Driving mechanism for a load with inertia

Claim 1

Apparatus for applying rotational driving torque to a load including in combination: a rotational load having predetermined inertia and presenting a first greater driving torque as said load is brought to an opening speed, and requiring a second lesser driving torque to maintain rotation of said load at the operating speed; a synchronous motor having an output shaft and capable of producing said second driving torque at its synchronous operating speed, said motor being incapable of producing said first greater driving torque at a speed below its synchronous speed and failing to rotate when a load requiring such greater torque is applied; and a slip torque clutch having a hollow cylindrical clutch drum and a clutch spring in engagement with the inner surface of said clutch drum, said spring resiliently urged outwardly into frictional contact with the inner surface of said drum for rotation therewith and including at least one projection thereon, a clutch shaft aligned with the axis of said clutch drum and carrying therewith a lever for engagement with said projection, said clutch drum connected for rotation with one of the output shafts of said motor and said rotational load and said clutch shaft connected with the other of the output shaft of said motor and said rotational load, and wherein the torque at which said clutch slips is selected to be less than the first greater driving torque which would prevent said synchronous motor from rotating upon initial energization.