Hosang Jung

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.

A Capacitive-Type Novel Six-Axis Force/Torque Sensor for Robotic Applications

This paper presents an innovative design of a six-axis force/torque sensor, which enables ease of manufacturing, cost reduction, and ruggedness in operation. The advantages are realized by simplifying the structure of the sensor and reducing manual labor during the manufacturing process. In order to achieve a simple sensor structure, we propose a capacitive-type force sensing scheme in which the sensing elements are aligned in-plane. By using this method, all the sensing elements can be fabricated on single printed circuit board, and thus, manual tasks, such as bonding and coating the sensing elements, can be eliminated. In order to verify the feasibility of the idea, a prototype six-axis force/torque sensor was manufactured, and its performances were evaluated. The characteristics of the prototype are analyzed in terms of condition number, static response, time domain response, hysteresis, repeatability, and time drift.

Printable monolithic hexapod robot driven by soft actuator

Aiming to apply soft actuators in driving a walking robot, the design, fabrication and locomotion of a bio-inspired printable hexapod robot are studied. The robot mimics the insects design and walking posture by driving six legs with alternating tripod gait which provides its locomotive adaptability on flat terrains. The versatile movements of the robots leg are achieved by using soft and multiple degree-of-freedom actuators. The actuators are made by dielectric elastomers with a simple mechanism based on antagonistic configuration. By using 3D printing method, the actuator can be embedded into the frame of the robot and a control system is developed. Finally, the robots locomotion is successfully demonstrated with variable speeds and stride lengths.

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.

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.

Development of a smart handheld surgical tool with tactile feedback

This paper presents a handheld surgical tool adapting a tactile feedback system. The tool consists of a 3-degree-of-freedom (DOF) force sensor and three tactile displays. The sensor is easily embedded in the tool by adopting the capacitive transduction principle. The sensor measures the direction and magnitude of the 3-DOF force applied to the tool tip. The fingertip grasping the tool is stimulated by the tactile display to transmit the contact force information measured by the sensor. The tactile display is actuated by employing a soft actuator technology based on a dielectric elastomer actuator such as a type of electroactive polymer actuator. In this work, a prototype of the tool is designed and fabricated. Its performance is experimentally validated.

Biomimetic robotic joint mechanism driven by soft linear actuators

From being soft, flexible and producing movement by contracting, soft linear actuators are said to have musclelike properties. Due to these similarities, they are often called “artificial muscle actuator.” However, the strain produced by these actuators is generally insufficient to be utilized in a large range of applications. Some solutions have been developed, but they sacrifice force to increase the displacement. Meanwhile, the force produced by skeletal muscles increases as it contracts due to its working principle, which is based on the “sliding filament mechanism.” The limitations of soft linear actuators could be overcome by mimicking the contraction process of skeletal muscles. Two types of muscle-inspired robotic joint mechanisms based on the sliding filament mechanism principle are proposed in this work. The mechanisms can be operated using any type of soft linear actuators as well as traditional actuators or motors, and this work realizes the implementation using shape memory alloy wires and 3D printed mechanical parts. The feasibility of both proposed mechanisms, and their capabilities were experimentally verified.