Bicode: A Hybrid Blinking Marker System for Event Cameras

In the field of robotics, tag systems play an important role in various applications, such as object identification and robot control in real-world environments. While typical visual markers use two-dimensional (2D) patterns and RGB cameras for recognizing object IDs and poses, achieving long-distance recognition necessitates increasing marker size and camera magnification to ensure the required resolution. Furthermore, the growing adoption of event cameras in robotics captures rapid changes in pixel brightness but faces limitations in recognizing stationary 2D markers. Although compact blinker markers using blinking light-emitting diodes (LEDs) achieve long-distance recognition, they are constrained by the number of IDs or recognition speed when used with standard RGB cameras. In addition, recognizing object pose using only a single blinking LED presents challenges. To address these challenges, we introduce ‘Bicode,’ an indoor visual marker designed for event cameras. Bicode seamlessly integrates 2D and blinker markers within a single marker unit. We have developed prototypes of 2.5, 5, and 10 cm square acrylic 2D markers, each equipped with a single LED blinking at 1 kHz, enabling recognition with an event camera. Our experiments revealed the effects of marker size, LED light quantity, recognition distance, and angle, external lighting conditions, and camera or marker movement on accuracy. Notably, using the 5 cm marker, we confirmed its compatibility to recognize IDs at distances exceeding 20 m, and pose recognition at 2.5 m was confirmed.