Design Studies 2005

An evaluation of haptic feedback modelling during industrial design practice Mark Evans, Department of Design and Technology, Loughborough University, Leicestershire, LE11 3TU, UK David Wallace, Room 3-455, Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts, 02139, USA David Cheshire, School of Engineering, Staffordshire University, Stafford ST18 0AD Bahar Sener, Department of Industrial Design, Middle East Technical University, Faculty of Architecture, Ankara, Turkey ABSTRACT Whilst new technologies in designing and rapid prototyping offer demonstrable benefits, their use can remove the potential for the designer to actively engage in the definition of form through tactile interaction with a physical material (as when working with foam or clay). This paper investigates the use of a haptic feedback device to facilitate interaction with virtual geometry and provide the designer with tactile cues during product modelling. The study concludes that limitations in the modelling capabilities of commercial haptic feedback technology restrict its ability to make a significant contribution to industrial design practice. Keywords: case study, computer-aided design, design practice, modelling, industrial design, conceptual design As a profession with responsibility for the appearance and human interface of manufactured products, industrial designers engage in the manipulation of form using a variety of two dimensional (2D) and three dimensional (3D) techniques. Whilst these may range from simple pencil sketches to sophisticated working prototypes, the advent of 3D computer-aided design (CAD) in the late 1980s has led to an increasing role for virtual modelling methods in professional practice. Reasons for this involve commercial pressure to reduce new product development (NPD) lead times and the efficiency gains achieved through the use of such technologies (Erhorn and Stark, 1994; Pasternack, 1999). However, increases in the use of virtual 3D modelling methods has not been without criticism: ‘designers are a notoriously touchyefeely lot to whom the ideal creative process is a multi-sensory one that supports direct, physical control of the artistic media. Traditional computer graphics don’t allow this. By adopting a 2D mouse or stylus as their design implement, artists have had to stifle their natural impulse to tactically explore and manipulate their creations’ (Mahoney, 2000).

1 Background The shaping of material by hand as part of the form-giving process has been at the core of industrial design education since the founding of contemporary design pedagogy at the Bauhaus after the First World War (Heskett, 1980; Whitford, 1984) and continues to the present day (Industrial Designers Society of America, 2001). When using workshopbased model making techniques, industrial designers have the opportunity to use their hands in the tactile exploration and development of form. This physical interaction with material has the potential to guide the designer’s decision making and direct, to varying degrees, the evolution of the design. In response to the increasing use of virtual design methods, McCullough (1998) cites the inability of computer systems to allow the user to more fully engage in the task being undertaken: ‘What

