Electrophotographic copying apparatus

An electrophotographic copying apparatus of the present invention is capable of copying a reduced original and forms an electro-static latent image of the reduced original image on a uniformly electrified photosensitive member so that the electrostatic latent image is sensible-imaged as a toner image and the toner image is transferred onto copying paper. In such operation, this apparatus can change corresponding to reduction rate the irradiation area of a side erase lamp for erasing unnecessary charge at both axial edge portions of photosensitive member, thereby enabling complete removal of unnecessary electrified portions on the photosensitive member which appear inevitably when the reduced copying is carried out, and reliable prevention of attaching of unnecessary toner to the photosensitive member.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an electrophotographic copying apparatus for 
exposure-scanning an original through a slit, and irradiating onto an 
electrified photosensitive member the reflected light from the original to 
thereby form on the photosensitive member an electro-static latent image, 
which is developed with toner, the image developed therewith being 
transferred to copying paper. 
2. Description of the Prior Art 
The electrophotographic copying apparatus electrifies the photosensitive 
member by applying thereto high voltage, and irradiates onto the 
electrified photosensitive member the reflected light from the original 
obtained by exposure-scanning thereof, thereby forming on the 
photosensitive member the electro-static latent image corresponding to the 
image of original. Then, the electro-static latent image is developed with 
the toner to thereby be sensible-imaged so that the sensible image is 
transferred to the copying paper. 
In such electrophotographic copying apparatus, the photosensitive member 
has a surface area corresponding to the overall area of an original 
supporting plate. In a case where the original is smaller than the 
original supporting plate and is copied by equal magnification, unless the 
light is adapted to be reflected from the portion at the plate not covered 
by the original thereon, when the original is exposure-scanned, the charge 
on the side edge of photosensitive member other than the image of original 
is not dissipated so that the side edge is attached with the toner to be 
developed. Therefore, a white lid covers the original supporting plate to 
reflect the light even when the side edge of the original is exposed, but 
when the lid is open, the unnecessary attaching of toner is not avoidable. 
When the charge on the abovementioned unnecessary portion is not 
dissipated, a very thick toner is attached onto the photosensitive member 
so that, when a copying paper larger than the original is copied in equal 
size, an unnecessary band-like image is formed around the image of 
original on the paper, resulting in deterioration of quality of copying. 
Also, even after copying, toner usually remains on the photosensitive 
member, which need be removed so as to prevent deterioration of the 
copying quality. Since the side edge portions other than the image of 
original on the photosensitive member are attached with the very thick 
toner as abovementioned, the toner is not completely transferred, but 
remains on the photosensitive member. For copying paper equal in size to 
the original, the toner at the side edge of photosensitive member is not 
transferred to the copying paper, but remains as a whole on the 
photosensitive member, whereby removal of the attached toner not only 
largely loads the machine but also produces much dust around the same, and 
further a large amount of toner is wasted so as to be not economical. For 
copying paper smaller than the original, the same problem as the above 
will be created. 
In order to solve the above problem, an erase light source has been 
proposed which dissipates charge on the side edge areas of the 
photosensitive member at first electrified at the overall surface, the 
side edge areas being positioned perpendicularly to the moving direction 
of photosensitive member and unnecessary for forming the image of 
original. 
Also, a device (disclosed in the U.S. Pat. No. 3,792,913) has been 
developed which detects the size of copying paper to change corresponding 
thereto the size of the projection areas of erase light source at the side 
edges perpendicular to the moving direction of photosensitive member, 
which dissipates the charge in the area of the photosensitive member not 
contacted by the copying paper during the transfer, thereby preventing 
unnecessary toner from attaching to the photosensitive member. 
