CA1037508A

CA1037508A - Paper feeding device

Info

Publication number: CA1037508A
Application number: CA235,482A
Authority: CA
Inventors: Santo Caenazzo
Original assignee: Honeywell Information Systems Italia SpA
Current assignee: Bull HN Information Systems Italia SpA
Priority date: 1974-09-27
Filing date: 1975-09-15
Publication date: 1978-08-29
Also published as: FR2286003A1; SE7510719L; IT1022388B; GB1484216A; JPS5850873B2; AU8481675A; NL7509868A; SE403198B; FR2286003B1; DE2540598A1; CH587727A5; JPS5158129A

Abstract

ABSTRACT OF THE DISCLOSURE
The undersirable effects of the relative displacement of different sheets of a multisheet web which occurs as they are moved over a platen roller in a printer by sprockets engaging the web upstream and downstream of the platen roller are avoided by mechanically coupling the platen roller to the sprockets so that the former has a peripheral speed at least as great as that imparted to the web by the sprockets.
The mechanical coupling is preferably resilient.

Description

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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- ~ -:, ,~ , .
~ 20 ~ion of a prior art feed device; ~ ~ -.~ . :
< 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 ~- .
and two side plates of which one only is shown at 2 0 The printing mechanism is mounted on the frameg and in 37~C~8 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 ::. .. ~ , ., . , .. , ,. . - . i ~ . .: . . . . .. . . . .

~03~7~8 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 - 5 ~
.: , ~75~3 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~
.. .,; ~ : .
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, ~ ~.
-- 6 -- .

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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.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A printer provided with a platen cylinder and a paper feed device for advancing a continuous web through an arc of about 180° about said cylinder, the web being provided with sprocket holes on the edges, where in the paper feed device com-prises motor actuated sprockets disposed to engage said web both upstream and downstream of said platen cylinder, and a mechanical coupling between said sprockets and said platen cylinder to impart to said platen a peripheral speed greater than that imparted to the web by said sprockets.

2. A printer as claimed in Claim 1 in which said mechanical coupling comprises a resilient coupling.