| 摘要 |
PURPOSE:To facilitate the optional changeover of a rotary section between the rotating state and secured state with a dynamic pressure bearing, by providing an ordinary spring, a spring made of a shape-memorizing alloy and a heater at a place where the rotary section is supported in contact with a secured section when the rotary section is stopped. CONSTITUTION:In an embodiment for a beam-scanning rotary polygonal mirror unit in a laser printer, a drive shaft 2 provided with numerous slender grooves 2a on the peripheral surface is supported on the lower end at the bottom of a casing 1. A sleeve 3, on which a permanent magnet 4 is mounted, is loosely fitted on the drive shaft 2. A thrust receiver 5a is attached to the upper end of the sleeve 3 to support the shaft 2 on the upper end. A polygonal mirror 5 is mounted on the upper end of the sleeve 3. A pusher 9 is provided coaxially with the drive shaft 2 and placed at a cover 1a. A helical spring 10 is provided on the shank of the pusher 9 to urge it downward. A helical spring 11, which is made of a shape-memorizing alloy that is elongated at high temperature, is provided between a nut 12 and the cover 1a for the shank of the pusher 9. |
