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TECHNICAL PAPERS

# Compliance Control for an Anthropomorphic Robot with Elastic Joints: Theory and Experiments

[+] Author and Article Information
Loredana Zollo

Biomedical Robotics & EMC Laboratory, Università Campus Bio-Medico Via Emilio Longoni 83 00155 Roma, Italyl.zollo@unicampus.it

Bruno Siciliano

PRISMA Lab, Dipartimento di Informatica e Sistemistica, Università degli Studi di Napoli Federico II, Via Claudio 21, 80125 Napoli, Italysiciliano@unina.it

Alessandro De Luca

Dipartimento di Informatica e Sistemistica,  Università degli Studi di Roma “La Sapienza,” Via Eudossiana 18, 00184 Roma, Italydeluca@dis.uniromal.it

Eugenio Guglielmelli

Biomedical Robotics & EMC Laboratory, Università Campus Bio-Medico Via Emilio Longoni 83 00155 Roma, Italye.guglielmelli@unicampus.it

Paolo Dario

Scuola Superiore Sant’Anna, ARTS Lab-c/o Polo Sant’Anna Valdera, Viale Rinaldo Piaggio 34, 56025 Pontedera (Pisa), Italyp.dario@arts.sssup.it

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J. Dyn. Sys., Meas., Control 127(3), 321-328 (Jul 09, 2004) (8 pages) doi:10.1115/1.1978911 History: Received August 06, 2003; Revised July 09, 2004

## Abstract

Studies on motion control of robot manipulators with elastic joints are basically aimed at improving robot performance in tracking or regulation tasks. In the interaction between robots and environment, instead, the main objective of a control strategy should be the reduction of the vibrational and chattering phenomena that elasticity in the robot joints can cause. This work takes into account working environments where unexpected interactions are experienced and proposes a compliance control scheme in the Cartesian space to reduce the counter effects of elasticity. Two theoretical formulations of the control law are presented, which differ for the term of gravity compensation. For both of them the closed-loop equilibrium conditions are evaluated and asymptotic stability is proven through the direct Lyapunov method. The two control laws are applied to a particular class of elastic robot manipulators, i.e., cable-actuated robots, since their intrinsic mechanical compliance can be successfully utilized in applications of biomedical robotics and assistive robotics. A compared experimental analysis of the two formulations of compliance control is finally carried out in order to verify stability of the two closed-loop systems as well as the capability to control the robot force in the interaction.

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## Figures

Figure 1

Elastic joint

Figure 2

The Dexter mechanical structure

Figure 3

A cable-actuated joint

Figure 4

Position error and orientation error in the case of compliance control in the Cartesian space with constant gravity compensation. The graph is related to a displacement in the negative vertical direction.

Figure 5

Position error and orientation error in the case of compliance control in the Cartesian space with on-line gravity compensation

Figure 6

Position error and orientation error in the case of compliance control in the Cartesian space with constant gravity compensation. The graph is related to a displacement in the positive vertical direction.

Figure 7

Position error and orientation error in the case of compliance control in the Cartesian space with on-line gravity compensation and lower KP

Figure 8

Impact force in the case of compliance control in the Cartesian space with on-line gravity compensation for higher (left) and lower KP values (right)

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