The webinar discusses the differences between flexible and rigid couplings, focusing on their applications, benefits, and limitations. It highlights the importance of addressing misalignments in shaft connections and presents specific coupling types suitable for various automation systems. The discussion also includes technical details about designing couplings for operational efficiency in high-precision environments.

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Flexible vs. Rigid
Couplings

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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

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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…

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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

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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

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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

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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

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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

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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

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

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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

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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

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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

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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

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THANKS FOR YOUR TIME!

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

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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.

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

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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.

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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:

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

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Metal Bellows Coupling!

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

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• 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!

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Servo Insert Coupling Application!

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• 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!

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Couplings Are Part Of A System!

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Couplings Are Part Of A System!

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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: (201) 666-3320
Email: edward.cole@ringfeder.com

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.
Edward.cole@ringfeder.com
Andy Lechner
Product Manager
R+W America
Alechner@rw-america.com
Flexible vs. Rigid Couplings
Bobby Watkins
Vice President of Sales
Ruland Manufacturing Co. Inc.
Robert.watkins@ruland.com
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