good are computers, except perhaps for mundane documentation, if you cannot even touch your work? The fact that traditional craft endures at all is because it satisfies some deep need for direct experience e and most computers are not yet providing that experience’. He goes on to comment that, ‘Without touch, currently the most common complaint about computers is not about overload, but deprivation. It is about the inability to touch one’s work. Being out of touch is considered an occupational hazard’ (McCullough, 1998). In addition to the increasing use of 3D CAD, rapid prototyping has enabled complex physical components to be produced without tactile interaction. Rapid prototyping is a relatively recent technological development, with the publication of research in this area commencing in the early 1980s and the first commercial system being launched in 1989 (Kochan, 1993). Rapid prototyping has been defined as ‘those activities and processes that significantly reduce the time between concept and the production of high quality prototype parts or tools’ (Bennet, 1995).What this definition fails to identify is the pre-requisite of a 3D computer model that fully defines the form to be produced. This requirement is noted by Wood (1993) who states that rapid prototyping ‘is the creation of three dimensional objects directly from CAD files, without human intervention’. A more complete definition of rapid prototyping can therefore be given as the use of 3D computer geometry in the production of components using a layer-based additive build process in condensed time-scales. In an attempt to re-establish the manipulative control of form as afforded through the production of physical models by hand, the use of a haptic feedback device was identified as a possible solution. Haptic devices have been defined as ‘technology that provides sensing and control via touch and gesture’ and a haptic feedback device translates these sensations to the operator (Hodges, 1998). Historically, work on haptic devices has been motivated by the desire to develop sensory substitution systems for people with visual or hearing impairments (Tan, 2000). People with such disabilities are known to respond well to learning through tactile or kinaesthetic experiences. Haptic devices can be broadly split into two groups: those providing 2D (planar) movement, and those providing 3D (spatial) movement1. They resemble pens, mice, joysticks, steering wheels, gloves, and body suits. For tasks requiring 3D-position sensing and feedback, finger thimble and pen-like styluses tend to be employed. For tasks requiring hand grasping actions or whole-hand sensitivity, gloves with sensors embedded in their fabric are used. Haptics-enabled gloves have been used in conjunction with VR technology since the early 1990s, with the combination of these technologies becoming known as ‘augmented virtuality’ (Drascic and Milgram, 1996; Oakley et al., 2000)2. The commercial use of haptics is now established in several areas, with systems supporting people with disabilities and entertainment, medical, educational and military applications. Haptics can be applied to create touch-enabled solutions that improve learning, understanding, creativity and communication, for example, in the training of surgical procedures, preparation and interpretation of seismic data, and in exploring and learning by feeling3. Force feedback is already an established feature in a wide range of handheld controllers, from laser guns to keypads and pilots’ joysticks. The entertainment industry is another key area currently developing haptic technology, both for stand-alone consoles and for cross communication over the Internet4. It is only recently that these devices have become of a practical size and sufficiently robust to be marketed as consumer products. The use of haptics in new product development (NPD) is now being actively explored (Tan, 2000). It is an emerging and relevant area of research, offering a new paradigm for the integration of physical and digital modelling. Haptics, as applied to industrial design, ranges from a capacity to perform a simple painting application to complex 3D form creation and virtual prototyping (Evans, 2000, 2004). Until recently, CAD tools would not allow industrial designers to physically touch 3D computer models, but collaborative research between academic and commercial groups (e.g. Massachusetts Institute of Technology and

SensAble Technologies) has led to the provision of computer-aided 3D form creation and evaluation tools that attempt to replicate the interaction experienced during physical 3D modelling (Sener et al., 2002). The SensAble Phantom/FreeForm system is the first CAD tool that allows designers to sculpt and form a block of ‘virtual clay’, emulating tools and techniques employed in the physical world of modelmaking (Ashwin, 1989; Hickey, 2001). By receiving instantaneous haptic as well as visual feedback, SensAble claim that precise and intuitive design changes can be easily made5. It has been suggested that if haptics technology were packaged into major CAD systems, it would speed up the product development cycle and significantly reduce cost (Larsson and To¨ rlind, 2001). Research is ongoing into the integration of haptic devices with established CAD packages, for example with 3DStudio Max (Marcy et al., 1998). As the only fully commercial desktop haptic feedback system, the SensAble Phantom/FreeForm has become the focus of research into design-related modelling. The Swedish company Reachin Technologies AB have developed a system that facilitates stereoscopic viewing by mounting the Phantom device on support structure that contains a monitor and semi-transparent reflective screen. The Reachin system has yet to find an application in industrial design, although the company’s current research is directed towards developing more intuitive ways of digital sketching, sculpting, modelling and painting for the designer craftsperson6. The system is currently being used for medical training, computer games and Internet collaboration. The MIT Spatial Imaging Group are developing a technique of haptic holography in which the Phantom device can be used for limited interaction with a deformable holographic shape7. At Glasgow School of Art’s Digital Design Studio (DDS) 3D interfaces are being developed to integrate haptic and 3D audio hardware and software8. The TACITUS project at the Edinburgh College of Art and Edinburgh Virtual Environment Centre is currently exploring the use of haptic interfaces for concept generation during craft activity9 and research at Loughborough University focuses on the evaluation of haptic feedback devices during industrial design practice (Evans, 2004). The SensAble Phantom allows the user to feel and press on the surfaces of virtual component geometry by applying force feedback when the cursor comes into contact with the digital object (see Figure 1).

