Dynamic digital human models for ergonomic analysis 5
capabilities and actual risks present in the work environments (Shahrokhi and Bernard,
2009).
However, in this paper, we are primarily interested in the DHM tools which are used
for workstation design. The main functions of such tools are:
1 The digital operator’s representation in the 3D CAD software tools. For this
purpose, the DHMs can be feminine and masculine models which are characterised
by anthropometrical or biomechanical factors (angular range of motion, maximum
exertion, etc.), which are selected by the designers from anthropometrical or
biomechanical databases.
2 Simulation of postures and/or activity sequences (gestures, posture changes, object
prehensions, motions, etc.). In other words, the DHMs can be animated by either
direct and/or inverse kinematic control, manually, from a database of predefined
movements or by motion analysis systems.
3 Anthropometric prescriptions verification, collision detection and task execution
time calculation. In other words, the operator’s reach area and visual field are
realistically and accurately included in the functionalities of the DHMs.
4 Biomechanical and/or physiological constraints assessment through the use of
common ergonomic indices. Various ergonomic evaluators such as revised
equations from NIOSH (1991), RULA methods (MacAtamney and Cortlett, 1993),
OWAS (Karu et al., 1977), EAWS (http://inderscience.metapress.com/
content/m850j18564428m27/) and Snook tables (Liberty MutualTables,
http://www.ccad.uiowa.edu/vsr/research/standard-ergonomicassesments/
liberty-mutual/) are used to evaluate the simulated tasks completed by the DHMs.
Table 1 sums up the main characteristics and functionalities of DHMs used by the main
industrial or academic stakeholders in the CAD field. Table 1 shows that there are two
groups of DHMs: on one hand those used in generic industrial contexts [for example,
Jack (Badler, 1997), DELMIA (http://www.3ds.com/products-services/delmia),
SAMMIE CAD (Porter et al., 2004) and ERGOMAN – PROCESS ENGINEER (Schaub
et al., 1997)] and those specifically designed for a specific type of application
(for example, RAMSIS (Seidl, 2004), BHMS (Rice, 2004), MAN3D (Monnier, 2004)
and SantosHuman (VSR Research Group, 2004; Vignes, 2004)). Table 1 includes the
DHMs’ names and their producers. Columns three to ten stand for ‘animation method’
(AM); ‘direct’ (D) stands for direct kinematics; ‘inverse’ (I) stands for inverse
kinematics; ‘field of view’ (FOV) stands for the extent of the observable world that is
seen at any given moment by the DHM; ‘reach area’ (RA) stands for objects and the parts
of the workstation that the DHM can reach; ‘collision detection’ (CD) stands for
detection of contacts between two or more objects or between humans and objects; ‘static
effort’ (SE) stands for human efforts in static conditions; ‘ergonomic assessment indices’
(EAI) stands for the types of workstation assessments; ‘motion capture’ (MC) stands for
optional modules that can record the movements of objects or people; ‘methods time
measurement’ (MTM) stands for calculation of standard times in which a worker can
complete a task.