Synchronization of Multiple Time-of-Flight Cameras Using Photodiodes

Abstract

Time-of-flight (ToF) cameras are an evolving technology, finding applications in a wide range of fields, including machine vision, automotive applications, face or hand recognition, and human-robot collaboration. A setup consisting of multiple ToF cameras can provide a 3-D model of the recorded scene with a larger field of view and avoid occlusion. The operating principle of ToF cameras' requires the emission of light to measure its round-trip time to the objects in the field of view and the reflection back to the camera. If multiple ToF cameras operate simultaneously, their light waves may interfere, resulting in erroneous depth measurements. In this paper, we propose a multi-camera time-of-flight system based on dynamic time-division multiple access (dynamic TDMA) to avoid any interference. The time synchronization is implemented optically, so that no further time synchronization, external to the cameras, is required. To achieve a high frame rate, every camera is extended with a photodiode, signaling a free channel. A synchronization protocol is implemented to allow for an autonomous operation of the ToF cameras.