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Articles from 1997 In September


Wescon-IC Expo 97

Wescon-IC Expo 97

The Wescon-IC Expo has expanded its bandwidth and for the first time in trade event history will utilize both the San Jose McEnry and Santa Clara convention centers. More than 1,400 booths will display electronics innovations and applications for next-generation electronic, computer, and communications systems.

In addition to focusing on communications, multimedia, power management, and application technologies, the conference will emphasize IC technologies, as well as networking and wireless communications topics. Attendees will find half-day workshops, sessions, and half- and full-day short courses on a range of topics encompassing processor/DSP, ASIC, and programmable chip design.

Three high-profile keynote event addresses will include John P. Morgridge, chairman of the board, Cisco Systems Inc.; Chet Silvestri, president of Sun Microsystems' Sun Microelectronics division; and Curtis Crawford, president, Microelectronics Group, Lucent Technologies Inc. The latter is part of Lucent Technologies' celebration of the 50th anniversary of the transistor, first invented by engineers at Bell Labs.

Continuous shuttle bus service during show hours and passes for the Silicon Valley light rail system's Guadalupe line are available at no cost.

Approximately 50,000 engineering professionals are expected to attend. Wescon is co-sponsored by the Los Angeles and San Francisco Bay Area Councils of the Institute of Electrical and Electronics Engineers (IEEE) and the Southern and Northern California Chapters of the Electronics Representatives Association (ERA). It is produced by Electronic Conventions Management.

Resettable devices

Line of surface-mount resettable devices now includes 30 and 60V radial-leaded polymeric PTCs. The 30R Series has an interrupting rate of 40A at 30V and offers 13 current ratings from 0.9 to 9.0A. The 60R Series features an interrupting rate of 40A at 60V. Choose from 17 current ratings from 0.1 to 3.75A. PTC products are suitable for overcurrent protection in applications including motors, process and industrial controls, test equipment, and security systems. Both Series have UL and CSA approvals. Bulk packaging as well as tape and reel options are available for most part numbers.
Littlefuse Inc.
800 East N.W. Highway
Des Plaines, IL 60016

Connectors

A series of self-latching circular connectors is now available for harsh environments. Housed in an aluminum-alloy shell with an anthracite conductive finish, these connectors can withstand temperatures from -65 to 200C and endure severe shock and vibrations. In addition, they are completely sealed against moisture and contaminating fluids by a sealing gasket and gland molded from fluorosilicone rubber. Features include a scoop-proof push-pull latching system, color-coded keyway identification, and an integral heatshrink boot adaptor. Connectors are suitable for aerospace, industrial, and military applications.
LEMO USA
Box 11488
Santa Rosa, CA 95406
FAX (707) 578-0869

Air conditioners

TechniCOOLTM line of thermoelectric solid-state air conditioners utilizes the Peltier effect to provide cooling for electronic enclosures and communications equipment. They provide up to 1,500 BTU/hr cooling each and can be arrayed in series or parallel configurations. Air conditioners can be mounted in any orientation as they contain no working fluids. Features include reliable solid-state operation, precision temperature-control capability, no acoustical/electrical noise, and dc operation.
MELCOR
1040 Spruce St.
Trenton, NJ 08648
FAX (609) 393-9461

LED assembles

Tri-level H-315C Series and quad-level H-400C Series of 3-mm T-1 LED assemblies have an interlocking feature that assures larger, more rigid arrays of up to 12 stations for uniform horizontal elevation and vertical alignment. As many as 64 LEDs can be mounted in a single array, with one insert. These tri- and quad-level LED arrays are suitable for network and telecommunications applications with high-density footprint requirements. All models are available in narrow-profile, individual or interlocking styles, in multiple color combinations.
Bivar Inc.
4 Thomas
Irvine, CA 92718
FAX (714) 951-3374

Temperature monitors

Tempilable temperature monitors provide temperature measuring accuracies to plus or minus 1%. No wires or readout boxes are required. Monitors are useful for measuring temperatures in isolated systems and on moving or rotating assemblies. Applications include monitoring operating conditions of electronic assemblies, transformers, resistors, and circuit-board components. Other products include Tempilaq temperature indicating liquid, Tempilstik temperature indicators, the Temprobe kit, and a semi-automatic label dispenser.
TEMPIL
2901 Hamilton Blvd.
S. Plainfield, NJ 07080
FAX (908) 757-9273

Composite cases

Val-An Composite Series of cases are for transporting electronics and other sensitive equipment. Superior stiffness and fatigue endurance provide dimensional stability against distortion, bowing, twisting, and impact. The cases, which are available in thousands of sizes, are watertight and offer inner panel options, a pressure-relief valve, and a wide choice of colors. Although they are lightweight, these cases feature high fracture and residual strength. Their low energy dissipation on impact provides excellent dampening properties through rapid decay of mechanical vibrations.
ZERO Enclosures
200 North 500 W.
North Salt Lake, Utah 84054
FAX (801) 299-7350

Switch

EVQ-WK edge-drive jog-encoder switch is for use in cellular telephone, pager, remote control, video camcorder, and computer mouse applications. The encoder has 15 detents and 6 output terminals. A push-on switch with a snap-action mechanism assures a short key stroke with a sharp click for secure input.
Panasonic Industrial Co.
Two Panasonic Way, Panazip 7H-4
Secaucus, NJ 07094
FAX (201) 392-6263

Potentiometers

GV4 Series of 12-turn, 4-mm SMD trimmer potentiometers are compatible with all surface-mount processes including flow and reflow procedures. A cheron shaft-seal design protects to Flourinert 85C, 1 minute. In addition, these potentiometers can withstand a variety of cleaning solvents and board-washing processes. GV4 incorporates a flush-adjustment screw allowing the use of pick-and-place equipment. The 4-mm design meets the EIA, EIAJ, IPS, VRCI SMD standard footprint. Electrically, the GV4 Series has a resistance range of 10 to 2 .
TOCOS America
1177 East Tower Rd.
Schaumburg, IL 60173
FAX (847) 884-6665

Keylock switches

SK Series keylock switches are available in pc-board and panel-mounting configurations. UL-recognized and CSA-certified for 3A at 125V and 1A at 250V ac, the panel- mounting version features a 12-mm bushing and takes up 27 mm behind the panel. Circuit options include: ON-NONE-ON and ON-OFF-ON. Pc-board versions feature sealed-body construction and a disposable boot that allows automated washing. Molded-in terminals seal out flux, solvents, and other contaminants.
NKK Switches
7850 E. Gelding Dr., Suite 100
Scottsdale, AZ 85260
FAX (602) 998-1435

