Mechanism for mounting and dismounting a screen-like photosensitive medium

A mechanism for mounting and dismounting a screen-like photosensitive medium having a number of fine openings with respect to an apparatus body. It is known to form a screen-like photosensitive medium into the shape of a drum, but according to the present invention, the photosensitive medium and a gear for driving the photosensitive medium are constructed independently of each other to leave the gear on the apparatus body side, and a device for directing a current applied to the photosensitive medium side is provided inside of the gear with a sliding member interposed therebetween. The side surface of the photosensitive medium which corresponds to the gear is provided with a construction similar to the gear portion, thereby facilitating the mounting and dismounting of the screen-like photosensitive medium with respect to the apparatus body.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a mechanism for mounting and dismounting, with 
respect to an apparatus body, a frame member supporting a screen-like 
photosensitive medium having a number of fine openings (hereinafter 
referred to as the screen). 
2. Description of the Prior Art 
The screen described herein is known from our U.S. Pat. No. 4,143,965 and 
U.S. Pat. No. 3,680,954. In an apparatus for forming an image by the use 
of such screen, it has been practised to form the screen into the shape of 
a drum as disclosed in U.S. Pat. No. 3,985,432. As an example of the means 
for forming the screen into the shape of a drum, use may be made of a 
partly cut-away cylindrical frame member 2 as shown in FIG. 1 in the 
accompanying drawings and the screen 1 may be stretched along the cut-away 
portion of the frame member 2 and adhesively secured thereto. In FIG. 1, 
reference character 3 designates cylindrical portions and reference 
character 4 designates a connection portion. Alternatively, such frame 
member may be constructed by joining the connecting portion 4 to the 
cylindrical portions 3. It is very difficult for the frame member 2 to 
maintain sufficient rigidity because of the limited positional relation 
between the frame member and a corona discharger disposed therewithin. 
Also, the screen itself is a net-like member comprising a plurality of 
very thin layers of several microns to several tens of microns and is 
structurally weak against extraneous forces. 
On the other hand, constituent members such as primary latent image forming 
means and latent image stabilizing means are disposed around and in 
proximity to the drum-shaped frame member supporting the screen 
(hereinafter referred to as the screen drum). Therefore, if a great 
extraneous force is exerted on the screen drum during the mounting or 
dismounting thereof with respect to the apparatus body, the frame member 
may be deformed to thereby twist and damage the screen or deform the 
configuration of the openings thereof. Also, during the mounting or 
dismounting, the screen is moved along the rotary center shaft thereof and 
in that case, there is a danger that the screen is brought into contact 
with the constituent members around the screen drum, whereby the screen is 
damaged. Further, it is necessary to dispose a corona discharger within 
the screen drum and this unavoidably complicates the construction for 
permitting the internal discharger to be disposed during the mounting or 
dismounting of the drum. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to solve the above-noted problems 
and to provide a construction which facilitates the mounting and 
dismounting of the screen and of the modulating corona discharger 
therewithin and which does not impart any undesirable stress to the screen 
during the mounting or dismounting thereof. 
It is a further object of the present invention to provide a construction 
which can easily set the home position of the screen drum when the drum is 
mounted on the center shaft. 
In connection with the above-described construction, it is an object of the 
present invention to provide a mechanism for preventing mal-insertion of 
the modulating corona discharger which is removably mountable with respect 
to the screen drum. 
The present invention which achieves these objects has a photosensitive 
medium frame member supporting the screen in the form of a drum (screen 
drum), a rotary center shaft for the screen which is fixed to the 
apparatus body, a drive unit provided on the rotary center shaft, and a 
screen drum side supporting unit. The drive unit has drive force 
transmitting means outside of a rotary bearing member and a fixed portion 
accompanying electrical wiring inside of the bearing member, and this 
fixed portion is fixed to the rotary center shaft. That side of the side 
supporting unit which is opposed to the drive unit has, outside of the 
rotary bearing member, a portion supporting the screen drum and has a 
fixed portion accompanying electrical wiring inside of the bearing member, 
and this fixed portion is slidable with respect to the rotary center shaft 
during the mounting or dismounting of the drum. The electrical wiring of 
the drive unit and the electrical wiring of the side supporting unit are 
connectible or disconnectible by a connector member. 
