JP3463221B2 - Roller drive for paper transport roller - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotation driving device for a sheet conveying roller, such as a fixing roller in a printer or a copying machine, which nips and conveys a sheet in cooperation with a pressure contact member.

[0002]

2. Description of the Related Art FIG. 12 is an overall view of an ordinary image forming apparatus (herein, a printer is shown as an example) adopting an electrophotographic method. This apparatus stacks and stores sheets of paper P and is detachably attached to a main body of the apparatus, a sheet feeding roller 2 for feeding the stacked sheets one by one, and a sheet fed by the sheet feeding roller 2. The slip roller pair 3 that is inherited and conveyed, the standby roller pair 4 that temporarily waits the sheet conveyed by the slip roller pair 3 and is reconveyed at a predetermined timing, and the image information is transmitted to the sheet conveyed by the standby roller pair 4. An image forming section 5 (photosensitive drum 5a, charging device 5b, optical writing head 5c, developing device 5d, transfer device 5e, cleaner 5) that forms a toner image based on
f)), a fixing roller pair 6 for fixing the toner image on a sheet, a sheet discharging roller pair 7 for discharging the fixed sheet to the outside of the apparatus, and the like.

In such an apparatus, for example, a slip roller pair 3, a standby roller pair 4, a fixing roller pair 6, and a paper discharge roller pair 7 are used as a paper conveying means for nipping and conveying the paper.
For example, various pairs of conveying rollers including a rotationally driven sheet conveying roller and a pressure contact roller that is pressed against the sheet conveying roller and is driven to rotate are provided. It is desirable that these pairs of conveying rollers have a configuration in which two rollers can be separated from each other or that at least one of the two rollers can be separated from the main body drive system in view of necessity of jam processing or the like. An example of such a configuration is shown in FIGS.

The example of FIG. 13 is a case of a fixing roller pair, for example, and is provided with a conveying roller pair consisting of a sheet conveying roller (fixing roller) 11 and a pressure contact roller 12 pressed against this by a spring or the like. A drive roller gear 13 that is connected to one end of the drive roller 11 is engaged with a drive gear 14 that rotates by receiving a drive force from a main body drive source. The rotation of the drive gear 14 drives the sheet transfer roller 11 to rotate. Accordingly, the pressure roller 12 is driven to rotate. In such a configuration, when a paper jam occurs between the rollers 11 and 12, the operation of temporarily releasing the pressure contact of the pressure contact roller 12 by a spring or the like is performed to remove the jammed paper, or the rollers 11 and 12 are pressed. The jammed paper sandwiched between them is forcibly pulled to remove it.

In the example of FIG. 14, in the configuration of FIG. 13, an idle gear 15 is interposed between the transport roller gear 13 and the drive gear 14, and the idle gear 15 is interlocked with the roof opening / closing operation of the apparatus main body. The gears 13 and 14 are movable in the direction in which they are separated from each other and in the direction in which they are engaged. In such a configuration, when a jam occurs and the roof is opened, the idle gear 15 is separated from the gears 13 and 14 in conjunction with the jam, so that the paper transport roller 11 (FIG. 13) can idle. In this state, the jammed paper between the rollers 11 and 12 is pulled and removed.

The example of FIG. 15 is, for example, in the case of a pair of discharge rollers (however, a pair of conveying rollers consisting of a sheet conveying roller and a pressure contact roller is not shown), and a roller shaft which is a rotating shaft of the sheet conveying roller. A pulley 22 is provided at one end of 21, and a pulley 25 is provided coaxially with another drive gear 24 that meshes with a drive gear 23 that is rotated by transmitting a driving force from a main body drive source. Two pulleys
2, 25 are connected by a belt 26.
In such a configuration, when a paper jam occurs between the pair of discharge rollers, if the jammed paper is pulled forcibly,
The belt 26 slides, the roller shaft 21 rotates, and the jammed paper can be removed.

