When used in shredding systems, programmable logic controllers can provide real-time information about the machinery and the process.
For a plant-based paper shredding system to run smoothly and produce the desired tonnage, dozens of mechanisms need to be running correctly and be synchronized with one another. One misstep and the entire day could be a loss. Operators are using programmable logic controllers (PLCs) to help keep things running smoothly. The industrial computers can be programmed to control input and output signals throughout a shredding plant.
Randy Beaudoin, service manager for Alpena, Mich.-based Ameri-Shred, says, “The PLCs allow for one-button system start and allow conveyors to stop and start automatically based on material flow. We also incorporate the metal detection system and discharge the metal and automatically restart the system.”
Todd Carswell, vice president of technical services for Archdale, N.C.- based Veccoplan, says, “The beauty of [a PLC] is that I don’t have to change any wiring. All I’m doing is hooking up a laptop and programming it.”
As plant-based document destruction systems become more complex, PLCs are being used to simplify the electrical system design for operator interface, safety and process control. However, PLCs are not necessarily used in every shredding plant. Dave Smith, senior control engineer for SSI Shredding Systems, Wilsonville, Ore., says, “PLCs are not just for complex systems.”
At the core, PLCs can be simple to use. “Normally you have a main motor, input conveyor and output conveyor,” Beaudoin says. However, PLCs can streamline an operation, and systems integrators are finding them useful.
Mike Davison, application manager for Shred-Tech, Cambridge, Ontario, Canada, says, “Today’s plant-based systems employ many components other than just shredders and balers. Bin tippers, conveyors and dust collectors are often included.” He adds, “All of these components can be controlled by PLCs.”
Shred-Tech has found PLCs to be necessary in all of its shredding systems, from basic, standalone shredders to the complete control and interfacing of all system components, Davison says.
Rick Cerra, system design coordinator, and Jeff Haley, senior electrician, for Allegheny Shredders, Delmont, Pa., also say they have found PLCs to be an important part of their business.
They describe PLCs as “very necessary, for monitoring the efficient functioning of the entire shredding system and allowing the end user to get the highest performance from the equipment. The process becomes more automated—the operator has to take a lunch break, but the shredder doesn’t.” Cerra and Haley add, “At Allegheny, we use PLCs in our larger systems, the 1000 Series shredders and beyond. We have one very sophisticated system that involves 17 conveyors, all monitored through a PLC.”
Jeff Dietterich, president of Souderton, Pa.-based Advanced Equipment Sales (AES), says, “When [PLCs] are used in shredders and shredding systems, one of their primary roles is to enhance the operator interface by providing real-time information about the machinery and the process.” He adds, “More sophisticated and complex systems rely heavily on PLCs for automatic process control.”
PLCs effectively can be used to control individual pieces of equipment, as Beaudoin has found. “The auto-tie balers require a PLC because you’re controlling pump motor, ram, bale tension, bale length, inserter, twister, wire shears, hydraulic pressure, lights, horns and limit switches and making decisions every second based on at least a couple dozen inputs.” He adds, “They allow control of auxiliary equipment, such as conveyors, metering systems, dumpers and warning devices.”
Form and Function
Simply put, PLCs replace relays to turn equipment and processes on and off. Beaudoin likens PLCs to switch boards. “Just think of the old-time switch boards that phone operators used. They would receive a call (input), make a decision based on that input (program) and then connect your call (output).”
Less simply put, a PLC is an industrial computer used to automate industrial processes by programming inputs and outputs to replace relays that would control timer and switching capabilities. Beaudoin continues, “You program the PLC to make decisions based on that input and then open or close outputs to energize relays, solenoid valves, motor starter coils, lights, bells and other devices that cause the equipment to work.”
Dietterich adds that PLCs are cost-effective and space-efficient ways to replace other electromechanical devices. Instead of having to take apart a piece of equipment, functions can be redirected by simply retyping the logic.
Cerra and Haley say, “Allegheny uses integrated controls to allow communication with any peice of equipment in the system, even if it’s from different manufacturers than Allegheny.” They say PLCs “get the most out of the machines” and alert operators to specific problem areas using alarms.
