Engineering News 7529

'Virtual company' hits the road

Paris--Intergraph, SAP, Siemens Automation, Digital Equipment Corp., and Microsoft have gotten together to put on a show. Their series of seminars, entitled Internet-enabled Manufacturing, will be rolling out across Europe this summer, starring live, real-time demonstrations of how the Web can impact the design-to-manufacturing process.

Essentially, these companies demonstrate how their products could work together to "Web-enable" an imaginary company called Write Right. In this case, Digital provides the hardware and networking know-how, Microsoft supplies the Windows operating system and interface, Intergraph provides the CAD/CAM design software and product data management (PDM) system, SAP links the supply chain, and Siemens Automation handles the factory-floor automation software.

The first seminar took place at the Digital/Microsoft Expertise Center in Valbonne, France, and attracted more than 75 industry leaders from companies such as Nokia, Ericsson, and Philips. Attendees found the live demo--with each of the participating partners playing a role in the sequence of events--particularly impressive.

In the Write Right scenario, one company partner plays a customer brow-sing the Web in search of a pen with an integrated communications paging device. He lands on the Write Right Web site, and sends them an e-mail message to ask if they can customize one of the fountain pens he's seen in their on-line catalog.

The request gets passed along to another partner, who plays the design engineer who has to modify the design of an existing product using Intergraph's Solid Edge 3-D CAD/CAM package. The designer goes out on the Web looking for existing pagers that might have parts he could integrate into a pen design.

He finds a standard pager in the on-line catalog at a telecom supplier's Web site, and decides that the display unit would be appropriate for the Write Right pen. The first step is dragging a copy of the pager from the Web site and dropping it into Solid Edge. There, he clicks on the part he wants, in this case the display unit; copies, resizes, and positions it with a few mouse clicks; and drops it into the pen barrel. Result: the basic design for a pen with an integrated pager.

A third partner plays a manufacturing engineer who accesses the 3-D model of the designer's proposal. He uses software from Siemens Automation to analyze factory-floor issues. Yet another partner uses SAP software to investigate issues like pricing, procurement, and shipping. All these tasks happen in real time as the audience watches the various processes unfold on the computer screens of each role player.

Seeing such a variety of partners interact in real time can be a mind-opener, and seminar organizers say the event may be extended to other regions of the world later in the year. But is it a viable scenario? Lisa Tomlinson, an industry analyst with Daratech, says it is. However, she cautions that at least in this example, the designer is part of a big company and is essentially looking for parts he can use.

Designers from small organizations can offer their ideas, products, geometries, and services on the Web. Today, many designers work alone or in a small office, she notes. It's important for these designers to share ideas with clients who may be much bigger. "For small designers, there's a lot of cheap, easy-to-do, high-impact things you can do on the Web," she says. Those with a bit of computer know-how can set up their own servers. She herself did this using a 386-based PC with all freeware software--all she bought was the phone line.

Another alternative is to find a small consultancy that will set up a server that the design firm can maintain itself. "Depending on your ambitions, there's a whole array of off-the-shelf applications for displaying products or geometries for less than US$3,000," she says. One ex-ample is Dr. DWG from California Software Labs for AutoCAD users.

One small design firm with a major client put its geometry on a Web server for the client to access, and even offered animations on how the parts could be used. This is one way, says Tomlinson, for small companies to be perceived as world-class players. "Wise use of this technology can enable the little guys to leapfrog the big guys," she adds, "by giving them a chance to demonstrate that they can be more mobile, flexible, and reactive." But whether you're offering services or looking for parts, the bottom line is that the Web should let designers focus on what they do best.

For more information on The Internet Enabled Manufacturing Company seminars, look on the Intergraph Web page for your country.

Technology links CAD applications

by Adele Hars, Contributing Editor, France

Hoofddorp, The Netherlands--Users of many Microsoft Windows applications have long enjoyed being able to drag and drop "objects" from one application to another. Parts of Excel spreadsheets drop into Word documents, and paragraphs from a Word document can be pasted into PowerPoint. This capability is in large part due to Microsoft's Object Linking and Embedding (OLE) technology, but has long eluded CAD users because CAD applications were too complicated to fit into the OLE framework.

