrow direction (direction γ) when viewed in the direction inFIG. 8AandFIG. 9A. Thus, in the second embodiment, the middle gear21and the second transfer roller driving gear22in the first embodiment are not provided.

In the second embodiment, a contact member of the intermediate transfer belt side includes a bearing36instead of the contact member26of the first embodiment. In this embodiment, the bearing36is a ball bearing having an inner lace36a, an outer lace36b, and balls36c. In this case, the inner lace36ais integrally attached to be rotatable with the rotational shaft9aof the intermediate transfer belt driving roller9. Accordingly, the outer lace36bcan rotate relatively with respect to the rotational shaft9a.

As shown inFIGS. 8A and 8B, on the side of the second transfer roller12, the partial circular shape outer peripheral surface25aof the contact member25contacts the outer peripheral surface36b1of the outer lace36bwhen the concaved portion14of the second transfer roller12is located on the transfer nip formation area. Accordingly, the elastic member12bof the second transfer roller12is separated from the intermediate belt8when the concaved portion14is located in the transfer nip formation area. Further, as shown inFIGS. 9A and 9B, on the side of the second transfer roller12, the partial circular shape outer peripheral surface25aof the contact member25is separated from the outer peripheral surface36b1of the outer lace36bwhen the concaved portion14of the second transfer roller12is located out of the transfer nip formation area. In this way, when the concaved portion14is located out of the second transfer nip11a, the elastic member12bof the second transfer roller12is contacted and pressed to the intermediate transfer belt8, and the second transfer nip11ais formed.

With further reference to the second embodiment, as shown inFIG. 10, the controller32controls the rotation of the intermediate transfer belt8and the rotation of the second transfer roller12by controlling the rotation of the intermediate transfer belt driving motor34and the second transfer roller driving motor35, on the basis of the second transfer roller position signal (the concaved portion position signal; ON signal) from the photo sensor23which detects the position of the second transfer roller12and the image forming operation finish signal (ON signal) from the image forming operation finish output section33, in the same manner as the first embodiment. Accordingly, the controller32controls the rotational position of the second transfer roller12(the rotational position of the concaved portion14) on the basis of the second transfer roller position signal (ON signal) and the image forming operation finish signal (ON signal).

Next, the description will be made regarding the sequence control which controls the driving of the second transfer roller12on the basis of the image forming operation finish signal and the rotational position of the concaved portion14of the second transfer roller12in the second embodiment.FIG. 11Ais an explanatory view showing the sequence control for the intermediate transfer belt driving motor34and the second transfer roller driving motor35, andFIG. 11Bis a flow chart showing the image forming operation until the intermediate transfer belt driving motor34and the second transfer roller driving motor35are turned off.

As shown inFIGS. 11A and 11B, when the image forming signal is input to the controller32as the user operates the operation button, the controller32sets the image forming apparatus1to the normal image forming mode. In this way, the image forming apparatus1starts the normal image forming operation. Accordingly, the intermediate transfer belt driving motor34and the second transfer roller driving motor35are driven respectively (ON). When the image forming apparatus1stops the image forming operation, the image forming operation finish signal is output from the image forming operation finish signal output section33to the controller32in the same manner to the first embodiment. After the image forming operation finish signal is output, from the photo sensor23to the controller32, when the concaved portion14is initially detected by the second transfer roller position detector, the second transfer roller position signal (ON signal) is output from the photo sensor23to the controller32. Thus, when the second transfer roller position signal (ON signal) is input to the controller32, each rotation of the intermediate transfer belt driving motor34and the second transfer roller driving motor35is stopped respectively (OFF). As described above, in the state that the intermediate transfer belt driving motor34and the second transfer roller driving motor35are stopped, the concaved portion14of the second transfer roller12is located in the transfer nip formation area and the elastic member12bof the second transfer roller12does not contact the intermediate transfer belt8as shown inFIGS. 8A and 8Bin the same manner as the first embodiment as shown inFIGS. 3A and 3B.

