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Descubra todo lo que Scribd tiene para ofrecer, incluyendo libros y audiolibros de importantes editoriales. Kristin L. Development of a Functional Basis for Design Functional models represent a form independent blueprint of a product. As with any blueprint or schematic, a consistent language or coding system is required to ensure others can read it. This paper introduces such a design language, called a functional basis, where product function is characterized in a verb-object function-flow format.
The set of functions and flows is intended to comprehensively describe the mechanical design space. Clear definitions are provided for each function and flow.
The functional basis is compared to previous functional representations and is shown to subsume these attempts as well as offer a more consistent classification scheme. Applications to the areas of product architecture development, function structure generation, and design information archival and transmittal are discussed.
Functional modeling is a key step in the product design process, whether original or redesign. This article reports on an inductive approach to create a common design language for use with functional models, focusing primarily on the mechanical and electromechanical domains. The common design language is termed a functional basis. It allows designers to describe a products overall function as a set of simpler sub-functions while showing their connectivity.
With such a set, designers can communicate product function in a universal language. Several factors motivate the creation of a functional basis for mechanical design. In particular, use of the functional basis described in this article significantly contributes to the following six product design areas. Product architecture development. The desire to move the product architecture decision i.
A modular architecture is then formed by grouping sub-functions from a functional model such as a function structure together to form modules. The modules identify opportunities for function sharing by components and lead to alternative layouts where concept generation techniques may be used to embody the layouts.
To systematically explore product architecture possibilities across a wide variety of products, a common functional design language is needed. Systematic function structure generation. The most common criticism of functional models particularly their graphical representation known as a function structure is that a given product does not have a unique representation.
Even within a systematic function structure generation methodology, different designers can produce differing function structures. A common set of functions and flows the connectivity of the products function significantly reduces this occurrence. It also provides a consistent basis for developing high-level physical models, and for teaching the abstract concepts of functional modeling to engineers.
Archival and transmittal of design information. Products are transient; their service lives range from days to hundreds of years, but are nevertheless transient. The design process behind a product is even more fleeting. The creation of each new product, though, adds to the collective design knowledge and needs to be recorded in a consistent manner.
A functional model is an excellent way to record and communicate design information. To do so consistently, a common set of functions and flows with clear and timeless definitions is necessary. Manuscript received August Associate Technical Editor: Jonathan Cagan. Comparison of product functionality. Few product designs are truly original.
Instead, they incorporate elements of other product designs that have accumulated in the corporate body of design knowledge. If functional descriptions of products, expressed in a common language, are accumulated in a repository, then that repository can be searched to find products similar in function. This offers obvious applications to benchmarking products and searching for form solutions. Creativity in concept generation. The ability to decompose a design task is fundamental to arriving at creative solutions 3.
Likewise, it is critical to represent abstract and incomplete information to make decisions early in a design process or product development. Functional models, with the addition of a functional basis, significantly aid the capacity of design teams to break problems down and make critical early decisions.
Product metrics, robustness, and benchmarks. An important aspect of product development is to formulate objective measures for benchmarking and quality endeavors. Functional models can greatly enhance methods, such as Quality Function Deployment, in identifying and choosing metrics. The flows or connections of functional models provide a high-level physical model of a products technical process. These flows, if suitably formalized, are directly measurable, reducing the guesswork and artistic nature of choosing metrics.
The scope of this article is limited to the functional modeling portion of conceptual design. Section 2 provides a glossary of common functional modeling terms. In Section 3, we review the design research leading up to the functional basis, which is presented in Section 4. A functional modeling methodology is given in Section 5 to demonstrate the placement of the functional basis within the design process. However, the functional basis for mechanical design presented in this article can be used across many methodologies.
The end result is always a functional model of a product expressed in a common design language, as the example in Section 6 demonstrates. The following terms are used throughout the article in reference to various parts of the design process. They are defined here for clarity. Sub-function: a description of part of a products overall task product function, stated in verb-object form. Sub-functions are decomposed from the product function and represent the more elementary tasks of the product.
