What to look for in a servocoupling

Torque, shaft misalignment, stiffness, rpm, and space requirements are some of the factors to consider when selecting a coupling for servo applications. Servocouplings come in a variety of designs but all have zero backlash. Servocouplings are typified by their ability to transmit torque with zero backlash. There are several different coupling designs with this property, so which one should you choose? Here are some basic guidelines to help decide. Beam-type couplings come in single and multiple-beam styles and are typically made from a single piece of aluminum. Single-beam couplings have one continuous helical cut about their OD spanning several rotations. They are highly flexible, transmit low bearing loads, and tolerate angular misalignment or axial motion. Parallel misalignment makes the coupling beam bend simultaneously in two directions, which develops high stresses and shortens service life. Single-beam couplers also tend to windup under torsional load and so are best for such lowtorque uses as connections to encoders and other light instrumentation. Multiple-beam couplings, as the name implies, use two or three overlapping short beams. The arrangement retains much of the misalignment capability of single-beam types yet boosts torsional stiffness and torque capacity. Of course the added stiffness also raises bearing loads when couplings are misaligned. On the upside, multiple beams better handle parallel misalignment than single-beam types. Stainless-steel units have improved corrosion resistance and double the torque capacity and stiffness of comparable aluminum parts. However, small drive motors can have trouble accelerating the added mass and inertia. Multiple-beam couplings work best for such light-duty applications as connecting a servomotor to a leadscrew. Oldham couplings consist of two hubs and a plastic or metal center insert. Drive tenons on the hubs transmit torque to mating slots in the insert located 90° apart on opposite sides. The three parts join with a slight press fit