JPH0680273A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent a generation of abnormality of a machine and an image owing to an excess or a shortage of bending amount by maintaining the bending amount of a transfer paper between a photosensitive body and a resist roller or a fixed roll to make in an adequate value constantly. CONSTITUTION:In a conveying passage of transfer papers between a photosensitive body drum 1 and a resist roller 4 or a fixed roller 11, transfer paper bending detecting devices 17a and 17b are provided, a transfer paper is passed for regulating, and from the difference between the detected bending of the transfer paper and an adequate bending amount, the speed of the resist roller 4 or the fixed roller 11 necessary to release the difference is operated. And one side member is moved to increase or decrease the width of a V-groove of two-piece V pulleys 22a and 22b provided at the shaft end of the resist roller 4 or the fixed roller 11, and the rotation speed of the rollers is controlled automatically so as to obtain an adequate bending.

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 in which a toner image formed on a photoconductor is transferred onto a transfer paper conveyed through a transfer portion along the photoconductor and is fixed by a heat roller fixing device.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as an electrophotographic copying machine, a facsimile, and an electrostatic printer, a toner image formed on a photoconductor by an electrophotographic process is transferred from a paper feed unit to a registration roller at a transfer unit. After being transferred by the action of the transfer charger onto the transfer paper that is fed so that the leading edge is aligned with the image formed on the photoconductor, the transfer paper is separated from the photoconductor and is conveyed to the fixing device and fixed. The image formation is completed and the paper is ejected outside the machine. As a fixing device, a heat roller fixing device including a fixing roller having a built-in heat source and a pressure roller in pressure contact with the heat source is widely adopted.

Conventionally, as a means for transporting a transfer paper carrying an unfixed toner image from a transfer portion in contact with a photoconductor to a heat roller fixing device without destroying the toner image, a transfer belt and a back surface of the transfer paper are attracted to the transfer belt. In most cases, a vacuum fan was used to make it happen. In this case, the distance between the photoconductor and the fixing section tends to be long, which leads to a reduction in the first copy time when performing continuous copying and an increase in the size of the machine. It becomes necessary to increase the number of parts, and the material cost and the assembly cost increase accordingly, resulting in cost increase. Therefore, by properly insulating the housing of the fixing device, the distance between the fixing device and the photoconductor can be made shorter than before, and the transfer paper from the transfer section can be directly fed without using a conveyor belt or a vacuum fan. It is conceivable to convey it to the fixing device. As described above, when the transfer sheet is conveyed to the transfer section along the photoconductor by the registration roller and the transfer sheet conveyed from the transfer section to the fixing device is sandwiched between the fixing roller and the pressure roller and conveyed, When the transfer paper is conveyed between the body and the registration roller, that is, when the transfer paper is conveyed under tension or under compression due to excessive deflection, magnification error or magnification error deviation, Transfer blurring, transfer dust, and rubbing noise between the transfer paper and the guide plate are generated.

The transfer state of the transfer sheet between the transfer section and the fixing device is substantially the same as the transfer state of the transfer sheet on the upstream side of the photoconductor, but the transfer blurring is affected. The transfer paper is bent between the fixing device and the photoconductor, and the flexure of the transfer paper is eliminated at the moment when the trailing end of the transfer paper passes through the registration roller, causing transfer blurring. Regarding the magnification error deviation, for example, when the diameter of the fixing roller is large and faster than the linear velocity of the photoconductor drum, the transfer paper is pulled by the fixing / pressurizing roller pair, and the deflection of the transfer paper between the fixing device and the photoconductor is caused. When it disappears, the magnification of the image before and after entering the fixing device is different, and the magnification error deviation increases.
Therefore, it is necessary for the transfer paper conveyed through the transfer paper conveyance path to maintain a predetermined optimum deflection amount.

6 and 7 show the results of actual measurement of the relationship between the magnification error deviation, the fixing roller diameter, and the registration roller diameter for an example of an image forming apparatus, and transfer blurring that occurs when the transfer paper leaves the registration roller. 8 shows the relationship between the resist roller diameter and the resist roller diameter.

From these figures, it can be seen that even if the diameter of the fixing roller and the diameter of the registration roller are changed very slightly, the magnification error deviation changes considerably and the rank of the transfer blur also changes.

Therefore, in the past, in order to prevent the magnification error deviation from increasing and prevent the degree of transfer blurring from deteriorating, the diameters of the fixing roller and the registration roller are accurately finished with strict tolerances. The increase in cost was unavoidable. In addition, deterioration in image quality due to changes in roller diameter over time cannot be avoided.

