Image forming apparatus having means for preventing toner deposit on photosensitive member

An image forming apparatus includes a movable photosensitive member; a toner image forming device for forming a toner image on the photosensitive member; a transfer device for electrostatically transferring the toner image from the photosensitive member to a transfer material at a transfer position; and a transfer material carrying member for carrying the transfer material to feed the transfer material to the transfer position. The transfer device transfers the image while the transfer material is on the transfer material carrying member, and after the image is transferred, the transfer material having the toner image transferred thereon and carried on the transfer material carrying member is contacted to the photosensitive member. There is also provided a charger for charging the photosensitive member, wherein at least a part of the photosensitive member making the contact is charged by the charger in a period between its passage through the transfer position and the contact, so as to be given an electric potential at which the toner image forming device does not deposit the toner to the photosensitive member.

FIELD OF THE INVENTION AND RELATED ART 
The present invention relates to an image forming apparatus of an 
electrophotographic type, and electrostatic recording type or the like, 
more particularly to an image forming apparatus usable as a multi-color 
electrophotographic copying apparatus having plural developing devices, a 
color printer or copying machine for a facsimile machine, an output 
terminal of a computer or the like. 
Various types of multi-color electrophotographic machines have been 
proposed. First, the description will be made as to a typical full-color 
image formation process. A surface of a photosensitive drum is uniformly 
charged by a charger, and thereafter is exposed to image light, so that an 
electrostatic latent image is formed. The latent image is developed by a 
developing device containing a developer of a predetermined color into a 
toner image, which is then carried to an image transfer station by 
rotation of the photosensitive drum. At the transfer station, the toner 
image is transferred onto a transfer material which has been supplied and 
carried on a transfer material carrying sheet of a transfer drum. The 
image is transferred onto the transfer material by the transfer charger. 
After the first color image is thus transferred, the transfer drum rotates 
through one full-turn (idle rotation) until the second color image 
transfer starts. The transfer material having the first color toner image 
and carrier on the transfer material carrying sheet is brought into 
contact with the non-latentimage area of the photosensitive drum surface. 
The period of the idle rotation is used for movement of an optical system 
or the developing device to make proper motions between the first color 
image formation and the second color image formation. 
The image formation, the transfer process and the idle rotation process are 
repeated for the plural color image transfers, so that a toner image 
constituted by multi-color images superposed, is formed. 
The experiments and investigations by the inventors have revealed problems 
arising, particularly when the transfer material carrying sheet of the 
transfer drum is made of polyvinylidene fluoride film or the like, and the 
transfer material P is made of paper, and particularly when the ambient 
humidity is high. 
Referring to FIG. 5, the problem will be described. After the transfer 
material P on the transfer drum 5 receives a first color toner image T, 
the transfer material P now having the toner image T is still retained on 
the transfer drum 5. It is rotated together with the transfer drum 5 for 
preparation of the transfer of the second color image. FIG. 5 shows the 
electric charge on the transfer material P at its trailing end Pa at this 
time. In this example, the electrostatic latent image is formed by 
negative charge; and the toner is charged to the negative polarity for the 
purpose of reverse development, and therefore, the transfer voltage 
supplied to the transfer charger 5b has a positive polarity. An outside 
discharger 5e and an inside discharger 5d are disposed to face each other 
across the transfer drum 5 at the outside and inside of the transfer drum 
5, respectively, immediately downstream of the transfer position where the 
transfer charger 5b is faced to the photosensitive drum 1, with respect to 
the peripheral movement direction of the transfer drum 5. The outside 
charger 5e is supplied with an AC voltage; and the inside charger 5d is 
supplied with an AC voltage biased with a DC voltage having a polarity 
opposite from the charging polarity of the transfer charger. 
In the example, a polyvinylidene fluoride film is used as the transfer 
material carrying sheet 501 of the transfer drum 5 with a sheet of paper 
as the transfer material P. The volume resistivity of the polyvinylidene 
fluoride resin film is 10.sup.13 ohm.cm, and the volume resistivity of the 
transfer sheet is 10.sup.9 (at high humidity condition of 85 
%RH)-10.sup.12 (low humidity condition of 10 %RH) ohm.cm. It has been 
found that when such materials are used, the positive charge is injected 
from the transfer charger 5b into the transfer material P through the 
transfer material carrying sheet 501, particularly at the high humidity 
condition, and the positive charge is accumulated in the surface region of 
the trailing edge Pa of the transfer material P. 
