Fin ray-inspired, Origami, Small Scale Actuator for Fin Manipulation in Aquatic Bioinspired Robots

TL;DR

The study explores the nuanced interplay between undulation patterns, power distribution, and locomotion efficiency, underscoring the potential of the actuator as a model system for the investigation of energy-efficient propulsion and control of bioinspired systems.

Abstract

Fish locomotion is enabled by fin rays-actively deformable boney rods, which manipulate the fin to facilitate complex interaction with surrounding water and enable propulsion. Replicating the performance and kinematics of the biological fin ray from an engineering perspective is a challenging task and has not been realised thus far. This work introduces a prototype of a fin ray-inspired origami electromagnetic tendon-driven (FOLD) actuator, designed to emulate the functional dynamics of fish fin rays. Constructed in minutes using origami/kirigami and paper joinery techniques from flat laser-cut polypropylene film, this actuator is low-cost at £0.80 (\$1), simple to assemble, and durable for over one million cycles. We leverage its small size to embed eight into two fin membranes of a 135 mm long cuttlefish robot capable of four degrees of freedom swimming. We present an extensive kinematic and swimming parametric study with 1015 data points from 7.6 hours of video, which has been used to determine optimal kinematic parameters and validate theoretical constants observed in aquatic animals. Notably, the study explores the nuanced interplay between undulation patterns, power distribution, and locomotion efficiency, underscoring the potential of the actuator as a model system for the investigation of energy-efficient propulsion and control of bioinspired systems. The versatility of the actuator is further demonstrated by its integration into a fish and a jellyfish.

Figures (8)

• Figure 1: Fin ray-inspired actuator for aquatic robots (A) A fin ray (lepidotrichium) at rest and while bending. The yellow parts represents the collagen fibrils. The red arrow represents the pulling force (B) FOLD actuator mimicking bending in fin ray. Pulling the tendon causes deflection in the fin ray actuator. (C) Aquatic locomotion, the yellow highlight indicates the propulsion mechanism. From top to bottom: Median paired fin (MPF) propulsion, body-caudal fin (BCF) propulsion, jet propulsion. (D) FOLD actuator integrated in three distinct bioinspired robot morphologies: cuttlefish, fish, jellyfish.
• Figure 2: Assembly of paired fin ray. (A) Folding assembly: 1. The polypropylene sheet is laser cut and engraved to create the desired profile; 2. The flat laser cut profile is folded to create the spine and ribs; 3. Tabs and slits are used to secure the structure. Tendon hooks are folded up. (B) The tendon: Laser-cut from the PP sheet and attached to the tab at the end of the backbone. (C) The assembly process of the coil: 1. The straw is laser cut to size; 2. The rings are glued on to create the coil bobbin; 3. Copper windings are added. The tendon is attached using the slits. (D) Magnets are attached on either side of the spine. (E) The coil is slid over the limiter (black) and magnets to complete the assembly.
• Figure 3: Characterisation of the fin ray in water. (A) Left: Composite side-view stills of the fin ray oscillating at a frequency of 0.5 Hz. Right: Asymmetric curvature profile at a frequency of 4 Hz. (B) Peak-to-peak deflection amplitude as a function of the current of the fin ray loaded with different weights at the tip at a frequency of 0.5 Hz. The dashed line at a current of 212 mA marks the upper current limit before the actuator enters the saturation regime due to the mechanical limit.(C) Step response of the fin ray loaded with different weights, excited with a current step of 212 mA amplitude and 1 s duration (the white region indicates when the signal is on).(D) Frequency response of the fin ray under various load conditions (unloaded, loaded at the tip, enclosed in a membrane) under sinusoidal excitation with a peak current of 212 mA.
• Figure 4: Assembly of the CuttleBot. (A) Folding of the body: The laser-cut skeleton is folded to create spine and ribs, tendons are inserted through the T-hooks and secured to the fin rays. (B) Blade casting of the 0.8 mm thick silicon elastomer film. (C) The CuttleBot skeleton is embedded into the liquid silicone film, cured for 30 minutes and the outline defined using a scalpel. (D) The coils and magnets for the VCAs are added to complete the assembly.
• Figure 5: Characterisation of the fin membrane. (A) Completed CuttleBot. (B) Side view of travelling wave on one fin. (C) Wave amplitude at wavelengths and frequencies combinations.