Readout conditioner

Model 7600A high-speed strain-gage readout conditioner allows the user to easily detect, store, and recall a peak input signal or runout. The parameters can be detected 1,000 times per second with up to 65,000 counts of resolution. Set-up and calibration are done with five front-panel switches, and a lockout feature prevents calibration corruption by unauthorized personnel. The standard unit has four alarm points which can be checked up to 1,000 times per second. Limits can be applied to channel 1, peak reading, or the runout reading.
DCI Inc.
Box 2877
Olathe, KS 66063

Power cords

Power cords and cordsets are available in 2- and 3-conductor styles with various insulations, voltage ratings, colors, lengths, plugs, connectors, and shielding. Alternate power cord and strain-relief configurations are available upon request. Other products include international power cords, multi-function modules, ac receptacles, fan accessories, and EMI/RFI powerline filters.
Qualtek Electronics Corp.
7675 Jenther Dr.
Mentor, OH 44060
FAX (216) 951-7252

Terminal blocks

32500 Series of 0.325-inch center-to-center spacing terminal blocks are made from durable polypropylene material, with a UL and CSA 94V-O flammability rating. Offset pins are available in numerous terminal choices including base mount, PC pin, wire wrap, turret, and right angle. The blocks are rated at 15A, 300V. Wire accommodations range from 22 to 14 AWG, and there are 1 to 26 terminal positions available. Eight top-termination or screw hardware options are available including: steel-combo head screws, brass screws, stainless-steel screws, quick connects, captivated steel-combo heads, captivated wire clamps, and less screws.
Curtis Industries Inc.
Box 343925
Milwaukee, WI 53234
FAX (414) 649-4279

Fastener

PEM(R) R' ANGLETM self-clinching fastener provides a strong right angle attachment point for aluminum sheets as thin as 0.040 inch/1.02 mm. The second sheet or component can be securely fastened to the PEM R' ANGLE with a thread-forming screw by using the self-clinching principle. This self-piloting screw forms its own thread as it is installed. The result: a thread fit which resists vibration and demonstrates excellent strip-out characteristics. In addition, the holding power of the fastener is not compromised by the repeated removal and re-installation of the screw.
Penn Engineering & Mfg. Corp.
5190 Old Easton Rd.
Danboro, PA 18916
FAX (215) 766-0143

Digital oscilloscopes

Series VC-5810 is a four-channel, color, digital oscilloscope. Measuring 280 x 80 x 335 mm and 4.5 kg, this Series features a 10-inch active-matrix color display. External and edge triggering are standard, as are GPIB, RS 232, Centronics, and PCMCIA interfaces. Features include a 150-MHz bandwidth, 64 kbytes of memory per channel, auto setup, 256 kW/channel, and glitch capture. Optional: hard drive, floppy drive, and memory.
Hitachi Denshi Americal Ltd.
371 Van Ness Way, Suite 120
Torrance, CA 90501
FAX (310) 328-6252

Subsystems

POWERTRAIN family of power-conversion subsystems for ac motors now includes two solutions for 1.5- and 7.5-hp ratings: IRPT2055 and IRPT4052, both accepting 460V ac inputs. The former features a complete power-inverter stage packaged in a chip-and-wire module; the latter supplies the inverter as a surface-mount assembly on an insulated metal substrate. Both include a Driver-Plus board which contains a driver function with fault protection and shutdown functions. This protects the circuitry from short circuits and ground faults, as well as over-temperature and over-voltage occurrences.
International Rectifier
233 Kansas St.
El Segundo, CA 90245

Dirty laundry's new spin

Dirty laundry's new spin

Every day, all year long, U.S. households wash some 77 million loads of laundry. Almost all of these piles of dirty clothes are stuffed into top-loading machines--washers that offer easy access and an appetite for big loads. Unfortunately, they also demonstrate an equally big thirst, consuming 40 or more gallons (151l) of water per single wash/rinse cycle. Added up, that's a lot of liquid down the drain for the sake of convenience.

Maytag's high-efficiency, front-loading Neptune washer uses 40% less water and 65% less energy than conventional top-loading machines. A tilted tub and large door match top-load accessibility and ease of use.

Maytag's "dependability" engineers, working in partnership with the Electric Power Research Institute, Palo Alto, CA, have confronted this problem with the company's first-ever, front-loading washer. Built about a horizontal axis, the "Neptune" washing machine substitutes the tumbling action of a clothes dryer for the push-pull agitation of top-load machines. Tumbling clothes instead of submerging them reduces the amount of water used in the wash cycle by 12-15 gallons (45.4-56.8 l).

While environmentally-conscious consumers can rest assured the design saves considerable water, as well as the energy needed to heat that water, convenience buyers will also be pleased. Thanks to some clever engineering plus attention to ergonomics, Neptune washers offer easy access and the largest capacity of any residential washer sold today. They are also said to clean clothes better and more gently than other models on the market.

Switched reluctance motor. While high-efficiency, front-load washers are common in European households, their series-wound, universal motor with variable speed control is not readily transferable to Maytag's design requirements. One reason: Significant cost is required to upgrade a series motor to the design life requirements of the Neptune washer. Any series motor, operating at 120V in the United States, will draw twice the current required by European 240V installations.

More current means a larger commutator with bigger brushes and associated brush wear and noise--"a built-in service call," claims Maytag's Curran Cotton, VP of Research and Development, and 1996 Design News Quality Award winner (see DN 3/4/96, p. 96). Because designers wanted a maintenance-free, low-noise motor, as well as speed controllability, they turned their attention to a switched reluctance (SR) motor design.

An electronic motor controller matches the SR motor and application. Working with Emerson Electric, St. Louis, MO, Maytag engineers developed a speed/torque profile to fit the specific wash and rinse cycles demanded by Neptune. These include the high spin speeds (800 rpm Vs 600 rpm) designed to extract up to 30% more water per load, reducing the amount of water the dryer has to remove, providing further energy savings.

"We could have achieved speed controllability with a variety of technologies," Cotton points out, "but we feel the switched reluctance motor and controller from Emerson Electric is the most cost-effective and efficient method available consistent with the quality we desired."

Tuned absorber. One of the challenges in designing any washer is vibration. This is particularly true in large-capacity machines like Neptune. If unbalanced loads are not handled properly, the washing machine transmits vibrational forces directly to the floor. And if the floor resonates, so may the china closet.

