A methodology to support elbow flesh deformation for ergonomics modelling

A human centric approach to the design of products and workplaces is essential to ensure the appropriate accommodation of the people who interact with such designs. Digital human models (DHM) in ergonomic simulation are commonly used within design and development to ensure product suitability. DHM for ergonomic simulation has improved in terms of its reliability and appearance in recent years. However, there appears to be a need to improve how the flesh of the DHM deformsaround the joint to support improved ergonomics simulations. Supported by data acquired through the use of a 3D body scanner, this PhD research aimed to address this need by developing a methodology to simulate body deformation due to joint movements that suited the needs of ergonomics simulation. To anticipate the large scope of the research, this research focused on modelling a single joint: the elbow. To ensure the suitability of the proposed flesh deformation method a literature review and user study was performed to derive a set of DHM specifications. Six DHM specifications were proposed i.e. accuracy, realism, minimum user intervention, accommodating different body types and sizes, real time, and whole body modelling. An existing flesh deformation method (FDM) which had the potential to conform to the DHM specifications was determined and chosen to be developed further so that it matched the requirements of DHM for ergonomics simulation. The development resulted in a new FDM which required the provision of several elements to create a surface flesh deformation at the elbow. These were: five cross sections and their locations from four key postures (full extension, 135o flexion, 90o flexion and maximum flexion); the carrying angle; and perpendicular profiles from all of the four key postures. To avoid having to obtain these elements for every person for whom the elbow was to be modelled, a supporting data framework was developed. The framework utilised a database and a limited number of inputs (race, gender, BMI and a 3D scan data of a fully extended arm) to predict the FDM’s elements from which flesh deformation at the elbow was created. The database stored five key cross sections, profiles, a parameter for the carrying angle and a parameter of the locations of UAF, UAM, LAM for two race groups i.e., Caucasian and Asian. A total of 23 subjects (11 males and 12 females) were carefully chosen to represent a variety of height and body type for each race and gender. The algorithm for the new FDM and the framework is supplied in the accompanying CD. DHM specifications were utilised to review the suitability of the new FDM for ergonomics simulation. The review results showed that the new FDM had a level of error < 3mm and was able to recreate flesh deformation around the elbow joint with a representative level of surface realism when compared to the 3D scan data. The review result also showed that the new FDM was able to accommodate different body types and sizes with a slightly larger error, < 4mm. The new FDM also demonstrated that it could be used to create flesh deformation with limited user intervention. A retrospective analysis for real time modelling and whole body modelling showed that the new FDM had a potential to conform to these two specifications. The overall result of the review demonstrated that the new FDM and framework had the potential to suit ergonomics simulation. The thesis has made a contribution to the field of DHM research for ergonomics simulation by proposing a flesh deformation approach for the elbow that allows the integration of carrying angle; and was built based on specification for the use of DHM’s in ergonomics simulation and the utilisation of 3D scan data.