Abstract:
Roll-to-roll printing on continuous plastic films could enable the production of flexible
electronics at high speed and low cost, but the granularity of feature sizes is limited by
the system accuracy.
Technologies such as gravure printing and nanoimprint lithography demand a level
of rotary motion precision that cannot be achieved with rolling element bearings. Manufacturing
tolerances of the rotating parts, thermal drift and process forces in combination
with structural compliance add up to additional error motions.
In this master by research an active magnetic bearing (AMB) solution is designed
for a new, super-sized roll-to-roll flexible electronics production machine, which was so
far based on hydrostatic bearings. The magnetic bearing could actively compensate the
accumulated synchronous error and maintain high accuracy under all conditions.
However, the asynchronous error of a conventional AMB with the required size and
power is a problem. In order to reduce the relatively high positioning uncertainty of active
magnetic bearings an innovative radial position measurement based on linear, incremental
encoders with optical conversion principle is proposed. A commercial encoder scanning
head faces a round scale with concentric, coplanar lines on its face. By counting these
lines the radial position can be measured.
Because such a scale is not readily available, it is made by micro-machining. In
experiments, different machining methods are compared. Then a magnetic bearing is
built to demonstrate the efficacy of the proposed sensor. As a result, the best measurement
noise is 3.5nm at 10kHz and a position uncertainty of approximately 0.25µm has been
achieved for the magnetic bearing. These promising results are especially interesting for
applications with high precision requirements at low speed of rotation.