Although the merits of electromyography (EMG)-based control of powered assistive systems have been certified, the factors that affect the performance of EMG-based human-robot cooperation, which are very important, have received little attention. This study investigates whether a more physiologically appropriate model could improve the performance of human-robot cooperation control for an ankle power-assist exoskeleton robot. To achieve the goal, an EMG-driven Hill-type neuromusculoskeletal model (HNM) and a linear proportional model (LPM) were developed and calibrated through maximum isometric voluntary dorsiflexion (MIVD). The two control models could estimate the real-time ankle joint torque, and HNM is more accurate and can account for the change of the joint angle and muscle dynamics. Then, eight healthy volunteers were recruited to wear the ankle exoskeleton robot and complete a series of sinusoidal tracking tasks in the vertical plane. With the various levels of assist based on the two calibrated models, the subjects were instructed to track the target displayed on the screen as accurately as possible by performing ankle dorsiflexion and plantarflexion. Two measurements, the root mean square error (RMSE) and root mean square jerk (RMSJ), were derived from the assistant torque and kinematic signals to characterize the movement performances, whereas the amplitudes of the recorded EMG signals from the tibialis anterior (TA) and the gastrocnemius (GAS) were obtained to reflect the muscular efforts. The results demonstrated that the muscular effort and smoothness of tracking movements decreased with an increase in the assistant ratio. Compared with LPM, subjects made lower physical efforts and generated smoother movements when using HNM, which implied that a more physiologically appropriate model could enable more natural and human-like human-robot cooperation and has potential value for improvement of human-exoskeleton interaction in future applications.

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Fuel cells are emerging as promising power sources and have attracted increasing attention from industries and academics worldwide. In particular, automotive manufacturers are replacing internal combustion engines in vehicles with fuel cell systems, which are advantaged by zero emissions, high efficiency, and various clean routes that generate pure hydrogen. However, current fuel cell systems are costly, and their corresponding infrastructures are not fully qualified to meet current market demand. This paper reviews the challenges and developments of automotive fuel cell hybrid power systems and their controls. It briefly summarizes the model, control, and optimization issue associated with the research and application of fuel cells in hybrid power systems. After presenting the basic knowledge and discussing the trending size and structure of fuel cells for automotive usage, the review describes models of automotive fuel cell systems, focusing on the electrochemical reaction dynamics and the key parameters influencing their efficiency and lifetime. The control problems associated with automotive fuel cell systems as well as the optimization issue associated with hybrid energy systems (comprising fuel cells, batteries, and ultra-capacitors) are elaborately analyzed. The review concludes with current problems and challenges faced by the energy control systems of fuel cell vehicles.

PurposeThe aim of this study was to document more appropriate electrode location of a four-electrode-based electrical impedance technology in the monitoring of bladder filling, and to characterize the relationship between bladder filling duration and the measured electrical impedances.MethodsA simulation study, based on a 2-dimension computational model, was conducted to determine the preferable locations of excitation and measurement electrodes in a conventional four-electrode setup. A human observation study was subsequently performed on eight healthy volunteers during natural bladder urine accumulation to validate the result of the simulation study. The correlation between the bladder filling time and the measured electrical impedance values was evaluated.ResultsThe preferable location of measurement electrodes was successively validated by the model simulation study and human observation study. Result obtained via the selected electrodes location revealed a significant negative correlation (R = 0.916 ± 0.059, P < 0.001) between the measured electrical impedance and the urine accumulation time, which was consistent with the result of simulation study.ConclusionsThe findings in this study not only documented the desirable electrodes location to monitor the process of bladder urine accumulation using four-electrode measurement, but also validated the feasibility of utilizing electrical impedance technique to monitor and estimate the bladder urine volume for those with urological disorders.

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