| 摘要 |
A dust cover comprises a plurality of shied plates which are equal in shape and progressively reduced in size. The shield plates are joined together such that they expand and retract along an axial direction; a linking device formed of a plurality of link rod units which have two rod members equal in length. The two rod members are pivoted together at the midpoint such that two ends of the two rod members form a pair of opening-closing arms. Two arms of each one end of each link rod unit are pivoted with two arms of other link rod unit to form two pivoting points pivoted in the lower side of the same shield plate.
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