设计英文论文

Haptic Modelling – An Alternative Industrial Design Methodology?

D.G.Cheshire, School of Engineering and Advanced Technology, Staffordshire University d.g.cheshire@https://www.wendangku.net/doc/058177604.html,

M.A.Evans,

Department of Design and

Technology,

Loughborough University

m.a.evans@https://www.wendangku.net/doc/058177604.html,

C.J.Dean,

Consultant Working for

Sensable Technologies,

chris.dean@https://www.wendangku.net/doc/058177604.html, Abstract

Physical models continue to form an essential outcome from industrial design practice. Whist the professional may be removed from the “hands-on” model build by employing the services of a model-maker, many designers consider such physical interaction as an important part of their idea development process. Visual and tactile feedback from model generation is considered by many as an essential part of the experience of physical interaction with form and material. However, the advent of remote model building technologies via rapid prototyping and computer controlled machining, has given professionals an alternative method of working which offers other advantages to the design process. This has meant that the designer is increasingly removed from such physical interaction with the model.

The emergence of three dimensional digital modelling via haptic feedback devices may offer a route whereby professional designers can gain the benefits of a digital process yet continue to be involved with tactile design modelling. Acknowledging the need to utilise digital design techniques, this paper investigates the capabilities of haptic modelling for use within industrial design practice. The research is based on an industrial design case study for a communication device that was undertaken by the authors.

The paper discusses the attempts made to emulate workshop-based modelling activities with Sensable Technologies Phantom haptic feedback device using Freeform software. Whilst the initial response to the system was not entirely satisfactory, the research identified the potential to use the haptic feedback device to produce forms that would be virtually impossible to specify using traditional digital techniques. Having gained some experience in the capabilities of the hardware and software, creative opportunities emerged that were a direct result of the application of this technology.

1. Introduction

As a profession involved in the definition of product form, industrial designers make extensive use of three- dimensional (3D) models. These may vary in sophistication from relatively simple study models to full prototypes ([1] Knoblaugh 1958 p15, [2] Kojima 1991 p38). The type of model most associated with industrial design practice is the appearance model, which embodies the form of the production item but none of the functionality ([3] Powell 1990 p11).

Prior to the advent of remote model building technologies such as rapid prototyping and computer controlled machining, models would be produced by manual working and craft-based techniques. Some designers take design decisions as they manually manipulate the material, modifying it accordingly.

As professional practice makes increasing use of remote model building technologies, the opportunity for the designer to be directly involved in the shaping of material decreases. This has been shown to be the case with the full range of models, from study models to prototypes ([4] Sharbaugh in Carrabine 1999 p24). In contrast the digital technology that enables remote model building has also enabled increasing use of virtual evaluation whereby 3D computer aided design (CAD) and computer aided industrial design (CAID) systems are used to provide photo-realistic visualisation and real-time animation.

One could argue that the experienced practitioner might have sufficient levels of skill and judgement to bypass the direct interaction with form. Indeed, personal experience has shown that such practice often takes place when deadlines are tight or resources are limited.

However there is a strong groundswell of opinion that tactile product development is beneficial to the final products form and so a way should be found to combine the craft based techniques with digital product development.

Recognising this need the emerging technology of digital modelling using a haptic feedback device may have the potential to develop and encourage the physical manipulation of form on a virtual level. Haptic feedback devices give the operator the “feel” of the virtual object. If the operator moves a cursor onto an object as seen via the monitor, they actually feel its presence via an electro-mechanical system attached to the pointing device.

The authors, having backgrounds as both design practitioners and educators, have explored the nature of haptic modelling, considering its potential for integration into industrial design practice and design education. There follows a record of a programme of research that involved the industrial design of a highly conceptual communication device that was produced as an entry for the Nagoya International Design Competition in May 2000. The structure of the case study follows the three phases of professional practice as identified by Pipes [5], involving concept generation, design development, and specification. These are now explored in some detail.

2. Concept Generation

The brief for the communication device specified that its form should cross the boundaries between what we consider to be jewellery and a consumer product. The design was to have some of the functionality of a mobile telephone, without the transient feel of a polymer consumer product. Concept generation was undertaken using paper-based sketching, examples of which can be seen in Figure 1.

Whilst CAID was available throughout the project, the industrial designer felt that the application of this technology was inappropriate at the concept generation stage due to the lack of spontaneity afforded by its modelling methods. This is identified by Pipes [5] when he states that “Conventional CAD at an early stage can stifle creativity by its insistence that the designer provides the system with exact dimensional and geometric information right from the start”.

A small brooch-like product emerged from the concept generation phase, its form based around an elliptical body with a large answer button. Other functionality was accessed via three smaller buttons positioned on one end. The speaker/microphone was located on the opposite edge.

