Warehouse Robots: Distance and Stored Energy

Tour Notes: Robots That Lift, Dock and Bump

Ms. Paloma Ventresca's eighth-grade class toured a regional supply warehouse where robots move plastic bins of goods. A tall lift robot raises bins onto shelves and lowers them to the floor again when an order comes in. Technician Soren Achterberg showed the class the robot's dashboard, which reports energy in joules (J). The robots work around the clock, so the company tries to waste as little battery energy as possible.

Every bin on that day's run had a mass of 20 kg. When the lift raised a bin, the battery supplied energy to the lift's motor. When the lift lowered a bin, the motor ran like a generator: the descending bin turned the motor, and the motor sent some energy back into the battery. Soren explained that some energy turns into heat and sound in the motor and gears, so the battery gets back less than it used. Student Jun Oyelaran copied the dashboard numbers for bins raised from the floor to four shelf heights and later lowered back to the floor. They are shown in Table 1.

When a robot's battery runs low, it drives to a charging dock. A pair of attracting magnets, one on the robot and one on the dock, pulls the robot's charging plate into place. Soren set up a demonstration with a small cart carrying a magnet on a level, low-friction track. A second magnet was fixed at the end of the track. He held the cart still at different gaps from the fixed magnet and then let go. Jun's classmate Ifeoma Strand filmed in slow motion and measured the cart's speed just before the two magnets met. The cart, the magnets and the track were the same in every trial. Her results are in Table 2.

Some robots also carry soft bumpers made of two magnets facing each other with like poles, so they repel. In a gentle bump against a wall, the bumper magnets were pushed only a little closer together, and the robot rolled back slowly. In a harder bump, the magnets were pushed much closer together, and the robot was pushed back faster. Soren said the bumpers protect both the robots and the shelves from damage.