Computer Manikins in Evaluation of Manual Assembly Tasks

Licentiate thesis, 2006

Time to market is a critical success factor in today’s business environment. The challange is to reduce the development cycle without sacrificing the performance and quality of products and production systems. With the short-lived products of today’s competetive global markets most of the engineering has to be done before the start of the production and simultaneous with product development – simultaneous engineering. Any use of computer software to solve engineering problems is called computer-aided engineering, and has become one of the most important tools for simultaneous engineering. Fast, high quality computer graphics now allow us to render lifelike images of people performing a multitude of tasks within various computer aided engineering programs. Thus it now is possible to position and move manikins to predict the performance capabilities of designated groups of people within a computer rendered environment. Digital human modelling tools have been introduced in industry to facilitate a faster and more cost efficient design process. Most of the tool users are in the fields of automotive and aerospace engineering. The tools are applied in the design, modification, visualization and analysis of human workplace layouts and/or product interactions. Focus of research within ergonomics simulation has primarily been related to improve the simulation tools with more enhanced functionalities resulting in better and more accurate posture and motion algorithms and biomechanical models. Considerably less research has been conducted to investigate the needs of organizations and end users and their experiences of using the digital human modelling tools. The aim of the research in this thesis is to enlighten the importance of some of the features which can make the manufacturing simulation results more realistic and increase their credibility. Two studies are presented. The aim of the first study was to investigate whether different appearances of manikins in detail levels and genders influence the observers’ ergonomics posture evaluations, as well as to see if the evaluations differ between the three working disciplines: manufacturing managers, simulation engineers and ergonomists. The primary aspect addressed by the second study was whether repeated simulation results achieved by using a posture prediction tool were more uniform than results achieved by manual manipulating of all body angles. The uniformity was compared both among users and within users. Another aspect addressed was time needed to carry out a simulation case when using a posture prediction tool or not. Results from the first study show that manufacturing managers and simulation engineers were influenced by the appearance whereas ergonomists showed no significance in being influenced by the appearance of the manikins. Moreover, only the ergonomists could distinguish between the different workpostures used in the study. These were different in workload and classified according to the OWAS-system. Results from the second study show that the use of a posture prediction tool, in such complex tasks as the study included, neither reduced time needed to fulfill a simulation, nor differences within or among simulation engineers, at least not significantly. Differences in simulation results often originate from the different assumptions the simulation engineers have of the task when positioning the manikins. The differences could be minimized by a more careful order description and by such activities as simulation engineering days at assembly plants and by bringing the people working with human simulation tools together in the organization.