Jungwon Yoon

A 6-DOF Gait Rehabilitation Robot With Upper and Lower Limb Connections That Allows Walking Velocity Updates on Various Terrains

This paper presents a 6-DOF gait rehabilitation robot that allows patients to update their walking velocity on various terrain types and navigate in virtual environments (VEs) through upper and lower limb connections. This robot is composed of an upper limb device, a sliding device, two footpad devices, and a body support system. The footpad device on the sliding device generates 3-DOF spatial motions on the sagittal plane for each foot. This allows the generation of various terrain types for diverse walking training. The upper limb device allows users to swing their arms naturally through the use of a simple pendulum link with a passive prismatic joint. Synchronized gait patterns for this robot are designed to represent a normal gait with upper and lower limb connections. To permit patients to walk at will, this robot allows walking velocity updates for various terrain types by estimating the interaction torques between the human and the upper limb device, and synchronizing the lower limb device with the upper limb device. In addition, the patient is able to navigate in VEs by generating turning commands with switches located in the handles of the upper limb device. Experimental results using a healthy subject show that the user can update the walking velocity on level ground, slopes, and stairs through upper and lower limb connections. In addition, the user could navigate in the VEs with walking velocity updates and turning input command allowing various rehabilitation training modes. During a pilot clinical test, a hemiplegic patient could use the suggested gait rehabilitation robot with a slow walking speed. The rehabilitation plan was also suggested for the patient and the possible therapeutic effects of the suggested rehabilitation robot system are discussed.

Design, fabrication, and evaluation of a new haptic device using a parallel mechanism

This paper presents design, fabrication, and evaluation of a new 6-DOF haptic device for interfacing with virtual reality by using a parallel mechanism. The mechanism is composed of three pantograph mechanisms that are driven by ground-fixed servomotors, three spherical joints between the top of the pantograph mechanisms and the connecting bars, and three revolute joints between the connecting bars and a mobile joystick handle. Forward and inverse kinematic analyses are performed and the Jacobian matrix is derived. Performance indexes such as global payload index, global conditioning index, translation and orientation workspaces, and sensitivity are evaluated to find optimal parameters in the design stage. The proposed haptic mechanism has better load capability than those of the pre-existing haptic mechanisms due to the fact that the motors are fixed at the base. It has also a wider orientation workspace mainly due to a RRR-type spherical joint. A control method is presented with gravity compensation and force feedback by a force/torque sensor to compensate for the effects of unmodeled dynamics such as friction and inertia. Also, the dynamic performance is evaluated for force characteristics. Virtual wall simulation with the developed haptic device is demonstrated.

A Novel Reconfigurable Ankle/Foot Rehabilitation Robot

This paper presents a novel reconfigurable ankle rehabilitation robot to cover various rehabilitation exercise modes. The designed robot can allow desired ankle and foot motions including toe and heel raising as well as traditional ankle rotations since the mechanism can generate relative rotation between the fore and rear platforms as well as pitch and roll motions. In addition, the robotic device can be reconfigured from a range of motion (ROM)/strengthening exercise device to a balance/proprioception exercise device by simply incorporating additional plate. Further, the action of the device is two folded in the sense that while a patient’s foot is fastened firmly to the ROM/strengthening device for task specific training, s/he can also stand on the balance/proproception device. The suggested ankle rehabilitation robot is expected to substitute not only the traditional therapy in various exercise modes but also supply the advanced functional exercises.

A Novel Locomotion Interface with Two 6-DOF Parallel Manipulators That Allows Human Walking on Various Virtual Terrains

This paper proposes a novel locomotion interface that can generate an infinite floor with various surfaces and can provide a user with proprioceptive feedback about walking. The interface allows users to experience life-like walking in virtual environments with various terrains. The interface consists of two platforms, each consisting of a three-degrees-of-freedom (3-DOF; x, y and yaw) planar device on which a 3-DOF (pitch, roll and z) footpad is mounted. Alternating current servomotors drive the planar devices to generate rapid motions, while pneumatic actuators drive the footpad devices to generate the impedances required for various virtual terrains, in addition to supporting the user’s weight. To simulate natural human walking, the locomotion interface design specifications are based on gait analysis, and each mechanism is optimally designed and manufactured to satisfy these requirements. The locomotion interface allows natural walking (step, 0.8 m; height, 20 cm; load capability, 100 kg; slope, 55°) on various terrains. In addition, a new walking control algorithm is proposed for generating continuous walking on an infinite floor involving various terrains. In this algorithm, each independent platform follows a human foot during the swing phase, while the other platform returns to the home position during the single-limb stance phase. During the double-limb stance phase, the two platforms assume neutral positions to compensate for the offset errors generated by velocity changes. Therefore, this algorithm can satisfy natural walking conditions in any direction. The transition phase between the swing and stance phases is detected using a simple switch sensor system, while human foot motions are sensed using a calibrated magnetic motion tracker attached to the shoe. Actual walking simulations on level ground, slopes, and stairs show that the proposed locomotion interface allows an average person to walk naturally on various virtual terrains in safety, without marked disturbances. This interface has various applications, such as in virtual reality (VR) navigation, rehabilitation, and gait analysis.

