Representative Papers


Representative Papers of RSC Lab


"WalkON Suit: A Medalist in the Powered Exoskeleton Race of Cybathlon 2016"

Author

Jungsu Choi, Byeonghun Na, Pyeong-Gook Jung, Dong-wook Rha, Kyoungchul Kong

Journal

IEEE Robotics and Automation Magazine

Abstract

The powered exoskeleton race in Cybathlon 2016 consisted of six challenging tasks that required a pilot with complete paraplegia to walk on a level floor, uphill, downhill, and on stairs; stand up and sit down; step on stones; and even pass through a tilted path. All of these tasks addressed exactly the requirements for a powered exoskeleton designed to assist with activities of daily living (ADL) for paraplegics. Every team brought unique technologies to achieve this goal. Team SG Mechatronics, a bronze medalist in the race, developed a powered exoskeleton called the WalkON Suit to participate in Cybathlon 2016. To accomplish all the tasks, the WalkON Suit was developed based on several special design and control technologies, such as a hybrid actuation mechanism, a biarticular transmission system, distributed batteries, and distributed actuators. In this article, the overall production of the WalkON Suit is discussed.

Link

https://ieeexplore.ieee.org/document/8097012


"High-Precision Robust Force Control of a Series Elastic Actuator"

Author

Sehoon Oh, Kyoungchul Kong

Journal

IEEE/ASME Transactions on Mechatronics

Abstract

A series elastic actuator (SEA) is a promising actuation method in force control applications that intelligently interacts with environments. The SEA is characterized by a spring placed between a load and an actuator, which is an electric motor in most cases. Since the spring plays the role of a transducer between position (i.e., the spring deflection) and force, it is able to control the output force (torque) precisely by utilizing typical position control methods. However, the force control performance of the SEA is considered to have limitations due to its elasticity, and thus, to be inferior to rigid actuators in terms of bandwidth. This paper proposes that the force control performance of the SEA can be improved by exploiting the dynamic model of the SEA. To this end, the SEA is modeled and analyzed utilizing the two-mass dynamic model, which is a well-known and widely accepted model of the flexible system. The disturbance observer and feedforward controller are introduced as the model-based control algorithms for the SEA to achieve the high-precision force control. In addition to high-bandwidth force control, the proposed controller can address the robust stability and performance against model parameter variance and exogenous disturbances. For the analytic and quantitative assessment of the proposed force control system, the dynamic characteristics of an SEA under various control algorithms are analyzed, and the experimental results are provided for an actual SEA system in this paper.

Link

https://ieeexplore.ieee.org/document/7579567


"A Wearable Gesture Recognition Device for Detecting Muscular Activities Based on Air-Pressure Sensors"

Author

Pyeong-Gook Jung, Gukchan Lim, Seonghyok Kim, Kyoungchul Kong

Journal

IEEE Transactions on Industrial Informatics

Abstract

Recognition of human gestures plays an important role in a number of human-interactive applications, such as mobile phones, health monitoring systems, and human-assistive robots. Electromyography (EMG) is one of the most common and intuitive methods used for detecting gestures based on muscle activities. The EMG, however, is in general, too sensitive to environmental disturbances, such as electrical noise, electromagnetic signals, humidity, and so on. In this paper, a new method for recognizing the muscular activities is proposed based on air-pressure sensors and air-bladders. The muscular activity is detected by measuring the change of the air pressure in an air-bladder contacting the interested muscle(s). Since the change of the air pressure can be more robustly measured compared with the change of electric signals appeared on the skin, the proposed sensing method is useful for mobile devices due to its great signal-to-noise ratio (SNR) and fast response time. The principle and applications of the proposed sensing method are introduced in this paper. The performance of the proposed method is evaluated in terms of linearity, repeatability, wear-comfort, etc., and is also verified by comparing it with an EMG signal and a motion sensor.

Link

https://ieeexplore.ieee.org/document/7045532


"Controller Design for Mechanical Impedance Reduction"

Author

Hanseung Woo, Kyoungchul Kong

Journal

IEEE/ASME Transactions on Mechatronics

Abstract

Mechatronic systems that physically interact with humans should guarantee safety, as well as stability and control performance. Mechanical impedance is an effective means to evaluate the safety of such systems. The mechanical impedance represents the magnitude of reaction forces by mechanical system when it is moved. Therefore, low mechanical impedance is one of the requirements of safe mechatronic systems. However, there exists a tradeoff between mechanical impedance, stability, and control performance. In this paper, a methodology to design control algorithms for reduction of the mechanical impedance with guaranteed stability is proposed. For the controller design, the mathematical definition of the mechanical impedance for open- and closed-loop systems is introduced in this paper. Various analyses on the mechanical impedance from the viewpoint of control systems are given. Then, the controllers are designed for systems with/without right-half complex plane poles and zeros such that they effectively lower the magnitude of mechanical impedance with guaranteed stability. The proposed method is verified through case studies including simulations and experiments.

Link

https://ieeexplore.ieee.org/document/6784001


"A Gait Monitoring System Based on Air Pressure Sensors Embedded in a Shoe"

Author

Kyoungchul Kong, Masayoshi Tomizuka

Journal

IEEE/ASME Transactions on Mechatronics

Abstract

Measurement of ground contact forces (GCFs) provides necessary information to detect human gait phases. In this paper, a new analysis method of the GCF signals is discussed for detection of the gait phases. Human gaits are complicated, and the gait phases cannot be exactly distinguished by comparing sensor outputs to a threshold. This paper proposes a method by fuzzy logic for detecting the gait phases continuously and smoothly. The smooth and continuous detection of the gait phases enables a full use of information obtained from GCF sensors. For advanced rehabilitation systems, this paper also introduces a higher level algorithm that quantitatively monitors the amount of abnormalities in a human gait. The abnormalities detected by the proposed method include an improper GCF pattern as well as an incorrect sequence of the gait phases. To realize the monitoring algorithm, the gait phases are analyzed as a vector and the abnormalities are detected by simple kinematic equations. The proposed methods are implemented by using signals from sensor-embedded shoes called smart shoes. Each smart shoe has four GCF sensors installed between the cushion pad and the sole. The GCF sensor applies an air pressure sensor connected to an air bladder. A gait monitoring system that integrates the proposed methods is shown in this paper and verified for both normal and abnormal gaits.

Link

https://ieeexplore.ieee.org/document/4813239


"Mechanical Parameter Tuning Based on Iterative Learning Mechatronics Approach"

Author

Joonyeong Jung, Kyoungchul Kong

Journal

IEEE/ASME Transactions on Mechatronics

Abstract

In most mechatronics applications, the best control performance cannot be obtained by only shaping a control input signal because, in practice, such control is effective within only the performance range realizable by the actuator and control system. Therefore, to obtain the best control performance, the mechanical parameters should be optimally selected such that the desired control performance can be achieved with minimal control effort. However, it is difficult to accurately predict the control performance without conducting an actual experiment because the control performance is dependent on not only the mechanical design parameters, but also on various practical factors, such as the input and output saturation of the actuator, the heat problem, and sensor limitations. For these reasons, a recursive mechanical parameter tuning process based on control experiments is proposed in this paper. Based on a set of control signals (e.g., a control input and a tracking error), the proposed mechanical parameter tuning method seeks a better mechanical design parameter for improving the control performance (i.e., to reduce the control input power). For verification of the proposed method, the method was applied to case studies including simulations and experiments.

Link

https://ieeexplore.ieee.org/document/8303218