Encoders and Resolvers Series:Motion Feedback 101

Select the Right Feedback for Your Application by Knowing the Basics

This webinar will be available afterwards at designworldonline.com & email

Q&A at the end of the presentation

Hashtag for this webinar: #DWwebinar

Before We Start

Moderator

Miles BudimirDesign World

Presenter

Mark LangilleTechnology Planner, Dynapar Corp.

Mark Langille is the Technology Planner for Dynapar.  He has worked in the encoder industry for 15years both on the manufacturing and commercial side of the business, with 7 years spent as a manufacturing engineer.  He holds a BS in Industrial Technology with an emphasis in manufacturing from Iowa State University.

Closed-loop feedback can deliver: Speed data—spindle applications,

CNC tools, conveyor belts Velocity data—web applications Position data—packaging, pick-and-

place

You can close the loop on: Shaft velocity/position provided from

an encoder or resolver The motor torque via motor current The load—high-performance apps

o removes lost motion, hysteresis

Knowledge is Powerposition velocity

Resolution (optical versus magnetic) Accuracy (optical or magnetic subtype) Velocity ripple- Symmetry specification Uptime/reliability (incremental

versus absolute) Cost of material/time during reset

(incremental versus absolute) Mechanical constraints—shaft type,

speed Environmental constraints (IP ratings)

How to Choose…

Different Horses for Different

CoursesEncoders vs. Resolvers

Special type of rotary transformero Stationary stator, rotor

moves with the loado Voltage from input

winding couples to output winding

o Ratio of voltages gives angular position

Resolvers

Single Speed Resolver Output

-1

-0.5

0

0.5

1

0 45 90 135 180 225 270 315 360 405

Degrees

Am

pli

tud

e

Sine

Mod Sine

Cosine

155ºC Rated Winding (Optional 220ºC) for High Temp Environments

Flux Shield Eliminates Crosstalk (pat. pend.)

Precision Laminations Help Assure High Accuracy

No On-Board Electronics Means Resolvers Can Be Used Where Encoders Cannot. Multi-Pole Versions in

Both Housed and Frameless Models to Size 55 Available

Housed Version

High res--no onboard electronics, very ruggedo Temperature extremeso Elevated radiation levels—no SEUso Contaminationo Shock and vibration

Analog—infinite resolution Good for tough applications like

aerospace, servo, and CNC.

But… The electronics have to go somewhere Skill required for integration

Resolver Trade-Offs

Linear or rotary feedback Moving load/motor modulates signal Output driver converts signal to

speed/velocity/position

Encoders

Complete – All digital electronic output Robust

o Potted electronicso Many design utilize ASIC’s

Lots of optionso Optical vs. magnetico Incremental vs. absoluteo IP ratedo Multiple mounting styles

But… Know your design criteria both electrical/mechanical.

Selecting the right device for specific for the applications can make the difference.

Encoder Tradeoffs

Poll Question #1In rugged environments it is best to specify:

a) Resolversb) Magnetic encodersc) Optical encodersd) Depends on the application

Optical vs. Magnetic

Disk—mounted on load or motor shafto Glass substrate patterned with metal thin filmo Mylar substrate (speed limitations--flutter)

Sensor—mounted on housingo LED to generate beamo Photodiode to detect beamo Board level or chip level integration

Turning/moving disk modulates beam Device uses this info to derive

velocity/position feedback

Optical Encoders

Mask (multichannel encoders only)o Prevent spillover between channelso Or introduces phase shift between channels

Phased-array encoder—onboard ASICo Array of detectors averages signalo Compensates for misalignmento More robust—shock loads up to 400 go Easier to integrate—no need for potentiometerso Larger air gap [give amount– millimeters?]o Batch processing keeps price down

Best for: Medical, semiconductor, elevators, oil and gas,

aerospace, heavy vehicles

Optical Encoders

High resolution (up to 10,000 PPR incremental direct read or 1×106 PPR for absolute versions (more on that later).

Ease of installation EMI immune Shock resistant Lower-cost

But… IP (ingress protection) is important Most optical encoders utilize bearings and

LED which can have a finite life.

