Design committee considers 737 rudder fixes
NTSB blames rudder's hydraulic power control unit for Pittsburgh crash
By Charles J. Murray, Senior Regional Technical Editor
Washington--Redundancy: It's a simple concept. Install an extra power unit, and if the first one fails, the backup handles the load. For decades, it's improved the safety and reliability of end products ranging from power plants to airplanes.
Recently, however, the concept of redundancy grew more complex. Investigators from the National Transportation Safety Board (NTSB), reviewing the 1994 air crash of a Boeing 737 near Pittsburgh, ruled that the accident was caused by the failure of a power component in the rudder. Their conclusion: The component needs a redesign to make it "reliably redundant."
For all engineers, the conclusion raises a key question: What exactly constitutes redundancy? In the case of the 737 rudder power control unit, many engineers were baffled by the NTSB conclusion. Even the Federal Aviation Administration (FAA) was surprised. "We believe that there's redundancy in the existing system," notes Federal Aviation Administration spokesman Les Dorr. "We think it's still the way to go on this aircraft."
In the interests of safety, however, NTSB investigators drew a fine distinction and determined that it wasn't redundant enough. As a result, Boeing and its vendors will probably need to undertake a major redesign of the power control unit (PCU) over the next few years.
One in a billion. The controversy began after the Pittsburgh air crash, which killed 132 people. NTSB devoted four and half years to the subsequent investigation, the longest in the agency's 32-year history. After culling through countless hours of tapes and digital data, agency investigators eventually singled out the rudder's power control unit as a primary cause of the crash.
They believe that the accident was caused by "rudder reversal." That is, the rudder did the opposite of what the pilot commanded.
In the Pittsburgh scenario, pilots were believed to be reacting to wake turbulence when rudder reversal allegedly occurred. The turbulence caused the 737 to roll left. When the pilot tried to compensate by rolling back to the right, however, the rudder reversed, and the aircraft rolled even harder to the left. Ten seconds later, it stalled, dove 5,000 feet, and crashed.
Sometime this year, a design committee is expected to recommend fixes that would prevent such accidents from occurring again. Because the existing power control unit is not "reliably redundant," the agency says, a major redesign will probably be required.
Observers say that the redesign will probably fall into one of two categories: Engineers might have to change the rudder itself, going to a two-panel configuration instead of single panel. Or they might employ two separate hydraulic actuators.
The rationale behind the changes is simple: Two separate systems are safer than one. According to Federal Aviation Regulations, a critical system that does not have redundancy must exhibit extraordinary levels of reliability. Specifically, the critical non-redundant component design must go a billion hours without a crash-related failure.
| The control valve in the rudder’s PCU employs two concentric servo ‘slides.’ The NTSB says that the concentric slides don’t constitute a redundant system.
Although that billion hours is distributed between thousands of power control units, it's still an incredible figure. Spread across 3,000 Boeing 737 rudders, it amounts to 38 years per aircraft, used 24 hours per day.
That, however, is where redundancy comes in. On a two-actuator system, the required time between component failures could drop as low as 100,000 hours. The reason: backup power makes the reliability of each individual component less critical.
Failure debate. Still, many engineers believe that the existing system is redundant.
The current power control unit employs a dual concentric servo valve. It consists of a primary hydraulic slide, which resides within a secondary slide. Both slides are contained within a single servo valve enclosure about the size of a Coke can.
To actuate the rudder, the pilot pushes on a foot pedal, which moves a linkage attached to the servo valve. The servo mechanism then shifts almost imperceptibly--total deflection is about the thickness of a dime--thus sending hydraulic fluid to the power components that move the rudder.
In most cases, the combination of primary and secondary slides offers some measure of redundancy. But experts say that in a rare few instances, the two concentric slides could malfunction together. Indeed, the National Transportation Board believes the two slides malfunctioned together in Pittsburgh.
In that accident, they cited a "secondary slide jam" and overtravel of the primary servo slide as the cause of rudder reversal. The primary, they say, traveled too far, causing hydraulic ports to misalign. That, in turn, caused hydraulic fluid to flow in the wrong direction.
NTSB officials believe the PCU was also at fault in a 1991 accident in Colorado Springs that killed 25, and in a non-fatal accident in Baltimore. As a result, they say that the current PCU design has failed three times in 90 million hours of flight. That's one in every 30 million hours--a far cry from the one-in-a-billion standard.
