Position detecting system for image forming appts. - includes two part photodiode providing two signals with difference proportional to position error

摘要

The position detector uses an optical system in order to detect the exact relative positions of the components of an image forming system. The image forming system includes a photo-sensitive surface on which an image is formed in the mfr. of electronic components. The detector may include a triangular reflecting prism (40) having a beam of light directed at one of its corners. The light is focussed by a lens (L3). The beam is split (41, 42) at the prism corner, and reflected towards two detectors (31, 32). The signals (s1, S2) provided by the two detectors are equal when the light is received symmetrically, corresponding to zero position error. For a non-zero position error, there is a difference in intensity between the two parts of the beam. The detector is intended to form part of a control loop.