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Articles from 2004 In January


Web-based document management gives new meaning to 'sharing

Web-based document management gives new meaning to 'sharing

For the 1,000 engineers worldwide who design oilfield equipment from more than 60 locations for Cooper Cameron Corp., a document management system has proven to be a valuable time-saver.

The company (www.coopercameron.com), headquartered in Houston, TX, manufactures oil and gas pressure control equipment, including valves, wellheads, chokes, blowout preventers and assembled systems for oil and gas drilling, production and transmission used in onshore, offshore and subsea applications. It also manufactures gas turbines, centrifugal gas and air compressors, integral and separable reciprocating engines, compressors and turbochargers.

The company uses the SAP R/3 business system integrated with eQuorum's ImageSite (www.eQuorum.com) document and image manager to share engineering documents worldwide.

"From SAP transactions, we launch into engineering documents and can view them or print them within our network printers around the world," explains Dave Whiting, manager of engineering systems, Cooper Cameron Corp. "Now we have one document file and people around the world can print or view it."

This integration of SAP R/3 with ImageSite provides users with a seamless solution to handle online viewing of complex engineering and technical documents as well as online collaboration and distributed printing. Users search for documents stored in the SAP R/3 repository using the SAP interface. Once the documents are retrieved, eQuorum's SAP Connector lets users view, distribute or print using ImageSite. ImageSite is used in PDM environments for the storage, management and distribution of "released documents" that are generated by the CAD modeling software after the design is complete.

Whiting adds that all engineers have access to the "latest revisions of all documents from one source, in a bill of materials. They can point and double-click and view it on screen, and elect to print or move on. This gives us the confidence that we are looking at the latest and greatest."

ImageSite lets users manage, share, distribute, and print engineering drawings and technical documents. Engineers can send an e-mail message to link users to documents in the ImageSite document repository. With the use of a Web browser, users can do collaborative viewing and mark up hundreds or thousands documents.


Cooper Cameron found that document management saved the company considerable time in design of its wellheads, such as this one.

What is notable about the product, says Dr. Joel Orr, vice president and chief visionary, Cyon Research Corp., (http://www.cyonresearch.com) Bethesda, MD, is that the technology is simple yet performs a necessary function.

"They aren't doing anything overly innovative," Orr says of eQuorum. They are doing a job that everybody needs, and apparently doing it very well," he says. "ImageSite seems to say what it is, and does what it says. It's a simple solution to a common problem."

Whiting says that the biggest payoff comes from his customers.

"What we're able to do, through ImageSite, is point and click and put together a whole package of bill of materials and print it all at once. Our customers can then send it to an Extranet, and their suppliers can access it through a URL," he explains.

Calculating ball screw load-life? Don't forget preload.

Can a ball screw with a reasonable amount of preload but no outside thrust last forever? Eschatological considerations aside, it's not likely. The balls still have to resist the internal, preload force.

Predicting ball screw load-life seems pretty straightforward: Compare the geometric average of loads and speeds to the dynamic load capacity. But determining equivalent loads - the critical issue, according to the folks at Steinmeyer, Inc. (Bedford, MA) - is where too many designers miss the boat.

"Almost all suppliers seem to forget about preload," contends Steinmeyer executive vice president George Jaffe. "In most applications, preload is the main factor that impacts fatigue life," he says. "Neglecting preload in load-life calculations isn't just a minor mistake. Ignore it and you risk potential disaster."

To help designers calculate preload, Steinmeyer (www.steinmeyer.com) offers both "rule of thumb" equations and a spreadsheet for greater precision. To illustrate the impact of preload, the firm examines the z-axis of a small lathe with a 32 mm diameter x 10 mm pitch ball screw using double or single nuts.

The double nut has 2x3 circuits with a 30.8 kN dynamic load capacity, a nominal preload of 10% of Cdyn (roughly 3,000 N) and 2,000 rpm speed. Rapid moves are estimated to occur 30% of the time, acceleration/deceleration 6%, and roughing 30%. Thrust is estimated at a worst-case, continuous 8,000 N; a positive load direction, because the thrust is against the chuck. Finishing occupies 40% of the lathe's time, with lighter loads and lower speeds. Dwell time is included for indexing the tool disk and loading work pieces.


When evaluating ball nuts, engineers must start by defining expected pre-load conditions.

