Je-Sung Koh

Flea-Inspired Catapult Mechanism for Miniature Jumping Robots

Fleas can jump more than 200 times their body length. They do so by employing a unique catapult mechanism: storing a large amount of elastic energy and releasing it quickly by torque reversal triggering. This paper presents a flea-inspired catapult mechanism for miniature jumping robots. A robotic design was created to realize the mechanism for the biological catapult with shape memory alloy (SMA) spring actuators and a smart composite microstructure. SMA spring actuators replace conventional actuators, transmissions, and the elastic element to reduce the size. The body uses a four-bar mechanism that simulates a fleas leg kinematics with reduced degrees of freedom. Dynamic modeling was derived, and theoretical jumping was simulated to optimize the leg design for increased takeoff speed. A robotic prototype was fabricated with 1.1-g weight and 2-cm body size that can jump a distance of up to 30 times its body size.

Omega-Shaped Inchworm-Inspired Crawling Robot With Large-Index-and-Pitch (LIP) SMA Spring Actuators

This paper proposes three design concepts for developing a crawling robot inspired by an inchworm, called the Omegabot. First, for locomotion, the robot strides by bending its body into an omega shape; anisotropic friction pads enable the robot to move forward using this simple motion. Second, the robot body is made of a single part but has two four-bar mechanisms and one spherical six-bar mechanism; the mechanisms are 2-D patterned into a single piece of composite and folded to become a robot body that weighs less than 1 g and that can crawl and steer. This design does not require the assembly of various mechanisms of the body structure, thereby simplifying the fabrication process. Third, a new concept for using a shape-memory alloy (SMA) coil-spring actuator is proposed; the coil spring is designed to have a large spring index and to work over a large pitch-angle range. This large-index-and-pitch SMA spring actuator cools faster and requires less energy, without compromising the amount of force and displacement that it can produce. Therefore, the frequency and the efficiency of the actuator are improved. A prototype was used to demonstrate that the inchworm-inspired, novel, small-scale, lightweight robot manufactured on a single piece of composite can crawl and steer.

Jumping on water: Surface tension–dominated jumping of water striders and robotic insects

How to walk and jump on water Jumping on land requires the coordinated motion of a number of muscles and joints in order to overcome gravity. Walking on water requires specialized legs that are designed to avoid breaking the surface tension during motion. But how do insects, such as water striders and fishing spiders, manage to jump on water, where extra force is needed to generate lift? Koh et al. studied water striders to determine the structure of the legs needed to make jumping possible, as well as the limits on the range of motion that avoids breaking the surface tension (see the Perspective by Vella). They then built water-jumping robots to verify the key parameters of leg design and motion. Science, this issue p. 517; see also p. 472 Specialized leg design and motions allow both insects and robots to jump on water. [Also see Perspective by Vella] Jumping on water is a unique locomotion mode found in semi-aquatic arthropods, such as water striders. To reproduce this feat in a surface tension–dominant jumping robot, we elucidated the hydrodynamics involved and applied them to develop a bio-inspired impulsive mechanism that maximizes momentum transfer to water. We found that water striders rotate the curved tips of their legs inward at a relatively low descending velocity with a force just below that required to break the water surface (144 millinewtons/meter). We built a 68-milligram at-scale jumping robotic insect and verified that it jumps on water with maximum momentum transfer. The results suggest an understanding of the hydrodynamic phenomena used by semi-aquatic arthropods during water jumping and prescribe a method for reproducing these capabilities in artificial systems.

Omegabot : Biomimetic inchworm robot using SMA coil actuator and smart composite microstructures (SCM)

Many researchers have developed various robots with novel gaits that can travel on rough terrain where conventional vehicles or other robots cannot. Many of these robots are bio-inspired since there is lots of amazing locomotions in nature that enable movement through various obstacles. This paper presents a robot based on the motion of ascotis selenaria, a type of inchworm with a locomotion that has an omega shape bending motion in between the extension motions. This type of inchworm can travel approximately its body length per stroke on a rough surfaces, leaf edges and branches of trees. The robot is built with smart composite microstructures, a fabrication method that uses laser micromachining to cut composites and assemble them into micro structures. The robot is actuated with a single shape memory alloy coil actuator. This robot can be used for search and rescue or gathering useful information in an area where only small scale robots can penetrate.

