Driven squeegee carriage and magnetic beam backup

A device for treating a web or the like adapted for screen printing including a magnetizable wiping roller or squeegee mounted on a working carriage, a printer's blanket carrying the web, a magnetic beam disposed below the printer's blanket, and rails rollably supporting the magnetic beam. The magnetizable wiping roller is urged towards the web through movement of the working carriage in the longitudinal direction of the printers blanket, and guided thereover by the magnetic beam in the course of printing on the web. The web is stationary during treatment. An electric motor is provided for moving the magnetic beam and the motor drives at least one drive wheel engageable with the rails for moving the beam. Speed and position of the wiping roller is determined by a sensor arrangement responsive to deviation of the working carriage from the magnetic beam path.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a device for the treatment of webs or the like, 
particularly for screen printing, comprising at least one magnetizable 
working element, particularly a wiper roller or squeegee urged by a 
magnetic beam towards the web and guided thereover, the web being 
stationary during the treatment process, the web being interposed between 
the wiper roller and the beam, the latter being movable on rollers. 
2. Description of the Prior Art 
Apparatus of this type is particularly used for flat screen printing and 
therein a magnetic beam is associated with each printing station and is 
movable along the web. A wiper roller of magnetizable material is 
displaced in a flat-type screen by displacement of the magnetic beam so 
that colorant is imprinted on the web. Subsequently, the magnets on the 
beam are switched off, the flat screen together with the wiper rollers 
disposed therein are lifted up, and the web, which is attached to a belt 
or printer's blanket is moved along. In printing machines employing a 
longitudinal table, the forward movement of the belt does not take place, 
and a single flat or curved screen is moved either stepwise, or 
continuously, above a single magnetic beam. According to an upublished 
proposal, the magnetic beam can also extend in the longitudinal direction 
of the web and be movable transversely to the latter. 
The movement of the magnetic beam has hitherto always been accomplished 
from the narrow side of the device, whereby a rigid coupling has been 
provided between the individual beams by means of longitudinally disposed 
tubes or the like. A rigid coupling of the magnetic beams of this type is 
always disadvantageous, if a change in the length of the screen is to be 
made. If only a single magnetic beam is to be employed, it is uneconomical 
to provide drive means, for example a chain drive, extending over the 
whole length of the device, since the length of such a device can easily 
reach 30 meters and more. 
SUMMARY OF THE INVENTION 
Devices of the above-described type are simplified, according to the 
invention, by the provision of at least one motor, preferably an electric 
motor, on the magnetic beam for effecting the movement of the beam, the 
motor driving at least one drive wheel. 
The invention is also particularly applicable to a printing device for 
film- or screen-printing having a longitudinal table, rails disposed at 
the longitudinal rims or edges of the table, and printing or auxiliary 
devices coupled to a drive motor and slidably or rollably arranged on the 
rails. 
In printing devices of this type, the web to be imprinted is pasted on the 
belt or printer's blanket which extends in the longitudinal and transverse 
directions of the longitudinal table. Curved or flat screens are 
displaceable on rails in the longitudinal direction of the table, the 
individual colors of a sample being sequentially coated on the web. 
Following the printing process, the product is taken off the table and 
transported to a drying device. Any color and paste residues must be 
cleaned from the table plate or the printer's blanket prior to pasting a 
new web on the plate or blanket. Special cleaning and pasting-carriages 
are used for cleaning off the table surface, for applying the paste 
coating on the blanket, and for attachment of the blanket onto the table 
surface. These carriages are denoted hereafter as "auxiliary devices," and 
these are continually moved in the longitudinal direction of the table. 
The flat screen printing carriages are displaced between successive 
printing stages over a length by manual action. Rotary printing rollers 
and/or printing-devices, as well as the auxiliary devices are displaceable 
at a uniform velocity in the longitudinal direction, the printing rollers 
rolling on said screen. 
If the magnetic beam of a device of this type is made to be self-propelling 
in accordance with the invention, then this is advantageous to the extent 
that the problem of synchronization with devices displaceable above the 
printer's blanket is easily solved. Preferably, contactless sensor means 
are provided for control of synchronization between the magnetic beam and 
the printing- or auxiliary-devices for determining the position of the 
printing- or auxiliary-devices relative to the magnetic beam, said sensor 
means controlling the drive motor of the magnetic beam or the printing- or 
auxiliary-devices upon detection of any deviation from the normal 
synchronized position. 
