Engineering News 7404

AC 'drives' ahead

Newton, MA--Though more than 100 years old, the electric motor remains in the vanguard of technology's march to the 21st century. Leading the charge are increasingly powerful, yet lower cost ac motor drives.

Cyclical applications such as high hp extruders and winders still require dc motors and drives, due to the ability to regenerate power. However, ac motors are penetrating the marketplace on two fronts: open-loop variable, or "selective speed" applications; and closed-loop vector control.

Benefits are many. For example, using an inverter to vary a pump's speed, instead of throttling output flow, can save 25% to 40% of the energy consumed. Vector drives, applied to closed-loop applications, allow high-performance motion control. "The point to remember," says Darryl Van Son, manager of Baldor Electric Company's Market Research & Planning group, "is that these motors have now become compliant rather than complacent."

Beyond fixed speed. Virtually every motor application runs better if the user can choose some speed other than the factory designed setting. The declining cost and increasing reliability of ac drives not only give users the option of variable speed, but the fixed speed of their choice.

"A major brewer tells us there's an upper threshold for mixer speeds, beyond which foaming occurs," states Ken Deken, ac drives marketing manager for Reliance Electric. "That's the speed they want to run at."

Commercial washing machines represent another application for open-loop inverter drives. Ideally, the operator wants to spin the basket at three speeds for light, medium, and heavy loads. Without a variable-speed drive, the washer motor runs full speed regardless of load.

Lower cost variable-speed drives provide a big incentive to accommodate such applications. "In 1981," Deken notes, "a one-horsepower ac drive and motor sold for $685. In 1994, the price was $465, even though motor costs (due to higher material costs) went up!"

Because the customer remains largely unaware of these price changes, Deken believes, only 5% of the three-phase motors used in commercial applications are equipped with variable-speed drives. The transition from fixed to variable-speed applications, therefore, represents a "huge" growth opportunity for ac drives. Deken predicts better than 10% over the next five years, with the greatest penetration in the HVAC, materials-handling, mixing, and packaging industries.

Baldor's Van Son agrees, citing the air-handling motors of a typical office building. Air-handling costs, he argues, may account for 30% of each month's electric bill. That's because most ventilation systems, sized for worst-case situations, are throttled back as much as 80% of the time.

Investing in variable-speed drives, he says, could reduce these costs by as much as 50%. In addition, such drives offer soft start/stop features, and control the high inrush of across-the-line motor starting.

Closed-loop control.With the advent of ac vector drives, ac motors began penetrating the traditional realm of dc motors and drives: closed-loop applications. A continued decrease in vector-drive cost, combined with the added value of increased performance, ensures an even greater share of that market

Adding a tachometer to communicate dc motor speed to a controller, for example, can deliver speed regulation within 1.00% of set speed. By contrast, vector-controlled ac motors, such as Kollmorgen's V-Series, can attain regulation on the order of 0.05% of base speed. Equipped with resolver feedback (no electronics in the motor), the V-Series provides full servo performance and excellent acceleration capabilities.

Cost, reasons Carroll Wontrop, manager of product marketing for Kollmorgen's Motion Technology Group, is often a wash. While dc SCR control remains less expensive than vector control, a dc motor prices significantly higher than an ac induction motor.

As for performance, Wontrop says V-Series motors are particularly good for spindle applications that require "zero-speed" positioning and high-torque position holding. They are also suited for applications featuring large load inertias that usually result in low bandwidth with traditional lower inertia, permanent magnet motors.

"The single biggest issue for converting to vector drives," says Baldor's Van Son, "is the absence of brushes and commutators, and the associated maintenance and repair responsibilities." Unlike dc motors, vector drives are not limited by environment or load considerations. The absence of brushes and commutators also makes them more suited for the higher speeds demanded by the motion-control industry.

Technology trends. Where does the future lie for ac motors and drives? Look for more applications involving non-propriety "open" networks. Already, more than 100 manufacturers, including Baldor, Reliance, and Kollmorgen, ship ac drives with DeviceNet-compatible network cards.

