Walmart has expanded its robot program to 50 stores across the country.

The autonomous robots go up and down the aisles, scanning for out-of-stock items, incorrect prices, and wrong or missing labels.

Walmart's vice president of innovation, John Crecelius, says the retailer is "very excited and very motivated" by the way the program has been performing.

Walmart's new robot fleet is having an impact on stores.

The retailer has expanded its initial test of its shelf-scanning robots to 50 stores across four states, including Arkansas and California. They're shaped like six-foot-tall roving towers on wheels and are equipped with cameras that can spot shelving errors. Walmart is working with the fully autonomous robots' manufacturer, Bossa Nova Robotics, for the program.

The robots scan aisles for out-of-stock items, things that were put in the wrong place by customers, incorrect prices, and wrong or missing labels. They continuously go up and down the aisles of the store, alerting human employees to the errors it sees.

The robots, which are often more efficient than employees performing similar tasks, are designed to free up workers' time so that they can use it to help customers.

But productivity is not what Walmart has been focused on with the pilot program, according to Walmart's vice president of innovation, John Crecelius.

"This has largely been about how we improve our performance and improve our service to our customers," he told Business Insider.

The robots go slow — about 2-3 mph. Walmart

One of those ways is being able to keep products in stock by noticing more quickly when items are running low. Crecelius says the information could even help customers shop Walmart's online offerings, as the store would have a more complete and accurate report of what exactly it has in stock.

During the initial testing phase, Walmart's store employees found new uses for the robot that corporate hadn't thought of, like using the information it's compiling to immediately rush certain items from the delivery truck to store shelves.

"[Store employees] are usually at the forefront for helping us identify things that improve our business that we hadn't thought of," Crecelius said.

Walmart is currently testing to figure out the best times to run the robots and what the best use for the data it provides would be. It's testing a three-run daily cycle: once in the early morning, once midday, and once in the evening.

The robots were developed by Bossa Nova Robotics. Walmart

Crecelius said the main reaction associates and customers have to the robot is "natural curiosity."

"People are just drawn to technology and what it does," he said. "Our associates naturally get drawn to: 'What is this going to provide, how can I use this in what I'm doing?'"

Store employees have taken a shine to the robots, according to Crecelius. Some employees say they see the machine as a member of the team, giving it a name and a name tag to wear.

"That's usually a good sign," Crecelius said. "It usually happens when they feel like something is helping them or making a meaningful difference."