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Articles from 1995 In September


European standards shine spotlight on EMI

European standards shine spotlight on EMI

A man opens his car hood and falls into a coma. Cause and effect? Yes. It's an extreme example of electromagnetic interference, or EMI.

The man was diabetic and had a computer-controlled insulin-injection system. Insulin demand is a function of activity rate, and the computer monitored the man's pulse rate and respiration and pumped out insulin accordingly. When he opened the car hood, an electromagnetic field from keying the ignition system interfered with the injection system's electronics. The result: three days' worth of insulin in 60 seconds.

The manufacturer (who shall remain nameless) took the medical device to Instrument Specialties' World Compliance Center (WCC) in Delaware Water Gap, PA. The Center tested it for susceptibility to external emissions. The end result was that the firm took the product off the market because there was no way to guarantee that under every possible circumstance such a tragedy wouldn't happen again.

EMI has become more and more of a problem as electronic products proliferate. Simply stated, EMI causes a piece of electrical equipment to misbehave due to unwanted electrical energy in the wrong place at the wrong time. (RFI, or radio-frequency interference, is a subset of EMI.)

Most people don't get bent out of shape when a hair dryer interferes with their TV picture. But, as in the above example, many EMI problems are not so benign. In the U.S., all airplanes ban the use of cellular phones because of possible interference with avionics equipment, and 50% of all hospitals ban cell phones. In fact, in a recent episode of the TV series ER, a cellular phone caused a wheelchair to spin around and an electromagnetic problem with a woman's pacemaker caused her arm to jerk up and down.

European standards. In the U.S., the FCC has set standards so that the emissions from certain electronics equipment don't interfere with allocated radio spectrum channels. The European Community has gone further by setting standards for both emissions and susceptibility to emissions for all electronic equipment.

"That's because the countries are so close," explains Instrument Specialties' Product Manager Art Johnson. "They wanted to control emissions more closely so you wouldn't have Germany doing one thing and Belgium doing something else, which could result in bad interference problems. In the U.S., we have one communications system, so there's no chance of anything happening between New York and Connecticut." But it should concern U.S. design engineers.

If you want to ship any electronic product to Europe after midnight December 31, 1995, your product must comply with the EC's electromagnetic compatibility (EMC) standards. If it doesn't, you'll be committing a criminal offense and be subject to fines and imprisonment. However, the main deterrent to not complying is the cost of losing access to the European marketplace--even for a short time.

Five U.S. industries--automotive, medical, industrial control, telecommunications, and test and measurement equipment--never had to meet any U.S. FCC requirements. But now they have to meet the more stringent EC regulations to ship to Europe. "It's been a real shocker for them," says Ron Brewer, vice president of EMC technical services at Instrument Specialties (IS).

Many testing facilities, such as Instrument Specialties' World Compliance Center, have been certified by an European Competent Body to test electronic systems to the European Community's EMC Directive. IS also manufactures standard and custom shielding products to help solve EMI problems.

It's most cost-effective to contact such a facility early so that you can avoid EMI problems. But human nature being what it is, many companies wait until a design is nearly finished and on the production line before addressing EMC. Some discover they have a major problem that requires a total redesign of their equipment. Others can get by with adding shielding or gasketing or doing some other simple retrofit.

Few passing grades. "About 90% of all products we test for EMC fail the first time," says Brewer. For example, a leading international maker of handheld cellular phones had Instrument Specialties' WCC test a model that had already passed FCC tests for compliance with the European EMC standards. They fully expected it to pass, thinking that the plastic housing's plated-nickel conductive coating provided sufficient grounding and shielding for the pc boards. They were wrong.

"The phone failed the emission portion of the testing," says Tony Sosnowski, manager of product development. "We designed a custom shield that not only acted as a barrier between the two circuit boards, but also grounded the top and bottom covers." The shield, made from beryllium copper 25 alloy, has 90o flanges that provide the contact between the covers. Using this first prototype shield, the phone passed the European tests. Within a week, Instrument Specialties was tooled up and making the custom part.

A surgical laser already used in the U.S. for trimming drooping eyelids and other delicate types of surgery was recently tested by the WCC. The power the laser puts out determines the depth of cut. EMI susceptibility testing for the EC EMC standard showed that the depth of cut could vary by almost .75 inch. "Instead of trimming your eyelid," says Brewer, "it could bore a hole through your skull and into the front part of your brain."

Instrument Specialties is working with the manufacturer on a major redesign. The two decided that just adding more shielding, which protects a device from EMI, wouldn't be the best solution. The shielding could degrade, and the manufacturer wanted a fail-safe design. Possible design changes include adding a power-regulator circuit, filtering circuits, and perhaps more shielding.

A European maker of telephone switching equipment approached Instrument Specialties during the early design phase to address EMC. The application: a cable access carrier. The company wanted end-users to have enough cable openings, but not have to worry about EMI problems if a cable slot wasn't being used.

Instrument Specialties engineers designed a nickel-graphite, conductive-elastomer shield that slides into unused cable access slots. "If there were nothing in the slot, RF energy could seep through the hole," explains Instrument Specialties' Art Johnson. Under pressure, the silicone-polymer-based elastomer makes contact with both sides of the metal carrier, prohibiting energy from passing through. If the part were metal, you'd need very fine tolerances to ensure electrical contact.

Testing for compliance. The World Compliance Center has a variety of rooms for performing different EMC tests. For instance, to find out the kind of radiation levels a piece of equipment is emitting, and not be confused by the ambient environment, WCC makes some preliminary measurements inside a shielded room, or enclosure. These enclosures exclude exterior RF ambient.

A typical measurement can have error due to antenna loading, reflections off the inside walls, and resonance that occurs when the wavelengths of frequencies happen to coincide with the dimensions of the enclosure. To minimize that problem, the floor, ceiling, and walls are covered with anechoic material. This material, in the form of bright blue cones, contains ferrite and carbon particles that match the impedance of free space. If a radio wave propagates along, what little reflection there is reflects into the cones and not back into the room.

"They're kind of wild places," says Ron Brewer, vice president of EMC technical services, of these rooms. "When the door is closed and the lights off, the sound-absorbing qualities of this material will let you hear your heart beat."

The Center also does susceptibility measurements in the shielded enclosures to prevent pollution of the environment. "The FCC and FAA take a dim view of squirting RF out into the ambient," notes Brewer.

A room without metal. If a product passes the shielded-enclosure tests, it proceeds straight to the top of the WCC. "We have a special area upstairs--our 10m open-area test site," says Brewer. The European EMC Directive states that radiated emission measurements must be performed in an environment where there are no reflections. Therefore, this room has no metal--not even nails--above the ground plane.