According to the image forming apparatus1of the second embodiment, each rotation of the intermediate transfer belt driving motor34and the second transfer roller driving motor35can be controlled independently, so that velocity of the intermediate transfer belt driving motor34and the second transfer roller driving motor35can be set properly, respectively.

Also, the elastic member12bof the second transfer roller12is not contacted with the intermediate transfer belt8when the intermediate transfer belt driving motor34is not driven and when the second transfer roller driving motor35is not driven. Therefore, in the state that the elastic member12bis not contacted with the intermediate transfer belt8, it can control the unstable sliding between the intermediate transfer belt8and the elastic member12bof the second transfer roller12when the intermediate transfer belt8starts the independent rotation or when the intermediate transfer belt8stops the independent rotation after the independent rotation.

Other than this, the constitution and effects of the image forming apparatus in the second embodiment are the same as those of the first embodiment.

Third Embodiment

Referring now toFIGS. 12A and 12B, an image forming apparatus and method in accordance with a third embodiment will now be explained. In view of the similarity between the second and third embodiments, the parts of the third embodiment that are identical to the parts of the second embodiment will be given the same reference numerals as the parts of the second embodiment. Moreover, the descriptions of the parts of the third embodiment that are identical to the parts of the second embodiment may be omitted for the sake of brevity.

FIG. 12Ais an explanatory view showing a signal in the sequence control for an intermediate transfer belt driving motor34and the second transfer roller driving motor35of the image forming apparatus of the third embodiment, andFIG. 12Bis a flow chart showing a management of the intermediate transfer belt8until the intermediate transfer belt driving motor34is turned off.

The third embodiment is directed to when the intermediate transfer belt8is driven in the state that the second transfer roller12is stopped, so that the intermediate transfer belt8undergoes a process such as cleaning or resist matching with respect to the intermediate transfer belt8. In this case, in the third embodiment, the intermediate transfer belt driving motor34and the second transfer roller driving motor35can use the block diagram ofFIG. 10in the same manner as the second embodiment.

The controller32controls the actuation of the intermediate transfer belt driving motor34, in the other words, the rotation of the intermediate transfer belt8on the basis of the second transfer roller position signal (the concaved portion position signal; ON signal) from the photo sensor23and the intermediate transfer belt processing signal (ON signal) from the intermediate transfer belt processing signal output section. More specifically, in the third embodiment, the controller32stops the second transfer roller driving motor35when the second transfer roller position signal (ON signal) is output from the photo sensor23to the controller32. Accordingly, the controller32controls the rotational position of the second transfer roller12(the rotational position of the concaved portion14) on the basis of the position signal (ON signal) of the second transfer roller12and the finish signal (ON signal) of the image forming operation.

Next, the description will be made regarding the sequence control which controls the actuation of the intermediate transfer belt8on the basis of the intermediate transfer belt processing signal and the second transfer roller position signal in the third embodiment.

As shown inFIGS. 12A and 12B, the controller32sets the image forming apparatus to the intermediate transfer belt processing mode, when the intermediate transfer belt processing signal is input to the controller32from the intermediate transfer belt processing signal output section. The intermediate transfer belt processing mode refers to a mode in which the intermediate transfer belt8undergoes cleaning or resist matching. The image forming apparatus1is set to the intermediate transfer belt processing mode, so that the controller32actuates the intermediate transfer belt driving motor34(ON) and the intermediate transfer belt8rotates in the direction β (shown inFIG. 8A). At this time, the second transfer roller12is stopped, so the concaved portion14is located on the second transfer nip11aposition. Accordingly, the elastic member12bof the second transfer roller12is not contacted with the intermediate transfer belt8and the intermediate transfer belt8rotates stably and smoothly. Thus, the intermediate transfer belt8is processed by the rotation of the intermediate transfer belt8as described above. The intermediate transfer belt processing finish signal is output from the intermediate transfer belt processing signal output section to controller32, when the processing regarding the intermediate transfer belt8is finished. Thus, the controller32stops the actuation of the intermediate transfer belt driving motor34, and the rotation of the intermediate transfer belt8is stopped.