It has also been found by the inventors that the positive charge 
accumulated in the surface of the trailing edge Pa of the transfer 
material forms a strong electric field between the surface of the 
photosensitive drum, and that, as shown in FIG. 6, when the trailing edge 
Pa is separated from the photosensitive drum 1, the separation discharge 
occurs. Then, the negative charge in the air is attracted by the positive 
charge of the transfer material P and moves to the transfer material. 
However, the positive charge in the air moves to the photosensitive drum 1 
having the negative charge, with the result that the photosensitive drum 1 
is damaged, in other words, an image transfer memory is retained in the 
photosensitive drum 1. The memory of the photosensitive drum 1 is not 
easily erased even by exposing the photosensitive drum 1 to light. 
Additionally, even if the photosensitive drum 1 is subjected to the 
negative charge, the amount of charge reduces in the memory region in the 
form of stripes along the width of the photosensitive drum 1. This 
prevents uniform charging of the photosensitive drum 1, and therefore, 
non-uniformity of the image results. 
Conventionally, and therefore, even if the memory region of the 
photosensitive drum 1 is discharged by exposure to light or is subjected 
to the charging by the primary charger for the image formation, after the 
first color image is transferred onto the transfer material P from the 
photosensitive drum during the transfer step, the potential distribution 
remains in accordance with the memory, and the memory is developed. 
Therefore, if the memory region exists in the region of the photosensitive 
drum that contacts the transfer material already having the transferred 
toner image during the transfer process being performed, such as during 
the idle rotation, the toner image corresponding to the memory region 
developed is transferred onto the transfer material, with the result of 
non-uniform resultant image. 
The memory particularly occurs when the photosensitive drum has a surface 
organic photoconductive layer. 
SUMMARY OF THE INVENTION 
Accordingly, it is a principal object of the present invention to provide 
an image forming apparatus wherein the non-uniformity of the image due to 
the transfer memory on the photosensitive drum is prevented to provide 
high quality images. 
It is another object of the present invention to provide an image forming 
apparatus capable of forming good images under substantially all 
conditions under which the apparatus is operated. 
These and other objects, features and advantages of the present invention 
will become more apparent upon a consideration of the following 
description of the preferred embodiments of the present invention taken in 
conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIG. 3, there is shown a multi-color electrophotographic 
copying machine as an exemplary image forming apparatus according to an 
embodiment of the present invention. 
The copying apparatus comprises an image bearing member in the form of a 
photosensitive drum 1 supported for rotation about an axis in a direction 
indicated by an arrow. Around the photosensitive drum 1, there are 
disposed image forming means. The image forming means may be of any known 
type. In this example, it includes a primary charger 2 for uniformly 
charging the photosensitive drum 1, exposure means 3 in the form of a 
laser beam exposure device, for example, for exposing the photosensitive 
drum 1 to a color separated light image in accordance with image 
information such as an image on an original document to form an 
electrostatic latent image on the photosensitive drum 1, and a rotary type 
developing device 4 for visualizing the electrostatic latent image on the 
photosensitive drum 1. 
The rotary type developing device 4 includes four developing devices 4Y, 
4M, 4C and 4BK containing four color developers, i.e., a yellow developer, 
a magenta developer, a cyan developer and a black developer, and a 
cylinder 4a rotatably supported and supporting the developing devices 4Y, 
4M, 4C and 4BK. The rotary type developing device 4 rotates a desired one 
of the developing devices a position facing the outer peripheral surface 
of the photosensitive drum 1 by rotation of the cylinder 4a to develop the 
electrostatic latent image on the photosensitive drum 1. By one full turn 
of the cylinder 4a, a full-color development in four colors is effected. 
The visualized image on the photosensitive drum 1, that is, the toner image 
is transferred onto the transfer material P carried on and supplied by a 
transfer device 5 (transfer material carrying means). In this example, the 
transfer device 5 includes a rotatably supported transfer drum 5 which, as 
shown in FIGS. 3 and 4, comprises a cylinder 5a having opposite rings and 
a connecting portion connecting the rings, a transfer charger 5b 
functioning as transfer means in the cylinder 5a, a transfer material 
gripper 5c for gripping the transfer material supplied by an unshown sheet 
feeding device. An inside discharging charger 5d and an outside 
discharging charger 5e which constitute discharging means are disposed 
inside and outside the transfer drum 5, respectively. The opening of the 
cylinder 5a is covered with a transfer material carrying sheet 501 
stretched thereover. The transfer material carrying sheet 502 is usually 
made of polyethylene terephthalate film or polyvinylidene fluoride resin 
film or the like. 
