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Searching For A Green Automated Warehouse

Automated storage/retrieval systems

Automated storage/retrieval systems can contribute to sustainability through reduced energy consumption.

Have you ever contemplated the warehouse of 2211?

My generation remembers all the episodes of Star Trek. We were captivated by the technology the writers created, like the communicators, talking computers, phasers and the tricorder. Today, a number of those futuristic devices are part of everyday life.

Do you remember scenes that took place in the cargo bay of the USS Enterprise? To me, this was the crew’s warehouse. But everything was sitting on the floor only one level high. So why didn’t they have product on multi-levels being held up by anti-gravity pallets? Could this be the warehouse of 2211?

Today, there are hundreds, if not thousands, of ways to store, retrieve and pick product in a warehouse. No matter what the design, we worry about environmental responsibility, cost reduction, carbon footprint and reducing energy consumption. The real trick is to design a facility that meets the needs of the supply chain and has little impact on future generations.

Reducing energy consumption ranks high on this list. As the material handling industry and those using it create new facilities, they must design systems and equipment that use the least amount of energy. There are new concepts and technology available from several automated storage/retrieval systems (AS/RS) manufacturers that can conceivably minimize consumption to a point where the system actually returns energy to the city power grid.

Coordinated Start-Up
In any automated warehouse designed with several stacker cranes, the control software should be integrated to a master function on the programmable logic control (PLC) level. The software should be coded to equalize the acceleration of the cranes within the system. No two stacker cranes should be allowed to start maximum acceleration within the same mil-second window. A defined coincidence factor to throughput should not be overridden. This allows the maximum currency peak to be exact. Because the provided power supply may be defined within tighter limits, no safety margin has to be calculated, resulting in a more cost-effective power supply. The energy savings need to be balanced with performance (pallets per hour) of the system. Similar concepts can benefit pallet conveyor systems.

Nissan Goes Green

Nissan Forklift announced its Green 2016 program in June. This follows on the heels of the company’s 2010 program, which focused on carbon dioxide reduction, emissions reduction and recycling. As part of the 2010 initiative, Nissan installed high-efficiency lighting in the factory. Adding variable frequency drives that allow the air compressor systems to run on demand instead of running constantly has saved more than $100,000 per year, according to Dale Mark, director of quality assurance. Nissan also put in heat exchangers to reclaim heat from its powder-coating oven, allowing the factory to use less natural gas. “All of these changes were supported with readily available rebate programs and have paid for themselves in less than two years,” Mark says.

Coordinated On-Board Motor Control
For each stacker crane, an onboard master function is considered, which equalizes the acceleration of the motors for lifting and driving. Controlling these functions, the peak of currency during acceleration can be reduced up to approximately 50 percent. Using this onboard master function, the priority lays on the limitation of the power consumption during the start-up phase of both motors, for lifting and driving. The result is a small reduction of the throughput of each stacker crane. However, peak currency during acceleration is reduced. Certain electrical components benefit by longer service life.

Coordinated Target Approach
Think about coordinating the stacker crane’s target approach. The destination of the X-coordinate should be reached at the exact same time as the Y-coordinate. If you control velocity and acceleration of both axes and the software’s algorithm varies motor characteristics based on the next location, absolutely no time is lost, which increases throughput and reduces energy consumption. This will also reduce mechanical stress on the stacker crane because the accelerations are reduced where possible.

Controlled Velocity
Every AS/RS has average, slow and peak operating days. If the higher-ranking material flow controller software is given the opportunity to control the acceleration and the velocity of each stacker crane dynamically based on actual business load of the warehouse, the stacker cranes could be driven with less power and therefore enjoy significant power reduction.

Of course, any transport order could be overridden. When the warehouse is busy, run the stacker cranes at full speeds. When the warehouse is slow, run the stacker cranes at slower speeds and accelerations to greatly save energy. This concept could also work during certain hours of a shift.

Four-Day Week Pays off for Jesco

A few years ago, Jesco Industries President Bonny DesJardin decided to implement a four-day work week as a benefit to her hard-working factory staff of 38 employees. “I gave them Friday off to be able to attend to personal business, which they were happy about,” she says. “Plus we found that it ended up having a huge price advantage on utilities and in energy savings.” Utility companies rate the usage on the biggest spike of the day, which for Jesco was each morning when the heavy manufacturing equipment turned on. Eliminating one of those spikes each week resulted in savings near 20 percent. Plus, eliminating operating costs and two employee breaks per week saved additional money and improved productivity. “We already do some energy co-ops, and this helps us save even more. It’s worked out really well for us,” DesJardin says.

On-Board Power Recovery
When designing an AS/RS system, consider using stacker cranes that can provide onboard power recovery. This means that for both motor units, driving and lifting have the possibility to feed their braking power into a common capacitor. At the same time, when one motor unit is running in generator mode, the other motor has the possibility of directly using the provided energy. Therefore, less energy is taken out of the power net.

The actual braking energy which is not consumed locally on the individual stacker crane could be fed back into the power net by means of a power recovery module. There are techniques which allow generating near sinusoidal currents for power recovery. Therefore, disturbances and harmonics are reduced to a minimum. Today, there is technology available that does not require special arrangements on the power supply side. The requirements on the power net do not go above the standard requirements of a motor-rated application.

As stated above, many of these strategies are employed in new technologies throughout the material handling industry. Employing them can help you and your customers boldly go where no material handling systems have gone before!

Material Handling Equipment Distributors Association
Daryl Hull Meet the Author
Daryl Hull is president of LTW Intralogistics, located in Emigsville, Pennsylvania, and on the Web at www.ltw.at.


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