Hyunchul Kim

Kinematic Data Analysis for Post-Stroke Patients Following Bilateral Versus Unilateral Rehabilitation With an Upper Limb Wearable Robotic System

Robot-assisted stroke rehabilitation has become popular as one approach to helping patients recover function post-stroke. Robotic rehabilitation requires four important elements to match the robot to the patient: realistic biomechanical robotic elements, an assistive control scheme enabled through the human-robot interface, a task oriented rehabilitation program based on the principles of plasticity, and objective assessment tools to monitor change. This paper reports on a randomized clinical trial utilizing a complete robot-assisted rehabilitation system for the recovery of upper limb function in patients post-stroke. In this study, a seven degree-of-freedom (DOF) upper limb exoskeleton robot (UL-EXO7) is applied in a rehabilitation clinical trial for patients stable post-stroke (greater than six months). Patients had a Fugl-Meyer Score between 16-39, were mentally alert (19 on the VA Mini Mental Status Exam) and were between 27 and 70 years of age. Patients were randomly assigned to three groups: bilateral robotic training, unilateral robotic training, and usual care. This study is concerned with the changes in kinematics in the two robotic groups. Both patient groups played eight therapeutic video games over 12 sessions (90 min, two times a week). In each session, patients intensively played the different combination of video games that directly interacted with UL-EXO7 under the supervision of research assistant. At each session, all of the joint angle data was recorded for the evaluation of therapeutic effects. A new assessment metric is reported along with conventional metrics. The experimental result shows that both groups of patients showed consistent improvement with respect to the proposed and conventional metrics.

Redundancy Resolution of the Human Arm and an Upper Limb Exoskeleton

The human arm has 7 degrees of freedom (DOF) while only 6 DOF are required to position the wrist and orient the palm. Thus, the inverse kinematics of an human arm has a nonunique solution. Resolving this redundancy becomes critical as the human interacts with a wearable robot and the inverse kinematics solution of these two coupled systems must be identical to guarantee an seamless integration. The redundancy of the arm can be formulated by defining the swivel angle, the rotation angle of the plane defined by the upper and lower arm around a virtual axis that connects the shoulder and wrist joints. Analyzing reaching tasks recorded with a motion capture system indicates that the swivel angle is selected such that when the elbow joint is flexed, the palm points to the head. Based on these experimental results, a new criterion is formed to resolve the human arm redundancy. This criterion was implemented into the control algorithm of an upper limb 7-DOF wearable robot. Experimental results indicate that by using the proposed redundancy resolution criterion, the error between the predicted and the actual swivel angle adopted by the motor control system is less then 5°.

Redundancy resolution of a human arm for controlling a seven DOF wearable robotic system

The human arm including the shoulder, elbow, wrist joints and exclusion scapular motion has 7 Degrees of Freedom (DOF) while positioning of the wrist in space and orientating the palm is a task that requires 6 DOF. As such it includes one more DOF than is needed to complete the task. Given the redundant nature of the arm, multiple arm configurations can be used to complete a task, which is expressed mathematically by none unique solution for the inverse kinematics. Despite this mathematical difficulty, the motor control provides a unique solution for the arm redundancy as the arm is moved in space. Resolving this redundancy is becoming critical as the human interacts with a wearable robotic system(exoskeleton) which includes the same redundancy as the human arm. Therefore, the inverse kinematics solution resolving the redundancy of these two coupled systems must be identical in order to guarantee a seamless integration. The redundancy of the arm can be formulated kinematically by defining the swivel angle — the rotation angle of the plane including the upper and lower arm around a virtual axis connecting the shoulder and wrist joints which are fixed in space. Analyzing reaching tasks recorded with a motion capture lab indicates that the swivel angle is selected such that when the elbow joint is flexed, the palm points the head. Based on these experimental results, selecting the point around the center of the head as a stationary target allows to calculate the swivel angle and in that way to resolve the human arm redundancy. Experimental results indicated that by using the proposed redundancy resolution criteria the error between the predicted swivel angle and the actual swivel angle adopted by the motor control system is less then 5 Deg. This criterion or a synthesis of several additional criteria may improve the synergistic relationships between an operator and a wearable robotic system.

