Document reader and image and image forming apparatus capable of reducing line-shaped noise

摘要

A document reading unit constituting an MFP reciprocates a reading glass holder in a direction of a vertical scanning at a low frequency (18 times per second) with use of a crank mechanism including a motor and gears. A stroke length of the reciprocating motion of a reading glass is 9 mm. This structure can make a line-shaped noise less noticeable, because a length of each portion of a line-shaped noise becomes 2.57 mm and a distance between adjacent portions of the line-shaped noise becomes 7.27 mm when a foreign object having a diameter of 100 mum adheres to the reading glass.