Drive customization is also on the rise. Reliance, for instance, plans on introducing a "flash" memory regulator in their product line later this year. "Flash memory," Senior Product Specialist Tom Lowery explains, "lets us load in everything under the sun; the customer selects only those parameters needed."

Flash memory also simplifies software updates. Used in conjunction with an open network, it permits changes to multiple drives from a single location. "You send the message across the network," Lowery says, "and actually change the memory in each of the drives."

And change is coming. Only 5% of ac motors in the North American market now use drives. With continued cost cutting, new features, and improved performance, that figure is expected to reach 20% by 2005.

Recessed light makes installation a snap

Crawfordsville, IN--Contractors can install Advantage Insta-Lite IC/Non-IC(TM) twice as fast as other downlighting fixtures on the market, according to their manufacturer, Lithonia Lighting. What makes this possible? The rugged, lightweight plastic design of the innovative lights, claims Okey Fields, Advantage Products VP.

To ensure light weight and ease of installation, Lithonia constructed the new downlight's frame and junction box of injection-molded Makrolon 6485 polycarbonate from Bayer Polymers Div., Pittsburgh. The material provides several key benefits to assist contractors with speedy installation.

For instance, total size of the junction box is one-third larger than standard products to make wiring quicker and easier. Also, captive gull-wing doors on the box swing up and stay up for easy access. In addition, factory-installed "poke-home" connectors save time, money, and hassle. And molded-in Romexclamps are secured without the need for added hardware.

"Bayer technicians aggressively participated in the research and prototyping," says Plant Manager Greg Yates of Casey Tool & Machine Co. "They helped us find answers."

Ancient technique helps quiet modern jet engine

Gloucester, MA--A centuries-old metal-forming technique is being used to create parts for the world's most powerful twin-engine commercial aircraft, the Boeing 777, according to subcontractor Bomco Inc.

Bomco engineers worked with Pratt & Whitney to develop 112-inch fan case liners for the P&W 4084 engine. And, they say that a metal-spinning process, believed to have originated in ancient Egypt with refinements by the Greeks and Romans, helped achieve fast start-up at low costs. The technique has been modified, Bomco officials note, with high-precision tooling replacing the simple wooden mandrels of early times.

For the fan case liner, a 112-inch aluminum cone is placed on the tooling. A precision craftsman cold forms perforated aluminum to the tooling as it rotates on a large lathe. The part is then trimmed using the same tooling and lathe. Had the fan case liner been press-formed, it would have cost four to five times more money and taken at least three times longer, estimates Mark L. Standley at Bomco.

The result from spinning: a precision fan case liner used as an integral part of the engine's sound-abatement system. The design was optimized, tooling created, and parts produced in only 12 weeks.

Comfort rules redesign

Santa Barbara, CA--For engineers designing the 1997 Park Avenue and Park Avenue Ultra, the paramount concern was comfort.

It shows.

The Park Avenue is slightly larger than the previous model. For example, the car is three inches higher and the wheelbase is three inches longer. This extra space translates into a roomy car that drives like a luxury sedan should, but doesn't feel or handle like a boat. The ride is quiet and comfortable; the steering makes you feel connected to the road.

Both cars feature Buick's new Hydra-matic 4T65-E 4-speed automatic transmission, the latest generation of the electronically controlled 4T60-E. Mileage is 19 mpg city, 29 mpg highway for the Park Avenue and 18/27 for the Ultra. The 3800 Series II V6 engine delivers 205 hp at 5,200 rpm; the Ultra's supercharged version produces 240 hp at 5,200 rpm. Torque is 230 lb-ft and 280 lb-ft, respectively.

Another new feature the cars share is a die-cast cross-car magnesium beam. This serves as a body structural member as well as the main instrument-panel mounting support, eliminating multiple secondary brackets. Magnesium is more expensive than more commonly used aluminum, but it's also one third to one half the weight, stronger, and stiffer. In fact, the beam delivered cost savings by eliminating separate parts.

The electrical system uses multiplexing technology, which reduces complexity and increases reliability. For example, designers were able to cut the number of wires going into each door by 75% and eliminate many wiring splices.

