Dr Gabriel Aguirre-Ollinger
Lecturer, School of Elec, Mech and Mechatronic Systems
Doc of Philosophy
Gabriel Aguirre-Ollinger is a Lecturer with a research–oriented appointment at the ARC Centre of Excellence for Autonomous Systems. Prior to his academic career he worked in the automotive components industry in Mexico as a manufacturing and design engineer, and as a project leader for the production launch of new products.
His early research at Carnegie Mellon University focused on AI–based computational tools to assist decision–making in the product design process. He developed RedesignIT, a computer program that uses model–based reasoning to generate and evaluate proposals of redesign plans for engineered devices. Subsequently he held a research appointment at Universidad Panamericana in Mexico, where he worked on dynamics of parallel manipulators, and served as a consultant for the automotive industry, particularly on surface treatments for automotive transmission components.
His doctoral research at Northwestern University focused on control methods for lower–limb exoskeletons and orthotic devices. He developed a novel exoskeleton controller based on active impedance display. Previous control methods control were often based on estimation on muscle forces from electromyography, which has reliability issues, or followed pre–programmed kinematic trajectories. Dr Aguirre-Ollinger's method focuses instead on shaping the impedance of the exoskeleton in order to modify the dynamic response of the human limbs, thereby reducing muscle effort and increasing the agility of the limbs' movements. He designed and built an experimental orthotic device to test his control methods on human subjects.
His current research plans include developing a hybrid passive–active exoskeleton for assisting the upper extremities of patients with motor disorders, and implementing control algorithms for task–specific assistance. A second project focuses on a powered exoskeleton for walking assistance, with the aims of reducing the metabolic cost of walking and enhancing the agility of compensatory movements. Other research interests of Dr. Aguirre-Ollinger include stability of physical human-robot interaction and compliant actuators.
Research supervision: Yes
Aguirre-Ollinger, G., Colgate, J.E., Peshkin, M. & Goswami, A. 2012, 'Inertia Compensation Control of a One-Degree-of-Freedom Exoskeleton for Lower-Limb Assistance: Initial Experiments', IEEE Transactions on Neural Systems and Rehabilitation Engineering, vol. 20, no. 1, pp. 68-77.
A new method of lower-limb exoskeleton control aimed at improving the agility of leg-swing motion is presented. In the absence of control, an exoskeleton+s mechanism usually hinders agility by adding mechanical impedance to the legs. The uncompensated inertia of the exoskeleton will reduce the natural frequency of leg swing, probably leading to lower step frequency during walking as well as increased metabolic energy consumption. The proposed controller emulates inertia compensation by adding a feedback loop consisting of low-pass filtered angular acceleration multiplied by a negative gain. This gain simulates negative inertia in the low-frequency range. The resulting controller combines two assistive effects: increasing the natural frequency of the lower limbs and performing net work per swing cycle. The controller was tested on a statically mounted exoskeleton that assists knee flexion and extension. Subjects performed movement sequences, first unassisted and then using the exoskeleton, in the context of a computer-based task resembling a race. In the exoskeleton+s baseline state, the frequency of leg swing and the mean angular velocity were consistently reduced. The addition of inertia compensation enabled subjects to recover their normal frequency and increase their selected angular velocity. The work performed by the exoskeleton was evidenced by catch trials in the protocol.
Aguirre-Ollinger, G., Colgate, J.E., Peshkin, M. & Goswami, A. 2011, 'A one-degree-of-freedom assistive exoskeleton with inertia compensation: the effects on the agility of leg swing motion', Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, vol. 225, no. 3, pp. 228-245.
Many of the current implementations of exoskeletons for the lower extremities are conceived to either augment the userÔ++s load-carrying capabilities or reduce muscle activation during walking. Comparatively little research has been conducted on enabling an exoskeleton to increase the agility of lower-limb movements. One obstacle in this regard is the inertia of the exoskeletonÔ++s mechanism, which tends to reduce the natural frequency of the human limbs. A control method is presented that produces an approximate compensation of the inertia of an exoskeletonÔ++s mechanism. The controller was tested on a statically mounted, single-degree-offreedom (DOF) exoskeleton that assists knee flexion and extension. Test subjects performed multiple series of leg-swing movements in the context of a computer-based, sprint-like task. A large initial acceleration of the leg was needed for the subjects to track a virtual target on a computer screen. The uncompensated inertia of the exoskeleton mechanism slowed down the transient response of the subjectsÔ++ limb, in comparison with trials performed without the exoskeleton. The subsequent use of emulated inertia compensation on the exoskeleton allowed the subjects to improve their transient response for the same task.
