ISA Transactions (00190578)
Crouch gait is a gait anomaly observed in youngsters with cerebral palsy (CP). Rehabilitation robots are useful for treating individuals with crouch gait. Multiple factors have impact on crouch, including contracture, spasticity, weak motor control, and muscle feebleness, which make the designing and controlling of these exoskeletons for this population a challenging job. A harsh kinematic trajectory enforced by an exoskeleton control strategy may place individuals with spasticity at a high risk of muscle tissue injury. Therefore, in this article, a multi-input multi-output (MIMO) control method is proposed to reduce this risk and improve crouch gait pattern. A constrained control law is used in the model since high power demands may threaten the wearer. In addition, the controller needs to be robust enough against external disturbances and uncertainties. Thus, a nonlinear disturbance observer (NDO) is presented to compute the wearer-generated muscular torque and the uncertainties in the modeling. In addition, a robust constrained MIMO backstepping sliding controller (CMBSC) based on NDO is used to deal with the effect of actuator saturation and uncertainties. A simulation test was used to validate the proposed model and controller. The results of Simulation confirmed the efficiency of the proposed control method when applied to crouch gait with subject specific gait reference. Then, some experimental tests were undertaken to validate the efficiency of the proposed controller. © 2021 ISA
Exoskeletons are new robotic systems that are in close contact with the human body. Thus, their performances are influenced by many factors, including the selection of its structure, actuators, measurement devices, parameters, and mechanism of coupling to the human body. The latter offers numerous challenges to its design, evaluation and modification, including analyzing the effectiveness of the exoskeleton, finding the optimal force for actuators and, discovering the effect of changes in design parameters on human muscle behavior, which are very difficult to measure. Therefore, numerical simulations play an important role in solving these challenges and have the potential to improve treatment strategies and medical decision-making. In this study, a simulation-based method is presented for the designing and analysis of the parameters of an exoskeleton and its wearer's kinetics and kinematics. Model-based design software, including OpenSim and Inventor, and mathematical software, such as MATLAB, are integrated. This method can assist in the modification of exoskeleton devices and allow physiologists, neuroscientists, and physical therapists to generate new solutions for rehabilitation programs using exoskeletons. • Using the movements parameters of each individual subject in her/his exoskeleton design. • Combining the power of OpenSim body movement and the ability of Matlab in mathematical calculations. • Considering the effect of exoskeleton parameters on each muscle-skeleton movement. © 2019 The Authors
In present study, a knee exoskeleton was designed to assist human movements in the flexion/extension of the knee. Moreover, a control method was proposed for the exoskeleton to track the desired position trajectory of the knee. Subsequently, an integrated human shank and exoskeleton model based on the sitting position was considered. A nonlinear disturbance observer (NDO) was used to reduce the influence of the uncertainties and external disturbance in modeling of the whole system. Furthermore, a backstepping sliding control (BSC) approach combined with the nonlinear observer was presented. To improve performance of BSC, genetic algorithm (GA) was employed to determine the optimal backstepping sliding control law parameters. The asymptotic stability of the presented controller and nonlinear disturbance observer convergence were mathematically verified based on the Lyapunov theory. The superiority of the proposed control method is shown in comparison to some recent new methods. The suggested controller can reduce the disturbance rejection time. The chattering and tracking error of NDO sliding mode control was also reduced. The proposed controller was simulated in MATLAB (a registered trademarks of The MathWorks, Inc.) and OpenSim was used to model the human knee. Moreover, some experimental results verified the designed system and its simulation and illustrated that the backstepping sliding mode controller based on the nonlinear disturbance observer can track the reference position by considering a nonlinear model of the identification errors and the external disturbances. © 2018 Elsevier Ltd
Yazdanian H.,
Mahnam, A.,
Edrisi, M.,
Abdar esfahani, M. Journal Of Medical Signals And Sensors (22287477)(1)
Measurement of the stroke volume (SV) and its changes over time can be very helpful for diagnosis of dysfunctions in the blood circulatory system and monitoring their treatments. Impedance cardiography (ICG) is a simple method of measuring the SV based on changes in the instantaneous mean impedance of the thorax. This method has received much attention in the last two decades because it is noninvasive, easy to be used, and applicable for continuous monitoring of SV as well as other hemodynamic parameters. The aim of this study was to develop a low-cost portable ICG system with high accuracy for monitoring SV. The proposed wireless system uses a tetrapolar configuration to measure the impedance of the thorax at 50 kHz. The system consists of carefully designed precise voltage-controlled current source, biopotential recorder, and demodulator. The measured impedance was analyzed on a computer to determine SV. After evaluating the system's electronic performance, its accuracy was assessed by comparing its measurements with the values obtained from Doppler echocardiography (DE) on 5 participants. The implemented ICG system can noninvasively provide a continuous measure of SV. The signal to noise ratio of the system was measured above 50 dB. The experiments revealed that a strong correlation (r = 0.89) exists between the measurements by the developed system and DE (P < 0.05). ICG as the sixth vital sign can be measured simply and reliably by the developed system, but more detailed validation studies should be conducted to evaluate the system performance. There is a good promise to upgrade the system to a commercial version domestically for clinical use in the future. © 2016 Journal of Medical Signals and Sensors.
