JP2000187397A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent transfer defects, owing to a stepped part of a surface potential on a photoreceptor, as a result of the large transfer current sharply flowing on the photoreceptor. SOLUTION: During the time while a leading edge side margin of a transfer paper sheet is transported on a transfer position, the image forming device is allowed to increase the transfer output up to the specified the stationary output value, and then, to gradually reduce the transfer output to the non- transfer time output value while a trailing end margin of the transfer paper sheet is transported on the transfer position.

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 facsimile, and a printer using an electrophotographic process.

[0002]

2. Description of the Related Art An image forming apparatus such as a copying machine, a facsimile, and a printer using an electrophotographic process generally includes:
Around the photoconductor having photoconductivity, a charger which applies a predetermined potential to the surface of the photoconductor by corona discharge from a charging wire to which a high voltage is applied in order along the rotation direction of the photoconductor. An exposure device that selectively attenuates the potential of the photoconductor surface by irradiating corresponding light to form an electrostatic latent image, and develops the electrostatic latent image formed on the photoconductor surface with toner to form a toner image A developing device for forming, a transfer device for transferring a toner image formed on the photoreceptor to transfer paper or the like, a static eliminator for removing charge on the surface of the photosensitive member, a cleaner for removing toner remaining on the surface of the photosensitive member, and the like are arranged. .

FIG. 8 shows a photosensitive drum 31 as a photosensitive member.
FIG. 3 is a perspective view showing the vicinity of a transfer roller 35 of a general image forming apparatus using a transfer roller 35 as a transfer device.

In this image forming apparatus, the photosensitive drum 31
The transfer sheet P is sent to the transfer position C, with a transfer position C between the transfer roller 35 and the transfer roller 35. Transfer roller 35
Is supplied with a transfer output from a transfer output applying means 67, and the transfer output
An electric field is formed between the photosensitive drum 31 and the photosensitive drum 31, and the toner image 311 on the photosensitive drum 31 is attracted to the transfer roller 35 side, so that the toner image 311 is transferred onto the paper P.

FIG. 9 shows a timing at which a transfer output is applied to a transfer roller 35 in a conventional image forming apparatus.

As shown in FIG. 1, in the conventional image forming apparatus, the transfer output is generally subjected to simple ON / OFF control, and a time T (sheet P) at which the leading edge of the sheet P is fed to the transfer position C is used. At the position indicated by the broken line in FIG. 8) so that the transfer can be started without fail.
Is located at a position A0 upstream of the transfer position C on the sheet transport path.
T0 (when the paper P is at the solid line position in FIG. 8)
, A predetermined transfer output is applied.

[0007]

However, when the transfer output is suddenly applied when the sheet P reaches the predetermined position A0 (time t = t0), the photosensitive member located at the transfer position C at this time. Since the transfer current suddenly flows into a predetermined portion on the surface of the body drum 31, a large potential difference is formed in this portion from the surrounding portion. If the potential step is large enough that the surface of the photosensitive drum 31 is not sufficiently eliminated by the charge eliminator, a toner density step occurs in the subsequent developing process, and the transferred image on the paper P has a width. There is a problem that an image defect occurs in which a plurality of stripes extending in the direction are formed.

Further, in a state where the sheet P is not interposed at the transfer position C (a solid line state in FIG. 8), the electric resistance between the photosensitive drum 31 and the transfer roller 35 is different from the case where the sheet P is interposed. If the transfer output is applied in this state, a very large transfer current flows into the surface of the photosensitive drum 31, and the above-described image defect is likely to occur in the transferred image.

In addition, the photosensitive portion of the photosensitive drum 31 generally has a charge elimination sensitivity characteristic in which a charge having a polarity opposite to the charge polarity by the charger is difficult to be removed. When the applied reversal developing method is used, the charge applied to the surface of the photoconductor drum 31 due to the flow of the transfer current is particularly difficult to be eliminated, and the above-mentioned image defects appear particularly remarkably. Specifically, in the developing step of the reversal developing method, a large amount of toner adheres to a portion of the photoconductor drum 31 where a charge of the opposite polarity is applied because a toner is attached to a low potential portion of the photosensitive drum 31. A plurality of black streaks extending in the width direction of the paper P are formed on the transferred image.

