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

POWER TRANSMISSION & MOTION CONTROL

DRIVE ELIMINATES WIND INVERTERS

GUSTS, STORMS, SUDDEN CALMS, AND CHANGES OF WIND DIRECTION KEEP WIND TURBINE ROTORS SPINNING AT VARIABLE RATES. That means their generators speed up and slow down too, producing electricity over a relatively broad range of frequencies. So before those generators can plug into an electrical grid, they must run their current through an inverter to match it to the grid’s frequency.

In fact, every wind turbine carries frequency converters that contribute to their size, weight, complexity, and cost. Now Voith Turbo Wind GmbH & Co. of Crailsheim, Germany, has developed a way to eliminate them entirely and send power directly to the grid.

Voith’s new WinDrive combines a hydrodynamic torque converter with a planetary gear system to convert the rotor’s variable speed into a constant, stable output speed for the generator. The innovative system won the 100,000-euro Hermes Award at this year’s Hanover Fair in Germany.

Eliminating the inverter obviously eliminates the cost of the unit. It generates several secondary benefits as well. The WinDrive system decouples the rotor from the generator, damping vibration and shock in the drive-line. This reduces loads and lets engineers downsize the wind turbine’s generator and other components. Reducing weight and size lowers not only the cost of the wind turbine, but also the cost of its installation.

WinDrive starts with a planetary gear situated between the rotor and the generator. Most of the power generated by the rotor goes into the planetary gear. WinDrive diverts some of that power to the hydrodynamic torque converter. It then superimposes that power back into the planetary gear in order to maintain a consistent speed.

By combining the continuously adjusting, stepless torque converter with the planetary gear, Voith can produce an almost unlimited range of conversion ratios between input and output speed. This flexibility enables the wind turbine to operate at peak efficiency for a given wind speed, yet always maintain the same rotational output speed.

Wind power drives a planetary gear (red) and torque converter (yellow), which superimposes power back on the gear (gray) to produce steady speeds.

Actually, most wind turbines try to do this now by adjusting the pitch of their blades. This often forces the units to run at less than optimal rates, and the process is slow. “The torque converter works 10 times faster than blade pitch adjustments,” explained Uwe Reimesch, general sales manager at Voith Turbo. “It reacts to sudden gusts just by adjusting the oil’s angle of flow.”

The technology itself is similar to the planetary gear/torque converter system used in gas compressors for the past 30 years, but the start-and-stop nature of wind power makes greater demands on drive fatigue life and efficiency.

Voith has several projects under way that suggest it is winning this war. The most impressive, said Reimesch, is a wind turbine installed for Barrick Gold in Veladero, Argentina, 4,300 meters above sea level in the Andes Mountains. “The power electronics in the inverters start to fail at that height, and the air pressure is so low that you need huge coolers to keep them running,” Reimesch said.

The turbine was installed in December 2007. Through January 2009, it had run for 2,400 hours synchronized with the grid, and continues to power the mine’s electrical system today.

SMALL ACTUATOR PACKS PUNCH

The new MLA Series mini-actuator from PBC Linear of Rockford, Ill., brings greater load capacity and lots of installation options to small, screw-driven linear actuators used in laboratory and small-scale automation.

The actuator housing is just 28 millimeters x 32 millimeters (just over 1 inch on a side) and up to 650 millimeters (26 inches) long. Yet when outfit with two linear guides, one on each side, it can handle loads up to 890 newtons (200 pound-force).

The optional linear guides are the key to MLA’s strength. Most actuators this small consist of an extruded aluminum housing holding the lead screw. The screw both supports and drives the carriage, which carries the load, as it runs along the length of the screw.

For heavier loads, PBC adds one or two guide rails. The carriage runs along these guides supported by an “L” or “U” bracket.  The U bracket, for example, runs on two guide rails the way a railroad car rests on the two rails of its track. This provides the extra support needed to carry heavy loads.

Most small actuators cannot use guide rails and brackets. “This is because small variations in the thickness of the as-extruded housing’s walls would cause the brackets to bind,” said PBC senior system design engineer Kevin Bischel.

“To prevent binding, we simultaneously machine the inside and outside of all four sides of the actuator’s extruded aluminum housing. This enables us to hold the outside surfaces and right angles to closer tolerances, so we can attach guide rails to the housing without causing binding,” Bischel said.

While dual guide rails are often used in industrial systems, Bischel said this is the first time he knows of its being done for such a small actuator.

PBC also machines the interior of the housing with dovetail mounts. The carriage’s profile slots into the dovetails, which position the part during assembly and keep it aligned during operation.

