Flexibile vs. Rigid Couplings

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.

1. #DWwebinar
Flexible vs. Rigid
Couplings

2. #DWwebinar
q This webinar will be available afterwards at
www.designworldonline.com & email
q Q&A at the end of the presentation

q Hashtag for this webinar: #DWwebinar
Before We Start

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. #DWwebinar

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. #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. #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. #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. #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. #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. #DWwebinar
BACKLASH
•  mechanical clearance which results in lost mo>on
•  necessary in most gears, but can be avoided in flexible couplings

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. #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. #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. #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. #DWwebinar
THANKS FOR YOUR TIME!

17. Selecting Couplings For
Your Servo Applications
Ed Cole, Engineering Manager

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. #DWwebinar
Servo Coupling Applications!
• Any automation system with shaft-driven linear motion, including:
• Machine tools.
• Packaging equipment.
• Test and measurement systems.
• Semiconductor manufacturing.

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. #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. #DWwebinar
Metal Bellows Coupling!
• Typically constructed of stainless steel bellows with aluminum hubs.
• Integrated clamping hubs or set screws in miniature models.

23. #DWwebinar
Metal Bellows Coupling!

24. #DWwebinar
Servo Insert Coupling!
• Typically consists of aluminum hubs and elastomer “spider” inserts.
• Clamping via set screws or integrated clamping hub

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. #DWwebinar
Servo Insert Coupling Application!

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. #DWwebinar
Couplings Are Part Of A System!

29. #DWwebinar
Couplings Are Part Of A System!

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. Thank You
Ed Cole
Engineering Manager
Tel: [phone]
Email: [email protected]

32. #DWwebinar
Presented by: Bobby Watkins www.ruland.com
Flexible vs. Rigid Couplings
Presented by: Bobby Watkins www.ruland.com

33. #DWwebinar
Presented by: Bobby Watkins www.ruland.com
Types of Misalignment
Presented by: Bobby Watkins www.ruland.com

34. #DWwebinar
Presented by: Bobby Watkins www.ruland.com
Why is misalignment a concern?
• Adds stress to system components
• Caused by tolerance mismatch

35. #DWwebinar
Presented by: Bobby Watkins www.ruland.com
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. #DWwebinar
Presented by: Bobby Watkins www.ruland.com
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. #DWwebinar
Presented by: Bobby Watkins www.ruland.com
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. #DWwebinar
Presented by: Bobby Watkins www.ruland.com
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. #DWwebinar
Presented by: Bobby Watkins www.ruland.com
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. #DWwebinar
Presented by: Bobby Watkins www.ruland.com
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. #DWwebinar
Mike Santora
Associate Editor -
Moderator
Design World
@DW_MikeSantora
Edward Cole
Engineering Manager
Ringfeder Power
Transmission USA Corp.
[email protected]
Andy Lechner
Product Manager
R+W America
[email protected]
Flexible vs. Rigid Couplings
Bobby Watkins
Vice President of Sales
Ruland Manufacturing Co. Inc.
[email protected]
Questions?

42. #DWwebinar
Thank You
q This webinar will be available at
designworldonline.com & email
q Tweet with hashtag #DWwebinar
q Connect with Design World
q Discuss this on EngineeringExchange.com