Design World

  • Home
  • Articles
    • 3D CAD
    • Electronics • electrical
    • Fastening & Joining
    • Factory automation
    • Linear Motion
    • Motion Control
    • Test & Measurement
    • Sensors
  • 3D CAD Models
    • PARTsolutions
    • TraceParts
  • Leadership
    • 2020 Winners
    • 2019 Winners
    • LEAP Awards
  • Resources
    • Subscribe
    • DIGITAL ISSUES
      • EE World Digital Issues
    • Future of Design Engineering
    • LEAP Awards
    • MC² Motion Control Classroom
    • Motion Design Guide Library
    • Podcasts
    • Suppliers
    • Webinars
  • Women in Engineering
  • Ebooks / Tech Tips
  • Videos
  • COVID-19

What are rotary actuators and how do they differ from other rotary tables?

By Danielle Collins | January 11, 2021

Share

When we think about actuators, we typically think about linear actuators — devices that move loads in a straight line, driven by a screw, belt, or other mechanical power transmission device. But there also exists a class of actuators that provide rotary motion for positioning a load radially around a fixed axis. While these rotary actuators can be driven by pneumatic, hydraulic, or electromechanical power, we’ll focus here on electromechanical versions.


rotary actuators
This rotary actuator from Harmonic Drive incorporates a pancake servo motor, gearing, crossed roller bearing output, and an integrated encoder.

Electromechanical rotary actuators are designed to move loads in angular increments with very high positioning accuracy and repeatability. Although all rotary actuators can provide up to 360 degrees of rotation, many designs can provide continuous rotation through multiples of 360 degrees.

There are two main design principles for rotary actuators: those that incorporate a mechanical drivetrain — such as a belt or gear — to transfer motion from the motor output to a rotating table, and those in which the motor is directly coupled to the rotating table. In either case, an absolute or incremental rotary encoder is often integrated into the actuator assembly, and brakes are typically offered as standard options. To support the rotating load, most designs use either a rotary ball bearing or a radial (ring-style) crossed-roller bearing.

The first type — those that use a mechanical drivetrain — most often use a belt, worm gear, or pinion gear coupled to a servo or stepper motor. In the case of belt-driven versions, gearing (torque multiplication and speed reduction) can be achieved through additional gear components or by using different diameters for the motor and table pulleys.

rotary actuators
Rotary actuators with mechanical drivetrains offer many options for configuration.
Image credit: Oriental Motor

Direct-drive rotary actuators use a style of rotary servo motor that has a flat construction principle, known as a torque motor, or a pancake motor. The actuator’s table top, where the load is attached, is directly mounted to the motor, so components that would introduce compliance and backlash — such as couplings, screws, or belts — are eliminated. This gives direct-drive versions very high positioning accuracy, repeatability, and stiffness.

Direct-drive rotary actuators are often based on torque or pancake-style motors, which have a flat, low-height design.
Image credit: ETEL S.A.

Rotary actuators — particularly direct-drive versions — are often used as the rotary axis in multi-axis systems such as Cartesian and gantry robots. And because electrical rotary actuators provide tight control over speed and positioning accuracy, they’re often chosen over pneumatic and hydraulic designs in printing, machining, assembly, and inspection applications.

Continuous versus fixed rotation

Another permutation of the rotary actuator is the rotary indexing table. In general, rotary actuators are used for moving loads at any angle, while rotary indexing tables are designed to move loads to pre-set, fixed positions, where the load dwells for some time and then moves to the next position. For example, an indexing table would be used for a part that required a machining operation to be performed around its circumference at 90 degree intervals.


As in the linear world, in the world of rotary motion, a distinction is often made between rotary actuators and a rotary stages. Rotary stages are commonly used in applications that require a very high flatness of travel during rotation — in other words, there should be no (or very little) “tilt” or “wobble” as the stage rotates. This is typically achieved by using highly-machined base and table structures with stringent requirements for flatness, along with high-precision radial bearings or crossed roller bearings. However, the distinction between rotary actuators, rotary stages, and even rotary tables is not strictly followed, so it’s not uncommon to see these terms used interchangeably.

MOTION DESIGN GUIDES

“motion

“motion

“motion

“motion

“motion

“motion

Enews Sign Up

Motion Control Classroom

Design World Digital Edition

cover

Browse the most current issue of Design World and back issues in an easy to use high quality format. Clip, share and download with the leading design engineering magazine today.

EDABoard the Forum for Electronics

Top global problem solving EE forum covering Microcontrollers, DSP, Networking, Analog and Digital Design, RF, Power Electronics, PCB Routing and much more

EDABoard: Forum for electronics

Sponsored Content

  • Drilling rig OEM benefits from a PLC with edge computing technology: IIoT case study
  • The industry shift to smart electromechanical actuators
  • Commemorating a great entrepreneurial personality – Oskar Lapp at 100 – A pioneer for the future
  • SE motor – uncompromised motion performance
  • With virtual commissioning, commissioning time and prototype waste is reduced
  • Master Bond Supreme 10HT High strength, NASA low outgassing approved epoxy
Engineering Exchange

The Engineering Exchange is a global educational networking community for engineers.

Connect, share, and learn today »

Tweets by @DesignWorld
Design World
  • Advertising
  • About us
  • Contact
  • Manage your Design World Subscription
  • Subscribe
  • Design World Digital Network
  • Engineering White Papers
  • LEAP AWARDS

Copyright © 2021 WTWH Media, LLC. 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. Site Map | Privacy Policy | RSS

Search Design World

  • Home
  • Articles
    • 3D CAD
    • Electronics • electrical
    • Fastening & Joining
    • Factory automation
    • Linear Motion
    • Motion Control
    • Test & Measurement
    • Sensors
  • 3D CAD Models
    • PARTsolutions
    • TraceParts
  • Leadership
    • 2020 Winners
    • 2019 Winners
    • LEAP Awards
  • Resources
    • Subscribe
    • DIGITAL ISSUES
      • EE World Digital Issues
    • Future of Design Engineering
    • LEAP Awards
    • MC² Motion Control Classroom
    • Motion Design Guide Library
    • Podcasts
    • Suppliers
    • Webinars
  • Women in Engineering
  • Ebooks / Tech Tips
  • Videos
  • COVID-19