Hosu Lee - Academia.edu (original) (raw)

Papers by Hosu Lee

IEEE Transactions on Neural Systems and Rehabilitation Engineering

Trunk rehabilitation exercises such as those for remediating core stability can help improve the ... more Trunk rehabilitation exercises such as those for remediating core stability can help improve the seated balance of patients with weakness or loss of proprioception caused by diseases such as stroke, and aid the recovery of other functions such as gait. However, there has not yet been any reported method for automatically determining the parameters that define exercise difficulty on a trunk rehabilitation robot (TRR) based on data such as the patient's demographic information, balancing ability, and training sequence, etc. We have proposed a machine learning (ML)-based difficulty adjustment method to determine an appropriate virtual damping gain (Dvirtual) of the controller for the TRR's unstable training mode. Training data for the proposed system is obtained from 37 healthy young adults, and the trained ML model thus obtained is tested through experiments with a separate population of 25 healthy young adults. The leave-one-out cross validation results (37 subjects) from the training group for validation of the designed ML model showed 80.90% average accuracy (R2 score) for using the given information to predict the desired difficulty levels, which are represented by the level of balance performance quantified as Mean Velocity Displacement (MVD) of the center of pressure. Statistical analysis (Repeated measures analysis of variance) of subject performance also showed that ground truth difficulty levels from the training data and predicted difficulty levels did not differ significantly under any of the three exercise modes used in this study (Hard, Medium, and Easy), and the standard deviations were reduced by 16.39, 41.39, and 25.68%, respectively. Moreover, the Planar Deviation (PD) of the center of pressure, which was not the target parameter here, also showed results similar to the MVD, which indicates that the predicted Dvirtual affected the difficulty level of balance performance. Therefore, the proposed ML model-based difficulty adjustment method has potential for use with people who have varied balancing abilities.

2022 22nd International Conference on Control, Automation and Systems (ICCAS)

2022 9th IEEE RAS/EMBS International Conference for Biomedical Robotics and Biomechatronics (BioRob)

IEEE Access

To achieve safe and immersive interface with a user-driven treadmill (UDT), robustness of the use... more To achieve safe and immersive interface with a user-driven treadmill (UDT), robustness of the user position must be ensured by sensitively estimating and accurately converging to the intentional walking speed (IWS). The existing IWS estimation using a linear observer with the cart model (1 st order dynamics) can exponentially converge to the true IWS. However, when the estimation sensitivity is increased by increasing the gain, this method causes severe postural instability due to the generation of excessive anomalous forces. Thus, the existing method has an implicit limitation with regards to increasing the position robustness because of the postural instability issues. In this paper, to simultaneously achieve sensitive and accurate IWS estimation while reducing postural instability on a UDT, in addition to the cart model, we have also utilized the inverted pendulum-based gait model (IPGM) as a 2 nd order dynamic to estimate the intentional walking acceleration (IWA) generated by the ankle torque. Thus, the proposed IWS prediction method uses the cart model for accurate convergence to IWS and the IPGM to follow sensitively the change in the IWS. In the proposed method, the internal states of the existing observers applied to the 1 st and 2 nd order dynamics are shared recursively to estimate the ankle torque acting as a disturbance for the IPGM and to sensitively predict the change in the IWS. Experiments show that the proposed method can significantly facilitate the users in following a profile of desired walking speeds more accurately than the existing IWS estimation method under the same position robustness setup.

2019 19th International Conference on Control, Automation and Systems (ICCAS)

The human core plays a key role in maintaining stability and allowing safe execution of movements... more The human core plays a key role in maintaining stability and allowing safe execution of movements. Stability of the core depends on the strength and control of its muscles. Hemiparesis due to stroke can compromise this control, thus reducing core stability of stroke survivors. Therefore, to allow stroke survivors to safely and independently perform activities of daily living, rehabilitation therapists focus on increasing their core stability. Core rehabilitation involves performing training exercises while sitting on stable or unstable surfaces. This paper presents the development and initial testing of a system that can provide both stable and controlled unstable surfaces for the performance of trunk rehabilitation exercises. It is a 4 DOF system that can gauge the position of the user's center of pressure (COP) using built-in instrumentation and can move according its movements. The system has a graphical interface that is used to provide movement targets to the user which they have to achieve by moving their COP. To judge the system's capability of generating an unstable exercise surface, the COP movement tracking performance of the system has been tested. Further evaluations with healthy and stroke subjects are required to elucidate the system's potential as a trunk rehabilitation tool.