According to the image forming apparatus of the third embodiment, in the state that the concaved portion14stops the rotation of the second transfer roller12at the transfer nip formation area, the intermediate transfer belt8is rotated. Thus, in the state that the elastic member12bof the second transfer roller12is not contacted with the intermediate transfer belt8, it is possible to rotate the intermediate transfer belt8. However, in the case of the image forming apparatus, in which the second transfer roller12always contacts presses the intermediate transfer belt, when the cleaning or resist matching of the intermediate transfer belt8is processed, the distance between the rotational shaft of the second transfer roller and the rotational shaft of the intermediate transfer belt driving roller9is changed, so that it is necessary to separate the second transfer roller12from the intermediate transfer belt8. Otherwise, in the image forming apparatus of the third embodiment, the second transfer roller12can be separated from the intermediate transfer belt8without substantially changing the distance between the rotational shaft12cof the second transfer roller12and the rotational shaft9aof the intermediate transfer belt driving roller9. Thus, the processing with respect to the intermediate transfer belt8described above can be processed easily.

Other than this, the constitution and effects of the image forming apparatus in the third embodiment are the same as those of the second embodiment.

Fourth Embodiment

Referring now toFIGS. 13A,13B,14,15A and15B, an image forming apparatus and method in accordance with a fourth embodiment will now be explained. In view of the similarity between the previous embodiments and the fourth embodiment, the parts of the fourth embodiment that are identical to the parts of the previous embodiments will be given the same reference numerals as the parts of the previous embodiment. Moreover, the descriptions of the parts of the fourth embodiment that are identical to the parts of the previous embodiments may be omitted for the sake of brevity.

FIG. 13Ais a partial view similar toFIG. 2Ashowing a second transfer section of the fourth embodiment of the image forming apparatus of the invention, andFIG. 13Bis an explanatory drawing a detection of the transfer material presence.FIG. 14is a block diagram similar toFIG. 10showing the control for each of the second transfer roller driving motor34and the intermediate transfer belt driving motor35of the fourth embodiment.

As shown inFIG. 13A, the image forming apparatus of the fourth embodiment has the transfer material presence/absence detector38using a reflective type sensor between the transfer nip formation area and the gate roller18. As shown inFIG. 13B, the transfer material presence/absence detector38outputs OFF signal when the transfer material19which is transported from the gate roller18is detected at the transfer material detection timing position detecting the transfer material19, and outputs ON signal when the transfer material19is not detected at the same position. Thus, the transfer material presence/absence detector38outputs ON signal, when the transfer material19is not detected at the detection timing position. In this case, ON signal output from the transfer material presence/absence detector38is the transfer material presence/absence signal (ON signal indicates the transfer material is absent at the detection position). Also, as the transfer material presence/absence detector38, for example, a photo interrupter from Sharp Corporation (GP2A25J0000F series) can be used.

As shown inFIG. 14, the photo sensor23detecting the position of the second transfer roller12, the transfer material presence/absence detector38, the transfer material belt driving motor34and the second transfer roller driving motor35are connected to the controller32.

Further, the controller32controls the actuation of the second transfer roller driving motor35, and controls the rotational position (the rotational position of the concaved portion14) of the second transfer roller12, on the basis of the second transfer roller position signal (the concaved portion position signal; ON signal) from the photo sensor23and the transfer material presence/absence signal (ON signal) from the transfer material presence/absence detector38. In other words, the transfer material presence/absence signal (ON signal) is input to the controller32from the transfer material presence/absence detector38, and it is determined that the transfer material19is jammed, then the second transfer roller position signal (ON signal) is input to stop the actuation of the second transfer roller driving motor35. In this way, when the jam of the transfer material19has occurred in front of the transfer material presence/absence detector38in the material transporting direction, the concaved portion14of the second transfer roller12is stopped at the transfer nip formation area. Thus, when the second transfer roller12is stopped due to the occurrence of the jam in the transfer material19, the elastic member12bof the second transfer roller12is not contacted with the intermediate transfer belt8.

