Automated storage: Shuttle technology is taking off
When automated storage and retrieval systems first appeared on the materials handling scene back in the 1960s, they were designed and built to handle heavy pallet loads, known as unit loads. As automated storage and retrieval system (AS/RS) technology progressed, system incarnations were introduced to handle smaller, lighter loads in totes, trays, cartons and bins. This more compact cargo became known as mini-loads.
Now, there’s another emerging storage technology known as shuttle technology, and it handles micro-loads. Like the mini-load AS/RS, shuttle technology is a computer-controlled system that uses moving vehicles known as shuttles to put away, store and retrieve goods in a racking structure.
But while there are similarities, there are also differences between the two solutions. For example, two significant differences between a mini-load AS/RS and the newer shuttle technology are weight and directional movement. Both systems can transport product in totes, trays, cartons and bins, but the load handling devices in a mini-load AS/RS system are capable of carrying loads of up to about 1,000 pounds. Shuttle systems are designed to carry even lighter loads, typically limited to about 100 to 110 pounds.
The mini-load AS/RS uses one stacker crane that moves horizontally and vertically, forward and back, and up and down an aisle. But in a shuttle system, two separate transport devices carry out vertical and horizontal movements. A lift, like an elevator, at one or both sides of the unit, moves up and down to the designated storage level within the system. Some lifts are designed to raise and lower more than one load at a time. Then, to move product horizontally—meaning to and from the lift and in and out of the storage aisle—each level is equipped with one or more load handling devices, or shuttles.
“Shuttles and lift systems work independently from each other,” explains Roman Schnabl, product manager for Knapp USA. “This guarantees a maximum utilization of lift capacity and optimized throughput.”
Another thing that makes the shuttle different from the typical mini-load crane is speed. Stephen Schwietert, integrated systems sales manager for TGW Systems, says shuttles can multiply throughput rates. “Because there can be a number of shuttles operating in a single aisle, and these shuttles are moving simultaneously, the throughput per aisle can be five to 10 times greater than a typical mini-load AS/RS,” he says.
So while the vehicles act concurrently on different storage levels and a high throughput can be reached, typically it is the vertical lift at the end of the aisle that sets the limit for the possible throughput per aisle. However, according to Kenneth Hayer, senior consultant for Swisslog, there can be several lifts per aisle depending on performance requirements. Lifts can be located at the front, middle or end of an aisle.
Still, the lifts also move at a fast rate. In fact, Hayer says that each lift can perform approximately 500 vertical lifts every hour and make it to the top of a 45-foot high rack structure in about three seconds.
These differences give shuttle technology some advantages over a mini-load system and can make it a better solution for certain automated materials handling applications.
Here’s the answer, what’s the question?
An AS/RS only brings value to an operation when an order is filled, says Dave Simpson, director of applications engineering for Schaefer Systems International. “It’s a holding tank for inventory, getting the right SKU to the right place at the right time.”
So why do the features and benefits of shuttle technology make it a good materials handling solution for certain operations with certain requirements and not the ideal solution for others? The best way to understand the answer is to ask the question: What are you moving and why?
If an operation that is handling a variety of goods in a variety of sizes, shapes and packages, shuttle technology could be the right match—especially if that operation is a warehouse or distribution center handling multi-channel order fulfillment.
Multi-channel order fulfillment is a term that we’re hearing a lot these days. Online shopping, smart phones, catalogs, 3:00 a.m. infomercials and brick and mortar stores offer shoppers more choices than ever. More options for consumers means a proliferation of SKUs for warehouses and distribution centers. It also means that more frequent and smaller orders are being shipped directly to individuals.
Filling more small orders means a lot more leg work and that’s where shuttle technology steps in. The idea is to take the leg work out of order fulfillment and replace it with a goods-to-person strategy, which is supported by shuttle technology.
