• 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 / Motors / Servo Motors / Servomotor basics video: Common motor types for closed-loop operation and motion applications

Servomotor basics video: Common motor types for closed-loop operation and motion applications

December 27, 2017 By Lisa Eitel Leave a Comment

Servomotors are electric motors that output motion under closed-loop control — so they rely on feedback from encoders or sensors … as well as a controller to process those signals for shaping the commands and corrections back to the motor. Usually these are rotary servomotors to output precise torque and speed — often for positioning.

So all servomotor systems include the aforementioned electric motor as well as feedback and electronic control of some form.

Servomotors work for machine axes that need to make complex moves or position loads with really high precision. Servomotors can also run at zero rpm while holding torque to keep a load at a set position, if that’s the goal.

Note that manufacturers classify motors for constant-speed tasks by horsepower — or torque at base speed. In contrast, servomotors operate over speed ranges so aren’t rated this way. Instead they have speed-torque curves that express continuous torque capabilities (that won’t threaten to overheat the motor) and intermittent or peak torque for acceleration.

So to pick a servomotor, define (using application inertia) how much load it will move. Then determine application speed or velocity — and how far and fast the load needs to travel. Calculating torque is next — and then plot them on the prospective motors’ torque-speed curves — as the servomotors’ continuous and peak torque limits over the axis’ full speed range. So is picking and sizing an appropriate servomotor complex? Often yes — but there are many manufacturer software programs out there to help make it easier. The other good news is that once a designer has the parameters for an axis and its motor, he or she can setup its drive to protect the rest of the system’s components by preventing excessive torques and other problematic conditions.

Many servomotors that aren’t direct drive have top speeds up to thousands of rpm — so to better leverage their full capabilities, designers will often combine such motors with gearing to trade an increase in output torque with lower output speed. Much of the time, this gearing takes the form of planetary or harmonic gearheads — precision arrangements with high accuracy and efficiency.

In a lot of cases, gearing even lets machine builders use smaller motors on axes — which equates to cost savings that may even offset the price of additional gearing.

Keep in mind that the term servomotor can mean different things depending on the context. Convention is that the term often (though definitely not always) refers to what industry calls dc motors — brushed and the costlier (but longer-lived) brushless servomotors.

Note that technically, dc brushless motors run off ac power — shaped into a square wave current that’s fed to the motor’s phases in a predefined sequence – so-called electronic commutation. What the industry calls an ac brushless motor is the same permanent-magnet synchronous design — just optimized to accept sinusoidal ac current into its phases instead. Some argue that we should forever rename dc brushless motors to trapezoidally wound motors — and (to be consistent) we should call ac brushless motors sinusoidally wound motors.

Just remember that brushed servomotors give linear and predictable performance that makes them easy to apply. Brushless motors usually run applications needing more torque; the only catch here is that their drives are more complex because commutation is done electronically and not mechanically as in brushed types. Industry also categorizes motors in part by their number of electrical phases. Brush DC servo motors as well as voice coil motors are in fact single-phase motors, whereas brushless servo motors most commonly have three phases.

Some sources classify induction-motor-based designs running off vector controls as servomotor setups where the design incorporates feedback (usually from an encoder) to track and control speed and sometimes even position. These induction motors typically adhere to NEMA or metric standards, whereas other servomotor offerings are less uniform, as their design roots are in application-specific setups.

You may also like:


  • Integrated motor basics video: Benefits, communications, and support of distributed…

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

  • Frameless motor basics video: Operation, integration, and application
  • cable
    How does cabling contribute to servomotor electrical noise problems?
  • direct drive motor
    Direct-drive motor designs: What variations are there?

Filed Under: FAQs + basics, Featured, Servo Motors

Reader Interactions

Leave a Reply Cancel reply

You must be logged in to post a comment.

Primary Sidebar

MOTION DESIGN GUIDES

“motion

“motion

“motion

“motion

“motion

POWER TRANSMISSION REFERENCE GUIDE

RSS Linear Motion Tips

  • Haydon Kerk Pittman launches compact Z-Theta motion platform
  • Three easy ways to specify application requirements for linear motion systems
  • Sourcing linear motion solutions from NSK’s global manufacturing sites
  • Ride the wave of electrification: Off-highway designs with linear actuators
  • What are capacitive sensors and where are they used?
Subscribe Today

RSS Featured White Papers

  • Identifying Best-Value Linear Motion Technologies
  • Learn how to reduce noise and distortion in encoders’ signals
  • Helical Planetary Gearboxes: Understanding The Tradeoffs
Tweets from https://twitter.com/Motion_Control/lists/motion-control-tweets

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 © 2021 · 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