Gait Analysis based on a Hidden Markov Model

Joonbum Bae 제어로봇시스템학회 2012 제어로봇시스템학회 국제학술대회 논문집 Vol.2012 No.10

For effective rehabilitation treatments, the status of a patient’s gait needs to be analyzed precisely. Since the gait motions are cyclic with several gait phases, the gait motions can be analyzed by gait phases. In this paper, a hidden Markov model (HMM) is applied to analyze the gait phases in the gait motions. Smart Shoes are utilized to obtain the ground contact forces (GRFs) as observed data in the HMM. The posterior probabilities from the HMM are used to infer the gait phases. The proposed gait phase analysis methods are applied to actual gait data, and the results show that the proposed methods can be used to diagnose the status of a patient and evaluate a rehabilitation treatment.

Network-Based Rehabilitation System for Improved Mobility and Tele-Rehabilitation

Joonbum Bae,Wenlong Zhang,Tomizuka, Masayoshi IEEE 2013 IEEE transactions on control systems technology Vol.21 No.5

<P>In this brief, a network-based rehabilitation system, which takes advantage of the Internet, wireless communication, and control, is proposed to increase the mobility of a rehabilitation system and to enable tele-rehabilitation. In the proposed system, control algorithms and rehabilitation strategies are distributed at the central location (physiotherapist) and the local site (patient) by communicating over the Internet, and the rehabilitation device is controlled wirelessly by the controller at the local site. In order to deal with possible packet losses over the local wireless network, a modified linear quadratic Gaussian controller and a disturbance observer are applied. The simulation and experimental results with an actual knee rehabilitation system show that the proposed network-based rehabilitation system can generate the desired assistive torque accurately in a network environment.</P>

Gait Phase-Based Control for a Knee Assistive System

Joonbum Bae,Kyoungchul Kong 제어로봇시스템학회 2012 제어로봇시스템학회 국제학술대회 논문집 Vol.2012 No.10

Actuators for physical human-robot interaction (pHRI) such as rehabilitation or assistive systems should generate the desired torque precisely. However, the resistive and inertia loads inherent in the actuators (e.g., friction, damping, and inertia) set challenges in the control of actuators in a force/torque mode. The resistive factors include nonlinear effects and should be considered in the controller design to generate the desired force accurately. Moreover, the uncertainties in the plant dynamics make the precise torque control difficult. In this paper, nonlinear control algorithms are exploited for a rotary series elastic actuator to generate the desired torque precisely in the presence of nonlinear resistive factors and modeling uncertainty. The performance of the proposed controller is verified by experiments with actual walking motions

Force-Mode Control of Rotary Series Elastic Actuators in a Lower Extremity Exoskeleton Using Model-Inverse Time Delay Control

Kim, Suin,Bae, Joonbum Institute of Electrical and Electronics Engineers 2017 IEEE/ASME Transactions on Mechatronics Vol. No.

<P>For a physical human-robot interaction (pHRI) system such as an exoskeleton, it has been an important issue to control the interaction force between the user and the actuators because it directly determines the accuracy of the realized impedance. However, the accurate force control of the exoskeleton system has not been fully achieved due to the difficulties caused by uncertainties from pHRI. To overcome this problem, in this study, the series elastic actuator (SEA) was operated by a time delay control (TDC), which directly compensated the uncertainties without an accurate model of them, realizing the designed model dynamics in the actuator. However, in spite of the successful application of TDC, the delays between the desired and model dynamics severely degraded the force control performance of the SEA. Thus, a new strategy named model-inverse time delay control was proposed by introducing a virtual reference predicted by the inverse of model dynamics in TDC. The proposed method significantly improved performance of the force control, and it was verified by demonstrating zero impedance control with pHRI, free oscillation of a pendulum, and force control in the exoskeleton.</P>

Lifetime Prediction of Silicone and Direct Ink Writing-Based Soft Sensors Under Cyclic Strain

Kyeongtaek Kim,Joonbum Bae 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.10 No.2

The softness and stretchability of soft sensors has generated much interest with respect to applying soft sensors for human activity monitoring and proprioception of soft robots. However, most of the research in this area has focused on electrical stability, despite the importance of mechanical failure, thus limiting practical application. In this study, the lifetime of silicone-based soft sensors was examined under accelerated cyclic strain conditions, to construct lifetime prediction models of crack nucleation and growth considering the failure properties of the sensor’s silicone elastomer. To establish the models, an accelerated life test was conducted, in which the lifetime was estimated according to a Weibull distribution under accelerated cyclic strain conditions. Specifically, a lifetime prediction model using the crack growth approach (CGA) was constructed by experimentally measuring the energy release rate (tearing energy) of the silicone elastomer due to crack propagation. Compared to the inverse power law-based model, the CGA-based model showed about 90% improvement in lifetime prediction accuracy in the strain ranges from 150 to 270% with root mean square error 456 and 4592 cycles, respectively, thus indicating that tearing energy is an important parameter for sensor lifetime prediction. The proposed model is expected to be useful for predicting the lifetime of soft sensors under various strain operating conditions.

