Power-and-free conveyors. Enclosed-track conveyors. Heavy-duty roller conveyors. Tow-line conveyors. Skid conveyors. Automatic guided vehicles (AGVs). Automatic electrified monorails (AEMs). Automated storage and retrieval systems (AS/RS)...You get the picture.
All of these systems are provided to industry by Jervis B. Webb Co. (Farmington Hills, MI), which has been at it since 1919 when an engineer, who is the namesake of the company, developed the forged rivetless chain conveyor.
Given that the company offers a vast assortment of this enabling material handling technology, the natural question to have answered from their perspective is, simply, "What's new?"
Robert A. Pierson, vp of Sales & Marketing, provides an answer that is somewhat surprising: "Not a whole lot of big different things." Indeed, with the exceptions of such things as controls that make devices like AGVs and AEMs a whole lot smarter (speaking of the former, Pierson remarks, "Originally, they were dumb vehicles") and mechanical modifications, such as the replacement of metal chain with rubber belts on belt-skid conveyor systems (Pierson ticks off the benefits: quieter, cleaner as no lube is necessary, and potentially requiring less maintenance), things pretty much have stayed the same. There are improvements, not revolutions.
Peaks & Valleys
Pierson explains that what tends to occur is that there are peaks and valleys of interest related to specific approaches to material handling. Some of it is personal, as when a plant gets a new manager who comes from a site where things were done with, say, overhead conveyors, and so a switch is made. Some of it is organizational, as when there is a tendency to stick with the status quo and not risk making a switch. Some of it is technological, as when there is a comparatively new technology that seems most appealing, such as was the case with AGVs in the 1980s. Some of it is cyclical, as unit-load AS/RS being more popular across all industries (not just automotive) 10 years ago as compared with today.
One interesting aspect of this is that fundamentally, the various types of material handling equipment tend not to go away. That is, there is no wholesale replacement of one type of equipment; there is no dominant approach significantly that takes over (think, for example, of the replacement of relays by programmable controllers). There tends to be coexistence. Which is, Pierson admits, one of the reasons why Webb is a full-line manufacturer of equipment.
"There are at least six ways to assemble a car with different systems," Pierson notes. "No one can say that this is the best way to do it."
"You can walk a vehicle from when it is flat steel and follow it until it is a driveable unit. Company to company, there are different theories about how to do it." Consequently, Ford engineers may opt for overhead chain systems while their peers at General Motors may be more inclined to implement skillet systems and so on, manufacturer to manufacturer.
"There are few places where there is only one way to do something," Pierson says. He adds, "And we've never found a product with a list of advantages and no disadvantages. One disadvantage may win over 100 advantages." It is all a matter of the particular conditions and context, where and by whom the equipment is to be used.
His recommendation for a good implementation? "It's important to meld the equipment with the skills and the comfort level of the plant," Pierson says, adding, "and you need buy-in to make the implementation successful."
"When it comes to material handling," Pierson observes, "people tend to be conservative. The cost of being wrong is too big. No one wants to have something installed that they discover, six months later, that it's unreliable or not the right choice for the job."
"Rarely have I seen a system that we couldn't offer a couple of different alternatives to," he remarks. It's all about the user's approach to production.
On the Rail
One of the more interesting material handling systems to come along in the past several years is the montamatic (that's right: small "m") from Bleichert, Inc. (Sterling Heights, MI), if for no other reason than its configuration. The first one we saw in action was back in 1993 at the Ford casting plant in Windsor, Ontario, which was being used to carry molds. The striking thing about this monorail-style system is the aluminum rail upon which the transport devices seem to be running. It is true that they are riding on the aluminum guide track, but from the inside of the track.
The configuration is such that there is rack-and-pinion drive: the carrier is equipped with a motor and a pinion gear and there's a gear rack on the inside of the guide rail. Consequently, there is positive drive.
According to Michael O'Brien, vice president of Sales at Bleichert, the primary difference between the montamatic today and the one that was installed five years ago is—yes—in the control. In the previous arrangement there is a main control panel that was PLC- or PC-based. But the carriers, he points out, "Never knew where they were." Stopping at a station is predicated upon optical sensors. Lots of I/O panels and sensors in the track are all part of the system. "If a carrier stops between stations," O'Brien says, "the control system doesn't know." If a carrier is removed from the system (one of the benefits of the individually powered units is the fact that the performance is distributed), the main controller thinks it lost some remote I/O. This setup is point-to-point.
The power for the motors on the carriers—then and now—is provided via a conductor bar. So to improve the performance of the system, they're taking advantage of the conductor bar and using it for communications. Consequently, there is real-time communication between the carriers and the main controller. Each carrier is equipped with a small PLC. Communication is based on CAN (Controller Area Network) technology. So the control topology is essentially control through an RS232 port to CAN, through CAN, then into an RS232 port and to the PLC on the carrier. An absolute encoder permits the carrier to know where it is, which it can, in turn, communicate back to the system. Not only is this advantageous from the standpoint of having full awareness of where all the carriers are all of the time and the ability to make changes on-the-fly to the schedule (for example, to skip a station), but there is an additional benefit in terms of quicker setups and reconfigurations because the amount of wiring is far reduced compared with the previous arrangement.
(What about using radio communication? O'Brien answers that it was considered but (1) there was a concern with interference with other equipment in a plant and (2) the CAN network provides faster communications.)
One of the problems that some people have with the montamatic system is the fact that there is a rail, which might just get in the way.
So the clever folks at Bleichert Foderanlangen, GmbH (Osterburken, Germany), the parent company, have come up with the montarail. Essentially, this is the montamatic, but the rail is placed in the floor. It requires a trench that's 20-in. wide and 6-in. deep. Then it is similar to the montamatic in terms of what it can do. Although the montarail may resemble an AGV, O'Brien says that it provides "all of the characteristics of an AGV without the expense and maintenance." With regard to the former, he says that the price is about half that of an AGV system. And in terms of maintenance, a big difference is that there are no batteries involved. (This also means that users can be more "liberal" in energy usage; the montarail has a top speed of 180 fpm, so if need be, it can really move—and yes, there are obstruction detection sensors.)
The guide path can be configured with curves; it can be interfaced with devices that can allow the carriers to be vertically lifted.
According to O'Brien, in Europe the montamatic (there are also side-running units) and the montarail systems are finding applications in engine assembly and body shops. Two reasons: one is the flexibility that is facilitated (e.g., multiple models can run down the same line in mixed lots) and the reusability provided (when a model changes, he says that conversion can be comparatively quick). These units are both pre-engineered, so this permits more cost-effective rearrangements and combinations.
However, he admits that these systems are not for everyone. "If they don't need this level of flexibility, we also build belt-driven conveyor systems," O'Brien says.