[0007]

If the paper is pulled forcibly to remove the jammed paper sandwiched between the rolls as in the example of FIGS. 13 and 15, the jammed paper may be torn.
Alternatively, there is a problem that it takes a lot of time for processing work because a strong force is required even if it is not broken.

Further, if a mechanism for separating the sheet conveying roller and the drive source is provided as in the example of FIG. 14, the above problem can be solved, but such a mechanism becomes considerably complicated and the apparatus is There was a problem that it would lead to an increase in size and cost.

In view of the above-mentioned conventional problems, it is an object of the present invention to provide a rotation driving device for a sheet conveying roller that can take out jammed paper with a simple mechanism by simply pulling lightly.

[0010]

In order to achieve the above object, the present invention is rotatably supported by a support member via a bearing, and rotates in a predetermined direction to cooperate with a pressure contact member to load a sheet. In a rotation driving device for a sheet conveying roller that nips and conveys, it has a gear portion on the outer periphery, engages with an engaging member formed on the sheet conveying roller, and rotates in the axial direction while rotating with respect to the sheet conveying roller. The transfer roller gear to be fitted as much as possible and the axial movement range of the transfer roller gear
A regulating member for regulating the position from the second position to the second position, and a biasing member for biasing the transport roller gear toward the first position,
A drive gear connected to a drive source, the drive gear having an outer periphery of a gear portion engageable with the transport roller gear, wherein the transport roller gear and the paper transport roller are Engage in a relationship of moving to the first position direction when trying to rotate in the predetermined direction with respect to the conveying roller, and moving to the second position direction when trying to rotate in the opposite direction to the predetermined direction The drive gears are arranged so as to mesh with each other when the transport roller gear is in the first position and disengage from each other when the transport roller gear is in the second position.

[0011]

When the drive gear to which the driving force is transmitted from the drive source tries to drive the transport roller gear to rotate in the predetermined direction for normal sheet transport, the transport roller gear moves in the first position direction, The drive gear and the transport roller gear are in mesh with each other. In this state, the driving force of the drive gear is transmitted to the transport roller gear, and the paper transport roller is rotationally driven in the predetermined direction, so that the paper is nipped and transported in cooperation with the pressure contact member.

On the other hand, at the time of jam processing, if the jammed paper sandwiched between the paper carrying roller and the pressure contact member is lightly pulled, the rotational force of the paper carrying roller is transmitted to the carrying roller gear, that is, the carrying roller. Since the drive gear is rotated in the direction opposite to the predetermined direction with respect to the paper transport roller, the transport roller gear moves in the second position direction against the biasing force of the biasing member, and the drive gear and the transport roller are moved. The mesh with the gear for gear is released. Therefore, by simply pulling the jammed paper lightly as it is, the paper conveyance roller idles accordingly and the jammed paper can be taken out without difficulty.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an exploded perspective view showing the configuration of the main part of the first embodiment of the present invention, and FIGS. 2 and 3 are diagrams for explaining the operation thereof. Note that this embodiment considers a case where it is applied to the fixing roller pair 6 shown in FIG. 12, and a sheet conveying roller (fixing roller) which is one of the rollers forming the fixing roller pair 6 is illustrated. A mechanism such as 1 is applied.

First, as shown in FIG. 2 or 3, a cylindrical sheet conveying roller (fixing roller) 30 is rotatably supported by a frame 32 as a supporting member via a bearing 31, and the arrow mark thereof. The rotation in the direction A cooperates with a pressure contact roller (not shown) to sandwich and convey the sheet for thermal fixing. As shown in FIG. 1, a pair of spiral grooves 30a and 30b as engaging members are provided axially symmetrically with each other on one end side of the cylindrical sheet conveying roller 30. A protrusion 33a engaging with the grooves 30a and 30b is formed on the inner circumference of the transport roller gear 33 that is fitted onto the shaft 30 so as to be slidable in the axial direction.
33b is provided. As a result, when the transport roller gear 33 is rotated with respect to the paper transport roller 30, the protrusions 33a and 33b are guided along the spiral grooves 30a and 30b, so that the transport roller gear 33 rotates. Axial direction (arrow C) depending on the direction (arrow B ₁ , B ₂ direction)
It is configured to slide in the ₁ and C ₂ directions).