"There were also other incidents in which the valves still functioned, but the potential for failure was there," notes John Clark, NTSB deputy director of aviation safety. "We found corrosion and shotpeen balls in the valves, which could have interfered with proper operation."
Not everyone agrees with the NTSB findings, however. The FAA, Boeing, and the PCU's vendor could not duplicate the failure scenario in flight tests. And investigation of the PCUs involved in the accidents gave no hard evidence to suggest that a mechanical or thermal jam occurred in the secondary slides. As a result, many industry observers said they were "astonished" by the NTSB findings. "To our knowledge, there was no hard evidence to show that the PCU on Flight 427 failed that way," Dorr says. "The decision was made by process of elimination."
Some experts believe that it's equally likely that the pilot or co-pilot stepped on the wrong rudder pedal.
To be safe, however, the FAA and Boeing have taken action to eliminate the possibility of rudder reversal. A 1997 directive called for a redesign of the dual concentric servo valve. The redesign prevents primary slide overtravel and hydraulic port misalignment on that unit. Boeing complied, and the redesigned units will be installed on all Boeing 737 aircraft by August 1999.
More to come. Still, the NTSB design committee is expected to call for the pending changeover to a "reliably redundant" PCU. That may mean that the redesigned dual concentric servo valve will ultimately require replacement.
Redundancy, Clark says, is particularly important for an aircraft such as the 737. Because the engines are out on the wings, it is subject to large, thrust-induced yawing moments. As a result, failure of the rudder is more critical than it would be on an aircraft with engines next to the fuselage.
Nor is the concept of redundancy a new idea in rudder design. Newer aircraft, such as the Boeing 757 and 767, have redundant rudder packages. Many more have redundant elevator packages. "It's the same reasoning that you use when you put two engines on an aircraft," Clark says. "Redundancy enables you to more easily handle a failure."
Engineers are looking at ways to provide that redundancy without tearing down the rudder and starting from scratch. Some believe that the existing manual stand-by actuator could be equipped with sensors, thus enabling it automatically react to a primary system failure. But it's not known whether the design committee would accept such a fix.
The larger question is whether any hydraulic actuator design can exceed the performance already achieved by the 737 PCU. First built in the mid-1960s, the 737 has become Boeing's best-selling, longest-lived product. More than a million people ride on 737s every day. Its safety record is considered one of the best in the industry.
Experts acknowledge that few, if any, hydraulic designs have exhibited such records. "Thirty million hours is an awfully big number," notes Bob Doll, a research engineer at Milwaukee School of Engineering. "It's a lot more than in the industrial world."
While they await the design committee's decision, Boeing engineers are considering alternatives that would meet the NTSB's demand for reliable redundancy. In the meantime, they're also examining how those alternatives would impact the aircraft's other flight surfaces. Says a Boeing spokesman: "We just want to be sure that everyone keeps the entire safety picture in mind."
What this means to you
More changes to come
Many experts believe that the NTSB design committee will call for one of two "reliably redundant" fixes in the coming year.
A two-panel, split rudder, each with its own control unit…
The redesigned PCU, installed on every 737 by August,
fixes the problems that could cause rudder reversal.
It accomplishes that by:
Eliminating primary slide overtravel
Tenderizer adds spice to meats
Reno, NV--Picture this. A sturdy tray with a spiked rolling pin that pierces meat, also lacing it with flavorful marinade. The system beats labor-intensive pounding or poking of the meat with forks and mallets.
Inventor Michael W. Thompson, president and CEO of Soaring T Inc., brought his Gourmet Tenderizing System from concept to market in just nine months. To make this possible, he got assists from RTP Co. (Winona, MN) and local business partners.
After a patent search, Thompson turned to Synergy Technology Inc., a design firm, to develop the complex tooling. "Early on, we brought in an RTP team from the company's nearby Dayton plant to help sample materials," says Synergy engineer Ray Bryan. "Although I try to stay neutral, the convenient location of RTP's lab and blending facility, combined with its successful track record on other projects, made it the best choice for this project."
RTP engineers formulated two specialty compounds that exceeded Soaring T's standards. They enabled Thompson to offer customers a 10-year system warranty against melting or warping, even if the product undergoes many cleanups in the bottom rack of a dishwasher.
Because of its good dimensional stability, engineers specified RTP 100 series mineral-reinforced polypropylene compound for the marinade tray. The FDA-compliant, pre-colored component has a visually appealing granite-fleck gray finish to add an extra touch of consumer appeal.
