JPH09202503A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce the shortening effect of a first copy time as a result of a transfer paper being discharged and conveyed at a high speed by a paper discharge roller group after the transfer paper passes through a fixing means and to maintain the shortening effect of the first copy time also during the continuous feed of paper sheets by a method wherein the conveyance speed of the fixing means is regulated without the occurrence of a slip between a paper discharge roller group and the transfer paper until the transfer paper passes through the fixing means. SOLUTION: A one-way clutch (a speed switching means) worked through a transfer paper 8 serving as a medium is located at roller groups 4 and 5, situated upper stream, positioned between fixing means 1 and 2 and roller groups 6 and 7 situated downstream and drive at the same speed as those of the fixing means 1 and 2. This constitution, even when paper sheets continuously pass through, discharges and conveys a preceding transfer paper 8 as it is without deceleration by the roller groups 6 and 7 situated downstream, and conveys a subsequent transfer paper 8 at a conveyance speed regulated by the fixing means 1 and 2.

Description

Detailed Description of the Invention

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine.

[0002]

2. Description of the Related Art Generally, in this type of image forming apparatus, an unfixed toner image carried on a transfer paper is transferred onto the transfer paper by passing a transfer paper on which a toner image is transferred from a photoreceptor or the like through a fixing means. After fixing, the sheet is conveyed and discharged to a sheet discharge tray or the like. In this case, the transport speed from the fixing unit to the paper discharge unit is set to be approximately the same. For this reason, when the discharge conveyance path is relatively long, the time from the trailing edge of the transfer sheet passing through the fixing unit to the sheet discharge to the discharge unit also becomes long, and after the operator instructs copying. There is a problem that it takes a long time to complete the copy (that is, the first copy time). Further, in order to prevent the transfer paper from slackening between the fixing unit and the paper discharge unit, it is also widely possible to set the speed relationship so that the conveyance speed on the paper discharge unit side is about several percent faster than that on the fixing unit side. Although it is known, the speedup is about several percent, and there is no big difference in that the first copy time is still long.

With respect to such a problem, Japanese Patent Laid-Open No. 4-2
According to Japanese Laid-Open Patent Publication No. 37075, the transfer paper is driven at the conveyance speed of the fixing unit so as not to impair the fixability until the transfer paper leaves the fixing unit, but when the transfer paper leaves the fixing unit, it is discharged and conveyed at high speed. A mechanism for driving a group of paper discharge rollers is disclosed. That is, an upstream roller group (intermediate roller) and a downstream roller group (paper ejection roller) are sequentially provided as a paper discharge roller group on the downstream side of the fixing roller, and the conveyance speed of the intermediate roller is higher than the conveyance speed of the fixing roller. In addition to setting it to a high speed, the transport speed of the discharge roller is set to be higher than the transport speed of the intermediate roller, and when the leading edge of the transfer paper leaves the fixing roller, the transport speed of the intermediate roller and the discharge roller is transported by the fixing roller. In accordance with the speed, when the trailing edge of the transfer paper leaves the fixing roller, the transport speed of the intermediate roller and the discharge roller is switched to the transport speed set for the intermediate roller, and when the trailing edge of the transfer paper exits the intermediate roller, it is ejected. A speed switching mechanism that switches the transport speed of the paper roller to the transport speed set for the paper discharge roller is provided. Specifically, a torque limiter is provided as a speed switching mechanism in the drive transmission system from the fixing roller to the intermediate roller. As a result, while the transfer paper is being conveyed by the fixing roller (until the trailing edge comes out)
Is slipped by the torque limiter, the transfer paper is conveyed at the conveyance speed of the fixing roller, and when the transfer paper is released from the fixing roller (when the trailing edge comes out), the torque is not absorbed by the torque limiter and the intermediate roller The transfer paper is conveyed at the set high conveyance speed.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
According to the paper discharge conveyance drive as disclosed in Japanese Unexamined Patent Application Publication No. 5, it is possible to discharge the paper at high speed without impairing the fixing performance and shorten the first copy time.

