Engineering News 7839

This mannequin is no dummy

Meet BioRID, a 'pain in the neck' that better mimics human physiology, leading to safer cars

By Rick DeMeis, Associate Editor

Trollhattan, Sweden--Think crash test dummies aren't smart? Well, think again. The latest of these human surrogates, introduced last fall and now in use at Saab, measures forces at many more points than its ancestors. And it also reacts more like a human for better crash-dynamics analyses.

Known as BioRID (Biofidelic Rear Impact Dummy), this dummy with a high IQ was developed by a Swedish consortium that included Saab, Volvo, Chalmers University of Technology (both Goteborg), and Autoliv Research (Vargarda). Co-developer Applied Safety Technologies Corporation (ASTC, North Milan, OH) made parts for the dummy.

According to Elisabet Karlsson, an engineer in Biomechanics and Crash Test Dummies at Saab Crash Safety Center, this mannequin had a long gestation period. The BioRID project began in the autumn of 1994, and the dummy was first "introduced" at a conference in Goteborg in September 1998. Reason for the development: the industry- standard Hybrid III dummy is designed for head-on front-impact research. Its measurement of head-to-torso angle without sufficient measurement of horizontal head displacement is inadequate for evaluating whiplash in rear impacts. Also the neck and spinal structure of the Hybrid III is too stiff to mimic the interaction of a compliant human spine with a seat back. But statistics indicate one out of four vehicular injuries is related to rear-end crashes, and almost 10% of these lead to permanent disability.

Recently, both Saab and Volvo introduced seats which counter the effects of whiplash. But until now, no dummy existed to fully test occupant protection in such accidents. According to Peter Bergqvist, who works on assessing legal requirements and certification in Saab's Technical Department, "The only specified rear-crash test is designed to evaluate the risk of fuel leakage." In the absence of a firm requirement for potential injury evaluation in rear collisions, up until now there has been little motivation to develop a new dummy. Saab made do with a Hybrid III outfitted with a special RID neck in testing its new seat designs.

While such necks went a step further, namely they have seven or nine vertebrae, the devices could be evaluated for angular displacement of the head relative to the torso, but not initial rearward translation of the head and neck, termed retraction motion or "head lag." Although the relationship between head/neck motion and neck injury is not completely understood, research suggests that rapid linear head displacement relative to the torso occurs in a majority of injury cases.

Researchers developed BioRID with greater human fidelity in mind. On the need for a dummy allowing the measurement of small effects in a rear collision, Saab safety engineer Kristina Wiklund, responsible for front-seat development, notes, "In whiplash-related injuries, the pressure changes are very small." The changes she refers to are those in the vertebral canal, thought to be the source of neck injuries. "Dummies of the past provide no scope for measuring pressure changes. They merely measure large movements and acceleration changes."

A dummy with backbone. The BioRID is aimed at measuring head movement and acceleration differences between the head and chest. The first models are average (50th percentile) males and feature 24 neck and spine vertebrae--the same number as in the human body. Based on software simulation results (TNO-MADYMO North America, Northville, MI), durable plastic vertebrae are connected by pin joints incorporating linear torsion springs and polyurethane bumpers to resist flexion and tension, mimicking the body's crash response. Designers tweaked the angular range of motion of the vertebrae relative to one another to account for that of a seated person. Through the adjustment of the torsion pin attachments, the angle of one vertebra to another can change to produce various spine curvatures, and thus different seating postures.

Spring-loaded and damped wires leading from the head down through the cervical vertebrae serve as posterior and anterior neck muscles, replicating head lag. A silicon-rubber molded torso, along with a Hybrid III head, arms, legs, and a modified pelvis, round out the mannequin. The torso accounts for about 40% of the upper body stiffness (most of which resides in the spine) and a 2l water-filled bladder in the abdomen is used to reduce torso bending resistance. A layer of Teflon between the "spine" and the torso reduces friction between the two. Finally, to duplicate the low friction found between human skin and clothing, Mr. BioRID is nattily dressed in two layers of elastic nylon and Lycra, both shirt and pants.

