For a long time, engineers have thought they could improve turbine efficiency by using a rotating heat exchanger. The concept is simple. Start with a circular filter. Expose the top half of the filter to hot exhaust gases. Then spin that hot section down to the inlet duct to preheat incoming air. Instead of just relying on conduction, the system puts the heat in front of the incoming air. The result is a big jump in efficiency, especially for microturbine engines.

The problem is getting it to work. High outlet duct temperatures quickly degrade metals. In fact, most recuperators precool their exhaust stream before it enters the heat exchanger to prolong the unit's operating life.

Ceramics, on the other hand, stand up to high outlet temperatures. Their higher thermal capability enables them to recover and reuse more heat than metals can. Unfortunately, constantly rotating ceramic heat exchangers soon grind away their seals. This allows hot air to escape through the gaps, losing any efficiencies that switching to ceramics might have gained.

A prototype of Wilson TurboPower's heat exchangers uses a rotating ceramic core that boosts efficiency to 97.5 percent while reducing the size of the regenerator.

A Massacusetts Institute of Technology professor emeritus, David Gordon Wilson, believes he has found a way to use ceramics in rotating heat exchangers and has founded a company, Wilson TurboPower Inc. in Woburn, Mass., to commercialize the results. His idea? Instead of rotating the heat exchanger at a constant speed, he lifts the seals about 10 micrometers and turns the circular ceramic core only partway around. The seals then drop down to reseal the heat exchanger.

Lifting the seals solves the wear problem, since the ceramic core doesn't grind against them while it is in motion. To maintain efficiency, though, Wilson has to move the seals and core quickly. Wilson has patented a cam and spring indexed rotation mechanism to rapidly rotate the disk in precise increments. Springs lift the flexible seals for a fraction of a second as the core repositions itself and then snap them shut again. Limiting clearance to a few micrometers allows smooth movement without sacrificing efficiency to leakage.

An indexed cam and spring mechanism rotates the Wilson regenerator 90 degrees at a time.

The core itself consists of a honeycomb with 1,100 open passages per square inch. It is made of cordierite, a ceramic used in automotive catalytic converters. This commercial application makes it widely available and relatively inexpensive. Cordierite also has a low coefficient of expansion, a high working temperature, and low conductivity. Users may be able to coat its surface with catalysts to reduce the emissions of nitrogen oxides, carbon monoxide, and unburned hydrocarbons.

According to Wilson, the ceramic heat exchanger is 97.5 percent efficient, withstands high temperatures that burn away metals, and is much smaller and less expensive to manufacture than conventional units. The company plans to team the heat exchanger with a microturbine of its own design to produce highly efficient power.

When it comes to precision positioning, piezoelectric motors—which measure steps in micrometers—have taken the world by storm. Now they are getting cheaper, as well.

One example of the race to make piezo linear drives more affordable is the tiny system developed by Physik Instrumente GmbH & Co. KG of Karlsruhe/Palmbach, Germany. The company's new P-652 micro piezomotor measures 11.6 x 11.0 x 2.2 millimeters. It reaches velocities of 80 mm a second, has a travel range of 3.2 mm, and costs about $12 each in high volumes.

What really sets it apart from rotary-motor leadscrew systems, however, is its self-locking design. The drive resembles a sled, with a load tray on top and piezo sliders coming down on either side. The sliders fit snugly into grooves on either side of the ceramic stator, which serves as a track.

When they are switched on, the piezo sliders propel the tray down the track. When turned off, they lock the unit in place. The result, the company says, is very high position stability. This eliminates the dither caused by gears and leadscrews in rotary motors as well as the heat dissipation common in conventional linear motors.

PI has optimized the system for moving small objects, such as fibers, optomechanical devices, and microelectromechanical systems rapidly and precisely. The unit runs on 3-volt current and requires no tuning because the driver automatically adjusts to the resonant frequency of the motor.

Engineers often turn to smart relays when they need more function than a relay, timer, or counter can deliver. But why stop there, asks Israel's Unitronics Ltd. The company's new Jazz is a full-function programmable logic controller that lists for $140, less than some smart relays.

According to the company, the controller provides enough features to automate small machines, water and filter systems, packaging lines, and even simple robots. The basic unit combines a PLC and an operator interface. It measures 5.8 inches by 4.6 inches.

On the PLC side, Jazz has six inputs and four outputs. It supports up to 24 kilobytes of virtual ladder logic code. This includes math, store/load, compare, clock, and vector operations, as well as immediate read/write to I/Os, interrupts, and loops.

Unitronics' small Jazz programmable logic controller costs about as much as a smart relay.

The interface supports up to 60 user-designed screens. It displays these screens on two 16-character lines on a backlit LCD display. A full alphanumeric keypad lets operators request data, input data, or respond to instructions or alerts.

The Jazz comes with PC software to program and download PLC ladder logic and screens. An optional kit lets Jazz send alerts and data requests to an operator's cell phone (or respond to cell phone queries for information), a feature useful for distributed facilities. Other options enable it to act as a slave on both MODBUS and SCADA systems.

Jazz has plenty of competition. Smart relays continue to grow smarter and more like true PLCs. PLCs, on the other hand, keep getting cheaper. Yet even in a world of ever more capable inexpensive electronics, Jazz turns in an impressive performance in terms of both function and price.

Most small robot controllers are roughly the same size as a college dorm refrigerator. The Epson Micro PowerDrive RC170 breaks the rule. It is small enough to fit inside an attaché case and weighs in at just under 20 pounds.

Although Epson bills the RC170 as an inexpensive entry-level controller, it still provides full-function, six-axis control. It operates as a stand-alone controller, programmable logic controller slave, or part of a PC-based system. It comes with 16 inputs and eight outputs, but expansion boards can provide up to an additional 128 inputs and 128 outputs.

The RC170 uses Epson's PowerDrive servo technology for path control and high-speed acceleration and deceleration. Epson's RC+ development software provides multitasking for up to 16 simultaneous operations, full SPEL+ programming language, project management, and source-level debugging.

The unit supports the Epson E2 SCARA wall, ceiling, shelf, and tabletop robots. Fully integrated options include Microsoft.NET, DeviceNet, and Profibus. The unit itself is small enough to mount next to a PLC inside a standard cabinet panel.

home | features | breaking news | marketplace | departments | about ME back issues | ASME | site search

© 2006 by The American Society of Mechanical Engineers