Dynamic Model of a 7-DOF Whole Arm Manipulator and Validation
from Experimental Data
Zaira Pineda Rico, Andrea Lecchini-Visintini and Rodrigo Quian Quiroga
Department of Engineering, University of Leicester, University Road, Leicester, U.K.
Keywords:
Whole Arm Manipulator Model, Friction Model, Friction Identification.
Abstract:
The present paper describes the design of the dynamic model of a 7 degrees of freedom whole arm manipulator
implemented in SimMechanics. The friction phenomena of the manipulator is identified, represented through
a fitted model and included in the system model with the aim of increment the accuracy of the model with
respect to the real system. The characteristics of the model make it suitable to test and design control strategies
for motion and friction compensation in MATLAB/Simulink.
1 INTRODUCTION
The computation of the dynamic model of a robot ma-
nipulator plays an important role in simulation of mo-
tion, analysis of the manipulator’s structure and de-
sign of optimal control algorithms. The inclusion of
the effects of friction in a mechanical system model
when simulating control strategies, helps to improve
the performance of the controller to be implemented
in the real system (Kostic et al., 2004; Indri, 2006;
Bompos et al., 2007). Most of the whole arm manip-
ulators mathematical models are based in the com-
putation of multi-links serial robot’s mathematical
equations. These equations are obtained using the
Newton-Euler recursive method to calculate the Cori-
olis, centrifugal and inertial forces observed when the
end-effector is in motion. Moreover, a Jacobian ap-
proach may be implemented in parallel for mapping
between Cartesian and joint space, in order to mini-
mize singularity conditions that increase the computa-
tion load of the control algorithm (Lau and Wai, 2002;
Sousa et al., 2009). This methodology involves both
operational and joint forces.
In most cases these mathematical models are
implemented using high level computing languages
as MATLAB (Corke, 1996), C/C++ or Fortran.
Nevertheless, in order to avoid significant com-
putation time, some authors have found in MAT-
LAB/SimMechanics a comfortable tool to design me-
chanical systems used for experimental verification.
The capability of this tool yields appropriate results
when working with joints with 1 DOF and when
all the manipulator’s inertial parameters are known
(MathWorks, 2011).
Section 2 offers a brief description of the real ma-
nipulator system. Section 3 gives insights on the de-
sign of the model and shows the importance of exper-
imental data in the development of the friction model.
In Section 4 the response of the real system is com-
pared to that of the model when simulating some ex-
periments. Finally, section 5 presents some conclu-
sions related to this work.
2 THE REAL SYSTEM
The real system is a 7-degrees-of-freedom whole arm
manipulator (WAM) from Barrett Technology Inc. It
is a joint torque controlled manipulator equipped with
configurable PD/PID control and gravity compensa-
tion. The information related to the joints configu-
ration, joint motor drives and the body part masses,
centre of gravity and inertia matrix is provided by the
manufacturer in the WAM ARM User’s Manual (Bar-
rett Technology Inc, 2008). Figure 1 shows the con-
figuration and attached frames of the 7-DOF system
with a grasper. All the joints of the manipulator are
1 DOF revolute joints. An image of the real system
is shown in Figure 2, consisting in a Barret 7-DOF
Whole Arm Manipulator with an attached BH8-series
BarrettHand.
For the developmentofthis projectthe 7-DOF ma-
nipulator is configuredwithjoint PD control and grav-
ity compensation given by Equation (1), where the
joint torque τ is expressed as the sum of the difference
217
Pineda Rico Z., Lecchini-Visintini A. and Quian Quiroga R..
Dynamic Model of a 7-DOF Whole Arm Manipulator and Validation from Experimental Data.
DOI: 10.5220/0004013002170222
In Proceedings of the 9th International Conference on Informatics in Control, Automation and Robotics (ICINCO-2012), pages 217-222
ISBN: 978-989-8565-22-8
Copyright
c
2012 SCITEPRESS (Science and Technology Publications, Lda.)