| 摘要 |
A mine-roof support has a floor beam, an advancing ram and a relay bar. A bell-crank lever is pivotally-connected to the floor beam and the advancing ram is pivotally-connected to the bell-crank lever. One arm of the bell-crank lever has a member which may be in the form of a ball. The pivotal connections are such that, on extension of the ram, when the relay bar is connected to part of a conveyor, the bell-crank lever is initially urged downwardly from an inoperative position away from contact with the relay bar, into an operative position in contact with the relay bar, thereby to apply an upward thrust to the front end of the support and to maintain an upward thrust during further extension of the ram and consequential advancing movement of the mine-roof support towards the conveyor. |
