FreeHex machining robot wins Rolls-Royce innovation award

The brainchild of engineers from The University of Nottingham and the Rolls-Royce University Technology Centre (UTC), FreeHex is a six-legged parallel kinematic machine tool capable of applying complex computerised milling processes to a range of in-situ maintenance jobs. The robot has attracted attention from the like of Formula One and is now being eyed up by Rolls-Royce for use in a range of applications, including aerospace. The idea for FreeHex came from a request made by Rolls-Royce's submarine business, which required in-situ repairs to be done in a very confined workspace. Its own machine was heavy and hard to move, so the company asked for something smaller and more flexible with the same functions. "Rolls-Royce presented us with a challenge that tested our abilities and gave us a chance to rethink traditional machine tools," explained UTC director Professor Dragos Axinte. "Many of these are still 'serial manipulators' like robot arms; a chain of rigid links in a series. These serial kinematic machines stack independent stages to provide multi-axis movement; but this can lead to compound errors. Prof Axinte continued: "Alternative parallel kinematic mechanisms driven by actuators, often telescopic 'jacks' and ball-screw drives linked in pairs, are flexible but also more complex. Our development of a Free-leg Hexapod, a unique parallel kinematic configuration without base platform so that the lower joints can be attached to the surfaces of various geometries, takes this kind of robotised in-situ processing machine a reality." Unlike other machines, FreeHex is designed to be flexible enough to tackle numerous tasks. Weighing in at less than five kilos, it has a small footprint and can be installed quickly and effectively. Its computer numerical control is said to ensure highly accurate and repeatable remote machining in dangerous working environments. Axite says the robot is mechanically very simple. Its design is based on a Stewart type hexapod structure, with six telescopic struts or legs with ball-screw drives that work in parallel to position the moving platform. A compact high speed spindle is mounted on the centre of the platform between the legs. Because the legs are gathered into pairs on three separate feet which can be temporarily attached to a work piece in any given position, the machine is said to offer much greater flexibility than competing designs and more variability. Ralph Anderson of Rolls-Royce commented: "Free-hex has served extremely well to demonstrate the practical potential for carrying out complex machining operations, such as profile milling and thread milling. The technology offers us a genuine alternative to our traditional bespoke machine designs."