  This paper presents a method for algebraic fault detection and identification
of nonlinear mechanical systems, describing rigid robots, by using an
approximation with orthonormal Jacobi polynomials. An explicit expression is
derived for the fault from the equation of motion, which is decoupled from
disturbances and only depends on measurable signals and their time derivatives.
Fault detection and identification is then achieved by polynomial approximation
of the determined fault term. The results are illustrated for a faulty SCARA.
