Electrostatic copying device

An electrostatic copying device comprises a transparent support plate onto which an original to be copied is placed. A slide carrying a recording cylinder provided on its peripheral surface with a photosensitive layer is movable beneath and parallel to the transparent support plate. At least one gear coaxially fixed to the recording cylinder meshes with a rack extending parallel to the path of movement of the slide to rotate the recording cylinder during movement of the slide. The slide carries also a raster objective stepwise scanning the original during movement of the slide to produce a latent image of the original on the photosensitive peripheral surface of the recording cylinder, which picture is transferred to an endless dielectric band forming an intermediate recording carrier and from the latter the picture is transferred to a photosensitive paper sheet fed onto the band along which also a plurality of usual treating stations are arranged for developing the image on the paper sheet.

BACKGROUND OF THE INVENTION 
The present invention relates to electrostatic copying devices in which an 
original is stripwise illuminated by means of a raster image reproducing 
system on a uniformly electrostatically charged emulsion carrier for the 
production of an electrostatic latent image. 
A device of this type is for instance disclosed in the German Pat. No. 23 
03 115 and the corresponding U.S. Pat. No. 3,592,592. Such copying devices 
provided with a raster image producing system have the advantage to 
produce with relatively little constructional expenditure a high-intensity 
image of the original on the copying carrier, whereby the original has to 
have only a small distance from the copy produced, which results in very 
small dimensions of the copying device. 
A so-called book copy in which the original during the illumination process 
rests on a planar transparent support face of the copying device, is with 
this arrangement practically only possible when the light sensitive layer 
is arranged on a carrier which has at least a planar portion of a length 
corresponding to that of the original. Such a copying device is for 
instance disclosed in the German Offenlegungsschrift No. 24 21 661 and the 
corresponding U.S. Pat. No. 3,972,609. The therein used band-shaped 
recording carrier is especially subjected to considerable wear if it is 
provided with a layer of selenium which is especially suitable for 
electrophotographic purposes, but which is however relatively brittle. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a constructively 
simpler raster copying system with small dimensions which eventually may 
operate with different copying scales, and in which the recording carrier 
is not subjected to increased mechanical wear. 
With these and other objects in view, which will become apparent as the 
description proceeds, the electrostatic copying device according to the 
present invention mainly comprises support means, a planar transparent 
support plate mounted on said support means for receiving a stationary 
original of predetermined length to be copied, a slide movable on a 
predetermined planar path along said transparent support plate, a 
recording cylinder having a photosensitive peripheral surface turnably 
mounted on the slide, raster objective means carried by said slide for 
producing an image of the original on the photosensitive surface of the 
cylinder, corona discharge means on said slide for uniformly charging the 
photosensitive surface before illuminating the same by the raster 
objective means, first drive means for moving the slide with a 
predetermined speed along said predetermined path from a starting position 
to an end position and for rotating said cylinder with a peripheral speed 
corresponding to the speed of the image produced by the raster objective 
means on the photosensitive surface of the cylinder, a band-shaped 
dielectric recording carrier extending along the predetermined path and 
having at least over the predetermined length of the original a planar 
portion, means on the slide for transmitting the charge image from the 
recording cylinder to said planar portion of the band-shaped recording 
carrier during movement of the slide in one direction along the 
predetermined path from the starting position to the end position, a 
plurality of treating stations arranged along the band-shaped recording 
carrier following the planar portion thereof for transmitting the image 
from the band-shaped recording carrier to a paper within a predetermined 
time period, and second drive means for moving, after transmission of the 
image from the recording cylinder to the band-shaped carrier, the 
recording cylinder in a direction opposite to said one direction back from 
the end to the starting position and simultaneously moving the band-shaped 
carrier in the same direction as the recording cylinder and both at the 
same speed corresponding to a speed according to the predetermined time 
period. 
In this arrangement, the latent electrostatic image is produced on the 
recording cylinder provided on its peripheral surface with a layer of 
selenium or another known photoelectric layer, in which the actual 
photoelectric layer is not subjected to any mechanical strain. The 
application of the powder image and the other operating steps act on the 
dielectric recording carrier, which consists of a relatively elastic 
wear-resistant plastic material. An exchange of the recording carrier can 
therefore be carried out at longer time intervals as is necessary with 
conventional apparatuses of this type. 
Despite the additional recording cylinder, there will result, with respect 
to known raster image reproducing systems, at only slightly increased 
distance between the original and the remaining image planes, if the 
recording cylinder has a sufficient periphery for the reception of the 
total intermediate picture. In so far as the timely regenerability of the 
photosensitive layer and the required copy speed permit, it is possible to 
improve this relationship by distributing the reproduction and transfer 
process onto a plurality of cylinder revolutions. The arrangement provides 
also advantageous possibilities for the exchangeable use of raster 
reproduction systems with different image scales, especially with regard 
to, in this case, simply obtainable drives for the recording carrier with 
corresponding transmission ratios for the different scales, and with 
regard to the possibility to arrange the practically short building 
one-to-one recording system closer to the recording cylinder than the 
longer building reducing systems. 
