Servo class couplings for high signal integrity
The operating principles of the Huco Dynatork flexible membrane - Flex M - and bellows couplings - Flex B, K and Ni - offer the highest performance available from a flexible coupling. With excellent kinematic properties and torsional stiffness of a very high order, they are suitable for servo drives and satisfy the criteria for highly dynamic position and velocity control systems.
Bellows couplings have the greater torsional stiffness while the flexible membrane, or disc coupling, has the more tolerant flexural system and features dynamically balanced construction. So what are the design and performance criteria governing the selection of these high performers?
They are the best choice where torsional stiffness is a critical parameter and when the backlash-free life requirement is beyond that of a sliding contact type coupling. Typically they serve applications with speeds of above 5,000rpm and when rotation is continuous or the duty cycle exceeds 50%.
Where a coupling with axial compliance is needed to protect fragile bearings from thrust loads and where environmental conditions favour an all-metal product, a Flex M or bellows type is ideal. They are best suited to applications where there is little risk of alignment errors exceeding prescribed limits during initial installation or on subsequent replacement of a motor or encoder.
The design of Flex M is characterised by thin, metallic membranes pressed from spring quality stainless steel that act as pivotal media. These are attached alternately to the drive and driven members and provide flex to compensate for misalignment. Any torque is resolved to simple tensile stresses as no secondary forming operations are involved in the coupling's manufacture.
Three versions of the Flex M are available: single stage (highest torsional rigidity), double stage and double stage with spacer (highest axial compensation). Typical applications for these products are in machine tools, robots, centrifuges, turbines and dynamometers.
The Flex B and Flex K stainless steel bellows couplings are available in three standard configurations: short, long and stretched - each with different characteristics to provide a wide choice for systems' designers.
Flex B flexible bellows are attached to the hubs by a unique swaging technique that overcomes the uncertainties of bonding or soldering. The convolutions are torsionally rigid but elastic in the lateral and longitudinal planes. This type of bellows coupling is limited to a peak torque of 12.5Nm and rated for continuous uni- and bi-directional rotation; up to 25,000rpm.
Flex K couplings have bonded hubs. The scope of this design, in terms of size and geometry, provides Huco Dynatork with greater opportunity to design and manufacture customised solutions.
Flex Ni is the popular electro-deposited nickel version of the bellows coupling, typically used in drives for sensitive instruments such as encoders, dynamometers and switches. Nickel bellows couplings accommodate a high degree of axial, angular and parallel misalignment through the flexure of their convolutions. These are formed by the electrolytic deposition of nickel to produce a stress-free and uniform, closely-controlled wall thickness.
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