A Faster but More Sensitive Conveyor
Among the most significant changes in conveyor technology is the move from mechanical sensors to electronic sensors. A move that has been driven by the conflicting demands for higher speed with increased sensitivity for handling smaller lighter weight cartons.
Electronic sensing has many advantages. It allows for higher speeds, reduces noise and lessens the need for maintenance because there are no moving parts to wear out. It also extends the range of items that can be handled via conveyor. With most mechanical sensors, cartons need to weigh several pounds to trigger a sensor. The new electronic sensors, by contrast, can be tripped by the cartons physical presents alone thus eliminating the weight factor.
Buyers need to be careful here because while some manufacturers have incorporated electronic sensors into their standard product line, others still offer them as optional to mechanical sensors. You need to make sure you know what’s being provided.
Kaffenberger, at HK systems, points out that in a zero pressure live roller accumulation conveyor, accumulation zone lengths are no longer based on how far apart the sensors are, but are instead determined by the size of the cartons conveyed.
Klueber agrees, saying that Intelligrated has developed “crowder functionality” that allows for even smaller gaps, further increasing carton accumulation density per lineal foot of conveyor while also increasing system throughput. Kind of a two-for-one benefit.
Good Looking, and Smart Too
Today's conveyors are faster, quieter, and more adaptable that ever before. You could also say that they’re smarter too, based on the liberal use of small, relatively inexpensive electronic photo sensors and micro-processors that communicate real-time critical information to higher level software systems such as a Warehouse Control System (WCS).
There are several different approaches to conveyor control. Primarily, system providers are using some form of network control. According to Kaffenberger, there is not a lot of discrete wiring out to photo eyes anymore. Instead, he says that HK Systems uses networks like DeviceNet, Ethernet, and ASI, which are commonly used in the industry to collect signals and to initiate commands to activate a conveyor device.
Kaffenberger points out that one of the most important considerations, relative to accumulation control, is that there are choices. There are several different approaches all involving the use of a photo sensor of one class or another, but each one of them according to the amount of control that needs to be exerted by the highest level including being networked in.
For example, there are simple DC and AC photo sensors that are available for applications where no network control is required. All they can do is control the accumulation zone immediately downstream of it. This is the least expensive, simplest to maintain sensor.
At the high end, networks are used to collect signals from “smart” sensors. These smart sensors, in addition to the actual control of the zones can provide diagnostic feedback. They can indicate exactly where an interruption in flow has occurred, as well as identifying equipment and/or system faults.
Faster and Easier Maintenance
All of this real-time operational information can be communicated directly to maintenance crews PDF or PDA, or via e-mail message to a laptop or text message to cell phone allowing for a quicker more informed response. Schematics and step-by-step tutorial videos can be stored within the system so that a maintenance technician with a wireless laptop can access repair information directly from the site. These immediate fault recognition and resolution features can reduce downtime for DCs with limited maintenance resources.
Other maintenance tasks have become easier as well. Conveyor components such as drives and belts that used to take hours to change out can now be serviced in less than half the time. Klueber points out that Intelligrated has recently developed a line of new live roller V-belt curves and spurs where the endless belt loop can be removed and replaced in just a few minutes.
As it relates to components like sensors and control valves, etc - all snap into the conveyor frame or mounting bracket. No nuts, bolts and hand tools are required to replace such components. Airlines also are equipped with snap connections while electric is “plug-n-play”.
Kaffenberger says that all components are “pinned” so that they cannot be installed incorrectly. However, AC motor drives are seldom equipped for plug-n-play as it is not cost effective given that there are relative few (dozens) of them in a typical system compared to hundreds or even thousands of components.
HK Systems emphasizes its version of auto calibration, meaning that the equipment will continue to self-adjust as it normally wears. It says that it tends to limit the amount of time maintenance people are working on adjustments.
As an example, on a belt driven live roller conveyor auto calibration would continue to apply proper driving pressure to the carrying rollers as the belt becomes thinner over time. Auto calibration is also used to provide critical feedback during initial setup, run-in, and ongoing real-time monitoring of specialized equipment like a sorter to compensate for chain stretch as it wears.
Automatic Speed Control
A popular accessory on automobiles for many years – now available on conveyors.
Conveyor speeds have been steadily increasing. Some conveyors are approaching speeds of 500 plus feet per minute, with sorters actually attaining blazing-fast speeds up to 700 feet per minute. At these speeds the system would be handling and sorting cartons in the 200 to 250 per minute range. Of course, that's not an advantage if the rest of the operation is unable to keep up. If you can't pick, pack and load at those rates, ultra-fast conveying and sortation may create bottlenecks that offset any gains achieved through greater velocity.
Kaffenberger says that requirements for ultra high rates above 150 cases per minute are rare. He points out that conveyor equipment running at those higher rates naturally generates more noise and cause accelerated ware and tear on major components.
In the typical DC logistics system operation there are times of slow or no volume followed by dramatic surges. In response to these highly fluctuating volume patterns, conveyor manufacturers are being pressured by their customers to better accommodate this operational reality.
As a result today’s conveyor systems can be equipped with automatic speed control through innovative solutions such as more responsive servo and VFD (variable frequency drive) control. Klueber says that at the beginning of a work shift, the operations manager enters the expected case volume into the Warehouse Control System (WCS). This then allows the conveyor system to automatically slow down or speed up to more closely match volume demand within system design parameters and constraints.
But, there is still room for improvement. Therefore, a highly competitive, industry-wide design initiative is underway to reduce the gap between cartons as they are being merged and inducted onto sorters. Smaller gaps serve to increase the population of cartons on the conveyor, producing higher throughput volume while at the same time reducing speed. Additional benefits are in lower noise level, lower maintenance cost, and improved system performance.
To a large degree these speed control and gap initiatives have been made possible due to the continued increase in relatively cheap computing power and faster processing capability. Thus allowing software engineers to develop more sophisticated logic based programs that optimize conveyor speed while minimizing carton gaps at critical merge and sorter induction points. Also, equipment like high capacity cross-belt sorters are now available that can sort at right angles, which further reduces gap and speed requirements.
In part 2 of this series next week, we will explore how conveyor systems are networked and integrated so that multiple sub-systems communicate and work as one unified system, advances in low voltage Motor Driven Roller and future technology, plus how one company moved from a manual operation to being fully automated.
What is your reaction to these advances in conveyor technology? Do you have any direct experience with them, good or bad? Which do you view as the most important? Let us know your thoughts at the Feedback button below.
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