The efficient sort
It’s not quite a perpetual motion machine, but Wegener + Stapel has built a highly energy-efficient package distribution system using leading-edge drive technology.
In 1967 Wegener + Stapel started building conveyor systems to handle in-house material flows. Over the years this company, based in Bergen in the German state of Lower Saxony, has earned an impressive reputation in the logistics industry as a specialist for high-efficiency sorting systems. One of the pivotal functions in such systems is performed by a so-called rotary diverter, which redirects packages from one roll conveyor to another.
For three years now, the conveyor and handling specialists have employed Rexroth technology and know-how. With Rexroth’s support, Wegener + Stapel has now realized a large-scale package distribution system for a leading logistics enterprise. It is capable of handling up to 4,500 packages, weighing up to 32 kilograms each, every hour. “In addition to precise, rapid and gentle handling of the packages, the focus in the planning phase was primarily on energy efficiency,” explains Wolfgang Bortels. As head of automation at Wegener + Stapel, Bortels headed up this project.
Intelligent motors
“In view of this requirements profile, we decided to deploy the IndraDrive Mi system for the 41 rotary diverters and their drive units,” recounts Karl-Heinz Gebhard, sector manager in the Rexroth General Automation division. Unlike conventional drives, the controllers are not installed in a central switchgear cabinet. Instead, the control electronics and servo motors are combined to form a single, space-saving unit. This technology offers a wide range of advantages. Since the drives can be connected in series, wiring requirements are reduced by up to 85 per cent. A single cable is sufficient to supply power and for programming and communication. As the intelligence and power electronics are located in the motors themselves, switchgear cabinet size is reduced by over two-thirds. The labor required to assemble those cabinets and to lay cable is also significantly less.
More performance – less energy
This sorting system sets new standards in energy efficiency: even though it uses up to 35 per cent less energy, the system’s handling capacities are significantly greater than for configurations with conventional drives. This considerable enhancement in system efficiency is due to a number of factors.
Connecting components in series reduces by 85 per cent the amount of wiring required.
For example, the concept makes systematic use of the kinetic energy present in the plant. Up to 20 IndraDrive Mi drives are connected in any given electrical circuit in this distribution system, making it possible to capture the braking energy to generate electricity that is then available for subsequent acceleration phases. The transfer of energy among the drives – functioning alternately as generators and motors – reduces energy consumption by up to 15 per cent.
Retaining energy in the system
A modern power supply concept contributes to further energy savings. This unit is capable of feeding excess power back into the mains, which means that the braking energy not used by the system is available for other uses. In a package sorting system this effect can quickly add up to savings of around 20 per cent, as a great deal of braking energy is reclaimed that would otherwise be lost in the form of heat.
And as a side benefit, the energy is no longer converted to heat at braking resistors in the switchgear cabinet, eliminating the need for power-hungry air conditioning. To further increase system efficiency, the drive specialists can also integrate storage modules. These briefly store excess braking energy and make it available for accelerations. “Maximum energy efficiency is attained by keeping the energy in the system, because returning recuperated energy to the grid always entails additional losses,” explains Gebhard.
Speed to fit the need
Using modern motor control technology to regulate the synchronous motors improves energy consumption even further. Here the drive specialists have created a motion profile optimized for acceleration. Just like an automobile engine, an electric motor can be accelerated in an energy-saving manner.
Braking energy is stored at the rotary diverter.
A driver who steps on the gas and “burns rubber” uses far more fuel than one who accelerates moderately. “In this way we reduce not only energy consumption, but wear and tear on the mechanical equipment and material being moved, as well. During testing we even sorted full egg cartons without a hitch,” reports project manager Bortels. He adds: “We also worked with Rexroth to optimize the design and the timing for the rotary diverter. These efforts resulted in a significant performance increase.” Optimizing rotary diverter motion made it possible to increase belt speed from 1.3 to 1.5 meters per second, so that the system is now able to sort an additional 500 packages per hour.
Decisive factor
Altogether, the energy-saving schemes have had a major effect: assuming 300 workdays per year and twelve hours of operation per day, the system uses around 23,400 kWh less power. At a price of € 0.12/kWh for electricity, this translates into savings of about € 2,800 and a reduction in CO2 emissions by over fourteen metric tons. “Energy efficiency is a key competitive factor for us and a major issue for both our customers and ourselves. If a drive lets us boost performance and at the same time significantly reduce energy consumption, then that’s certainly convincing,” concludes Wolfgang Bortels.
More information:
www.boschrexroth.com/energyefficiency
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