FAULT TOLERANCE OF ROBOT
MANIPULATORS
F. Noureddine
Ecole Nationale d’Ingénieurs de Tarbes
BP 1629, 65016 Cedex, France
Email : farid.noureddine@enit.fr
Abstract: This work is about the study of a fault tolerant rigid robot manipulator
having five degrees of freedom. All the stages in the design of a fault tolerant
system are described here. In order to simplify the fault detection process and
isolation module only faults a?ecting joint 3 are considered. Fault accommodation
relative to a locked joint 3 is established thanks to the kinematic redundancy of
this robot.
Keywords: Fault detection in robots, fault detection and isolation, fault
accommodation, fault tolerance, robotics
1. INTRODUCTION
Fault tolerance is one of the means available to enhance
dependability in systems. Any technological
system can prove to have malfunctions despite a
decent design. In some cases, these malfunctions
can have disastrous consequences. Fault tolerance
is mainly aimed at foreseeing the tasks to be
performed in order to ensure the continuity of
the system in a normal working mode despite the
faults and even, to some extent, prevent dangerous
situations to be generated by the blocking of
joint 3 or any other part of the robot. In order
to be real, fault tolerance requires the design of
two main stages. Fault detection and isolation,
FDI, which will allow the generation of indicators
showing the occurence of faults is called residuals.
The second stage should allow the accommodation
of the faults that have been detected and isolated
and thus permit the continuity of a given task.
The preliminary phase in the design of algorithms
is the phase consisting in analysing the di?erent
types of faults which can a?ect the whole system
and yet allow the creation of a model with faults.
As most of technological systems, robots are subject
to faults. According to the context in which
the robot is used and the environment of the
robot, detected faults could have repercussions
that are more or less serious. A detailed analysis of
the robot will permit one to anticipate the faults
and failures which may occur. See (Visinsky et
al., 1995) for a study of fault tolerance in robotics,
refer to (Filaretov et al., 2002) for more recent
works focussing on FDI in robotics.
Once the fault has been detected and isolated,
propositions of fault accommodation can then be
defined. The specificity of fault tolerant systems is
to design in line and even in real time accommodation
procedures. The specificity of robot manipulators
is such that their task generally includes
end-e?ector motion in the execution of a precise
task. The task is generally described in a task
space (cartesien space) and the consequences of
the fault must be analysed in this same space. So a
fault occuring on a joint can cause it to be blocked
and the loss of a freedom degree will significantly
reduce the workspace of the robot. Nevertheless
it is still possible to consider the robot as being
functioning correctly inspite of its performances
.....