Motion Control Couplings
STAINLESS BELLOWS | ALUMINUM DISC MEMBRANE | OLDHAM COUPLING
UNIVERSAL LATERAL COUPLING | MULTI BEAM COUPLING | MINI JAW COUPLING

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Bellows Type	Membrane Type	Oldham Type	Universal/Lateral Type	Multi Beam Type	Jaw Type
Bore Adapters
General Description
Precision couplers with excellent kinematic properties. Torsionally rigid, near infinite backlash-free life.	Precision couplers with excellent kinematic properties. Dynamically balanced construction. Single-stage versions make up into 'whirl' free Cardans. The 2-stage versions offer short envelopes and low bearing loads respectively. Near infinite backlash-free life.	General purpose, robust, easy to use 3-part couplers with replaceable wear elements. Generous radial compensation and pull-apart / re-engage facility for blind assemblies. Backlash-free to 108 revs.	Unique, general purpose light duty couplers with generous angular and radial misalignment compensation. Resists axial motion, can anchor unrestricted shafts and perform light push/pull duties. Backlash-free to 108 revs.	Single piece coupling, constant velocity and spring rate, zero backlash. Available in aluminum, stainless or acetyl.	General purpose elastometric 3-piece coupling with variable durometer spider elements. Zero backlash to preload limit of element.
Where to Use
High-precision servo drives, pulse generators, scanners, positioning slides, metering valves, etc.	High-precision servo drives, pulse generators, scanners, positioning slides, high speed dynamometers, unsupported drive shafts, etc.	Stepper drives for most applications including positioning slides, pumps, actuators, etc.	Encoder, resolver, tacho, potentiometer drives. Small positioning slides, dosing pumps & light drives.	Instrumentation, encoders, lead screws, small pumps, and feed rollers.	Stepper drives for most applications including positioning slides, encoders, resolvers, tachometers.
Speeds
Up to 10,000 rpm in standard form	Up to 25,000 rpm.	Up to 3,000 rpm.	Up to 3,000 rpm.	Up to 25,000 rpm.	Up to 40,000 rpm.
Peak Torque Largest Size
110 In#	530 In#	390 In#	31 In#	133 In#	185 In#
Standard Bores
0.118" to 0.787" (3 to 20mm)	0.118" to 1.102" (3 to 28mm)	0.078" to 1.181" (2 to 30mm)	0.118" to 0.629" (3 to 16mm)	.079" to 1.500" (2 to 38mm)	.118" to .945" (3 to 24mm)
Temperature Range
-40 to +248°F	-40 to +248°F	-4 to +140°F	-4 to +140°F	-40 to +248°F	-40 to +248°F
Electrically Isolating
No, unless used with insulating bore adapters		Yes	Yes	Yes (acetyl)	Yes
Connection
Clamp or set screw	Clamp or set screw	Clamp or set screw	Clamp or set screw	Clamp or set screw	Clamp or set screw

Several issues must be considered when selecting a flexible coupler: Does it provide adequate misalignment protection? Can it transmit the load torque? Can it sustain the required speed of rotation? Will it fit within the available space envelope? Can it operate at the designated ambient temperature? Does it provide the required torsional stiffness? Does it provide electrical isolation between shafts? Will it have the required life expectancy? Will it meet my cost expectations? Misalignment compensation and axial motion These properties differentiate a flexible coupler from a solid sleeve type. The nature of the enabling mechanism (i.e., bellows, membrane, Oldham, etc.) determines almost every other performance characteristic of the coupler, including its tolerance of misalignment and/or axial motion. Oldham and universal/lateral types can tolerate misalignments but their backlash-free life may reduce as a result; bellows types can absorb significant axial motion but their misalignment capacity may suffer accordingly; membrane couplers are irrevocably damaged if axial motion exceeds the catalogue specification, but can accommodate large misalignments with no reduction in life expectancy if the distance between membrane centers is increased, typically by linking a pair of single-stage couplers with an intermediate shaft. Incidental misalignment is caused by manufacturing tolerances, thermal expansion, wear, fitting difficulties and structural settlement. The resultant errors are small, generally in the range 0° - 1/2° angular and 0-0.008" parallel, and are difficult to predict. Be aware that a 0.008" parallel error can grow substantially due to adverse interaction with the angular component. When misalignment is incidental, it is more realistic to consider the effective radial error, being the radial distance between shaft center lines measured midway along the length of the coupler. In effect, this is the composite error and is what matters when determining a value for maximum misalignment. Only a radial-value need be specified. Axial motion can result from axial clearances in the shaft bearings, or from shaft growth due to thermal expansion. It is usually beneficial to absorb this with a suitable coupler. In some cases, however, it may be preferable to resist the axial motion of an unrestricted shaft, particularly if this has a positioning function, and anchor it to a stable motor shaft. Couplers such as the universal/lateral can be useful in these cases.

The reason we use flexible couplers is to protect the shaft support bearings from destructive radial and thrust loads due to misalignment and axial motion, it follows that those with least resistance can better protect the bearings. Fig. 1 compares the radial bearing loads of a number of popular couplers. Excluding the 1.125"Ø jaw coupler, all results were obtained with couplers of nominal outside 1"Ø. Load torque, inertia and torsional stiffness Applications in which couplers are used for driving so-called frictional loads, for example pumps, shutter doors, textile machinery, and so on, are not generally sensitive to coupler torsional stiffness because angular synchronization of the shafts is not an issue. When resonance is a problem, it is possible to reduce the coupler's torsional stiffness and thus avoid conflict with the natural resonant frequency of the machine which is most likely operating at constant speed. This is not a solution when the loads are inertial, typified by position and velocity control systems, where registration of input and output shafts is critical throughout the operating cycle. In these systems, motor, coupler and load form a resonant system. Its resonant frequency depends on the load inertia and on the coupler's torsional stiffness. Increasing the load inertia, or decreasing the coupler's torsional stiffness, lowers the resonant frequency. To control a resonant system you have to be working well below its resonant frequency. Imagine you are holding an elastic band with a weight suspended from it. You can control the vertical movement of the weight provided you move your hand slowly. Speed up the movement and the weight barely moves. To improve response, you need a less "elastic" elastic band, or you need to reduce the weight at the end of it. Substitute a coupler for the elastic band, and an inertial load for the weight, and you have a good analogy for an inertial system. When the focus is on performance, a stiffer coupler reduces setting times, improves positional accuracy, and raises the upper limit of dynamic performance. Fig. 2 compares torsional deflection tests (the inverse of torsional stiffness) for a number of popular couplers. Excluding the 1.125"Ø jaw coupler, all results were obtained with couplers of nominal outside 1"Ø.

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