IEEE Robotics and Automation Letters

2022 International Conference on Robotics and Automation (ICRA)

2020 17th International Conference on Ubiquitous Robots (UR)

This paper presents a performance comparison of the robust integral of sign of error (RISE) contr... more This paper presents a performance comparison of the robust integral of sign of error (RISE) controller with the cascade PID controller for the control of a 6-DOF heavy payload industrial robot. The 6-DOF heavy payload industrial robot is a highly nonlinear system. In this research, the dynamic simulation software ADAMS® is used to model the robot. The control systems are designed as joint space controllers and simulated using an ADAMS® and MATLAB/Simulink co-simulation platform. The simulation results are used to tune the controllers and to compare their performance under the best tuning conditions. The results show that when compared with the PID controller, the RISE controller with non-linear robust term provides robust control performance with asymptotic trajectory tracking and less overshoot in nonlinear systems. These results pave the way for implementation of the RISE controller in the real robotic system and verification of its performance.

2021 21st International Conference on Control, Automation and Systems (ICCAS)

Impaired postural control following muscle fatigue (MF) can result in falling, which can lead to ... more Impaired postural control following muscle fatigue (MF) can result in falling, which can lead to fracture or other trauma. Transcutaneous electrical nerve stimulation (TENS) can reduce the muscle weakness that occurs due to MF and electro-tactile feedback can help guide the user to achieve postural or movement goals by providing sensory augmentation. The aim of the presented work is to evaluate experimentally the concept that these two effects can be applied simultaneously through the use of TENS as electro-tactile feedback. In this proof-of-concept study, two healthy participants stood in the one-leg stance while in MF condition for 30 seconds under ‘No TENS’, ‘TENS Continuous' and ‘TENS Feedback’ conditions. Their medio-lateral trunk tilt was recorded during all trials. Electro-tactile feedback was achieved by modulating TENS intensity according to body sway in the medio-lateral direction. The results show that, as compared to the No TENS condition, there was no substantial improvement in postural stability under the TENS Continuous condition. However, the TENS Feedback condition resulted in the highest level of postural stability. Due to the small sample group in this pilot study, it is not possible to conclusively prove the benefits of using TENS as a feedback modality. However, results of both the male and female participants suggest that TENS may hold promise for use as a new electro-tactile biofeedback modality for postural improvement with the added benefit of alleviating the effects of muscle fatigue. In the future, studies with larger sample groups will be undertaken to demonstrate clearly the benefits of using TENS as electro-tactile biofeedback.

IEEE Transactions on Neural Systems and Rehabilitation Engineering, 2022

Performance of trunk rehabilitation exercises while sitting on movable surfaces with feet on the ... more Performance of trunk rehabilitation exercises while sitting on movable surfaces with feet on the ground can increase trunk and leg muscle activations, and constraining the feet to move with the seat isolates control of the trunk. However, there are no detailed studies on the effects of these different leg supports on the trunk and leg muscle activations under unstable and forcefully perturbed seating conditions. We have recently devised a trunk rehabilitation robot that can generate unstable and forcefully perturbed sitting surfaces, and can be used with ground-mounted or seat-connected footrests. In this study, we have evaluated the differences in balance performance, trunk movement and muscle activation (trunk and legs) of fourteen healthy adults caused by the use of these different footrest configurations under the different seating scenarios. The center of pressure and trunk movement results show that the seatconnected footrest may be a more suitable choice for use in a balance recovery focused rehabilitation protocol, while the ground-mounted footrest may be a more suitable choice for a trunk movement focused rehabilitation protocol. Although it is difficult to make a clear selection between footrests due to the mixed trends observed in the muscle activation results, it appears that the seat-connected footrest may be preferable for use with the unstable seat as it causes greater muscle activations. Furthermore, the results provide limited evidence that targeting of a particular muscle group may be Manuscript

