  This paper analyses the workspace of the three-revolute orthogonal
manipulators that have at least one of their DH parameters equal to zero. These
manipulators are classified into different groups with similar kinematic
properties. The classification criteria are based on the topology of the
workspace. Each group is evaluated according to interesting kinematic
properties such as the size of the workspace subregion reachable with four
inverse kinematic solutions, the existence and the size of voids, and the size
of the regions of feasible paths in the workspace.