Neptune, therefore, "adapts" to its structural environment. How? A simple spring-mass system, fixed inside the washer door, vibrates with the washer, but 180 degrees out-of-phase. Here's how it works:

The machine controller, which communicates with the motor controller, mounts rigidly to the cabinet. When the cabinet shakes side-to-side, so does the circuit board. An accelerometer on the board also vibrates, creating an electric signal proportional to the amplitude of vibration.

"Ideally, we want the tuned absorber's resonant frequency to be around our top spin speed of 800 rpm," Cotton explains, adding that unbalance is a product of the spin mode. As spin frequency approaches 800 rpm, the microprocessor on Neptune's machine controller monitors accelerometer output; it also monitors motor speed via tachometer feedback to the motor controller.

Once the motor has ramped to its top spin speed, the machine controller determines at which rpm accelerometer output is lowest. The motor controller then holds speed to that rpm where the tuned absorber is doing the best job at canceling machine vibrations.

Conservation and convenience. Two other features differentiate the Neptune washer from European front-load designs: 1) a 15-degree tilt to the wash basket, and 2) a 15-inch diameter tub opening.

Maytag's marketing people evaluated competitive front-load washers and found them hard to load. Consumer studies agreed--the public felt they had to bend and stoop too much, and were not happy with the smaller European-like door openings. Maytag engineers solved the problem by tilting the stainless steel tub to improve visibility and reach; by designing the cabinet, top cover, and door to interface with the tilted tub; and by expanding tub opening diameter. The latter required working with Medibeg of Belgium to manufacture the industry's largest rubber door boot.

"We've known for a long time that European high-efficiency washer technology has held promise with its cleaning ability as well as energy and water savings," concludes Cotton. "But we also knew there were certain features, such as capacity and accessibility, that North American consumers weren't willing to sacrifice. With a significant investment in tooling and targeted consumer research, we are debuting the best of both worlds in the Maytag Neptune washer."


Maytag's motor of choice

Switched reluctance motors feature rugged construction, few parts. Operating principle is equally simple: Applying current to opposing stator windings creates a flux that attracts opposite rotor poles, producing torque.

Not only do SR motors eliminate the wear and electrical interference problems normally associated with brushes, they are physically smaller than comparable ac motors, reverse without relays, and operate over a wider speed range.


Clean but green!

by Roy O'Connor, European Bureau Chief

German cleanliness is legendary, but in recent years environmental aspects have also loomed large on the horizon, affecting both domestic and industrial issues. How does one get clothes clean with the minimum environmental impact? AEG Domestic Appliances point to their Oeko Lavamat front-loading washer.

In this washer a smart, micro-computer controlled DC motor drive and neuro-fuzzy logic provide the intelligence and expertise needed for single-knob operation. The development objective was to obtain a washer efficient in terms of energy, washing agents, and water--not just at the nominal mixed-wash load of 5 kg, but also with loads down to 1 kg.

Because it is smart enough to decide how many rinses and how much water it needs for different loads, the washer only needs 48 l and 0.94 kWh of electrical energy for a standard 5 kg load. For a 1 kg load the washer gets by with just 20 l of water.

Once the program has been selected, fuzzy logic determines how much laundry has been loaded. This is done by soaking the clothes with a small amount of water which is then spun out again. Level measurement, comparing the volume of water extracted to that originally added, gives a measure of the weight of clothes loaded. This figure determines the number of rinses and the amount of water needed.

For the washing cycle itself, a four-jet spray system in the drum ensures that clothes are soaked right through to the center of the bundle. After about ten minutes, once the washing enzymes have done their job, a stain removal agent is added. This process allows the washer to use a lower temperature of 40 C compared to the standard 60 C for a mixed wash, giving corresponding savings in energy.

AEG employs their Advanced Rinsing Technology (ART) to the rinsing cycle. Once rinsing has lowered the suds concentration to a level where foaming is reduced, ART's intensive spinning helps reduce the amount of water needed to 10-12 liters for a 5 kg load.

Apart from optimizing the washing cycle, on-board fuzzy logic also helps reduce vibration by detecting down to 600 grams of unbalance during the spin cycle. This also helps save energy, because the washer can then spin at the relatively high speed of 1600 rpm, reducing drying time.

Differentiating amplifier helps detect small leaks

Differentiating amplifier helps detect small leaks

Columbus, OH--Users of high-efficiency particulate air (HEPA) filters and ultra low penetration air (ULPA) filters (used in the nuclear industry and in cleanrooms) need to detect leaks as quickly and reliably as possible. A widely employed method of detecting leaks relies upon a photometer that measures light scattered from an aerosol. Typically, engineers atomize what's called a challenge agent, for example, dioctyl phthalate (DOP), upstream of the filter to generate the aerosol. A probe moving across the surface of the filter captures aerosol at the leak and delivers it to the photometer.

To be sure of detecting leaks, the probe should reside over the center of the hole for several detector time constants, i.e. long enough to build up aerosol concentration in the photometer's optical chamber. When the operator encounters small leaks, or leaks not directly under the probe, such concentrations often don't develop satisfactorily. Until recently, when using any photometer, operators faced a choice of either missing some leaks or working very long hours scanning filters at very slow speeds.

Photometers gather aerosols and use light focused on a photomultiplier to measure aerosol concentrations. The light stop creates a shadow that keeps direct light out of the photomultiplier.

Designed by Bela Kovach, Eric Banks, and Walter Wikoff of NUCON International Inc., this scanning hand-held probe makes use of a differentiating amplifier to observe the first fraction of the rising signal produced by an aerosol. The amplifier also removes slow signal drift and zero offset, preventing them from interfering with a reading. This approach reduces the time required to detect leaks by 50% to 90%, according to the NUCON team.

A photometer basically consists of a light source and light stop, a sample chamber shaped like two cones joined at their apexes (the sensing zone), a lens that collects light scattered by particles in the sensing zone, and a photodetector. Drawn by a pump, the sample moves into the first cone-shaped region, passes through the sensing zone between the cones, and exits the chamber. Photodetector output is an analog signal, a varying voltage proportional to the density of the aerosol. A conventional system amplifies and displays that signal. It appears as a value added to photodetector drift and the constantly changing background signal.

In the system designed by NUCON's team, the probe's two op amps receive the signal. Any basic differential op amp produces an output signal equal to the difference in voltage appearing at its input terminals. In the NUCON design, an op amp with a gain setting of one drives the main display of an LCD meter to present the aerosol concentration seen by the photodetector to the operator.

