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.

/pdf/development-of-underwater-drilling-robot-based-on-earthworm-1fm7opslrx.pdf

Development of Underwater Drilling Robot Based on Earthworm Locomotion

Seabed mineral resources have been found on the bottom of the ocean, and to utilize them, samples must be taken and analyzed. This study develops a seafloor robotic explorer that can excavate and sample seafloor soil. In a previous study, we developed a drilling robot that could excavate 430 mm into the ground while underwater. However, excavation deeper than 430 mm was not possible because the discharging outlet became buried, making it difficult to discharge the drilled soil. In this paper, we develop a discharging mechanism utilizing water jetting to improve the excavation depth to 650 mm and potentially deeper.

Soil Discharging Mechanism Utilizing Water Jetting to Improve Excavation Depth for Seabed Drilling Explorer

Sampling of marine sediments is important in investigating ocean floor environments. In general sampling methods, equipment such as drills and pipes are made to penetrate the seafloor from ships and collect sediments. However, it is necessary to use large ship as existing exploration devices, resulting in enormous cost. In addition, this method is inefficient because the search range is limited to one point. To overcome this problem, we developed a sub-seafloor excavation robot called SEAVO that consists of an excavation unit and a propulsion unit. The excavation unit excavates and creates a borehole for propulsion. SEAVO is propelled by a propulsion unit based on the movement method employed by earthworms. In this paper, we present a setae propulsion subunit that imitates the earthworm's setae to realize underwater excavation and SEAVO II, which is equipped with the setae propulsion subunit. In the experiments conducted, SEAVO II effectively carried out underwater excavation, which verifies the usefulness of the developed subunit in underwater environments.

Underwater Excavation by Excavation Robot Equipped with Propulsion Unit Based on Earthworm Setae

Marine resources exist on the seabed, and sampling is useful for a detailed study of these resources. In general, a pipe-shaped sampler is used to collect marine resources for investigation. However, this is inefficient and expensive for investigating sediments, which are widely distributed, because the sampling range is limited to the pipe penetration part. Wide area exploration can be made possible by deploying multiple robots to autonomously search beneath the seabed. In a previous study, we developed a seabed robotic explorer called “SEAVO” and experimentally demonstrated the ability of SEAVO to produce curved boreholes with a turning radius of 1.67 m, and a depth of 613 mm, in the land environment. However, underwater excavation has not been successful. Reduction in the drilling torque is necessary for underwater excavation. In this paper, we propose a water jetting excavation method and consider the shape of the earth auger to reduce the drilling torque.

Water Jetting Excavation and Consideration of Earth Auger Shape to Reduce Drilling Torque for Seabed Robotic Explorer

In recent years, observations and explorations of the deep seafloor have been actively pursued. One goal of such explorations is to obtain the samples of seafloor mud and its inclusions. Mud that contains minerals and submarine microorganisms has great potential for studies in biology, geology, and marine science. To contribute to these efforts, we propose a robot using peristaltic crawling to excavate deep seafloor. The robot consists of three parts: excavation, propulsion, and extraction units. The propulsion actuator of the proposed robot must be able to function under water at high pressures. As the first stage in the development, we developed a subunit using an oil hydraulic artificial muscle intended for use in deep sea, and conducted a performance experiment under water pressure. Our results confirmed that the artificial muscle can be used in water pressures of up to 5 MPa.

Development of a Hydraulic Artificial Muscle for a Deep-Seafloor Excavation Robot with a Peristaltic Crawling Mechanism

The deep sea riser drilling vessel, CHIKYU started its scientific operation from 2007 after completed the shakedown and training cruises. It is capable of riser drilling up to 7,000m deep below sea floor at 2,500 water depth and aims to the seismogenic zone and mantle in the future. CHIKYU explores the Earth interior as the first riser equipped scientific drilling platform of the Integrated Ocean Drilling Program, to contribute such important scientific program as the Nankai Trough Seismogenic Zone Experiment, the Deep Hot Biosphere, the Japan Trench Fast Drilling, and the Deep Coal bed Biosphere off Shimokita. Any of these expeditions involve technological and operational difficulties related to strong current, high wave, strong wind, deep water, and deep penetration. This paper describes some topics of technological challenges for these expeditions.

Challenges to drill through seismogenic zone

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Challenges to drill through seismogenic zone