Development and Impact of Radio-frequency Identification-Based Workflow Management in Health Promotion Center: Using Interrupted Time-Series Analysis

Radio-frequency identification (RFID) technology is being used increasingly for its efficiency and safety. The goal of this study is to evaluate the RFID technology within a hospital information system (HIS) for better workflow management in a health promotion center. We developed an RFID (433 mHz) real-time tracking system to monitor patients at the room level. Then we implemented an automatic workflow management by integrating RFID system with HIS. If a patient has finished one examination, the next step is determined automatically by previous number of examined patients and duration in each examination room. We performed interrupted time-series analysis of the mean waiting time for patients in a health promotion center compared with a control group of outpatients in the hospitals radiology department before and after the implementation of an RFID-based system. After implementation of the RFID system, the mean waiting time of patients in the health promotion center decreased significantly (from 5.4 to 4.3 min, 20% decrease) compared with the control group (from 3.8 to 3.5 min, 8% decrease). The RFID system integrated with HIS increases workflow efficiency by shortening the mean waiting time during the workflow process and provides valuable real-time data for physicians and staff regarding workflow efficiency.

Resolving the redundancy of a seven DOF wearable robotic system based on kinematic and dynamic constraint

According to the seven degrees of freedom (DOFs) human arm model composed of the shoulder, elbow, and wrist joints, positioning of the wrist in space and orientating the palm is a task requiring only six DOFs. Due to this redundancy, a given task can be completed by multiple arm configurations, and there is no unique mathematical solution to the inverse kinematics. The redundancy of a wearable robotic system (exoskeleton) that interacts with the human is expected to be resolved in the same way as that of the human arm. A unique solution to the systems redundancy was introduced by combining both kinematic and dynamic criteria. The redundancy of the arm is expressed mathematically by defining the swivel angle: the rotation angle of the plane including the upper and lower arm around a virtual axis connecting the shoulder and wrist joints which are fixed in space. Two different swivel angles were generated based on kinematic and dynamic constraints. The kinematic criterion is to maximize the projection of the longest principle axis of the manipulability ellipsoid for the human arm on the vector connecting the wrist and the virtual target on the head region. The dynamic criterion is to minimize the mechanical work done in the joint space for each two consecutive points along the task space trajectory. These two criteria were then combined linearly with different weight factors for estimating the swivel angle. Post processing of experimental data collected with a motion capturing system indicated that by using the proposed synthesis of redundancy resolution criteria, the error between the predicted swivel angle and the actual swivel angle adopted by the motor control system was less then five degrees. This result outperformed the prediction based on a single criteria.

Epileptic seizure detection - an AR model based algorithm for implantable device

The algorithm of epileptic seizure is at the core of any implantable device aimed to treat the symptoms of this disorder. A training free (on line) epileptic seizure detection algorithm for implantable device utilizing Autoregressive (AR) model parameters is developed and studied. Pre-recorded (off line) epileptic seizure data are used to estimate the internal parameters of an AR model prior and following the seizure Principle Component Analysis (PCA) is used for reducing the dimension of the problem while allowing only the salient features representing the seizure onset to be saved into the implantable device. The implantable device estimates the AR model parameter in real time and compares the saved features of seizure onset with feature from the incoming signals using cosine similarity. In order to guarantee an efficient on line signal processing, Weighted Least Square Estimation (WLSE) model is utilized. Simulation result shows that the proposed method has average 96.6% detection accuracy and 1.2ms latency for the data sets under study. The proposed approach can be extended to multi channel approach using Multi-Variant Autoregressive (MVAR) model which enables seizure foci localization and the sophisticated seizure prediction.