An FDA-approved RTP 300 series polycarbonate forms the three-piece rolling pin assembly. Internal lubrication of the material allows the parts to glide smoothly with minimal wear. The polycarbonate has a flexural strength of 12,000 psi (83 MPa) and an unnotched impact strength of 35.0 ft lb/inch (1,869 J/m) at 1/8-inch. A heat-deflection temperature of 270F (132C) at 264 psi keeps the pieces from warping.
QVC, the popular cable TV marketing network, began selling the system late last year. "Without the aid of our partners, we wouldn't have met our extremely short delivery deadline with QVC," says Thompson. "They made our needs a priority, and our product fly."
'Safety first' circuit plugs into nylon
Long Island City, NY--Eagle Electric recently introduced its "safety first" ground fault circuit interrupter (GFCI). Before putting it on the market, however, the company launched a search for a material that would help the GFCI beat the competition.
The GF 15 device features a built-in LED lamp that serves as both a correct wiring indicator for installers and a "trip" indicator for consumers. During the installation test, the device lights to indicate proper line-to-load connections. If the indicator does not light, the contractor knows a wiring error exists that needs correcting before having to make a costly call back or an accident occurs.
After installation, the GFCI lights only when tripped to alert the user that a ground fault has been detected. The indictor light also helps educate homeowners about the protective function of the GFCI and how it works.
In addition to the safety features, the product offers other benefits to contractors: side and backwire installation holes, easy-access ground screw placement, a built-in wire stripper, and a long mounting strap. With all of these features, the device measures just 1.170-inch deep, 1.688-inch wide, and 2.670-inch high.
Eagle Electric needed to produce millions of the new product and still make it cost competitive. "We started the redesign with a 'wish list' based on years of feedback from the field," says Yuliy Rushansky, Eagle's manager of new product development. "The only viable material choice was nylon. We chose Capron® 8202 nylon 6 (AlliedSignal Plastics, Morristown, NJ) for its chemical resistance and because it flows easily to form a thin-wall part." The material also had to meet V2 electrical standards.
Capron 8202 has a tensile strength of 11,500 psi (80 MPA), a flexural strength of 15,700 psi (110 MPa), and a flexural modulus of 410,000 psi (2,825 MPa). It melts at 420F (215C).
How has the redesigned GFCI been received? It obtained a letter of commendation from the chairman of the U.S. Consumer Product Safety Commission, and Today's Homeowner magazine also selected it as one of the Best New Products for 1999.
Controller simplifies fabric manufacture
By Charles J. Murray, Midwest Technical Editor
Valdese, NC--In many applications, PLCs serve as an industrial brain, controlling acceleration, deceleration, timing, and positioning of actuators.
But not every application needs a full-fledged PLC. That's what engineers from the Valdese Weaver Co. learned when the firm recently updated its textile manufacturing operation. The company, which manufacturers high-end woven fabric for the fashion industry, sought to improve the speed and uptime of its machinery. Its existing operation required too much starting and stopping of machinery for monitoring, fabric repositioning, and resetting of dials.
After first considering a combination of industrial speed controllers and a master PLC, engineers ultimately selected five CX-1000 controllers from Contrex Motion Control Products, Maple Grove, MN.
Engineers located the five CX-1000 controllers at the system's five wash boxes, which wash fabrics after they leave the company's looms. Fabric passes through the five boxes in succession, then moves to so-called "tenter frames" for drying. In the application, the CX-1000 controllers track speed ratios and monitor the number of yards of material processed at each station, thus enabling them to "know" if the fabric is stretching.
Consultants who worked with Valdese Weavers say that the CX-1000 controllers helped them to simplify the design, reduce initial labor, and lower costs. Unlike full-fledged PLCs, which typically require dedicated HMIs, the CX-1000 speed controllers displayed data on small, integrated liquid crystal displays. "By eliminating the PLC, we got rid of the HMI, and all the associated wiring," notes Jack McManus of Bryant Electric Supply, a distributor who helped the system integrator, Industrial Controls (Hickory, NC).
McManus estimates that system integrators cut 50 hours from the 150-hour project by using the CX-1000s, instead of a conventional PLC. He says that the next such project would eliminate even more hours, as engineers grow accustomed to the CX-1000 setup. Ultimately, he says, the CX-1000 could reduce labor time to about 20% of what it would be with a conventional PLC-based system.
