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Articles from 2005 In February


Plan Ahead, Keep In Touch

With nearly two million square feet of floor space to cover, improving efficiency is perhaps more important during CONEXPO-CON/AGG and IFPE 2005 than during the normal workday. New tools will help attendees plan their visit in advance, then adjust their time in Las Vegas while staying in touch with home and office.

The personal itinerary planner is an advance-planning tool that lets attendees organize their visit, tracking educational sessions and maintaining a schedule of industry meetings. This planner works with the shows’ Virtual Trade Show, letting attendees search for exhibitors by name, product category, or booth number. They can make booth appointments and store them in their personal itinerary planner.

Once show-goers arrive, they can use information centers around the show floor to search the exhibitor directory. These kiosks will also provide dates, times and locations for industry association conventions and meetings, as well as technical sessions.

The information centers also let visitors access their e-mail from the show floor. “The ability to easily access e-mail from the show floor will also be extremely helpful,” said conference co-chair Gerald L. Shaheen, group president at Caterpillar Inc. of Peoria, IL.

Click here for an overview map of IFPE and CONEXPO-CON/AGG.

Wear Walking Shoes

The trade show and travel industries have been hit hard over the past few years, but many conferences are starting to set new highs for attendance. The IFPE 2005 International Exposition for Power Transmission and CONEXPO-CON/AGG shows are both setting records for attendance and floor space reservations, spurred in part by a heavy international presence.

Early registrations portend an onslaught of more than 110,000 attendees are expected to spend some time in Las Vegas between March 15-19. That will surpass the 108,000 of 2002, the last time the shows were held, and appears likely to surpass the record attendance set in 1999. Hotel reservation rates also point to a record turnout.

The shows have a strong international presence. Eight international exhibit pavilions include a pair from China as well as groups from Finland, Germany, Italy, Korea, Spain and the U.K. IFPE 2005 will host two international exhibit pavilions run by Chinese trade organizations as well as an Italian pavilion and a pavilion featuring exhibitors from Taiwan. Foreign attendees are also expected to rise. In 2002, nearly 16,000 attendees came from outside the United States.

CONEXPO-CON/AGG exhibit space sales surpassed 1.85 million net square feet, setting a new record as off-highway equipment makers and others plan to bring huge equipment to the show floor. IFPE, which doesn’t have the huge space requirements of the heavy equipment show, broke its previous space records with reservations for 110,000 net square feet of exhibit space.

Equipment from Caterpillar and others at CONEXPO will cover nearly 2 million square feet of floor space.

Adding Knowledge

Technical sessions offer a quiet spot away from the bustling show floor, giving attendees a chance to build their knowledge base. Scores of in-depth seminars give attendees at CONEXPO-CON/AGG and IFPE 2005 a chance to hear in-depth presentations on a host of topics.

The IFPE 2005 Technical Conference, organized by the National Conference on Fluid Power, comprises 98 presentations. They’re grouped into 22 subject tracks such as modeling and simulation, testing, filtration/contamination, biodegradable hydraulic fluids, mechanical drives and motion control. Speakers represent 44 companies and 21 universities from 15 countries.

Another alternative is the IFPE 2005 Best Practices Learning Center, a nine-part series of interactive sessions split into three tracks.  The fluid power basics session addresses hydraulics and other fluid power technologies. Electrohydraulics and motion control strategies examines a variety of control issues, while reliability, maintenance and troubleshooting for mobile hydraulics systems rounds out the sessions.

On the CON/AGG side, there are over 115 seminars addressing many issues surrounding concrete and other materials, as well as specific topics such as preventing truck rollovers. A number of sessions also address various aspects of corporate planning. Several sessions will be simultaneously translated into Chinese, Russian, Spanish and Portuguese.

Electrohydraulics will be among the many technical topics addressing in program sessions. Source: Sauer-Danfoss

Help Is On the Way

International sales are of growing importance for large and small companies, but expanding into new geographic regions often poses many vexing issues for many organizations. The U.S. government has a number of programs designed to help countries export, offering many services at low costs.

