  The subject of this paper is the optimal design of a parallel mechanism
intended for three-axis machining applications. Parallel mechanisms are
interesting alternative designs in this context but most of them are designed
for three- or six-axis machining applications. In the last case, the position
and the orientation of the tool are coupled and the shape of the workspace is
complex. The aim of this paper is to use a simple parallel mechanism with
two-degree-of-freedom (dof) for translational motions and to add one leg to
have one-dof rotational motion. The kinematics and singular configurations are
studied as well as an optimization method. The three-degree-of-freedom
mechanisms analyzed in this paper can be extended to four-axis machines by
adding a fourth axis in series with the first two.
