JP4790536B2 - Image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer apparatus, or a facsimile apparatus that employs an electrophotographic system, for example, when the leading end of a recording medium enters between an image carrier and a transfer unit, or the trailing end of a recording medium The present invention relates to an image forming apparatus configured to buffer an impact that occurs when a sheet passes.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, a printer apparatus, and a facsimile apparatus adopting an electrophotographic method, a toner image is carried on an image carrier such as a photosensitive drum or a transfer belt, and a recording paper is loaded by a transfer roller. There is one in which a toner image is transferred onto a recording sheet by being pressed against an image carrier.

  Thus, in the image forming apparatus, when the leading edge of the recording paper enters the nip portion between the image carrier and the transfer roller, the leading edge of the recording paper collides with the image carrier at the nip portion. Occurs, and the phenomenon becomes more prominent as the recording paper is thicker.

  In the image transfer means for transferring the toner image on the surface of the image carrier onto the recording paper, if the image carrier is a photosensitive drum, the exposure device, the developing device, the cleaning device, etc. installed around the photosensitive drum Since the image forming process such as exposure, development, and cleaning is performed on the same surface on the photosensitive drum, and primary transfer is also performed when the image carrier is a transfer belt, the conveyance speed of the image carrier is temporarily When it is slow, the line speed of the image forming process also fluctuates, and image defects called banding such as streak in the main scanning direction, band-like shading unevenness in the sub-scanning direction, and image shift occur.

  As a means for solving such a problem, there is known a technique in which a step as an impact buffering material is provided on the circumference of either the transfer roller or the pressure roller to mitigate the impact (for example, (See Patent Document 1).

  Also, an image carrier that is formed when the recording medium enters the pressure contact portion between the image carrier and the transfer member by forming a concave groove in the image carrier or the transfer member to form a gap that is narrower than the thickness of the recording medium. Are known in which the speed fluctuation is suppressed (for example, see Patent Document 2).

  Further, when an image is not formed on the image carrier, the pressure contact portion is separated by moving at least one of the image carrier and the pressure roll by a driving force from a driving unit that rotationally drives the image carrier. In synchronism with the timing when the recording medium enters between the pressure contact portion of the carrier and the pressure roll, the pressure contact portion is released using the biasing force of the biasing means that presses the image carrier and the pressure roll. Is known (for example, see Patent Document 3).

  In addition, the recording member enters the pressure contact portion between the image carrier and the transfer member by pushing down the transfer member with a push-down amount corresponding to the thickness of the recording medium to provide a gap between the image carrier and the transfer member. An image carrier that suppresses the speed fluctuation of the image carrier that is sometimes generated is known (for example, see Patent Document 4).

  However, in the case of the one described in Patent Document 1, since the gap to be formed is constant, if the thickness of the recording paper is thin, the conveyance force is insufficient, and the recording paper cannot reach the downstream side at a desired timing. There has been a problem that a slip phenomenon occurs or a problem such as a skew phenomenon (skew) occurs due to an imbalance of frictional forces at both ends of the roller.

  Further, the one described in Patent Document 2 forms a gap using a concave groove portion, and it can be expected that the rotational load of the image carrier when the recording medium enters is suppressed. Since the image carrier or the transfer member is in contact with only the provided part, there is a problem that stress concentration locally occurs only in that part, and plastic deformation may occur during long-term use. . That is, since the roller end portion is always in pressure contact with the roller, local stress concentration occurs, and the roller may be deformed when used for a long period of time.

  In addition, since the press contact portion is separated until the recording medium enters, the one disclosed in Patent Document 3 can be expected to suppress the rotational load of the image carrier when the recording medium enters, but the press contact portion When the separation is released, the image carrier, the recording medium, and the transfer roller collide with each other with a certain urging force, which causes a problem that a rotational load is generated on the image carrier and causes image deterioration. That is, when the clearance between the transfer roller and the image carrier is released, there is a problem that the transfer roller collides with the image carrier due to the urging force of the spring connected to the arm and a rotational load is generated. .

  Further, the one disclosed in Patent Document 4 is a method in which the transfer member is pushed down by a push-down amount corresponding to the thickness of the recording medium so that a gap is provided between the image carrier and the transfer member, thereby speeding up the recording medium. The effect of reducing fluctuations is considered to be obtained regardless of the thickness of the recording medium, but it must be equipped with a device that detects the thickness of the recording medium, or it must be driven by determining the adjustment amount according to the thickness of the recording medium. As a result, there is a problem that the apparatus is expensive and complicated. That is, since it is necessary to provide a motor for forming the gap separately from the driving of the roller, there is a problem that the cost is increased.

  Therefore, the present applicant has devised the following invention as a means for solving the above-mentioned problems, and has filed an application as Japanese Patent Application No. 2006-140333 or Japanese Patent Application No. 2006-140403.

  This case will be described with reference to FIG. In FIG. 22, the intermediate transfer belt 1 set to the main scanning width Wb (belt width) is sandwiched between the opposing roller 2 set to the main scanning width Wt and the secondary transfer roller 3 set to the main scanning width Wr. A toner image is carried on the surface of the intermediate transfer belt 1 by primary transfer.

  Further, an image forming area Wi and a non-image forming area Wo set outside the image forming area Wi are set with respect to the main scanning width Wt of the secondary transfer roller 3, and recording paper is set in the image forming area Wi. P is conveyed.

  A torque limiter 4 slides on the outer periphery of each end of the secondary transfer roller shaft 3 a of the secondary transfer roller 3, and a torque limiter holder 5 is press-fitted on the outer periphery of the torque limiter 4.

  The torque limiter holder 5 is integrally provided with a holding ring 6, and a pair of gap forming members 7 made of a flexible sheet are joined to the outer periphery of the holding ring 6. The gap forming member 7 is provided with an attaching portion 7a as an adhesive margin, and the attaching portion 7 is joined to the holding ring 6 by adhesion, welding, fusion or the like.

  Further, the gap forming member 7 has an arc shape along the outer periphery of the mounting portion 7a, and is free on the upstream side thereof, and thus is flat due to the restoring force of the elastic sheet material. Further, the gap forming member 7 is set to a width Wg, and is set in the non-image forming area Wo.

  A rotation locking claw 5a (see FIG. 23) (not shown) is provided on the outer periphery of the torque limiter holder 5, and the rotation locking claw 5a is locked to the locking claw 8a of the locking plate 8. It has become. An electromagnetic solenoid 9 is connected to the locking plate 8, and the locking plate 8 is positioned at a position where the locking claw 8 a is locked to the rotation locking claw 5 a by the electromagnetic solenoid 9 and a position separated from the rotation locking claw 5 a. Are moved in the main scanning direction.

  For this reason, when the locking plate 8 is locked to the rotation locking claw 5a, the torque limiter 4 slips and power is not transmitted from the secondary transfer roller shaft 3a to the holding ring 6, and the locking plate 8 is rotated and locked. When separated from the claw 5a, the power is transmitted from the secondary transfer roller shaft 3a to the holding ring 6, so that the gap forming member 7 moves together with the holding ring 6, and the gap forming member 7 is intermediate between the secondary transfer roller 3 and the intermediate transfer roller 3. It is inserted between the transfer belt 1.

  Next, a recording paper conveyance method will be described with reference to FIG. In FIG. 23, the counter roller 2 rotates as the intermediate transfer belt 3 is conveyed while the registration roller pair 10 starts to rotate. At this time, since the rotation locking claw 5 a is locked to the locking plate 8, the torque limiter 4 slips and the torque limiter holder 5 and the gap forming member 7 are nipped between the intermediate transfer belt 1 and the secondary transfer roller 3. It will be in a standby state, stopping before the part (refer to (a)).

  Next, when the leading edge of the recording paper P is detected by the registration sensor 11, the electromagnetic solenoid 9 is turned on and the locking claw 8a of the locking plate 8 is separated from the rotation locking claw 5a. As a result, the torque limiter holder 5 and the gap forming member 7 start to rotate counterclockwise (see (b)).

  Next, as shown in (c) and (d), when the leading edge of the recording paper P comes close to the intermediate transfer belt 1 and the secondary transfer roller 3, the gap forming member 7 is located between the intermediate transfer belt 1 and the secondary transfer roller 3. Enters the intermediate transfer belt 1 and the secondary transfer roller 3, so that a gap is formed between the intermediate transfer belt 1 and the secondary transfer roller 3, and the leading edge of the recording paper P passes through the gap formed in the intermediate transfer belt 1 and the secondary transfer roller 3. The toner enters the nip portion of the next transfer roller 3.

  Next, the recording paper P is conveyed while being sandwiched between the secondary transfer roller 3 and the intermediate transfer belt 1 (see (e)), and the gap forming member 7 is separated from the intermediate transfer belt 1 and the secondary transfer roller 3 to perform intermediate transfer. A gap corresponding to the thickness of the recording paper P is formed between the belt 1 and the secondary transfer roller 3 (see (f)).

  Next, before the torque limiter holder 5 rotates once, the electromagnetic solenoid 9 is turned off, and the locking claw 8a of the locking plate 8 is locked to the rotation locking claw 5a, so that the torque limiter 4 is slipped and torque is increased. By stopping the rotation of the limiter holder 5, the secondary transfer roller 3 is rotated together (see (g)). For this reason, the gap forming member 7 does not enter the nip portion between the intermediate transfer belt 1 and the secondary transfer roller 3.

Thus, in the image forming apparatus devised by the present applicant, the gap forming member 7 is provided in the non-image forming area Wo, and the gap forming member 7 is attached to the nip between the intermediate transfer belt 1 and the secondary transfer roller 3 at a predetermined timing. The leading edge of the recording paper P is caused to enter the nip portion of the intermediate transfer belt 1 and the secondary transfer roller 3 in a state where a gap is formed in the nip portion of the intermediate transfer belt 1 and the secondary transfer roller 3. be able to.
For this reason, it is possible to prevent the rotation speed of the intermediate transfer belt 1 from fluctuating, and to prevent image defects from occurring.
JP-A-61-90167 Japanese Utility Model Publication No. 56-47639 JP-A-6-274051 JP-A-4-242276

  However, in the image forming apparatus devised by the present applicant, since the gap forming member 7 is installed in the non-image forming area Wo, the recording paper having the maximum width in the main scanning direction as an object of image formation. On the other hand, when the width of the recording paper to be printed is extremely small, for example, in the case of a government postcard, the gap forming member 7 is present in the non-image forming area Wo. 7 distances away.

  Therefore, when the gap forming member 7 is inserted into the nip portion between the intermediate transfer belt 1 and the secondary transfer roller 3, the gap formed between the intermediate transfer belt 1 and the secondary transfer roller 3 is in the main scanning direction. The recording paper P enters the nip portion of the intermediate transfer belt 1 and the secondary transfer roller 3 or an impact occurs when the trailing edge of the recording paper P comes out, resulting in an image defect. There was still room for improvement.

  The present invention has been made to solve such a problem, and can prevent the fluctuation of the rotation speed of the image carrier regardless of the width of the recording medium and can form a good image. An image forming apparatus is provided.

