Learning from biological attachment devices: applications of bioinspired reversible adhesive methods in robotics

Abstract

Many organisms have attachment organs with excellent functions, such as adhesion, clinging, and grasping, as a result of biological evolution to adapt to complex living environments. From nanoscale to macroscale, each type of adhesive organ has its own underlying mechanisms. Many biological adhesive mechanisms have been studied and can be incorporated into robot designs. This paper presents a systematic review of reversible biological adhesive methods and the bioinspired attachment devices that can be used in robotics. The study discussed how biological adhesive methods, such as dry adhesion, wet adhesion, mechanical adhesion, and sub-ambient pressure adhesion, progress in research. The morphology of typical adhesive organs, as well as the corresponding attachment models, is highlighted. The current state of bioinspired attachment device design and fabrication is discussed. Then, the design principles of attachment devices are summarized in this article. The following section provides a systematic overview of climbing robots with bioinspired attachment devices. Finally, the current challenges and opportunities in bioinspired attachment research in robotics are discussed.

Graphical abstract

Keywords

adhesion / bioinspired attachment / biomimetic gripper / climbing robot

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Nomenclature

Abbreviations
AR	Aspect ratio
AUV	Autonomous underwater vehicle
BL	Body length per second moved
CPG	Central pattern generator
DC	Direct current
DEA	Dielectric elastomer actuator
DOF	Degree of freedom
IMU	Inertial measurement unit
IR	Infrared ray
JPL	Jet Propulsion Laboratory
MSAMS	Mushroom-shaped adhesive microstructure
PDMS	Polydimethylsiloxane
PMMA	Polymethyl methacrylate
PS	Polystyrene
PU	Polyurethane
PUA	Polyurethane acrylate
PVS	Polyvinyl siloxane
QDD	Quasi-direct drive
RCM	Remote center-of-motion
SDM	Shape deposition manufacturing
SEA	Serial elastic actuator
SMA	Shape memory alloy
VMC	Virtual model control
WBC	Whole-body control
Variables
A	Hamaker constant
d	Normalized separation in the multiple wet adhesion model
D	Separation distance between the two surfaces
f	Normalized total force in the multiple wet adhesion model
F	Shear force along the attached substrate in Fig.13(a)
Fa	Force per area between two planar surfaces in van der Waals force model
Fcap	Capillarity force
Fhyd	Hydrodynamic force
Fn	Multiple wet adhesion
h	Height of the liquid film
hasp	Depth of the center of the asperity as shown in Fig.13(a)
n	Number of small drops
rs	Radius of the microspine
rtip	Radius of the claw tip
R	Radius of the contact unit in wet adhesion model
Rasp	Radius of the asperity in Fig.13(a)
s	Scale factor in the multiple wet adhesion model
t	Separating time of the two surfaces in wet adhesion model
V	Volume of one large liquid droplet
W	Weight acting on the claw directed normal of the attached surface
α	Angle as shown in Fig.13(a)
θ1, θ2	Contact angles of the liquid film with contact unit and the surface respectively in Fig. 8
θload	Angle between the surface and the direction of external force
θmin	Critical attachment angle between the attached surface and the claw
γ	Surface tension
η	Liquid viscosity
µ	Friction coefficient between claw end and attached surface

Acknowledgements

This work was financially supported by the National Key R&D Program of China (Grant No. 2019YFB1309600), and the National Natural Science Foundation of China (Grant Nos. 51775011 and 91748201).

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