[0010] Further, such an image defect may be caused by transferring a photographic image or the like having a gradation property to the photosensitive drum 31.
Because the minute potential difference on the surface also appears as shading in the image,
It is a big problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an image forming apparatus capable of stably forming high-quality images.

[0012]

An image forming apparatus according to the present invention includes a transfer device for transferring a toner image formed on a photoreceptor to a sheet, and a transfer position between the photoreceptor and the transfer device. Based on the sheet position detecting means for detecting the sheet position and the sheet position information detected by the sheet position detecting means, the transfer area of the sheet gradually increases before being conveyed to the transfer position, and An output application unit for applying a transfer output, which becomes a steady transfer output value when the transfer area reaches the transfer position, to the transfer device (claim 1).

According to this image forming apparatus, since the transfer output applied to the transfer device gradually increases, the transfer current does not suddenly flow into the photosensitive member. Therefore, it is possible to suppress the occurrence of an image defect in a transferred image on a sheet due to the formation of a large potential step on the surface of the photoconductor, thereby stably forming a high-quality image.

The transfer area of the sheet is an area to which an image is to be transferred except for a peripheral portion of the transfer sheet which is a margin.

Further, the output applying section applies to the transfer device a transfer output that gradually increases from the time when the leading edge of the sheet passes through the transfer position until the area to which the sheet is transferred reaches the transfer position. It is desirable to configure as follows (claim 2).

With this configuration, when the transfer output is applied, the paper is already interposed between the photoconductor and the transfer unit, and the same electrical resistance value as at the time of transfer is secured between the photoconductor and the transfer unit. Therefore, the influence of the surface potential of the photoconductor due to the excessive transfer current flowing into the photoconductor can be reduced, and the occurrence of the above-mentioned image defects can be suppressed more reliably, thereby contributing to high-quality image transfer.

Further, the output applying unit is configured to apply a transfer output gradually decreasing to an output value at the time of non-transfer to the transfer unit after the transfer area of the sheet has passed the transfer position. It is desirable to perform (claim 3).

With this configuration, the transfer output does not sharply decrease after the image is transferred, and it is possible to suppress the occurrence of the step of the surface potential on the photosensitive member after the image is transferred.
Even in the case of performing continuous transfer on a plurality of sheets of paper, while suppressing the occurrence of image defects and performing high-quality image formation,
High transfer work efficiency can be obtained by narrowing the paper interval.

Further, the output applying section applies to the transfer device a transfer output that gradually decreases from the time when the transfer area of the sheet passes through the transfer position to the time when the rear end of the sheet reaches the transfer position. It is desirable to be configured so as to perform (claim 4).

With this configuration, while the paper is interposed between the photoconductor and the transfer device, the transfer output decreases to the output value at the time of non-transfer, so that an excessive transfer current flows into the photoconductor, and the surface of the photoconductor is charged. The influence on the potential can be further reduced.

The output applying unit includes a transfer output applying unit for applying a transfer output to the transfer unit, a transfer output setting unit for setting a transfer output to be applied to the transfer unit in accordance with a sheet position, The transfer output control means controls the transfer output application means so that the transfer output set by the transfer output setting means is applied to the transfer device.

On the other hand, the conductivity of the paper changes in accordance with the absolute humidity, and the transfer current flowing into the photoreceptor by the transfer output applied to the transfer unit differs depending on the absolute humidity of the apparatus installation environment. The output setting means sets a change amount of the transfer output per unit time according to the absolute humidity condition of the apparatus installation environment, and based on the change amount thus set, gradually increases or decreases the transfer output. It is desirable to set to (claim 6).

In this way, the transfer output is applied at an appropriate rate of change that can suppress the occurrence of the above-mentioned image defects, in consideration of the magnitude of the transfer current actually flowing into the photosensitive member with respect to the applied transfer output. Since the voltage can be applied, high-quality image formation can always be performed regardless of the absolute humidity condition.

Further, since the transfer current flowing into the photoreceptor varies depending on various transfer conditions such as the size and quality of the paper, the transfer output control means controls the transfer output unit in accordance with the transfer condition. Set the amount of change per hour,
It is desirable that the transfer output is set so as to gradually increase or decrease based on the set amount of change (claim 6).

