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Flexibile vs. Rigid Couplings


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When specifying a coupling for a mechanical system, many factors are involved in the decision. Andy Lechner of R +W America, Ross Rivard of Ringfeder and Bobby Watkins of Ruland Manufacturing Co. will each take some time to help us gain a better understanding of when the different types of couplings make the most sense for an application.

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Flexibile vs. Rigid Couplings

  1. 1. #DWwebinar Flexible vs. Rigid Couplings
  2. 2. #DWwebinar q  This webinar will be available afterwards at & email q  Q&A at the end of the presentation q  Hashtag for this webinar: #DWwebinar Before We Start
  3. 3. #DWwebinar Mike Santora Associate Editor - Moderator Design World Edward Cole Engineering Manager Ringfeder Power Transmission USA Corp. Andy Lechner Product Manager R+W America Flexible vs. Rigid Couplings Bobby Watkins Vice President of Sales Ruland Manufacturing Co. Inc. Meet the speakers…
  4. 4. #DWwebinar
  5. 5. #DWwebinar PARALLEL SHAFT MISALIGNMENT •  results from lack of pilots in moun>ng frames / coupling housings •  most harmful to bearings and couplings •  even small amounts (e.g., >0.001”) can place a large amount of stress on adjacent shaN bearings, contribute to vibra>on, and reduce system efficiency
  6. 6. #DWwebinar ANGULAR SHAFT MISALIGNMENT •  results from moun>ng surfaces not being flat or level •  slightly less harmful to bearings and couplings •  rarely exists without parallel misalignment
  7. 7. #DWwebinar AXIAL SHAFT MISALIGNMENT (END PLAY) •  results from thermal expansion of shaNing •  results from motor shaN end-play •  occurs to varying degrees independent of other types of misalignment
  8. 8. #DWwebinar MOUNTING WITH PILOTS •  protruding feature of a precision diameter and concentric to the shaN •  exists on almost all servo motors, stepper motors and precision gearboxes •  when used in conjunc>on with a precision machined housing, parallel shaN alignment within 0.001-0.003” should be guaranteed
  9. 9. #DWwebinar RIGID COUPLINGS •  disclaimer – R+W does not make rigid couplings •  very useful in joining shaNs which are not both bearing supported •  allows one shaN to support the other •  no misalignment loading if only one shaN is bearing supported •  useful when one connected component has a flexible frame •  (e.g., encoders with flexible mounts) •  allows that component to flex during shaN rota>on to compensate for misalignment •  some>mes used to couple a length of shaNing on each end •  works well when the shaN is long enough to flex slightly •  mostly for slower rota>onal speeds •  oNen used in cases where high precision rota>on is needed but then require difficult alignment procedures
  10. 10. #DWwebinar FLEXIBLE COUPLINGS •  disclaimer – R+W does make and sell flexible couplings •  generally considered to be a best prac>ce between supported shaNs •  reduces side loads, which are s>ll high at 0.001” misalignment •  helps extend bearing life •  can help with vibra>on damping •  many varie>es and moun>ng op>ons are available on the market •  torsionally rigid versions •  vibra>on damping versions •  high misalignment versions •  self-suppor>ng line shaN versions
  11. 11. #DWwebinar BACKLASH •  mechanical clearance which results in lost mo>on •  necessary in most gears, but can be avoided in flexible couplings
  12. 12. #DWwebinar TORSIONAL WIND-UP •  momentary deflec>on as a result of torque loading •  occurs to varying degrees in all drive components but is generally greater in flexible couplings than in rigid couplings
  13. 13. #DWwebinar BELLOWS COUPLINGS •  unlike other “spring” type couplings they are torsionally rigid •  used typically in highly dynamic or high precision applica>ons •  offers the benefits of reduced bearing loads with high performance •  s>ll not as torsionally s>ff as rigid couplings but worth considering
  14. 14. #DWwebinar PRECISION ELASTOMER COUPLINGS •  torsionally soN for vibra>on damping but preloaded for zero backlash •  offers compensa>on for small amounts of shaN misalignment •  high torque density compared with other flexible coupling types
  15. 15. #DWwebinar EXAMPLE: BALL SCREW / LEAD SCREW APPLICATION •  GIVEN: 10Nm torque load / 10mm lead •  10Nm bellows coupling •  torsional s>ffness of 157 Nm/deg = 0.064° angular deflec>on •  with a 10mm lead this results in 0.0018mm (0.00007”)linear error •  10Nm elastomer coupling (standard insert) •  sta>c torsional s>ffness of 4.54 Nm/deg = 2.2° angular deflec>on •  with a 10mm lead this results in 0.0611mm (0.00241”) linear error
  16. 16. #DWwebinar THANKS FOR YOUR TIME!
  17. 17. Selecting Couplings For Your Servo Applications Ed Cole, Engineering Manager
  18. 18. #DWwebinar Servo Coupling Requirements! •  Backlash-free to maintain positioning accuracy. •  Mass balanced for high rotational speeds. •  Designed for low to moderate torques—usually to 100 Nm. •  Tolerant of shaft misalignments. •  Maintenance free.
  19. 19. #DWwebinar Servo Coupling Applications! •  Any automation system with shaft-driven linear motion, including: •  Machine tools. •  Packaging equipment. •  Test and measurement systems. •  Semiconductor manufacturing.
  20. 20. #DWwebinar Servo Coupling Choices! •  Two types of servo couplings can meet these requirements: •  Rigid metal bellows couplings. •  For example, Ringfeder Gerwah EKN and DKN Series. •  Flexible servo insert couplings. •  For example, Ringfeder Gerwah GWE Series.
