Copying machine with original carriage moving device

In a copying machine having a movable carriage 5 for carrying the original, the correct velocity ratio between the carriage and the drive shaft 18 which advances the photosensitive sheet 21 (or photosensitive drum) is established by driving the carriage from a shaft 25 at overspeed through a friction clutch 38 and limiting the carriage velocity to the correct value by a coupling (rack 32, gears 40,43, one-way clutch 29) between the carriage 5 and the drive shaft 18. The correct velocity is thereby maintained irrespective of wear and tolerances in the drive to the carriage and the carriage guides.

BACKGROUND OF THE INVENTION 
1. Field of the invention. 
The present invention relates to a copying machine with a device for 
imparting motion to the carriage carrying the original, in particular, to 
a device for establishing the correct velocity of the carriage. 
2. Description of the prior art 
It is known, for example from U.S. Pat. No. 3,900,256, for the original 
which is to be reproduced to be located on a carriage having a transparent 
plane surface, which is transported over a scanning slit arranged 
transversely with respect to the motion of the carriage, so that a 
transverse strip of the original is illuminated. The corresponding image 
is transmitted through a fixed optical system which is located below and 
adjacent to this slit on to a photo-sensitive element which is moved at a 
velocity substantially equal to, or is kept at a constant ratio with 
respect to the velocity of the carriage. 
The photosensitive element may be a cylinder having a photoconducting layer 
on its outer surface which is electrostatically charged and on which the 
latent electrostatic image is formed, to be developed and transferred onto 
a copy of page of plan paper, or the copy sheet itself may have one face 
coated with a photoconducting material which is electrostatically charged 
and, after exposure to the image of the original, carries a latent image 
which is developed using developing powder or liquid and fixed on the copy 
sheet, as is known in the Electrofax copying process. 
Whatever the type of process used and consequently the type of 
photo-sensitive element used, copying machines which employ a movable 
carriage do suffer from the disadvantage that whilst the motion of the 
photosensitive element is taking place, at a constant velocity, at least 
during exposure to the luminous image, the velocity of motion of the 
carriage is not constant to the same degree, both as a result of play in 
the parts providing for transmission and conversion of the rotational 
movement of a drive shaft to a translatory motion of the carriage, and a 
result of play, wear, and irregularities in the guides on which the 
carriage slides. 
Strict constancy of the velocity ratio between the carriage and the 
photo-sensitive element is absolutely essential in order to ensure that 
the image of the original is transferred to the photo-sensitive element 
without any geometrical distortion. 
Electronic control systems for providing constancy of the carriage velocity 
suffer from the disadvantage of being too expensive, all the more so 
because the use of a movable carriage for transporting the original is a 
characteristic of less expensive copying machines, namely those machines 
which fall in the medium to low price range of the market for reprographic 
machinery. 
SUMMARY OF THE INVENTION 
The object of the invention is consequently to provide a copying machine 
comprising a drive element for advancing a photo-sensitive element at a 
first constant velocity in an exposure region, and a carriage for 
transporting the original at a second constant velocity along a scanning 
path, whereby the image of the original is transferred on to the 
photo-sensitive element. The invention is characterized by carriage drive 
means tending to drive the carriage at a velocity exceeding the second 
velocity, a coupling between the carriage and drive element limiting the 
velocity of the carriage to the second velocity, and a device allowing 
slip in the carriage drive means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the drawing, the carriage 5 carrying the original is slidable on 
ball-bearings 9 on guides 7 which are fixed to the frame 8 of the copying 
machine. For semplicity the term carriage is used herein to denote the 
member which carries and moves the original, regardless of whether the 
path of movement is rectilinear or not. The transparent illuminating 
surface 6, an illuminating window 11 is provided, through which a strip of 
the original is illuminated and the image of the strip is focused, using 
an optical system 14 which is shown diagrammatically in the drawing, on to 
an exposure window 15. Below and adjacent to the exposure window 15, a 
pair of drive rollers 16, 17 on shafts 18 and 19 is designed to advance a 
copy sheet 21 having its upper face coated with a photoconducting 
material. The image of the strip of original is projected through the 
exposure window 15 on to the sheet 21 and, after subsequent developing and 
fixing, the finished copy of the original is produced, as is known for 
example from the Electrofax copying process which is described in the U.S. 
Pat. No. 3,900,256 mentioned above. 
The roller 16 is driven from a drive shaft 22 via a toothed wheel 23 on the 
shaft 22, a toothed wheel 24 on shaft 18 and a toothed belt 28 which 
couples the two wheels 23 and 24. 
