| 摘要 |
A reversible drive mechanism comprises a shaft (18) provided with two axially spaced apart toothed rings (19,20). The teeth (21,22) extend in a generally radial direction and are inclined clockwise and anti-clockwise respectively. Hydraulic rams (23) are selectively actuated to engage the teeth (21,22) to rotate the rings (19,20) and the shaft (18) in either the clockwise or anti-clockwise direction. Continuous rotation of the rings (19,20) is achieved by operating the rams (23) in a phased relationship. The mechanism can be locked to prevent rotation of the shaft (18) by simultaneously actuating all of the rams (23) into engagement with the teeth (21,22). <IMAGE>
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