[0008]

SUMMARY OF THE INVENTION According to the present invention, a toner image formed on a photoconductor is transferred to a transfer paper fed to a transfer section along the photoconductor by a transfer paper conveying roller such as a registration roller. In view of the above-mentioned problems related to image transfer in the conventional image forming apparatus in which the transfer paper is directly conveyed from the transfer unit to the heat roller fixing device, in consideration of the above-mentioned problems between the transfer paper conveying roller and the transfer unit of the photoconductor and the transfer unit and the fixing unit. An object of the present invention is to provide an image forming apparatus capable of always automatically maintaining the optimum deflection amount of the transfer sheet conveyed through the transfer sheet conveying path between the pressure roller pair and the above-mentioned abnormality. Let's take the first challenge.

An image forming apparatus capable of achieving the above-mentioned object at a low cost by manually performing an operation for maintaining the optimum deflection amount of the transfer sheet conveyed through the transfer sheet conveying path. The second problem is to provide.

Although the allowable deflection amount and the maximum deflection amount of the transfer sheet conveyed on the transfer sheet conveying path between the photoconductor and the transfer sheet conveying roller or the fixing roller vary depending on the type and size of the transfer sheet. A third object is to provide an image forming apparatus capable of automatically reducing the amount of deflection of the transfer paper to the allowable amount of deflection in the shortest time even when the type and size of the transfer paper used differ. To do.

A fourth object is to provide an image forming apparatus suitable for manually reducing the amount of deflection of the transfer paper to an allowable amount of deflection.

[0012]

SUMMARY OF THE INVENTION An invention for solving the above-mentioned first problem is to provide a transfer paper conveying roller provided on the upstream side of a transfer section along a photosensitive member or a fixing roller provided on the downstream side,
In an image forming apparatus having a sensor provided between the transfer paper transport roller or fixing roller and the photoconductor and detecting the amount of deflection of the transfer paper at that position, the rotation of the transfer paper transport roller or fixing roller. The rotation speed control means is provided at the shaft end of the transfer paper conveying roller or the fixing roller so as to rotate together with the roller, and is divided into two in the axial direction, at least one of which is the shaft. A slidable surface of the V-shaped groove, which comprises a pulley having a variable interval between the opposite slopes of the V-shaped groove, and a V-belt wound around the pulley and driven at a constant speed by a drive source. The rotation speed of the shaft is changed by changing the interval of the transfer paper. When the deflection amount of the transfer sheet detected by the sensor exceeds a predetermined optimum deflection amount, the transfer sheet conveying roller or the fixing roller is set. It is possible to control the rotation speed by changing the width of the pulley groove so that the deflection of the transfer paper approaches the predetermined optimum deflection amount, and fixing the pulley groove width when the deflection amount reaches the optimum value. Characterize.

The invention for solving the above-mentioned second problem is similar to the invention for solving the above-mentioned first problem, in that the amount of deflection of the transfer paper is set between the photoconductor and the transfer-paper conveying roller or fixing roller. Although a sensor for detecting is provided and a means for changing the rotation speed of the transfer paper transport roller or the fixing roller having the above-described configuration is provided, the rotation speed of the transfer paper transport roller or the fixing roller is manually changed. In order to facilitate the above, the required amount of movement of one of the two divided pulleys for obtaining the rotational speed of the transfer paper transport roller or fixing roller at which the amount of flexure of the transfer paper detected by the sensor becomes a predetermined optimum amount of flexure. Is provided, and a means for displaying a required movement amount (for example, the number of rotations of the moving nut) based on this is provided.

According to the invention for solving the third problem, in the structure of the invention for solving the first problem, the sensor for detecting the amount of deflection of the transfer paper is a transfer paper conveying roller and a transfer section.
Alternatively, the maximum value of the difference between the deflection amount detected by each sensor and the permissible deflection amount at each sensor position is set in the transfer sheet conveyance path between the transfer section and the fixing roller in the transfer sheet conveyance direction. The control circuit is fed back to control the rotation speed of the transfer paper transport roller or the fixing roller.

According to the invention for solving the fourth object, in the structure of the above-mentioned invention for solving the second object, the sensor for detecting the amount of deflection of the transfer paper is a transfer paper conveying roller and a transfer portion.
Alternatively, the maximum value of the difference between the deflection amount detected by each sensor and the permissible deflection amount at each sensor position is set in the transfer sheet conveyance path between the transfer section and the fixing roller in the transfer sheet conveyance direction. It is characterized in that it is inputted to an arithmetic circuit to calculate a required movement amount of one of the two-split pulleys and displayed on a display unit.