The carriage 5 has racks 31 and 32 rigidly fixed to it. Using rack 31, the 
carriage has its translatory motion imparted to it from a drive shaft 25 
via a toothed wheel 33 on the shaft 25, a toothed wheel 34 which is free 
to rotate on a shaft 35 and is coupled to the wheel 33 by a toothed belt 
36, a friction clutch 38 of known type designed to transmit the motion of 
the wheel 34 to the shaft 35 by virtue of friction coupling between the 
disc 38a which is rigidly fixed to the wheel 34 and the disc 38b which is 
rigidly fixed to shaft 35, an intermediate clutch plate 38c being located 
between the two discs, and a toothed wheel 39 on the shaft 35 and which 
engages with the rack 31. 
During the exposure of the copy sheet to the image of the original via the 
illuminating window 11 with the optical system 14 and the exposure window 
15, in which the carriage is caused to advance in the direction of arrow 
50 and the copy sheet 21 is caused to advance in the direction of arrow 
51, the drive shafts 22 and 25 rotate in the same clockwise sense and at 
the same angular velocity, whilst the diameters and the tooth numbers of 
the toothed wheels are such that the rectilinear velocity imparted to the 
carriage 5 is slightly greater than the peripheral velocity of the drive 
roller 16. By way of example, the wheels 23, 24 and 33 may have the same 
diameter and the same number of teeth Z=14, while the wheel 34 has a 
smaller number of teeth Z=13 and the wheel 39 has the same effective 
diameter as the roller 16, as a result of which if VO is the peripheral 
velocity of the roller 16 then VI=(14/13) VO is the velocity of 
translation of the carriage 5, assuming that there is no slipping between 
the discs 38a and 38b of the clutch device 38. 
However, a toothed wheel 43 is further provided, which is free to rotate on 
shaft 18 and is identical in diameter and tooth number to the wheel 39, 
and this is coupled to the rack 32 by means of idler wheel 40, which is 
free to rotate on a shaft 41. The rack 32 consequently imparts, during the 
exposure stage, an anti-clockwise rotation at a peripheral velocity equal 
to that of the carriage 5, to the wheel 43. 
The wheel 43 has a device 29 fixed to it which provides unidirectional 
transmission of the motion between the wheel 43 and the shaft 18; such a 
device is known as a one-way clutch or a free-wheel. The device 29 
connects the wheel 43 to the shaft 18 when the wheel 43 rotates clockwise 
and this prevents the wheel 43 from having a peripheral velocity of 
rotation which is greater than the velocity VO of the roller 16. On the 
other hand, the device 29 allows the wheel 43 to idle on shaft 18 when the 
wheel 43 rotates anticlockwise. 
Consequently, during the exposure stage, the effect of the one-way clutch 
device 29 is to cause the wheel 43 to brake the motion of the carriage 5 
and keep its velocity down to the value VO. There is consequently 
continuous slip between the disc 38a which is driven at a velocity 
VI=(14/13) VO and disc 38b which is driven, as a result of the limiting 
action referred to above, at the velocity VO. Consequently, any possible 
variations in velocity in the transmission of drive to the carriage, as a 
result of the causes mentioned above, are compensated for and are 
reflected in greater or lesser slip between the discs 38a and 38b of the 
clutch device 38, whilst the carriage maintains a velocity of translation 
which is substantially constant and equal to the value VO. 
At the end of the exposure stage, when the copy sheet has left the exposure 
region and is no longer engaged between rollers 16 and 17, the rotation of 
the drive shaft 25 is reversed and the velocity of rotation is trebled as 
a result of which there is rapid travel of the carriage in the reverse 
direction from the arrow 50 until the rest position is reached, the wheel 
43 now rotating freely on the shaft 18 so that there is substantially no 
slip between the discs 38a and 38b of the clutch device 38. 
In one modification of the device described above, the shaft 18 may carry a 
photoconducting drum as is used in electrophotographic copying machines 
using plain paper, in place of a drive roller for a copy sheet of coated 
paper, the image of the original being developed on the drum for 
subsequent transfer on to a sheet of plain paper. 
According to another modification, the various parts constituting the 
transmission could be dimensioned in such a way as to maintain the 
velocity of the carriage during the exposure stage at a constant ratio 
with respect to the velocity of the photo-sensitive element, rather than 
at a velocity which is equal to it, so as to provide for enlargement or 
reduction of the copy with respect to the original. 
The device described above is not limited to use in the field of 
electrophotography but can be used in fields of photocopying where there 
is a problem of keeping constant the relationship between the velocity of 
the original and that of a photo-sensitive element.