| 摘要 |
<p>The concrete door (10) closes a semi circular shelter (12) and runs on friction rollers (14) carried on a steel rail embedded in the ground below the door. The drive chain (24) is fixed to both ends of the door, one of the fixings being adjustable (28) so that the chain tension can be regulated. The chain must have a length at least equal to the amount of opening required for the door. It is driven by the toothed drive shaft of a reduction motor (20), a guide (25) ensuring that the chain always engages the shaft.</p> |