A U.S. Export Pavilion operated by the U.S. Department of Commerce will help CONEXPO-CON/AGG and IFPE 2005 exhibitors increase their global sales and aid attendees making international purchases. Trade experts from the DOC and other federal agencies including the U.S. Commercial Service, Small Business Administration, and Export-Import Bank of the U.S. will be available at the Pavilion, which will be located just outside the shows' International Trade Center in the North Hall.

Pavilion services are geared to assisting smaller and medium-sized businesses. These services include research into export markets, information on international trade regulation compliance and shipping processes, and financing support. Many of the services cost less than fees charged by entities in foreign countries.

International offices of the Dept. of Commerce can provide lists that help companies find customers and business partners, also helping visitors manage foreign transactions. They also provide information on local customs regulation and other country-specific data. The U.S. Export-import Bank can help finance international sales, while export training seminars run by the Small Business Administration.

Electronics

MAGNETIC SENSORS

Mounted from above

The BIM-INR permaprox inductive magnetic sensors are engineered to fit into a 4-mm round-groove on extruded-style cylinders. They are mounted from above instead of sliding into the cylinders' groove, providing easy installation when the cylinder is located in a tight space or when other equipment problems prohibit access to the end of the cylinder. The product contains Magneto-Resistive technology, which is a solid-state construction that holds advantages over similar switch devices. TURCKhttp://rbi.ims.ca/4387-578

WIRE INSERTION

Screwless

Modular Terminal Blocks for two (part #8728) and three-wire (part #8729) insertion are designed to meet PCB, Test Set, and Quick-Connect requirements. The screwless, push-button devices reportedly assure positive, horizontal entry of solid or stranded #20-18 AWG wire, and feature stainless steel integrated springs from firm wire retention. They mount into pre-drilled or stamped holes and provide brass, tin-plated terminations with stainless steel contacts. Housings are made of Nylon 6/6, UL rated 94V-0. Keystone Electronics Corp.http://rbi.ims.ca/4387-579

LASER THROUGH-BEAM SENSOR

Provides simple focus adjustment

The company's sensor can reportedly recognize an object as small as a 0.5 mm at a distance of 50m. According to the company, the visible through-beam arrangement provides simple focus adjustment and a reaction time of 100 µsec. It is in a stainless steel housing, and can be used in a variety of applications. Uses include controlling overall height of object, presence or position check in hostile environment, remote sensing of tool breakage, and clear plastic bottle detection, among others. Component Engineeringhttp://rbi.ims.ca/4387-580

LIGHT ENGINES

Encased in aluminum housing

The company's LED Light Engines are engineered for designers who want to spread light from a single light source over a wide, flat area. It combines one or more of the company's high-power LEDs with a Lumitex® woven or UniGlo® fiber-optic panel. A special collimating lens captures, then focuses the light from the LEDs to the fiber-optic panel. Encased in an aluminum housing that acts as a heat sink, the assembly provides increased panel brightness by driving these LEDs at a higher current through more efficient heat management, according to the company. Lumitexhttp://rbi.ims.ca/4387-581

LDT

Programmable, non-contact

The Q21R version of the E-Z track line of programmable, non-contact linear displacement transducers is engineered to provide an enhanced internal resolution of 0.001-inch (16-bit analog output) in an accurate, auto-tuning, low-profile package. Features include the ability to sense a magnet other than the standard slide magnet and to adjust the signal strength accordingly. Using magnetostrictive technology, the product monitors the position of a magnet along the active stroke without causing any wear on the sensor parts, making it suitable for applications where continuous linear feedback and high resolution are necessary. TURCKhttp://rbi.ims.ca/4387-582

CO2 LASERS

All-metal design

The company's CO2 lasers are designed for use in a range of industrial processes, including cutting, welding, drilling, and marking. Like other traditional metal-cutting applications, CO2 last cutting requires the use of an assist gas, typically oxygen, to enhance cutting efficiency. The products feature the company's patented, all-metal tube. The all-metal, sealed tube design provides and maintains high gas purity, which is considered essential to achieve the long operating life required of the company's lasers. Synardhttp://rbi.ims.ca/4387-583