High on the list of features that make the car a pleasure to drive are rain-sensitive wipers that activate automatically when moisture accumulates on the windshield. Using an LED sensor, the system also responds to road splash by automatically increasing wiper speed when necessary, allowing drivers to keep their hands on the steering wheel.

--Julie Anne Schofield, Associate Editor

Acetal copolymer helps make subminiature regulator a hit

Racine, WI--Precision pressure regulators have traditionally been large, heavy devices made of metal. Such designs make it difficult for OEMs to squeeze the regulators into compact products, or use them where weight savings are important.

With these criteria in mind, Air Logic, a division of Fred Knapp Engraving, decided to create a modular subminiature regulator that would be compatible with the company's existing line of pneumatic accessories. The result: a molded plastic regulator, available in adjustable and factory-set versions, with a patented thin-walled supply stem. The new device measures just 3.50 inches high with an adjusting knob.

The plastic regulator holds set output pressures within 0.1 psi. The modular dovetail design allows the regulator and matching manifold to be used individually or combined.

To simplify manufacture and assembly, Air Logic designers specified dimensional tolerances within 3 thousandths of an inch on the injection-molded parts that go into each regulator. For the same reasons, they selected the polymer very carefully. The choice: a strong, easily processed, dimensionally stable, and self-lubricating acetal copolymer that could stand up to chemicals in a range of applications.

The regulator is assembled by hand in about five minutes from 36 precision parts. All the components snap, slide, and screw together, with no gluing or ultrasonic welding needed to keep them in place.

Nineteen of the parts are molded from Celconacetal copolymer from Hoechst Celanese, Dallas, TX. The adjusting screw consists of carbon-filled nylon 6/6, the springs of stainless steel, and the diaphragm and O-rings of soft Buna-N rubber.

The nylon adjusting screw was strong enough to carry loads from the 200-lb. spring, but carbon-filled nylon proved too expensive to use for most of the regulator parts. Therefore, Air Logic Designer John Boticki specified Celcon for most components "mainly because it offers many engineering grades to choose from. We are using four grades in the regulator. Each grade was chosen for its specific engineering quality."

Thinner dovetail slides had to be molded without warping to prevent air from leaking around the O-rings. As a result, they were made of low-warp Celcon GB25, a 25% glass-bead-filled grade generally used for flat, thin-walled parts. "We were amazed at how flat we could mold this part," says Boticki. However, for added strength, the vented pressure housing was molded of 10% glass-bead-filled Celcon M90 compounded in-house.

Comparisons of acetal copolymer with polysulfone and polycarbonate by Air Logic also documented a significant savings in materials. Based on per-pound costs, Celcon saved Air Logic about 38 cents per regulator.

"This is a low-cost, precision regulator," Boticki explains. "To do all the machining necessary to manufacture a metal regulator this small would probably double the price."

Demand for the subminiature pneumatic regulator was so great that Air Logic built a new assembly building at its Racine, WI, facility. The precision regulator also has passed a one-million-cycle test as part of Air Logic's quality assurance program. To date, the regulators have been incorporated in equipment for eye surgery, automotive engine diagnostics, semiconductor manufacturing, and other instrumentation applications.

Flash drive stores digital-camera images

Cambridge, MA--Rugged, reliable image storage is crucial for digital photography. With this in mind, Polaroid engineers looked to SanDisk, Santa Clara, CA, to supply embedded flash memory for the company's new digital camera. The PDC-2000 uses a 60-M byte IDE FlashDrive to store up to 60 uncompressed images, which users then download to a computer.

"We chose SanDisk's flash because of its storage capacity and reliability," says Maarten de Haan, program manager for the PDC-2000. "Protection against lost or damaged files is imperative in digital photography."

Key to the camera itself is the thumbnail-sized, 1-million-pixel CCD (charge-coupled device) sensor. The CCD's rectangular pixels represent a red, green, or blue value that is digitized to 8 bits (256 different levels). The camera's control circuitry combines the pixels into square 24-bit color pixels for a total of 16.7 million colors.