However, in the case of the structure shown in the publication, depending on the arrangement of the discharge roller group and the like, when the continuous paper is passed, the trailing edge of the preceding transfer paper is passed before the trailing end of the transfer paper passes through the paper discharge roller. The leading edge of the transfer paper may reach the intermediate roller, actuate the torque limiter, and the transport speed of the intermediate roller and the discharge roller may be reduced to the transport speed of the fixing roller. In this case, since the preceding transfer sheet, which has been accelerated once, is decelerated before being ejected to the sheet ejection unit, the effect of shortening the first copy time is halved. In order to avoid such an inconvenience, for example, it is conceivable that the interval between the intermediate roller and the discharge roller is shortened, the transport speed of the intermediate roller and the discharge roller is set to a higher speed, and the like. Any of these is not preferable because it imposes restrictions on the configuration of the device.

[0006]

According to a first aspect of the present invention, a fixing unit is rotatably driven by a driving unit to nip and convey a transfer sheet, and an unfixed toner image carried on the transfer sheet is fixed on the transfer sheet. And an ejection roller group that is connected to the drive unit through a drive transmission unit and ejects and conveys the transfer sheet that has been fixed by the fixing unit. According to the paper transport direction, the upstream roller group and the downstream roller group are divided into two, and the transport speed of the downstream roller group by the drive transmission means is set higher than the transport speed of the fixing means and the drive transmission means is set. The conveyance speed of the upstream side roller group is set to the same as the conveyance speed in the fixing means, and when the leading edge of the transfer paper reaches the downstream side roller group, the conveyance speed of the downstream side roller group. A speed difference absorbing mechanism for adjusting the conveying speed of the fixing means to the conveying speed of the fixing means, and the conveying speed of the upstream side roller group when the rear end of the transfer sheet passes through the fixing means by using the transfer sheet as the medium. And a speed switching mechanism for switching to the transport speed of.

Therefore, when the transfer sheet is conveyed across the fixing means and the discharge roller group, the transfer sheet is conveyed by the fixing means without slipping between the transfer sheet and the downstream roller group due to the action of the speed difference absorbing means. Transported at speed. When the trailing edge of the transfer paper passes through the fixing means, the downstream side roller group can be driven at the set high conveyance speed, and the upstream side roller group also uses the transfer paper as a medium to operate by the speed switching mechanism. Since the conveyance speed is switched so as to follow the conveyance speed of the downstream side roller group, the transfer sheet is ejected and conveyed at high speed. In this case, the transfer paper may be continuously passed, and the leading end of the succeeding transfer paper may reach the upstream roller group from the fixing unit before the trailing end of the preceding transfer paper passes through the downstream roller group. However, since the transfer paper is out of the intermediary state in which the speed switching mechanism acts, and the speed switching mechanism does not act on the upstream roller group, the preceding transfer paper is not decelerated and the downstream roller group continues to operate at high speed. At the same time as the sheet is discharged and conveyed, the succeeding transfer sheet is conveyed at a conveying speed regulated by the fixing means. Therefore, the transfer paper can be discharged at high speed without restricting the apparatus configuration, and the effect of shortening the first copy time can always be obtained.

According to the second aspect of the invention, the transport speed of the downstream roller group is set within the range of 1.1 to 3 times the transport speed of the fixing means. A transport speed of 1.1 times or more the transport speed of the fixing unit is effective for obtaining the minimum effect of shortening the first copy time. Further, if the conveying speed of the fixing means is within three times, the speed difference absorbing mechanism or the drive system will not be overloaded.

According to a third aspect of the invention, the speed difference absorbing mechanism is a torque limiter, and in the fourth aspect of the invention, the speed switching mechanism is provided on the roller shaft of the upstream roller group, and the transfer paper is conveyed to this shaft. Since the one-way clutch is provided so as to have a direction in which the roller idles in the direction, an inexpensive and simple mechanism is sufficient for all of them.

[0010]

An embodiment of the present invention will be described with reference to the drawings. The image forming apparatus of the present invention is applied to, for example, a copying machine as one of its embodiments.
FIG. 1 shows a schematic configuration of the fixing and discharging unit. First, a roller pair of a fixing roller 1 and a pressure roller 2 that constitute a fixing unit is provided in pressure contact with each other. These rollers 1,
A discharge roller group 3 is provided on the downstream side in the transport direction with respect to 2. This paper discharge roller group 3 follows the paper discharge conveyance direction.
A roller pair of an upper intermediate roller 4 and a lower intermediate roller 5 located upstream and forming an upstream roller group, and an upper paper discharging roller 6 and a lower paper discharging roller located downstream and forming a downstream roller group. It is divided into 7 roller pairs. Regarding these roller pairs, the fixing roller 1, the lower intermediate roller 5, and the lower paper discharge roller 7 side are the drive rollers, and the opposing pressure roller 2, upper intermediate roller 4, and upper paper discharge roller 6 side are the driven rollers. .