  The image forming apparatus according to the present invention includes an image carrier that rotates while supporting an image, an image forming unit that forms an image on a surface of the image carrier, and rotates while abutting the image carrier. A transfer means for transferring an image formed on the surface of the body to a recording medium; a recording medium transfer means for transferring the recording medium to a position where the image carrier and the transfer means abut; and the contact at a predetermined timing. A gap forming unit that forms a gap between the image carrier and the transfer unit by inserting a gap forming unit at a position in contact, and the gap forming unit forms an image in the main scanning direction at the contacting position. And the non-image forming area outside the main scanning direction with respect to the image forming area.

  With this configuration, the gap forming means is provided between the image forming area and the non-image forming area in the main scanning direction between the image carrier and the transfer means, and the gap is formed at a predetermined timing in the nip portion between the image carrier and the transfer means. Since a gap is formed between the image carrier and the transfer unit by inserting the forming unit, the timing at which the recording medium enters the nip portion of the image carrier and the transfer unit and the timing at which the trailing edge comes out If a gap is formed at the nip portion between the image carrier and the transfer means, the gap formed in the main scanning direction of the image carrier can be made uniform.

  Therefore, regardless of the width of the recording medium, it is possible to prevent an impact from being applied to the image carrier when the recording medium enters and exits the nip portion of the image carrier and the transfer means.

  As a result, it is possible to prevent the rotation speed of the image carrier from fluctuating, and image defects called banding such as streak in the main scanning direction, band-like shading unevenness in the sub-scanning direction, and image misalignment occur. Can be prevented.

Further, the gap forming means of the image forming apparatus of the present invention is configured such that the length in the sub-scanning direction is different between the non-image forming area and the image forming area.
With this configuration, when the gap forming means is inserted between the image carrier and the transfer means, and there is a small gap in the sub-scanning direction between the recording medium and the gap forming means, it is provided in the non-image forming area. Since the long portion of the gap forming means forms a gap between the image carrier and the transfer means for a relatively long time, the recording medium enters or leaves between the image carrier and the transfer means. Can be mitigated, and fluctuations in the rotational speed of the image carrier can be more reliably prevented.

  Further, the gap forming means of the image forming apparatus of the present invention comprises an external gap forming part provided in the non-image forming area and an internal gap forming part provided in the image forming area, and the image carrier A gap formed between the image carrier and the transfer means when the image forming member rotates in the sub-scanning direction so that the outer gap forming portion forms a long distance with respect to the inner gap forming portion. The inner gap forming part and the outer gap forming part are configured to set lengths in the sub-scanning direction.

  With this configuration, when the gap forming means is inserted between the image carrier and the transfer means, the external gap forming means is compared when there is a small gap in the sub-scanning direction between the recording medium and the gap forming means. Since a gap is formed between the image carrier and the transfer unit over a relatively long time, the impact when the recording medium enters or exits between the image carrier and the transfer unit can be reduced, and the image carrier It can prevent more reliably that the rotational speed of a body fluctuates.

  In the image forming apparatus of the present invention, the operation timing of the gap forming unit includes a first timing when the external gap forming unit starts forming the gap and a second timing when the gap forming unit ends. A third timing at which the internal gap forming means starts forming the gap and a fourth timing at which the formation of the gap is finished, and at least the first timing and the third timing, or the second timing. And the lengths in the sub-scanning direction of the internal gap forming portion and the external gap forming portion are set so that the fourth timing is different.

  With this configuration, the internal gap forming portion and the external gap forming portion are set so that the first timing and the third timing at which the gap formation is started, or the second timing and the fourth timing at which the gap formation is finished are different. Therefore, when the gap forming unit is inserted between the image carrier and the transfer unit, or when the gap forming unit comes out, a small gap in the sub scanning direction is formed between the recording medium and the gap forming unit. In some cases, the external gap forming means can form a gap between the image carrier and the transfer means over a relatively long time.

  For this reason, it is possible to mitigate the impact when the recording medium enters between the image carrier and the transfer means, and it is possible to more reliably prevent the rotational speed of the image carrier from fluctuating.

  The image forming apparatus of the present invention starts the formation of the gap at the first timing and the third timing before the leading edge of the recording medium reaches the transfer unit, and the leading edge of the recording medium is The internal gap forming section and the inner gap forming section and the second gap are finished immediately before or simultaneously with reaching the means at the fourth timing, and then finished at the second timing. The external gap forming unit is configured to set the length in the sub-scanning direction.

  With this configuration, when the gap forming means is inserted between the image carrier and the transfer means, the external gap forming means is compared when there is a small gap in the sub-scanning direction between the recording medium and the gap forming means. A gap can be formed between the image carrier and the transfer means over a relatively long time.

  For this reason, it is possible to mitigate the impact when the recording medium enters the image carrier and the transfer means, and more reliably prevent the rotation speed of the image carrier from fluctuating.

  In addition, the image forming apparatus of the present invention starts forming the gap at the first timing before the trailing edge of the recording medium reaches the transfer means, and the trailing edge of the recording medium acts on the transfer means. The internal gap is formed such that the formation of the gap is started at the third timing immediately before or simultaneously with the arrival, and then the formation of the gap is finished at the second timing and the fourth timing. It is configured to set the length in the sub-scanning direction of the forming portion and the external gap forming portion.

  With this configuration, when the gap forming means is inserted between the image carrier and the transfer means, the external gap forming means is compared when there is a small gap in the sub-scanning direction between the recording medium and the gap forming means. A gap can be formed between the image carrier and the transfer means over a relatively long time.

  For this reason, it is possible to mitigate the impact when the recording medium comes out between the image carrier and the transfer means, and it is possible to more reliably prevent the rotation speed of the image carrier from fluctuating.

  The image forming apparatus of the present invention starts the formation of the gap at the first timing before the leading edge or the trailing edge of the recording medium reaches the transfer unit, and the leading edge or the trailing edge of the recording medium is The formation of the gap is started at the third timing immediately before or at the same time as reaching the transfer means, and after the formation of the gap is finished at the fourth timing, the formation at the second timing is performed. The internal gap forming portion and the external gap forming portion are configured to set the length in the sub-scanning direction so as to finish the formation of the gap.

  With this configuration, when the gap forming means is inserted between the image carrier and the transfer means, the external gap forming means is compared when there is a small gap in the sub-scanning direction between the recording medium and the gap forming means. A gap can be formed between the image carrier and the transfer means over a relatively long time.

  For this reason, it is possible to alleviate the impact when the recording medium enters and exits between the image carrier and the transfer means, and more reliably prevent the rotation speed of the image carrier from fluctuating. it can.

  In the image forming apparatus of the present invention, the edge shape in the main scanning direction of the internal gap forming means that finishes forming the gap at the fourth timing is formed in a linear shape parallel to the main scanning direction. It is configured.

  With this configuration, the gap formed by the image carrier and the transfer means can be linearly formed parallel to the recording medium, so that the gap between the recording medium and the gap forming means can be set small, and the leading edge of the recording medium Can further reduce the impact when entering between the image carrier and the transfer means.

  In the image forming apparatus of the present invention, the edge shape in the main scanning direction of the internal gap forming means that finishes the formation of the gap at the fourth timing is scanned from the center in the main scanning direction of the image forming area. The fourth timing is delayed from the center in the main scanning direction toward the outside in the main scanning direction so that the fourth timing is delayed toward the outside in the direction.

  With this configuration, the gap formed by the image carrier and the transfer unit can be formed so as to widen from the center in the main scanning direction to the outside in the main scanning direction, so that recording can be performed regardless of the width of the recording medium. A gap can be formed between the image carrier and the transfer means at the leading end of both ends in the width direction of the medium. For this reason, it is possible to further reduce the impact when the leading edge of the recording medium enters between the image carrier and the transfer means.

  In the image forming apparatus of the present invention, the edge shape in the main scanning direction of the internal gap forming means that finishes the formation of the gap at the fourth timing is scanned from the center in the main scanning direction of the image forming area. Formed in a plurality of staircases that are symmetrically inclined outward in the main / sub-scanning direction across the central portion in the main scanning direction so that the fourth timing is delayed toward the outside in the direction, and formed by each staircase The gap is made to correspond to the length in the width direction for each size of the recording medium.

  With this configuration, it is possible to form a gap between the image carrier and the transfer unit on the leading end side of both ends in the width direction of the recording medium according to the size of the recording medium. For this reason, it is possible to further reduce the impact when the leading edge of the recording medium enters between the image carrier and the transfer means.

  In the image forming apparatus of the present invention, the edge shape in the main scanning direction of the internal gap forming means that finishes the formation of the gap at the fourth timing is scanned from the center in the main scanning direction of the image forming area. Consists of a continuous curve shape or a straight line shape that is symmetrically inclined outward in the main / sub scanning direction with the central portion in the main scanning direction sandwiched so that the fourth timing is delayed toward the outside in the direction. Has been.

  With this configuration, the gap formed by the image carrier and the transfer unit can be formed in a continuous curved shape or linear shape inclined from the central portion in the main scanning direction toward the outside in the main scanning direction. Regardless of the width, a gap can be formed between the image carrier and the transfer means at the leading end of both ends in the width direction of the recording medium. For this reason, it is possible to further reduce the impact when the leading edge of the recording medium enters between the image carrier and the transfer means.

  In the image forming apparatus of the present invention, the edge shape in the main scanning direction of the internal gap forming means that starts forming the gap at the third timing is formed in a linear shape parallel to the main scanning direction. It is configured.

  With this configuration, the gap formed by the image carrier and the transfer unit can be linearly formed parallel to the recording medium, so that the gap between the recording medium and the gap forming unit can be set small. It is possible to further alleviate the impact when the end comes out between the image carrier and the transfer means.

  In the image forming apparatus according to the present invention, the edge shape in the main scanning direction of the internal gap forming unit that starts forming the gap at the third timing is scanned from the central portion in the main scanning direction of the image forming area. The third timing is configured to spread from the center in the main scanning direction toward the outside in the main scanning direction so that the third timing is advanced toward the outside in the direction.

  With this configuration, the gap formed by the image carrier and the transfer unit can be formed so as to widen from the center in the main scanning direction to the outside in the main scanning direction, so that recording can be performed regardless of the width of the recording medium. A gap can be formed between the image carrier and the transfer means on the rear end side of both end portions in the width direction of the medium. For this reason, it is possible to further alleviate the impact when the trailing edge of the recording medium comes out between the image carrier and the transfer means.

  In the image forming apparatus according to the present invention, the edge shape in the main scanning direction of the internal gap forming unit that starts forming the gap at the third timing is scanned from the central portion in the main scanning direction of the image forming area. Formed in a plurality of staircases that are symmetrically inclined outward in the main / sub-scanning direction across the central portion in the main scanning direction so that the third timing is advanced toward the outside in the direction, and formed by each staircase The gap is made to correspond to the length in the width direction for each size of the recording medium.

  With this configuration, a gap can be formed between the image carrier and the transfer unit on the rear end side of both end portions in the width direction of the recording medium according to the size of the recording medium. For this reason, it is possible to further alleviate the impact when the trailing edge of the recording medium comes out between the image carrier and the transfer means.

  In the image forming apparatus according to the present invention, the edge shape in the main scanning direction of the internal gap forming unit that starts forming the gap at the third timing is scanned from the central portion in the main scanning direction of the image forming area. Consisting of a continuous curved shape or a linear shape inclined symmetrically outward in the main / sub-scanning direction across the central portion in the main scanning direction so that the third timing is advanced toward the outer side in the direction Has been.