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

Omegabot: Crawling robot inspired by Ascotis Selenaria

In this paper, we describe the design, fabrication processes, and control of a new biomimetic robot inspired by the inchworm, Ascotis Selenaria. The robot, called Omegabot, is named after the omega (Ω) shape of the crawling motion of the inchworm. This type of inchworm can travel approximately its body length per stroke along rough surfaces, leaf edges, and boughs of trees. The robot is built with smart composite microstructures (SCM), a fabrication method that uses laser micromachining to cut composites and assemble them into micro structures. We suggest a special pattern design for SCM to generate a two-dimensional turning motion, crawling motion, and a proleg design for climbing a tree. The robot is actuated with a shape memory alloy coil actuator activated by a PWM (pulse-width modulation) signal control electric current. As a result, Omegabot can crawl, turn, and grip a tree bough. This robot can be used for search and rescue or gathering useful information in an area where only small-scale robots can penetrate.

Design of an Optically Controlled MR-Compatible Active Needle

An active needle is proposed for the development of magnetic resonance imaging (MRI)-guided percutaneous procedures. The needle uses a low-transition-temperature shape memory alloy (LT SMA) wire actuator to produce bending in the distal section of the needle. Actuation is achieved with internal optical heating using laser light transported via optical fibers and side coupled to the LT SMA. A prototype, with a size equivalent to a standard 16-gauge biopsy needle, exhibits significant bending, with a tip deflection of more than 14° in air and 5° in hard tissue. A single-ended optical sensor with a gold-coated tip is developed to measure the curvature independently of temperature. The experimental results in tissue phantoms show that human tissue causes fast heat dissipation from the wire actuator; however, the active needle can compensate for typical targeting errors during prostate biopsy.

Flea inspired catapult mechanism with active energy storage and release for small scale jumping robot

Fleas have a unique catapult mechanism with a special muscle configuration. Energy is stored in an elastic material, resilin, and the extensor muscle. Force is applied by the extensor muscle to generate a torque. Energy is released as a small triggering muscle reverses the direction of the aforementioned torque. A flea can jump 150 times its body length using this elastic catapult mechanism. In this paper, a flea-inspired catapult mechanism is presented. This mechanism can be categorized as an active storage and active release elastic catapult. Owing to its unique stiffness change characteristic, a shape-memory-alloy coil spring actuator enables the mimicking of the fleas catapult mechanism. Two types of flea-inspired jumping mechanisms were developed for verifying the feasibility of applying the concept to an efficient jumping robot. The first prototype has a flea-like appearance and the second is simplified to contain just the essential components of the flea-inspired catapult mechanism. The two prototypes are 20-mm- and 30-mm-long and can jump 64 cm and 120 cm, respectively. This unique catapult mechanism can be used not only for jumping robots but also for other small-sized robots to generate fast-releasing motion.

Underactuated Adaptive Gripper Using Flexural Buckling

In gripping devices, adapting to highly unstructured environments such as irregularly shaped objects and surfaces continues to be challenging. To achieve safe and reliable gripping, many researchers have employed various underactuated mechanisms such as differential and compliant mechanisms. All these mechanisms have demonstrated successful gripping performances. They, however, have hardly considered scalability issues of underactuated mechanisms originating from additional force transmissions and onerous mechanism assembly. In this paper, we propose a structurally simple and scalable underactuated mechanism. The mechanism is demonstrated on a gripping device called the “Buckling gripper.” The Buckling gripper achieves adaptive gripping on rugged, uneven, and undulating surfaces typically found in the natural world. The key design principle of the Buckling gripper is inspired by a caterpillars proleg that highly deforms depending on the shape of the contact surface. This key principle is applied to the gripper via flexural buckling. Normally, buckling is avoided in mechanical designs, but the buckling behavior of a flexure with an adequately selected length provides wide gripping range with a narrow range of force variation, which provides a sufficient number of contacts with even contact forces. As a result, the Buckling gripper achieves adaptive gripping on various surfaces, similar to a caterpillar.

Towards a bio-mimetic flytrap robot based on a snap-through mechanism

This paper presents a bio-mimetic flytrap robot based on the Venus flytrap, which has rapid snap-through motion. The robot employs a bi-stable unsymmetrically laminated carbon fiber reinforced prepreg (CFRP) structure, which has a bi-stable mechanism that is similar to the Venus flytraps passive elastic mechanism. By embedding shape memory alloy springs, large deformation is induced and bi-stable structure can be triggered to snap through. The robots working performance shows that the leaves close in about 100ms, and this time for closure is almost the same as that of the Venus flytrap. This concept of the flytrap robot can be applied to rapid grippers of various sizes.