With such a basic roller system configuration, the transfer paper 8 on which the toner image on the photoconductor (not shown) is transferred is nipped and conveyed between the fixing roller 1 and the pressure roller 2 and heated / heated. The unfixed toner image is fixed by the pressure fixing action. After fixing, the transfer paper 8 is the intermediate roller 4,
5, the paper is conveyed by the paper discharge rollers 6 and 7 and is discharged to a paper discharge unit such as a paper discharge tray. Here, the transfer paper 8 is discharged and conveyed at a high speed by the configuration described below.

First, a drive gear 9 is provided on the shaft of the fixing roller 1.
The fixing roller 1 is directly connected to the fixing roller 1 by a drive motor (not shown), a motor gear, and a driving unit such as the drive gear 9 (not shown).
It is configured to be rotationally driven by V ₁ . The lower intermediate roller 5 and the lower sheet discharge roller 7 side are drivingly connected to a drive gear 9 by a drive transmission means 10. First, the transmission gear 11 meshed with the drive gear 9 and having the same number of teeth is fixed on the shaft 12 of the lower intermediate roller 5. Therefore, basically, the speed of the lower intermediate roller 5 is set so as to be driven at the same transportation speed as the transportation speed V ₁ of the fixing roller 1. Further, the transmission gear 11 also has a gear pulley portion 13 integrally therewith.
A timing belt 16 is stretched between 3 and a gear pulley 15 provided on the shaft 14 of the lower paper discharge roller 7. At this time, the gear pulley 1 is
5 has a small diameter, and the speed is set so that the transport speed V _{2 of the} lower discharge roller 7 (converted to the linear velocity of the transfer paper 8) is higher than the transport speed V ₁ of the fixing roller 1. Specifically, while the transport speed V ₁ is the same as or substantially the same as the transport speed on the photoreceptor side, the transport speed V ₂ is the transport speed V ₁
It is set to be 1.1 to 3 times faster than the above. The fixing roller 1
The gripping force of the transfer paper 8 between the pressure rollers 2 is
The pressing force is set so as to be larger than the holding force of the transfer paper 8 between the sheets 7.

Further, in the lower paper discharge roller 7, a shaft 14 is provided with a torque limiter 17, which is a speed difference absorbing mechanism integrally with a gear pulley 15. Further, in the lower intermediate roller 5, a one-way clutch 18 as a speed switching mechanism is provided between the lower intermediate roller 5 and its shaft 12.
Is interposed. The directionality of the one-way clutch 18 is set so that when the shaft 12 is fixed in FIG. 1, the lower intermediate roller 5 is locked in the clockwise direction and idled in the counterclockwise direction. That is, when the shaft 12 is rotationally driven in the counterclockwise direction by the transmission gear 11, the lower intermediate roller 5 is in the locked state and rotates in the counterclockwise direction together with the shaft 12, and the lower intermediate roller 5 itself rotates in the counterclockwise direction. When the rotational force is applied, the lower intermediate roller 5 rotates freely because it is in the idling direction with respect to the shaft 12.

The torque of the torque limiter 17 will be described below. The torque limiter 17 absorbs the speed difference between the conveying speed V ₂ in the conveyance speed V ₁ and the lower discharge roller 7 in the fixing roller 1, the lower discharge roller 7
Is for adjusting the conveying speed of V to V ₁ and the set torque T ₀ is N for the pressing force of the upper paper discharge roller 6, μ for the friction force of the lower paper discharge roller 7, and When the outer diameter is r and the torque for driving the entire downstream side of the lower paper discharge roller 7 is T, the range is set to T <T ₀ <μNr.

In such a structure, as shown in FIG. 3A, the leading end of the transfer paper 8 reaches the paper discharge rollers 6 and 7, and the fixing roller 1 and the pressure roller 2 discharge these paper discharge rollers 6 and 7. In the case where the transfer paper 8 is conveyed over 7 sheets, even if there is a speed difference between the fixing roller 1 side and the lower paper discharge roller 7 side, the transfer paper 8 is conveyed at the conveying speed V ₁ on the fixing roller 1 side having a large holding force. Is transported. In this case, no slip occurs between the transfer paper 8 and the discharge rollers 6 and 7, and roller marks and the like due to excessive rubbing are not attached to the transfer paper 8. That is, the torque limiter 1
Since the set torque T _{0 of} 7 is smaller than μNr, when the transfer sheet 8 is conveyed at the conveying speed V ₁ , the speed difference (V ₂ −
Since V ₁ ) is absorbed by the torque limiter 17, no slippage occurs between the transfer paper 8 and the paper discharge rollers 6, 7.

