Not Your Grandfather’s Conveyor Line!

As I sit, staring out of this airport window at a baggage handler unloading the belly of a not-so-jumbo jet, I’m struck by how woefully behind the times that baggage handling system really is. We have a human manually picking packages off a mobile conveyor belt that he earlier towed up to the jet with a little riding tractor.

By C.G. Masi, Control Engineering November 1, 2007

Sidebars: Robotic handlers cross lines Automatically guided vehicles Smart conveyors add flexibility

As I sit, staring out of this airport window at a baggage handler unloading the belly of a not-so-jumbo jet, I’m struck by how woefully behind the times that baggage handling system really is. We have a human manually picking packages off a mobile conveyor belt that he earlier towed up to the jet with a little riding tractor. He also towed along two or three double decker baggage trailers, like a little toy train from Disneyland. This equipment, developed during the 1950s, is motion technology with which your grandfather would have been familiar.

I compare this with technology I saw at Siemens’ airport technology development facility in Nuremberg, Germany, last year, and similar systems I’ve seen demonstrated at half a dozen places since. Material handling technology already in use in many facilities around the U.S. and around the world makes this stuff I’ve been watching bring to mind the comment by Mr. Spock in an early Star Trek episode about “stone knives and bear skins.”

The word “mechatronic” is smashing its way into material handling technology. The material-handling-systems that vendors now are developing are fast, powerful and, above all, highly automated. They come in all sizes and shapes, run on wheels, tracks, rollers, and even magnetic fields. No matter what the task, you can probably find something that will do it faster, safer, more reliably, and less expensively than anything guided by a human hand.

These technologies fall into three broad categories: robots, automatically guided vehicles (AGVs), and smart conveyors. Most material handling applications are hybrid systems whose designers deploy just the right technology to do the job at just the right place. The trick, therefore, is matching the technology to the job.

(Please scroll down for table and more article.)



Articulated arm
* Highly adaptable * Can manipulate work * Coordination possible * Multiaxis * Reconfigurable
* Fixed mounting * Slow * Limited weight capacity * Low throughput * No mobility

* Multiaxis * Very fast * Reconfigurable
* Limited weight capacity * No mobility * Limited throughput

* Highly adaptable * Multiaxis * Fast * Unlimited capacity
* Complex * Hard to reconfigure * Low throughput * No mobility

Automatically Guided Vehicles

* Highly mobile * Fast * Long distance * Large capacity * Unlimited paths
* Potential safety hazard * Expensive

* Highly mobile * Very large capacity * Provides work surface * Long distance * Unlimited paths
* Provides no grippers * Expensive * Must stay with load * Limited adaptability

* Unlimited capacity * Highly mobile * Inexpensive trailers * Unlimited paths * Long distances
* Provides no grippers * Limited adaptability

Smart conveyor

* Very fast * High throughput
* Hard to reconfigure * Provides no grippers * Limited weight capacity * Limited fixed paths * Limited distance

Author Information

C.G. Masi, senior editor, for machine control topics, is at .

Robotic handlers cross lines

Robots are an excellent choice to transfer loads from one vehicle to another. For example, when moving items from a conveyor to a pallet, or making up an order on a pallet from items picked from several other pallets. “Robots are a fantastic piece of equipment to sit at one spot and combine available products into one individual load,” says Yves Gazin, vice president of solutions and product support at Egemin Automation.

“We typically use robots when a change in orientation of a specific package is required,” reports Paul Moore, director of systems sales for FKI Logistex. “For direct transportation, a robot is not a cost-effective means for moving from one point to another point, but if you do need to orient the product, pick the product up off a conveyor and place it into a machine, pull it out of a machine, or put it into a case, the robot is very good.”

Robots start with the classic articulated arm models we’re used to seeing around automotive assembly lines. While these have grown eyes, brains and the ability to work together, even more versatile are free-form systems whose structures and dynamics follow exactly the needs of the task at hand. Most often, those structures take the shape of a gantry made up of two trundles or “bogeys” moving on parallel rails, which support a large crosswise “bridge” carrying a third bogey providing the robot’s second degree of freedom. A hoist or crane dangling from the bridge bogey provides the third spatial degree of freedom.

Moore also points out that in the last five years, there has been a trend to extend robots’ reach by mounting an articulated-arm robot on a servo-driven track so it can reach an extended number of positions. An example would be for tending multiple machines or for palletizing to multiple positions, which wouldn’t fit in the traditional robot work envelope.

Delta robots have a spider-like structure that uses clever geometry to provide stiffness with little mass, making them light and fast. They still have limited spatial range and payload capacity, but move those loads within that envelope with surprising speed and agility.

Automatically guided vehicles

Automatically guided vehicles (AGVs) are self-propelled and self-guided vehicles that can pick up, carry, or tow their loads from where they are to where they need to be. To perform these functions, an AGV needs considerable on-board intelligence and significant sensory capability. Of course, since AGVs are, by definition, free-roaming, they present significantly greater safety issues than other material handling technologies. Much of the AGV’s sensory capability and intelligence is devoted to mitigating that risk.

