Gecko adhesion based sea star crawler robot

Abstract

Over the years, efforts in bioinspired soft robotics have led to mobile systems that emulate features of natural animal locomotion. This includes combining mechanisms from multiple organisms to further improve movement. In this work, we seek to improve locomotion in soft, amphibious robots by combining two independent mechanisms: sea star locomotion gait and gecko adhesion. Specifically, we present a sea star-inspired robot with a gecko-inspired adhesive surface that is able to crawl on a variety of surfaces. It is composed of soft and stretchable elastomer and has five limbs that are powered with pneumatic actuation. The gecko-inspired adhesion provides additional grip on wet and dry surfaces, thus enabling the robot to climb on 25° slopes and hold on statically to 51° slopes.

Keywords: bio-inspired robots; gecko; gecko adhesion; sea star; soft-robots.

FIGURE 1

(A–E) Bioinspiration Images (A) Common sea star (Asterias rubens) (Image adapted from Heydari et al. (2020) (source: Shutterstock) with permission conveyed through Copyright Clearance Center, Inc.). (B) Tube feet of the sea star (Image adapted from Heydari et al. (2020), (source: Symbiotic Service, San Diego) with permission conveyed through Copyright Clearance Center, Inc.). (C) Ventral view of a tokay gecko (Gekko gecko). (D) Tokay gecko foot, showing array of setae-bearing scansors. (E) Microscale array of setae (Images adapted from (Autumn and Gravish, 2008) with permission conveyed through Copyright Clearance Center, Inc.).(F) Robot’s limb with gecko patch actuated. (G) Gecko Adhesion Based Sea Star (GASS) Crawler Robot. (H) GASS robot climbing a 25° slope.

FIGURE 2

(A) Gecko adhesive patch fabrication process. (B) Optical and atomic force microscopy (AFM) images of diffraction grating. (C) Scanning electron microscope (SEM) image of unpatterned silicone surface. (D) SEM images of patterned silicone surface. (E) AFM image of patterned silicone surface.

FIGURE 3

(A) Fabrication steps for the soft actuator. (B) Fabrication steps for the robot foot. (C) Fabrication process of the soft limb.

FIGURE 4

(A) Schematic vector diagram of limbs for movement of GASS Robot. Here l _limb and θ _limb denote the magnitude and angle of the movement vector for the limb, and θ _cmd denotes the commanded desired direction of movement of the robot. (B) The timing diagram for the basic crawling gait. Here, “Ext” and “Con” refer to extension and contraction of soft limbs respectively, and “E” and “DE” refer to engagement and disengagement of the gecko patch with the surface.

FIGURE 5

(A) Schematic of GASS robot. (B) Disengaged (left) and engaged (right) position of the gecko patch on the robot foot. (C) States of linear actuators. (D) Sequence of GASS robot motion phases for one cycle of motion.

FIGURE 6

(A) Schematic illustration of the limb adhesion test setup. (B) Gecko patch in the disengaged state (left) and in the engaged state (right).

FIGURE 7

Schematic illustration of static adhesion test measurement setup.

FIGURE 8

(A–C) Images of limb peel test taken from video footage. (A) Limb was placed on the test surface (B) The gecko patch was inflated with 2 mL of air and the initial position was noted. (C) Peel force was applied to the limb (Figure 6A). After a critical slipping force, the limb started slipping. The final position of the limb was noted after the Instron crosshead reached a displacement of 20 mm. (D) Limb peel test comparison on different surfaces (glass, acrylic and metal) in both, wet and dry conditions.

FIGURE 9

(A) Total distance traveled by the robot on dry and wet horizontal acrylic surfaces with and without adhesion in four cycles. (B) Initial position of the robot on horizontal, dry acrylic surface, image taken from video footage. (C) Final position of the robot on horizontal, dry acrylic surface, image taken from video footage. (D) Displacement of robot on horizontal, dry acrylic surface. (E) Initial position of the robot on horizontal, wet acrylic surface, image taken from video footage. (F) Final position of the robot on horizontal, wet acrylic surface, image taken from video footage. (G) Displacement of robot on horizontal, wet acrylic surface.

FIGURE 10

(A) Effect of increase in slope on the climbing speed of the robot. (B) Static adhesion test results for the robot. Error bars indicate standard deviation.