Laser guided vehicles (LGVs) area a flexible automated guided vehicle (AGV) solution. LGVs are a more flexible solution than older forms of AGVs that follows markers or wires in the floor or where navigation is based on following a magnet crumb trail. LGVs can move through a facility on multiple paths and the paths can change as needed. This article explains how a “typical” LGV implementation would take and the steps involved.
Different suppliers of LGVs have a somewhat different approach to laser navigation. At JBT, “LGVs have a navigational laser that is typically elevated 10 to 15 feet in the air, spinning at several revolutions per second,” Mark Longacre explains. Mr. Longacre is an Applications Engineering Manager at JBT Corporation. The range of the laser, 30 meters, roughly 100 feet, is an important factor because it limits the infrastructure required.
Each vehicle has one (or more) of these rotating laser sensors that interact with targets (reflective strips of tape) mounted along the path. The laser sensors receive the reflected signals and use that data to triangulate the vehicle’s position. At JBT, the navigation algorithms recalculate the vehicle position 40 times per second, which means path corrections stay small. The virtual guide paths are created and changed in Layout Wizard software.
In JBT implementations, the targets are usually installed on columns, that would alternate left and right every 50 feet or so. These targets have a center that is highly reflective center surrounded by a quarter inch border that is black. The targets need to be precisely surveyed in a facility. The survey locates the left most edge of the reflective surface and positions it on a CAD drawing with a precision that is usually within one millimeter of what is shown on the drawing. The survey is done using a transit survey tool, a theodolite. This is a precision optical instrument for measurement you may have seen being used surveying properties or at construction sites.
The survey might be done in four hours if the LGV was going to travel a relatively short distance on a simple loop. But in a big facility, which might be as large as two square miles, the survey will probably take about two weeks.
John Clark, Product Marketing for Mobile Automation in North America at Dematic, agrees that surveys for an “average” project probably is about two weeks. He points out, however, that the AGV companies are all busy. Once an AGV is ordered, it might take months to be delivered. At best, you would be looking at the delivery in a matter of several weeks. The initial survey can be done while the vehicles are being built.
Could a customer’s drawings be used? Mr. Clark says Dematic has learned they need to do their own survey. The facility may have been changed in some manner and that may not be reflected in the current CAD on file.
In addition to doing a target survey, a survey of the wireless infrastructure is also done. Reliable wireless coverage allows constant communication between the vehicles and the fleet management software. Reliable wireless coverage also is needed if the vehicle is doing automated barcode scans or is integrated to a warehouse management system.
With some LGV suppliers, a second survey may be done to validate the location of the initial targets. This is particularly advisable if an LGV is navigating not just based on XY coordinates but needs Z coordinates to be able to accurately place pallets in slots in a rack, or on top of each other, or on top of a conveyor. In locations where this kind of precision is needed, the number of targets needed increases. In a big warehouse, where there might be as many as 2000 locations where pallets could be placed, this kind of survey could take as long as two months.
The final step is integration testing. Here the vehicles are given a task and the project personnel ensure that the vehicle can go from an origin to a destination accurately. This testing can take from one to two days to three to four weeks depending on the number of paths and the difficulty involved in integrating to a warehouse management system.
So, across all steps, a customer is looking at an installation that will take some months.
The payback from any form of AGV comes in the form of labor savings that result from less time wasted in traveling across a facility. Warehouses and factories in the wealthy Western world are finding it increasingly difficult to hire workers. That is the primary reason the AGV companies are so busy.
LGVs are a form of robots, but an older form that does not get as much publicity. It is a reliable technology. And, despite its age, it remains a very cool technology.