The Use of Virtual Prototypes in Product
The use of virtual prototyping techniques can lead to competitive advantages in product development (Bernard, 2005; Cecil and Kanchanapiboon, 2007; Zorriassatine et al., 2003) The purpose of this literature review is to provide an overview of the methods and technologies that currently come under the banner of virtual prototyping, and to provide examples to illustrate the reasons why it is considered to be useful in reducing the time and cost to market. The potential shortfalls will also be discussed and where possible, examples of future solutions to these problems given.
2. What is Virtual Prototyping?
2.1.Characteristics and Methods
There is no single definition for the meaning of the terms "virtual prototyping," "virtual prototype" or the functions that a virtual prototype (VP) should include (Zorriassatine et al., 2003).
A paper by Pratt (1994) is considered to be one of the first to discuss virtual prototyping (Zorriassatine et al., 2003). In it, the purpose of a VP is described as to "provide answers to engineering questions" and computer models in the form of computer aided design (CAD), finite element (FE) simulation and graphical simulation models are all considered to be forms of VP (Pratt, 1994.)
Chua et al. (1999) further refines the definition of a VP from this broad consideration to be the usage of a CAD model to simulate a physical entity, such that analysis can be performed. FE analysis, mechanical simulation, form, fit, and interference checking, the application of virtual reality (VR), cosmetic modelling and ease of assembly are defined as the functional analyses to be performed (Chua et al., 1999)
Cecil and Kanchanapiboon (2007) also includes the application of VR as one of 4 characteristics of a VP, the other 3 essentially encompassed by the definition given by Chua et al. (1999) VR is listed as a key and essential characteristic (Cecil and Kanchanapiboon, 2007).
Zorriassatine et al. (2003) however, rejects the mandatory inclusion of VR on the grounds that it is not essential for all the desired tasks previously described, and instead classifies a VP as a non-physical model which uses computer aided engineering (CAE) software to achieve an objective. Five classes of objective are identified, within which the method used may include the use of VR alongside other tools;
b) fit and interference of mechanical assemblies,
c) testing and verification of functions and performance
d) evaluation of manufacturing and assembly operation
e) human factor analysis(Zorriassatine et al., 2003, pp 516)
As well as the use of CAE tools and software, and VR technology, a VP may also utilise haptic interfaces to provide a tactile experience and force feedback (Cecil and Kanchanapiboon, 2007).
The initial usage of virtual prototyping technologies was pioneered by the aerospace and automotive industries due to the initial cost of development (Zorriassatine et al., 2003). It is now suggested that it would be beneficial for small and medium enterprises to utilise techniques to provide competitive advantages (Zorriassatine et al., 2003).
Cugini, Bordegoni & Mana, (2008) recently speculate on the possible use of VPs in the fashion industry, to allow extensive virtual simulation of fabrics and designs. Tooling & Production (2006) details the advantage of use of VPs and CAE by a consumer tabletop gaming company, which had previously relied on traditional techniques.
Some key benefits of utilising VPs are discussed in Cecil and Kanchanapiboon (2007), Zorriassatine et al. (2003) and Jimeno & Puerta (2007). They include that the use of VPs allows the development time and cost to be reduced, since the production of multiple is VPs faster and cheaper than physical prototyping. Their use allows the effective use of concurrent engineering techniques; VPs can be more easily modified than physical prototypes, simulations can be run throughout the development process. Problems can be identified in the early development stages, resulting in a reduction in the cost to rectify them. (Chua et al., 1999 and Cecil and Kanchanapiboon, 2007).
VP use allows the simulation of multiple scenarios or configurations at reduced cost compared to the creation of physical models Jimeno & Puerta (2007), as demonstrated when applied to an assembly sequence in Yin, Ding & Xiong (2004).
The use of VPs also allows ease of communication through the ability to create realistic 3-D graphical representations (Zorriassatine et al., 2003) This is especially so between groups separated by geography, where collaboration using physical prototypes is particularly difficult, but a VP can be easily shared (Jimeno & Puerta, 2007). The development of the Dassault Falcon 7X business jet using VPs shows these benefits leading to tangible results, as manufacturing and tool costs were halved and the use of simulations resulted in the first production aircraft being without fault (Reid, 2005). Design World (2007) also highlights the possible cost and time reductions in the design of exhaust components, such that the introduction of virtual prototyping methods contributed to a reduction of cost per test iteration from $10,000 to $400, and a reduction in overall design time of between 20 to 30%.
Tooling & Production (2006) describes a tabletop gaming and miniature figurine company using haptic modelling to create VPs in the virtual sculpts of figures, compared to traditional solid hand sculpting techniques. Being able to pass this data directly to manufacturing has resulted in a reduction of time to produce mould tooling by a factor of 5 to 10.
A use of VPs in ergonomic simulations of a manufacturing assembly process reported by Dukic, Rnnng & Christmansson (2007) indicates that many potential problems were able to be identified earlier than would be achievable otherwise, and such identification meant that they could be consequently solved before entering the physical domain.
4. Shortcomings and Possible Solutions
A study by Dukic, Rnnng & Christmansson (2007) on the application of virtual prototyping simulations to manufacturing processes highlights the current difficulties in visualization of 3-d space and human/machine interfaces when dealing with virtual simulations. There were limitations when using the virtual simulation in judging distance and relating virtual data to reality, especially forces, pressure and sound. To counteract this, Ha et al. (2009) demonstrate the use of a haptic device incorporating both sound and touch feedback to improve the user experience when interacting with a virtual prototype.
The challenges of judging distance accurately were also by revealed in a study whose aim was to evaluate the ability to distinguish errors in geometry using a simulation (Wickman & Sderberg, 2007). The results reveal that the best solution depends on the problem itself, and the suggestion is that each individual problem is best solved by a separate model. It is not sufficient to aim to recreate a photorealistic reality; better results can be achieved by some augmentation of reality such as the use of artificial colours (Wickman & Sderberg (2007).
On the other hand, Dukic, Rnnng & Christmansson (2007) warns against the augmentation of reality as creating other problems when using a virtual prototype to visualize the feasibility of a task, and also discusses the limitations of virtual prototypes in detecting hazards such a sharp edges.
When attempting to create a virtual prototype of a manufacturing system, Vera, West & Harrison (2009), raise the issue that CAD models sometime provide more detail than is needed for the purpose of creating an effective prototype, resulting in increased complexityand time to model. The approach taken was to separate the geometry (provided by the CAD model) from the description of the kinematics (generated separately) to reduce the modelling time, which led to advantages in simulating different configurations. (Vera, West & Harrison, 2009).
Virtual prototyping is a rapidly developing field, indeed there is no one comprehensive description of the characteristics of a virtual prototype and the analytical methods involved. What can be seen is that their use can deliver key benefits in the product development process, centred on a reduction in cost and time to reach final production. They achieve this through ease and flexibility of modification. There are disadvantages compared to the use of physical prototypes focussed on a lack of functionality of human-computer interfaces, to represent real world sensations. As technology develops, so these shortcomings may be mitigated in time.
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