Technological advances enable the engineers to design more complex systems and manufacture them using new materials and techniques. Although bioinspired mechanisms and robots have attracted many researchers and several studies have been introduced, there are so much to consider improving the performance of robots to accomplish desired tasks such as rescue, pick and place and quick response. Biomimetic robots mimicking the motion of a real undulating fish have been the interest of researchers as they have better performance compared to the propeller-driven underwater vehicles by means of its maneuverability and speed .

Fish locomotion is propelled by the undulatory motion of the body from head to tail or by the caudal fin in the form of waves. Existing fish robots also mimic the swimming motion either through the undulatory motion of pectoral fins or flexing of the caudal fin while completing the swimming gait cycle.  The main difference between two is while the former can travel long distances, the latter can perform slow swimming motion. Performance of the developed bio inspired fish-like robots are considered by their swimming speed in terms of their body length per second (BL/s). 

Compliant mechanisms in other words flexible systems, having the tendency to bend when subjected to any loading or displacement are appealed to be great candidates in the design of biomimetic locomotive robots. A mechanism can be manufactured as a single piece if designed fully compliant. Fully compliant mechanisms incorporate either distributed or lumped compliance depending on the design to lower the stress distribution acting on the flexible members. Compliant mechanisms can be manufactured by injection molding using polysilicon. Alternatively, they can be also 3D printed monolithically or separately on a 3D printer and assembled with joints. Common materials preferred for flexible links while 3D printing are polylactic acid (PLA), polyethylene terephthalate glycol (PETG), thermoplastic polyurethane (TPU) or thermoplastic elastomer (TPE). Main difference between each material is PLA can be utilized for small length flexure hinge designs, PETG is suitable if more bending is required as it is more flexible however it will yield easily under large deformations and TPU is more elastic and durable compared to PETG and TPE can considered as a medium between PETG and TPU filament.

This study presents the design and analysis of monolithically designed two compliant swimming robots that are actuated and controlled by single motor. Each design incorporates large deflecting compliant members and rigid levers to transfer the input torque to the different parts of the robot. While the first design integrates flexible tail to perform swimming motion, the second design adopts snapping type motion for the same action. Both mechanisms are 3D printed and tested for forward motion. The first robot has a constant speed of 0.68 BL/s while the second has an average speed of 0.6 BL/s.  Kinematic model using pseudo rigid body modeling (PRBM) is derived to calculate the load-deflection curves of the flexible tail for Design I, finite element analysis for deflection analysis are performed for Design II.


Bioinspired Monolithically Designed Compliant Swimming Robots

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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