Janesville, WI--Anyone who has ever walked the floors of a large manufacturing operation has seen it: pallets, rolling down a conveyor line, then slamming into one another as they reach a mechanical stop. It's a crude method of material handling, but one that has satisfied manufacturing engineers for generations.
Giddings & Lewis engineer Paul Terpstra, however, wasn't satisfied with that status quo. Terpstra, who works for the company's Assembly Automation group in Janesville, WI, believed conventional conveyor stopping techniques were in-efficient. Increasingly, he noticed that they required considerable maintenance. "When you have that much weight banging into the stops all day long, you create a real maintenance headache," he observes.
Worse, conventional techniques required special clutching mechanisms, which sometimes seized up or needed adjustment. So Terpstra met with other Giddings & Lewis engineers and eventually devised a simple alternative--supplying each of the conveyor's rollers with its own electric drive motor.
Now known as the SmartConveyor, the concept offers users a multitude of advantages--some of which, even Terpstra hadn't foreseen. Because each motor drives a single roller, instead of a team of rollers, it eliminates clutches, belts, and drive chains. As a result, it vastly simplifies maintenance and improves uptime.
It also uses far less energy. When all of the motors are networked to a programmable logic controller, the conveyor operates like a giant inchworm, engaging only those motors in the vicinity of the load, then pushing it forward. In the meantime, the other rollers and their motors lie idle. In tests, the concept has reduced energy use from 25% to 75%. "By transferring power directly from the motor to the roller, you gain efficiency," Terpstra says.
The SmartConveyor concept requires few components: specially designed torque motors and gearheads; drive rollers; proximity switches; a programmable controller; and custom-built "motor blocks." Used in conjunction with networking protocols, such as DeviceNet, it also requires a network cable between motor blocks.
How it works. During operation, SmartConveyor's proximity switches sense the position of the load, then communicate with the controller. The controller activates motors in the area of the load and the rollers push it forward. Afterwards, the rollers stop and a new set of motors is engaged.
Giddings & Lewis engineers designed the system to accurately stop loads, as well as convey them. To accomplish that, SmartConveyor reverses its rollers, thus imparting a stopping force to the load. "If we merely shut off the power to each motor, the pallet will coast, instead of stopping" Terpstra explains. "But by reversing the motors, we can decelerate the pallet and stop it repeatably."
Among the keys to the success of the system were Giddings & Lewis' work with two suppliers: Bodine Electric, Chicago, IL, which provided the torque motors; and Turck, Inc., Plymouth, MN. Early on, Giddings & Lewis engineers teamed with Bodine to develop a motor and gearhead for the project. The engineering team wanted a motor that could operate in a stall condition for prolonged periods while not in use. Bodine provided a torque motor rated at 10 lb-inches for the application, then built a special gearhead, enabling the rollers to operate at a slower speed.
Working with Turck's engineers, Giddings & Lewis also selected a special square proximity switch, Turck's Q26. The Q26's square shape and relatively long sensing distance (about 10 mm) made it a desirable choice for the application, Terpstra says. "The square prox switch mounts right up against the side rail of the SmartConveyor and doesn't need adjustment," he says. "Conventional cylindrical switches would have required a height adjustment."
Turck engineers also designed the motor block, a sealed aluminum housing that contains eight receptacles for the plug-in connection of the motor, proximity switches, and DeviceNet cable. Each straight section of SmartConveyor "track" uses two motor blocks. By communicating with the PLC, the motor blocks help monitor the performance of the motor and prox switches. If, for example, a motor short circuits, the controller knows it immediately.
The SmartConveyor has been used extensively for trimming of engines at General Motors' Flint, MI, V-8 engine plant. Engineers there say that it has dramatically reduced maintenance time and improved throughput by as much as 10%. Similarly, engineers at Ford operated a SmartConveyor test loop for more than a million cycles, saying that it achieved an operating uptime of 99.6%. "Few conveyor lines of any kind have uptimes that high," notes Ken Smerecki, a production superintendent for Ford who was involved in testing the system.
Though Giddings & Lewis plans continued improvement of the system, its engineers say it has met its initial goals. It also minimized part count, simplified the drive train, and reduced downtime. Says Terpstra: "It has already exceeded all of our expectations."
Sensors scout the factory floor
..If an army of electromechanical components constitutes an assembly line or network of manufacturing cells, sensors serve as the advance guard. Constantly on the lookout for indicators critical to the manufacturing process, sensors provide a winning edge in the battle to build things faster, cheaper, better. The following are some of this year's new recruits.
John Lewis, New Technology Editor and David J. Bak, Executive Editor
Proximity sensor stands up to weld slag
Known for their rough environments, welding applications present proximity sensors with a variety of challenges. Allen-Bradley engineers designed the VersaCubeTM inductive proximity sensor with hassles, such as weld-slag build up and weld-field interference, in mind.
Welding applications typically require protective-boot changes every few weeks, increasing downtime and decreasing productivity, according to Kimber Lynn Drake, senior product marketing engineer for Allen-Bradley. "Our proprietary polymer housing material resists weld slag buildup on the sensor enclosure. Boots are disposed of entirely because most weld slag bounces off. Any sticking slag easily wipes away."
In addition, the sensor's internal electronic design alleviates affects from weld-field interference, short-circuits, overload, fast transients, and radio-frequency interference. A patented adjustable-mounting base lets users rotate the sensor head to any of five sensing positions, and helps users limit various sensor styles from their inventory. Multiple-mounting hole patterns simplify retrofits on existing equipment.
Measuring 40 x 40 x 65 mm, the VersaCube offers a sensing range up to 15 mm. Allen-Bradley engineers designed adjustable mini and micro connectors on the VersaCube that enable right-angle mating cables to rotate to almost any position. A rugged die-cast base offers durability, and over-molded grommets, fused to the cable, provide superior cable-strain relief.
