| 摘要 |
A roof support capable of being moved by a drive mechanism while under permanent load includes two pairs of carriages, each carriage carrying an articulated track. The carriages of each pair are arranged one above the other and the two pairs of carriages are disposed parallel. The upper carriages can then be applied against the roof and the lower carriages against the floor of an underground gallery. The upper carriages are connected by at least one cross-member and the lower carriages are connected by two cross-members, and means are arranged to apply a force to the cross-members to separate the upper carriages from the lower carriages. The cross-members and carriages are connected together by pivotal joints.
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