Intergraph's Jupiter technology overcomes this obstacle by extending OLE to make it suitable for integrating data created in technical applications. OLE for Design & Modeling Applications (OLE for D & M)--one part of Jupiter technology--has been endorsed by Microsoft and many CAD/CAM, CAE and GIS software vendors as the standard means of integrating geometric and geographic data in the Windows environment. OLE for D & M meet the needs of technical applications including: 3-D objects, frameless overlapping of objects, and transparent and translucent objects.

With applications based on Jupiter technology, users can create compound models using data generated in different CAD programs as easily as they can create compound documents using data generated in different business applications, explains Philip Wolffers, manager of marketing and business development for the manufacturing industry at Intergraph's European headquarters.

Landerholm & Lund, Arhus, Denmark, is using Intergraph's Solid Edge 3-D solid modeling system which is based on the Jupiter technology. "Since we have been using Solid Edge our company has clearly become more productive," says John Landerholm, managing director of Landerholm & Lund.

Adroit engineering quiets veteran airliners

Seattle--Fleets of older, noisier aircraft, such as the venerable Boeing 727 trijet, are getting a new lease on life. Due to be retired at the turn of the century because of noise regulations, these aircraft can now meet restrictions thanks to three options.

Replacing the engine is the most obvious, but also the most costly at $9 to $12 million--perhaps hard to justify on a 727 worth $2 to $3 million. The least costly choice at just under $700,000 was recently announced by Raisbeck Engineering. Its noise-abatement system permits FAA-certified procedural changes in 727 operation. The changes include cutting drag and aerodynamic noise by reducing the extensions of high-lift flaps on the leading and trailing edges of the wings during takeoff and landing. This lets the plane use lower levels of thrust, producing less engine noise.

The system allows reduced flap operation without triggering a warning horn. Flap control is restricted by a detent breakout wire, so full deflection and full power are available for emergencies.

But lowered thrust lengthens takeoff runs by 500 to 900 ft and limits takeoff weight to 167,000 lb, compared with the current 727-200 maximum of up to 191,500 lb. The weight reductions cut into fuel load and thus the payload/range envelope as well. Lower drag increases landing speed 5 mph, and extends landing-field distance 450 ft at a maximum landing weight of 154,000 lb.

James Raisbeck, company CEO, points out such performance limitations are moot--the cost of three-person crew and higher fuel consumption have pushed these aircraft into shorter routes or into corporate service with only several hundred yearly flight hours rather than thousands. On such routes, airport infrastructure expenses, not cost per mile, dominate operating cost, making older planes competitive. Raisbeck also cites studies of airline operations: "In 1995, 92% of all 727-200 takeoffs were at 167,000 lb or less and 100% of all landings were below 154,000 lb."

The third alternative is 727 hushkits from Federal Express Aviation Services, Memphis, TN. Costing $1.9 to $2.6 million, these kits modify the engines with acoustic treatments and an internal high- and low-velocity gas mixer to muffle the exhaust jet. "There is no change in performance nor in thrust with power setting," asserts FedEx Marketing Manager Phil Blum.

Photocopier goes 3-D

by Anna Kochan, Contributing Editor, England

Hazu-gun, Japan--Three-dimensional photocopying has almost become a reality. A rapid-prototyping machine from the Japanese company Kira uses proven laser-printing technology to automatically convert a 3-D computer model into a 3-D component using sheets of ordinary paper.

In appearance, the Kira machine resembles a large computer-controlled photocopier. In practice, it uses standard A3-size photocopier-quality paper. As with a photocopier, it takes one sheet at a time and applies toner to a selected area of the paper. This area corresponds to one particular cross-section or layer of the model being built.

Instead of appearing in the outlet tray, the "printed" sheet proceeds to another zone in the machine where it is assembled on top of others to create the solid model.

Here, the sheets are pressed together at a temperature that melts the resin powder of the toner. In this way, the toner acts as an adhesive to hold the sheets of paper together without the addition of any further substances. Once each sheet has been pressed onto the block, a tiny blade cuts around the contour of the "printed" area. It also makes additional cuts so that, once all the sheets have been assembled, the designer can pick out the model from the excess paper surrounding it.

The resulting model has the consistency of wood and can be used as an investment die-casting pattern to generate additional samples in plastic or metal materials.