  With this configuration, the gap formed by the image carrier and the transfer unit can be formed in a continuous curved shape or linear shape inclined from the central portion in the main scanning direction toward the outside in the main scanning direction. Regardless of the width, a gap can be formed between the image carrier and the transfer means on the rear end side of both end portions in the width direction of the recording medium. For this reason, it is possible to further alleviate the impact when the trailing edge of the recording medium comes out between the image carrier and the transfer means.

The image forming apparatus of the present invention is configured to vary the operation timing of the gap forming means in accordance with the width of the recording medium.
With this configuration, the operation timing of the gap forming means is made variable in accordance with the width of the recording medium, so that the recording medium can carry the image when the recording medium enters or leaves between the image carrier and the transfer means. The gap formed between the bodies can be optimized according to the width of the recording medium. For this reason, it is possible to further alleviate the impact when entering and exiting between the image carrier of the recording medium and the transfer means.

  In addition, the transfer unit of the image forming apparatus of the present invention includes a holding member that is connected to a transfer roller via a torque limiter and holds the gap forming unit. The holding unit is locked to the holding member and rotates the holding member. A holding member rotation control unit that moves between a permissible position that permits the rotation of the holding member and a prohibition position that prohibits rotation of the holding member away from the holding member, and a recording medium detection unit that detects the recording medium. The holding member rotation control means is configured to move between the allowable position and the prohibited position based on the detection information of the recording medium detection means.

  With this configuration, when a gap is formed between the image carrier and the transfer unit, the holding member rotation control unit is moved to an allowable position to allow the holding member to rotate, and the gap between the image carrier and the transfer unit is allowed. Since the holding member rotation control means is moved to the prohibited position to prohibit the rotation of the holding member when the image forming mechanism is not formed, the gap forming means can be inserted between the image carrier and the transfer means with a simple configuration. it can.

  As described above, it is possible to provide an image forming apparatus capable of preventing the fluctuation of the rotation speed of the image carrier regardless of the width of the recording medium and forming a good image.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIGS. 1 to 8 are diagrams showing a first embodiment of an image forming apparatus according to the present invention. In this embodiment, the image forming apparatus is applied to a copying machine that performs color printing. In addition to the copying machine, the image forming apparatus may be applied to a printer, a facsimile machine, a multifunction machine having a copying function and a facsimile communication function, and the like.

  In FIG. 1, a copying machine 100 includes a printer unit 101, a paper feeding unit 102, a scanner unit 103 and an automatic document feeder (hereinafter referred to as ADF) 104 fixed to the upper part of the printer unit 101, and each device in the copying machine 100. A controller 105 or the like for controlling the operation.

  The scanner unit 103 reads image information of a document placed on the contact glass 106, forms a light source for irradiating light on the document placed on the contact glass 106, and forms reflected light from the document. A reflection mirror that leads to a photoelectric conversion element such as a CCD image scanner through a lens is provided.

  The printer unit 101 includes an intermediate transfer unit 107 and an exposure device, an image forming unit, a fixing unit, a toner supply device, and the like, and transfers an image of a document read by the scanner unit 103 onto a recording sheet as a recording medium. It has become.

  The paper feed unit 102 includes a plurality of paper feed cassettes, a transport path, and the like, and feeds recording paper stored in the paper feed cassette to the intermediate transfer unit 107 through the transport path.

FIG. 2 is a diagram illustrating a configuration of the intermediate transfer unit 107. The intermediate transfer unit 107 uses the image forming units 21Y, 21M, 21C, and 21Bk as image forming units corresponding to four colors of yellow (Y), magenta (M), cyan (C), and black (Bk), respectively, to form a toner image. The toner image is primarily transferred onto an endless intermediate transfer belt 22 as an image carrier.
Specifically, the image forming units 21Y, 21M, 21C, and 21Bk are arranged on the photosensitive drum 21a by exposing the photosensitive drum 21a, the charger 21b that charges the photosensitive drum 21a, and the photosensitive drum 21a. An exposure device 21c that forms an electrostatic latent image corresponding to the original image, a developing device 21d that visualizes the electrostatic latent image by supplying toner onto the photosensitive drum 21a, and an intermediate transfer belt 22 are photosensitive. A transfer roller 21e for transferring the toner image on the body drum 21a and a cleaning blade 21f for removing residual toner on the photoreceptor drum 21a are provided.
Since the image forming units 21Y, 21M, 21C, and 21Bk all have the same configuration, only the image forming unit 21Bk is given a reference numeral.

  The intermediate transfer belt 22 is configured such that an inscribed belt driving roller 23 is driven by a belt driving motor 24 and a belt driving gear 25 to move around. The belt is driven by a belt driven roller 26, a counter roller 27, a belt stretching roller 28, and the like. It is stretched. The intermediate transfer belt 22 means rotation.

  Further, a secondary transfer roller 31 as a transfer means and a transfer roller is in sliding contact with the intermediate transfer belt 22, and the secondary transfer roller 31 presses the recording paper P against the intermediate transfer belt 22 so as to be on the intermediate transfer belt 22. The toner image is transferred onto the recording paper P.

  Specifically, the recording paper P stored in the paper feed cassette of the paper feed unit 102 is fed by a paper separation mechanism or a transporting unit (not shown), and then a registration roller pair as a recording medium transporting unit at a desired timing. 29 is conveyed to the intermediate transfer belt 22 side.

  When the leading edge of the recording paper P conveyed by the registration roller pair 29 is detected by the registration sensor 30 as a recording medium detection unit, the registration sensor 30 outputs a signal to the controller 105.

  Based on this detection information, the controller 105 stops a paper feed motor (not shown) that drives the registration roller pair 29 to stop registration of the recording paper P, and drives the paper feed motor in synchronization with the conveyance timing of the intermediate transfer belt 22. As a result, the recording paper P is conveyed to the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31, and an image is transferred to the recording paper P at the nip portion, and then the toner image on the recording paper P by the pair of fixing rollers 32. Is fixed by heating.

  3 and 4 are perspective views of the main part of the intermediate transfer portion. 3 and 4, the widths of the intermediate transfer belt 22, the opposing roller 27, and the secondary transfer roller 31 in the main scanning direction (the axial direction of the opposing roller 27 and the secondary transfer roller 31) are Wb, Wr, and Wt, respectively. The image forming area (in the recording paper transport area) in the main scanning direction at the position where the intermediate transfer belt 22 and the secondary transfer roller 31 are in contact is set to Wi, and the non-image forming area (recording paper transport area) outside both ends is set. The relational expression when the outer side is defined as Wo is Wr (the length of the opposing roller 27) = 2Wo + Wi.

  Further, the image forming area Wi is set to be slightly larger than the recording paper having the maximum recording width Wpmax, and an image can be transferred from the minimum size to the maximum size recording paper. Further, in the non-image forming area Wo of the secondary transfer roller 31, the non-image forming part of the opposing roller 27 and the non-image forming part 31 b of the secondary transfer roller 31 are located.

  A torque limiter 33 slides on each of the secondary transfer roller shafts 31 a provided at both ends of the secondary transfer roller 31. The torque limiter 33 is press-fitted into the outer periphery of the torque limiter 33, and the torque limiter A holding ring 45 is provided integrally with the holder 35. In the present embodiment, the torque limiter holder 35 and the holding ring 45 constitute a holding member.

  The torque limiter 33 and the torque limiter holder 35 are not moved in the main scanning direction, and the torque limiter holder 35 holds the holding ring 45 with the set torque of the torque limiter 33 by the rotation of the secondary transfer roller shaft 31a. Rotate with.

  Further, both end portions of the secondary transfer roller shaft 31a are rotatably supported by a bearing 34, and the bearing 34 is movable in the vertical direction (radial direction). The bearing 34 is attached to a bearing holder 36. The bearing holder 36 is engaged with a slide hole 101b formed in the main body 101a of the copying machine 100 so as to move in the vertical direction.

  A spring receiving portion 37 is provided on the lower surface of the slide hole portion 101b. A compression spring 38 is interposed between the spring receiving portion 37 and the bearing holder 36. The bearing holder 36 is moved upward by the compression spring 38. Is being energized.

  Therefore, the secondary transfer roller 31 is movable in the vertical direction via the secondary transfer roller shaft 31a and the bearing holder 36, and is always urged by the compression spring 38 so as to be in sliding contact with the intermediate transfer belt 22. It is pressed.

  When the recording paper P reaches the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31, the secondary transfer roller 31 moves downward in FIG. 22 and the secondary transfer roller 31 can enter the recording sheet P. In particular, when the leading edge and the trailing edge of the recording sheet P pass, the secondary transfer roller 31 can rapidly move up and down. .

  Further, the opposing roller shaft 27a of the opposing roller 27 is rotatably attached to the main body 101a via a bearing 40, so that the opposing roller 27 cannot move in the radial direction.

  On the other hand, a pair of flexible elastic sheets 39 as gap forming means are attached to the holding rings 45 provided at both ends of the secondary transfer roller 31. The elastic sheets 39 are polyethylene terephthalate (PET), It is composed of polycarbonate (PC), polyamide (nylon) or the like.

  The elastic sheet 39 is attached to the holding ring 45 by bonding, welding, fusion, or the like, and a part of the elastic sheet 39 in the width Wb of the intermediate transfer belt 22 in the non-image forming area Wo and the non-image forming area Wo. An external sheet portion (external gap forming portion) 39b provided and an internal sheet portion (internal gap forming portion) 39c provided in the image forming area Wi are provided, and the mounting portion 39a, the external sheet portion 39b, and the internal sheet are provided. 39c is integrally formed.

  Note that the attachment portion 39a, the outer sheet portion 39b, and the inner sheet 39c may be configured by joining separate members without being configured integrally. Further, it is needless to say that the elastic sheet 39 needs to secure rigidity so that at least the outer sheet portions 39b on both the left and right sides are twisted in the sub-scanning direction and the phase is not shifted.

  Further, the width of the external sheet portion 39b in the main scanning direction is set to Wg, and the width of the external sheet portion 39b in the sub scanning direction (conveyance direction of the recording paper P perpendicular to the axial direction of the secondary transfer roller 31) is The inner sheet portion 39c is set to be longer than the width in the main scanning direction. Further, the outer sheet portion 39b and the inner sheet portion 39c are formed to have the same thickness.

  Further, the outer sheet portion 39b has an arc shape along the outer periphery of the mounting portion 39a, and is free on the upstream side thereof, and thus has a planar shape due to the restoring force of the outer sheet portion 39b.

  Further, the left and right torque limiter holders 35 of the secondary transfer roller 31 are provided with a rotation locking claw 41 (only the left side is shown), and the rotation locking claw 41 has both end portions (only the left side). It is adapted to be engaged with an engaging claw 42a provided in the figure. The locking plate 42 is formed with a long elongated hole portion 42b extending in the main scanning direction, and a pin 43 fixed to the main body 101a is inserted into the elongated hole portion 42b.

  Further, an electromagnetic solenoid 44 is connected to the locking claw 42, and the locking plate 42 is driven by the electromagnetic solenoid 44, so that the locking claw 42 a is connected to the rotation locking claw 41 along the long hole portion 42 b. It moves in the main scanning direction between the position to be locked and the position separated from the rotation locking claw 41.

  Specifically, when the registration sensor 30 detects the leading edge of the recording paper P, the controller 105 turns on the electromagnetic solenoid 44 based on the detection signal from the registration sensor 30, thereby causing the locking plate 42 to move to the allowable position. The elastic sheet 39 is inserted into the intermediate transfer belt 22 and the secondary transfer roller 31 at the timing when the leading edge of the recording paper P enters between the intermediate transfer belt 22 and the secondary transfer roller 31.

