This article was written by Sam Shaw, a roboticist and the multipick technical lead, and Grant Aylward, a product manager for warehouse robotics.

The team behind Stretch, our autonomous mobile robot for the warehouse, is constantly learning from our customers and deployed robots. We’re continually leveraging those learnings when developing and deploying new capabilities that make the robot unload trailers and shipping containers faster.  

Today we announce a major advancement in unloading speed: Stretch will pick and place multiple boxes— currently up to four at once—with a feature we are calling multipick. Containers are often filled with thousands of boxes, so enabling Stretch to move multiple boxes instead of one with a single swing of the arm results in significantly higher productivity.

The Stretch robot is grasping 3 brown boxes simultaneously with the suction gripper at the end of an industrial arm, hovering over a conveyor belt inside a container.

Sensing and Planning to Optimize Efficiency

Stretch picks boxes in cycles, grasping a box and swinging its arm over to the conveyor, placing the box, and then repeating this series of movements. With multipick, Stretch continues to make all decisions in real time, deciding how many and which boxes to grasp each time it goes to pick. The robot considers properties of boxes including size, as well as properties of candidate groups of boxes that can be picked, such as how well aligned their faces are for simultaneous grasping. Stretch may end up picking one box at a time, but often will grab two, three, or more boxes at once.

Stretch’s perception system and gripper make this advanced behavior possible. When planning a grasp, Stretch will consider different candidate groupings of boxes in the environment that it could pick together, assessing the quality of the grasp between the gripper and each box.

Once Stretch has decided which boxes it will pick and how, context about which gripper suction cups the robot should use for which boxes is passed to the gripper controller. When the gripper makes contact with those boxes, Stretch’s software can assess whether sufficient suction has been made with each box, ensuring a secure grasp to prevent drops and protect customer product. Depending on the properties of the individual boxes held and how they’re held as a group, Stretch will choose a placement technique that enables each box to be placed in the desired orientation with appropriate spacing and centering on the conveyor. To drop boxes one by one, that original context about which cups go to which boxes is used again so that the gripper knows which cups should be turned off in order to release each box.

Additionally, the variety of intelligent box placement behaviors rolled out with multipick seamlessly integrate Stretch with downstream warehouse workflows: our advanced gripper doesn’t dump all the boxes on the conveyor, but places and spaces each box so they are better aligned for scanning and transportation with customers’ sortation systems.

Effortless Integration

Stretch was built with ease of use in mind. Training goes quickly, so associates who were manually unloading containers one week are operating Stretch robots the next week.

Operators don’t need to do anything to activate multipick, since the feature is now integrated into the robot’s behavior. They simply drive the robot into place and set the robot to start as usual. Assessing each grasp and placement in real time, Stretch will pick multiple boxes when that’s possible and single boxes when it’s not, as in the case of large boxes whose surface areas require all the gripper’s suction cups.

Pushing Innovative Boundaries

Multipick leverages Stretch’s core grasping algorithms, the ones used for picking and placing single boxes. As the team continues to develop that technology, multipick will benefit from those advances as well. And as we plan to expand the ways Stretch works further into the warehouse, multipick will be contributing value.

To learn more about why efficient container unloading matters, check out our latest whitepaper: Strengthening the Supply Chain with Automated Case Unloading.