As a member of robot families, climbing robots have become one of the research hot-spots in the robotic field recently and Gekko gecko (G. gecko) has been broadly seen as an ideal model for climbing robot development. But for gecko-mimic robots, one of the key problems is how to design the robot's foot. In this paper, (1) high-speed camera recording and electrophysiological method are used to observe motion patterns of G. gecko's foot when it climbs on different oriented surfaces; (2) nerve innervations of gecko's toes to motion and reception are studied. It is found that the five toes of the G. gecko can be divided into two motion and reception divisions, and also its motion and reception are modulated and controlled hierarchically. The results provide important information and exclusive ideas for the foot design and control algorithm of gecko-mimic robots.
Scanning electron microscopy (SEM) and histological techniques were used to observe and study the setae structures of two gecko species (G. gecko and G. swinhonis) and the relationships between these structures and the adhesive forces. The SEM results showed that the setae of these two species were densely distributed in an orderly fashion, and branched with curved tips. The setae of G. gecko had cluster structures, each cluster containing 4-6 setae whose terminal branches curved towards the center of the toes at ~ 10o, the tips of the branches like spatulae and densely arrayed at an interval of less than 0.2―0.3 μm. On the contrary, the branch tips in the setae of G. swinhonis were curled, and the terminal parts of setae curved towards the center of the toes at various angles. Usually the setae of these gecko species branch twice at the top at intervals greater than that of G. gecko. The histological observation found that inside the setae of these two species there were plenty of unevenly distributed contents, such as epithelia, fat cells, pigmental cells and muscle tissue, but no gland cells existed. The results of functional experiments suggested that modifying the structure of gecko’s setae could reduce its adhesive ability dramatically, demonstrating the positive correlation between the structure of the gecko’s setae and its adhesive ability. The above results provide important information in designing bio-mimic setae and bio-gecko robots.
GUO Ce1, WANG WenBo1, YU Min1, DAI ZhenDong1 & SUN JiuRong2 1 Institute of Bio-inspired Structure and Surface Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
To understand the mechanical interactions when geckos move on ceiling and to obtain an inspiration on the controlling strategy of gecko-like robot,we measured the ceiling reaction force(CRF) of freely moving geckos on ceiling substrate by a 3-dimensional force measuring array and simultaneously recorded the locomotion behaviors by a high speed camera.CRF and the preload force(FP) generated by the geckos were obtained and the functions and the differences between forces generated by fore-and hind-feet were discussed.The results showed that the speed of gecko moving on the ceiling was 0.17-0.48 m/s,all of the fore-and hind-legs pulled toward the body center.When geckos attached on the ceiling incipiently,the feet generated a very small incipient FP and this fine FP could bring about enough adhesive normal force and tangential force to make the gecko moving on ceiling safely.The FP of the fore-feet is larger than that of the hind-feet.The lateral CRF of the fore-feet is almost the same as that of the hind-feet's.The fore-aft CRF generated by the fore-feet directed to the motion direction and drove their locomotion,but the force generated by the hind-feet directed against the motion direction.The normal CRF of fore-and hind-feet accounted for 73.4% and 60.6% of the body weight respectively.Measurements show that the fore-aft CRF is obviously lager than the lateral and normal CRF and plays a major role in promoting the fore-feet,while the hind-feet of the main role are to provide a smooth movement.The results indicate that due to the differences of the locomotion function of each foot between different surfaces,the gecko can freely move on ceiling surfaces,which inspires the structure designing,gait planning and control developing for gecko-like robot.
On the basis of the microstructure of the cross-section of a beetle's elytra,three bio-inspired lightweight structures were designed and built from acrylonitrile butadiene styrene plastic with a three-dimensional printer.The mechanical properties of three lightweight structures were analyzed and compared employing the finite element method,and quasi-static compression experiments and a three-point bending test on the structure samples were carried out using an electronic universal testing machine to verify the effectiveness of the finite element method.The results show that all three bio-structures were lightweight and had excellent mechanical properties.In particular,the bio-structure with spherical holes and hollow columns perpendicular to the top and bottom surfaces best imitated the microstructure of the cross-section of the Cybister elytra and had the greatest specific strength/stiffness in compression and bending.Finally,a preliminary optimization design was obtained for this bio-structure to further improve its specific strength and specific stiffness to 31.82 kN m/kg and 108.73 kN m 2 /kg respectively.
The 3-dimensional interactions between toes of a gecko and substrates (ceilings or walls) were measured when it moves on ceilings or walls by using a 3-dimensional force measuring array,and the correspondent morphology of the gecko toes was recorded by a high speed camera.The study aims to understand the relationship between adhesive and shear forces generated by the toes of the gecko and the locomotion behavior when it walks on walls and ceilings.Results showed that shear force is along the toe-only 12.6° and 3.1° away from the toe for wall-climbing and ceiling-crawling,respectively while the adhesion is big enough to balance the body weight and moment.The shear forces generated by the first and the fifth toes are in opposite directions;this redundant force increases the reliability of adhesion and stability of locomotion.The support angles of toes are equal approximately for ceiling-crawling and wall-climbing.The study greatly inspires the design of a gecko-like robot.
WANG ZhouYi1,2,GU WenHua1,2,WU Qiang1,2,JI AiHong1 & DAI ZhenDong1 1 Institute of Bio-inspired Structure and Surface Engineering,Nanjing University of Aeronautics and Astronautics,Nanjing 210016,China
The study of the adhesion of millions of setae on the toes of geckos has been advanced in recent years with the emergence of new technology and measurement methods. The theory of the mechanism of adhesion by van der Waals forces is now accepted and broadly understood. However, this paper presents limitations of this theory and gives a new hypothesis of the biomechanism of gecko adhesion. The findings are obtained through measurements of the magnitude of the adhesion of setae under three different conditions, to show the close relationship between adhesion and status of the setae. They are reinforced by demonstrating two setal structures, follicle cells and hair, the former making the setae capable of producing bioelectrical charges, which play an important role in attachment and detachment processes. It is shown that the abundant muscular tissues at the base of the setae cells, which are controlled by peripheral nerves, are instrumental in producing the foot movement involved in attachment and detachment. Our study will further uncover the adhesion mechanism of geckos, and provide new ideas for designing and fabricating synthetic setae.
