JP2001282072A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of image deviation and rubbing by suppressing the loop of recording paper between a transfer belt and a fixing apparatus below a definite quantity and further controlling fixing transporting speed so that the recording paper during transfer is not drawn by the fixing apparatus. SOLUTION: An image forming device has an image forming means 6 which is provided with a photoreceptor drum and forms an image on the photoreceptor drum corresponding to image information, a transfer belt 5 which transports the recording paper 2 through a transfer position at which the image formed on the photoreceptor drum is transferred onto the recording paper 2, the fixing apparatus 8 which fixes the image transferred on the recording paper 2 while transporting the recording paper 2 at speed v1 being slower than transporting speed v of the transfer belt 5, a sensor 35 for detecting the loop of the recording paper 2 between the transfer belt 5 and the fixing apparatus 8 and a control means for switching-controlling the transporting speed of the fixing apparatus 8 based on detection information from the sensor 35. After the sensor 35 detects the loop of the recording paper 2, the transporting speed of the fixing apparatus 8 is changed over to speed v2 being faster than the transporting speed v of the transfer belt 5 for a definite time Δt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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, a facsimile, and the like.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus employing an electrophotographic system forms a plurality of image forming units for forming a latent image on a photosensitive drum and visualizing the latent image with toner to obtain a visible image; The image forming apparatus includes a transfer belt that conveys a recording sheet to each transfer position of the plurality of image forming units, a fixing device that fixes an image transferred on the recording sheet onto the recording sheet, and the like.

The recording paper is electrostatically attracted to the transfer belt, transported to a transfer position of each image forming section while being held on the transfer belt, and a toner image of each color is transferred.
Further, a full color image can be obtained by being conveyed to the fixing device and fixing the transferred toner image.

In the above-described conventional image forming apparatus, as shown in FIG. 9, the distance l from the end of the transfer belt 55 to the nip of the fixing device 58 is determined by the following formula: It is necessary to make the recording paper shorter than this recording paper size. For example, if the A6 size transverse feed is the minimum size, it is necessary to configure the distance l to be 105 mm or less.

The conveying speed v of the recording paper 52 of the transfer belt 55 is a process speed for forming an image. The conveying speed v ₁ of the recording paper by the fixing device 58 is lower than the process speed v. Set late. This is because the fixing conveying speed v ₁ is faster than the process speed v, it will pull the recording paper in the transfer of an image of each image forming unit, an image deviate.

The conveyance of the recording paper 52 by the fixing device 58 is fixed.
Roller component tolerances in the kimono 58, recording paper thickness, toner
It is difficult to set a constant transport speed depending on conditions such as presence or absence.
is there. As a result, the transport speed varies due to these conditions.
Fixing / conveying speed v ₁Is slower than the process speed v
It is set to become.

[0007]

[SUMMARY OF THE INVENTION However, in the above conventional example, since essentially the slower fixing conveying speed v ₁ relative to the process speed v, the recording paper 52 is the fuser and the transfer belt 55 by the speed difference A loop as shown in FIG. In particular, this loop becomes larger as the size of the recording paper 52 increases.

Therefore, when the loop of the recording paper 52 becomes large, the loop cannot be absorbed in the space 51 between the transfer belt 55 and the fixing device 58 as shown in FIG. There is a case where the unfixed image is rubbed by the image forming unit 56 or the like due to the occurrence of the floating 52a of the 52.

In the case of thick recording paper such as thick paper (200 g / m2), the recording paper itself has a strong stiffness and cannot form a sufficient loop in the space 51. The recording paper 52 may be pushed back. This allows
The recording paper 52 during the transfer may be displaced in the direction of arrow A, and image displacement may occur.

To prevent these problems, it is conceivable to increase the space 51 between the transfer belt 55 and the fixing device 58. However, since the space 51 is restricted to the minimum size of the usable recording paper as described above, It is difficult to widen the space 51.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to prevent a recording paper loop between a transfer belt and a fixing device from being enlarged by a predetermined amount or more, and to reduce the length of a loop during transfer. The purpose is to control the fixing conveyance speed so that the recording paper is not pulled by the fixing device, and to prevent image deviation and rubbing.

