  A new type of parallel robot mechanism with an extendable structure is
presented, and its kinematic properties and design parameters are analyzed. The
Triple Scissor Extender (TSE) is a 6 Degree-Of-Freedom robotic mechanism for
reaching high ceilings and positioning an end effector. Three scissor
mechanisms are arranged in parallel, with the bottom ends coupled to linear
slides, and the top vertex attached to an end effector plate. Arbitrary
positions and orientations of the end effector can be achieved through the
coordinated motion of the six linear actuators located at the base. By changing
key geometric parameters, the TSE's design can yield a specific desired
workspace volume and differential motion behavior. A general kinematic model
for diverse TSEs is derived, and the kinematic properties, including workspace,
singularity, and the Jacobian singular values, are evaluated. From these
expressions, four key design parameters are identified, and their sensitivity
upon the workspace volume and the Jacobian singular values is analyzed. A case
study in autonomous aircraft assembly is presented using the insights gained
from the design parameter studies.
