All manual systems have their breaking points. Picking errors increase with growing SKU counts. Labor costs per pick increase. Human walking speed caps the throughput. At that stage, automation is no longer a luxury, but the only way to justify the operation at scale.
Automated storage encompasses a variety of systems. Each has a unique cost profile, operational footprint, and a different way it influences operations. To justify these systems, it is critical to understand each one.
AS/RS — The Core Systems
Automated racking and Retrieval Systems has a number of distinct types of systems. The most common are narrow aisle stacker cranes. In this system, a single crane operates the length of a racking aisle and is able to pick and place totes and pallets. These systems are designed to maximize speed and accuracy while optimizing the storage density. A narrow aisle manual system (VNA) pales in comparison to a well-designed stacker crane system, especially when the aisle width is in the dimensions of 1.6 meters.
Pallet shuttle systems have a unique method. These systems use a motorized shuttle that runs on the racking rails in a deep lane. The shuttle carries the pallets in and out, negating the need for a crane to enter the aisle. Pallet shuttle systems work best in high throughput and low SKU operations. A good example is cold storage. The traditional purpose for this application is to achieve the highest storage density and reduce the time the doors are open. These systems are not flexible and handle FIFO and LIFO flows, but not mixed-SKU lanes.
Mini-load AS/RS systems are designed to handle smaller items. These can be totes, cartons, or individual picks, which are all smaller than a pallet. These systems have smaller cranes and footprints, with faster cycles, and can integrate with pick stations at the end of the aisle. In operations specializing in e-commerce and the fulfillment of pharmaceuticals, mini-load systems have been implemented at a larger scale than manual systems.
Vertical Lift Modules and vertical carousels are further down the small end of the AS/RS ranges. VLMs contain trays that are stored on both sides of a central extractor. The extractor can deliver the tray to a pick window. These systems are best used in high value, low storage spaces. These systems are modular, and more secure than traditional storage.
AGVs and Their Role Alongside Racking
Automated Guided Vehicles (AGVs) transport loads across a facility without the need for fixed guide paths. The first generation of AGVs used wired loops or magnetic tapes embedded into flooring. Modern AGVs tend to use some version of laser guided navigation or vision-based SLAM (simultaneous localisation and mapping). Because of this, the routes taken by modern AGVs can be changed by software, without the need for any changes to the flooring.
AGVs and racking have a specific relationship. AGVs, unlike racking, do not provide a substitute. AGVs, as stated previously, do the work of forklift trucks and operators by transporting loads to and from racking positions. Storage locations will still need to be occupied by either conventional or automated storage and retrieval systems (AS/RS) racking. In this case, the automation is housed in the transport layer and the storage layer is unautomated.
AGVs, in general, have a subset that is known as Autonomous Mobile Robots (AMRs). These AMRs have better obstacle avoidance, along with superior navigation flexibility. That is why they are predominant in goods-to-person fulfilment operations. In this case, the robot will bring a pod or a shelf unit to a picker, as opposed to the picker commuting to the goods. These robots will also replace the order picker by walking to the pod. At this moment, Ocado’s warehouse model is the most known example of this in the UK.
Furthermore, the integration question is significant. A fleet of AGVs interfacing with a Warehouse Management System (WMS) that does not manage automated traffic will cause disruption that will halt manual operations. Specifically, the WMS will have to provide automation for task prioritisation, battery management, and an automated traffic system that interfaces with the WMS for the positioning of inventories.
What Drives the Decision
Three common factors justify automation projects in UK warehousing: the need for labour, accuracy, and speed. The need for labour has become the most important factor post 2021. This is especially the case for logistics hubs in the Midlands and South East due to the competition to employ warehouse staff.
The cost of capital investment is considerable. For example, the price of installing a stacker crane system in a medium-sized distribution center starts in the millions of pounds. However, due to their modular design, AMR can be deployed with much greater flexibility for incremental scaling, thus changing the investment risk.
SEMA’s guidance addresses the structural needs for automated racking such as loading tolerances, flatness of the floor, and, for taller racking, the design for equilibrium. Retrofit projects often underestimate the required precision of the floor. A stacker crane’s throughput on a floor designed for counterbalance trucks will produce positioning errors resulting in degraded throughput and increased wear and mechanical damage of the crane.
The systems are functional, but the obstacles are in the implementation – integration gaps, floor specification, and WMS – rather than in the technology.