Farhad Aghili

Concordia University (Canada), Mechanical & Industrial Eingineering, Adjunct

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Farhad Aghili (SM'07) received his Ph.D. degree in Mechanical Engineering from McGill University, Canada, in 1998. Since 1998, Dr. Aghili has been Systems Engineer and Research Scientist at the Canadian Space Agency (CSA), where he contributed to the Canadian Space Exploration and the International Space Station (ISS) programs in various capacities. Currently, he leads a number of design and R&D activities for development of the iconic Canadara3 for the NASA-led lunar Gateway of the Artemis program. Dr. Aghili is also an Affiliate Professor in the Department of Mechanical, Industrial, and Aerospace Engineering at Concordia University.

Dr. Aghili has established a robust research and development program leading to many technology transfers to industry by applying his expertise in the areas of robotics, dynamics and controls, and mechatronics. His research resulted in over 160 scientific papers and book chapters, 12 patents and patent applications in US and Canada, and several technology transfers to industry. He also chaired and has been otherwise involved in several international conferences and professional activities as well as being the recipient of the best paper award and invited keynote speaker at international conferences. Dr. Aghili is Technical Editor of the IEEE/ASME Transactions on Mechatronics (TMech) and the Chair of the IEEE Montreal Robotics & Automation Chapter.

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Papers by Farhad Aghili

Projection-based modeling and control of mechanical systems using non-minimum set of coordinates

This paper presents a non-minimal order dynamics model for many analysis, simulation, and control... more This paper presents a non-minimal order dynamics model for many analysis, simulation, and control problems of constrained mechanical systems passing through singular configurations during their motion by making use of linear projection operator. The distinct features of this model describing dynamics of the dependent coordinates are: i) The mass matrix M̅(q) is always positive definite even at singular configurations; ii) matrix equation is skew symmetric, where all nonlinear terms are lumped into vector C̅(q, q̇)q̇ after elimination of constraint forces. Eigenvalue analysis shows that the condition number of the constraint mass matrix can be minimized upon adequate selection of a scalar parameter called “virtual mass” thereby reducing the sensitivity to round-off errors in numerical computation. It follows by derivation of two oblique projection matrices for computation of constraint forces and actuation forces. It is shown that projection-based model allows feedback control of dependent coordinates which, unlike reduced-order dependent coordinates, uniquely define spatial configuration of constrained systems.

Machine Learning for LiDAR-Based Navigation System

arXiv (Cornell University), Aug 9, 2022

This paper presents a robust 6-DOF relative navigation by combining the iterative closet point (I... more This paper presents a robust 6-DOF relative navigation by combining the iterative closet point (ICP) registration algorithm and a noise-adaptive Kalman filter (AKF) in a closed-loop configuration together with measurements from a laser scanner and an inertial measurement unit (IMU). In this approach, the fine-alignment phase of the registration is integrated with the filter innovation step for estimation correction while the filter estimate propagation provides the coarse alignment needed to find the corresponding points at the beginning of ICP iteration cycle. The convergence of the ICP point matching is monitored by a fault-detection logic and the covariance associated with the ICP alignment error is estimated by a recursive algorithm. This ICP enhancement has proven to improve robustness and accuracy of the pose tracking performance and to automatically recover correct alignment whenever the tracking is lost. The Kalman filter estimator is designed so as to identify the required parameters such as IMU biases and location of the spacecraft center-of-mass (CoM).

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Autonomous Sequential Sub-Manoeuvres in Pre- and Post-Capturing Space Objects Using Obstructed 3-D Vision Data

IEEE Transactions on Aerospace and Electronic Systems, 2023

Connectivity Preservation and Collision Avoidance in Multi-Agent Systems Using Model Predictive Control

IEEE Transactions on Network Science and Engineering, May 1, 2023

This paper proposes a unified error transformation strategy for the distributed formation trackin... more This paper proposes a unified error transformation strategy for the distributed formation tracking of networked uncertain nonholonomic mobile robots with different communication ranges. To guarantee the connectivity preservation and collision avoidance of all robots without employing any potential functions, a novel nonlinear formation error function using the relative distance and angles between robots is introduced. Then, the approximation-based local adaptive tracking design methodology using the dynamic surface design technique is recursively established to achieve (i) the connectivity preservation and collision prevention of initially connected robots, (ii) the collision avoidance of initially nonconnected robots, and (iii) the desired formation tracking of robots in a fully distributed manner. The stability of the total closed-loop control system is analyzed in the Lyapunov sense.