Users can save images in super high resolution at 1,600 1,200 pixels or in high resolution at 800 600 pixels, which results in a smaller image file--1.4M bytes versus 5.6M bytes. Given this amount of data, images enlarged to 8 10 inches still look crisp.

Three models, which differ based on their internal memory, are available. Two models have internal storage for 40 or 60 images. The PDC-2000/60 ($4,995) uses SanDisk's solid-state memory; the PDC-2000/40 ($3,695) has magnetic storage. The third model ($2,995) has no internal memory; it connects to a computer for immediate capture and image transfer. All three models let users delete one or more image on the spot and retake the pictures.

DMMs do lots for little

Beaverton, OR--Known primarily for its oscilloscope expertise in the test-and-measurement world, Tektronix has introduced a new family of handheld digital multimeters(DMMs). At the heart of the three units--the DMM830, DMM850, and DMM870-- is the TC8129/8131 chip from TelCom Semiconductor, Mountain View, CA.

This autoranging, autocalibrated DMM analog-to-digital converter, say Tektronix engineers, lets them achieve 4 .75 digit (or 40,000-count) resolution. Some competing units are limited to 3 .75-digit (or 4,000) resolution. The higher spec lets Tek up dc-volts accuracy to 0.06% for the model DMM870.

DMM800 Series meters perform continuity/diode testing and measure resistance, frequency, dc and ac voltage, dc and ac current, capacitance, and decibels. The DMM850 and DMM870 models also measure temperature in both Fahrenheit and Celsius. The dual numeric display of these two models lets users make two measurements at once. For example, engineers can measure the amplitude and frequency of a current or voltage without switching between signal displays.

Other features include:

Time stamp--The DMM850 amd DMM870 can label when minimum and maximum values occur during testing.

Tiny grabber eases IC testing

Santa Clara, CA--Connecting test equipment such as oscilloscopes to individual chip leads is a nuisance, especially if the leads are small and packed close together. Options include holding a probe to the lead and keeping it steady, or soldering a wire to the lead then attaching the probe to the wire--a time-consuming proposition.

Now there's a third alternative. The FP-2S-10 MicroGrabber provides hands-free connection to plastic and ceramic quad flat pack (QFP) and SOIC (small-outline IC) pins with pitches as small as 0.3 mm. (Pitch is the distance between the centers of adjacent pins.) The grabbers work with chips having up to 304 pins, and handle frequencies up to 100 MHz. Applications include telecommunications, data communications, military, industrial, medical, and automotive test and design.

Thin clip body width allows side-by-side placement of grabbers for simultaneous testing. A slide bar secures multiple grabbers in place, and insulated wire tips and nonconductive ABS plastic housings prevent grabbers from shorting out when attached side by side.

Beta tester Roy Wu, an engineering manager with Microtek Corp., Hillsboro, OR, used MicroGrabbers when designing an in-circuit emulator. He and his team attached the grabbers to 33-MHz field-programmable gate arrays in QFPs having 144 and 148 pins and 0.5- and 0.4-mm lead pitches. "MicroGrabbers saved us time, and we di't need a magnifying glass to make the connection," says Wu. He previously soldered wires to attach a scope to the pins of fine-pitch surface-mount devices.

A set of 10 MicroGrabbers costs $325 and includes the slide bar and standard leads to connect to oscilloscopes and other test instruments. They are also available in pairs.

Gas spring improves auto ergonomics

Detroit--A new gas spring is providing an alternative to "hydraulic-damped" gas springs in automotive applications. "Dynamic-Damped" springs from Stabilus, Colmar, PA, are being used on the 1996 BMW 3-Series, the Ford Explorer and Contour, the Mercury Mystique, and the forthcoming '97 Acura CL.

Unlike hydraulic springs that rely on oil reservoirs, the dynamic-damped configuration uses a pressed or rolled longitudinal groove on the pressure-tube inside-diameter area and a sealed piston. Nitrogen gas forced to travel from one side of the piston to the other via the groove serves as the damping medium.