Initial work with the BioRID is encouraging. While much closer than the Hybrid III to replicating results obtained with human volunteers, some Bio-RID adjustment looks to be necessary in the areas of upward head and thoracic vertebrae motion. Changes will likely include reduction in thoracic spine stiffness and extension of the "neck muscles" to include parts of the thoracic spine. And in a way, the research is complicated by working with human volunteers--they understandably "tense up" when they expect a collision, skewing the results. In addition to the consequences of such muscle activity, initial seating posture--a result of specific seat design--also greatly affects accident kinematics and loads on seat structures.

Saab is using one of the four BioRIDs currently in existence. Another is on loan to the Insurance Institute for Highway Safety (Arlington, VA) to test dummy usability and for seat evaluations, in which the Volvo seat design passed three crash tests (see DN 2/15/99, p. 24). Karlsson concludes that "Bio-RID technology will be made available to other companies after the validation program."

Thanks to dummies like BioRID, automotive engineers can design smarter, more effective occupant protection systems. And neck injuries from all kinds of auto accidents will be better evaluated and reduced.

For more information on Simulation software from TNO-MADYMO North America,
call 1-800-828-6344, x 011, product code 4674

Materials from DuPont, product code 4675

What this means to you

Have you driven a Volvo lately?

Where is the emphasis on safety headed? One Volvo official notes: After Ford announced in Goteborg its intention to buy Volvo's automobile operations, the first facility the Americans wanted to visit was Volvo's safety center. Ford is aiming to be an American leader in safety development. Ford Biomechanics Technical Fellow Priya Prasad is "proud of the fact that Ford has the highest number of vehicles with four- and five-star ratings in U.S. National Highway Traffic Safety Administration crash test results." He says safety has to go beyond regulations, noting, for instance, "We will do testing with 5th percentile (small woman) and 95th percentile dummies, with the seat in the full forward and rear positions--not just a head-on test at 30 mph with a 50th percentile dummy."

While study of human dynamics in auto collisions has benefited by BioRID development, the Swedes are also pushing ahead in direct analysis of vehicle collisions. To develop and validate collision models, Volvo is expanding its safety research center to the tune of $81 million. The centerpiece of the upgraded center when it opens in about a year will be a test facility that can hurl any two vehicles (cars, trucks, and buses) at each other (or other objects) at any angle, ranging from head-on to 90 degrees , and simulate rollovers.

Jan Ivarsson, Volvo property manager for new cars, notes there is always room to improve--as occupant protection increases in one area, the database will indicate other areas with potential for improvement. Thus when designing the new S80 sedan, he notes, "We had a solid base of cases focused on head protection, especially in side impacts." Result: introduction of the company's new Inflatable Curtain (IC) on the S80. Deploying down from the roofline, the IC protects both front and rear passengers during side impacts. In rollovers, sensors keep the curtain inflated for three seconds.

Polyimide washers give pickups added thrust

Livonia, MI--Ford Powertrain Operations' redesigned electronic, four-speed automatic overdrive transmission has added thrust, thanks to a washer. You'll find it on 1999 Ford Super Duty F-Series pickups equipped with 7.3l diesel turbo engines.

Ford engineers wanted a thrust washer that would experience low wear and friction for a long service life in a demanding torque converter environment. The washers prevent wear between a 12-inch-diameter converter clutch piston and a converter turbine hub. The engineers found the appropriate washer material in Aurum(R) JCL 3030 thermoplastic polyimide from Mitsui Chemicals (Purchase, NY). The self-lubricating, high-strength, carbon-fiber-reinforced polyimide cuts down on wear at high-pressure and velocity levels.

HPG Powertrain Systems, a unit of Huron Plastics Group (Port Huron, MI), injection-molds the washers on a standard 150-ton machine with a four-cavity mold equipped with a hot runner. "Processing attributes of Aurum, such as low mold shrinkage and hot-runner capability, allow tight tolerance at a reasonable component cost," notes Dan Evans, HPG engineering manager.

Before selecting the material, however, Ford engineers required that Aurum samples undergo ASTM heat-aging tests. The samples had to be immersed in two Exxon automatic transmission fluids at 350F for 1,760 hours. The polyimide exhibited no change in properties, including tensile strength, elongation, and Izod impact strength.

