Industrial Line
PAGE 228
Glossary
definition of some technical terms
Positioner vs. Scanner
Closed Loop Positioning
attocube uses the term positioner for all products that achieve motion
over macroscopic (mm sized) travel ranges via repetitive voltage drive
signals in sawtooth shape (see working principles on pages 238 and
312). While the step size can be as small as 10 nm (adjusted via the voltage amplitude), the speed (adjusted via the frequency and/or step size)
can still reach several mm/s when using drive frequencies in the kHz
range. The term scanner on the other hand is reserved for devices that
use DC voltages for expansions over microscopic ranges (below 1 mm;
typically several tens of µm up to 125 µm). With appropriate controllers
(e.g. ANM300 module or ANC350), the stepping type positioners can be
used in scan mode (with limited ranges) by applying a DC offset, but the
scanners cannot be used in stepping mode.
Positioners with an integrated or external encoder (/RES, /NUM,
/FPS), can be used for closed loop position control. A feedback loop
integrated into the electronics minimizes the difference between target position and actual position. Setpoints can either be defined in a
software interface (ANC350, ECC100) or on the front panel of the closed
loop electronics (ANC350).
Open Loop Positioning
In this mode, the positioner is simply driven forward or backward, without an encoder to read back the actual position or a feedback loop to
control the desired target position. Many applications don‘t require either of the latter or provide inherent external means of controlling the
position. Still, at least a rough estimate of the actual position can be
deduced by counting the number of steps (if the step size can be determined from an external measurement). The step size itself is relatively
uniform under fixed conditions (temperature, humidity, pressure, load,
etc) and typically within 5% over the full range. The forward/backward
asymetry is also typically 5%.
Guiding Accuracy
The guiding accuracy describes the deviation of the motion of a positioner from its ideal trajectory. These are typically given in terms of
roll, θx, pitch, θy, and yaw, θz. Vertical and horizontal runouts are frequently also considered when referring to the term guiding accuracy.
Single axis encoders as typically integrated into a positioner read back
the position along the direction of desired motion, but do not provide
information on the guiding accuracy. This usually requires additional
external means of measurement (e.g. via the IDS or FPS sensors).
z axis
θx
θz
x axis
θy
y axis
Industrial Line positioners pro vide highest guiding accuracy
due to crossed roller bearings.