Linear off-axis error introduced through amplification of tilt and wobble with a long
moment arm. This type of error occurs when the point under measurement is
at a relatively long distance from the axis of motion.
The maximum expected difference between the actual and a desired position for a given
input. Highly dependent on method of actual position measurement.
The output of a system versus the commanded or ideal input.
The uncertainty of position after all sources of linear error are eliminated. Linear errors
include: cosine error, leadscrew pitch error, abbe error and thermal expansion effects.
The maximum magnitude of an input that produces no measurable output upon
reversing direction. Typically the result of poor meshing between drivetrain
components as with lead screw threads.
The smallest motion detectable by a motion
device’s precision rule, micrometer or motor controls.
Sometimes called concentricity, eccentricity in a rotary device is the deviation of the
center of rotation from its mean position as the device turns.
The difference between an obtained performance parameter and the ideal or
desired result. Errors fall into two primary categories, on-axis and off-axis
Friction is defined as the resistance to motion between surfaces in contact.
Friction can be constant or it can vary with speed. Elements contributing to
overall friction may be in the form of drag, sliding friction, system wear or lubricant viscosity.
The friction that must be overcome to impart motion to a body at rest. Since static
friction is higher than sliding friction, the force which must be applied to
impart motion is greater than the force required to keep the body in motion. As a result, when
a force is initially applied, the body will begin to move with a jump in some
unpredictable and unrepeatable manner, producing non-linear, non-repeatable
Gear Ratio, Drive Train
A motion instrument’s drive train gear ratio is the relationship between received input
motion and the delivered output motion. Ratios are expressed in the numerical
notation a:b, where "a" represents the received motion or device input in
revolutions or some other unit, and "b" represents the delivered or resulting output
motion in revolutions for rotary devices or 1" of travel in linear motion instruments.
The difference in the absolute position of an object for a given commanded input when
approached from opposite directions. It is due to elastic forces accumulated in
various drivetrain components, leadscrew wind-up, for instance. Often confused with
Load Capacity, Stage
The maximum centered load that can be placed directly on an XYZ motion stage and
is typically limited by the load capacity of the bearings.
Load Capacity, Lateral or Moment
Also called side or bending load capacity, it is the maximum load that can be applied
perpendicular to a shaft’s axis of motion.
Load Capacity, Axial
The maximum centered and balanced compressive or tensile load that can be
applied to a stage’s or shaft’s longitudinal or parallel axis of motion.
Minimum Incremental Motion
The smallest motion a device is capable of delivering reliably, not the smallest display
Uncontrolled movement due to looseness of mechanical parts. Usually increases with
the components age. Play is a contributor to backlash.
The ability to maintain a constant position over time. Variation from stable position is
called drift. Contributors to drift include worn parts, migration of
lubricant, and thermal variation.
Also known as repeatability, it is the range of deviations in output position that will
occur for 95% of the motion excursions from the same error-free input. Accuracy
and precision are not the same.
The ability of a motion instrument to reliably achieve a commanded position over
many attempts regardless of the direction from which the position is
The linear, not angular, portion of off-axis error. It is the deviation between ideal
straight line motion and actual measured motion in a translation stage. Runout
has two orthogonal components, straightness, a measure of in-plane deviation, and flatness,
the out-of-plane deviation.
The minimum input required to produce output motion or the ratio between output
motion and input drive. Applicable particularly to manually actuated
The angular portion of off-axis error. It is the deviation between ideal straight line
motion and actual measured motion in a translation stage. Tilt and wobble have
three orthogonal components commonly referred to as roll, pitch, and yaw.
The torque present in an unenergized stepper motor caused by its magnetic rotor. Detent torque allows stepper motors to hold their position even when unenergized.
The maximum external force or torque that can be applied to a stopped, energized motor without causing the rotor to rotate continuously.
Wobble is the angular deviation of the axis of rotation over one complete revolution.
MDC precision micrometers measure along
unique plus-minus laser etched scales