[0001] The present invention relates to a plant for printing web materials, such as lengths
or runs of cloth.
[0002] Known in the art are plants in which the web material to be printed is fastened to
a feed belt to be lead to several printing stations in succession, each station printing
one of the desired colours on the fabric, for example.
[0003] Positioning of the web under each printing screen in the different stations (or in
the same station for several passages) must necessarily reach the highest degree of
precision in order to ensure alignment of the images as they are printed and an exact
colour matching.
[0004] In addition to being necessary to stop the feed belt under the printing screen in
a very precise manner, it is also required that the belt while travelling between
the different stations should not be subjected to side skiddings that would cause
a transverse misalignment of the impressions.
[0005] In order to limit side skiddings and try to keep the belt at its optimal position
relative to the printing screen which is fixed on supports, several devices have been
developed for guiding the belt sideways, which consist of side shoulders for example,
on which the belt edges rest and slide. Although increasingly more complicated devices
have been suggested in an attempt to keep the belt in place, the reached precision
is in any case relatively poor and this represents a limit to the quality of the obtainable
impressions.
[0006] It is a general object of the present invention to obviate the above mentioned drawbacks
by providing a printing plant ensuring a precise mutual positioning between the printing
screens and web material to be printed.
[0007] In view of the above object, in accordance with the invention, a plant for printing
web material has been devised which comprises a conveyor belt for moving the web material
to at least one printing station in turn comprising a printing screen and printing
means for printing of the screen on the web material, characterized in that the screen
is supported by power-driven means for moving it in the station in directions parallel
to the belt surface, a control device detecting a mutual shifting at least in one
direction between the printing position on the web and the screen and driving the
power-driven movement means of the screen to reduce this shifting.
[0008] For better explaining the innovatory principles of the present invention and the
advantages it offers over the known art, a possible embodiment of the invention practising
said principles will be given hereinafter by way of non-limiting example with the
aid of the accompanying drawings. In the drawings:
- Fig. 1 is a fragmentary diagrammatic plan view of a printing plant according to the
invention;
- Fig. 2 is a fragmentary diagrammatic and partly sectional view of part of the plant,
shown in Fig. 1;
- Fig. 3 is a partial view in section taken along line III-III in Fig. 2;
- Fig. 4 is a sectional view taken along line IV-IV in Fig. 2.
[0009] Referring to the drawings, diagrammatically shown in plan view in Fig. 1 is a plant
according to the invention and generally identified by 10, which comprises a conveyor
belt 11 driven to bring a fabric web 13 or similar web material under at least one
printing station 14. Each station 14 comprises a frame 15 on which support means is
provided for a known printing screen 17. The station is comprised of known printing
means, such as a doctor blade 18, not shown in detail as it can be easily imagined
by a person of ordinary skill in the art.
[0010] According to the invention, the screen is supported on the fixed frame 15 by supports
that are mounted on frame elements movable in directions parallel to the belt plane.
[0011] For example, the frame is movable at least in one direction transverse to the belt
by means of a motor 19. A sensor 20 is disposed integral with the screen supports
to be moved therewith, and it detects marks 21 integral with the web to be printed
so as to be a reference for the transverse position of the web. The reference marks
may consist for example of graphic elements having an edge parallel to the web edge
and being greatly contrasted, so that an easy detection of the same by the sensor
is enabled, said sensor thereby utilizing such an edge as an indicator of the web
side position.
[0012] The graphic elements may be a sequence of black rectangles on a white background
or the like, for example, printed on a narrow pressure-sensitive tape 73 applied to
the belt 11 at margin of the web to be printed, the web being fastened to the belt
so that it is integral with the reference marks. In the known art such a reference
tape or strip is usually employed for detecting the longitudinal position of the web
and operating stopping of the belt to the printing position.
[0013] The sensor 20 and side-displacement motor 19 are connected to a control device 22,
consisting of a known electronic circuitry for example, advantageously provided with
a microprocessor. Such a device is substantially known in the art and therefore will
not be herein further described or shown as it can be easily assumed by a person skilled
in the art, above all in the light of the following description relating to the plant
operation.
[0014] The device 22 receives information about the side position of the web from sensor
20 and drives the motor 19 in operation to translate the screen sideways, so that
the correct relative side position between the screen and web to be printed is maintained.
In this manner, the presence or not of small side skipping of the belt on running
of same is no longer of importance, the screen being shifted sideways so as to compensate
for any belt skipping.
[0015] As described in more detail in the following, the printing screen 17 supporting means
can be also advantageously comprised of translation means for moving the screen in
the belt running direction. For driving of said translation means, a connection between
the latter and the control device 22 is carried out. The reference marks 21 in this
case are made in such a manner that they provide edges directed transversely of the
web edge, thereby offering a detecting element for the web position in the running
direction as well.
[0016] In this way, the control device 22 detects the reference mark passage by means of
sensor 20 and when it detects passage relative to the stop position for printing,
it stops the belt 11. Typically, due to inertias and/or to its own elasticity, the
belt will surpass the desired stop position. At this point, the control device, still
using the edges of marks 21 as a reference, operates the transverse-translation means
to centre the screen relative to the belt side skippings and the longitudinal-translation
means to bring the screen exactly in register with the longitudinal printing position
on the web, compensating for the belt stop error.