Recently, an electrophotographic copying apparatus has been developed, in 
which the image of original can be copied in reduction or enlargement via 
selective variation of the copying magnfication. The image of original, 
when copied in reduction, is formed on the photosensitive member in 
reduction by a set reduction rate relative to the actual original, 
resulting in that the electrified portion (the toner-attaching portion) 
unnecessary for copying at the photosensitive member is expanded. However, 
the light is reflected from the portion at the original support plate 
except for the portion supporting the original during the 
exposure-scanning, so that when the side edges of photosensitive member 
are exposed to the light, the charge at the same is dissipated, thereby 
preventing the unnecessary toner from attaching thereto. The area for the 
erase light source at the side edges of photosensitive member is changed 
corresponding to the size of copying paper as above mentioned to thereby 
ensure that toner is prevented from unnecessarily attaching to the 
photosensitive member, but when the image of original is reduced 
unnecessary attachment of toner cannot be, fully prevented. In brief, in a 
case where the area for the erase light source is changed corresponding to 
the aforesaid copying size, the charge at the side edges of photosensitive 
member cannot completely be dissipated because the reduction rate is 
irrelevant to the size of copying paper. 
The image of the original can be exposed over the entire surface of the 
original support plate, and the photosensitive member is larger enough to 
be exposed to the entire image of the original on the original support 
plate, but when the original is copied in reduction, only the area 
corresponding to the reduction size of the plate is exposed to the 
reflected light therefrom, so that the side edges of photosensitive member 
are out of the exposure area so as to be not exposed. Hence, the side 
edges of photosensitive member, when reduced, are always electrified and 
attached with toner, whereby it is impossible in such a case to completely 
dissipate the side edge charge, resulting in unnecessary toner being 
attached to the side edges of the photosensitive member. 
An electrophotographic copying apparatus (disclosed in the U.S. Pat. No. 
3,724,940) has been developed for dissipating the charge on the side edges 
of photoelectric member even when reduced. This copying apparatus, which 
rotates a shade pivoted to one side of the copying apparatus to change the 
projection position of a correction light source, is not accurately 
controllable and causes unnecessary toner is attached to the 
photosensitive member. 
OBJECTS OF THE INVENTION 
A first object of the invention is to provide an electrophotographic 
copying apparatus which completely dissipates unnecessary charge around 
the image of an original formed on a photosensitive member when reduced 
and prevents attaching of unnecessary toner thereto, thereby saving the 
consumption of toner, largely reducing the amount of dust produced, and 
avoiding useless imaging on the copying paper. 
A second object of the invention is to provide an electrophotographic 
copying apparatus which is capable of reliably dissipating with simple 
construction and high accuracy the unnecessary charge existing around the 
image of an original formed on the photosensitive member when copied in 
reduction. 
A third object of the invention is to provide an electrophotographic 
copying apparatus which is capable of dissipating only from the areas 
centrally symmetrical to each other the unnecessary charge at each side 
edge of photosensitive member. 
A fourth object of the invention is to provide an electrophotographic 
copying apparatus which is capable of changing the charge dissipating area 
with high accuracy by use of racks, pinions, and a stepping motor, and of 
being controlled in the home position to change the charge dissipating 
area with accuracy. 
The above and further objects and features of the invention will more fully 
be apparent from the following detailed description with accompanying 
drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIGS. 1 and 2, reference numeral 1 designates a body of the 
copying apparatus, the body 1 providing at the upper portion thereof an 
original suport plate 2 of transparent glass fixed thereto and at the rear 
an automatic original transporting unit 3 mounted thereto in relation of 
being vertically movable through hinges 4, 4, the original transporting 
unit 3 is turned downwardly to abut against the upper surface of original 
support plate 2. At one side (rightward in the drawing) of automatic 
original transporting unit 3 is provided an original loader 6 on which 
originals 5, 5 . . . to be copied are loaded, and at the other side 
(leftward in the drawing) of the same is provided a tray 7 on which the 
copied originals are placed. A plurality of rollers 8, 8 . . . are 
provided at the original loader 6 side of automatic original transporting 
unit 3, an original transporting belt 9 is provided in continuation of the 
rollers 8, 8 . . . and about throughout the transporting unit 3 laterally 
thereof, and another roller 8 is provided in continuation of original 
transporting belt 9 at the tray 7 side thereof, the rollers 8, 8 . . . and 
belt 9 abutting against the uppermost original 5 at the loader 6, 
cooperating for placing the original 5 onto the original support plate 2, 
and the copied originals 5, 5 . . . being placed on the tray 7. 