Figure 1 SensAble haptic feedback device

Whilst the promotional literature for such devices may appear convincing, the use of a pen-like sensing device means that the tactile information delivered to the user is limited. This is summed up by Salisbury, a Principal Research Scientist at the MIT Artificial Intelligence Laboratory, when he states ‘to sense the shape of a cup we do not take a simple tactile snapshot and go away and think about what we felt. Rather, we grasp and manipulate the object, running our fingers across its shape and surfaces in order to build a mental image of a cup’ (Hodges, 1998). He goes on to acknowledge the use of haptic feedback devices in the fields of medical simulation (for surgical procedures), animation and computer games, but their contribution to industrial design has yet to develop (Hodges, 1998). As the only fully supported commercial design system, the SensAble FreeForm/Phantom system was selected as the haptic feedback device for evaluation in a product design case study. To ensure that the full modelling capabilities of the FreeForm/Phantom system were exploited, the project was supported by Christopher Dean of Freeform Studios10. Christopher Dean is an expert user of the FreeForm/Phantom system and former consultant to SensAble Technologies.

2 Research methods Case studies have been described as an approach to research as opposed to a research method (Moore, 1983), with a capability ‘to describe and understand the phenomenon ‘‘in depth’’ and ‘‘in the round’’ (completeness). In this role, case studies serve a useful purpose, since many important issues can be overlooked in a more superficial survey’ (Birley and Moreland, 1998). In addition, the way in which data are collected and analysed in case studies ‘implies the collection of unstructured data, and qualitative analysis of those data’ (Gomm et al., 2000). Such techniques are relevant to a comparative evaluation of design phenomena, and the principle of using case study methods to investigate the use of a haptic feedback device during industrial design practice forms the core of this study. In focusing on the specific methods applied as part of case study research, Moore (1983), Gomm et al. (2000), and Cohen and Manion (1980) identify action research. Action research has been defined as: ‘an on-the-spot procedure designed to deal with a concrete problem located in an immediate situation. This means that the step-by-step process is constantly monitored (ideally, that is) over varying periods of time and by a variety of mechanisms (questionnaires, diaries, interviews and case studies, for example) so that the ensuing feedback may be translated into modifications, adjustments, directional changes, redefinitions, as necessary, so as to bring about lasting benefit to the ongoing process itself’ (Cohen and Manion, 1980). The cyclical nature of action research has been identified by Birley who sees it as being conducted by a profession studying its activity, the aim of which is to bring about an improvement in practice (Birley and Moreland, 1998). Action research was therefore considered particularly appropriate in meeting the objectives of this study as it represents a recognised method for the facilitation of improvements in the execution and understanding of practice. In employing action research through case study, a strategy of reflective designing was adopted where one of the co-authors (Dr Mark Evans) undertook the role of industrial designer and articulated the process and outcomes. The activity of reflective designing is described by Schon when he states: “The designer’s moves tend, happily or unhappily, to produce consequences other than those intended. When this happens, the designer may take account of the unintended changes he has made in the situation by forming new appreciations and understandings and by making new moves. He shapes the situation, in accordance with his initial appreciation of it, the situation ‘talks back’, and he responds to the situation’s back-talk” (Schon, 1983).

3 Product design case study: toaster The case study involved the comparative evaluation of two strategies for the definition of product form through tactile interaction. One employed workshop-based sketch modelling using rigid foam (styrofoam), the other used virtual techniques via the FreeForm/Phantom haptic feedback device plus rapid prototyping.