In this way, a high-quality image can be formed by applying a transfer output at an appropriate change rate corresponding to various transfer conditions.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment in which an image forming apparatus according to the present invention is applied to a copying machine will be described.
First, an overall configuration of the apparatus will be described with reference to FIG. 1, and then a characteristic configuration of the present invention, that is, a configuration of a control system of a transfer output applied to a transfer device will be described.

FIG. 1 is a schematic diagram showing the overall configuration of the apparatus. In this copying machine, a paper feed unit 10 provided at a lower portion of the apparatus main body, a paper transport unit 20 provided above the paper feed unit 10, and a paper transport unit 20 provided above the paper transport unit 20 are provided. An image reading unit including an image forming unit 30, a fixing unit 40 disposed on the discharge side of the image forming unit 30, and an optical member disposed above the image forming unit 30 and the fixing unit 40. A section 50 is provided.

The paper supply unit 10 transfers the bundle of transfer papers 15 stacked and mounted on the paper supply cassette 11 to the outlet side of the paper supply cassette 11 (see FIG. 1) by rotating a paper supply roller 12 having an arc-shaped outer peripheral portion. (Right side) and feed cassette 1
1 a separating claw 16 provided at an upper portion of both ends in the width direction;
In this way, the uppermost transfer paper 15 is reliably fed to the paper transport unit 20 one by one.

The paper transport section 20 transports the transfer paper 15 fed from the paper feed section 10 to the image forming section 30 by a pair of transport rollers 22 and a pair of registration rollers 23 via a reversing guide 21 and further transfers the image. The transfer paper 15 on which an image has been formed in the forming unit 30 to the fixing unit 40 is discharged onto a discharge tray 24 by a discharge roller pair 25.

Immediately before the registration roller pair 23,
A registration switch 231 for detecting the leading end and the trailing end of the conveyed transfer paper 15 is provided.

The image forming unit 30 forms a predetermined toner image on the transfer sheet 15 by an electrophotographic process, and includes a photoconductive drum 31 rotatably supported on a photoconductive drum 31 and a photoconductive drum 31. Around the drum 31, a charger 32, an exposure device 33, a developing device 34, a transfer device 35, a cleaner 36, and a static eliminator 37 are provided along the rotation direction.

The charger 32 has a charging wire (not shown) to which a high voltage is applied, and applies a predetermined potential to the surface of the photosensitive drum 31 by corona discharge from the charging wire. The exposing device 33 includes an image reading unit 5 described later.
The laser light emitted from the laser light emitter 331 based on the image data of the original read by the laser light source 0 irradiates the photosensitive drum 31 via the polygon mirror 332 and the reflecting mirror 333, so that the surface of the photosensitive drum 31 is exposed. The potential is selectively attenuated to form an electrostatic latent image on the surface of the photosensitive drum 31. The developing device 34 develops the electrostatic latent image with toner to form a toner image on the surface of the photosensitive drum 31. The transfer device 35
This is for transferring the toner image on the surface of the photosensitive drum 31 to the transfer paper 15. As described later, in this image forming apparatus, the transfer unit 35 is configured by a transfer roller separated from the photosensitive drum 31 by a predetermined distance.
The cleaner 36 removes the toner remaining on the surface of the photosensitive drum 31 after the transfer. Static eliminator 37
Is for removing residual charges on the surface of the photosensitive drum 31.

In this embodiment, a toner having the same polarity as the charged polarity of the photosensitive drum 31 is used, and the transfer roller 35 is applied with a transfer output having a polarity opposite to that of the toner to perform transfer. Is used.

The fixing unit 40 is disposed downstream of the image forming unit 30 in the sheet conveying direction, and fixes the transfer paper 15 on which the toner image has been transferred in the image forming unit 30 to a heating roller 41.
The toner image is fixed on the transfer paper 15 by heating by sandwiching the pressure roller 42 pressed against the heating roller 41.

The image reading unit 50 includes a contact glass 51
The original placed above is irradiated with light from an exposure lamp 52, and the reflected light is guided to a photoelectric conversion unit 56 including a CCD line sensor or the like via reflecting mirrors 55a, 55b, and 55c, thereby forming an image of the original. It reads information. Note that the exposure lamp 51 and the reflecting mirror 55a are
The scanning operation part 57 scans the entire surface of the original placed on the contact glass 60 by moving the area of FIG. 58 in the horizontal direction of FIG. The image on the entire surface of the document can be read.