PROCESSOR

Intended for tech upgrades

The SVME/DMV-183 is designed as a high-performance, dual-processor, rugged 6U VMEbus single-board computer. It features faster processors, additional operating features, and a lower retail price than its predecessors. It offers single or dual 1.5 GHz FreeScale MPC7447A/7448 PowerPC processors, and is fit for technology upgrades. The construction-cooled SBC is targeted to the data processing needs of tactical aircraft, armored vehicles, and various harsh environment naval systems. Curtiss-Wright Controls Embedded Computinghttp://rbi.ims.ca/4387-584

ENCODER

With electronic reset capability

The HMT25, a multi-turn absolute encoder, is designed to feature electronic reset capability. Unlike manual rests, it can use system software for initialization; this reportedly improves machine set-up time, especially in systems with space constraints. Sending a timed pulse through the rest pin, the encoder value gets set to 0 through a non-volatile internal memory. The physical position at any time is precisely determined, even in prolonged power-down situations, according to the company. BEI Industrial Encoder Divisionhttp://rbi.ims.ca/4387-585

PROCESSORS

Doubles performance

Featuring quad 1.5 GHz FreeScale MPC7448 PowerPC processors, the CHAMP-AV IV doubles the processor performance of its predecessor, the CHAMP-AV II, while reducing cost by almost one-third. The AltiVec -based DSP engine also features the company's QuadFlow architecture. It drives DSP applications with up to 48 GFLOPs of peak computational power, 256 Mbytes or 512 Mbytes DDR-250 SDRAM, and dual 100 MHz 64-bit PCI-X interfaces. Each processing node of the product is provided with a Gigabit Ethernet connection, according to the company. Curtiss-Wright Controls Embedded Computinghttp://rbi.ims.ca/4387-586

EMBEDDED BOARDS

Deliver real-time control

The SCRAMNet GT PMC, PCI, and VME embedded boards are engineered to deliver real-time control and data networking 1,200 percent faster than boards based on its predecessor. The products are also engineered to enable networked heterogeneous computers to function as a single multiprocessor system. Each board features an industry standard 2.5 Gbytes/sec Small Form Factor Pluggable (SFP) transceiver and delivers data throughput rates exceeding 200 MBps. A secondary onboard SFP is available as an option to provide redundancy, according to the company. Curtiss-Wright Controls Embedded Computinghttp://rbi.ims.ca/4387-587

MINIATURE POWER RELAY

Features small seated height

Designed for applications where mechanical headroom is at a premium, the AZ9481 miniature power relay features a seated height of less than 0.45 inches. It has a 16A, 4,000 VA rating, a dielectric strength from contact to coil of 2,500 Vrms, and a coil that operates at 128 mW at pull-in. The product comes standard with a Class F insulation system that allows operating in ambient temperatures up to 85C; it is also available fully sealed and RoHS compliant. American Zettler Inc.http://rbi.ims.ca/4387-588

It Is All About Power

It Is All About Power

Tom Solon, Kerk Motion Control

Engineers know it all. At parties, after everyone has given their opinion, everyone asks the engineer to tell them the real answer. Engineers deal in facts, data, and probabilities. And engineers are trusted. The public may have lost trust in the medical profession, in our leaders, and in our favorite news reporters. But, though they make jokes about us, engineers are viewed as straight shooters. This trust gives us power. It also carries responsibility.

Our nation, our world, is in a crisis, a crisis of power. Specifically, our dependency on fossil fuels has the world at war. Regardless of one's politics, it is an irrefutable fact that oil drives much of our economy and has fueled many of the recent wars. The sad truth is that we have a solution that we are not using.

Nuclear energy is the answer. Current technology is capable of providing lower cost, safe energy in virtually infinite amounts. And the prospect of commercially viable fusion reactors is closer than most believe. (Read the article on cold fusion in the March 29, 2003 issue of New Scientist for details.) But the public has shut nuclear power down based on myth and fear.

We all know the list: Three Mile Island, Chernobyl, The China Syndrome (great movie, bad science), radioactive waste, and worst of all, that link between nuclear power and the atom bomb.

But, fossil fuels, both oil and coal, have killed and continue to kill every day. Coal mine disasters, black lung, acid rain, hydrocarbon emissions, oil spills, poisoned water and land, oil platform disasters, refinery accidents, the Gulf War, and arguably most fighting in the Middle East are directly attributable to our dependence on fossil fuels. Add to this the economic risks of a world economy inextricably linked to oil, and our current concerns about terrorism (think refinery or LNG tanker explosions), and it is hard to understand why we are willing to use oil and gas at all.

