1. Field of the Invention
The present invention relates to an optical scanning device for an image forming apparatus which scans an original document for forming a light image of the original document on an image carrier.
2. Description of the Related Art
A conventional optical scanning device for an image forming apparatus, such as a copying machine, is reciprocally moved by a driving mechanism to scan an original document. A light image is irradiated on an image carrier, for instance, a photoconductive drum, by the scanning of the original document with the optical scanning device.
In a first conventional optical scanning device, the device comprises a pair of shafts, a carriage on which a lamp, a reflector and a mirror are mounted, a pair of pipe-shaped supporting members mounted on the carriage, and a moving mechanism for moving the carriage. The pair of shafts is inserted into the pair of supporting members, and thus the pair of supporting members slidably moves along the shafts. The carriage is operatively connected to the moving mechanism to be reciprocally moved along the shafts via the pair of pipe-shaped supporting members.
In a second conventional optical scanning device, the device comprises a pair of guide rails, a carriage on which a lamp, a reflector and a mirror are mounted and having a pair of extended portions, a pair of slide members made of plastic with a low coefficient of friction mounted on the pair of extended portions, and a moving mechanism for moving the carriage. The carriage is movably placed on the pair of guide rails via the slide members. The carriage is operatively connected to the moving mechanism to be reciprocally moved along the rails via the pair of slide members.
However, the above-mentioned conventional optical scanning devices have many problems. That is, force moments occur about the leading edge in the moving direction of the carriages at the start of forward movement and at the start of backward movement during the scanning operation of the optical scanning devices. In the first conventional optical scanning device, although a certain amount of clearance is required between the shaft and the pipe-shaped supporting member, when a force moment occurs at the start of reciprocal movement, rattling occurs between the pair of shafts and the pipe-shaped supporting members due to this clearance. This leads to a problem of poor picture quality due to the occurrence of image blurring.
In the second conventional optical scanning device, since the carriage is held only on the guide rails by its own weight via the slide members, there is a problem in that the carriage is liable to jump up at the start of reciprocal movement or due to other external forces and thus image blurring will occur. In either case, the higher the copying speed, the greater the blurring, and thus there is a problem in that the system cannot be applied to high-speed models.