| 摘要 |
A mechanism for selective translation of an object along first and second axes comprises a frame, a carriage mounted on the frame for sliding movement with respect to the frame along the first axis, a holder for said object and an intermediate mounting means coupled to the holder and the carriage for mounting the holder on the carriage for sliding movement with respect to the carriage along the second axis. A motor is provided for selectively driving a first shaft and a drive/brake assembly provides a second shaft. In a drive mode of the assembly the second shaft is allowed to be driven synchronously with the first shaft and, in a brake mode of the assembly, is held non-driven while the first shaft is being driven. First and second endless belts are coupled to the first and second shafts, respectively, for receiving selective rotational movement therefrom. The first belt is also coupled to the intermediate mounting means for causing selective movement of the object holder along the second axis and the second belt is also coupled with the carriage for causing selective movement of the carriage along the first axis. In operation, when both belts are rotated, the second belt causes the carriage to move along the second axis, while the intermediate mounting means does not cause movement of the object holder due to the synchronous movement of the intermediate mounting means with the first belt due to coupling of the intermediate mounting means on the carriage. However, when the second belt is not driven during the brake mode of the drive/brake assembly, relative movement of said first belt with said intermediate mounting means causes sliding movement of the object holder along the second axis.
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