The aim was to explore the capacity of the FreeForm/Phantom system to emulate the tactile sculpting of form and produce a similar physical outcome to that of workshop-based techniques through the use of rapid prototyping. Styrofoam remains a popular material for the production of product mock-ups, and despite extensive use of digital techniques, industrial designers continue to maintain their enthusiasm for such media: ‘it is worth remembering that while it is easy to be romanced by all of this computer-aided design and virtual prototyping, the tried and tested foam model, generated in an afternoon from simple 2D drawings, will often beat out its hi-tech sister in both schedule and cost’ (ID Magazine, 1997). The comparative evaluation employed in the case study required the design methods to deviate from a typical design commission in that it was necessary to produce two forms of model: one from styrofoam in a workshop, the other in starch via haptic feedback modelling followed by rapid prototyping. Details of the case study will now be discussed. 3.1 Concept generation One of the key features of the toaster brief was a requirement to prevent the ingress of dirt by concealing the bread slots when not in use. Alternative configurations for this feature were modelled quickly and effectively through pencil sketching. Pipes (1990) refers to this activity as ‘concept sketching’ and sees it a analogous to the designer ‘thinking aloud with a pencil’. He goes on to point out that often these somewhat ambiguous marks on the page can lead to further design ideas. Soufi and Edmonds (1996) have defined this process as ‘emergence’. They discovered that the uncertainty and ambiguity that are characteristics of sketch work undertaken during concept generation perform a key role in the production of further ideas. Whilst this ambiguity can be present in a sketch model sculpted by hand, the rigour of the CAD modelling required for rapid prototyping makes this virtually impossible to reproduce. Examples of concept sketching can be seen in Figure 2.

Figure 2 Concept generation

3.2. Physical sketch modelling (conventional workshop) Having arrived at a proposal via 2D concept sketching, it was necessary to evaluate and progress the design as a physical form through the use of 3D sketch modelling. This transition from 2D to 3D would also provide an opportunity to engage in a comparative evaluation of sketch modelling using workshop-based and haptic feedback/rapid prototyping techniques. This was achieved through the adoption of three-phase strategies for each technique.

Workshop phase 1 - transpose elevational information Sketch views produced during concept generation were bonded onto a block of styrofoam (see Figure 3).

Figure 3 Elevational sketch drawing bonded onto Styrofoam block Workshop phase 2 - approximation of form The basic geometric form was roughed out using a band saw and sanding disc (see Figure 4).

Figure 4 Approximation of form using bandsaw and sanding disc Workshop phase 3 - fine surface definition Abrasive pads and papers were used to precisely define form through direct tactile sculpting. This required a high level of physical contact with the evolving form and resulted in a degree of emergence (see Figure 5) (Soufi and Edmonds, 1996).

Figure 5 Definition of from through tactile interaction On completion of the shaping of form by hand, black tape was used to identify the location of split-lines. The final styrofoam model can be seen in Figure 6.

Figure 6 Styrofoam model produced by hand in a workshop

3.3 Virtual sketch modelling (haptic feedback device/rapid prototyping) Having arrived at the required form through the tactile manipulation of material, the three-phase workshop-based strategy was transposed to a haptic feedback/rapid prototyping strategy to enable a comparative evaluation. Haptic feedback/rapid prototyping phase 1 - transpose elevational information The sketch views used in the workshop were scanned and incorporated into the virtual modelling environment using the ‘sketch planes’ functionality of the FreeForm software. This enabled the drawings to be positioned within the 3D environment and was analogous to manually cutting and pasting sketches onto the styrofoam block. The functionality of the software also enabled the transparency of the drawings to be adjusted to suit specific shaping operations (see Figure 7).

Figure 7 Sketch elevations translated into the Free-Form/Phantom virtual environment Haptic feedback/rapid prototyping phase 2 - approximation of form The basic geometric form was roughed out using the ‘wire cut’ and ‘smoothing’ functionality by shaping a quadrant of the design that was then ‘mirrored’ to produce the complete product (see Figure 8).

Figure 8 Basic form defined using FreeForm/Phantom Haptic feedback/rapid prototyping phase 3 e fine surface definition The final form was defined through the tactile shaping of surface geometry using the smoothing operations of the FreeForm/Phantom system. This included a degree of emergence as was the case with the styrofoam sketch model.

