Kyungjun Choi

This study proposes fabric muscles based on shape memory alloy (SMA) springs coiled with a thin diameter SMA wire of 80 μ m to improve heat dissipation under natural convection and forced air cooling. A new structure and its fabrication process are developed to create soft and flexible fabric muscles capable of supplying current and withstanding high external force, using a large number of thin SMA spring bundles. A total of 250 bundles of SMA springs weighing only 3.2 g constitute the fabric muscle that can lift a 1500 times-heavier mass, where each strand behaved like a muscle fiber. The fabric muscle generates a blocking force of up to 56.54 N and a power density of 2072 W kg ⁻¹ . In addition, an air-cooling structure similar to a showerhead is proposed to further improve the actuation speed of the fabric muscles and maintain the flexibility of the fabric muscles. The fabric muscle with forced air cooling is cooled 40.5% faster than that with natural cooling. Finally, the results confirm that forced cooling can drive the muscle with a cycle of 5.5 s.

In the field of robotics, sensors are crucial in enabling the interaction between robots and their users. To ensure this interaction, sensors mainly measure the user’s strength, and based on this, wearable robots are controlled. In this paper, we propose a novel three-axis force/torque sensor for wearable robots that is compact and has a high load capacity. The bolt and nut combination of the proposed sensor is designed to measure high-load weights, and the simple structure of this combination allows the sensor to be compact and light. Additionally, to measure the three-axis force/torque, we design three capacitance-sensing cells. These cells are arranged in parallel to measure the difference in capacitance between the positive and negative electrodes. From the capacitance change measured by these sensing cells, force/torque information is converted through deep neural network calibration. The sensing point can also be confirmed using the geometric and kinematic relation of the sensor. The proposed sensor is manufactured through a simple and inexpensive process using cheap and simply structured components. The performance of the sensor, such as its repeatability and capacity, is evaluated using several experimental setups. In addition, the sensor is applied to a wearable robot to measure the force of an artificial muscle.

This study proposes a soft inductive coil spring (SICS) strain sensor that can measure the strain of soft actuators. The SICS sensor, produced by transforming a shape memory alloy (SMA) wire with the same materials as that of an SMA spring bundle actuator (SSBA) into a coil spring shape, measures inductance changes according to length changes. This study also proposes a manufacturing method, output characteristics of the SICS sensor applicable to the SSBA among soft actuators, and the structure of the SICS sensor-integrated SSBA (SI-SSBA). In the SI-SSBA, the SMA spring bundle and SICS sensor have structures corresponding to the muscle fiber and spindle of the skeletal muscle, respectively. It is demonstrated that when a robotic arm with one degree of freedom is operated by attaching two SI-SSBAs in an antagonistic structure, the displacement of the SSBA can be measured using the proposed strain sensor. The output characteristics of the SICS sensor for the driving speed of the robotic arm were evaluated, and it was experimentally proven that the strain of the SSBA can be stably measured in water under a temperature change of 54 °C from 36 to 90 °C.