| 摘要 |
An overshot (10) comprises a latching mechanism (12) for latching a member such as a spear point (14); and, an actuator (16) which actuates the latching mechanism (12). The latching mechanism (12) has a number of different operational states. One of these is a neutral state in which latching mechanism (12) is able to latch or capture a spear point (14). In the neutral state, latching mechanism (12) is able to open in order to receive spear point (14) and then self- close to latch or retain the spear point (14). Latching mechanism (12) also has a locked state in which it is locked in a closed position by actuator (16) to prevent the release of a latched spear point (14). The third state is the release state where the overshot is locked in an open position by actuator (16) to release a previously latched spear point (14). The actuator (16) operates as a linear to rotary motion converter which converts linear motion of one part of the actuator to a rotary motion of another part of the actuator between a plurality of rotationally spaced positions. The rotational positions determine the state of the latching mechanism.
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