Remotely Operated Vehicles (ROVs) and Autonomous Underwater Vehicles (AUVs) are well known in the field of underwater robotics. Many of these vehicles use infinitely rotating propellers (thrusters) to move. However, while propellers are efficient in moving vehicles, they can cause malfunctions in underwater environments where debris, algae, and water plants are scattered about, and can become entangled in them. In such environments, a propeller that uses only reciprocating motion may be more useful than an infinitely rotating propulsion mechanism. Therefore, we are studying a snake-like robot for underwater swimming that uses only the reciprocating motion of its joints.
Generally, in order to realize an underwater robot, all motors, circuit boards, etc. are placed in a waterproof container and the gaps are filled with rubber seals to prevent water from entering the robot. However, the rubber seals rub against joints that must move relative to each other, resulting in a large energy loss and making it difficult to control weak forces.
For this reason, this study employs submerged geared electric servomotors that do not require waterproof seals in the joints of an underwater swimming robot, and examines the effect on underwater force control performance when water completely submerges the inside of the motor and reduction gear.
For general DC motors, the output torque is proportional to the current. The elimination of the waterproof seal reduces the effect of excess friction, making it easier to control the joint torque only by controlling the motor current. With these features, we are aiming to realize new interactions with the underwater environment, such as letting an underwater snake-like robot wrap itself around a structure, or moving forward in a narrow underwater crevice while successfully controlling the forces from the environment.
The motor is a brushless DC motor with anti-corrosion treatment, and the reduction gear is an S-bear DD plastic gear manufactured by Starlite Corporation. The motor does not require lubricating oil and has high sliding characteristics and heat resistance, making it suitable for underwater use. All bearings are made of ceramics.
※本成果は，科学研究費助成事業（基盤研究(B)）「トルクセンサレス・シーリングレス水陸両用柔軟アクチュエータの基礎研究」22H01456の支援を受けました．本研究の減速機にはスターライト工業株式会社製のS-BEAR DD4830を用いています．
Elemental studies related to this study
Related works
- Shah Darshankumar Rajendrakumar, Atsushi Kakogawa, and Shugen Ma, An Underwater Snake Robot that Does Not Consider Actuators’ Waterproof: Design and Primary Experiments, Proc. The 2023 IEEE Int. Conf. Robotics and Biomimetics (ROBIO 2023), pp.226-231, 2023