Even a relatively small movement between the magnetic beam driven below the 
printing blanket, and the printing- or auxiliary-devices, driven above the 
printer's blanket (by a separate drive), triggers a correction signal for 
the control circuit of one of the drives. Thus, complicated devices 
embracing the printer's blanket, such as, for example, rope lifts which 
are prone to malfunction, ae avoided.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a screen printing station of a screen printing machine having 
flat screens 1. In flat screen 1 there is disposed a wiper roller or 
squeegee 2 of magnetizable material, which is attracted by a magnetic beam 
3, the latter having an upper surface forming a printing support. A 
conveyor belt or printer's blanket 4 is disposed between the magnetic beam 
3, and the screen 1 and a web 5 to be screen-printed is adhesively secured 
to the belt and travels therewith. 
The wiper roller 2 is driven longitudinally by movement of the magnetic 
beam 3 on stationary rails 7 in the direction of the arrows 8 and/or 8' 
and the roller travels in contact on the screen 1 which is stationary 
relative to the conveyor belt 4. Due to the contact of the roller with the 
screen, the roller 2 rolls on the inner surface of the flat screen 1 in 
the course of its longitudinal travel and thereby imprints a colorant 9 
through sieve-like openings of the screen onto the web 5. 
The magnetic beam 3, best seen in FIG. 2, includes a plurality of magnetic 
cores 14 disposed successively in a row, the cores 14 being surrounded by 
respective windings 15. A motor 10 is carried on the underside of the beam 
to drive a toothed wheel 11 which meshes with teeth 12 on the lower 
surface of rails 7 to cause the beam to travel along the rails. The beam 
carries rollers 13 which roll on the smooth upper surface of the rails 7 
to facilitate the travel of the beam. If an attempt was made to directly 
drive the magnetic beam on the rails 7 by forming teeth on the upper 
surface there would not be obtained a smooth and quiet operation to the 
same degree as is required in screen printing. 
The rails 7 are carried by posts 16 disposed along web 5. The same 
arrangement is also provided on the left end of the magnetic beam 3 (not 
shown) where an additional toothed wheel corresponding to the toothed 
wheel 11, is driven by a shaft 17 from motor 10. 
In a modified arrangement shown in FIG. 3, the same reference numerals are 
employed to refer to similar structure in FIG. 1. The machine frame 
consists essentially of the posts 16, which are joined to one another in 
the longitudinal and transverse directions by braces, the frame carrying 
the rails 7 for the magnetic beam 3, as well as profiles or sections 18 
for the support and tensioning of a printer's blanket. Toothed racks 19 
are disposed on the longitudinal sides of sections 18. Inner flanges of 
sections 18 serve as rails for displacement of a carriage 21 provided with 
a drive means 20 for displacing the carriage in the longitudinal direction 
of the frame, together with printing- and auxiliary devices disposed on 
the carriage 21. The longitudinal displacement of the carriage 21 is 
achieved by driving toothed wheels 22 from drive means 20, the toothed 
wheels 22 being in mesh with the rack 19. The magnetic beam 3 is disposed 
on rails 7 for travel below the printer's blanket, and the beam 3 serves 
as an abutment for the devices moving above the web, as well as a bearing 
support for exerting counterpressure against wiper roller 23 which is 
supported on the carriage 21. The rotational speed of the drive means 20 
and the motor 10 are controlled so that the magnetic beam 3 and the 
carriage 21 always remain in the same longitudinal position with respect 
to one another. The synchronization provided between the magnetic beam 3 
and the carriage 21 is shown schematically in FIG. 3 of the drawing. 
A permanent magnet 24 is disposed on the magnetic beam carriage and is 
located a small distance from the web, said permanent magnet facing a 
magnetizable pendulum 25 disposed on the carriage 21 to cause the pendulum 
to pivot if it is displaced from a predetermined position with respect to 
the magnetic beam 3. A potentiometer 26 is connected to and operated by 
the pendulum 25 to furnish indication of the relative longitudinal 
positions of carriage 21 and beam 3 and in order to re-adjust the 
positions thereof to the pre-determined positions, the potentiometer acts 
in a control circuit of the motor 20 such that the speed of the motor 20 
is adjusted such that the carriage 21 will by synchronized in longitudinal 
position with the magnetic beam 3. 
It is also possible within the bounds of the invention to reverse the 
relative positions of the permanent magnet 24 and the pendulum 25.