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25 February, 2021

Simple coupling `cures back torque`

01 November, 2001

Simple coupling `cures back torque`

A Gloucestershire engineering firm claims to have developed a technique for stopping reverse torque from being transmitted back from the driven to the driving parts of a rotating mechanical system. Samar Systems of Coleford says that its simple, compact coupling device can be used for either in-line or concentric connections and can be incorporated in either conventional or epicyclic drives.

One traditional way to tackle back-driving is to rely on the frictional losses of large reduction gears. Samar asserts that its patented technique avoids the inefficiencies of this approach, and allows a direct (1:1) drive coupling speed ratio. It "grounds" any back-driven torque to its outside casting and thus to the machine frame, avoiding loading the prime mover and the risk of overloading a gear train.

The rotary torque management (RTM) system can withstand back-driven torque from either direction of rotation and is therefore suitable for applications where possible runaway of the driven side of the system must be avoided.

The sealed device contains a system of specially shaped rollers held by a planetary cage. If the input torque is larger than the back-driven torque and any frictional losses in the driven system, the device acts as a direct-drive coupling. If, however, the back-driven torque exceeds that of the input, the rollers automatically ground the output side to the casing. The transition between the two modes of operation is said to be smooth and jerk-free.

Samar envisages the coupling being used for a wide range of applications including the replacement of conventional sprog clutches, centrifugal brakes and backstops. It could be used as a safety device for cranes, hoists, lifts or escalators, as well as eliminating the need for ratchet-and-pawl mechanisms on equipment such as winches and capstans. Samar has built several prototypes and pre-production devices, and is developing the technology further. The company does not plan to put the RTM system into full-scale production itself, partly because of the cost and partly because the coupling needs to be tailored to each application. It hopes to form partnerships or licencing deals with coupling manufacturers and is already talking to several potential partners.

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