An additional advantage of the system according to the present invention 
consists in that, due to the image reversal at the first image producing 
step, the dielectric recording carrier may rest, in the case of a 
one-to-one reproduction, during the transmission of the charge image. 
The novel features which are considered characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the embodiment shown in FIGS. 1 and 6, there is provided at the upper 
side of the device housing 1 a transparent support plate 2 for a 
stationary original 3 to be copied. The original 3 is stripwise scanned by 
a raster objective 4. The raster objective 4 is combined with a reversing 
mirror 5, which transmits the image produced by the raster objective in a 
mirror-inverse manner. For reversing the image it is also possible to use, 
instead of the reversing mirror, raster reproduction systems as disclosed 
in German Pat. No. 1,298,407 and the corresponding U.S. Pat. No. 3,580,675 
or raster reproduction systems as disclosed in German Offenlegungsschrift 
No. 26 37 514, in which an uneven number of lens elements are combined 
with a mirror. The original 3 is illuminated during the scanning by 
illuminating tubes 6 and 7. 
The picture is produced on a recording cylinder 8 provided on its 
peripheral surface with a selenium layer. The recording cylinder 8 is 
mounted on a slide 11 which is guided by means of rolls 9 on guide rails 
10. The recording cylinder 8 is surrounded by a housing 11a mounted on the 
slide 11, which protects the surface of the recording cylinder from 
foreign exposure. The slide 11 is moved during the optical scanning 
process in the direction of the arrow A. For this purpose, the slide 11 is 
connected by means of a rope 26 with a rope pulley 23, which is mounted on 
a shaft 24 rotated by a non-illustrated motor. The rope pulley 23 can be 
coupled with the shaft 24 for rotation therewith by a magnet coupling 126 
which in turn is connected by conductors 129 and 130 to a central control 
unit 25. 
A gear 13 is mounted on the shaft 12 of the recording cylinder 8 for 
rotation therewith, and the gear 13 meshes with a stationary rack 14. The 
pitch diameter of the gear 13 corresponds to the outer diameter of the 
recording cylinder 8, which rotates in the direction of the arrow B, 
whereby the peripheral speed of the recording cylinder corresponds to the 
speed of the slide 11 in the direction of the arrow A. Due to the image 
reversal by the mirror 5, the image shift at the scale 1:1-producing 
raster objective 4 corresponds likewise to the peripheral speed of the 
recording cylinder 8 so as to produce a non-blurred reproduction of the 
original 3 onto the surface of the recording cylinder 8. A corona charging 
device 15 for uniformly charging the recording cylinder 8 is arranged 
upstream of the illuminating location, as considered in the direction of 
rotation of the cylinder 8. An infrared radiation device 16 provides for 
the regeneration of the photoconductive layer on the recording cylinder 
after such rotation of the same. 
A dielectric band 17 serving as an intermediate recording carrier is 
arranged beneath the path of the recording cylinder 8. The dielectric band 
17 is guided over an span rolls 18, 19 and 20. The peripheral surface of 
the rolls 18 and 20 are in a known manner slightly crowned, so that the 
band 17 may not laterally move. The band-shaped recording carrier, which 
for instance consists of a plastic film of 10-20 mm thickness, is driven 
over the span roll 20. For this purpose, the shaft 21 of the span roll 20 
is driven by means of a pulley 23 which is connected by a roll or cable 22 
with a pulley 125 mounted on the driven shaft 24. The pulley 125 may be 
connected at the suitable moment to the shaft 24 for rotation therewith by 
means of an electromagnetic coupling 127, which in turn is connected by 
conduits 128 and 130 to the control unit 25. 
The band-shaped intermediate recording carrier 17 is guided by metal guide 
sheets 27 on the slide 11 in order to maintain during the charge 
transmission, which for instance is produced in a known manner as 
disclosed in U.S. Pat. No. 2,982,647, by means of the corona discharge 
device 28, the necessary small distance between band 17 and the cylinder 8 
in an exact manner. In order to permit the recording cylinder 8 to roll 
without slipping on the recording carrier 17 during the transmission of 
the charge image, the latter has to remain at a standstill during the 
scanning and transmitting process. 
