Pulsed time-of-flight laser scanning techniques for industrial safety monitoring applications

Abstract

The pulsed time-of-flight laser scanner can be used to detect intrusions of humans or foreign objects into user-defined zones, give alarm or shut down hazardous equipment whenever the pre-defined zone is intruded. Working principles and system components of the laser scanner are introduced, and pulsed time-of-flight laser scanning techniques including laser transmitting, receiving, arrival time discrimination and time interval measurement are discussed in detail. High-repetition-frequency, narrow pulse semiconductor laser transmitting circuit is designed and realized to generate pulsed laser. Wide bandwidth and fast response time receiving circuit using avalanche photodiode is designed and realized to receive pulsed laser echo. Three time discrimination methods including leading edge, constant fraction and peak are discussed, and time discrimination circuits are designed. Experiment results indicate that constant fraction and peak time discrimination are not affected by changes in pulse amplitude. High resolution time interval and distance measurement is realized using integrated time-to-digital converter. By Comparing distance measurement value with distance setting value, the laser scanner can be used to realize both alarm and protection of user-defined zones.