Virtual 3D ground reaction force sensors for a gecko-inspired climbing robot with dry adhesive foot pads

The 11th International Symposium on Adaptive Motion of Animals and Machines. Kobe University, Japan. 2023-06-06/09. Adaptive Motion of Animals and Machines Organizing Committee.Poster Session P4

The use of clamping grips and friction pads by tree frogs for climbing curved surfaces

Most studies on the adhesive mechanisms of climbing animals have addressed attachment against flat surfaces, yet many animals can climb highly curved surfaces, like twigs and small branches. Here we investigated whether tree frogs use a clamping grip by recording the ground reaction forces on a cylindrical object with either a smooth or anti-adhesive, rough surface. Furthermore, we measured the contact area of fore and hindlimbs against differently sized transparent cylinders and the forces of individual pads and subarticular tubercles in restrained animals. Our study revealed that frogs use friction and normal forces of roughly a similar magnitude for holding on to cylindrical objects. When challenged with climbing a non-adhesive surface, the compressive forces between opposite legs nearly doubled, indicating a stronger clamping grip. In contrast to climbing flat surfaces, frogs increased the contact area on all limbs by engaging not just adhesive pads but also subarticular tubercles on curved surfaces. Our force measurements showed that tubercles can withstand larger shear stresses than pads. SEM images of tubercles revealed a similar structure to that of toe pads including the presence of nanopillars, though channels surrounding epithelial cells were less pronounced. The tubercles' smaller size, proximal location on the toes and shallow cells make them probably less prone to buckling and thus ideal for gripping curved surfaces

Mini Review: Comparison of Bio-Inspired Adhesive Feet of Climbing Robots on Smooth Vertical Surfaces

Developing climbing robots for smooth vertical surfaces (e.g., glass) is one of the most challenging problems in robotics. Here, the adequate functioning of an adhesive foot is an essential factor for successful locomotion performance. Among the various technologies (such as dry adhesion, wet adhesion, magnetic adhesion, and pneumatic adhesion), bio-inspired dry adhesion has been actively studied and successfully applied to climbing robots. Thus, this review focuses on the characteristics of two different types of foot microstructures, namely spatula-shaped and mushroom-shaped, capable of generating such adhesion. These are the most used types of foot microstructures in climbing robots for smooth vertical surfaces. Moreover, this review shows that the spatula-shaped feet are particularly suitable for massive and one-directional climbing robots, whereas mushroom-shaped feet are primarily suitable for light and all-directional climbing robots. Consequently, this study can guide roboticists in selecting the right adhesive foot to achieve the best climbing ability for future robot developments

The biomechanics of tree frogs climbing curved surfaces: a gripping problem

The adhesive mechanisms of climbing animals have become an important research topic because of their biomimetic implications. We examined the climbing abilities of hylid tree frogs on vertical cylinders of differing diameter and surface roughness to investigate the relative roles of adduction forces (gripping) and adhesion. Tree frogs adhere using their toe pads and subarticular tubercles, the adhesive joint being fluid-filled. Our hypothesis was that, on an effectively flat surface (adduction forces on the largest 120 mm diameter cylinder were insufficient to allow climbing), adhesion would effectively be the only means by which tree frogs could climb, but on the two smaller diameter cylinders (44 mm and 13 mm), frogs could additionally utilise adduction forces by gripping the cylinder either with their limbs outstretched or by grasping around the cylinder with their digits, respectively. The frogs' performance would also depend on whether the surfaces were smooth (easy to adhere to) or rough (relatively non-adhesive). Our findings showed that climbing performance was highest on the narrowest smooth cylinder. Frogs climbed faster, frequently using a 'walking trot' gait rather than the 'lateral sequence walk' used on other cylinders. Using an optical technique to visualize substrate contact during climbing on smooth surfaces, we also observed an increasing engagement of the subarticular tubercles on the narrower cylinders. Finally, on the rough substrate, frogs were unable to climb the largest diameter cylinder, but were able to climb the narrowest one slowly. These results support our hypotheses and have relevance for the design of climbing robots