Engineers preset the second display of the analog bar graph LCD meter to a value equal to 50% of meter range. Doing so enables the meter to display both positive and negative movement. It's fed by an ac-coupled op amp with a gain of 10. This ac-coupled differentiating op amp causes the display to show a positive movement as the probe passes over a leak, and a negative movement as the probe moves away from the leak. At the same time, an LED flashes to warn the operator of a sudden change in aerosol concentration. These signals enable the operator to realize that he or she just passed a leak. Next, the operator moves the probe back over the leak, and reads the leakage concentration value from the main LCD meter display.

According to the NUCON engineers, tests performed using a NUCON detector reduce the time needed to scan for leaks by 50% to 90%. Such time reduction allows operators to scan more filters per unit of time, and to reduce both their exposure to radiation fields and time spent in confined spaces.

Other Applications

  • Test equipment

  • Pollution monitoring

Additional details...Contact Curt Graves, NUCON International Inc., 7000 Huntley Rd., Columbus, OH 43229, (614) 431-0858.

Load cell technology boosts hardness tester's accuracy

Load cell technology boosts hardness tester's accuracy

Canton, MA--Rockwell hardness testers essentially measure hardness by determining the depth a steel ball or other penetrator moves into a specimen's surface under certain fixed test loads. Like the Brinell, Vickers, and Knoop tests, the Rockwell test defines a material's resistance to permanent indentation.

Although indentation hardness is not a fundamental material property, it has become one of the more reliable controls for the heat treatment and quality of manufactured parts. Unfortunately, correlating hardness test data taken with mechanical deadweight systems is challenging. Dirt, friction, and other mechanical parameters cause variations from tester to tester.

"Maintaining accuracy and repeatability means frequent disassembly, cleaning, and lubrication in the field," says Instron Corp.'s manager of hardness tester engineering, Jack Merck. By replacing mechanical deadweight mechanisms with load-cell technology and closed-loop servo controls, Instron engineers claim they've achieved the highest user-to-user and tester-to-tester displacement-measurement accuracy and repeatability ever attained.

Gauge Repeatability and Reproducibility (GR&R) is what General Motors uses to determine a given tester's contribution to error. The Wilson Series Rockwell 2000 Hardness Tester offers less than 7% GR&R with plus or minus 3 Rockwell-points tolerance. Significant reduction in test errors is evident from the GR&R certificate shipped with every tester. "No one in the industry does that," Merck asserts.

Series 2000's design eliminates all moving parts between the penetrator, force sensor, and displacement transducer. This arrangement defeats key error-contributing mechanisms found in traditional deadweight-type testers. Although Instron's engineers had experience designing load-cell-based tensile testing systems, they needed to create new algorithms to modify their load-cell technology for hardness testing.

A patent application was filed for the in-line servo system design. The load cell and displacement transducer mount directly above the penetrator; there are no levers, dashpots, or pivot points.

Texas Instruments' TMS 320-32C DSP controls the servo loop and provides operator interface functions. It uses load and position feedback to adjust the input current to the dc servo motor (manufactured by Worcester, MA-based K&D Magmotor). The motor drives a ball screw to apply load normal to the penetrator. This structure compensates for dirt, friction, and other mechanical contributors to error, and ensures application of the exact pre-set load to the specimen. Rockwell number determination relies on accurate displacement measurements obtained from a Heidenhain linear glass scale.

A concurrent design team used Silicon Graphics workstations with SDRC IDEAS to design the product for manufacturability. "Reducing parts count from 390 to 160 not only reduced inventory and lead time, but improved reliability so much that we doubled the warranty to two years," says Merck.

Other Applications

  • Tensile testing

  • Fatigue testing

  • Spring testing

Additional details...Contact Jack Merck, Instron Corp., 100 Royal St., Canton, MA 02021-1089, (617) 828-2500.

Shopping becomes a 'smart' experience

Shopping becomes a 'smart' experience

Ever wish you could make that trip to the supermarket an effortless experience? That day has arrived with a new shopping concept called the Smart BoxTM.

The revolutionary system enables consumers to use returnable, reusable grocery boxes they purchase for less than $2 in combination with a new grocery cart (trolley). The containers not only offer grocery retailers an opportunity to improve their customer service with a smarter way to shop and pack, but they help the environment at the same time.

Jointly developed by Buko Limited (Glenrothes, Scotland) and Dow Chemical Co. Limited (Winslow, England), the automated, self-scanning technology offers the convenience of not having to unload then repack groceries at the checkout line. And, since the technology won't work within a metal framework, plastics played a major role in the system's design.

In October 1994, Buko, an innovator in the shopping-equipment market, and Dow teamed to develop a supermarket cart that could be used with self-scanning technology. The system, based on a hand-held, battery-powered self-scanner, allows customers to check their own purchases as they shop. Scanner contents are downloaded at the cash register; the customers pay the bill and leave the store with the purchased items still in the box. And, since they can stack up to six boxes on the carts, customers not only don't have to unload items and repack them into grocery bags, but when they get home they don't have to separate them.

How it works. Various attempts to introduce forms of box shopping have been made over the past 20 years, according to David Butchart, sales and marketing director at Buko. However, until recently, stores have had little incentive to incur the expense to implement the system, which can run up to $100,000 for a store with 30,000 boxes, says Peter Merryweather, business and development manager at Dow--until the SuperTag, that is.

SuperTag is a passive radio frequency (RF) transponder marketed by the British Technology Group (London). The RF tag, attached to the grocery item, is "read" by passing the groceries still in the Smart Box through an "RF Loop" on the checkout belt. As a result, Smart Box creates a lasting plastic box shopping system that meets the new RF system's requirements (SuperTag will not work with metal baskets or carts), allowing the use of the self-scanning technology.

Buko and Dow began their business relationship by co-developing the concept. A manufacturer of metal carts, Buko brought more than 30 years of experience in the retail grocery industry to the table. Dow provided the plastic knowledge and materials that would enable the two companies to become an integrated supplier. In January 1995, Smart Box prototypes were completed and approved, followed by the submission of patent and registered design applications by the partners.

Mailbox Mouldings (Cheshire, England) part of the Stamford Group, molds the Smart Boxes for Buko and Dow. "Dow made the first global delivery of polypropylene to the Stamford Group in September 1996," Merryweather reports. "Since then, Mailbox Mouldings has constructed two 50-ton silos to store the polypropylene resin."