Is nuclear energy perfect? Of course not. But let's give it some time. At its worst, it has been much safer and it is in its infancy. The potential is even more hopeful with the possibility of fusion and improved processes. We live in a world of managed risks. If you look at the scorecard, the risks from nuclear power cannot match the real, proven and ever increasing dangers we accept with fossil fuels. But the public's ongoing fear of radioactivity has paralyzed us. For more information, visit the website http://www.ecolo.org.

People willingly inhale concentrated carcinogens (tobacco smoke), ingest poison (alcohol and others), subject themselves to all kinds of electromagnetic radiation (TVs, cell phones, microwave ovens, power lines) and seek out powerful sources of ultraviolet radiation (tanning booths and sunlight). Yet we have managed to shut down the most tightly regulated industry ever to have existed (nuclear power).

It is time to change this. We, as engineers, have the power, the public's trust. We need to tell the world that the emperor is naked! Look at the facts and decide for yourself. Then tell people what you have found. Write letters to your representatives and vote accordingly. Invest in companies that are developing nuclear energy. Explode the myth!

Or don't. But don't complain that you can't change things. Remember that it is your choice, your responsibility. Because you've got the power.

Reach Solon at [email protected].

Clive Emitted That Youthful Glow

Clive Emitted That Youthful Glow

Committed to a cleaner environment, Clive recycles plastic objects into funky jewelry-perfect to wear for a night out clubbing as long as you don't mind lugging along a power supply! First, he glues colored LEDs into holes he has drilled into an array of clear plastic objects-the more varied the shape, the better. He crafts the string from a pair of wires twisted together and terminated into a socket at regular intervals. A resistor limits the current through each LED, which requires about 20 mA.


Click here for Clive Mitchell's complete instructions on how to build your own LED charm lights.
LED Charm lights parts list
Amt Part Description Allied Part #
1 6V 300mA PSU 928-9625
1 6V 600mA PSU 928-9630
1 Two-crimp connector housing 863-3250
1 Female crimps 863-9969
1 24 AWG stranded wire (green) 696-9104
1 24 AWG stranded wire (brown) 696-9109
1 5-min Quik Stik epoxy glue 796-9851
1 220 ohms 1/4W resistors 832-0248
1 Clear 1/8 inch heatshrink tubing 617-0414
1 Red 3 mm LED 505-9999
1 Orange 3 mm LED 505-9715
1 Yellow 3 mm LED 505-0002
1 Ultra green 3 mm LED 505-9716
1 Blue 3 mm LED 505-9720

More for Less in Motion

Muhammad Mubeen, Senior Research Associate, Motion Tech Trends

Muhammad Mubeen has two decades of expierience in motion control. He says the use of permanent magnet brushless motors is a major trend.

What technologies have caught your eye in surveying motion control trends? You have to understand that the motion control business is not revolutionary. You can't point to a product that is going to shake up the whole world. Instead, we have incremental improvements in products, as well as cost savings. But having said that, I would point out that, for precise motion control in applications ranging from disk drives to medical to packaging machinery, the permanent magnet brushless dc motor has emerged as the clear winner. That's despite all the talk about other types, such as switched-reluctance motors and slotless motors, which are rarely seen in real-world applications. Brushless permanent magnet linear motors also are coming into their own, with some companies offering models with incredible precision at very attractive prices.

What is the impact of specialized microprocessors? Digital signal processors are having a tremendous impact, and it all boils down to delivering more features for less money. Who would have ever thought of putting a DSP in a sump pump for a house? But if you've got an expensive home, you want a pump that is not only reliable but has memory and communication capabilities. As costs of DSPs have fallen from $30 to $1.50, these very fast microprocessors are providing many rich features for motion control, such as higher speeds, programmable inputs/outputs, diagnostics, error history, coordinated motion, communications, and noise control. The leading DSP manufacturers—Texas Instruments and Analog Devices—are stressing these benefits, with the goal of putting a DSP in every motor. If you are a design engineer and are not considering a DSP in your motion control system, you are missing the boat.

