User-centred systems design engineering 91

According to the (INCOSE) definition of Systems Engineering (SE) [87], ‘SE is an interdisciplinary approach and means to enable the realization of successful systems. It focuses on defining customer needs and required functionality early in the development cycle, documenting requirements, then proceeding with design synthesis and system validation while considering the complete problem [87]. A Systems

Engineering approach to the design of a product or service ensures the creation and execution of an interdisciplinary process that guarantees the customer and stakeholder's needs are satisfied in a high quality, trustworthy, cost efficient and schedule compliant manner throughout a system's entire life cycle [87]. This process is usually comprised in parallel through a series of tasks, which are outlined in the diagram below.

Figure 2.9. The Systems Engineering Process from A. T. Bahill and B. Gissing

This thesis will be based on contributions to user centred-design and systems design engineering for product development made by ulrich-eppinger [88], Dieter [89], Taguchi [90] and Otto & Anthonson [91]. User-centred design (UCD) is a type of user interface design and a process in which the needs, wants, and limitations of end users of a product are given extensive attention at each stage of the design process. The user-centred design process is a multi-stage problem solving process that requires analysis and optimization of the product across capability, desire, and needs of users in respect to usability of the product rather than forcing the users to change their behaviour to accommodate the product.

The international standard for human-centred design process (ISO13407) defines a general process for including human-centred activities throughout a development life-

cycle. In this model, once the need to use a human-centred design process has been identified, four main stages comprise the user-centred development procedure:

• Identify and specify the context of use: Identify user of the product, purpose for use, and conditions of operation or usability.

• Specify performance requirements or user goals that must be met for the product to be successful.

• Create design solutions through developmental stages building from a preliminary concept to a complete design.

• Evaluate designs through usability testing with authentic users of the product

Systems engineering recognizes the following seven tasks: State the problem, Investigate alternatives, Model the system, Integrate, Launch the system, Assess performance, and Re-evaluate. These functions can be summarized with the acronym SIMILAR: State, Investigate, Model, Integrate, Launch, Assess and Re-evaluate [87]. Similarly, the UCD activities are broken down into four phases: Analysis, Design, Implementation and Deployment, with suggested activities for each phase [92]. For the application of design customisation of sports wheelchairs for the individual athlete, the extent to which systems engineering and user-centred design will be applied, will be limited to the ‘design methodology’ as product outcome for this application. According to a wheelchair-user combination optimisation study by Vegter et al. ‘there is no single ultimate design in general, but there is always a design that is adjusted to the user’ [31]. To fully understand the needs and requirements of the user ‘as the research develops’ this thesis will involve primary qualitative and quantitative data collected directly from the end-user (wheelchair rugby athletes and coaches) at the research phase of analysis which involve strategy and product planning (Chapter 3), design of experiments and testing (Chapter 4,5,6) in the design phase, and validation of results (Chapters 6,7) in the implementation and deployment

phases. This approach will enable the development of an appropriate wheelchair- design process to suit individual user’s demands.

In general, systems design engineering focuses on how to design and manage large and complex engineering projects during design development. Generally a systems engineering approach to the design of a specific product will assist the consideration and coordination of different areas of the complex product design such as reliability, logistics, coordination of different teams, and evaluation measurements. Systems engineering ensures that all likely aspects of a project or system are considered, and integrated into a whole by involving tools for work-processes, optimization methods, and risk management in complex projects in ensuring an end user-centred focus (satisfying user needs) throughout the development process. To this end, this investigation will make use of the following key methods for reliable user-centred research:

Qualitative function deployment (QFD): One of the well-known methods in systems

design engineering to gather and deploy product user’s data in the product development process is the qualitative function deployment (QFD) method [88, 89]. The QFD method has been used in the areas of sports technology [93] and daily wheelchair design [94] previously, to enable the identification of correlations between user requirements and product attributes, as well as to establish the relative importance to each other. There are other more simplistic approaches to qualitative analysis of user needs, which involve user needs matrixes. However, the QFD method includes positive and negative correlations between customer requirements and technical parameters of the product; which in the case of the current design intent are reflective con design parameter trade-offs providing a numerical value of correlation

and focus scale for design decisions as QFD result outcome. Hence, it will be useful to adopt this approach in the same fashion during research/product planning. The user-centre approach ensures that user’s functional requirements in terms of comfort, safety, and performance are assessed and validated as the investigation progresses.