The paper-based sketches provided the industrial designer with sufficient detail on form and size to progress to the second phase of design development. If operating to a more traditional design methodology, this phase may involve some modelling in “soft” materials such as Styrofoam, or even the manipulation of more resistant materials. For the purpose of the case study,

haptic modelling was to be introduced as an alternative. Figure 1. Concept generation using paper-based

techniques.

3. Design Development

Sensable Technologies based in Boston Massachusetts made the Phantom Desktop input device and Freeform software available. Twin Intel 450Mhz processors with 512MB of RAM were used to run the software, and Sensable Technologies UK consultant provided support.

The Phantom Desktop device can be seen in Figure 2.

Figure 2. Phantom Desktop input device with

Freeform 2 software.

As a precursor to the product being modelled, an exploratory use of the technology was undertaken. This involved an evaluation of the additive and subtractive (Boolean) modelling techniques, along with smoothing operations and manipulation of material density. The move from interacting with a physical object, to a virtual model, was initially found to be an unusual experience. However, as familiarity with the software and system developed, the modelling capabilities of the media emerged. Indeed it soon became apparent that the haptic

modelling system was capable of producing forms that could not be generated using CAID, although the value of these relatively abstract surfaces represent a separate issue. Figure 3 shows one of the models produced during the exploration of the media.

After a period of familiarisation, it became evident that the modelling system could be used on two levels. The first involved techniques closely associated with normal CAD modelling, whereby forms could be generated by non-haptic input e.g. creating standard shapes and modifying by stretching. The second technique was true haptic modelling which had the potential to produce forms via various shaping operations whilst receiving physical tactile feedback.

Following the evaluation of the haptic modeller, which only lasted some 2-3 hours (a credit to the usability of the system), the decision was taken to model the communication device using the using both of these methods. This was particularly appropriate for the communication device, as the basic outer form of the product was easily constructed from primitive shapes combined via Boolean operations. However to fulfil the design brief in removing the typical feel of a plastic injection moulded product the basic form was intended to be enhanced by surface finishes more normally associated with hand crafted products.

The basic outer form was first created in the modelling system by taking a sphere and distorting it to produce the required flat, curved form. Subtracting a suitable scaled cylinder created the central cutout for the ‘answer’ button. The speaker/microphone notches were to be modelled by haptic feedback techniques. The designer was attempting to create the effect one would achieve by taking a scoop of soft ice cream, leaving a cavity with smooth sides. When the operator performed a haptic scooping operation, the surfaces were excessively rippled, as there was no tight control of the motion. This was the first disappointment in the use of the modelling system, which will be discussed later in this paper. The notches were again produced using non-haptic techniques of subtracting forms generated by extruding curves.

At this point it was recognised that the form produced had been developed in the haptic system but had not used any of the benefits of the haptic feedback. The system was being used much like a traditional CAD system. As a parallel test the communication device was modelled using a surface modeller familiar to the operator in less than ? an hour and was imported into the Freeform software via an STL file (a standard file transfer format which transfers the shape information via triangular facets). The imported surface can be seen in Figure 4. This raises questions about the suitability of haptic techniques for developing certain forms. Again this will

be discussed later.

Figure 4. Imported CAID surface.

The surface finish to be applied to the model was not rigorously defined at the concept generation stage as it was intended to explore the possibilities of forming the virtual material using techniques closely related to craft-based interaction. The first finish to be explored was a hammered finish normally applied to soft metals such as copper. The desired result was achieved by using a rounded tool to repeatedly strike the surface. It was important for the operator to understand the parameters that could be varied to affect the material properties of the model. Using a soft material produced very smooth rounded and rather indistinct indentations whereas harder material settings produced shapes that resembled more closely cuts into the surface. The progression of the

hammering can be seen in Figure 5.

Figure 5. Haptic modelling of hammered effect. The haptic system was easily able to take advantage of other digital design techniques seen in other CAD systems. For example the hammer finish was only applied to ? of the model and mirroring reproduced the other quarters. Careful attention was paid to over striking the centre lines to ensure that they did not exhibit any mirror effects.

When completely hammered, the surface looked quite effective but the edges of the hammer marks were considered too sharp so the whole model was smoothed-out to soften corners. The final finish can be seen in

Figure 6.

Figure 6. Final hammered effect.

The final design features, the ‘answer’ button and three function buttons, were once again added using traditional CAD design techniques based on standard primitive shapes and extruded/revolved curves. The completed model was saved as an STL file and exported to a CAID system for rendering. The rendered product can be seen in Figure 7, and as a photomontage with user

in Figure 8.

Figure 7. Rendered hammer finish.

Figure 8. Photomontage of hammer finish product

with user.