CX-1000 controllers can be used on web drives and extruders, among others.
Contrex engineers say the systems targeted at single-station machines or retrofitting of older manufacturing lines. "This is for those applications where you don't need the custom touch screens and PLCs," notes Glen Gauvin, vice president of sales and marketing for Contrex.
Pressure-sensitive adhesive tapes help rearview mirrors stick together
Painesville, OH--Your car's rearview mirror, so indispensable when changing lanes, presents a manufacturing challenge: joining two dissimilar materials, the glass mirror and plastic housing.
Conventionally, manufacturers use RTV silicone adhesives to join the mirror and housing. While the compliant bonding material accommodates the thermal expansion mismatch, the adhesives require a minimum of 24 hours to cure.
In addition, while being shatterproof is not a requirement on rearview mirrors in the U.S., it is in Europe. This can present problems in today's global marketplace. Rearview mirrors take a beating from the environment, as they are exposed to heat, humidity, and moisture, among other extreme conditions.
Enter Avery DennisonTM FM 2453 pressure-sensitive adhesive (PSA) tape from the company's Specialty Tape Div., which bonds to PPO or PPE plastics with an instant cure to save the inventory time previously found with longer cure times. The PSA tape can be used anywhere an RTV silicone was previously used in a mirror bonding application. Avery tested the adhesive to meet temperature, salt spray, and heat requirements, according to Tom Epple, senior research associate for Avery Dennison.
The PSA tape is a black foam carrier coated with acrylic adhesive on both sides. The adhesive on the outside bonds the foam to the mirror, so the foam can get into the gap space between the plastic and glass materials, Epple says. The manufacturer applies one side of the tape to the glass mirror using a machine, then applies the other side of the tape to the plastic housing by hand.
An advantage is that mirrors bonded with the FM 2453 PSA meet international shatterproof requirements. Manufacturers who use RTV silicone apply it in heavy dabs and swirls, so it does not completely cover the mirror and therefore does not meet the shatterproof requirement, Epple notes.
When the PSA tape-bonded mirrors were put to the test, the tapes experienced different results. "When the testers swung the pendulum into the mirror to break the glass for the shatterproof test, the key is that the PSA adhesive tape stuck to every part of the back of the glass," Epple says. "With the foam filling in all the gaps, you can be sure that when you apply the mirror to the tape, you get 100% coverage."
While Avery developed the PSA, which General Motors uses on the rearview mirrors for two of its truck platforms and Daimler-Chrysler uses on Dodge Dakota rearviews for use in automotive applications, the adhesive tape is being trialed in others. Epple says the PSA may find future use in rubber bumper strips on boats because of its water resistance, and on bumper strips for vehicles like golf carts.
Cost top concern for auto engineers
Detroit--Cost reduction once again topped the list of challenges that face the automotive industry. So reports auto engineers and designers who responded to the fifth annual DuPont Automotive/SAE survey, announced at this year's a SAE International Congress and Exposition. Moving up the list of concerns, however, are emissions and safety regulations.
According to survey results, 31% of the respondents identified cost reduction as the number one challenge facing the automotive design and engineering community. Another 31% identified cost as the top capability an OEM looks for in a supplier. In fact, cost has consistently held the top spot on the survey list since the survey began.
| Survey reveals top priorities of automotive engineers and designers.
"The industry's emphasis on cost reduction has reduced vehicle prices relative to consumer purchasing power," explains Walter Fields, vice president of automotive engineering materials at DuPont Automotive (Troy, MI). He cites a Comerica Bank study where the purchase of an average-priced new vehicle last year required 24.6 weeks of median family income before taxes. That's a 10% drop from two years ago.
"This shows how the automotive supply chain can come together to better manage development programs and deliver real innovation that lowers final product costs," Field notes. "And these improvements add up to sustainable value that will keep vehicles cost-competitive far into the future."
New vehicle-emissions regulations coming onstream are increasingly important to engineers. Thirteen percent of the respondents selected such regulations as the number one challenge this year. That's up 62% from last year.
"DuPont is committed to helping customers meet new California Air Resources Board (CARB) evaporative-emissions regulations," Field adds. "We offer suppliers such advanced permeation-resistant materials as TefzelTM fluoropolymer and Selar® barrier resins for use in hoses and fuel-filler neck applications that can resist both permeation and static build-up."
Another 13% of respondents named safety regulations as the top challenge. That's a gain of 50% over the previous year's survey.