Using precise equations the modified, equivalent load in the example is 3,732 N, and the resultant life is 562 million revolutions, or 24,453 hours. Using the rule of thumb equation, the numbers are 3,525 N and 667 million revolutions. Neglecting preload, however, yields quite different numbers: Mean load is 2,746 N, and life goes up to 1.4 billion revolutions, or 61,403 hours - about 2.5 times the realistic value. The rule-of-thumb equations miss the correct value by 18%, whereas omitting preload misses by 150%. 

With a 1x4 circuit single nut with 39.4 kN dynamic load capacity, preload is 3000 N, or roughly 8% of Ca. The modified, equivalent load is 4,467 N by precise calculation, 4,288 N by rule of thumb. Calculated life expectancy is 686 million revolutions (775 million with the estimated modified loads), or 29,852 hours. If preload is ignored, the mean load is 2,749 N.  Since the single nut has a higher dynamic load capacity than the double nut, the calculated life goes up to 2.94 billion revolutions, or 128,052 hours - off by a factor of 4.

Network to link top nanotech labs

Network to link top nanotech labs

The National Science Foundation is making a big push to improve the nation's nanotechnology research, establishing a network that will link together 13 of the country's leading research facilities. The National Nanotechnology Infrastructure Network (www.nnin.org ), announced late last year, will help the universities continue pushing forward with research, potentially developing concepts and technology that can be commercialized.

Many companies are already in the process of pushing collegiate research programs into production. "The resulting research will be valuable to the country and to companies like NanoSys that commercialize technology developed in university labs," said Stephen Empedocles, director of business development at NanoSys Inc. of Palo Alto, CA (www.nanosysinc.com/technology.html ). NanoSys develops materials and manufacturing processes that it will license or sell to larger OEMs so they can gain the benefits of various nanotechnologies without making big investments in this fledgling field.

Cornell University is the administrator for NINN. Other members include the University of Michigan, Harvard University, Georgia Institute of Technology, Penn State, University of Minnesota, University of New Mexico, and Stanford University.

Professors and grad students will perform many tasks such as characterizing materials, developing new research and manufacturing tools, and devising manufacturing processes. There will also be a strong emphasis on improving educational materials. That thrust will include the creation of training programs for tools, processing, and synthesis techniques. Understanding the social and ethical concerns will also be a big part of the program, a Cornell spokesman says.

All the universities have strong nanotechnology departments that are already being funded by state governments, which will make the NSF investment more effective, an NSF spokesman says. The creation of a network is only one part of the U.S. effort to remain in the forefront of this new field. President Bush recently signed a bill that allocates $3.7 billion to nanotechnology programs from 2005 to 2008 (www.whitehouse.gov/infocus/technology/nano2.html ). Proponents feel that huge sum will help spark a takeoff in the field. "The $3.7 billion is more than what the government committed to the human genome project that fostered the biotech revolution," Empedocles said.


The playable nanoguitar fabricated by researchers at Cornell University, administrator for NNIN, demonstrates the precision of nanotechnology processing. The strings are 150 by 200 nanometers across and range from 6 to 12 micrometers in length. The entire guitar is the size of a red blood cell.

Flexible and rigid plastics join forces-inside a blow mold

Flexible and rigid plastics join forces-inside a blow mold

Hybrid injection molding technology, which joins metal and plastic inside the mold to produce structural components that offer the best of both materials, has been around for more than a dozen years now. But Bayer Polymers, a pioneer in this technology, has now come up with a brand new kind of hybrid based on extrusion blow molding. This patent-pending process can combine rigid and flexible materials inside the mold, creating components such as seat frames with integrated air-bladder cushions.

"Think of it as an evolution of our injection molding hybrid technology," says Chris Cooper, senior process engineer for Bayer and one of the inventors of the new process. Like the company's earlier technology, the new blow-molding hybrid starts with a rigid substrate placed inside the mold, usually robotically. This rigid inserted part would then be overmolded with a flexible plastic, which forms the bladder and other molded in features, And like the earlier hybrid technology, molded-in part features form a mechanical interlocks between the insert and overmolded plastic. As Cooper describes it, the flexible plastic flows through holes in the rigid inserts during the molding process, forming "chamfered buttons" that join the insert and overmolded bladder. Though their exact size and geometry would depend on the application, the buttons would typically range from 0.25 to 0.75 inches across. In early testing of one button design, Bayer found that each offered about 43.5 lb of pull-through strength. By varying the number and spacing of the buttons, engineers could meet a variety of mechanical requirements, Cooper reports.

