Ji-Suk Kim

The Deformable Wheel Robot Using Magic-Ball Origami Structure

In this paper, we present a deformable wheel robot using the ball-shaped waterbomb origami pattern, so-called magic-ball pattern. The magic-ball origami pattern is a well-known pattern that changes its shape from a long cylindrical tube to a flat circular tube. By using this special structure, a wheel with mechanical functionalities can be achieved without using many mechanical parts. Moreover, because of the characteristic that the structure constrains its own movement, it is possible to control the whole shape of the wheel using only few actuators. And also, from analysis of the wheel structure in kinematic model, the performance of the wheel and determine the condition for actuators can be predicted. We think that the proposed design for the deformable wheel shows the possibility of using origami structure as a functional structure with its own mechanism.Copyright

Toward a solution to the snapping problem in a concentric-tube continuum robot: Grooved tubes with anisotropy

The concentric-tube continuum robot generates distal end motions by translating and rotating the proximal ends of pre-curved tubes that overlap concentrically. This robot does not require additional actuators along the tubes because the overall curvature and distal end position are determined solely by interactions between the inner and outer tubes. However, under certain conditions, the rotation of the distal end is hindered as the actuation energy accumulates into torsional energy of the tubes. As the distal ends are rotated further, the accumulated energy from the twisting is suddenly released, which makes the tubes snap to a remote position. This is called the snapping problem, and it considerably limits the performance of the robot. In this paper, we propose a novel design for the concentric tubes to eliminate the snapping problem. The new design creates groove patterns on superelastic nitinol tubes to make the tubes more flexible to bending than twisting. Simulations and experiments were performed to verify that the tubes with our groove patterns had anisotropic structural characteristics, and video image analysis verified that this structural property can eliminate the snapping problem. A concentric-tube robot with this new tube design can have a larger workspace area because tubes with greater curvatures can be used without the snapping problem.

Anisotropic Patterning to Reduce Instability of Concentric-Tube Robots

As a steerable needle or robotic manipulator, the concentric-tube robot shows good potential for use in minimally invasive medical procedures. However, the torsional deformation of the precurved tubes comes at the price of instability, which not only limits the workspace and tool path but also potentially creates danger of tissue rupture when external load is applied. In this paper, we propose anisotropic patterning of tubes to solve the instability problem. Hole-patterning can tune the mechanical properties of the tubes so that the ratio of the torsional rigidity to the bending rigidity becomes higher. This study investigates the effect of pattern design parameters by building a lumped analytical model and examining it with finite-element analysis. The pattern is engraved via laser machining and we experimentally verify that material anisotropy reduces instability.

Component assembly with shape memory polymer fastener for microrobots

Adhesives are generally used for the assembly of microrobots, whereas bolts, screws, or rivets are used for larger robots. Although adhesives are easy to apply, lightweight, and small, they cannot be used for repeated assembly and disassembly of parts. In this paper, we present a novel microfastener composed of a polyurethane-based shape memory polymer (SMP) that is lightweight and small but that is easily detached for disassembly. This was achieved by using the shape recovery and modulus change of the SMP. A sheet of macromolded SMP was laser machined into an I-beam-shaped rivet, and notches were added to the structure to prevent stress concentration. Pull-off tests showed that, as the notch radius increased, the disengagement strength of the rivet fastener decreased and the reusability increased. Through the elastoplastic model, a single SMP rivet was calculated to have maximum disengagement strength of 150 N cm−2 in the elastic range, depending on the notch radius. The fasteners were applied to a jumping microrobot. The legs and body were assembled with ten fasteners, which showed no permanent deformation after impact during jumping movements. The legs were easily replaced with ones of different stiffness by heating the engaged sites to make the fasteners compliant and detachable. The proposed detachable SMP microfasteners are particularly useful for testing the isolated performance of microrobot components to determine the optimal designs for these components.

Fabrication of origami wheel using pattern embedded fabric and its application to a deformable mobile robot

The unique characteristics of origami to realize 3-D shape from 2-D patterns have been fascinating many researchers and engineers. This paper presents a fabrication of origami patterned fabric wheels that can deform and change the radius of the wheels. PVC segments are enclosed in the fabrics to build a tough and foldable structure. A special cable driven mechanism was designed to allow the wheels to deform while rotating. A mobile robot with two origami wheels has been built and tested to show that it can deform its wheels to overcome various obstacles.

