Motion Feedback 101: Select the Right Feedback for Your Application by Knowing the Basics

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Motion Feedback 101: Select the Right Feedback for Your Application by Knowing the Basics

  1. 1. Encoders and Resolvers Series: Motion Feedback 101 Select the Right Feedback for Your Application by Knowing the Basics
  2. 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
  3. 3. Moderator Miles Budimir Design World Presenter Mark Langille Technology Planner, Dynapar Corp.
  4. 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. 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. 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…
  7. 7. Different Horses for Different Courses Encoders vs. Resolvers
  8. 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. 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. 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. 11.  Linear or rotary feedback  Moving load/motor modulates signal  Output driver converts signal to speed/velocity/position Encoders
  12. 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. 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
  14. 14. Optical vs. Magnetic
  15. 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. 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. 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. 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. 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. 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. 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. 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
  23. 23. Incremental vs. Absolute
  24. 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. 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. 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. 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. 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. 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
  30. 30. Mounting Types
  31. 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. 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. 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
  34. 34. IP Ratings
  35. 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. 36. Know the Code IP 67 – 6 7 Pay attention to Time limits, Pressure limits, Depth limits, Angle dependence. Solids
  37. 37. Putting It All Together
  38. 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. 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
  40. 40. Questions? Design World Miles Budimir mbudimir@wtwhmedia.com Phone: 216.860.5271 Twitter: @DW_RapidMfg Dynapar Mark Langille mark.langille@dynapar.com Phone: 847.782.5211 Twitter: @encoders
  41. 41. Thank You  This webinar will be available at designworldonline.com & email  Tweet with hashtag #DWwebinar  Connect with  Discuss this on EngineeringExchange.com

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