Sungon Lee

EMG-Based Continuous Control Scheme With Simple Classifier for Electric-Powered Wheelchair

This paper presents an electromyographic (EMG)-based continuous control scheme including simple classifier for an electric-powered wheelchair, ultimately for quadriplegics. The proposed scheme utilizes three EMG signals as inputs for the muscle-computer interface. Since zygomaticus major muscles and transversus menti muscle of human face are able to move independently as well as to adjust contractile forces voluntarily, the surface EMG signals on these muscles are utilized for the electric-powered wheelchair control system. To extract the envelopes of the signal waveforms and to reflect the moving average activities, the root-mean-squares (RMS) operation and normalization are subsequently employed as initial signal processing. Then, an activation vector containing three normalized RMS signals is obtained in real time. The activation vector is applied to the simple classifier for finding out the motion command. Both desired linear acceleration and angular velocity are yielded from the linear combinations of the classification result and the magnitude of activation vector. Finally, desired wheel velocities of the wheelchair control system are obtained by using the integration and differential inverse kinematics. The effectiveness of the proposed control scheme is verified through several experiments such as avoiding obstacle cones and navigating long distance by the users.

A Coordinated Navigation Strategy for Multi-Robots to Capture a Target Moving with Unknown Speed

The paper proposes an algorithm for multi-robot coordination and navigation in order to intercept a target at a long distance. For this purpose, a limit cycle based algorithm using a neural oscillator with phase differences is proposed. The state of target is unknown, under the assumption that it is stationary or in motion with constant unknown speed along a straight line. Using the proposed algorithm, a group of robots is intended to move towards the target in such a way that the robots surround it. While moving to the target, self-collision between the robots is avoided. Moreover, a collision avoidance with static obstacles as well as dynamic target is realized. The robots reach the target at a desired distance, keeping uniformly distributed angles around the target. The algorithm is further extended so that a static interception point for the target can be estimated in place of pursuing a dynamic target, which is referred to as a virtual target in this paper. In other words, the robots move towards the virtual target instead of the actual target. The robots ultimately encircle the actual target when they arrive at the virtual target. The effectiveness of the proposed method is verified through simulation results.

Prolonged stimulation with low-intensity ultrasound induces delayed increases in spontaneous hippocampal culture spiking activity

Ultrasound is a promising neural stimulation modality, but an incomplete understanding of its range and mechanism of effect limits its therapeutic application. We investigated the modulation of spontaneous hippocampal spike activity by ultrasound at a lower acoustic intensity and longer time scale than has been previously attempted, hypothesizing that spiking would change conditionally upon the availability of glutamate receptors. Using a 60‐channel multielectrode array (MEA), we measured spontaneous spiking across organotypic rat hippocampal slice cultures (Nu2009=u200928) for 3u2009min each before, during, and after stimulation with low‐intensity unfocused pulsed or sham ultrasound (spatial‐peak pulse average intensity 780u2009μW/cm2) preperfused with artificial cerebrospinal fluid, 300u2009μM kynurenic acid (KA), or 0.5u2009μM tetrodotoxin (TTX) at 3u2009ml/min. Spike rates were normalized and compared across stimulation type and period, subregion, threshold level, and/or perfusion condition using repeated‐measures ANOVA and generalized linear mixed models. Normalized 3‐min spike counts for large but not midsized, small, or total spikes increased after but not during ultrasound relative to sham stimulation. This result was recapitulated in subregions CA1 and dentate gyrus and replicated in a separate experiment for all spike size groups in slices pretreated with aCSF but not KA or TTX. Increases in normalized 18‐sec total, midsized, and large spike counts peaked predominantly 1.5u2009min following ultrasound stimulation. Our low‐intensity ultrasound setup exerted delayed glutamate receptor‐dependent, amplitude‐ and possibly region‐specific influences on spontaneous spike rates across the hippocampus, expanding the range of known parameters at which ultrasound may be used for neural activity modulation.

Theoretical analysis and design for a multilayered ionic polymer metal composite actuator

Ionic polymer metal composites with a flexible large deformation have been used as biomimetic actuators and sensors in various fields. This work mainly focuses on the validation of the proposed theoretical prediction for various ionic polymer metal composite applications, such as a field needing a large resultant force, large tip deflection, or high response frequency. Such properties can be controlled by the number of layers and the thickness ratio of a multilayered ionic polymer metal composite actuator. Thus, we considered major design factors such as the number of layers and the thickness ratio in analysis of the proposed theoretical model and performed experiments to verify the static and dynamic electromechanical responses of multilayered (multimorph) ionic polymer metal composite structures acting as actuators. The relation between the polymer (Nafion) and electrode or substrate is represented by β. From this theoretical analysis, three properties were analyzed and predicted based on the Euler–Bernoulli beam theory, considering the dynamics of the ionic polymer metal composite, electrode, and bonding layers (substrate layers). The predicted results of a symmetric ionic polymer metal composite multimorph were compared with results of finite element analysis and experiments using ionic polymer metal composite multimorphs with one to five layers. Finally, this work examined how the number of layers and thickness affect the dynamic properties. This can contribute to predicting and optimally designing a multilayered ionic polymer metal composite actuator for satisfying a specific requirement.