“There’s a clear distinction,” says Yves Gazin, vice president of solutions and product support at Egemin Automation, “between two main AGV types: the classic forklift style (whether it has forks or clamps, multiple forks, single forks… basically anything that a forklift operator would drive); and more of a flatbed cart style. The big difference between them is that the former can pick the load up from the floor, and the other one can’t.”

Space then becomes the defining factor. How far does the load have to move? If loads have to move long distances (hundreds of feet), some kind of automated vehicle is usually the most economical means of transport. However, it is unlikely to be cost effective to have an AGV pick up a load to move 15 feet. For that, a conveyor makes more sense.

Another important consideration is time. How long does the load stay put when it reaches its destination? If it’s going right onto a truck for shipping, then an AGV fork lift is likely the best choice. If, however, the load will sit for a while in a warehouse, you want to drop it and get the AGV out of there. In such a situation, an AGV fork lift might or might not be the right choice depending on how much material is in the load.

Fork lifts, whether piloted by a human or a computer, can only carry a limited amount at one time, even if that amount is fairly large. When a lot of stuff has to go somewhere, then sit for a significant amount of time, the best choice might be to use an AGV tow vehicle. An amount of material that no reasonably sized fork lift could carry can be loaded onto a flatbed trailer, then towed by an AGV.

More significantly, trailers can be coupled in tandem like cars in a train, then towed by the AGV. Trailers may be more expensive than fork lifts, but they cost much less than powered vehicles—especially powered vehicles with brains.

When stuff needs to move often from station to station while staying at each station a relatively short time, Brian Stewart, senior vice president and chief operating officer of the Jervis B. Webb Co. cites an entirely different concept: “The SmartCart is an extremely low-cost, highly-reliable and very flexible method for delivery or manufacturing.” Essentially, one of these carts is an AGV tug with a load-supporting frame fitted over it. The tug stays with the frame and load to form a self-mobile unit.

“Typically,” says Paul Moore, director of systems sales for FKI Logistex, “we find uses for guided vehicles in our integrated systems where there are heavy loads that need to be transported over long distances and/or to multiple positions. It’s a math calculation to determine what’s the most cost-effective. If it’s a very infrequent move over long distance, running AGVs makes tremendous economic sense.”

Smart conveyors add flexibility

Smart conveyors seldom have belts anymore. Typically they drive loads via computer-controlled rollers that can speed up, slow down, and even steer packages to arrive at the right place at the right time.

“When moving material over very short distances and with extremely high throughput,” says Yves Gazin, vice president of solutions and product support at Egemin Automation, “it is much better to use a conveyor system. The congestion you would create with a number of vehicles moving back and forth make AGVs impractical. If the distance becomes too small, on the other hand, you’re not going to do it with forklift, but with a piece of conveyor.”

Similarly, installing a robot just to move stuff from A to B does not make economic sense if the distance is beyond its movement range. You may have a robotic handler at each end of the conveyor, but not just to traverse the space between.

“In the last five years,” says Paul Moore, director of systems sales for FKI Logistex, “we’ve seen a huge growth in smart conveyors. These conveyors are typically powered with 24-V rollers, and are very flexible.”

There are several reasons customers like to use them. When humans are present, such roller conveyors are inherently safer. There are a series of small motors built into roller sets laid out on three-foot centers. One roller is driven and the others slave off it. The roller sets’ motors are separately energized under command of a local controller.

This system provides a number of advantages. Safety is enhanced by having a number of relatively small independent drive motors, rather than one huge monster pushing the whole conveyor. Should a human tangle with the conveyor, the small motor driving just one roller set can do relatively little damage. The system can save energy by driving only when there is something to drive. In between individual loads, the rollers in a section can be powered down to save energy.

Another advantage is easier reconfigurability. When a conveyor is built with one large belt, that assembly must run a certain distance, and modifying the route by, say, introducing a new divert point in the middle, would require building an entirely new conveyor. With short powered-roller sections, it is possible to just yank one section out and install the diverting equipment.

Maintenance is easier because a mechanical or electrical failure only involves one small section, which is easier to remove and replace than an entire conveyor.

Finally, these computer-controlled conveyor lines allow on-the-fly package diversion. It is now possible to combine and split material flows, sending different items to different destinations and bringing items from different sources together for one destination.

What makes this possible is the ability to individually identify and track packages combined with sophisticated warehouse management software.

“One of the new products we’ve recently introduced,” says FKI’s Moore, “is a software package that allows us to space cases very closely going into a sorter. We can merge from multiple lines into a stream feeding a high-speed sorter at up to 400 cases per minute.”

Try THAT with a belt conveyor!

“With lean manufacturing everyone’s initiative, everyone wants to reduce the number of conveyors, but they still remain the most cost-effective way to transfer product from one point to another point,” Moore says.