Journal Of Medical Signals And Sensors (22287477)(4)
The purpose of this study was to estimate the torque from high-density surface electromyography signals of biceps brachii, brachioradialis, and the medial and lateral heads of triceps brachii muscles during moderate-to-high isometric elbow flexion-extension. The elbow torque was estimated in two following steps: First, surface electromyography (EMG) amplitudes were estimated using principal component analysis, and then a fuzzy model was proposed to illustrate the relationship between the EMG amplitudes and the measured torque signal. A neuro-fuzzy method, with which the optimum number of rules could be estimated, was used to identify the model with suitable complexity. Utilizing the proposed neuro-fuzzy model, the clinical interpretability was introduced; contrary to the previous linear and nonlinear black-box system identification models. It also reduced the estimation error compared with that of the most recent and accurate nonlinear dynamic model introduced in the literature. The optimum number of the rules for all trials was 4 ± 1, that might be related to motor control strategies and the % variance accounted for criterion was 96.40 ± 3.38 which in fact showed considerable improvement compared with the previous methods. The proposed method is thus a promising new tool for EMG-Torque modeling in clinical applications.
Yazdanian H.,
Mahnam, A.,
Edrisi, M.,
Abdar esfahani, M. Journal of Isfahan Medical School (10277595)(290)
Impedance cardiography (ICG) is a simple and inexpensive technique for non-invasive and continuous measurement of stroke volume and other hemodynamic parameters. In this method, an estimation of the changes in the aortic blood volume is obtained via measuring the electrical impedance of the thorax area during the cardiac cycle. In comparison to thermo-or dye-dilution methods, impedance cardiography has the inherent advantages of being non-invasive, simple and inexpensive. Compared to the non-invasive methods such as Doppler-echocardiography, the method does not require an expert to perform the test, and can be used for continuous measurement, and even during activity. Impedance cardiography is becoming increasingly used in research and clinical applications. A brief description of the research applications of the impedance cardiography method is given in this letter, and preliminary results of evaluation of an impedance cardiography system developed by the authors are reported. © 2014, Isfahan University of Medical Sciences(IUMS). All rights reserved.
Mediterranean Journal of Measurement and Control (17439310)10(3)pp. 252-259
In this paper, the control problem of underactuated systems in the presence of external disturbances and time varying model uncertainties is considered. Ensuring the stability and robust performance against uncertainties and disturbances arc the main problems in such systems. An adaptive fuzzy sliding mode controller (AFSMC) is proposed to solve the problem, satisfying the robustness properties against the perturbations. The designed controller can be applied to a wide class of underactuated systems with fewer restrictions, compared with many pervious works. To evaluate the performance of proposed algorithm, it is applied to an underactuated inverted pendulum and a Translational Oscillator/Rotational Actuator (TORA) system with two degrees of freedom. The simulation results are compared with a conventional method to demonstrate the effectiveness of the proposed strategy. The results show that the proposed controller guarantees the stability and robustness against time varying uncertainties and disturbances. Copyright © 2014 SoftMotor Ltd.
Cell Journal (22285806)(2)
Objective: Intra-peritoneal administration of riluzole has been shown to preserve the membrane properties and firing characteristics of Purkinje neurons in a rat model of cerebellar ataxia induced by 3-acetylpyridine (3-AP). However, the exact mechanism(s) by which riluzole restores the normal electrophysiological properties of Purkinje neurons is not completely understood. Changes in the conductance of several ion channels, including the BK channels, have been proposed as a neuro protective target of riluzole. In this study, the possible cellular effects of riluzole on Purkinje cells from 3-AP-induced ataxic rats that could be responsible for its neuro protective action have been investigated by computer simulations. Materials and Methods: This is a computational stimulation study. The simulation environment enabled a change in the properties of the specific ion channels as the possible mechanism of action riluzole. This allowed us to study the resulted changes in the firing activity of Purkinje cells without concerns about its other effects and interfering parameters in the experiments. Simulations were performed in the NEURON environment (Version 7.1) in a time step of 25 μs; analyses were conducted using MATLAB r2010a (The Mathworks). Data were given as mean ± SEM. Statistical analyses were performed by the student's test, and differences were considered significant if p<0.05. Results: The computational findings demonstrated that modulation of an individual ion channel current, as suggested by previous experimental studies, should not be considered as the only possible target for the neuro protective effects of riluzole to restore the normal firing activity of Purkinje cells from ataxic rats. Conclusion: Changes in the conductance of several potassium channels, including voltage-gated potassium (Kv1, Kv4) and big Ca2+-activated K+ (BK) channels may be responsible for the neuro protective effect of riluzole against 3-AP induced alterations in the firing properties of Purkinje cells in a rat model of ataxia.