[0012]

A typical configuration of the present invention for achieving the above object is an image forming means comprising an image carrier and forming an image on the image carrier according to image information; Conveying means for conveying the transfer material through a transfer position for transferring the image formed on the image carrier to the transfer material, and transferring the transfer material to the transfer material while conveying the transfer material at a speed lower than the conveying speed of the conveying means. Fixing means for fixing the image, a detecting means for detecting a loop of the transfer material between the conveying means and the fixing means, and a control for switching and controlling the conveying speed of the fixing means based on the detection information of the detecting means. And a switching unit that switches the transport speed of the fixing unit to a speed higher than the transport speed of the transport unit for a certain period of time after the detection unit detects the loop of the transfer material.

According to the present invention, the transfer material is fixed so that the loop of the transfer material between the transfer means and the fixing means is not increased by a certain amount or more, and the transfer material during transfer is not pulled by the fixing means. Since the speed is controlled, it is possible to prevent image displacement and rubbing.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus to which the present invention is applied will be described in detail with reference to the drawings.

[First Embodiment] First, referring to FIG. 8, a color printer 50 as an image forming apparatus according to the present embodiment will be described.
Will be described.

The recording paper 2 as a transfer material loaded on the cassette 1 is sent out by a pickup roller 1a, and the uppermost recording is made by a feed roller 1c and a reverse separation roller 1b rotating in a direction opposite to the feed direction. Only the paper is transported downstream.

Next, the recording paper 2 is conveyed along the conveyance path by a plurality of conveyance rollers 1d, the leading end is locked by the nip of the registration rollers 3 which are stopped, the recording paper 2 is curved, and the skew is corrected.

On the other hand, the image forming means 6a, 6b, 6c, 6
“d” forms yellow, magenta, cyan, and black toner images on the recording paper 2, respectively. Since the image forming means has the same configuration, only the image forming means 6a for forming a yellow image will be described in detail here as a representative. In the image forming means 6a, 6a1 is a photosensitive drum serving as an image carrier that rotates clockwise, 6a2 is a laser scanner that irradiates the photosensitive drum 6a1 with a laser beam to form an electrostatic latent image, and 6a3 is a photosensitive drum. The developing unit develops the electrostatic latent image formed on the surface of the drum 6a1 with yellow toner.

The registration roller 3 starts rotating at a timing synchronized with the toner image formed on the photosensitive drum 6a1, and sends out the recording paper 2. The fed recording paper 2 is pressed by a suction roller 4 against a charged transfer belt 5 as a conveying means, and the recording paper is electrostatically attracted to the transfer belt 5.

The yellow toner image formed on the photosensitive drum 6a1 is transferred by the transfer means 7a to the recording paper 2 conveyed by the transfer belt 5.

Similarly, the image forming means 6b, 6c, 6
(d) Magenta, cyan, and black toner images are sequentially transferred to the recording paper 2 by the transfer units 7b, 7c, and 7d.

Reference numeral 8 denotes a heat fixing device as fixing means having a halogen heater inside the roller, and fixes the toner image transferred onto the recording paper 2 conveyed by the transfer belt 5 onto the recording paper 2.

The recording paper 2 that has passed through the fixing device 8 is conveyed by an inner discharge roller 9 and is discharged onto a discharge tray 11 by an outer discharge roller 10 as discharge means.

When an image is to be formed on the second surface opposite to the recording paper 2 on which the image has been formed on the first surface, the flapper 13 is rotated counterclockwise to pass the inner discharge roller 9. The leading end of the recording paper 2 is guided to the reversing path 14 by the flapper 13.
The recording paper 2 is transported to the switchback path 21 by the first transport roller 15 and the second transport roller 16.

When the rear end of the recording paper 2 has passed through the reverse feed prevention guide 22 formed of a flexible sheet, the second transport roller 16 is rotated in the reverse direction to switch back the recording paper 2. The leading end of the recording paper 2 conveyed in the reverse direction is guided to the two-sided conveyance path 23 by the back-feed prevention guide 22, and is conveyed by the two-sided conveyance roller 20 until it reaches the conveyance roller 1d.

The transport roller 1d transports the recording paper 2 to the registration roller 3 again, and forms an image on the second surface in the same procedure as the above-described process, thereby completing the image formation on both surfaces.