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Optimal Control of Legged-Robots Subject to Friction Cone Constraints

arXiv (Cornell University), Aug 3, 2022

A hierarchical control architecture is presented for energy-efficient control of legged robots su... more A hierarchical control architecture is presented for energy-efficient control of legged robots subject to variety of linear/nonlinear inequality constraints such as Coulomb friction cones, switching unilateral contacts, actuator saturation limits, and yet minimizing the power losses in the joint actuators. The control formulation can incorporate the nonlinear friction cone constraints into the control without recourse to the common linear approximation of the constraints or introduction of slack variables. A performance metric is introduced that allows trading-off the multiple constraints when otherwise finding an optimal solution is not feasible. Moreover, the projection-based controller does not require the minimal-order dynamics model and hence allows switching contacts that is particularly appealing for legged robots. The fundamental properties of constrained inertia matrix derived are similar to those of general inertia matrix of the system and subsequently these properties are greatly exploited for control design purposes. The problem of task space control with minimum (point-wise) power dissipation subject to all physical constraints is transcribed into a quadratically constrained quadratic programming (QCQP) that can be solved by barrier methods.

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Design and control of direct-drive systems with applications to robotics

ABSTRACT

Analysis, optimization and control of an adaptive tuned vibration absorber featuring magnetoactive materials

Smart Structures and Systems, Oct 1, 2021

Excessive vibration may cause premature fatigue failure on structural components if it is not pro... more Excessive vibration may cause premature fatigue failure on structural components if it is not properly controlled. One effective way to attenuate vibration is to attach a tuned vibration absorber to the main structural component. Passive tuned vibration absorbers are mainly effective to attenuate vibration at a specific range of frequencies and thus they become infective under varied environmental conditions which can significantly alter the tuning frequencies. The present study aims at development of a wide-bandwidth and light-weight adaptive tuned vibration absorber (ATVA) featuring a magnetorheological elastomer (MRE) which is tuned to absorb the vibrations of a flexible beam. The accelerance transfer function is derived for both beam with and without ATVA. The effectiveness of the ATVA to control vibration of the flexible beam caused by external excitation under wide range of frequencies is demonstrated. The proposed ATVA consists of C-Shape frame with winding coils, two isometric MRE specimens with 40% volume fraction, and active mass. An empirical model for the MRE has been developed through an experimental identification method in order to predict the MRE's elastic modulus under various levels of excitation frequencies and applied magnetic fields. Using MRE models and magneto-circuit analysis, the frequency bandwidth of the ATVA is analytically obtained. The analytical model is then used to develop a multidisciplinary design optimization formulation to minimize the mass and maximize the frequency bandwidth of an ATVA featuring MRE given several geometrical and physical constraints. Finally, a tuning algorithm has been presented to determine the required applied magnetic flux density to the MRE layers based on the identified phase difference between the absolute acceleration of the host and relative acceleration of the host and ATVA's resonator.

Optimal and fault-tolerant torque control of servo motors subject to voltage and current limits

ABSTRACT This paper presents optimal torque control of brushless DC motor with any back-emk wavef... more ABSTRACT This paper presents optimal torque control of brushless DC motor with any back-emk waveform that mini- mizes power dissipation subject to voltage and current limits of the motor&#39;s drivers/amplifiers. When one or more phases reach the voltage or/and current limits, the controller optimally reshapes the stator currents of the remaining phases for continuing accurate torque production. This allow the motor to operate above the rated speed and torque that would be achieved without current reshaping. In the event that an open- circuit or short-circuit of a winding occurs, the torque controller can also isolate the faulty phase in order to generate torque as requested given the voltage and current constraints of the healthy phases. A closed-form solution for the optimal phase currents is obtained rendering the control algorithm suitable for real-time implementation. Experimental results illustrate the capability of the controller to achieve precise torque production during voltage/current saturation of the motor&#39;s drivers or a phase failure.

