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Motion Feedback 101: Select the Right Feedback for Your Application by Knowing the Basics
1. Encoders and Resolvers Series:
Motion Feedback 101
Select the Right Feedback for Your Application by Knowing the Basics
2. 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
4. 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.
5. 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 Power
position velocity
6. 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…
8. Special type of rotary
transformer
o Stationary stator, rotor moves
with the load
o 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
Amplitude
Sine
Mod Sine
Cosine
9. 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
10. High res--no onboard electronics, very rugged
o Temperature extremes
o Elevated radiation levels—no SEUs
o Contamination
o 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
11. Linear or rotary feedback
Moving load/motor modulates signal
Output driver converts signal to
speed/velocity/position
Encoders
12. Complete – All digital electronic output
Robust
o Potted electronics
o Many design utilize ASIC’s
Lots of options
o Optical vs. magnetic
o Incremental vs. absolute
o IP rated
o 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
13. Poll Question #1
In rugged environments it is best to specify:
a) Resolvers
b) Magnetic encoders
c) Optical encoders
d) Depends on the application
15. Disk—mounted on load or motor shaft
o Glass substrate patterned with metal thin film
o Mylar substrate (speed limitations--flutter)
Sensor—mounted on housing
o LED to generate beam
o Photodiode to detect beam
o Board level or chip level integration
Turning/moving disk modulates beam
Device uses this info to derive velocity/position
feedback
Optical Encoders
16. Mask (multichannel encoders only)
o Prevent spillover between channels
o Or introduces phase shift between channels
Phased-array encoder—onboard ASIC
o Array of detectors averages signal
o Compensates for misalignment
o More robust—shock loads up to 400 g
o Easier to integrate—no need for potentiometers
o 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
17. 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
18. 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
19. Variable reluctance
o Magnetic pickup—permanent
magnet wound with coil
o Changing magnetic field
generates voltage pulse
o Pro: simple; con: limited to 240 PPR
Magnetoresistive
o Resistor array changes resistance
when drum turns
o Pro: better resolution, lithographically
patterned
o Cons: larger, not actually integrated,
needs support circuitry
Magnetic Encoders
20. 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
21. Tough—unaffected by
o contamination
o Temperature extremes
o Shock/vibration
o Stable performance – no degradation
But…
Lower resolution than optical encoders
Can be affected by high magnetic fields
Magnetic Encoder
22. Which type of rotary feedback typically can provide the
highest accuracy resolver, optical encoder,
or magnetic encoder?
a) Resolver
b) Optical encoder
c) Magnetic encoder
d) Depends more on the
more on the application/environment
Poll Question #2
24. 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
25. 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
26. 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
27. 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
28. 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
29. Poll Question #3
Which device allows you sense the
absolute shaft position with in one rotation
a) Optical – Incremental with index
b) Optical - Absolute
c) Magnetic
d) Resolver
e) All of the above
31. Coupled to:
o non-loadbearing end of motor shaft
o 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
32. 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
33. 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
35. 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
36. Know the Code
IP 67 – 6 7
Pay attention to Time limits, Pressure limits, Depth limits, Angle dependence.
Solids
38. Performance requirements
o Accuracy
o Resolution
o Symmetry/Phase
o Electrical interface
Environmental conditions
o Temperature
o IP Rating
o Shock/vibration
o Overall reliability
Budget
o TCA versus TCO
Know your application…
39. 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
41. Thank You
This webinar will be available at designworldonline.com & email
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