Abbe Error – Motion errors caused by angular moments between the measuring feedback element and the point of interest.

Abbe Offset – The linear distance between the measuring feedback element and the point of interest.

Absolute Move – A move referenced from a fixed zero position.

Acceleration – Change in velocity as a function of time, going from slower to faster.

Accuracy – Difference between expected position and
achieved position.

Angular Errors – Moment errors at a point in space commonly caused by pitch, roll, yaw, and/or cosine offsets.

Axial Runout – Errors normal to the plane of rotation of a rotary stage, measured ± along its axis of rotation.

Axis of Rotation – An imaginary line about which rotation occurs.

Back emf, Ke – A voltage generated by relative motion between
a motor's permanent magnets and its coil windings.

Backlash – The non-responsive lost motion between a drive screw and its nut that occurs at the point of change in rotation direction.

Bearing – A support device that allows motion between two surfaces loaded against each other.

Cantilevered Load – A load that has its center of mass offset from the balance point of a bearing system.

Closed Loop – Implementing feedback to regulated position and/or velocity with respect to commanded.

Coefficient of Kinetic Friction (µk) – It is the proportional value of the force required to maintain motion to the normal force of the mass being moved.

Coefficient of Static Friction (µs) – It is the proportional value of the force required to overcome stiction to the normal force of the mass to be moved.

Cogging – Changes in force at low velocity, caused by magnetic “detenting” forces created by relative motion between a motor's permanent magnets and its ferrous core coil windings.

Commutation, Sinusoidal – The three phase currents applied to a motor closely follow the sine wave shape of the motor's natural back emf waves, thereby providing the lowest velocity ripple and the smoothest possible motion. This is a very important factor for scanning applications. Sinusoidal commutation is electronically generated at the servo controller.

Commutation, Trapezoidal – The three phase currents applied to a motor resemble a trapezoidal profile. Slight force ripple is present due to the mismatch between the three phase trapezoidal shape and the motor's back emf sinewave profile. Trapezoidal commutation is typically generated by Hall effect sensors secured near the motor's moving coils. Trapezoidal commutation is suitable for most high-speed motion applications.

Cosine Error – Results from a parallel misalignment between a linear bearing system and the linear feedback element.

Deceleration – Change in velocity as a function of time, going from faster to slower.

Duty Cycle, Motion – The percentage of the time in motion to the total time (motion time ÷ total time) x 100%.

Duty Motor Power – The percentage of the application process power to a motor's continuous power limits [(IRMS ÷ ICont)2 x 100%]. This value should not exceed 100% for a prolonged period of time.

Error Budget – An accounting of all the error contributing factors that could affect precision goals.

Error Mapping – A process of calibrating and storing positioning correction factors for later recall.

Flatness of Travel – Up and down deviation as a carriage moves along its axis.

Friction – Resistance to motion of two surfaces that touch.

Hall Effect Sensors – Typically three feedback elements that sense a motor's magnetic fields during motion. These signals, generated at the motor itself, are used by the servo amplifier to control the timing of the three phase currents applied to the motor coils.

Hysteresis – The non-responsive lost motion which may occur at the point of change in direction. The composite error results from many contributing factors (backlash, elasticity of structure, etc.).

Incremental Move – A move referenced from the current position.

Inertia – The property of an element's mass and shape that resists changes in velocity when exposed to an outside force. The larger an object's mass, the greater its inertia and the greater the magnitude of force required to accelerate it at a given rate.

Lead – The linear distance a nut advances through one complete revolution of a screw.

Leadscrew – A device that converts rotary motion to linear motion.

Mapping – Calibrating the motion system so that repeatable errors can be corrected from a lookup table.

Open Loop – A motion system which does not utilize a feedback element.

Orthogonality – The degree to which stages are aligned with their motion at right angles to one another. Motion of an X-Y system is typically 90° apart in a single plane. X-Y-Z systems are all mutually at a 90° relationship in a 3D space. The specification is typically the angle measured between the best-fit-straight-line of X-axis motion and the best-fit-straight-line of Y-axis motion.

Pitch, Angular – Front and back angular motion of a linear stage, about an axis which is across the bearing system and which is at right angles to the direction of travel.

Pitch, Leadscrew – The number or revolutions a leadscrew must turn for the nut to travel one inch.

Radial Runout – Errors within the plane of rotation of a rotary stage, along its radius and through its axis of rotation.

Repeatability, Bi-directional – The error from nominal when repeatedly approaching a position from opposite directions.

Repeatability, Uni-directional – The error from nominal when repeatedly approaching a position from the same direction.

Resolution, Electrical – The smallest increment that can be commanded by a servo system. The value results from the feedback's precision (encoder, laser, etc.) and the controller's logic multiplication factor.

Resolution, Mechanical – The smallest increment that can be controlled by a motion system. The value is affected by friction, stiction, driving mechanism precision, etc.

Resonance – Oscillatory behavior in a mechanical body when subjected to a periodic force occurring at its natural frequency.

Roll – Side to side angular motion of a linear stage, about an axis which is parallel to the bearing system and which is in-line with the direction of travel.

Scale Error – Errors associated with the precision of the feedback elements.

Servo Motor – A motor used in a closed-loop positioning system where feedback is used to control the motor's force, velocity, and position.

Settling Time – The time it takes to after a move completes to settle to within a specified tolerance band (i.e.: to within ± 1µm).

Stiction – Frictional resistance to initial motion.

Straightness of Travel – Side to side deviation as a carriage moves along its axis.

Torque – Product of a force perpendicular to the radius of motion that is applied at a distance from the axis of rotation that causes rotational motion about the axis.

Wobble – A conical projection of a rotary stage's imaginary axis of rotation as the table top's plate rotates. Typically the further away from the rotating plate's surface, the larger the error.

Velocity – A change in position as a function of time (speed).

Yaw – Angular motion of a linear stage, about an axis which is between to the bearing system and which is at right angles to the direction of travel.

Weight – The force of gravity acting on a body. Weight equals mass x acceleration due to gravity.