Next, the description regarding the sequence control of the fourth embodiment will be made wherein the sequence control controls the rotation of the second transfer roller12on the basis of the transfer material presence/absence signal and the second transfer roller position signal.FIG. 15Ais a flow chart showing a process of the second transfer roller driving motor35until the second transfer roller driving motor35is turned off when a jam of the transfer material19occurs, andFIG. 15Bis an explanatory view showing a signal in the sequence control for the intermediate transfer belt driving motor34and the second transfer roller driving motor35when a jam of the transfer material19occurs.

As shown inFIGS. 15A and 15B, when the image forming signal which set up the transfer material size is input to the controller32by a user operating the operation button, the controller32sets the image forming apparatus to the image forming mode. Accordingly the image forming apparatus starts the normal image forming operation. Thus, each of the intermediate transfer belt driving motor34and the second transfer roller driving motor35is driven respectively (ON), and the intermediate transfer belt8rotates in the direction β shown inFIG. 1, and the second transfer roller12rotates in the direction γ shown inFIG. 13A. As described above, after the leading edge19aof the transfer material19which is transported from the gate roller18is pinched by the gripper15, the transfer material19enters the second transfer nip11a. Thus, in the second transfer nip11a, the toner image which is transferred by the intermediate transfer belt8is transferred to the transfer material19.

At this time, the transfer material presence/absence detector38does not detect the transfer material19, and outputs the transfer material presence/absence signal (ON signal; signal that the transfer material is absent) until the transfer material19which is transported from the gate roller18reaches the detection timing position of the transfer material presence/absence detector38. When the transfer material19reaches the detection timing position of the transfer material presence/absence detector38, so that the transfer material presence/absence detector38detects the transfer material19, the transfer material presence/absence detector38outputs the transfer material presence/absence signal (OFF signal; signal that the transfer material is present). In other words, the jam of the transfer material19does not occur (when the jam does not occur). Moreover, when the transfer material presence/absence detector38does not detect the transfer material19at the detection timing position, regardless of whether the jam of the transfer material occurs or does not occur, the transfer material presence/absence detector38outputs ON signal, so that any of ON signals is indicated as the transfer material presence/absence signal (ON signal) for convenience of the description inFIG. 15B. As described above, even if the size of the transfer material19in the transfer material transporting direction is the maximum size used in the image forming apparatus1, the transfer material19is separated from the second transfer roller12until the concaved portion14reaches the position of the transfer nip formation area next time. Thus, the transfer material presence/absence detector38outputs the transfer material presence/absence signal (ON signal) again, until the next second transfer roller position signal (ON signal) is output.

If the transfer material19which is transported from the gate roller18is jammed, so that the transfer material19does not reach the detection timing position of the transfer material presence/absence detector38, the transfer material presence/absence detector38does not detect the transfer material19at the detection timing position. Because of this, the transfer material presence/absence signal from the transfer material presence/absence detector38does not become OFF, and the transfer material presence/absence detector38outputs the transfer material presence/absence signal (ON signal) to the controller32continuously (detection that the transfer material is absent). In other words, the jam of the transfer material19occurs (when the jam occurs). Then, the controller32determines that the jam of the transfer material19has occurred, and when the second transfer roller position signal (ON signal) is input subsequently, the actuation of the second transfer roller driving motor35is stopped. Accordingly, when the jam of the transfer material19occurs, the second transfer roller12is stopped in the state that the elastic member12bis not contacted to the intermediate transfer belt8. Then, the controller32stops the actuation of the intermediate transfer belt driving motor34, and the intermediate transfer belt8is stopped.