"Aurum's exceptional heat resistance and ability to withstand high pressure and velocities is founded on its high glass transition temperature of 482F," explains Lee J. Hyde, Mitsui's business manager for the Performance Polymers Div. "That's why the material also has entered other demanding automotive and off-highway applications, such as oil-seal rings and check balls, turbocharger bearings and retainers, and components for steering, suspension, small-motor, and braking systems."

Nylon improves pool heater performance

Westlake Village, CA--Raypak has replaced brass and glass-lined cast iron header manifolds in its residential pool and spa heaters with injection-molded nylon 6,6 resin. Result: longer-lasting, less expensive parts.

"Going into this project, our three main criteria were to eliminate machining operations in our own plant, use material impervious to corrosion, and have the freedom of design that metal forming processes didn't allow us," reports Terry Doyle, Raypak project engineer.

Mounted on either end of a bundle of copper-fin heat-exchanger tubes, the manifolds direct-cool water into the heat exchanger, then direct heated water out into the pool or spa. Under these working conditions, the manifolds encounter temperatures as high as 140F, chlorine levels up to 10 ppm, a pH range of 5 to 9, and water velocities up to 25 ft/sec. Industry standards also require that the manifolds withstand burst pressures of 150 psi (l,034 KPa) and water temperatures to 210F.

Raypak engineers evaluated several thermoplastics--including acetal, nylon 6, polysulfone, modified-polyphenylene ether, and polyester--before selecting Capron(R) nylon 6,6 supplied by AlliedSignal (Morristown, NJ). "AlliedSignal became a partner in the design process," Doyle explains. "We are just starting to get into plastics, and they stepped up to the plate and helped educate us so we could communicate with injection molders and get the results we needed. We were under a tight deadline on this project, and Allied kept us on track."

"Now, the internal manual bypass is more precise," Doyle says. "We have 100% repeatability of the seat closure, complete drainage of water for fast, simple winterization of the product, and screw-on plumbing connections for PVC pipe. We used surface-mount technology for the high limits because we could mold a boss into the heater, thus eliminating two threaded parts and possible water leaks."

In addition, the switch to plastics offers advantages on the manufacturing side. "We no longer have to machine in house, so we can dedicate more floor space to R&D and production," Doyle adds. "The turnaround time on plastic parts is much faster than cast, so we can reduce inventory and work more JIT."

Foam gasket battens down battery hatch

Beaverton, OR--The battery-hatch opening on Tektronix's newest portable TV radio-frequency (RF) signal analyzer required nearly half the 11 x 8-inch back side of the unit's case. The challenge for David Engquist, a Tektronix mechanical engineer: make the cover easy to open, and seal the closed hatch tight enough to make the instrument suitable for operation outdoors.

The SignalScout^TM RFM151 analyzer measures the digital and analog coaxial RF signal quality of cable TV networks, including signals of hybrid fiber/coaxial systems. It can isolate hard-to-detect shortwave or citizens-band radio interference in low-level, return-path frequencies. Such frequencies normally transmit data from converter boxes, such as when a consumer chooses a pay-per-view movie, or from a cable modem, when a user accesses the Internet through a cable TV service.

Technicians use the instrument outdoors for testing newly installed lines, performing semiannual FCC-required signal quality measurements over a 24-hour period, and troubleshooting cable plant problems, including those during recovery from major storms. The specification that technicians had to be able to open and close the analyzer's hatch effortlessly when changing the battery in the field increased the challenge of designing a weather-resistant seal. It ruled out using a gasket material that required significant compressive force.

One other material-qualifying requirement centered on the analyzer's UL rating. Because it is possible for an overcharged battery to generate excess heat, the analyzer incorporates two lines of safety defense: a load-current sensor that automatically turns the unit off at a specified amperage, and flame-resistant materials.

Working with Boyd Corp. (Modesto, CA), the company that makes the gasket, Tektronix chose a medium-modulus silicone foam for the seal. The Poron(R) material, supplied by Rogers Corp.'s Bisco Materials Unit (Elk Grove Village, IL), has a UL rating (UL94HBF) and also the right resistance to compression set (10% maximum when compressed to 50% for 22 hours).

