| 摘要 |
A head lift body (42) with a head assembly (30) mounted thereon has a nut (45) engaged with a lead screw (41). The head lift body has an integral structure formed by resin molding with a through hole, a hollow opening, and a guide portion (47). The through hole receives the lead screw inserted therethrough. The hollow opening is formed at the center of the head lift body to accommodate a backlash preventing mechanism (43). The guide portion inhibits the rotation of the head lift body and guides the head lift body moving up and down along a rotation center axis of the lead screw. The backlash preventing mechanism comprises a preload bushing (431) and a preload spring (432). The preload bushing has an internal thread to be engaged with the external thread of the lead screw. The preload spring presses the head lift body against the preload bushing along the rotation center axis of the lead screw.
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