A novel walking speed estimation scheme and its application to treadmill control for gait rehabilitation

BackgroundVirtual reality (VR) technology along with treadmill training (TT) can effectively provide goal-oriented practice and promote improved motor learning in patients with neurological disorders. Moreover, the VR + TT scheme may enhance cognitive engagement for more effective gait rehabilitation and greater transfer to over ground walking. For this purpose, we developed an individualized treadmill controller with a novel speed estimation scheme using swing foot velocity, which can enable user-driven treadmill walking (UDW) to more closely simulate over ground walking (OGW) during treadmill training. OGW involves a cyclic acceleration-deceleration profile of pelvic velocity that contrasts with typical treadmill-driven walking (TDW), which constrains a person to walk at a preset constant speed. In this study, we investigated the effects of the proposed speed adaptation controller by analyzing the gait kinematics of UDW and TDW, which were compared to those of OGW at three pre-determined velocities.MethodsTen healthy subjects were asked to walk in each mode (TDW, UDW, and OGW) at three pre-determined speeds (0.5 m/s, 1.0 m/s, and 1.5 m/s) with real time feedback provided through visual displays. Temporal-spatial gait data and 3D pelvic kinematics were analyzed and comparisons were made between UDW on a treadmill, TDW, and OGW.ResultsThe observed step length, cadence, and walk ratio defined as the ratio of stride length to cadence were not significantly different between UDW and TDW. Additionally, the average magnitude of pelvic acceleration peak values along the anterior-posterior direction for each step and the associated standard deviations (variability) were not significantly different between the two modalities. The differences between OGW and UDW and TDW were mainly in swing time and cadence, as have been reported previously. Also, step lengths between OGW and TDW were different for 0.5 m/s and 1.5 m/s gait velocities, and walk ratio between OGS and UDW was different for 1.0 m/s gait velocities.ConclusionsOur treadmill control scheme implements similar gait biomechanics of TDW, which has been used for repetitive gait training in a small and constrained space as well as controlled and safe environments. These results reveal that users can walk as stably during UDW as TDW and employ similar strategies to maintain walking speed in both UDW and TDW. Furthermore, since UDW can allow a user to actively participate in the virtual reality (VR) applications with variable walking velocity, it can induce more cognitive activities during the training with VR, which may enhance motor learning effects.

Gait pattern generation with knee stretch motion for biped robot using toe and heel joints

This paper presents a new alternative methodology to generate gait pattern with a knee stretched motion for biped robot utilizing toe and heel joints. During walking sequence, human heels act as passive joints that create some support area which enhances the stability of human walking. This research tries to replace human-heel like mechanism with a heel joint in the biped robot foot. The existence of heel joints in the biped robot feet has two main advantages. The first one is that the support area during double support phase will be increased. Secondly, singularity during knee stretch motion can be avoided. The loss of degree of freedom in the knee joint will not produce singularity in the inverse kinematics solution since there is still another degree of freedom in the heel joint. The effectiveness of the algorithm is being studied through a dynamic simulation tool. A stable knee stretch walking pattern utilizing toe and heel joints was generated, which has some similarity to the human walking pattern. Effectiveness of the proposed algorithm in terms of joint torque requirements as well as energy consumptions have also been shown.

A Portable Gait Asymmetry Rehabilitation System for Individuals with Stroke Using a Vibrotactile Feedback

Gait asymmetry caused by hemiparesis results in reduced gait efficiency and reduced activity levels. In this paper, a portable rehabilitation device is proposed that can serve as a tool in diagnosing gait abnormalities in individuals with stroke and has the capability of providing vibration feedback to help compensate for the asymmetric gait. Force-sensitive resistor (FSR) based insoles are used to detect ground contact and estimate stance time. A controller (Arduino) provides different vibration feedback based on the gait phase measurement. It also allows wireless interaction with a personal computer (PC) workstation using the XBee transceiver module, featuring data logging capabilities for subsequent analysis. Walking trials conducted with healthy young subjects allowed us to observe that the system can influence abnormality in the gait. The results of trials showed that a vibration cue based on temporal information was more effective than intensity information. With clinical experiments conducted for individuals with stroke, significant improvement in gait symmetry was observed with minimal disturbance caused to the balance and gait speed as an effect of the biofeedback. Future studies of the long-term rehabilitation effects of the proposed system and further improvements to the system will result in an inexpensive, easy-to-use, and effective rehabilitation device.