"With four thumbscrews to hold a fairly large battery hatch, we needed a material firm enough to form a very good water barrier, but soft enough to avoid having to exert a lot of force to close the hatch," Engquist explains. "A high-modulus material requiring a lot of compression would make it difficult to get the screws started properly in the threads of the fittings."

Using geometries of the hatch from his CAD system, Engquist did some quick tolerance analyses and decided on a 0.093-inch-thick gasket. "I knew I had to compress it a minimum of 10% to maintain a tight seal over time, and I needed a margin for process variability," he says. "Given these constraints, I determined that when the battery hatch was closed, I needed a compressed gasket thickness of just over two-thirds of the uncompressed thickness."

To ensure the material would meet its environmental challenges, Engquist did a "Danner boot test" on some early prototypes to determine water resistance. Just as a boot manufacturer fills its boots with water to test water tightness, Engquist filled the back half of the case with water to see if the closed hatch would leak.

"Of course, the instrument was put through environmental chamber tests that included a drenching spray," Engquist adds. "The gasket created an excellent seal."

Based on the success of this application, Tektronix plans to use the material on an upgrade kit for the RFM150 signal analyzer, a model that previously required technicians to return to the office to recharge a battery sealed inside. The new SignalScout analyzer comes with a three-year warranty.

Motion processor increases wafer throughput

Lexington, MA--Eaton Corp.'s Implant Systems Div. uses Performance Motion Devices' (PMD) MC1401A motion-processor chipset in two new wafer-handling controllers. Used for semiconductor manufacturing, the controllers provide quick and precise handling of delicate silicon wafers in medium- and high-current ion implanters. "Our motion processor helps achieve higher throughput, reduces size and cost, and increases system performance," says PMD Chief Technology Officer Chuck Lewin.

The MC1401A programmable chipset is available in 1-, 2-, or 4-axis configurations that perform complete motion sequences such as "move to a point at this velocity and acceleration" or "maintain position using PID control." It consists of a processor for profile and PID calculations and a logic device to handle motor-specific functions such as encoder feedback. As part of Eaton's Micro3 general-purpose, three-axis motion controller, the MC1401A controls low-current dc brush-type motors and associated sensors and actuators on Eaton's 300-mm medium-current ion implanter.

The ability to generate smooth trajectories was a key requirement for the motion controller, according to Eaton's Line Product Manager Mike Harris. "PMD's MC1401A motion processor was selected primarily for its S-curve motion profile capability," he says. "Previous-generation controllers were limited to trapezoidal moves, which can put increased stress on the load or the drive mechanism, resulting in vibration. By using S-curve profiles, the cycle time of certain moves was reduced by as much as 20%." PMD's Lewin says that the motion processor enables tighter positioning control throughout the move profile and improved positioning accuracy at the profile destination. Both are critical in improving throughput and performance.

According to Harris, Eaton chose the MC1401A after investigating alternative solutions such as off-the-shelf motion cards. "The high integration and PWM interface of the PMD chipset helped us achieve our goals by enabling a significant component-count reduction over previous designs."

Fasteners lock 'lucky ticket' printers

West Greenwich, RI--Lottery players rarely stop to think about the machine spewing out their lottery tickets, but it's GTECH Corp.'s business. The company is a leading supplier of online lottery terminals and printers in 29 states and 34 countries.

This spring GTECH will introduce the AccuTherm8^TM thermal printer, which is held together by 26 PEM(R) fasteners, in nine types, from Penn Engineering and Mfg. Corp. (Danboro, PA). The printer hooks up to wager-entering terminals in convenience stores and other venues that sell lottery tickets, and spits out the customer's receipt, or "lucky ticket."

Within the printer, a mechanism prints on the paper and cuts the tickets. PEM(R) fasteners get pressed into a sheet-metal frame, which serves as a "skeleton" for the printer since several of its parts, such as the drive train and pc-board, are attached to it, says Anestis Halkidis, principal mechanical engineer for GTECH.

The most common fasteners that GTECH used in the printer are type SOS stainless-steel threaded standoffs, located on two ends of a roller that guides the ticket paper within the printer.

Other fasteners include KEYHOLE(R) stainless-steel standoffs, which are points to hook extension spring loops with a groove on one end as part of the printer's spring-loaded latch.