Predicting Redundancy of a 7 DOF Upper Limb Exoskeleton Toward Improved Transparency between Human and Robot

For a wearable robotic system which includes the same redundancy as the human arm, configuring the joint angles of the robotic arm in accordance with those of the operators arm is one of the crucial control mechanisms to minimize the energy exchange between human and robot. Thus it is important to understand the redundancy resolution mechanism of the human arm such that the inverse kinematics solution of these two coupled systems becomes identical. In this paper, the redundancy resolution of the human arm based on the wrist position and orientation is provided as a closed form solution for the practical robot control algorithm, which enables the robot to form the natural human arm configuration as the operator changes the position and orientation of the end effector. For this, the redundancy of the arm is expressed mathematically by defining the swivel angle. Then the swivel angle is expressed as a superposition of two components, which are reference swivel angle and the swivel angle offset, respectively. The reference swivel angle based on the wrist position is defined by the kinematic criterion that maximizes the manipulability along the vector connecting the wrist and the virtual target point on the head region as a cluster of important sensory organs. Then the wrist orientation change is mapped into a joint angle availablility function output and translated to the swivel angle offset with respect to the reference swivel angle. Based on the inverse kinematic formula the controller can transform the position and orientation of the end-effector into the joint torque which enables the robot to follow up the operator’s current joint configuration. The estimation performance was evaluated by utilizing a motion capture system and the results show that there is a high correlation between the estimated and calculated swivel angles.

Admittance control of an upper limb exoskeleton - Reduction of energy exchange

The synergy of human arms and wearable robot systems (e.g. exoskeletons) is enabled by a control algorithm that maximizes the transparency between the two subsystems. The transparency can be improved by integrating the admittance control along with an arm redundancy resolution algorithm. Recent research effort resulted in a new criterion for the human arm redundancy resolution for unconstrained arm motions estimating the swivel angle with prediction errors of less than 5°. The proposed criterion for the arm redundancy resolution defines the mouth as the primary target of the the human hand during unconstrained arm motions in free space. It was postulated based on experimental data analysis that this criterion is based on a neural mechanism directing the hand towards the head for self-feeding. In conjunction with the proposed redundancy resolution criteria a task space admittance control algorithm is introduced based on multiple force sensor inputs obtained at the interface between the human arm and the exoskeleton system. The system performance was evaluated by five healthy subjects performing a peg-in-hole task for three different target locations. The velocities and interaction forces at the upper arm, lower arm, handle and tip were recorded and further used to power exchange between the subject and the device. Results indicated that the proposed control scheme outperforms the purely reactive task space admittance control with energy exchange reduced to 11.22%. Improving the quality of the human control of a wearable robot system may allow the robot to be a natural and transparent extension of the operators body.

A new distributed cooperative MIMO scheme for mobile ad hoc networks

In this paper, we introduce a new communication scheme based on cooperative multiple-input multiple-output (MIMO) communication for mobile ad hoc networks (MANETs) in which nodes are endowed with M antennas. According to our new approach, adjacent nodes no longer interfere with each other but rather cooperate attempting to communicate concurrently. In our scheme, during transmissions, the nodes send packets from only one of their antennas, while during reception, they use all of their antennas to receive and decode packets from multiple close nodes simultaneously. Therefore, each distributed MIMO system in this scheme consists of multiple transmitting nodes acting as a single-array of multiple antennas. We derive upper and lower bounds on the receiver node ergodic capacity in the network where the wireless channel is modeled with both large and small-scale fluctuations. These bounds are compared with Monte-Carlo simulation of point-to-point and cooperative MIMO communications in MANETs. We demonstrate that the capacity of MANETs with multiple antennas is improved using cooperation compared to non-cooperative schemes, i.e., point-to-point MIMO communication. In addition, under the above communication model, we demonstrate that the lower and upper bounds of the ergodic capacity grows linearly with the number of receiving antennas M.

Energy-efficient resource management in Wireless Sensor Network

This paper studies energy-efficient resource allocation schemes in Wireless Sensor Network (WSN) where sensor nodes are densely deployed on the network with infrastructure support. We first construct a network scheme and compute the energy consumption with no intelligent resource management scheme for a given quality-of-service constraint defined as Signal-to-Interference-plus-Noise Ratio (SINR). Under the SINR constraint, optimum energy saving strategies are introduced based on common and adaptive transmit power. Simulation results show that for a given channel bandwidth, minimum energy consumption can be achieved when nodes adaptively control transmit signal power depending on the channel condition.