Enhancing Human Mobility Exoskeleton Comfort Using Admittance Controller

Authors: Alexandre Rabaseda, Emelie Seguin, Marc Doumit

Abstract:

Human mobility exoskeletons have been in development for several years and are becoming increasingly efficient. Unfortunately, user comfort was not always a priority design criterion throughout their development. To further improve this technology, exoskeletons should operate and deliver assistance without causing discomfort to the user. For this, improvements are necessary from an ergonomic point of view. The device’s control method is important when endeavoring to enhance user comfort. Exoskeleton or rehabilitation device controllers use methods of control called interaction controls (admittance and impedance controls). This paper proposes an extended version of an admittance controller to enhance user comfort. The control method used consists of adding an inner loop that is controlled by a proportional-integral-derivative (PID) controller. This allows the interaction force to be kept as close as possible to the desired force trajectory. The force-tracking admittance controller modifies the actuation force of the system in order to follow both the desired motion trajectory and the desired relative force between the user and the exoskeleton.

Keywords: Mobility assistive device, exoskeleton, force-tracking admittance controller, user comfort.

References:

[1] A. Seguin, “Experimental Characterisation of Polyurethane Foam-Based Magnetorheological Elastomers”, Thesis submission, Ottawa-Carleton Institute for Biomedical Engineering, University of Ottawa, Canada, 2018.
[2] H. F.N. Al-Shuka, S. Leonhardt, W. Zhu, R. Song, C. Ding and Y. Li, “Active Impedance Control of Bioinspired Motion Robotic Manipulators: An Overview”, in Bionics and Biomechanics, Hindawi, Vol 2018, Article ID 8203054, 18 October 2018.
[3] K. Anam, A. Al-Jumaily, “Active Exoskeleton Control Systems: State of the Art”, International Symposium on Robotics and Intelligent Sensors 2012 (IRIS 2012), Procedia Engineering vol 41 pp.988-994.
[4] N. Berezny, “Design and Implementation of a Novel Rehabilitation Robot for Acute Stroke Patients”, thesis submitted to the University of Ottawa, Canada, Dept. Mechanical & Aerospace Engineering, September 20219.
[5] T. Nef, M. Mihelj, G. Kiefer, C. Oerndl, R. Müller, R. Riener. “ARMin – Exoskeleton for Arm Therapy in Stroke Patients”, International Conference on Rehabilitation Robotics, IEEE, June 2007.
[6] E. Rocon, J.M. Belda-Lois, A.F. Ruiz, M. Manto, J.C. Moreno, and J.L. Pons, “Design and Validation of a Rehabilitation Robotic Exoskeleton for Tremor Assessment and Suppression”, Transactions on neural systems and rehabilitation engineering conference, vol. 15, no. 3, September 2007.
[7] J. Veneman, R. Kruidhof, E. G. Hekman et al, “Design and Evaluation of the LOPES Exoskeleton Robot for Interactive Gait Rehabilitation”, presented at transactions on neural systems and rehabilitation engineering conference, vol. 15, no. 3, September 2007.
[8] W. Yu, J. Rosen, X. Li, “PID Admittance Control for an Upper Limp Exoskeleton”. In American Control Conference, July 2011.
[9] C. Carignan, J. Tang, and S. Roderick, “Development of an Exoskeleton Haptic Interface for Virtual Task Training”, in International Conference on Intelligent Robots and Systems, IEE, October 2009.
[10] G. Aguirre-Ollinger, J. Edward Colgate, Michael A. Peshkin and Ambarish Goswami, “Design of an active one-degree-of-freedom lower-limb exoskeleton with inertia compensation”, published in The Internation Journal of Robotics Research, December 2010.
[11] G. Li, H. Huang, and B. Li, “Robust Adaptive Force Tracking Impedance Control for Robotic Capturing of Unknown Objects”, in International Conference on Intelligent Robot and Applications, Vol 12, August 2019.
[12] K. Lee and M.Buss, “Force Tracking Impedance Control with Variable Target Stiffness”, presented at World Congress The International Federation of Automatic Control, Vol 17, pp.6751-6756, July 2008.
[13] K. Kiguchi and Y. Hayashi, “An EMG-Based Control for an Upper-Limb Power-Assist Exoskeleton Robot”, in Transactions on Systems, MAN, and Cybernetics-Part B, Vol 42, pp.1064-1071, August 2012.