In the above-described construction of the present invention, the drive 
gear of the drive unit has a projecting portion such as a pin or a 
recessed portion and by engagement of such projecting or recessed portion 
with a projecting or recessed portion formed in part of the screen drum, 
the drum may be rotated. Also, a connector member for supplying power to 
the power consuming member of the screen drum is disposed on the fixed 
portion of the drive unit, so that, when the screen drum is dismounted 
from the rotary center shaft, the screen drum and the drive unit can be 
electrically divided by the connector member. A position setting 
projecting portion such as pin or a recessed portion for determining the 
home position of the screen drum may be provided in the fixed portion of 
the drive unit. 
Further, when it is taken into account to independently remove the power 
consuming member within the screen drum during the mounting of the drum 
simultaneously with the dismounting of the drum from the rotary center 
shaft, and if the connector of the fixed portion of the drive unit is 
referred to as the first connector member, the power consuming member 
disposed within the drum and independently removable from the drum may be 
connected by the second connector member of the drum supporting unit, and 
the first connector member and the second connector member may preferably 
be disposed in electrically series relationship to provide an effect which 
will later be described. The power consuming member may be a modulating 
corona discharger which may be provided within the drum, or a heating 
member for heating the screen, or a lamp which may be provided if 
required. 
With the above-described construction, when the screen drum is to be 
removed from the rotary center shaft, the means for transmitting the drive 
force to the drum, namely, the drive unit can be left on the center shaft 
and thus, the weight of the member withdrawn can be reduced. Also, with 
the construction of the above-described drive portion, the member for 
supplying the power to the drum side can easily pass through the drive 
portion and so, the wiring design is not complicated and the safety is 
enhanced. By providing positioning means on the drive portion left, the 
home position of the screen can be easily found out and cumbersome 
adjusting operation can be eliminated. Further, the position is determined 
by a projecting portion such as a pin or a recessed portion and thus, any 
electrical member such as microswitch is not required, and a part itself 
such as a pin or the like supports the member and provides a drive source, 
thereby enabling effective utilization of the parts. 
In the electrical system of the above-described mechanism, the drive 
portion and the screen drum side are electrically divided by the first 
connector provided in the drive portion, and the screen drum and the power 
consuming member therewithin are divided by the second connector, so that 
these may be easily mounted or dismounted independently of each other and 
moreover, the connectors are all provided removably in the axial 
direction, thus providing good operability. That is, the reliability of 
electrical connection is enhanced by the use of the connector members 
while, at the same time, removal of individual parts and the mounting of 
the drum can be accomplished more reliably. 
In the construction of the present invention, the drum itself is supported 
independently of the member therewithin, so that the drum can be removed 
from its shaft while maintained in mounted condition, thus preventing 
unnecessary stress from being imparted to the screen. 
A safety device for mounting a corona discharger removably mountable with 
respect to the screen drum in the described manner will be fully explained 
in the following description. 
The invention will become more fully apparent from the following detailed 
description thereof taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention will hereinafter be described in greater detail with respect 
to an embodiment thereof. 
