Emerald Group Publishing Limited
Copyright © 2011, Emerald Group Publishing Limited
Holistic precision and the global economy
Article Type: Viewpoint From: Assembly Automation, Volume 31, Issue 4
Europe is confronted with major potential opportunities in the decades to come. These opportunities are created by the globalisation of markets, shorter product lifecycles, information technology progress and miniaturisation of products. Although often portrayed as threats, the symptoms being denoted in the European economy are, in fact, part of a shift in knowledge and technology infrastructures created by these trends. In this context, one of the major challenges of the future enlarged European Union will be to integrate and fully activate the existing capacities and knowledge across Europe in the high-tech industrial sector in order to reduce the potentially growing gap that may be created, in technological development, between Europe and other most technologically developed countries (USA, Japan and Korea). To counteract this, a vast number of initiatives have been started on micro and nano topics. Unfortunately, they generally refer to products, materials, specific technologies, but almost never production. This is alarming since micro and nano products will require new production and automation principles.
“Market dominance in micro & nano technologies, products and their production systems will not occur overnight. Moreover, micro and nano products will not always exist as purely independent entities but, also, as parts of larger products that still require some macro assembly and will integrate a growing service component. Therefore, the societies that intend to support the development of world-class micro and nano technologies will have to rely, in order to succeed, upon the coordinated fusion of new technologies and production strategies to existing production constraints, business paradigms and educational infrastructures: evolution rather than revolution” (Professor Jacques Jacot, Ecole Polytechnique Fédérale de Lausanne).
This becomes somewhat evident when one analyses what “precision” actually includes within its topical boundaries: measurement, manufacturing (including casting, moulding, etc.), assembly, functional performance, etc. In fact, one may quite clearly understand that precision has become possible due to the advances made in production technology and, more substantially, within measurement systems. Finally, even though lost authors will focus on micro/nano products when dealing with precision, the reality is that very large products require extreme precision as well: airframe assembly, turbine blade manufacturing, etc.
Hence, precision becomes a very holistic topic which should encompass the effects such requirements pose both upstreams and downstreams from the initial product conceptualisation. Design of precision products still have no adequate support, will affect the manufacturing and assembly quite seriously, and the final product quality and performance will need advanced measurement systems.
Within the micro-domain, for example, precision remains to be achieved at a cost-effective level, but it is not a new scientific issue. If assembly systems work in “open loop”, that is without any information regarding the position of the component, it is possible to position a part with an accuracy of 50-100 μm. This is a known fact for the leaders of assembly technology. To reach an accuracy of better than 10 μm, it is necessary to use a vision system, or other high-positioning sensory device, to detect the position of the part and the receptor before the assembly operation. If one uses a vision system to control the position during the assembly process, it is possible to reach a repetitivity of 500 nm (if one is able to release the component without moving). In this world, however, once under 1 μm, the macro-model is no longer valid. Unfortunately, it does not seem to be possible to use general rules for the conception of very flexible assembly systems at this precision level. Working at 0.5 μm is not new. The real challenge is to find good guidelines to be able to design a small, high precision, easily produceable product. This is where the “micro-model” discussion comes into view: one has to consider the robot, the grasping tool, the component and fixtures, all together, and that poses an almost unreachable objective when applying a “flexible” or “evolvable” approach to the assembly processes, from a modularity point of view. This is a granularity issue: by creating a micro-assembly system consisting of several modules, the chain of tolerances becomes unsustainable. In extreme micro assembly, the assembly unit will most probably have to be a single integrated unit.
This was just a small example of the challenges that remain ahead. A few things remain certain: one cannot venture into high-precision production without the capability to measure the actual results. As pointed out in several International Precision Assembly Symposium (IPAS) conferences, distinctions need to be made as to the type of product (macro/meso/micro/nano), the validation of the precision (measurement) as well as the highlighting of the fact that adequate design methods still do not exist. Once one includes the fact that, as stated earlier, most products are an integration of micro and macro components, the complexity of the requirements should become obvious. The encouragement of research within this field should, therefore, be most definitely supported.
Mauro OnoriProfessor at KTH Royal Institute of Technology, Stockholm, Sweden.