The molder produces the containers using two 1,300-ton Toshiba fast-cycling molding machines, automated hot-foil stamping and handle insertion, and palletization. With two new dual-cavity tools, the molder can turn out 80,000 boxes per week.

Due to the low density of polypropylene, finished parts require less raw material than other plastic materials, claims Kyle Lorton, senior product marketing manager at Dow. "Polypropylene is one of the most cost-effective commodity plastics available," he explains. "The combinations of properties--good fatigue resistance, greater strength and stiffness, and good chemical resistance to hydrocarbons, alcohols, and non-oxidizing agents--make the material ideal for the use and abuse the containers experience in the shopping arena."

Going commercial. Along with the design activities, Buko made systems presentations to several grocery retail organizations. J. Sainsbury (London), a leading UK supermarket owner, signed up in May 1995. Dow and Buko provided in-store promotions at Sainsbury's Camberly, UK, store launch in October 1996. Customers were offered a Smart Box container at a reduced cost when purchasing GB pound 20 ($33) of groceries.

"The launch was extremely successful," says Butchart. "We sold about 30,000 Smart Box containers. J. Sainsbury then decided to launch the concept in six more stores. He adds that if 15% to 20% of the customers buy the boxes, the store considers its investment a winner. Moreover, the system eliminates the cost of supplying shoppers with paper or plastic bags to tote their purchases home, as well as facing the added aggravation of having to dispose of the bags in an environmentally acceptable manner. And, unlike bags, the boxes won't leak if one of the liquid products breaks.

The system has since spread to more than 50 stores across several chains in Ireland, France, and Belgium. Butchart adds that Finnish and Norwegian chains are considering the system.

"In addition to marketing Smart Box containers throughout Europe, we are also working with several retail organizations to bring the containers' convenience to consumers in North America," Dow's Lorton reveals.


History behind the Smart Box

The concept of box shopping first appeared at the Food Marketing Institute (FMI) show in Chicago in 1983. Symbol Technologies, a U.S. company known for its airport baggage cart technology, exhibited a new trolley (cart) design and cardboard box at the show. The product proved commercially unsuccessful, but impressed many of the show's visitors.

Eleven years later at FMI, Symbol introduced a new concept of self-scanning at a seminar. The presentation noted that the first year's experience with public use of small, portable barcode readers proved highly innovative. Some cart makers predicted the technology would have a significant impact on future cart designs and the superstore environment.

In-Store Products, a Canadian company, also announced at the FMI show that year it had developed an environmentally conceptualized product called the Green BoxTM that would replace bags.

In January 1994, the British Technology Group (BTG) generated worldwide press interest with the news it had secured the licensing rights for the South African SuperTag. Many felt the ground-breaking invention could be used as a type of super-price barcode, allowing goods to be scanned by passing a shopping cart through a radio frequency (RF) field.

About this same time, a Dow representative visited the Buko company in Scotland to explore extending the use of polymers in shopping carts. The launch of Symbol self-scanning at FMI and the continuing publicity of SuperTag encouraged Buko and Dow to seriously consider their nontraditional cart system design. Carts with plastic baskets that worked with the SuperTag had already been developed, but it was concluded that a box and cart system offered more benefits to the shopper and the retailer., and the Smart Box system was born.

The Smart Boxes come with handles as well as hand-grips. Their absence of holes prevents inevitable spills that may stain clothes or car upholstery. Boxes are tailored to a UK average cart size that measures less than 650 mm wide.

Three cart sizes offer a two-, five-, or six-box capacity. The larger carts feature nestable newborn and twin-child versions that save space within stores.

The system debuted in October 1995 at a J. Sainsbury supermarket in Camberly, UK. It continues to win converts with as many as three new store rollouts a week throughout Europe.

Hot Spots in Cyberspace

Hot Spots in Cyberspace

Getting product information online

Call them "reader service cards," "bingo cards," or "those cards stuck in the middle of the magazine with all the numbers." Just how do they work on www.designnews.com?

Once you are on the Design News Online home page, click on the latest issue of the magazine. Scroll down to the bottom of the page, and you'll see a button that says "Search Advertised Products." Click it.

This takes you to a site where you can search through the last three issues of Design News, search by issue date, or search all issues. You can search by circle number, company name, or product description.

Type in a circle number, and in most cases you'll get a couple of hits. Click on the appropriate box for information and hit the submit button. This will take you to another page where you fill in your name, phone number, and e-mail address.

If no information is found, you will be requested to complete the registration information. Readers of Design News are already pre-registered, so you may be asked to input some additional information.

That's all there is to it!


Drop by Cafe Silica for ICs

Cafe Silica is open for business serving as an electronic trading center for integrated circuits. OEMs can buy ICs on the open market or sell their excess supply. Most products are priced 30% below current factory-direct prices. The site is password-protected and offers secure encrypted transactions. Check it out at www.cafesilica.com.

It keeps on going

A virtual community for the battery industry is now live at www.iBattery.com. The site is open to commercial battery users, manufacturers, suppliers, and services, and encompasses battery chargers, smart-chip technologies, and test equipment. Other features include electronic catalogs, yellow pages, publications, and online consulting services. The site is laid out much like a community, so you can visit the battery museum, the product screening room, or inventory trading post.

NIST Webbook available online

The National Institute of Standards and Technology now offers a new compilation of chemical and physical data in the NIST Chemistry Webbook at webbook.nist.gov. The web edition contains thermochemical properties, infrared spectral data, vapor pressure data, and mass spectral data. Access is currently free and is part of the more than 50 databases available from NIST.

Electronics design engineers have new web site

The Electronics Design & Technology Network, a joint venture between Aspect Development and CMP Media Inc., has a Web-based resource for electronics design engineers at www.edtn.com.The site offers news, notes, and briefings; how-tos and best-practices design information; and an integrated circuit and component database that you can search parametrically. There are also two fee-based services available: ICselector, with data on 440,000 ICs from more than 200 suppliers, and AspectOnline, with over 2 million components from 700 suppliers.

Looking for optics on line?

Edmund Scientific's Industrial Optics Division features a technical library, new product re-leases, a searchable database, and an online imaging calculator that allows visitors to perform calculations based on the Infinvar TM Imaging System. Visit the site at www.edsci.com.

SAE offers new Web service

The Society of Automotive Engineers (SAE) has updated their site to include a new product, WebDEX. This comprehensive electronic guide includes 63,000 complete bibliographic citations. Categories are:

  • Technical papers published by SAE since 1906.

  • Complete collection of current technical standards in aerospace and ground vehicles.

  • Articles from SAE magazines published since 1990. Information is updated monthly and searchable.

