This paper presents a contact force distribution feedback control system for developing safe wearable assistive robots. In order to ensure the safety of the user wearing an assist robot being different structure from the assisting part (e.g. entire torso assist with several actuators), a control system based on contact force distribution measured via tactile pressure sensors (pressure distribution sensors) is proposed. By utilizing the tactile sensors on the robot's surface, the robot can measure physical contact force distribution as pressure distribution and control it to suppress excessive. In our previous research, a control methodology with pseudo torque generated from maximum contact force measured by tactile sensors was proposed, however, amplitude of contact force needed to reduce according to pain tolerance of human body parts. A control methodology based on inverse kinematics, a known methodology on the field of serial link-type manipulators, is presented, and confirmed to be effective to improve safety from conventional torque-base control methodology on computer simulations.
This paper proposes an AAN VFC (Assist-as-Needed Velocity Field Control) approach for rehabilitation robots. Proposed controller includes an adaptive NN (neural network) term to compensate for the unknown dynamics of the system and the weight matrix update law of the adaptation NN term involves a forgetting factor which reduced the control effort for small tracking error. The dead-zone property together with the forgetting factor of the NN gives a liberty (a free torque tunnel) to the user to move the target limb with a velocity inside a velocity interval around the desired velocity. This property leads to the AAN property. The controller does not require the dynamic model of the system, and also delivers a priori bounded command. The latter has been featured by means of utilizing a saturated function in the proportional-type feedback term and a projection operator in the NN update law. The stability of the closed-loop system is studied well, and the performance of the controller is evaluated through experiments conducted on a lower-limb exoskeleton (TTI-Knuckle 1).
In this study, we focus on developing a computer - aided diagnosis (CAD) system which estimates dementia at home from electroencephalogram (EEG) data. In order to realize such a system, measurement with a small number of electrodes is necessary from the viewpoint of convenience. Furthermore, a short measurement time is required to reduce the burden on the patient. Therefore, we propose a method using average frequency and 3-electrode correlation value calculated from 1-minute data from 3 electrodes (P3, P4, Oz) on the occipital region at resting state with closed eyes. By using this method, it is shown that Alzheimer's disease and dementia with Lewy bodies (DLB) can be classified with an accuracy of 81% and 89% respectively.
SSVEP (steady-state visual evoked potential) is known as EEG response for alternated visual stimulation about 3.5-75Hz that used for signal source of the brain-computer interface. Whereas there are many studies for SSVEP or visual sensory system, little is known that how is central nerves system generate EEG response at high frequency visual stimulation such as SSVEP. To simplify the experimental neural pathway, we focused on the optic tectum of the Goldfish that receives direct visual inputs from the retina. For the Goldfish has been used as experimental animal for oculomotor reflex, thought to be suitable for experimental model for visual system. In this study, single unit activities of the optic tectum were recorded during flashing stimulation at 1Hz or 15Hz to pupil of the Goldfish. Most part of unit group 1 that only showed ON- or OFF-response at 1Hz showed abolished response at 15Hz stimulation. In contrast, most part of unit group 2 that showed ON-OFF response at 1Hz remained ON- or OFF-response at 15Hz stimulation. In addition, unit group 2 showed shorter latency of OFF response than ON response at 1Hz stimulation significantly. These results suggests unit group that showed ON-OFF response at low frequency have a following activity with high frequency stimulation.
Sleepiness causes human errors and traffic accidents. It accounts for about 20% of all traffic accident factors. Attempts have been made to detect sleepiness during driving by using electroencephalograms (EEG) and reaction time to auditory and visual stimuli. It is, however, not realistic to apply these methods during driving. In the present study, we investigated the effect of sleepiness on the muscle force generation pattern in foot that steps on a device simulating a gas pedal of an automobile as to explore for the possibility of sleepiness detection. During the 45min experiment, 13 subjects was instructed to continuously demonstrate a net 20N muscle force on the device simulating the automobile's gas pedal. We also investigated subjective sleepiness by Stanford Sleepiness Scale. The coefficient of variation (CV) in force every minute was counted for each subjective sleepiness value. As a result, the ratio of CV less than 0.2 was high when the subjective sleepiness was not felt. In turn, the ratio of CV of 0.2 or greater, or negative value became high when strong sleepiness is felt. It was suggested that sleepiness could be detected by using CV of foot muscle force against a gas pedal.
This paper presents a novel path-following feedback control method for a four-forked steering walker based on the Lyapunov's stability theory. The locomotor has a square base on which objects to be carried can be loaded. Links are connected through joints at each corner of the base, and a steering system is attached at the endpoint of each link. The locomotor is an undulatory locomotor which transforms the periodic driving of its four joints into its motion through the periodic operation of its four steering systems. Since all the wheels of the locomotor are passive, it is required for the locomotor to avoid singular attitudes in which it cannot move in some direction while maintaining its desired motion. In this control method, the desired angular velocities of the joints for causing the centroid of the base to follow a target point on the desired path and for causing the base to be directed in the orientation of the tangent of the path can be equalized to those for causing the links to be directed in their desired orientations periodically changed by control of the angles of its four steering systems. In other words, the locomotor has a particular structure which facilitates to achieve the desired motion of the base and the desired rotations of the links simultaneously. The asymptotic stability of this control method is guaranteed by the Lyapunov's second method. Especially, the cost of the control input calculation is much lower compared with that in a control method based on chained form which requires convergent calculations for the estimation of the locomotor position in a curvilinear coordinate system and high order Lie derivatives. The validity of this control method is verified in experiments where the locomotor follows a 9th-order Bezier curve path.
Renewable energy sources (RES) have been introduced in power systems since the feed-in tariff (FIT) was adopted. Especially, photovoltaic (PV) power has been widely installed in western Japan, causing a surplus of power that increases the frequency of the power system. Power outputs from PVs are unstable and the estimation of the outputs is difficult. Moreover, a ramp variation of PV outputs has also been observed. The frequency fluctuation caused by the variation is severe for a stable operation of the power system. A standard power system model for automatic generation operation and control was published by the Institute of Electrical Engineers of Japan (IEEJ). The standard model was named IEEJ AGC 30 model. The power system model is utilized to evaluate the results of a frequency control objectively. This study develops an expanded IEEJ AGC 30 model which can simulate for 24 hours. Also, the study simulates a load frequency control with a ramp down phenomenon of PVs on a large demand day and a small demand day. Moreover, the study suggests some approaches to suppress the frequency fluctuation caused by a ramp down phenomenon.
This note is concerned with the problem of designing observers for a first-order hyperbolic system that has a time lag in the nonlocal boundary condition. In our previous work, an infinite-dimensional observer could be constructed for the system by using a backstepping approach, and it was shown that the classical solution of the error system could be finite-time stabilized. In this note, we focus on the L2-stability of the error system and prove that the operator describing the error system generates a nilpotent semigroup on the augmented L2-space. As a result, the function space to which the initial value of the error system belongs is enlarged.