Specifying the Perfect Encoder: How to Avoid the Most Common Encoder Errors
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Specifying the Perfect Encoder: How to Avoid the Most Common Encoder Errors
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Join us during this webinar as Encoder Products and US Digital discuss ways to avoid the most common errors when specifying encoders. Topics covered will include how knowing the difference between position accuracy and resolution aides in selecting the right encoder, as well as important mechanical, electrical, and environmental considerations.
Transcript of Specifying the Perfect Encoder: How to Avoid the Most Common Encoder Errors
Specifying the Perfect Encoder: How to Avoid the Most Common Encoder Errors
Sponsored By:
q This webinar will be available afterwards at designworldonline.com & via email
q Q&A at the end of the presentation q Hashtag for this webinar: #DWwebinar
Before We Start
Moderator
Miles Budimir Design World
Presenter
Jim Stevens US Digital
Dan Craner Encoder Products
ENCODER SOLUTIONS THAT JUST MAKE SENSE EPC
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• Global designer and manufacturer of industrial incremental and absolute rotary encoders
• Established 1969 • 100,000 sq ft. facility in Sagle, Idaho
ABOUT EPC
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THE CHALLENGE
725i-S-S-1024-R-HV-1-F-1-SX-N-N
XH25D-SS-1024-ABZC-28V/V-SM18
HA52510240341
• Package Style • Mechanical • Electrical • Environmental
CRITICAL CONSIDERATIONS
PACKAGE STYLES
TWO TYPES
Shaft Bore
PACKAGE STYLE SELECTION: BORE Avoid specifying a shaft encoder when a through-bore will be the better choice. - Incurred additional hardware cost - Installation - Cost of ownership/operation– belts, pulleys, chains, sprockets too tight - Shaft couplings, set screws
PACKAGE STYLE SELECTION: SHAFT
In some applications the shaft style is preferred:
SEVERE CONDITIONS
MOBILE / OUTDOOR WASHDOWN
SEALING SHAFT VS. BORE
Maintaining seal integrity of a 3/8” shaft is much more certain than a ¾” bore
PACKAGE STYLE: SHAFT LOADS Hollow bore or through-bore devices are not commonly designed for shaft loads, but mount free floating with a flexible anti-rotation tether.
Shaft encoders are designed for heavy radial/axial shaft loading - Measuring wheel applications - Axial / radial loads
MECHANICAL SPECIFICATION: BEARINGS
Confirm bearings are adequate for operational axial/radial loads.
- Peak loads - Shock
5lbs axial/radial 80lbs axial/radial
Vs.
MECHANICAL SPECIFICATION: BEARINGS
WE GET SUSPICIOUS WHEN… “The encoder was bad out of the box.” “All the wiring checks out.” “Everything is fine until I get these intermittent missed counts…and sometimes extra counts.” “I sent the encoder back for repair and it checks out OK. I’m still having problems.” “It worked perfectly on the test bench, but when installed…”
COMMON PROBLEM: SIGNAL NOISE
Be sure to sufficiently account for electrical noise Preferred output type: Differential Line Driver
- Complementary signals - Error checking
COMMON PROBLEM: SIGNAL NOISE
Cable specifications - Shielded cable - Twisted Pair
Cable routing Termination practices
ENVIRONMENTAL CONSIDERATIONS
A word about IP ratings….
ENVIRONMENTAL CONSIDERATIONS
3 PATHWAYS OF INGRESS
Connector
Shaft Seal
Case/Hub interface
IP RATINGS - Specify an appropriate IP rating for all operating conditions - Consider all ingress pathways: shaft/bore, housing, connector - Understand the IP Ratings Standard - Understand the manufacturer specifications Shaft seals: more is not always better
- break away torque - heat generator
ENCODER SOLUTIONS THAT JUST MAKE SENSE EPC
The Truth Behind Kit Encoder Position Accuracy
Introductions – Who Are We? § Presenter: Jim Stevens, VP of Sales and Marketing at US Digital
§ US Digital is a US-‐based manufacturer of Motion Control Products in Vancouver, Washington for over 30 years.
Today we will talk about the positional accuracy of a kit or
modular style encoder.
Positional Accuracy Misconceptions
§ Accuracy is cumulative with every rotation of the encoder disk.
§ Accuracy is a function of disk to sensor gap spacing.
§ Calculating encoder accuracy is nearly impossible.
OR is “Optical Radius”
Optical Detector
Optical Detector Shaft
Optical Detector Shaft
Set Screw
Hubdisk
Optical Detector Shaft
Set Screw
Hubdisk
This distance indicates “optical
radius”.
TIR is “Total Indicated Runout”
Disk Error (none)
An example of a disk with a perfect center rotating correctly.
Perfectly centered disk. No disk error.
Disk Error (offset)
Disk off center rotating incorrectly.
Disk not perfectly centered can
cause disk errors Disk not perfectly centered affects
accuracy
(TIR) Hubdisk and Shaft Formula
How set screw can affect centering and accuracy.
Notice set screw.
Hubdisk and Set Screw
How set screw can affect centering and accuracy.
Set screw tightened.
Disk not perfectly centered affects
accuracy Hubdisk no longer
centered.
Error
Arc min.
Shaft L
A Sample Calculation
If OR = 0.433”
Disk Error = 0.001”
Hub ø = 0.2501” to 0.2506”
Shaft ø = 0.2498”
Solving TIR
Completing the Equation
14.3
180º 360º
Arc min.
Shaft L
Thank You!
Questions? Design World Miles Budimir [email protected] Phone: 440.234.4531 Twitter: @DW_Motion
US Digital Jim Stevens [email protected] Phone: 360-260-2468 Twitter: @USDigital
Encoder Products Dan Craner [email protected] Phone: 208-255-4700
Thank You q This webinar will be available at designworldonline.com & via
q Tweet with hashtag #DWwebinar
q Connect with q Twitter: @DesignWorld
q Facebook: facebook.com/engineeringexchange
q LinkedIn: Design World Group
q YouTube: youtube.com/designworldvideo
q Discuss this on EngineeringExchange.com
