US Patent 7256813 Optical scanner and image forming apparatus

An optical scanner for writing an electrostatic latent image on an image carrier includes a scanning optical system that forms an optical scanning path, a pair of optical detecting units arranged at two positions on the optical scanning path for detecting a write-start position and a write-end position to measure a time for scanning from the write-start position to the write-end position, and an optical housing that houses at least the scanning optical system and the optical detecting units. The optical detecting units are mounted on the optical housing via an intermediate member having a thermal expansion coefficient smaller than that of the optical housing.