Positional control is fundamental to most manufacturing processes as w
ell as a wide range of other applications. Many types of positional de
vices have been proposed and used, ranging from robotic arms to Stewar
t platforms. This paper discusses a new family of six degrees of freed
om positional control devices which generally combine simple designs,
high stiffness and strength, and a wider range of motion. Stiffness is
particularly advantageous in very small (submicron) positional device
s as thermal motion is a significant source of positional uncertainty.
The stiffness and thermally induced positional uncertainty of three d
esigns-a robotic arm, a Stewart platform, and one member of the new fa
mily-are analysed and compared. The Stewart platform provides the grea
test stiffness for a given structural mass but has the most restrictiv
e range of motion. The robotic arm is least stiff. The new proposal co
mbines greater stiffness than the robotic arm with a significantly gre
ater range of motion than the Stewart platform.