Optical Encoder Trade-Offs

Drum/strip with alternating magnetic—mounted to shaft/load

Readout electronics—mounted on housing Output based on responses system to

perturbed magnetic field

Best for: Mill applications, cranes, extruders, wash-

down environments

Magnetic Encoders

Variable reluctanceo Magnetic pickup—permanent

magnet wound with coilo Changing magnetic field

generates voltage pulseo Pro: simple; con: limited to 240 PPR

Magnetoresistiveo Resistor array changes resistance

when drum turnso Pro: better resolution, lithographically

patternedo Cons: larger, not actually integrated,

needs support circuitry

Magnetic Encoders

Hall-effect sensor arrays: Solid-state detector – applied

magnetic field separates charge carriers Separation triggers voltage spike Process to get speed/displacement

Pros: Sensor and processor on same chip Integrated – robust, compact, economical Data averaged over multiple detectors – lower

noise, higher sensitivity

Magnetic Encoders

Tough—unaffected byo contaminationo Temperature extremeso Shock/vibrationo Stable performance – no degradation

But… Lower resolution than optical encoders Can be affected by high magnetic fields

Magnetic Encoder

Which type of rotary feedback typically can provide the highest accuracy resolver, optical encoder, or magnetic encoder?a) Resolverb) Optical encoderc) Magnetic encoderd) Depends more on the

more on the application/environment

Poll Question #2

Incremental vs. Absolute

Can measure speed, velocity, and direction, depending

Track counts traveled from some home position

Generate pulse stream only—need PLCs, drives, etc. to convert to info

Incremental Encoders

2+ channels, 90° out of phase (in quadrature) One channel goes high first—directionally

dependent More channels equals more resolution Triggering (leading edge, trailing edge) ups

resolution Index channel monitors turns

Best for: Web apps, e.g. printing, paper Packaging equipment Motor/Drive application with tight PID

speed loops

Quadrature Encoders

Up to 32768 PPR with interpolation Simple to integrate Easy to maintain Variety of form factors and prices

But… Need to be re-homed on start up Can require 10 conductor cables

Incremental Encoder Trade-Offs

Output as a digital word corresponding to absolute position Code disc -- each ring corresponds to one bit of resolution Each ring read by separate LED/detector pair Standard resolution--12 bits (4096 PPR)

o As high as 22 bits (4.19 x 106 positions) Multi-turn designs to track multiple turns of shaft (to 4096) Support many bus/Ethernet based communication protocols

Best for: Hi-accuracy applications: Medical, aerospace, semiconductor Multi Axis machines with coordinated motion Serial versions are best for ultra low speed PID loop

Absolute Encoders

No need to re-home on start-up Faster start up time Greater accuracy Bus compatible Deliver real-time diagnostics 

But… Tend to be more expensive More complex to install

Absolute Trade-Offs

Poll Question #3

Which device allows you sense the absolute shaft position with in one rotation a) Optical – Incremental with indexb) Optical - Absolutec) Magnetic d) Resolvere) All of the above

Mounting Types

Coupled to: o non-loadbearing end of motor shafto gear box/measuring wheel.

Robust Greatest variety of options

Tip: Connect to rotating shafts via belts, wheels, or flexible coupler. Be mindful that the dynamic loads don’t exceed the encoders’ bearings rating.

Shafted Encoders

Fits over motor shaft with a pressure connection

Automatic alignment No need for couplers Rapid installation

But… Tether mounting shouldn’t be

shouldn’t be taken for granted

Best for: AC Induction Motor Feedback

Hollow-Shaft Encoders

Sensor unit on the motor shaft Housing connected to the motor

housing No bearing—less maintenance, fewer

failures, smaller, lighter Non-contact sensing

Application tip: Play close attention to shaft run out and end play under mechanically loaded conditions.

Bearingless Encoders

IP Ratings

IEC 60529 --protection against solid and liquid Two digit system

o first digit, solids----fingers to dust o second digit, liquids----droplets to high-

pressure Jets IP ratings specify time durations, depth, etc. , so

pay attention No one seal can do both----identify your

priorities

Know the Code

Know the CodeIP 67 – 6 7

Pay attention to Time limits, Pressure limits, Depth limits, Angle dependence.

Solids

Putting It All Together

Performance requirementso Accuracyo Resolutiono Symmetry/Phaseo Electrical interface

Environmental conditionso Temperatureo IP Ratingo Shock/vibrationo Overall reliability

Budgeto TCA versus TCO

Know your application…

Choose a resolver for the very harshest applications. Choose optical encoder when you need the best

resolution possible. Choose a magnetic encoder when you need the best of

both worlds. A high IP rating can’t compensate for the wrong choice of

encoder type. No one feedback device can do it all – decide what’s most

important and design to it.

In Summary

Questions?

Design WorldMiles Budimir mbudimir@wtwhmedia.com

Phone: 216.860.5271Twitter: @DW_RapidMfg

DynaparMark Langillemark.langille@dynapar.comPhone: 847.782.5211Twitter: @encoders

Thank You This webinar will be available at designworldonline.com

& email

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