Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a paper feed device for multiple
copy printers and more particularly for high speed impact printers,
teleprinters and likP equipment, used in data processing systems.
In such printers, a continuous papsr web having sprocket-
holes on the edges is commonly used as a printing mediumO
The movement of the paper web is ob-tained by means of
sprockets which engage with the paper perforation~ .
The sprockets are intermittently operated by means of es-
capement devices or preferably by means of stepping motors or low
inertia motors, so as to cause, on command, advance of the paper
web from a printing station every time a print line has been
impressed~
In order to assure adequate paper tension in proximity of
the printing station, two pairs of sprockets are generally used~
one of which is placed upstream of the printing station and the
other downstrea~. At the printi.ng station is a printing platan
in form o~ an idle cylinder~
Alternatively the paper web may wrap in an arc of about
180 around the platen cylinder and the same pair of sprockets
may engage the sprocket-holes both upstream and downstream of the
platen~ ~.
In the feed devices of this kind it has been found that ~ -
when a multi-sheet web is used to obtain multiple copies there
is relative shifting of the paper sheets which form the web.
This occurs particularly in the case of the sheet contact-
ing the platen
As a consequence, in the region of the downstream (relative
to the feed direction) sprocket, it often if not always occurs ~ c
that the sprocket holes tear, causing clogging of the feed
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mechanisrn and ian extreoely irrecJuli~r advance of the paper web.
The pre~ent invention has as its object the obviation of
such inconvenience and provides a paper feed device which is
xeliable, cheap and consistent in performance even where multiple-
copy webs are usedO
According to the invention these advantages are obtained
by mechanicall~ coupling the platen cylinder to the sprockets so
as to impart to it a peripheral velocity equal or slightly higher
than that of the sprocketsO
According to another feature of the invention the mechani-
cal coupling is achieved by means of elastic transmission means
so as to reduce the inertial couple applied to a motor which
actuates the sprockets.
These and other features will appear more clearly from the
following description of a preferred embodiment of the invention,
reference being had to the attached drawing, in which:
~ Figure 1 shows in perspective a printer provided with a
3 feed device according to the invention;
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Figure 2 illustrates the problems occurring in the opera- ~ -
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~ 20 ~ion of a prior art feed device; ~ ~ -
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< Figure 3 illustrates the operation of a feed device ac-
cording to the invention.
Referring to Figurs 1, a line printPr of the so-called
mosaic type is shown in perspective
The printer comprises a frameJ a print mechanism and a
feed mechanism~
s The frame in the exiample shown is built up from a base 1
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and two side plates of which one only is shown at 2 0
The printing mechanism is mounted on the frameg and in
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t~le ~xampl~ shown .it con~pris~s two guide ba.rs 3, 4 and a print
carriage 5 slidably mounted on said bars~ a printing head 6 being
mounted on the carriageO
The printing head shown in Figure 1 i9 of the type referred
to as a "needle-head" and it enables the printing of different
characters by combinations of dots obtained by tha selective
energization of different needles and transverse movement of the
carriage and printing headO However it is clear that different
printing devices may be usedO
Movement of the carriage is obtained by means of a flexible
drive cable 7, fixed to the carriage and wound on a driving pulley
8 and an idle pulley 9. The driving pulley 8 is fixed on the
drive shaft of a motor 10, which may be a stepping motor or a D~Co
low inertia motor so as to control the carriage and printing head
for movement in a continuous of intermittent way, in one direction
or the other depending on the mode oi. energization under the con-
trol of suitable electronic circuits~, Accordingly the printing
head moves along a generatrix of a platen cylinder 11 which is
freely rotatable on an axle 120 An ink ribbon 13 is interposed
between the printing head and the platen cylinder, the ink rib~
bon beiny drawn from a ~irst spool, not shown, and wound on a
second spool~ A printing medium 14, shown in dotted lines, is ~:
wound about cylinder 11 through an arc of about 180. ~;
The printing medium is a continuous web with lateral
sprocket holes, and may be composed by several superimposed sheets
of paper interleaved with carbon paperO AlternativelyJ pressure ~ :~
sensitive paper may be used or when printing other than by impact ~ .