In full-color image forming operation, the first primary charger 2 and the 
image exposure means 3 are operated to form a cyan color component latent 
image on the outer surface of the photosensitive drum 1. The electrostatic 
latent image is developed with a first color developer (yellow) 
accommodated in the developing device 4Y. The transfer material P supplied 
to the transfer drum 5 is gripped by a gripper 5c. The transfer material P 
is contacted to the yellow toner image on the photosensitive drum during 
rotation of the transfer drum 5 in the image transfer process. The toner 
image is transferred onto the transfer material P by the transfer charger 
5b, and simultaneously, the transfer material P is securedly attracted on 
the transfer material carrying sheet 501. 
During the period after the completion of the yellow color image transfer 
and before the start of the second color image transfer, the transfer drum 
5 rotates through one full-turn idly. In this period, the transfer 
material P having the yellow toner image on the transfer material carrying 
sheet 501 is contacted to the electrostatic latent image non-formation 
area on the surface of the photosensitive drum 1. The non-formation region 
is a region on the photosensitive drum in which no electrostatic latent 
image is formed when any image formation is applied on the photosensitive 
drum 1, even when the region extends downstream of the exposure position 
with respect to a movement direction of the surface of the photosensitive 
drum 1. During the idle rotation, the optical system for reading image 
information and the developing device is moved for preparation of the 
second color image formation. The yellow toner image on the transfer 
material P is contacted to the photosensitive drum 1 during the idle 
rotation, and the toner image is retained on the transfer material P by 
the operation of the transfer charger 5b. 
The image forming operation, the image transfer operation and the idle 
rotation are carried out for each of the magenta, cyan and black images. 
Until completion of the four color image transfers, the transfer charger 
5b is repeatedly operated. After completion of the superposed image 
transfers of the four color visualized images onto the transfer material 
P, the transfer material P is electrically discharged by the inside 
charger 5d and the outside charger 5e. Thereafter, the transfer material P 
is separated from the transfer material 5 and is subjected to an image 
fixing operation by a heat roller fixing device 6. Finally, the transfer 
material P now having a fixed full-color image is discharged to the 
outside of the apparatus. The residual toner remaining on the 
photosensitive drum 1 is removed by a cleaner 7, and the photosensitive 
drum 1 is electrically discharged by a discharging lamp, so that it is 
prepared for the next image formation process. 
In this embodiment, the diameter of the photosensitive drum 1 is 80 mm, and 
that of the transfer drum 5 is 160 mm (twice the diameter of the 
photosensitive drum 1). The photosensitive drum 1 has a surface organic 
photoconductive layer having a negative charging property and is rotated 
at a peripheral speed of 160 mm/sec in the direction indicated by an 
arrow. After the surface thereof is discharged by the discharging lamp 9, 
the surface is charged to a potential of -300--900 V by the primary 
charger. The surface potential of the photosensitive drum 1 is monitored 
by a drum surface potential sensor 10, and a proper surface potential is 
determined. 
Each of the developing devices of the rotary developing device 4 contains 
the toner electrically charged to a polarity which is the same as the 
charging polarity of the photosensitive drum 1 The toner is deposited onto 
a low potential portion of the electrostatic latent image on the 
photosensitive drum 1 by a developing electric field which is provided by 
the potential of the photosensitive drum 1 and a developing bias voltage 
applied to a developing sleeve for carrying the toner to the developing 
zone where the developing sleeve is disposed close to the photosensitive 
drum 1. Thus, the latent image is developed and visualized. 
FIG. 1 is a sectional view of the image forming apparatus of FIG. 3 around 
the transfer station. In this embodiment, the transfer material carrying 
sheet 501 is of polyvinylidene fluoride resin film (dielectric material) 
having a thickness of 100- 175 microns and a volume resistivity of 
10.sup.13 ohm.cm. The transfer charger 5b is a corona charger having a 
charging polarity which is opposite from the charging polarity of the 
toner and of the photosensitive drum 1. The transfer charger 5b is 
supplied with a voltage of +6 KV-+9 KV, so that the transfer current is 
+100 micro-ampere -+500 micro-amper. The visualized image or toner image 
on the photosensitive drum 1 is transferred onto the transfer material P 
supplied to the transfer station on the transfer drum 5. 