BK channels are large-conductance voltage and Ca 2+-activated K + channels available on the membrane of many types of neurons including cerebellar Purkinje cells. The role of these channels on electrophysiological behavior of Purkinje cells has been investigated in several experimental studies, including those that used Iberiotoxin as BK-specific channel blocker. However, these studies have not led to a conclusion about the role of BK channels. In this study, two realistic models of Purkinje cell with and without dendritic branches were used to investigate the functional contribution of BK channel currents to the firing activity of Purkinje cells. The results obtained from these models indicate that Purkinje cell spiking rate was slightly dependent on BK channel conductance. Block of the BK channel had no significant effect on the action potentials amplitude, but increased the duration of action potentials and the AHP amplitude. © 2011 IEEE.
Control Engineering Practice (09670661)16(9)pp. 1069-1080
A new systematic tuning method with a new structure to design a robust PID load frequency controller for multimachine power systems is presented. The control strategy is mainly based on a maximum peak resonance specification that is graphically supported by the Nichols chart. The proposed controller design is straightforward and effective. It also guarantees that the overall system performance is desirable. Comparative results of this new load frequency controller and a conventional PI one for a multimachine power system example show its robustness with a satisfactory response when the parameters of the system change. © 2007 Elsevier Ltd. All rights reserved.
Journal of Electromagnetic Waves and Applications (09205071)20(8)pp. 1051-1060
A simple methodology for computation of shielding effectiveness (SE) of conducting enclosures with apertures under external illumination is proposed. The methodology is suitable for prediction of electromagnetic compatibility (EMC) of the final product in the design stage. The exterior and interior regions of the enclosure are analyzed separately by employing the boundary conditions of Bethe's small aperture coupling theory [1]. The electric and magnetic SE of the enclosures is discretized using the finite elements method (FEM). Selected numerical results for the shielding effectiveness of rectangular cavity with apertures calculated by the new methodology are provided and compared with measured published data in order to show the effectiveness and the reliability of the proposed approach.
International Journal of Applied Electromagnetics and Mechanics (13835416)(3-4)
This paper addresses the modular decoupling methodology (MDM) [1]. It predicts EMC by the simulation of the effects of radiated emissions on an enclosure with a prescribed aperture and some contents. The proposed method could be a tool for preventing some possible EMI problems at the design stage. Computer simulations are developed using the finite element method and the investigation assesses the effectiveness of the shielding and susceptibility predictions. Exploration on an external emission source and its impact to lower stage is also considered.
Electronics Letters (00135194)(15)
A methodology is proposed to simulate and calculate the electric field inside enclosures. Use of this method not only gives information over a wide frequency range and for various apertures, but also predicts the variation in the electric field inside the enclosure. The method is less time-consuming than other methods.
In this paper, a saturated PD based Fault Tolerant Control is proposed for a quadrotor suffering a severe fault in one of its actuators, on top of a new control scheme assuming the fault has been already detected by the system. Whenever a severe fault occurs in system, the PD control is reconfigured by adding relevant trirotor control equations to the control laws. To tune the optimal parameters of the controllers, a Particle Swarm Optimization algorithm (PSO) is used. The stability of the upgraded PD is proved by using Lyapunov theorem. Simulation Results with some induced disturbance demonstrated the effectiveness of the proposed controller in controlling the damaged quadrotor until it finishes its path. © 2017 IEEE.
This paper proposes an active disturbance rejection control (ADRC) method based on generalized proportional integral (GPI) observer to control of a biped robot while considering its complicated structure and possible disturbances. These observers are used to estimate time-varying disturbances and possible uncertainties. Generally, implying GPI observer on robotic systems is accompanied by a PD-controller in feedback, which is not efficient enough due to abrupt velocity changes of the biped in impact phase, and consequently, a higher level of input torque is required. Thus, applying the back-stepping technique to the mentioned method is suggested. In this study, a two-nested control loop is designed for a 3D biped robot. The back-stepping method with a GPI observer is used in the inner control loop to improve the custom method. Joint trajectories are designed by an offline method and modified by an online method in the outer loop to maintain the stability of the biped. The efficiency of the proposed control strategy is depicted for the biped in the presence of time-varying disturbances through MATLAB simulation. © 2019 IEEE.
