November 2006 Mechanical Engineering Departments: Tech Focus, Pt. 2

This section was written by Associate Editor Alan S. Brown.

Technology Focus part 2:
Power Transmission and Motion Control

Batteries That Keep

Reserve batteries typically have a lifespan of five years. Now a new nanotechnology-based design promises to extend that to 15 to 20 years, or possibly even longer. A company developing the technology, mPhase Technologies Inc. of Little Falls, N.J., sees potential uses in remote communications, lab-on-a-chip diagnostic tests, chemical and biological sensors, and radio-frequency identification tags.

The key to long life is a property called superhydrophobicity. This occurs when a drop of electrolyte or other liquid sits on top of a roughened nanostructured surface instead of wetting it. Zap the droplet with a burst of electricity or heat, however, and it wets the surface in a matter of milliseconds.

The company builds its roughened surface from silicon with the same lithographic techniques used to pattern semiconductors. It produces what it calls nanograss, silicon stalks that are several hundred nanometers high and only a few nanometers in diameter. These stalks act as electrodes. The electrolyte sits atop the structure. As long as the two are not in intimate contact, there is no battery drain or corrosion. Once electricity jolts the electrolyte, it wets out the nanograss and begins producing electricity within 1 millisecond.

Another feature of the battery is its scalability. The company says it can make batteries with any number of separate cells. Each cell can turn on as power drains from the previous active cell. This could enable batteries in some applications to last for decades. It is also an ideal technology for applications that need bursts of power. A sensor, for example, may require only a small amount of power in the "monitor" mode, but, once triggered, needs a burst of energy to activate an alarm or send a warning.

The technology scales both large and small. Nanobatteries are small enough to fit on chips and power RFID tags. The same technology could be used in larger, more powerful batteries composed of multiple cells.

A spokesman said the company is also working on a design that uses a honeycomb structure as an alternative to nanograss. Neither has been commercialized yet.

According to mPhase, nanobatteries can take advantage of aqueous and nonaqueous chemistries. They can serve as primary and reserve power sources. The company and Lucent Technologies, which discovered the original chemistry, have applied for a patent on a system that enables the battery to neutralize the electrolyte before disposal.

Understand Multidrives

What's the best way to take advantage of multidrives? ABB Inc. has passed along some information that can help engineers take advantage of multidrives to reduce energy use through precision motor control.

Actually, any adjustable speed drive helps shave energy costs. Motors, after all, consume whatever energy they receive. Matching energy input to the load on the motor is certain to reduce energy use. According to ABB, end users can save 25 to 70 percent of their energy bill by using drives (although a majority of motors continue to chug along without them).

ABB says multidrives are simpler and less costly to implement than multiple individual drives, and enable users to reduce energy use.

Single drives convert ac power to dc, and then invert the dc back to ac output and into a motor. A multidrive is an array of drives that run multiple motors, but receive their dc current from a common dc bus bar connected to a single rectifier.

This setup is cheaper to install. It uses fewer components and less cabling. It runs at lower line currents. The common bus bar provides motor-to-motor braking without the need for a braking chopper or a regenerative supply unit. It eliminates the need for a separate motion control center, and it is more reliable.

According to ABB, multidrives make sense in single or integrated mechanical processes that use several drives or motors. In applications like paper machines, a common power supply simplifies control and safety while improving coordination of individual drive motors. The fast communication of torque and speed signals between the drives helps control the tension in the paper web. Multidrives also make sense where the shafts of the individual drive motors are not tightly coupled.

ABB's own modular multidrives combine a single rectifier with inverters connected in parallel to provide a range of output current.

Find the Right Motor Fast

Thanks to the Internet, engineers can get information on just about every motor made in the world. Many Web sites even aggregate the information, so it's all in one place as long as you don't mind sorting through long lists of specifications to find what you're really looking for.

Now Motion Tech Trends of Inglewood, Calif., has developed a site, www.motioninfo.com, which adds intelligence to this process. The site lets users rank as many as four specifications in order of importance. It then returns results based on how well they meet your criteria.

Motion Tech Trends' president, George Gulalo, explained how it works: "Your most important specifications might be motor diameter, torque, voltage, and motor constant, which is the ratio of torque to power input. The search lets you set minimum and maximum values."

According to Gulalo, "What makes us unique is our search algorithm. We try to assign each search a logic pattern that an intelligent engineer would use to evaluate how well the specifications match his or her targets.

"For example, when the search sees that you've specified torque, it knows that you want a motor close to your minimum so you don't pay for extra torque you don't need," Gulalo said. "If you put down diameter, it knows that smaller is usually better, so it says, 'I'm going to like results better if they are smaller.' "

The search produces a list of motors ranked with a single number that shows how well each result matches up with the search requirements. Clicking on a motor brings up what Gulalo calls a "super datasheet." Its consistent presentation simplifies finding such obscure or footnoted specifications as winding insulation class, encoder counts, heat sink size, or type of enclosure.

Motion Tech also includes several figures of merit, which it calculates based on its online data. They include motor constant, power rate, and power per volume or weight. "These are normalized figures that let you compare one motor to another," said Gulalo. "You can use them to compare motors across different technologies and devices, and see which one gives you the most bang for the buck."

Users can filter results based on motor configuration (assembled, with or without controller, etc.), technology (brushless, linear, etc.), and supplier. The system also lets users e-mail suppliers from within their search results. Suppliers receive search specifications and their product's ranking within the search. "It's not so much a sales lead as an application form," Gulalo said.

Gulalo said the system is just ending its beta testing and will soon go live. He plans to expand the number of motors and related products in his database.