As with the production of the styrofoam sketch model, this third and final phase of the digital design strategy required a high degree of control over the emerging shape to enable the final surface geometry to be modelled through tactile interaction. Whilst employing the Free-Form/Phantom system, this activity proved to be far from straightforward as it was impossible to achieve a geometrically smooth finish over the entire surface. Whilst it would have been possible to achieve this through the use of more controlled, non-

haptic modelling operations within FreeForm, such as ‘3D curves’, this was considered to be an inappropriate alternative as the objective of the haptic feedback/rapid prototyping strategy was to explore the tactile capabilities of the system. Unfortunately, the outcome of the FreeForm/Phantom tactile interaction was a degree of undulation on curved surfaces that was considered unacceptable for both rendering and downstream tooling operations. Having identified the limitations of the FreeForm/Phantom system, it was still necessary to complete the evaluation and translate the virtual geometry into physical components via rapid prototyping. The final definition of form (as geometrically smooth surfaces) during Phase 3 was therefore completed using the CAD-type functionality of Free- Form. This involved the use of ‘3D curves’ within the construction environment (see Figure 9).

Figure 9 Form precisely defined using FreeForm/Phantom Rapid prototyping Whilst the full haptic capabilities of the FreeForm/Phantom system proved ineffective when compared to workshop techniques, it was still possible to translate the virtual geometry into a physical model using a rapid prototype concept modeller. This was achieved through the use of the starch-based Z-Corporation rapid prototyping system (see Figure 10).

Figure 10 Z-Corporation concept model produced using FreeForm/Phantom geometry

3.4 Further evaluation Having demonstrated a significant shortcoming in the capability of the FreeForm/Phantom system to produce geometry required by industrial designers through haptic interaction, an opportunity for further evaluation emerged in the modelling of texture on the middle moulding of the toaster. This texture was to be similar to that of obscured vision glass and contribute to the industrial design proposal by breaking up the view of the product’s internal components. 3.4.1 Basic component geometry As the haptic modelling capabilities of the FreeForm/Phantom system were unable to deliver smooth surfaces, the NPD strategy reverted to CAD for the production of the basic 3D geometry that would be required for rendering, rapid prototyping and tooling. This was undertaken using the DeskArtes industrial design system with support from David Cheshire, an expert user and reader in design technology at Staffordshire University. When complete, the middle section was imported into the FreeForm/Phantom system as an stl file for the production of the obscured vision texture. The stl file format is the industry standard for the transfer of 3D computer geometry when employing rapid prototyping. 3.4.2 Hammered effect In producing a hammered effect for the obscured vision texture, an attempt was again made to employ the full haptic capabilities of the FreeForm/Phantom system. As a precursor to this, it was necessary to explore the characteristics of a number of different tools and levels of ‘clay’ hardness before the desired effect was achieved. The test piece produced as part of this process can be seen in Figure 11.

Figure 11 Test piece employed in the definition of the required surface finish Having defined the preferred tool and material properties, the production of the hammered finish was found to have an extremely close association to working with a physical material. Each individual blow delivered to the virtual surface was felt by the designer who could precisely control the positioning and depth of deformation. Nonetheless, some of the blows onto the component surface were unsatisfactory (i.e. too deep, shallow or in the wrong place). A major advantage of the FreeForm/SensAble system over workshop-based modelling techniques was that these errors could be easily deleted and another attempt made to achieve the required effect. Such immediate editing would obviously be impossible when working with a physical material. The ‘hammered’ effect was applied to the entire outer surface of the middle component before being digitally ‘smoothed’ using the Free-Form software. Again, such smoothing would not be possible when working a physical material. The final ‘hammered’ form can be seen in Figure 12.

Figure 12 Final ‘hammered’ form produced using the haptic interaction of FreeForm/Phantom

As the haptic interaction was of a local nature, the problem associated with producing geometrically smooth surfaces over relatively large areas was not encountered. This resulted in a highly satisfactory and original result that could not have been modelled using any other means.

3.4.3 Rendering To fully evaluate the design outcome, the hammered middle section was imported into the DeskArtes CAD system and integrated with the remaining components in preparation for rendering. The final rendering can be seen in Figure 13, and with a close up of the hammered effect in Figure 14.

Figure 13 CAD rendering of all components

Figure 14 Close up of ‘hammered’ effect

3.4.4 Rapid prototype components As the haptic interaction with form had been undertaken on the virtual model, no additional input of data was required for the production of rapid prototypes e.g. laser scanning, translation of sketches/models into a CAD system. The virtual components had been modelled using the most appropriate of the available techniques, but verification of the acceptability of the hammered finish was required prior to rapid prototyping using a production build system (e.g. resin-based stereolithography). This was achieved by producing a starch-based Z-Corporation component for half of the middle section (see Figure 15).

