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Ocado’s robot swarm

Ocado's "Hive" in Andover

Andover factory contains 400 robots controlled by “world’s densest” mobile communications network based on 4G technology.

Box-shaped robots sliding like rooks on chessboard made of crates, pulling the boxes up with “fingers” from the stack and into a cavity within them, before delivering them to pick stations. Welcome to Ocado Technology’s Andover factory.

The “swarm” – made up of 440 robots – live in a 2D world, Paul Clarke, Chief Technology Officer (CTO) explains; moving on a horizontal or vertical axis, collecting, delivering and replenishing storage on a SIL 3 safety certified grid or “hive”.

The robots are capable of accelerating at 2m/s2 and reaching speeds of 4m/s, with millimetre tolerances. Making a grid the size of a football pitch, while still ensuring the robots could pass each other at a 5mm distance and within 60cm of the roof beams was a huge design challenge, Clarke adds.

Each bot is exactly the same, meaning that one can be easily replaced by another if, for example, maintenance, charging or updates are required. The robots can also collaborate in “swarm” like behaviour to carry out tasks which require more than one bot to complete.

In terms of the software stack, the low-level software that controls the robot is written in C, while the high level overall control software is written in Java. The system uses OpenStack to provision an internal cloud infrastructure where Ocado uses Kubernetes to create containers for the various applications it needs to run. Log data is stored in Ceph and everything is streamed into Google Cloud where Ocado uses BigQuery for analytics.

To talk to the robots, Ocado Technology designed what it claims is the “world's densest mobile communications network based on 4G technology”. According to Ocado, the communications protocol guarantees a connection 10 times a second to each of the 1,000 robots per base station – all working within a 150-metre radius.

The communications network is said to be the world's first deployment of unlicensed 4G spectrum for warehouse automation.

The wireless protocol uses orthogonal frequency-division multiple access (OFDMA) which is used by LTE for the downlink air-interface. However, Ocado has replaced the media access control (MAC) layer with its own implementation and entirely removed the upper layers of the 4G cellular offering, which were not relevant for this particular project.

The system has the notion of a resource map where the frequency and time allocation for each node is described. Ocado’s wireless protocol's map is fixed for each client as it adds it to the system vs LTE or WiMAX where some element of scheduling is involved.

Before physically building this high-tech warehouse, Ocado’s simulation team created a 3D representation of the structure, which was used to develop and test software. The simulation was then transformed into a live monitoring system, meaning Ocado can track what every bot is doing in real-time and anticipate issues.

This technology is part of the Ocado Smart Platform (OSP), a solution designed to power the online grocery business of retailers around the world.

Previously, Ocado would purchase third party hardware from logistics companies and install them in the warehouses. A solution that worked well in both its Hatfield and Dordon factories, Clarke points out. But for the OSP, Clarke says it needed to control the supply chain and to design a solution that could easily be installed and scaled in any geography, as well as suitable for overseas operations. “We use one machine to design, evolve, manufacture and support, making it a much more flexible and accessible solution” he explains. “We want to be able to sell this system into territories where online grocery is more nascent. With OSP, a company is able to build upon its hive in stages, partially populating it until the need to expand arises, when they can just add more robots and crates.”

Ocado has already licensed its OSP to several companies, including Morrisons, and intends to increase its own swarm to 1,100. The online grocery store believes at full capacity, it will be able to process 65,000 Ocado orders every week.

Author
Bethan Grylls

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