Referring to FIG. 2 which is a cross-sectional side view showing primary 
and secondary latent image forming portions of an image formation 
apparatus to which the present invention is applied, reference character 5 
designates a hollow, fixed, rotary center shaft which provides the axis of 
the rotation of a screen drum 6 having a screen stretched over the outer 
surface thereof. The screen drum 6 comprises a screen stretched around a 
frame member 2, shown in FIG. 1, and the screen is a three-layer screen as 
disclosed in said Japanese Laid-Open Patent Application No. 341/1976. The 
screen drum 6 is rotated in the direction of arrow and is first subjected 
to application of light by a lamp 7 and simultaneously therewith, 
application of corona discharge by a discharger 8, thereby being charged 
to a predetermined potential. Subsequently, the drum 6 is irradiated with 
image light and simultaneously therewith, discharged by a corona 
discharger 9, whereafter it is subjected to uniform application of light 
by a lamp 10, whereby a primary latent image is formed on the screen. 
Within the screen drum 6, there is a stay 11 slidably supported relative to 
the center shaft 5, and the stay 11 has a cylindrical member 14 fixed at 
the axial ends thereof by screws 12 and 13. This cylindrical member 14 is 
concentric with the screen drum 6 and has a surface-like hot plate 15 
adhesively secured to the surface thereof which faces the center shaft 5. 
The surface-like hot plate 15 acts to stabilize the characteristic of the 
screen when heated and also to prevent the reflected light resulting from 
the application of light to the screen from affecting the other members 
than the screen. On the other hand, a corona discharger 16 which is a 
modulating corona discharger is disposed below the stay 11 and the corona 
ion flow emitted from the discharger 16 is modulated on an insulating drum 
17 rotated in the direction of arrow, correspondingly to the primary 
latent image on the screen. The above-described latent image formation 
unit is hermetically surrounded by an outer case 18 and the interior of 
the case 18 is always maintained at a positive pressure. 
As described above, both inside and outside of the screen drum, various 
members are in proximity to the screen drum. Therefore, the screen is 
exposed to the high risk of being damaged when the drum is mounted or 
dismounted with respect to the apparatus body for the purpose of 
replacement of the screen drum and maintenance of the apparatus. The 
present invention has solved this problem by a method which will 
hereinafter be described by reference to FIG. 3 and so on. 
The screen drum of the present invention is shown in the cross-sectional 
view of FIG. 3, which is taken along line III--III of FIG. 2. In FIG. 3, 
the modulating corona discharger 16 and insulating drum 17 of FIG. 2 are 
depicted by dots-and-dash lines. 
In FIG. 3, reference character 5 designates the center shaft. That end of 
the screen drum at which it may be removed (the left end as viewed in the 
Figure) is closed by a drum cap 19 which prevents each member on the shaft 
5 from being displaced. The other end of the shaft 5 is connected to 
blower means, not shown, so that compressed air is introduced into the 
shaft 5 as indicated by arrow 20. The warm wind or the dust-removing wind 
introduced into the shaft is blown out into the screen drum 6 through a 
plurality of openings (not shown) provided in the shaft. The blown out air 
stream reaches the dischargers 8, 9 (FIG. 2) and other members surrounding 
the drum, through the screen, to heat the screen 1 and prevent the screen 
from being stained by discharging. 
The rotary center shaft 5 is secured to the back plate 21 of the apparatus 
body by a shaft set member 23 secured to the back plate 21 by means of a 
screw 22. On the other hand, that end of the shaft 5 which is adjacent to 
a front plate 24 is fixed by a core positioning plate (not shown) 
removable during the mounting or dismounting of the screen drum 6. On the 
center shaft, a drive portion 25 for driving the screen drum 6 is provided 
adjacent to the back plate 21. The drive portion, as shown in FIG. 5, has 
on the outer side thereof a gear 27 for driving the screen drum through a 
bearing 26 which is a rotary bearing member, and a drive pin 28 secured to 
the gear 27 and has on the inner side thereof plug receptacles and a fixed 
portion 30 to which the positioning pin 29 of the screen drum is secured, 
and is mounted on the shaft 5 by fixing the fixed portion 30 to the center 
shaft 5 by means of a pin 31. With the above-described construction, the 
drive portion can have its fixed portion 30 fixed on the shaft 5 and at 
the same time can assume a construction in which the drive gear 27 is 
freely rotatable around the fixed portion. Also, since the fixed portion 
30 always assumes a determined position relative to the shaft 5, it is 
possible to provide a standard pin for positioning the screen drum or to 
mount plug receptacles. Designated by 32 is a plug receptacle embeded in 
the fixed portion 30 and supplied with a high voltage current by a cord 33 
from a power source section, not shown. On the other hand, a gear 34 
meshing with the gear 27 is a drive gear for the insulating drum 17. 