Next, the transfer belt 5 will be described with reference to FIGS.
The configuration and operation between the fixing device 8 and the fixing device 8 will be described in detail. The transfer speed v of the transfer belt 5 for the recording paper 2 is a process speed for forming an image.
The conveyance speed v ₁ of the recording paper by the fixing device 8 is set to be lower than the process speed v. This is the fixing conveyance speed v
_{If 1} is faster than the process speed v, the recording paper during transfer of the image of each image forming unit is pulled, and the image is shifted.

As shown in FIG. 1, a fixing entrance guide 31 for guiding the recording paper 2 from the transfer belt 5 to the fixing device 8 is provided between the transfer belt 5 and the fixing device 8. The fixing entrance guide 31 is rotatable by a rotation fulcrum 32 on the fixing device 8 side. The spring 36 presses the lower surface of the fixing entrance guide 31 in the direction of arrow B, whereby the fixing entrance guide 31 is lifted in the direction of arrow B. The stopper 37 is in contact with the fixing inlet guide side surface portion 33, thereby restricting the rotation of the fixing inlet guide 31 lifted in the direction of arrow B by the spring. A flag 34 is provided in the fixing entrance guide 31, and a sensor 35 as a loop detecting means for detecting the flag 34 is provided below the flag 34. That is,
The loop of the recording paper 2 is detected by the sensor 35 detecting the flag 34 of the fixing entrance guide 31 which has been swung by the loop of the recording paper 2.

According to the above configuration, the fixing inlet guide 31 is pressed by the spring 36 until the leading end of the recording paper 2 conveyed from the transfer belt 5 enters the fixing device 8, and the fixing inlet guide side surface portion 33.
Is in contact with the stopper 37, and is in a state as shown in FIG. Next, a loop is formed only on the recording paper 2 difference fixing conveying speed v ₁ and the process speed v to be conveyed by the recording paper 2 fuser 8, depressing the fixing inlet guide 31 in the direction of arrow C, FIG. 2 ( As shown in FIG. 2B, when the conveyance further proceeds, the fixing entrance guide 31 is further pushed down, and the flag 34 is detected by the sensor 35 as shown in FIG. That is, the above-described loop detecting means according to the present embodiment detects when the loop of the recording paper 2 becomes larger than a predetermined amount. Then, based on a detection signal of the sensor 35, a control unit (not shown) including a CPU and the like controls switching of the conveyance speed of the fixing device 8 as described later.

Next, a method of controlling the loop amount of the recording paper 2 will be described with reference to FIG. In FIG. 3, the horizontal axis is a time axis with the time when the recording paper 2 is conveyed by the fixing unit 8 as 0, and the vertical axis is detection (ON / OFF) of the sensor 35 and fixing conveyance speeds (v ₁ , v _2). ) And loop amounts (a, b). First, fixing the conveying speed for v _1, the recording paper 2 is difference loop the process speed v is formed. At time t1 when the loop amount of the recording paper 2 has changed from 0 to a, the sensor 35 detects the flag 34 (the state of FIG. 2C). Here, varying the fixing conveyance speed v _2. The fixing conveyance speed v ₂ is higher than the process speed v. Thereby, the loop amount of the recording paper 2 decreases. For this reason, the fixing entrance guide
31 is pushed up again by the spring 36, and the sensor 35 is also flagged.
34 will not be detected. The fixing device 8 sensor 35 until a predetermined time Δt since not detect the flag 34 carries the recording sheet 2 by fixing the conveying speed v _2, it switched to a fixing conveyance speed v ₁ again at time t2. At time t2, the loop amount of the recording paper 2 becomes b, and there is a state where some loops remain. This operation is repeated until the recording paper 2 has been conveyed.

As a result, the loop amount of the recording paper 2 formed between the transfer belt 5 and the fixing device 8 can be reduced to a predetermined amount (a in FIG. 3), and Δt which is a fixed time period
Fixing conveying speed by returning from v ₂ to v _1, it is possible to prevent that the recording paper 2 loops disappears after (in Fig. 3 b).

Here, a description will be given of the time Δt during which the apparatus operates at the fixing conveyance speed v ₂ .