This is a subscription site, $49/year for members, $99/year for non-members. For more information, see their website at www.sae.org/WEBDEX.


Hot link

Everything you always wanted to know about gears...

Billed as the largest international power transmission website on the planet, www.nord.com covers 48 countries and is available in three languages.

Visitors can check out more than 2,500 catalog pages from Nord Gear Corp. and review maintenance manuals, application notes, and training materials. Downloadable DFX drawings are also available.

Micromachines that work!

Micromachines that work!

MEMS Micro gearmotor

Clearwater, FL--Records are meant to be broken; champions dethroned. A few short months after reporting what was claimed to be the "world's smallest dc brushless motor" (see DN 5-5-97), along comes an even smaller motor.

Measuring a mere 1.9 mm in diameter by 5.5 mm long, this brushless dc motor offers a 0.5V dc nominal voltage with a no-load current of 73 mA. No-load speed is rated at 150,000 rpm with a stall torque of 7 muNm. Developed by Micro Mo(R) Electronics Inc. in cooperation with sister company Faulhaber GmbH, Schonaich, Germany, and its research partner IMM, Mainz-Hechtsheim, Germany, the micromotor features specially fabricated bearings, a rare-earth-magnet system, and proprietary lubricants.

Planetary gearheads, produced by LIGA technology, add only 2-4 mm to motor length, depending on the selected ratio (3.6:1 to 47:1). Based on deep X-ray lithography and electroplating, LIGA permits molded micro-range gears with very high aspect ratios.

"Comparative semiconductor-based techniques of surface and bulk machining," says Stephen O'Neil, Micro Mo vice president of Advanced Research & Planning, "are more appropriate for two-dimensional devices with low aspect ratios and little output power or load-bearing capabilities."

Gearhead numbers: Maximum output torques up to 300 muNm intermittent and 150 muNm continuous; efficiencies from 50% to 80% depending on ratio. Target and beta test applications: Medical diagnostic, treatment, and surgical devices; cell biology research tools; chemical analysis apparatus; micro-recording and data storage devices; reconnaissance and security equipment; and pumping/dispensing systems.


Fast printing head

Neuchatel, Switzerland--High-density arrays of microelectromagnets form the basis of a 700 page-per-minute magnetographic printing machine. Not only do they improve print speed, these silicon magnet arrays increase resolution to 480 dots per inch (dpi)--twice that of classical magnet arrays made from individually manufactured electromagnets.

An array of electromagnets writes magnetic pixels on a drum. These pixels pick up magnetic toner which is brought to the paper. The system then recovers residual toner and demagnetizes the drum.
Electromagnets integrated on a silicon chip (1,000 devices/cm2) have been successfully used in high-performance magnetographic printing heads producing a maximum induction of about 1 Tesla.

Developed by CSEM SA (Centre Suisse d'Electronique et de Microtechnique SA), each electromagnet consists of a flat multi-turn coil surrounding a magnetic circuit. A magnetic writing pole and a large, low-reluctance back plate form the circuit. The writing pole concentrates and guides the magnetic flux generated by the coil while the back plate provides a flux return path. Since the number of devices per chip is too high for addressing each inductive coil individually, an on-chip integrated diode matrix sequentially addresses the coils.

Magnetic poles pass through holes in the silicon chip. Coils magnetize the poles. On-chip diode matrices demultiplex the driving signals, directing information to the proper pixels.

Batch fabrication lowers costs. Starting with the silicon substrate: 1) Standard microelectronic processes build the addressing electronics; 2) Microelectrochemical deposition lays down the gold coils; and 3) Silicon bulk micromachining, followed by electrodeposition of the FeNi back plate and writing pole, form the magnetic circuit.

High-speed printing heads are presently in production at CSEM SA for Nipson Printing Systems, Belfort, France.


In-pipe micro inspection machine

Aichi, Japan--An eddy current sensor, multi-layer actuator, countermass, and three clamps comprise this miniature "pipe crawler," developed by DENSO Research Laboratories. Components reside in a 60"-mm-thick shell weighing 0.084g. Shell construction involves the same processes applied to integrated circuit manufacture: precision machining, plating, and etching.

When voltage increases slowly, the countermass moves, but the clamps do not. Decreasing voltage quickly moves the clamps, but not the countermass.

Each actuator layer comprises a piezoelectric element and elastic plate, arranged like a bi-metal. Because shell volume of the piezoelectric element is constant, the piezoelectric element expands in the direction of applied voltage, but contracts in the perpendicular direction. This bends the elastic plate, amplifying displacement. Layer number determines actuator force.

Actuator expansion/contraction moves the inspection machine forwards and backwards within a pipe. During expansion, static friction force between the clamps and pipe exceeds inertial force of the counter mass; inertial force overcomes stiction force during contraction.

Able to detect cracks approximately 10 mum in width, the micro inspection machine operates in both air and liquid.


Rotating micromirror

Dallas, TX--Video is now following in audio's footsteps by going digital for ease of storage and transmission. Digital light processing (DLP) enables digital displays for digital video formats, thus eliminating the digital-to-analog processing step. It works by transmitting a burst of light that the eye interprets as a color analog image.

Digital micromirror device (DMD) uses electrical signals to move a 16-mum-square aluminum mirror to reflect light. DMD arrays can produce black and white or with filters, color dispalys as part of a digital light processing system.

Key to DLP is a MEMS device from Texas Instruments called a DMD (digital micromirror device) light switch. Each DMD has a 16-mum-square aluminum mirror that can reflect light in one of two directions, depending on the state of the underlying CMOS SRAM memory cell. With the memory cell in the (1) state, the mirror rotates to +10 degrees; with the cell in the (0) state, the mirror rotates to -10 degrees.

The mirror is rigidly connected to an underlying yoke. The yoke connects via two mechanically compliant torsion hinges to support posts attached to the substrate. Address electrodes for the mirror and yoke are connected to the complementary sides of the memory cell.

Electrostatic fields develop between the memory cell and the yoke and mirror, creating an electrostatic torque. This torque works against the restoring torque of the hinges to rotate the mirror. The mirror and yoke rotate until the yoke comes to rest against mechanical stops that are at the same potential as the yoke.

By combining a DMD with a light source and projection optics, the mirror reflects light either into or out of the pupil of the projection lens. Thus, the (1) state appears bright and the (0) state appears dark. Binary pulse-width modulation of the incident light results in shades of gray. Stationary or rotating color filters in combination with one, two, or three DMD chips result in color.