MLA pairs with either standard stepper or servo drive motors, as well as a variety of gear reducers and screw sizes. Users can mount the housing from the bottom (straight or upside down) or from either side. PBC offers seal strips for contaminated and clean-room environments. By combining several mini-actuators, users can create x-y-z gantries and other complex configurations.

PBC designed the MLA Series for medical and life science applications, such as pick-and-place devices used to sort and move samples during automated laboratory testing. Another potential application is automated movement of small parts in manufacturing. “You can use it anywhere you need a lot of load capacity in a small package,” Bischel said.

HARVEST THOSE GOOD VIBRATIONS

ENERGY HARVESTING HAS BECOME THE TALK OF THE MANUFACTURING WORLD, AND NO WONDER. It’s like getting something for nothing. Using small devices to convert heat or vibration into electrical energy lets engineers install wireless sensors without running cable or worrying about charging or changing batteries. Energy harvesters could power machinery health monitoring, remote sensing, and active RFID tags, as well as replace bundled wiring in airframe and motor vehicle sensors and actuators.

One of the slickest commercial packages around is the Joule-Thief from AdaptivEnergy LLC of Hampton, Virginia. The company claims the small, self-contained device—just over 3 cubic inches and only 1.6 ounces—has the highest output per unit volume or weight of any commercially available vibration energy harvester.

AdaptivEnergy designed the module to produce an industry-standard 3.6 volt direct current output by optimizing its frequency response for devices running on 50/60 and 100/120 hertz alternating current. It says it can optimize the Joule-Thief for custom frequencies, and it also sells a model designed to harvest energy from random vibrations.

Energy harvesters let engineers run sensors without batteries or cables.

According to vice president/general manager Tim Michalski, Joule-Thief works even with machines that vibrate at amplitudes below the threshold of human perception. “We’ve tried this successfully on machines where you couldn’t feel the vibrations, where other energy harvesters produced little or no current,” Michalski said.

The key to the device’s sensitivity and longevity (150,000 hours mean time between failures) is its ruggedized, laminated piezoelectric power generator. Piezoelectrics are materials that convert vibration to electricity. This one is based on lead zirconate titanate (PZT), a ceramic piezoelectric material that has been used in sensors for decades.

The problem with piezoceramics is that, like all ceramics, they are brittle. AdaptivEnergy’s response was to prestress the ceramic through a process that laminates it onto a plastic substrate. Prestressing makes the ceramic tougher, so it handles greater strains and fails less often during use. The lamination process is scalable, making it economical to produce tens of thousands of prestressed piezoelectric sensing elements at a time.

The Joule-Thief consists of a laminated piezoelectric cantilever with a proof mass on the end that acts like a swimmer preparing to dive off a board. The added mass causes the vibration to apply greater force on the cantilever. That force produces an alternating current that is converted into direct current. The energy is stored in a battery or capacitor, which discharges periodically to provide the power needed for small sensors and communications devices.

INTEGRATION REDUCES CARRIAGE COSTS

The current recession has turned the normal focus on efficiency into an obsession. Engineers are being asked to deliver more value while reducing costs, and often that involves redesigning traditional products to work more efficiently.

One example is the new P3 linear motor actuator from Germany’s Schneeberger. The P3, which reaches speeds of up to 5 meters per second and accelerations of 10 gravities, was built for automation, packaging, paper converting, and semiconductor manufacturing. It comes in strokes of 125 millimeters to 1 meter long.

To improve efficiency, one aspect that the designers of the P3 paid particular attention to was thermal performance. According to Schneeberger’s Glenn Bythrow, heat buildup is often a limiting factor in linear motor operation. “For the P3, we mold the motor coil into the carrier assembly instead of bolting it onto a mating surface,” he said. “This improves heat transfer and thermal performance, and lets us get more force out of a smaller motor.”

Smaller motors cost less and use less power, a double savings. The integrated design also stiffens the carriage. Since the linear motor is made without iron to eliminate cogging (the slight catch as it moves between magnetic poles), the carriage moves smoothly at constant velocities, even at low speeds.

To provide better value, Schneeberger gives engineers a choice of P3 encoders for positioning. “Most people choose optical encoders because of their high resolution, since they have accuracies down to 0.1 microns,” said Bythrow.

For those who do not need such high resolutions, Schneeberger also offers magnetic encoders, which cost substantially less. Magnetic encoders deliver resolutions down to 1 micron and provide clean signals even in difficult environments.