Thus, when the jam of the transfer material19is detected, the second transfer roller12rotates until the concaved portion14reaches the position of the second transfer nip11a, and when the concaved portion14reaches the position of the second transfer nip11a, the second transfer roller12is stopped. At this time, when the second transfer roller12rotates after the jam of the transfer material19is detected, the intermediate transfer belt8rotates too. Also, when the second transfer roller12rotates after the jam of the transfer material19is detected, the intermediate transfer belt8does not necessarily have to rotate. However, it is preferable to rotate the intermediate transfer belt8when the second transfer roller12rotates after the jam of the transfer material19is detected to decrease the friction between the second transfer roller12and the intermediate transfer belt8.

According to the image forming apparatus of the fourth embodiment, when the jam of the transfer material19which is transported from gate roller18has occurred, the controller32stops the rotation of the second transfer roller12so that the concaved portion14is located to the position of the second transfer nip11aon the basis of the second transfer roller position signal (ON signal) and the transfer material presence/absence signal (ON signal) from the transfer material presence/absence detector38. Thus, it can be suppressed that the toner of the image transported on the intermediate transfer belt8may be attached on the second transfer roller12. In particular, as shown inFIG. 13A, the detection timing position of the transfer material presence/absence detector38for detecting the transfer material19is set immediately upstream of the detection position of the concaved portion14by the photo sensor23, so that it can be more effectively suppressed that the toner of the image carried on the meddle transfer belt8may be attached on the second transfer roller12.

In other respects, the constitution and effects of the image forming apparatus1in the fourth embodiment are the same as those in the second embodiment.

Fifth Embodiment

Referring now toFIGS. 16,17,18A and18B an image forming apparatus and method in accordance with a fifth embodiment will now be explained. In view of the similarity between the previous embodiments and the fifth embodiment, the parts of the fifth embodiment that are identical to the parts of the previous embodiments will be given the same reference numerals as the parts of the previous embodiments. Moreover, the descriptions of the parts of the fifth embodiment that are identical to the parts of the previous embodiments may be omitted for the sake of brevity.

FIG. 16is a partial view showing the image forming apparatus according to the fifth embodiment of the invention.FIG. 17is a block diagram similar toFIG. 14showing a control for each of the second transfer roller driving motor34and the intermediate transfer belt driving motor35of the fifth embodiment.

In the image forming apparatus of the fifth embodiment, in addition to the transfer material presence/absence detector38(herein after the first transfer material presence/absence detector38, in the fifth embodiment) of the fourth embodiment, the second air flow generator28has the second transfer material presence/absence detector39. The second transfer material presence/absence detector39detects the jam of the transfer material19which is already detected by the first transfer material presence/absence detector38. The second transfer material presence/absence detector39may be the same as the first transfer material presence/absence detector38, for example, a photo sensor may be used as described above.

As shown inFIG. 17, the photo sensor23which detects the position of the second transfer roller12, the first transfer material presence/absence detector38, the second transfer material presence/absence detector39, the intermediate transfer belt driving motor34and the second transfer roller driving motor35are connected to the controller32.

Further, the controller32controls the actuation of the second transfer roller driving motor35, and controls the rotational position (rotational position of the concaved portion14) of the second transfer roller12(rotational position of the concaved portion14), on the basis of the second transfer roller position signal (the concaved portion position signal; ON signal) from the photo sensor23, the first transfer material presence/absence signal (ON signal) from the first transfer material presence/absence detector38and the second transfer material presence/absence signal (ON signal) from the second transfer material presence/absence detector39. In other words, the first transfer material presence/absence signal (ON signal) from the first transfer material presence/absence detector38is input in the controller32in the state that the second transfer roller12rotates in the direction γ (forward rotational direction). If the determination is that the jam of the transfer material19has occurred, then the actuation of the second transfer roller driving motor35is stopped when the second transfer roller position signal (ON signal) is input initially in the same manner as described above in the fourth embodiment. Thus, the concaved portion14of the second transfer roller12is stopped on the position of the transfer nip formation area when the jam of the transfer material19has occurred ahead of the first transfer material presence/absence detector38in the moving direction of the transfer material. Accordingly, if the second transfer roller12is stopped, when a jam of the transfer material19occurs, the elastic member12bof the second transfer roller12is not contacted to the intermediate transfer belt8.