The new Kira machine is now being marketed in the UK for 100,000 pounds. In Japan, Konica has used it in APS camera development, Mitsubishi Electric has developed palm-top computer designs with it, Toyota has used the machine for automotive design.

Solenoid valve offers proportional control

Scherpenzeel, The Netherlands--As more design engineers incorporate microprocessor-based controllers into their applications, the need for precise control of fluid flow increases. Posiflow^TM proportional solenoid valves provide this function. Flow is directly related to electrical input, and can be adjusted from 0% to 100% of the valve's capacity.

Most flow-control valves work on an "all or nothing" basis. They are either fully open or fully closed. "The key to Posiflow's proportional control," claims Terrance Sarkees, marketing engineer for ASCO Valve, "is a uniquely designed core and plug nut." This simple concept, he explains, permits a linear relationship between electromagnetic pullforce and current.

Extensive engineering data now on CD-ROM

by Anna Kochan Contributing Editor, England

London--Engineering data that was previously available only in catalog form is now being issued on CD-ROM. The new medium will save engineers time and money by presenting validated data in a format they can access quickly and use immediately, claims Engineering Sciences Data Unit (ESDU) International PLC, a company that has collated engineering data in the mechanical, aeronautical, structural, and chemical engineering fields for more than 50 years. It is now launching the CD-ROMs.

Fluid mechanics--internal flow (aerospace) is the first data set available on CD-ROM. Although the data already existed in printed format, the data on the CD-ROM have been created from scratch--not by scanning printed copies, stresses ESDU Managing Director John Castle. In this way, he says, it has been possible to provide fully interactive diagrams, graphs, tables, and other display materials. Users need no special training to use the CD-ROM because it employs the Microsoft Access Interface, which provides industry-standard compatibility.

The new CD-ROM contains the first version of a program called ESDUscope, which lets engineers explore the database and interact with "live" versions of data items and computer programs.

The data set also includes equations. Engineers using the CD-ROM can introduce variables such as dimensions, speeds, and temperatures for specific calculations. They can view the text and graphics and can manipulate and alter the on-screen image using standard zoom facilities. A word-processing package allowing cut-and-paste and other editing features is also included.

A search facility helps locate topics of interest by scanning files and reviewing their abstracts before running the full file.

ESDU plans to make its other engineering data topics available on CD-ROM. As with the printed volumes, customers pay an annual subscription for the data.

Zinc alloy offers enhanced performance

Peterborough, Ontario, Canada--A ternary zinc-copper-aluminum alloy lets design engineers use hot-chamber zinc-alloy die casting to produce small components for use at elevated temperatures and in structural applications. Composed primarily of zinc, the ACuZinc(R) alloy contains 5 to 6% copper and 2.8 to 3.3% aluminum.

Fishercast, Division of Fisher Gauge Limited, was the first hot-chamber die-casting company to sign a comprehensive licensing agreement with the alloy's developer, General Motors Corp., for use of the alloy. Co-inventors M.S. Rashid and M. David Hanna of the metallurgy department at General Motors Corporation Research and Development Center, Warren, MI, developed ACuZinc after evaluating more than 40 alloy compositions.

Its copper content gives ACuZinc a tensile strength of 59,000 psi and a yield strength of 49,000 psi (338 MPa)--comparable to that of low-carbon steel. Another formulation, used in cold-chamber casting, contains about 10% copper.

Application Engineer Todd Ulrich of Fishercast says that ACuZinc is harder as well as stronger than traditional Zamak alloys and ZA-8 alloy. Its Brinell hardness of 118 is 36 points harder than Zamak 3, 38 points harder than Al380, and 25 points harder than brass. In high-load applications, conventional zinc alloys relax over time. This ternary zinc alloy, however, provides substantially higher creep resistance than such alloys. Using fillets and radii can further enhance the material's creep resistance, according to Ulrich.

ACuZinc's copper content reportedly gives it wear characteristics comparable to those of bearing bronzes. Fishercast's Ulrich says that in the standard block-on-rotating-ring test, the alloy loses 7.63 mg/hr, while Zamak 3 loses 23.76 mg/hr. Wear behavior of the new alloy is comparable to that of aluminum alloy 356 Al +5% SIC and aluminum alloy 339 Al. Furthermore, the material's friction coefficient is 0.06 against itself (the value for Zamak 3 is 0.24).