[0017] For better comprehension of the invention, a description of a possible embodiment
of the screen movement means is given.
[0018] In this embodiment, the screen supports comprise one side-bar element or front-bar
element 23 and a second side-bar element or rear-bar element 24 parallel to each other
and to the belt running direction, from which fitting groups for the screen denoted
by 25, 26 and 27, 28 respectively, project, which groups are directed towards each
other and the belt centre, so that opposite edges of the screen may rest thereon and
be connected thereto.
[0019] As best shown in Fig. 2, the front-bar element 23 comprises a section bar 29 supporting
several mechanisms protected by a housing 71, 72. The bar carries the fitting pieces
25, 26 and is connected at the ends to carriages 30, 31 sliding along respective slide
guides 32, 33 transverse to the belt. Motor 19 is integral with frame 15 and causes
rotation of a worm screw parallel to guides 32, 33 and engaging with a nut screw 35
integral with carriage 31.
[0020] In this manner, on rotation of motor 19, bar 29 moves transversely of belt 11.
[0021] The bar ends are connected with carriages 30, 31 by interposition of slidable inserts
36, 37 received in complementary seatings formed in the bar ends. A motor 38 is fastened
to the bar and causes rotation of a worm screw 39 on which a nut screw 40 integral
with the insert 37 slides, so that, upon command of motor 38 (powered by the control
device 22) the bar can slide axially to itself and therefore in a direction parallel
to the belt running direction.
[0022] The rear bar 24, instead, is freely slidable transversely of the belt 11 by means
of end carriages 41, 42 which run idly along respective slide guides 43. 44. The rear
fitting pieces 27, 28 are mounted freely slidable along bar 24. In this manner, when
the screen 17 is fastened to the respective supports 25, 26 and 27, 28, the transverse
and longitudinal movements of the front bar 23 also cause shifting, by means of the
screen, of the bar 17 and supports 27, 28 so that the screen is firmly supported on
either side during movement.
[0023] Turning back to Fig. 2, the fitting means 25 and 26 are each formed of a respective
carriage 45, 46 slidable in a guide 47 along the bar. Carriages 45, 46, in mirror
image relationship, carry rests 48, 49 on which the screen 17 edge comes to lie.
[0024] In addition, projecting from each carriage is an automatic fitting mechanism 50,
51 for complementary coupling elements on the screen. For example, the fitting mechanisms
comprise forks 52, 53 to be sideways fitted to mushroom-shaped pins 74 projecting
from the screen 17, as diagrammatically shown in chain line for fork 52 in Fig. 2.
[0025] As clearly shown in connection with fork 52, forks 52, 53 are pivoted at 54, 55 to
be moved towards an abutment 56, 57 by means of a lever mechanism operated by a thrust
action, acting in a direction parallel to the bar 29, of a screen portion supporting
the mushroom-shaped pin against rollers 62, 63.
[0026] As clearly shown in Figs. 3 and 4 as well, an electric motor 58 operates a pignon
gear 59 meshing with an opposite pair of superposed racks 60. 61, parallel to the
bar 29. Rack 60 has one end connected to carriage 45, whereas rack 61 has one end
connected to carriage 46. On operation of motor 58 (electrically powered by the control
device 22) the racks run in opposite directions, so that the carriages move close
to or away from each other.
[0027] In use, screen 17 is laid on rests 48, 49 whereas carriages 45, 46 are disposed between
a pair of mushroom-shaped pins projecting from the screen edge. Then motor 58 is operated
to move the carriages apart from each other and lead the forks 52, 53 (directed opposite
to each other) to be fitted under the mushroom heads of the pins.
[0028] A further movement of carriages 45, 46 brings the pin supports to push against rollers
62, 63, so that the forks move towards the abutments 56, 57 and lock the pin heads
against the abutments themselves. Thus the screen is firmly clamped to the bar 29
and the control device 22 can move the screen in a precise manner, as above said.
[0029] As shown in Fig. 2, a feeler element 64 may be also provided on the front bar 29,
for detecting the exact position of screen 17 along the bar 29. To this end, the feeler
element 64 runs on a worm screw moved by an electric motor 67 by means of a transmission
gear 68. On actuation of motor 67 by the control device 22, the feeler element moves
parallelly to the bar 29 until it touches an abutment present on the screen 17, as
shown in Fig. 1. For detecting the exact instant at which contact occurs, the worm
screw is supported for a small axial movement against the thrust of a spring 69. When
contact occurs, the feeler element stops against the screen and the worm screw, as
a result, moves against the thrust of the spring thereby operating an end-of-stroke
microswitch 70 signalling the occurred contact between the feeler element 64 and screen
17 to the control device 22. Thus the control device detects the exact stop position
of the screen on the bar.
[0030] At this point it is apparent that the intended purposes have been achieved, a printing
plant being provided which has a precision positioning mechanism for the screen relative
to the belt, so as to avoid printing errors due to side skippings of the belt for
example, and/or stop errors of the belt. The relatively light weight of the screen
and screen supports will enable very quick positionings.