2018 IEEE International Conference on Robotics and Automation (ICRA), 2018

To achieve immersive and natural navigation in a virtual environment through human locomotion, it... more To achieve immersive and natural navigation in a virtual environment through human locomotion, it is necessary to generate a 2-dimensional infinite ground for omnidirectional walking. However, the existing omnidirectional treadmills are heavy, complex and exhibit low acceleration due to power transmission inefficiency. In this paper, we present a novel fast-omnidirectional treadmill (F-ODT) with a new power transmission mechanism called the Geared Omni-pulley. This mechanism ensures higher power transmission efficiency for driving the belts of the multiple transversal treadmills for independent Y-axis motion. Due to the improved power transmission performance combined with a simpler and relatively light-weight structure, the proposed 2D treadmill can generate a maximum speed of 3m/sec with an acceleration of 3m/sec2. Based on the improved performance, the F-ODT system can be used as a locomotion interface platform in various virtual reality environments such as training of soldiers, gaming/educational experiences and gait rehabilitation.

IEEE Robotics and Automation Letters, 2022

Balance problems can be a major cause of falling. Existing gait balance rehabilitation devices us... more Balance problems can be a major cause of falling. Existing gait balance rehabilitation devices usually have limited overground usability due to low portability. Therefore, there is need for development of a portable gait balance rehabilitation system. To fulfill this need, a wearable balance biofeedback system is proposed that utilizes a pair of novel devices to deliver 2-dimensional hybrid haptic biofeedback to the neck that is a combination of indentation and stretching of the skin corresponding to the mediolateral (ML) and anteroposterior (AP) directions, respectively. The system's functionality is demonstrated through an experiment where 14 healthy subjects and 1 stroke patient performed stance and gait tasks under various feedback conditions. Provision of feedback to healthy subjects resulted in significant improvements in two-dimensional balance under all task conditions. It is also observed that provision of feedback during more difficult tasks resulted in more significant balance improvements. Furthermore, use of the system during gait balance evaluation trials did not cause any significant change in gait speed, meaning that it does not have any detrimental effect on the user's gait. Results of the stroke subject pilot trial showed similar trends. We expect that use of the proposed system may help to improve the overground gait balance of people suffering from the after effects of diseases such as stroke.

2021 21st International Conference on Control, Automation and Systems (ICCAS), 2021

An active knee orthosis can support a patient's weight and assist the knee during stance phas... more An active knee orthosis can support a patient's weight and assist the knee during stance phase for improved gait assistance. This paper presents the development of a lightweight active knee orthosis (AKO) for post-stroke gait rehabilitation that is capable of providing assistive torque in a pattern that is similar to the natural pattern of the human leg. The proposed system is designed to be lightweight and comfortable to use. The system utilizes a single series elastic actuator and is controlled using the patient-driven motion reinforcement (PDMR) control to provide assistive torque to the user's knee based on the force information gathered from its series elastic link. A pilot study was performed with one young healthy subject wearing an ankle weight (4 kg) on one leg, in order to identify the effects and potential implications of using the AKO for gait assistance of hemiplegic subj ects. No discomfort was reported by the participant during the gait trials. Addition of the ankle weight reduced the knee movements, gait speed and gait balance, while increasing the knee range of motion asymmetry. While using the AKO, the subject was able to overcome much of the detrimental effects of the ankle weight and show improvements in majority of the outcome measures. Thus, the developed AKO exhibited promising outcomes in this pilot study that warrant further studies to better understand the implications of using this system during gait rehabilitation of stroke survivors.

2020 20th International Conference on Control, Automation and Systems (ICCAS), 2020

For stroke survivors, the ultimate goal of rehabilitation training for community life is to incre... more For stroke survivors, the ultimate goal of rehabilitation training for community life is to increase the dynamic stability, which can be helped by increasing the walking speed or symmetry. Several researches have reported the use of haptic stimulation to increase the dynamic stability of gait. Haptic systems have many advantages such as, portability and low-cost, that make them extremely suited for rehabilitation applications. However, until now the use of these systems has been focused mainly on the lower limbs. Gait is a harmonic motion that includes both the upper and lower limbs. A study with people suffering from Parkinson’s Disease showed that it is possible to bring about spatiotemporal gait changes using an arm swing cueing device. Therefore, in this paper, we present the development and verification of a haptic bracelet designed to deliver arm swing based haptic feedback for the rehabilitation of stroke survivors. The presented system is portable, composed of inexpensive sensors and it can measure the arm swing angle correctly regardless of the location or direction of the sensor. The measurements made using the developed system were compared to those made using a standard motion tracking system and only an acceptable amount of error was found. The developed system may be used to characterize the effect of upper extremity motion modification during gait. It may also be used as a system for improving gait speed and symmetry of stroke patients using haptic vibration feedback.