Carbon monoxide sensor

Phoenix, AZ--Using silicon-based technology to detect gases has many advantages: sensors smaller than traditional devices, consistent performance, and lower device cost.

A silicon micromachined carbon monoxide sensor is available now from Motorola. Applications include home fire, smoke, and gas alarms; industrial monitoring and maintenance systems; and automotive emission and sensing.

A gas-sensitive, thin-film, tin-oxide layer sits on top of a micro-machined silicon diaphragm in Motorola's carbon monoxide sensor. An embedded heater raises the temperature of the tin oxide to be sensitive to the gas; the silicon diaphragm reduces power consumption.

Motorola makes the sensors using both bulk and surface micromachining technologies licensed from Switzerland-based Microsens S.A. Bulk micromachining involves single crystal silicon etching. Micromechanical structures developed this way are made either of silicon crystal or deposited or grown layers on silicon. Surface micromachining involves depositing or growing layers on top of the substrate to build micromechanical devices.

A thin film of tin oxide senses concentration of carbon monoxide. A heater sits below the film, embedded in a silicon oxide layer. The entire structure rests on silicon bulk-micromachined to 2 mm. This base layer decreases thermal mass and power needed to heat the structure to its 100 to 450C operating temperature.

Motorola plans to offer a line of chemical sensors for different gases. Soon to be available: a methane sensor and sensors to measure hydrogen sulfide.


Blood pressure sensor

Milpitas, CA--The highest-volume application for MEMS products in the medical industry is for measuring a patient's blood pressure in hospital intensive-care units.

One such sensor is the Model 1620 disposable blood-pressure sensor from EG&G IC Sensors. Here's how it works: Fluid from a saline bag passes through tubing into the MEMS sensor pack-age and then into the patient's arm. As the heart beats, a pressure wave moves up the fluid path and is detected by the sensor, which sends the information to a monitor.

Four resistors form a Wheatstonebridge to reflect the pressure seen by the silicon diaphragm.
The MEMS sensor itself consists of a pressure-sensing element mounted on a ceramic substrate. The element comprises a silicon diaphragm that moves under pressure and thick-film resistors that form a Wheatstone bridge. The resistors are arranged so that as the diaphragm moves, opposite sides of the bridge will change by similar magnitudes and in the same direction. When a constant current or voltage is applied to the bridge, the unbalance causes a change in the sensor's output voltage. Thus, the sensor's voltage output directly reflects the pressure.
Grooved bearings boost scanner performance

Grooved bearings boost scanner performance

Swindon, England --To function at the extreme speeds(>10,000 rpm) necessary for high-performance optical scanning, top-of-the-line scanners employ self-acting aerodynamic bearings. Such bearings incorporate herringbone (journal bearings) or spiral (thrust bearings) grooves to improve distribution of air or a fluid film. Better lubricant distribution, in turn, may be used to increase load-carrying capacity, stiffness, or stability.

Schematic Arrangement of EMM System
Electrolyte filtering and temperature control ensure there is no conductivity drift, which can alter the current level in successive machining operations.

H.K. Productions Ltd., London, wanted to improve the stiffness and stability of the optical scanners used in the company's digital enlargers. Unfortunately, conventional processes available for grooving of air bearings present problems: chemical etching is slow and difficult to control; milling can leave burrs; coining or rolling plastically deforms the component, compromising dimensional precision; and laser-beam etching is expensive.

Solution? Implementation of a patented electrochemical micromachining process. Developed by Loadpoint Ltd., EMM comprises a stationary workpiece, a stationary conforming electrode, an electrolyte, and power supply. A control system sequences the machining cycle and monitors key process parameters.

During operation, the electrolyte pumps through the gap between the electrode and workpiece. Current passing between the electrode and workpiece removes workpiece material. Groove depth is directly proportional to the product of current and time.

"The use of pulsed current in place of DC current," explains Loadpoint Technical Director Frank Wardle, "distinguishes EMM from traditional electrochemical machining (ECM) processes used to achieve high material removal rates." As a result, Wardle says EMM equipment design is more easily tailored to a wide range of engineering components. Other electrochemical micromachining characteristics include:

High speed. Typically it takes only a few seconds to machine a complete set of grooves on a bearing.

  • No tool wear. Since the tool is an electrode, it gives repeatable groove forms over long periods of operation.

  • Negligible distortion. There are no cutting forces to deform the workpiece surface, so grooving can be a final machining operation.

  • Precision. EMM is capable of meeting a tolerance of plus or minus 15% on groove depth.

Limitations? Electrochemical micromachining can only be used on electrically conductive materials, and a hot water rinse is necessary to remove electrolyte from the workpiece surface.

Other Applications

Computer disc drives

  • Surface texturing and patterning

  • Machining fragile components

  • Deburring

Additional details, England...Contact Frank Wardle, Loadpoint Ltd., Chelworth Industrial Estate, Cricklade, Swindon, Wiltshire SN6 6HE, England , Tel: +44 1793-751160, Fax: +44 1793-750155.

Additional details, U.S....Contact Gerald Marshall, 1808 Pinecone Court, Morgan Hill, CA 95037-7049, Tel: (408) 779-4828, Fax: (408) 779-4705.

Designer's corner

Designer's corner

Radial-load ball screw

Ballnut/screw assemblies accommodate axial loads; simultaneous side loads shorten the assembly's useful life. A second helical raceway, placed parallel to the primary balltrack, overcomes this problem.

As with conventional configurations, the new raceway features its own ball return. Unlike traditional designs, captive balls contact the secondary groove at its bottom, not sides.

Ball nut/screw assembly's axial- and radia-lad bearing circuits function independently of each other.

Result: the nut also accommodates loads perpendicular to the assembly centerline.

Mike Cossentine, Thomson Industries Inc., 2 Channel Drive, Port Washington, NY 11050, (516) 883-8000, Fax (516) 767-4570.


Wafer watch

Measurement system rapidly maps defects in silicon wafers for next-generation LSI circuits.

In general, microcrystal defects measuring 20-60 nm in size, and & 105 defects/cm3 are not considered a problem in today's silicon wafers; they may be, however, when manufacturing next-generation devices such as the 256-Mbit DRAM.

If so, the Optical Shallow Defect Analyzer (OSDA) should be ready. Two laser beams of different wavelengths scan the wafer surface. Because the beams have different absorption coefficients in silicon, OSDA calculates defect depth and size from the difference in scattered light intensities.

