5 Tips for a Successful Servo Crossover

Reprint of March 27, 2014, article  by Josh Bellefeuille Sales Application Engineer at Kollmorgen

Kollmorgen Servo Motor FamilyThere are a number of situations that call for crossing over and replacing an existing motor with a newer servo.  These can include: product obsolescence, cost savings, lead time issues, or upgrading to newer technology.  The specifics of each application could lead to an endless number of important factors to consider.  In this post I will try to (briefly) identify those that are most common and their correct order of concern.

1. Healthy Motivations

Whatever the reason for a replacement situation, it is important to understand (and never forget!) the most important aspect of the task.  Mitigating risk.  A good replacement is one that minimizes the potential number of issues that may be experienced amidst the upgrade.  If great care is not taken to manage the potential risk of a replacement, a higher potential for system failure will be introduced.

This means cost should not be the controlling factor for replacements! A good replacement is one that minimizes risk AND reduces the cost of a system, versus reducing cost and accepting a higher potential for risk.

2. Axis Stability

Inertia matching is very important and often overlooked.  A servo replacement should have the same rotor inertia as the existing motor, or be as similar as possible.  The goal is to keep the stability of a system consistent when the new servo is introduced.  This of course assumes the existing system already has the desired stability.

If replacing a lower resolution system (i.e. tachometer, commcoder, or older resolver based system) it is often worthwhile to consider a high resolution sine-encoder feedback device, with resolution ≥ 220 counts per revolution (CPR). Doing so will give more flexibility when matching rotor inertias.  As a general rule, when improving feedback resolution with a high resolution device, the servo replacement should have at least one third of the inertia of the existing motor, though it’s preferred to have one half.  This method has been successfully applied in many applications.

3. Speed and Torque

Speed and torque matching is equally as important.  The performance of the replacement motor should meet or exceed the performance of the existing motor.  It is important to review the catalog values of each (i.e. continuous torque, rated speed) to ensure there are no shortcomings.

It is also critical to compare torque values over the entire speed range of each motor.  Comparing graphically may be a helpful exercise.  This can be done by comparing motor speed/torque curves and manually plotting like-values in a spreadsheet.  For example, at 1000 RPM the continuous torque for motor A = X Nm and motor B = Y Nm, and so on for the entire speed range.

4. Motor Dimensions

Though not critical to the performance of the motor, a retrofit situation becomes streamlined if the mounting dimensions of the replacement servo are identical to the existing motor.  The outline drawings of both motors should be reviewed to ensure consistency.  This is good practice even when replacing motors with industry standard mounts, like NEMA or IEC.  Standards typically have consistent pilot and bolt circle dimensions, but often do not maintain the same shaft dimensions.  Though you are replacing a NEMA 34 motor, one manufacturer’s definition may be drastically different than another’s!

5. Other Considerations

Is the motor the only part of the machine being replaced?  Typically a servo replacement will mean replacing the drives, cables, and in rare instances even the controller.  In this case the difference in motor windings can become a secondary consideration assuming manufacturer recommendations are followed.

However careful review is in order if the replacement motor is intended to be used with an existing drive.  Winding data (including motor constants: Kt and Ke), feedback device type and resolution, and cable pin-outs are just a few of the pieces that must be closely examined and matched.  Furthermore, different servo motor manufacturers often utilize different units and commutation methods for these critical parameters.  This can leave a lack of clear distinction between definitions and units of the motors being compared. As a supplementary resource, this helpful article further details some of the common specification inconsistencies that should be considered during a servo replacement.

Other aspects worthy of comparison may include overall envelope size, environmental ratings, holding brakes, bearing and load life, and specials. As hinted at earlier, this short article is in no way meant to serve as a comprehensive “checklist” of crossover guidelines.  Instead, I hope it serves as a high-level starting point for effective servo crossovers, in which risk is carefully considered and managed.

 

Tags:  Servo Motor, BLDC Motor, Electric Motor, Kollmorgen, Electromate, Servo, Automation

Temperature Effects on Motor Performance

When applying DC motors to any type of application, temperature effects need to be considered in order to properly apply the motor.  Performance will change as the motor temperature changes.  When reviewing DC motor curves, the user needs to ask the question “Do these curves represent performance of the motor at room temperature, or do these curves illustrate performance at the maximum rated temperature?”  Depending on the temperature and the required operating point on the motor curve, the performance difference between “cold” and “hot” conditions can be significant.

Click on the link below to download this White Paper.

http://www.engineeringwhitepapers.com/companies/haydon-kerk/temperature-effects-motor-performance/

 

Tags:  Motor Performance, Servo Motor, BLDC Motor, Electric Motor, Temperature Effects

E-book: Motor Selection & Gearbox Matching Tech Tips

In this Tech Tip E-Book, access resources on servo selection, tips for quiet gear motor operation, gearbox matching, basics of motor selection and more on motors.  Included are case studies for automotive and medical applications.  Get motor selection tips, selection tools and resources from Groschopp in this issue.

Click on the link below to download this E-Book.

http://s3.amazonaws.com/2013_pdfs/Groschopp/Groschopp-Tech-Tip.pdf

For more information, please contact:

EDITORIAL CONTACT:

Warren Osak
sales@electromate.com
Toll Free Phone:   877-737-8698
Toll Free Fax:       877-737-8699
www.electromate.com

Tags:  Servo Motor, Servo Selection, Gearbox Matching, Motor Selection, Motor Tips, E-Book, Electric Motor, PMDC Motor

How to Select the Right Screw for your Linear Actuator

PowerPoint Presentation by Gary Rosengren, Director of Engineering at Tolomatic

The lead screw is an essential component in many electric linear actuators.  When selecting the type of lead screw a linear actuator should have, you need to strike a balance between purchase price and performance characteristics to get full value.