  In this embodiment, when the locking claw 42 a of the locking plate 42 is locked to the rotation locking claw 41, the torque limiter 33 slips and rotates only the secondary transfer roller 31, and the torque limiter holder 35 and the holding ring are rotated. 45 can be prohibited from rotating.

  When the locking claw 42 a is separated from the rotation locking claw 41, power is transmitted from the secondary transfer roller shaft 31 a to the torque limiter holder 35 to rotate the torque limiter holder 35 and the holding ring 45 together with the secondary transfer roller 31. Thus, the outer sheet portion 39 b and the inner sheet portion 39 c can be inserted between the secondary transfer roller 31 and the intermediate transfer belt 22.

  For this reason, a gap is formed between the intermediate transfer belt 22 and the secondary transfer roller 31 according to the plate thickness of the outer sheet portion 39b and the inner sheet portion 39c. However, the plate thickness of the outer sheet portion 39b and the inner sheet portion 39c must be thinner than the thinnest thickness of the recording paper P necessary for the outer sheet portion 39b and the inner sheet portion 39c to be activated.

  This is because if the plate thickness of the outer sheet portion 39b and the inner sheet portion 39c is made larger than the thickness of the recording paper P, the pressure for sufficiently transferring the toner image in the image forming area Wi to the recording paper P. This is because of insufficient transfer and transfer failure. For example, if the threshold cardboard for starting the elastic sheet 39 is 135 kg, the thickness is about 180 μm. In this case, the thickness of the outer sheet portion 39b and the inner sheet portion 39c is set to be less than 180 μm.

  As the secondary transfer roller 31 and the secondary transfer roller shaft 31a move up and down, the torque limiter holders 35 and the rotation pawls 41 provided on the left and right of the secondary transfer roller 31 also move up and down at the same time. The movement amounts of the transfer roller 31 and the secondary transfer roller shaft 31a and the rotation locking claw 41 are not necessarily equal, and in order to rotate the left and right torque limiter holders 35 simultaneously, the rotation locking claw 41 and the locking claw It is necessary to retract the locking plate 42 in such a direction that the timing at which the locking of the 42a is released is not affected by the secondary transfer roller 31 and the vertical movement position of the secondary transfer roller 31.

  In the present embodiment, the locking claw 42 and the locking claw 42a can be easily unlocked by shifting the locking claw 42a to the left. In the present embodiment, since the electromagnetic solenoid 44 is used as power, it can be operated instantaneously by an electric signal output from the controller 105. Specifically, it can be operated only by energizing for a moment (about several tens of milliseconds to several hundreds of milliseconds).

  In the present embodiment, the locking plate 42, the electromagnetic solenoid 44, and the controller 105 constitute a holding member rotation control means.

FIG. 5 is a diagram for explaining the dimensions of the elastic sheet 39 and the recording paper P and the positional relationship in the main and sub scanning directions.
In FIG. 5, the front end (left side in FIG. 5) of the recording paper P has a dimension A1 in the sub-scanning direction of the internal sheet portion 39c that is spaced by a dimension A2 of the gap between the front end of the recording paper P and the internal sheet portion 39c. The outer sheet portion 39b is set at both ends of the inner sheet portion 39c. The outer sheet portion 39b has a dimension A1 + A2 + A3 in the sub-scanning direction and a dimension Wg in the main scanning direction.

  That is, the outer sheet 39b is formed longer in the sub-scanning direction than the inner sheet 39c, and the dimension A1 of the inner sheet 39c in the sub-scanning direction is equal to the dimension A2 of the gap between the leading edge of the recording paper P and the inner sheet 39c. The outer sheet portion 39b is overlapped by the dimension A3 with respect to the leading end of the recording paper P, so that the outer end of the recording paper P is also externally immediately after passing the nip portion between the intermediate transfer roller 22 and the secondary transfer roller 31. The sheet portion 39b remains in the nip portion.

  The operation timing for forming the gap between the intermediate transfer roller 22 and the secondary transfer roller 31 by the elastic sheet 39 is the first timing (indicated by B1) when the external sheet portion 39b starts to form the gap and A second timing (indicated by B2) for ending the formation of the gap, a third timing (indicated by B3) at which the inner sheet portion 39c starts to form a gap, and a fourth timing (B4) at which the formation of the gap is finished. The lengths in the sub-scanning direction of the external sheet portion 39b and the internal sheet portion 39c are set so that the second timing B2 and the fourth timing B4 are different timings.

  Specifically, in the present embodiment, the edge shape in the main scanning direction of the internal sheet portion 39c, which finishes the formation of the gap at the fourth timing B4, is formed in a linear shape parallel to the main scanning direction, and the second The length in the sub-scanning direction of the outer sheet portion 39b that completes the formation of the gap at the timing B2 is formed longer than the inner sheet portion 39c.

  Next, a method for transporting the recording paper P will be described with reference to FIGS. 6 is a view showing a state in which the locking claw 42a of the locking plate 42 is locked to the rotation locking claw 41, and FIG. 7 is a view in which the locking claw 42a of the locking plate 42 is separated from the rotation locking claw 41. FIG. 8 is a diagram showing a recording paper transport procedure.

  First, the recording paper P stored in the paper feeding cassette is fed by a paper separating mechanism and a conveying means, and then conveyed to the intermediate transfer belt 22 side by a registration roller pair 29 as a recording medium conveying means at a desired timing. The

  When the counter roller 27 starts to rotate as the intermediate transfer belt 22 rotates, the secondary transfer roller 31 is in a state where the rotation locking claw 41 is locked to the locking claw 42a, so that the torque limiter 33 slips. As a result, only the secondary transfer roller 31 rotates with the intermediate transfer belt 22. For this reason, the elastic sheet 39 enters a standby state where it stops before the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31 (see FIG. 8A).

  Next, when the recording paper P is conveyed by the registration roller pair 29 and the leading edge of the recording paper P is detected by the registration sensor 30 (see FIG. 8B), the controller 105 turns on the electromagnetic solenoid 44.

  At this time, the locking plate 42 moves in the main scanning direction to separate the locking claw 42 a from the rotation locking claw 41. Therefore, the driving force is transmitted from the secondary transfer roller shaft 31a to the torque limiter holder 35 via the torque limiter 33, and the torque limiter holder 35 and the elastic sheet 39 start to rotate in the counterclockwise direction (FIG. 8 (c). )reference).

  When the torque limiter holder 35 further rotates, the outer sheet portion 39b and the inner sheet portion 39c enter between the intermediate transfer belt 22 and the secondary transfer roller 31 (see FIG. 8D), and the opposing roller 27 and the intermediate transfer belt. A gap corresponding to the plate thickness of the intermediate transfer belt 22, the outer sheet portion 39b, and the inner sheet portion 39c is formed across the main scanning direction between the two.

  Further, the bearing holder 36 moves downward against the urging force of the compression spring 38, and the secondary transfer roller 31 moves downward by an amount corresponding to the plate thickness of the elastic sheet 39, so that the elastic sheet 39 is smoothly moved. Insert into. The leading edge of the recording paper P enters between the intermediate transfer belt 22 and the secondary transfer roller 31 through this gap.

  When the torque limiter holder 35 further rotates, the internal sheet portion 39c having a short length in the sub-scanning direction is pulled out from between the intermediate transfer belt 22 and the secondary transfer roller 31, and is formed longer in the sub-scanning direction than the internal sheet portion 39c. The outer sheet portion 39b remains on the intermediate transfer belt 22 and the secondary transfer roller 31 to form a gap between the intermediate transfer belt 22 and the secondary transfer roller 31 (see FIG. 8E).

  When the torque limiter holder 35 further rotates, the external sheet portion 39b is pulled out from between the intermediate transfer belt 22 and the secondary transfer roller 31, and between the opposing roller 27 and the intermediate transfer belt 22, the intermediate transfer belt 22 and the recording paper P are removed. Only a gap corresponding to the plate thickness is formed, and the recording paper P is conveyed by the intermediate transfer belt 22 and the secondary transfer roller 31 while transferring the toner image from the intermediate transfer belt 22 to the recording paper P (FIG. 8 ( f)).

  Next, the controller 105 turns off the electromagnetic solenoid 44 before the torque limiter holder 35 makes one rotation, returns the locking plate 42 to the original position (home position position), and moves the locking claw 42a to the rotation locking claw 41a. Lock.

  At this time, the torque limiter 33 slips to stop the rotation of the torque limiter holder 33 and rotate the secondary transfer roller 3 (see FIG. 8G). For this reason, the elastic sheet 39 does not enter the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31, and only the recording paper P is conveyed.

  Thus, in the present embodiment, the elastic sheet 39 is provided across the image forming area Wi and the non-image forming area Wo in the main scanning direction between the intermediate transfer belt 22 and the secondary transfer roller 31, and the intermediate transfer belt 22. Since the elastic sheet 39 is inserted into the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31 at a predetermined timing, a gap is formed between the intermediate transfer belt 22 and the secondary transfer roller 31. If a gap is formed in the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31 at the timing of entering the nip portion between the transfer belt 22 and the secondary transfer roller 31, the intermediate transfer belt 22 extends over the main scanning direction. The gap formed can be made uniform.

  Therefore, regardless of the width of the recording paper P, it is possible to prevent the impact from being applied to the intermediate transfer belt 22 when the recording paper P enters the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31. it can.

  As a result, it is possible to prevent the rotation speed of the intermediate transfer belt 22 from fluctuating, and image defects called banding such as streak in the main scanning direction, band-like shading unevenness in the sub-scanning direction, and image misalignment occur. Can be prevented.

  In this embodiment, the elastic sheet 39 includes an external sheet portion 39b provided in the non-image forming area Wo and an internal sheet portion 39c provided in the image forming area Wi, and the intermediate transfer belt 22 is sub-scanned. So that the outer sheet 39b forms a gap formed between the intermediate transfer belt 22 and the secondary transfer roller 31 over a long distance with respect to the inner sheet 39c. The length of the portion 39b in the sub-scanning direction is longer than the length of the inner sheet portion 39c in the sub-scanning direction, and the inner sheet portion 39c forms the gap at the second timing B2 when the outer sheet portion 39b finishes forming the gap. The fourth timing B4 to be finished is different from the timing.

  For this reason, when the elastic sheet 39 is inserted into the nip portion of the intermediate transfer belt 22 and the secondary transfer roller 31, there is a small gap in the sub-scanning direction between the recording paper P and the elastic sheet 39. The sheet portion 39 b can form a gap between the intermediate transfer belt 22 and the secondary transfer roller 31 over a relatively long time, and the recording paper P enters between the intermediate transfer belt 22 and the secondary transfer roller 31. Impact can be further reduced. For this reason, it can prevent more reliably that the rotational speed of the intermediate transfer belt 22 fluctuates.

  In the present embodiment, the edge shape in the main scanning direction of the internal sheet portion 39c, which completes the formation of the gap at the fourth timing B4, is formed in a linear shape parallel to the main scanning direction. In addition, the gap formed by the secondary transfer roller 31 can be a linear shape parallel to the recording paper P.