Fiberglass bolts hold the walls together, and the windows have plastic frames. Lights and wiring are below floor level, with the light shining up through the shield. As far as radio waves are concerned, the room is outside.

During emissions testing, engineers set up a calibrated receiver with calibrated antennas. They measure the field intensity generated by the sample at a distance determined by the appropriate standard. A camera watches the sample on the turntable as it rotates 360 degrees, and the antenna moves up and down to gather a wide spectrum of data. This is the test most products fail.

Even if a product passes, that doesn't mean life will be rosy. "Passing EMC testing in the lab doesn't necessarily mean that the unit will operate properly in the field," stresses Brewer. A lab can't possibly duplicate all real-world conditions. Good design still applies.


EMC resources

Two helpful guides to the EC electromagnetic compatibility standards are The Guide to the EMC Directive 89/336/EEC and EDN's Designer's Guide to Electromagnetic Compatibility. The first describes the key features of the European Directive, their implications, and how to form a plan to achieve compliance. The second addresses design engineers who need to get up to speed on EMI, why it happens, and how to fix it.

The Guide to the EMC Directive 89/336/EEC, by Chris Marshman, IEEE Press, Piscataway, NJ, 1993 (ISBN 0-7803-0445-4).

  • EDN's Designer's Guide to Electromagnetic Compatibility, by Daryl Gerke and Bill Kimmel. To order, phone (800) 523-9654 or FAX (708) 390-2779.

Internal reflector improves solar cells

Internal reflector improves solar cells

Newark, DE--To make electricity from sunlight, you must capture photons in your solar cell. If photons pass through the cell, or get reflected out of it, cell efficiency suffers. By putting an irregular reflector on the back of a silicon cell, engineers enable a new photovoltaic cell to capture photons that would otherwise be lost. Photons can bounce back and forth between the front surface and the "mirror" until they are absorbed.

James Rand, AstroPower Inc.'s manager of product technology, explains that there are two types of silicon solar cells: Rather expensive, 400-aem-thick, polycrystalline cells, with an efficiency of about 14%; and super-thin amorphous silicon cells with an efficiency that ranges from 3 to 5%.

AstroPower has developed a new solar cell that combines the advantages of both types. It consists of silicon grown 35- to 50-aem-thick on sheets of inexpensive, ceramic-like substrate--which cuts costs. Current cell efficiency reaches 13% in the laboratory, 10 to 12% in the field. Its novel silicon/ceramic substrate combination makes extra light trapping feasible.

Silicon does not stop all the light that enters it. In fact, says Rand, "in 30 to 50 microns of silicon, about 15% of the light is not absorbed. Light passes into the substrate and is lost. So we put a reflector in the back."

The reflector must be randomly irregular. When a photon comes straight down, it passes through a non-reflective top coating. If it were to hit a flat reflector at the back of the cell, the photon could bounce straight back out of the top coating. By making the reflector irregular, the photon bounces off at an angle, and can't get through the top coating. "So we trap it, and the photon bounces about until it's absorbed," adds Robert Hall, Astro-Power's vice president of research and development.

In fact, a reflective layer can also keep electrons from escaping. "When photons strike the silicon, they generate huge clouds of electrons, which diffuse randomly," Rand explains. "When they reach the p-n junction at the front of the cell, they are collected and converted to useful electrical current." But at the back surface, any defects provide "holes" or places where there the cell's lattice structure lacks an electron, and the electrons can attach. So AstroPower engineers design their cell's rear reflective surface to be defect-free. It amounts to a barrier that holds in electrons until they diffuse to the front of the cell.

Other Applications
  • Remote village power

  • Bulk power generation

  • Water pumping

  • Battery charging

The natural, unpolished texture of the substrate is randomly irregular. AstroPower grows refractory-like oxides, nitrides, and carbides on the substrate. Next, a thin silicon layer grows in intimate contact with that combination of materials.

Light trapping should enable cells to reach 19% efficiency in the lab and 17% in the field. Prototypes demonstrated that the reflected light's path length is longer than in conventional cells. Engineers now want to make such a solar cell easy to manufacture.

Additional details...James Rand, Manager of Product Technology, AstroPower Inc., Solar Park, Newark, DE 19716-2000.

Screw pump regulates pressure precisely

Screw pump regulates pressure precisely

Egham, England--Start with a stepping motor-controlled screw pump. Add a pressure transducer and microprocessor. Then develop some simple control algorithms. This is how GDS Instruments transforms an ordinary hydraulic pump into a precise regulator of pressures as high as 150 Mpa (22,000 psi).

To work, the stepping motor and gearbox turn a ball screw through a captive ball nut. This action displaces the piston inside its cylinder. The transducer, which measures fluid pressure in the cylinder, informs the control circuit of the pressure changes. Finally, the control circuit and microprocessor instruct the motor to step forward or back to maintain target pressure.

Bruce Menzies, director of GDS, explains that the system can be programmed through a built-in control panel to ramp and cycle pressure linearly with respect to time. Additionally, the device offers a computer interface to accommodate a PC. Users, therefore, can input their own custom programs.

Such functions, says Menzies, not only apply to pressure, but to volume change as well. For example, he points out that with 200 steps/revolution of the stepping motor, a 25:1 reduction gearbox, and a 5 mm pitch on the precision ground screw, "it is a simple procedure to size the cylinder bore so that one step of the motor equals a volume change of one cubic centimeter."

Because of its ability to regulate volume change, the system allows precise dosing. Other possibilities include switching between two systems and a reservoir for unlimited flow, and using external transducers such as load cells, displacement sensors, and differential pressure sensors for closed-loop control of piston movement.

Additional details...Contact Bruce Menzies, GDS Instruments Ltd., Unit 12 Eversley Way, Thorpe Industrial Estate, Egham, Surrey, England TW20 8RG, Tel: +44 1784 439228, FAX: +44 1784 434644.


TECHNICAL SPECIFICATIONS

SIZE: 860 mm x 230 mm x 220mm

WEIGHT: FROM 20 kg

PRESSURE RANGES: 2, 3, 7, 10, 20, 32, 64, 150 Mpa

COMPUTER INTERFACE: IEEE-488 STANDARD AND RS 232

VOLUME CHANGE ACCURACY: 0.25% MEASURED VALUE

VOLUME CHANGE RESOLUTION: 1.0 cu-mm

PRESSURE MEASUREMENT ACCURACY: 0.1% FULL RANGE

PRESSURE MEASUREMENT RESOLUTION: +- 1 IN 10,000


Other Applications

  • Control of ultra-high pressure in hydraulically operated test systems

  • Computer-controlled dosing in industrial chemical processes

  • Control of small pressure differences at high line pressures

Step-motor drive reduces resonance problems

Step-motor drive reduces resonance problems

Rohnert Park, CA--Step motors find themselves in a variety of motion-control applications, from the mundane to the mission-critical. On board the X-Ray Astronomy Satellite, for instance, a step motor drives an essential telescope-calibration system. Out in the shop, step motors control the sheet-stock feeders used in metal stamping.