Impact dynamics in robotic and mechatronic systems

This paper presents an impact model of robotic manipulators subject to changing topology using th... more This paper presents an impact model of robotic manipulators subject to changing topology using the notion of linear projection operators. An oblique projection matrix is introduced in order to directly obtain: i) The acceleration of the constrained robotic system from unconstrained acceleration, ii) post-impact velocity of the robot from pre-impact velocity, and iii) impulse force during impact from pre-impact momentum. All solutions are provided in closed-form with elegant geometrical interpretations, e.g., the energy lost during contact is a quadratic function of pre-impact velocities. Moreover, the formulation seemingly works not only when the unilateral constraints remain active through a finite time interval but when changing topology occurs, i.e., unilateral constraints becomes inactive or vice versa, or even when the overall constraint jacobian becomes singular. The formulation is general enough to be applicable to robotic manipulators with chain, tree and close-loop topologies, or to handle simultaneous multiple contacts with non-identical restitution coefficients. The model is proven to be energetically consistent if a global restitution coefficient bounded between zero and one is assumed.

An Adaptive Kalman Filter for Motion Esitmation/Prediction of a Free-Falling Space Object Using Laser-Vision Data with Uncertain Inertial and Noise Characteristics

AIAA Guidance, Navigation and Control Conference and Exhibit, Jun 15, 2008

A computationally efficient, noise adaptive Kalman filter is presented for the motion estimation ... more A computationally efficient, noise adaptive Kalman filter is presented for the motion estimation and prediction of a free-falling tumbling satellite (target). The filter receives only noisy pose measurements from a laser vision system aboard another satellite (chaser) at a close distance in a neighboring orbit. The filter estimates the full sates, all the inertia parameters of the target satellite, as well as the covariance of the measurement noise. A comprehensive dynamics model that includes aspects of orbital mechanics is incorporated for accurate estimation. The discrete-time model, which involves a state-transition matrix and the covariance of process noise, is derived in closed form, thus rendering the filter suitable for real-time implementation. The statistical characteristics of the measurement noise is formulated by a state-dependent covariance matrix. This model allows additive quaternion noise, while preserving the unit-norm property of the quaternion. The convergence properties of the developed filter is demonstrated by simulation and experimental results. These results also demonstrate that the filter can continuously produce accurate estimates of pose even when the vision system is occluded for tens of seconds.

Adaptive motion estimation of a tumbling satellite using laser-vision data with unknown noise characteristics

A noise-adaptive variant of the Kalman filter is presented for the motion estimation and predicti... more A noise-adaptive variant of the Kalman filter is presented for the motion estimation and prediction of a free-falling tumbling satellite as seen from a satellite in a neighboring orbit. A complete dynamics model, including aspects of orbital mechanics, is incorporated for accurate estimation. Moreover, a discrete-time model of the entire system which includes the state-transition matrix and the covariance of

Non-Minimal Order Model of Mechanical Systems With Redundant Constraints for Simulations and Controls

IEEE Transactions on Automatic Control, May 1, 2016

This technical note presents a non-minimal order dynamics model for many analysis, simulation, an... more This technical note presents a non-minimal order dynamics model for many analysis, simulation, and control problems of constrained mechanical systems passing through singular configurations during their motion by making use of linear projection operator. The distinct features of this model describing dynamics of the dependent coordinates are: (i) The mass matrix M̅(q) is always positive definite even at singular configurations; (ii) matrix M̅-2C̅ is skew symmetric, where all nonlinear terms are lumped into vector C̅(q,q̇)q̇ after elimination of constraint forces. Eigenvalue analysis shows that the condition number of the constraint mass matrix can be minimized upon adequate selection of a scalar parameter called “virtual mass” thereby reducing the sensitivity to round-off errors in numerical computation. It follows by derivation of two oblique projection matrices for computation of constraint forces and actuation forces. It is shown that projection-based model allows feedback control of dependent coordinates which, unlike reduced-order dependent coordinates, uniquely define spatial configuration of constrained systems.