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Eor instance the~nally heat-sensitive paper may be used, or other
material suitable for the printing method employed.
The feeding of the web 14 is obtained by means of the
mechanism of the present invention.
The mechanism comprises two sprockets, each being assemb~
lies co~pr~ ~g a belt (or chain) 15 and 16 re~pectively~ external-
ly provided with sprocket teeth such as 17 and 18, and int~rnally
provided with teeth which engage re~pectively with toothed wheels
19, 20 and 21, 220 The toothed wheels 20 and 21 are keyed to a
drive shaft 23 actuated by a stepping or low inertia motor 24
The toothed wheels 19 and 22 are mounted for free rotation on
axel 24. The toothed wheels 19 and 20, togethex with the sprocke-
ted belt 15, are axially located in a pre-established position by
means of a frame or cage~ not ~hownO This frame or cage, is also
used as a support for two pressure shoes, respectively an upper
shoe 26 and a lower shoe 270 The toothed wheels 21 and 22, to-
~ether with the sprockeked belt 16, are mounted in a frame which
allo~s their axial movement alon~ the shaft 23 and axle 25 and -
which supports two pressure shoes 28 and 29v By this arrangement :~
i~ is possible to adjust the distance between the two sprocket
asssmblies so as to match the width of the web~ The web engages
the sprockets, both beneath the latter where it is interposed be-
tween the sprockets and the lower shoes 27~ 29, as well as above
where it i~ interposed between the sprockets and the upper shoes :
26, 28
Tn this way~ the web is driven, in which ever direction
it moves> both upstream and downstream of the platen cylinder and ; .
the line printerO This is desirable in order to assure adequate
paper tension without resorting to braking devicesO This is
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furthermore cssential where bi-directional movement of t:he web
is de~ired in order -to rnake correctionq, or to plot diagrams,
iOe~ to use the printer as a "plotter~"
According to the invention~ the platen cylinder 11 is
mechanically coupled to the sprockets~ so that the procket
movement causes rotation of the cylinder. In this way the dis-
placement of the cylinder corresponds to -that of th~ web. The
mechanical coupling to the sprockets may be achieved by fixing
a grooved pulley 30 to the drive sha~t 23 and by coupling the
10 pulley to the cylinder by means of a belt 31.
To achieve the purposes of the invention it is required
that the peripheral speed imparted to the cylinder be equal or
preferably slightly greater9 than the sprocket driving speed~ as
discussed below. Therefore the pulley 30 has a diameter suitably
chosen relative to the diameter of the platen cylinder. Alter-
natively, as shown in Figure 1, the belt 31 engages an end portion
of the cylinder having a reduced diameter such, relative to the
diameter of the driving pulley 30, as to provide a peripheral
speed o the platen cylinder slightly greater than that of the
20 sprocketsO
~ Although posi~ive mechanical coupling such as is provided
t by toothed belts or transmission chains or gears may be used,
accor~ng to another feature of the invention the coupling is
obtained by means of a resilient belt9 for instance a rubber
belt~ This expedient provides many advantages~ on the one hand
it eliminates the need for belt tensioning devices and on the ~ -
other it permits minor adjustment of the distance between the
platen cylinder and the sprockets~ It is known that the re-
lative distance between the printing head and the pla~en must be
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adjusted depending on the thickness of the printin~ web, the
LmpreSSiOn strength required and the number of copies to be
printed~ Obviously this may be done by moving the printing headJ :
for instance by mounting the head on a slide, but preferably
this is achieved more simply by moving the platen cylinder re-
lative to the sprockets and the printing headO Another advantage
is achieved by this mean~ through the reduction of the distance
between the platen cylinder and the sprockets which compensates
in part for the longer mean path which a web of greater thick-
ness is compelled to follow around the cylinder. This factorwill be considered in more detail belowO
Another advantage of a resilient transmission is that it ~ :
reduces significantly the inertial torque applied by the platen
cylinder to the motor 24, thus permitting faster starting and
stopping of the mechanism with the same motor power.
