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A jaw coupling is a type of motion control (servo) coupling designed to transmit torque (by connecting two shafts) while damping system vibrations, which protects other components from damage. Jaw couplings are composed of three parts: two metallic hubs and an elastomer insert called an element, but commonly referred to as a "spider". The three parts press fit together with a jaw from each hub fitted alternately with the lobes of the spider. The curved jaws of the hubs reduce deformation of the spider to maintain the zero-backlash fit.
The elastomer of the spider can be made in different hardnesses, which allows the user to customize the coupling so that it absorbs more or less vibration. The more damping ability the coupling has, the less torsional strength it possesses. Jaw couplings are best suited for applications that rely on a stop-and-go type of movement, where accuracy needs to take place upon stopping in order to perform any number of precision tasks, such as taking a high resolution picture (machine vision system). Absorbing vibrations decreases the settling time the system needs, which increases through-put. The jaw coupling is less suited for applications that rely on a constant scanning type of motion, where accuracy is required during movement, which requires a torsionally stronger coupling.
The drawback of the jaw coupling is the lack of misalignment capability. Too much axial motion will cause the coupling to come apart, while too much angular or parallel misalignment will result in bearing loads that are higher than most other servo/motion control couplings. Jaw couplings are also considered fail-safe. If the spider fails, the jaws of the two hubs will mate, much like teeth on two gears, and continue to transmit torque. This may or may not be desirable to the user depending on the application.
Jaw couplings are well balanced and able to tolerate high RPM. With its damping capability and interchangeable spiders, jaw couplings make a great solution for shock absorption.
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