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and
Machine Theory
Mechanism and Machine Theory 43 (2008) 1385–1400
ate/mechmt
Model-based control of a 6-dof electrohydraulic
Stewart–Gough platform
Ioannis Davliakos, Evangelos Papadopoulos *
Department of Mechanical Engineering, National Technical University of Athens, Athens 157 80, Greece
Received 26 June 2006; received in revised form 26 November 2007; accepted 2 December 2007
Available online 29 January 2008
Abstract
In this paper, a novel model-based controller for a six Degree-of-Freedom (dof) electrohydraulic Stewart–Gough plat-
form is developed. Dynamic models of plexity are employed that describe the salient dynamics of the main elec-
ponents. Rigid body equations of motion and hydraulics dynamics, including friction and servovalve
models are used. The developed feedback controller uses the system dynamic and hydraulic model to yield servovalve cur-
rents, so that the error dynamics converge asymptotically to zero, independent of load variations. In this approach, force,
pressure or acceleration feedback is not required. Simulations with typical desired trajectory inputs are presented and a
good performance of the controller is obtained. The proposed methodology can be extended to electrohydraulic serial
or closed-chain manipulators and simulators.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Stewart platform; Hydraulic servomechanisms; Parallel mechanisms; Model-based control
1. Introduction
The original Gough six Degree-of-Freedom (dof) platform was developed in 1954 [1,2]. In 1965, the pro-
totype parallel mechanism was used as a 6-dof motion platform for a flight simulator [3]. Since then, a number
of studies on this mechanism and its variations have been published, . [4]. The mechanism can be driven
electrically or electrohydraulically. The kinematics and dynamics of the Stewart–Gough (S–G) platform has
been studied by many researchers [5–9]. However, actuation dynamics have