Integrated Product Gestalt Design Method for the Analysis and Definition of Interface Elements Regarding Exterior and Interior
The exterior and interior of products are often considered as independent systems in the development process. But both the interior and the exterior gestalt are of great relevance for the usage and perception of a product. As a consequence of technological advance, such as increased automation, the borders between exterior and interior are becoming blurred. The Integrated Product Gestalt Design Definition proposed in this paper facilitates the consideration of the interrelations between and resulting complexity of different aspects of a gestalt integrating exterior and interior. We therefore distinguish between the subgestalts layout, shape, colour with surface and graphics to describe both the exterior and interior. The interdependencies between interior and exterior are characterized by functional-technical and aesthetical aspects. To derive essential relations between the exterior and interior view different products, covering investment goods and consumer goods, are analyzed. This analysis reveals the most common relations between the exterior and interior systems and allows for finding recurring patterns of relations between exterior, inner space and interior. This is a prerequisite for the predictive quality of the Integrated Product Gestalt Design. Thus, the approach facilitates the next step of a guided implementation of a method for the development process by highlighting the links between the disciplines.
KeywordsExterior and interior Development process Ergonomics
Vehicles are prominent product examples, for which both the exterior and the interior play a significant role during the design process. It is also clear from the example of the vehicle that the exterior and interior are often viewed and handled separately during the design process. This already commences with established vehicle design processes, where different design departments are responsible for the exterior and interior design .
Mega trends like digitalization or urbanization result in new requirements challenging existing product concepts, like e.g. in cars . Looking at the definition of the interior and exterior of a product disruptive change is to be expected in the future due to both technological progress and social changes. For example, a contribution to a more sustainable mobility is realized by electric drive trains and disruptive changes to single technical components. These changes are affecting, for instance, the installation space. In order to gain use of new design options, the packages have to be defined from scratch with effects on the interior, exterior, ergonomics and other properties. But this also affects the aesthetics of the product, since proportions and existing product specific harmonic relations are changed . Another example is an automated vehicle, where the interior will grow in importance for its use  and where the degree of freedom in designing an interior will also change . So it is foreseeable that the appearance and importance of the vehicle interior will also implicate changes of the exterior. The perception of the exterior can even influence the perception of the interior, so that “a tight, noisy, hard and poorly equipped sports car may cause environmental and ergonomic discomfort and [still] be a favorite car at the same time as the viewer is conditioned by visual information.” .
Other products where the interaction between the exterior and the machine interior is important are, for instance, machine tools. On the one hand, the exterior is important for the way the tool is operated and on the other hand due to safety regulations and design reasons, the interior of the machine has to be subject of the design process. It is thus evident that the boundaries between the exterior and the interior are becoming increasingly obliterated when handling them within the design process.
In order to better understand the mutual development of exterior and interior, the approach of the Integrated Product Gestalt Design (IPGD) is introduced. In Sect. 2, important definitions concerning the exterior and interior of a product are introduced. Therefore, a detailed distinction of the product gestalt into gestalt-views and subgestalts is presented. Based on these definitions it is possible to analyze the exterior and interior of different products (Sect. 3). For a detailed analysis, different vehicles for water, land and air were chosen. It was furthermore examined between which subgestalts interdependencies are observable. So the main goal of the introduced approach is to structure and highlight the interactions between these views and their subgestalts in order to support the collaboration of designers and engineers during the design process. Therefore, this research focuses on the technical-functional and formal-aesthetic interaction following this hypothesis: Understanding the interaction between exterior and interior design will support the identification of fields to focus on within the interdisciplinary work between engineers and designers and will help the latter to define trade-offs during the design process .
2 The Parameters of the IPGD-Method
The IPGD-Method is based on a sophisticated understanding of the product gestalt. According to Hammad, the gestalt of technical products is the ostensive, spatial and visual, noticeable appearance of the entity or the organized structure of a three-dimensional figure . The use of the German term “gestalt” for the appearance of the product in this study has two main reasons. On the one hand, there is no adequate equivalent in the English language [9, 10], and the denotation of the term “shape” constitutes too much of a reduction to a single aspect of the gestalt. On the other hand, the term “shape” is supposed to be one of the subgestalts alongside other subgestalts, which are introduced below in Sect. 2.2. Subsequently, the gestalt-views exterior, interior and the inner space are presented as well as the interrelations between these views. The subgestalts and the gestalt-views include the parameters for the description and analysis of the exteriors and interiors.
2.1 The Gestalt-Views Exterior, Interior and the Inner Space
Some technical products also have a perceptible inner appearance. This is the case when the observer or user is placed inside the product and the corresponding gestalt-view is called the interior. A typical example is the driver’s cabin of a car (see Fig. 1). The interior is – unlike the exterior – not inevitably existent for every product. A third view of the gestalt is the inner space describing the parts of the gestalt that are visible from neither the exterior nor the interior view. It is located between exterior and interior and often contains technical components (parts and assemblies) which are necessary to realize functionality. The components of the inner space are normally not perceptible to the user of the product, but are essential for the function of the product as a whole.