"From a safety standpoint, it's time we stopped accepting the inherent fragility of glass," says Fields. "It can be made stronger and safer at an excellent cost-benefit ratio." He cites DuPont's introduction of SentryGlas® inomeric interlayer for laminated safety glass in side windows as an example.
Nearly half the respondents said molded-in-color plastics will be used in more body exterior applications during the next five years. Anticipating the need for such applications, DuPont has introduced Surlyn® ReflectionTM Series supergloss alloy. The material will debut on the model year 2000 Dodge and Plymouth Neon fascias.
Automotive composites on growth spiral
| Thermoset automotive composites will experience a 27% growth over the next five years.
Troy, MI--The Automotive Composites Alliance (ACA) has projected a growth of 27% in the use of reinforced thermoset composites by automakers from 1999 to 2003. This represents an increase of 80 million lb--from 300 million lb today to 380 million lb in 2003.
"Much of the growth will be in exterior body panel applications and in structural and drivetrain components--and most will replace what have traditionally been steel components because of cost, weight, and styling advantages," predicts Don Kossak, ACA chairman and vice president of development at Cambridge Industries. "This is the first year we're tallying volumes for all thermoset reinforced composites, and we expect to see growth in all segments."
Reinforced thermoset composites reported in the industry group's annual components list include:
BMC (bulk molding composite)
Why will thermoset composites replace traditional steel components? Kossak lists these composite advantages:
Provide design engineers with the ability to make frequent body style changes to multiple car and truck lines at program costs much lower than steel.
Consolidate radiator supports, cowls, cross-vehicle beams, and other structural components made from several steel stampings into one- or two-piece composite assemblies.
ACA consists of 26 molders, raw materials suppliers, and toolmakers.
Suuundaaay thunder goes high(er) tech
Vista, CA--Drag racing may be the ultimate commute--only a quarter mile in about five seconds!
And while getting there may be half the fun, the design challenges are exacting. According to Paul T. Glessner, an aerodynamics and stability and control engineer who consults on the aerodynamics of various types of race cars, a top-fuel (nitromethane) drag racer can be going 100 mph in 60 ft. The current record is over 330 mph in the quarter mile.
There is no transmission. At the start, a centrifugal "slider" clutch slips to keep the wheels from spinning, maintaining traction--thus the flat-out V8 engine produces "only" 2,500 hp. The driver keeps the pedal down and a timer pneumatically engages the throw outs for the staged disks in the clutch. The latest titanium units from Applied Friction Technology (AFT, City of Orange, CA) have five disks for more friction and to spread out the heat generated. Halfway down the track: 260 mph and all disks are engaged, locking up the engine and drive shaft directly, and power reaches 6,000 hp.
According to Gary Kennedy, AFT field engineer, the pit crew usually replaces the disks after every run, and tear down and inspect the engine as well. With the next run in an hour, accessibility is vital. Among the many variables that a crew chief has to account for in programming the clutch timer: air and track temperatures and oil on the track.
Crews adjust the engine based on data from data-acquisition software such as from Pi Research (Indianapolis, IN). Company Drag Support Engineer Toby Graham says the firm entered the drag racing data-acquisition market in 1997. In addition to communication software Racer-PC and channel-configuration code, its Pi Analysis package gives engine, clutch, driveshaft, front wheel speed, and accelerometer data time histories. The software processes distance plots and maximum values as well. Graham notes that drag racers are newer users, many not having a computer background. The company streamlined its Windows interface for easier access and reaped the benefit of making its packages for other racing classes more user friendly.
Scaring the air. With the highest speeds of any racers, aerodynamics are vital. Top-fuel racers can weigh no less than 2,100 lb, including driver at the end of a run. Total downforce (weight plus aero) can be as high as 10,000 lb, according to Glessner, taxing the rear wing and its support structure. And all aero surfaces behind the front axles must not exceed 1,500 in2, with the rear wing itself limited to 60 inches in span and being mounted a maximum of 90 inches above the ground. Deflectors ahead of or behind the exhaust pipe headers divert air around the pipes or the tires. Glessner says both are not used because the drag will be too great.
