A new family of six degrees of freedom positional devices

Positional control is fundamental to most manufacturing processes as well as a wide range of other applications. Many types of positional devices have been proposed and used, ranging from robotic arms to Stewart platforms. This paper discusses a new family of six degrees of freedom 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 devices as thermal motion is a significant source of positional uncertainty. The stiffness and thermally induced positional uncertainty of three designs-a robotic arm, a Stewart platform, and one member of the new family-are analysed and compared. The Stewart platform provides the greatest stiffness for a given structural mass but has the most restrictive range of motion. The robotic arm is least stiff. The new proposal combines greater stiffness than the robotic arm with a significantly greater range of motion than the Stewart platform.