A retaining ring 3 is provided at the end of the sheet conveying roller 30.
4 is attached, and this stop ring 34 acts as a restricting member that prevents the transport roller gear 33 from falling off and restricts the movement in the arrow C ₁ direction. As a result, the transfer roller gear 33 can be moved in the arrow C ₁ direction up to the first position (the position shown in FIG. 2) where the transfer roller gear 33 contacts the retaining ring 34, while the transfer roller gear 33 is moved in the arrow C ₂ direction. Can be moved to the second position (the position shown in FIG. 3) where the protrusions 33a and 33b come into contact with the ends of the grooves 30a and 30b. Further, a compression spring 35 as an urging member is arranged between the transport roller gear 33 and the bearing 31 to constantly urge the transport roller gear 33 in the direction of the first position (direction of arrow C ₁ ). ing.

Further, as shown in FIG. 2 or 3, the drive gear 36 connected to the main body drive source can be engaged with the transport roller gear 33 in order to transmit the driving force to the transport roller gear 33. It is provided in. And this drive gear 36
Is in a position such that the gears 33 for the transport roller are in mesh with each other when the gear 33 for the transport roller is in the first position as shown in FIG. It is arranged. Moreover, both the transport roller gear 33 and the drive gear 36 use helical gears, and the meshing relationship of the gear teeth is such that the drive gear 36
When the drive roller 36 rotates in the direction of arrow D and transmits the driving force to the transport roller gear 33, the drive gear 36 causes the transport roller gear 3 to move.
3 is generated in the direction of arrow C ₁ , and conversely, when the transport roller gear 33 tries to rotate in the direction of arrow B _{1 with} respect to the drive gear 36 that is stopped, the drive gear 36 moves. It is set so as to generate a force that pushes the transport roller gear 33 in the direction of arrow C ₂ .

In the apparatus of this embodiment having the above-mentioned configuration
The operation to be performed will be described below with reference to FIGS. Well
First, as shown in Fig. 2, drive the main unit for normal paper transport.
The driving gear 36 receives the driving force from the power source and rotates in the direction of arrow D.
When rotated, the transport roller gear 33 is moved by the compression spring 35.
Arrow C₁The drive gear 36 while receiving a biasing force in the direction.
Arrow B₁Start rotating in the direction. Then, groove 3
0a, 30b and the protrusions 33a, 33b are engaged with each other.
And the conveyor roller gear 33 is indicated by the arrow B.₁Rotating in the direction
Arrow C ₁Slide in the direction, and drive as shown in Fig. 2.
Settle into the 1st position, which is the position that meshes securely with the
Ku. Then, in this state, the driving force of the drive gear 36 is transferred.
It is transmitted to the gear 33 for the feed roller, which causes the paper transport roll.
Since the roller 30 is driven to rotate in the direction of arrow A, it is not shown.
The paper is nipped and conveyed in cooperation with the pressure contact roller.

On the other hand, when a paper jam occurs between the paper conveying roller 30 and the pressure contact roller (not shown), the jammed paper sandwiched between the paper conveying roller 30 and the pressure contact roller is conveyed in the paper conveying direction. If it is pulled lightly, the paper transport roller 30 rotates in the direction of arrow A as shown in FIG. Then, the transport roller gear 33 causes the paper transport roller 3 to move.
Since it is rotated in the direction of the arrow B _{2 with} respect to 0, the conveying roller gear 33 resists the biasing force of the compression spring 35 due to the engagement relationship between the grooves 30a and 30b and the protrusions 33a and 33b. And slides in the direction of arrow C ₂ to settle at the second position where the engagement with the drive gear 36 is completely released, as shown in FIG. Therefore, if the jammed paper is continuously pulled lightly as it is, the paper conveying roller 30 idles accordingly, and the jammed paper can be taken out without difficulty.

