Sensors Today: Customer Profile

Roach Conveyors gets their zero pressure accumulation control in the zone.

by Todd M. Bissell
Sr. Technical Writer, Rockwell Automation

A world leader in conveyor systems since 1953, Roach Conveyors is known not only for their innovation and unsurpassed quality, but also for their technical expertise and willingness to address their customers’ needs. Whether those needs involve specialized turnkey solutions or quick, 24-hour shipment of standard conveyors, Roach Conveyors welcomes the opportunity. So when the engineers there were looking for a unique control solution for their next-generation accumulation conveyors, they looked to Rockwell Automation—a familiar colleague, and one who shared their dedication to quality, technology and partnership.

Located in Trumann, Arkansas, Roach Conveyors® uses a combination of the latest manufacturing processes and good, old-fashioned hard work to build material handling products of the highest quality, from belt and roller conveyors to high-speed diverters and sorters. And Charlie Parks, vice president of sales, marketing, purchasing and engineering, is involved in the design of every product Roach® offers. When he and electrical engineering manager LaRoy McCann began designing their new Smart Zone® series of zero pressure accumulation conveyors, they started looking for technology that would meet the industry’s growing demand for the transport of lighter packages at high speeds while streamlining the control system. “We’ve had accumulation conveyors for years,” says Parks, “and we always used pneumatic logic or mechanical linkages in our zone control.” But such technology wasn’t befitting of the trends taking place in today’s market.

The Roach Conveyor Smart Zone accumulation conveyor.

Photoelectric sensors have emerged in the last five years as the predominant technology in the industry, replacing the mechanical ‘sensor rollers’ most commonly found in accumulation conveyors. The problem with most photoelectric sensors, however, was that they still had to be wired back to the controller, where the necessary conveyor control logic was carried out. As Parks and McCann investigated the options on the market, they found that the available solutions involving sensors with embedded logic weren’t rugged enough for industrial applications. Parks elaborates: “Everything out there involved running ribbon cable along the conveyor and tapping off of it with little squeeze-type connectors--that didn’t look industrial duty to us.”

Having used Allen-Bradley Series 9000 photoelectric sensors extensively on their other conveyors, Roach contacted Rockwell Automation to discuss the possibility of combining sensor and logic in a simple solution that would be suitable for their full range of conveyors—light- and heavy-duty models alike.

Accumulating Knowledge – A Brief Description

Accumulation conveyors prevent product damage and jams by controlling the spacing between items as they move down the line.

Generally used in distribution centers to move materials from the warehouse to shipping, accumulation conveyors control product flow and optimize throughput while preventing packages from colliding. By preventing contact between packages, accumulation conveyors not only prevent damage to the items they are transporting, but also prevent jams along the line. The conveyor is divided into sections, or zones, each containing one sensor and one actuator typically wired to a central controller (PLC) that provides the desired control logic. Each zone’s behavior is dictated by that logic, which may include timing functions to allow for various operations such as counting and sorting.

The sensor is generally of the photoelectric type, but mechanical sensors are still quite common. Mechanically actuated sensors, however, have minimum weight restrictions that make them ineffective for the lightest packages. Actuators can be pneumatic or power rollers that initiate conveyor movement, turning on or off based on the presence of packages in other zones as reported by the sensors. To put it simply, each conveyor zone operates based on feedback from the other zones.

Conveyor logic, as mentioned previously, is typically performed by the PLC and is designed in such a way as to optimize product flow while preventing collisions. The logic may include system-wide or local zone timer functions to maximize or minimize gaps between products. And it is at the controller where the method of release at the discharge end of the conveyor is established; once product is accumulated at the discharge end of the conveyor, it can be released singly or as a group, referred to in the industry as a “slug.” Additional, advanced control functions may be required—at high-speed distribution hubs, for example—but the bulk of conveyor installations require only the most basic zone control. And based on this fact, the folks at Roach Conveyor wanted a combined sensor and logic solution that not only eliminated the need for a controller and the associated wiring, but which struck just the right balance between simplicity and functionality.

(See our Tech Talk article for further details on today's zone control technology.)

Back to the Story…
After evaluating several products that didn’t fit the bill, Charlie Parks and LaRoy McCann requested help from Jim Berry at Arkansas Industrial Electric, their local Allen-Bradley distributor, who in turn contacted Ray Archer, Sales Engineer, Rockwell Automation. Kerry Lee McCulloch, Standard Control Area Manager, and John Lang, Presence Sensing Area Manager, both from Rockwell Automation, were also brought in to discuss possible solutions. “The application was conveyor zone control, pure and simple,” says McCulloch, “and our other solutions were overkill for what Roach wanted. We didn’t have that product.” Or so they thought.