As for wind tunnel testing top-fuel dragster aerodynamics, many problems crop up, notes Glessner. The cars are relatively narrow and about 300 inches long, dictating a moving tunnel ground plane for proper boundary-layer effects and a large tunnel test section for any full-size tests. And he notes, any aerodynamic data acquired on an actual run (at a basic cost of $3,000 per quarter-mile run) would add extra instrumentation weight to a machine that is quite sensitive to inertia changes because of the high accelerations (see graph).
| Top-fuel racer acceleration can swing more than 10g.
But the wings themselves can be designed using computational fluid dynamics, says Glessner. The rear wing is mostly in clean air, easing analysis. Finally, the massive exhaust flow out of the headers entrains incoming air big time. This effect may be harnessed to act as "end plates" for the rear wing, reducing induced drag. But it is also the effect of the exhaust that makes wind tunnel testing less precise, unless a tunnel can be found that could handle lighting off the engine inside!
All-plastic design improves child seat
Colorado Springs, CO--It may be safe after all to put an infant in the front seat of a vehicle equipped with a passenger-side airbag. That's the promise of the Airbag Safe Infant Seat (ASIS) developed by Xportation Safety Concepts Inc.
Xportation engineers designed the rear-facing seat after studies showed that the front seat is a safer place for children. The survey revealed that putting infants in the front seat reduces driver distractions and accidents caused while tending a child in the back seat. What the engineers needed to overcome, however, was how to protect those infants from airbag deployment.
Designed to work with a safety belt, the ASIS redirects the airbag motion downward in the seat's frame, pushing it into the vehicle's seat cushion. In addition, the seat's cradle remains isolated from the frame by shock mounts. The shocks help elongate the crash pulse and dampen the energy that reaches the infant.
| Elevation view of Level VII seat (without infant cradle) highlights seat’s major components.
Xportation's current rear-facing, airbag-compatible infant seat prototypes consist of three primary components. A plastic infant cradle attaches to an aluminum 6061-T6 frame via four rubber mounts. Although proven crashworthy in sled tests worldwide, the engineers note that the Level VII design has "some cost, performance, and practicality limitations." Therefore, they have made a cost-effective, all-plastic design their goal.
Why plastic? In testing the Level VII seat, the engineers found that use of plastic (an ABS resin in the prototype models) could provide a significant improvement in the frame's and the shock-absorbent foam mounts' protective features. Plastic would also let them develop thinner, more complex shapes than cast and machine aluminum designs.
Moreover, the engineers point out that using injection molding reduces costs for a relatively complex seat attachment configuration. Most important, they say that the material properties of plastic would inherently reduce the peak shock load of the airbag or any sudden impact to the occupant.
Presently, Xportation has produced one plastic prototype, with another under development. One of the two models will be undergoing tests shortly. Xportation hopes to have a production model on the market late this year or early next year. The price: under $100.
FireWire-based drive network fires up CNCs
Newton, MA--Manufacturing Data Systems, Inc. (MDSI) of Ann Arbor, MI, and ORMEC Systems Corporation, Rochester, NY announced a joint development and marketing partnership for the integration of ORMEC's ServoWireTM Drive Network with MDSI's software CNC, OpenCNC®. This brings the first FireWire-based digital servo communications network to CNC machine tools and establishes a new benchmark for CNC machining: digital communications to servos at 200 megabit/second.
OpenCNC with ServoWire communications is 50 times faster than standard SERCOS and 10 times faster than current high-speed proprietary digital-drive interfaces, and reportedly will save thousands of dollars in hardware and integration costs.
"With ORMEC's FireWire-based digital servo communications, MDSI sets a new benchmark for speed and support of industry standards in CNCs," says James R. Fall, MDSI president and CEO. "MDSI's mission is to leverage industry standards to make our customers more productive and this technology will do just that. It's fast and open. We're pulling the manufacturing industry closer and closer to the day when a machine tool is an on-line peripheral to a network--just as your printer or plotter is today."
"We are pleased to join forces with ORMEC, another like-minded technology leader in the factory automation industry," he adds, "and to continue to break new ground in CNCs."
According to Gordon E. Presher, Jr., president and CEO of ORMEC, "In addition to lowering costs, ServoWire capitalizes on the strengths of IEEE-1394 to provide plug-and-play functionality and reliability. IEEE-1394 communications between our ServoWire drives and MDSI's OpenCNC software on a standard PC provides robust CNC control and real-time data collection with no proprietary hardware. The combination of the two technologies brings as fast, lean, and open a system for factory automation as you can get."
