Patent GB-158528-A (GB)
Title: Improvements in winding-gear for actuating automatic grabs
IPC: B66C3/12
Filed: 1920-07-29
Abstract: 158,528. Soc. de Construction et de Location d'Appareils de Levage et de Materiel de Travaux Publics. Jan. 30, 1920, [Convention date]. Addition to 147,524. Apparatus with jointly-controllable drums; brakes; driving-gear. - The mechanism for operating grabs described in the parent Specification is modified by the introduction of a ratchet wheel a mounted on the axle of the drum controlling the opening of the grab, a differential band brake d which prevents the movement of a pulley c in one direction only, and thus locks the central pinion of the planetary driving-gear, and a travelling nut f which is operated during the opening and closing movements of the grab hereinafter described. The whole of the mechanism is controlled from a single pedal. During hoisting of the grab, the differential brake is "on" and the consequential locking of the sun pinion of the differential gear allows the opening drum to be driven by the winding drum, both the winding and opening ropes being wound in at the same speed. To open the grab to dump the load, the pedal g is depressed for a half stroke, which is sufficient to engage the pawl b. On reversing the winding drum, the opening drum is retained by the pawl, and the transfer of the load from the winding to the opening rope allows the grab to open. Meanwhile the reversal of the winding drum tends to turn the pulley C in the reverse direction, and thus automatically relieves the brake and frees the central pinion, thus allowing the gearing to rotate idly during the opening movement without being disconnected from either drum. Prior to lowering the opened grab, it is raised sufficiently to allow the counterweight m to disengage the pawl b. The winding rope then is unwound, and the weight of the opening rope rotates the undriven opening-drum to pay out at the same rate as the winding-drum. If the opening drum over-runs, the effect is to cause a resultant rotation of pulley c in the direction for applying the brake and so coupling both drums for positive driving so long as the opening rope remains slack. When the grab rests on the heap and the ropes are slackened, the pedal g is depressed for a full stroke and then released again. Pawl b is engaged momentarily and disengaged again without affecting the apparatus, but the brake lever 0 is operated to put the brake in the "off" position in which it is held positively by the engagement of an arm q with a stop r irrespective of the rotation of the pulley c. The winding-drum then is operated for hoisting, and the grab is closed in the usual way. This. rotation of the winding-drum drives the gearing idly and the rotation of the central pinion traverses a nut f which removes the arm q at the end of the closing movement. The brake then is applied by rotation of the pulley c and the drums are coupled for the lifting of the grab. The nut f is restored to its original position by the rotation of the central pinion during the opening of the grab. In some cases the nut f may operate an electric switch to control an electromagnetically operated differential brake.