In this embodiment, as shown in FIG. 2A, the primary charger 2 is of a 
scorotron type supplied with a high voltage from a high voltage source 
2-2. The voltage is supplied particularly to the charging wire 2-1, and 
the amount of electric discharge is controlled by application of a control 
voltage to a grid wire 2-3 from a grid bias source 2-4. By doing so, the 
surface of the photosensitive drum 1 is charged to a desired potential. 
In the multi-color electrophotographic copying apparatus having the 
structure described above, the output voltage of the grid bias voltage 
source 2-4 is increased for the electrostatic latent image non-formation 
area of the photosensitive drum 1, that is, for example, the area facing 
the scorotron 2 after completion of the electrostatic latent image by the 
first color image exposure and before the start of the second color 
electrostatic latent image formation. By doing so, the amount of charge on 
the surface of the photosensitive drum 1 by the primary charger 2 is made 
larger than that in the electrostatic latent image formation area. 
Therefore, the potential of the photosensitive drum surface in the 
electrostatic latent image non-formation region is higher than that in the 
electrostatic latent image formation region. In this embodiment, the 
latent image non-formation region charged to a potential higher than that 
in the latent image formation region by the primary charger 2, is 
uniformly exposed to light by the laser beam exposure means 3. 
FIG. 7 shows a change of a surface potential of the latent image formation 
region of the photosensitive drum 1. The latent image formation region is 
a region in which an electrostatic latent image is formed on the 
photosensitive drum after exposure thereof to the beam from the laser beam 
exposure device 3. As will be understood from FIG. 7, in the left of 
"laser beam exposure", the latent image formation region does not have the 
electrostatic latent image as yet. 
After the image transfer process, the photosensitive drum 1 having residual 
electric charge is electrically discharged by the discharging lamp 9 so 
that the surface potential thereof becomes substantially 0 V. Thereafter, 
it is uniformly charged to a potential of -400 V by the primary charger 2. 
The developing bias for providing the developing electric field is set 
-250 V. The difference 150 V between the charge potential of the 
photosensitive drum 1 of -400 V and the developing bias voltage of -250 V 
is a fog removing voltage effective to prevent the toner from depositing 
on the background area of the image. Because of the electric field 
provided by the potential difference, the toner is normally attracted to 
the developing sleeve, and is prevented from depositing on the 
photosensitive drum 1, and therefore, the resultant image does not have 
the toner in the background area of the image (white portion). On the 
other hand, the area of the photosensitive drum 1 corresponding to the 
image pattern is illuminated by the laser beam at a light intensity 
corresponding to the image density by a laser beam exposure device 3. 
Therefore, the potential of the portion exposed to the laser beam lowers 
beyond the developing bias voltage By the electric field provided by the 
developing bias voltage and the surface potential of the photosensitive 
drum at the exposed area, the toner is deposited on the photosensitive 
drum 1, so that a toner image is formed. In FIG. 7, the broken line 
represent the portion having the surface potential of -50 V to which the 
potential is lowered by the image exposure. 
FIG. 8 shows a change of the surface potential in the electrostatic latent 
image non-formation area on the photosensitive drum 1. The photosensitive 
drum 1 having the residual charge after the image transfer is electrically 
discharged by the discharging lamp 9 so that the surface potential thereof 
becomes substantially 0 V. Thereafter, it is charged to a surface 
potential of -800 V which is higher than that in the latent image 
formation region, by the primary charger 2 Then, it is exposed to the 
laser beam from the laser beam exposure means 3, by which the surface 
potential lowers to -400 V. 
FIG. 9 shows a change of a surface potential when the same primary charging 
as for the latent image formation region is effected to the latent image 
non-formation region. The non-formation region is contacted to the 
transfer material P having the toner image on the transfer drum 5, during 
the idle rotation. As will be understood from FIG. 9, the potential of the 
memory region (approximately 200 V) remains even after the photosensitive 
drum 1 is electrically discharged. When the photosensitive drum 1 is 
charged by the primary charger to -400 V, the potential of the memory 
region becomes approximately -200 V. Therefore, in the memory region, the 
developing electric field is provided by the potential difference of 
approximately 50 V (hatched portion in the Figure), which is the 
difference between the memory region potential (-200 V) and the developing 
bias voltage (-250 V). In the conventional apparatus, the potential 
distribution appears by the memory where the electrostatic latent image is 
not formed In the low potential portion, the toner is deposited. As a 
result, during the idle rotation (non-transfer duration), the transfer 
material having the toner image and carried on the transfer drum 5 is 
brought into contact with a region of the photosensitive drum 1, at least 
a part of which is the memory region, and therefore, the toner deposited 
on the photosensitive drum 1 due to the memory is transferred onto the 
transfer material P with the result of a non-uniform image. 