[0016]

According to the structure of the above invention for solving the first problem, the transfer sheet is passed through for adjustment, and the transfer sheet is provided between the photoconductor and the transfer sheet conveying roller or the fixing roller detected by the sensor. If the deflection amount of the pulley is different from the predetermined optimum deflection amount, one member of the pulley is moved so as to increase or decrease the width of the V groove of the pulley divided into two in the direction in which the deflection amount becomes the optimum deflection amount. Since the distance between the grooves of the pulley is controlled to be fixed when the amount reaches the amount, the amount of deflection of the transfer paper is automatically maintained at the optimum value.

According to the configuration of the above invention for solving the second problem, the means for displaying the deflection amount of the transfer sheet detected by the above sensor, and the optimum deflection amount when the deflection amount is different from the optimum deflection amount. In order to do this, a circuit for calculating how much one of the two pulleys should be moved and means for displaying the required amount of movement are provided, so that a serviceman or the like manually bends the amount of deflection of the transfer paper to the optimum deflection. It will be easier to adjust to match the quantity.

In the configuration of the invention for solving the third and fourth problems, a plurality of sensors are provided in the transfer paper conveyance path between the photoconductor and the transfer paper conveyance roller or the fixing roller, and each sensor detects. The maximum value of the difference between the flexure amount and the allowable flexure amount at each sensor position is input to the control circuit and the arithmetic circuit of the invention for solving the first and second problems so that similar control or display is performed. Therefore, even when the type or size of the transfer paper used is different, it is possible to adjust the optimum deflection amount automatically or manually in a short time.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 mainly shows a photosensitive drum and a transfer paper conveying path of an embodiment of an image forming apparatus according to the present invention.
It is a figure which shows schematic structure.

Around the photosensitive drum 1, the developing unit 2, the pre-transfer charge eliminating lamp 3,
Transfer / separation charger 8, cleaning unit 13,
A charging charger 14, an exposure device 15, and an eraser 16 are provided. The transfer paper P stacked in the paper tray 7 passes through the feed roller 6, the vertical conveyance roller pair 5, and the registration roller pair 4, and is transferred onto the transfer member between the transfer / separation charger 8 and the photosensitive drum 1 onto the photosensitive member 1. The sheet is fed at the timing when the image leading edge position and the transfer sheet leading edge match. The toner image formed on the photoconductor drum 1 by the above-mentioned process unit by a known electrophotographic process is transferred to the transfer paper under the action of the transfer charger, and the transfer paper is separated from the photoconductor 1 by the separation charger. Guided by the paper conveying member 9 and inserted into the nip portion of the roller pair of the heat roller fixing device composed of the pressure roller 10 and the fixing roller 11, and sandwiched and conveyed by these to be fixed, and the paper discharge roller pair. It is discharged to the outside of the machine by 12. The configuration described so far is not particularly different from that of the conventional image forming apparatus.

However, in the image forming apparatus of the embodiment, according to the present invention, the transfer is carried to the transfer paper carrying path between the registration roller pair 4 and the photosensitive drum 1 and between the photosensitive drum 1 and the fixing roller 11, respectively. Sensors 17b and 17a for detecting the amount of bending of the paper are arranged. For adjustment, the detection outputs of these sensors obtained by passing the transfer paper through the conveyance path are connected to a deflection amount detection circuit 19, which detects the deflection amount of the transfer paper at each sensor position. It The detected deflection amount is compared with a preset optimum deflection amount in the arithmetic circuit 20, and is fed back to the roller rotation speed control circuit 21.

The roller rotation speed control circuit decreases the rotation speed of the registration roller when the deflection amount of the transfer sheet between the registration roller 4 and the photosensitive drum 1 exceeds the optimum deflection amount, and increases it when the deflection amount is below the optimum deflection amount. If the deflection amount of the transfer paper between the photoconductor drum 1 and the fixing roller 11 exceeds the optimum value, the rotation speed of the fixing roller is increased, and if it is less than the optimum value, the rotation speed is decreased to a predetermined optimum value. When the amount of deflection is reached, this is a circuit that controls the rotation speed to be maintained.

In the present invention, a mechanism using a known V-belt and a pulley with a variable width V groove is used as a mechanism for adjusting the rotational speed of the registration roller and the fixing roller.

