DUPONT — Robots do a lot of the heavy lifting at the new Amazon.com fulfillment center, helping 500 human employees fill orders for the Seattle-based Internet retailer.

The center is one of 50 around the country and three in the Puget Sound area. The others are at Bellevue and Sumner. A fourth is under construction in Kent.

The $100 million DuPont Fulfillment Center has been operating since last June, but Amazon held a grand opening ceremony Friday for political and economic development officials, The News Tribune reported.

The center is a showcase for Amazon’s robotic technology.

Robotic equipment improves safety because it operates without direct human control, minimizing the chance of injuries, said Greg Zielinski, the DuPont center’s general manager.

Computer-driven equipment follows wires embedded in the floor to select merchandise on a two-story warehouse floor equal in area to 59 football fields.

The order travels on a conveyer belt to where it is boxed and labeled for shipment through a computerized system that routes the boxes to one of two dozen package-delivery trucks.

An algorithm decides which delivery company will handle the shipment to ensure the order arrives on time at the least cost.