specifying the perfect encoder: how to avoid the most common encoder errors

Specifying the Perfect Encoder: How to Avoid the Most Common Encoder Errors

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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 mbudimir@wtwhmedia.com Phone: 440.234.4531 Twitter: @DW_Motion

US Digital Jim Stevens Jim.s@usdigital.com Phone: 360-260-2468 Twitter: @USDigital

Encoder Products Dan Craner danc@encoder.com Phone: 208-255-4700

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