But they have their limits. Highly undamped--most exhibit damping ratios of 0.02 to 0.04--step motors suffer stability problems. "The dynamic model is like a mass on a spring," says Stuart Goodnick, manager of the power products group at Compumotor. And as with springs and masses, step motors can resonate in ways that lengthen their settling time, fight high-speed moves, and cause instability in full-step motors at about 1.0 rps.

A new drive from Compumotor, called Zeta, is the first to address these issues throughout the operating range, the company says. And it does so without changes to the motor.

It incorporates several patentable features that greatly improve damping at both low and high speed, increase throughput, and provide more available torque. Engineers believe the drive may open doors to new applications or even replace servo motors in some cases.

Zeta's secret lies in three separate technologies: electronic viscosity, active damping, and stall detection. Uniquely, all three operate off signals generated by the motor, thus foregoing the need for separate sensors and encoders.

Electronic viscosity dampens system ringing that occurs when trying to stop, decreases the duration of individual moves, and increases throughput. "We found a way to detune the current loop at low speed," says electronics engineer Christopher Botka. "The net effect is that we introduce a very strong viscous term." At speeds less than 3 rps, electronic viscosity increases the damping ratio from 0.20 to 0.25, cutting settling time by an order of magnitude compared to undamped systems.

By contrast, active damping only functions at more than 3 rps (built-in hysteresis prevents it from conflicting with electronic viscosity at the crossover point). It reduces vibration, counteracts mid-frequency resonance at 15 to 20 rps, and increases the usable torque of the motor. Unlike competing passive damping techniques, active damping can be applied while driving the motor and not just at the end of a move. It can also be used with microstepping drives, whereas passive damping cannot.

Active damping requires a feedback signal to form a closed-loop system similar to that of a servo motor. The signal is usually supplied by a tachometer or other sensor. While this technique has been used since the 1980's, the expense and fragility of tachometers has limited its use.

With Zeta, however, engineers developed a sensorless active damping method that uses the signals produced by the motor's back-EMF. "You know this back-EMF is there," says Botka, "and we asked, is there anything we can do with these signals to extract position?'"

And indeed there is. Zeta uses the motor-terminal voltages and currents as a sort of electronic observer, Goodnick explains. By looking at the signals being sent and the signals coming back, engineers found a way to extract rotor dynamics. "We extract phase information that tells how much torque the rotor is seeing," he says. "We scale the signal, find the velocity of the rotor, and then difference that with the command signal to create an active loop."

Zeta contrasts with traditional solutions such as friction rings and ferrofluidic dampers. The former reduce usable torque and eventually wear out, and the latter add inertia and cost--the price of a ferrofluidic damper might be four times the cost of the step motor itself. With a damping ratio of 0.45 at speeds greater than 3 rps, "Zeta exceeds what ferrofluidic dampers give you with no changes to the motor," says John Walewander, product planning manager.

Active damping also eliminates the need for customers to choose an over-sized motor to account for mid-frequency (15 to 20 rps) resonance, ringing, and transient behavior. "We usually recommend that customers dial in a 50% torque-safety margin," says Goodnick, "but you don't need that with this drive."

During the 18 months spent studying sensorless active damping, engineers also discovered a way to detect stalls. "We use the motor terminals to look for an impulse of energy that arises when the rotor loses synchronization with the stator," explains Botka. This feature can save customers the expense of adding an encoder.

While the company makes no specific claims regarding improved high-speed performance, during a demo performed for Design News, engineers ran a standard size-23 motor to more than 300 rps. That compares with a maximum of 50 to 150 rps for a typical motor and drive, they claim.

Skeptical of Zeta's abilities? Don't take Compumotor's word for it. Mary Slaw-ski, an advanced design engineer at 3M, St. Paul, MN, has used Zeta in an R&D project. The application demands a linear positioning accuracy of 0.002-inch with the motor turning at 0.9 rps. "We were using Compumotor's S-Drive, and you could hear it whining," says Slawski.

After trying Zeta, she believes the application can now run open-loop. "The anti-resonance circuitry is pretty incredible," she says. "I've never seen a step motor run that quiet that slow."

Additional details...Contact John Walewander, Parker Hannifin, 5500 Business Park Drive, Rohnert Park, CA 94928, (800) 358-9068.


Other Applications

  • Electronic pick and place

  • Servo motor applications

  • Extremely high- and low-speed motion control

Coil gun drives high-speed-rail technology

Coil gun drives high-speed-rail technology

Albuquerque, NM--At first glance, Sandia National Laboratories' linear induction motor appears an unlikely candidate to solve the country's transportation woes. Surrounded by a heavy steel truss, it looks more like a shortened particle accelerator.

But when physicists demonstrate it, all skepticism disappears. A wheeled aluminum plate weighing 35 pounds streaks through the middle of the truss as if shot from a cannon. In a distance of just 13 feet, the plate's velocity reaches 33 mph.

And that's merely a fraction of the technology's ultimate potential. The offshoot of a Sandia coil-gun program, the linear induction motor has moved steel plates and cylinders at a speed of a kilometer per second. Physicists estimate that the technology could launch satellites at the incredible speed of six kilometers per second. The National Aeronautics and Space Administration has even considered it as a means to launch the Space Shuttle.

Now, however, Sandia scientists propose an unexpected new role for the technology: high-speed rail. A project called SERAPHIM (for SEgmented RAil PHased Induction Motor) would employ linear induction motors to propel trains at speeds of 200 mph or more. Using the new technology, high-speed trains could operate on existing rights-of-way, create less rail wear, reduce the need for track maintenance, offer improved grade-climbing capabilities, and provide a smoother, quieter ride than is now available.

What's more, the scientists say their system offers advantages over much ballyhooed magnetic levitation technology. "It requires neither powered guideways nor superconducting magnets," says Barry Marder, distinguished member of Sandia's technical staff. "As a result, this system offers a low-risk, cost-effective route to very-high-speed ground transportation."

Faster than a bullet. Unlike conventional high-speed-train technologies--such as those used on the French TGV (Design News, 7-24-95) and the Japanese Bullet Trains--the Seraphim concept employs passive steel wheels. No traction is needed--either for acceleration or braking.