Back-Drivability Recovery of a Full Lower Extremity Assistive Robot

Byeonghun Na,Joonbum Bae,Kyoungchul Kong 제어로봇시스템학회 2012 제어로봇시스템학회 국제학술대회 논문집 Vol.2012 No.10

Recently, walking assistance robots are receiving a great attention according to the increase of elderly population. Such systems are required to generate precise and large assistive torques to effectively assist human motions. Moreover, the assistive robots should be light and compact for the comfort and safety issues. In this paper we designed full lower extremity assistive robot with compact rotary series elastic actuators(cRSEAs) that are designed considering these factors. A worm gear is installed to amplify the motor torque in the limited space. Also, to generate assistive torque as desired, a torsional spring is used between the motor and the human joint. The device generates large assistive torques by utilizing worm gear, but the large friction introduced by the worm gear makes the controller design challenging. In this paper, a feedback control algorithm is proposed to compensate for such undesired disturbances. The proposed method is verified by experiments.

Kinematic Analysis of a 5-DOF Upper-Limb Exoskeleton With a Tilted and Vertically Translating Shoulder Joint

Yeongtae Jung,Joonbum Bae IEEE 2015 IEEE/ASME transactions on mechatronics Vol.20 No.3

<P>In this paper, an upper-limb exoskeleton with a tilted and vertically movable shoulder joint is proposed. By analyzing the biomechanics of the shoulder, the upper limb for the shoulder and the elbow was approximated to five degrees of freedom (DOFs) by including the vertical translation of the glenohumeral joint of the shoulder, in addition to the 3 DOFs of the shoulder and 1 DOF of the elbow, which are conventionally used to analyze the motion of the shoulder. The shoulder joint was tilted to avoid singularity problems in the workspace, i.e., by tilting the shoulder joint, the singularity position was placed outside of the normal range of motion. This configuration was analyzed using forward and inverse kinematics methods. Because the shoulder elevation affects all of the joint angles, the angles were calculated by applying an inverse kinematics method in an iterative manner. The performance of the proposed upper-limb exoskeleton and analysis methods was verified by simulations and experiments.</P>

Modified Preview Control for a Wireless Tracking Control System With Packet Loss

Wenlong Zhang,Joonbum Bae,Tomizuka, Masayoshi IEEE 2015 IEEE/ASME transactions on mechatronics Vol.20 No.1

<P>In this paper, a modified preview control technique is proposed to compensate packet loss in a wireless tracking control system, where future reference signals over a finite horizon can be previewed. In order to utilize future reference information for the controller design, the system model is augmented with a reference generator whose states are the future reference signals. As a response to the packet loss that occurs in the wireless network, the preview control technique is modified by employing Bernoulli variables to represent packet loss in both controller-actuator and sensor-controller channels. The Bernoulli packet loss model, along with tracking errors and control inputs, is included in a quadratic cost function, and the optimal controller gain that minimizes the cost function is obtained by dynamic programming. A modified Kalman filter considering packet loss is utilized for full-state estimation and state feedback control. The choice of preview horizon is discussed and the performance of the proposed controller is verified by simulation and experimental results.</P>

Application of a Disturbance Observer for Wireless Network Control Systems

Yeongtae Jung,Joonbum Bae 제어로봇시스템학회 2014 제어로봇시스템학회 국제학술대회 논문집 Vol.2014 No.10

In this paper, a control algorithm based on a disturbance observer (DOB) is proposed for wireless network control systems. In order to deal with possible packet losses over the wireless network, a modified linear quadratic Gaussian (MLQG) controller, which includes modeling of the packet loss as a Bernouilli variable, is applied. Since the packet loss of the control command can be considered as an external disturbance, the disturbance observer is added to deal with such virtual disturbance by the packet loss. Performance of the proposed control algorithm is verified by simulations.

Toward Fast and efficient mobility in aquatic environment: A robot with compliant swimming appendages inspired by a water beetle

Kwak, Bokeon,Bae, Joonbum Springer-Verlag 2017 Journal of bionic engineering Vol.14 No.2

<P>Water beetles are proficient drag-powered swimmers, with oar-like legs. Inspired by this mechanism, here we propose a miniature robot, with mobility provided by a pair of legs with swimming appendages. The robot has optimized linkage structure to maximize the stroke angle, which is actuated by a single DC motor with a series of gears and a spring. A simplified swimming appendage model is proposed to calculate the deflection due to the applied drag force, and is compared with simulated data using COMSOL Multiphysics. Also, the swimming appendages are optimized by considering their locations on the legs using two fitness functions, and six different configurations are selected. We investigate the performance of the robot with various types of appendage using a high-speed camera, and motion capture cameras. The robot with the proposed configuration exhibits fast and efficient movement compared with other robots. In addition, the locomotion of the robot is analyzed by considering its dynamics, and compared with that of a water boatman (Corixidae).</P>