• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer

Motion Control Tips

Automation • Motion Control • Power Transmission

  • News
    • Industry News
    • Editor Blogs
    • Video
  • Controls
    • HMIs
    • PC-Based Controllers
    • PLCs + PACs
    • Stand-Alone Controllers
    • Software
  • Drives
    • Servo Drives
    • Stepper Drives
  • Encoders
    • Absolute Encoders
    • Incremental Encoders
    • Rotary Encoders
  • Mechanical
    • Bearings
    • Brakes + Clutches
    • Belt + chain
    • Couplings
    • Gears + Gearing
    • Lubrication
    • Shock + Vibration Mitigation
    • Springs + Rings + Seals
  • Linear
    • Actuators
    • Linear Motors
    • Linear Encoders
  • Motors
    • AC Motors
    • DC Motors
    • Brushless Motors
    • Gearmotors
    • Piezo Motors
    • Servo Motors
    • Stepper Motors
  • Systems
    • Conveyors + linear transport systems
    • Gantries + Stages
    • Rotary Tables
    • Grippers + End Effectors
    • Robotics
  • Networks
    • Connections + Sliprings
    • Fieldbuses
    • I/O
    • Sensors + Vision
  • FAQs
    • Motion Casebook
    • Motion Selection Guides
  • Suppliers
You are here: Home / FAQs + basics / What are the key parameters to consider when sizing and selecting a rotary actuator?

What are the key parameters to consider when sizing and selecting a rotary actuator?

February 5, 2021 By Danielle Collins Leave a Comment

Rotary actuators — and their counterparts, rotary stages and rotary indexing tables — are designed to move loads radially with high positioning accuracy. Similar to linear actuators, sizing a rotary actuator requires evaluating parameters such as torque, speed, and inertia, as well as ensuring the actuator can meet the application requirements for positioning the load, such as repeatability and concentricity.

While the sizing process will vary slightly for different actuator configurations — mechanical drivetrain versus direct drive, servo versus stepper driven — there are some key parameters to consider when sizing and selecting any type of rotary actuator, stage, or indexing table.

This rotary actuator from IntelLiDrives includes a servo torque motor, crossed roller bearing support, and integrated encoder.

Inertia

Rotary actuator sizing generally begins with determining the load inertia — a function of the load’s mass, geometry, and any gear reduction applied between the motor and actuator. The load inertia must be within the selected actuator’s “allowable load inertia” — a parameter included in the technical specifications of most rotary actuators — otherwise, the motor may not be able to effectively move and control the load. This is especially important for highly dynamic applications that involve quick acceleration and deceleration rates or frequent changes in rotational direction.

rotary actuator sizing
Allowable load inertia and speed are often plotted on an inertia-speed chart.
Image credit: IAI

Torque, speed, and acceleration

Just as a linear actuator requires force to drive a load, a rotary actuator must produce sufficient torque to move the attached load during both the constant velocity and the acceleration phases of the motion profile. For rotary actuators, speed and acceleration are typically given in radians or degrees per unit time (rad/min or deg/s, for example). Because many rotary actuators are based on direct-drive torque motors or pancake motors, or have a separate servo or stepper motor integrated, their technical specifications often include torque-speed curves, although in some cases, the bearing or encoder may limit the maximum rotational speed of the actuator.


Moment stiffness is an actuator’s resistance to deflection when a moment load is applied.
Image credit: Harmonic Drive

Some rotary actuator manufacturers also include specifications for moment stiffness and torsional stiffness. Moment stiffness — typically given in units Nm/rad — indicates the output flange’s ability to resist tilting when a load is applied at some radial distance from the center of the actuator.

Torsional stiffness indicates the tendency of table to rotate when a load is applied while the actuator is in a “locked” position. Torsional stiffness is important when the load needs to be held at a precise location, such as during inspection or machining operations.


Load and bearing life

Although the attached load is a key factor in the required torque and inertia, it’s also important for determining the life of the radial bearing or crossed roller guide. When determining bearing life, both axial and radial loads should to be taken into account, as well as the combined moment load (often referred to as the tiling moment) that the radial and axial loads produce. And because rotary actuators often involve significant periods of dwell, where the load is held in a static position, static loads and moments on the bearing also need to be evaluated.

rotary actuator sizing
Radial, axial, and moment loads are all important parameters for rotary actuator sizing.
Image credit: SMC

Positioning

Along with the common specifications of positioning accuracy and repeatability, the positioning capabilities of rotary actuators are also defined by the axial and radial runout values of the output table, or flange, which are determined by the parallelism and concentricity of the output table to the base. (Runout indicates how much one surface or feature varies with respect to a datum when the actuator is rotated 360° around the datum axis.) Axial and radial runout determine how much the output flange “wobbles” — that is, how much a point on its surface varies in the vertical and horizontal directions — as it rotates.

rotary actuator sizing
Axial runout (1) and radial runout (2) are determined by the parallelism and concentricity between the output flange and the base.
Image credit: Harmonic Drive

You may also like:


  • What are rotary actuators and how do they differ from…
  • multi-turn encoder
    What happens when a multi-turn encoder reaches 4096 turns?
  • rotary indexing
    What is a rotary indexing table?

  • Torque motors basics video: Construction variations and sizing and selection…

  • New ways of controlling indexing tables for precision motion

Filed Under: FAQs + basics, Featured, Rotary Tables

Reader Interactions

Leave a Reply

You must be logged in to post a comment.

Primary Sidebar

POWER TRANSMISSION REFERENCE GUIDE

DESIGN GUIDE LIBRARY

“motion
Subscribe Today

RSS Featured White Papers

  • Specifying electric rodless actuators: Ten tips for maximizing actuator life and system performance
  • The truth about actuator life: Screw drive survival
  • Top Ten Tips: How to specify electric rod-style actuators for optimal performance, reliability and efficiency

Footer

Motion Control Tips

DESIGN WORLD NETWORK

Design World Online
The Robot Report
Coupling Tips
Linear Motion Tips
Bearing Tips
Fastener Engineering.

MOTION CONTROL TIPS

Subscribe to our newsletter
Advertise with us
Contact us
About us
Follow us on TwitterAdd us on FacebookAdd us on LinkedInAdd us on YouTubeAdd us on Instagram

Copyright © 2022 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy | RSS