Effect of penetration force on drilling efficiency for seabed drilling robot

Seabed mineral resources have been discovered on the bottom of the ocean; to utilize them, samples must be obtained and analyzed. In this study, a seafloor robotic explorer that can excavate and sample seafloor soil is developed. In a previous study, we developed a drilling robot that could excavate 650 mm into the ground while being underwater. And, we discovered that the excavation robot rotation speed, penetration force, and characteristics of the target ground affected the excavation resistance. In this paper, the effect of penetration force on excavation efficiency is verified experimentally using both dry and underwater silica sand ground with different ground characteristics. Results of the experiment indicated that the most efficient excavation was performed at 15 N in dry silica sand ground. In underwater silica sand ground, the excavation efficiency improved as the penetration force increased, and the most efficient excavation was achieved when the penetration force was 10 N. Hence, we concluded that controlling the excavation parameters, which are penetration force and rotational speed, enables an efficient excavation according to ground characteristics.