Tech Briefs Magazine - May 2024 - PIT-15

Precision Motion Control: Six Elements To Consider for Photonics and Optics
Alignment Applications
A
dvancements in silicon photonic
and micro-optic technologies are
driving the need to perform precision
alignments down to sub-micrometer levels.
As cutting-edge optical and photonic
processes demand increasingly smaller,
nanometer-scale tolerances, precision
motion control is more important than
ever. Achieving these alignments is crucial
to quality - misalignments of even a
few micrometers can result in significant
power losses. As emerging chip-level
functionalities and device miniaturization
intensify the demand for nanopositioning
technology, there is a correlated
need for solutions that balance speed
and precision - reducing process cycle
times without compromising on quality.
Precision Motion
Fundamentals
When considering a precision motion
control solution for any high-tolerance
photonics or optics application, it is
helpful to think in terms of accuracy and
repeatability. Accuracy describes how
close a measured or achieved position is
to the true or desired positional target.
Repeatability characterizes the range of
actual positions attained when the motion
system is repeatedly commanded to
a specific location. Because repeatability
is inherent to a stage's design and construction,
a repeatable stage's accuracy
can be improved by means of error-mapping
and calibration.
Several methods exist to define accuracy
and repeatability, but not all supplier
specifications are created equal.
Metrology standards such as ISO 2302,
ASME B5.64 and others apply statistical
treatments to a set of specifically
defined positioning data. Beyond this,
many motion suppliers have developed
their own reporting methods. When in
doubt, ask your motion supplier how
they are defining this and request sample
performance plots.
Sources of Error Motion
Accuracy and repeatability relate to errors
in the direction of motion (X), but
there are also five other degrees of freePhotonics
& Imaging Technology, May 2024
Figure 1. All linear stages exhibit five off-axis error motion components: horizontal and vertical straightness,
roll, pitch and yaw. (Image: Aerotech)
Figure 2. All rotary stages exhibit five off-axis error motion components: axial, radial (two directions) and tilt
(two directions). (Image: Aerotech)
dom (DOF) to evaluate. For the linear
stage, undesired linear motion perpendicular
to the direction of travel is called
straightness error, and it can occur in
both the horizontal (Y) and vertical (Z)
directions. Further, rotations about the
X, Y and Z axes are called roll, pitch and
yaw, respectively, as shown in Figure 1.
In the rotary stage, motion in the
Z-direction along the axis of rotation is
called axial error motion, while translation
in the X and Y directions is known
as radial error motion. Finally, rotation
about the X and Y axes is referred to
as tilt error motion, as shown in Figure
2. Note that error motions are differ15

Tech Briefs Magazine - May 2024

Table of Contents for the Digital Edition of Tech Briefs Magazine - May 2024