Digitization of Farm Tractors and Body Models for the Evaluation of Farm Tractors

Feature-envelope technique is a method that describes the spatial location and orientation of areas or landmarks of interest with respect to a well-defined, easily duplicated coordinate system. This technique has been tested in a NIOSH study in guiding tractor designers in their placement of tractor control components in order to best accommodate the user population. NIOSH recently measured the human body dimensions of 100 West Virginia farm workers, including whole body surface scans, to examine body size accommodation issues associated with safe farm tractor operation and rollover protective structures. Multivariate anthropometric models were derived from this population based on measurements related to the workstation. The Euclidian distance of each subject for each model was computed, and those that scored the closest were identified as “nearest neighbors.” Fifteen of these subjects, representing the extremes plus one mean, were re-recruited and seated in the tractor workstation and their anatomical landmarks were digitized using Faro arm technology. Fourteen landmark point clouds were further simplified using principal component analysis to generate feature ellipsoids for each landmark location with respect to the workstation. Each feature envelope can be thought of as an ellipsoid enclosing a cloud of three-dimensional data points representing the variability in a landmark location. Descriptions of how feature envelopes are created and implemented within the Computer Assisted Design environment will be presented. The technique can be used in other machine or product safety applications, such as in designing construction vehicle cabs, truck driver compartments, and aircraft cockpits.