Nylon beefs up Boxster manifold

Orbey, France--When the Porsche Boxster's motor reaches high revs, less than one-hundredth of a second is available to fill its 2.5 liters of cylinder capacity--six cylinders in horizontally opposed banks--with the right fuel-air mix. Twin air-intake manifolds made of nylon help beat the clock, even at top engine revolutions.

The two-seater, first shown to the public late last year (see Design News, 3/24/97), is powered by a water-cooled boxer motor with its characteristic low, flat silhouette and widely separated banks of cylinder heads. The aspirated air for the motor passes from a central distribution pipe in two manifolds, each of which supplies three cylinders. For the design, Porsche engineers decided to use two separate, symmetrical manifolds.

Development of the part was a joint project involving car-maker Porsche; France's Le Profil Industries (LPI), developer of the design and molder; and DuPont as the raw material supplier. To save weight as well as costs, the team decided at an early stage on a welded design. The material of choice: Zytel(R) 70G35 HSL, DuPont's heat-stabilized nylon with 35% glass-fiber reinforcement, formulated especially for air-intake manifold applications.

The nylon withstands continuous temperatures up to 130C and shorter excursions up to about 150C. The smooth internal flow surface the material produces in the manifold actually improves performance. One manifold weighs about 1.4 kg, or about half the weight of a comparable aluminum part.

However, in early tests the manifold's surface near the plenum chamber turned out to be a source of unwanted noise with high oscillation amplitude. DuPont engineers found that pulsations of the air stream at certain valve positions triggered the noise. On a lab scale, engineers tested the effect of changes to the stiffness of certain manifold sections to establish the data for an optimized design.

LPI incorporated the results of the lab's work into the final design, modifying the twin manifolds so that the unwanted resonance no longer occurred. As a result, the mid-engine Boxster now runs smoothly and quietly, though still with Porsche's typical sporting "snort."

Seal solves fowl problem

Lancaster, NY--A malfunctioning seal resulted in chickens on several farms not drinking enough water. Because of this, the chickens failed to gain weight--a costly situation for the farmers, as well as for the manufacturer who had guaranteed the feeders.

Hearing of the problem, personnel from Apple Rubber Products Inc. visited the manufacturer's facility. Investigation showed that an O-ring placed around a small rod often would stick and not allow water to pass through. The possibility also existed for the seal to be completely blown off the rod by the high pressure of the system, letting too much water spray through.

In designing a new seal several factors came into play. Water differed dramatically in various areas where the feeders operated. In some cases, the water contained heavy mineral content; in others, it was heavily chlorinated. Moreover, the feeders were regularly cleaned with high-pressure water and solvents. And farmers often administered nutrients and medicines through the water system.

Technicians at Apple Rubber, knowing that seals generally aren't effective force limiters, offered a rubber-bonded-to-metal seal. Here, the metal becomes the force limiter and the seal only has to seal. In other words, the metal bond added the needed stability to the seal, eliminating potential swelling and disfiguring.

The manufacturer chose the suggested solution. Al-though it required some tooling changes to the feeder, the seal combines two parts into one, eliminating an assembly step and associated costs. The result: a better, more functional seal for the same amount of money.

Traction control for your Rolls

Sutton Coldfield, West Midlands, UK--Designed to give good performance on surfaces where one driven wheel grips more easily than the other, Zytek Automotive's traction-control system uses the Engine Management System (EMS) microprocessor to collect and analyze wheel speed data from the existing ABS control module. Incorporating a viscous limited slip differential eliminates the need for individual control over driven wheels. This approach reportedly provides smoother action than a brake intervention system while yielding excellent vehicle stability.

If the EMS microprocessor detects traction loss, it calculates the extent of action required and selects a strategy to reduce engine power until restoration of traction. By using this processor to directly control flow metering, engineers see to it that gas-flow inertia does not affect response time, as it would in a conventional throttle-control system.

In the Rolls-Royce and Bentley application, the Zytek system adds four components to the vehicles: an on/off switch, connections to the switch, and connections to the ABS control module and driver information panel. Complexity resides in software and system calibration.

