| 摘要 |
The invention having a chassis includes a transverse guiding plate located at the front side of the chassis and two sliding rods running through a sliding member which is run through by two rods from the front side to the rear side. A moving cap that the two rods run through is provided to cover the sliding member having a slant plate at the front side. An anchor slat which is run through by a moving bar having a rear end movable along the jagged teeth of the guiding plate at the bottom is provided in front of the moving cap to be pivotally coupled with a handle bar having a rear end coupled with rollers which press the slant plate. By depressing the handle bar downwards, the moving cap can be moved forwards to make the moving bar to escape the jagged teeth of the guiding plate to be repositioned.
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