Flying in the face of convention – a new approach to the assembly of large fabricated products

Citation

(2005), "Flying in the face of convention – a new approach to the assembly of large fabricated products", Industrial Robot, Vol. 32 No. 3. https://doi.org/10.1108/ir.2005.04932caf.001

Flying in the face of convention – a new approach to the assembly of large fabricated products

Flying in the face of convention – a new approach to the assembly of large fabricated products

Keywords: Aerospace engineering, Robotics

Conventional robotic assembly systems are well established in high volume manufacturing industries such as automotive and consumer electronics. These are primarily designed on the assumption that there is a high degree of certainty within their operating environments. The position, orientation and precise geometry of each individual component are assumed to be well defined and known. The large size and inherent compliance of the components and assemblies used in industries such as aerospace, yellow goods and rail vehicle manufacture means that significant distortion occurs during handling and processing resulting in a high degree of geometric and positional uncertainty.

To assemble large structures requires multiple co-operative robots that are capable of handling a number of different components. The ability of these systems to adapt to any deviations is usually limited to time consuming search for edge and feature location. These functions are also usually confined to a single robot and only provide local corrections. The problem can be mitigated to some degree by the use of complex fixtures, but this increases the cost and reduces flexibility by making large parts of the cell hardware product specific (Plate 1).

Solving this problem has been the basis of a significant programme of UK Engineering and Physical Sciences Research Council funded research work supported by Comau at the University of Nottingham with close support from Bombardier Aerospace, Belfast. As a result of this a number of core technologies have been developed. The key enabler being a technique called Simulation Based Control. This technique combined with non-contact metrology, mathematical modeling techniques and innovative robot end- effectors offers a practical solution and allows the effective and safe use of industrial robots within a partially defined environment.

Plate 1 Example use of the assembly – with robot positioning components

The culmination is a working demonstrator cell. The cell contains four Comau robots, two S2 6 kg robots for assembly and a 200 kg H4 and Tricept for riveting. The robots are fully networked and also connected to the cell master controller using Interbus. This allows them to be precisely synchronised since the exact time of delivery of programmes to individual robots via the ethernet cannot be guaranteed as it is dependent on the amount of traffic on the network at any time.

The cell is currently being evaluated using fuselage components from the CRJ700 regional jet manufactured by Bombardier Aerospace. During operation of the cell the fuselage panel is mounted on a simple fixture and loaded into the cell on rails. Once in the approximate required position it is locked off and the cell is then ready to be started. The part does not need to be precisely located since the robots will, on initialisation, search for its position using laser scanners mounted on their end-effectors. This allows the position of the part relative to the robots to be obtained. After the panel has been found, control is then passed to the programme database and the required sequence of robot operations are completed according to the stored programme sequence. Before each operation the panel is rescanned to account for any local variations in position relative to the initial position obtained during initialisation of the cell caused by the previous manufacturing operations.

Each robot has a small software module loaded into its controller that interfaces it to the network and Interbus. This software is responsible for the loading of robot programmes and “hand shaking” with the other robots and the cell co-ordinator prior to programme execution. The final requirement is the availability of advanced robot end-effectors that can perform the required handling and assembly tasks. In the cell novel end- effectors have been developed for material handling and fastening. The handling end-effectors are highly reconfigurable allowing a large number of different components to be handled without the need for regular end- effector changes. To support the assembly of airframes a pair of end- effectors have been developed that can be used to drill, countersink and install solid rivets. These are mounted on a pair of opposing high payload industrial robots with the componets to be riveted being placed between them.

The system has been developed primarily for use in the manufacture of airframes, but the technique is applicable to any structures that are liable to deformation during assembly. A fully functional demonstrator cell has been built at the University of Nottingham. The performance of the cell has been good with the required assembly tolerances being reached. The techniques developed have the potential to revolutionise the way in which large structures such as airframes are manufactured. Much of the technology developed is also transferable to other industries such as the assembly of rail vehicles.