Manufacturers, engineers, architects, and researchers are using the precision, speed, and noncontact processes and achieve more control. Riegl Laser Systems of Horn, Austria, designed its 3-D LMS-Z210 imaging scanner to generate 240,000 laser measurement points within 30 seconds to create highly accurate images of complex structures without the need for conventional surveying. The National Institute of Standards and Technology in Gaithersburg, Maryland, is designing a laser-based system to track the myriad of tools, materials, and equipment on construction sites. Riegl Laser Measurement designed its LMS-Z210 3-D Imaging Scanner to serve in three-dimensional measurement applications that are too complex for traditional theodolites to survey, including shipyards, quarries, vineyards, and crime scenes. Riegl USA expects to begin several projects using the 3-D scanner to continuously monitor bulk material piles in the wood and corn processing industries to improve process management and control.

## Article

Manufacturer's, engineers, architects, and researchers are using the precision, speed, and noncontact properties of lase r beam sensors to improve processes and achieve more control. This is most notable in three laser sensor devices launch ed in the pas t eight months, and in a system still being developed. They incorporate the latest developments in laser technology to enhance their capabilities.

Riegl Laser Systems of Horn, Austria, designed its 3-D LMS-Z210 imaging scanner to generate 240,000 laser measurement points within 30 seconds to create highly accurate images of complex structures without the need for conventional surveying. Engineers at TSI Inc. in St. Paul, Minn., developed the Laservec diode velocimeter to take flow measurements more easily and conveniently than with costlier and bulkier research laser velocimeters.

Honeywell 's Micro Switch division in Freeport, Ill., introduced its convergent beam SVP2 Smart Value photoelectric sensors to provide a small er, more precise light beam to serve the booming electronic assembly market.

The National Institute of Standards and Technology in Gaith ersburg, Md., is designing a laser-based system to track the myriad of tools, mater ials, and equipment on construction sites.

At the dawn of the 21st century, most architects, builders, and engineers continue to rely on the traditional theodolite to survey objects and scenes. Today's theodolites consist of a laser rangefinder mounted on a tilt-and-pan platform that uses two axis encoders to provide range, azimuth, and elevation measurements. Although the theodolites yield accurate results, they are manually operated and relatively slow. In addition, the complexity of large-scale subjects can exceed the capabilities of the theodolite.

Riegl Laser Measurement designed its LMS-Z210 3-D lnnging Scanner to serve in three-dimensional measurement applications that are too complex for traditional theodolites to survey, including shipyards, quarries, vineyards, and crime scenes. Riegl introduced the scanner commercially in Europe last October, and in the United States this past February, through Riegl USA, a subsidiary based in Orlando, Fla.

The new 3-D scanner determines distance by emitting pulses of laser light to a surface along two axes over any field of view, and measuring the time it takes for the energy to return to a sensor. By generating nearly 8,000 such time-of-flight measurements per second, the scanner creates a high-fidelity, three-dimension al point cloud to represent the scene. This point cloud can be processed further to yield more traditional data formats by using standard computer-aided-design software packages, such as VR.ML or DXF.

The LMS-Z210 scanner is tripod-mounted to face the target object. When the device is activated, an electronic pulse generator periodically drives a semiconductor laser diode that emits the transmit beam. A rotating, three-sided mirror directs the range-finder beam over an 80-degree vertical line scan axis. The entire mirror assembly is rotated about the orthogonal frame axis by a high-precision stepper motor to provide a sharply defined 80 x 340- degree horizontal scan over the scene. The company claims the process yields measurement accuracy to within 25 mm at peak measurement rates of 20,000 Hz.

A portion of the outgoing light energy is reflected back from the target surface to the scanner's range-finder receiver lens. The lens focuses the energy to a photo diode receiver to generate an electric signal. A quartz-stabilized clock frequency measures the time interval between the transmitted and received laser pulse. An internal, eightbit parallel data output microprocessor converts the data for display and output as an image on a personal computer or laptop. Equipping a PC with Riegl-Scan software provides data acquisition and real-time display.

The scanner provides surveying data that include range, bearing angle, inclination angle, and the distance between any two points. In addition, the laser scanner is able to color code its images because it can measure the intensity of the reflected optical signal. For example, black means that no laser measurement could be performed because of low reflectivity, signifying that the objects are close to the ground, while blue means images are more than 77 meters away. Operators can adjust range limits, varying from 7 mm to 70 meters, to improve the resolution of color coding.