Downloaded 22 Jul to Function: a description of an operation to be performed by a device or artifact, expressed as the active verb of the sub-function. Flow: a change in material, energy or signal with respect to time.
Expressed as the object of the sub-function, a flow is the recipient of the functions operation. Functional model: a description of a product or process in terms of the elementary functions that are required to achieve its overall function or purpose. Function structure: a graphical form of a functional model where its overall function is represented by a collection of subfunctions connected by the flows on which they operate. Functional basis: a design language consisting of a set of functions and a set of flows that are used to form a sub-function.
In function-based design methodologies, functional modeling of a device is a critical step in the design process 4,5. The systematic approach of Pahl and Beitz 4 and Hubka 6, which represents European schools of design, has spawned many variant methodologies in recent American design literature 3, Similarly, the field of value engineering has significantly advanced our understanding of basic functions, especially with respect to economic measures Regardless of the variation on methodology, all functional modeling begins by formulating the overall product function.
By breaking the overall function of the device into small, easily solved subfunctions, the form of the device follows from the assembly of all sub-function solutions.
The lack of a precise definition for small, easily solved subfunctions casts doubt on the effectiveness of prescriptive design methodologies such as those by Pahl and Beitz 4, Ullman 3, and Ulrich and Eppinger 7 among engineers in more analytical fields. For instance, within a given methodology how does one reconcile different functional models of a product generated by different designers?
Typically, such differences arise from semantics or poor identification of product function. The development of a standard set of functions and flows referred to here as a functional basis, others may call it a function taxonomy and a systematic approach to functional modeling offers the best case to erase remaining doubt.
Much of the recent work on a functional basis stems from the results of value engineering research that began in the s Value analysis seeks to express the sub-functions of a product as an action verb-object pair and assign a fraction of a products cost to each sub-function.
Sub-function costs then direct the design effort specifically, the goal is to reduce the cost of high value subfunctions. However, there is no standard list of action verbs and objects. Recognizing that a common vocabulary for design was necessary to accurately communicate helicopter failure information, Collins et al.
Here, the mechanical functions are limited to helicopter systems and do not utilize any classification scheme. As systematic, function-based design methodologies gained influence, the development of function taxonomies continued.
Now, though, the development is based on the related needs for a clear stopping point in the functional modeling process and, hence, a consistent level of functional detail. Pahl and Beitz 4 list five generally valid functions and three types of flows, but they are at a very high level of abstraction.
Hundal 18 formulates six function classes complete with more specific functions in each class, though does not claim to have an exhaustive list of mechanical design functions. Another approach uses the 20 subsystem representations from living systems theory to represent mechanical design functions Malmqvist et al.
TIPS uses a set of 30 functional descriptions to describe all me Vol. Kirschman and Fadel 22 propose four basic mechanical functions groups, but vary from the standard verb-object sub-function description popular with most methodologies. However, this work appears to be the first attempt at creating a common vocabulary of design that leads to common functional models of products.
Building on the above work, the concept of a functional basis is described in this paper, significantly extending our previous research 13,23, A functional basis is a standard set of functions and flows capable of describing the mechanical design space for our focus. Our work expands the set of functions and groups them into eight classes. Also, for the first time, a definition for each function is given.
This initial functional basis subsumes all other classification schemes discussed above along with the 30 basic sub-functions found in TIPS. It is from this point that the functional basis in this article picks up. Accepting the functions of Little, we add a standard list of flows with definitions in Section 4. In addition to conceptual design work, functional models represent a means of archiving and communicating design knowledge. Altshuller 21 recognized that patents provided a valuable store of design knowledge while developing TIPS, but are not easy to search or categorize.
Currently, product databases are being developed that facilitate easier search and retrieval of product design knowledge, all based on a standard set of functions and flows
Development of a functional basis for design.pdf
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