When the drive gear 36 starts to drive again from this state, the compression roller 35 pushes the transport roller gear 33 in the direction of arrow C ₁ to engage with the drive gear 36, and thereafter, as described above. Due to the meshing relationship between the helical gears, the transport roller gear 33 moves to the first position,
It is possible to nip and convey sheets. Therefore, the compression spring 35 may urge the conveying roller gear 33 in the direction of arrow C ₁ so as to mesh with the drive gear 36 even slightly, and it is not necessary to use a strong spring.

As described above, according to the present embodiment, at the time of jam processing, the paper conveying roller 30 is rotated only by lightly pulling the jammed paper, and the jammed paper can be easily taken out without breaking the jammed paper. Smooth processing work is possible. Moreover, since it suffices to add the extremely simple structure as shown in FIG. 1, it is possible to suppress the increase in size and cost of the apparatus.

In the first embodiment, the grooves 30a, 3
0b is a notch that penetrates from the inner circumference to the outer circumference of the paper transport roller 30.
If a groove engageable with the protrusions 33a and 33b is provided on the outer periphery of the same, the same effect can be obtained.

Further, the transport roller gear 33 and the drive gear 36 may be composed of spur gears by using a compression spring having an urging force sufficient to move the transport roller gear 33 to the first position.

Next, FIG. 4 is an exploded view showing the structure of the main part of the second embodiment of the present invention, and FIGS. 5 and 6 are diagrams for explaining the operation thereof. Note that this embodiment also considers the case of being applied to the fixing roller pair 6 shown in FIG.
The mechanism shown in FIG. 4 is applied to the sheet conveying roller (fixing roller) which is one of the rollers forming the fixing roller pair 6, and has a simpler structure than that of the first embodiment. is there.

First, although not shown in the drawing, the cylindrical sheet conveying roller (fixing roller) 40 is rotatably supported by a supporting member such as a frame via a bearing, as in the first embodiment. By the rotation in the arrow E direction, the heat fixing is performed while the sheet is nipped and conveyed in cooperation with a pressure contact roller (not shown). As shown in FIG. 4, a pair of protrusions 40a and 40b as engaging members are provided on the outer periphery of the cylindrical sheet conveying roller 40 on the one end side at axially symmetrical positions with each other. A cylindrical portion 42 coaxial with the gear 41 for the conveying roller, which is fitted onto the conveying roller 40 so as to be slidable in the axial direction, is integrally provided. The cylindrical portion 42 has the protrusions 40a and 40b, respectively. Helical grooves 42a, 42b are provided for engagement. Accordingly, when the transport roller gear 41 is rotated with respect to the sheet transport roller 40, the protrusions 40a and 40b are engaged with the spiral grooves 42a and 42b, whereby the transport roller gear 4 is engaged.
1 is configured to slide in the axial direction (arrows G ₁ and G ₂ directions) according to its rotation direction (arrows F ₁ and F ₂ directions).

The end portion of the sheet conveying roller 40 has a step portion 4 having a small diameter.
0c, a retaining portion 43 having a diameter larger than that of the step portion 40c is provided at the outermost end portion, and the step portion is provided on the flange surface of the conveying roller gear 41 on the side opposite to the cylindrical portion 42. A retaining claw 44 slidable along the portion 40c and capable of contacting the retaining portion 43 is integrally provided. The retaining portion 43 and the retaining claw 44 are connected to the transport roller gear 41. And acts as a restricting member that restricts the movement in the arrow G ₁ direction. This allows
The conveyance roller gear 41 can be moved in the direction of the arrow G ₁ to the first position (the position shown in FIG. 5) where the retaining claw 44 of the conveyance roller gear 41 contacts the retaining portion 43, while the arrow The movement in the G ₂ direction is possible up to the second position (the position shown in FIG. 6) where the protrusions 40a and 40b come into contact with the ends of the grooves 42a and 42b. Further, a spring portion 45 as an urging member is integrally provided at the end of the cylindrical portion 42 of the transport roller gear 41 to move the transport roller gear 41 in the direction of the first position (arrow G ₁ direction). Always urged.

