Abstract:
The machining of brittle materials such as glasses and ceramics is an area of rising
interest in the 'Precision Engineering' field due to the advantageous characteristics of
ceramics and demands for glass machining from optical component manufacturers. In
general the 'ductile mode' machining of brittle materials requires cut-geometry to be
sub-micrometre. In order to improve machining accuracy of single-point diamond
turning for brittle materials in the ductile mode, a controlled micro-tilt stage system was
proposed for improvement of the motion accuracy and dynamic stiffness of an aerostatic
spindle.
Mechanical arrangements for the proposed controlled micro-tilt stage system including
slip rings for transferring voltage signals to a rotating body were developed together
with a strategy for spindle metrology using three optical fibre sensors. Algorithms for
averaging and spacial filtering were applied to remove random noise caused by the
variation of surface texture.
The micro-tilt stage was designed to satisfy specifications in respect of travel range,
resolution, stiffness, and resonant frequency. Efforts were also made to minimize static
and dynamic cross-coupling-interference between the required three degrees of freedom.
The micro-tilt stage showed satisfactory performance, and the effectiveness of non-crosscoupling
design was seen.
After considering various control strategies, hardware and software were arranged with
PID and repetitive controllers. The diagonal dominance of the micro-tilt stage control
system permitted 'SISO' system design.
The performance of the controlled micro-tilt stage was investigated both stationary and
during rotation. The stationary controlled micro-tilt stage worked satisfactorily; the
controlled rotating micro-tilt stage demonstrated its error-correcting capability with some
speed limitations, primarily due to the spacial filtering and time averaging required to
reduce the surface texture noise.