Time required to inspect a six-inch wafer is one hour. Defects to 0.5 mum below the surface can be detected with a depth resolution of 0.1 mum.

Hitachi, Ltd.,6 Kanda-Surugadai 4-chome, Chiyoda-ku, Tokyo 101-10, Japan, Fax: +81-3-3258-5217, Ref: Hitachi Review 45, No. 6.


Health ring

Prototype ring warns of potential heart problems. Multiple LEDs and photo diodes could measure blood flow speed for continual blood-pressure readings. A patent application has been filed.

A battery-powered light-emitting diode and wireless transmitter, wrapped around the ring finger, may one day monitor patient vital signs. Here's how:

The LED emits light into the finger; a photo diode captures light reflected back from the blood. Because blood vessels expand when the heart beats, the amount of reflected light corresponds to the pulse rate.

Embedded circuitry "cleans" and amplifies the signals, which are transmitted to a remote receiver. Rhythm and shape of the pulse rate, processed on a home computer and available to doctors via the Internet, indicate cardiac condition.

Elizabeth Thomson, Massachusetts Institute of Technology, Room 5-111, 77 Massachusetts Ave., Cambridge, MA 02139-4307, (617) 253-2700.


Sensor bearings

With the exception of total width, FAG sensor bearings offer the same main dimensions and inner construction as standard deep-groove ball bearings of the dimension series 62.

Why bother fitting a separate speed encoder to your drive shaft when an integrated sensor/bearing will do?

Phase-shifted Hall-effect sensors, positioned opposite the bearing seal, measure rotational speed and direction of rotation. Quoted savings: Up to 50% when compared to solutions using a separate encoder.

Sensor bearings operate from a direct voltage of 5V to 24V and are intended for electrical machines, materials handling equipment, and packing machines.

Rocco Docimo, FAG Bearings Corp., 200 Park Ave., PO Box 1933, Danbury, CT 06813-1933, (203) 830-8133.


Convenient coupling

Available in 3- and 6-beam models,positive drive couplings can be removed without disturbing shaft position.

One-piece couplings can be a maintenance headache. Replacement requires pulling drive and driven shafts apart, and that means realignment later.

Removable end caps, clamped in place with socket-head cap screws, eliminate the problem. Cap removal exposes the shaft on its centerline; the drive assembly can be disconnected without moving motors or driven equipment.

Other benefit: Because the end cap fits across a D-shaped flat machined on the shaft, there is no backlash.

Hunt Power Drives Ltd., 2 Freemans Way, Wetherby Rd., Harrogate, North Yorkshire HG3 1DH, +44 1423-889984.

Plastic bearings a design option

Plastic bearings a design option

With the constant pressures on design engineers to provide cost savings without compromising quality, any new technology that can do this must be considered.

Plastic rolling element bearings are a relatively new concept which provide an alternative to the more traditional steel bearings. These bearings are generally molded and this process allows for more flexibility in terms of design and manufacture, turning a bearing into an assembly through the integration of any number of features such as gears, shafts, fixing clips and housings.

Sarnatech BNL are the leading exponents of this technology, designing and manufacturing products for major OEMs throughout the world. Their expertise in developing this new technology is based on the ability to analyze the application rather than simply the bearing or moving element within it. The more opportunities there are to offer the customer cost savings through parts reduction and reduced assembly time.

The business is very much project based with every customer having different requirements and requiring varying design solutions. Typically, when a project is introduced into the company it would be accompanied by all parts surrounding the bearing or moving element (mating parts) and an initial assessment would be made to see which components could be integrated within the assembly. There are a number of areas that need to be considered to ensure that the time and effort that goes into the project is fully justified. These "design considerations" include:

  • Speed - It is important to understand the speed at which the bearing assembly will be run and included in this both the running time and the dwell time are important. Although excessively high speeds are generally prohibitive, there are other factors, particularly environmental, which influence how the product will perform at high speeds.

  • Materials - There are a number of engineering polymers available for the manufacture of plastic bearings depending on the end requirements and environment. Chemicals, temperatures and radiation will all require particular consideration when a selecting a plastic material. Additionally, the balls used will be dependent on the environment. Stainless steel balls of varying grades, carbon steel, glass and polymer are all available to meet specific customer requirements.

  • Environment - Various environmental situations can affect the performance of a bearing and consequently the design. Traditional steel bearings have problems running in liquids, chemicals and even in dry situations when contaminants such as paper dust are prevalent. These areas can be addressed when designing plastic bearings through the inclusion of specific ball types, raceway material and of course by the fact that plastic does not corrode. Additionally, plastic bearings with glass or plastic balls can be used in areas where a non-metallic component is required i.e. the medical industry. Another common technique in the medical industry is sterilization using high-energy radiation and the choice of materials in such an area is yet another design consideration.

  • Temperature - is a further area that needs careful consideration at the design stage. It is fair to say that plastic bearings have generally been limited to maximum temperature levels of 100?C although this will change somewhat depending on the speed and local environment in which the bearing will work. However, there are now engineering polymers that have higher temperature limits and these can now be considered during the design process.

  • Dimensional stability - It is a fact that thermal expansion and the absorption of fluids significantly affect most engineering polymers. These areas have to be considered during the initial design stage and any likely expansion can then be allowed for with the integration of special features on the design. The absorption of liquids into the polymer can cause both dimensional and performance changes and where this is likely particular care has to be taken in choosing the raceway.

  • Size constraints - In the majority of cases, the objective is to injection mold the finished bearing tracks. Very high dimensional accuracy is required to produce an effective bearing and this generally means that the maximum size of a bearing is limited to 150 mm. Similarly, at the small end of the scale bearing raceways have to be sufficiently thick to allow satisfactory plastic material flow and to provide adequate support for the bearing loads. Typically, this means that the minimum bearing O/D is 11 mm.

  • Loads - Clearly plastic bearings cannot withstand the same loads as steel bearings. However, there are various options available to increase the load capacity of plastic bearings. Increasing ball size and pitch circle diameter will improve load capacity that can also be increased by omitting the cage thus making the bearing a full complement bearing. Again, dependent on space available, the bearing can be designed to include two rows of balls instead of the more usual single row.

Once all these options are taken into consideration and a product is finally designed, a free of charge prototype can be produced and life tested in the application to prove it works or alternatively highlight some area which requires further consideration.

These are some of the areas to be considered during the design process of plastic rolling element bearings and assemblies and they clearly highlight the options open to Design Engineers. They say that for every problem there is a solution and the design options available through plastic rolling element bearings and assemblies clearly confirm this.