Role of compliant leg in the flea-inspired jumping mechanism

Jumping locomotion has been widely employed in milliscale mobile robots to help overcome their size limitations by extending their range and enabling them to overcome obstacles. During jumping, the robots legs experience acceleration that is up to an order of magnitude greater than the gravitational acceleration. This large force results in bending of the jumping legs. In this paper, we study how the bending of the leg affects the jumping performance of a flea-inspired jumping robot. To judge the effect of the leg compliance, the amount of energy lost during jumping is determined by examining the ratio of kinetic energy to input energy, which we define as the mechanical efficiency. The bending leg is dynamically modeled using a pseudo-rigid-body model in order to precisely analyze the energy transfer. Jumping experiments are performed for five different legs, each with a different stiffness. Shape memory polymer rivets, which are lightweight and compact, were used to easily switch out the legs. The mechanical efficiency of the robot with appropriately chosen leg compliance was 41.27% compared with 36.93% for the rigid case and 21.51% for the much more compliant case. The results show that optimizing the compliance of a jumping leg can improve the performance of a jumping robot.

Design of deformable-wheeled robot based on origami structure with shape memory alloy coil spring

In this research, a novel concept of a deformable wheel robot using the origami structure is proposed. The word, origami, comes from the traditional Japanese art of paper folding. The unique characteristic of origami that realizes three-dimensional structures from two-dimensional materials have long attracted attention from various fields such as design, education and mathematics [1-6]. Among many researches on engineering applications of origami, some suggest that origami structure can be treated as a kinematic system [7-8]. The research in this paper focus on this characteristic - origami structure is a morphing structure, but it is kinematically designable and can be used as mechanical system. The research present how to deal with three major issues in this topic - pattern design, fabrication and actuation - when the deformable wheel mechanism is realized. The pattern design is key design parameter in determining the function of the mechanism. Desired function can be achieved by appropriate design of pattern. Specially designed magic-ball pattern was developed for achieving desired function. Material and fabrication are also important issue. Depending on the material and the fabrication method, the properties of final origami structure are determined. Therefore, to realize desired functionality of final origami structure, appropriate fabrication method should be selected as well as origami pattern need to be designed properly. In this robot, paper coated with Kapton film and pattern by laser machine was used. Third is actuation design. The wheel structure should be rotate and also has limited space. Shape memory alloy coil spring with slip ring was used for this purpose. Integration of solutions of each issues goes to final product of the deformable wheel robot as in figure 1. It shows adoptability with environment that the diameter of the wheel is 70-mm in normal state but by deforming of the wheel, the robot can pass through the 55-mm slit. The result of the research shows the possibility that origami structure can be a mechanical system.

Meso-scale robot assembly using shape memory polymer rivet fastener

This paper describes a novel rivet fastener made with shape memory polymer (SMP). Shape recovery and modulus change are main two properties of SMPs that enable themselves to be promising base materials for fasteners. The new type of fastener was used to join two composite parts of a meso-scale robot. The fabrication procedure includes macro molding and subsequent laser machining in order to enhance manufacturability, and change size and design on demand. By pull-off experiment it was demonstrated that one single rivet can endure 8N of disengagement force. We applied this fastener to meso-scale flea robot and verified its feasibility.

Design, Fabrication and Analysis of Walking Robot Based on Origami Structure

Recently, there have been many researches about applications of origami to mechanical engineering, which realizes a 3D sturcture by folding a 2D plane material. With this simple manufacturing process, origami was even adopted by some roboticists as a way to build an entirely new robot with benefits in terms of cost, weight, and structural simplicity. In this paper, we propose a new type of a walking robot based on origami structure. Because all the components of the robot that generate gait motion are mechanically connected, it can actually walk forward with only a single actuator. We also showed the similarity of gait trajectories between a kinematic analysis and the actual gait motion measured by video tracking. This result proved the possibility of designing an origami-based robot with the identical gait trajectory as we plan.

Design and Fabrication of Soft Deformable Wheel Robot using Composite Materials and Shape Memory Alloy Coil Spring Actuators

In order to operate a search and rescue robot in hazardous area, the robot requires high mobility and adaptable locomotion for moving in unpredictable environments. In this paper, we propose the deformable soft wheel robot that can produce three kinds of driving modes; caterpillar driving mode, normal wheel driving mode, legged-wheel driving mode. The robot changes its driving mode as it faces the various obstacles such as a small gap, stairs etc. Soft film and composite materials are used for fabrication of deformable wheel structure and Shape Memory Alloy (SMA) coil spring actuators are attached on the structure as an artificial muscle. Film lamination and an composite manufacturing process is introduced and the robot design is required to be modified and compromised to applying the manufacturing process. The prototype is developed and tested for verifying feasibility of the deformable wheel locomotion.