In this image forming apparatus, a temperature sensor 61 for detecting the temperature of the installation environment and a relative humidity sensor 62 for detecting the relative humidity are provided in order to detect the absolute humidity condition of the installation environment. ing. Note that the temperature sensor 61 and the relative humidity sensor 62 may be provided outside the device as long as the absolute humidity condition of the device installation environment can be detected.

Next, a control system of the transfer output applied to the transfer roller (transfer device) 35 in this image forming apparatus will be described.

FIG. 2 is a schematic explanatory diagram of a control system of the transfer device. As described above, the transfer device 3 of this image forming apparatus
5 is a toner image 311 formed on the photosensitive drum 31
Is transferred from the surface of the photosensitive drum 31 via a gap L that is equal to or more than the thickness t of the sheet P,
The closest portion between the photosensitive drum 31 and the transfer roller 35 is the transfer position C. Further, since the transfer roller 35 is arranged from the photosensitive drum 31 via the gap L, even when the paper P is interposed between the photosensitive drum 31 and the transfer roller 35, the transfer roller 35 is An air layer having a predetermined resistance value is always formed between the transfer rollers 35 to prevent an excessive transfer current from flowing.

Specifically, the thickness t of the general transfer paper P
Is about 0.1 to 0.15 mm, while the transfer roller 35 is separated from the surface of the photosensitive drum 31 by about 0.5 mm. The transfer roller 35 is made of conductive solid urethane having a volume resistance of 4.0 to 25.1 MΩ and a diameter of 14.2 mm, and a core material 351 having a diameter of 8 mm is inserted into a central shaft portion thereof. I have.

When a predetermined transfer output is applied to the core material 351 by the transfer output applying means 67, an electric field is formed between the photosensitive drum 31 and the transfer roller 35. The toner image on the body drum 31 is transferred to the paper P.

The transfer output applying means 67 is controlled by the transfer output control means 66, and the transfer output control means 66
Is based on the transfer voltage control signal, the timing signal, and the polarity signal sent from the CPU 60 so that the transfer voltage applied to the transfer roller 65 becomes the target voltage value set by the CPU 60 indicated by the transfer voltage control signal. , And controls the transfer output applying means 67. That is, in this image forming apparatus, the transfer output is controlled at a constant voltage.

On the other hand, the CPU 60 has a difference between a character transfer mode for transferring characters and a photo transfer mode for transferring an image such as a photograph, the size and paper quality of a transfer sheet, and the like. Various transfer conditions, such as whether the surface is the first surface or the second surface, are transmitted to the transfer condition detecting means 6.
31, 632, and 633. These transfer condition input means 631, 632, 633
May be configured as means for direct input by the user, or may be configured as a predetermined detecting means such as a sensor.

The CPU 60 also converts the temperature information of the apparatus installation environment detected by the temperature sensor 61 and the relative humidity information detected by the relative humidity sensor 62 into digital values by A / D converters 611 and 621, respectively. The input data is converted and input to the CPU 6.
A value of 0 calculates the saturated water vapor amount at this temperature from the temperature information, and calculates the absolute humidity, which is the absolute amount of water vapor, by multiplying the saturated water vapor amount by the relative humidity.

These various transfer conditions and the absolute humidity conditions of the apparatus installation environment affect the optimum value of the transfer output when transferring to the paper P. For this reason, the CPU 6
0 sets an optimum transfer output as a steady transfer output value using a function or the like stored in the memory 65 in accordance with the transfer condition and the absolute humidity condition. At the time of transfer, a constant voltage control signal is set by a transfer voltage control signal. It is sent to the transfer output control means as a target voltage value.

Further, the CPU 60 stores the position information of the transfer sheet P with respect to the transfer position C in the transfer timing detecting means 6.
4 is input. The transfer timing detecting means 64 can be constituted by the above-described registration switch 231 for detecting the leading edge and the trailing edge of the sheet P, a controller for each roller for transporting the sheet P, and the like.

