"Taking the Mechanical Pulse," Feature Article, May 2004

taking the mechanical pulse

Data acquisition systems go well beyond just counting the numbers.

by Jean Thilmany, Associate Editor

Let's say you work for a company that makes small actuators that control an airplane's wing flaps. Naturally, before you make even one actuator, you need assurance they'll actually work for the life of the plane. You want to know the actuators will still operate after 40,000 flights.

How will you know that in advance? Sure, you could put your actuators in an airplane, and have it take off and land 40,000 times. The more realistic answer is a data acquisition system specifically tailored to get the answers you need.

Railroad clamps have to hold up to the stress of trains rolling over them. Engineering software and hardware help to prevent derailment.

Today, most scientists and engineers use personal computers with ports configured to collect data from their test electronics or prototype designs, like the actuators.

The process is very roughly like getting a physical. Just as a doctor uses a stethoscope to listen to your heart, engineers outfit the prototypes they want to study with sensors connected to a data acquisition system to learn what's going on inside. Software interprets the readings to make the hard numbers digestible. After engineers review the readings, they better understand how to revise their design to meet specifications.

Because data acquisition hardware is coupled with the software, which users can adapt for their own unique applications, data acquisition systems can be configured to fulfill a range of purposes. They're used for test and measurement and for industrial automation, and also can serve as the eyes of a production line or the nose of a sensor.

Check on the Computer

One company, Innoventor Inc. of St. Louis, has worked on the actuator question, as well as on many other engineering problems. The engineering-company-for-hire solves design, process, and manufacturing problems across many disciplines.

Innoventor's engineers have created vision inspection systems and pick-and-pack equipment for customers; they've designed machine control systems and robotics. All the while, they've relied heavily on data acquisition test and measurement hardware and software to create systems specific to a customer's needs, said Sam Hammond, the chief engineer. Data acquisition systems are a check on the confidence that today's computer-aided design and analysis software engender.

Hammond's engineers, for example, might design a part with CAD software and use accompanying software to perform thermal analysis. They analyze the part on the computer, before it's built, to ensure how it will perform once it is produced.

"But you get too confident, sometimes, about the analysis capabilities of the software," Hammond said. "So you want to go back to the hardware to check it."

Though seemingly simply made, a wooden pencil can include a number of defects.

To check analysis results with a data acquisition system, engineers build a design prototype and— if performing, say, thermal analysis— put sensors on the part, then expose it to different temperatures.

The sensors are tied to the data acquisition system that receives information. Accompanying software interprets and analyzes that information.

The thermal data acquired that way should match the software's thermal analysis results, Hammond said. In this way, engineers check hardware against software to make sure everything is performing as expected.

The aerospace company that wanted Innoventor to test its actuators that control wing flaps was essentially asking the engineering services company to run what Rob Humfeld, a senior program engineer, calls an endurance test.

Innoventor's engineers used data acquisition hardware and software to build a system that could run the actuators through 40,000 flights; they programmed the system to imitate the conditions the actuators would meet through the course of all those flights.

"We apply real-world loads as if there's actually wind resistance on the actuators," Humfeld said. "The system actually pushes the flaps in and out, and rotates them as if they're taking off in wind resistance or as if the pilot is flying and using the flaps."

Soliton Automation Ltd. of Coimbatore, India, created a vision system that uses data acquisition software and hardware to sort pencils and automatically reject the defective ones.

The data acquisition system records all the feedback from the actuators. The software graphs actuator performance over 40,000 flights and can highlight information of particular interest to the engineers, such as how the actuators performed in particularly cold temperatures or in strong winds.

Innoventor carried out a similar project for a company that makes mechanical clamps that affix to railroad tracks to keep the tracks on the ties. The clamps, or rail anchors, provide stress relief from the compression that's applied by a passing train.

"You have to know your clamp will perform well or you'll have a derailment," Humfeld said. "We mimicked a real-world situation from a train and slammed an anchor against the tie as if the train were going over that. We recorded that data over a long length of time and used that to revise the clamp."

Humfeld explained, "What we were doing is applying forces to a section of rail that had an anchor clamped to it. The anchor would pound up against the tie as the forces were applied, in the exact same way as an anchor is pounded against the tie as a train passes over it. If the anchor does not hold, it shoots off of the rail. The purpose of the testing was to prove that the anchor would hold. The company wanted to be able to show proof of their product performance to their customers, and also to evaluate new designs before taking them to market."