Aguirre-Ollinger, G., Colgate, J.E., Peshkin, M. & Goswami, A. 2011, 'Design of an active one-degree-of-freedom lower-limb exoskeleton with inertia compensation', International Journal Of Robotics Research, vol. 30, no. 4, pp. 486-499.
Limited research has been done on exoskeletons to enable faster movements of the lower extremities. An exoskeleton's mechanism can actually hinder agility by adding weight, inertia and friction to the legs; compensating inertia through control is particularly difficult due to instability issues. The added inertia will reduce the natural frequency of the legs, probably leading to lower step frequency during walking. We present a control method that produces an approximate compensation of an exoskeleton's inertia. The aim is making the natural frequency of the exoskeleton-assisted leg larger than that of the unaided leg. The method uses admittance control to compensate for the weight and friction of the exoskeleton. Inertia compensation is emulated by adding a feedback loop consisting of low-pass filtered acceleration multiplied by a negative gain. This gain simulates negative inertia in the low-frequency range. We tested the controller on a statically supported, single-degree-of-freedom exoskeleton that assists swing movements of the leg. Subjects performed movement sequences, first unassisted and then using the exoskeleton, in the context of a computer-based task resembling a race. With zero inertia compensation, the steady-state frequency of the leg swing was consistently reduced. Adding inertia compensation enabled subjects to recover their normal frequency of swing.
Aguirre-Ollinger, G., Colgate, J.E., Peshkin, M. & Goswami, A. 2007, 'A 1-DOF Assistive exoskeleton with virtual negative damping: Effects on the kinematic response of the lower limbs', IEEE/RSJ International Conference on Intelligent Robots and Systems, San Diego, USA, October 2007 in Proceedings of the 2007 IEEE/RSJ International Conference on Intelligent Robots and Systems, ed NA, IEEE, Piscataway, USA, pp. 1938-1944.
View/Download from: UTSePress | Publisher's site
We propose a novel control method for lowerlimb assist that produces a virtual modification of the mechanical impedance of the human limbs. This effect is accomplished through the use of an exoskeleton that displays active impedance. The proposed method is aimed at improving the dynamic response of the human limbs, while preserving the user's control authority. Our goal is to use active-impedance exoskeleton control to improve the user's agility of motion, for example by reducing the average time needed to complete a movement. Our control method has been implemented in a 1-DOF exoskeleton designed to assist human subjects performing knee flexions and extensions. In this paper we discuss an initial study on the effect of negative exoskeleton damping (a particular case of active-impedance control) on the subject's time to complete a target-reaching motion. Experimental results show this effect to be statistically significant. On average, subjects were able to reduce the time to complete the motion by 16%.
Aguirre-Ollinger, G., Colgate, J.E., Peshkin, M., Goswami, A. 2007, 'Active-Impedance Control of a Lower-Limb Assistive Exoskeleton', IEEE International Conference on Rehabilitation Robotics, The Netherlands, June 2007 in Proceedings of the 2007 IEEE 10th International Conference on Rehabilitation Robotics, ed Bart Driessen, Just L. Herder, Gert Jan Gelderblom, IEEE, USA, pp. 188-195.
View/Download from: UTSePress | Publisher's site
We propose a novel control method for lower-limb assist that produces a virtual modification of the mechanical impedance of the human limbs. This effect is accomplished by making the exoskeleton display active impedance properties. Active impedance control emphasizes control of the exoskeleton's dynamics and regulation of the transfer of energy between the exoskeleton and the user. Its goal is improving the dynamic response of the human limbs without sacrificing the user's control authority. The proposed method is an alternative to myoelectrical exoskeleton control, which is based on estimating muscle torques from electromyographical (EMG) activity. Implementation of an EMG-based controller is a complex task that involves modeling the user's musculoskeletal system and requires recalibration. In contrast, active impedance control is less dependent on estimation of the user's attempted motion, thereby avoiding conflicts resulting from inaccurate estimation. In this paper we also introduce a new form of human assist based on improving the kinematic response of the limbs. Reduction of average muscle torques is a common goal of research in human assist. However, less emphasis has been placed so far on improving the user's agility of motion. We aim to use active impedance control to attain such effects as increasing the user's average speed of motion, and improving their acceleration capabilities in order to compensate for perturbations from the environment.