Under the original support plate 2, an exposure lamp 10 as an 
exposure-scanning unit is axially disposed widthwise of the plate 2 and 
movable lengthwise thereof, and under the exposure lamp 10 is mounted a 
reflector 11 for reflecting the light from the lamp 10 toward the original 
support plate 2, the reflector 11 being provided at the rear side with a 
first movable mirror 12 for reflecting the reflected light from the 
original 5 on the original support plate 2. Also, a pair of second movable 
mirrors 13 and 14 are vertically disposed at the leftward upper portion of 
the body 1 to thereby reflect toward the center of body 1 the reflected 
light from the first movable mirror 12. Near the central portion of the 
body 1 is disposed an image lens 15, so that when the exposure lamp 10 
moves in reciprocation for scanning rightwardly in FIG. 2, the original 5 
on the plate 2 is slit-exposed and the image of original 5 is reflected 
toward the image lens 15 through the first movable mirror 12 and pair of 
second movable mirrors 13 and 14, the image lens 15 comprising a zoom lens 
changeable of the copying magnification. A stationary reflector 17 is 
provided rightwardly of image lens 15 and a photosensitive drum 16 is 
disposed rightwardly downwardly of image lens 15, so that the image of 
original 5 having passed the image lens 15 is reflected toward the 
photosensitive drum 16 through the stationary reflector 17, and then 
reflected thereby to transmit through an infrared absorption filter 18 
disposed between the stationary reflector 17 and the photosensitive drum 
16, thereby being exposed thereon. In addition, a zoom ratio of image lens 
15 is decided by a copying magnification setting switch (not shown). 
The photosensitive drum 16 is adapted to rotate clockwise as shown by the 
arrow in FIG. 2 and a side erase lamp 53 is provided at the upstream side 
in the rotation direction of the exposure position of the image of 
original 15 at the photosensitive drum 16, the side erase lamp 53 serving 
to eliminate (side-erase) charge on the portion corresponding to the side 
edges of copying paper on the photosensitive drum 16. Around the side 
erase lamp 53 there is provided a shading means, to be detailed below, is 
provided around the side erase lamp 53. 
At the upstream side to the side erase lamp 53 in the rotation direction of 
photosensitive drum 16 there an electrifying corotron 21 is housed in a 
support casing 70, and functions for uniformly plus-electrifying (up to 
about 600V) the photosensitive drum 16. 
A development unit 23 is disposed at the downstream side to the exposure 
position in the rotation direction of photosensitive drum 16 so as to 
develop with toner electro-static latent images formed on the 
photosensitive drum 16. The development unit 23 is provided with screw 
conveyors 22 and 24 for agitating carriers with toner, and in front with a 
toner container 25 (see FIG. 1) for feeding the toner to the development 
unit 23. The toner container 25 is mounted swingably laterally through a 
support shaft 26. 
At the downstream side to the development unit 23 in the rotation direction 
of photosensitive drum 16 there is provided a transfer corotron 27 for 
transferring the toner image on the photosensitive drum 16 to the copying 
paper. At the downstream side to the transfer corotron 27 there is 
provided adjacent thereto a separating corotron 28 for separating the 
copying paper from the photosensitive drum 16, the corotrons 27 and 28 
being integral with each other to move toward or away from the 
photosensitive drum 16. 
A cleaning unit 35 for removing from the photosensitive drum 16 the 
remaining toner not transferred to the copying paper is disposed 
leftwardly and upwardly of the separating corotron 28, which comprises a 
rubber blade 36 for scraping off the toner from the photosensitive drum 
16, and a screw conveyor 38 for discharging the scraped-out toner into a 
discharged toner collector 37 (see FIG. 1). 
Furthermore, an erase lamp 39 for eliminating the remaining charge on the 
photosensitive drum 16 is provided in advance of cleaning unit 35 in the 
rotation direction of drum 16, the electrifying corotron 21 being disposed 
in advance of erase lamp 39 in the rotation direction of the same. 