  Therefore, the gap between the recording paper P and the elastic sheet 39 can be set small, and the impact when the leading edge of the recording paper P enters between the intermediate transfer belt 22 and the secondary transfer roller 31 can be further reduced. Can do.

  In the present embodiment, the torque limiter holder 35 and the holding ring 45 that are connected to the secondary transfer roller 31 via the torque limiter 33 and hold the elastic sheet 39, and the rotation lock provided on the torque limiter holder 35. A locking claw 42a that moves between a permissible position that allows the rotation of the torque limiter holder 35 by locking the claw 41 and a prohibited position that prohibits the rotation of the torque limiter holder 35 from the rotation locking claw 41. And a registration sensor 30 for detecting the recording paper P, and the electromagnetic solenoid 44 is operated based on detection information from the registration sensor 30 to move the locking plate 42 to an allowable position. I tried to make it.

  For this reason, when a gap is formed between the intermediate transfer belt 22 and the secondary transfer roller 31, the locking plate 42 is moved to an allowable position to allow the torque limiter holder 35 to rotate, and the intermediate transfer belts 22 and 2. When no gap is formed between the next transfer rollers 31, the locking plate 42 can be moved to the prohibition position to prohibit the rotation of the torque limiter holder 35, and the elastic sheet 39 can be connected to the intermediate transfer belt 22 with a simple configuration. It can be inserted between the secondary transfer rollers 31.

  9 to 11 are views showing a second embodiment of the image forming apparatus according to the present invention. In the present embodiment, only the shape of the elastic sheet is different from that of the first embodiment, and other configurations are the same as those of the first embodiment, and therefore only different configurations will be described.

  In FIG. 9, an elastic sheet 51 as a gap forming means includes an attaching portion (not shown) attached to the holding ring 45, an external sheet portion (external gap forming portion) 51a installed in the non-image forming area Wo, and an image forming area. And an internal sheet portion (internal gap forming portion) 51b installed on the Wi.

  Further, the edge shape in the main scanning direction of the internal sheet portion 51b that finishes the formation of the gap at the fourth timing B4 is the fourth timing as it goes outward from the central portion in the main scanning direction of the image forming area Wi. It is formed so as to spread outward from the central portion in the main scanning direction so that B4 is delayed.

  In particular, in the present embodiment, the edge shape in the main scanning direction of the inner sheet portion 39c, which completes the formation of the gap at the fourth timing B4, is symmetrically outward in the main sub-scanning direction across the central portion in the main scanning direction. The gap formed by the stepped portion 52 of each staircase corresponds to the length in the width direction for each size of the recording paper P.

  For this reason, the leading ends of the widthwise ends of the recording paper P of each size are the gaps in the main scanning direction between the intermediate transfer belt 22 and the secondary transfer roller 31 defined by the respective step portions 52 of the internal sheet portion 51b. Rush into.

  In the present embodiment, when the length in the width direction of the recording paper P is detected by a recording paper size detection sensor (not shown) or input from the operation panel, the controller 105 performs electromagnetic solenoid 44 based on the detection information of the registration sensor 30. The timing for turning on is changed for each size of the recording paper P. That is, in the present embodiment, the operation timing of the elastic sheet 51 is varied according to the width of the recording paper P.

  For example, the A6 size recording paper P is conveyed in the sub-scanning direction by being sandwiched between the step portions 52 having the same interval as the length in the width direction for each size of the A6 recording paper P at the leading ends of the widthwise ends of the recording paper P. A gap formed between the intermediate transfer belt 22 and the secondary transfer roller 31 reaches a region suitable for the A6 size recording paper P.

  Further, at the leading ends of both ends in the width direction of the A3 size recording paper P having the maximum width, it is sandwiched between the external sheet portions 51a having the same interval as the width direction length for each size of the A3 recording paper P and conveyed in the sub-scanning direction. Therefore, the gap formed between the intermediate transfer belt 22 and the secondary transfer roller 31 reaches a region suitable for the A3-sized recording paper P.

  For this reason, when the elastic sheet 51 is inserted into the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31, the leading ends of both ends in the width direction of the recording paper P are defined by the step portions 52 of the internal sheet portion 51b. The intermediate transfer belt 22 and the secondary transfer roller 31 can be inserted into the nip portion through the gap.

  As described above, in the present embodiment, the edge shape in the main scanning direction of the internal sheet portion 51b, which finishes the formation of the gap at the fourth timing B4, is symmetrically left and right outside the main sub-scanning direction across the central portion in the main scanning direction. Are formed in a plurality of staircases inclined so as to spread toward the direction, and the gap formed by the stepped portion 52 of each staircase is set so as to correspond to the length in the width direction for each size of the recording paper P. Depending on the size of the paper P, a gap can be formed between the intermediate transfer belt 22 and the secondary transfer roller 31 at the leading end of both ends in the width direction of the recording paper P. For this reason, it is possible to further reduce the impact when the leading edge of the recording paper P enters between the intermediate transfer belt 22 and the secondary transfer roller 31.

  In the present embodiment, the edge shape in the main scanning direction of the internal sheet portion 51b, which finishes the formation of the gap at the fourth timing B4, is stepped. However, the present invention is not limited to this, and FIGS. It may be formed as shown.

  In FIG. 10, an elastic sheet 53 as a gap forming means includes an attaching portion (not shown) attached to the holding ring 45, an external sheet portion (external gap forming portion) 53a installed in the non-image forming area Wo, and an image forming area. And an internal sheet portion (internal gap forming portion) 53b installed in Wi.

  The edge shape in the main scanning direction of the internal sheet portion 53b that finishes the formation of the gap at the fourth timing B4 is such that the fourth timing B4 increases from the central portion in the main scanning direction of the image forming area Wi toward the outside in the main scanning direction. In order to be delayed, it is formed in a curved shape so as to spread outward from the central portion in the main scanning direction.

  Further, in FIG. 11, an elastic sheet 54 as a gap forming means includes a mounting portion (not shown) attached to the holding ring 45, an external sheet portion (external gap forming portion) 54a installed in the non-image forming area Wo, And an internal sheet portion (internal gap forming portion) 54b installed in the image area Wi.

  The edge shape in the main scanning direction of the inner sheet portion 54b that completes the formation of the gap at the fourth timing B4 is such that the fourth timing B4 increases from the central portion in the main scanning direction of the image forming area Wi toward the outside in the main scanning direction. In order to be delayed, it is formed in a linear shape so as to spread outward from the central portion in the main scanning direction.

  Even in this case, the operation timing of the elastic sheet 53 or the elastic sheet 54 is varied according to the width of the recording paper P according to the size of the recording paper P, and a gap is formed according to the size of the recording paper P. The impact when the leading edge of the recording paper P enters between the intermediate transfer belt 22 and the secondary transfer roller 31 can be further reduced.

12 to 15 are views showing a third embodiment of the image forming apparatus according to the present invention. The same reference numerals are given to the same components as those in the first embodiment, and the description thereof will be omitted.
12 and 13, an elastic sheet 61 as a gap forming means includes an attachment portion 61 a as a glue margin joined to the holding ring 45 by adhesion, welding, fusion, or the like, a non-image forming region Wo, and an intermediate portion. Two external sheet portions (external gap forming portions) 61b partially provided within the width Wb of the transfer belt 22 and an internal sheet portion (internal gap forming portion) 61c provided in the image forming area Wi are provided. The mounting portion 61a, the outer sheet portion 61b, and the inner sheet 61c are integrally formed.

  In the present embodiment, when the trailing edge of the recording paper P comes out of the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31, an impact is prevented from being generated on the intermediate transfer belt 22. 61b extends in the clockwise direction of the secondary transfer roller 31 from the internal sheet portion 61c.

  Further, as shown in FIG. 14, the rear end (right side in FIG. 14) of the recording paper P has a dimension C3 in the sub-scanning direction of the internal sheet 61c that is the gap between the rear end of the recording paper P and the internal sheet 61c. The outer sheet portion 61b is set to have a dimension C1 + C2 + C3 in the sub-scanning direction and a dimension Wg in the main scanning direction at both ends of the inner sheet portion 61c.

  That is, the outer sheet 61b is formed longer in the sub-scanning direction than the inner sheet 61c, and the dimension C3 of the inner sheet 61c in the sub-scanning direction is equal to the dimension C2 of the gap between the trailing edge of the recording paper P and the inner sheet 61c. The outer sheet portion 61b is overlapped with the rear end of the recording paper P by a dimension C1 so that the rear end of the recording paper P passes immediately after the nip portion between the intermediate transfer roller 22 and the secondary transfer roller 31. In addition, the external sheet portion 61b remains in the nip portion.

  The operation timing for forming a gap between the intermediate transfer roller 22 and the secondary transfer roller 31 by the elastic sheet 61 is a first timing (indicated by D1) when the external sheet portion 61b starts to form a gap, and A second timing (indicated by D2) for completing the formation of the gap, a third timing (indicated by D3) at which the inner sheet portion 61c starts to form a gap, and a fourth timing (D4) at which the formation of the gap is completed. The lengths in the sub-scanning direction of the outer sheet portion 61b and the inner sheet portion 61c are set so that the first timing D1 and the third timing D3 are different from each other.

  Specifically, in the present embodiment, the edge shape in the main scanning direction of the internal sheet portion 61c that starts forming the gap at the third timing D3 is formed in a linear shape parallel to the main scanning direction.

Next, a method for conveying the recording paper P will be described with reference to FIG.
First, the recording paper P stored in the paper feeding cassette is fed by a paper separating mechanism and a conveying means, and then conveyed to the intermediate transfer belt 22 side by a registration roller pair 29 as a recording medium conveying means at a desired timing. The

  When the counter roller 27 starts to rotate as the intermediate transfer belt 22 rotates, the secondary transfer roller 31 is in a state where the rotation locking claw 41 is locked to the locking claw 42a, so that the torque limiter 33 slips. As a result, only the secondary transfer roller 31 rotates with the intermediate transfer belt 22.

  The recording paper P conveyed to the registration roller pair 29 is nipped and conveyed by the intermediate transfer belt 22 and the secondary transfer roller 31. At this time, the bearing holder 36 moves downward against the urging force of the compression spring 38, and the secondary transfer roller 31 moves downward by an amount corresponding to the plate thickness of the elastic sheet 61. Insert smoothly.

  In addition, a gap corresponding to the thickness of the intermediate transfer belt 22 and the recording paper P is formed in the main scanning direction between the opposing roller 27 and the intermediate transfer belt 22 (see FIG. 15A).

  When the toner image is transferred from the intermediate transfer belt 22 to the recording paper P and the trailing edge of the recording paper P is detected by the registration sensor 30, the controller 105 counts the driving pulses of the driving motor driving pulses (FIG. 15). (See (b)). When this drive pulse reaches a predetermined pulse, the controller 105 turns on the electromagnetic solenoid 44.

  At this time, the locking plate 42 moves in the main scanning direction to separate the locking claw 42 a from the rotation locking claw 41. For this reason, the driving force is transmitted from the secondary transfer roller shaft 31a to the torque limiter holder 35 through the torque limiter 33, and the torque limiter holder 35 and the elastic sheet 61 start to rotate counterclockwise (FIG. 15C). )reference).

  When the torque limiter holder 35 further rotates, first, the external sheet portion 61b enters between the intermediate transfer belt 22 and the secondary transfer roller 31, and is intermediate in the main scanning direction between the opposing roller 27 and the intermediate transfer belt 22. A gap corresponding to the plate thickness of the transfer belt 22 and the external sheet portion 61b is formed.