A Novel Electromagnetic Actuation System for Magnetic Nanoparticle Guidance in Blood Vessels

Targeted drug delivery using magnetic nanoparticles (MNPs) is a new therapeutic method and is being improved continually. However, recent improvements have focused mainly on the introduction and synthesis of special drugs and there are still limitations getting a drug to desired locations in the body, primarily owing to the small size of nanoparticles and the difficulty of controlling their movement in the body. This paper introduces a new electromagnetic actuation system for guiding MNPs in blood vessels. This system uses six electromagnets powered by currents that can generate a high-gradient magnetic field in the desired direction. A differential current coil (DCC) approach is used to calculate the current applied to each coil. Due to properties of the DCC approach, it is possible to use soft iron cores at the centers of the coils to amplify and concentrate the magnetic field in the desired region and generate a stronger magnetic force than the existing coil systems. To evaluate the performance of the actuation system, a model that guided nanoscale magnetic particles inside special channels was studied using commercial software. To improve the efficiency of the electromagnets for MNP guidance, the structural parameters of the cores and coils were chosen based on the simulation results to get the largest magnetic force in the region of interest, which was set as size of the mouse brain. The proposed actuation system is very compact and less expensive than previous systems. Furthermore, the simulation results demonstrated that the actuation system can generate adequate magnetophoretic forces for nanoparticle steering in a Y-shaped vascular model and can be potentially used as a propulsion tool for MNP guidance in blood vessels.

A Novel Scheme for Nanoparticle Steering in Blood Vessels Using a Functionalized Magnetic Field

Magnetic drug targeting is a drug delivery approach in which therapeutic magnetizable particles are injected, generally into blood vessels, and magnets are then used to guide and concentrate them in the diseased target organ. Although many analytical, simulation, and experimental studies on capturing schemes for drug targeting have been conducted, there are few studies on delivering the nanoparticles to the target region. Furthermore, the sticking phenomenon of particles to vessels walls near the injection point, and far from the target region, has not been addressed sufficiently. In this paper, the sticking issue and its relationship to nanoparticle steering are investigated in detail using numerical simulations. For wide ranges of blood vessel size, blood velocity, particle size, and applied magnetic field, three coefficient numbers are uniquely generalized: vessel elongation, normal exit time, and force rate. With respect these new parameters, we investigated particle distribution trends for a Y-shaped channel and computed ratios of correctly guided particles and particles remaining in the vessel. We found that the sticking of particles to vessels occurred because of low blood flow velocity near the vessel walls, which is the main reason for low targeting efficiency when using a constant magnetic gradient. To reduce the sticking ratio of nanoparticles, we propose a novel field function scheme that uses a simple time-varying function to separate the particles from the walls and guide them to the target point. The capabilities of the proposed scheme were examined by several simulations of both Y-shaped channels and realistic three-dimensional (3-D) model channels extracted from brain vessels. The results showed a significant decrease in particle adherence to walls during the delivery stage and confirmed the effectiveness of the proposed magnetic field function method for steering nanoparticles for targeted drug delivery.

The simplest passive dynamic walking model with toed feet: A parametric study

This paper presents a passive dynamic walking model with toed feet that can walk down a gentle slope under the action of gravity alone. The model is the simplest of its kind with a point mass at the hip and two rigid legs each hinged at the hip on the one end and equipped with toed foot on the other end. We investigate two cases of the model, one with massless legs and another with infinitesimal leg masses. Rotation of the stance foot about the toe joint is initiated by ankle-strike, which is caused by the inelastic collision of the stance leg with a stop mounted on the stance foot. Numerical simulations of walking show that larger step lengths, higher speeds, stability, and energy efficiency can be achieved than what is achievable by a point-feet walker of same hip mass and leg lengths. Period-two gait of a point-feet walker is compared with period-one gait of the toed-feet walker and the mechanism responsible for achieving longer step lengths is described. It is shown that the advantage of the proposed walker comes from its relation to arc-feet walker. The characteristics of deterministic gait with infinitesimal leg masses is compared with that of nondeterministic gait with zero leg masses. It is shown that deterministic gait does not give maximum speed and efficiency compared to nondeterministic gait with swing leg control. Finally, active dynamic walking of the proposed walker is discussed.