RASCAL: Novel robotics for scalable and highly available automated storage and retrieval

This research paper was presented at the 
41^st IEEE International Conference on Robotics and Automation (opens in new tab) (ICRA 2024), the premier international forum for robotics research.

Over the past decade, robotics has revolutionized numerous industries that rely on storage systems, such as manufacturing and warehousing. In these contexts, robotics streamlines operations and increase efficiency, and automated storage and retrieval systems (ASRS) are at the heart of this technological shift, exemplifying the transition to smarter, computer-controlled logistics solutions. These systems quickly move items from storage to fulfilment stations, helping to increase speed and accuracy in the overall process. Yet despite these advances, current ASRS—whether rail-based, fixed, or free-roaming—continue to face challenges, often sacrificing scalability and availability for higher throughput capacity. For instance, the use of fixed robots in traditional tape storage libraries, typically used for archival storage, can lead to availability limitations, as the robots cannot pass each other, and a single robot failure can restrict access to a significant portion of the library.

Our paper, published at ICRA 2024, introduces RASCAL: A Scalable, High-redundancy Robot for Automated Storage and Retrieval Systems, which addresses these concerns. RASCAL is an untethered robot that improves the efficiency of vertical storage systems by operating across evenly spaced, parallel shelves and horizontal rails. Designed to maximize scalability and redundancy, it handles the storage and retrieval of small objects. RASCAL was inspired by the challenges of managing archival storage media in datacenters, and it’s the key component of Project Silica’s storage and retrieval system. However, RASCAL’s modularity enables it to be used in other scenarios as well. 

An innovative approach to archival storage

RASCAL’s design is based on four key principles:

• Addressability: This allows any robot to access any item being stored on the shelves. 
• Scalability: The system can adjust retrieval capacity and storage space by adding or removing robots and shelving with negligible downtime.  
• Availability: A single robot failure minimally impacts access to items and routing, and it does not obstruct the operation of other robots.  
• Serviceability: Robots can easily be added or removed from the rails without the need for special training.   

RASCAL’s motion system supports horizontal and vertical movement along storage panels assembled from contiguous storage racks. The parallel rail system enables independent and flexible movement. These rails are designed to be passive—functioning without the need for active power or energy sources, relying instead on their physical structure and positioning to guide and support the robot’s movement along the storage panels. The robot can travel along and between these rails using various pathways to reach a given item. Video 1 shows how RASCAL operates multiple robots on a single storage panel.

RASCAL utilizes a special rail geometry, allowing the robot to passively latch onto the rails with opposing wheels mounted on each end, as illustrated in Figure 1. This design ensures that the robot is securely held in place by gravity alone. The passive nature of this latching mechanism simplifies the process of adding or removing robots from the rails, as it does not require any tools or power.

The robot features two rotating assemblies known as wings, each equipped with wheels that allow it to move horizontally. The wings rotate in a choreographed sequence to enable ascent and descent. RASCAL climbs by unlatching one wing from its current rail while remaining attached to the other. It then rotates and secures its free wing to a new rail either two levels up or down. This is shown in Video 2.

Video 3 demonstrates RASCAL’s item-selection system, or picker interface, which is designed to handle various robotic tool attachments for precise pick-and-place operations. This interface can rotate in alternating directions during climbs, ensuring that the robotic tool attachment, or end effector, remains oriented towards the shelving while stationary, preventing the cables from tangling.

Advancing robotics and automation

As digital economies grow, the need for efficient storage and retrieval systems becomes increasingly urgent. Breakthroughs in robotics technology are poised to drive productivity, efficiency, and innovation across numerous industries. Developments like RASCAL, with its flexible design and advanced capabilities, are leading the way for the next generation of robotics and automation.

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