Furthermore, if the controller32determines there is no jam occurrence of the transfer material19because the first transfer material presence/absence signal (OFF signal) is input from the first transfer material presence/absence detector38, and the controller32determines there is a jam occurrence of the transfer material19because the second transfer material presence/absence signal (ON signal) is input from the second transfer material presence/absence detector39, the concaved portion14passes through the transfer nip formation area, so that the second transfer roller driving motor35rotates in reverse. Thus, the second transfer roller12is controlled to rotate in reverse (reverse to the direction γ). After that, when the second transfer rotational position signal (ON signal) is input, the actuation of the second transfer roller driving motor35is stopped. Thus, after the first transfer material presence/absence detector38detects the transfer material19and when the second transfer material presence/absence detector39does not detect the transfer material19, the second transfer roller12rotates in reverse so that the concaved portion14is stopped at the position of the second transfer nip11a. Thus, after the second transfer material presence/absence detector39detects the jam occurrence of the transfer material19, the elastic member12bof the second transfer roller12is not contacted to the intermediate transfer belt8when the second transfer roller12is stopped.

Next, the description regarding sequence control in the fifth embodiment will be made wherein the sequence control controls the actuation of the intermediate transfer belt8on the basis of the first transfer material presence/absence signal, the second transfer material presence/absence signal and the second transfer roller position signal in the fifth embodiment.FIG. 18Ais a flow chart showing a process of the second transfer roller driving motor35until the second transfer roller driving motor35is turned off when a second jam of the transfer material occurs, andFIG. 18Bis an explanatory view showing a signal in the sequence control for each of the intermediate transfer belt driving motor34and the second transfer roller driving motor35when a second jam of the transfer material occurs.

As shown inFIGS. 18A and 18B, when the image forming signal which sets up the transfer material size is input to the controller32when a user operates the operation button, the controller32sets the image forming apparatus1to the image forming mode. Thus, the image forming apparatus1starts normal image forming operation. Then, the intermediate transfer belt driving motor34and the second transfer roller driving motor35are driven respectively (ON), so that the intermediate transfer belt driving motor34rotates in the direction β (forward direction), and the second transfer roller driving motor35rotates in the direction γ (forward direction). After the leading edge19aof the transfer material19which is transported from the gate roller18is pinched by the gripper15as described above, the transfer material19enters the second transfer nip11a. Also, the toner image transported on the intermediate transfer belt8is transferred to the transfer material19at the second transfer nip11a.

At this time, the first transfer material presence/absence detector38does not detect the transfer material19, and outputs the first transfer material presence/absence signal (ON signal) until the transfer material19which is transported from the gate roller18reaches the detection timing position of the first transfer material presence/absence detector38. When the first transfer material presence/absence detector38detects the transfer material19as the transfer material19reaches the detection timing position of the first transfer material presence/absence detector38, the first transfer material presence/absence signal from the first transfer material presence/absence detector38becomes OFF. In other words, the transfer material19does not jam (when the jam does not occur). Further, the second transfer material presence/absence detector39does not detect the transfer material19and outputs the second transfer material presence/absence signal (ON signal), until the transfer material19reaches the detection timing position of the second transfer material presence/absence detector39. When the transfer material19reaches the detection timing position of the second transfer material presence/absence detector39, so that the second transfer material presence/absence detector39detects the transfer material19, the second transfer material presence/absence signal from the second transfer presence/absence detector39becomes OFF. That is to say, the jam of the transfer material19does not occur (when the jam does not occur).

If the transfer material19from the gate roller18is jammed, so that the transfer material19does not reach the detection timing position of the first transfer material presence/absence detector38, the first transfer material presence/absence detector38does not detect the transfer material19at the detection timing. At this time, the rotation of the second transfer roller12is stopped in the state that the elastic member12bdoes not contact the intermediate transfer belt8in the same manner as the fourth embodiment described above.

