One of the most revolutionary concepts in machine control technology became reality recently at the site of a new Wal-Mart Supercenter in Rogers, Ark. A Gomaco GT 3600 curb machine was modified to operate without a string line for 3-D guidance.

Proper curbing placement is critical for the success of paving operations that follow and the advantages of automated curb construction are obvious. Curbing directs storm water drainage, provides grade control for subsequent surfacing and strengthens the edge of asphalt pavements. Preparing for machine-placed curb has always been a time-consuming task. Offset staking and string line placements are frequently sources of human error. Overruns of base material and water ponding are just two of the problems that can result from misplaced curb.

Four years ago, two companies joined their fields of expertise to develop new machine control solutions for asphalt and concrete paving applications. Sauer-Danfoss was in the business of developing and designing electro-hydraulic operating systems for construction equipment. Its primary customers were OEMs like Gomaco. Topcon, a worldwide leader and innovator in precision positioning technology, was developing and manufacturing machine control systems based on laser, sonic and GPS guidance technologies. Its primary customers were after-market purchasers, primarily contractors. The fit was a natural and a joint venture agreement between the two companies created TSD Integrated Controls.

Crossland Construction Company, Inc., based in Columbus, Kan., is the one of the most prominent general contractors in the Midwest. They have numerous projects under way in the Bentonville-Rogers area of Arkansas. Crossland maintains their own site work equipment and personnel in order to retain control over preparatory phases of their building projects. They also perform their own site concrete construction, but subcontract asphalt paving operations. With literally miles of curb under contract on all their projects, they were looking for ways to reduce their manpower costs for curb staking and string line setting. Working with local Topcon dealer Ozark Laser and Shoring, Crossland arranged a demonstration of TSD's automated control system on their Gomaco GT 3600 curb machine. But how can a curb machine be modified to work without a string line?

The conversion is not very complicated. First, software programs created by TSD are uploaded into the control system of the GT 3600, enabling it to respond to Topcon's 3D-LPS machine control components. Next, a two-piece receiver mast is attached to a central mounting point on the frame of the curb machine. On this particular machine, the feed conveyor had to be repositioned slightly to prevent contact with the mast. The mast is plumbed and mounting bolts are tightened securely. A Topcon LS-2000 receiver is then mounted on top of the mast and connected to the GT 3600's operating system by cable.

Topcon's 3D-LPS system provides 3-D guidance to the GT 3600. A Topcon GRT-2000 laser-tracking total station is set up at a control point on the perimeter of the project site. A computer file containing horizontal and vertical data for the proposed curb is loaded into the field controller attached to the instrument. The GRT-2000 automatically tracks the position of the LS-2000 receiver on the curb machine. Laser signals communicate curb location and elevation data to the GT 3600.

The GT 3600, as manufactured, is equipped with a cross slope sensor. Since the 3D-LPS guidance system needs to know the exact 3-D orientation of the machine, a long slope sensor is required. This additional component is mounted to the receiver mast with a bracket and attached with another cable to the machine's operating system.

Once these components are in place, a few adjustments are necessary. The machine is leveled, and the long slope sensor is set accordingly. Topcon's Pocket 3-D software, which controls the laser guidance system, needs to know where the LS-2000 sensor is in relation to the machine and curb mold. These measurements are taken, entered into the field computer and the system is ready to go.

Mike Olson, senior engineer for TSD, led the installation and made the electronic modifications to the GT 3600. Doug Comstock, field service representative for Gomaco, assisted Mike and installed the hardware components. Brian Lingobardo, Topcon support manager, Technical Service Group, handled the total station and field computer operation. Ryan Zweerink, owner of Ozark Laser and Shoring, the Topcon distributor for the area, assisted the setup crew. Take-off Professionals, located in Peoria, Ariz., prepared the specialized curb data file loaded into the field computer.

By the end of the first day, the GT 3600 was ready to go. Several trial runs without concrete were made that evening to see how the machine tracked.

Though the next morning brought gloom, overcast skies and the possibility of rain, Matt O'Brien, head of Crossland's concrete operations, confidently set up 30 yards of concrete for late afternoon. Beginning at 7 a.m., systems were checked and double-checked. After lunch, the GT 3600 was sent on a trimmer run down a long straight section of curb that rolled up and down to low points for drainage release. The completely unmanned machine tracked perfectly to the end of the parking lot while everyone went about other business.

Three concrete trucks and the finishing crew arrived at 4 p.m. The overcast skies and fall's early sunset provided just enough daylight to get started. The last truck poured out under the headlights of pickups and cars. The perfectly positioned curb that was created that day is the signature of innovative technology.

O'Brien was pleased with the results. "The performance exceeded our expectations," he said. The demonstration convinced Crossland of the productivity they could expect from the system and their purchase decision is pending.

The Gomaco GT 3600 used for the demo is actually the third machine in existence to be modified for 3D-LPS control. The first machine ran at Topcon's test site in California. The second belongs to a contractor in Nashville. With the extensive work that lies ahead for Crossland, their GT 3600 will likely be the most intensively used 3D-LPS machine in the nation.