“If an operation has products that are handled in case or unit quantities, and you have associates walking or riding to pick this merchandise, shuttles may eliminate the need for walking and increase productivity two to six times greater than your current process,” explains Schwietert. “This is where technology moves beyond the ‘wow’ factor, to a technology solution that integrates with an operation to deliver results.”
With this solution, the integration of shuttle technology results in getting orders to customers quickly and accurately. Shuttle technology supports goods-to-person order fulfillment configurations.
According to Ken Ruehrdanz, warehousing and distribution market manager for Dematic, “shuttle technology supports higher order and inventory accuracy, increased productivity and controlled access to inventory.” It also accommodates the growing trend to improve the performance of the replenishment task, meaning the replenishment of inventory into the pick modules.
The goods-to-person picking concept has gained traction over the past couple of years. “Because of their speed and ability to sequence, shuttles have opened up the idea of goods-to-person picking. Almost anyone with a traditional multi-floor pick module, may have an opportunity for goods-to-person picking using shuttle technology,” Schwietert adds.
The demand creating the opportunity for this technology is a constant struggle to balance storage effectiveness, throughput capacity and SKU representation, Ruehrdanz says.
When operations were only filling large orders for wholesalers or retailers, he points out, unit-load AS/RS systems were a fine solution. But unit-load systems that handle pallets are not as effective in this case. It’s comparable to using a service elevator to deliver a cup of coffee when you could have used a dumbwaiter.
Using shuttles to deliver product to the operators in a goods-to-person operation uses the right equipment to handle the job, and the shuttle’s lightweight design and advanced controls contribute to reduced energy consumption.
In comparing the weight of mini-load crane, which is about 20,000 pounds, to a shuttle carrier, which is less than 100 pounds, the difference is significant and so is the ratio of energy needed to move the load.
The shuttle system has extremely low energy consumption at full speed. This is because carriers are driven by super capacitors and the system has energy recuperative features for both the carriers and the lifts that feed energy back into the system, Swisslog’s Hayer explains. Additionally, the control software continually optimizes transport routes and transport movements, making an added and important contribution to energy conservation.
The interplay between lift system and shuttles makes a constant level of performance possible, avoiding energy consumption peaks and providing an even supply of containers, says Knapp’s Schnabl. “One rack line of the [shuttle] performs 800 storage and retrieval movements in one hour and consumes approximately 2 kWh, which corresponds to the energy consumption of two vacuum cleaners.”
Multi-benefits of shuttle
In addition to being fast and energy-efficient, shuttle systems are flexible, explains Dematic’s Ruehrdanz. With the ability to handle totes, trays, bins, cartons, cases and trays, shuttle systems can accommodate different load types in variable sizes and the load handling device can ‘flex’ to multiple load widths.
Flexibility is also gauged by the system’s ability to work within the confines of an irregular building space. A traditional mini-load AS/RS doesn’t have the same modular design options because it needs a square form of racking, but the shuttles’ modular rack structures can be adapted to existing irregular building shapes which optimizes the storage space inside the building’s cube.
Because shuttles can go in and out both ends of aisle, the system can be configured to accommodate unusual or irregular facility dimensions. Modular rack can be designed around building components on the ceiling like air conditioning units or designed to bridge floor-level concerns like lift truck traffic routes.
Still, shuttle technology should be treated like another tool in the toolbox. This tool, for example, works well in ambient environments but has not yet been perfected for use in the deep freeze warehouse environment, says Swisslog’s Hayer. This is because the vehicles have electronic components that don’t function well in temperatures that dip below 32 degrees Fahrenheit. Keeping freezer temperatures low is a high operational expense, so you don’t want to introduce anything in the freezer environment to heat up the components that could add to the cost of temperature control.
With virtually unlimited design possibilities, Knapp’s Schnabl says, a system can be tailor-made to fit the customer’s requirements today and in the future can be adjusted simply and effectively to meet changes in their market sector.
“Shuttle technology will allow integrators to have a bit more flexibility in developing the most cost effective solution for end users,” says Schaefer’s Simpson.