U.S. contact: Performark, Tel: (612) 946-7330, FAX: (612) 942-6940, E-mail [email protected]
European contact: Rockwell Automation/Sprecher + Schuh, Tel: +41-62-837-2121, FAX: +41-62-837-2903.
Sensor exploits single-channel processing
Aromat Corp.'s LM-10 micro-laser sensor is targeted to meet an OEM's growing need for small, cost-effective sensors. Its single-channel processing method (patent pending) employs a single chip to do the work formerly done by two dedicated circuit paths. This reduces size, number of components, cost and weight. Sensor applications include: thickness measurement in paper, lumber, film, and gypsum manufacturing, and electronic applications for board warpage detection.
To maintain a consistent and defined light beam, the LED projects through a transmitter lens. Focused light hits the target's surface, scattering the beam. Some diffused light enters the receiver lens, and is refocused on a position-sensitive diode (PSD).
If the distance to the target changes, so does the position of the refocused spot on the PSD. The LM-10 reads the spot's position, and, using a triangulation method, converts the analog signal to a digital output proportional to the distance from the sensor's face. The 35- x 96- x 55-mm sensor offers three response frequencies: 10Hz, 100Hz, and 1kHz, and provides resolution to 5mu.
U.S. contact: Aromat Corp., Tel: 908/464-3550, Ext. 2086
European contact: Tel: +49-08024-648-0
Pre-programmed sensor detects 5mu movements
Providing resolution to 5mu, Omron Electronics Inc.'s new Z4D-F micro-displacement sensor has a built-in microprocessor. It's available in both analog and digital versions for applications such as presence/absence detection of small parts or solder points, double-feed detection in printers and copiers, and vibration detection.
Integrating the analog output version with Omron's K3TX intelligent signal processors allows digital outputs for monitoring applications. "This scheme is good for applications that have several thresholds requiring voltage variation verification," says Omron's product marketing specialist Nazario Biala.
The Z4D-F04A analog model includes a power alarm indicator that immediately identifies sensing problems. And the Z4D-F04D digital version with ON/OFF output includes a stability/operation indicator and a distance adjuster for precision sensing. It uses a 12- to 24-Vdc plus or minus 10% supply voltage, 10-mV ripple voltage, 35-mA current consumption, and has a 1.5-mm spot diameter at a 4-mm sensing range. Cost: $285.
U.S. and European contact: Omron Electronics Inc., Tel: 314/281-2129, FAX: 314/281-1517
Beam power doubled
.Despite availability of one-touch automatic calibration, many users of fiber-optic sensors prefer trimmer pot designs. Why? Stable detection and the ability to make slight changes in sensitivity.
Keyence Corp.'s FS-M Series FO amplifier gives operators another reason: improved trimmer linearity at longer detecting distances. For example, operating in the FINE mode (standard power) with a Model FU-4F Fiber Unit, the FS-M amplifier obtains specified trimmer linearity to distances of 100 mm. Switching to the TURBO mode (high power) extends that detecting distance to 200 mm.
Three components make this possible: a high-intensity LED, an extra-sensitive photodiode, and proprietary circuitry the company calls "Super EX." Other FS-M features include:
High-speed response. In the FINE mode, 250 microseconds; 500 microseconds, TURBO.
Interference prevention. As many as eight units can operate side-by-side.
Eight-turn trimmer. "Super EX" circuit ensures linearity between detecting distance and number of trimmer turns, even in TURBO mode.
U.S. contact: Keyence Corporation of America, Tel: 201-930-1400, FAX: 201-930-0088.
European contacts: Keyence United Kingdom, Tel: +44 1908-696900, FAX: +44 1908 6967777.
Keyence Germany: Tel: +39 711 796061, FAX: +39 711 797799
Relative humidity measured
When placed in an air path, the ERH 300 from Elmwood Sensors detects changes in relative humidity--within seconds, without drift. A combination of material and construction accomplishes this measurement task.
The ERH 300 Series Sensor operates by generating a resistive output as a proprietary doping material on the surface of the base alumina absorbs moisture. Output impedance of the thick film changes according to the amount of water vapor present.
Unlike polymer-based humidity sensors, the ceramic-based design does not lose accuracy over time, eliminating the need for recalibration. In addition, it will not clog, and is unaffected by temperature and most gases--the cause for delamination of some polymer-based sensors.
U.S. contact: Elmwood Sensors Inc., Tel: 401-727-1300, FAX: 401-728-5390. 2 European contact: Elmwood Sensors Ltd., Tel: +44 191-258-2821, FAX: +44 191-258-7040
Pressure sensor spurns hostile media
Glass fusing a micro-machined, silicon strain gage to a stainless-steel diaphragm makes this piezo-resistive pressure sensor virtually impervious to most hostile media environments, both physical and electrical. The latter includes radio frequency interference (RFI), electromagnetic interference (EMI), as well as electrical transient problems.
Developed by Measurement Specialties, Inc., the MSP 400 features a diaphragm and pressure port machined from a single piece of high-strength stainless steel. The absence of O-rings, internal welds, or silicone oil-filled cavities means corrosion-, shock-, vibration-, and leak-proof operation. Input pressure simply deflects the diaphragm to generate a directly-proportional change in electrical output.
Good for liquids or gases, the MSP 400 is offered in several pressure ranges from 0-100 psi (7 bar) to 0-10,000 psi (700 bar). Output signal levels of 0.5 to 4.5 VDC (ratiometric), 1.0 to 5.0 VDC (fixed), and 4 to 20 mA (two-wire) are available.
U.S. and European contact: Measurement Specialities Inc., Tel: 201-808-1819, FAX: 201-808-1787.