Högskolan i Skövde

Use of digital human modeling (DHM) tools enables early assessment of ergonomic risks in the production development process. This early risk assessment can indicate needs for preventive actions in order to decrease risks for work-related musculoskeletal disorders. A method for the assessment of physical workload has been developed, for the analysis of wrist joint data produced by a DHM tool. The method is tested in a simulation model of an actual manual assembly station in industry where it is assumed that physical workload problems exist. The results show that the method can be successfully applied on an industrial case. In addition, presumptive risks and possible diagnoses are predicted based on the similarity of the simulated task’s motions with motions from other known work class profiles stored in a database based on epidemiological research.

Simulation and visualisation software such as digital human modelling (DHM) tools have been designed to predict and evaluate ergonomics within a virtual environment. Today’s DHM tools typically include observation-based evaluation methods, initially designed for visual observation. Direct measurement techniques enable assessment of quantitative data similar to the information derived from the DHM. Such technique allows detailed and time-dependent risk aspects to be considered in the ergonomics evaluation. No methods in commercial DHM software calculate time-dependent information, which is shown as an important risk factor in the development of work-related musculoskeletal disorder (WMSD). This paper presents and discusses an ergonomics assessment approach based on the theory of a dose-response relationship between exposure and the risk of arising injury. The focus of the approach presented is on the wrist-joint.

Digital human modelling (DHM) systems are used to simulate production processes and analyse the human-machine interaction, particularly at early development stages. Consideration of anthropometric variation is central in DHM simulations due to the necessity of ensuring intended accommodation levels. This paper describes the process of how digital human models are created and defined within the IMMA software. The process begins with the definition of a number of key measurements, which acts as the basis for the definition of several boundary manikins using a confidence ellipsoid methodology. These manikins represents the appropriate confidence region and hence the anthropometric diversity. Key measurements are then entered into regression equations to define the complete set of measurements for each manikin. These measurements are based on the appropriate ISO-standard. Finally, measurements are used to define the size and alignment of each segment in the biomechanical model of the manikin. The manikins are then used to automatically simulate and analyse human-machine interaction.

Software tools as Digital Human Modelling (DHM) has been designed to simulate and visualize the human work and to assess ergonomics conditions. No methods in commercial DHM software calculate time-dependent information, which is adequate in defining the relations between exposure and risk of disorders. The paper presents and discusses how an assembly task can be analysed with the help from a DHM-tool. Out comes from the study revealed that it is possible to generate output files with time-dependent wrist exposure data from a manikin in a DHM-tool. However, current evaluation methods do not take time-dependent information into consideration.

The increased computerisation of design and engineering work has led to the development of software such as digital human modeling (DHM) tools. These tools can be used to simulate and visualise human work and for evaluating ergonomic conditions. Observational-based ergonomics methods, such as RULA and OWAS, may be used for characterizing workload and are typically integrated in DHM tools. However, using observational-based methods usually means that ergonomics evaluations are based on assessing static postures, i.e. not taking time-related aspects into account. This is usually also the case when industrial companies choose to customize the DHM software and integrate their own company specific ergonomics methods. Since time-sensitive aspects, such as frequency and angular velocity, are of importance in the ergonomics evaluation, it is necessary to be able to predict these variables also in an early stage of the design process. As observation methods are poor in terms of sensitivity they give rough estimations of ergonomic conditions. Consequently, researchers aim to develop dynamic evaluation methods where also time-dependent aspects, such as repetitiveness, velocity and duration in exposed positions, are considered. The objective of this study is to focus on the assessment of the wrist since a large amount of work related disorders is caused by this joint and also due to the fact that this is a relatively uncomplicated joint to explore from a biomechanical perspective. This paper displays initial findings from the literature for how to adequately and quantitatively assess wrist movements, appropriate evaluation criteria and for how to calculate cumulative load. Moreover, the paper illustrates how time significant wrist exposure data obtained from a DHM may be used for ergonomics assessment. This involves a proposed time consideration concept, based on a combination of modified and established evaluation methods, including suggestions for how to identify fundamental cycles.