The ergonomics suites available within computer aided design and digital human modelling programs are increasingly being used to predict and prevent ergonomic and human factors risk due to poor design. To further aid the reduction in poor design, it is of importance to understand the need for user input and the limitations of these software programs. These limitations include: the small number of available anthropometric population samples; and the disconnect between what a designer perceives as possible, and what is possible within a manufacturing environment. A method of mitigating these limitations is the use of user input using virtual reality suites, mock-ups and motion capture technology

Fletcher, Sarah R.

Johnson, Teegan L.

English

Cranfield CERES

THE LIMITATIONS OF USING ONLY CAD AND DHM INDESIGN RELATING TO HIGH VALUE MANUFACTURINGTeegan L. Johnson and Sarah R. FletcherIndustrial Psychology and Human Factors Group, Cranfield University,The ergonomics suites available within Computer Aided Designand Digital Human Modelling programs are increasingly beingused to predict and prevent ergonomic and human factors risk dueto poor design. To further aid the reduction in poor design, it is ofimportance to understand the need for user input and thelimitations of these software programs. These limitations include:the small number of available anthropometric population samples;and the disconnect between what a designer perceives as possible,and what is possible within a manufacturing environment. Amethod of mitigating these limitations is the use of user inputusing virtual reality suites, mock-ups and motion capturetechnology.IntroductionPoor design for ergonomics has been shown to negatively impact worker health(Broberg, 1997) and workplace performance (Wang and Lau, 2013). As a resultthe integration of human factors (HF) into the planning process of productdevelopment has been identified as a major strategy for mitigating work relatedinjuries and illness (Broberg, 1997). Despite the availability of ergonomicguidelines for engineers (Lehto, Landry and Buck, 2008), ergonomic methodsand tools have historically not been available in accessible formats for designengineers, hampering the integration of HF into the design process (Broberg,1997). The integration of Digital Human Modelling (DHM) and human activityanalysis suites into Computer Aided Design (CAD), has given designers accessto HF methods and tools (Broberg, 1997). This has led to CAD human modellingtools becoming a common technique for predicting and preventing ergonomicrisk within manufacturing (Lockett, Fletcher and Luquet, 2014).The aim of this paper is to discuss some of the ways HF tools in CAD are used indesign and redesign within manufacturing. Some of the issues and limitationsthat should be considered when using these tools to reduce negative impacts onworker health and performance will be highlighted.CAD and DHMCAD can be used in the design and redesign of structures within manufacturing.Structures are the parts and the framework that holds these parts in place. Withinmanufacturing these structures tend to be large and occlude operators and theirpostures, making it difficult to accurately assess for muskulo-skeletal risk. TheDHM and ergonomic assessment capabilities in CAD enables the easy variationof anthropometric and biomechanical parameters of virtual manikins (Paul andWischniewski, 2012). Helping to improve design and usability of products andwork systems (Paul and Wischniewski, 2012) by allowing designers to identifyhow their structure will be used by individuals of different physiologies.Designers can identify how operators will likely interact with their structure;allowing problem areas to be identified such as those that may cause thedevelopment of musculo-skeletal disorders (MSD). This reduces the need forlarge participant pools and mock-ups in the early stages of the design processwhen assessing structure accessibility. There are however limits in theapplication of CAD and DHM in practice that should be taken into account.Designers using DHM to inform their design decisions should be aware of theanthropometric differences between countries (Cavelaars, et al, 2008). CADprograms are limited on the types of pre-set manikins available, which canvaried based on the percentiles within the specific populations. However, thenumber of population groups is limited, meaning that designers looking todevelop structures for specific populations not represented in the program willneed to identify and interpret the relevant anthropometric data. This requires anawareness of how to manually make changes to the manikins, and createmanikins that fit the percentiles of interest; this can be a time consuming processin relation to the ease of use for the preprogramed populations.When modelling the postures of manikins while interacting with structures, thepostures adopted through the task from beginning to end should be modelled. Forsome activities the working posture may be judged as acceptable by a posturalanalysis tool; while MSD risk lies in the transition postures. It is therefore ofimportance that the entire interaction is modelled to identify problem areas. CADsoftware has the ability to record frame by frame the activity of the manikin andergonomically assess every frame rapidly (Johnson and Fletcher, 2014), makingassessment much faster than traditional forms of postural analysis and allowingthe designer to identify exact problem areas in a design.Operator/user perception and feedbackCAD can be used at the start of a project to design a structure and design outobvious problems using DHM and HF tools available. However, input should begained from individuals outside of the design process to identify the more subtleor missed issues with a design. Ideally this would include representative users.An issue with DHM is that it is