What impact is globalization having on motion control? China is becoming more and more of a factor. It is a major supplier of precise, powerful, and low-cost permanent magnets for motors as well as machined motor parts, such as stators and rotors. In the motion control business, it is getting to be the case that, if you don't have China in the equation, you are going to lose.

Are you seeing more applications with distributed control? Often, the ideal solution is distributed control, especially for more sophisticated, multiaxis systems. The question is: Can you afford it? But we are seeing progress here, too. For example, you now see more motors with integrated controls that are performing functions that once were the responsibility of the central controller.

Isn't motion control becoming more difficult for design engineers to keep up? That is particularly true of smaller companies, which is why more of them are turning to integrators for assistance. But there is a cost associated with this, with markups ranging from 30 percent to 100 percent. Many large companies, however, still have the resources to hire in-house specialists to handle motion control tasks.

Valve Maker Drops a Bomb on Cost

The engineers who design Marotta Controls' precision pneumatic components sit just a few yards away from the company's manufacturing plant. And that proximity paid off when they designed parts of a new ejection mechanism for the U.S. Air Force's Small Diameter Bomb (SBD) system. This forthcoming system will allow existing fighter jets, including the F-15E, to rack up more kills per sortie by equipping them with a weapons carriage that holds four small bombs rather than one large one. At 250 lbs, each one of the new 70-inch-long small bombs will weigh only half as much as the smallest bomb currently used by the Air Force. Size aside, the new bombs will feature advanced GPS guidance and other targeting systems designed to improve accuracy. And they will feature a new pneumatic bomb ejection system.

Which is where Marotta enters the picture. The company will supply the pneumatic firing valve and accumulator that release these small but potent bombs from the plane. In some ways, the valves represent business as usual for the company. It already supplies precision fluid control components for military, aerospace, and demanding industrial applications. And this lineup of components includes balanced-poppet solenoid valves similar in operation principle to the one used for the SDB firing valve (see http://rbi.ims.ca/4387-556 for more information on balanced poppet designs).

But this particular valve proved especially challenging from both design and manufacturing standpoints. Richard Molesworth, Marotta’s manager for aerospace systems, is intentionally vague about many of the design and performance details, citing confidentiality requirements. But he does note that the SDB approach in general does try to pack a lot of components in a small space. After all, it does squeeze four small bombs and their weapons carriage in roughly the space normally occupied by one big bomb. This packaging constraint ultimately made the valve design more difficult because the valve has to contribute to overall space savings by integrating functions unrelated to its own operation. For example, the valve includes mounting points for and actuates an over-center latch used when the bombs are loaded into the carriage. “The packaging constraints required us to do more mechanical interface work with other parts of the system,” Molesworth says.

From a manufacturing standpoint, the company’s engineers also faced additional challenges with this valve. First, the valve body has tight tolerances and surface finish requirements that are stringent even by Marotta’s standards. Some of the concentricity specifications on the bores are less than 0.001 inch, and the finish requirements for the entire part average 16 rms.

Making just one of these valves bodies would be tough enough, but the second of Marotta’s manufacturing challenges involves much larger production volumes than the company normally encounters. “A lot of our production runs are for two or three units,” Molesworth says. Yet the valves for the SBD will have volumes measured in the “thousands” once the program ramps up fully.

Finally, Marotta had to make this difficult part while meeting a hard-and-fast cost target—an “average unit production price,” as it’s known in the defense business. “The price expectation of our customer is fixed,” Molesworth says diplomatically. Marotta didn’t start this project anywhere near that desired cost. “We wouldn’t have been able to meet our target price with our existing processes and supply model,” says Tony DiGiovanna, a senior program manager.

So Marotta engineers made some changes, taking what boils down to a three-pronged approach to getting this job right.

Focus on Component Design First
Adherence to Design for Manufacturing (DFM) principles played a key role in driving toward production and cost goals. Marotta’s own design team and an independent reviewer scoured the valve design for any threats to manufacturability. And the design aspect that counted the most in this case turned out to be dimensional tolerances.