The CPU 60 sets the transfer output to be applied to the transfer roller 35 based on the position information of the sheet P detected in this manner, and transfers the transfer output to the transfer output control means 66 by a transfer voltage control signal. The magnitude of the output, the timing of application of the transfer output by the timing signal, and the polarity of the transfer output are indicated by the polarity signal. That is, the CPU 60 constitutes a transfer output setting unit.

Next, the transfer output set by the transfer output setting means will be specifically described. FIG. 3 is a perspective view of the sheet P. As shown in this figure, on the sheet P, the transfer area P0 to which the image is to be transferred is a central portion excluding the upper, lower, left, and right peripheral portions serving as a margin (margin).
Here, for the sake of convenience in the following description, the leading end of the sheet P is L1, the leading end of the transferred area P0 is L2, the trailing end of the transferred area P0 is L3, and the The edge is referred to as L4, the margin on the leading end side in the transport direction of the sheet P is referred to as a leading end margin P1, and the margin on the trailing end side in the transport direction is referred to as a trailing end margin P2.

FIGS. 4A to 4D are explanatory diagrams showing the position of the sheet P with respect to the transfer position C at each time t when the sheet P is transported at the transfer position C.

More specifically, FIG. 4A shows a time t1 immediately after the leading end L1 of the sheet P has passed the transfer position C, and FIG.
FIG. 4C is a time t2 when the leading end L2 of the transfer area P0 of the sheet P is transported immediately before the transfer position C, and FIG. 4C is a time t3 when the leading end L2 of the transfer area P0 reaches the transfer position C. 4
4D is a time t4 when the rear end L3 of the transfer area P0 reaches the transfer position C, and FIG. 4E is a time t5 immediately after the rear end L3 of the transfer area P0 passes the transfer position C. FIG. 4 (f)
The state at time t6 immediately before the rear end L4 of the sheet P reaches the transfer position C is shown.

FIG. 5 is a graph showing a time change of the transfer output. It should be noted that the times t = t1 to t6 in this figure respectively correspond to the above-mentioned time t in FIG.

As shown in FIG. 5, the transfer output increases stepwise to a predetermined steady-state transfer output value when the sheet P is carried into the transfer position C, and when the sheet P is carried out from the transfer position C. A predetermined non-transfer output value (here, 0)
It is controlled to decrease step by step.

More specifically, at time t1 immediately after the leading end L1 of the sheet P has passed the transfer position C, the application of the transfer output is started, and the leading end L2 of the transfer target area P0 is transported to just before the transfer position C. Until time t2, the transfer output increases stepwise.

As described above, since the transfer output is not applied suddenly but is applied so as to increase in a stepwise manner, a large transfer current suddenly flows into the surface of the photoreceptor drum 31 and is transferred to the transfer position C. The formation of a potential step with respect to the periphery of the corresponding surface portion of the photosensitive drum 31 is suppressed. Therefore, it is possible to suppress the occurrence of image defects such as stripes extending in the width direction in the transferred image in the subsequent transfer process due to the step of the surface potential of the photosensitive drum 31.

Further, when the transfer output is applied (time t1), the leading end L1 of the sheet P is sent to the transfer position C, and the leading end margin P1 of the sheet P is set between the photosensitive drum 31 and the transfer roller 35. Between the photosensitive drum 31 and the transfer roller 35, the same electrical resistance value as when the transfer area P0 is located at the transfer position C is secured. Therefore, when the application of the transfer output is started, it is ensured that an excessive transfer current suddenly flows toward the photoreceptor drum 31, and the occurrence of the above-mentioned image defects is suppressed, so that a higher quality image is formed. It is possible to do.

As described above, the transfer output is increased stepwise, but from the time t3 when the leading end L2 of the transfer area P0 of the paper P reaches the transfer position C, the rear end L3 of the transfer area P0 moves to the transfer position C. Until a time t4 when a predetermined steady-state transfer output value is applied. For this reason, it is possible to reliably transfer the image to the transfer area P0 of the sheet P.

From time t5 immediately after the rear end L3 of the transfer area P0 passes the transfer position C to time t6 immediately before the rear end L4 of the sheet P reaches the transfer position C, the transfer output is stepwise. It is going to decrease. As described above, since the transfer output does not suddenly decrease, formation of a large step of the surface potential on the photosensitive drum 31 after the end of the transfer step is suppressed.

