Kyeong Ho Cho

A robotic finger driven by twisted and coiled polymer actuator

Previous studies reported that a twisted and coiled polymer actuator (TCA) generates strong force and large stroke by heating. Nylon 6,6 is known to be the most suitable polymer material for TCA because it has high thermal expansion ratio, high softening point and high toughness which is able to sustain gigantic twisting. In order to find the optimal structure of TCA fabricated with silver-coated nylon sewing threads, an equipment for twist-insertion (structuralization), composed of single DC motor, a slider fabricated by 3D printer and a body frame, is developed. It can measure the behaviors of TCAs as well as fabricate TCAs with desired characteristics by structuralizing fibers with controlled rotation per minutes (RPM) and turns. Comparing performances of diverse structures of TCAs, the optimal structure for TCA is found. For the verification of the availability of the optimal TCA, a TCA-driven biomimetic finger is developed. Finally, we successfully demonstrate the flexion/extension of the finger by using the actuation of TCAs.

Inspection Robot for Hanger Cable of Suspension Bridge: Mechanism Design and Analysis

Periodic maintenance of suspension bridge is critical to the safety of the bridge structure. Because most of the load on the bridge is supported by the cables, inspections on main cable or hanger are very important. In this paper, we propose a cable-climbing robot enabling convenient and safe visual inspection of the hanger cable. The robot is comprised of three identical modules assembled 120 ° apart circumferentially on a frame around the cable, and each module has three functional mechanisms, that is, driving, adhesion, and safe landing. The robot is controlled wirelessly by an operator on the ground, though ac power is supplied via a tether cable. In addition, the vision sensor consisting of three cameras provides images taken from three different directions covering the cable and the odometer made with a soft idler wheel locates the robot on the cable. The robot is able to transmit the visual images of the cable surfaces in realtime at a position, while climbing up and down. In this paper, the kinematic and force analysis of the robot is performed and its feasibility is experimentally demonstrated.

Caterpillar-based cable climbing robot for inspection of suspension bridge hanger rope

Periodic inspection of a hanger rope is needed for the effective maintenance of suspension bridge. However, it is dangerous for human workers to access the hanger rope and not easy to check the exact state of the hanger rope. In this work we have developed a wheel-based robot that can approach the hanger rope instead of the human worker and carry the inspection device which is able to examine the inside status of the hanger rope. Meanwhile, a wheel-based cable climbing robot may be badly affected by the vibration that is generated while the robot moves on the bumpy surface of the hanger rope. The caterpillar is able to safely drive with the wide contact face on the rough terrain. Accordingly, we developed the caterpillar that can be combined with the developed cable climbing robot. In this paper, the caterpillar is introduced and its performance is compared with the wheel-based cable climbing robot.

Development of cable climbing robot for maintenance of suspension bridges

In this paper, we introduce a wheel-based cable climbing robot system developed for maintenance of the suspension bridges. The robot consists of three parts: a wheel based driving mechanism, adhesion mechanism, and safe landing mechanism. The driving mechanism is a combination of pantograph mechanism, and wheels driven by motors. In addition, we propose a special design of safe landing mechanism which can assure the safety of the robot on the cables when the power is lost. Finally, the proposed robotic system is manufactured and validated in the indoor experimental environments.

Development of Cable Climbing Robotic System for Inspection of Suspension Bridge

In this paper, we propose a wheel-based cable climbing robotic system which can climb up and down the vertical cylindrical cables in the suspension bridges. Firstly, we develop climbing mechanism which includes wheels driven by motors and adhesion system.In addition,we propose a special design of adhesion mechanism which can maintain adhesion force even when the power is lost.Finally, an additional mechanism is developed for guaranteeing the safety of the robot during operations on cables.

Fabrication and modeling of temperature-controllable artificial muscle actuator

Research about the artificial muscle made of fishing lines or sewing threads, called the twisted and coiled polymer actuator (abbreviated as TCA in this paper) has collected many interests, recently. Since TCA has a specific power surpassing the human skeletal muscle theoretically, it is expected to be a new generation of the artificial muscle actuator. In order that the TCA is utilized as a useful actuator, this paper introduces the fabrication and the modeling of the temperature-controllable TCA. With an embedded micro thermistor, the TCA is able to measure temperature directly, and feedback control is realized. The safe range of the force and temperature for the continuous use of the TCA was identified through experiments, and the closed-loop temperature control is successfully performed without the breakage of TCA.

Development of novel multifunctional robotic crawler for inspection of hanger cables in suspension bridges

This paper introduces a novel robot which is able to climb hanger cables of long span suspension bridges. The robot has been developed for inspection purpose, and it can help us remotely inspect the state of cables by using cameras and Non-Destructive Testing (NDT) devices. The robot consists of two traction modules, two sub modules, and an adhesion mechanism. The unique design of the traction module ensures the stable movement of the robot on the twisted surface of the hanger cable. In this paper, we describe the structure and environmental situation of hanger cables and the mechanisms of the robot. Also, the results of experiments in the indoor and outdoor environments are included.

Twisted Dielectric Elastomer stack Actuator

The purpose of this research is to make an actuator which is easily adaptable to use as artificial muscle by improving structure of stack-type Dielectric Elastomer Actuator (DEA). In contrast with previous stack-type actuator, Single body Dielectric Elastomer stack Actuators (SDEAs) is connected as single body without external frame so that it can be actuated in twisted and bended state like human muscle. Consequently, it is applicable with no design limitations of rigid frame and has the advantages of flexibility and weight lightening. Using the advantages of SDEAs, we fabricate 2-ply structure SDEAs which can amplify the contraction rate and compare the performance with the non-ply SDEAs and evaluate that SDEAs is effective for use as artificial muscle application.

Super stretchable soft actuator made of twisted and coiled spandex fiber

Twist and Coiled soft Actuator (TCA) is simply fabricated by twisting a polymer fiber. In the previous researches, TCA was mainly fabricated with Nylon 6,6 fiber, and Nylon-TCA (NTCA) showed strong force outputs. However, the strain from NTCA was not much enough for practical application. This paper introduces SPX-TCA (STCA) which is fabricated with Spandex fibers. NTCA and STCA were fabricated, and their performances were compared by using the performance evaluation device. STCA showed larger strain, and it was actuated lower temperature than NTCA.

Multifunctional Robotic Crawler for Inspection of Suspension Bridge Hanger Cables: Mechanism Design and Performance Validation

This paper presents a robotic system, called multifunctional robotic crawler for cable INspection II, which is developed for inspection of hanger cables of suspension bridges. The robot can move over hanger cables and perform inspections with instruments such as cameras, nondestructive testing tools, etc. The novel mechanisms for the robotic system are proposed under the consideration of the environmental conditions of suspension bridges. Its driving mechanism adopts a crawler type one driven by brushless direct current motors, and the detachable adhesion tool ensures simple and quick installation procedures. The safe-landing mechanism for emergency situations guarantees the retrieval of the robot while preserving the safety of operators. This paper presents the robot system and its field test results under a super long-span suspension bridge, called Yeong-Jong Grand Bridge in South Korea. For practical applications, the real environmental conditions of a suspension bridge and the other fields where the robot can be applied are discussed.