Further, as in the above embodiment, the main body drive source is connected.
As shown in FIG. 5, the coupled drive gear 46 causes the transport roller to move.
When the gear 41 for gear meshes with each other when in the first position,
When the transport roller gear 41 is in the second position as shown in
It is arranged at a position where the meshing is released.
Also in this embodiment, the conveyance roller gear 41 and the drive gear
Both 46 use helical gears and their gear teeth
The drive gear 46 rotates in the direction of arrow H
Drive force when transmitting the driving force to the transport roller gear 41.
The moving gear 46 moves the conveyance roller gear 41 to the arrow G.₁Push in the direction
Force is generated, and conversely, the drive gear 46 is stopped.
On the other hand, the conveyance roller gear 41 is indicated by an arrow F. ₁Rotate in the direction
In this case, the drive gear 46 is set to the transport roller gear 41.
Arrow G ₂It is set to generate a pushing force in the direction.

In the apparatus of this embodiment having the above-mentioned configuration
The operation to be performed will be described below with reference to FIGS. 5 and 6. Well
Instead, for normal paper transport, drive the main unit as shown in Fig. 5.
The drive gear 46 receives the driving force from the drive source and rotates in the direction of arrow H.
When rolled, the transport roller gear 41 is moved by the spring portion 45.
Mark G₁Bites with the drive gear 46 while receiving a biasing force in the direction
Fit arrow F ₁Start rotating in the direction. Then, the protrusion
By the engagement relationship between the grooves 40a, 40b and the grooves 42a, 42b.
The transport roller gear 41 is indicated by the arrow F.₁Rotating in the direction
Arrow G₁Slide in the direction, and as shown in Fig. 5, drive gear
Settles in the first position, which is the position where it engages securely with A.
Ku. Then, in this state, the driving force of the drive gear 46 is transferred.
It is transmitted to the feed roller gear 41, which causes the paper conveyance roll
Since the roller 40 is driven to rotate in the direction of arrow E, it is not shown.
The paper is nipped and conveyed in cooperation with the pressure contact roller.

On the other hand, when a paper jam occurs between the paper transport roller 40 and the pressure contact roller (not shown), the jammed paper sandwiched between the paper transport roller 40 and the pressure contact roller is moved in the paper transport direction. If it is pulled lightly, the paper transport roller 40 is rotated in the direction of arrow E as shown in FIG. Then, the transport roller gear 41 moves to the paper transport roller 4
Since it is rotated in the direction of the arrow F _{2 with} respect to 0, the conveyance roller gear 41 resists the urging force of the spring portion 45 due to the engagement relationship between the protrusions 40a and 40b and the grooves 42a and 42b. continue to slide in the arrow G ₂ direction Te, settles to the second position is a position where the engagement is completely released with the drive gear 46 as shown in FIG. Therefore, if the jammed paper is continuously pulled lightly as it is, the paper conveying roller 40 idles accordingly, and the jammed paper can be taken out without difficulty.

When the drive gear 46 starts to drive again from this state, the transport roller gear 41 is pushed by the spring portion 45 in the direction of the arrow G ₁ and meshes with the drive gear 46. After that, in the same manner as described above. The transport roller gear 41 moves to the first position, and the sheet can be nipped and transported.

Therefore, according to this embodiment, the same effect as that of the first embodiment can be obtained, and in addition, the gear 41 for the conveying roller is obtained.
Since the cylindrical portion 42, the retaining claw 44, and the spring portion 45 are integrally formed, the number of parts can be significantly reduced, and the configuration can be further simplified.

