1. Field of the Invention
The present invention relates to an optical writing device and an image forming apparatus.
2. Description of the Background Art
It is known to use a laser writing device in an image forming apparatus such as a laser printer, a digital copying machine, a digital facsimile machine, and a multifunction machine. In a known laser writing device, a roller bearing for a polygon mirror is placed directly on a driving base plate. The polygon mirror rotates on the base plate, which is not surrounded by a barrier, such as a wall or a case. In another known laser writing device, the polygon mirror rotates within a case. The laser writing device that is not surrounded by the barrier is used only for limited applications in which the polygon mirror rotates at a relatively low speed. Because rotation of the polygon mirror at a relatively high speed is preferred, the laser writing device within the case is frequently used. Generally, the case is almost fully enclosed around the polygon mirror, such that noise caused by rotation of the polygon mirror is reduced or suppressed
In such a laser writing device, the case includes a housing which surrounds the polygon mirror and a cover disposed on an open top of the housing. Such an arrangement can be easily assembled. The cover is in the shape of a flat plate, and the cover is connected to the housing with bolts inserted through a peripheral portion of the cover into the housing. However, considerable noise is produced in the conventional case because of sympathetic vibration (resonance) or forced vibration, as well as other vibrations caused by a variety of factors. The factor includes air movement caused by rotation of the polygon mirror, and misalignment of a body of rotation such as the polygon mirror, among other factors. Accordingly, the known laser writing device including the housing and cover cannot effectively decrease noise and vibration.