The time: the late-1990s.

The place: a Midwest automotive plant.

Earl, a tug vehicle operator, is pulling a 60-foot long dolly train loaded with panel racks from an outside rack storage area, and is headed toward a rack loading cell. As he approaches an intersection in the plant, Earl notices an unmanned, parts-carrying, automated guided vehicle (AGV) moving perpendicularly in another aisle toward the same intersection.

Earl, hold up!

Instead of stopping, Earl guns his tug truck, hoping he can clear the intersection before the AGV arrives at the crossing.

He doesn’t make it.

The AGV bumps into the side of the dolly train, compressing a hoop-shaped, flexible plastic bumper on the AGV’s front end, which triggers limit switches that bring the AGV safely to a halt. But the AGV bumper, already stressed from several earlier collisions, has been cracked. And as Earl’s dolly train continues through the crossing, one trailer snags the plastic and literally tears the bumper away.

While the AGV itself is OK, its safety bumper is gone, and the vehicle can’t move until a maintenance technician arrives to repair or replace it. Meanwhile, the stalled unit is blocking the aisle, and a production line somewhere in the plant is left waiting for the parts it is carrying.

Different outcome

Fast forward to the present day, at the same automotive plant. Earl is still on the job, and the same scenario occurs.

This time, however, when Earl’s dolly train moves into the intersection, the AGV senses its presence and automatically slows down well ahead of the crossing. The AGV creeps along, though not stopping, until the train clears the intersection, then speeds up again when the way is clear.

Still, just as the AGV arrives at the crossing, another careless worker steps directly in front of the vehicle, this time causing the AGV to stop suddenly, but without any physical contact. No one is hurt, nothing is broken, and once the errant worker passes by, the AGV resumes its motion and is safely on its way.

AGVs get smarter

What makes today’s AGVs smarter about obstacle avoidance than the previous generation? Increasingly, the mechanical bumpers used to ensure safety and negate impact damage on earlier AGVs are being replaced with non-contact, sensor-based collision avoidance systems, such as the Laser Bumper system supplied by Sick Inc., of Minneapolis. These systems rely on optical sensors that scan their surroundings using infrared laser beams, and detect obstacles based on reflected light. They can slow down or stop vehicles as necessary—without making contact—when obstructions enter their protective fields.

FMC Technologies Inc., for one, has been installing Sick Laser Bumpers on most AGVs it manufactures since about 2001, says Mark Longacre, marketing manager for FMC’s Automated Systems Group, in Chalfont, Pa. Prior to that time, there was a question as to whether proximity laser scanning systems such as the Laser Bumper met the American National Standards Institute (ANSI) B56.5 standard governing AGV safety, says Longacre. “Before, the standard specifically called out mechanical bumpers,” he notes. But subsequent revisions now allow for such “electronic bumpers,” Longacre relates.

The Sick Laser Bumpers are significantly more costly than the mechanical, plastic bumpers used earlier, Longacre confirms. Each Laser Bumper can scan an area of 180 or 190 degrees in a single plane, so AGVs typically are equipped with either one or two of the Sick systems, he says—with one looking forward and the second mounted on the rear of the vehicle to avoid back-up accidents. At a cost of $4,000 to $5,000 each for the Laser Bumpers, that can add up to around $10,000 to the price of the AGV. And some complex vehicles use side-mounted and top-mounted scanner units as well, raising the price further, Longacre notes.

AGVs sold by FMC are typically priced the in $60,000 to $150,000 range, and are used in automotive, printing and other industrial applications. FMC claims the largest North American AGV market share, with some 250 units shipped last year, says Longacre, out of a total market of 605 AGVs sold here in 2004.

Quick paybacks

Despite the added cost of the Laser Bumpers, however, Longacre is quick to point out that the laser scanning units provide benefits that enable the technology to quickly pay for itself.

One big advantage is reduced maintenance costs. The older mechanical bumpers were designed to flex upon impact, triggering limit switches that stopped the vehicle. But the bumpers were prone to cracking after several collisions. “Whatever you used—different kinds of plastic, or ...