As shown in FIGS. 2 (a) and 2 (b), this rotation speed varying mechanism has a registration roller 4 and a fixing roller 1.
For example, a pulley 22 having a V groove that integrally rotates with the shaft 25 and a spline shaft at the end of the shaft 25 of the roller whose rotation speed is to be changed, such as 1 is divided into two in the axial direction and two members 22 are provided.
a and 22b, one of which is slidable along the axis,
The drive motor 23 can move the pulley 22a in the axial direction via the pinion gear 24a and the cylindrical rack 24b and rotate the pulley 22a integrally with the shaft 25. The opposing slopes of the V-shaped groove of the pulleys 22a and 22b thus make it possible to change the spacing, and if the V-belt 26 driven at a constant speed is wound around this V-shaped groove, the pulley 22a, By changing the spacing of 22b, the effective position of V belt 26, that is, the effective radius of V belt 26 from the center of shaft 25, changes,
When the belt moves at a constant speed, the rotation speed of the shaft 25 changes in inverse proportion to the effective radius of the pulley.

Therefore, by the roller rotation speed control circuit, the movement amount of one pulley 22a for changing the rotation speed of the registration roller or the fixing roller to a rotation speed such that the deflection amount of the transfer paper becomes a predetermined optimum deflection amount. By giving the obtained rotation amount to the motor 23, the deflection of the transfer paper can be made to match a predetermined optimum deflection amount. The rotation of the motor is stopped when the amount of deflection of the transfer sheet matches a predetermined optimum amount of deflection, and the pulley 22a is axially fixed at that position by a fixing means (not shown). The distance between the slopes on both sides of the V-groove and thus the effective radius are kept constant, so that the amount of deflection of the transfer sheet can be maintained at the optimum amount of deflection.

FIG. 3 is a diagram showing a second embodiment of the present invention. In this embodiment, the arithmetic circuit 20 allows the sensor 17
a, 17b and the required movement amount of one member of the two-divided pulleys required to make the deflection amount detected by the deflection detection circuit 19 the optimum deflection amount are calculated and displayed on the display unit 28.

Then, the serviceman, looking at this display, displaces one of the two-divided pulleys 22a in the axial direction by the instructed movement amount. FIG. 4 shows a pulley arrangement suitable for this purpose. One member 22a of the pulley is the shaft 2
5 is free to slide in the axial direction by a spline, etc.
It is provided to rotate with. The end portion of the shaft penetrates the member 22a, the end portion is threaded, and the nut 27 is screwed. Since the member 22a is always urged by a spring (not shown) so as to be pressed against the nut 27, the nut 27 is rotated by a spanner or the like to change the axial position of the two pulley portions 22a, 2a.
The distance between the opposite slopes 2b changes, the effective radius of the V-belt changes, and the rotation speed of the fixing roller or the registration roller changes to a speed at which the required deflection is obtained.

In the example of the two V-pulleys shown in FIGS. 2 and 4, the means for directly adjusting the rotation speed is attached to the shaft 25 of the fixing roller or the registration roller that conveys the transfer paper. The rotation speed is not necessarily limited to this, and the rotation speed of the fixing roller or the registration roller may be adjusted through a portion different from the fixing roller or the registration roller to change the rotation speed of the fixing roller or the registration roller via the transmission unit. It is possible.

Further, since the tension of the V-belt changes as the effective radius of the pulley changes, a mechanism such as a tightener for making the belt tension uniform or a means for constantly pressing one of the pulleys against the nut 27 as described above. However, since these are known, the detailed description of the mechanism is omitted.

The difference between the deflection amount of the transfer sheet and the allowable deflection amount in the transfer sheet conveyance path between the photoconductor 1 and the registration roller 4 or between the photoconductor 1 and the fixing roller 11 changes depending on the position in the conveyance direction. . FIG. 5 shows an example thereof. The solid line shows the actual deflection of the transfer paper, and the broken line shows the allowable deflection.
a, b, and c are the differences between the actual deflection amount and the allowable deflection amount at each point. The position where the difference in the amount of deflection at each of these positions is maximum varies depending on the type and size of the transfer paper.

Therefore, a plurality of sensors 17a (a sensor for the transfer path on the registration roller side is not shown in FIG. 5) is provided in the transfer paper transfer path between the photosensitive member and the fixing roller or the registration roller. By feeding back the largest difference between the actual deflection amount and the allowable deflection amount to the control circuit of FIG. 1 to control the pulley, the deflection of the transfer sheet can be set to the allowable value in the shortest time. .

