Aug 28, 2018 | By Thomas

A bio-inspired robotic fish A bio-inspired robotic fish, which has flexible tail mechanism, can swim among its living counterparts quietly with lower consumption and higher maneuverability in water, where a conventional propeller AUV cannot reach. These kinds of robots are preferred for underwater exploration, observation andresearch purposes, especially where maneuverability is required. A group of engineering researchers from the University of Firat in Turkey are using biomimetic design and 3D printing to construct an intelligent robotic fish for real-world exploration and survey missions.

3D printed robotic fish prototype

The team published their work in a paper, titled “Mechatronic Design and Manufacturing of the Intelligent Robotic Fish for Bio-Inspired Swimming Modes,” authored by Mustafa Ay, Deniz Korkmaz, Gonca Ozmen Koca, Cafer Bal, Zuhtu Hakan Akpolat, and Mustafa Can Bingol.

This paper presents mechatronic design and manufacturing of a biomimetic Carangiform-type autonomous robotic fish prototype (i-RoF) with two-link propulsive tail mechanism. For the design procedure, a multi-link biomimetic approach, which uses the physical characteristics of a real carp fish as its size and structure, is adapted. Appropriate body rate is determined according to swimming modes and tail oscillations of the carp. ... the characteristics of the robotic fish are performed with forward, turning, up-down and autonomous swimming motions in the experimental pool. Maximum forward speed of the robotic fish can reach 0.8516 BLs-1 and excellent three-dimensional swimming performance is obtained. 

Important factors in the design of 3D printed biomimetic robotic fish are primarily the swimming modes and the body structure of the fish. In ichthyology, more than 85% of fish swim by bending their bodies and/or caudal fins (BCF) and about 15% of fish swim by median and/or pectoral fins (MPF). These biological properties indicate that BCF type Carangiform robot model is an appropriate approach for AUV design.

"There are two basic approaches in robotic fish design," the researchers wrote. "First is the biomimetic design which has certain requirements such as a tail with the size and number of joints to provide body travelling wave, and the ability to stay at a certain depth with the control of the center of gravity. The second design approach uses only the movement effects of fish, but it is not physically inspired by real fish."

The detailed mechanical configuration of the robotic fish.

Their robotic fish mimics BCF-type Carangiform swimming modes with a propulsive tail mechanism driven by servo motors. The robotic fish prototype consists of five basic components including anterior rigid main body, two-link tail mechanism, control unit performing Central Pattern Generator (CPG) model, the front sight unit and a flexible caudal fin. The anterior rigid torpedo-shaped body is designed for housing the electronics, sensors and Center of Gravity (CoG) control mechanism. CoG control mechanism successfully provides up-down motion abilities. The CPG-based locomotion controller is adapted to generate robust, smooth and rhythmic oscillatory swimming patterns. Tail links driven by high-powered servo motors and one flexible caudal fin fixed to peduncle are designed to generate a body travelling wave of the prototype. These links connected to each other in the shape of a series chain structure produce the thrust force needed for swimming motions. As robotic fish should be able to perceive static and/or dynamic obstacles in the environment as they move through the water, the team placed three Sharp infrared distance sensors in the left, right and front of the robotic fish.

Detailed mechanical configuration of the second tail link: unmounted and mounted models.

The 3D models of the robotic fish were designed in SolidWorks. The STL files were then converted to voxel format in Voxelizer where its layer, print and support point settings are configured. Each part of the prototype is 3D printed with PLA filament, and the flexible caudal fin is produced by using mold silicone. The outer caudal fin mold is also designed and produced with 3D-printing technology. All parts are covered with epoxy resin to prevent possible leakage from the micro pores formed in the production process. After the assembly phase, the outer surface is covered with synthetic paint to prevent leakages that may be caused by capillary cracks during assembly.

The 3D printed caudal fin.

The robotic fish prototype is approximately 500 mm long, 76 mm wide and 215 mm high. The prototype mass is also approximately 3.1 kg.

"The robotic fish prototype for three-dimensional motion abilities is investigated in the real experimental system. In these analyses, more than 72 different experimental studies were performed to obtain the characteristics of the prototype," the researchers explained. "In order to test the sealing performance of the mounted parts, they run during 6 hours in a water-filled test pool. The success of sealing tests is observed."

In the future work, the closed loop control performances of the prototype will be examined with different control structures, and swimming performance of the robot will be tested in different watercourses.

This robotic fish design provides versatile solutions for various different marine applications, such as examination of underwater resources, determination of pollution, observation of living forms, survey of submerged areas, fault detection in electricity or oil pipelines, coastline security and military missions.



Posted in 3D Printing Application



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