Model predictive control with angular acceleration constraint of proportional servo-hydraulic lower extremity robotic device

Lower Extremity Robotic Device (LERD) is a four-degree of freedom hydraulic exoskeleton that assists the paralysed patient to walk. The nonlinear dynamic model of the hydraulic exoskeleton system used in Model Predictive Control (MPC) is challenging to be modelled, especially in the state-space mode...

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Main Author:	Onn, Nurfarahin
Format:	Thesis
Language:	English
Published:	2021
Subjects:	TJ Mechanical engineering and machinery
Online Access:	http://eprints.utm.my/id/eprint/102388/1/NurfarahinOnnPhDSKM2021.pdf.pdf
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spelling	my-utm-ep.1023882023-08-21T08:25:48Z Model predictive control with angular acceleration constraint of proportional servo-hydraulic lower extremity robotic device 2021 Onn, Nurfarahin TJ Mechanical engineering and machinery Lower Extremity Robotic Device (LERD) is a four-degree of freedom hydraulic exoskeleton that assists the paralysed patient to walk. The nonlinear dynamic model of the hydraulic exoskeleton system used in Model Predictive Control (MPC) is challenging to be modelled, especially in the state-space model form. Traditional torque constraint technique restricts the exoskeleton to provide wide variability of wearers’ weight. For a heavy wearer, the torque constraint could limit the system’s performance where the hydraulic force will be cut off when exceeds the predetermined torque. Angular acceleration constraint could be an alternative method to overcome the weight variations among different wearers. However, this technique has not been reported elsewhere in the literature. This study aimed to develop mathematical models of the empiric relationship between the median of absolute angular accelerations and pulse width modulation duty cycle of the LERD exoskeleton to facilitate system interfacing. An optimal motion constrained MPC controller for trajectory tracking was designed first, and the results were benchmarked with Proportional-Integral-Derivative (PID) controller. Using cross-correlation analysis, the dynamic models were then selected and used to analyse the designed controllers. The average absolute trajectory tracking error (AATTE) was chosen as the performance parameter with the AATTE closer to zero-degree reference point indicates better trajectory tracking. Results of the simulation study for both MPC and PID controllers at three different speeds showed that AATTE became farther as the walking speed increased. Benchmarked for simulation result showed that the PID controller produced closer AATTE of all joints compared to the MPC controller at the slowest speed (0.3m/s). However, as the speed increased, the MPC controller achieved closer AATTE of all joints than the PID controller. The simulation results were further validated with an experimental study at 0.3m/s. After cross-correlation analysis between reference and output trajectories, the PID controller has produced all joints’ AATTE of 2.64 degrees nearer to zero degrees than the MPC controller’s AATTE of all joints (2.99 degrees). In overall, the MPC controller exhibits a smoother control signal compared to the PID controller where the latter produces fluid hammer during operation which can harm the wearer and potential to cause possible damage to the exoskeleton system’s components. The proposed control system is able to avoid the need to derive several important parameters such as valve’s orifice area, flow coefficient, frictions, etc. Based on the findings of this study, it can be concluded that the proposed simulation and prototype models together MPC controller are acceptable for use in the exoskeleton control system. 2021 Thesis http://eprints.utm.my/id/eprint/102388/ http://eprints.utm.my/id/eprint/102388/1/NurfarahinOnnPhDSKM2021.pdf.pdf application/pdf en public http://dms.library.utm.my:8080/vital/access/manager/Repository/vital:147311 phd doctoral Universiti Teknologi Malaysia Faculty of Engineering - School of Mechanical Engineering
institution	Universiti Teknologi Malaysia
collection	UTM Institutional Repository
language	English
topic	TJ Mechanical engineering and machinery
spellingShingle	TJ Mechanical engineering and machinery Onn, Nurfarahin Model predictive control with angular acceleration constraint of proportional servo-hydraulic lower extremity robotic device
description	Lower Extremity Robotic Device (LERD) is a four-degree of freedom hydraulic exoskeleton that assists the paralysed patient to walk. The nonlinear dynamic model of the hydraulic exoskeleton system used in Model Predictive Control (MPC) is challenging to be modelled, especially in the state-space model form. Traditional torque constraint technique restricts the exoskeleton to provide wide variability of wearers’ weight. For a heavy wearer, the torque constraint could limit the system’s performance where the hydraulic force will be cut off when exceeds the predetermined torque. Angular acceleration constraint could be an alternative method to overcome the weight variations among different wearers. However, this technique has not been reported elsewhere in the literature. This study aimed to develop mathematical models of the empiric relationship between the median of absolute angular accelerations and pulse width modulation duty cycle of the LERD exoskeleton to facilitate system interfacing. An optimal motion constrained MPC controller for trajectory tracking was designed first, and the results were benchmarked with Proportional-Integral-Derivative (PID) controller. Using cross-correlation analysis, the dynamic models were then selected and used to analyse the designed controllers. The average absolute trajectory tracking error (AATTE) was chosen as the performance parameter with the AATTE closer to zero-degree reference point indicates better trajectory tracking. Results of the simulation study for both MPC and PID controllers at three different speeds showed that AATTE became farther as the walking speed increased. Benchmarked for simulation result showed that the PID controller produced closer AATTE of all joints compared to the MPC controller at the slowest speed (0.3m/s). However, as the speed increased, the MPC controller achieved closer AATTE of all joints than the PID controller. The simulation results were further validated with an experimental study at 0.3m/s. After cross-correlation analysis between reference and output trajectories, the PID controller has produced all joints’ AATTE of 2.64 degrees nearer to zero degrees than the MPC controller’s AATTE of all joints (2.99 degrees). In overall, the MPC controller exhibits a smoother control signal compared to the PID controller where the latter produces fluid hammer during operation which can harm the wearer and potential to cause possible damage to the exoskeleton system’s components. The proposed control system is able to avoid the need to derive several important parameters such as valve’s orifice area, flow coefficient, frictions, etc. Based on the findings of this study, it can be concluded that the proposed simulation and prototype models together MPC controller are acceptable for use in the exoskeleton control system.
format	Thesis
qualification_name	Doctor of Philosophy (PhD.)
qualification_level	Doctorate
author	Onn, Nurfarahin
author_facet	Onn, Nurfarahin
author_sort	Onn, Nurfarahin
title	Model predictive control with angular acceleration constraint of proportional servo-hydraulic lower extremity robotic device
title_short	Model predictive control with angular acceleration constraint of proportional servo-hydraulic lower extremity robotic device
title_full	Model predictive control with angular acceleration constraint of proportional servo-hydraulic lower extremity robotic device
title_fullStr	Model predictive control with angular acceleration constraint of proportional servo-hydraulic lower extremity robotic device
title_full_unstemmed	Model predictive control with angular acceleration constraint of proportional servo-hydraulic lower extremity robotic device
title_sort	model predictive control with angular acceleration constraint of proportional servo-hydraulic lower extremity robotic device
granting_institution	Universiti Teknologi Malaysia
granting_department	Faculty of Engineering - School of Mechanical Engineering
publishDate	2021
url	http://eprints.utm.my/id/eprint/102388/1/NurfarahinOnnPhDSKM2021.pdf.pdf
_version_	1776100911310962688

Model predictive control with angular acceleration constraint of proportional servo-hydraulic lower extremity robotic device

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