Impedance control based on optimal adaptive high order super twisting sliding mode for a 7-DOF lower limb exoskeleton

Mokhtari, M.; Taghizadeh, Mohammad Javad; Mazare, Mahmood

doi:10.1007/s11012-021-01308-4

Cited by 37 publications

(20 citation statements)

References 36 publications

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“…Meanwhile, machine learning is also employed in adjusting the parameters of impedance model to minimize the interactive force for more comfortable human-exoskeleton coupling [29]. However, instead of revealing the physical relationship between the interactive movements and forces, impedance model uses artificial inertia, damping and stiffness coefficients, and it cannot be regarded as a constitutive equation but a filter [30]. Therefore, the impedance model does not yield accurate prediction of the interactive force and cannot be used to study the human-exoskeleton coupling dynamics.…”

Section: Introductionmentioning

confidence: 99%

Modelling and Analysis of Coupling Dynamics of a Lower Limb Exoskeleton

Yan

Chen

Huang

et al. 2022

Preprint

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Exoskeleton is a promising technology to enhance the mobility of aged and disable people. With comfortable human-exoskeleton interaction, mechanical and control designers aim at accurately tracking a desired trajectory, while saving the wearer's energy expenditure is the preference from the viewpoint of biomechanics. Given all of these effects, we propose a new model, consisting of the swing dynamics of both human and robot's lower extremities coupled by damped springs representing elastic and viscous properties of band and human tissue. With the coupling coefficients identified with an experimental platform, the analytical model yields consistent results compared with an experimental exoskeleton, especially in the prediction of the interactive forces. Further analyses are then performed based on this validated model, revealing the influences of desired trajectory, mass ratio, misalignment, coupling points, health condition and band tightness on the human-exoskeleton coupling dynamics. It is found that introducing gravity compensation and tuning the feedback gain improve the tracking accuracy, but hardly change the interactive force. The most comfortable interaction requires a healthy wearer coupled with a light-weight exoskeleton without any misalignment, but properly changing the trajectory, coupling points and tightness can partly reduce the interactive forces if the ideal condition is unachievable.

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Section: Introductionmentioning

confidence: 99%

Modelling and Analysis of Coupling Dynamics of a Lower Limb Exoskeleton

Yan

Chen

Huang

et al. 2022

Preprint

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“…It produces a continuous control function, which conducts the sliding surface and its derivative to zero in finite time in the existence of the smooth matched disturbances with bounded gradient and known boundary. Several variants of STSMC have been proposed in the literature in order to overcome the difficulties previously discussed for lower extremity exoskeleton [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] by considering a standard reference signal. In [25], a comparative study of different SMC such as conventional 1st order sliding mode control (SMC), 2nd order SMC (STW), fast terminal SMC (FTSMC), and integral SMC (ISMC) were done.…”

Section: Introductionmentioning

confidence: 99%

Modeling and Evaluation of Adaptive Super Twisting Sliding Mode Control in Lower Extremity Exoskeleton

Ezhilarasi

Nair

2021

Int. J. of Precis. Eng. and Manuf.-Green Tech.

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In this paper, an integrated human-in-the-loop simulation paradigm for the design and performance analysis of a 6 DOF lower extremity exoskeleton is presented. An adaptive Super Twisting Sliding Mode Controller (ASTSMC) is designed for the trajectory tracking control of the exoskeleton by considering the human motion as reference trajectory. The dynamic model, that include linear and rotational displacement of hip, knee and ankle joints of both the legs is developed using Lagrange energy formulation. The position and angular velocity error of the wearer and the exoskeleton are being considered to establish the control law. Super twisting SMC is a robust control scheme that works effectively in the presence of external disturbances and parameter variations. However, the STSMC introduces chattering in the closed loop because of its high gain, to overcome this drawback, an adaptive STSMC is proposed for the control of exoskeleton against unknown disturbances without chattering. An adaptation scheme using Lyapunov criterion is derived that ensures the stability of the system in closed loop. The performance of the proposed control strategy is verified by implementing on the integrated CAD model of the exoskeleton along with the wearer. The effectiveness of the controller is tested under wind disturbance of varying velocity and direction. The results demonstrate improved tracking performance of the proposed control scheme with least error and less control effort compared to constant gain STSMC in normal and uneven terrain.

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“…For this reason, in various controllers an adaptation law is implemented to handle the adverse effect of uncertainties and disturbances with unknown and infinite bounds. [20][21][22][23][24] For example, Baek et al proposed a new adaptive sliding-mode control scheme based on timedelay estimation (TDE) for a robot manipulator. 25 A model-free robust adaptive controller is proposed by Jin et al to control a humanoid robots with flexible joints.…”

Section: Introductionmentioning

confidence: 99%

“…However, this assumption is not the case in practice, as the pre-knowledge of the uncertainties, disturbances and faults is not available. As a solution to this problem, adaptive backstepping nonsingular fast integral type terminal sliding mode control law is proposed as equation (20).…”

mentioning

confidence: 99%

Fault tolerant control based on backstepping nonsingular terminal integral sliding mode and impedance control for a lower limb exoskeleton

Mokhtari

Taghizadeh

Ghanbari

2021

Proceedings of the Institution of Mechanical Engineers, Part C:

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In this paper, an active fault-tolerant control scheme is proposed for a lower limb exoskeleton, based on hybrid backstepping nonsingular fast terminal integral type sliding mode control and impedance control. To increase the robustness of the sliding mode controller and to eliminate the chattering, a nonsingular fast terminal integral type sliding surface is used, which ensures finite time convergence and high tracking accuracy. The backstepping term of this controller guarantees global stability based on Lyapunov stability criterion, and the impedance control reduces the interaction forces between the user and the robot. This controller employs a third order super twisting sliding mode observer for detecting, isolating ad estimating sensor and actuator faults. Motion stability based on zero moment point criterion is achieved by trajectory planning of waist joint. Furthermore, the highest level of stability, minimum error in tracking the desired joint trajectories, minimum interaction force between the user and the robot, and maximum system capability to handle the effect of faults are realized by optimizing the parameters of the desired trajectories, the controller and the observer, using harmony search algorithm. Simulation results for the proposed controller are compared with the results obtained from adaptive nonsingular fast terminal integral type sliding mode control, as well as conventional sliding mode control, which confirm the outperformance of the proposed control scheme.

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Impedance control based on optimal adaptive high order super twisting sliding mode for a 7-DOF lower limb exoskeleton

Cited by 37 publications

References 36 publications

Modelling and Analysis of Coupling Dynamics of a Lower Limb Exoskeleton

Modelling and Analysis of Coupling Dynamics of a Lower Limb Exoskeleton

Modeling and Evaluation of Adaptive Super Twisting Sliding Mode Control in Lower Extremity Exoskeleton

Fault tolerant control based on backstepping nonsingular terminal integral sliding mode and impedance control for a lower limb exoskeleton

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