| Notes on Specifications for Motorized Actuators |
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Active axes
Specifications given in the data sheet are measured in relation to the defined motion axis. A different motor orientation may result in modified data.
Motion and Positioning
Travel Range
limited by the length of the drive screw in a spindle/motor combination. Given in the data sheet is the distance between the two limit switches, if present.
Integrated sensor
Rotary or linear encoder
Encoder resolution
Rotary encoder: counts per drive-screw revolution
Linear encoder: interpolated minimum increment that can be distinguished
Design resolution
The theoretical minimum movement that can be made, based on the selection of the mechanical drive components (drive screw pitch, gear ratio, angular motor resolution etc.). Design resolution is usually better than the practical position resolution (minimum incremental motion). For linear encoders, the design describes the resolution of the of the position feedback sensor system.
Minimum incremental motion
The minimum motion that can be repeatably executed for a given input, which is sometimes referred to as practical or operational resolution. Design resolution and practical resolution have to be distinguished. Design resolutions of 1 nm or better can be achieved with many motor, gearbox and leadscrew combinations. In practical applications, however, stiction/ friction, windup, and elastic deformation limit operating resolution. Several PI motorized micropositioners are available with additional piezo fine positioners for applications where repeatable nanometer scale resolution and / or fast response are required.
The data table states typical measured values.
For repeatable nanometer or sub-nanometer resolution see the "Piezo Flexure Stages / High-Speed Scanning Systems" (see link) and "Piezo- Walk® Motors / Actuators" (see link) Sections.
Backlash
Position error that appears upon reversing direction due to error in the drivetrain. See here for details. The data table states typical measured values.
Rotation / linear input, tangent-arm length
Angular displacement of tangentarm rotation stages is determined by the arm length and the linear motion input pushing the arm (see link) for information on how to calculate angular displacement from linear input).
Unidirectional / bidirectional repeatability
Values are typical results (RMS, 1 sigma), see also Glossary
Pitch / yaw
The maximum angular deviation around Y- (pitch) and Z-axis (yaw) over the whole travel range, with X being the direction of motion. Pitch and yaw are usually given as ± values. The data table states typical measured values. See "Definition of Axes and Angles" (see link).
Max. velocity
This is the short-term peak value for horizontal mounting, with no load, and not intended for continuous operation. The average velocity and continuous velocity are lower than the peak value and depend on the load conditions and other environmental parameters.
Origin repeatability
Repeatability of the reference switch (if present)
Mechanical properties
Motor resolution
Resolution with micro-stepping specified for PI's stepper motor controllers.
Stiffness in motion direction
Typical tolerance: ±20%
Max. normal load capacity
Centered, vertical load (horizontal installation).
Max. push / pull force
Active and passive force limit in operating direction, at center of stage. Some stages may be able to generate higher forces at the cost of reduced lifetime.
Drive properties
Drive type / Operating voltage
ActiveDrive™: The operating voltage (usually 24 VDC) for the ActiveDrive™ motors is provided by an external power supply (included in the delivery).
DC motors: DC servo motors require a supply voltage of up to 12 VDC. The operating voltage is usually given as differential value where the magnitude determines the velocity, and the sign determines the motion direction.
Stepper motors: PI stepper motors are usually driven in chopper mode.
Electrical power
Motor manufacturer’s information.
Torque
Motor manufacturer’s information.
Miscellaneous
Operating temperature range
Safe operation, no damage to the mechanics. All technical data specified in the data sheet refer to room temperature (22 °C ±3 °C).
Material
Micropositioning stages are typically made of anodized aluminum or stainless steel. Small amounts of other materials may be used (for bearings, preload, coupling, mounting, etc.). For special applications other materials are possible like Invar.
Al: Aluminum
N-S: Nonmagnetic stainless steel
St: Steel
I: Invar
Mass
Typical tolerance: ±5%
Cable length
Typical tolerance: ±10 mm
Recommended motor controller
Compatible motor controllers are described in the "Servo & Stepper Motor Controllers" (see link) Section.
For further information read "Micropositioning Fundamentals" Section (see link).
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