Also in the embodiment of FIG. 3, a plurality of sensors are similarly provided, and the deflection amount at the position where the difference between the actual deflection amount and the allowable deflection amount is the maximum is put in the arithmetic circuit and one of the pulleys is inserted. It is preferable that the required movement amount of the member is calculated, and a serviceman or the like adjusts the pulley based on the calculated movement amount to adjust the rotation speed of the roller.

As described above, even when the rotational speed of the registration roller or the fixing roller is adjusted by automatic control or manual operation by a service person, the transfer paper enters the conveyance path between the photoconductor and the registration roller. However, until the leading edge of the transfer paper contacts the photoconductor and the trailing edge of the transfer paper leaves the registration roller, or when the leading edge of the transfer paper contacts the photoconductor and the leading edge contacts the fixing roller, The deflection of the transfer paper between the photoconductor and the registration roller or the fixing roller until it is separated is not constant and changes with time.

However, since the transfer paper is a cut paper and its length is limited, the change in the amount of deflection is not great, and it takes place from the contact of the leading end of the transfer paper with the photosensitive member until the trailing end of the transfer paper passes through the registration roller. Or the maximum value of the difference between the allowable deflection amount detected by the sensor provided on the conveyance path and the actual deflection amount between the time when the leading edge of the transfer paper contacts the fixing roller and the time when the rear edge leaves the photoconductor. It is sufficient to make adjustments based on.

[0036]

As described above, according to the present invention, the deflection amount of the transfer sheet conveyed between the photoconductor and the registration roller or the fixing roller is properly maintained, so that the machine caused by the deflection amount being too large or too small. Alternatively, it is possible to prevent abnormalities in the image. Also, unlike the conventional case, it is not necessary to tighten the tolerance of the diameter of the registration roller or the fixing roller, which contributes to cost reduction, and the outer diameter of the roller changes with time, or the outer diameter changes due to replacement of parts. Can also be easily adjusted.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a schematic configuration centered on a photoconductor and a transfer paper conveyance path according to an embodiment of the present invention.

2A and 2B are a front view and a side view, respectively, showing an example of a rotation speed varying mechanism for a registration roller and a fixing roller in the above embodiment.

FIG. 3 is a schematic diagram showing a schematic configuration centering on a photoconductor and a transfer paper conveyance path according to another embodiment of the present invention.

FIG. 4 is a front view showing an example of a rotation speed varying mechanism for a registration roller and a fixing roller in the embodiment.

FIG. 5 is a schematic diagram showing an example in which a plurality of transfer paper deflection amount detection sensors are provided in a transfer paper transport path between a photoconductor and a fixing roller or a registration roller.

FIG. 6 is a graph showing an example of a relationship between a fixing roller diameter and a magnification error deviation in a conventional image forming apparatus.

FIG. 7 is a graph showing an example of the relationship between the registration roller diameter and the magnification error deviation in the conventional image forming apparatus.

FIG. 8 is a graph showing a relationship between a registration roller diameter and a rank of transfer blur in a conventional image forming apparatus.

[Explanation of symbols]

 1 photoconductor drum 4 registration roller pair (transfer paper transport roller pair) 8 transfer / separation charger 11 fixing rollers 17a, 17b transfer paper deflection amount detection sensor 19 deflection amount detection circuit 20 arithmetic circuit 21 roller rotation speed control circuit 22a, 22b 2 Split pulley 23 Pulley moving motor 24a, 24b Gear 25 Roller shaft 26 V-belt 27 Nut 28 Indication of required movement amount of one member of pulley

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location G03G 15/20 107

Claims (6)