Gecko-inspired robot with body-height adaptability

The 9.5th international symposium on Adaptive Motion of Animals and Machines. Ottawa，Canada (Virtual Platform). 2021-06-22/25. Adaptive Motion of Animals and Machines Organizing Committee

Equivalent Dynamic Analysis of a Cable-Driven Snake Arm Maintainer

In this paper, we investigate a design method for a cable-driven snake arm maintainer (SAM) and its dynamics modelling. A SAM can provide redundant degrees of freedom and high structural stiffness, as well as high load capacity and a simplified structure ideal for various narrow and extreme working environments, such as nuclear power plants. However, their serial-parallel configuration and cable drive system make the dynamics of a SAM strongly coupled, which is not conducive to accurate control. In this paper, we propose an equivalent dynamics modelling method for the strongly coupled dynamic characteristics of each joint cable. The cable traction dynamics are forcibly decoupled using force analysis and joint torque equivalent transformation. Then, the forcibly equivalent dynamic model is obtained based on traditional series robot dynamic modelling methods (Lagrangian method, etc.). To verify the correctness of the equivalent dynamics, a simple model-based controller is established. In addition, a SAM prototype is produced to collect joint angles and cable forces at different trajectories. Finally, the results of the equivalent dynamics control simulation and the prototype tests demonstrate the validity of the SAM structural design and the equivalent dynamics model

Design of a Variable Stiffness Gecko-Inspired Foot and Adhesion Performance Test on Flexible Surface

Adhesion robots have broad application prospects in the field of spacecraft inspection, repair, and maintenance, but the stable adhesion and climbing on the flexible surface covering the spacecraft has not been achieved. The flexible surface is easily deformed when subjected to external force, which makes it difficult to ensure a sufficient contact area and then detach from it. To achieve stable attachment and easy detachment on the flexible surface under microgravity, an adhesion model is established based on the applied adhesive material, and the relationship between peeling force and the rigidity of the base material, peeling angle, and working surface stiffness is obtained. Combined with the characteristics of variable stiffness structure, the adhesion and detachment force of the foot is asymmetric. Inspired by the adhesion-detachment mechanism of the foot of the gecko, an active adhesion-detachment control compliant mechanism is designed to achieve the stable attachment and safe detachment of the foot on the flexible surface and to adapt to surfaces with different rigidity. The experimental results indicate that a maximum normal adhesion force of 7.66 N can be generated when fully extended, and the safe detachment is achieved without external force on a flexible surface. Finally, an air floating platform is used to build a microgravity environment, and the crawling experiment of a gecko-inspired robot on a flexible surface under microgravity is completed. The experimental results show that the gecko-inspired foot with variable stiffness can satisfy the requirements of stable crawling on flexible surfaces

Wall-Climbing Mobile Robot for Inspecting DEMO Vacuum Vessel

The vacuum vessel (VV) inside and outside inspection of the Demonstration Fusion Power Plant (DEMO) is very difficult due to various constraints, such as non-magnet effect material requirements, constrained space, and neutrons on its surfaces. We propose a design method for wall-climbing mobile robots (WMR) based on the vortex principle and investigate key technologies to meet VV inspection requirements. We developed a kinematic model based on the robot’s motion control requirements and a trajectory tracking control algorithm according to the tractrix principle, enabling the robot to follow the path for autonomous inspection. The impeller is designed based on the vortex principle. The aerodynamic characteristics and structural strength of the impeller were also analysed and optimised. A sliding-mode robust pressure control system was designed for the robot’s negative pressure adsorption, and its effectiveness was verified by simulation. Finally, an initial test prototype verified the structural design and vortex adsorption performance. We also addressed the potential applications of the WMR in DEMO and other fusion reactors