| 摘要 |
A rotary mechanism for incrementally advancing a rotary element (13) with respect to a ground member (12) comprises a unidirectional clutch (41) and a rotary actuator (21, 33, 39). Actuation of the actuator is against a resilient bias (34), and overcomes friction between the rotary element and the ground member to advance the rotary element with the unidirectional clutch locked. Release of the actuator allows re-setting thereof by the resilient bias, the friction between the rotary element and the ground member resisting further relative movement. |