Instead, the SERAPHIM concept propels the train through magnetism. Electrified coils on the train react against a segmented reaction rail mounted on the roadway. The reaction rails can be one of two types: single- or double-sided. In either case, the coils for the linear induction motor mount on the train.

SERAPHIM's linear induction motor provides motive force by magnetic interaction with the reaction rail. Unlike linear induction motors of the past, however, it operates not by embedding flux in a conductor, but by excluding it. In the double-sided version, pairs of closely spaced coils on the vehicle straddle a segmented aluminum rail. As the train moves forward, on-board sensors "watch" for the approach of an aluminum reaction plate. When the coils overtake the plate, the system's modulator pulses current to the coil, creating a magnetic field, which induces surface currents on the plate. Those surface currents repel the coil.

In essence, Sandia scientists say, the pulsed coils push off the edges of the plate. How? At high frequency operation, the flux has insufficient time to penetrate.

Operating in this fashion, each coil can produce 3.5 kN of thrust. With 30 coil pairs mounted on each powered railroad car, the system can provide 6 MW (8,000 hp).

During operation, each powered rail car would employ two gas turbine power units. Power modulators would supply the pulsed voltage to the coils, with each modulator powering six coil pairs.

A sense-and-fire circuit would control the pulsing of the power modulators. Each modulator, in turn, would provide 1.2 MW average power in pulses 2 ms half-width at frequencies ranging from 100-230 Hz.

Sandia scientists say that the system's maximum cruise speed is limited primarily by available power, aerodynamic drag, and grade. Cruise speeds of 200 mph on straight and level track could be achieved with a supplied power of 6.3 MW (8,500 hp).

In their New Mexico labs, Sandia scientists have constructed working models of the SERAPHIM concept. Using a three-stage motor, they accelerated a 14.4 kg aluminum plate along a 4m track to speeds of 15 m/sec. In the test, they achieved peak thrusts of 18 kN per coil, using coils with two windings of 51 turns each. The windings employed copper straps insulated with DuPont's Kapton(R) film and Dacron(R) polyester.

Air travel alternative. Sandia's concept isn't the first of its kind. During the 1970s, engineers working for the Federal Railroad Administration conducted tests on a similar concept at the Transportation Test Center in Pueblo, CO. Using demonstrator vehicles with linear induction motors and passive steel wheels, trains reached speeds of 200 mph.

By developing the new linear induction technology, Sandia scientists have resurrected the idea, but have added one important twist. Up to now, linear motors have had inherent velocity limitations related to their lengths. That is, the longer they were, the greater their speed. But by employing rapidly-pulsed magnetic fields and segmented reaction rail--instead of low-frequency fields and continuous rails--the scientists eliminated the inherent speed limitation.

"There's really no practical limit to the speed you can achieve with this technology," Marder says. "If you had the power to do it, you could launch the train at any speed. All it requires is faster switching of the coils."

The technology, Marder says, also offers other important advantages:

It requires no new rail technology. Its construction would cost about one-fourth as much as a comparable maglev system.

  • Its track would be subjected to less wear, because SERAPHIM doesn't rely on wheel adhesion.

  • It would offer greater grade climbing capabilities, because it doesn't suffer from wheel slippage.

  • Its locomotives would be lighter, because no extra weight is needed to improve traction.

Sandia scientists hope to test the concept at the Pueblo, CO, Test Center. Plans are to build a "ladder-like" reaction rail with aluminum plates that lie horizontally within the track bed. This configuration would provide single-sided linear motor technology, allowing downward-facing coils to "push off" the aluminum plates. Though it's not as efficient as the double-sided configuration, it should easily allow test trains to run at 200 mph.

Ultimately, Sandia scientists believe that the technology could offer a viable alternative to air travel. Because airline costs are highest for planes as they ascend and descend, short flights might one day be less cost effective than rail travel. Concludes Marder: "A train travelling at these speeds could certainly compete."


A smokeless Space-Shuttle launch?

Since the glory days of the Redstone rockets, NASA has launched its space missions amid great plumes of smoke and fire. Now comes a completely different idea.

Instead of a great belch of smoke, some NASA scientists are looking at a huge pop of electrical current to launch the Space Shuttle. Using Sandia's coil gun technology, they could replace the first stage of the Shuttle with a re-usable "MagLifter," they say.

If it were ever deemed feasible, the MagLifter would propel the Space Shuttle up a mountainside using the magnetic coil-gun technology. Employing a technology similar to SERAPHIM's, electrical coils on the ground would react magnetically with specially-designed plates on the Shuttle's first stage. This magnetic propulsion scheme could ultimately push the Shuttle up a track to a speed of 600 mph, giving it sufficient speed for a mountainside launch. "Then you could bring the launch vehicle back down for the next launch," says Barry Marder, distinguished scientist for Sandia National Laboratories.

According to the researchers, the MagLifter could supply sufficient thrust for higher-speed launches, were it not for excessive G-force build-up on the crew. Using the coil gun for satellite launches, they estimate a build-up of more than 2,000 Gs on the satellite--a figure that's obviously excessive for passengers.

How likely is the MagLifter concept to see action? All Marder will say: "We've proposed this propulsion scheme to NASA, and they're considering it."


Polyimide film keeps ac motors humming on Alpine rail link

Sandia's linear induction motor isn't the only electromotive train technology to employ DuPont's Kapton(R) polyimide film as an insulation medium.

The material also plays a vital role in the most powerful universal four-axle locomotive in the world, the Re 465. Designed by ABB Transportation Systems Ltd., Zurich, Switzerland, and Swiss Locomotive and Machine Works, the 82-ton engine has a top speed of 140 mph and can pull a 650-ton train at 60 mph up a 2.7% gradient. The new locomotive runs on a Swiss trans-Alpine rail link between northern and southern Europe. For the Re 465's traction motor, DuPont engineers developed a special, corona-resistant version of the material, known as Kapton CR. Kapton CR helps insulate the copper conductors in the motor's stator from steep voltage peaks that can lead to partial electrical discharges, or corona. These discharges can break down organic insulation materials.

To develop Kapton CR, DuPont engineers undertook a joint program with traction motor manufacturers ABB and Siemens AG. The result: Corona resistance is said to be orders of magnitude better than that of standard Kapton, and thermal conductivity is twice as high.

Corona resistance is now said to be 100,000 hours at 20 kV/mm at 50 Hz. The propulsion system employs power thyristors and three-phase ac motors.

Designer's Productivity Kit: How to choose & use fasteners & adhesives

Designer's Productivity Kit: How to choose & use fasteners & adhesives

Admit it: When you think about design--whether it be an intricate electronic component or a straight-forward enclosure--you probably don't think about how you're going to hold it all together until the end of the design cycle.

