Adhesion performance test and trajectory optimization for gecko-inspired footpad under simulated micro-gravity environment

Abstract

The extraordinary locomotory abilities of geckos are attributed to striking adhesive setae segmented into scansors or pads on the undersides of the toes or legs, have been well-known for many centuries due to van der waals force. The outstanding climbing performances of the animal inspired the engineers and researchers for the design of artificial systems, such as adhesive materials, which in turn enabled the construction of climbing robots that are capable of climbing smooth walls and ceiling. The robot based on van der waals force has a wide prospect for execution space task application. Legged climbing robot involves the controlled application of forces during the leg-substrate contact and release, in order to propel the body forwards. The achievement of strong attachment and easy removal of the adhesive is the critical issues, when we apply the adhesive to the robot’s footpad. Here, by using a custom-built force platform, adhesion performance of the bio-inspired adhesive which directly apply to the footpad were investigated. The effect of footpad stiffness, contact area and trajectory on adhesion force and real contact area is investigated. Results show that normal force and shear force increased as stiffness increase up to 68.9 N/m. After that, normal force and shear force decrease as stiffness increase. Both normal force and shear force increase as real contact area increase, but not increase linearly. Additionally, different attaching trajectories are applied to explore the adhesion characteristic of the footpad. The result indicates that for the robot, the footpad of this kind does not need much load control: the pad just needs to contact the surface, in order to produce substantial adhesion force and meet the requirement of the attaching phase. This characteristic of footpad is extremely beneficial for applying it at zero gravity, when the robot cannot rely on gravity to load the adhesive pad. Furthermore, normal force and shear of the footpad during one cycle are tested. The force is compared with the frictional-adhesion model. Stable adhesion region under different conditions can be obtained by adjust peeling angle and effective real contact area. Finally, optimized footpad stiffness, area and trajectory are selected and stable adhesion region is analyzed. By using gravity compensation method to simulate micro-gravity environment and designing attachment and detachment trajectory, the robot can climb stably under zero gravity environment up to 1 cm/s. This paper presents adhesion performance test and trajectory optimization of gecko-inspired footpad under simulated micro-gravity environment. The experimental tests demonstrated that the robot can climb under mimic zero gravity at the velocity of up to 1 cm/s. The major contribution of this work is the application of the biological principle of footpad to the legged robot, and the demonstration of the feasibility and reliability of this design. To the best of our knowledge, the legged robot, climbing under nearly zero gravity, is demonstrated here for the first time. We also explore the effect of the stiffness, contact area and attaching trajectory on the reliability of the robot locomotion. This research could be a basis for the space application of micro-adhesion robot.