In the trenching, one of the working targets of underwater construction robots, a long ditch for cable laying is dug by rotational torque of the trenching cutter generated by the force of bringing the trenching cutter into contact with the underwater ground. This contact force is generated by operating the boom cylinder which enables up and down movement of the trenching cutter or by the propulsive force of the track. This contact force applied to trenching cutter for trenching work should be maintained properly because when this force is excessive or insufficient, the trenching cutter stops or the work efficiency is not ensured, respectively. For the remote-controlled underwater construction robot, the operator should maintain the optimum torque of the trenching cutter by repeatedly operating the proportional control valve for driving the track drive motor or boom cylinder. This work requires a period of skill practice for proficient performance even on the ground and also causes fatigue quickly by repeated work even to expert. In the case of the seafloor, the work condition is more severe by the difficulty in obtaining visibility due to high concentration of float in the water caused from trenching work. The present paper proposes an active control technique for maintaining the optimal torque and speed for the trenching work. In order to evaluate the effect of the proposed control method for the trenching work, the experiments were performed.
As the marine energy and plant projects attract increasingly more attention of government and businesses, the need for construction equipment to develop the oceans has been raised, which led to the development of deep-sea robots to perform various tasks required for marine construction work [Lee et al., 2015]. Deep sea robots, based on the moving method, are divided into, into thruster-based underwater swimming robot, waterjet propelled skid-based mobile robot, and track- based mobile robot [Hettinger et al., 2005, Kim et al., 2016].
Track-based underwater construction robots are designed to perform underwater works such as pipeline burial and rock crushing under underwater ground conditions of compressive strength of 20 MPa or more. The track-based underwater construction robots are required to have impact resistance because of such need for heavy works. The underwater construction robot uses valve control type hydraulic system, a flexible power transmission system that has higher impact resistance than electric motor system and that generates power in Hydraulic Power Unit (HPU) and supplies the power to each actuator by adjusting the proportional control valve [Cho et al., 2010, Kim et al., 2016, Wang et al., 2012].