The new traction-control system will be an option on the non-intercooled turbo Rolls-Royce and Bentley cars, and standard on intercooled turbo vehicles.

Find the motor, they'll sell you the drive

by David J. Bak Senior Technical Editor

Feuerthalen, Switzerland-- Need a 450-kW motor with intelligent drive? No problem, says Daniel Berg, director of sales and marketing for Baldor Motors and Drives. "Find the motor and we'll sell you the drive." Berg can state this with confidence since Baldor's recent acquisition of Optimised Control Ltd. (Bristol, UK), a leading designer of motion-control products.

The acquisition meets the growing demand for complete motion-systems solutions. Optimised Control's product line, claims Berg, gives Baldor the engineering resources to support the transition to integrated drives and controls, and open automation systems.

SmartMove, for example, is a fully integrated machine controller that offers motion, I/O, operator interface, and serial communication in a single CE-compliant panel-mount enclosure. Able to provide up to three axes of closed-loop control, the SmartMove controller is programmed using MINT^TM (Machine INTelligence).

Flexible, yet easy to use, the MINT language supports event-driven and scanned I/O tasks, along with communication features for connecting to MMIs, host controllers, and other serial devices.

SmartMove controllers offer standard network connectivity in the form of a Control Area Network (CAN), which provides a 1-Mbps serial link for connection of sensors, I/O expansion, and direct control of digital drives.

John McFarland, President of Baldor Electric Company, explains that "by bringing position-control products and engineering capability in-house, we have the opportunity to develop much stronger relationships with our customers. It makes us the only vendor that can offer complete motion control solutions right through the spectrum." Baldor expects to sell Optimised Control products to customers worldwide.

Crack detection cuts paper-mill downtime

by Charles J. Murray Senior Midwest Editor

Marietta, GA--When a paper roll tears, large paper mills can lose as much as 30 minutes to downtime at costs approaching $1,000 per minute.

To eliminate that problem, engineers from Ryeco Inc. have devised a system that detects tiny cracks in paper rolls moving as fast as 8,000 feet per minute. Using the system, mill operators can detect edge cracks as small as 1/16 inch. As a result, they can fix an edge crack before the tear grows larger, ultimately preventing downtime.

To accomplish that, the Edge Crack Detection System uses a combination of photoelectric sensors, high-speed electric actuators, small air jets, and microprocessor-based control. Three basic systems perform the unit's primary functions: A tracking module uses infrared photoelectric sensors to monitor side-to-side movement of the paper as it passes; an edge-crack detection module with visible-light photoelectric sensors finds defects in the passing paper; and a marker module color codes those defects. Two air jets blow streams of air under the paper to temporarily separate the edge crack so the angled optics can detect it.

Key to the system is its ability to move the edge-crack detection module back and forth in a direction perpendicular to the paper as it passes. The photoelectric sensors in the module, which are positioned within 0.375 to 1.375 inches of the paper's edge, must be kept close enough for accurate detection. "They need to stay as close to the edge of the paper as possible because you can't afford to miss anything when the paper is flying by at 8,000 feet per minute," notes David Lawrence, engineering manager for Ryeco.

The problem in achieving close proximity is that fast-moving paper rolls often wander from side to side. During this drifting, the roll's edge may move as fast as two inches per second.

To properly position the sensors, the system's edge-tracking module monitors side-to-side movement of the paper, then sends position information to the microprocessor. The microprocessor, in turn, sends a signal to an electrically driven actuator, which moves the edge-crack detection module with respect to the moving target. All of this takes place in about 40 msec.

Key to the success of the Edge Crack Detection System is the use of an electric screw drive actuator made by Tol-O-Matic Inc., Hamel, MN. Known as the BCES, the actuator offers two important performance advantages: Its self-lubricating carrier bearing system provides longer cycle life, and an outer dust band in the actuator body encloses the ball nut screw drive, thus protecting it from the environment. The patented actuator design draws on Tol-O-Matic's experience in rodless pneumatic cylinders, which use similar dust bands for protection against dirt and moisture.

The actuator's advances enable it to withstand the equipment washdowns that regularly occur in pa-per mills. Earlier actuators employed oil-impregnated bronze bearings and offered about one-third the life-cycle performance of the new actuator. "With this design, when the paper ma-chine is washed down, it doesn't damage the actuator," Lawrence says.

