September 2010 | Case Studies | DC Solutions

Xylophones, Checkerboards, and Gestalt Theory

Tags: Warehousing, Materials Handling, Picking Solutions

Using colors, shapes, numbers, and mnemonics in warehouse signage can help reduce training and picking errors, while improving service.

Winston Churchill once said, "we shape our buildings; thereafter they shape us." How you design your warehouse locator system, pick flow, and slotting strategy has profound ramifications on productivity throughout a building's lifetime. Using colors, numbers, and shape mnemonics in signage can produce immediate benefits.

Mispicks often occur because a slight distraction disrupts a picker's train of thought. A casual conversation or looking ahead to the next pick can cause a miscalculation; then a product is selected from a location directly next to, or above, the target. Rarely do workers mispick from a location catty-corner to the target.

Voice and pick-to-light technology helps workers keep their eyes on the task, but these expensive investments can run up to $100 per pick face, hardly a cost-effective solution for low- or moderate-velocity SKUs.

Lack of attention and focus contribute to mispicks, but so does signage. Poor visual indicators within a warehouse can get a new hire lost quicker than a sailor's paycheck on shore leave. Good, clear signage improves picking accuracy.

Think about it. When you're driving and get lost, what type of information do you want from your GPS or co-pilot? Do I go left, right, or straight? Where is the next turn? How far away is it? Will my reference point be a building, street sign, or traffic light? The quicker you receive this information, the better prepared you are to make the correct move.

It seems simplistic, but take a walk through your warehouse with a new hire's eye. Can you quickly identify building, zone, or aisle signs from all areas? The number of blind spots, especially within an aisle, will surprise you. Try asking observant new hires to identify possible oversights. How quickly can they see the next destination sign? How distinguishable are the signs? If signs are all the same color and shape, their meaning may be camouflaged to an untrained eye.

Pick sequences can be a directional beacon, but how fast will employees move if they are not sure when the next turn is? Some pickers work best from a numeric approach—vertical and horizontal, latitude and longitude. Others have an affinity to colors; still others to shapes. But why choose one when you can use all three?

Using Color and Shapes to Improve Accuracy

Simple visual hints reinforce accuracy. Consider how we learn as children and eventually are trained to perform tasks. Some people learn best by reading documentation, others by observing, and some by doing. Most early learning tasks leverage this knowledge. Why are toy building blocks and xylophones colored and often numbered?

While the true cause of some mispicks will continue to give warehouse managers gray hair and remain a mystery, others can be diagnosed and mitigated by sticking to a continually replicated methodology that uses common denominators.

Pick methods vary by technology and equipment, but you can always improve the human factor. Take, for example, a multi-layered approach that supports the basic numeric location (the "target" destination of pickers). This tactic introduces a universal, second tier of location information using color and shape mnemonics. With modern labeling and printing capabilities, it's a low-cost solution that rivals radio frequency, pick-to-light, and voice-directed picking technologies in some environments.

The Gestalt Laws of Organization (Gestalt is German for shape) analyze how we perceive visual factors as "structured" patterns or wholes, rather than as many disparate parts. There are six factors that dictate how things may be grouped, according to our visual perception: common fate, continuity, proximity, similarity, closure, and symmetry.

Throughout history, these ideas have been translated into simple forms to facilitate identification. From items such as playing card suits and dartboards, to critical communication devices including traffic lights and road signs, colors and shapes play a paramount role. We have the ability to distinguish more shades of green than any other color (thus the green light on traffic signals). Red, another traffic light color, is the most visible color to humans, likely from the emergency survival skills needed to identify the flow of blood.

Evolution has allowed the human eye to identify some colors more effectively than others, and we can apply these naturally honed selective tools to choosing product and location colors in the warehouse.

Imagine training a new DC worker in this scenario: If each color in Figure 1 (below) was a SKU, which pattern is most unique to best identify a specific destination? For example, "pick the top yellow square" versus "pick the black box on the third row from the bottom, four columns over from the left in the right section." Which could you describe or do quicker?

Adding location numbers as identifiers makes it easier, but then you must look closer and spend more time reading and distinguishing characters. Now try the matrix shown in Figure 2 (below), which leverages four distinct tiers: numbers, letters, colors, and shapes.

I developed this matrix for shelf, zone, or section tags in an industrial building. A picker looking from a distance in a dark warehouse can more quickly and accurately identify a location or level within a rack column by a "standard" color, as opposed to gleaning details from the often faded and scratched text of a paper label.

From my experience, recognition occurs about 15 to 20 feet earlier using this approach. For constant visual anchors, I use red at the 5 column to split the difference of 10 digits. Repeat the colors if the shelf section exceeds 10 slots. I use white and black as 1 and 2 to control label print costs on rack sections housing smaller SKU volumes. The shapes also employ alphabetic name mnemonics to help associate the level to the shape's nomenclature (D level = Diamond, C level = Circle).

Finding the Perfect Slot

After you identify areas where you can improve visual indicators in your warehouse, use these simple tips to optimize slotting and signage methods and increase accuracy, efficiency, and productivity.

Slotting

  • Store like items close—but not too close. You can reduce mispicks by up to 60 percent through thoughtful and non-contiguous slotting of similar style items. Store SKUs from the same vendor together to speed putaway, but use a checkerboard strategy to avoid horizontal or vertical SKU assignments that look alike or include different consumer sizes of the same item. Storing them adjacently confuses rookie pickers and increases mispicks.
  • If you speed picking, you reduce fatigue. Most warehouses store high-velocity items in their "golden zones" but fail to assign these SKUs to ergonomically convenient levels where pickers don't have to stretch or stoop. Conversely, slot slow-moving products in low or high locations. Fatigue ultimately reduces quality and speed.

Signage

  • Use shapes and colors with large, bold fonts to identify all unique identifiers that add value: building, zone, section, rack, aisle, level, column, pick direction (arrows on the floor or on signs), and non-pickable areas (departments, exits, and common spaces).
  • If you can't produce colored or shaped labels with your own printing technologies, buy pressure-sensitive labels and stickers to support signage efforts. Try working on a section a week to minimize constraints on your daily workload.
  • Use square labels for diamonds, then cut them in half for triangles.
  • Identify all blind spots where a section is not clear and add signs as required.
  • Use simple forms of number sequences on labels and in your numbering system for your locator. It's not a NASA project, so don't turn it into one.
  • Have clean copies of your locator map on posters, clipboards, and picking carts to reinforce new-hire learning and impress new visitors to your facility.