The time from when the leading edge of the recording paper 2 enters the fixing device 8 and starts to be conveyed at the fixing conveyance speed v ₁ to when the recording paper 2 is conveyed at the fixing conveyance speed v ₂ by detecting the flag 34 with the sensor 35 is t.
(See FIG. 3), since the process speed v <the fixing conveyance speed v ₂ , the loop formed between the transfer and the fixing is reduced, but the loop amount is set to 0 or more (in the fixing device 8). (V-
v ₁ ) t> (v ₂ −v) Δt. Therefore, the fixed time Δt is Δt <(v−v ₁ ) t /
(V ₂ −v). Here, since (v−v ₁ ) t = a (see FIG. 3), Δt <a / (v ₂ −v), and
Loop amount of the recording sheet 2 a, process speed v, it is possible to set the predetermined time Δt from the fixing conveying speed v _2.

As described above, according to the present embodiment, the loop of the recording paper 2 between the transfer belt 5 and the fixing device 8 is not increased by a certain amount or more, and the recording paper 2 being transferred is fixed by the fixing device 8. Since the fixing / conveying speed is controlled so as not to be pulled, it is possible to prevent image displacement and rubbing.

[Second Embodiment] Next, a second embodiment will be described with reference to FIG. FIG. 4 is an explanatory view of a main part showing a configuration between the transfer belt 5 and the fixing device 8 according to the second embodiment.

The fixing device 8 has a heater 8a inside and heats the fixing roller 8b. Pressing roller 8
c is pressed against the fixing roller 8b by an urging means (not shown). Thus, the toner on the recording paper 2 is fixed on the recording paper by heat and pressure.

However, a color printer 50 as shown in FIG.
In this case, since an image is formed with a large amount of toner (a plurality of colors), a large amount of heat is required to melt the large amount of toner by heat. In addition, since the heat of the fixing roller 8b is taken away by the recording paper 2 in addition to the toner, a larger amount of heat is required than when thick recording paper is used. More OH
When a T film is used as recording paper, it is necessary to completely dissolve the toner to make it transparent, and also in this case, more heat is required. However, there is an electric power limit in increasing the amount of heat of the heater, and usually, the speed of conveying the recording paper 2 by the fixing unit 8 is reduced. For example, if the normal transport speed is 1, the transport speed of thick recording paper is 1
The transport speed of the OHT film is set to 1/4 in order to make the recording paper thicker and to completely dissolve the toner.

Here, the fixing conveyance speed v ₁ of the first embodiment is used.
In the thick recording sheet v _1/2, the OHT film v ₁ /
It becomes 4. Also, the difference between the process speed v and the fixing conveyance speed v _1/2 of thick recording paper becomes too large,
A recording paper loop between transfer and fixing is immediately formed.
Therefore, as with the process speed v also in fixing conveying speed v _1, the thick recording sheet and v / 2, v / 4 in OHT film, and corresponds slowing down.

Here, based on the loop control of the recording paper described in the first embodiment with reference to FIG. 3, the loop control of the recording paper according to the type of the recording paper in the present embodiment will be described.

The thick recording paper is conveyed by the fixing device 8 and
The fixing conveyance speed v_ThreeTransport by
Time t '(corresponding to t in the first embodiment).
And the fixing conveyance speed v_ThreeTransport time Δt '(first implementation
(Corresponding to the form Δt) is ((v / 2) − (v₁/ 2))
t ′> Δt ′ (v_Three− (V / 2)), ((v / 2) −
(V ₁/ 2)) From t '= a, Δt' <a / (v_Three− (V
/ 2)) = 2a / (2v_Three-V), which is the first embodiment.
Similarly, the loop amount a of the recording paper 2, the process speed v, the constant
Incoming transport speed v_ThreeTherefore, it is possible to set a certain time Δt ′.
it can.

[0041] Here, the fixing conveyance speed _{v 3 v 2/2 (v} ,
Assuming _１ ／ as in v ₁ , Δt ′ <2a / (v ₂ −
v), which is Δt × 2 times. Also, a =
'From _{= (v-v 1) t} , t' - ((v / 2) (v 1/2)) t becomes = 2t. That is, the fixing conveyance speed v ₃ also velocity v, if you slow similarly to v _1, would be that if long inverse number of time Δt late the speed ratio. Also OHT
For v _1/4, v / 4 of the film is the same.

