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On the use of positive feedback for improved torque control

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Abstract

This paper considers the torque control problem for robots with flexible joints driven by electrical actuators. It is shown that the achievable closed-loop tracking bandwidth using PI torque controllers may be limited due to transmission zeros introduced by the load dynamics. This limitation is overcome by using positive feedback from the load motion in unison with PI torque controllers. The positive feedback is given in terms of load velocity, acceleration and jerk. Stability conditions for designing decentralized PI torque controllers are derived in terms of Routh-Hurwitz criteria. Disturbance rejection properties of the closed system are characterized and an analysis is carried out investigating the use of approximate positive feedback by omitting acceleration and/or jerk signals. The results of this paper are illustrated for a two DoF (degrees of freedom) system. Experimental results for a one DoF system are also included.

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Correspondence to Houman Dallali.

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This work was supported by the AMARSI (Adaptive Modular Architecture for Rich Motor Skills, FP7-ICT-248311) and Walk-Man (FP7-ICT-611832) European projects.

Houman DALLALI obtained the M.Sc. degree from the Department of Automatic Control and Systems Engineering at the University of Sheffield with distinction, and subsequently was admitted to the University of Manchester for pursuing his Ph.D. in modelling and stabilization control of a compliant humanoid robot, COMAN. Following the award of his Ph.D. in 2012, he was accepted for postdoctoral fellowship at the Advanced Robotics Department, the Italian Institute of Technology (IIT), Genova, Italy. In his postdoctoral fellowship in addition to work on applied control theory, he has been developing an accurate humanoid dynamic simulator for studying whole body motion and locomotion of COMAN and WALKMAN humanoid robots. His research interests are in dynamic modelling, multivariable impedance and force control of safe humanoid robots with flexible joints.

Gustavo A. MEDRANO-CERDA received the B.Sc. degree in Electro-mechanical Engineering from the Universidad Nacional Autonoma de Mexico in 1977, and the M.Sc. and Ph.D. degrees in Control Systems from Imperial College, London, in 1979 and 1982, respectively. From 1982 to 1985, he was an associate professor at the Division de Estudios de Postgrado, Facultad de Ingenieria, Universidad Nacional Autonoma de Mexico. From 1985 to 1986, he was a research fellow at the Department of Engineering, University of Warwick. From 1986 to 2002, he was a lecturer at the Department of Electronic and Electrical Engineering at the University of Salford. During this period, he set up the Advanced Control and Robot Locomotion Laboratory at the University of Salford. In 1999, he became a control systems consultant at Las Cumbres Observatory (formerly Telescope Technologies Ltd.) and later in 2002 he joined the company as a senior control engineer pioneering work in Hinfinity control system design and implementation for astronomical telescopes. Since 2009, he has been a senior research scientist at the Advanced Robotics Department, Istituto Italiano di Tecnologia. His research interests are in the areas of robust control, adaptive control, modelling and identification, fuzzy systems and advanced robotic applications, in particular to walking robots.

Michele FOCCHI was born in Rimini, Italy. He holds the M.Sc. in Control System Engineering from Politectico di Milano in 2007. His final project dealt with dynamic modelling of hydraulic turbines for energy generation carried out at the Federal University of Santa Catarina, Brazil. Until 2008 he worked at the R&D department of Indesit company where he worked with design and dynamic modeling of hydraulic, thermal and mechanical phenomena and system identification for house appliances. In 2009, he was employed as a fellow at the Advanced Robotic Department (ADVR) at IIT developing a prototype of Novel concept for an air-pressure driven micro-turbine for power generation for which he obtained an international patent and several awards. He also gained some experience with force control with pneumatic muscles. In 2010, he started a Ph.D. getting involved in the Hydraulically Actuated Quadruped Robot project at the Dynamic Legged Systems Laboratory at ADVR where he was involved on development of low-level controllers for locomotion purposes. Currently, his research interests range from dynamic locomotion with legged robots, whole body control and planning, to actuation technologies.

Thiago BOAVENTURA received his B.Sc. and M.Sc. degrees in Mechatronic Engineering from the Federal University of Santa Catarina, Brazil, in 2009. He received his Ph.D. degree in Robotics, Cognition, and Interaction Technologies from a partnership between the Italian Institute of Technology and University of Genoa, Italy, in 2013. He is currently a post-doctoral researcher at the Agile & Dexterous Robotics Lab, at ETH Zurich, in Switzerland. He is mainly involved in the EU FP7 BALANCE project with focus in the collaborative impedance control of exoskeletons. His research interests include impedance and admittance control, model-based control, legged robotics, passivity of sample-based systems, hydraulic actuators and systems, variable stiffness actuators, and wearable robotics.

