Mechanical torque limiters have been employed for many years as a simple and reliable means of torque overload protection in case of machine jams and crashes. They provide sound insurance against costly machine down time resulting from broken tooling, components, etc; and not to mention replacement of expensive, long lead time components. For this purpose, ball-detent style torque limiters have proven to be a compact and very dependable form of overload protection, reacting quickly (<3msecs) and accurately (+/- 5% of preset torque value). Most designs also offer zero-backlash and a high repeatability in terms of rotational position accuracy after re-engagement.
Ball-detent torque limiters normally incorporate a series of ball bearings, driven by a retaining ring machined around the base of the unit, and spring loaded into conical detents on a hardened steel output plate. At torque overload, the balls overcome the spring load, and roll out of their detents, allowing the output plate to spin freely over an integral bearing. The output plate is normally either a piloted flange or a flexible coupling for connecting to (and disconnecting from) another shaft.
Currently the ESL is available in the form of an elastomer insert coupling, which is a low cost but robust and backlash free form of flexible coupling. They are however designed for specific OEM applications and there is a certain degree of flexibility in design when manufactured in volume. Currently torque overload values from 0.1 ‚– 1,100 Nm (0.885 – 9735 in lbs) and shaft bore diameters of 3 ‚– 70 mm (1/8 to 2.75 in) are available.
::Design World::
Filed Under: Couplings, Motion control • motor controls
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