MAGNETIC COMPRESSOR CUTS ENERGY USES

When vendors talk about oil-free compressors, they usually mean systems that segregate motors and gears (which use lubricants) from air-moving equipment such as rotary screw and centrifugal compressor assemblies. CompAir UK Ltd., of Redditch, England, has a very different definition. It has developed a compressor that has only one moving part and does away with all lubricants, gearboxes, and contacting components.

CompAir’s new Quantima compressor instead relies on magnetic fields. Using magnetic bearings, it levitates and stabilizes its direct drive centrifugal compression assembly while spinning its impellers at up to 60,000 revolutions per minute. The magnetic design eliminates the possibility of engine lubricants contaminating process air.

More importantly, claims Comp-Air, Quantima uses up to 25 percent less energy than comparable systems. It does this by eliminating the gearbox, a well known energy parasite, as well as other contact parts. Instead, it uses a variable speed drive to adjust motor speed to match demand. Quantima also has low off-load power consumption, just 2.5 percent of full power (equal to 7.5 kilowatts for a 300-kilowatt compressor).

According to CompAir key account manager Kai Doth, energy accounts for 80 percent of the money spent on a compressor over its lifetime. A 25 percent reduction in that amount is equivalent to reducing the total compressor spend by 20 percent. It is also enough to slash CO₂ emissions by 1,920 metric tons over ten years.

Quantima is about half the weight and size of comparable conventional compressors. It is also much quieter. A 300-kilowatt Quantima produces only 69 dBA of noise, compared with 74 dBA for most similarly sized compressors, Doth noted. Since decibels are measured logarithmically, this is a big enough difference to enable companies to locate Quantima near its point of use, rather than in a separate building. In fact, CompAir claims Quantima is so quiet, operators can work near it without ear protection.

The company has several compressors in operation. Continental AG’s Regensburg, Germany, factory installed a unit to expand air capacity. Hochwald Nahrungsmittelwerke GmbH, a German dairy cooperative, opted for the oil-free design to meet international food quality standards and reduce energy use. CompAir also says an unnamed automaker has replaced two older piston compressors with a new Quantima unit in its paint shop and other factory sections.

Quantima comes with its own touch screen controller and predictive maintenance software. It was one of five semifinalists for this year’s Hermes Award for industrial innovation.

DRIVES INTEGRATE CONTROL AND ENERGY SAVINGS

When German industrial giant Siemens AG introduced its Sinamics motor drive/motion controllers, it wanted to create cost-effective modular products that engineers could mix and match for both the simplest and the most complicated machines. It has certainly gone a long way toward reaching that goal.

Sinamics’ big driver remains energy savings. This is especially true for pumps, fans, and compressors. Motor drive frequency converters can reduce energy use in those applications up to 70 percent. 

That is because their motors typically run full out and throttles and valves adjust flow. This often sets off a cascade of other energy-wasting events, such as pressure surges, eddies, vibration, and temperature swings in pipes. Motor drives solve the problem a better way: Instead of running full out and throttling back, they continuously match motor speed with actual demand, so the motors use less energy.

The drive system also can recover energy for reuse. This is particularly effective in multiaxis machinery. “If one motor is braking, then that motor works like a generator,” Siemens marketer Sigmund Förstl explained.

“Normally, that energy is changed to heat by a resistor. Now we capture the energy in a capacitor and supply it to the next motor. The controller analyzes when the power is needed, then starts an axis a little earlier so it can ramp up more slowly and with less power,” he said. (Siemens previously used a flywheel to capture energy, but decided a capacitor was more cost-effective.)

Siemens also integrates safety functions into Sinamics drives. Most come with an embedded safe torque off function and safety-limited speed.

The company’s integration strategy is atypical. In the 1990s, many competitors exited or deemphasized their controls business because they feared hardware was becoming a low-cost commodity. They sought to differentiate their offerings through easier and more intelligent software.

Siemens improved its software, to be sure, but it also found a way to deliver more value through its hardware. It did this by standardizing its product range so engineers spent less time and money learning, programming, commissioning, stocking, and repairing Siemens products.

Combining drives with controllers, for example, reduces the cost and the amount of wiring associated with the two systems, Förstl said. Modular components that let users match power output and controller sophistication to their specific needs provide more customizable solutions while simplifying spare parts management. Siemens also uses a single set of software tools to size, configure, commission, test, and wire its products, so engineers only have to learn one set of interfaces.

The result, Siemens asserts, is that Sinamics saves engineering time and money, especially for large companies that want a single, modular, standardized solution that works across a broad range of products.