Common 3DOF motions include pure translation (3T) and pure orientation or
rotation (3R). Less familiar motions involving both translation and
rotation, i.e., (1T2R) and (2T1R), are difficult to classify, analyze
and design. We call (1T2R) tasks ``mining'' since these involve following
a space curve or ``tunnel'' while the end effector is capable of 2DOF
orientation or ``excavation''. 2T1R tasks are called ``sculpting'' since
freedom of movement on some surface as well as a 1DOF rotation is implied.
A special case, planar motion, is the only familiar member of this class. 3DOF
manipulation is useful in manufacturing where such reduced mobility is
sufficient and a stiff, simple and accurate mechanism is desired.
The design of parallel manipulators for this pupose is particularly
P. Zsombor-Murray, M. Husty, J. Hayes, P. Gervasi