Quadratically Constrained Quadratic-Programming Based Control of Legged Robots Subject to Nonlinear Friction Cone and Switching Constraints

IEEE-ASME Transactions on Mechatronics, Dec 1, 2017

Optimal Design Parameters of Reconfigurable Robots with Lockable Joints

Transactions of The Canadian Society for Mechanical Engineering, Mar 1, 2017

This paper presents a global optimization methodology to find the optimal Denavit–Hartenberg para... more This paper presents a global optimization methodology to find the optimal Denavit–Hartenberg parameters of a serial reconfigurable manipulator minimizing a cost function over a pre-specified workspace volume and given lower and upper bounds on the design parameters. Different cost functions such as the manipulability measure, maximum force capability of the manipulator’s end-effector, and maximum velocity capability of the manipulator within the operating workspace of the manipulator are considered to optimize the kinematic design. Based on a combination of genetic algorithm (GA) and sequential quadratic programming (SQP), a modified global and posture-independent parameter of singularity (MPIPS) is presented. Finally, a weighted objective function is proposed to balance between the conflicting requirements for manipulator’s force and velocity capabilities.

Editorial: Robotic Manipulation and Capture in Space

Frontiers in Robotics and AI

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Dumping Momentum on the Lunar Gateway Using a Robotically Steerable Solar Sail

Journal of Guidance Control and Dynamics, 2020

Emulation of space robot through hardware-in-the-loop simulation

As a partner in the International Space Station (ISS), Canada is responsible for the verification... more As a partner in the International Space Station (ISS), Canada is responsible for the verification of all tasks involving the Special Purpose Dextrous Manipulator (SPDM). The verification is done in three stages: pure real-time simulation, hardware-in-the-loop simulation and non real-time simulation. The second stage refines the analysis of the contact portion of the task (e.g., insertion) using a real robot. This component is the main addition to existing facilities. In previous publications the STVF concept and the proposed controller used for the hardware-in-theloop sequence have been thoroughly discussed. This paper concentrates on the design and the development of the STVF Manipulator test-bed and on the implementation of the hardware-in-the-loop control on the robot.

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Configuration Control and Recalibration of a New Reconfigurable Robot

Proceedings, Apr 1, 2007

The advantages of reconfigurable robots have been discussed in the specialized literature. Conven... more The advantages of reconfigurable robots have been discussed in the specialized literature. Conventionally, reconfigurability was a direct result of using modular joints. In this paper we discuss the configuration control and recalibration of a different class of reconfigurable robots, one which is equipped with lockable cylindrical joints with no actuators or sensors. Such a robot can be as versatile and agile as a hyperredundant manipulator, but with a simpler, more compact, lighter design. A passive joint becomes controllable when the robot forms a closed kinematic chain and the joint lock is released. After reconfiguration, the values of the passive joints are computed from the value of the active joints using inverse kinematics of the closed chain. That problem is solved using a globally uniformly asymptotically stable scheme based on Closed-Loop Inverse Kinematics (CLIK). An asymptotically stable reconfiguration controller is also devised that takes the robot from one configuration to another by directly regulating the values of the passive joints. The controller has a rather simple structure, which only relies on the robot gravity and kinematics models. Conditions for the observability and the controllability of the passive joints are also derived in detail, and some numerical results are reported.

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Quadratically constrained quadratic programming: Some applications and a method for solution

Zeitschrift für Operations Research, 1982

A constructive method is used to prove that n C. is not empty and that x (fi) with i~_M ~ fl ~ n ... more A constructive method is used to prove that n C. is not empty and that x (fi) with i~_M ~ fl ~ n C. chaxacterizes an optimal solution to (QPQR). Quite attractive numerical results have i~ t been reached with this method. Zusammenfassung: Die vorliegande Arbeit befatM sieh mit Anwendungen und einer neuen L6sungsmethode des folgenden Aufgabe (QPQR): man minimiese eine konvoxe quadratische Zidfunktion Q1 (x) untes Beriicksichtigung konvexer quadratischer Restriktionen Qi (x) < 0, i EMI := {2 ..... m}, und/odes lineaxes Resttiktionen.

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Robot Manipulators Control with Parameters Adaptation and State Estimation

2018 3rd International Conference on Advanced Robotics and Mechatronics (ICARM), 2018

Robot manipulator control considering parameter uncertainty and velocity estimation is address in... more Robot manipulator control considering parameter uncertainty and velocity estimation is address in this paper. An adaptive controller using state estimation feedback is provided in this paper, which can adapt the dynamic parameters and estimate the velocity with imprecise system model simultaneously. The stability of the proposed controller is discussed and a 2-links robot manipulator is adopted as an example to illustrate and validate the provided control scheme. In the simulation, all the observer performance, parameter adaptation, and the trajectory tracking are validated.