As Molesworth points out, overly tight tolerances can in general be a big threat to manufacturing yields and ultimately drive up costs. So long before the valve body went into production, Marotta engineers reviewed every single dimensional tolerance and looked for places where those tolerances could be eased up a bit. “You don’t want the tightest tolerances where you don’t need them,” Molesworth says. Of course, this valve still has its share of tight tolerances—largely because it has to operate with response times less than 50 msec and at pressures over 6,000 psi. Most critical were the tolerances that involve sealing surfaces. “But everything else was up for grabs,” Molesworth says.

The company’s engineers didn’t stop there. They also looked for other design features that could be simplified for manufacturing’s sake. For example, they considered a couple of different methods of retaining one of the valve’s O-rings—either a machined undercut in the valve body or a split bushing. They ultimately picked the bushing; though it required an additional component, it avoided a potentially difficult and expensive machining operation.

To meet its cost and production volume requirements, Marotta created a stand-alone production cell for teh firing valve and instituted a Kanban supply system.

Get the Right Machine Tools
Of all the costs associated with the valve, the valve body represents the single biggest cost driver. Molesworth notes that it alone is responsible for 65 percent of the hardware cost, and it’s easy to see why given its machining requirements. Made from hardened heat-treated 17-4 PH steel, the valve body has 18 tight tolerance bores, some of them angled, and nine thread holes. Many of the bores have concentricity requirements of 0.001 inch, and a few have even tighter requirements. And the part, which starts off as an investment cast blank, has to be machined on all six sides.

To machine this tricky part without driving up costs, Marotta engineers knew they needed to create an extremely capable manufacturing cell. So they started with an exhaustive search for the right machine tools. DiGiovanna recalls that eight machine tool vendors initially looked good. Yet all but three quickly fell out of contention. “Five of them just couldn’t meet our requirements,” he says. Marotta engineers went on to study four solutions from the three remaining vendors (see table for a detailed look at the evaluation criteria).

One solution, a pair of SuperMiller 400’s from Mori Seiki, “stood above the rest,” DiGiovanna says. These machines feature a five-axis machining center with integrated turning (see http://rbi.ims.ca/4387-557 for the full specs). It’s worth noting that all four of the final machining solutions did pass muster from a technical standpoint; all could produce the valve body parts. But the Mori Seiki shined when it came to operator costs. The SuperMillers can run unattended for up to eight a day, while the other solutions could run for an hour or less without attention.

Smart about Assembly
While most of the valve’s cost can be found in the body, assembly and testing represent the second largest share of the cost. Marotta has contained some of these costs by changing its supply model. For example, some of the soldering and wire harness work that Marotta does in house for lower volume products has been outsourced to a supplier. “Some of the electronics now come in as a module,” Molesworth says.

To further lower assembly and testing costs while contending with the larger production volumes, Marotta also created a stand-alone production cell that makes use of a Kanban supply system. In that cell, Marotta has invested in assembly systems that may have cost more upfront but will ultimately save time and money. The cell includes computerized assembly benches, for instance. These graphically display the correct assembly procedures and collect assembly data—such as bolt torque—for statistical quality control.

Molesworth cites the cell’s laser marking system as another good example. Its initial cost certainly exceeds the cost of a few nameplates, but the laser-marking machine ultimately saves the cost of buying, storing, and affixing those nameplates. And it avoids the cost of mistaken labeling. “Our focus in this cell has been to spend more on upfront tooling that will lower our production costs,” he says.

And it looks like this approach has paid off. Since the beginning of the project, the company has halved the total cost of making these valves, DiGiovanna reports. And he expects that number to fall even further as the production line starts to ramp up next month.