Innocuous as they may seem, fasteners and adhesives are critical to the success of any product. For optimum joint design, engineers must balance performance, cost, and manufacturability. Factors such as availability, joint life-expectancy, handling, safety, and design for serviceability also come into play.

With so much to consider and an endless variety of fastening options to chose from, it's not surprising that some designs don't take advantage of ideal fasteners or adhesives. To avoid being overwhelmed at the choices and to improve your design, look to the experts. What follows is their advice on how to avoid common mistakes, cut costs, save time, and get the most out of new fastening technologies.

Think of the end use

If you haven't already chosen between mechanical fasteners and adhesives, tapes, or welds, focus on the product's end-use. "Parts subject to wear will need access and service, and require mechanical fasteners," says Larry Kline, senior product engineer at SPS Technologies, Newtown, PA. Mechanical fasteners can also provide a reusable solution in some applications.

Adhesives offer other benefits: Where a permanent bond is desirable, they can lower manufacturing costs, add shock protection and sealing characteristics, or improve the aesthetics of an exterior surface.

"Obviously, in any application the engineer has to carefully consider parameters and physical requirements such as stress, shock, load, and temperature," says Randy Ladutko, General sales manager for Avdel Textron, Parsippany, NJ. But Design for Serviceability should also influence the decision, he says. Will the product require frequent maintenance or replacement parts? Clearly, permanent adhesive bonds aren't suitable for an access panel. "But don't forget that modular products and upgrade options also mean that the product may require disassembly down the road," adds Ladutko.

Remember to evaluate the surfaces you're intending to bond, cautions Jeff Travis, senior market development administrator at 3M, St. Paul, MN. Says Travis: "Are you working with two rigid substrates? One flexible and one rigid? What about material compatibility?" For example, vibration can spell disaster for a mechanical fastener, yet leave certain adhesive bonds intact. Likewise, different coefficients of thermal expansion can wreak havoc on joints that include dissimilar substrates.

Although engineers are typically well-informed about the adhesive bond performance requirements of their application, they tend to be unfamiliar with important manufacturing issues such as surface preparation and time-to-cure, adds Travis. Such elements can have a profound influence on installed cost, bond strengths, and production speed.

Get suppliers involved early

Manufacturers agree: No matter which fastening technology you choose, early supplier involvement is vital. "The fastener supplier is rarely called in at the 'paper napkin' stage," reflects Avdel's Randy Ladutko. "Fastening is probably the most critical area of design, but most engineers relegate it to something they'll find in the corner hardware store." Supplier involvement can help the designer take advantage of the wide variety of sophisticated fastening systems available.

For example, extensive handbooks, such as SPS Technologies' 76-page reference for aerospace self-locking nuts, provide specifics about swaging, plating, and fatigue properties of hundreds of products. Likewise, 3M's updated Designer's Reference Guide and Loctite's intensive Design Guide for Bonding Plastics walk you through the selection of suitable adhesive chemistry and application and cure methods, as well as highlighting advantages and disadvantages of dozens of products.

Even the most detailed guide is no substitute for supplier engineering support, however. "Excluding the supplier from the early stages of design diminishes the possibility of using a standard--and therefore less expensive--product," says Jim Grady, manager of corporate engineering for Southco, Concordville, PA. "When the designer contacts us at the end of the development cycle, there are already set criteria and we're limited in what we can provide," he observes. "Early in the cycle, it's easy to specify an off-the-shelf product. If necessary, we have the lead time to pursue custom development and tooling, and everything can happen on the same launch schedule. Because you don't want to be waiting on a $4 latch for a $100,000 computer system."

Analyze installed cost

When banished to the end of the design cycle, fastening systems often bear severe budget and design constraints. There's more to specifying fastening technology than screws and glues, warns Ladutko at Avdel. "If the design engineer takes a hands-off approach with the idea that a fastener is a low-cost item, that mind-set can turn out to be very expensive."

For example, specifying a less-costly substrate can actually add expense if it's incompatible with conventional bonding methods or not sufficiently strong for a threaded fastener. And while a custom mechanical fastener may be only slightly more expensive on a piece-part basis, single-side access for installation or elaborate custom tooling can cause installed cost to skyrocket.

Tim McGuire, Manager of Product Engineering at Camcar Textron, Rockford, IL, advises engineers to "look at the overall design. Are you designing the fastener in your component where there's room for tooling? It's easy to locate a fastener in an engineering drawing, but maybe a component will prevent the drive gun or a person's hand from getting in to install it." By including fasteners in conceptual drawings, engineers can avoid such a scenario, says McGuire.

Avoid overkill in your specifications

Frequently, hidden costs stem from design overkill. That's where a supplier's expertise can save money. Penn Engineering and Manufacturing, Danboro, PA, halved the cost of most of the fasteners in an automatic bank teller machine in one instance, says Application Engineering Manager Pat Kelly. "The engineering group hadn't contacted us, and they were specifying stainless-steel fasteners throughout the assembly," recalls Kelly. "In 80% of the fastener locations, they didn't need stainless steel. They were spending more than twice the cost of an equivalent non-stainless-steel part with no benefit."

Likewise, balance the cost and performance of plating or other finishes when addressing corrosive environments, says Kelly. "We often see applications where our customers have specified products that work, but they're over-designed." Thread size is especially prone to such excess, he adds. Unless a metric M6 or M8 fastener gives the benefit of having a single fastener size in your component, it may be too large a thread. "When engineers over-specify, they don't get additional benefit, just additional cost," reflects Kelly.

Choosing an over-qualified adhesive, over-specifying bond overlap, and over-spraying are also budget thieves. For example, the lower tensile strengths of plastics make it common to create bonded joints that are stronger than the plastic itself, explains Richard Thompson, Senior Product Engineer with Loctite Corp., Rocky Hill, CT. Engineers can achieve equal overall assembly strength with a narrower overlap and less adhesive. Many engineers aren't aware that shortening bond overlaps actually reduces the bend and differential shearing effects of lap joints, says Thompson.

Use specials to beat design limitations

When a custom fastener or adhesive formula is genuinely called for, the extra expense and engineering effort during design can prevent failures and costly delays down the line. In fact, a well-designed special fastener can compensate for limitations of a design. Says Camcar's Tim McGuire: "Custom fasteners can reduce overall fastening cost in some applications. The overall piece-price is higher, but the fastener may be faster to drive, such as the Torx Plus[super{TM}], so it reduces overall installed cost."

Soft joints also benefit from custom fasteners. Plastic components, thin cross-sections, and gasketed joints aren't well-suited to proper fastening techniques. But custom fasteners tailored to the correct seating torque can overcome the restraints of such designs and prevent fasteners from stripping out or cracking the substrate, says McGuire.