In the second embodiment, the grooves 42a, 4
Although the notch 2b penetrates from the inner circumference to the outer circumference of the cylindrical portion 42, the projection 4 is formed at least on the inner circumference of the cylindrical portion 42.
If a groove that can be engaged with 0a, 40b is provided, the same effect can be obtained.

Further, in the second embodiment as well, a helical gear is used as the conveying roller gear and the driving gear, but the helical gear is used for sliding the conveying roller gear as described above. Although a pushing force is generated in the assisting direction, which can be said to be convenient, a sufficient action can be obtained even with a normal spur gear without using such a helical gear.

With respect to such a gear, in the case of a conventional gear, grease is applied between the gears to prevent wear, but the grease is unevenly attached to the gears or applied to the tooth surface. If dust such as paper powder or toner adheres to the grease and the quality of the grease deteriorates, the rotation of the gear is burdened with a secondary problem later. Therefore, in order to solve such a problem, it is very effective to introduce the following configurations to the above-mentioned transport roller gear and drive gear.

That is, normally, by the rotation of two gears (especially spur gears) meshing with each other, excess grease attached to the tooth tips of each gear moves to the tooth roots and is further discharged from the tooth roots to the outside of the flange. In view of the fact that excess grease that did not move to the tooth root moves to the next tooth surface, and the movement from the tooth tip to the tooth root is repeated,
A groove for discharging excess grease is provided at the tooth tip and the tooth root of at least one gear. An example thereof is shown in FIGS. In this example, two gears (spur gears) 5
Of the gears 1 and 52, one gear 51 is an ordinary spur gear, and the other gear 52 is provided with grooves 53 and 54 at the tooth tip center and tooth root, respectively, as shown in FIG.
In FIG. 9, the central portion of the meshing surface of the gear 51 seems to be slightly swollen, but it is actually a flat surface. In such a configuration, excess grease attached to the tooth tips of the gears 51 and 52 moves to the tooth root through the groove 53 and is further discharged from the tooth root to the outside of the flange through the groove 54. Extremely smooth discharge of grease and dust-laden grease. Another example is shown in FIGS. 10 and 11. In this example, two gears (spur gears) 61,
62 both have a groove 63 at the tooth tip and a groove 63 at the tooth root, respectively.
64 is provided. In such a configuration, since the excess grease attached to the tooth tips of the gears 51 and 52 is discharged to the outside of the flange through the grooves 63 at the both ends of the tooth tips and the grooves 64 at the tooth roots, the same as in the above example. The unnecessary grease can be discharged smoothly. As described above, unnecessary grease is quickly discharged simply by providing grooves on the tips and roots of the gears, so the amount of grease adhered is constant and the gear torque is also kept constant. It is possible to effectively prevent a backlash failure due to the above.

In the above embodiments, the case where the sheet carrying roller is the fixing roller has been described as an example, but the present invention is not limited to the fixing roller, and in addition, as shown in FIG.
The present invention can be applied to each paper transport roller that constitutes the slip roller pair 3, the standby roller pair 4, the paper discharge roller pair 7 and the like as shown in FIG.

Further, the pressure contact member for nipping and conveying the paper in cooperation with the paper conveyance rollers does not necessarily have to be the pressure contact roller, and various shape members capable of conveying the paper without trouble can be used.

[0037]

According to the present invention, at the time of jam processing, the jam paper can be easily taken out without breaking it by simply pulling the jam paper lightly, so that extremely smooth processing work can be performed. Moreover, since it is only necessary to add an extremely simple structure, it is possible to suppress an increase in size and cost of the device.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing a main part configuration of a first embodiment of the present invention.

FIG. 2 is a diagram showing a state during sheet conveyance in the first embodiment.

FIG. 3 is a diagram showing a state at the time of jam processing in the first embodiment.

FIG. 4 is an exploded view showing a main part configuration of a second embodiment of the present invention.

FIG. 5 is a diagram showing a state when a sheet is being conveyed in the second embodiment.

FIG. 6 is a diagram showing a state during jam processing in the second embodiment.

