  Presented in this paper is the kinematic analysis of a symmetrical
three-degree-of-freedom planar parallel manipulator. In opposite to serial
manipulators, parallel manipulators can admit not only multiple inverse
kinematic solutions, but also multiple direct kinematic solutions. This
property produces more complicated kinematic models but allows more flexibility
in trajectory planning. To take into account this property, the notion of
aspects, i.e. the maximal singularity-free domains, was introduced, based on
the notion of working modes, which makes it possible to separate the inverse
kinematic solutions. The aim of this paper is to show that a non-singular
assembly-mode changing trajectory exist for a symmetrical planar parallel
manipulator, with equilateral base and platform triangle.