In critical applications such as automotive airbags and seatbelts, price and production volume support custom parts. The technology is available, says McGuire, and "the more dramatic the impact of the failure, the more technology you can afford to put into place."

With adhesives and tapes, getting what you want out of a custom formula can be as simple as knowing what you need, says 3M's Jeff Travis. "Customers come to us and say they need a longer open time, or higher viscosity, or faster set, and we tweak a formula to make it work."

Examine manufacturing issues

Of course, even the best prototype joint design doesn't always prove sound in production. With adhesives, engineers need to be aware of issues such as bond curing techniques, shelf-life limits, and handling requirements. For both adhesives and mechanical fasteners, assembly time and automation and tooling expenses are important elements of a bond design's feasibility.

For instance, some adhesives shrink during curing. Flexible adhesives are better able to adjust to shrinkage than rigid systems. In applications that don't tolerate shrinkage, engineers should select 100% solids adhesives such as one-component epoxies, says Kelvin Yee, market development manger at Grace Specialty Polymers, Woburn, MA. For example, Grace's AMICON(R) epoxies are designed specifically to bond surface-mount devices in electronics applications, where they protect components from contaminants and excess solder filling once cured.

To address safety standards and OSHA requirements, engineers should consider automatic mixing and dispensing equipment to minimize worker exposure, says Ken Cressy, Industry Manager for Ciba-Geigy's Aerospace group in Los Angeles. In some cases, liquid adhesives can be replaced with alternative products. "If heat cures are suitable, as is often the case with pre-preg composite structures, you can go to a film adhesive, which gives higher strength and better application control," he says.

Many designers don't take into account that some substrates require surface preparation such as plasma- or chemical-etch, says Len Rantz, Director of Polymer R&D at Grace Specialty Polymers. Engineers should be aware that design constraints such as available heat, time, and dispensing techniques limit automation choices, he adds. "We're seeing a lot of infrared curing, induction curing, and hot air blowing, because engineers are looking for shorter cure times. There are more demands on the chemistry, because in some applications, there's no time to wait around while a part goes through a tunnel oven."

Design for Assembly isn't simply a matter of inexpensive, easy-to-install fastening systems, says Avdel's Ladutko. Engineers should consider not only the cost of fastening materials, but also the quality and integrity of the final joint. In an automotive fastener, for example, an anti-rattle feature such as one designed by Avdel can improve the fastener's function and may reduce parts count without any assembly-speed penalty. Not surprisingly, many high-volume automotive applications demand compatibility with automated assembly equipment. Hence, fasteners from Penn Engineering are available with tapered or dog-point ends, or an orientation feature for rapid, high-volume track-feeding in automated assembly lines.

Explore new fastening technologies

Adhesive and fastener suppliers are always introducing new products to answer application needs. For instance, to join magnesium components, engineers needed a thread-forming fastener rather than a thread-cutting part that would create debris from the flaky substrate, says Camcar's Tim McGuire. So Camcar developed thread-forming TapTite(R) "Magscrews" especially for magnesium.

For applications where loose hardware is a problem, Southco engineers designed the "Captive Nut." The N7 fastener replaces wingnuts or mounting nuts in installations where lost hardware can't be retrieved or would cause equipment damage. The fastener is suitable for joining aluminum, low-carbon steels, and annealed stainless steel. To speed assembly, an internal thread and ferrule help position panels being fastened. A through-hole version accommodates frame and panel thickness variations and gasket compression set.

As application demands change, fastening systems must adapt, observes Larry Kline of SPS. "Car engines today run a lot hotter than they were running ten years ago, for fuel-efficiency reasons. That requires high-strength, high-temperature fasteners." Similarly, aerospace manufacturers seeking to boost engine thrust run aircraft engines hotter. To meet those requirements and accommodate existing designs, SPS offers fasteners made from multi-phase materials such as AEREX 350, an alloy suited to high-strength service to 1,300F. "New materials come out every six months, and a lot of them are directed at fastener applications," says Kline.

New technologies are constantly developing for adhesive uses, as well. For example, Ciba-Geigy's Urelane 5774 FST adhesive meets flame, smoke, and toxic-gas emission limits, which are required for automotive, aircraft, and other applications for safety. The adhesive is slow to burn and releases no toxic fumes, says Industry Manager Ken Cressy.

If you run into a snag when designing a joint, call on suppliers for technical expertise. Says Penn's Pat Kelly, "We don't expect our customers to be experts in the fastener field. We welcome their calls and questions because, ultimately, it's going to be better for everyone." Many adhesives suppliers, such as Grace and 3M, devote R&D resources and engineering experience to customer-support labs. Says Grace's Len Rantz, "That's why the lab is here. If it was easy, engineers wouldn't need us."

Digital technology comes to motion control

Digital technology comes to motion control

In 1989, Korte became general manager/president of Heidenhain, the North American subsidiary of Dr. Johannes Heidenhain GmbH, Traunreut, Germany. In this capacity, he authors many technical articles on linear- and rotary-encoder technology on behalf of Heidenhain. Korte began his career at the company as a salesman, and became national sales manager in 1986. Before joining Heidenhain, he worked for MXM Corp. Korte served as a sales technician at Trionics Corp. from 1978 to 1981. His experience with electronics began in the Air Force in 1971.

Solid and mature, motion-control has been around as long as there has been motion to control. But Rick Korte explains that the industry has also benefited greatly from digital techniques, leveraging computer technology to improve performance.

Design News: What are some current trends in rotary encoder designs and applications?

Korte: One of the most prevalent new trends is the move to digital speed control. If you review a typical numerically controlled machine, you will find a microprocessor is controlling the position loop. However, the velocity loop is probably using an analog circuit, which uses feedback from a tachometer and employs Hall sensors for commutation of the brushless motor.

At Heidenhain we see a move in the newer control systems to a fully digital solution to both position feedback and velocity control. With the demand to reduce the number of components and the number of lines running between the motor and the control, it is desirable to let the encoder provide position, speed, and commutation data.

Q: How is Heidenhain improving resolution and accuracy?

A: Our continued work in the area of optical gratings and special scanning methods has allowed us to produce finer gratings with higher accuracy--and the ability to have large interpolation values producing higher resolutions. Our use of optical filtering allows increased accuracy in the signal; net quality by using a special scanning method that eliminates various signal elements caused by diffracted light.

Q: What should engineers look for when choosing encoders?

