June 2003 Mechanical Engineering Departments: Tech Focus, Pt. 2

This section was written by
Associate Editor John DeGaspari.

Instrumentation and Control

Tire Check
by Paul Sharke

Machine-vision maker LMI Selcom of Detroit and Commercial Timesharing Inc. of Akron, Ohio, have formed a partnership to bring laser sensors to the sidewall inspection machines used in tire manufacturing.

According to CTI president Ron Symens, at least one U.S. tire manufacturer is using the partnership's latest laser inspection system on a tire uniformity machine to re-inspect tires failed by other, older machines. Two out of three tires that fail inspection end up passing when examined by the lasers, Symens reports. As a result, the tire builder is saving hours in manual inspection time.

According to LMI sales manager Mike Snow, the latest machines use two opposing lasers to measure tire sidewalls for bulges, dents, and depressions. The lasers also identify the location of lettering. As the tire spins between the two sensors at 60 rpm, a spot 200 microns in diameter determines the relative distance from the tire surface to the sensor. Four thousand readings go into generating each tire profile, and as many as five can be made during any given test.

An algorithm developed by CTI can even distinguish the tire surface lying beneath any raised lettering, something that older systems, relying on contact with the wall of the tire, can't do.

The laser sensors are unaffected by surface conditions, such as color or oiliness, Symens said. The company retrofits its laser-based control system to existing tire uniformity machines, Symens explained.

Keeping Water Pure

Water monitoring is typically a manual endeavor, in which water samples are collected in the field and analyzed back at the laboratory. It is an important function that ensures a pure water supply. It is also expensive and time-consuming, and can miss short-duration events, such as the release of pollution or other toxins. Fear of terrorist acts, such as a deliberate release of a toxin into the water supply, has heightened the awareness of real-time monitoring.

A group of researchers at Pennsylvania State University in University Park is working on an aqueous sensor network that can function in real time. The system also gets around a problem of underwater data transmission. Water interferes with radio signals, so Penn State's idea is to use acoustic communication to connect the immersed parts of the system.

An acoustic sensor network being developed at Penn State could help to protect water supplies.

Craig Grimes, an associate professor of electrical engineering and materials science and engineering, is heading the project. He said that the network can deploy many types of sensors. For example, optical sensors could monitor algae, which have a characteristic signature that changes very slowly over time. In the event of a toxin release, that signature would change rapidly, raising a red flag and prompting further investigation.

The network consists of a fleet of nodes submerged in the water. Each node in the network serves two functions. It has a sensor to monitor its environment, and also contains hardware and software that enable it to act as a data router. Beneath the surface, the nodes remain unattached but communicate with each other acoustically.

Grimes said that the network is adaptable. If a unit is lost, the network will keep working.

In the communication scheme, nodes send data to each other acoustically. The acoustic signals are transferred to an uplink node floating on the surface. The uplink node contains the radio transmitter that communicates to a computer off-site. When the network of nodes is first deployed, it sets up an identification tree, in which the uplink node broadcasts a signal containing its identity.

The nodes send their environmental data through the system. They pass data along until all of the information is received by the uplink node. The collected data is then transferred over the air to the central computer, where it can be displayed and evaluated.

The nodes themselves are fairly large, measuring roughly six inches in diameter and a foot long. Each node works on standard D batteries and can operate for months.

The underwater network has been under development for about a year.

Tracking Sticky Chemicals in Tests

Chemicals known as semi-volatiles are present in diesel fuels, pesticides, and herbicides, and also could be used to produce chemical weapons. They are the sort of thing that people need to keep a close eye on, in order to handle them safely. Yet they are difficult to manipulate and to observe in a lab, because they are sticky. They cling to the walls of chemical reaction chambers and sampling lines of chemical analysis equipment, making them hard to measure.

A team of scientists, headed by David Maughan at Pacific Northwest National Laboratory in Richland, Wash., developed a chemical reaction chamber designed to handle volatile and semi-volatile chemicals. The chamber is intended to help experts understand what happens to semi-volatiles when they are exposed to conditions such as intense sunlight or moisture, as well as what they degrade into. The information has important environmental implications, but could also help design better sensors, according to Kathy Probasco, an environmental engineer and senior research scientist who helped to design the chamber.

Pacific Northwest National Laboratory's chemical testing chamber is capable of characterizing volatile and semi-volatile chemicals.

The chamber was developed to simulate what happens to certain chemicals in reactions that take place in the environment. Computer modeling provides a pretty good idea of what goes on, but the chemical chamber could better characterize how chemicals react under tightly controlled conditions, Probasco explained. In addition to characterizing semi-volatile chemicals, the chamber could have wider uses, such as characterizing particles, aerosols, and molds.

The chemical testing chamber consists of two sections arranged side by side. Each section has a volume capacity of about 10 cubic meters. The walls are made of inert Teflon fluorinated ethylene propylene sheet supplied by DuPont Engineering Polymers of Wilmington, Del. The Teflon minimizes the interaction of the chemicals with the walls. Fused silica lines and valves also minimize line losses when sampling chemicals, Probasco said.

The chamber has a group of high-caliber analytical equipment, including gas chromatograph and mass spectrometer, long-path Fourier transform infrared spectrometer, chemoluminescence, particle counting, and acoustic gas analyzer. The chamber is hooked up to a clean air pack that provides an ultrapure environment. It could measure chemical concentrations in parts per trillion. The setup allows flexibility. Chemicals can be mixed, isolated, and compared.

The lab says that its chemical testing chamber could help solve complex atmospheric problems. Some potential applications are testing air for "sick building" syndrome, analyzing airplane cabin air, and chemical and automotive emissions monitoring. The chamber also could be used to improve test chemical sensors by exposing them to very minute amounts of various chemicals. The chemical chamber came on line in October 2002. It is undergoing performance testing, which should be complete by this September, Probasco said.