Thereafter, the transfer paper 8 is further conveyed, and as shown in FIG.
As shown in (b), when the rear end of the transfer paper 8 comes out between the fixing roller 1 and the pressure roller 2, the transfer paper 8 is sandwiched by the paper discharge rollers 6 and 7 and is discharged and conveyed. In this case, the set torque T ₀ of the torque limiter 17 is equal to the driving torque T
Since the torque T is not absorbed, the lower paper discharge roller 7 is set to its own set transport speed V.
_{At 2} , the transfer paper 8 is conveyed. At this time, the rear end side of the transfer paper 8 straddles the intermediate rollers 4 and 5, and the lower intermediate roller 5 transfers the transfer force through the transfer paper 8 which is about to be transferred by the lower transfer roller 7 at the transfer speed V _2. receive. Since the action direction of the carrying force is the direction in which the lower intermediate roller 5 idles with respect to the shaft 12 due to the interposition of the one-way clutch 18, the carrying speed by the lower intermediate roller 5 is also switched to V ₂ . In this way, the intermediate rollers 4, 5 and the discharge rollers 6, 7
Is driven at a high speed so that the transfer speed is V ₂ and the transfer paper 8 that has passed through the fixing roller 1 and the pressure roller 2 is discharged and transferred at a high speed.

Therefore, the first copy time can be shortened. If the transport speed V ₂ is less than 1.1 times the transport speed V ₁ , the discharge transport speed will be slightly higher after the transfer paper 8 leaves the fixing section. Therefore, it is not very effective in reducing the first copy time, but at least 1.1 with respect to the transport speed V ₁ .
Since the speed is more than doubled, it is effective to obtain the minimum effect of shortening the first copy time. Further, when the transport speed V ₂ is three times or more faster than the transport speed V ₁ , the effect of shortening the first copy time increases, but
As the speed difference increases, the torque limiter 17 is overloaded and its deterioration becomes severe. In this respect, if it is within 3 times, there is no particular problem.

Further, according to the present embodiment, it is possible to deal with the case where the transfer paper 8 is continuously fed. That is, FIG. 3 (c)
As shown in, before the trailing edge of the preceding transfer sheet 8a passes through the discharge rollers 6 and 7, the leading edge of the succeeding transfer sheet 8b reaches the intermediate rollers 4 and 5 from the fixing roller 1 and the pressure roller 2. In any case, the preceding transfer paper 8a is already out of the intermediary state in which the one-way clutch 18 is acted (it does not straddle the intermediate rollers 4 and 5 side), and the one-way clutch is applied to the lower intermediate roller 5. 18 is in a non-operating state. As a result, the preceding transfer sheet 8a is discharged and conveyed as it is by the discharge rollers 6 and 7 at a high conveyance speed V ₂ without being decelerated, and the succeeding transfer sheet 8b is conveyed by the fixing roller 1. The sheet is conveyed at the speed V ₁ (the speed transmitted through the drive gear 9, the transmission gear 11, and the shaft 12). Therefore, the transfer paper 8 can be discharged at high speed without restricting the apparatus configuration, and the effect of shortening the first copy time can always be obtained.

In the present embodiment, the fixing means is constituted by the pair of fixing roller 1 and pressure roller 2, but the fixing means is not limited to such a structure, and the transfer paper can be sandwiched and conveyed. Any combination of rollers and a belt, a combination of a roller and a plate material, or the like may be used. Further, the configuration of the drive transmission means 10 is not limited to the one using the timing belt 16, but may be a gear train or the like.