After transmitting of the charge image, the recording carrier 17 is moved 
in the direction of the arrow C. The slide 11 is at the same time returned 
to its starting position by means of a rope 29 guided over guide rolls 
30-32 and a pulley 44 on the shaft 21 connectable thereto by an additional 
magnet coupling 140 connected by the conduits 129 and 141 to the control 
unit 25. The slide 11 is thereby moved with the same speed as the 
intermediate recording carrier 17 so that the recording cylinder 8 during 
the return movement of the slide 11 contacts the recording carrier 17 only 
with a single line contact, so as not to disturb the transmitted charge 
image, and in order not to transmit charge particles onto the following 
portion of the recording carrier 17. The recording carrier is freed, 
before entering the charge transmitting stretch indicated by the two 
arrows D and E, of any residual charge, thus electrically neutralized, by 
two corona discharge devices 34 and 35 operated by alternating current. 
The distance between the arrow F and D indicates the lead distance which 
has to be passed through until the first surface portion of the recording 
carrier 8, which is charged from the corona charging device 15 and 
according to the image discharged by the raster objective 4, comes into 
contact with the recording carrier 17. 
The further processing of the charge image transmitted to the recording 
carrier 17 proceeds in the usual manner. For this purpose, a magnet 
developing device 36, a paper stack 37 with a strip roll 38, a 
transmitting and take-off recording device 39 and 40, a quick fixing 
device 41, a receiving stack 42 and a scraper cleaning device 43 with a 
toner return spiral 45 are provided in the usual manner. The thereby 
resulting advantage with the arrangement according to the present 
invention is that, by the mentioned operating processes, especially by the 
scraper cleaning device, the sensitive and expensive selenium layer of the 
recording cylinder 8 is not mechanically stressed, but such stresses are 
transmitted only to the plastic band 17. The recording cylinder 8, which 
does not come into contact with the powder image, needs therefore 
eventually to be exchanged only at relatively long time intervals. 
The distance between the original 3 and the intermediate recording carrier 
17 is, due to the intermediate recording cylinder 8, even when the latter 
makes only one revolution per image length, only slightly enlarged with 
respect to directly copying raster copying systems. The constructive 
expenditure is thereby essentially smaller than in book copying devices 
with the usual equalizing mirrors. 
FIGS. 2 and 3 illustrate an arrangement in which, besides the first at a 
scale 1:1 reproducing raster copying system 4, a second raster copying 
system 45 is provided, which for instance copies the original at the scale 
1:.sqroot.2. For simplification reasons, the last lens before the 
reversing mirror is constructed in the copying system 45 as a lens 46 
combined with a mirror surface. 
As can be ascertained from FIGS. 4 and 5, the reproduction scale of a 
raster projection system M is equal to K/B, and is given by 
EQU m=b/a.multidot.d/c, 
that is, any desired reproduction scale can be obtained by any combination 
of the distances a-d. Thus, for instance it is possible to make the 
distance d substantially equal to the distance c and to choose both 
dimensions in such a manner as to bridge a relatively large distance to 
the rerecording carrier, whereby a desired reproduction scale is obtained 
solely by suitable choice of the distances a and b. However, it is also 
possible, as shown in the illustrated example, to choose the distance a 
substantially equal to the distance b, and to produce the desired 
reproduction scale by the relationship of the distances d and c. 
On the other hand, the lattice constants or parameters of the individual 
raster planes have to be chosen in such a manner that the central rays of 
the partial systems of the raster reproduction system meet at a projection 
point P, which is spaced at the distances e and f respectively from the 
plane of the original and the plane of the intermediate recording carrier, 
as shown in FIG. 5, and which satisfy the equation 
EQU m=f/e. 
In the case of a 1:1 reproduction, the projection center P.sub.ml is at 
infinity, and the overall length of a 1:1 reproduction system can be 
chosen so small as is possible with respect to the arrangement of the 
illumination device. For other reproduction scales, the overall length 
l.sub.2 is to be chosen in such a manner that the angle .alpha. of the 
central ray at the edge of the reproduction system becomes not too great. 
Therefore, the overall length of an enlarging or a reducing reproduction 
system is usually to be chosen slightly greater than the overall length of 
a 1:1 reproduction system, so that it is advisable to arrange the lattice 
system closer to the recording cylinder and to guide the rays of the other 
system around the 1:1 reproduction system. 
The changeover between the two reproduction systems 4 and 45 is made 
possible in that the reversing mirror 61 is mounted on a tilting lever 47 
and in that a tiltable shutter 48 is provided which covers one of the 
reproduction systems, and which is connected by a pin-and-slot connection 
47a, 48a with the tilting lever 47. The tilting lever 47 is moved as will 
be described later on by means of a push rod 49. 
