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On the use of positive feedback for improved torque control 
H.Dallali,G.A.Medranocerda,M.Focchi,T.Boaventura,M.Frigerio,C.Semini,J.Buchli,D.G.Caldwell 

(Department of Advanced Robotics, Istituto Italiano di Tecnologia (IIT), Genova, Italy) 

摘要: 
This paper considers the torque control problem for robots with flexible joints driven by electrical actuators. It is shown that the achievable closedloop 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 RouthHurwitz 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. 
关键词: Forcetorque control, load motion compensation, decentralized control 
DOI： 
Received:October 28, 2014Revised:May 14, 2015 
基金项目: 

On the use of positive feedback for improved torque control 
H. Dallali,G. A. Medranocerda,M. Focchi,T. Boaventura,M. Frigerio,C. Semini,J. Buchli,D. G. Caldwell 
(Department of Advanced Robotics, Istituto Italiano di Tecnologia (IIT), Genova, Italy;Agile and Dexterous Robotics Lab, Institute of Robotics and Intelligent Systems, ETH, Z\"{u}rich, Switzerland) 
Abstract: 
This paper considers the torque control problem for robots with flexible joints driven by electrical actuators. It is shown that the achievable closedloop 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 RouthHurwitz 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. 
Key words: Forcetorque control, load motion compensation, decentralized control 