A: Rather than describing specific technical details, the most important decision when choosing an encoder is the vendor itself. Engineers today must be able to have a strong partnership with their supplier. It is important that the encoder manufacturer be able to provide a full range of solutions. The manufacturer must be reliable and dependable, able to provide the best possible technical solution for numerous applications, and forward-thinking. The manufacturer's R&D group must be one step ahead of the requests of the engineers. When a vendor/customer partnership is established on mutual trust and confidence, the outcome can be very dynamic and rewarding.

Q: What is being done to toughen encoders and provide better mechanical performance?

A: One area we have recently addressed is the coupling between the encoder and the motor shaft. The conventional way of connecting an encoder is with a coupling located on the rotor side of the encoder. This configuration is more often becoming unsuitable. The problem is that even the best coupling acts as a torsional spring which, in conjunction with the moment of inertia of the encoder rotor, makes up a spring-mass system. Upon reaching its natural frequency, this design limits drive stability.

Heidenhain now incorporates a coupling on the stator side of the encoder between the scanning unit and the encoder housing. This coupling is not strained during acceleration. The encoder rotor can then rigidly mount to the motor shaft. The stator side coupling sees only the low torque of the bearings. An internal spring-parallelogram coupling compensates axial motion and radial misalignment between the motor shaft and the encoder.

Q: Which areas for encoders will show the greatest growth during the next five years?

A: The area of digital speed control shows very promising potential. And we expect continued growth in the use of higher accuracy encoders for angular position applications.

Q: What changes in encoder design should engineers expect in the future?

A: Watch for the introduction of encoders (both linear and rotary) that can handle higher vibration environments. The continued push toward higher output frequency will also be a dominant trend. Encoders with built-in commutation signals and new ab solute data transmission formats, such as ENDAT (encoder-data-interface), will be available. Rotary encoders will now have internal, programmable memory to store data on the parameters of the system, along with details of the machine application itself.

Design News

This CAD company is a family affair

This CAD company is a family affair

Everyone in the Hills-of-Skyline area of Wilmington, DE, knew Tom and Bonnie Bentley's five sons when they were growing up. Keith, Barry, Greg, Scott, and Ray were popular, industrious, and good students.

They shared the same paper routes. They all worked at Wassam's variety store. They built go-carts. Two were Presidential Scholars at John Dickinson high school in successive years, while two others were on the wrestling team. They were often together, so no one was surprised when the five brothers started a business.

Bentley Systems, Inc., founded in 1984, sprang from their shared love of computers, programming, and working together. Today, the Exton, PA, company's flagship product, MicroStation(R), has over 200,000 users with full licenses, and Bentley is the second largest developer of PC CAD software, after Autodesk. Revenues from MicroStation, which is used in mechanical, architectural, construction, plant, process, and mapping applications, exceeds $100 million annually, and are growing at better than 20% a year. First half 1995 Bentley sales were triple the first half of 1994.

The reasons for its success: Broadly, it's the company's strong technical vision, says Bruce Jenkins, of the Cambridge, MA, research firm Daratech. Now that the company is marketing MicroStation under its own name instead of exclusively through Intergraph Corp., its revenues should grow even more, he says. First-half 1995 results bear that out.

President Greg Bentley cites the software's features, particularly its ease of use, as a primary reason for its popularity. "MicroStation was the first PC CAD product with a complete graphical user interface," he asserts. "And, it has the same look and feel across all platforms." He says the software requires 30-40% fewer mouse clicks, which means users can get more work done faster.

Customers agree, but add another reason for the success of MicroStation. "They treat us all like we're part of the family too," says Marco Wo, senior designer at Item New Product Development, Providence, RI. "If we ever have a problem, we just call them. Sometimes we just chat."

Family roots. CEO Keith Bentley, an electrical engineer, first wrote the software that was to become MicroStation in 1982 for DuPont. His objective was to develop a CAD product that would enable the company to do physical and chemical plant designs and schematics on machines other than expensive, dedicated hardware. The product, which Bentley called PseudoStation, emulated the VAX-based Interactive Graphics Design System from Intergraph Corp. on generic terminals. Eventually, DuPont let Keith commercialize the software.

Meanwhile, brother Barry was finishing his Ph.D. studies in chemical engineering at the California Institute of Technology, and running a company he co-founded (Dynamic Solutions Corp.) to develop software for the laboratory chemistry market. He and Keith joined forces in a new company (Bentley Systems) in 1984 to further develop and commercialize PseudoStation as a new product for IBM-compatible PCs. It wasn't long before sales of MicroStation, the name they gave the enhanced product, overtook sales of the laboratory instrumentation software, so they sold Dynamic Solutions to Millipore, Bedford, MA, and concentrated on the new product.

In 1987, Scott joined as vice president of operations and sales and Ray came on board with responsibility for 3-D and rendering functionality and, ultimately, the MicroStation solids modeler.

Initial users, besides DuPont, included Renault, Molex, and others who used the software for machine tooling, among other applications. But, it became apparent to the founders that further growth would depend on marketing prowess they didn't have. "At the time, it was a company of programmers who never worried about sales," says brother Greg. In 1987, Integraph bought 50% of the company and exclusive sales and marketing rights. "Intergraph users had been seeking out MicroStation," he says, "so Keith and Barry saw the liaison with Intergraph as mutually beneficial."

In 1991, Greg joined the other four brothers after selling his own financial software company, Devon Systems. In 1995, the brothers consolidated MicroStation development, marketing, and sales at Bentley.

"Our original vision was to bring to engineering easy-to-use graphics and modeling that didn't depend on an expensive proprietary platform," asserts Greg. "Now, we've done it with five products, and all are hardware independent." Along with Unix, he says, Bentley was the first to support Windows NT, and its products also run on Macs and OS/2.

Early in 1995, Bentley shipped three new products: MicroStation Modeler(TM) a solids modeling product; MicroStation PowerDraft(TM), and MicroStation V5 for the Power Macintosh(TM) platform. The company also announced Objective MicroStation(TM) an object-based expanded architecture for all MicroStation products, and its "Open Space" initiative. The latter is a strategy under which Bentley partners with one important developer in each of several fields to provide industry-specific development tools for third parties in those fields.

Programmer driven. That's a lot of product introduction in one quarter, but then again, it's a company founded and run by programmers. Technical continuity is important in code development of long-lived software such as CAD, says Greg, "and few companies can boast that their founders wrote the original code and are still in charge of technical development several product generations later."

Keith, Barry, and Ray lead the 75-member code-development team. "They set the example for hard work," says Gary Cochrane, product manager for MicroStation Modeler.

It may be that they are just following the example they had at home growing up. Tom Bentley, their recently deceased father, was a mechanical engineer at DuPont who taught his sons to develop inventive skills and to be civic-minded. Their mother, Bonnie, a former school teacher, passed along to them her love of learning and a bookishness that Greg says spawned their inclination toward programming.