Further, the rear end margin P2 of the sheet P is interposed at the transfer position C until the transfer output decreases to the non-transfer output value (here, 0). Since a sudden change in the transfer current is suppressed, it is possible to prevent a step from being formed in the surface potential of the photosensitive drum 31.

Accordingly, when the transfer to one sheet of paper P is completed, there is no step in the surface potential of the photosensitive drum 31 and the photosensitive drum 31 can be immediately subjected to the transfer process to a new sheet of paper P. Multiple sheets of paper P
Even when continuous transfer is performed, a plurality of sheets P are fed to the transfer position C at a narrow sheet interval without causing image defects, and high-quality image formation is performed with high transfer operation efficiency. be able to.

Since the conductivity of the paper P changes in accordance with the absolute humidity, the transfer current flowing into the photosensitive drum 31 by the transfer output applied to the transfer roller 35 differs depending on the absolute humidity condition of the installation environment of the apparatus. It is. Further, the transfer current flowing into the photosensitive drum 31 varies depending on various transfer conditions such as the size and quality of the paper P. That is, the level difference of the potential formed on the surface of the photoconductor drum 31 with respect to the amount of change per unit time of the transfer output varies depending on the absolute humidity condition of the apparatus installation environment and various transfer conditions.

Therefore, the transfer output setting means CP
U60 is configured to set a change amount of the transfer output per unit time according to the absolute humidity condition and the transfer condition, and to gradually increase or decrease the transfer output based on the set change amount. Have been.

For this reason, the transfer output is applied at an appropriate rate of change that can suppress the occurrence of image defects, and a high-quality image can be always formed regardless of the absolute humidity condition and various transfer conditions. .

The amount of change in the transfer output per unit time is, if the transfer output is increased or decreased stepwise as shown in FIG. 5, the height or width per step of the stairs. Can be realized by appropriately setting.

Although the present invention has been described with reference to the embodiment, the image forming apparatus according to the present invention is not limited to the above embodiment, and may be configured as follows.

(1) In the above embodiment, the amount of change in the transfer output per unit time is set according to the absolute humidity condition or the like. However, the amount of change is constant regardless of these conditions. It may be. At this time, if the transfer output is changed stepwise as in the above embodiment,
By fixing the height and width of one step to a constant value and adjusting the number of steps, it is possible to easily respond to the steady transfer output value.

(2) In the above embodiment, the transfer output is changed in a stepwise manner with the same height and width in each step, but the height and width are changed in each step. May be.

(3) In the above embodiment, the transfer output is changed in a discontinuous manner in a stepwise manner, but may be changed continuously.

FIGS. 6 and 7 show examples of transfer output changes in which the transfer output is continuously changed. At time t = t1 ~
t6 corresponds to time t in FIG. As shown in these figures, the transfer output may be changed linearly or in a curved line.

(4) In the above-described embodiment, the transfer output is started to be applied after the leading end L1 of the paper P has passed the transfer position C.
If a steady transfer output value is obtained before the leading edge L2 of the sheet P reaches the transfer position C, the application of the transfer output may be started before the leading edge L1 of the paper P reaches the transfer position C.

(5) In the above embodiment, when the transfer output is reduced after the transfer to one sheet of paper P is completed,
The transfer output is gradually reduced. However, when it is not necessary to continuously perform transfer to a plurality of sheets of paper P, or when a sufficiently large sheet interval is secured, the photosensitive drum 37 or the like is used during this time. If the step of the surface potential of the body drum 31 can be eliminated, ON / OF is required in the process of decreasing the transfer output after the transfer.
The transfer output may be momentarily reduced by the F-type control. Further, the transfer output may be reduced after the rear end L4 of the sheet P has passed the transfer position C.

(6) In the above embodiment, the output applying section for applying the transfer output corresponding to the sheet position to the transfer device (transfer roller) 35 is provided by the transfer output setting means (CPU 6).
0), the transfer output control means 66, the transfer output application means 67, etc., and the transfer output is gradually increased and decreased by electronic control by the transfer output setting means constituted by the CPU 60. For example, the transfer output applying means 67 composed of a high-voltage transformer or the like can be realized by delaying the rise and fall of the transfer output by configuring the transfer output applying means 67 with a circuit whose output rises and falls slowly.