The screen drum 6 also removable with respect to the drive portion 25 is of 
a double drum construction in which the inner drum is formed by the 
surface-like hot plate 15 which is also supported by the peripheral 
surface of a front support 35 and a rear support 36, which in turn are 
supported on an insulative stepped member 38 against axial sliding or 
rotation relative to the member 38, said stepped member 38 being supported 
by a stay 39 and provided on the shaft 5. An electrically conductive stay 
11 for mounting the modulating corona discharger 16 is supported on the 
supports 35 and 36, and a plate spring 49 for urging the discharger 16 
toward the screen is mounted on the stay 11. The plate spring 40 has 
applied thereto a bias voltage, and the bias voltage from the stay 11 to 
the shield plate of the discharger 16 is also applied from here. 
The screen drum 6 lies outside of the substantially drum-shaped hot plate 
15 and that end of the drum 6 which is adjacent to the back plate is 
supported by an inner flange 41 provided on the stepped member 38, a 
bearing 42 provided on the peripheral surface of the flange 41, and a back 
plate side flange which constitutes a drum side supporting unit comprising 
an outer flange 43 on the bearing 42. The inner flange 41 has therein an 
opening 44 fitted over the positioning pin 29, and the outer flange 43 has 
therein an opening for receiving the drive pin 28. On the other hand, a 
plug 45 corresponding to the plug receptacle 32 is fitted in the inner 
flange and when the screen drum is mounted, this plug is electrically 
connected as shown in FIG. 3. This will hereinafter be referred to as a 
first connector. 
An intermediate member 46 constituting a second connector is supported on 
the stepped member 38 between the back plate side flange and the support 
36. This intermediate member is formed of an insulating material, and a 
plug receptacle 47 into which the plug of the corona discharger 16 side 
may be inserted is provided at the opposite side from the plug 45. 
The front plate side of the screen drum is supported by an electrically 
conductive wheel member 48 provided on said support 35, a bearing 49 on 
the peripheral surface thereof, and a front plate side flange comprising 
an outer flange 50 provided on the peripheral surface of the bearing 49. 
Application of a bias voltage to the screen drum is effected from the stay 
11 through the wheel member 48 and the bearing 49 using electrically 
conductive grease and through the flange 50. That portion of the back 
plate side flange which is in contact with the drum 6 is formed of an 
insulating material to prevent the bias current from flowing to the 
apparatus body side. 
To remove the discharger 16 in the above-described construction, the drum 
cap 19 may be removed and a flange 51 may be removed, and then the plug of 
the discharger may be axially withdrawn from the plug receptacle 47 
through an opening 52 in the flange 50, whereby the discharger may be 
singly removed. To remove the entire drum 6 from the drive portion, the 
drum cap 19 may be removed and a shaft having the same diameter as that of 
the shaft 5 may be connected to the cap portion, and then the entire drum 
may be forced leftwardly as viewed in the Figure, whereby the drum 6 may 
slide on the shaft 5 with the stepped member 38 to assume a position as 
shown in FIG. 4. Mounting the screen drum 6 on the apparatus body may be 
easily and smoothly accomplished by carrying out procedures reverse to the 
aforementioned procedures. During the dismounting of the screen drum, the 
drum can be withdrawn outwardly in this manner as it is in mounted 
condition and this enables the presence of damages or wrinkles on the 
screen to be readily and fully checked up. 
