Conveyors are basically beasts of burden. But that doesn’t mean they have to be dumb beasts.
Digital technology has enhanced all kinds of equipment in food & beverage plants, and conveyors are no exception. Digitization opens new possibilities for conveyors, both for contributing to overall automation and for their own maintenance.
In a way, conveyors are an excellent target for digitization because they’re the plant’s circulatory system. Keeping track of what’s on them and how smoothly it’s flowing are ways to take the pulse of the plant.
“Our Iso-Flo shakers and other vibratory conveyors work in conjunction with different types of sensors and systems, including weigh belts, load cells and product height sensors, that transmit data to the control system about product flowing through the line,” says Jim Ruff, vice president for process systems and integrated solutions at Key Technology.
There are many variations available in conveyor performance, but at the end of the day, it’s all about moving stuff from point A to point B. That’s why digital enhancement of conveyors usually starts with the motors that are driving them.
Simply keeping track of when they start and stop is the most basic bit of information. A common source for this kind of data is the PLCs that usually operate the conveyor motors.
“For most applications, we utilize Allen-Bradley and other PLCs that are used by virtually all our customers,” Ruff says. “Leveraging PLC software, we can monitor both digital and analog sensors to determine product height, product speed and volume of product within any given section of one of our shakers, belt conveyors or hoppers. With this information, we can create application-specific algorithms within the PLC software to optimize product flow.”
At its most basic, conveyor control is uncomplicated. Conveyors are nearly always segmented, with the segments picking up product or packages at one station and delivering them to another. Each segment has three critical components or data points: motor, input and output. Monitoring input and output for each segment, and controlling the motor accordingly, adds flexibility to the whole operation.
“On a sophisticated line that’s fully integrated, data collected by the sensors on one machine automatically triggers all the necessary adjustments to other machines on the line without human intervention,” Ruff says. “For example, if downstream equipment sends data about changes to product flow, it can trigger upstream gates or diverters on distribution shakers to control feed rates.”
Variable speeds
Motor control is especially important when the conveyor is running at variable speeds. Mono-speed conveyors used to be the norm, and in many cases they still are. But increasingly, conveyors need to vary speeds to meet the changing demands of a given application for flexibility.
Photo Credit: Multi-Conveyor
“Occasionally we need to interface with a machine that ramps up or down depending on external conditions or prompts inline or offline accumulation, which can affect conveyor speeds,” says George Packard, account manager at Multi-Conveyor.
The traditional way to vary speeds has been mechanical, by switching the drive chain gearing. But that is inflexible and entails considerable work and downtime. An increasingly common strategy is to use three-phase AC motors with variable-frequency drives (VFDs) that can speed up or slow down the motor by controlling the frequency of the current fed to it. VFDs often have smart capability, enabling them to communicate with upstream or downstream controls.
“Variable speeds are required on a regular basis,” Packard says. “Generally speaking, this is achieved using recipes in the programming and [operator interface] to store jobs by product, size, line speeds and other variables. The operator cues up jobs by touchscreen controls, and the programmed conveyors automatically adjust to loaded input parameters.”
This works for both discrete units such as packages and a continuous stream of product, such as powder or small particulates.
“Our conveyors can be equipped with sensors that have the capability to transmit data to the control system, which can collect and analyze that data to monitor product weight, product height, mass flow, product volume and more,” Ruff says.
Modernizing maintenance
Digital capabilities for conveyors go beyond control. Due to their size, conveyors are among the hardest plant components to maintain. But digital technology has the potential to revolutionize maintenance of components like conveyors and make it more proactive or predictive.
Machine components that are susceptible to wear often exhibit symptoms, like heat or vibration, that serve as warnings of impending failure. Reading those signs is an important part of predictive maintenance, and VFDs are a good potential source of this information. Fluctuations or other anomalies in the current used by the drive can be an indication of impending trouble.
“By monitoring devices such as VFDs, we can analyze motor current, motor voltage, motor speed and any digital or analog input to look for trends that will alert maintenance personnel to issues such as product buildup on shaker pans, changes in motor loads and more,” Ruff says. “We can also capture this data to look for long term trends that can impact overall plant production.”
Directly monitoring the motor itself is also an option, made easier when it’s a drum motor specifically designed to pull conveyors. “Although the drum motor is simply a motor and gearbox located inside the drive shell of the conveyor, we’ve embraced technology to make our drive intelligent,” says Rick Zander, business development manager of VDG (Van der Graaf). “Over the years, we’ve noticed a demand for information at the operational and maintenance levels.”
VDG has equipped its motors with oil life indicators and sensors for motor temperature and vibration, along with what Zander describes as “a ‘conditional monitoring’ device that takes what the sensors are sending (1’s and 0’s) and decodes into usable data.” End users can set limits and parameters and decide what gets done – alarms, shutdowns or other actions – when they are exceeded.
Digital technology has the potential to make conveyors run more smoothly, both operationally and in terms of maintenance. And a smooth-running conveyor system is vital to a smooth-running plant.
