Theoretical analysis of a special purpose miniature machine tool with parallel kinematics architecture: Free-leg hexapod

This paper introduces a unique hexapod-type miniature machine tool. This machine, referred to as Free-leg Hexapod (FreeHex), is intended for in-situ maintenance of large mechanical systems. In the investigated machine design, the positions of the joints at the lower ends of the extensible actuators can be varied in order to fit the machine onto different workpieces. The high flexibility of this machine design greatly enhances its versatility, but also increases the variability of its kinematics. A theoretical analysis of this machine design is presented including a full inverse kinematics model which can overcome the immense flexibility of this design. The paper goes on to present a method for work volume calculation based on the inverse kinematics model, motion limits of the machine, and collision detection. The variability of the work volume of the FreeHex, depending on its arrangement on a workpiece, is illustrated by a range of work volume plots for different machine set-ups. The impact of machine collisions on the working envelope is also demonstrated by example.