Ming-Shaung Ju

A rehabilitation robot with force-position hybrid fuzzy controller: hybrid fuzzy control of rehabilitation robot

The goal of this study was to design a robot system for assisting in the rehabilitation of patients with neuromuscular disorders by performing various facilitation movements. The robot should be able to guide patients wrist to move along planned linear or circular trajectories. A hybrid position/force controller incorporating fuzzy logic was developed to constrain the movement in the desired direction and to maintain a constant force along the moving direction. The controller was stable in the application range of movements and forces. Offline analyses of data were used to quantitatively assess the progress of rehabilitation. The results show that the robot could guide the upper limbs of subjects in linear and circular movements under predefined external force levels and apply a desired force along the tangential direction of the movements.

Estimation of Mass, Stiffness and Damping Matrices from Frequency Response Functions

A frequency-domain method for estimating the mass, stiffness and damping matrices of the model of a structure is presented. The developed method is based on our previous work on the extraction of normal modes from the complex modes of a structure. A transformation matrix is obtained from the relationship between the complex and the normal frequency response functions ofa structure. The transformation matrix is employed to calculate the damping matrix of the system. The mass and the stiffness matrices are identified from the normal frequency response functions by using the least squares method. Two simulated systems are employed to illustrate the applicability of the proposed method. The results indicate that the damping matrix can be identified accurately by the proposed method. The reason for the good results is that the damping matrix is identified independently from the mass and the stiffness matrices. In addition, the robustness of the new approach to uniformly distributed measurement noise is also addressed.

Wavelet-based fractal features with active segment selection: Application to single-trial EEG data

Feature extraction in brain-computer interface (BCI) work is one of the most important issues that significantly affect the success of brain signal classification. A new electroencephalogram (EEG) analysis system utilizing active segment selection and multiresolution fractal features is designed and tested for single-trial EEG classification. Applying event-related brain potential (ERP) data acquired from the sensorimotor cortices, the proposed system consists of three main procedures including active segment selection, feature extraction, and classification. The active segment selection is based on the continuous wavelet transform (CWT) and Students two-sample t-statistics, and is used to obtain the optimal active time segment in the time-frequency domain. We then utilize a modified fractal dimension to extract multiresolution fractal feature vectors from the discrete wavelet transform (DWT) data for movement classification. By using a simple linear classifier, we find significant improvements in the rate of correct classification over the conventional approaches in all of our single-trial experiments for real finger movement. These results can be extended to see the good adaptability of the proposed method to imaginary movement data acquired from the public databases.

High sensitivity ethanol gas sensor integrated with a solid-state heater and thermal isolation improvement structure for legal drink-drive limit detecting

Abstract The paper reports the successful fabrication of ethanol gas sensors with tin-dioxide (SnO 2 ) thin films integrated with a solid-state heater, which is realized with technologies of micro-electro-mechanical systems (MEMS), and are compatible with VLSI processes. The main sensing part with dimensions of 450×400 μm 2 in this developed device is composed of a sensing SnO 2 film, which is fabricated by electron-gun evaporation with proper annealing in ambient oxygen gas to yield fine particles and good structure. An integrated solid-state heater with a 4.5 μm-thick cantilever bridge (1000×500 μm 2 ) structure is made of silicon carbide (SiC) material by MEMS technologies. The sensitivity for 1000 ppm ethanol gas reaches as high as 90 with 10 s and 2 min for the response and recovery time, respectively, at an operating temperature of 300°C. Those experimental results also exhibit a much superior performance to that of a popular commercial ethanol gas sensor TGS-822. Therefore, the developed sensor with high performance is a good candidate for some specific application in automobile to detect drink-drive limit and allows an array integration available with various films for controlling each element at separate resistance.

A contact-type piezoresistive micro-shear stress sensor for above-knee prosthesis application

A prototype contact-type micro piezoresistive shear-stress sensor that can be utilized to measure the shear stress between skin of stump and socket of above-knee (AK) prosthesis was designed, fabricated and tested. Micro-electro-mechanical system (MEMS) technology has been chosen for the design because of the low cost, small size and adaptability to this application. In this paper, the finite element method (FEM) package ANSYS has been employed for the stress analysis of the micro shear-stress sensors. The sensors contain two transducers that will transform the stresses into an output voltage. In the developed sensor, a 3000/spl times/3000/spl times/300 /spl mu/m/sup 3/ square membrane is formed by bulk micromachining of an n-type [100] monolithic silicon. The piezoresistive strain gauges were implanted with boron ions with a dose of 10/sup 15/ atoms/cm/sup 2/. Static characteristics of the shear sensor were determined through a series of calibration tests. The fabricated sensor exhibits a sensitivity of 0.13 mV/mA-MPa for a 1.4 N full scales shear force range and the overall mean hysteresis error is than 3.5%. In addition, the results simulated by FEM are validated by comparison with experimental investigations.

Time-course analysis of stretch reflexes in hemiparetic subjects using an on-line spasticity measurement system.

Spasticity after a stroke is usually assessed in a score form by subjectively determining the resistance of a joint to an externally imposed passive movement. This work presents a spasticity measurement system for on-line quantifying the stretch reflex of paretic limbs. Four different constant stretch velocities in a ramp-and-hold mode are used to elicit the stretch reflex of the elbow joint in spastic subjects. The subjects are tested at supine position with the upper limb stretched towards the ground, in contrast with the horizontally stretched movement used in other studies. By subtracting the baseline torque, reflex torque measured at a selected low stretch velocity of 5 deg/sec, the influence of gravity torque and inertial in vertical stretching mode can be minimized. The averaged speed-dependent reflex torque (ASRT), defined as the measured torque deviated from the baseline torque, is used for quantifying the spastic hypertonia. Four subjects having incurred cerebrovascular accident (CVA) are recruited for time-course study in which the measurements are taken at 72 hours, one week, one month, three months, and six months after onset of stroke. During the development of spasticity, the changes of ASRT and velocity sensitivity of ASRT of the involved and the intact elbow joints are discussed.