Design of experiments (DOE): (also known as factorial design) is used as a

systematic approach to finding a combination of design parameters that best suit the requirements of the individual athlete. DOE is commonly used as a technique for investigating all possible conditions in an experiment involving multiple factors and levels of measurement; in this study, the experimental design investigates the influence of wheelchair key dimensions (design factors) on desired performance variables. However, the DOE for this application requires careful analysis; in a standard DOE, both the number of experiments and the size of the data sample required to gain statistical significance increase with the number of design factors and dimensional levels tested. This represents a limitation for the sports wheelchair design application as the data sample can be highly affected due to the variability associated to nature of the human subjects, posing a higher data sample requirement on an experimental design based on repetitive testing of athlete subjects who are prone to fatigue. Hence, the numbers of design factors and dimensional levels to be tested need careful consideration.

Taguchi method: The Taguchi method is applied to overcome the issues associated

with a full factorial design and repetitiveness of testing with athlete subjects [89], as it simplifies and standardizes fractional factorial experimental designs by using standard orthogonal arrays [95]. Orthogonal arrays tests pairs of key controlled design combinations allowing: a) the collection of the required data using a minimum

amount of testing, b) identification of the individual contribution of each design factor on a particular quality characteristic (in this case propulsion performance) which is a kind of analysis that cannot normally be performed in other experimental designs [89]. Additionally, the Taguchi method emphasizes the importance of minimizing variation to improving the quality of the product by taking into consideration the likely influence of ‘error’ or ‘noise’ on the performance of the final product [96]. In product design, noise factors are described as design elements which are expensive or difficult to control [97]. The idea is to reach higher quality designs that are less sensitive to changes in operating conditions or environments [97]. The ‘noise’ in the current study is the ‘variability’ with respect to a) the athlete’s performance across experimental trials, and b) the variability of the performance of athletes within a group. The challenge in engineering a DOE for a specific market or product application is in finding the right balance between the theoretical design of the tests, and their practical implementation in the product’s environment [98]. Hence, for any Taguchi design, it is essential to have a deep understanding of the problem at hand in order to identify the source of noise in the system. Herrmann presented an engineering approach to designing a product highly affected by uncontrollable noise [98]; where the main focus was to analyse and define the specifications of the parameters that would eventually control the product's output performance using separate arrays for noise and design factors, instead of the ordinarily preferred combined inner and outer arrays for noise tests. This approach can be transposed to the current study allowing noise to be post-measured rather than predetermined; eliminating the difficulty of quantifying noise factors that are undetermined and athlete subjective prior to testing. This approach is validated through Taguchi’s variation noise and turning parameter measurement [99]. Variation noise is the type of noise that is not due to the operating

environment or to the product architecture, but due to variations in the supplied materials and manufacturing processes. Respectively, turning parameters are often set in Taguchi designs by the manufacturing company or the ‘product user’ once the confounding effects of the noise have occurred [91].

In the current case, variation noise is non-quantifiable prior to testing as it is related to athlete's physical capacity, which is a dependent of athlete’s classification category, fatigue, and comfort. Henceforth, to account for confounding influences of the noise parameters and to compensate for the lack of predetermined noise levels, turning parameters are introduced as qualitative ergonomic assessment of comfort and fatigue at the end of each experimental design trial.

Chapter Summary

The aim of this chapter was to establish the theoretical framework surrounding the design and customisation process of court based sports wheelchairs. The review of the literature presented in this chapter highlighted research findings that are relevant to this research. Particularly, this chapter partially addressed the first research question in this thesis from the perspective of the specialists and scientists in the field of wheelchair propulsion. The first research question refers to the principal concepts of interest for wheelchair configuration of the sports wheelchairs. The literature reviewed included sports wheelchair designs and configuration effects on the system’s performance, biomechanics propulsion, vehicle mechanics, and performance demands across court-based wheelchair sports. In addition, the review included dynamic and static models and tests that have been performed for athlete’s characterisation of performance, results obtained and correlation to biomechanical analysis of athletes. This chapter identified the body of knowledge relevant to this investigation and established the knowledge base for the methods developed in this thesis.

Most importantly, the knowledge generated through this chapter includes state of art knowledge on the potential of a systematic and evidence-based design method applicable to wheelchair design; capable of merging all confounding effects of the wheelchair configuration process for individual users and sports. As evident from the literature and as stated by some of the reviewed specialists research groups in wheelchair propulsion biomechanics; the main challenge of sports wheelchair configuration is on enabling the conjunct application of the many research findings for a practical outcome due to the numerous differences in methodologies, studied populations, wheelchair characteristics, and outcomes measured, in the available literature. [51], [14], [49].

Additionally, the review of the literature highlighted a few methods that might be useful for implementation in some of the fundamental research stages outlined in Chapter 1. Primarily during data collection, the methodological consideration highlighted in this chapter will be taken into account as they have shown a positive impact in previously reported studies and their use is within the scope of the research presented in this thesis.

Finally, this thesis has a particular focus on wheelchair rugby. The level of specificity required for wheelchair rugby is an example of the level of comprehension required to undertake focused research in any other court-based wheelchair sports.

Chapter 3. Identification of Performance and Design