Bouillon Inc. of Seattle used a single Riegl scanner to measure the dimensions of ship hulls in dry dock. This task previously required the installation of a vast array of reflectors over a ship 's hull to enable measurements to be taken by a theodolite, in what was ordinarily a six-week process. The LMS-Z210 did the job for an estimated cost of$5,000, a fraction of the previous cost of$300,000.

Ferrotron, a German provider of measurement equipment to the steel industry, used an LMS-Z210 scanner to measure the interior dimensions of vessels that transport molten steel. This enables the steel manufacturer to maximize the service life of each vessel at a significant cost saving. Units also have been sold to clients in Austria, Spain, Israel, Australia, and Japan.

Riegl USA expects to begin several projects using the 3-D scanner to continuously monitor bulk material piles in the wood and corn processing industries to improve process management and control. Reality Capture Technologies Inc. in San Fran cisco, a group of engineers working under contract for the National Aeronautics and Space Administration, used the 3-D scanner to capture virtual reality scenes of NASA's Mars Lander vehicle. The scanner eventually may be used to replace the stereoscopic systems currently installed on the Lander.

There are also signs that the LMS-Z210 scanner may be going Hollywood, because an emerging entertainment market for the 3-D scanner is acquiring scenes for the virtual reality program used in making movies.

## One Head is Better than Two

Engineers at TSI Inc., in St. Paul, Minn., combined the laser transmitter and receiver in a single optical head on their Laservec Diode Velocimeter, introduced last September. Like similar devices, the Laservec uses the principle of laser Doppler velocimetry to measure the flow of solids, gases, or liquids. "Briefly, this involves crossing two laser beams to measure velocity at the area they cross," explained Rajan Menon, an aerospace engineer and marketing engineer at TSI.

The Laservec is aimed at the flow diagnostic applications in chemical and pharmaceutical processing, and the electronic cooling and testing in wind and water tunnels that are often served by argon ion laser velocimeters. The latter devices produce the tri-colored beams-green, blue, and violet- needed to differentiate the three axes of velocity, namely up and down, in and out, and side to side.

## Where Did I Put that Trowel

Optics and automation experts continue to extend the application for laser sensors. One promising technology being developed by the National Institute of Standards and Technology is a laser system that will keep track of materials, machines, and tools on construction sites. This project is headed by William C. Stone, leader of the Construction Metrology and Automation Group at NIST, who said the cost of tracking equipment and material that is moved on a daily basis is considerable.

"Several members of my team are members of technical committees for the Construction Industry Institute based in Austin, Texas, an industry/ owner-led consortium of about 100 of the country's largest contractors," Stone said. "At a recent meeting in Houston, where we discussed a typical $100 million oil refinery upgrade, we determined that it cost approximately$500,000 for workers to count materials and keep track of about 10,000 parts."

NIST is using infrared pulsed lidar technology that measures. the time of flight of reflected laser light to calculate distance. "Our research focuses on faster data acquisition rates, higher data density, and wireless communication links that can accommodate the necessary real-time bandwidth," explained Stone.

The lidar instrumentation Stone's team is using emits a beam that contacts a target surface. and captures the reflected light to produce a two-and- one-half dimensional image of the site; that is, the devices obtain information on the X and Y position and the front face range of objects within the imaging instrument's field of view. Line-of-sight restrictions mean the lidars cannot see what is behind a physical object. By scanning, the systems can create a cloud made of up of tens of thousands of data points to form a detailed picture.

"By taking such pictures from many different viewpoints, we can extract important knowledge about the construction site—for example, the cut-and-fill status of landscapers and excavators," Stone said. "In fact, we are developing an autonomous vehicle for the lidar system that can collect this data without the need to have a survey team on the site." In addition to lidars, the NIST researchers are using other sophisticated instruments, including global positioning systems, and a new approach 'developed at NIST known as non-line-of-sight, or NLS, surveying for tracking the location of objects through solid walls. "NLS is based on sending time-synchronized, wideband electromagnetic impulses through the walls to a roving measurement system inside the building," explained Stone.

There are several prototype tracking systems in use, with the field-mobile lidar system, human guided at first, scheduled for deployment this summer. "We will be using that system for a full-scale field test during the excavation and assembly of a \$6 million process plant at NIST," Stone said. "We will be uplinking live status data to the prime building contractor in this case."

According to Stone, commercial applications for the tracking system should open up in the next three to five years. He noted that a pressing need for full commercialization is the development of both field metrology and dynamic construction database communication protocols and standards. To that end, NIST is seeking cooperative research and development partners from the metrology and construction areas to develop database communication protocols and standards.

"These standards will pave the way for third-party software development to leverage the utility of live construction data, much like the computer-aided design data exchange standards being adopted by most software houses," said Stone.