Skin Impedance Estimation System for Voltage-mode Electrical Stimulator with an AC Bridge Circuit.

Neuromuscular electrical stimulation is used to improve the motor function of paralyzed limbs and prevent muscle atrophy in stroke patients. The system for electrical stimulation is broadly classified into current-mode stimulators and voltage-mode stimulators. The current-mode stimulator adjusts the amplitude of the current, whereas the amplitude of the voltage is adjusted for voltage-mode stimulators. Voltagemode stimulators have the advantage that there is little risk of burns even if the electrode is partially detached. To perform arbitrary current-mode stimulation with voltage-mode stimulators, it is necessary to generate a stimulating voltage based on the skin impedance. As a primary experiment, the frequency characteristics of the electrode-skin impedance were measured using an impedance analyzer on 6 subjects, and the frequency band in which the skin impedance is equivalent to a parallel connection between resistance and capacitance was determined. A prototype bridge circuit with a skin impedance equivalent circuit implemented was designed, assembled, and tested to estimate the skin impedances of 3 subjects. The residuals were computed from the estimated skin-impedance resistance and capacitance of the bridge circuit, and the impedance-analyzer-measured resistance and capacitance. The residuals between the estimated and measured were up to 4.4 % in the resistance component, and up to 8.2 % in the capacitance component of the skin impedance measurements by the impedance analyzer.

Analysis of Pressure Distribution in Transfemoral Prosthetic Socket for Prefabrication Evaluation via the Finite Element Method.

In this study, we estimated and validated the pressure distribution profile between the residuum and two types of prosthetic sockets for transfemoral amputees by utilizing a finite element analysis. Correct shaping of the socket for an appropriate load distribution is a critical process in the design of lower-limb prosthesis sockets. The pressure distribution profile provides an understanding of the relationship between the socket design and the level of subject comfortability. Estimating the pressure profile is important, as it helps improve the prosthesis through an evaluation of the socket design before it undergoes the fabrication process. This study focused on utilizing a magnetic resonance imaging (MRI)-based three-dimensional (3D) model inside a predetermined finite element simulation. The simulation was predetermined by mimicking the actual socket-fitting environment. The results showed that the potential MRI-based 3D model simulation could be used as an estimation tool for a pressure distribution profile due to the high correlation coefficient value (R2 > 0.8) calculated when the pressure profiles were compared to the experiment data. The simulation also showed that the pressure distribution in the proximal area was higher (~30%) than in the distal area of the prosthetic socket for every subject. The results of this study will be of tremendous interest for fabricators through the use of a finite element model as an alternative method for the prefabrication and evaluation of prosthetic sockets. In future prosthetic socket fabrications, less intervention will be required in the development of a socket, and the participation of the subject in the socket-fitting session will not be necessary. The results suggest that this study will contribute to expanding the development of an overall prefabrication evaluation system to allow healthcare providers and engineers to simulate the fit and comfort of transfemoral prosthetics.

Multimodal sensor controlled three Degree of Freedom transradial prosthesis.

This paper describes the basic concept of our multimodal sensor control system for 3-Degree-of-Freedom transradial prosthesis. The target of developing the controller is to reduce the mental effort of planning operating multiple joints in the conventional multifunctional myoelectric controller and reduce the compensating motion of conventional myoelectric prosthesis. An accelerometer is installed in the socket and the angles of the gravitational force are computed to drive the pronation/spination joint and the palmar flexion/dorsifelxion joint of the prosthesis. A threshold On/Off control using the posture information is implemented with the triggering of a co-contraction EMG signal. Through experiment with able-body subjects, we confirmed that this controller has a potential of reducing compensating shoulder movements for pick-raise-place tasks, when compared to the task conducted with conventional locked-wrist prostheses. Yet modification is required for stability.

Powered orthosis and attachable power-assist device with Hydraulic Bilateral Servo System.

This paper discusses the developments and control strategies of exoskeleton-type robot systems for the application of an upper limb powered orthosis and an attachable power-assist device for care-givers. Hydraulic Bilateral Servo System, which consist of a computer controlled motor, parallel connected hydraulic actuators, position sensors, and pressure sensors, are installed in the system to derive the joint motion of the exoskeleton arm. The types of hydraulic component structure and the control strategy are discussed in relation to the design philosophy and target joints motions.

Neural machine interfaces for controlling multifunctional powered upper-limb prostheses.

This article investigates various neural machine interfaces for voluntary control of externally powered upper-limb prostheses. Epidemiology of upper limb amputation, as well as prescription and follow-up studies of externally powered upper-limb prostheses are discussed. The use of electromyographic interfaces and peripheral nerve interfaces for prosthetic control, as well as brain machine interfaces suitable for prosthetic control, are examined in detail along with available clinical results. In addition, studies on interfaces using muscle acoustic and mechanical properties and the problem of interfacing sensory information to the nervous system are discussed.