Glossary
Backlash
Position error caused by mechanical play in that drivetrain that occurs when changing the
direction. Backlash is caused by mechanical play in drivetrain components such as
gearheads, bearings or by friction in the guides. In contrast to hysteresis, backlash can lead
to instability in position-controlled systems because it causes dead time in the servo loop.
Backlash depends on the temperature, acceleration, load, leadscrew position, positioning
direction, wear etc. Backlash is suppressed by preloading the drivetrain. A position
measuring method that can detect the position of the platform directly, eliminates all errors
in the drivetrain (direct measuring). The data table shows typical measured values. Data for
vacuum versions can differ.
Design Resolution
The theoretical minimum movement that can be made. Design resolution must not be
confused with minimum incremental motion. In indirect position measurement methods,
values for drive screw pitch, gear ratio, motor or sensor/encoder resolution, for example, are
included in the calculation of the resolution. Normally, the design resolution is considerably
below the minimum incremental motion of the mechanics. In direct measurement methods,
the resolution of the sensor system is specified.
Hysteresis
Hysteresis is a position error that occurs when reversing direction. It can be caused by
elastic deformation resulting from applying and relieving friction-based tension. Hysteresis
of a positioning system changes mostly with load, acceleration and velocity.
Lateral Force
Also: lateral load capacity
Maximum permissible force orthogonally to the positioning direction. This value is valid
directly for the motion platform and is reduced when the force acts above the platform.
Limit Switch
Each limit switch sends its signal to the controller on a dedicated line. The controller then
interrupts the motion avoiding that the positioner moves until the hard stop and gets
damaged. PI positioners have mechanical, noncontact optical or Hall-effect limit switches.
Linear Encoder
The linear encoder is an incremental sensor for capturing changes in position. Signals from
the sensor are used for axis position feedback. After the controller is switched on, a
reference point definition must be performed before absolute target positions can be
commanded and reached.
Load Capacity
Maximum load in the vertical direction when the L-412.xx9211E0 is mounted horizontally. The
contact point of the load is at the center of the motion platform.
L412M0016EN
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3/14/2019
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