Peter Cicchetto, Senior Product Marketing Engineer at Rockwell Automation’s Sensing, Safety and Connectivity Business, got the phone call asking if there was anything available fitting the profile Roach was looking for. Cicchetto informed them that no, there wasn’t—but that one was in the conceptual stage. According to Cicchetto, “end users have been looking for ways to reduce the material and labor costs associated with traditional PLC-based accumulation conveying applications, leading us to develop a lower cost, simpler product that reduces wiring.” As a result, Rockwell Automation was developing a full range of solutions to address accumulation conveyor applications of varying complexities, from complete network approaches to a simple sensor solution with basic on-board logic functions. Cicchetto told them about the latter—the Bulletin 44N zone control photoelectric sensor—and it sounded like the ideal solution for the Smart Zone conveyor. Within a few weeks, Roach Conveyors headquarters would have prototypes in hand.

Introducing a Simple, Logical Solution
Based on the popular Allen-Bradley Series 9000 photoelectric sensor, the 44N Zone Control Photoelectric Sensor features built-in accumulation zone control in an easy-to-use and economical stand-alone package. Outfitted with multiple cable leads, each 44N has connections for an actuator and the two neighboring sensors immediately upstream and downstream. The leads carry 24V DC power while allowing communication between sensors for effective control of up to 50 conveyor zones (25 zones may be powered on each side of the power supply). So each sensor is able to ‘talk’ to the sensors in adjacent zones, informing each other when to turn their respective roller mechanisms on and off based on zone status. The use of photoelectric sensing technology eliminates the need for mechanical switches, whose minimum package weight restrictions have proved a hindrance for many applications with extremely light packages or empty cartons. The polarized retroreflective sensing mode of the 44N also ensures reliable sensing of even shiny packages at distances up to 16 feet. The on-board variable time delay, selectable singulation mode/slug release mode and “dual zone” logic function for the minimization of gaps between packages were also there, rounding out the features that Roach Conveyors desired—and that the 44N already had when Cicchetto presented it for the first time.

Bulletin 44N zone control sensors talk to their neighbors to control gaps between cartons on a conveyor.

“When Peter came in with what we were looking for wrapped in that Series 9000 package, it really struck a chord with us,” says Mr. Parks. “We immediately knew that it was versatile enough to use on all our conveyors, light-, medium- or heavy-duty.” Having used thousands of Series 9000 sensors on their conveyors in the past, the Roach engineers were confident knowing that in addition to providing zone control, the 44N would be capable of withstanding applications in moist environments—a characteristic that would also give them a competitive edge in the marketplace.

Since Roach conveyors are shipped in sections, the 44N’s quick-connect leads offered plug-and-play capability that would allow conveyors to be connected at the joints quickly and easily without requiring a licensed electrician. The 44N eliminated loads of hard wiring that had previously made installation and maintenance not only difficult, but expensive. Now these savings could be passed down to the end user. Parks can confirm the numbers: “In addition to building conveyors, we also install them. The modular nature of the 44N-based control system saves you a minimum of 15 to 20 percent of the total equipment cost when compared to other photoelectric logic installations, mainly because you don’t need an electrician.”

The only request Roach had, however, involved the actuator lead. The standard 44N would have micro connectors on the upstream and downstream sensor leads, but the actuator lead was a straight pigtail. A connector compatible with the pneumatic valve actuators regularly used by Roach would make the 44N even easier for them to use. Rockwell Automation offered to install the appropriate valve connector on the 44N, making it an all-around perfect fit for the Smart Zone conveyors.

The custom 44N built for Roach Conveyors bears the Smart Zone name.

But ultimately it was the functionality of the 44N that sold Parks and McCann. The built-in logic of this ‘smart sensor’ allowed them to eliminate the controller and associated wiring while maintaining the flexibility and control Smart Zone conveyors were designed to provide. The 44N’s internal timing functions would allow box spacing to be customized to best suit the application while facilitating loading/unloading of the conveyor. Settings could be adjusted via a potentiometer right on the sensor, as opposed to having to employ and configure an external timer. Plus, slug release and singulation modes could be selected simply through the use of external contact closures. Basically, the 44N proved to be the easiest solution for customers to configure and maintain when compared to traditional sensor-based solutions, yet it provided the functionality previously only available in more complex system architectures.

Exercising control
With the introduction of the 44N Zone Control Sensor, Roach Conveyors had found what seemed to be the ideal solution, but it had yet to be truly tested. The engineers knew that the 44N would reduce wiring and had the required logic functions, but how would it truly perform? When the first Smart Zone conveyors were tested at the plant, the Roach team started by conveying boxes, then catalogs, and finally individual sheets of paper. The result: even single sheets of notebook paper were successfully conveyed and accumulated by the cutting-edge new system. The team instantly knew they had a complete, versatile solution that answered the call in the industry and that their customers would embrace.

Today, each Smart Zone conveyor is outfitted with Allen-Bradley zone control photoelectric sensors that themselves now carry the Smart Zone name. Charlie Parks’ philosophy captures it best: “When designing a solution, we always think in terms of what we would be looking for in a product.” The complete solution is the result of a strong partnership between two companies dedicated to making their customers more successful. And in this case, the road to success was paved with good communication between people--and between sensors.

Special thanks to Charlie Parks and LaRoy McCann of Roach Conveyors, Jim Berry of Arkansas Industrial Electric and Ray Archer, Kerry Lee McCulloch and John Lang of Rockwell Automation for their assistance with this article.