Aside from the fact that it's based on extrusion blow molding, the new hybrid also differs from the injection molding technology in another key respect. Whereas hybrid technology has traditionally relied only on metal stampings for the inserts, the blow-molded hybrids can use metal or rigid plastic inserts. In fact, Cooper believes injection molded plastics-including glass-filled nylon, PC/PBT, or others with good structural properties-will be more common than metal in the seating and cushioning applications that the new technology targets.

Though it could also work with a variety of elastomers for the flexible material, thermoplastic urethane (TPU) grades will likely dominate. Gerry DiBattista, Bayer's market channel manager for TPU and another one of the inventors, notes that TPU has well-recognized combination of tear, puncture, chemical, thermal, and UV resistance. These make it well suited to all sorts of rugged seating applications. Consider, for example, the guy who plunks down in his tractor seat with a screwdriver sticking out of his back pocket. Seats on lawn-and-garden equipment, recreational vehicles, and personal watercraft can also benefit from the same TPU attributes, DiBattista says. And the blow-molding hybrid doesn't just lend itself to seating. "It could be used in any area needing cushioning," he adds.

Size wise, the blow-molding hybrid can tackle some pretty big parts. Bayer has tried it with components measuring as much as 6 feet long and about 2.5 feet in diameter. And DiBattista believes that even larger parts are possible. The only limitations he cites relate to the size of the molding machine and to TPU's possible melt strength limitations in truly gargantuan parisons.


This seating concept shows the integration of a flexible TPU cushioning bladder (lighter color) would be integrated with a rigid thermoplastic substrate (black).

Capable of running on standard blow-molding machines and requiring mostly conventional processing expertise, the blow-molding hybrid promises several important advantages. The most important has to do with cost avoidance. Traditional seating or cushioning components need some assembly-such as attaching frame to a foam cushion and adding a covering. The hybrid process turns out an integrated frame and bladder without the need for foam or a covering. "The bladder and seating surface can be one and the same," DiBattista says, though he adds that the method can incorporate fabric coverings if the application requires them. "We can add fabrics right in the mold," he says. Bayer has also experimented with foam filled bladders as an alternative to air.

Other components can be assembled inside the mold as well. The process can mold in nozzles for inflating the bladder, to take one example. And the inserts can be molded with built-in attachment points, such as boltholes.


A cross section of a blow-molded hybrid part shows how the molded-in buttons lock together the flexible TPU bladder with a rigid substrate.

The process could also enhance design flexibility. In one study, for instance, Bayer engineers come up with hybrid parts that use a living hinge-a molded-in hinge made from the TPU itself-to join a seat bottom insert to a seatback insert. The same approach could work with a storage console, using the TPU to form both a cushioned air bladder for the top of the console and a living hinge to join the top the rigid box underneath.

For general information Bayer Polymers, visit www.bayerpolymers.com. Email [email protected] for more information about the hybrid blow-molding technology.

Silver still rules the road-but for how long?

Silver still rules the road-but for how long?


This Mercedes sports the color of choice, according to a DuPont report.

This should come as no surprise to anyone who ever goes for a drive, but silver for the second year in a row ranked as the most popular automotive color in the annual DuPont Automotive Color Popularity Report. But the survey also suggests that some automotive color shifts may be on the horizon.

In addition to reaffirming the car buying public's love affair with silver, the survey also revealed an increasing popularity for rich colors, with medium and dark grays in particular gaining ground. In North America, 11.5% of vehicles made during the 2003 model year sported gray, up from 7% last year.

Why so gray? "It's a pull-through from silver, which is a kind of gray," explains Robert Daily, DuPont's automotive color manager. And he attributes this shift to today's "chiseled, sharp-edged" automotive designs. "Darker colors make those designs look better," he says, noting that some of the newest grays will be enhanced with coarser metallic effects than in years past.

The DuPont survey, which has offered color analysis for more than 50 years, also highlighted an increasing use of reds and other high-chroma colors. Yellow has even emerged as a top-10 color in the sport-compact segment.
Daily believes that the upswing in high-chroma colors signals a forthcoming change in automotive color palette. And he predicts that more vibrant hues will serve as an increasingly popular alternative to silver and neutrals as "more people become adventurous about color," he says.

