| 摘要 |
A roller assembly includes an elongated casing with a shaft longitudinally provided within it. A U-shaped bracket with two opposed sides and a bottom connecting the two sides is fixed in the elongated casing. A threaded rod is sleeved on the shaft in such a way that it can rotate along with the shaft. A guiding block having a first face, a second face and an internally threaded through-hole is sleeved on the threaded rod. Each of the face have a guiding wheel. The block is sized and designed so as to sit flush on the U-shaped bracket and prevent the bracket from rotating with the threaded rod, but allowing instead the block to move axially along on the threaded rod. One end of a first string connects to one end of the threaded rod and winds on the same to a position adjacent to the first face whereat the first string is held straight between the guiding wheel on the first face and the threaded rod. A second string is also held straight between the guiding wheel on the second face of the block and the threaded rod in the same manner.
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