Advantages & Disadvantages
Besides being much smaller than most relays, these space savers also offer other advantages. Dietterich says they also are fairly inexpensive and typically less time consuming to change than tearing apart a system that uses relays.
Operators would have “the ability to change the operational features of the equipment or system with a few keystrokes,” he says. “When used with a touch screen or other human/machine interface (HMI) the operation of a piece of equipment or system is simplified due to the intuitive graphics that can guide a machine operator or service technician,” Dietterich adds.
“In a simple system [PLCs] are not necessary if you don’t have a lot of input points, just two or three conveyors,” Carswell says. “The only thing that makes [PLCs] wise to use in a simple system is the cost. The cost has plummeted in the last 10 years. A simple system may have up to four relays and two timers. Those four relays could cost me $400. A PLC could cost me $200.”
Carswell adds, “On the more sophisticated systems, ease of expansion is a key issue,” that makes PLCs preferrable to relays and timers.
Allegheny Shredder’s Cerra and Haley, who refer to PLCs as “very user friendly,” say, “They require much less panel space in your facility. They are very reliable compared to conventional relays—they don’t have moving parts, wires, etc. They allow you to have information at your fingertips so you can monitor the operation.” They add, “The information they provide helps the customer to troubleshoot—to tell if a belt is ripped, for example, and where it’s located.”
PLCs also can track maintenance needs, either based on operating hours or from an input sensing a problem, and can alert an operator when a machine needs attention, Beaudoin says. They also interpret and respond to digital and analog process variables.
Secure destruction companies can integrate their shredding and baling operations with PLCs. A PLC will allow the machines to communicate with one another. Smith explains, “The PLC can help control the security of sensitive material destruction by ensuring that all systems within the shredding facility are ready to accept the materials prior to opening the secured container.
“Additionally, the PLC can receive information from the baler to modulate or stop the flow of shredded material to the baler, either by pausing when the baler is between cycles or by slowing its rate of throughput,” Smith adds. “An uninterrupted stream is a more secure stream.”
Dietterich gives an example of how a shredder and baler can communicate with the use of a PLC. “If the baler is in a tie cycle, it may tell the shredder to stop running if the baler chute becomes overfilled with paper. Otherwise, the PLC may allow for remote operator control, observation or troubleshooting.”
He continues, “Additionally, if equipped with the right communication capabilities, a manufacturer can remotely troubleshoot a piece of equipment or an entire system.”
Davison shares a second example. “For instance, if you have a system that has a shredder and conveyor feeding the baler, the baler’s PLC can send a permit signal to start or stop the conveyor and shredder,” he says. “This means that the shredder or conveyor will not run if the baler is not operational or the high-level switch in the baler hopper is reached. It can even be set up to automatically start the shredder/conveyor once the level drops in the hopper,” Davison adds.
Cerra and Halley say, “PLCs control internally rather than externally [and] this wasn’t feasible with earlier control systems.”
Beaudoin says PLCs are not necessarily needed to ensure communication between the shredder and baler. “Normally the only thing the shredder needs to know from the baler is that it can accept material,” he says. “This is simply accomplished by placing a sensing device in the baler hopper to detect paper level.”
Like any computer, PLCs store certain information that may be beneficial to a company interested in fine-tuning its process. Depending on the PLC model, operators can track operation hours, start/stop cycles, amp draws, baler strokes and jams among other things. This information could assist operations in evaluating their production costs and in planning maintenance.
Carswell says, “It’s also the data acquisition,” that makes PLCs useful in shredding plants. “I can tell you if first shift is working harder than third shift by going to a touch screen. You could get that by weighing your trucks as they’re leaving, but it’s easier this way,” he says.
There is something to be said for convenience and productivity, as most equipment suppliers say they would not choose to switch back to the old ways of doing things.
“At Shed-Tech we have found the use of PLCs to be economical, reliable and flexible, we could not imagine going back to the old technology,” Davison says.
The author is assistant editor of Recycling Today and can be reached by email at email@example.com. This article was first printed in Storage & Destruction Business, a sister publication of Recycling Today.