Machining Capabilities Score Card
Criteria Vendor
0 = No, 1=Yes Mori Seiki A* B* C*
Capability to produce production volumes 1 1 1 1
Machinery must be in place by 10/1/04 1 1 1 1
Technical risk - scale 1-5 with 5 representing the least risk 4 5 5 5
Machine quality - scale 1-5 with 5 representing the best 4 4.5 4.5 4.5
Machine service - scale 1-5 with 5 representing the best 4 4 5 4
Includes programming software 0 1 1 0
Warranty - scale 1-5 with 5 representing the best 5 5 4 5
Time study guarantee 1 1 1 1
Perishable tool consumption - scale 1-5 with 5 representing the best 4 3 3 4
Manpower required - scale 1-5 with 5 representing the least manpower 5 4 4 5
Single point four ports - scale 1-5 with 5 representing the best 5 4 4 5
Hard tooling cost - scale 1-5 with 5 representing the least cost 5 4.5 4.5 2.5
Unattended machining - scale 1-5 with 5 representing the most 5 2.5 2.5 2.5
Machinery cost - scale 1-5 with 5 representing the least cost 5 4 3 4
Score 49 44.5 43.5 44.5
Time study estimate (hrs) 3.7 3.7 3.7 4.25
Length of warranty 2 years 2 years 1 year 2 years
Number of proposed machines 2 3 4 2
Manpower required (FTE) 1 2 2 1
Hours of unattended machining per day 8 50 mins. 40 mins. 1
Adv. Completed parts per day 12 13 13 8
*A: lathe, horizontal mill, and vertical mill
*B: lathe, two horizontal mills, and veritcal mill
*C two turning Machine centers

Non-Cogging Motor Improves Grinding

Introduction

Mating a non-cogging motor with an ultra-precision air-bearing spindle enabled a micro-grinder spindle/indexing system for outside diameter (OD) grinding and profiling of parts with diameters as small as 25 microns. The non-cogging motor eliminated flat spots caused by conventional brushless motor cogging, while improving accuracy, repeatability, and surface finish.

Problem

A customer of Nelson Air Corp. developed a computer-controlled micro-grinding system to grind extremely small parts in a proprietary manufacturing process. The parts are microscopic so the tolerances are an order of magnitude tighter than can be achieved with conventional equipment.

Solution

The ThinGap motorized air-bearing spindle is the key component of the solution. Three Nelson Air motorized air bearing spindles are mounted on ultra-high-resolution positioning stages and the grinding and dressing operation is monitored using a high-powered video microscope with machine vision system. The air-bearing spindles include the grinding, dressing, and tool spindles. The grinding spindle spins a 3-inch diameter diamond-impregnated grinding wheel at speeds up to 13,000 rpm. The dressing spindle uses another abrasive wheel to dress and profile the grinding wheel. A tool spindle with a non-contact optical encoder rated at 8192 counts per revolution holds the part being ground. The tool spindle with encoder is used for grinding part profiles down to 25-micron diameter, which is too small to be seen without a microscope. The tool spindle allows multi-tasking, spinning the part for concentric grinding, and indexing the part to a precise position for grinding flat profiles at different angles. The micro grinder reduces cycle time and part handling.

While the grinding and dressing spindles have a runout tolerance of ±20 µinches, the tool spindle needed to achieve a tolerance of ±2 µinches. "When we first built the tool spindle, we used a conventional brushless dc motor to drive it," says Brad Engel, president of Nelson Air. "But when we looked at the parts ground with the conventional brushless dc motorized air-bearing spindle under a microscope, we saw it had created a part that was not round but had flats where the cogging occurred." Magnetic attraction between the iron in the motor stator and the magnets in the rotor was causing a radial deviation of the spindle as it rotated past each motor pole. When the part in the spindle moved radially, the grinder took a deeper cut and it created a flat. A ThinGap brushless motor achieves zero cogging with a coreless circular copper coil replacing the iron core and wire windings used by conventional brushless motors. The coil is a thin, freestanding composite structure made of copper sheet, glass fiber, and polyimide. Since there are no magnetic materials in the air gap, there would be no magnetic attraction to cause radial motion of the spindle. The ThinGap motor also eliminates cogging due to the moving magnetic field. Generally, most brushless motors (iron core and ironless) rely on a rotating magnetic field, which causes hysteresis losses. ThinGap brushless motors eliminate relative motion between the rotor and housing return path by using a fixed magnetic field with a rotating return path, which results in hysteresis losses that are barely measurable. This eliminates cogging, which enables very precise control. The unique geometry of the ThinGap motor allows the rotor to be mounted directly to the air-bearing shaft, eliminating the use of ball bearings, which would degrade the accuracy of the spindle.

Because the inside and outside surfaces of the coil are exposed to moving air, it quickly dissipates. The maximum stator winding temperature is 100C. By eliminating the iron core, eddy current losses are eliminated and efficiency is improved.