But, they're not all work and no play. Four of the brothers are regulars in the company's bowling league, and, says Cochrane, they encourage the blue-jean-bedecked employees to include some unwinding time in their hectic work days.

"When we were all working long hours finalizing MicroStation V5," recalls Cochrane, "Keith sent around a note saying he had $200 in his desk drawer and that anyone working late could just take money from the pile and go get a burger if they needed to."

It's all in the family.

Helixâ„¢

Helixâ„¢

Helix's solid modeling engine and parametric design capabilities, coupled with MICRO CADAM's intelligent user interface structure, offer powerful solid modeling tools with an easy-to-use menu. The menu structure allows multiple input options for performing operations, rather than a lengthy menu scheme prior to user-interaction with the system.

Helix has integrated the 3-D operation into two existing abilities found in the 2 .50-D product. These two abilities are the use of auxiliary views and the ability to hide and then reveal geometry from the screen with a quick command rather than relying on layers for entity blanking.

Spec Box

Helix

Helix runs on IBM systems with AIX 3.2.5.1 and HP systems with HP-UX 9.05. Requirements: Motif v1.2, X11R5; Intel-based Windows NT 3.5, and 64M bytes physical memory.

List Price: $3,495.00

MICROCADAM, Inc., 355 S. Grand Avenue, 23rd Flr., Los Angeles, CA 90071; ph: (213)-613-2300; fax: (213) 613-2350.

Auxiliary views are the means to create, manipulate, and edit planar graphic entities such as points, lines, arcs, circles, and splines. These entities relate to each other in the context of model views that can be orthographic, isometric, or true at an arbitrary location or orientation. Each view is characterized by its position and orientation within a drawing and by a scale and transformation reflecting its orientation in three dimensional space. Using the familiar techniques of descriptive geometry, operators can project from one view to another or use two views to define a third view.

The auxiliary view concept is the basis for the mathematical relationship for all CADAM and MICRO CADAM models. It is used by Helix for its solid model creation functions performed on existing 2 .50-D or 2-D files from other CAD products.

With Helix, each Auxiliary view is brought in within a separate window. Solids are created by selecting the geometry from any view or window. The system will then automatically convert this geometry into a profile. These profiles or outlines of an object are extruded along an axis to faces that are defined in another auxiliary view. All interaction is by simply selecting existing geometry or by keying in values.

Since other views are on the screen, selecting existing geometry to define the depth is more accurate than trying to figure out values to type in. Each extruded profile may be combined or removed from others through traditional Boolean operations to create a complete part. Any DXF, DWG, or IGES file may be imported into and quickly converted a solid by extruding similar to the method described above.

Helix's solid engine provides remarkable filleting functions for blending edges and corners. DESIGNBASE also provides for special edge and face editing called "local operations." It allows the operator to easily create and manipulate edges, faces, and vertices to model geometry. By selecting the components of a solid, the part can be quickly and easily modified without the use of Boolean operations or the need to first create other primitive shapes.

The engine also keeps a history of a parts creation process. Any step of the part may be viewed and reverted back to with Helix's feature tree operation, which lists graphical operations. The tree can be edited to insert a different operation; the old tree may be kept intact, or a new version started that will purge out unused operations.

Documentation and support. With Helix, the only printed manual is the installation guide. All other documentation is in electronic format via the on-line, context-sensitive help. While the on-line help was very thorough, I still would like to have a book in front of me.

New solid modeling users will find Helix's construction techniques from 2-D images very handy and easy to use. While surfaces are not supported in this current release, the product itself offers almost every solid creation tool available on the market. Its support for dynamic shaded image rotation is very helpful, along with its ease of assembly building. Local editing of solid edges and faces makes the product very productive for almost every type of solid modeling application.


A similar product:

AutoCAD Designer-Autodesk Inc., 111 McInnis Pkwy., San Rafael, CA 94903; ph. (415) 507-5000; fax: (415) 507-5100.

Application Digest

Application Digest

Specify linear motors for smooth, direct drives

Nicolas Wavre, General Manager, ETEL SA

Because advances in electronics and magnet quality have outpaced improvements in mechanical power transmission subsystems, ball screws or gearing have become limiting factors for engineers trying to improve servo-actuator performance. With a linear motor, however, load is driven directly by the magnetic field. This characteristic eliminates the need for a mechanical transmission system.

A promising area of activity is the command of X and Y tool machines. Replacing conventional ball screws and gearboxes by using direct drives with linear servo motors provides a considerable increase in performance. With the increase in bandwidth, it is possible to suppress elasticity, backlash, hysteresis, and maintenance by a factor of five to ten.

The technology used by ETEL is based on the permanent magnet synchronous motor, also known as a brushless dc motor. Motors with strokes to 50 mm are single phase, while motors with strokes exceeding 50 mm are polyphase. The power stages are IGBT or MOSFET configurations. Commutation frequencies run from 20 to 100 kHz, depending upon power, while control electronics can be analog, digital, or a combination of both.

High-force linear motors with fully integrated water cooling are drastically improving grinding machines, pc-board drilling, and wire bonding equipment in the chip-manufacturing industry.

To speak with an applications engineer from ETEL, call: +41 38 61 18 58 or FAX +41 38 61 24 19.


Ten reasons to consider metal belts

David Huntley, Belt Technologies, Europe

Design engineers who specify metal belts have options not available with other products or materials. Used for conveying, timing, indexing, positioning, power transmission, and automated manufacturing operations, metal belts offer many features and benefits.

High strength-to-weight and durability are also inherent to metal belts. Available in a variety of alloys, metal belts can withstand sustained exposure to temperature extremes, vacuum, and hostile environments.

Unlike the links of a chain, a metal belt does not generate component friction. As a result, a metal belt doesn't require lubrication. Spring steels with a high modulus of elasticity will not stretch, a characteristic that makes metal belts ideal for precision positioning.

Some other advantages of metal belts:

Smooth operation: Free from the pulsation of chordal action, metal belts precisely translate the control system motion profile.

  • Accurate and repeatable: Metal timing belts can be fabricated with a pitch accuracy of plus or minus 0.013 mm station-to-station.

  • Precise construction: Edges are smooth and dimensions are tightly toleranced.

  • Good conductivity: Metal belts can transmit energy in the form of heat, cold, and electricity.

Because metal belts experience no static buildup, they can be useful in the manufacture of ICs, SMDs, and other electronic components. Further, metal belts do not generate particulates, making them ideal for food and pharmaceutical processing. They are also clean-room compatible.

To speak with an applications engineer at Belt Technologies, Europe, dial: +44 91 383 1830.