Erhardt+Leimer develops web guider for the production of printed circuits
Web guiding with an accuracy of +/- 5 µm
Typically accuracies of +/- 0.1 mm are achieved with web guiders, in special cases the
control accuracy is as much as twice as high at +/- 0.05 mm. However, absolute position
tolerances of maximum 10 µm are allowed during the production of printed circuits – a real
challenge for the engineers. Erhardt+Leimer, the specialist for web guiding in a very wide
range of sectors, is now offering a sophisticated solution.
At the recent meeting of the oe-a (Organic Electronics Association, a VDMA working group) in
Japan, Dirk Schröder, Sales Division Manager at Erhardt+Leimer, presented the high precision
web guider. The task was as follows: a web already printed is printed again with components to
give the material the required characteristics. During this second printing process an absolute
position accuracy of 10 µm is required. The contrast edge (white-gray contrast) that is to act as the
guiding criterion is not continuous, but is often interrupted; there is interference in the background.
First the web is unwound on the unwinder, during this process the web tension is typically
controlled using a dancer roller. The next process step, a traction unit with web tension control and
web guiding, is now crucial: the web guider must ensure the web is fed to the subsequent printing
process with the required accuracy of +/- 5 µm.
The pivoting frame used by E+L here for the web guiding is the ELGUIDER DRS 24. This system
provides an actuating speed of up to 70 mm/s and a control accuracy of < +/- 0.1 mm as standard.
To acquire the position of the two web edges, 2 CCD line scan cameras of type OL 82 with 5150
pixels and 8-times subpixeling are used.
Adaptation of mechanics, optics and software
A resolution of 0.013 mm/pixel can be achieved using the standard lens on the OL 82 CCD camera
with a focal length of 50 mm – in this case insufficient. The engineers at E+L therefore
supplemented the lens with various ancillary lenses such that the distance to the web could be
reduced from the normal 500 mm to 180 mm. Thanks to the subpixeling a resolution of 1.2 µm is
achieved in this manner.
The mechanics were also adapted: the gearbox ratio for the actuator motor was increased by 10
times. Also play-free bearings were provided in the control frame, and the play in the bearings for
the rollers was also eliminated by fitting springs.
In the software area the settings for the controller were adapted such that all "dead zones" on the
controller characteristic are suppressed. In this way it is possible to achieve an even more precise
reaction from the actuator.
Due to the stated optimizations the pivoting frame system guides the web with an accuracy of at
least +/- 5 µm and is suitable for usage in the production of printed circuits.
Limits of the application
However, under certain conditions the solution from Erhardt+Leimer comes up against its limits: if
the web arrives at the web guide with an excessively large position error, if the web tension varies
or is not constant transverse to the direction of web travel, or if the web is not of even thickness,
the required guiding accuracy may not be achieved.
The accuracy achieved with standard geared motors of +/- 5 µm is already a major success. Even
higher accuracies can be achieved with the aid of piezo actuators.
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The pivoting frame ELGUIDER DRS 24 with two CCD line scan cameras of type OL 82
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http://www.erhardt-leimer.de/Aktuell/Pressemitteilungen
Press contact:
Name: Corporate Communications Erhardt+Leimer
E-mail: [email protected]
Erhardt+Leimer GmbH
Albert-Leimer-Platz 1 • 86391 Stadtbergen • Germany •
Tel.: +49 821 2435-0 •
[email protected] • www.erhardt-leimer.com
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