Nowhere are these two color trends more apparent than in the North American luxury segment, which has traditionally been a bellwether for other vehicle categories. Medium-gray jumped from sixth place to the lead color in this category, while red surpassed the traditionally more popular blue. Medium-dark green, by contrast, has fallen out favor in this segment. This former color leader from the 1990's has dropped out of the Top 10 luxury-vehicle colors, though it did post small gains in other segments.

Darker grays also rose significantly outside the luxury segments as well. It jumped from sixth to third place in the sport-compact category, and it climbed four places to become the third most popular color for intermediate-full size cars.

Silver, meanwhile, stayed firmly on top in North America, where it colored 20.2% of 2003 vehicles. It was followed by white at 18.4% and black at 11.6%. "Neutrals will always be a major part of the automotive color palette," Daily says. The question now is how big a part. For all of its popularity, silver slipped about two percentage points from last year. "It should remain strong for a couple of years, but we do see it plateauing," he says.

For more information on the DuPont Automotive Color Popularity Survey, visit www.automotive.dupont.com and click on "News and Events."

Electronics

Electronics

I/O interface

With LED status indication

The e2C interface is designed for passive actuator/sensor distribution boxes for the company's e2C product line. Allowing a user to connect passive distribution boxes to the e2X system via an M23 connection, the product features the same bus system independence and is designed to be used across all e2C compatible bus systems. It handles either eight inputs or eight outputs and can also be used to connect multi-port valve manifolds to an e2C network. Lumberg Inc.http://rbi.ims.ca/3843-583

PCB LED indicators

Rugged housings

The right-angle 3-mm products reportedly feature rugged housings and sturdy pins, and can withstand the stress of automated positioning machinery. Available in bi-, tri-, and quad-level, and in single-column units to four-column configurations, the LEDs are resistant to shock, frequent switching, environmental extremes, and vibration. They are made for applications that require the precise alignment of status indicators. LEDtronics Inc.http://rbi.ims.ca/3843-584

Compressed air sensor

Improves energy efficiencies

The efector Metris(R) monitors compressed air systems on a regular basis, intending to identify leakage areas, improve system performance, reduce energy costs, and optimize compressed air usage. The product can be mounted in a supply pipe to monitor one machine, or in a plant zone to monitor several machines. Based on the calorimetric flow sensing principle that ensures a constant temperature difference between two sensing elements, the technology is designed to allow for greater sensitivity in air consumption. ifm efectorhttp://rbi.ims.ca/3843-585

Test measurement software

Over 30 new features

TestStand 3.0, the newest version of the company's test management software, was created to help engineers build and deploy automated prototype, validation, and manufacturing test systems 75 percent faster. Some of the new features include an enhanced LabVIEW adapter interface for instant connectivity to LabVIEW test programs, and a new deployment utility for quickly deploying software to test systems in local and worldwide locations. Engineers using the software can develop custom interfaces for test applications in minutes instead of days, according to the company. National Instrumentshttp://rbi.ims.ca/3843-586

Pressure and Temperature

Steam sterilization

The ebro(TM) Model EBI-125A-PT has a built-in temperature-compensated ceramic pressure-sensing element and the PT 1000 temperature sensor, combined with WINLOG 2000 software. It is designed to offer improvement over existing methods of measurement and documentation of sterilization procedures. Weighing 3.5 oz and operating on a 3.6V lithium battery, the product has a reported working service life of three to five years. Dresser Instrumentshttp://rbi.ims.ca/3843-587

LDO

Microcontroller reset function

The TC1302A/B integrates two low-dropout regulators (150 and 300 mA), while the TC1301A/B also has a microcontroller reset function. The company asserts that combining these parts into one device will require fewer passive and discrete components for the products, and will reduce the amount of board real estate, lowering overall project cost. Additional features include an over-current limit, an over-temperature protection, and low crosstalk between the voltage output channels. Microchip Technology Inc.http://rbi.ims.ca/3843-588

White LEDs

Up to 50-degree viewing angle

Made for high temperature indoor and outdoor environments, the UW3804X and UW5805S white through-hole LEDs deliver a luminous intensity of up to 2000 mcd. Designed with an InGaN die for superior brightness, the products are available in either a 3- or 5-mm package. They are ideal for applications, such as indoor/outdoor displays, indicators in appliances, automotive, signs and symbol illumination, and medical devices. Stanley Electric Sales of Americahttp://rbi.ims.ca/3843-589