The higher life-cycle performance of the Tol-O-Matic actuator reduces downtime for the paper mills because it requires less frequent servicing and replacement. That, in turn, allows the Edge Crack Detection System to dramatically reduce downtime by spotting minuscule tears in the paper before operators separate the sheet and allow the paper roll to run free. "With this system, operators don't have to stop for 30 minutes to clean up and re-thread their winding machine," Lawrence says. "And that's critical for most paper mills, because they simply cannot afford the downtime."

Simulation cuts time and costs, delivers European feel

Los Angeles and Raymond, OH--Honda R&D North America, Inc. had one major performance factor in mind when designing the Acura CL: a handling feel similar to that of a BMW. The design team wanted to promote a feeling of high body rigidity and high damping when hitting a bump, for example. And handling was to be linear and natural for everyday driving.

Jim Jamieson, senior engineer at the Ohio center, says the team also wanted to expand its simulation capabilities on this project. Their main goal was to perform simulation prior to prototype development. "This would cut down on the number of prototypes built because the majority of the design problems would be solved during simulation," he says. "It would also reduce development costs and decrease development time, or at the very least, make it easier to meet the design deadline."

The simulation group used its existing software system for structural simulation during the CL's early prototype stages, but it became increasingly difficult as the work became more complex. Among the software's weaknesses were the lack of an in-depth geometry base, no solid modeling capabilities, and an inability to manage large parts assemblies.

Jamieson and his team needed new software that included:

Ease of use so new associates with backgrounds in physics and thermal dynamics could learn the package quickly.

And the program had to be easy to administer. The Ohio R&D center decided on I-DEAS Master Series^TM software from Structural Dynamics Research Corporation (SDRC), Milford, OH.

One of the first things the CL team did was to create surface geometry to match the wireframe design coming from Dassault Systemes' CATIA software. The I-DEAS translator made direct translation between the two packages possible.

I-DEAS' surface modeling capabilities came in handy in devising a white-body development strategy, a critical simulation task. A two-person team constructed a structural model of the CL white body to have a working simulation prototype. "Without I-DEAS' surface modeling capabilities, we would have had trouble meeting our schedule of 32 months," comments Jamieson.

n the construction of the model, all parts were managed using I-DEAS project libraries capabilities. The simulation team had access to all part components and was able to control all the data. Once the parts were created, each was meshed using the surface-free mesher.

To create an entire finite element (FE) vehicle model, all the FE part models were merged and part meshes attached to create a complete vehicle mesh. With the finer mesh capabilities in I-DEAS, a half-vehicle mesh contained more than 30,000 elements and had an average length of 30 mm, compared to the previous 100 mm.

Other simulation activities included designing a new bulkhead. The CL's early bulkhead designs had large rotations, making this a weak area in the car. "With I-DEAS, we de-signed a more efficient bulkhead that met our objectives as well as those of manufacturing," says Jamieson.

After that, the simulation team went on to more detailed component-level analysis, such as looking at the aluminum road wheel for the 3.0 CL and the front strut bar. "The I-DEAS solver let us look at the full car with very complex loading conditions and in much more detail to ascertain what was driving design, and which features our test engineers were telling us were important," says Jamieson. "We actually made these parts and found the trends we were seeing on the computer matched those found when the CL was test driven," he adds.

Overall, I-DEAS software has made life easier for Honda's simulation engineers, says Jamieson, and with each new set of I-DEAS enhancements, various simulation tasks have become much faster to perform. Static deflection for half-vehicle meshing, for example, has dropped from eight hours to one, while natural frequency analysis has decreased from 16 hours to two.

"Without I-DEAS, we wouldn't have been able to meet our objectives to the level we wanted," says Jamieson. "There's no doubt we would have had a vehicle, but it wouldn't have been as good as we wanted or as it turned out to be."

Circuit breakers replace auto blade fuses

by Roy O'Connor European Bureau Chief

Brighouse, UK--The large amount of electrical equipment installed in emergency vehicles makes enormous demands on the vehicles' electrical systems. With lights, siren, monitoring equipment, Laerdal suction units, incubators, and vehicle heating/air conditioning, the total load on the electrical system in an ambulance can reach 120 amperes. In addition, dependence on the overall system reliability is a critical factor in saving lives.

