Plausible 3D Human Hand Modeling for Virtual Ergonomic Assessments of Handheld Product : Construction, Contact simulation and Variational Modeling

Handheld products, such as portable digital appliances, have been widely used in daily life and production activities. For their customers, an ergonomic design is always desired for better user experience and high productivity. Therefore, during the developmentprocess of handheld products, many grasp factors need to be assessed, for instance, grasp stability, grasp comfort, and grasp safety.3D human hand modeling and simulation providesignificant advantages for ergonomic assessments when incorporated into the early stage of the design process of handheld products. They can, especially, reduce the need for sensory tests on human subjects and also for expensive prototypes, thus reducing costs and time tomarket. However, current 3D human hand modelingtechnique that mainly aims to provide visual simulation for game or movie industry (e.g. in famous movie Avatar(2009), CG technique was used to make one lifelike character including hand models) cannot provide aplausible hand model for virtual ergonomic assessment.Therefore the purpose of this research is to model the human hand for virtual ergonomic assessments of handheld products with an acceptable accuracy.First, the main properties of human hand includingsurface skin, joint-link structure, and skin contactdeformation property need to be modeled to generate a fine template hand model.Moreover, based on a fine template hand model owning the main properties mentioned above, hand model instances, with individual hand size or with specific people’s anthropometric statistical characteristics, need to be generated by hand variational modelingmethod. This thesis mainly includes the followingfour topics:(1)Based on MRI measurements of human hand, 3D precise human hand modeling for product ergonomic assessments was proposed. The surface skin, the joint-linkstructure, and the skin deformation caused by joint motion were modeled and experimentally verified. (2)The skin deformation caused by contact was efficiently simulated for virtual ergonomic assessment of handheld products. The main properties of human hand skin, nonlinear elasticity and compressing-swelling effect, were realized for precise simulation. The results including estimated contact force, contact area,contact pressure distributions in grasping posture were experimentally verified.(3)Variational hand modeling based on image-based 3D model reconstruction was proposed for modeling a handof a particular person. Experimental verificationindicated that the modeling method could model individual hands including hand surface and joint-link structure in a relatively shorter period and with acceptable accuracy for virtual ergonomic assessments of handheld products.(4)Based on correlation analysis between anthropometricdimensions from subjects, two major dimensions, hand length and circumference, which can be sampled from a Japanese hand database, are used to predict other hand dimensions for enerating hand model instances.By grasping products using these instances in our Digital Hand software, the statistical grasping evaluation indices such as contact area and contact pressure distribution are given.