GTECH also used Type BSOS steel blind-threaded standoffs to align the printing head bracket to the ticket paper-cutter assembly. Type TPS^TM stainless-steel, flush-mounted pilot pins further align the printing head bracket. Type CLC stainless-steel threaded nuts attach the ground strap to the printing head bracket.

Type FE miniature self-locking threaded fasteners attach the printer's plastic outer skin to the metal frame, while Type LAC stainless-steel floating-thread fasteners anchor the plastic outer skin to the metal frame. GTECH engineers used Type PFC2 pre-assembled, spring-loaded, stainless-steel panel fasteners to attach the power supply to the plastic base at the unit's bottom.

GTECH selected PEM fasteners for use in various parts of the printer because they are an industry standard, says Halkidis. Since the machine will be taken apart for maintenance, adhesives were not an option due to their permanence.

Other deciding factors included the fasteners' availability. "We can go to one company to satisfy all our needs," he adds.

Switch to PC-based CAD brings unexpected benefits

Atlanta, GA--Electromagnetic Sciences switched from UNIX-based CAD systems to Gateway PCs and Solid Edge CAD from Unigraphics Solutions (St. Louis, MO). The company was hoping for savings in hardware costs. It got that and more. Productivity went up by 20%, and the company became more competitive.

Electromagnetic Sciences manufactures microwave communications equipment. The mechanical engineering department produces machined parts, such as specialty wave guide and antenna products and packaging for electronic systems--all components of larger communications systems.

Reasons for the company's increased productivity after the CAD switch include the software's ease of use and ability to model complex parts.

"Our engineers spend only 25% of their time on the CAD system, so they need something they can pick up again quickly," says John Voss, mechanical engineering manager at Electromagnetic Sciences. "Solid Edge's functions are all similar in how they operate, and it's easy to know what to do next. You can leave Solid Edge and come back to it and be productive right away."

Solid Edge can accurately model the most complex parts the company produces, says Ike Chapman, senior systems analyst. "There's a very common part, called a microwave switch, that's in just about every product that goes out the door," explains Chapman. "It has no moving parts, and typically it's machined as a single piece or as a split housing and then assembled. The problem is a raised portion in the middle of a Y that must be machined to very tight tolerances. But the raised portion has a radius that is not a full blend radius, and we couldn't model it in any CAD system until Solid Edge."

The ability to model this part in Solid Edge eliminates the extra work previously needed to document and manufacture it, says Chapman. In the past, the designer left the corners on the solid model square, and "fooled" the drawing into seeing the radius by disassociating the drawing from the model. A draftsman would doctor the graphics to make the blend look right and then send the drawing to the shop where special techniques were developed to machine that surface.

"Now that we can fully model the part, we don't have to modify the drawing views to get those surfaces in there," Chapman says. "We know we have good clean data and an associative link that lets us take the model, put it on a drawing sheet, put the dimensions on it, and we're done."

From the solid model, Electromagnetic Sciences also derives accurate weight estimates. In space work, every gram is critical. "In the past, we would analytically estimate weight, so we used a large contingency factor to account for any uncertainty," says Voss. "Now that we're able to prepare an accurate solid model so quickly, we can use precise weights. As a result, we've reduced the contingency factor to a fraction of what it was. That's another way the software helps us be more competitive."

Engineers are also more productive because they spend less time moving paper around the building. Before engineers had their own CAD systems, designers and drafters printed out drawings for engineers to review. Now engineers call up models on their own computers.

Don't forget analysis. Electromagnetic Sciences also purchased five seats of MSC/Nastran for Windows from The MacNeal-Schwendler Corp. (Los Angeles) to perform structural and thermal analysis of its designs. FEMAP, the pre- and post-processor for MSC/Nastran for Windows, generates finite element models directly from Solid Edge models. Not only does this result in analysis models that accurately match original designs, it saves engineers time because finite element models no longer need to be generated by hand.

This year, Electromagnetic Sciences says it will extend its use of Solid Edge. The company plans to purchase a program that lets Solid Edge import 3D pc-board assembly models and incorporate them into mechanical models. The company also plans to install a product-data-management system and start handling configuration management electronically--part of the larger, company-wide move to go paperless.