In order to assure that the peripheral speed of the recording cylinder 8 
corresponds to the chosen reproduction scale, two racks 49 and 50 are 
provided in the embodiment shown in FIGS. 2 and 3, which alternatingly can 
be brought into meshing engagement with a gear 52 or a gear 53 mounted on 
the shaft 51 of the recording cylinder 8 for rotation therewith. The 
engagement of the two racks 52 and 53 with the respective gear 52 or 53 is 
controlled by means of tilting levers 55 tiltably mounted on the side wall 
54 of the housing, and which are connected to each other by a rod 56. A 
pin 57 at the bottom end of the push rod 49 abuts under the influence of a 
tension spring 58 onto the bottom face of the rack 49, so that during 
downward movement of the latter, or during the upward movement of the rack 
50 which controls the 1:1 reproduction, the tilting mirror 61 is moved 
into the path of the rays of the reproduction system 4 while the 
reproduction system 45 for the other reproduction scale is covered by 
means of the shutter 48. 
Since the relative speed between the recording cylinder 8 and the 
intermediate recording carrier 17 changes with the change of the 
reproduction scale, the recording carrier 17 is, in the embodiment shown 
in FIGS. 2 and 3, sliplessly connected with the movement of the recording 
cylinder 8. For this purpose, a sprocket wheel 59 is coaxially fixed, as 
best shown in FIG. 3, to one end of the recording cylinder 8, which 
engages in corresponding perforations provided along one edge of the 
recording carrier 17. Proper engagement between the sprocket wheel 59 and 
the perforations in the recording carrier 17 is assured by a counterwheel 
60 turnably mounted on the slide 11. Evidently in this case all other 
drive connections of the recording carrier 17, that is the drive 
connection of the recording carrier 17 by means of the pulleys 125 and 33 
as described in connection with the embodiments shown in FIGS. 1 and 6, as 
well as the drive connection with the respective racks 49 or 50, have to 
be disconnected from the recording carrier 17, which, with the exception 
of a reproduction at a scale of 1:1, does not remain any longer at 
standstill. As soon as the drive movement of the recording carrier 17 by 
means of the shaft 24, the coupling 107, the pulley 125, the rope 22 and 
the pulley 33 and roll 20 starts, the racks 49 or 50 must be disconnected 
from the respective gear in order to avoid a redundancy in the 
determination of the drive relations. 
The tilting levers 55, which selectively bring the racks 49 and 50 into and 
out of engagement with the gears 53 and 59, are actuated by magnets 131 
and 132 which are connected by conductors 133-135 with the control unit 
25. The magnets 131 and 132 act on a common rod 136 which carries a pin 
136a engaging in a slot provided on an arm 56a projecting laterally from 
the rod 56. One of the tilting levers 55 is further connected to one end 
of a return spring 138 which is connected at the other end to a stationary 
pin 137 and which holds when neither of the magnets 131, 132 is energized, 
the tilting levers 55 in an intermediate position in which both racks 49 
and 50 are out of engagement with the corresponding gears 53 and 59. 
The return movement of the slide 11 is produced as described in connection 
with the embodiment shown in FIG. 1. During this return movement of the 
slide it is not necessary to interrupt the drive connection of the carrier 
17 with the sprocket wheel 59. 
The further processing of the latent image is carried out in the same 
manner as described in connection with the embodiment shown in FIG. 1. 
If in the embodiment illustrated in FIGS. 2 and 3 the length of the 
recording cylinder 8 and the length of the transparent support plate 2 are 
chosen in such a manner that originals of the size A3, that is 
297.times.420 mm (according to German Industrial Norm DIN 476), may 
lengthwise be placed on the transparent support plate 2, then it is 
possible to produce the following copying operations, provided that the 
respectively correct paper formats are arranged in the stack 38 and that 
the control device 25 correctly controls the movement of the slide 11 and 
that of the recording carrier 17: 
copying at a scale of 1:1 an original of the dimensions according to DIN A4 
(210.times.297 mm) placed in transverse direction on the transparent plate 
2 on a sheet of equal size taken in transverse direction from the stack 
37; 
copying at a scale of 1:1 a sheet with the dimensions DIN A3 (420.times.297 
mm) placed in longitudinal direction on the transparent plate 2 on a 
corresponding sheet taken in longitudinal direction from the stack 37; 
copying at a reduced scale of 1:.sqroot.2 a single sheet of the dimensions 
DIN A3 placed in longitudinal direction on the transparent plate 2 or two 
sheets of the dimensions DIN A4 side-by-side in transverse direction on 
the transparent plate 2 on a single sheet of the dimensions DIN A4 taken 
in longitudinal direction from the stack 37. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
electrostatic copying devices differing from the types described above. 
While the invention has been illustrated and described as embodied in an 
electrostatic copying device which includes a recording cylinder on a 
slide movable with respect to an intermediate recording carrier 
constituted by an endless dielectric band and a transparent support plate 
on which the original to be copied is to be placed, it is not intended to 
be limited to the details shown, since various modifications and 
structural changes may be made without departing in any way from the 
spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features, that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.