1 Introduction
2 Dry adhesion
2.1 Biological devices and mechanism
Fig.2 Illustration of hierarchical structure of the gecko adhesive pad from macroscale to nanoscale: (a) ventral view of a tokay gecko (Gekko gecko), (b) foot, (c) setae, (d) single seta, and (e) arrays of spatular tips of a single seta. Reproduced with permission from Ref. [33] from Oxford University Press. |
2.2 Dry adhesives and their applications in robotics
2.2.1 Dry adhesives
Fig.3 Artificial adhesives used in robotics: (a) MSAMS adhesive used in TBCP-II, reproduced with permission from Ref. [53] from IOP Publishing, (b) MSAMS adhesive used in Mini-Whegs, reproduced with permission from Ref. [54] from IEEE, (c) MSAMS adhesive used in gecko robot_7, reproduced with permission from Ref. [55] from ACTA Press, (d) adhesives with wedged structure, reproduced with permission from Ref. [56] from Royal Society, (e) adhesives with wedged structure used in Stickybot, reproduced with permission from Ref. [24] from IEEE, (f) adhesives with wedged structure used in the space gripper, reproduced with permission from Ref. [57] from The American Association for the Advancement of Science, and (g) adhesives with wedged structure used in soft gripper, reproduced with permission from Ref. [58] from IEEE. |
2.2.2 Multilegged climbing robots
Fig.4 Multilegged climbing robots with dry adhesives: (a) Stickybot and its foot, reproduced with permission from Ref. [24] from IEEE, (b) LEMUR 3, reproduced with permission from Ref. [57] from The American Association for the Advancement of Science, (c) gecko robot_7 and its foot, reproduced with permission from Ref. [55] from ACTA Press, (d) Abigaille-III and its foot, reproduced with permission from Ref. [80] from Springer Nature, and (e) AnyClimb II and its flat adhesive foot, reproduced with permission from Ref. [81] from Elsevier. |
2.2.3 Wheeled and tracked climbing robots
Fig.5 Climbing robots with dry-adhesive wheels or tracks: (a) Waalbot II, reproduced with permission from Ref. [88] from IEEE, (b) Mini-Whegs, reproduced with permission from Ref. [54] from IEEE, (c) MultiTank, reproduced with permission from Ref. [89] from John Wiley and Sons, and (d) TBCP-II, reproduced with permission from Ref. [53] from IOP Publishing. |
2.2.4 Gripper
Fig.6 Robotic grippers with dry adhesives: (a) sucker covered with dry adhesive [93], copyright 2017, (b) gripper for manipulation in microgravity, reproduced with permission from Ref. [57] from The American Association for the Advancement of Science, (c) gecko-adhesive elastomer actuator grippers, reproduced with permission from Ref. [94] from IEEE, (d) soft gripper with dry adhesives and electrostatic adhesives, reproduced with permission from Ref. [58], (e) adaptive soft exoskeleton gripper with the directional adhesive, reproduced with permission from Ref. [95] from IEEE, and (f) farmHand, reproduced with permission from Ref. [96] from The American Association for the Advancement of Science. |
3 Wet adhesion
3.1 Mechanisms of wet adhesive
Fig.7 Tree frog toe from macro to micro, reproduced with permission from Refs. [11] from Springer Nature: (a) whole toe pad, (b) toe pad epidermis showing largely hexagonal columnar epithelial cells, the channels between them and a mucus pore, (c) view of a single epithelial cell showing evidence of nanostructuring on its surface, and (d) view of part of the surface of a single epithelial cell showing nanoscale peg-like projections. |
3.2 Wet adhesives
3.3 Applications in robotics
Fig.10 Applications of wet adhesion in robotics: (a) hexapod climbing robot, reproduced with permission from Ref. [104] from IEEE, (b) insect-scale climbing robot with wet adhesives, reproduced with permission from Refs. [122] from IEEE, (c) illustration of the robot climbing by hydrogel, reproduced with permission from Refs. [123] from The American Association for the Advancement of Science,and (d) soft gripper with wet adhesives, reproduced with permission from Refs. [124] from IEEE. |
4 Mechanical adhesion
4.1 Biological devices
4.2 Applications of mechanical adhesion in robotics
4.2.1 Bioinspired spine mechanisms
Fig.14 Bioinspired spine mechanisms: (a) compliant long-flexure spine mechanism with two types of materials, reproduced with permission from Ref. [19] from John Wiley and Sons, (b) compliant long-flexure spine mechanism with a single material, reproduced with permission from Ref. [141] from Springer Nature, and (c) cross-section of a linearly-constrained spine mechanism. |
