Design and fabrication of a gecko-inspired surface for improving the grasping ability of a humanoid dexterous hand

Many studies have examined the design,fabrication and characteristics of gecko-inspired adhesives,but applied research on gecko-inspired surfaces in humanoid dexterous hands is relatively scarce.Here,a wedged slanted structure with a curved substrate suitable for humanoid dexterous fingers was designed and manufactured via ultraprecision machining and replica molding.The adhesion and friction properties of the wedged slanted structure show obvious anisotropic characteristics in the gripping and releasing directions,and the influence of structural parameters and motion parameters on the adhesion and friction was systematically studied.The humanoid dexterous fingers with gecko-inspired surfaces greatly increased the grasping force limit(increase to 4.02 times)based on the grasping of measuring cups with different volumes of water and improved the grasping stability based on the picking up of smooth steel balls of different diameters.This study shows that this process,based on ultraprecision machining and replica molding,is a green,high-efficiency,and low-cost method to fabricate large-area biomimetic surfaces that has potential applications in dexterous humanoid hands to improve grasping ability,stability and adaptability.

Fabrication and Characterization of Gecko-inspired Dry Adhesion, Superhydrophobicity and Wet Self-cleaning Surfaces

In this study, gecko-inspired polydimethylsiloxane （PDMS） microfiber surfaces were fabricated by combining Inductively Coupled Plasma （ICP） and micro-mold casting. The effect of roughness and surface energy of counterface on the adhesion of gecko-inspired microflber surfaces and its superhydrophobicity and wet self-cleaning were studied. The adhesion of gecko-inspired microfiber surfaces depended on the roughness of the eounterfaces due to the influences of contact area and interlocking mechanism. SEM images of interfaces between counterfaces with different roughness and gecko-inspired mi- crofiber surfaces revealed the matched and dis-matched contact directly. The gecko-inspired microfiber surface got the larger adhesive force from the higher surface energy counterface, which is consisted with Johnson-Kendall-Roberts （JKR） theory. The smaller dimension and lower duty ratio of microfibers on PDMS resulted in the increasing of Water Contact Angle （WCA） and the decreasing of Sliding Angle （SA） compared to those of smooth PDMS. Particularly, sample P-8-28-20 had the biggest WCA （155°） and SA （7°）, which displayed the superhydrophobicity and the best wet self-cleaning efficiency in all samples. The present studies showed that the roughness and surface energy of counterface both affected the adhesion of gecko-inspired microfiber surfaces. The smaller dimension and lower duty ratio of microfibers on PDMS endowed it with the superhydro- phobicity and the wet self-cleaning abilities.

Detachment Behavior of Gecko Toe in Functional Strategies for Bionic Toe

Geckos can efficiently navigate complex terrains due to their multi-level adhesive system that is present on their toes.The setae are responsible for the gecko’s extraordinary adhesion and have garnered wide attention from the scientific community.The majority of the reported works in the literature that have dealt with the peeling models mainly focus on the gecko hierarchical adhesive system,with limited attention given to investigating the influence of gecko toe structure on the detachment.Along these lines,to gain a deeper understanding of the rapid and effortless detachment abilities of gecko toes,the peeling behavior of gecko toes on vertical surfaces was primarily investigated in this work.More specifically,the detachment time of a single toe on a smooth acrylic plate was measured to be 0.41±0.21 s.Moreover,it was observed that the toe assumed a"U"-shaped structure upon complete detachment.Additionally,Finite Element Analysis(FEA)models for three different types of gecko toes were developed to simulate both the displacement-peel and the moment-peel modes.Increasing the segmentation of the adhesive layer led to a gradual decrease in the resultant force,as well as the normal and tangential components.Lastly,a gecko-inspired toe model was constructed and powered by Shape Memory Alloy(SMA).A systematic comparison between the vertical drag separation and the outward flip separation was also conducted.From our analysis,it was clearly demonstrated that outward peel separation significantly necessitated the reduction of the peeling force,thus confirming the advantageous nature of the outward motion in gecko toe detachment.Our data not only contribute to a deeper understanding of the gecko detachment behavior but also offer valuable insights for the advancement of the wall-climbing robot feet.

Geckos Distributing Adhesion to Toes in Upside-down Running Offers Bioinspiration to Robots

Discoveries in geckos locomotion have advanced the bio-inspired robotics.However,the gecko-inspired robots still lag behind animals in attachments and maneuvers due to our failure to understand and implement gecko bionics thoroughly.Here,we studied the toe deployments that facilitate the upside-down motion of geckos by focusing on the directions and contact area of toes to offer inspirations for the design and control of feet of legged robots that must operate on inverted surfaces.Instead of clustering toes,geckos align toes in varying directions.They distribute adhesion to toes by controlling the magnitude of contact area,with one square millimeter setae generating〜153.8 mN shear force and〜39.5 mN attractive force on ceilings.Front feet deploy toes in a〜190°span that centers on〜16°from the motion direction.Toes distribute uniformly and contribute similarly.Whereas,hind feet deploy toes in a〜220°span centering around^90°relative to the fore-aft direction.The last two toes point toward the rear and contribute most in hind feet while the first two toes adhere barely.Such deployments involving distributed control among toes not only provide insight into biological adhesion but will also deliver useful information to the next generation of climbing robotics.