Multi-Object Grasping - Efficient Robotic Picking and Transferring Policy for Batch Picking

Abstract

In a typical fulfillment center, the order fulfilling process is managed by a warehouse management system (WMS). For efficiency, WMS usually applies batch picking, also called multi-order picking, to collect the same items for multiple orders. Suppose an item appears in multiple orders, instead of repeatedly revisiting the exact picking location multiple times, a picker will be instructed to pick up multiple same items at once and bring them to a sorting station, also called a re-bin station. It is at the re-bin station, where the workers sort the picked items into separate orders. We have seen many robotic technologies being developed for sorting. However, we have not seen any feasible robotic technology for batch picking. Transferring multiple objects between bins is a common task. In robotics, a standard approach is to transfer a single object at a time. However, grasping multiple objects and transferring them at once is more efficient. This paper presents a set of novel strategies for efficiently grasping and transferring multiple objects. The grasping strategies enable a robotic hand to grasp multiple objects by identifying an optimal ready hand configuration (pre-grasp), calculating a flexion synergy based on the desired quantity of objects to be grasped, and utilizing a deep learning model to signal the completion of a grasp. The transferring strategies demonstrate an approach that models the problem as a Markov decision process (MDP) and defines specific grasping actions to efficiently transfer objects when the required quantity is larger than the capability of a single grasp. Using the MDP model, the approach can generate an optimal pick-transfer policy that minimizes the number of transfers. The complete proposed approach has been evaluated in both a simulation environment and on a real robotic system. The proposed approach reduces the number of transfers by 59% and the number of lifts by 58% compared to an optimal single object pick-transfer solution.