The open standard IEEE-1394 FireWireTM technology was first developed by Apple Computer as a high-speed serial data bus for moving large amounts of data between computers and peripherals. Because the IEEE-1394 FireWire standard has already been adopted by a broad range of consumer electronics and computer companies, including Sony, Toshiba, Philips, Compaq, Adaptec, IBM, Microsoft, Intel, Sun, Apple, and others, many new computers already come standard with Firewire ports. By the year 2000, nearly 150 million FireWire ports will be available.
Thermoplastic expands joint design
Newton, MA--C/S Group Inc. (Muncy, PA) has developed the largest portal design expansion joint of its kind. While it conceals the space between buildings, during earthquakes the joint allows up to 30 inches of movement in each direction. Its first application is for the corridors that connect the 10-story-high Hoaf Presbyterian Memorial Hospital (Newport Beach, CA) with the adjacent elevator tower. As the primary means of exit for the building, these corridors must withstand seismic activity.
The need for such an expansion joint materialized after the devastating North Ridge earthquake prompted the California Senate to pass a bill that requires hospital structures to perform to a certain level before, during, and after a seismic event. The legislation, enforced by the California Office of State Health and Planning Development, calls for hospitals to use base isolation technology that can increase building sway from 3 to 6 inches to 18 to 24 inches. The 4-inch-wide corrugated expansion joint cover, made of Santoprene 8000 thermoplastic rubber by Advanced Elastomer Systems (Akron, OH) ties the corridors to the exit towers.
After considering a number of materials including silicone, neoprene, and EPDM during the material selection process, engineers specified Santoprene 8000 thermoplastic rubber based on performance and movement criteria. The material is easy to process, says C/S General Manager Bill Sampsell, and meets the needed tolerances.
In order to maintain a weather-tight seal for the building, the portal system must also stand up to high winds and heavy rains. After engineers developed a prototype portal, CS built an exact duplicate of the Hoag corridor and tower. Then a carnival-ride manufacturer created a cycling machine to simulate earthquake-type conditions. At the test facility, the experimental setup simultaneously moves each of the two simulation building sections distances of 6, 11, and 22 inches through a combination of movements in tension, compression, and lateral sheer. "Our test facility allows clients to see these expansion joints work even before the project begins," says Sampsell.
Over a four-year period, contractors will replace the expansion joints in the Hoag Hospital, Newport Beach's tallest building, two floors at a time, starting at the top. "The heat weldability of Santoprene 8000 rubber makes it easy to connect the joint sections as each phase of the project is completed," says Sampsell. Other medical facilities in California are in the process of upgrading with these expansion joints to meet the new regulations.
FEA moves beyond verifying designs
By Laurie Toupin, Associate Editor
Paris--Today, finite element analysis (FEA) verifies what engineers design. Tomorrow, it may help the engineer actually do the design work.
Engineers use FEA primarily for building better prototypes or replacing them altogether with computer models, says Chris Kelley, CAE Marketing Manager of Structural Dynamic Research Corp. (SDRC, Milford, OH). Tomorrow, FEA will provide design guidance for the engineer and improve performance of a model. "The missing link up until now has been a deductive reasoning process that gives relationships between design parameters and performance criteria," says Kelley.
Sollac, a consultant for Usinor Group (Paris, France) found its missing link when it won back an important client for Usinor using I-DEAS Variational Analysis from SDRC. Usinor lost a contract for a steel brake pedal to a competitive brake pedal produced in plastic. The new pedal not only met the client's requirements for durability and deflection, but at a lower weight than Usinor's steel one. "Weight was a very important factor to the automotive OEM who was buying the pedals," says Kelley. Usinor naturally wanted to win back the contract with an even lighter steel design.
Sollac fed the fundamental criteria into the I-DEAS Variational Analysis program: stiffness, deflection, and weight. They designed the brake pedals around the design curve information. In two weeks, Usinor had a new design and won back the business. The whole process reduced the company's normal product development by 90%.
Kelley describes the Variational Analysis process like this: Suppose an engineer is designing a simple structure, like a beam. When the design concept is initially established, he knows the beam's geometric envelope. He also knows the overall environment, including loads, boundary conditions, and other parameters. Finally, he has some idea about how the beam must perform, including allowable stresses and deflection. Variational Analysis takes what is known (geometric envelope, operational environment, performance targets), and produces data that can be directly used to make design decisions in the form of design curves.
"This is in stark contrast to more traditional FEA approaches which require that the design be fixed before an analysis can be performed," Kelley says.