MCAD MODELLING METHODS: Human Factors Engineering30 Jun, 2004 By: Joe Greco
Virtual prototyping boosts safety, comfort, and ergonomics.
Since our first creative ideas, humans have probably used prototypes for design, engineering, and manufacturing to prove a concept before committing time, materials, and other resources. As concepts and products became more sophisticated, so did the prototypes, making them more time-consuming and expensive to build. These physical prototypes led to improved products, and so fit in with the "better" part of the "better, faster, cheaper" philosophy for designing products, although not with the "faster and cheaper" part. To reduce the time and expense of creating physical prototypes, designers have turned to virtual prototypes.
Technically, an operation as simple as an interference check performed inside a mechanical CAD application is considered a form of virtual prototyping. In addition, any sort of FEA (finite-element analysis) or motion analysis software also falls into the realm of virtual prototyping. Because so many programs fit these definitions, I'm focusing the scope of this article on an area of virtual prototyping commonly referred to as human factors engineering, which includes safety, comfort, and ergonomics. Let's explore these different areas as well as some of the companies whose products support this specialized area of virtual prototyping.
Safety Comes FirstWhen it comes to safety, generally there are two categories-safety when manufacturing and maintaining a product and safety when using it. Employing virtual prototyping to make sure a vehicle is safe in a collision is important, but the manufacturing process of the same automobile, or any other object, should also be safe for those involved. For this type of safety analysis, UGS PLM Solutions (www.ugs.com) has a series of products such as Manual Handling Limits, Low Back Spinal Force Analysis, Static Strength Prediction, and NIOSH (The National Institute for Occupational Safety and Health) Lifting Analysis. The Manual Handling Limits application helps determine the maximum acceptable weight that typical men and women can handle when performing various lifting, lowering, pushing, pulling, and carrying tasks. It's based on 20 years of research conducted at the Liberty Mutual Research Center (www.libertymutual.com/research).
Another developer, Dassault Systèmes (www.3ds.com), has a similar product called ENVISION/ERGO, which is part of its DELMIA product line. Capabilities include analyzing human range of motion, NIOSH lifting guidelines, Garg energy expenditure, upper-limb repetitive motion assessment, and MTM-UAS (Methods Time Measurement). To actually create digital humans, Dassault offers its DELMIA Human products.
Another Dassault Systèmes company, SAFEWORK (www.safework.com), offers SAFEWORK Pro. You specify an initial and final task posture, and from that input it determines variables such as the lifting, lowering, pushing, and pulling weight limits suggested by NIOSH. SAFEWORK also provide tools to create various types of people who may manufacture and assemble a product. Its technology is integrated into CATIA, DELMIA, and is also used in PTC's DIVISION MockUp prototyping software.
Once manufacturing is complete, whether a particular product is as safe as it can possibly be should already be determined. One company on the leading edge of this technology is the ESI Group (www.esi-group.com), which develops more than a dozen products relating to vehicle safety alone. One of its most popular applications is PAM-CRASH 2G for crash simulation. In addition to automobiles, it simulates roadside safety features, such as guardrails, and how they interact with cars in an accident. The software also works with other transportation vehicles such as railroads and boats. PAM-CRASH 2G allows the deformation of a variety of materials such as composites, high-strength steels, and aluminum. The software is also capable of predicting how car interior components, such as dashboard and trims, behave on impact, saving the time and expense of building a physical prototype.
ESI Group offers PAM-SAFE for simulating the effect of restraint systems such as seatbelts and airbags (figure 1, p. 38). New to the application is a Belt Generator utility, which helps you model a complete seatbelt mechanism, including sliprings, retractors, and pretensioners, and then calculate how the parts interact with the occupant. The company's Biomechanics application houses digital models of the human body for use in these applications.
Figure 1. The ESI Group develops PAM-SAFE, which simulates the effect of restraint systems, as with this airbag deployment simulation.
Many programs handle motion analysis, but the only other major product that includes a fairly wide array of safety simulation capabilities is MSC.Dytran 2004 from MSC.Software Corp. (www.mscsoftware.com). Version 2004 is the first MSC.Dytran release to integrate the LS-DYNA solver, which MSC co-develops with LSTC (www.lstc.com). It combines the fluids capabilities of the former with the structural analysis tools of the latter. The update also includes general enhancements to airbag and occupant safety tools such as consideration for out-of-position occupants. In addition, new algorithms make possible calculations that involve the simulation of multi-compartment airbags, fuel tank sloshing, underwater shock analysis, and general fluid-structure interactions. LS-DYNA also works with tools from ANSYS.