Marco FRIGERIO graduated in Computer Science in 2008, at the University of Milano Bicocca (Italy). In 2013, he obtained a Ph.D. degree in Robotics at the Advanced Robotics Department (ADVR) of Istituto Italiano di Tecnologia (IIT, located in Genoa, Italy). His thesis focuses on a novel approach for optimized code generation for the kinematics and the dynamics of articulated robots. Since 2013, he has been a postdoctoral researcher at the Dynamic Legged Systems Lab of ADVR at IIT. He is responsible for the software development efforts of the lab, which focus on control, legged locomotion, autonomous robots. His research interests include robotics software, software architectures and robot dynamics.

Claudio SEMINI is currently the head of IIT’s Dynamic Legged Systems Lab that developed the HyQ and HyQ2Max robot platforms, which are able to perform highly dynamic tasks such as running and jumping. After his M.Sc. at ETH Zurich, he spent 2 years in Japan for robotics research. Since the beginning of 2007, he has been a member of the Advanced Robotics Department at the Italian Institute of Technology (IIT). In spring 2007, he started the HyQ project as his Ph.D. research under the supervision of Nikos Tsagarakis and Darwin Caldwell. In 2010, he finished the design and construction of the first version of HyQ and successfully defended his Ph.D. with the title “HyQ–Design and Development of a Hydraulically Actuated Quadruped Robot”. His current research focus lies on the design and control of hydraulically actuated high-performance robots with arms and legs, compact hydraulic actuation and hydraulic force control.

Jonas BUCHLI is an SNSF Assistant Professor for Agile and Dexterous Robotics at ETH Zurich since May 2012. He holds a Diploma in Electrical Engineering from ETH Zurich (2003) and a Ph.D. from EPF Lausanne (2007). He has contributed to research in diverse fields such dynamical systems approaches to motion generation and control, the theory of coupled oscillators, planning and control of dynamic locomotion, machine learning, whole body control, whole body force and impedance control and modeling of human motor control. He was involved in the development of robotic platforms as well as software engineering projects for robotic control software. His current research interests include model based control of legged robotic and human locomotion and manipulation, optimal and learning control, and dynamic and versatile service and field robots.

Darwin G. CALDWELL (born in Ballymena, Northern Ireland) is a noted international researcher and academic in Robotics who is currently Research Director at the Italian Institute of Technology in Genoa, Italy. He has been heavily involved as project leader in the development of the iCub, a smallsize humanoid robot being designed by the RobotCub Consortium. He has published over 170 papers and has received awards at several international conference and events. He is a visiting professor at the University of Sheffield, King’s College London, University of Wales Bangor and University of Manchester. He studied at Ballymena Academy and then completed his B.Sc. and Ph.D. in Robotics from the University of Hull in 1986 and 1990, respectively, and completed an M.Sc. in Management at the University of Salford in 1994. His research interests include innovative actuators and sensors, haptic feedback, force augmentation exoskeletons, dexterous manipulators, humanoid robotics (iCub), bipedal and quadrupedal robots, biomimetic systems, rehabilitation robotics, telepresence and teleoperation procedures, and robotics and automation systems for the food industry. He was previously at the University of Salford between 1989 to 2007 as a Lecturer, Senior Lecturer, Reader and finally Professor of Advanced Robotics in the Centre for Robotics and Automation between 1999 and 2007. He is currently Chair of the IEEE Robotics and Automation Chapter (UKRI) and a past co-chair of the IEE (IET) Robotics and Mechatronics. He is on the editorial board of Industrial Robot as well as being guest editor of several journals. In association with Professor John Gray of the University of Salford, he was responsible for the establishment of the Yorkshire Forward funded Centre for Food Robotics and Automation (CenFRA).

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Dallali, H., Medrano-Cerda, G.A., Focchi, M. et al. On the use of positive feedback for improved torque control. Control Theory Technol. 13, 266–285 (2015). https://doi.org/10.1007/s11768-015-4146-y

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  • DOI: https://doi.org/10.1007/s11768-015-4146-y

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