Referring to FIG. 5 which shows the members constituting the 
above-described drive portion, reference character 53 designates a bias 
voltage connector for the shield plate of the discharger 16 and the drum 
6, and reference characters 54a and 54b designate connectors for the 
surface-like hot plate 15. Each connector has a construction which permits 
the screen drum side plug to mesh therewith reasonably during the mounting 
of the drum. 
The above-described construction enables bias application to the 
complicated screen drum, corona discharger and other members to be 
effected reliably and stably and further enables each member to be readily 
mounted or dismounted with respect to the drum drive portion and moreover, 
during the mounting, the home position of the drum can be easily found 
with the aid of the pin member, thus eliminating any cumbersome 
adjustment. 
In FIG. 5, a recess formed in a flange 55 is for detecting the position of 
the screen drum. Such recess is detected by the detecting portion 57 of 
FIG. 3 and used to control the operation of image formation means, not 
shown. The aforementioned positioning pin may be provided on the screen 
drum and a pin may be provided on the drive portion and a recess may be 
formed in the drum 6. 
Description will now be made of a mounting safety device for the modulating 
corona discharger which is removably mountable with respect to the screen 
drum 6. 
The modulating corona discharger 16 may be removed or mounted with respect 
to the screen drum 6 even when the drum 6 is or is not supported on the 
rotary center shaft 5. The purpose of removal of the discharger is to 
clean or replace the discharger and when the discharger is again inserted 
into the screen drum 6, it must be reliably and fixedly disposed at its 
accurate position. The reason is that in an image formation apparatus 
using such a screen, the screen drum 6 is rotated but the discharger 16 is 
fixedly disposed at a perdetermined position within the screen drum 6 and 
therefore, if the discharger 16 is not completely inserted into the 
predetermned position, it will strike against the drum side flange portion 
which is rotated with the screen 1. Thereby, the screen 1 which is usually 
made up with a thickness of several tens of microns will be twisted with 
the screen drum 6, thus being damaged. A first example for solving this 
problem will be described by reference to FIG. 6. 
FIG. 6 is a cross-sectional view showing the interior of the screen drum 6 
with the discharger 16 inserted thereinto. After the discharger 16 has 
been deeply pushed into its shown position (rightwardly as viewed in the 
Figure), a mal-insertion preventing lid 58 is fitted into the opening 52 
(see FIGS. 2 and 3) of the outer flange 50 of the screen drum 6 by a 
finger or the like. In this case, the mal-insertion preventing lid 58 is 
elastically deformed toward the interior of the screen drum 6, thus 
forcing the discharger 16 into its predetermined accurate position. Then, 
when the finger is released, the mal-insertion preventing lid 58 restores 
its original configuration and comes off the end face of the discharger 
16, so that even if the screen drum 6 is rotated, the screen 1 and other 
members forming the screen drum 6 may be protected from any damage which 
would otherwise result from insufficient insertion of the discharger 16, 
thus precluding occurrence of any accident. 
FIGS. 7 and 8 are a cross-sectional view and a perspective view, 
respectively, showing an example of such mal-insertion preventing lid 58 
which is formed of rubber. In FIG. 7, the portion depicted by dot-and-dash 
lines shows the range of the lid 58 which can be elastically deformed by 
pushing it by a finger. 
With such a construction, it is possible to eliminate leakage of wind from 
the opening 52 of the flange 50 of the screen drum by the mal-insertion 
preventing lid 58 when the wind is blown into the screen drum 6 through 
the interior of the rotary center shaft 5 to prevent adherence of dust or 
toner to the screen 1 or to prevent production of impurities and thus, the 
interior of the drum is substantially hermetically sealed to enable the 
wind to be blown into the screen 1 further efficiently. During the 
downtime of the apparatus, it is often the case that the wind is not blown 
into the screen drum and the presence of the opening allows suspended 
toner or dust to enter the interior of the drum and adhere to the 
discharger 16 and/or the screen 1, but again in such case, the 
mal-insertion preventing lid 58 is effective to prevent such entry and 
adherence of the toner or dust. 