FIG. 7 is a diagram showing an example of a gear provided with a groove for discharging grease.

8 is a cross-sectional view of the gear shown in FIG.

9 is a perspective view of a main part of the gear 52 shown in FIG.

FIG. 10 is a diagram showing another example of a gear provided with a groove for discharging grease.

11 is a perspective view of essential parts of the gears 61 and 62 shown in FIG.

FIG. 12 is an overall view of a normal image forming apparatus adopting an electrophotographic method.

FIG. 13 is a perspective view showing an example of a conventional rotation driving mechanism for a sheet conveying roller.

FIG. 14 is a diagram showing another example of a conventional rotation driving mechanism for a sheet conveying roller.

FIG. 15 is a perspective view showing still another example of the conventional rotation driving mechanism of the sheet conveying roller.

[Explanation of symbols]

3 Slip roller pair 4 Standby roller pair 6 fixing roller pair 7 Paper ejection roller pair 30 paper transport rollers 30a, 30b groove 31 bearings 33 Transport roller gear 33a, 33b Projection 34 retaining ring 35 Compression spring 36 Drive gear 40 Paper transport roller 40a, 40b protrusion 41 Transport roller gear 42 Cylindrical part 42a, 42b groove 43 retaining part 44 retaining claw 45 Spring part 46 drive gear

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-1-303264 (JP, A) JP-A-2-175533 (JP, A) JP-A-5-119665 (JP, A) Actual Kaihei 5- 24636 (JP, U) Actual development 59-181452 (JP, U) Actual development 58-50225 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) B65H 5/06 B41J 13 / 00 B41J 13/02 G03G 15/00 510

Claims (6)

(57) [Claims] 1. A rotary drive device for a paper transport roller, which is rotatably supported by a support member via a bearing, and cooperates with a pressure contact member to nip and transport a paper by rotation in a predetermined direction. A transport roller gear that has a portion and that engages with an engagement member formed on the paper transport roller and that is fitted onto the paper transport roller so as to slide in the axial direction while rotating with respect to the paper transport roller; A restricting member that restricts a movement range of the gear in the axial direction from a first position to a second position; an urging member that urges the transport roller gear toward the first position; and the transport roller gear A drive gear connected to a drive source, the drive gear having an engageable gear portion on the outer circumference, wherein the transport roller gear and the paper transport roller are the transport roller gear and the paper transport roller. Trying to rotate in a given direction The drive gear for the transport roller is engaged in a relationship of moving in the first position direction and moving in the second position direction when trying to rotate in a direction opposite to the predetermined direction. A rotation driving device for a sheet conveying roller, wherein the gears are arranged to mesh with each other when the gear is in the first position and release the mesh when the gear is in the second position. 2. The rotation drive device for a sheet transport roller according to claim 1, wherein the pressure contact member is a pressure contact roller that is in pressure contact with the sheet transport roller and is driven to rotate. 3. The rotation driving device for the paper carrying roller according to claim 1, wherein the paper carrying roller is a fixing roller of an image forming apparatus. 4. The rotation driving device for a sheet carrying roller according to claim 1, wherein the carrying roller gear and the drive gear are helical gears. 5. The engaging member of the paper carrying roller is a spiral groove provided on the outer circumference of the paper carrying roller, and the protrusion provided on the inner circumference of the carry roller gear is the spiral. 2. The rotation driving device for the sheet conveying roller according to claim 1, wherein the conveying roller gear is slidable in the axial direction while rotating with respect to the sheet conveying roller by engaging with the groove of the sheet conveying roller. 6. The engaging member of the paper carrying roller is a protrusion provided on the outer periphery of the paper carrying roller, and the spiral groove provided on the inner periphery of the gear for the carry roller is the protrusion. 2. The rotation driving device for the sheet carrying roller according to claim 1, wherein the gear for the carrying roller is slidable in the axial direction while rotating with respect to the sheet carrying roller by engaging with the sheet carrying roller.