  21. 21. #DWwebinar Servo Coupling Choices! •  Many servo applications do not strongly favor one type of coupling over another. •  Either a metal bellows and servo insert coupling can satisfy basic torque, shaft size and lifecycle requirements. •  But each type of coupling has its subtle advantages:
  22. 22. #DWwebinar Metal Bellows Coupling! •  Typically constructed of stainless steel bellows with aluminum hubs. •  Integrated clamping hubs or set screws in miniature models.
  23. 23. #DWwebinar Metal Bellows Coupling!
  24. 24. #DWwebinar Servo Insert Coupling! •  Typically consists of aluminum hubs and elastomer “spider” inserts. •  Clamping via set screws or integrated clamping hub
  25. 25. #DWwebinar •  Adjustable flexibility by changing elastomer inserts. •  Harder inserts approach metal bellows stiffness. •  Softer inserts maximize damping and misalignment tolerance. •  Optimize vibration damping through insert selection. •  Excellent tolerance of radial, axial and angular misalignment. •  Good torque transmission and angular positioning performance. Servo Insert Coupling!
  26. 26. #DWwebinar Servo Insert Coupling Application!
  27. 27. #DWwebinar •  Keep in mind that servo couplings often work in conjunction with other power transmission components, such as gear boxes and linear actuators. •  It’s important to choose couplings whose 
 designs work well with related power transmission components. •  Shrink discs •  Locking assemblies Couplings Are Part Of A System!
  28. 28. #DWwebinar Couplings Are Part Of A System!
  29. 29. #DWwebinar Couplings Are Part Of A System!
  30. 30. #DWwebinar Metal Bellows Servo Insert Product Examples! EKN, DKN, AKN Series! GWE Series! Adjustable Rigidity! Torque Transmission! Backlash Free! Misalignment Tolerance! Damping! Low Inertia! Servo Couplings At A Glance!
  31. 31. Thank You Ed Cole Engineering Manager Tel: (201) 666-3320 Email:
  32. 32. #DWwebinar Presented by: Bobby Watkins Flexible vs. Rigid Couplings Presented by: Bobby Watkins
  33. 33. #DWwebinar Presented by: Bobby Watkins Types of Misalignment Presented by: Bobby Watkins
  34. 34. #DWwebinar Presented by: Bobby Watkins Why is misalignment a concern? •  Adds stress to system components •  Caused by tolerance mismatch
  35. 35. #DWwebinar Presented by: Bobby Watkins Backlash, Windup, and Bearing Loads Coupling with Windup •  Windup is not backlash •  Backlash refers to power transmission error •  Windup is posi>on error without torque error •  All couplings have windup •  Zero-backlash means zero loss in power transmission •  Bearing loads increase wear •  Excessive bearing loads result in bearing wear and •  premature failure •  Couplings designed to flex during misalignment produce bearing load •  Coupling misalignment ra>ngs oNen result from bearing loads Coupling with Misalignment
  36. 36. #DWwebinar Presented by: Bobby Watkins Bearing Loads •  Misalignment exists between the motor and the driven system due to tolerances and/or system incompa>bility •  Bearing loads are generated as a result and are harmful to system performance •  Other system design factors must be considered when selec>ng a coupling
  37. 37. #DWwebinar Presented by: Bobby Watkins Managing Misalignment •  Selec>on of the correct coupling is cri>cal •  Must address the applica>on misalignment type or types •  Must stay within the coupling specifica>ons •  Must install the coupling properly •  Other applica>on criteria must also be addressed
  38. 38. #DWwebinar Presented by: Bobby Watkins Rigid Couplings Benefits •  Best torque transmission capabili>es •  Almost zero-windup = the most precise coupling available •  Suitable for shaN support and push-pull applica>ons •  Low cost Drawbacks •  No misalignment capabili>es •  No allowance for thermal expansion •  Extremely high bearing loads if used incorrectly •  Poten>al for damage to system components •  Very high iner>a - not suitable for high RPM applica>ons
  39. 39. #DWwebinar Presented by: Bobby Watkins Flexible Couplings Benefits •  Accommodate misalignment •  Different styles allow the user to select the best fit for the applica>on •  High RPM capabili>es •  Many standard size op>ons are available •  Most have low iner>a Drawbacks •  Some require maintenance •  Installa>on can require specialized alignment systems •  Limited torque capabili>es •  Both shaNs must be bearing supported •  High cost Oldham Coupling Bellows Coupling Beam Coupling Jaw Coupling Disc Coupling
  40. 40. #DWwebinar Presented by: Bobby Watkins Product SelecFon •  Mul>ple solu>ons may exist when selec>ng a coupling •  Specific couplings are beser suited for each type of misalignment, for example: oldhams with parallel misalignment or beam couplings for angular misalignment •  Bearing loads and windup are a side effect of all couplings •  Proper coupling selec>on requires a full understanding of the system requirements
  41. 41. #DWwebinar Mike Santora Associate Editor - Moderator Design World @DW_MikeSantora Edward Cole Engineering Manager Ringfeder Power Transmission USA Corp. Andy Lechner Product Manager R+W America Flexible vs. Rigid Couplings Bobby Watkins Vice President of Sales Ruland Manufacturing Co. Inc. Questions?
  42. 42. #DWwebinar Thank You q  This webinar will be available at & email q  Tweet with hashtag #DWwebinar q  Connect with Design World q  Discuss this on