| 摘要 |
an optical sensor (10) of simple, low cost construction for detecting the entry of the leading edge (41) of a light-reflective surface (40) into the sensor's field of view includes an infrared sensitive phototransistor (20) positioned at the end of a light-collimating channel (16). A pair of pulse-powered, infrared, light-emitting diodes (30, 32) are also positioned at the phototransistor end of the collimating channel and bracket the phototransistor to highly illuminate an axially extending sector of the phototransistor field of view immediately adjacent the other end of the collimating channel. A pulse generating circuit stabilized for temperature and ambient light variations is connected to the phototransistor to provide a fast rise-time pulse in response to the detected leading edge. Proper dimensioning of the collimating channel length (L) and width minimizes errors caused by wandering of the reflective surface to and away from the sensor as the surface moves past it. |