4. Specification

The specification of product form to design engineers and manufacturers who are conversant with digital design techniques is relatively straightforward, requiring the transmission of digital geometry in a mutually compatible format e.g. IGES or STL.

The proposition for the hammered product was for a low-volume, jewellery-like product. It would therefore be straightforward to output the surface geometry of the body to an STL file and utilise this information to produce the components in wax using a rapid prototyping system such as Sanders. Investment casting could then be used to manufacture the components as a direct copy of the model.

5. Conclusions

This design project has raised a number of issues, both positive and negative, relating to haptic modelling.

The ease of use of the software makes it very straightforward for even inexperienced computer operators to start modelling very quickly. The software does however require a high level of hand-eye coordination for the tools to be used effectively. This should not be considered as a problem since this skill is expected of designers as part of their repertoire and so they should feel quite at home with the input methods used. It does tend to alienate other groups from using the software. For example, experience with engineers attempting to use the system has shown that in general they lack the skill to operate it effectively although they appreciate the value of tactile feedback.

The apparent ease of use should not disguise the fact there is a technical element to the software that need to be understood. This is especially apparent when dealing

with aspects such as the variable hardness and ‘density’ of the material. Even in the relatively small modelling exercise undertaken for this project it was necessary to vary material properties to achieve the desired results. Although this is relatively easy to achieve in terms of the user interface the user needs to understand the knock on effects such modifications have on the model. For example reducing the ‘density’ of the model enables finer detail to be produced but the size of the storage space for the model increases dramatically (100 Mb files are common) and even using relatively powerful computers performance reduces dramatically. This can be very frustrating to a designer who does not want to be concerned with such ‘technical’ details.

At the beginning of the project, the expectations of the haptic modelling system were high. Assumptions were made that the modelling techniques would be very close to those of conventional foam and clay concept modelling. Unfortunately, the functionality of the software and hardware made it difficult to obtain the surface quality needed for both rendering and production. This was highlighted by the attempts made to produce a clean scoop when modelling the speaker/microphone detail. These shapes were easily reproduced by other techniques but these duplicated more traditional methods of modelling found in traditional CAD systems and so did not benefit from haptic feedback. The fact that the system can model in this manner is advantageous but it is disappointing that haptic modelling could not reproduce the same effects. It is almost an admission that haptic techniques are not yet able to model large smooth surfaces effectively.

Another related area that concerned many operators of the system was the reproduction of sharp edges. This is highlighted in Figure 8, which shows feathering on the

edges of the button cutouts.

Figure 8. Edge feathering.

The method of representing the model in the Freeform software means that edges between surfaces can never be perfectly sharp. They are always feathered to some extent. This feathering can be reduced by increasing the accuracy of the model (with the consequences already mentioned) but will always be present. This always concerns operators as they zoom in to the model closely. In practice the feathering is not a problem as when viewed at normal scale the feathering is not visible and has never shown up in derived rapid prototype models.

The responsiveness of the haptic modelling system to the generation of the hammered effect was impressive. The production of the hammered effect was very closely associated with traditional hands-on modelling, whereby the designer controlled the manipulation of material whilst responding to tactile feedback.

For industrial design practitioners, the findings of the case study indicate that haptic modelling as currently implemented in the Freeform software has its limitations. Whilst the stylistic trends within industrial design require smooth, crisp surfaces, the authors feel that haptic modelling has significant limitations. However, the principle of haptic feedback being used in the model process is unquestionable and when the product shapes being designed are appropriate then the Freeform software and haptic modelling are the only realistic modelling method. The only alternative method for reproducing the hammered finish would be to use greyscale pictures to generate a bump mapped surface but the results are unlikely to be as effective. One can only assume that future development in the hardware and software for haptic modelling will address the shortcomings identified in the case study. Further work will then be required to re-evaluate such capabilities.

In terms of the generation of random, almost craft effects, haptic modelling has much to offer. The authors feel that such a system may be of interest to practitioners in may areas of design such as jewellery. This would be particularly relevant if the virtual material could emulate the characteristics of precious metals that may be too expensive to use. Indeed it may be possible to use haptic modelling to practice on a virtual material before working on the real (and expensive) precious metal.

6. Bibliography

[1] R R Knoblaugh, Modelmaking For Industrial Design,

New York, 1958.

[2] T Kojima, S Matsuda, Y Shimizu, M Tano, Models & Prototypes, Graphic-sha Publishing, Tokyo, 1991.

[3] D Powell, Presentation Techniques, Macdonald London, 1988.

[4] Sharbaugh in Carrabine, C3, Media Directories International, London, March 1999.

[5] A Pipes, Drawing For Three Dimensional Design, Thames and Hudson, New York, 1990.