Patent ID: 8412081

Claim:
A belt meandering preventing device, comprising: a belt displacement detection unit detecting an amount of displacement in a belt width direction of an endless belt rotatably stretched over support parts; and a belt meandering correction unit correcting the displacement in the belt width direction of the endless belt based on the amount of displacement detected by the belt displacement detection unit, wherein the belt displacement detection unit includes a moving part moving in association with the displacement of the endless belt or an edge of the endless belt in the belt width direction, and optical sensors outputting signals with output levels corresponding to proportions of the moving part in optical paths of the optical sensors; the optical sensors are arranged such that the output levels of the optical sensors change as the endless belt is displaced in the belt width direction in a predetermined high-resolution detection range; and the belt displacement detection unit is configured to combine the output signals of the optical sensors such that a rate of change of an output level of the combined signal with respect to the amount of displacement in the belt width direction of the endless belt within the high-resolution detection range becomes greater than rates of change of the output levels of the respective optical sensors and to detect the amount of displacement based on the combined signal.