Down-Home ComfortVibration analysis is frequently done to ensure that a product such as an automobile will last longer- an engine that shakes less places fewer stresses on its mounting brackets and other areas. However, vibration analysis is also important for the comfort of the passengers in the vehicle and is often grouped together with noise and harshness analysis, otherwise known as NVH (noise, vibration, and harshness).
Several companies develop NVH software. ESI Group offers four products, including RAYON for low-frequency noise prediction, analysis and design, and AutoSEA2, which is used to reduce noise and vibration.
Cambridge Collaborative (www.seam.com/cclayout.htm), has three products: SEAM, visiSEAM, and SEAM 3D. SEAM is the engine behind the other two products, but can also be a front end for analysis templates that a product development company creates in a program such as Microsoft Excel. visiSEAM (figure 2, p. 38) is a network-based pre- and postprocessor for model development and parameter studies for analyzing systems at a component level-for example, studying transmission loss through a panel with damping and absorption treatments. SEAM 3D is a useful supplement to visiSEAM for prototyping the geometry of individual components and the entire model, and for model checking and presenting results.
Figure 2. visiSEAM, from Cambridge Collaborative, analyzes systems at a component level. For example, you can use it to optimize the sound absorption system inside an automobile.
The company's recent efforts aim at bringing acoustical analysis to the front of the design cycle, as opposed to considering it only after other aspects, such as structure and key component placement, are determined. Toward this end, SEAM 3D can read a VRML file generated by a CAD program and view it without the user having to first create an FE (finite element) mesh, as in some other products. The 3D components of the models are assigned materials and acoustical elements (plates, beams, ducts, foams, and so on), and SEAM 3D runs the analysis. After you study the results, you can change the model-adjusting the thickness of an acoustical panel, for example. However, these changes don't update the model. They update in the analysis and you then send these changes to the CAD designer to apply them.
Another player in the NVH market is LMS International (www.lmsintl.com). Its product, LMS Virtual.Lab Noise and Vibration, uses data collected from real-world tests and applies them to a 3D model. After the analysis runs, you can recognize the most critical contributors to noise and vibration and then identify design modifications needed to correct the problem. You can use LMS Virtual.Lab Acoustics to tweak a design to achieve a desired sound-such as a distinctive roar when a motorcycle starts.
LMS also has an application called Virtual.Lab Desktop that ties everything together. For instance, as a CATIA CAA v5 application, the Desktop environment can run inside CATIA with the model it's analyzing. At the same time, you can use Desktop to import FEA results from packages such as MSC.Nastran, ANSYS, ABAQUS, and CATIA's Structural Analysis product. This makes it easy to use the same FE mesh for both structural and NVH analysis while determining how the two affect each other.
ErgonomicsThough ergonomics involves safety and comfort, it's primarily the study of how humans interact with machines, equipment, and consumer products. Because of this overlap, the SAFEWORK product in the Safety section also has tools that you can use as ergonomic design aids.
For creating digital humans for ergonomic studies, there is ManneQuinPRO from NexGen Ergonomics. (www.humancad.com/products/mqpro.html). With a few clicks of the mouse, I found it easy to generate digital humans (figure 3, p. 40). You can move these digital people to any human-compatible position to perform field-of-vision and other studies, including reach and kick simulations.
Figure 3. NexGen Ergonomics ManneQuinPRO lets you complete ergonomic studies in its virtual prototyping environment.
UGS PLM Solutions is also a player in ergonomics with a product called Jack. Jack is the name of the biomechanically accurate digital human, who, along with his counterpart, Jill, you can position in a 3D model. For instance, when used by an automotive designer, Jack and Jill can provide information on possible problems when occupants enter a vehicle or reach for certain controls, as well as pinpoint line-of-sight issues. Virtual humans created in Jack can have various sizes and shapes and are made up of 69 segments, 68 joints, a 17-segment spine, 16-segment hands, coupled shoulder and clavicle joints, and 135 degrees of freedom. The models, based on studies done by the U.S. Army and NASA, can be represented as stick figures, wire frames, and shaded models with varying degrees of transparency.
Dassault Systemes also partners with Immersion Corp. (www.immersion.com), the makers of haptic feedback devices, to help CATIA users with ergonomic studies. The VirtualHand for Design and the VirtualHand for DMU work with Immersion's CyberGlove, CyberTouch, and CyberForce products to enable designers to test and manipulate 3D models in a virtual space.