possible to make a task look feasible that whentranslated into a manufacturing environment, can only be accomplished with ahigh level of discomfort. Physical discomfort is indicative of poor biomechanics(Helander and Khalid, 2012) which can contribute to the development of MSD.The movement of a manikin in a CAD program can be limited by fixing thedegrees of freedom and applying collision detection to limit unnaturalmovements. The discomfort levels while completing the task have to be inferredby the designer or engineer. If possible representative users, such as those thatwill be directly interacting with the structure, should be consulted aboutperceived discomfort levels of the structure. Virtual reality (VR) and physicalmock-ups can be used to gain this information on the accessibility and comfortassociated with a structure.Virtual RealityA CAD model can be presented in an immersive VR suite or on a screen and therepresentative user can either point out where they perceive problem areas to beor physically enact how they would interact with the structure. For individualsphysically enacting their interaction, a motion capture (MoCap) suit can be usedto capture postures and input that data into CAD. This gives the user visualfeedback which can inform their movement and can be ergonomically assessed.This data will be limited because interactions are devoid of tactile information;the structures used for support, guidance or as a barrier are unavailable. Howeverproblem areas can still be identified, which can aid in refining the design of thestructure. A solution to the need for tactile information is to use mock-ups.Mock-upsUpon the reduction of problems using DHM and VR suites, the structure can beconstructed using inexpensive materials with a degree of assembly flexibility.This gives operators a more realistic idea of what interacting with the structurewill involve, helping to inform data on physical discomfort. Gaining both thephysical movements as well as the qualitative discomfort data involved withinteracting with the structure would be advantageous. Discomfort can be used toidentify where the structure could be causing stress which may play a role in thedevelopment of MSDs (Gielo-Perczak, Karwowski, Hancick, Marras,Karwowski, and Bonato, 2012). A limitation when using mock-ups to gain anunderstanding of how operators interact with a structure is that the activity of theindividual may be occluded. This can make it difficult to pinpoint the exactproblem areas on or in the structure that require redesign. Non-optical MoCapsuits, particularly where the data can be fed into the CAD program, would allowthe whole posture to be captured and translated to a manikin. Problem areas andstructures essential for task completion can be identified with the removal of thestructures surfaces within CAD. Postural assessment suites within the CADprogram can be applied to the data captured giving postural information aboutthe task.ConclusionCAD modelling with DHM can be used at the start of a design process toimprove design and usability. However it is limited to the perceptions of thoseworking on the design, their understanding of how a structure will beimplemented and used on a shop floor may be limited. Therefore, representativeuser input is essential to identify problems that may be missed. User input can begained through the use of VR and mock-ups to identify physical usability andease of access for structures along with qualitative comfort data. Thisinformation can be used to improve design and help to mitigate work relatedinjuries and stress, helping to reduce cost relating to injuries and improve workerperformance.AcknowledgementsThis work was supported by the UK EPSRC Centre for InnovativeManufacturing in Intelligent Automation.ReferencesBroberg, O. (1997). Integrating ergonomics into the product development process.International Journal of Industrial Ergonomics. 19, 317-327.Cavelaars, A. E. J. M., Kunst, A. E., Geurts, J. J. M., Crialesi, R., Grötvedt, L.,Helmert, U., et al. (2000). Persistent variations in average height betweencountries and between socio-economic groups: an overview of 10 Europeancountries. Annals of Human Biology, 27, 407-421.Gielo-Perczak, K., Karwowski. W., Hancock, P.A., Marras, W.S., & Bonato, P.(2012). Multidisciplinary Concepts in Ergonomic Design and IndividualDifferences in Performance. Proceedings of the Human Factors and ErgonomicsSociety Annual Meeting, 56, 1034-1038.Helander M. G. & Khalid, H. M. (2012). Affective Engineering and Design. In In G.Salvendy (Eds.) Handbook of Human Factors and Ergonomics, Fourth Edition.New Jersey: John Wiley & Sons, Inc.Johnson, T. L, & Fletcher, S. R. (2014). A Computer Software Method forErgonomic Analysis Utilising Non-Optical Motion Capture. In Sharples, S &Shorrock, S (Eds.), Contemporary Ergonomics and Human Factors. (pp. 93-100). Croydon: CRC Press.Lehto, M. R., Landry, S.J. & Buck J. (2008). Introduction to Human Factors andErgonomics for Engineers. New York: Lawrence Erlbaum AssociatesLockett, H., Fletcher, S., & Luquet, N. (2014). Applying Design for AssemblyPrinciples in Computer Aided Design to Make Small Changes that Improve theEfficiency of Manual Aircraft Systems Installations. SAE Int. J. Aerosp. 7.Paul, G., & Wischniewski, S. (2012). Standardisation of digital human models.Ergonomics, 55, 1115-1118.Wang, L., & Lau, H.Y.K. (2013). Digital Human Modeling for Physiological FactorsEvaluation in Work System Design. In V.G. Duffy (Eds.), Digital HumanModeling and Applications in Health, Safety, Ergonomics, and RiskManagement. Heidelberg: Springer.

The limitations of using only CAD and DHM in design relating to high value manufacturing

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The limitations of using only CAD and DHM in design relating to high value manufacturing

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