The above matters will now be considered in more detail
with reference to Figures 2 and 3~ ]Figure 2 is a simplified side
view of a conventional feed device known in the prior art. The .
sprocket assembly ~0 advances a continuous web comprising a
plurality of superimposed sheetsO Only the inner sheet 50 and
the outer sheet 51 are shown, separated by a distance ~O The
web engages the sprocket teeth 18, both in a lower zone 52 and :`~
an upper zone 53, and wraps about freely rotating platen cylinder ~.-
11 through an arc of abou~ 180o The direction of advance is as ~:
shown by arrow Fl~
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In order to assure good print quality it is required that :: :
tha web make perfect contact with the platen cylinder 11 and
this is achieved by subjecting the web to an appreciable~ even
if slight~ tension~ .
In the rest condition, when the paper ig stationary, ~ ~.
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the tension i9 distributed uniformly over the whol~ portion of
the web between its points of engagement with the sprocket~
This web portion must have the same length both at the innermost
sheet and the outermost sheetO However, due to the thickness
of the paper, and due to its wrap around cylinder 11) which
involves a shorter wrapping arc for the innermost sheet the
innermost sheet is in practice not subject to tension, indsed
it will develop a wrinkle 54 at least at some point on its
lengthO
When the feed device is operated and due to the inertia
of the platen cylinder and to the friction between it and the
module, the distribution of tension is modified and becomes
greater in the portion indicated by 55 and lesser in the portion
indicated by 56. This results in the contact pressure between
the sheets of the web and between the web and the platen cylin-
der decreases as between the zone 57 and the zone 580 Therefore
relative shifting between the different sheets occurs more readi-
ly in the zone 58 than in the zone 57. On the other hand such - .
shifting necessarily occurs along the wrapping arc~ because the
length of the arc is diferent for the inner and the outer sheet. ~ :
The consequences of such shifting are that the platen
cylinder tends to transfer different length~ of the innermost and
outermost sheet through the wrapping arcJ and concentrates the
length of the untransferred paper between the lower traction ~:
zone 52 and the cylinder, in form of a wrinkle 54
The other and more serious consequence which derives from
this phenomenon is that the relative shifting of the sheets is
not corrected and therefore the web enters the traction zone 53 ~:
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with a relativ~ shift arnongst sheets, so that the sprocket holes
of the various sheet are out of register and therefore are sub-
ject to considerable stress as the sprocket teeth attempt to
correct the offsetO This cause~ tsaring of the paper and jamming
of the web~
In the apparatus of the invention~ however (see Figure 3)
the platen cylinder is mechanically coupled to the sprockets so
as to move with a peripheral speed at least equal to the speed
of the sprocketsO In consequence the movement of the platen -
cylinder lea~s that of the web causing a tension distribution in ;~
the web providing greater tension in zone 58 and lesser tension
in zone 57, This encourages the necessary and unavoidable re-
lative shiting of the different sheets of the web to occur in
zone 57 and the transfer of the wril~le 54 to the zone 59 between
the platen cylinder and the upper traction zone 53. In this way
the sprocket holes of the diffexent sheets are automatically re-
aligned in the region of the sprockets and malfunctioning and
paper tearing is avoided. ~ ~:
Additionally~ by this means, the effective tension in
the web in the zone 59 is reduced so that the risk of tearing
is further reduced, even when the tension in the web is sub- .: ;
stantially sustained by the outermost sheet alonea
According to another feature of the invention, the
leading action of the platen cylinder may be further increased -~
by adopting a transmission ratio such as to impart to the
platen cylinder a peripheral speed slightly higher than the
sprocket speed~ This results on one hand in a lesser tension
of the module in zone 59 and on the other hand it enables .:~ :
adoption of a resilient transmission. The utilization of a
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resilient tran~mission results in a certain hysteresis in
the acceleration of the platen cylinder during starting of
the drive, and in its deceleration during stoppingJ so that
the inertial torque applied to the motor is reduced compared
to that applied to a rigid transmission.
