An online ergonomic evaluator for 3D product design

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482 been applied to guide the design of hand tools, furniture, and other consumer products [31,32]. The latter is focused on analyzing the action angles, trajectories, and reaching spaces of the body parts under specified human motions. It contributes to the design of work environment, machines, production lines, and other occupational equipments [33,34]. Ergonomic assessment for the car interior design mainly concerns static anthropometry. In this study, a digital model is constructed with a local anthropometry database in Taiwan [35], which serves as a complete data source for characterizing the 3D human body of both male and female adults in the country. This human model can be customized according to different body sizes chosen by the user. The customization is performed based on the template approach [36] previously developed in which human models at different scales are controlled by a set of anthropometrical parameters. The design of this anthropometry database follows three important guidelines: (1) design for extreme individuals, (2) design for adjustable range, and (3) design for average. 2.4. Posture generation The digital human can be placed in a set of postures that are recognized in a motion capturer and modeled with the captured data [37]. The human motion is comprised of a set of rigid parts connected by joints, referred to as a human template, as shown in Fig. 1.A different human template is generated from each anthropometry data set that corresponds to a specific C.-F. Kuo, C.-H. Chu / Computers in Industry 56 (2005) 479–492 percentage of the body size. These rigid parts are allowed to rotate and translate with respect to the connected joints under biomechanical constraints. Complex and realistic postures are thus created with minimal user’s interactions. Moreover, compounding homogeneous transformations are applied to generate the postures of body extremity [38]. For instance, the posterior segments, like wrist’s final position, are determined by a series of the anterior segment’s rotations including forearm, upper arm, and torso. Note that the use of the human templates helps a nonskilled designer easily create realistic character postures by learning only a small set of key parameters. 2.5. Posture evaluation The mechanism for the posture evaluation is based on a musculoskeletal load assessment method proposed by Chaffin and Baker [39]. This twodimensional static sagittal model (see Fig. 2) divides human body into seven major parts [40]. The dimensions of each part are collected and stored in the anthropometric database. Ignoring the influence of inertia, we compute the angle of each joint and combine the result with the dimensional data. In the posture assessment, the focus is on shoulder, elbow, wrist, hip, knee, and toe. The relative positions between important body points and the product are Fig. 1. 3D human template based on motion capture data. Fig. 2. Chaffin’s biomechanical model [39].
calculated after the user has accommodated the digital human template to the simplified 3D model in the viewer. The stress induced by the posture on lumbar vertebra is then estimated. 3. System architecture The on-line ergonomic evaluator proposed in this study consists of five major software components: 3D viewer, posture generator, ergonomic evaluation engine, interface to CAD system, and the web-based GUI’s. Fig. 3 illustrates the corresponding system architecture. Each module and the data flows among them are described as follows. 3.1. 3D viewer Actify SpinFire TM [21] is an integral part of the system. It provides Software Development Kits (SDK) C.-F. Kuo, C.-H. Chu / Computers in Industry 56 (2005) 479–492 483 Fig. 3. System architecture of the online ergonomic evaluation system. in a number of programming languages (JavaScript, VB, and C++) for customized development tasks. This software converts commercial CAD model into its proprietary file format—.3D for better file transmission and manipulation over the Internet. The conversion process produces a set of 2D meshes from the geometry of the CAD model, usually according to Delaunay Triangulation algorithms [41]. Most topological information and other engineering attributes are not retained in the .3D file for file size reduction. Such a light-weighted model is more suitable to network transmission and online manipulation. This software also provides a graphical environment for real-time rendering .3D models. Simple dimensional data such as length and angle can be calculated interactively in 3D GUI’s or programmatically via API’s. In addition, this viewer can serves as a plug-in in Windows TM application programs, so its customization and integration with other systems are convenient.
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An online ergonomic evaluator for 3D product design

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