A paper feed cassette 29 is mounted to the rightwardly lower portion of the 
body 1, is detachable from the inner bottom thereof, and contains copying 
papers 19, 19 . . . of A-3 size in layers, for example. At the inner 
bottom of cassette 29 there are provided a compression spring 29a and a 
support plate 29b for biasing upwardly the copying papers 19, 19 . . . 
within the cassette 29. A paper feed roller 32 is provided at the 
leftwardly upper portion of cassette 29, the uppermost copying paper 19 in 
the cassette 29 abutting against the paper feed roller 32. Above the paper 
feed cassette 29 there is detachably mounted a paper feed cassette 33 
having the same construction as the cassette 29, in the latter of which 
copying papers 19, 19 . . . of A-4 size are contained in layers. The 
papers 19, 19 . . . and biased upwardly by a compression spring 33a and a 
support plate 33b, the uppermost paper 19 abutting against a paper feed 
roller 31. 
The root of a manual paper feeder 34 is mounted rotatably in the vicinity 
of paper feed roller 31 at the upper paper feed cassette 33. The fore end 
of the latter projects outwardly from the right side of body 1, so that 
the fore end is turned downwardly and copying paper 19 is placed on the 
manual paper feeder 34, thereby enabling manual paper feeding. 
The copying paper 19 placed on each paper feed cassette 29 or 33, or the 
manual paper feeder 34. The paper 19 is transported by the paper feed 
roller 32 or 31, to a pair of register rollers 61 and 62, and then 
transported via the latter to above the transfer corotron 27 and 
separating corotron 28, so that the toner image on the photosensitive drum 
16 is transferred and the copied paper is separate from the drum 16. 
A vacuum conveyor 41 is disposed at the horizontally left side of 
separating corotron 28, that is, at the downstream side in the 
transportation direction of copying paper 19, and a fixing unit 40 is 
disposed at the downstream side of vacuum conveyor 41, so that the copying 
paper 19 on which the toner image is transferred is transported to the 
fixing unit 40 through the vacuum conveyor 41. 
The fixing unit 40 contains therein a heating roller 43 housing therein a 
heater 42 and a pressure roller 44 in press-contact with the heating 
roller 43, the toner not yet fixed to the copying paper 19 being heated 
and pressurized by both rollers 43 and 43, thereby being fixed to the 
copying paper 19. At the downstream side to the fixing unit 40, a pair of 
discharge rollers 45 and 46 are provided for discharging the copying paper 
19 from the fixing unit 40 into a paper discharge tray 47 extending at the 
lefthand end outwardly from the body 1. 
Above the fixing unit 40 is disposed a control box 49 containing therein 
control parts 50. At a side of control box 49, a ventilating fan 51 is 
mounted. 
Referring to FIGS. 3 to 5, at the upstream side to the exposure position at 
the photosensitive drum 16 in the rotation direction thereof, in other 
words, at the downstream side to the electrified corotron 21, there is 
provided a hollow-box-like guide rail 56 integral with a support casing 70 
for corotron 21, extending in parallel to the axis of photosensitive drum 
16, and open at the surface opposite thereto. At the upper and lower 
portion of opposite inner surfaces of guide rail 56 are formed guide 
grooves 56a, 56a extending lengthwise of guide rail 56, the guide rail 56 
providing therein a pair of shading members 52, 52 engageable slidably 
with each guide groove 56a. The shading members 52, 52 are the same in 
construction and symmetrical with respect to the center of guide rail 56, 
one shading member 52 comprising a shading plate 52a of about 1/4 the 
length of guide rail 56, covering the opening at one side thereof and 
opposite to the photosensitive drum 16 and a side plate 52b rising at the 
side of shading plate 52a in the rotation direction of photosensitive drum 
16. The upper portions of side plates 52b at the other side of shading 
plate 52a extend in parallel thereto so that racks 52c, 52c are formed at 
the extensions of side plates 52b, 52b, respectively. A pinion 57 is 
provided at the lengthwise center of guide rail 56 and between the racks 
52c, 52c in relation of engaging with both the racks 52c, 52c, the pinion 
57 rotating to move the shading members 52, 52 at equal speed toward or 
away from each other. 