FIG. 10 is a graph showing a change of the surface potential when the 
present invention is used, that is, when the electrostatic latent image 
non-formation region of the photosensitive drum 1 having the memory region 
is subjected to the primary charging with a potential higher than that for 
the latent image formation region The latent image non-formation region is 
contacted to the transfer material P having the toner image during the 
idle rotation. In this embodiment, the surface of the photosensitive drum 
1 has been subjected to the primary charging, and the surface potential of 
the latent image non-formation region is -800 V which is higher than the 
potential of the latent image formation region. Therefore, as will be 
understood from the Figure, the potential in the memory region is 
approximately -600 V. Then, the non-formation region is uniformly exposed 
to light by the laser beam exposure means 3 to lower the surface potential 
(-800 V) in the uniformly charged region to -400 V similarly to the 
conventional example. The surface potential of the memory region lowers 
only to -290 V. The voltage level of -290 V is higher than -250 V which is 
the developing bias voltage, and therefore, no developing electric field 
is formed. For this reason, the disturbance of the image due to the toner 
deposited on the memory region and then deposited to the transfer material 
P during the idle rotation of the transfer drum 5. 
The problem arises from the fact that the lowering degrees of the surface 
potential are different even by the same amount of exposure because of the 
potential difference before the exposure in the uniformly charged region 
without memory than the memory region. 
FIG. 11 shows the relation between the surface potential and the amount of 
exposure of the photosensitive drum 1 having the organic photoconductor 
used in this embodiment. As will be understood from this Figure, even if 
the amount of exposure is kept constant, the degree of the potential 
lowering by the exposure increases with increase of the surface potential 
before the exposure It is also understood from this Figure that if the 
amount of exposure is such that the surface potential of -800 V before the 
exposure lowers to -400 V after the exposure, the surface potential of 
-600 V before the exposure lowers only to -290 V after the exposure. Thus, 
the potential lowering of the memory region beyond that of the nonmemory 
region decreases so that it remains higher than the developing bias 
voltage (-250 V), and therefore, the developing electric field is not 
formed in the memory region. Therefore, the toner is prevented from being 
deposited on the memory region, so that even if the memory region contacts 
the transfer material P which is carried on the photosensitive drum 5 
during the idle rotation, the image non-uniformity does not occur. 
FIG. 13 shows operational sequence including a primary charging, laser beam 
exposure or the like for each rotation corresponding to the positions of 
the photosensitive drum and the transfer drum in this embodiment. In this 
Figure, the time required for a certain position of the photosensitive 
drum moves from the primary charger position to the developing device 
position through the exposure position, and the same abscissa position 
means the same position of the photosensitive drum 5. The potential by the 
primary charging in the memory region is omitted. 
FIG. 12 shows a change of a surface potential of electrostatic latent image 
non-formation region of the photosensitive drum 1 which has a memory 
region. The image non-formation region is brought into contact with the 
transfer material P having the toner image and carried on the transfer 
drum 5, during the idle rotation of the transfer drum 5. In this 
embodiment, after the residual charge is removed by the discharging lamp 
9, the latent image non-formation region of the photosensitive drum 1 is 
charged by the primary charger so that the region is given a potential 
which is higher than that in the latent image formation region. Then, it 
is exposed to the laser beam, by which the surface potential of the latent 
image non-formation region is lowered to a potential lower than that in 
the latent image formation region. In addition, the developing bias 
voltage is lowered to a proper level corresponding to the surface 
potential after the exposure. The change of the surface potential in the 
latent image formation region of the photosensitive drum in this 
embodiment is the same as in the first embodiment, and therefore, it is as 
shown in FIG. 7. 
As shown in FIG. 12, in this embodiment, the surface of the photosensitive 
drum 1 not having the memory region is discharged by the discharging lamp 
9 so that the potential thereof becomes substantially 0 V, and 
thereafter, the primary charger 2 charges the latent image non-formation 
region having the memory region so that the non-memory region has -800 V. 