4.2.2 Applications in feet of legged climbing robot
Fig.15 Applications of bioinspired spine mechanism in legged robots: (a) RiSE V2, its foot and toes, reproduced with permission from Ref. [18] from John Wiley and Sons, (b) CLIBO, reproduced with permission from Ref. [143] from Elsevier, and (c) BOB 2.0, reproduced with permission from Ref. [144] from IOP Publishing. |
4.2.3 Applications in wheeled and tracked climbing robots
4.2.4 Applications in robotic grippers
Fig.17 Application of mechanical adhesion in robotic grippers: (a) LEMUR IIB and its gripper, reproduced with permission from Ref. [19] from John Wiley and Sons, (b) JPL-Nautilus gripper, reproduced with permission from Ref. [150] from John Wiley and Sons, (c) pneumatic gripper with claws, reproduced with permission from Ref. [151] from Springer Nature, (d) soft spiny gripper, reproduced with permission from Ref. [152] from IOP Publishing, and (e) Treebot, reproduced with permission from Ref. [132] from John Wiley and Sons. |
5 Sub-ambient pressure adhesion
5.1 Biological suckers
Fig.18 Morphology and hypothesis adhering process of octopus sucker: (a) scanning electron micrograph of infundibulum of the octopus sucker, reproduced with permission from Ref. [166] from Oxford University Press, (b) internal diagram of octopus sucker, reproduced with permission from Ref. [168] from The Royal Society, and (c) attachment process of the octopus sucker, reproduced with permission from Ref. [168] from The Royal Society. |
Fig.20 Hierarchical structures from macroscale to microscale of clingfish sucker (Gobiesox maeandricus), reproduced with permission from Ref. [176] from The Royal Society, (a) clingfish and its sucker, (b) SEM of the ventral surface of the sucker, (c) SEM of a papilla, consisting of many rods subdivided apically into fibrils, and (d) SEM of the fibrils on the tips of the rod. |
5.2 Bioinspired suckers
Fig.21 Bioinspired suction cups: (a) sucker actuated by DEA and its attachment process, reproduced with permission from Ref. [181] from IOP Publishing, (b) CAD model of an octopus-inspired sucker actuated by SMA [182], copyright 2009, (c) magnetically actuated sucker, reproduced with permission from Ref. [183] from John Wiley and Sons, (d) octopus-inspired gripper [184], copyright 2019, (e) remora-like suction disc, reproduced with permission from Ref. [12] from The American Association for the Advancement of Science, and (f) clingfish-inspired sucker, reproduced with permission from Ref. [22] from IOP Publishing. |
6 Summary and discussion
6.1 Bioinspired adhesion devices
6.2 Focus on bionic climbing robot
6.2.1 Adhesive system and configuration
Tab.1 Typical climbing robots with dry adhesives |
Reference | Weight/g | Size/mm | Climbing angle and surface | Speed/(mm∙s−1) | BL/s | Configuration | Attachment device |
---|---|---|---|---|---|---|---|
Geckobot [82] | 100.0 | L = 190.00, W = 110.00 | 85° and acrylic surface | 10.00 | 0.053 | Four legs driven by linkage, six motors and an active tail | Gecko-like PDMS adhesive pad driven by tendons |
Stickybot [24] | 370.0 | L = 600.00, W = 200.00, H = 60.00 | 90° and glass, tile, acrylic, polished granite | 40.00 | 0.067 | A flexible body, four legs, 12 motors, and a passive tail | Gecko-like PU anisotropic adhesive pads driven by tendons |
CLASH [85] | 19.0 | L = 100.00 | 75° and acrylic surface | 100.00 | 1.000 | Six legs, a motor, and a scaled smart composite microstructure constructed body | RCM ankle and a wedge-shape PDMS adhesive pad |
Abigaille II [86] | 260.0 | D = 90.00 | 90° and PMMA | 1.00 | 0.011 | Six legs with three active DOFs | MSAMS PDMS adhesive pads |
Abigaille-III [80] | 634.6 | L = 200.00, W = 210.00, H = 90.00 | 90° and PMMA | 0.44 | 0.002 | Six legs with four active DOFs | MSAMS PDMS adhesive pads |
AnyClimb II [81] | 138.0 | L = 140.00, W = 120.00,H = 49.00 | 90° and acrylic surface | 12.50 | 0.089 | Eight legs, a steering mechanism with a motor and two bevel gears, and a passive tail | Vytaflex-10 flat adhesive pads |
UNIclimb [83] | 363.0 | L = 230.00, W = 200.00, H = 55.00 | 180° and glass | 14.00 | 0.061 | Four legs with three active DOFs | Multilayered footpad with MSAMS adhesives and SiO2-F hydrophobic coating |