Another embodiment of the mal-insertion preventing mechanism will now be 
described in detail. 
FIG. 9 is a perspective view showing a flange different in configuration 
from the flange 50, FIG. 10 is a perspective view showing the 
configuration of a discharger for this embodiment, and FIG. 11 is a 
fragmentary cross-sectional view showing the engagement relationship 
therebetween. A flange 59 is formed with a sloping-surfaced projecting 
portion 60 which may contact a roller 62 attached to the end of a 
modulating discharger 61 shown in FIG. 9. At this time, even if the 
discharger 61 is not in completely inserted condition, the projecting 
portion 60 forming the sloping surface acts to insert the discharger 61 
completely deeply when the drum 6 is rotated with the flange 59. After 
that, the projecting portion 60 of the flange and the roller 62 of the 
discharger are brought into non-contact relationship. 
Reference is now had to FIG. 12 to describe a third embodiment. 
In this embodiment, a sliding portion 64 facing the screen drum 6 and the 
flange 63 is slidably constructed so that, even if the discharger 16 is 
not fully deeply inserted into the screen drum 6 and is projected from the 
opening 65 of the flange 63, only the drum 6 continues to rotate due to 
the presence of the sliding portion 64, whereby the screen drum 6 may be 
prevented from being damaged. In FIG. 12, the position indicated by broken 
line is the regular position of the discharger 16. 
A fourth embodiment will now be described with reference to FIG. 13. 
A reflecting surface 66 is formed on a part of the end of the discharger 16 
so that, when the discharger 16 is disposed at its regular position, the 
light from a light source 67 may be reflected by the reflecting surface 66 
and enter a light-receiving portion 68 and that when the discharger 16 is 
not at its regular position, the light may not enter a predetermined 
position of the light-receiving portion 68 and that when the discharger is 
not at its predetermined position, a current may not flow to a drive 
source such as a motor for driving the screen drum 6, thereby preventing 
occurrence of any accident which would otherwise result from mal-insertion 
of the discharger 16. 
Instead of reflection of light, reflection of ultrasonic wave or other may 
of course be utilized. 
Reference is now had to FIGS. 14 and 15 to describe a fifth embodiment. 
Apertures 69, 70, 71, 72, 73 and 74 are formed through the screen drum 6, 
the discharger 16, the electrically conductive wheel member 48, the 
support 35 and the rotary center shaft 5 and these apertures are 
substantially in line with one another when the screen drum 6 is at its 
basic stop position. When the light from a light source 75 does not pass 
to a light-receiving portion 76, the motor or the like for driving the 
screen drum 6 is not rotated. Thus, when the discharger 16 is not at its 
regular position, namely, when the discharger 16 is mal-inserted, the 
screen drum 6 is not rotated and no damage occur to the screen 1. Each of 
the aforementioned apertures for passage of light may preferably be sealed 
by a transparent material to provide a dust-proof effect. 
Since a high bias voltage necessary during the modulation is applied to the 
interior of the screen drum 6, using an ordinary microswitch to prevent 
mal-insertion of the discharger 16 would be very dangerous in causing 
malfunctioning or leak and would also be difficult to do and therefore, 
the detection by non-contact as in the present embodiment may be said to 
be preferable. Also, a modification as shown in FIG. 15 would occur to 
mind. That is, it is possible to provide a practical type of construction 
in which apertures 77 and 78 are formed through part of the screen drum 6 
and discharger 16. 
With the above-described construction, mal-insertion of the discharger may 
be simply prevented and any damage to the screen may be eliminated while, 
at the same time, escape of the blast from the interior of the screen drum 
and entry of dust or the like into the drum may also be prevented, thereby 
achieving the aforementioned objects. Thus, the present invention is 
highly useful.