Actuatable stop

Claim 1

A stop for use with a crane having a rotatable pedestal mounted on a rigid base and driven in rotation by electrically powered means comprising: A. a stop ring circumscribing the pedestal and rigidly mounted on said base, 1. said ring being disposed concentrically of the rotatable pedestal and having upwardly disposed teeth of predetermined width measured circumferentially of the ring separated by interstices of substantially the saMe width; a pair of stops selectively positionable about the circumference of said ring B. locking means including, 1. a bracket mounted on said pedestal in spaced relation to the stop ring, 2. a pair of pins mounted in the bracket above the stop ring and in juxtaposition thereto for reciprocal elevational movement to and from ring engagement, a. the pins being adapted to be received by the interstices and b. having centers spaced a distance equal to an odd numbered multiple of the tooth width whereby when one pin is aligned with a tooth the other registers with an interstice, 3. resilient means urging the pins downwardly into ring engagement, and 4. electromagnetic means individual to the pins adapted when energized to retract their respective pins upwardly from the ring in opposition to the resilient means; and C. an electric circuit for supplying electrical energy to the electrically powered means and simultaneously to the electromagnetic means whereby the pins are retracted whenever the powered means in energized, 1. said circuit including a switch having actuating means engageable with said stops when said pedestal has been rotated through a predetermined rotation for simultaneously interrupting energization of the powered means and the electromagnetic means for release of the pins for receipt of one thereof into an interstice upon de-energization of the powered means.