Sensor

Sorts parts, detects object orientation

Ultralinear(TM) analog prox technology was created to combine prox sensor toughness with a highly linear analog feedback signal (without an external switching device) proportional to target distance from the sensor face, providing resolution down to 1.5 microns. The product enables a variety of process control and positioning applications to be solved, such as the measurement of distance, thickness, concentricity, circularity, wobble, and deflection. It also allows the detection of object orientation; part sorting by size, shape, or material; and monitoring thermal expansion of ball screws and shaft imbalance on rotating machinery. Balluff Inc.http://rbi.ims.ca/3843-590

Data bus transformer

High electrical performance

The 4260-1646 and 4260-1647 series data bus transformers have a minimum input impedance of 3,000V or 7,200V over the full temperature range of up to -55 to +130C. They support a wide range of instrumentation, data collection, and communications equipment, and feature common mode rejection at 45 dB minimum and droop at less than 20 percent. Both products are available in flat-pack through-hole and compact surface-mount packages; they are also available in both single and dual packages. Datatronics Romoland Inc.http://rbi.ims.ca/3843-591

Fiber optic panel

Simplifies assembly

The UniGlo(R) is designed to improve the backlighting of the control panel LCD used in portable instruments for locating underground cables and pipes, while allowing the manufacturer to assemble the device quickly. The RD4000Rx receiver operates by sensing the electromagnetic field produced by underground cables and pipes. The control panel is a backlit LCD that reduces power consumption and improves reliability. The product reportedly provides an operating range of -40 to +80C. Poly-Optical Productshttp://rbi.ims.ca/3843-592

Retractile power cordage

Available on-demand

Using the company's Direct stocking program, customers now have access to same day shipping on a wide range of severe duty retractile power cord products. These include products from 12-18 AWG, 2-5 conductors, and 1-6 ft retracted, and 5-30 ft extended lengths. The products are designed to provide excellent resistance to oil, solvents, detergents, and moisture, and they feature outdoor approved jacket material. Northwirehttp://rbi.ims.ca/3843-593

PC mount switch line

Miniature and sub-miniature

The company's new line of miniature and sub-miniature switches are toggle, rocker, slide, and pushbutton. Many are certified to UL/CUL under file number E7560, are sealed to IP67, and are available as surface mount. The new switches are included in the company's new catalogue, which is designed for product selection. Carling Technologieshttp://rbi.ims.ca/3843-594

Mezzanine card

Features complete oscilloscope

The M78, an M-Module mezzanine card, was created to enable system designers to add multi-channel oscilloscope functionality to systems based on a large variety of open buses (it can also be installed in bus-less, standalone systems). It is a complete four-channel oscilloscope in the 50- x 150-mm, ANSI standard, M-Module form factor. It contains 12 bits of resolution, a sampling speed of 50 MS/s, and a 10 MHz bandwidth. It is designed for systems designers who require oscilloscope functionality. MEN Micro Inc.http://rbi.ims.ca/3843-595

Telecom relay

Low power consumption

The AZ8222 two-pole telecom relay with the industry standard 16-pin DIP footprint has bifurcated cross-bar contacts and a high switching capacity of 60W or 125 VA. With dc coils from 3 to 48V dc, the product has three sensitivities: standard (320 mW), sensitive (200 mW), and ultrasensitive (150 mW). It reportedly meets FCC Part 68 requirements for 1,000 VRms dielectric strength and 1,500V lightning surge. American Zettlerhttp://rbi.ims.ca/3843-596

Sub-miniature DIP relay

Small, lightweight

Providing high sensitivity switching with a 0.15W coil option, the WJ102 subminiature DIP relay is designed to be a perfect fit for high density PC boards. It has gold-plated bifurcated contacts that reportedly provide designers with reliable switching. The product is manufactured and quality controlled to ISO-9002 and QS-9000 standards. CIT RELAYhttp://rbi.ims.ca/3843-597

Connectors

For damaged molded cord sets

Designed as a replacement for in-field repairs, the 3- and 4-pin M8 picofast IACs reportedly provide easy assembly. As no soldering is required, the "tool-less" design has color-coded contact holders and can handle 22-26 AWG conductors. They are rated for 4.0A at 60V ac/75 dc and are offered in male or female configurations. With a cage clamp strain relief that provides an IP68 seal, the product is ideal for the company's junction boxes and receptacles. TURCK Inc.http://rbi.ims.ca/3843-598

Lasers dish dirt

Lasers dish dirt

Laser technology is expanding in construction, helping bulldozer operators smooth sites. Caterpillar Inc. (www.cat.com) is now offering the AccuGrade laser system, which can guide dozers to create surfaces that have only a 6 mm deviation. Once a transmitting laser is set to the desired elevation, it sends signals to masts mounted on the dozer blade. That input is sent to the controller module, which directs the hydraulic system that moves the blade.