[0031] Obviously, the above description of an embodiment applying the innovatory principles
of the present invention is given for purposes of illustration only and must not be
considered as a limitation of the scope of the invention as herein claimed.
[0032] For example, the structure of the fixed frame and movable frame for screen fastening,
as well as the mutual movement means, can be different from those shown. In addition,
sensor 20 may be made as any type of known sensor enabling exact identification of
the web position based on the references thereon. While the sensor has been shown
as a single device for the sake of simplicity, generally it will consist of two separated
sensors for detection of the transverse and longitudinal positions.
[0033] Finally, while the apparatus according to the invention can be provided to advantage
with both transverse and longitudinal screen movements to compensate for positioning
errors in both directions, should compensation for positioning errors be deemed necessary
only in one direction, it would be possible to equip the apparatus with translation
means for movement in that direction alone.
1. A printing plant for web material comprising a conveyor belt (11) for moving the web
material (13) to at least one printing station (14), in turn comprising a printing
screen (17) and printing means (18) for printing of the screen on the web material,
characterized in that the screen is supported by power-driven means (23, 36, 37, 38)
for moving it in the station in directions parallel to the belt surface, a control
device (22) detecting a mutual shifting at least in one direction between the printing
position on the web and the screen and driving the power-driven movement means (23)
of the screen to reduce this shifting.
2. A plant according to claim 1, characterized in that the control device (22) detects
shifting by means of a sensor (20) identifying reference marks (21) integral with
the web.
3. A plant according to claim 1, characterized in that the power-driven means comprises
first translation means (23) for moving the screen in a direction transverse to the
belt.
4. A plant according to claim 1, characterized in that the power-driven means comprises
second translation means (36, 37, 38) for moving the screen in a direction longitudinally
of the belt.
5. A plant according to claim 1, characterized in that the first translation means (23)
comprises frame elements (23, 24) on which the screen is mounted, the frame elements
(23, 24) being driven so as to slide along guides (32, 33, 43, 44) transverse to the
web.
6. A plant according to claim 5, characterized in that the frame elements comprise a
first (23) and a second (24) bars disposed on opposite sides of the screen (17) parallelly
to the belt running direction.
7. A plant according to claim 6, characterized in that the first bar (23) and second
bar (24) are supported at the ends by carriages (31, 31; 41, 42) for a powered movement
along respective transverse guides (32, 33; 43, 44).
8. A plant according to claim 7, characterized in that the first bar (23) is connected
to an electric motor (19) for its movement along the respective transverse guides
(30, 31) and the second bar (24) is freely slidable along the respective transverse
guides (41, 42).
9. A plant according to claim 2, characterized in that the reference marks (21) consist
of a plurality of marks aligned along a side edge of the web (13).
10. A plant according to claim 9, characterized in that the marks (21) are rectangles
having contrasted edges, one transverse position of the web detected by sensor (20)
being defined by the position of a side edge of the rectangle, and one longitudinal
position of the web being defined by the position of a leading or trailing edge of
the rectangle with respect to the movement direction.
11. A plant according to claim 9, characterized in that the marks (21) are printed on
a pressure-sensitive tape (73) applied to the belt along a side edge of the web.
12. A plant according to claims 4 and 7, characterized in that the first bar (23) is supported
on the respective end carriages (30, 31) by interposition of joints (36, 37) sliding
in a direction longitudinal to the belt to embody said power-driven longitudinal-translation
means.
13. A plant according to claim 6, characterized in that the first bar (23) supports the
screen (17) by interposition of fitting groups (25, 26) of the screen, which are power-driven
to slide along the first bar for fitting of complementary coupling elements (74) disposed
on the screen.
14. A plant according to claim 13, characterized in that the fitting groups (25, 26) comprise
fork-shaped elements (52, 53) directed in opposite directions, parallelly to the sliding
direction of the fitting groups for coupling with the complementary elements on the
screen, embodied by pins (74) having mushroom-shaped heads.
15. A plant according to claim 13, characterized in that each fork-shaped element (52,
53) is movable by means of a linkage (50, 51) to clamp a mushroom-shaped head (74)
between itself and a facing abutment (56, 57), said linkage being driven by a thrust
action of a portion of the screen (17) against one operating end (62, 63) of the linkage
(50, 51) during sliding of the fitting group.
16. A plant according to claim 13, characterized in that the first bar (23) supports an
electric motor (58) having a pinion gear meshing with a pair of racks (60, 61) parallel
to the bar, one rack (60) having one end fastened to a fitting group (25) and the
other rack (61) having an opposite end fastened to the other fitting group (26), so
that on actuation of the motor (58) movement of the fitting groups (25, 26) takes
place in a synchronized manner in opposite directions along the bar.
17. A plant according to claim 5, characterized in that detection means (64, 70) is mounted
on the frame elements, for detection of the longitudinal position of the screen (17)
with respect to the frame elements.
18. A plant according to claim 2, characterized in that the sensors (20) are such positioned
that they move integrally with the screen.