As a result, the fixing transport speed v _3, which has been increased in accordance with the process speed v / 2 and the fixing transport speed v _1/2,
By also with v _2/2, that the overall transport speed is in the 1/2, t '= 2t, Δt' = 2Δt, if the size of the same recording sheet, the thickness of the recording sheet regardless _{of, v / 2, v 1/} 2, v 2/2, v / 4, v 1/4,
v _2/4 and v, v _1, the number of times the v sensor 35 in all cases ₂ detects the flag 34 becomes the same, the number of accelerating the same.

Third Embodiment Next, a third embodiment will be described with reference to FIGS. FIG. 5 is an explanatory view of a main part showing a configuration between the transfer belt 5 and the fixing device 8 according to the third embodiment.

As shown in FIG. 5, in the third embodiment, a first sensor 39 as a first detecting means for detecting a loop of the recording paper 2 between the transfer belt 5 and the fixing device 8, and the recording paper 2
And a second sensor 38 for detecting a loop larger than the first loop.
And a flag 34a corresponding to the second sensor 38.

When the second sensor 38 detects the loop of the recording paper 2, the fixing conveyance speed is made faster than the process speed. When the first sensor 39 detects the loop of the recording paper 2, the fixing conveyance speed is increased. Is returned to a speed lower than the original process speed.

That is, as shown in FIGS. 6 and 7, a loop is formed by the recording paper 2 and the flag 34a is set to the second sensor 38.
, The fixing conveyance speed of the fixing device 8 is increased (see FIG. 6B). Next, the recording paper 2
When the flag 34b is detected by the first sensor 39, the fixing conveyance speed of the fixing device 8 is returned to a speed lower than the normal process speed (see FIG. 6C). Then, similarly to the above-described embodiments, this operation is repeated until the recording paper 2 is conveyed.

Thus, in the above-described embodiment, the speed-up time is fixed (Δt, Δt ′). However, since the loop amount is directly detected, fixing by paper type (thin paper, thick paper, etc.) is performed. It is possible to control the loop amount without considering variations in the transport speeds v ₁ and v ₂ .

[Other Embodiments] In the above-described embodiment,
Although four image forming units are used, the number of used units is not limited, and may be appropriately set as needed.

In the above-described embodiment, the laser scanner is used as the exposure means. However, the present invention is not limited to this. For example, an LED array may be used.

Further, in the above-described embodiment, the photosensitive drum serving as the image carrier, the charging means as the process means acting on the photosensitive drum, and the developing means (or the cleaning means) are individually incorporated. But,
The present invention is not limited to this. For example, an apparatus in which a process cartridge integrally including a photosensitive drum serving as an image carrier and a charging unit, a developing unit, and a cleaning unit as process units acting on the photosensitive drum, Alternatively, in addition to the photosensitive drum, a process cartridge having one of the charging unit, the developing unit, and the cleaning unit may be detachably attachable, or each component may be detachable. It may be a device.

In the above-described embodiment, the printer is exemplified as the image forming apparatus. However, the present invention is not limited to this. For example, another image forming apparatus such as a copying machine or a facsimile apparatus, or a function thereof. May be selectively combined, and the same effect can be obtained by applying the present invention to the image forming apparatus.

[0052]

As described above, according to the present invention,
The amount of the transfer material loop formed between the conveying means and the fixing means is detected, and accordingly, the transfer material loop is not increased by a certain amount or more, and the transfer material being transferred is pulled by the fixing means. By switching and controlling the conveyance speed of the fixing unit so as not to cause a problem, it is possible to control the loop amount so as not to affect the color shift or the like of the transfer unit.

[Brief description of the drawings]

FIG. 1 is a principal part explanatory view showing a configuration between a transfer belt and a fixing device according to a first embodiment.

FIG. 2 is an explanatory diagram showing a loop state of recording paper between a transfer belt and a fixing device.

FIG. 3 is a timing chart for controlling a loop amount of recording paper.

FIG. 4 is an explanatory view of a main part showing a configuration between a transfer belt and a fixing device according to a second embodiment.

FIG. 5 is an explanatory view of a main part showing a configuration between a transfer belt and a fixing device according to a third embodiment.

FIG. 6 is an explanatory diagram showing a loop state of recording paper between a transfer belt and a fixing device.

FIG. 7 is a timing chart for controlling a loop amount of recording paper.

FIG. 8 is a schematic configuration diagram of a color printer.