Further, after the first transfer material presence/absence detector38detects the transfer material19at the detection timing position, so that the first transfer material presence/absence signal from the first transfer material presence/absence detector38becomes OFF, when the jam of the transfer material19occurs and the transfer material19does not reach the detection timing position of the second transfer material presence/absence detector39, the second transfer material presence/absence detector39does not detect the transfer material19at the detection timing position. Therefore, the second transfer material presence/absence signal from the second transfer material presence/absence detector39does not become OFF, and the second transfer material presence/absence detector39outputs the second transfer material presence/absence signal (ON signal) to the controller32continuously (the second transfer material jam occurs). In other words, the jam of the transfer material19occurs (when the jam occurs). Then, the controller32determines that the second transfer material jam of the transfer material is occurring, and the second transfer roller driving motor35rotates in reverse. Namely, if the jam is detected after the second transfer roller12rotates forward; the roller12is stopped instantly and is then rotated in reverse. Also, at this time, the controller32rotates the intermediate transfer belt driving motor34in reverse, so that the intermediate transfer belt8is also rotated in reverse. After that, each actuation of the second transfer roller driving motor35and the intermediate transfer belt driving motor34is stopped respectively when the second transfer roller position signal (ON signal) is input initially. Accordingly, the second transfer roller12is stopped in the state in which the elastic member12bis not contacted to the intermediate transfer belt8, when the second transfer material jam of the transfer material19occurs.

As described above, when the second transfer material jam of the transfer material19occurs, the second transfer roller12rotates in reverse until the concaved portion14reaches the transfer nip formation area, and it is stopped when the concaved portion14reaches the transfer nip formation area. At this time, when the second transfer roller12rotates in reverse after the second transfer material jam of the transfer material19occurred, the intermediate transfer belt8also rotates in reverse. Also, the intermediate transfer belt8does not necessarily need to rotate in reverse when the second transfer roller12rotates in reverse after the second jam of the transfer material19occurs. However, it is preferable to rotate the intermediate transfer belt8when the second transfer roller12rotates in reverse after the jam of the transfer material19is detected to decrease the friction between the second transfer roller12and the intermediate transfer belt8.

According to the image forming apparatus in the fifth embodiment, after the transfer material19is detected at the first transfer material presence/absence detector38, and when the second transfer material jam of the transfer material19occurs, the controller32controls the second transfer roller12so as to rotate in reverse, on the basis of the second transfer roller position signal (ON signal) and the second transfer material presence/absence signal (ON signal) from the second transfer material presence/absence detector39. Then, the reverse rotation of the second transfer roller12is stopped when the concaved portion14is located at the transfer nip formation area. Thus, it can suppress the toner which is transported by the intermediate transfer belt8that may attach the second transfer roller12.

In other respects, the constitution and effects of the image forming apparatus in the fifth embodiment are the same as those of the fourth embodiment. In this case, the second transfer material presence/absence detector39can be located at any one of the inner side of the endless shaped transfer material transport belt29aof the transfer material transporter29, the third air flow generator30, the front side of the image fixing section31, and the rear side of the image fixing section31.

Moreover, the image forming apparatus and the image forming method of the invention are not limited to the above described preferred embodiments. For example, in the above described embodiments, the intermediate transfer belt8is used as the image carrier, however, the intermediate transfer drum or photo sensor can be used as the image carrier. In the case where a photosensitive body is applied as the image carrier, the toner image of the photosensitive body is directly transferred to the transfer material. Also, the image forming apparatus has 4 colors; however the image forming apparatus may have a single color.