  Further, when the torque limiter holder 35 further rotates, the inner sheet portion 61c having a short length in the sub-scanning direction is inserted into the intermediate transfer belt 22 and the secondary transfer roller 31, and the intermediate sheet transfer is performed by the outer sheet portion 61b and the inner sheet portion 61c. A gap is formed between the intermediate transfer belt 22 and the secondary transfer roller 31 remaining on the belt 22 and the secondary transfer roller 31 (see FIG. 15D). For this reason, the trailing edge of the recording paper P comes out from between the intermediate transfer belt 22 and the secondary transfer roller 31 through this gap (see FIG. 15E).

  Next, the controller 105 turns off the electromagnetic solenoid 44 before the torque limiter holder 35 makes one rotation, returns the locking plate 42 to the original position (home position position), and moves the locking claw 42a to the rotation locking claw 41a. Lock (see FIGS. 15 (f) and 15 (g)).

  At this time, the torque limiter 33 slips to stop the rotation of the torque limiter holder 35 and rotate the secondary transfer roller 3, so that the elastic sheet 61 enters the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31. No, and only the recording paper P is conveyed.

  As described above, in this embodiment, the elastic sheet 61 is provided between the intermediate transfer belt 22 and the secondary transfer roller 31 over the image forming area Wi and the non-image forming area Wo in the main scanning direction. Since the elastic sheet 61 is inserted into the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31 at a predetermined timing, a gap is formed between the intermediate transfer belt 22 and the secondary transfer roller 31. If a gap is formed in the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31 at the timing of entering the nip portion between the transfer belt 22 and the secondary transfer roller 31, the intermediate transfer belt 22 extends over the main scanning direction. The gap formed can be made uniform.

  Therefore, regardless of the width of the recording paper P, it is possible to prevent the impact from being applied to the intermediate transfer belt 22 when the recording paper P comes out of the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31. .

  As a result, it is possible to prevent the rotation speed of the intermediate transfer belt 22 from fluctuating, and image defects called banding such as streak in the main scanning direction, band-like shading unevenness in the sub-scanning direction, and image misalignment occur. Can be prevented.

  In the present embodiment, the elastic sheet 61 includes an external sheet portion 61b provided in the non-image forming area Wo and an internal sheet portion 61c provided in the image forming area Wi, and the intermediate transfer belt 22 is sub-scanned. So that the outer sheet 61b is formed over a long distance with respect to the inner sheet 61c with a gap formed between the intermediate transfer belt 22 and the secondary transfer roller 31 when moving in the direction. The length of the portion 61b in the sub-scanning direction is made longer than the length of the inner sheet portion 61c in the sub-scanning direction, and the inner sheet portion 61c forms the gap at the first timing D1 when the outer sheet portion 61b starts to form the gap. The third timing B3 to be finished is set to a different timing.

  For this reason, when the elastic sheet 61 comes out of the intermediate transfer belt 22 and the secondary transfer roller 31, the external sheet portion 61b is compared when there is a small gap in the sub-scanning direction between the recording paper P and the elastic sheet 61. A gap can be formed between the intermediate transfer belt 22 and the secondary transfer roller 31 over a relatively long time.

  For this reason, the impact when the recording paper P enters between the intermediate transfer belt 22 and the secondary transfer roller 31 can be reduced, and the rotation speed of the intermediate transfer belt 22 can be prevented more reliably. can do.

  In addition, since the edge shape in the main scanning direction of the internal sheet portion 61c that starts forming the gap at the third timing D3 is formed in a linear shape parallel to the main scanning direction, the intermediate transfer belt 22 and the secondary transfer roller 31 are formed. Can form a straight line parallel to the recording paper P.

  Therefore, the gap between the recording paper P and the internal sheet portion 61c can be set small, and the impact when the trailing edge of the recording paper P slips out between the intermediate transfer belt 22 and the secondary transfer roller 31 is further alleviated. be able to.

  FIG. 16 is a view showing a fourth embodiment of the image forming apparatus according to the present invention. In the present embodiment, only the shape of the elastic sheet is different from those of the first and third embodiments, and the other configurations are the same as those of the first and third embodiments. Therefore, only different configurations will be described.

  In FIG. 16, an elastic sheet 71 as a gap forming means includes an attaching portion (not shown) attached to the holding ring 45, an external sheet portion (external gap forming portion) 71a installed in the non-image forming area Wo, and an image forming area. And an internal sheet portion (internal gap forming portion) 71b installed in Wi.

  Further, the edge shape in the main scanning direction of the internal sheet portion 71b that starts the formation of the gap at the third timing E3 is the third timing as it goes outward from the central portion in the main scanning direction of the image forming area Wi. It is formed so as to spread from the center in the main scanning direction toward the outside in the main scanning direction so that D3 is accelerated.

  In particular, in the present embodiment, the edge shape in the main scanning direction of the internal sheet portion 71b that starts forming the gap at the third timing D3 is symmetrically outward in the main sub-scanning direction across the central portion in the main scanning direction. The gap formed by the stepped portion 72 of each staircase is set so as to correspond to the length in the width direction for each size of the recording paper P.

  Therefore, the rear ends of both end portions in the width direction of the recording paper P of each size are in the main scanning direction between the intermediate transfer belt 22 and the secondary transfer roller 31 defined by the respective step portions 72 of the internal sheet portion 71b. Exit through the gap.

  In the present embodiment, when the length in the width direction of the recording paper P is detected by a recording paper size detection sensor (not shown) or input from the operation panel, the controller 105 performs electromagnetic solenoid 44 based on the detection information of the registration sensor 30. The timing for turning on is changed for each size of the recording paper P. That is, in the present embodiment, the operation timing of the elastic sheet 71 is varied according to the width of the recording paper P.

  For example, the A6 size recording paper P is transported in the sub-scanning direction by being sandwiched by the stepped portions 72 having the same interval as the length in the width direction for each size of the A6 recording paper P at the rear end of both ends in the width direction. The gap formed between the intermediate transfer belt 22 and the secondary transfer roller 31 reaches a region suitable for the A6 size recording paper P.

  In addition, at the rear end of both ends in the width direction of the A3 size recording paper P having the maximum width, it is sandwiched between the outer sheet portions 71a having the same interval as the length in the width direction for each size of the A3 recording paper P in the sub scanning direction. Since the sheet is conveyed, a gap formed between the intermediate transfer belt 22 and the secondary transfer roller 31 reaches a region suitable for the A3-sized recording paper P.

  For this reason, when the elastic sheet 71 comes out of the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31, the rear ends of both ends in the width direction of the recording paper P are defined by the step portion 72 of the internal sheet portion 71b. The intermediate transfer belt 22 and the secondary transfer roller 31 can be pulled out through the gap.

  As described above, in the present embodiment, the edge shape in the main scanning direction of the inner sheet portion 71b that starts forming the gap at the third timing D3 is symmetrically left and right outside the main sub-scanning direction across the central portion in the main scanning direction. Are formed in a plurality of staircases that are inclined so as to spread toward the direction, and the gap formed by the stepped portion 72 of each staircase is set so as to correspond to the length in the width direction for each size of the recording paper P. Depending on the size of the paper P, a gap can be formed between the intermediate transfer belt 22 and the secondary transfer roller 31 on the rear end side of both ends in the width direction of the recording paper P. For this reason, it is possible to further alleviate the impact when the trailing edge of the recording paper P comes out between the intermediate transfer belt 22 and the secondary transfer roller 31.

  In this embodiment, the edge shape in the main scanning direction of the internal sheet portion 71b that starts the formation of the gap at the third timing D3 is stepped. However, the present invention is not limited to this, and FIGS. It may be formed as shown.

  In FIG. 17, an elastic sheet 73 as a gap forming means includes an attaching portion (not shown) attached to the holding ring 45, an external sheet portion (external gap forming portion) 73a installed in the non-image forming area Wo, and an image forming area. And an internal sheet portion (internal gap forming portion) 73b installed on the Wi.

  The edge shape in the main scanning direction of the internal sheet portion 73b that starts to form a gap at the third timing F3 is such that the third timing D3 increases from the central portion in the main scanning direction of the image forming area Wi toward the outside in the main scanning direction. The curve is formed so as to spread from the center in the main scanning direction toward the outside in the main scanning direction.

  Further, in FIG. 18, an elastic sheet 74 as a gap forming means includes a mounting portion (not shown) attached to the holding ring 45, an external sheet portion (external gap forming portion) 74a installed in the non-image forming area Wo, And an internal sheet portion (internal gap forming portion) 74b installed in the image area Wi.

  The edge shape in the main scanning direction of the internal sheet portion 74b that starts to form the gap at the third timing D3 is such that the third timing D3 increases from the central portion in the main scanning direction of the image forming area Wi toward the outside in the main scanning direction. In order to advance, it is formed in a linear shape so as to spread from the center in the main scanning direction toward the outside in the main scanning direction.

  Even in this case, the operation timing of the elastic sheet 73 can be varied according to the width of the recording paper P according to the size of the recording paper P, and a gap can be formed according to the size of the recording paper P. The impact when the trailing edge of the paper P slips out between the intermediate transfer belt 22 and the secondary transfer roller 31 can be further reduced.

  19 to 21 are views showing a fifth embodiment of the image forming apparatus according to the present invention. In the present embodiment, only the shape of the elastic sheet is different from those of the first and third embodiments, and the other configurations are the same as those of the first and third embodiments. Therefore, only different configurations will be described.

  In FIG. 19, an elastic sheet 75 as a gap forming means includes an attaching portion (not shown) attached to the holding ring 45, an external sheet portion (external gap forming portion) 75a installed in the non-image forming area Wo, and an image forming area. And an internal sheet portion (internal gap forming portion) 75b installed in Wi.

  Further, the elastic sheet 75 is configured to prevent an impact from being generated on the intermediate transfer belt 22 when the trailing edge of the recording paper P comes out of the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31. The outer sheet portion 75a extends further in the counterclockwise direction of the secondary transfer roller 31 than the inner sheet portion 75b.

  In addition, the dimension H3 in the sub-scanning direction of the inner sheet portion 75b is spaced by the dimension H2 of the gap between the trailing edge of the recording paper P and the inner sheet portion 75b, and the outer sheet 75a is in the main scanning with the dimension H1 + H2 + H3 in the sub-scanning direction. The direction dimension Wg is set.

  That is, the outer sheet portion 75a is formed longer in the sub-scanning direction than the inner sheet portion 75b, and the dimension H3 of the inner sheet portion 75b in the sub-scanning direction is equal to the dimension H2 of the gap between the trailing edge of the recording paper P and the inner sheet portion 75b. The outer sheet portion 75a is overlapped with the trailing edge of the recording paper P by the dimension H1, so that the trailing edge of the recording paper P passes immediately after the nip portion between the intermediate transfer roller 22 and the secondary transfer roller 31. In addition, the external sheet portion 75a remains in the nip portion.