IEEE addresses security

IEEE addresses security

The IEEE is helping the National Institute of Standards and Technology address certification and accreditation of systems by opening work on a standard that will enhance security. The P1700 security architecture standard (http://ieeeia.org/scaiswg/) will create a basis for ensuring a system's techniques for maintaining quality of service are in line with its security risks. The overall standard architecture and some versions that implement it should be done this year.

Real-time profinet

Real-time profinet

The PROFIBUS Trade Organization (PTO) now offers a PROFInet real-time extension for general automation applications. Based on Ethernet, PROFInet is a modern standard for distributed automation standards that integrates existing fieldbus systems, specifically PROFIBUS. The new extension is called Soft Real Time, which features cycle times of 5 to 10 msec. It is compatible with the TCP/IP Ethernet protocol. In addition, a second PROFInet real-time extension is being developed, and is scheduled to be available in 2005 for high-performance motion control applications. For more information, visit the PTO website at www.us.profibus.com.

MEMS' Fantastic Voyages

Journey with us now to the ultra-miniature world of MEMS, where microscopically small accelerometers, valves, switches, and gears perform much of the same work as their bigger brothers but in impossibly small spaces.

Born in R&D labs more than a generation ago, MEMS devices took their nurturing from the semiconductor-manufacturing industry and have grown steadily in status if not stature. They rule the airbag-sensor world where, as extremely small accelerometers, they detect the slightest change in acceleration, and the ink-jet printer domain where, as miniature flow valves, they direct the dispersion of ink to produce printed pages.

They also act as pressure sensors inside tire-valve stems, inertial sensors, resonators and mechanical filters, micro-capacitors, micro-inductors, micro-probes, DNA sequencers, and chemical- and biological-agent sensors.

And that's just the beginning. Researchers and engineers alike say that MEMS are like early teens, continually asserting themselves and their worth and poised for explosive growth. Says market research firm In-Stat/MDR, they'll grow in consumer electronics to nearly 190 million devices in 2006 from about 5 million in 2001. In the automotive world, the firm predicts, there will be twice as many MEMS applications in 2007 as there were in 2002. The firm also predicts MEMS use in gyros to grow from $279 million in 2002 to $396 million in 2007.

With numbers like that, it's only natural that the tools for designing MEMS would likewise grow in number and sophistication. In the last ten years, software developers have been incorporating algorithms in their codes to handle the special problems inherent in MEMS design. On the CAD side, SolidWorks now has customers using its software in the design of commercial MEMS-based products as does ANSYS on the analysis/simulation front. MSC.Software and ALGOR also are working with customers in analysis of products.

While MEMS share many of the same design problems as products in the macro world, they pose a few different challenges that software developers have had to take into account in their codes. For example, says MSC's Brian Cheung, surface-to-volume ratios are different in the micro world from what they are in the macro world.


Direct Route: Microfabrica used new 3D CAD capabilities from SolidWorks to develop micro-manufacturing technology. A three-step process generates each devicelayer. First, metal is deposited in a pattern corresponding to the cross-section of the device. Next, a second material is electroplated into the substrate. Then the two materials are planarized for a single two-material layer. The process continues until all cross sections of the 3D CAD design have been constructed in the material.

"In the macro world, thickness could be comparable to length and width, but micros are very thin and can be out of scale to the others," he says. Additionally, he says, because mechanical MEMS devices live in an electrical world, MEMS designers have to simulate electronics as well as mechanics.

Paul Lethbridge of ANSYS says fluid damping effects are different too. "They can be a thousand times greater," he says, "so MEMS designers have to think like aerospace engineers, figuring out how the device might move through a fluid."

Electrostatic forces are also greater on MEMS devices than macro devices. And, say Motorola engineers Dave Monk and Andrew McNeil, engineers have to be especially concerned with variations in manufacturing processes.

But, what makes MEMS especially challenging in analysis, says Lethbridge, is dealing with all of these issues and more simultaneously. "In the macro world, engineers have to consider maybe one or two physics," he says. "With MEMS, you have to look at several, including electrostatic, structure, and fluid, and they're all interrelated—a multi-physics approach."