With the image forming apparatus according to the illustrated embodiments, there is provided an image forming apparatus and the image forming method. An elastic member is installed in the circumferential surface of the transfer roller having a concaved portion, along with which a transfer nip formation area is formed where the transfer roller is pressed against the image carrier when the image is transferred. In this case, the width of the concaved portion is larger than the width of the transfer nip formation area in the circumferential direction of the transfer roller. The transfer roller is stopped when the concaved portion is in the transfer nip formation area, so as not to have contact between the transfer roller and the image carrier when the image is not transferred. Thus, the transfer nip is not formed in the transfer nip formation area between the transfer roller and the image carrier when the image forming operation of the image forming apparatus is not performed. Accordingly, the elastic member of the transfer roller is not twisted, even when the image forming apparatus is not operated for a long time. Thus, the image defect and the occurrence of the banding caused by the twisting of the elastic member are suppressed effectively and a higher quality image can be obtained.

In addition, when the rotation of the transfer roller is stopped, the concaved portion is reliably positioned on the transfer nip formation area so that the transfer roller can be reliably stopped in a constant position. Accordingly, the rotational position of the transfer roller can be controlled when the next image forming operation is performed, and the positional alignment between the rotational position of the transfer roller and the transfer material which is transported to the apparatus is easily accomplished.

Additionally, each rotation of the image carrier driver driving the image carrier and the transfer roller driver driving the transfer roller may be controlled independently, so that the rotation velocity of the image carrier driver and the transfer roller driver can be controlled properly and individually.

Also, the elastic member of the transfer roller is not in contact with the image carrier when the image carrier is driven and the transfer roller driver is stopped. In the state in which the elastic member is not in contact with the image carrier, unstable sliding between the elastic member of the transfer roller and the image carrier can be suppressed when the image carrier starts to rotate independently or when the image carrier is stopped after rotating independently.

Also, in the state in which the rotation of the transfer roller is stopped, the image carrier can be rotated in the state that the elastic member of the transfer roller is not in contact with the image carrier by placing the concaved portion in the transfer nip formation area. However, in the case that the transfer roller of the image forming apparatus is always in press-contact with the image carrier, it is necessary for the transfer roller to be separated from the image carrier to change the distance between the rotational axis of the transfer roller and the rotational axis of the image carrier, when the image carrier is cleaned or registration alignment thereof is performed. Meanwhile, the image transfer apparatus of the illustrated embodiments has a transfer roller separating from the image carrier without substantially changing the distance between the rotational axis of the transfer roller and the rotational axis of the image carrier. Thus, the operation as described above can be accomplished with easily and quickly.

In addition, when a jam of the transfer material occurs, the controller stops the rotation of the transfer roller so that the concaved portion is located in the transfer nip formation area, on the basis of the transfer roller position signal and the transfer presence/absence signal from the transfer presence/absence detecting section. Accordingly, it can be suppressed that the toner of the image being carried by the image carrier is attached on the transfer roller. In particular, by setting the location of the transfer material detecting timing position of the transfer material presence/absence detecting section to immediately upstream of the concaved portion detecting position (the position of the concaved portion when the concaved portion is placed in the transfer nip formation area) on the front of the transfer roller position, the toner of the image being carried by the image carrier can be more effectively suppressed from being attached on the transfer roller.

Also, when a jam of the transfer material passing through the transfer nip at the transfer presence/absence detecting section is detected, the controller stops the reverse rotation of the transfer roller when the concaved portion is located on the transfer nip position after reverse rotation of the transfer roller, on the basis of the transfer roller position signals and the transfer material presence/absence signals of the transfer presence/absence detecting section. Accordingly, it can be more effectively suppressed that the toner of the image being carried by the image carrier is attached on the transfer roller.

Also, in the state in which the transfer material is pinched by the transfer material gripper, the transfer material passes through the transfer nip, so that separation of the transfer material from the image carrier can be reliably accomplish after the image is transferred.

Also, the image carrier has an elastic layer, so that the transfer efficiency can be enhanced even though the transfer material has high surface roughness. Even if this image carrier has the elastic layer, the transfer nip is not formed in the case that the image carrier and the transfer roller is stopped for a long time, so that it is possible to suppress the occurrence of twisting occurrence between the elastic layer of the image carrier and the elastic layer of the transfer roller.

General Interpretation of Terms