(7) In the above embodiment, the transfer output applied to the transfer unit 35 is controlled by the constant voltage control. However, the transfer function applied to the transfer unit 35 is controlled. The transfer output applied to the transfer device 35 may be controlled by current control.

(8) In the above embodiment, the transfer device 3
5, a gap L from the photoreceptor 31 to the sheet t of the sheet P or more
Although the configuration using the transfer roller arranged with the opening is shown, the photosensitive member 3 is activated by applying a predetermined transfer output.
Any known transfer device such as a transfer device using a contact-type transfer roller, a transfer belt, or a corona discharge device can be used as long as the transfer device transfers the toner image on the sheet P onto the paper P. .

(9) In the above embodiment, the reversal developing method is used. However, a positive developing method in which a transfer output having the same polarity as the charging polarity of the photosensitive member is applied may be used.

[0074]

As described above, according to the image forming apparatus of the present invention, since the transfer output applied to the transfer device is gradually increased or decreased, the transfer current flows into the photosensitive member rapidly, and It is possible to suppress the occurrence of an image defect due to the formation of a step in the potential, whereby it is possible to always perform stable and high-quality image formation.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram of a transfer output control system in the apparatus.

FIG. 3 is a perspective view of a sheet P.

FIG. 4 is an explanatory diagram showing a position of a sheet P with respect to a transfer position C;

FIG. 5 is a graph showing a temporal change of a transfer output.

FIG. 6 is a graph showing an example in which a transfer output is continuously changed linearly.

FIG. 7 is a graph showing an example in which a transfer output is continuously changed in a curved line.

FIG. 8 is a perspective view showing the vicinity of a transfer unit in a general image forming apparatus.

FIG. 9 is a graph showing a time change of a transfer output in a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Paper feed part 20 Paper conveyance part 231 Registration switch (paper position detection means) 30 Image formation part 31 Photoconductor drum (photoconductor) 35 Transfer roller (transfer device) 40 Fixing part 50 Image reading part 60 CPU (Transfer output setting means) 66) Transfer output control means 67 Transfer output applying means

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tetsuya Ichigaya 1-2-28 Tamazo, Chuo-ku, Osaka-shi F-term in Mita Corporation (reference) 2H032 AA05 CA02

Claims (7)

[Claims] A transfer unit configured to transfer a toner image formed on a photoconductor to a sheet; a sheet position detection unit configured to detect a sheet position with respect to a transfer position between the photoconductor and the transfer unit; Based on the sheet position information detected by the position detecting means, the transfer area of the sheet gradually increases before being conveyed to the transfer position, and when the transfer area of the sheet reaches the transfer position, the steady transfer output value Transfer output
An image forming apparatus, comprising: an output applying unit for applying the output to the transfer unit. 2. The transfer application unit applies a transfer output to the transfer device, the transfer output gradually increasing from the time when the leading edge of the sheet passes through the transfer position until the transfer area of the sheet reaches the transfer position. The image forming apparatus according to claim 1, wherein: 3. The output application unit is configured to apply a transfer output gradually decreasing to an output value at the time of non-transfer to the transfer unit after the transfer area of the sheet has passed the transfer position. The image forming apparatus according to claim 1, wherein: 4. The transfer application unit applies a transfer output to the transfer unit, the transfer output gradually decreasing from the time when the transfer area of the sheet passes through the transfer position to the time when the rear end of the sheet reaches the transfer position. The image forming apparatus according to claim 3, wherein the image forming apparatus is configured to perform the operation. 5. The transfer output applying unit that applies a transfer output to the transfer unit; a transfer output setting unit that sets a transfer output to be applied to the transfer unit according to a sheet position; 5. A transfer output control means for controlling the transfer output applying means so as to apply the transfer output set by the output setting means to the transfer device.
The image forming apparatus according to any one of the above. 6. The transfer output setting means sets a change amount of the transfer output per unit time according to the absolute humidity of the installation environment of the apparatus, and gradually sets the transfer output based on the change amount thus set. 6. The image forming apparatus according to claim 5, wherein the setting is made to increase or decrease. 7. The transfer output setting means sets a change amount of the transfer output per unit time according to the transfer condition, and gradually increases or decreases the transfer output based on the set change amount. The image forming apparatus according to claim 5, wherein the image forming apparatus is set to perform the setting.