Valve Module Controls Conveyors Without a Central Computer

Clip on: The valve module clips to the side of a conventional conveyor.

Engineers searching for a simple means of controlling miles of pneumatically actuated conveyor lines may now have a way. A new valve module from Humphrey Products Co. (Kalamazoo, MI) eliminates that need for programmable logic controllers (PLCs) or centralized computer control, and yet still provides automated conveyor motion. The module, targeted at the giant warehouse conveyor lines operated by retail distributors, enables developers to apply a "zone control" technique to the automated movement of packages on a conveyor. By "talking" to pneumatic modules in upstream and downstream zones, the system can control movement of packages across miles of conveyor lines.

"We've broken down the distributed control of a conventional conveyor, and brought that distributed intelligence to each of our zones," says Rich McDonnell, business development manager for Humphrey Products.

To accomplish that, the system employs a valve module, a photoelectric sensor, air supply line, and a puck-like pneumatic actuator in each zone. During operation, the "photo eye" in each zone searches for approaching packages. When it spots one, it signals the module, engaging a three-way pneumatic valve. The valve, in turn, pressurizes the puck-like actuator. Operating in the manner of a conventional pneumatic diaphragm, the pressurized puck moves through its half-inch stroke, contacting a rotating drive belt, which engages the conveyor's rollers. As a result, the drive belt can then spin the conveyor's rollers.

By operating in this way, the system engages the rollers in its zone, typically about 3 ft long. The key to the system, however, is that as each zone activates, it also communicates with the next two upstream zones and the next two downstream zones. In that way, adjacent zones are always "prepared" for approaching packages, despite the fact that those zones are not connected to a central computer. The architecture of the system allows for 100 of the valve modules to be daisy-chained together.

"Essentially, there's a wave," McDonnell says. "The rollers come alive just before a box gets to them."

Known as the Gen2, the module incorporates a three-way pneumatic valve, a 5-MHz Motorola microprocessor, and associated electronics for communications and voltage regulation. For diagnostics purposes, each hundred modules also work with a so-called "interpreter," which provides an interface between Humphrey's communication protocol (known as H-flex) and common field bus protocols, such as DeviceNet. As a result, the system can communicate with a centralized computing system employing Ethernet.

Big savings

Humphrey engineers claim that the system offers advantages in terms of labor, time, and cost, when compared to more traditional pneumatically driven conveyor systems. They estimate it is approximately 30 percent less costly to purchase and install.

"With the old way, there was a lot of heartache involved in the installation," McDonnell says. "And it was more difficult to troubleshoot."

"Now, you can program the system down at the rudimentary level, where it needs to be, and eliminate all of the programming that goes on in the higher-level computing systems," McDonnel says. "Essentially, we're getting rid of the PLC and all the associated overhead, but still automating the conveyor operation."