Automation
M
odern motion overall system (stage mechanics along and appropriate encoder interpolation.
control with controls and drive electronics) can Even though the controller will be able
applications achieve reliably. However, this to detect a 10 nm implied move from
are typically characteristic (commonly defined the rotary motor’s encoder, the stage
defined by a independently as ‘minimum incremental mechanics almost definitely will not
broad set of specifications. Accuracy, move’) is often far different than system realize a commanded 10 nm move.
repeatability, velocity regulation, and resolution. The respective terms are Backlash, wind-up, and other
many other characteristics are more precisely defined as: compliance in the mechanical drive train
painstakingly highlighted in system will prevent most or all of the motor’s
requirements. Most of these Resolution: Smallest value that a rotation from repeatably manifesting as
performance metrics are well defined, motion system can be commanded to linear motion. What causes a stage’s
intuitive, or both, others are sometimes move and/or detect, as determined by smallest achievable step size to diverge
misinterpreted or incorrectly specified. the feedback device (encoder, etc.) and from its system resolution value?
Resolution is one such benchmark. controller. This can be thought of as a Clearly, a firm understanding of
Stage resolution is often called out theoretical minimum incremental move. true system resolution, as well as what
in motion control system application contributes to the limits of minimum
requirements as well as in vendor Minimum Incremental Move: incremental motion, is crucial to
catalog and website specifications. Smallest move a stage can consistently understanding performance of precision
Many users, and some manufacturers, and reliably deliver. Often defined by a positioning systems.
misinterpret what is truly encompassed value of uniformity, i.e., ‘non-uniformity
by this term. Most assume that this in step size to be less than…’. Drive Element Effects
value represents the smallest move the Perhaps the most obvious source of
In other words, a complete differences between resolution and
24
electromechanical system may be incremental motion is motion generated
devised such that a resolution of 10 nm by the stage’s motor but wasted before
www
is established, for instance, using a 2 it is converted into linear translation of
.eur mm/rev ball screw along with a 1000 the stage carriage. This manifests from
oasiasemiconductor
line sinusoidal output rotary encoder compliance in the coupling, backlash in
the screw, and other mechanical
.com
square4
Issue II 2009
Resolving resolution
Motion control in high tech manufacturing is now a key
factor for successful manufacturing of devices that are
now measured at the atomic scale. Although most of the
performance metrics in motion control have been well
defined, some can be misinterpreted leading to a
performance that is below expectations. Aerotech
discusses how resolution is one such benchmark that can
impact on the final result.
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