6 - 4
6.2.4 Local Accuracy
For some applications, it is important to know not just the positioning
Accuracy
over the entire travel but also over a small distance. To illustrate
this case, Figure
6.2-2 and Figure
6.2-3 show two extreme cases.
A
B
Position
max. error
Error
0
Figure 6.2-2 — High Accuracy for Small Motions
A
B
Position
max. error
Error
0
␣
Figure 6.2-3 — Low Accuracy for Small Motions
Both error plots from Figure
6.2-2 and Figure
6.2-3 have a similar maximum
Error
. But, if you compare the maximum
Error
for small distances, the
system in Figure
6.2-3 shows significantly larger values. For applications
requiring high accuracy for small motions, the system in Figure
6.2-2 is
definitely preferred.
“Local Error” is a relative term that depends on the application; usually no
Local Error
value is given with the system specifications. The user should
study the error plot supplied with the motion device and determine the
approximate maximum
Local Error
for the specific application.
6.2.5 Resolution
Resolution
is the smallest motion that the controller attempts to make. For
all DC motor and all standard stepper motor driven stages supported by
the ESP6000 controller card, this is also the resolution of the encoder.
Keeping in mind that the servo loop is a digital loop, the
Resolution
can be
also viewed as the smallest position increment that the controller can
handle.
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