[Claims] 1. A photoconductor, a transfer paper transport roller provided upstream of a transfer unit along the photoconductor in the transfer paper transport direction, and a position provided between the transfer paper transport roller and the photoconductor. In the image forming apparatus having a sensor for detecting the amount of deflection of the transfer paper, the rotation speed control means has a means for controlling the rotation speed of the transfer paper conveyance roller, and the rotation speed control means is a shaft end of the transfer paper conveyance roller. Is provided so as to rotate together with the roller, and is divided into two in the axial direction, at least one of which is slidable on the shaft, and the distance between the slopes facing the V-shaped groove is variable, and the pulley is wound around the pulley. It is composed of a V-belt that is rotated and driven at a constant speed by a driving source, and changes the rotation speed of the shaft by changing the interval between the slopes facing each other in the V-shaped groove. The transfer paper detected by the above sensor. The maximum amount of deflection is When the amount of deflection exceeds, the rotational speed of the transfer paper transport roller is reduced, and when the amount of deflection is less than the predetermined optimum amount, the rotational speed of the transfer paper transport roller increases, and one of the divided pulleys is rotated. An image forming apparatus characterized in that when one of the deflection amounts of sliding in a predetermined direction reaches a predetermined optimum deflection amount, one of the pulleys is fixed and the rotational speed of the transfer sheet conveying roller is controlled. 2. A photoconductor, a fixing roller provided on the downstream side of a transfer section along the photoconductor in the transfer paper conveying direction, and a transfer paper provided at the position between the fixing roller and the photoconductor. An image forming apparatus having a sensor for detecting the amount of flexure of the fixing roller has means for controlling the rotation speed of the fixing roller, and the rotation speed control means is arranged to rotate with the roller at the shaft end of the fixing roller. The pulley is provided in the axial direction, at least one of which is slidable on the shaft, and the distance between the opposing slopes of the V-shaped groove is variable, and the pulley is wound around the pulley at a constant speed. It is composed of a driven V-belt, and changes the rotation speed of the shaft by changing the interval between the slopes facing each other in the V-shaped groove. The deflection amount of the transfer paper detected by the above sensor is a predetermined optimum deflection. When the amount is exceeded The deflection amount by sliding one of the divided pulleys in the axial direction is increased so that the rotation speed of the fixing roller is increased and the rotation speed of the fixing roller is decreased when the rotation amount is lower than a predetermined optimum deflection amount. An image forming apparatus characterized in that, when the amount of deflection is optimum, the one pulley is fixed and the rotation speed of the fixing roller is controlled. 3. A photoconductor, a transfer paper transport roller provided on the upstream side of a transfer unit along the photoconductor in the transfer paper transport direction, and a position provided between the transfer paper transport roller and the photoconductor. In the image forming apparatus having a sensor for detecting the amount of deflection of the transfer paper, the means for changing the rotation speed of the transfer paper conveyance roller is provided, and the means for changing the rotation speed is A pulley provided at the shaft end so as to rotate together with the roller and divided into two in the axial direction, at least one of which is slidable on the shaft and in which the distance between the slopes of the V-shaped grooves facing each other is variable; It is composed of a V-belt wound around the V-shaped groove and driven at a constant speed by a driving source, and changes the rotation speed of the shaft by changing the interval between the slopes facing each other in the V-shaped groove. The amount of paper deflection Means for calculating the required movement amount of one of the two-divided pulleys for obtaining the rotation speed of the transfer paper transport roller required to obtain a predetermined optimum deflection amount, and means for displaying the required movement amount based on this An image forming apparatus characterized by being provided. 4. A photosensitive member, a fixing roller provided on the downstream side of a transfer portion along the photosensitive member in the transfer paper conveying direction, and a transfer paper at the position provided between the fixing roller and the photosensitive member. An image forming apparatus having a sensor for detecting the amount of flexure of the fixing roller, having means for changing the rotation speed of the fixing roller,
The means for changing the rotation speed is provided at the shaft end of the fixing roller so as to rotate together with the roller, and is divided into two in the axial direction, at least one of which is slidable on the shaft and is opposed to the V-shaped groove. And a V-belt wound around the pulley and driven at a constant speed by a driving source. The rotation speed of the shaft is changed by changing the interval between the opposite slopes of the V-shaped groove. The required amount of movement of one of the two-divided pulleys is calculated to obtain the rotational speed of the fixing roller required for the deflection amount of the transfer paper detected by the sensor to reach a predetermined optimum amount of deflection. An image forming apparatus comprising means and means for displaying a necessary movement amount based on the means. 5. A plurality of sensors for detecting the amount of flexure of the transfer paper are arranged in the transfer paper transport direction in a transfer paper transport path between the transfer paper transport roller and the transfer section or between the transfer section and the fixing roller, The maximum value of the difference between the deflection amount detected by each sensor and the allowable deflection amount at each sensor position is fed back to the control circuit to control the rotational speed of the transfer sheet conveying roller or the fixing roller. Or the image forming apparatus according to 2. 6. A plurality of sensors for detecting the amount of flexure of the transfer paper are arranged in the transfer paper transport direction in a transfer paper transport path between the transfer paper transport roller and the transfer section or between the transfer section and the fixing roller. The feature is that the maximum value of the difference between the deflection amount detected by each sensor and the allowable deflection amount at each sensor position is input to the arithmetic circuit, and the required movement amount of one of the two-split pulleys is calculated and displayed on the display unit. The image forming apparatus according to claim 3 or 4.