Improve Productivity with Ergonomic Storage System Design
Strategic SKU placement reduces injuries and increases picking and assembly productivity
For order pickers, packers and others in industrial facilities, warehouse ergonomics is critical to both safety and effectiveness. The way you store and pick can enhance productivity — or hamper it. In an age of labor shortages and spiraling costs, it pays to design for ergonomics. The core of that is where you place items for picking and processing.
What’s the impact of poor warehouse ergonomics?
Over 34% of missed workdays are due to musculoskeletal issues, such as sprains and strains in the manufacturing and processing sectors. OSHA statistics underline the problem even more: musculoskeletal disorders, or MSDs comprise over a third of all worker compensation claims in the United States. The agency specifically mentions inadequate ergonomic protection as a driving force in these injuries, so evaluating the way your storage systems impact ergonomics is always worthwhile.
Those injury statistics don’t get into what may be even bigger: the impact of bad ergonomics on productivity. People who must constantly repeat awkward and difficult movements are less productive. They work slower and make more mistakes.
Wasted motions are wasted time
Any function that requires people to manually choose an item, access it, move it and use it can cause injuries, but also presents an opportunity to ramp up productivity. Consider the act of removing one part from a bin, turning and placing that part on a conveyor belt or into a carton. That motion occurs hundreds of times a day, hundreds of days a year, for years. Shaving off precious seconds from it adds up to massive gains in speed and productivity.
Any constantly-repeated motion should be evaluated, measured and improved to improve safety and productivity. Tiny efficiencies add up over time.
Picking and access “reach” zones
To understand the idea of the “golden zone” picture a space in front of yourself that starts just beneath your shoulders and ends the waist and forms an arc in front of you that doesn’t require you to turn. Things you have to access at those heights are relatively easy to grab. You can do it effortlessly if the item isn’t too heavy. You’ll be fast. If you need to swivel, you’re a little slower. If the item is below your waist, but not below your knees, it’s not bad, but you will be slower and it will take more effort. Movements outside this area require you to bend, stretch, reach or strain.
Minimizing those movements will reduce injuries and will increase the pace of work without causing extra strain.
While this illustration indicates fewer storage positions in the “golden zone” than in the less accessible zones, there are techniques and storage systems that increase gold-zone density for active SKUs and parts. The green, infrequent zones are reasonably good positions, particularly for larger, easier to grab items that fit a light-to-medium weight category. Store resupply stock or slow movers on the lower and upper zones.
Focusing on the golden zone
The zone you want is the “most frequent” area between the waist and shoulders. While the ergonomic zone extends to the top of knees for relatively easy movement and accessibility, the gold area means the least possible effort and time to achieve a pick or other process. This keeps arms from going over the workers’ head and prevents many back or knee bends. If the process involves moving with a heavy item (in this case, the worker could be picking and pivoting to a conveyor line, for instance), this reduces the amount of time he’s “cantilever'” lifting since the item is pulled from storage at the right height. If the item is particularly heavy, consider assistance such as hoists or balancers. If possible, extend the picking area so that it’s as brief a lift/hold as possible.
Slot your fastest moving, most important items into golden zone positions in your shelves or carton flow.
Accessing pallets: when is depalletizing worth it?
Sometimes you don’t depalletize at all and pick cases directly from a pallet. While this decision is made during putaway, it affects the downstream picking and packing processes and should be evaluated for efficiency and ergonomics. If you can store the pallet in an accessible manner, and items are easily reached, you can pick directly from it without stocking its contents into a storage system. We see this frequently next to conveyor lines for fast-moving SKUs.
Above: for pallet picks, use a positioner that adjusts as layers of cartons are removed. At least one layer is always above the level of the picker’s knees to reduce bending and stretching.
If you can, use a pallet positioner to raise the pallet for ergonomic ease. When the top layer is picked, the positioner elevates the pallet so that your people don’t need to stoop or bend to reach the contents. They also rotate, meaning workers don’t need to walk around the pallet and can reach everything from one spot. The benefits of depalletizing aren’t worth it if the items can be left on it and effectively picked from there.
Shelving: slower movers should be stored on static shelves
Shelving is a common way to store items for picking, and serve the right product in the right process. For improved ergonomics, consider the following:
- Always store the fastest-moving items in the golden zone, but if they are higher volume, consider flow storage.
- Tighter shelf spacing may give you more positions in the zone. If people can see/reach the products, you might get 3-4 shelves inside the golden zone.
- Case picks work well on shelving, particularly if it’s easy to reach items and slide them off the shelves. Shelves with lips should be avoided.
- When it comes to dimensions, don’t make the shelves too deep. Reaching deep into a shelving unit can be as slow and awkward as reaching down to the floor. Taller shelves give you more storage, but what can it be used for? If you can use it as overflow or restock areas, it can be helpful. Wider shelves give you a longer side-to-side run of golden zone pick areas, but will take up more space.