Perform on the Line

Data acquisition systems can be customized for a testing situation or environment, Humfeld said. His company uses software and hardware from National Instruments of Austin, Texas, to create systems unique to each application. In fact, Humfeld is one of 10 certified architects on LabView, National Instruments' software. He's passed a series of tests to prove his ability to work with the LabView tools and modules.

In addition to acquiring data from prototypes, a system can be configured to measure products on a manufacturing line or measure the line itself. For instance, Hammond and other engineers created a system that became part of the production line for a company that makes oxygen respirators. The system's oxygen bottle rests on a small cart that patients are able to wheel with them.

"Our test system validates that the pump is delivering the right amount of oxygen," Hammond said. "The oxygen monitor has a dial that's set to six different settings. Our test system verifies that the monitor delivers the amount of oxygen that corresponds with the dial setting, within tolerances."

With a patient's life depending on the oxygen, the company has to ensure that the dial is calibrated exactly.

Software also can be configured to act as a vision system on a production line.

Software that accompanies data acquisition hardware interprets and analyzes test results.

Soliton Automation Ltd. of Coimbatore, India, makes automated test and inspection systems. It developed one inspection system to sort through two million pencils per day for its customer, a wooden pencil manufacturer. Because there were pencils of different wood types, textures, and lead colors, the system had to be easily changeable to account for differences among the products. Engineers used a vision development module tied to LabView as well as digital image acquisition hardware to build the system.

To make pencils, a machine sandwiches a long cylinder of graphite between two half-cylinders of wood. Then a saw uniformly cuts them to length. A pencil can include a number of defects. The lead might be missing or the two wooden slats might not be aligned correctly, said Anand Chinnaswamy, an engineer at Soliton Automation. The wood might include defects, too, such as chips or holes.

Before the pencil maker asked Soliton for a vision-based sorting system, the company employed more than 120 people to look over the pencils as they came down the line and remove the ones that didn't pass muster.

"Even though a large number of people were involved, the quality of segregation was far from good," Chinnaswamy said.

For more demanding pencil markets, the lead can't be more than 300 micrometers off center, or the pencil can't be sharpened correctly. Obviously, inspectors couldn't eyeball these parameters. And they certainly aren't able to catch all the faults as they come down the line.

The pencil maker needed to have a visual inspection system that could sort more than 23 pencils per second into different bins, based on the type of defect and where it appeared on the pencil. The automation company created a system made up of two high-resolution, high-speed monochrome line-scan cameras focused at opposite sides of the pencil. They connected the conveyor control to the data acquisition system to coordinate the speed of the conveyor with the inspection system.

A Set of Mechanized Eyes

Application software within a personal computer processed the data acquired from both cameras. The image processing software classifies images as either good or bad, depending on definitions programmed into the software. The software had to be sophisticated enough to detect the different defect types under various conditions with lightning speed. The system synchronizes the different pencil ejectors in the sorting line.

Soliton engineers built the system in 16 weeks, Chinnaswamy said. The customer expects it to pay for itself within one year.

A data acquisition system can act as a visual inspector. But, in at least one case, the system has functioned almost like a nose. Researchers at Argonne National Laboratory in Illinois used data acquisition software and hardware to develop their Smart Sensor Developer Kit, a chemical microsensor that can identify almost any air-bound gaseous chemical.

The researchers developed the sensor because exposure to toxic chemicals accounts for many respiratory illnesses and deaths around the world, said Michael Vogt, the sensor's instrumentation developer. The remedy lies in identifying harmful chemical agents before they can be inhaled. But isolating the harmful chemicals among the multitude of chemicals that make up the Earth's atmosphere is no easy task.

The researchers developed the advanced gas microsensor that uses a chemical analysis technique to identify harmful chemicals. The microsensor comprises measurement software, a miniature sensing element, and specialized hardware.

The system uses solid electrolytes that translate chemical reactions into electrical outputs. The resulting signals, or voltammetric signatures, include information that identifies the chemicals to which the sensor was exposed. The voltammetric readings help scientists detect minute quantities of gaseous chemicals—something that was not previously possible, Vogt said. His team used software from MathWorks of Natick, Mass., and their own specialized hardware to develop their data acquisition system.

Once it is acquired, the data from a device—whether mechanical, electronic, or a mix of the two—can serve a myriad of purposes. And getting the specialized data isn't difficult in this age of easily customizable software and hardware.