Optical sensor for interval control of vehicle windscreen wiper - directs light beam into internal face of windscreen acting as waveguide using TIR, and detects light reflected by rain drop and refracted into air at internal face towards sensor

摘要

A pulse of radiation from an emitter (1.1) impinges on the windscreen (1.5) at an acute angle ( alpha ) selected to give total internal reflection at the opposite, external face. A drop of water (1.4) on the outside modifies the boundary layer so that some light is transmitted and the remainder refracted through the incident face on to a photodetector (1.2) at a different acute angle ( beta ). The detector can be shielded (1.6) from direct sunlight and stray light emitted from other sources. ADVANTAGE- Wiper is set in motion in accordance with amount of rainfall windscreen.