Development of a computational human hand model for ergonomic product design

Human hand is one of the most sophisticated tools that can be owned by a human. One of the main functions of the human hand is its interaction with physical environment where the most important is the prehensile grasp of a physical object. In this sense the human hand can be effectively used as a tool for different tasks or as an interface to use different powered and non-powered hand tools and products. In order to increase productivity, satisfaction and lower the risk of acute and cumulative trauma disorder development, which are product use induced, it is necessary to consider ergonomics in the development stage of the product. Considering mechanical properties of biological tissue of a human hand during grasping is crucial, since forces and torques are transferred from the product to the whole hand-arm system. Acute and cumulative trauma disorders present one third of sick leaves of the workforce. Most ergonomic analyses of products and hand tools are done using physical prototypes and costly measurement systems and therefore iterative design process, which increases development time and cost. Extensive ergonomic knowledge, which is needed during the development phase of a new product and its poor integration with existing, established software in the field of computer aided design has affected that companies do not, or in low scales, address the ergonomic principles in the design phase of a new product. Therefore, the aim of this research project is a development of a finite element digital human hand model (FE-DHHM), which would allow simultaneous studying of biomechanical behaviour of human hand during moving and grasping, analyses of biological tissue deformations, internal stresses, contact pressures and also effects of vibration on hand. This will allow direct evaluation of the product inside the virtual environment with the possibility of topological modifications of the product to improve the ergonomics and therefore lower the development times and costs. Safety and effectiveness of a product could be predicted and design mistakes could be eliminated in the development phase for increased performance, comfort and avoidance of cumulative trauma disorders. Anticipated research methods include mostly the correct definition of hand geometry using medical imaging. Segmentation will be performed on obtained images to allow distinguishing between typical anatomical structures such as bones, nails, skin, subcutaneous tissue, etc. Based on the segmented images, 3D reconstruction will be performed to obtain the 3D model of a human hand. This model will be then transferred to a commercial software for numerical simulations based on finite element method. Material model and parameters will be determined based on each anatomical structure of the hand and based on available results of previous authors. Each depth of field (DOF) of the human hand will be studied in detail, which would allow to determine correct joint definitions, which would allow realistic hand movement and numerical stability. Simplifications in terms of geometry, boundary conditions and material properties will be introduced, which will allow the development of a robust and numerically stable FE-DHHM while ensuring the accuracy of the results. On the other hand, the FE-DHHM will be developed robustly to allow future updates in terms of geometry, material properties and boundary conditions. Results from experiments using motion capture system will be used to determine realistic joint movements and therefore realistic movement of the FE-DHHM. Numerical model will be verified and validated with the help of already developed digital human hand models and results of numerous experiments.

New product development and ergonomic analyses currently rely on outdated manual methods (design using anthropometric data, iterative design process using prototypes, etc.) and do not allow the use of full data of potential users of a product. The result are products with bad ergonomics and great potential for improvement. Several authors have shown that numerical models of human parts, which assist in development of new products, have a crucial role in development of improved products (numerical model of human foot for gait analysis and footwear development, numerical model of human head for impact analysis and helmet design development, etc.). In that manner, a developed numerical model of a human hand would significantly contribute to the development of science and professional work in the field of biomechanics and ergonomics, since appropriate numerical models of human hand have not been developed yet. Cumulative trauma disorder development mechanisms are still largely uninvestigated field. With the use of the developed numerical model of human hand this area could be also investigated. The results in terms of stresses on biological tissues could be correlated to the injury development, which would allow new knowledge generation. Scientific results will be collected an arranged to be able to publish them in contemporary scientific journals with high impact factor and good ranking, which will also enable an appropriate dissemination of generated scientific knowledge into the scientific community and profession.

The developed numerical human hand model would be directly applicable in the process of new product development and would allow ergonomic amylases and identification of problematic areas and their correction inside the virtual environment in the development phase of the product. Additionally, the developed numerical human hand model would allow researching the phenomena of human hand movement and grasping and provide an insight into the mechanisms of various cumulative trauma disorder development (carpal tunnel syndrome, hand-arm vibration syndrome, white finger syndrome, bursitis, etc.), which are the result of badly designed products and tools and present high costs for companies with sick leave of the workers, injury diagnostics and their treatment. With ergonomic analyses using the numerical human hand model ergonomic value of a product would increase, which would also increase the competitiveness of the product and company on the market. Slovenia with the European Union and other developed countries present an increasingly aging population, which results in a reduction of productivity and performance of the working population and therefore increases the risk of various cumulative trauma disorder development. This, it is essential that future products will optimize the human-product interaction and thereby maintain or even increase productivity, comfort, satisfaction, and safety.  The developed numerical human hand model could be also commercialized and therefore also kickstart a new company. With appropriate further development after the project finish it would be possible to integrate the numerical human hand model into existing computer tools and thereby enable a comprehensive approach to product development. Used methodology and findings could also be easily transferred to other applications in the research field of biomechanics, such as numerical modeling of human foot, knee, etc. Additionally, methods and findings could be also transferred to the safety industry, where determination of the correct shape (helmet shape design, wheelchair design, hand tools for high precision (medical devices), high-performance products, sports equipment, military equipment, etc.) and correct material parameter determination of interface materials (energy absorption liners in helmets, liners in prostheses, equipment of disabled, seat cushions) is crucial. Identified mechanisms of cumulative trauma disorder development in the hand could be also transferred to other anatomical structures, which would allow their identification and prevention.