To improve the vehicle's reliability and reduce downtime in the event of a fault, the Ambulance Division of Universal Vehicles at Brighouse, UK, has been replacing automotive blade fuses with circuit breakers manufactured by E-T-A, Altdorf, Germany, and supplied via the group's UK subsidiary. The main advantage of circuit breakers over fuses is that they can easily be reset once the fault or overload has cleared. On a vehicle responding to an emergency, the time taken to replace fuses can be critical, particularly if the fault recurs a number of times during an emergency call.

A typical circuit-protection configuration on a Lazer ambulance consists of several subsystems. Three E-T-A 413 Series high-performance thermal circuit breakers guard against overload on the battery power cables. Four 1658 Series thermal circuit breakers protect on-board incubator equipment. And a panel of about 30 miniature 1170 circuit breakers protects low-voltage wiring to lights, sirens, fans, and medical equipment. E-T-A engineers developed the 1170 Series specifically for direct replacement of automotive blade fuses, and the devices fit into standard fuse sockets.

To overcome the problems of fire and battery draining, a battery isolator switch with remote cut-off enables the driver to shut off the power supply from the dashboard. This overcomes the problem of under-hood access to any isolator switch in the event of a fire. The driver can also operate the switch to reduce battery drain when the vehicle is to be left standing for a long period of time.

Flexible blanket GaAs/Ge array nears end of tests

Redondo Beach, CA--Engineers at TRW Space & Electronics Group are completing tests on what the company describes as the first operational flexible blanket solar array made from gallium arsenide germanium (GaAs/Ge). Generating 25 to 35% more energy per pound than an array made from conventional silicon cells, the 200x351-inch array consists of 26 panels and 36,480 cells, each measuring 1.60x0.95 inch. With harnesses it weighs approximately 160 lb, some 20 to 25% lighter than a comparable array built using silicon technology.

TRW will deliver the array to Lockheed Martin this summer for integration into NASA's 11,000-lb Earth Observing System AM-1 (EOS AM-1) spacecraft. There are to be three earth-observing satellites--EOS AM-1, EOS PM-1, and EOS Chemistry. Satellite AM-1 will cross the equator at noon at a specific point on the earth. Satellite PM-1 will follow at midnight. The EOS chemistry satellite will observe chemical environments around the globe. Each satellite is the first of two in NASA's longer-term plans.

At the beginning of its life in low earth orbit (LEO), the new array will produce 7.5 kW at 127V. Over time, array output changes in a nonlinear fashion. "It's exponential," explains Mike Herriage, EOS AM solar-array program operations manager at TRW's Space & Electronics Group. "You're losing more power in the first year or two. Then it becomes asymptotic through 5 kW out to something approaching 4,500 or 4,000W, if it survives 7.5 to 10 years in orbit. Our requirement is to have 5,000W at end of life, which is five years in LEO."

Engineers can accommodate future spacecraft needs by expanding the array design to produce as much as 20 kW in a two-wing configuration. "You can easily increase the size of the blanket by 50% in each wing without changing the fundamental frequency significantly," Herriage asserts.

The GaAs/Ge solar cells are bonded to a laminate of carbon fiber and epoxy captured between two sheets of Kapton^TM polyimide film. Engineers protect the substrate from the LEO environment (basically atomic oxygen) by sputtering a germanium coating onto it. TRW then bonds the solar-cell stack--a 6-mil-thick cell secured to a 6-mil-thick borosilicate cover glass--to the 0.007-inch-thick laminate. A silicone adhesive secures the cell to its cover, and also bonds the cell to the germanium coating on the substrate.

Two types of hinges allow the array to fold like an accordion. In the photo, "you can see the lines between the dark blocks of solar cells," says Herriage. "Those lines consist of fold hinges and piano hinges. At every third hinge line a graphite rod serves as a hinge pin. Two out of every three are fold hinges. There are openings in the substrate material where we do not apply cells, and we have no graphite in that area. We allow the plastic film to carry the load."

Awarded in 1993, the contract to develop the array included the design phase, developmental phase, qualification, and flight hardware. Current contract value is $38 million. In June 1998, the EOS AM-1 spacecraft will be launched from Vandenberg AFB.