Gecko robot_7 [55] | 700.0 | L = 400.00, W = 260.00, H = 80.00 | 180° and glass surface | 1.70 | 0.004 | Four legs with three active DOFs | Feet with four MSAMS PVS adhesive pads driven by tendon |
Gecko-like robot [193] | 1980.0 | L = 440.00, W = 260.00 | 90° and glass and Teflon | 6.00 | 0.014 | Four legs with three active DOFs | PVS MSAMS adhesive pad |
Waalbot II [90] | 85.0 | L = 95.60 | 180° and glass, acrylic, and wood | 50.00 | 0.523 | Two whegs, two motors, a passive joint in the pivot, and two passive tails | Whegs with three MSAMS PU adhesive pads and passively peeling ankles |
Mini-Whegs [54] | 21.8 | L = 47.00 | 180° and glass | 85.00 | 1.805 | Two whegs, a single motor, and a passive tail | Whegs with four MSAMS PVS adhesive pads |
Orion [91] | 71.5 | L = 59.04, H = 34.90 | 180° and acrylic surface | 30.00 | 0.508 | Two whegs, a single motor, and a passive tail | Whegs with bilayer adhesive pads made by PDMS and 3M VHB tape |
Tankbot [92] | 115.0 | L = 190.00 | 180° and wooden door, glass | 120.00 | 0.632 | Two tracks, a motor, and an active tail | Vytaflex-10 adhesive tracks |
TBCP-II [53] | 240.0 | L = 215.00, W = 200.00 | 90° and PMMA, glass and painted steel | 34.00 | 0.158 | Four actuated tracks and an active waist | MSAMS adhesive tracks made by PDMS |
Notes: L, body length; H, body height; W, body width; PMMA, Polymethyl methacrylate. |
Tab.2 Typical climbing robots with microspines |
Reference | Weight/g | Size/mm | Climbing angle and surface | Speed/(mm∙s−1) | BL/s | Configuration feature | Attachment device |
---|---|---|---|---|---|---|---|
Spinybot II [139] | 400 | N/A | 90° and rough wall | 23.00 | 0.053 | Six legs, seven servo motors, and a passive tail | Toe with spine mechanism fabricated by SDM |
RiSE V2 [18] | 3800 | L = 600 | 90° and rough wall | 40.00 | 0.067 | Six legs with two active DOFs and an active tail | Toe with spine mechanism fabricated by SDM |
ROCR [194] | 550 | L = 460 | 90° and rough wall | 157.00 | 0.340 | A pendulum-like tail and a main body with two claws | Steel claws |
CLIBO [143] | 2000 | L = 750 | 90° and rough wall | 60.00 | 0.080 | Four legs with four DOFs | Toes with steel claws |
DynoClimber [146] | 2600 | L = 400, W = 116, H = 70 | 90° and textile wall | 670.00 | 1.675 | Two four-bar linkage arms driven by a motor | Toes with spine mechanism fabricated by SDM |
BOB 2.0 [144] | 300 | Length of leg: 200 | 90° and textile wall | 250.00 | 1.250 | Two arms, a motor, and a passive tail | Toes with spine mechanism fabricated by SDM |
BOBCAT [195] | 5000 | L = 600 | 90° and textile wall | 170.00 | 0.283 | Four five-bar legs with two active DOFs | Toes with spine mechanism fabricated by SDM |
Wall climbing robot [194] | 400 | L = 480, W = 240, H = 30 | 90° and board | 46.00 | 0.096 | A body and four four-bar legs with two active DOFs | Flexible rubber pads with claws |
Soft climbing robot [147] | 37 | L = 120, W = 124, H = 42 | 90° and rough wall | 2.00 | 0.017 | An SMA driven body and two spiny feet | PDMS feet with steel microspines |
SpinyCrawler [148] | 208 | L = 242, W = 124, H = 42 | 180° and rough wall | 18.00 | 0.074 | A spiny track driven by a motor and two compliant tails | Spiny tracks |
Tbot [141] | 60 | L = 120, W = 110 | 100° and rough wall | 100.00 | 0.833 | Two wheels, a motor, and a passive tail | Spiny wheels printed by nylon |
TriDROP [149] | 394 | L = 470, W = 220, H = 100 | 90° and rough wall | 300.00 | 0.638 | Three wheels and an active waist | Spiny wheels made by SDM |
Treebot [132] | 600 | L = 325, W = 175, H = 135 | 105° and tree trunk | 300.00 | 0.004 | Two spiny grippers and continuum body | Passive spiny gripper with four fingers |
LEMUR IIB [19] | N/A | N/A | 105° and rock | N/A | N/A | Four legs with active three DOFs | Spiny grippers with 16 fingers and four DC motors |
LEMUR 3 [25] | 35000 | N/A | N/A and cliff face | 0.04 | N/A | Four legs with seven active DOFs | Spiny grippers with 16 fingers and four DC motors |
Free-climbing robot [132] | 1600 | W = 1600, H = 130 | 90° and artificial rock face with 1/3 gravity | 2.83 | 1.805 | Four legs with three active DOFs | Passive spiny gripper with six fingers and a motor for detaching |
Notes: N/A, not available; L, body length; H, body height; W, body width. |