FIG. 9 is an explanatory view showing a schematic configuration between a conventional transfer and fixing.

FIG. 10 is an explanatory view showing a schematic configuration between a conventional transfer and fixing.

FIG. 11 is an explanatory diagram showing a schematic configuration between a conventional transfer and fixing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cassette 1a ... Pickup roller 1b ... Reverse separation roller 1c ... Send roller 1d ... Conveyance roller 2 ... Recording paper 3 ... Registration roller 4 ... Suction roller 5 ... Transfer belt 6a, 6b, 6c, 6d ... Image forming means 6a1,6b1 .., 6c1, 6d1... Photosensitive drums 6a2, 6b2, 6c2, 6d2... Laser scanners 6a3, 6b3, 6c3, 6d3. … Pressure roller 9… Inner discharge roller 10… Outer discharge roller 11… Discharge tray 13… Flapper 14… Reverse path 15… Convey roller 16… Convey roller 20… Double-side conveying roller 21… Switchback path 22… Reverse feed Prevention guide 23 ... Double-sided conveyance path 31 ... Fixing entrance guide 32 ... Rotating fulcrum 33 ... Fixing entrance guide side surface 34 ... Flag 34a ... Flag 34b ... Flag 35 ... Sen 36 ... spring 37 ... stopper 38 ... second sensor 39 ... first sensor 50 ... color printer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) 9A001 F-term (Reference) 2H027 DA20 DC05 DE02 DE07 DE10 EC06 ED16 ED24 ED25 EE03 EE04 EF09 2H032 AA02 BA12 BA13 BA18 BA19 BA21 BA23 2H033 AA14 BA09 BA11 BA59 BB01 BB28 BB37 CA01 CA09 CA13 CA17 CA22 CA30 CA36 CA37 CA40 2H072 AA16 AA22 AB09 CA06 JA02 JA03 3F049 AA10 DA01 DA12 EA10 EA13 LA02 LA05 LA07 LB03 9A001 HH34 JJ35 KK42 LL

Claims (5)

[Claims] An image forming unit that includes an image carrier and forms an image on the image carrier in accordance with image information; and a transfer unit that transfers an image formed on the image carrier to a transfer material. Conveying means for conveying the material, fixing means for fixing the image transferred to the transfer material while conveying the transfer material at a speed lower than the conveying speed of the conveying means, transfer between the conveying means and the fixing means Detecting means for detecting a loop of the material, and control means for switching and controlling the conveyance speed of the fixing means based on the detection information of the detecting means, after the detecting means detects the loop of the transfer material, An image forming apparatus, wherein the conveying speed of the fixing unit is switched to a speed higher than the conveying speed of the conveying unit for a predetermined time. 2. The method according to claim 1, further comprising: changing a conveying speed of the conveying unit and the fixing unit according to a type of the transfer material, and increasing a conveying speed of the fixing unit in accordance with the conveying speed of the conveying unit and the fixing unit. 2. The image forming apparatus according to claim 1, wherein the time is changed. 3. The method according to claim 1, wherein the conveying speed of the fixing unit is returned to a speed lower than the original conveying speed after the lapse of the predetermined time.
An image forming apparatus according to claim 1. 4. An image forming means having an image carrier and forming an image on the image carrier in accordance with image information, and transferring the image formed on the image carrier through a transfer position for transferring the image to a transfer material. Conveying means for conveying the material, fixing means for fixing the image transferred to the transfer material while conveying the transfer material at a speed lower than the conveying speed of the conveying means, transfer between the conveying means and the fixing means A first detecting unit for detecting a loop of the transfer material; and a second detecting unit for detecting a loop larger than the loop of the transfer material. When the second detecting unit detects the loop of the transfer material,
When the transport speed of the fixing unit is higher than the transport speed of the transport unit, and when the first detection unit detects a loop of the transfer material,
An image forming apparatus, wherein the conveying speed of the fixing unit is returned to a speed lower than the original conveying speed of the conveying unit. 5. A detecting means for detecting a loop of the transfer material, wherein a swingable guide member for guiding the transfer material from the transfer means to the fixing means swings by the loop of the transfer material.
The loop of the transfer material is detected by detecting a flag provided on the guide member.
The image forming apparatus according to claim 1.