In one shading member 52, a home position shutter 61 is mounted to the 
upper surface of side plate 52b at the guide rail 56 end side and projects 
at the upper portion outwardly through an elongate slot 56b formed at one 
upper end surface of guide rail 56. A home position sensor 60 is mounted 
onto the upper surface of guide rail 56 at a side of the lengthwise end of 
elongate slot 56b, and has a photocoupler 60b which is mounted to a base 
plate 60a. The former comprises a light emitting element and a light 
receiving element vertically opposite to each other, and is mounted to a 
mounting member 60c which is mounted upon a holder 60d fixed to the upper 
surface of guide rail 56 and slidable lengthwise of guide rail 56. Also, 
the mounting member 60c is biased one-sidedly by a push spring 60e 
interposed between the mounting member 60c and the holder 60d, capable of 
being regulated in position through an adjusting screw 60f. The screw 60f 
is rotated to change the position of the mounting member 60c, and in turn 
the position of photocoupler 60b. The home position shutter 61 is adapted 
to be positioned at the upper portion thereof between the light emitting 
element and the light receiving element at the photocoupler 60b, and when 
both the shading members 52, 52 reach the separation limit position, 
photocoupler 60b is positioned between both the elements, causing the 
photocoupler 60b to be in its off condition. 
Within the pair of shading members 52, 52 disposed symmetrically with 
respect to the center of guide rail 56 there is fitted a transparent 
box-like-shaped lamp casing 54 that is slidable with respect to each 
shading member 52. A shading film 54a is stuck to the surface of lamp case 
54 opposite to the side plate 52b at each shading plate 52, and a shading 
film 54b is stuck at the lengthwise center of the open side surface (the 
lower surface) of guide rail 56, except at both lengthwise end portions 
thereof, in other words, at the center except for both the portions of 
guide rail 56 opposite to both axial end portions of photosensitive drum 
16. 
A substrate 53a is disposed in the lamp casing 54 and provided at both 
lengthwise sides with three side erase lamps 53, 53, 53 respectively in 
relation of being disposed lengthwise of substrate 53 so as to project at 
the lower portion, the light projection areas of three side erase lamps 
53, 53, 53 at the lengthwise end portions of substrate 53a being out of 
the shading film 54 stuck to the lower surface of lamp casing 54 and 
corresponding to the both axial side edges of photosensitive drum 16. 
Accordingly, the light from each side erase lamp 53, 53 . . . passes 
through the lamp casing 54 to reach each axial side edge of photosensitive 
drum 16, and exposures the side edge of photosensitive drum 16 to the 
light to thereby dissipate charge on the side edge of the same electrified 
by the corotron 21. Also, when the shading plate 52a covers the light 
projection area of side erase lamp 53, the light is shaded to prevent 
light from striking the photosensitive drum 16, whereby the portion 
covered by the shading plate 52a is not exposed. 
The pinion 57 projects at a shaft thereof upwardly from the guide rail 56 
so that the shaft supports at its upper end a gear 67. A stepping motor 59 
is mounted above one lengthwise end (at the slot 56b side) of guide rail 
56, so that an output shaft 59a of motor 59 extends downwardly and carries 
a gear 68. A timing belt 58 is stretched across the gear 68 and the 
aforesaid gear 67 so that rotation of stepping motor 59 is transmitted to 
the pinion 57 through the gear 68, timing belt 58 and gear 67, to thereby 
move the pair of shading members 52, 52 toward or away from each other. 
When the shading members 52, 52 move toward each other, the shading plates 
52a, 52a provided under the shading members 52, 52 reduce the portions for 
covering the light projection areas of side erase lamps 53, 53 . . . 
within the lamp casing 54 to enlarge the charge dissipation areas at both 
axial edges of photosensitive drum 16. On the contrary, the shading 
members 52, 52 move away from each other to expand the portions for 
covering the side erase lamps 53, 53 . . . light projection areas to 
restrict the charge dissipation areas at both axial edges of the same. 
FIG. 6 is a flow chart explanatory of operation of the shading members 52, 
52 provided under the side erase lamps 53, 53 . . . . When a copy starting 
button (not shown) is pushed, an output of photocoupler 60b of the home 
position sensor 60 at first is examined, thereby putting the shading 
members 52 in the condition of moving farthest away from each other. In 
other words, in the condition of most reducing the light projection areas 
of side erase lamp 53, 53 . . . , that is, in condition of most 
restricting the charge eliminating areas at the axial edges of 
photosensitive drum 16, whereby when the photocoupler 60b is on, both the 
shading members 52, 52 are assumed not to be in the home position where 
they are most far apart from each other, so that the stepping motor 59 is 
reversely rotated, and when the photocoupler 60b at the home position 
sensor 60 is off, the stepping motor 59 is stopped of its rotation. 