Figure 15 Half of ‘hammered’ section of middle moulding

The Z-Corporation model represented the first physical embodiment of a component that had been shaped (at least in part) by hand but never directly touched during the modelling process. Having been seen and touched as a physical object, the design was approved and a full set of production rapid prototypes produced using stereolithography (see Figure 16).

Figure 16 Full set of components produced using stereolithography

4 Discussion There are a number of factors that may have contributed to the difficulties in achieving a geometrically smooth surface over relatively large areas with the FreeForm/Phantom system. One issue may be related to the encoding resolution of the Phantom hardware device as it often appeared that the fine details one was trying to ‘feel’ were on the same scale as the resolution of the system. However, this issue is not fundamental and can be resolved at a cost as demonstrated by a similar device for tele-operated surgery (Madhani, 1998). Additionally, the mathematical geometric representation used within FreeForm does not seem to readily support globally smooth deformation. Again, this is probably more of an implementation

issue rather than a fundamental limitation of the force-feedback concept. For example, Celniker (1990) developed ‘soap bubble-like’ energy minimising surfaces that were manipulated through the application of force or pressure. This representation, which could also address the smoothness issues experienced in this study, seems well suited to the haptic technology. Though the issues related to smoothness could be rationalised as implementation details, the experience, and the relative effectiveness of traditional CAD modelling environments lead the authors to wonder about the validity of the assumption that virtual sculpting will add value to the form design process. Perhaps simply providing tactile feedback about the resulting surfaces is more important than a literal emulation of feeling the sculpting process. If so, other forms of haptic feedback devices (such as gloves) may be more appropriate.

5 Conclusions A product design case study has identified the capabilities and limitations in desktop haptic feedback modelling. Specifically, it has highlighted the capacity to engage in tactile interaction with virtual geometry, but more significantly, demonstrated severe limitations in applying this to industrial design practice. The inability of the FreeForm/Phantom system to allow the industrial designer to sculpt form through touch and produce acceptable curved surfaces brings into question the relevance of this generation of technology to the profession. Despite the fact that the system was extremely capable in replicating workshop activity in the production of the hammered surface, this must be regarded as somewhat esoteric and only of relevance to localised surface effects. However, whilst geometric surface continuity is a requirement for industrial design modelling, this is not necessarily the case for the designer craftsperson where slight (or even significant) disruptions to surface finish may be required and very much the norm. The use of the haptic feedback device by this profession may therefore provide an opportunity to maintain a relevant tactile relationship with material (albeit virtual) and assist this group in exploiting the advantages of working in a digital 3D geometry format with the associated benefits (e.g. capacity to employ rapid prototyping). In moving this debate and technology forward, it may be appropriate to reflect on the way CAD has evolved to its current state. The first 2D systems were designed to emulate the production of paper-based engineering drawings, but through a combination of increases in computing power and fundamental rethink of modelling paradigms, the modelling metaphor changed to a more capable and productive 3D format. Evidence from this research indicates that a similar rethink may now be required for haptic interaction with virtual models. Instead of attempting to adapt established practice into a digital format (e.g. workshop-based form-giving translated to a haptic feedback device), it may be more appropriate to identify what the industrial designer is attempting to achieve through tactile interaction. Advanced CAD tools such as Alias Studio provide an extremely high level of modelling capability with a precise analysis of form through supporting visualisation and surface diagnosis. Having identified limitations in the only commercially viable haptic feedback system, by acknowledging the sophistication of state of the art CAD it is necessary to question the need to engage in tactile interaction during the development and definition of form and shift the emphasis to the tactile interpretation of the virtual design outcome i.e. enabling the designer to run their fingers over the surface and feel the shape. Whilst this is possible via downstream rapid prototyping, this requires a significant delay between the design action and sensory reaction. A future direction for the use of haptic devices in industrial design practice may therefore be based around the use of glove-type devices that enable the industrial designer to take sensory cues after defining form using CAD tools.

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