Locking bushes clamp workholding fixtures for aerospace project

ETP-Express locking bushes are playing a key role in the Neuron project to build a UCAV (Unmanned Combat Aerial Vehicle) demonstrator. Neuron is one of the most ambitious and high-profile aeronautical projects in Europe this decade. The project is led by Dassault of France, with partners in Sweden, Italy, France and Switzerland. Test flights are scheduled to take place in 2011. The build makes use of reconfigurable fixtures that rely on the holding properties of ETP-Express locking bushes. These adaptable fixtures, known as hexapods, support the fuselage during assembly. As additional parts to the fuselage are built in different assembly stages, new fixtures are added or moved to new locations on the structure, thereby providing support and, at the same time, good access for the operators.

The six-legged hexapod structure is well known in robotics and flight simulators for the ability to achieve true movement with six degrees of freedom (x, y and z axes, plus yaw, pitch and roll). Hexapods are more commonly found with powered actuators, but a project between the University of Linkoping, ETP and Saab sought to develop hexapods for workholding. Here the additional advantages of high rigidity, an ability to accept side loads, very precise adjustment and a small footprint become relevant. On each leg is fitted an ETP-Express locking bush that permits sliding movement until tightened - at which point it becomes rigid and free from backlash. Hexapod holding fixtures can be laser-aligned and locked in position. When the time comes to reconfigure the fixture, the ETP bushes are simply loosened, giving immediate free release of the legs.

Hexapod clamping application

ETP-Express shaft locking bushes are more commonly used for the connection of hubs, sprockets, cams and gears to rotating shafts without using keyways. They work by pressurisation of a cylindrical chamber that sits between thin inner and outer walls, causing them to expand and grip the hub and the shaft. Pressurisation that sets the rated performance is easily achieved by tightening a single radially-mounted screw. ETP-Express bushes have features that are well matched to the hexapod application. As well as transmitting torques, ETP-Express bushes are equally good at transmitting the axial forces present in the hexapod. Partial tightening of the pressurisation screw achieves a light resistance to movement - which is useful when setting the position. Once set, the full tightening torque is applied without any resulting axial movement that could disturb the set position. Loosening the single screw gives immediate and free release. In the UK the ETP-Express bush is available from Techdrives to suit shafts of 15 to 100mm diameter.

The Neuron project will produce an unmanned aerial vehicle to serve as a technology demonstrator, with the first flight expected in 2011. Its 6700kg weight, 12.5m wingspan and Star Wars appearance is based on a high degree of build precision thanks to the reconfigurable hexapod fixtures with ETP-Express locking bushes.

Follow the link for more information about ETP-Express locking bushes and to view a short animation.