- Don’t load heavy items on upper shelves, even if the SKUs are relatively slow-moving. Don’t set up pickers to pull heavy items from above their heads.
- Lower shelves, down to knee level, are relatively good for picking. Below the knees, store very slow movers or reserve stock.
- If you’re piece-picking, the right bin or container can make a difference, especially for small items picked in quantity. Bins with tilted fronts and easy-to-grip edges will make it easier and increase safety.
Ideally, you should be placing infrequent items on shelves, but the right configuration can make a difference.
Carton Flow: faster movers, higher density, easier access
Above: This Unex carton flow rack has three shelves in the gold or near-gold zones. While the fifth shelf is above the picker’s shoulder height, the tilted rollers deliver bins so that he can retrieve them with relative ease. Even the lowest two shelves are in the green zone. The top shelf is an empty bin return slot and is never picked. This design delivers more positions in the gold zone than outside it.
Carton flow is ideal for items that fall between fast and slow movers, and by their nature present higher density storage and faster picking that increases retrieval efficiency. Your fastest movers should be stored in your golden zone carton flow shelves. This places them where the golden zone is maximized to its best use. Those picks that drive the most orders and most value should be stored in the zone.
Your midrange items can go into the green zones, where they are picked less often. While your gold zones should be occupied by your most important, fastest movers (in Pareto, the 20% of stock that drives 80% of orders), this flips the script: the green zones should hold the 80% of SKUs that drive 20% of picks. These aren’t slow movers, but they are retrieved much less often and with more trouble and reaching. A picker may pick something from this zone every day, but not everything in the zone every day.
Automated systems: carousels and ASRS
Carousels are perhaps the most ergonomic of these options because the picker is always at a pick window, which is set at ideal ergonomic height. The product rotates within a vertical cabinet and is delivered to workers in exactly the right position. Vertical carousels typically set their picking window square in the golden zone, where pickers are always at the optimum place. If the volume supports it, that picker should never have to leave her position.
Horizontal carousels are live shelves–their rotating baskets are at various heights which must be accessed by the picker. The rules for storage should be similar for them: fast-movers in the gold with medium and slow movers on the upper or lower levels.
The golden zone drives efficiency, which also drives ergonomics. These are complementary goals that always produce better outcomes.
Dealing with the exceptions
Keep in mind that these are general guidelines and that many factors–headcount, replenishment rates, facility design, throughput and customer demand–will dictate the actual solution. People who are very tall or very short will not necessarily benefit from the golden zone without other equipment and considerations. The golden zone tends to hold true most of the time, for most facilities and most picks. What are some of the exceptions?
Heavy items pose special challenges
Heavy items can be difficult for pickers, particularly if they are high-volume. If you’re constantly picking heavy items, look for a way to slot them into a place that requires little or no lifting. A full case of bottled beverages isn’t that heavy when picked a few times a day, but should use the golden zone if constant. Picking heavy items shouldn’t require bending, squatting or lifting. We’ve seen carton flow feed to a table that lets pickers slide it to the conveyor line or directly to a cart, for instance. Store large, heavy items in a way they can be accessed with a hoist or other lifting options. You can also leave them palletized as mentioned above, and use a pallet positioner to elevate them to ergonomic height.
For infrequent but heavy picks, use the lower level (knee or below) of carton flow or shelving and train your pickers to lift correctly with their legs. When they stand, the conveyor or cart height shouldn’t force them to lift the item much higher. Why the bottom and not the top? Depending on the reach, an average person can lift about 50 pounds if it’s right in front of their stomach, which they can achieve from that position. The amount of weight reduces dramatically with reach, so these items should mostly be stored at the bottom level.
Right: the upper level is stocked with large, light cases of potato chips.
Large & bulky items
Even when they’re light enough to be hand-picked, very large items are harder to grip and move. If the item is large and lightweight, store it on the top level, where pickers have easier clearances to grasp and move it. If the bulky/light item is a frequent pick, slot it into the golden zone. Storing bulky items in that zone isn’t ideal for storage density, but works for ergonomic access and picking efficiency.
Work with your people: they know more than you do
As you work to improve ergonomics, always consult your people on the line. They can tell you where the difficult picks, stresses and problems are. Some may have even tried an ad-hoc fix. You must still evaluate the operation from a management and safety perspective, but you’ll learn a lot by talking with your order pickers. Making changes without picking team input is never advisable. Employees may resist changes they disagree with, or suffer morale issues because they weren’t asked about a process they understand deeply. Always involve them.
- First-in, First-out Storage Considerations
- Order Fulfillment is the First Line of a Great Customer Experience
- Order Picking Velocity: Storage and Picking Method Comparisons
Scott Stone is Cisco-Eagle's Vice President of Marketing with more than thirty years of experience in material handling, warehousing and industrial operations. His work is published in multiple industry journals an websites on a variety of warehousing topics. He writes about automation, warehousing, safety, manufacturing and other areas of concern for industrial operations and those who operate them.