Motion characterization scheme to minimize motion artifacts in intravital microscopy

Abstract. Respiratory- and cardiac-induced motion artifacts pose a major challenge for in vivo optical imaging, limiting the temporal and spatial imaging resolution in fluorescence laser scanning microscopy. Here, we present an imaging platform developed for in vivo characterization of physiologically induced axial motion. The motion characterization system can be straightforwardly implemented on any conventional laser scanning microscope and can be used to evaluate the effectiveness of different motion stabilization schemes. This method is particularly useful to improve the design of novel tissue stabilizers and to facilitate stabilizer positioning in real time, therefore facilitating optimal tissue immobilization and minimizing motion induced artifacts.

Underactuated finger mechanism for natural motion and self-adaptive grasping towards bionic partial hand

This paper presents an underactuated finger mechanism enabling both self-adaptive grasping and natural motion such as flexion and extension. It has three degrees-of-freedom mechanism composed of one actuator and a couple of passive components including torsional springs and mechanical stoppers. In detail, the proposed mechanism consists of two five-bar and one four-bar linkages. Since each five-bar linkage contains passive components, it is allowed to have adaptive grasping as well as natural motion for human finger-like behavior. Kinematics and static force analysis are performed to reveal the operational principle of the proposed mechanism. Finally both simulation and experiments are conducted to show the design feasibility of the proposed mechanism.

Development of a Wearable Robotic Positioning System for Noninvasive Transcranial Focused Ultrasound Stimulation

Transcranial ultrasound neuromodulation has been attracting more and more interest from researchers as a novel modality for brain stimulation. Typical manual positioning for brain stimulation requires the patient to sit still during stimulation for extended periods and readily loses its positioning accuracy if the patient moves. To address these problems of inconvenience and inaccuracy, we proposed a robotic positioning system for targeted ultrasound brain stimulation. The proposed device automatically moves the ultrasound transducer to a desired position and orientation, enabling far more accurate and comfortable automatic positioning of the transducer than when using traditional manual positioning. The device was developed as a wearable design, because it eliminates the necessity for troublesome motion compensation for the users unintentional movements. Parallel and serial mechanisms were combined and a torque optimization method was proposed so as to obtain a lightweight design, and to implement a sufficient number of degrees of freedom of motion.

Load distribution algorithms for redundantly actuated manipulator resembling the human upper-extremity

This paper presents the optimization of muscle forces in the human upper extremity for the desired trajectory. The proposed kinematic model of the human upper extremity is a force redundant mechanism, implying that number of actuators are more than number of outputs. During the trajectory, the torque is generated for each joint by antagonistic activation of muscles. The biological actuators (muscles) can only generate forces in one direction (unidirectional). Based on this fact and considering the maximum forces limit for each muscle, we proposed a dynamic optimization technique in which only positive muscles forces not exceeding their maximum limits are generated to follow the desired trajectory.

Design of a kinematically redundant Schönflies-motion generator with auxiliary grasping task

This paper introduces a novel kinematically redundant five-degree-of-freedom (DOF) parallel mechanism (PM) which can be fully gravity balanced. The kinematic redundancy can be used to generate large rotational workspace or perform auxiliary grasping task. The grasping task is selected as an example to be investigated in this work. Firstly, description of structure and principle of gravity balancing are introduced. Secondly, closed-form inverse and forward kinematic models are presented in detail. Thirdly, an example trajectory that includes the auxiliary grasping task is demonstrated using a commercially available multi-body dynamic simulator. Analysis results show that the proposed PM has quite a few potential applications.

Retractor mechanics in open-surgery

In this study, we investigate a retractor mechanics in open-surgery. Retracts are being used to acquire open space for conducting surgery. It is discovered that regardless of retractors number, retractors should be located at the vertices of regular polygon in order to secure the largest operating space. Based on this result, retractor mechanics that describes the correlation among the operating area, retraction force, and the number of retractors is suggested. The estimated retraction forces based on retractor mechanics match well with experimental data based on the porcine skin.