Ergonomics and Warehouse Robots

I believe mobile robots will eventually change the face of warehousing. Kiva Systems, for example, has developed robots for each picking that can retrieve a small, square rack with multiple slots. The robot brings the rack to the worker, spins it so the correct facing is towards the picker, and then the slot to be picked lights up. Alternatively, if you were building mixed SKU case pallets, the robots would retrieve a pallet and bring it to you at your work station to pick the cases and build the pallet. This is “goods-to-man” material handling. 

But I have wondered about goods-to-man material handling from an ergonomics perspective. If a worker is sitting in one position all day long making repetitive picking motions, couldn’t this lead to more injuries –e.g., more hand, wrist, and elbow injuries for each picking?

To get an answer this question, I talked to Steve Lavender, an Associate Professor of Integrated Systems Engineering and Orthopedics at Ohio State University.  Here are some of Steve’s thoughts.

Man-to-goods distribution centers (DCs) have a lot of variability built into them. For example, in a food distribution DC, there might be 6,000 SKUs located in 6,000 slots. That means there are, in effect, 6,000 work sites. There is a lot of variability in what muscles are used to pick at all of these different work sites, which can help prevent repetitive stress disorders. But it also means that it is harder for safety experts to build in safety because the environment is so dynamic. 

For example, imagine you are building a mixed SKU pallet. You go to a slot where there is a pallet of coffee on the floor with cases weighing 35 pounds. When the pallet is full and you are picking from the front, it is pretty safe. But as the cases from the front of the pallet get picked, and you have to lean over and stretch to pick from the rear, the risk for back injuries go up.   

But in goods-to-man, there is tremendous opportunity to improve the ergonomics. Imagine a worker standing in a small pit but working from an adjustable height platform. The robot brings the pallet. If it is full, the worker pushes a button to raise the platform. If the goods are on the back of the pallet, he pushes a button to make the robot turn the goods towards him. 

Now let’s look at each picking. In general, Steve does not see many hand or wrist injuries in a warehouse; back and shoulder injuries are more common. But each picking in a zone, where some of the slots are high and workers stand on their toes and repetitively flex their wrist to pick, wrist injuries can occur. 

In goods-to-man each picking, you can design the movable pallet to be at a height where workers don’t have to repetitively flex their wrist in a strenuous manner. As long as there are enough robots to keep workers fully occupied, the height of the rack may not matter so much.

In conclusion, man-to-goods material handling could be worse—e.g., you could force someone to repetitively bend all day to each pick from the low slots on the rack. But ergonomically, it is an environment where building in safety is much easier. Thirty years ago manufacturing was much more dangerous than it is today. Automation and ergonomic practices, as well as off-shoring, have dramatically decreased manufacturing injuries. Factory welding, for example, used to be particularly dangerous. Now robots do the welding in automotive factories. As automation comes to the warehouse, the same sorts of safety improvements could occur.

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