This new slideshow from Tolomatic shares the advantages and limitations of acme, ball and roller screws (the three screw types used in linear actuators.)  The slideshow also describes the application characteristics most suited to each screw type.

Acme Screws

acmme screw for linear actuatorAcme screws have a trapezoidal tooth form that’s very strong.  They come in a variety of leads and diameters to fit many electric linear actuator applications.  Nuts can be made from metals (which require lubrication to overcome friction) and self-lubricating plastics.

Acme screws operate quietly and are usually low cost.  They can be very inefficient because they need high motor torques to drive them due to the friction inherent in the sliding action between screw and nut.  But because of this friction and thread geometry, acme screws may reduce or eliminate back driving.

An acme screw is a good choice in applications that require slow speeds and low duty cycles.  However, variables such as nut material, environmental factors and the demands of the application affect the wear characteristics of acme nuts, so it can be difficult to predict the service life of these screw/nut systems.

Ball Screws

Ball screws are very popular in linear actuators.  They get their name from the re-circulating ball screw for linear actuatorball bearings that fit between the arch-shaped screw and nut threads.  The ball bearings transmit force and relative motion very efficiently as they roll through one or more circuits in the nut.

Ball screws are available in many diameters, leads and accuracies.  Under ISO 3408, they’re classified by lead accuracy in one of five grades – 1, 3, 5, 7 or 10 – with grade 1 being the most accurate.

Ball screws have higher thrust capabilities, longer service lives and higher efficiency than acme screw systems.  On the downside though, some ball screws can be back driven easily (depending on the lead), are higher cost and can be noisy.  They’re ideal for applications that require high duty cycles, high thrust and high speeds.

Roller Screws

roller screw for linear actuatorRoller or planetary screws have triangular-shaped threads which match up with multiple threaded rollers in the nut.  These rolling elements create a highly effective system for transmitting force, even better than that of a ball screw.  Like ball screws, roller screws are classified by lead accuracy into five grades.

Roller screws have very high force transmission capabilities since the rollers have significant contact with the screw threads.  They come with a higher price tag though, which is balanced by the fact that they are long lasting, capable of high speeds and quick acceleration, and require little maintenance. Some roller screws may be back driven, though, depending on the lead.

Roller screws are best suited to applications where their high performance and long service life outweigh their initial purchase price.

More information on Tolomatic’s Product Family can be viewed at-

http://www.electromate.com/products/?partner=1175527175

For more information, please contact:

EDITORIAL CONTACT:

Warren Osak
sales@electromate.com
Toll Free Phone:   877-737-8698
Toll Free Fax:       877-737-8699
www.electromate.com

 

Tags:  Electromate, Tolomatic, Linear Actuator, Electric Linear Actuator, Rodless Cylinder, Rod Style Cylinder

 

Motion Control Technology Handbook

Published by Manufacturing Automation

Manufacturing AUTOMATION’s ‘Motion Control Technology Handbook’ is a digital magazine that focuses on Automation and Motion Control products and systems.  Posted on MA’s website as an interactive flip-style magazine, the Technology Handbook provides market information, technical product information, tutorial video’s, white papers as well as trends within the Motion Control Industry.

Motion Control Technology Handbook

 

This is a must-read for all to OEM machine builders, end users and system integrators.  Click on the link below to view the Handbook.

http://mfgautomation.techhandbook.dgtlpub.com/2013/2013-11-30/home.php

Tags:  Motion Control, Motor Control, Machine Control, Servo Systems, Stepper Systems

Linear Bearings and Guiderails ship in less than 1 week

 

LinTech announces an increase in its profile rail component product line.  Sizes from 15 to 45 mm are now available in both the ARC & HRC series.   Available in short, normal and long block lengths, most models ship < 1 week.

Competitive pricing and dimensional drop-in interchangeability make switching to Lintech a breeze.

Click on the link for more information.

http://www.electromate.com/products/series.php?&series_id=105163

EDITORIAL CONTACT:
Warren Osak
sales@electromate.com
Toll Free Phone:   877-737-8698
Toll Free Fax:       877-737-8699
www.electromate.com

Tags:  Lintech, Electromate, Linear Bearing, Guiderail, Square Rail, Recirculating Linear Bearing, Rails, Profile Rail

 

Live Webinar: Designing an Optimal Rotary Motion Joint for Robotics & Factory Automation

 

Space is limited. Reserve your Webinar seat now.

Register now to watch this webinar live or anytime after July 29, 2014.

Harmonic Drive® gearing is a dominant technology used in precision rotary motion applications in the field of robotics and factory automation as well as other industries such as machine tool, semiconductor, and medical equipment.   Basic principles and technical considerations will be reviewed leading to a discussion of rotary actuator joint design optimized for the application requirements while minimizing size & weight.

Webinar Content to Include:
-Overview of Harmonic Drive gearing principles and operation
-Technical considerations of joint performance
-Application design examples
-Design enhancements and customization

Title: Designing an Optimal Rotary Motion Joint for Robotics and Factory Automation
Date: Tuesday, July 29, 2014
Time: 11:00 AM – 12:00 PM EDT
Presenter: Bob Mullins, VP of Sales, Harmonic Drive LLC

 

Tags:  Harmonic Drive, Electromate, Strain Wave Gearing, Rotary Motion, Automation, Motion Control, Webinar, HD, Robotics, Factory Automation

 

 


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