Development of Underwater Drilling Robot Based on Earthworm Locomotion

In this paper, a drilling robot based on earthworm locomotion was developed for seafloor exploration. Seabed mineral resources are found on the bottom of the ocean. The drilling robot developed herein can excavate and obtain samples of seafloor soil. This paper was inspired by the results of the previous study, in which a drilling robot based on earthworm locomotion developed for land successfully demonstrated the ability to create curved boreholes of 1670-mm turning radius and 613-mm depth. By principle, earthworm locomotion is propelled without rubbing the side of the robot against the wall of the borehole. That is, the movement is not affected by earth pressure, and thus it is facilitated deep into the soil region, which makes it is suitable for underground exploration robots. Seafloor explorations, in essence, could be realized by improving the gripping torque of the drilling robot and reducing its drilling torque. To resolve the problem, in this paper, three points were addressed. First, a setae-attached propulsion unit patterned to an earthworm structure was designed to attain an improved gripping torque for a subunit, typically at 30 kPa, by 1.7 times compared to that without setae. Second, the drilling resistance was reduced by the adjustment of the penetration and rotational speeds of the drilling robot based on the drilling properties of underwater ground. Lastly, the shape of the earth auger was considered for the reduction of the drilling torque. Following these solutions, the developed robot succeeded in drilling 430 mm into an underwater soil.