  The operation timing for forming the gap between the intermediate transfer roller 22 and the secondary transfer roller 31 by the elastic sheet 75 is the first timing (indicated by E1) when the external sheet portion 75a starts to form the gap and A second timing (indicated by E2) at which the formation of the gap is finished, a third timing (indicated by E3) at which the inner sheet portion 75b starts to form a gap, and a fourth timing (E4) at which the formation of the gap is finished. And the formation of a gap is started at the third timing E3 immediately before or at the same time when the trailing edge of the recording paper P reaches the secondary transfer roller 31, and then the fourth timing. After the formation of the gap at E4, the lengths in the sub-scanning direction of the outer sheet portion 75a and the inner sheet portion 75b are set so that the formation of the gap is finished at the second timing E2. To have.

  Further, in the present embodiment, the edge shape in the main scanning direction of the internal sheet portion 75b that starts forming the gap at the third timing E3 is formed in a linear shape parallel to the main scanning direction.

  The elastic sheet 75 is configured to prevent an impact from being generated on the intermediate transfer belt 22 when the leading edge of the recording paper P enters the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31. The outer sheet portion 75a extends in the clockwise direction of the secondary transfer roller 31 from the inner sheet portion 75b.

  Further, the dimension H3 in the sub-scanning direction of the inner sheet portion 75b is separated by the dimension H4 of the gap between the leading edge of the recording paper P and the inner sheet portion 75b, and the outer sheet portion 75a has a dimension A3 + A4 + A5 in the sub-scanning direction. The dimension Wg is set.

  That is, the outer sheet portion 75a is formed longer in the sub-scanning direction than the inner sheet portion 75b, and the dimension H3 of the inner sheet portion 75b in the sub-scanning direction is equal to the dimension H4 of the gap between the leading edge of the recording paper P and the inner sheet portion 75b. The outer sheet portion 75a is overlapped by the dimension A5 with respect to the leading end of the recording paper P, so that the outer end of the recording paper P is also externally immediately after passing the nip portion between the intermediate transfer roller 22 and the secondary transfer roller 31. The sheet portion 75a remains in the nip portion.

  The operation timing for forming a gap between the intermediate transfer roller 22 and the secondary transfer roller 31 by the elastic sheet 75 is just before or at the same time when the leading edge of the recording paper P reaches the secondary transfer roller 31. The formation of the gap is started at the third timing E3, and then the formation of the gap is finished at the second timing E2 after the formation of the gap is finished at the fourth timing E4. The length of the sheet portion 75b in the sub-scanning direction is set.

  In the present embodiment, the edge shape in the main scanning direction of the internal sheet portion 75b that finishes the formation of the gap at the fourth timing E4 is formed in a linear shape parallel to the main scanning direction.

Next, a method for transporting the recording paper P will be described with reference to FIGS.
First, the recording paper P stored in the paper feeding cassette is fed by a paper separating mechanism and a conveying means, and then conveyed to the intermediate transfer belt 22 side by a registration roller pair 29 as a recording medium conveying means at a desired timing. The

  When the counter roller 27 starts to rotate as the intermediate transfer belt 22 rotates, the secondary transfer roller 31 is in a state where the rotation locking claw 41 is locked to the locking claw 42a, so that the torque limiter 33 slips. As a result, only the secondary transfer roller shaft 31 a rotates with the intermediate transfer belt 22.

  The recording paper P conveyed to the registration roller pair 29 is nipped and conveyed by the intermediate transfer belt 22 and the secondary transfer roller 31. At this time, the bearing holder 36 moves downward against the urging force of the compression spring 38, and the secondary transfer roller 31 moves downward by an amount corresponding to the plate thickness of the elastic sheet 61. Insert smoothly.

  In addition, a gap corresponding to the thickness of the intermediate transfer belt 22 and the recording paper P is formed in the main scanning direction between the opposing roller 27 and the intermediate transfer belt 22 (see FIG. 20A).

  When the toner image is transferred from the intermediate transfer belt 22 to the recording paper P and the trailing edge of the recording paper P is detected by the registration sensor 30 (see FIG. 20B), the controller 105 detects the drive pulse of the paper feed motor. Count drive pulses. When this drive pulse reaches a predetermined pulse, the controller 105 turns on the electromagnetic solenoid 44.

  At this time, the locking plate 42 moves in the main scanning direction to separate the locking claw 42 a from the rotation locking claw 41. Therefore, the driving force is transmitted from the secondary transfer roller shaft 31a to the torque limiter holder 35 through the torque limiter 33, and the torque limiter holder 35 and the elastic sheet 75 start to rotate counterclockwise (FIG. 20 (c). )reference).

  When the torque limiter holder 35 further rotates, first, the external sheet portion 75a enters between the intermediate transfer belt 22 and the secondary transfer roller 31 (see FIG. 20D), and between the opposing roller 27 and the intermediate transfer belt 22. A gap corresponding to the thickness of the intermediate transfer belt 22 and the external sheet 75b is formed over the main scanning direction.

  When the torque limiter holder 35 further rotates, the inner sheet portion 75b having a short length in the sub-scanning direction is inserted into the intermediate transfer belt 22 and the secondary transfer roller 31, and the intermediate sheet transfer is performed by the outer sheet portion 75a and the inner sheet portion 75b. A gap is formed between the intermediate transfer belt 22 and the secondary transfer roller 31 remaining on the belt 22 and the secondary transfer roller 31. For this reason, the trailing edge of the recording paper P comes out between the intermediate transfer belt 22 and the secondary transfer roller 31 through this gap.

  Next, the controller 105 turns off the electromagnetic solenoid 44 before the torque limiter holder 35 makes one rotation, returns the locking plate 42 to the original position (home position position), and moves the locking claw 42a to the rotation locking claw 41a. Lock (see FIG. 20 (e)).

  At this time, the torque limiter 33 slips to stop the rotation of the torque limiter holder 35 and rotate the secondary transfer roller 3, so that the elastic sheet 75 enters the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31. The trailing edge of the recording paper P is completely pulled out from between the intermediate transfer belt 22 and the secondary transfer roller 31.

  At this time, the succeeding recording paper P enters a standby state stopped before the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31. Next, when the recording paper P is conveyed by the registration roller pair 29 and the leading edge of the recording paper P is detected by the registration sensor 30, the controller 105 turns on the electromagnetic solenoid 44 (see FIG. 21A).

  At this time, the locking plate 42 moves in the main scanning direction to separate the locking claw 42 a from the rotation locking claw 41. For this reason, the driving force is transmitted from the secondary transfer roller shaft 31a to the torque limiter holder 35 via the torque limiter 33, and the torque limiter holder 35 and the elastic sheet 75 start to rotate counterclockwise.

  When the torque limiter holder 35 further rotates, the outer sheet portion 75a and the inner sheet portion 75b enter between the intermediate transfer belt 22 and the secondary transfer roller 31 (see FIG. 21B), and the opposing roller 27 and the intermediate transfer belt. A gap corresponding to the plate thickness of the intermediate transfer belt 22, the outer sheet portion 75a, and the inner sheet portion 75b is formed in the main scanning direction between the two.

  Further, the bearing holder 36 moves downward against the urging force of the compression spring 38, and the secondary transfer roller 31 moves downward by an amount corresponding to the plate thickness of the elastic sheet 39, thereby smoothly moving the elastic sheet 75. Insert into. The leading edge of the recording paper P enters between the intermediate transfer belt 22 and the secondary transfer roller 31 through this gap.

  When the torque limiter holder 35 further rotates, the inner sheet portion 75b having a short length in the sub-scanning direction comes out from between the intermediate transfer belt 22 and the secondary transfer roller 31, and is formed longer in the sub-scanning direction than the inner sheet portion 75b. The outer sheet portion 75a remains on the intermediate transfer belt 22 and the secondary transfer roller 31 to form a gap between the intermediate transfer belt 22 and the secondary transfer roller 31 (see FIG. 21C).

  When the torque limiter holder 35 further rotates, the external sheet portion 75 a comes out from between the intermediate transfer belt 22 and the secondary transfer roller 31, and the intermediate transfer belt 22 and the recording paper P are placed between the opposing roller 27 and the intermediate transfer belt 22. Only the gap corresponding to the plate thickness is formed, and the recording paper P is conveyed by the intermediate transfer belt 22 and the secondary transfer roller 31 while transferring the toner image from the intermediate transfer belt 22 to the recording paper P.

  Next, the controller 105 turns off the electromagnetic solenoid 44 before the torque limiter holder 35 makes one rotation, returns the locking plate 42 to the original position (home position position), and moves the locking claw 42a to the rotation locking claw 41a. Lock.

  At this time, the torque limiter 33 slips to stop the rotation of the torque limiter holder 35 and rotate the secondary transfer roller 3 (see FIG. 21D). For this reason, the elastic sheet 75 does not enter the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31, and only the recording paper P is conveyed.

  Thus, in the present embodiment, the elastic sheet 75 is provided across the image forming area Wi and the non-image forming area Wo in the main scanning direction between the intermediate transfer belt 22 and the secondary transfer roller 31, and the intermediate transfer belt 22. Since the elastic sheet 75 is inserted between the intermediate transfer belt 22 and the secondary transfer roller 31 at a predetermined timing, a gap is formed between the intermediate transfer belt 22 and the secondary transfer roller 31. If a gap is formed in the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31 at the timing when the belt 22 and the secondary transfer roller 31 enter and the timing when the belt 22 exits, the intermediate transfer belt 22 The gap formed in the main scanning direction can be made uniform.

  Therefore, regardless of the width of the recording paper P, it is possible to prevent the impact on the intermediate transfer belt 22 when the recording paper P enters and exits the nip portion between the intermediate transfer belt 22 and the secondary transfer roller 31. can do.

  As a result, it is possible to prevent the rotation speed of the intermediate transfer belt 22 from fluctuating, and image defects called banding such as streak in the main scanning direction, band-like shading unevenness in the sub-scanning direction, and image misalignment occur. Can be prevented.

  In the present embodiment, the gap formed between the intermediate transfer belt 22 and the secondary transfer roller 31 when the intermediate transfer belt 22 rotates in the sub-scanning direction is set to the outer sheet with respect to the inner sheet portion 75b. The length of the external sheet 75a in the sub-scanning direction is made longer than the length of the internal sheet 75b in the sub-scanning direction so that the portion 75a is formed over a long distance, and the outer sheet 75a finishes the formation of the gap. The second timing E2 and the fourth timing E4 at which the inner sheet portion 75b finishes the formation of the gap, and the first timing E1 and the inner sheet at which the outer sheet portion 75a starts to form the gap. The third timing E3 at which the part 75b starts to form the gap is set to a different timing.

  For this reason, when the elastic sheet 75 is inserted into the intermediate transfer belt 22 and the secondary transfer roller 31, there is a small gap in the sub-scanning direction between the recording paper P and the elastic sheet 75. Can form a gap between the intermediate transfer belt 22 and the secondary transfer roller 31 over a relatively long time, and the recording paper P enters between the intermediate transfer belt 22 and the secondary transfer roller 31. It is possible to mitigate the impact when it comes out, and more reliably prevent the rotation speed of the intermediate transfer belt 22 from fluctuating.

  In the present embodiment, the edge shape in the main scanning direction of the internal sheet portion 75b, which finishes forming the gap at the fourth timing E4, is formed in a linear shape parallel to the main scanning direction. In addition, the gap formed by the secondary transfer roller 31 can be a linear shape parallel to the recording paper P.

  In addition, since the edge shape in the main scanning direction of the internal sheet portion 75b that starts forming the gap at the third timing E3 is formed in a linear shape parallel to the main scanning direction, the intermediate transfer belt 22 and the secondary transfer roller 31 are formed. Can form a straight line parallel to the recording paper P.