"Before this advancement, the ability to offer variably controlled opening and closing speeds on hatches, gates, hoods, flip-windows and decklids was limited because of the governed flow rate of damping oil through a piston," explains Stabilus Application Engineer Peter Birk. "A significant benefit of the new spring is a reduction of annoying 'flutter' and 'bobble' sometimes associated with gas springs."

Only a small amount of oil--typically 2 to 4 cc--provides critical seal lubrication in the new design. This reduced oil volume allows for a larger gas volume in the spring and helps extend spring life, adds Birk.

In some applications using hydraulic-damped springs, the point at which the piston first encounters the damping oil column is evidenced by a change in extension speed due to the density difference between nitrogen gas and oil. This condition can be more pronounced at cold temperatures as the oil viscosity changes.

A longitudinal groove in the dynamic-damped gas spring consists of two sections: a "constant groove" depth section and a "ramping groove" depth section. At a prescribed point in the gas spring's travel, the piston exits the constant-depth area and enters the ramping section at a smooth gradual speed--regardless of temperature, says Birk. Groove depth and the length of both the constant and ramping groove sections can be specified as required.

HP brings new plotter features to the low end

Palo Alto, CA--Hewlett-Packard has announced two inkjet plotters that are its first to bring roll-feed paper and film media to the low-end CAD market.

The DesignJet 330 is a monochrome plotter that can be upgraded later to color. It sells for $2,195 for the D-size model and $2,995 for E-size. The DesignJet 350C is priced at $2,695 for D-size and $3,495 for E-size. Roll-feed options are extra. The new plotters offer more features at the same price as their predecessors.

HP officials say the new DesignJet 350C can generate images rendered in full color, in any of three modes (fast, normal, and best). The plotter creates a D-sized draft drawing in less than three minutes, and normal-mode output in six minutes.

The 350C uses four ink cartridges (cyan, yellow, magenta, and black) -- the same ones as are used in the high-end DesignJet 750C. Engineers say improved printhead design, ink formulations, special software algorithms, and some mechanical enhancements have all helped boost color quality. An AutoCAD driver offers extra features, such as status feedback and notification of problems like missing cartridges.

For more information about HP plotters, see the company's WWW site at http://www.hp.com

Stratasys offers desktop-prototyping device

Minneapolis--Stratasys Inc. has expanded its rapid-prototyping offerings, with one system that offers quick conceptual models on the desktop, and another later this year that will boost prototyping speed up to six-fold.

Genisysjoins ACTUA from rival 3D Systems in offering a new kind of prototyping for the industry. Vendors have traditionally focused on providing a high degree of precision, so engineers could validate and even test their designs; but these machines are aimed at use much earlier in the design cycle. Here, 0.1-mm accuracy is less important than a machine that is smaller and easy to use.

"We want to get these systems into the design engineers' hands, within the office environment, so the design engineer doesn't have to rely on a central resource or third party for prototypes," explains Paul Blake at Stratasys. So, instead of residing in a separate department, these systems can attach to a workstation much like any other peripheral.

Genisys is based on technology purchased from IBM last year. A cassette system holding 52 wafers feeds material through an extrusion head, which deposits 0.33 inches of material at a time, at a rate of 102 mm/sec (4 in/sec). It uses a Stratasys proprietary polymer.

AutoGensoftware orients and scales the CAD model, slices the data, and automatically constructs the parts with a single point-and-click command. The company says part accuracy is 0.356 mm (0.14 in). A small part might take five to eight hours to produce and cost $15 or $20. Production units are scheduled to be available next month, at prices around $50,000. Systems will work with Sun, Hewlett-Packard, and Silicon Graphics workstations; and will be available for Windows-NT in June.

The Genisys system is significantly smaller and lighter than early ACTUA systems from 3D Systems, according to Terry Wohlers, an analyst with Wohlers Associates, Fort Collins, CO. Genisys parts are also less brittle. The tradeoff: ACTUA offers significantly higher resolution, with crisp corners and fine detail, he says.

