It’s easy to agree that the products around us should use resources in as efficient way as possible. When it comes to complex products, however, such as cars and aircraft, many aspects must be considered during the early engineering and design phases. The aspects to be considered include hydraulic design, mechanical design, electronic design, software, many different types of hardware, choice of materials, how the parts are manufactured and the methods used, how the product is used, how it can be recycled or reused, how it can be maintained in an efficient manner, whether it must be possible to upgrade the software, etc.
Life cycle perspective“If products are to become more resource-efficient, the complete life cycle must be considered, from the initial design phase to the final resting place, be it recycling or reuse. Many want to have their say and make their wishes known, and it becomes a complicated puzzle that is extremely important to solve, if this is to work,” says Sara Nilsson.
There are many stumbling blocks along the way: the various requirements influence each other and the designers cannot always predict how different parts, designed and built by different groups, will work together.
“When we bought a second-hand car, the warning light for low oil pressure was lit all the time, but it turned out that the upgraded software was not compatible with the original sensors,” she gives as an example.
In collaboration with some of the companies involved in the Mistra REES research programme, Sara Nilsson has developed a process that she hopes can solve some of the problems.
Step by step processThe first step is to define unambiguous and clear objectives that everyone in the organisation knows. This is extremely important. The objectives must specify how the product is to work and which requirements are to be given highest priority.
“Sustainability or resource-efficiency must be discussed at this stage: if our objective is to manufacture the safest car in the world, for example, it will be useless to bring up sustainability requirements later on,” says Sara Nilsson.
After this, it is necessary to collect and convert the requirements from all the different actors into technical specifications. What is involved here is to obtain the points of view of all parts of the chain, from the end-user to the people involved in recycling or using the various parts of the product for remanufacturing.
Subsidiary requirements are then coupled to the principal requirements. For example, an external requirement for a maximum speed of 180 km/h can be coupled to a requirement for maximum permitted fuel consumption or maximum permitted emissions (which may not always be compatible). One of Sara’s suggestions it to label the various types of requirements, e.g. by using different colours: environmental requirements have one colour, material and strength requirements another colour, etc. This makes it easier in a subsequent step to assign priorities, since requirements are coupled in order to investigate how they influence each other. If one requirement is problem-free operation for 10 hours a day, this can be achieved through continual maintenance or through a more robust design, for example.
Sara Nilsson Photo credit: Monica Westman
A specification of requirements is then drawn up after negotiation with all parties involved to ensure that all support it, before arriving at the definitive solution.
Testing next step“This process must be iterative: it may be necessary to go back and forth, or work with different aspects in parallel,” says Sara Nilsson.
She has presented the method at the Mistra REES annual conference attended by partner companies and concluded that the method is primarily suitable for use by large companies, which are accustomed to work in a process-oriented manner.
“It would be possible also for small companies to benefit by using parts of the model, in order to compare different generations of a product and reveal what the various parts of the manufacture influence,” she says.
“We don’t, however, have any evidence yet that it actually works: the next step is that one of the companies involved in REES will test the method.”
Research into how requirements can be specified for complex systems is scarce, but Saab has worked extensively in the field. This is where Sara Nilsson plans to continue working with system integration.
“I realised after a while that the expertise I had developed makes me attractive on the labour market. Not many people have an understanding for the differences in the various links in the chain: design, engineering and manufacture, and few know how they work,” she says.
“I am, however, hoping to come back to LiU in the future and work as an industry-sponsored PhD student.”
Sara Nilsson will defend her licentiate thesis on 7 December 2017: How requirements development could support design of effective and resource-efficient offerings, Sara Nilsson 2017. The research has been financed within the Mistra REES programme, coordinated by Professor Mattias Lindahl, Division of Environmental Technology and Management and supervised by Professor Mats Björkman from the Division of Manufacturing Engineering.