A Wheeled Robot Chain Control System for Underground Facilities Inspection Using Visible Light Communication and Solar Panel Receivers

The underground facilities require to be inspected regularly for long term and safe-use. Several mobile inspection systems are widely used, but some crucial problems with the limited inspection distance still exist due to the unstable wireless communication and cable restrictions in complex facilities. To solve these problems, we propose a wheeled robot chain control system (RCCS) for underground facilities inspection based on visible light communication (VLC) and solar panel receivers. The RCCS consists of a leader and follower robot and can extend the inspection range with special 'optical signal relay' technology. VLC can provide not only illumination for inspection but also less attenuation, higher information security, and stronger antielectromagnetic interference capability, compared with conventional radio communication in complex underground facilities. Using solar panels can increase the receiving area of optical signals, environmental adaptability, and system robustness, compared with conventional photodiode (PD) receivers. Moreover, to ensure longer and more stable communication, we develop an optical signal relay mechanism along-side an attenuation control module. We performed several experiments to evaluate the signal waveform, communication quality, effective communication region, and cooperative movement. The results indicated that the proposed system could extend the inspection range with higher communication quality and environmental adaptability than VLC-based system with PD receivers.