[0020]

According to the first aspect of the present invention, the fixing unit is rotatably driven by the driving unit to nip and convey the transfer sheet, and the unfixed toner image carried on the transfer sheet is fixed on the transfer sheet. An image forming apparatus, comprising: a discharge roller group that is connected to the drive unit via a drive transmission unit and discharges and conveys the transfer sheet that has been fixed by the fixing unit. According to the direction, it is divided into an upstream roller group and a downstream roller group, and the conveying speed of the downstream roller group by the drive transmitting means is set to be higher than the conveying speed of the fixing means, and the conveying speed by the drive transmitting means is set. The conveyance speed of the upstream side roller group is set to the same as the conveyance speed in the fixing means, and when the leading edge of the transfer paper reaches the downstream side roller group, the conveyance speed of the downstream side roller group is fixed. A speed difference absorbing mechanism adapted to the conveying speed of the transfer means, and a conveying speed of the upstream side roller group through the transfer paper when the rear end of the transfer sheet passes through the fixing means. Since the transfer sheet is provided with a speed switching mechanism, the transfer sheet can be regulated to the conveying speed of the fixing unit without slipping between the discharge roller group and the transfer sheet until the transfer sheet leaves the fixing unit. After exiting the printer, the first copy time can be shortened by discharging and transferring the transfer paper at a high speed by the discharge roller group, and in particular, it is located between the fixing unit and the downstream side roller group. Since the upstream side roller group which is driven at the same speed as the means has the speed switching means intervening the transfer paper, the preceding transfer paper is decelerated even when continuously passing the paper. Without that Subsequent transfer paper can be conveyed sheet discharging at a high speed by the downstream rollers can be conveyed by the conveying speed is restricted by the fixing means, therefore, without adding a constraint to the device configuration,
The transfer paper can be discharged at high speed, and the effect of shortening the first copy time can always be obtained.

According to the second aspect of the present invention, the conveying speed of the downstream roller group is set within the range of 1.1 to 3 times the conveying speed of the fixing means, so that the minimum first copy time is shortened. It is effective for obtaining the effect and does not overload the speed difference absorbing mechanism or the drive system.

According to the invention described in claim 3, the speed difference absorbing mechanism is a torque limiter, and according to the invention described in claim 4, the speed switching mechanism is provided on the roller shaft of the upstream roller group with respect to this shaft. Since a one-way clutch provided with the directionality to idle the roller in the transfer paper conveyance direction,
In either case, the purpose can be achieved with a cheap and simple mechanism.

[Brief description of drawings]

FIG. 1 is a schematic side view of a transport system configuration of a fixing and discharging unit of a copying machine showing an embodiment of the present invention.

FIG. 2 is a plan view mainly showing a drive transmission system.

FIG. 3 is a side view for explaining switching of the transport speed according to the state of the transfer paper.

[Explanation of symbols]

 1, 2 fixing means 3 paper discharge roller group 4, 5 upstream roller group 6, 7 downstream roller group 8 transfer paper 10 drive transmission means 12 shaft 17 torque limiter, speed difference absorption mechanism 18 one-way clutch, speed switching means

Claims (4)

[Claims] 1. A fixing unit that is rotationally driven by a driving unit to nip and convey a transfer sheet to fix an unfixed toner image carried on the transfer sheet onto the transfer sheet, and a driving transmission unit to the driving unit. In an image forming apparatus including a discharge roller group that is connected and discharges and conveys the transfer sheet that has been fixed by the fixing unit, the discharge roller group includes an upstream roller group and a downstream roller in a sheet discharge direction. And the conveyance speed of the downstream roller group by the drive transmission means is set to be higher than the conveyance speed of the fixing means, and the conveyance speed of the upstream roller group by the drive transmission means is fixed to the fixing group. A speed that is set to be the same as the conveying speed in the means, and adjusts the conveying speed of the downstream side roller group to the conveying speed of the fixing means when the leading edge of the transfer paper reaches the downstream side roller group. A differential absorption mechanism and a speed switching mechanism that switches the transport speed of the upstream roller group to the transport speed of the downstream roller group through the transfer paper when the trailing edge of the transfer paper passes through the fixing unit. An image forming apparatus characterized by being provided. 2. The image forming apparatus according to claim 1, wherein the conveying speed of the downstream side roller group is set within the range of 1.1 to 3 times the conveying speed of the fixing unit. 3. The image forming apparatus according to claim 1, wherein the speed difference absorbing mechanism is a torque limiter. 4. The speed switching mechanism is a one-way clutch provided on the shaft of the upstream roller group so as to have a direction to idle the roller in the transfer paper transport direction with respect to this shaft. The image forming apparatus according to claim 1, 2, or 3.