Underwater Robotics - Science and Technology for Subsea Exploration

Why do You Need Underwater Robotics?

Before the development of robots to explore the ocean, submarine pipelines and cables must be repaired when they are damaged or broken, or when the infrastructure of oil rigs and harbor terminals under the sea is checked for safety and stability, divers were relied on. These divers must risk dangerous dives into the deep sea to perform repairs, inspections, and even salvage tasks.

With the advancement of technology, these dangerous tasks have gradually been transferred to underwater robots, including oil extraction, submarine mineral exploration, underwater search, and salvage operations. Or inspection of submarine pipelines, underwater structures, submarine cables, oil drilling Underwater facilities such as platforms and harbors, and military operations have greatly reduced the risks faced by personnel when performing these tasks.

Exploring the deep sea can help humans analyze the evolution process of the earth and life, discover new biological species, and understand how biological groups survive in extremely dangerous environments. Even today, in the face of energy catastrophe, the detection and exploitation of new energy also need to rely on Sufficient deep-sea exploration capability. To meet the needs of developing oceans and sustainable oceans, underwater robots have become an important tool for exploring the unknown deep sea, and it is also the goal of competition and research and development among advanced countries in the world.

Uncharted Ocean Territories:

Due to the limitations of darkness, cold and high pressure, most of the deep-sea areas are unexplored by humans. Because seawater absorbs and scatters light, particles suspended in seawater also scatter light, making the deep ocean dark. The ocean also engulfs other types of electromagnetic radiation besides light, including radio signals. In addition, the deep sea is extremely cold, and the temperature in the water at a depth of 500 meters is usually only 4 to 6 degrees Celsius. In the deep ocean, devastating pressure restricts everything that enters it. This force is similar to atmospheric pressure on the ground, but because water is much denser than air, it increases by about 1 atmosphere for every 10-meter increase in water depth in seawater.

With the assistance of high technology, scientists have designed underwater robots that can overcome the high pressure and dark environment, and help humans to complete tasks in and out of the deep sea. Or stay in specific areas of the deep sea such as ridges and trenches for a long time to collect and detect data. Working at these deep-sea levels, combined with the high risks of using oil and gas, means many tasks are done autonomously, with ROVs, autonomous underwater vehicles (AUVs), and robotics leading the way.

What is Underwater Robotics?

• Underwater robots can be divided into two types: remote-controlled underwater robots and autonomous underwater robots. Autonomous underwater gliders are the deformation of autonomous underwater robots.
• Remotely controlled underwater vehicles: Also known as ROVs (remotely operated vehicles), they rely on a tether with copper wires or fiber optic bundles inside to connect to working research vessels on the sea to provide underwater robot motion required power, transmit control commands, and send back information gathered under the sea. ROVs have gradually replaced divers and become the mainstream of underwater operations. Because they can be equipped with robotic arms for exploration purposes, they are used for sample collection, seabed salvage, and my sweeping.
• Autonomous underwater vehicles: Also known as autonomous underwater vehicles (AUVs), they communicate freely in seawater through their batteries and autonomous navigation programs through sound wave communication. AUVs are often used in surveys and mapping operations under ice, military science applications, sonar deployment and safety monitoring posts, surveys of hazardous waste sites, geological vibration surveys and recordings of volcanic earthquakes, submarine shipwreck detection, port surveillance, environmental monitoring, submarine cable detection, etc. ROV is an underwater robot that can be remotely controlled. Generally, large ROVs have basic equipment such as the main computer, propellers, cameras, lights, and robotic arms. After transmitting power and signals through communication cables, the ROV pilot can be on board. For remote operation, and because the power is provided by the ship, the ROV has no working time limit in the water. ROV can be divided into 5 levels according to size and function, namely the first-level observation type, the second-level loadable observation type, the third-level working type, the fourth-level towed type, and the fifth-level prototype.
• Subsea seismograph: A subsea seismograph is a seismic observation system that places seismic sensors on the seabed. It can monitor and record seismic data, improve the location accuracy of earthquake hypocenters, and understand the structure of seabed stratigraphic profiles.

Features of the Underwater Robotics:

• Structure: To operate in the deep sea, the underwater robot must have a good structural design to withstand the increased seawater pressure due to the depth. Secondly, it is necessary to apply and integrate cutting-edge technologies such as sensing and control technology, signal processing, dynamic estimation, navigation and positioning, and communication, so that underwater robots can become intelligent individuals and can flexibly face the challenges of the harsh environment of the deep sea.
• Navigation and positioning: The underwater robot use the method of network dialogue with the acoustic transponder installed on the seabed to confirm its position. Every few seconds, the underwater robot transmits a sound wave signal to the transponder network, and each transponder responds to the underwater robot with its unique signal. From the information reflected by the three transponders in the network, the underwater robot can use simple trigonometric function calculations and rely on navigation technology to know the current position and orientation.
• Speed: Using Doppler sonar, the underwater robot sends fixed-frequency sound waves to the bottom, front, rear, left, right, left, and right directions of the seabed below, and then listen to the difference in sound frequency when they bounce back and can calculate its speed.
• Relying on ultrasound to snorkel in the deep sea: AUV underwater robots rely on the action of gravity and buoyancy to shuttle back and forth between the sea surface and the seabed. When diving from the sea, it uses gravity to glide down. When it reaches the target point, it throws out part of the counterweight lead block to balance its weight with the buoyancy and then turns on the thrust of the propeller and dives under the sea at maximum speed. With the help of ultrasonic sensors, AUV underwater robots can evaluate the distance of obstacles and maintain a certain altitude with the seabed. Then, the sonar or camera mounted on the bottom of the AUV body is started one after another, and the captured underwater image data is stored in the computer memory. When the power is about to run out, the AUV will throw away the last weight of the lead and float up gently, returning to the sea when it started.

What Substrates are Typically Used in Subsea Technology?

• BK7 (or equivalent): Typically used in submersible ROVs in the form of optical domes, the BK7 substrate has two main properties in underwater environments - durability and high transmittance. With excellent transmittance from 300nm to 2µm, BK7 is a relatively stiff material with excellent chemical durability, commonly used in high-pressure viewports and underwater cameras.
• Sapphire (Al2O3): Sapphire (Al2O3), known as one of the hardest materials on Earth, is another substrate used for viewports in windows and submersible applications.

How to Carry Out the Observation Task of the Vast Sea Area?

The concept of assembling a variety of underwater robots and organizing them into an ocean detection team is a feasible direction. At a low cost, small underwater robots that can be mass-produced can be used to observe a specific small-scale sea area, and then the observation data can be integrated into a large-scale observation result, which can effectively achieve the observation task of a large sea area.

Due to the maintenance of the formation of the underwater robot team, the relative positioning between adjacent underwater robots can be used, so there is no need for expensive navigation and communication equipment. And there is no need to worry about having to spend a lot of computing time to carry out the navigation control program. A network motion control method formed by the entire underwater robot team can also reduce the relative position error between each underwater robot, which is conducive to the collection and analysis of marine data. The collaborative division of work of the group robot network under the sea, and the concept of multi-machine division of labor to jointly complete larger sea areas and more complex tasks, it is an important trend in the development of underwater robot technology in the future.

Through the integration of the information collected by the sensors of different underwater robots, the research and development of team formation control technology, and the establishment of the underwater communication network, underwater robots of different models and functions can communicate, connect, and communicate with each other. , complete the group behavior control, monitoring management, system fault diagnosis, and other operations of underwater robots, and realize the ideal of group operation.