Journal of Institute of Control, Robotics and Systems, 2017

IEEE Access, 2020

Physical therapy involving the use of varying types of seating surface and visual input is recomm... more Physical therapy involving the use of varying types of seating surface and visual input is recommended for individuals suffering from trunk instability. Some robots have been developed to assist in such therapy protocols, but none of them fully constrains the user's lower extremities to move with the seat, which is required to fully transfer the task of maintaining balance to the trunk. To fulfill this requirement, we have developed a robot that can provide a static, unstable or forced perturbation seating surface. The instability of seating surface is provided by having the robot follow movements in the user's center of pressure (COP) and forced perturbations are provided by moving the surface according to an operator's commands irrespective of the COP position. The system is also capable of providing visual feedback of the user's COP. This paper presents a study conducted using this novel robot aimed at evaluating the effect of the different seat modes on the balance of healthy subjects under different visual conditions (blindfold, eyes open and visual feedback). Various COP and trunk movement parameters were observed and the results indicate that the system can elicit similar responses in the unstable mode as the conventional devices, showing that it may be used as a controllable alternative to such devices for the training and objective evaluation of stroke survivors. The results under perturbation conditions showed deviations from the generally held notions about the use of visual feedback. Thus, revealing the need for further studies on the implications of using visual feedback under perturbation conditions. The observation of effects similar to conventional systems that may be beneficial for stroke survivors and the system's ability to help assess recovery progress show that the system holds promise for use as a trunk training and objective performance evaluation tool for stroke survivors. INDEX TERMS Center of pressure (COP), rehabilitation robotics, seated balance, trunk rehabilitation, visual feedback.

IEEE Transactions on Neural Systems and Rehabilitation Engineering, 2021

The conventional cane (single cane) is widely used to promote gait ability of stroke survivors as... more The conventional cane (single cane) is widely used to promote gait ability of stroke survivors as it provides postural stability by extending the base of support. However, its use can reduce muscle activity in the user's paretic side and cause upper limb neuropathies due to the intermittent and excessive loading of the upper limb. The provision of low magnitude support and speed regulation may result in collective improvement of gait parameters such as symmetry, balance and muscle activation. In this paper, we developed a robotic Haptic Cane (HC) that is composed of a tilted structure with motorized wheels and sensors to allow continuous haptic contact with the ground while moving at a regulated speed, and carried out gait experiments to compare the HC with an Instrumented conventional Cane (IC). The results show that use of the HC involved more continuous ground support force of a comparatively lesser magnitude than the IC, and resulted in greater improvements in the swing symmetry ratio and significant improvements in the step length symmetry ratio. Percentage of Non-Paretic Activity (%NPA) of paretic muscles (vastus medialis obliquus (VMO), semitendinosus (SMT), tibialis anterior (TBA) and gastrocnemius medialis (GCM)) in swing phase was significantly improved by the use of either device at fast speed. However, the use of HC improved %NPA of paretic VMO and SMT more than the use of IC at both preferred and fast speeds. It also significantly improved %NPA of paretic GCM in stance phase. Further

2019 19th International Conference on Control, Automation and Systems (ICCAS), 2019

In order to explore mobile applications of kinesthetic cues, we recently developed a system for g... more In order to explore mobile applications of kinesthetic cues, we recently developed a system for generating kinesthetic cues on the user's back. Carrying on from that work, in this paper we present a completely redesigned system that utilizes a pair of reaction wheels to generate torques on the system which in-turn are perceived by the user as directed force cues being delivered to their back. It is a wearable device that wirelessly takes commands from a PC and can generate leftward and rightward directed cues. The system was tested with healthy adults with two distinct objectives. The first was to determine how well they can perceive the cues and also to determine the effect of training on cue perception. The second was to determine the effect on standing balance of directed force cues delivered as biofeedback by the system. The results show that the device can effectively deliver directed kinesthetic cues to the user without becoming a source of discomfort, and biofeedback delivered through this system aids in maintaining balance. Thus, it is indicated that the device presented here is a viable means of delivering directed kinesthetic cues to a user and thus warrants further exploration of its possible applications.