The control of shading members 52, 52 is started on the basis of the above 
conditions. The copying magnification is decided from the output of a 
copying magnification setting switch so that, when the copying 
magnification is 0.64 times to a minimum, the stepping motor 59 is 
normally rotated only by 99 pulses. Also, when the same is 0.75 times, the 
motor 59 is normally rotated only by 69 pulses, when 0.78 times, only by 
59 pulses, and when 0.93 times, only by 18 pulses. Hence, the pinion 57 
rotates by the predetermined amount to thereby move both the shading 
members 52, 52 toward each other. In this case, since the rack 52c at each 
shading member 52 is formed in equal in pitch, both the shading members 
52, 52 move in equal distances and approach each other, whereby the light 
projection areas under the side erase lamps 53, 53 . . . disposed at both 
lengthwise end portions are expanded and the central portion of 
photosensitive drum 16 is not exposed only by length corresponding to each 
reduction rate, but other side edge portions of the same are exposed. 
On the other hand, the photosensitive drum 16 rotates to be uniformly 
electrified at the axially overall area by the electrification corotron 
21, and the original 5 on the original support plate 2 is exposed to the 
light by the exposure lamp so that the original image reduced into the 
predetermined magnification by the image lens 15 exposes the electrified 
photosensitive drum 16, whereby the charge on the exposed portion thereof 
is dissipated to form the electro-static latent image on the 
photosensitive drum 16. In this case, since the latent image is reduced 
from the original 5, both axially end portions of photosensitive drum 16 
are larger than those at the original support plate 2, thereby being not 
exposed and left electrified. 
The photosensitive drum 16 on which the reduced original image is formed 
further rotates to reach the side erase lamps 53, 53 . . . disposing 
position, then each axially end portion of photosensitive drum 16 is 
exposed to the light projected from the side erase lamps 53, 53 . . . , 
thereby dissipating the charge at the same. In this case, the light 
projection area by the side erase lamps 53, 53 . . . is restricted by the 
shading member 52a, 52a at each shading member 52. Hence, the axial 
portions at the photosensitive drum 16 corresponding to the reduction 
rate, in other words, a width, when the original support plate 2 is 
reduced by the predetermined magnification, only is adapted not to be 
exposed to the side erase lamps 53, 53 . . . , whereby both the axially 
end portions of photosensitive drum 16 except for the above portion only 
are reliably exposed, thus dissipating the charge on the side edge portion 
only. 
The electro-static latent image on the photosensitive drum 16 is 
sensible-imaged with toner by the developing unit 23. In other words, the 
electrified portion at the photosensitive drum 16 not exposed to the light 
is attached with toner so as to be sensible-imaged, but each side portion 
at the photosensitive drum 16 where no original image is formed, is 
exposed to the side erase lamps 53, 53 . . . corresponding to the 
reduction magnification to thereby dissipate the charge, thus attaching no 
toner to the side portion. 
The toner image on the photosensitive drum 16 is transferred to the copying 
paper 19 through the transfer corotron 27, the copying paper 19 being 
separate from the drum 16 by the separating corotron 28. Also, the toner 
image on the copying paper 19 is fixed by the fixing unit 40, the 
remaining toner and charge on the drum 16 being removed by the cleaning 
unit 35 and the charge-erase lamp 39, respectively. 
Alternatively, the shading members 52 of the side erase lamps 53, 53 . . . 
each may be changed in movement on the basis of the reduction 
magnification and the size of copying paper 19. 
As this invention may be embodied in several forms without departing from 
the spirit of essential characteristics thereof, the present embodiment is 
therefore illustrative and not restrictive, since the scope of the 
invention is defined by the appended claims rather than by the description 
preceding them, and all changes that fall within meets and bounds of the 
claims, or equivalence of such meets and bounds thereof are therefore 
intended to be embraced by the claims.