2.2 The Subgestalts
The most abstract subgestalt called layout (L) is a view describing the basic assembly of the product, so that the cup is a mere buildup of a big and small cylinder. A specification of this subgestalt is defined by the shape (S), which includes lines and surface transitions. As shown in the example the cup is tapered and raised. The third subgestalt colour and surface (CS) includes texture elements and the fourth also includes graphics (G) with symbols and letters like the coffee bean in the example. The subgestalts can be used to precisely describe the interrelations between the different gestalt-views.
2.3 Technical-Functional and Aesthetic Interrelations
technical-functional interrelations between exterior, interior and inner space
aesthetic interrelations between exterior, interior and inner space
3 Integrated Gestalt Analysis of Different Products
With the definitions and theoretical knowledge of interior and exterior an analysis of the interior and exterior of different products could be operationalized. It is firstly described how the analysis was carried out (Sect. 3.1) and secondly the results showing the interdependencies between interior and exterior are presented. At this point it is also considered in what way the interior and exterior are connected, which means that it will be apparent which subgestalts and technical-functional and aesthetic interrelations are involved.
The examination of interrelations is similar to the depiction of interrelations of Lindemann  or the design structure matrix of Browning . It is only examined whether a change determination exists. The quality or intensity of interdependency is not evaluated in this context. It is more about determining where there is a connection at all.
There also exists an approach that tries to align the interior with the exterior . A generally applicable understanding of the interrelationships between interior and exterior is not the focus of that study, however. The approach in the present study is intended primarily to clarify and define the interrelations and to connect the two thematic priorities of interior and exterior so that engineers, designers and ergonomists can holistically design the increasingly merging worlds of interior and exterior. As already described, the major aim of the analysis is to identify from the variety of the vehicles examined whether there are differences with regard to the product categories. The second aspect is focusing on the type of interrelations between exterior and interior. This raises the question of whether certain interrelations such as the interface occur frequently and if so which subgestalts are involved?
3.2 Examples of Vehicles with Interrelations of Exterior and Interior
Numerous vehicles have been analyzed using the different elements of the gestalt described before. Vehicles are used as examples since they usually have a distinctive exterior and interior. The consideration of vehicles from different fields takes into account that a balanced picture of the respectively varying importance of the exterior and interior is included. Within the analysis, seven land vehicles, two aircrafts and one watercraft were considered. The choice of land vehicles included classic consumer products such as the Audi S4, the Mercedes-Benz C-Class Cabriolet and the Pickup Ford Raptor. The rather unusual vehicle KTM X-Bow was also analyzed as a land vehicle, because of its open interior and its special relation between exterior and interior. Finally, investment goods such as a Claas Axion, the Mercedes-Benz Bus Tourismo or the Voegele tar machine were analyzed. The used aircrafts were the Airbus H155 Civil and the Bombardier CRJ1000. The vessel used was the yacht Princess 62.
It is particularly interesting to see where the interface plays a special role. This concerns vehicles in which the relative position and thus the appearance of the exterior in the vehicle interior play a major role, such as in aircrafts or agricultural machines. One example of this is the conversion of the lateral inclination via an appropriate miniaturization of the aircraft in the interior. All in all, it can be seen that the technical-functional aspects make up a large part of the interdependencies on many vehicles.
This is a typical example, as the radiator grille is still a very distinctive element of vehicle design and Design-DNA [11, 13], and it is likely that this will continue to be the case, even though its objective might change with the use of electric vehicles . Here, we can also see the link between functional-technical and aesthetical aspects of the interdependencies. This connection is not part of the IPGD but will be considered in further research projects.
3.3 Analysis of the Overall Interrelations Concerning the Different Subgestalts
The analysis was focused on different products; a quantitative weighting of the observed interrelations was not conducted. As a result, no statement about the frequency of interdependencies within the products is possible. However, it becomes clear which substructures are fundamentally important across different products.
It can be discerned that the most connections occur between same subgestalts, such as layout to layout or shape to shape. This relation was to be expected, because the technical-functional or aesthetical links often can be found in the same subgestalt. But it is furthermore interesting to see that there are many interdependencies within the Design-DNA. This elucidates how important the relationships between exterior and interior are already today. A stronger technical-functional connection between the exterior and the interior will in all likelihood also increase the aesthetic connection between the exterior and the interior. As explained below, an in-depth understanding and a software-based operationalization of the links is therefore expedient.
This work formulates a precise definition of the interior and exterior gestalt. For this purpose, the view of the interior and the exterior of the gestalt including the inner space were presented. A detailed definition of both the interior and the exterior is provided by the subgestalts layout, shape, colour with surface and graphics. The relationships between interior and exterior were specified by technical-functional and aesthetic interrelations. These design definitions render the analysis and comparison of different products possible, which in this case were performed for vehicles. In the case of investment goods, the technical-functional interdependencies usually predominate; for consumer goods, the aesthetic aspects in the form of Design-DNA also have a major influence. In the overall view of all subgestalts, the interrelations of the same subgestalts predominate. Future technological advancements and requirements will in all likelihood increase the magnitude of the technical-functional links between the exterior and interior, which might in turn increase their aesthetic connections.
Based on the presented definitions and gained knowledge, a methodical procedure will be derived. To this end, it should be investigated which interrelations are important in the development process at which stages. For a meaningful presentation of the links during the development process, a software solution should be developed, which also ought to be linked with other software tools in the development process. Since this is an interdisciplinary topic we are planning on cooperating with project partners from other stakeholders of the product development process.
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