Cool as a moose

By Rick DeMeis, Associate Editor

Trollhattan, Sweden--An area of what Saab calls "real-life safety" is highlighted by Tony Landh, Saab product improvement area manager. In going beyond mandated tests, the company does its "moose test." Here a 900-lb rig of steel cables simulates the body mass and dynamics of this tall-standing animal. The test simulates a collision where the nose of the car goes between the side legs of the animal and the torso impacts the windshield and the supporting A pillars of the structure--the animal's body must not penetrate the passenger cabin. Folks in New Hampshire, where one state motto is "Brake for moose, it could save your life," and other northern states know how hazardous such encounters can be. The test came about after company rally driver Erik Carlsson hit a moose while testing a car. The joke among Saab engineers is it's a good thing there are no elephants native to Sweden.

Bus stop?

Rohnert Park, CA--"In the future, no one will be putting motion control inside the bus," predicts John Walewander, marketing manager for the Compumotor Div. of Parker Hannifin Corp. "In fact, a bus is the worst place to put a board-level motion controller."

Why? Excess cabling, for one thing, says Walewander. With a bus, which is a PC-backplane, all communication connections are outside the computer, requiring signals to be transferred to and from the box. "The more axes of control, the worse it gets," he says.

As a point of comparison, Walewander estimates that a motion controller with eight axes of control would require a jumble of 200 discrete wires. A network, on the other hand, requires only a single cable.

As an alternative, Compumotor is betting on the standard Ethernet LAN. A serial bus, a network is an extension of a PC's backplane and is designed to move more data, faster. The company's first Ethernet-based product is the 6K Motion Controller, which delivers up to eight axes of control. "With a single cable, engineers can get bus-like performance," Walewander says. "As a consequence, we expect network-based products to quickly eclipse bus-based systems."

Other companies are also jumping on the network bandwagon. Galil Motion Control, for example, has a stand-alone controller called the DMC-2000. It uses Universal Serial Bus (USB) as the backplane.

Not all companies, however, agree that networks will supplant the bus. "We think there is room for both types of systems," says Curt Wilson, president of engineering and research at Delta Tao. "In fact, we believe that a network pays off in only a minority of the applications today."

If you're wondering what those applications are, Wilson has this advice: "If you are basically happy putting all of your electronics in the same cabinet, there is no point of going to the extra expense and complexity of a network. In fact, nothing achieves tight integration better than putting the controller onto the backplane."

As for the wiring, Wilson says that a network doesn't really reduce the number of wires. Rather, it just reduces the length of the wires. "People go to great expense to install a network," he says, "and wind up with a bunch of 6-inch-long optical fibers."

Prototype system speeds auto R&D

Basildon, U.K.--Ford Motor Co.'s Advanced Vehicle Technology (AVT) teams are incorporating Helisys' LOM^TM 2030 rapid-prototyping system into their design processes. This change is in line with Ford's continuing effort to improve productivity and streamline design and development.

Engineers initially acquired the LOM 2030 to support body trim and design development, producing parts for visualization, form, fit, and function purposes. Now designers also use the machine to fine-tune component designs such as steering wheels, bumpers, and grills. In addition, the LOM 2030 produces patterns for limited production parts such as exhaust manifolds.

Ford's prototyping process begins when one of the company's R&D centers sends a solid CAD design to the Basildon design workshop. The model is then post-processed as an STL file and checked for discrepancies.

Before downloading data to the Helisys system, an engineer programs the profiling laser's speed and power and the size of any cross-hatching. Next, a laser beam profiles and cuts separate laminations of polymer-coated paper of plastic sheets. The layers are then bonded and compressed under a heated roller to create a finished, laminated 3D model. Sanding removes any rough edges.

Ford engineers note that a key advantage of using the LOM technology is the reduction of product and production costs. Helisys' stereolithography processes use adhesive paper, which is easier to store and handle than liquid plastic. And, the paper doesn't produce toxic fumes.

At the same time, using the system has increased productivity, according to Ford. The LOM 2030 has helped turn weeks of work into days, and in some cases, the machine has rendered prototypes in 24 hours, say company engineers.