The majority of analytical tools available today -to assist the designer in designing a maintainable product -are related to modeling the human being. Since the late 1970's more than 50 different human models have been developed. Electronic representations of human forms are used in simulation of equipment assembly, operation, and maintenance during the design process in order to "walk through" these activities in order to identify and resolve human interface problems before hardware is built. Early human models used only hands or arms to check clearances for tool manipulation. Today's models create whole-body representations using a basic "link" system resembling a human skeleton to enable posturing of the model within the work environment.
Although a large variety of human models have emerged to support the design effort, there is little agreement about how the human form should be configured, what constitutes valid data, what are acceptable levels of accuracy, and what software/communications standards should be adopted. Earlier human models focused on the physical or ergonomic aspects of human/machine interaction. The focus today is on integrating this information with visual and cognitive information processing requirements and with human modeling simulation to create an integrated modeling technology. This provides additional realism not only through accurate replication of human anthropometry, biomechanics and movement, but also in simulating purposeful and logical behaviors in response to external stimuli and workload.
The purpose of all of these models is to integrate human performance analysis with Computer-Aided Design (CAD) to provide the design team with a high degree of visualization of human performance capabilities and limitations with respect to the product design. Through integration of graphic human models with CAD product models, "rapid prototyping" of human/product simulations or their results can be passed back to equipment designers for resolution of identified problems.
Designing equipment that is easy to operate, assemble, and maintain is often hindered by poor communications between the design team and personnel familiar with the operation, assembly, or maintenance of similar or existing equipment. Improved communication among integrated product development (IPD) team members can be accomplished by simulating equipment operation, assembly, and maintenance using human modeling technology. Human models combine animated 3-D human mannequin geometry with equipment geometry in order to "walk through" designs so that problems can be solved early in the design process. They help to ensure that human-centered design information is readily and accurately documented and preserved to aid in human resources and related logistics planning requirements for system support. The models are used first to influence a product's design for supportability, and then to document the product requirements for human and logistics resources. Another major objective is the development and implementation of design evaluation technology for performance of "design checking" and prescriptive human performance information for recommending corrective action to equipment designers to conform to human performance requirements.
The term "human model" in this context refers to the 3-D, computer-graphic representation of a human form for analysis purposes. It does not address human performance models that are independent of the geometric aspects of the human body, e.g., human error models.
Human modeling systems can support both the design-requirements definition and design evaluation when concepts are only represented in 3-D computerized form. The human design-requirement definition can be accomplished using reach or vision envelops that describe the minimum conditions a designer must satisfy for physical or visual access. Design evaluations, on the other hand, usually focus on critical task segments in which the human/equipment interface is tested for compliance with stated design requirements and freedom from "won't-fit" or "won't-work" conditions.
Some of the important benefits of using human modeling in CAD are:
- Elimination of most physical-development fixtures by performing evaluations electronically
- Reduction of design costs by enabling the IPD team to prototype more rapidly and test a design among themselves
- Avoidance of costly design fixes later in the program by considering human factors requirements early in the design effort
- Improvement of customer communications at every step of product development by using compelling animated graphics to review and confirm equipment function.
Application of human modeling technology is likely to impact how engineers design, build, and test products in the future. Those who are responsible for manufacturing planning, tool design, or maintenance engineering will be able to communicate with structural and systems engineering effectively to illustrate assembly or maintenance problems associated with new designs. It is expected that human model applications will spread beyond what is traditionally called engineering and be used by various IPD team members from factory-built units to product support groups.
Human modeling software programs are available from a variety of suppliers. Unfortunately, they have created models which are very different: both in functionality and in user interface, and in the underlying data driving the mannequins. This diversity has created not only models that look and behave differently, but also models that produce distressingly different results when performing the same engineering analysis.
For these reasons, the Society of Automotive Engineers (SAE) has formed an ad hoc committee to formulate standards to promote the orderly growth of this technology. The SAE Human Modeling Technology committee has established three major subcommittee activities: user requirements, human model definition, and software standards. A fourth subcommittee activity is being considered on the topic of human performance models that would address human error prediction, human workload, and task time estimation.