# Designing Fault Tolerant Manipulators: How Many Degrees-of-Freedom?

** Abstract: ** One of the most important parameters to consider when
designing a manipulator is the number of degrees-of-freedom (DOFs). This
article focuses on the question: How many DOFs are necessary and sufficient
for fault tolerance and how should these DOFs be distributed along the length
of the manipulator? A manipulator is fault tolerant if it can complete its
task even when one of its joints fails and is immobilized. The number of
degrees-of-freedom needed for fault tolerance strongly depends on the
knowledge available about the task. In this article, two approaches are
explored. First, for the design of a General Purpose Fault Tolerant
Manipulator, it is assumed that neither the exact task trajectory, nor
the redundancy resolution algorithm are known a priori and that the
manipulator has no joint limits. In this case, two redundant DOFs are
necessary and sufficient to sustain one joint failure as is demonstrated
in two design templates for spatial fault tolerant manipulators. In a second
approach, both the Cartesian task path and the redundancy resolution algorithm
are assumed to be known. The design of such a Task Specific Fault Tolerant
Manipulator requires only one degree-of-redundancy.
To appear in:
*The International Journal of Robotics Research,
*
1996.

paredis@cmu.edu