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Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

[ EN ]


The subject of this invention is a method and apparatus for printing on sheet material such as w eb s o f t e x t i l e ma t e r i a l a n d s h e e t s o f p ap e r .

Various methods for the high speed printing of sheet material both in black and white and in colour have been proposed. one form of apparatus employing a Laser device includes a rotating mirror structure so arranged that the beam from a Laser directed on to the rotating mirror is caused to scan across a light sensitive printing drum while the
output of the laser is controlled by a computer to produce sensitized points on the printing drum in the form of a line of dots. The laser is so switched that the spacing of the dots in each scanning line is determined to form a line of the desired pattern, the pattern being built up by the addition of subsequent scanning lines of dots on the printing drum so that the lines of dots come together on the printing drum to delineate the pattern to appear on the web.
Toner, i.e. printing pigment, is then applied to
the printing drum and adheres to the points where the laser light has fallen on the drum so that as the drum is rotated in contact with the web the pattern is printed on the web. this device which so far
has been mainly or only used for printing on sheets of paper suffers from the disadvantage that because pf parallax and angularity effects at the ends of each scanning line distortion is introduced. To
overcome this difficulty another proposal has been to provide a continuous light source having its light directed as a line across a series of liquid crystal (LCS) units, each shutter unit being controlled by a control computer to be open or shut according to whether or not a beam of light is to be allowed to pass through at that point so as to provide a dot or a blank space at that point. In this device the light beams passing through the shutter units are not subjected to parallax or angularity effects so there is no distortion anywhere along each line of dots.

A disadvantage of the known apparatus using liquid crystal shutters is that the pattern is created by a continuous operation of successive line formation. Since every line has a different spacing of dots
from the dot spacing in the preceding line in the formation of most patterns the line of shutters has to be reset to a new configuration for each succeeding line of the pattern and even in forming repeat patterns each repeat is a completely fresh pattern-forming operation. As it is necessary in forming patterns of high quality to provide at least 120 dots per
cm it will be understood the rate of emission of
shutter control impulses by the controlling computer must be very high, at least 120 times the width of the web of material being printed in cm times the depth of the design in cm times the number of patterns to be reproduced per second. The rate at which the control impulses have to be applied by the control computer to the shutters for operation at commercial speeds of printing may thus be as high as 100 mHz for each printing colour. For colour printing at least found separate colour printing units are required, For high quality work even more colours are often required. Thus the control computer must be able to operate at a speed of at least 400 mHz and often cons i de rab l y faster. A computer able to operate at this speed is extremely expensive, possibly so
expensive as to r e n d e r the whole operation uneconomic.

It is an object of the present invention to provide a method and apparatus capable of printing on sheet material at commercially acceptable speeds yet using a low cost computer capable only of operating at low rates of impulse generation.

According to the invention a method of
printing paper or textile material by directing light on to a light sensitive printing surface through
electronically operated light shutter units and applying printing medium to the light sensitive printing surface whereby the printing medium adheres to the portions of the printing surface on which the light has fallen and then bringing the printing surface into contact with the material to be printed is characterized
by arranging the shutters in an array forming a two dimensional area disposed in proximity to the light sensitive surface and setting the shutters in a pre arranged pattern for passage or non-passage of light through the shutters of the array then applying light to whatever portion of the array is at any particular time adjacent to the light sensitive printing surface.

The light sensitive printing surface may
be a rotatable printing drum and the two-dimensional area constituting the array of shutters may be constituted by at least a portion of the surface of a second
and hollow control drum the axis of which is p a r a l l e l to the axis of the printing drum the light being
applied to that portion of the inner surface of said control drum which is for the time being adjacent
to the printing drum, said printing drum and said
control drum being arranged to rotate in opposite directions at the same peripheral speed.

A machine for printing sheet material according to the invention incorporating a rotatable light
sensitive printing drum arranged to be sensitized
to retain printing medium applied thereto at any
point on the surface where a beam of light falls
on that point on the surface, electronically operated shutter units operable to permit or block the passage of light therethrough to the printing drum, a light source arranged to apply light to the shutters and means for applying printing medium to the printing drum at a position where it can be retained at sensitized points is characterized in that the shutter units
are arranged to form at least a portion of the wall of a second and hollow control drum disposed parallel to the printing drum and arranged to rotate in a
direction opposite to that of the printing drum and at the same peripheral speed, the light projecting means being located within said control drum and
being arranged to project light against the light shutter units forming that portion of the wall of
.the control drum which is at that instant closest to the printing drum.

A practical embodiment of the invention
is illustrated diagrammatically in the accompanying drawing in which 1, 2, 3 and 4 denote hollow drums the wall of at least a portion of each of which is constituted by an array of electrically operated
light shutters 5, 6, 7 and 8 respectively. The hollow drums 1, 2, 3 and 4 contain within them light sources (not illustrated). 9, 10, 11 and 12 denote light sensitive printing drums each arranged with its axis parallel to the axis of the a s s o c i a t e d control drums 1, 2, 3 and 4, the light source inside the drums 1, 2, 3 and 4 being located to direct the light against the portion of the wall of the associated
drum 1, 2, 3 or 4 closest to the associated drum
9, 10, 11 and 12. Means (not shown) is provided
for directing printing medium (toner) of the appropriate colour against each drum. The printing drums 9,
10, 11 and 12 are in contact with the sheet 13 of material to be printed. A control computer (not
shown) is operatively connected to the individual light shutters of the arrays 5, 6, 7 and 8 to set open o r closed each individual shutter according
to the pattern to be printed.

In practice, the light sources within the control drums 1, 2, 3 and 4 direct light continually towards the shutter devices adjacent to the printing drums 9, 10, 11 and 12. Each shutter device if open allows a dot of light to pass through to the associated light sensitive printing drum or prevents light from passing through at the point of that particular shutter device. A pattern is thus built up on each printing drum as it rotates along with the associated control drum so that each printing drum carries on its surface an electrical pattern of the entire presentation of the design in a particular colour. Toner of that particular colour applied to each printing drum adheres to the printing drum at the electrified points and as the printing drum rotates the toner is transferred to the sheet of material to be printed 13.

The control computer sets up the entire pattern on each control drum 1, 2, 3, 4 by arranging for the shutters to be open or shut over the entire surface of the drum, the shutters being left in that position until that pattern is no longer required.

Each control drum is then illuminated by the associated light source and as each portion of the array of light shutters is brought successively across the associated light sensitive printing drum that portion of the pattern appears on the light sensitive printing drum in the form of sensitized spots to which printing medium applied to the drum adheres for transfer to the sheet 13 as the drum rotates. There is thus no question of a pattern having to be built up of individual dots applied fast enough to allow the printing to take place at normal commercial speeds and since the pattern setting operation requires to be done just once it can be set in advance before any printing is done at all by a comparatively s l ow and cheap control computer. Also by the method and apparatus of the invention the speed of printing is limited only by the normal mechanical li m i tat i ons of the app ratus.