The potential in the memory region at this time was approximately -300 V. 
Then, the latent image non-formation region is uniformly exposed to light 
by the laser beam exposure means 3, by which the surface potential of -800 
V in the uniformly charged region (non-memory region) is lowered to -200 V 
which is lower than -400 V in the latent image formation region. 
Correspondingly, the developing bias voltage is lowered to -50 V so as to 
provide a proper fog preventing voltage. By the exposure, the surface 
potential of the memory region lowers to -90 V. Since the -90 V voltage in 
the memory region higher than -50 V which is the developing bias voltage, 
and therefore, no developing electric field is formed. Accordingly, the 
image disturbance due to the transfer of the toner to the memory region 
and then to the transfer material P during the idle rotation, can be 
prevented. 
FIG. 14 shows sequential operations such as primary charging, laser beam 
exposure or the like corresponding to each rotation at the positions of 
the photosensitive drum and the transfer drum. 
In the embodiment of FIGS. 1 and 2, the primary charger is of a scorotron 
type as shown in FIG. 2A, and the amount of charging of the photosensitive 
drum 1 is controlled by controlling the grid bias voltage for the charger. 
When the corotron type charger as shown in FIG. 2B is used, the voltage 
applied to the charging wire 2-1 is controlled to effect the same control 
of the charging amount for the photosensitive drum 1. In the foregoing 
embodiments, as shown in FIGS. 13 and 14, the amount of charge and the 
amount of exposure on the entirety of the latent image non-formation 
region of the photosensitive drum 1 is controlled to prevent the 
deposition of the toner on the memory region and the transfer thereof. 
FIG. 15 shows a further alternative, wherein the amount of charge for the 
memory region is increased by the primary charger beyond that in the 
non-memory region of the latent image non-formation area of the 
photosensitive drum 1, and after the primary charging, only the memory 
region is uniformly exposed to light, thus preventing the formation of the 
developing electric field. In FIGS. 13-15, the image pattern shown in the 
second, fourth, sixth and eighth rotations of the transfer drum is only an 
example. The above described surface potential of the photosensitive drum 
after the primary charging, the surface potential after exposure to the 
laser beam, the developing bias voltage or the like in the foregoing 
embodiments in the latent image formation region and in the latent image 
non-formation region, are not limited to those exemplified. They may be 
properly determined by one skilled in the art in consideration of the 
ambient conditions or the like. The exposure means is not limited to the 
laser beam type exposure means, but it may be in the form of LED head or 
liquid crystal shutter array or the like. The present invention is 
applicable not only to the multi-color electrophotographic copying 
apparatus but also various image forming machines such as copying machines 
or printers. 
It is a possible alternative for the purpose of reducing the memory of the 
photosensitive member to operate the discharging means (inside charger 5d 
and outside charger 5e) each time the toner image is transferred onto the 
transfer material P, thus electrically discharging the trailing end of the 
transfer material P. However, if the discharging is too strong, the toner 
image transfer is disturbed with the result of disturbance in the image. 
Therefore, it is preferable that this is incorporated in addition to the 
structure of the present invention. 
Additionally, in order to reduce the memory, a separate charger is provided 
upstream of the cleaning means and downstream of the transfer means with 
respect to the movement direction of the surface of the photosensitive 
drum so as to pre-charge the memory region after the transfer process to 
the polarity which is the same as the polarity of the primary charging. 
The reduction of the memory has been confirmed. However, since the toner 
remaining on the photosensitive drum is also charged, the improper 
cleaning may occur. Additionally, the provision of the additional charger 
requires a high voltage source, which leads to increase of the cost, and 
requires additional space. Therefore, it is desirable that the memory 
region be charged by the primary charger provided for the image formation, 
as in the foregoing embodiments. 
As described in the foregoing, according to the present invention, at least 
of a part of that region of the photosensitive member which contacts the 
transfer material already having the toner image, during the non-transfer 
action period, is charged and then exposed to light in the period between 
passage by the transfer position during the transfer action before the 
contact. Accordingly, the production of the image non-uniformity 
attributable to the transfer memory can be prevented. 
In addition, the good images can be provided under wide varieties of 
ambient conditions. 
While the invention has been described with reference to the structures 
disclosed herein, it is not confined to the details set forth and this 
application is intended to cover such modifications or changes as may come 
within the purposes of the improvements or the scope of the following 
claims.