Stratasys also unveiled the FDM1650 based on the company's existing fused-deposition modeling technology. The 1650 creates parts three times faster than prior systems, and offers several different kinds of materials--ABS, MABS, investment-casting wax, and polyamide. It will create parts up to 10 10 10 inches, boasts accuracy within 0.127 mm (0.005 in), and sells for about $100,000.

The Stratasys 8000, to be available in the fourth quarter, will offer a six-fold speed increase.

Auto engineers call cost their top priority

Detroit--Cost is the number-one challenge facing the automotive design community. At least that was the concern voiced most (34%) by engineers and designers canvassed in the second annual DuPont Automotive/SAE survey. The poll was taken just prior to the recent SAE International Congress & Exposition.

Nearly 70% of those surveyed by the Automotive Consulting Group, Ann Arbor, MI, also identified low cost as one of the top qualities automakers look for in suppliers, while about half rated cost issues as the greatest concern when its comes to automaker and supplier relationships.

"The cost issue permeates the entire industry," says Henry Voigt, DuPont Automotive's director of sales, marketing, and development. "The message is loud and clear. Materials suppliers must help customers find ways to reduce overall costs."

New fuel-emissions regulations were cited by 24% of respondents as a key challenge facing the automotive industry, just behind cost reduction. Last year, it was the number-one concern, followed closely by cost.

Quality and engineering-support capabilities also ranked high in the survey when it comes to automaker/supplier relations. Two-thirds of respondents listed quality as one of the top capabilities an automaker looks for in a supplier. Last year, quality ranked number one, just ahead of cost. Among the choices presented, engineering support, cited by 21% of those surveyed, was identified as the key quality automakers look for in suppliers.

In an attempt to address these concerns, DuPont Automotive introduced several technologies at SAE designed to help improve automakers' quality and performance, while reducing overall cost. They included:

F200 barrier hose, composed of four DuPont materials, that addresses new evaporative-emissions regulations.

To maintain its industry momentum, DuPont has invested $100 million to open a Zytel PA 66 nylon resin manufacturing plant in Singapore; spent more than $1 billion annually in research; and joined with Dow Chemicals to develop elastomeric technologies.

"The secret here is to ensure that the dollars we have invested create winning solutions," says Voight.

Hydrofoil-rigged trimaran to challenge sailing records

Paris--Under construction in France, a flying-sailing vessel, the Hydroptere, encompasses the latest in both aeronautical and naval technology. The goal: a series of record-breaking attempts at crossing the Mediterranean, Atlantic, and Pacific in 1997.

The project has the support of the French Ministry of Higher Education and Research, Matra Defense, Dassault Aviation, and veteran French sailboat racer Eric Tabarly. To create such a technological breakthrough in sailing vessels, the 60-ft-long hydrofoil trimaran has its foils mounted under the sponsons between the hulls. When the vessel moves, the foils experience a vertical (Archimedes) force, which lifts all three hulls out of the water.

According to its engineers, at a speed of 10 knots only the boat's foils and rear stabilizers will remain in the water. They believe the small, wetted surface and hydraulic drag should allow the Hydroptere to reach record speeds for a sailboat.

Racer Tabarly experimented with a Hydroptere prototype in 1976. However, the current project hopes to guarantee the absolute stability of the boat, regardless of wind or sea conditions during high-speed runs.

To make this possible, the builders must overcome three main constraints. First, because stress on the foils is as important as that applied on a combat airplane's wing, the boat cannot be constructed with conventional materials or technology. Next, since the boat can only "take off" if its weight is very low (the Hydroptere will weigh 5.3 tons), use of a keel is excluded. Finally, the conjunction of these two elements creates the third major difficulty: achieving stability.

To limit weight while optimizing rigidity, high-performance composite materials such as carbon- and glass-fiber sheets make up the foils, the 90-ft-high main mast, the central hull, and the 2,700 square feet of sail. To limit ventilation and cavitation, the foil shape was progressively refined through several hydrodynamic wind-tunnel sessions using a one-third-scale model. Testing sessions suggest this newest idea in sailing vessels should now be able to lift hulls completely clear of the water.