  Therefore, the gap between the recording paper P and the elastic sheet 75 can be set small, and the impact when the leading edge of the recording paper P enters and exits between the intermediate transfer belt 22 and the secondary transfer roller 31 is further increased. Can be relaxed.

  In the present embodiment, the edge shape in the main scanning direction of the inner sheet portion 75b that finishes the formation of the gap at the fourth timing E4 and the main shape of the inner sheet portion 75b that starts the formation of the gap at the third timing E3. The edge shape in the scanning direction is formed into a plurality of staircases that are symmetrically inclined outward in the main sub-scanning direction across the central portion in the main scanning direction, and the gap formed by the step portions of each staircase is the recording paper It may be set so as to correspond to the length in the width direction for each size of P, and a linear shape or a linear shape inclined symmetrically outward in the main sub-scanning direction with the central portion in the main scanning direction interposed therebetween. good.

  As described above, the image forming apparatus according to the present invention has the effect of preventing the fluctuation of the rotation speed of the image carrier regardless of the width of the recording medium and forming a good image. And is useful as an image forming apparatus such as a copying machine, a printer apparatus, and a facsimile apparatus adopting an electrophotographic system.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. 1 is a schematic configuration diagram of an intermediate transfer unit of an image forming apparatus according to a first embodiment of the present invention. 1 is a perspective view of a main part of an intermediate transfer unit of an image forming apparatus according to a first embodiment of the present invention. 1 is a front view of a main part of an intermediate transfer unit of an image forming apparatus according to a first embodiment of the present invention. 2 is a diagram showing a positional relationship between the elastic sheet and the leading edge of the recording paper P of the image forming apparatus according to the first embodiment of the present invention. 1 is a perspective view of a main part of an intermediate transfer unit showing a state in which a locking claw of a locking plate is locked to a rotation locking claw of the image forming apparatus according to the first embodiment of the present invention. 1 is a perspective view of a main part of an intermediate transfer unit showing a state where a locking claw of a locking plate is separated from a rotation locking claw of an image forming apparatus according to a first embodiment of the present invention. FIG. 4 is a diagram illustrating a procedure for conveying the leading edge of a recording sheet of the image forming apparatus according to the first embodiment of the present invention. The figure which shows the elastic sheet of the image forming apparatus which concerns on the 2nd Embodiment of this invention The elastic sheet of the other shape of the image forming apparatus which concerns on the 2nd Embodiment of this invention is a figure. The elastic sheet of the other shape of the image forming apparatus which concerns on the 2nd Embodiment of this invention is a figure. FIG. 9 is a perspective view of main parts of an intermediate transfer unit of an image forming apparatus according to a third embodiment of the present invention. FIG. 9 is a perspective view of main parts of an intermediate transfer unit showing a state in which recording paper is conveyed by an intermediate transfer unit of an image forming apparatus according to a third embodiment of the present invention. The figure which shows the positional relationship of the elastic sheet of the image forming apparatus which concerns on the 3rd Embodiment of this invention, and the rear end of the recording paper P FIG. 10 is a diagram illustrating a procedure for conveying the trailing edge of a recording sheet of an image forming apparatus according to a third embodiment of the present invention. The figure which shows the structure of the elastic sheet of the image forming apparatus which concerns on the 4th Embodiment of this invention. The figure which shows the structure of the elastic sheet of the other shape of the image forming apparatus which concerns on the 4th Embodiment of this invention. The figure which shows the structure of the elastic sheet of the other shape of the image forming apparatus which concerns on the 4th Embodiment of this invention. The figure which shows the structure of the elastic sheet of the image forming apparatus which concerns on the 5th Embodiment of this invention. The figure which shows the conveyance procedure of the front-end | tip of the recording paper of the image forming apparatus which concerns on the 5th Embodiment of this invention. The figure which shows the conveyance procedure of the trailing end of the recording paper of the image forming apparatus which concerns on the 5th Embodiment of this invention. Perspective view of main part of intermediate transfer unit of image forming apparatus previously filed by the present applicant The figure which shows the conveyance procedure of the recording paper of the image forming apparatus which this applicant applied for earlier

Explanation of symbols

21Y, 21M, 21C, 21BK Image forming unit (image forming means)
22 Intermediate transfer belt (image carrier)
29 Registration roller pair (recording medium conveying means)
30 Registration sensor (recording medium detection means)
31 Secondary transfer roller (transfer means, transfer roller)
33 Torque limiter 35 Torque limiter holder (holding member)
39, 51, 53, 54, 61, 71, 73, 74, 75 Elastic sheet (gap forming means)
39b, 51a, 53a, 54a, 61b, 71a, 73a, 74a, 75a External sheet part (external gap forming part)
39c, 51b, 53b, 54b, 61c, 71b, 73b, 74b, 75b Internal sheet part (external gap forming part)
42 Locking plate (holding member rotation control means)
44 Electromagnetic solenoid (holding member rotation control means)
45 Retaining ring (holding member)
100 Copying machine (image forming device)
105 controller (holding member rotation control means)
P Recording paper (recording medium)
Wi imaging area Wo non-imaging area

Claims (17)

An image carrier that carries an image and rotates;
Image forming means for forming an image on the surface of the image carrier;
Transfer means for rotating in contact with the image carrier and transferring an image formed on the surface of the image carrier to a recording medium;
A recording medium conveying means for conveying the recording medium to a position where the image carrier and the transfer means abut;
A gap forming means for forming a gap between the image carrier and the transfer means by inserting a gap forming means at a position where the contact is made at a predetermined timing;
The gap forming means is provided in an image forming region in the main scanning direction at the abutting position and a non-image forming region outside the main scanning direction with respect to the image forming region. apparatus. The image forming apparatus according to claim 1, wherein the gap forming unit is configured such that the non-image forming area and the image forming area have different lengths in the sub-scanning direction. The gap forming means includes an external gap forming part provided in the non-image forming area, and an internal gap forming part provided in the image forming area,
When the image carrier rotates in the sub-scanning direction, a gap formed between the image carrier and the transfer unit is formed over a long distance with respect to the internal gap forming portion. The image forming apparatus according to claim 1, wherein lengths in the sub-scanning direction of the internal gap forming portion and the external gap forming portion are set. The operation timing of the gap forming means includes a first timing at which the external gap forming means starts to form the gap and a second timing at which the formation of the gap is completed, and an internal gap forming means at which the gap is formed. And a fourth timing to end the formation of the gap,
The lengths in the sub-scanning direction of the internal gap forming portion and the external gap forming portion are set so that at least the first timing and the third timing, or the second timing and the fourth timing are different. The image forming apparatus according to claim 3, wherein the image forming apparatus is set. Before the leading edge of the recording medium reaches the transfer means, the formation of the gap is started at the first timing and the third timing,
The formation of the gap is finished at the fourth timing immediately before or at the same time as the leading edge of the recording medium reaches the transfer means, and then the formation of the gap is finished at the second timing. 5. The image forming apparatus according to claim 4, wherein lengths in the sub-scanning direction of the internal gap forming portion and the external gap forming portion are set. Before the trailing edge of the recording medium reaches the transfer means, the formation of the gap is started at the first timing,
The formation of the gap is started at the third timing immediately before or at the same time as the trailing edge of the recording medium reaches the transfer means, and then the gap is reached at the second timing and the fourth timing. 5. The image forming apparatus according to claim 4, wherein lengths in the sub-scanning direction of the internal gap forming portion and the external gap forming portion are set so as to finish the formation of the image forming apparatus. Before the leading or trailing edge of the recording medium reaches the transfer means, the formation of the gap is started at the first timing,
The formation of the gap is started at the third timing immediately before or at the same time as the leading or trailing end of the recording medium reaches the transfer means, and then the formation of the gap is finished at the fourth timing. The sub-scanning direction lengths of the internal gap forming part and the external gap forming part are set so that the formation of the gap is finished at the second timing after Image forming apparatus. 8. The edge shape in the main scanning direction of the internal gap forming means that finishes forming the gap at the fourth timing is formed in a linear shape parallel to the main scanning direction. The image forming apparatus described in 1. The edge shape in the main scanning direction of the internal gap forming means that finishes forming the gap at the fourth timing is changed from the central portion in the main scanning direction to the outside in the main scanning direction of the image forming area. 8. The image forming apparatus according to claim 5, wherein the image forming apparatus is configured to spread from the central portion in the main scanning direction toward the outside in the main scanning direction so that the timing is delayed. The edge shape in the main scanning direction of the internal gap forming means that finishes forming the gap at the fourth timing is changed from the central portion in the main scanning direction to the outside in the main scanning direction of the image forming area. In order to delay the timing, it is formed in a plurality of staircases that are symmetrically inclined outward in the main sub-scanning direction with the central portion in the main scanning direction interposed therebetween, and the gap formed by each staircase is formed for each size of the recording medium. The image forming apparatus according to claim 5, wherein the image forming apparatus corresponds to a length in a width direction of the image forming apparatus. The edge shape in the main scanning direction of the internal gap forming means that finishes forming the gap at the fourth timing is changed from the central portion in the main scanning direction to the outside in the main scanning direction of the image forming area. 8. A continuous curved shape or a linear shape inclined symmetrically outward in the main sub-scanning direction with the central portion in the main scanning direction sandwiched so as to delay the timing. The image forming apparatus described. 8. The edge shape in the main scanning direction of the internal gap forming means that starts forming the gap at the third timing is formed in a linear shape parallel to the main scanning direction. The image forming apparatus described in 1. The edge shape in the main scanning direction of the internal gap forming means that starts forming the gap at the third timing is shifted from the center in the main scanning direction of the image forming area toward the outside in the main scanning direction. 8. The image forming apparatus according to claim 6, wherein the image forming apparatus is configured to spread from the central portion in the main scanning direction toward the outside in the main scanning direction so that the timing is advanced. The edge shape in the main scanning direction of the internal gap forming means that starts forming the gap at the third timing is shifted from the center in the main scanning direction of the image forming area toward the outside in the main scanning direction. A plurality of staircases that are symmetrically inclined outward in the main sub-scanning direction across the central portion in the main scanning direction so as to advance the timing are formed, and the gap formed by each step is formed for each size of the recording medium. The image forming apparatus according to claim 6, wherein the image forming apparatus corresponds to a length in a width direction of the image forming apparatus. The edge shape in the main scanning direction of the internal gap forming means that starts forming the gap at the third timing is shifted from the center in the main scanning direction of the image forming area toward the outside in the main scanning direction. 8. A continuous curve shape or a linear shape inclined symmetrically outward in the main sub-scanning direction with the central portion in the main scanning direction interposed therebetween so as to advance the timing. The image forming apparatus described. The image forming apparatus according to any one of claims 9 to 11, and 13 to 15, wherein the operation timing of the gap forming means is varied according to the width of the recording medium. The transfer unit includes a holding member that is connected to a transfer roller via a torque limiter and holds the gap forming unit.
A holding member rotation control means that moves between an allowable position that locks the holding member and allows rotation of the holding member, and a prohibited position that is spaced apart from the holding member and prohibits rotation of the holding member;
A recording medium detecting means for detecting the recording medium;
The said holding member rotation control means moves between the said permissible position and a prohibition position based on the detection information of the said recording-medium detection means, The any one of Claims 1-16 characterized by the above-mentioned. Image forming apparatus.

Images