In practical terms, that means engineers might have to use a different finite-element mesh for each physics problem. "In the macro world, you can get good analysis results with a coarse mesh," Lethbridge says. "But with a MEMS device, you may have to solve for a fluid domain and that requires computational fluid dynamics, a much more complex process."

One other difference in the use of software for design of MEMS devices is the lack of inter-operability among different software packages, particularly 2D and 3D packages. MEMS design work is generally 2D. The missing dimension is thickness, but you need to know thickness to construct finite-element models. Motorola engineers extrude the 2D models and add the required thickness, then use CIF (Caltech Intermediate Form) and GDSII (Graphic Data System file format) to translate the models to an analysis software. "Getting the different software packages to talk to each other is a bigger problem than it is in the macro world," says Motorola's McNeil.


Multi-Tasking microsystem (MEMs) devices challenge engineers with several interrelated physics problems, rather thant the one or two independent physics that macros devices offer. This packaged device contains several analysis problems that would typically be solved by different engineers using different software for each. The ANSYS multiphysics approach allows engineers to solve each of the physics problems here with the same software, allowing the physics problems to be coupled together either directly or sequentially. ANSYS says that saves time and cost of recreateing the model for each problem.

Motorola has used ANSYS multi-physics software in the development of low-g Z- and X-access accelerometers. Among other goals, they wanted to ensure the accuracy of the devices in the face of the high sensitivity of low-g parts. For example, they used the software to model performance of various metals before choosing the best one for minimizing the effect of metal-stress hysteresis on device performance. They also have been using ANSYS software to analyze how their MEMS devices would work in applications other than those they were designed for. In one case, they analyzed a medium-g (about 40g) device originally designed for airbag deployment to see if they could modify it to produce a low-g (1.5g to 8g) or high-g (100 to 500g) device.

Engineers at SiWave Inc. have used ALGOR to calculate stress and displacement for applied shock loads on their MEMS optical switches. They have also used that software for electrostatic analysis. Meanwhile, engineers at the University of Alberta have used ALGOR to demonstrate the usefulness of FEA in design of MEMS pumps.

On the CAD side, the emergence of 3D design capability is facilitating MEMS design. Because of its origin in the semiconductor-manufacturing world, MEMS design has traditionally been a 2D process. The typical sequence is to begin with a model of the component created out of multiple semiconductor layers, followed by photo masks and 2D layouts for each layer, which match each specific cross-section configuration to drive manufacturing. Often, there can be photo masks for several cross sections of a solid model at the micron and sub-micron level for a device that's eventually going to wind up in a larger assembly. SolidWorks' Ilya Mirman says MEMS-specific CAD functionality allows engineers to move back and forth between different dimensional scales for 3D visualization of the complete assembly.

Axsun Technologies' Chief Technology Officer Dale Flanders uses SolidWorks in design and manufacture of the company's miniaturized optical micro-instrumentation devices. He says he and his team use the assembly and interference-checking capabilities of the software and the associative nature of 3D solid models to support mechanical, thermal, and electro-magnetic analyses as well as rapid prototyping activities. In fact, he says the associativity of the software is key for fast design.

The benefits of 3D design are extending to manufacturing too, helping MEMS designers break the stranglehold semiconductor-manufacturing process have held on them. For a long time, says Microfabrica Inc. Applications Engineering Director Nelsimar Vandelli, micro devices could only be created by experts using specialized tools and exotic silicon-based micro-machining techniques. Now, he says, Microfabrica Inc. is using SolidWorks to create arbitrary geometries. That opens up lots of new possibilities for engineers, he says. As an example, he points to helical springs. They're efficient for controlling force and displacement, but tough to produce based on four or five layers of silicon. "We're eliminating that restriction," he says.

National Editor Paul E. Teague can be reached at[email protected].

Research on MEMS
Sandia National Laboratories has an extensive research program on micro electromechanical systems (MEMS. The research has resulted in several breakthroughs. For information on one of the Lab's most recent MEMS projects, click on the following: http://www.sandia.gov/ldrd/stacelmi.htm

The Massachusetts Institute of Technology also has several programs on MEMS. For information, click on http://www-mit.edu/mtlhome/mems/opticalmems.shmtl

Occupying a package no bigger than a grain of sand, new smart-dust circuits combine sensing, computing, and communications functions.
http://www.reed-electronics.com/ednmag/article/ca336870?text=mems