Improving Elbow Torque Output of Stroke Patients with Assistive Torque Controlled by EMG Signals

This paper develops an assistive torque system which uses homogeneic surface electromyogram (EMG) signals to improve the elbow torque capability of stroke patients by applying an external time-varying assistive torque. In determining the magnitude of the torque to apply, the incorporated assistive torque algorithm considers the difference between the weighted biceps and triceps EMG signals such that the applied torque is proportional to the effort supplied voluntarily by the user. The overall stability of the assistive system is enhanced by the incorporation of a nonlinear damping element within the control algorithm which mimics the physiological damping of the elbow joint and the co-contraction between the biceps and triceps. Adaptive filtering of the control signal is employed to achieve a balance between the bandwidth and the system adaptability so as to ensure a smooth assistive torque output. The innovative control algorithm enables the provision of an assistive system whose operation is both natural to use and simple to learn. The effectiveness of the proposed assistive system in assisting elbow movement performance is investigated in a series of tests involving five stroke patients and five able-bodied individuals. The results confirm the ability of the system to assist all of the subjects in performing a number of reaching and tracking tasks with reduced effort and with no sacrifice in elbow movement performance.

Performance of elbow tracking under constant torque disturbance in normotonic stroke patients and normal subjects

OBJECTIVE In this study, the influences of externally imposed constant torque on the voluntary elbow movements of stroke and normal subjects were investigated quantitatively. BACKGROUND Muscle weakness, spasticity and incoordination are the major factors that interfere with stroke patients limb functions. Imposing external torque disturbance may worsen the motor performance. This experiment was designed to investigate the effects of small constant external torque on the performance of voluntary elbow movements. METHODS Tracking of a ramp-and-hold angle trajectory in the direction of extension was used as the main task for performance assessment. Each subject repeated the same tracking movement six times in each of three loading conditions: no, assistive or resistive loading. Five normal and six stroke subjects were recruited for this study. We used parameters extracted from movement trajectory and processed electromyograms as the performance indicators. RESULTS For normal subjects, there was no difference in the tracking performance in the three loading conditions. For stroke patients, the affected side had inferior performance to the healthy side in the free loading condition and the difference diminished in assistive and resistive loading conditions as the performance of the affected side improved. Integrated electromyograms of biceps or triceps did not show significant changes in different loading conditions. CONCLUSIONS Small externally imposed constant torque, either resistive or assistive, may improve motor performance of affected elbows in stroke patients. RELEVANCE Most of the currently available prostheses are passive devices, aiming at providing better support and improving stability. The results of the current study imply that an active prosthetic device that applies a small constant torque to the hemiparetic elbow can improve its motor performance in stroke patients. The direction of external torque is to assist the weaker side of the antagonistic muscle pair.

Control of Ionic Polymer-Metal Composites for Active Catheter Systems via Linear Parameter-Varying Approach

The ionic polymer metal composite (IPMC) is one type of electro-active material with the characteristics of low electric driving potential, large deformation, and aquatic manipulation. It is highly attractive to biomedical applications as an actuator or a sensor. The main purpose of this study is to explore closed-loop control schemes to an IPMC actuator for active catheter systems. In this article, by measuring frequency responses of a 20 mm × 5 mm × 200 μm IPMC, an empirical model is developed and used for closed-loop control. From previous work, two resonant peaks ranged at 3—4 Hz and 18—20 Hz are found in the Bode diagram for the frequency responses of IPMC. Based on this fact, a 4th order transfer function was modeled to describe the system. A parameter-dependent transfer function was then created to describe the bending dynamics of IPMC in response to different driving voltages. As IPMC actuators are nonlinear and slow time-varying systems, the controller was designed using linear parameter varying (LPV) approach. Compared with the conventional closed-loop PID control, the maximum overshoot and steady-state error was decreased to 2% and 1.32%, respectively. The rise time was about 0.186 s, which is within the limit for many biomedical applications.

Neuro-rehabilitation robot-assisted assessments of synergy patterns of forearm, elbow and shoulder joints in chronic stroke patients.

BACKGROUND Abnormal synergy is one of the major motor deficits in stroke patients. Abnormal muscle synergies, in conjunction with weakness and spasticity, interfere with voluntary movements and restrict the range of motion. This study aimed to quantify abnormal synergies in the affected upper limbs of chronic stroke patients by using a neuro-rehabilitation robot. METHODS Twelve chronic stroke patients and eight age-matched control subjects were recruited to perform rectilinear tracking movements in four horizontal directions (back-forth, two oblique directions at 45 degrees , and right-left). Kinematic, kinetic and electromyogram data were recorded and used to develop two biomechanical indices and one electromyogram assessment index based on principal component analysis. FINDINGS Significant differences between upper limbs of control subjects and the affected side of stroke patients were observed in all three assessment indices. Higher correlation between the elbow joint angle and the forearm pronation/supination torque, higher variation of the forearm torque, and abnormal co-contraction of the elbow and shoulder muscles were observed in the affected limbs of stroke patients. The difference was more prominent in the right-left direction and the oblique direction contra-proximal to ipsi-distal. INTERPRETATION The proposed assessment indices could be employed to quantify the abnormal synergies in stroke patients. Rectilinear tracking along the right-left direction and the oblique direction of contra-proximal to ipsi-distal is more suitable for assessing abnormal synergies.